ATMOSPHERE AIR FURNACES TECHNICAL CONTENT

Heat Treat Radio #105: Lunch and Learn: Batch IQ Vs. Continuous Pusher, Part 2

/ ATMOSPHERE AIR FURNACES TECHNICAL CONTENT, CARBURIZING TECHNICAL CONTENT, FEATURED NEWS, HEAT TREAT RADIO, MANUFACTURING HEAT TREAT TECH

Have you decided to purchase batch or continuous furnace system equipment? Today's episode is part 2 of the Heat Treat Radio lunch & learn episode begun with Michael Mouilleseaux of Erie Steel. Preceding this episode were Part 1 (episode #102) and a Technical Tuesday piece, so listen to the history of these systems, equipment and processing differences, and maintenance concerns before jumping into this episode about capability and throughput.

Doug Glenn, Heat Treat Today publisher and Heat Treat Radio host; Karen Gantzer, associate publisher/editor-in-chief; and Bethany Leone, managing editor, join this Heat Treat Today lunch & learn.

Below, you can watch the video, listen to the podcast by clicking on the audio play button, or read an edited transcript.

The following transcript has been edited for your reading enjoyment.

An Example: Carburizing (00:52)

Michael Mouilleseaux:  What we want to do here is just compare the same part, the same heat treating process, processed in a batch furnace and processed in a pusher.

Figure 1: Carburizing Load Example (Source: Erie Steel)

Here we’re just going to make an example:

Pusher Load Description (00:58)

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I’m going to take a fictious gear: it’s 2 ¾ inch in diameter, it’s got an inside diameter of an inch and a quarter, it’s an inch and a half tall, and it weighs 1.25 pounds. For our purposes here, we’re going to put these in a cast basket. For the furnace that we’re going to put them in, the basket size is 36 inches square — so, it’s 36 x 36. The height in this pusher furnace is going to be 24 inches; the inside dimensions of a 36-inch basket (actually it’s a 35-inch basket that sits on a 36-inch tray) is 32 ½ inches.

Michael Mouilleseaux General Manager at Erie Steel, Ltd. Sourced from the author

If I take 10 rows of parts — that’s 27 ½ inches — that gives me about a half inch between parts. That’s going to be our loading scheme. So, in one layer, it’s going to be 10 pieces of 10 rows of 10 pieces each; that gives us about a half inch between parts. It doesn’t matter why, that’s just what we’re going to do so that we have some standard to do that.

We’re going to say that this basket is 18 inches tall, so we’re going to get 7 layers of parts so that there’s approximately 1 inch between each layer of parts. This loading scheme gets us 700 pieces in a basket; it gets us 875 pounds net.

So the 36-inch basket that’s 18 inches tall and we’ve got 10 rows of 10 pieces, and we’ve got 7 layers of these things, so we have some room in between them. The reason for that is circulation of atmosphere and quenchant. This is what’s going to constitute the pusher load.

Batch Load Description (03:09)

Now, when we go to the batch load, we’re going to take four of these, because the batch furnace that we’re going to compare this to is going to be 36 inches wide and it’s going to be 72 inches long. We have two baskets on the bottom, 36, and then two of them is 72, and two on top. They’re 18 inches high, so 18 and 18 is 36 — a standard 36 x 72. It’s got 40 inches of height on it. I can take that 36 inches, put it on a 2 ½-inch tray and I can get it in and out of the furnace.

What is this four baskets? 2800 pieces in a load and 3500 pounds. That’s the difference. I’m comparing one basket, 700 pieces and 875 pounds and we’re going to compare that to what we would do if we ran a batch load, which is significantly more. It’s 2800 pieces and 3500 pounds.

What do we want to do with this?

Let’s say that we’re going to carburize this, and we want 50 thousandths case (total case depth of 0/050”). Now, I will show you very soon why we’ve chosen 50 thousandths case. Because at 1700°F (which is what we’re going to carburize at), the diffusion rate is 25 thousandths of an inch times the square root of time.

Now, I can do that math in my head. 25 thousandths times 2 is 50 thousandths. That means we need four hours. So, the part would have to be in the furnace for four hours, at temperature, carburizing, in order to achieve 50 thousandths case.

Figure 2: Batch IQ Carburizing Load (Source: Erie Steel)

Batch Furnace Time (04:59)

Let’s look at the next section. As we said, the furnace is 36 x 72 x 36 and we have 2800 pieces in the load. So, that is 1700°F. We’re going to say that there is 3500 pounds and there is probably another 800 or 900 pounds in fixturing so that’s about 4500 pounds. It’s very conservative; in a 36 x 72 furnace, you could probably get away with running 6,000 pounds. This is just a load that is well within the capability of that.

Furnace recovery is going to take two hours.

Doug Glenn:  Meaning, it’s going to take you two hours to get up to temperature.

Mike Mouilleseaux:  Until the entirety of the load is at 1700°F, that’s right. Inside, outside, top to bottom.

We’re going to carburize this at four hours, as we described previously; we calculated that and we need four hours to get our 50 thousandths case. Then we’re going to reduce the temperature in the furnace to 1550°F so that we can quench it.

So, we have two hours of furnace recovery, four hours at carburizing, two hours to reduce the temperature and attain a uniform 1550°F. That’s eight hours, and that’s what you would term an 8-hour furnace cycle.

We know that we have 2800 pieces in the load. In eight hours (2800 divided by 8) you’ve got 350 pieces/hour. That’s what the hourly productivity would be in this load.

We won’t talk about “what could we do.” There’s a lot of things that we could do. This is simply an example.

Pusher Furnace Time (07:05)

Now, in the pusher load, as previously described, it’s 36 x 36 and it’s 24 inches high. Now, we know that we have a basket that’s 18 inches high. Again, it’s going to sit on a 2-inch tray, so we’ve got 21 inches of the top of the basket that is going to fit in the furnace; there are going to be no issues with that whatsoever.

When we looked at the first description of that furnace, there were two positions in recovery, there were four positions to boost to diffuse, and there were two positions to reduce the temperature.

The controlling factor is that we want four hours at temperature. In the boost and diffuse, we have four positions. The furnace cycles once per hour.

We get one load size (700 pieces, 875 pounds) every hour. So, in this example (an 8-position, 36-square pusher) this process would yield 700 pieces an hour, and a batch furnace loaded as we described (same exact loading and number of pieces/basket) would yield 350 pieces/hour. In this scenario, the pusher furnace is going to produce twice the number of parts/hour that the batch would.

So, you would say, “Well, let’s just do that.” What you have to understand is that every hour, you are going to produce 700 pieces. If we went back and we looked at that description of what that pusher system looked like, you would see there are 23 positions in that. When I load a load, it’s going to be 23 hours before the first load comes out.

What we’re talking about is whether or not there were 700 pieces and 800 pounds, 23 of those[ET10] [BL11]  load.

The point would be, you either have to have enough of the same product or enough of similar product that can be processed to the same process to justify using something like this. Because if we want to change the cycle in the furnace. So, can we do that? The answer is absolutely, yes.

The preheat there, that stays at relatively the same temperature. The first zone in the furnace where we’re preheating the load, that temperature can be changed, as can the temperature in the boost diffuse and/or cycle time.

Figure 3: Pusher Furnace System (Source: Erie Steel)

So, in our example, we used an hour. What if you wanted 40 thousandths case and you’re going to be closer to 45 minutes or 50 minutes of time, how would you accomplish that? That can be done.

Typically, commercial heat treaters would come up with a strategy on how to cycle parts in and hold the furnace, or how many empties you would put in the furnace before you would change the furnace cycle.

Obviously, in the last two positions, where you’re reducing temperature, you could change the temperature in either the first two positions, where you’re preheating the load, or you could change the carburizing temperature, because when we’re dropping the temperature, it doesn’t have a material effect upon that.

Typically, in an in-house operation, you would not do that kind of thing, for a couple of reasons, not the least of which would be considering the type of people that you have operating these furnaces. They come in and out from other departments, and this is the kind of thing that you would want someone experientially understanding the instructions that you’ve given them. The furnace operator is not necessarily going to be the one to do it; this may be a pre-established methodology. You want them to execute that. But if you have somebody that is running a grinder and then they’re running a plating line and then they’re coming and working in the heat treat, that would not be the recipe for trying to make these kinds of changes.

As I described to you before, I worked in another life where we had 15 pushers. They were multiple-row pushers. We made 10,000 transfer cases a day. The furnace cycle on every furnace was established on the 1st of January, and on the 31st of December it was still running the same furnace cycle. You never changed what you were doing. The same parts went into the same furnaces and that’s how they were able to achieve the uniform results they were looking for.

Pusher Furnaces and Flexibility (12:45)

So, the longer the pusher furnace is, the less flexible it is.

In this example, you have eight. You know, there are pusher furnaces that have four positions. If you think about it, in a 4-position furnace, you could empty it out pretty quickly and change the cycle.

There are a lot of 6-position pusher furnaces in the commercial heat treating industry; that seems to be a good balance. The number of multiple-row pushers in the commercial industry, they’re fewer and far between. I’m not going to say they’re nonexistent, but enough of the same kind of product to justify that is difficult.

Doug Glenn: You could put two 8-stations in a pusher side by side so that there’s two baskets going through side by side or three baskets side by side, or four. That increases the productivity even more. There are multi-row setups.

Distortion, Quenching, and Furnace Choice (14:28)

I think the bottom line here is, for companies that are having high variability, low quantity, low volume loads, generally speaking, your batch is going to be good because it’s very flexible, you can change quickly.

However, with a company like the one you were describing where there is low variability and very high volume, pushers are obviously going to make sense. But there is a whole spectrum in between there where you’re going to have to figure out which one makes more sense — whether you’re going to go with a batch or a continuous.

Mike Mouilleseaux: Possibly underappreciated is the aspect of distortion.

Figure 4: Pusher Furnace Sequence (Source: Erie Steel)

In that carburizing example, you’d say, “We have an alloy steel, we’re aiming for 50 thousandths case — what’s the variation within a load?” And I’m going to say that it is going to be less than 5 thousandths, less than 10%. From the top to the bottom, the inside to the outside, it’s going to be less than 5 thousandths. That same process, in the pusher furnace is going to be less than 3 thousandths.

That’s one aspect of the metallurgy. The other aspect is quenching.

Doug Glenn: 5 thousandths versus 3 thousandths — 3 thousandths is much more uniform, right?

Mike Mouilleseaux:  Correct.

Doug Glenn: And that’s good because that way the entire load is more consistent (in the continuous unit, let’s say).

Mike Mouilleseaux:  That is correct.

Then there is the consistency in quenching. In the batch furnace, you’re quenching 36 inches of the parts. If we had seven layers in the pusher, we have 14 layers of parts in the batch. What are the dynamics involved in that?

We have experience that the ID of a gear (it’s a splined gear) in a batch furnace, we were able to maintain less than 50 microns of distortion. There is a lot involved in that, that’s not for free; there’s a fair amount involved in that and it’s a sophisticated cycle, if you will. That same cycle in a pusher furnace, same case depth, similar quenching strategy, will give you less than half that amount of distortion.

To the heat treater, where we’re talking about the metallurgy of this, you’re going to think 5 thousandths or 3 thousandths is not a big deal.

To the end-user, that reduction in distortion all of a sudden starts paying a number of benefits. The amount of hard finishing that has to be done or honing or hard broaching or something of that nature suddenly becomes far more important.

Doug Glenn:  Yes. That adds a lot of money to the total process, if you’ve got to do any of those post heat treat processes.

Mike Mouilleseaux:  To a large extent, that is due to the fact that you have a smaller load. If you have a smaller load, you have less opportunity for variation — it’s not that it’s all of a sudden magic.

Doug Glenn:  And for the people that don’t understand exactly what that means, think about a single basket that goes into a quench tank and four baskets, arranged two on top and two on bottom. The parts in the middle of that are going to be quenched more slowly because the quench is not hitting it as much.

So, the cooling rates on a stacked load are going to be substantially different than for a single basket, and that’s where distortion can happen.

Mike Mouilleseaux: There are a tremendous number of components that are running batch furnaces successfully. The transportation industry, medical, aerospace, military — are all examples. I’m simply pointing out the fact that there is an opportunity to do something but what we have to keep in mind is — how many of those somethings are there available?

The one thing you would not want to do is try to run four loads in a pusher furnace that could hold 10 because the conditions are not going to be consistent. The front end (the first load) has nothing in front of it so it’s heating at a different rate than the loads in the center, and the last load is cooling at a different rate than the loads that were in the center. That which I just described to you about the potential improvement in distortion, that would be negated in that circumstance.

Doug Glenn:  If you’re running a continuous system at full bore and you’re running a batch system at full capacity, especially when you get to the quench, there are a lot of other variables you need to consider in the batch.

This is simply because of the load configuration, and the rates of cooling from the outer parts — top, bottom, sides, as opposed to the ones in the middle. Whereas with a single basket, you still have to worry about the parts on the outside as they’re going to cool quicker than the parts on the inside, but it’s less so, by a significant degree.

Mike Mouilleseaux: Something that I have learned — which is totally counterintuitive to everything that I was educated with and everything that I was ever told— we’d always thought that it was the parts in the top of the load where the oil had gone through and had an opportunity to vaporize and you weren’t getting the same uniform quench—those were the parts that you had the highest distortion.

Counterintuitively, it’s the parts in the bottom of the load that have the greatest degree of distortion. It has very little to do with vaporizing the oil and it has everything to do with laminar flow versus turbulent flow.

Doug Glenn: In the quench tank, is the oil being circulated up through the load?

Mike Mouilleseaux:  Yes.

Doug Glenn:  So, supposedly, the coolest oil is hitting the bottom first.

Mike Mouilleseaux:  Yes.

Thoughts on the Future of Furnace Improvement (22:20)

Doug Glenn:  What about the future on these things?

Mike Mouilleseaux:  Where do we think this thing is going? Obviously, you’re going to continue to see incremental improvement in furnace hardware: in burners, in controllers, in insulation, in alloys. These things will be more robust; they’re going to last longer. If we looked at a furnace today and we looked at a furnace that was made 50 years ago, and we stood back a hundred yards, almost no one could tell what the difference was, and yet, it would perform demonstrably different. They are far more precise and accurate than ever.

For the process control systems, we’re going to see real-time analysis of process parameters. We don’t have that now. I think that machine learning is going to come into play, to optimize and predict issues and prevent catastrophic things.

Heating rates that we talked about: Why are we not going to see machine learning or AI finding the problem sooner, rather than my looking at it and seeing it a week later and thinking, “You know, it looks like these things are starting to take longer to heat up.” Why can’t that be noticed by some kind of machine learning or something like that?

In terms of atmosphere usage, if you’re running the same load, and you run it a number of times, the heating rate should be the same, and the amount of gas that you use to carburize that load should be exactly the same. But if you have a problem with atmosphere integrity — you got a door leak, you got a fan leak, or you got a water leak on a bearing — those things are going to change. Now, by the time it gets your attention, you could’ve dealt with that much sooner and prevented other things from happening.

"For the process control systems, we’re going to see real-time analysis of process parameters. We don’t have that now. I think that machine learning is going to come into play, to optimize and predict issues and prevent catastrophic things."

So, did it cause a problem with the part? By the time it causes a problem with the part, it’s really serious. The point is that there is something between when it initiated and when it’s really serious. With the right kind of analysis, that could be prevented. I think that that kind of thing is coming.

Motor outputs, transfer times — I see all of those things being incorporated into a very comprehensive system whereby you’re going to understand what’s happening with the process in real-time. If you make adjustments, you’re going to know why. Then you’re going to know where you need to go and look to fix it.

And last but not least, the integration of the metallurgical results in the process. Before you have a significant difference in case depth or core hardness. There are reasons that these things happen. Again, this machine learning, expert analysis, AI (whatever it is we’re going to call that) we’re going to see that that’s going to do it, and we’re not relying on somebody to figure why it’s happening.

The other thing I see happening in the future is all about energy and greenhouse gases. Our Department of Energy has an industrial decarbonization roadmap today, and it’s being implemented, and we don’t even know it. One of the targets in this industrial decarburization roadmap is reduction in greenhouse gases: 85% by 2035, net zero by 2050.

So, what does that mean? I’ve listened to the symposiums that they have put on. There are three things that they’re looking for and one is energy efficiency. I’m going to say that we’ve been down that road and we’ve beat that dog already. Are there going to be other opportunities? Sure. It’s these incremental things, like burner efficiency. But there is no low hanging fruit in energy efficiency.

The other thing is going to be innovative use of hydrogen instead of natural gas because the CO₂ footprint of hydrogen is much lower than that of natural gas. If you look at how the majority of hydrogen is generated today, it’s generated from natural gas. How do you strip hydrogen out of there? You heat it up with natural gas or you heat it up with electricity. Hydrogen is four times the cost of natural gas as a heating source.

The other thing that they’re talking about is electrifying. It’s electrify, electrify, electrify. The electricity has to be generated by clean energy. So, does that mean that we run our furnaces when the wind is blowing or the sun is out, or we’re using peaker plants that are run off hydrogen, and the hydrogen is generated when the sun is shining or the wind is blowing, and we’re stripping out the natural gas?

From what I, personally, have seen with these things, these are absolutely noble goals. You could not disagree with them whatsoever. The way that they want to go about accomplishing it, and the timeline that they wish to accomplish that in, is unrealistic.

If you look at how the majority of hydrogen is generated today, it’s generated from natural gas. How do you strip hydrogen out of there? You heat it up with natural gas or you heat it up with electricity. Hydrogen is four times the cost of natural gas as a heating source.

Doug Glenn:  Well, Michael, don’t even get me going on this! There are a lot of different things that are going on here but it’s good to hear you say this stuff. I agree with you on a lot of this stuff. They are noble goals; there is absolutely nothing wrong with electrifying.

Now, I do know some people — and even I would probably fall into the camp of one of those guys — that questions the premise behind the whole decarbonization movement. I mean, is CO₂ really not our friend? There’s that whole question. But, even if you grant that, I agree with you that the timeframe in which they’re wanting to do some of these things is, I think, fairly unrealistic.

It’s always good to know the reality of the world, whether you agree with it or not. It’s there, it’s happening, so you’ve got to go in with eyes wide open.

Safety Concerns (29:41)

Mike Mouilleseaux:  The safety concerns on these are all very similar. You know, the MTI (Metal Treating Institute) has some pretty good safety courses on these things, and I think there are a lot of people who have taken advantage of that. The fact that it’s been formalized is much better.

When I grew up in this, it was something that you learned empirically, and making a mistake in learning it, although the learning situation is embedded in you, sometimes the cost of that is just too great, so that the probability of being hurt or burnt or causing damage to a facility, is just too great.

There are definitely things that need to be addressed with that, and there are some very basic things that need to be done.

Doug Glenn: Michael, thanks a lot. I appreciate your expertise in all these areas, you are a wealth of knowledge.

Mike Mouilleseaux:  My pleasure. It’s been fun.

Doug Glenn:  You bet, you bet.

About the Expert:

Michael Mouilleseaux is general manager at Erie Steel LTD. Mike has been at Erie Steel in Toledo, OH since 2006 with previous metallurgical experience at New Process Gear in Syracuse, NY and as the Director of Technology in Marketing at FPM Heat Treating LLC in Elk Grove, IL. Having graduated from the University of Michigan with a degree in Metallurgical Engineering, Mike has proved his expertise in the field of heat treat, co-presenting at the 2019 Heat Treat show and currently serving on the Board of Trustees at the Metal Treating Institute.

Contact: mmouilleseaux@erie.com

 

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Heat Treat Radio #105: Lunch and Learn: Batch IQ Vs. Continuous Pusher, Part 2 Read More »

Continuing the Dialogue: Michael Mouilleseaux on Batch/Continuous Furnace Maintenance

/ ATMOSPHERE AIR FURNACES TECHNICAL CONTENT, CONTROLS, CONTROLS TECHNICAL CONTENT, MANUFACTURING HEAT TREAT TECH

Our readers and Heat Treat Radio listeners will remember a recent episode entitled "Heat Treat Radio #102: Lunch & Learn, Batch IQ Vs. Continuous Pusher, Part 1." Today's Technical Tuesday article is a continuation of this dialog, with Michael Mouilleseaux, a boot-on-the-ground North American heat treat expert from Erie Steel here to answer your questions on the maintenance of batch and continuous pusher furnace systems.

Doug Glenn, Heat Treat Today's publisher, Karen Gantzer, associate publisher/editor-in-chief, join in this Technical Tuesday article.

Stay tuned for a Part 2 continuation of the Lunch and Learn Heat Treat Radio episode, coming to Heat Treat Radio in a couple weeks.

Below, you can watch the video or read from an edited transcript.

https://player.vimeo.com/video/900890450?badge=0&autopause=0&player_id=0&app_id=58479
Michael Mouilleseaux
General Manager at Erie Steel, Ltd.
Sourced from the author

Introduction to Maintenance

Doug Glenn: We would like to move on to maintenance of the batch furnace and the continuous furnace. What is the cost of maintaining and operating these furnaces?

Michael Mouilleseaux:  When they are utilized in a carburizing environment, there is always excess carbon that falls out or precipitates out of the atmosphere, and it ends up as elemental carbon in the bottom of the furnace.

What do you do with that? In furnaces that are using a carburizing environment, the burnout of the furnace is easily the single most important piece of preventative maintenance that you can perform. How is that performed? First, the furnace is vacated; there is no product in the furnace, the temperature is reduced — typically, you want it down around 1500°F or 1550°F — and you introduce room air into the furnace. The room air ignites the carbon. It’s a very primitive operation.

So, what temperature does carbon burn at? It burns at 3000°F.

You need to be very careful. It’s a controlled burn because you can actually damage the furnace through refractory, through the alloy that’s in the furnace, or it can get away. How do you do control it? On one level, you’re just looking at the temperature control. If you have it set at 1550, you’re going to say, “I’m only going to put air as long as the temperature of the furnace does not go up more than 25°F or 50°F.” It’s somewhat dependent upon the piece of equipment and is one of those things that you learn empirically; there is not a hard and fast rule for it.

Then, you can shut off the air. If there is no oxygen, then the source for combustion is taken away and you stop that operation. If you need to do it more rapidly than that, you may need to flood the furnace with nitrogen. Typically, if you have to flood the furnace with nitrogen to do it, you’ve been a little too aggressive in your burnout.

How long do you perform that? The great thing with oxygen probes is that you can utilize your oxygen probe to help you learn when you have burnt out the furnace. You’re not getting an actual carbon atmosphere, but what you do get is a readout from the probe. What you can do is perform the burnout operation until you attain that level and then you know that you’ve done a sufficient job in burning it out. That’s the single most important piece of preventative maintenance that’s done on a furnace used for carburizing.

Doug Glenn: Is that both in batch and in continuous?

Michael Mouilleseaux: Identical, yes.

Doug Glenn: I’ve got a couple other questions about furnace burnouts as someone who’s not a furnace operator. You said that there’s “carbon dropout” in the furnace. I know that in some furnaces, parts of the atmosphere may precipitate onto the coolest part of the furnace. Is that what is happening, or are we talking about carbon powder at the bottom of a furnace?

Michael Mouilleseaux: It is carbon powder, and it becomes more egregious. The powder then begins to accumulate into pebbles, nuggets, and larger size pieces. That’s more problematic. When it is in a powdered form, that is the best.

The question will be: How often do you have to do this? As with everything, the answer is — it depends. It depends on what you’re doing; it depends on how aggressive you are in your carburizing.

In the boost phase, we talked about carburizing at upwards of 1%. As soon as you exceed the saturation level of carbon, you’re going to precipitate out the excess carbon. What is that number? It’s different for every temperature. At 1500°F, it’s .9 or .85; at 1750°F, it’s 1.25. But to attain that, you’re actually putting natural gas into the furnace, and the amount of natural gas that you put into the furnace and its dissociation rate — the rate that it breaks down — can then subsequently be diffused into the parts; all of that comes into play.

With saturation levels of carburizing, there is always some residual carbon that’s in the furnace.

Doug Glenn: You mentioned that carbon burns at around 3,000 degrees. Are you taking the furnace up to that temperature?

The great thing with oxygen probes is that you can utilize your oxygen probe to help you learn when you have burnt out the furnace. You’re not getting an actual carbon atmosphere, but what you do get is a readout from the probe. What you can do is perform the burnout operation until you attain that level and then you know that you’ve done a sufficient job in burning it out. That’s the single most important piece of preventative maintenance that’s done on a furnace used for carburizing

Michael Mouilleseaux: No. The burnout cycle is at 1500 or 1550. You raise that carbon to that level and introduce oxygen, and what you want is a slow burn.

We next think about the systems involved in the furnace. First there is the heating system. In a gas-fired furnace, some critical things to consider are burner recovery, burner adjustment, and the amount of excess air that results in that burner adjustment. That’s a preventative maintenance operation that needs to be performed on a regular basis. It probably doesn’t need to be done daily, but monthly is optimal. If everything is very steady, including the barometric pressure, then you don’t need to do all of those adjustments.

Now, electric furnaces have SCRs that fire the elements, and you have to pay attention to the tuning of those things to make sure that they’re operating at optimum performance. One of the ways that you can do that, in a batch furnace, is if you look at the recovery time.

For example, if you have a load that weighs 4000 lbs. and you put it in the furnace and you know that it takes an hour and a half for the furnace to recover to temperature, but then all of a sudden, it takes an hour and 45 minutes, or an hour and 50 minutes, or two hours, obviously the burners are not producing the same amount of heat. The burners are not pumping the requisite amount of BTUs to achieve that recovery time. Could that be related furnace circulation? Could it be related to the insulation in the furnace? At an extreme, it could. Typically, though, it’s related to burner or SCR tuning.

Those are the kinds of things that are very easy to pay attention to.

"Electric furnaces have SCRs that fire the elements, and you have to pay attention to the tuning of those things to make sure that they’re operating at optimum performance. One of the ways that you can do that, in a batch furnace, is if you look at the recovery time."

Setting up PM Through Controls System

The control schemes in the PLC are typically very robust. So, you can establish a program and the PLC is going to say, “I want to heat it at this rate, I want the carbon potential to be .4%, I want to hold this at two hours at temperature, and then I want to initiate a quenching cycle.” Typically, PLCs are quite robust.

The thing you have to be careful with is obviously not just power outages, but brownouts. Brownouts are when you don’t quite lose all voltage, but you lose some of it. If you don’t have some kind of a filter on the power you can mitigate with, or have an uninterruptable power supply for the PLC, you can damage those things, resulting in some major work on the PLC.

The other part of that is the furnace circulation. We’ve got fans in these furnaces, and we circulate the atmosphere. The primary stages of heating in the furnace are convection, until we get to 1200 degrees. How do we convect the heat? We have the atmosphere in the furnace, the fan circulates, it washes the atmosphere down the radiant tubes, it heats up the atmosphere, the atmosphere comes into contact with the components, and we’re convection-heating the parts.

Once we get to 1200 degrees or more, then the primary method of heating becomes radiant heating. That’s where the radiant tubes are then the primary means of transferring energy. But the fans become very important. Are they balanced? Is the RPM correct? Is the amp reading on the fan? Those are areas to look at.

You have to understand how the furnace operates when it’s healthy — the furnace manufacturer can help you and/or you just learn empirically. For instance, what would it mean if, all of a sudden, I’m drawing much fewer amps on a circulating fan and it’s running very rough? Quite possibly, we’ve lost a fan blade.

Then there is the atmosphere control system. All that we just described is applicable to both continuous and batch furnaces. The furnace needs to be sealed and you want a couple inches of water column pressure — excess pressure — in the furnace relative to atmosphere pressure, since safety is the number one concern.

The atmosphere that we’re talking about in most of these furnaces is endothermic atmosphere. It’s a reducing atmosphere, meaning that it’s combustible. If, of course, we have combustion in a closed vessel, that’s called an explosion.

The reducing atmosphere, in and of itself, is if you look in a furnace that is at anything above 1200 degrees where it’s red, up to 1700–1800 degrees where it’s going to be yellow to white — and there is no flame . . . . People are absolutely amazed when they look in an atmosphere furnace and they see no flame. What you should see is everything in a relative, uniform color. The parts should be a uniform color. If you look at the tubes, they should be a little lighter because the tubes will always be somewhat above the temperature of the parts . . . .

Back to the atmosphere: We want to be sure that the atmosphere stays in the furnace and that we maintain that pressure in the furnace. So, what would be a cause to lower the pressure in the furnace? A door leak or a leak in a fan. It could be, if you have a mechanical handling system, a leak through that system. Those are all places to look.

The PM on that? For maintaining the level of lubrication in the fan bearings, see that they’re cooled so that the outlet temperature of the coolant — be it air or water — should be higher than the inlet temperature; that shows that they’re being cooled.

I can’t tell you an absolute number, but I can say that for the equipment that we have, we have numbers that we’ve developed; we know that if the outlet temperature of the water is 20 degrees higher than it is going in, we’re doing a good job of cooling the bearings.

The door seals in furnaces, typically, are brick on brick. Typically, they use a wedge system to seal the doors in the furnace. But, of necessity, these are wear items. Therefore, in preventative maintenance, you might notice a burnout around a door where you hadn’t had one before. That tells you that atmosphere is leaking out of that door and so a repair is needed in the near future.

An interesting thing about a batch furnace: Most of them only have one door. So, it’s quite easy — you can open the vestibule and, in a maintenance operation, if you gassed up the furnace, you could see.There is always going to be some atmosphere coming around the door because that’s where the atmosphere goes into the vestibule, but it should be at the top; it shouldn’t be around the sides, and it definitely shouldn’t be at the bottom. It should be very consistent.

That’s one of those things that, again, you empirically learn. You look at it — it’s a visual operation to say what you’re doing.

There are two other systems: First, the quench system. We talked about how critical the quench system is. The RPMs of the prop, the amp draw of the motors for the props — those things should be very consistent. I think they should be monitor and data logged. The reason for that is you want to know when you quench a load that the RPMs of those props are what you have set it for. When you introduce a load into the quench, the amp draw is, of necessity, going to increase. That’s because you’ve put something in the path of the quenchant so, in order to maintain that flow, you’ve increased the amount of work that it takes to rotate those props.

That’s the kind of thing that you want to monitor. If the amp draw is changing, that means that there’s something in the quench system. Could it be the bearings? Could it be the motor? Those are some things that you’d need to take a look at and be certain of. Obviously, the props need to be in balance; you don’t want any vibration in them.

Doug Glenn: This is also true on the continuous furnace. You’ve got three or four green props in the batch furnace, and it would be the same in the continuous furnace.

Source: Erie Steel, Ltd

Maintenance of Quenchant

Michael Mouilleseaux: Also, there is the maintenance of the quenchant. I’m of the belief that the quench should be continuously filtered. I’m not a fan of batch filtering. I’ve been doing this long enough that I’ve done that, and it just isn’t successful. Quite possibly there are operations that allow it.

If you’re carburizing, you’re going to have particulate in the quenchant because that same atmosphere precipitation of carbon finds its way into the quench. It’s going to be on the parts, it’s going to be on the trays, it’s going to be dragged in there. So, you have this particulate carbon in the quench and it acts as a catalyst to break down the oil.

One way to extend the life of the oil is to make sure that you’re continuously filtering that out. People say 50 microns or 100 microns or 25 microns. Experientially, I’m going to say that it’s going to be 25 microns. If you have a 100-micron filter, that’s great for getting the pebbles out of the quench or the scale, if that were to be an issue with your customer’s parts, but that’s not sufficient to filter out the particulate that’s going to be of the size that’s going to catalyze the breakdown of your quenchant.

Doug Glenn: I assume that if you’re providing for some sort of continuous filtering of your quench, that’s built into the quench structure. The quench tank is built for that, right, and you’re continually flowing it through this filter?

Michael Mouilleseaux: I’m not going to say that no manufacturers offer sufficient quench filtering, but I am not aware of anyone that offers a quench filtration system that’s sufficient. Most of these things end up being standalone. You want to draw the quenchant from the bottom of the tank in one quarter, you want to put it through a series of filters, and you want to put it back into the furnace at the opposite end of the quench tank.

I can say with certainty, that a batch furnace which has not been filtered well, if you remove the quenchant from the furnace after six months — definitely after 12 months — of using it in daily carburizing, you’re going to take 55-gallon drums of sludge out of the furnace, and the sludge is essentially carbon that’s mixed in with the oil.

For that same furnace, with a sufficient quench filtration system, there will be little pockets in the four corners of the quench tank, but that’s about it.

CQI-9, Nadcap and all of those standards have a requirement for monitoring of quenchant. One of the monitors should be particulate because that lets you know how good a job you’re doing in filtering.

Having done it properly, one can say, “Well, I have to replace my quench oil,” — fill in the blank — “once a year, once every six months, once every two years.” Properly maintained and filtered, the quenchant does not have to be replaced very often.

You’re going to drag out a little oil on every load. You want to let the load drip so that you’re not taking that precious quench oil and just putting it in the wash and washing it off. But in a batch furnace, you could have a couple hundred gallons a month to four hundred gallons, depending on the size of the furnace, of add-back that you’re putting in there. Is that sufficient to maintain all of the additives that are in the quenchant? Is that something that you need to monitor? Typically, the manufacturer can do that for you. You get monitoring and you see what the quench speed is, what is the viscosity, flash – all of those important pieces of information.

Now, it doesn’t come for free. A filtration system is costly, and the filters are costly. A year’s worth of quenchant is five years’ worth of filters. In my mind, that’s a good tradeoff.

Karen Gantzer:  So, Michael, when the process is filtering the quench, does this happen during production downtime?

Karen Gantzer
Associate Publisher/ Editor in Chief
Heat Treat Today

Michael Mouilleseaux:  No, it’s done continuously. Even when the furnace is not running on the weekend, you’re still filtering the oil. You’re going to be taking 20-50 gallons out of the quench tank but you’re putting it right back in. It just passes through filters.

Some people have utilized centrifuges. It’s a very successful way of filtering out carbon particles in oil. The caveat on that is you don’t want the oil above 140 degrees. If you get the oil above 140 degrees and for every 20 degrees you go up, you start doubling the oxidation rate of the oil.

In high-temperature oil, we do a fair amount of modified marquenching. We do it in closed canisters. The seals must be temperature-tolerant, but it is very successful.

The last part is going to be the quench heating and cooling. Typically, at the first part of the week when you’re starting up the furnace or if you’re going from operation A to operation B and it requires a higher temperature quenchant, you’re going to use either gas or electric elements that are going to heat it. Those things need to be monitored so that they’re available when you need them. The last thing that you want to do is start out the week and find out that the quench heaters don’t work; then, you’re trying to find a couple of dummy loads that you can heat up to put into the quench to heat up the quenchant before proceeding with operations.

Then, of great, importance is quench cooling. In petroleum-based quenchants, you’ve got a flashpoint of 400 degrees plus or minus — could be 350, could be 450, depending upon the quenchant that you’re using. You don’t want the temperature of that oil to approach that flashpoint. You do that by using a quench-cooling system. It’s a big radiator. You’ve got a pump, and you set it when you want the pump to go on. You pump the oil out to the quench coolant, and when it comes back, once you’ve attained what your temperature is, then you stop.

Doug Glenn: I’ve got a couple quick questions on this. First, is the quench heater an immersion tube?

Michael Mouilleseaux: Yes. Gas-fired tubes and gas-fired units are very small u-tubes that go into the quench tank. Electrical units have got elements that are tolerant to that.

Doug Glenn: Typically, you’re using those because you’re actually using the quenchant and always putting hot things into it, so once the quench fluid is up to temperature, it’s not a problem. You’re using that quench heater just to get the thing up to temperature. So after that, most of the time, you’re using the cooler to keep it cool, correct?

Michael Mouilleseaux: Absolutely. That’s a control scheme. The last thing that you want to do is set the quench heater so that it’s within five degrees of setpoint and set the quench cooling so that it’s within five degrees of setpoint — then, the temperature just sits there, with heating and cooling fighting each other. You’re heating and cooling oil unnecessarily. You want to give yourself some bandwidth on that.

Material Handling System

Last is going to be the material handling system. In the batch furnace, many have what we call a “rear handler.” We saw the cart and it would push the load into the vestibule, the inner door would open, and it would push the load into the furnace. It’s always preferable to push hot loads, not to pull on them. The reason is that the base trays are alloy and the compressive strength is much higher than the tensile strength is. If you’re pulling on loads, you’re going to break trays.

Once the load is in the furnace, you would have a rear handler so when the cycle is terminated and the inner door opens, you would have a mechanism — it may have a flat bar that’s half the width of the tray — that actually pushes the load into the quench vestibule.

There it’s pushed by the charge car and the inner door is open. That same handler, from the charge car, pushes it into the furnace. Now, when the cycle is terminated, there is a handler in the rear of the furnace that pushes it into the vestibule for quenching.

The exception is right here: When it’s taken out of the vestibule, typically the charge car goes in and grabs it and pulls it out. But, at that point, you’re at 100 or 200 degrees so, at that temperature, you have no material effect upon the strength of the alloy.

Doug Glenn: Okay, the motion it took it from the tray on the left inside is going to push it in and then the next step it’s also going to push it into this “hot zone,” correct?

Michael Mouilleseaux: Yes.

Doug Glenn: But what you’re saying is, when it’s coming out of the hot zone, there’s probably a mechanism on the far righthand side of the hot zone that’s going to push it back. Nothing is going in to pull it out because it’s hot.

Michael Mouilleseaux: Extended reach cars put the load into the vestibule and then put it into the hot zone.

There are some rear handlers that, rather than being a simple push function, have a dog mechanism that allows them to go and get the load in the vestibule and pull it into the furnace. Personally, I am not a fan of that; I like the extended reach car because when you’re pushing something, it is very easy to determine if you’ve put it in the right location. If you grab a load and pull it, you could lose the attachment on that load and then it’s not put exactly where you want it to be.

You can put amp meters on these things so that the amount of force that the motors require to pull in or push out a load. The one thing you need to be cognizant of is that it’s going to take more power — a higher amp draw — to push a 4000-pound load than it is a 2000-pound load. Once you understand what that is, you can monitor these furnaces and then they start making sense to you.

Source: Erie Steel, Ltd

 

Continuing the Dialogue: Michael Mouilleseaux on Batch/Continuous Furnace Maintenance Read More »

Traveling through Heat Treat: Best Practices for Aero and Auto

/ AEROSPACE HEAT TREAT, AEROSPACE HEAT TREAT TECHNICAL CONTENT, ATMOSPHERE AIR FURNACES TECHNICAL CONTENT, AUTOMOTIVE HEAT TREAT, AUTOMOTIVE HEAT TREAT TECHNICAL CONTENT, CONTROLS TECHNICAL CONTENT, FEATURED NEWS, HARDENING TECHNICAL CONTENT, INSTRUMENTATION TECHNICAL CONTENT, MANUFACTURING HEAT TREAT, TECHNOLOGY

Thinking about travel plans for the upcoming holiday season? You may know what means of transportation you will be using, but perhaps you haven't considered the heat treating processes which have gone into creating that transportation. 

Today’s Technical Tuesday original content round-up features several articles from Heat Treat Today on the processes, requirements, and tools to keep planes in the air and vehicles on the road, and to get you from one place to the next. 

Standards for Aerospace Heat Treating Furnaces 

Without standards for how furnaces should operate in the aerospace, there could be no guarantee for quality aerospace components. And without quality aerospace components, there is no guarantee that the plane you're in will be able to get you off the ground, stay in the air, and then land you safely at your destination.

In this article, written by Douglas Shuler, the owner and lead auditor at Pyro Consulting LLC, explore AMS2750, the specification that covers pyrometric requirements for equipment used for the thermal processing of metallic materials, and more specifically, AMEC (Aerospace Metals Engineering Committee).

This article reviews the furnace classes and instrument accuracy requirements behind the furnaces, as well as information necessary for the aerospace heat treater.

See the full article here: Furnace Classifications and How They Relate to AMS2750

Dissecting an Aircraft: Easy To Take Apart, Harder To Put Back Together 

Curious to know how the components of an aircraft are assessed and reproduced? Such knowledge will give you assurance that you can keep flying safely and know that you're in good hands. The process of dissecting an aircraft, known as reverse engineering, can provide insights into the reproduction of an aerospace component, as well as a detailed look into the just what goes into each specific aircraft part.

This article, written by Jonathan McKay, heat treat manager at Thomas Instrument, examines the process, essential steps, and considerations when conducting the reverse engineering process.

See the full article here: Reverse Engineering Aerospace Components: The Thought Process and Challenges

Laser Heat Treating: The Future for EVs?

If you are one of the growing group of North Americans driving an electric vehicle, you may be wondering how - and how well - the components of your vehicle are produced. Electric vehicles (EVs) are on the rise, and the automotive heat treating world is on the lookout for ways to meet the demand efficiently and cost effectively. One potential solution is laser heat treating.

Explore this innovative technology in this article composed by Aravind Jonnalagadda (AJ), CTO and co-founder of Synergy Additive Manufacturing LLC. This article offers helpful information on the acceleration of EV dies, possible heat treatable materials, and the process of laser heat treating itself. Read more to assess the current state of laser heat treating, as well as the future potential of this innovative technology.

See the full article here: Laser Heat Treating of Dies for Electric Vehicles

When the Rubber Meets the Road, How Confident Are You?

Reliable and repeatable heat treatment of automotive parts. Without these two principles, it’s hard to guarantee that a minivan’s heat treated engine components will carry the family to grandma’s house this Thanksgiving as usual. Steve Offley rightly asserts that regardless of heat treat method, "the product material [must achieve] the required temperature, time, and processing atmosphere to achieve the desired metallurgical transitions (internal microstructure) to give the product the material properties to perform it’s intended function."

TUS surveys and CQI-9 regulations guide this process, though this is particularly tricky in cases like continuous furnace operations or in carburizing operations. But perhaps, by leveraging automation and thru-process product temperature profiling, data collection and processing can become more seamless, allowing you better control of your auto parts. Explore case studies that apply these two new methods for heat treaters in this article.

See the full article here: Discover the DNA of Automotive Heat Treat: Thru-Process Temperature Monitoring

Find heat treating products and services when you search on Heat Treat Buyers Guide.com

Traveling through Heat Treat: Best Practices for Aero and Auto Read More »

Heat Treat Radio #102: Lunch & Learn, Batch IQ vs. Continuous Pusher, Part 1 – Heat Treat Today

/ ATMOSPHERE AIR FURNACES TECHNICAL CONTENT, FEATURED NEWS, HEAT TREAT RADIO, MANUFACTURING HEAT TREAT

Batch or continuous — which equipment is better for your operations? Today’s Heat Treat Radio episode is a lunch & learn to answer your burning question about batch IQ vs. continuous pusher furnace systems. Michael Mouilleseaux of Erie Steel is a boots-on-the-ground expert in North American heat treat, and he’ll share a bit about the history of these systems before getting into the equipment and heat treat processing differences.

Doug Glenn, Heat Treat Today's publisher and the Heat Treat Radio host, Karen Gantzer, associate publisher/editor-in-chief, and Bethany Leone join this Heat Treat Today lunch & learn.

Below, you can watch the video, listen to the podcast by clicking on the audio play button, or read an edited transcript.

 


 

HTT · Heat Treat Radio #102: Lunch & Learn, Batch IQ vs. Continuous Pusher Systems Part 1

The following transcript has been edited for your reading enjoyment.

The History of Batch and Pusher Furnaces (00:52)

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DOUG GLENN: Can you talk with us a little bit about the whole history of batch furnace versus pusher furnace?

MICHAEL MOUILLESEAUX:  Sure. And thank you for having me!

Interestingly enough, the pusher furnace — which we might say is a more complex piece of equipment than a batch integral quench furnace — preceded the batch furnace. Atmosphere pushers were around prior to World War II. I spoke with a number of folks in the industry and asked, “How could that possibly be, given the level of complexity?” Interestingly, pushers were available because the atmosphere was generated by a charcoal generator.

If you think back to pack carburizing, we used charcoal and some accelerator. You would put it in a closed container, you’d heat it up, and that’s how you carburized things before you had atmosphere furnaces. Utilizing that same concept, they generated an atmosphere, put it in a furnace, and pushers were the first ones to do that.

So, who were the folks who did that? They were AFC-Holcroft,  Surface Combustion, and Ipsen, all the usual characters and suspects there.

Pusher furnaces were available in single row and multiple row configurations.

They were heated with gas or electricity. I have to think that the earlier ones were heated by gas. Typically, they employed oil quenching. Although atmosphere cooling could be in the works, to find something of that vintage is very difficult. Maybe someone listening to this will weigh in and say, “Well, let me help you with that.”

The batch integral quench furnace is post World War II. What precipitated the development of the batch integral quench furnace was the development of the atmosphere generator, and that’s thanks to and around 1941 he actually published a book on atmosphere generators. I’m not sure where to find documentation of the patent he was granted for this generator. It might be interesting to discover. But again, Lindberg, Surface, Ipsen, — all these folks had these furnaces in the late 40s/early 50s.

When they started out, these furnaces were relatively small. The furnace might have had a tray that was 12 inches x 12 inches x 8 inches tall. You’d struggle to fit a hundred pounds into something like that.

But the batch furnace is by far the most popular atmosphere furnace that is available. You’ve got a variety of processing capabilities, which makes very flexible. There are a wide variety of sizes, even today; it can be heated with electricity or gas (we’ll talk about that a little bit later). You can have an oil quench furnace, you can use a polymer quench, and you can have a furnace where you atmosphere-cooled the load after it was processed in the primary furnace.

During this discussion, I’m going to use “batch,” “batch IQ,” and “batch integral quench” semi-interchangeably. So, if I say “batch” and I forget the “IQ” or if I say “batch integral quench” — these are all the same pieces of equipment. We have numerous names for the same thing.

DOUG GLENN:  Gotcha. You said the continuous furnace came first because the atmosphere was being created by burning charcoal inside the furnace, that created a carbon rich environment?

MICHAEL MOUILLESEAUX:  Actually, it was a generator that was pumped into the furnace.

DOUG GLENN:  Got it. That was confusing; I was wondering how they were burning charcoal inside a furnace.

MICHAEL MOUILLESEAUX:  Actually, it was explained to me that because the pusher furnace was so much larger, when you would open the doors to place or extract a load, the relative pressure drop of opening a door wasn’t that great. So, these primitive charcoal generators could accommodate that.

But in a batch furnace, arguably, the door is one wall of the furnace, and you couldn’t create a sufficient amount of pressure in the furnace. So, it had to wait until we had endothermic generators so that we could establish a furnace pressure higher than atmospheric pressure to make batch furnaces. It’s fascinating.

Basics of the Batch Furnace (05:41)

DOUG GLENN:  And as you said, it is probably the most popular furnace used today by many, many heat treaters. Let’s talk about batch furnaces, here we go.

MICHAEL MOUILLESEAUX:  Let’s look at the CAD drawing for a batch furnace. The batch furnace is primarily two components. You can see the hot zone — that is the furnace proper. It’s highly insulated, it has radiant tubes in it (so we can put atmosphere in the furnace), and the heating portion does not affect the atmosphere.

It is loaded through a vestibule, and the vestibule is pressurized as well. A load can go into a vestibule, you can close the door, you open the inner door, the load goes into the furnace, you can process it and then, as you can see, you can either quench the load or you can top cool the load.

CAD drawing of a batch furnace.

Common Processes in a Batch Furnace (06:31)

What kind of things can we do in an atmosphere furnace? Answer: operations that do not require quenching. We could stress relieve, we could subcritically anneal, we could supercritically anneal (so, above and below 1350/1400 Fahrenheit), and then we can normalize.

Normalizing is utilized for products like forgings or castings which are made at a very high temperature. You’ve got a number of structures in the component and what you want is a “normal” structure. You want a uniform structure throughout the part so that it can be machined.

Normalizing is typically performed at a high temperature, and it’s put into this top cooled/atmosphere cooled chamber. In the old days, that was termed “air cooling” — it was a rate equivalent if you just set it out in air. These top cooled chambers are somewhat insulated; they have cooling jackets that are in the side, and there is a fan in them so you can circulate the atmosphere through it so that you get uniform cooling throughout the load.

DOUG GLENN:  Michael, this isn’t considered high pressure gas quenching though, right?

MICHAEL MOUILLESEAUX:  Not even close.

In this animation, we have the load going into the furnace, the vestibule door closes, the furnace door opens, the furnace door closes, we perform whatever process we want, we extract the load out of the furnace, and it goes up into the top cool chamber. It’s then atmosphere cooled. When that is completed, we take the load out.

The time in the furnace could be four hours (plus or minus). The time up in the top cool chamber would probably be an hour or two. Once the load is extracted from the furnace and is put into the top cool chamber, and you reestablish pressure in the vestibule, you actually open the outer door, put another load in and start processing the next load while the initial load is being cooled.

Then, there are processes that require quenching. In degree of simplicity, first there is neutral hardening. Neutral hardening implies that the atmosphere in the furnace is neutral with the carbon content of the steel. So, for a 30-carbon steel, you’d want a 30-carbon atmosphere; for a 40-carbon steel, you’d want a 40-carbon atmosphere. The optimum is to neither enrich nor to deplete the surface carbon; you don’t want to change the chemistry. Typically, neutral-hardened parts are subsequently oil-quenched.

Then, there is carbonitriding. In carbonitriding, you have a high carbon atmosphere. You also introduce ammonia into the furnace. The ammonia dissociates right in the furnace. The carbon and nitrogen diffuse into the surface of the component. is held at a sufficient temperature to attain the case step that is desired, then, again, it is extracted into the vestibule, and it is quenched.

Carburizing would be another process. It’s similar to carbonitriding, except there is no ammonia. It’s only carbon that’s diffused into the surface of the part. Typically, parts that are carburized are oil-quenched.

There are, however, strategies and components where you would carburize, and then you would take the part and you would top cool it. You might take the part out of the furnace, and you may reorient it. So, parts that are distortion-critical may be oriented in one direction for carburizing, and then reoriented for hardening. You may carburize twice as many parts as you harden, so the hardening load would be half the size.

A low temperature process which is more complex is ferritic nitrocarburizing. That, typically, is performed around 1000°F. It is performed in batch furnaces, as well. Typical process cycles for that are going to be, at temperature, an hour and a half/two hours. That process can either be atmosphere cooled or it can be quenched; it depends on whether you’re looking for solid solution hardening or if you’re just looking for the nitrided layer and you’re not trying to do anything to the substrate.

I think that we have an animation for this.

Diagram of a batch system load.

Again, the load is loaded in the vestibule, the vestibule pressure is reestablished, the load is put into the furnace and, at that point, we perform whatever operation it is that we want to do of those previously described operations.

In the animation, you can see that the load is immersed in the quench. Following the quenching operation, it’s withdrawn from the furnace.

The total time for quenching is 10 minutes. When the load is brought up out of the oil, typically you let it sit there and allow it to drip so the precious quench oil you’ve paid your money for can go back into the quench. You’re washing and removing as little quenchant as is possible. In the heat treating operation, quenching is the single most critical portion of the operation.

A Note on Quenching (12:32)

MICHAEL MOUILLESEAUX:  When we’re carburizing, we have a portion of an hour where there would be no significant change in the case depth of the part. When we temper the parts, we have hours. You could temper it for three hours, you could temper it for five hours, and you’re not going to have a material change in what’s performed. In the quenching operation, the latitude that you have in quenching is in seconds.

Our typical protocol is that when a load is extracted from the furnace, from the time that the furnace door opens into the vestibule to when the load bottoms out at the bottom of the quench, in a batch furnace, must be 40 seconds maximum.

DOUG GLENN:  40?

MICHAEL MOUILLESEAUX:  40 seconds maximum. Typically, it’s done in 20 or 25 seconds. But it’s 40 seconds maximum. In a pusher, that number is 30 seconds maximum. This is something that you track; it’s data logged. If it exceeds that, at that point, you’re going to have to perform some inspection on that load that is much higher and much more intense had it not taken that much longer.

DOUG GLENN:  Can you, very briefly, explain why is it so important? I’m assuming it has something to do with martensite start and martensite finish and all that good stuff, but is there a layman’s way of explaining why the time to quench is so important?

MICHAEL MOUILLESEAUX:  Essentially, you want to have the load at a uniform temperature when it goes into the quenchant. If we have a significant variation in the low temperature, from the top to the bottom or the front to the back — even if the quenching operation is completely uniform — we’re going to have a variation in properties, variation in hardness, and certainly the probability of variation in core hardness.

For those things that are distortion-critical, it is absolutely important that the load has a similar temperature, across the load, top to bottom, inside to out, when it’s quenched.

Batch Furnace Systems (15:00)

MICHAEL MOUILLESEAUX: You typically don’t have a singular furnace, you have a system. What’s involved in a system?

What we’re looking at here is a relatively simple system. You have a loading operation. Obviously, the parts need to be loaded in baskets or fixtures. In some way, the load needs to be built. Typically, there is a station for that.

Diagram of a batch system furnace line.

Following  loading, it’s put into a preheat furnace. A preheat furnace is identical to what we would call a “temper” or a “draw.” You can thermally clean the parts by heating them up to 800°F. The other thing is that those that you put into that part are 20% the cost of getting those BTUs when you’re putting it in the high heat furnace, so it just makes economic sense. You’re cleaning the parts and you’re preheating the parts.

Then you’re going to put it into the furnace to perform the furnace operation; it’s either going to be top cooled or quenched. If it’s top cooled, you’re going to stop that top cooling operation at 300°F or 400°F. You’re going to put it in a cooling station and allow it to cool to room temperature. If you quench the part, if you’re modified marquenching it, it’s 250°F plus; if it’s quenched in regular oil, it could be 150–180°F.

The next operation is to wash the part. Typically, you don’t want to wash hot parts; you want to allow them to cool to room temperature. Sometimes you do, but more often than not, no.

Then there’s the wash station; you’re washing the parts. Then, you’re taking them out of the washing station and allowing them to drip. Then, you’re going to put them into a temper and you’re going to temper it for three to seven or eight hours, or something of that nature. You extract the load from the tempering furnace, put it in a cooling station, and allow it to cool down to room temperature so you can then unload it.

As you can see, the way that is accomplished is with this transfer cart. The transfer cart extracts the load from the loading table, pushes it into the preheat furnace, pulls it out of the preheat furnace, and pushes it into the batch furnace. Then the batch furnace quenches it, but when the outer vestibule door is opened, the transfer car must go in and get the load and pull it back onto the transfer car. The car pushes it across the aisle into the cooling station, picks it up, puts it in the wash, takes it out of the wash, puts it into the temper, takes it across the aisle when the tempering is finished, extracts it from the temper, and puts in on the cooling station. That transfer cart is an important piece of equipment.

But you can see there are a lot of moving parts to this. And you might ask, “Why would you do this?” Well again, because of the flexibility of the batch furnace. In this example, batch furnace #1 can be performing neutral hardening; batch furnace #2, at the same time, can be carbonitriding; the neutral hardening load finishes and the next load that goes in there could be annealed; after the load is annealed, then you could take a load and it could be normalized; then you could go back and you could neutral harden again.

So, if you don’t have multiple loads of the same thing, this offers a degree of flexibility that almost is not available in any other type of atmosphere processing equipment.

DOUG GLENN:  Right. And the fact that you have more than one furnace, more than one high heat furnace, more than one temper furnace, gives you almost (not exactly, but closer to) a continuous process even though each furnace is a “batch,” if you will.

MICHAEL MOUILLESEAUX:  Correct.

There are charge cars that are automated, so the charge car knows where the loading station is — it goes to that loading station. You could either have a human unload it or, in the highest degree of automation, it gets there and you have a PLC that is overseeing or supervising this entire operation, and it would know to take that load onto the cart, where to take it next, and what to do. It becomes a semi-automated method of heat treating.

Properties of the Pusher Furnace (19:53)

DOUG GLENN:  Let’s move on to the pusher furnace, the continuous system.

MICHAEL MOUILLESEAUX:  The pusher furnace, as you can see in this description, contains the vestibule, the furnace, and the quench. We’ve just broken it down into the pusher furnace proper.

Diagram of a pusher furnace.

Loads are put into the vestibule and then, sequentially, they move their way through the furnace. The first zone of the furnace would be what we would call the “preheat” and that’s where we bring the part up to temperature.

In this example, we’re showing boost-diffuse. This is an example where we would be carburizing. The first couple of positions would be a boost. We carburize at a higher carbon content because it diffuses more rapidly at the initial point of carburizing. Then, at the tail end of the carburizing cycle, we reduce the carbon content to what our desired surface carbon content would be.

An example might be: We would start out and we’d boost at 1% or 1, and the diffuse cycle would be .8% carbon. You do that for a couple of reasons:  You want to mitigate any retained austenite, so the bar is quenched at a higher carbon. You have opportunity for development of an unacceptable amount of retained austenite. At the extreme, you could start developing carbides and those become very difficult to re-solution. That’s the rationale for having a boost-diffuse. You do that same thing in a batch furnace; I just didn’t describe that as such.

And then the drop zone. We want to reduce the temperature prior to quenching so that we have very uniform quenching properties and if the components that we’re heat treating are distortion-critical, it’s very important as to what the temperature is prior to quenching.

So, we carburize at a high temperature (1700 Fahrenheit/1750 Fahrenheit), because the diffusion rate is much higher at that temperature. But we only want to quench these parts at 1500 or 1550 Fahrenheit because we want to have an absolute minimum amount of distortion.

Every hour, the vestibule door to the quench is going to open and you would cross-push that load into the quench vestibule, you would close the door, and just as the animation described in the batch furnace, that load would drop on an elevator into the quench.

Now that we’ve done that, we have an opening. That last position is open. So, we go to the vestibule on the front end of the furnace, we open that door, we put a load in there, we close the door, and we’ll close it long enough for us to reestablish the furnace pressure (no more than 3–5 minutes). Once we’ve established furnace pressure, we can open the door between the vestibule and the first preheat zone, and then to the left of the vestibule is going to be a mechanism for pushing these loads, hence the term “pusher”? Could it be hydraulic? It could. Could be mechanical? Both are employed.

What you’re doing is pushing it further by one position. Because the last position is open, the second to the last load progresses into the last position, the load that you put in the vestibule goes into the first position.

DOUG GLENN:  A couple quick questions: Really, the sequence starts with the load being pushed out of the furnace into the quench vestibule and then dropped in. That leaves that last spot open in the furnace. Then everything else starts and we push it all down, correct?

MICHAEL MOUILLESEAUX:  You are correct.

DOUG GLENN: In this illustration, it looks like there are divisions between each of these different locations. In the preheat, it looks like there are three or four; in the boost-diffuse, it looks like you’ve got two or three. Those aren’t actually physical barriers; You’re just showing where the load would progress to, correct?

MICHAEL MOUILLESEAUX:  You are correct.

DOUG GLENN:  Are there any chamber divisions in a pusher furnace?

MICHAEL MOUILLESEAUX:  In a pusher furnace, you have arches above the load and that helps to compartmentalize. The key word there is “helps.” You don’t have an actual compartmentalization.

Let’s say that we want to perform a carburize at 1700°F in this furnace. If you had three preheats, you may want to perform these somewhere below the 1700°F with the last position being at 1700°F so that the load that goes into the carburizing zone is at temperature and it’s ready to accept carbon.

The carburizing zone would all be at the same temperature, but you have to understand these parts are all at 1700°F and we want to quench it at 1550°F, let’s say. We have two positions that we are going to allow the load to cool down to 1550°F.

So, would you want a zone arch there? I think that you would, yes. Would you want a fan in those zones? If you had a fan in those zones, and you are circulating the atmosphere through those loads, you have a better opportunity to attain a uniform temperature from the top to the bottom of the load than if you did not.

Diagram of a pusher furnace system.

MICHAEL MOUILLESEAUX:  Here’s a pusher furnace system. Typically, but not always, pushers are put into a system because you have multiple operations that you must perform. This example is in a U-shape. The loading and unloading are next to each other. This could be a linear layout.

In another life, I worked for a company in Syracuse, New York that had 14 furnaces that were all linearly oriented. So, the person on the front of the furnace did one thing, the person on the back of the furnace did another thing, and they really didn’t communicate.

I, personally, am not a fan of that. I like this operation because you can have one or two people performing the loading and unloading operation, and you could have a furnace operator who would be responsible for the overall control of this piece of equipment.

You can see that we have four loads here that are in whatever way we chose to fixture them — baskets, fixtures, or whatever it might be. We’ve put a couple of parts in a preheat so we could perform that same cleaning that we talked about in preheating the load with low-cost BTUs. The preheat then goes into the vestibule, the loads progress down through the furnace as we described, you get to the end and that load is quenched. When the load comes out of the quench, just as in the batch furnace, it’s going to be 150–200°F plus. We want that to cool down to room temperature because the next operation is going to be washing.

After the load to cools down to room temperature, we then put it in the wash. Following the wash operation, you might have a drip station. So, whatever it was that you have washed off in the water, you don’t want that to go into the temper. Following the drip station, then you would go into the tempering furnace. Here we’re showing three positions; it could be three, it could be six, it could be nine. This is just an example.

Following the tempering operation, we would go out and in that first position, you might have a blower underneath and you would be circulating, room temperature air through it up into a duct work ahead and that’s how you would cool the room down to low temperature. Those loads would progress down that unload station so, at the very end, you are unloading the parts, perhaps for a subsequent shop blast cleaning operation or development of rust preventative or maybe they’re just put back into the customer’s container.

In a captive operation, they might go into a container where the parts would go on to a subsequent grinding or hard-turning operation.

This can be automated. Here you can see that the loads progress into the preheat, they progress through the furnace, they go into the quench, and they’re put into the wash. It’s quick.

Diagram of a pusher furnace load.

DOUG GLENN:  Yes. It doesn’t happen this fast in real life, everyone!

MICHAEL MOUILLESEAUX:  In the temper, the load exits the temper and goes into the unloading station. The point of this is to show that it progresses through the furnace.

The advantage is that you have relatively small loads that you’re processing, there is a very consistent process in the pusher furnace, and what you’re on for is that however you’ve designed this system, every load goes through every station. You don’t have an opportunity to easily extract a load as quenched and not wash it. It can be done. You could have a furnace designed to do that, but it’s not easy. After it’s washed, as you can see in this animation, typically it’s going to progress into the temper. Could you design a station that would allow you to offload it? You could, but normally that’s not how that’s done.

So, the load progresses through the temper and then you go in to where it is then subsequently unloaded.

If the batch furnace’s strong suit is the fact that it is extremely flexible — particularly in a “systemic” way — the pusher furnace’s strength is its productivity. °

DOUG GLENN:  Yes, higher levels of productivity. But you’ve got to have, if not the same product, at least the same process on whatever it is you’re putting in there.

MICHAEL MOUILLESEAUX:  Bingo. That’s exactly what you must have there, yes.

About the expert: Michael Mouilleseaux is general manager at Erie Steel LTD. Mike has been at Erie Steel in Toledo, OH since 2006 with previous metallurgical experience at New Process Gear in Syracuse, NY and as the Director of Technology in Marketing at FPM Heat Treating LLC in Elk Grove, IL. Having graduated from the University of Michigan with a degree in Metallurgical Engineering, Mike has proved his expertise in the field of heat treat, co-presenting at the 2019 Heat Treat show and currently serving on the Board of Trustees at the Metal Treating Institute.

Contact: mmouilleseaux@erie.com

To find other Heat Treat Radio episodes, go to www.heattreattoday.com/radio.

Search heat treat equipment and service providers on Heat Treat Buyers Guide.com  

Heat Treat Radio #102: Lunch & Learn, Batch IQ vs. Continuous Pusher, Part 1 – Heat Treat Today Read More »

Sustainability Insights: Reducing the Carbon Footprint of Your Heat Treating Operations

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OC

Renewable fuels or hydrogen have entered the scene as these are fuels that contain little or no carbon. So, no carbon in the fuel means no CO2! These fuels present an excellent opportunity to significantly reduce carbon.

This Sustainability Insight article was composed by Brian Kelly, manager of Application Engineering at Honeywell Smart Energy and Thermal Solutions (SETS) and president of the Industrial Heating Equipment Association. It can be found in Heat Treat Today's August 2023 Automotive Heat Treating print edition.

The need to understand the impact of greenhouse gases (GHGs), especially carbon-based emissions, on climate change is gaining much more interest recently from organizations that have industrial heating processes. Most industrial heating processes are fueled by carbon-based fossil fuels such as natural gas, propane, fuel oil, diesel, or coal. In basic terms, if you have combustion processes in your organization, you are emitting carbon (CO2). Impacts on climate change due to these carbon emissions have prompted government and corporate actions to reduce carbon. These actions are creating unique new opportunities for more sustainable and lower carbon process heating methods. In this article, we will focus on ways to reduce carbon in typical fossil fuel fired heat treat thermal processes. First step: Figure out where you are today. Do you know?

Assess Your Carbon Footprint

Brian Kelly
Image Source: Honeywell

More and more companies are interested in understanding their GHG/carbon footprints, so they can determine what processes are their biggest CO2 offenders, and on what assets to focus on in order to have the largest impact on reducing carbon. Whether your thermal processes are being heated by fossil fuels (typically natural gas) or electrically, each will have a carbon footprint. Fuel gases are being burned to provide the heat and they produce CO2 as a result. Most electrical power is currently being produced by fossil fuels, so electricity will have a CO2 amount associated per kW. What can be done to burn less fuel in your furnaces or ovens, which directly relates to reducing CO2?

Tune Your Combustion Systems

Radiant tube burner with plug recuperator in a U-tube
Source: Honeywell

Over time combustion systems drift and are not at their optimum air/fuel ratio. By simply tuning your burner system on a routine basis, you can fire at the optimum air/fuel ratio for the process and be as efficient as possible. For example, if a furnace is firing on natural gas, operating at 1800°F, and currently operating at 35% excess air, tuning your burners to 10% excess air could save approximately 15% in fuel consumed. The fuel costs will be reduced, and the resulting CO2 will be reduced by that same percentage!

Maintain Your Furnaces/Ovens

A simple review of your furnaces or ovens to observe any hot spots, openings, faulty seals, or refractory issues will identify areas that will cause your systems to operate less efficiently, thus using more energy. Repairing these problems and consistently maintaining them will have the systems running more efficiently and producing as little carbon as possible.

Upgrade Your Firing Systems To Be More Efficient

Direct fired self-recuperative burner
Source: Honeywell

Incorporating preheated combustion air into furnace combustion systems can significantly reduce fuel consumption and therefore the resulting carbon. The two main methods for introducing hot air into a combustion system are recuperation and regeneration. The most popular air preheating method in heat treating applications is recuperation. For a direct fired furnace, this can take the form of a central stack recuperator or self-recuperative burners. Self-recuperative burners have grown in popularity in recent years as they get rid of the need for hot air piping, recuperator maintenance, and most are often pulse fired, which will not only maximize efficiency but also promote temperature uniformity in the furnace and often be lower in emissions. For indirect fired (radiant tube) furnaces, you can apply/add a plug recuperator to an existing cold air fired burner in a furnace that has a U or W-tube to preheat the combustion air or apply self- recuperative burners installed in Single-Ended Radiant (SER) tubes to optimize your furnace firing. The SER tube material can be upgraded to silicon carbide which allows higher temperatures/flux rates that can provide the opportunity to increase throughput and reduce the possible CO2 per cycle.

Combustion air preheating can result in energy savings of close to 25% over cold air combustion.

Renewable Fuels/Hydrogen

Renewable fuels or hydrogen have entered the scene as these are fuels that contain little or no carbon. So, no carbon in the fuel means no CO2! These fuels present an excellent opportunity to significantly reduce carbon. Hydrogen has been of interest because it has the opportunity to be a zero-carbon industrial fuel when produced with renewable energy such as wind, solar, hydro, or nuclear power. As these methods become more prevalent, they bring down the price of hydrogen and increase its availability. This could be a significant driver to greatly reduce CO2 in thermal processes. These topics as well as many others are being discussed in an on-going Sustainability Webinar series hosted by IHEA to provide education and insight into the ever-changing sustainability landscape.

Single ended self-recuperative radiant tube burner
Source: Honeywell

About the author:

Brian Kelly is manager of Application Engineering for Honeywell Smart Energy and Thermal Solutions (SETS) and current president of the Industrial Heating Equipment Association (IHEA).

Find heat treating products and services when you search on Heat Treat Buyers Guide.com

Sustainability Insights: Reducing the Carbon Footprint of Your Heat Treating Operations Read More »

Heat Treat Radio #97: Lunch & Learn, Ovens vs. Atmosphere Furnaces

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Are you trying to figure out what heat treat equipment investments you need to make in-house and what is better being outsourced? This conversation marks the continuation of Lunch & Learn, a Heat Treat Radio podcast series where an expert in the industry breaks down a heat treat fundamental with Doug Glenn, publisher of Heat Treat Today and host of the podcast, and the Heat Treat Today team. This conversation with Dan Herring, The Heat Treat Doctor®, zeros in on heat treat ovens versus atmosphere furnaces.

Below, you can watch the video, listen to the podcast by clicking on the audio play button, or read an edited transcript.


The following transcript has been edited for your reading enjoyment.

Contact us with your Reader Feedback!

Doug Glenn: Welcome everybody. This is another Lunch & Learn event with the staff of Heat Treat Today and the illustrious Dan Herring, The Heat Treat Doctor®. Dan, we’re always very happy to spend some time with you.

We are here to learn a little bit about some basics about heat treat equipment, mostly ovens, air and atmosphere furnaces, and possibly vacuum furnaces.

Dan Herring: It’s always a pleasure, Doug, and hello everybody.

It is an exciting topic for me because I happen to love heat treat equipment. Let’s start with industrial ovens.

All About Ovens (01:42)

Years ago, industrial ovens were very easy to differentiate from furnaces. I’m going to give you my understanding of the differences between ovens and furnaces, and then talk a little bit about some general characteristics of all types of heat-treating equipment.

Ovens are typically designed for low-temperature operation. When I talk about low-temperature operation, years ago the definition was “under 1,000° F.” That definition has changed over the years. We now usually say either under 1250°F or under 1400°F. All of that being said, there are some ovens that run all the way up to 1750°F. But what we’re going to concentrate on are, what I call, “the classic temperature designations for ovens.”

Universal oven from Grieve
Source: Grieve

First of all, ovens are typically rated at 500°F, 750°F, 1000°F, or 1250°F. If you see a heat treat operation that’s running — certainly under 1450°F — but even under 1250°F, it may be being done in either an oven or a furnace.

Let’s talk about some of the distinguishing characteristics of ovens, so everyone gets a feel for it.

Ovens always have a circulating fan. If you see a piece of equipment without a circulating fan, it can’t be an oven. At these low temperatures, the heat transfer — in other words, how you heat a part — is done with hot air or circulating hot air. So, ovens always have fans.

In most cases — and years ago in all cases, but today in most cases — ovens are metal lined. If you were to open the door of an oven and look in, and you see a metal-lined chamber, that would typically be an oven.

The fan and the type of insulation or lining that’s used is very characteristic for distinguishing features of ovens.

Today, however, there are ovens that use fiber insulation and even some ovens that have refractory-insulated firebricks, refractory in them. The lines are a little bit blurred, but typically you can distinguish them by the fact that they have fans and are metal lined.

Ovens come in either “batch” or “continuous” styles. If the workload inside the unit, the piece of equipment, is not moving, we call that a batch style furnace. If the workload is somehow being transferred through the unit, we call that a continuous furnace. Ovens and furnaces can be both batch and continuous.

Ovens and furnaces can both be either electrically heated or gas fired.

One of the distinguishing characteristics of ovens is that if they are gas fired, they are, what we call, “indirectly heated.” This means your burner, your combustion burner, is firing into a closed-ended tube, a radiant tube, as we call it, so that the products of combustion do not “intermix.” They do not create an atmosphere that’s used inside the oven. In fact, the majority of ovens run with an air atmosphere – that’s another distinguishing feature.

However, there are ovens that can run inert gases. Those ovens typically have continuously welded shells. Again, that’s an exception rather than a rule, but there are ovens of that type.

There are also vacuum ovens out there. We actually have an oven chamber on which we can pull a vacuum. They are less common than their cousins, the air ovens, but they are out there in industry.

We have the method of heating and type of movement of the hearth or movement of the load that typically is consistent between ovens and furnaces.

What I’d like to do is just show everybody a couple of pictures of some very typical, what I’m going to call, “batch ovens.”

Doug Glenn: Because ovens are typically low temperature, you’re able to have metal on the inside, right? If it was higher temperature, you’d start experiencing warping. Is that the primary reason why you tend to see metal in an oven and not in a furnace?

Dan Herring: That’s correct, Doug.

"Metal lined oven"
Source: Dan Herring

The lining can be made of steel: it can be made of “aluminized’ steel,” it can be made of zinc-gripped steel (those are just coatings), it can be just steel, and they can be made of stainless steel (a 300 series stainless steel). That’s why you have the different temperature ratings and the different types of materials that this metal interior can be made from.

If you open the door of a metal-lined oven or an oven that had a metal lining, you would typically see what’s pictured here.

"Double door shelf oven"
Source: Dan Herring

Ovens can be very small or they can be very, very large. What you’re seeing on the screen is a “double door shelf” oven.

It is very similar to your ovens at home. You open the door, there are shelves, and you can put trays on the various shelves. These can be small, to the point where, sometimes, they can sit on a benchtop. Sometimes they can be very, very large and be floor-mounted, as this one is.

This is an example of a batch oven, something that you would load, and the load stays stationary within the oven. Then, when you’re ready, you unload it.

Ovens can come in slightly larger sizes.

"A larger horizontal oven . . . . a fan system sitting at back"
Source: Dan Herring

That’s a picture of a larger, horizontal oven. The door on this particular oven is closed shut, but you can see the fan system — that’s that yellow arrangement that’s sitting in back of this particular oven.

There is another style of oven.

"Walk in oven"
Source: Dan Herring

We call this a “walk-in” oven — very creative, because you can walk into it. I’ve seen batch ovens that are very, very small and very, very large — ones that will fit on a benchtop and ones that are a hundred feet long.

You can see the heat source on the right hand side. Remember, whether it’s electrically heated with sheathed elements or if it’s gas-fired with, typically, an atmospheric-type burner, again, you have circulating air past either the electric elements or circulating air past the tube into which the burner is firing. You’re relying on convection — or moving hot air — to transfer that heat energy to your load.

These are just some different styles of different types of ovens, so everyone can see them. I don’t want to take too long, but I’ll show you another picture of one.

"Industrial oven . . . . typical oven in typical heat treat shop"
Source: Dan Herring

This is an industrial oven. You can see the fan; it has a yellow safety cover on it. You can see the fan mounted on top, and this is a typical oven that you’d find at a typical heat treat shop.

Ovens have the characteristics that I pointed out. I’ll bring up one more picture which you might find interesting.

"Monorail conveyor oven . . . . with u-shaped radiant tubes"
Source: Dan Herring

Since there are a variety of oven shapes and sizes, this happens to be a monorail conveyer oven. What you’re looking at is the inside of the oven. You’ll notice that in the ceiling there are hooks. The loads are actually placed on the hooks and sent through or pulled through the oven. This happens to be a gas-fired unit, and you can see that it has U-shaped radiant tubes into which you’re firing.

This oven is fiber-lined and not metallic-lined. You’ll also notice that because you see different colors of the tubes, this particular shot was taken and you destroyed the uniformity of temperature within the oven. Usually, they’re very tight.

Ovens are typically in the ±10°F range for temperature uniformity, sometimes in the ±5°F range.

Those are basically some pictures of ovens, whether they be batch or continuous, for everyone to see and think about, from that standpoint.

Q&A on Ovens (16:58)

Bethany Leone: What is the reason for the increase in temperature range for what classifies an oven?

Dan Herring: The main reason is the materials of construction have gotten better, so we’re able to withstand higher temperatures. But going to some of these temperature ratings, one of the things that heat treaters look at is if I have a process that runs at 1,000°F or 970°F (let’s take an aluminum heat treat example where a process is running at 970°F), I could run that in an oven rated at 1,000°F but I’m right at the upper limit of my temperature.

It's much better to buy an oven rated at 1250°F and then run a process such as 970°F where I have a margin of safety of the construction of the oven, so the oven will last longer.

However, industrial ovens tend to last forever. I’m the only person on this call old enough to have seen some of these ovens retired. It’s not unusual that an oven lasts 40 or 50, or sometimes 60 years.

Ovens are used in the heat treating industry for processes such as tempering, stress relief, for aluminum solution heat treatment, aluminum aging operations, and to do some precipitation hardening operations that run in these temperature ranges. Ovens are also commonly found in plating houses where you’re doing a hydrogen bake-out operation after plating. You also do various curing of epoxies and rubbers and things of this nature in ovens.

There are a variety of applications. Ovens are used also for drying of components. Ovens are used for drying of workloads, these days, prior to putting in your heat treating furnace. Many times, our washers are inefficient when it comes to drying. You take a wet load out of a washer and put it into a low-temperature oven, maybe running between 300°F and 750°F. Consequently, you both dry the washing solution off the parts and you even preheat the load prior to putting it into the furnace.

Heat Treat Today team enjoying a Lunch & Learn session

Doug Glenn: One of the things I’ve always distinguished ovens by is the term “panel construction” opposed to “beam construction.”

If you can imagine a sheet of metal, some insulation, and another sheet of metal – that’s a panel. It’s got enough insulation in it because the temperatures are not excessively high, but you really only need those three layers. You take those panels, you put them in a square or whatever, put a lid on it, put a bottom on it, and you basically have an oven, right?

Where furnaces are not typically constructed that way; they are constructed more where you have a support structure on the outside and then a heavy metal plate and then you build insulation on the inside of that. It doesn’t even need to have metal on the inside — it can be brick or another type of insulation.

Many people claim — and I’m sure there are some very strong ovens — that the oven construction is not as hardy, not as rugged. That’s one other minor distinction, but the main distinction is ovens tend to be lower temperature.

Dan Herring: Yes, that’s very correct, Doug. In panel-type construction, there is typically mineral wool insulation in between the two panel sheets; and it’s rated for obviously very low temperature.

There are, what we call, “light duty” and “heavy duty” ovens. Heavy duty ovens have that plate and support structure — those I-beams or channels — supporting the external structure.

Doug Glenn: You reminded me of something, Dan: We talk about ratings – oven ratings, furnace ratings, and that type of stuff. That’s pretty important and we haven’t really discussed that much. But if a furnace is rated at a certain temperature, you do not want to take that furnace beyond that temperature because there are real safety issues here.

There was one picture that Dan showed where you could see the metal interior, and there was like a gasket, if you will, around the whole opening. That gasket is only rated to go up so high in temperature. If you go over that temperature, you’d end up deteriorating that gasket, if you will. It could cause a fire, it could cause a leak, it could cause all kinds of issues. And that’s only one example.

One other one he mentioned was fans. There is almost always a fan in an oven, and if you take the temperature of that oven over its rated temperature, all of sudden the bearings in that fan start . . . well, who knows what’s going to happen.

You always want to know the rating of your oven and furnace, and don’t push the rating.

Dan Herring: Yes, if you exceed temperature in an oven, typically the fan starts to make a lot of noise and you know you’re in trouble. You only do that once. But those are excellent points, Doug, absolutely.

So, the world of ovens -- although it’s they’re an integral part of heat treating -- are a “beast unto themselves,” as I like to say. Construction is a factor, and other things.

All About Atmosphere Furnaces (24:50)

Furnaces, interestingly enough, can be rated both to very, very low temperatures all the way up to very, very high temperatures. In other words, you can see industrial furnaces running at 250° or 300°F or 500°F or 1000°F, — at typical temperatures that you would associate with oven construction — but you can also see furnaces running at 1700°F, 1800°F, 2400, 2500, 3200°F. There are some very interesting furnaces out there.

But furnaces, although they can run in air — and there are a number of furnaces that do — they typically run some type of either inert or combustible atmosphere inside them. Furnaces typically have an atmosphere, and they do not always have a fan. The rule is the higher you go up in temperature, the more any moving part inside your furnace becomes a maintenance issue. Many times, furnaces do not have fans in them.

They can be electrically heated. They could also be gas-fired. In this particular case, they can either be direct-fired or the burners are actually firing into the chamber; and the products of combustion become your atmosphere. They could be indirect-fired — like we discussed with ovens — into a radiant tube as a source of heat or energy.

Furnaces typically have plate construction. It’s typically continuous welded, they have channels or I-beams surrounding the structure to make it rigid, insulation is put on the inside. Traditionally it’s been insulating firebrick, but in what I’ll call recent years (20 years or so) fiber insulations have come about, and they perform very, very well.

Fiber insulations reduce the overall weight. They have advantages and disadvantages. A refractory-lined unit can have a great thermal mass due to the storage of heat inside the insulation, so when you put a cold load into a brick-lined furnace, the heat from the lining will help heat the load up quickly.

You don’t have quite the same heat storage in a fiber insulation. At the same time, when you go to cool a furnace, a fiber-lined furnace will cool very quickly as opposed to a refractory furnace which cools a lot slower.

Again, furnaces can be batch style, they can be continuous style, they can be fairly small in size. The smallest ones that I’ve seen, typically, are about the size of a loaf of bread. Conversely, you have furnaces that are so large you can drive several vehicles or other things inside of them.

A 14-foot long car bottom furnace
Source: Solar Atmospheres of Western PA

As a result of that, what distinguishes them are typically their temperature rating and the fact that they use an atmosphere. Some of the atmospheres are: air, nitrogen, argon. I’ve seen them run endothermic gas and exothermic gas which are combustible atmospheres, or methanol or nitrogen-methanol which are also combustible atmospheres; they can run steam as an atmosphere. I’ve seen furnaces running sulfur dioxide or carbon monoxide or carbon dioxide as atmospheres. The type of atmosphere that is used in an industrial furnace can be quite varied.

We have several different furnace categories that typically are talked about: Batch style furnaces are configured as box furnaces. They are very similar in shape to the ovens that we looked at. Pit style furnaces are where you have a cylindrical furnace that actually is quite tall and fits down, usually, into a pit that’s dug in the factory floor.

You also have mechanized box furnaces. Those, typically, today, would be called integral quench furnaces or sometimes batch quench furnaces or “IQs.” There are belt style furnaces, gantry, tip-up, and car-bottom furnaces. There is a wide variety of batch style furnaces, all of which have the characteristic that once you put the load into the chamber, it sits there until it’s been processed and until it's time for you to remove it.

The exception is in an integral quench furnace. You push the load typically either directly into the heating chamber or into a quench vestibule and then into a heating chamber; you heat it in one chamber, you transfer it out, and you quench it into another chamber.

Those are some of the distinguishing features of batch style equipment. I’ve got a couple of pictures here that you might find interesting.

"A box furnace . . . . sometimes difficult by sight alone to tell an oven or box furnace"
Source: Dan Herring

Here is a “box furnace.” You might say, “Oh, my gosh, it looks like an oven!” I see a fan on top, and it’s a box style. From the outside, it’s hard to tell whether it’s an oven or a furnace.

When you look at this unit, you might see that it’s made of plate construction. It would be difficult to tell if this unit were a heavy-duty oven or furnace unless you, of course, opened the door and looked inside. You would typically see either fiber insulation or insulating firebrick in these types of units.

Sometimes, just by sight alone, it’s very difficult to tell if it’s an oven or a furnace. But there are other telltale signs.

"A box furnace with retort"
Source: Dan Herring

Now, this is a box furnace with a retort inside it. The workload is placed, in this case, into a metal container that’s physically moved on a dolly into the furnace itself. This is what we call a box furnace with a retort.

The process takes place inside the retort. You’ll notice that there’s a flow-meter panel there, of different gases, that are introduced directly into the retort. This style of furnace is very interesting because the furnace itself, outside the retort, is simply heated in air. It’s a relatively inexpensive construction. Also, when the time comes that the process is finished, usually you can remove the retort and introduce or put a second retort into the furnace while the first retort is cooling outside the furnace. It lends to increased production, from that standpoint.

But this is typically a box furnace; it looks like a big box. The shell does not have to be continuously welded because the process takes place inside the retort. You might be able to see, just past the dolly, there is a dark color and that is the blackish retort that’s actually being put in.

Doug Glenn: I think the reasoning of the retort is to protect the airtight atmosphere, right?

Dan Herring: That’s correct, Doug. The idea is the fact that it’s an effective use of your atmosphere.

The other thing you can do with a box furnace with a retort is you can pull a vacuum on the retort. As a result of this, you can actually have a “hot wall” vacuum furnace. That is what is defined as a hot wall vacuum.

The next type of atmosphere furnace we’re going to look at is pretty distinct or pretty unique: This is a pit style furnace.

"A pit style furnace . . . . there is probably 4X as much furnace below the floor"
Source: Dan Herring

What you’re seeing here is only that portion of the furnace that is above the floor. There is probably four times as much furnace below the floor as there is above. OSHA has certain requirements: there must be 42 inches above the floor not to have a railing or a security system around the pit furnace, because you don’t want to accidentally trip and fall into a furnace at 1800°F. We don’t want to say, “Doug was a great guy, but the last time I saw him . . .”

In this particular case, there is a fan which is mounted in the cover of this pit style furnace. Most pit furnaces are cylindrical in design; however, I have seen them rectangular in design. Some of them have a retort inside them; unlike the picture of the box furnace with the retort, the retort is typically not removable, in this case. Of course, there are exceptions. There are nitriding furnaces that have removable retorts.

I think this is a very distinctive design. If you walked into a heat treat shop, you’d say, “You know, that’s either a box furnace or an oven.” Or, if you looked at this style of furnace, you can clearly see it’s a pit furnace, or what we call a pit furnace.

Two other examples, one of which is just to give you an idea of what we call an “integral quench furnace.” I think this is a good example of one:

"An integral quench furnace, an in-out furnace"
Source: Dan Herring

They’re made by a number of manufacturers. The integral quench furnace is probably one of the more common furnaces you’re able to see. It has, in this case, an oil quench tank in front and a heating chamber behind.

This would be an “in-out” furnace; the workload goes in the front door and comes out the front door. But once the workload is loaded into an area over the quench tank (which we call the vestibule), an inner door will open. The load will transfer into the heating chamber in back. That inner door will close, the workload will be heated and either brought up to austenitizing temperature, carburized or carbonitrided, the inner door will then open, the load will be transferred onto an elevator and either lowered down into a quench tank (typically oil) or, if the unit is equipped with a top cool, the load is brought up into the top cool chamber to slowly cool.

These styles of furnaces do processes like hardening, carburizing, carbonitriding, annealing, and normalizing. You typically don’t do stress relief in them, but I’m sure people have. These furnaces have a wide variety of uses and are quite popular. Again, the style is very distinctive.

They typically run a combustible atmosphere, and you can see some of that atmosphere burning out at the front door area.

There are also, what we call, continuous furnaces or continuous atmosphere furnaces. They are furnaces where you have a workload and somehow the workload is moving through the furnace. A good example of that is a mesh belt conveyor furnace.

There are also what we call incline conveyor, or humpback-style furnaces. The mesh belts are sometimes replaced, if the loads are very heavy, with a cast belt: a cast link belt furnace. The furnaces can sometimes look like a donut, or cylindrical, where the hearth rotates around. We put the workload in, it rotates around, and either comes out the same door or comes out a second door.

A lot of times, rotary hearth furnaces have a press quench associated with them. You’re heating a part, or reheating a part in some cases, getting it up to temperature, removing it, and putting it into a press that comes down and tries to quench it by holding it so that you reduce the distortion.

There are other styles of furnaces typical of the “faster” industry which are rotary drums. Those furnaces you would load parts into, and you have an incline drum (typically, they’re inclined) with flights inside it. The parts tumble from flight to flight as they go through the furnace, and then usually dump at the end of the furnace into a quench tank.

For very heavy loads, there are what we call walking beam furnaces where you put a workload into the furnace. A beam lifts it, moves it forward, and drops it back down. Walking beam furnaces can handle tremendous weights; 10,000 to 100,000 lbs in a walking beam is not unusual. Any of the other furnaces we’re looking at wouldn’t have nearly that type of capacity.

There are some other fun furnaces: shaker furnaces. How would you like to work in a plant where the furnace floor is continuously vibrating, usually with a pneumatic cylinder so it makes a tremendous rattle, all 8 or 10 hours of your shift? That and a bottle of Excedrin will help you in the evening.

As a last example, the monorail type furnaces where we saw that you hang parts on hooks. The hooks go through the furnace and heat the parts.

I’ll show you just a couple of examples of those. These are not designed to cover all the styles of furnaces but this one you might find interesting.        

"A humpback style furnace"
Source: Dan Herring

This is a typical continuous furnace. This would be a humpback style furnace where the parts actually go up an incline to a horizontal chamber and then go down the other side and come out the other end. These furnaces typically use atmospheres like hydrogen, which is lighter than air and takes advantage of the fact that hydrogen will stay up inside the chamber and not migrate (or at least not a lot of it) to floor level.

Atmosphere Furnaces Q&A (47:30)

Evelyn Thompson: Are the inclined sections of the furnace heated? Why do the parts need to go up an incline? Just to get to the heated part of the furnace?

Dan Herring: If you’re using an atmosphere such as hydrogen, it’s much lighter than air. If you had a horizontal furnace just at, let’s say, 42 inches in height running through horizontally, the hydrogen inside the furnace would tend to wind up being at the top of the chamber or the top of the furnace, whereas the parts are running beneath it! So, the benefit of hydrogen is lost because the parts are down here, and the hydrogen tends to be up here.

By using an incline conveyor, once you go up the incline, the hydrogen covers the entire chamber and therefore the parts are exposed to the atmosphere.

I did a study a few years ago: About 5–6% of the types of mesh belt furnaces in industry are actually this incline conveyor type.

Another good example is the fact that people like to run stainless steel cookware. I’ve seen pots, pans, sinks, etc. Sometimes you need a door opening of 20 or 24 inches high to allow a sink body to pass into it. Well, if that were a conventional, horizontal furnace, you’re limited to, perhaps, 9 to maybe, at most, 12 inches of height.

Typically you never want to go that high, if you can help it. 4–6 inches would be typical. So, there would be a tremendous safety hazard, among other things, to try to run a door opening that’s 24 inches high. But in an incline furnace, the height of the door can be 20, 24, 36 inches high. The chamber is at an 11° angle, and you must get up to the heat zone, but they run very safely at that.

Karen Gantzer: Could you explain what a retort is?

Dan Herring: Think of a retort — there are two types — but think of one as a sealed can, a can with a lid you can open, put parts in and then put the lid back on. The retort we saw in that box style furnace is that type. It is a sealed container. We typically call that a retort.

Now, in that pit furnace we saw, there could be a retort inside that one and they could be sealed containers, but typically they’re just open sides, that are made of alloy. Sometimes we call those “retorts” as opposed to “muffles” or “shrouds,” in another case. Muffles don’t have to be a sealed container, but they typically are. That’s the way to think of them.

Karen Gantzer: Thank you, Dan, I appreciate that.

Bethany Leone: Dan, thank you for joining us. It was really a valuable time.

Dan Herring: Well thank you, my pleasure.

For more information:

www.heat-treat-doctor

dherring@heat-treat-doctor.com

To find other Heat Treat Radio episodes, go to www.heattreattoday.com/radio.

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Heat Treat Radio #97: Lunch & Learn, Ovens vs. Atmosphere Furnaces Read More »

On-Site Hydrogen Generation Essential for Riverhawk Company’s Heat Treat Operations

/ ATMOSPHERE AIR FURNACES TECHNICAL CONTENT, ATMOSPHERE GENERATORS TECHNICAL CONTENT, BULK GASES & SYSTEMS TECHNICAL CONTENT, FEATURED NEWS, MANUFACTURING HEAT TREAT

OC

For heat treat operations, use of hydrogen comes with questions about price-point, safety, and storage or delivery. Read this case study to learn how a manufacturer with in-house heat treat, Riverhawk Company, contended with these questions and decided to meet stringent production requirements for pivot bearings by leveraging on-site hydrogen and a hydrogen furnace.

This original content article was written by Marie Pompili, a freelance writer, for Heat Treat Today's May 2023 Sustainable Heat Treat Technologies print edition.

For companies using hydrogen furnaces for heat treating operations, questions always surface surrounding the provision of the necessary hydrogen. Should we have it delivered in cylinders? Do we have the room outdoors for a large storage tank? Can we generate it ourselves? For Randy Gorman, maintenance supervisor at Riverhawk Company, the overriding question is always, “How do we handle hydrogen safely?” The ultimate solution the company chose was the installation of an on-site hydrogen generator. How and why the in-house heat treater came to that conclusion is an interesting story.

Making a History

Riverhawk staff (L to R): Spencer Roose, Flex Pivots Manager; Randy Gorman, Maintenance Supervisor; and Josh Suppa, Pivot Department Engineer
Source: Nel Hydrogen

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Located in New Hartford, NY, Riverhawk Company was established in 1993 as a value-added provider of hydraulic tooling. The company quickly grew from a “buy and assemble” operation to a manufacturer with 14 CNC machine tools, 21 conventional machines, and all the necessary peripheral devices, tools, and software. Through a period of smart acquisitions and the development of new product lines, Riverhawk became one of the leading manufacturers of tensioners, powertrain couplings, and accessories for the turbomachinery industry; the instrumentation product line of legacy torque and vibrations measuring instruments; and the Free- Flex® pivot bearings, which are very well known in high performance industry sectors.

Pivot Bearing Line Requires Improved Heat Treat Abilities

The Free-Flex® pivot bearing line is the focus in this heat treat/hydrogen story. Riverhawk purchased this line from Goodrich in 2004. It is the same product that was developed by Bendix more than 60 years ago. In fact, many of the original part numbers are the same, and the manufacturer strives to maintain the quality and performance characteristics that Bendix established more than six decades ago. Many of the manufacturer’s clients have been purchasing flex pivots for long-running applications, some of which are 25 to 50 years old.

Cantilevered-double ended thick spring. Riverhawk purchased the Free-Flex® pivot bearing line from Goodrich. Many of the company’s clients, in a wide range of critical industries, have been purchasing flex pivots for long-running applications.
Source: Nel Hydrogen

If a product line could talk, the flex pivots could share some tales and compelling accounts about all it has seen and done in the world’s most critical and sophisticated applications — many in the military, commercial aerospace, outer space, industrial robotics, medical, clean rooms, information technology, semiconductors, and many more. In all of these challenging sectors, clients are well-known and demand exacting results.

Shortly after integrating the pivot line into its existing production processes, it became clear that the company needed to improve its heat treat function. After researching several options, Riverhawk purchased a new Camco batch hydrogen furnace.

The pivot line consists of flat springs crossed at 90° and supporting cylindrical counter-rotating sleeves. Standard Free-Flex® pivots are made from 410 and 420 stainless steel; however, certain special material compositions include 455 stainless, Inconel 718, titanium, and maraging steel. During the manufacturing process for the flexure bearings, Riverhawk uses the batch atmosphere heat treat furnace to braze the springs to the body halves using a braze alloy, and to simultaneously heat treat certain components in the assembly. The atmosphere used for the heat treating and brazing is a 100% hydrogen atmosphere — chosen because it is universally applicable to all the different metallurgy used for the flex pivots.

The Tension: Delivered vs. On-site Hydrogen?

The use of a batch atmosphere heat treat furnace requires that the hydrogen atmosphere be flushed from the furnace with inert nitrogen when a finished batch is unloaded and a new load is added. Likewise, the furnace must return to inert atmosphere again with nitrogen after the new load is added, and before hydrogen is again injected; hence, hydrogen is used in a batch-wise fashion. The function of the hydrogen atmosphere is to prevent oxidation of the metal surfaces, and to promote fluxing of the braze alloy during the thermal cycle.

Until 2009, Riverhawk used hydrogen-filled cylinders to provide hydrogen to their batch heat treat furnace. Each run of the furnace would use several cylinders of hydrogen. Increases in production rates required careful management of hydrogen gas supply to the furnace. Running out of hydrogen mid-run could sacrifice a whole batch of nearly completed parts.

In 2009, the company elected to move away from hydrogen cylinders and transition to a hydrogen supply approach less disruptive to their production process. The choices were either bulk stored hydrogen or on-site hydrogen generation. After extensive consideration, they chose a model H2 hydrogen generator from Nel Hydrogen because the zero-inventory hydrogen generation saved the company money as compared to the cost of permitting, construction, and compliance for bulk stored hydrogen approaches.

The approach that was not chosen — delivered, stored bulk hydrogen — was unappealing for several reasons. Chief among these were the capital cost of the hydrogen storage infrastructure, the requirement for permitting for the necessary hydrogen storage, the accompanying project schedule risk for permitting, the continuous compliance issues with stored hydrogen, and the price volatility of delivered hydrogen that would have made cost accounting more difficult.

“The state and local regulations were likely necessary; however, there was a lot to wade through to become compliant,” said Gorman.

Finding the Best Way

Fast forward 14 years to today and Riverhawk is once again analyzing its approach to handling its hydrogen requirement.

“The H2 model generator that we have has served us well for 14 years, several years beyond the typical life of a cell stack,” said Gorman. “But we need more capacity and redundancy due to the increased demand for our Free-Flex® products and to cost-effectively mitigate the risk of a hydrogen generator issue, leaving us without the use of our furnace.”

The company decided to go with a model H4 hydrogen generator from Nel Hydrogen, which doubles their capacity with two cell stacks and the capacity for three if and when needed. The new system features the same footprint as the former H2 model, which is important to them, and they are even gaining floor space as they will eliminate the number of cylinders formerly stored nearby. The additional free space to move about also appeals to Gorman’s top mandate for safety.

Josh Suppa — engineer of the Pivot Department at Riverhawk — has had hands-on experience with this particular generator series (pictured above). “The maintenance of it is easy, and if there ever is a rare issue, Nel is quick to respond either in person or if it’s something that they can walk us through, they take all the time we need to resolve the matter and get us back online quickly. From a product line and customer satisfaction perspective, we cannot take the risk of our heat treat operation to go down for long. It’s that integral to our success. It’s essential, really, and one of our core competencies.”

Riverhawk will soon use a model H4 hydrogen generator from Nel Hydrogen, which doubles their capacity with two cell stacks and the capacity for three if and when needed. The new system features the same footprint as the former H2 (pictured here).
Source: Nel Hydrogen

Choosing On-Site Hydrogen Generation

Looking back on the initial decision to generate on site, one of the important issues that Riverhawk and Nel personnel had to determine was the most cost-effective configuration of the hydrogen generator and ancillaries to supply the hydrogen required for thermal processing. Had the manufacturer used a continuous furnace such as a belt furnace, then the calculations would have been easy, as the flow rate required would have been level and continuous. Instead, the batch furnace required more complex calculation because the hydrogen flow rate varies depending on the stage of the furnace cycle: fast hydrogen flow to fill the furnace, then slow to maintain the atmosphere, then no flow during parts removal and during loading. Additionally, there were many factors that affected the precise furnace cycles employed, including the size of the pivots in each batch, the number of parts loaded, and the specific metallurgy of the flex pivots in the batch. Overall, the cycle times can vary between 6 and 12 hours per batch.

It is important to seek out a knowledgeable hydrogen partner in this endeavor to specify exactly what’s needed, no more and no less. For heat treat applications, users generally would want compact equipment, extreme hydrogen purity, load following, near-instant on and instant off, and considerable hydrogen pressure that make it flexibly suited for a variety of thermal processes.

By combining on-site hydrogen generation with a small amount of in-process hydrogen surge storage if needed, on-site hydrogen generation can be used to meet the needs of batch processes, such as batch furnaces. By carefully choosing generation rate and pressure, and surge storage vessel volume, the process can provide maximum process flexibility while minimizing the amount of hydrogen actually stored.

In practice, client priorities such as minimum hydrogen storage, or lowest system capital cost, or highest degree of expandability, or least amount of space occupied can be met by choosing the specific hydrogen generator capacity and surge storage system employed for any particular production challenge.

In this case study, the optimum solution chosen was based on lowest capital cost and operating cost (including maintenance) while preserving the maximum possible expandability for production increases, and safety. These sound like common reasons and may be yours as well. Success continues at Riverhawk with the arrival of the new H4 generator in the coming weeks.

 

About the Author: Marie Pompili is a freelance writer and the owner of Gorman Pompili Communications, LLC.

For more information: 

Visit nelhydrogen.com and riverhawk.com.

 

 

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On-Site Hydrogen Generation Essential for Riverhawk Company’s Heat Treat Operations Read More »

Tip-Ups: A Viable Solution To Customize Your Heat Treat Department

/ ATMOSPHERE AIR FURNACES TECHNICAL CONTENT, FEATURED NEWS, MANUFACTURING HEAT TREAT

OCHeat Treat Today asked tip-up manufacturers to help heat treaters understand the variability of tip-up options in the market today. In this article, Gasbarre Thermal Processing Systems and Premier Furnace Specialists share unique approaches on how their own gargantuan furnaces serve heat treaters. As you read, note that customization is the critical component to operating a tip-up in your heat treat department.

This original content article is drawn from Heat Treat Today's February Air & Atmosphere Furnace Systems print edition. Have something to share about tip-up furnaces? Our editors would be interested in sharing it online at www.heattreattoday.com. Email Bethany Leone at bethany@heattreattoday.com with your own ideas!

Gasbarre Thermal Processing Systems

What is your system and how does it differ from historic tip-up systems?

Gasbarre has a unique offering of tip-up style furnaces. We offer systems for conventional applications such as austenitizing, solution treating, stress relieving, and tempering. In addition, we also offer atmosphere processes such as annealing and ferritic nitrocarburizing (FNC). For us, tip-up systems are not one-size-fits-all type systems. Systems are designed around our customer’s specific processing requirements. This would include thermal process requirements, load geometry and weight, temperature ranges and uniformity requirements, as well as time to quench specifications.

What are its operational advantages?

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When evaluating a tip-up furnace system, they are typically compared against box-style furnaces and car bottom furnaces. So, what differentiates a tip-up from these other style furnaces? First, you can achieve the main goal of large capacity batch processing, while gaining advantages over box furnaces with wider temperature ranges and tighter uniformity requirements. Box furnaces are more challenging to evenly distribute heat due to the large space requirement for the furnace door, where it is difficult to include heating elements or gas fired burners. Second, you can achieve faster time-to-quench speeds in a tip-up furnace over a car bottom furnace. Car bottom furnaces require the load to be pulled out of the furnace and then the load is typically manually moved from the furnace hearth to the quench. In a tip-up, this process can be automated and completed in 60 seconds or less. Finally, when special atmosphere processes are required, a tip-up furnace offers a superior atmosphere seal to the other furnaces mentioned. With tip-up furnaces, you can seal the furnace using its own weight. Other furnaces require additional mechanical assemblies to achieve a proper seal, which ultimately is more susceptible to leaks and requires more maintenance than a tip-up furnace seal.

Tip-up furnace from Gasbarre Thermal Processing Systems
Source: Gasbarre Thermal Processing Systems

Why should people be paying attention to what you have to offer?

Gasbarre’s broad product offering gives us the ability to evaluate your requirements objectively and offer the best solution for you and your company, whether that be box furnace, car bottom, or tip-up. Tip-up furnace systems are usually not one-off installations. These systems usually involve quenching equipment, material handling, load staging, and other integration. Gasbarre has the experience and personnel to manage such large projects and support the customer to effectively implement a system.

Premier Furnace Specialists

What is your system and how does it differ from historic tip-up systems?

The controls and automation capabilities of our furnaces set us above many older systems still in use today. On the control panel of an older system, you’re likely to see paper chart recorders, maybe a PanelView screen, and dozens of switches, pushbuttons, and pilot lights. Some of our customers prefer these control systems for their familiarity, and that’s fine because we are capable of building this style of enclosure, but most come to us for improvements or new systems entirely. Our standard panel comes with a 23.8” color touchscreen display that lets operators manage or record almost every aspect of the furnace’s operation. This package can be added to existing furnaces as well, as we have performed many control and combustion upgrades on older systems to keep them functional and reduce operating costs. We also offer tip-up furnaces that operate via jackscrews for customers who want to avoid the maintenance and flammability of hydraulics.

Open indirect gas-fired atmosphere furnace used to handle a variety of parts
Source: Premier Furnace Specialists

Modern burner technology also offers a massive improvement over older systems. With rising energy costs for all fuel types, any increase in efficiency will quickly become a source of savings which can be redirected into other areas of your company. Improvements to burner design offer increased preheat, recuperative, and regenerative possibilities, which offer fuel savings across multiple temperature ranges and reduce emissions to keep in line with changing regulations. A standard burner can heat up and cool down faster, take less time to tune, and reduce maintenance hours and headaches compared to older models of burners with knowledgeable air and gas train design coupled with modern burners.

What are its operational advantages?

Our systems allow greater flexibility for integration with existing and future equipment as well as simplified operation. One of the largest complaints we hear in every industry is about the struggle to retain maintenance and equipment operators’ knowledge once a senior member leaves a company. For this reason, it is important to have a simplified controls interface that allows new operators to get up to speed quickly. As a service company as well as an OEM, we have extensive experience working on and upgrading many brands of equipment. This enables us to easily integrate our solutions to match what customers are familiar with while also reducing maintenance requirements.

Closed furnace with work chamber of approx 31' x 9' x 9' with load capacit of 90,000 lbs.
Source: Premier Furnace Specialists

Why should people be paying attention to what you have to offer?

Despite OEMs trying to convince you, sometimes a standard “cookie cutter” model just isn’t the right fit for a job. It can take years to build up a budget for a new furnace system. Don’t invest those hard earned dollars into a piece of equipment that won’t do everything you need, exactly how you need it done. We are willing to take on the jobs that require creative solutions and extensive automation. Premier’s custom engineered systems live up to our namesake. Some of our recent projects have included a 130 ft long roller hearth furnace system with automated cooling/sequencing/handling of over 40 loads simultaneously; and a car bottom furnace with a 15’ x 15’ x 15’ work chamber capable of controlled heating and cooling of 160,000-pound loads.

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Tip-Ups: A Viable Solution To Customize Your Heat Treat Department Read More »

How Tip-Ups Forever Transformed Brake Rotor Manufacturing

/ ATMOSPHERE AIR FURNACES TECHNICAL CONTENT, AUTOMOTIVE HEAT TREAT, AUTOMOTIVE HEAT TREAT TECHNICAL CONTENT, FEATURED NEWS, NITROCARBURIZING TECHNICAL CONTENT

OC

Are your brake rotors heat treated? Travel back in time to discover how ferritic nitrocarburizing (FNC) became the heat treatment of choice for automakers’ brake rotors and why the tip-up furnace forever altered the production process for this part.

This Technical Tuesday article is drawn from Heat Treat Today's February Air & Atmosphere Furnace Systems print edition. If you have any information of your own about heat treating brake rotors, our editors would be interested in sharing it online at www.heattreattoday.com. Email Bethany Leone at bethany@heattreattoday.com with your own ideas!

The Problem: Brake Rotor Corrosion

Michael Mouilleseaux
General Manager at Erie Steel, Ltd.
Sourced from the author

In the early 2000s, corrosion was one of the top three issues that U.S. automotive manufacturers found negatively affected the perception of the quality of their cars. Brake rotors are made of cast iron. These components sit out in the elements, and in places like the U.S. Midwest where salt is often used on the roads, unprotected steel or iron will corrode or rust. Even on the coast, there is salt water in the air.

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What does rusting cause? The rotor rusts, and first, the cosmetics are negatively affected (i.e., rusty appearance). But more importantly, the first time you step on the brakes, it squeals like a pig, the vehicle shudders, and the driver feels pulsing in the pedal. He’ll also feel it in the steering wheel because the amount of rust coating one area is different from the amount of rust that’s on another. So, these brand new, forty- to seventy-thousand-dollar cars have orange rust over the brake rotor and a shaky drive. . . it’s not a good look!

Now, this is just a superficial coating of rust that will eventually abrade away; the rotor will look alright, the vehicle will stop better, and it won’t squeal. However, since the rust on the rotor wears off unevenly, the car may never have smooth braking.

A Move to FNC

In the early 2000s, all the big players were looking to FNC (ferritic nitrocarburizing) as a solution to corrosion, including Bosch Braking Systems, Ford, General Motors, Akebono, and the truck manufacturers. FNC was becoming popular since the process adds a metallurgical layer — called the “white layer” or “compound zone” — to the part, providing corrosion resistance and the bonus of improving wear.

Source: Oleksandr Delyk/Adobe Stock

To the OEMs, the benefits were perceived as:

  1. The corrosion issue had an answer.
  2. The life of the rotor doubled from roughly 40,000 to 80,000 miles. Although that meant half as many aftermarket brake jobs compared to before, consumers perceived it as a real advantage.
  3. The rotors generated less dust. Brakes generate dust particles as the result of abrasion of the pads and the rotors. This particulate dust has been identified as both an environmental and a health concern. Now, flash forward to 2022: Electric vehicles are largely displacing the need to control emissions from ICE (internal combustion engine) vehicles. So, the new European standard on vehicle emissions implemented a requirement to control this dust that is harmful to the environment and which EV and traditional brake systems can emit.

But there were certain technical and practical challenges that automotive manufacturers faced when trying to implement this process at scale.

#1 Distortion. Brake rotors may distort during FNC. Since rotors are (gray iron) castings, the process temperature for FNC may stress relieve the rotor, causing it to change shape or distort, rendering it unusable as a disc brake rotor. It was determined that if the rotor castings were stress relieved prior to machining and FNC, the distortion issue was rendered moot.

#2 Loss of Necessary Friction. FNC gives the white layer on the surface of a part with a diffusion zone underneath. The compound zone has a very low coefficient of friction, which means excellent wear properties. However, manufacturers want friction between the rotor and the brake pads to slow the car down. Reducing the friction on the rotors extends the braking distance of the car.

". . .[M]anufacturers want friction between the rotor and the brake pads to slow the car down."
Source: Unsplash.com/Craig Morolf
Let me illustrate this: I ferritic nitrocarburized a set of brake discs for Bosch Braking Systems, which eventually went to Germany and then on a vehicle. The customer absolutely loved the corrosion resistance, but when it was time for the downhill brake test, the car went straight through an instrument house because the brakes couldn’t stop the car! Lesson: For rotors treated with FNC, the brake pads need to be made from a different frictional material!

#3 Cost. Overcoming the technical issues is simple. Stress relieving the casting at FNC temperatures before machining it would help the parts machine better and would eliminate distortion. Modifying the FNC process could reduce the depth of the white layer and, paired with the correct friction material, the acceptable braking capabilities were restored. Yet these additional steps presented a new challenge: higher costs.

The practical constraints of FNC in conventional batch or pit furnaces strained efforts to be cost-effective. The load (size) capacity of the conventional equipment, in conjunction with the time constraints of the FNC process presented a dilemma, as the OEMs’ benchmark was about one dollar per rotor.

Here Comes the Tip-Up

With traditional furnaces for FNC, there was just no way to reach the economics that were necessary for it. A bigger pit furnace might be the way to go, but they really weren’t big enough. So, here comes the tip-up.

Traditionally, a tip-up furnace has been used for processes with just air, no atmosphere. With direct fired burners, the furnace is used for tempering, stress relieving, annealing, and normalizing. Everything loads into the box, gets fired, and unloads, similar to a car-bottom furnace. With the appropriate external handling systems parts could be retrieved from the furnace and then quenched. This additional process increased the usefulness of the equipment and allowed for the processing of tubes, bars, big castings. . . big forgings for the oil industry and the like.

The question of how to heat treat brake rotors on a large scale still needed to be answered. It required a large, tightly sealed furnace with atmospheric integrity for excellent temperature uniformity. In ferritic nitrocarburizing, the processing range is about 950°F to 1050°F. It is well known that properties vary significantly across the temperature range. And they needed to be optimized to create the appropriate frictional properties for the rotors.

So, the answer was: Let’s make a tip-up furnace that can be sealed for atmospheric integrity, has the appropriate temperature uniformity, and can circulate gas evenly. A lot of this would have to be iterative — create, test, compare, repeat.

Tip-up furnace from Gasbarre Thermal Processing Systems
Source: Gasbarre Thermal Processing Systems

The development of the perfect tip-up was essentially the work of one furnace manufacturer and one heat treater who together changed the industry.

American Knowhow Makes the Perfect Tip-Up

In the early 2000s, heat treaters worked with OEMs to develop a cost-efficient process in a tip-up. Manufacturers and service providers tested different methods, including atmosphere FNC and salt bath FNC.

By 2009, the perfect atmosphere furnace was complete and high volume brake rotors began to be processed for General Motors. The furnace manufacturer was JL Becker, Co., acquired by Gasbarre in 2011. The commercial heat treater was Woodworth, Inc., located in Flint, MI. Together, they spent a lot of time and money looking into FNC and figuring out how to make it work in a tip-up furnace.

General Motors was the first one to get on board, utilizing the FNC processed rotors on their pickup trucks and big SUVs, like the Escalade and Tahoe. Ford was not far behind using it on their F150 pickup truck. I was shocked the first time I saw the commercial: a Silverado pickup truck, out in the snow, and the speaker saying, “We now have an 80,000-mile brake system because of a heat treating process called FNC!”

It’s a great story of American knowhow and a collaborative effort between someone who saw a need and someone else who saw the way. To this day, if you want to get a replacement set of brake rotors for your car, go to a place like AutoZone; they will tell you that the difference in cost between the OEM parts and an off-brand is the fact that the off-brand is not heat treated.

About the author: Michael Mouilleseaux has been at Erie Steel, Ltd. in Toledo, OH, since 2006 with previous metallurgical experience at New Process Gear in Syracuse, NY, and as the Director of Technology in Marketing at FPM Heat Treating LLC in Elk Grove, IL. Having graduated from the University of Michigan with a degree in Metallurgical Engineering, Michael has proved his expertise in the fi eld of heat treat, co-presenting at the Heat Treat 2019 show and currently serving on the Board of Trustees at the Metal Treating Institute.

Contact Michael at MMouilleseaux@erie.com

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Air & Atmosphere Heat Treat Tips Part 4: Carbon Control

/ ATMOSPHERE AIR FURNACES TECHNICAL CONTENT, FEATURED NEWS, MANUFACTURING HEAT TREAT

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Let’s discover new tricks and old tips on how to best serve air and atmosphere furnace systems. In this series, Heat Treat Today compiles top tips from experts around the industry for optimal furnace maintenance, inspection, combustion, data recording, testing, and more. Part 4, today's tips, examines carbon probes and carbon control. Look back to Part 1 here for tips on seals and leaks, Part 2 here for burners and combustion tips, and Part 3 here for data and record keeping tips.

This Technical Tuesday article is compiled from tips in Heat Treat Today's February Air & Atmosphere Furnace Systems print edition. If you have any tips of your own about air and atmosphere furnaces, our editors would be interested in sharing them online at www.heattreattoday.com. Email Bethany Leone at bethany@heattreattoday.com with your own ideas!

1. Slight Positive Pressures Are Best

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Atmosphere furnace pressure should be only slightly above ambient. The range should be between 0.25-0.35 inches water column. Higher pressures in multiple zone pusher furnaces will cause carbon control issues. High pressures in batch furnaces will cause high swings when doors and elevators move.

Source: AFC-Holcroft

#atmosphericpressure #furnacezones #batchfurnace #multizone

2. Carbon Probe Trouble Shooting

If you’re having atmosphere problems with a furnace that has been operating normally for some time, avoid the temptation to remove the carbon probe. There are several tests you can run on nearly all carbon probes while the probe is still in the furnace, at temperature, in a reducing atmosphere. Super Systems Inc. provides an 11-step diagnostic procedure in a white paper on their website, in a paper titled, “Carbon Sensor Troubleshooting” by Stephen Thompson.

Source: Super Systems Inc.

#troubleshoot #reducingatmosphere #diagnostictest

3. What To Do When Parts Are Light on Carbon

"Review process date for abnormalities."
Source: Super Systems Inc.

Many factors can contribute to why parts are not meeting the correct hardness readings. According to Super Systems Inc., here is a quick checklist of how to start narrowing down the culprit:

  • Review process data for abnormalities. The first thing to do is make sure the parts were exposed to the right recipe. Check the recorders to make sure the temperature prof le and atmosphere composition were correct. Make sure all fans and baffes were working correctly. Determine if any zones were out of scope and that quench times were acceptable. If any red flags appear, hunt down the culprit to see if it may have contributed to soft parts.
  • Check the generator. Next, check the generator to make sure it is producing the gas composition desired for the process. If available, check the recorders to make sure the gas composition was on target. If not, check the generator inputs and then the internal workings of the generator.
  • Check the furnace atmosphere. If the generator appears to be working correctly, the next step would be to check the furnace itself for atmosphere leaks. Depending on what type of furnace you have, common leak points will vary; for continuous furnaces, common leak points are a door, fan, T/C, or atmosphere inlet seals. Other sources of atmosphere contamination may be leaking water cooling lines in water-cooled jackets or water-cooled bearings. More than likely, if the generator is providing the correct atmosphere but parts are still soft, there is a leak into the furnace. This will often be accompanied by discolored parts.
  • Check carbon controller to make sure it matches furnace atmosphere reading (verify probe accuracy and adjust carbon controller). This can be done using a number of different methods: dew point, shim stock, carbon bar, three gas analysis, coil (resistance), etc. Each of these methods provides a verification of the furnace atmosphere which can be compared to the reading on the carbon controller. If the atmosphere on the carbon controller is higher than the reading on the alternate atmosphere check, that would indicate the amount of carbon available to the parts is not as perceived. The COF/PF on the carbon controller should be modified to adjust the carbon controller reading to the appropriate carbon atmosphere. If the reading is way off, it may require the probe to be replaced.
  • Check the carbon probe.
  • Replace the probe – CALL SSI.

Source: Super Systems Inc.

#checklist #hardening #carbon #furnaceatmosphere #probes #controller

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