Dr. Valery Rudnev

The Chemistry Behind the Process: 6 Heat Treat Tips for Brazing, Induction, and Quenching

/ BRAZING TECHNICAL CONTENT, FEATURED NEWS, INDUCTION HEATING EQUIPMENT TECHNICAL CONTENT, MANUFACTURING HEAT TREAT, QUENCHING TECHNICAL CONTENT

OCWe’ve assembled some of the top 101 Heat Treat Tips that heat treating professionals submitted over the last three years into today’s original content. If you want more, search for “101 heat treat tips” on the website! Today’s tips will remind you of the importance of materials science and chemistry.

By the way, Heat Treat Today introduced Heat Treat Resources last year; this is a feature you can use when you’re at the plant or on the road. Check out the digital edition of the September Tradeshow magazine to check it out yourself!

Induction Hardening Cast Iron

Induction hardening of cast irons has many similarities with hardening of steels; at the same time, there are specific features that should be addressed. Unlike steels, different types of cast irons may have similar chemical composition but substantially different response to induction hardening. In steels, the carbon content is fixed by chemistry and, upon austenitization, cannot exceed this fixed value. In contrast, in cast irons, there is a “reserve” of carbon in the primary (eutectic) graphite particles. The presence of those graphite particles and the ability of carbon to diffuse into the matrix at temperatures of austenite phase can potentially cause the process variability, because it may produce a localized deviation in an amount of carbon dissolved in the austenitic matrix. This could affect the obtained hardness level and pattern upon quenching. Thus, among other factors, the success in induction hardening of cast irons and its repeatability is greatly affected by a potential variation of matrix carbon content in terms of prior microstructure. If, for some reason, cast iron does not respond to induction hardening in an expected way, then one of the first steps in determining the root cause for such behavior is to make sure that the cast iron has not only the proper chemical composition but matrix as well.

(Dr. Valery Rudnev, FASM, Fellow IFHTSE, Professor Induction, Director Science & Technology, Inductoheat Inc.)

14 Quench Oil Selection Tips

Here are a few of the important factors to consider when selecting a quench oil. 

  1. Part Material – chemistry & hardenability 
  2. Part loading – fixturing, girds, baskets, part spacing, etc. 
  3. Part geometry and mass – thin parts, thick parts, large changes in section size 
  4. Distortion characteristics of the part (as a function of loading) 
  5. Stress state from prior (manufacturing) operations 
  6. Oil type – characteristics, cooling curve data 
  7. Oil speed – fast, medium, slow, or marquench  
  8. Oil temperature and maximum rate of rise 
  9. Agitation – agitators (fixed or variable speed) or pumps 
  10. Effective quench tank volume 
  11. Quench tank design factors, including number of agitators or pumps, location of agitators, size of agitators, propellor size (diameter, clearance in draft tube), internal tank baffling (draft tubes, directional flow vanes, etc.), flow direction, quench elevator design (flow restrictions), volume of oil, type of agitator (fixed v. 2 speed v. variable speed), maximum (design) temperature rise, and heat exchanger type, size, heat removal rate in BTU/hr & instantaneous BTU/minute.
  12. Height of oil over the load 
  13. Required flow velocity through the workload 
  14. Post heat treat operations (if any) 

(Dan Herring, “The Heat Treat Doctor®”, of The HERRING GROUP, Inc.)

How to Achieve a Good Braze

In vacuum brazing, be certain the faying surfaces are clean, close and parallel. This ensures the capillary action needed for a good braze.

A good brazing filler metal should:

  1. Be able to wet and make a strong bond on the base metal on which it’s to be applied.
  2. Have suitable melt and flow capabilities to permit the necessary capillary action.
  3. Have a well-blended stable chemistry, with minimal separation in the liquid state.
  4. Produce a good braze joint to meet the strength and corrosion requirements.
  5. Depending on the requirements, be able to produce or avoid base metal filler metal interactions.

(ECM USA)

Pay Attention to Material Chemistry

When trying to determine a materials response to heat treatment, it is important to understand its form (e.g., bar, plate, wire, forging, etc.), prior treatments (e.g. mill anneal, mill normalize), chemical composition, grain size, hardenability, and perhaps even the mechanical properties of the heat of steel from which production parts will be manufactured. The material certification sheet supplies this basic information, and it is important to know what these documents are and how to interpret them.

Certain alloying elements have a strong influence on both the response to heat treatment and the ability of the product to perform its intended function. For example, boron in a composition range of 0.0005% to 0.003% is a common addition to fastener steels. It is extremely effective as a hardening agent and impacts hardenability. It does not adversely affect the formability or machinability. Boron permits the use of lower carbon content steels with improved formability and machinability.

During the steelmaking process, failure to tie up the free nitrogen results in the formation of boron nitrides that will prevent the boron from being available for hardening. Titanium and/or aluminum are added for this purpose. It is important, therefore, that the mill carefully controls the titanium/nitrogen ratio. Both titanium and aluminum tend to reduce machinability of the steel, however, the formability typically improves. Boron content in excess of 0.003% has a detrimental effect on impact strength due to grain boundary precipitation.

Since the material certification sheets are based on the entire heat of steel, it is always useful to have an outside laboratory do a full material chemistry (including trace elements) on your incoming raw material. For example, certain trace elements (e.g. titanium, niobium, and aluminum) may retard carburization. In addition, mount and look at the microstructure of the incoming raw material as an indicator of potential heat treat problems.

(Dan Herring, The Heat Treat Doctor®)

Aqueous Quenchant Selection Tips

Determine your quench: Induction or Immersion? Different aqueous quenchants will provide either faster or slower cooling depending upon induction or immersion quenching applications. It is important to select the proper quenchant to meet required metallurgical properties for the application.

  1. Part material: Chemistry and hardenability are important for the critical cooling rate for the application.
  2. Part material: Minimum and maximum section thickness is required to select the proper aqueous quenchant and concentration.
  3. Select the correct aqueous quenchant for the application as there are different chemistries. Choosing the correct aqueous quenchant will provide the required metallurgical properties.
  4. Review selected aqueous quenchant for physical characteristics and cooling curve data at respective concentrations.
  5. Filtration is important for aqueous quenchants to keep the solution as clean as possible.
  6. Check concentration of aqueous quenchant via kinematic viscosity, refractometer, or Greenlight Unit. Concentration should be monitored on a regular basis to ensure the quenchant’s heat extraction capabilities.
  7. Check for contamination (hydraulic oil, etc.) which can have an adverse effect on the products cooling curves and possibly affect metallurgical properties.
  8. Check pH to ensure proper corrosion protection on parts and equipment.
  9. Check microbiologicals which can foul the aqueous quenchant causing unpleasant odors in the quench tank and working environment. If necessary utilize a biostable aqueous quenchant.
  10. Implement a proactive maintenance program from your supplier.

(Quaker Houghton)

Container Clarity Counts!

Assure that container label wording (specifically for identifying chemical contents) matches the corresponding safety data sheets (SDS). Obvious? I have seen situations where the label wording was legible and accurate and there was a matching safety data sheet for the contents, but there was still a problem. The SDS could not be readily located, as it was filed under a chemical synonym, or it was filed under a chemical name, whereas the container displayed a brand name. A few companies label each container with (for instance) a bold number that is set within a large, colored dot. The number refers to the exact corresponding SDS.

(Rick Kaletsky)

Check out these magazines to see where these tips were first featured:

The Chemistry Behind the Process: 6 Heat Treat Tips for Brazing, Induction, and Quenching Read More »

Tips #13 – 23 – 33 – 43

/ HARDNESS TESTERS TECHNICAL CONTENT, HEAT TREAT NEWS INDUSTRIES

One of the great benefits of a community of heat treaters is the opportunity to challenge old habits and look at new ways of doing things. Heat Treat Today’s 101 Heat Treat Tips is another opportunity to learn the tips, tricks, and hacks from some of the industry’s foremost experts.

Heat Treat Today’s latest round of 101 Heat Treat Tips is featured in Heat Treat Today 2020 fall issue (also featuring the popular 40 Under 40).

Today’s selection includes four tips from Leybold Vacuum USA, Young Metallurgical Consulting, Dr. Valery Rudnev, and Chiz Bros. Increase output, decrease production costs, hit target temperature, and avoid thermal shock with these four tips.

Heat Treat Tip #13

New Diffusion Pump Technology Increases Production Output

Gain immediate positive net cash flow with a lease to own finance option by upgrading your diffusion pumps with the new immersion heater technology. The new style heater will extend oil life and reduce energy consumption. New heater technology can increase production by eliminating the need of dropping your pump every time you change oil for faster maintenance turn around. Drop in place pump design with improved performance.

NEW-DIJ Diffusion Pumps with smart heater technology by Leybold Vacuum
Source: Leybold Vacuum USA

(Leybold Vacuum USA)

Heat Treat Tip #23

Inspection Mistakes That Cost

Rockwell hardness testing requires adherence to strict procedures for accurate results.  Try this exercise to prove the importance of proper test procedures.

  • A certified Rc 54.3 +/- 1 test block was tested three times and the average of the readings was Rc 54 utilizing a flat anvil.  Water was put on the anvil under the test block and the next three readings averaged Rc 52.1.
  • Why is it so important that samples are clean, dry, and properly prepared?
  • If your process test samples are actually one point above the high spec limit but you are reading two points lower, you will ship hard parts that your customer can reject.
  • If your process test samples are one point above the low spec limit but you are reading two points lower, you may reprocess parts that are actually within specification.
  • It is imperative that your personnel are trained in proper sample preparation and hardness testing procedures to maximize your quality results and minimize reprocessing.
Properly preparing a hardness sample can save time and money.

Source: Young Metallurgical Consulting

(Young Metallurgical Consulting)

Heat Treat Tip #33

Not Able to Hit Target Temperature — What To Do

Situation: Customer had an available 100kW/1kHz inverter and needed to heat 1-in.-diameter carbon steel bar to hot working temperature (2000°F). It was a low production application and cycle time was not critical. However, regardless of the heat time and irrespective of using maximum available output power, it was not possible to reach required target temperature. Actually, after reaching about 1470o°F there was no noticeable temperature rise regardless of increased heat time.

Solution: Severe eddy current cancellation was responsible for a failure to reach target temperature. The use of frequencies 6 kHz and greater can easily help to accomplish the goal. As a simple “rule-of-thumb,” in order to provide an efficient heating and avoid eddy current cancellation in through heating applications (e.g., through hardening or hot working), it is necessary to choose a frequency that will guarantee that the “bar diameter-to-penetration depth” ratio exceeds 3.6 at a target temperature.

(Dr. Valery Rudnev, FASM, Fellow of IFHTSE/Professor Induction/Director Science & Technology, Inductoheat Inc., An Inductotherm Group company)

Heat Treat Tip #43

Brick to Fiber to Avoid Thermal Shock

Thermal shock is a regular issue with hard refractory and brick-lined furnaces due to the constant changes in temperature for batch annealing. Switching an old furnace over to ceramic fiber is an easy process that can save time and money.

(Chiz Bros)

Tips #13 – 23 – 33 – 43 Read More »

Take a Tip or Two

/ MANUFACTURING HEAT TREAT

One of the great benefits of a community of heat treaters is the opportunity to challenge old habits and look at new ways of doing things. Heat Treat Today’s 101 Heat Treat Tips is another opportunity to learn the tips, tricks, and hacks from some of the industry’s foremost experts.

Heat Treat Today’s latest round of 101 Heat Treat Tips is featured in Heat Treat Today fall issue (also featuring the popular 40 Under 40).

Today’s selection includes tips from Dr. Valery Rudnev, Grammer Vacuum Technologies, Inc., and L & L Special Furnace Co., Inc. This selection includes tips related to induction heating, vacuum furnaces, and temperature uniformity.

Heat Treat Tip #3

Avoid Axle Shaft Cracks After Induction Tempering

Situation: In induction scan hardening of axle shafts, there was NO cracking occurred after scan hardening (case depth varies from 5 mm to 8 mm). Cracks appeared in the spline region after induction tempering.

Solution: Most likely, the cause of this problem is associated with a reversal of residual stress distribution during induction tempering. Reduce coil power for tempering and increase time of induction tempering. Multi-pulse induction tempering applying lower power density might also help. As an alternative, instead of modifying temper cycle, you can also try to reduce quench severity by increasing the temperature of the quenchant and/or its concentration.

 

(Dr. Valery Rudnev, FASM, Fellow of IFHTSE, Professor Induction, Director Science & Technology, Inductoheat Inc., An Inductotherm Group company)

Heat Treat Tip #26

TZM Moly Grids

Source: Grammer Vacuum Technologies, Inc.

A very commonly observed failure mechanism with a moly post hearth assembly is bending of the moly posts. They will stay fairly straight at the center of the hearth area, but they can distort badly toward the outer sides of the work zone. The outer rows of vertical posts end up leaning away from each other. This is due to the very high linear thermal expansion coefficient of nickel-iron alloy grids (usually 330 SS or Inconel). With a high load on the nickel alloy grid, it is not able to slide on the perpendicular hearth beams as the temperature rises. The outer hearth post rows are forced in an outward direction. The quenching of the furnace load does not reverse all of this effect and over time results in the severe bending of the hearth posts.

By replacing the stainless steel or nickel alloy grids with a moly or TZM alloy moly grid, which exhibits very low thermal expansion, the hearth life can be increased. For comparison, the figure shows the coefficients of linear thermal expansion for commonly used grid materials. For example, a 36” wide 330 SS grid at 70°F grows to 36.6” wide at 2200°F.

Another significant benefit of TZM moly grids is use at higher furnace process temperatures without the problem of a softened, sagging grid that cannot support the load properly.

Source: Grammer Vacuum Technologies, Inc.

 

(Grammer Vacuum Technologies, Inc.)

Heat Treat Tip #41

Ways to Increase Temperature Uniformity in Heat Treat Furnaces

  1. A (sometimes) simple way to increase uniformity in a furnace is to add a circulation fan. Circulation fans can be a quick way to add an additional 5°F tighter uniformity on a batch furnace application.
  2. Be sure that the furnace is tuned optimally to reduce/eliminate any overshoot and oscillation around setpoint.
  3. Eliminate any thermal lag by making sure that the control thermocouple and TUS thermocouples have similar sensitivity. If not, the control thermocouples can fall behind and cause the TUS thermocouples to overshoot and fail.

 

(L & L Special Furnace Co., Inc.)

 

Take a Tip or Two Read More »

10 Heat Treat Tips to Whet Your Appetite

/ FEATURED NEWS, MANUFACTURING HEAT TREAT, MANUFACTURING HEAT TREAT NEWS

Heat Treat 2019 is coming, and one of the great benefits of gathering with a community of heat treaters is the opportunity to challenge old habits and look at new ways of doing things. Heat Treat Today’s 101 Heat Treat Tips is another opportunity to learn the tips, tricks, and hacks shared by some of the industry’s foremost experts.

For Heat Treat Today’s latest round of 101 Heat Treat Tips, click here for the digital edition of the 2019 Heat Treat Today fall issue (also featuring the popular 40 Under 40), and to be distributed in print at Heat Treat 2019, in Detroit, Michigan, October 14-17, 2019.

Today’s Technical Tuesday features 10 Tips from a variety of categories, including SCR Power Controls (56), Cooling Systems (64), Combustion (66, 101), Induction Heat Treating (71), Thermocouples (79), AMS2750 (86), Vacuum Furnaces (92), and Miscellaneous (41, 87). These tips come from the 2018 list of 101 Heat Treat Tips published in the FNA 2018 Special Print Edition. This special edition is available in a digital format here.

If you have a heat treat-related tip that would benefit your industry colleagues, you can submit your tip(s) to doug@heattreattoday.com or editor@heattreattoday.com—or stop by to see us at Booth #2123 in Detroit!

 

Heat Treat Tip #41

Discolored Part—Who’s to Blame?

If your parts are coming out of the quench oil with discoloration and you are unsure if it is from the prewash, furnace, or oil quench, you can rule out the quench if the discoloration cannot be rubbed off. Check this before the part is post-washed and tempered.

Other possible causes:

  • Can be burnt oils as parts go through the quench door flame screen
  • Poor prewash
  • Furnace atmosphere inlet (particularly if it is drip methanol)

Submitted by AFC-Holcroft

Heat Treat Tip #56

Electrical Energy Savings

When we buy a pint of beer we don’t expect the head (or foam) to be ½ the glass. We can get this situation when we pay for our plant’s electricity; we pay for both the working power that drives the process (analogy: beer) and reactive power that doesn’t directly drive the process (analogy: foam/head). The lower the Power Factor the worse this situation. The latest SCR devices can help combat this while maintaining precise control and reducing overall peak load demands (using flexible firing methods).

Submitted by Eurotherm

 

Heat Treat Tip #64

Buy a Cooling System Capable of Growth

Plan for future growth. It is more cost-effective to provide additional capacity while equipment is being installed. Simple planning for the addition of future pumps (e.g. providing extra valved ports on tanks) and space for heat transfer equipment (e.g. pouring a larger pad or adding extra piers) can save considerable money down the road with little upfront expenditure. Consider installing one size larger piping for the main distribution supply and return. If this is not possible make sure you can add an additional piping run on the hangers you will install now.

Above all, be sure to include all necessary drains, vents, isolation valves, and plenty of instrumentation. These items are critical aids in maintenance and troubleshooting and future system expansion.

Submitted by Dry Coolers

Heat Treat Tip #66

Tune That Burner!

Don’t neglect burner tuning—a 1% reduction in excess O2 in the flue products can save you $1,000.00/year on your IQ batch or $2,000.00/year on a 2000-pound/hour continuous furnace—not to mention consistent temp uniformity, better heat-up rates. Pretty good payback for a couple of hours’ work.

Submitted by Combustion Innovations

Heat Treat Tip #71

Tube & Pipe Heat Treatment Is Different Than Solid Cylinder Heat Treating

Induction heating of tubes and pipes is somewhat different from the heating of solid cylinders. There is a difference in the frequency selection that would maximize energy efficiency for heating tubular products as compared to solid cylinders. In tube and pipe heating, the frequency, which corresponds to maximum coil efficiency, is typically shifted toward lower frequencies providing larger current penetration depth than the tube wall thickness (except for heating of tubes with electromagnetically small diameters). This condition can produce an improvement in electrical efficiency of 10–16 % and even higher. One simplified formula that is used in industry for rough estimate of the electrically efficient frequency is shown in the image, where:

  • ρ – electrical resistivity of heated metal (Ω*m)
  • Am = average diameter; Am = (Tube O.D. – h) (m)
  • h = wall thickness (m)

In cases when induction heaters cannot be considered to be electromagnetically long coils, the values of the optimum frequency will be higher than the values suggested according to formula, and computer modeling can help determining its exact value.

Submitted by Dr. Valery Rudnev, FASM, Fellow of IFHTSE Professor Induction Director Science & Technology, Inductoheat Inc., An Inductotherm Group company

Heat Treat Tip #79

Order SAT Probes All at Once

Place a yearly blanket order for your SAT probes and ask that they are made from the same coil. This will give you the same correction factors and temperature tolerances.

Submitted by GeoCorp

Heat Treat Tip #86

AMS2750 Is Golden

This standard is gold and unfortunately has a bad rap today because companies feel it’s just added cost into the process. Today’s technology means you can afford AMS2750E compliant controllers and digital recorders for only a few hundred dollars above a standard offer. This investment will be paid back many times over due to the longer lifetime expected with a quality instrument as well as the quality benefits from better drift performance between calibration intervals, redundant recording (in case of record loss), and overall accurate temperature control, leading to less rejects and reduced rework.

Submitted by Eurotherm

Heat Treat Tip #87

Pay Attention to Material Chemistry

When trying to determine a materials response to heat treatment, it is important to understand its form (e.g., bar, plate, wire, forging, etc.), prior treatments (e.g. mill anneal, mill normalize), chemical composition, grain size, hardenability, and perhaps even the mechanical properties of the heat of steel from which production parts will be manufactured. The material certification sheet supplies this basic information, and it is important to know what these documents are and how to interpret them.

Certain alloying elements have a strong influence on both the response to heat treatment and the ability of the product to perform its intended function. For example, boron in a composition range of 0.0005% to 0.003% is a common addition to fastener steels. It is extremely effective as a hardening agent and impacts hardenability. It does not adversely affect the formability or machinability. Boron permits the use of lower carbon content steels with improved formability and machinability.

During the steelmaking process, failure to tie up the free nitrogen results in the formation of boron nitrides that will prevent the boron from being available for hardening. Titanium and/or aluminum are added for this purpose. It is important, therefore, that the mill carefully controls the titanium/nitrogen ratio. Both titanium and aluminum tend to reduce machinability of the steel, however, the formability typically improves. Boron content in excess of 0.003% has a detrimental effect on impact strength due to grain boundary precipitation.

Since the material certification sheets are based on the entire heat of steel, it is always useful to have an outside laboratory do a full material chemistry (including trace elements) on your incoming raw material. For example, certain trace elements (e.g. titanium, niobium, and aluminum) may retard carburization. In addition, mount and look at the microstructure of the incoming raw material as an indicator of potential heat treat problems.

Submitted by Dan Herring, The Heat Treat Doctor®

Heat Treat Tip #92

Hacksaw Your Hearth!

When loading parts, carefully place the workload on the center of the hearth (front-to-back and side-to-side). Make sure it is stable and no part of the load is close to or touching the heating elements. This can create arcing and damage your parts. Tip: Once the load is in place, mark the hearth posts with a hacksaw to quickly find the front and back measurements each time.

Submitted by Ipsen USA

Heat Treat Tip #101

Can We Achieve Perfect Combustion?

Perfect combustion is based upon the concept of neither excess oxygen or a deficiency of oxygen in the combustion process. This is known as stoichiometric or theoretical combustion. Why is this considered as theoretical and not possible under normal field conditions? Consider the factors that can affect your combustion process: temperature of air or gas, pressure fluctuations, gas composition or supply changes, operating conditions, etc. Therefore theoretical combustion is just that: perfect combustion is only possible in a lab setting. Burner adjustment and calibration normally maintains a minimum of 10% excess air to compensate for these variables and avoid operating gas-rich with high levels of CO in the combustion process.

Submitted by WS Thermal

10 Heat Treat Tips to Whet Your Appetite Read More »

Heat Treat Tips: Safety and Cost-Saving Hacks

/ HARDENING, MANUFACTURING HEAT TREAT, MANUFACTURING HEAT TREAT NEWS

During the day-to-day operation of heat treat departments, many habits are formed and procedures followed that sometimes are done simply because that’s the way they’ve always been done. One of the great benefits of having a community of heat treaters is to challenge those habits and look at new ways of doing things. Heat Treat Today‘s 101 Heat Treat Tips, tips and tricks that come from some of the industry’s foremost experts, were initially published in the FNA 2018 Special Print Edition, as a way to make the benefits of that community available to as many people as possible. This special edition is available in a digital format here.

Today we continue an intermittent series of posts drawn from the 101 tips. The tips for this post come from a variety of categories but all generally address safety or cost-saving ideas. 

Dr. Valery Rudnev, FASM, Fellow of IFHTSE, Professor Induction, Director Science & Technology, Inductoheat Inc., An Inductotherm Group company

Heat Treat Tip #2

Avoid axle shaft cracks after induction tempering

Situation: In induction scan hardening of axle shafts, there was NO cracking occurred after scan hardening (case depth varies from 5 mm to 8 mm). Cracks appeared in the spline region after induction tempering.
Solution: Most likely, the cause of this problem is associated with a reversal of residual stress distribution during induction tempering. Reduce coil power for tempering and increase time of induction tempering. Multi-pulse induction tempering applying lower power density might also help. As an alternative, instead of modifying temper cycle, you can also try to reduce quench severity by increasing the temperature of the quenchant and/or its concentration.

Submitted by Dr. Valery Rudnev, FASM, Fellow of IFHTSE, Professor Induction, Director Science & Technology, Inductoheat Inc., An Inductotherm Group company

Heat Treat Tip #4

Closed Loop Water System on Top

When designing a vacuum furnace installation with a closed loop water system, elevate the tank and pump about 9 feet, then cage the space underneath for thermocouple storage, spares, and tools. Saves shop floor space.

Submitted by AeroSPC

IR Cameras are inexpensive and worth the price.

Heat Treat Tip #6

Don’t Be Cheap. Buy an IR Camera.

IR cameras have come way down in price—for a thousand dollars, you can have x-ray vision and see furnace insulation problems before they cause major problems—also a great diagnostic tool for motors, circuit breakers, etc. (And you can spot deer in the dark!)

Submitted by Combustion Innovations

 

 

Heat Treat Tip #7

An Engineer’s Design Checklist

Get an SCR design checklist and avoid mistakes.

When SCRs are involved in the design of a new piece of equipment, questions arise. Control Concepts Inc of Chanhassen, MN, offers a 20-point design checklist to help engineers who don’t specialize in power controllers. Good reading. Search for “design checklist” at the website.

Submitted by Control Concepts, Inc.

Heat Treat Tip #9

Question the Spec! Save Money!

Before you specify a heat treatment, stop and consider your options. Rather than reusing an old specification, ask the design engineer to determine the stress profile, and base the hardness or case depth on real stress data. Is this complicated? Maybe. But especially for carburizing, why pay for more depth than you need, and why take the risk of inadequate strength? The 21st century is here. We have ways to help with the math. Let’s move beyond guess and test engineering methodology.

Submitted by Debbie Aliya

 

 

Heat Treat Tips: Safety and Cost-Saving Hacks Read More »

Dr. Valery Rudnev on Equipment Selection for Scan Hardening, Part 3

/ FEATURED NEWS, INDUCTION HEATING, MANUFACTURING HEAT TREAT, MANUFACTURING HEAT TREAT NEWS

Dr. Valery Rudnev on . . . 

Induction Hardening Tips: Equipment Selection for Scan Hardening, Part 3

This is the third installment of a multi-part column on equipment selection for induction heat treatment. Part 1, Dr. Valery Rudnev On . . . Induction Hardening Tips: Equipment Selection for Scan Hardening, covered types of scanners, scan hardening system setup, quenching challenges, maximizing process flexibility, and computer modeling. In Part 2, Dr. Valery Rudnev discussed another critical aspect of induction scan hardening: inductor design subtleties and a comparison of different fabrication techniques (brazing vs. CNC
machining vs. 3D printing).

In this installation, Dr. Rudnev focuses on Moveable Inductor versus Moveable Part.

Moveable Inductor versus Moveable Part

As stated in one of the previous installments of this column, when a scan processing mode is chosen, either the inductor or the part or both may be moved during the heating and quenching. This installment discusses the applicability of those approaches (movable inductor vs. movable part), as well as pros and cons associated with both techniques.

Figure 1. An example of scan hardening of track shoes for earth-moving machines that often specify deep hardness case depths (up to the 24 mm).

The choice to move the inductor or to move the part is primarily based on required production rate as well as on the size, weight, and geometry of the component compared to the size, weight, and geometry of the inductor: in other words, it depends on which of the two is easier to move.

Weight is an important factor because the movement can occur several hundred times each day and, in some cases of high production, even several thousand times per day. For example, during induction surface hardening of track shoes for earth-moving machines that often specify deep hardness case depths (up to 24 mm), it is much easier to move the inductor around the workpiece instead of moving the track shoes, the weight of which can exceed several thousand pounds. (Figure 1)

When moving the inductor, both flexible cables and hoses are used or the inductor is hard-bused to the transformer and the transformer or heat station moves with the inductor. In some cases, the power supply itself may be moved at a moderate rate to scan a stationary workpiece [1]. Another example of moving the inductor is surface hardening of trailer axles. (Figure 2)

 

Figure 2. (Left image) Horizontal scanner to induction harden both ends of a trailer axle. A walking beam system was incorporated into the machine for part transfer. At the heating station, the axle is lifted off the beam and the power supply and inductor are indexed to position for scan hardening. After the completion of surface hardening of one end, the axle is then lifted off the transfer mechanism and rotated 180° to induction harden the opposite end. Heavy-duty precision shafting and bearings are used for stability and consistency. (Right image) shows a close-up of a movable inductor to scan harden trailer axle ends. Heating time is less than 8 s per axle end.

 

The length of the part to be heated is also an important consideration When a component is of moderate weight, it is obviously preferable to move the part rather than the inductor. For example, it is much easier and more cost-effective to design a hardening system that anticipates moving a workpiece that weighs less than 0.25 kg (<0.5 lb) rather than moving an entire power supply, as it is shown in Figure 3.

Figure 3. Horizontal scanner that provides a maximum scan rate up to 200 mm/s (8 in./s). (Courtesy of Inductoheat Inc., an Inductotherm Group company.)

 

In other cases, it may not be practical to move very large and elongated components. It would consume too much floor space to move the part through a stationary inductor. In the case of low production rates, the best choice might be to move the inductor, but the length of the high-frequency power leads could become a problem with respect to voltage drop and power loss. In this case, it is preferable to move the inductor with the power supply attached. Then, the moving cables are operating at a low frequency (50–60 Hz) with lower voltage drop and power loss. In the case of high production, continuous horizontal systems may be more suitable.

The consideration of the length of the leads (e.g., cables or buses) from the power source to the inductor is important. They should be as short as possible to conserve energy and to allow the power source to operate properly without reaching any limits (for example, voltage limit). If these leads are too long, the inductance increase can be so significant that it may result in a substantial power loss and voltage drop. The voltage drop in the leads may even exceed the voltage at inductor’s terminals. Long leads could net an excessive total needed power, a measurable reduction in energy efficiency, and potential concerns regarding the process repeatability owing to the possibility of an appreciable inductance change of the flexible leads during their motion, that in some cases may negatively impact process repeatability.

Whether moving the inductor or moving the part, the induction system can be designed to be efficient and robust in order to ensure smooth and consistent operation and the production of quality parts.

I recommend Reference #1 to readers interested in further reading on this subject.

  

References

  1. V. Rudnev, D. Loveless, R. Cook, Handbook of Induction Heating, 2nd Edition, CRC Press, 2017.

 

Dr. Valery Rudnev, FASM, IFHTSE Fellow, is the Director of Science & Technology, Inductoheat Inc., and a co-author of Handbook of Induction Heating (2nd ed.), along with Don Loveless and Raymond L. Cook. The Handbook of Induction Heating, 2nd ed., is published by CRC Press. For more information click here.

Dr. Valery Rudnev on Equipment Selection for Scan Hardening, Part 3 Read More »

Heat Treat Today Contributor to Present Webinar on Induction Heating Challenges

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Heat Treat Today Technical Tuesday contributor, Dr. Valery Rudnev, FASM, IFHTSE Fellow, “Professor Induction”, and Director of Science and Technology at Inductoheat, Inc, is the featured speaker of an ASM International Materials Solutions webinar titled “Simple Solutions for Common Induction Heating Challenges: Lessons Learned”.

Dr. Rudnev will present this webinar on Thursday, January 24, 2019, 2 pm, and address:

  • Induction hardening of powertrain transmission and engine components
  • Failure analysis
  • How to avoid cracking in induction hardening
  • Subtleties of heating parts with holes, fillets, and other geometrical irregularities
  • Re-hardening (re-austenitization) of previously hardened parts
  • Novel inverters that allow instant and independent adjustment of both frequency and power
  • Selected challenges when applying induction tempering
  • Reducing process sensitivity and improving robustness and flexibility of induction systems.

Note: Attendees will earn a professional development hour for attending the webinar.

This webinar is sponsored by Inductoheat, Inc. For more information and to register, click here.

Heat Treat Today Contributor to Present Webinar on Induction Heating Challenges Read More »

Heat Treat Tips: Induction Heating — Stuff You Should Know

/ FEATURED NEWS, INDUCTION HEATING, INDUCTION HEATING TECHNICAL CONTENT, MANUFACTURING HEAT TREAT, MANUFACTURING HEAT TREAT NEWS

During the day-to-day operation of heat treat departments, many habits are formed and procedures followed that sometimes are done simply because that’s the way they’ve always been done. One of the great benefits of having a community of heat treaters is to challenge those habits and look at new ways of doing things. Heat Treat Today‘s 101 Heat Treat Tips, tips and tricks that come from some of the industry’s foremost experts, were initially published in the FNA 2018 Special Print Edition, as a way to make the benefits of that community available to as many people as possible. This special edition is available in a digital format here.

In today’s Technical Tuesday, we continue an intermittent series of posts drawn from the 101 tips. The category for this post is Induction Heating, and today’s tips–#29, #73, and #83–are from Dr. Valery Rudnev, FASM, Fellow of IFHTSE, “Professor Induction”, Director of Science & Technology at Inductoheat Inc., an Inductotherm Group company. Dr. Rudnev is a regular contributor to Heat Treat Today. 

Heat Treat Tip #29

Induction Heating Non-Ferrous Metals & Alloys

Dr. Valery Rudnev, FASM, Fellow IFHTSE, Professor Induction, Director Science & Technology, Inductoheat Inc., an Inductotherm Group company
Dr. Valery Rudnev, FASM, Fellow IFHTSE, Professor Induction, Director Science & Technology, Inductoheat Inc., an Inductotherm Group company

Steel components by far represent the majority of hot worked and heat-treated parts for which electromagnetic induction is used as a source of heat generation. At the same time, many other non-ferrous metals and alloys are also inductively heated for a number of com­mercial applications. Induction heating of low electrically resistive metals such as Al, Mg, Cu, and others typically require using lower electrical frequencies compared to carbon steels, cast irons, or high resistive non-magnetic metals (such as Ti or W, for example) and metallic alloys. The lower value of electrical resistivity results in smaller current penetration depth (depth of heat source gen­eration), making it possible to apply much lower frequencies without facing the danger of eddy current cancellation.

Heat Treat Tip #73

Induction Hardening Powder Metal

When induction hardening powder metallurgy (P/M) materials, it is good practice to have a minimum density of at least 7.0 g/cm3 (0.25 lb/in.3). This will help obtain consistent induction hardening results. When hardening surfaces that have cuts, shoulders, teeth, holes, splines, slots, sharp corners, and other geometrical discontinuities and stress risers, it is preferable to have a minimum density of 7.2 g/cm3 (0.26 lb/in.3). Low-density P/M parts are prone to cracking due to a penetration of the gases into the subsurface areas of the part through the interconnected pores. Interconnected pores contribute to decreased part strength and rigidity compared with wrought materials. In addition, the poor thermal conductivity of porous P/M parts encourages the development of localized hot spots and excessive thermal gradients and also requires the use of quenchants with intensified cooling rates to obtain the required hardness and case depths. This is so because an increase in pore fraction and a reduction in density negatively affect the hardenability of P/M materials compared to their wrought equivalents.

Heat Treat Tip #83

Induction Hardening Cast Iron

Induction hardening of cast irons has many similarities with hardening of steels; at the same time, there are specific features that should be addressed. Unlike steels, different types of cast irons may have similar chemical composition but substantially different response to induction hardening. In steels, the carbon content is fixed by chemistry and, upon austenitization, cannot exceed this fixed value. In contrast, in cast irons, there is a “reserve” of carbon in the primary (eutectic) graphite particles. The presence of those graphite particles and the ability of carbon to diffuse into the matrix at temperatures of austenite phase can potentially cause the process variability, because it may produce a localized deviation in an amount of carbon dissolved in the austenitic matrix. This could affect the obtained hardness level and pattern upon quenching. Thus, among other factors, the success in induction hardening of cast irons and its repeatability is greatly affected by a potential variation of matrix carbon content in terms of prior microstructure. If, for some reason, cast iron does not respond to induction hardening in an expected way, then one of the first steps in determining the root cause for such behavior is to make sure that the cast iron has not only the proper chemical composition but matrix as well.

 

These tips were submitted by Dr. Valery Rudnev, FASM, Fellow IFHTSE, Professor Induction, Director Science & Technology, Inductoheat Inc, an Inductotherm Group company.

If you have any questions, feel free to contact the expert who submitted the Tip or contact Heat Treat Today directly. If you have a heat treat tip that you’d like to share, please send to the editor, and we’ll put it in the queue for our next Heat Treat Tips issue. 

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Heat Treat Today’s Induction Expert Dr. Valery Rudnev Recognized at TPiM 2018

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Dr. Valery Rudnev, who writes Heat Treat Today‘s column, “Dr Valery Rudnev On . . . “, was recognized during the opening ceremony of the American Society for Materials (ASM International) Thermal Processing in Motion 2018 (TPiM 2018) conference held this month in Spartanburg, South Carolina, and received two prestigious awards for his contributions in the field of induction heating and heat-treating.

Dr. Rudnev, Director of Science and Technology at Inductoheat Inc., an Inductotherm Group Company, was elected as a Fellow to the International Federation for Heat Treatment and Surface Engineering (IFHTSE) “[f]or his preeminence in induction heat treating and modeling of the induction heat treating process” (IFTSE, 2018). As a Fellow of ASM International with more than 30 years of experience, he is considered by many to be one of the leading global figures in the induction heating and is known among induction heating professionals as “Professor Induction.” His credits include a great deal of “know-how”, more than 50 patents and inventions (U.S. and International), and more than 250 engineering/scientific publications.

Dr. Richard D. Sisson Jr., George F. Fuller Professor, Director of Manufacturing and Materials Engineering and the Director of the Center for Heat Treating Excellence at Worcester Polytechnic Institute, and Professor Rafael Colás, Professor and Metallurgist Engineer, Universidad Autónoma de Nuevo León, were awarded fellowships with IFHTSE.

Dr. Rudnev was also presented with the ASM International “Best-Paper in Heat Treating” award for co-authoring an article entitled “Revolution – Not Evolution – Necessary to Advance Induction Heat Treating.” The article was published in the September 2017 issue of Advanced Materials & Processes Magazine (HTPro quarterly newsletter) and co-authored with Gary Doyon, Collin Russell, and John Maher. The ASM International Heat Treating Society, Research and Development Committee, established this award to recognize the best papers in the heat treat industry each year.

IFHTSE is a nonprofit group of scientific/technological societies and associations, groups and companies and individuals whose primary interest is heat treatment and surface engineering.

We at Heat Treat Today congratulate Dr. Valery Rudnev on these accomplishments!

Heat Treat Today’s Induction Expert Dr. Valery Rudnev Recognized at TPiM 2018 Read More »

Dr. Valery Rudnev on Equipment Selection for Scan Hardening, Part 2

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Dr. Valery Rudnev on . . . 

Induction Hardening Tips: Equipment Selection for Scan Hardening, Part 2

This is the second installment of a multi-part column on equipment selection for induction heat treatment. Part 1, Dr. Valery Rudnev On . . . Induction Hardening Tips: Equipment Selection for Scan Hardening, covered types of scanners, scan hardening system setup, quenching challenges, maximizing process flexibility, and computer modeling. In this installment, Dr. Valery Rudnev discusses another critical aspect of induction scan hardening: inductor design subtleties and a comparison of different fabrication techniques (brazing vs. CNC
machining vs. 3D printing).

Introduction

Hardening inductors are often considered the weakest link in an induc­tion hardening system because they may carry significant elec­trical power and operate in harsh environments exposed to high temperatures, water, and other coolants while being subjected to mechanical movement and potential sudden part con­tact.

Single-turn or multiturn inductors may be used in scan hardening (Figure 1). Copper profiling and the number of turns is determined by the workpiece geometry, required hardness pattern, and the ability to properly load match the coil to the power supply without reaching the operational limits or by other specific process requirements, such as the production rate or the hardness pattern runout/pattern cutoff. [1]

Figure 1: Single-turn or multiturn inductors may be used in scan hardening.

The longer (in case of horizontal arrangement) or the higher (vertical arrangement) the scan coil is, the faster the scan rate can be. This is due to the simple fact that the longer inductor leads to a longer period when the part will be inside the coil; therefore, the scan rate can be greater. However, limitations on the maximum length of the inductor’s heating face may be associated with the maximum permissible runout.

Hardness Pattern Runout Control

Single-turn inductors with narrow heating faces (3mm-6mm wide) are used where a sharp pattern runout is needed. An example of this would be the case where a pattern must end near a snap ring groove. Inductors with wider heating faces or two-turn coils can be used when a faster scan rate is desired and an extended runout is permitted. The main disadvantage to the excessively wide heating face is that it may result in an unspecified shift of coil current density when hardening complex geometric parts due to an electromagnetic proximity effect. [1]

Inductor Fabrication Techniques

In applications where high process repeatability is critical (including automotive, aerospace, defense and other industries), the great majority of scan hardening inductors are CNC machined from a solid copper block, thus making them rigid, durable, and repeatable. CAD/CAM/CNC software pro­grams are created that provide appropriate cutter-to-copper spatial relationships, which produce inductors of the re­quired shape and precision regard­less of complexity. Figure 2 shows a variety of fin­ished and semi-finished CNC-machined hardening inductors. [2]

Figure 2: fin­ished and semi-finished CNC-machined hardening inductors

In other cases, copper tubing (square, rectangular, round, or die-formed shaped tubes) may be used for coil fabrication (Figure 3). Copper tubing is typically annealed to improve its ductility, bending properties, and workability. When sharp bends or complex coil shapes are required, inductor segments made from tubing are assembled by brazing. Joints are often overlapped, creating tongue-and-groove joints. Butt-joints should not be used.

Figure 3: Copper tubing (square, rectangular, round, or die-formed shaped tubes) may be used for coil fabrication.

A complex geometry inductor that contains numerous brazed joints, and elbow-type 90° joints in particular, could experience impeded water flow in the cooling coil turns, shortening coil life. Poor quality brazed joints are prime candidates for water leaks affecting not only the coil life expectancy but also a quality of hardened components due to a potential soft spotting in the areas of water leaks. Eliminating braze joints or dramatically reducing their number, particularly in current-carrying areas, is the key to fabricating durable, reliable, and long-last inductors.

Additive manufacturing (AM), or 3D printing, delivers successful fabrication of fixtures, tooling, holders, etc. Recently, some inductors have been fabricated using 3D printing as well. It is important to keep in mind that AM is not a single technology but it comprises a number of processes including direct metal laser sintering, electron beam melting, directed energy deposition, direct and indirect binder jetting, and others.

Depending upon a particular AM technique used in fabricating hardening inductors, it may face major challenges to match properties of pure copper. This includes (1) obtaining sufficiently high thermal conductivity (2) or low electrical resistivity, (3) ensuring high volumetric density, and (4) having minimum amount of residuals, just to name a few. All these factors affect coil life. Therefore, if you compare 3D printed inductors with brazed coils comprising numerous brazed joints, in the majority of cases, the life of 3D printed coils will surpass life of brazed inductors because of elimination of brazed joints in current-carrying regions. In addition, fabrication accuracy and repeatability of AM inductors typically surpasses the accuracy of brazed or bended coils.

The situation is different when comparing life of 3D printed coils vs. CNC machined inductors. Fabrication accuracy of both processes is very similar, however, in high-power density applications even small degradation of above discussed four factors associated with AM might become essential causing greater probability of stress-fatigue and stress-corrosion copper failure of 3D printed coils compared to CNC machined inductors fabricated from pure copper. Another factor to consider is repairability of 3D printed inductors. If you need to do a revision then it would be most likely required you to re-manufacture 3D printed coils. Regardless of a fabrication method and for quality assurance purposes, it is beneficial to apply computerized 3D metrology laser scanner technology (Figure 4) to verify coil dimensional accuracy and alignment precision after inductor fabrication and assembly.

Figure 4: It may be beneficial to apply computerized 3D metrology laser scanner technology to verify accuracy and alignment after inductor fabrication and assembly.

Material Selection

Copper and copper alloys are almost exclusively used to fabricate induction coils due to their reasonable cost, avail­ability, and a unique combination of electrical, thermal, and mechanical properties. Proper selection of copper grade and its purity is crucial to minimize the deleterious effects of factors that contribute to premature coil failure including stress-corrosion and stress-fatigue cracking, galvanic corro­sion, copper erosion, pitting, overheating, and work hardening. Cooling water pH also affects copper sus­ceptibility to cracking.

Oxygen-free high-conductivity (OFHC) copper should be specified for most hardening inductors. In addition to superior electrical and thermal properties, OFHC copper dramatically reduces the risk of hydrogen em­brittlement and developing localized “hot” and “cold” spots. The higher ductility of OFHC copper is also im­portant because coil turns are subjected to flexing due to electromagnetic forces. The higher cost of OFHC copper is offset by improved life expectancy of hardening inductor.

For scan inductors that are intended to heat fillets, an appropriate copper heating face region must be focused into the fillet area. Coil copper profiling and the use of flux concentrators (flux intensifiers) are beneficial to focus the magnetic field into the fillet. These applications require careful design because the induced current has a tendency to take the shortest path and stay in the shaft area rather than flowing into the fillet [1]. Therefore, all efforts must be made to focus the heat generation into the fillet. Typically, higher frequencies work better for this purpose.

Copper Wall Thickness

It is important to maintain sufficient wall thickness to carry the electrical currents. The wall thickness of an inductor’s heating face should increase as frequency decreases. This fact is directly related to both the current penetration depth in the copper δCu. [1] It is highly desirable for the current-carrying copper wall thickness to be 1.6 times greater than the δCu calculated at maximum working temperature. Increased kilowatt losses in the copper, which are associated with reduced coil electrical efficiency and greater water-cooling requirements, will occur if the wall is thinner than 1.6∙δCu.

The table below shows the variation of δCu vs. frequency at room temperature (20°C/68°F).

In some cases, the copper wall thickness can be noticeably thicker than the recommended value of 1.6∙δCu. This is because it may be mechanically impractical to use a tubing wall thickness of, for example, 0.25 mm (0.01 in.).

I recommend Reference #1 to readers interested in further discussion on design of hardening inductors.

References

  1. V.Rudnev, D.Loveless, R.Cook, Handbook of Induction Heating, 2nd Edition, CRC Press, 2017.
  2. V.Rudnev, A.Goodwin, S.Phillip, W.West, S.St.Pierre, Keys to Long-lasting Hardening Inductors: Experience, Materials and Precision, Advanced Materials & Processes, October, 2015, p.48-52.

______________________________________________

Dr. Valery Rudnev, FASM, is the Director of Science & Technology, Inductoheat Inc., and a co-author of Handbook of Induction Heating (2nd ed.), along with Don Loveless and Raymond L. Cook. The Handbook of Induction Heating, 2nd ed., is published by CRC Press. For more information click here.

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