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Exo Gas Composition Changes, Part 1: Production

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Exothermic gas undergoes a few metamorphoses from the time it is produced to the time it is cooled down after use. Explore the transformations that occur within the combustion chamber to discover the impact these phases can have on the heat treatment atmosphere of your workpieces.

This Technical Tuesday article was composed by Harb Nayar, president and founder, TAT Technologies LLC. It appears in Heat Treat Today's August 2023 Automotive Heat Treating print edition.

Background

Harb Nayar
President and Founder
TAT Technologies LLC
Source: LinkedIn

Exothermic gas, more commonly referred to as Exo gas, is produced by partial combustion of hydrocarbon fuels with air in a well-insulated reaction or combustion chamber at temperatures well above 2000°F. Immediately after they exit the combustion chamber, the reaction products are cooled down using water to a temperature below ambient temperature to avoid condensation. The typical dew point of the cooled down Exo gas is about 10°F above the temperature of the water used to cool down. The cooled down Exo is then delivered to the heat treat furnaces where it gets reheated to the operating temperatures between 300°F and 2100°F.

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A simplified schematic flow diagram of Exo gas production followed by its cool down below ambient temperature and its final use in heat treat furnaces is shown in Figure 1.

The following aspects of the Exo gas production are clear from Figure 1:

  1. There is lot of energy lost out of the reaction chamber.
  2. There is additional heat lost during cooling using water.
  3. A good deal of water is used for cooling.
  4. The cooled down Exo gas is re-heated to the process temperature in heat treat furnaces.

Exo gas has been predominantly used and is still being used as a source of nitrogen rich atmosphere for purging, blanketing, and mildly oxide reducing applications in the heat treat and metal working industries.

Figure 1. Schematic flow diagram showing Exo production, cool down, and its use.
Source: Morris, “Exothermic Reactions,” 2023

Examples of applications:

  • Brazing
  • Annealing
  • Hardening
  • Normalizing
  • Sintering
  • Tempering, etc.

Examples of materials:

  • Irons
  • Steels
  • Electrical steels
  • Copper
  • Copper-base alloys
  • Aluminum
  • Jewelry alloys

Examples of product sizes and shapes:

  • Tubes
  • Rods
  • Coils
  • Sheets
  • Plates
  • Components
  • Small parts, etc.

Exo is the lowest cost gas used in furnaces operating at temperatures above about 700°F to keep air out and provide a protective atmosphere with some oxide reducing potential to the materials being thermally processed.

There are two types of Exo gases: lean Exo gas, with mostly nitrogen and carbon dioxide and very little hydrogen, and rich Exo gas, with a little less nitrogen and carbon dioxide and substantially more hydrogen and some carbon monoxide. Typical compositions are given below:

  • Lean Exo: 80–87% Nitrogen; 1–2% Hydrogen; 2–4% H20; 1–2% CO; 10–11% CO2
  • Rich Exo: 70–75% Nitrogen; 9–12% Hydrogen; 2–4% H20; 7–9% CO; 6–7% CO2
Figure 2. Exo gas operating range
Source: SECO/WARWICK

Figure 2 shows graphs of Exo gas composition at various air to natural gas ratios. H2, CO, and residual CH4 decreases with increasing air to natural gas ratio whereas CO2 goes in the opposite direction. H20 content not shown in the graphs is typically in the 2–4% range depending upon the temperature and cooling efficiency of the cooling system. N2 is the balance which increases with increasing air to natural gas ratio.

The generator designs to produce lean and rich Exo gases are slightly different as shown in the schematic flow diagrams below in Figures 3 and 4.

Objective

This paper will demonstrate a simplified software program (harb-9US) developed recently by TAT Technologies LLC that can easily calculate the reaction products composition, temperature, exothermic energy released, various ratios, and final dew point for various combinations of air and fuel flows entering the reaction chamber at a predetermined temperature and pressure.

The data presented in this paper is under thermodynamically equilibrium conditions only, captured when the reaction is fully completed. It does not tell how long it will take for the reaction to reach completion. However, it can be safely said that reactions are completed relatively fast at temperatures above about 1500°F and very slow at temperatures below about 1000°F. The current software program uses U.S. units: flow in SCFH, pressure in PSIG, temperature in degrees Fahrenheit, and heat as enthalpy in BTU.

The composition of the Exo gas for a fixed incoming air to hydrocarbon fuel ratio changes from production in the combustion chamber to the cool down equipment to bring the Exo gas to below the ambient temperature and finally into the furnace where the material is being heat treated.

Understanding the changes in gas composition from Step 1 (Production in the Combustion Chamber) to Step 2 (Cool Down to Ambient Temperature) to Step 3 (At Temperature of Heat Treated Part) can help to improve the composition, quality, and control of Exo gas that will surround the metallic products being heat treated in the furnace.

Figure 3. Lean Exo generator schematic flow diagram
Source: SECO/WARWICK

Step 1: Composition of Exo Gas as Produced in the Combustion Chamber

Table A shows the Exo gas compositions as generated within the combustion chamber at various air to natural gas ratios supplied at 100°F and 0.1 PSIG. In these calculations natural gas composition is assumed as 100% CH4 and air is assumed as 20.95% oxygen and balance nitrogen. CH4 is fixed at 100 SCFH and air flow is varied to give air to natural gas ratios between 9 and 6. Typically a ratio of 9 is used for lean Exo and 7 is used for rich Exo applications. Other ratios are used in some special applications.

Table A: Exo gas compositions in reaction chamber based on 100 SCFH of CH4 with air 900, 850, 800, 750, 700, 650, and 600 SCFH to give air to natural gas (CH4) ratios of 9, 8.5, 8, 7.5, 7, 6.5 and 6 respectively. Air and natural gas (CH4) are at 100°F before entering the combustion chamber.
Source: TAT Technologies LLC

The following key conclusions can be made from Table A as one moves from air to natural gas (CH4) ratio of 9 down to 6:

  1. The peak temperature in the reaction chambers goes from a high of 3721°F down to low of 2865°F. Because of high temperatures, good insulation around the combustion chamber is a must. A significant portion of the exothermally generated energy within the reaction chamber is lost to the surroundings.
  2. There is no residual CH4 in the Exo gas composition at these high temperatures. There is no soot (carbon residue) under equilibrium conditions.
  3. H20 content in the natural gas (CH4) gas in the reaction chamber is very high — from high of 19.11% to low of 15.87%. These correspond to dew point 139°F to 132°F — well above the ambient temperature. Because of the very high dew point, the Exo gas coming out of the reaction chamber must be cooled down below the ambient temperature to remove most of the H20 in the Exo gas to avoid any condensation in the pipes carrying the Exo gas toward the furnace and into the
    furnace.
  4. H2% changes significantly from 0.67% to 9.96%.
  5. The oxide reducing potential (ORP) as measured by H2/H20 ratio changes from a very low of 0.035 to 0.628. ORP in the reaction chamber is overall quite low because of high percentage of H20.
  6. Nitrogen content varies from 70.34% to 61.26% of the total Exo gas in the reaction chamber.
  7. Exothermic heat generated varies from 95.3 MBTU to 54.34 MBTU — it gradually becomes a less exothermic reaction. Gross heating value of CH4 (at full combustion) is 101.1 MBTU/100 cubic foot of CH4.
Figure 4: Rich Exo generator schematic flow diagram
Source: SECO/WARWICK

Question: What happens to the composition of Exo gas as it cools from peak temperature in the combustion chamber to different lower temperatures after it exits from the combustion chamber?

Answer: It changes a LOT, assuming enough time is provided to reach its equilibrium values during cooling down to any specific temperature. Whenever there is a mixture of gases, such as CH4, H2, H20, CO, CO2,O2, N2, there are a variety of reactions going on between the constituents in the reactant gases to produce different combinations of gas products and heats (absorbed or liberated) at different temperatures. The most popular and well-known reactions are:

  • Partial Oxidation Reaction: CH4+ 1/2O2 → CO + 2H2 — exothermic. The reaction becomes more exothermic as O2 increases from 0.5 to 2.
  • Water Gas Shift Reaction: CO + H20 → CO2 + H2 — slightly exothermic. It usually takes place at higher temperatures faster. A catalyst in the reaction chamber can help to lower the high temperature requirement. There are many catalysts. Commonly used are either Ni or precious metals.
  • Steam Reforming Reaction: CH4 + H20 → CO + 3H2 — highly endothermic.
  • CO2 Reforming Reaction: CH4 + CO2 → 2CO + 2H2 — endothermic.

All of these reactions have different degrees of influences from changes in temperature. One could say that the final equilibrium composition of the Exo gas is a continuously moving target as temperature changes. Only the N2 portion stays constant. One can make the following generalized statements covering a broad range of Exo gases (lean and rich) in the reaction chamber:

a) N2 content does not change. It remains neutral at all temperatures.
b) H2 content decreases with increasing temperature.
c) H20 (vapor) content increases with increasing temperature.
d) CO content increases with increasing temperature.
e) CO2 content decreases with increasing temperature.
f) Residual CH4 decreases with increasing temperature.
g) Soot decreases with increasing temperature.
h) Catalysts facilitate the speed of reactions at any temperature.

Conclusion

Exo gas composition changes during its time in the combustion chamber. Reaction products composition, temperature, exothermic energy released, various ratios, and final dew point are all items that need to be taken into consideration to protect the metallic pieces that will be heat treated in the resulting atmosphere. Part 2 will demonstrate this principle and discuss Step 2 (Cool Down to Ambient Temperature) and Step 3 (At Temperature of Heat Treated Part).

About the author:

Harb Nayar is the founder and president of TAT Technologies LLC. Harb is both an inquisitive learner and dynamic entrepreneur who will share his current interests in the powder metal industry, and what he anticipates for the future of the industry, especially where it bisects with heat treating

For more information:

Contact Harb at harb.nayar@tat-tech.com or visit www.tat-tech.com.

References:

Herring, Dan. “Exothermic Gas Generators: Forgotten Technology?” Industrial Heating, 2018. https://digital.bnpmedia.com/publication/m=11623&i=534828&p=121&ver=html5.

Morris, Art. “Exothermic Reactions.” Industrial Heating (June 10, 2023), https://www.industrialheating.com/articles/91142-exothermic-atmospheres.

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

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“The light at the end of the tunnel” — Monitoring Mesh Belt Furnaces

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OCAccording to "Dr. O" – Dr. Steve Offley, product marketing manager at PhoenixTM – temperature control of the heat treatment application is critical to the metallurgical and physical characteristics of the final product, and hence its ability to perform its intended function. Explore today's Technical Tuesday article to find the light at the end of your mesh belt furnace tunnel.

This article first appeared in Heat Treat Today’s February 2022 Air & Atmosphere Furnace Systems print edition.

Dr. Steve Offley, “Dr. O"
Product Marketing Manager
PhoenixTM

Introduction – The Need for Accurate Product Temperature Measurement

Even though modern furnaces are supplied with sophisticated control systems, they are still not always capable of truly giving an accurate picture of the actual product temperature as it passes through the process. Temperature sensors positioned along the furnace give a snapshot of what the environmental temperature is possibly zone by zone. Furnace controllers, as the name suggests, can give confidence that the process heating is performed in a controlled manner but will never give an accurate view of what the actual product temperature is. When monitoring, it is important to be able to distinguish between process and product.

The challenge to any process engineer is understanding how the product heating cycle relates to the operation of the furnace. A furnace environment may be well controlled, but very different product temperatures can be experienced with variation in key properties such as product material, size, shape, thermal mass, and position/orientation in the furnace. Infrared (IR) pyrometers and thermal imagers can provide surface temperature measurements only and require line of sight, so they limit the areas of the product that can be measured. Setup can sometimes be complex considering surface characteristics (emissivity) and process background/atmosphere compensation. As with air sensors, being fixed, typically IR sensors only give information at that specific furnace location which prevents accurate calculation of soak times at critical temperatures. Without additional information, soak times and temperatures may need to be extended well beyond the target to guarantee the heat treat process is completed with confidence with an obvious compromise to throughput and energy conservation.

Product Temperature Profiling

To fully understand the operational characteristics of the heat treat process it is necessary to measure both the environment and product temperature continuously as it travels through the process. Such technique provides what is referred to as a “temperature profile” which is basically a thermal fingerprint for that product in that furnace process. This thermal fingerprint will be unique but will allow understanding, control, optimization, and validation of the heat treat process.

Table 1. Table showing the numerous benefits of thru-process temperature monitoring over traditional trailing thermocouples methodology for a mesh belt furnace

Historically, trailing thermocouples have been the go-to technique for product temperature monitoring. A very long thermocouple is attached to the product in the furnace. The data logger measuring the live temperature reading is kept external to the furnace. Although possible for static batch processes, the technique has significant limitations in a continuous/semicontinuous process, especially mesh belt furnaces (See Table 1).

Fig 1. Robust multichannel data logger designed specifically for thru-process temperature profiling

In thru-process temperature profiling the data logger travels with the product through the furnace. The data logger (Figure 1) is protected by an enclosure, referred to as a thermal barrier, which keeps the logger at a safe operating temperature (Figure 2). Temperature readings recorded by the data logger from multiple short length thermocouples can be retrieved post run. Alternatively, if feasible, the data can be read in real time as the system passes through the furnace using a two-way radio frequency (RF) telemetry communication option. The resulting temperature profile graph (Figure 3) provides a comprehensive picture — product thermal fingerprint — of the thermal process.

Fig 2. Thermal barrier protecting the data logger safely entering the conveyor furnace during the temperature profile run. Barrier size is customized to suit process credentials.

Fig 3. Typical temperature profile recorded for an aluminum CAB brazing line giving a complete temperature history for a brazed radiator at different product locations.(1)

Monitoring Your Heat Treat Process Temperature at the Product Level

Applying thru-process temperature monitoring product temperature measurement can focus on the micro product level which at the end of the day is most important. Static control thermocouples give an environmental temperature of the furnace in a zone, but this only reflects the true temperature wherever the thermocouple is located. This may be some distance from the product and may give some bias to its position if located on one side of the furnace. The thru-process monitoring system allows simultaneous product and/or air temperature measurement directly at the mesh belt. Monitoring can be performed across the belt with thermocouple placement on and in the core of the product and can be made to identify areas of different thermal mass resulting in differing heating characteristics.

A useful strategy to use before looking at the product temperature is to thermally map the furnace. Thermocouples, connected to the data logger protected within the thermal barrier, are positioned across the mesh belt using a mount jig such as that shown in Figure 4. The jig guarantees reliable location of the measurement sensor run to run and adjustment means it can be adapted to different belt widths. Applying this principle, the thermal uniformity of air across the belt width through the entire furnace can be measured.

Fig 4. Thermocouple mount jig allowing accurate positioning of thermocouples (1) across the mesh belt width with adjustment to suit different belt dimensions (2).

Such data can be compared with zone control thermocouples to see what temperature differential the product may be experiencing at the belt level. Temperature imbalances across the belt and hot or cold spots along the process journey can be identified.

Furnace mapping can be further developed to satisfy either CQI-9/CQI-29 or AMS2750F pyrometry standards where a two-dimensional jig is constructed to perform the temperature uniformity survey (TUS).2 Employing the plane method, a frame jig is constructed to match the furnace work zone with the necessary number of thermocouples to satisfy the furnace cross section dimensions. Temperatures recorded over the working zone are compared to the desired TUS levels to ensure that they are within tolerance as defined in the standards.

Discover the True Root Cause of Your Furnace Problems

When it comes to product quality and process efficiency in any mesh belt furnace applications, temperature monitoring is only part of the story. Gaining an insight into what is physically happening in the product’s furnace journey can help you understand current issues or predict issues in the future, which can be corrected or prevented. To allow true root cause analysis of temperature related issues, it is sometimes necessary to “go to Gemba” and inspect what the product is experiencing, directly in the furnace. This is not always possible under true production conditions.

For a classic mesh belt furnace application such as controlled aluminum brazing (CAB), internal inspection of the furnace is not a quick and easy task. Operating at 1000°F, the cool down period is significant to allow engineers safe access for inspection and corrective action and then further delay to get the furnace back up to a stable operating temperature. Such maintenance action may mean one or two days lost production, from that line, which is obviously detrimental to productivity, meeting production schedules, satisfying key customers, and the bottom line.

In addition to process temperature problems there are many other production issues that can be faced relating to the furnace operation and safe reliable transfer of the product through the furnace. In the CAB process a day-to-day hazard is the build-up of flux debris. Flux materials used to remove oxides from the metal surface and allow successful brazing can accumulate within the internal void of the furnace. These materials are most problematic at the back end of the muffle section of the furnace where, due to the drop in temperature entering the cooling zone, materials condense out. Flux buildup can create many different process issues including:

  • Physical damage to the conveyor belt or support structure requiring expensive replacement
  • Reduction in belt lubricity creating jerky movement and causing unwanted product vibration
  • Lifting of the mesh belt creating an uneven transfer of products causing possible excessive product movement, clumping, or clashing
  • Reduction in inner furnace clearance creating possible product impingement issues and blockages

To prevent such problems, regular scheduled inspection and clean out of the furnace is necessary. This is not a pleasant, quick operation, and requires chipping away flux debris with pneumatic tools. Often requiring a furnace down time of 1 to 2 days, this task is only performed when essential. Leaving the clean-up operation too long can be catastrophic, causing dramatic deterioration in product quality or risk of mid-production run stoppages.

Figure 5. PhoenixTM Optical profiling ‘Optic’ System - Optical Profile View. System adaptable for both temperature and optical profiling.

Optical Profiling – The Efficient Alternative

Optical profiling is a new complementary technique to that of thru-process temperature profiling. The innovative technology allows for the first-time process engineers to view the inner workings of the furnace under normal production conditions. Traveling through the furnace with the products being processed, the optic system gives a product’s eye view of the entire heat treatment journey. A thermal barrier, similar in design to that used in temperature profiling, protects a compact video camera and torch that are used to record a video of what a product would see traveling through the furnace (Figure 5). The principle is just like your car’s dash cam, the only difference being that your journey is being performed in a furnace at up to 1000°F. The resulting video, “Optical Furnace Profile,” shows process engineers so much about how their process is operating without any need to stop, cool, and dismantle the furnace. This allows safe routine furnace inspection without any of the problems of costly lost production and days of furnace down time.

Summary

Monitoring your mesh belt furnace from a temperature and optical perspective allows you to fully understand what truly happens in that black box. Understanding leads to better control, which helps you get the optimal performance out of your heat treat process from a quality, productivity, and energy efficiency perspective.

Don’t get left in the dark. Consider the power of temperature and optical profiling which will literally provide a light at the end of your furnace tunnel!

References:

[1] Steve Offley, “Unveiling the Mystery of Your Al Brazing Furnace with ‘Thru-Process’ Temperature Profiling," Heat Treat Today Magazine, June 2020, p40.

[2] Steve Offley, “Applying ‘Thru-process’ Temperature Surveying To Meet the TUS Challenge of CQI-9.” HeatTreatToday.com. June, 2019. https://www.heattreattoday.com/heat-treat-news/automotive-heattreat-news/applying-thru-processtemperature-surveying-to-meet-thetus-challenges-of-cqi-9/

About the Author:

Dr. Steve Offley, “Dr. O,” has been the product marketing manager at PhoenixTM for the last 4 years after a career of over 25 years in temperature monitoring focusing on the heat treatment, paint, and general manufacturing industries. A key aspect of his role is the product management of the innovative PhoenixTM range of ‘thruprocess’ temperature and optical profiling and TUS monitoring system solutions.

For more information, contact Dr. O at Steve.Offley@phoenixTM.com.

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Mesh Belts 101

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OC

Heat Treat Today surveyed mesh belt industry manufacturers asking for feedback on information heat treaters should know. In this article, Abelard Escura, manager of Export at Codina, gives recommendations when to use specific belts, explains belt vocabulary, and shares trends they are excited about.

This article first appeared in Heat Treat Today’s February 2022 Air & Atmosphere Furnace Systems print edition.

What mesh belt materials, belt weaves, and belt loading (lbs./linear foot or lbs./square foot) are recommended for various heat treatment processes and atmospheres?

For quench tank belts (oil, salt, water), annealing and normalizing applications, and hardening and case hardening (carburizing and carbonitriding in particular), Abelard Escura of Codina said, “Normally for these applications, the parts are small, so we usually go for models with several rods inside one spiral, to close the opening area of the belt. The basic material recommended is AISI 314/AISI 330CB.”

“Because the parts can be large or in baskets during the sintering (specifically irons, stainless steels) and brazing (silver, copper, nickel) processes, it is recommended that balance or double balance weave (models AE or AE-A) with just one rod inside one spiral be used. The basic material recommended is AISI 314. By the way, in the EU, the model B1ES is popular for brazing because it’s stronger and allows heavy loads on the mesh belt.” Escura added.

Photo Credit: Codina

Explain the “vocabulary” of belts:

Understanding the mesh belt lingo is critical for achieving successful results.

Heat Treat Today asked, What about the types of belt weaves (open versus closed weaves), upturned edges — when/why are they recommended, and why are certain alloys (e.g., 316 SS) such a popular choice for general purpose belts? Escura responded, “The closed weave belts are used for small products like fasteners. Open weave belts are used for larger products.” He continues, “The material content, for heat treatment in general, needs to be high in nickel and chromium to be strong enough to resist high temperatures and oxidation.”

What is the typical belt life for processing running in the 1600°F–1800°F temperature range in a nitrogen or nitrogen/hydrogen atmosphere? Escura weighed in, “This will always depend on the process, application, and how the belt is used on the furnace. However, as a rule, the lifetime of the mesh belt can be from 6 to 12 months.”

What about the pre-conditioning (prestretching) of the belt — when is it recommended and for what applications?

Escura explained, “We do not believe this preconditioning is helpful. It’s also an extra cost. If the belt is produced properly, pre-conditioning is not necessary.”

What are a few common problems encountered when operating mesh belts?

“The main problems are belt deformations from extra load, cuts on the mesh belt due to parts stacking on the furnaces and cutting the belt. Another problem we see is lateral plates break, fall out, and come into contact with the ‘floor’ of the furnace,” Escura shared.

Are there any advances or trends in the mesh belt world that you’re excited about? What is one thing that you believe is vital for people to know about mesh belts?

Escura concluded, “We are excited about looped edges instead of welded edges terminations. These looped edges prevent the breaking of the welding, and belts can last longer in sintering and brazing applications.”

For more information

Contact Abe: abe@codinametal.com

Website: Codinametal.com

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Don’t Vacuum-Braze Metals Containing Zinc

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Source: Kay & Associates Brazing Consultants 

Are you sure you should vacuum braze that? As the title of this best of the web article suggests, vacuum brazing materials containing zinc is not a good idea. Volatized zinc can contaminate, and maybe even ruin, your vacuum furnace. But what about cadmium, lead, chromium, and magnesium? Is vacuum brazing safe for those materials?

In this article by Dan Kay, examine the vapor pressure curves of common metallic elements to be sure you know exactly when you need to worry about vaporization. And remember, operating your furnace at partial pressure does not offset the effects of vaporization.

An excerpt: 

Many people braze stainless steels (which contains chromium) at vacuum levels approaching 10-5 Torr [. . . ] You can readily see that at 10-5 Torr the temperature at which Cr volatilizes has dropped down to only about 1800F (950°C). Since nickel-brazing of stainless typically takes place at about 2000-2100°F (1095-1150°C), please understand that you will indeed be volatilizing chromium during this brazing operation, which will condense on the furnace walls, giving them a greenish/bluish coloration.

Read more: Don't Vacuum-Braze Metals Containing Zinc

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

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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 »

Celebrate January 6th: National Technology Day!

/ BRAZING TECHNICAL CONTENT, FEATURED NEWS, HARDENING TECHNICAL CONTENT, HIPING TECHNICAL CONTENT, INDUCTION HEATING TECHNICAL CONTENT, MANUFACTURING HEAT TREAT, NITRIDING TECHNICAL CONTENT

OCWhat’s new in heat treat? A LOT.

Over the past year, we’ve seen numerous new technologies in the way of research, new partnerships, and conversations throughout the industry. So in honor of today being #NationalTechnologyDay, we’re sharing an original content article about just several of these new technologies that are changing the work of heat treaters across North America.

Research

Using HIP to Advance Oregon Manufacturing Innovation Center Programming – “‘Today’s globally competitive manufacturing industry demands rapid innovations in advanced manufacturing technologies to produce complex, high-performance products at low cost,’ observes Dr. Mostafa Saber, associate professor of Manufacturing & Mechanical Engineering Technology at Oregon Tech.”

College Students Implement a NEW Heat Treat Solution with Induction? – “‘We were in shock,’ Dennis admitted, ‘because we didn’t expect it to [work].’ The expectation, Dennis continued, was that something would go wrong, like the lid would not be able to clamp down, or the container would leak.”

The Age of Robotics with Penna Flame Industries – “The computerized robotic surface hardening systems have revolutionized the surface hardening industry. These advanced robots, coupled with programmable index tables, provide an automation system that helps decrease production time while maintaining the highest quality in precision surface hardening.”

New Partnerships

Captive Extrusion Die Maker Levels Up With 11 New Furnaces – Heat treaters are leaning into the benefits of nitriding and vacuum technology.

Auto Partner Enters Agreement for New Nitriding Technology – As nitriding technology becomes more popular, heat treaters are brushing up on their understanding of case hardening processes across the board. (Read this article comparing 5 common case hardening processes.)

Vacuum Heat Treat Supplier Partners with Neota to Advance MIM Technology – Learn how this partnership produced solid and strong metallic parts with near 100% density.

Conversations in the Industry

Heat Treat Radio: Five experts (plus Doug Glenn) discuss hydrogen combustion in this episode. An easily digestible excerpt of the transcript circulated by Furnaces International here and is available to watch/listen/read in full for free here.

Heat Treat Radio: Get on-the-ground projections of what technologies Piotr Zawistowski believes will be bringing in the future. Watch/listen/read in full here

Heat Treat Radio: HIP. The Revolution of Manufacturing, that is, according to Cliff Orcutt. Watch/listen/read in full here

Heat Treat Radio: Will indentation plastometry find its way into North America? If you’ve been listening to James Dean, it seems like it already has. Watch/listen/read in full here

Heat Treat Radio: Fluxless inert atmosphere induction brazing. That’s a mouthful! But what is it? Watch/listen/read in full here

Learn More About New Tech!

Everything You Need to Know About HIPing eBook

Metal Hardening with Mark Hemsath Podcast

Stories About Heat Treaters Implementing New Hardening Methods Article

 

 

Celebrate January 6th: National Technology Day! Read More »

Have You Seen These 18 Heat Treat Technical Resources?

/ BRAZING TECHNICAL CONTENT, CARBURIZING TECHNICAL CONTENT, FEATURED NEWS, FOUNDRY CASTING TECHNICAL CONTENT, HARDENING TECHNICAL CONTENT, HIPING TECHNICAL CONTENT, MANUFACTURING HEAT TREAT, NITRIDING TECHNICAL CONTENT, PARTS CLEANING TECHNICAL-CONTENT

OCWelcome to another Technical Tuesday for 18 hard-hitting resources to use at your heat treat shop. These include quick tables, data sets, and videos/downloadable reports covering a range of heat treat topics from case hardening and thermocouples to HIPing and powder metallurgy.

Defining Terms: Tables and Lists

  1. Table #3 Suggested Tests and Frequencies for a Polymer Quench Solution (in article here)
  2. Case Hardening Process Equipment Considerations (bottom of the article here)
  3. Nitriding vs. FNC comparative table here
  4. 9 Industry 4.0 Terms You Should Know here
  5. Table 1: Limits of Error Thermocouple Wire (in article here)
  6. Table 2: Limits of Error Extension Grade Wire (in article here)
  7. Thermocouple Color Code Chart (in article here)
  8. International Thermocouple Lead Colors (in article here)

Free Downloadable Reports

  1. FREE ebook—High Pressure Heat Treatment: HIP here
  2. FREE ebook – On-site Hydrogen Generation here
  3. Forging, Quenching, and Integrated Heat Treat: DFIQ Final Report here

Visual Resources

  1. HISTORIC VIDEO: Aluminum Heat Treatment here
  2. Two simulations of a moving billet through heating systems (in article here)
  3. Fourier’s Law of Heat Conduction (in article here)
  4. Webinar on Parts Washing (link to full webinar at the top of the review article here)
  5. Materials 101 Series from Mega Mechatronics, Part 4, Heat Treatment/Hardening here
  6. Heat Treat TV: Press-and-Sinter Powder Metallurgy here

BONUS: 39 Top Heat Treat Resources

Heat Treat Today is always on the hunt for cutting-edge heat treat technology, trends, and resources that will help our audience become better informed. To find the top resources being used in the industry, we asked your colleagues. Discover their go-to resources that help them to hone their skills in the 39 Top Heat Treat Resources on this page of the September print magazine.

 

Have You Seen These 18 Heat Treat Technical Resources? Read More »

The “Next Leap”: Diffusion Bonding for Critical Component Manufacturing

/ BRAZING TECHNICAL CONTENT, FEATURED NEWS, MANUFACTURING HEAT TREAT

OCWith "advances in electric vehicle transportation, semiconductor fabrication, novel material development, and miniaturization, the ‘performance envelope’ continues to broaden." This requires revisiting some tried and true heat treating techniques and their applications.

Read on to see what Tom Palamides, senior sales and product manager at PVA TePla America, Inc., has to say about how diffusion bonding may replace brazing for certain applications. Check out other Heat Treat Today original content or Technical Tuesday articles in the search bar to the right.

Tom Palamides with diffusion bonding furnace
Source: PVA TePla

As we begin to see the light at the end of the tunnel from the devastating economic shock of the COVID pandemic, engineering companies, heat treaters, and material process engineers must work in unison to adopt refined manufacturing processes to meet the demands of critical component design. Harnessing new tools and techniques allows for real operational enhancements and is an increasing trend across many industries.

Brazing historically has been, and remains, the stalwart technique for joining precision-machined components. However, with advances in electric vehicle transportation, semiconductor fabrication, novel material development, and miniaturization, the “performance envelope” continues to broaden. Two of the most common limitations of brazing are that it is challenging to prevent alloy flow in small diameter micro-channels. When such a part is used in higher temperature operating conditions, the joint can introduce elemental cross-contaminants for ultraclean environments. To this end, diffusion bonding, which uses pressure and relatively low heat (about 50%-90% of the absolute melting point of the parent material) to join similar, or dissimilar materials, holds promise.

If one examines the aerospace, semiconductors, energy, medical devices, and electronic component markets, new and higher performance demands have become the norm. Next-generation product designers are, therefore, evaluating new bonding processes to achieve improved performance goals. Many now view diffusion bonding as the “next leap” for metallic materials processing; it offers several unique advantages for complex geometric structures and materials that can operate under strenuous high-performance conditions.

Solid-state diffusion bonding results from the controlled combination of three (3) key processing parameters: pressure, temperature, and cycle time. The careful balancing of these three parameters promotes bonding at the joining surfaces. The result is a virtually invisible uniform interface, devoid of metallurgical discontinuities and porosity.

PVA TePla’s commercial diffusion bonding furnace for joining similar and dissimilar materials
Source: PVA TePla

Process engineers have evaluated solid-state diffusion bonding at a research-level for more than fifty years; however, much has changed recently. Building on twenty-five years of successful commercial product solutions, such as aircraft disk brakes and specialized heat exchangers, diffusion bonding is now an “upgraded” process. With advancement in the use of high-strength carbon matrix composites and advanced furnace designs that leverage sophisticated electronics and hydraulic systems controllable to within thousandth-of-an-inch, commercial interest now extends far beyond aerospace and energy.

The most sophisticated global companies in electronic instrumentation and semiconductors view diffusion bonding as the wave of the future. The functional-value that 21st-century diffusion bonding technology now offers is a unique-and-beneficial solution in a class by itself; designers came to this realization after being confronted with component performance issues that could not be resolved by traditional brazing. Materials currently under consideration include pure aluminum, aluminum alloys, stainless steels, and nickel-based alloys as well as any other material, such as coated substrates for power electronics or glass and special material combinations (dissimilar joints).

Today is an exciting time for any engineer who wants to upgrade or produce new and/or higher performance designs, and heat treaters need to be aware of a new process emerging in their midst. It is essential for the heat treater to know the various types of capital equipment and the performance specifications that have and are evolving with the diffusion bonding process. Companies are learning to operate with smarter devices and more intelligent methods. Why not evaluate diffusion bonding to improve productivity, product quality, and material performance for your next-generation products?

About the Author: Thomas Palamides, senior sales and product manager at PVA TePla America, Inc., has a background in materials science and international marketing.  He holds two U.S. patents.  He is passionate about facilitating a broader understanding of how material processes fundamentally influence design and manufacturing cost, as well as how they improve business.

 

(source: Michael Fousert at unsplash)

(source: thisisengineering Raeng at unsplash)

 

 

 

 

 

 

 

The “Next Leap”: Diffusion Bonding for Critical Component Manufacturing Read More »

Washing and Heat Treat: What Did You Miss?

/ BRAZING TECHNICAL CONTENT, CARBURIZING TECHNICAL CONTENT, FEATURED NEWS, MANUFACTURING HEAT TREAT, PARTS CLEANING TECHNICAL-CONTENT

OCIn January 2021, Hubbard-Hall hosted a free webinar with Thomas Wingens of Wingens International and Michael Onken of SAFECHEM. These two experts described the influencing factors for technical cleanliness and some solutions for washing. This Technical Tuesday, we are sharing an Original Content overview of what happened at the virtual event.

To learn more, watch the recorded webinar here. Additionally, listen to Thomas Wingens on "Parts Washing" on Heat Treat Radio.

This year, we are seeing a lot of online-adapted education for the heat treat industry. One of these webinars was "Solving The 4 Most Common Metal Cleaning Challenges In Heat Treatment" hosted for free by Hubbard-Hall. Jeff Davis, SVP of business development and distribution at the chemical supplier, introduced experts Thomas Wingens, longtime metallurgist with a lifetime of exposure in the heat treating industry, and Michael Onken, market development manager at SAFECHEM. Here is a brief rundown of what they talked about.

The concluding slide from Hubbard-Hall's webinar, Tuesday February 2, 2021.
Source: Screen shot from Hubbard-Hall Webinar February 9, 2021

How Do You Clean | Why Do You Clean | Who Cleans

The audience indicated that if they cleaned, they overwhelming used water-based cleaners on their products.

The experts then gave four clear reasons why heat treaters should clean:

  • Optics -- get rid of stains
  • Achieve Uniformity -- resolve soft spots and stop-off paint issues
  • Brazing Voids -- prevent the appearance of bubbles on your part
  • Contamination of the Furnace -- all furnaces, even vacuum furnaces, are susceptible to contamination
  • Smoking Parts -- if not cleaned well, left-over oil on a part can smoke up

With all of these reasons and with the specificity of the part, all heat treaters should pay attention to how they clean their products, but especially commercial heat treaters. The reason? Commercial heat treaters are in the most challenging situation with cooling fluid contamination, corrosion protection, chips, dirt, and dust as they treat a variety of different parts at their facility. As a note, the experts noted that commercial heat treaters could remove these contaminants with sandblasting, pickling, and sputtering.

4 Challenges - 4 Solutions

One by one, Wingens shared a cleaning challenge that Onken immediately responded to.

1 - Residual Contamination Results in Insufficient Hardening (T.W.)

Residual contamination may be because the cleaning method you are using is insufficient or non-existent. Still, Wingens noted there is clear evidence that insufficient cleaning for nitriding and ferritic nitro caburizing (FNC) leads to white spots. This, among other things, is a cause for concern and may compromise the part quality.

1 - Consider Cleaning Factors, Regulations, and Requirements (M.O.)

If you are running into this cleaning challenge, you have to first consider specific factors, regulations, and requirements for implementing optimal cleaning, says Onken.

  1. Time. You want cleaning to be as short as possible because "time is money."
  2. Temperature.
  3. Mechanics of the cleaning machine.
  4. Chemistry of the Cleaning Agents. Alkaline, neutral, or and organic solvents? You must know what type of contaminations you have on the surface -- if it's polar or non-polar -- in order to use the correct solvent in cleaning the part.
    • Are the contaminants fat, resins, oil, petroleum or salts, emulsions, emulsions?

Additionally, there are several factors of the part itself, pricing, and Environmental Health & Safety standards that do come into play, as Onken lists in the slide below.

Michael Onken sharing factors influencing technical cleanliness.
Source: Screen shot from Hubbard-Hall Webinar February 9, 2021

2 - Surface Stains on Finished Product (T.W.)

This is a pretty straight forward challenge: you don't want the surface stain, so what do you do?

2 - Type of Contamination: Polarity (M.O.)

First, you want to clean "like-with-like." That is, if you have a water insoluble/non-polar contaminant like petroleum or wax, you want to clean with an insoluble/non-polar cleaner like halogenated solvents. Likewise, if the contaminants are water soluble/polar like salts or emulsion residues, then you clean with water-based cleaners. Check out the chart below that Onken shared at the webinar to see how specific cleaners are non-polar, polar, or even hybrid.

Polarity of cleaners and contaminants presented by Michael Onken at SAFECHEM.
Source: Screen shot from Hubbard-Hall Webinar February 9, 2021

Additionally, the way your load is situated can influence what cleaner you use. For a basket load, you'll want to use a cleaner with low surface tension like solvents since those can penetrate and move through the complex geometry of the load.

3 - Inconsistent Cleaning (T.W.)

The impact of a cleaner decreases in strength over time, particularly with solvents, leading to an oily surface. (See the example below.) What to do?

Oily parts before hat treating and after quenching.
Source: Screen shot from Hubbard-Hall Webinar February 9, 2021

3 - Process Stability (M.O.)

There are preventative measures, Onken highlights, that emphasizes process stability that can handle high through-put that will clean all of the parts you have uniformly:

  • Solvents: These are 100% composed of solvent with a stabilizer. Monitor build up of acids only, not the concentration of cleaner itself.
  • Water cleaner: These are 90-99% water mixed with other chemical(s). Therefore, they are much more complex. Check out alkalinity.

Bottom line: keep an eye on how your cleaners are doing so that you always know their quality before you use them.

4 - The Cost. (T.W.)

Wingens pointed out that it is costly to invest in a cleaner, and so how is a heat treater to mitigate this practical challenge?

4 - Efficient Product Use (M.O.)

First, look at efficiency of aqueous cleaning. Solvent cleaning is now in closed machines, not open machines. It is simply not that efficient to use an open machine because a lot of the cleaner disperses into the atmosphere when it is in use. That is why it is more common to see closed cleaning process. Vacuum Tight Machines close the processes even more.

Do what can to conserve material and keep the process efficient and effective.

Final Comments

The experts left the live webinar with a few final comments, noting that there is a move away from water-based cleaning because of the constraints of being able to do batch part cleaning (see solution #2). Additionally, they reiterated that investment costs are higher for closed system with a vacuum; but due to their efficiency, that investment can be paid-off fairly quickly.

If you are interested in catching the next webinar, "Do You Know Your Real Cost of Cleaning?" is happening next week, February 23, 2021 at 2:00pm ET. Again, the recorded webinar can be accessed here.

 

All images were captured during the live webinar on February 2, 2021.

Washing and Heat Treat: What Did You Miss? Read More »

Heat Treating and Fishing: New Applications with Induction and Brazing

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

Source: The Ambrell Blog

How does this heat treat equipment supplier help a fishhook heat treater with their brazing and induction needs? Find out in today’s Best of the Web featured case study from Ambrell Induction Heating Solutions.

The client needed to heat two pairs of fishhooks within a steel tube to form an anchor. This brief case study demonstrates the value in testing new methods to optimize heat treating results.

An excerpt:

[blockquote author=”Bret Daly, The Ambrell Blog” style=”1″]It took 35 seconds or less to heat each sample to temperature. For one of the samples, to prevent overheating of the tube, braze wire was cut up and put inside the tube along with the fishhooks. That way, the entire assembly would…[/blockquote]

Read more: “Induction Brazing Fishhooks”

 

 

 

 

(photo source: Sebastian Pena Lambarri at unsplash.com)

Heat Treating and Fishing: New Applications with Induction and Brazing Read More »