In this installment of Answers in the Atmosphere, David (Dave) Wolff, an independent expert focusing on industrial atmospheres for heat treat applications, explores the practical role of argon as a truly inert alternative to nitrogen in thermal processing.
This informative piece on argon’s unique properties, production challenges, and applications — from vacuum heat treating of titanium to powder metallurgy and additive manufacturing —was first released in Heat Treat Today’sFebruary 2026 Annual Air & Atmosphere Heat Treating print edition.
Akin Malas Business Development Manager / Metallurgist Linde
In this column, I’ve invited Akin Malas, business development manager and metallurgist at Linde, to bring his deep expertise in the subject of argon gas. What follows is the fruit of our discussion and continued conversations about this specialized yet indispensable industrial gas in thermal processing applications.
Compared to nitrogen (the industrial gas this column last covered), argon exhibits actual inertness, enabling its use in high-temperature environments and for processing metals that cannot tolerate nitrogen atmospheres, such as titanium and certain high-performance stainless steels. While argon is significantly higher cost than nitrogen, it remains far more economical than helium, another highly inert alternative.
Argon plays a vital role across multiple stages of metal processing, including:
Primary metallurgy: ladle stirring
Powder metallurgy: atomization of metal powders
Additive manufacturing: laser and electron-beam processes requiring inert chamber atmospheres
Vacuum heat treating: backfill gas for titanium and specialty alloys
Argon is used differently than nitrogen in most cases. Inexpensive nitrogen is often used as a utility pressurization gas, for scavenging, and blended with other gases (such as hydrogen); however, argon is most often used in pure form. Nitrogen is considered inert for heat treatment applications except in extraordinarily high temperatures or heat treatment of reactive metals, such as titanium and stainless steels. In this case, using an actual inert gas like argon or helium is necessary. Also, while nitrogen is virtually the same density as air and thus will diffuse throughout a vessel, argon is much denser than air and can be used to form a stratified inert layer.
Linde gas storage tanks | Image Credit: Linde
Both argon and nitrogen are separated from air in a cryogenic air separation unit (ASU), but there are three main factors that make argon much harder to make than nitrogen and thus much more expensive:
Argon is only 1% of air while nitrogen is 78% of air. Argon boils at nearly the same temperature as oxygen, making a separate purification process necessary. Those two factors mean that only the largest ASUs make enough argon to make it worth purifying.
Argon cannot economically be separated from air non-cryogenically (primarily because the percentage in air is so low), so there is no low-cost competition to cryogenic argon. Also, because argon is prized for its inertness, there is much less interest in argon that might be lower purity.
Because argon is made in only the largest ASUs (typically those serving very large steel mills) and because those plants tend to be geographically grouped, shipping distances for argon tend to be much farther than for nitrogen and oxygen, further driving up the costs.
Processors of titanium parts and parts made of some stainless steels, such as the 300 series stainless alloys (SS), cannot be processed in nitrogen-containing atmospheres, because the metals will nitride at heat treating temperatures. Hence these metals may be processed in a pure argon (for Ti) or hydrogen (for SS) atmosphere blends.
We’ll pick up this discussion next month to see what market options are available, particularly in the U.S.
About The Author:
David (Dave) Wolff Industrial Gas Professional Wolff Engineering
Dave Wolff has over 40 years of project engineering, industrial gas generation and application engineering, marketing, and sales experience. Dave holds a degree in engineering science from Dartmouth College. Currently, he consults in the areas of industrial gas and chemical new product development and commercial introduction, as well as market development and selling practices.
In this installment of Answers in the Atmosphere, David (Dave) Wolff, an independent expert focusing on industrial atmospheres for heat treat applications, highlights the practical value of smartphone apps designed for industrial gas calculations and conversions.
This informative piece on mobile tools that simplify gas property calculations, unit conversions, and storage or flow-rate estimations — drawing attention to apps developed by major gas suppliers and equipment providers that help heat treaters access critical data in the field —was first released in Heat Treat Today’sJanuary 2026 Annual Technologies to Watch print edition.
The field of industrial gases is complicated by the fact that the physical characteristics of gases depend on the temperature and pressure at the time of measurement. Industrial gases may be delivered and stored as cryogenic liquids and highly pressurized gases, though they are generally used in relatively low-pressure gaseous form. Additionally, gases may be used for different purposes; for example, hydrogen may be used as a metallurgical atmosphere or as a burner fuel. As such, users need a ready source of data on various industrial gases to make necessary calculations.
Image Credit: Open Library/Internet Archive
Years ago, industrial gas users had to rely on data tables in publications like the CRC Handbook of Chemistry and Physics — the nearly 8 lb, $195 hardbound handbook that has been published continuously since 1914 and is currently on its 106th edition.
Today, there are many more mobile solutions in the form of smartphone applications. Several of the major gas providers have developed handy apps available for both Apple and Android operating systems to simplify gas conversions and calculations. Equipment providers have also developed apps to help understand the specifics of their equipment. All of these can be helpful to metals thermal processors, including heat treaters at in-house processing operations.
Some examples follow:
Air ProductsandLinde both provide powerful conversion engines that enable users to convert from imperial to metric units, from mass to volume measurements, and from liquid to gaseous volumes for common industrial gases. For example, users can calculate how many hours of atmosphere coverage 6,000 gallons of liquid hydrogen stored in a tank will provide.
Cyl-Tec, Inc. has developed an app that focuses on calculations primarily specific to cryogenic and pressurized gas storage. In addition to unit of measure conversions for each common industrial gas, the app provides detailed information on each of the storage vessels that the company makes.
WITT-Gasetechnik of Germany has developed an app to support their gas safety and controls business. Their products include gas mixers, gas analyzers, regulators, and other controls. The app provides a variety of gas blending and measurement information, including welding gas blend suggestions, unit conversion, and flow rate calculators.
Gasmet of Finland has developed an app that simplifies calculation of dewpoint and combustion products depending on the fuel being combusted.
While these suppliers hope that you will buy their products, be assured that the measurements and conversions performed with their tools, and the recommendations generated, will be equally applicable to products and systems supplied by others.
I suggest you create a folder called “calculations and conversions” on your smartphone and load it up with several of these apps while you are connected to your home or office internet, so that you will have the apps handy when you are away from your standard technical resources.
About The Author:
David (Dave) Wolff Industrial Gas Professional Wolff Engineering
Dave Wolff has over 40 years of project engineering, industrial gas generation and application engineering, marketing, and sales experience. Dave holds a degree in engineering science from Dartmouth College. Currently, he consults in the areas of industrial gas and chemical new product development and commercial introduction, as well as market development and selling practices.
In this installment of Answers in the Atmosphere, David (Dave) Wolff, an independent expert focusing on industrial atmospheres for heat treat applications, explores the versatile role of nitrogen gas in thermal processing.
This informative piece on nitrogen’s flow rate considerations, sourcing strategies, and cost factors — drawing on insights from Air Products engineers to help heat treaters make informed, cost-effective supply decisions —was first released inHeat Treat Today’sDecember 2025 Annual Medical & Energy Heat Treat print edition.
We’re picking up the topic of nitrogen this month with a continued discussion of several key aspects of flow rate, expert assistance, and atmosphere costs that I had the pleasure of hearing about from several key industry experts. My thanks to these Air Products individuals: John Dwyer, principal engineer; Bryan Hernandez, commercial technology sales engineer; and Emily Phipps, strategic marketing manager.
First, the experts shared that in a typical thermal processing operation, the required instantaneous nitrogen flow rate may vary significantly depending on several factors including number of furnaces in operation, flowrate required per furnace, and materials being processed. The nitrogen supply system must be capable of meeting these varying flowrate requirements, from minimum to maximum, on demand.
Although non-cryogenically generated nitrogen may be acceptable for some processes and materials, they emphasized that varying flowrate demands may make sizing a nitrogen operation system challenging.
Additionally, because nitrogen purity from non-cryogenic generation may vary depending on required flowrate (with purity decreasing as flowrate demand increases), it is important to prevent changes in nitrogen purity, which can cause quality issues with the material being heat treated.
Dwyer and his colleagues advise securing expert assistance when evaluating nitrogen needs prior to choosing a new or modified supply approach. This might involve going to your industrial gas provider or to an independent consultant. If you are working with an industrial gas provider, make sure that you are getting the technical assistance needed to determine the most cost-effective nitrogen supply system to meet your requirements.
There are upfront costs involved with both delivered and generated nitrogen supplies. According to the Air Products team, users may prefer a lower initial cost approach of dealing with a full-service industrial gas provider to provide a nitrogen system with higher operating costs (for delivered gas), versus a more complex generated nitrogen gas system with higher upfront costs that may offer significant long term savings through lower nitrogen costs. An industrial gas provider may also offer you a lease option for an on-site generation system that could offer you reliability at lower cost.
Besides the costs and investment timing, there are other considerations the experts shared:
NFPA 86 (and your insurance provider) may require sufficient nitrogen to be available for purging and inerting regardless of whether your electricity is operating.
Because delivered nitrogen production and delivery costs are a significant fraction of the nitrogen price, depending on where the nitrogen producing plant is, some suppliers may offer better prices than others.
Electricity costs are a significant fraction of the cost of both delivered and on-site generated nitrogen. If your local electric costs are high but the nitrogen comes from an area with lower electric costs, that may affect potential nitrogen costs and supply decisions.
Nitrogen tanks may require meaningful site investments in foundations and piping. If you are leasing your building, consider if a delivered or generated nitrogen supply solution minimizes your site investment.
An onsite nitrogen generation system requires large volumes of clean, dry air. In addition to buying a nitrogen generator, you may need to invest in additional air compression capacity. You also need to maintain your compressed air system, because oily air will destroy the expensive air separation media in a PSA nitrogen generation system. Consider your staff’s capabilities carefully.
It is important to take the time to think about a reliable supply that will avoid sending workers home due to lack of available nitrogen. Onsite nitrogen generation allows nitrogen users to make their own nitrogen, without the need for a tank and deliveries. At the same time, nitrogen generation requires large amounts of clean, dry compressed air. For companies that can commit to maintaining their air compression and nitrogen generation equipment, nitrogen generation can be a powerful approach to cost savings. But be realistic. If you can’t commit to 100% uptime for your air supply system, you need to plan for nitrogen downtime and production interruptions.
As a final note, the ideal nitrogen supply approach for your operations may be different from others in your industry. Dwyer, Hernandez, and Phipps say it is important to consider your process needs, ability to invest, interest in ownership vs. delivered utility, staff’s ability to manage a generation system, and the specific costs. Take the time to evaluate and understand that you can choose a different solution at a later time if your needs change.
About The Author:
David (Dave) Wolff Industrial Gas Professional Wolff Engineering
Dave Wolff has over 40 years of project engineering, industrial gas generation and application engineering, marketing, and sales experience. Dave holds a degree in engineering science from Dartmouth College. Currently, he consults in the areas of industrial gas and chemical new product development and commercial introduction, as well as market development and selling practices.
In this installment of Answers in the Atmosphere, David (Dave) Wolff, an independent expert focusing on industrial atmospheres for heat treat applications, explores the versatile role of nitrogen gas in thermal processing.
This informative piece on nitrogen’s critical functions in safety, as a diluent, and as an atmosphere component — including production methods and purity requirements —was first released inHeat Treat Today’sNovember 2025 Annual Vacuum Heat Treating print edition.
As discussed in the introduction for this series of gas-focused columns, nitrogen gas is ubiquitous in thermal processing — by far the most-used delivered or generated gas in secondary metallurgy. This column covers many important considerations for the use and availability of nitrogen gas, featuring the insights from my recent interview with Air Products experts: John Dwyer, principal engineer; Bryan Hernandez, commercial technology sales engineer; and Emily Phipps, strategic marketing manager. Because of its key role in thermal processing, we expect to have additional columns on nitrogen gas in this series.
Nitrogen serves three important purposes in secondary metallurgy:
Safety
Diluent
Atmosphere
Regarding safety, the Air Products experts shared important attributes of nitrogen and several applications it is most often used in. According to them, nitrogen:
will not react with most metals used in fabrication applications until reaching extremely high temperatures
will not support combustion or oxidation
has about the same density as air (which is 78% nitrogen)
is the least expensive industrial gas on a volumetric basis.
For those reasons, nitrogen is used as a purging and inerting gas in metallurgical applications, such as inerting the furnace in preparation for a flammable atmosphere to be introduced, as well as expelling flammable atmosphere at the end of a furnace cycle. They further noted that the National Fire Protection Association (NFPA) Standard 86 for Ovens and Furnaces mandates that nitrogen be always available for furnace inerting except for very specific exceptions where alternative approaches are used (burn in and burn out). Beyond the strict safety considerations, nitrogen protects furnace linings and components from high temperature oxidation.
Dwyer, Hernandez, and Phipps emphasized that when used as a diluent, nitrogen makes it possible to use relatively small volumes of a more expensive reactive gas or gas blend and ensure that the diluted active gas can provide benefits for an entire furnace load of parts. Examples include nitrogen/hydrogen atmospheres where nitrogen gas can enable a relatively small volume of very powerful reducing gas hydrogen to be mixed with a higher volume of nitrogen to fill the furnace interior. I would add that a blended atmosphere of nitrogen/hydrogen will have a higher density than hydrogen alone, and hence may distribute more widely in the furnace rather than just pooling at the ceiling level.
They further discussed how nitrogen can be used as a sole constituent in a furnace atmosphere in many cases, especially at lower temperature ranges, such as tempering and stress relief. In situations where surface finish is a secondary consideration, or where additional operations are going to be performed, they note that the part lower finish quality provided under inert nitrogen alone might be acceptable.
The team then reported that nitrogen forms the bulk of the atmosphere and cryogenic air separation is now available virtually worldwide; because of this, liquified or gaseous compressed nitrogen can also be delivered to clients virtually worldwide. Cryogenically separated nitrogen is, by the nature of the process, extremely pure, and can be assumed to be 99.999% or purer as delivered into the client’s storage vessel. Nitrogen can also be made at the client’s site, using non-cryogenic or cryogenic air separation techniques. For secondary metallurgy, non-cryogenic techniques are the most common because the volumes of nitrogen required are too low for a dedicated cryogenic air separation unit.
Continuing along this line, they explained that while both pressure swing adsorption (PSA) and hollow fiber membrane techniques can be employed to generate nitrogen for a single customer site, the PSA technology is the one primarily used to supply generated nitrogen for thermal processes. This is because the membrane technique for non-cryogenic nitrogen generation makes relatively impure nitrogen, with too much oxygen to achieve the desired surface properties sought by heat treaters. As such, membrane generated nitrogen is primarily used for chemical blanketing and similar low temperature air displacement applications.
The final discussion point I will share from the interview today is about the variability in accepted purity based on the planned usage of nitrogen. The three Air Products experts pointed out that NFPA86 mandates that the atmosphere in a furnace must be below 1.0% oxygen before any flammable gas species can be introduced. So, they continued, nitrogen used solely for safety purging can be relatively impure and still achieve the 1.0% maximum oxygen allowed. When used as the sole atmosphere component (i.e., 100% N₂), or as a carrier gas blended with an active gas like hydrogen, they explained that nitrogen purity must be much higher in order to achieve acceptable surface quality. In general, for atmosphere uses, it should be assumed as a general rule that the purer the nitrogen is, the easier it is to achieve satisfactory heat treat results. The three concluded this thought noting that in blended atmospheres it may be possible to use slightly higher levels of active gases (like hydrogen) to react with excess oxygen in the nitrogen supply, but that approach is unlikely to make sense economically since nitrogen is typically far less expensive than an active gas.
In the December 2025 installment of Answers in the Atmosphere, I’ll share further insights that my interview uncovered. Until then, consider your unique nitrogen needs and therefore whether having direct access to this gas for the benefit of your heat treat operations is essential.
About The Author:
David (Dave) Wolff Independent expert focusing on industrial atmospheres for heat treat applications
Dave Wolff has over 40 years of project engineering, industrial gas generation and application engineering, marketing, and sales experience. Dave holds a degree in engineering science from Dartmouth College. Currently, he consults in the areas of industrial gas and chemical new product development and commercial introduction, as well as market development and selling practices.
Heat Treat Todayis pleased to welcome this regular column spot, Answers in the Atmosphere, to David (Dave) Wolff, an independent expert focusing on industrial atmospheres for heat treat applications. This column explores various atmospheres with Dave and different industry specialists.
This informative piece on the critical role of atmosphere control in metal thermal processing was first released inHeat Treat Today’sOctober 2025 Ferrous & NonFerrous Heat Treatments/Mill Processing print edition.
Thermal processing of metals is critical to successful production of fabricated metal parts and assembled systems. Characteristics of parts and devices, including blades, springs, wire and cable, medical implants, and electric motors, all depend on successful thermal processing to produce metallic components with specific properties to meet the requirements of the part, assembly, or device. What is sometimes overlooked, however, is that atmosphere is as critical as the heat itself. The wrong furnace atmosphere can undo the best processing recipe, while the right one ensures that parts achieve their intended properties consistently.
Tune into the news, and you will find stories about metal parts incorrectly handled during thermal processing: gears that degrade to powder, camshafts that were too soft, electric switches that fail, materials with the wrong magnetic properties, knives that cannot hold an edge, and so on. These are all problems that occur too frequently and are expensive to resolve, because metal parts are often components in a more complex and expensive assembly. (Imagine the responsibility of parts-making for military jet engines or body-implanted parts. You do not want to be the shop supplying inadequate parts!) It is imperative that heat treating and sintering processes are completed correctly the first time.
Metals thermal processing requires more than just heat. As indicated above, atmosphere is essential to the heat treating process, coming alongside temperature, time, and a specific sequence of operations in a recipe that will ensure the material yields the desired performance. Much like baking bread, thermal processing of metals requires equipment, materials, conditions, and recipes. The furnace is the main equipment (other operations may be performed in a less expensive thermal processing oven). Then there are the materials — the parts being heat treated — which may be bulk metals, alloys, or compacted powder parts with unique blends and surface morphology. The conditions of time, temperature, atmospheres, and perhaps a quenching step come together in a specified recipe. Properly done, heat treating and sintering operations will yield parts that meet the hardness, toughness, appearance, surface finish, shape, dimensions, and other specialized and specified properties.
Since cost is an important driver, metals thermal processors strive to produce compliant parts in as few steps as possible. Innovations can assist in making it possible to consolidate steps, too. But mistakes in thermal processing may result in defective parts or require expensive rework or even additional (secondary) operations to correct deficiencies.
Each issue, this column will focus on the atmospheres component of heat treating. You’ll read interviews with industry experts focused on the atmospheres used in thermal processing — from relatively inert atmospheres, such as vacuum, nitrogen, and argon, to chemically active atmospheres used for annealing, hardening, and sintering. We will assist thermal processors by explaining how various atmospheres work, what the key properties are that determine successful results, how to buy and utilize the atmospheres, and precautions and alternatives for that atmosphere.
My hope is that this column will help Heat TreatToday readers become better buyers and users of atmospheres, so that you can run a smoother, more reliable, and more profitable operation.
About The Author:
David (Dave) Wolff Independent expert focusing on industrial atmospheres for heat treat applications
Dave Wolff has over 40 years of project engineering, industrial gas generation and application engineering, marketing, and sales experience. Dave holds a degree in engineering science from Dartmouth College. Currently, he consults in the areas of industrial gas and chemical new product development and commercial introduction, as well as market development and selling practices.
Have you faced complications from inadequate quenching, tempering, or documentation? You’re not alone. Small oversights can compromise part quality and performance. In this Technical Tuesday installment Ryan Van Dyke, metallurgical engineering manager at Paulo, addresses the top five pitfalls that in-house heat treating operations encounter and when to find another solution.
This informative piece was first released inHeat Treat Today’sJuly 2025, Heat Treat Super Brands print edition.
When dealing with high-volume production, running an in-house heat treating operation may seem like it makes financial and logistical sense. The ability to immediately process large batches of the same parts, minimize handling time, and tightly integrate heat treatment into the manufacturing workflow can provide critical advantages over outsourcing.
Industries involving high-volume machining of parts (e.g., automotive fasteners and bearings) rely on heat treating in-house to maintain efficiency and cost control. When parts are produced in the millions, outsourcing heat treating risks working with an inadequate supplier, introducing unacceptable lead time delays, transportation risks, and logistical complexities that do not align with high-throughput manufacturing.
Gas nitriding furnace at Paulo
Conversely, in-house heat treat operations often lack the flexibility, specialized equipment, and process control systems that commercial heat treaters develop over years of refining best practices. I have worked with countless manufacturers with in-house heat treat who have faced challenges they were unable to solve internally — from unpredictable distortion to process inconsistency, failed audits, and more. When they turn to a commercial heat treater for help, we often find the same core issues at play.
While commercial heat treating is not always the best fit for high-volume operations, there are real risks if you choose to run heat treating in-house. Here are the five most common pitfalls I’ve seen.
Pitfall #1: Inconsistent Mechanical Properties
Understanding the Problem
Gas flow gauges for heat treating furnace
Heat treating sets the foundation for a part’s hardness, toughness, and overall performance. This is done by the controlled heating and cooling of materials in a special atmosphere and then locking in the desired microstructure.
One major challenge that impacts consistency in parts is furnace temperature uniformity. Older or improperly calibrated furnaces can create hot and cold spots, leading to localized variations in hardness and mechanical properties within the same batch. This is a common challenge in-house heat treaters face. To avoid hot spots, heat treaters must go beyond just considering equipment age — they should implement robust preventative maintenance programs and routinely calibrate furnaces to ensure consistent thermal performance across all zones.
Real-World Consequences
Distortion issues from non-uniform heating: Variations in temperature cause inconsistent thermal profiles, leading to unpredictable warping and dimensional instability. For example, a die used for stamping operations requires excessive rework after heat treatment because some areas of the part distorted unevenly due to poor furnace temperature uniformity.
Inconsistent hardness in a load: Hot and cold spots in austenitizing and tempering furnaces can cause parts in some areas to have a different final hardness than others. For example, a load of larger diameter structural bolts was tempered in a furnace with poor uniformity. Bolts located in a hot spot in one corner of the furnace showed below specification mid-radius hardness due to over-tempering.
Pitfall #2: Surface Contamination from Incorrect Gas Atmosphere Control
Understanding the Problem
Many manufacturers with in-house heat treating operations use gas atmospheres to control oxidation and facilitate processes like carburizing and nitriding. However, if the gas atmosphere is not properly monitored, it can lead to oxidation, decarburization, or uncontrolled case hardening.
Heat treaters often rely on Endothermic gas generators that produce a carbon-rich atmosphere. Without precise control of carbon potential, parts may develop non-uniform case depths, excessive soot buildup, or — the opposite extreme — decarburization, in which the surface loses carbon and thus its strength and hardness. Therefore, it’s imperative to monitor and adjust atmosphere parameters in real time using carbon probes to maintain precise control of carbon potential.
Real-World Consequences
Decarburization leading to soft surfaces: If the furnace atmosphere lacks sufficient carbon potential, the steel loses carbon at the surface, reducing hardness and durability. For example, aerospace landing gear components could be rejected if surface hardness tests show excessive decarburization, making them unsuitable for service.
Scaling and oxidation issues: Excess oxygen in the furnace leads to surface oxidation, requiring costly post-processing like machining or pickling. For example, stainless steel medical implants can develop scale during heat treatment, requiring extensive rework to restore a clean finish.
Uneven carburizing creating case depth variations: Fluctuations in furnace gas composition lead to inconsistent carbon diffusion, making case depth unpredictable. For example, a batch of industrial gears can fail inspection because some parts have insu cient case depth while others are over-cased, leading to production delays.
Quenching is one of the most stress-inducing steps in heat treatment. Rapid cooling causes phase transformations and volume changes within the steel, leading to internal stresses and distortion.
Manufacturers with in-house heat treaters often struggle with choosing the right quench medium, optimizing agitation rates, and positioning parts correctly during quenching. Additionally, many only have access to one quench medium, such as oil, and will attempt to apply it to all materials and geometries — even when a slower or faster quench rate is required. This mismatch can cause excessive distortion, high residual stresses, and even quench cracking.
Another issue is poor part orientation during quenching. If a part is improperly positioned, different areas will cool at different rates, creating non-uniform hardness and residual stress buildup, which can later cause warping or failure in service.
Real-World Consequences
Incorrect quenchant selection: If the wrong quench medium is used, such as oil when polymer or water would be more suitable, the parts could end up having inconsistent hardness in various sections due to insufficient cooling. Conversely, selecting a fast oil as a quenchant when hot oil would be more suitable could cause excessive distortion due to the faster cooling rate. For example, lifting shackles quenched in oil will not have sufficient hardening response throughout the cross-section, causing them to be rejected for service due to low strength values in the center of the part.
Insufficient quenchant agitation: If the quenchant in the quench tank is not sufficiently agitated when the parts are submerged, then cooling rates throughout the load of parts could vary, causing different amounts of hardening. For example, parts near the edges of a batch load show hardness testing within specification, while parts in the center of the load show hardness below specification.
Incorrect positioning of parts: How a part is oriented during quenching can have a large impact on the amount of distortion after heat treatment. If a part is laid horizontally rather than vertically, the amount of distortion can dramatically increase. For example, if a hollow cylinder was laid horizontally for processing, rather than vertically, the cylinder would likely be at risk of material creep during austenization, as well as deformation from the bottom of the part quenching before the top. The result would be distortion in the inner diameter and along the length in excess of the amount of additional material le for machining, causing the part to become scrap.
Pitfall #4: Brittle Failures from Inadequate Tempering
Understanding the Problem
Tempering is a critical post-quench process that reduces residual stresses and brittleness while fine-tuning hardness and toughness. After quenching, steel is in a highly stressed martensitic state, which, if left untreated, can lead to catastrophic failures in service.
If heat treaters are working under tight production schedules or have an incomplete understanding of tempering curves for different steels, then they may fall into the trap of rushing or even omitting tempering cycles. For some in-house heat treat operations, a single tempering cycle may be employed when a double temper is required, particularly for high-alloy steels like D2, H13, or certain aerospace-grade alloys.
Real-World Consequences
Brittle fracture under load: If a part is left untempered or under-tempered, the high internal stresses from quenching remain, making it prone to sudden brittle fracture when subjected to impact or fatigue loading. For example, an induction-hardened gear used in heavy machinery can snap under torque loading due to excessive quench-induced stresses. It is very common to skip tempering on induction-hardened parts, especially in in-house heat treat operations where cycle times are minimized as much as possible.
Reduced wear resistance due to over-tempering: If a steel is over-tempered (held at too high a temperature or for too long), excessive softening can occur, reducing wear resistance and surface hardness. For example, a die used in stamping operations can wear prematurely because it was tempered above its recommended range, leading to a loss of edge retention.
Excessive retained austenite leading to dimensional instability: Some steels, particularly high-carbon and high-alloy grades, require a secondary tempering cycle to stabilize the microstructure. Skipping this can leave excessive retained austenite, which converts to untempered martensite over time, causing unexpected distortion or possibly cracks forming in the material in service. For example, a precision-ground shaft can warp and develop cracks weeks after heat treatment because retained austenite transforms to untempered martensite in service, altering the part’s geometry and encouraging fractures to form.
Pitfall #5: Lack of Process Documentation & Repeatability Issues
Understanding the Problem
Heat treating is a process-sensitive operation where small variations can lead to major differences in final part properties. If a heat treat operation does not have detailed documentation and tracking systems, this will lead to inconsistencies in cycle parameters, atmosphere control, and quenching conditions.
One of the most common issues is manual adjustments without proper record-keeping, which can lead to process drift. Operators may tweak furnace temperatures, quench delays, or gas flow rates without logging the changes, creating batch-to-batch variability.
Automotive Gear
Additionally, compliance and traceability may present a challenge for manufacturers facing ISO, Nadcap, or AS9100 audits. When an auditor asks for process records, lacking verifiable data is a red flag for non-compliance.
Real-World Consequences
Batch-to-batch variability: When process parameters are not documented or followed precisely, parts in one batch may have different hardness, case depth, or dimensional stability than parts in the next batch — leading to field failures or quality escapes. For example, a manufacturer of automotive control arms may and that some components fail impact testing while others pass, leading to a full production hold to investigate process inconsistencies.
Failed audits and compliance issues: Without traceable process documentation, heat treat operations can fail compliance audits, especially for industries with strict quality requirements. For example, an aerospace supplier could lose Nadcap certification because they cannot provide accurate records of furnace temperature control, atmosphere composition, and quench parameters for critical landing gear components.
Difficulty troubleshooting heat treat issues: When a batch of parts fails post-heat treatment inspection, the root cause can be nearly impossible to determine if there are no detailed process records. For example, a fastener manufacturer might experience high rejection rates due to inconsistent case depths, but if the atmosphere carbon potential wasn’t recorded, they will not be able to pinpoint whether it was a gas mix issue, furnace drift, or soak time variance.
Expensive scrap and rework costs: A lack of process repeatability leads to high scrap rates and expensive rework to bring parts back into spec. For example, a tooling manufacturer might have to scrap an entire run of die components after discovering that an unrecorded furnace temperature deviation softened the steel below acceptable hardness levels.
Lack of lot traceability: When a heat treatment problem does occur, being able to trace it back to exactly which piece of equipment it ran in and when is critical for determining root cause. For example, many automotive seating brackets exhibit low hardness after heat treatment. However, if lot traceability to the furnace cycle was not maintained, root cause of factors like incorrect furnace temperature, inadequate carbon control, or insufficient quench agitation are much more difficult to identify.
When To Call a Commercial Heat Treater
If limited resources and/or lack of specialized expertise are in question, these five pitfalls can easily occur. Even the most well-run in-house heat treat operations must balance production efficiency, heat treat quality, and high-volume demands; additionally, it can be challenging to regularly invest in the most advanced equipment, process monitoring, or specialized personnel.
There are commercial heat treaters that have built their entire business around controlling these variables with precision. These heat treaters have invested decades into refining their heat treating processes, equipment, and metallurgical expertise to eliminate these issues before they ever become problems.
If these five pitfalls are ones your operations cannot easily avoid, consider a partnership with the right commercial heat treater to maintain parts with extreme precision, low distortion, and strict compliance specifications.
About The Author:
Ryan Van Dyke Manager of Metallurgical Engineering Paulo
Ryan Van Dyke is the manager of metallurgical engineering at Paulo, where he works closely with customers to solve challenging thermal processing issues. He’s dedicated to pushing the limits of heat treating performance, continuously innovating more efficient, reliable ways to process critical parts. Ryan was an honoree in Heat TreatToday’s 40 Under 40 Class of 2023.
For more information: Contact Ryan Van Dyke at RVanDyke@paulo.com.
La baja efi ciencia energética en los hornos industriales suele impactar los costos de producción de las empresas, ya que se requiere más consumo de energía para alcanzar la temperatura deseada. Esto, a su vez, tiene un impacto tangible en su huella de emisiones de carbono.
This article was originally published inHeat Treat Today’sMay 2024 Sustainable Heat Treat Technologies 2024print edition.
De acuerdo a la Agencia Internacional de Energía, el sector industrial es uno de los principales culpables en lo que respecta al consumo global de energía. En muchas situaciones, los hornos industriales tienden a ser los equipos que más la consumen.
En este artículo, compartiremos una serie de soluciones que pueden implementarse para mejorar la efi ciencia energética, reducir los costos de producción y ser social y ambientalmente responsables.
Factores que pueden estar afectando tu efi ciencia energética
Existen un par de factores obvios que pueden estar perjudicando tus índices de eficiencia energética.
Pérdidas de calor en el proceso del horno
Estas pueden deberse a daños estructurales en el aislamiento o a una distribución incorrecta del fl ujo de gas dentro del horno.
Procesos de combustión inefi cientes
Contact us with your Reader Feedback!Gran atención al detalle en el mantenimiento predictivo
Probablemente debido a relaciones aire/combustible inadecuadas o excesivas, o a una mala mezcla causada por daños internos en el quemador.
Algunos consejos que podemos brindarte para ayudarte a mejorar el ahorro de energía en el horno son: Monitorear la temperatura en el lado frío del horno, verifi cando cuidadosamente que no haya puntos calientes.
Analizar periódicamente la composición de los gases de combustión del horno, asegurándose de mantener los niveles esperados de oxígeno y CO.
Verifi car periódicamente que los fl ujos de aire de combustión y combustible estén en una relación estequiométrica.
Revisar al menos dos veces al año que los quemadores estén en buenas condiciones y no presenten daños.
Evitar la infi ltración de aire frío en el horno que pueda afectar la efi ciencia del proceso.
Mantener ajustados los lazos de control de temperatura. Si no hay un lazo de control de temperatura, recomendamos integrarlo.
Monitorear periódicamente el consumo, ya sea manual o automáticamente.
Garantizar un programa de mantenimiento predictivo en el sistema de combustión.
¿Cómo funciona el mantenimiento predictivo?
Revisión de fl ujos de hornos industriales
Este tipo de mantenimiento se basa en el almacenamiento, monitoreo y análisis de datos y variables cuantifi cables de los equipos en tiempo real, como temperatura, vibración y frecuencia.
Para que este enfoque funcione, es necesario comprender a fondo los procesos e identifi car qué aspectos necesitan ser analizados. Estos aspectos incluyen:
Temperatura: monitorear la temperatura puede revelar cambios anormales, indicando un posible sobrecalentamiento o falla de componentes.
Vibración: una vibración inusual puede indicar desgaste o desequilibrio de la maquinaria, lo que resultará en daños más severos si no se aborda a tiempo.
Frecuencia: analizar patrones y comportamientos particulares puede proporcionar una idea de lo que puede convertirse en futuros problemas potenciales.
Estas acciones dependerán de sistemas de control de medición y detección adecuados. Los sensores y algoritmos constituyen los principales sistemas de medición de variables y detección de problemas.
Por un lado, los sensores juegan un papel fundamental en el mantenimiento predictivo, ya que pueden detectar cambios sutiles en el desempeño del equipo, permitiendo identifi car posibles fallas antes de que ocurran. Es recomendable tener acceso a un inventario de marcas reconocidas de sensores y repuestos, lo que te permitirá medir las variables de tu equipo.
Por otro lado, los algoritmos identifi can patrones y tendencias indicativas de posibles problemas mediante el procesamiento de grandes cantidades de datos, lo que permite intervenciones oportunas y planifi cadas. Factores que infl uyen en el tiempo de medición.
El tiempo que puede llevar medir variables durante un proceso de mantenimiento predictivo depende de muchos f actores internos y externos. A continuación, abordamos algunos de ellos.
Factores externos
El proceso. Cada procedimiento industrial tiene sus propias características y requerimientos particulares. Por ejemplo, en un proceso continuo se podría requerir un monitoreo constante y en tiempo real, mientras que en otras situaciones un enfoque de intervalos específi cos podría ser el mejor.
El producto. Algunos productos pueden requerir un monitoreo frecuente o estricto debido a su naturaleza y características.
La fi losofía del cliente. Algunos clientes pueden tener estándares más estrictos o solicitar un monitoreo más frecuente para garantizar la calidad y confi abilidad de sus productos.
Factores internos
Capacidad. Puede ser necesaria una planifi cación estratégica y una programación de las mediciones si el equipo es limitado o se emplea para otros procesos.
La disponibilidad de personal califi cado. Es fundamental garantizar que haya personal califi cado disponible en el momento adecuado para interpretar los datos obtenidos.
Soluciones de ahorro de energía para hornos industriales. Aquí es donde necesitas poder confi ar en tu socio experto en combustión para que lo asesore sobre las soluciones de.
Sistemas de recuperación de energía
Personal altamente capacitado de NUTEC Bickley
Hoy por hoy, se pueden implementar algunos sistemas que pueden ayudar signifi cativamente a reducir el consumo de energía en hornos, previniendo así pérdidas y/o eliminando procesos inefi cientes. Estos son algunos de los que manejamos en NUTEC Bickley:
Sistemas de recuperación de energía
Se pueden agregar a los hornos para recuperar el calor de los gases de combustión y reutilizarlos calentando el aire de combustión. Algunas opciones para estos sistemas son quemadores autorrecuperativos y quemadores regenerativos.
Sistemas de medición de gases de combustión
Garantizan que los hornos siempre tengan la proporción correcta de aire y gas en su sistema. Con ellos, puede monitorear continuamente el estado y así tomar decisiones basadas en estos datos para luego ajustar cualquier nivel desproporcionado.
Servicios de mantenimiento preventive
Además de los consejos y sistemas de ahorro de energía ya mencionados, existen otras acciones que pueden ayudar a prevenir fallas en hornos industriales, mejorar su funcionamiento y más.
Servicio de auditoría y diagnóstico: Se miden las variables de entrada y salida del horno para indicar los niveles de eficiencia actuales e identifi car posibles áreas de mejora.
Servicio de calibración de quemadores: Se verifi a la relación aire/combustible para asegurar que los quemadores operen en el rango correcto.
Conclusión
En resumen, si deseas mejorar la efi ciencia energética en hornos industriales y reducir signifi cativamente tus costos operativos, recuerda seguir nuestras recomendaciones.
Acerca del autor
Alberto Cantú, Vice President of Sales, NUTEC Bickley
Alberto Cantú es vicepresidente de Ventas de NUTEC Bickley. Cantú tiene más de veinte años de experiencia profesional y ha escrito prolífi camente para una gran variedad de revistas y publicaciones. Cantú es uno de los galardonados por Heat Treat Today’s 40 Under 40 Class del 2020.
Para mayor información: Contactar a Alberto escribiendo a albertocantu@nutec.com.
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Poor energy efficiency in industrial furnaces usually impacts companies’ production costs since more energy consumption is required to achieve the desired temperature. This, in turn, has a tangible impact on their carbon emission footprint. In this Technical Tuesday by Alberto Cantú, VP of Sales at NUTEC Bickley, learn energy-saving solutions for industrial furnaces.
This article was originally published inHeat Treat Today’sMay 2024 Sustainable Heat Treat Technologies 2024print edition.
According to the International Energy Agency, the industrial sector is one of the main culprits when it comes to global energy consumption. In many situations, industrial furnaces tend to be the pieces of equipment that consume the most energy.
In this article, we will share a series of solutions you can implement to improve energy efficiency, reduce production costs, and be socially and environmentally responsible.
Factors that May Be Affecting Your Energy Efficiency
There are a couple of obvious factors that may be harming your energy efficiency ratings.
Heat Losses in the Furnace Process
These may be due to structural damage to the insulation or incorrect gas flow distribution inside the furnace.
Inefficient Combustion Processes
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Inefficiencies here are probably due to inadequate or excessive air/fuel ratios or poor mixture caused by internal damage to the burner.
Some tips we can pass on to help you improve furnace energy savings are:
Monitor the temperature on the cold side of the furnace, carefully checking that there are no hot spots.
Periodically analyze the composition of the furnace combustion gases, ensuring you are maintaining the expected levels of oxygen and CO.
Periodically check that the combustion air and fuel flows are in a stoichiometric ratio.
Check at least twice a year that the burners are in good condition and show no damage.
Avoid infiltration of cold air into the furnace that could affect the efficiency of the process.
Keep the temperature control loops tuned. If there is no temperature control loop, we recommend integrating one.
Periodically monitor consumption, either manually or automatically.
Ensure there is a program of predictive maintenance on the combustion system.
How Does Predictive Maintenance Work?
Attention to detail during predictive maintenance
This type of maintenance is based on the storage, monitoring, and analysis of data and quantifiable equipment variables in real time, such as temperature, vibration, and frequency.
It is necessary at the outset to understand the processes thoroughly and identify which aspects need to be analyzed, to make this approach work. These aspects include:
Temperature — monitoring the temperature may reveal abnormal changes, indicating possible overheating or component failure.
Vibration — unusual vibration may indicate machinery wear or imbalance, resulting in more severe damage if not addressed in time.
Frequency — analyzing particular patterns and behaviors during heat treat processing can provide insight into what may evolve into future potential problems.
Th ese actions will depend on appropriate measurement and detection control systems, the primary variable for these being sensors and algorithms. Firstly, sensors play a fundamental role in predictive maintenance, as they can detect subtle changes in the equipment’s performance, making it possible to identify potential failures before they occur. It is advisable to have access to an inventory of recognized sensor and spare parts brands, allowing you to measure your equipment’s variables.
Secondly, algorithms identify patterns and trends indicative of possible issues by processing large data amounts, allowing timely and planned interventions.
Factors Influencing Measurement Time
The time it can take to measure variables during a predictive maintenance process depends on many internal and external factors. Below we address some of them.
External Factors
Data analysis is a key component for effective preventative maintenance
The process — each industrial procedure has its own characteristics and requirements. For example, constant and real-time monitoring might be required in a continuous process, while a specified intervals approach might be best in other situations.
The product — some products may require frequent or strict monitoring due to their nature and characteristics.
Customer philosophy — some customers may have stricter standards or request more frequent monitoring to ensure the quality and reliability of their products.
Internal Factors
Capacity — strategic planning and scheduling measurements may be necessary if the equipment is limited or employed for other processes.
Availability of qualified personnel — ensuring that qualified staff are available at the right time to interpret the data obtained is crucial.
Energy-saving solutions for industrial furnaces — this is where you need to be able to rely on your combustion expert partner to advise on the most up-to-date energy-efficiency solutions you can implement in order to improve furnace performance and to help you reduce production costs.
Systems To Improve Furnace Energy Efficiency
Today, some systems that can significantly assist in reducing energy consumption can be implemented in your furnaces, thus preventing losses and/or eliminating inefficient processes. Here are some systems that can be implemented:
Energy Recovery Systems
These can be added to your furnaces to recover the heat from the flue gases so that they can be used again, heating the combustion air. Some options for these systems are self-recuperative burners and regenerative burners.
Flue Gas Measurement Systems
These guarantee that your furnaces always have the correct proportion of air and gas in their system. With them, you can continuously monitor the status and thus make decisions based on these data to adjust any out-of-proportion levels.
Preventive Maintenance Services
Besides the tips and systems for energy saving already mentioned, there are other actions that save energy, reduce costs, prevent failures in your industrial furnaces, improve their operation, and more.
Two of these are:
Audit and diagnosis service: The furnace input and output variables are measured in order to indicate current efficiency levels and to identify possible areas for improvement.
Burner calibration service: The air/fuel ratio is checked to ensure burners operate in the correct range.
Conclusion
In summary, if you consider implementing any of the tips and systems presented here, you can improve energy efficiency in your industrial furnaces and significantly reduce your operating costs. Be sure to check out the International Energy Agency if you are looking for further information on this topic.
About the Author
Alberto Cantú, Vice President of Sales, NUTEC Bickley
Alberto Cantú is the vice president of Sales at NUTEC Bickley. Cantú has more than twenty years of professional experience and has written prolifically for a variety of journals. Cantú is an honoree from Heat Treat Today’s40 Under 40 Class of 2020.
For more information: Contact Alberto at albertocantu@nutec.com.
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The search for sustainable solutions in the heat treat industry is at the forefront of research for industry experts. Michael Stowe, PE, senior energy engineer at Advanced Energy, one such expert, offers some fuel for thought on the subject of how heat treaters should prioritize the reduction of their carbon emissions by following the principles of reuse, refuel, and redesign.
This Sustainability Insights article was first published in Heat Treat Today’sJanuary/February 2024 Air & Atmosphereprint edition.
Reduce
Michael Stowe PE, Senior Energy Engineer Advanced Energy
We explored why the question above has come to the forefront for industrial organizations in Part 1, released in Heat Treat Today’s December 2023 print edition. Now, let’s look at the four approaches to managing carbon in order of priority.
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The best way to manage your carbon footprint is to manage your energy consumption. Therefore, the first and best step for reducing your carbon footprint is to reduce the amount of energy you are consuming. Energy management tools like energy treasure hunts, energy assessments, implementation of energy improvement projects, the DOE 50001 Ready energy management tool, or gaining third party certification in ISO 50001 can all lead to significant reduction in energy consumption year over year. Lower energy use means a smaller carbon footprint.
Additionally, ensuring proper maintenance of combustion systems will also contribute to improved operational efficiency and energy savings. Tuning burners, changing filters, monitoring stack exhaust, controlling excess oxygen in combustion air, lubricating fans and motors, and other maintenance items can help to ensure that you are operating your combustion-based heat treating processes as efficiently as possible.
Reuse
Much of the heat of the combustion processes for heat treating goes right up the stack and heats up the surrounding neighborhood. Take just a minute and take the temperature of your exhaust stack gases. Chances are this will be around 1200–1500°F. Based on this, is there any effective way to reuse this wasted heat for other processes in your facility? One of the best things to do with waste heat is to preheat the combustion air feeding the heat treating process. Depending on your site processes, there are many possibilities for reusing waste heat, including:
Space heating
Part preheating
Hot water heating
Boiler feed water preheating
Combustion air preheating
Refuel
Once you have squeezed all you can from reducing your process energy consumption and reusing waste heat, you may now want to consider the possibility of switching the fuel source for the heat treating process. If you currently have a combustion process for a heat treat oven or furnace, is it practical or even possible to convert to electricity as the heating energy source? Electricity is NOT carbon free because the local utility must generate the electricity, but it typically does have lower carbon emissions than your existing direct combustion processes on site. Switching heating energy sources is a complex process, and you must ensure that you maintain your process parameters and product quality. Typically, some testing will be required to ensure the new electrical process will maintain the metallurgical properties and the quality standards that your customer’s specific cations demand. Also, you will need a capital investment in new equipment to make this switch. Still, this method does have significant potential for reducing carbon emissions, and you should consider this where applicable and appropriate.
Redesign
Finally, when the time is right, you can consider starting with a blank sheet of paper and completely redesigning your heat treating system to be carbon neutral. This, of course, will mean a significant process change and capital investment. This would be applicable if you are adding a brand-new process line or setting up a new manufacturing plant at a greenfield site.
In summary, heat treating requires significant energy, much of which is fueled with carbon-based fossil fuels and associated-support electrical consumption. Both combustion and electricity consumption contribute to an organization’s carbon footprint. One of the best ways to help manage your carbon footprint is to consider and manage your energy consumption.
For more information: Connect with IHEA Sustainability & Decarbonization Initiatives www.ihea.org/page/Sustainability Article provided by IHEA Sustainability
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In Part 1, the author underscored the importance of understanding the changes in gas composition through three steps of its production: first, the production in the combustion chamber; second, the cool down of gas to bring the Exothermic gas (Exo gas) to below the ambient temperature; and third, the introduction of the gas to the heat treat furnace. Read Part 1, published in Heat Treat Today’sAugust 2023Automotive Heat Treat print edition, to understand what Exo gas is and to learn about the composition of gas in the first step.
Harb Nayar
Founder and President TAT Technologies LLC Source: TAT
As the author demonstrated in Part 1, Exo gas composition changes in its chemistry for heat treatment; this first step is how the gas composition changes when it is produced in the combustion chamber. The composition of reaction products, temperature, Exothermic energy released, various ratios, and final dew point are all factors that need to be considered to protect metal parts that will be heat treated in the resulting atmosphere.
Now, we’ll turn to Steps 2 and 3.
Step 2: Composition of Exo Gas after Exiting the Reaction Chamber Being Cooled Down
The two examples that follow demonstrate how lean and rich Exo under equilibrium conditions change as they are cooled from peak equilibrium temperature in the combustion chamber down to different lower temperatures (Table B). This cool down brings the Exo down to below ambient temperatures to avoid water condensation.
Example 1: Lean Exo Gas with a 9:1 Air to CH₄ Ratio
The first column highlighted in blue shows the composition of the lean Exo gas as generated in the reaction chamber with an air to natural gas ratio of 9:1. The peak temperature as generated in the combustion chamber is 3721°F. The next four columns show how the composition changes when the lean Exo gas is slowly cooled from 3721°F to 2000°F, 1500°F, 1000°F, and 500°F under equilibrium condition. The following key changes take place as the temperature of the lean Exo is lowered from the peak temperature to 500°F:
Hydrogen volume almost triples from 0.67% to 1.97%.
H₂O volume decreases slightly from 19.1% to 17.5%, but still is very high at all temperatures.
Oxidation-reduction potential (ORP) changes as the H₂ to H₂O ratio increases from 0.035 to 0.111. At all temperatures, it is very low.
CO and the CO to CO₂ ratio drop in a big way, making lean Exo from being decarburizing at higher temperatures to being highly decarburizing at lower temperatures.
The percentage of N₂ remains at 70.34 at all temperatures.
There is no C (carbon, i.e., soot) or residual CH₄ at all temperatures.
For all practical purposes, at an air to natural gas ratio of 9:1, the Exo gas as generated is predominantly an N₂ and H₂ (steam) atmosphere with some CO₂ and small amounts of H₂ and CO.
Table B. Air to Natural Gas at 9:1 and 7:1, cooled to various temperatures
Example 2: Rich Exo Gas with a 7:1 Air to CH₄
The column under ratio of seven is highlighted as red to show the composition of the rich Exo gas as generated in the reaction chamber with an air to CH₄ ratio of seven. The peak temperature is 3182°F — significantly lower than that for lean Exo. The next four columns show how the composition changes when the rich Exo gas is slowly cooled from 3182°F to 2000°F, 1500°F, 1000°F, and 500°F. The following key changes take place as temperature of the rich Exo is lowered from the peak temperature to 500°F:
Hydrogen volume almost doubles from 5.58% at peak temperature to 9.91% at 1000°F, and then it drops to 5.70% at 500°F. The overall volume of H₂ in rich Exo is significantly higher than in lean Exo.
H₂O volume decreases slightly from 17.9% to 15.1%, but it is still very high at all temperatures.
Oxidation-reduction potential (ORP) changes as the H₂ to H₂O ratio increases from 0.312 at peak temperature to 0.737 at 1000°F before decreasing to 0.377 at 500°F. Overall, ORP in rich Exo is significantly higher than that in lean Exo.
CO and the CO to CO₂ ratio drop in a big way, making it mildly decarburizing to more decarburizing
The percentage of N₂ remains at 65– 67%, which is lower than lean Exo.
There is no C (carbon, i.e., soot) at any temperature. However, there is residual CH₄ at 1000°F and lower. This increases rapidly when cooled slowly below 1000°F.
For all practical purposes, the rich Exo gas (at air to natural gas ratio of 7:1) generated is still predominantly a H₂
and H₂O (steam) atmosphere, but with more H₂; hence, it has somewhat higher oxidation-reduction potential (ORP) than lean Exo and a bit higher CO to CO₂ ratio (less decarburizing than lean Exo).
In summary, rich Exo as generated in the combustion chamber differs from lean Exo as follows:
It has a little less N₂ % as compared to lean Exo.
It has significantly more H₂ , but a little less H₂O than lean Exo. As such, it has a significantly higher H₂ to H₂O ratio (ORP).
It is decarburizing, but less than lean Exo.
It has residual CH₄ at temperatures below 1000°F. Therefore, it must be cooled very quickly to suppress the reaction of developing too much residual CH₄.
Discussion
Let us take the example of rich Exo (an air to natural gas of 7:1) exiting from the reaction chamber in Table B (see column highlighted in red). The total volume is 853.3 SCFH and has H₂O at 152.4 SCFH (17.9% by volume). This is equivalent to dew point of 137°F. Its H₂ content is 47.6 SCFH (5.58% by volume). And the H₂ to H₂O ratio is 0.312.
If this were quenched to close to ambient temperature “instantly,” this composition would be “frozen,” except most of the H₂O vapor will become water. Let us assume the Exo gas was instantly quenched to 80°F (3.6% by volume after condensed water is removed). Rough calculation shows that the final total volume of H₂O vapor has to be reduced from 152.4 SCFH to about 26.0 SCFH in order to meet the 80°F dew point goal. This means 152.4 – 26.0 = 126.4 SCFH of H₂O vapor got condensed to water.
Now the total volume of Exo gas after cooling down to 80°F= 853.35 – 126.4 = 726.95 SCFH, or almost 15% reduction in volume of Exo gas as compared to what was generated in the reaction chamber.
Of course, the composition of Exo gas will not be the same as calculated above. The exact composition after being cooled down depends upon the following:
a. Cooling rate of the reaction products from the peak temperature in the reaction chamber to some intermediate temperature, typically around 1500°F.
b. Cooling rate of the gas from the intermediate temperature to the final (lowest) temperature via water heat exchangers — typically 10–20°F below ambient temperature unless a chiller or dryer is installed on the system.
Depending upon the overall design of the generator, especially how Exo gas coming out of the combustion chamber is cooled and maintained during the period of its use, the expected Exo gas composition should be in the range of the light red columns in Table B — where temperatures are between 1500°F to 1000°F — however:
Total volume closer to 727 SCFH (since a major portion of H₂O was condensed out)
N₂ between 74–77%
Dew point between 80–90°F
CH₄. between 0.1–0.5%
H₂ percentage between 7–9%
Step 3: Composition of Exo Gas after Being Introduced into the Heat Treat Furnace
The cooled down Exo gas will once again change its composition depending upon the temperature inside the furnace where parts are being thermally processed.
As an illustration, let us assume the following composition of the rich Exo gas (with a 7:1 air to natural gas ratio) at ambient temperature just before it enters the furnace:
Total volume: 727 SCFH
H₂: 8% (58.16 SCFH)
Dew Point 86°F or 4.37% (31.77 SCFH)
CO: 6% (43.62 SCFH)
CO₂: 6% (43.62 SCFH)
CH₄ : 0.4% (2.91 SFH)
Balance N₂ (%)
75.23% (546.92 SCFH)
Table C shows how the composition changes once it reaches the high heat section of the furnace where parts are being thermally treated. The column highlighted blue shows the composition of Exo gas as it is about to enter while it is still at the ambient temperature. The next three columns show the composition of the Exo gas in the high heat section of furnaces operating at three different temperatures depending upon the heat treat application — 1100°F like annealing of copper, 1500°F like annealing of steel tubes, and 2000°F like copper brazing of steel products. The H₂ to H₂O ratio decreases as temperature increases.
Other general comments on Exo generators:
Generally, they are horizontal.
Size ranges from 1,000 to 60,000 SCFH.
Rich Exo generators use Ni as a catalyst in the reaction chamber. Lean Exo does not.
Lean Exo generators typically operate at a 9:1 air to natural gas ratio. There is no carbon/soot buildup.
Rich Exo generators typically operate at a 7:1 air to natural gas ratio. Below about 6.8 and lower ratios, soot/carbon deposits start appearing that require carbon burnout as part of the maintenance procedure.
Table C. Exo gas compositions in heat treat furnaces
Conclusions
A walkthrough of the entire cycle of gas production to cool down to use in the high heat section of the furnace clearly shows that as temperature changes, so does the Exo gas composition for any air to natural gas ratio.
Having a well-controlled composition of Exo gas requires the following:
Well-controlled composition of the natural gas used
Air supply with controlled dew point
Highly accurate air and natural gas mixing system
Highly controlled and maintained cooling system
A reliable ORP analyzer or the H₂ to H₂O ratio analyzer as part of the Exo gas delivery system.
Protecting metallic workpieces is paramount in heat treating, and in order to do this, the atmosphere created by Exothermic gas must be understood, both in the cool down phase and within the heat treat furnace. For further understanding of the good progress made in the improvement of Exo generators, see Dan Herring’s work in the reference section below.
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.
