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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.

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

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

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

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

Making a History

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

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

Pivot Bearing Line Requires Improved Heat Treat Abilities

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

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

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

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

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

The Tension: Delivered vs. On-site Hydrogen?

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

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

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

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

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

Finding the Best Way

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

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

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

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

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

Choosing On-Site Hydrogen Generation

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

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

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

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

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

 

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

For more information: 

Visit nelhydrogen.com and riverhawk.com.

 

 

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On-Site Hydrogen Generation: A Viable Option for Reducing Atmospheres in Heat Treating

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OCHydrogen is a reducing gas used in thermal processing atmospheres for brazing, annealing, metal injection molding, metal additive manufacturing, and glass-to-metal and ceramic-to-metal sealing. Recent supply chain issues, safety concerns surrounding storage, and the growing metal additive manufacturing parts market are making on-site generated hydrogen a burgeoning trend among thermal processors.

This article first appeared in Heat Treat Today’s February 2022 Air & Atmosphere Furnace Systems print edition and was written by Lynn Gorman, a freelance writer.

Reliance on Hydrogen Delivery Can Be Risky

We learned in 2020 that when the pandemic hit, hydrogen gas supply declined, and liquid hydrogen production slowed accordingly.

Hydrogen is a byproduct of refineries processing crude oil, and when demand for gasoline and other crude oil-based products slows, so does hydrogen production. Even as the economy fights back post COVID-19 the long-term trends in crude oil processing are negative because of increasing fleet electrification.

Hydrogen scavenges oxygen, counteracting minor furnace leaks.
Photo Credit: Nel Hydrogen

Besides having more control and assurance that hydrogen will be available on demand as needed, there are other benefits to generating hydrogen on site. According to David Wolff, regional manager at Nel Hydrogen, the only raw materials required to produce hydrogen on site are water and electricity, which are among the most reliable of supply chains. “Essentially the hydrogen becomes another utility with little personnel attention required,” he said. “Electricity and water come into a plant in pipes and wires and are highly reliable. Additionally, there are no hydrogen storage tanks taking up a large amount of unusable space.” He added further that electrolyzers produce ultra-pure, extremely dry hydrogen for best processing results; companies can move the electrolyzers if they relocate to another facility; generating hydrogen eliminates the supply interruptions and contract issues; and producing hydrogen reduces costs over time.

Hydrogen cleans part surfaces to enhance processing results.
Photo Credit: Nel Hydrogen

Hydrogen Generation Facilitates Processing Atmospheres

For thermal processors, the ultimate priorities for a thriving business are parts and profits. Satisfying customers with high quality, heat treated components keep them coming back. To that end, generating hydrogen on site can play a significant role . For instance, hydrogen has the highest heat transmission of any gas, resulting in faster heating, faster cooling, and faster cycle times in both continuous and batch furnaces. Hydrogen atmospheres clean parts, and clean part surfaces enhance sintering/fusion. Hydrogen also scavenges oxygen which counteracts potential furnace leaks. Companies that make their own pure hydrogen, already formulated for their thermal process atmospheres and always available, can potentially improve plant productivity and part quality with the desired properties demanded by their customers.

“The many positives of hydrogen generation work for companies experiencing environmental pressures to choose alternatives to delivered and stored gases,” said Wolff. For instance, he cited a case in which a specialty wire producer in an urban area used dissociated ammonia for wire annealing for decades. However, a gradual shift in their neighborhood to less industry and more housing, schools, and places of worship made it risky to continue storing the toxic ammonia gas to make dissociated ammonia. The company chose to invest in hydrogen and nitrogen generation to replace their ammonia storage and dissociator. According to Wolff, the company is now using less electricity, and can use a leaner atmosphere blend because hydrogen is drier than dissociated ammonia. They are getting cleaner wire, saving money using less electrical power, and eliminating ammonia purchases and tank rental.

Dave Wolff
Regional Sales Manager
Nel Hydrogen
Photo Credit: Nel Hydrogen

In another case, a different specialty wire producer suffered a catastrophic fire that involved hundreds of hydrogen cylinders stored at their historic facility. The company had to replace the plant. To meet current safety and fire code standards, the decision to generate hydrogen was a great choice to comply with the demands of the local fire marshal. According to Wolff, “Authorities having jurisdiction are some of the best advocates for hydrogen generation versus storage.”

Certain Growing Applications Prefer Generated Hydrogen for Best Part Quality

The newest powder-based manufacturing technology is metal AM (metal additive manufacturing) which expands on the learnings and foundations of PM (powder metallurgy) and MIM (metal injection molding). Metal AM is growing rapidly in applicability. Several metal AM techniques are commercialized, and even more are in development. There are several ways that metal AM is revolutionizing fabrication by eliminating complex set-ups, molds, and fixtures, and thereby reducing the costs of short runs. The method allows for continuous design improvements, practically in real time. Metal AM enables parts to be very lightweight through internal strengthening, and parts can be directly translated and produced from a CAD file. In other words, metal AM can create parts that are impossible to make by other approaches. While there is a range of techniques that can be applied to the general category of metal AM parts, most of them use powder, as powder provides the best part finish quality. And, like previous powder fabrication technologies such as PM and MIM, metal AM uses sintering to adhere the metal powder particles together with metal-to-metal bonds.

Metal AM powders are miniscule (20 - 100 microns) and are highly susceptible to oxidation if unprotected by an inert or reducing atmosphere.
Photo Credit: Nel Hydrogen

Metal AM powders are miniscule (20–100 microns), uncoated, and handled gently during fabrication. They are highly susceptible to oxidation if unprotected by an appropriate atmosphere. These tiny particles have an enormous surface area (3kg of typical metal AM 316 SS powder has the surface area of a tennis court). Pure hydrogen (or blended with N2 or Ar gas) is the optimal reducing atmosphere for sintering metal AM parts in both atmosphere furnaces and vacuum furnaces. According to  Wolff, a company having the capability to produce its own hydrogen will have the best results with these kinds of parts that will grow in demand in the coming years.

Compliance Considerations in Hydrogen Use

While generating hydrogen for on-site use without storing inventory is far safer than storing hydrogen or ammonia, there are still rules to follow. There are issues surrounding exhaust, pressure balancing, air flow, heating/cooling, and other considerations. Safety, of course, is paramount when using hydrogen. Helpful publications to review include NFPA 2, NFPA 55, ASME Code for Pressure Piping B31.1, and FM Global Property Laws Hydrogen Data Sheet. Additionally, if the building is leased, the landlord should be aware of the use of hydrogen as should the insurance agent.

Water electrolyzers are available in a variety of sizes and configurations to meet the hydrogen requirements of any thermal processing facility.
Photo Credit: Nel Hydrogen

“Thousands of hydrogen users have proven that, given the right set of circumstances, it’s in their interest and their customers’ interest to generate hydrogen on site,” said Wolff. “And that’s because hydrogen generators produce high purity, pressurized, dry hydrogen with zero hydrogen storage. It’s also a compact, portable, and reliable system, that provides a range of flow rates to suit any thermal processing requirement. And, the hydrogen cost is relatively fixed, so as production goes up, the cost per part goes down.”

For more information: Please send your inquiry to info@nelhydrogen.com or visit www.nelhydrogen.com.

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Industrial Gases: Advancing 3D Printing Processes for Aerospace

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Curious about proper gas atmospheres needed to meet high-tolerance standards for additive manufactured parts before, during, and after the heat treating process?

Learn about them in this detailed original content article from Heat Treat Today’s Aerospace 2021 print magazine. The author, Lisa Mercando, Ph.D., is the marketing manager of strategic marketing & development at Air Products. You can access the other articles in our digital edition here. Enjoy the Technical Tuesday!

Lisa Mercando - Air Products - BRANDED - provided by Air Products
Lisa Mercando, Ph.D.
Marketing Manager, Strategic Marketing & Development
Air Products

In a world of rapid prototyping and production of metal components, it is imperative to have the proper gas atmosphere to produce quality parts. Argon, nitrogen, and helium are commonly used to create inert atmospheres in order to meet the high-tolerance standards required for additive manufactured (AM) aerospace parts. Industrial gases are used every step of the way from powder production to various additive manufacturing techniques to finishing processes that include heat treating and hot isostatic pressing (HIPing).

Inert gas atomization is the best method to obtain dense, spherical particles, which are best for AM applications where the desired particle size is usually less than 100 microns. Additionally, inert gas atomization greatly reduces risk for oxidation, providing a high level of powder purity and quality. Helium provides the best results when its superior heat transfer capabilities are needed. This process achieves the following properties: dense and spherical particles; high quality and purity metal powders; and narrow particle size distribution. We can provide high pressure gases for powder atomization and hydrogen-based atmospheres for powder reduction and annealing.

Image demonstrating metal additive manufacturing

To meet the high-tolerance standards required in additive manufacturing–particularly for aerospace–nitrogen and argon are commonly used to provide inert atmospheres. The use of helium, with its high thermal conductivity, offers an interesting option for minimizing the thermal distortion of elongated parts during printing. An inert atmosphere provides numerous benefits on a printed part by:

  • reducing oxidation of printed parts by lowering the oxygen concentration in the build chamber
  • improving safety through the inerting of combustible dust during powder handling and sieving
  • creating a stable printing environment by maintaining constant pressure in the print chamber
  • mitigating powder clumping in the feed tube
  • preventing part deformation by controlling thermal stress through effective cooling

Gas requirements differ based on the process being used and the material being printed.

Often, AM aerospace parts require additional processing to achieve the desired final properties. This is done mainly in the form of heat treating, sintering, or HIPing. All three processes have industrial gas requirements for preventing oxidation. Heat treating with argon, nitrogen, hydrogen, or a nitrogen/hydrogen blend can relieve internal stresses and enhance part properties such as strength, ductility, and hardness. In sintering applications, nitrogen/hydrogen blends or argon/hydrogen blends are important in producing near-net shape parts with increased strength and uniformity. High pressure argon is used in HIPing applications to provide fully dense parts with increased strength and reliability.

Image of a furnace heating metal parts

In addition to providing the bulk industrial gases required, the company has developed state-of-the-art process intelligence systems. These systems monitor atmosphere composition parameters to ensure the process is running with the desired gas atmospheres and provide alerts for any needed maintenance or adjustments. Decades of metals processing experience in gas supply, applications, process knowledge, and safety are applied to help improve heat treating efficiency and part quality.

Remote tank monitoring is one example of the company’s Process Intelligence™. Operators increasingly rely on data to closely track critical process parameters, such as the use and inventory of vital industrial gases. This tank monitoring system enables operators to remotely check their supply levels and monitor usage from a touch screen in the plant, on their laptop, or on their mobile device. Customized daily reports are a common way to stay current on their industrial gas supply.

For heat treatment operations using a furnace atmosphere that is flammable or potentially flammable, an inert purge gas – typically nitrogen – is utilized to help ensure safe operation. This system alerts operators to the condition of the liquid nitrogen supply and helps them remotely track their supply and usage of gases. Optional system alarms allow operators to safely initiate a controlled purge shutdown, enabling compliance with NFPA 86 by confirming they have adequate liquid storage levels, or ensuring their nitrogen piping temperature remains at a safe level. Typically installed near the furnace operation, the remote touch screen on the base station displays conditions of all bulk gas storage tanks and can use both audible and visual alarms to warn the operator of a potentially critical situation.

Tank Monitoring

In addition to using inert gases, such as nitrogen and argon for the 3D printing processes, GE Additive Manufacturing, located in Cincinnati, OH and a major manufacturing center for additive manufacturing, also performs post processing heat treatment/sintering on the metal parts to enhance part quality. Their capabilities allow for the production of quick, precise parts with high levels of accuracy, even on intricate shapes and geometries across multiple applications.

Conclusion

If you are prototyping and producing metal components, be sure to consider the importance of achieving the optimum gas atmosphere to efficiently make quality parts. The heat treat postprocessing of AM metal parts is often required to produce the high-quality parts specified for the aerospace industry.

About the Author: Dr. Lisa Mercando is the marketing manager, Strategic Marketing & Development, for Air Products’ metals processing industry. She has worked at Air Products for 28 years in a variety of roles and responsibilities and is the author of several patents and technical articles.

All images were provided by Air Products.

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Heat Treat Tips: Atmospheres, Gas Chambers, and Thermocouples

/ ATMOSPHERE GENERATORS TECHNICAL CONTENT, HEAT TREAT NEWS INDUSTRIES, MANUFACTURING HEAT TREAT, OVENS-HIGH-TEMPERATURE, THERMOCOUPLES TECHNICAL CONTENT

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

For Heat Treat Today’s latest round of 101 Heat Treat Tips, click here for the digital edition of the 2019 Heat Treat Today fall issue (also featuring the popular 40 Under 40).

Today’s tips come to us from Nel Hydrogen covering atmospheric solutions and Wisconsin Oven Corporation with a tip on gas chamber issues. Additionally, Pelican Wire provides 4 quick tips on Thermocouples.

Heat Treat Today welcomes you to submit your own heat treat tip for Heat Treat Today's 2020 Fall issue to benefit your industry colleagues. You can submit your tip(s) to karen@heattreattoday.com  or editor@heattreattoday.com.

Heat Treat Tip #11

Compliance Issues? Try On-Site Gas Generation

On-site gas generation may help resolve compliance issues. Growth and success in thermal processing may have resulted in you expanding your inventory of reducing atmosphere gases. If you are storing hydrogen or ammonia for Dissociated Ammonia (DA), both of which are classed by the EPA as Highly Hazardous Materials, expanding gas inventory can create compliance issues. It is now possible to create reducing gas atmospheres on a make-it-as-you-use-it basis, minimizing site inventory of hazardous materials and facilitating growth while ensuring HazMat compliance. Modern hydrogen generators can serve small and large flow rates, can load follow, and can make unlimited hydrogen volumes with virtually zero stored HazMat inventory. Hydrogen is the key reducing constituent in both blended hydrogen-nitrogen and DA atmospheres—hydrogen generation (and optionally, nitrogen generation) can be used to provide exactly the atmosphere required but with zero hazardous material storage and at a predictable, economical cost. (Nel Hydrogen)

Generate H2 and N2 on-site – saving money, improving safety, and reducing carbon footprint.

Heat Treat Tip #12

Oven Chamber Failing the Test? Try This!

When having difficulties passing a temperature uniformity test, check the pressure of the heating chamber. This can be done with a pressure gauge that reads inches of water pressure. The best uniformity is achieved when the pressure is neutral or slightly positive (0” to +.25” wc). If the pressure is negative (even slightly), it can draw a stream of outside cold air into the chamber, causing cold spots. For the best results and ease of analysis, permanently mount a gauge to read the pressure. Any issues with pressure can be easily recognized and corrected. (Wisconsin Oven Corporation)

Heat Treat Tip #70

Type N Thermocouple (Nicrosil / Nisil)

Type N Thermocouple (Nicrosil/Nisil): The Type N shares the same accuracy and temperature limits as the Type K. Type N is slightly more expensive and has better repeatability between 572°F to 932°F (300°C to 500°C) compared to Type K. (Pelican Wire)

Heat Treat Tip #71

Know Your Thermocouple Wire Insulations

Know your thermocouple wire insulations. When is Teflon® not Teflon®? Teflon® is a brand name for PTFE or Polytetrafluoroethylene owned by Chemours, a spin-off from Dupont. FEP is Fluorinated Ethylene Propylene. PFA is Perfluoroalkoxy Polymer. All three are part of the Fluoropolymer family but have different properties. Of the three compounds, PTFE has the highest heat resistance, PFA second highest and FEP third. The higher the heat resistance the more expensive the insulation. Keep that in mind when specifying the insulation and only pay for what you need. (Pelican Wire)

Heat Treat Tip #72

Resistance Temperature Detectors (RTDs)

Resistance Temperature Detectors (RTDs) are replacing thermocouples in applications below 1112°F (600°C) due to higher accuracy and repeatability. Typical constructions are multiconductor cables with nickel-plated copper conductors. (Pelican Wire)

Heat Treat Tip #74

When to Use Type K Thermocouples

Type K thermocouples should only be used with the appropriate Type K thermocouple wire. Type K measures a very wide temperature range, making it popular in many industries including heat treating. An added benefit with Type K is that it can be used with grounded probes, ungrounded probes, and exposed or uncoated wire probes which are attached to the probe wall, measure without penetration, and have a quick response time respectively. (Pelican Wire)

Heat Treat Tip #100

The Right Furnace Atmospheres Will Pay Dividends

Precision blended gas system provides the atmosphere needed at the most economical cost.

Save money on your furnace atmospheres by employing the driest and leanest furnace atmosphere blends possible. Furnace atmospheres are a compromise between keeping it simple and supplying exactly the atmosphere to meet the unique requirements of each material processed. Organizations have different priorities when it comes to atmospheres—heat treat specialists may want to be able to run as many different materials as possible using a limited array of atmosphere types, while captive heat treating operations often want exactly the atmosphere approach to maximize the benefits for their specific processes/products.

The dewpoint (water content) of the atmosphere in the furnace is a key factor in its performance. At high temperatures, water in the atmosphere can break down, releasing oxygen that can cause oxidation. You must maintain a high degree of reducing potential to achieve the surface finish and processing results desired. If the furnace atmosphere gas is wet, you’ll need a gas blend richer with hydrogen than you would if your atmosphere blend had a lower dewpoint (less water vapor content). Since hydrogen costs 10 times more than nitrogen, it is more economical to run a leaner atmosphere than a richer atmosphere. By running the driest atmosphere blend possible, you may find that you can lean down your atmosphere (consistent with the metallurgical needs of your product/process) by reducing the proportion of hydrogen and increasing the nitrogen. In doing so, you may recognize meaningful savings.

Check your furnace atmosphere raw materials and process and obtain the driest atmosphere possible. Control your atmosphere dewpoint by adding humidity as needed to the driest starting blend possible rather than accepting a wet atmosphere and trying to process your parts. You’ll achieve the best compromise of excellent results at the lowest cost. (Nel Hydrogen)

 

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Women’s History Month: Alice Parker’s Gas Furnace Patent

/ ATMOSPHERE GENERATORS TECHNICAL CONTENT, ENERGY HEAT TREAT, FEATURED NEWS

Alice H. Parker’s gas furnace design, as patented in 1919.

Heat Treat Today is pleased to join in the celebration of Women’s History Month by turning the spotlight on Alice H. Parker, an African-American woman from Morristown, New Jersey, who received a patent for a gas furnace heating system that played a key role in the development of the central heating systems most of us have in our homes today.

It was nearly 100 years ago that U.S. Patent No. US132590A was issued to Parker, whose furnace design shows gas being used as a power source when most homeowners were stocking up on wood and coal, and includes the idea of using air ducts to deliver the heat to different parts of a home. Officially granted on December 23, 1919, Parker’s patent was not the first for a gas furnace design, but it was unique in that it incorporated a multiple yet individually controlled burner system (see the text of the patent here). Although this exact design was never implemented due to safety issues with the regulation of heat flow, this structure was an important precursor to the modern heating zone system and thermostats as well.

Parker was a 1910 graduate of Howard University.

Sources: Face2FaceAfrica.com, TheFrisky.com,

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