Scientists from the Alliance for the Development of Additive Processing Technologies (ADAPT) at Colorado School of Mines who took part in an international research team have helped develop a nickel-titanium elastocaloric cooling shape memory alloy (SMA) that is highly efficient, eco-friendly, and easily scaled up. The alloys, in which hafnium acts as a strengthening precipitate, hold the promise of requiring only heat treatment to attain functional shape memory performance.
The international team, led by University of Maryland Professor Ichiro Takeuchi, developed the improved elastocaloric cooling material using a blend of nickel and titanium metals, fabricated by a 3D printer, that is not only potentially more efficient than current technology, but is completely “green.” Moreover, it can be quickly scaled for use in larger devices.
Dr. Aaron Stebner, Rowlinson Associate Professor of Mechanical Engineering
“The key finding of the research is that while elastocaloric materials typically used for solid-state cooling show a degradation in cooling behavior after hundreds of cycles, laser melting these metals creates fatigue-resistant nanocomposite microstructures that can cycle, with consistent cooling capacity, a million times,” said Aaron Stebner, Rowlinson Associate Professor of Mechanical Engineering and a co-author of the paper.
Professor Ichiro Takeuchi, Graduate Program Director in Materials Science and Engineering, University of Maryland
“Dr. Stebner’s expertise played a crucial role in developing understanding of the fundamental mechanism behind fatigue-resistant behavior of additively manufactured shape memory alloys. His group’s in situ synchrotron diffraction and finite element modeling capabilities gave us unique insight into the inner workings of the material,” Prof. Takeuchi said.
The work, which was published in the Nov. 29 issue of Science, is the result of a collaboration led by researchers from the University of Maryland, together with Ames Laboratory, Mines, Iowa State University, and China’s Xi’an Jiaotong University.
Welcome to another episode of Heat Treat Radio, a periodic podcast where Heat Treat Radio host, Doug Glenn, discusses cutting-edge topics with industry-leading personalities. Below, you can either listen to the podcast by clicking on the audio play button, or you can read an edited version of the transcript. To see a complete list of other Heat Treat Radio episodes, click here.
Audio: A Discussion with David Wolff, Nel Hydrogen, Part 2
In this episode, Heat Treat Radio host, Doug Glenn, continues his conversation with Nel Hydrogen Heat Treat Manager David Wolff about the use of hydrogen in heat treat processes. Listen to this second part of a two part conversation to find out more about the various delivery systems available, the economics of using hydrogen, and whether using hydrogen might make sense for your specific heat treat application. If you missed Part 1 of the series, click here.
Click the play button below to listen.
Transcript: A Discussion with David Wolff, Nel Hydrogen, Part 2
The following transcript has been edited for your reading enjoyment.
This Heat Treat Radioepisode/transcript is based on the e-book shown above. Click on the image above if you'd like to get your own download of this 18-page e-book.
Doug Glenn (DG): Welcome to part two of this 2-part series on the use of hydrogen in heat treat processes. Today we are wrapping up a conversation we started last time with David Wolff of Nel Hydrogen. This 2-part series is based on the content of an eBook recently published by Heat Treat Today in cooperation with Nel Hydrogen entitled “Hydrogen Generation and its Benefits for Heat Treaters.”
In part one, we discussed some hydrogen fundamentals. Things like what purpose hydrogen plays in the heat treat process. We hit on safety issues, the processes where hydrogen is typically used, and other atmosphere generation systems and how they compare to hydrogen, as well as several other hydrogen basics. In this episode we're going to dig deeper into several topics, including the various delivery systems available, the economics of using hydrogen, and whether or not using hydrogen might make sense for your specific heat treat application.
We're going to get back to our discussion with David Wolff of Nel Hydrogen. Remember, this is part 2. If you'd like to read the transcript or listen to part 1, click here. Now back to the interview.
DG: Let's talk about typical modes of delivery for hydrogen. My understanding is we're talking about bulk delivery from some of your gas companies, generated hydrogen, which, as you mentioned, could be endo or exo, that does produce some percentage of hydrogen, but then also we've got a product that you guys are offering, which is a hydrogen generator. Let's talk about those delivery methods just briefly, maybe summarize them, their advantages/disadvantages, etc.
Delivered atmosphere options
David Wolff (DW): While nitrogen and argon, the diluent gases are available anywhere on earth because they are components in the air, hydrogen is only available by generating it from a hydrogen containing material, such as methane or from water. Delivered hydrogen needs to come from a hydrogen plant that may be hundreds of miles away from any particular customer. In most cases, if you're buying hydrogen, say from an industrial gas provider, that hydrogen has come from a plant where it's made, cleaned, and then packaged or processed in a way for efficient delivery. It might be liquefied or it might be compressed and then it's trucked to thermal processing customers for storage and subsequent use. Your delivered hydrogen is coming from some chemical or other facility, which may be quite far away.
As you mentioned, Doug, the two historically significant sources of generated, what I will call “blended atmospheres,” typically fall under the name "generated atmospheres," and I'll group endo and exo together because they're really made in a very similar way, and then dissociated ammonia. Endo and exo are made by thermally cracking natural gas, which is primarily methane, and endo and exo describe two very similar processes for making an atmosphere which consists of hydrogen, water, carbon monoxide, and carbon dioxide. The ratios of those gases differ whether you're using endo or exo gas, but both gases contain all four-hydrogen, water, CO2, and CO. As long as your process can utilize all four of those gases, then endo and exo are quite economical, particularly today when methane or natural gas is so cheap. You don't have to be that old to remember that natural gas at one time was not so cheap. I remember not so long ago where natural gas was about five times what it costs today. There was a period of time when endo and exo were not attractive in industry because of the cost.
Now ammonia dissociation or DA (dissociated ammonia) has a popular and cost-effective technique for generating a kind of general use furnace atmosphere where you store ammonia and then you use a heated catalytic reactor to crack that ammonia into a gas which is 75% hydrogen balance nitrogen. DA has been used for many, many decades, and in fact there are many methods which have standardized on DA. It is still popular. The challenge with DA is it requires the storage of ammonia, and ammonia is ever more unwelcome in communities because if it leaks, it creates a hazardous material response incident.
DG: You've got storage issues there. It's very obvious when ammonia leaks, you can tell with your nose, it is a harmful gas, so you've got to be very careful with the storage of it. That is the point.
DW: And there is one other issue, and that is if you're using DA, you can't get pure hydrogen. Because you're starting with a gas which is 25% nitrogen, so no matter how much you dilute it by adding pure hydrogen, it is still going to have nitrogen in it. If you want pure hydrogen for the ultimate in flexibility, it can be helpful to generate pure hydrogen.
The final thing you asked me to talk about was the equipment that Nel Hydrogen provides, which is electrolytic on-site generation of pure hydrogen. That has become newly attractive because we've managed to reduce the capital cost of electrolysis equipment and we've managed to improve the energy efficiency, the hydrogen production versus the electricity used. And in an environment where it is harder and harder to store hazardous materials like ammonia or pure hydrogen, it is interesting and attractive to be able to make cost-effective, process pressure, dry, pure hydrogen which you can then custom blend into whatever diluent gas you want, whether it's nitrogen or argon, in the exact ratio needed for your parts.
Atmosphere generation systems
DG: Exactly, because you're talking about the endo or exo, you've got a range there of how much hydrogen, or what percentage of hydrogen you can have, whether you run it rich or lean, and things of that sort. With DA (dissociated ammonia), your looking at 75% hydrogen/25% nitrogen, basically very little deviation from that. With a system where you are on-site hydrogen generating, you can dilute it at whatever percentage tickles your fancy.
DW: Exactly. And by definition, the metallurgist will assist you to run the most dilute mixture that meets your metallurgical needs. Because that's how you save the most money, by diluting the hydrogen as much as the metallurgy will allow.
DG: Very briefly, for those who might not know, tell us about the technology inside of your equipment, the proton exchange membrane and things of that sort. Explain how it works, and then I'd like to ask you what kind of capacities can these systems that you supply, how many CFH or however you measure it, how much can you produce for a process.
DW: It is easy to explain because we've all done it in high school chemistry. Virtually every person among us, in high school chemistry, has used a direct current from a battery and two electrodes to crack water with an acid or base in it to make hydrogen and oxygen bubbles. We're doing exactly the same thing, but we're doing it on an industrial level. Our equipment uses an electrolyte, which is made by Dupont, to enable us to crack water into hydrogen and oxygen and maintain the two gases on two different sides of a solid membrane. That has important safety advantages because the hydrogen and oxygen can never mix. We make very pure hydrogen. The only impurity in that hydrogen is water. As manufactured in our equipment, the hydrogen is wet with water. The only purification that we do to that hydrogen is we dry it. And we dry it to the specification for industrial grade either gas or liquid hydrogen. In essence, it is a replacement for gaseous compressed, or liquefied hydrogen, that you might have delivered to your facility.
The raw materials that we require are simply electricity and de-ionized water, and we require also cooling water for some of our larger scale equipment.
DG: The contention is that there are some real potential benefits to some heat treaters by having on-site hydrogen generation. What are the advantages and then, are there some heat treaters who shouldn't even consider using hydrogen?
Stored atmosphere raw materials by the numbers
DW: Getting rid of the need for on-site hazardous material storage is a huge benefit. That is a major benefit- zero hazardous materials inventory. Cost predictability is often even more important than having the lowest absolute cost at any point in time. With hydrogen generation, most of the cost is in the capital and in the electricity that you use to drive the equipment. So cost predictability is much better, for example, than with ammonia, natural gas, or with delivered hydrogen.
On-site electrolytic hydrogen generation makes pure hydrogen as compared with exo, endo, or DA. And the hydrogen that you're using is very, very pure. It is 99.9995% or better, so it's the equivalent of very, very pure delivered hydrogen. We provide very dry hydrogen. One of the drawbacks to the generated hydrogen in exo, endo, and DA is that those gases are not as dry, so you often need a higher hydrogen level in order to achieve similar scavenging of oxygen. People find, for example, when they replace DA with generated hydrogen and nitrogen, they can often use a more dilute blend. So rather than having to use 75/25, they might be able to use 50/50, saving money.
Finally, the generated hydrogen from Nel equipment is available at considerable pressure, 200 to as high as 435 Psi. That makes it easier to use a pressure-based blender to selectively blend hydrogen and nitrogen to your desired furnace atmosphere blend.
DG: How big are these systems?
DW: We have equipment anywhere from 4 cubic feet an hour of pure hydrogen up to 19,000 cubic feet/hour of pure hydrogen. The cost of the equipment goes up as you get bigger. I think the 'sweet spot' for generated hydrogen is probably not to try to compete with the largest endo and exo facilities. I think a thermal processor might choose to utilize a generated hydrogen for those materials and processes that require pure hydrogen or a purity of atmosphere unattainable with endo or exo.
Endo and exo are really good technologies and especially today with inexpensive natural gas. If you can use those, God bless you, use them. But if today you're using DA or you're using delivered hydrogen, then I think you might find it very worthwhile to choose a hydrogen generator which might have a capacity of 200 or 400 or 1000 cubic feet an hour for your process. And, in doing so, you might find that, as compared with certainly DA, you can use a leaner blend and save money as well as get better process results.
DG: What are the maintenance issues that we're seeing with on-site generation equipment?
DW: There are two types of normal maintenance required. All of our equipment is designed with internal flammable gas detectors. That's important from a safety point of view. That protects you from any leaks within the equipment, it also protects the facility if there was any flammable gas in the facility atmosphere, the hydrogen generator would shut down. Those internal flammable gas detectors need to be calibrated once every 3 months. The nice thing is that it only takes 15 minutes, but it is a planned, required maintenance operation that must take place every 3 months and takes 15 minutes. And of course, we train you how to do that.
In terms of schedule maintenance of a more involved type, our equipment is designed to be maintained once per year. Again, we train our customers to do that, or we can offer to come in and do it ourselves. It is a kind of maintenance that is very straightforward and can be done by a mechanical or electrical technician. It includes replacing parts, such as the water pump, that have a defined life-time. And we recommend that those parts be replaced on a proactive point of view in order to eliminate nuisance failures. For example, a water pump might last 3 years or 25,000 hours, for example. And really, that's it. Like any process equipment, you can have failures and we have set up a robust service capability so that we can diagnose and get people parts as quickly as possible so that they can keep their equipment running with the highest on-stream time possible. Especially for customers in other countries, we often recommend that they have on-hand a kit of parts that we call 'recommended spares kit', which is a very cost-effective way to have the parts available that we have seen fail in the field, so that they don't have to wait for shipped parts to show up. As soon as a failure is diagnosed, they can put in the parts and they can be right back on-stream and then we can replace any parts that were taken from the recommended spares kit.
DG: I next asked Dave to address the economics of the system. How does on-site hydrogen generation compare to other gas delivery systems?
DW: In terms of economics, the cost of on-site generated hydrogen is really very straightforward. It is the capital cost of the equipment, the cost of the electricity and water inputs and the cost of annual maintenance. The equipment can be a purchase or a lease. And because you're acquiring the equipment, of course there is an economy of scale to consider. Small volumes of hydrogen is smaller equipment. And then, in that case, we find that most people find the generator capital cost for smaller users might be around $2.00/hundred cubic feet. That is the capital cost of the equipment depreciation. As the size of the hydrogen generator increases (that would be tube trailer users or liquid hydrogen users), the capital cost of the equipment drops below $1.00/hundred cubic feet. So as equipment gets bigger, the capital cost per unit of production falls. Our largest capacity equipment, intended for very large scale manufacturing, which might be used, but might be too large for most thermal processors, has a fixed cost as low as 20 cents/hundred cubic feet. So you can see there is economy of scale.
Now the energy cost of the hydrogen is most of the variable cost. Water is almost nothing. Depending on the specific model of the system chosen, it requires between 15 and 19 kilowatt hours of electricity to make a hundred cubic feet of hydrogen. Here in the US, in 2018, the US industrial electrical rate was about .07/kilowatt hour average. So the average in the US in 2018 was 7 cents. If you multiply that by 15 – 19 kilowatt hours/hundred cubic feet, then you get an electric variable cost of between $1.05 and $1.53/hundred cubic feet. So you add that variable cost to the fixed.
Your annual maintenance is somewhere between $2,000 and $5,000. Obviously, that is a bigger hit for the smaller users than your larger users. Altogether, the cost of hydrogen for on-site water electrolysis in the medium volume range of interest to the thermal processing industry ranges from a high, at the low end of the use, of about $4/hundred to as little as $2/hundred for users of larger volumes, say your liquid hydrogen users.
DG: Best candidates for on-site generation and then, are there some people who shouldn't?
DW: The best candidates for on-site hydrogen generation are those for whom the technique, equipment, and product quality, the hydrogen quality, provide competitive advantage. So very compact equipment, zero hydrogen inventory, very pure hydrogen with relatively low maintenance, highly predictable costs and the ability to blend any hydrogen atmosphere to pure hydrogen down to forming gas, are all advantages of on-site electrolysis hydrogen.
We observe that captive heat treating operations often prioritize the characteristics of on-site hydrogen generation because they see a direct effect on product quality and ease of integrating heat treating processes into their facility. So they are more interested in- is it safe, is it pure, is it easy to operate than is it the cheapest possible hydrogen. Because of the capital cost (this equipment is not cheap), the best candidates for on-site hydrogen are going to use the equipment hard. The closer to 24/7, the less expensive, the capital cost contribution to your cost structure. So use it hard.
There are a few usage characteristics that argue against on-site hydrogen and similarly would make endo, exo, or DA less attractive. If you've got a temporary requirement for hydrogen, or a batch process that occurs irregularly or with long time gaps between batches, or you have a portable requirement, or where your actual atmosphere required might still be under development. In all of those cases, frankly, you'd be better to start out with delivered gases, at least until you understand the requirements of the process and the scheduling for the gas use until you establish a predictable pattern.
Finally, endo, exo, and DA are really good technologies to make a hydrogen containing atmosphere. If the cost of the atmosphere is the most important factor and the safety issues of ammonia storage and CO containing atmospheres are acceptable, and the characteristics of the exo, endo, or DA atmosphere are acceptable to your processes, then those may be a good choice.
Doug Glenn, Heat Treat Today publisher and Heat Treat Radiohost.
End of Part 2.
Part 1 of this two-part series aired on January 30, 2020. To find that episode, click here. To find other episodes, go to www.heattreattoday.com/radio and look in the list of Heat Treat Radio episodes listed.
A Hauck HT plant located in the Netherlands recently received a unique high vacuum furnace. The all-metal high vacuum furnace from SECO/WARWICK with the working chamber size of 47.2″ x 47.2″ x 78.7″ was delivered to Hauck’s newly expanded plant in Eindhoven. At the same time, it is the largest furnace of that type currently in operation in that region.
According to Marcus Wendel, Hauck Heat Treatment Executive Director, “The all-metal vacuum furnace with diffusion pump was designed to achieve high vacuum conditions and ensure the highest possible purity of the heat treated parts. Accordingly, we had some special requirements regarding used components and solutions. All have been implemented by SECO/WARWICK.”
Sławomir Woźniak CEO SECO/WARWICK
Sławomir Woźniak, SECO/WARWICK Group CEO, also commented, “From the very beginning, our company philosophy has been based on meeting the highest expectations of product and technology development for our customers, including first class organizations such as Hauck Heat Treatment Group. This partnership proves that knowledge and experience are not just empty marketing slogans, but valuable features in business.”
This was the third furnace delivered there, and the two companies are discussing next steps together.
Welcome to another episode of Heat Treat Radio,a periodic podcast where Heat Treat Radio host, Doug Glenn, discusses cutting-edge topics with industry-leading personalities. Below, you can either listen to the podcast by clicking on the audio play button, or you can read an edited version of the transcript. To see a complete list of other Heat Treat Radio episodes, click here.
Audio: A Discussion with David Wolff, Nel Hydrogen, Part 1
In this conversation, Heat Treat Radio host, Doug Glenn, engages Nel Hydrogen Heat Treat Manager David Wolff in a conversation about hydrogen generation and its purposes. Find out more about what hydrogen is best used for, what hydrogen can do for your company, why hydrogen is preferred to nitrogen, and how to safely use it to the best effect.
Click the play button below to listen.
Transcript: A Discussion with David Wolff, Nel Hydrogen, Part 1
The following transcript has been edited for your reading enjoyment.
Doug Glenn (DG): We're here today with David Wolff from Nel Hydrogen and we're going to be talking a bit about on-site hydrogen generation. This really has come about because of an eBook that David and one of his colleagues, a gentleman by the name of Chris Van Name, and Heat Treat Today worked on together. The eBook was based on a presentation that you gave at FNA 2018.
Dave Wolff (DW): You're correct. The eBook was based on the FNA (Furnaces North America). I did an expansion on it for Fabtech 2019.
DG: I want our readers to know you before we jump into the content of the book. If you don't mind, Dave, would you just give us your name, rank, serial number, etc.
This Heat Treat Radioepisode/transcript is based on the e-book shown above. Click on the image above if you'd like to get your own download this 18-page e-book.
DW: I've been in the industrial gas industry for my whole career, (hard to believe), going well over 40 years now. I've been a little over 20 years at Nel Hydrogen. Before we were called Nel, we were called Proton Onsite. I joined relatively early in Proton's history. Proton was begun in order to commercialize attractively cost on-site hydrogen using water electrolysis. I found that incredibly exciting, as I came from the industrial gas industry, and I witnessed first hand the importance of having cost effective access to hydrogen in order to succeed in materials processing. Prior to Proton, I was with Messer, who is now back in the United States; and I was with Air Products for about 13 years prior to my time with Messer.
DG: So you've spent, let's say, 40 years in the industrial gases industry and most recently, and a good bulk of that time, with what was called Proton Onsite, now called Nel Hydrogen. For our reader's sake, Nel in the US is headquartered out of New England?
DW: Yes. Nel, in the US is headquartered in Wallingford, Connecticut, which was where Proton was based. Nel's worldwide corporate headquarters is in Norway. Nel is a corporation related to the historical Norsk Hydro, which has been around since 1927 and involved with water electrolysis since the early 20's.
DG:So today we want to talk about hydrogen, but we're going to talk specifically about on-site hydrogen generation. But before
Delivered atmosphere options
we get there, if you don't mind Dave, give us a quick rundown on just the role of hydrogen in your normal, typical heat treat process. What does hydrogen do for us?
DW: You start with the fact that hydrogen is a reducing gas, which means that it can prevent or even reverse oxidation. For example, you can put oxidized parts through a hydrogen atmosphere furnace and they'll come out the other end, say if it's a belt furnace, bright and shiny. At the elevated temperatures used in metal thermal processing (heat treating), the rate of oxidation is increased, so you have to protect the metal so that it doesn't discolor from oxidation. And more concerning, oxidation will interfere with braze material flow in brazing and will prevent proper sintering of powder metal fabricated parts, so oxidation is a real problem in thermal processing.
DG: Right. So the reason of the brazing and whatnot is because of contamination on the surfaces, right? You don't get a solid braze or a solid sinter.
DW: Exactly. Now hydrogen is not the only reducing gas. CO (carbon monoxide) can also be used. But CO is highly toxic, so it is not routinely used, except if it's created incidentally in the process of making endo or exo gas.
Some people wonder why nitrogen alone is not sufficient as a heat treating atmosphere. It's inert, right? But it's essentially impossible to flow enough nitrogen through an atmosphere furnace to eliminate all of the oxygen molecules. And if you did try to flow that much nitrogen through the furnace, you would rob all of the heat out of the furnace. So the attractiveness about hydrogen is it grabs and immobilizes the stray oxygen molecules preventing oxidation but still enables you to manage the flow rate in your furnace.
DG: There are some vacuum furnace heat treaters who place a piece of metal or some substance inside of their furnace (they call it a 'getter'), which basically attracts those undesirable elements out of the atmosphere. In a sense, hydrogen (not exactly, but in a sense) can be kind of that 'getter' that goes and 'gets,' if you will, the oxygen pulls it out of that atmosphere, where nitrogen you have to be pushing it out. You'd have to be putting so much nitrogen through, you still might not get rid of all of the oxygen, whereas if you have some hydrogen, it pulls it out.
DW: You're exactly right. The hydrogen acts as a chemical 'getter' and so it's analogous. A couple of other things I should mention. In addition to its role as a reducing gas to prevent or reverse oxidation, hydrogen has the highest heat conductivity of any gas. So the high heat conductivity of hydrogen means that parts heat up faster in a hydrogen containing atmosphere, and they cool off faster too. The high heat conductivity allows for higher productivity by faster cycles in batch heat treating and faster transport speed through continuous furnaces likes belts and pushers. Parts heat up fast and they cool down quickly. The alternative, if you have lower hydrogen content in your atmospheres, is longer furnaces, slower belt speeds, or longer back furnace cycles.
DG: Coefficient heat transfer hydrogen is the best for pulling heat out or putting heat in, so you're looking at process efficiencies there as well.
DW: Productivity. One final thing. While vacuum furnaces are widely used and yield terrific results, a vacuum furnace creates an inert atmosphere, not a reducing atmosphere. So a high vacuum furnace can prevent oxidation, but typically not reverse it. So in many cases, a wisp of hydrogen is often used to create a partial pressure hydrogen atmosphere in vacuum furnaces. For example, for powder metallurgy, you enhance the sintering by reducing the surface oxidation on the powder particles.
DG: We've hit on what hydrogen can do, and I think we've already hit on this next question, which is the typical heat treat processes. Brazing you've mentioned, sintering you've mentioned; what else would we typically use a hydrogen atmosphere for?
DW: Let's start with making sure that people are aware that hydrogen is used only in furnaces which are designed for hydrogen
Atmosphere generation systems
atmosphere. They have to have the right flow path, they have to have electrical parts and safety systems such as flame curtains, which are expressly designed to safely use hydrogen. Also, and importantly, the newest thermal processing equipment is highly automated for safe use of hydrogen. While hydrogen can be used safely in older equipment that is also designed to use hydrogen, it's important to follow procedures which are specifically designed around hydrogen use. So those are key considerations.
DG: I think we ought to emphasize the caveat that you're issuing. Hydrogen does have its issues, and we need to be careful with the use of hydrogen. So don't just go throw hydrogen into your furnace. It is very, very important that the safety concerns be followed.
DW: So hydrogen is used to provide atmospheres for processes like annealing, brazing, glass metal sealing and all types of sintering including PM, MIM, and AM. Hydrogen is also widely used for processing magnetic materials, motor laminations and things like that. Keep in mind that both synthetic or blended atmospheres and also generated -- and by "generated" we typically refer to exo, endo and DA (dissociated ammonia) -- those atmospheres contain hydrogen as the primary reducing gas. As I mentioned earlier, exo and endo gas also contain CO, which is also a reducing gas, and exo and endo are often used in atmospheres for hardening. Typically you don't use a pure hydrogen atmosphere for that because that will tend to soften your parts.
DG: We've covered some of the processes that are involved, and you've alluded to this Dave, but let's flesh this out a little bit
Stored atmosphere raw materials by the numbers
more--we don't often use hydrogen alone. Often it is used as one component with other gases. Let's talk about why that is. Besides the obvious safety issues of using 100% hydrogen, let's talk about why we don't see 100% hydrogen and what we're often mixing with.
DW: I like to use an analogy here. Think of hydrogen gas in a furnace atmosphere, kind of like dish washing detergent. When you're washing dishes or processing parts, the function is to clean the parts, either the metal parts or cups and saucers. Dish washing detergent is diluted with water. Hydrogen is typically diluted with nitrogen or possibly with argon. In both cases, whether you're washing dishes or processing metal parts, the detergent is more expensive than the diluent. Hence, the idea is to use only as much detergent (hydrogen) as is needed to get the job done.
There are major differences between thermal processing and washing dishes. One major consideration is that the metal that is being thermally processed is actually chemically and metallurgically interacting with the furnace atmosphere. So you have the surface effect, which is the chemical effect, but also you have a metallurgical effect. That's how metals are softened and also, in the case of carbon, hardened. Obviously dishes are unaffected by the dish washing process other than having their surface cleaned. So that is part of the reason that atmosphere composition is greatly dependent on the metallurgy of the parts that you're processing. That is also the area where metallurgists have the greatest knowledge and provide unique process knowledge and value.
DG: So basically, you're going to use as little, if you will, or an appropriate portion of hydrogen to get the job done, and that is very much dependent on materials being run, processes being performed, etc. Correct?
DW: Exactly. The workhorse thermal processing atmosphere is a nitrogen atmosphere with a variable amount of hydrogen depending on the metal being processed. Carbon steel, for example, can be processed in a 4–5% hydrogen blend with the balance of the atmosphere being 95–96% nitrogen. This blend is so widely used that it has been given a nickname, so called forming gas. Some metals react adversely with hydrogen and cannot be processed in a hydrogen containing atmosphere at all. An example of that would be titanium. Titanium, which is so widely used for aerospace and also medical applications, is not processed in hydrogen at all, and that is why batch vacuum heat treating is so popular in aerospace and medical because there is a lot of titanium use.
DG: My understanding is that hydrogen causes embrittlement when we're dealing with titanium.
DW: Exactly. It causes damage to titanium parts. Batch processing also enables you to do lot tracking and other things which are important in both aerospace and medical.
Aluminum is another commonly heat treated metal that doesn't require hydrogen. Aluminum is basically generally heat treated in pure nitrogen. But other metals that do use hydrogen containing atmosphere include copper and brass, as I mentioned, magnetic steels and stainless steels. Generally, the steels, other than carbon steel, will require an atmosphere in the 30–60% range of hydrogen in nitrogen while certain grades of stainless must be heat treated in 100% hydrogen. Often the 300 series of stainless, people prefer to use 100% hydrogen for that.
Doug Glenn, Heat Treat Today publisher and Heat Treat Radio host.
End of Part 1.
Part 2 is scheduled to be released on February 13th. Check back here for a link to that episode or go to www.heattreattoday.com/radio after February 13, 2020, and look for Part 2 in the list of Heat Treat Radioepisodes listed.
Nitrex, a global provider of fully integrated heat-treating solutions and technologies based in Montreal, Canada, acquired G-M Enterprises, a manufacturer of vacuum furnaces, headquartered in Corona, California.
Mrs. Veena Jhawar, G-M Enterprises COO; Mr. Jean-François Cloutier, Nitrex CEO; Mr. Suresh Jhawar, G-M Enterprises President
The addition of G-M Enterprises will further expand Nitrex’ integrated heat treatment solutions to customers; both share the same goal of providing technologies that focus on customer workflow and efficiency while maximizing the life span and quality of engineered parts and components.
Jean-Francois Cloutier, Nitrex CEO
“This acquisition will allow Nitrex to bolster its turnkey solutions business by bringing a new, innovative and broader mix of heat treatment systems to our customers,” said Jean-Francois Cloutier, Nitrex CEO. “We also look forward to welcoming the entire G-M Enterprises’ team into the Nitrex family.”
“Joining forces with Nitrex and becoming part of its family of companies will ensure we keep pace with our customers’ evolving needs and expectations,” says Suresh Jhawar, G-M Enterprises President. “What this means for the future of G-M Enterprises is an opportunity to enhance our products and services, expand our international presence further by leveraging the resources, expertise, and capital of Nitrex.”
A global technology group, an industrial gases company, an additive and design company, and an engineering university in Germany have entered into a research partnership with the end goal of supporting the aerospace and automotive industries through their research and development of aluminum based-alloys.
Oerlikon, a global technology group, entered into a research partnership with Linde, an industrial gases company, GE Additive, an additive and design company, and the Technical University of Munich (TUM), a leading German university in engineering, to conduct additive manufacturing (AM) research with the aim of developing new high-strength, lightweight aluminum-based alloys that can serve the safety and weight reduction needs of the aerospace and automotive industries.
Dr. Marcus Giglmaier, Project Manager for the AM Institute
This collaboration seeks to address the challenge of aluminum AM. “There are significant challenges during the AM of aluminum alloys because the temperatures reached in the melt pool create an extreme environment that leads to evaporation losses of alloying elements that have comparatively low boiling temperatures — such as magnesium,” said Dr. Marcus Giglmaier, project manager for the Additive Manufacturing Institute and research funding manager. “Additionally, the cooling rates of more than 1 million °C per second, create high stresses during the solidification process, which can cause micro cracks in the solid material.”
The project draws on the strengths of each of its members. Oerlikon’s experience in powder and material science will contribute to the development of the novel material; Linde’s technology and expertise in gas atmosphere control and evaporation suppression during the AM process – including the processing of aluminum-based alloys – overcomes impurities within the print chamber, which will help manufacturers achieve optimal 3D-printing conditions; GE Additive will assist in the collaboration; and, for its part, the Institute of Aerodynamics and Fluid Mechanics (AER) at TUM will be able to provide a detailed understanding of the physical phenomena taking place during the AM process using numerical simulations.
From left to right: Dr Sven Hicken (Business Unit Head, Oerlikon AM), Prof Thomas Hofmann (President, TUM), Jason Oliver (President and CEO, GE Additive), Dr Wolfgang Dierker (CEO, GE Germany), Dr Christoph Laumen (Executive Director R&D, Linde AG), Prof Michael Suess (Chairman of the Board of Directors, Oerlikon Group), Dr Christian Haecker (Head of Industrialisation, Oerlikon AM), Dr Andreas Lessmann (Managing Director, GE Additive Germany GmbH, Senior Leader, Legal Operations), Dr Christian Bruch (Executive Vice President & CEO, Linde Engineering), Andreas Rohregger (Head of Global Properties, GE Additive), Dr Alice Beck (Deputy Director, TUM ForTe) (Courtesy Oerlikon)
A global materials engineering group explored alternative methods of applying a hard surfacing alloy at the ITSC conference in Japan.
Engineers from Wall Colmonoy Corp. discussed in a conference presentation how the properties of a hard surfacing alloy change when applied by different methods. Alloy Ni-15Cr-15W-3B-4Si-3.5Fe-0.6C is a hard surfacing alloy designed to extend the life of OEM parts that are subjected to various wear mechanisms in service. The alloy can also be used to repair/rebuild those worn parts and extend service life.
This hard-surfacing alloy can be applied by various methods, including thermal spray processes, laser cladding, PTA welding, GTAW, OFW, and GMAW. This study compared the properties of the alloy applied by different methods using various test procedures, and also included the cost/benefit ratio of each.
Test procedures included abrasion testing by ASTM G-65; erosion testing by ASTM G-76; Vickers hardness by ASTM E-92; and Rockwell hardness by ASTM E18. In addition, metallographic examples of the test specimens were prepared.
A steel producer based in Fort Wayne, Indiana, recently announced the expansion of their rolling mill, which will include a 3-MW induction furnace to heat the stock coming from the existing mill.
Steel Dynamics USA announced the expansion at their Columbia City, Indiana, location. Among other equipment being added are a 70-m conveyor connecting the existing medium section mill to the new spooler line, six housingless SHS 180 roller stands, complete with quick stand-changing table, a 6-pass Delta-type finishing block driven by a low-voltage- 2.5-MW motor and finishing services.
SDI and Danieli teams studied a temporary removable solution, steel support structure to support the existing furnace-exit roller table, allowing the execution of the Billet Welder concrete foundation with only minor impact to the MSM (Medium Section Mill) production schedule.
A western Pennsylvania heat treat provider recently completed construction of a new brazing and assembly room, built primarily to accommodate a large aluminum brazing project for a specific customer.
Bob Hill, president of Solar Atmospheres of Western PA
Solar Atmospheres of Western PA, based in Hermitage, Pennsylvania, stated that the room will also be used for other brazing and assembly work.
“During successful development and prototype runs, our customer, along with Solar management, understood that in order to bring this critical aluminum brazing project to full production a separate braze/assembly room would be needed,” said Bob Hill, president of Solar Atmospheres of Western PA. “We worked together with our customer to develop the best space that is in close proximity to the vacuum furnace being utilized.”
Main photo credit/caption: Solar Atmospheres / The inspection of critical braze joints being analyzed within Solar’s newly constructed Braze-Assembly room.
This article continues the ongoing discussion on Equipment Selection for Induction Hardening by Dr. Valery Rudnev, FASM, IFHTSE Fellow. Six previous installments in Dr. Rudnev’s series on equipment selection addressed selected aspects of scan hardening and continuous/progressive hardening systems. This post is the third in a discussion on equipment selection for one of four popular induction hardening techniques focusing on single-shot hardening systems.
Previous articles in the series on equipment selection for single-shot hardening are here (part 1) and here (part 2). To see the earlier articles in the Induction Hardening series at Heat TreatToday as well as other news about Dr. Rudnev, click here.
Single-Shot Inductors for Non-Cylinder Parts
Single-shot inductors can be successfully used for hardening not only components of classical cylinder geometries but other geometries as well. This includes workpieces of general conical shapes, such as elliptic, parabolic, hyperbolic geometries—and the list can grow. As an example, Figure 1 shows induction surface-hardened ball joints (ball studs) and the single-shot inductors used to harden them. Ball studs are used in automotive, off-road, and agricultural machinery and can be different in shape and size (Compare images on the left in Figure 1 with images on the right.), requiring noticeably different hardness patterns.
Figure 1. Surface-hardened ball joints (ball studs) and single-shot inductors used for its hardening. (Courtesy of Inductoheat Inc., an Inductotherm Group company.)
In any attempt to scan harden workpieces with appreciable diameter changes, the scan coil must have a sufficient gap to clear the largest diameter. When scanning the section(s) of the workpiece with smaller diameters, an inductor-to-shaft air gap might be very large, resulting in low electrical efficiency and potentially exhibiting difficulties in load matching as well as in controlling the austenitizing pattern along the length of the part producing "cold" and "hot" spots. Additional difficulties may appear in controlling the hardness pattern in regions (e.g., near geometrical irregularities) where good control is most needed.
Thus, the substantially different workpiece-to-inductor electromagnetic coupling variations might not permit using classical multiturn solenoid coils or scan inductors. In contrast, single-shot inductors allow not only better electromagnetic coupling along the entire length of heat treated components (Figure 2) but also better address the geometrical irregularities of heat treated workpieces, producing the required hardness patterns at minimum process times with superior metallurgical quality.
Figure 2. Single-shot inductors allow better electromagnetic coupling along the length of heat treated components properly addressing the geometrical complexity of the workpiece. (Courtesy of Inductoheat Inc., an Inductotherm Group company.)
As stated in Part 1 of this series, in contrast to scan hardening, a single-shot inductor can be contoured along the length of the part properly addressing the geometrical complexity of the workpiece. Furthermore, the use of flux concentrators helps drive the current into the desired areas and allows producing a well-defined hardness profile with minimum distortion. The trade-off here is that more finesse is required in the design stage to produce the properly profiled single-shot inductor at the lowest possible cost.¹ Errors are costly since these inductors are each custom made for a given part or application and modifications can be quite costly. Thus, computer modeling is a helpful assistant as an attempt to keep the development cost down and shorten the "learning curve".
Proper hardening of such components as output shafts, flanged shafts, planet carriers, yoke shafts, sun shafts, intermediate shafts, driveshafts, turbine shafts, and some others may require extensive copper profiling, making a single-shot hardening inductor a complex electromagnetic device.
Certain geometrical features such as flanges, diameter changes, bearing shoulders, grooves, undercuts, splines, etc., may distort the magnetic field generated by an inductor, which, in turn, can cause temperature deviations, making it challenging to achieve certain hardness patterns.
For components containing fillets, it is often necessary to increase the heat intensity in the fillet region owing to the geometrical specifics. Also, the larger mass of metal in the proximity of the heated fillet and behind the region to be hardened produces a substantial thermal “cold sink” effect.¹ This draws heat from the fillet due to thermal conduction, which must be compensated for by generating additional heating energy in the fillet area.
Needed energy surplus can be achieved by narrowing the current-carrying face of the crossover segment of the single-shot inductor (Figure 3). Here is a simplified illustration of an impact of a copper profiling of the inductor’s heating face: if the current-carrying portion of the inductor heating face is reduced by 50 percent, there is a corresponding increase in current density. This will be accompanied by an increase of the eddy current density induced within the respective region. According to the Joule effect, doubling the induced eddy current density increases the induced power density roughly by a factor of four. Also, attaching a magnetic flux concentrator to certain areas of the hardening inductor further enhances the localized heat intensity.
Figure 3. Longitudinal leg sections of single-shot indicators and their crossover segments can be profiled by relieving selected regions of the copper to accommodate workpiece geometrical features. Attaching a magnetic flux concentrator to certain areas of the inductor further enhances localized heat intensity. (From V. Rudnev, A. Goodwin, S. Fillip, W. West, J. Schwab, S. St. Pierre, Keys to long-lasting hardening inductors: Experience, materials, and precision, Adv. Mater. Processes, October 2015, pp. 48–52.)
When using a single-shot inductor, it is particularly important that the workpiece is properly located in the heating position because seemingly minor dislocations may noticeably affect the heat treat pattern and metallurgical quality of hardened parts.
Traditionally designed single-shot inductors may exhibit high process sensitivity that is associated with the electromagnetic proximity effect.¹ A change in positioning of the workpiece inside the single-shot inductor attributed to excessive bearing wear of the centers, improper machining of the centers and fixtures, incorrect part loading, and other factors may produce a correspondent appreciable variation in the hardness pattern (particularly within the fillet region, undercut areas, and the part’s end zone). A reduced hardness case depth and the formation of unwanted microstructural products associated with incomplete phase transformation may be the result of that. Magnitude and distribution of transient and residual stresses might also be altered. Thus, attention should be paid to part’s reliable positioning during heating and quenching cycles.
As can be concluded, there are good reasons for using single-shot hardening, scan hardening, or continuous/progressing hardening approaches in induction hardening applications. The decision must be well thought out based on many factors such as geometry specifics, product quality, production rate, design proficiency, limitations of available equipment, reliability requirements, cost considerations, and some other factors.
The next installment of this series, “Dr. Valery Rudnev on . . . ”, will continue the discussion on design features of induction single-shot hardening systems.
