ATMOSPHERE AIR FURNACES TECHNICAL CONTENT

Heat Treat Radio #102: Lunch & Learn, Batch IQ vs. Continuous Pusher, Part 1 – Heat Treat Today

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Batch or continuous — which equipment is better for your operations? Today’s Heat Treat Radio episode is a lunch & learn to answer your burning question about batch IQ vs. continuous pusher furnace systems. Michael Mouilleseaux of Erie Steel is a boots-on-the-ground expert in North American heat treat, and he’ll share a bit about the history of these systems before getting into the equipment and heat treat processing differences.

Doug Glenn, Heat Treat Today's publisher and the Heat Treat Radio host, Karen Gantzer, associate publisher/editor-in-chief, and Bethany Leone join this Heat Treat Today lunch & learn.

Below, you can watch the video, listen to the podcast by clicking on the audio play button, or read an edited transcript.

 


 

HTT · Heat Treat Radio #102: Lunch & Learn, Batch IQ vs. Continuous Pusher Systems Part 1

The following transcript has been edited for your reading enjoyment.

The History of Batch and Pusher Furnaces (00:52)

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DOUG GLENN: Can you talk with us a little bit about the whole history of batch furnace versus pusher furnace?

MICHAEL MOUILLESEAUX:  Sure. And thank you for having me!

Interestingly enough, the pusher furnace — which we might say is a more complex piece of equipment than a batch integral quench furnace — preceded the batch furnace. Atmosphere pushers were around prior to World War II. I spoke with a number of folks in the industry and asked, “How could that possibly be, given the level of complexity?” Interestingly, pushers were available because the atmosphere was generated by a charcoal generator.

If you think back to pack carburizing, we used charcoal and some accelerator. You would put it in a closed container, you’d heat it up, and that’s how you carburized things before you had atmosphere furnaces. Utilizing that same concept, they generated an atmosphere, put it in a furnace, and pushers were the first ones to do that.

So, who were the folks who did that? They were AFC-Holcroft,  Surface Combustion, and Ipsen, all the usual characters and suspects there.

Pusher furnaces were available in single row and multiple row configurations.

They were heated with gas or electricity. I have to think that the earlier ones were heated by gas. Typically, they employed oil quenching. Although atmosphere cooling could be in the works, to find something of that vintage is very difficult. Maybe someone listening to this will weigh in and say, “Well, let me help you with that.”

The batch integral quench furnace is post World War II. What precipitated the development of the batch integral quench furnace was the development of the atmosphere generator, and that’s thanks to and around 1941 he actually published a book on atmosphere generators. I’m not sure where to find documentation of the patent he was granted for this generator. It might be interesting to discover. But again, Lindberg, Surface, Ipsen, — all these folks had these furnaces in the late 40s/early 50s.

When they started out, these furnaces were relatively small. The furnace might have had a tray that was 12 inches x 12 inches x 8 inches tall. You’d struggle to fit a hundred pounds into something like that.

But the batch furnace is by far the most popular atmosphere furnace that is available. You’ve got a variety of processing capabilities, which makes very flexible. There are a wide variety of sizes, even today; it can be heated with electricity or gas (we’ll talk about that a little bit later). You can have an oil quench furnace, you can use a polymer quench, and you can have a furnace where you atmosphere-cooled the load after it was processed in the primary furnace.

During this discussion, I’m going to use “batch,” “batch IQ,” and “batch integral quench” semi-interchangeably. So, if I say “batch” and I forget the “IQ” or if I say “batch integral quench” — these are all the same pieces of equipment. We have numerous names for the same thing.

DOUG GLENN:  Gotcha. You said the continuous furnace came first because the atmosphere was being created by burning charcoal inside the furnace, that created a carbon rich environment?

MICHAEL MOUILLESEAUX:  Actually, it was a generator that was pumped into the furnace.

DOUG GLENN:  Got it. That was confusing; I was wondering how they were burning charcoal inside a furnace.

MICHAEL MOUILLESEAUX:  Actually, it was explained to me that because the pusher furnace was so much larger, when you would open the doors to place or extract a load, the relative pressure drop of opening a door wasn’t that great. So, these primitive charcoal generators could accommodate that.

But in a batch furnace, arguably, the door is one wall of the furnace, and you couldn’t create a sufficient amount of pressure in the furnace. So, it had to wait until we had endothermic generators so that we could establish a furnace pressure higher than atmospheric pressure to make batch furnaces. It’s fascinating.

Basics of the Batch Furnace (05:41)

DOUG GLENN:  And as you said, it is probably the most popular furnace used today by many, many heat treaters. Let’s talk about batch furnaces, here we go.

MICHAEL MOUILLESEAUX:  Let’s look at the CAD drawing for a batch furnace. The batch furnace is primarily two components. You can see the hot zone — that is the furnace proper. It’s highly insulated, it has radiant tubes in it (so we can put atmosphere in the furnace), and the heating portion does not affect the atmosphere.

It is loaded through a vestibule, and the vestibule is pressurized as well. A load can go into a vestibule, you can close the door, you open the inner door, the load goes into the furnace, you can process it and then, as you can see, you can either quench the load or you can top cool the load.

CAD drawing of a batch furnace.

Common Processes in a Batch Furnace (06:31)

What kind of things can we do in an atmosphere furnace? Answer: operations that do not require quenching. We could stress relieve, we could subcritically anneal, we could supercritically anneal (so, above and below 1350/1400 Fahrenheit), and then we can normalize.

Normalizing is utilized for products like forgings or castings which are made at a very high temperature. You’ve got a number of structures in the component and what you want is a “normal” structure. You want a uniform structure throughout the part so that it can be machined.

Normalizing is typically performed at a high temperature, and it’s put into this top cooled/atmosphere cooled chamber. In the old days, that was termed “air cooling” — it was a rate equivalent if you just set it out in air. These top cooled chambers are somewhat insulated; they have cooling jackets that are in the side, and there is a fan in them so you can circulate the atmosphere through it so that you get uniform cooling throughout the load.

DOUG GLENN:  Michael, this isn’t considered high pressure gas quenching though, right?

MICHAEL MOUILLESEAUX:  Not even close.

In this animation, we have the load going into the furnace, the vestibule door closes, the furnace door opens, the furnace door closes, we perform whatever process we want, we extract the load out of the furnace, and it goes up into the top cool chamber. It’s then atmosphere cooled. When that is completed, we take the load out.

The time in the furnace could be four hours (plus or minus). The time up in the top cool chamber would probably be an hour or two. Once the load is extracted from the furnace and is put into the top cool chamber, and you reestablish pressure in the vestibule, you actually open the outer door, put another load in and start processing the next load while the initial load is being cooled.

Then, there are processes that require quenching. In degree of simplicity, first there is neutral hardening. Neutral hardening implies that the atmosphere in the furnace is neutral with the carbon content of the steel. So, for a 30-carbon steel, you’d want a 30-carbon atmosphere; for a 40-carbon steel, you’d want a 40-carbon atmosphere. The optimum is to neither enrich nor to deplete the surface carbon; you don’t want to change the chemistry. Typically, neutral-hardened parts are subsequently oil-quenched.

Then, there is carbonitriding. In carbonitriding, you have a high carbon atmosphere. You also introduce ammonia into the furnace. The ammonia dissociates right in the furnace. The carbon and nitrogen diffuse into the surface of the component. is held at a sufficient temperature to attain the case step that is desired, then, again, it is extracted into the vestibule, and it is quenched.

Carburizing would be another process. It’s similar to carbonitriding, except there is no ammonia. It’s only carbon that’s diffused into the surface of the part. Typically, parts that are carburized are oil-quenched.

There are, however, strategies and components where you would carburize, and then you would take the part and you would top cool it. You might take the part out of the furnace, and you may reorient it. So, parts that are distortion-critical may be oriented in one direction for carburizing, and then reoriented for hardening. You may carburize twice as many parts as you harden, so the hardening load would be half the size.

A low temperature process which is more complex is ferritic nitrocarburizing. That, typically, is performed around 1000°F. It is performed in batch furnaces, as well. Typical process cycles for that are going to be, at temperature, an hour and a half/two hours. That process can either be atmosphere cooled or it can be quenched; it depends on whether you’re looking for solid solution hardening or if you’re just looking for the nitrided layer and you’re not trying to do anything to the substrate.

I think that we have an animation for this.

Diagram of a batch system load.

Again, the load is loaded in the vestibule, the vestibule pressure is reestablished, the load is put into the furnace and, at that point, we perform whatever operation it is that we want to do of those previously described operations.

In the animation, you can see that the load is immersed in the quench. Following the quenching operation, it’s withdrawn from the furnace.

The total time for quenching is 10 minutes. When the load is brought up out of the oil, typically you let it sit there and allow it to drip so the precious quench oil you’ve paid your money for can go back into the quench. You’re washing and removing as little quenchant as is possible. In the heat treating operation, quenching is the single most critical portion of the operation.

A Note on Quenching (12:32)

MICHAEL MOUILLESEAUX:  When we’re carburizing, we have a portion of an hour where there would be no significant change in the case depth of the part. When we temper the parts, we have hours. You could temper it for three hours, you could temper it for five hours, and you’re not going to have a material change in what’s performed. In the quenching operation, the latitude that you have in quenching is in seconds.

Our typical protocol is that when a load is extracted from the furnace, from the time that the furnace door opens into the vestibule to when the load bottoms out at the bottom of the quench, in a batch furnace, must be 40 seconds maximum.

DOUG GLENN:  40?

MICHAEL MOUILLESEAUX:  40 seconds maximum. Typically, it’s done in 20 or 25 seconds. But it’s 40 seconds maximum. In a pusher, that number is 30 seconds maximum. This is something that you track; it’s data logged. If it exceeds that, at that point, you’re going to have to perform some inspection on that load that is much higher and much more intense had it not taken that much longer.

DOUG GLENN:  Can you, very briefly, explain why is it so important? I’m assuming it has something to do with martensite start and martensite finish and all that good stuff, but is there a layman’s way of explaining why the time to quench is so important?

MICHAEL MOUILLESEAUX:  Essentially, you want to have the load at a uniform temperature when it goes into the quenchant. If we have a significant variation in the low temperature, from the top to the bottom or the front to the back — even if the quenching operation is completely uniform — we’re going to have a variation in properties, variation in hardness, and certainly the probability of variation in core hardness.

For those things that are distortion-critical, it is absolutely important that the load has a similar temperature, across the load, top to bottom, inside to out, when it’s quenched.

Batch Furnace Systems (15:00)

MICHAEL MOUILLESEAUX: You typically don’t have a singular furnace, you have a system. What’s involved in a system?

What we’re looking at here is a relatively simple system. You have a loading operation. Obviously, the parts need to be loaded in baskets or fixtures. In some way, the load needs to be built. Typically, there is a station for that.

Diagram of a batch system furnace line.

Following  loading, it’s put into a preheat furnace. A preheat furnace is identical to what we would call a “temper” or a “draw.” You can thermally clean the parts by heating them up to 800°F. The other thing is that those that you put into that part are 20% the cost of getting those BTUs when you’re putting it in the high heat furnace, so it just makes economic sense. You’re cleaning the parts and you’re preheating the parts.

Then you’re going to put it into the furnace to perform the furnace operation; it’s either going to be top cooled or quenched. If it’s top cooled, you’re going to stop that top cooling operation at 300°F or 400°F. You’re going to put it in a cooling station and allow it to cool to room temperature. If you quench the part, if you’re modified marquenching it, it’s 250°F plus; if it’s quenched in regular oil, it could be 150–180°F.

The next operation is to wash the part. Typically, you don’t want to wash hot parts; you want to allow them to cool to room temperature. Sometimes you do, but more often than not, no.

Then there’s the wash station; you’re washing the parts. Then, you’re taking them out of the washing station and allowing them to drip. Then, you’re going to put them into a temper and you’re going to temper it for three to seven or eight hours, or something of that nature. You extract the load from the tempering furnace, put it in a cooling station, and allow it to cool down to room temperature so you can then unload it.

As you can see, the way that is accomplished is with this transfer cart. The transfer cart extracts the load from the loading table, pushes it into the preheat furnace, pulls it out of the preheat furnace, and pushes it into the batch furnace. Then the batch furnace quenches it, but when the outer vestibule door is opened, the transfer car must go in and get the load and pull it back onto the transfer car. The car pushes it across the aisle into the cooling station, picks it up, puts it in the wash, takes it out of the wash, puts it into the temper, takes it across the aisle when the tempering is finished, extracts it from the temper, and puts in on the cooling station. That transfer cart is an important piece of equipment.

But you can see there are a lot of moving parts to this. And you might ask, “Why would you do this?” Well again, because of the flexibility of the batch furnace. In this example, batch furnace #1 can be performing neutral hardening; batch furnace #2, at the same time, can be carbonitriding; the neutral hardening load finishes and the next load that goes in there could be annealed; after the load is annealed, then you could take a load and it could be normalized; then you could go back and you could neutral harden again.

So, if you don’t have multiple loads of the same thing, this offers a degree of flexibility that almost is not available in any other type of atmosphere processing equipment.

DOUG GLENN:  Right. And the fact that you have more than one furnace, more than one high heat furnace, more than one temper furnace, gives you almost (not exactly, but closer to) a continuous process even though each furnace is a “batch,” if you will.

MICHAEL MOUILLESEAUX:  Correct.

There are charge cars that are automated, so the charge car knows where the loading station is — it goes to that loading station. You could either have a human unload it or, in the highest degree of automation, it gets there and you have a PLC that is overseeing or supervising this entire operation, and it would know to take that load onto the cart, where to take it next, and what to do. It becomes a semi-automated method of heat treating.

Properties of the Pusher Furnace (19:53)

DOUG GLENN:  Let’s move on to the pusher furnace, the continuous system.

MICHAEL MOUILLESEAUX:  The pusher furnace, as you can see in this description, contains the vestibule, the furnace, and the quench. We’ve just broken it down into the pusher furnace proper.

Diagram of a pusher furnace.

Loads are put into the vestibule and then, sequentially, they move their way through the furnace. The first zone of the furnace would be what we would call the “preheat” and that’s where we bring the part up to temperature.

In this example, we’re showing boost-diffuse. This is an example where we would be carburizing. The first couple of positions would be a boost. We carburize at a higher carbon content because it diffuses more rapidly at the initial point of carburizing. Then, at the tail end of the carburizing cycle, we reduce the carbon content to what our desired surface carbon content would be.

An example might be: We would start out and we’d boost at 1% or 1, and the diffuse cycle would be .8% carbon. You do that for a couple of reasons:  You want to mitigate any retained austenite, so the bar is quenched at a higher carbon. You have opportunity for development of an unacceptable amount of retained austenite. At the extreme, you could start developing carbides and those become very difficult to re-solution. That’s the rationale for having a boost-diffuse. You do that same thing in a batch furnace; I just didn’t describe that as such.

And then the drop zone. We want to reduce the temperature prior to quenching so that we have very uniform quenching properties and if the components that we’re heat treating are distortion-critical, it’s very important as to what the temperature is prior to quenching.

So, we carburize at a high temperature (1700 Fahrenheit/1750 Fahrenheit), because the diffusion rate is much higher at that temperature. But we only want to quench these parts at 1500 or 1550 Fahrenheit because we want to have an absolute minimum amount of distortion.

Every hour, the vestibule door to the quench is going to open and you would cross-push that load into the quench vestibule, you would close the door, and just as the animation described in the batch furnace, that load would drop on an elevator into the quench.

Now that we’ve done that, we have an opening. That last position is open. So, we go to the vestibule on the front end of the furnace, we open that door, we put a load in there, we close the door, and we’ll close it long enough for us to reestablish the furnace pressure (no more than 3–5 minutes). Once we’ve established furnace pressure, we can open the door between the vestibule and the first preheat zone, and then to the left of the vestibule is going to be a mechanism for pushing these loads, hence the term “pusher”? Could it be hydraulic? It could. Could be mechanical? Both are employed.

What you’re doing is pushing it further by one position. Because the last position is open, the second to the last load progresses into the last position, the load that you put in the vestibule goes into the first position.

DOUG GLENN:  A couple quick questions: Really, the sequence starts with the load being pushed out of the furnace into the quench vestibule and then dropped in. That leaves that last spot open in the furnace. Then everything else starts and we push it all down, correct?

MICHAEL MOUILLESEAUX:  You are correct.

DOUG GLENN: In this illustration, it looks like there are divisions between each of these different locations. In the preheat, it looks like there are three or four; in the boost-diffuse, it looks like you’ve got two or three. Those aren’t actually physical barriers; You’re just showing where the load would progress to, correct?

MICHAEL MOUILLESEAUX:  You are correct.

DOUG GLENN:  Are there any chamber divisions in a pusher furnace?

MICHAEL MOUILLESEAUX:  In a pusher furnace, you have arches above the load and that helps to compartmentalize. The key word there is “helps.” You don’t have an actual compartmentalization.

Let’s say that we want to perform a carburize at 1700°F in this furnace. If you had three preheats, you may want to perform these somewhere below the 1700°F with the last position being at 1700°F so that the load that goes into the carburizing zone is at temperature and it’s ready to accept carbon.

The carburizing zone would all be at the same temperature, but you have to understand these parts are all at 1700°F and we want to quench it at 1550°F, let’s say. We have two positions that we are going to allow the load to cool down to 1550°F.

So, would you want a zone arch there? I think that you would, yes. Would you want a fan in those zones? If you had a fan in those zones, and you are circulating the atmosphere through those loads, you have a better opportunity to attain a uniform temperature from the top to the bottom of the load than if you did not.

Diagram of a pusher furnace system.

MICHAEL MOUILLESEAUX:  Here’s a pusher furnace system. Typically, but not always, pushers are put into a system because you have multiple operations that you must perform. This example is in a U-shape. The loading and unloading are next to each other. This could be a linear layout.

In another life, I worked for a company in Syracuse, New York that had 14 furnaces that were all linearly oriented. So, the person on the front of the furnace did one thing, the person on the back of the furnace did another thing, and they really didn’t communicate.

I, personally, am not a fan of that. I like this operation because you can have one or two people performing the loading and unloading operation, and you could have a furnace operator who would be responsible for the overall control of this piece of equipment.

You can see that we have four loads here that are in whatever way we chose to fixture them — baskets, fixtures, or whatever it might be. We’ve put a couple of parts in a preheat so we could perform that same cleaning that we talked about in preheating the load with low-cost BTUs. The preheat then goes into the vestibule, the loads progress down through the furnace as we described, you get to the end and that load is quenched. When the load comes out of the quench, just as in the batch furnace, it’s going to be 150–200°F plus. We want that to cool down to room temperature because the next operation is going to be washing.

After the load to cools down to room temperature, we then put it in the wash. Following the wash operation, you might have a drip station. So, whatever it was that you have washed off in the water, you don’t want that to go into the temper. Following the drip station, then you would go into the tempering furnace. Here we’re showing three positions; it could be three, it could be six, it could be nine. This is just an example.

Following the tempering operation, we would go out and in that first position, you might have a blower underneath and you would be circulating, room temperature air through it up into a duct work ahead and that’s how you would cool the room down to low temperature. Those loads would progress down that unload station so, at the very end, you are unloading the parts, perhaps for a subsequent shop blast cleaning operation or development of rust preventative or maybe they’re just put back into the customer’s container.

In a captive operation, they might go into a container where the parts would go on to a subsequent grinding or hard-turning operation.

This can be automated. Here you can see that the loads progress into the preheat, they progress through the furnace, they go into the quench, and they’re put into the wash. It’s quick.

Diagram of a pusher furnace load.

DOUG GLENN:  Yes. It doesn’t happen this fast in real life, everyone!

MICHAEL MOUILLESEAUX:  In the temper, the load exits the temper and goes into the unloading station. The point of this is to show that it progresses through the furnace.

The advantage is that you have relatively small loads that you’re processing, there is a very consistent process in the pusher furnace, and what you’re on for is that however you’ve designed this system, every load goes through every station. You don’t have an opportunity to easily extract a load as quenched and not wash it. It can be done. You could have a furnace designed to do that, but it’s not easy. After it’s washed, as you can see in this animation, typically it’s going to progress into the temper. Could you design a station that would allow you to offload it? You could, but normally that’s not how that’s done.

So, the load progresses through the temper and then you go in to where it is then subsequently unloaded.

If the batch furnace’s strong suit is the fact that it is extremely flexible — particularly in a “systemic” way — the pusher furnace’s strength is its productivity. °

DOUG GLENN:  Yes, higher levels of productivity. But you’ve got to have, if not the same product, at least the same process on whatever it is you’re putting in there.

MICHAEL MOUILLESEAUX:  Bingo. That’s exactly what you must have there, yes.

About the expert: Michael Mouilleseaux is general manager at Erie Steel LTD. Mike has been at Erie Steel in Toledo, OH since 2006 with previous metallurgical experience at New Process Gear in Syracuse, NY and as the Director of Technology in Marketing at FPM Heat Treating LLC in Elk Grove, IL. Having graduated from the University of Michigan with a degree in Metallurgical Engineering, Mike has proved his expertise in the field of heat treat, co-presenting at the 2019 Heat Treat show and currently serving on the Board of Trustees at the Metal Treating Institute.

Contact: mmouilleseaux@erie.com

To find other Heat Treat Radio episodes, go to www.heattreattoday.com/radio.

Search heat treat equipment and service providers on Heat Treat Buyers Guide.com  

Heat Treat Radio #102: Lunch & Learn, Batch IQ vs. Continuous Pusher, Part 1 – Heat Treat Today Read More »

Sustainability Insights: Reducing the Carbon Footprint of Your Heat Treating Operations

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Renewable fuels or hydrogen have entered the scene as these are fuels that contain little or no carbon. So, no carbon in the fuel means no CO2! These fuels present an excellent opportunity to significantly reduce carbon.

This Sustainability Insight article was composed by Brian Kelly, manager of Application Engineering at Honeywell Smart Energy and Thermal Solutions (SETS) and president of the Industrial Heating Equipment Association. It can be found in Heat Treat Today's August 2023 Automotive Heat Treating print edition.

The need to understand the impact of greenhouse gases (GHGs), especially carbon-based emissions, on climate change is gaining much more interest recently from organizations that have industrial heating processes. Most industrial heating processes are fueled by carbon-based fossil fuels such as natural gas, propane, fuel oil, diesel, or coal. In basic terms, if you have combustion processes in your organization, you are emitting carbon (CO2). Impacts on climate change due to these carbon emissions have prompted government and corporate actions to reduce carbon. These actions are creating unique new opportunities for more sustainable and lower carbon process heating methods. In this article, we will focus on ways to reduce carbon in typical fossil fuel fired heat treat thermal processes. First step: Figure out where you are today. Do you know?

Assess Your Carbon Footprint

Brian Kelly
Image Source: Honeywell

More and more companies are interested in understanding their GHG/carbon footprints, so they can determine what processes are their biggest CO2 offenders, and on what assets to focus on in order to have the largest impact on reducing carbon. Whether your thermal processes are being heated by fossil fuels (typically natural gas) or electrically, each will have a carbon footprint. Fuel gases are being burned to provide the heat and they produce CO2 as a result. Most electrical power is currently being produced by fossil fuels, so electricity will have a CO2 amount associated per kW. What can be done to burn less fuel in your furnaces or ovens, which directly relates to reducing CO2?

Tune Your Combustion Systems

Radiant tube burner with plug recuperator in a U-tube
Source: Honeywell

Over time combustion systems drift and are not at their optimum air/fuel ratio. By simply tuning your burner system on a routine basis, you can fire at the optimum air/fuel ratio for the process and be as efficient as possible. For example, if a furnace is firing on natural gas, operating at 1800°F, and currently operating at 35% excess air, tuning your burners to 10% excess air could save approximately 15% in fuel consumed. The fuel costs will be reduced, and the resulting CO2 will be reduced by that same percentage!

Maintain Your Furnaces/Ovens

A simple review of your furnaces or ovens to observe any hot spots, openings, faulty seals, or refractory issues will identify areas that will cause your systems to operate less efficiently, thus using more energy. Repairing these problems and consistently maintaining them will have the systems running more efficiently and producing as little carbon as possible.

Upgrade Your Firing Systems To Be More Efficient

Direct fired self-recuperative burner
Source: Honeywell

Incorporating preheated combustion air into furnace combustion systems can significantly reduce fuel consumption and therefore the resulting carbon. The two main methods for introducing hot air into a combustion system are recuperation and regeneration. The most popular air preheating method in heat treating applications is recuperation. For a direct fired furnace, this can take the form of a central stack recuperator or self-recuperative burners. Self-recuperative burners have grown in popularity in recent years as they get rid of the need for hot air piping, recuperator maintenance, and most are often pulse fired, which will not only maximize efficiency but also promote temperature uniformity in the furnace and often be lower in emissions. For indirect fired (radiant tube) furnaces, you can apply/add a plug recuperator to an existing cold air fired burner in a furnace that has a U or W-tube to preheat the combustion air or apply self- recuperative burners installed in Single-Ended Radiant (SER) tubes to optimize your furnace firing. The SER tube material can be upgraded to silicon carbide which allows higher temperatures/flux rates that can provide the opportunity to increase throughput and reduce the possible CO2 per cycle.

Combustion air preheating can result in energy savings of close to 25% over cold air combustion.

Renewable Fuels/Hydrogen

Renewable fuels or hydrogen have entered the scene as these are fuels that contain little or no carbon. So, no carbon in the fuel means no CO2! These fuels present an excellent opportunity to significantly reduce carbon. Hydrogen has been of interest because it has the opportunity to be a zero-carbon industrial fuel when produced with renewable energy such as wind, solar, hydro, or nuclear power. As these methods become more prevalent, they bring down the price of hydrogen and increase its availability. This could be a significant driver to greatly reduce CO2 in thermal processes. These topics as well as many others are being discussed in an on-going Sustainability Webinar series hosted by IHEA to provide education and insight into the ever-changing sustainability landscape.

Single ended self-recuperative radiant tube burner
Source: Honeywell

About the author:

Brian Kelly is manager of Application Engineering for Honeywell Smart Energy and Thermal Solutions (SETS) and current president of the Industrial Heating Equipment Association (IHEA).

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

Sustainability Insights: Reducing the Carbon Footprint of Your Heat Treating Operations Read More »

Heat Treat Radio #97: Lunch & Learn, Ovens vs. Atmosphere Furnaces

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Are you trying to figure out what heat treat equipment investments you need to make in-house and what is better being outsourced? This conversation marks the continuation of Lunch & Learn, a Heat Treat Radio podcast series where an expert in the industry breaks down a heat treat fundamental with Doug Glenn, publisher of Heat Treat Today and host of the podcast, and the Heat Treat Today team. This conversation with Dan Herring, The Heat Treat Doctor®, zeros in on heat treat ovens versus atmosphere furnaces.

Below, you can watch the video, listen to the podcast by clicking on the audio play button, or read an edited transcript.


The following transcript has been edited for your reading enjoyment.

Contact us with your Reader Feedback!

Doug Glenn: Welcome everybody. This is another Lunch & Learn event with the staff of Heat Treat Today and the illustrious Dan Herring, The Heat Treat Doctor®. Dan, we’re always very happy to spend some time with you.

We are here to learn a little bit about some basics about heat treat equipment, mostly ovens, air and atmosphere furnaces, and possibly vacuum furnaces.

Dan Herring: It’s always a pleasure, Doug, and hello everybody.

It is an exciting topic for me because I happen to love heat treat equipment. Let’s start with industrial ovens.

All About Ovens (01:42)

Years ago, industrial ovens were very easy to differentiate from furnaces. I’m going to give you my understanding of the differences between ovens and furnaces, and then talk a little bit about some general characteristics of all types of heat-treating equipment.

Ovens are typically designed for low-temperature operation. When I talk about low-temperature operation, years ago the definition was “under 1,000° F.” That definition has changed over the years. We now usually say either under 1250°F or under 1400°F. All of that being said, there are some ovens that run all the way up to 1750°F. But what we’re going to concentrate on are, what I call, “the classic temperature designations for ovens.”

Universal oven from Grieve
Source: Grieve

First of all, ovens are typically rated at 500°F, 750°F, 1000°F, or 1250°F. If you see a heat treat operation that’s running — certainly under 1450°F — but even under 1250°F, it may be being done in either an oven or a furnace.

Let’s talk about some of the distinguishing characteristics of ovens, so everyone gets a feel for it.

Ovens always have a circulating fan. If you see a piece of equipment without a circulating fan, it can’t be an oven. At these low temperatures, the heat transfer — in other words, how you heat a part — is done with hot air or circulating hot air. So, ovens always have fans.

In most cases — and years ago in all cases, but today in most cases — ovens are metal lined. If you were to open the door of an oven and look in, and you see a metal-lined chamber, that would typically be an oven.

The fan and the type of insulation or lining that’s used is very characteristic for distinguishing features of ovens.

Today, however, there are ovens that use fiber insulation and even some ovens that have refractory-insulated firebricks, refractory in them. The lines are a little bit blurred, but typically you can distinguish them by the fact that they have fans and are metal lined.

Ovens come in either “batch” or “continuous” styles. If the workload inside the unit, the piece of equipment, is not moving, we call that a batch style furnace. If the workload is somehow being transferred through the unit, we call that a continuous furnace. Ovens and furnaces can be both batch and continuous.

Ovens and furnaces can both be either electrically heated or gas fired.

One of the distinguishing characteristics of ovens is that if they are gas fired, they are, what we call, “indirectly heated.” This means your burner, your combustion burner, is firing into a closed-ended tube, a radiant tube, as we call it, so that the products of combustion do not “intermix.” They do not create an atmosphere that’s used inside the oven. In fact, the majority of ovens run with an air atmosphere – that’s another distinguishing feature.

However, there are ovens that can run inert gases. Those ovens typically have continuously welded shells. Again, that’s an exception rather than a rule, but there are ovens of that type.

There are also vacuum ovens out there. We actually have an oven chamber on which we can pull a vacuum. They are less common than their cousins, the air ovens, but they are out there in industry.

We have the method of heating and type of movement of the hearth or movement of the load that typically is consistent between ovens and furnaces.

What I’d like to do is just show everybody a couple of pictures of some very typical, what I’m going to call, “batch ovens.”

Doug Glenn: Because ovens are typically low temperature, you’re able to have metal on the inside, right? If it was higher temperature, you’d start experiencing warping. Is that the primary reason why you tend to see metal in an oven and not in a furnace?

Dan Herring: That’s correct, Doug.

"Metal lined oven"
Source: Dan Herring

The lining can be made of steel: it can be made of “aluminized’ steel,” it can be made of zinc-gripped steel (those are just coatings), it can be just steel, and they can be made of stainless steel (a 300 series stainless steel). That’s why you have the different temperature ratings and the different types of materials that this metal interior can be made from.

If you open the door of a metal-lined oven or an oven that had a metal lining, you would typically see what’s pictured here.

"Double door shelf oven"
Source: Dan Herring

Ovens can be very small or they can be very, very large. What you’re seeing on the screen is a “double door shelf” oven.

It is very similar to your ovens at home. You open the door, there are shelves, and you can put trays on the various shelves. These can be small, to the point where, sometimes, they can sit on a benchtop. Sometimes they can be very, very large and be floor-mounted, as this one is.

This is an example of a batch oven, something that you would load, and the load stays stationary within the oven. Then, when you’re ready, you unload it.

Ovens can come in slightly larger sizes.

"A larger horizontal oven . . . . a fan system sitting at back"
Source: Dan Herring

That’s a picture of a larger, horizontal oven. The door on this particular oven is closed shut, but you can see the fan system — that’s that yellow arrangement that’s sitting in back of this particular oven.

There is another style of oven.

"Walk in oven"
Source: Dan Herring

We call this a “walk-in” oven — very creative, because you can walk into it. I’ve seen batch ovens that are very, very small and very, very large — ones that will fit on a benchtop and ones that are a hundred feet long.

You can see the heat source on the right hand side. Remember, whether it’s electrically heated with sheathed elements or if it’s gas-fired with, typically, an atmospheric-type burner, again, you have circulating air past either the electric elements or circulating air past the tube into which the burner is firing. You’re relying on convection — or moving hot air — to transfer that heat energy to your load.

These are just some different styles of different types of ovens, so everyone can see them. I don’t want to take too long, but I’ll show you another picture of one.

"Industrial oven . . . . typical oven in typical heat treat shop"
Source: Dan Herring

This is an industrial oven. You can see the fan; it has a yellow safety cover on it. You can see the fan mounted on top, and this is a typical oven that you’d find at a typical heat treat shop.

Ovens have the characteristics that I pointed out. I’ll bring up one more picture which you might find interesting.

"Monorail conveyor oven . . . . with u-shaped radiant tubes"
Source: Dan Herring

Since there are a variety of oven shapes and sizes, this happens to be a monorail conveyer oven. What you’re looking at is the inside of the oven. You’ll notice that in the ceiling there are hooks. The loads are actually placed on the hooks and sent through or pulled through the oven. This happens to be a gas-fired unit, and you can see that it has U-shaped radiant tubes into which you’re firing.

This oven is fiber-lined and not metallic-lined. You’ll also notice that because you see different colors of the tubes, this particular shot was taken and you destroyed the uniformity of temperature within the oven. Usually, they’re very tight.

Ovens are typically in the ±10°F range for temperature uniformity, sometimes in the ±5°F range.

Those are basically some pictures of ovens, whether they be batch or continuous, for everyone to see and think about, from that standpoint.

Q&A on Ovens (16:58)

Bethany Leone: What is the reason for the increase in temperature range for what classifies an oven?

Dan Herring: The main reason is the materials of construction have gotten better, so we’re able to withstand higher temperatures. But going to some of these temperature ratings, one of the things that heat treaters look at is if I have a process that runs at 1,000°F or 970°F (let’s take an aluminum heat treat example where a process is running at 970°F), I could run that in an oven rated at 1,000°F but I’m right at the upper limit of my temperature.

It's much better to buy an oven rated at 1250°F and then run a process such as 970°F where I have a margin of safety of the construction of the oven, so the oven will last longer.

However, industrial ovens tend to last forever. I’m the only person on this call old enough to have seen some of these ovens retired. It’s not unusual that an oven lasts 40 or 50, or sometimes 60 years.

Ovens are used in the heat treating industry for processes such as tempering, stress relief, for aluminum solution heat treatment, aluminum aging operations, and to do some precipitation hardening operations that run in these temperature ranges. Ovens are also commonly found in plating houses where you’re doing a hydrogen bake-out operation after plating. You also do various curing of epoxies and rubbers and things of this nature in ovens.

There are a variety of applications. Ovens are used also for drying of components. Ovens are used for drying of workloads, these days, prior to putting in your heat treating furnace. Many times, our washers are inefficient when it comes to drying. You take a wet load out of a washer and put it into a low-temperature oven, maybe running between 300°F and 750°F. Consequently, you both dry the washing solution off the parts and you even preheat the load prior to putting it into the furnace.

Heat Treat Today team enjoying a Lunch & Learn session

Doug Glenn: One of the things I’ve always distinguished ovens by is the term “panel construction” opposed to “beam construction.”

If you can imagine a sheet of metal, some insulation, and another sheet of metal – that’s a panel. It’s got enough insulation in it because the temperatures are not excessively high, but you really only need those three layers. You take those panels, you put them in a square or whatever, put a lid on it, put a bottom on it, and you basically have an oven, right?

Where furnaces are not typically constructed that way; they are constructed more where you have a support structure on the outside and then a heavy metal plate and then you build insulation on the inside of that. It doesn’t even need to have metal on the inside — it can be brick or another type of insulation.

Many people claim — and I’m sure there are some very strong ovens — that the oven construction is not as hardy, not as rugged. That’s one other minor distinction, but the main distinction is ovens tend to be lower temperature.

Dan Herring: Yes, that’s very correct, Doug. In panel-type construction, there is typically mineral wool insulation in between the two panel sheets; and it’s rated for obviously very low temperature.

There are, what we call, “light duty” and “heavy duty” ovens. Heavy duty ovens have that plate and support structure — those I-beams or channels — supporting the external structure.

Doug Glenn: You reminded me of something, Dan: We talk about ratings – oven ratings, furnace ratings, and that type of stuff. That’s pretty important and we haven’t really discussed that much. But if a furnace is rated at a certain temperature, you do not want to take that furnace beyond that temperature because there are real safety issues here.

There was one picture that Dan showed where you could see the metal interior, and there was like a gasket, if you will, around the whole opening. That gasket is only rated to go up so high in temperature. If you go over that temperature, you’d end up deteriorating that gasket, if you will. It could cause a fire, it could cause a leak, it could cause all kinds of issues. And that’s only one example.

One other one he mentioned was fans. There is almost always a fan in an oven, and if you take the temperature of that oven over its rated temperature, all of sudden the bearings in that fan start . . . well, who knows what’s going to happen.

You always want to know the rating of your oven and furnace, and don’t push the rating.

Dan Herring: Yes, if you exceed temperature in an oven, typically the fan starts to make a lot of noise and you know you’re in trouble. You only do that once. But those are excellent points, Doug, absolutely.

So, the world of ovens -- although it’s they’re an integral part of heat treating -- are a “beast unto themselves,” as I like to say. Construction is a factor, and other things.

All About Atmosphere Furnaces (24:50)

Furnaces, interestingly enough, can be rated both to very, very low temperatures all the way up to very, very high temperatures. In other words, you can see industrial furnaces running at 250° or 300°F or 500°F or 1000°F, — at typical temperatures that you would associate with oven construction — but you can also see furnaces running at 1700°F, 1800°F, 2400, 2500, 3200°F. There are some very interesting furnaces out there.

But furnaces, although they can run in air — and there are a number of furnaces that do — they typically run some type of either inert or combustible atmosphere inside them. Furnaces typically have an atmosphere, and they do not always have a fan. The rule is the higher you go up in temperature, the more any moving part inside your furnace becomes a maintenance issue. Many times, furnaces do not have fans in them.

They can be electrically heated. They could also be gas-fired. In this particular case, they can either be direct-fired or the burners are actually firing into the chamber; and the products of combustion become your atmosphere. They could be indirect-fired — like we discussed with ovens — into a radiant tube as a source of heat or energy.

Furnaces typically have plate construction. It’s typically continuous welded, they have channels or I-beams surrounding the structure to make it rigid, insulation is put on the inside. Traditionally it’s been insulating firebrick, but in what I’ll call recent years (20 years or so) fiber insulations have come about, and they perform very, very well.

Fiber insulations reduce the overall weight. They have advantages and disadvantages. A refractory-lined unit can have a great thermal mass due to the storage of heat inside the insulation, so when you put a cold load into a brick-lined furnace, the heat from the lining will help heat the load up quickly.

You don’t have quite the same heat storage in a fiber insulation. At the same time, when you go to cool a furnace, a fiber-lined furnace will cool very quickly as opposed to a refractory furnace which cools a lot slower.

Again, furnaces can be batch style, they can be continuous style, they can be fairly small in size. The smallest ones that I’ve seen, typically, are about the size of a loaf of bread. Conversely, you have furnaces that are so large you can drive several vehicles or other things inside of them.

A 14-foot long car bottom furnace
Source: Solar Atmospheres of Western PA

As a result of that, what distinguishes them are typically their temperature rating and the fact that they use an atmosphere. Some of the atmospheres are: air, nitrogen, argon. I’ve seen them run endothermic gas and exothermic gas which are combustible atmospheres, or methanol or nitrogen-methanol which are also combustible atmospheres; they can run steam as an atmosphere. I’ve seen furnaces running sulfur dioxide or carbon monoxide or carbon dioxide as atmospheres. The type of atmosphere that is used in an industrial furnace can be quite varied.

We have several different furnace categories that typically are talked about: Batch style furnaces are configured as box furnaces. They are very similar in shape to the ovens that we looked at. Pit style furnaces are where you have a cylindrical furnace that actually is quite tall and fits down, usually, into a pit that’s dug in the factory floor.

You also have mechanized box furnaces. Those, typically, today, would be called integral quench furnaces or sometimes batch quench furnaces or “IQs.” There are belt style furnaces, gantry, tip-up, and car-bottom furnaces. There is a wide variety of batch style furnaces, all of which have the characteristic that once you put the load into the chamber, it sits there until it’s been processed and until it's time for you to remove it.

The exception is in an integral quench furnace. You push the load typically either directly into the heating chamber or into a quench vestibule and then into a heating chamber; you heat it in one chamber, you transfer it out, and you quench it into another chamber.

Those are some of the distinguishing features of batch style equipment. I’ve got a couple of pictures here that you might find interesting.

"A box furnace . . . . sometimes difficult by sight alone to tell an oven or box furnace"
Source: Dan Herring

Here is a “box furnace.” You might say, “Oh, my gosh, it looks like an oven!” I see a fan on top, and it’s a box style. From the outside, it’s hard to tell whether it’s an oven or a furnace.

When you look at this unit, you might see that it’s made of plate construction. It would be difficult to tell if this unit were a heavy-duty oven or furnace unless you, of course, opened the door and looked inside. You would typically see either fiber insulation or insulating firebrick in these types of units.

Sometimes, just by sight alone, it’s very difficult to tell if it’s an oven or a furnace. But there are other telltale signs.

"A box furnace with retort"
Source: Dan Herring

Now, this is a box furnace with a retort inside it. The workload is placed, in this case, into a metal container that’s physically moved on a dolly into the furnace itself. This is what we call a box furnace with a retort.

The process takes place inside the retort. You’ll notice that there’s a flow-meter panel there, of different gases, that are introduced directly into the retort. This style of furnace is very interesting because the furnace itself, outside the retort, is simply heated in air. It’s a relatively inexpensive construction. Also, when the time comes that the process is finished, usually you can remove the retort and introduce or put a second retort into the furnace while the first retort is cooling outside the furnace. It lends to increased production, from that standpoint.

But this is typically a box furnace; it looks like a big box. The shell does not have to be continuously welded because the process takes place inside the retort. You might be able to see, just past the dolly, there is a dark color and that is the blackish retort that’s actually being put in.

Doug Glenn: I think the reasoning of the retort is to protect the airtight atmosphere, right?

Dan Herring: That’s correct, Doug. The idea is the fact that it’s an effective use of your atmosphere.

The other thing you can do with a box furnace with a retort is you can pull a vacuum on the retort. As a result of this, you can actually have a “hot wall” vacuum furnace. That is what is defined as a hot wall vacuum.

The next type of atmosphere furnace we’re going to look at is pretty distinct or pretty unique: This is a pit style furnace.

"A pit style furnace . . . . there is probably 4X as much furnace below the floor"
Source: Dan Herring

What you’re seeing here is only that portion of the furnace that is above the floor. There is probably four times as much furnace below the floor as there is above. OSHA has certain requirements: there must be 42 inches above the floor not to have a railing or a security system around the pit furnace, because you don’t want to accidentally trip and fall into a furnace at 1800°F. We don’t want to say, “Doug was a great guy, but the last time I saw him . . .”

In this particular case, there is a fan which is mounted in the cover of this pit style furnace. Most pit furnaces are cylindrical in design; however, I have seen them rectangular in design. Some of them have a retort inside them; unlike the picture of the box furnace with the retort, the retort is typically not removable, in this case. Of course, there are exceptions. There are nitriding furnaces that have removable retorts.

I think this is a very distinctive design. If you walked into a heat treat shop, you’d say, “You know, that’s either a box furnace or an oven.” Or, if you looked at this style of furnace, you can clearly see it’s a pit furnace, or what we call a pit furnace.

Two other examples, one of which is just to give you an idea of what we call an “integral quench furnace.” I think this is a good example of one:

"An integral quench furnace, an in-out furnace"
Source: Dan Herring

They’re made by a number of manufacturers. The integral quench furnace is probably one of the more common furnaces you’re able to see. It has, in this case, an oil quench tank in front and a heating chamber behind.

This would be an “in-out” furnace; the workload goes in the front door and comes out the front door. But once the workload is loaded into an area over the quench tank (which we call the vestibule), an inner door will open. The load will transfer into the heating chamber in back. That inner door will close, the workload will be heated and either brought up to austenitizing temperature, carburized or carbonitrided, the inner door will then open, the load will be transferred onto an elevator and either lowered down into a quench tank (typically oil) or, if the unit is equipped with a top cool, the load is brought up into the top cool chamber to slowly cool.

These styles of furnaces do processes like hardening, carburizing, carbonitriding, annealing, and normalizing. You typically don’t do stress relief in them, but I’m sure people have. These furnaces have a wide variety of uses and are quite popular. Again, the style is very distinctive.

They typically run a combustible atmosphere, and you can see some of that atmosphere burning out at the front door area.

There are also, what we call, continuous furnaces or continuous atmosphere furnaces. They are furnaces where you have a workload and somehow the workload is moving through the furnace. A good example of that is a mesh belt conveyor furnace.

There are also what we call incline conveyor, or humpback-style furnaces. The mesh belts are sometimes replaced, if the loads are very heavy, with a cast belt: a cast link belt furnace. The furnaces can sometimes look like a donut, or cylindrical, where the hearth rotates around. We put the workload in, it rotates around, and either comes out the same door or comes out a second door.

A lot of times, rotary hearth furnaces have a press quench associated with them. You’re heating a part, or reheating a part in some cases, getting it up to temperature, removing it, and putting it into a press that comes down and tries to quench it by holding it so that you reduce the distortion.

There are other styles of furnaces typical of the “faster” industry which are rotary drums. Those furnaces you would load parts into, and you have an incline drum (typically, they’re inclined) with flights inside it. The parts tumble from flight to flight as they go through the furnace, and then usually dump at the end of the furnace into a quench tank.

For very heavy loads, there are what we call walking beam furnaces where you put a workload into the furnace. A beam lifts it, moves it forward, and drops it back down. Walking beam furnaces can handle tremendous weights; 10,000 to 100,000 lbs in a walking beam is not unusual. Any of the other furnaces we’re looking at wouldn’t have nearly that type of capacity.

There are some other fun furnaces: shaker furnaces. How would you like to work in a plant where the furnace floor is continuously vibrating, usually with a pneumatic cylinder so it makes a tremendous rattle, all 8 or 10 hours of your shift? That and a bottle of Excedrin will help you in the evening.

As a last example, the monorail type furnaces where we saw that you hang parts on hooks. The hooks go through the furnace and heat the parts.

I’ll show you just a couple of examples of those. These are not designed to cover all the styles of furnaces but this one you might find interesting.        

"A humpback style furnace"
Source: Dan Herring

This is a typical continuous furnace. This would be a humpback style furnace where the parts actually go up an incline to a horizontal chamber and then go down the other side and come out the other end. These furnaces typically use atmospheres like hydrogen, which is lighter than air and takes advantage of the fact that hydrogen will stay up inside the chamber and not migrate (or at least not a lot of it) to floor level.

Atmosphere Furnaces Q&A (47:30)

Evelyn Thompson: Are the inclined sections of the furnace heated? Why do the parts need to go up an incline? Just to get to the heated part of the furnace?

Dan Herring: If you’re using an atmosphere such as hydrogen, it’s much lighter than air. If you had a horizontal furnace just at, let’s say, 42 inches in height running through horizontally, the hydrogen inside the furnace would tend to wind up being at the top of the chamber or the top of the furnace, whereas the parts are running beneath it! So, the benefit of hydrogen is lost because the parts are down here, and the hydrogen tends to be up here.

By using an incline conveyor, once you go up the incline, the hydrogen covers the entire chamber and therefore the parts are exposed to the atmosphere.

I did a study a few years ago: About 5–6% of the types of mesh belt furnaces in industry are actually this incline conveyor type.

Another good example is the fact that people like to run stainless steel cookware. I’ve seen pots, pans, sinks, etc. Sometimes you need a door opening of 20 or 24 inches high to allow a sink body to pass into it. Well, if that were a conventional, horizontal furnace, you’re limited to, perhaps, 9 to maybe, at most, 12 inches of height.

Typically you never want to go that high, if you can help it. 4–6 inches would be typical. So, there would be a tremendous safety hazard, among other things, to try to run a door opening that’s 24 inches high. But in an incline furnace, the height of the door can be 20, 24, 36 inches high. The chamber is at an 11° angle, and you must get up to the heat zone, but they run very safely at that.

Karen Gantzer: Could you explain what a retort is?

Dan Herring: Think of a retort — there are two types — but think of one as a sealed can, a can with a lid you can open, put parts in and then put the lid back on. The retort we saw in that box style furnace is that type. It is a sealed container. We typically call that a retort.

Now, in that pit furnace we saw, there could be a retort inside that one and they could be sealed containers, but typically they’re just open sides, that are made of alloy. Sometimes we call those “retorts” as opposed to “muffles” or “shrouds,” in another case. Muffles don’t have to be a sealed container, but they typically are. That’s the way to think of them.

Karen Gantzer: Thank you, Dan, I appreciate that.

Bethany Leone: Dan, thank you for joining us. It was really a valuable time.

Dan Herring: Well thank you, my pleasure.

For more information:

www.heat-treat-doctor

dherring@heat-treat-doctor.com

To find other Heat Treat Radio episodes, go to www.heattreattoday.com/radio.

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Heat Treat Radio #97: Lunch & Learn, Ovens vs. Atmosphere Furnaces Read More »

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 Essential for Riverhawk Company’s Heat Treat Operations Read More »

Tip-Ups: A Viable Solution To Customize Your Heat Treat Department

/ ATMOSPHERE AIR FURNACES TECHNICAL CONTENT, FEATURED NEWS, MANUFACTURING HEAT TREAT

OCHeat Treat Today asked tip-up manufacturers to help heat treaters understand the variability of tip-up options in the market today. In this article, Gasbarre Thermal Processing Systems and Premier Furnace Specialists share unique approaches on how their own gargantuan furnaces serve heat treaters. As you read, note that customization is the critical component to operating a tip-up in your heat treat department.

This original content article is drawn from Heat Treat Today's February Air & Atmosphere Furnace Systems print edition. Have something to share about tip-up furnaces? Our editors would be interested in sharing it online at www.heattreattoday.com. Email Bethany Leone at bethany@heattreattoday.com with your own ideas!

Gasbarre Thermal Processing Systems

What is your system and how does it differ from historic tip-up systems?

Gasbarre has a unique offering of tip-up style furnaces. We offer systems for conventional applications such as austenitizing, solution treating, stress relieving, and tempering. In addition, we also offer atmosphere processes such as annealing and ferritic nitrocarburizing (FNC). For us, tip-up systems are not one-size-fits-all type systems. Systems are designed around our customer’s specific processing requirements. This would include thermal process requirements, load geometry and weight, temperature ranges and uniformity requirements, as well as time to quench specifications.

What are its operational advantages?

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When evaluating a tip-up furnace system, they are typically compared against box-style furnaces and car bottom furnaces. So, what differentiates a tip-up from these other style furnaces? First, you can achieve the main goal of large capacity batch processing, while gaining advantages over box furnaces with wider temperature ranges and tighter uniformity requirements. Box furnaces are more challenging to evenly distribute heat due to the large space requirement for the furnace door, where it is difficult to include heating elements or gas fired burners. Second, you can achieve faster time-to-quench speeds in a tip-up furnace over a car bottom furnace. Car bottom furnaces require the load to be pulled out of the furnace and then the load is typically manually moved from the furnace hearth to the quench. In a tip-up, this process can be automated and completed in 60 seconds or less. Finally, when special atmosphere processes are required, a tip-up furnace offers a superior atmosphere seal to the other furnaces mentioned. With tip-up furnaces, you can seal the furnace using its own weight. Other furnaces require additional mechanical assemblies to achieve a proper seal, which ultimately is more susceptible to leaks and requires more maintenance than a tip-up furnace seal.

Tip-up furnace from Gasbarre Thermal Processing Systems
Source: Gasbarre Thermal Processing Systems

Why should people be paying attention to what you have to offer?

Gasbarre’s broad product offering gives us the ability to evaluate your requirements objectively and offer the best solution for you and your company, whether that be box furnace, car bottom, or tip-up. Tip-up furnace systems are usually not one-off installations. These systems usually involve quenching equipment, material handling, load staging, and other integration. Gasbarre has the experience and personnel to manage such large projects and support the customer to effectively implement a system.

Premier Furnace Specialists

What is your system and how does it differ from historic tip-up systems?

The controls and automation capabilities of our furnaces set us above many older systems still in use today. On the control panel of an older system, you’re likely to see paper chart recorders, maybe a PanelView screen, and dozens of switches, pushbuttons, and pilot lights. Some of our customers prefer these control systems for their familiarity, and that’s fine because we are capable of building this style of enclosure, but most come to us for improvements or new systems entirely. Our standard panel comes with a 23.8” color touchscreen display that lets operators manage or record almost every aspect of the furnace’s operation. This package can be added to existing furnaces as well, as we have performed many control and combustion upgrades on older systems to keep them functional and reduce operating costs. We also offer tip-up furnaces that operate via jackscrews for customers who want to avoid the maintenance and flammability of hydraulics.

Open indirect gas-fired atmosphere furnace used to handle a variety of parts
Source: Premier Furnace Specialists

Modern burner technology also offers a massive improvement over older systems. With rising energy costs for all fuel types, any increase in efficiency will quickly become a source of savings which can be redirected into other areas of your company. Improvements to burner design offer increased preheat, recuperative, and regenerative possibilities, which offer fuel savings across multiple temperature ranges and reduce emissions to keep in line with changing regulations. A standard burner can heat up and cool down faster, take less time to tune, and reduce maintenance hours and headaches compared to older models of burners with knowledgeable air and gas train design coupled with modern burners.

What are its operational advantages?

Our systems allow greater flexibility for integration with existing and future equipment as well as simplified operation. One of the largest complaints we hear in every industry is about the struggle to retain maintenance and equipment operators’ knowledge once a senior member leaves a company. For this reason, it is important to have a simplified controls interface that allows new operators to get up to speed quickly. As a service company as well as an OEM, we have extensive experience working on and upgrading many brands of equipment. This enables us to easily integrate our solutions to match what customers are familiar with while also reducing maintenance requirements.

Closed furnace with work chamber of approx 31' x 9' x 9' with load capacit of 90,000 lbs.
Source: Premier Furnace Specialists

Why should people be paying attention to what you have to offer?

Despite OEMs trying to convince you, sometimes a standard “cookie cutter” model just isn’t the right fit for a job. It can take years to build up a budget for a new furnace system. Don’t invest those hard earned dollars into a piece of equipment that won’t do everything you need, exactly how you need it done. We are willing to take on the jobs that require creative solutions and extensive automation. Premier’s custom engineered systems live up to our namesake. Some of our recent projects have included a 130 ft long roller hearth furnace system with automated cooling/sequencing/handling of over 40 loads simultaneously; and a car bottom furnace with a 15’ x 15’ x 15’ work chamber capable of controlled heating and cooling of 160,000-pound loads.

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Tip-Ups: A Viable Solution To Customize Your Heat Treat Department Read More »

How Tip-Ups Forever Transformed Brake Rotor Manufacturing

/ ATMOSPHERE AIR FURNACES TECHNICAL CONTENT, AUTOMOTIVE HEAT TREAT, AUTOMOTIVE HEAT TREAT TECHNICAL CONTENT, FEATURED NEWS, NITROCARBURIZING TECHNICAL CONTENT

OC

Are your brake rotors heat treated? Travel back in time to discover how ferritic nitrocarburizing (FNC) became the heat treatment of choice for automakers’ brake rotors and why the tip-up furnace forever altered the production process for this part.

This Technical Tuesday article is drawn from Heat Treat Today's February Air & Atmosphere Furnace Systems print edition. If you have any information of your own about heat treating brake rotors, our editors would be interested in sharing it online at www.heattreattoday.com. Email Bethany Leone at bethany@heattreattoday.com with your own ideas!

The Problem: Brake Rotor Corrosion

Michael Mouilleseaux
General Manager at Erie Steel, Ltd.
Sourced from the author

In the early 2000s, corrosion was one of the top three issues that U.S. automotive manufacturers found negatively affected the perception of the quality of their cars. Brake rotors are made of cast iron. These components sit out in the elements, and in places like the U.S. Midwest where salt is often used on the roads, unprotected steel or iron will corrode or rust. Even on the coast, there is salt water in the air.

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What does rusting cause? The rotor rusts, and first, the cosmetics are negatively affected (i.e., rusty appearance). But more importantly, the first time you step on the brakes, it squeals like a pig, the vehicle shudders, and the driver feels pulsing in the pedal. He’ll also feel it in the steering wheel because the amount of rust coating one area is different from the amount of rust that’s on another. So, these brand new, forty- to seventy-thousand-dollar cars have orange rust over the brake rotor and a shaky drive. . . it’s not a good look!

Now, this is just a superficial coating of rust that will eventually abrade away; the rotor will look alright, the vehicle will stop better, and it won’t squeal. However, since the rust on the rotor wears off unevenly, the car may never have smooth braking.

A Move to FNC

In the early 2000s, all the big players were looking to FNC (ferritic nitrocarburizing) as a solution to corrosion, including Bosch Braking Systems, Ford, General Motors, Akebono, and the truck manufacturers. FNC was becoming popular since the process adds a metallurgical layer — called the “white layer” or “compound zone” — to the part, providing corrosion resistance and the bonus of improving wear.

Source: Oleksandr Delyk/Adobe Stock

To the OEMs, the benefits were perceived as:

  1. The corrosion issue had an answer.
  2. The life of the rotor doubled from roughly 40,000 to 80,000 miles. Although that meant half as many aftermarket brake jobs compared to before, consumers perceived it as a real advantage.
  3. The rotors generated less dust. Brakes generate dust particles as the result of abrasion of the pads and the rotors. This particulate dust has been identified as both an environmental and a health concern. Now, flash forward to 2022: Electric vehicles are largely displacing the need to control emissions from ICE (internal combustion engine) vehicles. So, the new European standard on vehicle emissions implemented a requirement to control this dust that is harmful to the environment and which EV and traditional brake systems can emit.

But there were certain technical and practical challenges that automotive manufacturers faced when trying to implement this process at scale.

#1 Distortion. Brake rotors may distort during FNC. Since rotors are (gray iron) castings, the process temperature for FNC may stress relieve the rotor, causing it to change shape or distort, rendering it unusable as a disc brake rotor. It was determined that if the rotor castings were stress relieved prior to machining and FNC, the distortion issue was rendered moot.

#2 Loss of Necessary Friction. FNC gives the white layer on the surface of a part with a diffusion zone underneath. The compound zone has a very low coefficient of friction, which means excellent wear properties. However, manufacturers want friction between the rotor and the brake pads to slow the car down. Reducing the friction on the rotors extends the braking distance of the car.

". . .[M]anufacturers want friction between the rotor and the brake pads to slow the car down."
Source: Unsplash.com/Craig Morolf
Let me illustrate this: I ferritic nitrocarburized a set of brake discs for Bosch Braking Systems, which eventually went to Germany and then on a vehicle. The customer absolutely loved the corrosion resistance, but when it was time for the downhill brake test, the car went straight through an instrument house because the brakes couldn’t stop the car! Lesson: For rotors treated with FNC, the brake pads need to be made from a different frictional material!

#3 Cost. Overcoming the technical issues is simple. Stress relieving the casting at FNC temperatures before machining it would help the parts machine better and would eliminate distortion. Modifying the FNC process could reduce the depth of the white layer and, paired with the correct friction material, the acceptable braking capabilities were restored. Yet these additional steps presented a new challenge: higher costs.

The practical constraints of FNC in conventional batch or pit furnaces strained efforts to be cost-effective. The load (size) capacity of the conventional equipment, in conjunction with the time constraints of the FNC process presented a dilemma, as the OEMs’ benchmark was about one dollar per rotor.

Here Comes the Tip-Up

With traditional furnaces for FNC, there was just no way to reach the economics that were necessary for it. A bigger pit furnace might be the way to go, but they really weren’t big enough. So, here comes the tip-up.

Traditionally, a tip-up furnace has been used for processes with just air, no atmosphere. With direct fired burners, the furnace is used for tempering, stress relieving, annealing, and normalizing. Everything loads into the box, gets fired, and unloads, similar to a car-bottom furnace. With the appropriate external handling systems parts could be retrieved from the furnace and then quenched. This additional process increased the usefulness of the equipment and allowed for the processing of tubes, bars, big castings. . . big forgings for the oil industry and the like.

The question of how to heat treat brake rotors on a large scale still needed to be answered. It required a large, tightly sealed furnace with atmospheric integrity for excellent temperature uniformity. In ferritic nitrocarburizing, the processing range is about 950°F to 1050°F. It is well known that properties vary significantly across the temperature range. And they needed to be optimized to create the appropriate frictional properties for the rotors.

So, the answer was: Let’s make a tip-up furnace that can be sealed for atmospheric integrity, has the appropriate temperature uniformity, and can circulate gas evenly. A lot of this would have to be iterative — create, test, compare, repeat.

Tip-up furnace from Gasbarre Thermal Processing Systems
Source: Gasbarre Thermal Processing Systems

The development of the perfect tip-up was essentially the work of one furnace manufacturer and one heat treater who together changed the industry.

American Knowhow Makes the Perfect Tip-Up

In the early 2000s, heat treaters worked with OEMs to develop a cost-efficient process in a tip-up. Manufacturers and service providers tested different methods, including atmosphere FNC and salt bath FNC.

By 2009, the perfect atmosphere furnace was complete and high volume brake rotors began to be processed for General Motors. The furnace manufacturer was JL Becker, Co., acquired by Gasbarre in 2011. The commercial heat treater was Woodworth, Inc., located in Flint, MI. Together, they spent a lot of time and money looking into FNC and figuring out how to make it work in a tip-up furnace.

General Motors was the first one to get on board, utilizing the FNC processed rotors on their pickup trucks and big SUVs, like the Escalade and Tahoe. Ford was not far behind using it on their F150 pickup truck. I was shocked the first time I saw the commercial: a Silverado pickup truck, out in the snow, and the speaker saying, “We now have an 80,000-mile brake system because of a heat treating process called FNC!”

It’s a great story of American knowhow and a collaborative effort between someone who saw a need and someone else who saw the way. To this day, if you want to get a replacement set of brake rotors for your car, go to a place like AutoZone; they will tell you that the difference in cost between the OEM parts and an off-brand is the fact that the off-brand is not heat treated.

About the author: Michael Mouilleseaux has been at Erie Steel, Ltd. in Toledo, OH, since 2006 with previous metallurgical experience at New Process Gear in Syracuse, NY, and as the Director of Technology in Marketing at FPM Heat Treating LLC in Elk Grove, IL. Having graduated from the University of Michigan with a degree in Metallurgical Engineering, Michael has proved his expertise in the fi eld of heat treat, co-presenting at the Heat Treat 2019 show and currently serving on the Board of Trustees at the Metal Treating Institute.

Contact Michael at MMouilleseaux@erie.com

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How Tip-Ups Forever Transformed Brake Rotor Manufacturing Read More »

Air & Atmosphere Heat Treat Tips Part 4: Carbon Control

/ ATMOSPHERE AIR FURNACES TECHNICAL CONTENT, FEATURED NEWS, MANUFACTURING HEAT TREAT

OC

Let’s discover new tricks and old tips on how to best serve air and atmosphere furnace systems. In this series, Heat Treat Today compiles top tips from experts around the industry for optimal furnace maintenance, inspection, combustion, data recording, testing, and more. Part 4, today's tips, examines carbon probes and carbon control. Look back to Part 1 here for tips on seals and leaks, Part 2 here for burners and combustion tips, and Part 3 here for data and record keeping tips.

This Technical Tuesday article is compiled from tips in Heat Treat Today's February Air & Atmosphere Furnace Systems print edition. If you have any tips of your own about air and atmosphere furnaces, our editors would be interested in sharing them online at www.heattreattoday.com. Email Bethany Leone at bethany@heattreattoday.com with your own ideas!

1. Slight Positive Pressures Are Best

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Atmosphere furnace pressure should be only slightly above ambient. The range should be between 0.25-0.35 inches water column. Higher pressures in multiple zone pusher furnaces will cause carbon control issues. High pressures in batch furnaces will cause high swings when doors and elevators move.

Source: AFC-Holcroft

#atmosphericpressure #furnacezones #batchfurnace #multizone

2. Carbon Probe Trouble Shooting

If you’re having atmosphere problems with a furnace that has been operating normally for some time, avoid the temptation to remove the carbon probe. There are several tests you can run on nearly all carbon probes while the probe is still in the furnace, at temperature, in a reducing atmosphere. Super Systems Inc. provides an 11-step diagnostic procedure in a white paper on their website, in a paper titled, “Carbon Sensor Troubleshooting” by Stephen Thompson.

Source: Super Systems Inc.

#troubleshoot #reducingatmosphere #diagnostictest

3. What To Do When Parts Are Light on Carbon

"Review process date for abnormalities."
Source: Super Systems Inc.

Many factors can contribute to why parts are not meeting the correct hardness readings. According to Super Systems Inc., here is a quick checklist of how to start narrowing down the culprit:

  • Review process data for abnormalities. The first thing to do is make sure the parts were exposed to the right recipe. Check the recorders to make sure the temperature prof le and atmosphere composition were correct. Make sure all fans and baffes were working correctly. Determine if any zones were out of scope and that quench times were acceptable. If any red flags appear, hunt down the culprit to see if it may have contributed to soft parts.
  • Check the generator. Next, check the generator to make sure it is producing the gas composition desired for the process. If available, check the recorders to make sure the gas composition was on target. If not, check the generator inputs and then the internal workings of the generator.
  • Check the furnace atmosphere. If the generator appears to be working correctly, the next step would be to check the furnace itself for atmosphere leaks. Depending on what type of furnace you have, common leak points will vary; for continuous furnaces, common leak points are a door, fan, T/C, or atmosphere inlet seals. Other sources of atmosphere contamination may be leaking water cooling lines in water-cooled jackets or water-cooled bearings. More than likely, if the generator is providing the correct atmosphere but parts are still soft, there is a leak into the furnace. This will often be accompanied by discolored parts.
  • Check carbon controller to make sure it matches furnace atmosphere reading (verify probe accuracy and adjust carbon controller). This can be done using a number of different methods: dew point, shim stock, carbon bar, three gas analysis, coil (resistance), etc. Each of these methods provides a verification of the furnace atmosphere which can be compared to the reading on the carbon controller. If the atmosphere on the carbon controller is higher than the reading on the alternate atmosphere check, that would indicate the amount of carbon available to the parts is not as perceived. The COF/PF on the carbon controller should be modified to adjust the carbon controller reading to the appropriate carbon atmosphere. If the reading is way off, it may require the probe to be replaced.
  • Check the carbon probe.
  • Replace the probe – CALL SSI.

Source: Super Systems Inc.

#checklist #hardening #carbon #furnaceatmosphere #probes #controller

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Air & Atmosphere Heat Treat Tips Part 4: Carbon Control Read More »

Air & Atmosphere Heat Treat Tips Part 3: Data and Record Keeping

/ ATMOSPHERE AIR FURNACES TECHNICAL CONTENT, FEATURED NEWS, MANUFACTURING HEAT TREAT

OC

Let’s discover new tricks and old tips on how to best serve air and atmosphere furnace systems. In this series, Heat Treat Today compiles top tips from experts around the industry for optimal furnace maintenance, inspection, combustion, data recording, testing, and more. Part 3, today's tips, examines AI and record keeping. Look back to Part 1 here for tips on seals and leaks and Part 2 here for burners and combustion tips.

This Technical Tuesday article is compiled from tips in Heat Treat Today's February Air & Atmosphere Furnace Systems print edition. If you have any tips of your own about air and atmosphere furnaces, our editors would be interested in sharing them online at www.heattreattoday.com. Email Bethany Leone at bethany@heattreattoday.com with your own ideas!

1. Use AI To Simplify Your Maintenance

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"cloud view of heat treating operation"
Source: NITREX

Simplify your maintenance! Today, using artificial intelligence (AI) software allows the “Cloud” to do the hard work. NITREX has introduced QMULUS, a web-based software solution, with each of its nitriding systems, which examines key parameters  to determine if your furnace is having any issues. Gas flows, amperage, motors, and cycles are all monitored for health factors. But QMULUS is so much more than that. It also analyzes input usages and calculates the cost of each run; logs all data relevant to running processes more efficiently; and provides an easy and seamless cloud view of heat treating operations.

Source: NITREX

#maintenance #iiot #AI #costsavings

2. Record System Settings Before Issues Arise

This is a very simple tip that is often overlooked when customers are focused on meeting production goals instead of the maintenance of their equipment. It is critical to record the operating settings of their furnace systems when parts are coming out at their best, or simply before issues arise. When something goes awry in the process and troubleshooting is required, service technicians hear all too often that there is no record of what the ideal or correct setpoints are for various systems. Nearly every item on a modern heat treating furnace (or in its control panel) has a setpoint or position that can be recorded or physically marked. Now, clearly some items are more critical than others when it comes to air and atmosphere settings. Below are a few items you’ll want to have setpoint/positioning records of before they require troubleshooting:

  • Flowmeter setpoints (at the furnace and generator)
  • Blower/pump/motor VFD setpoints (primarily frequency setpoints and ramp rates)
  • Manual or actuated damper positions on flues
  • Regulator setpoint (from pressure gauge or in-line test port)
  • High/low pressure switch setpoints
  • Any air/gas/atmosphere ratios for various recipe steps
  • Burnout frequency and duration (if applicable)

An added incentive to record these settings is the preventative maintenance benefit. The best way to avoid supply chain issues and delivery delays is to fix a problem before it grows into a bigger issue. When a setpoint/setting is correct but product quality begins changing, it is a warning sign that consumables may be approaching end of life (such as nickel catalyst in endothermic gas generators) or components require maintenance (such as air inlet filter replacements).

Source: Premier Furnace Specialists

#preventativemaintenance #troubleshooting #furnaceequipment

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Air & Atmosphere Heat Treat Tips Part 3: Data and Record Keeping Read More »

Air & Atmosphere Heat Treat Tips Part 2: Burners and Combustion

/ ATMOSPHERE AIR FURNACES TECHNICAL CONTENT, FEATURED NEWS, MANUFACTURING HEAT TREAT

OC

Let’s discover new tricks and old tips on how to best serve air and atmosphere furnace systems. In this series, Heat Treat Today compiles top tips from experts around the industry for optimal furnace maintenance, inspection, combustion, data recording, testing, and more. Part 2, today's tips, examines burner and flame safety. Look back to Part 1 here for tips on seals and leaks.

This Technical Tuesday article is compiled from tips in Heat Treat Today's February Air & Atmosphere Furnace Systems print edition. If you have any tips of your own about air and atmosphere furnaces, our editors would be interested in sharing them online at www.heattreattoday.com. Email Bethany Leone at bethany@heattreattoday.com with your own ideas!

1. Operating with a Multiple Burner System

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If a furnace or oven has a multiple burner combustion system with only one valve train, a multi-burner combustion safeguard should be used. This ensures that if one burner fails, they all go out.

Source: Bruce Yates, "Ten Tips for Safeguarding Combustion Processes"

#multiburner #combustion #safety

2. Regularly Inspect Retort Alloys

Source: Nitrex

Retort alloys must be inspected on a regular basis. Hot spots can be identified by bulges. Plastic deformation occurs due to overheating, causing the hotter section to bulge because it is surrounded by stronger metal. Inspect your retorts or radiant tubes for deformations. In addition, constant thermal cycling can cause problems with some alloys. Look for cracks in welds or near welds. Some leak detection methods can also detect alloy issues or overheating.

Localized overheating could indicate a problem with the burner or the heating element. Early detection and correction can save you a lot of money on expensive alloys.

Source: Nitrex

#retortalloys #maintenance #burner #moneysaving

3. Understand What Flame Detection Is

Flame supervision may be defined as the detection of the presence or absence of flame. If a flame is present during the intended combustion period, the supervisory system will allow a fuel flow to feed combustion. If the absence of flame is detected, the fuel valves are de-energized.

This basic definition does not consider the hazard potential during startup or ignition, however. A dangerous combustible mixture within a furnace or oven consists of the accumulation of combustibles (gas) mixed with air, in proportions that will result in rapid or uncontrolled combustion (an explosion). It depends on the quantity of gas and the air-to-fuel ratio at the moment of ignition.

Source: Bruce Yates, "Ten Tips for Safeguarding Combustion Processes"

#flamedetection #combustion #valves

4. Remember that Flame Safety Starts with Purging

The sequence for flame safety starts with purging the furnace or oven. Purge time should allow for four air changes.

Fuel valves can — and do — leak gas. The purpose of purging is to remove combustible gases from the combustion chamber before introducing an ignition source. The four air changes in the combustion chamber are based on a worst-case scenario that includes having a burner chamber that is completely filled with gas.

Once airflow for purge is verified, the proof-of-valve closure is confined and safety limits are proven. Then the purge timer — which may or may not be integral to the combustion safeguard — determines the period of time required to evacuate the combustion chamber.

Source: Bruce Yates, "Ten Tips for Safeguarding Combustion Processes"

#combustion #fuelvalves #combustionchamber #safety

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Air & Atmosphere Heat Treat Tips Part 2: Burners and Combustion Read More »

Air & Atmosphere Heat Treat Tips Part 1: Seals and Leaks

/ ATMOSPHERE AIR FURNACES TECHNICAL CONTENT, FEATURED NEWS, MANUFACTURING HEAT TREAT

OC

Let’s discover new tricks and old tips on how to best serve air and atmosphere furnace systems. In this series, Heat Treat Today compiles top tips from experts around the industry for optimal furnace maintenance, inspection, combustion, data recording, testing, and more. Part 1, today's tips, examines seals and leak points.

This Technical Tuesday article is compiled from tips in Heat Treat Today's February Air & Atmosphere Furnace Systems print edition. If you have any tips of your own about air and atmosphere furnaces, our editors would be interested in sharing them online at www.heattreattoday.com. Email Bethany Leone at bethany@heattreattoday.com with your own ideas!

1. Tip-Up Furnace Perimeter Insulation Maintenance Is Key to Efficiency & Quality

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Due to their construction, the insulation at the perimeter of a tip-up furnace is subject to more abuse than typical furnace insulation. Whether from the repeated stress of cycling the case open and closed — or from high temperature operation — fiber modules will eventually begin to shrink/compact. Be watchful for high case temperatures (or worse: case discoloration and paint damage) as a signal that insulation issues are present in that area.

Heat-damaged case wall
Source: Premier Furnace Specialists

An air/atmosphere tight seal is critical for maintaining heating efficiency and process quality. Inspect the seal material around the furnace perimeter often and replace sections that are worn. Common perimeter seals are sand seals, fiberglass tadpole tapes, and insulating fiber blankets. These sealing materials are easy to keep on hand to ensure a quality seal is never delayed by lengthy lead times or supply chain issues.

Source: Premier Furnace Specialists

#tip-up #maintenance #insulation #heatingefficiency

2. Mind Your Seals

Seals are everywhere on any furnace. Do you know where all the seals and leak points are? Rope gaskets is an obvious example; high temperature gaskets need to be flat, smooth, and unbroken. Another clear example is in the world of vacuum furnaces: O-rings need to be clean and protected from abrasion. Almost every item of your furnace is sealed in some manner. It is best to replace seals as part of a preventative maintenance program. While your nose can detect ammonia, vacuum leaks require special helium leak detectors and a lot of training. Your furnace manufacturer’s service technician can assist in identifying problem areas and developing a maintenance routine to keep your furnace running. And a simple electronic manometer is great to have handy for running leak-down tests using positive pressures. Auto supply stores sell inexpensive halogen detectors, and some people use smoke bombs to detect leaks.

Source: Nitrex

#leaks #tests #preventativemaintenance

3. Out of Control Carburizing? Try This 11-Step Test

Source: AFC-Holcroft

When your carburizing atmosphere cannot be controlled, perform this test:

  • Empty the furnace of all work.
  • Heat to 1700°F (926°C).
  • Allow endo gas to continue.
  • Disable the CP setpoint control loop.
  • Set generator DP to +35°F (1.7°C).
  • Run a shim test.
  • The CP should settle out near 0.4% CP.
  • If CP settles out substantially lower and the CO2 and DP higher, there’s an oxidation leak — either air, water, or CO2 from a leaking radiant tube.
  • If the leak is small, the CP loop will compensate, resulting in more enriching gas usage than normal.
  • Sometimes, but not always, a leaking radiant tube can be found by isolating each tube.
  • To find a leaking radiant tube, not only the gas must be shut off but combustion air as well.

Source: AFC-Holcroft

#carburizingheattreat #radianttubes #checklists #endogas #carburizingatmosphere

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Air & Atmosphere Heat Treat Tips Part 1: Seals and Leaks Read More »