Three elements in the T6 aluminum heat treatment process — high temperature solution heat treatment, drastic temperature change in the water quench, and a long age hardening process — challenge accurate temperature monitoring. Thru-process technology gives in-house heat treaters the power to control these variables to overcome the unknowns. In the following Technical Tuesday article, Dr. Steve Offley, “Dr. O”, product marketing manager at PhoenixTM, examines the path forward through the challenges of aluminum heat treating.
This informative piece was first released in Heat Treat Today’s August 2024 Automotive print edition.
Aluminum Processing Growth
In today’s automotive and general manufacturing markets, aluminum is increasingly becoming the material of choice, being lighter, safer, and more sustainable. Manufacturers looking to replace existing materials with aluminum are needing new methodology to prove that thermal processing of aluminum parts and products is done to specification, efficiently and economically.
To add strength to pure aluminum, alloys are developed by the addition of elements dissolved into solid solutions employing the T6 heat treatment process (Figure 1). The alloy atoms create obstacles to dislocate movement of aluminum atoms through the aluminum matrix. This gives more structural integrity and strength.
FIgure 1. Critical temperature phase transitions of the T6 aluminum heat treatment process Source: PhoenixTM
Process temperature control and uniformity is critical to the success of T6 heat treat to maximize the solubility of hardening solutes such as copper, magnesium, silicon, and zinc without exceeding the eutectic melting temperature. With a temperature difference of typically 9–15°F, knowing the accurate temperature of the product is essential. Control of the later quench process (Figure 1, Phase 3) is also critical not only to facilitate the alloy element precipitation phase but also to prevent unwanted part distortion/warping and risk of quench cracking.
T6 Process Monitoring Challenges
The T6 solution reheat process comes with many technical challenges where temperature profiling is concerned. The need to monitor all three of the equally important phases — solution treatment, quench, and the age hardening process — makes the trailing thermocouple methodology impossible.
Figure 2. Thru-process temperature monitoring of the three T6 heat treatment phases Source: PhoenixTM
Even when considering applying thru-process temperature profiling technology, sending the data logger through the process, protected in a thermal barrier (Figure 2), the T6 heat treat process comes with significant challenges. A system will not only need to protect against heat (up to 1020°F) over a long process duration but also withstand the rigors of being plunged into a water quench. Rapid temperature transitions create elevated risk of distortion and warping which need to be addressed to give a reliable and robust monitoring solution.
Certain monitoring systems can provide protection to the data logger at 1022°F for up to 20 hours (Figure 3).
Figure 3. Thru-process temperature profiling system installed in the product cage monitoring the T6 heat treatment (solution treatment, quench, and age hardening) of aluminum engine blocks
Thermal Protection Technology
To meet the challenges of the T6 heat treat process, the conventional thermal barrier design employing microporous insulation is replaced with a water tank design, with thermal protection using an evaporative phase change temperature control principle. Evaporative technology uses boiling water to keep the high temperature data logger (maximum operating temperature of 230°F) at a stable operating temperature of 212°F as the water changes phase from liquid to steam. The advantage of evaporative technology is that a physically smaller barrier is often possible. It is estimated that with a like for like size (volume) and weight, an evaporative barrier will provide in the region of twice the thermal protection of a standard thermal barrier with microporous insulation and heat sink. The level of thermal protection can be adjusted by changing the capacity of the water tank and the volume of water. Increasing the volume of water increases the duration at which the T6 temperature barrier will maintain the data logger temperature of 212°F before it is depleted by evaporation losses.
The TS06 thermal barrier design (Figure 4) incorporates a further level of protection with an outer layer of insulation blanket contained within a structural outer metal cage. The key role of this material is to act as an insulative layer around the water tank to reduce the risk of structural distortion from rapid temperature changes both positive and negative in the T6 process.
Figure 4. TS06 thermal barrier design showing water tank, housing the data logger at its core, installed within structural frame containing the insulation blanket surface layer; water tank shown with traditional compression fitting face plate seal Source: PhoenixTM
Obviously, the evaporative loss rate of water is governed by the water tank geometry. A cube shaped tank will provide the best performance, but this may need to be adapted to meet process height restrictions. A TS06 thermal barrier with dimensions 8.5 x 18.6 x 25.2 inches (H x W x L) offering a water capacity of 3.5 US gallons provides 11 hours of protection at 1022°F. A larger TS06 with approximately twice the capacity 12.2 x 18.6 x 25.2 inches (H x W x L) and 7.7 US gallons gives approximately twice the protection (20 hours at 1022°F).
Innovative IP67 Sealing Design
Passing through the water quench, the data logger needs to be protected from water damage. This is achieved in the system design by combining a fully IP67 sealed data logger case and water tank front face plate through which the thermocouples exit. Traditionally in heat treatment applications, mineral insulated thermocouples are sealed using robust metal compression fittings. Although reliable, the compression seals are difficult to use, requiring long set-up times. The whole uncoiled straight cable length must be passed through the tight fitting which, for the 10 x 13 ft thermocouples, takes some patience. Thermocouples can be used and installed for multiple runs, if undamaged. Unfortunately, as the ferrule in the compression fitting bites into the MI cable, removal of the cable requires the thermocouple to be cut, preventing reuse.
To overcome the frustrations of compression fitting, an alternative innovative thermocouple sealing mechanism has been designed for use on the T6 thermal barrier (Figure 5).
Figure 5. TS06 thermal barrier IP67 bi-directional rubber gasket seal; installation of mineral-insulated (MI) thermocouples and RF antenna aerial
Thermocouples can be slotted easily and quickly, tool free, into a precision cut rubber gasket without any need to uncoil the thermocouple completely. The rubber gasket has a unique bi-directional seal, allowing both sealing of each thermocouple but also sealing of the clamp face plate to the data logger tray, which is then secured to the water tank with a further silicone gasket seal. The new seal design allows thermocouples to be uninstalled and reused, reducing operating costs significantly.
Accurate Process Data considerations
The T6 applications come with a series of monitoring challenges which need to be considered carefully to guarantee the quality of the data obtained. Although the complete process time of the three phases can reach up to 10 hours, it is necessary to use a rapid sample interval (seconds) to provide a sufficient resolution. The data logger is designed to facilitate this with a minimum sample interval of 0.2 seconds over 20 channels and memory size of 3.8 million data points, allowing complete monitoring of the entire process. A sample interval of 0.2 seconds provides sufficient data points on the rapid quench cooling curve. The high resolution allows full analysis and optimization of the quench rate to achieve required metallurgical transitions yet avoid distortion or quench cracking risks.
Employing the phased evaporation thermal barrier design, the high temperature data logger with maximum operating temperature of 230°F will operate safely at 212°F. During the profile run, the data logger internal temperature will increase from ambient temperature to 212°F. To allow the thermocouple to accurately record temperature, the data logger offers a sophisticated cold junction compensation method, correcting the thermocouple read out (hot junction) for anticipated internal data logger temperature changes.
Data logger and thermocouple calibration data covering the complete measurement range (not just a single designated temperature) can be used to create detailed correction factor files. Correction factors are calculated by interpolation between two known calibration points using the linear method as approved by CQI-9 and AMS2750G. This method ensures that all profile data is corrected to the highest possible accuracy.
Addressing Real-Time, Thru-Process Temperature Monitoring Challenges
For a process time as long as the T6, real-time monitoring capability is a significant benefit. The unique two-way RF telemetry system used on the PhoenixTM system helps address the technical challenges of the three separate stages of the process. The RF signal can be transmitted from the data logger through a series of routers linked back to the main coordinator connected to the monitoring PC. The wirelessly connected routers are located at convenient points in the process (solution treatment furnace, quench tank, aging furnace) to capture all live data without any inconvenience of routing communication cables.
A major challenge in the T6 process is the quench step from an RF telemetry perspective. An RF signal cannot escape from water in the quench tank. To overcome this limitation, a “catch up” feature is implemented. Once the system exits the quench and the RF signal is re-established, any previously missing data is retransmitted guaranteeing full process coverage.
Process Quality Assurance and Validation
In the automotive industry, many operations will be working to the CQI-9 special process heat treat system assessment accreditation. As defined by the pyrometry standard, operators need to validate the accuracy and uniformity of the furnace work zone by employing a temperature uniformity survey (TUS).
The thru-process monitoring principle allows for an efficient method by which the TUS can be performed employing a TUS frame to position a defined number of thermocouples over the specific working zone of the furnace (product basket). As defined in the standard with particular reference to application assessment process Table C (aluminum heat treating), the uniformity for both the solution heat treatment and aging furnace needs to be proven to satisfy ±10°F of the threshold temperature during the soak time.
Complementing the TUS system, the Thermal View Survey software provides a means by which the full survey can be set up automatically allowing routine full analysis and reporting to the CQI-9 specification as shown in Figure 6.
Figure 6. View of TUS for T6 aluminum processing in Phase 1 Solution Re-heat Source: PhoenixTM
Interestingly, a significant further benefit of the thru-process principle is that by collecting process data for the whole process, many of the additional requirements of the process Table C can be achieved with reference to the quench. From the profile trace, key criteria such as quench media temperature, quench delay time, and quench cooling curve can be measured and reported with full traceability during the production run.
Summary
To fully understand, control, and optimize the T6 heat treat process, it is essential the entire process is monitored. Thru-process monitoring solutions, designed specifically, allow not only product temperature profiling of all the solution heat treatment, water quench, and age hardening phases, but also comprehensive temperature uniformity surveying to comply with CQI-9.
About the Author:
Dr Steve Offley (“Dr O”), Product Marketing Manager, PhoenixTM
Dr. Steve Offley, “Dr. O,” has been the product marketing manager at PhoenixTM for the last five years after a career of over 25 years in temperature monitoring focusing on the heat treatment, paint, and general manufacturing industries. A key aspect of his role is the product management of the innovative PhoenixTM range of thru-process temperature and optical profiling and TUS monitoring system solutions.
United States Air Force personnel stationed at Royal Air Force (RAF) Base Mildenhall in the United Kingdom recently commissioned and received full training on the use and maintenance of a heat treating furnace for aerospace parts. The furnace will help maintain KC-135, CV-22, C-130 aircraft, and F-15 fighter jets assigned to RAF Mildenhall or nearby RAF Lakenheath air stations. The installation was interrupted by an impromptu visit from the U.S. President.
Richard Conway Chief Technology Officer Delta H Technologies
The DELTA H® TECHNOLOGIES dual chamber heat treating furnace for aerospace (DCAHT®) was designed by the supplier to rapidly heat treat all common aviation grade metals and alloys necessary for aircraft maintenance and is fully compliant with USAF/NAVAIR Tech Order 1-1A-9 and SAE-AMS2750F. The training received by the USAF airmen at RAF Mildenhall included essential instructions in heat treating, as well as furnace calibration practices like temperature uniformity surveys (TUS) and system accuracy tests (SAT) and culminated with each airman receiving Certificates of Training.
The specialized furnace features an upper chamber convection system, 18" wide x 12" high x 48" deep, capable of Class 1 (+/-5°F) from 200°F to 1200°F and a lower chamber radiant heat system, 12" wide x 12" high x 36" deep, capable of Class 3 (+/-15°F) from 1000°F to 2000°F with air or argon atmosphere. A roll-away quench tank features dual baths for water and oil quenchant. The controls and data acquisition provide detailed batch records of heat treated parts, including quench delay, as well as automatic tracking of thermocouple usage and calibration intervals.
Air Force One at RAF Mildenhall
The training was interrupted by an unexpected visitor to RAF Mildenhall. The hangar next to the Metals Tech Shop, where the furnace was being commissioned and the training was being conducted, was the epicenter for the arrival of a top-secret VIP. When the Air Force Band began practicing "Hail to the Chief," it became obvious that U.S. President Joe Biden would be making an unexpected visit to the base. While the President’s visit was not related to the furnace commissioning, Richard Conway, DELTA H® founder and chief technology officer, and wife Mary Conway, witnessed this presidential visit and got a few candid photographs of Air Force One (see above).
Heat TreatToday provides many different ways for you to keep current on heat treating technical content, news, trends, and specifications within the industry. Heat TreatRadio is one of those outlets. Publisher and Heat TreatRadio host, Doug Glenn, talked with James Hawthorne from Acument Global Technologies and Justin Rydzewski of Controls Service Inc., both of whom served on the committee, with Hawthorne being the chairman, of the latest revisions (Rev. 4) to CQI-9.
This column appeared in Heat TreatToday'sAugust 2021 Automotiveprint edition.
Check out this article for a summary of the topics and insights discussed during this four-part series, and then listen to the individual episodes to learn all you need to know about understanding and complying with CQI-9 Rev. 4.
Process tables from Rollout Webinar (Source: Rollout Webinar PowerPoint)
Heat Treat Radio:
Justin Rydzewski on CQI-9 Rev. 4
(Part 1 of 4) – Pyrometry
In this first episode, Doug Glenn and Justin Rydzewski provide an overview of CQI-9 and the “why” behind the new revision as well as talking down through the pyrometry section which covers things like sensors, thermocouples, calibration, SATs, and TUS. Rydzewski was an active participant in the writing of the new revision. His company, Controls Service Inc., is an ISO/IEC 17025 accredited provider of process control systems, calibration, maintenance, and services.
Here’s an excerpt taken from the transcript of the first podcast:
Doug Glenn (DG): Give us information about CQI-9. Give us a brief history. When did it start? Who owns it? Who maintains its updates? To whom does it apply? What is its scope?
Justin Rydzewski (JR): The best way I know to describe it (because, perhaps the most widely known pyrometry specification is AMS2750) is CQI-9 is the automotive equivalent of AMS2750. There are obviously some differences between the two documents, but, in a nutshell, that’s the comparison. It is a document supported by the AIAG, the Automotive Industry Action Group. They oversee the publication of it, the drafting of it, and supervise the whole thing through that process. CQI-9 is the number. Officially, it’s called the Special Process Heat Treat System Assessment and that kind of gets the nomenclature of CQI-9 that applies to automotive heat treaters, or any performing heat treat work within the automotive industry; and several processes fall into that category. It can be from commercial heat treat to in-house heat treat, to organizations like mine that support it. It applies to anyone participating in that effort of heat treat.
DG: Let’s talk about Rev. 4. You said as soon as “3” was out, you started on “4” and it took eight to nine years to get done with “4.” What was the main reason why you needed to abandon “3”?
JR: They schedule these things out to be rewritten on a routine basis. Like most specifications, they are reviewed on some established interval of time. The biggest difference between the second edition of CQI-9 and the third edition was that the third edition removed all references to AMS2750. When 2750 was in the document, it created a world of confusion, and the guidance and errata sheets that followed were just so numerous that they made it a somewhat difficult document to adhere to.
One of the ideas we brought to the table was that maybe we should just remove all reference to it [2750] and write our own specification. So, the third edition removed the 2750 references. In doing so, it ended up being a very well written document. It was effective. The OEMs—your GMs, Fords, FCAs—were happy with the results of the document.
The prolonged active interval of that document allowed us to collect a lot of really good data about what was working, what wasn’t, what was confusing, and where additional clarity was needed. The more data we collected, the more confident we were that the fourth edition would truly make a stride toward being a more effective document.
DG: What are the major sections?
JR: It is structured very similar to the way of AMS2750 in that regard. You have four sections that divvy up a pyrometry section: thermocouples, instrumentation, system accuracy testing, and temperature uniformity survey. But, unlike AMS2750, CQI-9 is a system assessment, it is a process, it is a heat treat management system. It encompasses more than just pyrometry. Where AMS2750 is a pyrometry specification, CQI-9 is a process specification; it encompasses everything. It also includes your heat treat system assessment, which is three sections of questions regarding your heat treat operation, then you have your pyrometry which is those four sections I mentioned. Then you have your process tables. Your process tables drive all of your requirements for your particular operation, in terms of frequencies and tolerances.
To listen or read more about the CQI-9 pyrometry section, go to www.heattreattoday.com and search “Heat Treat Radio CQI-9”
Heat Treat Radio:
James Hawthorne and Justin Rydzewski on CQI-9 Rev. 4
(Part 2 of 4) – HTSAs & Job Audits
In this second installment, Doug Glenn, Justin Rydzewski, and James Hawthorne of Acument Global Technologies discuss heat treat system assessments and job audits in CQI-9 Rev. 4.
Hawthorne is a heat treat specialist in Acument’s North American facilities and handles the heat treat systems, the system’s compliance, and quality assurance for heat treat within his organization. (Acument makes fasteners—nuts, bolts, rivets, washers— for the auto industry.)
Here’s an excerpt taken from the transcript of the second podcast:
DG: James, how would you explain CQI-9 to someone who has essentially zero understanding of what it is?
James Hawthorne (JH): CQI-9 is Continuous Quality Improvement. The purpose behind it is to put together a system that will help you manage and control your process, and at the end of it, the product that you’re delivering to the end user. The intent is to give you those guidelines to help avoid potential spills or escapes or whatever else may come with that.
DG: It’s mostly heat treat related, yes? Or is there more than just heat treat there?
JH: It is the entire system of heat treat. If you look at the heat treat system assessment, the first portion of it is quality based. The second portion (Section 2) is the floor responsibilities, things that are on task that are being completed. And third, you get into the maintenance and the pyrometry portion of it, very specific to the pyrometry and very specific to atmosphere control. At the end of it, there are some very specific induction questions, because when it comes to induction, there is no real furnace at that point, so you want to focus on those key elements of induction.
DG: James, we’d like to pick your brain a bit on this. Let’s jump into some questions on the HTSAs, as we’ll refer to them, heat treat system assessments, and job audits. Let’s go right to the basics: What is an HTSA and what is its purpose?
JH: HTSA, heat treat system assessment, is a tool that has been developed to help you evaluate how you manage your heat treat system for effectiveness: effectiveness in quality management and effectiveness in the floor responsibilities. Like I mentioned earlier, understanding that through aspects of training and training effectiveness and into the final section of atmospheric control and atmosphere management and reaction to those.
The purpose here is to have one system, one document that is the rules of engagement for doing heat treat in the automotive world. What this does is allows the automotive industry to give you one spec, one thing to follow. As opposed to having, say Ford, give you ten questions where none of them are exactly the same as FCA or nine of them are the same as Ford Motor Company, where one of them has a specific question. This encompasses all of those wants and needs from the auto industry to protect themselves, to protect the end user out there in the field that may be using that heat treated component.
To listen or read more about the CQI-9 pyrometry section, go to www.heattreattoday.com and search “Heat Treat Radio CQI-9”
Heat Treat Radio:
Justin Rydzewski and James Hawthorne on CQI-9 Rev. 4
(Part 3 of 4) – Process Tables & New Resources
In this third episode, the trio talks about process tables, their importance, and key information on how to read this revision of CQI-9.
Here’s an excerpt from part 3:
JH: The heat treat system assessment (HTSA) covers the heat treat system and its assessment. There are very unique processes that are covered by CQI-9 and are captured in the process table section of the CQI-9 document.
Process Table A covers carburizing, carbonitriding, carbon restoration, austempering, and precipitation hardening or aging. Section B covers nitriding and ferritic nitrocarburizing. Process Table C covers aluminum. Process Table D covers induction. Process Table E includes annealing and normalizing the stress relief. It goes up to process Table I.
AIAG Cover CQI-9 Edition, 2020
There is a process table for each unique type of heat treat that is out there in the industry and this allows some very specific topics to be covered in those types of processes.
The first portion of it is Process and Test Equipment Requirements. What are the rules of engagement for those items? The same thing for pyrometry. There are specific call outs in the process tables. If this is part of your system, you have to play by these rules. Some of them will point you to specific sections of pyrometry. So, if you’re looking at the thermocouple and calibration of thermocouples, the process table is going to tell you that you shall conform to section P3.1 which covers all of those.
It also covers the process monitoring frequency. How often do you have to check your temperatures? What are the rules of engagement? If you have a batch style furnace that covers that process, it has certain rules for you to manage your batch process.
Then you get into things like inspection – Section 5 of the process table covers things like quenchant and solution test parameters, and the rules for checking that.
What’s really nice about the document is that it’s set up in a way where you can go to the HTSA right from the process table to see if you’re compliant to what’s listed there as the shell statement and the requirements or the frequency for checking those.
To listen or read more about the CQI-9 pyrometry section, go to www.heattreattoday.com and search “Heat Treat Radio CQI-9”
Heat Treat Radio:
Justin Rydzewski and James Hawthorne on CQI-9 Rev. 4
(Part 4 of 4) – Expert Advice
In this final installment, Doug Glenn, Justin Rydzewski, and James Hawthorne field opinion questions as well as practical implementation questions of the new CQI-9 Rev. 4.
Here’s an excerpt from the transcript:
DG: Has CQI-9 been effective in the automotive industry?
JH: I think, 100%, Doug. It’s like IATF—all of the automotive industry has to be compliant to that. Same thing with CQI-9. It provides that commonality for all heat treaters in all the different processes that are employed at their facilities, or the multiple facilities that they may have. For a company like ours, we have eight companies in North America. For the North American side of things that have heat treat furnaces in them, we have induction furnaces, we have carbonitriding furnaces, and we have stress relief furnaces. So that commonality even helps us internally with our management system and how we take steps to provide that common approach and compliance to CQI-9.
JR: I think that also bodes well up the ladder for the OEs. The more people, the more sources that you can go to in order to have work done and have it what you expect it to be, from a quality standpoint.
I think one of the things that CQI-9 has done really well is they’ve made a concerted eff ort to make that document easier to understand and to simplify things down to just its bare bone necessities, whereas some of the other specifications that exist in industry can be lacking.
The intent of CQI-9 was, to a large extent, to be something that you can do yourself and implement yourself. We’ll provide you with the guidance, put it in simple terms, and give you all the research you need to support this on your own.
To listen or read more about the CQI-9 pyrometry section, go to www.heattreattoday.com and search “Heat Treat Radio CQI-9”
Heat Treat Radio host Doug Glenn continues his conversation with AMS2750F expert Andrew Bassett. This final discussion revolves around changes in temperature uniformity survey (TUS) specifications.
Below, you can either listen to the podcast by clicking on the audio play button, or you can read an edited version of the transcript.
The following transcript has been edited for your reading enjoyment.
Doug Glen (DG): In this episode, Andrew Bassett and I have our third and final conversation about AMS2750F. Andrew Bassett is president of ATP and directly contributed his expertise to the latest revisions of AMS2750. If you haven’t heard the previous two episodes, you can find them by Binging or Googling Heat Treat Radio or by simply typing www.heattreattoday.com/radio into your browser.
In the first episode, you and I did some talking about just the AMS2750 generally; what it was, how it’s done, who was on the committee obviously, the fact that it’s not just a minor rewrite, but that it’s a major rewrite and then specifically in that first episode, we talked about thermocouples and calibration. Once we were done with that, we went into the second episode where we talked about system accuracy tests.
Andrew, again, tell our listeners who was involved on the committee. I know that from our perspective, the good folks over at GeoCorp had James LaFollete on the committee and I know Doug Shuler from Pyro Consulting was on there, but who else was on the committee that was responsible for putting this revision F together?
Andrew Bassett (AB): We had Marcel Cuperman from PRI (Performance Review Institute). He is one of the lead staff engineers for the NADCAP heat treat task group. We had Doug Matson from Boeing. Doug Matson, after the release of Rev F went into retirement. He has still been very active on any questions that have been arising with the Rev F. He’s retired, but he’s still in the loop with the specification. We had Brian Reynolds from Arconic. Again, we were looking for various people within the industry, so Brian Reynolds gave us a perspective from the raw material suppliers. We also had Cyril Vernault from Safran Aerospace. We wanted some European influence on the specification, and he is also the task group chairman for heat treat. We had a good, well rounded group of guys that were experts on this, to try to get this next revision put together.
DG: And yourself, of course. Let’s not forget that.
AB: I always like to say that I wrote the good stuff in there.
DG: Before we jump into TUS specifics and some of the major changes there, I want to hit just briefly on training. You and I were talking about this before we hit the record button. The fact of the matter is, there are several different training courses out there. Obviously, these three episodes ought to be helpful to you. A direct call to your cell or to Aerospace Testing and Pyrometry probably wouldn’t be a bad idea if somebody needed help with it. Does ATP also provide a training course?
AB: Yes, we do. We’ve always prided ourselves on providing AMS2750 training. Our training has always been customized to what our customers requirements would be, so every course is not the same. We like to take it to more than just AMS2750. You have to remember, there are other aerospace primes out there that have their own pyrometry requirements. For instance, GE Aviation has their own pyrometry requirements, P10TF3. Rolls Royce has their own pyrometry requirements. Or Pratt & Whitney might have some other things that need to be addressed. We actually sit down with our customers prior to any training and kind of take out the information that is needed, and then we perform the training onsite at the client’s facilities. So that if any other questions arise – “Hey, you’re talking about the SAT stuff” – then I can say, “Hey, let’s go for a field trip” and we can walk right out to the customer’s equipment and kind of demonstrate how to do, let’s say, a proper SAT or proper calibration. Again, we’ll cover various different specifications. For instance, one thing we like to do is find out what types of heat treating they’re doing. If they’re strictly a vacuum heat treating, I’m not going to talk about any of the aluminum requirements. There are some pyrometry requirements when it comes to aluminum, but we’ll talk about vacuum gauge calibrations, which is not covered under 2750, but is covered under AMS2769. Again, each one of our courses is customized to what our client’s needs are.
So, yes, they can feel free to reach out to us. There is myself and Collin Thomas who is an ex-NADCAP auditor for the two instructors for the course, and we’re more than willing to help out with that at any time.
DG: And just so everyone knows, at the end of this podcast, we will mention a couple of other companies and resources that you can go to for training on AMS2750F. I would like to mention, though, just a little self-serving note – and I did this with Google just a minute ago, though I don’t know that it will work on everybody’s location and what not… I Googled “AMS2750F” and Heat Treat Today came up as the second item with an article that we posted back on July 21st called AMS2750F expert analysis of which, Andrew, you were one of the contributors. We had five contributors, I believe, to that article, Doug Shuler being one of them, Peter Sherwin from Eurotherm being another, yourself being one and we had two others, Jim Oakes from SSI and Jason Schulze. I think you had to answer two or three questions and we compiled that. So that’s also a good resource to go to, if you have a moment to do so.
Let’s jump into temperature uniformity surveys (TUS). As we’ve done in the past, basically what we’re doing is asking you, “what were the major changes in this area?” So we’ve broken TUS into five basic questions. Let’s hit the first one now. Looking for the major changes in modifications and repairs section, tell us about that.
AB: In Rev E (the previous revision), there were two sections broken out called furnace modifications and furnace repairs. We put in there the caveat “but not limited to the following things.” If you replaced a hot zone in a vacuum furnace, or you changed thermocouple locations, these would trigger a major modification where you would have to do an initial uniformity survey. We basically took out the repairs function and just left in modification. If any kind of preventive maintenance, or some sort of maintenance function that is done, that would be considered a repair, it’s going to be up to the user’s quality organization to determine if any other testing is going to be required. For instance, if they replace a door seal around a door, quality is going to have to get involved and ask, “Do we need to do a uniformity survey?” What I always tell suppliers out there that are compliant with this is, get with your maintenance team, because the maintenance team typically will know whatever repair they did will have a major impact to maybe a uniformity survey. At that standpoint, repairs will have to be documented, as always, and then quality is going to have to sign off and ask, “Do we need another calibration, an SAT or a TUS?” We’ve put the onus back on the users now to determine if a test needs to be conducted. And then they’re going to have to defend that if they have an audit.
It was kind of silent in the previous revisions of the spec, but it was kind of mentioned that when you move a piece of thermal processing equipment from one corner of the building to the other corner of the building, that you were going to be required to do an initial uniformity survey. I brought up to the team, that these days, they actually make furnaces and ovens with wheels on them. This is for cellular manufacturing. If they have wheels on them to be moved to different locations, it again will have to be on the onus of the quality department to determine if another uniformity or initial survey needs to be done. Maybe they do a quick test on the furnace to make sure it’s within the same realm as the previous testing. We did say that initial TUS may be waived if the furnace is designed to be portable.
Some of the other major changes/modifications were people were always thinking if you changed your control thermocouple, when you replace it with a new one, that you have to do an initial survey. We always said no, you don’t have to do that as long as you put it back in the documented location. But I did see a problem with this when if they change the type of sensor, basically the thickness of the sensor. Maybe they went from a 3/16th sensor down to a 1/8th sensor. Well the 1/8th sensor is going to be more sensitive to temperature change and that could have a major impact on the uniformity. Or if they went from a hot junction that was not exposed to an exposed junction, this again increases the sensitivity. So we added in that as a major modification. If you do change that type of scenario on your thermocouples, then yes, you’d better do an initial uniformity survey.
And lastly, since we’re getting more and more advanced control systems, if you change the PLC logic, the PLCs that control a vacuum furnace or any other type of thermal processing equipment, then you better do an initial uniformity survey. So we kind of beefed up a little bit of the major modifications to address some of the newer technology that is out there.
DG: You said a lot of that was up to the quality department? Is that true, for example, when you went from a hot junction to not? Is that still up to the quality department?
AB: No. That’s now been changed under the major modifications that would trigger an initial uniformity survey. Changing from different types of sensors is not a repair, that is a modification.
DG: How about the way vacuum furnaces and the TUS’s need to be performed there? What were the major changes?
AB: There was really only one major change that we changed for when you conduct a survey on a vacuum furnace. Before, all you had to do was just do your typical uniformities within your temperature ranges for your qualified range of use and your vacuum pressure. If you had a diffusion pump, it had to get below one micron and then just do your survey. But then, I think it was Dr. Shuler, that brought up the idea that said, if people use a back fill gas or use partial pressure, maybe they just need to have one test under partial pressure.
At first, we got a lot of push-back from the suppliers on that saying this is going to cost them extra money and they would have to do an extra test. And we said, no, this is just part of your routine temperature uniformity survey schedule. We’re just saying, at least on an annual basis, you choose a single operating temperature within a defined partial pressure range that you use during production. We just want a survey done that way. You get to choose what gas you’re using, if you’re using argon or nitrogen. The thought process behind this was, if you had a needle valve that maybe was leaking and creating a cold spot in your furnace and you didn’t know about it, it’s more of a preventive thing to ask are those needle valves leaking and are you getting a cold spot in your furnace that you don’t know about. That’s all we’re asking, is just for one survey to be done in any one of your single set point temperatures with any partial pressure gas in the range that you define as your partial pressure. Once we explained it that way, we were able to get over that hump and move forward.
DG: It wasn’t as onerous as it initially sounded, apparently.
AB: Yes, I think the wording in the original draft sounded like it was going to be an extra survey, and I can understand the pushback from the suppliers. We explained that it was not an extra survey, it’s just one during your regular routine survey.
DG: Right. It replaces another one.
AB: Correct.
DG: Question 3. Location of the test thermocouples when you’re under 3 cubic feet.
AB: This was something that I always had an issue with in AMS2750, in the previous revision. How it was stated was that when you have a furnace less than 3 cubic feet, you can do a survey with five sensors. And it said that the five sensors shall be placed in the corners. Well, in a cylindrical furnace, you have eight corners, so what five corners do you choose? My understanding was that when NADAP PRI was teaching their pyrometry course, it was basically the central plane of the furnace. So you would have two thermocouples in the front that were in the center plane and then two in the back in the center plane and one in the center.
And I said, that doesn’t really work so well because you’re not really getting what’s on the top of the furnace or the bottom of the furnace. So, what we ended up doing was putting some new diagrams in the specification that showed that you’re going to go opposite corners. Let’s say you’re going to put one thermocouple in the top left corner in the front and then diagonally across from that will be one in the bottom right corner. Then in the back you would reverse those. So we are covering the top and bottom of the furnace. And the last thermocouple will be in the center. We spelled out a little bit better way of testing these smaller furnaces.
Source: ATP
In a cylindrical furnace, it is stated that those thermocouples should be 180 degrees apart. Again, the NADCAP course would basically put five thermocouples in the center plane of a cylindrical furnace. And we said, no, we want two thermocouples on the top directly 180 degrees apart from each other and then two on the bottom, again, 180 degrees apart from each other, but they should be offset 90 degrees from the top one. You’re getting a better test of your full work zone dimension. I’ve always been doing these testings with these small furnaces in this method because that’s actually an older requirement from an old Boeing specification; the old BAC5621 actually spelled it out this way. We kind of adopted the old Boeing requirement of the smaller furnaces to show a better test for your small furnaces now.
Source: ATP
DG: Right. And let’s be clear, that is for a 3ft3 or smaller furnace. I assume, over 3ft3, you’ve still got nine thermocouples.
AB: Yes, greater than 3ft3 and less than 225ft3, you’ve still got the nine sensors. Once you get above 225 ft3, then the formula is in place in 2750F that spells out how many more thermocouples. I believe we don’t allow it to go past 40 thermocouples in some of those big monster furnaces.
DG: Let’s talk about aluminum for a little bit here. We’ve got radiation test surveys in aluminum furnaces, anything above 800°F; let’s talk about that.
AB: This is actually a surprise that this didn’t get some more pushback when we were putting the drafts out there. Originally, in previous revisions, it said all aluminum solution heat treating furnaces where the heat source is located in the wall, you had to do what’s called a radiation test survey. But we’ve changed the requirement to say all aluminum alloy thermal processing equipment used above 800, also with the heat source located in the furnace wall, ceiling or floor. This is a game changer because this will now put those aluminum vacuum braze furnaces into play. This was typically only a requirement for solution heat treating of aluminum alloys, but now it’s going to be for aluminum brazers. I’m very curious of how this is going to work. A radiation test survey is basically you have to have one 6061 aluminum panel that is 12 inches square with a test thermocouple peened into the middle of it and there is one panel for every 10 cubic feet of wall area. Basically, what we’re looking for is if there is any kind of direction radiation of heat to an aluminum panel as your panels are going to get extremely hot. What they’re looking for is eutectic melting. All aluminum heat furnaces, it’s required by AMS2770 which is the aluminum processing spec that says if you’re processing aluminum, there can’t be any direct radiation to the parts. But in a vacuum furnace, how is it heated? Direct radiation. I’m very curious as to how this is going to play out for those suppliers. Again, I was really surprised there wasn’t a whole lot of pushback from the aluminum vacuum braze facilities that have these types of furnaces that are now going to be required to do this test. It’s going to be interesting how that plays out once 2750 is in full force for everybody.
DG: Yes, and I guess we ought to say that it is not always radiation in a vacuum furnace. If you don’t have back fill gases, ok, it’s going to be all radiation. But if you’ve got some convective heat going on with back fill gases, that is possible. It doesn’t change the point that we’re making here. This is something for people to be aware of if you’re working with a vacuum furnace above 800°F, you’re doing any type of aluminum, then you’ve got a new requirement to do this radiation test.
AB: Yes. It’s the change of the words of ‘solution heat treating’ to ‘all aluminum alloy thermal processes.’
DG: Last question of the five. Documentation requirements. You mentioned there have been some changes. Tell us about those.
AB: We made a few changes to the documentation requirement. Basically from the standpoint of Rev E, we left everything from the original requirements in there, but people were unfamiliar with right after the section that talked about documentation. (The funny thing is we had to change it from reports to documentation. There was somebody that said we don’t want to call it a report because that quantitates that it has to be all in one package, we want to call it documentation. So we appeased that one.) Anyway, in Rev E, it was not part of the documentation records, but should be accessible on site, which were the control instrument tuning parameters, the PIDs or the proportional band reset rate, depending on the instrument manufactures, that those had to be documented for each thermal processing equipment. We thought this is being missed. There are a lot of places that I’ve been to where they don’t even know what the tuning parameters are. So we said from now on you’re going to have to document that in your TUS reports.
It also required to have a diagram of your TUS thermocouple location. That has always been a requirement, but we also now require you to show where the control thermocouple is placed and if you have any recording sensors. If you have type A instrument A or C instrumentation to have the high and low, those would have to be denoted on the diagram for part of the documentation package. We want to make sure that the supplier is aware that we don’t just need to see where your nine thermocouples are located, we also need to see where the control is and any applicable other sensors in the furnace that qualify for A, B or C.
We also want to find out, too, what type of atmosphere is being used in the furnace. Is it air? Is it a vacuum? Are you putting it under carburizing? You now have to list the atmosphere that was done during the testing as well. And then we’re also saying that the TUS test instrument that you’re using, you have to let us know what the correction factors are, even if you electronically apply them to the TUS instrument. You’re allowed to put in the correction factors prior to starting the TUS for your test instrument. A lot of people are saying it’s already been put into the recorder, I don’t need to document it. But we’re saying we still need to know what that correction factor is. So you need to document what those correction factors are.
There are two other things that are new to the documentation requirements. If you have types A or C instrumentation, again with the hot and cold thermocouples placed in there from the last uniformity survey, there shall be an analysis done to make sure that those locations have not changed. There are some requirements in Rev F that say if your uniformity survey is half your uniformity tolerance. In other words, if you’re testing for ∓10 and your final results come out less than ∓5, you can make an easy statement that my survey is within ∓5. No relocation of my hot and cold sensors are required. But you have to do an analysis of those two sensors for types A and C.
[blockquote author=”Andrew Bassett” style=”1″]We also want to find out, too, what type of atmosphere is being used in the furnace. Is it air? Is it a vacuum? Are you putting it under carburizing? You now have to list the atmosphere that was done during the testing as well.[/blockquote]
The other change deals with more of shaker type furnaces or continuous type furnaces, we call them continuous or semicontinuous furnaces. You have to list out what the traversing speeds are during your uniformity survey, maybe whatever your bump rate is for your shaker or the traverse rate. Then you’re going to have to recalculate what your work zone is. With a continuous type furnace, obviously your work zone will shrink the faster the belt goes through the furnace. There needs to be a recalculation of the work zone dimensions based on the survey based on what the belt speed should be.
And then lastly, like we’ve done with all the other documentation, if your service is being performed by a third party, the quality organization of the third party must also approve the reports as well.
Those are the major changes when it came to the documentation for temperature uniformity surveys.
DG: Basically, we’ve hit on three major areas. The first episode – thermocouples and calibration, the second episode – system accuracy tests, and this episode – temperature uniformity surveys. Are there any other odds and ends that you think our listeners should know about?
AB: Absolutely. There are a couple last minute things towards the end of this specification that already passed all the testing requirements.
The biggest pain when it came to Rev E is that we had the requirement for rounding, and that was to the ASTME29 method. That caused a lot of problems. I think we put a number on all the thermocouple suppliers because typically the thermocouple suppliers – when they’re doing their calibration of thermocouples – put everything into Excel. Well, Excel rounds .5 up, like we all learned in grade school. But, E29 doesn’t like that. They like to have if your next significant digit is odd, it rounds up; if it’s even, it stays the same. That put a little hamper on all of the thermocouple guys and we kind of didn’t think that one through.
So, now we’ve changed it in Rev F. The methods that you can use are ASTME29 using the absolute method, that still can stay the same, or you can use an equivalent international standard such as ISO 8001 rule B which is .5 round up, or you round to any commercial spreadsheet, in other words .5 round up. As long as you have documented procedures and you have to use it in a consistent manner. I should say we’ve relaxed the rules, so now you can choose what kind of rounding method you want to use.
We wanted to make sure that we spelled out, too, that all the tolerances in 2750F, if you look at Rev F compared to Rev E, all the tolerance requirements, we used to say plus or minus 10, now it says plus or minus 10.0. It’s an absolute. If you have a survey that you do that is 10.2 and you want to try to round that down, you can never round anything back into compliance. If something does fall out of tolerance by a 10th of a degree, or whatever, you cannot using the rounding function to bring it into compliance.
We addressed a hole that was left in Rev E on your test interval extensions. In previous revisions, we forgot about adding bimonthly and every four months, how many days you can go past an extension for a due date, so we finally addressed that in this revision. It used to be Table 10 and now it’s Table 25. The only thing that’s added onto this is if you do use an extension for any reason, there must be a written justification approved by the user’s quality organization. It can be as simple as: my test came due on Sunday, but I came in and did the test on Monday. You’re just going to have to write a note saying the due date was Sunday and you did it on Monday. You just have to write some justification of that.
Lastly, and I think this is a big thing, as well, is under the quality assurance provision. It is basically the section that says what happens if you have a pyrometry failure and so on. We didn’t change anything in there except two years after the release of Rev F, any third party pyrometry service organization must have a quality system approved to ISO 17025. Also, the scope of accreditation shall include laboratory standards and/or the field services applicable.
Third party service providers, two years after the release, will now have to be 17025 accredited. If they are, there is also no procedural oversight from the supplier. For example, since we’re 17025 accredited for our laboratory, we actually hold two different accreditations, one for our laboratory and one for our field service work for calibrations for uniformity surveys and system accuracy testing. Now, since we are third party accredited, our clients will not be required to have any oversight on us. Personally, I don’t think that’s the best option; I think the supplier should still be able to audit us and look at our procedures to make sure it’s compliant with the industry standards. But according to Rev F, there is no more oversight if we’re third party accredited.
I wasn’t a big fan of adding this in. Again, you would think people that are 17205 like ourselves would be happy to have this in there as it might weed out some other companies, but I’ve actually worked with some really good smaller shops – a two-man father and son that’s located in New York, and then a gentleman in California that is just a single guy, and these guys are very versed in the specification and do thing right. Unfortunately, now they’re going to have to be 17025 accredited. I talked to one of them and he said, “This may put me out of business. I don’t know if I can afford swinging this. I do a good job.” And I said, “I know, I’m trying to fight for you on this,” but it ended up going in. At least we put the caveat that they have two years to get it down, so it’s not something immediate.
DG: Yes, that is the danger when you start requiring certain accreditations, licenses or whatever. It’s typically the small guy that takes the beating. That’s too bad, but that’s the way it is… I shouldn’t be so flippant about that, should I? It is too bad!
AB: I really struggled. Originally, the first draft was going to be immediately, and I said, no, let’s put a moratorium on it for at least two years so people can queue up for that.
DG: I guess the moral of the story for the end user is within two years you need to be asking your third party survey companies/accreditation folks, whoever is coming in to do your pyrometry and whatnot, if they have this 17025.
Anything else? Any other odds and ends?
AB: The last thing I want to add about the 17025 is that this is only for third party suppliers. We’ve received questions like, We do our pyrometry internally, do I have to go get 17025? No, you don’t. It’s only for third party suppliers.
DG: Let’s wrap up with a couple of quick things here. Training. If there are listeners out there who want additional training. We talked at the beginning of this episode about what Aerospace Testing and Pyrometry, your company Andrew, what you guys can do. I’m going to list a couple of other places, I believe, have training, and then if you know of any others you’re comfortable mentioning, please feel free to do so.
I do know, you mentioned, PRI does some sort of training here on this. I believe, a good friend of Heat TreatToday, Jason Schulze up at Conrad Kacsik, have something, and I’m sure they can do custom. I don’t know if they have standard courses or not, but I’m sure they can do some custom stuff. And, I believe that Super Systems also has some sort of training on this. I believe GeoCorp does, or will. But those are the only sources I know. Correct me if I’m wrong on any of those and let me know if there are any other places that people could get training.
AB: I wasn’t familiar with Super Systems or GeoCorp, but everybody is getting onto this bandwagon. But the other course I would also know of is Doug Shuler’s Pyro Consulting as well. He does teach an advanced pyrometry course.
DG: First of all, Andrew, we really appreciate your time doing these three episodes. If people want to get a hold of you, what are you comfortable giving out? We don’t want to give out your cell phone, unless you’re comfortable with it, but certainly emails and things of that sort.
AB: They can give me a call on our office line which is 844-828-7225. If you press 1, that’s supposed to actually ring my cell phone, but sometimes it doesn’t and sometimes it does. You can try the office line or you can reach me through email which is abassett@atp-cal.com or you can hit us up on the website www.atp-cal.com and you can just hit one of the emails of support and let me know what you’re looking for from pyrometry training, or anything else for that matter, and I’ll be more than happy to reach out to you.
DG: If you’re interested in reaching out to Andrew, please try the above. Of course, I’m always willing to take emails and put you directly in touch with Andrew, if you’d like. You can do that by emailing doug@heattreattoday.com.
Doug Glenn, Heat Treat Today publisher and Heat Treat Radio host.
To find other Heat Treat Radio episodes, go to www.heattreattoday.com/radio and look in the list of Heat Treat Radio episodes listed.
