What is the connection between AMS2750 specifications and furnace classifications? With tight specifications, what does the heat treater need to know to be compliant? Follow along as we take a brief look into this often-overlooked topic.
This Technical Tuesday article, written by Douglas Shuler, owner and lead auditor, Pyro Consulting LLC, was first published in Heat Treat Today's March 2023 Aerospace Heat Treating print edition.
Doug Shuler Lead Auditor Pyro Consulting
AMS2750 is the specification that covers pyrometric requirements for equipment used for the thermal processing of metallic materials. AMEC (Aerospace Metals Engineering Committee) is one of the committees which oversees the changes and revisions of AMS2750. There are five main sections in the technical requirements of the specification: sensors, instrument calibrations, thermal processing classification, SAT (system accuracy testing), and TUS (temperature uniformity surveys). Additionally, there are quality provisions that detail what happens if a calibration or test is either past due or fails.1
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Revisions to the original requirements have occurred over the years, with the newest being Revision G. The structure of Revision G has carried over from Revision F and has remained the current structure of the AMS2750 specification. This structure includes furnace classes, which are based on the minimum requirements for temperature uniformity.
Furnace classes are defined in Figure A of Revision D Figure 1.
Figure 1. AMS2750G furnace class uniformity tolerances Source: Doug Shuler
Originally, furnace classes were based on temperature uniformity, but also subzero transformation, refrigerated storage of aluminum alloys, and embrittlement relief, Figure 2.
Figure 2. Original AMS2750 instrument accuracy requirements, no class structure Source: Doug Shuler
AMS2750 Revision C was released in May 1990 and started to implement the class and instrumentation type structure and differentiated between furnaces for heat treating parts versus furnaces for heat treating raw materials. Furnaces for heat treating parts were classified based on uniformity, but also on a readability requirement. Furnaces for heat treating raw materials were classified based on a readability requirement alone.
AMS2750 Revision D was released in September 2005 and continued to define equipment class (Figure A)* and instrumentation type (Section 3.3.1.1)*. It also clarified chart recorder resolution (Table 4)*, print and chart speed (Table 5)*, and testing frequencies for SAT (Tables 6, 7)* and TUS (Tables 8, 9)* for the processing of parts versus raw materials.
AMS2750 Revision E was released in July 2012 and continued to build on the clarity presented in Revision D by adding an instrumentation type table (Figure 3)* instead of a simple text description in the body of the specification.
Figure 3. AMS2750 Revision C: distinguishment between furnaces for heat treating parts versus raw materials Source: Doug Shuler
Moving to AMS2750 Revision F, the specification saw a major rewrite and restructuring where the tables were moved from the end of the document to the first area text that called out the specific table. Revision F also put into place a sunset date for analog instruments.
That brings us to the current revision of AMS2750, Revision G, which has carried forward the structure of Revision F and only sought to further clarify the intent of the requirements.
Over the years, the technology of sensor, instrument, and furnace manufacture and capability has continued to produce better and tighter controls for the process of heat treating. The evolution of AMS2750 has recognized these advancements and has kept pace with them in technology. The understanding of the origins of AMS2750 and how it has evolved is vital in understanding its application to today’s heat treat special processes.
*Specified figure, table, or section is associated with the AMS2750 revision being discussed.
About the Author: In 2009, Douglas (Doug) Shuler became the owner of Pyro Consulting LLC and also began working with Performance Review Institute (PRI), first as an instructor and course developer and later as an auditor for the Nadcap program. As a lead auditor for Nadcap, he has conducted over 380 Nadcap special process and aerospace quality management system audits on behalf of the Aerospace Primes over the past 10+ years. Doug continues to focus on instruction, training, and education for the heat treat industry, developing courses, authoring exams, and employing the PIE method: “Procedures that Include all requirements, and Evidence to show compliance.”
The Metal Treating Institute (MTI) hosted a special meeting for members at the Embassy Suites by Hilton in Downtown Pittsburgh, PA, on Monday, October 17, to review key Nadcap and AMEC topics. During the meeting, members addressed challenges that heat treaters face in Nadcap/audit compliance, how to navigate audits more effectively, and what suggestions to present to the Nadcap committee so that heat treaters would be better equipped for audits.
MTI’s Technical Standards Committee Co-Chairs Bob Ferry, VP of Engineering and Quality at FPM Heat Treat, and Edward (Ed) Engelhard, VP of Corporate Quality at Solar Atmospheres, facilitated the meeting. It was hosted by Tom Morrison, CEO MTI Management, and Jim Orr, president of Penna Flame Industries and current president of MTI. Several attendees who made particularly significant contributions to the discussion were; Doug Shuler, lead auditor at Pyro Consulting, LLC; and Roy Adkins, director of Corporate Quality at Braddock Metallurgical and recipient of the 2022 MTI Award of Industry Merit.
A Room Full of MTI members Including (l-r): Doug Glenn, Ed Engelhard, Bob Ferry, and Doug Shuler
At the meeting, attendees identified the number one challenge in Nadcap/audit compliance is understanding and implementing new Nadcap revisions; a close second was the challenge of ensuring quality when auditors give different feedback. These challenges were addressed in the meeting, especially when discussing two specific topics: first, Auditee Advisories – Type P (Potential Product Impact) and Type C (Confirmed Product Impact) as well as Audit Observations.
Several key points that came out of these discussions were to (1) always read up on the most recent revisions in order to be confident in your compliance with quality standards; (2) be sure to reference objective evidence on the Nadcap Checklist questions to help facilitate the audit; (3) let the Nadcap auditor do their job but address any clarifications/follow-ups to the staff engineer immediately; (4) investigate immediately when receiving a Type P write-up so that you can ask the auditor to add a comment on the limits of that product impact; and finally (5) always push-back on findings that are clearly not valid so that they are “voided” by the Performance Review Institute (PRI).
Another main point of the meeting was to address AMS2750H, an update consisting of editorial and language updates for added clarity.
Lastly, the facilitators of the meeting addressed aerospace standard AS13100: AESQ Quality Management System Requirements for Aero Engine Design and Production Organizations. The standard seeks to harmonize and simplify supplier quality requirements among the major aero engine manufacturers, supplemental to standard AS9100. This standard is in the process of being flowed down to the supply chain and compliance is required January 1 of 2023, meaning that heat treaters have a couple months to get up to standard.
This special meeting happens each year during the October Nadcap meeting in Pittsburgh, PA. MTI encourages heat treaters to attend the Nadcap meetings to share their invaluable voice to guide industry standards.
Photo caption for main image: Jim Orr speaks to members of MTI.
Find heat treating products and services when you search on Heat Treat Buyers Guide.com
One of the great benefits of a community of heat treaters is the opportunity to challenge old habits and look at new ways of doing things. Heat TreatToday’s101 Heat TreatTipsis another opportunity to learn the tips, tricks, and hacks shared by some of the industry’s foremost experts.
Today’s offering includes tips from Quaker Houghton to help you select aqueous quenchant, Pyro Consulting LLC to check your flow, and Nel Hydrogen on how to solve certain compliance issues.
Heat TreatTip #9
Aqueous Quenchant Selection Tips
Aqueous Quenching
1. Determine your quench: Induction or Immersion? Different aqueous quenchants will provide either faster or slower cooling depending upon induction or immersion quenching applications. It is important to select the proper quenchant to meet required metallurgical properties for the application.
2. Part material: Chemistry and hardenability are important for the critical cooling rate for the application.
3. Part material: Minimum and maximum section thickness is required to select the proper aqueous quenchant and concentration.
4. Select the correct aqueous quenchant for the application as there are different chemistries. Choosing the correct aqueous quenchant will provide the required metallurgical properties.
Greenlight Unit
5. Review selected aqueous quenchant for physical characteristics and cooling curve data at respective concentrations.
6. Filtration is important for aqueous quenchants to keep the solution as clean as possible.
7. Check concentration of aqueous quenchant via kinematic viscosity, refractometer, or Greenlight Unit. [Image: Hougton Intn'l Greenlight Unit and/or Houghton Int'l GL Display B] Concentration should be monitored on a regular basis to ensure the quenchant's heat extraction capabilities.
8. Check for contamination (hydraulic oil, etc) which can have an adverse effect on the products cooling curves and possibly affect metallurgical properties.
Greenlight Display
9. Check pH to ensure proper corrosion protection on parts and equipment.
10. Check microbiologicals which can foul the aqueous quenchant causing unpleasant odors in the quench tank and working environment. If necessary utilize a biostable aqueous quenchant.
11. Implement a proactive maintenance program from your supplier. (Quaker Houghton)
Heat TreatTip #10
Go with the Flow!
In the absence of specific calibration requirements, how do you know your flow meters are working properly? Certainly, AS9100D requires gauges that can affect fit, form, or function to be calibrated, and Nadcap requires the meters to be correct for the gas used and checked for proper function as part of the PM schedule. Often generator issues can reveal problems with flow meters. Check the meter when the furnace gas is off. If the float does not drop to the -0- mark, it’s an indication that carbon soot has built up inside the chamber of the meter. This condition can be detected early by looking for tiny black carbon particles floating around in the flowmeter oil. Proper PM should include removing the float for cleaning and replacing the float oil regularly. (Pyro Consulting LLC)
Heat TreatTip #11
Compliance Issues? Try On-Site Gas Generation
On-site gas generation may help resolve compliance issues. Growth and success in thermal processing may have resulted in you expanding your inventory of reducing atmosphere gases. If you are storing hydrogen or ammonia for Dissociated Ammonia (DA), both of which are classed by the EPA as Highly Hazardous Materials, expanding gas inventory can create compliance issues. It is now possible to create reducing gas atmospheres on a make-it-as-you-use-it basis, minimizing site inventory of hazardous materials and facilitating growth while ensuring HazMat compliance. Modern hydrogen generators can serve small and large flow rates, can load follow, and can make unlimited hydrogen volumes with virtually zero stored HazMat inventory. Hydrogen is the key reducing constituent in both blended hydrogen-nitrogen and DA atmospheres—hydrogen generation (and optionally, nitrogen generation) can be used to provide exactly the atmosphere required but with zero hazardous material storage and at a predictable, economical cost. (Nel Hydrogen)
Generate H2 and N2 on-site – saving money, improving safety, and reducing carbon footprint.
AMS2750F, a rewrite of the specification that covers pyrometric requirements for equipment used for the thermal processing of metallic materials, was released at the end of June. For this Technical Tuesday feature, Heat Treat Today asked a few experts in the aerospace industry to share their insights of this much anticipated revision that helps to better clarify issues with the previous revision. Specifically, Heat Treat Today wanted to know what they perceived to be the top 2-3 most important changes in revision F; what companies should do to prepare for these changes; and additional thoughts about the revision as it relates to aerospace heat treating.
Andrew Bassett was on the subteam for AMS2750F as well as the previous revision AMS2750E and has been a member of AMEC and SAE Committee B since 2006. He shares some “inside baseball” background about this four year process, “The AMS2750F subteam utilized the Nadcap Pyrometry Reference Guide, the Nadcap Heat Treat Audit Advisories that pertained to Pyrometry, and the collective experience from the sub-team which dealt with the previous revision issues and problems. The AMS2750F sub-team had a broad range of backgrounds, with representatives from Boeing, Safran, Arconic, GeoCorp Inc, Nadcap-PRI, and Aerospace Testing & Pyrometry.”
What do you believe to be important changes in revision F?
Jason Schulze, Director of Technical Services; Special Process – Metallurgy, Conrad Kacsik Instrument Systems, Inc.
Jason Schulze comments on offsets saying, “Offsets have often been a confusing subject throughout the years. How they are applied, removed and documented has caused confusion and has been a source of Nadcap findings. With the changes to the offsets section of AMS2750 in the new revision, these issues will be greatly reduced. Offsets have now been split into two categories; correction offsets and modification offsets. It will be important for suppliers to understand and implement the new requirements as well as use the same verbiage as this will hopefully alleviate further confusion.”
Andrew Bassett, President, Aerospace Testing and Pyrometry
Andrew agrees this is an important change regarding the offsets and further clarifies, “A “Modification Offset” is when an instrument is purposely, either through electronic means or manual means, shifts the accuracy away from the nominal temperature. This is typically done to “center a temperature uniformity” that may be skewed in one direction or another. The modification offset, when used properly, will shift the temperature uniformity more towards the set point of the thermal processing equipment. A “Correction Offset” is used to bring the instrument back to the nominal temperature. As always, a well defined procedure will be required on how the “Correction Offset” and “Modification Offset” will be introduced into your system.”
“One of the biggest changes that caused a lot of controversy was the restricted re-use of expendable test thermocouples,” Andrew notes. “The AMS2750F subteam provided studies and data that showed that there was considerable drift of certain types of base metals thermocouples, especially when it came to Type “K” thermocouples. The previous revision of AMS-2750 already had restrictions on these types, but after providing data of the drift of these thermocouples, the team felt further restrictions were required for Expendable Base Metal SAT & TUS Sensors. Section 3.1.7.3 describes the limitations of these type thermocouples. Types “M”, “T”, “K” & “E” shall be limited to 3 months or five uses, whichever occurs first between 500F and 1200F (260C and 650C) and is limited to single use above 1200F (650C). Types “J” and “N” shall be limited to 3 months or ten uses, whichever occurs first between 500F and 1200F (260C and 650C) and is limited to single use above 1200F (650C).”
Peter Sherwin, Global Business Development Manager for Heat Treat, Eurotherm by Schneider Electric
Peter Sherwin comments on instrumentation, “From an instrument perspective our no.1 focus is the instrument accuracy specification. This has not changed for Field Test or Control and Recording Instruments (now in Table 7), however the impact of the decimal place for digital recorders could cause some issues for less precise instrumentation. In 3.2.3.1 All control, recording and overtemp instruments shall be digital 2 years after release of AMS2750F – this was not a surprise, and today’s overall cost (paper, pens, storage etc.) of paper chart recorders cannot match their digital counterparts. Digital time synchronization (3.2.3.19) is also sensible to ensure you have an accurate time record across a number of Furnaces/Ovens and charts – we are used to this for other regulations (e.g. FDA 21 CFR Part 11) and offer a SNTP/Time Synchronization feature in our Recorders.”
Jim Oakes, President, Super Systems, Inc.
Jim Oakes shared his pleasure with section 3.2.3.12, “I was happy to see the document address integrated recording/controlling data. It states in section 3.2.3.12when the control and recording system is integrated such that the digitally displayed control value and digitally recorded value are generated from the same measurement circuit and cannot be different, it is only necessary to document a single displayed/recorded value for the control reading. This is happening through direct communications, so what you see on the controller is what you are recording electronically. This saves a step and eliminates the need for additional documentation.”
Doug Shuler, Lead Auditor, Owner, Pyro Consulting LLC
Doug Shuler cites the auditor advising piece, “The top of the list has to be the overall progress we made by incorporating auditor advisories and pyrometry reference guide FQS into the body of the specification so users don’t have to ask themselves “What did I miss.”
How should companies prepare for these changes?
Jason Schulze’s advice to companies focuses on training, “Companies should receive concise training regarding the revisions within AMS2750F, including administrative and technical. As with any training, continuous courses may be necessary to ensure comprehension. I recommend performing a characteristic accountability for each and every requirement stated within AMS2750F.”
Peter Sherwin encourages companies to ready instrumentation for the standards, “Recent feedback from the MTI indicated that 3rd party audits to the new standard would probably start next year. However, if you are in the market for a new instrument then it only makes sense to ensure this meets the requirements of the updated standard.”
Doug Shuler sees the benefit of analysis, “Users should prepare by performing an internal or perhaps an external gap analysis to establish where their pyrometry system is today, and what has to be changed going forward. Users don’t have to wait until AMS2750F and AC7102/8 Rev A are released and in effect before making changes. The key is that if a user has an audit before the revised Nadcap Checklist AC7102/8 Rev A becomes the law of the land, they will have to declare compliance to AMS2750E or AMS2750F in full and will be held to that revision’s requirements. Once AC7102/8 Rev A takes effect (best guess after January 1, 2021) all audits will be done to AMS2750F.”
Andrew Bassett recommends, “First and foremost, get a copy of AMS2750F and start the review process. Since the document was a complete re-write, there is no change summary or change bars to point the supplier in the direction of what has changed. Spend time creating a matrix of the previous requirements (AMS2750E) and comparing to the new requirements (AMS2750F). I would suggest breaking this matrix down into four main sections: Thermocouples, Calibrations, System Accuracy Testing, and Temperature Uniformity Surveys. This will allow suppliers to work on each section without getting overwhelmed by the entirety of the specification. Currently at the time of writing this, there is no formal implementation requirement for AMS2750F. Typically this will either be dictated by the suppliers’ customers, or in the case of Nadcap, they will issue a “Supplier Advisory” as to when their expectation for implementation will be.”
Final Thoughts
Planning for the future will serve companies well for the long term encourages Doug Shuler, “With a number of significant changes, nearing a complete rewrite, now is a good time to take a look at your internal procedures that may have become fragmented over the years and streamline them to the new revision. Auditing for Nadcap for over 10 years has shown me one thing for sure. Those companies that have a thermocouple procedure, a calibration procedure, a SAT procedure, an alternate SAT procedure, a TUS procedure, and maybe even multiple TUS procedures for different kinds of furnaces (Air, Vacuum, Atmosphere, etc.) usually have a more difficult time with audits because the SAT procedure also addresses thermocouples, but doesn’t address correction factors because that’s in the instrument calibration procedure… See where this is going? Consider writing one pyrometry procedure with sections in it just like the specification. Then, the SAT section can refer to the thermocouple section for test thermocouples and to the instrument section for test instruments, etc. It’s like re-writing AMS2750, but customized for your facility, your equipment, and your practices. In the end, remember that the pyrometry portion of your Nadcap audit follows my P.I.E. acronym. Procedures that Include all requirements and Evidence to show compliance.”
Paying close attention to the right data solution will alleviate potential headaches when dealing with both the new AMS2750F revision and the CQI9 (V.4 update) says Peter Sherwin, “Many commercial heat treaters will also have to cope with the update to CQI9 Version 4 at the same time! According to the MTI, your ‘end’ customers may request you perform your self-audit to the new standard from this point forward. There is a bit more time allocated to move to digital (3 years), but my advice would be to take advantage of digital solutions sooner rather than later. The right data solution should save you money over time compared to the paper alternative.”
Finally, amidst all the new changes AMS 2750F has offered, Jim Oakes assures, “…the pyrometric requirements that most of us are used to will still be very familiar as this document becomes the new standard.”
Our Reader Feedback feature allows us to facilitate discussion between Heat Treat Today‘s content contributors and hard-working folks in the shop who have questions about an article.
This Reader Feedback exchange followed an inquiry to our publisher Doug Glenn about government regulation of heat treatment of firearms which we threw out to a few of our consultants and individuals who have knowledge and expertise in this field — and we added a few questions of our own. Our experts are Doug Shuler, lead auditor with Pyro Consulting LLC;John Quaglia, president of Bennett Heat Treating and Brazing; and Jamie Jones, president of Solar Atmospheres. If you have any questions about this or other topics you’ve seen covered on any Heat Treat Today platform, please submit them to editor@heattreattoday.com.
Do you know if any type of firearms license is required to heat treat firearm components?
Doug Shuler
Doug Shuler: It depends on which components are being heat treated. Barrels, slides, etc. do not require a license, but if the receiver (the part with the serial number) is heat treated, a license is required and the heat treater is subject to ATF audits. . . . Basically, if serialized parts are heat treated it must be done under an FFL (Federal Firearms License) so the ATF can audit the whereabouts of any firearm at any time.
John Quaglia
John Quaglia: To the best of my knowledge, based upon some pretty extensive experience heat treating firearm components for one of my customers, the only license I am aware of is an FFL which is required toheattreatserializedreceivers. If the components are military or ITAR controlled, you must be registered with the DDTC and have ITAR certification, [as well as] for domestic (commercial firearms) if you are heat treating serialized components of a firearm (the receiver). Barrels, slides, sights, magazines, springs, firing pins, etc., are all easily acquired and interchangeable between firearms and therefore require no special permitting.
Jamie Jones
Jamie Jones: The US Department of Justice authorizes the ATF to regulate those who are manufacturers, dealers, collectors, and importers of firearms and destructive devices. Part of that regulation requires a license (Federal Firearms License [FFL]) be applied for and held by those who are involved with any of the above. For a contract heat treat company, this essentially only pertains to serialized components. Under the “manufacturing” definition, the ATF considers any activity which results in the manufacture of firearms for sale or distribution (including installing parts in or on firearm frames and receivers, and processes that primarily enhance a firearm’s durability), constitutes firearms manufacturing, and requires a manufacturer’s license. The FFL does not include components related to fully automatic firearms or suppressors. In order to possess and process those serialized items, the ATF requires a manufacturer’s FFL plus a special occupational tax stamp (SOT). Prior to issuance of the FFL, the ATF will conduct an on-site audit of the operation and person(s) applying for the license/stamp. The FFL needs to be renewed every three years.
What is the most challenging part of heat treating gun parts?
Spring Loaded Firing Pin thetruthaboutguns.com
JQ: Managing distortion is probably the most challenging as most components are very close to being finished machined. Special racking and methodizing is often required. Marquenching, ausquenching, and vacuum processing are often employed to minimize or eliminate the possibility of distortion. Also, due to the small size and complex geometry present, inspection of the parts is difficult. It is important to clarify the testing location with the manufacturer prior to punching hardness holes into areas of the parts that may be exposed after assembly. After all, manufacturers want their guns to look nice afterward. We have experienced delayed rusting on barrels due to the combination of steel wire and the 4150 barrel reacting to cause anodic corrosion after processing in a salt bath which would only expose itself after a few days. We would ship parts that were perfect, and two days later I would be on the phone with my customer trying to explain a mysterious rust line through the rifling in the barrel. We solved this with some tooling changes.
JJ: Frankly, it is no more challenging or different than heat treating any other parts for any other industry. Some parts are routine and some are challenging. Some materials are more challenging than others and some designs are more challenging than others.
Which parts are the most difficult and why?
BCM PNT™ Trigger Assembly Bravo Company USA
JQ: They all present challenges. Slides and barrels present challenges due to the non-symmetrical nature which require special setup procedures. These also tend to have lots of crevices and blind or small holes which trap quenchants, salts, cleaning materials which tend to lead to unhappy customers unless the parts are thoroughly cleaned. Magazines present challenges because they are thin steel stampings which tend to distort due to the quench and induced stressed relieving themselves during heating. I could write a book on the challenges we have faced with the processing of gun parts.
JJ: Parts that require carburizing which have been machined to a finished or near-finished state, with intricate designs, cut-outs, and varying cross sections are the most challenging; a perfect example of this is an AR bolt carrier. This kind of challenge is why we developed our version of low-pressure vacuum carburizing, as we now don’t need to worry about severe quench distortion or carbon potential control. With traditional carburizing, the austenitizing temperature of the steel can change if too much carbon diffuses into the corners and edges. This can lead to retained austenite and carbide formation. Our process negates that phenomenon by using precisely controlled boost-diffuse controls instead of carbon potential. Our process also leaves the parts bright, with no post carburizing blasting or cleaning operations required.
Is it the materials that make it difficult or is it the configuration of the part?
JQ: The materials tend to be common that most heat treaters have worked with before so from a metallurgical standpoint I would say that the materials are not the problem. The configuration of the parts is definitely worse. Non-symmetrical parts tend to distort more than symmetrical parts. It also makes it difficult to inspect the parts. Test in the wrong area and you have spring-back or rocking. As I mentioned earlier, if you test in the wrong area the customer cannot sell the part. Some gun manufacturers have test methods that are unconventional, testing a shallow case depth using an HRC scale, so that the hardness reading is a combination of the case hardness, case depth, and core hardness.
JJ: It seems like you are assuming it is difficult all of the time! Please see my answer to question 2 above.
Are there any other special processes or regulations that need to be followed when heat treating gun parts? If so, what are they?
JJ: This answer is not to be taken as legal advice. If you want to apply for an FFL, or you get an FFL, you need to know the regulation. It is serious business: if you don’t follow regulation, you could end up in prison. You need to keep detailed records of EVERY serialized component that you receive, process, and ship. You don’t want to be on the tail end of a missing part or parts, especially if you don’t know about it. If something goes missing you need to report it immediately. Of course, reporting it could mean losing your license. So my advice to anyone considering this is: BE GOOD AT TRACEABILITY and RECORD KEEPING!
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What is the connection between AMS2750 specifications and furnace classifications? With tight specifications, what does the heat treater need to know to be compliant? Follow along as we take a brief look into this often-overlooked topic.
Find heat treating products and services when you search on Heat Treat Buyers Guide.com
