Achieving the elimination of oxidation during thermal treatment has driven heat treaters for decades and resulted in a wide variety of approaches. The obvious method is to flow an inert gas such as nitrogen into the furnace in order to drive out both air and moisture. By itself, however, this technique is inadequate.
The zirconia carbon sensor has been used for nearly three decades to control the carbon potential in many carburizing applications. Today’s best of the web article examines the use of the zirconia carbon sensor in a variety of annealing and special treatment applications and considers how the sensor millivolt output is preferred because it relates directly (not empirically) to the free oxygen concentration in the surrounding environment.
An Excerpt:
“While it is desirable to avoid oxidation during thermal treatment, the achievement of adequate control using one of the ‘getter’ gases requires that the sensor millivolts achieved be established at some value higher than the vee formed by the iron reaction at temperatures below 1375ºF and the carbon reaction above that temperature. The vee will demonstrate the lower limit, but the practical level should be established by evaluation of product quality, getter cost and possible sooting. The appropriate level will be limited by such things as furnace leaks, atmosphere agitation, work porosity, time of treatment, etc.”
Heat treat industry players from across a spectrum of facilities, suppliers, and manufacturing specialties landed in Pittsburgh, Pennsylvania, on Monday, September 24, 2024, to kick off Heat TreatBoot Camp 2024. Attendees networked, gained new practical knowledge, and participated in a tour of a local commercial heat treating facility. It wasn’t all work; an opportunity to get to know one another at a meet-and-greet reception upon arrival and later on a trip up Pittsburgh’s Duquesne Incline allowed boot campers to relax and connect, balancing work with fun.
A day and a half of sessions led by instructors Doug Glenn, publisher and founder of Heat TreatToday, and Thomas Wingens, president/CEO and founder of WINGENS International Industry Consultancy, brought the 39 trainees up-to-speed on “Processes & Materials,” “Heat Treat Players,” “Latest Heat Treat Developments,” and more. Questions and discussion were encouraged during the formal sessions, and heat treaters had plenty of informal, additional learning time through interactions with each other and the instructors.
At the end of the first day of lectures, nearly all of the attendees boarded a school bus to visit the Duquesne Incline on Mount Washington and enjoy the view of Pittsburgh. Following another day packed with training and resources, attendees had the option to visit Solar Atmospheres in Hermitage, Pennsylvania, to tour the in-house vacuum heat treating and brazing facility.
Ike Okoh Product Engineer Dry Coolers
“I’ve enjoyed talking about the different types of heat processes and the types of furnaces — vacuum and atmosphere air systems,” said Ike Okoh, a product engineer with Dry Coolers, Inc, based in Michigan. “The questions I had before the course started were answered during the course, and the most beautiful part of the program was that it’s not always you get to see CEOs and or business owners in the training sessions with you. It’s wonderful to get to meet them and find out more about them and their companies.
“The instructors, Doug and Thomas, were really nice, went through the course and broke down some of the issues, took questions and answered them,” Okoh added. “All in all, it’s been an enlightening experience.”
“Every group that’s been here is different,” said Glenn. “This group has been really fantastic; it’s an engaging group, and overall, we’ve heard positive feedback that the sessions and networking have been helpful. So, thanks to everyone who has come, and we look forward to seeing others next year.”
Highlights of the Event
Monday evening’s meet-and-greet allowed participants to network and connect.
Days 1 and 2 of instruction from Doug Glenn and Thomas WingensField trip to Pittsburgh’s Duquesne Incline after Day 1 of instructionHTBC 2024 team and attendees
Keep your eyes open for your invitation to join us in 2025 for our fourth year of training up heat treaters of the future. Be sure to register early and bring friend and coworkers!
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.
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.
"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.
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.
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.
You can’t always get what you want. With frequently changing specifications and a volatile economy, what heat treaters want is always evolving. But what they need changes, too. Steven Christopher of Super Systems, Inc. discusses how to balance what vacuum furnace operators NEED and what they WANT. Is the difference between those two things too great?
This article originally appeared inHeat TreatToday’sMarch 2022 Aerospace print edition.
Steven Christopher West Coast Operations Manager Super Systems, Inc. Photo Credit: Super Systems, Inc.
I love metaphors and think of vacuum furnaces as automobiles. As an owner, the goal is to keep our cars on the road for 100,000+ miles — and why not the same for furnaces? Accomplishing this feat requires the same in both cases: (1) routine maintenance — literally changing oil and (2) addressing warnings before they become problems — such as check engine lights or vacuum leaks.
The similarities stop there, however, with a key difference in how each is upgraded. In the near future, if you want a self-driving vehicle you will have no choice but to turn in the keys of your 10-year-old sedan and buy a shiny new Tesla, opting for the autonomous driving upgrade.
But what about your vacuum furnace? As the industry releases all these new standards and specifications, do we also need a newer furnace? Or can we retrofit what we have? That answer is complicated because so much is influenced by what we WANT versus what we NEED.
Day-to-day production shapes what we want. We learn from both experiences and failures, shaping features we want to improve operations, customer experience, and reduce rejected work. Specifications and customers drive what we need. Most recently AMS2750F (and 2769C) have been revised and place a burden on operating aging equipment while maintaining compliance. Before these, NFPA86 was modified in 2019, improving furnace design and safety “best practices."
These requirements levy real costs in terms of both hardware investment and increased labor (additional quality employees). We are expected to perform additional labor with the same workforce; however, the reality is that a worsening domestic labor shortage often means we are doing more work with even fewer people. This article navigates this delicate balance, maximizing each investment dollar’s impact while reducing our reliance on labor.
What We Need
It becomes impossible to completely address such large specifications in a short article, so let me highlight a few important considerations from AMS2769C:
Section 3.2.3.2 requires decimal precision for thermocouples (AMS2750F)
Section 3.3.1 reviews partial pressure and dew point requirements
Section 3.5.2.1 addresses permissible outgassing
Section 3.5.3 covers load thermocouples
Perhaps the most talked about change is the requirement of thermocouples to record to a tenth of a degree. It is important to distinguish the difference between a temperature controller and recorder. Section 3.2.3.2 does not require a furnace to control with decimal precision, only record to it. However, best practice lends itself to controllers supporting this ability as well.
Exposure to oxygen at elevated temperatures is detrimental to part metallurgy, be it aesthetics or integrity. Leak-up rates are so important because they prove such exposure is eliminated (or significantly reduced). AMS2769C attempts to mitigate this exposure by standardizing the best practices for performing such tests. Leak-up rate tests are required weekly for (minimum) 15 minutes. Figure 1 identifies a maximum allowable leak-up rate based on the material being processed.
Historically this requires an operator to initiate a cycle, stop the evacuation (pumping), then document the beginning and ending vacuum levels by hand. While simple, this requires both time and attention, preventing any operator from performing other tasks.
AMS2769C proceeds by addressing outgassing, requiring ramp/soak controllers to either be placed on hold or to disable the heating elements if the vacuum level exceeds (1) the partial pressure target or (2) the diffusion pump operating range. Aging controllers require well-trained operators, constantly monitoring vacuum instrumentation and manually adjusting the controller. This introduces potential for operator error, again limiting their ability to perform other tasks.
Section 3.5.3 details placement and requirements for load thermocouples. Assuming load thermocouples are required, runs may be rejected should thermocouples fail below the minimum processing temperature. Disconnected control systems monitor load thermocouples using a recorder separate from the ramp/soak controller. This complicates the control system’s ability to alert operators to such failed conditions — the recorder not knowing which thermocouples are required.
AMS2769C progresses to cover partial pressure. Partial pressure has been automated for years with minimal changes to control mechanisms, though some have replaced solenoid valves with mass flow controllers (MFCs). System upgrades should strongly consider automatic gas type compensation and digital communications of vacuum levels.
Thermocouple (or pirani) vacuum sensors estimate the heat emitted from a heating filament within the sensor. This measurement represents an exact vacuum level, though the gaseous media separating the fi lament from the measuring tip influences the reading (thermodynamics heat transfer). This phenomenon (represented in Figure 2) explains why nitrogen and argon result in very different vacuum estimates.
Figure 2. Gas compensation graph Photo Credit: Televac MM200 User Manual
NOTE: Thermocouple gauges operate in vacuum ranges where enough gas molecules remain (e.g., in excess of 1 micron) to influence this reading; unlike cold cathode sensors which operate under complete vacuum, excluding them from such compensation.
As an example, consider a vacuum furnace operating under nitrogen partial pressure. The vacuum instrument correctly displays 200 microns (refer to the AIR curve). Now consider the same cycle, only the operator introduces argon. The display now incorrectly displays (and controls to) 200 microns; however, the furnace is truly operating closer to 100 microns (refer to the ARGON curve).
Figure 3. Dew point requirements Photo Credit: AMS2769 Section 3.3.1.1
Historically vacuum signals have transmitted a 0-10vdc analog signal representing the vacuum level. As with all analog signals, error is introduced by both the accuracy of the instrument generating the signal as well the recorder interpreting it. This error is mitigated by routine calibrations — often aligned with temperature uniformity survey (TUS) schedules. Modern control systems replace such signals with vacuum instrumentation supporting digital communications, eliminating error in the process. As a bonus, the reduction in calibration points reduces time when performing calibrations. Such systems may even automatically compensate thermocouple sensors resolving the sensitivity of thermocouple sensors to multiple gas types.
AMS2769C references other specifications, namely AMS2750 and the Compressed Gas Association (CGA). CGA establishes minimum requirements ensuring inert gas quality. In addition to supplier certification, gas quality is proven by dew point. All gasses have a dew point, with outside air relatively high (e.g., +50°F) and inert gas very low (e.g., -100°F). Purchasing supplier certified gas results in a facilities bulk storage tank having a very low dew point, with any leaks in gas delivery system (pipe threads, fittings, etc.) resulting in a less negative dew point. The concept that dew point can only raise once exiting the storage tank illustrates the importance of sampling “as the gas enters the furnace” — measurements taken upstream fail to detect leaks downstream. The intensity of this increase directly correlates to the amount of air (oxygen) entering the gas supply, compromising the gas purity, which as previously discussed negatively impacts the parts being processed. Proving a dew point below -60°F proves the inert gas mostly free of oxygen. Measurements have long been a manual process; an operator samples gas using a portable sensor and records the findings in an entry log. Modern systems seamlessly integrate dedicated sensors continuously sampling gas quality which alert upon compromised gas.
What We Want
This article’s first draft opened this section listing a handful of features — that was November. Fast forward three calendar months (what feels like an entire year), it is now January, and priorities have changed. Three months ago we wanted features, now we just want parts. The growing supply chain disruption is feeling less temporary and more permanent. This final draft opens with availability. Any upgrades should factor both (1) component lead-time and (2) their flexibility. Lead-time should focus not just on immediate project delivery, but the long-term availability of the product. Is it in its infancy? Or near the end of its life? What is the current lead-time and strategies to maintain inventory? Flexibility should focus on limitations of the product. Is it limited to specific applications? Or can it be used in other equipment? Flexibility paired with planning results in standardization. Keeping with the automobile theme, standardization is what made Henry Ford’s Model T so special. Standardization reduces on-site spare parts, as the same component can be installed in many locations. Standardization should be a primary focus when purchasing programmable logic controllers (PLCs), vacuum instruments, and temperature controllers.
As if the supply chain worries are not enough, the U.S. faces a labor shortage projected to worsen over the next decade. This highlights another late addition to this article, stressing the importance that any upgrade considers the availability of the most important resource: people. New furnaces and upgrades alike (like it or not) develop a co-dependence between multiple parties. This relationship may be internal, between operations and engineering; or external, between an end user and a supplier. No matter the specific situation, all parties should discuss availability and access to information. Failure to discuss this early on is often exacerbated, especially when upgrades are performed by a supplier who is considered (1) unresponsive or slow to respond and (2) unwilling to share information. Purchase orders should document expectations in terms of deliverables (PLC logic, schematics, etc.) and support.
Figure 4. Projected US labor deficit Photo Credit: US Department of Labor
This third paragraph was that ill-fated November draft’s first. Today’s buzzword, the Internet of Things (IoT ). As we are well on our way to the quarter mark of the 21st century, we have all become accustomed to a lot of quickly accessible information. Why should vacuum furnace recorders not meet the same lofty expectations? Control system upgrades should be capable of recording information and displaying it in an easily retrievable format. Recorded data should expand beyond the required process data into the status of the furnace itself (valve position, state of limit/thermal/vacuum switches, motor status, etc.). Such data can be evaluated postmortem to troubleshoot a failed production run’s root cause of the failure. Advanced systems should be able to notify personnel of issues via email or text messaging.
Often the information gathered above is passed into a Supervisory Control and Data Acquisition (SCADA) System. This system must meet industry compliance for data integrity and security. As every new software seems to have its own system, daily operation requires most to juggle many of these systems, often sharing common data. A SCADA System should be designed to operate in this unknown environment and be capable of sharing data between itself and Enterprise Resource Planning (ERP) and other supervisory systems. The first step here is to build upon common platforms; and today the most widely accepted platform is Microsoft SQL Server. SCADA Systems should be able to “offer up” data using any number of industry standard protocols (Modbus, API, OPC, etc.).
The biggest invisible threat to our industry is internet security. For those fortunate enough to have avoided a cybersecurity attack, IT’s work seems a burden. For those unfortunate to have experienced such an event, IT’s work is beloved. This rapidly changing frontier is our reality and programs like Cybersecurity Maturity Model Certification (CMMC) become a necessary (even required) precaution. Hardware for upgrades should be vetted for compliance with these evolving precautions.
Thus far this article has focused on people, hardware, and features. I now turn the focus to the vacuum furnace itself. Furnaces routinely struggle with passing TUS at both lower (<1000°F) and elevated (>2000°F) temperatures. The issue itself varies between graphite and molybdenum hot zones but the root cause remains the same: inflexibility with rheostats to adjust across a wide temperature range or the furnace’s incapability of reaching elevated temperatures. Users manually adjust the applied power to each zone in attempt to minimize the difference between the coldest and hottest TUS thermocouples. Rheostats force the user to settle for a configuration “just good enough” for all temperatures but “not perfect for any.” Modern systems replace rheostats with individual silicon controlled rectifiers (SCRs) driving each variable reactance transformer (VRT), a feature commonly called digital trim. All furnaces are candidates for digital trim, though older VRT packages using slide wire (or “corn cob”) resistors may require the addition of direct current (DC) rectifiers in addition to SCRs. The benefit of digital trim is these settings can automatically adjust with temperature allowing for the ideal configuration at every temperature.
How Do We Get There?
Resurrecting the automobile analogy which opened this article, have you ever wondered why so many people love Jeep Wranglers (and I realize Jeep could easily have been Harley Davidson or a new home purchase)? The reason is not what they are, rather what they can become. Owners see upgrades and features in their mind long before anything is modified. The key concept here is customization. This same vision applies to vacuum furnaces, any upgrades should consider robust and powerful control systems, flexible enough to evolve with the industry.
PLCs and process instrumentation should always be sourced with room to grow. Modular designed platforms easily expand to integrate new hardware. Ask suppliers how their hardware handles additional inputs, outputs, and sensors. Instrumentation should be integration-friendly and be capable of monitoring the entire vacuum ecosystem — considering the temperature, load thermocouples, and vacuum and gas control systems. Ideally, instrumentation will communicate with each other, passing relevant information between each while simultaneously eliminating calibration points.
Control systems should be sourced with an Evolution Plan in place; compliant solutions today in no way assure compliance tomorrow. Suppliers should be asked their plan for AMS2750G, H, and I. Doing so positions you to make large investments once, then grow hand-in-hand with the industry rather than fight it every time it changes.
Summary: Have a Plan
Modern controllers consolidate a furnace’s self-contained subsystems (vacuum, load thermocouples, valve control, etc.) into a singular control system. This provides the transparency necessary for the controller to alert operators or place itself on hold when necessary. The outcome is that operators require less time monitoring the subtleties of production, meaning they focus their time on more urgent tasks. A happy byproduct becomes the natural progression of data (the recorded values from all these subsystems) into information (meaningful, document values presentable to customers, reviewable by auditors, or referenced for troubleshooting).
I was once told to either open or conclude an article with a poignant quote, so let me offer this advice: When considering upgrades for any furnace “have a plan or become part of someone else’s.” Early conversations between engineers/suppliers and quality/production ensures the delivered product shares everyone’s goals.
About the Author
Steven Christopher is a Purdue University engineering graduate and a 15-year veteran of the heat treating industry. He began his career in pharmaceutical maintenance before joining a commercial heat treat facility focusing on the automotive and aerospace industries. He now manages Super Systems' West Coast operations supporting all types of industries west of the Rocky Mountains.
For more information, contact Steven at schristopher@supersystems.com
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A batch sintering furnace will be installed at Mueller Brass Co., a major supplier of brass rod and forgings in the United States. The 60" wide x 90" deep x 30" tall atmosphere box sintering furnace includes an accelerated gas cooling system to improve floor-to-floor cycle time and meet their demanding production needs.
This Gasbarre Thermal Processing Systems box furnace is designed with a maximum operating temperature of 1650°F, a capacity of 14,000 lbs., and utilizes a nitrogen atmosphere. The system incorporates an Allen-Bradley PLC with SSi 9130 control and 12.1" HMI display. Additionally, the indirect fired gas heating system incorporates parallel positioning control for efficiency and process flexibility, and an integrated oxygen analyzer gives Muller Brass Co. the proper furnace environment prior to heating.
Tall atmosphere box sintering from Gasbarre Thermal Processing Systems Photo Credit: Gasbarre Thermal Processing Systems
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.”
A Pennsylvania producer and provider of steel wire and rod products, Liberty Wire in Johnstown, PA, underwent an intensive nitrogen-methanol controls upgrade for a continuous furnace line. The process included a new control system and panel for a continuous annealing furnace line to process coiled wire products.
SSI Controls Matrix (photo source: Super Systems Inc.)
Mike Cassidy, the Liberty Wire Controls Analyst, led the installation with Super System Inc. (SSI) project engineers, “I’m very pleased with SSI and the new system... I’m looking forward to working with them in the future.”
The SSI Matrix control system was incorporated to control the automated flow and mixing of the process gases. SSI HMI and eFlo 2.0 meters were also integrated to provide Liberty with the latest in hardware, software and communications technology.
One of the great benefits of a community of heat treaters is the opportunity to challenge old habits and look at new ways of doing things. Heat Treat Today’s101 Heat TreatTipsis another opportunity to learn the tips, tricks, and hacks shared by some of the industry’s foremost experts.
Today’s Technical Tuesday features a tip from Jim Oakes of Super Systems, Inc, covering Probes. Jim's tip suggests some fundamental procedures that should be performed properly to maximize carbon/oxygen probe life.
If you have a heat treat-related tip that would benefit your industry colleagues, you can submit your tip(s) to doug@heattreattoday.com or editor@heattreattoday.com.
Jim Oakes, Super Systems, Inc
Are you not getting the life that you would expect from your carbon/oxygen probe? There are some fundamental procedures that should be performed properly to maximize probe life.
1. Clean reference air. The probe needs a fresh source of air provided in the reference air fitting to ensure that the partial pressure of air is consistent. This will provide accuracy in the carbon calculation, and assuming the air does not contain any contaminates, it will lead to longer life under normal use.
2. Proper burnoff procedures. Make sure that you follow the manufacturer's recommendation on probe burnoff. Frequency and duration are dependent on the application (temperature, atmosphere, cycle time, and furnace), but regardless of these, ensuring a probe burnoff's effectiveness can be measured by watching what happens during the burnoff.
a. Probe mV. The probe mV is the best indication that a burnoff is effectively performed. Soot deposition occurs in two critical locations: the annular space between the sheath and the measuring surface, and at the measuring junction between the zirconia and the contact point with the sheath, which is the measuring electrode. The burnoff is performed to remedy this. Burnoff air is forced down the probe on the inside of the sheath but the outside of the probe substrate to force any buildup of soot/carbon on the probe where it can cause electrical connection issues and attack the probe sheath or create a carbon ring internal to the probe. By watching the mV during the burnoff, you should see them drop to 200mV or below during the burnoff process. This information will provide evidence that the burnoff is effective. If you are not getting the mV below that value, then there is not enough air flowing through the airway to force out any soot. Reasons could be:
i. The burnoff pump is not providing enough flow (Super Systems Inc.-SSI recommends 10 scfh or greater.).
ii. The pressure/agitation of the furnace is greater than what the burnoff pump can provide. If the burnoff pump is sized properly and properly working, the timing of the burnoff may need to occur when there is a relief in pressure (inner door opens) or temporarily turning the fan off during the burnoff.
iii. The probe has already been sooted up and should be evaluated for a carbon ring and blockage in that airway.
b. Assuming you have a thermocouple in the tip of the probe, you can monitor the temperature. If the tip superheats, it can damage the tip and in some cases oxidize the tip of the probe. The probe tip should not exceed the furnace temperature by more than 100 degrees.
3. Frequency is dependent upon the environment the probe is exposed to. At the least, SSI recommends performing a burnoff once a day but will suggest increasing that based on the atmosphere setpoint, use of stop-off paint, and length of heat treat cycles. Avoid a frequency of fewer than 6 hours if possible. The duration of the burnout should not exceed 90 seconds. A good way to measure the effectiveness is based on the mV reading dropping below 200.
The Class of 2019 40 Under 40, revealed online on October 4, was featured at the Heat TreatTodaybooth at the Heat Treat Show in Detroit, Michigan. Here is a group photo of most of those still present on the last day:
Matt Watts (Ultra Electronics Energy), Mike Harrison (Gasbarre), Ben Gasbarre (Gasbarre), Tom Zimmerman (ATP), Chris Davidson (SSi), Neal Conway (Delta H), Brandon Sheldon (Plibrico), Kyle Hummel (Contour), Sergio Cantu (Quaker Houghton), Uwe Rahn (Rubig), Justin Dzik (Fives)
You can’t always get what you want. With frequently changing specifications and a volatile economy, what heat treaters want is always evolving. But what they need changes, too. Steven Christopher of Super Systems, Inc. discusses how to balance what vacuum furnace operators NEED and what they WANT. Is the difference between those two things too great? 
