“Communication is key.” As heat treating equipment and processes evolve, it becomes critical that the accompanying control systems also develop to maintain “communication.” In this Technical Tuesday installment, guest columnist Stanley Rutkowski III, senior applications engineer at RoMan Manufacturing, Inc., discusses how digital control system communications have improved to increase energy efficiency for manufacturers with in-house heat treat operations.
This informative piece was first released inHeat Treat Today’sMay 2024 Sustainability Heat Treat print edition.
Industrial furnace applications that rely on resistive heating will consume large amounts of electrical energy when processing their loads. Utilizing digital controls technologies to maximize this type of heating allows for a cleaner-and thus greener-approach to energy demands.
Typically, heat treat processes have a long duration (hours to days in length), and each load can have its own unique recipe in the amount of power required. With unique recipes, there tends to be a ramp-up phase (getting the vessel to temperature), followed by a soak phase (which demands more control over the power system), and then a cool-down phase (an even more controlled state). As the power is controlled through the furnace system, disturbances occur with different technologies. This starts with “tube technology,” then variable reactance transformer (VRT) technology, then silicon controlled rectifier (SCR) technology, and finally IGBT (insulated-gate bipolar transistor) technology. As these technologies have evolved, their ability to communicate information digitally has allowed for less disturbance in the power system and allowing both a less expensive energy bill and a cleaner energy usage for the process.
Definitions
Electrical Power
Power losses in an electrical system are defined by five aspects (Figure 1):
Resistance (R): a function of the material cross section and the length of an electrical conductor.
Reactance (XL): a function of the area in a circuit and is a vector 90 degrees offset from resistance.
Capacitance (XC): a vector 180 degrees offset from reactance. In inductive circuits, capacitance can be added for power factor correction.
Impedance (Z): the vector sum of resistance, reactance, and capacitance.
Power Factor [cos(F)]: the ratio of resistance to impedance. In industrial applications, displacement power factor (DPF), the offset of the current to voltage waveforms, is used in the billing of electrical power.
There are five unique aspects that define electrical power usage (Figure 2):
Real power (kW): the amount of power that is generated.
Reactive power (kVAR): the amount of power that is wasted.
Total power (kVA): the rate at which power is consumed. This is also referred to as apparent power.
Power factor (cos(F)): the ratio of real power to total power. In industrial applications, the displacement power factor (DPF) is the offset of the current to voltage waveforms and is used to bill for electrical power.
Peak demand: the capacity required when the power grid experiences the highest power demand in a specified period of time.
3 Most Popular Types of Control Systems
For the most part, today’s furnace manufacturers use three main types of control systems: VRT, SCR, and IGBT. Each operates with slightly different methods to control how power goes into the heat treat furnace and creates heat.
VRT Control System
One traditional resistance heating setup uses a VRT control system that incorporates a saturable reactor, which controls the power applied to the transformer in the system (Figure 3). The control transformer on the output side of the transformer feeds back to the reactor to set the limit on the input power to the transformer.
Figure 3. VRT Control and Transformer Schematic (CT=control transformer); Source: RoMan Manufacturing, Inc.
SCR Control System
Figure 4. SCR Control and Transformer Schematic; Source: RoMan Manufacturing, Inc.
Another traditional resistance heating setup uses an SCR control system that includes dual thyristors (gated diodes) to control the amount of power applied to the primary of a transformer.
The SCR control delays the start of the waveform, and the control point is reset when the waveform crosses the zero line.
Figure 5. Comparison of Sine Waves; Source: RoMan Manufacturing, Inc.
IGBT Control System
Finally, an IGBT control system uses a diode bridge, capacitor, and switching transistors to control the amount of power applied to the primary (i.e., main power input of a transformer). The input frequency to the transformer is controlled by the switching transistors. Since the IGBT control system utilizes all three phases of the power system, the IGBT control can be set to a particular phase for the zero cross (for phase orientation in the application, synchronous mode) or left floating (non-synchronous mode), as is demonstrated in Figure 6. The input voltage to the transformer is increased by the operation of the IGBT control. As such, potential energy savings may be had with these types of controls as compared to tradition controls (such as on-off contractors, time proportioning controls, or other types of current proportioning control systems).
Figure 6. IGBT Control and Transformer Schematic; Source: RoMan Manufacturing, Inc.
Synchronization with the IGBT can be to the incoming lines (A, B, or C phase) and can be offset from each of the phases. The ability to offset from a phase allows for traditional arrangements (Single Phase, Scott-T, Delta and Wye) as well as unique offsets allowing for additional vector heating in the application with AC outputs. The unique arrangements beyond the traditional systems could allow for more uniform heating of the part and less energy being consumed during the process.
Advantages of Utilizing Communications
As technology for controlling heating systems has evolved, and with an emphasis on clean energy sources, the ability to communicate with the control system has increased as well. This communication allows for more precise control of the run for the load, improved power usage (better power factors and less peak power usage as well as less total power usage), and inputs into a preventive maintenance program.
Table A. Analog vs. Digital IGBT Systems
With an IGBT system, both analogue and digital control communications are available today. See Table A for a comparison on how each control option works.
In addition to the EIP defined pieces, there is the ability to access the FPGA system for graphical outputs that can be downloaded into another system in your process for storage, comparisons, or general record keeping for a part run. The FPGA is an internal processor in the control that allows for more data, charting, and diagnostics to be captured and used by the system for both energy consumption and possible preventative maintenance purposes.
Why does this matter? Let’s turn to some possible ways of using the data generated from digital controls systems:
Evaluate average, minimum, and maximum DC bus voltages to plan for the best time and day to run heat treat jobs. For high power draw jobs, planning ahead can minimize power costs; similarly, knowing power trends can be helpful to plan jobs requiring sensitive control of the heating.
Evaluate transformer output voltage to allow the system to detect any shorts in the process. If the controller output and transformer output diverge from the known turns ratio, a change has occurred in the system. This could be corroborated if controller on time and output power do not trend.
Track furnace run records with EIP communications and FPGA data. This will be most helpful in processing lots of data, as is the case for Milspec records.
Evaluate changes in power factor to monitor any loose cables, and so avoid reactive power losses.
Evaluate the current versus the voltage to monitor the resistance of the system. If there is an increase in the resistance, you could project the trends in wear of the heating elements, therefore predicting future required maintenance.
Evaluate the critical control temperatures of the system to know if it is being run close to, or above, its ratings or if there is a disturbance in the cooling systems.
Use knowledge of power usages and power stability to update recipes for load runs so they use less power over the total run; this allows for a less costly power-savings solution. With less power usage, more output of the total facility can be had as each station contributes less to energy consumption
Even more benefits can be realized when users and builders of furnace systems and component manufacturers collaborate in the design of the total system. Such dialogues lead to the creation of more interactive and intuitive solutions that minimize power consumption, minimize downtime, and maximize outputs. These practical benefits are the foundation of a greener system.
About the Author:
Stanley F. Rutkowski III Senior Applications Engineer RoMan Manufacturing, Inc.
Stanley F. Rutkowski III is the senior applications engineer at RoMan Manufacturing, Inc., working on electrical energy savings in resistance heating applications. Stanley has worked at the company for 33 years with experience in welding, glass and furnace industries from R&D, design, and application standpoints. For more than 15 years, his focus has been on energy savings applications in industrial heating applications.
Sludge, scale, and dirt are all undesirables in quench oils that can cause detrimental effects during quenching. Bag filtration and centrifuge filtration are put to the test in this investigation. Compare the results before you make your next purchase.
This Technical Tuesday article, written by Greg Steiger, senior account manager, and Michelle Bennett, quality assurance specialist, at Idemitsu Lubricants America, was originally published in November 2023’s Vacuum Heat Treatmagazine.
Introduction
The primary role of a quench oil is to dissipate the heat from a quenched load safely, quickly, and uniformly. Both sludge and heat scale have a higher heat transfer coefficient than quench oil and dissipate heat more than this quench medium. This can affect the performance of a quench oil.
To obtain the desired metallurgical results, the operation of a quench system must be both consistent and uniform. The presence of sludge from quench oil oxidation and scale within the quench oil, pump, and heat exchangers can lead to variability in key parameters such as grain size, hardness, case depth and surface finish. The best way to minimize the detrimental effects of sludge and scale is to remove these contaminants by filtration. This article will compare the two most popular types of commercial filtration available for oil quench systems: bag filters vs. centrifuge filtrations.
This article will compare the two most popular types of commercial filtration available for oil quench systems: bag filters vs. centrifuge filtrations.
Test Methods
To simulate a two-stage bag filter, the following lab procedure was followed.
A 300-mL sample of used quench oil was passed through a 75-micron filter paper. The filtrate from the 75-micron filter was then filtered through a 25-micron filter paper. To simulate the pressure typically found in an industrial bag filter, the filtration in both the 75-micron and 25-micron papers was aided by a vacuum pump that pulled used quench oil through the filter paper.
To simulate the effects of centrifugal separation, a benchtop centrifuge was used. A 300-mL sample of used quench oil was placed in a centrifuge tube and centrifuged for 25 minutes at a speed of 3,500 RPM. An additional 300-mL sample was placed in an identical centrifuge tube and centrifuged for 180 minutes at 3,500 RPM as well.
In addition to the lab testing of dirty quench oil samples, we monitored the particle count and pentane insolubles in samples from an in-use heat treating furnace. This study began with charging the furnace with clean quench oil that was filtered using a single stage 25-micron filter and collected after each filtration. At the conclusion of each timed centrifuge session, the filtrate and the centrifuged sample were tested across five tests, see Table 1.
Table 1. Tested parameters after simulated bag or centrifuge filtration (Source: Idemitsu Lubricants America) Note on Table 1: Pentane insolubles measure sludge and scale present in the quench oil after the filtration through the barrier filter or after the centrifuge. Millipore testing is a measure of the overall cleanliness of the quench oil after either filtration or centrifuging. Carbon residue testing measures the Conradson carbon in the filtered or centrifuged quench oil and is designed to determine if any of the quench speed improver additive in the quench oil has been removed via filtration or centrifuging. By measuring the total acid number (TAN) of the quench oil, it is possible to determine if the quench oil is becoming oxidized and beginning to create unwanted sludge. The ISO Particle Count tests for solids contamination, providing a quantitative value for the number of particles that are larger than 4 μm, 6 μm, and 14 μm.
Filtration Results
Because industrial quench oil filters are under a slight pressure, it would be very difficult to replicate this in a laboratory setting. To simulate the slight pressure found in industrial oil filters, we used a Buchner funnel connected to a vacuum pump to simulate the industrial pressure vessel. A similar setup is depicted in Figure 1.
The results post-filtration are depicted in Table 2 and Table 3.
Table 2. Tested parameters after filtering 300 mL of quench oil through 75-micron filter (Source: Idemitsu Lubricants America)Table 3. Tested parameters after filtering 300 mL of quench oil through 25-micron filter (Source: Idemitsu Lubricants America)
Another popular method of filtration in a heat treating facility is through a centrifuge. While it is impractical to use a full-size industrial centrifuge in a lab, the same results can be achieved through the use of a smaller sample size and a benchtop centrifuge. A benchtop centrifuge similar to the one seen in Figure 2 was used to produce the results in Tables 4 and 5 (below).
Understanding the Test Methods: Bag/Barrier Filtration
Figure 3. Polyethylene felt filter bag and filter canister (Source: SBS Corporation)
Bag (or barrier) filtration is the most common type of filtration used in quench oil filtration. For the heat treater, there are many different size filters available, as well as different configurations varying in the number of canisters and filters. The filter creates a barrier that particles greater than the pore size in the barrier cannot pass. The primary reasons for its popularity are economics, simple operation, and design. A typical polyethylene bag filter and filter cannister can be seen in Figure 3.
The most common filter sizes are 50-micron and 25-microns. Both 5-micron and 25-micron filters were used in this investigation because the test sample contained a high level of pentane insoluble. Additionally, since it is commonly thought that using a 50-micron filter will cause blinding and clogging, we chose a 75-micorn filter and a subsequent filtration step of using a 25-micron filter to simulate a common two-stage quench oil filter.
Understanding the Test Methods: Centrifuge Filtration
Using a centrifuge to filter out sludge and scale is also commonly used in many heat treating operations. The difference between centrifugal filtration and barrier filtration is centrifugal filtration relies on gravity, friction, and centrifugal force to separate the particles from a quench oil instead of a physical barrier (Figure 4).
Figure 4. Horizontal centrifugal filtration (Source: SBS Corporation)
In the horizontal centrifugal filtration diagram, the dirty oil enters the tangential opening (section #1) and is forced into a spinning motion. A centrifugal force (occurring in section #2) is based on the spinning pentane insolubles, scale, and any other solids contained in the dirty oil.
In section #3, the friction created by the flow of the solids, scale, and other undesirables encountering the steel body of the centrifugal separator creates a low viscosity shear layer. In section 4, the clean liquid travels through a vortex and leaves through a side discharge. The slowing velocity of the undesirables allows gravity to pull them into the debris collection area in section #5. The now cleaned oil regains its velocity and continues through the vortex created by the centrifugal forces acting on the solids to a center discharge and back to the quench tank. As the debris fills section 6, a light will illuminate, indicating the receptacle is full and needs to be emptied.
Once the undesirables fill the debris collection area, an indicator light signals the receptacle is full and a gate knife control valve (section #7), is manually closed so the debris collector can be opened via the closure (section #8).
Discussion
Table 4. Tested parameters after centrifuging 300 mL of quench oil sample @ 3,500 RPM for 25 minutes
(Source: Idemitsu Lubricants America)Table 5. Tested parameters after centrifuging 300 mL of quench oil sample @ 3,500 RPM for 3 hours
(Source: Idemitsu Lubricants America)
As seen in Tables 2 and 3, filtration does improve the overall cleanliness of the dirty quench oil. The weight percent of the pentane insolubles showed a significant improvement when filtered through the 25-micron fi lter. However, the level of pentane insolubles was still outside of the suggested limits for the quench oil.
This was not seen when the quench oil was filtered through a 75-micron filter. The 75-micron filter had little or no effect on the Millipore results. The Millipore results increased when filtered through a 75-micron filter. This leads us to believe some of the particles within the dirty oil were forced through the 75-micron filter and not through the 25-micron filter, as the 25-micron filter showed an improvement in Millipore results.
An ISO particle count was not possible on the original used samples or the filtered samples because the filter clogged on all three test samples.
The largest difference in results lies in the carbon residue testing. The level of carbon residue is essentially the same after both the 75-micron and 25-micron filter samples. Both of the carbon residue levels are within the normal suggested limits. However, the high level of sludge in the original dirty sample is likely removing some of the quench speed improver from the quench oil. The removal of the quench speed improver changes the performance of the quench oil over time.
In examining the results of the centrifuge testing in Tables 4 and 5, it is clear centrifuging for 25 minutes has better effect on the cleanliness of the oil sample than filtering through a 25-micron filter. The level of pentane insolubles after centrifuging for 25 minutes at 3,500 RPM is still outside of the suggested limit. However, running the centrifuge for three hours under the same conditions not only brings the pentane insolubles within the suggested limits, the Millipore and particle counts also see an improvement over the virgin oil sample results. The carbon residue levels behave much the same as they do in the filtration tests.
What is significant is the year-long study we conducted using actual customer data. In this study, a furnace was dumped, cleaned, and then filled with clean virgin oil. The authors then tested the ISO particle counts and pentane insolubles for one year after the furnace was charged with clean oil. These results are seen in Table 6. These data show essentially no change in the particle counts and a slight improvement in the level of pentane insolubles over the one-year period.
Table 6. Particle count and pentane insolubles on a clean quench oil (Source: Idemitsu Lubricants America)
Conclusion
From the testing conducted, it is clear the filtration through a 75-micron filter has little to no effect upon the tested parameters and the performance of the quench oil. The high levels of pentane insolubles will likely clog heat exchangers, pumps, and valves within the quench system. The dirty oil will also likely cause metallurgical issues such as isolated soft spots due to the slower heat transfer of the dirty oil. The results of filtering a dirty oil through a 25-micron filter show some improvement in the pentane insoluble levels. However, the result is still outside of the recommended limits for the oil. Additionally, the ISO particle counts were not able to be tested due to the overall dirty condition of the filtered sample.
In contrast to the bag filter samples, the centrifuge samples showed a marked improvement over the dirty sample. While the pentane insoluble level was slightly out of the recommended limit for the 25-minute centrifuge sample, all results were within the recommended specifications for the three-hour centrifuge sample. In some cases, such as the particle count, the centrifuge sample had better results than the virgin sample.
While the centrifuge and filter results both show how hard it is to effectively clean a dirty quench oil, the results from the year-long study show very little difference in particle counts and a slight decrease in pentane insolubles, which can be explained through the normal addition of virgin make up oil to the quench system.
It is clear both centrifuge separation and bag filtration can improve the overall condition of a dirty quench oil. However, if your level of dirt, sludge, and scale reaches near the levels of the tested sample, a centrifuge is better at removing these than filtration. Overall, the data show the most important and efficient method is to begin filtering a clean quench oil as soon as the quench tank is charged.
About The Authors
Greg Steiger is the senior account manager at Idemitsu Lubricants America. Previous to this position, Steiger served in a variety of technical service, research and development, and sales and marketing roles for Chemtool Incorporated, Witco Chemical Company, Inc., D.A. Stuart Company, and Safety-Kleen, Inc. He obtained a BS in Chemistry from the University of Illinois at Chicago and recently earned a master’s degree in Materials Engineering at Auburn University. He is also a member of ASM International.
Michelle Bennett is the quality assurance specialist at Idemitsu Lubricants America, supervising the company’s I-LAS used oil analysis program. Over the past 12 years, she has worked in the quality control lab and the research and development department. Her bachelor’s degree is in Chemistry from Indiana University. Michelle is a recipient of Heat Treat Today’s 40 Under 40 Class of 2023 award.
The appeal of additive manufacturing (AM) for producing orthopedic implants lies in the “ability to design and manufacture complex and customized structures for surgical patients in a short amount of time.” To complement speed of production, learn how an innovative hot isostatic pressing (HIP) application is confronting the challenges of post-processing heat treatments when creating high quality AM medical parts.
Today’s Technical Tuesday article, written by Andrew Cassese, applications engineer; Anders Magnusson, manager of Business Development; and Chad Beamer, senior applications engineer, all from Quintus Technologies, was originally published in Heat Treat Today’sDecember 2023’s Medical and Energy Heat Treat magazine.
AM is playing a significant role in the medical industry. It gives manufacturers the ability to create customized and complex structures for surgical implants and medical devices. Additionally, medical device manufacturers have different material factors to consider – such as biocompatibility, corrosion resistance, strength, and fatigue – when selecting a material for a given application. Each of these factors plays a significant role. It’s no wonder that the most common metallic biomaterials in today’s industry are stainless steels, cobalt-chrome alloys, and titanium alloys (Trevisan et al., 2018).
In this article, learn about the application of Ti6Al4V in the medical industry, as well as ways to address some of the challenges when producing AM medical components.
The Future Demands Orthopedic Implants
Figure 1. Example of AM trabecular structure on a Ti6Al4V
acetabular cup (Source: Quintus Technologies)
The medical market for orthopedic implants is predicted to grow annually by approximately 4% where joint replacement, spine, and trauma sectors are reported to account for more than two-thirds of the market. The largest portion is joint replacement with over a third of global turnover, reaching in excess of 20 million U.S. dollars in 2022 (ORTHOWORLD® Inc., 2023). This confirms an earlier study by Allied Market Research where spine, knee, and hip implants made up over 66% of the entire market, with knee implants leading the way at 26% (Allied Market Research Study, 2022). This fact, combined with the expectation that the global population aged 60+ is predicted to double between 2020 and 2050, adds to the increasing demand on manufacturers to produce better quality and longer lasting orthopedic implants (Koju et al., 2022).
These factors have increased the predicted medical implant market for Ti6Al4V and other common orthopedic materials. Using AM processes such as electron beam melting (EBM) and laser powder beam fusion (L-PBF), manufacturers can produce thin-walled trabecular structures that are fabricated to promote bone ingrowth in a growing market that is in competition with traditional production methods.
Titanium-based alloys have been increasingly used in orthopedic applications due to their high corrosion resistance and a Young’s modulus similar to that of human cortical bone (Kelly et al., 2021). The high strength-to-weight ratio and bioinert-ness of Ti6Al4V has proven it to be an ideal candidate for orthopedic and dental implants. It is a titanium alloy with 6% aluminum and 4% vanadium that has low density, high weldability, and is heat treatable. Ti6Al4V demonstrates good osteointegration properties, which is defined as the structural and functional connection between living bone and the surface of a load carrying medical implant.
Many manufacturers are using L-PBF to create thin-walled complex structures on the surface of the implant. This makes use of the osteointegration properties as the implant integrates itself into the body over time without the need for bone cement (Kelly et al., 2021). Introducing a large metallic foreign body leads to challenges such as promotion of chronic inflammation, infection, and biofilm formation. Instead, porous AM Ti6Al4V implants have a biomimetic design attempt towards natural bone morphology (Koju et al., 2022).
AM Yields Production Solutions for Medical Alloys
The medical industry has been increasing the use of AM over traditional processing methods. AM facilitates weight reduction, material savings, and shortened lead-time due to reduced machining, but these are only a few of the benefits. Improved functionality and patient satisfaction are also key aspects through tailoring of designs to take advantage of AM over traditional forging and casting techniques. Additionally, the costs of machining a strong alloy like Ti6Al4V can be expensive, and any wasted material and time in turn lead to higher cost.
One of the main reasons for the interest in AM is the ability to design and manufacture complex and customized structures for surgical patients in a short amount of time. For example, if a patient needs an implant for surgery, an MRI scan can help reverse engineer a customized implant. Engineers prepare a design of a patient-specific implant according to the patient’s anatomy that is then printed, HIPed, and finished for surgery with a reduced lead time. This is especially important for trauma victims, where the speed of repair can mean the difference between losing a limb or returning to a fully functional life. Cancer victims and those requiring aesthetic surgery to the skull, nose, jaw, etc., can also benefit from this (Benady et al., 2023).
Some of the current challenges with AM titanium in the medical industry are related to the post-processing heat treatments that are required. These treatments can leave an oxide layer on thin-walled structures that is hard to remove by machining or chemical milling. Quintus Purus®, a unique clean-HIP solution, has proven to overcome this challenge and provide clients with a robust solution that both densifies and maintains a clean surface.
When HIP Meets AM
Figure 2. AM Ti6Al4V components HIPed without getter using conventional HIP (left) and Quintus Purus® (right) (Source: Zeda)
HIP is important in the AM world as a post-process that closes porosity and increases fatigue life. For medical implants, high and low cycle fatigue life properties are key as they affect the longevity of the repair. The mechanical strength and integrity are improved significantly by HIPing the implants, reducing the need for further surgery on the same patient. Modern HIP cycles have been developed to further increase this performance. When combined with Quintus Purus®, modern HIP cycles can minimize the thin, oxygen-affected layer that can result from thermal processing on surfaces of high oxygen-affinitive materials, such as titanium.
For Ti6Al4V, this layer is often referred to as alpha-case. The brittle nature of the alpha-case negatively impacts material properties resulting in medical manufacturers requesting their AM parts in the “alpha-case free” state. Alpha-case can be formed during heat treatment. As surfaces of the payload and process equipment are exposed to oxygen at elevated temperatures, they may be oxidized or reduced, depending on the oxide to oxygen partial pressure equilibrium. During heat treatment, evaporating compounds become part of the process atmosphere, and solids are deposited or formed on other surfaces, either as particles or as surface oxides.
For titanium alloys, surface oxides are formed at logarithmic or linear rates, depending on temperature and oxygen partial pressure. At the same time, oxygen can diffuse into the surface to form the brittle alpha-case, which is detrimental to the part’s fatigue performance. Changes of the surface color can often be seen as an indication that surface reactions have occurred during processing when using traditional thermal processes (Magnusson et al., 2023).
The HIP furnace atmosphere contaminants that cause this oxidation can originate from various sources including the process gas, equipment, furnace interior, and, most importantly, the parts to be processed. The payload itself often absorbs moisture from the surrounding atmosphere before being loaded into the furnace, which is subsequently released into the HIP atmosphere during processing. Industrial practice today attempts to solve the issue by wrapping parts in a material such as stainless steel foil or a “getter” that has a high affinity to oxygen protecting the Ti6Al4V component from exposure to large volumes of process gas, thus helping minimize the pickup of the contaminates.
This method adds material, time, and labor to wrap and unwrap parts before and after each HIP cycle. Also, wrapping in getter cannot guarantee cleanliness and may result in some uneven oxidation. This is where the tools of Quintus Purus® are of assistance; these tools allow the user to define a maximum water vapor content that can be accepted in the HIP system before the process starts. The tool utilizes the Quintus HIP hardware together with a newly developed software routine, ensuring that the target water vapor level is met in the shortest time possible. The result is a cleaner payload, without the need to directly wrap components with getter (Magnusson et al., 2023).
Table 2. Results from case study productivity analysis
(Source: Quintus Technologies)Table 1. Input to case study (Source: Quintus Technologies)
Alpha-Case Avoided: Comparing Conventional HIP and Optimized HIP Technologies
Quintus Technologies performed a study with Zeda, Inc. to evaluate Quintus Purus® on L-PBF Ti6Al4V medical implant parts. The study was performed in the Application Center in Västerås, Sweden in a QIH 21 HIP. A conventional HIP cycle was performed as well as an optimized Quintus Purus® HIP cycle, both without the use of getter. No presence of alpha-case was found on the part processed with the Quintus Purus® cycle as shown in Figure 2 below (Magnusson et al., 2023).
Quintus Purus® can be further enhanced with the use of a Quintus custom-made getter cassette supplied as part of the installation, which consumes or competes for the remainder of contaminant gaseous compounds still present in the system after all other measures such as best practice handling, adjustment of gas quality, etc., have been implemented.
Titanium is considered the getter of choice for Quintus Purus® and is included as an optional compact getter cassette placed at the optimum position in the hot zone of the HIP furnace. Although the custom-made getter cassette occupies a small space, its use can significantly increase loading efficiency. The traditional way of individually wrapping components with stainless steel or titanium foil will consume more furnace volume, through reduced packing efficiency, leading to less components per cycle when compared to the Quintus Purus® titanium getter cassette strategy. Using an average spinal implant size of 2 in3 (32 cm3), one can calculate the packing density in a standard HIP vessel assuming two shifts per day and a 90% machine uptime. For example, a Quintus Technologies QIH 60 URC with a hot zone diameter of 16 in (410 mm) and a height of 40 in (1,000 mm) can pack up to 1,280 implants per cycle, with clearances for proper spacing and load plates.
Figure 3. Quintus Technologies QIH 60 URC outfitted with
Quintus Purus® technology (Source: Quintus Technologies)
The typical Ti6Al4V HIP parameters include a soak time of two hours at 1688°F with 14.5 ksi argon pressure (920°C with 100 MPa). Accounting for heat up and cool down time, this HIP cycle can take less than eight hours, allowing two cycles per day on a two-shift work schedule. A typical case of wrapping each component in getter material adds time, cost, resources, and uses up to an estimated 50% of the load capacity. With the increased efficiency enabled by Quintus Purus®, clients have the opportunity to HIP 552,960 spinal implants per year (Tables 2 and Figure 3).
In conclusion, the growing Ti6Al4V market in the medical industry demands innovative developments to keep up with ever-increasing production volumes, whilst quality demands in lean production are becoming more significant. Solutions like the Quintus Purus® will allow manufacturers to have control over the quality of their titanium parts during a HIP cycle. It can be applied to produce alpha-case free components ensuring the optimal performance of orthopedic implants with increased service life.
References Ahlfors, Magnus, Chad Beamer. “Hot Isostatic Pressing for Orthopedic Implants.” (2020): https://quintustechnologies.com/knowledge-center/hiporthopedic-implants/. Allied Market Research Study performed for Quintus Technologies, 2022. Benady, Amit, Sam J. Meyer, Eran Golden, Solomon Dadia, Galit Katarivas Levy. “Patient-specific Ti-6Al-4V lattice implants for critical-sized load-bearing bone defects reconstruction.” Materials & Design 226 (Feb. 2023): https://www.sciencedirect.com/science/article/pii/S0264127523000205?via%3Dihub. Kelly, Cambre N., Tian Wang, James Crowley, Dan Wills, Matthew H. Pelletier, Edward R. Westrick, Samuel B. Adams, Ken Gall, William R. Walsh, “High-strength, porous additively manufactured implants with optimized mechanical osseointegration.” Biomaterials (Dec.2021): 279, https://www.sciencedirect.com/science/article/abs/pii/.
About the Authors
Andrew Cassese is an applications engineer at Quintus Technologies. He has a bachelor’s degree in welding engineering from The Ohio State University.
Anders Magnusson is the business development manager at Quintus Technologies with an MSc in engineering materials from Chalmers University of Technology.
Chad Beamer
Applications Engineer
Quintus Technologies
Chad Beamer is a senior applications engineer at Quintus Technologies, and one of Heat Treat Today’s 40 Under 40 Class of 2023 award winners. He has an MS from The Ohio State University in Materials Science and has worked as a material application engineer with GE Aviation for years and as a technical services manager with Bodycote. As an applications engineer, he manages the HIP Application Center located in Columbus, Ohio, educates on the advancements of HIP technologies, and is involved in collaborative development efforts both within academia and industry.
Our readers and Heat Treat Radiolisteners will remember a recent episode entitled "Heat Treat Radio #102: Lunch & Learn, Batch IQ Vs. Continuous Pusher, Part 1." Today's Technical Tuesday article is a continuation of this dialog, with Michael Mouilleseaux, a boot-on-the-ground North American heat treat expert from Erie Steel here to answer your questions on the maintenance of batch and continuous pusher furnace systems.
Doug Glenn, Heat TreatToday's publisher,Karen Gantzer, associate publisher/editor-in-chief, join in this Technical Tuesday article.
Stay tuned for a Part 2 continuation of the Lunch and LearnHeat Treat Radio episode, coming to Heat Treat Radio in a couple weeks.
Below, you can watch the video or read from an edited transcript.
Michael Mouilleseaux
General Manager at Erie Steel, Ltd.
Sourced from the author
Introduction to Maintenance
Doug Glenn: We would like to move on to maintenance of the batch furnace and the continuous furnace. What is the cost of maintaining and operating these furnaces?
Michael Mouilleseaux: When they are utilized in a carburizing environment, there is always excess carbon that falls out or precipitates out of the atmosphere, and it ends up as elemental carbon in the bottom of the furnace.
What do you do with that? In furnaces that are using a carburizing environment, the burnout of the furnace is easily the single most important piece of preventative maintenance that you can perform. How is that performed? First, the furnace is vacated; there is no product in the furnace, the temperature is reduced — typically, you want it down around 1500°F or 1550°F — and you introduce room air into the furnace. The room air ignites the carbon. It’s a very primitive operation.
So, what temperature does carbon burn at? It burns at 3000°F.
You need to be very careful. It’s a controlled burn because you can actually damage the furnace through refractory, through the alloy that’s in the furnace, or it can get away. How do you do control it? On one level, you’re just looking at the temperature control. If you have it set at 1550, you’re going to say, “I’m only going to put air as long as the temperature of the furnace does not go up more than 25°F or 50°F.” It’s somewhat dependent upon the piece of equipment and is one of those things that you learn empirically; there is not a hard and fast rule for it.
Then, you can shut off the air. If there is no oxygen, then the source for combustion is taken away and you stop that operation. If you need to do it more rapidly than that, you may need to flood the furnace with nitrogen. Typically, if you have to flood the furnace with nitrogen to do it, you’ve been a little too aggressive in your burnout.
How long do you perform that? The great thing with oxygen probes is that you can utilize your oxygen probe to help you learn when you have burnt out the furnace. You’re not getting an actual carbon atmosphere, but what you do get is a readout from the probe. What you can do is perform the burnout operation until you attain that level and then you know that you’ve done a sufficient job in burning it out. That’s the single most important piece of preventative maintenance that’s done on a furnace used for carburizing.
Doug Glenn: Is that both in batch and in continuous?
Michael Mouilleseaux: Identical, yes.
Doug Glenn: I’ve got a couple other questions about furnace burnouts as someone who’s not a furnace operator. You said that there’s “carbon dropout” in the furnace. I know that in some furnaces, parts of the atmosphere may precipitate onto the coolest part of the furnace. Is that what is happening, or are we talking about carbon powder at the bottom of a furnace?
Michael Mouilleseaux: It is carbon powder, and it becomes more egregious. The powder then begins to accumulate into pebbles, nuggets, and larger size pieces. That’s more problematic. When it is in a powdered form, that is the best.
The question will be: How often do you have to do this? As with everything, the answer is — it depends. It depends on what you’re doing; it depends on how aggressive you are in your carburizing.
In the boost phase, we talked about carburizing at upwards of 1%. As soon as you exceed the saturation level of carbon, you’re going to precipitate out the excess carbon. What is that number? It’s different for every temperature. At 1500°F, it’s .9 or .85; at 1750°F, it’s 1.25. But to attain that, you’re actually putting natural gas into the furnace, and the amount of natural gas that you put into the furnace and its dissociation rate — the rate that it breaks down — can then subsequently be diffused into the parts; all of that comes into play.
With saturation levels of carburizing, there is always some residual carbon that’s in the furnace.
Doug Glenn: You mentioned that carbon burns at around 3,000 degrees. Are you taking the furnace up to that temperature?
The great thing with oxygen probes is that you can utilize your oxygen probe to help you learn when you have burnt out the furnace. You’re not getting an actual carbon atmosphere, but what you do get is a readout from the probe. What you can do is perform the burnout operation until you attain that level and then you know that you’ve done a sufficient job in burning it out. That’s the single most important piece of preventative maintenance that’s done on a furnace used for carburizing
Michael Mouilleseaux: No. The burnout cycle is at 1500 or 1550. You raise that carbon to that level and introduce oxygen, and what you want is a slow burn.
We next think about the systems involved in the furnace. First there is the heating system. In a gas-fired furnace, some critical things to consider are burner recovery, burner adjustment, and the amount of excess air that results in that burner adjustment. That’s a preventative maintenance operation that needs to be performed on a regular basis. It probably doesn’t need to be done daily, but monthly is optimal. If everything is very steady, including the barometric pressure, then you don’t need to do all of those adjustments.
Now, electric furnaces have SCRs that fire the elements, and you have to pay attention to the tuning of those things to make sure that they’re operating at optimum performance. One of the ways that you can do that, in a batch furnace, is if you look at the recovery time.
For example, if you have a load that weighs 4000 lbs. and you put it in the furnace and you know that it takes an hour and a half for the furnace to recover to temperature, but then all of a sudden, it takes an hour and 45 minutes, or an hour and 50 minutes, or two hours, obviously the burners are not producing the same amount of heat. The burners are not pumping the requisite amount of BTUs to achieve that recovery time. Could that be related furnace circulation? Could it be related to the insulation in the furnace? At an extreme, it could. Typically, though, it’s related to burner or SCR tuning.
Those are the kinds of things that are very easy to pay attention to.
"Electric furnaces have SCRs that fire the elements, and you have to pay attention to the tuning of those things to make sure that they’re operating at optimum performance. One of the ways that you can do that, in a batch furnace, is if you look at the recovery time."
Setting up PM Through Controls System
The control schemes in the PLC are typically very robust. So, you can establish a program and the PLC is going to say, “I want to heat it at this rate, I want the carbon potential to be .4%, I want to hold this at two hours at temperature, and then I want to initiate a quenching cycle.” Typically, PLCs are quite robust.
The thing you have to be careful with is obviously not just power outages, but brownouts. Brownouts are when you don’t quite lose all voltage, but you lose some of it. If you don’t have some kind of a filter on the power you can mitigate with, or have an uninterruptable power supply for the PLC, you can damage those things, resulting in some major work on the PLC.
The other part of that is the furnace circulation. We’ve got fans in these furnaces, and we circulate the atmosphere. The primary stages of heating in the furnace are convection, until we get to 1200 degrees. How do we convect the heat? We have the atmosphere in the furnace, the fan circulates, it washes the atmosphere down the radiant tubes, it heats up the atmosphere, the atmosphere comes into contact with the components, and we’re convection-heating the parts.
Once we get to 1200 degrees or more, then the primary method of heating becomes radiant heating. That’s where the radiant tubes are then the primary means of transferring energy. But the fans become very important. Are they balanced? Is the RPM correct? Is the amp reading on the fan? Those are areas to look at.
You have to understand how the furnace operates when it’s healthy — the furnace manufacturer can help you and/or you just learn empirically. For instance, what would it mean if, all of a sudden, I’m drawing much fewer amps on a circulating fan and it’s running very rough? Quite possibly, we’ve lost a fan blade.
Then there is the atmosphere control system. All that we just described is applicable to both continuous and batch furnaces. The furnace needs to be sealed and you want a couple inches of water column pressure — excess pressure — in the furnace relative to atmosphere pressure, since safety is the number one concern.
The atmosphere that we’re talking about in most of these furnaces is endothermic atmosphere. It’s a reducing atmosphere, meaning that it’s combustible. If, of course, we have combustion in a closed vessel, that’s called an explosion.
The reducing atmosphere, in and of itself, is if you look in a furnace that is at anything above 1200 degrees where it’s red, up to 1700–1800 degrees where it’s going to be yellow to white — and there is no flame . . . . People are absolutely amazed when they look in an atmosphere furnace and they see no flame. What you should see is everything in a relative, uniform color. The parts should be a uniform color. If you look at the tubes, they should be a little lighter because the tubes will always be somewhat above the temperature of the parts . . . .
Back to the atmosphere: We want to be sure that the atmosphere stays in the furnace and that we maintain that pressure in the furnace. So, what would be a cause to lower the pressure in the furnace? A door leak or a leak in a fan. It could be, if you have a mechanical handling system, a leak through that system. Those are all places to look.
The PM on that? For maintaining the level of lubrication in the fan bearings, see that they’re cooled so that the outlet temperature of the coolant — be it air or water — should be higher than the inlet temperature; that shows that they’re being cooled.
I can’t tell you an absolute number, but I can say that for the equipment that we have, we have numbers that we’ve developed; we know that if the outlet temperature of the water is 20 degrees higher than it is going in, we’re doing a good job of cooling the bearings.
The door seals in furnaces, typically, are brick on brick. Typically, they use a wedge system to seal the doors in the furnace. But, of necessity, these are wear items. Therefore, in preventative maintenance, you might notice a burnout around a door where you hadn’t had one before. That tells you that atmosphere is leaking out of that door and so a repair is needed in the near future.
An interesting thing about a batch furnace: Most of them only have one door. So, it’s quite easy — you can open the vestibule and, in a maintenance operation, if you gassed up the furnace, you could see.There is always going to be some atmosphere coming around the door because that’s where the atmosphere goes into the vestibule, but it should be at the top; it shouldn’t be around the sides, and it definitely shouldn’t be at the bottom. It should be very consistent.
That’s one of those things that, again, you empirically learn. You look at it — it’s a visual operation to say what you’re doing.
There are two other systems: First, the quench system. We talked about how critical the quench system is. The RPMs of the prop, the amp draw of the motors for the props — those things should be very consistent. I think they should be monitor and data logged. The reason for that is you want to know when you quench a load that the RPMs of those props are what you have set it for. When you introduce a load into the quench, the amp draw is, of necessity, going to increase. That’s because you’ve put something in the path of the quenchant so, in order to maintain that flow, you’ve increased the amount of work that it takes to rotate those props.
That’s the kind of thing that you want to monitor. If the amp draw is changing, that means that there’s something in the quench system. Could it be the bearings? Could it be the motor? Those are some things that you’d need to take a look at and be certain of. Obviously, the props need to be in balance; you don’t want any vibration in them.
Doug Glenn: This is also true on the continuous furnace. You’ve got three or four green props in the batch furnace, and it would be the same in the continuous furnace.
Source: Erie Steel, Ltd
Maintenance of Quenchant
Michael Mouilleseaux: Also, there is the maintenance of the quenchant. I’m of the belief that the quench should be continuously filtered. I’m not a fan of batch filtering. I’ve been doing this long enough that I’ve done that, and it just isn’t successful. Quite possibly there are operations that allow it.
If you’re carburizing, you’re going to have particulate in the quenchant because that same atmosphere precipitation of carbon finds its way into the quench. It’s going to be on the parts, it’s going to be on the trays, it’s going to be dragged in there. So, you have this particulate carbon in the quench and it acts as a catalyst to break down the oil.
One way to extend the life of the oil is to make sure that you’re continuously filtering that out. People say 50 microns or 100 microns or 25 microns. Experientially, I’m going to say that it’s going to be 25 microns. If you have a 100-micron filter, that’s great for getting the pebbles out of the quench or the scale, if that were to be an issue with your customer’s parts, but that’s not sufficient to filter out the particulate that’s going to be of the size that’s going to catalyze the breakdown of your quenchant.
Doug Glenn: I assume that if you’re providing for some sort of continuous filtering of your quench, that’s built into the quench structure. The quench tank is built for that, right, and you’re continually flowing it through this filter?
Michael Mouilleseaux: I’m not going to say that no manufacturers offer sufficient quench filtering, but I am not aware of anyone that offers a quench filtration system that’s sufficient. Most of these things end up being standalone. You want to draw the quenchant from the bottom of the tank in one quarter, you want to put it through a series of filters, and you want to put it back into the furnace at the opposite end of the quench tank.
I can say with certainty, that a batch furnace which has not been filtered well, if you remove the quenchant from the furnace after six months — definitely after 12 months — of using it in daily carburizing, you’re going to take 55-gallon drums of sludge out of the furnace, and the sludge is essentially carbon that’s mixed in with the oil.
For that same furnace, with a sufficient quench filtration system, there will be little pockets in the four corners of the quench tank, but that’s about it.
CQI-9, Nadcap and all of those standards have a requirement for monitoring of quenchant. One of the monitors should be particulate because that lets you know how good a job you’re doing in filtering.
Having done it properly, one can say, “Well, I have to replace my quench oil,” — fill in the blank — “once a year, once every six months, once every two years.” Properly maintained and filtered, the quenchant does not have to be replaced very often.
You’re going to drag out a little oil on every load. You want to let the load drip so that you’re not taking that precious quench oil and just putting it in the wash and washing it off. But in a batch furnace, you could have a couple hundred gallons a month to four hundred gallons, depending on the size of the furnace, of add-back that you’re putting in there. Is that sufficient to maintain all of the additives that are in the quenchant? Is that something that you need to monitor? Typically, the manufacturer can do that for you. You get monitoring and you see what the quench speed is, what is the viscosity, flash – all of those important pieces of information.
Now, it doesn’t come for free. A filtration system is costly, and the filters are costly. A year’s worth of quenchant is five years’ worth of filters. In my mind, that’s a good tradeoff.
Karen Gantzer: So, Michael, when the process is filtering the quench, does this happen during production downtime?
Karen Gantzer
Associate Publisher/ Editor in Chief
Heat Treat Today
Michael Mouilleseaux: No, it’s done continuously. Even when the furnace is not running on the weekend, you’re still filtering the oil. You’re going to be taking 20-50 gallons out of the quench tank but you’re putting it right back in. It just passes through filters.
Some people have utilized centrifuges. It’s a very successful way of filtering out carbon particles in oil. The caveat on that is you don’t want the oil above 140 degrees. If you get the oil above 140 degrees and for every 20 degrees you go up, you start doubling the oxidation rate of the oil.
In high-temperature oil, we do a fair amount of modified marquenching. We do it in closed canisters. The seals must be temperature-tolerant, but it is very successful.
The last part is going to be the quench heating and cooling. Typically, at the first part of the week when you’re starting up the furnace or if you’re going from operation A to operation B and it requires a higher temperature quenchant, you’re going to use either gas or electric elements that are going to heat it. Those things need to be monitored so that they’re available when you need them. The last thing that you want to do is start out the week and find out that the quench heaters don’t work; then, you’re trying to find a couple of dummy loads that you can heat up to put into the quench to heat up the quenchant before proceeding with operations.
Then, of great, importance is quench cooling. In petroleum-based quenchants, you’ve got a flashpoint of 400 degrees plus or minus — could be 350, could be 450, depending upon the quenchant that you’re using. You don’t want the temperature of that oil to approach that flashpoint. You do that by using a quench-cooling system. It’s a big radiator. You’ve got a pump, and you set it when you want the pump to go on. You pump the oil out to the quench coolant, and when it comes back, once you’ve attained what your temperature is, then you stop.
Doug Glenn: I’ve got a couple quick questions on this. First, is the quench heater an immersion tube?
Michael Mouilleseaux: Yes. Gas-fired tubes and gas-fired units are very small u-tubes that go into the quench tank. Electrical units have got elements that are tolerant to that.
Doug Glenn: Typically, you’re using those because you’re actually using the quenchant and always putting hot things into it, so once the quench fluid is up to temperature, it’s not a problem. You’re using that quench heater just to get the thing up to temperature. So after that, most of the time, you’re using the cooler to keep it cool, correct?
Michael Mouilleseaux: Absolutely. That’s a control scheme. The last thing that you want to do is set the quench heater so that it’s within five degrees of setpoint and set the quench cooling so that it’s within five degrees of setpoint — then, the temperature just sits there, with heating and cooling fighting each other. You’re heating and cooling oil unnecessarily. You want to give yourself some bandwidth on that.
Material Handling System
Last is going to be the material handling system. In the batch furnace, many have what we call a “rear handler.” We saw the cart and it would push the load into the vestibule, the inner door would open, and it would push the load into the furnace. It’s always preferable to push hot loads, not to pull on them. The reason is that the base trays are alloy and the compressive strength is much higher than the tensile strength is. If you’re pulling on loads, you’re going to break trays.
Once the load is in the furnace, you would have a rear handler so when the cycle is terminated and the inner door opens, you would have a mechanism — it may have a flat bar that’s half the width of the tray — that actually pushes the load into the quench vestibule.
There it’s pushed by the charge car and the inner door is open. That same handler, from the charge car, pushes it into the furnace. Now, when the cycle is terminated, there is a handler in the rear of the furnace that pushes it into the vestibule for quenching.
The exception is right here: When it’s taken out of the vestibule, typically the charge car goes in and grabs it and pulls it out. But, at that point, you’re at 100 or 200 degrees so, at that temperature, you have no material effect upon the strength of the alloy.
Doug Glenn: Okay, the motion it took it from the tray on the left inside is going to push it in and then the next step it’s also going to push it into this “hot zone,” correct?
Michael Mouilleseaux: Yes.
Doug Glenn: But what you’re saying is, when it’s coming out of the hot zone, there’s probably a mechanism on the far righthand side of the hot zone that’s going to push it back. Nothing is going in to pull it out because it’s hot.
Michael Mouilleseaux: Extended reach cars put the load into the vestibule and then put it into the hot zone.
There are some rear handlers that, rather than being a simple push function, have a dog mechanism that allows them to go and get the load in the vestibule and pull it into the furnace. Personally, I am not a fan of that; I like the extended reach car because when you’re pushing something, it is very easy to determine if you’ve put it in the right location. If you grab a load and pull it, you could lose the attachment on that load and then it’s not put exactly where you want it to be.
You can put amp meters on these things so that the amount of force that the motors require to pull in or push out a load. The one thing you need to be cognizant of is that it’s going to take more power — a higher amp draw — to push a 4000-pound load than it is a 2000-pound load. Once you understand what that is, you can monitor these furnaces and then they start making sense to you.
Discover expert tips, tricks, and resources for sustainable heat treating methods Heat Treat Today's recent series. And, if you're looking for tips on combustion, controls systems, or induction in general, you'll find that too! Part 1, today's tips, digs into cleaning and maintenance
This Technical Tuesday article is compiled from tips in Heat Treat Today's May Focus on Sustainable Heat Treat Technologiesprint edition. If you have any tips of your own about induction and sustainability, 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. Maintenance of Induction Coils Used in Hardening Applications
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Soap and hot water will remove sticky quench and debris. Source: Induction Tooling, Inc.
How should you maintain induction coils used in hardening applications? Elbow grease — a little goes a long way. After each use, a simple solution of soap and hot water will remove sticky quench and debris. Scrub hardened dirt with a Scotch-Brite pad. Check for pitting, arcing, and insulator damage. If all is good, use a hot water rinse, and it’s ready for use. If the inductor is to remain on the machine for an extended period, it is advised to wash it and the associated bus daily. Check for damage. Following this simple procedure will reduce business waste.
As industry tries to become more “green,” a number of companies are switching from lubricants that are petroleum or mineral oil-based to water-based (“aqueous”) lubricants instead. However, some of these companies then make the mistake of not changing their degreasing fluids that they use to remove these lubricants prior to their next processing operations, and stay with their standard degreasing fluids, such as acetone or alcohol, which are not effective at fully removing water-based lubricants. Instead, they need to run tests to find an appropriate alkaline-based degreasing fluid for such water-based lubricants, since alkaline-based degreasers will be effective at removing such lubricants. Commonly available dish-detergents (alkaline-based) have been shown to be highly effective for such use.
On site at heat treat operations, gas-fired furnaces can be a significant source of carbon emissions. But depending on the desired heat treatment, an alternative approach that combines induction through heating and intensive quenching could be the “green ticket.” Learn about the ITH + IQ technique and discover how certain steels may benefit from this approach.
This Technical Tuesday article was composed by Edward Rylicki, Vice President Technology, and Chris Pedder, Technical Manager Heat Treat Products and Services, at Ajax TOCCO Magnethermic Corp., and Michael Aronov, CEO, IQ Technologies, Inc.It appears in Heat Treat Today's May 2023 Sustainable Heat Treat Technologiesprint edition.
Introduction
Chris Pedder, Technical Manager Heat Treat Products and Services, Ajax TOCCO Magnethermic Corp. Source: Ajax TOCCO Magnethermic Corp.
Induction heating is a green, environmentally friendly technology providing energy savings and much greater heating rates compared to other furnace heating methods. Other advantages of induction heating include improved automation and control, reduced floor space, and cleaner working conditions. Induction heating is widely used in the forging industry for heating billets prior to plastic deformation. Induction heating is also used for different heat treatment operations such as surface and through hardening, tempering, stress relieving, normalizing, and annealing. However, the amount of steel products subjected to induction heating in the heat treating industry is much less compared to that processed in gas-fired furnaces.
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Gas-fired heat treating equipment is a major source of carbon emissions in the industry. As shown in Reference 1, induction through heating (ITH) followed by intensive quenching (IQ) (an “ITH + IQ” technique) eliminates, in many cases, the need for a gas-fired furnace when conducting through hardening and carburizing processes — the two most widely used heat treating operations for certain steel parts. Eliminating gas-fired furnaces will result in significant reduction of carbon emissions at on-site heat treat operations.
Dr. Michael Aronov, CEO, IQ Technologies, Inc. Source: Ajax TOCCO Magnethermic Corp.
The goal of this article is twofold: 1) to evaluate carbon emissions generated during through hardening of steel parts and carburizing processes when conducted in gas-fired furnaces, and 2) to discuss how these emissions can be reduced to zero using the ITH + IQ process.
Evaluation of Carbon Emissions for Through Hardening and Carburizing Processes
Ed Rylicki, Vice President Technology, Ajax TOCCO Detroit Development & Support Center Source: Ajax TOCCO Magnethermic Corp.
Most through hardening and carburizing operations for steel parts are conducted in batch and continuous integral quench gas-fired furnaces. Assumptions made for evaluating CO2 emissions produced by a typical integral quench furnace are presented in Table 1. Note: The values of carbon emissions presented Table 1 are conservative since they don’t consider the amount of CO2 produced by furnace flame screens and endothermic gas generators used to provide a controlled carburizing atmosphere in the furnace. Also, it’s assumed that the furnace walls are already heated through when loading the parts, so there are no heat losses associated with the thermal energy accumulated by the furnace walls.
Table 1. Assumptions for calculating of carbon emissions by integral quench furnace Source: Ajax TOCCO Magnethermic Corp.
Emissions Generated During the Through Hardening Process
A furnace time/temperature diagram for the through hardening process considered is presented in Figure 1. Carbon emissions Ehard produced by the furnace considered during heating of the load to the austenitizing temperature prior to quenching are calculated by using the following equation,
(Equation 1) Ehard = k • Qhard
where:
■ k = the emission coefficient (equal to 0.050 • 10-3 kg per 1 kJ of released energy when burning natural gas (see Reference 2) ■ Qhard = thermal energy required for heating up the above load from ambient to the austenitizing temperature
A value of Qhard is calculated by the equation below,
■ M = load weight, kg ■ C = steel specific heat capacity (kJ/kg°C) ■ Ta = part austenitizing temperature (°C) ■ To = part initial temperature (°C) ■ Eff = furnace thermal efficiency (a ratio of the furnace thermal losses to the gross heat input)
From equations (1) and (2), the amount of carbon emissions produced by the above furnace during one hardening operation is 40.2 kg. To determine an annual amount of carbon emissions, calculate the number of hardening cycles per year (Nhard) run in the furnace. From Figure 1, a duration of one hardening cycle is 4 hours (3 hours for austenitizing of the parts plus 1 hour for quenching the parts in oil and unloading/loading the furnace). Thus, Nhard is equal to:
Nhard = 360 day • 24 hour • 0.85 / 4 hour = 1826
Figure 1 Source: Ajax TOCCO Magnethermic Corp.
Annual CO2 emissions from one integral quench batch gas-fired furnace are 40.2 • 1836 = 73,807 kg, or more than 73 t
Emissions Generated During Carburizing Process
A simplified furnace time/temperature diagram for the carburizing process considered is presented in Figure 2. Carbon emissions (Ecarb) produced by the above furnace during the carburizing process are calculated by the following equation,
(Equation 3)
Ecarb = k • Qcarb
where:
■ Qcarb = a thermal energy expended by the furnace during the carburizing process. A value of Qcarb amounts to two components:
(Equation 4)
Qcarb = Qcarb1 + Qcarb2
Qcarb in the following equation is:
■ Qcarb1 = energy required for heating up the load to the carburizing temperature
■ Qcarb2 = energy needed for maintaining the furnace temperature during the remaining duration of the carburization process (for compensation of the furnace thermal losses since the parts are already heated up to the carburizing temperature)
A value of Qcarb1 is calculated using equation (2) where the part carburizing temperature Tc is used instead of part austenitizing temperature Ta (see Table 1):
A value of Qcarb2 is a sum of the flue gas losses and losses of the thermal energy through the furnace walls by heat conduction. Qcarb2 is evaluated from the following considerations. Since the assumed furnace thermal efficiency is 65%, the furnace heat losses are equal to 35% of the gross heat input to the furnace. Hence, the furnace heat losses Qloss1 during the load heat up period (the first 3 hours of the carburizing cycle, see Figure 2) are the following:
Thus, the total amount of the thermal energy expended by the furnace during the carburizing cycle is Qcarb = 0.887 • 106 + 0.827 • 106 = 1.71 • 106 kJ. The total amount of the CO2 emissions from carburizing of the load in the furnace considered according to equation (3) is: Ecarb = 0.050 • 10-3 • 1.71 • 106 = 85.7 kg. To determine an annual amount of carbon emissions from one carburizing furnace, calculate the number of carburizing cycles run in the furnace per year. Per Figure 2, a duration of one carburizing cycle is 12 hour (1 hour for the furnace recovery plus 10 hour for carburizing of parts at 927°C plus 1 hour for quenching parts in oil and for unloading and loading the furnace). Thus, the number of carburizing cycles per year Ncarb is:
Ncarb = 360 day • 24 hr • 0.85 / 12 hr = 612
Figure 2 Source: Ajax TOCCO Magnethermic Corp.
Annual CO2 emissions from one integral quench batch carburizing furnace is about 85.7 • 612 = 52,448 kg, or more than 52 t.
Reducing Carbon Emissions Using the ITH + IQ Process
Reference 1 presents results of two case studies of the ITH + IQ process on automotive input shafts and drive pinions. The study was conducted with a major U.S. automotive part supplier. A two-step heat treating process was used for the input shafts, consisting of batch quenching parts in oil or polymer using an integral quench gas-fired furnace for core hardening followed by induction hardening. This two-step method of heat treatment is widely used in the industry for many steel products. It provides parts with a hard case and tough, ductile core.
Substituting the “ITH + IQ” method for the two-step heat treating process not only eliminates the batch hardening process, but also requires less alloy steel for the shafts that don’t require annealing after forging. Thus, in this case, applying the ITH + IQ technique eliminates two furnace heating processes for the input shafts, resulting in the reduction of the CO2 emissions to zero for the shafts’ heat treatment. Per client evaluation, as mentioned in Reference 1, the hardness profile in the intensively quenched input shafts was similar to that of the standard shafts. Residual surface compressive stresses in the intensively quenched shafts were greater in most cases compared to that of the standard input shafts, resulting in a longer part fatigue life of up to 300%.
Per Reference 1, the environmentally unfriendly carburizing process can be fully eliminated in most cases for automotive pinions when applying the ITH + IQ method and using limited hardenability (LH) steels that have a very low amount of alloy elements. A case study conducted for drive pinions with one of the major U.S. automotive parts suppliers demonstrates the intensively quenched drive pinions met all client’s metallurgical specifications and passed both the ultimate strength test and the fatigue test. It was shown that the part’s fatigue resistance improved by about 150% compared to that of standard carburized and quenched in oil drive pinions. In addition, distortion of the intensively quenched drive pinions is so low that no part straitening operations were required.
Conclusion
Coupling Ajax TOCCO’s induction through heating method with the intensive quenching process creates a significant reduction of CO2 emissions produced during heat treatment operations for steel parts. For the through hardening process, eliminating just one batch integral quench gas-fi red furnace will reduce carbon emissions by more than 73 ton per year. For the carburizing process, eliminating just one batch carburizing furnace will reduce carbon emissions by more than 52 ton per year. Note that for continuous gas-fired furnaces, the carbon emission reduction will be much greater due to higher continuous furnaces production rates (hence a much higher fuel consumption).
Per our experience, the ITH + IQ process can be applied to at least 20% of the currently through-hardened and carburized steel parts. Per two major heat treating furnace manufacturers in the U.S., there are thousands of atmosphere integral quench batch and continuous furnaces in operation in the U.S. That means hundreds of gas-fired heat treating furnaces can be potentially eliminated, drastically reducing carbon emissions in the U.S., supporting a lean and green economy.
Ed Rylicki has been in the induction heating industry for over 50 years. He is currently Vice President Technology at Ajax TOCCO Detroit Development & Support Center in Madison Heights, Michigan.
Mr. Chris Pedder has over 34 years of experience at Ajax Tocco Magnethermic involving the development of induction processes in the heat treating industry from tooling concept and process development to production implementation.
Dr. Michael Aronov has over 50 years’ experience in design and development of heating and cooling equipment and processes for heat treating applications. He is CEO of IQ Technologies, Inc. and a consultant to the parent company Ajax TOCCO Magnethermic.
Induction heat treating: no harsh chemicals, gases, or even CO2 emissions. But to get there, heat treaters should first understand how to plan for an induction design and fabrication project upfront. Consider these five important factors before you dive into induction.
This Technical Tuesday article was composed by John Chesna, general manager at Induction Tooling, Inc. and honoree in Heat Treat Today's 40 Under 40Class of 2022. It appears in Heat Treat Today's May 2023 Sustainable Heat Treat Technologiesprint edition.
Introduction
John Chesna General Manager at Induction Tooling Source: Induction Tooling, Inc.
There are many less than obvious factors to consider when preparing and planning for induction. So where to start? There are five important factors that manufacturers with in-house heat treat operations should understand in order to successfully prepare an induction heating project and design.
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But first, what is induction heating? Induction heat treating is the process in which a high frequency conductor (induction tool) induces currents (eddy currents) into an electrically conductive workpiece. Without ever touching the work-piece, the current generated and the resistance causes heating. Ever since its proven usefulness around the time of World War II, induction has been chosen as the go-to heat treatment for a variety of applications across many industries including agricultural, medical, and transportation. Now, it seems that most industries have taken advantage of induction heat treating, and its popularity will likely only continue to increase with the push for the use of “clean” and “green” energy.
#1 Plan for Inductor Wear
One of the most important factors to an induction project is realizing the inductor/ coil is a wear item. It can be highly engineered, hand fabricated, machined, or even 3D printed. Yet, in the overall process, it is still a wear item: an item that will eventually require replacement or repair. The inductor is exposed to the worst of the elements during the induction process and can fail from standard use, accidents, or unforeseen circumstances. Inductor designers are constantly being challenged to create tools that will last longer, require less maintenance, or run more cycles. All of those can be achieved, but the inductor will eventually require replacing and that is not a bad thing!
A properly serviced and maintained inductor will ensure quality parts are being produced. As the inductor wears, the efficacy degrades, leading to undesirable results. Repair of the inductor will correct this issue and ensure the parameters required for the desired heat treat pattern are restored. Depending on production needs, a good principle is to have more than one inductor on hand so that while one is being repaired the spare inductor can remain on the machine to keep up with manufacturing demand. Planning for this is important for the project’s timing and budget.
#2 Types of Inductor Designs
Determining a specific inductor design will be necessary to properly heat parts. The inductor creates the magnetic field in the workpiece, and typically the inductor is shaped to couple closely where heat treatment of the part is desired. Additionally, if quenching is required for the heating application, this function will be considered in the inductor’s design. The inductor’s design must deliver the electrical energy and quench medium to the workpiece while allowing accessibility for material handling purposes. For this reason, inductors take on many different designs.
Six turn multi-turn inductor Photo Source: Induction Tooling, Inc.
Pancake inductor with strap supports Photo Source: Induction Tooling, Inc.
MIQ (Machined Integral Quench) scanning inductor with removable quench plate Photo Source: Induction Tooling, Inc.
Common inductor designs include:
Pancake: used for heating flat surfaces
Single turn or multi-turn: commonly shown as copper tubing wrapped around cylindrically around the workpiece
Hairpin: typically, a simple back and forth loop used to heat long lengths internally or externally on the workpiece
Split return: used to focus the energy in particular areas of the workpiece
MIQ (machined integral quench) paddle: the most commonly used design for scanning applications
#3 Power and Frequency
Know the power supply and/or work-head power and frequency. Depending on the composition of the part that requires processing, the power and frequency of the equipment will help estimate the depth of the pattern that can be achieved, as well as help determine how successful the part will be for induction heating. Irregularly shaped geometries with points, holes, or sharp edges sometimes cause difficulty establishing eddy currents where the induction pattern is desired. Some parts, after review, are good candidates for induction heat treatment but cannot be processed with the existing power supply and/or work-head setup.
If an inductor is being built to mount to existing induction equipment, it is important to know the scope of parts that are currently being processed or expected to be processed on the machine. The electrical circuit of the power supply, work-head, and inductor must load match to the part. If a variety of parts are being run then multiple styles of inductors may exist or will be required to be used. Different designs of inductors, e.g., single-turn, multi-turn, or split return used on the machine will change the transformer effect and capacitor requirements of the system. Availability to tune the system capacitance and inductance becomes vitally important for operation. Please note that adjusting capacitance can be dangerous and should only be done by a trained technician. Newer power supplies function differently than older models, yet load tuning needs to be considered.
#4 Part Details
A detailed pre-induction print is needed. The print should list the material as well as the desired heat treatment pattern to determine the inductor design. As the print specifies the pattern, it should also provide limits. Inductors are then typically designed to the shape of the part. The inductor may require an integrated quench, electrically insulating protective coating, locators, or additional assembly fixturing depending on the part’s size. An inductor built for one part may be used or tried on a similar part. However, the same results cannot be expected to render on the part for which it was not designed. If the manufacturer knows that a family of parts will be run, the full scope should be presented to inductor designers for consideration before the build.
#5 Material Handler
Ideally an inductor supplier would be contacted to develop the induction heating process for a part; then, that information should be shared with the material handling designer. That would be the ideal, but that’s not the way it usually happens. Sometimes, a machine is built to process a part that no longer is in use, so the machine is now being retrofitted to process different parts. The design of a new inductor is needed to accommodate this existing machine which may create size constraints to the inductor’s design.
The contact style, how the inductor mounts to the work-head, will need to be determined. There are a variety of commonly used power supplies and work-heads available from OEMs in the market. As each OEM keeps their contacts standard to their equipment, there is no singular standard footprint in the market. Once the contact style has been determined, the inductor can be designed for maximum power delivery efficiency. How the part and inductor are presented to each other is important. The centerline distance, a measurement from where the inductor mounts to where the part will be processed, needs to be known. The centerline determines the required length of the inductor and indirectly how much room is available for the inductor’s design.
Conclusion
Due to the variety of factors, no two projects are ever the same. Induction heating is an exciting technology, and I encourage everyone to learn more about it.
About the Author: John Chesna is the general manager of Induction Tooling, Inc. and has been involved with the induction heat treating industry for over 8 years. He is a graduate of the University of Akron with a Bachelor of Science in Mechanical Engineering Technology. His responsibilities include overseeing day-to-day operations including the design, manufacturing, and testing of induction heat treating inductors. Additionally, John was a recipient of Heat Treat Today's 40 Under 40 award in 2022.
Heat Treat Today’s Technical Tuesday feature means that on just about any given Tuesday, there will be an article that aims to educate our heat treating readers—be it in a process, equipment, metals, analysis, critical parts, or more. Enjoy this sampling of Technical Tuesday articles from the past several months.
Case Study: Heat Treat Equipment Meets the Future Industry Today
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Construction and schematic furnace cross-section CMe-T6810-25 Source: SECO/WARWICK
How has one heat treat furnace supplier contended with modern challenges of manufacturing? In this case study about a shift away from traditional forms of heat treat, explorehow vacuum furnace technology has more technological horizons to bound.
Several key features discussed will be the various challenges that characterize modern industry; the differences between historical heat treat furnaces and vacuum furnaces; furnace features that can meet these obstacles; and a close look at what one equipment option from SECO/WARWICK helps. Additionally, explore the case study of a process that resulted in the following assessment: "all technological requirements have been met, obtaining the following indicators of efficiency and consumption of energy factors calculated for the entire load and per unit net weight of the load (700 kg)."
Eric Yeager of Cleveland Electric explaining the 101 of all things thermocouple Source: Heat Treat Today
How do thermocouples work? How would you tell if you had a bad one? Those ever present temperature monitors are fairly straightforward to use, but when it comes to how it works — and why — things get complicated.
This transcript Q&A article was published in the print edition last year (2022), but there was too much information to fill the pages. Online, read the full-length interview, including the final conversation about how dissimilar metals create EMF. Included in the discussion is proper care of the T/C and knowledge of when it’s time to replace.
Trends in the heat treat industry Source: Unsplash.com/getty images
What’s “hot” for heat treaters in recent months? The trends are pointing towards streamlining upgrading information systems, more efforts to reduce carbon footprint, and ensuring processes in salt quenching and electricity use are as efficient as they can be.
Each of the 6 trends included in the article demonstrates that heat treaters are making thoughtful and responsible decisions and purchases. Considerations include care for the environment and methods to help employees share and receive information needed for each job.
Read more about each of the trends to see what’s happening with equipment purchases and technology decisions and how companies are pushing to make that carbon footprint smaller.
A Quick Guide to Alloys and Their Medical Applications
Sneak peak of this medical alloys resource Source: Heat Treat Today
If you're pining for a medical heat treat quick resource in our "off-season," we have a resource for you. Whether you are a seasoned heat treater of medical application parts or not, you know that the alloy composition of a part will greatly determine the type of heat treat application that is suitable. Before you expand your heat treat capabilities of medical devices, check out this graphic to quickly pin-point what alloys are in high-demand within the medical industry and what end-product they relate to.
The alloys addressed in this graphic are: titanium, cobalt chromium, niobium, nitinol, copper, and tantalum.
Resource -- Forging, Quenching, and Integrated Heat Treat: DFIQ Final Report
Examples of DFIQ equipment Source: Joe Powell
How much time and energy does it take to bring parts through forging and heat treatment? Have you ever tried to integrating these heat intensive processes? If part design, forging method, and heat treat quenching solutions are considered together, some amazing results can occur. Check out the report findings when the Direct from Forge Intensive Quenching (DFIQTM) was studied.
Forgings were tested, in three different locations, to see if immediate quenching after forging made a difference in a variety of steel samples. The report shares, “The following material mechanical properties were evaluated: tensile strength, yield strength, elongation, reduction in area and impact strength. Data obtained on the mechanical properties of DFIQ forgings were compared to that of forgings after applying a conventional post-forging heat-treating process.”
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.”
Consider the numerous systems in your heat treat operations. What makes up the anatomy of each furnace? In this "Anatomy of a Furnace" series, industry experts indicate the main features of a specific heat treatment system. For this inaugural feature, note how the schematics demonstrate how the tip-up furnace is able to process massive loads in an atmospheric sealed environment at highly controlled temperatures.
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Annotations for this furnace corpus were provided by Dan Herring, The Heat Treat Doctor®, The HERRING GROUP, Inc. A front view of a tip-up furnace as well as a back view of a different tip-up are provided along with the labels.
Download the full graphics by clicking the images below.
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This Technical Tuesday article is drawn from Heat Treat Today's February's Air & Atmosphere Furnace Systems print edition.
