Improving Hardening and Introducing Innovation for In-House Heat Treat

/ AEROSPACE HEAT TREAT, HARDENING TECHNICAL CONTENT

In this Technical Tuesday by Paulo Duarte, project manager, Metalsolvus, explores how digital tools lead the way in vacuum hardening operations to ensure energy efficiency and processing repeatability.

This piece was originally published in Heat Treat Today’s March 2025 Aerospace print edition.

Vacuum hardening has been the chosen process for hardening tools used in plastic injection, die casting, and metal sheet stamping over the past few decades. Although widely used and accepted, there is still room for improvement in tool performance through quality-driven procedures. By employing easy methods of measurement, study, and testing, it is possible to enhance part integrity and mechanical properties, while simultaneously reducing heat treatment time and energy consumption. Advanced metallurgical analyses of heat treatment cycles and equipment can introduce better tools on the market, as well as provide time and cost saving heat treatments.

Basics of Vacuum Hardening

In vacuum hardening furnaces, temperature and time are carefully controlled at specific load locations to ensure optimal hardening. Optimal
practices focus on heating and soaking the metal parts during heat treatment. The controlled introduction of vacuum and inert gases during the process ensures the right protective atmosphere for treatment, resulting in steel that is mainly free from oxidation and decarburization. This preserves the surface integrity of the tools.

Cooling is achieved through the injection of an inert gas into the heating chamber, with controlled pressure and adequate recirculation between the heat exchanger and the hot zone (Figure 1). Different gas injection directions are utilized depending on the load being treated, ensuring optimal cooling.

Figure 1. Cooling parts in vacuum hardening furnaces — inert gas injection on the hot chamber during cooling

Hardening of Large Tools

Heating and quenching large tools is one of the most challenging situations for vacuum hardening, as temperature control and part microstructure integrity are more difficult to obtain, which affects part quality. Large tools, typically made of hot work tool steels, are hardened in large furnaces. To minimize deformation, parts are preferably positioned vertically inside the furnace (Figure 2).

Figure 2. Large molds positioned inside the vacuum hardening furnace, two parallel cavities

Surface soaking times for big tools can significantly exceed standard austenitization and tempering times due to thermal gradients existing within the
parts. Mold cores usually achieve the right soaking and tempering recommendation through accurate temperature control, monitored by well-positioned core thermocouples. A tool’s microstructure and performance will depend heavily on geometry, size, and temperature uniformity achieved during treatment. See Figure 3 for the core and surface typical hardening cycles for large tools.

Figure 3. Heating and soaking cycle for the hardening of large tools (“Heat Treatment of a AISI H11 Premium Hot-Work Tool Steel”)

The cooling phase is crucial in determining the final properties of both the surface and core of the tool. Higher gas injection pressures result in faster
cooling and increased toughness, but this also introduces greater deformation risks, when directly cooled from austenitization temperature, so martempering done at low pressures is usually required.

Balancing cooling pressure is one of the most secret topics in vacuum hardening. With a variety of parameters and procedures used among heat treaters, measuring and testing is essential for achieving consistent quality for better controlling the hardening process and attaining the best part quality.

Figure 4. Microstructure and toughness obtained after the use of different hardening cooling rates (image from Transactions of the 15th NADCA Congress, 1989)

The use of higher or lower inert gas pressures directly affects the cooling rate, making it faster or slower, respectively. Regulating the gas injection pressure during the cooling phase significantly impacts the material’s toughness, even when cooling occurs within the bainitic-martensitic domain commonly observed in vacuum hardening practices. Faster cooling leads to finer microstructures, which in turn results in tougher materials. However, fully martensitic microstructures are rarely achieved in industrial vacuum hardening furnaces and are typically limited to smaller loads composed of
small parts. In larger parts, the risk of pearlite formation increases, especially when cooling rates fall around 3°C/min (5°F/min) at the core, as illustrated in Figures 4 and 5.

Figure 5. Microstructure of Uddeholm Orvar Supreme steel after quenching using different cooling rates

In industrial heat treatments of large tools, accurately monitoring core temperature is challenging, as it is difficult to position a thermocouple hole exactly at the innermost location or a nearby region. This makes it harder to control the hardening process and prevent pearlite formation. Therefore, studying the process to establish effective control measures is essential for achieving the highest possible quality.

Heat treatment simulation simplifies this task by allowing the hardening process to be predicted, with thermal gradients estimated and compensated through furnace control parameter adjustments. Figure 6 presents a real case study, where the temperature distribution inside a large mold was fully characterized during the entire heat treatment cycle using FEM (Finite element method) simulation and validated through actual thermocouple measurements. FEM simulation, as a proven and highly effective technique for predicting heat treatment cycles, enables heat treaters to implement optimized, computer-supported heat treatment practices.

Figure 6. Mold temperature gradients during vacuum hardening: a) FEM mesh, b) gradients during heating at lower temperatures, c) gradients at the last pre-heating steps, and d) gradients during austenitization from Maia et al. “Study of Heating Stage of Big Dimension Steel Parts Hardening”; e) gradients during mold cooling from Pinho et al. “Modelling and Simulation of Vacuum Hardening of Tool Steels”

Vacuum Hardening Standard Block
Size and Cycle Forecast

When working with loads composed of small to medium-sized parts, the core temperature of the load can be monitored using dummy standard blocks. These blocks have a central hole to accommodate the thermocouple used to control the heat treatment cycle. The dummy block should be selected to
closely match the size of the largest part in the load. However, in commercial heat treatment settings, part sizes can vary widely, making it di cult to maintain a comprehensive set of dummy blocks that represents all possible heat treatment scenarios.

Once again, simulation proves valuable in helping heat treaters gather useful data to anticipate the heat treatment cycle and determine the appropriate range of dummy blocks to have available on the shop floor. The procedure for selecting the dummy block range and forecasting the corresponding
heat treatment times is outlined in the following equations. Ideally, the standard block should be made from the same material as the largest part in the load. If the materials differ, the characteristic length of the block can be calculated using the first of the following equations.

Table 1. Proposed dimensional distribution range for cubic and cylindrical standard blocks and expected cycle times in a typical 600 x 600 x 900 mm hardening furnace (data from Figueiredo et al., “Study of a Methodology for Selecting Standard Blocks for Hardening Heat Treatments”)

Table 1 lists a range of proposed dummy block sizes to be used for monitoring the load temperature during heat treatment. The time to end of soaking at higher temperature is also given by Table 1 for a typical 600 x 600 x 900 mm hardening furnace. Times were obtained by FEM simulation and can be used to forecast the end of austenitization in a hardening process of each dummy block.

The simulated times were validated by using real parts temperature measurement by thermocouples. These were the calculated errors based on simulation and heat treat validation trial:

  • Plate Example: 20 x 300 x 200 mm
  • Ideal standard block: diameter or edge: 51 mm
  • Maximum Error — same material block:
    • Cylindrical: -0.2% (-0.7 min)
    • Cubic: -0.1% (-0.4 min)
  • Maximum Error — block — Stainless steel 304:
    • Cylindrical: +2.2% (+9.2 min)
    • Cubic: +1.65% (+6.9 min)
  • EDM Block Example: 200 x 200 x 200 mm
  • Ideal standard block: diameter or edge: 200 mm
  • Maximum Error — same material block:
    • Cylindrical: -3.9% (-22.6 min)
    • Cubic: 0% (0 min)
  • Maximum Error — block — stainless steel 304:
    • Cylindrical: +17.3% (+100.3 min)
    • Cubic: +12.2% (+70.8 min)

Optimizing the Vacuum Hardening of Tools

Figure 7. Effect of selecting different temperature (T) range for starting to control the isothermal stage time. a) T criteria and respective cycle time reduction; b) surface mechanical properties obtained by using different T; and c) core properties after tempering at different T range (Miranda et al., “Heat Treatment of a AISI H11 Premium Hot-Work Tool Steel,” MSC)

FEM simulation can also be used to optimize the heat treatment process, but metallurgical testing remains crucial for providing reliable insights into safely reducing cycle time and energy consumption. Typically, for setting the isothermal stage time, a tolerance of -5°C relative to the temperature setpoint is used, leading to savings in both heat treatment duration and power consumption, as shown in Figure 7a. However, Figure 7b demonstrates that higher tolerance values (ΔT) can be considered. Tolerances of up to -10°C or even -20°C can be applied for controlling the soaking time without significantly affecting the hardness and toughness of the parts. Naturally, these results depend on the desired setpoints for the isothermal stages, but Figure 7c reflects the worst-case scenario for ΔT, referring to the use of lower austenitizing and tempering temperatures commonly applied in the hardening of hot-work tool steels.

Future Trends of Vacuum Hardening

Innovations like digitalization, automation, and resource reduction, as part of Industry 5.0 initiatives, are expected to drive advancements in heat treatment processes. Long martempering, a heat treatment under development for hardening hot-work tool steels, shows promise as an alternative to traditional quenching and tempering. This process offers a balance of high hardness and toughness in significantly less time, providing energy savings and faster turnaround.

Figure 8. New long martempering heat treatment cycle: AISI H13 premium toughness for two different long martempering temperatures (“Study of The Bainitic Transformation of H13 Premium Steel”)

New Vacuum Hardening Process — Long Martempering

Long martempering is a heat treatment under development that can be used to harden hot-work tool steels. Long martempering is a process somewhat similar to austempering but is applied to steels rather than cast irons. Performed at temperatures within the martempering range, long martempering corresponds to an interrupted bainitic heat treatment with a specific process window (Figure 8) where high toughness is achieved at hardness levels exceeding those obtained through traditional quenching and tempering. Table 2 lists the mechanical properties attained for 5Cr hot-work premium tool steels.

The transformation during long martempering is not yet fully characterized in terms of microstructure, however, curved needles of bainitic ferrite are observed without carbide precipitation. This phenomenon is generally not associated with steel but rather with ausferrite in cast irons. Nonetheless,
it is evident in at least H11 and H13 premium steel grades. This one day martempering treatment could potentially replace the traditional two- to three-day heat treatment cycle for large tools, offering significantly faster lead times and reduced energy consumption. Moreover, the mechanical properties achieved through long martempering are notable, as high levels of both hardness and toughness are obtained simultaneously, as demonstrated in Table 2.

Table 2. Mechanical properties of the new hardening process — long martempering

Industry 5.0

The integration of heat treatment equipment with management software enhances furnace utilization, quality control systems, and maintenance practices. Industry 5.0 can be implemented in heat treatment plants through the connection of databases that collect inputs from furnaces (e.g., temperature, time, pressure, heating elements, and auxiliary equipment performance) and production data (e.g., batch numbers, order details, operator
information, cycle setup, and load weight). This data is analyzed by software to generate valuable insights for plant management, process optimization, predictive maintenance, and quality control.

Figure 9. Heat treatment plant supervision solution

A supervision interface for a 5.0 solution can monitor furnaces and control them
remotely in real time (Figure 9). Operators receive updates on tasks, alerts, and production schedules. Additionally, plant productivity, efficiency, and maintenance
can be tracked through the same supervision software, whether on site or remote. Automatic reporting is also possible, enabling the approval or rejection of cycles based on criteria that are not typically used in heat treatment plants. This not only
improves quality but also facilitates process optimization and cost reduction.

Conclusion

Figure 10. Heat treatment quality automatic report including automatic approval

Acquiring a full understanding of furnaces in operation through data measurement and analysis allows full control over the heat treatment process. This facilitates process development, enabling cycle optimization and improvement in part quality. Additionally, testing and simulation practices can lead to cost reduction and shorter lead times.

The introduction of long martempering and Industry 5.0 will significantly enhance heat treatment processes, leading to improved delivery times and reduced operational risks. Automation and digitalization bring more data to the shop floor, improving plant management and resulting in greater efficiency, higher quality parts, and simplified task execution.

Finally, current personnel are busy with routine operations that are based on longestablished practices and may be limiting opportunities for innovation. Therefore, new teams or external consultants can be leveraged to focus on designing, studying, testing, and implementing each new heat treatment solution.

References

Fernandes, José, Laura Ribeiro, and Paulo Duarte. “Study of the Bainitic Transformation of H13 Premium Steel.” MSC thesis, Faculty of Engineering of Oporto University, 2021.

Figueiredo, Ana, Paulo Coelho, José Marafona, and Paulo Duarte. “Study of a Methodology for Selecting Standard Blocks for Hardening Heat Treatments.” MSC thesis, Faculty of Engineering of Oporto University, 2022.

Kind & Co. “Vacuum Hardening with Highest Levels of Precision.” Accessed January 30, 2025. https://www.kind-co.de/en/company/technologies/vacuum-hardening.html.

Maia, Pedro, Paulo Coelho, José Marafona, and Paulo Duarte. “Study of Heating Stage of Big Dimensions Steel Parts Hardening.” MSC thesis, Faculty of Engineering of Oporto University, 2013.

Metaltec Solutions. “Brochure Presentation.” Accessed January 30, 2025. https://www.metalsolvus.pt/en/wp-content/uploads/2019/01/plant-supervisionbrochure-V3.pdf.

Miranda, Isabel, Laura Ribeiro, and Paulo Duarte. “Heat Treatment of AISI H11 Premium Hot-Work Tool Steel.” MSC thesis, Faculty of Engineering of Oporto University, 2024.

Pinho, José Eduardo, Gil Andrade Campos, and Paulo Duarte. “Modelling and Simulation of Vacuum Hardening of Tool Steels.” MSC thesis, Aveiro University, 2017.

Ramada. “New Hardening Furnace up to 4 Tons.” Accessed January 30, 2025. https://www.ramada.pt/pt/media/noticias/novoforno-de-tempera-vacuo—ate-4-tons-.html.

Schmetz. “Schmetz Heat Treatment Furnaces.” Accessed January 30, 2025. https://edelmetal.com.tr/en/heat-treatmentfurnaces.

Schmetz. Sketch of the Cooling Process in the Vacuum Hardening Furnace: Schmetz Commercial Proposals Drawing – Metalsolvus Training Courses
Documentation.

Seco/Warwick. Vector 3D Hardening Furnace Commercial Brochure.

Solar Manufacturing. “Solar Vacuum Hardening Furnace.” Accessed January 30, 2025. https://solarmfg.com/vacuum-furnaces/horizontal-iq-vacuumfurnaces.

Wallace, J.F., W. Roberts, and E. Hakulinen. “Influence of Cooling Rate on the Microstructure and Toughness of Premium Grade H13 Die Steels.” Transactions of the 15th NADCA Congress (1989).

About the Author:

Paulo Duarte is a researcher and consultant on heat treat technologies. His education and expertise in metallurgy has culminated in several articles and patents. He was a former technical manager within bohleruddeholm group for the Portuguese market and heat treatment manager with the same group. Currently, Paulo efforts focus on helping heat treaters by providing innovative, more efficient, and profitable heat treatment services to companies.

For more information: Contact Paulo Duarte at paulo.duarte@metalsolvus.pt.

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    Major Auto Maker Pledges $20 Billion for US

    / AUTOMOTIVE HEAT TREAT NEWS, MANUFACTURING HEAT TREAT NEWS

    A major automaker announced a $20 billion investment in United States-based manufacturing.

    Hyundai‘s investment, which the automaker described as a pledge to increase localized production in the United States, will create over 1,000 jobs. As part of the pledge, the company will open a $5.8 billion steel plant in Louisiana.

    This near-shoring move by Hyundai is one among many automakers who are currently planning major U.S. investments, including Stellantis, which promised $5 billion to U.S manufacturing and Honda, which is expected to produce new Civic hybrids in Indiana.

    Press release is available in its original from here.

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    1 Big Event vs. 7 Industry Events

    / EDITOR

    Heat Treat Today publishes twelve print magazines a year and included in each is a letter from the editor, Bethany Leone. In this installment, which first appeared in the March 2025 Aerospace Heat Treating print edition, Bethany gives a preview of important events ahead in 2025 for the heat treating industry.

    Feel free to contact Bethany at bethany@heattreattoday.com if you have a question or comment. 

    Just about now, the demands of one big event — welcoming a newborn into our family — will be monopolizing my time for the next few months. While I am more than happy to set aside work to get to know this little person, let’s not deny that I’m missing out on quite a few amazing industry events!

    The late spring period of the year sees more people willing to travel, and so events abound for our industry. This editor’s page highlights just a few things that you can enjoy (and that I will be missing) between now and June.

    March Highlights

    The end of March kicks off the trade show season in Las Vegas, NV. At TMS 2025, metallurgists gather from March 23 to 27 to discuss industrial innovations. With more than 100 symposia on the docket, the sessions are divided into 11 tracks. These categories include additive manufacturing, advanced characterization methods, and light metals. The exhibition includes a poster presentation space. Suffice it to say, this event is intended for heat treat researchers and implementers who are looking to hear about practical innovations in the materials space.

    April Highlights

    Four years ago, I attended the International Conference on Hot Isostatic Pressing (HIP) in Ohio. This April 6 to 10, the city of Aachen, Germany, will be hosting the conference. Attend sessions and tour plants in the area over the course of several days. Additive manufacturing coupled with HIP as well
    as heat treating with HIP vessels will be part of the discussion. The event page says, “Improvements in HIP technology … have the potential to strengthen the competitiveness of many companies which are active in emerging industrial areas.”

    During that same week, heat treaters will be gathering in Detroit, MI, for RAPID + TCT from April 8 to 10. For those interested in staying at the top of industrial innovation in additive manufacturing and industrial 3D printing, this is the event to watch. Browse real-world solutions at the show and dig into the details at technical sessions. Being that this is the largest AM show in North America, it is worth a visit if this is a technology your operations are curious about or interested in understanding better.

    The following week, CastExpo will be attracting suppliers, peers, and customers to the casting market. Happening in Atlanta, GA, from April 12 to 15, this is primarily a time once every three years to network and advance strategy. Among the different topics addressed through exhibits, presentations, and featured events, two are particularly noteworthy for the U.S. manufacturing industry in 2025: reshoring and supply chain & logistics. Of ever-growing importance are topics such as artificial intelligence & machine learning and simulation.

    If you are interested in any part of the ceramics supply chain — be it sourcing material or implementing new technologies, the Ceramics Expo USA in Novi, MI, will be the event to attend from April 28 to 30.  is annual event, like many, offers space to collaborate and new partners to create solutions.

    May Highlights

    Launch your May with AISTech 2025 returning to Nashville, TN. The annual iron and steel conference offers opportunities to connect and hear advances
    happening in the industry. There are so many opportunities to connect with suppliers in the industry and advance one’s understanding of what is happening. From May 5 to 8, you can take the pulse of what direction this segment of American manufacturing is headed and how to prepare.

    Bonus Event

    While nominations are always open, Heat Treat Today’s 40 Under 40 launch will be happening in May 2025. Jayna McGowan led the charge last year,
    and the team already is excited to see what in-house heat treat professionals in North American manufacturing will be nominated and recognized this year. Visit www.heattreattoday.com/40under40 for more information about how to nominate.

    I’m looking forward to reconnecting with the industry folks later this summer. In the meantime, there are a few Heat Treat Kids onesies I’m needing to sort …

    Bethany Leone
    Managing Editor
    Heat Treat Today

    Contact Bethany at bethany@heattreattoday.com.

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    Walk-In Batch Ovens Shipped To Energy Industry

    / ENERGY HEAT TREAT NEWS, Featured

    A shipment of six (6) heavy-duty walk-in batch ovens was delivered to a manufacturer of products for the energy industry. These industrial ovens will be used for baking glue onto products.

    Mark Schahczinski, Senior Sales Engineer, Wisconsin Oven Corporation

    The batch ovens, from Wisconsin Oven Corporation, have a maximum operating temperature of 500°F and guaranteed temperature uniformity of ±5°F at 285°F. A combination airflow configuration ensures even heat distribution throughout the chambers to optimize heating rates and temperature uniformity. Nine (9) point profile tests were conducted in each empty chamber under static operating conditions to verify temperature uniformity. 

    “We are proud to continue our partnership with this valued customer who has purchased multiple ovens from Wisconsin Oven over the years. Their trust in our products is a testament to our commitment to providing high quality equipment and building long term relationships with our customers,” said Mark Schahczinski, Senior Sales Engineer, Wisconsin Oven Corporation.

    Press release is available in its original form here.

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    News from Abroad:

    / MANUFACTURING HEAT TREAT NEWS

    In today’s News from Abroad installment, we highlight processing and initiatives that aim to improve operations and improve sustainability. Read more about a method used in the production of parts with complex geometries; a venture to create the world’s first fossil-free, ore-based steel with renewable electricity and green hydrogen; and a production plant that will generate around 9,000 tons of green hydrogen a year to be used for the production of carbon-reduced steel.

    Heat Treat Today partners with two international publications to deliver the latest news, tech tips, and cutting-edge articles that will serve our audience – manufacturers with in-house heat treat. Furnaces International, a Quartz Business Media publication, primarily serves the English-speaking globe, and heat-processing, a Vulkan-Verlag GmbH publication, serves mostly the European and Asian heat treat markets.

    Investing In the Future

    A commitment to technical excellence and innovation in metalworking

    “To meet the growing demand for qualified experts and to impart knowledge in a practical and timely manner, the OTTO JUNKER Academy has been offering a comprehensive professional training program for the planning, modernization, operation, repair and maintenance of industrial furnaces since 2014. The program covers key areas such as induction melting and heat treatment of metals, as well as universal topics such as economy and energy efficiency. In addition to the technical content, participants are also introduced to theoretical peripheral subjects directly related to industry and development. Safety aspects at all levels are also given priority.”

    READ MORE: “OTTO JUNKER Academy: Practical professional training for the future of the metal industry for more than ten years” at heat-processing.com

    EAF Replaces Blast Furnace at SSAB’s Site in Sweden

    Swedish steelmaker SSAB blast furnaces in Oxelösund, Sweden, replaced with an electric arc furnace.

    “Swedish steelmaker SSAB is replacing its blast furnaces in Oxelösund, Sweden, with an electric arc furnace and associated raw material handling. The aim is for the new production system to be up and running towards the end of 2026. The Oxelösund mill is the first in the green transition of SSAB’s entire Nordic production system….

    SSAB has obtained all the required permits and secured the availability of sufficient amounts of fossil-free electricity.”

    READ MORE: “SSAB to replace Oxelösund blast furnaces with EAF“ at Furnaces International. 

    Celsa Barcelona Enhances Operational Efficiency

    State-of-the-art Condoor® systems for electric arc furnace (EAF)

    “SMS group has been awarded a contract by Celsa Barcelona to supply two state-of-the-art Condoor® systems for electric arc furnace (EAF) #2, along with relevant modifications to the electrics and automation. This collaboration marks another milestone in the long-standing partnership between the two companies, aimed at enhancing operational efficiency and sustainability in steel production.

    The Condoor® technology is set to improve the performance of electric arc furnace #2 by increasing the yield and improving safety with manless operation on the floor. These enhancements are expected to provide Celsa Barcelona with OPEX savings and operational efficiencies, aligning with their commitment to sustainable steelmaking practices. The delivery of the Condoor® system is planned for November 2025.”

    READ MORE: “Condoor® technology for CELSA Barcelona’s electric arc furnace” at heat-processing.com

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    Aviation Industry Supplier Expands with HPGQ Furnace

    / AEROSPACE HEAT TREAT NEWS, VACUUM FURNACES NEWS

    A screws and fasteners manufacturer for the aviation industry is expanding its heat treating operations with a vacuum furnace with high-pressure gas quenching (HPGQ) and high vacuum for multipurpose and dedicated applications. The vacuum’s heating chamber is 16x16x24 in (400x400x600 mm), a compact design that accommodates the company’s small in-house hardening plant while still being large enough to enable efficient heat treatment of multiple components at once.

    Maciej Korecki
    Vice President of Vacuum Business Segment
    SECO/WARWICK

    The SECO/WARWICK furnace is designed with the ability to work on both nitrogen and argon and includes a round heating chamber with a temperature uniformity of +/-9oF (+/-5oC), and convection heating up to 1590°F (850°C). The Vector HV (high vacuum) furnace meets standards required in the heat treatment of components intended for the aviation industry; material heating processes require cleanliness (which is why an additional argon-partial pressure system was used) and a high heating temperature of 2192oF (1200oC).

    “The Client required very short cooling times, which are possible with the use of a 15 bar abs gas blower,” said Maciej Korecki, vice president of the vacuum segment, SECO/WARWICK Group. “Our advantage is that it is a proven solution (our standard but adapted to the partner’s specific requirements). Vector offers wide personalization possibilities, which significantly reduces project costs and ensures faster implementation time.”

    Press release is available in its original from here.

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    Basics of Vacuum Furnace Leak Detection, Part 2

    / Manufacturing Heat Treat Technical Content, VACUUM PUMPS GAUGES VALVES TECHNICAL CONTENT

    Part 1 of this article by Dave Deiwert, owner and president of Tracer Gas Technologies, was published in Heat Treat Today’s November 2024 Vacuum Heat Treat print edition and online and explored finding leaks with and without a leak detector, the best equipment for leak detection, and 10 tips for finding a leak with a helium leak detector. In this week’s Technical Tuesday we bring you part 2, where Dave further addresses leak detection using a helium leak detector including modern advancements in helium leak detector technology, the best place to connect a leak detector, maintaining a leak detector, and discerning whether to repair or replace components with a leak.

    This informative piece can be found in Heat Treat Today’s March 2025 Aerospace print edition.

    Past Challenges in Leak Detector Operation

    When I started my career in 1989, helium leak detectors required frequent maintenance, often caused by improper shutdown or power outage. Another problem with the older detectors is how easily someone can improperly disconnect the test line while it is still in test mode. These situations could cause backflow of diffusion pump oil. An improper shutdown or power loss often required a major overhaul of the leak detector before you could use it again.

    If an operator or maintenance technician forgot the leak detector was still in test mode and disconnected the test line from the leak detector to the furnace, the inrush of air to the leak detector also would require a major overhaul of the leak detector. Sometimes the inrush of air would cause the filament in the mass spectrometer to burn out. Additionally, in the days of diffusion pump leak detectors, significant backflow of diffusion pump oil could enter the valve block and possibly the mass spectrometer.

    Modern Advancements in Helium Leak Detectors

    The first major improvement in leak detector design targeting reliability and significantly lowering the cost of ownership was replacing the diffusion pump in the detector with a turbo pump. Replacing the diffusion pump with a turbo pump in modern leak detectors allows that leak detector to get into test mode sooner at a higher crossover pressure.

    Figure 1. Evaluating a vacuum furnace for leaks

    In addition, the turbo pumped leak detectors are much less at risk for pressure bursts due to opening the test line while still in test mode or operating some process gas valve while the leak detector is in test mode. With diffusion pumped leak detectors, these events cause a significant maintenance event. But with a turbo pumped leak detector, most likely it will drop out of test mode but be ready to go back into it once the pressure burst event has been solved.

    A third benefit of the turbo pumped leak detectors is they typically have a much better helium pumping speed during testing which helps with response time, reaching base leak rate sooner, and recovering more quickly after detecting a leak.

    Lastly, leak detectors with greater helium pumping speed benefit with a greater signal-to-noise ratio.

    The next major advancement in leak detector design was replacing tungsten filaments with thoria-coated iridium; today the whole leak detector industry is using yttria-coated iridium filaments. The newer fi lament materials operate at a lower temperature but the most significant benefit is how much more robust they are to pressure bursts. Tungsten filaments used in older leak detector mass spectrometer designs would “burn out,” creating an open circuit and loss of operational capability of the leak detector. My experience and that of others shows you can expect to get thousands of hours of more use from each modern filament vs. the old tungsten filaments. This development further aided the reliability and cost-effective ownership of leak detectors.

    Another advancement is that modern detectors can now respond to sudden rises in test pressure. If an operator accidentally leaves the leak detector in test mode and then proceeds to disconnect the hose from the furnace, the leak detector will likely sense the sudden rise in test pressure, close the test valve, and then turn off the mass spectrometer filaments and amplifier to protect them and the turbo pump from the pressure spike. The leak detector will document the event as an alarm but soon be ready for the next test with no maintenance required.

    Older technology leak detectors gave the user no status signals beyond:

    • Filament on or off
    • High vacuum for mass spectrometer gauge or status light
    • Sight glass for the rotary vane pump

    Most likely an end user with an older leak detector has to rely on the manufacturer or other third-party service company to repair or provide preventative maintenance.

    Newer technology leak detectors have a full range of alarms and status messages for any issues of concern. For example:

    • Filament on or off
    • Filament life or condition
    • Test port pressure
    • High vacuum gauge
    • Turbo pump controller status readings
    • Error messages for any problems detected
    • Next maintenance date required
    • Last calibration performed
    • Many other messages per the manufacturer’s manual
    Figure 2. Dave with a vacuum pumping system recently remanufactured by Midwest Vacuum Pumps Inc. in Terre Haute, Indiana

    Maintaining an Older vs. Modern Leak Detector

    An end user or OEM still using diffusion pumped leak detectors with tungsten filaments is probably overhauling their leak detector every one to two years at best, or multiple times per year at worst. Depending on how much they use it and how knowledgeable their operators are, the obsolete leak detectors are probably costing them at least several thousands of dollars per event, not to mention the time lost in production as they wait to get a leak detector working so they can find the leak in their furnace.

    On the other hand, an end user or OEM with a modern helium leak detector may be fortunate enough to have their model still in production by their supplier today. They can most likely go several to many years without maintenance beyond maintaining the oil quality and level in the rotary vane pump of the leak detector.

    Where To Connect the Leak Detector

    Figure 3. Leak testing a vacuum furnace

    Th ere has been much discussion over the years on where to connect the leak detector to a vacuum furnace. Some think that because they are leak testing a furnace they should connect the leak detector directly to the furnace. While you can do that, you are asking a leak detector — typically with an NW25 vacuum connection or some type of hose barb connector — to compete with the typically very large port of the diffusion pump; in systems without a diffusion pump, the leak detector competes with the blower. In molecular flow level of vacuum, the conductance of helium to that 1” target is significantly lower than the conductance to the port of the valve to the diffusion pump or the blower (imagine a 1” vs. a 10” connection, for example).

    It is best to connect to a port near the inlet of the blower, which is typically available. You would still be using an NW25 vacuum connection or smaller hose barb fitting, but you will be sampling the flow to the blower. The recommended connections from the leak detection to the blower should all be the same as to the leak detector test port. Using smaller connectors to the leak detector diminishes conductance to the leak detector from the furnace. This, in turn, decreases the performance of the leak detector.

    It is also best to have a manually operated NW25 ball valve that is permanently installed at this point, which would be closed normally with a “blank” fitting clamped to the port on that valve. This would facilitate the following recommendation that preventative maintenance leak checks be completed during long furnace processes.

    How To Conduct Preventative Maintenance Leak Checks During Operation

    While the furnace is under vacuum in a long furnace process, place the leak detector in test mode. While in test mode, the leak detector creates a vacuum to the closed ball valve on the furnace, as previously recommended. Next, place the leak detector momentarily in standby mode. This closes the test valve of the leak detector but does not vent the test port. Then, open the ball valve. This lets the leak detector test port gauge show the current vacuum level now that it’s connected to the furnace. Now put the leak detector back into test mode.

    At this point, you are ready to spray helium at potential leak points on the furnace. While many often begin checking with the leak detector hose at the ball valve to ensure they did not create a leak during assembly, then it is best to move to the opposite side of the furnace — to the furthest point of the vacuum system of the furnace — and slowly work back to the pumps.

    A common question is how much helium should you spray? People often say they were taught to adjust the helium spray so that they get one or two bubbles in a glass of water per second or to adjust the spray so that they can barely feel it on their lips or tongue. That last one makes some people nervous. Then, it is basically like playing the hot and cold game as you spray the potentially leaking points of the furnace. More information on helium spray technique can be found in part 1 of this article.

    Finding a Leak

    The closer you get to a leak, the larger and faster the response will be on the leak rate meter of the leak detector. To confirm that you have located a leak, repeatedly spray the point of leakage and ensure that you get the same peak leak rate display and response time with each spray at that leak point.

    Earlier we mentioned that you can accomplish preventative maintenance leak checks on furnaces while in a long process. This is because helium is inert, as mentioned in part 1 of this article. Many times, operators have told me they know of a persistent leak and have not been able to repair it; as the leak is so small, they say it does not affect their product quality. Therefore, it is possible for any furnace operator to: (a) do a preventative maintenance leak check and discover a leak they did not know they had, and then (b) have the option of marking or tagging that leak to do a preemptive repair at their convenience, as opposed to discovering it aft er it degrades to the point of causing a production shut down.

    Figure 4. Dave in the front of a vacuum furnace at Mercer Technologies, Inc., in Terre Haute, Indiana

    To Repair or Replace?

    If you find a leak in a component like a valve, fitting, or thermocouple, you must then consider if the component is something that can be repaired or needs to be replaced. Often components that can be repaired may have a repair kit available from the manufacturer. If you have a leaking door seal, for example, you may be able to clean and, if appropriate, relubricate the seal. If it is damaged or worn, then replacement would be necessary.

    The only temporary repairs that come to mind are, for example, a cracked weld or substituting a failed pump with a lower performing pump. For the cracked weld, you may discover that applying some vacuum-appropriate putty or similar material may help the furnace back to approvable vacuum capability. However, a repair like this should only be considered a temporary solution with plans to repair the weld at the earliest opportunity.

    For a failed pump, you may replace it with another pump that might not have the same performance but is capable of the same vacuum level. While your process time might be slower, at least you can continue producing product until appropriate repairs can be made to the failed pump or you can replace it with the same type of pump.

    Importance of Leak Detection

    A leak on a vacuum system introduces air, thereby affecting the quality of the product or even ability to reach the process vacuum level. To ensure the quality of heat treated parts and prevent long delays in production, it is critical that heat treat operations with vacuum furnaces are well-versed in their equipment and leak detection resources, whether they own and operate helium leak detectors or hire a manufacturer or a third-party service company to detect and repair leaks.

    About The Author:

    Dave Deiwert
    President
    Tracer Gas Technologies

    Dave Deiwert has over 35 years of technical experience in industrial leak detection gained from his time at Vacuum Instruments Corp., Agilent Vacuum Technologies (Varian Vacuum), Edwards Vacuum, and Pfeiffer Vacuum. He leverages this experience by providing leak detection and vacuum technology training and consulting services as the owner and president of Tracer Gas Technologies. Dave is a Heat Treat Consultant. Click here for more about Dave and other consultants Heat Treat Today consultants.

    For more information: Contact Dave Deiwert at ddeiwert@tracergastechnologies.com or tracergastechnologies.com.

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    Modernized Walking Beam Furnace at thyssenkrupp Steel

    / MANUFACTURING HEAT TREAT NEWS

    thyssenkrupp Steel, a supplier of high-grade flat steel, recently upgraded with the modernization of a walking beam furnace installed at the company’s hot strip mill. The plant enhancement will improve production capability, increase quality of the electrical steel strip, and reduce specific consumption.

    The modernized furnace is provided by Tenova Italimpianti, a Tenova division with technologies for reheating, heat treatment, strip processing, acid regeneration plants, and cold rolling mills. thyssenkrupp Steel‘s new overhauled system includes an improved refractory lining design and an optimized fixed and walking beam system, which lead to a more uniform temperature distribution along the entire slab length. This reduces temperature loss in the slab’s center and minimizes contact points (rails) between the slabs and the fixed and walking beam system, preventing surface defects.

    “The modernization of this walking beam furnace supports our goals for efficiency and sustainability. Tenova has played a key role in this process,” said Viktor Schlecht, head of Hot Strip Mill 1, at thyssenkrupp Steel in Duisburg Bruckhausen, Germany. “We had already successfully collaborated on a new walking beam furnace at our Beeckerwerth Hot Strip Mill 2 in Duisburg, where Tenova’s contribution was crucial in helping us potentially reduce CO2 emissions by more than 20% through the use of hydrogen.”

    “We are proud to have partnered with thyssenkrupp Steel for this project, which supports their forward-looking strategy,” said Alessandro Sicher, project engineer coordinator for Reheating Technologies at Tenova. “Our equipment ensures the maximum production of high-quality electrical steel strips while enhancing the sustainability of the heat treatment process.”

    The upgrade includes new state-of-the-art UltraLowNOx burners for coke oven gas fuel application. The customized design, enhanced with a modern control system, ensures optimal heating distribution in the furnace with significantly reduced nitrogen oxide (NOx) emissions. Additionally, a new automatic descaling concept was incorporated, reducing the cleaning intervals and optimizing heat treatment processes. The safety systems were upgraded to meet the latest standards for industrial furnaces.

    Main image caption: thyssenkrupp Steel Bruckhausen plant, Duisburg, Germany

    Press release is available in its original form here.

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    Time for Company Leaders To Refocus on Profits

    / OP-ED, PUBLISHER'S PAGE

    Heat Treat Today publishes twelve print magazines a year and included in each is a letter from the publisher, Doug Glenn. This letter first appeared in March 2025 Aerospace Heat Treating print edition.

    Feel free to contact Doug at doug@heattreattoday.com if you have a question or comment. 

    The world is a better place when people know what their job is and then stick to that job. When the carpenter knows that their job is working with wood and then works with wood, things go well. When the pipefitter doesn’t try to be an electrician but sticks to pipefitting, things go well. It’s only when we forget (or never knew) who we are or why we’re here that things begin to go terribly wrong.

    This is just as true in the C-suite as it is on the shop floor when it comes to running a business. CEO, CFO, COO, presidents, and VPs all benefit the business by sticking to their huckleberry bush just as the welder, the electrician, and the plant operations guys prosper the business when they do what they’re called to do.

    In the C-suites, however, there seems to be more confusion about what it is they are there to do and company leaders more frequently get distracted from their huckleberry bush than do the guys in the shop. Here are some good, yet ultimately unhelpful things that have kept company leadership from focusing on profits — which ought to be their huckleberry bush.

    Environmental Concerns

    If ever there was a worthy cause, caring for the planet should be toward the top of the list, coming in second only behind caring for people. Business leaders proceed at their own risk if they completely ignore environmental issues. But elevating “saving the planet” over profits is a common mistake made by well-meaning leaders. The driving question that should underlie all business questions is whether or not profits will increase, not only what impact the decision will have on the environment. The EV craze, which has petered out significantly since this time last year, is a great example of company leaders losing sight of profits in favor of the environment. The number of car manufacturers who boldly announced electric-only or significantly enhanced EV fleets in 2024 only to have the two-by-four of company profits hit them squarely upside the head is astounding. Most of them have backtracked or are in financial hardship for not backtracking.

    Well-meaning environmentalism should never come at the expense of profits.

    Diversity, Equity, Inclusion (DEI)

    Another distraction from focusing on profits has been, while to a lesser degree now as compared to this time last year, the DEI movement. DEI, to its credit, is people-focused and, undoubtedly, was well-motivated by many. Nonetheless, kowtowing to externally imposed social norms in order to avoid becoming a corporate pariah carries with it the seeds of failure, because profits and overall corporate health will suffer. Such was the case for countless large and small companies, including McDonalds and Harley Davidson, that elevated DEI above profits. The primary (though not the only) factor that should drive hiring and promotional concerns within a company should be competency and effectiveness. Will the individual help enhance company profits or not?

    “Profit” Is NOT a Four-Letter Word

    In her classic work, Atlas Shrugged, Ayn Rand makes this very point. When we vilify “profits,” we do not do ourselves or our fellow man any good. One might say, “It is not profitable to vilify the word ‘profit.’” Profit is good, and it is enormously comforting to see company leaders of all stripes returning to a good, healthy embrace of the profit motive.

    Obviously, the ill-founded desire for profits at all costs regardless of the impact on the freedoms and liberties of others is not good and is the exact reason why we have courts of law. Profit cannot and ought not be at the expense of others’ freedoms. Further, the profit motive should not go right up to the line of violating personal freedoms. A true and good profit motive is not devoid of compassion and long-term thinking. It values human life and liberty and tempers its decisions based on what is good in the long run for human flourishing. Sound, profit-motivated decisions are often not easy black and white decisions. There are countless intricacies and complexities. Nonetheless, our default position ought not to be the disparaging of profits. Quite the opposite.

    Company leader, stand strong as you do all that you can to build your company profits and don’t be ashamed to say so.

    Doug Glenn
    Publisher
    Heat Treat Today

    Contact Doug Glenn at doug@heattreattoday.com.

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    High-Purity Alumina Calcining Processes Support Expansion

    / ALUMINUM PROCESSING NEWS, MANUFACTURING HEAT TREAT NEWS

    One of North America’s leading producers of ultra-high-purity alumina and associated products recently boosted its advanced manufacturing operations with a 50m-long electric tunnel kiln. This installation will support the company’s expansion into the production of a variety of high specification lines.

    Alberto Cantú Br<> Vice President of Sales
    NUTEC Bickley

    The calcination kiln, which was broken down into modules and transported by NUTEC Bickley, has an operating temperature of 2190°F (1200°C) and maximum temperature of 2460°F (1350°C) and processes the material in saggars sitting in six-high stacks that are loaded on to 33 cars. With a firing cycle of 23.6 hours, approximately 5000kg of calcined material is processed each day. In addition, special provisions to prevent equipment wear due to chemical attack that follows degassing of hydrochloric acid during the alumina heating process has been designed by NUTEC Bickley.

    “The nature of the material being processed means that tight tolerances and demanding specifications have had to be met,” said Alberto Cantú, vice-president of ceramics at NUTEC Bickley. “[This] demonstrates once again how, when all necessary design parameters are in place, electric heating in continuous kilns can deliver for a wide range of manufacturing processes.”

    The use of electric heating is increasingly in demand. Extremely tight thermal control is necessary in the kiln chamber, operating under an oxidizing atmosphere, and this particular kiln has 14 automatic control zones for heating, plus two automatic zones for cooling. To ensure maximum flexibility and management of the temperature profile, the control systems are arranged so that the exhaust, heating zones, and cooling zones are all independently regulated.

    Image 1. 3D view of the electric tunnel kiln, showing its structural design and distribution of key components.
    Image 2. External view of the electric tunnel kiln installed in the plant.

    The heating system comprises a combination of silicon carbide and metal alloy elements. These hang down vertically through the roof and are sited on either side of the load, with distribution configured to deliver a well-balanced temperature uniformity throughout the kiln. The electrical connection design means that elements can be replaced while the furnace is at operating temperature.

    Hot gases are drawn towards the kiln entrance and are evacuated from the tunnel through exhaust ports positioned in the kiln sidewalls, via the exhaust fan. Cooling is achieved by direct air movement in the cooling zones. The temperature set points from the cooling zones are controlled automatically with cooling nozzles positioned to blow a stream of cold air above and below the load setting. The kiln walls use lightweight insulation for rapid thermal response and fuel economy, with the lining rated for use up to 2350ºF (1290°C). The roof is lined with high thermal efficiency ceramic fiber system, and the roof insulation combines modules of polycrystalline fiber and zirconia grade fiber.

    Kiln car operation is based on a semi-continuous feed electromechanical pusher with push speed adjustment. The push speed is configurable by selecting the appropriate firing schedule at the kiln control panel. A vestibule arrangement serves to reduce exchange of air and gases between the factory and the kiln. When a car is being introduced into the kiln, the door at the entry end opens, while the door at the kiln entrance is closed.

    The vestibule has two sections: the first accommodates a single car and is separated by two vertical lift doors to separate the factory’s atmosphere from the kiln atmosphere. This is managed by installing an exhaust hood which is connected to the entry exhaust fan, thus ensuring a negative pressure in the vestibule to avoid any gases from the kiln from leaving the chamber. The second section functions as a transition from the vestibule door sections to the kiln’s pusher.

    Press release is available in its original form here.

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