Manufacturing Heat Treat Technical Content

Diffusion Bonding Innovation Advancing Aluminum Manufacturing

As this author notes, “Aluminum’s unique blend of lightness, strength, and purity makes it indispensable across various industries.” Especially for aerospace components, bonding aluminum alloy materials to achieve premium structural integrity is essential to keep pace with the demands of new component designs.

In this Technical Tuesday installment, Horst-Gunter Leng, product manager at PVA TePla discusses recent developments in diffusion bonding technology with increased bonding speed of aluminum and aluminum alloys by up to 50%, decreased energy use by 30%, and improved quality.

This informative piece was first released in Heat Treat Today’s February 2025 Air/Atmosphere Furnace Systems print edition.


Background: Aluminum Innovations and Joining

Aluminum, and its broad family of alloys, is prized as a lightweight metal with high purity, strong structural integrity, high electrical and thermal conductivity, corrosion resistance, and a malleability that makes it easy to shape. In aerospace, its high strength-to-weight ratio is crucial for structural components. For semiconductor equipment, aluminum enables the fabrication of intricate, contamination free channels essential for gas and fluid flow, avoiding the impurities inherent in traditional joining methods like brazing or welding.

Many developments in high demand or high quality industrial sectors involve aluminum as one or more of the layers of metals that are bonded. Diffusion bonding is a joining method used to achieve a high-purity interface when two similar or dissimilar metals require superior structural integrity and a traditional brazing approach fails to yield optimum results. The process involves applying high temperature and pressure to metals mated together in a hot press, which causes the atoms on solid metallic surfaces to intersperse and bond, typically (but not exclusively) in vacuum furnaces.

Aluminum’s compatibility with diffusion bonding has allowed for the creation of complex cooling channels in high-power electronics, injection molds, and specialized heat exchangers — designs often impossible to achieve through conventional machining.

Unfortunately, the thermal conductivity characteristics of aluminum present a challenge for the traditional diffusion bonding process, which involves the application of radiant heat into the metal layers while in a vacuum furnace.

This article explores a new bonding technology that overcomes this challenge with a conductive heating method which more rapidly reaches bonding temperature.

Traditional Diffusion Bonding: Challenges with Aluminum

Figure 1. Depiction of a c.BOND machine

In the traditional diffusion bonding process, a vacuum furnace provides radiant heat to the surface of the part. Subsequently, the heat is conducted through the assembly and transmitted to the faying surface (i.e., surfaces in contact at the joint) where required. Aluminum excels at conducting heat, particularly at lower temperatures, making it ideal for applications requiring efficient heat dissipation, such as in electronics and automotive components. However, when radiation is the dominant form of heat transfer, particularly at relatively lower temperatures in vacuum below 1112°F (600°C), aluminum’s thermal conductivity is time consuming.

Aluminum’s high reflectivity poses a challenge in traditional diffusion bonding. It is like trying to heat a mirror with a spotlight — the energy is reflected away instead of being absorbed into the material using the traditional diffusion bonding process.

Diffusion bonding of aluminum requires superior temperature control throughout the process. To prevent overheating of the load, slow heating rates traditionally are applied, leading to long process times.

In addition, aluminum alloys have a narrow processing temperature range for successful bonding. When temperatures fall outside that critical temperature band, a poor bond is produced.

New Diffusion Solution with Conductive Heating

To overcome the existing challenges of bonding aluminum, a global manufacturer of both industrial furnaces and PulsPlasma nitriding systems alongside its partner initiated an extensive development program. The result was an innovative solution: integrating heating elements directly into the press platens. This approach speeds up the bonding process and significantly reduce enhances efficiency by directly transferring heat to the aluminum components.

The culmination of this research and development is the c.BOND machine. The machine features a combination of direct conduction heating through the top and bottom platens, which are in contact with the assembly. This design ensures bi-directional homogenous heating and more precise temperature at the bonding interface where it is required.

The machine utilizes a hot-press tool with advanced software and feedback sensors to achieve micrometer-precise pressure control across the entire component surface. This ensures uniform bonding over large areas. Furthermore, the system allows for selective heating of specific areas, preventing unnecessary heat exposure to other parts of the component.

The high-vacuum atmosphere within the chamber eliminates contamination and prevents voids in the bonded joint.

With this machine, the time to heat the part to the ideal temperature for bonding is cut in half compared to traditional radiant heating. With less processing time required, the energy requirements are reduced by up to 30% as well. Multilayer stacking is also possible, which can further increase productivity.

With the size of components continually getting smaller in sectors like semiconductors and electronics, controlling the amount of time, and by extension heat, introduced into the part becomes more critical.

Horst-Gunter Leng

The technology demonstrates significant quality improvement of bonded aluminum components. It improves temperature homogeneity in the load by 70%, enhancing bonding across the entire surface. This method also improves the parallelism of parts by 50%, which enhances the accuracy of geometric dimensions, tolerances and product specifications.

As this new machine is commercially available for high-volume production, heat treaters can leverage this furnace technology alongside another unique feature that is incorporated within the system: proprietary automatic bonding software (ABP).

With the automatic bonding software, after parts can be placed in the furnace and a few parameters (such as the size of the bonding area) input, the software automatically calculates the optimum processing parameters. No specific diffusion bonding knowledge from the operator is required. The recipes can be modified according to the type of material being bonded, the thickness of the material, its surfaces and other factors. During the process, the software continuously monitors the process in real time and adjusts parameters accordingly.

Real-World Applications

A unit was installed at a national research facility in Germany, The Günter Köhler Institute for Joining Technology and Materials Testing (ifw Jena), an independent, non-university industrial research institution that conducts research in diffusion bonding, additive manufacturing, brazing, welding, laser processing, material science and other forms of bonding.

The system is compact, requires minimal maintenance, and enables high-volume production of aluminum components for diverse industries. Its benefits are being realized in aerospace, where it creates lightweight yet strong aircraft components. In the semiconductor industry, it provides a cleaner alternative to brazing, eliminating the risk of solder contamination. There is also growing demand for diffusion-bonded aluminum heat sinks, crucial for cooling high-power silicon carbide (SiC) electronics.

Figure 2. Example of the c.BOND machine

Diffusion bonding also has applications for conformal cooling. The concept is to bond layers of sheet metal that contain machined channel/microchannel structures. When combined, the channels provide a path for heat dissipation. Current applications include power electronics for effective heat management and rapid cooling of molds utilized in injection and blow molding processes.

With the size of components continually getting smaller in sectors like semiconductors and electronics, controlling the amount of time, and by extension heat, introduced into the part becomes more critical.

As the features of the internal channels become more miniaturized, it becomes even more important to control the heating during the diffusion bonding process to avoid any distortion in the part. Shortening the cycle time means introducing less heat into the part. This will facilitate creating parts with conformal cooling channels that have finer and finer features.

As mentioned earlier in this article, diffusion bonding is increasingly valuable for joining dissimilar metals, such as aluminum to steel or titanium. This allows engineers to design components and assemblies with the best properties of each metal. For example, one metal might offer superior corrosion resistance while the other provides greater strength. This “packaging” of dissimilar metals opens up new possibilities in design, particularly for overall weight reduction of design and enhancing performance in challenging environments.

When joining dissimilar surfaces, a liquid-phase diffusion bonding process is utilized, particularly when the bonding interface extends beyond R&D-sized samples. This often involves an interlayer of an alloy that typically melts at the faying surfaces. When the interlayer includes aluminum, the machine can deliver controlled heat to increase the bonding speed.

Conclusion

This new approach to diffusion bonding offers an alternative to the traditional method by circumventing the slow process of radiant heating structural assemblies in a vacuum environment. Although the technology in c.BOND is designed to improve the diffusion bonding of aluminum, it can be modified to the specific needs of the client and customized for the alloy, including copper, an alloy that has many applications in specialized heat exchanger and products used in the microelectronics industry. PVA TePla is exploring options to modify the machine to achieve even higher temperatures above the current maximum of 1472°F (800°C).

As diffusion bonding of aluminum gains importance across industries, contract manufacturers and design engineers must embrace the latest advancements to remain competitive. By adopting fast, energy efficient diffusion bonding technologies for aluminum and other materials, they can unlock higher production volumes, reduce costs, improve or achieve global sustainability targets, and increase profitability.

About the Author:

Horst-Gunter Leng
Product Manager
PVA TePla

Horst-Gunter Leng is the product manager for PVA TePla, a global manufacturer of industrial furnaces and PulsPlasma nitriding systems.

For more information: Contact PVA TePla at www.pvatepla.com/en.



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What Will Heat Treating in the Mid-21st Century Look Like?

The Heat Treat Doctor® has returned to offer sage advice to Heat Treat Today readers and to answer your questions about heat treating, brazing, sintering, and other types of thermal treatments as well as questions on metallurgy, equipment, and process-related issues.

This informative piece was first released in Heat Treat Today’s January 2025 Technologies to Watch print edition.


As a very young engineer, I vividly recall our company president had a statue of a three-headed elephant in his office. One head faced forward, one faced slightly to the right, one faced slightly to the left. The moral: looking backwards is not the path forward! Let’s learn more about what the heat treatment industry will look like by the middle of this century.

The Market

A number of market studies and economic forecast models suggest that the global heat treatment market will grow to between 130–150 billion U.S. dollars by no later than 2030 and to around 200–220 billion U.S. dollars by 2040, barring another significant or sustained global economic event. These forecasts assume several minor downturns in the economy of various countries and in manufacturing segments due to economic and geopolitical factors in the coming decades.

Heat Treatment Market Shift

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The most significant and fundamental shift that is and will continue is in the makeup of the heat treatment equipment segment of the North American market. What began in the late 1990s and early 2000s as a transition from older, long-established practices and processes to equipment capable of meeting the rapidly evolving demands of technological innovation will continue. Standardization (for cost containment), changes in manufacturing methods and methodologies, and environmental considerations are also fueling this change.

A demand for higher performance products, end-of-life expectations (in some but not all products), an emphasis on systems with single-piece flow or small batch productivity are just a few examples of this change. Other factors such as equipment obsolescence, the need for even higher manufacturing efficiencies, long term operator health and safety concerns, predictive (as opposed to preventative) maintenance, and adaptation to both the speed at which the manufacturing landscape is changing and the type of flexible equipment/processes reinforce these conclusions.

From an equipment standpoint, vacuum furnaces and applied energy systems are and will continue to experience rapid growth at the expense of more traditional atmosphere furnaces. Safety, open flames and emissions of any kind (NOx, CO2, particulates) are driving this change. As such, the dramatic reduction and control of greenhouse gases and the cooling of our planet by the mid-century will be metamorphic. This trend is not only expected to continue but to accelerate (Figures 1–2).

Figure 1. North American Industry by Equipment Segment, 2012–2018 (see Herring, Atmosphere Heat Treatment, Vol. 1, 2014)

For example, the driving force behind the development, use and integration of vacuum technology into manufacturing is not only due to the fact that it is lean, green, and agile, but also that vacuum technology best addresses the identified needs of the heat treatment industry, namely:

  • Energy efficient equipment
  • Processing with minimal part distortion
  • Optimization of heat treatment processes (especially diffusion-related processes)
  • Environmentally friendly by-products and emissions
  • Adaptability/flexibility for new and advanced materials
  • Process controls incorporating intelligent sensors
  • Designs based on heat treat modeling and simulation
  • Equipment/process integration into manufacturing

Change — Its Pace and Form

A paradigm shift in the workforce has occurred, transitioning to a vastly more mobile and younger group of individuals relying on the growing role of automation and communication in manufacturing. This shift is principally responsible for accelerating the pace of change in the heat treatment industry, from what has traditionally been a slow moving and slow-to-adapt industry, to one capable of meeting the need for rapid deployment of new products and one that keeps pace with technological innovations.

Moving forward, equipment manufacturers and suppliers to the industry will continue to look at product standardization to maximize profitability, thus driving the industry to “cookie cutter” solutions or, in a diametrically opposite philosophy, looking to provide highly customized solutions, often with risk factors incorporated into the pricing as specialized solutions with high profit margins to application-specific needs.

Figure 2. North American Industry by Equipment Segment, 2024–2035 (see Herring, Atmosphere Heat Treatment, Vol. 1, 2014)

Technology/Innovation Drivers and Industry Trends

Heat treatment will always be a core manufacturing competency, and as such, decisions will continue to be made to either heat treat in-house or outsource to commercial heat treatment shops. It is significant that the percentage of manufacturers with in-house heat treat departments (80–85%) to commercial (10–15%) heat treat shops hasn’t really changed in the last six decades! The consolidation of companies is a trend that is expected to continue.

What is more prevalent today than ever is the tremendous pressure being exerted on manufacturing from senior management to increase product velocity and lower unit cost. While recalls seem to be a way of life these days, product liability and consume demands for product performance are forcing change, even in the most extreme applications.

As a result, the most identifiable trends in today’s North American heat treatment industry are:

  • Growing the manufacturing portion (percentage) of GDP through mobility and adaptability, coupled with more sophisticated and higher paying jobs
  • Lowering product unit cost through technology adaptation
  • Obsoleting older equipment and technologies and replacing them with innovative new and/or high productivity heat treatment systems. Examples include:
    • New materials development allowing for different processing methods and/or lower temperature heat treatments while maintaining environmentally friendly equipment and processes
    • Transition of carburizing/ carbonitriding from atmosphere to low pressure vacuum processes with either oil or high-pressure gas quenching, or both
    • Use of single-piece heating and quenching of parts and/or small (versus large) batch processing to improve product velocity
    • Changes in product materials and/or designs to allow more low temperature atmosphere treatments (e.g., nitriding, nitrocarburizing)
  • Use of advanced quenching techniques and quenching technologies to better manage distortion
  • Implementing artificial intelligence-based modeling and simulation software capable of equipment control and process optimization
  • Implementing the next generation of intelligent sensors, real-time data collection methods and analytics (including cloud-based computing)
  • Changing the focus of companies from “generalization” toward “specialization” with respect to products, services, processes (proprietary or unique) and new or innovative technologies to capture greater market share or present opportunities to generate higher profit margins
  • Accelerating the implementation of lean manufacturing strategies and applying these strategies to heat treatment:
    • Eliminate high labor costs (via automation and controls), simplify operations (i.e., reduce the number of manufacturing steps), and adopt “build to order” strategies.
    • Conservation of energy, on-demand part production, shortening of process cycles, and the move toward smaller lot sizes is the order of the day.
  • Continuing the transition from heat treatment departments to integrated manufacturing cells

In Summary

It is, and will be for decades to come, a truly magical time in the heat treatment industry. The slow-moving, plodding, three-headed elephant has been replaced by a lean and agile animal — technology. This will not only ensure a greener workplace but an environment of innovation for future generations. And as I am fond of saying about the future, there’s “magic in the aire!”

References

ASM International, Vision 2020. 1999.

Herring, Daniel H. “Esoteric Heat Treatment Industry Critique: 2019 and Beyond.” Industrial Heating, January 2019.

Herring, Daniel H. Atmosphere Heat Treatment, Volume 1. BNP Media, 2014.

Wolowiec-Koreka, Emilia. Carburising and Nitriding of Iron Alloys. Springer, 2024.

About the Author

Dan Herring
“The Heat Treat Doctor”
The HERRING GROUP, Inc.

Dan Herring has been in the industry for over 50 years and has gained vast experience in fields that include materials science, engineering, metallurgy, new product research, and many other areas. He is the author of six books and over 700 technical articles.

For more information: Contact Dan at dherring@heat-treat-doctor.com.

For more information about Dan’s books: see his page at the Heat Treat Store.


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Avoid Costly Refractory Repairs with Proper Maintenance 

Refractories, “the unsung hero of the manufacturing process,” can’t measure up to that moniker if their superpowers are worn down and not getting due maintenance. Guest columnist Pamela Gaul, director of marketing at Plibrico Company, LLC, examines the critical role the refractory lining plays in the success of manufacturing aluminum, why a refractory is susceptible to cracking under extreme conditions, and how to select and prepare refractory linings to achieve a longer service life.

Read more Maintenance columns in previous Heat Treat Today’s issues here.


As the old saying goes, “An ounce of prevention is worth a pound of cure.” This is certainly true when it comes to your refractories. 

Manufacturers around the world rely on refractories to safeguard their multi-million dollar industrial-grade boilers, incinerators and furnaces from thermal damage and corrosion brought on by operating temperatures that can reach 3000°F (1650°C). 

Without refractories — the unsung hero of the manufacturing process — it would be impossible to process the raw materials that go into automobiles, chemicals, power-generation equipment, buildings, roads and much more. As such, it only makes good financial and business sense to provide basic refractory maintenance for your machinery. By protecting your critical heat-processing equipment, you can minimize costly downtime, reduce energy losses, prevent employee injuries and, more importantly, avert a catastrophic equipment failure. 

Given refractories’ importance to operations, it is important to remember that they are consumables and will wear out. This is significant because without proper maintenance your processing equipment may fail at the most inopportune time, and downtime for a furnace or dryer — even one day — can cost a company hundreds or thousands of dollars. The rewards of proper maintenance far outweigh the expense. 

It is also important to remember that refractories are not commodities. Even within the general classification of refractories, there are significant variances in chemical compositions. As a result, refractories will have different maintenance schedules and repair practices. 

Refractory maintenance has a cost. That is why maintenance needs must be factored in when evaluating which refractories to install in your application. For example, the upfront costs of engineered shapes may be 20-30% more than monolithic refractories. However, they require little to no dryout, are easy to install and in some cases last longer than some traditional castables. Also, if there are high-wear areas that may be difficult to reach due to their location or geometry, financially it is well worth going with the precast shapes to minimize future maintenance expense. 

The Wear Factor 

What causes refractories to wear? Time, temperature, corrosive gases, slag and operational practices will all take their toll, as will the overall engineering of the heat-processing equipment. Other culprits leading to the degradation of a refractory lining can be incorrect combustion controls, improper flame set-up, anchor failure or thermal shock resulting from severe temperature fluctuations. More times than not it is a combination of these or other factors that lead to refractory damage — not a single cause. 

Not following the manufacturer’s recommended curing and dryout schedule can also lead to degradation. If an end-user is looking to accelerate the process due to production demands, quick dryout products might be a good option. 

Some manufacturers offer refractory materials that provide reductions in dryout time and may offer nearly the same properties as their traditional, non-fast dryout counterparts. The benefit to these quick-cure/dryout products are that dryout times are cut about in half, which can represent a time savings of up to 40-50 hours. While they offer an easy, time-saving solution, however, there are limitations to their material properties as well as cautions on dryout. 

It is a good idea to use the dryout time to check items such as the vessel pressurization, exhaust system, temperature monitor, thermocouple position and moisture wicking. 

How You Can Help with Refractory Longevity 

The goal of periodic inspection, maintenance and repair is to ensure the longevity and performance of refractories (Fig. 1). During maintenance, worn parts and areas of excessive wear are repaired before turning into bigger issues. 

Figure 1. During the inspection process, the refractory team will provide a comprehensive condition assessment to help determine the need for repair.  Source: Plibrico Company

Depending on operational make-up, skills and budget, employing a permanent staff to perform these services might not make financial sense. Instead, working with an outside professional refractory contractor with extensive industry expertise who can provide maintenance services, emergency response and repair operations might be far more cost-efficient for the end-user. 

Under either service structure, there are precautionary steps that can be taken in-house to extend refractory operation and increase longevity. 

  • Furnace heat up and cool down: Follow procedures established by the furnace manufacturer. Proper heating creates positive pressure in a furnace, ensuring an equal distribution of temperature. Expansion or contraction control is vital to avoid damage to the refractory. 
  • Dust removal: Keep the dust off the steel in roofs that have an exposed anchoring structure. This simple step keeps the stainless steel hardware from becoming too hot and fatiguing. 
  • “Good” cracks vs. “bad” cracks: Understand the important differences between good cracks and bad cracks. Good cracks in the refractory are created and visible as part of the natural cool-down process. These should be left alone because they will disappear during the heat-up process. If the end-user fills “good” cracks, they will have problems down the road with shell bulge because the refractory will naturally expand during heat-up and production. 

An Ounce of Prevention 

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Develop a relationship with a reliable, knowledgeable and nimble professional refractory expert who has your best interests at heart. During the inspection process, your expert and their refractory team should provide you with a comprehensive condition assessment to help determine the need for repair. Assessments allow the refractory contractor to analyze the state of the refractory and select the proper solution to ensure durable repair. 

Often, the first indication that there might be a problem with the refractory lining is the appearance of a “hot spot” on the shell. A hot spot is where an area of the shell is found to be operating at a higher temperature than the surrounding area. This can be due to cracking, spalling or other issues that result in deterioration of the refractory lining. 

When hot spots are identified, the refractory professional will typically pack, grout, caulk or “stuff” the area if it is accessible from the outside. They may also “hot gun” from the inside. 

The number and severity of hot spots, usually found using an infrared camera and heat-flow analysis, can help the refractory professional or engineer determine the integrity of the refractory lining. Depending on the results, the manager/engineer should perform a full cost-benefit analysis to help evaluate which is the best option — repair or complete lining replacement (Fig. 2). 

Figure 2. Depending on the inspection results, the plant manager should perform a full cost-benefit analysis to help evaluate which is the best option: repair or a complete lining replacement. Source: Plibrico Company

When faced with any type of refractory repair, best practice will come down to scope and timetable. A quick repair may be addressed using a gunning (cold/hot) or shotcrete refractory technique. Another possibility might be ramming plastic refractory just to fill a hole/spall or resurface the lining. 

A more time-consuming and sometimes better option would be a full lining repair. These repairs are done to a more thorough degree, which allows for proper cure, dryout and anchoring. 

A Pound of Cure – Premature Failure 

Without proper refractory maintenance, you run the risk of premature failure of the refractory lining. The funny, or not so funny, thing about refractory failures is that you will usually not receive a notice on that day telling you that one of your critical systems will be failing. And once a failure occurs, it is all-hands-on-deck to address the issue and bring your operation back online as quickly as possible. 

During the process, you or your refractory expert should collect samples of the existing refractory material to help identify the causes of failure. For example, glazing and excessive shrinking indicate exposure to excessive temperatures. Shearing away of the top refractory service can be evidence of thermal shock. 

In addition, calculating a base-to-acid ratio will show if the type of refractory installed should have been selected in the first place. Refractory materials are manufactured to operate in different environments. A properly selected and installed refractory lasts longer, helps minimize shutdowns and leads to better fuel efficiency. 

Lastly, fuel should be checked to determine if it is contributing to the degradation of the refractories. For instance, moisture content in fuel may be too high or contain chemicals that damage the lining. 

Financial Implications of Non-Compliance 

Compliance with CMMC 2.0 can be financially burdensome. Implementing measures such as multi-factor authentication, encryption and continuous monitoring can be costly, especially for businesses with limited resources. The lack of in-house cybersecurity expertise compounds this issue, requiring companies to hire or train specialized personnel, further increasing costs. 

Failing to comply with CMMC 2.0 could result in losing valuable DoD contracts, which can be a significant portion of SMB revenue. Such losses could lead to layoffs, revenue declines or even business closures. 

Drama-Free Refractory Removal and Replacement 

In some cases, the maintenance needed for heat-processing equipment is more than repairs can handle. This leaves complete refractory lining replacement as the only option. This is highly specialized work requiring the skills of an experienced refractory installer. 

To ensure drama-free refractory removal and replacement, follow these five key tips: 

  • Enlist the support of a seasoned, knowledgeable and professional refractory contractor. Not all contractors are experts in refractory work. Make sure the contractor has quick access to refractory material. 
  • Obtain a complete scope of work (SOW) and a solid plan. Some of the items that should appear in a good SOW include: 
    • Amount of material needed and on hand 
    • List of equipment supplied 
    • Schedule and details for the tear-out plan 
    • Proper curing/dryout plan 
  • Prepare for the unforeseen. Often, problems do not reveal themselves until the unit has cooled and the tear-out begins. This reality necessitates contingency plans to be in place. Further, it underscores the importance of working with a fully stocked professional refractory contractor who has access to a refractory manufacturer that uses just-in-time manufacturing principles. 
  • Where applicable, install and use precast shapes. These shapes are ready to install and require little to no dryout. 
  • Discuss with your refractory expert if fast-dryout refractory material may be an option for you. Incorporating quick-dryout materials like Plibrico’s FastTrack® can cut traditional dryout time in half. 

When working with your refractory installer, it is important to focus on your specific application to drive refractory material requirements. It is easy to get caught up in flashy new refractory compositions and features. The application should determine the refractory material, not the other way around. 

Good for Your Equipment, Good for Your Wallet 

Proper refractory maintenance is not only good for your critical heat-processing equipment, but also for your wallet. The reality is that the life of your refractory can be reduced by as much as 50% (or more) without proper maintenance. In fact, failing to provide basic refractory maintenance for an aluminum furnace, for example, can leave the end-user with an unbudgeted and unexpected bill for $150,000 or more to fully replace the roof. This is an expense that might have been put off many years with properly maintained refractory. It could then have been scheduled, budgeted and drama-free. 

Worse yet, in the event of catastrophic refractory failure where the anchor tile system or full wall is snapped, the repair bill can easily top $200,000. Keep in mind these figures only address repairs. Add on the large cost of lost production and the total skyrockets quickly! 

As Benjamin Franklin would agree, take care of your refractory — the unsung hero of the manufacturing process — and it will take care of you with a safe and efficient work environment, minimized downtime, reductions in energy losses and, more importantly, avoidance of catastrophic critical heat-processing equipment failure. 

About the Author

Pamela Gaul
Director of Marketing
Plibrico Company

Pamela Gaul is the director of marketing at Plibrico Company LLC.

For more information: Visit www.plibrico.com. 

This article was initially published in Industrial Heating. All content here presented is original from the author.


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Claim the Power with SCRs and VSC

Processes that utilize electric-powered industrial heaters instead of fossil fuels will necessitate improved power consumption management. Therefore, advanced technologies in power management systems are critical, as in-house operations think about cost savings and electric power requirement compliance.

Janelle Coponen, senior product marketing program strategist, and Christian Schaffarra, director of research and development — Power Control Solutions’ Engineering Team, both of Advanced Energy, address the key to the discussion, SCRs and VSC, in this Technical Tuesday. Read more to understand how the reduction of harmonics allows operations to better manage energy consumption.

This informative piece was first released in Heat Treat Today’s January 2025 Technologies To Watch in Heat Treating print edition.


Processes are increasingly converting to electric-powered industrial heaters instead of fossil fuels to improve process control and comply with the latest energy policies. This transition enables greater operational efficiencies but necessitates improved power consumption management by companies and their heat treat operations.

The integration of advanced technologies in power management systems is critical for both cost savings and to comply with electric power requirements. Among these technologies, silicon-controlled rectifiers (SCRs) and voltage sequence control (VSC) play a pivotal role in optimizing energy consumption. This article explores the significance of the reduction of harmonics by using a special energy-efficient mode to allow facilities to better manage and reduce their energy consumption.

What Are SCR Power Controllers?

Figure 1. SCR power controller

SCR power controllers regulate the power delivered to resistive or inductive loads. Unlike traditional mechanical switches, SCRs offer faster switching times and greater reliability. They are commonly used in applications requiring heating, melting, or bending such as heating elements, motors, and lighting systems.

These devices control electrical power, current, or voltage with high precision and reproducibility. They adjust the phase angle of the AC supply, allowing for finer control over the amount of power sent to the load. This reduces energy consumption and minimizes wear on the equipment, thereby extending its lifespan. Phase-angle firing is designed for high dynamic loads with small thermal inertia and allows for high control dynamic, soft and bump-less loading, and exact current-limit setting.

SCR power controllers produce high manufacturing quality and efficiency through:

  • Energy efficiency of approximately 99.6%
  • Power density of approx. 18 W/in3 (for 3-step VSC SCR)
  • High accuracy up to 1% for output power, 0.5% output voltage
  • Flexibility
  • EtherCAT Interface

Traditional SCR operation can be inefficient, especially under partial loads. An energy-efficient mode optimizes the SCR firing angle based on load requirements, reducing energy waste. By adapting to varying loads, these controllers improve system efficiency, lower energy costs, and reduce environmental impact.

Figure 2. Phas-angle firing control mode

Understanding Power Factor

Power factor (PF) is a critical component, representing the ratio of real load power (kW, the actual power consumed) to apparent load power (kVA, the total power supplied). It is a measure of how effectively electrical power is being converted into useful work output. A power factor of 1 (or 100%) indicates maximum efficiency, while lower values indicate wasted energy due to reactive power.

In many industrial settings, a low power factor can lead to higher electricity bills and additional charges from utility companies. Utilities must generate more power to compensate for the inefficiencies caused by reactive power, which does not perform useful work.

Benefits of Improved Power Factor and Reduced Harmonics

One significant advantage of using SCR power controllers is the ability to minimize harmonic distortion. Harmonics are voltage or current waveforms that deviate from the ideal sinusoidal wave, often caused by non-linear loads like electronic devices. These distortions can lead to overheating, equipment damage, and inefficiencies within the electrical system.

Figure 3. Power triangle

Reducing harmonics improves the overall efficiency of power systems and smoother equipment operation, which can prevent costly downtime. Additionally, improving power factor can result in financial savings by reducing energy loss, lowering demand charges, and increasing the capacity of existing electrical infrastructure.

This results in lower energy bills, less wasted energy, and better system reliability. Improved power factor can also help meet regulatory standards requiring specific power factor levels.

Special Energy-Efficient Mode, Voltage Sequence Control (VSC)

VSC complements SCR technology to enhance power system performance by managing voltage levels more effectively. It systematically sequences voltage application to loads, which improves power quality and extends the lifespan of equipment.

VSC is particularly beneficial for applications with inductive loads, where voltage management can significantly reduce inrush currents and mitigate harmonics. By integrating VSC with SCR technology, industries can harness the benefits of both systems, ensuring a stable and efficient power supply.

Combined Advantages of SCRs with Voltage Sequence Control

  • Improved energy efficiency: By optimizing firing angles and managing voltage sequences, facilities can achieve substantial reductions in energy consumption.
  • Cost savings: Lower energy usage translates directly into reduced operational costs, making these technologies economically attractive for businesses.
  • Enhanced equipment longevity: By reducing stress on electrical components through better voltage management, both SCRs and VSC can prolong the operational lifespan of machinery.
  • Environmental impact: Energy-efficient systems contribute to lower greenhouse gas emissions, aligning with global sustainability goals and regulatory standards.
Figure 4. Comparison phase-angle firing versus VSC

Advantages and Disadvantages of Using SCR in Voltage Sequence Control Mode

Here are several of the advantages:

  • Improved stability: Helps maintain voltage stability across the system, reducing the risk of voltage fluctuations and outages.
  • Enhanced performance: Optimizes the performance of electrical equipment by ensuring they operate within their rated voltage range, improving efficiency.
  • Protection against voltage imbalances: Monitors and adjusts for voltage imbalances in three-phase systems, which can prevent equipment damage and reduce wear.
  • Energy efficiency: By maintaining optimal voltage levels, VSC can lead to energy savings and lower operational costs.
  • Automated control: Often incorporates automation, allowing for real-time adjustments without manual intervention, thus improving response times.
  • Lowest level of harmonics: VSCs can help minimize harmonic distortion in electrical systems.
  • Lowest level of reactive power: The specific control design of the VSC can significantly impact the minimum achievable reactive power level, even in a weak grid.
Figure 5a. Standard circuit VAR (phase angle) / Figure 5b. VSC circuit

Compare with a few disadvantages:

  • Large footprint: Larger power controller footprint versus standard SCR power control system.
  • Initial cost: The initial investment in VSC systems and related technology can be higher, but payback time is less than a year.

Conclusion

Figure 6. Power factor over outpower in VAR (phase angle) blue line vs. VSC red line

In-house heat treat operations aiming for greater efficiency and cost reduction can benefit from VSC, the energy-efficient mode for SCR power controllers. By enhancing power factor and reducing harmonics, these devices optimize energy use and support sustainable, cost-effective operations. Adopting such technologies leads to significant improvements in industrial power consumption and enhanced savings for end users.

About the Author:

Janelle Coponen
Senior Product Marketing Program Strategist
Advanced Energy

With more than 21 years of experience in the industrial and energy sectors, Janelle Coponen bridges the gap between technical solutions and market needs. At Advanced Energy, she works alongside engineering teams to translate complex technologies into market ready strategies ensuring alignment between engineering innovations and business objectives.

For more information: Contact Janelle at Janelle.Coponen@aei.com.

Christian Schaffarra
Director of Research and Development
Power Control Solutions’ Engineering Team
Advanced Energy

With more than 30 years of experience, Christian Schaffarra leads a research team dedicated to developing and advancing innovative power control technologies, ensuring optimal performance and reliability. He has a deep understanding of both the technical and marketing requirements that drive successful product development and engineered solutions.



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What Is Thermal Expansion?

The Heat Treat Doctor® has returned to offer sage advice to Heat Treat Today readers and to answer your questions about heat treating, brazing, sintering, and other types of thermal treatments as well as questions on metallurgy, equipment, and process-related issues.

This informative piece was first released in Heat Treat Today’s December 2024 Medical & Energy Heat Treat print edition.


The subject of thermal expansion and contraction is a very important one to most heat treaters given that the materials of construction of our furnaces and our fixtures experience these phenomena every day. However, to find a simple explanation of what it is and how we can help minimize the issues caused by it can be difficult. What we need is an explanation in laymen’s terms, along with some simple science and a few examples. Let’s learn more.

Thermal Expansion Effects

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When exposed to a change in temperature, whether heating or cooling, materials experience a change (increase or decrease) in length, area, or volume. This not only changes the material’s size but also can influence its density. The freezing of ice cubes is a common example of a volume expansion (on freezing or cooling), while as they melt (on heating), we see a volume contraction.

As most of us recall from our science classes, as temperature increases, atoms begin to move faster and faster. In other words, their average kinetic energy increases. With the increase in thermal energy, the bonds between atoms vibrate faster and faster creating more distance between themselves. This relative expansion (aka strain) divided by the change in temperature is what is known as the material’s coefficient of linear thermal expansion.

We must also be aware, however, that a number of materials behave in a different way upon heating. Namely, they contract. This usually happens over a specific temperature range. Tempering of D2 tool steel is a good example (Figure 1). From a scientific point of view, we call this thermal contraction (aka negative thermal expansion).

Figure 1. Change in length of D2 tool steel as a function of tempering temperature (Image courtesy of Carpenter Technology — www.carpentertechnology.com)

A related fact to be aware of is that thermal expansion generally decreases with increasing bond energy. This influences the melting point of solids, with higher melting point materials (such as the Ni-Cr alloys found in our furnaces and fixtures) more likely to have lower coefficient of thermal expansion. The thermal expansion of quartz and other types of glass (found in some vacuum furnaces) is, however, slightly higher. And, in general, liquids expand slightly more than solids.

Effect on Density

As addressed above, thermal expansion changes the space between atoms, which in turn changes the volume, while negligibly changing its mass and hence its density. (In an unrelated but interesting fact, wind and ocean currents are, to a degree, effected by thermal expansion and contraction of our oceans.)

What Is the Effect of the Coefficient of Thermal Expansion?

In laymen’s terms, the coefficient of thermal expansion (Table 1) tells us how the size of an object changes with a change in temperature. Specifically, it measures the fractional change in size per degree change in temperature at a constant pressure. Lower coefficients describe lower tendency to change in size. There are several types of thermal expansion coefficients — namely linear, area, and volumetric. For most solid materials, we are typically concerned in the heat treat industry with the change along a length, or in some cases a change in volume (though this is mainly of concern in liquids).

Table 1. Comparative values for linear and volumetric expansion of selected materials

Heat Treat Furnace Examples

When calculating thermal expansion, it is necessary to consider whether the design is free to expand or is constrained. Alloy furnace muffles, retorts, mesh and cast link belts, and radiant tubes are good examples. The furnaces that use them must be designed to allow for linear growth and changes in area or volume. If not, the result is premature failure due to warpage (i.e., unanticipated movement).

If a component is constrained so that it cannot expand, then internal stress will result as the temperature changes. These stresses can be calculated by considering the strain that would occur if the design were free to expand and the stress required to reduce that strain to zero, through the stress/strain relationship (characterized by Young’s modulus). In most furnace materials it is not often necessary to consider the effect of pressure change, except perhaps in certain vacuum furnaces or autoclave designs.

A Little Science

For those that are interested, here are the formulas most often used by heat treaters to calculate the coefficient of thermal expansion.

Estimates of the Change in Length (L), Area (A), and Volume (V)

Linear expansion is best interpreted as a change in only one dimension, namely length. So linear expansion can be directly related to the coefficient of linear thermal expansion (αL) as the change in length per degree of temperature change. It can be estimated (for most of our purposes) as:

where:

  • ΔL is the change in length
  • ΔT is the change in temperature
  • αL is the coefficient of linear expansion

This estimation works well as long as the linear expansion coefficient does not change much over the change in temperature and the fractional change in length is small (ΔL/L <<1). If not, then a differential equation (dL/dT) must be used.

By comparison, the area thermal expansion coefficient (αA) relates the change in a material’s area dimensions to a change in temperature by the following equation:

where:

  • ΔA is the change in area
  • ΔT is the change in temperature
  • αA is the coefficient of area expansion

Again, this equation works well as long as the area expansion coefficient does not change much over the change in temperature ΔT(ΔT), if we ignore pressure and the fractional change in area is small (ΔA/A <<1)ΔA/A<<1. If either of these conditions does not hold, the equation must be integrated.

For a solid volume, we can again ignore the effects of pressure on the material, and the volumetric (or cubical) thermal expansion coefficient can be written as the rate of change of that volume with temperature, namely:

where:

• ΔV is the change in volume
• ΔT is the change in temperature
• αV is the coefficient of volumetric expansion

In other words, the volume of a material changes by some fixed fractional amount. For example, a steel block with a volume of 1 cubic meter might expand to 1.002 cubic meters when the temperature is raised by 90°F (32°C). This is an expansion of 0.2%. By contrast, if this block of steel had a volume of 2 cubic meters, then under the same conditions it would expand to 2.004 cubic meters, again an expansion of 0.2% for a change in temperature of 90°F (32°C).

Thermal Fatigue

In many instances, we must consider the effect of thermal fatigue as well as thermal stress. One example is on the surface of a hot work die steel as H11 or H13: one must ensure that in service, when it experiences a (rapid) change in temperature, it will avoid cracking.

The equation for thermal stress is:

where:

  • σ is the thermal stress
  • E is the Young’s modulus of the material at temperature
  • α is the coefficient of linear thermal expansion at temperature
  • ΔT is the change in temperature

Here both E and α depend on temperature and the resultant stress will either be compressive if heated or tensile if cooled, so we must use these constants at both maximum and minimum temperatures. Considering the temperature dependent stress-strain curve, this stress may exceed the elastic limit (tensile or compressive) and contribute eventually to thermal fatigue failure. There are software programs to aid in the calculation of the resultant thermal stresses. Thermal expansion at a surface at a higher temperature than the core results in a compressive stress, and vice versa.

Final Thoughts

The effects of thermal expansion will be highlighted in a forthcoming article in Heat Treat Today, but it suffices for all heat treaters to remember that this phenomenon is responsible for a great deal of downtime and maintenance in our equipment. It also can affect the end product quality (disguising itself as distortion) and hence create additional cost or performance issues for our clients.

References

Chandler, Harry, ed. Heat Treater’s Guide: Practices and Procedures for Irons and Steels, 2nd Edition. ASM International, 1995.

Herring, Daniel H. Vacuum Heat Treatment. BNP Media, 2012.

Herring, Daniel H. Vacuum Heat Treatment Volume II. BNP Media, 2016.

Special thanks to Professor Joseph C. Benedyk for his input on the topic.

About the Author

Dan Herring
“The Heat Treat Doctor”
The HERRING GROUP, Inc.

Dan Herring has been in the industry for over 50 years and has gained vast experience in fields that include materials science, engineering, metallurgy, new product research, and many other areas. He is the author of six books and over 700 technical articles.

For more information: Contact Dan at dherring@heat-treat-doctor.com.

For more information about Dan’s books: see his page at the Heat Treat Store.


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Case Study: The Metallurgy Within a Reheating Furnace at DanSteel

In this article, a team of researchers describe the technical, technological, and metallurgical characteristics in heating large-sized continuous cast slabs made of low carbon microalloyed steels, using the operation at DanSteel’s rolling complex 4200 as a case study. These characteristics ensure high quality heating process of slabs used for production of high-quality heavy plates weighing up to 63 tonnes*, which are particularly in demand in the offshore wind energy and bridge construction industries.

On the research team are the following: Eugene Goli-Oglu, Sergey Mezinov and Andrei Filatov, all of NLMK DanSteel, and Pietro della Putta and Jimmy Fabro of SMS group S.p.A.

This informative piece was first released in Heat Treat Today’s December 2024 Medical & Energy Heat Treat print edition.

*1 metric ton = 2204.6 pounds


The production of structural heavy plate steel is a complex multi-step process, the technological steps and operations of which have an impact on product quality and production economics. Slab reheating for rolling is one of the key process steps in the technological chain, directly linked to the quality and cost efficiency of heavy plate production process.

At DanSteel’s rolling complex 42001, continuously casted (CC) slabs are heated either in pusher type furnaces or walking beam furnaces depending on their cross section. In the case of big-size and heavy tonnage slabs with a cross-section of H x B up to 400 x 2800 mm, heating takes place in the latest generation of the SMS group walking-beam reheating furnace, installed in 2022. The main objectives of the installation of the new reheating furnace were the expansion of the product range towards the production of XXL high-quality heavy plates weighing up to 63 tonnes, which are most in demand in the offshore wind power and bridge construction industries, as well as improving the quality, economic, and environmental parameters of slab reheating process.

Figure 1. Effect of reheating temperature on particle size (a) and austenitic grain size (b) in steels (see reference 5) microalloyed simultaneously with Ti and Nb:
1 — steel with low titanium additions (Ti/N=3.24)
2 — steel with 0.02% Nb and Ti (Ti/N=3.33)
3 — steel with increased titanium content Ti/N=4.55

The aim of this article is to describe the technical, technological, and metallurgical characteristics in heating large-sized continuous cast slabs made of low carbon microalloyed steels and how this looks at the DanSteel’s rolling complex 4200.

Metallurgical Characteristics of Slab Heating

Heating of low carbon microalloyed steel slabs is one of the key technological steps in forming the optimal microstructural condition of heavy plates and their surface quality. In conjunction with microalloying, the technological parameters of heating affect such important characteristics as average grain size and uniformity of the austenitic structure, the composition of the solid solution and the type/thickness of the surface scale. In terms of heavy plate quality, the main realized task at the reheating stage is to obtain at the exit a slab with a setup temperature, the minimum temperature gradient along the thickness, width and length of the slab, optimal quality and quantitative condition of the surface scale.

The heating temperature and its uniformity are important to form a microstructure of increased uniformity. It is known2 that a fine-grained austenitic steel structure has an increased grain boundary surface per volume unit, which leads to an excess of free energy of the system, which creates a driving force that determines the subsequent grain growth. The austenitic grain grows exponentially when heated in certain temperature ranges and this grain growth tendency is always present in low carbon microalloyed steels.

Figure 2. Growth pattern of austenitic grains in steels containing various microalloying elements

There are two general mechanisms of austenitic grain growth when heating slabs: normal and abnormal growth. That is, when reaching a certain temperature, which depends on the chemical composition, the austenite grain begins to increase very rapidly in apparent diameter. Abnormal grain growth can be observed in austenitizing steels containing strong CN-forming elements. Anomalous grain growth is not observed in simple low alloyed Si-Mn steels but at heating temperatures of 2102°F–2192°F, the grain grows to very large sizes (200 μm and larger).3

To avoid exponential grain growth of austenite during heating for rolling, dispersed particles that inhibit grain boundary migration are effectively used.4 The undissolved particles inhibit the migration of grain boundaries and thus inhibit the growth of austenitic grains. The nature of the release of particles and their effect on the average size of the austenitic grains of Ti and Nb alloyed low carbon steels is shown in Figure 1. It is important that the slab at the exit of the furnace has a given heating temperature without gradient limit deviations.

The main microalloying elements that form the optimal (fine grain) austenite structure as a result of the solid-solution effect and the formation of nitrides and carbides during slab heating are titanium, niobium, and vanadium (Figure 2).5 Titanium forms nitrides, which are stable at high temperatures in the austenitic range and allow control of the austenite grain size during heating before hot deformation. The binding of free nitrogen (which has a high affinity for carbide forming elements) by titanium has a positive effect on steel ductility and makes niobium more effective. Niobium is an effective microalloying element for refining the austenite grain during heating for rolling.6 It also has the positive effect of inhibiting austenite recrystallization during thermomechanical rolling.7

It is worth noting a number of works8, 9, 10, in which it was shown that increasing the heating temperature of V-Ti-Nb steel and the associated austenite grain enlargement does not significantly affect the size of the recrystallized grain, formed in the temperature range of complete recrystallization after repeated deformation under the same temperature and deformation conditions. This experimental result at first sight contradicts most recrystallization models11, 12, according to which the size of recrystallized austenite grain depends on the initial (before deformation) grain size and deformation temperature.

The microstructure and mechanical properties of the finished product directly depend on the heating temperature and are determined by the size and homogeneity of the austenitic grains, the stability of the austenite itself, influencing the condition of the excess phase and, consequently, the kinetics of its subsequent transformation. For timely recrystallization processes and control of dispersion hardening, it is necessary to balance the uniform fine grained austenitic microstructure and the transition of dissolved particles into solid solution when defining the heating temperature. Also, the heating temperature must be sufficiently high to fully undergo recrystallization in the interdeformation pauses.13 It should also be considered the possible negative phenomena of local and general overheating that occur when heating a slab above a certain temperature for a given steel and lead to a sharp increase in the austenitic grain size. The decreased heating temperature allows for a number of technological advantages: The possibility of reducing the pause time for cooling before the finishing step of rolling, increasing productivity of furnaces due to reduced heating time for rolling, and therefore the mill as a whole, as well as reducing the cost of the product due to saving fuel and reducing losses on scale. However, it should be remembered that some groups of low carbon steels have an optimal temperature range for heating, target temperatures above or below, which increase the heterogeneity of the microstructure. Thus, ensuring uniform heating to a given holding temperature and discharging slabs from the reheating furnace for subsequent rolling is an important technological task and contributes to the formation of austenitic microstructure and solid solution state of low carbon microalloyed steel with increased uniformity.

DanSteel Walking Beam Reheating Furnace

In 2022, DanSteel and SMS commissioned a new walking-beam reheating furnace (Figure 3) with a design capacity of up to 100 tonnes/hour, expanding the range of slabs heated to a maximum cross section of H × B 400 × 2800 mm and improving heating quality. The maximum temperature difference between the coldest and the hottest points on the slabs is not more than 30°C. The new furnace has been designed with a focus on environmental and energy efficiency and has reduced CO2 emissions by 17–18% compared to the furnaces already in operation in the plant.

Figure 3. DanSteel walking beam reheating furnace no. 3, (left) general view of the furnace and (right) slab discharging area

The walking beam reheating furnace is for heating cast carbon, low-carbon, and low-alloy steel slabs weighing up to 63 tonnes. The main production characteristics of the furnace as part of DanSteel 4200 rolling complex are shown in Table 1.

Slabs are moved through the furnace by moving the walking beam in four steps: lifting, moving forward, lowering below the level of the fixed beams, and moving the walking beams backwards. The speed of the slab moving in the furnace is controlled by changing the movement intervals between the movement cycles of the beams and depends on the variety of heated slabs. Slab discharging from the furnace is carried out shock-free, using a special machine that moves the slabs from the furnace beams to the mill roller conveyor. The furnace is equipped with a modern automated process control system and a system of instrumentation and sensors that allows the heating of steel without the direct involvement of technical personnel and provides for the measurement, regulation, control, and recording of all operating parameters.

The furnace type is reheating, walking beam, regenerative, multi-zone, double-row, double-sided heating, frontal charging, and discharging furnace. The furnace is designed for natural gas operation with the possibility of a quick conversion, within three weeks, of up to 40% of the capacity for hydrogen operation. The conversion is carried out by means of a minor modernization of the burner’s inner circuit, the installation of hydrogen storage auxiliary equipment and the regulation of the hydrogen supply to the modified nozzles. It is planned that the replacement of natural gas by hydrogen will also reduce the consumption of natural gas by ~40% and hence reduce the negative impact of the process on the environment. Feeding control as well as optimum pressure is controlled by a special automated control system. Table 2 shows the main technical characteristics of the furnace.

The air is heated in a metal recuperator, located on the furnace roof. The combustion products pass between the tube and the air passes through the recuperator tubes. The air is blown by a blower into the recuperator and transported to the burners through thermally insulated air ducts. The gas and air from the common pipelines are supplied to each zone via zone headers, on which flow meters and actuators for flow controllers are installed to ensure an ideal furnace atmosphere with an O2 content of about 0.7–1.0 %.

The furnace has 6 heating zones, 3 upper and 3 lower, with 24 SMS-ZeroFlameTM burners (Figure 4a) for ultra-low nitrogen oxide concentrations and high thermal efficiency.14 The burners consist of a metal casing with external cladding for heat protection, several fuel and combustion air lines, a pre-combustion chamber and an air deflector made of refractory material with high alumina content.

Figure 4. SMS-ZeroFlameTM burners used in DanSteel’s walking beam furnace: a – burner structure; b – flame operation; c – flameless (“invisible flame”) operation

The particular design of the installed burners allows them to operate using three modes:

  • Flame mode (Figure 4b), used for ignition and at low temperature, but even then, the NOx level remains low thanks to the triple-stage air supply
  • Flameless mode (“aka invisible flame,” Figure 4c), which ensures high slab heating uniformity over the cross section creating a homogeneous, invisible flame with minimum NOx emissions
  • Mixed “booster” mode, allowing a 15% to 20% increase in nominal heat input, and a rapid increase in zone temperature if the furnace setting is changed due to a change in steel grade or increased capacity
Figure 5. Heating curves of a 250 x 2800 mm slab in the new reheating furnace no. 3

The combustion gases from the gas combustion heat the metal through direct radiant heat transfer, as do the combustion gases heat the burner units, the furnace roof and walls, which in turn heat the slabs in the furnace through indirect radiant heat transfer. The optimum combination of burner arrangements ensures intensive and uniform heating. The mutual movement of combustion gases and metal is counter current. Combustion gases from the recuperation zone are conveyed by a waste gas duct to the heat exchanger (where they heat the air) and then through a waste gas intake to the chimney and exhausted to the atmosphere. The rotating valve is installed in the exhaust duct between the recuperator and the chimney and is used to control the pressure in the heater.

Figure 6. Heating curves of a 400 x 2800 mm slab in the new reheating furnace no. 3

The skids are cooled by chemically treated water, which circulates in a closed circuit. A dry fan cooling tower is used to dissipate the heat from the cooling water. Steel is charged into the furnace by a charging machine that moves the slabs from the charging roller table to the furnace skids.

Technical Features of Slab Heating

The highly even heating of slabs in furnace 3 of DanSteel is ensured by the optimum arrangement of the burners, flameless fuel combustion, triple skids shift, and warm riders on the skids. The evenness of the slab heating corresponds to a maximum temperature difference in the longitudinal section of up to 20°C, and the maximum difference between the coldest and hottest points of the slab must not exceed 30°C.

Earlier in work15, it was shown that when heating a 250 mm slab in the old furnace no. 2, the maximum temperature gradient was for a long time within 250-300°C, and at the exit of the furnace the slab had a sensitive temperature difference in cross section. Figure 5 shows an industrial schedule of heating slabs cross-section 250 x 2800 mm in the new furnace no. 3. Analyzing thermal and technical data of slab heating for heavy plate production using the new furnace, it should be noted that the slab temperature uniformity distribution during the whole heating period is essential. When heating slab cross-sections 250 x 2800 mm in the new furnace, the maximum temperature gradient does not exceed 130°C (Figure 5). The peak values of temperature gradients are situational in nature and appear only for a short period of time and at times of adaptation of the control model of heating for each specific slab in the active zones of the furnace. For slabs with a thickness of 250 mm the most critical time is the time interval between approx. 90 and 120 minutes during which the upper and lower surfaces of the slab are actively heated. During the last 20 minutes in the soaking and equalizing phase, the temperatures at ¼, ½, and ¾ of the slab thickness reach a maximum gradient of no more than 20°C. As can be seen from the graph in Figure 5, heating of 250 x 2800 mm slabs to a given temperature of 1150°C takes no more than 4.5 hours. It is possible to reduce the heating time, however, with a certain decreasing of quality.

Figure 7a-b. Temperature gradients of 120 mm heavy plate, produced using TM+ACC modes: a, b — top surface thermoscanner data

A similar schedule for heating 400 x 2800 mm slabs is shown at Figure 6. For large cross-section slabs with a thickness of 400 mm, the heating time is in the range of 9–10 hours. The heating time can be reduced to 8 hours, but also with a decrease in the quality of heating towards an increase in the temperature gradient across the thickness of the slab. It should be noted that the temperature increases smoothly in the heating curves at ¼, ½, and ¾ of the slab thickness. From the peaks of the upper furnace temperature curve, the discreteness of the adaptation adjustments of the furnace heating control model can be evaluated.

Heavy Plate Temperature Profile

The DanSteel 4200 Rolling Complex is equipped with twelve control pyrometers and three thermo scanners that measure the temperature of 100% of the top surface of the plate at reference points in the heavy plate production process. The data obtained can be used to accurately and in real time evaluate the temperature uniformity of the plate in width and length direction.

Figure 7 c-f. Temperature gradients of 120 mm heavy plate, produced using TM+ACC modes: c, d (top) — temperature profile of top surface from pyrometer; e, f (bottom) — temperature profile of bottom surface of plate from pyrometer

As an example, Figure 7 shows the results of a scan of the surface temperature of 120 mm thick rolled steel heavy plate after deformation stage is completed and before the start of final cooling in an accelerated cooling unit. Two states of temperature gradients occurring during production are considered: uneven heating and uniform heating. Figure 7a shows the temperature field of a plate with expressed temperature irregularity. The main reason for the marked irregularity in the temperature field of the rolled plate is non-optimal modes of heating of the slab. It can be seen that the central part of the plate has the temperature specified by the technology, while the head and tail overheated by 50-60° C relative to the specified temperature at a maximum permissible deviation of not more than 30°C. Figure 7b shows the temperature field of a plate with a high degree of uniformity. Approximately 95% of the surface of such a plate is at the process-specified temperature with a deviation of ±3°C. The maximum temperature gradient does not exceed 10°C.

The temperature profiles of the top (Figure 7c and Figure 7d) and bottom (Figure 7d and Figure 7e) rolled surfaces, obtained from control pyrometers, show that the nature of the temperature non uniformity is repeated on the upper and lower surfaces of the plate. In the first “non-optimal” case the temperature gradient of the top surface reaches about 76°C, and on the bottom surface: -54°C. In the case of uniform heating, the gradient of the top surface of the plate does not exceed 3–6°C and the bottom surface: 5–11°C.

Preventive Maintenance System

The DanSteel new walking beam furnace is also equipped with an innovative maintenance support tool named SMS Prometheus PMS (Preventive Maintenance System). It consists of a software platform collecting and elaborating the data provided by an extended number of sensors strategically placed over several mechanical components of the furnace, with the goal of predicting possible malfunctioning. The monitored equipment includes the key handling devices, like the slab charger, the slab extractor or the walking beam system, as well as the hot air recuperator, the combustion air fans of the main components of the water treatment fan. The software algorithm is able to extrapolate some data from the sensor measurements to assess the key performance trends of the related component and anticipate the necessity of intervention for maintenance or repair before any actual damage happens.

Figure 8. Dashboard handling — monitoring of the walking beam system

In the example of Figure 8, the trends are shown that correlate the walking beam movement and the cylinders pressure to the slab load inside the furnace. Any significant deviation in respect to the foreseen pattern denotes a movement anomaly and will trigger a notification to the control system, that allows the plant maintenance team to act preventively in view of a potential failure.

Conclusion

A new walking-beam reheating furnace with a designed productivity of up to 100 t/h was put into operation at DanSteel rolling complex 4200. This allowed expanding the range of heated large-size slabs with a maximum cross-section of H x B 400 x 2800 mm and weighing up to 63 tonnes. The implemented project has provided increased uniformity of heating along the thickness, width and length of slabs with average maximum values of temperature gradients in the three directions not exceeding 30°С (80°F) and reduced consumption of natural gas to the level of 31–32 m3/t of finished product. More uniform heating of slabs ensured improved temperature field uniformity of rolled heavy plates. The constructive possibility of a partial transition to the use of hydrogen instead of natural gas was taken into account.

References

  1. I. Sarkits, Y. Bokachev, E. Goli-Oglu, “Production of heavy plates on the rolling mill 4200 DanSteel A/S,” Stahl und Eisen. 2014. no. 4, 57–61.
  2. Imao Tamura, Hiroshi Sekine, Tomo Tanaka, Chiaki Ouchi, Thermomechanical Processing of High-strength Low-alloy Steels (Butterworth-Heinemann, 2013), 256.
  3. Antonio Augusto Gorni and José Herbert Dolabela da Silveira, “Accelerated Cooling of Steel Plates: The Time Has Come,” Journal of ASTM International 5, no. 8 (2008): 358–365.
  4. Y. I. Matrosov, “Complex microalloying of low-pearlite steels subjected to controlled rolling,” Met Sci Heat Treat No. 28 (1986): 173–180.
  5. S. V. Subramanian,, G. Zhu, C. Klinkenberg, K. Hulka, “Ultra Fine Grain Size by Dynamic Recrystallization in Strip Rolling of Nb Microalloyed Steel,” In Materials Science Forum. Vols. 475–479 (2005): 141–144.
  6. S.C. Hong, S. H. Lim, “Inhibition of Abnormal Grain Growth during Isothermal Holding after Heavy Deformation in Nb Steel,” ISIJ International 42, no. 12 (2002): 1461–1467.
  7. K. Hulka, A. Kern, U. Schriever, “Application of Niobium in Quenched and Tempered High-Strength Steels,” Materials Science Forum vols. 500–501 (2005): 519-526.
  8. C. M. Sellars, J. A. Whiteman, “Recrystallization and Grain Growth in Hot Rolling,” Metal Science no. 13 (1979): 87–194.
  9. H. Tamehiro, N. Yamada, H. Matsuda, “Effect of the Thermo-Mechanical Control Process on the Properties of High-strength Low Alloy Steel,” Transactions of the Iron and Steel Institute of Japan Vol. 25, Issue 1 (1985): 54–61.
  10. Sh. Liang, F. Fazeli, H. S. Zurob, “Effects of solutes and temperature on high-temperature deformation and subsequent recovery in hot-rolled low alloy steels,” Materials Science and Engineering A., vol. 765 (2019): 138324.
  11. H. Yada, “Prediction of Microstructural Changes and Mechanical Properties in Hot Strip Rolling,” Proceeding of the International Symposium on Accelerated Cooling of Rolled Steel. Winnipeg, Canada. 1988. 105-119.
  12. W. Roberts, A. Sandberg, T. Siweski, T. Werlefors, “Prediction of Microstructure Development during Recrystallization Hot Rolling on Ti-V-steels,” ASM HSLA Steels Technology and Applications Conference. Philadelphia, USA. 1983. 35–52.
  13. R. Wang, C. I. Garcia, M. Hua, K. Cho, H. Zhang, A. J. Deardo, “Microstructure and precipitation behavior of Nb, Ti complex microalloyed steel produced by compact strip processing,” ISIJ international 46, no. 9 (2006): 1345-1353.
  14. “Innovation in combustion process,” SMS group, https://www.sms-group.com/en-gb/insights/all-insights/innovation in-combustion-process (date of review 2023-03-20).
  15. V. A. Tretyakov, Bokachev, A. Yu, A. N. Filatov, E. A. Goli-Oglu, Development of a digital twin of the process of controlled rolling of thick plate from high-strength low-alloy steels. Message 1. Simulation of slab reheating in continuous furnace with a prediction of austenite grain size before rolling. // Problems of ferrous metallurgy and materials science. 2022. no. 2, P. 30-40.

This article content is used with permission by Heat Treat Today’s media partner Furnaces International, which published this article in September 2023.

About the Authors:

Eugene Goli-Oglu has worked at NLMK DanSteel since 2013 and has led Product Development, Technology and Technical Sales Support functions for steel heavy plate production. Eugene received his Master degree in Metal Forming in 2007, a second Master’s degree in Economy in 2009, and a PhD in Metallurgy and Thermal Processing of Metals and Alloys in 2012. He has authored/co-authored 90+ publications in technical journals.

Sergey Mezinov has worked at NLMK DanSteel since 2007 as an engineer of the Project Department and process engineer of the Quality Department. In 1995, Sergey graduated as an heat-power engineer. He has authored/co-authored of 2+ publications in technical journals and authored/co-authored two patents.

Andrei Filatov has worked at NLMK DanSteel since 2019 as a metallurgist in the Product Development and Technical Sales Support department. In 2015, Andrei graduated as an engineer physicist, and in 2019, he completed postgraduate studies in Metallurgy and Thermal Processing of Metals and Alloys. He has authored/co-authored 20+ publications in technical journals.

Pietro della Putta is the vice president of the Reheating and Heat Treatment Plants department at SMS group S.p.A. Jimmy Fabro is the head of the Technical Department – Furnace Division at SMS group S.p.A.

Jimmy Fabro is the head of the Technical Department – Furnace Division at SMS group S.p.A.



Case Study: The Metallurgy Within a Reheating Furnace at DanSteel Read More »

The Heat Treat Robotic Paradigm Shift

As Thomas Bauernhansl, professor of Production Technology & Factory Operations at the University of Stuttgart, aptly states, “We are going from more supply-oriented production to a demand-oriented one. In many cases, the customer determines which version he wants to have [of] a product — the manufacturer adapts to this and his processes accordingly.”

This shift is critical for the heat treat industry, where the need for advanced automation and robotics integration is paramount to achieve higher efficiency, consistent quality, and reduced costs. In this Technical Tuesday, Dennis Beauchesne, general manager at ECM USA, discusses the increase in use and installation of automation and robotics in manufacturing and specifically how companies within the heat treat industry have adapted to their implementation—and become innovators in their usage.

This informative piece was first released in Heat Treat Today’s January 2025 Technologies To Watch in Heat Treating print edition.


Industry Automation

In the last 10–15 years, an upward trend is consistent with the increased investment value of integrated automation within a heat treatment plant. At the beginning of the 2000s, it was common to have an automatic transport car transporting batches to different stations, but, in the last five years, far more complex automation solutions are in demand. In order to meet the requirements of future industry robotics and automation, our industry must adapt to the new and improved technology offerings and standards that are being used in other industries.

Figure 1. Annual robotics installation by industry 2021-2023

According to World Robotics, there has been a significant increase in robotics usage and installations since 2020 (Figure 1). For example, the automotive industry shows installations almost doubled from 2020 to 2022 with 83,000 installations in 2020, compared to 136,000 installations in 2022. The industrial robot market was expected to grow by 7% in 2023 to more than 590,000 units worldwide. Although it exceeded 500,000 installations, robotics were down 2% (possibly due to COVID-19) compared to the prior record year. Of interest to note for the automotive industry, the industry increased its robotics demand in 2023 to surpass electronics with a 25% share (electronics was close with 23%, down by 5% due to inventory levels stabilizing after supply chain bottlenecks mostly vanished).

Table 1. North America’s robotics comparison 2022 to 2023
Source: World Robotics

Specifically for the United States and Mexico, peak robotics installation demand was documented in 2022, but demand has been consistent within +/-5% (Table 1). The future of robot installations is trending to grow and exceed 50,000 units in North America for 2024. Nearshoring of supply chains will create demand for automation technology in the years to come, according to Christopher Müller in his World Robotics 2024 – Industrial Robots presentation.

Manufacturing Concepts

The company SEW has previously published its ideas and concepts of autonomous transporters distributing the raw parts to the production cells, after the soft processing to the hardening plant, and finally the hard machining (Figure 2). All steps are configured within the component so the process steps can be well documented on a component basis.

Figure 2. SEW concept from Hiller, “The networked hardening shop,” 2019
Source: ECM GmbH

As can be seen in the SEW Figures, the original hardening plant is shown as a continuous furnace. However, this type of plant technology can be seen as contradictory to current production needs. To be compliant with this new philosophy, plant technology must be as modular, flexible, and automatable as the rest of the production layout and components. Heat treatment must also be controllable and unloadable with automatic transport units. Robots must be able to load batches and navigate the plant (according to CHD, steel, part numbers, etc.). The smaller the batch size, the larger the value of robotic component documentation. Furthermore, a reduction in batch size is advantageous for flexibility, costs, and heat treatment of many requirements for production runs.

Heat Treatment & Robotics

A heat treatment plant can implement
recommendations for the future of industry
automation by acquiring technology for:

  • Automatic loading/unloading
  • Component recognition systems
  • Automatically loaded/read recipe systems
  • Smaller batch sizes with a wide variety of variants
  • Heat treatment of different applications or steels in small quantities
  • Maintenance/repair detection

Benefits of automating part or all production line steps include:

  • Shorter process times
  • High CHD (Case Hardening Depth) uniformity and lower distortion
  • Lower operating costs and labor reduction

These technologies have existed and are being implemented in heat treat operations for a few years now. The results are clear and the benefits are proven through higher quality parts, highly efficient heat treat operations, and overall more efficient production facilities.

As many machining operations have been robotized, this allows the downstream heat treat operations to easily take advantage of part placement in dunnage and plant transport systems, whether manual or automated.

Figure 3. ECM Vision System
Source: ECM Robotics

Batch Loading with Robotics

Bulk goods-loading (such as clips, links, and other small parts via weight detection) as well as loading and unloading of truck shafts in fixtures and in straightening machines are just a few examples of production areas that can benefit from robotics/automation. Visual recognition systems can identify gears/parts based on the diameter or by the number of teeth on the gear and can then sort them by these features (Figure 3).

Like the visual locating of the parts by cameras, they can also be used for tracking parts and loads within a heat treatment cell. A good amount of work has been done in this area for heat treating. This work covers part marking, tray/fixture encoding, and part weighing scenarios, and allows the heat treat system to accurately process all the different parts coming through the heat treat system with the correct process recipe.

Some of the work being done has been implemented with a QR code marking system for each part before heat treatment. To ensure the correct recipe or heat treatment is performed on the proper part, this scanned code works with the heat treatment system controls to upload the correct recipe to the proper cell. This information can be further analyzed to indicate precise placement in the heat treat tray through virtual tracking.

Figure 4. QR code heat treat test picture
Source: ECM USA Synergy Center

In Figure 4, you can see in the details that this client has reviewed and tested to assure the code is visible before and after heat treating with a carburizing and hardening process.

These parts are tracked when entering the system and also noted as to which heat treat tray they are on by using a binary code with holes in a tray or on a strategically placed bar code plate on the tray. With this system, they can be scanned by a camera before entry and upon exit of the furnace (Figure 5). This tray scanning can also indicate how many cycles the trays have on them to ensure the trays stay in good condition and can be cycled efficiently.

Figure 5. Lohmann Steel barcode scan plate (Images courtesy of Lohmann Steel, heat resistant castings — grates, trays, baskets, fixtures and more)
Source: Lohmann Steel

Networked Hardening

Let’s look at the SEW production concept again and re-imagine it with a more efficient vacuum furnace technology with robotic integration. In this concept, the vacuum furnace system forms the “spatially distributed production reserve” which helps autonomous transport units as “situationally self-controlling” material is delivered.

The QR code on the component represents the “knowledge-based” running card. The robots recognize the components by means of the QR code and are loaded onto the appropriate heat treat trays. The heat treatment can then be carried out on a component-related, flexible, and documented basis. Traceability of production can also be ensured (Figure 6).

Figure 6. Robotics concept
Source: ECM Technologies

Loading of the parts can be done efficiently through a series of dunnage that hold the part in specific locations which assist the robot to locate, lift, and place the parts in the heat treat tray. This method doesn’t always need to be a perfect location for the incoming work as we now have 2D and 3D cameras that can work in tandem to locate parts, even in odd stacking or randomly loaded bins.

In a recent installation, a heat treater automated their gear cutting operation to prepare the dunnage before heat treat. Therefore, the heat treat robotics phase was simplified by storing each part in a specification location for the robot to “see” with its vision system. These parts are then scanned and automatically connected to the part’s recipe as stored in the system. In a modular system using low pressure carburizing, individual cells are utilized, and production is recipe driven. These recipes are pre-developed and stored to allow each cell to utilize the recipes for many different parts. In this case, after a part is scanned, the recipe is uploaded into the next available cell and the scanned parts and heat treat fixture is moved to the cell (Figure 7).

Figure 7. Modular vacuum furnace for low pressure carburizing
Source: ECM USA

Figure 8 was designed to use over 175 different parts with nine different heat treat processes which included carburizing and slow cooling, hardening, tempering, cooling after tempering and cryogenic treatment.

With further considerations for additional benefits of the automated system, fixtures were optimized by using CFC (carbon fiber composite) base trays. These trays are not only extremely stable and have non-existent growth/warpage, but they also help with robotic placement before and after heat treatment. CFC trays are flat, or can be machined to conform to part geometry, which helps to reduce or minimize distortion related to fixture warpage or creep.

Figure 8. LPC and robotics configuration
Source: ECM USA

Many system designs have been proposed to a variety of clients; however, the end goal is to design a system that is “standard.” This standard design needs to incorporate different forms of dunnage, bins, boxes, and pallets to allow a commercial heat treater to easily program the system whenever the next part comes in from their client, whatever it may be. This is a challenging task and needs to be broken out by weight category to design the robot’s reach and end tool design. In this case a robot cell offline of the heat treat furnace can be built and utilize, and ultimately use, an AMR (automated mobile robot) or AGV (automated guided vehicle) to bring the built loads to the furnaces (Figure 9).

Figure 9. AGV configurations
Source: ECM GmbH & ECM Technologies

Vacuum Advantages

Vacuum furnace systems have a clear advantage over traditional atmospheric systems with many features which lend themselves to integrate into the machining area with robotics and automation.

The fact that an LPC (low pressure vacuum) furnace system can process loads via a recipe input and each cell can be used to process a different case depth, or hardening cycle is highly advantageous when processing a wide variety of parts. In addition, the LPC process provides a more uniform case depth throughout the part to make a stronger part along with high quality processing. The vacuum furnace cells can be arranged in many ways to fit into existing facilities and to be able to use many methods of automation especially including robotics.

Quenching is also a key element in any hardening heat treat process. LPC furnace systems are usually associated with high pressure gas quenching (HPGQ) in a separate chamber to provide the best quenching performance. This gas quenching technique provides a clean process for each part and allows the use of CFC fixtures. There is also no requirement for post cleaning as is necessary with oil quenching.

Providing quality low pressure carburizing, clean and precise gas quenching, CFC trays for better uniformity and keeping the parts flat, and the automation benefits of robotics makes for a state-of-the-art heat treating production operation and thus completes the heat treat paradigm shift.

Figure 10. Robot loading
Source: ECM USA

Conclusion

The heat treat industry wants and needs automation and robotics integration to advance production, reduce costs, and improve the overall quality of production. With traditional technology, process data evaluation and self-configured recipe values are not possible. Therefore, component analysis should be automated to meet and achieve consistent and reliable recipe values (mass flow, time). With the increase in robotics demand, vacuum furnace technology meets the variable requirements of “demand-oriented” production. Due to the flexibility of this technology, small batch size systems can be automated with robots or as bulk material.

References

  • Hiller, Gerald. “The networked hardening shop – the challenge to the hardening plant in the world of Industry 4.0.” ECM GmbH. Paper presentation, 2019.
  • Müller, Christopher. “World Robotics 2024 – Industrial Robots.” IFR Statistical Department, VDMA Services GmbH, presentation in Frankfurt am Main, Germany, 2024.

About the Author:

Dennis Beauchesne
General Manager
ECM USA

Dennis Beauchesne brings experience of over 200 vacuum carburizing cells installed on high pressure gas quenching and oil quenching installations. He has worked in the thermal transfer equipment supply industry for over 30 years, 23 of which have been with ECM USA.

For more information: Contact Dennis at DB@ECM-USA.com.



The Heat Treat Robotic Paradigm Shift Read More »

Digitalization Propels Heat Treating to Industry of the Future

If you work in a standards-driven industry, you may already feel the imperative of digitalization. In today’s Technical Tuesday, Mike Loepke, head of Nitrex Software & Digitalization, posits how, even if you aren’t necessitated to track compliance digitally, you are probably looking to synthesize and leverage the strengths of multiple advanced operations — furnace and process record-keeping, knowledge of furnace past operations, juggling different new equipment capabilities — across just one platform. In other words, you are looking to bring digitalization system management to your operations.

This informative piece was first released in Heat Treat Today’s December 2024 Medical & Energy Heat Treat print edition.


The Future of Heat Treatment Relies on Digitalization

The ultimate goal for heat treaters, whether commercial or captive, is to uphold the quality of their product and meet client expectations while remaining profitable. Digitalization supports these efforts as it synthesizes and presents detailed, transparent, and accessible data that allows heat treaters to better manage their equipment, processes, and product quality. In addition, the collection of detailed information can serve as a database of knowledge to be used by the next generation of heat treaters, supporting future viability and advancement in the field.

There are necessary steps to take to establish a digital solution and essential components to look for when choosing a software platform that assists heat treaters in optimizing equipment and processes, effectively creating the digitalization of the heat treat operations. Let’s explore these now.

How Digitalization Optimizes Heat Treatment Processes

Digitalization in the heat treatment industry relies on the integration of industrial internet of things (IIoT) technologies with traditional and modern heat treatment processes. Using enabling devices such as sensors, modern connectivity methods, analytics, machine learning, and IIoT software platforms, it is possible for heat treaters to collect and process data that, after analysis, drives informed decisions to optimize equipment, processes, and product quality. To put a finer point on it, digitalization occurs when a manufacturing system is digitally integrated to capture and preserve human experience and knowledge, forming a holistic virtual representation of heat treat operations.

Figure 1. QMULUS Shop Layout enables visual inspection of the current production status, the location of goods and parts, as well as the real-time status of assets and their ongoing processes.
Source: Nitrex

While digitalization varies from industry to industry and plant to plant, there are some common ways in which heat treaters can employ digital technologies to build such a system. Firstly, digitally integrated solutions can optimize process management and control. For example, when a sensor detects a temperature anomaly during a heat treatment process, the integrated software platform picks up that reading, analyzes it in real time, recognizes it as an error based on historical data or programmed parameters, and alerts the operator.

This integration also facilitates predictive, condition-based maintenance. For example, if collected data and analysis suggests that a furnace is behaving abnormally, the system can automatically generate a work order along with a list of potential failure causes, so that a technician can troubleshoot, identify, and correct small issues — such as a failing thermocouple — before they impact quality or result in equipment failure. By addressing these proactively, heat treaters can avoid extended periods of costly unplanned downtime and ensure continuous operation.

Secondly, artificial intelligence through machine learning plays a crucial role in optimizing quality control in a digitalized system. By analyzing data collected during heat treating processes, it learns to detect patterns and identify anomalies. As in the examples above, this capability enables the system to identify deviations from the desired outcomes, allowing heat treaters to quickly rectify any issues before they impact quality.

Figure 2. The heart of the IIoT data platform needs to be thoughtfully planned and designed. Illustrated are 5 steps to follow to ensure the cloud data system properly engages with the data generated from your specific heat treat operations, ultimately delivering actionable insights. Step 1 depicts the various data sources; Step 2 shows the data transformation, integration, and processing stages; Step 3 highlights the central QMULUS database where data is indexed and organized; and Steps 4 and 5 demonstrate how data is further processed, distributed, and accessed by different end-users.
Source: Nitrex

Thirdly, algorithms can be programmed into a comprehensive management system to identify the most energy-efficient operating conditions for the heat treating process, helping heat treaters reduce their carbon footprint, minimize energy costs, and comply with sustainability goals.

In addition to these types of operational advantages, digitalization technologies can also be used to create a database of knowledge before experienced operators and experts leave the workforce. Traditionally, a handful of experts in the plant oversee the furnaces and equipment and understand how to best control and maintain them based on experience. However, passing down this knowledge to the next generation of heat treaters can take years, which may not be possible due to a company’s workflow demands and cost pressures. Digitalization addresses this challenge by creating a streamlined and accessible database of knowledge, offering less experienced operators and technicians immediate access to detailed information about what may be happening in the equipment or process for an issue at hand. This ensures that essential insights are not lost and enables quicker problem-solving and decision-making on the shop floor.

Making the Digitalization Transformation

While digitalization presents obvious advantages, the heat treatment industry, often conservative in its approach to technology, has some initial work and investment required before realizing the full benefits.

Going “paperless” in order to unlock the full potential of the available data is an important first step. All reports, histories, drawings, and other paperwork associated with equipment, processes, maintenance activities, product quality, and other relevant information should be digitized to provide a comprehensive view of both historical and current data.

Connectivity and integration between machine and higher-level systems are essential for effective data acquisition, monitoring, and remote control. SCADA systems, Manufacturing Execution Systems (MES), and other higher-level systems are rich sources of machine and process data. Gathering and analyzing this data can provide actionable insights that operators can use to make smarter decisions about the control and maintenance of equipment and processes.

Figure 3. A comprehensive overview displays all detected control loop anomalies, indicating possible root causes as well as recommended actions. Incorporating feedback from the responsible maintenance personnel further improves accuracy and delivers more effective recommendations for future occurrences.
Source: Nitrex

Finally, just having data is not enough. The data must be accessible, transparent, and relevant to be valuable. Achieving a complete picture of all the collected data, known as data consolidation, is necessary.

To build an IIoT platform with a well-architectured data engine, heat treaters should begin by identifying and understanding the different sources of data provided by sensors and high-level systems. This involves integrating the data through interfaces adapted to the data type and source, as well as documenting the integrated data sources, data fields, and data streams. Next, a “data lake” should be created to store the collected raw data. From this foundation, a data warehouse can be established to store enriched or analyzed data, derived values, data models, and forecasts in an organized way. For heat treaters, this type of contextualized data might be grouped by parts, loads, or orders.

Once the data engine is in place, the information stored in the data warehouse must be presented in a way that makes sense to operators and technicians for them to make informed decisions for heat treatment processes. To facilitate this, a universal data interface should be considered.

Building from this well-architectured data engine, the IIoT platform can then be expanded with statistical analytics, remote monitoring, KPI tracking, machine learning, artificial intelligence, and other applications to optimize processes and increase profitability.

What Heat Treaters Need in a Digitalization Solution

Harnessing modern technologies tomake digitalization a reality presents heat treaters with the opportunity to implement a solution based on a complete and well documented data system. It also means that the solution creates a holistic solution to data analysis, interpretation, reporting, and action that supports the real-world actions of heat treaters on the plant floor and in the office.

For this reason, a digitalization solution that has cloud and on-premises allows real-time access to analysis and alert messages for operators on the floor as well as managers who are away from the plant, ensuring quick problem-solving and maximum uptime in the event of process or machine issues.

Additionally, heat treaters should look for a solution that offers the freedom to integrate all the various platforms and equipment from which data are gathered from. These may include relevant machinery and production data from the shop floor as well as third-party and custom controllers. This flexibility to synthesize information from multiple sources will ensure the digitalization efforts lead to a comprehensive solution with actionable process overviews, recipe control, batch tracking, and other customization options.

To further this intent of a holistic solution, heat treaters should consider various data capabilities with different portal views, such as a manufacturer portal, a plant portal, and a client portal. However, considering the historic value of a comprehensive software solution, it may be worthwhile to consider how each user could transfer direct feedback and add new rules into the system, creating a repository of knowledge that bridges the knowledge of outgoing generations to future heat treaters.

Finally, any platform that directs the digitalization of a plant must prioritize robust security measures. Several features to look for are:

  • enhanced encryption standards to keep data confidential and tamper-proof during transmission and storage;
  • secure protocols based on industry best practices to safeguard data integrity;
  • a granular access control system (ACS) to allow IT administrators to define and manage user permissions of authorized personnel, thereby minimizing the risk of data breaches and unauthorized data manipulation; and
  • intrusion detection and prevention systems to continuously monitor network and system activities, enabling instant identification and mitigation of suspicious behavior. This serves as an additional layer of defense against potential cyber threats.

Beyond the software setup, be sure to use best practices by conducting regular security audits to assess the platform’s vulnerabilities and ensure compliance with evolving cybersecurity standards. While digitalization of heat treat operations may seem like a task for the next generation to complete, secure software options that integrate the hard work of digitizing plant activities can make this endeavor just a step away.

About the Author:

Mike Loepke
Head of Nitrex Software & Digitalization
Nitrex

Drawing from a background in Mathematics and Physics, coupled with extensive R&D experience and metallurgical modeling, Mike Loepke specializes in AI and process prediction. He has led Nitrex’s initiative in developing QMULUS, a pioneering IIoT cloud-based platform. Mike’s relentless pursuit of knowledge keeps him at the forefront of evolving technology.

.

For more information: Contact Mike at mike.loepke@nitrex.com



Digitalization Propels Heat Treating to Industry of the Future Read More »

Heat Treat Radio #116: Basic Practices for Successful Leak Detection

In this Heat Treat Radio episode, Dave Deiwert, a seasoned expert in leak detection, shares key steps to locate leaks in a vacuum furnace. Host Doug Glenn and his guest specifically look at helium as a tracer gas. From Dave’s extensive experience starting as a field service engineer to founding his own company, Tracer Gas Technologies, listen as he identifies systematic approaches, the influence of air currents, and cost-effective strategies for effective leak detection.

Below, you can watch the video, listen to the podcast by clicking on the audio play button, or read an edited transcript.



The following transcript has been edited for your reading enjoyment.

Meet Dave Deiwert (01:10)

Doug Glenn: Welcome to another episode of Heat Treat Radio. We’re talking today about leak detection in vacuum, and we’re happy to have Dave Deiwert with us who is a leak detection expert.

Dave, would you give our listeners a little bit of background about you and your qualifications in the industry, and then we’ll jump into some questions about leak detection?

Dave Deiwert: I’ve been in leak detection since 1989. I started off my career as a field service engineer. I did that for about 10 years, then moved into sales engineering for probably the second third of my career. And for the last number of years, I’ve been a product manager and applications manager, working with several of the major vacuum and leak detection companies in the world. I thoroughly enjoy what I do and helping others with their leak testing applications.

Doug Glenn: And now you’ve got your own company. Could we hear a bit about that?

Dave Deiwert: Sure, Tracer Gas Technologies had its birth in September of this year. My focus will be on providing training and applications assistance to industrial clients, research and development labs, and government and university labs.

Doug Glenn: What’s the best way for people to reach you?

Doug Glenn and Dave Deiwert discuss his new position as president of Tracer Gas Technologies.

Dave Deiwert: We are new and still working on the website, but in the meantime, you can reach me at my phone at (765) 685-3360 or email me at DDeiwert@gmail.com.

Doug Glenn: Dave recently published an article in the November 2024 print issue of Heat Treat Today called, “Basics of Vacuum Furnace Leak Detection, Part One.” The article includes ten tips for vacuum leak detection using a helium leak detector.

Indicators of Leaks (03:45)

We’re going to cover some of those tips today. But before we get started, what are the most common symptoms that we have a leak when operating a vacuum furnace?

Dave Deiwert: I’ve been helping these clients for a number of years. And typically, one or two things happen: So, the client is following the furnace manufacturer’s recommendations to do a periodic “leak up test,” where they pump the furnace down towards base vacuum; they isolate the pumps to look for the pressure to rise after the pump’s been isolated, and if the pressure rises at a faster rate over a test period of time, which might be ten minutes, then they determine they have a leak that they should be looking for.

It’s either during that test that they discover they have a leak that they should be looking for before it impacts quality. Or the problem develops while they’re using the furnace, and it begins to affect the quality of the product. They start to see a difference in the appearance of the product because there’s some type of contaminant gas from atmosphere, water vapor, or maybe their product is sensitive to oxygen and such. It also could be as simple as they used to pump down to base pressure for the process in “x” amount of time, and it seems like it’s taking longer.

One of those two things will get their attention, and that’s okay. Let’s look for the leaks.

Isolating the Source of the Leak (05:11)

Doug Glenn: Most of the discussion we’re going to have today is going to be on using helium leak detectors. But let’s assume you don’t have a helium leak detector. What would be your checklist of things to run through to try to isolate the source of the leak?

Dave Deiwert: My perception is that end users that only have maybe one or two furnaces might not have their own leak detector, and calling for help might be quite a pricey option. They may try to do some things on their own without the leak detector or help from somebody outside the organization.

The first thing you’re going to do is consider where most leaks typically would be on a furnace. You’re going to think of things like the door is opened and closed on every cycle of the furnace, so the gasket or O-ring type material there can get worn over time.

Or maybe while the door was open, something came to rest on the O-ring: a piece of fuzz, hair, or slag metal. Something may be there that creates a leak path when they close the door. To look at that in greater detail, they get some extra light on it and see if they can determine something there. They may go ahead and remove that O-ring and just clean it up really well. Many might put a light coating with some vacuum grease or some type on it and then reinstall it.

Of course, we recommend that you try not to use vacuum grease. That could be a whole other discussion. But many will try that and see if it’s helpful to them.

The vent valve for the system also opens up after every test. So, there’s another gasket that can get worn or dirty.

Another thing would be process gases. If they filled their furnace with some back stream with argon or something, those process gas valves can leak past the seal.

So they think about each of these things and go through them one at a time and inspect them. And if they’re not quite sure what they’re seeing, they might replace the gasket or seal and then hope that they’re successful. And if they continue to not be successful, they ultimately end up calling for help.

Somebody could get very frustrated looking for leaks if you don’t know for sure that it’s only picking up helium. It’s not reacting to Dave Deiwert’s aftershave or cologne, or something else… the fork truck that went by, or something else. I can say with 100% certainty it’s reacting to helium.

Understanding Leak Detector Technology (07:14)

Doug Glenn: I want to ask for a further explanation on the first tip in this article.You say, “Understand how your leak detector works to the point that you can confirm it is working properly.” How does a company do that?

Dave Deiwert: If you’re going to go to the expense of having a leak detector — which many should — they should understand how it works properly and how to tell that it’s working properly or not before you start spraying helium to look for leaks.

Every manufacturer of leak detectors today, and for quite a number of years, has a leak detector that will let you know whether you’re in the test mode or in a standby mode. If you ever approach somebody that is leak testing and the leak detector is in standby mode and they’re spraying helium, you can suggest, “I bet you haven’t found any leaks yet, have you? Well then, you might want to put your leak detector in test mode.”

Understanding it’s in test mode and understanding how to calibrate the leak detector are good tools to help your success in finding leaks on the system. You have to at least be familiar enough with the leak detector to understand its operation and knowing that it’s sensitive to helium and the calibrating procedure increases and supports this understanding.

Doug Glenn: That makes a lot of sense: Make sure it’s turned on.

Dave Deiwert: Right, turned on and connected to your system. If you don’t have a hose going from the leak detector to the furnace and you’re spraying helium, that’s also going to be a problem.This might sound silly, but sometimes people think, “Hey, this sounds easy. You just spray helium and look for leaks.” They may ask some person who doesn’t really have much experience, “Hey, go over and test the furnace.” They may be embarrassed to say that they don’t know how to use the leak detector, so they may give it a go. Because they don’t understand the leak detector, they might not be successful.

Doug Glenn: That leads me to my next question because I would be that guy that doesn’t really know how they work. When you’re performing a leak detection using a helium leak detector, how does that process work? Where is the leak detector? Where are you spraying the helium?

Dave Deiwert: Sure. In my career I’ve seen people choose a few different points of connection to the furnace, but you’ll find our industry that we teach people that the best place would be to connect the hose from the leak detector to point in front of the blower if they’ve got a blower on their system. If they don’t have one, it’s going to go at a connection point near the inlet of the pump of gas pumping through this system. But you want to sample that flow of gases from the furnace towards the pumps. That way, you can get a sample to the leak detector as you’re spraying the helium.

When you talk about how the leak detectors work… at every class I teach, I think it’s important to at least give enough information so that you have confidence that the leak detector can help you. How’s it sensitive to helium and why? With these leak detectors, no matter who manufactures them, typically you’ll see that inside there’s a mass spectrometer that’s tuned to the gas mass weight of a helium molecule. And because it’s dependent on the mass weight of a helium molecule, not the mass weight of oxygen, nitrogen, argon, or whatever, you can be 100% sure that when the leak detector reacts, it’s getting helium from somewhere.

I stress that because somebody could get very frustrated looking for leaks if you don’t know for sure that it’s only picking up helium. It’s not reacting to Dave Deiwert’s aftershave or cologne, or something else… the fork truck that went by, or something else. I can say with 100% certainty it’s reacting to helium.

You might be surprised how often in my career somebody said, “Dave, the leak detector’s reacting, and I haven’t even started spraying helium yet.” I will tell them helium is coming from somewhere, and it could be the tank of helium that you’ve rolled up to the furnace is spraying helium and you didn’t realize it. Maybe the spray gun is still spraying helium even though the trigger is not pulled. Maybe the regulator’s leaking.

Leak detector hooked up to vacuum furnace
Source: Dave Deiwert

And if that furnace has got a leak, it’s the whole reason you brought the leak detector over. You’re not spraying helium yet, but helium is being sprayed by the tank or the regulator. The leak detector is going to react to the helium regardless of how it got into the system. So that can be very frustrating.

Let me back up: If you know beyond the shadow of a doubt the leak detector will only respond to helium and you haven’t sprayed helium yet, you know immediately it’s coming from somewhere.That is to say, I need to figure out what’s going on there. Otherwise I might spin my wheels looking for a leak while something else is a distraction for me.

Does that make sense?

Understanding Helium (11:53)

Doug Glenn: Yes, it does. Let me ask you this, though, because I’ve never done a helium leak detection as a publisher of a magazine — we don’t have a lot of helium in this business. You’ve got this box called the helium leak detector. It’s got a hose. You connect the hose near the blower or someplace close to the vacuum pump. I assume the leak detector is sampling the air as it’s coming towards the pump or towards the blower. Correct?

Dave Deiwert: Absolutely.

Doug Glenn: Then you’re spraying helium on the outside of the furnace somewhere to see if it’s being pulled into the furnace through some hole and therefore heading towards the pump.  Correct?

Dave Deiwert: Yes.

Doug Glenn: I wasn’t ever sure how that worked — whether you spray the helium inside the furnace then you’re checking around the outside of the furnace with the leak detector; I know that sounds silly, but I thought that might be how it worked. But the truth is you’re sampling the air inside, and you’re spraying helium on the outside. If that’s the case, with a canister of helium on the outside of the furnace, won’t the detector be detecting the gas because it is going from that helium canister through and into the furnace, right?

Dave Deiwert: Yes, that’s correct.

When we get into the idea of spraying helium — where does the helium go when I spray it? When I started my career way back in 1989 as a field service engineer, I was taught that helium rises because it’s the lightest gas. And so I was taught, as were many other people, to start at the top of the furnace and work your way down.

The problem with teaching that is (remember, there’s five parts per million of helium naturally in the air we breathe) that if I start spraying helium, I can tell you with 100% confidence that the air currents in the room are going to impact that helium. If you can feel the air blowing from your right towards your left, and when someone’s got a floor fan on you can be sure of it, the predominant helium you’re spraying is going to move that way. It’s going to dissipate over time, but starting somewhere methodical to spray the helium is important and to not spray too much.

Be Patient with Leak Detection! (13:14)

Doug Glenn: I did want to ask a little bit about that because in your second and third tip in this article you expressed the need to be patient when doing a leak detection. Just exactly how patient do we need to be, and why do we need to be so patient?

Dave Deiwert: Frequently throughout my career, I’ve run into people who say, “I’m not sure if I’ve got a leak, so I’m going to spray a lot of helium so I can determine it pretty quickly.” But if you spray that helium like you’re trying to dust off the equipment, you will have so much helium in the air the leak detector will definitely react if there’s a leak. However, now you have to wait forever and a day; it could be quite a while until the helium that you just sprayed all over the system and in the room dissipates before you can continue looking for a leak.

I always ask this question when I’m teaching a class with people who have been doing leak testing: “How do you set your helium spray nozzle?” The ones that’ve been doing it for quite a while will say that they’ll get a glass of water, for example, and they’ll put the spray nozzle down in the water and adjust the flow to where they get one bubble every two to three seconds. I see some variation on that, one to ten seconds. But they’ll try to meter it down. Somebody might say, “I’ll put the nozzle up to my lip and spray so I can barely feel it.”

I’ve run into people who say, “I’m not sure if I’ve got a leak, so I’m going to spray a lot of helium so I can determine it pretty quickly.” But if you spray that helium like you’re trying to dust off the equipment, you will have so much helium in the air the leak detector will definitely react if there’s a leak. However, now you have to wait forever and a day.

To those people, I’ll say, “That’s a good start. If you put that nozzle in that glass of water and it looks like a Ken and Barbie jacuzzi, you’re spending way too much helium into that.” I would meter that down to a very small amount, whether it’s a bubble every three seconds or you can barely feel it on your lip is a good place to start.

And because I made the comment that helium doesn’t necessarily rise but can go different directions based on the wind, air currents in the room, and fresh air makeup, eventually somebody says, “Where should I start?” I’ll say, “I don’t have a problem with you starting at the top of the furnace and working your way down. Be methodical.”

Some people will start at the leak detector they just hooked up because they might have put a leak in the bellows connection from the leak detector. You might start there to make sure the assembly you just did is leak tight.

But start somewhere, be methodical as you move across the system, and remember that helium can go up, down, left, back, or forward depending on what the air currents are.

Doug Glenn: I was actually going to ask you about the air currents, because I thought that was an interesting tip that you had made. In fact, I think that’s like tip four and five in this article. I think we’re dealing with air currents and things of that sort. So, we’ll skip over that, because I think you’veaddressed that.

The Dead Stick Method (16:48)

Doug Glenn: You mention an interesting thing called a “dead stick method” in tip number six. Can you explain what that is?

Dave Deiwert: I’m glad you asked that because I looked back on that later and thought I don’t think I elaborated on that enough for somebody that’s never done the dead stick method. That is a term for when you spray just a little squirt of helium away from you and the furnace, and then stop spraying. Then you’re going to rely on the residual helium that’s coming out of the tip of the nozzle for some period of time.

In my training classes, I typically have a plastic bottle that has a little right-angle nozzle on it. You may have used them back in high school in chemistry; it might have had alcohol in it. I will squirt a little helium in that plastic bottle and then screw the cap on; that will last me for two or three days at a trade show or a training event. I don’t have to squeeze the bottle. There’s enough helium coming out of the nozzle that you can detect leaks.

To demonstrate, I’ll put hair on an O-ring on a test for the leak detector. (It’s the cause of my receding hairline.) I can take that nozzle without squeezing the bottle and move it near the hair that I put in there, and it will detect it very impressively every single time, at least over the course of two to three days.

Perspective looking up into the world’s largest vacuum chamber at NASA’s facility in Sandusky, Ohio
Source: Dave Deiwert

My point of demoing that is people tend to spray away too much helium. If there’s five parts per million naturally in the air we breathe, you only need enough delta difference so that as you go past where the leak’s at you can see a reaction from the leak detector and pinpoint it.

Backtrack to if somebody sprays a lot of helium to prove they have a leak. Now they have to wait a long time for the helium to dissipate. And by the way it’s not just dissipating from the room. You’ve sprayed a lot of helium that is now feeding that leak. And as it goes through the leak path in the furnace, it expands back out in front of you. It’s got to pump away from the furnace, too. It’s also got to clear the system and go out to the pumps before you get back to baseline so that you can continue leak checking.

Therefore, if you spray just very small amounts,, you have to get close to where the leak is before you start to get a response. This way you have less concern of helium drifting to the opposite side of the furnace and going through a leak path there — that can really distract. You may think you’re near the leak, but it’s really on the other side of the furnace because you’ve sprayed way too much helium.

Spraying little amounts might make you feel like it’s taking longer. But the fact is, when you start to get a reaction at the leak detector, you can be comfortable that you’re getting close to the where the leak is.

Doug Glenn: If you know you’re in a room with air currents in it (let’s just say there’s a flow of some sort from left to right), does it make sense to always start downwind, and then work your way back across the system?

Dave Deiwert: Yes. If I can feel a fan — Joe’s got his fan on because it’s keeping him cool, and it’s blowing over towards where I’m leak testing, I might say, “Hey Joe, could you turn your fan off a little bit while I’m testing?” He may say, “No, it’s making me comfortable.” All right, now I’ve got to work with that. I know that I can feel the air currents moving from my right towards my left. So, yes, starting downwind and working my way up could be helpful. You want to pay attention to what the air is doing if you can tell. It may be a very calm environment, and you’re not sure what the air currents are doing; just be methodical. Pick somewhere to start in the furnace.

Here’s something else about spraying helium: Once you think you know where the leak is at, every time you put the spray nozzle there you should get the same response. You spray the helium, you get a response, you stop spraying and wait until it drops back to baseline, and then you go back to where you think the leak is. If that’s where the leak is, every time you put the probe there, you should get the same response time at the leak detector. If even one time you put the spray gun there and don’t get a response or not nearly the same, then that’s not where the leak is at. Yeah, you should know beyond a shadow of a doubt when you pinpoint the leak.

Doug Glenn: How often do you see more than one leak at a time? Let’s say you isolate a leak, you think you got it, then say you take the gasket off or whatever you do, do the test again, and there’s still a leak.How often does that happen?

Dave Deiwert: It happens most of the time. When I was a field service engineer and somebody called me in to help, I almost never found one leak. That tells me they were working with one leak that maybe wasn’t large enough to affect their quality or the cycle time, and they were living with it. And the day comes where they have a leak that gets their attention or the leak got larger. It can be more challenging if you’ve got more than one leak. It’s a short-lived celebration when you think you found a leak and then you go to start the process, and, oh, it looks like you still have a leak. That wasn’t the one. So, you might make a case for looking to see if you can pinpoint another leak while you’re in the leak testing mode.

Doug Glenn displays the cover of the November 2024 issue of Heat Treat Today, in which Dave Deiwert’s article, “Basics of Vacuum Furnace Leak Detection, Pt 1,” is featured.

Saving on Helium Gas (21:35)

Doug Glenn: Besides the fact that a helium leak detector can save you all kinds of time because typically you can find a leak faster with a helium leak detector then in a process of elimination, you also mentioned a tip for saving money regarding the mixing of the gas. Could you elaborate on that and any other cost savings tips?

Dave Deiwert: I already mentioned that people tend to spray way too much helium at least until they’re sensitive to that concern and cut back. But when they buy the tanks of helium, they’re buying 100% helium. And remember my comment that you just need enough delta increase in the helium that you’re applying to where the leaks at to be able to pinpoint it. The possibility that you could buy your tanks of helium at a lesser percentage, maybe 25% helium and 75% nitrogen, would help you save on some helium and help your efforts to not be spraying too much.

People have not been saying that in this industry, and so that can make folks nervous. “I don’t know, Dave. We’ve never done that before. I’ve never heard anybody else say that before.” I suggest if you are going through a lot of helium, you could cut down how much helium you’re spraying. You could save some significant money, especially these larger facilities with many furnaces and so forth. Give it a try. Buy one tank of it with a mix gas and pick something that you’re comfortable trying, whether it be 25% or 50% helium and buy one bottle. And the next time you test your furnace and find a leak, then try to look at that leak with the lower percentage helium and prove to yourself whether using a lower percentage of helium is going to save you money.

Doug Glenn: You’re suggesting people get themselves comfortable with it, use their 100% until they find the leak, and then try the lower helium.

Dave Deiwert: When they show the proof to themselves, that they can still have the capability to find leaks like that, then they could save a little money. Plus, there’s the added benefit of not spraying so much helium and having to wait as long for the area to clear up before you can start spraying again to continue to pinpoint a leak.

Doug Glenn: And that would save you additional time. Dave, thank you very much. Is there anything else you’d like to add before we wrap up?

Dave Deiwert: Only that if you know you’ve got a leak in the system — it failed the leak up test or quality or whatever, you sprayed it around the entire system, and you can’t find any leaks — then you’re probably looking at an internal leak most likely past the seat of a valve. Or maybe you’ve got a vent valve that’s leaking past the seat, but your plumbing to that vent valve maybe goes out of the building, so you don’t really have an easy access to spray helium past that.

For example, with an argon valve, you may need to disconnect the argon supply from that valve so you can get access to that side of the valve to spray helium to see if you can detect a leak past the seat of that valve.

Doug Glenn: Dave, thanks very much, I appreciate it. I’m sure we’ll be talking again. I know vacuum leak detection is an important thing.

About The Guest

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.

Contact Dave at ddeiwert@gmail.com.


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Understanding Inductance in a Furnace Heating System

In this installment of the Controls Corner, we are addressing inductance in a furnace heating system, and the critical role it plays in various industrial systems, including furnace load systems. Impedance acts as a measure of how much a circuit resists the flow of AC current. In this guest column, Brian Turner, sales applications engineer at RoMan Manufacturing, Inc., explains how impedance applies in electrical circuits.

This informative piece was first released in Heat Treat Today’s November 2024 Vacuum Heat Treat print edition.


Inductance is a fundamental concept in electrical engineering, and it plays a critical role in various industrial systems, including furnace load systems. In furnaces used for heating, inductance is a key factor influencing the system’s electrical performance, energy efficiency, and overall operational behavior.

To talk about inductance, let’s first address impedance and how it applies:

In electrical circuits, impedance refers to the total opposition to the flow of alternating current (AC), which is a combination of both resistance (from resistors) and reactance (from inductors), essentially acting as a measure of how much a circuit resists the flow of AC current, taking into account both the resistive component (like a resistor) and the reactive component (like an inductor at a specific frequency) within the circuit.

Load configuration, power source (IGBT, VRT, ERT) to the furnace feedthrough
Source: RoMan Manufacturing Inc.

Inductance

Inductance is the property of an electrical conductor that opposes a change in the current flowing through it. It arises from the magnetic field generated around the conductor when an electric current passes through it. The unit of inductance is the Henry (H).

In an AC circuit, inductance creates a phenomenon known as inductive reactance, which resists the flow of current. Inductive reactance (XL) is given by the formula:

XL = 2πƒL

Where:
XL is the inductive reactance (in ohms)
f is the frequency of the AC supply (in hertz)
L is the inductance (in Henrys)

This reactance influences how the current behaves in the system, which is particularly important in furnace load systems where high current flows are common.

Resistance

Electrical resistance is the opposition that a material offers to the flow of electric current. It is measured in ohms (Ω) and depends on factors such as the material’s properties, its temperature, and the geometry of the conductor (length, cross-sectional area). In heating systems like vacuum furnaces, resistance is harnessed to convert electrical energy into heat through Joule heating (also known as resistive heating).

The relationship between electrical power, voltage, current, and resistance is governed by Ohm’s law:

V = IR

Where:
V is the voltage across the heating element(in volts)
I is the current through the element (inamperes)
R is the electrical resistance of theelement (in ohms)

The heat generated by the furnace’s heating elements is a function of the power dissipated in the resistance, given by the equation:

P = I2 x R

This shows that the heat produced is directly proportional to the resistance and the square of the current flowing through the heating elements

Close Couple

  • Reducing the material in the secondary* reduces resistance (HEAT = I2 x R)
  • Reducing the area in the secondary reduces inductive reactance increasing power factor

To be most efficient, use the shortest amount of conductor material from the electrical system secondary to the furnace feedthrough. Additionally, keep the distance between those conductors as small as possible.

Power Factor and Efficiency

Inductance in a furnace load system causes the current and voltage to be out of phase. This phase difference results in a lower power factor, which is a measure of how effectively the system converts electrical power into useful work. A lower power factor means that more apparent power (the combination of real power and reactive power) is required to achieve the same level of heating.

In practical terms, a furnace with a high inductive load will draw more current from the power supply for a given amount of heating, leading to increased energy losses and inefficiency.

In practical terms, a furnace with a high inductive load will draw more current from the power supply for a given amount of heating, leading to increased energy losses and inefficiency. Power factor correction techniques, such as the use of capacitors, are often employed to counteract the effects of inductance and improve system efficiency.

Conclusion

Inductance is a fundamental factor in the operation of furnace load systems, influencing everything from heating performance to energy efficiency and power quality. By understanding and managing inductance, furnace operators can optimize their systems for maximum performance while minimizing energy losses and operational costs. Controlling inductance is essential for ensuring that furnace load systems operate reliably and efficiently in demanding industrial environments.

*The connection from a vacuum power source to the furnace’s feedthroughs, this connection can be made using air-cooled cables, water-cooled cables, or copper bus.

About the Author:

Brian Turner
Sales Applications Engineer
RoMan Manufacturing, Inc.

Brian K. Turner has been with RoMan Manufacturing, Inc., for more than 12 years. Most of that time has been spent managing the R&D Lab. In recent years, he has taken on the role as applications engineer, working with customers and their applications.

For more informationContact Brian at bturner@romanmfg.com.



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