Manufacturing Heat Treat Technical Content

Basics of Vacuum Furnace Leak Detection, Part 1

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

If you have the right leak detection equipment, the process of detecting leaks can be more time efficient. In this Technical Tuesday installment, learn more about the practical side of leak detection, from potential sources of leaks to equipment and methods of effective leak detection. Guest columnist Dave Deiwert, president of Tracer Gas Technologies, also provides 10 tips for identifying the most common sources of leaks. Stay tuned for his follow-up article that will focus on operating and maintaining a helium leak detector and repairing the leaks that are found.

This informative piece can be found in Heat Treat Today’s November 2024 Vacuum print edition.

When leaks develop in a vacuum furnace, they can inhibit the furnace’s ability to achieve the desired process vacuum level. Without an appropriate leak detector, an operator and maintenance team are limited to guessing where the leak might be, a time-consuming process of elimination evaluating each component or possible leak point one at a time. Alternatively, if you have the right leak detection equipment, the process of detecting leaks can be more time efficient.

First, a team needs to know the possible sources for leaks — especially if they are troubleshooting without a leak detector. Then, selecting the appropriate equipment can speed up the leak detection process. Ultimately, that equipment is most useful if a team is informed on how to best use and maintain the equipment.

Troubleshooting Without a Leak Detector

If a team does not have a leak detector, they first must disassemble potentially leaking components to clean and replace gaskets and seals. For some products, like valves and pumps, they might use a supplier-provided repair kit.

After reassembling, if they discover they still have a leak in their furnace, they will continue to select possible leaking components for maintenance.

The team would then start with the components most likely to be leaking — for example, the door seal. The door to the furnace is opened and closed every cycle of the furnace as the operator removes products that were under process for the previous cycle and then places the next product, or batch of products, into the furnace. This opening and closing of the door creates wear on the gasket and also provides opportunity for foreign materials and debris to land on the seal and cause a leak. As this is just one possible source of a leak, continuing to troubleshoot can become a lengthy process. (See sidebar for more information on possible sources for leaks.)

Selecting Equipment To Support Vacuum Furnace Leak Detection

Having a leak detector on-site allows a team to identify the source of the leak more efficiently. Typically, major OEM furnace suppliers, their field service teams, and major end-users of vacuum furnaces have selected “fixed magnetic sector mass spectrometers” optimized for using helium as a tracer gas to look for leaks in vacuum furnaces. These are also the tool of choice for OEM companies and end-users in other vacuum applications such as glass coaters, solar panel manufacturing, automotive, medical, aerospace, and others. In industrial manufacturing plants and R&D, we commonly call these tools “helium leak detectors.”

Helium leak detectors are the well-established method for leak testing because helium — the second smallest molecule and a safe, inert gas that does not react with other gasses or material — is useful for finding the smallest of leaks.

Figure 1. Leak detector hooked up to vacuum furnace
Source: Dave Deiwert
Figure 2. Perspective looking up into the world’s largest vacuum chamber at NASA’s facility in Sandusky, Ohio
Source: Dave Deiwert

10 Practical Tips for Leak Detection

The following tips for leak detection pertain to using helium leak detectors:

  1. Understand how your leak detector works to the point that you can confirm it is working properly.
  2. A common question is, “How long after I spray a point on the furnace should I wait for a reaction on the leak rate meter to ensure that point doesn’t leak?” The answer is to characterize your system so that you know what the longest time constant can be for a leak to be detected. For example, purposefully apply a leak at the furthest point on the furnace from where the leak detector is installed. Then, spray helium and count the seconds to when the leak detector reacts to helium from the leak. Now you will know that you never have to wait longer than that without a reaction before moving on to the next point of leak testing.
  3. Avoid moving along too quickly around the furnace as you spray helium. If there is a reaction at the leak detector when you stop spraying, you may have passed the point of leakage. After the leak detector leak rate drops back to baseline, you will try respraying the point of concern. If there is no reaction, consider that you may have moved along too quickly, and retrace the area you had sprayed more slowly. If you do not get a reaction again, it is very possible that the air currents of the room had carried the helium towards a point that you have not even reached yet.
  4. Remember: There are naturally five parts per million of helium in the air we breathe. Therefore, when you spray helium, it becomes the victim of the air currents in the air and the fresh air makeup of the room. Helium can go up, down, left, right, away from you, and towards you depending on the air currents of the room. 
  5. Because helium spreads so pervasively, it is better to spray very small amounts of helium so that when you get a reaction from the leak detector, you know you are getting closer to the leak. If you spray helium like you are trying to dust off the system at the same time, you will quickly confirm there is a leak but will be forced to wait forever and a day for the helium to clear up in the room to the point that you can continue looking for the leak.
  6. If you have confirmed the location of the leak to a small area, but there are still several points of possibility within it and you are unable to pinpoint the leak, diminish the amount of helium you are spraying. You can try to further restrict the flow of helium by using the “dead stick” method. This is where you spray helium from the spray nozzle away from the area of interest, then you place the nozzle near the potential leak points one at a time, relying on the residual helium that is present at the nozzle. This can still work well because (if you remember that there are 5 parts per million of helium in the air we breathe) there could still be hundreds, if not thousands or more, parts per million of helium present at the tip of the nozzle — at least long enough for using the dead stick method.
  7. If you are looking to minimize the costs of helium, consider buying your tanks of helium at a lower percentage using nitrogen as the balance gas in the cylinder. People already tend to spray too much helium when conducting leak detector tests, and we are not trying to measure the severity of the leaks. So, decreasing the percentage of helium will save money without negatively impacting leak detection. If you are not yet comfortable with this but interested in testing it, simply buy one tank with a lower percentage of helium. Next time you find a leak with your 100% tank of helium, roll the tank with a lower percentage of helium over, spray the same leak on your system, and determine the difference (if any) in the effectiveness of detecting any leaks found.
  8. Learn the “wellness” checks from your leak detector’s manufacturer. This can help you establish preventative maintenance for your leak detector before it has a problem that makes it unavailable for use when your furnace needs a leak check. Your leak detector manufacturer should be able to recommend what points of interest on their leak detector need regular scrutiny.
  9. Calibrate your leak detector when you start it up and check calibration when you are finished to confirm it is working properly.
  10. If you are fortunate to not need your leak detector for many months, I recommend you schedule a few times per year to start it up and ensure it is still working well. Occasionally, I hear of someone who needed their leak detector after months to a year of disuse who found that it was not working well. Leak detectors, like pumps, should not be neglected indefinitely.
Figure 3. Blower mounted atop pump
Source: Dave Deiwert

The Value of Efficiency

While it is possible to identify and repair leaks without a helium leak detector, a team with one is likely to net significant time savings if they operate and maintain it intentionally. An operation with many furnaces typically will have their own leak detector — and probably a spare. Operations with just one or two furnaces may choose to hire a service company to find the leaks in their system; this works well if they rarely encounter leaks on their systems.

“Basics of Vacuum Furnace Leak Detection, Part 2” will cover advancements in helium leak detector technology, operating and maintaining a leak detector, and comparing whether it would make sense to repair vs. replace a leak detector.

About the Author:

Dave Deiwert
President
Tracer Gas Technologies
Source: Dave Deiwert

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.  

For more information: Contact Dave at ddeiwert@gmail.com.

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Ask the Heat Treat Doctor®: How Do Parts Fail?

/ AEROSPACE HEAT TREAT TECHNICAL CONTENT, ATMOSPHERE AIR FURNACES TECHNICAL CONTENT, Manufacturing Heat Treat Technical Content

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.

Product failures (Figure 1) can often be traced to deficiencies in design, materials, manufacturing, quality, maintenance, service-related factors, and human error to name a few. Examples of failures include misalignment, buckling, excessive distortion, cracking, fracture, creep, fatigue, shock, wear, corrosion, and literally hundreds of other mechanisms. Let’s learn more. 

Figure 1. Image of damage to left fuselage and engine; fire damage to nacelle.
Source: National Transportation Safety Board
Figure 2.: Model of material science depicting— key interactions and /interrelationships
Source: The HERRING GROUP, Inc.

Whatever the source, it is important to recognize that it is next to impossible to separate the product from the process.  Performance, design (properties and material), metallurgy (microstructure), heat treatment (process and equipment), and maintenance are all interconnected (Figure 2).  

When considering ways to prevent failures from occurring, one must determine the factors involved and whether they acted alone or in combination with one another. Ask questions such as, “Which of the various failure modes were the most important contributors?” and “Was the design robust enough?” and “Were the safety factors properly chosen to meet the application rigors imposed in service?” Having a solid engineering design coupled with understanding the application, loading, and design requirements is key to avoiding failures. If failures do happen, we must know what contributed to them.  

Let’s review a few of the more common failure modes. 

Fracture Types on a Macroscopic Scale  

Applied loads may be unidirectional or multi-directional in nature and occur singularly or in combination. The result is a macroscopic stress state comprised of normal stress (perpendicular to the surface) and/or shear stress (parallel to the surface). In combination with the other load conditions, the result is one of four primary modes of fracture: dimpled rupture (aka microvoid coalescence), cleavage, decohesive rupture, and fatigue. 

Virtually all engineering metals are polycrystalline. As a result, the two basic modes of deformation/fracture (under single loading) are shear and cleavage (Table 1). The shear mechanism, which occurs by sliding along specific crystallographic planes, is the basis for the macroscopic modes of elastic and plastic deformation. The cleavage mechanism occurs very suddenly via a splitting action of the planes with very little deformation involved. Both of these micro mechanisms primarily result in transgranular (through the grains) fracture. 

Fracture Types — Ductile and Brittle  

Numerous factors influence whether a fracture will behave in a ductile or brittle manner (Table 2). In ductile materials, plastic deformation occurs when the shear stress exceeds the shear strength before another mode of fracture can occur, with necking typically observed before final fracture. Brittle fractures occur suddenly and exhibit very little, if any, deformation before final fracture. (The following is based on information found in Wulpi, 1985.)

Ductile fractures typically have the following characteristics: 

  • Considerable plastic or permanent deformation in the failure region 
  • Dull and fibrous fracture appearance 

Brittle fractures typically have the following characteristics:

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  • Lack of plastic or permanent deformation in the region of the fracture 
  • Principal stress (or tensile stress) is perpendicular to the surface of the brittle fracture 
  • Characteristic markings on the fracture surface pointing back to where the fracture originated  

When examined under a scanning electron microscope, fracture surfaces seldom exhibit entirely dimpled rupture (i.e. ductile fracture) or entirely cleavage (i.e. brittle fracture), although one or the other may be more prevalent. Other fracture modes include intergranular fractures, combination (quasi-cleavage) fractures and fatigue fractures. 

Fracture Types — Wear 

Wear (Table 3) is a type of surface destruction that involves the removal of material from the surface of a component part under some form of contact produced by a form of mechanical action. Wear and corrosion are closely linked, and it is important not only to evaluate the failure but to take into consideration design and environment and have a good understanding of the service history of a component. 

Fracture Types — Corrosion 

Corrosion is the destruction of a component by the actions of chemical or electrochemical reactions with the service environment. The major types of corrosion include galvanic action, uniform corrosion, crevice corrosion, stress-corrosion cracking, and corrosion fatigue. The mechanisms and effects created by each of these are well documented in the literature, as in Fontana and Greene’s Corrosion Engineering (1985) and Uhlig’s Corrosion and Corrosion Control (1985). It is critical to understand that the effects of corrosion are present to some degree in every failure analysis, which is one of the reasons why protecting fracture surfaces is so critical when sending parts for failure analysis. 

Table 1. Differences between shear and cleavage fracture (Data referenced from page 23 of Wulpi, see References.)
Source: The HERRING GROUP, Inc.
Table 2. Typical characteristics of ductile and brittle fractures
Source: The HERRING GROUP, Inc.
Table 3. General categories of wear
Source: The HERRING GROUP, Inc.

Final Thoughts

To avoid failures or their reoccurrence, it is important to document each step in the design and manufacture process (including heat treatment). In addition, careful documentation of failures if/when they occur is of critical importance as is assembling a team of individuals from different disciplines to perform a comprehensive investigation. This includes a thorough failure analysis to assist in determining the root cause (there is only one) and to avoid it from happening in the future. 

References

Airline Safety. www.AirlineSafety.com. Accessed September 2024.

Fontana, M. G., and N. D. Greene. Corrosion Engineering, 3e. McGraw-Hill Book Company, 1985.

Herring, Daniel H. Atmosphere Heat Treatment, Volume Nos. 1 & 2. BNP Media, 2014/2015.

Lawn, B.R. and T. R. Wilshaw. Fracture of Brittle Solids. Cambridge University Press, 1975.

Shipley, R. J. and W. T. Becker (Eds.). ASM Handbook, Volume 11: Failure Analysis and Prevention. ASM International, 2002.

Uhlig, H. H. Corrosion and Corrosion Control. John Wiley & Sons, 1963. 

Wulpi, Donald J. Understanding How Components Fail. ASM International, 1985.

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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Parts Distortion: How To Predict It and How To Account for It

/ Manufacturing Heat Treat Technical Content

Source: Paulo

No matter the craft, disappointment is inevitable when the end result doesn’t turn out as planned. But in heat treatment, distortion is more than just a disappointment, it could contribute to weakness in a component, putting lives at risk. The industry can be credited for its commitment to determining the causes and manners in which parts distort and how to eliminate the risk.

Today’s best of the web article examines the inevitability of distortion in heat treating and demonstrates how to predict changes in size and shape of parts during processing, acknowledging that “maintaining dimensional accuracy is essential, especially for mission-critical and safety-critical components with the tightest tolerances.”

An Excerpt:

“Every part you heat treat will have some degree of ‘ballooning’ and distortion, but there are ways to predict how much your parts will deform. Knowing how your parts will change during heat treatment allows you to account for that change in the design of the part and, in a perfect world, avoid an additional round of machining after heat treatment.”

Read the entire article from Paulo by clicking here: “How Much Distortion To Expect in Heat Treating”

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Dual Chamber Vacuum Furnaces vs. Single Chamber Vacuum Furnaces — An Energy Perspective

/ FEATURED NEWS, GUEST COLUMN, Manufacturing Heat Treat Technical Content, OP-ED, VACUUM FURNACES TECHNICAL CONTENT

The need to understand how certain furnace designs operate comes at a time when heat treaters are weighing each energy cost and benefit of their systems and processes. Read on for a quick summary on how dual chamber furnaces preserve energy.

On April 17-19, 2024, TAV VACUUM FURNACES provided a speaker at the 4th MCHTSE (Mediterranean Conference on Heat Treatment and Surface Engineering). The speech focused on the energy aspects of vacuum heat treatment, a subject towards which all of us within the industry need to pay attention for reducing the carbon emissions aiming at a zero net emissions future.

We have already analyzed the essential role that vacuum furnaces will play in this transition, with a focus on the optimization of energy consumption in our previous article. With this new presentation, we wanted to emphasize how selecting the right vacuum furnace configuration for specific processes may impact the energy required to perform such process. For doing so, we compared two different furnace designs — single chamber vs. dual chamber vacuum furnaces — detailing all of the components’ energy consumption for a specific process.

TAV DC4, dual chamber vacuum furnace for low pressure carburizing and gas quenching
Source: TAV VACUUM FURNACES

As a sneak peek into our presentation, we will summarize below how the main features of the two vacuum furnaces design are affecting their energy performance.

Let’s start by introducing the protagonist of our comparison: a single chamber, graphite insulated vacuum furnace, model TAV H4, and a dual chamber furnace TAV DC4, both having useful volume 400 x 400 x 600 mm (16” x 16” x 24”) (w x h x d).

In a single chamber vacuum furnace, like the TAV H4, the entire process is carried out with the load inside the furnace hot zone. This represents a highly flexible configuration that can perform complex heat treatment recipes with a multiple sequence of heating and cooling stages and to precisely control the temperature gradients at each stage.

Configuration of the TAV DC4 dual chamber vacuum furnace
Source: TAV VACUUM FURNACES

Alternatively, a dual chamber vacuum furnace, like the TAV DC4, is equipped with a cold chamber, separated from the hot zone, dedicated for quenching. Despite the greater complexity of this type of vacuum furnace, the dual chamber configuration allows for several benefits.

First, in dual chamber furnaces, the graphite insulated hot chamber is never exposed to ambient air during loading and unloading of the furnace; for this reason, the hot chamber may be pre-heated at the treatment temperature (or at a lower temperature, to control the heating gradient). But in single chamber vacuum furnaces, the hot zone must always be loaded and unloaded at room temperature to avoid damages due to heat exposure of graphite to oxygen.

Because dual chamber furnaces have more controlled heating, this will result in both faster heating cycles and lower energy consumption, as a substantial amount of energy is required to heat up the furnace hot zone. This advantage obviously will be more relevant in terms of energy savings the shorter the time is between subsequent heat treatments.

View of the cold chamber of the TAV DC4 dual chamber vacuum furnace
Source: TAV VACUUM FURNACES

Secondly, since the quenching phase is performed in a separated chamber, the hot zone insulation can be improved in dual chamber vacuum furnaces by increasing the thickness of the graphite board without compromising cooling performance. This translates into a significantly lower heat dissipation, to the extent that at 2012°F (1100°C) the power dissipation per surface unit (kW/m2) is reduced by 25% compared to an equivalent single chamber vacuum furnace.

Additionally, quenching in a dedicated cold chamber allows to obtain higher heat transfer coefficients and higher cooling rates compared to a single chamber vacuum furnace. Since the cold chamber is dedicated solely to the quenching phase, it can be designed for optimizing the cooling gas flow only without the need to accommodate all the components required for heating. All things considered, the heat transfer coefficient achievable in the TAV DC4 can be, all other things being equal, even 50% higher compared to a single chamber vacuum furnace. Secondly, since the cold chamber remains at room temperature throughout the whole process, only the load and loading fixtures need to be cooled down; as a result, the amount of heat that needs to be dissipated is significantly less compared to the single chamber counterpart.

CFD simulation showing a study on the cooling gas speed in a section of the cooling chamber for the TAV DC4 dual chamber vacuum furnace
Source: TAV VACUUM FURNACES

For heat treatments requiring high cooling rates, it is possible to process significantly higher loads on the dual chamber furnace compared to the single chamber model; translated into numbers, the dual chamber model can effectively quench as much as double processable in a single chamber furnace, depending on the alloy grade, load configuration and overall process. The savings in terms of energy consumption per unit load (kWh/kg) achievable in the dual chamber furnace for such processes can be as high as 50% compared to the single chamber furnace.

In the end, the aim of the speech was to highlight how the energy efficiency of vacuum furnaces is highly dependent on the machine-process combination. Choosing the right vacuum furnace configuration for a specific application, instead of relying solely on standardised solutions, will improve significantly the energy efficiency of the heat treatment process and drive the return on investment.

About the Author

Giorgio Valseccchi
R&D Manager
TAV VACUUM FURNACES

Giogio Valsecchi has been with the company TAV VACUUM FURNACES for nearly 4 years, after having studied mechanical engineering at Politecnico di Milano. 

For more information: Contact Giorgio at info@tav-vacuumfurnaces.com.

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Sustainability Insights: Forging a Sustainable Path to Decarbonization

/ Manufacturing Heat Treat Technical Content, OP-ED

The search for sustainable solutions in the heat treat industry is at the forefront of research for industry experts. In this article, provided by IHEA Sustainability Initiatives, a path to sustainable decarbonization is suggested that cuts through the murky waters of changing terms and shifting protocol and charts instead a navigable course with updated definitions and industry resources, such as IHEA’s upcoming Decarbonization SUMMIT in Indianapolis, IN, this fall.

This Sustainability Insights article was first published in Heat Treat Today’s May 2024 Sustainability print edition.

There is no hotter topic (no pun intended) than decarbonization. Just about everywhere you go and everything you read or listen to talks about sustainability and decarbonization. As leaders and stewards in the industrial heating industry, the Industrial Heating Equipment Association (IHEA) is committed to being at the forefront of providing valuable information and developments around the topics of sustainability and decarbonization. For the past 18 months, IHEA has been developing and delivering a highly successful Sustainability Webinar Series; continuously updating terms and definitions, frequently asked questions, and resources for the industry on the IHEA website; and, in its biggest step, is now offering a comprehensive Decarbonization SUMMIT from October 28–30, 2024 in Indianapolis, IN.

Current IHEA President and Sustainability Committee Chair Jeff Rafter states, “All IHEA members are continuously being asked about ways to decarbonize their processes. As the industry association dedicated to all things ‘heating,’ we feel it is our duty to present an unbiased view of what’s happening now, how companies can begin the process of lowering their carbon emissions on their current equipment, while beginning to look at all the alternatives that are coming and how those might fit into their operations. There is no question that change is imminent. We want to be the resource that the industry uses for information on all options to begin to decarbonize operations.”

While not much is going to happen overnight, “Legislation is going to be coming,” notes IHEA Board Member Mike Stowe, who is serving on the ISO Decarbonization Committee. “The best thing companies can do is begin preparing now. Take a look at your current operations and start making changes that improve efficiency now. Educate yourself and your staff on technologies that will help you lower carbon emissions. Be ready for what lies ahead.”

IHEA is ready to help the industry take the next step by hosting its first Industrial Heating Decarbonization SUMMIT. This event is designed to start shaping the future of manufacturing heating processes. It will include keynote addresses by industry visionaries; ways to begin your decarbonization process now; a look ahead at various technologies that can also help you decarbonize; case histories and a panel discussion on decarbonization collaboration; networking with industry leaders, and a tabletop exhibition that showcases cutting-edge technology.

Themes Running Throughout the SUMMIT Will Focus On:

  • Low Carbon Fuels in Industrial Processes
  • Carbon Capture and Storage Technologies
  • Global Benchmarking
  • Economics and Business Concerns
  • Innovations in Clean Technologies
  • DOE (Department of Energy) Programs and Tools
  • Policy Frameworks for Decarbonization

Target Audience for the SUMMIT:

  • CEOs and Executives from Industrial Companies
  • Sustainability Officers and Environmental Managers
  • Government Officials and Policymakers
  • Researchers and Academics in Clean Technology
  • Sustainability Engineers and Program Managers
  • Directors of Sustainable Manufacturing
  • Utility Representatives

“We are in a unique position,” comments IHEA President Jeff Rafter. “There has never been an issue like this that has faced our industry. Working together and bringing the industry together at a SUMMIT gives everyone a forum to learn, share ideas and best practices, review recent technologies, and begin lowering carbon emissions as an industry. No one is going to do this alone.”

IHEA’s tabletop exhibits that will accompany the SUMMIT programming will allow attendees to get a close look at a wide array of information that will help them in their decarbonization efforts. Those interested in reserving a tabletop should visit summit.ihea.org. Tabletops are expected to sell out quickly.

As IHEA works its way towards the SUMMIT in the fall, the Sustainability Webinar Series is still underway. Nearly 1,000 people have logged on over the past year since the first webinar was launched. Upcoming Webinars include:

May 16Increasing Available Heat to Lower CO2 Emissions
June 20Understanding Carbon Credits & Net Zero
July 18U.S. Codes & Standards
August 15Renewable Fuels

Additional webinars will be supplemented to this list regularly. IHEA’s webinars are free to attend. You can register by going to IHEA’s website (www.ihea.org) and clicking on the Sustainability logo on the home page. Then scroll down and click on the “Sustainability Webinar Series” to review and register for the upcoming webinars. If you have a sustainability topic you would like us to address, please email the topic to anne@goyermgt.com, and we’ll work to create a webinar.

For more information:

Connect with IHEA Sustainability & Decarbonization Initiatives https://www.ihea.org/page/Sustainability

Article provided by IHEA Sustainability Initiatives

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Basic Definitions: Power Pathways in Vacuum Furnaces

/ CONTROLS TECHNICAL CONTENT, FEATURED NEWS, Manufacturing Heat Treat Technical Content, OP-ED, VACUUM FURNACES TECHNICAL CONTENT

Ever wish you had a map to follow when navigating your power source? In the following Technical Tuesday article, Brian Turner, sales applications engineer at RoMan Manufacturing, Inc., charts the route that power takes from the source to the load and back again in a vacuum furnace.

This informative piece was first released in Heat Treat Today’s June 2024 Buyers’ Guide print edition.

In a vacuum furnace, the journey from the load (the material being heat treated) to the incoming power involves a complex arrangement of components that deliver, control, and monitor electrical energy. Here’s a breakdown of the path from the source to the load and back to the source of incoming power of a vacuum furnace:

Load

The material — either an item or batch of items — that is undergoing heat treatment; can be metals, ceramics, or composites.

Heating Elements

Common materials for heating elements include graphite, molybdenum, or tungsten, depending on the temperature range and application.

Electrical Feedthrough

These are used to transmit electrical power or signals through the vacuum chamber wall. They often contain insulated conductors and connectors to ensure safe transmission without leaking air into the vacuum environment.

Conductors

The most common methods to connect power from a vacuum power source to the furnace’s feedthrough include air-cooled cables, water-cooled cables, and copper bus bar. Power efficiency can be improved when selecting the length, size, and area between conductors. This can be achieved by close coupling the power system to the electrical feedthroughs, reducing resistance and inductive reactance, and improving the power factor.

Machined Copper Bar
Source: RoMan Manufacturing, Inc.

Controlled Power Distribution Systems

The furnace market today generally relies on three primary types of control power distribution systems: VRT, SCR, and IGBT. Each of these technologies employs different methods to regulate the power input to the furnace, which in turn generates the required heat.

VRT (Variable Reactance Transformer)

  • The VRT controls AC voltage to the load, this is accomplished by a DC power controller that injects DC current into the reactor within the transformer.

SCR (Silicon Controlled Rectifier)

IGBT (Insulated-Gate Bipolar Transistor)

  • Balanced three-phase voltage is rectified through a bridge circuit to charge a capacitor in the DC bus. The IGBT network switches the DC bus at 1000Hz to control the AC output voltage to a Medium Frequency Direct Current (MFDC) power supply.
  • MFDC power supply transforms the AC voltage to a practical level and rectifies the secondary voltage (DC) to the heating circuit.
  • A line reactor on the incoming three-phase line mitigates harmonic content.

Control Systems

These systems manage the furnace’s operation, including driving the setpoint of the power system, temperature control, vacuum levels, and timing. They often consist of programmable logic controllers (PLCs), human-machine interfaces (HMIs), sensors, and other automation components.

Incoming Power

This is the origin of the furnace’s electrical energy, typically from a utility grid. It provides alternating current (AC), which is distributed and transformed within the furnace system to power all necessary components. In industrial settings, power companies usually charge for electricity based on several factors that reflect both the amount of electricity used and how it’s used. Some common charges/penalties are energy consumption (kWh), demand charges (kW), power factor penalties, and time-of-use (TOU) reactive power.

Conclusion

The careful arrangement of heating elements, electrical feedthroughs, conductors, and controlled power distribution systems allows for precise temperature control, ultimately impacting the quality of the processed material. Understanding the role of various control systems, such as VRT, SCR, IGBTs, and transformers is crucial for optimizing furnace performance and managing energy costs

About the Author:

Brian Turner
Sales Applications Engineer
RoMan Manufacturing, Inc.
Source: 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 information: Contact Brian at bturner@romanmfg.com.

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