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.
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.
Maintaining clear communication for high precision processing, critical with medical component heat treating, requires sophisticated operations. In today’s Technical Tuesday, Mike Grande, vice president of Sales at Wisconsin Oven Corporation, provides an overview of how the industrial internet of things (IIoT) advances heat treat performance capabilities and ensures accurate, repeatable results.
Today’s technology is evolving at an exponential rate. Over the last several years, digital technology has provided more and more connectivity between devices and processes. One of the most impactful is IoT technology. From smartphones to virtual assistants, touchscreen refrigerators to thermostats and interconnected home management systems, these products are quickly changing the way people interact and connect.
In addition to consumer products, the industrial world is also seeing increased reliance on this technology to improve throughput, decrease energy use, and increase equipment longevity by capturing and analyzing the data generated by their machines.
What Is IoT and IIoT Technology?
IoT (internet of things) refers to everyday items that have been equipped with sensors that transfer data over a network. Refrigerators, lights, thermostats, smart speakers, and entire homes are now available with IoT technology. Devices equipped with IoT options provide conveniences like remote monitoring, advanced programming, and smart learning, which make daily and household tasks easier. What seemed like science fiction just a few years ago has become reality.
This impressive technology does not only apply to the consumer world. The application of IoT to the manufacturing sector is even more impactful. Industrial internet of things (IIoT) is the term used to describe the application of connected IoT technology to industrial machinery. These systems collect and analyze data, learn from that data (“machine learning”), perform predictive maintenance, and then share that information with personnel, manufacturers, including manufacturers of the machines being monitored, and even other devices. This type of data collection and analysis gives valuable insight into the facilities, processes, and equipment to ensure that everything from energy usage in a facility to equipment performance for a process is optimized.
Figure 1. The IoT gateway collects the data from oven-mounted sensors and wirelessly transmits it to the cloud. Source: Wisconsin Oven Corporation
How Is IIoT Used in Industrial Ovens and Furnaces?
IIoT technology tracks the performance and health of the most critical components and conditions in the ovens and furnaces they are monitoring. The system utilizes an IoT gateway (Figure 1), which collects information from predictive maintenance sensors that gathers performance data and stores it over time. The gateway also wirelessly transmits the data to a cloud platform where it can be displayed in dashboards, designed for easy viewing and monitoring. Thresholds are set at warning or alarm conditions. When exceeded, the system alerts the user or the oven manufacturer that there is a problem. This type of system predicts component failures before they occur, allowing time to schedule maintenance and minimize unplanned downtime.
Figure 2: An example of a dashboard used on an oven IIoT system Source: Wisconsin Oven Corporation
The data is displayed in a dashboard format (Figure 2) which permits visual analysis of the information, and intuitive understanding of the process being performed in the oven. In the example of an oven used to process parts in an inert atmosphere, the x-axis represents the elapsed time, which can be expanded or collapsed by the user in order to provide a more (or less) detailed view of the process. The y-axis tracks variables such as temperature, pressure, oxygen level, nitrogen flow rate, and humidity level.
A few examples of the oven data gathered and analyzed by an IIoT system are as follows:
The output of the temperature controller is monitored. If, for example, the controller output is normally running at 30% for a specific oven (meaning the oven is using 30% of its full heat capacity), and for no apparent reason it increases to 60% output, this indicates either an exhaust damper is stuck open and causing the oven to exhaust too much of its heat, there is a heater failure, or a door is not closing fully, or something else.
Vibration sensors installed on recirculation blowers can monitor the health of the oven. Since blowers are rotating machines, they have a predictable vibration frequency and amplitude. As the blower bearings wear over time, these vibration parameters change. The IIoT system uses proprietary algorithms to determine acceptable vibration levels at different temperatures and RPMs. As the vibration values change over time, the system can predict when blower failure is likely, prior to it occurring. This allows replacement parts to be ordered before a “hair on fire” situation where the equipment suddenly stops working, interrupting production and workflow.
In order to monitor the burners on gas-fired ovens, the flame safety system is wired to the IIoT system. This allows remote evaluation of the flame sensor, purge timer, and other components that are critical to safe and proper burner operation. On older ovens, nuisance shutdowns can occur due to a dirty combustion blower, dirty flame rod, faulty airflow switch, or other reasons. An IIoT system allows the oven manufacturer to remotely diagnose this type of issue without ever sending a service technician to the job site, saving time and money.
An oven IIoT system is often used to measure the oven chamber pressure. Ovens can be intentionally operated at a neutral pressure, a slightly negative, or slightly positive pressure, for various process-related reasons. A pressure sensor measures this value and, via the IIoT gateway, delivers it to the dashboard in real time. If the chamber pressure strays outside of a predetermined range, this indicates a failure such as an improper damper setting or a malfunctioning exhaust blower.
The Benefits of IIoT Technology
Predictive maintenance is one of the most important benefits of IIoT. The ability to prevent potential equipment breakdowns and resulting process bottlenecks is invaluable. Not only does IIoT allow plant managers and operators to schedule maintenance ahead of time, it also reduces maintenance hours by knowing exactly what the issue is that needs to be serviced. This reduction in unplanned downtime increases productivity, which translates to higher profits.
The quantity of detailed, relevant data available (real time and retroactive) via the IIoT system exceeds the information a service technician can gather oven side, especially if the oven has stopped working. Using IIoT to remotely gain information to service the equipment, the problem can often be resolved the same day.
Perhaps the most impressive benefit of IIoT is remote diagnostics. Whether a furnace or oven is experiencing occasional unexplained shutdowns, or is completely out of commission, it typically takes days or weeks to schedule a service technician to inspect the equipment and diagnose the problem. However, if the oven is equipped with IIoT, a call can be made to the oven manufacturer who can remotely log into the system dashboard. They will be able to view and analyze the data gathered by all the sensors going back over time, without sending a service technician to the job site. Also, the quantity of detailed, relevant data available (real time and retroactive) via the IIoT system exceeds the information a service technician can gather oven-side, especially if the oven has stopped working. Using IIoT to remotely gain information to service the equipment, the problem can often be resolved the same day. Further, the IIoT system gathers and records the data going back in time for months, which is invaluable when trying to diagnose a chronic or intermittent failure.
Another use of IIoT technology is energy management. Through IIoT monitoring, facilities and equipment can be set to optimize energy efficiency. By ensuring the oven uses only the amount of heat energy necessary, and no more, its energy consumption is minimized. The system can reveal, for example, that a second shift oven operator opens the oven doors for five minutes to unload the parts and then load the next batch, while the first shift operator takes ten minutes to do the same process, wasting a great deal of energy as heated air spills out of the oven for an extra five minutes with every batch.
Data Security
IIoT devices use encryption to protect against unauthorized access to the oven operational data. Data transmitted between IIoT devices and the cloud is encrypted using protocols like Transport Layer Security (TLS). This provides confidence that only approved parties can access the information, safeguarding it from those with malicious intent. This ensures that even if data is intercepted, it will appear as jumbled information that cannot be read without the decryption key.
Because the data collected relates to the oven or furnace being monitored, and is not descriptive of the parts being processed, it would be of limited use to anyone who gained unauthorized access. If a malicious actor discovered, for example, the vibration levels, temperature controller output, or the status of the burner system while the oven is processing a load, it would be of limited proprietary value and would not directly reveal information about the parts being processed since no information about the load is included in the data.
In considering the security risk of an IIoT system collecting and transmitting data to the cloud, it must be compared to the alternative, which is bringing a service technician to the job site to perform the required maintenance or troubleshooting. When a service technician is invited on site, they have the opportunity to view the parts being processed, which temperature profiles apply to which parts, material handling methods, ancillary processes performed before or after heating, and even unrelated proprietary processes performed in the facility. This level of intrusion is much greater than simply sending the oven IIoT data to the cloud and avoiding the service technician entirely.
The Future of IIoT
Since the introduction of IIoT to the industrial oven market, it has gained acceptance by a wide range of manufacturers, and it is expected to continue to grow. Artificial intelligence (AI) is becoming a part of IIoT, as it can optimize the algorithms used in predictive maintenance. Also, IIoT can incorporate AI’s cognitive capabilities to better be able to learn at what thresholds of vibration, pressure, etc., to send alert notifications.
To Summarize
Consider purchasing an IIoT system with your next industrial oven. The successful implementation and use of IIoT provides a competitive advantage to the owner of the equipment. In today’s world of “doing more with less,” IIoT can increase productivity, reduce maintenance costs and unplanned downtime, and decrease energy use, all at minimal cost, and with no additional personnel required.
About the Author:
Mike Grande Vice President of Sales Wisconsin Oven Corporation
Mike Grande has a 30+ year background in the heat processing industry, including ovens, furnaces, and infrared equipment. He has a BS in Mechanical Engineering from University of Wisconsin-Milwaukee and received his certification as an Energy Manager (CEM) from the Association of Energy Engineers in 2009. Mike is the vice president of Sales at Wisconsin Oven Corporation.
Did you know that November 6 was National Stress Awareness Day? It seems an appropriate designation to cover the days and weeks that follow Election Day as well as those leading up to the holidays. For many who are well aware of the stress of the events of the season, Heat Treat Todaywants to help with a different kind of stress relief.
Today we’re highlighting technical content that we’ve published over the last couple of years about stress relieving processes. Read an overview about stress relieving stainless steel components, listen to a Lunch & Learn dialogue about this underrated process, and explore a mechanical testing method for measuring material strength.
It is critical to provide things like stainless steel appliances and the Tesla truck with proper maintenance to keep the corrosion resistance and appearance lasting as long as possible.
Stainless steel shines in our kitchens and is becoming more popular in auto showrooms, mostly because of the promise that it is corrosion resistant. What most people don’t realize is that stainless steel will rust in a lot of circumstances. Sarah Jordan explores how stainless steel can be compromised by improper heat treatment and the steps heat treaters can take to prevent corrosion:
“Improper heat treating can also contribute to stress corrosion cracking. When material is quenched, it can cause residual stresses that, if not relieved, can become an issue.
“Corrosion in stainless steel can often be traced to improper heat treatment. When stainless steel is heated between 842–1562°F (450–850°C), chromium carbides can form at the grain boundaries, depleting the surrounding areas of chromium and making them susceptible to corrosion.”
Click on the image to hear this episode of Heat Treat Radio and read the transcript.
In this Lunch & Learnepisode from Heat Treat Radio, Dave Mouilleseaux discusses the three most underrated heat treat processes, including stress relieving manufactured components. If a comprehensive analysis of a heat treat operation needs to be performed on a manufactured component, such as a gear or a shaft, it is necessary to take into consideration any prior existing stresses in the part and what effect that has on the part.
The detrimental effects of not having stress relieved Source: pixabay
“Many times during the course of my career, I’ve had a customer come to me and say, ‘The part I gave you was correct, and you’ve given it back to me and then fill-in-the-blank. It’s warped, it’s changed size, it’s shrunk, all of those things.’
“What have you done in your heat treating process?” asked Mouilleseaux. “You have to back up all the way to the beginning of how this part was manufactured and deal with all of those component steps in order to answer that question properly. Stress relieving is one of the answers. It’s not the answer. It’s not the only answer, but it is one of them that has to be considered.”
To listen to this episode of Lunch & Learn, click here.
Photograph of the Hardox steel samples, with and without the WC insert attached, showing high levels of oxidation following from the brazing process. Source: Plastometrex
Mechanical testing is a standard production step in heat treating operations, but conventional methods of testing don’t always yield stress values consistent with the testing calculations.
Indentation plastometry allows users to obtain material strength characteristics in a way that is faster, cheaper, and simpler than conventional mechanical testing procedures. James Dean explores this novel mechanical testing method developed to infuse efficiency and accuracy into the process.
“The testing process is fully automated and involves three simple steps. The first is the creation of an indent using the indentation plastometer which is a custom-built, macromechanical test machine. The second is measurement of the residual profile shape using an integrated stylus profilometer.
“The third is the analysis of the profile shape in a proprietary software package called SEMPID, which converts the indentation test data into stress-strain curves that are comparable to those that would be measured using conventional mechanical testing methods. The entire procedure takes just a few minutes, and the surface preparation requirements are minimal.”
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 inHeat Treat Today’sNovember 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 DeiwertFigure 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:
Understand how your leak detector works to the point that you can confirm it is working properly.
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.
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.
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.
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.
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.
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.
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.
Calibrate your leak detector when you start it up and check calibration when you are finished to confirm it is working properly.
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 Deiwerthas 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.
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 BoardFigure 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.
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. UnderstandingHow 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.
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.”
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.
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 inHeat Treat Today’sMay 2024 Sustainabilityprint 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 16
Increasing Available Heat to Lower CO2 Emissions
June 20
Understanding Carbon Credits & Net Zero
July 18
U.S. Codes & Standards
August 15
Renewable 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.
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.
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.
The SCR controls the AC output voltage and can be paired with a transformer to step the voltage up or down and close couple to the furnace feedthroughs.
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.
