INDUCTION HEATING TECHNICAL CONTENT

Induction Hardened Case Depth Measurement Using Ultrasonic Backscattering

/ INDUCTION HEATING TECHNICAL CONTENT

By Jose Miguel Equihua Toral, Head of the New Projects and Development, BOINSA Mexico and Manager, InTech NDT, USA.

Nondestructive testing (NDT) techniques have been used exclusively to detect defects in structures and components after they have been manufactured. To protect public safety and security, it is imperative to test parts efficiently and ensure their quality. Nondestructive evaluation, like ultrasonic backscattering, serves an important role in this area. 

This informative piece was first released in Heat Treat Today’s April 2025 Annual Induction Heating & Melting print edition.

Introduction

Figure 1a. Induction hardening (top)
Figure 1b. UT backscattering testing (bottom)

Induction hardening is a critical process in manufacturing automotive, agricultural, and aeronautical components, such as crankshafts, camshafts, constant velocity joints, and axle shafts (Figure 1a). The procedure for the evaluation of metallurgical characteristics is carried out in the laboratory and is destructive testing (Bernard, “Methods of Measuring Case Depth in Steels”). This means the component will be unusable. Additionally, this procedure is time-consuming, expensive, and cannot be integrated into the production line. Over time, the industry has sought faster and more efficient methods to evaluate metallurgical characteristics, such as eddy current testing, magnetic methods, and ultrasound. Having the capability of monitoring material properties after each key process can help minimize the cost of processing out-of-specification material. A combination of nondestructive testing methods can help to guarantee the quality of induction heat treatment operations (ASM Handbook, vol 4c).  

Ultrasonic methods, for example, can be used to determine microstructural differences in metals. For this, contact testing with pulse-echo technique is used. For inductive-hardened parts, the ultrasonic backscattering method works because the hardened layer (martensite) is almost transparent to ultrasonic waves (in range of 20 MHz), while bulk material (ferrite-pearlite) scatters ultrasonic waves very strongly.  

In this article, we will address the use of industrial ultrasound applying the backscattering technique, which offers a direct determination of the depth. This method is simple and does not require prior calibration to evaluate the components (Figure 1b). 

The Ultrasonic Backscattering Technique  

Figure 2a. Ultrasonic backscattering technique (top)
Figure 2b. Time-of-flight measurement (bottom)

Iron crystals exhibit notable acoustic anisotropy, meaning the acoustic velocity (c) varies depending on the direction of travel within the crystal. Grain boundaries represent transitions between crystal structures with varying orientations. The resulting variation in impedance causes the ultrasonic pulse to scatter at the grain boundaries. The ultrasonic technique for measuring hardness depths (SHD) utilizes this grain boundary scattering effect. This technique is known as the ultrasonic backscattering method (Kruger et al., “Broadband Ultrasonic Backscattering”).  

The ultrasonic backscattering method for hardness depth testing relies on finding the ultrasound frequency that does not scatter at the fine-grained hardened microstructure of the outer layer but at the coarse-grained core material (Figure 2a). The different scattering properties from the varied grain sizes of the hardened surface layer and the core material are seen in the backscattering measurement. The connection between scattering and the material’s grain size is utilized to produce a detectable backscattering echo when the ultrasound penetrates the core material.  

The depth (SHDUS) of the interface can be determined using the time (t) it takes for the sound pulse to reach the scattering interface, the angle of the shear wave (βT), and the velocity (c) of the shear wave in steel. Therefore, the following equation is relevant for a flat shape:  

SHDUS=1/2∙c∙t∙cos∙βT  

Based on this equation, the acoustically measured surface hardness depth (SHDUS) is always found before the sound exit point of the probe wedge. To guarantee an accurate measurement of this location during destructive testing, this distance (A) must be calculated. The next equation is used for a plane geometry:  

A=1/2∙c∙t∙sin∙βT  

The backscattered ultrasonic amplitude depends on the actual gradient of the microstructure. In the transition zone, grain boundaries, grain size, and second phases change the acoustic impedance value discontinuously, depending on the ultrasonic frequency. Different backscattering signals in the hardened and bulk material occur (Yanming Guo, “Effects of material”). Th ese amplitude characteristics can be used to evaluate the case depth by using simple time-of-flight measurements (Figure 2b). Contact testing is generally done by using portable equipment, using a contact wedge where the transducer is mounted to be inclined at a certain angle, and shear waves are emitted into the component. Ultrasonic backscatter takes place at the surface of the component due to surface roughness and results in the return of the energy to the transducer (first echo). Ultrasonic energy enters the hardened surface layer made of fine martensitic structure, and thus, no scatter of ultrasonic waves takes place in this region. However, when the shear waves reach the transition zone where martensitic structure is gradually converted into ferrite-pearlite structure, which has a larger grain size, once again energy is scattered at the grain boundaries, and the transition zone backscatter forms the second echo. The difference in time-of-flight of these two echoes is proportional to the case depth of the component. 

Technical Requirements  

Technical requirements for testing hardness depth using the ultrasonic backscattering method will produce optimal results in the following conditions:  

  • The test parts should be induction-hardened.  
  • The test parts must be forged, not cast.  
  • There is minimal or no microstructure present between the hardened martensitic microstructure and the core material. 
  • The grain size of the core material is significantly larger than the grain size of the hardened microstructure, leading to considerable backscattering of shear waves at a frequency of 20 MHz. 
  • The minimum hardness depth that can be measured is 1.2 mm. Smaller hardness depths need special considerations, such as adjustments to the wedge design.  

Practical Correlation Between NDT and DT

Destructive hardness depth testing is a method to determine the thickness of the case depth of hardened parts. In the process, the parts are destroyed, or their surface is altered rendering each tested part unusable. Hardness depth profiles are usually determined by using the Vickers test to measure the hardness of a reference sample at different points in a line from the surface to the core.  

If you compare the acoustically measured surface hardness depth SHDUS with the surface hardness depth measured with destructive methods SHDDT, you will see a basic difference: Independent of the hardness limit and the minimum hardness, the acoustic testing always determines the depth of the core material that has not been affected by the hardening process. As a consequence, this value tends to be slightly higher than the surface hardness depth measured with destructive methods SHDDT. This difference can be compensated by means of a correction term ΔT (“Off set”):  

SHDUS = SHDDT – ΔT  

In the case of hardness curves with rapidly decreasing hardness values just above the interface, the transit time is measured at 20% of the height of the backscattering signal’s amplitude, and the results of the acoustic and the destructive hardness depth tests will match. The reason for this is the slightly shorter sound path in the marginal ray of the divergent sound field, which induces the backscattering echo.  

If cases occur regularly in which the hardness curve deviates significantly from the characteristics, reference tests must be conducted to determine the correction factor ΔT. Reasons for this could be material and/or process related. The calculated correction factor can then be integrated in the respective test task as a test parameter.  

Technical Description and Measurement Highlights  

The manual device includes a four-channel ultrasonic board managed by a software package for program settings, signal processing, reporting, and overall quality assurance requirements. The parts are put together in an industrial notebook meant for tough industrial settings. The probe systems allow testing of components with complex shapes. The wedge of the probe system is adjusted to fit the geometry of the specific test location. Testing can be done before or after machining.  

The primary cause of measurement error is the evaluation of surface position; the shape of the surface signal relies on proper coupling and the operator’s skill. Another source of error is the placement of the marker that indicates the time-of-flight when the pulse hits the interface. The sharper the signal rises, the less the error. Therefore, a shear wave angle as low as reasonable is employed, and scanning in the direction of decreasing SHD is advised. Achievable accuracy of better than ±0.1 mm is possible for standard parts with high-quality surfaces. Nevertheless, the operator must monitor the “good” shape of the A-scan during data collection. Accuracy based on microindentation hardness profiles compared to the backscatter method is slightly lower, estimated at ±0.2 mm on average, based on the material microstructure (Bogaerts et al., “Surface Hardness Depth Measurement”). We are able to test different geometries like crankshafts (Figure 3), camshaft s (Figure 4), tulips (Figure 5), and barshafts (Figure 6), to mention some components. 

Figure 3. Crankshaft
Figure 4. Camshaft
Figure 5. Tulip
Figure 6. Barshaft

Feasibility Testing

Situation: During induction hardening, an unanticipated variation on the case depth was detected on the shaft of an axle bar (Figure 7). We were requested to examine the case depth in this important area using a P3123 Hardness Depth Tester to find out if the case depth met specifications.  

Figure 7. Induction case-depth variation
Figure 8. Axle bar inspection

Results: During the testing, we noted the case depth was insufficient compared to the minimum required case depth of 5.5 mm. This meant all induction hardened parts made before the discovery had to be paused while a complete check of the case depth was performed. All axle bars hardened after the discovery were analyzed (Figure 8), starting with the most recently hardened parts. Case depth was also evaluated by making a microindentation hardness profile in the hardened area, showing a case depth consistent between ultrasound readings with the P3123 and the destructive testing measurements. In Figure 9, we can observe the measurement of the out of specification case depth, and in Figure 10, we have the measurement within specification case depth. 

Hardness depth testers are used for optimizing production parameters, reducing downtimes after inductor changes, fast production control, and quality management. The techniques discussed in this article offer the technical advantages to ensure quality assurance for both steel and induction hardened components. Feasibility testing is required, which can be performed with prompt review of the ultrasound behavior in components. 

Figure 10. Case depth within specification
Figure 9. Case depth out of specification

References  

ASM International. ASM Handbook Volume 4C: Induction Heating and Heat Treatment. 2014.  

Bernard, William J. “Methods of Measuring Case Depth in Steels.” Steel Heat Treating Fundamentals and Processes (2013): 405-416. https://doi.org/10.31399/asm.hb.v04a.a0005795. 

Bogaerts, Mike, Michael Kroening, Paul Kroening, and Tobias Mueller. “Surface Hardness Depth Measurement Using Ultrasound Backscattering.” AM&P Technical Articles 177, no. 8 (2019): 58-62. https://doi.org/10.31399/asm.amp.2019-08.p058. 

Guo, Yanming. “Eff ects of material microstructure and surface geometry on ultrasonic scattering and fl aw detection.” Dissertation, Iowa State University, 2003. 

Kruger, S.E., J.M.A. Rebello, and J. Charlier. “Broadband Ultrasonic Backscattering Applied to Nondestructive Characterization of Materials.” IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control 51, no. 7 (2004): 832-838. https://doi.org/10.1109/tu c.2004.1320742.

About The Author:

Jose Miguel Equihua Toral
Head of New Projects and Development
BOINSA Mexico
Manager,
InTech NDT, USA

Jose Miguel Equihua Toral graduated as a mining engineer from Guanajuato University and obtained his Master’s Degree in Engineering from the National Technology Institute of Mexico. He currently works as head of the new projects and development department of BOINSA de Mexico, involved in technological and operational advances in the design, manufacture, and repair of induction coils, as well as advances in the application of non-destructive testing methods for the quality assurance of components for the automotive, agricultural, and energy industries. This experience has led to the formation of InTech NDT, to serve the U.S. market.  

For more information: Contact Jose Miguel Equihua Toral at miguel.equihua@intech-ndt.com. 

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How 3D Printing Coils Exceeded R&D Expectations

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In this Technical Tuesday installment, Josh Tucker, Manager of Induction Heating, Tucker Induction Systems, Inc., relates new research conducted on the strength of coils which have been produced through 3D printing.

This informative piece was first released in Heat Treat Today’s April 2025 Induction Heating & Melting print edition.

To read the article in Spanish, click here.

Research on 3D printing induction coils finds that coils are stronger and have a longer life when compared to traditionally manufactured coils. Read about how additive manufacturing removes steps like brazing the joints and provides new design capabilities. 

Tucker Induction Systems began exploring the possibility of using 3D printing technology to manufacture coils and found that, in many cases, 3D printed coils were stronger and longer lasting than traditionally manufactured counterparts. 

The quest to develop 3D printed coils began in 2020. When COVID-19 hit, Macomb County, Michigan, started an initiative called Project DIAMOnD, which stands for Distributed, Independent, Agile Manufacturing on Demand. It provided small-to-medium-sized area manufacturers with Markforged Fused Deposition Modeling-style 3D printers as both a way to quickly manufacture much needed personal protective equipment for the pandemic and to help small-to-mid-sized manufacturers overcome the supply chain issues that plagued industry during the crisis. 

We were eager to gain hands-on additive manufacturing experience through the DIAMOnD initiative and, in doing so, found that it sparked our curiosity about the possibility of 3D printing our coils and new ways to design them that go beyond the capabilities of traditional machining. 

In 2021, we began a two-year research and development process of printing coils and discovered that by 3D printing induction coils we were able to drastically increase the strength of the coils and potentially lengthen the useful life of the coil. The experience has opened new realms in designing our coils, as well as giving us the ability to design coils using methods that go beyond the capabilities of traditional machining. 

It is common industry knowledge that the weakest parts of a coil are the braze joints, but through the R&D process, we have learned that by 3D printing the coils, it is possible to eliminate most, if not all, braze joints in the head of a coil. This increases the strength and, potentially, the life of a coil. After years of testing and evolving, the end results were better than we expected, proving that the coils can be printed and will last in the field. 

Figure 1. 3D printed single-shot hardening induction coil heads

However, there were some challenges in adapting to using 3D printing technology. For example, the type of copper printing we required was not being done in the United States, which was an obstacle in trying to form a process that resulted in a successfully printed coil. But one of the biggest challenges after we locked down the process and material was in designing the internal cooling passages for the coils. The passages needed to be designed in a way that was self-supporting and non-restricting. We had to produce the same flow rate as traditionally made coils and ensure we were driving the cooling into the right areas. Figuring that out took many failed attempts — learning opportunities — before achieving success. 

Once that goal was achieved, we installed a metal 3D printer at Tucker Induction in January 2024 and have been successfully printing all different types of coils. Some examples include two turn ID, spindle, single-shot, and scanning coils. 

The Benefits of Using 3D Printed Coils 

While traditional coils (such as our interchangeable, quick-change coil for two-turn induction systems and single-shot designs with accurate clamping pressure) have changed the industry, the additional capability of 3D printing allows us to print dimensionally accurate, durable parts that are capable of performing in the field and that can go beyond the barriers of traditional machining. 

Figure 2. 3D printed single-shot induction coil with keepers

3D printed coils bring several worthwhile benefits to the table including time savings, longevity, and faster coil repair. Time savings is one of the biggest advantages. Because the 3D printer can run “lights out,” the processing time from the printer to the client is far shorter when compared to traditionally fabricated coils. We refer to the processing time as the additional time needed to complete the coil assembly after printing. In some situations, it is possible to print a completed coil assembly with the coil immediately ready to be sent to the client. Other times, additional brazing or supplemental details may be required to complete the assembly. 

Since all coils are different, the processing time varies from coil to coil. However, by printing as much of the assembly as we can, we are able to limit the amount of additional work needed to complete the job. 

Strength and potential longevity of 3D printed coils are additional advantages. The weakest parts of the coil are the braze joints, but the process we use to print the coils drastically reduces the amount of braze joints, thus making the workforce of the coil a solid construction. This results in a product that will be stronger in the induction environment and has the potential to outlast its traditionally manufactured counterpart. 

When it comes to the lifetime of the 3D printed coils, our baseline is that the printed coils need to last at least as long as traditionally manufactured coils. However, in our research, we have seen, on average, that our 3D printed coils can last two to three times longer than traditionally manufactured coils. While the longevity of each coil is case dependent, as there are many factors that go into the lifespan of a coil, one of our original test coils is still running in the field with over one million heat cycles. 

While continuing to improve processes and designs, we are also pushing to decrease the time for repairs. Getting our clients’ coils repaired and returned in an effort to limit their downtime has always been something we strive for with our traditional coils, but we have found that 3D printed coils are easier to repair. Since multiple braze joints are not an issue in printed coils, it reduces the chance of causing additional problems as you work on the original repair. If the repair consists of replacing the head of the coil, we are able to recall the original print and run it again, as opposed to having to re-machine and re-assemble and braze the entire coil, significantly reducing the repair time of many 3D printed coils. 

Limitations of 3D Printing Coils 

Despite the advantages of 3D printing induction coils and the fact that the capability to print coils gets you into the mindset that every coil needs to be printed, there are some instances when it is still more effective to use traditional manufacturing. 

Figure 3. 3D printed sample structures

For example, coils that are larger than the machine is capable of printing — our print bed size is roughly 12 x 12 x 13 inches — can be a limiting factor. Other times, the coil may be manufactured faster using traditional methods. The printer does have limitations, and it is not the best option for certain coils. For example, coils that are less intricate and made from tubing is one type that would be a better candidate for traditional manufacturing; these coils simply require wrapping copper tubing around a mandrel. 

The Future of 3D Printed Coils 

We are continuing to research and fine tune the processes of 3D printing our coils and strive to provide our clients with the best possible product. In order to do that, we must stay vigilant and be willing to continuously learn and improve our designs and processes.  

As we learn more and perfect our 3D printing coil processes, I believe 3D printed coils will play a vital role in the future of the industry. We have proven that 3D printing coils is not just possible, but that in some cases 3D printed coils can outperform their traditionally manufactured counterparts. 

About The Author:

Josh Tucker
Manager of Induction Heating
Tucker Induction Systems, Inc.

Josh Tucker graduated with a bachelor’s degree from Grand Valley State University and was then hired as the head of Purchasing at Tucker Induction Systems. Since starting eight years ago, Josh’s role and capabilities have expanded to machining, wire EDM, 3D printing, and laser engraving. He also organizes the day-today operations and flow of the shop floor. Josh was recognized in Heat Treat Today’s 40 Under 40 Class of 2024.


For more information: Contact Josh Tucker at JTucker@tuckerinductionsystems.com

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Settling in for the Season with Sustainability Suggestions

/ BURNERS & COMBUSTION SYSTEMS TECHNICAL CONTENT, FEATURED NEWS, INDUCTION HEATING TECHNICAL CONTENT, MANUFACTURING HEAT TREAT, VACUUM FURNACES TECHNICAL CONTENT / Leave a Comment

As we get further into the heart of fall, it’s time to turn up the heat (treat)! – but how can this be done in an optimized and sustainable way?

Today’s Technical Tuesday original content round-up features tips and tricks from our summer print editions on how to optimize and sustain your heat treat operations, even during the chilly months. So, bundle up, grab a hot drink, and review these insightful pieces!

Sustainability Insights Corner 

In May, Heat Treat Today began publishing "Sustainability Insights" from the IHEA editorial team. Here's a brief overview of the recent insights all in one place:

May: New Sustainability & Decarbonization Initiatives for Heat Treat. Learn from industry-leader Brian Kelly about the stages of getting started with suitability and planning for the future of the industry.

June: NEW Sustainability and Carbonization Webinar Series. Although this year's IHEA Webinar series may have come and gone, it's not too late to establish a foundational understanding of carbon and sustainability here!

August: Reducing the Carbon Footprint of Your Heat Treating Operations. Brian Kelly of Rockford Combustion is back with yet another suitability insight, here exploring ways to assess your heat treating operation's carbon footprint, tune your combustion systems, explore renewable fuels, and much more.

September: Process Heating and the Energy-Carbon Connection. Explore the issue of greenhouse gases and how recent conversations are affecting the heat treating industry with Michael Stowe of Advanced Energy.

In Case You Missed the May Issue: Induction and Sustainability Tips  

Looking for sustainability tips for your heat treating operation, but lacking in time? Heat Treat Today's May Issue has you covered with a quick read: "13 Induction and Sustainability Tips." We'll highlight a few below which made it into a recent Technical Tuesday feature:

Induction and Sustainability Tips Part 1: Cleaning and Maintenance

Induction and Sustainability Tips Part 2: Efficient Power

Induction and Sustainability Tips Part 3: Combustion

Induction and Sustainability Tips Part 4: Vacuum Furnace and Heat Treat Energy Savings

Sustainable Energy for Furnaces? What does the Future Hold? 

What will the future run on? With growing discontent around current energy sources like natural gas and other fossil fuels, power sources for furnace equipment are due for a makeover.

Explore the question of sustainable energy for furnaces in the future with industry experts John Clarke of Helios Electric, Philippe Kerbois of Glass, various authors from Watlow, and Stuart Hakes of F.I.C. (UK) Limited.

Read the article by Heat Treat Today's Editorial Team: Energizing the Future of Furnaces - 4 Perspectives.

Saving Power and Dollars in Vacuum Processing 

How much electrical power is being used in the typical heat treatment plant? And how can power (and money) be saved in these operations? If these questions peak your interest, explore further with Roger A. Jones and William Jones of Solar Atmospheres.

Learn about savings in electricity and money in areas of electric motors, high vacuum diffusion pumps, gas blowers, building lighting, AC/heating, and more in this article.

Read the article, "Conserve Electric Power and Save Dollars in Vacuum Processing" here!

Find heat treating products and services when you search on Heat Treat Buyers Guide.com

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Induction and Sustainability Tips Part 4: Vacuum Furnace and Heat Treat Energy Savings

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Discover expert tips, tricks, and resources for sustainable heat treating methods Heat Treat Today’s recent series. Part 4, today’s tips, covers induction heating, quench, and insulation tips. We’ve added resources towards the end of today’s post for further enrichment.

This Technical Tuesday article is compiled from tips in Heat Treat Today’s May Focus on Sustainable Heat Treat Technologies print edition. If you have any tips of your own about induction and sustainability, our editors would be interested in sharing them online at www.heattreattoday.com. Email Bethany Leone at bethany@heattreattoday.com with your own ideas!

1. Tips for Induction Hardening

 

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What are the benefits of induction hardening? Here are a few:

  • Saves space: Induction hardening requires minimum space required in comparison with furnaces
  • Saves energy: Induction heating equipment does not need to be kept running when not in use
  • Clean: Induction heating equipment requires no combustion gases
  • Energy-efficient: Only a small proportion of the material needs to be heated
  • Minimize deformation: Induction hardening requires no applied force
  • Save maintenance costs: Inductor coils have a long life, reducing the need for maintenance

Source: Humberto Torres Sánchez, Chief Metallurgist, ZF Group

#induction hardening #deformation #zerocombustiongas

2. Insulation = Key for Energy Savings in Vacuum Furnaces

Look for insulation quality in your next vacuum furnace.
Source: NITREX

Improvements in insulation materials are also contributing to greater energy efficiency of vacuum furnaces. Most furnaces on the market today have a 1” (25.4 mm) graphite board with bonded Grafoil and two layers of graphite felt. However, the insulation performance of a 1” (25.4 mm) graphite board is about 25% less efficient than a 1” (25.4 mm) graphite felt. For processes that require high operating temperatures, typically over 2,200°F (1,204°C), an all graphite felt that is 2” or 2.5” thick (50.8 mm or 63.5 mm) minimizes heat loss inside the hot zone. Efficiency gains of up to 25% are possible over the standard 1” (25.4 mm) board and 1” (25.4 mm) graphite felt insulation and an even greater gains at higher operating temperatures. To safeguard the graphite felt from mechanical harm and localized compression, these thicker all-graphite felt insulation configurations are usually covered with a carbon fiber composite (CFC) sheet about 0.050” (1.27 mm) thick.

Source: NITREX

#insulation #energysavings #graphite

3. Thinner Steel, Lighter Car

Fuel efficiency (and the stringent requirement for passenger safety) has raised the bar for the automotive industry to procure steel with high strength, hardness, and ability to fabricate. Reduction of weight requires lighter cars with thinner body material which can absorb impact. These dual contradictory properties of high hardness material which can be easily shaped can normally be achieved either by heat treat or through addition of alloys. These two processes are described below.

Normal heat treatment to produce small grains in the material will increase the hardness in steel but also create a propensity to fracture. Thus, a process known as quench and partition — where carbon diffusion from martensite to retained austenite to stabilize the latter — has been introduced. Further verification and prediction of the phases has been conducted using thermodynamics modeling for phase characteristics by Behera & Olsen at Northwestern University, Materials Science and Engineering.

The process starts with full automatization (or in some cases intercritical annealing) followed by fast quench to a defined quench temperature (QT) between the martensite start, Ms, and martensite finish, Mf, temperature. The steel is then reheated to the partition temperature (PT) and held there for a certain partition time followed by a quenching step again to room temperature, as shown in the image.

Quench and partition process
Source: Speer et al. The Minerals, Metals, & Materials Society 2003

The quenching step establishes the largely martensite matrix while the partition step helps stabilize the retained austenite by carbon partitioning. During the holding step, carbon diffuses from martensite to retained austenite and thus improves its stability against subsequent cooling or mechanical deformation. The final microstructure consists predominantly of tempered martensite and stabilized retained austenite with possibly a small amount of bainite formation and carbide precipitation during the partition step and fresh martensite formation during final quenching.

The other process to achieve high hardness and high ductility is by alloy addition in carbon steel. Over, 2,000 different types of steel exist. A new type of steel that is extremely strong, but simultaneously ductile is used in the automotive industry. Small quantities of elements like vanadium or chrome in steel promotes ductility. They are not brittle; however, up until now they have not been strong enough to enable the construction of car bodies with thinner sheets.

In the crystals of steels, the atoms are more or less regularly arranged. Steels become particularly ductile though if they can switch from one structure to another. This is because this process allows energy absorption, which can then no longer initiate any damage in the material. In a car body or other steel components, tiny areas then alternate with the two different atom arrangements.

Ductile steels have two coexisting crystal structures. The search produced an alloy made from 50% iron, 30% manganese and 10% respectively of cobalt and chrome (Max Planck Institutes).

Source: Madhu Chatterjee, President, AAT Metallurgical Services LLC

#quenchandpartition #quenchtemp

4. Tips for Selecting Induction Heating Equipment

“The following factors typically influence equipment design:

  • Material
  • Prior microstructure
  • Part geometry
  • Austenitizing temperature
  • Production rate
  • Power requirements, kW (typically selected by vendor based on information provided)
  • Frequency selection, kHz (typically selected by vendor based on information provided)
  • Pattern/profile (i.e., shape of heating area)
  • Coil design (typically selected by vendor based on information provided)
  • Process-development requirements
  • Application-specific criteria (e.g., water vs. polymer quenching)
  • Method of loading and unloading the workpiece (e.g., manual or robotic)
  • Stock removal after heat treatment
  • Type of tempering (i.e., furnace/oven vs. induction)”

Source: Dan Herring, The Heat Treat Doctor®, Atmosphere Heat Treatment, vol. 1, 2014, pp. 656.

#inductionequipment #inductiondesign

5. Additional Resources on Induction Heating, Quench, and Insulation

Read more about the processes when you click on these articles:

Find heat treating products and services when you search on Heat Treat Buyers Guide.com

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Complex Geometries – A Simple Heat Treat Reality

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What makes the geometry of a part “complex”? With the increasing use of AM and 3D printing for parts along with typically complex parts, heat treaters in many industries must acquire the equipment and technical know-how for precise applications.

This Technical Tuesday article is compiled from Heat Treat Today articles and industry news releases. Email Bethany Leone at bethany@heattreattoday.com or click the Reader Feedback button below to chime in on the topic.

What Are Complex Geometries?

 

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Complex geometries in industrial parts are often defined by their intricate patterns and structures, which entail specialized heat treat processing. As Inductoheat describes in a case study with Stellantis, “Many times, complex geometries of components are linked to intricate hardness patterns and specific requirements for magnitude and distribution of residual stresses.”

Heat Treat Equipment for Processing Parts with Complex Geometries

Be it for highly customized medical implants or for engine components in the burgeoning electric vehicle industry, complex geometries need to heat treated carefully. Fasteners in the medical device industry can be quite intricate and susceptible to creep or other dimensional changes; one method heat treating these parts — particularly titanium alloy parts — would be in a vacuum furnace. In vacuum and in hot isostatic presses, the environment allows for complex geometries that are 3D printed to be made into a unified whole piece. “Heat conduction can be carefully monitored [in induction heating coils] to confirm that an overheat condition does not occur at the target temper areas,” making induction a key candidate for heat treating your parts with complex geometries (“Tempering: 4 Perspectives — Which makes sense for you?“). To accommodate the complexities of certain parts, designing an induction coil for the desired case hardening may entail simulation to “[predict] coil heating, which altogether results in a longer coil lifetime,” (“Simulation Software and 3D Printers Improve Copper Coils”). For more on induction coils, check out this article by Dr. Valery Rudnev.

Suffice it to say, there is a great diversity of heat treatment options to explore when it comes to identifying the appropriate equipment for your application.

What Processes Are Used in Heat Treating Complex Geometries?

Perhaps you have all of your equipment needs necessary for heat treating your parts with complex geometries. Are you completing your heat treat processing in the most technically sound manner? Check out the following excerpts that speak to processing complex geometries.

“[Forging] at elevated temperatures enables reaching high strains and forming complex geometries in a single stroke. Additionally, thermal and mechanical influence during the forging can lead to improving local mechanical properties and the quality of the resulting joining zone.” (“Thermomechanical Processing for Creating Bi-Metal Bearing Bushings“)

“In some cases, such attempts result in a component’s geometries that might be prone to cracking during heat treating or might be associated with excessive distortion . . . .  The subject of induction hardening of complex geometry parts (including but not limited to gears, gear-like and shaft-like parts, raceways, camshafts, and other critical components) is also thoroughly discussed, describing inventions and innovations that have occurred in the last three to five years.” (“Heat Treat Training Benefits Stellantis“)

“LPC [low pressure carburizing] with gas quenching can be an attractive option for distortion prone complex geometries as the cooling rates are slower than oil quenching; however, given the slower cooling rate, it becomes very important to choose a higher alloyed steel that will achieve the desired hardness.” (“Elevate Your Knowledge: 5 Need-to-Know Case Hardening Processes“)

Complex Geometries In the News

See how your peers are solving complex geometries needs in these real-life partnerships with industry suppliers. From additive manufacturing (AM) and precision manufacturing parts to heat treat technology, maybe your company is next to leverage manufacturing equipment to “wow” the industry.

Find heat treating products and services when you search on Heat Treat Buyers Guide.com

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Induction and Sustainability Tips Part 2: Efficient Power

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Discover expert tips, tricks, and resources for sustainable heat treating methods Heat Treat Today’s recent series.  And, if you’re looking for tips on combustion, controls systems, or induction in general, you’ll find that too! Part 2, today’s tips, digs into energy and electricity. We’ve added another resource towards the end of today’s post to further enrich your knowledge of induction heating.

This Technical Tuesday article is compiled from tips in Heat Treat Today’s May Focus on Sustainable Heat Treat Technologies print edition. If you have any tips of your own about induction and sustainability, our editors would be interested in sharing them online at www.heattreattoday.com. Email Bethany Leone at bethany@heattreattoday.com with your own ideas!

1. Maximizing Energy Efficiency of Vacuum Furnaces

 

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The use of AC to DC transformers is an energy-efficient innovation that can significantly lower energy consumption of the heating system. Typically, a system uses alternating current as the primary source, which fluctuates output during each half cycle. Using AC to DC transformers limits these fluctuations, reducing the amount of energy used. Furthermore, transformers operate at optimal efficiency when under a reduced load – i.e., less than 70% output in steady-state heating – rather than ramping up to the full operating temperature. Another advantage of the DC-type transformer is that its operating power factor is very close to 1.0, which lowers the utility company’s calculation of peak demand surcharges

Source: Nitrex

#ACDCtransformers #inductiondesign

2. Want a More Consistent Heat Control?

Try power feedback for your electric heating elements. Power feedback is ideal for variable resistance heating elements. Kilowatts are used as the unit of control, rather than just current or voltage.

Source: Tony Busch, Sales Application Engineer, Control Concepts, Inc.

#heat elements #powerfeedback

3. Give Sustainability the Green Light

GPC Controller
Source: GEFRAN, Inc.

Conserving energy is not only good for the environment, but it can mean more money in your pocket and less downtime. Here are three tips to improve furnace efficiency with diagnostic technology:

  • Do you have tight and secure terminal connections? Poorly connected power cables waste electricity and can cause fires. An SCR power controller monitors terminal temperature changes and will alert you before failures happen. It also monitors heat sink temperatures and ensures the control’s cooling fan is working properly.
  • Do you have a heater-break alarm? Heating zones typically have multiple heating elements, wired in parallel. A broken element is difficult to detect and will impact the heater’s circuit, reducing the power of the process. This can waste energy and affect product quality. A heater-break alarm will alert you to a failing heater circuit.
  • Do you pay high electricity bills? You could benefit from a factory load management system. It’s now possible to limit peak current loads and power usage across your factory and multiple furnaces. These systems communicate by sharing important power-demand information and providing more effective power distribution.

A connected and automated factory network saves electricity and improves operational efficiency by establishing powerful furnace management systems.

Source: John Thoma, Sales Manager, GEFRAN, Inc.

#automation #efficiency #sustainability

4. Additional Reading Material

After absorbing today’s tips, you may want to take one step farther to read up on induction heating. Take a look at “Why Induction Heating is a Green Technology” to help broaden the horizon.

Find heat treating products and services when you search on Heat Treat Buyers Guide.com

Induction and Sustainability Tips Part 2: Efficient Power Read More »

Induction and Sustainability Tips Part 1: Cleaning and Maintenance

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Discover expert tips, tricks, and resources for sustainable heat treating methods Heat Treat Today's recent series.  And, if you're looking for tips on combustion, controls systems, or induction in general, you'll find that too! Part 1, today's tips, digs into cleaning and maintenance

This Technical Tuesday article is compiled from tips in Heat Treat Today's May Focus on Sustainable Heat Treat Technologies print edition. If you have any tips of your own about induction and sustainability, our editors would be interested in sharing them online at www.heattreattoday.com. Email Bethany Leone at bethany@heattreattoday.com with your own ideas!

1. Maintenance of Induction Coils Used in Hardening Applications

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Soap and hot water will remove sticky quench and debris.
Source: Induction Tooling, Inc.

How should you maintain induction coils used in hardening applications? Elbow grease — a little goes a long way. After each use, a simple solution of soap and hot water will remove sticky quench and debris. Scrub hardened dirt with a Scotch-Brite pad. Check for pitting, arcing, and insulator damage. If all is good, use a hot water rinse, and it’s ready for use. If the inductor is to remain on the machine for an extended period, it is advised to wash it and the associated bus daily. Check for damage. Following this simple procedure will reduce business waste.

Source: William Stuehr, President/CEO, Induction Tooling, Inc.

#partscleaning #inductorcoil #hardening

2. Maintaining Tooling Fixtures for Induction Hardening

Tooling fixtures are usually maintained simply by storing them inside a mandrel and a box. This system will prevent coils from getting distorted.

Most tooling should be rinsed in hot water to wash off the polymer and then dried and stored away for future use.

It is a good practice to use deionized water for cooling the power supplies.

Source: Madhu Chatterjee, President, AAT Metallurgical Services LLC

#partscleaning #toolingfixtures

3. Switch to Aqueous

As industry tries to become more “green,” a number of companies are switching from lubricants that are petroleum or mineral oil-based to water-based (“aqueous”) lubricants instead. However, some of these companies then make the mistake of not changing their degreasing fluids that they use to remove these lubricants prior to their next processing operations, and stay with their standard degreasing fluids, such as acetone or alcohol, which are not effective at fully removing water-based lubricants. Instead, they need to run tests to find an appropriate alkaline-based degreasing fluid for such water-based lubricants, since alkaline-based degreasers will be effective at removing such lubricants. Commonly available dish-detergents (alkaline-based) have been shown to be highly effective for such use.

Source: Dan Kay, Owner, Kay & Associates

#aqueouscleaner #gogreen #lubricants

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10 pasos para solucionar las fallas en un equipo de inducción

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Nikola Tesla afirmó: <<Si quieres descubrir los secretos del universo, concéntrate en la energía, la frecuencia y la vibración.>>

Al revisar los mecanismos internos de un sistema de inducción es posible evidenciar cada uno de estos tres elementos. Los 10 pasos de esta guía servirán para apoyar a los operadores de departamentos internos de tratamiento térmico en entender los secretos de la inducción para así identificar posibles escollos en tales sistemas y dar solución a problemas comunes que se puedan presentar.

This original content article was first written by Alberto Ramirez, engineer of Power Supply and Automation at Contour Hardening, Inc. and an honoree from Heat Treat Today’s 40 Under 40 Class of 2021, for Heat Treat Today's May 2023 Sustainable Heat Treat Technologies print edition. Read the Spanish version below, or click the flag above right for the English version.

Puedes hacerlos llegar a Bethany Leone al correo bethany@heattreattoday.com

Alberto Ramirez
Power Supply and Automation Engineer
Contour Hardening, Inc.

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Los metales pueden calentarse mediante el proceso de inducción electromagnética, mediante el cual un campo magnético alternativo cerca de la superficie de una pieza de trabajo metálica (o conductora de electricidad) induce corrientes de Eddy (y, por lo tanto, calentamiento) dentro de la pieza de trabajo.

Los sistemas de inducción pueden llegar a ser sistemas complejos que tienen como objetivo endurecer piezas o secciones específicas de un componente mecánico, dependiendo del grado de complejidad de la pieza a tratar; para el profesional, el desafío será el diagnóstico de los problemas que se lleguen a presentar.

1. Familiarízate con el proceso

Figura 1. Proceso de endurecimiento por inducción
Source: Contour Hardening, Inc.

El proceso de inducción envuelve muchas características tales como: posición de la pieza dentro de la bobina de inducción, posiciones de carga, posiciones de enfriamiento, tiempos de ciclo, potencia eléctrica aplicada, entre otras. Es importante que el profesional sea capaz de identificar la falla y la situación particular en el momento en el que se está presentando.

En algunas ocasiones las fallas no son evidentes y, por ende, es indispensable analizar la pieza que ha sido tratada; este análisis puede ser clave para entender situaciones tales como: falta de profundidad de capa por potencia eléctrica o disminución en la frecuencia de salida, entre otros posibles escenarios.

Adicional al análisis de la pieza, es vital inspeccionar la “escena del crimen” ya que muchos de los sistemas de inducción, dada la naturaleza del proceso y el peligro que implica manejar altos potenciales eléctricos, suelen ser en extremo automatizados y las estaciones de trabajo de difícil acceso para el personal, así que una buena estrategia de trabajo consiste en observar detenidamente las condiciones generales del equipo para determinar el punto de inicio para la resolución del problema.

2. Identifica los componentes principales de tu sistema de inducción, así como los mecanismos de seguridad para ciertas zonas en particular

Entender la interrelación del sistema es importante para comprender qué elemento realiza cierta acción, así como los canales de comunicación entre ellos. Una vez que se genere este conocimiento, se puede asociar una falla a un componente en particular. Usualmente los sistemas de inducción se componen de los siguientes elementos:

Figura 2. Componentes de un sistema de inducción
Source: Contour Hardening, Inc.

Como mencionamos con anterioridad el proceso implica altos potenciales eléctricos, y para eso la naturaleza de las fuentes de alimentación involucra dispositivos electrónicos de potencia, como capacitores eléctricos, los cuales almacenan energía y, por ende, es importante descargar eléctricamente el sistema antes de comenzar a inspeccionar un equipo.

3. Ten preparadas las herramientas necesarias para realizar un buen análisis del problema

Figura. Capacitores
Source: Contour Hardening, Inc.

Al igual que cualquier problem técnico, el uso de la herramienta mecánica es indispensable al realizar algún tipo de proyecto, pero para el diagnóstico de una falla en un equipo de inducción es importante contar con:

  • Osciloscopio
  • Generador de funciones
  • Amperímetro
  • Multímetro digital y analógico.
  • Sondas de alto voltaje

Sin estos elementos es muy difícil llegar a un diagnóstico fiable, y  la posibilidad de encontrar la falla es mínima. Por ende, tener estos medidores en buen estado y, sobre todo, calibrados nos da una perspectiva más clara del problema.

4. Verifica que los sensores del proceso, los monitores de energía y las bobinas de inducción funcionen correctamente

Existen distintos medidores que recogen información acerca del proceso; esta información en su mayoría puede ser visualizada a través del HMI (Human Machine Interface), y, en muchas ocasiones, una buena manera de comenzar a entender el problema es recopilar la información del proceso. Si los medidores no funcionan correctamente, te pueden llevar a conclusiones erróneas.

Verifica que los medidores de energía estén funcionando correctamente, así como tus señales de entrada y de salida.

Las bobinas de inducción son un elemento clave en el proceso de inducción ya que acorde a su geometría generan los campos magnéticos adecuados para lograr los resultados metalúrgicos esperados. Si existen fugas de agua o los elementos de transmisión eléctrica se encuentran sueltos o sucios, seguramente podrán ser la raíz del problema. Es importante comenzar a realizar el diagnóstico de la falla una vez se haya descartado este circuito en particular.

Figura 4. Ejemplo de parámetros de energía
Source: Contour Hardening, Inc.

5. Realiza estudios de energía constante en tu subestación para identificar posibles problemas en tu suministro de energía, así como tiempos críticos

La energía eléctrica es la fuente principal en un proceso de inducción; las fuentes de alimentación transforman y potencializan este recurso para crear campos electrónicos lo suficientemente fuertes para generar el calor en la pieza.

Por ende, es importante descartar con evidencia que el problema en cual nos encontramos no se debe a una falla del sistema eléctrico del cual nuestro sistema de inducción forma parte. De igual manera entender cómo se comporta nuestro sistema eléctrico nos puede ayudar a generar patrones de comportamiento que puedan determinar la solución en momentos específicos en los que se lleguen a presentar.

6. Trabaja de forma metódica documentando tus movimientos y realiza un paso a la vez

Los sistemas de inducción pueden ser muy intimidantes si no has tenido experiencia previa, y, al igual que con cualquier elemento o situación, es importante abordar de manera lógica el problema analizando el modo de la falla, identificando las partes principales que interactúan en ese preciso momento, y, a partir de este análisis, documentar y realizar pequeños pasos, uno a la vez, ya que, de no ser así, es muy probable que pierdas todo el trabajo realizado y la situación empeore.

Figura 5. Antes y durante un arco eléctrico dentro de la línea de transmisión
Source: Contour Hardening, Inc.

Si los movimientos no son exitosos, siempre puedes regresar a tu punto de partida e intentar otro acercamiento. La idea consiste en que el modo de la falla se mantenga estable sin importar los movimientos realizados hasta que se resuelva el problema. De esta manera lograrás contener la falla; de otra manera podrías estar dañando otros elementos sin darte cuenta.

Es muy importante entender que los procesos son secuencias que anteceden y preceden a nuevos eventos; si entiendes el proceso y, una vez resuelto el problema, ahora tienes una nueva falla, es importante analizar si esta falla es la continuación del proceso ya que, de ser así, es posible que te encuentres frente al caso de un evento que está desencadenado una serie de fallas y se haga necesario practicar un análisis más profundo. La idea general es llegar a la raíz del problema y mitigar el riesgo.

7. Intenta cualquier posibilidad relacionada con el proceso sin importar que la relación entre ésta y el problema no sea directa

Un pensamiento lógico puede resolver la mayoría de las fallas técnicas de un sistema, pero, para fallas excepcionales, es necesario utilizar la imaginación y agotar todos los recursos posibles ya que el área de interés más insignificante o el lugar menos pensado puede ser la clave para resolver un problema.

8. Conoce tus fuentes de alimentación

Uno de los factores claves en cualquier equipo de inducción son sus fuentes de alimentación. Las fuentes de alimentación son equipos que no requieren un mantenimiento tan arduo en comparación con otros sistemas en la industria, pero, de no presentarse las condiciones mínimas de mantenimiento, pueden generar altas pérdidas para la organización.

Figura 6. Diagrama de flujo del proceso eléctrico en una fuente de alimentación
Source: Contour Hardening, Inc.

En los casos en los que el problema se encuentra en las fuentes de alimentación, es vital que se siga el mismo proceso metódico previamente descrito. Entender cómo funciona el proceso de transformación de la energía te dará una ventaja, al igual que conocer los componentes empleados o el tipo de tecnología utilizado en el proceso de rectificación, en la inversión (estado sólido o tubos de electrones) y en el circuito resonante. Generalmente las fuentes de alimentación siguen el siguiente patrón de transformación (Figura 6).

9. Identifica las partes críticas de tu equipo de inducción y prepara un inventario de éstas

Figura 7. Daño en una bobina de inducción
Contour Hardening, Inc.

Usualmente los componentes que forman parte de las fuentes de alimentación son difíciles de conseguir dependiendo de la antigüedad de tu equipo, y con la reciente crisis de microchips en el mercado, existen tiempos de entrega muy largos para los elementos de control y automatización; de igual manera, los precios de los mismos se han disparado. Por ende, es vital que exista una lista de partes críticas y un inventario de éstas.

Adicionalmente a los elementos descritos, las bobinas de inducción suelen ser elementos muy característicos e importantes en el proceso de inducción. Éstas bobinas son elementos complejos que han sido diseñados exclusivamente para la pieza, por lo que su fabricación puede tomar varias semanas, y es importante tomar las precauciones necesarias para mantener un movimiento de mantenimiento constante.

10. Realiza mediciones preventivas al sistema para generar un patrón de comportamiento

Figura 8. Ejemplo de posibles mediciones
Contour Hardening, Inc.

Cuando el sistema se encuentre trabajando en óptimas condiciones, genera un plan de medición el cual te permita recopilar información de puntos específi cos dentro del sistema. Una vez que se vuelva a presentar una nueva falla puedes comparar las mediciones de falla contra las del buen funcionamiento. Algunos ejemplos de mediciones pueden ser:

  • Temperatura
  • Voltaje
  • Corriente eléctrica
  • Resistencia y capacitancia
  • Formas de onda

En resumen

Una metodología de trabajo ordenada y documentada, un buen catálogo de piezas de recambio, junto con las herramientas de trabajo necesarias, pueden ser elementos clave para entender un problema y, lo que es más importante, resolverlo de forma eficaz.

Es vital que los profesionales se capaciten de manera constante para mejorar los tiempos de paro debido a fallas en los sistemas de inducción. La capacitación relacionada con procesos metalúrgicos sería una buena forma de complementar tus habilidades de resolución de problemas permitiéndote interpretar las características de los sistemas de inducción, al igual que de los elementos que los componen.

 

Bibliografía

Valery Rudnev and George Totten, ed., ASM Handbook Volume 4C: Induction Heating and Heat Treatment, (Materials Park, OH: ASM International Heat Treating Society, 2014), 581- 583

 

Sobre el autor: Alberto C. Ramirez es ingeniero en Mecatrónica egresado del Instituto Tecnológico Nacional de México Campus León con una maestría en Administración de Tecnologías de la Información por el Instituto Tecnológico de Monterrey. Cuenta con más de 8 años de experiencia en fuentes de alimentación, gestión de proyectos, mantenimiento y automatización. Actualmente se desempeña como ingeniero de fuentes de alimentación y automatización en Contour Indianapolis. Alberto inició su carrera en la fi lial de Contour en México y debido a su dedicación forma parte del staff en los Estados Unidos.

He is also an honoree from Heat Treat Today's 40 Under 40 Class of 2021.

Para más información:

Contacta a Alberto escribiendo a: aramirez@contourhardening.com.

 

 

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10 Steps To Troubleshoot Your Induction System

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Nikola Tesla said, “If you want to find the secrets of the universe, think in terms of energy, frequency, and vibration.” These three components are evident in getting to know the inner workings of an induction system. When it comes to troubleshooting such a system at in-house heat treat departments, this 10 step guide will help heat treat operators understand the secrets of induction and solve common problems that may arise.

This original content article was first written by Alberto Ramirez, engineer of Power Supply and Automation at Contour Hardening, Inc. and an honoree from Heat Treat Today’s 40 Under 40 Class of 2021, for Heat Treat Today's May 2023 Sustainable Heat Treat Technologies print edition.

Alberto Ramirez
Power Supply and Automation Engineer
Contour Hardening, Inc.

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Metals can be heated by the process of electromagnetic induction, whereby an alternative magnetic field near the surface of a metallic (or electrically conductive) workpiece induces eddy current (and thus heat) within the workpiece. Induction systems can be complex systems that aim to heat treat specific parts or sections of a mechanical component; depending on the degree of complexity of the part to be treated, it will be the challenge of a professional to detect any problem.

1. Familiarize Yourself with the Process

Figure 1. Induction hardening process
Source: Contour Hardening, Inc.

The induction process involves many characteristics such as: position of the piece within the induction coil, load positions, cooling positions, cycle times, applied electric power, and others. It is important that the professional can identify the failure and the particular situation at the moment in which it is occurring.

On some occasions, the failures are not evident and therefore it is essential to analyze the part that has been treated. This analysis can be key to understanding situations such as poor depth due to electrical power or decrease in output frequency, among other possible scenarios.

In addition to the analysis of the piece, it is vital to inspect the “crime scene,” since many of the induction systems — given the nature of the process and the danger involved in handling high electrical potentials — are usually highly automated and the work stations are difficult for staff to access. A good work strategy consists of carefully observing the general conditions of the equipment to determine where the problem will begin to be solved.

2. Identify Main Components and Certain Security Mechanisms of Your Induction System

Understanding the interrelationship of the system is important to comprehend which element performs a certain action, as well as the communication channels between them. Once this knowledge is generated, a failure can be associated with a particular component. Induction systems are usually made up of the elements in Figure 2.

Figure 2. Induction system components
Source: Contour Hardening, Inc.

As we mentioned before, the process involves high electrical potentials, and for this reason, the nature of the power supplies involves power electronic devices such as electrical capacitors, which store energy. Therefore, it is important to electrically discharge the system before beginning to inspect a piece of equipment.

3. Have the Necessary Tools Ready To Carry Out a Good Analysis of the Problem

Figure 3. Capacitors
Source: Contour Hardening, Inc.

Like any technical problem, the use of a mechanical tool is essential when carrying out some type of project, but for the diagnosis of failure in induction equipment it is important to have:

  • Oscilloscope
  • Function generator
  • Ammeter
  • Digital and analog multimeter
  • High voltage probes

Without these elements it is exceedingly difficult to reach a reliable diagnosis, and the possibility of finding the fault is minimal. Therefore, having these meters in good condition and above all, calibrated, gives a clearer perspective of the problem.

4. Verify that the Process Sensors, Power Monitors, and Induction Coils Are Working Properly

There are different meters that collect information about the process. This information can mostly be viewed through the HMI (human machine interface). On many occasions, a good way to begin to understand the problem is by collecting the information on the process. If these meters do not work correctly, they can lead you to wrong conclusions.

Verify the energy meters are working correctly, as well as your input and output signals.

Induction coils are a key element in the induction process since, according to their geometry, they generate the appropriate magnetic fields to achieve the expected metallurgical results. If there are water leaks or the electrical transmission elements are loose or dirty, it could be the root cause of the problem. It is important to start troubleshooting once this circuit is ruled out.

Figure 4. Energy parameters example
Source: Contour Hardening, Inc.

5. Carry Out Studies of Constant Energy in Your Substation To Identify Possible Problems in Your Energy Supply, Including Critical Times

Electrical energy is the main source in an induction process, power supplies transform and potentiate this resource to create electronic fields strong enough to generate heat in the piece.

Therefore, it is important to find evidence that rules out failures of the electrical system that the induction system is a part of. In the same way, understanding how our electrical system behaves can help us generate behavior patterns that can determine the solution at specific times when it may arise.

6. Document Your Work Methodically and Take One Step at a Time

Induction systems can be very intimidating if you have not had previous experience, and, like any element or situation, it is important to logically approach the problem by analyzing the failure mode, identifying the main parts that interact at that specific moment. From there, document and take small steps, one at a time. If you don’t, it is very likely you will lose all the work you have done, and the situation will get worse.

Figure 5. Before and after of an arc at the transmission line
Source: Contour Hardening, Inc.

If the moves are unsuccessful, you can always return to your starting point and try another approach. The idea is that the failure mode remains the same no matter what moves you make until the problem is resolved. In this way you will have the failure contained, otherwise you could be damaging other elements without realizing it.

It is very important to understand that the processes are sequences that precede and proceed new events. If you understand the process and solve a problem, but now have a new failure, it is important to analyze if this failure is the continuation of the process. If so, it is possible that you find yourself in a case where an event is triggering a series of failures. Therefore, a more in-depth analysis must be carried out. The idea to generate is to get to the root cause and mitigate the risk.

7. Try Any Possibility Related to the Process Regardless of Whether the Relationship Between It and the Problem Is Not Direct

Logical thinking can solve most of the technical failures of a system. For exceptional failures, however, it is necessary to use your imagination and exhaust all possible resources, since the smallest area of interest or the least thoughtful place can be the key to solving a problem.

8. Get To Know Your Power Supplies

One of the key factors in any induction equipment is its power supplies. Power supplies are equipment that do not require such arduous maintenance compared to other systems in the industry, but if the minimum maintenance conditions are not present, they can generate high losses for the organization.

Figure 6. Flow diagram of the energy process at the power supply
Source: Contour Hardening, Inc.

In cases where the problem is the power supplies, it is vital that the same methodical process previously described is followed. Understanding how the energy transformation process works will give you an advantage, as will knowing the elements that compose them or the type of technology used in the rectification process, in the inversion (solid state or electron tubes) and in the resonant circuit. Generally, power supplies follow the transformation in Figure 6.

9. Identify the Critical Parts of Your Induction Equipment and Prepare an Inventory

Figure 7. Coil damage
Contour Hardening, Inc.

Usually, the elements that belong to the power supplies are difficult to obtain depending on the age of your equipment. With the recent microchip crisis in the market, control and automation elements have very long delivery times or the prices are very high. Therefore, it is vital that there is a list of critical parts and an inventory of these.

In addition to the elements described, induction coils are usually very characteristic and important elements in the induction process. These coils are complex elements that have been designed exclusively for the piece, so their manufacture can take several weeks, and the necessary precautions must be taken to maintain a constant maintenance movement.

10. Perform Preventative Measurements to the System To Generate a Pattern of Behavior

Figure 8. Possible examples of measurements
Contour Hardening, Inc.

When the system is working in optimal conditions, generate a measurement plan which allows you to generate information on specific points within the system. Once a new failure occurs again you can compare the measurements of failure against those of good performance. Some examples of measurements can be:

  • Temperature
  • Voltage
  • Current
  • Resistance and capacitance
  • Waveforms

Summary

An orderly and documented work methodology, a good spare parts catalog, and the necessary work tools can be key elements to understand a problem and, more importantly, to solve it effectively.

It is vital that professionals are in continuous training in order to decrease downtime due to failures in induction systems. Training related to metallurgical processes would be a good way to complement your resolution skills by being able to interpret the characteristics of induction systems with the elements that compose it.

 

References

Valery Rudnev and George Totten, ed., ASM Handbook Volume 4C: Induction Heating and Heat Treatment, (Materials Park, OH: ASM International Heat Treating Society, 2014), 581- 583.

 

About the Author: Alberto C. Ramirez graduated from the National Technical Institute of Mexico as a mechatronics engineer. He earned his master’s degree in information technology administration from Monterrey Institute of Technology. With more than eight years of experience in power supplies, project management, maintenance, and automation, he currently works as a Power Supply and Automation Engineer at Contour Indianapolis. Alberto began his career at the Contour subsidiary in Mexico and due to his dedication, he is part of the staff in the United States. He is also an honoree from Heat Treat Today's 40 Under 40 Class of 2021.

For more information:

Contact Alberto at Contact Alberto at aramirez@contourhardening.com.

 

 

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Induction Through Heating + Intensive Quenching: A “Green Ticket” for Steel Parts

/ CARBURIZING TECHNICAL CONTENT, FEATURED NEWS, INDUCTION HEATING EQUIPMENT TECHNICAL CONTENT, INDUCTION HEATING TECHNICAL CONTENT, MANUFACTURING HEAT TREAT, QUENCHING TECHNICAL CONTENT

OCOn site at heat treat operations, gas-fired furnaces can be a significant source of carbon emissions. But depending on the desired heat treatment, an alternative approach that combines induction through heating and intensive quenching could be the “green ticket.” Learn about the ITH + IQ technique and discover how certain steels may benefit from this approach.

This Technical Tuesday article was composed by Edward Rylicki, Vice President Technology, and Chris Pedder, Technical Manager Heat Treat Products and Services, at Ajax TOCCO Magnethermic Corp., and Michael Aronov, CEO, IQ Technologies, Inc. It appears in Heat Treat Today's May 2023 Sustainable Heat Treat Technologies print edition.

Introduction

Chris Pedder,
Technical Manager Heat Treat Products and Services, Ajax TOCCO Magnethermic Corp.
Source: Ajax TOCCO Magnethermic Corp.

Induction heating is a green, environmentally friendly technology providing energy savings and much greater heating rates compared to other furnace heating methods. Other advantages of induction heating include improved automation and control, reduced floor space, and cleaner working conditions. Induction heating is widely used in the forging industry for heating billets prior to plastic deformation. Induction heating is also used for different heat treatment operations such as surface and through hardening, tempering, stress relieving, normalizing, and annealing. However, the amount of steel products subjected to induction heating in the heat treating industry is much less compared to that processed in gas-fired furnaces.

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Gas-fired heat treating equipment is a major source of carbon emissions in the industry. As shown in Reference 1, induction through heating (ITH) followed by intensive quenching (IQ) (an “ITH + IQ” technique) eliminates, in many cases, the need for a gas-fired furnace when conducting through hardening and carburizing processes — the two most widely used heat treating operations for certain steel parts. Eliminating gas-fired furnaces will result in significant reduction of carbon emissions at on-site heat treat operations.

Dr. Michael Aronov,
CEO, IQ Technologies, Inc.
Source: Ajax TOCCO Magnethermic Corp.

The goal of this article is twofold: 1) to evaluate carbon emissions generated during through hardening of steel parts and carburizing processes when conducted in gas-fired furnaces, and 2) to discuss how these emissions can be reduced to zero using the ITH + IQ process.

Evaluation of Carbon Emissions for Through Hardening and Carburizing Processes

Ed Rylicki,
Vice President Technology, Ajax TOCCO Detroit Development & Support Center
Source: Ajax TOCCO Magnethermic Corp.

Most through hardening and carburizing operations for steel parts are conducted in batch and continuous integral quench gas-fired furnaces. Assumptions made for evaluating CO2 emissions produced by a typical integral quench furnace are presented in Table 1. Note: The values of carbon emissions presented Table 1 are conservative since they don’t consider the amount of CO2 produced by furnace flame screens and endothermic gas generators used to provide a controlled carburizing atmosphere in the furnace. Also, it’s assumed that the furnace walls are already heated through when loading the parts, so there are no heat losses associated with the thermal energy accumulated by the furnace walls.

Table 1. Assumptions for calculating of carbon emissions by integral quench furnace
Source: Ajax TOCCO Magnethermic Corp.

Emissions Generated During the Through Hardening Process

A furnace time/temperature diagram for the through hardening process considered is presented in Figure 1. Carbon emissions Ehard produced by the furnace considered during heating of the load to the austenitizing temperature prior to quenching are calculated by using the following equation,

 

(Equation 1)
Ehard = k • Qhard

where:

■ k = the emission coefficient (equal to 0.050 • 10-3 kg per 1 kJ of released energy when burning natural gas (see Reference 2)
■ Qhard = thermal energy required for heating up the above load from ambient to the austenitizing temperature

A value of Qhard is calculated by the equation below,

(Equation 2)

Qhard = M • C • (Ta -To) / Eff = 1,135 • 0.56 • (843 - 20) / 0.65 = 0.805 • 106kJ

where:

■ M = load weight, kg
■ C = steel specific heat capacity (kJ/kg°C)
■ Ta = part austenitizing temperature (°C)
■ To = part initial temperature (°C)
■ Eff = furnace thermal efficiency (a ratio of the furnace thermal losses to the gross heat input)

From equations (1) and (2), the amount of carbon emissions produced by the above furnace during one hardening operation is 40.2 kg. To determine an annual amount of carbon emissions, calculate the number of hardening cycles per year (Nhard) run in the furnace. From Figure 1, a duration of one hardening cycle is 4 hours (3 hours for austenitizing of the parts plus 1 hour for quenching the parts in oil and unloading/loading the furnace). Thus, Nhard is equal to:

Nhard = 360 day • 24 hour • 0.85 / 4 hour = 1826

Figure 1
Source: Ajax TOCCO Magnethermic Corp.

Annual CO2 emissions from one integral quench batch gas-fired furnace are 40.2 • 1836 = 73,807 kg, or more than 73 t

Emissions Generated During Carburizing Process

A simplified furnace time/temperature diagram for the carburizing process considered is presented in Figure 2. Carbon emissions (Ecarb) produced by the above furnace during the carburizing process are calculated by the following equation,

(Equation 3)

Ecarb = k • Qcarb

where:

■ Qcarb = a thermal energy expended by the furnace during the carburizing process. A value of Qcarb amounts to two components: 

(Equation 4)

Qcarb = Qcarb1 + Qcarb2

Qcarb in the following equation is:

■ Qcarb1 = energy required for heating up the load to the carburizing temperature
■ Qcarb2 = energy needed for maintaining the furnace temperature during the remaining duration of the carburization process (for compensation of the furnace thermal losses since the parts are already heated up to the carburizing temperature)

A value of Qcarb1 is calculated using equation (2) where the part carburizing temperature Tc is used instead of part austenitizing temperature Ta (see Table 1):

Qcarb1 = 1,135 • 0.56 • (927 – 20) / 0.65 = 0.887 • 106 kJ

A value of Qcarb2 is a sum of the flue gas losses and losses of the thermal energy through the furnace walls by heat conduction. Qcarb2 is evaluated from the following considerations. Since the assumed furnace thermal efficiency is 65%, the furnace heat losses are equal to 35% of the gross heat input to the furnace. Hence, the furnace heat losses Qloss1 during the load heat up period (the first 3 hours of the carburizing cycle, see Figure 2) are the following:

Qloss1 = Qcarb1 • 0.35 = 0.887 • 106 • 0.35 = 0.31 • 106 kJ.

The furnace heat losses during the remaining 8 hours of the carburizing cycle Qloss2 are proportionally greater and are equal to:

Qloss2 = Qloss1 • 8 hr /3 hr = 031 • 106 • 8 /3 = 0.827 • 106 kJ

Thus, the total amount of the thermal energy expended by the furnace during the carburizing cycle is Qcarb = 0.887 • 106 + 0.827 • 106 = 1.71 • 106 kJ. The total amount of the CO2 emissions from carburizing of the load in the furnace considered according to equation (3) is: Ecarb = 0.050 • 10-3 • 1.71 • 106 = 85.7 kg. To determine an annual amount of carbon emissions from one carburizing furnace, calculate the number of carburizing cycles run in the furnace per year. Per Figure 2, a duration of one carburizing cycle is 12 hour (1 hour for the furnace recovery plus 10 hour for carburizing of parts at 927°C plus 1 hour for quenching parts in oil and for unloading and loading the furnace). Thus, the number of carburizing cycles per year Ncarb is:

Ncarb = 360 day • 24 hr • 0.85 / 12 hr = 612

Figure 2
Source: Ajax TOCCO Magnethermic Corp.

Annual CO2 emissions from one integral quench batch carburizing furnace is about 85.7 • 612 = 52,448 kg, or more than 52 t.

Reducing Carbon Emissions Using the ITH + IQ Process

Reference 1 presents results of two case studies of the ITH + IQ process on automotive input shafts and drive pinions. The study was conducted with a major U.S. automotive part supplier. A two-step heat treating process was used for the input shafts, consisting of batch quenching parts in oil or polymer using an integral quench gas-fired furnace for core hardening followed by induction hardening. This two-step method of heat treatment is widely used in the industry for many steel products. It provides parts with a hard case and tough, ductile core.

Substituting the “ITH + IQ” method for the two-step heat treating process not only eliminates the batch hardening process, but also requires less alloy steel for the shafts that don’t require annealing after forging. Thus, in this case, applying the ITH + IQ technique eliminates two furnace heating processes for the input shafts, resulting in the reduction of the CO2 emissions to zero for the shafts’ heat treatment. Per client evaluation, as mentioned in Reference 1, the hardness profile in the intensively quenched input shafts was similar to that of the standard shafts. Residual surface compressive stresses in the intensively quenched shafts were greater in most cases compared to that of the standard input shafts, resulting in a longer part fatigue life of up to 300%.

Per Reference 1, the environmentally unfriendly  carburizing process can be fully eliminated in most cases for automotive pinions when applying the ITH + IQ method and using limited hardenability (LH) steels that have a very low amount of alloy elements. A case study conducted for drive pinions with one of the major U.S. automotive parts suppliers demonstrates the intensively quenched drive pinions met all client’s metallurgical specifications and passed both the ultimate strength test and the fatigue test. It was shown that the part’s fatigue resistance improved by about 150% compared to that of standard carburized and quenched in oil drive pinions. In addition, distortion of the intensively quenched drive pinions is so low that no part straitening operations were required.

Conclusion

Coupling Ajax TOCCO’s induction through heating method with the intensive quenching process creates a significant reduction of CO2 emissions produced during heat treatment operations for steel parts. For the through hardening process, eliminating just one batch integral quench gas-fi red furnace will reduce carbon emissions by more than 73 ton per year. For the carburizing process, eliminating just one batch carburizing furnace will reduce carbon emissions by more than 52 ton per year. Note that for continuous gas-fired furnaces, the carbon emission reduction will be much greater due to higher continuous furnaces production rates (hence a much higher fuel consumption).

Per our experience, the ITH + IQ process can be applied to at least 20% of the currently through-hardened and carburized steel parts. Per two major heat treating furnace manufacturers in the U.S., there are thousands of atmosphere integral quench batch and continuous furnaces in operation in the U.S. That means hundreds of gas-fired heat treating furnaces can be potentially eliminated, drastically reducing carbon emissions in the U.S., supporting a lean and green economy.

 

References

[1] Michael Aronov, Edward Rylicki, and Chris Pedder, “Two Cost-Effective Applications of Intensive Quenching Process for Steel Parts,”Heat Treat Today, October 2021, https://www.heattreattoday.com/processes/quenching/quenching-technical-content/two-cost-effective-applications-for-intensive-quenching-of-steel-parts/.

[2] U.S. Energy Information Administration.

About the Authors:

Ed Rylicki has been in the induction heating industry for over 50 years. He is currently Vice President Technology at Ajax TOCCO Detroit Development & Support Center in Madison Heights, Michigan.

Mr. Chris Pedder has over 34 years of experience at Ajax Tocco Magnethermic involving the development of induction processes in the heat treating industry from tooling concept and process development to production implementation.

Dr. Michael Aronov has over 50 years’ experience in design and development of heating and cooling equipment and processes for heat treating applications. He is CEO of IQ Technologies, Inc. and a consultant to the parent company Ajax TOCCO Magnethermic.

For more information: Contact info@ajaxtocco.com or 800.547.1527

 

 

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