Inductoheat Inc.

Tips #13 – 23 – 33 – 43

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One of the great benefits of a community of heat treaters is the opportunity to challenge old habits and look at new ways of doing things. Heat Treat Today’s 101 Heat Treat Tips is another opportunity to learn the tips, tricks, and hacks from some of the industry’s foremost experts.

Heat Treat Today’s latest round of 101 Heat Treat Tips is featured in Heat Treat Today 2020 fall issue (also featuring the popular 40 Under 40).

Today’s selection includes four tips from Leybold Vacuum USA, Young Metallurgical Consulting, Dr. Valery Rudnev, and Chiz Bros. Increase output, decrease production costs, hit target temperature, and avoid thermal shock with these four tips.

Heat Treat Tip #13

New Diffusion Pump Technology Increases Production Output

Gain immediate positive net cash flow with a lease to own finance option by upgrading your diffusion pumps with the new immersion heater technology. The new style heater will extend oil life and reduce energy consumption. New heater technology can increase production by eliminating the need of dropping your pump every time you change oil for faster maintenance turn around. Drop in place pump design with improved performance.

NEW-DIJ Diffusion Pumps with smart heater technology by Leybold Vacuum
Source: Leybold Vacuum USA

(Leybold Vacuum USA)

Heat Treat Tip #23

Inspection Mistakes That Cost

Rockwell hardness testing requires adherence to strict procedures for accurate results.  Try this exercise to prove the importance of proper test procedures.

  • A certified Rc 54.3 +/- 1 test block was tested three times and the average of the readings was Rc 54 utilizing a flat anvil.  Water was put on the anvil under the test block and the next three readings averaged Rc 52.1.
  • Why is it so important that samples are clean, dry, and properly prepared?
  • If your process test samples are actually one point above the high spec limit but you are reading two points lower, you will ship hard parts that your customer can reject.
  • If your process test samples are one point above the low spec limit but you are reading two points lower, you may reprocess parts that are actually within specification.
  • It is imperative that your personnel are trained in proper sample preparation and hardness testing procedures to maximize your quality results and minimize reprocessing.
Properly preparing a hardness sample can save time and money.

Source: Young Metallurgical Consulting

(Young Metallurgical Consulting)

Heat Treat Tip #33

Not Able to Hit Target Temperature — What To Do

Situation: Customer had an available 100kW/1kHz inverter and needed to heat 1-in.-diameter carbon steel bar to hot working temperature (2000°F). It was a low production application and cycle time was not critical. However, regardless of the heat time and irrespective of using maximum available output power, it was not possible to reach required target temperature. Actually, after reaching about 1470o°F there was no noticeable temperature rise regardless of increased heat time.

Solution: Severe eddy current cancellation was responsible for a failure to reach target temperature. The use of frequencies 6 kHz and greater can easily help to accomplish the goal. As a simple “rule-of-thumb,” in order to provide an efficient heating and avoid eddy current cancellation in through heating applications (e.g., through hardening or hot working), it is necessary to choose a frequency that will guarantee that the “bar diameter-to-penetration depth” ratio exceeds 3.6 at a target temperature.

(Dr. Valery Rudnev, FASM, Fellow of IFHTSE/Professor Induction/Director Science & Technology, Inductoheat Inc., An Inductotherm Group company)

Heat Treat Tip #43

Brick to Fiber to Avoid Thermal Shock

Thermal shock is a regular issue with hard refractory and brick-lined furnaces due to the constant changes in temperature for batch annealing. Switching an old furnace over to ceramic fiber is an easy process that can save time and money.

(Chiz Bros)

Tips #13 – 23 – 33 – 43 Read More »

Dr. Valery Rudnev on Equipment Selection for Induction Hardening: Single-Shot Hardening, Part 2

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

This article continues the ongoing discussion on Equipment Selection for Induction Hardening by Dr. Valery Rudnev, FASM, IFHTSE Fellow. Six previous installments in Dr. Rudnev’s series on equipment selection addressed selected aspects of scan hardening and continuous/progressive hardening systems. This post is the second in a discussion on equipment selection for one of four popular induction hardening techniques focusing on single-shot hardening systems.

The first part on equipment selection for single-shot hardening is here; the third part is here. To see the earlier articles in the Induction Hardening series at Heat Treat Today as well as other news about Dr. Rudnev, click here. 

Traditional Designs of Single-Shot Inductors

Figure 1 shows a typical shaft-like component (Figure 1,top-left) suitable for a single-shot hardening inductor, as well as a variety of traditionally designed single-shot inductors for surface hardening shaft-like workpieces. Sometimes, these inductors are also referred to as channel inductors.

A conventional single-shot inductor consists of two legs and two crossover segments, also known as bridges, “horseshoes,” or half-loops [1]. The induced eddy currents under the legs primarily flow along the length of the part (longitudinally/axially) with the exception of the regions of the workpiece located under the crossover segments where the flow of the eddy current is half circumferential. Unlike scanning inductors, traditional designs of single-shot inductors can be quite complicated.

Figure 1. A typical shaft-like component (top-left image) suitable for a single-shot hardening and a variety of traditionally designed single-shot inductors for surface hardening shaft-like workpieces (Courtesy of Inductoheat Inc., an Inductotherm Group company)
Figure 1. A typical shaft-like component (top-left image) suitable for a single-shot hardening and a variety of traditionally designed single-shot inductors for surface hardening shaft-like workpieces (Courtesy of Inductoheat Inc., an Inductotherm Group company)

With a predominantly longitudinal eddy current flow, the heat uniformity in the diameter change areas of the stepped shafts is dramatically improved and the tendency of corners and shoulders to be overheated is reduced significantly compared to applying a single-turn or multi-turn solenoid coils commonly used in scan hardening and continuous/progressive hardening.

Because the copper of single-shot inductors does not completely encircle the entire region required to be heated, rotation must be used to create a sufficiently uniform austenitized surface layer along the workpiece perimeter. Upon quenching, a sufficiently uniform hardness case depth along the circumference of the part will be produced. For single-shot inductors, the rotation speed usually ranges from 120 to 500 rpm.

Different types of magnetic flux concentrators (also called flux intensifiers, flux controllers, flux diverters, magnetic shunts, etc.) complement the copper profiling of an inductor, helping to achieve the required hardness pattern. Flux concentrators may provide several considerable benefits when applied in single-shot inductors. This includes an increase of coil electrical efficiency, a noticeable reduction of coil current, and a significant reduction of the external magnetic field exposure.

As an example, Figure 2 shows a transverse cross-section of a single-shot inductor and a straight shaft. Computer-modeled electromagnetic field distribution of a bare inductor (Figure 2, left) compared to an inductor with a U-shaped flux concentrator (Figure 2, right) is shown. Note that the magnitude of magnetic field intensity on both images is different. The use of U-shaped magnetic flux concentrators in single-shot hardening applications typically results in a 16% to 27% coil current reduction compared to using a bare inductor while having a similar heating effect. A reduction of the external magnetic field exposure while applying flux concentrator is even more dramatic (Figure 2, right).

Figure 2.  Computer-modeled EMF distribution in the transverse cross-section of a bare inductor (left) compared to an inductor with U-shaped flux concentrator (right). Note: the scale of magnetic field intensity on both images is different [1].
Figure 2.  Computer-modeled EMF distribution in the transverse cross-section of a bare inductor (left) compared to an inductor with U-shaped flux concentrator (right). Note: the scale of magnetic field intensity on both images is different [1].
Different applications may call for various materials used to fabricate magnetic flux concentrators including stacks of silicon-steel laminations, pure ferrites, and various proprietary multiphase composites. The selection of a particular material depends on a number of factors, including the following [1]:

  • applied frequency, power density, and duty cycle;
  • operating temperature and ability to be cooled;
  • geometries of workpiece and inductor;
  • machinability, formability, structural homogeneity, and integrity;
  • an ability to withstand an aggressive working environment resisting chemical attack by quenchants and corrosion;
  • brittleness, density, and ability to withstand occasional impact force;
  • ease of installation and removal, available space for installation, and so on.

It should be noted that, though in most single-shot hardening applications flux concentrators will improve efficiency, there are other cases where no improvement will be recorded, or efficiency may even drop. A detailed discussion regarding the subtleties of using magnetic flux concentrators is provided in [See References 1, 2.].

Sufficient rotation is critical when using any single-shot inductor design. As an example, Figure 3 shows the sketch of a single-shot induction hardening system.

Figure 3.  Sketch of single-shot induction hardening of an axle shaft. Note: The right half of this induction system is computer-modeled in Fig. 4 [3].
Figure 3.  Sketch of single-shot induction hardening of an axle shaft. Note: The right half of this induction system is computer-modeled in Fig. 4 [3].
Taking advantage of symmetry, only the right side of such a system was modeled using finite-element analysis. Figure 4 shows the result of computer simulation of initial, interim, and final heating stages, taking into consideration the shaft rotation. Insufficient part rotation resulted in a non-uniform temperature distribution along the shaft perimeter (Figure 4, left). Proper shaft rotation results in a sufficiently uniform temperature pattern (Figure 4, right).

Figure 4.  Results of numerical simulation of heating an axle shaft by using a single-shot inductor [3].
Figure 4.  Results of numerical simulation of heating an axle shaft by using a single-shot inductor [3].
There should be at least eight full rotations per heat cycle (preferably more than 12 rotations), depending on the size of the workpiece and the design specifics of the inductor, though, as always in life, there are some exceptions. Shorter heating times and narrower coil copper heating faces require faster rotation during the austenitization cycle.

An appropriate inductor design with a closely controlled and monitored rotation speed will produce a hardness pattern with minimum circumferential and longitudinal temperature deviations, which will result in sufficiently uniform hardness patterns (Figure 5, left four images). Failure to ensure proper rotation as well as the use of worn centers (lacking grabbing force resulting in slippage and excessive part wobbling) could lead to an unacceptable heat non-uniformity, severe local overheating, and even melting (Figure 5, right). Manufacturers of induction equipment such as Inductoheat have developed various proprietary tools, holders, fixtures, and monitoring devices to ensure proper rotation and high quality of single-shot hardened parts.

Figure 5.  Inductor design with closely controlled rotation speed will produce a hardness pattern with minimum circumferential temperature deviations (left four images). Failure to ensure proper rotation speed as well as the use of worn centers (lacking grabbing force resulting in slippage) could lead to unacceptable heat non-uniformity and can even cause a localized melting (right image).
Figure 5.  Inductor design with closely controlled rotation speed will produce a hardness pattern with minimum circumferential temperature deviations (left four images). Failure to ensure proper rotation speed as well as the use of worn centers (lacking grabbing force resulting in slippage) could lead to unacceptable heat non-uniformity and can even cause a localized melting (right image).

The next installment of this column, "Dr. Valery Rudnev on . . . ", will continue the discussion of design features of induction single-shot hardening systems.

References

  1. V.Rudnev, D.Loveless, R.Cook, Handbook of Induction Heating, 2nd Edition, CRC Press, 2017.
  2. V.Rudnev, "An objective assessment of magnetic flux concentrators", Heat Treating Progress, ASM Intl., December 2004, pp 19-23.
  3. V.Rudnev, "Simulation of Induction Heat Treating", ASM Handbook, Volume 22B, Metals Process Simulation, D.U. Furrer and S.L. Semiatin, editors, ASM Int’l, 2010, pp 501-546.

 

Dr. Valery Rudnev on Equipment Selection for Induction Hardening: Single-Shot Hardening, Part 2 Read More »

Dr. Valery Rudnev on . . . Equipment Selection for Induction Hardening: Single-Shot Hardening, Part 1

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This article continues the ongoing discussion on Equipment Selection for Induction Hardening by Dr. Valery Rudnev, FASM, IFHTSE Fellow. Six previous installments in Dr. Rudnev’s series on equipment selection addressed selected aspects of scan hardening and continuous/progressive hardening systems. This post continues a discussion on equipment selection for induction hardening focusing on single-shot hardening systems.

The first part on equipment selection for continuous and progressive hardening is here. The second part in this series on equipment selection for single-shot hardening is here; the third part is here. To see the earlier articles in the Induction Hardening series at Heat Treat Today as well as other news about Dr. Rudnev, click here. This installment continues a discussion on equipment selection for continuous and progressive hardening applications.

Why Single-Shot Hardening?

With the single-shot method, neither the workpiece (cylinder shaft, for example) nor the coil moves linearly relative to each other; the part typically rotates instead.¹ The entire region that is to be hardened is heated all at once rather than only a short distance, as is done with scan hardening.

With conventional scan hardening of cylindrical parts, induced eddy currents flow circumferentially. In contrast, a single-shot inductor induces eddy currents that primarily flow along the length of the part. An exception to this rule would be the half-moon regions (also called the crossover or bridge sections) of a single-shot inductor, where eddy current flow is circumferential.

Normally the single-shot method is better suited for hardening stepped parts where a relatively short (1.5–2 in. [38–50mm] long heated area is commonly minimum) or moderate length area is to be heat treated. This method is also better suited to cylindrical parts having axial symmetry and complex geometry including various diameters.

When scanning these types of parts, improper austenitization of certain areas may occur due to localized electromagnetic field distortion, for example. Insufficient quenching due to the deflection of quench flow not allowing it to properly impinge on the surface in various diameter regions may also occur. Both factors are considered undesirable and can cause low hardness, spotted hardness, or even cracking. For example, the use of scan hardening on stepped shafts with large shoulders, multiple and sizable diameter changes, and other geometrical irregularities and discontinuities (including fillets, flanges, undercuts, grooves, etc.) may produce severely non-uniform hardened patterns. In cases like this, a scan hardening inductor or progressive/continuous hardening system would be designed around the largest diameter that would have sufficient clearance for safe part processing.¹ However, variations in the shaft’s diameter, to a significant extent, will result in a corresponding substantial deviation in the workpiece-to-coil coupling in different sections of the shaft, potentially causing irregular austenization.

Besides that, sharp corners have a distinct tendency to overheat owing to the buildup of eddy currents, in particular when medium and high frequencies are used. The electromagnetic end and edge effects may also cause the shoulders to severely overheat while the smaller-diameter area near the shoulder (including undercuts and fillets) may have noticeable heat deficit. These factors may produce a hardness pattern that might grossly exceed the required minimum and maximum case depth range, making it unacceptable. Single-shot hardening is usually a better choice in such applications. As an example, Figure 1 shows some examples of components for which single-shot hardening would be a preferable method of heat treating.

Examples of components for which a single-shot hardening would be a preferable method of heat treating. (Courtesy of Inductoheat Inc., an Inductotherm Group company)

 

In some not so frequent cases, when hardening larger parts, there are advantages to the single-shot method over the scanning method, such as the reduction of shape/size distortion, enhanced metallurgical quality, and increased production rate.

Single-shot hardening may also be the preferred choice when shorter heat times/high production rates are desired. For example, in some applications, the time of heating for single-shot hardening can be as short as 2 s, though 4 to 8 s is more typical.

However, the single-shot method has some limitations as well. One of them is cost. Single-shot inductors are typically more expensive to fabricate compared to the coils used for scanning. This is because the single-shot inductor, to some degree, must follow the contour of the entire region required to be heated. Additionally, a single-shot inductor is usually able to harden only one specific part configuration, whereas a coil used for scanning may be able to harden a family of parts.

Besides that, in some case hardening applications using a scanning method, it is possible to apply certain pre-programmed pressure/force on a workpiece during heat treating. This allows distortion to be controlled. Single-shot hardening might also permit applying this technique but there might be some limitations.

Design Features of Single-Shot Inductors

Single-shot inductors are made of tubing, either 3-D printed or CNC-machined from solid copper to conform to the area of the part to be heated. This type of inductor requires the most care in fabrication because it usually has an intricate design and operates at high power densities, and the workpiece’s positioning is critical with respect to the coil copper profiling. Figure 2 shows several examples of induction heating of different components using single-shot inductors.

Several examples of induction heating of different components using single-shot inductors. (Courtesy of Inductoheat Inc., an Inductotherm Group company)

 

In order to provide the required temperature distribution before quenching, heat is sometimes applied in several short bursts (pulse heating) with a timed delay/soaking between them to allow for thermal conduction toward the areas that might be difficult to heat.

Single-shot inductors typically require higher power levels than used in scan hardening because the entire area of the workpiece that needs to be hardened is austenitized at once. This is the reason why single-shot hardening normally requires having a noticeably larger power supply compared to scan hardening, resulting in increased capital cost of power source. Additionally, the increased power usage and power densities combined with complex geometry can reduce the life of the inductor. For this reason, single-shot inductors often have shorter lives than scan inductors.

It is always important to keep in mind that, electrically speaking, the inductor is typically considered the weakest link in an induction system. For this reason, most single-shot inductors have separate coil-cooling and part-quenching circuits. The inductor will fail if power is increased to the point at which the water cannot adequately cool it. Additional cooling passages may be needed with high-power density, single-shot inductors. A high-pressure booster pump is also frequently required.

The next several installments of Dr. Valery Rudnev on . . . will continue the discussion on design features of single-shot inductors and equipment selection.

 

References

  1. Rudnev, D.Loveless, R.Cook, Handbook of Induction Heating, 2nd Edition, CRC Press, 2017.

 

Dr. Valery Rudnev on . . . Equipment Selection for Induction Hardening: Single-Shot Hardening, Part 1 Read More »

Dr. Valery Rudnev on … Equipment Selection for Induction Hardening: Continuous and Progressive Hardening, Part 3

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This article continues the ongoing discussion on Equipment Selection for Induction Hardening by Dr. Valery Rudnev, FASM, IFHTSE Fellow. Dr. Rudnev previously reviewed equipment selection for scan hardening in three parts. The first part on equipment selection for continuous and progressive hardening is here; the second part is here. To see the earlier articles in the Induction Hardening series at Heat Treat Today as well as other news about Dr. Rudnev, click here. This installment continues a discussion on equipment selection for continuous and progressive hardening applications.

Inductor Designs

So far, I have discussed the application of conventionally designed solenoid coils in continuous/progressive hardening applications. However, even multiturn solenoid-type coil geometries may have quite complex shapes accommodating the shape of induction hardened components. One illustration of this is shown in Figure 1 where two in-line multiturn solenoid-type inductors are used for heat treating of an irregular shape component.

Figure 1. Two in-line multiturn solenoid inductor of a complex shape. (Courtesy of Inductoheat Inc., an Inductotherm Group company)
Figure 1. Two in-line multiturn solenoid inductor of a complex shape. (Courtesy of Inductoheat Inc., an Inductotherm Group company)

Besides multiturn solenoid coils, channel-type multiturn inductors (also called slot or skid inductors) are frequently used in continuous/progressive heat treating. The channel inductor gets its name from its similarity to a long channel. This shape allows parts to be passed through the coil in a number of ways, such as a conveyor, shuttle, indexing, rotary or carousel table, turntable, or any other indexing system.

Channel coils permit easy entry and exit of the heated components to/from the inductor. Figure 2 shows images of some examples of multiturn channel inductors. The crossover ends of channel coils are bent away to allow the part to pass through. In some cases, the crossover ends are made high enough to ensure minimum impact on the heating of the part at the ends of the coil, minimizing electromagnetic forces when workpieces enter and exit the inductor. In other cases, the opposite might be true, and crossover coil regions play an important part in providing the needed temperature distribution.

Figure 2. Images of different examples of multiturn channel inductors. (Courtesy of Inductoheat Inc., an Inductotherm Group company.)
Figure 2. Images of different examples of multiturn channel inductors. (Courtesy of Inductoheat Inc., an Inductotherm Group company.)

Channel coils are used to heat treat selected regions of parts, as well as entire components. These inductors are often used for through hardening, annealing, and tempering applications. However, if a specific case depth is required, rotation of the workpiece may be needed to even case depth.

Figure 3 shows a “state-of-the-art” continuous fed induction system for heat treating fasteners [2]. This system is adjustable for a wide range of fastener/bolt diameters and lengths (0.5–4.0 in. [12–102 mm]) and is capable of production rates of up to 600 fasteners per minute. The unique proprietary coil design developed by Radyne Corporation maximizes electrical efficiency and system flexibility while preventing stray heating of electrically conductive surroundings that may potentially cause undesirable heating of structures and malfunction of electronic devices. The rotary dial tooling is designed to accept bolt fasteners from the in-line vibratory feeder. The adjustable speed rotary table contains advanced safety features to prevent damage and meltdown.

The quench assembly allows adjusting the quench flow for the utmost in quench control. After spray quenching, parts are stripped from the traverse assembly and dunk quenched into the tank for final cooling to room temperature.

Figure 3 shows a “state-of-the-art” continuous fed induction system for heat treating fasteners [2].
Figure 3 shows a “state-of-the-art” continuous fed induction system for heat treating fasteners [2].
The tooling is designed with a quick change feature to ensure that all tooling can be changed for a different part size in less than 15 minutes. The system is controlled through a controls package and HMI for part setup and part storage of different programs. Through this HMI, the power source coil “Z” adjustment can also be stored and adjusted for different bolt lengths assuring superior quality fasteners. This unit includes four sizes of tooling required for the rotary heat treat fixture and the traverse tooling: M6, M8, M10, and M12.

Besides solenoid coils and channel inductors, other inductor styles are used including split-return, hairpin and double hairpin inductors, transverse flux, and traveling wave inductors. However, an application of those inductors is not as frequent for continuous/progressive induction hardening.

References

  1. V.Rudnev, D.Loveless, R.Cook, Handbook of Induction Heating, 2nd Edition, CRC Press, 2017.
  2. J.Mortimer, V.Rudnev, Bernhard,A., Induction Heating and Heat Treating of Fasteners, Fastener International, February, 2019, p.50-53.

Dr. Valery Rudnev on … Equipment Selection for Induction Hardening: Continuous and Progressive Hardening, Part 3 Read More »

15 Quick Heat Treat News Items to Keep You Current

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15 Quick Heat Treat News Items to Keep You Current

Heat Treat Today offers News Chatter, a feature highlighting representative moves, transactions, and kudos from around the industry.

Personnel and Company Chatter

  • Thomas Persson recently joined Therma-Tron-X Inc. as their newest HTF (Heat Treat Furnace) sales engineer.
  • Chromalox has announced the opening of its new sales and operations office in Korea.
  • Thomas “Tucker” Hamling II was recently appointed to the position of sales manager with ZIRCAR Refractory Composites, Inc., responsible for domestic technical sales while also providing technical guidance to the company’s customers.
  • A definitive agreement has been reached between Tenaris S.A. and PAO TMK, a Russian company and manufacturer of steel pipe, to acquire 100% of the shares of PAO TMK’s wholly owned U.S. subsidiary IPSCO Tubulars, Inc.
  • Beaumont Machine has relocated to a new larger manufacturing facility, still in the Cincinnati area, to expand the machine line for components for new markets such as semiconductor materials processing and land-based power generation, particularly turbine blades.
  • The American Foundry Society is pleased to welcome Tom Dore as Technical Director. Formerly a vice president at AFS Corporate Member Alu-Bra Foundry, Dore has years of hands-on experience in foundry operations, including plant engineering, heat treating, sand casting, customer quality, and sales.
  • Mike Winkelmann, an industry veteran, has been appointed the new General Manager of the fast-growing Mechanical Services division of Plibrico Company, LLC.
  • Paulo recently announced three leadership changes to the Operations team. Kyle Moore has been promoted to Plant Manager of the St. Louis Division, Tim Mohr has been promoted to Director of Strategic Programs, and Tee Rassieur has been promoted to Vice President Operations.

 Equipment Chatter

  • A Tier 1 automotive manufacturer recently chose Can-Eng Furnaces International Ltd to design and commission a high-capacity, heat-treatment system, providing T-6 and T-7 processing capabilities for lightweight aluminum High Pressure Die Casting (HPDC) automotive components.
  • A medical device manufacturer required an oven to preheat an aluminum mold for a silicone part that was to be filled and cured in the next manufacturing step and contracted with Despatch. The company develops innovative products that improve patient outcomes by enabling minimally invasive surgery.
  • A company that requires the heat treating of automotive parts in baskets recently purchased the No. 1040, a 2200°F (1204°C), inert atmosphere pit furnace, from Grieve Corporation.

Kudos Chatter

  • Dr. Valery Rudnev, FASM IFHTSE Fellow, the Director of Science & Technology at Inductoheat Inc., was recently appointed this year’s speaker at the Woodside Lecture of the Detroit Chapter of ASM. The Woodside Lecture is named for William P. Woodside, the founder of ASM in Detroit (1913). Dr. Rudnev will be discussing “Recent Theoretical and Practical Novelties in Induction Heat Treatment.”
  • Saint-Gobain recently announced that Neha Dave, business manager of Specialty Materials at Saint-Gobain Ceramics & Plastics, has been named a 2019 STEP Ahead Emerging Leader by The Manufacturing Institute. Additionally, the institute is recognizing Silham El Kasmi, operational director for Saint-Gobain Crystals in France, as a 2019 STEP Ahead Award Honoree. Dave and El Kasmi were recently honored during an Awards Dinner Gala in Washington, D.C.
  • The world’s largest wind-turbine blade—351 feet (107 meters) long—has been manufactured by LM Wind Power in Cherbourg, France, as part of a GE Renewable Energy Haliade-X 12-MW offshore turbine. The blade is comprised of multiple thin layers of glass-and-carbon fibers with wood, fused together with resin.
  • In addition, the largest rotary tilting furnace in the world has been manufactured and supplied by GHI Smart Furnaces, in a project subsidized by the Basque Government in which the company has worked together with Befesa and Tecnalia. This is the second time the company has reached a world record.
  • Heat Treat Today is pleased to join in the announcements of growth and achievement throughout the industry by highlighting them here on our News Chatter page. Please send any information you feel may be of interest to manufacturers with in-house heat treat departments especially in the aerospace, automotive, medical, and energy sectors to the editor at editor@heattreattoday.com.

15 Quick Heat Treat News Items to Keep You Current Read More »

Heat Treat Tips: Safety and Cost-Saving Hacks

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During the day-to-day operation of heat treat departments, many habits are formed and procedures followed that sometimes are done simply because that’s the way they’ve always been done. One of the great benefits of having a community of heat treaters is to challenge those habits and look at new ways of doing things. Heat Treat Today‘s 101 Heat Treat Tips, tips and tricks that come from some of the industry’s foremost experts, were initially published in the FNA 2018 Special Print Edition, as a way to make the benefits of that community available to as many people as possible. This special edition is available in a digital format here.

Today we continue an intermittent series of posts drawn from the 101 tips. The tips for this post come from a variety of categories but all generally address safety or cost-saving ideas. 

Dr. Valery Rudnev, FASM, Fellow of IFHTSE, Professor Induction, Director Science & Technology, Inductoheat Inc., An Inductotherm Group company

Heat Treat Tip #2

Avoid axle shaft cracks after induction tempering

Situation: In induction scan hardening of axle shafts, there was NO cracking occurred after scan hardening (case depth varies from 5 mm to 8 mm). Cracks appeared in the spline region after induction tempering.
Solution: Most likely, the cause of this problem is associated with a reversal of residual stress distribution during induction tempering. Reduce coil power for tempering and increase time of induction tempering. Multi-pulse induction tempering applying lower power density might also help. As an alternative, instead of modifying temper cycle, you can also try to reduce quench severity by increasing the temperature of the quenchant and/or its concentration.

Submitted by Dr. Valery Rudnev, FASM, Fellow of IFHTSE, Professor Induction, Director Science & Technology, Inductoheat Inc., An Inductotherm Group company

Heat Treat Tip #4

Closed Loop Water System on Top

When designing a vacuum furnace installation with a closed loop water system, elevate the tank and pump about 9 feet, then cage the space underneath for thermocouple storage, spares, and tools. Saves shop floor space.

Submitted by AeroSPC

IR Cameras are inexpensive and worth the price.

Heat Treat Tip #6

Don’t Be Cheap. Buy an IR Camera.

IR cameras have come way down in price—for a thousand dollars, you can have x-ray vision and see furnace insulation problems before they cause major problems—also a great diagnostic tool for motors, circuit breakers, etc. (And you can spot deer in the dark!)

Submitted by Combustion Innovations

 

 

Heat Treat Tip #7

An Engineer’s Design Checklist

Get an SCR design checklist and avoid mistakes.

When SCRs are involved in the design of a new piece of equipment, questions arise. Control Concepts Inc of Chanhassen, MN, offers a 20-point design checklist to help engineers who don’t specialize in power controllers. Good reading. Search for “design checklist” at the website.

Submitted by Control Concepts, Inc.

Heat Treat Tip #9

Question the Spec! Save Money!

Before you specify a heat treatment, stop and consider your options. Rather than reusing an old specification, ask the design engineer to determine the stress profile, and base the hardness or case depth on real stress data. Is this complicated? Maybe. But especially for carburizing, why pay for more depth than you need, and why take the risk of inadequate strength? The 21st century is here. We have ways to help with the math. Let’s move beyond guess and test engineering methodology.

Submitted by Debbie Aliya

 

 

Heat Treat Tips: Safety and Cost-Saving Hacks Read More »

Dr. Valery Rudnev on . . . Equipment Selection for Induction Hardening: Continuous and Progressive Hardening, Part 2

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This article continues the ongoing discussion on Equipment Selection for Induction Hardening by Dr. Valery Rudnev, FASM, IFHTSE Fellow. Dr. Rudnev previously reviewed equipment selection for scan hardening in three parts. The first part on equipment selection for continuous and progressive hardening is here; the third part is here. To see the earlier articles in the Induction Hardening series at Heat Treat Today as well as other news about Dr. Rudnev, click here. 

Frequency Selection

Depending on the application specifics, continuous and progressive hardening lines may use the same frequency for various in-line coils. In other cases, power levels and frequencies may be different at different heating positions. The presence of three general process stages (described in Part 1) makes a marked impact on a selection of process parameters and the design of an induction system.

When using different frequencies for the various heating stages, the coil design may need to change as well (e.g., a number of coil turns may need to be adjusted for load matching purpose). Just as the eddy current penetration depth in the heated part is affected by the frequency, the current flow in the inductor is affected as well. The wall thickness of the inductor turns (i.e., copper tubing wall) might need to be adjusted to accommodate different frequencies to maximize the coil electrical efficiency.¹

The wall thickness of an inductor’s heating face should be increased as frequency decreases. It is highly desirable for the current-carrying copper wall thickness to be 1.6 times greater than the current penetration depth in the copper (δCu). Increased kilowatt losses in the copper, which are associated with reduced electrical efficiency and greater water-cooling requirements, will occur if the wall is thinner than 1.6∙δCu. In some cases, the copper wall thickness can be noticeably thicker than the recommended value of 1.6∙δCu. This is because it may be mechanically impractical to use a tubing wall thickness of, for example, 0.25 mm (0.01 in.).

As an example, Figure 1 shows a number of continuous in-line multi-coil systems for induction heat treating wire products.²

Several continuous in-line systems for heat treating wire products (Courtesy of Radyne Corp., and Inductotherm Heating & Welding, UK. Both are Inductotherm Group companies.)

There are noticeable benefits of compact induction systems compared to fluidized beds, infrared heaters, and gas furnaces, such as quick response and the ability to provide a rapid change in the process operating parameters to accommodate the required temperature of the wire/cable being processed at speeds up to 5 mps. Frequencies that are in the range of 10 to 800 kHz are commonly applied. A dual-frequency concept can be beneficial to enhance electrical efficiency of while heating different diameters/thicknesses or it can be advantageous for through heating of metallic alloys that exhibit low toughness/high brittleness.

According to the dual-frequency concept, a lower frequency is used during the initial heating stage when the steel is magnetic. In the final heating stage, when the steel becomes nonmagnetic with significantly increased current penetration depth δsteel and becomes substantially more ductile, it is beneficial to use a higher frequency.

Case study¹:

As an example, consider the induction heating of a 1/8 inch-diameter (3.2 mm-diameter) steel rod from ambient to 2000°F (1100°C) using both a single 10-kHz frequency and dual 10-kHz/200-kHz frequencies (see Figure 2). When using the single frequency of 10 kHz (Figure 2, left), the rod’s final temperature experiences very little change regardless of the coil power that is increased more than fivefold (from 17 to 90 kW). The only noticeable difference is related to the initial slope of the temperature-time curve, where the steel is ferromagnetic. Upon reaching the Curie point, there is no noticeable temperature rise. This is the result of severe eddy current cancellation making the steel rod transparent (practically speaking) to the electromagnetic field of the induction coil.

Illustration of the dual-frequency concept when induction heating a 1/8 inch-diameter (3.2 mm-diameter) carbon steel rod from room temperature to 2012°F (1100°C) using both a single frequency of 10 kHz (a) and dual frequencies of 10 kHz/200 kHz (b). (Source: V.Rudnev, Systematic analysis of induction coil failures, Part 11c: Frequency selection, Heat Treating Progress, January/February, ASM Intl., 2008, pp. 27–29.)

In contrast, Figure 2, right, shows that a dual-frequency approach provides a remarkable improvement in the ability to heat the rod above the Curie temperature. A power of 14 kW/10 kHz was used to heat the rod below the Curie point and a power of 19 kW/200 kHz was used above it. The total required power is only 33 kW, compared with 90 kW using just 10 kHz, which was still unable to provide the required temperature rise.

Note: The target temperature of 2000°F (1100°C) is above typical target temperatures when hardening plain carbon or low alloy steels and it is more suitable for hot forming applications. This temperature was selected here to better illustrate a dual-frequency concept and the importance of avoiding eddy current cancellation when choosing operating electrical frequencies. It should be noted though that it is not unusual that the heat treating protocols/recipes for some alloyed steels and stainless steels may require target temperatures of 1900°F to 2100°F (1050°C to 1150°C) range.

In some not too often cases, three frequencies may be used. Lower frequency is applied for preheating inductors, a medium frequency is used for mid-heat inductors, and a high frequency is used for final heat inductors.

Sometimes, it is required that the induction system should be able to heat a variety of sizes using a single frequency. In these cases, in order to provide efficient steel heating, it is necessary to choose a frequency that will guarantee that the “diameter-to-current penetration depth (δsteel)” ratio exceeds 3.6 for any workpiece diameter or heating stage. Thus, it is important to remember that when calculating δsteel, the values of electrical resistivity and relative magnetic permeability of the heated material should correspond to their values at the highest temperature that occurs during the entire heating cycle.

The next installment of this column will review a variety of styles of inductors used in continuous and progressive induction hardening applications.

 

 

References

  1. V.Rudnev, D.Loveless, R.Cook, Handbook of Induction Heating, 2nd Edition, CRC Press, 2017.
  2. J.Mortimer, V.Rudnev, D.Clowes, B.Shaw, “Intricacies of Induction Heating of Wires, Rods, Ropes, and Cables”, Wire Forming, Winter, 2019, p.46-50

Dr. Valery Rudnev, FASM, IFHTSE Fellow, is the Director of Science & Technology, Inductoheat Inc., and a co-author of Handbook of Induction Heating (2nd ed.), along with Don Loveless and Raymond L. Cook. The Handbook of Induction Heating, 2nd ed., is published by CRC Press. For more information click here.

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Dr. Valery Rudnev on . . . Equipment Selection for Induction Hardening: Continuous & Progressive Hardening, Part 1

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This article continues the ongoing discussion on Equipment Selection for Induction Hardening by Dr. Valery Rudnev, FASM, IFHTSE Fellow. Previously, Dr. Rudnev reviewed equipment selection for scan hardening in three parts. This first installment in a new sub-series addresses equipment selection for continuous and progressive hardening. The second part in this series on equipment selection for continuous and progressive hardening is here; the third part is here. To see the earlier articles in the Induction Hardening series at Heat Treat Today as well as other news about Dr. Rudnev, click here. 

Introduction

The hardening of steels, cast irons, and P/M materials represent the most popular application of induction heat treatment. There are four primary methods for induction hardening [1]:

  • Scan hardening,
  • Continuous and progressive hardening,
  • Static hardening, and
  • Single-shot hardening.

These methods are related to the heating mode, essentials of inductor design, part geometry, and processing specifics. The previous three installments of this column, “Dr. Valery Rudnev on …”, discussed select subtleties associated with induction scan hardening. This article is devoted to continuous and progressive induction hardening techniques.

Continuous and Progressive Hardening

This method is commonly applied when heat treating elongated workpieces, such as bars, tubes, rods, wires, plates, beams, pins, and others. Long parts are more readily processed in a horizontal manner and heated as they progressively pass through multiple inductors. Inductors are positioned in-line or side by side. Each inductor may have a different design and power/frequency setting. This type of hardening is not limited to horizontally processed parts; vertical processing and arrangements at certain angles are also possible, if suitable.

There are also cases when a workpiece is statically heated to a certain temperature and then progressively moved to another heating position or static inductor for the next heating stage. These processes are referred to as progressive processing/heat treatment.

Induction practitioners sometimes consider continuous or progressive horizontal hardening systems as horizontal scanners. The difference is vague and it is a matter of terminology. Some heat treaters feel that it would be appropriate to differentiate these systems based on the number of inductors included in the induction machine design. Horizontal systems consisting of a single inductor are commonly referred to as horizontal scanners. In contrast, if a system consists of two or more heat treat inductors, then it might be referred to as a continuous or progressive heat treat system.

With the continuous hardening method, the workpiece is moved in continuous motion through a number of in-line inductors. Multiturn solenoid coils and, to lesser a degree, channel-style inductors and split-return inductors are most typically used in continuous heat treating lines. As an example, Figure 1 shows a side view of a horizontally arranged continuous induction system consisting of three in-line coils. Each coil consists of three turns.

Figure 1

As another example, Figure 2 shows a top view of a continuous heat treating line that comprises four in-line hardening coils and a spray quench device positioned after the last inductor. Workpieces (e.g., bars, shafts, rods, pins, etc.) are processed end-to-end through the inductors in a continuous motion.

Figure 2

Progressive multi-stage hardening is used when multiple workpieces are moved (via a pusher, indexing mechanism, robot, walking beam, etc.) through a number of coils. Therefore, the entire component or its portions are sequentially heated (in a progressive manner) at certain predetermined heating stages inside the in-line horizontal (being more typical) induction heater or a multi-position horizontal or vertical heater where coils are positioned side by side.

Continuous or progressive hardening methods are typically used for through hardening of elongated or moderate-length parts processing end to end and, to a lesser degree, for surface hardening. Outside diameters for case hardening (surface hardening) usually vary from 1/2 in. (12 mm) to 4 in. (100 mm). In through hardening applications of solid cylinders, the diameters may be as small as 1/8 in. (3 mm).

It is possible to recognize three heating stages in through hardening applications [1]:

  1. Initial or magnetic stage,
  2. Interim stage, and
  3. Final heating stage.

Initial or magnetic stage. Temperatures anywhere within the workpiece are below the A2 critical temperature (Curie point); thus, the steel is ferromagnetic and the current penetration depth is typically quite small. Skin effect is fairly pronounced at this stage and the heat source distribution resembles a conventional exponential distribution. The maximum power density is located at the surface and sharply decreases toward subsurface and the core. Heat source generation is localized by the fine surface layer of the workpiece. This leads to a rapid increase in temperature at the surface with a minor change in the core. This stage is characterized by high electrical efficiency often reaching 90% or so.

Interim stage. During this stage, the austenized surface layer and near-surface area is heated above the A2 critical temperature; however, the internal region, having temperatures below the Curie point, retains its ferromagnetic properties. At this stage, the power density distribution along the radius has a unique non-exponential “wave-like” distribution, which is very different from the commonly assumed exponential distribution. The cause for this behavior has been explained in Ref.1.

Final heating stage. The thickness of the austenized surface layer that exhibits nonmagnetic properties becomes greater than the current penetration depth in hot steel at a given frequency, and the “wavelike” distribution disappears. The classical exponential power density distribution will then take place. As expected, heat source generation depth has increased dramatically compared to an initial stage resulting in a more in-depth heating effect. With time, the core temperature exceeds the Curie point and the entire cross section will be nonmagnetic.

In surface hardening applications, there are typically only the first two heating stages.

Depending on the application specifics, the same frequency may be used for various coils or process stages. In other cases, power levels and frequencies may vary at the different heating stages. The presence of above-described process stages makes a marked impact on a selection of process parameters and design of an induction system and will be discussed in the next installment of this column.

References

1. V. Rudnev, D. Loveless, R. Cook, Handbook of Induction Heating, 2nd Edition, CRC Press, 2017.

Dr. Valery Rudnev, FASM, IFHTSE Fellow, is the Director of Science & Technology, Inductoheat Inc., and a co-author of Handbook of Induction Heating (2nd ed.), along with Don Loveless and Raymond L. Cook. The Handbook of Induction Heating, 2nd ed., is published by CRC Press. For more information click here.

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Heat Treat Today Contributor to Present Webinar on Induction Heating Challenges

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Heat Treat Today Technical Tuesday contributor, Dr. Valery Rudnev, FASM, IFHTSE Fellow, “Professor Induction”, and Director of Science and Technology at Inductoheat, Inc, is the featured speaker of an ASM International Materials Solutions webinar titled “Simple Solutions for Common Induction Heating Challenges: Lessons Learned”.

Dr. Rudnev will present this webinar on Thursday, January 24, 2019, 2 pm, and address:

  • Induction hardening of powertrain transmission and engine components
  • Failure analysis
  • How to avoid cracking in induction hardening
  • Subtleties of heating parts with holes, fillets, and other geometrical irregularities
  • Re-hardening (re-austenitization) of previously hardened parts
  • Novel inverters that allow instant and independent adjustment of both frequency and power
  • Selected challenges when applying induction tempering
  • Reducing process sensitivity and improving robustness and flexibility of induction systems.

Note: Attendees will earn a professional development hour for attending the webinar.

This webinar is sponsored by Inductoheat, Inc. For more information and to register, click here.

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Heat Treat Tips: Induction Heating — Stuff You Should Know

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During the day-to-day operation of heat treat departments, many habits are formed and procedures followed that sometimes are done simply because that’s the way they’ve always been done. One of the great benefits of having a community of heat treaters is to challenge those habits and look at new ways of doing things. Heat Treat Today‘s 101 Heat Treat Tips, tips and tricks that come from some of the industry’s foremost experts, were initially published in the FNA 2018 Special Print Edition, as a way to make the benefits of that community available to as many people as possible. This special edition is available in a digital format here.

In today’s Technical Tuesday, we continue an intermittent series of posts drawn from the 101 tips. The category for this post is Induction Heating, and today’s tips–#29, #73, and #83–are from Dr. Valery Rudnev, FASM, Fellow of IFHTSE, “Professor Induction”, Director of Science & Technology at Inductoheat Inc., an Inductotherm Group company. Dr. Rudnev is a regular contributor to Heat Treat Today. 

Heat Treat Tip #29

Induction Heating Non-Ferrous Metals & Alloys

Dr. Valery Rudnev, FASM, Fellow IFHTSE, Professor Induction, Director Science & Technology, Inductoheat Inc., an Inductotherm Group company
Dr. Valery Rudnev, FASM, Fellow IFHTSE, Professor Induction, Director Science & Technology, Inductoheat Inc., an Inductotherm Group company

Steel components by far represent the majority of hot worked and heat-treated parts for which electromagnetic induction is used as a source of heat generation. At the same time, many other non-ferrous metals and alloys are also inductively heated for a number of com­mercial applications. Induction heating of low electrically resistive metals such as Al, Mg, Cu, and others typically require using lower electrical frequencies compared to carbon steels, cast irons, or high resistive non-magnetic metals (such as Ti or W, for example) and metallic alloys. The lower value of electrical resistivity results in smaller current penetration depth (depth of heat source gen­eration), making it possible to apply much lower frequencies without facing the danger of eddy current cancellation.

Heat Treat Tip #73

Induction Hardening Powder Metal

When induction hardening powder metallurgy (P/M) materials, it is good practice to have a minimum density of at least 7.0 g/cm3 (0.25 lb/in.3). This will help obtain consistent induction hardening results. When hardening surfaces that have cuts, shoulders, teeth, holes, splines, slots, sharp corners, and other geometrical discontinuities and stress risers, it is preferable to have a minimum density of 7.2 g/cm3 (0.26 lb/in.3). Low-density P/M parts are prone to cracking due to a penetration of the gases into the subsurface areas of the part through the interconnected pores. Interconnected pores contribute to decreased part strength and rigidity compared with wrought materials. In addition, the poor thermal conductivity of porous P/M parts encourages the development of localized hot spots and excessive thermal gradients and also requires the use of quenchants with intensified cooling rates to obtain the required hardness and case depths. This is so because an increase in pore fraction and a reduction in density negatively affect the hardenability of P/M materials compared to their wrought equivalents.

Heat Treat Tip #83

Induction Hardening Cast Iron

Induction hardening of cast irons has many similarities with hardening of steels; at the same time, there are specific features that should be addressed. Unlike steels, different types of cast irons may have similar chemical composition but substantially different response to induction hardening. In steels, the carbon content is fixed by chemistry and, upon austenitization, cannot exceed this fixed value. In contrast, in cast irons, there is a “reserve” of carbon in the primary (eutectic) graphite particles. The presence of those graphite particles and the ability of carbon to diffuse into the matrix at temperatures of austenite phase can potentially cause the process variability, because it may produce a localized deviation in an amount of carbon dissolved in the austenitic matrix. This could affect the obtained hardness level and pattern upon quenching. Thus, among other factors, the success in induction hardening of cast irons and its repeatability is greatly affected by a potential variation of matrix carbon content in terms of prior microstructure. If, for some reason, cast iron does not respond to induction hardening in an expected way, then one of the first steps in determining the root cause for such behavior is to make sure that the cast iron has not only the proper chemical composition but matrix as well.

 

These tips were submitted by Dr. Valery Rudnev, FASM, Fellow IFHTSE, Professor Induction, Director Science & Technology, Inductoheat Inc, an Inductotherm Group company.

If you have any questions, feel free to contact the expert who submitted the Tip or contact Heat Treat Today directly. If you have a heat treat tip that you’d like to share, please send to the editor, and we’ll put it in the queue for our next Heat Treat Tips issue. 

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