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.

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