Designing quench systems for induction hardening: Part 2; The success of the of induction hardening is closely related to using an optimal quench process, which depends on design considerations including quenchant cooling rate remediation mechanisms, material effects, and spray and immersion quench systems.(Induction Heat Treating)

Induction hardening is accomplished by the use of a suitable quenchant, which provides the required cooling rate to achieve the desired hardness. The selection of a specific quenchant depends on such factors as material, shape, crack-sensitivity and hardness pattern. The basic elements of the quench process were discussed in Part 1 of this article (see November 2005 IH). This article discusses the factors to be considered in designing a quench system.

Induction heating process

Two primary ways to apply heat inductively to a component are single-shot (static) and progressive scanning (shooting). In progressive scanning, the part is progressively moved through the inductor during the heating process versus static heating with single-shot. Typically, the component is rotated during heating and quenching cycle in both processes. Recently developed non-rotating systems are not discussed here [1].

It is important to understand the induction heating system design because it impacts quenching system design. Induction quenching systems are classified as direct or separate [2]. In a direct system, it is possible to heat and cool concurrently. The quenching system is built into the inductor by constructing a spray quench ring with quench holes facing the rotating part placed around a multiturn coil. The quench ring may be concentric with (Fig. 1), below or beside the coil [3,4]. Figure 2 illustrates cross section of a single turn scan coil to show the quench and coil cooling chambers. This system is often preferred for in-line production processes. In a separate system, the component is quenched into an agitated bath containing the desired quenchant, which is not an integral part of the induction heating system. Other coil and quench ring arrangements are summarized in Fig. 3 [4,5].

Material considerations

Several important material effects must be taken into consideration in the design of an induction heat treating system including part size and shape, whether through or surface hardening is performed, whether single-shot or scanning heating and hardenability [4].

Part size and geometry. Complex shaped parts containing holes, sharp corners, grooves, undercuts and diameter changes may lead to cracking and hardness distribution problems [6, 7]. In addition, cooling rate …