Induction heating has been extensively applied to processes like heat treating, brazing and soldering, shrink fitting and more. In such applications, the metal part is electrically conductive and is generally heated directly by induced current when it is placed in the electromagnetic field established by a high frequency current flowing through the induction heating coil. However, metallic and non-metallic parts may also be heated indirectly by the use of a susceptor, heated by induction.
The term ‘susceptor’ as used in induction heating denotes an electrically conductive material placed between the induction heating coil and the work piece. In its simplest form, it may be a metal tube interposed between the coil and the material to be heated. Such a susceptor is readily heated by the electromagnetic field establish by the induction coil, but essentially shields the part within it so that the part is heated primarily by radiation or conduction from the heated susceptor. Use of a susceptor provides an effective means for heating non-conductive materials like ceramics or plastics using an induction heating generator.
Susceptors may be designed to protect against damage to conductive surfaces by inductive heating or to help control the heat pattern obtained. IN such instances, the susceptor cover the portion of the part to be protected, electromagnetically shielding it. If a susceptor does not completely encircle the part, heating will take place simultaneously by direct induction heating as well as by radiation and conduction from the susceptor.
Fundamentally, susceptor heating using an induction heating source is simply radiation and/or conduction heating. However, many features make it highly adaptable. Firstly, the susceptor is heated electromagnetically, permitting heating through quartz, glass, or other non-conducting chambers for atmosphere control. Secondly, a thin susceptor acts as a radiation source that can be rapidly heated and cooled if desired, creating a heat source that can change temperature very rapidly. The susceptor may be of any size and highly localized in placement for shielding or use as an integral susceptor. In parts with complex geometry, a susceptor improves the uniformity of heating, as compared to direct induction heating. Susceptors allow for very thin materials such as steel strips or wired to be heated to elevated temperatures using nominal frequencies.
The use of susceptors in induction heating applications is extensive. Susceptors make induction heating applicable for heating all non-metallic and metallic materials, allowing induction heating to become an important tool in the electronics, glass, plastics, and rubber industries.