Susceptor heating by Induction has been extensively applied to processes where the material to be heated is not electrically conductive or not easily heated evenly with induction heating. Both metallic and non-metallic parts may be heated indirectly with the use of a susceptor, heated by induction. Susceptors may be in contact with or separated from the part or material to be heated. When in contact heating is via conduction, when separated heating is by radiation.
The term ‘susceptor’ as used in induction heating denotes an electrically conductive material placed between the induction heating coil and the material to be heated such as a workpiece, either a solid, a slurry, a liquid, a gas, or some combination of the foregoing. In its simplest form, an Induction Susceptor Heater 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 established by the induction coil so that the part is heated primarily by radiation or conduction from the heated susceptor. The use of a susceptor provides an effective means for heating non-conductive materials like ceramics, glass, plastics, semiconductors, organic and non-organic chemicals, foods, and beverages. Induction susceptor heating provides control precision, efficiency, rapid ramp-up, and reliability benefits.
Susceptors may be designed and employed to protect/shield areas of a part that should not be subjected to an induction field. This to control the heat pattern obtained. In some cases, these are referred to as diverters or shields. In such instances, the susceptor covers the portion of the part electromagnetically shielding it. If a susceptor does not completely encircle the part, heating will take place simultaneously by direct induction heating in the unshielded zones as well as by radiation and conduction from the susceptor. In many cases shielding susceptors are constructed of water-cooled copper where the shielded zones of the part are not to be heated at all.
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 magnetically transparent chambers for atmosphere containment and control. Secondly, a thin susceptor acts as a radiation source that can be rapidly heated and cooled if desired. Induction heating the susceptor allows for higher reliability since the high-temperature susceptor does not have to be connected to a high current conductor to impart the energy required for heating. The susceptor may be of any size. 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 wires to be heated to elevated temperatures using more economical low and medium magnetic field frequencies. When considering a susceptor heating design there are a number of factors that go into selecting the appropriate susceptor material, these include reactivity with the environment that the susceptor is in contact with. Choosing the right material leads to a reliable system, choosing the wrong materials can lead to contamination and low-reliability performance.
Induction Susceptor heating has become an important tool in the production of Foods and Beverages, Chemicals, Electronics, Glass, Plastics, Rubber, Construction, Consumer Medical, and industrial products.
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