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Design and Fabrication of Long-Lasting Inductors. Prevention of Coil Failures.
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Systematic analysis of induction coil failures. Part 10: Contactless inductors.

Authors: Valery Rudnev
Publication: Heat Treating Process, Professor Induction Series
Date: 3/1/2007

This article is one of series of articles devoted to a systematic scientific/engineering analysis of failures of induction heating coils and prevention. The previous entry in this series discussed split or clamshell inductors used for hardening irregular shapes that do not allow an inductor to encircle the part. At the same time, in other applications such as strip or plate heat treating and coating (galvanizing, galvannealing, galvaluming, nonmetallic coating, and paint drying, for example), the ability to move the induction coil from the heating position to an off-line position is considered an important system requirement. Solenoid induction heaters with water-cooled "doors" are sometime used for such applications. Article discusses patented doorless induction coils that allow increasing coil life and eliminating the maintenance problems associated with high-frequency current interrupting a doored inductor.

Systematic analysis of induction coil failures. Part 9: Clamshell inductors.

Authors: Valery Rudnev
Publication: Heat Treating Process, Professor Induction Series
Date: 1/1/2007

This article is one of series of articles devoted to a systematic scientific/engineering analysis of failures of induction heating coils and prevention. When hardening irregularly shaped components, adjoining areas may sometimes exclude the possibility of positioning the component inside a cylindrical coil. In other cases, the required "coil-to-part" air gap that would provide enough clearance for loading and unloading the workpiece is so large that it dramatically reduces electrical efficiency of induction coil or may even prevent obtaining required hardened patterns. An example is the hardening of camshaft lobes that have a sharp "nose" and undersized "base circle" in combination with large bearings or eccentric journals. In cases such as this, split or clamshell inductors sometimes provide a solution. Article discusses advantages and drawbacks of split or clamshell inductors for induction heating irregular-shaped parts, as well as its failure modes.

Systematic analysis of induction coil failures. Part 8: "Gap-by-gap" gear hardening coils.

Authors: Valery Rudnev
Publication: Heat Treating Process, Professor Induction Series
Date: 11/1/2006

This article is one of series of articles devoted to a systematic scientific/engineering analysis of failures of induction heating coils and prevention. Gears are induction hardened by either encircling the part with a coil (so-called spin hardening) or, for larger gears, hardening them "tooth-by-tooth" or "gap-by-gap." Article concentrates on analyzing main coil failure modes of "gap-by-gap" inductors for hardening large and medium size gears. Several case studies are discussed including degradation of laminations, copper overheating, distortion, arcing, coil abuse and improper handling.

Systematic analysis of induction coil failures. Part 7: Fabrication of hardening inductors.

Authors: Valery Rudnev
Publication: Heat Treating Process, Professor Induction Series
Date: 9/15/2006

This article is one of series of articles devoted to a systematic scientific/engineering analysis of failures of induction heating coils and prevention. Intricacies of fabrication of long-lasting coils for induction heating and heat treating applications will be discussed here. Helpful hints are shared here for designing variety of hardening inductors.

Systematic analysis of induction coil failures. Part 6: Coil end effect.

Authors: Valery Rudnev
Publication: Heat Treating Process, Professor Induction Series
Date: 5/1/2006

This article is one of series of articles devoted to a systematic scientific/engineering analysis of failures of induction heating coils and prevention. Non-uniform coil current density distribution resulting from various electromagnetic phenomena has a dramatic effect on induction heating coil life and crack development in the copper. Coil electromagnetic end effect and copper electromagnetic edge effect are critical factors that should be taken into account when designing "long-lasting" induction coils. The coil copper edge effect that is primarily responsible for copper edge cracking was discussed in Part 4 of this series. This column concentrates on the other important electromagnetic phenomenon: the coil end effect, magnetic forces, current density distribution, and distortion of electromagnetic field inside induction coil.

Systematic analysis of induction coil failures. Part 5: Effect of flux concentrator on coil life.

Authors: Valery Rudnev
Publication: Heat Treating Process, Professor Induction Series
Date: 3/1/2006

This article is one of series of articles devoted to a systematic scientific/engineering analysis of failures of induction heating coils and prevention. Magnetic flux concentrators (also called flux intensifiers, diverters, or flux controllers) are made from high permeability, low-power-loss materials. They are used in induction heat treating applications in a manner similar to that of magnetic cores in power transformers. Article concentrates on effect of magnetic flux concentrators on life of induction coils.

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