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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 4: Coil copper electromagnetic edge effect.

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

Non-uniform coil current distribution resulting from various electromagnetic phenomena has a dramatic effect on induction coil life and crack development in the coil copper. This article is one of series of articles devoted to a systematic scientific/engineering analysis of failures of induction heating coils and prevention. Article concentrates on coil copper electromagnetic edge effect, effect of frequency and coil copper tubing geometry on current density distribution. Other factors that affect electromagnetic edge effect (i.e., flux concentrators, magnetic flux intensifiers, flux controllers, frequency selection, etc.) are discussed here as well.

Systematic analysis of induction coil failures. Part 3: Coil copper selection.

Authors: Valery Rudnev
Publication: Heat Treating Process, Professor Induction Series
Date: 11/1/2005

In induction heating applications longevity of inductor depends upon several factors, including coil copper selection. This article discusses how different copper grades used for fabrication of induction heating coils affect physical properties, main electrical parameters, copper losses, reliability and longevity of induction heaters. Among other phenomena article discusses copper stress-corrosion cracking, stress-fatigue cracking, galvanic corrosion, and some other important phenomena that have a marked effect on coil failure. Effect of copper residual elements and alloying elements on performance of induction coil is discussed here as well.

Systematic analysis of induction coil failures. Part 2: Effect of coil current flow on crack propagation

Authors: Valery Rudnev
Publication: Heat Treating Process, Professor Induction Series
Date: 9/1/2005

In induction heating applications longevity of inductor or induction coil depends upon several factors, including coil current orientation, frequency, power density and other factors. This article is one of series of articles devoted to a systematic scientific/engineering analysis of failures of induction heating coils and prevention. Several case studies were presented using induction hardening coils as an example.

Systematic analysis of induction coil failures. Part 1: Introduction.

Authors: Valery Rudnev
Publication: Heat Treating Process, Professor Induction Series
Date: 8/1/2005

Article discusses an effect of nonuniform coil current distribution on coil failure mode.

Electromagnetic forces in induction heating

Authors: Valery Rudnev
Publication: Heat Treating Progress, Professor Induction Series
Date: 7/1/2005

Electromagnetic (EM) forces play the major part in many modern technologies. Motors, magneto-hydro-dynamic (MHD) seals, electromagnetic pumps, levitators, electrical bearings, and springs are some of the modern technologies in which EM forces play a leading role. In some applications, EM forces can reach tremendous values. For example, thanks to a capability to develop incredibly large electromagnetic forces, electric guns or launchers can fire materials to higher velocities than are achievable by rockets or chemical/powder guns. In the majority of induction heating applications, coil current also can reach appreciable values. For example, currents of 10 kA and higher are not unusual for many induction heat treating applications including shaft hardening and gear hardening. High currents produce significant forces that have a pronounced effect on coil life. Without proper consideration, those forces can physically move the heated workpiece, flux concentrator, and even bend induction coil, or fixture, which may negatively affect overall system's reliability and repeatability as well as dramatically reduce a coil life. Unfortunately, electromagnetic forces are rarely discussed in induction heating publications. Endless variety of heat treated parts required a specific coil geometry adds a difficulty to study EM forces. This column is intended to at least partially remedy this by providing an introduction to the topic.

Designing inductors for heating internal surfaces

Authors: Valery Rudnev
Publication: Heat Treating Progress, Professor Induction Series
Date: 1/1/2005

Induction heating of the internal surfaces of a workpiece for applications such as hardening, tempering, annealing, shrink fitting, and brazing has several unique features related to the physics of the process and the selection of process parameters, compared with heating of external surfaces. There are four main coil styles for heating internal surfaces: solenoid-type cylindrical coils (single-turn and multiturn), rod-type coils, hairpin inductors (single or double), and "C"-core coils. This article reviews design features of solenoid-type internal coils (also called inside diameter or ID coils), which are the most popular inductors for heating internal surfaces.

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