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Magnetic Flux Concentrators [.pdf format]

Systematic analysis of induction coil failures. Part 14: Split-return inductors and butterfly inductors

Author: Valery Rudnev
Publication: Heat Treating Progress, Professor Induction Series
Date: 3/1/2009

The main considerations when choosing an inductor style are the shape of the part, the desired heat-treat pattern, and the material handling to be used for production (i.e., how the part is moved into the coil or the coil indexes into the part, whether rotation of the part is required, or how is the part transferred after heat treatment). Over the years, induction practitioners have established a family of special or specialty inductors. Common names have been coined to describe their appearance or function, such as pancake, channel, hairpin, split-return, and butterfly inductors [1]. This column is devoted to the analysis and prevention of failures of split-return and butterfly-type inductors.

Systematic analysis of induction coil failures. Part 12: Inductors for heating internal surfaces.

Authors: Valery Rudnev
Publication: Heat Treating Process, Professor Induction Series
Date: 7/1/2008

This article is one of series of articles devoted to a systematic scientific/engineering analysis of failures of induction heating coils and prevention. Four of the most typical coil failure modes when induction heating internal surfaces of a workpiece (for example, holes or inside diameters)are discussed here. Induction heating of internal surfaces of a workpiece can be used in such applications as hardening, tempering, annealing, shrink fitting, stress relieving, brazing, and others. Ways to prevent premature coil failures and making robast and long-lasting internal inductors are discussed here as well.

Innovative induction heating of oil country tubular goods

Authors: Peter Ross, Valery Rudnev, Rich Gallik, George Elliott
Publication: Industrial Heating
Date: 5/1/2008

The stress relieve operation is an important step in the manufacture of a quality connection of tubes and pipes. Improper heat treatment could result in several undesirable phenomena from total joint failure to a type of bi-metallic corrosion known as "ring-worm corrosion" that occurs in improperly stress relieved or normalized pipes. Stress relieving is typically done prior to machining of the thread. In order to achieve the best stress relief, the upset end must be uniformly heated along the entire swage length as well as through the entire wall thickness of the pipe. Article discusses novel induction heating technology - FluxManager that provides superior axial and radial temperature uniformity that is imperative for manufacturing quality tubular goods.

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.

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.

An objective assessment of magnetic flux concentrators

Authors: Valery Rudnev
Publication: Heat Treating Progress, Professor Induction Series
Date: 11/1/2004

Magnetic flux concentrators (also called flux intensifiers, diverters, or controllers) are made from high-permeability, low-power-loss materials. They are routinely used in induction heat treating applications in a manner similar to that of magnetic cores in power transformers. This article presents basic information about magnetic flux concentrator materials, its limitations and advantages, and provides design and selection guidelines for their use in induction heat treating.

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