Induction Heat Treatment & Role Of Simulation Software

How simulation software can help companies save time and money on induction coil and process design

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1. Induction Heating

1.1. Induction Heating - Brief History

English scientist Michael Faraday is credited with the discovery of the underlying principles of electromagnetic induction in 1831. The induction heating was applied firstly in the industry for melting metals by Sebastian Z. de Ferranti in 1887. But it was F.A. Kjellin from Sweden, who first presented successful mains frequency induction furnace in 1903. In 1915 the American J.R. Wyatt develops the idea of the vertical channel induction furnace.

An early application was the melting of tiny charges utilizing a device called a spark-gap oscillator. Another early application was the heating of various metallic elements of vacuum tubes in order to drive off the absorbed gases prior to the sealing process. The heating of these elements helped to determine their melting points. The Curie point was also discovered - the Curie point is the temperature at which certain magnetic materials undergo a sharp change in their magnetic properties. The Curie point of steel, for example, is about 760 °C (1400 °F) depending on steel grade.

First high frequency furnace was designed by E.F. Northrup in the Palmer lab at Princeton in 1916. Year later he obtained a patent for determination of the relation between skin depth and frequency for the high frequency induction furnaces. Next biggest push for induction heating was invention of high frequency generators (initially designed for radio applications), by Prof. Valentin P. Vologdin in Russia - he put a first large HF machine generator of 50kW, 20 kHz into operation and used it for induction melting in 1930.

The development of powerful car and aircraft engines gave next impulse for induction heating and specifically induction hardening - methods for partial hardening were not efficient enough, so more accurate methods were required. In 1929 V.P. Vologdin patented and published first results of his experience with the high frequency induction surface hardening - therefore he is considered as an inventor of this process.

Induction heating use and development grew rapidly during the years of World War II. This was because an immediate need arose for manufacturing large quantities of parts with minimal labor and costs involved. Further developments during the WWII showed very clearly the advantages of induction heating, including the very accurately adjustment of heated depth and surface areas. Some of the currently most recognized induction heating companies were founded in U.S. and Europe - “Ajax/TOCCO”, “Elotherm GmbH.” (currently part of SMS Group), “Brown, Boveri & Cie” (current ABB Group) to mention a few.

1.2. Induction Heating - Basics

Induction starts with a coil of conductive material (for example, copper). As alternating current flows through the coil, a magnetic field in and around the coil is produced. The ability of the magnetic field to do work depends on the coil design as well as the amount of current flowing through the coil.

Induction heating is a contactless heating method of bodies, which absorb energy from an alternating magnetic field, generated by induction coil (inductor).

How induction is used to heat metals? Induction heating is an efficient way to quickly heat electrically conductive metals with pinpoint accuracy. Induction generates heat directly in the workpiece by creating eddy currents with alternating electric and magnetic fields in the material that is heated. The depth of penetration depends on the frequency of the alternating current applied on the inductor. As a basic rule, the higher the frequency, the lower the penetration of eddy currents in the material, and the higher is concentration of current within the penetration depth (aka skin layer).

1.3. Induction Heating - Applications

Today induction heating is used in many industrial processes, such as heat treatment in metallurgy, Czochralski crystal growth and zone refining used in the semiconductor industry, and to melt metals which require very high temperatures.

  • Induction heating of bars, billets or slabs for hot forming has been one of the main applications for many years.

  • Induction hardening - offers excellent hardness distribution with minimal deformations.

  • Induction brazing – the joining procedure for high-quality joints of metallic parts.

  • Joining/Separating - joining and separating shrink-fit connections.

  • Preheating - preheating for welding, e.g. gears, oil pipelines.

  • Induction melting/vacuum melting - induction melting is fast and efficient. Vacuum or controlled atmosphere enables processing of reactive metals (Ti, Al), specialty alloys, silicon, graphite, and other sensitive conductive materials.