In induction heating, an alternating current (AC) source is used to supply current to an induction heating coil. As a result, the coil generates an alternating magnetic field. When an object is placed in this field, two heating effects occur:
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Both effects result in the heating of the treated object, but the second one is most commonly the main heat source in IH processes. Moreover, hysteresis is not observed in non-magnetic materials, and magnetic materials lose their magnetic specificities if heated above a specific temperature (the so-called Curie point).
Eddy currents also depend on the magnetic field frequency due to the skin effect – at high frequencies, the currents flow close to the conductor surface. This specificity is used to control the penetration depth of the induction heating process. As a result, either the whole object or only a specific part of it (only the surface, for example) can be heated. Thus, induction heating can be used for different applications – from metal melting to brazing and surface hardening.
Induction heating was first discovered by Michael Faraday as he studied the induction of currents in wires by a magnet. The fundamental principles of induction heating were later established and developed by James C. Maxwell in his unified theory of electromagnetism. James P. Joule was the first to describe the heating effect of a current flowing through a conductive material.
In , Sebastian Z. de Ferranti proposed induction heating for metal melting and filed the first patent on the industrial applications of induction heating. The first fully-functional induction furnace was presented in by F. A. Kjellin, and the first high-frequency furnace application of induction heating was implemented by Edwin F. Northrup in .
During the Second World War and afterward, the use of induction heating technology was boosted by the aircraft and automotive industries. Induction heating was not only used for metal melting but also for advanced material treatment, which significantly increased the range of induction heating applications.
The development of solid-state generators using new power semiconductor technologies provided the potential for IH beyond the industrial environment. Since the late s, different domestic applications have appeared. In recent years, a particular interest in induction heating for medical treatments has emerged, as this method provides precise and targeted local heating.
Today, induction heating technology provides highly efficient and reliable systems for a wide variety of applications.
What's is Induction Heating?
Induction heating is a process for heating metals and other electrically conductive materials that is precise, repeatable and a safe non-contact method. It involves a complex combination of electromagnetic energy and heat transfer that passes through an induction coil, creating an electromagnetic field within the coil to metal down materials. Materials such as Steel, Copper, Brass, Graphite, Gold, Silver, Aluminum, & Carbide can be heated for a range of applications, which include various heat-treating applications such as hardening, annealing, tempering, brazing, soldering, shrink fitting, heat staking,bonding, curing, melting and many more.
How Does Induction heating work?
The induction phenomenon has two important consequences:
Induced force: Where a permanent magnet is dropped into a copper tube. The induced force according to Faraday’s law tries to stop the magnet’s motion inside the tube.
Induced heat. When an electrically conductive material is exposed to an alternating magnetic field, depending on the material, heat is induced by two mechanisms: Joule Heating and Magnetic Hysteresis. The latter occurs in the magnetic metals (such as Carbon Steel below Curie temperature) in which the rotation of the adjacent magnetic dipoles due to the direction change of the imposed magnetic field will lead into friction and heat. This effect increases by increasing the frequency of the imposed magnetic field.
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What are the main components of induction heating?
A typical induction heater system includes a power supply, impedance matching circuit, tank circuit, and applicator. The applicator which is the induction coil can be a part of the tank circuit. A tank circuit is usually a parallel set of capacitors and inductors. The capacitor and inductor in the tank circuit are reservoirs of electrostatic energy and electromagnetic energy, respectively. At the resonance frequency, the capacitor and the inductor start to swing their stored energy to each other. In the parallel configuration, this energy conversion occurs at high current. The high current through the coil helps to have a good energy transfer from the induction coil to the workpiece.
What Is Operating Frequency?
Induction heating systems rely on operating frequency to determine heat generation and depth of penetration. Higher frequencies provide less heat with shallower penetration, while lower frequencies generate more heat and deeper penetration. The ideal frequency is based on material and desired heating rate.
Does Induction Heat Magnetic Materials?
Induction heating takes place in an electrically conducting object (not necessarily magnetic steel) when the object is placed in a varying magnetic field. Induction heating is due to the hysteresis and eddy-current losses. Hysteresis losses only occur in magnetic materials such as steel, nickel, and very few others.
Advantages of Induction Heating
Induction heating is particularly useful where highly repetitive operations are performed. Once an induction heating machine is properly adjusted, part after part is heated with identical results. The ability of induction heating to heat successive parts identically means that the process is adaptable to completely automatic operation, where the workpieces are loaded and unloaded mechanically.
Induction heating has made it possible to locate operations, such as hardening, in production lines along with other machine tools instead of in remote, separate departments. This saves the time of transporting the parts from one part of the factory to another. Induction heating is clean. It does not throw off unpleasant heat. Working conditions around induction heating machines are good. They do not give off the smoke and dirt which are sometimes associated with heat-treating departments and forge shops.
Another desirable characteristic of induction heating is its ability to heat only a small portion of a workpiece, offering advantages where it is unnecessary to heat the whole part. This advantage is critical in essential parts with a few localized high-wear areas during normal operation. Previously, a higher quality, more expensive material would be required to withstand the wear of operation. With induction, less expensive materials can be locally processed to achieve the durability required.
Induction heating is fast. A properly tuned induction heating machine can process high part volumes per minute by utilizing efficient coil design and part handling. Since induction heating machines are well suited to automation, they can easily integrate with existing part production lines. Unlike radiant heating solutions, induction heating heats only the part inside the coil without wasting energy on unnecessary heating.
Induction heating is clean. Without flame operations that leave soot or otherwise require cleaning after heating, induction is a choice for parts that require clean heating, such as in brazing operations. Because induction heating utilizes magnetic fields that are permeable through glass or other materials, controlled atmosphere heating through induction is a possibility.
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