Magnetic Flux Controllers in Induction Heating and Melting
MAGNETIC FLUX CONTROLLERS are materials other than the copper coil that are used in induction systems to alter the flow of the magnetic field. Magnetic flux controllers used in power supplying components are not considered in this article. Magnetic flux controllers have been in existence since the development of the induction technique. Michael Faraday used two coils of wire wrapped around an iron core in his experiments that led to Faraday’s law of electromagnetic induction, which states that the electromotive force (emf) induced in a circuit is directly proportional to the time rate of change of the magnetic flux through the circuit. After the development of the induction principle, magnetic flux controllers, in the formof stacks of laminated steel, found widespread use in the development of transformers for more efficient transmission of energy (Ref 1, 2). Magnetic cores gained widespread use in the transformer industry because they increased the amount of magnetic flux produced with the same alternating current. The higher the magnetic flux, the higher the emf, which results in an increase in energy transfer efficiency from the primary winding to the secondary winding. Similar to transformers, magnetic cores were used on early furnaces for induction melting (Ref 1, 2). The benefits of magnetic flux controllers vary depending on the application. For induction heating, magnetic flux controllers can provide favorable and unfavorable paths for magnetic flux to flow, resulting in increased heating in desired areas and reduced the heating in undesirable areas, respectively. Magnetic flux controllers are not used in every induction heating application, but their use has increased (Ref 3, 4).
Design Principles for Induction Heating and Hardening
The induction technique has been around for almost 100 years, but only now have all of the pieces in place reached their full potential. Induction heating (IH) established itself as one of the key manufacturing technologies, especially in the automotive, metal production, forging, tube welding, and other metal processing industries. The current growth of induction heating includes the medical, food, chemical, electronics, and agricultural industries, to name a few. The first industrial applications of induction heating were for melting and were developed in the United States near the dawn of the 20th century. Induction heating then became the method of choice for new metal melting installations. However, it was not until the mid-1930s that the first induction heat treating process was developed. Nearly simultaneously, TOCCO USA and Russia developed commercial processes for the induction hardening of crankshaft pins and journals. This very successful development helped to spur a new age of induction heating, and a great number of new heating and heat treating applications emerged throughout the world. Despite the complicated mathematical description of induction heating, intensive efforts yielded the development of the theory and methods for the calculation of induction heating devices. The first profound technical book on induction heat treating, titled Surface Hardening by Induction Method [1], was published in 1939 in Russia. Shortly after, several other books on the theory and application of induction heating were published in the United States and Russia [2–5]. These publications described the physical effects in induction systems and provided design guidelines for heating time, power, and frequency selection for typical applications, including mass heating, melting, and hardening (gears and other parts). They established a good basis for increased penetration of the induction technique into different industries such as automotive, military, railway transport, metallurgy, and some others. Many new revolutionary processes appeared in the 1950s including crystal growth and induction tube welding. A long period of technology evolution followed the initial pioneering period [5–12]. At the end of the 20th century, a new period of rapid expansion emerged due to the following four factors:
Physical Metallurgy Handbook
Chapter 1: Iron-Carbon Alloys Chapter 2: Diffusion in Metals and Alloys Chapter 3: Solidification Chapter 4: Plastic Deformation Chapter 5: Recovery, Recrystallizaiton, and Grain Growth Chapter 6: Nucleation in Solids Chapter 7: Pearlite and Proeutectoid Phases Chapter 8: Martensite Chapter 9: Bainite Chapter 10: Austenite Chapter 11: Isothermal and Continuous Cooling Transformation Diagrams Chapter 12: Basic Heat Treatment Chapter 13: Hardening and Hardenability Chapter 14: Tempering Chapter 15: Thermomechanical Treatment Chapter 16: Surface Hardening Treatments Chapter 17: Defects and Distortion in Heat-Treated Parts Chapter 18: Surface Modification and Thin-Film Deposition Chapter 19: Thermal Spray Coatings Appendix A: Conversion Table for Units, Constraints, and Factors in Common Use Appendix B: Temperature Conversions INDEX