Research on the mechanism of magnetic flux concentrator in the gap-to-gap induction heating of wind power gear

Gear quality is one of the factors that determine the stability of the wind turbine. Electromagnetic heating is a green and efficient heating method, which has been used to heat wind power gears. Good mechanical properties could be obtained by induction hardening on the surface of wind power gears. And a uniform hardened layer along the tooth profile is needed. In this paper, research on the effect of the Magnetic Flux Concentrator (MFC) in gap-to-gap induction heating of wind power gear was carried out. The study and the experimental tests refer to the heat treatment of an inner gear ring of a wind turbine transmission of modulus m = 16 at frequency 6000 Hz. The calculated hardened depth is 3 mm inward from the side of the tooth profile, and reaches 2 mm at root of the tooth. The mechanism of the concentrator, and the relationship between MFC characteristics and the heating results are explored. The study found the heating time and quality could be significantly affected by the geometrical dimensions thickness "t", height "h" and material of the MFC. The Magnetocaloric Capacity "Mc" was proposed to describe the ability of the MFC to influence the heating process. The characteristics of the magnetic flux concentrator that affect the heating quality and efficiency are discussed. Meanwhile, this study found that the heating efficiency is related to the strength of the magnetic field in the MFC and the distribution of magnetic field lines. By adjusting t, h and the materials, the heating efficiency and quality could be significantly changed. The maximum temperature difference along the tooth contour was changed to 39.6%, and the average temperature was changed to 6%. When the relative permeability of the material is matched with the frequency, a better heating quality and higher speed could be obtained. The research provides a theoretical support for the precise control of the gap-by-gap induction heating of wind power gear, especially for quality control by the MFC.