INDUCTION HARDENING METHOD AND SEMI-OPEN TYPE INDUCTION HEATING COIL

PROBLEM TO BE SOLVED: To provide an induction hardening method capable of uniformly hardening a barrel-shaped work piece having a hole provided in the center.SOLUTION: A support member 73 dispersedly supports an end part 55b in the axial direction of a work piece 40, and a pressing member 69 dispersedly supports an inner peripheral surface 40b. An external surface induction heating coil 1 is close to an outer peripheral surface 40a of the work piece 40, and an internal surface induction heating coil 61 is arranged in an open hole 56 of the work piece 40. The external surface induction heating coil 1 has a plurality of circumferential direction lines 20a etc., including many circumferential direction components A1 around a rotating axis 41 of the work piece 40. The length of each of the circumferential direction lines 20a etc., is longer as it is faced on the central portion side in the axial direction of the work piece 40. A central interval between adjacent circumferential direction lines on the central portion side is narrower than that between adjacent circumferential direction lines on the end portion side. When the work piece 40 is rotated and electricity is conducted to heating coils 1 and 61, the outer peripheral surface 40a and the inner peripheral surface 40b are approximately, uniformly induction-heated.