Heat treatment method for ring-shaped member and heat treatment equipment for ring-shaped member

Abstract

In a heating step (S 1 ) of inductively heating a steel outer ring (OR) to a target temperature, a plurality of outer rings (OR) retained coaxially by a retaining unit ( 3 ) are caused to sequentially pass through an opposing region of a pre-heating coil ( 22 ) having a variable output, and through an opposing region of a heating coil ( 21 ) having a constant output and being arranged coaxially with the pre-heating coil ( 22 ) on an exit side of the pre-heating coil ( 22 ). Thus, the plurality of outer rings (OR) are sequentially and inductively heated to the target temperature.

1 . A heat treatment method for a ring-shaped member, comprising a heating step of inductively heating a steel ring-shaped member to a target temperature,
 the heating step comprising causing a plurality of the steel ring-shaped members, which are retained coaxially by a retaining unit, to sequentially pass through an opposing region of a pre-heating coil having a variable output, and through an opposing region of a heating coil having a constant output and being arranged coaxially with the pre-heating coil on an exit side of the pre-heating coil, to thereby sequentially and inductively heat the plurality of the steel ring-shaped members to the target temperature.   
     
     
         2 . The heat treatment method for a ring-shaped member according to  claim 1 ,
 wherein the heating step comprises:
 an output increasing step of increasing the output of the pre-heating coil in a stepped manner; and 
 an output decreasing step of decreasing the output of the pre-heating coil in a stepped manner, and 
   wherein an output increase pattern of the pre-heating coil in the output increasing step and an output decrease pattern of the pre-heating coil in the output decreasing step are different from each other.   
     
     
         3 . The heat treatment method for a ring-shaped member according to  claim 1 , wherein the output of the pre-heating coil is varied in accordance with a relative position of the retaining unit with respect to the heating coil. 
     
     
         4 . The heat treatment method for a ring-shaped member according to  claim 2 , wherein, of the output increasing step and the output decreasing step, at least in the output increasing step, the output of the pre-heating coil is varied in accordance with a number of the steel ring-shaped members present in the opposing region of the heating coil. 
     
     
         5 . The heat treatment method for a ring-shaped member according to  claim 1 , wherein the heating coil and the pre-heating coil are electrically connected to separate high-frequency power sources, respectively. 
     
     
         6 . The heat treatment method for a ring-shaped member according to  claim 1 , further comprising a cooling step of cooling the steel ring-shaped member inductively heated to the target temperature. 
     
     
         7 . The heat treatment method for a ring-shaped member according to  claim 1 , wherein the steel ring-shaped member comprises a raceway ring of a rolling bearing made of a steel material having a carbon content of 0.8 mass % or more. 
     
     
         8 . A heat treatment apparatus for a ring-shaped member, comprising:
 a heating unit configured to inductively heat a steel ring-shaped member to a target temperature;   a retaining unit configured to retain a plurality of the steel ring-shaped members thereon under a state in which the plurality of the steel ring-shaped members are aligned in an axial direction of each of the plurality of the steel ring-shaped members; and   a driver configured to move the retaining unit in the axial direction relatively to the heating unit,   the heating unit comprising:
 a pre-heating coil having a variable output; and 
 a heating coil having a constant output and being arranged coaxially with the pre-heating coil on an exit side of the pre-heating coil, 
   the driver being configured to move the retaining unit in the axial direction relatively to the heating unit so as to cause the plurality of the steel ring-shaped members, which are retained by the retaining unit to be aligned in the axial direction, to sequentially pass through an opposing region of the pre-heating coil and an opposing region of the heating coil.