Method and apparatus for shaft diameter enlargement

Abstract

To radially enlarge an intermediate portion of a shaft, the shaft is held by a pair of holders with a gap between the pair of holders in an axial direction of the shaft, compression force is applied in the axial direction to the intermediate portion arranged between the pair of holders, and alternating load is applied in a direction intersecting the axial direction to the intermediate portion to enlarge the intermediate portion. When enlarging the intermediate portion, a temperature of the intermediate portion is set to be above a blue brittleness temperature range of the shaft, and a temperature of the holders is set to be below a tempering temperature range of the holders.

1 . A shaft diameter enlarging method for enlarging an intermediate portion of a shaft, the shaft diameter enlarging method comprising:
 holding the shaft by a pair of holders with a gap between the pair of holders in an axial direction of the shaft;   applying compression force in the axial direction to the intermediate portion arranged between the pair of holders; and   applying alternating load in a direction intersecting the axial direction to the intermediate portion to enlarge the intermediate portion,   wherein, when enlarging the intermediate portion, a temperature of the intermediate portion is set to be above a blue brittleness temperature range of the shaft, and a temperature of the holders is set to be below a tempering temperature range of the holders.   
     
     
         2 . The shaft diameter enlarging method according to  claim 1 , wherein, when enlarging the intermediate portion, the temperature of the intermediate portion is set to be equal to or above 400° C., and the temperature of the holder is set to be below 580° C. 
     
     
         3 . The shaft diameter enlarging method according to  claim 1 , wherein, when enlarging the intermediate portion, the temperature of the intermediate portion is set to be in a range of 400° C. to 700° C. 
     
     
         4 . The shaft diameter enlarging method according to  claim 1 , wherein, when enlarging the intermediate portion, the temperature of the intermediate portion is set to be above the blue brittleness temperature range of the shaft and below the tempering temperature range of the holders. 
     
     
         5 . The shaft diameter enlarging method according to  claim 1 , further comprising heating at least a portion of the shaft including the intermediate portion before the enlarging of the intermediate portion. 
     
     
         6 . The shaft diameter enlarging method according to  claim 1 , further comprising heating the intermediate portion during the enlarging of the intermediate portion. 
     
     
         7 . A shaft diameter enlarging apparatus comprising:
 a pair of holders configured to hold a shaft with a gap between the pair of holders in an axial direction of the shaft;   a presser configured to apply compression force in the axial direction to the intermediate portion arranged between the pair of holders;   an alternating load generator configured to apply alternating load in a direction intersecting the axial direction to the intermediate portion to enlarge the intermediate portion; and   a heating device configured to heat at least a portion of the shaft such that, during a period in which the compression force and the alternating load are applied to the intermediate portion of the shaft, a temperature of the intermediate portion is above a blue brittleness temperature range of the shaft, and a temperature of the pair of holders holding the shaft is below a tempering temperature range of the holders.