PURPOSE: To prevent the shape precision of balls from being deteriorated with elapse of time, so as to decrease the degree of deterioration of acoustic property of a ball bearing in which the ball are incorporated with elapse of time by specifying the surface treatment process of the balls.
CONSTITUTION: When balls 8, 8 of ball bearings 3, 3 are manufactured, the tempering treatment is performed under the conditions of the specific temperature after the surface treatment. First, the normal hardening treatment is applied on the front surfaces of the balls 8, 8 processed into a secific shape. In this hardening treatment, the balls are left in a heating furnace having the temperature 860°C for ten minutes and then immersed in cooling oil having the temperature 60°C±5°C for ten minutes. Next, the pre-tempering treatment is applied on the balls at 125°C for 120 minutes, and the balls are bumped against a plate after applying rough grinding to the balls, thereby a method for hardening the front surfaces of the balls is performed. Then, after the front surface hardening treatment, the tempering treatment is performed at 125°C for 120 minutes, and then the finish grinding is performed, so as to complete the balls for the ball bearing.
HIRAKAWA KIYOSHI
HIWATARI MICHIHARU
