Study on Fatigue Life of Ball Screw (2nd Report)

Fatigue Life and Growing Characteristics of Fatigue Failure of Preloaded Ball Screw with Double Nut

Abstract

Fatigue life characteristics of ball screw with a single nut was discussed in the first report. The present report deals with the experimental results on the fatigue life of preloaded ball screw with a double nut, the relationship between the fatigue life and preload, and the dependency of friction torque with the growth of fatigue failure. The main results are as follows : (1) The dispersion in the fatigue life of preloaded ball screw with a double nut is fairly small same as that of ball screw with a sigle nut. (2) The mean value of Weibull slope e is 6.5 from the life tests of 75 ball screws in the 1st and 2nd reports. (3) Growth of the initial fatigue failure in ball screw is fairly slow because ball screws have large number of active balls compared with ball bearings. (4) Ball screw is maintained at a mechanical efficiency above 90%, until the ball screw revolutions exceed about 2.4 times the initial fatigue life. (5) The exponent p in the life formula L=(C/F)^p for ball screws is 3 same as ball bearings.