The Effect of Thread Angle on Loosening by Impact : 1st Report, Theoretical Analysis

Abstract

The purpose of this research is to find out a certain angle of the thread unloosening under repeated impacts. In the last report⁽²⁾, the author described the general theory of fastening and loosening process of screw threads qualitatively. In this report, he induces theoretical formulae by using a three-dimensional analytical geometry to make clear the effect of thread angle on loosening quantitatively. He performed numerical calculations on 10 metric screw threads used popularly by changing their thread angle from 65° to 55° and obtained the following conclusions. (1) When the pitch-diameter ratio is 0.15 (M8, M10, M12, M14), 0.125 (M16, M8×1, M10×1.25) or about 0.1 (M12×1.25, M14×1.5, M16×1.5) and thread angles are 63°, 62.5° or 62° respectively, the strongest fastening action is obtained for each of them. These screw threads are insensitive to angle error. (2) When the thread angle is 60° or 55°, a comparatively strong loosening action is obtained.