Optimizing study of SLBs for higher anti-loosening performance

The authors had earlier proposed the concept of an SLB (step–lock–bolt), which has some steps on the lead helix, with an objective of developing an anti-loosening screw fastener. The SLB produced had eight steps in a pitch and 45% flat part in which the lead angle is nil. It was found that the SLB does not easily loosen when it was fastened with a clamping force of 16±4 kN, because it suppresses the bolt torsion which is one of the causes of loosening. In this paper, a newly produced SLB, which has 10 steps and 50% flat part, is reported. The aim of developing this screw fastener is to prevent loosening even when a high clamping force cannot be applied, which is the case when wooden or rubber plates are fastened. The importance of the number of steps in a pitch and the ratio of the flat part in the anti-loosening performance of the SLB are discussed. The matching of the hardness of bolt and nut for preventing loosening is also discussed. The contact state between the bolt screw thread and nut is investigated carefully. As a result, the newly produced SLB prevents loosening even when the applied clamping force is 4 kN. The higher ratio of the flat part makes the SLB exhibit better performance.