A Study on Anti-Loosening Characteristics of Different 3/8 BSW Threaded Fasteners

A significant advantage of the threaded fastener is its capability of being dismantled using simple tools. However, threaded fasteners have an inherent and inevitable limitation that they loosen eventually under vibrating environment. The loosening of screw fasteners is caused by two factors mainly. One is the relative slip between the bolt and nut screw threads, and the other is the relative slip between the nut or bolt surface and the surface of the fastened material. In the present work, the antiloosening ability of various 3/8 BSW locking screw fasteners with nylock nut, flat washer, nylon washer, serrated washer and spring washer are tested under accelerated vibrating conditions. The experiment has been carried out in an indigenously made testing machine. The initial clamping force given has been around 0.82 ton. Under vibrating condition, the loss of tightening force has been measured at regular intervals to adjudge the loosening of threaded fastener. From the results, it is observed that only small improvement has been obtained using flat washer over conventional nut. Outside serrated, spring and nylon washers show marginal anti-loosening ability. Nylock nut is seen to have better resistance to loosening than the other popularly known anti-loosening fastening elements tested, and hence, may be quite effective to use in vibrating conditions. However, other popularly known anti-loosening nuts or washers are found not to be that effective.