An investigation on the anti-loosening characteristics of threaded fasteners under vibratory conditions

A significant advantage of the screw fastener is its capability of being mantled and dismantled using simple tools. However, threaded fasteners have inherent and inevitable limitations that they loosen eventually under vibrating environment leading to higher frequency of routine maintenance of the components, the absence of which may result in fatal accidents. In the present work, an attempt has been made to test the anti-loosening ability of various locking screw fasteners, such as nylock nut, aerotight nut, chemical lock, cleveloc nut, flat washer, nylon washer, serrated washer and spring washer with bolts of different materials, sizes and types with different initial clamping forces under the accelerated vibrating conditions obtained in an indigenously made testing rig. The loss of clamping force gives an indication of the extent of loosening. Their anti-loosening characteristics are compared with respect to initial clamping forces. On the basis of the test results, chemical locking has been found to show best anti-loosening characteristics followed by nylock and aerotight nut. Loosening is found to be considerably less, when the initial clamping force is more than 1.1 ton for metric threaded bolts, and the same for BSW bolts is found at a force above 0.8 ton, when the bolts are fastened with conventional nuts.