66 wwwenerpaccom What is Torque It is a measure of how much force acting on an object which causes that object to rotate What is Torque Tightening The application of preload to a fastener by the turning of the fasteners nut Torque Tightening and Preload The amount of preload created when torqueing is largely dependant on the effects of friction Principally there are three different torque components torque to stretch the bolt torque to overcome the friction in bolt and nut threads torque to overcome friction at the nut spot face bearing contact surface Torque Tightening Friction points should always be lubricated when using the torque tightening method Preload residual load Applied Torque minus Frictional Losses Lubrication Reduces Friction Lubrication reduces the friction during tightening decreases bolt failure during installation and increases bolt service life Variation in friction coefficients affect the amount of preload achieved at a specified torque Higher friction results in less conversion of torque to preload The value for the friction coefficient provided by the lubricant manufacturer must be known to accurately establish the required torque value Lubricant or antiseizure compounds should be applied to both the nut bearing surface and the male threads Frictional Losses Example of how a lubricant can reduce the effect of friction and convert more torque to bolt preload Frictional Losses dry steel bolt T urning movement Torque Tightening Stretch of F astener Preload F orce 50 a t nut face Lubrica ted with Moly grease 01 Light oil 015 Dr y unlubrica ted 02 Residual Bolt L oad t ons T or que ftlbs Applied load Lubrication Reduces Friction 40 in threads 10 converted to preload 11 10 9 8 7 6 5 4 3 2 1 0 0 20 40 60 80 100 120