Effect of Control Fluid on Surface Treatments of High Strength Bolts

This paper presents results of a series of tests performed using ¾ in. diameter A325 and A490 bolts. The resulting relationship between torque – tension for the bolt – nut – washer assembly is used to explain its behavior as the length and location of treatment surface are varied. Tests were performed upon one hundred sixty four bolts; eighty A325 of three inches in length, fifty-two A325 of six inches in length, twenty A490 of three inches in length, and twelve A490 of six inches in length. One hundred sixty four nuts and washers were tested, one hundred nuts type 2H, and fifty six nuts type C and eight nuts type D to determine the effect of the variables (nut type, bolt length, bolt type and Control Fluid) on the torque-tension relationship of the bolt-nut-washer assembly. Hundreds of experiments using replicate samples for statistical reliability were conducted to establish the effect of the variables on the tension-torque relationship of the bolt-nut-washer assemblage. The principal relationship in turn-of-nut installation is that between elongation and bolt pretension, the tension -torque relationship is the factor that reflects the bolt pretension in an installation to be expected in a properly tightened connection. Control Fluid was found to decrease the coefficient of friction on coated parts and to control the tension obtained with a given torque upon assembly.