عنوان مقاله [English]
In marine diesel engine, main bearing bolts (M18×1.5) withstand large tensile and cyclic loads to keep the crank shaft, bearing whit acceptable clearance and precision clamping force at high crank speed like 3100 rpm. In this research, the relationship between torque and clamp force, the friction coefficient, the effect of number of tightening and bearing conditions on the new manufactured bolt (with and without coating) and the original bolt were studied and compared. Also, the experimental results show that the new bolt designed and manufacture at maximum level of bolts standard (DIN 898 class 12.9). The process of manufacturing of new bolt was cold forging and heat treatment method after thread rolled. In order to determine the behavior and compering the performance of the new and original bolt, the tightening torque and clamping force were measured according to clamping process using a digital torque-wrench and load cell. Finally, the coefficients of friction were calculated using Motoch relationship for a bolt with and without coating in several stages of tightening. In addition, the amount of k constant (Torque coefficient) estimated. Also the bearing clearance measured with the micrometer. The results showed that about 10% of the tightening torque was converted to the clamping force, and the new bolt had the same functional condition with the original bolt. Also, the value of the diameter deviations of the bearing caps was acceptable.