Reamer bolts are widely used for the bolted joints subjected to large shear forces. The most important application is the case of clamping rigid flanged shaft couplings which deliver large torques. The body diameter of a reamer bolt is basically equal to the bolt hole diameter. When installing into the joint, reamer bolts are cooled in order to temporarily reduce its diameter for easy insertion. Dry ice or liquefied nitrogen is commonly used to lower the bolt temperature. It is customary in the actual tightening operation that to save working hours, the tightening torque is applied to the reamer bolt while its temperature is still well below the ambient temperature. Accordingly, the reamer bolt inevitably elongates as its temperature increases to the ambient one, which leads to the reduction of axial bolt force. In this paper, an equation of simple form is derived, which can estimate the amount of bolt force reduction occurred during the tightening operation of reamer bolts by cooled fitting. It is shown that the reduction rate in axial bolt stress, per unit of temperature difference between the reamer bolt and the fastened plate, gradually increases as the grip length is increased, ranging from about 1MPa/K to somewhat in excess of 2MPa/K. If the target joint tightened by cooled fitting has an excessive strength, the derived equation is useful from the practical point of view. It can determine the excessive torque that compensates the bolt force reduction due to the elongation during the tightening operation. The effectiveness of the derived equation is demonstrated by experiments. Based on the derived equation and the experimental results, a guide line is proposed to securely tighten reamer bolts using cooled fitting.
Unit of Temperature