冷やしばめによるリーマボルトの締め付け過程の評価

Abstract

A reamer bolt is widely used in the marine engineering field, bolted joints being subjected to large shear forces. The most important application is in the joint couplings, composing the propeller shaft system. The diameter of a reamer bolt is basically equal to that of the bolt-hole. When installed into the joint a reamer bolt is cooled in order to temporarily reduce its diameter for easy insertion. Dry ice or liquefied nitrogen is commonly used to lower the bolt temperature. In actual practice it's customary that a tightening torque is applied to the reamer bolt when its temperature is below that of the ambient one. Accordingly, the reamer bolt elongates with the temperature increase, during the tightening operation. In the final state, the axial bolt force is reduced to some extent.In this paper, an equation that estimates the amount of bolt force reduction due to the temperature increase is proposed. For joints with sufficient strength, the proposed equation is both practical and useful. It will determine the amount of excess torque that compensates for the bolt force reduction. The validity of the equation is demonstrated by experimentation. Based on the proposed equation and the experimental results, a guideline is shown for securely tightening the reamer bolt using a cooled fitting.