Tightening bolt with accurate preloading and tightening procedure using such bolts

摘要

A tightening bolt with accurate preloading has a first threaded portion 1B adjacent to its free end and a second threaded portion 1A of greater diameter and lesser pitch adjacent to or corresponding to its head T. A ring 2 is screwed onto the portion of greater diameter and in the tightened condition this rests against one of the two members 3, 4 which are being connected. In this condition head T is at a distance from its supporting plane, so the friction between the head and the supporting plane does not affect the link between the tightening torque and the tension stress produced in bolt 1. Having then determined the amount of friction on the threads by partial tightening, it is possible to determine the final tightening torque so as to ensure that the bolt can be rotated through the necessary angle to ensure the desired preloading on the shank of the bolt. IMAGE