Research On High Strength Bolt Failure And Measurement Of Torque Coefficient

In recent years, the wind power industry is developing rapidly in China, thequality and safety of wind turbines is paid more and more attention. Because the windpower accident caused by high strength bolt failure has occurred, wind power plantsconcerned high-strength bolts about the measurement of torque coefficient and thecontrol of tighten torque. It is very critical to determine the torque coefficient of boltinstalled in large castings. Generally, the wind turbine manufacturers consider thestandard experimental results of nut torque coefficient, then according to experienceto estimate the torque coefficient of high strength bolt installed on the casting. Beforedelivery, bolt factory will measure the torque coefficient by test, but tests carrythrough in laboratory, is not same as wind turbine installation factory, and the way ofoperation is either different. Because of these factors, it is different between measuredtorque coefficient and the actual coefficient.This paper proposes a new method to measure torque coefficient used in fieldassembly, developed a set of lightweight, portable measuring equipment, this set ofequipment including: hydraulic pump, axial force sensor, digital display meter, torquesensor, digital display meter, etc. Using axial force sensor measure the axial forcewhen bolt tightening, sleeve sensor measure the torque when the bolt tightening,displaying axial force and torque at the time of the bolt tightening. According to theformula, the torque coefficient could be calculated. At the wind turbine assemblyscene, this method is used to measure torque coefficient. In view of the effect factorsto torque coefficient, test is done respectively. The test focuses on factors includingthread matching precision, surface treatment, surface lubrication, etc.. Then theorderliness of the influence factors is analyzed on the torque coefficient. At the scene,167experiments are carried out using this method, the details of the original data isget. The failure reasons of bolt are obtained by data analysis, the correspondingsolution is found. According to this method, the high strength bolt tightening torquecould be determined. This can improve the safety and reliability of the wind turbine,and also could improve the market competitiveness of the turbine.