Causes Analysis on Fracture of Valve Springs of Motors

The physical and chemical testing and SEM analysis of the fracture were carried out on three typically fractured valve springs of motors. It was concluded that all the fracture mechanisms of the three valve springs were the fatigue fracture. The reasons causing the fracture were related to surface quality of valve springs. The fracture reason of No.1 valve spring was that non-metallic inclusions exsited in the surface. The fracture reason of No.2 valve spring was that corrosion pits exsited in the surface. The fracture reason of No.3 valve spring was that the folding defect exsited in the surface. Therefore, the key measures to improve the service life of valve springs were to control the quality of raw materials and avoid the surface defects of the valve springs.