Study On Factors Affecting Fatigue Life Of Coil Spring For Railway Truck Bogie

Coil spring is one of the main parts of bogie in railway truck. Its capability and life time decide security and stability of railway truck bogie operation. In order to bring spring life into accord with quailty assurance period of railway truck, that is 9 years, a period of factory repair under normal usage, Railway Ministry assued No.[2004]342 technique condition of helical spring for railway truck bogie to prescribe spring fatigue life no less than 3000 thousand times. It is main reason that now Science and Technology Department and Transportation Bureau of Railway Ministry require to spot-check fatigue trial life of springs made by every manufacturer every year. So it is highly important for improvement of fatigue life that analyze and study effect factors.Spring rupture occured on operation mainly due to spring fatigue under the condition of alternative stress. Spring fatigue strength is a key performance index. Fatigue strength is less than static stress strength such as elasticity limit,yield strength. Spring is seldom endured pure static stress in motion. It is usually deemed static stress when it changes slowly or its change extent and less in degree,moreover the spring under above static stress is endured No.III load when designed. For the spring under No. I and II load, stress change extent and degree are more.At the same time fatigue strength must be taken into account. Now Chinese railway truck is running at a speed of 120Km/h. So the spring for railway truck bogie is endured No. I and II load and its fatigue strength must be taken into account.The factors affecting spring fatigue strength are various. It includes properties of spring steel, manufacturing technologies etc. It is necessary to systematically analyze above-mentioned factors.According to what coil spring(for example ZK2 spring) fractured during normal operation and fatigue test,this text comprehensively analyzes many factors affecting spring fatigue strength(life),such as fracture character,nonmetal inclusions in spring steel,grain size,content of harmful gas, heat treatment cycle,surface quality and metallographical structure etc, comparing of fracturing spring under reaching fatigue life and not reaching fatigue life by some test equipments. It also needs to take the correct technologes to improvement the fatigue life of coil spring.