What are the factors that affect the spring fatigue strength?

The service life of a spring is related to its own fatigue strength, and the fatigue strength of a spring is closely related to many factors. Therefore, in order to ensure the spring can work effectively for a long time, we must start from the various factors that affect the fatigue strength of the spring. So what are the factors that affect the spring fatigue strength?

1, yield strength There is a certain relationship between yield strength and fatigue limit of the material, in general, the higher the yield strength of the material, the higher the fatigue strength, therefore, in order to improve the fatigue strength of the spring should try to improve the yield of the spring material Strength, Nantong Precision Precision Co., Ltd. processing or use of high yield strength and tensile strength of the material. For the same material, the fine grain structure has a higher yield strength than the fine grain structure.

2, the maximum surface stress occurs in the surface of the spring material, so the surface quality of the spring fatigue strength of great impact. Spring material in the rolling, drawing and rolling process caused by cracks, defects and scars and other defects are often the cause of spring fatigue fracture. The smaller the material surface roughness, the smaller the stress concentration, the higher the fatigue strength. Effect of Material Surface Roughness on Fatigue Limit. As the surface roughness increases, the fatigue limit decreases. In the case of the same roughness, different types of steel and different winding methods to reduce the degree of fatigue limit is different, such as the degree of reduction of cold coil spring coil spring is smaller. Because the steel coil spring and its heat treatment heating, due to oxidation of the spring surface roughness and decarburization phenomenon, thus reducing the fatigue strength of the spring. Grinding the surface of the material, strong pressure, shot blasting and rolling, can improve the fatigue strength of the spring.

3, the size effect The larger the size of the material, due to a variety of cold and hot processing technology caused by the higher the possibility of defects, the possibility of surface defects are also greater, these reasons will lead to fatigue performance decline. Therefore, in calculating the fatigue strength of the spring to consider the size effect of the impact.

4, metallurgical defects Metallurgical defects refers to the non-metallic inclusions in materials, bubbles, segregation of elements, and so on. The inclusions existing on the surface are the sources of stress concentration, leading to premature fatigue cracks between the inclusions and the interface of the substrate. Using vacuum smelting, vacuum casting and other measures, can greatly improve the quality of steel.

5, corrosive medium Spring in the corrosive medium, due to surface pitting or grain boundary corrosion has become a source of fatigue in the role of stress will gradually expand and lead to fracture. For example, spring steel working in fresh water has a fatigue limit of only 10% to 25% of the air. The influence of corrosion on the spring fatigue strength is not only related to the number of times the spring is subjected to varying loads, but also to the service life. Therefore, the design and calculation of the spring affected by corrosion should take into account the working life.

Springs that work under corrosive conditions may be made of highly corrosion-resistant materials such as stainless steel, non-ferrous metals, or surface protective coatings such as coatings, oxidation, spray and paint to ensure their fatigue strength. Practice shows that cadmium plating can greatly increase the fatigue limit of the spring.

6, the temperature Fatigue strength of carbon steel, from room temperature to 120 ℃ when the decline, from 120 ℃ to 350 ℃ and then rise, the temperature is higher than 350 ℃ after the decline in high temperature without fatigue limit. Spring work in high temperature conditions, to consider the use of heat-resistant steel. At temperatures below room temperature, the fatigue limit of steel increases.