Several factors influencing spring fatigue strength.Elastic electrode Production

　　1. Yield strength There is a certain correlation between the yield strength of the material and the fatigue limit. Generally speaking, the higher the yield strength of the material, the higher the fatigue strength. Therefore, in order to better improve the fatigue strength of the spring, every effort should be made to improve the spring material. Or select materials with a high ratio of yield strength to compressive strength. For the same material, fine crystal structures have higher yield strength than large and small crystal structures.

　　2. The surface condition is large. The ground stress is mostly generated on the surface of the spring material, so the surface quality of the spring is very harmful to the fatigue strength. The defects such as cracks, defects and scars caused by the spring material in the whole process of cold rolling, drawing and production are usually caused by the fatigue and rupture of the spring.

　　The smaller the surface roughness of the material, the smaller the stress and the higher the fatigue strength. The surface roughness of the material is harmful to the fatigue limit. As the surface roughness increases, the fatigue limit decreases. Under the same surface roughness, different steel grades and different production methods have different fatigue limit reduction levels. For example, the reduction level of cold-rolled coil springs is smaller than that of hot-coiled springs. As the steel hot-rolled coil spring and the heat treatment process are heated, the surface of the spring material becomes matte and carburized due to air oxidation, which reduces the fatigue strength of the spring.

　　Carry out cutting, air brake, shot blasting, rust removal and extrusion molding on the surface of the material. Both can improve the fatigue strength of the spring.

　　3. Specification utility The larger the specification of the material, the higher the probability of defects caused by various cold drawing and hot processing, and the greater the probability of causing surface defects, which will cause the fatigue characteristics to decrease. Therefore, when estimating the fatigue strength of the spring, the harm of the specification effect should be considered.

　　4. Disadvantages of the metallurgical industry The disadvantages of the metallurgical industry refer to the non-metallic material impurities, vapor bubbles, and shrinkage of elements in the material. The impurities on the surface are the source of stress, which will cause fatigue cracks between the impurities and the substrate page. The use of vacuum pump smelters, vacuum casting and other countermeasures can further improve the quality of stainless steel plates.

　　5. Eroding material When the spring is working in an etched material, the surface will cause crevice corrosion or surface dislocations to be eroded and become a source of fatigue. Under the effect of variable geostress, the spring will gradually expand and cause rupture. For example, when talking about spring steel working in water, the fatigue limit is only 10%~25% of that in air. The damage of erosion to the fatigue strength of the spring is not only related to the frequency of the spring subjected to variable loads, but also to the service life of the spring. Therefore, the service life during operation should be taken into consideration when calculating the design plan for the springs that are damaged by erosion.

　　In order to better ensure the fatigue strength of the spring working under the erosion standard, materials with high corrosion resistance characteristics can be selected, such as stainless steel plates, non-ferrous metal materials, or surface protection layers, such as coatings, air oxidation , Electrostatic spraying, painting, etc. Practical activities show that cadmium plating can further increase the fatigue limit of the spring.

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