When the spring or elastic element is under the necessary condition of constant strain, the spring stress decreases with time. This phenomenon is called stress relaxation. To improve the anti relaxation ability of the spring, the elastic limit value and load-bearing capacity of the spring must be improved. In addition to steel alloying and appropriate heat treatment, mechanical strong pressure treatment can also be selected to improve the anti relaxation performance of the spring. The operation method is to add a higher load on the spring, so that the production circlip stress generated by the surface layer exceeds the elastic limit value of the raw material, resulting in plastic spring or elastic element. Under the necessary condition of constant strain, the stress decreases with the extension of time. This phenomenon is called stress relaxation.
  To improve the anti relaxation ability of the spring, the elastic limit value and load-bearing capacity of the spring must be improved. In addition to the alloying and proper heat treatment of steel used for the inner sleeve hydraulic valve spring, mechanical strong pressure treatment can also be selected to improve the anti relaxation performance of the spring. The operation method is to add a higher load on the spring, so that the stress generated by the surface layer exceeds the elastic limit value of the raw material and plastic deformation occurs. When the external load is unloaded, the center of elastic deformation tries to restore to the original state, and will be restrained by the plastic deformed surface layer in the process of restoration. After recovery, the stress on the surface layer is opposite to the load, and the superposition of the two reduces the macro stress in the spring section. The spring treated by strong pressure does not appear the first stage with large relaxation rate, but only the second stage with small relaxation rate, which effectively improves the stress relaxation resistance of the spring and makes the load loss rate of the spring working for 10 years less than 5%.