Under the condition of constant strain, the stress of spring or elastic element decreases with the extension of time tower spring. This phenomenon is called stress relaxation. To improve the anti-relaxation ability of the spring, it is necessary to improve the elastic limit and bearing capacity of the spring. In addition to steel alloying and proper heat treatment, mechanical strong pressure treatment can also be used to improve the anti-relaxation performance of the spring. The operation method is to apply a high load on the spring, so that the stress of the production circlip produced by the outer layer exceeds the elastic limit of the material, causing plasticity

Under the condition of constant strain, the stress of spring or elastic element decreases with time, which is called stress relaxation.

To improve the anti-relaxation ability of the spring, it is necessary to improve the elastic limit and bearing capacity of the spring. In addition to the alloying and proper heat treatment of the steel used for the inner hydraulic valve spring, mechanical strong pressure treatment can also be used to improve the anti-relaxation performance of the spring. The operation method is to apply a high load on the spring, so that the stress produced by the outer layer exceeds the elastic limit of the material, and plastic deformation occurs. When the external load is removed, the center of the elastic deformation will try to recover to its original state, and will be restrained by the outer layer of the plastic deformation during the recovery process. After recovery, the stress of the surface layer is opposite to the effect of the loaded load, and the superposition of the two will reduce the macro stress in the spring section. The spring treated by strong pressure does not appear in the first stage with large relaxation rate, but only in 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%.

Strong pressure treatment methods include: ① cold strong pressure treatment, that is, strong pressure treatment at room temperature for several hours to dozens of hours; ② Heat and strong pressure treatment: put the strong pressure device into a constant temperature furnace at a certain temperature, hold it for a proper time, take it out and unload it and quickly cool it to room temperature; ③ Magnetic field strong pressure treatment, that is, the strong pressure spring device is placed in the bath furnace with magnetic field around it for treatment; ④ Electric strong pressure treatment, that is, put the strong pressure spring device between the two plates and heat it for a short time, then take it out for quick cooling.