The spring should ideally conform to hooke's law, that is, the relationship between stress and strain in the elastic range is linear.However, since the actual spring steel is a polyphase and polycrystalline material, there must be inconsistencies in composition, structure, elasticity, etc., and the stress and strain deviated from the linear relationship within the elastic range, which is called elastic incompleteness or anelastic.The phenomena such as elastic after effect, elastic lag, stress relaxation and elastic modulus decrease are produced.After tempering, the stabilization process can reduce the elastic imperfection.
(1) the fixing process for the compression spring is to compress the spring to the working limit height or to tighten the height several times;For the stretching spring, the length of the spring is drawn to the working limit several times;For the torsional spring, it turns the spring in the working direction several times to the ultimate torsion Angle.After 7 times of such action, the spring will tend to stabilize, field operation, generally take 3 to 5 times.
Pressure treatment also has a stabilizing effect on the spring.
(2) the calculation of the prefabricated height of the spring shall be reduced after the spring is set up and treated with strong pressure.In order to make the spring reach the free height specified on the pattern, the rolling height of the spring should be set aside for deformation except the free height. This height is called precast height.Because there are many factors influencing the setting and the strong pressure treatment, the deformation amount cannot be calculated accurately.Two empirical formulas for calculating the height of prefabrication are introduced as references for determining the process parameters.
The prefabricated height of the coiled compression spring is fixed
After the fixing process, such as low temperature tempering, the spring's proportional limit and load-bearing capacity will be improved, especially for the precision spring and the spring with slightly higher temperature, which have obvious effects in improving the spring performance and improving the pass rate.
After the low temperature tempering, the tempering temperature should be a little lower than that of the de-stressed annealing, considering the residual strain between the metal lattices in the processing and the drop of the macroscopic residual stress without strengthening.In general, copper spring of tempering temperature for 160-200 ℃, 1 h heat preservation;Steel springs tempering temperature is 200-400 ℃, the heat preservation about 30 min.