1. The standing treatment of the compression spring is to compress the spring to the working limit height or to tighten the height several times, usually 3 to 5 times;For the stretching spring, the length of the spring is drawn to the working limit several times;Torsion spring, is the spring in the working direction of the 5522 for the ultimate torsion Angle several times.

2. Strong pressure (strong tension and strong torsion) treatment for compression spring is to press the spring into the material layer and the stress exceeds the yield point, resulting in negative residual stress on the surface and positive residual stress on the heart.

There are two technological methods: one is the static pressure, which presses the spring to the required height.This method takes up more process equipment and equipment and takes up a larger site.But the performance is more stable. Suitable for some small springs.

Another method is to press the spring to the specified height at a slower speed (about 1min), and then release it slowly (about 1min), causing the spring to undergo plastic deformation.Then, the vertical processing is carried out at this height.This method has the same effect as the static pressure and is applicable to all kinds of large springs.

FIG. L shows the stress distribution on the cross section of the helical compression spring material in the process of high pressure treatment.FIG. 1-a shows that the spring is in a free state (i.e. before the pressure treatment) and the stress on the material section is zero.FIG. 1-b shows that the spring is subjected to load F1, which is less than the elastic limit of the material, and the material is subjected to non-uniform shear stress. The maximum value is at the surface of the material, and the central stress of the material is zero.FIG. 1-c refers to the continuous loading of the spring to F2 and the compression of the spring. At this time, the material surface stress exceeding the elastic limit of the material produces plastic deformation.FIG. 1-d when the load F on the spring is removed, the elastic deformation part of the inner layer of the material begins to recover, but cannot be completely recovered due to the influence of plastic deformation of the outer layer of the material.In this way, the residual shear stress is left in the inner and outer layers of the material.The direction of shear stress is the same near the core of the material.FIG. 1-e refers to the situation where the material is subjected to shear stress when the spring is loaded again to the rated working load F(lower than the strong pressure load). At this point, the stress increases after adding the shear stress at the core of the material and the residual shear stress, and the surface working stress is opposite to the residual shear stress, and the shear stress decreases.This variation in stress distribution gives full play to the material's core potential.

Different types of spring have different ways of dealing with strong pressure.The torsion bar spring is the torque that places the torsion bar in the direction of the working load, and exceeds the elastic limit of the torsion bar shear.Compression and tension loads are applied to the compressed and stretched spring separately exceeding the shear elastic limit of the spring material.The torsion spring is applied to the torque exceeding the elastic limit of the spring material.In conclusion, the type and direction of load applied to the spring should be consistent with the type and direction of load applied to the spring.Residual stress is determined by the degree of residual deformation, which makes the size tolerance of the spring difficult to control. Therefore, the size of the load must be considered in the design.

FIG. 1 cross section stress distribution in the compression spring under strong pressure

A) the stress before the strong pressure is o b) the linear distribution of the initial stress under the strong pressure and c) the stress distribution at the time of turns

D) residual stress after high pressure e) stress distribution during reloading after high pressure

Under the same working conditions, the fatigue life of the spring can be increased by 5% ~ 35% if the reinforcement is properly handled.On the contrary, if not handled properly, if the pre-load load is too large, fatigue life will be reduced.In addition, after working for a certain period of time, with the residual deformation and the change of spring performance, the normal operation of the spring will be damaged.

In order to prevent creep and relaxation of the spring under high temperature conditions, the spring should be subjected to enhanced pressure or creep tempering.The warm and strong pressure treatment is the strong pressure treatment under the condition that the spring is higher than the working temperature.The process of low temperature tempering under load loading (usually in the deformed or coiled state at work) is called creep tempering.The main difference between the two is the stress and the heat preservation time.This is beneficial for springs operating in a warmer environment, preventing relaxation on the one hand and increasing fatigue strength on the other.

Heating and strong pressure treatment and creep tempering are mainly used in the spiral spring formed by cold machining.Their treatment conditions (temperature, stress, time) are selected according to the design requirements of the spring.Steel spring, usually used in 200 ~ 200 ℃ temperature, creep tempering time for about 30 min, heating can crush processing time is 2 ~ 6 h.For heat-resistant spring materials, the temperature can be higher, the time can be longer.

After standing or strong pressure treatment, 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.

The temperature of tempering should be slightly lower than that of de-stressing annealing, considering the residual strain of the microstructure between the metal lattices and the decreasing of the macroscopic residual stress.In general, copper spring tempering temperature is 160 ~ 200 ℃, 1 h heat preservation;Steel springs tempering temperature is 200 ~ 400 ℃, the heat preservation about 30 min.

3. The calculation of the prefabricated height of the spring is that the free height of the spring should be reduced after the fixing treatment and the strong pressure treatment.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.