After the spring is formed, it generally needs to be subjected to low temperature stress removal annealing or bluing treatment at 220-330 ℃, or according to the requirements of the operating conditions of the spring and the nature of the selected material, it needs to be hardened and tempered to improve the spring force. However, clamps should be used during the heat treatment of the spring to prevent the ring from shrinking and jamming with the shaft when working. Others, such as removing the corners of the two outer ends, radial burrs, etc., cannot be ignored. In the event of a spring with a tendency to bend, a coil of strips can be used to rub the tensioned spring along the longitudinal direction of the axis repeatedly until the surface is locally hardened.
In actual work, we often encounter that the spring cannot push the moving object to the set position, which means that the calculated free length of the spring becomes shorter. The main reason is that there is no initial compression treatment, that is, a spring is compressed to its compression height or tight height (if necessary) with a relatively large force, and it cannot be restored to its original shape after being released. The free length of the operation. The amount of shortening is called "initial compression". Generally after 3-6 times of compression, the length is no longer shortened, that is, the spring is "positioned". The spring undergoes permanent deformation after initial compression.
In actual work, the standard compression spring should be able to maintain its working length even if it is subjected to a force beyond the elastic limit of the material. Therefore, the length of the finished spring should be equal to the calculated length of the spring plus the initial compression, which can prevent the spring from being out of place, so as to avoid dangerous stress when the coil is tightened, which may cause the spring indicator line to be abnormal and not in place. In the heat treatment process of the finished spring, especially the hardening and tempering process, the workpiece must be placed horizontally in the furnace to prevent the spring from being shortened due to its own weight and the operation is not in place.
Insufficient spring force: The requirement for springs is that a certain spring force must be generated under specified deformation. Once the load is removed, the spring returns to the free length and smoothly moves the moving parts to the set position. But sometimes it cannot be in place due to insufficient spring force.
Among them are technological factors. For example, the spring must overcome the friction generated between the ring and the ring, between the ring and the mandrel or sleeve, and between the moving pairs during the stretching process. Sometimes the friction force varies widely (up to ±50%), it will lead to insufficient spring force, unable to overcome the friction force to make the moving parts in place, resulting in spring failure. To this end, each process in the production process specification, such as screening materials, spring forming, flattening of both ends, removing edges and corners, heat treatment, correction and adjustment, initial compression treatment, inspection and refueling, must be strictly implemented.
In addition, the spring force is also related to design factors and material selection factors. The two main calculation formulas of the spring are the deformation formula: λ=8PD32n/Gd4 and the stress formula τ=K8PD2/πd3. It can be seen that the spring force is greatly affected by the wire diameter, coil diameter, deformation and number of turns, depending on the characteristics of the material and temperature, load characteristics and dynamic effects are closely related, and can all cause abnormalities in the indication lines of spring force and deformation.