After spring forming, the general need to go through the 220 ~ 330 ℃ low temperature to remove stress annealing or hair blue treatment, or according to the spring operating conditions and the nature of the selected material requirements, the need for hardening and tempering to improve the spring force. But the spring heat treatment should use the fixture to prevent the circle to shrink, work and shaft bar stuck. Other such as the removal of the two ends of the angular edge, radial inside and outside the burr, etc., can not be ignored. When there is a tendency to bend the spring, you can use a circle, in the tension on the spring along the axis of the vertical force several times to friction, to the surface of local hardening.
Spring is not in place, failure mode and reason
In the actual work, we often encounter the spring can not push the moving object to the set position, that is to say the spring free length of the calculation of the shorter. The main reason is that there is no initial compression treatment, is to make a spring made, with a larger force to compress it to his compression height and tightness (if necessary), can not be restored after the original Of the free length of the operation. The amount of shortening is called "initial compression". Generally repeat the 3 ~ 6 times after compression, the length is no longer shortened, that is, the spring "positioning." After the initial compression of the spring permanent deformation.
In practice, the compression spring should be able to maintain its working length even if it is subjected to forces 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, to avoid the spring is not in place, so as to avoid the coil and tight when the dangerous stress, resulting in abnormal spring line and not in place. Finished spring in the heat treatment process, in particular, need to be hardened and tempered process, we must press the workpiece (lying) in the furnace, to prevent the spring due to the role of shortening caused by the job is not in place.
Insufficient spring force For springs, it is necessary to produce a certain spring force under the specified deformation. Once the load is removed, the spring is restored to the free length and the moving element is smoothly moved to the set position. But sometimes due to insufficient spring force can not be in place.
There are process factors, for example, the spring in the process of stretching, must overcome the circle and the circle, between the circle and the mandrel or sleeve, the movement between the friction between the friction, and sometimes a large range of friction changes (up to ± 50 %), Will lead to lack of spring force, can not overcome the friction to make the moving parts in place, resulting in spring work failure. To this end, must be in accordance with the production process specifications in each process such as screening materials, spring forming, both ends of grinding, removal of edges and corners, heat treatment, calibration adjustment, early compression treatment, inspection and other strict implementation.
In addition, the spring force and design factors, selection factors and so on. From the two main formulas of the spring, ie, the deformation formula: λ = 8PD32n / Gd4 and the stress formula τ = K8PD2 / πd3 we can see that the spring force is affected by the wire diameter, circle diameter, deformation and the number of turns, with the material characteristics, Environmental temperature, load characteristics and dynamic effects are closely related, and can lead to spring force and deformation of the indicative line of abnormal.