In the actual work, we often encounter that the spring cannot push the moving object to the set position, that is to say, the length of the spring's computational freedom becomes shorter.The main reason is that there is no initial compression, that is, a spring is made into a spring, which is compressed to its compression height or to its compression height (if necessary) with a greater force, and cannot be restored to its original free length upon release.Its shortened quantity is called "initial compression quantity".After repeating 3-6 times of compression, the length is no longer shortened, that is, the spring is "positioned".The spring is permanently deformed after initial compression.

In practice, the spring should maintain its working length even if it is subjected to forces beyond the elastic limit of the material.Therefore, the length of finished spring of spring preventive measures should be equal to the calculated length of spring plus the amount of initial compression, which can avoid the spring not in place, avoid the risk stress when the spring coil is tightened, and lead to abnormal and not in place of the spring indicating line.In the heat treatment process of finished spring, especially after quenching and tempering, the workpiece must be placed horizontally (horizontal) in the furnace to prevent the operation of the spring from being short due to the action of gravity.