The coil spring can be divided into compression spring, torsion spring and tension spring according to the different loading conditions. The defects of coil spring in use are: plastic deformation due to the stress relationship, which causes the free length of spring to change or skew; or insufficient elasticity due to high temperature; fatigue fracture due to long-term use, etc. Next, the identification method of compression spring will be described, and the other two types of spring can be implemented by reference.

(1) Visual view:

Check whether the spring is skewed due to fatigue fracture and plastic deformation. For the spring deflection, it can also be measured by placing the spring on the flat plate with a square, and the deflection shall not exceed 2 ° generally.

(2) Inspection of spring free length:

The free length can be measured with a steel ruler to see if it meets the requirements; the new and old springs can also be compared for inspection.

(3) Elasticity test:

Measure with elastic tester, compress to a certain length according to regulations, and observe whether its elastic force meets regulations. When there is no tester, place the spring on the platform scale, press down a certain length with a bar, and determine its elastic force from the size of the indicated force on the platform scale; or clamp the new and old springs on the same vice, and compare the elastic force to determine whether to continue to use or replace them.