1. Stress relief annealing targets: Spring coiled by cold coiling process is commonly used as lead bath isothermal quenching cold-drawn steel wire (carbon spring steel wire, piano steel wire) and oil tempered spring steel wire. These springs do not need quenching treatment, they need stress relief annealing. Generally referred to as tempering, also known as stress relief tempering or stress relief tempering.
(1)To eliminate the internal stress in wire cold drawing and spring cold coiling.
(2) Stable spring size. Springs without stress relief annealing will cause external diameter and size increasing and instability in the subsequent processing and using.
(3) Improve the tensile strength and elastic limit of wire;
(4) Use stress relief annealing to control the size of spring.
Note: Under the same material diameter, if some materials have high strength and poor toughness, the temperature may be higher. The second tempering of tension spring and torsion spring should be about 20 C lower than that of the first one, and the holding time can also be shortened.
2. Stress relief annealing technology: The temperature of stress relief annealing and the holding time of torsion spring have a great influence on the initial pulling force of spring. If the temperature is low and the holding time is short, the retained initial pulling force will be large; otherwise, the retained initial pulling force will be small. Fig. 3-10 is the experimental value of the relationship between temperature and initial tension. Generally, it can be selected in the range of 200-300 C, holding for 20-30 minutes. The temperature can be as low as 180 C if the initial pulling force is retained. It should be pointed out that the initial pulling force should be mainly coiled spring force, and the stress relief annealing temperature only plays an auxiliary role.
Note: The stress relief annealing temperature of the springs after shot blasting is generally 180-220 C, and the holding time is 20-30 minutes. Tempering must not be higher than 250 C. If the dimension is adjusted by tempering method, the temperature should be about 20 C higher than that generally introduced.
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