What is the cause of spring stress relief?

Spring Factory tells you why the spring is de stressed: the heat treatment equipment used for stress relief annealing of spring is as follows.
 

1) Continuous hot air tempering electric furnace. This electric furnace has been widely used in spring manufacturing in recent years. Its advantage is that it can accurately control temperature and time, and save electricity. If the electric furnace is arranged in front of the spring coiling machine, the automatic production line of spring coiling and stress relief annealing can be realized.

2) Hot air circulating tempering electric furnace, box type electric furnace. The furnace temperature is relatively uniform, but the holding time is much longer than that of the nitrate furnace.

3) Nitrate tempering furnace. The furnace is generally manufactured by the spring manufacturer. Nitrate furnace has the advantages of fast heating speed and shorter holding time than other furnaces. The disadvantage is that the temperature is uneven, and the liquid in the furnace tends to invade the surface of the spring, which is especially bad for oil quenching and tempering spring steel wire. The springs treated by the nitrate furnace should be cleaned by water cooling, and then immersed in the antirust water for several minutes to prevent rust. When electric furnace is used for stress relief annealing, its holding time should be appropriately longer than that of nitrate furnace. Springs shall be neatly arranged when heated in the furnace. Springs with special shape or easy deformation shall be equipped with corresponding auxiliary tools.

Determination of stress relief annealing temperature and time The stress relief annealing temperature is usually selected in the range of 150~350 ℃. The general principle is that the material with thin diameter should use a lower temperature, and the material with thick diameter should use a higher temperature. Under the condition of the same material diameter, some materials have high strength and slightly poor toughness, so the temperature can be higher. The spring made of oil quenched and tempered spring steel wire has a higher temperature than that made of carbon spring steel wire and piano steel wire. The stress relief annealing temperature and holding time of the spiral tension spring have a great influence on the initial tension of the spring. If the temperature is low and the time is short, the retained initial tension is large; On the contrary, the retained initial tension is small.

Generally, it can be selected within the range of 200~300 ℃, and kept for 20~30min. If you want to retain more initial tension, the temperature can be as low as 180 ℃. It should be pointed out that the initial tension of the spiral tension spring should be mainly controlled by the coil spring, and the stress relief annealing temperature only plays an auxiliary role. The second stress relief annealing temperature of spiral tension spring and spiral torsion spring should be about 20 ℃ lower than the first, and the holding time can also be shortened. The stress relief annealing temperature of the spring after shot blasting is generally 180~220 ℃, and the holding time is 20~30min. When it is necessary to adjust the spring size by means of stress relief annealing, the temperature should be about 20 ℃ higher than that generally introduced. 2. The influence of stress relief annealing on spring diameter and total number of coils After the carbon spring steel wire and piano steel wire are rolled into springs, the diameter should be reduced and the total number of coils should be increased after the stress relief annealing process. The diameter shrinkage is related to the winding ratio. The larger the winding ratio, the larger the shrinkage. Therefore, the first sample shall be taken before mass production, and can be put into mass production only after the sample is determined. Shrinkage of spring diameter after stress relief annealing treatment Δ Increase of D2 and total turns Δ N can be estimated according to the following empirical formula