What are the reasons for the destressing of springs? The following spring manufacturers will answer them for you.
1) Continuous hot air tempering electric furnace. This kind of electric furnace has been widely used in the spring manufacturing industry in recent years. Its advantage is that it can precisely control temperature and time and save power. An automated production line for coil springs and stress relief annealing can be realized if the electric furnace is placed in front of the coil spring machine.
2) Hot air circulation tempering electric furnace and box-type electric furnace. The furnace temperature is relatively uniform, but the holding time is much longer than that of the nitric acid furnace.
3) Nitrate tempering furnace. The furnace is generally manufactured by a spring factory. The salt furnace has the advantages of fast heating speed and short holding time. The disadvantage is that the temperature is not uniform, and the liquid in the furnace easily invades the surface of the spring, especially the oil-quenched and tempered spring steel wire. Springs treated with nitrate furnaces should be cooled and cleaned with water first, and then immersed in anti-rust water for a few minutes to prevent rusting. When using an electric furnace for stress relief annealing, the holding time should be appropriately extended. The spring should be heated neatly in the furnace, and the spring with special shape or easily deformed should be equipped with corresponding auxiliary tools.
The determination of stress relief annealing temperature and time is usually selected in the range of 150~350℃. The general principle is that lower temperatures should be used for smaller diameter materials and higher temperatures should be used for larger diameter materials. In the case of the same material diameter, if some materials have high strength and poor toughness, the temperature can be higher. The temperature of spring steel wire rolled by oil quenching and tempering is higher than that of carbon spring steel wire and piano steel wire rolled by spring steel wire. The stress relief annealing temperature and holding time of the helical tension spring have a great influence on the initial tension of the spring. When the temperature is low and the holding time is short, the retained initial tension is large. Otherwise, the remaining initial tension is small.
Generally, it can be selected in the range of 200~300℃, and keep it for 20~30 minutes. If you want to maintain a greater initial tension, the temperature can be as low as 180°C. It should be pointed out that the initial tension of the helical extension 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 the helical tension spring and helical torsion spring should be about 20°C lower than the initial temperature, and the holding time can also be shortened. The stress relief annealing temperature of the spring after shot peening is generally 180~220℃, and the holding time is 20~30 minutes. When stress relief annealing is required to adjust the size of the spring, the temperature should be about 20°C higher than the temperature generally introduced.
The effect of stress relief annealing on the diameter and coil number of spring carbon steel wire and piano wire coil spring after stress relief annealing process Generally speaking, the diameter should be reduced and the coil number should be increased. The shrinkage of the diameter is related to the winding ratio. The larger the winding ratio, the larger the shrinkage. Therefore, the first sample should be prepared before mass production, and the mass production can only be carried out after the sample is confirmed.
