After the oxidation process of the shell hook spring can reduce the residual stress, the steel wire is cold-wound to form a spring, and residual stress is generated inside, and the residual tensile stress is formed on the inner side of the spring, and the value is related to the spring winding ratio C (C=D2/d); The smaller the C value, the greater the residual tensile stress. The C-hook of the shell hook is small, generally 5.8.
According to the spring theory, the maximum stress is inside the coil, so the inner side of the coil is a dangerous point. If the residual tensile stress can be reduced, it is beneficial to improve the life of the hook spring. After the shell hook spring is oxidized, the oxide film has a compressive stress on the surface of the spring steel wire, and can offset some residual tensile stress, which is beneficial to improve the spring bearing capacity.
The hook-and-loop hook spring is subjected to repeated impact torsion and bending during the shooting process. Due to the thinner spring wire, fine cracks and scratches may occur during the cold-rolling or winding of the steel wire, and the material is damaged. Multiple alternations can also produce very fine cracks, which become the origin of cracks. The tip of the crack has severe stress concentration, which leads to the crack propagation under the alternating stress. During the crack propagation process, the material on both sides of the crack is sometimes separated or sometimes pressed, and a grinding-like effect occurs. After a long-term action, The crack propagates and the effective section gradually decreases, eventually breaking, resulting in early failure of the shell hook spring.
In the process of oxidizing the hook spring, the surface of the steel wire is chemically corroded, which not only smoothes the unevenness of the surface of the steel wire, but also makes the micro crack and the sharp corner of the scratch become smooth, which is beneficial to prevent early failure of the spring.
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