The standard treatment for compression springs in their set position involves compressing the spring to its solid height several times, meaning it is compressed until the coils are fully engaged (both in terms of pressure and height). Typically, this process is repeated three to five times, after which the free length is adjusted. Under the test load, the spring’s free height should remain stable without causing permanent deformation. However, some manufacturers only apply one press cycle without fully compressing the spring to its solid height. This practice can reduce the initial height of the spring and save material, but it often leads to issues such as shortening, softening, or bending during use.
Surface blasting treatment of springs is not simply about shot blasting. It involves projecting high-speed projectiles onto the spring’s surface to plastically deform the outer layer, creating a strengthened surface layer that improves fatigue resistance. This process typically increases the spring's fatigue life by 20% to 35%. During visits to some spring manufacturers, it was observed that many either lack shot blasting equipment or only have small machines suitable for small springs. Large springs cannot be effectively treated, resulting in lower fatigue strength and fewer cycles before failure. Additionally, bending often occurs at the junction between tightly wound and loosely wound coils. To prevent this, the transition from dense to sparse coils should be gradual, with more transition turns to minimize stress concentration and reduce deformation. Unfortunately, some manufacturers skip this step, especially when there is a large difference in pitch between the tight and loose sections, making the spring prone to bending at the joint.
Manual grinding of the spring’s end face does not guarantee proper perpendicularity. Some manufacturers do not use specialized grinding machines and instead manually grind the ends, which often results in excessive tolerance deviations. Moreover, if the coiling machine lacks precision, the spring may not be straight, and the pitch may be uneven, increasing the likelihood of bending or deformation during operation. Ensuring quality requires attention to every detail in both manufacturing and finishing processes.
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