There are many manufacturers in the machinery industry or automobiles that require employees to tighten the screws when assembling. “Turn three turns and retreat half a circle”. Many people don't quite understand what it means. Why do you want to retire? Everyone tightens the screws and tightens them up. Why do you want to “snap and retreat”? Today, stainless steel screw manufacturers tell you why this is:
After tightening, the stainless steel screws should be additionally applied with a pre-tightening force to prevent loosening. Therefore, the pre-tightening force will be eliminated after loosening half a turn, and the screws will be elastically deformed after tightening, especially in the case of high temperature and shock load. Under the long-term, such continuous pressure will produce creep, and after the screw becomes plastically deformed, its strength will drop or even fail. Retracting a half turn is to restore the elastic deformation and eliminate the pre-tightening stress. After the screw is subjected to continuous pressure deformation or elastic deformation, the probability of plastic strain and failure is greatly reduced, so that the screw can maintain a constant high-strength pressure. And directly twisting two and a half turns can not achieve this effect.
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