1. Thread forming: all are rolled (ie, "thread r […]
1. Thread forming: all are rolled (ie, "thread rolling" in other answers), and no turning is allowed, because the surface of the thread is more likely to have microscopic defects, which will have a large impact on the fatigue life;
2. It is required to roll the thread after heat treatment, otherwise, bimetallic screw barrel if the thread is rolled first, some micro-defects may be deteriorated during the heat treatment process; although RAHT will cause the thread rolling process to be more expensive due to the increase in hardness after heat treatment, the thread rolling process is more expensive, but the industry has been Strict this requirement, so I did it;
3. Surface anti-corrosion treatment: zinc-chromium coating (Dacromet) is widely used, which can be understood as multiple layers of zinc flakes repeatedly coated on the surface. On the one hand, zinc oxygen passivation is used to protect the internal steel, and the other On the one hand, multiple layers of scales form a labyrinth-like effect, which greatly lengthens the path for air/moisture to enter the contact steel.