Common materials and materials for the requirements of the screw
A cylinder with a helical groove on its outer surface or a cone with a conical helical groove. The screw has a different head, like the picture in the head called the hexagonal screw. There are other, such as large flat screws, hex screws, and so on.
Screw Common materials
At present, China commonly used screw material 45 steel, 40Cr, ammoniated steel, 38CrMOAl, high temperature alloys.
1) 45 steel cheap, good processing performance, but poor wear resistance and corrosion resistance.
Heat treatment: quenched and tempered HB220-270, high frequency quenching HRC45--48.
2) 40Cr performance is better than 45 steel, but often to be coated with a layer of chromium, in order to improve its corrosion resistance and wear resistance. But the higher requirements of the chrome layer, the coating is too thin easy to wear, too thick is easy to peel off, but after the spill off the corrosion, has been less applied.
Heat treatment: quenched and tempered HB220-270, hard chrome HRC> 55
3) nitrided steel, 38CrMoAl comprehensive performance is relatively good, more widely used. General nitride layer of 0.4-0.6 mm. But this material is resistant to hydrogen chloride corrosion is low, and the price is higher.
4) high temperature alloy material is superior to other materials, the material without plating, mainly used for injection molding machine halogen-free screw, the material anti-oxidation corrosion resistance, heat treatment hra55 `60.
Screw The requirements of the material
From the extrusion process we can see that the screw is in high temperature, a certain corrosion, strong wear and tear, work under high torque, so the screw must:
1) high temperature, high temperature is not deformed;
2) wear resistance, long life;
3) corrosion resistance, the material is corrosive;
4) high strength, can withstand high torque, high speed;
5) has good cutting performance;
6) heat treatment after the residual stress is small, small heat distortion.