Explanation of screw
A cylinder with a spiral groove or a cone with a spiral groove.
Material requirements
It can be seen from the extrusion process that the screw works under high temperature, certain corrosion, strong wear and large torque. Therefore, the screw must:
screw
1) High temperature resistance, no deformation at high temperature;
2) Wear resistant, long life;
3) Corrosion resistance, material is corrosive;
4) High strength, can bear large torque, high speed;

5) Good cutting performance;
6) After heat treatment, the residual stress is small and the thermal deformation is small.
Common materials
At present, the commonly used screw materials in China are 45 steel, 40Cr, ammoniated steel, 38CrMoAl, high temperature alloy, etc.
1) 45 steel is cheap and has good processability, but it has poor wear and corrosion resistance.
Heat treatment: quenching and tempering hb220-270, high frequency quenching hrc45-48
2) The performance of 40Cr is better than that of 45 steel, but a layer of chromium is often plated to improve its corrosion and wear resistance. However, the requirement of chromium plating is high, the coating is too thin and easy to wear, and too thick is easy to peel off. After peeling off, it will accelerate corrosion, which has been rarely used at present.
Heat treatment: Hardened and tempered hb220-270, hard chrome plating HRC > 55
3) Nitriding steel and 38CrMoAl have excellent comprehensive properties and are widely used. Generally, the nitriding layer is 0.4-0.6mm. However, the material has low resistance to hydrogen chloride corrosion and high price.
4) The superalloy material is superior to other materials. It does not need coating, and is mainly used in the production of halogen-free screw of injection molding machine. The material has high oxidation resistance and corrosion resistance, heat treatment hra55 ` 60