From the extrusion process, it can be seen that the screw operates under high temperature, certain corrosion, strong wear, and high torque. Therefore, the screw must:

screw

1) High temperature resistance, without deformation at high temperatures;

2) Wear resistance and long service life;

3) Corrosion resistant, materials have corrosiveness;

4) High strength, capable of withstanding high torque and high rotational speed;

5) Has good cutting performance;

6) After heat treatment, the residual stress is small and the thermal deformation is small.

At present, the commonly used screw materials in China include 45 steel, 40Cr, ammoniated steel, 38CrMOAl, high-temperature alloys, etc. 1) 45 steel is cheap and has good processing performance, but its wear and corrosion resistance are poor. Heat treatment: quenched and tempered HB220-270, high-frequency quenched HRC45-48. 2) The performance of 40Cr is better than that of 45 steel, but it often requires a layer of chromium plating to improve its corrosion and wear resistance. However, high requirements are placed on the chrome plating layer. If the plating layer is too thin, it is prone to wear and tear, while if it is too thick, it is prone to peeling off. After peeling off, it actually accelerates corrosion and is less commonly used. Heat treatment: quenched and tempered HB220-270, plated with hard chromium (HRC>553), nitrided steel, and 38CrMoAl have excellent comprehensive properties and are widely used. The general nitride layer reaches 0.4-0.6 millimeters. But this material has low resistance to hydrogen chloride corrosion and is relatively expensive. 4) High temperature alloy materials are superior to other materials. This material does not require coating and is mainly used for producing halogen-free screws in injection molding machines. This material has high corrosion resistance,

heat treatment

Quenching and tempering HB220-270, nitriding HRC>65. The method of using titanium carbide coating abroad to improve the corrosion resistance of screw surface is useful, but according to reports, its wear resistance is not good enough.

screw

A series of measures have been taken abroad to improve the wear and corrosion resistance of screws. One approach is to use highly wear-resistant and corrosion-resistant alloy steel. Such as 34CrAlNi, 31CrMo12, etc. There is also a method of spraying Xaloy alloy on the surface of the screw. This Xaloy alloy has high wear and corrosion resistance.