Screw: a cylinder with spiral grooves cut on the outer surface or a cone with conical spiral grooves cut on the outer surface. The screw has different heads. The head like the one in the picture is called an external hexagonal screw. There are others, such as large flat screws, hexagon socket screws, etc.

Currently commonly used screw materials in my country include No. 45 steel, 40Cr, ammoniated steel, 38CrMOAl, high-temperature alloys, etc.

1. No. 45 steel is cheap and has good processing performance, but 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 No. 45 steel, but it is often coated with a layer of chromium to improve its corrosion and wear resistance. However, the requirements for the chromium plating layer are relatively high. If the plating layer is too thin, it is easy to wear, and if it is too thick, it is easy to peel off. After peeling off, it will accelerate corrosion and is rarely used. Heat treatment: quenched and tempered HB220-270, hard chromium plating HRC>55.

3. Nitride steel and 38CrMoAl have excellent comprehensive properties and are widely used. Generally, the nitride layer reaches 0.4-0.6 mm. However, this material has low resistance to hydrogen chloride corrosion and is expensive.

4. High-temperature alloy materials are superior to other materials. This material does not require coating and is mainly used to produce halogen-free screws for injection molding machines. This material has high oxidation and corrosion resistance and has a heat treatment of hra55`60.

Screw heat treatment:

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

Foreign countries have taken a series of measures to improve the wear and corrosion resistance of screws. One way 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 screw surface. This Xaloy alloy has high wear and corrosion resistance.