The twin-screw extruder is composed of many parts, amon […]
The twin-screw extruder is composed of many parts, among which the screw is a more critical part, and its quality directly affects the extrusion effect. So what kind of steel is used for the screw of the twin-screw extruder? What are the common types?
What kind of steel is used for the screw of the twin screw extruder
The commonly used screw materials in our country are No. 45 steel, 40Cr, ammoniated steel, 38CrMOAl, high temperature alloy and so on.
1. No. 45 steel is cheap and has good processing performance, but poor wear resistance 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 plated with a layer of chromium to improve its corrosion resistance 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, it will accelerate the corrosion. It has been less used. Heat treatment: tempered HB220-270, hard chrome plating HRC>55.
3. Nitrided steel and 38CrMoAl have excellent comprehensive properties and are widely used. Generally, the nitride layer is 0.4-0.6 mm. However, this material has low resistance to hydrogen chloride corrosion and is relatively expensive.
4. The high-temperature alloy material is superior to other materials. This material does not require coating and is mainly used for halogen-free screw of injection molding machine. This material has high oxidation and corrosion resistance and heat treatment hra55`60.
Common types of screws
1. The common structural feature of the split-flow screw is that a boss is milled on the rod or a mirror nail is installed, and a splitter ditch or splitter hole is opened. The model assembled with the screw has high plasticization efficiency, good mixing uniformity and good product quality, and it has been widely used at home and abroad.
2. The structural feature of the barrier type cricket rod is to set a "barrier" at a certain position on the screw to achieve the purpose of preventing the solid phase of the material from passing and promoting the solid phase to melt. One of the simplest is to configure a barrier-type mixing element at the head of an ordinary screw. Mainly used for polyolefin materials.
3. The structural feature of the variable flow passage screw is that the cross-sectional shape or cross-sectional area of the screw flow passage is the angle of change. Its representative is the corrugated screw. Due to the frequent compression, shearing and relaxation of this kind of screw, it is not suitable for heat-sensitive plastic processing. Although the double groove screw is difficult to process and manufacture, it has better plasticization and mixing quality, suitable for difficult-to-process plastics, and has high plasticization efficiency.
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