The material of the main parts of the screw pump should be selected according to the chemical and physical properties of the conveyed medium and the pressure of the pump:
1. Materials such as cast iron, cast steel and stainless steel can be used for the flow-passing parts (suction chamber, discharge chamber, sealing box, etc.);
2. The shaft is made of 45 high-quality carbon steel, 40Cr alloy structural steel or stainless acid-resistant steel;
3. The rotor can be made of 40Cr, 45 steel, 38CrMoAl, 1Cr18Ni12Mo12Ti and other materials;
4. The material of the rotor should be selected mainly according to the characteristics of the medium. Commonly used materials include natural rubber (NR), styrene-butadiene rubber (SBR), nitrile rubber (NBR), polyurethane rubber (UR), ethylene-propylene rubber (EPM), fluoro rubber (FPM), chlorosulfonated polyethene rubber (CSM), etc.
5. There are several kinds of stator rubber sleeves for screw pumps:
1) Natural rubber: high elasticity, excellent tear resistance, and good wear resistance, it is the material of the stator. However, its poor oil resistance and solvent resistance, low acid and alkali corrosion resistance, and low heat resistance limit its application. The use temperature is within 60°C.
2) Nitrile rubber: It has particularly good resistance to gasoline and aliphatic hydrocarbon oils, good heat resistance, good wear resistance, lower elasticity than natural rubber, and general acid and alkali resistance. It is a stator material with the same utilization rate as natural rubber. The use temperature is within 90°C.
3) Silicone rubber: non-toxic and tasteless, mainly used in occasions with hygienic requirements such as food and pharmaceutical industries. It has high stability to thermal oxidation and ozone and is chemically inert. The use temperature is within 100°C.
4) Fluorine rubber: acid and alkali resistance, oil resistance is the best in oil-resistant rubber; chemical corrosion resistance, ozone resistance, and atmospheric ageing resistance are all excellent. Expensive compared to other rubbers. It is mainly used in occasions where the medium is highly corrosive.
5) Solvent rubber: no swelling or very slight swelling in organic solvents, specially developed for transporting organic solvents.