A water pump is a pumping machine that uses the centrifugal movement of water. It consists of a pump casing, impeller, pump shaft, motor, etc. The function of the pump casing exhaust is to discharge air so that the pump can be filled with water before starting the pump for the first time. , So what are the materials for the volute of the pump body and how to choose it?
The consideration factors for the selection of the volute material of the pump body are: a strength; b corrosion resistance; c wear-resistant particle wear; d casting and machining performance; e welding repair performance; f cost.
1.Bronze
In many water pump applications, bronze materials are also used as the pump body. Lead bronze is commonly used in small low-pressure pumps, and lead helps the sealing of the pump body. Tin bronze is used as the body material for larger centrifugal pumps. Although nickel aluminum bronze has the best mechanical properties and corrosion resistance, it is expensive and not competitive.
2. Cast steel
For corrosive and harmful petroleum products, or when the outlet pressure of the multi-stage pump reaches 138Mpa, the specified cast steel or cast stainless steel must be used. In boiler feed pumps and many hydrocarbon applications, martensitic stainless steel is often used. Martensitic stainless steel has good mechanical properties and is suitable for high-pressure working conditions, but its corrosion resistance is not as good as other types of stainless steel. In chemical applications and other corrosive environments, austenitic stainless steel (CF-8M, CF-3M, etc.) is often used as a pump housing material. In addition, austenitic stainless steel can resist corrosion due to high speeds, and It is relatively easy to carry out on-site welding repairs. High-pressure shallow sea water injection pumps have higher requirements for corrosion resistance and mechanical properties. The pump casing is made of duplex stainless steel (50% ferrite + 50% austenite).
As the strength of cast steel becomes higher, usually when the pressure is greater than 16Mpa, the pressure-bearing parts are mostly cast steel. The national standard code is ZG, and the most commonly used grade is ZG230-450. Japan and the United States usually use CS to represent cast steel.
3. Cast iron
For most liquid transportation applications, gray cast iron is a better material for the pump housing. For single-stage pumps, gray cast iron is usually strong enough to resist the pressure generated. In the medium pressure and temperature range, ductile iron is widely used. In applications where gray cast iron and ductile iron cannot achieve sufficient corrosion resistance, corrosion-resistant high-nickel cast iron is often used as the pump body material. In recent years, a new type of corrosion-resistant high-nickel cast iron material (named D2W) with good welding performance has been developed, which contains a small amount of niobium to improve its welding performance. Typical austenitic cast iron contains 15% to 20% nickel and is widely used in salt water.
Gray cast iron is the most commonly used cast iron, the national standard code is HT. Generally, the pump body, impeller, pump cover, suspension, etc. of clean water pumps are all made of this material, and three types of grades are usually used: HT150, HT200, and HT250. For non-main parts such as base and backing plate, HT150 is mostly used, HT200 is mostly used for pump body, pump cover, suspension, etc., and HT250 is mostly used for impeller, mouth ring, and shaft sleeve. Different countries have different ways of expressing gray iron, such as Japan's code name is FC, Germany's code name is GG, and the United States is Class4
Nodular cast iron is a kind of cast iron with better comprehensive performance, and the national standard code is QT. Because its mechanical properties are close to steel, and its casting properties and processing properties are better than steel, it is usually used as a substitute for cast steel. The most commonly used grades are: QT450-10, QT500-7, QT600-3. Due to the limitation of casting and other reasons, the impeller of the current water pump adopts this material, especially the cut-type open impeller is superior in cost performance. The expression method for ductile cast iron in the DIN standard is GGG, and the expression method in the United States is Ductile iron.
4. Composite materials
In order to improve the chemical resistance of the pump, a lining can be installed in the volute. The materials used for the lining are polytetrafluoroethylene, rubber, etc. Monolithic ceramic and graphite pumps are used in particularly corrosive liquids, such as hydrofluoric acid. In the paper and pulp industry, metal finishing industry, composite materials (such as epoxy resin) are used to make pump bodies.
5. Non-metallic materials
Non-metallic materials for pumps are mainly used for sealing, such as polytetrafluoroethylene, fluorine rubber, nitrile rubber, etc. Among them, polytetrafluoroethylene has excellent corrosion resistance and high temperature resistance and is used for chemical pump gaskets and static seals of mechanical seals. It is suitable for almost all chemical media within 250°C. Its disadvantages are high hardness and difficulty in assembly. Large fluorine rubber is also a kind of good temperature resistance and corrosion resistance material. The upper limit of temperature resistance is 160 ℃. When the user has no special requirements, chemical pumps are recommended to use the sealing ring of this material; and nitrile rubber is mainly used for oil resistance. Or static seal in the case of clean water medium.
6. Stainless steel
The most widely used stainless steel is austenitic stainless steel, such as 0Crl8Ni9, 1Crl8Nij9Ti, 0Crl8Ni2Mo2IIi and so on. Except for a few media such as hydrochloric acid and dilute sulfuric acid, austenitic stainless steel is an excellent corrosion-resistant material and the most commonly used corrosion-resistant material for chemical pumps. Japan and the United States usually use SS304, SS316, and SS316L to represent austenitic stainless steel. Martensitic stainless steels such as 2Cr3 and 3Cr13 have better mechanical properties than austenitic stainless steels. They are usually used as materials for pump shafts and bushings. The corresponding codes in Japan and the United States are SS420. In addition, high-alloy stainless steel (alloy 20) and Double stainless steel is also an ideal corrosion-resistant material.
7. Carbon structural steel
Usually divided into ordinary carbon structural steel and high-quality carbon structural steel. The most representative ordinary carbon-bonded steel is Q235, which is mostly used in various steel plates and section steels; the most representative high-quality carbon steel is No. 45 steel, which is widely used as a pump shaft material when no corrosion is required.
8. Alloy steel
The most representative alloy steel is 40Cr, which is usually used as a material for high-strength pump shafts.
