The pump body materials of centrifugal pumps are commonly cast iron, stainless steel, cast steel, bronze, composite materials, carbon structural steel, alloy steel and non-metallic materials. These factors should be considered when selecting materials: a strength; b corrosion resistance; ε resistance Abrasive wear; d casting and machining performance; ε welding repair performance; f cost. Now we come to the specific introduction.
One, cast iron
For most liquid transportation applications, gray cast iron is a better material for 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 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 15920% nickel and is widely used in salt water.
Gray cast iron is the most commonly used cast iron, and the national standard code is HT. Generally, the pump body, impeller pump cover, suspension, etc. of clean water centrifugal pumps are made of this material, and three grades are usually used: HT150, HT200, HT250. HT150 is mostly used for non-main parts such as base and backing plate, pump body, pump Covers, suspensions, etc. mostly use HT200, while impellers, spigots, bushings, etc. mostly use HT250. The representation of gray iron varies from country to country. For example, the code name of Japan is FC, the code name of Germany is GG, and the United States is Cass4.
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 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 limitations of casting and other reasons, the impeller of the current water pump uses this material, especially the cutting-type open impeller. DN standard expresses nodular cast iron as GGG, and the American express method is Ductile iron
Two, stainless steel
stainless steel is the most widely used stainless steel is austenitic stainless steel. 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. In addition, high-alloy stainless steel (alloy 20) and double stainless steel are also ideal corrosion-resistant materials
Three, cast steel
For corrosive and harmful petroleum products, or when the outlet pressure of the multi-stage pump reaches 13.8Mpa, the specified cast steel or cast stainless steel must be used. In boiler feed water 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 applications. In the environment, austenitic stainless steel (CF-8M, CF-3M, etc.) is often used as a pump casing material. In addition, austenitic stainless steel can resist corrosion due to high speed and can be relatively easily welded on site. repair. 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, the most commonly used grade is ZG230-450 Japan and the United States usually use CS to represent cast steel
Fourth, carbon structural steel
is usually divided into Katong carbon structural steel and high-quality carbon structural steel. The most representative ordinary carbon structural 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.
Five, alloy steel
The most representative alloy steel is 40Cr, which is usually used as a material for high-strength pump shafts.
6. 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. Big
Fluorine rubber is also a kind of better temperature resistance and corrosion resistance material. The upper limit of temperature resistance is 160℃. When the user has no special requirements, the company’s chemical pumps all use the sealing ring of this material; while the nitrile rubber is mainly used for oil resistance or Static sealing for clean water medium.
Seven, 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
8. 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 PTFE, 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, and composite materials (such as epoxy resin) are used to make pump bodies.
