Reasonable selection of wear and wear resistant materials for slurry pump

The abrasive wear of solid particles is the fundamental difference between the design and application of slurry pump and ordinary centrifugal pump. Wear is a complex phenomenon which depends on many inherent characteristics of pump and pumped slurry. Scholars at home and abroad have been doing theoretical and experimental research on wear mechanism for many years. However, it is still not fully understood. There are many wear design factors of slurry pump, and the wear mechanism of different parts and different parts is not the same, but in general, it can be summarized into three categories:

1. Erosion wear

During the operation of slurry pump, solid particles carried in the liquid impact on the surface of flowing parts at a certain speed, resulting in material loss. The erosion wear mechanism can be divided into cutting wear, deformation fatigue wear and cutting + deformation composite wear. The failure analysis of volute and protective plate of slag slurry pump for iron mine shows that the cutting mechanism is the main reason of volute wear, and the deformation fatigue wear is the main reason of protective plate wear.

2. Cavitation damage

In the operation of the pump, the local area of the flow parts (usually the impeller inlet later), for some reason, the absolute pressure of the liquid into the drop to the vaporization pressure of the temperature at that time, the liquid will begin to vaporize, produce steam, the formation of bubbles. These bubbles flow forward with the liquid, and when they reach a high pressure, they shrink sharply and collapse. At the same time of bubble condensation, liquid particles fill the pores at high speed and have a strong impact on the metal surface. The metal surface due to the impact of fatigue and peeling, resulting in material loss, serious metal surface appears honeycomb. Usually cavitation occurs at the impeller outlet and volute inlet.

3. Corrosion and wear

When the conveying medium has a certain ph, the slurry pump flowing parts will also have corrosion wear, that is, corrosion and wear under the joint action of material loss phenomenon. Corrosion can be divided into chemical corrosion and electrochemical corrosion. Chemical corrosion is the direct reaction between metal and liquid medium to cause metal loss, while electrochemical corrosion is the formation of microcells on metal surface under the action of liquid medium to cause material loss. Due to the actual use of metal materials are polycrystalline polyphase materials, therefore, mainly electrochemical corrosion, the occurrence of corrosion, especially the crystal boundary corrosion, the formation of cracks between the metal surface grains, and the grain or hard phase isolation, loss of support, so that will fall off under the erosion of solid particles; And the erosion of solid particles makes the metal surface due to corrosion of the passivation layer is worn away, the liquid medium and the new surface of the metal contact increased corrosion. Corrosion has been found in the failure analysis of slurry pump. The wear rate is closely related to the following three factors:

A. Slurry characteristics. Including solid properties, liquid properties and comprehensive properties depending on the above and other factors;

B. Structural material properties for pumps;

C. Contact characteristics of pumped slurry.

In the above three factors, only the structural material characteristics of the pump can be controlled, so the reasonable choice of pump materials has become the primary task of today's pump industry.

The wear-resistant materials commonly used in slurry pumps are metal wear-resistant materials, rubber and ceramics. Each material has different wear characteristics, and also has its own adaptive economy of return on investment. The selection of materials cannot rely solely on the initial input of the pump.

Metal wear-resistant material: mainly used in slurry containing thick and sharp mineral processing and ore processing industry. The hardness of general alloys determines the resistance to particles. With higher shear hardness and compressive strength will improve the wear resistance of pump parts. The commonly used metal materials of slurry pump are shown in Table 1.

Hard nickel material has better wear resistance to sharp particle wear, but the material is brittle, easy to suffer from large Angle deformation wear, usually not applied to transport larger particles of dredging pump. Hard nickel no. 1 and No. 4 are commonly used in high-lift pumps that require higher toughness. Cr15Mo3 is an excellent abrasion resistance material recognized in the world at present. It has better abrasion resistance to coarse particles and strong abrasion slurry, but it has high price and is more brittle. Rubber material: there are natural rubber and synthetic rubber two categories. Rubber is suitable for conveying slurry pump with maximum particle size less than 10 m (average particle size 3 m). Its wear resistance is better than metal material. Therefore, glue pump is mostly used for conveying fine granule slurry without edges and corners.

Ceramic surface coating: although ceramic materials have high hardness, wear resistance, corrosion resistance and other characteristics, but because of its own brittleness and large shortcomings, so that it is difficult to apply in the slurry pump. However, using surface coating method to form ceramic coating on metal surface can not only exert the wear resistance and corrosion resistance of ceramic materials, but also improve the service life of metal materials, which can be regarded as a direction of material research and development of slurry pump flowing parts. H. X. Z H A O et al. formed Cr O coating on the surface of SUS329J1 dual-phase stainless steel by plasma spraying method, and carried out tests. The results show that Cr O coating significantly improves the wear resistance of corrosion and erosion wear of SUS329J1 dual-phase stainless steel. Although ceramic coating can improve the wear resistance of metal, there are still many problems to be solved in the practical application of this method in slurry pump.

With the development of industrialization and environmental protection, more and more slurry pumps are used, and the choice of material is more and more important. Reasonable material selection can not only reduce material consumption, but also reduce maintenance costs and energy consumption, thus improving production efficiency and economic benefits. As you know, no matter how high the quality of pump design and manufacturing, if the material selection is not reasonable, it will not achieve the ideal operation effect, life is difficult to achieve the ideal state. Therefore, the reasonable choice of slurry pump wear and material should be considered comprehensively from the actual conditions of working conditions.