What are the causes of pick failure

The pick is divided into shearer pick and roadheader pick. It is a part of the mining roadheader. It is used together with the shearer and is suitable for coal mining. The main failure forms of the pick are the falling off of the cutter head, the collapse of the cutter head and the wear of the cutter head and the cutter body. Under some working conditions, the pick often fails due to the breakage of the cutter body. The mechanical performance of the cutter body directly affects the service life of the pick, Therefore, reasonable selection of the material and effective heat treatment method of the cutter body is of positive significance to reduce the wear and fracture of the cutter body, reduce the consumption of shearer cutters, improve the operation rate of coal mining machinery and increase the comprehensive economic benefits of coal mining production. Among them, the cutter of the roadheader requires high hardness. Next, let's talk about the causes of the cutter failure.

1. quality problem of cemented carbide head. The cemented carbide head contains graphite impurities, the grain distribution is uneven, and cracks exist in some cemented carbide. Under the impact load, the pick cutter head is in a high stress state. When encountering hard coal and rock, the high-pressure stress exceeds the strength limit of cemented carbide, brittle fracture will occur, which is the main reason for the cracking of cemented carbide head. If the content of CO in cemented carbide is insufficient, resulting in insufficient toughness, under the action of impact load, the cemented carbide head is also prone to brittle fracture. The density difference between the upper and lower parts of the alloy is large, there are many pores, and the hardness is low, which is also easy to cause cracking.

2. the brazing residual stress is large, and copper zinc brazing filler metal is mostly used for the pick, and its welding temperature reaches more than 920 ℃. The expansion coefficients of cemented carbide, brazing filler metal and base metal are very different, and the shrinkage degree of the three materials is different when cooling. The copper shrinkage is the largest, the base metal is the second, and the cemented carbide is the smallest. Thus, there must be a large tensile stress between the cemented carbide and the filler metal, and between the filler metal and the base metal. Because the thermal expansion coefficient of the alloy cutter head and the tooth body material is quite different, and the shrinkage difference during cooling increases with the increase of brazing temperature. As a result, the weld strength decreases, and the carbide head is subject to strong impact load during cutting, resulting in brittle fracture.

3. abrasive wear. Some alloy elements in the alloy can not meet the requirements, the cobalt content is high, the structure is incomplete, the density is low, the hardness is not high, and the structure is uneven, resulting in the poor wear resistance of the pick alloy cutter head, which is the main reason for the wear of the cemented carbide head; Due to the unstable quality and performance of the raw materials of the tooth body and the improper control of the heat treatment process, the head of the pick has cracks and the hardness is low, which affects its wear resistance.

4. wear caused by low red hardness. Red hardness refers to the ability of prop materials to maintain high hardness at high temperature. Theoretically, cemented carbide can maintain high hardness at high temperature of 800-1000 ℃. However, due to some practical problems in the production of cemented carbide, the red hardness of the pick is low. When cutting coal and rock, the surface temperature of the cutter head can reach 600-800 ℃, and its hardness decreases by about 50%. The softening of the material accelerates the wear of the pick, The alloy head fell off due to welding and shape design.