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25 мая 2021 г. 12:29

Why Choose cemented carbide as the material of mining tool

An excellent hard alloy for mining should have high strength, high hardness required for abrasion resistance and high toughness required for resistance to impact fracture. Because of the high hardness, wear resistance, and stable chemical properties, tungsten carbide mining tool is widely used.

tungsten carbide mining buttons

1. Wear resistance of WC alloy

The shearer of the shearer is in direct contact with the coal seam during the working process. The abrasive wear characteristics of the shearer are closely related to the coal seam structure and hardness. The hardness of the coal is low, generally 100 to 420 HV, but the coal often contains different hardness. Impurities such as quartz and pyrite (900 to 1100 HV) have high hardness and have a great influence on the abrasive wear characteristics of picks.

In most of the operating examples, wear resistance is a basic function of material hardness. The higher the hardness, the higher the abrasive wear resistance. Pure WC is very hard and similar to diamond. In cemented carbide, WC particles form a strong skeleton, so WC cemented carbides exhibit very high hardness. In addition, WC belongs to the hexagonal crystal system and has anisotropy in hardness. The Vickers hardness of the bottom surface and the edge surface is 2 100 HV and 1 080 HV, respectively. In the coarse-grained cemented carbide, the proportion of WC grains on the plane is high, and thus the carbide containing the coarse-grained WC shows higher hardness. At the same time, at a high temperature of 1 000°C, coarse-grained WC hard alloys have higher hardness than ordinary hard alloys and show good red hardness.

In the coal cutting process, WC particles are exposed on the surface of the cemented carbide after cemented phases of the cemented carbide in the tool nose protected by the built-up edge have been squeezed away or are carried away by abrasive scraping. Bonded phase-supported WC particles are easily crushed, destroyed and released. Due to coarse WC grains, the cemented carbide has a strong holding force with respect to the WC, and the WC grains are difficult to pull out and exhibit excellent wear resistance.

carbide mining tips

2.Toughness of WC Alloy

When the cutter bit cuts the coal rock, the cutter head is subjected to high-stress stress, tensile stress and shear stress under the action of the impact load. When the stress exceeds the strength limit of the alloy, the alloy cutter head will be fragmented. Even if the generated stress does not reach the strength limit of the cemented carbide, the fatigue cracking of the cemented carbide will occur under the repeated action of the impact load, and the expansion of the fatigue crack may cause the tool head to fall off or chipping. At the same time, when cutting the coal seam, the shearer pick produces high temperature of 600-800°C on the cutting surface, and the cutting cutting coal seam is a periodic rotary motion. The temperature rise is alternating, and the temperature increases when the cutter head contacts the coal rock. , cool down when leaving the coal rock. Due to the constant change of the surface temperature, the dislocation density increases and concentrates, and the surface of the serpentine pattern appears.

The depth of cracks and the rate of propagation decrease with increasing carbide grain size, and the morphology, direction, and depth of cracks also vary with WC grain size. The cracks in fine-grained alloys are mostly straight and small and long; coarse-grained alloy cracks are irregular and short. The cracks mainly extend at the weak grain boundary. In the coarse-grained cemented carbide, if the micro-cracks bypass the coarse-grained WC grains, they are zigzag-shaped and must have energy that matches the fracture area; if they pass through When WC grains are expanded, they must have considerable fracture energy. As a result, the coarse-grained WC grains have enhanced deflection and bifurcation of cracks, which can prevent the further propagation of micro-cracks and increase the toughness of the cemented carbide. With the same content of cementitious phase, the coarse-grained alloy has a thicker bonding phase, which is beneficial to the plastic deformation of the bonding phase, inhibits the extension of cracks, and shows good toughness.

Studies on the strength and structure of WC-Co cemented carbide also show that there is a certain rule between the strength of tungsten carbide and the grain size of WC. When the cobalt content is constant, the strength of conventional low-cobalt alloys always increases as the grain size of WC in the cemented carbide becomes coarser, and the strength of the alloy with higher cobalt content peaks with WC grain coarsening.

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Автор: Статус: offline pinkledstone
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