Cutting picks are cutting tools in the construction process of tunnel boring machines, coal mining machines, and road planers, and they are also one of the commonly used consumable parts of mining equipment. However, excessive consumption of cutting picks will reduce work efficiency and increase mining or construction costs. Therefore, it is meaningful to analyze the cause of cutting pick failure and improve it.
The failure mode of cutting pick
Cutting picks work in rotary mode by contacting with ore and relative movement, and they are subjected to high compressive and shear stresses, high temperature, corrosion, mineral wear, and periodic impact loads. Therefore, the failure modes of the pick include wear, fracture, loss of picks and wear of carbide button, etc. What are the reasons for the failure of cutting picks?
Causes of cutting pick failure
Wear of cutting pick
The poor wear resistance of cutting pick includes the poor wear resistance of the pick skirt body material and cemented carbide.
1. The wear resistance of cutting pick skirt body is due to the improper selection of alloy steel for making the pick material, the low hardenability of the material, and the improper heat treatment process, resulting in low surface hardness of cutting pick after heat treatment, which cannot reach the cutting pick product standard requirements, poor wear resistance.
2. The poor wear resistance of the cemented carbide at the head of cutting pick is due to the frictional heat generated by the carbide button of the shearer cutting the coal seam, which makes the surface of the carbide button generate high temperature and the alternately changing temperature make the cutting pick bear thermal fatigue wear, alternating the impact load will deform the surface of the carbide button and gradually form microcracks. The microcracks will continue to expand under the action of periodic impact loads. Because the cobalt phase in the surface layer is preferentially consumed, the WC particles will fall off due to the loss of the cohesive effect of the cobalt phase and finally show that the alloy particles will peel off in a large area and cause wear. The service life of coal-pick cemented carbide can be improved by improving the purity of raw materials, changing the carbide composition, optimizing the forming and sintering process, controlling the grain size of the carbide, and performing heat treatment on the carbide.
Fracture of cutting pick
The main reason for cutting pick fracture is that the strength or impact value of cutting pick is low due to improper material selection or heat treatment. In actual production, most of the fractures of cutting picks are the impact value of the material that does not meet the requirements. When the impact value is low, the cutting picks are prone to fracture when encountering overload impact during coal mining. Due to the particularity of cutting pick production, the cutting pick blank not only needs to be die forged but also brazed with cemented carbide. During brazing, it is generally heated by induction, the heating temperature is difficult to control, which will cause the cutting pick material to be coarse, and improper heat treatment will cause the impact value of cutting pick to be low.
Cutting pick loss
Causes of cutting pick loss are the improper brazing process of the carbide button and the poor pre-welding treatment. The carbide head of cutting pick falls off in the later stage because the excessive wear of the front end of cutting pick body makes the carbide head protrude too much, and the weld area decreases, which leads to the insufficient strength of the welding seam and causes the carbide head to fall off. Therefore, it is necessary to improve the brazing quality and weld strength to solve the problem of late falling off of the carbide head of cutting pick, and it is more important to improve the wear resistance of the front end of the skirt body covered with cemented carbide.
