Analysis of pick loss and its influencing factors

Pick is a cutter installed on the working mechanism of shearer and roadheader for direct cutting of coal and rock. In the process of coal production, a large amount of pick consumption not only increases the cost per ton of coal and affects the economic benefits of coal production, but also reduces the output of the working face due to the increase of the time to replace the pick. Therefore, it is very necessary to analyze and determine the main factors causing the damage of the pick and take effective measures to reduce the consumption of the pick. However, at present, there are no exact records and statistical analysis on the damage forms of pick in China, and the consumption of pick has always been estimated, or determined according to the records of picking at ordinary times until the end of the year. These methods are inaccurate, unscientific and unpredictable. It is not convenient to accurately formulate the plan of coal production cost, and it is also impossible to take effective measures against the main influencing factors to reduce the consumption of pick. This paper will give the calculation method of the consumption of pick damage due to wear from determining the main form of pick damage. On this basis, the influence of various factors on pick consumption is systematically analyzed.

1. Main forms of pick damage and determination of its consumption

The damage forms of pick include breaking, loss, wear, alloy falling off and so on. The investigation results show that the damage caused by wear accounts for about 50% of the total consumption of pick. It can be seen that wear is the main form of pick damage. Further analysis shows that the breaking and loss of pick belong to sudden faults, and there are many random factors, so it is not suitable to predict. Wear is the normal fault form of pick, which is related to its structure, working condition and other factors. Therefore, it is more practical to determine the consumption of pick according to wear and scrap.

2. Analysis of factors affecting pick loss

2.1 coal rock characteristics

In order to analyze the influence of the characteristics of coal and rock on the pick consumption, the above calculation formula is used to simulate the relationship between the pick consumption N and the grindability of coal and rock, the uniaxial instantaneous compressive strength ay and the density p of coal and rock, as shown in Figure 1 (curves 1, 2 and 3 in the figure respectively).

It can be seen from the figure that the consumption of pick is linear with the grinding performance and uniaxial instantaneous compressive strength of coal and rock, and changes in direct proportion. The greater the grinding performance and instantaneous compressive strength of coal and rock, the more serious the wear and loss of pick; Moreover, when the grinding performance of coal and rock is weak, the pick damage caused by compressive strength is more, and with the enhancement of grinding performance, the pick damage increases significantly; The consumption of pick decreases with the increase of coal and rock density. After reaching a certain degree, the change tends to be gentle.

2.2 motion parameters of Shearer

The motion parameters of the shearer include the traction speed V of the shearer and the rotating speed n of the spiral drum. In order to analyze the relationship between the consumption of the pick and the motion parameters of the shearer, the simulation curve is obtained as shown in Figure 2.

2.3 drum structure parameters

The diameter and width of the drum are two parameters reflecting its shape and structure. The influence of its size on the consumption of pick is shown in Figure 3 (curves 1 and 2 in the figure respectively). The simulation results show that the pick consumption increases with the increase of drum diameter and decreases with the increase of drum width. This is because when the diameter of the drum increases, the number of teeth in contact with coal and rock increases, resulting in increased pick wear and loss; The increase of drum width means that the productivity of shearer is improved (when the traction speed does not change), so the pick consumption per unit output will be reduced.

2.4 the number of pick teeth and the working conditions

The number and arrangement of picks installed on the drum also have a certain impact on the cutting process. Figure 4 shows the influence of different pick numbers (curve 1) and the time constant of the contact between the pick and the coal wall (related to the arrangement of the pick and the height of the drum coal cutting) (see curve 2) on the pick consumption. It can be seen from the figure that the more the number of picks on the drum, the more the picks involved in cutting, so the greater the loss of picks; The longer the contact time between the pick and the coal wall, the greater the wear, and the consumption of the pick increases accordingly. Therefore, it is not suitable to install too many pick on the drum. At the same time, the phenomenon that the cutting height of the drum exceeds its diameter should be avoided in the work.

2.5 status and wear resistance of pick

Figure 5 shows the total wear area of the pick (the difference between the maximum wear area allowed by the pick and the initial wear area), the wear resistance of the alloy, and the relationship curve between the pick type constant (related to the shape of the tip) and the pick consumption (curves 1, 2 and 3 in the figure respectively). It can be seen from the figure that the lighter the wear of the pick when it starts working (the smaller the initial wear area), the larger the area available for wear before scrapping, the longer its service time and the less the consumption of the pick; The better the alloy wear resistance of the pick, the smaller the wear amount, the less the tooth consumption; For different types of pick, due to the difference of the structural shape and geometric size of the tooth tip, the allowable maximum wear area and initial wear area are different in the working process, so the consumption is also different.

2.6 stress of pick

During the cutting process of the pick, the force also has a great impact on its wear. The relationship between the traction resistance (or feed force, equivalent to positive pressure) of the sharp pick and the pick consumption is shown in curve 1 in Fig. 6. It can be seen that there is a proportional relationship between the two, that is, the greater the force on the pick, the greater the wear, and the more the pick consumption.

Because the cutting resistance and traction resistance of the pick are linear, the consumption of the pick also increases linearly with the increase of cutting resistance.

2.7 mining height of working face

Mining height is the height of the working face cut by the shearer. The influence of its size on the consumption of pick is shown in curve II in Figure 6. The results show that the consumption of pick decreases with the increase of mining height, and the smaller the mining height, the more the tooth consumption. The reason for this phenomenon is that due to the extrusion effect (or crisp effect) of coal and rock in the working face, the greater the mining height, the more obvious the effect, the less labor-saving the pick cutting, the less its wear, and the less the consumption of the pick.