(1) The amount of abrasion of the grinding body

The loading of the grinding body in the ball mill is usually determined according to the filling factor or the filling rate, and the filling factor of the general ball mill is mostly 0.28-0.32. Many studies and practices have proved that the filling factor of the grinding body can be appropriately increased, that is, the loading amount of the grinding body can be appropriately increased, especially in the fine grinding bins. Firstly, increasing the filling volume of the grinding body can increase the probability of grinding or grinding without changing the gradation; secondly, after the filling rate increases, the center of gravity of the grinding body approaches the axis of the mill, and the total acting moment is not obvious. Increased, it will not affect the power transmission. In fact, the power reserve of the motor associated with the mill completely allows the load to be increased within a certain range. It has been proved that the mill output can be increased by about 20% after properly increasing the grinding volume.

(2) The gradation optimization of the grinding body

The gradation optimization of the grinding body in the mill has been one of the hot topics in the cement grinding technology. In recent years, there have been many reports on the practice of steel ball grading. There are also many regular experiences, such as the average ball diameter method and Steiner curve method. Several important parameters to be solved in the grading determination are: large diameter, average diameter, and number of steel balls (or segments), and the proportion of each level. In fact, there are many factors that affect the grading of the grinding body, and many methods are only a better choice under certain materials and process conditions. Here are some views on the issues that should be considered in the determination of the grinding body grading.

1) The calculation of large diameter and average diameter should take into account the grindability or brittleness of the material.

The friability of materials calcined by different kiln types is different. Even if the clinker is calcined with the same kind of clinker, the processability and firing conditions are different, and the friability is often not the same. In addition, when the slag is used as the slag ball mill, the particle size is relatively small and it is difficult to grind. Therefore, the proportion of the small-sized grinding body must be appropriately increased in the ball.

2) In the pre-crushing grinding process, the adjustment of the average ball diameter and the number of stages of the grinding body in the coarse grinding bin should be determined depending on the pre-grinding equipment.

Specifically, the crushing clinker by roll pressing and extruding has a large number of crack defects in addition to the smaller particle size, and therefore it is easier to crush after entering the grinding; and the clinker particles after impact crushing are more uniform. At the same time, the crushing is mainly caused by the internal crack propagation, and there are relatively few internal defects in the particles, so it is relatively difficult to crush them after entering the grinding. Therefore, the two pre-shredding systems should be treated differently when equipped with balls.

3) The fineness and properties of the milled cement.

Finished cement fineness is one of its direct quality indicators. For an open circuit system, this index depends on the grading of the grinding body in the grinding mill. For a closed circuit system, if the fineness of the grinding cement is too coarse, it will inevitably lead to an excessive cyclic load rate and increase the pressure on the separator. On the other hand, the separator's critical separation particle size is defined by 0.08mm, which is 80um. It is impossible to change the content of each particle size class that is smaller than this particle size. For some cements, it is required to increase the early strength or to increase 28d strength, so the particle size distribution of the cement has a corresponding requirement, if the former, it is hoped that the content of fine particles <10um larger, to achieve this, you must increase the proportion of the grinding body within the small size.

4) Liner and grinding material

The stable grinding process conditions depend to a large extent on the material of the liner and the grinding body. If the hardness, wear resistance and impact resistance of the liner material are poor, the inner surface of the liner material will quickly change the original geometry; Similarly, the grading of the grinding body is dynamic and constantly changing during the operation of the mill. If the wear resistance and mechanical strength of the grinding body do not meet the requirements, after a period of grinding operation, the original good grade Matching is obviously difficult to guarantee. Although people have summarized many ways to make up the ball, after all, the wear laws of grinding bodies of different sizes are different during the grinding process, so the compensating ball can only maintain the relative balance of the load and can not maintain the consistent grading. . Therefore, the improvement of the material of the liner and the grinding body is the fundamental guarantee for the long-term stability of the grinding body grading and the working conditions of the mill and the improvement of its operation rate and production efficiency.

For liners, the material conditions necessary for long-term work are: uniform hardness and structure, high impact fatigue strength, low wear rate, no deformation, and no fracture. Obviously, ordinary steel liners are difficult to have these characteristics. The high-chromium white iron lining plate has high hardness and wear resistance, but its stress concentration sensitivity is high. The bainitic iron ball lining plate has high bending fatigue resistance and excellent wear resistance compared with the high manganese steel liner plate. The service life can be increased by more than 1 time; the service life of the multi-element low-alloy steel liner is more than 4 times that of the high-manganese steel liner.

5) Grinding media consumption is the main material consumption in the cement grinding process. It includes abrasion due to mutual friction between the grinding bodies and their materials, and loss due to self-fragmentation. Excessive loss of the grinding body not only affects the grinding ability of the grinding machine, but also results in a low operating rate and unstable working conditions caused by frequent stoppages of the ball, and directly increases the grinding cost. Grinding 1t cement ordinary ball grinding body loss is roughly 1000g, the ball filling cycle is mostly about 15d, while the wear ball, such as bearing steel ball, high chromium ball, low alloy steel ball loss can be reduced to 30g/t-40g /t, the average wear is about 60g/t, the loss is only 1/15—1/20 of the former, and the ball filling period can reach more than 180d. Considering factors such as the operating rate and the improvement of the grinding efficiency, the economic benefits are self-evident.

It is not difficult to see that although the price of the wear-resistant ball is more expensive, its excellent performance can not only greatly reduce the working strength of the clearance filling ball, but also greatly stabilize the working status of the grinding mill, improve the grinding ability of the grinding mill machine, and at the same time significantly reduce the powder. Grinding costs can bring considerable economic benefits.

It is worth mentioning that when the material is finely pulverized, the influence of the density of the grinding body is greatly weakened, and the importance is its hardness and surface area. In the test mill, the slag of the same size steel balls and ceramic balls of φ10mm and φ5mm are used respectively. The results of the grinding test show that under the same grinding conditions, the particle size distribution of the materials after grinding (especially 10um-30um and <10um) is basically the same, which is positive for reducing transmission power and reducing power consumption of grinding.