The grinding efficiency of the ball mill is affected by many factors, including: the movement form of the steel ball in the barrel, the rotation rate, the addition and size of the steel ball, the material level, and the use of grinding aids. These factors have an impact on the efficiency of the ball mill to a certain extent.
Five reasons for the low grinding efficiency of the ball mill
1. The movement form of the steel ball in the barrel To be precise, to a certain extent, the movement form of the grinding medium in the barrel affects the grinding efficiency of the ball mill. The working environment of the ball mill is divided into the following categories:
(1) In the surrounding and falling movement area, the filling amount in the barrel is small or even non-existent, so that the material can make uniform circular motion or falling motion in the barrel, and the probability of collision between steel balls becomes larger, causing wear between the steel balls and the liner, further making the ball mill inefficient; (2) In the falling movement area, the filling amount is appropriate. At this time, the steel balls impact the materials, making the ball mill relatively efficient;
(3) In the area around the center of the ball mill, the steel balls move in a circular motion or a mixture of falling and throwing motions, which limits the range of motion of the steel balls and reduces wear and impact;
(4) In the blank area, the steel balls do not move. If the filling amount is too much, the steel balls will move in a small range or not at all, which will cause a waste of resources and easily cause the ball mill to malfunction. From (1), it can be seen that when the filling amount is very small or even zero, the ball mill will suffer greater losses, and the losses mainly come from the impact of the steel balls on the materials. At present, the general ball mill is horizontal. In order to effectively reduce the loss of the ball mill to the material, the vertical ball mill has emerged. In traditional ball mill equipment, the barrel of the ball mill rotates, while the barrel of the stirring type equipment is stationary. It mainly relies on the spiral stirring device to disturb and stir the steel balls and materials in the barrel. The balls and materials rotate in the equipment under the action of the vertical stirring device. In this way, the materials will only interact with the steel balls until they are crushed, so it is very suitable for fine grinding and fine grinding operations.
2. Rotation rate An important working parameter of the ball mill is the rotation rate, and this working parameter directly affects the grinding efficiency of the ball mill. When considering the rotation rate, the filling rate should also be considered. The size of the filling rate is positively correlated with the rotation rate. When discussing the rotation rate here, keep the filling rate constant. Regardless of the motion state of the ball load, there will be an optimal rotation rate at a certain filling rate. When the filling rate is constant, the energy obtained by the steel ball is low, and the impact energy on the material is low. It may be lower than the threshold of mineral particle crushing and cause ineffective impact on the mineral particles, that is, the mineral particles will not be crushed, so the grinding efficiency at low speed is low. As the speed increases, the impact energy of the steel ball increases when it impacts the material, thereby increasing the crushing rate of coarse ore particles and improving the grinding efficiency of the ball mill. If the speed continues to increase, when it approaches the critical speed, the coarse particle product is not easy to be crushed. This is because after the speed is too high, although the impact energy of the steel ball increases, the number of cycles of the steel ball decreases a lot, the number of steel ball impacts per unit time decreases, and the crushing rate of coarse ore particles decreases.
3. The addition and size of steel balls If the amount of steel balls added is inappropriate, the ball diameter and ratio are unreasonable, then the grinding efficiency will be reduced. The ball mill is subject to greater wear during operation, and a large part of the reason is that the manual addition of steel balls is not well controlled, resulting in the accumulation of steel balls and the phenomenon of ball jamming, which in turn causes certain wear on the machine. Steel balls are the main grinding medium of the ball mill, and it is necessary to control not only the amount of steel balls added but also their ratio. The optimization of the grinding medium can increase the grinding efficiency by about 30%. In the process of grinding, the ball with a large diameter has greater impact wear and less grinding wear; the ball with a small diameter has less impact wear and greater grinding wear. When the ball diameter is too large, the number of balls loaded in the cylinder is reduced, the grinding area of ​​the balls is small, and the wear on the liner and the consumption of the balls will increase. If the ball diameter is too small, the buffering effect of the material will increase, and the impact grinding effect will be weakened. In order to further improve the grinding efficiency, some people have proposed a precise filling and replenishing ball method:
(1) Screen the specific ore and group it according to the particle size;
(2) Analyze the ore's anti-crushing performance and use the ball diameter semi-theoretical formula to calculate the precise ball diameter required for each group of ore particles;
(3) According to the particle size composition characteristics of the material to be ground, the principle of crushing statistical mechanics is used to guide the ball matching, and various steel balls are matched according to the principle of obtaining the maximum crushing probability;
(4) The calculation of replenishing balls is based on the calculation of replenishing balls, and the number of replenishing balls is reduced to 2~3.
4. Material level The material level affects the filling rate, which in turn affects the grinding effect of the ball mill. If the material level is too high, the ball mill will be blocked by coal. Therefore, effective monitoring of the material level is very important. At the same time, the energy consumption of the ball mill is also related to the material level. For the intermediate storage type milling system, the power consumption of the ball mill accounts for about 70% of the power consumption of the milling system and about 15% of the power consumption of the plant. There are many factors that affect the intermediate storage type milling system, but under the influence of many factors, effective inspection of the material level is very necessary.
5. The liner of the ball mill can not only reduce the damage to the cylinder, but also transfer energy to the grinding medium. One of the factors affecting the grinding efficiency of the ball mill is determined by the working surface of the liner. In practice, it is known that in order to reduce the damage to the cylinder and improve the grinding efficiency, it is necessary to reduce the sliding between the grinding medium and the liner. Therefore, the main method is to change the shape of the working surface of the liner and increase the friction coefficient between the liner and the grinding medium. High manganese steel liners were used before, and now there are rubber liners, magnetic liners, angle spiral liners, etc. These modified liners are not only higher than high manganese steel liners in performance, but also can effectively extend the service life of the ball mill. Targeted improvements in the movement of the ball mill's steel balls, rotation speed, addition and size of the steel balls, material level, and liner material can effectively improve grinding efficiency.
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