Ball mill is one of the commonly used equipment in mineral processing equipment. For the ball mill, the reasonable amount of ball loading not only affects the improvement of grinding efficiency and productivity, but also relates to the service life of the ball mill. Therefore, mastering the reasonable ball loading amount and ball loading ratio of the ball mill is a very important link in the use of the ball mill.

Selection of ball loading quantity

When the ball mill is working, its efficiency generally depends on the sum of work done by each steel ball (number of impacts and impact force). Therefore, it is necessary to give full play to the efficiency of each steel ball, which is to make the steel ball moving along different tracks (tracks) to avoid collision as much as possible.

The amount of ball loading is too much, and the steel balls are stacked against each other, which can not give full play to the crushing capacity of each steel ball, and increase the kinetic energy consumption; Too little, although the crushing capacity of each steel ball has been fully developed, the total crushing capacity is still limited; Therefore, it is necessary to choose the appropriate ball loading amount.

When the speed of the ball mill is fixed and the ball loading amount is 30%, the movement of the ball is mainly sliding, but it has begun to pour; When the ball load exceeds 40%, the ball movement is mainly in the form of tilting. When the amount of ball loading reaches 50% of the total capacity of the cylinder, because the surface of the ball group is right on the diameter line of the cylinder, it is easy to produce tipping. Tilting is required for ball mill production, so it is more appropriate to load the ball between one-third and one-half, and close to one-half is ideal.

According to the actual results of the laboratory, when the filling amount of steel balls in the cylinder is 40%, the output is the highest, and the filling rate of steel balls in the production is generally about 35%, that is, the volume of the ball is lower than the horizontal center line.

Selection of ball filling ratio
Determine the appropriate ball loading amount, but also choose the appropriate ball loading ratio, considering factors mainly include the size of the steel ball, the ball diameter series, the proportion of various specifications of the ball. Reasonable steel ball grading is the key to meet the requirements of grinding, which directly affects the grinding efficiency and ultimately affects the output of the ball mill.

The main function of the steel ball in the ball mill is to impact the crushing of the material, and it also plays a certain role in grinding. Determining the steel ball grading in addition to considering the size of the ball mill, the internal structure of the ball mill, product fineness requirements and other factors, but also consider the characteristics of the grinding material (grindability, particle size, etc.), generally follow the following principles:

1, the steel ball should have a large enough impact force, the hardness of the material is large, the diameter of the steel ball is large;

2, under the premise of ensuring sufficient impact force, minimize the diameter of the grinding body, increase the number of steel balls to improve the number of impact on the material, in order to improve the crushing efficiency;

3, the steel ball must have a certain ability to control the flow rate of the material to ensure that the material in the mill has enough residence time to be fully crushed.

When grinding powder in the ball mill, the following steel ball ratio grinding efficiency is the highest, which is an economic operation state:
More common in production is the two-stage ratio and multi-stage ratio, the general multi-stage ratio follows, large, small balls, middle balls, that is, "less at both ends, more in the middle" principle (as shown in the table above); The so-called two-stage ball method is to use two different sizes and large diameters of the two steel balls for grading.

The theoretical basis is that the gap between large balls is filled by small balls to fully increase the packing density of steel balls. The large ball can impact the material to break, improve the impact capacity and impact times of the mill, in line with the functional characteristics of the grinding body; The ball can fill the gap between the big balls, increase the packing density of the grinding body, and control the flow rate of the material; In addition, the coarse particle material in the gap can be squeezed out and placed in the impact zone of the large ball.

Generally, coarse ore particles should be hit by large steel balls, and fine ore particles need to be mill by small steel balls, too many large balls, and the grinding is not fine, which is manifested as "undergrinding"; On the contrary, too many small balls, large surface area, too much crushing will increase, and at the same time, due to too few large balls and insufficient ball striking force, the so-called "over-grinding and under-grinding" will be formed. Therefore, it is very important to correctly determine the size of the maximum and minimum balls for reasonable ball loading and improving the grinding efficiency.
Two-stage ball matching method needs to determine the following parameters:



(1) Determination of the diameter of the big ball. Depends on the size of the ball mill, the particle size of the grinding material and the ease of grinding. Generally, the second level ball diameter in the multi-level ball matching shall prevail. If the maximum ball diameter of a billiard mill is 100mm in the multi-stage ball matching, a steel ball with a diameter of 90mm should be selected when the two-stage ball matching is carried out.



(2) Determination of ball diameter. Depends on the size of the space between the big balls, that is, depends on the diameter of the big balls. Under normal circumstances, the diameter of the ball is 20%-30% of the diameter of the large ball.



(3) The ratio of large and small balls. In principle, it should be ensured that the amount of pellet incorporation does not affect the filling rate of the large ball. Generally, small balls account for 3%-5% of the weight of large balls.

How to judge whether the proportion of ball loading is reasonable?
In addition, in actual production, the rationality of the loading ratio can be checked from the following two aspects:

1, the amount of ore and classifier overflow fineness is unchanged, and the amount of sand return is reduced, which means that the grinding effect of the ball mill is strengthened, and the amount of ore can be increased at this time.

2, if according to the screening analysis results of the classifier sand return, it is found that the ore particles close to the overflow size increase, indicating that the number of pellets is insufficient; On the contrary, if the coarse grain is increased, it indicates that the number of large balls is insufficient.