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Factors affecting grinding efficiency of ball mill

With simple structure, stable performance and large crushing ratio (3~100), the ball mill can be wet-ground and dry-ground. It is widely used in mining, building materials, chemical industry, metallurgy, materials and other industrial fields.This paper introduces five factors that affect the grinding efficiency of ball mill.

01, the motion form of the steel ball in the cylinder

Precisely speaking, to a certain extent, the movement of the grinding medium in the cylinder 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 motion area, there is little or no filling in the cylinder, which enables the materials to move in the barrel in a uniform circular motion or falling motion. The collision probability between the steel ball and the steel ball increases, resulting in wear between the steel ball and the lining plate, which further reduces the efficiency of the ball mill.

(2) drop the moving area and fill it appropriately.At this time, the steel ball has an impact effect on the material, which makes the efficiency of the ball mill relatively high.

(3) in the area around the center of the ball mill, the circular motion or dropping motion of the steel ball is mixed with dropping motion, so that the motion range of the steel ball is limited and the abrasion and impact effect is small;

(4) in the blank area, the steel ball does not move. If the amount of filling is too much, the ball's motion range is small or does not move, which will cause a waste of resources and easily cause fault of the ball mill.

It can be known from (1) that, when the filling amount is very little or even no, the ball mill suffers a large loss, which mainly comes from the impact of the steel ball on the material.Now the general ball mill is horizontal, in order to effectively reduce the loss of the ball mill to no material, they invented a vertical ball mill.Traditional ball mill equipment, ball mill cylinder body is rotating, the mixing barrel type equipment is stationary, rely mainly on steel ball inside the barrel and the material of screw device for disturbance and stirring, sphere and material under the action of vertical mixing device in the device, so the material only in conjunction with the effect between steel ball, until the crushing, so in the fine grinding operation and fine grinding operation is very applicable.

02. Speed of revolution

One of the important working parameters of the ball mill is the rotation rate, which directly affects the grinding efficiency of the ball mill.The filling rate should also be considered when considering the rate of rotation.The filling rate is positively correlated with the rotation rate.Keep the fill rate constant when talking about speed of revolution here.No matter what the ball load is in motion, there will be an optimal rotation rate at a certain filling rate.When the filling rate is certain and the rotation rate is low, the energy obtained by the steel ball is low and the impact energy on the material is low. It may be lower than the crushing threshold of ore particles, resulting in ineffective impact on the ore particles, that is, the ore particles will not be broken, so the grinding efficiency of low rotating speed is low.With the increase of rotating speed, the impact energy of the steel ball on the material increases, which increases the crushing rate of the coarse ore particles and improves the grinding efficiency of the ball mill.If the rotational speed continues to increase, when approaching the critical rotational speed, the coarse grain products are not easy to be broken. This is because after the rotational speed is too high, although the impact of the steel ball can be improved, the circulation number of the steel ball drops a lot. The impact number of the steel ball per unit time decreases, and the crushing rate of the coarse ore particles decreases.

03. Addition and size of steel ball

If the amount of steel ball is not appropriate, and the ball diameter and proportion are not reasonable, the grinding efficiency will be reduced.In the process of working, the ball mill suffers a great deal of wear and tear, which is largely due to the failure to control the manual adding of steel ball, which leads to the accumulation of steel ball and the phenomenon of ball sticking, and then produces some wear and tear on the machine.

As the main grinding medium of the ball mill, it is necessary to control not only the amount of steel ball but also its ratio.In the grinding process, the ball diameter is large, the impact wear is larger, the grinding wear is smaller;Ball diameter is small, impact wear is small, grinding wear is large.When the ball diameter is too large, the number of loading in the cylinder decreases, the grinding area of the ball charge is small, the wear of the lining plate and the consumption of the ball will increase.If the ball diameter is too small, the cushioning effect of the material increases and the impact grinding effect is weakened.In order to further improve the grinding efficiency, some people put forward the accurate make-up ball repair method:

(1) screen and analyze specific ores and group them according to their particle size;

(2) analyze the crushing resistance of ore and calculate the precise diameter of each group of ore particles by using the semi-theoretical formula of spherical diameter;

(3) according to the composition characteristics of granule size of materials to be grinded, use the principle of crushing statistical mechanics to guide the mixing of balls, and carry out the mixing of various steel balls according to the principle of obtaining the maximum crushing probability;

(4) as the basis for the calculation of supplementary balls, the types of supplementary balls can be reduced and 2-3 kinds can be added.

04, material level

The material level affects the filling rate, which will affect the grinding effect of the ball mill.Material level is too high, will cause the ball mill block material.Therefore, effective monitoring of material level is very important.At the same time, the ball mill energy consumption and material level has an indelible relationship.For the intermediate storage type pulverizing system, the power consumption of the ball mill accounts for about 70% of the power consumption of the pulverizing system and about 15% of the auxiliary power consumption.There are many factors that affect the intermediate storage-type pulverizing system, but under the influence of many factors, it is very necessary to check the material level effectively.

05, lining plate selection

The lining plate of the ball mill can not only reduce the damage of the cylinder, but also transfer energy to the grinding medium.One of the factors that affect the grinding efficiency of the ball mill is the working surface of the lining plate.In order to reduce the damage of the cylinder and improve the grinding efficiency, it is necessary to reduce the sliding between the grinding medium and the lining plate. Therefore, changing the working surface shape of the lining plate and increasing the friction coefficient between the lining plate and the grinding medium are mainly adopted.Before the use of high manganese steel lining board, now has a rubber lining board, magnetic lining board, Angle screw lining board and so on.These modified linings are not only superior to high manganese steel linings in performance, but also can effectively extend the service life of the ball mill.

By improving the ball ball movement state, speed of rotation, ball addition and size, material level, lining material, can make targeted transformation, better improve the grinding efficiency.