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Working principle of ball mill and movement analysis of ball

Date:2019-05-30 13:40     writer:admin     Views:

 

  Working principle of ball mill:

  The main working part of the ball mill is a rotating cylinder mounted on two large bearings and placed horizontally. The cylinder is divided into several compartments with compartments, in which grinders of a certain shape and size are installed.

  The grinding body is generally steel ball, steel forging, steel bar, pebble, gravel and porcelain ball, etc.

  In order to prevent the cylinder from being worn, lining plates are installed in the inner wall of the cylinder.

  When the ball mill turning, grinding medium in a centrifugal force and the lining board face to cylinder under the action of friction, attached on the cylinder body wall lining board face, together with the cylinder, and taken to a certain height (as shown in figure 1), free fall under gravity, whereabouts of grinding medium, like a projectile impact at the bottom of the material to material.

  The upward and downward circular motion of the abrasive body is repeated.

  In addition, in the turning process of the mill, the grinding body also produces sliding and rolling, so the grinding body, the lining plate and the material between the grinding effect, so that the material grinding fine.

  Due to the continuous feeding of new materials at the feed end, there is a material surface difference between the material at the feed end and the material at the discharge end, which can force the material flow. In addition, when the grinding body falls, the axial thrust produced by the impact on the material also forces the material flow. In addition, the air flow in the mill also helps the material flow.

  Therefore, although the mill barrel is placed horizontally, the material can flow slowly from the feeding end to the discharging end to complete the grinding operation.

  Ii. Basic state of grinding body movement:

  The rotary speed and filling rate of ball mill barrel have great influence on grinding materials.

  When the cylinder rotates at different speeds, the grinding body in the cylinder may appear in three basic states, as shown in figure 2.

  FIG. 2(a) the rotation speed is too slow. When the grinding body and material are brought to the height equal to the dynamic friction Angle by the cylinder due to friction force, the grinding body and material will slide, which is called "pouring state".

  Figure 2(c), the rotating speed is too fast, the grinding body and the material are attached to the cylinder body under the action of the inertial centrifugal force and rotate together (in a circular motion), known as the "turnover state", the grinding body has no impact and grinding effect on the material;

  FIG. 2(b) shows that the rotation speed is relatively appropriate. The abrasive body is lifted to a certain height and then dropped, which is called "dropping state".

  In fact, the movement state is very complex, attached to the mill drum wall upward movement;

  Sliding downward along the cylinder wall and grinding body layer;

  A drop motion similar to that of a projectile;

  Rotation motion around its own axis, rolling, etc.

  The basic effect of abrasive body on material is exactly the result of the comprehensive effect of the above various movements on material, which can be mainly attributed to the impact and grinding effect.

  The purpose of analyzing the basic function of grinding material is to determine the reasonable motion state, which is the basis of choosing and calculating the suitable working speed, required power, production capacity and mechanical calculation of the mill.

  Three, ball mill internal motion analysis:

  The grinding effect of ball mill is mainly the impact and grinding of abrasive body to material.

  Mill operation in order to further understanding the essence of the grinding medium on material, in order to determine the working parameters of grinding machine, such as the suitable work speed, power consumption, production capacity, grinding medium loading amount as well as to master the various factors that influence efficiency of mill grinding, cylinder force and strength calculation, etc., must be within the grinding medium in the mill on the motion state of analysis and research.

  The actual state of abrasive body movement is very complicated. In order to simplify the problem analysis, the following basic assumptions are made:

  (1) when the grinding machine is working normally, there are only two kinds of motion trajectories of the grinding body in the barrel according to its position: one is to take the geometric center of the cross section of the barrel as the center of the circle layer by layer, and move upward along with the rotation of the barrel according to the concentric arc trajectory;

  The other is to fall down one parabolic trajectory after another;

  (2) the relative sliding between grinding body and cylinder wall and between grinding body layer and layer is very small, which is omitted in the specific calculation;

  (3) the influence of materials in the grinding barrel on the movement of grinding body is omitted;

  (4) the grinding body is a particle, so the outermost turning radius can be expressed by the effective inner diameter of the cylinder.

  The grinding body moves upward according to the circular arc rotation with the cylinder body. When it reaches a certain height, it starts to leave the arc track and fall along the parabolic track. The instantaneous center of the grinding body is called the detachment point, and the line connecting the detachment points of each layer of grinding body is called the detachment point track, as shown in figure 3, line AB.

  When the abrasive body falls in a parabolic trajectory and reaches the landing destination, the instantaneous center point of the abrasive body is called the landing point, and the line connecting the landing points of each layer of abrasive body is called the landing point trajectory, as shown in figure 3, line CD.

 

  (more professional analysis of abrasive motion)

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