The large vertical roller mill is mainly composed of cylinder, screw agitator, transmission device and frame. The vertical structure of the vertical roller mill can improve the grinding energy efficiency. In the vertical roller mill, the screw agitator rotates slowly, and the speed will not fluidize the medium and gravity settlement will not occur. The vertical structure is conducive to the internal differential stage of particles and reduces over grinding. Therefore, the efficiency is improved.
On the other hand, the main force application mode of vertical roller mill is friction grinding, which does not need large-size balls. Therefore, a relatively small medium can be added to the mill to increase its grinding area by 3 times compared with the ball mill with the same load.
The grinding action of the vertical roller mill mainly occurs in two areas, one is the area on the spiral blade, and the other is the annular area composed of the outer edge of the spiral blade and the inner wall of the cylinder. There are three kinds of grinding and stripping in the two areas:
(1)grinding between grinding media;
(2)Mutual grinding between spiral blade and grinding medium;
(3)Grinding and stripping between the inner wall of the cylinder and the grinding medium.
Vibration caused by insufficient preheating. If the preheating is insufficient, part of the heat input into the mill will be absorbed by the mill body, resulting in insufficient heat exchange, broken heat balance, increased friction of materials on the grinding plate, reduced fluidity, and the material bed becomes lumped. The powder discharge rate of materials rolled by the grinding roller decreases and cannot be taken away from the grinding plate by hot air, resulting in fluctuation of the material bed and vibration;
Vibration caused by insufficient feeding. The output of the vertical roller mill can be adjusted within a certain range, but when the feeding amount is too low, the moisture in the mill decreases, the absorbed heat is lower than the supplied heat, the materials are dried quickly, the plasticity of the material bed decreases, and it is not easy to form a stable material layer and cause vibration;
Vibration caused by over grinding. The improvement of raw material grindability, high grinding pressure and high separator speed may increase the suspended fine materials above the grinding plate, increase the density of dusty gas, increase the probability of collision between particles, interfere with the powder selection process of the separator, prevent the materials meeting the fineness standard from being brought out of the vertical roller mill, break the material balance and increase the proportion of fine materials on the material bed, Cause vibration.
Other possible causes of vibration: failure of vibration measuring element; Loose roll cover and lining plate; The feeding amount is too large, too small or unstable; Insufficient or unstable air volume of the system; Grinding pressure is too high or too low; The speed of powder concentrator is too high; Serious blockage of nozzle ring, etc.
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