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Five factors to increase the output of vertical mill

The level of vertical mill production not only affects production schedules and targets, but also affects energy consumption, enterprise costs and benefits. This paper discusses the impact on the vertical mill output from the aspects of mill structure, scraper plate, hydraulic system, material and differential pressure.
How to improve vertical mill production? These 5 factors need to understand

01 mill internal structure wear


The parts of the mill that affect the output are: grinding rolls directly involved in grinding, grinding discs, retaining rings for controlling the material layer, and spout rings for controlling hot air and wind direction.

1.1 Grinding roller and disc liner wear


According to the working principle of the mill, the vertical mill is used to grind the material by applying pressure to the grinding roller. After a long time of operation, the grinding roller and the grinding disc become uneven and irregular due to wear, and the grinding efficiency is lowered. The output will drop.

In this case, the wear of the lining should be checked regularly. When the wear amount of the grinding roller approaches 25 mm and the wear amount of the grinding disc approaches 10 mm, the size of the grinding roller and the grinding disc can be repaired by surfacing to ensure the output.

Avoid the increase of vibration due to the wear of the lining plate, thus affecting the operation safety of the main reducer. If it is found that the base disc is damaged by the base disc, the liner should be replaced in time.

1.2 retaining ring wear


The function of the retaining ring is to enable the material to be fully ground on the grinding disc. The height of the retaining ring determines the thickness of the layer. When the thickness of the layer is large, the vibration of the mill will increase. When the coarse powder is not fully ground, it will enter the outer circulation under the action of centrifugal force, so that the total amount of grinding will increase, the output at the time will be reduced, and the grinding will be reduced. The machine vibrates greatly. When the retaining ring is too low, it is difficult to ensure a smooth thickness of the layer. Under the action of the pressure of the grinding roller and the weight of the grinding roller, intermittent rolls and discs may directly collide and cause vibration, which may affect the normal operation of the production.

Properly setting the height of the retaining ring has a positive impact on increasing production. At the same time, since the mill retaining ring is composed of three steps, the bottom step is 45 mm wide and the opposite grinding disc is 50 mm high, and it forms an effective grinding space with the large end of the main roller in the grinding state. The wear of the bottom step of the retaining ring will destroy the formation of the effective grinding space. Therefore, in addition to the reasonable setting of the height of the retaining ring, the size of the retaining ring is also very important.

1.3 spout ring wear


The main function of the spout ring is to change the wind direction through the guide vanes to ensure the uniform swirling of the airflow. The inclination, height, and wear of the guide vanes have an effect on the airflow. The angle of the air deflector determines the time from the separation of the wind material to the powder selection zone. The length of time affects the internal working conditions of the mill.

The damage of the guide vane will not evenly distribute the air volume passing through the spout ring, and it will not form a steady upward spiraling airflow. The airflow will be disordered, and the ability of the gas to carry the ore powder will be weakened. The material will return to the grinding disc or scrape into the bottom of the spout ring. The material cavity causes the thickness of the material layer to be uneven, which increases the circulation amount and reduces the production time of the grinding machine. After the shutdown, the damaged nozzle ring must be repaired to avoid disturbing the inner circulation.

02 added scraper


In order to reduce the accumulation and slab of the material in the center of the grinding disc and improve the control of the material layer of the auxiliary roller, a scraping plate is added at the center of the grinding disc, and the height of the grinding disc is 20 cm. It can flatten the material in the center of the grinding disc, better stabilize the material layer, ensure the material is evenly ground, and can effectively reduce the wear of the mill body.

03 hydraulic system pressure


In the case of other factors, the grinding pressure is proportional to the output. The greater the grinding pressure, the greater the positive pressure acting on the material on the grinding disc, and the better the grinding effect. However, if the pressure is too high, the probability of vibration will increase, and the motor load will increase accordingly. Therefore, the operator should consider the set value of the grinding pressure according to the material's grindability, output and fineness index, bed thickness and vibration.

Failure of the hydraulic system valve, abnormal pressure switch or internal leakage will cause pressure drop. The pressure value in the nitrogen cylinder and the accumulator will not meet the requirements, which will affect the production time.

With each downtime, check the pressure of the nitrogen cylinder to ensure that the nitrogen pressure of the piston accumulator is 8 bar. Insufficient pressure will lead to increased vibration and frequent shutdown. The nitrogen pressure of the bladder accumulator is 40 bar. The roller timed out and the system responded slowly. During production, the leakage of the positive and negative pressure oil pipes of each hydraulic cylinder should also be checked and treated during shutdown maintenance.


04 material


The material requirements of vertical mill are mainly manifested in the wearability and particle size. The higher the hardness of the material, the longer the material is milled into a finished product, the more cycles the mill has, and the greater the wear of the equipment. The slag containing moisture accumulates and squashes on both sides of the blanking pipe, causing blockage of the inlet and outlet pipes, and the rotary feeder frequently stops due to overload, which makes the mill unable to produce normally.

An inspection hole is added under the rotary feeder, and the simple dredging is performed once every 4 days; the shutdown is performed once every 15 days, and the manpower is used to unblock the material of the discharge pipe, and the air cannon is used to assist the cleaning, and the production of the mill is fully guaranteed.

05 pressure difference


The pressure difference is composed of the difference between the internal pressure difference of the mill and the differential pressure of the bag collector, which is a key factor for improving product quality and output.

5.1 Internal pressure difference


It is mainly composed of two parts, one is the local ventilation resistance caused by the hot air vent ring, and the other is the fluid resistance of the suspended material from the top of the nozzle ring to the pressure point. The sum of these two resistances constitutes the internal pressure difference.

The amount of feed and the amount of circulating material in the grinding chamber will cause a change in the fluid resistance in the grinding chamber, resulting in a change in the pressure difference. In order to measure pressure changes more accurately, compressed air can be used to clean the measuring lines.

5.2 Bag collector pressure difference


The fluid resistance of the suspended material in the bag collector is determined by the factors such as the poppet valve, the pulse valve, the filter bag permeability, the flow direction of the air flow in the filter bag, and the sealing property of the cover plate. By repairing damaged poppet valves, pulse valves and regularly changing filter bags, adjusting the position of bag cages, repairing damaged casings, etc., the transportation efficiency of materials in the bag collector is ensured and the output is increased.
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