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The output of vertical grinding mill not only affects the production schedule and target, but also affects energy consumption, enterprise cost and benefit. Here we will discuss the influence of mill structure, scraper plate, hydraulic system, and material and pressure difference on the output of vertical grinding mill.
1. Wear of internal parts of the grinding mill
After a long time of operation, the grinding roller and disc become uneven and irregular due to wear, the grinding efficiency and output decreases accordingly.
Regularly check the wear condition of the lining plate, and repair it in time when the wear of the grinding roller approaches to 25 mm and that of the grinding disc approaches 10 mm. If the base metal of the grinding plate liner is damaged, it should be replaced in time.
（1） Wear of retaining ring
As the grinding mill retaining ring is composed of three steps, it forms an effective grinding space with the big 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. Besides the reasonable height of the retaining ring, it is also very important to repair the size of retaining ring.
（2） Nozzle ring wear
The main function of the nozzle ring is to change the wind direction through the guide vane to ensure the consistent rotation direction of the air flow. The inclination angle, height and wear condition of guide vane have influence on air flow.
The damage of the guide vane will make the air flow through the nozzle ring not evenly distributed, and cannot form a stable rotating upward flow. The airflow will be disordered, which will weaken the ability of gas to carry mineral powder. The material will return to the grinding plate or fall into the scraping cavity at the bottom of the nozzle ring, causing uneven thickness of the material layer, increasing the circulation volume and reducing the per hour output of the vertical grinding mill. After shutdown, the damaged nozzle ring must be repaired to avoid disturbing the internal circulation of grinding.
2. Add scraper plate
In order to reduce the accumulation and hardening of the materials in the center of the grinding plate and improve the control of the material layer by the auxiliary roller, a scraping plate is added in the center of the grinding plate with a height of 20cm from the grinding plate. It can smooth the material in the center area of the grinding plate, stabilize the material layer better, ensure the material is evenly grinded, and effectively reduce the wear of the mill body.
3. Hydraulic system pressure
When other factors remain unchanged, the grinding pressure is directly proportional to the output. However, if the pressure is too high, the probability of vibration will be increased, and the motor load will also increase accordingly. Therefore, the operator should consider the setting value of grinding pressure according to the grindability, output and fineness index, bed thickness and vibration.
Hydraulic system valve failure, pressure switch malfunction or internal leakage will cause pressure drop, and the pressure value in nitrogen cylinder and accumulator cannot meet the requirements, which will affect the hourly output.
During production, the leakage of positive and negative pressure oil pipes of each hydraulic cylinder should be checked and treated during shutdown and maintenance.
The higher the material hardness, the longer the grinding time, the more the number of internal cycles, and also increase the wear of the grinding mill.
The slag containing moisture accumulates and hardens on both sides of the discharge pipe, resulting in blockage of the feeding and discharging pipe of the vertical grinding mill. The rotary feeder is frequently shut down due to overload, which makes the grinding mill unable to operate normally.
In order to ensure the grinding mill operating normally, a manhole is added under the rotary feeder for regular maintenance, and centralized manpower is used to dredge the accumulated material in the discharge pipe, and the air gun is used to assist in cleaning up the blockage.
5. Pressure difference
The pressure difference is composed of two parts: the pressure difference inside the vertical grinding mill and the pressure difference of bag collector, which is the key factor to improve the product quality and output.
（1） pressure difference in vertical grinding mill
One is the local ventilation resistance caused by the hot air nozzle ring into the mill, and the other is the fluid resistance of suspended materials between the nozzle ring and the pressure point. The sum of these two resistances constitutes the pressure difference in the mill.
The feed rate and circulating material volume will cause the change of fluid resistance and pressure difference in the grinding chamber. In order to measure the change of pressure more accurately, compressed air can be used to clean the measuring pipeline.
（2） pressure difference of bag collector
It is determined by the fluid resistance of the suspended material in the bag collector. By repairing the damaged lifting valve and pulse valve, replacing the filter bag regularly, adjusting the position of bag cage and repairing the damaged shell, the transportation efficiency of materials in the bag collector will be ensured and the output will be increased.
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