6 reasons and solutions about the capacity reduction of vertical roller mill

Vertical roller mill is a set that combines drying, grinding, classification and conveying into one. And because of its less area coverage, vertical roller mill is quite popular among customers. However, some customers feedback said that after a period of use, the production is highly affected, which directly affects economic benefits. In this article, we mainly introduce factors that affect the production of vertical mill and how to prevent production reduction.

Wear of grinding roller and grinding disc liner plate

During the working process of vertical roller mill, grinding pressure is exerted by grinding roller, and the material is under the extrusion and shearing force of grinding roller and grinding disc to achieve the purpose of grinding, so the wear of grinding roller surface and grinding disc surface liner plate is inevitable. With the prolong of grinding time, the more severe the wear of the liner plate, the wear of lining plate will be more serious, the gap between grinding roller and disc will become small inside and large outside or unevenness, the grinding efficiency will be greatly reduced, resulting in a sharp decline of the output capacity of vertical roller mill.

In this case, the wear of the liner plate should be checked regularly, and when the grinding roller and the grinding disc liner plate are worn to a certain extent, it must be replaced in time, so as not to affect the operation of the vertical roller mill due to the vibration or other problems caused by the wear of the liner plate.

The liner plate wear should be checked and treated in time, and the service life of the liner plate can be prolonged by changing the liner plate face and appropriately lowering the height of the material retaining ring.

Grinding disc liner plate

Wear of material retaining ring

The function of the material retaining ring of vertical roller mill is to make the material to be fully ground on the grinding disc. If the material retaining ring is worn or lost, the thickness of the material layer will be reduced, and the vibration of the vertical roller mill will be stronger. The coarse powder is not fully ground and be thrown out of the mill under the action of centrifugal force, which increases the amount of returned material and the total amount of material need to be ground. In this way, the output of the vertical roller mill can only be reduced, and the vibration is largeaffecting the operation of the mill. Therefore, it is necessary to check the retaining ring regularly and deal with problems in time.

Retaining ring

Wear of nozzle ring

The main function of the nozzle ring is to change the wind direction through the guide blade, to ensure that the airflow is spiraling up and take away the material. If the nozzle ring is worn or partially worn, the airflow will become chaotic, the stable rotational upward airflow will not be formed, and the wind speed will also be reduced, the material cannot be taken away in time, and return to the grinding disc or fall into the scraping cavity at the bottom of the nozzle ring, increasing the circulation and affecting the output capacity of the vertical roller mill.

Properties of the raw material

Materials with high hardness, such as high silicon materials have poor grindability. In order to achieve the required fineness, the grinding time of materials is inevitably prolonged and the internal circulation of the grinding mill is increased. The materials in the grinding cannot be discharged in time, so the production capacity can only be reduced.

The particle size of the material entering into the vertical roller mill is too large, which increases the grinding times and the cycle amount, leading to the pressure difference is high, and the grinding is difficult. Moreover, it can also cause large vibration and unbalanced operation.

Therefore, customers should control the operation of the vertical roller mill according to the actual situation and the wear resistance and particle size of the material, so as to avoid affecting the production capacity.

Air leakage of the system

Air leakage of the mill body is bound to cause small pressure difference, insufficient wind speed, making the powder cannot be taken away in time, affecting the output capacity of vertical roller mill. In addition, air leakage in other parts of the system will also reduce the wind speed, which will cause the accumulation of raw materials in the pipeline. After the material accumulates, the ventilation area will become smaller, and the insufficient air volume will also affect the output capacity of the vertical roller mill. So it is necessary to check and deal with the air leakage problem in time.

Thickness of material layer

After the material is fed into the grinding disc, a certain material layer is formed. When the thickness of the material layer reaches a certain thickness, the grinding roller begins to grind.

If the material layer is too thin, the grinding stress is too concentrated, and the grinding ability will drop. It will lead to the impact of roller liner plate and disc liner plate, the vibration is strong, and will also damage lining plate, tension bar, etc.

If the thickness of the material layer is too thick, the grinding force will be transformed into lateral stress, sliding shear will be formed between the materials, the collapse degree of the material bed increases, the grinding efficiency is reduced, and the vibration will increase;

The material will be extruded from the grinding disc before they are fully ground, and falling into the nozzle ring, increasing the circulation, and the pressure difference is large, the material ca not be discharged in time, forming a vicious cycle, the production capacity will inevitably reduce.

The thickness of the material layer is generally controlled at about 50-80mm. The principle is that the material fed into the vertical roller mill should be ground in time and flow to the next process in time. The pressure difference of the system should not be controlled too high to ensure that the vibration is in a reasonable range.

In addition to the above factors, there are many other factors that affect the output capacity of vertical roller mill, such as material segregation caused by mixture structure, air volume control, hot air temperature control, batching control, etc., will all affect the output capacity of vertical roller mill. In the actual production, operators should solve the problems according the specific situation of the factory.