Cause Analysis and Treatment Measures of Vertical Roller Mill Vibration

Vertical roller mill has compact internal structure and few external equipment, which can save a lot of space and reduce the initial investment. Vertical mills also have the advantages of low dust, low noise, and low environmental pollution, and are widely used in milling powder production.

 

Vertical roller mills run smoothly under normal conditions, and the noise basically does not exceed 90 decibels, but if the operation is not proper, it will cause vibration and generate a lot of noise. For the vertical grinding mill, reasonable vibration is allowed to exist, but if the vibration is too large, it will inevitably cause damage to some accessories, so the vertical mill vibration needs to be strictly controlled in the production process.

 

Analysis of Vertical Mill Vibration Cause

In actual production operations, many vibrations are caused by improper operation, such as vibrations caused by unstable material layer control. Because the material layer is too thin, there will be few materials that can be ground, and the output will be reduced. At the same time, the material layer is too thin will also cause rigid contact between the grinding disc and the grinding roller, which will cause a lot of vibration, resulting in serious wear of the vertical grinding equipment and increased energy consumption. If the material layer is too thick, the grinding capacity of the vertical roller mill will be reduced, and the internal circulation load will increase, causing the grinding roller to jump up and down, causing serious damage to the equipment and affecting the safe use of the equipment. Therefore, the control of the material layer is very important. There are many reasons that affect the change of the material layer. The characteristics of the material include the moisture of the material, the friction factor, and the particle size of the material. In addition, there are factors such as temperature and pressure difference.

 

Material characteristics

Material friction factor: it directly reflects the internal friction produced when grinding various materials. It is directly related to whether the material layer can form a stable abrasive layer thickness, and whether it can maintain a stable material layer thickness directly affects the degree of vertical grinding. The material with small friction factor will be extruded out of the groove due to the extrusion, which will inevitably lead to the material layer is too thin, and it is easy to cause the direct contact between the grinding plate and the grinding roller, which will cause the equipment to vibrate and damage the internal equipment; if the friction factor is large, the material will be crushed to form a cake shape, which is difficult to loosen, causing the grinding difficulty.

 

Grinding particle size of the material: the particle size of the material entering the grinding plate shall match with the grinding roller and the grinding plate. With the increase of the diameter of the grinding roller, the speed of the outer circumference of the grinding roller is also increasing, so the generated friction is also increasing, so the grinding roller is easier to engage with the material, and the material is more easy to be rolled into the material layer, so the particle size of the material into the grinding can be appropriately increased. However, when the material particles are too large, the grinding roller will be greatly impacted, resulting in the vibration caused by the imbalance of the three rollers; because the material particles are too small, the material will enter the powder concentrator with the hot air machine, and the material layer cannot be formed on the grinding plate, resulting in the vibration caused by the direct contact between the grinding plate and the grinding roller. Generally speaking, the particle size entering the vertical mill should be about 5% of the diameter of the grinding roller.

 

Material moisture content: The amount of moisture in the material has a great influence on the vertical roller mill. If the moisture content is too large, the material is not easy to dry. The excessively wet material grinding will wrap and adhere to other materials, even wrapping the grinding roller, resulting in material accumulation on the grinding disc , making the grinding roller difficult to press down, causing vibration to stop. If the moisture content of the material is too small, the viscosity of the material will be too low, and the friction factor between the materials will be reduced, which makes it difficult for the material to stay on the grinding plate for a long time and cannot form a certain thickness of material layer, which will cause rigid contact between the grinding plate and the grinding roller and increase the vibration.

Pressure difference

The difference between the in-grinding pressure and the out-grinding pressure is the pressure difference, which is one of the main factors affecting the vertical roller mill vibration.The change of pressure difference directly reflects the change of internal circulation load rate of vertical roller mill, which is related to many factors such as material size, material characteristics, grinding pressure, ventilation in mill, material moisture, mill feeding amount, etc. For example, if the material is too small to enter the abrasive particles, the grinding pressure is large, the water content is low, the feeding amount is large and the ventilation is insufficient, the differential pressure will rise and the material layer will become thick; on the contrary, the differential pressure will decrease and the material layer will become thin, which will cause the vibration of the vertical roller mill, and the mill will jump and stop if not adjusted in time.

 

Hot air temperature

The temperature of the hot air will have a great influence on the mill vibration, because in the fixed vertical mill, the ventilation volume should ensure the drying efficiency of the materials. Therefore, it is necessary to control the temperature of the hot air entering the mill, which is mainly based on the moisture content of the materials entering and leaving the mill. However, poor air temperature control will also affect the grinding efficiency of the vertical mill to a certain extent. If the air temperature is too high, it can achieve good drying effect and grinding effect, but it will cause the material layer to be too thin. If the air temperature is too low, it will make it difficult to dry the materials, and it is difficult to carry out grinding. The materials are easy to be pressed into a cake shape, resulting in vertical roller mill vibration 

 

In general, the air temperature at the inlet is 200 ℃ ~ 250 ℃, and at the outlet, the temperature should be controlled at 80 ℃ ~ 120 ℃ according to the moisture content of the material and the water spray in the mill. Under this parameter, the vertical mill runs smoothly and efficiently, and does not produce much vibration.

 

Grinding pressure

Grinding pressure is mainly the sum of the pressure exerted by the center frame, hydraulic system and the weight of the grinding roller. The grinding pressure is directly related to the compression ratio of the material and the thickness of the material layer. The grinding pressure increases and the thickness becomes thinner. 

 

Measures to control vertical roller mill vibration

Feeding operation

 

When the moisture content of the material is very high, the outlet temperature of the tower should be properly increased to raise the internal pressure difference of the mill to an ideal value. In case of insufficient feeding and less return, the feeding shall be increased to ensure the normal pressure difference in the mill, so as to avoid vibration. If the material layer is too thick, the feeding amount shall be reduced in time and the outlet shall be smooth; on the contrary, the feeding amount shall be increased.

 

Grinding pressure control

 

If the grinding pressure feedback value of the vertical mill is less than the set value, it is proved that the accumulator pressure is too low, and nitrogen needs to be supplemented in time.

 

temperature control

 

If the temperature is too high, the power of the mill can be adjusted properly or the cold air valve can be opened directly.

 

Differential pressure control

 

When the feeding amount is large and the grinding capacity is insufficient, the pressure difference in the mill will rise. At this time, the feeding amount should be reduced appropriately according to the power of the mill. If the product is too fine, it will increase the internal circulation load and cause vibration due to the rise of differential pressure. Therefore, it is necessary to properly reduce the speed of the powder concentrator.

 

As a professional manufacturer of grinding mills, Shuguang Heavy Machinery sells a variety of different types of mill equipment, including ball mills, Raymond mills, vertical mills, etc.Welcome to contact us for more details.

 

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