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Various problems and solutions in the production process of vertical mills
Date: 2021-03-26  Click:
Various problems and solutions in the production process of vertical mills
1. Reasons for high differential pressure of vertical mill and treatment measures
 
1) The feeding amount is large, and the grinding capacity is not enough.
Treatment: According to the power of the mill, reduce the output appropriately.
 
2) The product is too thin and the internal circulating load value is high.
Treatment: Reduce the speed of the separator.
 
3) The powder concentrator may be blocked.
Treatment: stop grinding and check.
 
4) The guide angle of the powder separator is too narrow or the length is too long, which restricts the smooth passage of the material through the outlet.
 
5) The retaining ring is too high, resulting in high internal circulation load.
Treatment: stop grinding and adjust.
 
6) The scraper is broken or dropped, and no return material is formed. The material baffle is broken or dropped, forming a large amount of return material.
Treatment: stop grinding for maintenance.
 
7) The air flow in the mill is small, which affects the material passing through the separator.
Treatment: Increase the suction volume of the fan of the mill and adjust the inlet damper of the fan.
 
8) The grinding pressure pipe is blocked, and the grinding pressure (negative pressure value) returns to decrease, causing the display value of the differential pressure in the mill to be higher.
Processing: Notify the instrument worker to deal with it.
 
9) The temperature of the wind entering the mill is too high and the wind speed is too fast, and the material cannot form a layer on the grinding disc, and it is suspended in the mill, resulting in a high pressure difference.
Treatment: adjust the temperature of the humidification tower or adjust the outside wind (or circulating wind), reduce the temperature of the inlet wind, and slow down the wind speed.
 
10) During operation, too much external wind is used or the side door of the return material (zipper machine) is opened, resulting in a drop in the grinding pressure, slowing down the internal circulation of the mill system, increasing the return material of the external circulation, making it enriched, and causing the inside of the mill to be enriched. The differential pressure becomes higher.
Treatment: During operation, adjust the internal circulation of the mill system, increase the return of the external circulation, close the doors, and prevent air leakage.
 
11) The abrasiveness of the material is very poor, and the material is difficult to grind, resulting in a high pressure difference in the mill.
Treatment: Reduce production and run or increase the grinding pressure appropriately or check the pressure tank on site.
 
12) The long-term operation of the vertical mill increases the quartz crystal content in the mill, which makes the material difficult to grind and the differential pressure increases.
Treatment: Reduce production operation or discharge this part of the material out of the mill.
 
2. Causes of high vibration of vertical mill and treatment measures
 
Failure to maintain the proper material layer and surface shape of the vertical mill during normal operation will cause the vertical mill to vibrate. Through practical analysis, we believe that the causes of vertical mill vibration and treatment measures are as follows:
 
1) Foreign matter enters the mill to cause vibration.
Metal foreign objects from inside and outside the mill, such as wind guide blades, tools left over after maintenance, etc. If it is a small metal, you can lift the grinding roller, reduce the air draft, and take it out from the feeding port of the return material; if it is a large metal, open the grinding door and take it out.
 
2) The material layer is too thick to cause vibration.
The amount of incoming material is too large → the material layer becomes thick → the grinding ability is reduced → the material cannot be ground in time → there are too many unqualified powders in the grinding, and the system air volume is insufficient, and the wind speed of the spray ring decreases → the qualified powder cannot be removed Take it out of the system in time → increase the circulating concentration in the grinding chamber → return the powdered material to the grinding plate → thicken the material layer. Such a vicious circle causes the material layer to lift the grinding roller too high and cause vibration. At this time, the amount of feed should be reduced in time to ensure that the system is well ventilated and the discharge is unblocked.
 
3) The material layer is too thin to cause vibration.
The amount of incoming grinding material is small or the incoming grinding material is too fine, and there are many powdery materials. At this time, the material has strong fluidity and poor adhesion, and the rolling of the grinding roller, so that the material on the grinding disc is quickly ground into a qualified product. Excessive air volume will soon take the fine powder out of the system, making the material layer on the grinding disc too thin or unable to form an effective material layer, causing the grinding roller and the grinding disc to contact and cause vibration. At this time, the feed rate can be increased, the air flow rate can be reduced, and the water spray rate can be increased to maintain a certain material layer of the vertical mill to make it stable.
 
4) The material entering the mill is unstable, and the thickness of the material layer fluctuates too much.
Failure to maintain a reasonable material layer and material surface shape, such as migrant workers feeding, the feeding scale is blocked, causing large fluctuations. The measure is to feed evenly.
 
5) The air volume of the system is unreasonable.
When the air volume of the system is too large, the material stays in the mill for a short time, the output volume is large, and the material is small and vibrates; if the air volume is too small, the material stays in the mill for too long. Repeated grinding will cause the material to be too fine, high differential pressure and vibrate.
In addition, when the moisture of the material entering the mill increases or decreases, the inlet temperature suddenly increases or decreases, and the tail exhaust air door suddenly becomes larger or smaller, which will directly affect the ventilation volume of the vertical mill. If the adjustment is not timely, it will inevitably cause vibration. Therefore, when the moisture of the material entering the mill increases, it should be solved by reducing the feeding amount, reducing the water spray, increasing the air temperature of the entering mill, and increasing the ventilation of the vertical mill.
 
6) The speed of the powder separator is too high.
The speed of the powder separator is too high → the finished material cannot be discharged out of the mill in time, and the material is repeatedly ground → the internal circulation is increased → the differential pressure is high → the buffer layer of the vertical mill becomes thin, causing vibration.
 
7) Small amount of spray water causes vibration. Small water spray → high differential pressure → thin material layer causes vibration.
 
8) Too large or too small particle size of the material to be milled will cause vibration.
Due to the fixed speed of the grinding disc, the larger the particle size of the material to be ground, the more obvious the centrifugal effect. At this time, the grinding efficiency will decrease, and the surface shape of the material cannot be maintained.
The treatment measures are: control the material layer to be slightly thicker than normal, reduce the air volume and inlet temperature, and reduce the grinding pressure.
When the grinding material is too fine, most of it will be suspended in the grinding mill. However, the capacity of the classifier is limited, and the small amount of material on the grinding disc will also cause vibration. The treatment measures are: lower the temperature, reduce the ventilation, reduce the speed of the powder separator, and increase the water spray.
 
9) The pressure setting is unreasonable or the pressure of the nitrogen bag is unbalanced.
The grinding pressure setting is too large or too small, or the pressure of the nitrogen bag is insufficient or unbalanced during normal production, which causes the upstream and downstream movement of the grinding roller to cause vibration when it is working. The treatment measures are: adjust the pressure and check the pressure of the nitrogen bag.
 
10) The retaining ring is too high or too low.
The baffle ring is too low to maintain a certain material layer, and the material is thin, causing vibration; the baffle ring is too high, the material is thick, the air volume is reduced, the discharge is not smooth, and the differential pressure is high, causing vibration.
 
3. What effect does the inlet temperature of the vertical mill have on the operation of the vertical mill
 
The high inlet temperature of the vertical mill will cause the materials in the mill to dry too quickly, the suspended materials will increase, the differential pressure will increase, and the material bed will become thinner and unstable. At this time, the amount of spray water should be appropriately increased to stabilize the material layer, or the feeding amount should be appropriately increased. If it does not work, adjust the amount of water sprayed in the humidification tower to reduce the outlet temperature; if the inlet temperature of the vertical mill is low, the driving power of the main motor will increase, the material layer will become thicker, and the output will decrease. At this time, the water spray volume should be reduced, the inlet temperature should be increased, and the feed volume should be appropriately reduced.
 
4. The influence of the outlet temperature of the vertical mill on the operation of the vertical mill
 
The outlet temperature of the vertical mill is a basis for us to judge the status of the vertical mill. We can judge whether the operation adjustment methods we adopt are reasonable according to the level of the outlet temperature of the mill and other changing trends.
 
1) Grinding conditions when the outlet temperature of the vertical mill is too high: the material layer becomes thinner, the material layer is unstable, the mill power fluctuates greatly, and the vibration is large; the amount of return material increases; the product fineness becomes coarser.
2) Grinding conditions when the outlet temperature of the mill is too low: the material layer is thick; the power of the mill is high; the grinding movement is large; the output of the mill decreases.
3) The relationship between the outlet temperature change of the mill and the circulating load of the vertical mill: Under the condition that the air volume of the system and the speed of the separator remain unchanged, the change of the circulating load reflects the change of the material characteristics and the grinding efficiency of the mill.
A. The cycle load increases and the outlet temperature drops. When the cycle load rate becomes larger, the average fineness of the material in the mill becomes finer, which increases the heat transfer area. At the same time, the increase in the amount of material in the grinding will also increase the heat transfer area, thereby speeding up the heat transfer between the airflow and the material, resulting in The outlet temperature of the mill drops.
B. The circulating load decreases and the outlet temperature rises. At this time, the mill has a higher grinding efficiency.
C. Factors affecting the circulating load rate of the mill: the larger the air volume, the lower the circulating load rate; the faster the speed of the separator, the higher the circulating load rate; the grindability of materials and the thickness of the material layer also affect the circulating load rate. In normal production, a proper material layer is formed by setting a reasonable inlet air temperature and spray water volume. This is beneficial to improve the grinding efficiency and reduce the cycle load rate.
 
4) The relationship between the optimal grinding condition of the mill and the output temperature:
During the operation of the vertical mill, sometimes when the mill temperature is controlled at 92℃, the mill has the best grinding condition, and sometimes it is necessary to control the mill temperature at 98℃. Because the moisture, particle size and other physical characteristics of the raw materials and the ratio of the raw materials are different, the moisture required to form a stable and reasonable material layer is different. Therefore, in operation, the grinding temperature should not be regarded as the control target, but the grinding condition of the mill should be regarded as the control target. The change trend of the grinding temperature should be paid attention to, and the temperature value should not be overestimated.
 
5) Reasonably adjust other parameters according to the change of mill temperature:
A. The initial adjustment of the grinding. At the beginning of milling, as the fineness of the material in the mill decreases, the outlet temperature of the mill gradually decreases. When the outlet temperature stops falling and rises, it indicates that the amount of circulating materials inside and outside the mill is reduced, and the feeding amount can be gradually increased.
B. Adjustment in normal grinding. Because the output temperature of the mill reacts very quickly to the amount of material in the mill, after the mill has been pulverized for a period of time, if the outlet temperature is found to continue to decrease, we can preliminarily conclude that there is too much material in the mill at this time; when the current of the powder machine drops, the bucket The current of the air pump decreases, the power of the mill rises, and the material layer becomes thicker. At this time, it can be confirmed that the material in the mill is indeed too much, and the feeding amount can be reduced to the right place. When the export spy starts to rise and the power of the mill decreases, the feed volume can be gradually increased.
 
5. Influence of Vertical Abrasive Layer Thickness Control on Vertical Grinding Operation
 
1) Factors affecting material thickness:
A. The amount of water sprayed. When the water spray is large, the material layer is thick.
B. Into the mill temperature. The temperature is high and the material layer is thin.
C. Feeding amount. The feed volume is large and the material layer is thick.
D. Grinding pressure. The grinding pressure is large and the material layer is thin.
E. System ventilation. If the air volume is large, the material layer is thin.
F. Cycle load rate. When the speed of the separator is adjusted or the grinding condition of the mill changes, or the cyclic load rate is changed due to the change of the grindability of the material, the thickness of the material layer will also change. The specific manifestation is that the cycle load rate becomes larger and the material layer changes. thick.
 
2) Optimal material layer thickness: Due to instrument reasons or equipment wear, changes in material characteristics, etc., we cannot expect an exact value of the material layer thickness control target value. The optimal material layer thickness is embodied in the following aspects:
A. The output of the mill is high.
B. The power of the mill is high and stable, but the fluctuation is not large.
C. The material layer fluctuates little.
D. The grinding vibration is small.
 
3) How to control the thickness of the material layer:
A. Appropriate amount of spray water.
a. The material layer is thin, and the water spray can be increased when the power of the main motor is small.
b. The material layer is thin, and the water spray volume should not be increased when the power of the main motor is high.
c. The material layer is thick, and the water spray can be reduced when the main motor power is high.
d. The material layer is thick, and the grinding pressure should be increased when the power of the main motor is low.
B. Higher grinding pressure.
The higher grinding pressure can make the vertical mill obtain higher grinding efficiency, which can reduce the circulating load, which is beneficial to the stability of the material layer.
C. Appropriate feeding amount.
According to the amount of return material, adjust the feeding amount at the right time, so that the feeding amount and cycle load rate are always stable at the level that enables the vertical mill to exert the best grinding efficiency.
D. Appropriate wind temperature for entering the mill.
Adjust the inlet air temperature according to the water content of the raw materials. The basis is that after a certain inlet temperature is determined, if the outlet air temperature drops and the thickness of the material layer becomes larger, the inlet air temperature should be increased, otherwise the inlet air temperature should be reduced accordingly.
Appropriate ventilation.
On the premise that the fineness is qualified, increasing the ventilation is beneficial to reduce the cycle load rate and reduce the thickness of the material layer.
 
6. The influence of the height of the retaining ring of the vertical mill on the operation of the vertical mill
 
1) The vertical mill has a high retaining ring, and the corresponding vertical mill disc has a thicker material layer and a thick buffer layer, which reduces the relative grinding efficiency. In order to improve the grinding efficiency, the only way to increase the grinding pressure is to increase the power of the main motor. When the inner material layer of the mill becomes thicker, the relative ventilation capacity is also reduced, and the finished material cannot be taken out of the mill in time, and the output is low at this time.
 
2) The vertical mill has a low retaining ring, and the corresponding vertical mill disc has a thin material layer, a low buffer layer, and a large vertical mill vibration. In order to reduce the vibration, the only way to reduce the grinding pressure is to reduce the grinding pressure. At this time, the power of the main motor is low, the external circulation rate increases, the residence time of the material in the mill is prolonged, and the burden of the mill is increased. The efficiency is also low, and the raw meal is coarse in fineness at this time.
In order to maintain the high efficiency and high output of the vertical mill, the retaining ring should be selected reasonably.
 
7. The influence of raw material particle size on vertical mill operation
 
In order to ensure the high-efficiency operation of the raw material mill, the particle size of the incoming material should be kept within a reasonable range. The ATOX50 mill is 2%>95mm. If the particle size of the raw material is large, most of which exceed 95mm, due to the constant speed of the grinding disc, the material will segregate under the rotation of the grinding disc, and the material cannot be crushed into a finished product at a time. The external circulation rate of the vertical mill will increase, and the material will stay in the mill for a long time. Excessive drying hot air is needed. At this time, it often leads to:
1) The output of vertical mill is low, and the grinding time of coarse material is longer than that of fine material.
2) The outlet temperature of the vertical mill is relatively high, the contact area between the coarse material and the airflow is less than that of the fine material, and the heat exchange is less.
3) The vibration value is too large, the gap between the large material is large, the material layer is different, and the grinding roller vibrates greatly.
4) The power of the main motor fluctuates greatly, which is mainly affected by vibration.
 
8. Judgment and Treatment of the Phenomenon of Vertical Mill Scraper
 
After the scraper of the vertical mill is dropped, the long iron block may be picked up in the return material, or even stuck, and the conveying (returning) equipment may be stopped. At the same time, the power of the mill is obviously increased under the same output, and the output is difficult to increase. , The amount of return material is too small. During processing, the grinding can be stopped, and the grinding can be processed and welded.
 
9. The effect of high moisture content of raw materials on vertical mill operation
 
Impact: The high moisture content of the raw materials firstly affects the unobstructed delivery of the raw materials, which is easy to cause blockage of the raw material storage, resulting in large changes in the amount of material entering the grinding, frequent operations, and fluctuations in the composition of the raw material exiting the grinding; To form a high material layer, it is bound to increase the imported hot air and grinding pressure. The motor power will increase accordingly and the output will be relatively large. If the material contains more viscous substances, it will affect the output of the vertical mill.
 
Operation adjustment: control feeding moisture. The temperature of the humidifying tower is set a little higher, that is, to increase the temperature of entering the mill, so that there is enough heat in the mill, increase the temperature of the mill, reduce the water spray appropriately, and increase the grinding.
 
10. The handling of the feeding amount skipping during the operation of the vertical mill
 
1) If any scale of the limestone library is stopped, first add the scale to another scale, and then notify the post to check whether the scale is blocked; if the material is blocked, immediately clear the block; if it is not blocked, restart it again. Failed to start, notify the electrician to check.
 
2) If the sandstone or iron ore storage stops, notify the post to check whether the material is blocked. If the material is blocked, clear the blockage in time (note that during the process of clearing the blockage, be sure to start the scale once every 3 minutes); if it is not blocked Material, restart again. If it fails to start, notify the electrician to check it and prepare to stop grinding.
 
11. The effect and influence of vertical mill water spray on operation
 
Function: The vertical mill sprays water, mainly to stabilize the material layer, reduce the outlet gas temperature, reduce vibration, and stabilize operation.
 
Impact: A certain amount of water spray can form a stable material layer on the material on the grinding disc in time, reduce the vibration frequency of the grinding roller in operation, and have a very intuitive effect on stabilizing the system operation, increasing output and running. If the amount of water spray is small, the material layer is not easy to form, the vibration is large, and it is not easy to operate; if the amount of water spray is large, it is easy to cause a thick material layer, although the pressure difference can be reduced in time, but if the time is long, the material in the mill cannot be discharged for a long time , The internal circulation of the mill is increased. If the output or water is not reduced in time, it is easy to overcurrent and skip grinding.
 
12. Phenomenon, causes and treatment measures of vertical mill cyclone blockage
 
Phenomenon: Due to improper operation, the temperature of the mill is controlled to be low, resulting in a large moisture in the raw material of the mill, which will cause the cyclone to be blocked (the current is reduced, the material in the mill is gradually accumulated, the differential pressure is getting higher and higher, and the power of the main motor is increased. , There are more and more materials in the scraper room, and the current rises), the power of the circulating fan increases, and the grinding pressure decreases.
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