The Reasonable Operation of Vertical Grinding Mill for Producing Calcium Carbonate Micro Powder
With its unique advantages such as small floor space, low noise, high production capacity, easy operation, and integration of drying, grinding, and classifying, vertical grinding mill has been increasingly used in calcium carbonate micro powder production. In recent years, the development of ultra-fine calcium carbonate powder technology has also applied calcium carbonate micro powder in various industries. Because of the high power consumption and production cost of the ball mill for producing ultrafine/micro powder, and the it is not easy to control the whole production process.
The points to operation will are as following:
Keep stable amount of calcium carbonate between vertical grinding mill roller and grinding table:
Maintaining a stable material bed is the basis for normal grinding and operation. When the material bed is unstable, the calcium carbonate that enters the vertical grinding mill will be squeezed out in a large amount and cannot be ground. The thickness of the calcium carbonate layer can be adjusted by adjusting the height of the ring. The appropriate height and the corresponding relationship between them and the output of the vertical grinding mill should be noted firstly in the debugging stage. If the material layer is too thick, the grinding efficiency is reduced, and the grinding result is very difficult to meet the requirements. If the material layer is too thin, it will cause vibration, increase wear and cost. If the roller pressure is increased, more fine powder will be produced; and the material layer will become thinner, and the roller pressure is reduced, the material of the grinding disc becomes coarser, the corresponding return material is more, the grinding efficiency is reduced, and the material layer becomes thicker. A decrease in the air volume in the vertical grinding mill or an increase of the rotation speed of the classifier will increase the internal circulation and thicken the material layer; an increase in the air volume in the vertical grinding mill or a decrease of the rotation speed of the classifier will reduce the internal circulation and reduce the material layer, which should be adjusted according to actual conditions. Under normal operation, the thickness of the material between roller and grinding table should not be less than 25~40mm. The machine can run stably. If the material bed is unstable during feeding, the vertical grinding mill will not operate normally.
Grinding Roller Pressure Control
Grinding roller pressure is the main factor that affects mill output, grinding efficiency and mill power consumption. The vertical grinding mill applies high pressure to the material bed to grind the material between rollers and grinding table. The pressure increases, the grinding capacity increases, and the output will also increase. In order to protect the reducer, the vertical grinding mill has a maximum pressure to achieve this. Because the ground calcium carbonate bed is generally stable and the pressure control is relatively stable, but the increase in pressure is accompanied by an increase in power, which leads to an increase in power consumption and an increase in the wear of roller and grinding table. Therefore, reasonable roller pressure is required. And the output, quality and power consumption are balanced. This output depends on the grindability, feeding amount and specific surface area requirements. In the trial production, to find the appropriate grinding roller pressure and negative pressure is very important. Reasonable air speed and air volume can form a good internal circulation, so that the material layer on the grinding table is appropriate and stable, and the grinding efficiency is also higher. When encountering instability of the grinding material or other abnormal conditions, the grinding pressure should be appropriately reduced to ensure that the vertical grinding mill runs within the normal vibration range.
Reasonable Air Temperature to the Vertical Grinding Mill
Vertical grinding mill is a system that integrates drying, grinding and classifying. The outlet air temperature is a comprehensive indicator that measures whether the drying operation is normal. In order to ensure that the calcium carbonate is dried well, the moisture of the calcium carbonate should be less than 0.8%, and the outlet temperature of the vertical grinding mill is generally controlled at less than 60-80°C. If the temperature is too low, the moisture in the finished product will be higher, which will reduce the grinding efficiency and the powder classifying efficiency, and will increase the load of the main motor and classifier motor, and may also cause condensation in the dust collection system. As well as the different powder classifying ability, the grinding condition changes greatly, and the temperature requirements are also different.
Reasonable Air Volume and Speed Control
Vertical grinding mill mainly relies on airflow to circulate materials. In order to form a good internal circulation, the material layer on the grinding table should be appropriate, stable to achieve higher grinding efficiency. However, there are many factors that affect air volume: the exhaust fan, the rotation speed of classifier, and the circulating air valve opening degree, etc.. And the air volume is also related to the feeding volume, if the feeding volume is large, the air volume should be higher; on the contrary, the air volume should decrease. The air volume of the blower is affected by the resistance of the vertical grinding mill system.
The pressure difference of the vertical grinding mill, the pressure difference of the dust collector, and the amount of recycled material can all reflect the air volume. A large pressure difference indicates a large air volume: on the contrary, the air volume is small. These parameters stability indicates the stability of the air volume, thus ensuring the stability of the material bed. In addition, the pressure difference is also an important parameter that reflects the internal resistance of the vertical grinding mill.
Specific Surface Area Control of Superfine Calcium Carbonate Powder
The surface area of superfine calcium carbonate powder is affected by the speed of vertical grinding mill classifier and air speed, internal load, operating pressure, and feeding volume. Under the condition that the vertical grindinig mill operating pressure and the feeding amount remain the same, it can manually change the speed of the vertical grindinig mill classifier to adjust the fineness, the maximum increase each time during adjustment should at 4r/min. Increasing the specific surface area can also increase the operating pressure and reduce the feeding amount and reduce the air volume, etc.. These four factors can be coordinated according to the actual situation.