1. Material Moisture
Due to its speciality, bentonite requires a certain amount of water to exert its application activity. The difference in the water content of the grinding material will affect the running stability of the vertical mill. The grinding moisture of bentonite is usually 10% to 18% (the moisture after drying), or even higher. Passing hot air into the grinding process can effectively solve the problem of grinding efficiency, otherwise the material on the grinding disc will be easily damaged by the grinding roller The high pressure of the mill produces a material cake, which makes the material layer continue to thicken, resulting in reduced grinding efficiency, large mill vibration, serious slag spitting, and ultimately low mill output.
To this end, according to the actual situation in the mill, a special scraping device for grinding discs is installed at the front end of the material entering the rolling area of the grinding roller, which is installed on the inner wall of the mill shell.
By adjusting the height of the scraper bar and keeping the gap between the scraper bar and the disc lining plate at 2-2.5cm, the problem of cake formation in the disc material layer can be effectively controlled, and maintaining the material layer within a reasonable range of 2-3cm is conducive to the efficient grinding of the mill. , to ensure the stable operation of the mill and stable output.
2. The Grinding Temperature Of The Mill
The vertical mill operates under negative pressure, and a large amount of air is required for material conveying, drying and grading. The appropriate air temperature entering the mill when the mill is running will directly affect the output and quality of the final product.
The grinding moisture of bentonite is generally high. If there is no special requirement for the moisture content of the finished product, it can be ground without hot air; Gas stoves are available (depending on fuel type).
Due to its layered structure, bentonite will be deactivated or deactivated if it loses too much water during production, reaching below 8%. Therefore, the temperature of the hot air entering the mill should be controlled within a reasonable range.
According to the debugging, the air temperature entering the mill is controlled at 140 ~ 160 ℃ (the air temperature entering the mill is too low, the drying capacity of the mill is insufficient, resulting in low grinding efficiency, and the material layer of the abrasive disc becomes thicker, resulting in a large current of the mill; if the air temperature is too high, the As a result, the moisture content of the mill will be low, which will seriously reduce the performance of the product. Eventually lead to low yield), the moisture of the product is basically 8% to 12%, which will not affect the intrinsic activity of the powder. If the temperature of the air entering the mill exceeds 300 °C, the bentonite will begin to lose crystal water, and the microstructure will change, affecting the activity or even deactivation.
3. The Height Of The Disc Stopper Ring
The height of the retaining ring directly affects the thickness of the inner material layer and the grinding efficiency. The height of the stopper ring is too high, which is not conducive to the centrifugal overflow of the material on the grinding machine, which makes some qualified products stay on the grinding table for too long, which increases the energy consumption of over-grinding, and also causes the material bed to thicken and weaken the grinding efficiency. ; If the height of the stopper ring is too low, the overflowing flow rate of the powder will increase, and a part of the material will be thrown out of the grinding table without being ground, which will increase the slag discharge of the mill, which may cause the circulating elevator to block and cause the material bed to be too thin. It makes the grinding roller unable to operate under high pressure, and the mill is prone to vibration.
The height of the self-contained retaining ring is 5cm when the mill leaves the factory. During the initial strip production, it was found that the current of the mill motor was high and fluctuated, the output was low, and the mill also had large vibration. Further increasing the grinding pressure could not effectively reduce the mill. load.
After analysis, the bentonite powder and fine particles on the top of the grinding disc have good fluidity, while the bentonite below has not been effectively ground, and is agglomerated and bonded on the grinding disc. 2cm, which is conducive to the rapid overflow of the surface powder from the grinding disc and is carried away by the wind, reducing the thickness of the material layer, the current of the mill is immediately reduced and stabilized, the output of the mill is significantly improved, and the vibration is also very slight.
4. Milling Disc Wind Speed
The size of the air ring gap of the grinding disc determines the wind speed and material carrying capacity of the air ring . The airflow entering from the air inlet of the mill will be sprayed upwards evenly from the wind ring, and the large particles and impurities in the materials that pass over the baffle ring will fall into the lower wind ring due to their weight. There are several scrapers fixed on the frame, large particles and impurities are discharged from the scraper through the slag discharge port of the mill; small particles and fine powder are brought into the powder separator on the top of the mill by the airflow for powder selection.
The cross-sectional wind speed at the wind ring is determined by the gap area and the ventilation volume of the system. If the wind speed is too small, the material carrying capacity will be insufficient, which will lead to a large amount of slag discharge and low output; if the wind speed is too large, the amount of slag discharge will be small, and the circulation volume in the mill will increase, which is not conducive to the fine sorting of finished products. Under normal circumstances, in order to ensure a constant output, the air volume of the system is constant, and what can be changed is the area of the air ring gap.
Usually, the air ring gap area is fixed when the mill leaves the factory, and the wind speed ranges from 40 to 60 m/s. In production, the wind speed of the air ring should be inferred according to the amount of material returned by the mill. If the amount of slag returned is large, the air ring gap can be appropriately reduced (the simple method is to repair the round steel or flat steel on the outer edge of the upper wind ring), increase the wind speed at the air ring, and increase the material carrying capacity, so as to achieve the effect of increasing production and reducing emissions; If the amount of slag returned is small, it means that the flow field in the mill is smooth, keep the air ring gap unchanged, and appropriately increase the feeding amount. As long as the current of the mill allows, increasing the pressure of the grinding roller can continue to increase the production.
In this case, the vertical grinding of bentonite has a smooth process, simple operation, environmentally friendly production, strong adaptability, and is technically feasible. A single mill can reach 200 meshes, 95% pass rate, 10-12t/h output, and system electricity. The consumption is 28-34kWh/t (from the belt scale to the discharge port of the finished dust collector), and its performance is superior to the traditional Raymond mill in all aspects, providing an alternative for the large-scale and intensive development of the bentonite industry.