What are the precautions for a vertical mill operation?

1 vibration value

Vibration is a common situation in the operation of roller mills. Reasonable vibration is allowed, but if the vibration is too large, it will cause mechanical damage to the grinding disc and grinding roller, as well as damage to ancillary equipment and measuring instruments. The uneven thickness of the material layer is the main cause of vibration. Other reasons include: large metal objects in the grinding mill; too much grinding pressure; damaged wear-resistant parts; uneven charging pressure of the energy storage device; insufficient ventilation of the grinding mill, etc. In operation, vibration should be strictly controlled within the allowable range to create prerequisites for stable operation.

2 Material layer thickness

Another important factor for the stable operation of the vertical mill is the stability of the material bed. Only when the material layer is stable can the air volume, air pressure and feeding volume be stable. Otherwise, the thickness of the material layer must be maintained by adjusting the air volume and feeding volume. If the adjustment is not timely, it will cause problems such as intensified vibration, increased motor load, or system tripping and stopping. Theoretically, the material layer thickness should be 2% ± 20 mm of the grinding roller diameter. The vertical grinding roller diameter is 3000 mm, so 60 ± 20 mm is a suitable material layer thickness. In addition, the thickness of the material layer mainly depends on the quality of the raw materials, such as moisture content, particle size, particle distribution and grindability.

In the early stage of operation, in order to find the optimal material layer thickness, the height of the retaining ring must be adjusted. Under the condition that the height of the retaining ring is constant, one of the important conditions for stabilizing the thickness of the material layer is reasonable feeding particle size and particle size gradation. If the average particle size of the feed is too small or there are too many fine powders, the material layer will become thinner; if the average particle size is too large or there are too many bulk materials, the material layer will become thicker and the mill load will increase. The material layer can be stabilized by adjusting parameters such as water spray volume, grinding pressure, circulating air volume and powder separator rotation speed. Water spraying is the prerequisite for forming a solid material bed. Appropriate grinding pressure is the condition for maintaining the stability of the material bed. Ventilation in the mill is a means to ensure the fineness and moisture of the raw material.

3 pressure difference

The pressure difference refers to the pressure loss at the air ring and is also one of the important control parameters. Since the wind has a great influence on the operation of the vertical mill, the operating condition of the mill can only be good if the pressure difference is kept constant. The pressure difference is also a mirror of the situation inside the grinding mill. The operator can understand the situation inside the grinding mill by observing the pressure difference and judge whether there is more material, less material, high or low wind, grinding efficiency, etc. Moreover, as the feeding amount changes, the size of the grinding air volume and the stable value of the pressure difference also vary. This should be observed and accumulated experience in daily operations.

If the pressure difference is too large, it means that the resistance inside the mill is large and the internal circulation volume is large. At this time, measures should be taken to reduce the material, increase ventilation, increase water spray, stabilize the material layer, and temporarily reduce the number of revolutions of the powder separator. The fine powder accumulated in the grinding mill is discharged out of the grinding mill. After the pressure difference returns to normal, various parameters are restored appropriately to avoid over-grinding and prevent the grinding machine from skipping and stopping due to aggravated vibration, and the occurrence of full grinding accidents.

If the pressure difference is too small, it means that there is too little material in the grinding mill, and the grinding layer will be thinned quickly, causing increased vibration. Therefore, the material should be added immediately and water spray should be increased to form a stable material layer.

4 Grinding power consumption

The transmission power of the vertical mill is determined by the pressure exerted by the grinding roller on the grinding disc and related design parameters. If there is too much material on the grinding disc and the grinding pressure does not keep up, the grinding efficiency will be low and the grinding power consumption will be high; if the grinding pressure is too high, It will also increase the grinding power, which will have adverse effects on the equipment.

5 Mill outlet temperature

Supplying hot air into the mill is necessary for drying and lifting materials. The temperature of the gas at the outlet of the mill is an important factor in measuring the operating status of the mill. Overheating will cause damage to the internal machinery; if it is too low, the drying purpose will not be achieved. According to our factory’s operating experience, the mill outlet temperature is controlled at around 95°C. If the outlet temperature is high, open the circulation fan baffle appropriately or open the cold air baffle; if the outlet temperature is low, increase the hot air supply appropriately to ensure that the moisture content of the raw material does not exceed the standard.

6 Product fineness

The fineness of the product is mainly adjusted by the rotation speed of the powder separator. If the rotation speed is large, the product will be fine; if the rotation speed is small, the product will be coarse. The amount of air used in the mill also has a great impact on the fineness of the product.

7 output

Whether the vertical mill output is properly calibrated is also important for stable operation and giving full play to its advantages of energy saving, consumption reduction and cost reduction.