The Main Factors to the Grinding of the Bead Mill

Reasonably operating and using the bead mill according to the grinding process can achieve the desired grinding result, among which the output particle size, the selection of grinding media, the grinding temperature and pressure, and the appropriate grinding tank are important.

1. The Targeted Output Particle Size

The first to be noted when using the bead mill is the confirmation of the targeted output particle size(the final particle size of the solid content discharged from the bead mill). It determines the suitable type of bead mill, the time of grinding and circulation, and the appropriate separation method. For example, if the output particle size is required to meet the nano level, usually the pin type of rod type as the rotor structure is applied in the bead mill, which can meet the excellent fineness in the extremely narrow particle size distribution. At the same time, it is also featured in high grinding efficiency with great throughput and low energy consumption.

2. Selection of grinding media

The grinding media varies from different grinding slurry and the types of bead mills. Generally, 0.8-2.0mm zirconium beads are used for the output particle size from 5 μm to 15 μm. For the desired output fineness in 50-150nm, it is better to use 0.05-0.6mm while about 0.03mm is selected to reach 30nm.

There are also differences in selecting grinding media in bead mills using screen separation to centrifugal separation. The particle size separated using screen separation is limited. If the grinding media is too small, it may get carried out through the screen. 

However, the particle size separated using centrifugal separation allows smaller grinding media or zirconium beads since there is no screen. It adopts an independent electric motor for separation. When the bead mill is running, most of the zirconium beads are distributed to the periphery of the grinding vessel inside moving in the same direction as the slurry due to the centrifugal force while some rotate around the separator. The pressure on the zirconium beads generated by the separator during high-speed rotation keeps them in the grinding tank. At the same time, the centrifugal force on the slurry generated by the separator is less than the pressure generated by the pump, forcing the slurry to flow out of the separator.

3. Control of the Grinding Temperature and Pressure

Some materials or slurries require strict temperature control, as their physical or chemical properties may change when the temperature is high. Generally, the maximum temperature can be set on the electric temperature sensor at the product outlet. When the discharge temperature reaches the maximum temperature set, the bead mill will automatically shut down to protect the material or slurry from excessive temperature. Therefore, setting the appropriate maximum temperature is necessary. Besides, it can reach the best cooling by increasing the heat exchange area and lowering the cooling water temperature.

The movement of the grinding media through collision and shear generates a lot of heat energy when the mill runs. The large will gather and aggregate as the temperature rises,  adverse to the internal particles. In such cases, adjusting the cooling water temperature can effectively control the working temperature inside the grinding chamber, thereby greatly improving the grinding efficiency. The comparison of the experiment under all the same external factors except the temperature shows the grinding efficiency of using 15℃ chilled water is 30% higher than that of using 22℃ circulating water. Proprietary control of the cooling water temperature can greatly improve the grinding efficiency.

The grinding pressure is controlled by adjusting the air pressure of the bead mill, which can affect the fluidity of the solvent and slurry. Appropriately adding the grinding pressure can increase the grinding efficiency and output, but excessive pressure may increase the wear of the grinding media, thereby affecting product quality.