1. External reasons
1. Addition of dispersant
In the sand mill, the crushing of material particles mainly relies on the collision, extrusion and shearing between the high-speed moving grinding beads to achieve the reduction of the particle size of the material particles and the increase of the specific surface area. In the process of gradual refinement of the particle size, the particles will re-agglomerate under the influence of van der Waals force, double electric layer electrostatic action, etc. Therefore, it can be considered that after the particles are ultra-finely crushed to a certain extent, accompanied by a series of qualitative changes in the microscopic physical and chemical properties of the particles, a reversible process of "crushing ⇌ agglomeration" will appear. When the speeds of the positive and negative processes are equal, the dynamic balance in the crushing process is reached, and the particle size reaches the limit value. At this time, it is futile to further extend the crushing time. Because the mechanical force at this time is not enough to disaggregate the agglomerates and further break the particles, it can only be used to maintain the crushing balance, and it is possible to cause more small particle agglomerates, so the so-called "reverse grinding" and "re-coarsening" phenomenon will appear. To a certain extent, the appropriate selection of dispersants is an effective way to solve the "reverse grinding" and "re-coarsening" phenomenon. Dispersants can affect the van der Waals force between particles, the electrostatic force of the double electric layer, the spatial repulsion of the solvation film and the adsorption layer.
Therefore, the selection of dispersants in the ultrafine grinding process is a complex and difficult project. All factors must be considered comprehensively. Only when the dispersant has no effect on the product performance and system, the appropriate dispersant and its dosage can be selected to reduce the soft agglomerates between particles in the ultrafine grinding slurry, so that the particles are dispersed and stable in the system, and the grinding fineness of the sand mill can be achieved.
2. Internal reasons
The structure and technical design of the sand mill itself. As a highly efficient and energy-saving ultrafine grinding equipment, the sand mill has developed rapidly in the past decade. However, the equipment produced by different manufacturers is different, and the grinding fineness of different models of equipment produced by the same manufacturer is also different.
