How to choose appropriate glass beads, zirconium beads or other grinding media?

With the higher and higher requirements for the fineness of materials, the use of sand mills is becoming more and more common, and there are more grinding media in the market. How to choose a grinding medium that is more suitable for its own production process and conditions is a key and laborious thing. Here is a brief analysis of the following aspects


1、 Chemical composition

Grinding media can be divided into glass beads, ceramic beads (including zirconium silicate beads, zirconium dioxide beads, alumina beads, rare earth metal stabilized zirconium dioxide beads, etc.) and steel beads according to different materials. Due to the difference of chemical composition and manufacturing process, the crystal structure of grinding beads is determined. The dense crystal structure ensures the high strength, high wear resistance and low ink absorption of beads. The different percentage content of various components determines the specific gravity of grinding beads, and the high specific gravity ensures the high grinding efficiency; The chemical composition of the grinding bead and the natural wear during the grinding process will have a certain impact on the performance of the slurry. Therefore, in addition to considering the low wear rate, the chemical elements to be scruples about are also factors to be considered. For example, grinding tape powder or other electronic component slurry, metal elements such as Fe and Cu should be avoided, and grinding beads containing Fe2O3 or CuSO4 are not included in the selection, so choosing zirconium beads is often a common choice in this industry; For example, in terms of grinding pesticides, medicine and biochemistry, heavy metals are taboo elements, and PbO is the most common component. In short, some physical properties (hardness, density, wear resistance) determined by the chemical composition of the beads and the pollution of their own wear to the slurry are the factors to be considered in the selection of grinding medium.

2、 Physical properties:

1. The density of grinding beads is expressed by specific gravity (true specific gravity) and bulk weight (false specific gravity) in the usual documents. The molecular weight and percentage composition of various oxides determine the grinding density. The commonly used grinding density is shown in Table 1. Table I type glass bead zirconium silicate bead pure zirconium bead alumina bead steel ball rare earth zirconium bead specific gravity 2.5 4.3 5.5 5.7 7.8 6.1 bulk weight 1.5 2.5 3.2 3.4.4 3.7 under normal circumstances, the larger the specific gravity of the grinding beads, the greater the impulse, and the higher the grinding efficiency. However, the wear of the contact parts of the sand mill (inner cylinder, dispersion plate, etc.) is relatively large, so the matching of slurry viscosity and flow becomes the key. Low density grinding beads are suitable for low viscosity slurry, and high density grinding beads are suitable for high viscosity slurry.

2. Hardness of grinding beads

Mohs hardness (Mohs) is a commonly used index. The higher the hardness of grinding beads, the lower the wear rate of beads in theory. For example, from the wear of grinding beads on the contact parts of the sand mill (dispersion disc, rod pin and inner cylinder, etc.), although the wear of grinding beads with high hardness to the contact parts is greater, the best optimization point can be achieved by adjusting the filling amount of beads, viscosity and flow of slurry and other parameters.

The particle size of grinding beads determines the number of contact points between grinding beads and materials. The more contact points of beads with small particle size under the same volume, the higher the grinding efficiency in theory; On the other hand, when grinding materials with relatively large initial test particles, for example, for 100 micron slurry, beads with d = 1mm are not necessarily used because the impulse of small beads can not reach the energy of full grinding dispersion. At this time, beads with larger particle size should be used. Note: This article was published in the 4th issue of "Southern painting" in 2001.