The principles of choosing grinding beads
1. Chemical principles
Beads will wear during the operation,so the beads should be chosen according to the chemical composition of the beads and the loss amount.As well,the chemical elements in the beads are the key factor should be considered,such as the beads used for pesticides,pharmaceuticals,food,cosmetics etc.,but the beads should not contain heavy metals.For the grinding of some non-metallic mine,the components of beads should be similar(using zirconium silicate beads or composite ceramic beads for grinding zirconium silicate,and using alumina beads for grinding Al2O3 powder).
2. The key performance indications of beads
Higher density always means greater grinding efficiency. High viscosity slurry should choose larger density beads, for example the offset inks and printing inks generally using Y-TZP beads of Ø0.2-Ø0.8.
The hardness of beads should be higher than the one of raw materials. On the other hand, high hardness beads will increase the wear of the exposed parts of the equipments. Certainly this wear can be optimized by controlling the amount of filled beads, the viscosity of slurry and the rate of flow.
Try to use beads with less wear-resistant. The wear-resistant does not only base on the materials of the beads themselves, but also bases on the test conditions. The manufactures of beads always measure the wear values under the environment with water medium, which is self-abrasion wear. If the beads are harder than raw materials, the self-abrasion wear may relate with the actual-abrasion wear; and vice versa. So it is suggested that before choosing the type of beads, the actual wear should be tested.
The beads must be not broken in the running, especially for the sand mills with high-density energy. The higher bending strength the beads have, the less possibility of fragmentation there will be. Y-TZP beads are the strongest products on the market.
The size of beads will decide the number of contact points between beads and raw materials. On the premise of having enough power, the smaller size, the higher efficiency. As well, the media separation systems of equipments decide the sizes. For the screen separation system, the minimum diameter of beads should be 3 times bigger as the one of sieve pore; for the ring type separation systems, the minimum diameter of beads should be 4 times bigger as the one of ring gap; for current dynamic centrifuge systems, Ø0.1- Ø0.2 ultrafine grinding beads are allowed. Moreover, the size of raw materials and the requested size will control the diameter of beads. For feeding large size raw materials but requesting ultrafine products, multiple stage process, which is choosing larger size beads in the front and smaller size beads at the end, should be designed. In addition, choosing beads with a narrow distribution of diameter do improve the grinding effect.