How to Achieve a Smooth and Reflective Surface on Ceramic Grinding Balls?

Ceramic grinding balls have a shiny surface, some even reflecting light, what is the small secret behind this? In fact, the main factor that determines whether the surface of the ceramic grinding ball has a shiny effect is the flatness of the ball surface; the smoother the ball surface, the better the mirror effect; the rougher the ball surface is, the worse the mirror effect. The factors that affect the flatness of the ball surface mainly include: the internal structure of the material and the degree of external processing of the ball surface. Among them, understanding the external processing of the ball surface is relatively simple, for example, the grinding balls that have just been sintered are matte, and the ball surface may have a mirror effect only after polishing. The internal structure of the material includes: pores, grain size, liquid phase, etc., which affect the flatness of the ball surface as follows.

Pores of ceramic grinding balls

Since the sintered ceramic grinding balls nowadays generally have high density, there are few pores caused by sintering, so the pores mentioned here generally refer to large defects caused by molding and other reasons. For example, the powder used for rolling balls includes airflow powder, spray-dried powder, granulated powder, etc., which are essentially pseudo-particles composed of countless individual grains. However, due to different powder production processes and different particle strengths, there will be some pseudo-particles that cannot be completely crushed during use, which leads to the inability of the grains to fully approach during the sintering process, resulting in large pores and other defects.

Grain size of ceramic grinding balls

When the material type is different, the grinding degree of each manufacturer’s material is different, and the formula and firing process are different, the internal grain size of the sintered grinding balls will be different. The finer the grain, the flatter the ball surface; the coarser the grain, the less flat the ball surface, just like using stones and sand to pave the road. The grain size of the zirconia grinding ball is mostly between 0.3um-0.5um, while the grain size of the alumina grinding ball is mostly between 1um-5um. The zirconia grains are finer, and the ball surface is flatter, so the zirconia ball surface is brighter than the alumina ball surface.

Liquid phase of ceramic grinding balls

Taking alumina ceramics as an example, in production, some additives are added to lower the sintering temperature of ceramics. Some of these additives can generate a liquid phase in high alumina ceramics, such as kaolin, magnesium borate, silicon powder, etc. They can form binary, ternary, or more complex low-melting co-melts with other additives. After adding an appropriate amount of additives, on the one hand, the sintering temperature of the ceramic can be lowered, and the grain can be made finer; on the other hand, the formed liquid phase is similar to the asphalt on the road, making the ball surface of the ceramic grinding ball flatter, and naturally, the ball surface will be brighter.

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