Many of the surfaces of the grinding balls that we usually see are shiny and even have a mirror effect, which is due to the specular reflection of light.
Reflection occurs when light travels to the surface of the object. Reflection is divided into specular reflection, diffuse reflection and direction reflection.
1. Specular reflection: If the surface of the object is smooth, the reflected light is parallel when it is incident on a smooth surface. This reflection is called specular reflection.
2. Diffuse reflection: If the surface of the object is rough, parallel rays are incident on the uneven surface, and the reflected light is directed in all directions. This reflection is called diffuse reflection.
3. Directional reflection: The reflection between diffuse reflection and specular reflection is called directional reflection, also called non-Lambertian reflection, which is reflected in all directions, and the intensity of each reflection is not uniform.
It can be seen from the above that the factor that determines whether the surface of the grinding ball has bright light is the smoothness of the spherical surface; the smoother the spherical surface, the better the mirror effect; the rougher the spherical surface, the worse the mirror effect. There are many factors affecting the smoothness of the spherical surface, which are mainly divided into: the internal structure of the material and the degree of processing outside the sphere. Among them, the spherical outer surface processing is relatively easy to understand, for example, the grinding ball just after sintering, the spherical surface is matte, and the spherical surface may have a mirror effect after polishing. The internal structure of the material includes: pores, grain size, liquid phase, etc., and their effects on spherical flatness are as follows:
Stomata
Since the grinding balls after sintering are generally highly densified, the pores caused by sintering are few, so the pores we refer to here usually refer to large defects caused by molding and the like.
For example, the powder for rolling balls has air flow powder, spray dry powder, granulated powder, etc., which are essentially pseudo-particles composed of numerous individual crystal grains. However, due to the different milling process, the particle strength of the powder is not the same. In the use, some fake particles may not be completely crushed, resulting in the grain not being completely close during the sintering process, causing defects such as atmospheric pores.
Grain size
When the types of raw materials are different, the degree of grinding of the raw materials by different manufacturers, and the different formulation and firing processes, the internal grain size of the grinding balls after sintering is different. The finer the grain, the flatter the sphere; the thicker the grain, the less uneven the sphere, just like paving with stones and paving with sand.
Most of the zirconia grinding balls are 0.3um-0.5um, the alumina grains are mostly 1um-5um, the zirconia grains are finer, and the spherical flatness is higher, so the zirconia spherical surface is brighter than the alumina spherical surface.
Liquid phase
Taking alumina ceramics as an example, in order to reduce the sintering temperature of ceramics in general production, some additives are added. Some of them are admixtures capable of forming a liquid phase in high-alloy porcelain, such as kaolin, boehmite, silica fume, etc., which together with other admixtures can form binary, ternary or more complex low-melting co-melts. After adding an appropriate amount of admixture, on the one hand, the sintering temperature of the ceramic can be lowered to make the crystal grains small; on the other hand, the liquid phase formed on the other hand can also be like the paving asphalt, so that the spherical surface is flatter and the spherical surface is naturally brighter. It is.
