Ball milling grinding medium

Mixing. The most widely used mixing method is wet ball milling, which is a slow process, but it can be left unattended for the whole procedure. A ball mill is a barrel that rotates on its axis and is partially filled with a grinding medium (usually of ceramic material) in the form of spheres, cylinders, or rods. It mixes the raw oxides, eliminates aggregates, and can reduce the particle size. 

Material and Ball Charges The load of a grinding medium can be expressed in terms of the percentage of the volume of the mill that it occupies i.e., a bulk volume of balls half filhng a mill is a 50 percent ball charge. The void space in a static bulk volume of balls is approximately 41 percent. Since the medium expands as the mill is rotated, the ac tual running volume is unknown. 

PEBBLE MILL. A jacketed steel cylinder rotating on a horizontal axis and containing flint or porcelain pebbles as the grinding medium. Its operation is similar to that of a ball mill. It is used for grinding and mixing of dry chemicals, pigments, food products, and the like. Pebble mills are usually lined with alumina, buhrsione, or similar material to protect the walls from wear. 

The tube mill originated in the cement industry, where an extremely fine product is required. Originally flint pebbles were employed as the grinding medium, and the mills were lined with silex or silex brick, a hard siliceous material. Recently, however, it has been found that the efficiency is greatly increased by using a hard-iron or steel liner and steel balls, the output per horsepower being far greater. 

Ball and Pebble Mills. Ball mills are hardened steel shells with closed ends that use steel balls as the grinding medium (Figure 4). Pebble mills have steel shells and ends but they are lined with burrstone or synthetic stone (porcelain) and they use natural or porcelain balls as the grinding media (8) (Figure 5). 

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