the container wall, and then pulled back down by gravity to accomplish a grinding action
by a combination of impact and attrition. These operations are often carried out with water
added to the mixture, so that the ceramic is in the form of a slurry. In a roller mill,
stock is compressed against a flat horizontal grinding table by rollers riding over the table
surface. Although not clearly shown in our sketch, the pressure of the grinding rollers
against the table is regulated by mechanical springs or hydraulic-pneumatic means. In impact
grinding, which seems to be less frequently used, particles of stock are thrown against
a hard flat surface, either in a high velocity air stream or in a high-speed slurry. The impact
fractures the pieces into smaller particles.