Ball Mills

Ball Mills

From here, the pieces of rock go to the ball mills. These mills are giant revolving cylinders which are partly filled with heavy steel balls. As the cylinders revolve, the balls are carried upward by the centrifugal force holding them in place on the steel plates, or ribs, set into the sides of the cylinders. When the balls near the top of the mill they are hurled back by gravity onto the charge of raw material, which is ultimately ground to small particles.

Before the raw material is ground in the ball mills, it has been carefully proportioned to include the right amounts of limestone and clay, shale or slag.

The proportioning of the limestone and other ingredients is done under laboratory control by clever automatic devices. Thus, any single sack of finished cement taken at random will have the identical characteristics of the day's output of the mill, even though the production is thousands of barrels.

After this mixing process, the combined materials are again ground to a fine powder in another battery of tube mills. These are sometimes divided into several compartments, the material passing through screens from one to another until just the right stage of fineness is reached.