As a construction, a ball milling device usually consists of a cylindrical vessel mounted on an appropriate basis at both ends which allows rotation of the vessel around the center axis. The mill is driven by a girth gear bolted to the shell of the vessel and a pinion shaft moved by a prime mover. The prime movers are usually synchronous motors equipped with an air clutch or gear transmission. After the mill is charged with the starting material (ore, rock, etc.) and the grinding media (balls), the milling process takes place during rotation as a result of the transfer of kinetic energy of the moving grinding media into the grinding product.
The design of a ball mill can vary significantly depending on the size, the equipment used to load the starting material (feeders), and the system for discharging the output product. The size of a mill is usually characterized by the ratio “length to diameter” and this ratio most frequently varies from 0.5 to 3.5. The starting material can be loaded either through a spout feeder or by means of a single or double helical scoop feeder. Several types of ball mills are distinguished depending on the discharge system and these types are commonly known as overflow discharge mill, diaphragm or grate discharge mill and center-periphery discharge mill. In industrial applications, the inner surface of the mill is lined with mill liners protecting the steel body of the mill and incorporating mill lifters which help to raise the content of the mill to greater heights before it drops and cascades down. There are three types of grinding media that are commonly used in ball mills:
- steel and other metal balls;
- metal cylindrical bodies called cylpebs;
- ceramic balls with regular or high density.
Steel and other metal balls are the most frequently used grinding media with sizes of the balls ranging from 10 to 150 mm in diameter. Cylpebs are slightly tapered cylindrical grinding media with rounded edges and equal length and diameter with sizes varying from 8×8 to 45×45 mm. Their shape is developed to maximize the grinding efficiency due to their high density and specific surface area. Ceramic balls with regular density are usually porcelain balls and the high density balls are made with a high alumina oxide content and they are more abrasion resistant. The basic properties of the grinding system are their mass and size, ware rate, influence on the particle breakage rate and energy efficiency of the grinding process.