A ball mill is a method for grinding where small balls or beads are placed in a rotating drum. The media to be grinded is inserted and the balls will be lifted and dropped by the rotating motion of the drum. As the grinding balls fall, they break up the substance to be ground. The process can be used for wet or dry grinding.
Ball mill grinding has multiple uses including cement, paint pigments, semiconductor materials and is widely used in the pharmaceutical industry. It is a safe method for reducing hard substances to a powder form. It can also be used for polishing hard metal parts or removal of burrs and rough edges to form a smooth surface.
The material used for grinding balls or beads varies, depending on the drum and the material to be ground. Nylon and polyurethane are used to polish or grind softer materials. Zirconia, magnesium and chrome steel balls are used for harder substances.
Alumina oxide balls are a favorite in the grinding industry because of their versatility and durability. Alumina oxide in its crystalline form is corundum, the same material that forms rubies and sapphires. Some of the factors that make Alumina oxide attractive as a grinding media are:
• Hardness- Alumina oxide is one of the hardest substances used in the grinding industry, with an elasticity rate of 45 million lbs. per square inch, Hardness is important not only from a grinding and durability concern. It is especially important for a purity factor. The harder the substance, the less likely it is to flake off and intermingle with the material to be ground;
• Thermal properties- as a ceramic material, it can withstand high temperatures. Alumina oxide is commonly used as an electrical insulator;
• Corrosion resistance- Except for some acids, Alumina oxide possesses excellent anti-corrosive properties;
• Non-porous- This property is important to ensure the material to be ground does not accumulate into the grinding media;
• Expense- Alumina oxide is relatively inexpensive in comparison to other grinding media.
No grinding media is suitable for every grinding or polishing job. A quality grinding media manufacture will carry a large number of media materials to meet a variety of grinding needs. It is wise for any business operating a ball mill to discuss the material to be ground, the type of mill used and the production budget of the operation. If Alumina oxide is not right for the job the manufacturer will most likely have the appropriate grinding media.