How Do Ball Mills Work?

Ball mills are cylinders that rotate a grinding medium within them.

In the same way that a mortar and pestle can be used to crush ingredients between two solid objects, ball mills grind material between a rotating cylinder and a series of solid balls. These specialized grinding devices come in a variety of sizes but are all very efficient at reducing materials into a fine powder.

Features

Ball mills work on a similar principle to rock tumblers

A typical ball mill is made up of a cylinder containing a grinding medium. The type of medium used will depend on the function of the ball mill, but typically includes lead, steel and aluminum balls or even flint pebbles.

The cylinder rotates at high speed, causing the grinding medium to rotate in the opposite direction. The cylinder can rotate up to the speed where centrifugal forces cause the grinding medium to stop rotating and cling to it.

Functions

The ball mill is an effective grinding device because it crushes the material to be ground between the surface of the ball and the inside of the cylinder at high speeds. The high velocity of the impact combined with its regularity can reduce material to particles as small as five nanometers across.

History

The first recorded use of ball mills was to grind flint

The concept of a grinding device that crushes material by shaking it with hard objects is old but came to the fore during the Industrial Revolution. At this time, large devices could be made to run the grinding process continually. The first ball mills were recorded in operation in 1870, grinding flint.

The vibrating ball mill was developed in Germany in the 1930s. Unlike the traditional mill, it does not rotate, instead shuffling balls back and forth. Recently, the planetary ball mill was developed. This rotates the cylinder on a sun wheel, allowing the grinding medium to rotate at higher speeds.

Safety Considerations

To avoid explosions, use a non-sparking grinding medium

Ball mills are widely used in the production of black powder but can be dangerous. In order to minimize the chance of explosions, a non-sparking grinding medium is required. It is also is important to seal the ends of the ball mill when using one at home, to reduce the chance of spillage when the cylinder is rotating.

Useful Facts

Because of their small size and high rotational speed, ball mills are a cost-effective way of producing nano-scale powder for use in laboratories. On a more historical note, some of the earliest industrial-sized ball mills were churning out copper sulfate from mines in Michigan in 1915. At this time, other mines were still using far less effective, traditional grinding methods.

References

• "The History of Grinding"; Alban J. Lynch and Chester A. Rowland; 2005