5/26/2018 ball mill

1/2

Discussion

The operation of above experiment is based on size reductionand screening.

The term size reductionis applied to all the ways in which particles of solid are cut or broken

into smaller pieces. Throughout the process industries, solids are reduced by different methodsfor different purposes. Reducing the particle size increases the reactivity of solids, it permits

separation of unwanted ingredients by mechanical methods, it reduces the bulk of fibrous

material for easier handling and for waste disposal.

Solids may be broken in many different ways but only four are commonly used in size reduction

machines: (1) compression, (2) impact, (3) attrition or rubbing and (4) cutting.

In screen analysis standard screens are used to measure the size of particles in the size range

between about 3 and 0.0015 inches.

In making a screen analysis, a set of standard screens are arranged serially in a stack, with the

smallest mesh at the bottom and the largest at the bottom. The sample is placed on the top

screen and the stack shaken mechanically for a definite time. The particles retained on each

screen are removed and weighed, and the masses of the individual screen increments are

converted to mass fractions or mass % of total sample. Any particles that pass the finest screen

are caught in the pan at the bottom of the screen.

In the above experiment the equipment we used for size reduction was ball mill.

Ball mill is a type of tumbling mill. Tumbling mills consist of a cylindrical shell slowly turningabout a horizontal axis and filled to about one-half its volume with a solid grinding medium. The

grinding medium is balls of metal for ball mill.

Large ball mill shells might be 10 ft in dia and 14 ft long. The balls are 1 to 5 inches dia. The load

of the balls in ball mill is normally such that when the mill is stopped, the balls occupy about

one-half the volume of the mill. The void fraction in the mass of balls, when at rest is typically

0.40. When the mill is rotated, the balls are picked up by the mill wall and carried nearly to the

top, where they break contact with wall and fall to the bottom to be picked up again.

Centrifugal force keeps the balls in contact with the wall and with one another during the

upward motion. While in contact with the wall the balls do some grinding by slipping and rolling

over one another, but most of the grinding occurs at the zone of impact, where free falling balls

strike the bottom of the mill.

Theball mill is widely used in the fields of building materials, mineral processing, chemical

industry, electricity, etc, it can grind ores or other materials with certain granularity into fine

powder

http://www.greatwallmill.com/http://www.greatwallmill.com/

5/26/2018 ball mill

2/2