Grinder

Grinder has several meanings:

• In machining operations grinding refers to an abrasive operation to refine the surface of materials. See grinding machine.

• In the military, "grinder" is a slang term for a drill field, typically a hard surface upon which troops are marched or drilled in a manual of arms .

• This article concerns grinding in materials processing, typically use to reduce the particle size of bulk materials.

In materials processing grinding is the fine particle size reduction through attrition and compressive forces at the grain size level. See also crusher for mechanisms producing larger particles.

Contents

1 Ball milling 2 Rod milling 3 SAG milling 4 Autogenous milling 5 Pebble milling 6 High pressure grinding rolls 7 Buhrstone mill

Ball milling

A typical type of fine grinder is the ball mill. A slightly inclined or horizontal rotating cylinder is partially filled with balls, usually stone or steel, which grinds material to the necessary fineness by friction and impact with the tumbling balls. The feed is at one end of the cylinder and the discharge is at the other. Ball mills are commonly used in the manufacture of portland cement.

Rod milling

A rotating drum causes friction and attrition between steel rods and ore particles.

SAG milling

A rotating drum throws large rocks and steel balls in a cataracting motion which causes impact breakage of larger rocks and compressive grinding of finer particles. Attrition in the charge causes grinding of finer particles.

Autogenous milling

A rotating drum throws large rocks in a cataracting motion which causes impact breakage of larger rocks and compressive grinding of finer particles. Attrition in the charge causes grinding of finer particles.

Pebble milling

A rotating drum causes friction and attrition between rock pebbles and ore particles. May be used where product contamination by iron from steel balls must be avoided.

High pressure grinding rolls

The ore is fed between two rollers which are pushed firmly togther while their rotating motion pushes the ore through a small gap between them. Exteme pressure causes the rocks to fracture into finer particles and also causes microfracturing at the grain size level.

It consists of a pair of horizontal cylindrical rollers through which material is passed. The two rollers rotate in opposite directions, "nipping" and crushing material between them. A similar type of intermediate crusher is the edge runner, which consists of a circular pan with two or more heavy wheels known as mullers rotating within it; material to be crushed is shoved underneath the wheels using attached plow blades.

Buhrstone mill

Another type of fine grinder commonly used is the Buhrstone mill , which is similar to old-fashioned flour mills .