Laboratory mills work with different particle size reduction principles.
Which type of mill is used for a particular particle size reduction task
always depends on the breaking properties of the sample material.
Size reduction machines for large particle sizes above 40 mm are
known as crushers or shredders while particle sizes below this
are processed with mills.
The most common mechanisms for the particle size reduction of solids are explained below.
Please also note that usually, various particle size reduction principles are combined in
one mill, such as impact and friction in planetary ball mills or shearing and impact in rotor mills.
Hard-brittle materials are best pulverized with impact, pressure and friction effects to be successfully comminuted.
Force is applied between two solid surfaces that either represent the grinding tool surfaces directly or may be the surfaces of adjacent particles. Pressure is exerted by the grinding tools.
Examples: jaw crushers, toggle crushers
Force at a solid surface. This could either be that of a grinding tool, or be represented by other particles. Strain by impact is mainly caused by one-sided and opposing particle acceleration.
Examples: mixer mills, planetary mills, impact mills, jet impact mills, drum mills
Force between two solid surfaces. Caused by the vertical pressure of one surface and the simultaneous movement of the other surface.
Examples: mortar grinders, disc mills, hand mortars, rod mills
Soft and elastic substances require cutting and shearing effects to be successfully comminuted.
Force between two or more solid surfaces moving in opposing directions which results in a shearing effect. At least one fixed and one moving surface.
Examples: rotor beater mills, cross beater mills, ultra centrifugal mills
Force between two or more sharpedged surfaces. At least one fixed and one moving cutting edge.
Examples: shredders, cutting mills, knife mills