SIZE REDUCTION | COMMINUTION

                     Comminution / Size Reduction operation is generally employed in industries for reducing the size of the raw material so that it can be processed further. The equipments used for achieving size reduction are termed as size reduction equipments. There are several types of such equipments depending upon what feed size is to be crushed and up to what extent is it to be crushed. The roughest equipments for size reduction that can handle any size of feed are crushers. The size reduction equipments are specific and are been discussed below.

Size Reduction Machines can be classified as follows :

(A) Crushers (for coarse and fine crushing)

      1. Jaw Crushers

      2. Gyratory Crushers

      3. Crushing Rolls.

(B) Grinders (for intermediate and fine crushing)

      1. Hammer Mills, Impactors.

      2. Rolling Compression Mills :

         (a) Bowl Mills

         (b) Roller Mills

      3. Attrition Mills

      4. Tumbling Mills :

         (a) Rod Mills

         (b) Ball Mills, Tube Mills

         (c) Pebble Mills, Compartment Mills.

(C) Ultrafine Grinders

     1. Fluid Energy Mills

     2. Agitated Mills.

(D) Cutting Machines

     1. Knife Cutters.

CRUSHERS 

• Slow speed machines for coarse reduction of large quantities of solids.
• Main types are jaw crushers, gyratory crushers, smooth roll crushers and toothed roll crushers.
• All of them have specific type of force involved for size reduction.
• Toothed roll crushers tear feed apart as well as crushing it, they handle softer feeds like coal, soft shale, etc.

GRINDERS

• Size reduction machines for an intermediate duty.
• Product from a crusher is often fed to a grinder in which it is reduced to powdered form.
• Size reduction by crushing may not meet the size requirements that we need, if we want further reduction in size, we have to use the process of grinding.
• The outcome of grinding is usually the pulverised material i.e the powdered form of material.
• It makes the use of forces like attrition, compaction, shearing, impact, etc.
• Grinding is usually carried out by tumbling, vibrations and stirring.
• Some examples of are tumbling mills, impactor, roller mill, attrition mill, etc.

ULTRAFINE GRINDERS

• When particles of size 1-20 μm are required, ultrafine grinders are employed.
• These particles can easily pass via a standard 325 mesh screen.
• Both - dry and wet grinding can be done in these grinders.
• Some examples are fluid energy mills, jet mills, high speed hammer mills, etc.