Size reduction

Definition: is mechanical process of reducing a solid to small state of subdivision.

Reasons for size reduction:

1. To increase surface area exposed for chemical reaction

2. To allow material to be mixed

3. To enable material to be dispersed in liquid as suspension

4. To allow rapid penetration of solvent

5. To increase

absorption

6. To allow rapid solution of drug

  Wet and dry grinding:

Many material tend to cake with a moisture content of 5-50% they don't flow, these two factors oppose effective grinding

Dry grinding is carried out for material with low content of moisture.

 Advantage of wet grinding:

1. Elimination dust problems

2. Easier to handle material

3. Consumer less energy

4. Increase the capacity of the mill

Disadvantage:

1. It causes more wear of the grinding medium

2. It cannot be applied to material soluble in the liquid for grinding      

Size Reduction Methods

1. Cutting methods

 •Size reduction range 100-100000

 •Principle of operation: A cutter mill consists of a series of     knives attached to a horizontal rotor which act against a   series of stationary knives attached to the mill casing.        

 Cutter mill

2. Compression Methods

Size reduction range   •

 750-100000 (Roller mill)

•Size reduction range

40-100000 (End runner mill)

•Principle of operation: size reduction by compression can be carried out on a small scale using a mortar & pestle

 a. Roller mill

b. End runner mill

The later mills are not enclosed then cannot be used for drug with strong odor.

3. Impact Methods

Size reduction range 8-7500   •

•Principle of operation: size reduction by impact is carried        out using a hammer mill.

Hammer mill