This document summarizes the mechanism of size reduction using a hammer mill. It operates using the principle of impact, with hammers fitted horizontally or vertically that rotate at high speeds of 8,000-15,000 rpm. Materials are crushed when they impact the rotating hammers. Particle sizes obtained are typically 10-400mm. Hammer mills are versatile, occupy small spaces, and allow for closed systems to reduce dust. However, they can generate heat and screens may become clogged. Ball mills also use impact and attrition for size reduction and consist of a horizontal cylinder containing balls.

1. TOPIC: Mechanism of SIZE Reduction & Hammer Mill
PHARMACEUTICAL ENGINEERING
Prepared by kashish Wilson
Assistant Professor,
MM College of Pharmacy,
MM(DU),Mullana Ambala

2. Modes of size reduction:
Cutting: The material is cut by means of a sharp blades
Eg : cutter mill
Compression:
 In this mode material is crushed between roller by the application of
pressure Eg : roller mill
Impact:
 This involve the operation of hammer/bars at high speeds.
 When a lump of material strikes the rotating hammers, the material splits
apart. Eg : fluid energy mill
Attrition: breaking down by the rubbing action between two surfaces.
Eg : fluid energy mill, ball mill

3. Principle: Impact
Construction: hammers are fitted horizontally or
vertically made up of hardened steel
Hammers blades can be flat edges or sharp edges or both
on each side
Working: Rotates at 8000 to 15000rpm
variants:
Fitz patrick communicating mill.
Stokes tornado mill
;
Hammer mill

4. Uses: Obtained particle size is 10 to 400mm.
 Used to mill dry materials, ointment, filter press cakes.
Advantages:
It is versatile, occupies small space.
 Operation in close system,dust can be reduced
 Easy to setup and scale up.
Disadvantages: Screens may get clogged.
 More heat is generated.
 Not to mill sticky, fibrous, hard materials
Ball mill :
Principle: In the ball mill, Impact or attrition or both are responsible for the
size reduction.
Construction: consists of horizontal cylinder containing balls that occupy 30 to
50% of the mill volume.
Working: The drug is placed upto 60% of volume.

5. Thank you