Ball Mill , Principle , Construction , Working

Ball Mill :

This mill is also known as the pebble mill , tumbling mill .

Principle :

1. Impact between the rapidly moving balls and the powder material .

2. At low Rates speeds the ball roll over the each other and attrition will be the predominant mode of mechanism .

Mechanism :

Impact or Attrition or Both .

Construction :

1. It Consist of hollow cylinder , which is mounted on  a metallic frame in such a way that it can be rotated on its longitudinal Axis .

2. Length is slightly grater then its diameter .

3. balls can occupy 30-50% of the mill volume  .

4. weight of the ball is constant  .

5. ball size will be varied  .

6. Balls are made up of steel , iron , stoneware .

7. The balls used may be in the size of the Round , Banded, Cube , Cylinder (rod) .

Working :

1. The Sample to be placed in cylinder about 60 % .

2. Fixed number of balls are introduced .

3. Speed of rotation is very important .

1. At Low Speed 

1. Balls are roll over each other attrition .

2. Used For Wet Grinding .

Example : -  Surfactant to prevent agglomeration .

2. Optimum Speed 

1. Balls are picked up by the mill wall to the top , where they break contact with the wall and fall to the bottom .

2. Both impact and attrition .

3. High Speed  

1. Balls are thrown out to the wall by centrifugation force grinding will not occur . Compression occur but not sufficient .

Advantages :

1. Can Produce very fine Powder .

2. Suitable for both wet and Dry Grinding  .

3. Potent Drug can be Grounded .

Disadvantages :

1. Batch Process

2. Very noisy machine and wear .

3. Time taking process 

4. Soft and fibrous material cannot  be milled  .