Size separation can be done by various methods as follows,
Agitation:
Sieves may be agitated in a number of different ways.
Oscillation (move back and forth)
The sieve is mounted in a frame that oscillates.
Advantages: Simple method
Disadvantages: The material may roll on the surface of the sieve and fibrous materials tend to “ball”.
Vibration:
The mesh is vibrated at high speed, often by an electrical device.
Advantages: The rapid vibration is imparted to the particles on the sieve and the particles are less likely to “blind” the mesh.
Gyration:
Sieve is rubber mounted and is connected to an eccentric flywheel which gives gyrating movement which helps particles passing the sieve.
Brushing:
A brush can be used to move the particles on the surface of the sieve and to keep the meshes clear.
A single brush across the diameter of an ordinary circular sieve, rotating about the midpoint, is effective;
In large-scale production a horizontal cylindrical sieve is employed, with a spiral brush rotating on the longitudinal axis of the sieve.
Useful for separating sticky powder particles.
Centrifugal Force:
Use a vertical cylindrical sieve with a high speed rotor inside the cylinder, so that particles are thrown outwards by centrifugal force.
The current of air created by the movement helps sieving.
Is especially useful with very fine powders.
Commonly asked question.
Write a short note on different mechanisms involved in mechanical size separation.