Why size reduction is important?
In the process industry reactant, solid is broken or reduced to increase the reaction rate, the product reduces for handling, storage, and packaging purpose.
There are four different size Reduction principles :
(1) compression: compression force is applied for size Reduction. Solid particles which have to reduce size place between two solid walls and force is applied by both sides.
(2) Impact: I this generally one wall side is fixed and from second impact force is applied on solid particles.
(3) attrition or rubbing: same as the compression but here tangential force is created attrition or rubbing.
(4) Cutting: In this cutter is used by various machinery for cutting solid particles.
Based on the above four principles there are various types of size reduction equipment are used :
(A)Crushers
(B)Grinders
(C)Cutters
(A)Crushers :
for the making of coarse particles, size Crushers are used. Generally operated in compression action.
The main types of Crushers are:
1.Jaw crusher
2. Gyratory crusher
3. Roll crusher
Let take a look at one by one
1.Jaw crusher :
- Compression force between two jaws is given for size reduction.
- On the feed side, jaws are open for taking large size particles, And as size reduce the gap between the two jaws is less creates a V shape at the bottom side.
- One jaw is fixed and the other will give reciprocating motion horizontally.
- The angle of the fixed jaw is around 20-30°. Here reciprocating jaw closed and open in the range of 200-400 times per minute.
2. Gyratory crusher :
- This crushing is done by gyratory action means the circular motion of the shaft with some oscillation.
- The shaft is in conical shape making V shape for solid particles inlet. This shaft is also called a crushing head.
- Solid particles are inlet at the top and caught between the V shape of the crushing head and casing around it and because of gyratory action particle size is reduced.
- The advantage compare to the jaw crusher is that it can operate continuously, less maintenance requires and also power require for gyratory action is less.
3.Roll crusher :
- on this two roles are rotates oppositely for crushing of particles.
- Particles are caught between two rotating roles and because of compression action particles are crushed.
- Desire particle size can get by adjusting space between two roles. If thoughts are on rolls then it is called tooth crusher.
(B)Grinders :
- Used for the intermediate and fine size of the product. Mostly all types of mills come into this category.
1.Roller mill :
- solid particles are Crushed between roller and casing. This vertical roller rotates and creates a force to crush solid particles with the anvil or stationary ring.
2. Ball mill :
- The horizontal cylindrical drum contains some metal balls.
- As the cylindrical drum rotates balls are carried with the inner part of the drum wall and as balls are reached to the upper portion then because of gravity comes to the bottom and gives impact on solid particles. This impact can give fine particle size of the product.
- The mill is run at critical speed because at high speed balls give a whole round of mill with drum and give less impact,and at a lower speed, balls can't go with the drum to the top for impact.
- If in place of balls pebbles are used then it is called pabble mill.
3.Hammermill :
- a cylindrical horizontal casing contains a central shaft with hammers. As the shaft rotates hammer impact on solid particles and size is reduced.
(C) Cutters :
- Rubber, plastic, and other sticky material which size can't be reduced by compression, and impact is reduced by cutting.
- In Cutters knife Cutters are most common. The horizontal rotor contains some knife on it in the chamber.
- Particles are feed from the top and size is reduced by rotating the rotor with a knife. At the bottom screen is placed, so undesired size can feedback and get the desired size.
- Plate cutters are also used for size reduction. In this knives are arranged in parallel in manner. Used for getting uniform size.