• Size-reduction equipments are divided into four principal types as given in Table.
• Crushers are employed for breaking large pieces of solid materials into small lumps.
• A primary crusher is the one which crushes very large lumps to yield a product 150 to 250 mm in size. A secondary crusher is the one which takes the product from a primary crusher and reduces it to particles of about 6 mm size.
• Grinders are the machines which reduce crushed feed to powder. An intermediate grinder yield a product that might pass a 40 mesh screen. A fine grinder gives a product most of which would pass a 200 mesh screen. Ultrafine grinders are the machines which accept feed particles having a size less than 6 mm and yield a product of size 1 to 50 µm.
• Cutters are size-reduction machines which give particles of definite size and shape, usually 2 to 10 mm in length.
Table : Principal types of size-reduction machines
1. Crushers (coarse and fine)
(a) Jaw crusher
(b) Gyratory crusher
(c) Crushing rolls
2. Grinders (Intermediate and fine)
(a) Hammer mills
(b) Rolling-compression mills
(i) Bowl mills
(ii) Rolling mills
(c) Attrition mills
(d) Revolving mills
(i) Rod mills
(ii) Ball mills; pebble mills
(iii) Tube mills
3. Ultrafine grinders
(a) Hammer mills with internal classification
(b) Fluid-energy mills
(c) Agitated mills
4. Cutting machines
(a) Knife cutters, dicers, slitters.
• The size reduction machines perform their work in distinctly different ways. Crushers
employ compression while grinders employ impact and attrition. Ultrafine grinders
employ attrition. A cutting action is the characteristic of knife cutters, dicers and
slitters.
• The factors to be considered while selecting the equipment for size reduction are :
(i) Properties of the feed to be handled such as hardness, crushing strength, etc.
(ii) Nature of the product required.
(iii) Quantity of the material to be handled.
(iv) Size of the material to be handled.
(v) Speed of the size reduction equipment.
keywords :-
- What is size reduction ?
- Application of size reduction.
- Factors affecting size reduction.
- Fluid energy mill diagram.