BUILDING MATERIALS                


An abrasive is a substance, which is used to remove excess material by cutting. It polishes soft material and gives it an attractive appearance. Abrasives are the hardest materials.
They are used for engineering purpose in the following forms:
1. an abrasive papers or cloths,
2. as abrasive stones,
3. as grinding pastes with oil,
4. in grinding wheels, and
5. With some suitable bonding materials.

Abrasive may broadly be divided into the following two categories:
1. Natural Abrasives
2. Artificial Abrasives

Natural abrasives occur in nature. The most commonly used natural abrasives are diamond, garnet, flint, emery, corundum, carbonado and sandstone. Diamond is used for polishing precious stones. Garnet is used for polishing glass. Emery is used in papers and cloths and in grinding stones. Carbonado is used in rock drills, grinding wheels and cutting stones.
With the development of industries, it was found necessary to prepare artificial or synthetic abrasives. These abrasives possess the following advantages:
1. The amount of abrasive material is more in synthetic wheels.
2. The manufacture of synthetic abrasives permits exact duplication of the product.
3. The synthetic abrasive can be prepared of desired quality.
4. The synthetic wheels of desired size and shape can be prepared.

The most commonly used synthetic abrasives are carbides of aluminium, boric acid and silicon.