Write short notes.
The manufacturing process of glass consists of four major operations: (1) Melting, (2) Shaping, (3) Annealing, (4) Finishing. Each operation is being discussed briefly as follows:
1. Melting: The ingredients called batch materials are mixed in the appropriate proportion and heated to fusion in a furnace. For glass production, a mixture of sand(silicon dioxide), lime and a small quantity of magnesium oxide is added. The two most commonly used furnaces are (i) Pot furnace and (ii) Tank furnace.
i. Pot Furnace: In this furnace, the charge is fused in fire clay pots. The pots may be opened or closed. The closed pots are used when the-glass is to be protected from the products of combustion.
(ii)Tank Furnace: It consists of a large rectangular tank built of fire clay blocks. The batch materials are fed into the tank and producer gas is used as a fuel in the furnace.
2. Shaping: The plastic glass formed in the furnace is next shaped or formed into the desired articles. It is accomplished by blowing from the mouth or by means of a machine.
Shaping of glass lump.
3. Annealing: It is a process of cooling slowly the newly shaped articles. If they are cooled quickly they become brittle on account of the high internal strain. Annealing allows the molecules to arrange themselves in such a way that there is no internal strain when the mass is cooled. Annealing is done in a tunnel-like oven called lehr
4. Finishing: The articles obtained from the lehr are subjected to a number of operations such as cleaning, polishing, grinding, rounding edges, etc., for bringing them to a useable form.