a. Glass production:
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, mixture of sand(silicon dioxide), lime and 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. (Fig. 4.2).
2. Shaping: The plastic glass formed in the furnace is next shaped or formed into the desired articles. It is accomplished by blowing from mouth or by means of a machine.
Shapinq 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.
Optic glass is high-quality, homogeneous, color-free glass, as flint or crown glass, having specified refractive properties, used in lenses and other components of optical systems.
Optic glass is produced, when we mixed sand(silicon dioxide), soda, limestone, barium oxide and boron.
These glasses are useful in the production of microscopeic lenses, spectacle4s, lenses etc.
c. Uses of plastics are :
1.Melamine is used in domestically useful items like cup, saucers, plates, trey, spare parts of airplane engine and sound insulating coverings etc.
2.Polyurethane is used in surfing boards, small boats, furniture, seats in vehicles etc.
3.Bakelite is used for making cabinets of radio, T.V., telephones, electric switches, toys, coverings over handles of cookers etc.
4.Polyester is used for making fiber glass, toners of laser printers, textile industry etc.
5.Polypropylene is used for making parts of loudspeakers & vehicles, ropes, mattresses, laboratory appliances stc.
6.Polyethylene is used for making milk bags, packing bags, flexible garden pipes etc.
7. polystyrene is used for making thermo-insulating parts of electric appliances like refrigerators, gears of machine, toys, protective coverings like covers of CD and DVD etc.
8.Polyvinyl chloride is used for making bottles, raincoat, pipes, handbags, shoes, electric cable insulation, furniture, ropes, toys etc.