Processing of Glass Products
Glass is made from natural and abundant raw materials (sand, soda ash, and limestone) thatare mixed together and heated in a furnace at a very high temperature to produce molten glass. When in molten state, it is then shaped and allowed to cool so as to form a hard piece,by blowing air into the mixture. The hard glass is then reheated again and allowed to cool gradually, in a process called annealing.
The articles obtained are then subjected to a number of operations, such as cleaning, polishing, grinding, rounding edges, in order to bring them to a useable form.
Stages Involved in Glass Processing:
Stage 1: Preparation/Crushing and Mixing: Solid materials like sand, soda, lime, potash, and lead oxide together with recycled glass are crushed and grounded into a fine paste. This is followed by sieving of the paste to remove any coarse materials.
Stage 2: Firing: This involves heating the mixture in a furnace, for about 5 to 6 hours, in order to melt it. Meanwhile, additives and flux materials are added as the mixture is being stirred continuously. The impurities in the mixture, called cullet, are then removed. This process turns the mixture into a plastic molten glass.
Stage 3. Forming: At this stage, the molten glass is forced into either a flat sheet form or a desired geometrical shape. It is usually done when the gas is hot. The different shaping methods are blowing, pressing, and casting.
Stage 4. Annealing and Polishing: Annealing is a process of cooling glass slowly, so that the molecules of the molten glass crystallizes, without cracking suddenly. Polishing, on the other hand, is necessary to give the cooled glass a high-quality smooth surface.