Glass Manufacturing

1. PRESSING
This is a widely used process for mass producing glass pieces such as dishes, bake
ware, headlight lenses, TV tube faceplates, and similar items that are relatively flat.
Glass gob is fed into mould from furnace, pressing into shape by plunger and
plunger is retracted, and finished product is removed

2. GLASS BLOWING
A hollow blowing-iron or pipe is dipped into a pot containing molten glass and the
glass is assembled at the end of the pipe by rotating it, similar to gathering treacle
onto a spoon. The collected glass, known as the gather, cools to about 1000°C and
is rolled on an iron slab to form a parison.
The parison is then operated by allowing it to extend, re-heating it and blowing air
into it to bring it into a shape that resembles the final article. It is then placed in an
iron or wooden mould, which is kept wet by water, and the glass is blown to the
final shape of the interior of the mould.
There is no contact between the glass and the mould, due to the water which
forms a cushion of steam. During the blowing, pipe is rotated continuously,
preventing mould joints.

3. The blowing process is used to make hollow thin-walled glass items, such as bottles and flasks.
There are two methods for blowing;
• Press-And-Blow Method
• Blow-And-Blow Method
The press-and-blow method is a pressing operation followed by a blowing operation. The process
is suited to the production of wide-mouth containers.
A split mould is used in the blowing operation for part removal.
The blow-and-blow method is used to produce smaller-mouthed bottles.

4. Annealing of Glass;
Glass products usually have undesirable internal stresses after forming, which
reduces their strength. Annealing is done to relieve these stresses; the treatment
therefore has the same function in glass working as it does in metalworking.
Annealing involves heating the glass to an elevated temperature and holding it for
a certain period to eliminate stresses and temperature gradients, then slowly
cooling the glass to conquer stress formation. Annealing temperature is around
500 °C