The drawing illustrates the process by which plate glass and bottle glass are manufactured. [Crack IELTS with Rob]
In general, the initial stages of glass production are the same for both two kinds of glass.
The first step in making plate glass is to combine sand, soda and limestone in a furnace. [Crack IELTS with Rob] These raw materials are heated at approximately 1700oC until they melt and form molten glass. From the furnace, this mixture flows through piping to a reservoir, at the bottom of which is a valve. The glass comes out of this valve onto rollers, which perform the function of straightening the glass.
For producing bottles, the liquified glass coming out of the furnace flows into moulds. [Crack IELTS with Rob] As the liquid goes into each mould, compressed air is also introduced, thereby forcing the glass onto the inside walls of the mould, leaving the rest of it empty. After a cooling process, the mould can be removed and the final product – the bottle – can be taken out.