Glass is most commonly used for making windows. Today, windows are made using the float glass process, a technique invented in the 1950s.
Earlier methods of glass-making produced sheets of rough glass that had to be ground and polished to make them smooth enough for windows. This was expensive because a lot of energy was needed. In the float process, the resulting glass is perfectly smooth. This is because the glass floats on a bath of molten metal which is smooth and shiny like a mirror. The bath is surrounded by an inactive gas so there is also nothing to spoil the top surface of the glass.
Float glass process
The raw materials are melted in a furnace. A ribbon of molten glass then goes into the float bath where it floats on the surface of molten tin. The thickness of the glass can be varied by controlling the rate at which it flows through the float bath.
If glass cools too quickly it becomes brittle and is no good for normal use. It must therefore be reheated (but not so much as to change its shape) and cooled slowly. This process is known as annealing. Annealing takes place in a long tunnel called a lehr.
The float glass process has revolutionized the manufacturing of glass windows.
From the annealing lehr, the glass is first washed and then cut up into huge sheets which are lifted off by machine. Any waste glass is collected to be used again. The cutting process and the moving and stacking of the glass are all controlled by computer.