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Float Glass

 

The float glass method, which accounts for 90% of flat glass production worldwide, was pioneered in the 1950s by Sir Alastair Pilkington. This innovative process involves pouring molten glass over a bath of molten tin. The glass floats on the surface, spreading out evenly and cooling down to form a continuous ribbon with smooth, parallel surfaces as it moves along the bath. It is then annealed in a special oven known as a lehr, which ensures the finished product maintains its perfect flatness.

A minute fraction of tin embeds itself on the side of the glass that touches the tin bath, which is then often used to manufacture mirrors due to its ease of silvering. This side is also notably softer and more prone to scratching. Glass produced via this method comes in various standard thicknesses ranging from 2 to 22 mm.

To achieve the desired glass thickness, the process involves controlling the spread of molten glass on the tin under a nitrogen/hydrogen atmosphere, which naturally stops at about 6 mm due to surface tension. Making thinner glass requires stretching the glass, while making it thicker involves compressing it during the cooling phase.