The Float Process
At the heart of the world's glass industry is the float process - invented by Sir Alastair Pilkington in 1952 - which manufactures clear, tinted and coated glass for buildings, and clear and tinted glass for vehicles. The process, originally able to make only 6mm thick glass, now makes it as thin as 0.4mm and as thick as 25mm. Molten glass, at approximately 1000ºC, is poured continuously from a furnace onto a shallow bath of molten tin. It floats on the tin, spreads out and forms a level surface. Thickness is controlled by the speed at which solidifying glass ribbon is drawn off from the bath. After annealing (controlled cooling) the glass emerges as a 'fire' polished product with virtually parallel surfaces.
There are around 260 float plants worldwide with a combined output of about 800,000 tonnes of glass a week. Pilkington operates 25 plants and has an interest in another ten.
A float plant, which operates non-stop for between 11-15 years, makes around 6000 kilometres of glass a year in thicknesses of 0.4mm to 25mm and in widths up to 3 metres. The float process has been licensed to more than 40 manufacturers in 30 countries. It has earned Pilkington more than £600 million in licensing revenue, although most licences are now paid up.