Glass Manufacturing - the Float Process
At the heart of the world’s glass industry is the float glass 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 0.4 mm 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.
Click here to enlarge image of Float Glass process
A float plant, which operates non-stop for between 10-15 years, makes around 6000 kilometres of glass a year in thicknesses of 0.4 mm to 25 mm and in widths up to 3 metres. The float process has been licensed to more than 40 manufacturers in 30 countries. Over 380 float lines are in operation, under construction or planned worldwide with a combined output of about 1,000,000 tonnes of glass a week. The NSG Group operates or has interests in 51 float lines worldwide.
Modified Basic Manufacture
There are three main forms of modification to the basic manufacturing processes.
Tinted
Extra ingredients are added to the raw materials of glass at the melting stage to produce tinted products. Cobalt and nickel tint glass grey; ferrous oxide tints glass blue, while ferric iron generates a yellow tint - both together tint glass green. Tinted glass is used in buildings and vehicles to control heat and light transmission.
Coated (On-line)
Modified properties are produced from the basic glass by means of surface coatings. Glass can be coated on-line in the float process as the ribbon of glass is being formed in the float glass bath. The technology uses chemical vapour deposition to apply a microscopically thin coating on the glass at a temperature of about 600ºC. Pilkington K Glass™, Pilkington Energy Advantage™and Pilkington Activ™ are produced by this process.
Wired
Wired glass is made by the rolling processes. In one such process steel wire mesh is sandwiched between two separate ribbons of glass in a semi-molten state and passed through a pair of consolidating rollers which may also impress a required pattern. The rough cast surface may be polished to obtain clear transparency. Its uses include fire resistance and safety glazing.