About 90 % of the world's flat glass is currently formed via the float method, which produces glass with extremely flat, parallel surfaces. Float glass has many application in commercial and residential construction, the automotive industry, and specialty applications such as mirror manufacturing.
Float glass is formed from a 'batch' that typically consists of silica sand, soda and lime. At the beginning of the float process, these materials are digitally weighed and mixed with cullet crushed ,recycled glass that is left over from previous float cycle.
Small amounts of other material such as metals and metal oxides may be added to tint the glass. Conveyor transfers the batch mixture into the batch house. From there, it is continuously fed into the furnace, where it melts at a temperature of approximately 2800°F.
From the furnace, the molten glass mixture moves through a canal and onto a pool of liquid tin. Since tin has a higher specific gravity than glass ribbon, its edges helping to control both its width and its speed. The speed at which the glass ribbon moves will determine the ultimate thickness of the cooled glass.
At this point, specialized metallic oxide coatings such as low-emissive or reflective coatings can be applied to the 'atmosphere' surface of the glass, in order to improve its performance or to enhance its appearance. This online coating process is known as chemical vapor deposition and these coatings are called paralytic or 'hard' coats.
Whenever or not the molten glass is coated, it must be cooled to approximately 1100°F as it progresses through the tin bath, finally reaching a solid state where it is possible to lift it out with the help of rollers.
The float glass is cooled slowly or 'annealed' in order to remove any residual stresses. After annealing, the solidified ribbon of float glass is cool enough for further processing and cut into pieces.
Cooled float glass passes through inspection booths to ensure that it has the uncompromising quality needed for its end use. Defects are marked, and the rough edges where knurls pulled the glass through the molten tin are trimmed for use as cullet in a future batch of float glass. The reminder of the glass ribbon is cut for packaging.
Float glass can be cut into large standard sheets or cut to size, according to its ultimate use. The glass is then inventoried, stored, ready to be shipped.
Float glass include clear float, heavy float, low-iron, and tinted glass.