The Float Process

FIG. 107. The principle of sheet glass manufacture by the float process (Pilkington, 1969). 

By the nfid 1900s these three processes were responsible for the world s entire production of flat glass, with 12% being made by the Fourcault process, 20% by the Colburn-Libbey-Owens process, and 8% by the Pittsburgh process. These processes have now been replaced almost entirely by the float process. 

In practice, it is possible to produce glass thicknesses between about 2 mm and 20 mm using the float process, depending upon the glass viscosity and the drawing speed. At the exit, the temperature of the glass is decreased to 600°C, at which point the tin is still fluid, but the glass can be removed... 

One routinely uses floated glass, which is somewhat less smooth than a silicon wafer and less pure as well because of the incorporation of inorganic substances during the floating process. Its advantage is to be much cheaper. Additionally, it is optically transparent. Its surface composition (silanols) is compatible with the various surface treatments described earlier, including cleaning and silanization. 

The surface finish quality and thickness uniformity is generally insufficient for mirror, automotive, and architectural applications. Prior to the development of the float process, described below, rolled glass sheet was ground and polished on both sides, sometimes simultaneously, to meet these requirements. These products were known as plate glass. The process was inherently wasteful and expensive. 

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