Float Glass

Seven years ago Alastair Pilkington, a glass expert, whose father Sir Harry is chief of Britain's great Pilkington glass company, was helping his wife wash dishes. Watching the suds floating on the dishwater, he got an idea that is likely to revolutionize the manufacture of flat glass. Last week Alastair Pilkington explained his "float glass" process in the New Scientist.

Ordinary window glass is made by drawing a wide ribbon of glass vertically from a reservoir of syrupy melted glass. It cools in the air and has a brilliant "fire finish." But the process of drawing produces stresses that make flaws and irregularities. To make the glass smooth enough for mirrors, auto windshields and store windows, manufacturers are forced to an elaborate process of grinding and polishing glass sheets on both surfaces. The plate glass made in this way is expensive, and its surface lacks fire brilliance.

The suds in his wife's dishpan reminded Alastair Pilkington that the surface of a liquid is ideally flat. Back at the plant he floated molten glass on molten metal and found that its bottom side took on a shiny finish. In the full-scale machine, which took seven years to get working properly, a wide ribbon of soft glass is floated in a tank of molten metal (the metal or alloy used is a trade secret). As the ribbon moves to the far end of the tank, it is cooled by a controlled atmosphere and finally solidifies. The result is a sheet of glass that is mirror-flat and fire-bright.

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