Page 50 - Curriculum Visions Dynamic Book

In the float glass process the molten glass is spread out across a spout, run between rollers, and then floated on the bath of molten tin. The glass runs out onto the tin at a temperature of over 1,000°C. The glass spreads out under its own weight to yield a perfectly flat sheet. Controlling the speed the glass moves over the
tin controls the thickness. Such glass needs
no grinding or polishing. The surface is
smooth and shiny. Because glass will
shatter if cooled too quickly, the glass
is then cooled in a controlled way, a
process called annealing.
The electrofloat process was developed in 1967. It allows small amounts of metals (metal ions) to be put on the surface of the glass as it floats over the tin. Coated glass was also developed to add to the versatility of the float process.
A float glass machine runs continuously and can produce tens of thousands of kilometres of glass a year.
Hot gases
Hard coating
Hot glass
Molten tin
(Above) Reflective coatings are added to modern glass to improve its heat efficiency.
Molten glass from furnace
Thin sheet of glass floats on a very shallow layer of molten tin
Rollers
Heaters
Controlled atmosphere in which nitrogen and hydrogen gas mix is added.
Cooling zone
Glass ribbon
Heating zone
Float bath
Fire polishing zone
(Above) Diagrammatic representation of a modern float glass process.
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