Staying On-line: Coated Glass
All About Glass
Glass windows are great, but they waste energy. A glass pane provides only slightly more insulation than nothing at all. Even so, builders were using more, and bigger, windows. Then, in 1973, the energy crisis hit.
Harvard University chemist Roy Gordon knew that a tin oxide coating would make windows more energy-efficient. The challenge was in making the coating invisible. Gordon tried a two-phase chemical vapor deposition (CVD) process. He combined gases above a hot glass sheet. The gases reacted and deposited solid layers that formed a nonreflective coating of tin oxide on the surface of the glass.
Gordon’s innovation worked in the lab, but would it work in a float glass factory? The chemical reaction that formed the tin oxide fought the float process. Nevertheless, American glassmaker Libby-Owens-Ford risked finding out. It took ten years, but in 1989, the company unveiled its on-line CVD coating process.
Energy-saving windows are not the only on-line coated glass we see around us. Coatings for reflective building glass, tarnish-free mirrors, and electrically conducting glass are all applied on-line, by CVD.
Putting on a Coat
There are several ways to coat glass, but Roy Gordon's invention of on-line chemical vapor deposition (CVD) is the most efficient. Traditional processes apply a coating after the glass is cool and has left the manufacturing line. The continuous on-line process deposits a thin coating on the glass while it's still hot during the manufacturing process.
- Hot glass emerges from a furnace and is formed into a continuous ribbon of glass that floats on a bath of molten %%metal%%. One or more coating machines, located above the ribbon of glass near the end of the bath, release a mixture of gases.
- Under high temperatures, the gases react to form a solid substance that is deposited on the surface of the hot glass. The resulting coating is hard, uniform, extremely thin—and too tough to easily scratch off.
- The hot glass moves through an annealer, where it cools slowly.
Published on October 20, 2011