Glass from a cross fired regenerative melter flows over a refractory spout on to the mirror-like surface of molten tin, entering at 1,100 °C and leaving the float bath as a solid ribbon at 600°C. Tin is suitable for the float glass process because it has a high specific gravity, is cohesive, and is immiscible with molten glass. Tin, however, oxidises in a natural atmosphere to form tin dioxide.
Nitrogen and Hydrogen Atmosphere
In order to prevent oxidation, the tin bath is provided with a positive pressure protective atmosphere of nitrogen and hydrogen. Hydrogen reacts with oxygen that diffuses into the float bath atmosphere and keeps the tin from reacting with oxygen. If it reacts with oxygen, tin forms an oxide that will cause flaws in the glass surface. Molten glass is held in a controlled atmosphere composing N2 and approximately 5 -10% H2 and once cooled, the flat glass becomes hard enough to be removed. The hydrogen in the controlled atmosphere acts as a scavenging agent to ensure an oxygen-free environment, because the molten tin is highly sensitive to oxidation, even in trace quantities. A recycling system of the offgas allows to recycle up to 50% of the total fresh atmosphere injected in the tin bath (N2 + H2).
At the exit of the float bath, the glass ribbon is taken out by lift-out rollers, and is passed through a temperature-controlled tunnel, the lehr, to be annealed. At the beginning of the lehr, SO2 is sprayed on both sides of the ribbon, providing a surface treatment to protect the glass against the contact of the rollers. Here the chemistry of the glass is changed on the surface in order to affect the surface characteristics of the glass, improving its quality and durability.
Oxipyr - F
Oxipyr - Flat
Oxipyr - Flex3
Oxipyr - P / P LON
Oxipyr - Advanced regulation
Oxipyr - Basic+, Basic regulation
Oxipyr - 400 regulation