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By using such a flame, we are able to remove most if not all of the foam and reduce the bubbles in the resultant glass to commercially acceptable levels for general glazing or even automotive glazing. Use of the invention permits oxy-fuel firing to be used as the sole heat source in a flat glass furnace rather than, as at present, only for boost heating in combination with other firing techniques.
In conventional oxy-fuel burners, as used in container glass and glass fibre furnaces, the oxygen and fuel are introduced through co-axial or otherwise adjacent conduits and their mixing is almost instantaneous; a very turbulent gas mixture is formed which leads to almost instantaneous and substantially complete combustion with a clean (i.e. low luminosity), well-defined flame being produced. Similar burners may be used to melt the glass batch in oxy-fuel fired flat glass furnaces according to the invention, but result in the production of foam as described above. However, to achieve the diffuse, luminescent flame required by the present invention to disperse the foam resulting from such burners, we prefer to use ports for the fuel and oxygen which are spaced apart from each other such that delayed mixing of the fuel and oxygen occurs in a region remote from the ports, and takes place over a larger area. This leads to the production of flames which are considerably more diffuse and luminescent than conventional oxy-fuel flames and generally cooler; in fact, a flame dispersing the foam will generally be cooler than the surface of the molten glass it contacts. The flame impinges on the surface of the glass and destroys foam which has built up thereon. The exact mechanism by which the flame disperses the foam is not understood; it is possible that, because the flame is luminescent, it contains small particles of carbon which physically burst the foam.
According to a further aspect of the present invention, there is provided a flat glass making furnace including a melting zone into which glass-making batch components are 