Patent ID: 7386999

Claim:
A molten glass delivery system for use in producing sheet glass by a fusion process comprising: (a) a first conduit which has a first characteristic cross-sectional dimension; and (b) a second conduit which has an exit end and a second characteristic cross-sectional dimension; wherein: (i) the first conduit receives molten glass from the second conduit; (ii) a portion of the first conduit surrounds a portion of the second conduit; (iii) the first characteristic cross-sectional dimension is larger than the second characteristic cross-sectional dimension so that a free surface of molten glass is formed between the first and second conduits; and (iv) the first and second conduits are positioned relative to one another so that the spatial relationship between the exit end of the second conduit and the free surface of the molten glass results in neither substantial numbers of devitrification defects nor substantial numbers of blister defects in the finished sheet glass for a glass that is devitrification sensitive, and wherein: (A) the portion of the second conduit which is surrounded by the first conduit is substantially vertically oriented; (B) the molten glass between the first and second conduits defines a nominal free surface; and (C) the exit end of the second conduit is located in a spatial range that extends from 5 millimeters below to 30 millimeters above said nominal free surface.