JP2952255B

Apparatus for forming a cased glass stream having an inner core glass surrounded by an outer casing glass that includes a spout (14) for delivering core glass from a first source through a first orifice (24). A second orifice (30) is vertically spaced beneath and aligned with the first orifice, and is surrounded by an annular chamber (32) that communicates with the second orifice through a gap between the first and second orifices. A tube (34) delivers casing glass from the outlet opening (36) of a casing glass spout (38) to the annular chamber in such a way that glass flows by gravity through the orifices from the first and second sources to form the cased glass stream. A hollow tube (40) within the casing glass spout is positioned with respect to the spout outlet opening for metering flow of casing glass through the outlet opening and delivery tube to the annular chamber surrounding the orifices. The interior of the hollow tube is coupled to a source (60 or 72) of gas under pressure so as to maintain the tube interior, and the interior of the thin fall of casing glass through the spout outlet opening, at a pressure above ambient pressure surrounding the casing glass spout. This elevated gas pressure within the casing glass fall reverses the pressure differential between the interior and exterior of the spout outlet opening, so that any tendency for air to migrate through the refractory material surrounding the outlet opening and into the casing glass fall is eliminated.