Method and apparatus for controlling flow of casing glass in cased glass stream

Apparatus (10) for forming a cased glass stream having an inner core glass surrounded by an outer casing glass includes a first orifice (24) for receiving core glass from a first source (12). A second orifice (26) is vertically spaced beneath and aligned with the first orifice, and is surrounded by a chamber (30) that communicates with the second orifice through a gap between the first and second orifices. A spout (36) delivers casing glass from a second source (40) through a tube (32) to the chamber in such a way that glass flows by gravity from the first and second sources through the orifices to form the cased glass stream. Rate of glass flow through the second or casing glass source (40) is measured and compared with one or more preset limits (78). Rate of casing glass flow from the second source to the chamber surrounding the orifices is adjusted when rate of flow through the second source departs from the preset limit. In this way, a desired ratio of casing glass to core glass, and consequently the desired thickness of the casing glass layer, is automatically maintained.