Method and apparatus for pressure control of glass-making thickness-control zone

A method of producing a glass sheet with reduced thickness variation, the method comprising:

• drawing a glass ribbon from a forming body that is disposed within an enclosure;
• delivering fluid to a housing, that is disposed within the enclosure and facing the forming body, so as to control local thickness of the ribbon, wherein delivering fluid to the housing comprises delivering fluid from a fluid source through a plurality of tubes having outlets within the housing;
• maintaining a first pressure at a location that is in the housing, and maintaining a second pressure at a second location that is in the enclosure as well as both outside and adjacent to the housing, so that the second pressure is greater than the first pressure;
• and
• separating a glass sheet from the ribbon,
• wherein maintaining the second pressure greater than the first pressure comprises reducing the first pressure by managing a flow of fluid out of the housing, and
• wherein managing the flow of fluid out of the housing comprises disconnecting one or more of the plurality of tubes from the fluid source so that fluid may flow out of the housing through the disconnected one or more of the plurality of tubes.

A method of producing a glass sheet with reduced thickness variation, the method comprising:

• drawing a glass ribbon from a forming body that is disposed within an enclosure;
• delivering fluid to a housing, that is disposed within the enclosure and facing the forming body, so as to control local thickness of the ribbon, wherein delivering fluid to the housing comprises delivering fluid from a fluid source through a plurality of tubes having outlets within the housing;
• maintaining a first pressure at a location that is in the housing, and maintaining a second pressure at a second location that is in the enclosure as well as both outside and adjacent to the housing, so that the second pressure is greater than the first pressure;
• and
• separating a glass sheet from the ribbon,
• wherein maintaining the second pressure greater than the first pressure comprises reducing the first pressure by managing a flow of fluid out of the housing, and
• wherein a chamber is disposed around a portion of the enclosure in which is disposed the housing, and the method further comprises:
• managing the flow of fluid out of the housing by passively coupling the housing with the chamber, and
• maintaining a third pressure in the chamber so that the third pressure is less than the first pressure.