Patent ID: 8113015

Claim:
A method of causing the bow of a vertical glass ribbon produced by a downdraw process comprising: (a) passing the ribbon through a gas-filled vertical enclosure, wherein: (i) the enclosure comprises a wall that defines an internal volume, (ii) the bottom of the internal volume is open so that the pressure at the bottom is the pressure of the surrounding atmosphere, and (iii) the ribbon acts as a septum that divides the enclosure's internal volume into a first sub-volume and a second sub-volume; (b) producing a difference between a pressure of the first sub-volume and a pressure of the second sub-volume along at least a portion of the length of the enclosure, the pressure of the first sub-volume being greater than the pressure of the second sub-volume, by creating, over a vertical zone along the length of the enclosure, a difference between (i) the average density of gas which is on the first sub-volume side of the ribbon and (ii) the average density of gas which is on the second sub-volume side of the ribbon, the average density on the first sub-volume side of the ribbon being less than the average density on the second sub-volume side of the ribbon; and (c) constraining the edges of the ribbon so as to prevent movement of the edges into the second sub-volume over at least the vertical zone, said positive pressure difference causing bowing of the sheet.