PICT:1088062/C1/1 In the vertical-drawing process for the formation of glass sheets, the passage of gases from the melting and refining chamber 1 to the drawing chamber 2 is reduced by forming the screen 8 separating the chambers as a double wall. The screen may be formed with an open-topped slot which extends to a position below the level of the molten glass and through which a current of air can be passed; alternatively, the slot may be closed and excess or reduced pressure applied. In other forms, a second screen spaced from the first, a partition of refractory material spaced from the screen, or a U-shaped screen of a cross-sectional area greater than normal can be used.
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