Isopipe sag control using improved end support conditions

Abstract

The invention is directed to a method of preventing isopipe sag when using the overflow drawdown fusion process for making flat glass sheets. The method applies a vertical restraint on at least one end of an isopipe resting on a support to thereby reduce sage and/or the rate of sag during use of the isopipe. Using the vertical restraint block in accordance with the invention, the sag and/or rate of sag has been found to be reduced by at least 40 percent relative to an isopipe that does not use the vertical restraints of the invention or a compressive force along the sides of the isopipe.

1 . A method for reducing the sag rate of an isopipe used in the fusion glass-making process, said method comprising:
 providing a pipe having a longitudinal axis, a middle region and a first and second end region,   supporting the first and second end regions by placing said end regions on top of a support to thereby prevent the downward vertical motion of said end, and   placing a vertical restraint above and in contact with at least one of said first and second ends of said pipe to oppose sag due to gravitational forces;   wherein said vertical restraint above and in contact with said pipe applies a force to said pipe to prevent vertical motion of said pipe and reduce sag and/or the rate of sag of said isopipe.   
   
   
       2 . The method according to  claim 1 , wherein said force-applying vertical restraint is a fixed, rigid restraint. 
   
   
       3 . The method according to  claim 1 , wherein said force-applying vertical restraint is an adjustable restraint so as to control to control the force applied to the pipe by the restraint. 
   
   
       4 . The method according to  claim 1 , where in said vertical restraint is placed above and in contact with, and applies a downward force to, the first end of said pipe. 
   
   
       5 . The method according  claim 1 , wherein the vertical restraint is placed above and in contact with, and applies a downward force to, both the first end and the second end of said pipe. 
   
   
       6 . The method according to  claim 1 , wherein said method reduces the sag or sag rate of an isopipe at least 40% relative to a method that does not include use of said at least one vertical restraint or a compressive force applied along the sides of the isopipe. 
   
   
       7 . An isopipe for use in a fusion drawing process wherein said isopipe is a longitudinally-extending refractory element having an opening extending longitudinally there-through to facilitate the unobstructed flow of molten glass along opposite sides of said element, and said element is supported on its first and second end by a support under said ends,
 the improvement comprising the addition of a vertical support member above and in contact with at least one of said first and second ends of said pipe to oppose sag due to gravitational forces;   wherein said vertical restraint above and in contact with said pipe applies a force to said pipe to prevent vertical motion of said pipe and reduce sag and/or the rate of sag of said isopipe.   
   
   
       8 . The isopipe according to  claim 7 , wherein said vertical restraint member is selected from the group consisting of a fixed, rigid vertical restraint member and an adjustable vertical restraint member.