Overflow downdraw glass tube forming apparatus

Abstract

An apparatus for forming glass tubing is described. The apparatus for forming glass tubing comprises an endless former with an outer surface and an inner passage defining an inner surface. The apparatus for forming glass tubing further comprises two chambers from which molten glass may flow. One chamber flows molten glass to the outer surface of the endless former and another chamber flows molten glass to the inner surface of the endless former. The two flows of molten glass meet at the bottom of the former to form glass tubing.

1 . An apparatus for forming glass tubing comprising:
 an endless former, a first molten glass hold, and a second molten glass hold,   wherein the endless former is positioned substantially vertically and comprises an upper portion, an outer surface, and a first inner passage with a first inner surface, the upper portion of the endless former comprises an extension configured to be fixed in order to fix the endless former in a substantially vertical position;   wherein the first molten glass hold comprises a first floor, the first floor comprises a first opening configured for positioning of the endless former; the first molten glass hold is positioned so that the first floor is spaced below the extension of the endless former and the endless former is positioned within the opening in the first floor defining a glass flow gap between the endless former and the first floor of the first molten glass hold; the first floor is configured to permit the flow of molten glass toward the endless former such that molten glass may pass through the glass flow gap and down along the outer surface of the endless former; and   wherein the second molten glass hold comprises a second floor spaced above the first floor and above the extension of the endless former, the second floor comprises a second opening and a first neck extending downwardly from the second opening; the first neck comprises a second inner passage with a second inner surface; the second floor is configured to permit the flow of molten glass toward the second opening such that the molten glass may flow into the second opening and down along the second inner surface of the first neck; the second molten glass hold is positioned such that the molten glass flowing into the second opening and the down along the second inner surface of the first neck will flow down along the first inner surface of the endless former to meet the molten glass flowing down along the outer surface of the endless former to form glass tubing.   
     
     
         2 . The apparatus for forming glass tubing of  claim 1 , wherein the first molten glass hold is fixed separately from the endless former to permit adjustment of the first molten glass hold relative to the endless former; and the second molten glass hold is fixed separately from the endless former to permit adjustment of the second molten glass hold relative to the endless former. 
     
     
         3 . The apparatus for forming glass tubing of  claim 1 , wherein the endless former has a lower portion, the lower portion includes a bottom and a wedge-shaped portion such that the outer surface and first inner surface form a taper and meet at the bottom of the lower portion. 
     
     
         4 . The apparatus for forming glass tubing of  claim 1 , wherein the first floor includes a first endless upward extension adjacent the first opening, the first endless upward extension is configured to impede the flow of molten glass and to cause the molten glass to flow over the first endless upper extension before passing into the glass flow gap. 
     
     
         5 . The apparatus for forming glass tubing of  claim 1 , wherein the second floor includes a second endless upward extension adjacent the second opening, the second endless upward extension configured to impede the flow of molten glass and to cause the molten glass to flow over the second endless upper extension before passing into the second inner passage of the first neck to flow down along the second inner surface of the first neck and the first inner surface of the endless former. 
     
     
         6 . The apparatus for forming glass tubing of  claim 1 , wherein the first floor includes a first means for regulating the flow of molten glass and the second floor includes a second means for regulating the flow of molten glass. 
     
     
         7 . The apparatus for forming glass tubing of  claim 6 , wherein
 the first means for regulating flow of molten glass comprises the first floor having a first endless upward extension adjacent the first opening, the first endless upward extension is configured to impede the flow of molten glass and to cause the molten glass to flow over the first endless upper extension before passing into the glass flow gap, the first endless upward extension of the first floor includes a non-uniform height configured to impede the flow of molten glass to a greater extent from one direction relative to the flow of molten glass from a different direction; and   the second means for regulating flow of molten glass comprises the second floor having a second endless upward extension adjacent the second opening, the second endless upward extension is configured to impede the flow of molten glass and to require the molten glass to flow over the second endless upper extension before passing into the second opening, the second endless upward extension of the second floor includes a non-uniform height configured to impede the flow of molten glass to a greater extent from one direction relative to the flow of molten glass from a different direction.   
     
     
         8 . The apparatus for forming glass tubing of  claim 1 , further comprising a third molten glass hold, the third molten glass hold comprises a third floor spaced above the second floor of the second molten glass hold; the third floor comprises a third opening and a second neck extending downwardly from the third opening; the second neck has a third inner passage with a third inner surface; the third floor is configured to permit the flow of molten glass toward the third opening such that molten glass may flow into the third opening and down along the third inner surface of the second neck; the third molten glass hold is positioned such that the molten glass flowing into the third opening and down along the third inner surface of the second neck will flow down along the second inner surface of the first neck, down along the first inner surface of the endless former to meet the molten glass flowing down along the outer surface of the endless former to form glass tubing. 
     
     
         9 . The apparatus for forming glass tubing of  claim 1  wherein the third opening and the second neck of the third molten glass hold are aligned substantially axially with the first inner passage of the endless former and the second opening and first neck of the second floor.