Stain-resistant glass and method of making same

Abstract

The present invention provides a method for making a stain-resistant float glass and an apparatus for carrying out such a method. In keeping with this method, SO 3 is applied to the upper surface of float glass in an amount efficacious to materially reduce staining of the upper surface of the glass. Optimally, SO 3 gas can be applied directly onto the upper surface of the glass. An apparatus of the invention generally includes a downwardly open hood positioned above the upper surface of the glass and having walls defining an enclosure. SO 3 gas (either as such or as a reactive mixture of SO 2 gas and an oxygen-containing gas) is delivered through a delivery tube to the enclosure.

What is clamed is:  
     
         1 . In the manufacture of float glass in which a glass ribbon is drawn across a molten metal surface, a method of reducing staining of the upper surface of the float glass comprising applying to that surface an amount of SO 3  efficacious to reduce staining of the upper surface of the glass.  
     
     
         2 . The method of  claim 1  wherein the SO 3  gas is supplied to a hood positioned above the upper surface of the glass.  
     
     
         3 . The method of  claim 1  wherein the glass is passed through an annealing lehr after exiting the metal surface, the SO 3  gas being applied to the upper surface of the glass in said lehr.  
     
     
         4 . The method of  claim 3  wherein SO 2  gas and an oxygen-containing gas are supplied to the lehr at a temperature of at least about 800° F. to promote the oxidation of the SO 2  gas to create said SO 3  gas.  
     
     
         5 . In a float glass production apparatus in which float glass is horizontally supported and has an exposed upper surface, an apparatus for applying SO 3  gas to the upper surface of the float glass including a downwardly open hood comprising a frame and walls depending from the frame, a supply of SO 3  gas, and an SO 3  delivery tube communicating with the SO 3  supply and positioned within the enclosure for delivery of SO 3  gas to the upper surface of the glass.  
     
     
         6 . The apparatus of  claim 5  including an annealing lehr, the hood being disposed above the float glass within the annealing lehr.  
     
     
         7 . The apparatus of  claim 5  wherein the SO 3  delivery tube is carried horizontally beneath said frame.  
     
     
         8 . The apparatus of  claim 5  including a mounting shaft rotatably carried by the frame, the SO 3  delivery tube comprising a sparge pipe adapted to deliver SO 3  gas to the enclosure, the sparge pipe being attached to the mounting shaft and being rotatable therewith.  
     
     
         9 . The apparatus of  claim 8  wherein the sparge pipe is rotatable with the mounting shaft between a first position wherein it depends generally vertically downwardly from the mounting shaft and a second position wherein it is disposed away from vertical and is spaced away from the surface of the float glass.