Method and apparatus for homogenizing a glass melt

Abstract

The present invention is directed toward a method of reducing contamination of a glass melt by oxide particulates, such as particulates of platinum oxide, which may condense on the inside surfaces of a stir chamber, particularly the stir shaft, and fall back into the glass melt. The method includes causing a flow of gas through an annular space between the shaft and the chamber cover. In one embodiment, the flow of gas through the annular space is caused by drawing a vacuum in the chamber. An apparatus for practicing the method is also provided.

1 . A method of stirring a glass melt comprising: 
 flowing molten glass through a stir chamber, the stir chamber having at least one wall and a cover, the cover having a passage therethrough, the stir chamber further including a stirrer comprising a shaft which extends through the cover passage, thereby forming an annular gap between the shaft and the cover;    flowing a gas through the annular gap; and    wherein the gas flows through the annular gap at a rate of at least about 100 sccm.    
   
   
       2 . The method according to  claim 1  wherein the gas is air.  
   
   
       3 . The method according to  claim 1  wherein the gas flow rate is at least about 400 sccm.  
   
   
       4 . The method according to  claim 1  wherein the gas flow rate is at least about 900 sccm.  
   
   
       5 . The method according to  claim 1  further comprising heating the cover with a heater.  
   
   
       6 . The method according to  claim 1  further comprising heating the shaft with a heater.  
   
   
       7 . The method according to  claim 1  further comprising heating the stir chamber by flowing a current through an inside surface of the stir chamber.  
   
   
       8 . The method according to  claim 1  wherein the step of flowing a gas comprises forming a vacuum within the stir chamber above a surface of the glass.  
   
   
       9 . The method according to  claim 1  wherein the step of flowing a gas comprises pressurizing the stir chamber.  
   
   
       10 . The method according to  claim 8  wherein the gas flow is everywhere downward through the annular gap.  
   
   
       11 . The method according to  claim 8  wherein the vacuum is formed by evacuating the chamber through at least one gas flow tube, the gas flow tube terminating at an end within the chamber which does not extend over a surface of a molten glass within the chamber.  
   
   
       12 . The method according to  claim 9  wherein the chamber is pressurized through at least one gas flow tube, the gas flow tube terminating at an end within the chamber which does not extend over a surface of a molten glass within the chamber.  
   
   
       13 . The method according to  claim 8  wherein the vacuum is formed by evacuating the chamber through at least one gas flow passage, the gas flow passage being located in a spacer plate between the chamber wall and the chamber cover.  
   
   
       14 . An apparatus for stirring a glass melt comprising: 
 a stir chamber configured to hold molten glass, the stir chamber including a cover defining a passage therethrough;    a stirrer having a shaft extending through the passage into the stir chamber, the space between the cover and the shaft defining an annular gap;    at least one gas flow tube for flowing a gas through the stir chamber, the gas flow tube having an end within the stir chamber, the end of the gas flow tube not extending overtop a surface of the molten glass.    
   
   
       15 . The apparatus according to  claim 14  wherein the gas flow tube is connected with a vacuum system.  
   
   
       16 . The apparatus according to  claim 14  wherein the gas flow tube is connected with a compressor.  
   
   
       17 . The apparatus according to  claim 14  wherein a distance between a center of the annular gap and a center of the shaft is no more than about 0.15 inches.  
   
   
       18 . A method of stirring a glass melt using the apparatus of  claim 14  comprising: 
 flowing molten glass through the stir chamber;    drawing a vacuum in the stir chamber through the gas flow tube;    flowing a gas through the annular gap in a direction into the stir chamber; and    wherein the gas flows through the annular gap at a rate of at least about 100 sccm.    
   
   
       19 . The method according to  claim 18  wherein the gas flow rate is at least about 400 sccm.  
   
   
       20 . The method according to  claim 18  wherein the step of flowing a gas comprises forming a vacuum within the stir chamber.