Method of improving quality of flat glass formed on molten tin

Claim 2

IN A PROCESS OF FORMING FLAT GLASS WHICH COMPRISES THE STEPS OF FUSING A GLASS BATCH TO ORM MOLTEN GLASS, DELIVERING THE MOLTEN GLASS TO A POOL OF MOLTEN TIN IN A FORMING CHAMBER, ATTENUATING THE MOLTEN GLASS ALONG THE SURFACE OF THE TIN WHILE COOLING TO FORM A CONTINOUS SHEET OF FLAT GLASS HAVING A DESIRED, PREDETERMINED, FINAL SHAPE AND THICKNESS, ADVANCING SAID SHEET OF GLASS ALONG THE POOL OF MOLTEN TIN AND EVENTUALLY OUT OF SAID FORMING CAMBER, SAID GLASS ABOSRBING INTO ITS TIN-CONTACTING SURFACE STANNOUS TIN WHICH IS CAPABLE OF CAUSING TOP SURFSCE DISTORTION IN THE GLASS, THE IMPROVEMENT COMPRISING: INTERFUSING WITH SAID GLASS AN OXIDIZING AGENT WHICH IS CAPABLE OF OXIDIZING STANNOUS TIN TO STANNIC TIN IN AN EVIRONMENT OF MOLTEN GLASS, SAID OXIDIZING AGENT BEING PRESENT IN THE GLASS, IN AN AMOUNT SUFFICIENT TO MAINTAIN SAID GLASS SUBSTANTIALLY FREE OF TOP SURFACE DISTORTION BUT IS PRESENT IN AN AMOUNT INSUFFICIENT TO IMPART HEAT-ABSORBING CHARACTERISTICS TO THE GLASS, SAID OXIDIZING AGENT BEING SELECTED FROM THE GROUP CONSISTING OF THE HIGHER OXIDES OF CHROMIUM, MANGANESE, CERIUM, ARSENIC, AND ANTIMONY.

Claim 3

The method of claim 1 in which the glass being formed is a soda-lime-silica glass.

Claim 4

The method of claim 1 in which the molten glass is delivered to the pool of molten tin and is freely spread over the surface of the tin to form a fluid pool of glass followed by attenuating said fluid pool of glass to form a continuous sheet of flat glass.

Claim 5

The process of claim 1 in which the molten glass is delivered to the pool of molten tin as a layer of molten glass.

Claim 6

The method of claim 4 in which the layer of molten glass is delivered to the pool of molten tin in a substantially horizontal manner from a region of molten glass which is at substantially the same elevation as that of the molten tin.

Claim 7

The process of claim 4 in which the layer of molten glass is delivered downwardly from a region of molten glass which is at a higher elevation than the molten tin.

Claim 8

The process of claim 1 in which the oxidizing agent is one which has a standard Gibbs Free Energy substantially more positive than -125.5 kilocalories per mole O2 for the reaction: lower oxide (of oxidizing agent) + O2 -> higher oxide

Claim 9

The process of claim 1 in which the oxidizing agent is mixed with the glass batch ingredients before melting of the batch.

Claim 10

The process of claim 1 in which the oxidizing agent is present in the final glass composition in a concentration of 0.01 to 5 percent by weight based on total weight of the glass.

Claim 11

In a process of forming flat glass which comprises the steps of fusing glass batch to form molten glass, delivering the molten glass to a pool of molten tin in a forming chamber, attenuating the molten glass along the surface of the tin while cooling to form a continuous sheet of flat glass having a desired, predetermined, final shape and thickness, advancing said sheet along the molten tin and eventually out of said forming chamber, said glass, after it is initially delivered to the pool of molten tin, absorbing into its tin-contacting surface stannous tin which is capable of creating top surface distortion in the glass, the improvement comprising: intErfusing with said glass batch an oxidizing agent which is capable of and is present in an amount sufficient to oxidize stannous tin which has penetrated the bottom surface of the glass to stannic tin while the glass is being attenuated and has not attained its final shape and thickness, whereby the top surface of the glass is maintained relatively free of distortion, said oxidizing agent being present in the glass in an amount insufficient to impart heat-absorbing characteristics to the glass, said oxidizing agent being selected from the group consisting of the higher oxides of chromium, manganese, cerium, arsenic, and antimony.

Claim 12

In a process of forming flat glass which comprises the steps of fusing glass batch to form molten glass, delivering the molten glass to a pool of molten tin in a forming chamber, attenuating the molten glass along the surface of the tin while cooling to form a continuous sheet of flat glass having a desired, predetermined, final shape and thickness, advancing said sheet along the molten tin and eventually out of said forming chamber, said glass, after it is initially delivered to the pool of molten tin, absorbing into its tin-contacting surface stannous tin which is capable of creating top surface distortion in the glass, the improvement comprising: intErfusing with said glass batch an oxidizing agent which is capable of and is present in an amount sufficient to oxidize stannous tin which has penetrated the bottom surface of the glass to stannic tin while the glass is being attenuated and has not attained its final shape and thickness, whereby the top surface of the glass is maintained relatively free of distortion, said oxidizing agent being present in the glass in an amount insufficient to impart heat-absorbing characteristics to the glass, said oxidizing agent being selected from the group consisting of the higher oxides of chromium, manganese, cerium, arsenic, and antimony.

Claim 13

The process of claim 1 wherein said oxidizing agent is selected from the group consisting of the higher oxides of manganese, cerium, and arsenic.

Claim 14

The process of claim 11 wherein said oxidizing agent is CeO2.

Claim 15

The process of claim 10 wherein said oxidizing agent is selected from the group consisting of the higher oxides of manganese, cerium, and arsenic.

Claim 16

The process of claim 13 wherein said oxidizing agent is Ceo2.