Method and apparatus for reducing tin defects in float glass

In a method of making flat glass by a float process wherein molten glass is delivered onto a pool of molten metal containing tin within an enclosed chamber and formed into glass ribbon and oxygen gas dissolved in the pool of molten metal combines with the tin to form tin oxide which vaporizes and collects within the chamber resulting in defects in the glass ribbon, the improvement comprising:

• positioning an elongated porous graphite member in the pool of molten metal, such that it extends along at least selected portions of the edge of the glass ribbon;
• wherein a non-porous, heat resistant coating is on selected portions of the graphite member;
• and
• delivering hydrogen gas directly to the pool of molten metal through the porous graphite member to react the hydrogen within the oxygen gas and tin oxide with the pool of molten metal to form water and elemental tin resulting in a reduction in the amount of tin oxide within the pool of molten metal.

A gas delivery apparatus for delivering gas within a pool of molten metal containing tin, that supports a glass ribbon, comprising:

• an elongated, heat resistant delivery member for submersion in the molten metal pool having a bore extending along at least a portion of said delivery member, and a non-porous heat resistant coating applied to selected portions of said delivery member;
• a plurality of outlets through said delivery member to provide passages from said bore through the outlets of said delivery member so that with the delivery member positioned with the bore generally parallel to the glass ribbon gas flow from the outlets is controlled to avoid trapping gas beneath the glass ribbon;
• means to provide for connection of said delivery member to a gas source;
• and
• a gas supply source.

A gas delivery apparatus for delivering gas within molten tin, comprising;

• an elongated, heat resistant delivery member having a bore extending along at least a portion of said delivery member, said delivery member constructed from medium grain porous graphite having a sealant, a heat resistant coating applied to selected portions of said delivery member;
• to provide a plurality of outlets through said delivery member to provide passages from said bore through a wall of said delivery member;
• means to provide for connection of said delivery member to a gas supply source;
• and
• a gas supply source.

In a method of making a flat glass ribbon by a float process wherein molten glass is delivered onto a pool of molten metal containing tin within an enclosed chamber and formed into a glass ribbon, the glass ribbon having opposed edges as it moves through the chamber in a predetermined direction with the edges of the ribbon spaced from walls of the enclosed chamber such that the space between the edge of the ribbon and the adjacent wall of the chamber defines an uncovered portion of the pool of molten metal, wherein oxygen gas dissolved in the pool of molten metal combines with the tin in the molten metal to form tin oxide which vaporizes and collects within the chamber above the molten glass and glass ribbon resulting in defects in the glass ribbon, the improvement comprising:

• positioning within the enclosed chamber an elongated porous member having a longitudinal axis and an elongated hollow passageway extending through the elongated member so that the member is submerged in the pool of molten metal in the space between the edge of the glass ribbon and the adjacent wall of the chamber such that the longitudinal axis of the elongated porous member generally parallels an adjacent edge of the glass ribbon and extends along the predetermined direction of the glass ribbon, wherein gas passing into the passageway flows through the elongated porous member into the pool of molten metal and is concentrated away from the glass ribbon so as to avoid trapping the gas beneath the glass ribbon;
• and
• moving hydrogen gas through the passageway and the elongated porous member directly into the pool of molten metal at a rate of about 3 to 20 standard cubic feet of hydrogen per hour per ton of tin within the molten metal to react the hydrogen with the tin oxide within the pool of molten metal to form water and elemental tin to reduce the amount of tin oxide within the pool of molten metal.

In a method of making a flat glass ribbon by a float process wherein molten glass is delivered onto a pool of molten metal containing tin within an enclosed chamber and formed into a glass ribbon, the glass ribbon having opposed edges as it moves through the chamber in a predetermined direction with the edges of the ribbon spaced from walls of the enclosed chamber such that the space between the edge of the ribbon and the adjacent wall of the chamber defines an uncovered portion of the pool of molten metal, wherein oxygen gas dissolved in the pool of molten metal combines with the tin in the pool of molten metal to form tin oxide which vaporizes and collects within the chamber above the molten glass and glass ribbon resulting in defects in the glass ribbon, the improvement comprising:

• positioning an elongated porous member within the enclosed chamber in the pool of molten metal in the space between the edge of the glass ribbon and the adjacent wall of the chamber such that the elongated porous member generally parallels an adjacent edge of the glass ribbon and extends along the predetermined direction of the glass ribbon, the elongated porous member having:
• i)an elongated hollow passageway extending therethrough such that the hollow passageway extends generally parallel to the adjacent edge of the glass ribbon and along the predetermined direction of the glass ribbon, and ii) a non-porous heat resistant coating applied to selected portions of said elongated porous member for control of gas flow so that gas flowing into the passageway flows through the porous member into the pool of molten metal and is concentrated away from the glass ribbon so as to avoid trapping gas beneath the glass ribbon;
• and
• moving hydrogen gas through the passageway and the elongated porous member directly into the pool of molten metal to react the hydrogen with the tin oxide within the pool of molten metal to form water and elemental tin to reduce the amount of tin oxide within the pool of molten metal.

In a method of making a flat glass ribbon by a float process wherein molten glass is delivered onto a pool of molten metal containing tin within an enclosed chamber and formed into a glass ribbon, the glass ribbon having opposed edges as it moves through the chamber in a predetermined direction with the edges of the ribbon spaced from walls of the enclosed chamber such that the space between the edge of the ribbon and the adjacent wall of the chamber defines an uncovered portion of the pool of molten metal, wherein oxygen gas dissolved in the pool of molten metal combines with the tin in the pool of molten metal to form tin oxide which vaporizes and collects within the chamber above the molten glass and glass ribbon resulting in defects in the glass ribbon, the improvement comprising:

• positioning within the enclosed chamber a non-porous delivery tube in the pool of molten metal in the space between the edge of the glass ribbon and the adjacent wall of the chamber such that the delivery tube generally parallels an adjacent edge of the glass ribbon and extends along the predetermined direction of the glass ribbon, wherein the delivery tube has a passageway extending therethrough such that the passageway extends generally parallel to the adjacent edge of the glass ribbon and along the predetermined direction of the glass ribbon;
• providing a plurality of outlets along the delivery tube, wherein the outlets extend through a wall of the delivery tube such that gas passing into the passageway flows through the outlets and into the pool of molten metal;
• and
• moving hydrogen gas through the passageway and outlets directly into the pool of molten metal so that the gas is concentrated away from the glass ribbon so as to avoid trapping gas beneath the glass ribbon, whereby the gas can react with the tin oxide within the pool of molten metal to form water and elemental tin to reduce the amount of tin oxide within the pool of molten metal.

An apparatus for delivering gas within a pool of molten metal containing tin comprising;

• a manifold having:
• feeder tube,
• connector for the feeder tube, wherein any porous portions of the feeder tube and connector are coated with a sealant to prevent diffusion of hydrogen gas therefrom;
• a heat resistant elongated, heat resistant delivery member for submersion in the molten metal connected in gas supply relation with the connector and feeder tube for submersion having a bore extending along at least a portion of said delivery member, and a heat resistant coating applied to selected portions of said delivery member;
• a plurality of outlets along said delivery member to provide passages from said bore through the outlets of said delivery member;
• and
• means to provide for connection of said delivery member to a gas source.