An apparatus and method of refining molten glass are disclosed. An upstream vessel contains molten glass, a downstream vessel is arranged downstream of the upstream vessel, and vacuum refining vessels are located between the upstream vessel and the downstream vessel and are in separate, alternating fluid communication with the upstream vessel and in separate, alternating fluid communication with the downstream vessel.

The present invention relates to an alkali-free glass substrate in which when the alkali-free glass substrate is melted, and while holding a temperature at 1400° C., reduced in pressure from an atmospheric pressure to 33.33 kPa at a constant pressure reduction rate for 20 minutes and held at 33.33 kPa for 5 minutes, a diameter of a grown bubble is at least 3 times a diameter of an initial bubble. A bubble having a diameter of 0.1 to 0.3 mm contained in a molten glass at 1400° C. before starting pressure reduction is defined as the initial bubble. A bubble after held at 33.33 kPa for 5 minutes corresponding to the initial bubble is defined as a grown bubble.

An apparatus for manufacturing glass includes a furnace. A doghouse of the furnace receives and melts solid-glass forming material using one or more submerged combustion burners. An elongated tank positioned downstream of the doghouse includes a melting chamber, a refining chamber, and a thermal conditioning. The melting chamber has in inlet through which molten glass is received from the doghouse. The refining chamber is positioned downstream of the melting chamber and receives molten glass from the melting chamber. The thermal conditioning chamber is positioned downstream of the refining chamber and receives molten glass from the refining chamber. Additionally, the thermal conditioning chamber delivers molten glass to a glass forming machine.

An apparatus and methods of refining glass, in a multi-stage, downwardly cascading manner, include a melting chamber housing molten glass and having an outlet, a first refining chamber downstream from the melting chamber and having a first outlet and a first inlet below the outlet of the melting chamber, and a second refining chamber downstream from the first refining chamber and having a second outlet and a second inlet below the first outlet of the first refining chamber. The first refining chamber has a first negative pressure and the second refining chamber has a second negative pressure.

An apparatus for refining molten glass that includes a housing having a vertically oriented longitudinal axis and a transverse axis perpendicular to the longitudinal axis. Molten glass is received at an upper end of the housing and is discharged from a lower end of the housing. A guide extends at least partway across the housing and directs molten glass in a generally downward direction through the housing and in a parallel or oblique direction relative to the transverse axis of the housing.

A process and apparatus for manufacturing glass. A mixture of solid glass-forming materials comprising at least one fining agent are introduced into a doghouse located upstream of an elongated tank. The glass-forming materials are melted in the doghouse at a temperature at or above a fining-onset temperature of the at least one fining agent by application of heat from one or more submerged combustion burners. The resulting molten glass is relatively foamy and may comprise greater than 25 vol. % gas bubbles. The molten glass is directed from the doghouse into an upstream end of the tank where it is refined to produce molten glass having on average less than 20 seeds per ounce.

An alkali-free glass substrate contains, as represented by mass % based on oxides: 54% to 68% of SiO.sub.2; 10% to 25% of Al.sub.2O.sub.3; 0.1% to 5.5% of B.sub.2O.sub.3; and 8% to 26% of MgO+CaO+SrO+BaO. The alkali-free glass substrate has -OH of 0.15 mm.sup.1 to 0.35 mm.sup.1, and a Cl content of 0.15 to 0.3 mass %. A bubble growth index I of the alkali-free glass substrate given by the following formula is 320 or more: I=590.5[-OH]+874.1[Cl]5.7[B.sub.2O.sub.3]33.3. In the formula, [-OH] is -OH of the alkali-free glass substrate in mm.sup.1, [Cl] is the Cl content of the alkali-free glass substrate in mass %, and [B.sub.2O.sub.3] is a B.sub.2O.sub.3 content of the alkali-free glass substrate in mass %.

An alkali-free glass substrate contains, as represented by mass % based on oxides: 54% to 66% of SiO.sub.2; 10% to 23% of Al.sub.2O.sub.3; 6% to 12% of B.sub.2O.sub.3; and 8% to 26% of MgO+CaO+SrO+BaO. The alkali-free glass substrate has -OH of 0.15 mm.sup.1 to 0.5 mm.sup.1, and a Cl content of 0.1 to 0.35 mass %. A bubble growth index I of the alkali-free glass substrate given by the following formula is 280 or more: I=590.5[-OH]+874.1[Cl]5.7[B.sub.2O.sub.3]33.3. In the formula, [-OH] is -OH of the alkali-free glass substrate in mm.sup.1, [Cl] is the Cl content of the alkali-free glass substrate in mass %, and [B.sub.2O.sub.3] is a B.sub.2O.sub.3 content of the alkali-free glass substrate in mass %.

A method for removing bubbles from molten glass is provided and involves subjecting the surface of the molten glass to at least one fining sequence wherein the fining sequence comprises subjecting the surface of the molten glass to a sub-atmospheric pressure (relative vacuum less one atmosphere of pressure) for a time followed by subjecting the surface of the molten glass to super-atmospheric gas pressure (greater than one atmosphere of pressure) for additional time. The fining sequence can be repeated as needed to produce a high quality optically clear glass that is substantially free of bubbles.

An apparatus for manufacturing glass includes radially inner and outer flaw channels physically separated from each other by a common wall that allows heat transfer to occur between molten glass flowing through the outer flow channel and molten glass flowing in the opposite direction through the inner flow channel.