A large melting furnace suitable for borosilicate glass. The melting furnace includes a melting area, a reinforcing area, an ascending area and a clarifying area. The melting area includes no furnace crown, a surface of molten glass in the melting area is not covered by any wall and exposed for feeding. The reinforcing area includes a first furnace crown, the first furnace crown includes a first partition wall and a second partition wall, and the reinforcing area and the melting area are separated by the first partition wall, and a lower end of the first partition wall goes deep below a surface of molten glass but is not in contact with a bottom of the melting furnace, so as to guarantee that the molten glass in the melting area and the reinforcing area is interconnected.

A process and an apparatus for refining molten glass. The apparatus includes a porous body having an inlet, an outlet, and a plurality of pores through which molten glass can flow between the inlet and the outlet. The plurality of pores are defined by walls having wall surfaces that are configured to interact with the molten glass as the molten glass flows between the inlet and the outlet to help refine the molten glass.

A method of making glass having a basic soda-lime-silica glass portion, and a colorant portion, the colorant portion including total iron as Fe.sub.2O.sub.3 in the range of at least 0.00 to no more than 0.02 weight percent, a redox ratio in the range of 0.35 to 0.6, and tin metal providing tin in an amount within the range of greater than 0.005 to 5.0 weight percent; the glass product has a tin side and an opposite air side, said tin side of the glass having a higher concentration of tin than the air side, the air side having a uniform concentration of tin from the air side of the glass product towards the tin side of the glass product.

A process and an apparatus for refining molten glass. The apparatus includes a porous body having an inlet, an outlet, and a plurality of pores through which molten glass can flow between the inlet and the outlet. The plurality of pores are defined by walls having wall surfaces that are configured to interact with the molten glass as the molten glass flows between the inlet and the outlet to help refine the molten glass.

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.

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 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.

A glass fining system, multi-stage vacuum housing, and method are disclosed. The glass fining system includes a multi-stage vacuum housing comprising a first melt receipt tank configured to receive molten material, where the first melt receipt tank is disposed in a first vacuum chamber; a first refining channel configured to flow the molten material from the first melt receipt tank through a second vacuum chamber; a second melt receipt tank configured to receive the molten material from the first refining channel, where the second melt receipt tank is disposed in a third vacuum chamber; and a second refining channel configured to flow the molten material from the second melt receipt tank and through a fourth vacuum chamber; and a glass melter coupled to the multi-stage vacuum housing.

There is provided a process for producing molten glass, which is capable of easily increasing the H.sub.2O content in glass melt with excessive generation of convection of the glass melt being reduced. One mode of the process for producing molten glass according to the present invention is characterized to include a material melting step for melting a raw glass material in a melting furnace to prepare glass melt; a water-molecules supply step for supplying a water-molecules supply gas into the glass melt flowing from an upstream end of the melting furnace toward a downstream end of the melting furnace; and a refining step for degassing, under a reduced pressure atmosphere, the glass melt flowing out of the downstream end; wherein a position where the water-molecules supply gas is supplied in the water-molecules supply step includes a first position and a second position from downstream to upstream in a flowing direction of the glass melt in this order; the first position is a position away from both of the upstream end and the downstream end; and the second position is a position closer to the upstream end than a center of a distance between the upstream end and the first position in the flowing direction of the glass melt.

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.