A method of manufacturing a glass sheet stably reduces a variation in a thermal shrinkage rate to 15 ppm or less. The method includes a melting step of melting, in an electric melting furnace, a glass batch prepared so as to give glass comprising 3 mass % or less of B.sub.2O.sub.3, a forming step of forming a molten glass into a sheet-shaped glass, an annealing step of annealing the sheet-shaped glass in an annealing furnace, and a cutting step of cutting the annealed sheet-shaped glass into predetermined dimensions, to thereby obtain a glass sheet having a -OH value of less than 0.2/mm and a thermal shrinkage rate of 15 ppm or less. The method includes measuring a thermal shrinkage rate of the glass sheet and adjusting a cooling rate of the sheet-shaped glass in the annealing step depending on variation in thermal shrinkage rate with respect to a target value.

In various embodiments, refractory-metal glass melt electrodes are single-crystalline, at least within an outer layer thereof.

In various embodiments, refractory-metal glass melt electrodes are single-crystalline, at least within an outer layer thereof.

A method for reconditioning a glass manufacturing system includes establishing a reducing atmosphere in a glass melting vessel and draining a glass melt composition from the melting vessel while the reducing atmosphere is in the vessel. The pressure of the reducing atmosphere is greater than the pressure of the atmosphere surrounding the melting vessel and the reducing atmosphere is established by operating at least one combustion burner in the melting vessel in a fuel-rich condition.

A method for reconditioning a glass manufacturing system includes establishing a reducing atmosphere in a glass melting vessel and draining a glass melt composition from the melting vessel while the reducing atmosphere is in the vessel. The pressure of the reducing atmosphere is greater than the pressure of the atmosphere surrounding the melting vessel and the reducing atmosphere is established by operating at least one combustion burner in the melting vessel in a fuel-rich condition.

Provided is an alkali-free glass substrate having a high strain point and excellent bubble count, and a method for manufacturing the alkali-free glass substrate. The method includes: a batch preparing process of preparing a raw material batch so as to obtain alkali-free glass containing, in mass %, 50 to 80% of SiO.sub.2, 15 to 30% of Al.sub.2O.sub.3, 0 to 4.5% of B.sub.2O.sub.3, 0 to 10% of MgO, 0 to 15% of CaO, 0 to 10% of SrO, 0 to 15% of BaO, 0 to 5% of ZnO, 0 to 5% of ZrO.sub.2, 0 to 5% of TiO.sub.2, 0 to 15% of P.sub.2O.sub.5 and 0 to 0.5% of SnO.sub.2 as a glass composition; a melting process of melting the prepared raw material batch; a fining process of fining the molten glass; and a forming process of forming the fined glass into a sheet shape. The raw material batch is melted such that a bubble enlarging temperature of the obtained glass is lower than a maximum temperature of the fining process.

Provided is an alkali-free glass substrate having a high strain point and excellent bubble count, and a method for manufacturing the alkali-free glass substrate. The method includes: a batch preparing process of preparing a raw material batch so as to obtain alkali-free glass containing, in mass %, 50 to 80% of SiO.sub.2, 15 to 30% of Al.sub.2O.sub.3, 0 to 4.5% of B.sub.2O.sub.3, 0 to 10% of MgO, 0 to 15% of CaO, 0 to 10% of SrO, 0 to 15% of BaO, 0 to 5% of ZnO, 0 to 5% of ZrO.sub.2, 0 to 5% of TiO.sub.2, 0 to 15% of P.sub.2O.sub.5 and 0 to 0.5% of SnO.sub.2 as a glass composition; a melting process of melting the prepared raw material batch; a fining process of fining the molten glass; and a forming process of forming the fined glass into a sheet shape. The raw material batch is melted such that a bubble enlarging temperature of the obtained glass is lower than a maximum temperature of the fining process.

A sealing system for isolating the environment inside a vitrification container from the outside environment comprises a vitrification container with a lid. The lid comprises two or more electrode seal assemblies through which two or more electrodes may be operatively positioned and extend down through the lid into the vitrification container. The electrodes may move axially up and down through the electrode seal assemblies or lock into place. The electrode seal assemblies each comprise a housing having two halves with recessed ring grooves. Sealing rings with a split may be placed into the grooves. Gas galleries may be machined or cast into the housing such that they are adjacent to the ring grooves. The gas galleries distribute gas onto the external faces of the sealing rings causing a change in pressure resulting in the sealing rings compressing onto the electrodes and forming a seal.

A sealing system for isolating the environment inside a vitrification container from the outside environment comprises a vitrification container with a lid. The lid comprises two or more electrode seal assemblies through which two or more electrodes may be operatively positioned and extend down through the lid into the vitrification container. The electrodes may move axially up and down through the electrode seal assemblies or lock into place. The electrode seal assemblies each comprise a housing having two halves with recessed ring grooves. Sealing rings with a split may be placed into the grooves. Gas galleries may be machined or cast into the housing such that they are adjacent to the ring grooves. The gas galleries distribute gas onto the external faces of the sealing rings causing a change in pressure resulting in the sealing rings compressing onto the electrodes and forming a seal.

A method for manufacturing an alkali-free glass substrate capable of manufacturing an alkali-free glass substrate having a higher strain point by decreasing the -OH value of the glass is provided. The method for manufacturing an alkali-free glass substrate is a method for continuously manufacturing a SiO.sub.2Al.sub.2O.sub.3RO (RO is one or more of MgO, CaO, BaO, SrO, and ZnO) based alkali-free glass substrate, which includes a step of preparing a raw material batch containing a tin compound and substantially not containing an arsenic compound or an antimony compound, a step of electric melting the prepared raw material batch in a melting furnace capable of conducting electric heating by a molybdenum electrode, and a step of forming the molten glass into a plate shape by a downdraw method.