A glass substrate comprising a rectangular glass sheet having a first main surface and a second main surface opposite the first main surface, the glass substrate having a first side and a second side which are adjacent to each other in a view along a thickness direction of the glass sheet, in which a thickness tolerance is less than 6.26 m in a first cross section which is a cross section in the thickness direction of the glass sheet along a straight line parallel to the first side, the thickness tolerance being a difference between the maximum value and the minimum value of the thickness of the glass sheet.

A glass substrate comprising a rectangular glass sheet having a first main surface and a second main surface opposite the first main surface, the glass substrate having a first side and a second side which are adjacent to each other in a view along a thickness direction of the glass sheet, in which a thickness tolerance is less than 6.26 m in a first cross section which is a cross section in the thickness direction of the glass sheet along a straight line parallel to the first side, the thickness tolerance being a difference between the maximum value and the minimum value of the thickness of the glass sheet.

The present invention relates to an alkali-free glass substrate, in which when two arbitrary sites in one main surface thereof are selected, an absolute value of a difference between a thermal shrinkage ratio in an arbitrary direction at one site and a thermal shrinkage ratio in a direction orthogonal to the arbitrary direction at another site is 2 ppm or less, provided that the thermal shrinkage ratio is calculated by measuring a deformation amount in a measuring direction of the glass substrate between before and after a heat treatment of raising a temperature from normal temperature to 600 C. at 100 C./hour, holding the glass substrate at 600 C. for 80 minutes, and lowering the temperature from 600 C. to normal temperature at 100 C./hour.

The present invention relates to an alkali-free glass substrate, in which when two arbitrary sites in one main surface thereof are selected, an absolute value of a difference between a thermal shrinkage ratio in an arbitrary direction at one site and a thermal shrinkage ratio in a direction orthogonal to the arbitrary direction at another site is 2 ppm or less, provided that the thermal shrinkage ratio is calculated by measuring a deformation amount in a measuring direction of the glass substrate between before and after a heat treatment of raising a temperature from normal temperature to 600 C. at 100 C./hour, holding the glass substrate at 600 C. for 80 minutes, and lowering the temperature from 600 C. to normal temperature at 100 C./hour.

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.

Provided is a manufacturing method for a glass article, including: a pre-heating step (S1) of heating a transfer pipe (7); and a transfer step (S4) of causing molten glass to flow through the transfer pipe (7) after the pre-heating step (S1). The transfer pipe (7) includes a main body portion (8) having a tubular shape and a flange portion (9a, 9b) formed on an end portion of the main body portion (8). The main body portion (8) is retained by a refractory (10). In the pre-heating step (S1), the main body portion (8) is heated while the flange portion (9a, 9b) is movably supported so that the flange portion (9a, 9b) is moved in accordance with extension of the main body portion (8).

According to one embodiment, a method for thermally treating glass articles may include holding a glass article at a treatment temperature equal to an annealing temperature of the glass article 15 C. for a holding time greater than or equal to 5 minutes. Thereafter, the glass article may be cooled from the treatment temperature through a strain point of the glass article at a first cooling rate CR1 less than 0 C./min and greater than 20 C./min such that a density of the glass article is greater than or equal to 0.003 g/cc after cooling. The glass article is subsequently cooled from below the strain point at a second cooling rate CR.sub.2, wherein |CR.sub.2|>|CR.sub.1|.

According to one embodiment, a method for thermally treating glass articles may include holding a glass article at a treatment temperature equal to an annealing temperature of the glass article 15 C. for a holding time greater than or equal to 5 minutes. Thereafter, the glass article may be cooled from the treatment temperature through a strain point of the glass article at a first cooling rate CR1 less than 0 C./min and greater than 20 C./min such that a density of the glass article is greater than or equal to 0.003 g/cc after cooling. The glass article is subsequently cooled from below the strain point at a second cooling rate CR.sub.2, wherein |CR.sub.2|>|CR.sub.1|.

Provided is a method for manufacturing a glass substrate, comprising steps of: cooling a glass substrate transported by a plurality of rollers rotating at a predetermined speed; predicting a crack defect rate of the glass substrate in accordance with a plurality of predictive factors related to crack defects of the glass substrate and rotational speed information of the respective rollers, in the transport process; and adjusting the rotational speed of each roller so that the crack defect rate of the glass substrate is lowered. Also provided is an apparatus for manufacturing a glass substrate, comprising a transport part for cooling a glass substrate transported by a plurality of rollers rotating at a predetermined speed, a prediction part for predicting a crack defect rate of the glass substrate through a partial least squares regression analysis, and a control part for controlling the rotation speed of each roller.

Provided is a method for manufacturing a glass substrate, comprising steps of: cooling a glass substrate transported by a plurality of rollers rotating at a predetermined speed; predicting a crack defect rate of the glass substrate in accordance with a plurality of predictive factors related to crack defects of the glass substrate and rotational speed information of the respective rollers, in the transport process; and adjusting the rotational speed of each roller so that the crack defect rate of the glass substrate is lowered. Also provided is an apparatus for manufacturing a glass substrate, comprising a transport part for cooling a glass substrate transported by a plurality of rollers rotating at a predetermined speed, a prediction part for predicting a crack defect rate of the glass substrate through a partial least squares regression analysis, and a control part for controlling the rotation speed of each roller.