A strengthened glass article (100), such as a substrate for a p-Si based transistors, includes first and second glass cladding layers (104, 106) and a glass core layer (102) disposed therebetween. A coefficient of thermal expansion [CTE] of each cladding layer (104, 106), which can be made of the same glass, is at least 1×10.sup.−7° C..sup.−1 less than that of the core layer (102). Each of the core and cladding layers has a strain point less than 700° C. A compaction of the glass article (100) is at most about 20 ppm [see FIG. 1]. A method includes forming a glass article and/or heating a glass article to a first temperature of at least about 400° C. The glass article has a glass core layer (102) and a glass cladding layer (104, 106) adjacent to the core layer. The glass article is maintained at a temperature within a range of from 400° C. to 600° C. for a holding period from 30 to 90 minutes and subsequently cooled to a temperature of at most 50° C. over a cooling period from 30 seconds to 5 minutes. The glass article (100) for heat strengthening may have been produced by the fusion overflow down draw process, e.g. as depicted in FIG. 3.

An isothermal drop speed cooling method and an apparatus for same. A glass ribbon carried with glass passes through the forced convection area of the glass annealing lehr, and the glass ribbon is moving while the glass is being air-cooled in the forced convection area. The glass is air-cooled by different air volume according to the temperature of the glass, so that the glass is allowed to be cooled at isothermal drop speed during the moving process of the glass. According to the cooling method and apparatus, the specification size of the opening section of multi-row air nozzles longitudinally arranged is increased along the moving direction of the glass ribbon, so that the cooling air volume from the front to the rear can be gradually increased, thereby allowing the temperature drop speed of a glass plate to be uniform from the front to the rear.

An isothermal drop speed cooling method and an apparatus for same. A glass ribbon carried with glass passes through the forced convection area of the glass annealing lehr, and the glass ribbon is moving while the glass is being air-cooled in the forced convection area. The glass is air-cooled by different air volume according to the temperature of the glass, so that the glass is allowed to be cooled at isothermal drop speed during the moving process of the glass. According to the cooling method and apparatus, the specification size of the opening section of multi-row air nozzles longitudinally arranged is increased along the moving direction of the glass ribbon, so that the cooling air volume from the front to the rear can be gradually increased, thereby allowing the temperature drop speed of a glass plate to be uniform from the front to the rear.

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 glass for chemical strengthening that is a float-formed glass for chemical strengthening includes, as represented by mass percentage based on oxides, from 65 to 72% of SiO.sub.2, from 3.6 to 8.6% of Al.sub.2O.sub.3, from 3.3 to 6% of MgO, from 6.5 to 9% of CaO, from 13 to 16% of Na.sub.2O and from 0 to 0.9% of K.sub.2O. In the glass for chemical strengthening, (Na.sub.2O+K.sub.2O)/Al.sub.2O.sub.3 is from 2.2 to 5. The glass for chemical strengthening has a sheet thickness (t) of 0.1 mm or more and 2 mm or less. A SnO.sub.2 amount of a bottom surface in an unpolished state of the glass for chemical strengthening is 6.2 μg/cm.sup.2 or less (0.1≦t≦1 mm) or (2t+4.2) μg/cm.sup.2 or less (1<t≦2 mm).

The present invention relates to a float-glass manufacturing apparatus including a float bath and a heat treatment furnace, in which the heat treatment furnace includes: a dross box including a plurality of lift-out rolls; an annealing furnace including a plurality of lehr rolls; a first partitioning part; a second partitioning part; a gas ejection nozzle; and a guide member.

The present invention relates to a float-glass manufacturing apparatus including a float bath and a heat treatment furnace, in which the heat treatment furnace includes: a dross box including a plurality of lift-out rolls; an annealing furnace including a plurality of lehr rolls; a first partitioning part; a second partitioning part; a gas ejection nozzle; and a guide member.

A method for finishing a glass or ceramic article includes applying a force to the glass or ceramic article. The force is applied to the glass or ceramic article at least when the glass or ceramic article is at a temperature that is greater than or equal to a creep temperature of the glass or ceramic article. Holding the force to the glass or ceramic article as the glass or ceramic article is cooled to a temperature that is less than the creep temperature of the glass or ceramic article.

Methods and systems are provided for automated shaping of a glass sheet. The methods comprise preheating the glass, bending the glass through selective, and focused beam heating through the use of an ultra-high frequency, high-power electromagnetic wave, and computer implemented processes utilizing thermal and shape (positional) data obtained in real-time, and cooling the glass sheet to produce a glass sheet suitable for use in air and space vehicles.