Methods for producing a glass ribbon include drawing a quantity of molten material from a forming vessel into a glass ribbon with the forming vessel positioned within a first portion of a housing located within an upper chamber. The methods further include drawing the glass ribbon along a draw path passing through a second portion of the housing at least partially located within a lower chamber. The methods further include venting gas from an interior of housing through a wall of the second portion of the housing. In one example, the method further includes maintaining a pressure difference between the lower chamber and the upper chamber. In another example, the method includes maintaining a pressure difference between the interior of the housing and the upper chamber.

Glass forming apparatuses which decrease dimensional variations in glass ribbons are disclosed. In embodiments, a glass forming apparatus may include a forming body defining a draw plane that extends in a draw direction. An enclosure may extend in the draw direction below the forming body. The enclosure may include a compartment positioned below the forming body in the draw direction. The compartment may include a cooled wall positioned adjacent to the draw plane, a fluid conduit positioned within the compartment and adjacent to the cooled wall, an extraction port extending through the cooled wall and positioned in the draw direction from the fluid conduit, and an injection port extending through the cooled wall and positioned in the draw direction from the fluid conduit.

A method of manufacturing a sheet of glass comprises: (a) forming a vertically oriented ribbon of glass that moves downward as a function of time, the ribbon of glass having a first primary surface and a second primary surface that face in generally opposite directions and a core disposed between the first and second primary surfaces; (b) as the ribbon of glass moves downward, passing the ribbon of glass adjacent to a first raised temperature zone liquefies the first primary surface while a temperature of the core remains below a softening temperature; and (c) after the ribbon of glass moves below the first raised temperature zone, separating a sheet of glass from the ribbon of glass. Passing the ribbon of glass adjacent the first raised temperature zone reduces total thickness variation, surface roughness, and other surface defects of the ribbon of glass.

A method of forming a glass ribbon includes flowing a molten glass into a caster having a width (W.sub.cast) and a thickness (T.sub.cast) to form a cast glass, cooling the cast glass in the caster to a viscosity of 10.sup.8 Poise or more, conveying the cast glass from the caster, volumetrically heating the cast glass to an average viscosity of 10.sup.6 Poise or less using a gyrotron microwave heating device, and drawing the cast glass into a glass ribbon having a width (W.sub.gr) that is less than or equal to the width (W.sub.cast) of the caster and a thickness (T.sub.gr) that is less than the thickness (T.sub.cast) of the caster.

A method of forming a glass sheet comprises: (a) forming a ribbon of glass from molten glass with a pair of forming rollers; (b) reducing horizontal temperature variability of the ribbon of glass to be 10° C. or less across 80 percent of an entire width of the ribbon of glass before the ribbon of glass cools to a glass transition temperature; (c) controlling a cooling rate of the ribbon of glass while the ribbon of glass moves vertically downward within a setting zone such that the ribbon of glass has a first average cooling rate before the ribbon of glass cools to the glass transition temperature and a second average cooling rate after the ribbon of glass cools to the glass transition temperature, the first average cooling rate being less than the second average cooling rate; and (d) separating a glass sheet from the ribbon of glass.

Apparatuses and methods are described for cooling glass forming rolls during the glass manufacturing process. The apparatus and methods mix a liquid, such as water, and a gas, such as air, to form a liquid and gas mixture that is provided to an inside surface of the glass forming rolls to dissipate heat. In some examples, the apparatus and methods control the amount of liquid and air provided to the glass forming roll based on detecting temperatures of the glass forming rolls. In some examples, a computing device automatically controls the amount of liquid and gas mixture provided to the glass forming rolls, and may further control the proportions of each of the liquid and gas to be mixed. The apparatus and methods may allow for a more consistent glass thickness across the glass sheet, as well as a reduction in glass sheet defects.

A method for producing thing glass strips is provided that avoids camber defects. The method includes using a glass strip forming device that has a drawing device; drawing, using the drawing device, the thin glass strip away from the glass strip forming device; measuring, using a measuring device, variables that are dependent on a differing length of edges of the thin glass strip at at least two measurement locations spaced apart transversely to a longitudinal extension of the thin glass strip; determining a difference or a quotient of the variables. The difference or the quotient is used to determine a control variable by which the glass strip forming device is controlled so as to counteract a difference in velocities of the thin glass strip between the two opposite edges.

An alkali-free glass includes, as represented by mole percentage based on oxides, SiO.sub.2: 57 to 70%, Al.sub.2O.sub.3: 5 to 15%, B.sub.2O.sub.3: 15 to 24%, MgO: 0.2 to 10%, CaO: 0.1 to 7%, SrO: 0.1 to 2.5%, BaO: 0 to 10%, and ZnO: 0 to 0.1%, or includes, as represented by mole percentage based on oxides, SiO.sub.2: 57 to 70%, Al.sub.2O.sub.3: 5 to 15%, B.sub.2O.sub.3: 15 to 24%, MgO: 0.1 to 10%, CaO: 0.1 to 10%, SrO: 0.1 to 10%, BaO: 0.1 to 10%, and ZnO: 0 to 0.1%. Formula (A) is [Al.sub.2O.sub.3]/[B.sub.2O.sub.3], and a value of the formula (A) is larger than 0.35 and 1.4 or smaller.

Embodiments of glass forming apparatuses are disclosed herein. In one embodiment, a glass forming apparatus may include a forming body defining a draw plane extending from the forming body in a draw direction. An actively-cooled thermal sink may be positioned below the forming body in the draw direction and spaced apart from the draw plane. An infrared-transparent barrier may be positioned between the actively-cooled thermal sink and the draw plane. The infrared-transparent barrier may comprise an infrared-transparent wall positioned proximate the actively-cooled thermal sink or an infrared-transparent jacket positioned around the actively-cooled thermal sink.

A molding apparatus for forming a glass article comprises a mold shell comprising a cooling surface comprising at least a first zone and a second zone; an adjustable nozzle system comprising a mold-facing surface having a plurality of apertures sized to receive a nozzle or a plug; a plurality of nozzles, each coupled to one of the apertures to direct a stream of fluid onto the cooling surface; and a fluid supply providing a fluid through the plurality of nozzles. The fluid is jetted through the nozzles to impinge against the first zone or the second zone of the cooling surface, and a number of nozzles through which the fluid is jetted to impinge against the first zone of the cooling surface is different than a number of nozzles through which the fluid is jetted to impinge against the second zone of the cooling surface.