Apparatuses for thermally tempering glass using liquid conduction

#This application relates generally to thermally treating glass, defined as including glass and glass ceramics and materials comprising glass, and specifically relates to apparatuses and systems for the thermally strengthening or treating glass using liquid-mediated thermal conduction.

#In thermal (or “physical”) strengthening of sheets comprising glass (“glass sheets”), a glass sheet is heated to an elevated temperature above the glass transition temperature of the glass and then the surfaces of the sheet are rapidly cooled (“quenched”) while the inner regions of the sheet cool at a slower rate. The inner regions cool more slowly because they are insulated by the thickness and the fairly low thermal conductivity of the glass. The differential cooling produces a residual compressive stress in the sheet surface regions, balanced by a residual tensile stress in the central regions of the sheet.

#Thermal strengthening of glass is distinguished from chemical strengthening of glass, in which surface compressive stresses are generated by changing the chemical composition of the glass in regions near the surface by a process such as ion diffusion. In some ion diffusion based processes, exterior portions of glass may be strengthened by exchanging larger ions for smaller ions near the glass surface to impart a compressive stress (also called negative tensile stress) on or near the surface.

#FIG. 1 is a cross sectional diagram of a thermal tempering apparatus according to the present disclosure performing a thermal tempering process according to the present disclosure.

#FIG. 2 is a cross sectional diagram of another embodiment or aspect of a thermal tempering apparatus according to the present disclosure capable of performing another aspect of a thermal tempering process according to the present disclosure.

#FIG. 3 is a cross sectional diagram of yet another embodiment or aspect of a thermal tempering apparatus according to the present disclosure capable of performing yet another aspect of a thermal tempering process according to the present disclosure.

#In embodiments, a process is provided by which a glass article (herein, the term “glass” includes glass ceramic) is positioned between opposing liquid bearings and is conveyed from one zone to an adjacent zone which is at a different temperature in order to heat or cool a surface of the article predominantly by heat conduction across the fluid gap. The liquid bearings may be of a discrete hole type with or without added compensation restrictors, or they may be a bulk porous media type. Exemplary liquids are molten salts and molten metals. The gaps of the liquid bearings may be changeable, either during set-up, or during the actual heat transfer process (e.g., the glass may be conveyed into a zone and then the gaps may be opened or closed at a prescribed rate to achieve a desirable heat transfer profile as a function of time).

#Additionally, embodiments include an article supported by liquid bearings that is traversed at a prescribed speed through a heat exchange region which includes heat transfer lands in order to cause a heating or a cooling to the surface of the article that is predominantly by heat conduction across the liquid gap.

#Embodiments enable the article to be thermally processed with rates of heat transfer (heating or cooling) that are higher, more uniform, more deterministic, and more controllable than can be achieved by immersion into a liquid bath (whether stirred or otherwise agitated or flowed or not) or by being sprayed or otherwise contacted with a moving liquid. In the case of glass articles that are prone to distortion and warping during different stages of their thermal treatment, embodiments allow the thermal processing to occur without contacting the article with a solid form (roller, grid, etc.) and yet while constraining the article in a desired shape by the stiffness of the centering action of the liquid bearings.