TEMPERING GLASS SHEETS BY COOLING COMPRISING SUBLIMATION QUENCHING

摘要

AbstractIn tempering a glass sheet to a high temper by heating the sheetto approximately its softening point followed by rapid chilling using aquenching composition that comprises a tempering medium having high heattransfer characteristics, the heat-softened glass sheets are protected frombreakage during fabrication and resulting optical distortion by applyingthe tempering medium through exit orifices of a delivery system toward theheated glass in a novel cycle. The initially applied tempering medium havinga low heat transfer rate and is mixed with a second tempering medium havinga higher heat transfer rate to gradually increase the heat transfer rate ofthe mixed tempering medium. In a specific embodiment, dry air is the firsttempering medium and a sublimable mateial, such as carbon dioxide, is thesecond tempering medium. The delivery system has an unisulated portionthat assures that initially the sublimable material is applied as a gas.Dry air which has a lesser heat transfer coefficient than the sublimablematerial in its gaseous state, may be supplied to the uninsulated portionif humidity conditions require so that dry air having a lesser heat trans-fer coefficient is initially directed through the exit orifices followedby mixtures of dry air with increasing concentrations of said sublimablematerial in the gaseous state followed by increasing concentrations ofsolid particles of said sublimable material. Movement of the glass sheetis coordinated with movement of the delivery system for said quenchingcomposition to avoid "batter".