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AssigneePPG Industries, Inc.
InventorsTerry A. Bennett, Herbert W. Eilenfeld, Dewitt W. Lampman
Estimating the term…
In tempering a glass sheet to a high temper by heating the sheet to approximately its softening point followed by rapid chilling using a quenching composition that comprises a tempering medium having high heat transfer characterisitcs, the heat-softened glass sheets are protected from breakage during fabrication and resulting optical distortion by applying the tempering medium through exit orifices of a delivery system toward the heated glass in a novel cycle. The initially applied tempering medium has a low heat transfer rate and is mixed with a second tempering medium having a higher heat transfer rate to gradually increase the heat transfer rate of the mixed tempering medium. In a specific embodiment, dry air is the first tempering medium and a sublimable material, such as carbon dioxide, is the second tempering medium. The delivery system has an uninsulated portion that assures that initially the sublimable material is applied as a gas. Dry air which has a lesser heat transfer coefficient than the sublimable material in its gaseous state, may be supplied to the uninsulated portion if humidity conditions require so that dry air having a lesser heat transfer coefficient is initially directed through the exit orifices followed by mixtures of dry air with increasing concentrations of said sublimable material in the gaseous state followed by increasing concentrations of solid particles of said sublimable material. Movement of the glass sheet is coordinated with movement of the delivery system for said quenching composition to avoid "batter".
A method of tempering a glass sheet comprising heating said sheet to an elevated temperature range sufficient for tempering and rapidly cooling said glass sheet from said elevated temperature range by directing a first tempering medium at a temperature significantly below said elevated temperature range at the opposite major surfaces of said glass sheet, said tempering medium having an initial heat transfer capacity sufficient to cool said major surfaces at a rate such that said sheet develops a maximum temporary tensile stress insufficient to cause said glass sheet to fracture and gradually changing the composition of said cold tempering medium by mixing a second tempering medium at a temperature significantly below that of said glass sheet and having a greater heat transfer capacity than said initial heat transfer capacity in such a manner as to increase gradually the heat transfer capacity of the resulting mixture of cold tempering media directed toward said opposite major surfaces.
A method of tempering a glass sheet comprising heating said glass sheet to an elevated temperature range sufficient for tempering and rapidly cooling the heated glass sheet by exposing the glass sheet to cold, soft, solid particles of a cold sublimable material delivered through exit orifices of a tempering medium delivery system, characterized by first delivering said cold, sublimable material to the opposite major surfaces of said glass sheet from storage container means storing said cold sublimable material in liquid form under pressure through a delivery system comprising exit orifices via an uninsulated portion of sufficient length to convert the initial portion of said sublimable material to gas before its arrival in the vicinity of the major surfaces of said glass sheet from said exit orifices of said delivery system and the subsequent portion of said sublimable material in the form of soft, solid particles, whereby the glass sheet is initially subjected to tempering medium of relatively small heat capacity and subsequently to soft, solid particles of sublimable material having relatively large heat capacity to initially harden the glass sheet surface sufficiently to withstand said subsequent impingement of said soft, solid particles of said sublimable material and develop a high temper in said glass sheet without developing substantial surface damage that impairs the optical properties of the tempered glass sheet.
A method of tempering a glass sheet comprising heating said glass sheet to an elevated temperature range sufficient for tempering and moving said glass sheet in a given direction into a quenching position between a pair of sets of exit orifices while said exit orifices are stationary, and tempering medium is applied therethrough toward the opposite major surfaces of said glass sheet and, when the glass sheet decelerates as it approaches said quenching position, starting to reciprocate said exit orifices in unison with an initial stroke in the direction opposite said given direction and continuing to reciprocate said orifices after said glass sheet stops at said quenching position so as to insure continuous relative movement between the glass sheet and said exit orifices during both the entry of the glass sheet into said quenching position and its subsequent quenching at said quenching position.
Apparatus for tempering a glass sheet comprising glass sheet heating means, a cooling station including a source of dry, pressurized air, means to store a sublimable material under pressure at a temperature sufficiently cold to store said sublimable material in a liquid state, a delivery system comprising an uninsulated portion containing dry air, a pair of opposite sets of exit orifices and means to selectively deliver said dry air under pressure to said exit orifices for delivery toward said glass sheet, means to convey said glass sheet from said heating means into a quenching position between said sets of exit orifices in said cooling station while delivering said pressurized air through said exit orifices, valve means to discontinue the application of dry air to said delivery system, means to selectively deliver said sublimable material through said delivery system including valve means constructed and arranged to control the delivery of said sublimable material to said uninsulated portion to purge said dry air from said delivery system through said exit orifices and then deliver said sublimable material initially in gaseous form mixed with said dry air in increasing concentrations of said sublimable material in the gaseous state and finally to deliver a mixture of said sublimable material in a mixture of gas and soft, solid, cold, sublimable particles of increasing concentration of said particles.
Apparatus for tempering a glass sheet comprising glass sheet heating means, a cooling station and means to convey said glass sheet to a quenching position between said opposed sets of exit orifices within said cooling station, means to reciprocate said exit orifices in unison in response to control means actuated by entry of said glass sheet into said cooling station, and means for adjusting the phase of said reciprocating means to support said opposed sets of exit orifices at the downstream end of said path of reciprocation, whereby when said glass sheet decelerates to a stop at said quenching position, said reciprocating means starts to operate to move said exit orifices in an upstream direction to insure continuous relative movement between said glass sheet and said exit orifices during both the entry of said glass sheet into said quenching position and its subsequent quenching at said quenching position.
Dependencies are inferred from the claim text.