Glass manufacturing – Processes – Reshaping or surface deformation of glass preform
Patent
1992-11-19
1994-12-27
Woodard, Joye L.
Glass manufacturing
Processes
Reshaping or surface deformation of glass preform
65273, C03B 23035
Patent
active
053761588
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to vacuum forming of heated glass sheets.
BACKGROUND ART
Vacuum forming of heated glass sheets against a curved mold surface has been performed for many years. Such vacuum forming is usually performed by drawing a vacuum within openings in the mold surface. The extent of vacuum utilized is normally on the order of about several to 10 inches (about 10 to 25 cm.) water column. Such a conventional vacuum can be provided by commercially available hot operating fans that are positioned within a heated environment in which the vacuum forming is performed and can also be provided by a gas jet pump such as disclosed by U.S. Pat. No. 4,222,763 McMaster wherein a primary gas flow is introduced into a passageway through jet openings which have axial and circumferential components that are substantially tangent to the inner surface of the passageway such that the primary gas flow induces a secondary gas flow that generates the vacuum through suitable communication passageways.
Prior art glass sheet vacuum forming systems are disclosed by U.S. Pat. No. 3,778,244 Nedelec et al; U.S. Pat. No. 4,661,141 Nitschke et al; U.S. Pat. No. 4,711,653 Frank et al; U.S. Pat. No. 4,746,348 Frank et al; and U.S. Pat. No. 4,859,225 Kuster et al.
DISCLOSURE OF INVENTION
An object of the present invention is to provide a method for providing improved vacuum forming of heated glass sheets by the use of a vacuum impulse which involves a substantially greater vacuum than has been heretofore utilized in vacuum forming of glass sheets.
In carrying out the above object and other objects of the invention, apparatus for forming a heated glass sheet includes a vacuum mold having a full surface that defines a shape to which the glass sheet is to be formed and also includes a peripheral mold for forming and sealing the periphery of the glass sheet against the surface of the vacuum mold. A conduit provides a preferred means for communicating the vacuum mold surface within the sealed periphery of the glass sheet with at least one vacuum reservoir to provide a vacuum impulse that forms the glass sheet to the shape of the vacuum mold surface.
Since the hot glass sheet has viscoelastic characteristics, the greater vacuum for a shorter time, as compared to conventional forming of glass sheets by vacuum, reduces optical distortion resulting from the glass surface engagement with the mold surface. More specifically, the vacuum drawn at the vacuum mold surface within the sealed periphery of the glass sheet is large enough to fully form the glass sheet to the shape of the mold surface but is not applied long enough to overcome the large viscous characteristics of the glass such that reduced optical distortion results at the interface of the glass sheet and the mold.
The conduit that provides the preferred means for communicating between the vacuum mold and each vacuum reservoir preferably includes valving that controls the communication in applying the vacuum impulse. This valving includes at least one valve for: (a) closing the conduit to isolate the vacuum mold from each vacuum reservoir; (b) initially opening the conduit to commence the vacuum impulse at a first level of vacuum; and (c) finally opening the conduit to provide the vacuum impulse to the vacuum mold at a second greater level of vacuum. A pair of vacuum reservoirs of the apparatus provide the initial vacuum impulse at the first level of vacuum and the subsequent vacuum impulse at the second greater level of vacuum. A vacuum pump of the apparatus draws a vacuum within each vacuum reservoir.
Different embodiments of the apparatus are disclosed with the vacuum mold having its full surface facing both upwardly and downwardly and having both convex and concave shapes.
One of the embodiments of the apparatus with the upwardly facing vacuum mold surface has this mold surface provided with a convex shape and has its peripheral mold facing downwardly with a concave shape. Another embodiment of the apparatus with the upwardly facing vacuum mold surface has
REFERENCES:
patent: 3778244 (1973-12-01), Nedelec et al.
patent: 3826381 (1974-07-01), Kulig et al.
patent: 4222763 (1980-09-01), McMaster
patent: 4561688 (1985-12-01), Tsutsui
patent: 4575390 (1986-03-01), McMaster
patent: 4661141 (1987-04-01), Nitschke et al.
patent: 4711653 (1987-12-01), Frank et al.
patent: 4746348 (1988-05-01), Frank
patent: 4840657 (1989-06-01), Orain
patent: 4859225 (1989-08-01), Kuster
Hersch Christopher A.
Shetterly Donivan M.
Glasstech, Inc.
Woodard Joye L.
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