Glass manufacturing – Glassworking or preform by or with reheating means – Planar sheet preform
Reexamination Certificate
1996-08-28
2001-05-08
Vincent, Sean (Department: 1731)
Glass manufacturing
Glassworking or preform by or with reheating means
Planar sheet preform
C065S106000, C065S287000, C294S064200
Reexamination Certificate
active
06227008
ABSTRACT:
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 apparatus 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 having a periphery 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 to provide a sealed periphery of the glass sheet. A vacuum system of the apparatus: including at least one vacuum reservoir, conducting including at least one conduit for communicating the vacuum reservoir and the vacuum mold within the sealed periphery of the glass sheet, and valving including at least one valve located between the vacuum reservoir and the vacuum mold and operable to (a) initially communicate the vacuum mold surface within the sealed periphery of the glass sheet with at least one vacuum reservoir to provide a vacuum impulse in the range of 0.1 to 0.7 atmospheres of vacuum to elastically form the glass sheet to the shape of the vacuum mold surface; and (b) thereafter terminates the vacuum impulse at a predetermined time so as to reduce optical distortion of the heated glass sheet as a result of engagement with 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 vacuum system includes a 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 greater than the first level of vacuum. A pair of vacuum reservoirs of the apparatus initially provide the vacuum impulse at the first level of vacuum and subsequently provide the vacuum impulse at the second level of vacuum greater than the first 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 this mold surface provided with a concave shape and has its peripheral mold facing downwardly with a convex shape. The embodiments of the apparatus with the upwardly facing mold surface each include an actuator that moves the peripheral mold downwardly to press the periphery of the glass sheet against the upwardly facing vacuum mold surface.
One of the embodiments of the apparatus with the downwardly facing vacuum mold surface has this mold surface provided with a concave shape and has its peripheral mold facing upwardly with a convex shape. Another embodiment of the apparatus with the downwardly facing vacuum mold surface has this mold surface provided with a convex shape and has its peripheral mold facing upwardly with a concave shape. The embodiments of the apparatus with the downwardly facing vacuum surface each include an actuator that moves the vacuum mold downwardly such that the upwardly facing peripheral mold presses the periphery of the glass sheet against the downwardly facing vacuum mold surface.
Both the upwardly and downwardly facing embodiments of the vacuum mold surface are disclosed as having versions with straight line elements over the entire extent thereof, curved shapes in directions that are transverse to each other, and inversely curved portions.
The peripheral mold that presses the periphery of the glass sheet against the vacuum mold surface is preferably constructed as a ring mold with an open center.
In carrying out the above mentioned object and other objects of the invention, the method for forming a heated glass sheet by the apparatus includes sealing the periphery of the glass sheet against a full surface vacuum mold and communicating the vacuum mold surface within the sealed periphery of the glass sheet with at least one vacuum reservoir to provide a vacuum impulse in the range of 0.1 to 0.7 atmospheres of vacuum to elastically form the glass sheet to the shape of the vacuum mold surface, and the vacuum impulse is thereafter terminated at a predetermined time so as to reduce optical distortion of the hot glass sheet as a result of engagement with the mold surface.
In performing the method, the vacuum impulse is preferably provided at the vacuum mold surface initially at a first level of vacuum and thereafter at a second greater level of vacuum. The first and second levels of vacuum are disclosed as being provided by communicating the vacuum mold surface with a pair of vacuum reservoirs. Two different versions are disclosed for performing the method. In one version, the glass sheet periphery is sealed against the vacuum mold surface by a pressing operation of a peripheral mold which maintains the pressing relationship as the vacuum impulse is provided at the vacuum mold surface to form the glass sheet. In another version, the glass sheet periphery is initially sealed against the vacuum mold surface by a pressing operation of a peripheral mold which is thereafter positioned out of engagement with the glass sheet as the vacuum impulse is provided at the vacuum mold surface to form the glass sheet.
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
Hersch Christopher A.
Shetterly Donivan M.
Brooks & Kushman P.C.
Glasstech, Inc.
Vincent Sean
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