Glass manufacturing – Processes – Reshaping or surface deformation of glass preform
Reexamination Certificate
2000-11-03
2003-10-07
Colaianni, Michael (Department: 1731)
Glass manufacturing
Processes
Reshaping or surface deformation of glass preform
C065S102000, C065S103000, C065S288000, C065S289000, C065S290000, C065S291000, C065S374110, C065S374120, C065S374130
Reexamination Certificate
active
06629436
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to an apparatus and method useful in thermally treating glass sheets or panels for tempering, annealing and/or shaping of the glass which can include quenching to remove heat. The shaping of the glass can involve bending glass sheets, placing curves in glass sheets and otherwise changing the contour of glass sheets and panels, such as in bending float glass sheets. Also the invention is directed to the resultant thermally treated glass sheets.
TECHNICAL CONSIDERATIONS
Glass sheets, panes, panels or parts have been heated for tempering, for annealing and for shaping as in bending, or placing curves or contours in the glass in industry by use of various processes and accompanying apparatus. Conventional tempering and annealing processes involve heating the glass with subsequent cooling of the heated glass at particular rates while the glass is supported on support members such as rings or outline molds. Shaping processes for glass include gravity bending, press bending, roll bending and like processes. These are as opposed to any production of glass bottles through blowing. In these glass shaping methods the heated glass is at a temperature for non-breaking deformation so that the glass accepts a shape or curve or bend given through one or more supporting and/or contacting members acting as a mold.
For instance, in gravity bending, bending fixtures or irons carry the glass through a furnace or a lehr to support the glass sheet during heating and usually also during subsequent cooling. The fixture usually supports the underside or bottom surface of the glass sheet in such a manner to allow for its bending or sagging due to gravity. The outlying shaping rail of the fixture provides the support and also can have an upper surface with elevational contours corresponding to at least part of the final desired shape of the glass sheet. With bending irons the main area of the glass is usually untouched during the bending process since the support is along the marginal end of the one or more glass sheets. The heated glass at its heat softening temperature sags by gravity to adopt the desired configuration. Also, bending irons can have movable parts to assist in the shaping of the glass. The shaping rails themselves can be segmented and/or made to pivot from an open, rigid sheet supporting position to a closed, heat-softened glass sheet supporting position for more difficult or complex bends or curves for the shaped glass. Such a technique is suitable for simultaneous shaping of two sheets of glass or doublet that will be used as the inner and outer plies of conventional laminated glass such as a windshield. For instance, automotive windshields can be made by placing one or more flat glass sheets on the support surface of the bending iron with appropriate spacing material for doublet sheets as that available in U.S. Pat. No. 6,076,373 (Grodziski); U.S. Pat. No. 4,066,429 (Reese et al.); U.S. Pat. No. 3,880,636 (Tobeman et al.); U.S. Pat. No. 6,006,549 (Safka et al.). These are all incorporated herein by reference.
As the glass sags or bends due to gravity the glass contacts an increasing surface of the shaping rails along the bottom marginal edge of the glass. This increasing contact is as opposed to the fewer contact points for the cold precut single or multiple glass sheets placed on the rigid non-articulating or articulating metal shaping rails of the bending iron. The rails themselves are usually pre-shaped to have a shape to support the unbent sheet while also supplying the mold for the curved or bent sheets. The contact of the glass with the rail in bending can give rise to infrequent slight surface markings along the periphery of the bent glass sheet. In addition to these types of scuff markings, other markings on the glass can occur from indentations occurring from inappropriate time and/or temperature experienced by the heated glass on the irons. Other markings can arise from transfer defects on the irons themselves; such as burrs of glass deposited on the rail from previous glass sheets that were shaped. Such surface markings can be accommodated for in laminated windshield products by concealing and glazing or framing parts for the bent glass.
Additionally, shaped glass can be produced from pressure forming which is usually the process used for making curved automotive side windows and back windows although gravity forming equipment could also be used. In the pressure forming of glass sheets pressurized gas assists in shaping the heat-softened glass sheet(s). The glass sheet first can be pre-shaped; for instance by sagging by gravity bending onto a ring or outline mold in a support frame. The mold with the glass and an upper mold of a molding device are moved relative to each other. This movement is to position the molds either in close proximity to each other or to press the upper mold itself against the heated glass. Hot air issues either selectively or more uniformly from the upper mold to flow towards the glass surface. A useful pressure forming process is shown in U.S. Pat. No. 5,669,952 (Claassen et al.). In this patent the mold includes a rail member having a support surface that generally conforms to the elevation and outline of the final longitudinal and transverse shape desired for the bent glass sheets. The rail member itself may be a bar member that supports the glass sheets slightly inboard of the glass sheets periphery or it may be an “L” or “T” shaped member. In pressure forming similar markings can occur on the shaped glass similar to those that can occur in gravity bending.
Additionally, with gravity and press bending, cooling of the shaped glass sheets usually occurs through natural convection or low level forced air cooling.
It is an object of the present invention to provide an apparatus and method and the resulting thermally treated glass having reduced bottom surface defects in particular reduced surface marks which can result when glass is tempered, annealed, shaped or bent on support apparatus or equipment.
SUMMARY OF THE INVENTION
The invention relates to an apparatus and method useful in the thermal treatment of glass sheets or panels and the resulting treated glass sheets and panels. The apparatus is capable of supporting the glass during thermal treatment such as tempering, annealing, bending, and/or shaping which can include any cooling or quenching to remove heat or any combination of these. In one aspect of the invention the apparatus useful for thermal treatments such as tempering and annealing, including the cooling step, is a ring or outline mold. The ring has a horizontal surface suitable for contacting the glass. The horizontal surface can be configured so that it is not just horizontal but may be somewhat non-planar to have an elevational configuration for certain portions or segments. For heat treatments for bending or shaping the apparatus of the present invention can have a support frame and one or more support members attached to the support frame. The support members like the horizontal surface of the ring can conform in elevation, outline or contour, and shape to provide support to one or more glass sheets or panels during thermal treatment. Also the support members can provide support during cooling.
At least the surface of the ring and the support members with or without a coating for contact with the glass are of one or more metals having a thermal conductivity such that the glass heated for shaping cools at a rate not much slower than the cooling rate of unsupported sections of the glass. For instance suitable metals include those with a thermal conductivity of greater than around 60 BTU/(hour×feet×° F. so that the shaped glass can have the requisite edge stress levels desired. In the units above, “x” indicates multiplication. The shape and dimensions of the ring and the support member provide the necessary rigidity to support the glass. These parameters and this characteristic are balanced with the thermal characteristics of the metal for the ring and the support
Horcicak Steven M.
Karlo Rudolph A.
Lampman DeWitt W.
Letzkus Lawrence S.
Savka Mark M.
Colaianni Michael
PPG Industries Ohio Inc.
Siminerio Andrew C.
Stachel Kenneth J.
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