Method and apparatus for bending thin glass

Abstract

The present invention provides for a method and apparatus for bending multiple sheet of thin glass at the same time on a single set of molds. Multiple sheets of thin glass are stacked onto a full surface female mold. A partial surface male mold is placed onto the thin glass stack. The male mold serves to hold the edges in place and prevents the formation of wrinkles as the glass is heated and sags to conform to the shape of the female mold. Optionally, the top mold can be enclosed and pressurized to provide a pneumatic pressure assist to form the glass. In addition, the bottom mold can be enclosed to allow for vacuum assist to form the glass.

Claims

1. A method for bending automotive thin glass sheets, comprising: providing a full surface bottom concave mold and a partial surface top mold; stacking at least one thin glass sheet onto the full surface bottom concave mold such that the periphery area of said at least one thin glass sheet is in contact with the bottom concave mold; applying the partial surface top mold to said at least one thin glass sheet, said partial surface top mold contacting the periphery area of said at least one thin glass sheet; and heating said at least one thin glass sheet to its glass transition point such that the at least one thin glass sheet sags under the force of gravity, adopting the shape of the full surface bottom concave mold.

2. The method of claim 1, wherein the thickness of said at least one thin glass sheet is of less than 1.8 mm.

3. The method of claim 1, further comprising applying a clamping force to the at least one thin glass sheet to force said at least one thin glass sheet to conform to the full surface bottom concave mold.

4. The method of claim 1, further comprising aligning said at least one thin glass sheet and molds.

5. The method of claim 1, wherein the step of providing a full surface bottom concave mold comprises: bending a sheet of glass having a glass transition point that is sufficiently higher than that of said at least one thin glass sheet and having a thickness sufficient for said mold to retain its shape during bending of said at least one thin glass sheet.

6. The method of claim 1, wherein the step of providing a partial surface top mold comprises: providing a partial surface top mold having a ring type structure.

7. The method of claim 1, further comprising applying pneumatic pressure to said partial surface top mold constructed such as to enclose a volume of air and serve as a plenum.

8. The method of claim 1, further comprising applying vacuum to said full surface bottom concave mold constructed such as to enclose a volume of air and serve as a plenum to allow evacuation of air between full surface bottom concave mold and said at least one thin glass sheet.

9. The method of claim 1, further comprising adding additional weight to the partial surface top mold.

10. The method of claim 1, further comprising covering the edge of the partial surface top mold that comes in contact with the at least one thin glass sheet with a layer of glass cloth to prevent marking of said at least one thin glass sheet.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a view of the female bending mold;

(2) FIG. 2 is a view of the female bending mold with flat sheet of glass having a higher glass transition point than the thin glass to be bent;

(3) FIG. 3 is a view of the female bending mold with the higher glass transition point bent to shape;

(4) FIG. 4 is a view of the female bending mold loaded with thin flat glass;

(5) FIG. 5 is a detailed view of the female bending mold loaded with thin flat glass;

(6) FIG. 6 is a detailed view of the mold with male ring in place;

(7) FIG. 7 is a view of the top plenum in raised position;

(8) FIG. 8 is a view of the top plenum and mold;

(9) FIG. 9 is a view of the bottom plenum;

(10) FIG. 10 is a view of the full surface female mold with vacuum holes.

REFERENCE NUMBERS

(11) 2 Bending mold base 4 Bending mold female ring 6 Thin glass 8 Male ring mold 20 Flat sheet of glass used to form full surface female mold 22 Full surface female mold 30 Vacuum holes 32 Top plenum air inlet 34 Top plenum back 36 Bottom plenum back 38 Bottom plenum vacuum inlet

DETAILED DESCRIPTION OF THE INVENTION

(12) Referring now in detail to the illustrative embodiment depicted in the accompanying drawings for carrying out this invention, FIG. 1 shows a bending mold base 2 and a bending mold female ring 4 for bending sheets of glasses. It should be noted, that the bending mold base 2 can vary its shape, geometry, dimensions, and area depending on the type of glass required to be manufactured. Bending mold base 2 is shown for reference, but it should be noted that any type of base can be used to carry out the invention.

(13) In order to carry out the method of the present invention, a female mold has to be formed. The method and apparatus of the present invention avoid glass wrinkles and provide uniformity to form the sheet of glasses. In FIG. 2, a flat sheet of glass 20 with higher glass transition point that the thin glass to be bent has to be provided in the lower part of the set of glasses. That flat glass 20 can be bended in a separate step, in a separate tool. In additional embodiments of the present invention, the flat glass 20, as shown in FIG. 3, is subject to its glass transition point, so that it is bent to shape the bending mold female ring 4. Once the flat glass 20 has reached the shape of the ring 4, it is then allowed to cool. Once the flat glass 20 has been let to be cooled, it serves as a full surface female mold 22 when pressing the thin glass, as can be seen in FIG. 4. The flat glass 20 must have a thickness sufficient for said full surface mold 22 to retain its shape during bending of said thin glass. Alternately, other type of molds can be used, for example, a ceramic or metal full surface mold can be fabricated and used as a mold for carrying out the method of the present invention. The full surface female mold 22 can be formed by any means and of any suitable material known in the art.

(14) As can be seen in FIG. 5, one or more sheets of thin glass 6 are loaded and placed onto the full surface female mold 22. It should be noted that the number of sheets that can be bent at the same time will depend upon the thickness of the glass and the complexity of the shape. In a preferred embodiment, the thickness of the thin glass 6 is of less than 1.8 mm. Then, the thin glass sheets 6 will tend to sag and conform to the periphery of the full surface female mold 22 under their own weight.

(15) As can be seen in FIG. 6, a partial surface top mold 8, which contacts the thin glass 6 in at least the periphery area of said thin glass 6, is implemented as a male ring type mold. The male ring 8 is then placed on the stack of thin glass 6. The male ring 8 serves to hold the edge of thin glass 6 down, preventing wrinkling. In additional embodiments, the male ring 8 is held in place by its own weight, or additional weight can be added to the male ring 8 if needed. In addition, clamps may be used to force the thin glass 6 to conform to the full surface female mold 22 if needed (not shown). Furthermore, aligning means may be used to align said thin glass 6 and molds. In preferred embodiments, the male ring mold 8 is open to allow for radiant heating of the thin glass 6 and accelerate the cycle time. This step prevents wrinkles from forming near the edges of thin glass 6. The edges of male ring 8 and female ring 4 may be covered with a material that is softer than glass to prevent marking of the glass.

(16) Optionally, after the thin glass 6 has sagged to a pre-determined point, a backing plate 34 (top plenum back) is lowered onto the male ring 8 and docked so as to enclose a volume of air and form a top plenum, as shown in FIG. 7. The top plenum is then pneumatically pressurized, and then heated by means of a hot air flow entering into a top plenum air inlet 32. The heat forces the thin glass 6 to conform to the shape of the full surface female mold 22.

(17) In additional embodiments, as the one shown in FIG. 8, the top plenum is pressurized using hot air, forcing the soft thin glass 6 to conform to the full surface female mold 22. The point of application, duration, air temperature and pressure are varied as needed to obtain the desired shape. The application of heating should be performed until reaching the glass transition point. Optionally, the bottom side of the bottom female ring 4 may be enclosed with a backing plate 36 (bottom plenum back) to form a bottom plenum, as shown in FIG. 9.

(18) In addition to the previous step or in place of, vacuum can be applied to the full surface female mold 22 in order to press so as to assist in the bending of the thin glass 6. Vacuum can be also applied with the glass cold, to help the glass to conform to the ring and/or at any point during bending, using the vacuum holes 30 shown in FIG. 10. Vacuum can be used alone or in conjunction with the top plenum. Optionally, rather than or in addition to the vacuum holes 30, a bottom plenum vacuum inlet 38 (FIG. 9) can be provided to apply vacuum to the full surface female mold 22 and the thin glass 6, allowing the air between them to evacuate.

(19) The method of the present invention has a number of advantages: The pneumatic and/or vacuum assist decreasing the bending cycle time by up to half The male ring mold results in prevents wrinkles from forming. The male ring mold also serves to hold the thin glass in place preventing it from sagging to soon. The use of a bent glass full surface mold reduces the tooling cost as compared to a machine cut or cast mold. The use of the full surface female mold results in dimensional surface control sufficient to allow for lamination of plies of different types of glasses that were not bent on the same mold at the same time, increasing the capacity of bending thin glass. The present invention improves yield especially on optic due to reduced temperature. The present invention improves optic in transmission due reduced temperature. This also improves reflection. The present invention also maintains glass edge during complete bending process.

(20) In a first embodiment, a sheet of 8 mm thick Lithium silicate glass 20 is used as the material for the full surface female mold 22. The flat glass 20 is formed on a cast ceramic mold. The bent flat glass 20 is then supported on a bending mold female ring 4 and serves as the full surface female press. The full surface female mold 22 is covered with a layer of glass cloth to help prevent marking of the thin glass. Such a press can be used for at least several hundred bending cycles. Six sheets of 0.7 mm aluminosilicate glass 6 are placed on the full surface female mold 22. The male ring 8 is then applied. The edge of the male ring 8, that comes into contact with the thin glass 6, is covered with glass cloth or and equivalent material to prevent marking of the thin glass 6. No additional weight or clamping is needed to hold the male ring 8 in place although it may be needed on some parts.

(21) In a second embodiment, the steps of embodiment one are repeated. When the thin glass 6 has been heated and softened, the top plenum back 34 is lowered onto the male ring 8. The top plenum is pressurized using hot air from a low pressure blower. The pneumatic pressure forces the softened thin glass 6 to conform to the full surface of the female mold 22.

(22) In a third embodiment, the steps of embodiment one are repeated and vacuum is applied to the bottom plenum to assist in the bending of the thin glass 6.

(23) In a forth embodiment, the steps of embodiment two are repeated and vacuum is applied to the bottom plenum to assist in the bending of the thin glass 6.

(24) The forms of the invention shown and described in this specification represent illustrative preferred embodiments and it is understood that various changes may be made without departing from the spirit of the invention as defined in the following claimed subject matter.