GB2232976A

GB2232976A - Toughened, curved glass

Info

Publication number: GB2232976A
Application number: GB8906625A
Authority: GB
Inventors: Derek W Leveridge
Original assignee: TREND ALUMINIUM PROD
Current assignee: TREND ALUMINIUM PROD
Priority date: 1989-03-22
Filing date: 1989-03-22
Publication date: 1991-01-02
Also published as: GB8906625D0

Abstract

A method of forming a curved sheet of toughened glass comprising the step of: (a) heating the sheet of glass; (b) bringing the sheet of glass into contact with a mould before, during or after the heating so that the glass is supported on the mould; (c) so cooling the sheet of glass that layers of the sheet become compressed in a way which serves to toughen the sheet of glass.

Description

CURVED TOUGHENED GLASS Field of the Invention The invention relates to a method and apparatus for producing curved sheets of toughened glass.

The superior optical qualities and resilience of toughened glass make it preferable in many applications to the alternatives of glass laminates and acrylic screens. Toughened glass may be used, for example, in windshields for sea-going motor cruisers since the windshield's relatively large surface area and large curvature tend to highlight the deficiencies of the alternative materials.

A sheet of toughened glass derives its strength from the com pression of its outer layers. This effect can be achieved by heating the glass, and then arranging that the surface layers of the sheet cool more rapidly than its inside.

Summary of the Invention In one broad aspect, the invention provides a method of forming a curved sheet of toughened glass comprising the steps of a) heating the sheet of glass; b) bringing the sheet of glass into contact with a mould before, during or after the heating so that the glass is supported on the mould; c) so cooling the sheet of glass that layers of the sheet become compressed in a way which serves to toughen the sheet of glass.

Preferably the sheet is brought into contact with the mould by being initially supported above the mould on a pair of conveyors which are slidably mounted with respect to one another, and which subsequently slide apart, while maintaining the sheet in overlay with the mould.

Preferably, while the conveyors are sliding apart, the mould is raised and/or the conveyors are lowered so that the weight of the glass gradually comes to rest on the mould.

The sheet of glass is preferably cooled by being carried on the mould to a cooling station where, while still being supported on the mould, the glass is cooled by, for example, directing compressed air jets on the upper face of the glass and on the underside of the mould.

In another broad aspect, according to the invention, apparatus for producing a curved sheet of toughened glass comprises a pair of conveyors, so arranged as to be movable between a closed position in which the conveyors, in effect, form a single conveyor unit, and an open position in which a gap is defined between the conveyors; and a mould so mounted as to be movable between a cooling station and a position beneath the conveyors in which, with the conveyors in their open position, the mould is situated under the gap.

Brief Description of the Drawings The invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 Is a schematic plan view of apparatus according to the invention at various stages of the method according to the invention.

Figures 2 and 3 are schematic side views of parts of the apparatus during the heating and cooling stages of the method, res pectivel y.

Description of the Preferred Embodiment Referring to Figures 2 and 3, a metal mould 1 is mounted via a pair of bogeys 2 on rails 3, which run between a cooling station (shown in Figure 3) and a heating/moulding station (shown in Figure 2).

When correctly positioned in the heating/moulding station, the mould 1 is situated beneath a pair of conveyors 4. Each conveyor 4 is slidably mounted on its own support block 5. A system of hydraulic motors (not shown) is used to move the conveyors 4 between an open position, indicated by the dotted lines, and a closed position in which a sheet of glass 6 may be supported on the conveyors 4. Each bogey 2 includes a known kind of hydraulic lift which may be used to raise or lower the mould 1.

The source of heat which is used in the heating/moulding station is provided by two sets of radiant heating elements 7 mounted above and beneath the conveyors 4.

The mould 1 may be propelled from the heating/moulding station to the cooling station in a known way, for example by using a system of cables and winches to tow the mould 1 between the two stations. The cooling station includes two sets of compressed air jets respectively directed to the upper and lower faces of the mould 1.

The apparatus is used in the following way: Referring to Figure 1, the sheet of glass 6 which is to be curved and toughened is placed on the conveyors 4 using a pallet 9. Once the glass 6 has been correctly positioned, the heating elements 8 heat the sheet of glass until it reaches a temperature at which the glass may be shaped and toughened.

This temperature will depend upon the relative proportions of the glass's constituent materials, but would be apparent to a skilled addressee of this specification.

During the heating process, the conveyors 4 impart to the glass a reciprocating motion in the directions indicated by arrow A and B. This is done in order to prevent the glass sagging on, and hence being deformed by, the rollers of the conveyors 4.

Once the glass has reached the desired temperature, the conveyors 4 separate, and the mould 1 is simultaneously raised so that the glass is gradually transferred from the conveyors 4 to the mould 1. Under its own weight, the glass 6 is formed into a shape which corresponds with the upper face of the mould 1.

The glass 6 is then carried on the mould 1 to the cooling station, where air from the jets 8 serves to cool the mould rapidly enough for its outer layers to become compressed.

In this embodiment, the underside of the glass 6 is cooled indirectly as a result of the compressed air cooling of the mould 1, which is preferably made from a material with a high thermal conductivity so that the m6uld is quickly and uniformly cooled. Alternatively, to assist in the cooling of the underside of the glass, the mould 1 may include a number of apertures.

Claims

CLAIMS:

1. A method of forming a curved sheet of toughened glass comprising the steps of: (a) heating the sheet of glass; (b) bringing the sheet of glass into contact with a mould before, during or after the heating so that the glass is supported on the mould; (c) so cooling the sheet of glass that layers of the sheet become compressed in a way which serves to toughen the sheet of glass.

2. A method according to Claim 1 in which the sheet is brought into contact with the mould by being initially supported above the mould on a pair of conveyors which are slideably mounted with respect to one another, and which subsequently slide apart, while maintaining the sheet in overlay with the mould.

3. A method according to Claim 2 in which, while the conveyors are sliding apart, the mould is raised and/or the conveyors are lowered so that the weight of the glass gradually comes to rest on the mould.

4. A method according to Claim 3 in which the sheet of glass is cooled by being carried on the mould to a cooling station where, while still being supported on the mould, the glass is cooled by, for example, directing compressed air jets on the upper face of the glass and on the underside of the mould.

5. An apparatus according to Claim 1 for forming a curved sheet of toughened glass comprising a pair of conveyors, so arranged as to be movable between a closed position in which the conveyors, in effect, form a single conveyor unit, and an open position in which a gap is defined between the conveyors; and a mould so mounted as to be movable between a cooling station and a position beneath the conveyors in which, with the conveyors in their open position, the mould is situated under the gap.

6. A method of forming a curved sheet of toughened glass, substantially as described herein with reference to and as illustrated in the accompanying drawings.

7. An apparatus for forming a curved sheet of toughened glass substantially as described herein with reference to and as illustrated in the accompanying drawings.