GB2232631A

GB2232631A - Making flat plates

Info

Publication number: GB2232631A
Application number: GB9000443A
Authority: GB
Inventors: Robert Joseph Stephen Lundy
Original assignee: RINGWAY SIGNS Ltd; SPACESAVER SIGNS
Current assignee: RINGWAY SIGNS Ltd; SPACESAVER SIGNS
Priority date: 1989-01-13
Filing date: 1990-01-09
Publication date: 1990-12-19
Also published as: GB9000443D0; GB8900769D0

Abstract

An apparatus and method for making flat plates of GRP or other heat-curable material. Upper and lower plates (12, 18) define the top and bottom surface of the plate and an separate annulus (14) defines the shape of the perimeter. Layers of e.g. GRP are built up in the hollow interior (16) between the plates (12, 18) and the annulus (14). Pressure may be applied to the plates (12, 18) to aid dispersion of resin through the glass fibre, and heat from e.g. a liquid contained in the bed (24) of the support structure (10) of the apparatus may be applied to the plate. Pressure can be applied using a vacuum system, wherein a cover (20) forming part of a sealed enclosure is placed over the upper sheet (18) and air is evacuated from the enclosure (24). The cover may be rigid or flexible. <IMAGE>

Description

MAKING FLAT PLATES The present invention relates to the making of flat plates of e.g. GRP which may be used, for example, as the plate of a sign.

There are two known ways of making articles of GRP.

Firstly, sheets of GRP may be made by an extrusion system, which extrudes continuously a sheet of GRP which can then be cut to shape. As may be imagined, such systems involve machines which are complex and therefore expensive. The other way of making GRP articles is via shaped moulds, and there the problem is that the two mould halves must be accurately matched if the article is to be the right shape.

The present invention seeks to provide a simple way of forming a flat sheet of GRP, or other heat-curable material. It proposes that the material to be formed into a sheet is positioned between a pair of plates, with the periphery of the sheet being defined by an "annular" member. That annular member is not fixed to either; plate, but simply acts as a boundary. Then, the carrier plates are forced togethér änd the material is compressed. Of course, some material may flow between one of the plates and the annulus, since the plates and the annulus are not sealed together except by pressure, but such leakage has been found to be minimal.

It should be noted that, in the present specification, the word "annulus" is not restricted to circular shapes, but could refer to triangular, square, rectangular, or other shapes. What is needed, however, is that the hole within the "annulus" has a shape corresponding to the desired shape of the flat plate, and the lateral thickness of the annulus is sufficient to both support the plates and permit slight leakage of material as discussed above, without significant amounts of the material leaking beyond the outer limit of the annulus. The shape of the outer periphery of the annulus is not critical.

As was mentioned above, the present invention is particularly concerned with the manufacture of signs, in which case true annuli may be used to produce circular signs.

Once the article is compressed between the plates, with the lateral expansion limited by the annular member, material may then be heat-cured. For example, if the lower carrier plate is of metal, it may be positioned above a tank of heated liquid, such as oil or water, so that the heat is conducted from the liquid through the plate to the article. Alternatively, of course, heat may be supplied from above or both from above and below.

In a preferred development of the invention, the pressure is applied to the plates via a vacuum system. A cover is placed above the upper plate and sealed to the lower plate, or a support of the lower plate, and the interior evacuated. If the cover is rigid, e.g. by making it of steel, the seals are flexible so that they deform to force the cover onto the upper plate. However, it has been found that particularly advantageous results are obtained if the seals are relatively rigid and the cover is of a flexible material such as rubber. Then, the cover deforms around the plates to achieve very high pressures. Furthermore, the heating of the article may then be achieved through the (relatively thin) rubber cover.

To produce a GRP article using the system of the present invention, layers of glass fibre are placed on the lower plate, and surrounded by an annulus with a suitable shape. It is preferable for those fibres to be in the form of a chopped strand mat, which has a random pattern of glass fibres, but continuous filament mats may also be used as an alternative. A suitable amount of resin is placed on the layers of glass fibres, or may be added at an intermediate stage in the formation of the layers, and the upper plate placed over the layers. A vacuum pressure is then applied and this forces the resin throughout the glass fibre layers. The application of the heat will then cure the resin and catalyst, forming the article.

An embodiment of the invention will now be described in detail, by way of example, with reference to the accompanying drawings, in which the sole figure shows an apparatus for forming a GRP article according to the present invention.

Referring to the figure, a support structure generally indicated at 10 support a lower carrier plate 12. Loosely positioned on that carrier plate 12 is an annulus 14, the hollow interior 16 of which is shaped to conform to the shape of the flat article to be produced.

Layers of e.g. chopped strand mats are placed within this space 16, as is a suitable amount of resin and catalyst.

For example, two layers of chopped strand mat may be positioned on the lower carrier plate 12, a glass tissue layer placed thereon, a suitable amount of resin and catalyst located on the tissue, and then two further layers of chopped strand mat placed above the tissue layer. Then, an upper carrier plate 18 is loosely positioned above the lower carrier plate 12, the annulus 14, and the layers of chopped strand mat.

A cover 20 is then positioned above the upper carrier plate 18-, which cover 20 is sealed to the support 10 by seals 22. In this embodiment, the cover 20 is a steel plate, and the seals 22 are flexible. The interior 24, within the plate 20 and the seals 22 is then evacuated by a suitable vacuum system, and this forces the cover 20 onto the upper carrier plate 18, forcing that plate downwards towards the lower carrier plate 12, and thereby compressing the chopped strand mat layers within the space 16. The resin and catalyst then flows under that pressure so that the mats are fully impregnated.

Heat is then applied to cure the resin and so form the flat article. To apply such heat, the bed 24 of the support structure 10 may contain ducts for the passage of heated fluid such as oil or water. The heat passes through the lower carrier plate 12 and thereby cures the resin. Furthermore, this method may also be used to extract the heat produced by the curing of the resin, so that the resin can be maintained at the desired temperature during curing.

In a modification of the embodiment shown in the figure, the cover 20 is flexible, and the seals 22 are rigid. Then, the cover 20 flexes when a vacuum is applied to the space 24, and is forced onto the upper carrier plate 18. This has the effect of forcing the upper carrier plate 18 towards the lower carrier plate 12. Heat may then be applied through the cover 20.

The present invention provides a simple, but effective, way of producing flat shaped articles of GRP.

Since the carrier plates 12,18, and the annulus 14 are not fixed together, it is possible to replace one annulus 14 of a first shape with an annulus of another shape, to change the shape of the flat article. To do this with moulding techniques would be extremely expensive, since a whole new mould would be needed. Furthermore, assemblies consisting of upper and lower carrier plates 12,18, annuluses 14, and layers of chopped strand mat within the space 16 may be assembled separately, then placed on the support 10. In this way, the production of the articles may be on a semi-continuous basis.

It is desirable that the opposing surfaces of the carrier plates 12,18 and the surfaces of the annulus 14 are treated with a suitable resin releasing agent, such as wax, to prevent the article sticking thereto.

Claims

CLAIMS:

1. An apparatus for making a flat plate of heat-curable material comprising upper and lower flat plates for defining the upper and lower surfaces of a sheet being formed, a separate annular member between the plates for defining the periphery of the sheet, means for applying pressure to force the upper and lower plates together, and heating means for applying heat to the heat-curable material.

2. An apparatus according to claim 1 wherein the means for applying pressure comprises a sealed enclosure surrounding the upper and lower plates and means for evacuating air from the sealed enclosure arranged so as to apply pressure to the upper and lower plates when air is evacuated from the sealed enclosure.

3. An apparatus according to claim 2 wherein the sealed enclosure has a rigid cover over the upper plate and there are flexible seals connecting the rigid cover to the remainder of the enclosure.

4. An apparatus according to claim 2 wherein the sealed enclosure comprises a flexible cover over the upper plate.

5. An apparatus according to either claim 3 or 4 wherein heat from the heating means passes through the cover.

6. An apparatus according to any one of claims 1 to 4 wherein the heating means comprises a tank of heated liquid.

7. An apparatus for making a flat plate of heat-curable material substantially as herein described with reference to the accompanying drawings.

8. A method of producing a flat plate of heat curable material comprising; placing layers of glass fibre on a lower plate; surrounding the glass fibre with an annulus of a shape corresponding to the finished plate; placing resin on or between the glass fibre layers; placing an upper plate on the layers; and applying heat to one or both plates.

9. A method according to claim 7 further comprising the application of pressure to the plates.

10. A method of producing a flat plate of heat curable material substantially as herein described with reference to the accompanying drawing.