GB2053785A - Method of manufacturing panels - Google Patents

Abstract

A method for manufacturing panels, for example prefabricated roof panels, includes making a first skin (1) of reinforced plastics material in an open mould, spraying a liquid thermosetting plastics foam (2) onto the first skin once it has gelled, machining the top surface of the thermosetting plastics foam (2) once it has set, making a second skin of reinforced plastics material (3) in situ on the machined surface of said thermosetting plastics foam (2) and subsequently removing the completed panel (4) from the mould. The process described ensures that the foam completely fills the space between the two skins and bonds completely to each. <IMAGE>

Description

SPECIFICATION Method of manufacturing panels This invention relates to a technique for the manufacture of sandwich panels with reinforced plastic skins and foamed plastic core.

The use of foam-cored sandwich panels with reinforced plastic skins offers considerable benefits in buildings, container manufacture, vehicles etc.

Reinforced plastic is a strong but flexible material and can be used much more efficiently as the skin of a sandwich panel than as a solid material. Sandwich panels in reinforced plastic have good strength, stiffness and stability combined with low weight and freedom from distortion. When a plastic foam core is used, in particular a polyurethane foam, the level of thermal insulation achieved is superior to almost any other form of construction.

For a structural sandwich panel to perform satisfactorily over long periods it is essential that the skins are bonded to the core material as completely as possible. The presence of voids or unbonded areas causes a loss of strength and stiffness and can lead to further peeling off due to pressure generated inside the void by a rise in temperature. Large unbonded areas eventually show as blisters on the outside of the panel and spoil its appearance, as well as degrading its performance.

Existing methods of manufacturing foam-cored reinforced plastic sandwich panels usually rely on either the use of pre-cut foam slabs which have to be bonded to one or both skins in a press, or on injecting the liquid components into the cavity between the two skins, which requires a foaming jig massively reinforced to withstand the pressures generated. With both these techniques incomplete adhesion is possible; in the first method by trapping air between the foam slab and the skin; in the second by producing an incomplete fill. There are also economic penalties with both methods - slabstock foam is expensive and fragile, while cavity filling requires two moulds and a foaming jig - for large panels this is expensive and occupies a large area.Another disadvantage of both methods is that the manufacture of the skins is a separate operation requiring further equipment and space.

The invention described here is a system for manufacturing a complete sandwich panel with high structural integrity, at relatively low cost. The proce ydure is essentially as follows: 1. A skin of reinforced thermosetting plastic is manufactured on an open mould.

2. When the skin has gelled, a thermosetting plastic foam is sprayed onto the first skin as evenly as possible.

3. When the foam has set, its top surface is machined flat and all loose material removed.

4. A second skin of reinforced thermoset-ting plastic is manufactured on the aforementioned machined foam surface.

5. When the second skin has adequately cured, the complete sandwich panel is removed from the mould.

This technique has the following advantages over conventional methods of reinforced plastic sandwich panel manufacture.

(a) All operations are carried out on a single open mould, ensuring minimal floor space requirements and minimal jig and tool costs.

(b) No significant pressure is required or generated at any stage in the process, eliminating the need for cumbersome jigs or presses.

(c) Manufacture is directly from liquid foam components and liquid skin resins, ensuring low raw material costs and easy storage and handling of materials.

(d) Spraying on foam ensures an excellent bond to the first skin and a complete fill, with visual confirmation.

(e) A machined foam surface provides an excellent key for the second skin, with a complete bond ensured by laying the skin wet onto the cut foam surface.

(f) Although best suited to shallow, tray-like shapes, there is almost no restriction on the size and shape of panels which can be made.

(g) The process is particularly well suited to automation for example by using a robot or overhead gantry to deposit the materials consolidate the skin laminates and/or machine the foam.

In order to understand the invention more fully, a particular embodiment will be described by way of example only with reference to Figures 1 to 8 enclosed, of which: Figure 1 is a cut away perspective view of a sandwich construction roof unit to be manufactured.

Figure 2 is a sectional view of the mould used to manufacture the unit shown in Figure 1.

Figure 3 to s are cross-sections of the mould illustrating successive stages in the manufacture of the roof.

Referring to Figure 2, this is a conventional mould (5) for cold curing reinforced plastic, which can be made from timber, reinforced plastic, metal or any other suitable material. It must be coated with a release agent before manufacture commences.

(i) The first operation is to apply the first skin of reinforced thermosetting plastic (1 ) (typically glassfibre reinforced unsaturated polyester resin) to the mould (5) as shown in Figure 3. The resin can be applied by spray (6) or brush or roller; reinforcement by chopper gun(7) or by hand, using sheets of reinforcement cut from a roll. If required a layer of resin can be applied and allowed to gel (a gel coat) before any reinforcement is added.

(ii) Following application of resin and reinforcement the lay-up(1) is consolidated using a metal washer roller (8) or other suitable device as shown in Figure 4. The procedure described so far is well known and accepted practice for the manufacture of a reinforced plastic skin in any open mould.

The reinforced plastic skin must be allowed to gel and cure sufficiently before the core material is applied. If the core is applied too soon it can react with the skin resin which can inhibit the foaming action and cause undercure. The minimum cure time depends on resin type, ambient temperature, cure system etc, but is normally not less than 15 minutes after gellation.

(iii) The plastic foam core (9) (usually polyurethane) is sprayed on as shown in Figure 5. To avoid wastage it is important to obtain an even coverage and this is best achieved by fitting the spray gun (10) to a controlled-speed traversing device.

(iv) Figure 6 shows the next stage of manufacture - machining the foam surface (11) level. In the embodiment described here this is carried out with a rotating abrasive disc (12) mounted horizontally and fitted to a traversing machine, but other tools such as belt sanders or rotary planers could be used.

After machining all loose foam material must be removed from the machined surface, for example by vacuum cleaner.

(v) The second skin (13) of reinforced plastic is next applied in the same way as the first skin, as shown in Figure 7 and this is then consolidated as shown in Figure 8, without applying so much pressure as to crush the foam.

The component is then essentially complete and should be allowed to cure for the normal time before being removed from the mould and trimmed (if this has not been completed earlier).

The traversing device or machine may suitably be the one described in our copending UK application entitled "Manipulating Portable Tools" and filed on 9th July, 1979.

Claims (9)

1. A method of manufacturing panels including the steps of making a first skin of reinforced thermosetting plastics material in an open mould, applying a liquid thermosetting plastics foam onto the first skin once it has gelled, machining the top surface of the thermosetting plastics foam once it has set and making a second skin of reinforced thermosetting plastics material in situ on the machined surface of said thermosetting plastics foam, subsequentaly removing the competed panel from the mould.

2. A method according to claim 1 wherein the reinforced thermosetting plastics material is a glassfibre reinforced plastics resin.

3. A method according to claim 1 or claim 2 wherein the liquid thermosetting plastics foam is applied to the reinforced thermosetting plastics material not less than 15 minutes after gelation of the reinforced thermosetting plastics material.

4. A method according to any of the preceding claims wherein the thermosetting plastics foam is a polyurethane foam.

5. A method according to any of the preceding claims wherein at least one of the constituent layers of the panel is applied by spraying.

6. A method according to claim 5 wherein the liquid thermosetting plastics foam is applied by spraying.

7. A method according to any of the preceding claims wherein the machining of the thermosetting plastics foam is carried out by a rotating abrasive disc, a belt sander or rotary plane.

8. A method according to any of the preceding claims wherein at least one of the manufacturing operations is carried out by a tool or tools attached to a controllable robot or gantry which enables the speed and position of the said tools to be controlleti.

9. A method of manufacturing panels substantially as described herein with reference to the accompanying drawings.