A COMPOSITE PANEL

Field of the Invention

This invention relates to a composite panel and, more specifically, to a composite panel having a relatively light weight whilst displaying desirable mechanical properties, in particular flexibility and resistance to shear forces so that such panels exhibit long term dimensional stability.

Background to the Invention

Composite panels for use in constructing, for example, a dish for a radio telescope typically include two fibreglass sheets that are separated by an intermediate layer made up of honeycomb-shaped units. The intermediate layer is manufactured from a synthetic plastics material or from aluminium.

A problem associated with such composite panels is that the intermediate layer is subjected to shear forces once the panel forms part of a telescope dish due to the curvature of the panel as well as external forces acting on the dish. The intermediate layer can become distorted, as a result of which it no longer provides the desired support to the fibreglass sheets.

Furthermore, composite panels as described above are costly as well as time- consuming to manufacture, as well as being relatively heavy, making them difficult to handle.

The inventors believe that a need exists for a composite panel which overcomes at least some of the shortcomings of the prior art described above.

Summary of the Invention

According to the invention there is provided a composite panel including:- first and second spaced apart sheets, which sheets are manufactured from a metal or metal alloy; dividers located between and attached to the first and second sheets, which dividers are sufficiently flexible to accommodate a desired curvature of the sheets and which form a grid to divide the area between the sheets into a plurality of zones; and - flexible support members for supporting the sheets, the members being configured and dimensioned to fit snugly into the zones; wherein the dividers retain the support members in place and inhibit distortion of the members under the influence of shear forces.

The sheets may be linear when viewed in side elevation or they may be curved.

The maximum curvature of each sheet may vary between about 37 and 42 degrees and is typically 38,5 degrees, or 40,3 degrees, or 41 ,6 degrees.

The spacing between the sheets may be about 20 mm and is dictated by the desired stiffness of the panel.

The sheets may be generally in the form of a sector of a circle when viewed in plan having two linear sides extending between first and second arcuate sides.

The length of each linear side may be between about 2000 and 3000 mm.

The radius of an arc defining the first arcuate side may be between about 700 mm and 5300 mm, depending on the maximum curvature of the sheets.

The radius of an arc defining the second arcuate side may be between about 2800 mm and 7600 mm, again depending on the maximum curvature of the sheets.

The lengths of the radii of the first and second arcuate sides may be proportional to the maximum curvature that the sheets are able to adopt.

The larger the radii of the first and second arcuate sides, the smaller the maximum curvature that the sheets are able to adopt.

The thickness of each sheet may be about 0,5 mm and the sheets may be manufactured from steel.

The dividers may be in the form of elongate strips folded to form a zig-zag shape in plan view.

The strips may be provided with flanges along their edges that in use abut on the first and second sheets to facilitate attachment of the strips to the sheets.

Prior to attachment to the sheets, the flanges of the strips may be positioned at an angle of between 91 and 93 degrees relative to the strips. This ensures that the flanges make good contact with the first and second sheets during assembly of the composite panel.

The dividers may be attached to the first and second sheets by applying an adhesive to the flange surfaces exposed to the sheets. Alternatively, the adhesive may be applied to the surfaces of the sheets that will be in contact with the flanges. The adhesive may be an industrial strength adhesive such as, for example, Araldite 420 A/D two component epoxy adhesive.

Slots may be defined in each strip in predetermined intervals along the length of the strip. The slots may extend about midway into the width of the strip.

The slots may be defined every 100 mm along the length of each strip and may be about 11 mm deep, depending upon the width of the strips, which is typically about 20 mm. It is to be appreciated, that the spacing between the slots may be varied in accordance with the desired dimensions of the zones.

During assembly of the panel, the dividers may be arranged in a grid to define the zones. Slots of dividers that cross each other may be aligned so that the dividers may be slotted into each other to form the grid. The zones formed when the slots are spaced apart 100 mm are therefore square with a side length of 100 mm.

The strips may be manufactured from a metal or metal alloy, typically steel, and may be between 0,3 mm and 0,5 mm thick.

The flexible support members may be in the form of blocks having a honeycomb structure when viewed in plan. The honeycomb structure allows for the effective distribution of forces acting on the panel whilst providing a lightweight support for the sheets.

Such honeycomb blocks are commercially available in sheet form, for example, from NIDA-Core. The honeycomb blocks may manufactured from PVC, nylon, aluminium, or polypropylene. In order to minimise the cost and weight of the panel, aluminium is rarely used.

In an alternative embodiment, the blocks may be solid and may be manufactured from any suitable lightweight material such as a foam or polystyrene.

The thickness of each block may be about 20 mm and the dimensions of each block may be 100 mm by 100 mm so as to fit snugly into the zones.

Each block may be provided with a sheet or layer on either side thereof to facilitate attachment of the blocks to the first and second sheets. The blocks may be attached to the first and second sheets by applying an adhesive to the surfaces exposed to the sheets. The adhesive may be an industrial strength adhesive such as, for example, Araldite 420 A/D two component epoxy adhesive.

It is to be appreciated, that the thickness of the support members and accordingly, the width of strips and the spacing between the first and second sheets, is selected according to the desired stiffness of panel.

In use, a plurality of composite panels as described above may be arranged to form a dish of a radio telescope.

The invention extends to a method of manufacturing a composite panel in accordance with the present invention, as will be described in more detail below.

Detailed Description of the Invention

The invention will now be described by way of the following non-limiting example with reference to the accompanying drawings.

In the drawings:-

Figure 1 shows an elevation view of a portion of a composite panel in accordance with the present invention;

Figures 2 a to c show plan, perspective and side elevation views of a sheet of a composite panel having a first size and curvature in accordance with the present invention;

Figures 3 a to c show plan, perspective and side elevation views of a sheet of a composite panel having a second size and curvature in accordance with the present invention;

Figures 4 a to c show plan, perspective and side elevation views of a sheet of a composite panel having a third size and curvature in accordance with the present invention;

Figure 5 shows a plan view of a section of a divider in accordance with the present invention;

Figure 6 shows a side elevation view of the divider of Figure 5;

Figure 7 shows an enlarged view of area A in Figure 6;

Figure 8 shows a perspective view of a portion of a first sheet, dividers and flexible support members in an assembled condition; and

Figure 9 shows a plan view of Figure 8.

It is to be appreciated, that since only small portions of a panel 10 in accordance with the invention are shown in Figures 1 and 8, the curvature of the panel 10 is not visible.

A composite panel 10 according to the invention includes first and second spaced apart curved sheets 12 and 14, which sheets 12, 14 are manufactured from steel.

Dividers 16 are located between and attached to the first and second sheets 12 and 14 and form a grid dividing the area between the sheets 12,14 into a plurality of zones 18. The dividers 16 are sufficiently flexible to accommodate the curvature of the sheets 12, 14.

Flexible support members 20 for supporting the sheets 12, 14 are provided in dimensions that permit the members 20 to fit snugly into the zones 18 (see Figures 8 and 9) so that the dividers 16 inhibit the support members 20 from becoming distorted under the influence of shear forces, whilst retaining them in place.

The spacing between the sheets 12, 14 is about 20 mm and is dictated by the desired stiffness of the panel 10.

As can be seen in Figures 2 to 4 a, the sheets 12, 14 are generally in the form of a sector of a circle when viewed in plan and have two linear sides 22.1 and 22.2 extending between first and second arcuate sides 24 and 26.

In Figure 2, the maximum curvature of the sheet 12 shown is 38,5 degrees, whilst the maximum curvature of the sheets 12 shown in Figures 3 and 4 is 40,3 and 41 ,6 degrees as indicated by the letter "M".

In Figure 2, the length of each linear side 22.1 and 22.2 of the sheet 12 is 2239mm, whilst it is 2235 mm and 2983 mm respectively in Figures 3 and 4.

In Figure 2, the radius R ¹ of an arc defining the first arcuate side 24 is 5227 mm whilst it is 2988 mm and 749 mm respectively in Figures 3 and 4.

In Figure 2, the radius R ² of an arc defining the second arcuate side 26 is 7467 mm whilst it is 5226 mm and 2983 mm respectively in Figures 3 and 4.

The radii of the first and second arcuate sides 24 and 26 are thus proportional to the maximum curvature that the sheets 12, 14 are able to adopt.

The thickness of the sheet 12, 14 is about 0,5 mm and it is manufactured from steel.

Referring now to Figures 5 to 7:

The dividers 16 are in the form of elongate strips 28 folded to form a zig-zag shape in plan view as can be seen in Figure 5.

The strips 28 are provided with flanges 30 along their edges that abut on the first and second sheets 12 and 14 to facilitate attachment of the strips 28 to the sheets 12, 14.

The flanges 30 are positioned at and angle of between 91 and 93 degrees relative to the strips 28. This ensures that the flanges 30 make good contact with the first and second sheets 12 and 14 during assembly of the composite panel 10.

The dividers 16 are attached to the first and second sheets 12 and 14 by applying an adhesive to the flange surfaces exposed to the sheets 12, 14 or to the sheets 12, 14 themselves. The adhesive is an industrial strength adhesive such as, for example, Araldite 420 A/D two component epoxy adhesive.

Slots 32 are defined in each strip 28 in predetermined intervals along the length of the strip 28. The slots 32 extend about midway into the width of the strip 28 as shown in Figure 7.

In the embodiment shown, the slots 32 are defined every 100 mm along the length of the strip 28 and are about 11 long.

During assembly of the panel 10, the dividers 16 are arranged in a grid to define the zones 18 as shown in Figures 8 and 9. Slots 32 of dividers 16 that cross each other are aligned so that the dividers 16 can be slotted into each other to form the grid. The zones 18 formed in the embodiment shown are square with a side length of 100 mm.

The strips 28 are manufactured from steel and are between 0,3 mm and 0,5 mm thick.

The flexible support members 20 are in the form of blocks 34 having a honeycomb structure when viewed in plan as can be seen in Figures 8 and 9. The honeycomb structure allows for the effective distribution of forces acting on the panel 10 whilst providing a lightweight support for the sheets 12, 14.

Such honeycomb blocks 34 are commercially available in sheet form, for example, from NIDA-Core. The honeycomb blocks 34 are manufactured from PVC, nylon, aluminium, or polypropylene. In order to minimise the cost and weight of the panel 10, aluminium is rarely used.

The thickness of each block 34 is about 20 mm and the dimensions of each block 34 are about 100 mm by 100 mm so as to fit snugly into the zones 18.

The composite panels 10 are manufactured according to a method as set out below:

Moulds for receiving the first and second sheets 12 and 14 respectively therein having a desired curvature are prepared.

The moulds are installed in a light force press, with one of the moulds being fixed and the other mould being displaceable. The displaceable mould is coated with a resilient material, for example 3mm neoprene rubber, to ensure that an even pressure is applied to the panel during assembly.

The sheets 12 and 14 are cut to a desired size either by a laser (for low volumes) or by blanking (for high volumes).

The dividers 16 are arranged to form a grid as described above and the support members 20 or blocks 34 are inserted into the zones 18 formed by the dividers 16. The edges of the divider-support member arrangement are trimmed so that the arrangement is approximately 10-15mm smaller than the sheets 12, 14.

The edges are covered by a channel-shaped sheet metal. The edges will most likely be welded at the four comers of the divider-support member arrangement.

The sheets 12,14 and the divider-support member arrangement are cleaned using a suitable cleaning agent such as, for example, acetone whereafter these are only handled by users wearing suitable gloves to avoid contamination. The time between cleaning and final bonding should be limited and is typically not more than 30 minutes.

ARALDITE 420 A/D two component epoxy adhesive, is prepared and applied to inner surfaces of the sheets 12, 14. The thickness of the applied adhesive is about 0.1mm.

The first sheet 12 is then placed into the fixed mould with the adhesive-covered surface facing upwards. The divider-support member arrangement is placed onto the adhesive whereafter the displaceable mould containing the second sheet 14 is lowered onto it. The pressure exerted by the displaceable mould is the minimum pressure required to form the panel 10 into the mould profile.

The pressure is applied for the required curing time of the adhesive. The moulds can optionally be heated accelerate the curing cycle. Heating the moulds can reduce the curing time by a factor of ten.

Holes for panel supports and alignment targets, using either the bottom or top mould as a jig are drilled while the panel 10 is located in the moulds.

When curing is complete, the panel 10 is removed from the moulds and allowed to cool after which excess adhesive is removed from the panel edges.

Panel support and alignment target mechanisms can now be glued into the drilled holes, after appropriate cleaning. Heat is applied locally if require to accelerate curing.

The panel 10 is then cleaned for painting after which a suitable primer and high reflectance top coat are applied.

Once the top coat has cured, the panel 10 can be packaged for transport.

Advantages of the present invention include that due to the first and second sheet being manufactured from metal instead of fibreglass, the curing time required for the adhesive bonding the support members to the sheets is significantly reduced. The curing time can be further reduced by the application of heat during curing.

The inclusion of the dividers inhibit distortion of the support members due to shear forces acting on said members, which could otherwise lead to distortion of the first and second sheets. The panels thus have a good dimensional stability that is maintained during long-term use.

The use of metal sheets in combination with non-metallic support members significantly reduces the cost of the composite panel when compared to presently available panels.

It is to be appreciated, that the invention is not limited to any particular embodiment or configuration as hereinbefore generally described or illustrated.