Background of the invention Roof sheeting is typically attached to a portion of the underlying roof structure and conveniently to the rafters or purlins making up said roof structure, either in steel or timber. The roof sheeting is affixed to the roof structure using screw fasteners which penetrate the sheeting and embed into the members of the roof structure. On application of an external load to the roof, usually wind load, there would normally be a significant concentration of stress at the head of the fastener leading to failure of the sheet. To avoid this it is well known to use a washer assembly with the fastener, a steel backing member is attached to the fastener proximate the fastener head so as to distribute the load over a larger area. To ensure good contact and thus load distribution between the steel backing member and the roof sheeting, a more compliant member is placed between the backing member and roof sheeting, and so maintaining good contact. More importantly, the compliant member further acts as a sealing gasket to ensure that water ingress through the fastener hole is prevented and so maintains the integrity of the roof.

For even a small roof installation, the number of washer assemblies can run to the many hundreds. In an extreme example, under cyclonic conditions every crest of roof sheeting requires a washer assembly. For a width of sheeting of 750 mm with a "wave length"of 50 to 75 mm, one row of fasteners per sheet will require between ten and fifteen assemblies. Clearly for temperate conditions the number is substantially less, but nevertheless a large number of washer assemblies will be required. With a typical construction of a rubber sealing member, a steel backing member assembled with the insertion of a fastener through the centre, assembling the assembly is time consuming, which is in addition to the typically automated fabrication of each individual component.

Further problems with the conventional washer assemblies include corrosion of the steel backing member caused by detritus collecting around the projecting washer

and fastener head. Further, markedly differential thermal expansion of the backing and resilient members may lead to minor fatigue problems and even leakage of the roof.

Under significant loading the steel backing member is known to contact the fixed roof sheeting as the sheeting flexes under a wind load and can cause premature fatiguing of said sheet. Further, a steel backing member is incompatible with plastic roof sheeting as any contact between the steel backing member and the sheeting will tend to shear the softer plastic material.

Object and Statement of the Invention It is therefore an object of the present invention to provide an improved washer and assembly.

In a first aspect the invention provides a sealing washer for use in fastening a sheeting material or the like to a substrate said washer including a rigid backing member and a compliant sealing member wherein said backing member and said sealing member are provided with co-axial apertures to receive a fastener and are adapted to cooperate during fastening such that when said washer is applied to a section of said sheeting said sealing member is compressed between said backing member and said sheeting characterised in that said backing member and said compliant member are engaged and bonded during fabrication of said washer to provide a unitary washer which may have distinct physical characteristics for said backing and said sealing members thereof.

In another aspect the invention provides a sealing washer assembly for securing a section of roof sheeting to a roof structure said assembly including a rigid backing member, a compliant sealing member and a fastening means, the two members being co-engaged and apertured to receive the fastener such that on securing the roof sheeting to the roof structure, the compliant sealing member is compressed between the roof sheeting and said backing member wherein the stiff backing member and the resilient sealing member are made from dissimilar polymer materials and are co-engaged during fabrication of the members.

In another aspect the invention provides a sealing washer assembly for fastening a section of roof sheeting or the like to a supporting structure said assembly including a sealing washer as previously described and a fastening means.

Preferably, the co-engagement of the members during fabrication may involve a co-injection moulding of the members in a single two-stage process. Thus, in this embodiment the compliant member and the backing member are formed in an automated two-stage process whereby the stiffer polymer is injected followed by the

compliant polymer and consequently ejected from the co-injection mold will be an assembled unitary dual member ready for insertion of the fastener.

Thus, the present invention firstly adopts the advantages of a polymer backing member and thus avoids the inherent problems of a steel backing member being the shearing effect of the backing member against certain forms of roof sheeting, and the corrosion resistance of suitable polymers. Any number of suitable polymers may be selected including PVC, homopolymer polypropylene, ABS, or other consumer polymer having a low glass transition temperature, and thus may be relatively stiff at ambient temperature. Further, the use of a polymer backing member permits a range of different manufacturing processes to make it compatible with the manufacturing process for the resilient member.

Any number of suitable processes may be used including blow moulding, rotational moulding and injection moulding etc. The use of a moulding process not only increases the production rate of the backing member, but may also permit the use of complex shapes to mold the backing member.

It may be beneficial to manufacture a backing member which is adapted for use for a particular roofing profile wind loading condition or different roofing material.

Generally the types of elastomeric polymer materials previously used for the compliant member would also be applicable including EPDM, polyurethane and may be applicable to more diverse materials such as silicone.

In another preferred embodiment co-engagement of the members may further include partial mechanical engagement or encapsulation of the backing member by the sealing member. Thus, in addition to the bond between the members being of a fusion of the two members at the interface thereof, the sealing member may further physically encapsulate a portion of the backing member so as to provide a mechanical engagement. Alternatively, the backing member may act to encapsulate at least a portion of the sealing member.

The backing member may be a flat disc, or alternatively a substantially frusto- conical member. As discussed, various processes may permit more complex shapes for the backing member for particular applications. In general terms however, for the backing member to act as a load distribution means, a flat disc or a frusto-conical shaped member may be all that is required subject to the load distribution characteristics of the sealing member.

The sealing member may further include means to aid in the sealing and load distribution. These various means may be located on a face in contact with the roof sheeting. Preferably, the means may include fins, ridges or ring portions. Said portions

may be adapted to undergo substantial deformation when the resilient member undergoes compression. Thus, the means may provide for a differential stiffness and/or resiliency in the sealing member by being able to deform to a greater degree as compared to the remaining portion of the sealing member.

The sealing member may act both as a load distribution portion and/or a means to seal the roof sheeting from water ingress through the penetration caused by the fastener. Further, the sealing member may also include a collar isolating the fastener from the backing member. The collar may act as further sealing means about the shaft of the fastener. Thus, the collar may prevent any ingress through for instance, capillary action between the members and the fastener down the shaft of the fastener, by acting as an O-ring type gasket. Further, the sealing member may incorporate a lip that protrudes from the backing member and, under load, may further aid to seal the washer against the surface being fixed to.

In another embodiment, the sealing washer may further include a portion extending from a lower surface of the washer, and acting as an integral fastener. It follows that an extension from the stiff backing member may be formed to extend through the resilient sealing member and shaped so as to act as a self-tapping fastener.

Alternatively, a steel fastener may also be molded into the washer so that an entire washer assembly may be formed from the moulding of a stiff polymer backing member, a resilient polymer sealing member and a steel fastener within an automated moulding process. This has the clear advantage of negating the need for a final assembly stage as is necessary for conventional prior art systems.

Accordingly, in another aspect the invention provides a sealing washer assembly for fastening a section of roof sheeting or the like to a supporting substrate including a washer as previously described wherein said backing member includes an integral fastening means adapted for projection through the aperture of said engaged sealing member.

In another aspect the invention provides a method of manufacturing a washer or assembly as previously described comprising the steps of : (a) fabricating said backing member from a polymer having a low glass transition temperature; (b) fabricating said sealing member from an elastomeric polymer; (c) co-engaging said backing and sealing members to form a unitary washer.

The co-engagement may be effected by chemical adhesion, fusion or bonding and is most preferably effected during fabrication of the backing and sealing members.

Description Of Preferred Embodiment It will be convenient to further describe the present invention with respect to the accompanying drawings which illustrate possible arrangements of the invention. Other arrangements of the invention are possible and consequently the particularity of the accompanying drawings is not to be understood as superseding the generality of the preceding description of the invention.

Figure 1 is an elevation view of the washer assembly according to the present invention; Figure 2 is an elevation view of the washer assembly of Figure 1, securing a sheet of roof material to a purlin.

Figure 1 shows the washer assembly (1) the washer of the present invention having a rigid backing member (2) co-engaged with a compliant sealing member (3) through which is placed a fastener (4). The members (2) and (3) are made from dissimilar polymers with the backing member (2) made from a rigid polymer such as PVC, homopolymer polypropylene or ABS, and the compliant sealing member (3) made from an elastomeric polymer such as EPDM, polyurethane or similar.

The fastener (4) is of the conventional type, being manually inserted in the assembled or members (2) and (3). The combined members (2) and (3) in this preferred embodiment are the result of a co-injection moulding in a single two-phase process whereby the backing member (2) is injected within the moulding followed by the injection of the sealing member (3) immediately after. At an appropriate time the finished combined members (2) and (3) are ejected from the mold ready for the next batch. As a result the members (2) and (3) are co-engaged through a fusion of the two polymers along an interface (6a) between the two. In this preferred embodiment there is a further co-engagement with the sealing member (3) physically engaging the backing member (2) and so providing an additional co-engagement through a mechanical interference. Thus, the two members function together in an essentially composite manner.

In this embodiment the backing member (2) is molded into a substantially frusto conical shape, but the advantage gained in using a molded polymer material provides the flexibility to mold the backing member into a variety of complex shapes which may be advantageous for various applications of different roofing profiles, conditions or materials.

The sealing member (3) in this embodiment is shaped so as to provide additional sealing means being deformable ridges forming a circumferential lip which can aid in the sealing of the penetration in the roof sheet caused by the fastener (4). The sealing member (3) further functions to fully distribute the load applied to the backing member (2) to the roof sheeting and in this embodiment further includes a raised neck (8) defining the aperture which terminates in a bearing portion in the form of a collar (9) which supports the head (7) of the fastener (4). Consequently, load transmitted through the head (or screw flange thereof) (7) passes through the collar (9) to the backing member (2), and consequently, through the remaining portion of the sealing member (3) to the roof sheeting.

The raised neck of the sealing member also forms an indented rim (10) on the exterior surface of the neck defined by the top of the sealing member and the projecting collar. This rim provides the cooperative means for mechanical engagement with the aperture region of the backing member to ensure snug and secure engagement of the respective sealing and backing members.

Figure 2 shows the washer assembly (1) according to the present invention in an installed condition whereby the fastener (4) has a portion embedded into a substrate in the form of a purlin (13) so as to affix the roof sheeting (12) to said purlin. The washer assembly (1) is attached to the top of the trough of the sheeting (12). The contact between the sealing member (3) and the roof sheeting (12) is clear whereby both the load is transmitted to the roof sheeting (12) and the penetration caused by the fastener (4) is completely sealed.

Referring now to Figures 3 and 4, an alternative embodiment of the invention is detailed, showing the washer assembly including a washer comprising a rigid backing member (2) engaged to a compliant sealing member (3), where the backing member includes an integral fastening means (4) provided as part of the fabrication of the backing member. The fastening means will be formed during the fabrication of the backing member as an integral projecting part thereof, which effectively replaces the aperture in the backing member. The projecting fastener is configured to fit the aperture of the engaged sealing member and project therethrough and may take the form of a self tapping screw or any other convenient fastening device. In this manner, the separate incorporation of a fastener to the assembled washer of the invention can be eliminated or incorporated as an integral step in the manufacture of the washer components. Such a manufacturing process and product, eliminates the need to separately assemble a fastener into the washer and thereby provides a more efficient manufacturing technique and a more efficient and cost effective product.

Referring now to Figure 4, an alternative embodiment of the previously described assembly is shown, where the fastening means takes the form of a discrete steel fastener (4) which is moulded into the washer of the invention during fabrication process. The steel fastener may be moulded into either the backing member (2) as shown, or the resilient sealing member (3) during fabrication, but is most preferably moulded into the stiff backing member so as to provide an analogous product to that described with reference to Figure 3.

The invention provides for the first time, a highly economical method of manufacture and fabrication of a sealing washer, particularly adapted for use in the fastening of a roof sheeting and similar materials. The fabrication and method of the invention provides an effective one step manufacturing process, which replaces the existing prior art products, which currently require the assembly of multiple components. The method and product of the invention provides highly economical product and also provides clear advantages and improvements by virtue of the integral nature of the washer and the washer assembly, which when fabricated, form an effective unitary assembly thereby involving the use, assembly and handling of minimal components, not only in the manufacture, but also in the packaging, presentation and end use of this type of product. While the washer and assembly of the invention find particular application in the construction industry, alternative uses of the invention can be found in a range of engineering, automotive and general fabricating industries.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.