Static structures (e.g. – buildings) – Lapped multiplanar surfacing; e.g. – shingle type – Interfitted sections
Reexamination Certificate
1998-02-06
2001-02-13
Kent, Christopher T. (Department: 3635)
Static structures (e.g., buildings)
Lapped multiplanar surfacing; e.g., shingle type
Interfitted sections
C411S386000, C411S387400, C411S411000, C411S414000
Reexamination Certificate
active
06185896
ABSTRACT:
TECHNICAL FIELD
This invention relates to the fastening of material to thin metal structures. It will be convenient to hereinafter describe the invention with particular reference to the fixing of roofing or cladding material to battens of thin material section, but the invention has wider application. The invention is concerned with fastening systems of the foregoing kind and is also concerned with a fastening screw for use in such a system.
In the context of this specification the expression “thin metal” is to be understood as referring to metal having a thickness not significantly greater than one millimeter, and more generally in the range 0.4 to 0.8 mm.
BACKGROUND
It is common practice to secure metal roofing material to thin metal battens by means of self-tapping threaded fasteners of the kind having a drilling tip. Selection of such a fastener from the available range of such fasteners is largely determined by the speed with which the fastening operation can be achieved, but the security or strength of the fastened assembly may be compromised in the process. Fastenings of the aforementioned kind have been found to fail particularly in situations involving relatively high wind loading. It has been discovered that such failures are due at least in part to the distorting effect of the thread form of conventional fasteners on the thin metal battens.
OBJECTS SUMMARY OF THE INVENTION
It is an object of the present invention to provide a screw threaded fastener having a modified thread form which enables relatively rapid fastening of one member to another and which provides a secure fastening between those members. It is a further object of the invention to provide a fastening system which is highly resistant to failure.
SUMMARY OF THE INVENTION
According to a first aspect of the invention there is provided a screw threaded fastener including an elongate shank having a longitudinal axis, a drilling tip at one end of the shank and a head at the opposite end, and a screw thread extending over at least a part of the length of the shank, wherein the screw thread includes a leading flank having an angular disposition relative to the longitudinal axis whereby it slopes outwardly relative to the longitudinal axis in a direction away from the drilling tip and a trailing flank directed outwardly relative to the longitudinal axis at a different angular disposition to that of the leading flank, wherein the angular disposition of the trailing flank is closer to 90° than is the angular disposition of the leading flank.
A screw threaded fastener according to the invention is characterized in that the angle subtended between the longitudinal axis of the screw and the trailing flank of the screw thread is greater than the corresponding angle subtended between said longitudinal axis and the leading flank of the screw thread and wherein the trailing flank angle is closer to 90° than is the leading flank angle. This angular disposition of the trailing flank relative to the leading flank of the screw thread, in use of the fastener, reduces the angle between the trailing flank and the adjacent thin metal section of a batten surrounding the fastener. This has a decreased distorting effect on the thin metal batten under pull out loads on the fastener to that produced by the screw thread of a conventional fastener wherein the leading and trailing flanks slope at substantially the same angle relative to the longitudinal axis of the fastener.
In an example arrangement according to the invention the trailing flank angle is substantially 83° as compared with substantially 60° for the leading flank angle. In each case the angle is the inner subtended angle of the relevant flank so that in the example referred to the angle subtended between the two flanks is substantially 37°. It will be appreciated from the foregoing that in the example referred to the trailing flank slopes outwardly from the fastener axis in a direction towards the tip of the fastener shank.
It is preferred that the fastener includes a drilling portion which terminates at the drilling tip and which has two flutes formed therein on diametrically opposite sides of the fastener axis, wherein each flute extends generally in the direction of the longitudinal axis of the fastener. The terminal end of the fastener shank is formed by the tip of the drilling portion, and that tip preferably comprises two terminal end faces each of which slopes outwardly from the fastener axis in a direction towards the head of the fastener.
The maximum cross sectional dimension of the drilling portion, which portion may be substantially cylindrical, may be selected to suit requirements, but it is preferably substantially equal to the root diameter of the thread of the fastener. In some circumstances the aforementioned dimension could be greater or less than the root diameter.
The threaded portion of the screw fastener extends over a suitable part of the shank length and is located between the drilling portion and the head of the fastener. It is preferred that a section of the threaded portion adjacent the drilling portion is tapered so that the crest diameter of the thread progressively increases from a minimum at the end of the threaded portion adjacent the tip portion to a maximum at a location towards the head of the fastener.
According to a second aspect of the invention there is provided a fastening system including at least one thin metal batten having a support wall, a sheet of roofing or cladding material, and at least one screw threaded fastener as described above, wherein the fastener extends through the sheet and its screw thread is threadably engaged in the support wall of the batten so as to thereby attach the sheet to the batten, wherein the trailing flank of the thread extends outwardly approximately parallel to an adjacent surface of the support wall of the batten surrounding the fastener, and wherein further, the trailing flank subtends an angle relative to the adjacent surface of no more than about 10°.
BRIEF DESCRIPTION OF THE DRAWINGS
It will be convenient to hereinafter describe the invention with particular reference to the accompanying drawings which show an example embodiment of the invention. The particularity of the drawings and related description is not to be understood as superseding the preceding broad description of the invention. More particularly, various other objects, features, and attendant advantages of the present invention will be more fully appreciated from the following detailed description when considered in connection with the accompanying drawings in which like reference characters designate like or corresponding parts throughout the several views, and wherein.
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Doneddu Mark
Roberts David James Alexander
Kent Christopher T.
Maddox Nkeisha J.
Schwartz & Weinrieb
W. A. Deutsher Pty. Ltd.
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