Description of Invention

This invention relates to a threaded fastener. A fastener in accordance with the invention has been devised primarily, but not exclusively, for use in wood or materials having similar properties to those of wood.

Numerous types of threaded fasteners, commonly called screws, are known; there are different types of screw-thread varying in respect at least of their thread configuration and/or pitch according to their intended use. What such threaded fasteners have in common, however, is that they are all intended to be driven into the material with which they are to be used by rotation of the fastener so that the thread causes the fastener to penetrate the material. Thus the use of such fasteners to secure components together is a relatively time consuming operation. The time taken to drive a fastener may be reduced by the use of a power screw-driver or the like, but is still significant. Further, access to the fastener to drive it rotationally is not always easy, for example if a person driving the fastener has to reach up to it.

It is one object of the present invention to provide a fastener which enables these problems to be overcome or reduced.

According to the present invention, there is provided a fastener having a shank portion, a head portion at one end of the shank portion, and a tip portion at the other end of the shank portion; wherein at least a part of the shank portion is provided with a screw-thread which does not extend to the tip portion.

Preferably, the head portion has a driving formation therein for cooperation with a tool for driving the fastener by rotation thereof. Such a driving formation may be of any conventional type, e.g. a single elongate slot or a cruciform recess formation. There are different types of cruciform recess formations known for screws: for example that known as the "POZIDRIV" (Registered Trade Mark) recess may be utilized.

Preferably the tip portion of the fastener is substantially symmetrical about the longitudinal axis of the shank portion. Preferably the tip portion is

pointed to a sufficient extent to enable it to penetrate a material such as wood when the fastener is driven by a hammer in the manner of a nail. Thus the tip portion may be generally conical, and may have a substantially smooth outer surface.

The screw-thread preferably extends on the shank portion of the fastener from a position at or near the tip portion, and it may extend therefrom along the entire length of the shank portion to the head portion or may terminate at a position spaced from the head portion.

The thread is preferably a stepped thread, comprising at least one helical thread formation having flanks of which that facing the tip portion of the fastener is inclined at a relatively small angle to the axis of the shank portion, compared with the inclination of the flank facing the head portion of the fastener. The flank of the thread formation facing the head portion of the fastener may afford a shoulder, which may be at an angle at or near 90° to the axis of the shank portion.

Thus penetration of a fastener in accordance with the invention into a material such as wood solely by application of force in the direction of the length of the fastener, e.g. by hammering the head of the fastener, is possible. Withdrawal of the fastener, however, is not readily possibly by mere application of force to the fastener in the opposite direction of its length, since the shoulder afforded by the thread resists such removal. The fastener can, however, be removed by turning it so that it "unscrews" in conventional manner.

The thread may have a pitch which is generally like that of a known type of woodscrew or screw intended for another similar material; it will be appreciated that woodscrews are available having different thread pitches to render them especially suitable for different intended uses, and a fastener in accordance with the invention may similarly have its pitch selected in accordance with its intended use.

In a fastener in accordance with the invention, the difference between the major and minor diameters of the thread will be selected to suit the material

with which the fastener is intended to be used. For a hard wood, the difference between the major and minor thread diameters would be less than if the fastener is intended to be inserted into a soft wood. It is envisaged that fasteners having a major thread diameter of between 2 and 12mm may be provided.

The fastener is preferably produced by rolling in a thread rolling die, and preferably the head portion and tip portion are formed at the same time as the thread. The driving formation in the head may be provided by a subsequent punching operation.

Thereafter, the fastener is preferably heat treated by a process involving heating and then quenching the fastener. The heat treatment process may involve subjecting the fastener to a temperature in the range 400°C to 500°C, for example.

Preferably the fastener is formed from a low carbon steel, e.g. steel with a carbon content of between 0.07% and 0.15%.

The invention will now be described by way of example with reference to the accompanying drawings, wherein:-

FIGURE 1 is a side view of a fastener in accordance with the invention;

FIGURE 2 is a view of part of the fastener, inserted into a material such as wood;

FIGURE 3 is a perspective view of the head portion of the fastener.

Referring to the drawings, a fastener indicated generally at 10 comprises a shank portion 11, a head portion 12, and a tip portion 13. A helical screw thread 15 is provided on a part of the shank portion 11, the thread extending on the shank portion 11 from a region adjacent an upper part 15 of the tip portion to a position spaced beneath the head portion 12.

The head portion 12 has a frusto-conical undersurface 25 like that of a countersunk wood screw, and a flat upper end surface 16. In the head, extending into it from its surface 16, there is a driving recess 26 which, as illustrated, is a cruciform recess of the type known by the registered trade mark

"POSIDRIV". However, it will be appreciated that alternative driving formations, eg a single elongate slot or a recess of other cruciform or, indeed, any other known configuration, could be provided.

The tip portion 13 of the fastener is substantially conical, tapering to a point of sufficient sharpness to enable the fastener to be driven into a material by application of force thereto in the manner of hammering a nail. The tip portion is symmetrical about the axis of the fastener and its external surface is substantially smooth. In particular, it will be noted that the screw thread does not extend to the surface of the tip portion. This enables the fastener to enter a material such as wood in the manner of a nail and since the tip portion is substantially symmetrical about the axis of the fastener, no sideways bias to the fastener is imparted by the tip portion when axial force is applied to the fastener. This contrasts with conventional wood screws which have a thread running fully to the pointed tip of the fastener: in such a case, the thread of helical configuration on the tip would present an angled surface which would impede straight entry of the fastener to a material such as wood if an attempt were made to drive such a fastener by hammering it axially.

The screw thread 14 is provided by a helical thread formation on the shank portion 11, such thread formation being generally of the configuration which is sometimes known as a buttress thread or is herein referred to as a stepped thread. The helical thread formation has its flank (indicated at 14a in Figure 2) which faces the tip portion of the fastener inclined at a relatively shallow angle to the axis of the shank portion of the fastener compared with the inclination of its other flank (14b) which faces the head portion of the fastener. The thread formation thus provides a helical shoulder, indicated at 17, facing the head portion of the fastener and such shoulder may extend at an angle at or near 90° to the axis of the shank portion.

Figure 2 further illustrates the major and minor diameters Dl and D2 of the thread. The difference between such major and minor diameters may be greatest when the fastener is intended for insertion into a relatively soft material.

During insertion of a fastener into a piece 21 of material such as wood, such insertion being by driving the fastener by application of a force thereto, eg by hammering, in the direction Fl, the material 21 is able to be displaced outwardly transversely of the fastener. Due to the resilience of the material 21 it partially returns in the opposite direction so as to occupy regions 18 adjacent the shoulder 17 of the thread. Thus, the fastener remains tightly held by the material 21. To remove the fastener, torque must be applied thereto, as indicated by the arrow F2, so that the fastener is "unscrewed" in the manner of a conventional wood screw.

Insertion of a fastener in accordance with the invention by a hammering action rather than by rotationally driving it is a quick and easy operation, and particularly facilitates use of the fastener when access thereto is restricted, ie when application of a screw driver to the fastener is difficult.

Since the fastener, in accordance with the invention, is made by a thread rolling process, rather than having a pinch-pointed tip portion, manufacture of the fastener is simplified and manufacturing times are reduced

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse forms thereof.