AU734237B3 - Screw - Google Patents

Description

AUSTRALIA

Patents Act 1990 SFS Industrie Holding AG

ORIGINAL

COMPLETE SPECIFICATION PETTY PATENT Invention Title: Screw The following statement is a full description of this invention including the best method of performing it known to us:- S ,.zt-J 2 The invention relates to a screw for joining thin workpieces, with a shank and a washer-like head provided with a tool drive, wherein the shank is provided with a thread and at its free end remote from the head has a holeforming or hole-boring point, and wherein the head, measured in the axial direction of the screw, has a height which is smaller than twice the pitch of the thread formed on the shank.

Self-boring and self-tapping screws are usually used precisely for mutual fastening of relatively thin materials or for fastening of thin materials to a fixed substructure, where for technical reasons it is not possible to use countersunk head screws, because an appropriate recess cannot also be formed simultaneously in a workpiece in a single boring and driving process.

If a lining element, such as a plate, is to be subsequently attached in this fastening region, either a corresponding countersunk opening must be made beforehand or screw heads with correspondingly large height must be tolerated, even though they do not allow subsequently mounted plates to rest almost flat on the substructure over a large area.

One object of the present invention is therefore to provide an improved screw.

A screw for joining thin self tapable workpieces, said screw having a 20 shank and a washer-like head provided with a tool drive, wherein said shank is provided with a thread and at its free end remote from the head has a holeforming or hole-boring point, and wherein said head, measured in the axial direction of the screw, has a height which is smaller than twice the pitch-of the thread formed on the shank, characterised in that an external tool drive is formed on said head and that, between said head and said thread provided on the shank there is formed an unthreaded shank portion whose length is dimensioned to allow said threaded portion to substantially traverse said workpieces so as to provide slight engagement or contiguous contact between said remaining thread and the innermost of said workpieces when said screw is finally set.

Heretofore it has always been assumed among experts that, for selfboring and self-tapping screws, the screw head must have an appropriate height in order that the torque for the boring and thread-forming process can be transmitted. Even in the arrangement comprising a socket drive, the head must have an appropriate height, since the socket drive must not penetrate _1P I 2a into the region of the shank of the screw in the very case in which no countersunk head structure is provided.

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*ooo ooo *o By means of the present invention it has been made possible to construct the head of a screw with extremely low height, so that this low head height does not pose a hindrance even during subsequent placement and assembly of lining plates or the like. It has also been shown that the torque for the boring and thread-forming process can be transmitted optimally with an external tool drive, especially when the head of the screw has such a low height.

In the case of fastenings which will subsequently be covered, for example by lining plates, it is usually unimportant if slight assembly traces are left behind under certain circumstances by the tool used. Even when the head has such a low height, it can be held properly until final setting is achieved.

The unthreaded shank portion has been carefully dimensioned such that when the screw is finally set the threaded portion has penetrated the thin workpieces and is left with only a slight engagement or bit or the innermost workpiece or contiguous contact with the innermost workpiece. Therefore the screw can be stripped after is has been finally set and still retains a *permanent joining of the workpiece. A permanent joint between the two or S more workpieces is then ensured, and the screw can no longer be loosened 20 even by turning it in reverse direction. Precisely in the case of such fastenings, in fact, it is merely necessary that the two workpieces be pressed against each other in the fastened position. An additional advantage is that disconnection of the driving tool does not absolutely have to be torquedependent manner or caused by a stop.

25 One advantageous embodiment of the invention provides that the head, measured in axial direction of the screw, has a height which is smaller than the pitch of the thread formed on the shank. In this way there is provided an extremely low height of the head of the screw, which on the one hand permits optimal seizing in a tool by means of the external tool drive, and on the other hand achieves the special advantages that a countersunk opening does not have to be present or to be formed and the projecting head does not cause a hindrance for the subsequent assembly of plates.

In the structural respect, it is advantageous when the head has a polygonal external tool drive. Such a construction can be qualified as particularly simple from the viewpoint both of manufacture and of handling in an appropriate tool.

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.

It is also entirely possible, however, for the head to have a noncircular, curved external tool drive. The features according to the invention make it possible to design a particular external tool drive specific to the user in this case, since the main requirement is to have available a relatively shallow head and, in some or another, an external tool drive.

In this connection it is also conceivable for the head to be provided on its outside periphery with raised structures and/or depressions for forming an external tool drive. In this way the joint between the head and the shank of the screw is always sufficiently good that the necessary torque can be transmitted. This is possible because in contrast to a construction with a socket drive no kind of additional material weak spots are present in the transition region between the head and the shank.

:In order additionally to create the capability of holding the screw S: captively beforehand in a special tool, it is provided that the tool can emerge 20 with the head from behind, at least to a slight extent. This is achieved according to the invention by chamfering the head conically in the direction of the shank.

By further providing that an imaginary inscribed envelope circle on the head is at least approximately as large in diameter as the major diameter of the 25 thread on the shank, it can be additionally brought about that the screw is already guided with its alignment in axial direction when initially started on the workpiece. For example, if the head is square, practically only the corner regions of this square head, which are seized by the appropriate tool, project beyond the major diameter of the thread. When the screw is inserted into 30 this tool, the opening, which then has substantially square cross section, can also be used as a guide for the threaded region of the shank. As the driving-in process progresses, the head of the screw is drawn gradually out of the opening in the driving tool, but the shank itself no longer needs to be guided in this advanced driven-in stage.

Further features according to the invention and special advantages will be illustrated in more detail in the description hereinafter with reference to the drawing, wherein: Figure 1 shows a side view of a screw according to the invention; Figure 2 shows a face view of this screw from the head end; Figure 3 shows, in finally set condition, a screw joining two workpieces to one another; Figure 4 and Figure 5 show two special embodiments of the head of the screw.

Figure 6 shows an embodiment where contiguous contact only occurs between the thread and the inner most workpiece.

Screw 1 comprises a shank 2 and a head 3 provided with a tool drive.

The shank is provided at least partly with a thread 4. In the embodiment shown here, a boring part 5 is formed at the free end of shank 2 remote from head 3. Measured in axial direction of screw 1, head 3 has a height LK which is smaller than twice pitch S of thread 4 formed on shank 2, and it has an external tool drive 6. From the illustrated practical example it is evident that height LK of head 3 is even smaller than pitch S of thread 4. In the S.alternative embodiments according to Figure 1 to 3 there is therefore achieved 20 a head 3 which is constructed substantially in the form of a washer and has a polygonal external tool drive 6, which in the very special case here is a foursided polygon, meaning that in top view head 3 has square shape. If an inscribed envelope circle 7 (Fig. 2) is imagined in such an embodiment of head 3, then obviously it is at least approximately equal in size to major 25 diameter D of thread 4 or, as in the illustrated example, somewhat larger than the said diameter. if an appropriately deep socket which must have square "0 cross section in order to be able to seize head 3 is then provided in a tool in order to allow insertion of a screw, additional guidance for starting the screw on workpieces 8 and 9 to be joined together is achieved in the front region of the tool by its ability to enclose thread 4, even though only a relatively short "'.axial region of the tool is available for engaging appropriately with head 3.

The guidance for the screw itself becomes better the smaller the difference between width B of screw head 3, which is square in this case, and major diameter D of thread 4. The best guidance of all is therefore achieved when width B practically corresponds to diameter D, or in other words when envelope circle 7 has the same diameter as major diameter D of thread 4.

Between head 3 and the thread provided on shank 2 there is expediently provided an unthreaded shank portion 10. In the case of correspondingly thin workpieces 8 and 9 to be joined together, this embodiment permits stripping of the screw without excessive increase in torque. Even if the screw is stripped, workpieces 8 and 9 will be held firmly together, and for practical purposes it is no longer possible for this screwed joint to be loosened by turning screw 1 in reverse direction.

If the special embodiment of a tool permits screw head 3 to be firmly held, then it can be additionally provided that head 3 is conically chamfered in the direction of shank 2. In this case, an undercut as viewed from the screw head 3 toward workpiece 8 would be formed in the final set condition, thus permitting the head to be seized by, for example, radially opening or closing jaws.

In the embodiments according to Fig. 4 and 5, head 3 of screw 1 is also constructed in the form of a washer, but has a noncircular, curved external tool drive 6. The most diverse geometric options for an external tool drive 6 are possible here and, under certain circumstances, it is also conceivable that such screws can be driven in and if necessary loosened again only by :authorised persons. Precisely such forms require a special tool, in order to 20 have any possibility whatsoever of seizing such an external tool drive 6 properly.

The embodiment according to Fig. 5 shows that, in this case, an imaginary envelope circle inscribed in tool drive 6 on head 3 of screw 1 has the same size as diameter D of the thread 4. In such an embodiment, the 25 opening in the corresponding tool is matched to the shape of external tool drive 6, while nevertheless aligned guidance is available for shank 2 in the region of thread 4.

Within the scope of the invention, various embodiments can be provided precisely in the region of head 3. Instead of a polygonal external tool drive or instead of noncircular, curved external tool drives, various ""*raised structures and/or depressions are also possible for forming an appropriate external tool drive.

In the foregoing description it was assumed for screw 1 that a boring part 5 is formed at one end of shank 2. It is equally conceivable to use an appropriate boring tip here or else to provide a hole-forming point. The screw itself can be made in one piece, and of the same material throughout.

It is also conceivable, however, to make boring part 5 or an appropriate boring tip or a hole-forming point from another material and to weld it to the remaining shank portion.

The extremely low head height provided according to the invention proves advantageous in particular if ling plates or the like must be mounted subsequently on workpieces 8 and 9 joined to one another. In the case of elements flush with the wall, for example, no problems of any kind are then encountered with the screw heads, which protrude to only a small extent.

The features according to the invention are naturally also usable in screws which are used in any form as fastening elements. Even if the low head height is chosen not because other plates will also be mounted subsequently, such a shallow head proves to be esthetic even for other types of fastening and, in particular, appropriate security is achieved, since tools suitable for loosening such a screw are hardly available.

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Claims (3)

1. A screw for joining thin self tapable workpieces, said screw having a shank and a washer-like head provided with a tool drive, wherein said shank is provided with a thread and at its free end remote from the head has a hole- forming or hole-boring point, and wherein said head, measured in the axial direction of the screw, has a height which is smaller than twice the pitch of the thread formed on the shank, characterised in that an external tool drive is formed on said head and that, between said head and said thread provided on the shank there is formed an unthreaded shank portion whose length is dimensioned to allow said threaded portion to substantially traverse said workpiece so as to provide slight engagement or contiguous contact between the remaining thread and the innermost of said workpieces when said screw is finally set. C..

2. A screw according to claim 1, characterised in that the head measured in axial direction of the screw has a height (LK) which is smaller than the pitch of the thread formed on the shank.

3. A screw according to claim 1, characterised in that the head has a square external tool drive •Dated this fourth day of April 2001 SFS Industrie Holding AG Patent Attorneys for the Applicant: F B RICE CO F BRICE &GCO