Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Externally threaded fastener element – e.g. – bolt – screw – etc. – Pilot end having means enhancing fastening or installation
Patent
1999-11-01
2000-12-26
Wilson, Neill
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Externally threaded fastener element, e.g., bolt, screw, etc.
Pilot end having means enhancing fastening or installation
411399, 411409, 411919, F16B 2500, F16B 3506
Patent
active
061648876
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
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 hole-forming 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.
2. Description of the Related Art
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, while 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.
The object of the present invention is therefore to provide a screw of the type mentioned in the introduction, with which there can be achieved secure fastening in which the screw is not weakened by a socket drive and a sound joint is not prevented by stripping of the thread.
BRIEF SUMMARY OF THE INVENTION
According to the invention, it is proposed for this purpose that an external tool drive be formed on the head and that, between the head and the thread provided on the shank, there be formed an unthreaded shank portion, whose length is equal to or slightly smaller than the total thickness of the workpieces to be joined to one another.
Heretofore it has always been assumed among experts that, for self-boring 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 into the region of the shank of the screw in the very case in which no countersunk head structure is provided.
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 raises the possibility that the screw can be stripped after it has been finally set. A permanent joint between the two workpieces is then ensured, and so the screw can no longer be loosened 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 torque-dependent manner or caused by a stop.
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 cou
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DIN 7976, Dec. 1972, pp. 371 & 372.
DIN 912, Dec. 1983, p. 1,2, pp. 156 & 157.
DIN 479,Jul. 1968, pp. 73.
SFS Industrie Holding AG
Wilson Neill
LandOfFree
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