Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Externally threaded fastener element – e.g. – bolt – screw – etc. – Thread or shank structure
Patent
1999-06-21
2000-09-05
Saether, Flemming
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Externally threaded fastener element, e.g., bolt, screw, etc.
Thread or shank structure
4113874, F16B 3504
Patent
active
061133310
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a screw, formed by cold rolling, with a self-tapping single-flight thread, for screwing, in particular, into thermoplastics, with an essentially continuously cylindrical thread bottom and with thread teeth which have a vertex of continuously equal height, the free spaces between adjacent thread teeth being made the same along the thread.
BACKGROUND AND SUMMARY OF THE INVENTION
A screw of this type is known from German patent specification 39 26 000. This screw, regarding which the patent specification expressly points out that it is particularly suitable for setting and adjusting devices, that is to say for so-called movement threads, is to have a high-quality thread, by means of which a continuous and exactly meterable screw-in torque can be achieved. The outlay in terms of forming during the production of the screw by cold rolling is, at the same time, to be lower than in the case of conventional types of screw. In order to achieve this object, the screw possesses a vertex angle of about 40.degree., thus making it easier for the screw material to flow during the cold-rolling process.
The present invention is to provide a screw which, in contrast to the action of a movement thread, is particularly suitable for screwing, in particular, into thermoplastics for fastening purposes. When screws of this type are screwed into plastic, the latter is displaced by the thread teeth penetrating into the plastic, for which purpose the thread cross section must make sufficient free space available. During this time, the plastic displaced by the thread teeth is squeezed into this free space. In this case, German patent specification 27 54 870, column 2, paragraph 1, started from the idea of penetrating as deep as possible into the respective plastic workpiece (high bearing depth), for which purpose, in the case of a flank angle of about 30.degree., a correspondingly large free space must then be made available. To this effect, in the screw according to German patent specification 27 54 870, the thread bottom has a contraction, so that a correspondingly large free space is available for the plastic displaced by the thread teeth. In this case, the plastic displaced by the thread teeth has to cover, from the region of the thread tooth which is penetrated into the plastic, into the thread bottom, a distance over which the displaced plastic loses the direct intimate bond with the non-displaced plastic due to the length of this distance, thus making the said displaced plastic less capable of contributing to the pull-out force. The term "pull-out force" refers to the force necessary for tearing out the screwed-in screw. However, a large free space for receiving displaced plastic results in a correspondingly small thread-bottom diameter (core diameter), and a consequence of this may be that, when such a screw is screwed in, in particular when it is screwed in over a relatively large number of thread flights, it is overloaded by the torque acting on it and breaks off.
The idea of displacing the plastic is also of primary importance in the design of the screw according to European patent specification 0,589,399. This screw, which is designed expressly for a high bearing depth of the thread flanks, is to achieve a material displacement such that the material is compacted on the thread flanks, specifically on those flanks which, as so-called load flanks, have to absorb tear-out forces acting on the screw. In order to influence the flow of material in this way, the screw possesses a conical thread bottom, the smaller core diameter of which is adjacent to the said load flank. The flow of the plastic is thereby to be directed towards the load flank, where the plastic is then to be compacted. This intended flow of plastic presupposes that the material is sufficiently heated and converted into flow and solidification, while the screw is being screwed in. The design of the known screw is therefore based on considerably softening, shifting and compacting the plastic while the screw is be
REFERENCES:
patent: 2742074 (1956-04-01), Rosan
patent: 3726330 (1973-04-01), Adler
patent: 3748949 (1973-07-01), Dreger
patent: 4544313 (1985-10-01), Grossberndt
Grossberndt Herman
Konig Gottfried
EJOT Verbindungstechnik GmbH & Co. KG
Saether Flemming
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