Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Externally threaded fastener element – e.g. – bolt – screw – etc. – Thread or shank structure
Patent
1999-06-14
2000-12-12
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, F16B 2500
Patent
active
06158939&
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a cold-rolled screw which is intended for screwing into plastic, has a self-tapping thread and of which the thread turns are configured approximately in the manner of knife blades in cross section. The invention also relates to such a screw in which the free end of its shank forms a guide for screwing the screw into a bore.
BACKGROUND AND SUMMARY OF THE INVENTION
Such screws are widely used. As an example, you are referred to the screw according to German Patent 27 54 870. When such a screw is screwed into plastic, the latter is displaced by the thread turns penetrating into the plastic, for which purpose the thread cross section has to provide a sufficient clearance, to be precise a spacing between a screw-receiving bore and the core diameter of the screws. In the case of the known screw, this is also achieved in that the thread root has a narrowed fraction. This means that the plastic material displaced by the thread has to cover the distance between that region of the thread turn which has penetrated into the plastic and the thread root. In this case, the displaced plastic material loses the direct, intimate contact with the undisplaced plastic material, this reducing its capability of contributing to the drawing-out force. The drawing-out force is to be understood as that force which is necessary for pulling out the screwed-in screw.
Furthermore, EP Patent 133 773 describes a screw which is intended for screwing into plastic, has a self-tapping thread and in the case of which, for the purpose of increasing the release torque, the thread flanks, in axial section are rectilinear on one side and are provided with an outwardly directed inflection on the other side. With this thread configuration, it is not possible, during displacement of the plastic, to counteract the loss of contact between displaced and undisplaced plastic. Furthermore, EP Patent 476 831 likewise presents a non-symmetrical configuration of the thread of a screw which is intended for screwing into plastic and has a self-tapping thread, it being the case that this configuration results in the thread turns, in axial section, being rectilinear on one side and being allowed to run in arculate form into the thread root on the other side, the flank angle of the thread thus increasing constantly in the region of the arc. This is intended to improve the displacement of the plastic material with the effect of increasing the drawing-out force.
You are additionally referred to German Utility Model 79 25 469, which discloses a welding tip which is provided with a thread and in the case of which the thread serves for pressing a workpiece, which is provided with an opening, onto the welding tip and for securing the workpiece in that sharp-edged thread crests press into the material of the workpiece and secure the latter against a drawing-out force. In the case of the known welding tip, the thread is provided with sharp edges in that a peripheral phase [sic] is pressed laterally onto the thread crest, said phase [sic] merging with a sharp-edged formation into one thread flank. This necessarily gives a particularly large flank angle of approximately 75.degree. on the thread crest. This configuration means that the thread provided on the known welding tip is not suitable for a screw which is intended for screwing into plastic and has a self-tapping thread since screws for screwing into plastic only ensure a sufficient penetration depth of the thread turns when the cross section of the thread turns is designed approximately in the manner of knife blades (see abovementioned German Patent 27 54 870).
European Patent Application 102 605 presents a thread form which is similar to the configuration of German Utility Model 79 25 469, is intended for a wood screw, but does not have a sharp-edged thread crest, and thus does not have any properties which could make it suitable for screwing into plastic.
The object of the invention is for the self-tapping thread of a cold-rolled screw to be configured, in terms of
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Grossberndt Herman
Konig Gottfried
EJOT Verbindungstechnik GmbH & Co. KG
Saether Flemming
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