Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Externally threaded fastener element – e.g. – bolt – screw – etc. – Head having counter-sinking means
Patent
1997-05-15
1998-06-30
Wilson, Neill R.
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Externally threaded fastener element, e.g., bolt, screw, etc.
Head having counter-sinking means
411188, F16B 2300, F16B 3506
Patent
active
057723761
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a countersunk head screw having ribs which are arranged on the conical underside of its screw head, project relative to the underside, are present in an even number and have countersinking cutting edges.
Such a countersunk head screw is able by means of its ribs to cut free the countersink in a workpiece for the countersunk head of the screw. German Utility Model 92 02 650 and German Offenlegungsschrift 33 34 212, for example, disclose such countersunk head screws. A common feature of both countersunk head screws is that they have an even number of radial ribs identical to one another, the important factor according to the former publication being to provide a larger number of ribs, namely more than 8. This is intended to permit good distribution of the screwing forces over the countersinking cutting edges formed by the ribs. In the latter publication, it is a matter of configuring the ribs like a milling cutter. In both countersunk screws, all the ribs extend from the outer rim of the screw head to the screw shank.
Such countersunk screws are a mass product which is manufactured with tools which must have a long tool life. In this case, the cold forming of the underside of the screw head is effected by an embossing operation. The configuration of the underside of the screw head has to allow for this, since the embossing tool forms the negative image of the underside of the screw head and accordingly has to be designed with prominences and recesses, which then cause the material of the screw head to flow during the cold forming and in the process are subjected to high loads.
SUMMARY OF THE INVENTION
The object of the invention is to configure the countersunk head screw with regard to the conical underside of its screw head in such a way that, while achieving a good cutting action on the workpiece to be fastened and a favorable chip flow, the ribs have a configuration which permit a robust, rigid design for the embossing tool. According to the invention, this is achieved in that the ribs are present in an even number, of which every second rib, at its end facing the screw shank, has a step which is formed by shortening the relevant rib relative to the adjacent ribs.
On account of the shortening in each case of the second rib, a rib configuration is obtained in which a clearance space results between two unshortened ribs, which clearance space is formed by the latter and the step of the shortened rib and is relatively large in the area where the rib ends facing the screw shank run toward one another so that the ends of the ribs would come very close to one another there if every second rib were not shortened. A correspondingly large projection of the embossing tool can project into this relatively large clearance space; that is, the embossing tool has no especially narrow projections which tend to break away under prolonged loading. However, the rib configuration according to the invention not only makes it easier to design the embossing tool in such a way as to ensure a long tool life, it also enables chips to collect in the clearance spaces when screwing the countersunk head screw into a workpiece, which chips would otherwise have to escape or could exert an undesirable pressure on the material of the workpiece on account of their volume.
The length of the relevant rib following the step is expediently selected in such a way that this length corresponds to about 2/3 of the length of the adjacent ribs. At this length, the shortened rib, in its outer area, is in particular able to participate fully in the cutting of the material of the workpiece when the countersunk head screw is being screwed in and can remove the material cut in this area together with the chips arriving from the inside, while in the radially inner area the material cut there can largely remain in the abovementioned clearance spaces so that a substantially smaller volume of chips is to be conveyed away in this area.
The countersunk head screw dealt with here is often used to screw a
REFERENCES:
patent: 1151861 (1915-08-01), Brumback
patent: 4655661 (1987-04-01), Brandt
patent: 5199839 (1993-04-01), DeHaitre
EJOT Verbindungstechnik GmbH & Co. KG
Wilson Neill R.
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