Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Externally threaded fastener element – e.g. – bolt – screw – etc. – Head driving structure
Patent
1993-09-30
1994-11-15
Wilson, Neill R.
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Externally threaded fastener element, e.g., bolt, screw, etc.
Head driving structure
411919, 81460, F16B 2300, F16B 3506, B25B 2300
Patent
active
053642120
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates primarily to a threaded fastening member including an actuating end having a head, the head having a diameter projecting beyond a diameter of the thread of the fastening member and being coaxial with a thread axis; and a centrally located recess within the head for the application of interior forces.
The recesses of these types of prior art screws which are intended for the application of force from the interior, are configured symmetrically. Their axis of symmetry is the axis of the screw thread. The recesses of known screws of this type have different shapes. They may be cruciform, hexagonal, square, rectangular or circular with notched toothing, wedge-shaped toothing or arcuate toothing.
It is known that significant improvements in securing screws against loosening and with respect to their fatigue strength are obtained if they are pre-tensioned to the highest possible level of their pre-tensioning force, i.e., approaching the force at which their shank would break. This high pre-tensioning force cannot be realized with many of the known types of force application to a screw, because the tightening torque is limited. This torque limitation, for example, has the following mechanical causes: reaming of the interior-force application zone, severing of the head due to insufficient strength of the material between the head and the transition to the shank and the base of the interior-force application zone, and breakage of the screwing tool.
One important cause for the limit of the pre-tensioning force of conventional screws of this type is also that the screwing tool, due to axial forces during the assembly process, is pushed axially out of its force application zone. This cam-out effect is the result of a succession of reactive forces between the screwing tool and the force application zone, i.e., in the last analysis, it is the result of the screw torque that is applied.
A further drawback of most configurations of interior-force application zones for a screw is that different tools are required for screwing in different nominal diameters. For example, for mounting many different types of conventional Phillips screws having a nominal diameter ranging from 1.6 to 10 mm, five different sizes of screwdrivers are required. Frequently, each size of screw requires a screwdriver whose size specifically matches the screw.
SUMMARY OF THE INVENTION
It is an object of the invention to provide fastening members, particularly, screws of the above-mentioned type, with a novel geometry of the screw's recess for the application of force from the interior, such that the axial reactive forces are minimized, even if very high torque is applied during the screwing process. This makes it possible for the screwdriver to generate a pre-tensioning force that comes close to the force under which the screw shank would break. This problem is solved by the provision of a recess comprising radial outwardly projecting slots each having two flanks lying in respective planes, each flank plane being essentially tangential to an imaginary cone being co-axial with the thread axis; a pair of segmented circumferential faces separating each slot from an adjacent slot; and a transitional linear inner edge formed between each pair of segmented circumferential faces and each flank of a respective slot, wherein each inner edge converges towards a common point on the thread axis at a position within the fastening member, and each face of each pair is inclined relative to the other face of the pair at an angle, whereby the inner edges define the radially innermost limits of the recess and are for the reception of the interior forces.
Axial reactive forces are prevented on account of this solution. A further advantage is that this geometry of the interior-force application zone may be used in the same manner for screws of any size, so that all screws may be tightened with the same screwing tool.
To facilitate the realization of the above object with respect to manufacturing technology, the interio
REFERENCES:
patent: 2046343 (1936-07-01), Phillips
patent: 2402342 (1946-06-01), Phillips
patent: 2445525 (1948-07-01), Gulden
patent: 2764197 (1956-09-01), Torresen
patent: 3575080 (1971-04-01), Hannay
Julius Soled, P. E., Fasteners Handbook, 1957, p. 111, Chapter Entitled "Screws, Bolts and Studs", Reinhold Publishing Corp.
Richard Bergner GmbH & Co.
Wilson Neill R.
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