Expanded – threaded – driven – headed – tool-deformed – or locked-thr – Having separate expander means – Including sleeve and distinct tapered expander
Reexamination Certificate
2002-07-24
2004-04-06
Shackelford, Heather (Department: 3673)
Expanded, threaded, driven, headed, tool-deformed, or locked-thr
Having separate expander means
Including sleeve and distinct tapered expander
C411S080500
Reexamination Certificate
active
06715976
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an expansible fixing plug.
Such expansible fixing plugs are known per se. They comprise a fixing plug sleeve, into which an expansion screw can be screwed, wherein the expansion screw, as it is screwed in, widens the fixing plug. Normally, the fixing plug sleeve has longitudinal slits or slits running at an angle to the lengthwise direction, which divide the fixing plug sleeve into expansible tongues, which are expanded by screwing in the expansion screw. A further possibility is to manufacture the fixing plug sleeve from a resiliently and/or plastically expandable material, especially from a plastics material. As a consequence of the widening or expansion, the expansible fixing plugs are anchored in a drilled hole, for example in masonry.
The known expansible fixing plugs have the drawback that they become loose when the drilled hole becomes enlarged, for example, as a consequence of cracks developing in the masonry, and their anchoring or withdrawal force decreases.
The invention is based on the problem of constructing an expansible fixing plug of the kind mentioned in the introduction in such a way that it has a high anchoring or withdrawal force when the drilled hole becomes enlarged.
SUMMARY OF THE INVENTION
That problem is solved in accordance with the present invention. The expansion screw of The inventive expansible fixing plug has a screw thread, the rear flank of which in the screwing-in direction runs at a shallow angle of about 45° or less to the axial direction of the expansion screw. The flank of the screw thread at the rear in the screwing-in direction forms an oblique or expansion surface, which additionally widens or expands the fixing plug sleeve when the expansion screw is subjected to axial loading in the withdrawal direction. The screw thread forms a cone-like expander body. If a drilled hole in which the expansible fixing plug according to the invention is anchored becomes enlarged, then—when the expansion screw is loaded axially—the expansion screw is pulled a little way axially out of the fixing plug sleeve. As this happens, the flank of the screw is pulled a little way axially out of the fixing plug sleeve. As this happens, the flank of the screw thread at the rear in the screwing-in direction standing at a shallow angle of about 45° or less to the axial direction expands the fixing plug sleeve further, the expansible fixing plug is expanded further remains anchored in the drilled hole with more or less unchanged anchoring force.
The expansible fixing plug according to the invention has the advantage that it has the ability to expand subsequently and is therefore suitable for use in zones subject to tensile forces. A further advantage is a high anchoring force also in a drilled hole that has not become enlarged, and an advantageous ratio between screwing-in torque of the expansion screw necessary to expand the fixing plug sleeve and the anchoring force of the expansible fixing plug in the drilled hole.
Furthermore, the expansion screw of the inventive expansible fixing plug has a core diameter that increases over the length of its screw thread from the front to the rear. The core diameter can increase in steps or gradually. The rearwardly increasing core diameter has the advantage that the screw thread is able to accommodate a relatively large transverse force (bending and shearing stress) in the rear region. The expansion screw is therefore capable of supporting a relatively large load suspended on its rear end and subjecting the expansion screw to transverse load. In addition, a relatively large tensile stress on the expansion screw is also possible, of course, which decreases towards the leading end over the length of the screw thread. Furthermore, the screw thread can be formed right up to the rear end of the expansion screw without sharply reducing the ability of the screw thread to withstand stress as a consequence of a reduction in cross-section of and a stress concentration in of the screw thread. This has the advantage that the fixing plug sleeve can be expanded and subsequently expanded by means of the expansion screw close to a surface, for example of masonry, in which the expansible fixing plug according to the invention is anchored.
In a preferred construction of the invention, the screw thread has a saw-tooth profile, the shallower and longer flank of which, forming the expansion surface, is directed rearwards in the screwing-in direction of the expansion screw. This construction of the invention exhibits good screwing-in behaviour of the expansion screw into the fixing plug sleeve. A further advantage is a large expansion area, formed by the thread flank at the rear in the screwing-in direction, in relation to the axial length of the screw thread.
In a preferred construction of the invention, the core diameter at the rear end of the screw thread corresponds approximately to the diameter of the threadless screw shank adjoining the rear end of the screw thread. In this way, a substantially progressive transition from screw thread to screw shank is achieved. A cross-sectional weakening or stress concentration at the transition from screw thread to screw shank is largely avoided in this construction of the invention. This is particularly advantageous because the transition from screw thread to screw shank is normally located close to a surface, for example of masonry, in which the expansible fixing plug is anchored. Transverse stress on the expansion screw is greatest at the surface of the masonry.
In one construction of the invention, the angle at which the flank of the screw thread at the rear in the screwing-in direction runs is about 28° at the leading end of the screw thread. This produces an angle of taper of approximately 56°, angle of taper referring to the angle of the flank at the rear in the screwing-in direction at opposite points on the screw thread. The angle at which the flank at the rear in the screwing-in direction runs decreases towards the rear end of the screw thread to about 7°, which corresponds to an angle of taper of about 14°. The said angles produce a good ratio between axial force exerted on the expansion screw in the withdrawal direction and expansion force exerted by this force from the expansion screw on the fixing plug sleeve.
If the expansion screw is used in combination with a fixing plug sleeve manufactured from a relatively hard plastics material, it is advantageous to give the shallower and longer thread flank of the screw thread a concave form. The point angle of the thread therefore becomes somewhat smaller, so that the thread cuts its way more easily into the material. Furthermore, the run-out of the thread flank becomes shallower by virtue of the concave construction, which reduces friction at the start of axial displacement of the expansion screw in the fixing plug sleeve for subsequent expansion of the expansible fixing plug and increases it only as the axial displacement progresses. A subsequent-expansion behaviour in which the expansion force of the expansible fixing plug increases progressively with axial displacement is thereby achieved. A further advantage of a concave flank of the screw thread at the rear in the screwing-in direction is a reduced stress concentration by virtue of the relatively small flank angle at the root of the thread.
To create the necessary axial ability to move of the expansion screw for widening and subsequent expansion of the expansible fixing plug, in one construction of the invention the fixing plug sleeve has a yield and/or rupture point, which enables the fixing plug sleeve to elongate axially or to separate into two parts when the fixing plug sleeve is subjected to axial loading. If the fixing plug sleeve of the expansible fixing plug according to the invention is axially loaded, it elongates axially or is separated into two parts. When subjected to axial loading, the rear part of the fixing plug sleeve moves axially, together with the expansion screw located therein, a little way away from a front part of the f
Fischer Rainer
Haug Willi
fischerwerke Artur Fischer GmbH & Co. KG
Saldano Lisa M.
Shackelford Heather
Striker Michael J.
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