Expandable Screw with Separate Expansion Fingers

Abstract

A screw includes a shank where a thread helix receiving groove winds around the shank and is disposed in the shank. A thread helix is disposed in the thread helix receiving groove where the thread helix has an expandable helix section. The shank has, at the thread helix receiving groove, a wedge flank for radially expanding the expandable helix section as the shank is moved relative to the expandable helix section. The expandable helix section has a helical back and a plurality of expansion fingers projecting axially from the helical back towards the wedge flank. The wedge flank of the thread helix receiving groove is configured for radially displacing the plurality of expansion fingers outwardly as the shank is moved relative to the plurality of expansion fingers.

Claims

1.-15. (canceled)

16. A screw, comprising: a shank (10), wherein a thread helix receiving groove (12) that winds around the shank (10) is disposed in the shank (10); and a thread helix (20) which is disposed in the thread helix receiving groove (12); wherein the thread helix (20) has an expandable helix section (25); wherein the shank (10) has, at the thread helix receiving groove (12), a wedge flank (41) for radially expanding the expandable helix section (25) as the shank (10) is moved relative to the expandable helix section (25); wherein the expandable helix section (25) comprises a helical back (27) and a plurality of expansion fingers (30) that project axially from the helical back (27) towards the wedge flank (41), wherein the helical back (27) interconnects the plurality of expansion fingers (30), and wherein the wedge flank (41) of the thread helix receiving groove (12) is configured for radially displacing the plurality of expansion fingers (30) outwardly as the shank (10) is moved relative to the plurality of expansion fingers (30).

17. The screw according to claim 16, wherein at least some of the plurality of expansion fingers (30) are thread-engaging expansion fingers (31) which each comprise a thread engagement element (37) which radially protrudes on the respective thread-engaging expansion finger (31) and wherein the wedge flank (41) of the thread helix receiving groove (12) is configured for radially displacing the thread engagement elements (37) outwardly as the shank (10) is moved relative to the thread-engaging expansion fingers (31).

18. The screw according to claim 17, wherein the thread engagement elements (37) are projecting helical ribs and wherein the thread engagement elements (37) of the thread-engaging expansion fingers (31) form a discontinuous thread.

19. The screw according to claim 17, wherein on at least one thread-engaging expansion finger (31), the respective thread engagement element (37) is disposed at a free axial end of the at least one thread-engaging expansion finger (31).

20. The screw according to claim 17, wherein at least three adjoining expansion fingers (30) of the expandable helix section (25) are thread-engaging expansion fingers (31).

21. The screw according to claim 17, wherein the thread-engaging expansion fingers (31) each have a friction surface (38) and wherein the wedge flank (41) of the thread helix receiving groove (12) is configured for radially displacing the friction surfaces (38) outwardly as the shank (10) is moved relative to the thread-engaging expansion fingers (31).

22. The screw according to claim 21, wherein on at least one thread-engaging expansion finger (31), the respective thread engagement element (37) is located axially between the respective friction surface (38) and a free axial end of the at least one thread-engaging expansion finger (31).

23. The screw according to claim 21, wherein at least some of the friction surfaces (38) have an arcuate cross-section throughout.

24. The screw according to claim 16, wherein the expandable helix section (25) is a ribbon and wherein an axial width (a) of the ribbon is larger than a radial height (f) of the ribbon.

25. The screw according to claim 16, wherein the helical back (27) and at least some of the plurality of expansion fingers (30) are monolithic.

26. The screw according to claim 16, wherein the expandable helix section (25) comprises 2 to 10 expansion fingers (30) per turn of the thread helix (20).

27. The screw according to claim 16, wherein the plurality of expansion fingers (30) are separated by a respective separation slot (50).

28. The screw according to claim 27, wherein the separation slot (50) extends parallel to a longitudinal axis (99) of the screw.

29. The screw according to claim 27, wherein the separation slot extends in a longitudinal plane of the screw.

30. A method of using the screw according to claim 16, comprising the steps of: screwingly inserting the screw into a borehole; and subsequently to the screwingly inserting, loading the shank (10) in a pull-out direction of the screw to radially bias the plurality of expansion fingers (30) via the wedge flank (41).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG. 1 is a perspective representation of a screw.

[0038] FIG. 2 is a perspective representation, similar to FIG. 1, of the screw of FIG. 1, but with the thread helix omitted.

[0039] FIG. 3 is a perspective representation, similar to FIG. 1, of the thread helix of the screw of FIG. 1 only.

[0040] FIG. 4 is a detail side view of the screw in a middle region of the shank.

[0041] FIG. 5 is a cross-sectional view of a detail of a middle region of the screw, in which the cross-sectional plane is a longitudinal plane that runs through one of the separation slots.

DETAILED DESCRIPTION OF THE DRAWINGS

[0042] The figures show an embodiment of an inventive screw. The screw comprises a shank 10 having a tip 11 at its front end. The screw further comprises a drive 19 for transmitting torque to the shank 10 for rotating the shank 10 around the longitudinal axis 99 of the screw. In the present embodiment, the drive 19 is a hex drive provided at a screw head. However, this is an example only, and any type of drive could be used, such as a slotted drive, a cruciform drive, a lobular drive, an internal polygon drive, an external polygon drive or a special drive.

[0043] The screw furthermore comprises a helical thread helix 20, wherein the thread helix 20 and the shank 10 are separate elements. Both the thread helix 20 and the shank 10 can consist of metal.

[0044] The shank 10 is provided with a helical thread helix receiving groove 12, winding around the shank 10 and around the longitudinal axis 99 of the screw. The thread helix 20 is positioned in this thread helix receiving groove 12.

[0045] The thread helix 20 comprises an expandable helix section 25, which can be radially, with respect to the longitudinal axis 99, expanded by the shank 10, as will be explained in detail further below. The expandable helix section 25 is a ribbon, wherein the axial width a of the ribbon is larger than the radial height f of the ribbon. In the present embodiment, the expandable helix section 25 extends along the entire thread helix 20. But this is an example only. The expandable helix section 25 could as well span only a fraction of the thread helix 20.

[0046] The expandable helix section 25 comprises a helical back 27 and a plurality of expansion fingers 30, wherein the helical back 27 and the expansion fingers 30 are preferably monolithic. The expansion fingers 30 axially project from the helical back 27 towards the tip 11 of the screw, i.e., in the forward direction. Neighboring expansion fingers 30 are separated by separation slots 50 which intersect the expandable helix section 25, which separation slots 50 originate at the forward face, i.e., at the tipward face, of the expandable helix section 25, and extend from there rearwardly towards the helical back 27. Neighboring expansion fingers 30 are non-overlapping in the circumferential direction of the screw. The expansion fingers 30 form a helix structure which is intersected by the separation slots 50.

[0047] In the shown embodiment, each of the separation slots 50 extends parallel to the longitudinal axis 99 of the screw, and each of the separation slots 50 extends in a longitudinal plane of the screw, i.e., in a plane that contains the longitudinal axis 99. As can be seen in FIG. 5, the separation slots 50 extend, radially, all the way through the thread helix 20.

[0048] The forward, i.e., the tipward, end of the thread helix receiving groove 12 is delimited by a wedge flank 41. At this wedge flank 41, the radius of the shank 10 increases towards the tip 11. The wedge flank 41 thus faces rearwardly, away from the tip 11. When the shank 10 is moved rearwardly, i.e., in the pull-out direction, relative to the thread helix 20, the wedge flank 41 can abut against the expansion fingers 30 and force them radially outwards, thus expanding the expandable helix section 25 of the thread helix 20.

[0049] In the shown embodiment, all of the expansion fingers 30 are thread-engaging expansion fingers 31. A thread-engaging expansion finger 31 is characterized in that it has a thread engagement element 37, wherein the thread engagement elements 37 of all thread-engaging expansion fingers 31 are so arranged that they can engage into a single, common first female thread groove 67 provided in the wall of a borehole in a substrate 6, in particular a concrete or masonry substrate. Accordingly, all of the thread engagement elements 37 are arranged on a virtual thread helix. The thread engagement elements 37 are projecting helical ribs in the present embodiment, and therefore, the thread engagement elements 37 form, in an overall view, a discontinuous thread crest. The thread engagement elements 37 are arranged at the free forward, i.e., tipward, ends of the thread-engaging expansion fingers 31, so that they can be displaced by the wedge flank 41.

[0050] Adjacent to the thread engagement element 37, which means rearwardly in the present embodiment, each thread-engaging expansion fingers 31 comprises a friction surface 38 intended for frictionally acting in two dimensions against the cylindrical borehole wall 68 of the borehole in the substrate 6. Accordingly, the friction surfaces 38 are intended for pressing against the cylindrical borehole wall 68 on extended surface region. In the present embodiment, the friction surface 38 has arcuate cross-section throughout and has the shape of a cut-out of a cylinder. The friction surfaces 38 are located adjacent to the helical back 27, axially between the helical back 27 and the thread engagement element 37 of the respective thread-engaging expansion finger 31.

[0051] In use, the shank 10 of the screw is placed in a borehole in a substrate 6, in particular a concrete or masonry substrate, so that the thread engagement elements 37 of the thread-engaging expansion fingers 31 all engage into a first female thread groove 67 provided in the wall of the borehole. If the screw is a tapping screw, the first female thread groove 67 can be cut by the screw itself, in particular by its thread helix 20, preferably by the thread engagement elements 37. In an alternative embodiment, the screw could, however, also be non-tapping—in this case, the first female thread groove 67 could also be provided by a separate thread cutting tool. Torsional load transfer between the shank 10 and the thread helix 20 for screwing-in and, if required, tapping action could for example be realized by geometrically interlocking the thread helix 20 with the shank 10 or/and by local joining through welding or brazing.

[0052] The shank 10 is then loaded in the pull-out direction, i.e., away from the tip 11. This loading will cause the wedge flank 41 to load the thread-engaging expansion fingers 31 radially outwardly, forcing the thread engagement elements 37 deeper into the first female thread groove 67 and/or pressing the friction surface 38 against the cylindrical borehole wall 68 of the borehole, both of which mechanisms can improve anchorage of the screw within the substrate.

[0053] In particular, the friction surface 38 can provides additional load transfer due to friction between the deformed expandable helix section 25 and the substrate 6. Moreover, the friction surface 38 can introduce a compressive pressure situation in the substrate 6 that can further increase the loading capacity of the substrate 6, in particular if the substrate 6 is a concrete substrate.

[0054] The expansion fingers 30 and in particular the thread-engaging expansion fingers 31 form a discontinuous helical structure, separated by the separation slots 50. The discontinuous character facilitates radial displacement of the expandable helix section 25 by the wedge flank 41, in particular by reducing circumferential tension.