Screw with axial thread play

Abstract

A screw including a shank having a tip, a rear end, which is located opposite the tip, and a longitudinal axis, which extends through the tip and through the rear end, and a screw thread helix, which is arranged on the shank, wherein the screw thread helix has a screw thread ridge for engaging into an internal screw thread groove. The screw thread helix has axial tipward play with respect to the shank, wherein the tipward play increases as the axial distance of the screw thread helix from the tip increases.

Claims

1-15. (canceled)

16. A screw comprising: a shank having a tip, a rear end located opposite the tip, and a longitudinal axis extending through the tip and through the rear end; and a screw thread helix arranged on the shank and having a screw thread ridge for engaging into an internal screw thread groove; the screw thread helix having axial tipward play with respect to the shank, the tipward play increasing as an axial distance of the screw thread helix from the tip increases.

17. The screw as recited in claim 16 wherein the shank has a rearwardly facing flank for axially engaging the screw thread helix, and further comprising a gap between the screw thread helix and the rearwardly facing flank, wherein the gap becomes wider as the axial distance of the adjacent screw thread helix from the tip increases.

18. The screw as recited in claim 17 wherein the rearwardly facing flank is a wedge flank for radially loading the screw thread helix as the shank is loaded rearwardly.

19. The screw as recited in claim 17 further comprising a screw thread helix receiving groove winding around the longitudinal axis of the shank in the shank, the screw thread helix being arranged in the screw thread helix receiving groove, and the rearwardly facing flank delimiting the screw thread helix receiving groove.

20. The screw as recited in claim 19 wherein the screw thread helix receiving groove accommodates the screw thread helix, a width of the screw thread helix receiving groove increasing as the axial distance of the screw thread helix receiving groove from the tip increases.

21. The screw as recited in claim 20 wherein the screw thread helix receiving groove accommodates the screw thread helix, the width of the screw thread helix receiving groove increasing by at least 5% as the axial distance of the screw thread helix receiving groove from the tip increases.

22. The screw as recited in claim 19 wherein the shank has, at the screw thread helix receiving groove, a tipwardly facing flank, wherein the screw thread helix abuts against the tipwardly facing flank.

23. The screw as recited in claim 22 wherein the tipwardly facing flank has constant pitch.

24. The screw as recited in claim 16 wherein the screw thread helix has constant ribbon width.

25. The screw as recited in claim 16 wherein the screw thread ridge has constant pitch.

26. The screw as recited in claim 16 wherein the tipward play continuously increases as the axial distance of the screw thread helix from the tip increases.

27. The screw as recited in claim 16 wherein the screw thread helix has axial tipward play with respect to the shank alongside a fraction of the screw thread helix.

28. The screw as recited in claim 16 wherein the screw thread helix has axial tipward play with respect to the shank alongside all of screw thread helix.

29. The screw as recited in claim 16 wherein the screw thread helix has a helical back, wherein the screw thread ridge radially protrudes from the back, and wherein the back axially protrudes from the screw thread ridge towards the rear end of the shank.

30. The screw as recited in claim 16 wherein the screw thread ridge is free of any mating thread engagement.

31. The screw as recited in claim 16 wherein the screw is a concrete tapping screw, and the shank is a steel shank.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The invention is explained in greater detail below with reference to preferred exemplary embodiments, which are depicted schematically in the accompanying drawings. Individual features of the exemplary embodiments presented below can be implemented either individually or in any combination within the scope of the present invention.

[0040] FIG. 1 is a side view of a screw in an unloaded state.

[0041] FIG. 2 is a sectional view, according to A—A in FIG. 1, of the screw of FIG. 1 in an unloaded state.

[0042] FIG. 3 is a side view of the screw of FIGS. 1 and 2, with the screw thread helix omitted, in an unloaded state.

[0043] FIG. 4 a sectional view, according to A—A in FIG. 3, of the screw of FIGS. 1 to 3, with the screw thread helix omitted, in an unloaded state.

[0044] FIG. 5 is a sectional view of the screw of FIGS. 1 to 4, similar to that of FIG. 2, but in a highly loaded state.

DETAILED DESCRIPTION

[0045] The figures show an embodiment of a screw. The screw comprises a shank 10 having a tip 11 at its front end, and, at its opposite other end, a rear end 18. The tip 11 is that end of the shank 10 which is intended to be inserted first into a borehole. The longitudinal axis 99 of the shank 10 extends through the tip 11 and through the rear end 18.

[0046] 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 shank 10 for installing the screw. In the present embodiment, the drive 19 is a hex drive head connected to the rear end 18. 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.

[0047] The screw furthermore comprises a screw thread helix 20, wherein the screw thread helix 20 and the shank 10 are separate elements. Both the screw thread helix 20 and the shank 10 can consist of metal, preferably of steel.

[0048] The shank 10 is provided with a screw thread helix receiving groove 12, which winds around the shank 10 and around the longitudinal axis 99 of the shank 10. The screw thread helix 20 is positioned in this screw thread helix receiving groove 12.

[0049] The screw thread helix 20 is a ribbon, wherein the ribbon width w.sub.h, of the ribbon, measured parallel to the longitudinal axis 99 of the shank 10, is preferably larger than the ribbon height of the ribbon, measured perpendicular to the longitudinal axis 99 of the shank 10. The screw thread helix 20 might have non-shown additional elements connected thereto, e.g. slanted end elements for avoiding sharp ends, or elements for positioning or fixing the screw thread helix 20 on the shank 10. These additional elements might be helical or non-helical, and/or integral or non-integral with the screw thread helix 20.

[0050] The shank 10 has a rearwardly facing flank 41 and a tipwardly facing flank 42, which delimit opposite sides of the screw thread helix receiving groove 12 (see, e.g., FIG. 3). The rearwardly facing flank 41 and the tipwardly facing flank 42 border the screw thread helix receiving groove 12, and the screw thread helix receiving groove 12 is located between the rearwardly facing flank 41 and the tipwardly facing flank 42. When seen from a location within the screw thread helix receiving groove 12, the adjacent rearwardly facing flank 41 is located closer to the tip 11 than the adjacent tipwardly facing flank 42.

[0051] The rearwardly facing flank 41 thus faces rearwardly, away from the tip 11, whereas the tipwardly facing flank 42 faces forwardly, towards the tip 11. The rearwardly facing flank 41 encloses an acute angle with the longitudinal axis 99, e.g. an angle of about 20°. At the rearwardly facing flank 41, the radius of the shank 10 increases as the axial distance from the tip 11 decreases. When the shank 10 is loaded relative to the screw thread helix 20 rearwardly, in the pull-out direction, i.e. in the direction pointing from the tip 11 of the shank 10 to its rear end 18, the rearwardly facing flank 41 can wedge the screw thread helix 20 to force it radially outwards, away from the longitudinal axis 99. Accordingly, in the present embodiment, the rearwardly facing flank 41 is a wedge flank for radially loading the screw thread helix 20 as the shank 10 is loaded rearwardly. In order to facilitate radial expansion of the screw thread helix 20, not-shown expansion slots can be provided in the screw thread helix 20, for intentionally weakening the screw thread helix 20.

[0052] The tipwardly facing flank 42 includes a relatively high angle with the longitudinal axis 99. In the present embodiment, the tipwardly facing flank 42 is, by way of example, arranged approximately perpendicular to the longitudinal axis 99.

[0053] The screw thread helix 20 comprises a helical back 27 and a helical screw thread ridge 28, which protrudes radially outwardly from the back 27. The screw thread ridge 28 can engage into a single, common first internal thread groove provided in the wall of a borehole in a substrate, in particular a concrete or masonry substrate. The screw thread ridge 28 is arranged at the forward, i.e. tipward, edge of the screw thread helix 20, so that it can be wedged by the rearwardly facing flank 41. In the present embodiment, the screw thread ridge 28 is continuous. Alternatively, it could also be discontinuous and e.g. consist of a plurality of ribs. The helical back 27 can define a friction surface, which can frictionally act against the cylindrical borehole wall.

[0054] As can e.g. be taken from FIG. 2, the screw thread helix 20 has constant ribbon width w.sub.h throughout, with the ribbon width w.sub.h, measured parallel to the longitudinal axis 99. In particular, the ribbon width w.sub.h, can be considered to be the extent of the helically wound ribbon which forms the screw thread helix 20, measured parallel to the longitudinal axis 99.

[0055] As can e.g. be further taken from FIG. 2, the screw thread ridge 28 has constant pitch p.sub.tr, i.e. distance between threads, throughout, with the pitch p.sub.tr, measured parallel to the longitudinal axis 99. The pitch p.sub.t, of the screw thread ridge 28 is equal to the pitch of the forward ribbon edge and/or to the pitch of the rearward ribbon edge of the screw thread helix 20.

[0056] The screw thread helix receiving groove 12 has a width w.sub.g, measured parallel to the longitudinal axis 99. In particular, the width w.sub.g can be considered to be the extent parallel to the longitudinal axis 99 of the screw thread helix receiving groove 12, determined at the surface of the shank 10 which is interrupted by the screw thread helix receiving groove 12. In particular, the width w.sub.g is the axial distance between the foreward edge of the rearwardly facing flank 41 and the rearward edge of the tipwardly facing flank 42.

[0057] As can e.g. be taken from FIG. 4, the width w.sub.g varies in the region where the screw thread helix receiving groove 12 accommodates the screw thread helix 20. In particular, the width w.sub.g continuously increases towards the rear end 18 of the shank 10, i.e. the width w.sub.g continuously increases as the axial distance from the tip 11 increases, in the region where the screw thread helix receiving groove 12 accommodates the screw thread helix 20. Therefore, the width w.sub.g(z2) at location z2 is larger than the width w.sub.g(z1) at location z1, wherein z1 is, along the longitudinal axis 99, located closer to the tip 11 and farther from the rear end 18 than z2.

[0058] As can further be taken e.g. from FIG. 4, the tipwardly facing flank 42 has constant pitch p.sub.tff, at least in the region where the screw thread helix receiving groove 12 accommodates the screw thread helix 20. Pitch p.sub.tff of the tipwardly facing flank 42 can for example be determined at the rearward edge of the tipwardly facing flank 42, which can also be the rearward edge of the screw thread helix receiving groove 12. Pitch is the distance between threads, determined parallel to the longitudinal axis 99.

[0059] Before installation, i.e. in the state shown in FIGS. 1 to 4, the screw thread helix 20 abuts, at the rearward edge of its ribbon, against the tipwardly facing flank 42 of the screw thread helix receiving groove 12 all along the screw thread helix 20. Since the ribbon width w.sub.h, of the screw thread helix 20 is constant, whereas the width w.sub.g of the screw thread helix receiving groove 12 increases as the screw thread helix receiving groove 12 approaches the rear end 18 of the shank 10, a helical gap 44 is formed between the front edge of the screw thread helix 20 and the rearwardly facing flank 41, which gap 44 becomes wider as it approaches the rear end 18 of the shank 10. Due to the gap 44, the screw thread helix 20 has axial forward play on the shank 10, which axial play increases as the distance of the screw thread helix 20 from the rear end 18 decreases.

[0060] If the shank 10 is rearwardly loaded with respect to the screw thread helix 20 during installation or use of the screw, the threads of the screw thread helix 20 that are located closest to the tip 11 of the shank 10 will be axially loaded and radially displaced by the rearwardly facing flank 41 first, since their associated gap width is relatively small or zero from the beginning. On the other hand, threads of the screw thread helix 20 that are located further to the rear, have a wider associated gap 44 and thus a higher distance to travel before hitting the rearwardly facing flank 41, and consequently, they will become loaded and radially displaced by the rearwardly facing flank 41 only at higher loads, when deformation, in particularly of the substrate, becomes significant. This can lead to preferential load transfer starting deep within the borehole in which the screw is located, and progression of the load transfer up the borehole as the screw is becomes more highly loaded.

[0061] In use, the shank 10 of the screw is placed in a borehole in a substrate, in particular a concrete or masonry substrate, so that the screw thread ridge 28 of the screw thread helix 20 engages into an internal screw thread groove provided in the wall of the borehole. If the screw is a tapping screw, this internal screw thread groove can be cut by the screw itself, in particular by its screw thread helix 20, preferably by the screw thread ridge 28. In an alternative embodiment, the screw could, however, also be non-tapping—in this case, the internal screw thread groove could also be provided by a separate thread cutting tool.

[0062] The shank 10 is then loaded in the pull-out direction, i.e. away from the tip 11. This loading will cause the rearwardly facing flank 41 to engage and load the screw thread helix 20 axially rearwardly, and, since the rearwardly facing flank 41 is inclined, also radially outwardly, forcing the screw thread ridge 28 into the borehole wall of the borehole. Due to the varying width of the gap 44 between the front edge of the screw thread helix 20 and the rearwardly facing flank 41, said radial displacement will be initiated at the front end of screw thread helix 20, i.e. deep within the borehole. As the load of the shank 10 is increased, local deformation will occur in the vicinity of the screw. As a result of this deformation, regions of the screw thread helix 20 located closer to the rear end 18 of the shank 10 also overcome the gap 44 and get into axial contact with the rearwardly facing flank 41. As a consequence, load transfer propa-gates rearwards towards the mouth of the borehole as the shank 10 is loaded more and more strongly. FIG. 5 schematically illustrates a very high load situation, in which the shank 10 is so highly loaded that generally all of the gap 44 is closed and that generally all of the screw thread helix 20 abuts against the rearwardly facing flank 41. Due to the progressive load transfer mechanism, concrete loading can be much more homogeneous, in particular with concrete cone failure occurring at relatively deep embedment depths and at relatively high loads.

[0063] As can be taken from FIGS. 1 and 2, the tipward end region of the screw thread helix 20 abuts against the rearwardly facing flank 41 already from the beginning, i.e. the tipward end region, the screw thread helix 20 abuts against the rearwardly facing flank 41 also in an unloaded state of the screw. The gap 44 therefore does not reach into the tipward end region of the screw thread helix 20 and there is no axial play in the tipward end region of the screw thread helix 20. The gap 44 and the axial play are only provided further to the rear.