Screw with axially compressible thread

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, wherein the shank has a rearwardly facing abutment structure, which extends alongside the screw thread helix, for axial abutment of the screw thread helix. The pitch of the screw thread ridge increases as the axial distance of the screw thread ridge from the tip increases, and the screw thread helix has axial tipward play with respect to the rearwardly facing abutment structure, so as to permit axial compression of the screw thread helix.

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, the screw thread helix having a screw thread ridge for engaging into an internal screw thread groove; the shank having a rearwardly facing abutment structure extending alongside the screw thread helix for axial abutment of the screw thread helix; a pitch of the screw thread ridge increasing as an axial distance of the screw thread ridge from the tip increases; and the screw thread helix having axial tipward play with respect to the rearwardly facing abutment structure, so as to permit axial compression of the screw thread helix.

17. The screw as recited in claim 16 wherein the screw thread helix is compressively preloaded.

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

19. The screw as recited in claim 16 wherein the screw thread helix has axial tipward play with respect to the rearwardly facing abutment structure alongside a fraction of the screw thread helix only.

20. The screw as recited in claim 16 wherein the pitch of the screw thread ridge increases continuously as the axial distance of the screw thread ridge from the tip increases.

21. The screw as recited in claim 16 wherein the shank has a tipwardly facing flank and wherein the screw thread helix abuts against the tipwardly facing flank.

22. The screw as recited in claim 21 wherein the screw thread helix abuts against the tipwardly facing flank, the pitch of the tipwardly facing flank increasing as the axial distance of the tipwardly facing flank from the tip increases.

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

24. The screw as recited in claim 16 wherein the rearwardly facing abutment structure is a rearwardly facing flank.

25. The screw as recited in claim 24 wherein the rearwardly facing flank is a wedge flank for radially loading the screw thread helix as the shank is loaded rearwardly.

26. The screw as recited in claim 16 further comprising a screw thread helix receiving groove winding around the longitudinal axis of the shank and provided in the shank, the screw thread helix being arranged in the screw thread helix receiving groove.

27. The screw as recited in claim 26 wherein the screw thread helix receiving groove accommodates the screw thread helix, the width of the screw thread helix receiving groove increasing as the axial distance of the screw thread helix receiving groove from the tip increases.

28. 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.

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

30. The screw as recited in claim 16 wherein the screw is a concrete tapping screw, or a ratio of an outer thread diameter of the screw thread ridge to the pitch of the screw thread ridge is between 1 and 2 at least in some regions of the screw thread ridge.

31. The screw as recited in claim 30 wherein the ratio is between 1.2 and 1.6.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] 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.

[0041] FIG. 1 is a side view of a screw before installation of the screw, i.e. in a pre-installation state.

[0042] FIG. 2 is a sectional view, according to A-A in FIG. 1, of the screw of FIG. 1, before installation of the screw.

[0043] FIG. 3 is a side view of the screw thread helix of the screw of FIG. 1, before it is attached to the screw.

[0044] FIG. 4 is a sectional view similar to FIG. 2 of the screw of FIG. 1, but with the screw thread helix omitted.

[0045] FIG. 5 is a side view of the screw of FIG. 1, but in an installed state (i.e. in a state which is present after the screwing installation of the screw in a hole in a substrate has taken place,).

[0046] FIG. 6 is a sectional view, according to A-A in FIG. 5, of the screw of FIG. 1 in the installed state of FIG. 5.

DETAILED DESCRIPTION

[0047] 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.

[0048] 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.

[0049] 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.

[0050] The shank 10 is provided with a helical 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.

[0051] 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.

[0052] 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.

[0053] 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. 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.

[0054] 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 forms a rearwardly facing abutment structure, intended for abutment of the screw thread helix 20 when the shank 10 is rearwardly loaded, and for tensile load transfer between the shank 10 and the screw thread helix 20.

[0055] 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.

[0056] 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.

[0057] 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 screw 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.

[0058] The screw is a concrete or masonry tapping screw. Accordingly, either the screw thread ridge 28 or not—shown cutting elements, attached preferably to the screw thread helix 20 or elsewhere, are able to cut the internal screw thread groove for the screw thread ridge 28 into a concrete or masonry substrate.

[0059] As can be e.g. derived from comparing FIGS. 3 and 1, the free axial length l.sub.0 of the screw thread helix 20 (see FIG. 3) is greater than the length l.sub.1 of the screw thread helix 20 present on the assembled, but yet non-installed screw (see FIGS. 1 and 2). The screw thread helix 20 is therefore compressively preloaded in the assembled, but yet non-installed state of the screw shown in FIGS. 1 and 2.

[0060] In the assembled, but yet non-installed state of the screw shown in FIGS. 1 and 2, the screw thread helix 20 rests, at the rearwardly facing flank of the screw thread helix 20, against the tipwardly facing flank 42 of the shank 10. As can further be taken e.g. from FIG. 4, the tipwardly facing flank 42 has variable pitch p.sub.tff, at least in the region where the screw thread helix receiving groove 12 accommodates the screw thread helix 20. In particular, the pitch p.sub.tff of the tipwardly facing flank 42 increases as it approaches the rear end 18 of the shank 10 (accordingly, the pitch p.sub.tff(z2) of the tipwardly facing flank 42 at location z2 is greater than the pitch p.sub.tff(z1) of the tipwardly facing flank 42 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). Since the screw thread helix 20 rests against the tipwardly facing flank 42, since the screw thread helix 20 has constant ribbon width w.sub.h and since the relative position of the screw thread ridge 28 on the ribbon of the screw thread helix 20 remains constant along the screw thread helix 20, the pitch p.sub.tr of the screw thread ridge 28 also increases as it approaches the rear end 18 of the shank 10, i.e. as the axial distance of the screw thread ridge 28 from the tip 11 increases. Accordingly, as shown e.g. in FIG. 2, the pitch p.sub.tr(z4) of the screw thread ridge 28 at location z4 is greater than the pitch p.sub.tr(z3) of the screw thread ridge 28 at location z3, wherein z3 is, along the longitudinal axis 99, located closer to the tip 11 and farther from the rear end 18 than z4. (Note that in both cases, pitch is the distance between threads, determined parallel to the longitudinal axis 99 of the shank 10. The 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).

[0061] As can for example be taken from FIG. 4, the pitch p.sub.rff of the rearwardly facing flank 41 is, at almost constant, at least in the region where the screw thread helix receiving groove 12 accommodates the screw thread helix 20. Since, however, the pitch p.sub.tff of the tipwardly facing flank 42 increases as its distance from the tip 11 increases, the width w.sub.g (measured parallel to the longitudinal axis 99 of the shank 10) of the screw thread helix receiving groove 12 (which is formed between the rearwardly facing flank 41 and the tipwardly facing flank 42) likewise increases with increasing distance from the tip 11, at least in the region where the screw thread helix receiving groove 12 accommodates the screw thread helix 20. Accordingly, the width w.sub.g(z2) of the screw thread helix receiving groove 12 at location z2 is greater than the width w.sub.g(z0) of the screw thread helix receiving groove 12 at location z0, wherein z0 is, along the longitudinal axis 99, located closer to the tip 11 and farther from the rear end 18 than z2. (Note that, again, pitch is the distance between threads, determined parallel to the longitudinal axis 99 of the shank 10. The pitch p.sub.rff of the rearwardly facing flank 41 can for example be determined at the forward edge of the rearwardly facing flank 41, which can also be the forward edge of the screw thread helix receiving groove 12. In particular, the width w.sub.g of the screw thread helix receiving groove 12 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 forward edge of the rearwardly facing flank 41 and the rearward edge of the tipwardly facing flank 42.)

[0062] The screw thread ridge 28 has an outer thread diameter d.sub.tr. (See, e.g., FIG. 2). At least near the tip 11 of the non-installed screw, a ratio of the outer thread diameter d.sub.tr of the screw thread ridge 28 to the pitch p.sub.tr of the screw thread ridge 28 is between 1 and 2, in particular between 1.2 and 1.6.

[0063] Since the width w.sub.g of the screw thread helix receiving groove 12 increases towards the rear end 18 of the shank 10, whereas the ribbon width w.sub.h of the screw thread helix 20 remains constant, and since the screw thread helix 20 abuts against the tipwardly facing flank 42 before the screw is installed, a helical axial gap 44 is formed between the screw thread helix 20 and the adjacent rearwardly facing flank 41. This gap 44 provides the screw thread helix 20 with axial tipwards play, which allows that the screw thread helix 20 can be axially compressed when screwing-in the screw, namely in such a way that the pitch p.sub.tr of more rearwardly located sections of screw thread ridge 28 decreases towards smaller pitch values, which pitch values are present near the tip 11 already before installation. The gap 44 widens with increasing distance from the tip 11, i.e. as it approached the rear end 18 of the shank 10, which considers the increasing difference in pitch p.sub.tr of the screw thread ridge 28 towards the rear end 18. In the present embodiment, the most tipward region of the screw thread helix 20 abuts both against the rearwardly facing flank 41 and against the tipwardly facing flank 42, i.e. this region does not have an associated gap 44 and therefore does not have axial play, even before the screw is installed.

[0064] When the screw is installed, the shank 10 with the screw thread helix 20 attached thereto is screwed, tip 11 first, into a generally cylindrical hole in a concrete or masonry substrate. In this process, the screw thread ridge 28 of the screw thread helix 20 starts cutting an internal screw thread groove into the wall of the hole. The pitch of this mating internal screw thread groove will be about the same as the pitch p.sub.tr of screw thread ridge 28 at the tipward end of the screw thread helix 20, since this tipward end engages the substrate first, and since this tipward end is relatively tightly held between the tipwardly facing flank 42 and the rearwardly facing flank 41.

[0065] As the screw-in depth increases, more rearwardly located regions of the screw thread ridge 28 become threaded into the internal screw thread groove which is forming in the hole wall. These more rearwardly located regions of the screw thread ridge 28 initially have pitch mismatch with respect to the internal screw thread groove (the pitch of the screw thread ridge 28 is greater there than the pitch of the internal screw thread groove). However, the axial play (provided by the rearwardly-widening gap 44 located in front of the rearwardly located regions of the screw thread helix 20) allows the rearwardly located regions of the screw thread helix 20 to move forward relative to the shank 10, and therefore allows the pitch p.sub.tr of more rearwardly located regions of the screw thread ridge 28 to adjust to the pitch of the internal screw thread groove. As a result of this pitch adjustment, the screw thread helix 20 will become axially compressed, which axial compression adds to the axial compressive preload of the screw thread helix 20 which is already present before installation of the screw.

[0066] When the screw is fully installed, as shown in FIGS. 5 and 6, the screw thread ridge 28 has finally more or less constant pitch p.sub.tr throughout, the screw thread helix 20 abuts or is at least close to abutting on the rearwardly facing flank 41 throughout, and the screw thread helix 20 is compressed to length l.sub.2 and thereby tensioned with respect to the substrate to an amount resulting from the preloading and the additional compression caused by the pitch alignment. As a consequence, the screw thread helix 20 and the screw thread ridge 28 attached thereto have significant axial tension with respect to the surrounding substrate.

[0067] When the shank 10 is finally axially rearwardly loaded, its rearwardly facing flank 41 abuts against the screw thread helix 20, thereby transferring tensile force from the shank 10 into the screw thread helix 20, and further via the screw thread ridge 28 into the substrate. Since the screw thread helix 20 abuts or is at least close to abutting on the rearwardly facing flank 41 throughout after installation, force transfer from the rearwardly facing flank 41 into the screw thread helix 20 will be relatively uniform all along the screw thread helix 20. The significant axial tension provided between the screw thread helix 20 and the surrounding substrate can allow the system to adjust to varying conditions, for example to dynamic load situations or to non-static cracks in cracked concrete substrates.

[0068] In a preferred embodiment, the pitch p.sub.rff of the rearwardly facing flank 41 is not precisely constant, but has some variations to account for different expansion of the shank 10 and the surrounding substrate, respectively, when the shank 10 is axially loaded.