Hybrid screw with compartmentalized wedge groove

A screw having a shank, wherein the shank has a tip end, a rear end, and a longitudinal axis extending through the tip end and through the rear end, wherein the tip end and the rear end are opposite ends of the shank, and a screw thread, which is connected to the shank, and which winds around the shank, wherein a wedge groove is provided in the shank, which wedge groove winds around the shank and extends alongside at least a section of the screw thread, wherein the wedge groove is delimited by a rearwardly tapered wedge flank for wedging a grout shell surrounding the shank. At least one ridge is provided within the wedge groove, wherein the ridge compartmentalizes the wedge groove.

BACKGROUND

DE 10311471 A1 as well as EP 2138728 A2, EP 2354567 A1, U.S. Pat. No. 5,885,041 A1 and DE 19820671 A1 each describe screw-like elements which are intended to be installed in boreholes filled with chemical masses.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a screw with an additional grout wedge mechanism, which screw has particularly good performance at particularly low effort.

The invention relates to screws provided with an additional anchor mechanism, namely with a wedge-mechanism. This wedge-mechanism comprises a grout shell that surrounds the shank of the screw and a wedge flank, which is located at a helical wedge groove within the shank of the screw, and which is intended to wedge the grout shell radially outwardly as the shank is axially loaded in the pull-out direction (i.e. as the shank is rearwardly loaded). The invention is based on the fact that typical hardened grouts might have only a limited degree of extensibility. As a consequence, a continuous helical string of hardened grout arranged in the corresponding helical wedge groove cannot readily expand—rather, the helical string needs to, first of all, fracture before the string can be wedged out. Separation of the helical grout string into individual segments (i.e. lamella) might thus be essential for activating the wedge-mechanism.

In view of this, it is proposed to provide at least one axially extending ridge within the wedge groove, which ridge, depending on its height and geometry, can function as a predetermined breaking line for the helical grout string, or can subdivide the helical grout string into segments from the beginning. Accordingly, the at least one ridge provides segmentation of the helical grout string, which activates the wedge mechanism—and it does so in a particularly well-defined manner (in contrast to random fracturing). As a consequence, particularly good performance, in particular a particularly low variance of load bearing capacity, can be achieved in a particularly easy manner.

The shank is an elongate member and can, and in particular, be generally cylindrical, more preferably circular cylindrical. The tip end and the rear end, respectively, constitute opposite ends of the shank. The shank comprises a longitudinal axis, which extends through the rear end and through the tip end of the shank. The tip end is that end of the shank that is intended to be inserted first into a borehole when the screw is installed. The shank might be pointed at the tip end, but is preferably blunt or frustoconical at the tip end, in particular if the screw is a concrete screw. The screw would also comprise a drive for imparting torque on the shank. The drive could be located at the rear end of the shank, for example if the drive is a head, but it could also be located within the shank, for example if the screw is a headless screw.

The screw thread is usually generally helical, but could deviate from a strict mathematical helix, e.g. in order to provide additional functionality. The screw thread winds around the shank and the longitudinal axis of the shank, i.e. it turns helically around the shank, in particular by one or more turns, more preferably by at least two or three turns. The screw thread is an external thread. It radially protrudes from the shank and can engage a mating internal thread. The screw thread is connected to the shank so as to transfer rearwardly directed pull-out loads. The screw thread can be monolithic with respect to the shank, or it can consist of one or more separate parts, which are non-monolithically connected to the shank.

The screw thread is preferably continuous, but could also have interruptions. For example, it could have a sawtooth structure at least in some regions, in particular within a start of the thread. The screw could also be provided with cutting bodies embedded in the screw thread, in particular in the start of the screw thread. For a particular easy design, the screw can comprise only a single screw thread. However, additional screw threads might also be provided, e.g. for additional functionality.

The wedge groove is usually generally helical, but could deviate from a strict mathematical helix, e.g. in order to provide additional functionality. The wedge groove winds around the shank and the longitudinal axis of the shank, i.e. it turns helically around the shank, in particular by one or more turns, more preferably by at least two or three turns. The wedge groove cuts into the shank, namely the lateral surface thereof. The wedge groove extends alongside at least a section of the screw thread, i.e. the screw thread and the wedge groove wind around the shank next to each other in at least a section of the shank. The wedge groove is, amongst others, delimited by the rearwardly tapered wedge flank. This wedge flank, which faces rearwardly (i.e. which faces the rear end of the shank), delimits the wedge groove towards the tip end. In addition, the wedge groove can be delimited, towards the rear end of the shank, by a forwardly facing flank, and optionally at the groove bottom by a bottom surface. The wedge flank, the forwardly facing flank and/or the bottom surface wind around the shank. Usually, these flanks are generally helical, but could deviate from a strict mathematical helix, e.g. in order to provide additional functionality. The wedge flank tapers rearwardly, i.e. it tapers towards the rear end of the shank. Accordingly, the distance of the wedge flank from the longitudinal axis may decrease as it approaches the rear end of the shank in the axial direction. Thus, the wedge flank forms a wedge that can wedge a grout shell surrounding the shank radially outwardly when the shank is loaded axially rearwardly.

The grout shell is a shell of hardened mass arranged within a borehole. The grout can e.g. be a mortar or a synthetic resin.

Throughout this document, wherever the terms “axially”, “longitudinally”, “radially” and “circumferentially” are used, this can, in particular, refer to the longitudinal axis of the shank, which usually coincides with the longitudinal axis of the screw.

The ridge can, preferably, extend parallel to the longitudinal axis. This can efficiently counteract undesired interaction of the grout segments.

The ridge, preferentially, projects from the wedge flank. Accordingly, there are adjacent wedge flank regions located on both sides of the ridge. Thus, the ridge is provided particularly close to the location where separation is required, which can further improve effectiveness of the wedge mechanism. When the ridge projects from the wedge flank, the ridge might also extend into other regions of the wedge groove.

The ridge can be sunk into the wedge groove. In this case, the ridge does not separate the helical grout string from the beginning, but can rather provide a predetermined breaking line, at which the grout string breaks into segments. Alternatively, the ridge can be flush with its surroundings (i.e. adjacent regions). In this case, the ridge might provide a higher degree of separation into segments already from the beginning of the installation process.

According to another preferred embodiment of the invention, a plurality of ridges is provided within the wedge groove, wherein the ridges compartmentalize the wedge groove. Preferentially, at least one ridge is provided per turn of the wedge groove. This leads to a particularly finely granulated segmentation, which might further increase the effectiveness of the wedge mechanism. If a plurality of ridges is provided, at least one of the ridges can be configured as described here in connection with a single ridge. Preferably, all of the ridges are configured in this manner.

As already hinted at above, the screw is preferably a concrete screw, i.e. the screw, in particular the screw thread thereof, is able to, at least partly, tap its mating internal screw thread groove in a concrete substrate. In particular, a ratio of the maximum outer thread diameter of the screw thread to the pitch of the screw thread can be between 1 and 2, in particular between 1.2 and 1.6, at least in some regions of the screw thread, more preferably at least in some regions of the screw thread located near the tip end, most preferably throughout the screw thread. These are typical dimensions for concrete screws.

DETAILED DESCRIPTION

FIGS.1to7illustrate a first embodiment of a screw. The screw comprises an elongate shank10, which has a tip end11. The tip end11is the leading end of the shank10and the shank10is intended to be inserted with the tip end11first into a borehole90when the screw is installed. The shank10also has rear end18, which is located opposite the tip end11. In particular, the shank10can be generally circular cylindrical. The screw furthermore has a screw drive19that is connected to the shank10, monolithically in the present case by way of example, for applying torque to the shank10. In the shown embodiment, the screw drive19is a hex head located at the rear end18, but this is an example only. Any other type of screw drive19can be used, such as an external type, for example hex, line (ALH), square, or a socket head, for example Bristol, clutch, double hex, hex socket, hexalobular socket, line (ALR), polydrive, Robertson, spline, TP3, and others. The screw drive19could also be located within the shank10and/or remote from the rear end18, in particular if the screw is headless and/or internally threaded.

The elongate shank10comprises a longitudinal axis99, extending in the longitudinal direction of the shank10and through both the tip end11and through the rear end18.

The screw furthermore comprises a screw thread30, which is located on the shank10, which winds around the shank10and/or the longitudinal axis99, and which projects radially, with respect to the longitudinal axis99, from the shank10. In particular, the screw thread30is arranged coaxially with respect to the longitudinal axis99. The screw thread30is an external screw thread. The screw thread30is generally helical. However, it could also deviate from a strict mathematical helix, e.g. for additional functionality. In the present embodiment, the shank10and the screw thread30are monolithic. However, alternatively, at least a section of the screw thread30, or all of the screw thread30, might be separate from the shank10. Whereas in the present embodiment, the screw thread30is shown to be a monolithic part, it might also consist of separate elements. In particular, the shank10and/or screw thread30consist of a metal material, preferably a steel material, most preferably a stainless steel. The shank10and/or screw thread30could also be provided with a respective coating, comprising one or more layers.

In the present embodiment, the screw thread30is shown to be continuous. However, it could also be non-continuous, for example in order to provide a serration.

Whereas in the shown embodiment, no additional screw threads are shown, the screw might also have additional screw threads, formed monolithically or non-monolithically with respect to the shank10.

A wedge groove40is provided in the shank10, wherein the wedge groove40projects radially, with respect to the longitudinal axis99, into the shank10. The wedge groove40extends alongside the screw thread30and it flanks the screw thread30, at least a section thereof. Like the screw thread30, the wedge groove40thus winds around the shank10and/or around the longitudinal axis99, and the wedge groove40is generally helical (again with possible deviations from a strict mathematical helix). The helical wedge groove40is arranged coaxially with respect to the longitudinal axis99. In particular, the wedge groove40extends parallelly alongside the screw thread30. In particular, the wedge groove40and the screw thread30have the same pitch.

The wedge groove40is delimited by a forwardly facing flank41and a rearwardly facing flank44. Whereas in the shown embodiment, the forwardly facing flank41merges into the rearwardly facing flank44, there might also be provided a bottom surface adjoining both flank41and flank44, and located between flank41and flank44, which bottom surface delimits the bottom of the wedge groove40. Since the wedge groove40is generally helical, so are the forwardly facing flank41, the rearwardly facing flank44and/or the bottom surface.

The rearwardly facing flank44(see, e.g,FIG.5) is rearwardly tapering, i.e. when seen in a longitudinal section including the longitudinal axis99, its distance from the longitudinal axis99decreases towards the rear end18of the shank10. In other words, the rearwardly facing flank44converges towards the rear end18of the shank10, wherein a focus of convergence can preferably be the longitudinal axis99of the shank10.

The rearwardly facing flank44forms a helical wedge, which is able to wedge a grout shell91that surrounds the shank10radially outwardly as the shank10is rearwardly loaded (Rearwards can be considered the direction pointing, parallel to the longitudinal axis99, from the tip end11to the rear end18of the shank10, which is the direction indicated with a thick arrow inFIG.7. The rearward direction is also the pull-out direction). The flank44can thus form an additional anchoring mechanism for anchoring the shank10in a grouted borehole90, which is effective in addition to an interlock of the screw thread30with the wall of the borehole90. The flank44is thus a wedge flank44for wedging the grout shell91surrounding the shank10.

Wedge-shaped lamellae of the grout shell91may be radially displaced in case of axial displacement of the shank10in the substrate, which for example occurs during tensile loading and especially in cracked concrete condition. As a consequence, a friction and/or deadlock reaction between the shank10and the borehole wall can emerge, which can provide an additional load transfer mechanism between the screw and the substrate.

As can be seen particularly well inFIG.7, a buffer zone49is provided between, in particular axially between, the wedge flank44and the screw thread30located adjacent to the wedge flank44. The buffer zone49adjoins, namely at its rear edge, the wedge flank44, and further adjoins, namely at its front edge, the screw thread30, in particular the rearwardly facing flank of the screw thread30. The buffer zone49is thus sandwiched between the wedge flank44and the screw thread30. In the buffer zone49, the shank10has less rearward taper as compared to the wedge flank44. Accordingly, the cone angle, measured with respect to the longitudinal axis of the shank10, is smaller in the buffer zone49than it is at the wedge flank44. In particular, the taper and/or the cone angle might be zero in the buffer zone49, which is shown in the present embodiment. In this case, the buffer zone49can have a generally circular cylindrical lateral surface, as shown in the present embodiment.

The buffer zone49provides an offset, in the longitudinal direction, between wedge flank44and the screw thread30. This offset can counteract large-surface collision of grout shell lamellae wedged by the wedge flank44with the screw thread30when the shank10is rearwardly loaded, i.e. loaded in the pull-out direction illustrated with the thick solid arrow shown inFIG.7. As a consequence, the lamellae can retain contact with both the shank10and the surrounding substrate, and continue to transfer radial loads.

The rearward taper of the rearward flank of the screw thread30is larger than the rearward taper of the buffer zone49.

The screw is a concrete screw, i.e. the screw thread30is able to tap, in particular cut, a corresponding mating thread in a concrete substrate. In particular, the screw can be so configured that it is able to be anchored within a concrete borehole by means of engagement of the screw thread30only (i.e. without grout). A grout shell91, i.e. a shell of hardened mass, can be provided in order to provide additional anchoring by means of the mechanism described above.

The screw thread30has an outer thread diameter dtr. The ratio of the maximum outer thread diameter dtrof the screw thread30to the pitch ptrof the screw thread30is preferably between 1 and 2, in particular between 1.2 and 1.6. At least one of the following thread parameters can preferably be employed for the screw thread30:dtr/db=1.1 to 1.3 (ratio outer thread diameter to borehole diameter);ptr/db=0.7 to 1.1 (ratio screw thread pitch to borehole diameter);flank angle of the screw thread30=30° to 60°, wherein the screw thread30can have non-symmetric thread cross section, as shown, or, in an alternative embodiment, symmetric cross-section.

The screw thread30has a plurality of turns, namely approximately six turns in the shown embodiment. Preferably, it has at least two turns. In the present embodiment, the screw thread30spans, longitudinally (i.e. in the direction parallel to the longitudinal axis99), approximately 80% of the length lsof the shank10. The screw thread30thus forms a main thread of the screw.

The wedge groove40, on the other hand, has less turns than screw thread30has (the wedge groove40has approximately three turns in the present embodiment), and the wedge groove40spans approximately 40% of the length lsof the shank10. In particular, the screw thread30extends closer to the rear end18of the shank10than does the wedge groove40(and/or the wedge flank44). In particular, the screw thread30extends closer to the rear end18of the shank10than does the wedge groove40(and/or the wedge flank44) by at least one turn of the screw thread30(by approximately two turns in the present embodiment). Accordingly, the screw thread30has at least one turn (two turns in the present embodiment) that is located axially between the rear end18of the shank10and the wedge groove40and/or the screw thread30has at least one turn that is located axially between the rear end18of the shank10and the wedge flank44. In other words, the screw thread30extends closer to the rear end18of the shank10than does the wedge groove40and/or the wedge flank44by at least one time the pitch ptrof the screw thread30. Due to this offset, the wedging mechanism provided by the wedge flank44is concentrated deep within the borehole90, where the loading capacity of the substrate is usually highest, and/or where the substrate can usually absorb radial loads particularly well.

As already mentioned above, the screw thread30might be strictly mathematically helical, but might also deviate from a helical form, which can e.g. provide additional functionality. Likewise, the wedge groove40and/or the wedge flank44might be strictly mathematically helical, but might also deviate from a helical form, which can e.g. provide additional functionality

The screw comprises a plurality of axially extending ridges46(see, e.g.,FIG.1), which are located, at least partly, within the wedge groove40, and which divide the wedge groove40into a helical succession of compartments or bays. In case of the first embodiment shown inFIGS.1to7, the ridges46do not completely cover the longitudinal cross-section of the wedge groove40, and the ridges are slightly sunk into the wedge groove40, as can be for example taken fromFIGS.2and3. In contrast, in the second embodiment shown inFIG.8, the ridges46completely cover the longitudinal cross-section of the wedge groove40, and they are flush with their surrounding regions of the shank10, at least they are flush with buffer zone49. Moreover, in case of the second embodiment, the ridges46are broader as compared to the first embodiment.

In both embodiments, the ridges46form predetermined breaking locations (in particular predetermined breaking lines) or separator locations (in particular separator lines) for the grout shell91that surrounds the shank10, which can cause the grout shell91to divide into individual segments when the shank10is rearwardly loaded, thereby activating the wedging mechanism.

In both embodiments, the ridges46extend longitudinally, in particular they extend generally parallel to the longitudinal axis99. In both embodiments, they project radially outwardly from the wedge flank44and/or from the forwardly facing flank41of the wedge groove40.

Except for the different design of the respective ridges46, the two shown embodiments are generally identical. Therefore, with regards to the details of the embodiment ofFIG.8, reference is made to the description of the embodiment ofFIGS.1to7, which can be applied mutatis mutandis.

The screws of both embodiments can be screwingly inserted into a non-grouted borehole90in a concrete substrate, and the screw thread30can provide sufficient anchoring action. Alternatively, the respective screws can also be installed together with grout (i.e. a hardenable chemical mass) that is filling the gaps between shank10and borehole wall. In this case, grout fills also the individual cone-shaped compartments, so that wedge-shaped grout segments, separated by the ridges46, are formed. In particular, the grout is chosen so that it does not glue or bond to the (steel) surface of the shank10. Any bonding action with the shank10has usually to be minimized (optionally using surface treatment or coatings, e.g. organic wax coatings). In contrast, the grout should bond to the borehole wall, by chemical bonding and/or by mechanical interlock that is provided by any small geometrical “imperfection” such as roughness, local breakouts, corrugations or the like. When the shank10is rearwardly loaded in the axial direction, loads are transferred into the substrate both via mechanical interlock between the screw thread30and the borehole wall and via the wedging mechanism provided by the wedge flank44acting on the (hardened) grout.

In both embodiments, at least one of the following thread parameters can preferably be employed for the wedge groove40:Wgroove/ptr=0.5-0.95 (ratio of width of wedge groove40in axial direction to pitch of screw thread30)Woffset/ptr=0.1-0.5 (ratio of width of buffer zone49in axial direction to pitch of screw thread30)Cone angle α of wedge flank44=5°-30°dr/dc=0.6-1.1 (ratio of diameter of the ridges46to core diameter of screw thread30) Number of ridges46per turn of the wedge groove40: at least one per turn, preferably two ridges46or more per turn