Thread-forming screw with separate thread sprial and different part flank angles

Abstract

A thread-forming screw has a shank which, in a front region of the shank, has a tip for insertion into a bore in a substrate, and in a rear region of the shank, has a drive for transmitting a torque to the shank. The shank has a spiral-shaped groove and a thread spiral which is inserted into the spiral-shaped groove. The spiral-shaped groove has a front flank and a rear flank disposed opposite the front flank. The front flank, at least regionally, has a different part flank angle than the rear flank.

Claims

1. A thread-forming screw, comprising: a shank, wherein the shank has a tip in a front region of the shank for insertion into a bore in a substrate, a drive in a rear region of the shank for transmitting a torque to the shank, a spiral-shaped groove, and a thread spiral disposable in the spiral-shaped groove; wherein the spiral-shaped groove has a front flank and a rear flank disposed opposite the front flank and wherein the front flank has a part flank angle, at least in a region, that differs from a part flank angle of the rear flank.

2. The thread-forming screw according to claim 1, wherein the part flank angle of the front flank differs from the part flank angle of the rear flank by at least 5.

3. The thread-forming screw according to claim 1, wherein the part flank angle of the front flank is greater than the part flank angle of the rear flank.

4. The thread-forming screw according to claim 1, wherein the thread spiral has a first outer flank and a second outer flank, wherein a thread tip is formed between the first and second outer flanks, and wherein the first and second outer flanks have different part flank angles.

5. The thread-forming screw according to claim 1, wherein the thread spiral is movable along the spiral-shaped groove.

6. The thread-forming screw according to claim 1, wherein the thread spiral is axially fixed on the shank at the tip of the shank.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a perspective representation of the shank of a screw according to the invention without thread spiral;

(2) FIG. 2 is a perspective representation corresponding to FIG. 1 of the screw from FIG. 1 with partly fitted thread spiral;

(3) FIG. 3 is a perspective representation corresponding to FIG. 1 of the screw from FIG. 1 with thread spiral in the operationally ready state;

(4) FIG. 4 is a detail view of the screw from FIG. 3 in the axial section in the region of the rectangle shown in FIG. 3, the tip and the drive of the screw also being roughly schematically represented to illustrate the directions;

(5) FIG. 5 is a detail view corresponding to FIG. 4 of the screw from FIG. 3, the screw being screwed into a hole in a substrate; and

(6) FIG. 6 is a detail view corresponding to FIG. 5, the hole wall, for example, however, being further remote from the shank of the screw than in the case of FIG. 5 due to a tear opening in the case of an earthquake.

DETAILED DESCRIPTION OF THE DRAWINGS

(7) An exemplary embodiment of a screw according to the invention is represented in the Figures. As is shown in particular in FIGS. 1 to 3, the screw has a roughly cylindrical shank 10 at whose front end a tip 11 is provided for insertion into a bore and at whose rear-end region situated opposite the front end, a drive 12 is provided by means of which a torque can be transferred to the shank 10. The drive 12 can, for example, have an inner polygonal structure or an outer polygonal structure. In the present exemplary embodiment, the drive 12 is designed as an end screw head with an outer hexagonal structure. A spiral-shaped groove 20 is provided in the shell surface of the shank 10 which originates from the tip 11 of the shank 10.

(8) The screw also has a thread spiral 30. This thread spiral 30 has the same pitch as the spiral-shaped groove 20 and is arranged in the spiral-shaped groove 20 in the completely fitted state of the screw (see FIG. 3). The thread spiral 30 forms a cutting thread, which cuts a counter thread when the screw is screwed into the substrate.

(9) As is shown in particular in FIG. 1, an end face retaining groove 19 is provided at the tip 11 of the shank 10. As is shown in particular in FIG. 2, the thread spiral 30 has an angled retaining web 39 at its front end at which the thread spiral 30 deviates from a purely helix shape. As is shown in particular in FIG. 3, the retaining web 39 is inserted into the retaining groove 19 when the screw is completely fitted. The thread spiral 30 is hereby fixed on the shank 10 at its front end axially in relation to the longitudinal axis 100 of the shank 10. Otherwise, the thread spiral 30 is arranged in the spiral-shaped groove 20 so as to be displaceable along the spiral-shaped groove 20, which means that the thread spiral 30 can shift helically forward and backward in the spiral-shaped groove 20.

(10) As is shown in particular in FIG. 4, the spiral-shaped groove 20 has two flanks, namely a flank 21 near the tip that is at the front in the longitudinal section of the screw and facing the drive 12 and a flank 22 near the drive that is at the rear in the longitudinal section of the screw and facing the tip 11, the flank 22 being situated opposite the front flank 21. The front flank 21 has the part flank angle .sub.f and the rear flank 22 has the part flank angle .sub.r. Corresponding to the invention, the two part flank angles are different from each other, which means that .sub.f.sub.r. The part flank angle .sub.f of the front flank 21 is in particular greater than the part flank angle .sub.r of the rear flank 22, .sub.f>.sub.r. The two part flank angles preferably differ by at least 2, by at least 5, or by at least 10, in particular .sub.f>.sub.r+2, .sub.f>.sub.r+5 or .sub.f>.sub.r+10. As is customary in the specialist field, the respective part flank angle can, in particular, be understood as the angle between the respective flank and a vertical to the longitudinal axis 100.

(11) A thread base which is, for example, flat, convex or concave can also still be located in the longitudinal section between the two flanks 21 and 22 of the shank 10; the thread base is, however, not represented in the drawings.

(12) The thread spiral 30 has two inner flanks 31 and 32 facing the spiral-shaped groove 20 and/or facing the longitudinal axis 100 of the shank 10, namely a flank 31 near the tip that is at the front in the longitudinal section of the screw and a flank 32 near the drive that is at the rear in the longitudinal section of the screw. The front flank 31 of the thread spiral 30 is adjacent the front flank 21 of the spiral-shaped groove 20 and in particular has at least approximately the same part flank angle as the front flank 21 of the spiral-shaped groove 20. The rear flank 32 of the thread spiral 30 is adjacent to the rear flank 22 of the spiral-shaped groove 20 and in particular has at least approximately the same part flank angle as the rear flank 22 of the spiral-shaped groove 20.

(13) The thread spiral 30 also has two outer flanks 33 and 34 facing away from the spiral-shaped groove 20 and/or facing away from the longitudinal axis 100 of the shank 10, namely a flank 33 near the tip that is at the front in the longitudinal section of the screw and a flank 34 near the drive that is at the rear in the longitudinal section of the screw. The thread tip 38 of the cutting thread of the screw is formed between these two flanks 33 and 34. The front flank 33 of the thread spiral 30 has the part flank angle .sub.f and the rear flank 34 has the part flank angle .sub.r. In the represented exemplary embodiment, these two part flank angles are different from each other, which means that .sub.f.sub.r. The part flank angle .sub.f of the front flank 33 is in particular greater than the part flank angle .sub.r of the rear flank 34, .sub.f>.sub.r, preferably by at least 5 or 10, .sub.f>.sub.r+5 or .sub.f>.sub.r+10.

(14) FIG. 5 shows a detail of the screw after it has been screwed into a hole in a substrate 90. The screw is a thread-forming screw, which means that it and in particular its counter spiral 30 are designed such that they can themselves produce their counter thread when being screwed into a cylindrical hole in the substrate 90. The substrate 90 can in particular be a mineral material, preferably concrete, which means that the screw can preferably be a concrete screw.

(15) FIG. 6 shows a detail corresponding to FIG. 5, according to FIG. 6, however, the hole wall being further remote from the shank of the screw than shown in FIG. 5. The situation of FIG. 6 can, for example, arise in the case of an earthquake when a tear running through the hole in the substrate opens and thus the hole diameter increases sectionally. Since the tensile force F.sub.z represented in FIG. 6 with an arrow acts on the shank 10 of the screw, the front flank 31 of the thread spiral 30 slides off at the front flank 21 of the spiral-shaped groove 20 in the case of a tear opening. In this case, the thread spiral 30 shifts and preferably reversibly shifts radially outward relative to the longitudinal axis 100 and remains in positive-locking engagement with the substrate 90 such that the load-bearing capacity can be largely maintained. As a result of the part flank angle .sub.f of the front flank 21 of the spiral-shaped groove 20 being selected to be greater than the part flank angle .sub.r of the rear outer flank 34 of the thread spiral 30, .sub.f>.sub.r, the relative displacement can be selectively shifted from the contact surface of substrate 90-thread spiral 30 to the contact surface of thread spiral 30-shank 10.