Thread-forming screw

Abstract

A thread-forming screw which is provided in particular for thin, perforated sheet metal contains a threaded shank which below the screw head is initially configured so as to be cylindrical and then continues to a conical forming portion. The screw shank within the forming portion has a rib forming an incomplete counter thread.

Claims

1. A thread-forming screw for screwing into ductile materials comprising: a screw head including a screw-driving configuration; a screw shank which extends from the screw head to a front screw end, wherein the front screw end is rounded; and a screw thread, wherein a front forming portion of the screw shank has a cross section that decreases in the direction of the front screw end, wherein the screw thread reaches to the front screw end, wherein the screw thread is configured as a sheet metal thread and further wherein at least one rib which intersects the screw thread is configured in the forming portion, wherein the cross section of the screw shank has a trilobular shape.

2. The thread-forming screw as claimed in claim 1, wherein the rib runs obliquely to a longitudinal axis of the screw.

3. The thread-forming screw as claimed in claim 1, wherein the rib runs in an orientation that is reverse to the orientation of the screw thread.

4. The thread-forming screw as claimed in claim 1, wherein an angle (γ) between the rib and the screw thread is greater than 0 degrees and smaller than 180 degrees.

5. The thread-forming screw as claimed in claim 1, wherein the rib runs so as to be steeper than the screw thread.

6. The thread-forming screw as claimed in claim 1, wherein, when viewed in a direction from the front screw end toward the screw head, the rib begins at a spacing (A) from the beginning of the screw thread.

7. The thread-forming screw as claimed in claim 1, wherein, when viewed in a direction from the front screw end toward the screw head, the rib ends ahead of the transition of the forming portion to a cylindrical portion of the shank.

8. The thread-forming screw as claimed in claim 1, wherein the rib extends across two to four thread turns of the screw thread.

9. The thread-forming screw as claimed in claim 1, characterized in that a height of the rib is smaller than the height of the thread turns of the screw thread.

10. The thread-forming screw as claimed in claim 9, wherein a height of the rib is approximately half the size of the height of the thread turns of the screw thread.

11. The thread-forming screw as claimed in claim 1, wherein a plurality of obliquely running ribs that are preferably distributed uniformly across the circumference are provided.

Description

(1) Further features, details, and merits of the invention are derived from the claims and from the abstract, the wording of both being incorporated in the content of the description by way of reference, from the following description of a preferred embodiment of the invention, and by means of the drawing. Individual features of the various embodiments herein can be combined in an arbitrary manner without departing from the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

(2) In the drawing:

(3) FIG. 1 shows a partially sectional lateral view of a screw according to the invention;

(4) FIG. 2 shows a schematic illustration of a thread-forming screw according to the prior art, together with the sectional view of a pre-bored component prior to and after driving in the thread-forming screw;

(5) FIG. 3 shows a schematic illustration of the thread-forming screw according to the invention of FIG. 1, together with the sectional view of a pre-bored component prior to and after driving in the thread-forming screw; and

(6) FIG. 4 shows a schematic illustration of a thread-forming screw according to the invention, according to a further embodiment, together with the sectional view of a pre-bored component prior to and after driving in the thread-forming screw.

(7) FIG. 5 shows a schematic illustration of a thread-forming screw according to the invention, according to a further embodiment.

DETAILED DESCRIPTION

(8) The screw illustrated in FIG. 1 contains a screw head 1 having a flat lower side 2. A screw-driving configuration 4 in the form of a depression, which is one of the usual configurations enabling a transmission of torque, is configured in the end side 3 that is opposite the flat lower side 2. The screw shank 5 extends from the lower side of the screw head 1 to a front end 6 which is configured so as to be rounded in an approximately hemispherical manner.

(9) The screw shank 5 can be roughly subdivided into two portions, specifically a first cylindrical portion 7 that proceeds from the lower side 2 of the screw head 1, and a forming portion 8, adjoining the latter, in which the shank 5 has a continuously decreasing cross section and diameter. In the case of the embodiment illustrated and described, this portion 8 can also be referred to as being shaped in the manner of a truncated cone.

(10) A screw thread 9 extends across the entire length of the shank 5, said screw thread 9 being configured continuously to the front screw end 6. The beginning of the screw thread 9 at the screw end 6 in the illustration of FIG. 1 herein is on that side of the shank 5 that faces away from the observer, and cannot be seen.

(11) In the case of the embodiment illustrated, a rib 10 which extends across approximately three thread turns of the screw thread 9 is configured within the cone-shaped forming portion 8. The rib 10 runs in an orientation that is reversed in relation to the orientation of the screw thread 9. The thread 9 in the exemplary embodiment illustrated is a right-hand thread, while the rib 10 is disposed approximately in the manner of an incompletely configured left-hand thread.

(12) The pitch of the thread formed by the rib 10 is significantly steeper than the pitch of the screw thread 9. The angle α between the longitudinal direction of the rib 10 and the longitudinal axis of the screw in the example illustrated is approximately degrees. The angle γ between the longitudinal direction of the rib 10 and the screw thread 9 is approximately 40 degrees. The angle β between the longitudinal axis of the screw and the screw thread 9 is approximately 95 degrees. The angle γ is the result of the difference between β and α.

(13) When proceeding from the front screw end 6 and the beginning of the screw thread 9, the rib begins only at a spacing A from said front screw end 6 and ends ahead of the transition of the forming portion 8 to the cylindrical portion 7 of the screw shank 5. The axial length B of the region in which the rib 10 is present is smaller than the front rib-free portion A.

(14) As can be likewise derived from the drawing, the height of the rib 10, that is to say the radial spacing of the external edge of said rib 10 from the thread groove of the screw thread 9, is smaller than the thread height of the screw thread. On account thereof, the thread edge of the thread 9 remains present in an undisturbed manner also in the region B.

(15) FIG. 1 shows the screw seen from one side. An identical rib 10 can be present on the opposite side of the screw that is not visible in the figure.

(16) The illustration of FIG. 2 shows a thread-forming screw 20 according to the prior art. It can be immediately seen that the screw thread of this screw 20 does not have any rib which cuts the screw thread.

(17) FIG. 2 furthermore schematically shows a component 22 in which a prepared through opening 24a is provided. The thread-forming screw 20 is driven into the component 22, or into the through opening 24a, respectively.

(18) FIG. 2 furthermore schematically shows the component 22 after screwing in the thread-forming screw 20. The through opening 24a has now been widened to a through opening 24b, the latter having a larger diameter, on the one hand, and a greater length, on the other hand. A passage protrusion 26 which proceeding from the original shape of the component 22 extends in the advancing direction of the screw 20 has been created by driving in the thread-forming screw 20.

(19) However, the passage protrusion 26 is configured so as to be very short and specifically in the case of components 22 having a low material thickness cannot ensure a high resistance to overwinding the screw 20.

(20) The illustration of FIG. 3 shows the thread-forming screw 12 according to the invention as has already been illustrated in FIG. 1. As has already been explained with reference to FIG. 1, the screw 12 has the rib 10 which extends in an orientation reverse to the screw thread 9 over approximately three thread turns of the screw thread 9.

(21) FIG. 3 again shows the component 22 having the prepared through opening 24a.

(22) FIG. 3 furthermore shows the component 22 once the thread-forming screw 12 according to the invention has been driven in. By driving in the thread-forming screw according to the invention, the through opening 24a has been widened to a through opening 24c, the latter in relation to the through opening 24a prior to driving in the screw having a larger diameter and also a greater length. Thus a passage protrusion 28 which in relation to the passage protrusion 26 of FIG. 2 has a significantly greater length has been generated by driving in the thread-forming screw according to the invention. In the case of the schematic illustration of FIG. 3, the length of the passage protrusion 28 is approximately the size of the material thickness of the component 22. The thread-forming screw according to the invention can thus be connected to the component 22 by way of significantly more thread turns, such that a very high resistance to overwinding the screw according to the invention, and also a significantly improved holding force in relation to the conventional screw is achieved.

(23) The enlargement of the passage protrusion herein is created by the effect of the rib 10. When driving in the thread-forming screw according to the invention, the rib 10 displaces material in the region of the wall of the through opening 24a in the advancing direction, thus in a downward manner in FIG. 3. On account thereof, the passage protrusion 28 is elongated in relation to the passage protrusion 26 of FIG. 2.

(24) The illustration of FIG. 4 shows a further thread-forming screw 30 according to the invention. In principle, the screw 30 is configured so as to be identical to the screw 12 according to the invention in FIG. 3, only a rib 32 being disposed not as is the case with the screw 12 in the reversed orientation to the screw thread 9, but in the same orientation as the screw thread 9. The rib 32 with a longitudinal axis of the screw 30 thus forms an angle of −55°.

(25) When driving the screw 30 into the component 22, the through opening 24a on account thereof is not only enlarged in terms of the diameter of the latter, but a first passage protrusion 34 is formed on the lower side of the component 22 that faces away from the screw head, and also a second passage protrusion 36 is created on the side of the component 22 that faces the screw head 30. When driving in the screw 30, the rib 32 acts in a manner that material is displaced from the wall of the through opening 24a upward, counter to the advancing direction, such that the passage protrusion is formed. Surprisingly, however, the rib 32 simultaneously also ensures that the passage protrusion 34 is configured in the advancing direction, and that the passage protrusion 34 is indeed shorter than the passage protrusion 28 of FIG. 3, but still longer than the passage protrusion 26 of FIG. 2.

(26) Specifically in the case of thin sheet metal, a significantly higher holding force and a significantly higher resistance to overwinding can thus be achieved compared with a conventional thread-forming screw 20 by way of the thread-forming screw 12 according to the invention of FIG. 1 and FIG. 3, as well as by way of the thread-forming screw 30 according to the invention of FIG. 4, since on account of the configuration of the passage protrusions 28, and 34, 36, respectively, more thread turns of the screw thread 9 engage in the component 32 once the screws 12, 30 according to the invention have been driven completely into the component 22.

(27) The illustration of fig. 5 shows a further thread-forming screw 50 according to the invention. The screw 50 is configured to have a trilohular shank 52 below the screw head 54.