HK1124105B - Self-tapping and thread-forming screw - Google Patents

Abstract

The invention relates to a self-tapping and thread-forming screw (1), having a screw shank (2) with a screw tip (4) at one end and a force application point (6) at the other end for the transmission of torque. The screw shank (2) is composed of a thread section (10), which has the screw tip (4), and an adjoining thread-free shank section (12) which has the force application point (6). The thread section (10) is composed of a shank core (14) and a thread-forming thread (16). The thread section (10) has, in a region remote from the screw tip (4), a core section (20) with a polygonal core cross section which, with its corners (22), defines a circular envelope (24) with a circular envelope diameter (DH) which is greater than the shank diameter (DS) of the thread-free shank section (12).

Description

Self-drilling and thread-forming screw

Technical Field

The invention relates to a self-drilling and thread-forming screw with a screw shank, which has a screw tip at one end and a torque-carrying force-receiving grip (Kraft standard) at the other end. The lead screw is formed of a threaded portion having a screw tip and an unthreaded screw portion having a force-receiving handle attached thereto. The threaded portion is formed by a screw core (Schaftkern) and a single or multiple thread forming the thread.

Background

Such a screw is also referred to as a partially threaded screw due to its unthreaded shank portion. It can be drilled into soft materials, such as wood or similar materials, without prior drilling. It has been found in practice that the unthreaded shank portion produces severe friction when entering the threaded bore formed by the threaded portion, which can lead to a strong detrimental drilling torque.

It is known to provide a so-called screw milling cutter, which is formed by a plurality of radially outwardly projecting milling cutter blades, in the region of the unthreaded shank portion of such partially threaded screws adjacent to the threaded portion. These inserts enable the threaded hole to be enlarged as the screw is drilled, the friction of the shank portion as it enters the threaded hole is reduced and thus the drilling torque will be reduced. However, problems arise in the manufacture of such screws by rolling. Bending deformations of the screw occur in the region of the screw cutters during rolling. That is, such a screw cannot be straightly manufactured without a certain additional process.

Disclosure of Invention

The object of the invention is to create a screw of the type mentioned, which on the one hand can be drilled into material with a low drilling torque and on the other hand can also be produced in a simple and economical manner with high precision, in particular in the straight direction.

According to the invention, the thread portion has a core portion (Kernabschnitt) in a region remote from the thread tip, which core portion has a polygonal core cross-section. The core cross-section forms, at its corners, a shielding ring (hullkreis) with a shielding ring diameter which is greater than the screw diameter of the non-threaded screw portion. The polygonal core cross-section enlarges the threaded bore at its corners during drilling, so that the friction and the drilling torque are reduced during the subsequent drilling of the unthreaded shank portion. According to the invention, the polygonal core is arranged in the region of the threaded portion (not in the region of the unthreaded shank portion), which has the advantage that the screw can be made straight (tight) between the rolling plates in the direction of the thread in the region of the polygonal cross-section of the core, so that no bending in the axial direction of the screw is possible, when the screw is produced by rolling. Thus, the invention makes it possible to manufacture a high-precision screw simply and quickly by a rolling method.

Other advantageous features of the invention will be mentioned in the following claims and in the subsequent description.

Drawings

The invention will be explained more clearly with the aid of two preferred embodiments which are described in detail in the attached drawings. The diagram is as follows:

FIG. 1: according to a side view of the screw in the first preferred embodiment of the present invention,

FIG. 2: according to the enlarged cross-sectional view in plane II-II of figure 1,

FIG. 3: a side view of a second preferred embodiment of a screw according to the invention, an

FIG. 4: according to fig. 3, in an enlarged cross-sectional view in the plane IV-IV.

Detailed Description

A screw 1 according to the invention is formed in both embodiments by a long screw shank 2, which at one end is a screw tip 4 and at the other end is a force-bearing handle 6 for taking up torque. The force-receiving grip 6 is in the embodiment described made as a built-in force-receiving grip and is therefore not visible in the side view. Furthermore, the force-receiving handle 6 is arranged on the side of or in the screw head 8, which is preferably countersunk. The force-bearing handle 6 may be formed as a cross, an inscribed hexagon, an inscribed star, or other similar shapes. In addition, the stressed handle can also be an external stressed handle, such as an external hexagon.

The lead screw 2 is formed by a threaded portion 10 with a screw tip 4 and an associated non-threaded shank portion 12 with a forced grip 6 and a screw head 8. The non-threaded shank portion 12 has a cylindrical surface with a shank diameter DS. The threaded portion 10 is formed of a shank core 14 and a preferably single start thread 16 as described which forms a thread having a helically extending radial peak (Erhebung). The thread 16 with its outer thread edge 18, which is clamped between the two thread flanks, forms an external thread diameter DG.

According to the invention, the threaded part 10 has a core 20 in a region remote from the screw tip 4, which has a polygonal core cross section. As shown in fig. 2 and in cross-section in fig. 4, the polygonal core portion 20 forms a shielding ring 24 with a shielding ring diameter DH at a plurality of corners 22 thereof. This shroud ring is larger in diameter than the screw diameter DS of the unthreaded screw portion 12, but is preferably smaller than the flight diameter DG. Preferably, the diameter DH of the screening ring should be at or below 1.4 times the diameter DS of the screw, preferably 1.1 to 1.2 times. For example, an 8mm screw has a thread diameter DG of 8mm and a screw diameter DS of about 5.6 mm. Thus the diameter DH of the screening ring according to the invention should be about 6.2mm to 6.4 mm.

In a first embodiment, which is shown in detail in fig. 1 and 2, the thread 16 runs through the entire screw core 14, which also includes a polygonal core part 20. The polygonal core portion 20 can thus be directly connected to the unthreaded shank portion 12, preferably at the end region of the shank side of the threaded portion 10 (at the end of the threading). In order to achieve a precise straight line when producing the screw 1 by the rolling method, the polygonal core 20 is drawn precisely, in practice taut, in the two rolled plates by the continuous thread 16. The thread 16 with its outer thread edges 18 runs over the area of the polygonal core 20 in the form of a circular ring (viewed in axial projection) with a constant radius (see fig. 2). Unlike the embodiment shown in fig. 1, a polygonal core 20 provided with flights 16 can also be arranged on the flight portion 10 remote from the non-threaded screw portion 12, a part of the "normal" flight being visible between the portions 20 and 12, with a cylindrical screw core 14.

In the arrangement according to fig. 3 and 4, the polygonal core portion 20 interrupts the thread 16, which is not threaded thereon. Intermediate the polygonal core portion 20 and the unthreaded shank portion 12 is an end region of the threaded portion 10, which preferably has at least one full thread (Gewindegang). According to fig. 3, there may also be at least four complete threads thereon. Therefore, there is a portion of the threaded portion 10 on both axial sides of the polygonal core portion 20, and in this embodiment, precise drawing is also possible at the time of thread rolling, preventing buckling deformation.

The polygonal core portion 20 has an axial length L in both embodiments. The length of L corresponds approximately to the length of a part of the threaded portion 10. This portion has about 1 to 6 threads.

As shown in fig. 2 and 4, the polygonal core cross-section of the core portion 20 preferably has four sides (quadrilateral or square). In principle, it can also be arbitrary, but preferably equilateral triangles up to equilateral hexagons. Thus, the concave-convex amplitude of the side surface is not large in the manufacturing process. The corners 22 should be made as sharp as possible, but may also be rounded.

According to a preferred mode of the invention, the screw tip 4 also has a core 26 with a polygonal core cross-section. The thread 16 passes with its outer thread edge 18 (viewed in axial projection) through the region of the conical screw tip 4 and with a helically continuously decreasing radius through the core 26 to a pointed end 28. Preferably, a transition 30 is provided next to the screw tip 4, which transition has a core 32, which also has a constant polygonal core cross section in the axial direction. This core cross section is adapted in particular to the core cross section which is present in the region of the core 26 of the screw tip 4 directly adjacent to this core cross section. The thread 16 with its outer thread edge 18 passes over the region of the core 32 of the transition portion 30 (also viewed in axial projection), similarly to the other thread portions 10 which are circular in shape with a constant radius.

The core cross section of the core 26 of the screw tip 4 and the core cross section of the core 32 of the transition portion 30 is also preferably a square or a square, or an arbitrary, in particular an equilateral triangle to an equilateral hexagon. The polygonal core 32 of the transition section 30 forms a shadow ring with its corners. The diameter of the shielding ring is greater than the diameter of the screw core 14 but less than the shielding ring diameter DH of the core part 20 according to the invention.

By means of the preferred mode, the screw tip 4 is a drill tip which ensures a centralized and easy drilling.

The present invention is not limited to the embodiments described above, but encompasses all the equivalent means to the present invention. Furthermore, the invention is not limited to the combination of features defined in claim 1, but encompasses any combination of all disclosed features, which means that each feature of claim 1 can be deleted or at least replaced by some other feature of the application, such that claim 1 is only a preliminary description of the invention.

Claims (10)

1. Self-drilling and threading screw (1) having a screw shank (2) with a screw tip (4) at one end and a force-receiving torque handle (6) at the other end, said screw shank (2) being formed by a threaded portion (10) with a screw tip (4) and an unthreaded screw shank portion (12) with a force-receiving torque handle (6) connected thereto, said threaded portion (10) being formed by a screw shank core (14) and threading (16), said threaded portion (10) having a core portion (20) which is located in a region remote from the screw tip (4) and has a polygonal core cross-section, said core portion (20) forming with its corners (22) a shielding ring (24), the shielding ring (24) having a shielding ring Diameter (DH) which is larger than the screw shank Diameter (DS) of the unthreaded screw shank portion (12),

characterized in that said screw flight (16) extends over the entire screw core (14) and also comprises a polygonal core portion (20), which polygonal core portion (20) is provided in the end region of the screw flight portion (10) adjacent to the non-threaded screw portion (12).

2. The screw as set forth in claim 1,

characterized in that the shroud ring Diameter (DH) of the polygonal core portion (20) is 1.4 times or less the screw Diameter (DS) of the unthreaded screw portion (12).

3. The screw as set forth in claim 1,

characterized in that the shroud ring Diameter (DH) of the polygonal core portion (20) is 1.1 to 1.2 times the screw Diameter (DS) of the unthreaded screw portion (12).

4. The screw as set forth in claim 1,

the thread (16) is characterized in that the external thread edges (18) of the thread pass through the area of the polygonal core part (20), and the external thread edges (18) form a circle with a constant radius when viewed in axial projection.

5. The screw as set forth in claim 1,

characterized in that the screw tip (4) has a core (26) with a polygonal core cross section, the thread (16) having its outer thread edges (18) passing through the region of the conical screw tip (4), the outer thread edges (18) passing through the core (26) with a helically tapering radius in axial projection.

6. A screw as in claim 5, which is,

characterized in that a transition section (30) is provided next to the screw tip (4), which transition section has a core (32), which core (32) has an axially constant polygonal core cross section, which core cross section is adapted to the core cross section present in the region of the core (26) of the screw tip (4) directly adjacent to the core cross section, the thread (16) having its outer thread edge (18) passing through the region of the core (32) of the transition section (30), the outer thread edge (18) forming a circle with a constant radius, viewed in axial projection.

7. Screw according to one of claims 1 to 6,

characterized in that said polygonal core portion (20) has an axial length (L) corresponding to the length of a portion of the threaded portion (10) having one to six threads.

8. Screw according to one of claims 1 to 6,

the polygonal core is characterized in that the cross section of the polygonal core is from an equilateral triangle to an equilateral hexagon.

9. Screw according to one of claims 1 to 6,

characterized in that the polygonal core cross-section is square.

10. Screw according to one of claims 1 to 6,

characterized in that the non-threaded shank portion (12) is gradually transformed into a screw head (8) with a stressed handle (6), which is countersunk.