HK1084172B - Thread-cutting screw - Google Patents

Description

Tapping screw

Technical Field

The invention relates to a thread-tapping screw for screwing into a bore hole wall of a bore hole.

Background

A screw of this general type is known, for example, from EP 1129297a (corresponding to us patent No. 09/831707). Wherein a cutting element designed in the form of a blade spindle (Schneid-Einsatz-Schift) is provided in the thread of the screw. Such screws have a good cutting action but are relatively difficult to manufacture, especially in connection with the attachment of the inserted cutting pin to the core.

Furthermore, by the use of the previous disclosure it is known to use a threaded screw which has been carburized to increase the strength, i.e. to increase its carbon content to harden it. Practice has shown that such screws are susceptible to brittle fracture. This is believed to be due to hydrogen permeating into the core and thereby destroying the microstructure of the screw material.

Disclosure of Invention

It is an object of the invention to improve a screw of the type mentioned at the outset in such a way that: i.e., the combination of the cutting element and the core is less demanding in terms of manufacturing costs, while the risk of brittle fracture that occurs in other known tapping screws is avoided.

According to the invention, this object is achieved by a thread-tapping screw for screwing into a bore hole wall of a bore hole, comprising: a cylindrical metal core having a longitudinal central axis; a thread formed integrally with the core; at least one cutting element disposed in the thread for cutting engagement with the bore hole wall, the core being composed of a metal having a carbon content of between 0% and 0.5% by weight and not including 0%, and the at least one cutting element being fixedly attached to the core, characterized in that the cutting element of the thread forming screw is a welded structure in combination with the thread, the cutting element being made of a steel having a carbon content of more than 0.8% by weight, wherein the cutting element projects beyond the thread in a radial direction with respect to the longitudinal center axis.

The invention proceeds from the idea that: i.e. at least one cutting element can be realized by means of a welded construction, which makes it possible to combine the cutting element and the screw by means of welding to form a relatively simple connection which at the same time fully meets the cutting requirements required when screwing the screw into the concrete wall. Providing the screw with a cutting element having a higher carbon content only in well-defined parts, any prior art carburization process may be omitted. Tests have surprisingly shown that: this helps to avoid the risk of brittle fracture. The reason for this is the fact that: welding of the cutting elements causes the screw to be heated only in well-defined localized areas, which may significantly prevent the formation of hydrogen induced (wasserstoffinduzieren) cracks. Core materials having a carbon content of between 0% and 0.5% by weight can be shaped at reasonable cost. Cutting elements made of materials with carbon contents above 0.8% by weight have a hardness that is sufficient for tapping/thread cutting.

According to an aspect of the invention, the core is composed of a metal having a carbon content of less than 0.35% by weight, in particular less than 0.25% by weight, particularly preferably less than 0.2% by weight, more preferably less than 0.15% by weight, even more preferably less than 0.1% by weight. The lower the carbon content, the better the core material can be shaped. It is also conceivable to use a non-carbonaceous material, for example a pure metal such as aluminum or brass, as the core material.

According to a further aspect of the invention, the cutting element consists of steel with a carbon content of more than 1.0% by weight, in particular more than 1.5% by weight or more than 2.0% by weight. The higher the carbon content, the more hard the cutting element is for cutting.

The arrangement and number of such cutting elements has proven to be sufficient for a reliable cutting entry of the screw, i.e., the cutting elements are provided only on the last five thread leads of the thread, in particular on the last three thread leads, particularly preferably on the last two thread leads, and in total less than 15 cutting elements, in particular less than 10 cutting elements, particularly preferably less than 5 cutting elements are provided.

Preferably, there is provided a pilot cutting element at the end of the thread which mates with the cutting end of the screw. Such a pilot cutting element also ensures that the cutting process can be carried out in a controlled manner.

Preferably, the pilot cutting element is longer along the length of the thread than the other cutting elements. Such a pilot cutting element is particularly robust.

The following projections have proved to be a very good compromise between a good cutting action of the cutting element and a tight fit of the screw after cutting. That is, at least one cutting element projects radially beyond the thread with respect to the longitudinal center axis, and the projecting portion of the cutting element is at most 15% of the thread depth; furthermore, at least one cutting element projects axially beyond the thread in the direction of the longitudinal centre axis, and the projecting portions of the cutting elements project maximally 15% of the distance between one another at the transition of the flanks of the thread into the core. But these projections are not required.

The core and/or the cutting element is quenched and tempered after being formed. The tempering of the core material after manufacture and shaping (Verguten) further improves the cutting properties of the screw. However, this subsequent conditioning is not necessary for all applications and designs. Welding the cutting elements to the tempered core material does not cause any change in the structure of the tempered material.

Drawings

The details of the invention will be apparent from the following description of exemplary embodiments, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a side view of a screw;

fig. 2 shows a sectional view on an enlarged scale, broken along the line II-II in fig. 1 and 3;

fig. 3 shows a sectional view on an enlarged scale, broken along the line III-III in fig. 2;

FIG. 4 is a cross-sectional view, similar to FIG. 3, of another embodiment of a screw; and

FIG. 5 is a cross-sectional view, similar to FIG. 3, of yet another embodiment of a screw.

Detailed Description

The tapping screw 1 shown in fig. 1 is a concrete screw which is particularly suitable for screwing into a bore hole wall 1a of a bore hole 1 b. The screw 1 has a cylindrical core 2 made of structural steel with a carbon content in the range of 0.18% by weight. Such steels are well known. The core diameter of the screw 1 is adapted to a drill diameter of 10 mm. The core diameter may also be other diameters within 30 mm. A hexagonal head 3 is integrally formed at one end of the core 2 in a known manner. The core 2 has a longitudinal centre axis 4 which is diagrammatically shown in fig. 1 by means of a dot-dash line.

From the end of the screw 1 opposite the head 3 to approximately the centre of the two ends, the core 2 comprises a thread 5 formed integrally with the core. The thread 5 is a trapezoidal thread (see fig. 3).

The part of the thread 5 that is used for guiding the screw 1 when it enters the borehole is designed as a guide-cutting element 6. The pilot cutting element is embodied as a high speed steel weld structure with a carbon content in excess of 0.8% by weight, in this example 0.85%, as is the case with cutting elements 7 that are disposed immediately following the pilot cutting element 6 within the three thread leads (gewinnergang) of the thread 5. As shown in fig. 1, pilot cutting element 6 is longer along the length of thread 5 than other cutting elements 7. When screwing in, the cutting-guide element 6 immediately forms a thread with a defined pitch on the wall of the bore hole, which allows a precise guidance of the screwed screw 1. The function of the pilot cutting element 6 may be similar to that of the tip of a wood screw. Three cutting elements 7 are arranged on each thread lead behind the pilot cutting element 6, wherein only the first three thread leads of the thread 5 are provided with cutting elements 7, so that there are nine cutting elements 7 in total, two of which can be seen in fig. 1.

The cutting elements 6, 7 are mounted in the thread 5 by welding to continue the thread in unison. The cutting elements 6, 7 project slightly beyond the rest of the thread 5 in both the axial and radial direction of the longitudinal centre axis 4.

The above-mentioned projecting portions are clearly shown in fig. 2 and 3. Due to the welding process when mounted on the thread 5, the cutting element 7 is approximately cup-shaped, while the cup-shaped bottom of the cutting element 7 is inserted into the core 2. The cutting elements 7 project beyond the flanks 8 and the end wall 9 of the thread 5. The radial projection of the cutting element 7 on the thread 5 is indicated with a in fig. 2. In the screw 1, the cutting element has a protrusion a of 5% of the thread depth.

Fig. 3 is a partial cross-sectional view of a screw 1 containing a longitudinal central axis 4, the cross-section being proximate to the cutting element 7 of fig. 2. Fig. 3 shows, in addition to the radial projection a, an axial projection b of the cutting element 7 beyond the thread 5. In fig. 3, the axial projections b are marked and denoted b in the direction of the distance a between each other where the (two) flanks 8 of the thread 5 transition into the core 2. In the screw 1, the size of the convex portion b is 5% of the distance a.

In the thread 5, the thread depth and the distance a are about 2 mm. The bulges a, b are thus about 0.1mm other bulges, for example 0.2mm or 0.3mm, can also be chosen depending on the core diameter and the thread depth.

Other steels may be used for the core 2, the carbon content of which is, for example, less than 0.5% by weight, for example 0.42% by weight; or less than 0.35% by weight, for example 0.30% by weight; or less than 0.25% by weight, for example 0.22% by weight; or less than 0.2% by weight, for example 0.18% by weight; or less than 0.15% by weight, for example 0.12% by weight. Depending on the requirements of the formability of the material used for the manufacture of the core 2 and the thread 5 before the cutting elements 6, 7 are mounted, a steel may be selected whose carbon content meets the respective requirements.

Non-carbonaceous materials such as aluminum or brass may also be used as the core material.

Other steels may also be used as material for the cutting elements 6, 7, said steels having a carbon content of more than 1.0% by weight, for example 1.2% by weight; or more than 1.5% by weight, for example 1.8%, 2.0% or 2.5% by weight. The higher the carbon content, the harder the cutting elements 6, 7.

In an alternative screw, fewer cutting elements 7 may be used, for example four cutting elements or six cutting elements.

In an alternative screw, the cutting elements 7 may be distributed over fewer thread leads, for example only over the last two thread leads. In other designs of the screw, the cutting elements 7 can also be distributed over the last five thread leads.

The number and distribution of cutting elements 6, 7 on the thread 5 depends on the geometry of the screw 1, the thread 5 and the material of the borehole wall. Especially in the case of larger core diameters, a plurality of cutting elements 6, 7 can be provided per thread lead.

The screw 1 is manufactured as follows: a core 2 is first preformed by rolling and pressing, the core having an unprocessed thread and a head 3 integrally formed therewith. The core material is tempered and this step may be omitted for larger diameter screws, for example screws whose core diameter may be used for drilling holes larger than 16 mm. After the thread 5 has been formed, the cutting elements 6, 7 are incorporated into the thread 5 by welding.

Fig. 4 and 5 show other embodiments of screws according to the invention. Elements corresponding to those described with reference to fig. 1 to 3 have the same reference numerals with prime notation and will not be described again in detail.

Fig. 4 shows a thread 5' in the form of a triangular thread. The cutting elements 7 project beyond both flanks 8 'of the thread 5'. The projecting part of the cutting element 7 on the tip of the thread 5 'perpendicular to the longitudinal centre axis 4 is marked with a'.

Fig. 5 shows another embodiment with a thread 5 "in the form of a square thread. The cutting elements 7 project beyond the thread flanks 8 "and the end walls 9" which are parallel to one another in the present case.

Claims (21)

1. A tapping screw (1) for screwing into a bore hole wall (1a) of a bore hole (1b), comprising:

a cylindrical metal core (2) having a longitudinal central axis (4);

a thread (5, 5') integral with said core (2);

at least one cutting element (7) arranged in the thread (5, 5') for cutting engagement with the borehole wall,

the core (2) consists of a metal having a carbon content of between 0% and 0.5% by weight and not including 0%, and

the at least one cutting element (7) is fixedly connected to the core (2);

characterized in that the cutting element (7) is a welded structure in combination with the thread (5, 5 ', 5 "), the cutting element being made of steel having a carbon content of more than 0.8% by weight, wherein the cutting element (7) projects beyond the thread (5, 5', 5") in a radial direction with respect to the longitudinal centre axis.

2. A screw according to claim 1, characterised in that the core (2) consists of a metal having a carbon content of less than 0.35% by weight.

3. A screw according to claim 2, wherein the core (2) is formed of a metal having a carbon content of less than 0.25% by weight.

4. A screw according to claim 3, wherein the core (2) is formed of a metal having a carbon content of less than 0.2% by weight.

5. A screw according to claim 4, in which the core (2) consists of a metal having a carbon content of less than 0.15% by weight.

6. A screw according to claim 5, in which the core (2) consists of a metal having a carbon content of less than 0.1% by weight.

7. A screw according to claim 1, characterized in that the cutting element (7) consists of steel with a carbon content of more than 1.0% by weight.

8. A screw according to claim 7, characterized in that the cutting element (7) consists of steel with a carbon content of more than 1.5% by weight.

9. A screw according to claim 8, characterized in that the cutting element (7) consists of steel with a carbon content of more than 2.0% by weight.

10. A screw according to claim 1, wherein the cutting elements (7) are provided only on the last five thread leads of the threads (5, 5', 5 ").

11. A screw according to claim 1, wherein the cutting elements (7) are provided only on the last three thread leads of the threads (5, 5', 5 ").

12. A screw according to claim 1, wherein the cutting elements (7) are provided only on the last two thread leads of the threads (5, 5', 5 ").

13. A screw according to claim 1, characterized in that less than 15 cutting elements (7) are provided in total.

14. A screw according to claim 13, characterized in that less than 10 cutting elements (7) in total are provided.

15. A screw according to claim 14, wherein less than 5 cutting elements (7) are provided in total.

16. A screw according to claim 1, characterized in that there is provided a pilot cutting element (6) at the end of the thread (5, 5', 5 ") which matches the cutting end of the screw (1).

17. A screw according to claim 16, wherein the pilot cutting element (6) is longer along the length of the thread (5, 5', 5 ") than the other cutting elements (7).

18. A screw according to claim 1, wherein the protruding portion (a, a ', a ") of the at least one cutting element (7) protruding radially beyond the thread (5, 5', 5") with respect to the longitudinal centre axis (4) is at most 15% of the thread depth.

19. A screw according to claim 1, characterised in that at least one cutting element (7) projects axially beyond the thread (5, 5 ', 5 ") in the direction of the longitudinal centre axis (4), and that the projecting part (b, b ', b") of the cutting element (7) amounts to at most 15% of the distance (A, A ', a ") between the flanks (8, 8 ', 8") of the thread (5, 5 ', 5 ") at the transition into the core (2).

20. A screw according to claim 1, wherein the core (2) and/or the cutting element (7) is shaped and then subjected to a thermal refining process.

21. A screw as claimed in claim 1, wherein the screw is a concrete screw.