The invention relates to a method for producing a screw, in particular a concrete screw, comprising a shaft and screw thread arranged on the lateral surface of the shaft, wherein at least one cut-out recess is provided in the lateral surface of the shaft on a tip of the shaft. Such a method provides that:
The invention relates further to a concrete screw. Such a concrete screw is equipped with a shaft and a screw thread arranged on the lateral surface of the shaft, wherein at least one cut-out recess is provided in the lateral surface of the shaft on the tip of said shaft.
A generic method is known from US 2011274516 A. This document teaches a method for producing a concrete screw, in which initially a screw thread is formed on a shaft, and in which subsequently grooves are milled out of the shaft by means of oblique milling wheels. The milled-out grooves, which are a reflection of the milling wheels, are bounded by sharp edges. As explained in EP 2 233 757 A2 for example, these edges can serve as cutting edges, which can widen a non-ideal cylindrical borehole when the screw is screwed, and which can therefore make it possible to insert concrete screws with a relatively large core diameter and thus with relatively high loading capacities.
The object of the invention is to disclose a method for producing screws, in particular concrete screws, which can be used to simply and inexpensively manufacture screws that can handle a load and are easy to insert, and to disclose a corresponding concrete screw.
A method according to the invention is characterized in that,
A first basic idea of the invention can be seen in arranging the recesses such that at least one of the recesses, preferably all recesses, are not opposite from a corresponding recess so that the cross-section of the workpiece in the area of the recesses is asymmetrical with respect to a mirroring on the longitudinal axis of the workpiece. Accordingly, at least one of the recesses, preferably all recesses, are each opposite from an area that is free of recesses, in other words, an area without a recess, at which the workpiece is configured to be convex, in particular cylinder-segment-like, and/or projecting spherically to the outside. A further basic idea can be seen in that recesses arranged in such a way are rolled over during the thread rolling process, in other words, that at least one, preferably both opposing rolling tools also act on the immediate vicinity of the recesses.
It was surprisingly shown that, in the case of such a procedure, a deformation can occur in the area of the recesses and even in the axial direction going beyond this area, in which a formerly circular shaft cross-section with a uniform curvature is transformed into a non-round cross-section with a curvature, in particular into a cross-section, which approximates a polygonal line. Moreover, it was surprisingly shown that the resulting screws are especially easy to insert with good loading capacities. The formation of a non-round cross-section in the vicinity of the recesses can be attributed under the circumstances to the fact that the free end of the workpiece, at which at least one recess is designed to be asymmetrical, carries out a type of wobbling motion during rolling due to the asymmetrical cross-sectional design, which can possibly build up over the course of the rolling process. The good insertability, in turn, can be attributed to the fact that with the resulting cross-sectional shape in the area of the tip, a friction between the screw core and the borehole wall occurs only locally, without the capability of the screw to widen the borehole being lost.
The method according to the invention is preferably used to produce a concrete screw, i.e., a screw having a self-tapping thread, which can be screwed into a concrete substrate with the formation of a counter thread. Suitably, at least one threaded coil forms, as the case may be after a post-processing, the screw thread in the finished screw, and/or the recess in the lateral surface of the workpiece forms, as the case may be after a post-processing, the cut-out recess in the finished screw. The invention is especially suitable for producing concrete screws with a relatively thick shaft, i.e., for example for such screws, in which the ratio of the outer diameter of the screw thread to the core diameter of the shaft is 1.1 to 1.4. The workpiece and/or the screw are preferably made of a metal material.
The shaft and/or the workpiece expediently have a cylindrical lateral surface at least in sections. The tip of the shaft can be understood in particular as the end of the shaft, which is first introduced into the substrate with proper use of the screw, i.e., the area where the self-tapping screw thread begins. The lateral surface can be understood by definition as especially that outer surface that has a sleeve-like shape.
It is especially expedient that the piece of rod, from which the method according to the invention originates, has a circular cross-section. The piece of rod is preferably configured to be cylindrical, especially preferably circular cylindrical, in particular in the shape of a straight circular cylinder. This makes it possible to further reduce the manufacturing expense, in particular because an alignment of the workpiece can be dispensed with due to the high level of symmetry.
Furthermore, it is advantageous for an uneven number of recesses to be formed in the lateral surface of the workpiece, in particular at least three recesses, preferably precisely three recesses. This makes it possible to maintain the asymmetrical original shape according to the invention especially simply in terms of manufacturing for the thread rolling. Three recesses are preferably provided. Recesses with a relatively large opening can be realized hereby, which can accommodate especially well the stone dust that accrues during cutting.
If a plurality of recesses is provided, it is especially advantageous that the recesses, when seen in the cross-section of the workpiece, are arranged equidistantly. In particular, the workpiece, at least chronologically immediately before the thread rolling process, can have a rotationally symmetric cross-sectional shape, i.e., a shape in which a rotation of the cross-sectional shape around a specific angle brings the cross-sectional shape into congruence with itself. A three-fold rotational symmetry is preferably provided. The manufacturing expense can be reduced even further by this embodiment and/or the insertability and/or load-bearing capacity of the finished screw can be improved even further.
The thread rolling process is preferably a flat-die rolling process, in which two rolling dies, which are moved linearly towards each other, act as rolling tools on the workpiece. This makes an especially favorable and efficient process control possible and the effect in accordance with the invention, whereby a non-round cross-section is generated in sections during thread rolling, can be especially pronounced. The two rolling tools act, according to the invention on diametrically opposite sides of the workpiece. The rolling tools put the workpiece into motion in a rolling rotational direction of the workpiece.
An expedient embodiment is that the recess is introduced in the lateral surface of the workpiece by forming, in particular cold forming, i.e., by a non-machining manufacturing process, in which the workpiece is permanently modified plastically in terms of its shape while retaining its mass and cohesion. This type of non-machining forming process can be integrated especially simply into the manufacturing sequence of the screw and be combined with other steps. In addition, in certain circumstances in the case of a cold forming process, a local strain hardening can occur which can further strengthen the mechanism producing the non-round tip shape.
According to the invention, the recess is introduced in an end area of the workpiece in the lateral surface of the workpiece. It is expedient that the recess be open toward the front side of the workpiece. A design of the recess that is open towards the front can further support the effect in accordance with the invention, whereby a non-round cross-section is generated in sections during thread rolling. Moreover, this design makes an especially simple fabrication using a die possible. Accordingly, it is especially advantageous that the cut-out recess is open towards the front side of the screw.
The recess and therefore the cut-out recess are situated preferably in the tip region of the workpiece or the screw.
It is advantageous that the recess be introduced by compression forming, in particular by impact extrusion. This can be advantageous with respect to the manufacturing expense. By definition, the compression forming process is understood to be forming with predominant compressive stress. To introduce the recess, the workpiece is pressed appropriately into or by a die.
It is especially expedient that the screw have a screw head that is widened with respect to the shaft. This screw head can be used for rotationally fixed coupling with an insertion tool. The screw head can have a polygonal structure for example, preferably an external hexagon, for rotationally fixed coupling with an insertion tool.
It is advantageous in this connection that the workpiece be compressed and a thickening be thereby fabricated at the end. The thickening at the end can be formed in order to form the screw head of the finished screw or to form the screw head immediately.
The manufacturing expense can be reduced by the thickening at the end being fabricated or formed at the same time that the recess is introduced in the lateral surface of the workpiece. To this end, an axial force can be applied with a punch on the end of the workpiece, where the thickening is formed, wherein the axial force drives the workpiece into a die, which forms the recess.
An advantageous design of the method according to the invention is that the recess, which is introduced in the lateral surface of the workpiece, when seen in the cross-section of the workpiece, is asymmetrical. In particular the recess can be asymmetrical to the radial direction of the screw. Because of the asymmetrical design, it is possible for resistance to forming to be reduced when forming the recess, without producing substantial functional losses in the finished screw.
It is especially preferred that a flank of the recess leading in the rolling rotational direction of the workpiece run more steeply with respect to the lateral surface of the workpiece than a flank of the recess trailing in the rolling rotational direction of the workpiece. The resulting asymmetric flow of material can further strengthen the effect which produces the non-round cross-section in the tip region. The rolling rotational direction of the workpiece is understood as the rotational direction in which the workpiece is put into motion by the two rolling tools during the thread rolling process.
A concrete screw according to the invention is characterized in that the shaft has a greater eccentricity in the cross-section of the shaft in a tip region than in a center region, with the tip region being located axially closer to the tip of the concrete screw than the center region. As already explained above, such a shape makes it possible to achieve a good cutting effect with low friction and thus a good insertability with simultaneously high loading capacities. For example, the shaft can have a circular cross-section in the center region and a cross-section in the tip region that approximates a spherical polygon. Eccentricity can be understood in particular as the average or maximum deviation from an ideal circular shape.
It is especially preferred that in the tip region, the shaft have an uneven number of curvature maximums in the cross-section of the shaft, in particular at least three curvature maximums, preferably precisely three curvature maximums. This can result in an especially simple fabrication in a method according to the invention. The screw preferably has an uneven number of cut-out recesses, in particular at least three cut-out recesses, preferably precisely three cut-out recesses.
It is furthermore preferred that the tip region with the greater eccentricity as opposed to the center region extends axially beyond the cut-out recess. In accordance with this embodiment, the non-round tip region extends in particular further away from the screw tip and/or further toward the screw head than the cut-out recess. This can further improve insertability. This embodiment can take into consideration that the cutting effect is frequently concentrated on the end of the cut-out recess, whereas the non-round shape can be in a position to accommodate concrete dust that accrues over its entire length.
The features cited in conjunction with the screw according to the invention can also be used in the method according to the invention, just as, conversely, features cited in conjunction with the method according to the invention can also be used in the screw according to the invention. A concrete screw according to the invention can preferably be manufactured in a method according to the invention.
If one refers to the cross-section of the shaft in conjunction with the invention, this should relate in particular to the cross-section of the shaft exclusively. The screw thread and the cut-out recess are preferably not part of the shaft in the definition of this text, in other words, the screw thread and the cut-out recess can be irrelevant within the meaning of the invention in the consideration of the shaft cross-section, and the shaft cross-section must be interpolated in these areas. A cross-section can be understood in particular as a section perpendicular to the longitudinal axis of the workpiece and/or the screw.
The invention is explained in more detail in the following on the basis of preferred exemplary embodiments, which are depicted schematically in the attached figures, wherein individual features of the exemplary embodiments shown in the following can be realized individually or in any combination in conjunction with the invention. The figures show the following schematically:
As
In the subsequent step of the process, a thickening 19 with an external hexagon is compressed on an end of the workpiece 11, thereby obtaining the intermediate product shown in
In the next step of the process, the thickening 19 is formed further to a screw head 39. During the same step of the process, at the end of the workpiece 11, which is opposite from the thickening 19, three recesses 16 are formed in the cylinder surface of the workpiece 11 by means of a forming process, for example by the end of the workpiece 11 that is opposite from the thickening 19 being pressed into a die. The intermediate product that is obtained hereby is depicted in
Then, as shown in
A threaded coil 13 or even a plurality of threaded coils is formed on the cylinder surface of the workpiece 11 by means of the rolling tools 61 and 62. As
The stage shown in
As
The solid lines in
The measured eccentricity Δr, i.e., the deviation from an ideal circular shape, is plotted in mm in
As
A possible mechanism that can produce the observed locally non-round shaft shape in the case of an uneven number of recesses is evident in
As
The screw-in direction of the threaded coil 13 or the screw thread 33 is shown with an arrow in
Number | Date | Country | Kind |
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10 2013 203 148.3 | Feb 2013 | DE | national |
This application claims the priority of International Application No. PCT/EP2014/052690, filed Feb. 12, 2014, and German Patent Document No. 10 2013 203 148.3, filed Feb. 26, 2013, the disclosures of which are expressly incorporated by reference herein.
Filing Document | Filing Date | Country | Kind |
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PCT/EP2014/052690 | 2/12/2014 | WO | 00 |