Self-tapping screw The contents of German patent application DE 10 2021 211 692.2 are in- corporated here by reference.
The invention relates to a self-tapping screw.
Screws which can be screwed into a borehole in a material in a self-tapping manner are known in the art, in particular from WO 2019/194920 A1, DE
202016 107016 Ul and DE 20 2012 101 482 U1. These self-tapping screws have a cutting thread suitable for cutting a thread, on which the screw 1s anchored, in an inner borehole wall.
The object of the present invention is to provide a self-cutting screw which can be screwed into a borehole in an uncomplicated, failsafe manner.
This object is achieved according to the invention by a screw having the features set out in claim 1.
— According to the invention, it has been found that various measures regard- ing the configuration of a self-tapping screw have an advantageous effect on its screw-in properties.
The screw comprises a core, which has a longi- tudinal axis, a nominal diameter and an insertion end.
The core is formed in particular cylindrically about the longitudinal axis.
A first measure is to form the insertion end without a thread and with an in- sertion length.
The insertion end is in particular tapered at least in portions with respect to the core.
The insertion end simplifies inserting the self-tap- ping screw into a borehole.
Because the insertion end is formed without a thread, tilting of the screw with respect to a borehole longitudinal axis is prevented.
By way of the insertion end, the self-tapping screw is arranged stably in the borehole and facilitates the start of the screw-in process.
It is advantageous if the insertion length is at least 15% of the nominal diameter and at most 75% of the nominal diameter, in particular between 20% and 70% of the nominal diameter, in particular between 20% and 60% of the nominal diameter, in particular between 25% and 50% of the nominal di- ameter and in particular between 30% and 40% of the nominal diameter.
A further measure is for at least one longitudinal groove to be arranged on the insertion end.
The longitudinal groove extends in particular along the longitudinal axis of the core, in other words in the axial direction of the screw.
The longitudinal groove is formed as an outer groove on the outer surface of the screw.
The longitudinal groove extends in particular from an outer end face of the screw, the outer end face in particular being arranged on the insertion end.
It is possible for a plurality of longitudinal grooves, in particular two, three or more, to be arranged on the insertion end.
The lon- gitudinal grooves may be formed identically, in particular in terms of groove shape and/or groove length.
The longitudinal grooves are spaced apart, in particular uniformly spaced apart, in the circumferential direction in terms of the longitudinal axis.
The at least one longitudinal groove makes it possible to receive material which may still be arranged in the borehole, for example in the form of — bore dust, after the drilling process and/or which is cut out from the bore- hole by the screw-in process as a result of the thread being cut.
The risk of the self-tapping screw being blocked by material in the borehole when be- ing screwed in is reduced.
It has been found that the screw-in properties of the self-tapping screw are improved if both of the aforementioned measures are implemented. The self-tapping screw is in particular a concrete screw. The self-tapping screw is produced from a metal material, in particular from a steel material, which is in particular galvanized and/or zinc-flake-coated. In particular, the self-tapping screw is produced from a material having designation 1.4401,
1.4404, 1.4571, 1.4578 and/or 1.4529. Other metal, in particular steel, ma- terials are possible. The cutting thread is arranged in a cutting-thread portion, which is formed integrally on the core. In the cutting-thread portion, the screw has a shaft diameter. The self-cutting screw further comprises a torgue-transmission portion, which is formed integrally on the core. The torque-transmission portion serves in particular to transmit a torque to the screw, in particular by means of a tool. — The self-cutting screw is for screwing into a borehole in a material which is in particular hard and/or porous in form, in particular concrete. The self- cutting screw is in particular a concrete screw. The screw is in particular produced in one piece. The screw is in particular — for screwing into a borehole in a hard material, in particular concrete. The screw is produced in particular with a nominal diameter dn of 5 mm, 6 mm, 8 mm, 10 mm, 12 mm, 14 mm or 16 mm. Other nominal diameters are also possible.
A screw in which the at least one longitudinal groove has a groove length which is greater than the insertion length enables reliable removal of mate- rial, in particular bore dust.
Because the groove length is greater than the insertion length, it is ensured that material, in particular bore dust, can be transported from the cutting-thread portion to the end-face end of the screw during the screw-in process.
It is advantageous if the at least one longitudi- nal groove ends before the cutting thread.
The cutting thread is formed without a longitudinal groove.
The cutting thread is not interrupted by the longitudinal groove.
The longitudinal groove does not detract from the cut- ting performance of the screw.
In particular, the at least one longitudinal groove and the cutting thread are arranged in succession, and in particular not overlapping, along the longitudinal axis of the screw.
A screw according to claim 2 can be inserted into the bore hole particularly stably.
The screw is inserted into the borehole by the insertion end and thus radially braced and centred.
The risk of the screw tilting with respect to the borehole is reduced and in particular eliminated.
In particular, the contact pressure on the screw during screwing into the borehole, in particular at the
— start of the screw-in process, can be reduced.
This additionally reduces the risk of the screw tilting.
In particular, the screw can be screwed in without contact pressure.
In a screw according to claim 3, the cutting thread has a thread pitch which
1s at least 50% of the nominal diameter and at most 95% of the nominal di- ameter.
In particular, the thread pitch is at least 60% of the nominal diame- ter, in particular at least 70% of the nominal diameter, in particular at least 75% of the nominal diameter and in particular between 80% and 85% of the nominal diameter.
Surprisingly, it has been found that setting the thread pitch in this manner makes it possible to screw in the screw more easily, it simultaneously being ensured that the screwed-in screw is anchored stably in the material.
It has been found that a reduction in the thread pitch brings about a reduction in the screw-in torgue.
However, it has also been found that the carrying capacity of the remaining material between the incised thread spirals is reduced if the thread pitch is reduced.
In particular in the event of a tensile load on the screwed-in screw, there is the risk of the re- maining material shearing off if the thread pitch is too low and the screwed-in screw being torn out of the borehole if the thread pitch is too
— small.
The aforementioned range for the thread pitch is thus small enough to bring about a reduced screw-in torgue and thus to facilitate screwing in the screw.
However, the thread pitch is also large enough to prevent the webs of the thread from shearing off and thus to guarantee sufficient carry- ing capacity for the self-cutting screw in the material.
A screw according to claim 4 reduces the risk of a material blockage and thus an increased screw-in torgue for the screw.
It has been found that the end face arranged at the insertion end may be formed so as to be concave at least in portions, in particular using a fillet.
The fillet may advantageously
— be formed during the production process of the screw, in particular in a rolling process.
The fillet has in particular a maximum axial depth which is in particular at most 30%, in particular at most 25%, in particular at most 20% and in particular at most 15% of the nominal diameter of the screw.
For example, the depth of the fillet is between 0.8 mm and 2.0 mm.
A screw according to claim 5 has a reduced screw-in resistance.
In particu- lar the shaft diameter is formed small in terms of the nominal diameter.
It is advantageous if the shaft diameter is at least 60% of the nominal diameter.
The shaft diameter is formed stable.
A screw according to claim 6 makes uncomplicated torque-transmission possible.
The torque-transmission portion may for example have a non- round external contour and/or a non-round internal contour.
In particular,
— the torgue-transmission portion may be formed as a screw head, in particu- lar with a hexagonal external contour.
The screw head has in particular a width across flats which is greater than the nominal diameter of the screw.
However, the external contour of the torque-transmission portion may also be formed with a hexagonal contour of a width across flats which is less
— than the nominal diameter of the screw.
If the torgue-transmission portion has a non-round internal contour, this may advantageously be formed as a hexagonal internal contour or as a hexalobular internal contour.
Other non- round contours are also possible, for example triangular or square contours.
A screw according to claim 7 is particularly stable and robust.
The screw is produced in particular from steel and in particular from high-grade steel.
In particular, the screw is produced from high-grade steel having corrosion- inhibiting properties, in particular A2 high-grade steel or A4 high-grade steel, in particular chromium steel or nickel steel, in particular a material
— having designation 1.4301, 1.4401, 1.4404 or 1.4571. Alternatively, an aus- tenitic, stainless high-grade steel in accordance with material No. 1.4529 may also be used.
In particular, the screw is not heat-treated and in particular not tempered
— and/or hardened.
The screw is in particular produced in a rolling process.
A screw according to claim 8 has improved cutting properties.
A screw according to claim 9 simplifies inserting the screw into a borehole.
In particular, a minimum diameter of the screw is arranged externally, in other words in particular on the lower end face on the insertion end.
The minimum diameter is arranged externally.
In particular, the minimum di- ameter at the insertion end is approximately 1 mm less than the shaft diam-
eter and in particular 2 mm less than the nominal diameter.
A screw according to claim 10 has improved cutting properties, in particu- lar an increased cutting performance.
A cutting element is in particular
— formed as a cutting tooth, which is formed projecting on the cutting thread, in particular in a radial direction.
A cutting tooth of this type may be rolled onto the cutting thread in the rolling process.
However, the cutting tooth may also be applied to the cutting thread retroactively as a welding dot.
A cutting element may also be formed by way of a cutting notch recessed at
— the cutting thread.
A screw according to claim 11 has improved material transport properties along the longitudinal groove.
The longitudinal groove has in particular a V, U or rectangle shape along the groove longitudinal axis.
A groove
— depth, which extends from the outer wall of the screw to the groove base, is at least 3% of the nominal diameter, in particular at least 5%, in particular at least 8%, in particular at least 10% and in particular at most 15%. The groove width, which is defined by the distance between the groove flanks at the outer surface of the screw, is in particular at most 20%, in particular at most 15%, in particular at most 12%, in particular at most 10% and in particular at most 5% of the circumference of the screw at the core.
Both the features set out in the claims and the features set out in the follow- ing example embodiment of the screw according to the invention are each suitable, alone or in combination, for developing the subject matter accord- ing to the invention. The respective feature combinations do not constitute a limitation on the developments of the inventive subject matter, but rather are merely exemplary in nature. Additional features, advantageous embodiments and details of the inven- tion will be apparent from the following description of an embodiment with reference to the drawings, in which:
Fig.1 is a side view of a screw according to the invention and
Fig. 2 is a side view rotated through 90* about the longitudinal axis of the screw. A screw 1 shown in Fig. 1 and 2 is a self-tapping screw produced in a sin- gle piece from high-grade steel. The self-tapping screw 1 is for screwing into a borehole in concrete. The screw 1 is a concrete screw. The screw 1 has a cylindrical core 2. The core 2 is formed without a thread. The core 2 has a longitudinal axis 3 and a nominal diameter dn. A torgue-transmission portion 4 is formed integrally on the core 2, and in the embodiment shown is formed as a hexagonal screw head. The torque- transmission portion 4 has a width across flats SW which is orientated transverse to the longitudinal axis 3 and is greater than the nominal diame- ter dn. The torque-transmission portion 4 is arranged on a first outer end 5 of the screw 1. The torque-transmission portion 4 is for placing a tool for screwing the screw 1 into a borehole.
It is also conceivable for the torque-transmission portion 4 to have a width across flats SW which is less than the nominal diameter dn.
In particular, the torque-transmission portion 4 may be arranged spaced apart from an upper end face of the screw 1. This is the case in particular if the torque- transmission portion 4 has a non-round internal contour and in particular is formed offset inwards on the screw 1 and in particular on the core 2. The screw head has a ring plate 6, which in particular has a plate diameter dp which is greater than the width across flats SW.
The ring plate 6 is for placing on a surface on the material.
A transition portion 7 between the ring plate 6 and the core 2 is formed with a transition radius R.
A groove effect due to the diameter transition from the nominal diameter dy to the plate diameter dp is minimized.
At a lower outer end 8 opposite the upper outer end 5, the screw 1 has an inser- tion end 9. The screw 1 can be inserted by the insertion end 9 into the bore- hole.
The insertion end 9 is formed without a thread.
The insertion end 9 has an insertion length Lg along the longitudinal axis 3. In the embodiment shown: Lg = 0.375 x dn.
The insertion end 9 is formed so as to be conical with a cone angle k, which is 20° in the embodiment shown.
The insertion end 9 is formed tapering towards the lower outer end 8. Ac- cordingly, the insertion end 9 has a minimum diameter dmin, which is ar- ranged at the lower end face 10. In the embodiment shown, the minimum diameter dmin is reduced by comparison with the nominal diameter dn.
The minimum diameter dmin is 75% of the nominal diameter dn.
The lower end face 10 is formed concave in the form of a fillet.
The fillet has a depth T which extends along the longitudinal axis 3 and is 1.0 mm for the screw shown.
Along the longitudinal axis 3, the screw has a cutting-thread portion 11 be- tween the core 2 and the insertion end 9. The insertion end 9 has the shaft diameter ds at its upper end which faces the cutting-thread portion 11. The cutting-thread portion 11 is formed integrally on the core 2. The cutting- thread portion 11 is connected to the core 2 via a cone portion 12. The cone
— portion 12 is formed without a thread.
The cutting-thread portion 11 comprises a cutting thread 13 which has a thread diameter dg and a thread pitch h.
The cutting thread 13 extends in particular along the entire cutting-thread portion 11. What is essential is
IS — that the cutting thread 13 ends before the insertion end 9 starts.
A cutting thread start 14 is arranged in the cutting-thread portion 11 and in particular outside the insertion end 9. Proceeding from the cutting thread start 14, the thread diameter dg is formed increasing.
The increase in the thread diame- ter dg extends over at least a half and in particular at least a whole rotation of the cutting thread 13. The cutting-thread portion 11 has a shaft diameter ds which is less than the nominal diameter dn.
In particular, the shaft diameter ds is at most 95% of the nominal diameter dx.
The thread diameter dc is at least 110% of the nominal diameter dn.
The thread pitch h is in particular between 80% and 85% of the nominal di- ameter dx.
As is indicated in Fig. 1 and 2 by the interruptions, the cutting-thread por- tion 11 and/or the core 2 may have a variably settable axial length.
The cutting thread 13 has a plurality of cutting elements 15. In the screw 1 shown, the cutting elements 15 are formed as welding spots which have been welded retroactively to the rolled thread spiral.
In the embodiment shown, the cutting elements 15 extend over 1.5 rotations of the thread spi- ral of the cutting thread 13. In the embodiment shown, a plurality of cutting elements 15 are provided.
In particular, at least two, in particular at least four, in particular at least eight or more cutting elements 15 may be pro- vided.
It is conceivable for the cutting elements to extend along the thread spiral of the cutting thread 13 over at least 0.5 rotations, in particular over at least one rotation, in particular over at least two rotations and in particu-
lar over three rotations.
In particular, the cutting thread 13 has a portion formed without cutting ele- ments.
In this region, the cutting thread 13 serves in particular as a support thread when the screw 1 is arranged anchored in the borehole.
Two longitudinal grooves 16 are arranged at the insertion end 9. The longi- tudinal grooves 16 are formed identically, and have a groove length Ly ex- tending along the longitudinal axis 3. The groove length Ly is greater than the insertion length Lk.
Because the groove length Ly is greater than the insertion length Lg, the longitudinal grooves 16 extend at least in part into the thread portion 11.
It is possible to provide only one longitudinal groove 16 or more than two longitudinal grooves 16. The longitudinal grooves 16 are arranged spaced apart in the circumferential direction about the longitudinal axis 3 on the outer surface of the screw 1, in particular of the insertion end 9. The longi- tudinal grooves 16 each have a groove longitudinal axis 17 orientated par- allel to the longitudinal axis 3. The longitudinal grooves 16 are orientated parallel to the longitudinal axis 3 and in particular mutually parallel.
The longitudinal grooves 16 extend from the lower end face 10 along the longi- tudinal axis 3. The longitudinal grooves 16 are formed as external grooves — on the outer surface of the screw 1.