Thread-forming or self-tapping screw, in particular for use in light metal

Abstract

The invention relates to a screw (1), having a shank (3) which is provided with a thread (2) with at least one asymmetrical thread turn (4) with a plurality of windings, wherein the thread has an external diameter (Da), a core diameter (Dk) and a thread pitch (P), wherein the thread turn (4) has thread flanks (7, 8) with a flank angle (phi), wherein the thread flanks (7, 8) have a load-bearing flank (7) and a counter-flank (8) which abut one another directly or indirectly in a thread bottom (9) and at a thread tip (10), and wherein a flank angle (phiL) of the load-bearing flank (7) is smaller than a flank angle (phiG) of the counter-flank (8). The flank angle (phiL) of the load-bearing flank is at least 25°, preferably from 25° to 35°, in particular 30°, and the flank angle (phiG) of the counter-flank is at least 40°, preferably from 40° to 60°, in particular 50°, wherein the flank angle (phi) is from at least 65° to at most 95°. Screws of said type are used, in particular, for direct screw connection in light metal cast components.

Claims

1. A thread-forming or self-tapping screw, comprising: a shank provided with a thread with at least one asymmetric thread turn with a plurality of windings, wherein (i) the thread has an external diameter (D.sub.A), a core diameter (D.sub.K) and a thread pitch (P), (ii) the thread turn has thread flanks with a flank angle phi, (iii) the thread flanks have a load-bearing flank and a counter-flank which abut one another at a thread bottom and at a thread tip, wherein the load-bearing flank and the counter-flank form a transition region at the thread bottom with a longitudinal extension of at least 0.01 times and at most 0.2 times the pitch P, and (iv) a flank angle phiL of the load-bearing flank is smaller than a flank angle phiG of the counter-flank, wherein a ratio Q1=D.sub.A/P of the external diameter (D.sub.A) in relation to the thread pitch (P) is from 3.0 to 3.6, and a ratio Q2=D.sub.K/P of the core diameter (D.sub.K) in relation to the thread pitch (P) is from 2.0 to 2.5.

2. The screw according to claim 1, wherein the flank angle phiL of the load-bearing flank is at least 25°, the flank angle phiG of the counter-flank is at least 40°, and the flank angle phi is at least 65°.

3. The screw according to claim 2, wherein the shank has a threaded end with a thread beginning and a groove region is present with a thread profile fully formed in relation to the thread tip and to the load-bearing flank at the threaded end at the thread beginning over 0.5 to 2 windings.

4. The screw according to claim 3, wherein the thread profile increases in the groove region from zero to a full profile height P.sub.H.

5. The screw according to claim 1, wherein the transition region and has a tip radius Rs of at most 0.15 mm.

6. The screw according to claim 1, wherein the transition region has a fillet in the thread bottom.

7. The screw according to claim 6, wherein the transition region has a different radius RgL and RgG in the thread bottom for the load-bearing flank and for the counter-flank which is smaller than 1 mm, wherein the radius RgL of the load-bearing flank in the thread bottom is greater than the radius RgG of the counter-flank by at least 1.5 times and at most 3 times.

8. The screw according to claim 1, wherein a profile of the loadbearing flank and a profile of the counter-flank is a straight line.

9. The screw according to claim 1, wherein a ratio of the flank angle phiL of the load-bearing flank to the flank angle phiG of the counter-flank is at least 0.4 and at most 0.85.

10. The screw according to claim 1, wherein an angle bisector of the flank angle phi with a perpendicular to a central axis of the screw forms a positive angle epsilon in a head direction in a range of 2.5° to 17.5°.

11. The screw according to claim 1, wherein the thread has a circular geometry.

12. The screw according to claim 1, wherein the shank has a threaded end with a thread beginning, an attachment tip is formed at the threaded end before the thread beginning, a length L.sub.A of the attachment tip is at least 0.3 times the thread pitch P and a diameter D.sub.AS of the attachment tip is at most 0.95 times the core diameter (D.sub.K).

13. The screw according to claim 1, wherein the thread has a conical increase of the external diameter in a head direction.

14. The screw according to claim 1, wherein the screw is made of hardened steel, stainless steel, or corrosion-resistant materials for direct screw connection into light metal or alloys thereof, brass, or non-ferrous metals.

15. A thread-forming or self-tapping screw, comprising: a shank provided with a thread with at least one asymmetric thread turn with a plurality of windings, wherein (i) the thread has an external diameter (D.sub.A), a core diameter (D.sub.K) and a thread pitch (P), (ii) the thread turn has thread flanks with a flank angle phi, (iii) the thread flanks have a load-bearing flank and a counter-flank which abut one another at a thread bottom and at a thread tip, wherein the load-bearing flank and the counter-flank form a transition region at the thread bottom with a longitudinal extension of at least 0.01 times and at most 0.2 times the pitch P, (iv) a flank angle phiL of the load-bearing flank is smaller than a flank angle phiG of the counter-flank, and (v) the flank angle phiL of the load-bearing flank is at least 25°, the flank angle phiG of the counter-flank is at least 40°, and the flank angle phi is at least 65°, wherein a ratio Q1=D.sub.A/P of the external diameter (D.sub.A) in relation to the thread pitch (P) is from 3.0 to 3.6, and a ratio Q2=D.sub.K/P of the core diameter (D.sub.K) in relation to the thread pitch (P) is from 2.0 to 2.5.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The screw according to the invention is explained based on the drawing. It shows:

(2) FIG. 1 a screw according to the invention with a head and a screw tip and a thread in a side view;

(3) FIG. 2 the screw from FIG. 1 in a plan view to the screw tip;

(4) FIG. 3 the forming of the thread of the screw from FIG. 1 in the region of a thread tip in detail;

(5) FIG. 4 the forming of the thread of the screw from FIG. 1 in the region of a thread bottom in detail;

(6) FIG. 5 the forming of the thread at the screw tip in detail;

(7) FIG. 6a-c different embodiments of the thread with a conical increase of the external diameter in the head direction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(8) The screw 1 according to the invention represented in FIG. 1 in a side view for the screw connection, in particular in light metal casting has a shank 3 provided at least partially with a thread 2 extending along a longitudinal axis 1′ with an external diameter Da and a core diameter Dk. A head 4 of the screw arranged at one end of the screw 1 with interior force application surfaces, not represented, is also represented, but is not relevant for this invention. A threaded end of the shank 3 opposite the head 4 is formed as the screw tip 5.

(9) The shank 3 has been provided with an asymmetric thread turn 6 with a plurality of windings to produce the thread 2, said thread turn extends at least along a part of the shank 3 with a fully-developed thread profile.

(10) The thread turn 6 has thread flanks 7, 8 with a flank angle phi which abut one another in a thread bottom 9 and at a thread tip 10 forming, respectively, a transition region 11, 12 discernible in FIGS. 3 and 4.

(11) The thread 2 has an external diameter Da, a core diameter Dk and a thread pitch P.

(12) The thread flank 7 is a load-bearing flank since it receives the pretensioning forces caused by the screw between the screw head 4 and the thread in the nut component.

(13) The thread flank 8 is a counter-flank which supports the load-bearing flank 7 against the core of the screw.

(14) The thread 2 has a flank angle phi of approx. 80° and is formed asymmetrically, the flank angle phiL of the load-bearing flank 7 at approx. 30° being smaller than the flank angle phiG of the counter-flank 8 at approx. 50° is represented in FIG. 3. The ratio of the flank angle phiL of the load-bearing flank to the flank angle phiG of the counter-flank is 0.6. Since the flank angle phiL of the load-bearing flank is smaller than the flank angle phiG of the counter-flank, the thread 2 seems tilted towards the head 4, see FIG. 5.

(15) The thread pitch P is at 1.5 mm, in the case of a nominal diameter of 5 mm, 1.9 times the pitch of a metric standard thread of the same nominal diameter, which is 0.8 mm in the case of this nominal diameter.

(16) The core diameter is at 3.5 mm, in the case of a nominal diameter of 5, 0.87 times the core diameter of a metric thread of the same nominal diameter which is 3.995 mm in the case of this nominal diameter in the tolerance class 6 g.

(17) The screw 1 has an attachment tip 13 formed without a thread with a length La at the threaded end before the thread beginning, which is roughly 0.3 times the thread pitch P. The attachment tip 13 has a diameter D.sub.AS which is roughly 0.95 times the core diameter Dk.

(18) The shank 3 also has a thread beginning at the threaded end which extends, as represented in FIG. 2, over approx. 320°, i.e. over approx. 0.9 windings and forms a groove region 14 with a thread profile 10′ fully formed in relation to the thread tip and the load-bearing flank. A profile of the thread turn is present in the groove region 14 with a contour of the external diameter that is increasing more or less uniformly which leads to progressive forming of the thread into the nut component.

(19) However, in the groove region 14 it is irrelevant whether the counter-flank is already fully formed. The thread 2 adjoining the groove region 14 facilitates the further forming of the nut thread introduced into the nut part by means of the groove region 14 and is thus also formed in a thread-forming or self-tapping manner, even if the primary deformation takes place by way of the groove region 14 and smoothening and calibrating then takes place.

(20) In the case of an external diameter of the thread increasing in the head direction, as can be provided for example by conicity (FIG. 6a-c), further deforming of the material of the nut component also takes place after the groove region with progressive screwing of the screw into the nut component.

(21) FIG. 2 shows the screw from FIG. 1 in a plan view to the screw tip 5. It can be discerned that the thread 2 has a circular geometry with the thread tips 10 and the thread bottom 9, just like the head 4 which has no significance here for the invention.

(22) In the groove region 14, the thread profile 10′ runs proceeding from the thread bottom 9 with the core diameter Dk (FIG. 1) at a height of the thread tip from zero to the full height of the thread tips 10 on the external diameter Da (FIG. 1).

(23) The ratio Q1=Da/P of the external diameter Da in relation to the thread pitch P, in the case of an external diameter Da of 5 and a thread pitch P of 1.5, is approx. 3.3 and the ratio Q2=Dk/P of the core diameter Dk of 3.5 in relation to the thread pitch P is approx. 2.3.

(24) It is discernible in FIG. 3 that the profile of the load-bearing flank 7 and the profile of the counter-flank 8 is a straight line and that the load-bearing flank 7 and the counter-flank 8 abut one another in the thread bottom 9 and at the thread tip 10 indirectly forming a transition region 11, 12 with a longitudinal extension of roughly 0.01 times the pitch P at the thread tip 10 and at most 0.2 times the pitch P in the thread bottom 9.

(25) The transition region 12 at the thread tip 10 should be as sharp-edged as possible which is provided with a tip radius Rs of at most 0.15 mm.

(26) As already explained, the flank angle phi is divided asymmetrically, the flank angle phiL of the load-bearing flank 7 being indicated with respect to a perpendicular 15 to the longitudinal axis 1′ of the screw 1 and being smaller than the flank angle phiG of the counter-flank 8 which is also indicated with respect to the perpendicular 15 to the longitudinal axis 1′ of the screw 1, but in the other direction.

(27) The transition region 11 in the thread bottom 9 represented in FIG. 4 in detail Z from FIG. 3 has a fillet, a different radius RgL and RgG being present for the load-bearing flank 7 and the counter-flank 8 which is 0.05 and 0.1 mm here. The radius RgL in the thread bottom of the load-bearing flank 7 is thus double the size of the radius RgG of the counter-flank 8.

(28) The threaded end of the screw 1 from FIG. 1 is represented in FIG. 5 in detail. An attachment tip 13 formed without a thread with a length La is formed before the thread 2 beginning which is roughly 0.4 times the thread pitch P. The attachment tip 13 has a diameter D.sub.AS which is roughly 0.9 times the core diameter Dk.

(29) The shank 3 also has a thread beginning with a thread turn 6′ at the threaded end which has a thread profile increasing from zero up to the profile height P.sub.H and which, as represented in FIG. 2, extends over approx. 320°, i.e. over approx. 0.9 windings and forms a groove region 14. The thread profile of the thread turn 6′ is fully formed in relation to the thread tip 10′ and the load-bearing flank 7, however, the load-bearing flank 7′ does not directly adjoin the counter-flank 8 of the subsequent thread turn 6 in the groove region 14, but rather there is a gap present such that the groove region 14 has the pitch P.

(30) In the bearing region of the thread, which adjoins the groove region 14, the profile height P.sub.H increases by 1.05 times to 1.5 times with respect to a metric thread, for example in the case of DN 5 by 1.1 times. This is achieved by the core diameter D.sub.K being smaller than in the case of a metric thread.

(31) A transition region 15, formed conically in the present case, is between the groove region 14 and the attachment tip 13. The diameter increases from the diameter D.sub.AS to the core diameter Dk in the groove region 14. The attachment tip itself is rounded, but it is also possible to provide a bevel.

(32) Proceeding from the angle phiL of the load-bearing flank 7 of 30° and the angle phiG of the counter-flank 8 of 50°, the flank angle phi of 80° results and the angle bisector 21 of the flank angle phi with a perpendicular 22 to a central axis 20 of the screw forms a positive angle epsilon of 10° in the head direction.

(33) FIG. 6A-C show three different embodiments of the thread with a conical increase of the external diameter D.sub.A in the head direction. FIG. 6A shows an increase of the core diameter D.sub.K and of the external diameter D.sub.A with a cone angle beta with constant pitch and profile height P.sub.H.

(34) FIG. 6b shows an increase of the profile height P.sub.H with a cone angle beta of the external diameter D.sub.A with constant core diameter D.sub.K, FIG. 6c shows an increase of the profile height P.sub.H and of the core diameter D.sub.K, the cone angle beta′ of the core diameter D.sub.K being smaller than the cone angle beta of the external diameter D.sub.A.

(35) Hardened steel, stainless steels or highly corrosion-resistant austenitic materials are, in particular, considered as screw material, the listing being only exemplary and not exhaustive.