Self-tapping screw

Abstract

A self-tapping screw (10, 30) comprising a drive (12) and a shank (14) bearing a thread comprising a main thread (16, 32), wherein the main thread (16, 32) has a maximum main thread external diameter (D.sub.AF) and a cutting area (F) and a supporting area (T) following in the direction of the drive (12), wherein the shank (14) has a threaded end (18) at an end opposite the drive (12), with the screw end (18) having a diameter (DE) of at least 20% of the maximum main thread external diameter (D.sub.AF), The shank further has, in the region of the screw end (18), a tap flute (20), wherein the tap flute (20) comprises at least two tapping thread turns (20a, 20b, 20c) which attain, in their external diameter (D.sub.AA), no more than 90% of the maximum main thread external diameter (D.sub.AF) and form a tap region in which the tapping thread turns (20a, 20b, 20c) have the same diameter development, and in addition in that the diameter of the main thread (16, 32) in the tap flute region (AB) is less than or equal to the diameter (D.sub.AA) of the tapping thread turns (20a, 20b, 20c).

Claims

1. Self-tapping screw (10, 30), comprising: a drive (12), a shank (14) bearing a thread comprising a main thread (16, 32), said main thread (16, 32) has a maximum main thread outer diameter (D.sub.AF), cutting area (F) and a bearing area (T) following in the direction of said drive (12), said shank (14) has a screw end (18) at an end thereof opposite said drive (12), said screw end (18) has a diameter (D.sub.E) of at least 20% of said maximum main thread outer diameter (D.sub.AF), said shank has, in the region of said screw end (18), a tap flute (20), said tap flute (20) comprising at least two tapping thread turns (20a, 20b, 20c) which attain, in their outer diameter (D.sub.AA), no more than 90% of said maximum main thread outer diameter (D.sub.AF) and form a tap region, in said tap region said tapping thread turns (20a, 20b, 20c) have the same diameter, said diameter of said main thread (16, 32) in said tap flute region (AB) is less than or equal to said diameter (D.sub.AA) of said tapping thread turns (20a, 20b, 20c), said tap flute (20) has an obtuse flank angle in said tap flute region (AB), said main thread (16) has an obtuse flank angle outside said tap flute region (AB), and, said tap flute (20) has a flank angle in said tap region (AB) which is more obtuse than said flank angle of said main thread outside said tap flute region (AB).

2. Self-tapping screw according to claim 1, further comprising: said diameter of said main thread (16, 32) in said tap flute region (AB) is identical to said diameter (D.sub.AA) of said tap flute.

3. Self-tapping screw according to claim 1, further comprising: said tapping thread turns (20a, 20b, 20c) are provided, said diameter of said main thread (D) in said flute region being smaller than said diameter (D.sub.AA) of said tap flute (20).

4. Self-tapping screw according to claim 1, further comprising: said tapping thread turns (20a, 20b, 20c) in the area of said screw end (18) start at a core and constantly increase in diameter.

5. Self-tapping screw according to claim 1, further comprising: said tapping thread turns (20a, 20b, 20c) of said same outer diameter (D.sub.AA, D) are equally distributed around the circumference of said tap flute region (AB).

6. Self-tapping screw according to claim 1, further comprising: said screw end (18) has a diameter (D.sub.E) of at least 20% of said main thread outer diameter (D.sub.AF).

7. Self-tapping screw according to claim 1, further comprising: all thread turns in said tap flute region (AB) start in the same cross-sectional plane.

8. Self-tapping screw according to claim 1, further comprising: all thread turns (20a, 20b, 16) in said tap flute region (AB) are of identical thread shape.

9. Self-tapping screw according to claim 1, further comprising: said tap flute (20) starts immediately following said end of said screw (18).

10. Self-tapping screw according to claim 1, further comprising: said tap flute (20) starts at a distance from said screw end (18).

11. Self-tapping screw according to claim 1, further comprising: said tap flute (20) and said thread (16) are rolled threads.

12. Self-tapping screw according to claim 1, further comprising: said tap flute (20) runs out abruptly.

13. Self-tapping screw according to claim 1, further comprising: said tap flute (20) extends over a maximum of two turns.

14. Self-tapping screw according to claim 1, further comprising: said main thread has its maximum outer diameter (D.sub.AF) in said cutting area (F), with its outer diameter (D.sub.AT) being smaller in said bearing area (T).

15. Self-tapping screw according to claim 14, further comprising: the cross-sectional profile (38) of the thread in the area of said maximum main thread outer diameter (D.sub.AF) is larger at least in its radially outer area (E) of said cross-sectional profile of said thread than said cross-sectional profile (36) of said thread in said bearing area (T) in said radially outer area (E).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the Drawings,

(2) FIG. 1 is a lateral view of a screw according to the invention;

(3) FIG. 2 is a view of a cross-section through the screw shank of FIG. 1 taken along line B-B in the tap flute region of the screw;

(4) FIG. 3 is a lateral view of a screw according to the invention having three tapping thread turns;

(5) FIG. 4a is a view of a cross-section through the screw shank of FIG. 3 taken along line A-A in the tap flute region;

(6) FIG. 4b is a view of a cross-section through the screw shank of FIG. 3 taken along line B-B in the tap flute region;

(7) FIG. 5 is a comparative view of the thread profile contour in the cutting area and a thread profile contour in the bearing area of the main thread.

DESCRIPTION OF THE INVENTION

(8) The view of FIG. 1 shows a self-tapping screw 10 with a screw shank 14 and a screw drive 12. The threaded shank 14 has a main thread 16, which has a cutting area F and a bearing area T. The cutting area F ends at the point on the main thread 16 where the female thread has been completed, after which the bearing area T then follows. This is the case after about two turns of the main thread 16 starting from the free end of the screw 18.

(9) In this example, the cutting area F and the bearing area T are parts of the same thread turn, so that there is no actual transition between the bearing area T and the cutting area F. At the end of the screw opposite the drive, i.e. at the “tip”, a tap flute region AB is provided according to the invention. In this example, the tap flute region AB is formed by two thread turns 20a, 20b extending from the screw core directly at the screw end 18 and continuously increasing their diameter D.sub.AA towards the drive 12 up to the end of the tap flute region AB. The tapping thread turns 20a, 20b have their maximum outer diameter D.sub.AA at the end of the tap flute region AB. This diameter is less than 90% of the diameter D.sub.AF of the main thread 18. As a result, the holding properties of the tap flute 20 are not impaired and a centered and straight initial insertion of the screw 10 is still possible. In the tap flute region AB, the main thread 18 runs in the same way as the tapping thread turns 20a, 20b.

(10) Shown in FIG. 2 is a cross-sectional view taken along line B-B approximately through the middle of the tap flute region AB. This cross-sectional view shows the tapping thread turns 20a, 20b and the main thread 16. At this point all threads have the same diameter D.sub.AA. Although diameter D.sub.AA increases steadily from the end of the screw towards the drive, this diameter is the same in every cross-sectional plane in the tap flute region AB.

(11) FIG. 3 is a lateral view of another embodiment of a screw according to the invention, which screw is provided with three tapping threads 20a, 20b, 20c, and its main thread 32 in the tap flute region AB has a smaller diameter than the tapping threads 20a, 20b, 20c.

(12) The main thread 32 thus begins in the tap flute region AB between the tapping thread turns 20a, 20b, 20c and increases in diameter in such a way that at the end of the tap flute region AB it will eventually be the same as the diameter of the tapping thread turns 20a, 20b, 20c. From the end of the tap flute region AB, the tap flute 20 runs out and the main thread 32 extends further along the shank. The thread turn diameters are shown in the cross-sectional view of FIG. 4a, taken along line A-A, of the end of the tap flute region AB, and in the cross-sectional view of FIG. 4b, taken along line B-B, of the shank. Furthermore, following the tap flute region AB, the main thread turn 32 has a cutting area F and a bearing area T in the direction of the head.

(13) The maximum main thread outer diameter D.sub.AF is in the cutting area F, after which the female thread has been produced after cutting area F. The bearing area T following the cutting area in the direction of the drive has an outer diameter D.sub.AT which is smaller than the maximum main thread outer diameter D.sub.AF.

(14) This thus reduces the friction experienced by the bearing area T which follows after the cutting area F during the screw insertion process. This results in a low screw insertion torque.

(15) It is to be noted that the invention also relates to screws which have a cutting area F of the design illustrated in FIG. 1 and a main thread 32 of the design illustrated in FIG. 3 having a maximum main thread outer diameter D.sub.AF in the cutting area F and a smaller outer diameter D.sub.AT in the bearing area.

(16) FIG. 4a is a view of a cross section, taken along line A-A, through the screw shank at the end of the tap flute region AB. All threads have the same outer diameter D.sub.AA at this position.

(17) FIG. 4b is a view of a cross-section, taken along line B-B, approximately in the middle of the tap flute region AB. This view clearly shows that the main thread 32 is within the outer diameter D.sub.AA defined by the tapping thread turns 20a, 20b, 20c.

(18) FIG. 5 is a comparative view of the thread profile contour in the cutting area and a thread profile contour in the bearing area of the main thread. The view of FIG. 5 further shows that the cross-sectional profile 38 of the thread in the area of the maximum outer diameter D.sub.AF of the main thread is larger at least in its radially outer area E of the thread cross-sectional profile than the cross-sectional profile 36 of the thread in the bearing area T in this area E.