SELF-TEARING SCREW

Description

[0001] The invention relates to a self-tapping screw according to the preamble of claim 1.

[0002] In a manner known, such as from EP 0948 719 B1, a screw, particularly for fastening in plastic, comprises a drive and a threaded shank. The screw further comprises a main thread, the main thread having a maximum main thread outside diameter. The main thread has a bearing and a grooved section, the grooved section terminating at the point of the thread turn where the nut thread is fully formed.

[0003] The screw has a screw end on its shaft at its end facing away from the drive, the screw end having a diameter of at least 20% of the maximum main thread outer diameter.

[0004] US Patent 3,861,269 B discloses a self-tapping and hole-forming screw with a multi-start tip area, enabling the screw to create a hole in the components to be joined, thereby allowing simplified penetration.

[0005] JP 2001 107932 A discloses a self-tapping screw with a three-start insertion thread and a single- or double-start bearing thread, wherein the bearing thread is designed as a continuation of the insertion thread.

[0006] The object of the invention is to provide a screw whose screw-in behavior is improved.

[0007] The problem is solved by the characterizing features of claim 1 in conjunction with its preambles.

[0008] The dependent claims constitute advantageous further developments of the invention.

[0009] The shaft has a threaded insert in the area of ​​the screw end.

[0010] According to the invention, the starter thread comprises at least three starter threads, wherein the diameter of the main thread in the starter area is smaller than the diameter of the starter thread. In this embodiment, only the starter threads fulfill the centering function, with the main thread subsequently engaging the nut thread.

[0011] The initial threads have an outer diameter of at most 90% of the maximum outer diameter of the main thread. This creates a starting area on the screw in which the initial threads have the same diameter profile and, furthermore, the diameter of the main thread is smaller than the diameter of the initial threads in this starting area.

[0012] This has the advantage that the starting threads enable a quick and straight engagement with a pilot hole in a component, particularly a plastic component, so that a bearing area following the grooved area is aligned as precisely as possible and thus follows the pre-grooved nut thread, resulting in less friction during the screwing process. Furthermore, according to the invention, the starting thread extends over a maximum of two turns. This ensures sufficient guidance while still guaranteeing effective screw engagement.

[0013] Preferably, the starting threads begin at the screw end on the core and steadily increase in diameter from the beginning of the core. This ensures even and rapid centering of the screw during installation.

[0014] In particular, the threads with the same outer diameter are evenly distributed around the entire area where they start. This also helps to center the screw.

[0015] Furthermore, it can be provided that the diameter of the screw end has at least 30%, at least 40%, at least 50%, or at least 60% of the main thread's outer diameter. This creates a blunt screw end, so that guidance is already provided by the pilot hole after a short insertion distance.

[0016] It is particularly advantageous for all threads in the starting area to originate in the same cross-sectional plane. This ensures uniform thread engagement across the entire starting area.

[0017] According to a further advantageous embodiment, all threads in the starting area can have the same thread design, in particular the same thread profile.

[0018] Preferably, the threaded insert connects directly to the end of the screw. This allows for quick centering.

[0019] Alternatively, the starting thread can begin at a distance from the screw end. In this way, the area towards the screw end can fulfill a search function.

[0020] The starting threads and the main thread can be rolled threads, which enables cost-effective manufacturing.

[0021] The starting thread and the main thread can have a flank angle in the starting area that is more obtuse than the flank angle of the main thread outside the starting area. This allows for specific consideration of the centering function of the starting area and the cutting function of the main thread.

[0022] Once the threaded insert reaches its maximum outer diameter, it can taper off abruptly. This reduces friction, especially when screwing it into a narrow pilot hole.

[0023] According to the invention, interruptions in the thread sections can also occur, whereby the interpolated progression of the thread outer diameter remains the same.

[0024] According to the invention, the tightening torque can be further reduced by locating the maximum main thread outer diameter in the grooved area, while also having a smaller outer diameter in the bearing area. This results in the threads of the bearing area following the grooved area being screwed into a slightly larger grooved nut thread, thereby reducing the friction of the thread sections. This has a particularly positive effect when screwing into plastic.

[0025] Preferably, the thread cross-sectional profile in the region of the maximum main thread outer diameter is larger, at least in its radially outer region, than the thread cross-sectional profile in the bearing area within this region. The radially outer region is approximately 85% of the maximum main thread diameter.

[0026] Further advantages, features and application possibilities of the present invention will become apparent from the following description in conjunction with the exemplary embodiments shown in the drawings.

[0027] In the drawing, this means: Fig. 1 a side view of a screw not according to the invention; Fig. 2 a cross-section BB through the screw shank in the insertion area according to Fig.1 Fig. 3 a side view of a screw according to the invention with three starting threads; Fig. 4 a cross-section AA through the screw shank in the starting area according to Fig. 3 ; Fig. 4 leg cross-section BB through the screw shaft in the insertion area according to Fig. 3 ; Fig. 5 a comparison of the thread profile contour in the forming area and a thread profile contour in the bearing area of ​​the main thread.

[0028] Fig. 1 Figure 1 shows a self-tapping screw 10 not according to the invention, with a shank 14 and a drive 12. The threaded shank 14 has a main thread 16, which has a cutting section F and a bearing section T. The cutting section F ends at the point on the main thread 16 where the complete nut thread is formed, followed by the bearing section T. This occurs after approximately two turns of the main thread 16 starting from the free end of the screw 18.

[0029] In this example, the groove area F and the bearing area T are parts of the same thread, so there is no physical transition between the bearing area T and the groove area F. A starting area AB is provided at the end of the screw opposite the drive, i.e., the "tip." In this example, the starting area AB is formed by two starting threads 20a, 20b rising directly from the screw core at the screw end 18 and continuously increasing in diameter D AA towards the drive 12 until the end of the starting area AB. The starting threads 20a, 20b have their maximum outer diameter D AA at the end of the starting area AB. This is less than 90% of the diameter D AF of the main thread 18. Accordingly, any impairment of the holding properties by the starting thread 20 can be avoided, while still promoting centered and straight insertion of the screw 10.The main thread 16 runs in the insertion area AB in the same way as the insertion threads 20a, 20b.

[0030] Fig. 2 Figure BB shows a cross-section approximately in the middle of the starting area AB. The cross-section shows the starting threads 20a, 20b and the main thread 16. All threads have the same diameter D AA at this point. The diameter D AA increases continuously from the screw end towards the drive, but the diameter is the same in every cross-sectional plane within the starting area AB.

[0031] Fig. 3 Figure 1 shows a side view of a screw according to the invention, wherein three insertion threads 20a, 20b, 20c are provided and the main thread 32 in the insertion area AB has a smaller diameter than the insertion threads 20a, 20b, 20c.

[0032] The main thread 32 thus begins in the starting area AB between the starting threads 20a, 20b, 20c and increases in diameter such that at the end of starting area AB it reaches the diameter of the starting threads 20a, 20b, 20c. From the end of starting area AB, the starting thread 20 terminates and the main thread 32 continues along the shaft. The diameters of the threads are shown in cross-sections AA in Fig. 4a for the end of the insertion area AB and for the cross-section BB of the shaft in Fig. 4b depicted.

[0033] Furthermore, the main thread 32 has a groove area F and a bearing area T following the insertion area AB in the direction of the head.

[0034] The maximum main thread outer diameter DAF lies within forming area F, after which the nut thread is produced. The bearing area T following the forming area in the direction of the drive has an outer diameter DAT that is smaller than the maximum main thread outer diameter DAF. This reduces friction for the bearing area T following the forming area F during the screwing-in process. Consequently, a low screwing-in torque is required.

[0035] It is understood that the invention also relates to screws that comply with Fig. 1 trained form area F and one according to Fig. 3 The main thread 32 is designed with a maximum main thread outer diameter D AF lying in the form area F and a smaller outer diameter D AT in the bearing area.

[0036] Fig 4a Figure 1 shows a cross-section AA through the screw shank at the end of the insertion area AB. All threads at this position have the same outer diameter D AA.

[0037] Fig. 4b The diagram shows a cross-section BB approximately in the middle of the starting area AB. The main thread 32 is clearly visible here within the outer diameter D AA defined by the starting threads 20a, 20b, 20c.

[0038] Fig. 5 shows a comparison of the thread profile contour in the forming area and a thread profile contour in the bearing area of ​​the main thread. Fig. 5 further shows that the thread cross-sectional profile 38 in the area of ​​the maximum main thread outer diameter D AF is larger at least in its radially outer area E of the thread cross-sectional profile than the thread cross-sectional profile 36 in the bearing area T in this area E.

Claims

1. Self-tapping screw (10, 30) comprising a drive (12) and a threaded shaft (14) comprising a main thread (16, 32), which main thread (16, 32) has a main thread maximum outer diameter (DAF) and includes a thread-forming area (F) and a bearing area (T) following the former in the direction of the drive (12), with the shaft (14) having a screw end (18) at an end facing away from the drive (12), which screw end (18) has a diameter (DE) of at least 20% of the main thread maximum outer diameter (DAF), with the shaft furthermore having a setting thread (20) in the region of the screw end (18), characterized in that the setting thread (20) comprises at least three setting thread turns (20a, 20b, 20c), the outside diameter (DAA) of which reaches at most 90% of the main thread maximum outside diameter (DAF) and which form a setting area in which the setting thread turns (20a, 20b, 20c) have the same diameter profile and, moreover, in the setting area (AB) the diameter of the main thread (16, 32) is smaller than the diameter (DAA) of the setting thread turns (20a, 20b, 20c), with the setting thread (20) extending over at most two turns.

2. Self-tapping screw according to any one of the preceding claims, characterized in that the setting thread turns (20a, 20b, 20c) start at the core in the region of the screw end (18), with their diameter continuously expanding.

3. Screw according to any one of the preceding claims, characterized in that the thread turns (20a, 20b, 20c, 16) having the same outside diameter (DAA) are evenly distributed around the circumference in the setting area (AB).

4. Self-tapping screw according to any one of the preceding claims, characterized in that the diameter (DE) of the screw end (18) is at least 20%, at least 30%, at least 40%, at least 50%, at least 60% of the main thread outer diameter (DAF).

5. Self-tapping screw according to any one of the preceding claims, characterized in that all thread turns in the setting area (AB) start in the same cross-sectional plane.

6. Self-tapping screw according to any one of the preceding claims, characterized in that all the threads (20a, 20b, 16) in the setting area (AB) are of the same thread design.

7. Self-tapping screw according to any one of the preceding claims, characterized in that the setting thread (20) directly adjoins the free shaft end (18).

8. Self-tapping screw according to any one of claims 1 to 6 above, characterized in that the setting thread (20) starts at a distance from the free shaft end (18).

9. Self-tapping screw according to any one of the preceding claims, characterized in that the setting thread (20) and the main thread (16) are rolled threads.

10. Self-tapping screw according to any one of the preceding claims, characterized in that the setting thread (20) and the main thread (16) in the setting area (AB) have a more obtuse flank angle than the main thread (16) outside the setting area.

11. Self-tapping screw according to any one of the preceding claims, characterized in that the setting thread (20) runs out abruptly.

12. Self-tapping screw according to any one of the preceding claims, characterized in that interruptions of the thread turns are provided, with the interpolated course of the thread outer diameter remaining the same.

13. Self-tapping screw according to any one of the preceding claims, characterized in that the main thread maximum outer diameter (DAF) is located in the thread-forming area (F), with the outer diameter (DAT) being smaller in the bearing area (T).

14. Self-tapping screw according to claim 13, characterized in that the thread cross-sectional profile (38) in the region of the main thread maximum outer diameter (DAF) is larger, at least in its radially outer region (E) of the thread cross-sectional profile, than the thread cross-sectional profile (36) in the bearing area (T) in this region (E).