DE29720751U1 - Anchor screw and screw connection - Google Patents

Description

EJOT Verbindungstechnik GmbH & Co KG , P.O. Box 1 2 60, 57302 Bad Berleburg

Anchor screw and screw connection

The invention relates to an anchor screw, the head of which has internal engagement surfaces for a tool and the shaft of which is equipped with a cutting thread, as well as a screw connection in which an anchor screw engages in a hard material such as concrete or brick.

As their name suggests, anchor screws are used to anchor the frame of a door or window in the surrounding masonry, for example. An important property of an anchor screw is its universal usability with various masonry materials, such as concrete, sand-lime brick, solid brick, lattice brick, lightweight concrete or pumice, as well as various frame materials such as wood, metal or PVC. An anchor screw should also enable stress-free spaced assembly, in which a gap remains between the masonry and the frame. Known anchor screws have a continuous cutting thread on their shaft, the flanks of which have a smaller flank depth in a cutting zone starting from the thread tip than in the rest of the thread. In addition, the thread flanks are interrupted at regular intervals by recesses that result from two cutting grooves.

which run helically around the shaft in the same direction as the thread and with a greater pitch than the thread. The depth of the cutting grooves corresponds to the flank depth of the thread, so that the cutting grooves reach to the thread base, i.e. to the core diameter of the shaft. The cutting grooves extend over the full length of the shaft.

Anchor screws have a head at the end of the shaft opposite the thread tip. Anchor screws are known to have different head shapes tailored to the intended use. For wooden frames, a head is provided that connects to the shaft with a conically widening support surface and merges into a cylindrically shaped head surface. The diameter of the head surface corresponds to the outer diameter of the thread. Such a head is suitable for being countersunk into the wood of the frame.

For PVC frames - whether with or without an internal metal tube frame - a head is provided that has a flat support surface towards the shaft, the diameter of which is larger than the outer thread diameter and which is connected to a conically widening head surface. Such a head rests on the frame surface instead of being sunk into it.

Both heads have internal tool engagement surfaces for the engagement of a TORX tool. The latter head for plastic frames has a larger engagement than the former head for wooden frames with the same core and thread outer diameter, so that greater torques can be transmitted with the head for plastic frames than with the one for wooden frames.

For the user, the different head shapes have the disadvantage that different types of anchor screws have to be kept in stock for different applications. It is also disadvantageous for a manufacturer of fasteners such as anchor screws to produce different variants in correspondingly smaller quantities.

The invention is therefore based on the object of creating a universally applicable anchor screw that is easy to process.

The task is solved by an anchor screw with a head with internal tool engagement and flat support surface, the diameter of which is essentially

ally corresponds to the outside diameter of the thread and to which a head surface widens slightly conically towards the front surface of the head.

An anchor screw with such a head can be used universally for both wood and plastic frames and can be fully or partially countersunk in wood, plastic or metal frames or can rest on metal or plastic frames. Because the head can be countersunk, the anchor screw can also be used in holes that run at an angle to the frame surface. In addition, the extent of the tool engagement can be greater than with the well-known wood anchor screws, so that larger torques can be transmitted more reliably and a significantly longer service life of the tools (bits) is achieved. Compared to the well-known PVC anchor screws, the head requires less material. The anchor screw therefore offers the greatest possible maximum drive torque with minimal material use in the head.

Due to its universal applicability, the universal anchor screw saves the user from having to keep different anchor screws in stock for different areas of application. On the other hand, a manufacturer of the anchor screw can produce one type in larger quantities and thus more cost-effectively.

An anchor screw is preferred in which the cone pitch of the head surface in the longitudinal direction of the anchor screw is approximately 20% or 1/5. The diameter of the support surface preferably corresponds to 0.8 to 1.0 times and the head height preferably to one third of the thread outer diameter.

The solution to the problem also consists in an anchor screw, in particular of the type described above, which has a threaded shaft with helical cutting grooves and is characterized in that the shaft has no cutting grooves in a section adjoining the head and more than three cutting grooves in the rest, the depth of which is less than the flank depth of the thread. An anchor screw of the above type is preferred with a first section starting from the shaft tip with a reduced flank depth, the length of which corresponds to four to seven times and particularly preferably five to six times the outer thread diameter. The preferred anchor screw has - with a constant core diameter - three sections: a first section with cutting grooves and reduced flank depth, a second section with cutting grooves and full flank depth and a third section reaching up to the head.

» ·» »■ · »■♦ -if»

-4-

with full thread without cutting grooves. The two sections with cutting grooves, namely the first and second sections, together form the cutting zone of the anchor screw.

Such an anchor screw - especially in its preferred variant - can be processed with a significantly lower screwing torque than conventional anchor screws under otherwise identical conditions. This reduces bit wear and the risk of overloading both the tool including the drive and the anchor screw.

Specifically, the screwing torque required to screw in the preferred anchor screw in particularly hard wall materials, such as concrete, drops to approximately half the previously usual value. Since the required screwing torque increases with the screwing depth, it was previously necessary to choose the length of the anchor screw so that the minimum screwing depth was reached but not significantly exceeded. This meant that an anchor screw with a different shaft length was required for practically every application. Due to the significantly reduced screwing torque, a precise selection of the shaft length is hardly necessary anymore; instead, the anchor screws with the longest shaft length can be used regularly without overloading the anchor screw.

In the preferred variant of the anchor screw, the first section with reduced flank depth is longer than the minimum screw-in depth in concrete. As long as the anchor screw is only screwed into a concrete wall with its first section, the screw-in torque required is reduced considerably. As the first section is longer than the minimum screw-in depth required for concrete and the thread of the first section with reduced flank depth is more than sufficient in a material as hard as concrete, it is sufficient to screw the anchor screw into concrete with only its first section, which is achieved with a considerably reduced screw-in torque compared to what was previously usual. Studies have shown that the reduction in the required screw-in torque, even when the flank depth is not reduced, is not only due to the increase in the number of cutting grooves, but in conjunction with this measure also to the reduction in the cutting groove depth, which no longer reaches to the base of the thread. The reduction in the cutting groove depth leads to less deep notches in the flanks, so that only comparatively fine-grained material can settle in them when the thread is cut.

5 -

At the same time, the reduction in the cutting groove depth means that the full flank load-bearing capacity is retained, since the flanks are not notched down to the thread base. The load-bearing thread therefore remains unchanged.

Anchor screws are preferred which have six cutting grooves and whose first section is preferably approximately 40 mm with a thread diameter of 7.5 mm. A further preferred variant of the anchor screw is characterized in that the shaft has a second section between the first section and the section near the head, in which the thread has the full flank depth ( _pitch ) and is provided with cutting grooves, and whose length corresponds to approximately four times the outer thread diameter. For an anchor screw with an outer thread diameter of 7.5 mm, the length of the second shaft section is preferably approximately 30 mm. The length of the cutting zone provided with cutting grooves (first and second section) is then preferably approximately 70 mm in total. The rest of the threaded shaft up to the head of the anchor screw has no cutting grooves.

The interaction of the optimized head and shaft shape of the anchor screw means that, on the one hand, the torque with which the screw can be driven is greater than usual, but, on the other hand, the required (screwing-in) torque is considerably lower than before. The safety against overloading of the anchor screw is thus improved in two respects. This also makes the anchor screw more universally usable, since anchor screws with a long shaft length can now also be used where a shorter anchor screw was previously used, in order not to exceed its maximum possible screwing-in torque.

The invention also consists in a screw connection in which an anchor screw is screwed directly into a hard material such as concrete or brick with only the first section. Such a screw connection can be produced with a particularly low screw-in torque - measured against the material - since only the shaft section with a reduced thread flank depth engages the hard material. However, since the first shaft section is longer than the minimum screw-in depth in the hard material and the thread does not tear out due to the hardness of the material, the screw connection is secure.

An embodiment of the anchor screw according to the invention will now be explained in more detail below with the aid of a drawing. The figures in the drawings show

tψ · &psgr; ·

-6 -

figure 1 figure 2 Fig.3 - 8th Fig.9

a side view of the anchor screw,

the cross-section through the shaft of the anchor screw shown in Figure 1,

different applications for the anchor bolt from Fig. 1 and 2 and in

a screw connection with the anchor screw from Fig. 1 and 2 in a particularly hard material.

The anchor screw 10 shown in Figure 1 has a head 12 and a shaft 14.

The shaft 14 is provided with a cutting thread throughout, which is characterized by the dimensions shown in the figure: thread core diameter d _core , thread outer diameter dg _ew and by the flank depth &idiagr;&rgr;^&eegr;^ = ^Q _ew ' ^core' : 2. The shaft 14 has the shaft length 'shank ^unc ' ^we ' ^st three sections along ^its length from the thread tip to the head 1 2, namely:

a first section 1 6 in which the thread has notched flanks 1 8 with a smaller flank depth and thus also a smaller outer diameter,

a second section 20 in which the thread has the full outer diameter and the full flank depth, but the flanks 18 of the thread are interrupted by notches as in the first thread section 16 (the cutting zone), and

a third section 24 extending to the head 12, in which the thread from the second section 20 continues without notches (which can, however, be omitted in the case of relatively short screws).

The first and second sections together form a cutting zone of the anchor screw 10. In the cutting zone, i.e. in the first and second sections, the thread flanks 18 are notched. The notches enable self-tapping thread cutting with the anchor screw 10. The notches are created by six cutting grooves 22 that run helically around the shaft 14 in the same direction as the thread and with a greater pitch than the thread. The cutting grooves 22 are therefore manifested in the notches of the thread flanks.

The length of the first section 16 in the embodiment is 40 mm and that of the second section 20 is 30 mm. The core diameter d _core of the shaft is just under 5.5 mm and the thread outer diameter d _{Gew is} approximately 7.5 mm.

In the cross section of Figure 2 it can be seen that the depth of the cutting groove 22 is smaller than the flank depth, so that the cutting groove 22 does not reach to the thread root 26 or the thread core diameter.

Now to the head 12 of the anchor screw 10 (Fig. 1) The head 12 of the anchor screw 10 is connected to the shaft 14 of the anchor screw 10 with a head support surface 30. The head support surface is flat except for a transition curve 32 towards the shaft 14 and has an outside diameter d^ _uf | which corresponds to the thread outside diameter d _Gew . The head support surface 30 is followed by a slightly conical head surface 36,

whose diameter increases slightly towards the head face 34. The head face 34 has the diameter dg _tjrn . The distance between the head support surface 30 and the head face 34 is the head height h _{Ko f} . The slope of the conical head surface 36 results from ((dg _tjrn - d _Auf |) : (2h _{K f} )) and is 20% or 1/5 in the embodiment.

The head 1 2 has internal tool engagement surfaces for the engagement of a TORX® tool.

Figures 3 to 8 show the universal applicability of the anchor screw 10 shown in Fig. 1 and 2.

Fig. 3 shows a cross-section through a window frame 40 with an anchor screw 10. The frame 40 consists of an outer frame 42 made of PVC and an inner frame 44, which is formed by a rectangular metal tube. The anchor screw 10 penetrates both the outer frame 42 and the inner frame 44. The head 1 2 of the anchor screw 10 rests with its support surface 30 on the surface of the outer frame 42. It is therefore not countersunk. The head 1 2 of the anchor screw 10 can be covered with a cover cap 50.

Fig. 4 also shows a window frame 40 consisting of a metal inner frame 44 and a PVC outer frame 42. In contrast to Fig. 3, the anchor screw 10

ii *♦»·

screwed into the window frame 40 so far that the head 12 of the anchor screw 10 is countersunk in the surface of the PVC outer frame 42. The head face 34 of the anchor screw 10 is flush with the surface of the plastic outer frame 42. The head face 34 of the anchor screw 10 can be covered with a cover cap 52.

Fig. 5 shows the same frame 40 as Fig. 3 to 4. However, the anchor screw 10 in Fig. 5 is screwed so far into the frame 40 that the head 1 2 of the anchor screw 10 rests with its support surface 30 on the surface of the metal inner frame 44 and thus disappears completely inside the PVC outer frame 42. Above the head 1 2, the outer frame 42 has an opening 46 through which the anchor screw 10 is inserted into the frame 40. This opening can be closed with a cover cap 54.

Fig. 6 shows a cross section through a wooden frame 60. An anchor screw 10 is screwed into this wooden frame 60 so that its head 12 is countersunk in the wooden frame 60. The head face 34 of the anchor screw 10 is flush with the surface of the wooden frame 60. The head 12 of the anchor screw 10 can be covered with the cover cap 52 known from Fig. 4.

Fig. 7 shows the same wooden frame 60 as Fig. 6. In contrast to the situation in Fig. 6, however, the anchor screw 10 is screwed further into the wooden frame 60, so that the head end face 34 is also countersunk in the wooden frame 60. The opening remaining above the head end face 34 in the wooden frame 60 is closed with the cover cap 54 known from Fig. 5.

Fig. 8 again shows the wooden frame 60, through which an anchor screw 10 passes at an angle. In contrast to the applications shown in Figs. 3 to 7, the head face 34 does not run parallel to the surface of the wooden frame 60. The anchor screw 10 is screwed into the wooden frame 60 so far that the head face 34 lies below the surface of the wooden frame 60, so that a hole is formed in the wooden frame 60 above the head face 34. This hole is closed by means of a cover cap 56.

Fig. 9 shows a screw connection in which the frame 40 is fixed by means of the anchor screw 10 at a distance from a wall 70 made of a hard material, such as concrete or brick. Fig. 9 shows, on the one hand, that the

-9 -

Anchor screw 10 with its thread extending over the entire length of the shaft 14 is suitable for the distance mounting of components such as the frame 40. Mounting, for example, a window frame in the corresponding opening in the masonry of a building using the screw connection shown in Fig. 9 is particularly simple. First, the window frame is aligned in the wall opening. Then a core hole is drilled through the frame and into the masonry. The frame does not have to be backed up at the corresponding point for this. Finally, the anchor screw 10 is screwed into the core hole. It grooves its thread in both the frame 40 and the masonry 70 itself. Since the frame 40 is also in threaded engagement with the anchor screw 10 in this way, the distance between the frame 40 and the surface of the wall 70 is fixed and cannot be reduced even by strongly tightening the anchor screw 10. Therefore, it is not necessary to backfill the frame 40 at the points where it is to be connected to the wall 70. Since in the screw connection shown in Fig. 9 only the first section 16 of the shaft, in which the flank depth of the thread is reduced, engages the wall 70, the anchor screw 10 can be screwed in with a relatively low screw-in torque despite the hardness of the wall material. For the safety of the screw connection it is only important that the screw-in depth is as large as possible than the minimum screw-in depth for the corresponding wall material. This can be easily achieved for concrete or brick, since the first section 16 of the shaft 14 is longer than the minimum screw-in depth for these materials.

Claims (11)

- 10- PROTECTION CLAIMS 1. Anchor screw with a head (12) with internal tool engagement and flat bearing surface (30), the diameter (d^ _uf |) of which corresponds essentially to the outer thread diameter (dQ _ew ), and to which a head surface (36) widening slightly conically towards the front surface (34) of the head (12) is connected. 2. Anchor screw according to claim 1, characterized in that the cone pitch in the longitudinal direction of the anchor screw (10) is approximately 20%. 3. Anchor screw according to claim 1 or 2, characterized in that the diameter of the support surface (30) corresponds to 0.8 to 1.0 times the thread outer diameter. 4. Anchor screw according to one of the preceding claims, characterized in that the head height (h _head ) corresponds to approximately one third of the thread outer diameter (d(3 _evv ). 5. Anchor screw in particular according to claim 1 with a threaded shaft (14) with helically circumferential cutting grooves (22), characterized in that the shaft (14) has no cutting grooves (22) in a section (24) adjoining the head (12) and more than three cutting grooves (22) in the rest, the depth of which is less than the flank depth (&iacgr;&rgr;| _3&eegr; |<_&bgr; ) of the thread. 6. Anchor screw according to claim 5 with a first shaft section (16) extending from the shaft tip with a reduced flank depth (with an unchanged core diameter), characterized in that the length of the first section (16) corresponds to four to six times the outer thread diameter. 7. Anchor screw according to claim 5 or 6, characterized in that the shank (14) has six cutting grooves (22). 8. Anchor screw according to one of claims 5 to 7, with an outer thread diameter of 7.5 mm, characterized in that the length of the first section (16) is approximately 40 mm. 9. Anchor screw according to one of claims 6 to 8, characterized in that the shaft (14) has a second section (20) between the first section (16) _and the section near the head (24), in which the thread has the full flank depth (t _flank ) and is provided with cutting grooves (22), and whose length corresponds to approximately four times the outer thread diameter. 10. Anchor screw according to claim 9, with 7.5 mm thread outer diameter, characterized in that the length of the second section (20) is approximately 30 mm. 11. Screw connection in which an anchor screw according to one of claims 6 to 10 is screwed directly into a hard material such as concrete or brick exclusively with the first section (16).