Lifting and / or construction machine such as a crane

Abstract

The present invention relates to a lifting and / or construction machine such as a crane (1), comprising a multi-piece longitudinal structural part (2), in particular a tower (3) or boom (4), the pieces (3a, 3b.. 3n; 4a, 4b.. 4n) of which comprise corner posts (5) or longitudinal belts which can be placed against one another and have connecting heads (6) which can be moved into one another for releasable connection to one another, wherein the connecting heads are provided with fixedly attached toothing sections (7) which can be brought into and out of toothing engagement with one another by movement transverse to the longitudinal axis (8) of the longitudinal structural part and, in the engagement position, transfer tensile and compressive forces in the longitudinal direction of the longitudinal structural component.

Description

[0001] Lifting and / or construction machinery such as cranes

[0002] The present invention relates to a lifting and / or construction machine, in particular in the form of a crane, with a multi-piece longitudinal structural part, in particular a tower or boom, the pieces of which comprise corner posts or longitudinal belts which can be placed next to one another and which have connecting heads which can be moved into one another for detachable connection to one another.

[0003] In cranes, their longitudinal structural components, such as the tower or boom, are regularly assembled from multiple pieces to improve transportability. These longitudinal structural components, which can be designed as lattice or rod-and-beam girders, often comprise longitudinal chords or corner posts that are joined together at the ends during assembly of the longitudinal structural component and connected in a form-fitting manner by means of connecting heads that can be moved into one another. Similar longitudinal structural components are also known in other construction machinery, such as rope excavators or leaders with lattice booms, or even slot cutters whose cutters are suspended from a lattice boom. Such multi-piece longitudinal structural components are primarily used in tower cranes, whose towers and booms often have to be disassembled for transport and reassembled at the site of use due to frequent changes of installation location.In order to enable rapid assembly, which requires either connecting or disconnecting the pieces of the longitudinal structural component, and to achieve a stable, play-free connection in the assembled state, various connection types have been proposed. A classic joint is a tenon joint, in which a projecting tenon is provided on the longitudinal chord or corner post of one piece. This tenon engages a tenon receptacle provided on the other longitudinal chord or corner post to be connected to it. This tenon receptacle can be formed, for example, by the interior of the longitudinal chord or corner post, which is often designed as a hollow profile. To secure the tenons in the tenon receptacles, cross bolts are inserted through the tenon receptacles and the tenons sitting therein.In order to lock the tenon joints without play, the said cross bolts can, for example, be conical or have conical clamping sections, or can be composed of several bolt parts that are wedge-shaped or can be spread apart by a wedge located between them, see, for example, DE 10 2013 012 468 A1 .

[0004] As an alternative to such tenon joints, the longitudinal chords can also be connected to each other using screw bolts extending in the longitudinal direction of the longitudinal chords. For example, eyelets or sleeve-shaped bolt guides projecting outwards can be welded to the ends of the longitudinal chords. These are aligned with each other when the longitudinal chords are stacked on top of each other, allowing a bolt to be inserted through and tightened with a bolt nut, thus clamping the longitudinal chords together by tightening the bolt nut.

[0005] Internal tensioning bolts can also be used for longitudinal belts that are slotted or have a lateral recess.

[0006] It is also known to connect the longitudinal chords of the lattice sections of a tower crane using shell couplings, which have a so-called elephant foot. In this case, coupling shells are pivoted open and closed to lock or unlock the couplings. Even though such connectors between the longitudinal chords or corner posts have been tried and tested for many years, they still show potential for improvement. Firstly, the loose connecting parts such as screw bolts or cross bolts are sometimes quite laborious to thread in. In the case of the aforementioned expansion bolts or the longitudinal screw bolts with nuts, for example, several loose parts must be handled simultaneously, which makes assembly time-consuming and laborious, especially under harsh conditions on a construction site. At the same time, the multi-part design increases manufacturing and maintenance costs.

[0007] Secondly, the connectors must be individually adapted to the loads to be transferred, depending on the size of the crane. On the one hand, the connectors must be sufficiently robust and stable to be able to transfer the resulting forces and achieve the expected service life even under the harsh conditions of a construction site. On the other hand, the connectors should be slim and lightweight to avoid unnecessary weight and unnecessarily weakening the longitudinal chords themselves, for example, through excessively large cross-holes.

[0008] Even though the main loads on the longitudinal chords of such longitudinal structural components usually act in the longitudinal direction of the longitudinal chords or along the longitudinal axis of the longitudinal chords, they must be at least partially transferred via the aforementioned transverse bolts or screw bolts, at least when they occur as tensile forces. Since the aforementioned longitudinal structural components are also subject to bending stresses, be it due to wind forces or the load attached to the boom of a crane, some of the longitudinal chords are subjected to compressive stress and others to tensile stress. While compressive forces can be transferred via the superimposed end faces of the longitudinal chords or their connecting heads, the tensile stress must always be transferred via the locking devices. In practice, the locking of the connecting pieces must also be free of play, so that high loads occur under both tensile and compressive forces.The present invention is therefore based on the object of creating an improved lifting and / or construction machine of the type mentioned, which avoids the disadvantages of the prior art and advantageously develops them further. In particular, simple assembly and disassembly of the longitudinal structural components should be ensured while simultaneously creating a stable and robust connection that achieves the desired service life even under harsh construction site conditions, without requiring oversized connecting parts or sacrificing low manufacturing and maintenance costs due to a large number of components. Preferably, the connector system should be equally suitable and easily scalable across different sizes.

[0009] According to the invention, the stated object is achieved by a lifting and / or construction machine according to claim 1. Preferred embodiments of the invention are the subject of the dependent claims.

[0010] It is therefore proposed to provide tensile and compressive force-transmitting engagement means at the end sections of the longitudinal structural sections, which can be brought into locking engagement by a locking movement of the structural sections relative to one another, so that no loose plug-in parts have to transmit the main forces acting on the longitudinal structural part. According to the invention, the connecting heads of the corner posts or longitudinal chords that can be inserted into one another are provided with rigidly attached toothed sections that can be brought into and out of toothed engagement with one another by movement transversely to the longitudinal axis of the longitudinal structural part and, in the engaged position, transmit tensile and compressive forces in the longitudinal direction of the longitudinal structural part. The toothed sections can be formed onto the connecting heads orform an integral one-piece part thereof, whereby a favorable flow of forces and a robust connection can be achieved without overstressing the cross connectors at certain points or having to excessively weaken the longitudinal chords or corner posts through oversized cross holes.

[0011] In particular, the aforementioned toothed sections of the connecting heads can be designed to transmit the main loads of the longitudinal structural part, i.e., tensile and compressive forces acting in the longitudinal direction, completely across the interfaces between the pieces of the longitudinal structural part, so that any securing elements provided to secure the engaged position of the toothed sections, such as locking pins, clamping clips, or retaining rings, do not have to transmit any main loads in the longitudinal direction of the longitudinal structural part. Such securing elements, such as locking pins, screw bolts, clamping clips, or retaining rings, can nevertheless be used to hold the toothed sections in the engaged position and prevent unintentional slippage of two engaged toothed sections transversely to the longitudinal axis of the longitudinal structural part, or even disengagement.However, such securing elements can be installed in the longitudinal direction of the longitudinal structural part, for example with play, in order not to have to bear the main loads.

[0012] Since such securing elements only have to absorb transverse forces or only have to prevent the toothed sections from shifting relative to each other transversely to the longitudinal direction of the longitudinal structural part, the securing elements can be dimensioned significantly smaller than conventional socket pins of, for example, tenon joints and can also be used for different sizes of cranes or construction machinery or special adaptations, since different sizes mainly affect the main loads to be transferred, but not the required securing forces transversely to the longitudinal axis.

[0013] In a further development of the invention, the said toothing sections of the connecting heads can each have a rack-like toothing with a plurality of teeth projecting transversely to the longitudinal axis of the longitudinal structural part and tooth gaps in between, wherein the running direction of the toothing, i.e. the direction in which teeth and tooth gaps follow one another, can be aligned parallel to the longitudinal direction of the longitudinal structural part or inclined at an acute angle thereto, so that the teeth can be arranged one above the other in the longitudinal direction of the longitudinal structural part or can rise in a step-like manner. In principle, a toothing with only one tooth or only two teeth and one tooth gap could also be provided, but a toothing with several teeth and tooth gaps each allows better force distribution and introduction into the longitudinal belts or their connecting heads while at the same time avoiding excessive surface pressures at the tooth contact points.

[0014] In particular, the toothings can extend diagonally to the longitudinal direction of the respective longitudinal chord or corner post through the connecting head, or define a diagonal cutting plane through the connecting head. The teeth of a toothing can be arranged diagonally above one another in a stepped manner to distribute the longitudinal forces across the connecting head cross-section and utilize the connecting head cross-section as fully as possible.

[0015] The toothing need not have a truly straight path or define a flat envelope, although it can do so, but can also extend along a curved running direction and / or define a concave or convex envelope. Preferably, however, the toothing can have a straight running direction or, viewed in a longitudinal section through the longitudinal flange or corner post, define a straight tangent with its tooth tips. In particular, the teeth of the toothing can lie on a virtual envelope plane, similar to a rack.

[0016] Alternatively, the teeth may have a straight running direction, i.e., viewed in a longitudinal section through the longitudinal belt, the tooth tips may define a straight tangent, but may be curved in an arcuate manner in cross-sectional planes transverse to the longitudinal axis of the longitudinal structural part. In particular, the teeth may be designed like thread teeth, which describe an arc around the longitudinal center axis of the respective section of the longitudinal structural part.

[0017] In a further development of the invention, the toothed sections of the connecting heads are designed and oriented in such a way that the toothed sections can be brought into engagement and disengaged again by rotating the longitudinal structural part pieces to be connected relative to one another about an axis of rotation parallel to the longitudinal axis of the longitudinal structural part.

[0018] For example, the aforementioned toothing sections can be configured as internal and external toothings, similar to thread toothing, located on virtual circumferential surfaces, with one of two connecting heads to be connected having external toothing and the other having internal toothing. If the longitudinal structural components are aligned appropriately, in particular aligned coaxially with each other, placed on top of each other, and then rotated slightly relative to each other around the longitudinal axis, the internal and external threads interlock.

[0019] The aforementioned internal and external threads can actually have a pitch on the tooth flanks, similar to a screw thread, so that when the gears engage, they are axially tightened due to the pitch. Alternatively, the teeth of the gears can also be designed without a pitch and have tooth flanks aligned parallel to the cross-sectional planes and perpendicular to the longitudinal axis.

[0020] As an alternative to arranging the toothings on circumferential surfaces, the toothings can also be arranged in longitudinal planes that are aligned parallel to the longitudinal axis of the longitudinal structural part and, if necessary, tilted at an acute angle to a radial direction, although a radial alignment of the aforementioned longitudinal planes would also be possible. For example, the toothings can be arranged in longitudinal planes that are aligned parallel to the respective longitudinal belt and perpendicular to a transverse belt plane in which transverse belts extend from the longitudinal belt.

[0021] Advantageously, the toothed sections on the several longitudinal belts of a piece can be designed to be open or open towards the same circumferential direction, so that by rotating the pieces to be connected, the toothed sections of the connecting heads of one piece can move into the toothed sections of the connecting heads of the other piece.

[0022] The teeth of the gears can be designed in different ways. Classic tooth shapes, for example, with flat tooth flanks or with crowned or convex tooth flanks, can be used to achieve surface contact between the teeth of meshing gears and thus better force distribution. However, tooth flank shapes in which meshing teeth only have linear contact with each other are also possible.

[0023] Preferably, the tooth flanks can extend, at least in sections, approximately parallel to cross-sectional planes perpendicular to the longitudinal direction of the longitudinal structural part, or can be inclined at only a slight acute angle to such cross-sectional planes in order to avoid generating significant transverse forces or shear stresses as a reaction when transferring the main loads acting in the longitudinal direction. For example, the tooth flanks can extend over at least three-quarters of their tooth height at an angle of less than 15°, less than 10°, or less than 5° to the aforementioned cross-sectional planes perpendicular to the longitudinal axis.

[0024] To facilitate assembly and disassembly, insertion aids can be provided on the toothed sections, for example in the form of insertion chamfers on the teeth of the toothed sections. An element can be used as a disassembly aid on the toothed sections, for which a cylindrical, conical, or wedge-shaped opening can be provided on the toothed sections, so that disassembly can be facilitated by pulling in or pushing through a cylindrical element, for example, a cone, or a wedge.

[0025] Advantageously, the connecting heads at one end of a longitudinal structural part can be designed to complement the connecting heads at the other end of the part. For example, the connecting heads can have external thread-type toothed sections at one end and internal thread-type toothed sections at the other end, which would be engageable with each other if they were not mounted on the same part, i.e., they are mounted in a mirror-image arrangement and spacing.

[0026] Alternatively, identically designed connecting heads can also be provided at opposite end sections of a longitudinal structural component, in particular such that identical toothed sections are arranged at the same positions or spacings facing in the same direction. In particular, these can be rack-like toothed sections extending in longitudinal planes that are, as mentioned, parallel to the respective longitudinal chord and perpendicular to a transverse chord plane extending therefrom.

[0027] The connecting heads with the attached toothed sections can be designed as identical parts, which significantly simplifies the production and inventory of the longitudinal structural parts.

[0028] The invention is explained in more detail below using a preferred embodiment and the accompanying drawings. In the drawings:

[0029] Fig. 1: a side view of a lifting and / or construction machine in the form of a tower crane according to an advantageous embodiment of the invention, wherein a tower of the crane is designed as a multi-piece longitudinal structural part, the pieces of which comprise corner posts or longitudinal belts that can be placed on top of one another,

[0030] Fig. 2: a partial, enlarged, perspective view of the tower of the crane from Fig. 1 in the area of ​​the interface between two longitudinal structural sections, showing the engaged toothed sections of the connecting heads,

[0031] Fig. 3: a partial side view of two connecting heads at the ends of two longitudinal chords of the tower from the preceding figures, wherein the partial view a shows the toothed sections of the connecting heads before assembly in a non-engaged position and the partial view b shows the toothed sections of the connecting heads in engagement,

[0032] Fig. 4: a side view of two meshing connecting heads in partial section, showing the locking bolt for securing the meshing,

[0033] Fig. 5: a side view of the meshing connecting heads similar to Fig. 4, showing a disassembly aid in the form of a cylindrical opening,

[0034] Fig. 6: a partially enlarged view of the disassembly aid from Fig. 5, and

[0035] Fig. 7: a plan view of a longitudinal structural part showing the arrangement of the toothed connecting heads of the corner posts rotated by 90°.

[0036] As Figure 1 shows, the crane 1 can be designed as a tower crane and comprise, as longitudinal structural parts 2, on the one hand a tower 3 and, on the other hand, a boom 4 hinged thereto and projecting therefrom, from which a load-handling device, for example in the form of a load hook, can be lowered and raised via a hoist rope, wherein, for example, a trolley can be provided for moving along the boom 4.

[0037] The tower 3 is composed of several tower sections 3a, 3b, ...3n and the boom 4 is composed of several boom sections 4a, 4b, ...4n. The tower 3 and / or the boom 4 or their sections can each be designed as lattice girders. For example, the tower sections 3a, 3b, ...3n can each comprise four corner posts 5 running in the longitudinal direction of the tower, which can be connected to one another by cross connectors in the form of transverse and diagonal bars, so that the tower sections and thus the tower 3 as a whole have a quadrangular cross-section. Similarly, the boom 4 or the boom sections can comprise three longitudinal chords, which are arranged in the longitudinal direction of the boom and can be connected to one another by corresponding cross connectors in the form of transverse and diagonal bars, so that the boom 4 as a whole can have a triangular cross-section. It is understood, however, that other cross-sectional shapes with other corner posts orLongitudinal belt arrangements may be provided.

[0038] As Figures 2 and 3 show, the tower sections 3a and 3b of the tower 3 - and similarly the sections of the boom 4 - can be placed together with their longitudinal chords or corner posts 5 and locked together in a form-fitting manner in order to be able to transfer the forces acting on the tower 3 or the boom 4.

[0039] The longitudinal chords or corner posts 5 comprise connecting heads 6, each of which is provided with toothed sections 7, via which the connecting heads 6 can be brought into tooth engagement with one another on the corner posts 5 to be connected of two tower sections or boom sections to be connected.

[0040] The aforementioned toothed sections 7 can be molded onto the aforementioned connecting heads 6, in particular, formed integrally therewith. For example, the toothed sections 7 can be machined into the metallic connecting heads 6, although non-cutting manufacturing processes are also possible.

[0041] The toothed sections 7 are designed such that they can be brought into or out of engagement with one another by moving transversely to the longitudinal axis 8. Said longitudinal axis 8 can be the longitudinal axis of the longitudinal structural part 2 and / or the longitudinal axis of the longitudinal belts 5 to be connected to one another.

[0042] The toothed sections 7 are designed such that, in the engaged position, they transmit the main loads across the interface between two pieces of the longitudinal structural part 2, in particular also tensile forces acting in the longitudinal direction of the longitudinal chords or corner posts 5 and attempting to pull two interconnected corner posts 5 apart. Since the toothed sections 7 can be brought into engagement or disengaged from one another by transverse movement, the toothed sections 7 can be rigidly formed or fastened to the longitudinal beam pieces, in particular forming a rigid part of the connecting heads 6 and thus of the end sections of the corner posts 5.

[0043] As a comparison of Figures 2, 3 and 7 shows, the toothing sections 7 can each have a rack-like toothing 9, which each has a plurality of teeth 10 projecting transversely to the longitudinal axis 8 and tooth gaps 11 therebetween, wherein the toothings 9 with their teeth 10 can define a flat envelope surface which can extend diagonally to the longitudinal axis 8 through or on the end faces of the connecting heads 6.

[0044] For example, the parting line between the toothings 9 of two coupled connecting heads 6 can be inclined at an angle of 5° to 40° or 10° to 30° or 15° to 25° to the longitudinal axis 8, see Figure 3b.

[0045] Considering the multiple connecting heads 6 at one end of a longitudinal structural part (see Figures 2 and 7), the toothings 9 can be rotated from corner post to corner post, for example, by 90°, particularly if four such corner posts 5 are provided. Considering the boom 4, the toothings 9 can be correspondingly rotated by 120° relative to one another, particularly if said boom 4 comprises three longitudinal chords. Generally, the toothings, viewed from connecting head 6 to connecting head 6 at one end of a support piece, can be rotated by an angle corresponding to 360° divided by the number of longitudinal chords. In principle, however, other arrangements or rotations would also be possible.

[0046] In particular, the toothings 9 of the connecting heads 6 are arranged such that they can be brought into engagement or disengaged by rotating the two tower sections or boom sections to be connected relative to each other about the longitudinal axis 8. To secure the toothing sections 7 of two coupled connecting heads 6 in the engaged position, locking elements 12 can secure the engaged toothing pairs relative to each other against slipping or even disengaging. For example, locking pins or bolts 13 can be provided as locking elements 12, which pass through two coupled connecting heads 6 and hold the toothing sections 7 in the engaged position. For example, such locking bolts 13 can extend through the toothings 9, see Figure 4.

[0047] The connecting heads 6 can have bores that are aligned with each other when the connecting heads 6 are in the intended meshing position, so that a corresponding locking bolt 13 can be inserted through and secured therein, for example by a nut screwed on the opposite side.

[0048] The securing elements 12 can extend in a direction transverse to the longitudinal axis 8 of the longitudinal belts to be connected and transverse to the parting line between two meshing toothed sections 7, see Figure 4.

[0049] Independently of this, the securing elements 12 are designed to prevent slippage of the toothed sections 7 in the transverse direction along which the toothed sections can be brought into and out of engagement. In addition, the securing elements 12 can also absorb shear forces that can arise due to inclined tooth flanks when the engaged toothed sections 9 are subjected to strong tensile or compressive stresses. However, the aforementioned securing elements 12 do not serve to transfer the main loads transmitted by the toothed sections 9.

[0050] To aid in climbing into tower sections when erecting the crane, pockets on the inside or lugs on the outside can be attached to the tower sections 3a, 3b, 3n as assembly aids.

Claims

Claims 1. Lifting and / or construction machine such as a crane (1), with a multi-piece longitudinal structural part (2), in particular a tower (3) or boom (4), the pieces (3a, 3b .. 3n; 4a, 4b .. 4n) of which comprise corner posts (5) or longitudinal belts which can be placed next to one another and which have connecting heads (6) which can be moved into one another for detachable connection to one another, characterized in that the connecting heads (6) are provided with fixedly attached toothed sections (7) which can be brought into and out of toothed engagement with one another by movement transversely to the longitudinal axis (8) of the longitudinal structural part (2) and which, in the engaged position, transmit tensile and compressive forces in the longitudinal direction of the longitudinal structural component (2).

2. Lifting and / or construction machine according to the preceding claim, wherein the toothed sections (7) are designed to absorb the main loads of the longitudinal structural part (2) in the form of tensile forces and compressive forces in the engaged position. ten in the direction of the longitudinal axis (8) of the longitudinal structural part (2), and the connection between the longitudinal structural part pieces is designed free of loose or movable main load-bearing elements.

3. Lifting and / or construction machine according to one of the preceding claims, wherein securing elements (12) are provided for securing two coupled connecting heads (6) against slipping transversely to the longitudinal axis (8) of the longitudinal structural part (2) and loosening of the toothed sections (7) in tooth engagement, preferably comprising securing bolts (13) which are inserted or screwed through two coupled connecting heads (6) in each case.

4. Lifting and / or construction machine according to the preceding claim, wherein the securing elements (12) are mounted on the connecting heads (7) with play in the direction of the longitudinal axis (8) of the longitudinal structural part (2) and / or are designed to transfer only transverse forces in directions transverse to the longitudinal axis (8) of the longitudinal structural part (2).

5. Lifting and / or construction machine according to one of the preceding claims, wherein the toothed sections (7) are designed to be brought into engagement and disengaged by rotating two pieces of the longitudinal structural part (8) to be connected to one another about its longitudinal axis (8).

6. Lifting and / or construction machine according to one of the preceding claims, wherein the toothing sections (7) each have a rack-like toothing (9) with a plurality of teeth (10) projecting transversely to the longitudinal axis (8) and tooth gaps (11) located therebetween.

7. Lifting and / or construction machine according to the preceding claim, wherein the toothings (9) lie with their tooth tips on a preferably flat envelope surface which is inclined at an acute angle to the longitudinal axis (8) of the longitudinal structural part (2) and / or extends diagonally through a respective connecting head (8).

8. Lifting and / or construction machine according to the preceding claim, wherein said envelope surface is inclined to the longitudinal axis (8) at an angle of 10° to 30° and the teeth (10) are arranged one above the other in a stepped manner.

9. Lifting and / or construction machine according to one of the two preceding claims, wherein the teeth (10) of the toothings (9) extend with their tooth tips parallel to cross-sectional planes perpendicular to the longitudinal axis (8).

10. Lifting and / or construction machine according to the preceding claim, wherein the toothings (9) with their teeth (10) extend perpendicularly to a respective transverse belt plane in which transverse belts are arranged which extend from the respective longitudinal belt on which the toothing (9) is formed.

11. Lifting and / or construction machine according to one of the preceding claims, wherein the toothed sections (7) of the connecting heads (6), which are provided at one end of the respective longitudinal structural part, are arranged rotated relative to one another in such a way that the toothed sections (7) are arranged rotationally symmetrically to the longitudinal axis (8) of the longitudinal structural part (2) and / or can be transferred into congruent positions by rotating the longitudinal structural part.

12. Lifting and / or construction machine according to one of the preceding claims, wherein the toothed sections (7) of the connecting heads (6), which are provided at one end of the respective longitudinal structural part, are arranged rotated relative to one another from connecting head (6) to connecting head (6) by a respective pitch angle depending on the number of longitudinal belts, in particular by an angle of 90° in the case of four longitudinal belts and by an angle of 120° in the case of three longitudinal belts.

13. Lifting and / or construction machine according to one of the preceding claims, wherein the toothed sections (7) have tooth flank angles which indicate an inclination of the respective tooth flank relative to a cross-sectional plane perpendicular to the longitudinal axis (6) and are less than 20° or less than 10°.

14. Lifting and / or construction machine according to one of the preceding claims, wherein the toothed sections (7) have tooth flanks whose tangential plane is aligned approximately parallel to the said cross-sectional plane perpendicular to the longitudinal axis (6).

15. Lifting and / or construction machine according to one of the preceding claims, wherein the connecting heads (6) at opposite ends of a longitudinal structural part are designed as identical parts and / or all connecting heads (6) including their toothed sections (7) of a longitudinal structural part are designed identically to one another.

16. Lifting and / or construction machine according to one of the preceding claims, wherein insertion aids, in particular insertion bevels, are provided on the toothed sections (7) as an assembly aid.

17. Lifting and / or construction machine according to one of the preceding claims, wherein disassembly aids in the form of an insertion opening for inserting a disassembly element are provided on the toothed sections (7).

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