Clamp arrangement for crack limitation in tree trunks

Description

[0001] The invention relates to a clamp arrangement for limiting cracks in tree trunks.

[0002] EP 3 287 647 A1 discloses a clamping arrangement for tree trunks, with a base body on which at least three spaced-apart retaining tongues are formed, wherein the base body and the retaining tongues are aligned as cutting edges in a common cutting direction, and wherein at least two locking lugs for a releasable connection with a setting device are formed on the base body and / or on at least one retaining tongue.

[0003] The object of the invention is to provide a clamping arrangement that can also be used with high-density logs.

[0004] This problem is solved for a clamping arrangement of the type mentioned above by the clamping arrangement having two cutting edges, each extending from a back surface to a cutting edge along a cutting direction and tapered in the cutting direction, wherein the cutting directions of the two cutting edges are aligned parallel to each other and wherein the two cutting edges are connected, in particular exclusively, by a first connecting web extending between first end regions of the two cutting edges and by a second connecting web extending between second end regions of the two cutting edges.

[0005] The cutting direction refers to the direction in which the cutting edge can be driven into a log with the least resistance. The two cutting edges are connected to each other via the first and second connecting ribs in such a way that their cutting directions are aligned parallel to each other, thus ensuring minimal resistance for both cutting edges during the driving process into a log. Preferably, the two cutting edges are connected to each other exclusively at a first end section by the first connecting rib and at a second end section by the second connecting rib.This allows the two cutting edges to deform freely elastically or elastically and plastically in a central section between the two end regions during the driving process. This ensures advantageous adaptation of the cutting edges to the conditions of the log, which does not necessarily have a homogeneous density in the area into which the clamp assembly is to be driven. Furthermore, the two cutting edges can also deform elastically or elastically and plastically independently of each other in the central section between the two end regions even after the driving process into the log. This deformation capability of the two cutting edges is particularly advantageous if a crack in the log, which is bridged by the clamp assembly, widens, for example, due to the log drying out.In this case, an individual geometric adaptation of the respective central section of the two cutting edges promotes a homogeneous load transfer from the log to the respective cutting edge, so that local overloads of the cutting edges can at least be largely avoided.

[0006] Preferably, the first connecting web and the second connecting web each extend over a fraction of the total length of the respective cutting edge. Particularly preferably, this fraction is not greater than 25 percent, and especially not greater than 20 percent. This ensures that the cutting edge has the possibility to deform freely over at least a fraction of 50 percent or more.

[0007] The cutting edge can be tapered along its entire length in the cutting direction, resulting in an essentially wedge-shaped profile for the cutting edge in a cross-sectional plane that includes the cutting direction. Alternatively, the cutting edge extends from the back surface for 50 to 80 percent of the distance between the back surface and the cutting edge along the cutting length with a constant thickness and only tapers in the adjacent area extending to the cutting edge.

[0008] Advantageous further developments of the invention are the subject of the dependent claims.

[0009] It is advantageous if the first connecting web and the second connecting web each extend between the back surfaces of the two cutting edges. Preferably, the first connecting web has a first back surface and the second connecting web has a second back surface, which together with the back surfaces of the two cutting edges form a common surface. Furthermore, it is provided that both the first connecting web and the second connecting web extend from their respective first and second back surfaces along the cutting direction, this extension being only a fraction of the distance between the back surface and the cutting edge. Preferably, this fraction lies within an interval between 30 and 50 percent of the distance between the back surface and the cutting edge.

[0010] It is advantageous if the two cutting edges exhibit a curvature in a cross-sectional plane oriented perpendicular to the cutting direction, with a radius of curvature that is 5 to 10 times greater than the distance between the back surface and the cutting edge. In the application scenario for the clamp arrangement, crack propagation in the end face of a log is to be prevented, with the clamp arrangement spanning an existing crack or a zone where a crack is expected. If crack propagation occurs, for example due to a drying process of the log, the distance between the first end regions of the cutting edges and the second end regions of the cutting edges increases.Since the two cutting edges between the two opposite end regions are curved, the radius of curvature of both cutting edges increases because a kind of stretching process takes place for the two cutting edges in the cross-sectional plane perpendicular to the cutting direction. This creates a resulting force acting radially in the direction of the respective curvature, which is exerted by the respective cutting edge on the surrounding wood of the log. This results in a bracing effect between the respective cutting edge and the log, which in turn leads to an increase in the reaction forces provided by the clamping arrangement to the log.Accordingly, the curvature of the two cutting edges ensures an improved stabilizing effect that the clamp assembly can exert on the log, without requiring a significant increase in the amount of material used to manufacture the clamp assembly. For example, the clamp assembly is intended to be manufactured from a plastic material using injection molding. Alternatively, the clamp assembly can also be manufactured using additive manufacturing (3D printing) or as a stamped and bent part from a sheet metal part.

[0011] Preferably, a first distance between the first end regions of the two cutting edges and a second distance between the second end regions of the two cutting edges are greater than a distance between the two cutting edges in a central region between the first and second end regions. This results in the essentially band-shaped cutting edges facing each other with convexly shaped side surfaces, and in the application of the clamp arrangement, forces directed radially and in opposite directions from the respective cutting edges can be introduced into the surrounding wood of the log via the concave side surfaces of the two cutting edges that deflect each other.

[0012] In a further development of the invention, at least one cutting edge is provided with a centering mandrel that extends beyond the cutting edge in the cutting direction and has a centering tip that tapers in the cutting direction. The at least one centering mandrel facilitates the driving process for the clamp assembly, since the single centering mandrel assigned to one of the cutting edges, or the multiple centering mandrels assigned to one or both cutting edges, have a significantly smaller cross-section compared to the two cutting edges and therefore need to displace less wood to ensure at least initial adhesion of the clamp assembly to the log. By way of example, the centering mandrel has a conical geometry that tapers to a point with increasing distance from the back surface.Alternatively, the centering mandrel is partially cylindrical, particularly circular, and tapers conically at its ends. To ensure that, during the driving process for the clamp assembly, at least one centering mandrel is initially in contact with the surface of the log, the at least one centering mandrel projects beyond the cutting edge along the cutting direction. It is advantageous if at least three centering mandrels are attached to the clamp assembly, with the centering mandrels preferably being assigned to the first and / or second end regions of the cutting edges. It is particularly preferred that a total of four centering mandrels are arranged on the clamp assembly, each assigned in pairs to the first end region and the second end region.For example, it is provided that the centering mandrel is an integral part of the cutting edge, so that the centering mandrel projects symmetrically from the cutting edge transversely to the cutting direction or is integrated into the cutting edge in such a way that it only projects beyond the cutting edge in the cutting direction.

[0013] In a further embodiment of the invention, the centering mandrel is arranged transversely to the cutting direction adjacent to the cutting edge, and / or the centering mandrel has a recess on its rear side, facing away from the centering tip, with a geometry corresponding to that of the centering tip. With such an embodiment of the centering mandrel, it is advantageous that the centering function of the centering mandrel is separate from the cutting function of the cutting edge, so that these two components can each be optimally adapted to their respective purposes. Additionally or alternatively, the centering mandrel can be provided with a recess on its rear side, which is at least largely identical to the tapered area of ​​the centering mandrel.This facilitates stacking of the clip assembly, allowing a large number of such clip assemblies to be accommodated, for example, in a linear arrangement within a magazine designed for holding wooden marker plates. Preferably, when several clip assemblies are stacked, the centering pins of a preceding clip assembly define the edges of the subsequent clip assembly and engage in the recesses of the centering pins of the subsequent clip assembly, thus creating a stable stack connection between the clip assemblies.

[0014] In an advantageous embodiment of the invention, the centering mandrel is designed as an extension of the cutting edge in the cutting direction. The centering mandrel thus forms a projection directly associated with the cutting edge and can also be described as a partially projecting projection of the cutting edge in the cutting direction. The centering mandrel is therefore supported centrally on the cutting edge, so that undesirable lateral forces, which would otherwise have to be transferred from the centering mandrel to the cutting edge, are avoided during the driving process for the clamp assembly into a log. Instead, this arrangement of the centering mandrel ensures a linear force flow from the back surface of the cutting edge, through the cutting edge body, to the centering mandrel.

[0015] It is advantageous if the two cutting edges are aligned symmetrically to each other, with a mirror plane for the two cutting edges being oriented perpendicular to a minimum distance between the two cutting edges. This is intended to achieve at least a largely deformation-resistant behavior for the clamping arrangement. The underlying consideration is that, ideally, the clamping arrangement is driven into a log in such a way that the minimum distance between the two cutting edges is parallel to the crack and preferably directly above the crack, and the first and second end regions of the cutting edges are positioned as far away from the crack as possible. Preferably, the minimum distance between the cutting edges is less than the extent of the respective cutting edge between the back surface and the cutting edge, and in particular lies in a range between 60 percent and 90 percent of the extent of the respective cutting edge.

[0016] In an advantageous embodiment of the invention, each of the two cutting edges is provided with a transverse cutting edge at the first end region and / or the second end region, the transverse cutting edge of which is oriented at an angle between 70 degrees and 110 degrees to the cutting edge. The purpose of the transverse cutting edge is to prevent slippage of the associated cutting edge, such as can occur with increasing cracking forces in the log. The transverse cutting edge forms a barb with which forces, for example, those directed from the first end region of the cutting edge towards the second end region of the cutting edge, can be absorbed by anchoring it in the wood of the log. Preferably, the length of the transverse cutting edge is significantly shorter than the length of the cutting edge. The transverse cutting edge can be designed such that its edge lies at the same level as the cutting edge of the cutting edge.Alternatively, it can be provided that the cross-cutting edge extends beyond the cutting edge of the cutting tool in the cutting direction, thus ensuring a function similar to that of the centering mandrel.

[0017] In a further embodiment of the invention, the first connecting web and the second connecting web are each formed in an arc shape, with opposite end regions of the first connecting web and opposite end regions of the second connecting web being oriented perpendicular to the convex inner surfaces of the two cutting edges. The arc shape of the first and second connecting webs, as well as the orientation of their respective end regions relative to the convex inner surfaces of the two cutting edges, promotes advantageous deformation of the cutting edges during use.This assumes that the clamp arrangement spans a crack and that, as the crack propagates, the distance between the first and second end regions of the cutting edges increases, leading to a stretching or straightening of the arc-shaped cutting edges. The arc-shaped connecting webs counteract this stretching or straightening, as the force flow via the connecting webs acts on the inner surfaces in a normal direction.

[0018] It is particularly advantageous if the first connecting bridge and the second connecting bridge are arranged on a common oval.

[0019] Preferably, the first connecting web has a first support plate and the second connecting web has a second support plate, wherein the first support plate and the second support plate, together with the back surfaces of the two cutting edges, form a striking surface, in particular a flat one. The first support plate and the second support plate each extend from the first connecting web and the second connecting web, respectively, and from the two support plates to allow for the large-area application of striking forces, which are applied with a hammer, in particular a marking hammer designed for use with wooden marking plates, to the back surfaces of the cutting edges and the two support plates in order to drive the clamping arrangement into the log.

[0020] It is advantageous for the concave inner surfaces of the cutting edges to have radially outward-projecting protrusions. The purpose of these protrusions is to prevent the cutting edges from slipping in the surrounding wood. Preferably, the protrusions have a triangular profile in a cross-sectional plane oriented perpendicular to the cutting direction. The first side of the triangular profile is parallel to the inner surface, and the second side forms an angle of 45 to 90 degrees with the inner surface. This design of the protrusions acts as undercuts or barbs to prevent slippage in the wood, thus ensuring a particularly secure hold of the cutting edge in the wood.

[0021] In a preferred embodiment of the invention, retaining tongues are formed at the first end regions of the two cutting edges and at the second end regions of the two cutting edges, projecting from the back surface in the opposite direction to the cutting direction. The inner surfaces of opposing retaining tongues are each provided with a concave recess. The retaining tongues serve to positively engage the clamping arrangement with a marking hammer designed for use with wooden marking discs. For this purpose, the retaining tongues are designed in the same manner as corresponding retaining tongues of wooden marking discs.Preferably, the marking hammer has a circular cylindrical hammerhead with a flat striking surface and a circumferential groove is formed adjacent to the striking surface on the cylindrical outer circumferential surface of the hammerhead, into which the retaining tongues can engage with radially inwardly projecting end sections.

[0022] Advantageous embodiments of the invention are shown in the drawing. Here, the drawing shows: Figure 1 shows a perspective view of a first embodiment of a clamp arrangement from a top oblique angle; Figure 2 shows the clamp arrangement according to the Figure 1 In a perspective view from a low angle, Figure 3 shows a top view of the clamp arrangement according to the Figures 1 and 2 Figure 4 shows a bottom view of the bracket arrangement according to the Figures 1 to 4Figure 5 shows a top view of a second embodiment of a clamp arrangement, and Figure 6 shows a perspective view from below of a third embodiment of a clamp arrangement.

[0023] One in the Figures 1 to 4 The first embodiment shown, a clamp arrangement 1, is in the same way as one in the Figure 5 The second embodiment of a clamping arrangement 51 shown is designed to be driven into a cut surface of a log (not shown) in order to either prevent an existing crack from propagating further or to prevent crack formation at a crack-prone location. An orientation of the clamping arrangement 1, which can also be chosen for the clamping arrangement 51, is shown in the schematic representation of the Figure 3 to be seen, in which a previously existing crack 2 is indicated purely schematically.

[0024] The clamp arrangement 1 and the clamp arrangement 51 are preferably made from a base material, with the plastic injection molding process being used as the manufacturing method in particular.

[0025] The following description of the clamp arrangement 1 applies in the same way to the clamp arrangement 51, except for the arrangement of centering mandrels, so that a further description of the properties of the clamp arrangement 51 is omitted.

[0026] The clamp arrangement 1 comprises a first cutting edge 11 and a second cutting edge 12, which are mirror-symmetrical to each other. A mirror plane 3 is located in the Figure 4The first cutting edge 11 and the second cutting edge 12 are shown and are oriented perpendicular to a minimum distance 4 between the first cutting edge 11 and the second cutting edge 12. The minimum distance 4 is smaller than a first distance 6 between the first end regions 16 of the two cutting edges 11, 12 and smaller than a second distance 7 between the second end regions 17 of the two cutting edges 11, 12. Each of the cutting edges 11, 12 comprises a ribbon-shaped cutting body 18, which extends with a constant profile from a back surface 13 of the respective cutting edge 11, 12 in a cutting direction 15 to a tapered section 19. In the tapered section 19, the respective cutting edge 11, 12 tapers from the cutting body 18 to a cutting edge 14.By way of example only, it is provided that in the case of the cutting edges 11, 12 the tapering takes place exclusively from an inner surface 20 of the cutting edge 11, 12, while an outer surface 21 of the respective cutting edge 11, 12 is formed in a straight extension of the cutting edge body 18.

[0027] By way of example, both cutting edges 11, 12 point in a cross-sectional plane 5 that is parallel to the representation plane of the Figure 3The curvature of the concave inner surface 20 and the convex outer surface 21 is preferably aligned such that the inner surface 20 and the outer surface 21 are aligned parallel to each other, at least in certain areas, and in particular over their entire extent. By way of example, it is provided that the curvatures of the inner surface 20 and the outer surface 21 each follow circular segments (not shown) and thus each have a constant radius of curvature 27, 28.

[0028] The two cutting edges 11, 12 are connected to each other at a first end region 16 by a first connecting web 25 and at a second end region 17 by a second connecting web 26. By way of example, the first connecting web 25 follows a circular segment (not shown) and has a first radius of curvature 29, and the second connecting web 26 follows a circular segment (not shown) and has a second radius of curvature 30, which, purely by way of example, coincides with the first radius of curvature 29. Preferably, the two radii of curvature 29, 30 are matched to the radius of curvature 27 of the inner surface 20 such that the two connecting webs 25 and 26 each meet the respective inner surfaces 20 of the cutting edges 11, 12 in a normal direction.As an alternative to alignment with a circular segment, it can also be provided that the two connecting bridges 25, 26 are designed as sections of an oval not shown.

[0029] As an example, the connecting webs 25, 26 are each associated with support plates 32, 33 designed as plane-parallel plates. These support plates 32, 33 extend parallel to a striking plane (not shown) defined by the back surfaces 13 of the two cutting edges 11, 12 and, like the connecting webs 25, 26, serve to connect the two cutting edges 11, 12. Each of the two support plates 32, 33 is penetrated by a guide bore 38, so that the clamping arrangement 1 can be threaded onto guide mandrels (also not shown) with further clamping arrangements (not shown) for support purposes.

[0030] Each of the two cutting edges 11, 12 is provided with a transverse cutting edge 41 at both the first end region 16 and the second end region 17. For example, the transverse cutting edge 41 projects at a right angle to the first end region 16 and the second end region 17 of the respective cutting edge 11, 12. Accordingly, a transverse cutting edge 42 is also oriented at a right angle to the cutting edge 14. For example, the transverse cutting edge 41 is tapered on both sides in the cutting direction 15, unlike the cutting edges 11, 12, and the angle of an outer transverse cutting edge surface 49 relative to the cutting direction 15 can be greater than the angle of an inner transverse cutting edge surface 50 relative to the cutting direction 15.The transverse cutting edge 41 forms an end-side thickening for the cutting edge 11, 12, wherein this thickening, in the manner of an anchor, enables a tensile force introduction into the clamp arrangement 1 for tensile forces that are directed in the direction of a distance between the first connecting web 25 and the second connecting web 26 and preferably transverse to a crack direction of a crack to be limited in a tree trunk.

[0031] Adjacent to a back surface 43 of the transverse cutting edge 41 extends a plate-shaped support section 44, from which a retaining tongue 45 projects in the opposite direction to the cutting direction 15. Each of the retaining tongues 45 is provided with a recess 46, which forms a retaining projection 47. The four retaining tongues 45 (shown here as an example) allow the clamping assembly 1 to be positively clipped onto a marking hammer (not shown), which can then be used to drive in the clamping assembly 1.

[0032] On the inner surface 20 of the cutting edges 11, 12, six radially inwardly projecting projections 39 are formed, as shown in the illustration. Figures 3 and 4 exhibit a triangular profile. The projections 39, like the transverse cutting edges 41, serve to prevent movement of the respective cutting edge 11, 12 in a direction tangential to the outer surface 21.

[0033] As an example, each of the cross-cutting edges 41 is assigned a centering mandrel 34, which extends in the cutting direction 15 over the cutting edge 14 of the respective cutting edge 11, 12 and has a centering tip 35 at its end. Purely by way of example, a recess 37 is formed on the back side 36 of the centering mandrel 34 facing away from the centering tip 34, the geometry of which is adapted to the geometry of the centering tip 35. Furthermore, a recess 48 is formed between the respective support plate 32, 33 and the support sections 44 assigned to the cross-cutting edge 41, so that when several clamp arrangements 1 are arranged along the cutting direction 15, the centering mandrels 34 of a preceding clamp arrangement 1 can be received in the recesses 37 of the subsequent clamp arrangement 1. As shown, for example, in the illustrations of the Figures 1 and 2The centering mandrels 34 are each designed as halved bodies of revolution, with a rotation axis of the centering mandrel 34 (not shown in detail) being aligned parallel to the cutting direction 15.

[0034] By way of example, the two cutting edges 11, 12 are each freely movable in a central section 22, since they are only connected to each other at their first and second end regions 16, 17. Preferably, the extent of the support plate 32 and the second support plate 33 along the cutting edge 14 is smaller than the extent of the respective central sections 22.

[0035] For example, it is provided that the radius of curvature 27 of the inner surface 20 and the radius of curvature 28 of the outer surface 28 is 5 to 10 times the distance 31 between the back surface 16 and the cutting edge 14.

[0036] The one in Figure 5The second embodiment of a clamp arrangement 51 shown differs from the first embodiment of the clamp arrangement 1, as shown in the Figures 1 to 4 This is shown by the arrangement of the centering mandrels 54, which, unlike the clamp arrangement 1, are not arranged on the transverse cutting edges 41, but directly on the two cutting edges 11, 12.

[0037] The one in Figure 6 The embodiment of a clamping arrangement 61 shown is a variant of the second embodiment of the clamping arrangement 51, as shown in the Figure 5 as shown. In the clamp arrangement 61, the centering pins 64 are arranged away from the cross-cutting edges 41, in accordance with the clamp arrangement 51.

[0038] In contrast to the clamp arrangement 51, the centering pins 64 are designed as extensions of the cutting edges 11, 12 and extend along the cutting direction 15. By way of example, the centering pins 64 have a rectangular, in particular a square, cross-section in a cross-sectional plane (not shown) that is oriented transversely to the cutting direction 14.

[0039] By way of example, each of the centering mandrels 64 is provided at one end region facing away from the cutting edge 11 or 12 with a symmetrically wedge-shaped centering cutting edge 65 tapered in the cutting direction. Alternatively, in an embodiment not shown, the respective centering mandrel can have an asymmetrical wedge shape, in particular a wedge shape on only one side, like the cutting edge 11, 12.

[0040] A cutting edge 66 of the centering cutting edge 65 is aligned parallel to the cutting edge 14 of the respective cutting edge 11, 12. This prevents undesirable torsional stresses from being caused in the cutting edges 11, 12 and in the log after the centering pins 64 have penetrated the log to be stabilized, as could happen if the cutting edges 66 of the centering pins 64 were not aligned parallel to the cutting edges 14 of the cutting edges 11, 12.

[0041] Furthermore, in the embodiment according to the Figure 6It is provided, purely by way of example, that an inner surface 67 of the centering mandrel 64 is flush with the inner surface 20 of the cutting edge 11 or 12. It is also provided, purely by way of example, that an outer surface 68 of the centering mandrel 64 is flush with the outer surface 21 of the cutting edge 11 or 12. This ensures that, in a state where the clamping arrangement 61 is driven into the log (not shown) as intended, the centering mandrels 64 have the same profile as the cutting edges 11, 12 in a cross-sectional plane oriented transversely to the cutting direction 14, thus facilitating the penetration of the clamping arrangement 61 into the log. In other words, the arrangement and design of the centering tips 64 ensure that a projection of the centering tips 64 onto a projection plane oriented transversely to the cutting direction, which is aligned with the cross-sectional plane 5 according to the Figure 3coincides, is in overlap with a projection of the respective cutting edge 11 or 12.

[0042] By arranging the centering pins 64 in line with the cutting edge 11 or 12, an advantageous force flow within the clamp assembly 61 is ensured during the driving process. For illustrative purposes, it is assumed that the driving process for the clamp assembly 61 is carried out with a marking hammer (not shown) designed for processing wooden marking plates and featuring, for example, a circular cylindrical hammer head with a circumferential annular groove into which the retaining projections 47 of the retaining tongues 45 can engage in a form-fitting manner. In this process, a flat end face of the marking hammer rests at least substantially flush against the back surfaces 13 of the cutting edges 11, 12.If the marking hammer, with the clamp assembly 61 attached to it, is accelerated during a striking motion and the clamp assembly 61 with its centering pins 64 strikes the at least substantially flat end face of the log, a force is transmitted between the marking hammer, the clamp assembly 61, and the log. This results in a substantially linear force flow originating from the back surface 13, through the cutting edges 11, 12, and into the centering pins 64. Undesirable tilting forces caused by mutually inclined cutting edges, which would increase the driving forces required to drive the clamp assembly 61 into the log, are thus avoided.

[0043] In the embodiment of the clamping arrangement 61 according to Figure 6, a concavely curved profile surface 69 extends, particularly in the cutting direction 15, from the recess 48 to a transverse cutting step 70. The transverse cutting step 70 projects transversely to the cutting direction from the profile surface 69 and forms an undercut against the cutting direction 15. Thus, the transverse cutting step 70 reduces the risk of the clamping arrangement 61 working its way out of the log (not shown) against the cutting direction 15, for example due to temperature fluctuations and the associated different expansion changes of the clamping arrangement 61 and the log.

[0044] In another embodiment of a clamping arrangement, not shown, the transverse cutting edges extend beyond the cutting edges of the cutting blades in the cutting direction and can thus also serve as centering elements, whereby in this case separately designed centering mandrels can be dispensed with.

Claims

1. Clamp (1; 51; 61) for limiting cracks in logs, having two blades (11, 12) which each extend from a back surface (13) to a cutting edge (14) along a cutting direction (15) and which are tapered in the cutting direction (15), the cutting directions (15) of the two blades (11, 12) are aligned parallel to one another and wherein the two blades (11, 12) are connected, in particular exclusively, by a first connecting bar (25) which extends between first end regions (16) of the two blades (11, 12) and by a second connecting bar (26) which extends between second end regions (17) of the two blades (11, 12).

2. Clamp (1; 51; 61) according to claim 1, characterized in that the first connecting bar (25) and the second connecting bar (26) each extend between the back surfaces (13) of the two blades (11, 12).

3. Clamp (1; 51; 61) according to claim 1 or 2, characterized in that the two blades (11, 12) have a curvature with a radius of curvature (27, 28) which is 5 times to 10 times greater than a distance (31) between the back surface (13) and the cutting edge (14) in a cross-sectional plane aligned transversely to the cutting direction (15).

4. Clamp (1; 51; 61) according to claim 1, 2 or 3, characterized in that a first distance (6) between the first end regions (16) of the two blades (11, 12) and a second distance (7) between the second end regions (17) of the two blades (11, 12) are greater than a distance (4) between the two blades (11, 12) in a central region between the first end region (16) and the second end region (17).

5. Clamp (1; 51; 61) according to claim 1, 2, 3 or 4, characterized in that at least one blade (11, 12) is provided with a centering mandrel (34; 54; 64) which extends beyond the cutting edge (14) in the cutting direction (15) and which has a centering tip (35; 65) which is tapered in the cutting direction (15).

6. Clamp (1; 51; 61) according to claim 5, characterized in that the centering mandrel (34; 54; 64) is arranged transversely to the cutting direction (15) adjacent to the blade (11, 12) and / or in that the centering mandrel (34; 54) has, on a rear side facing away from the centering tip (16), a depression (37) with a geometry which corresponds to a geometry of the centering tip (35).

7. Clamp (1; 51; 61) according to claim 5, characterized in that the centering mandrel (64) is designed as an extension of the blade (11, 12) extending in the cutting direction (15).

8. Clamp (1; 51; 61) according to one of the preceding claims, characterized in that the two blades (11, 12) are aligned mirror-symmetrically with respect to one another, a mirror plane (3) for the two blades (11, 12) being aligned normal to a minimum distance (4) between the two blades (11, 12).

9. Clamp (1; 51; 61) according to one of the preceding claims, characterized in that the two blades (11, 12) are each provided at the first end region (16) and / or at the second end region (17) with a transverse blade (41), a transverse blade cutting edge (42) of which is aligned at an angle of between 70 degrees and 110 degrees to the cutting edge (14)10. Clamp (1; 51; 61) according to one of the preceding claims, characterized in that the first connecting bar (25) and the second connecting bar (26) are each of arcuate design, with mutually opposite end regions of the first connecting bar (25) and mutually opposite end regions of the second connecting bar (26) each being aligned normal to convexly shaped inner surfaces (20) of the two blades (11, 12).

11. Clamp (1; 51; 61) according to claim 10, characterized in that the first connecting bar (25) and the second connecting bar (26) are arranged on a common oval, in particular on a circle.

12. Clamp (1; 51; 61) according to claim 10 or 11, characterized in that the first connecting bar (25) has a first carrier plate (32) and in that the second connecting bar (26) has a second carrier plate (33), the first carrier plate (32) and the second carrier plate (33) together with the back surface (13) of the two blades (11, 12) forming an, in particular flat, impact surface.

13. Clamp (1; 51; 61) according to one of the preceding claims, characterized in that projections (39) projecting outwards in the radial direction are formed on concave inner surfaces (20) of the blades (11, 12).

14. Clamp (1; 51; 61) according to claim 13, characterized in that the projections (39) each have a triangular profiling in a cross-sectional plane aligned transversely to the cutting direction (15), a first triangular side of the profiling being aligned parallel to the inner surface (20) and a second triangular side of the profiling enclosing an angle in an interval of 45 to 90 degrees with the inner surface.

15. Clamp (1; 51; 61) according to one of the preceding claims, characterized in that the first end regions (16) of the two blades (11, 12) and the second end regions (17) of the two blades are each formed with retaining tongues (45) projecting from the back surface (13) in the direction opposite to the cutting direction (15), inner surfaces of mutually opposite retaining tongues (45) each being provided with a concave recess (46).