MX2013005063A

MX2013005063A - Clamp for attaching a rail and system provided with such a clamp.

Info

Publication number: MX2013005063A
Application number: MX2013005063A
Authority: MX
Inventors: Nikolaj Krieg
Original assignee: Vossloh Werke Gmbh
Priority date: 2010-11-04
Filing date: 2011-10-17
Publication date: 2013-06-28
Also published as: JP2013541655A; SG189555A1; BR112013011066A2; AU2011325351B2; CN103201430A; EA201300427A1; DE202010016149U1; MX338004B; AU2011325351A1; UA109455C2; IL225942A0; EP2635743B1; JP5778292B2; CA2815760A1; WO2012059318A1; ES2753165T3; DE102010050200A1; EA021499B1; PL2635743T3; AP3570A

Abstract

The invention relates to a clamp for attaching a rail S having a middle segment (3), having at least one torsional segment (9, 10) extending in the sideways direction from the middle segment (3), having at least one transition segment (11, 12) adjoining the torsional segment (9, 10), and having at least one retaining arm (13, 14) adjoining the transition segment (11, 12), an end segment (19, 20) being formed at the free end thereof.

Description

RAIL CLAMP TO JOIN A RAIL AND SYSTEM PROVIDED WITH A RAIL CLAMP OF THIS TYPE DESCRIPTION OF THE INVENTION The invention relates to a rail clamp for joining a rail, the clamp comprises a central portion, at least one torsional portion that branches out laterally from the central portion, at least a transitional portion joining the torsional portion and the less a retaining arm that is connected to the transitional portion and at the free end of which an end portion is configured by which the rail clamp is supported on the foot of the rail that will be joined in each case during use. Rail clamps of this type are normally curved in one piece from spring steel.

The invention also relates to a system for joining a rail having a rail foot, a rod placed in the same and a rail head, the system comprises a guide plate, a rail clamp held in the guide plate and a tension means to embrace the rail clamp against a base supporting the rail.

Rail systems and rail clamps of the type mentioned above are described, for example in US 3, 690.55 1 A or in US 3, 439, 874 A. Seen in a plan view, the retaining arms of the rail clamps in form of ? Known from these patents have a curved path with end portions, the end faces of which are directed towards each other. In this respect, the end portions themselves can be curved or straight, parallel to the associated torsional portion respectively of the rail clamp.

In the final assembly position, the free ends of the retention arms rest on the foot of the rail that will be joined.

The central portion of the rail clamp is wrapped around the arm of the clamping screw. Once the rail has been placed, the rail clamp is moved to the foot of the rail and pressed into the final assembly position when the screw is screwed. This pressure action is made by adjusting for an embrace of the rail arm that produces the retaining force required to retain the rail and is elastically transmitted by the retention arms on the foot of the rail. rail An additional rail clamp and system of the type indicated in the introduction are known from DE 1 0 2007 046 543 A l. In . In the known system, a rail clamp is used as an elastic element to generate the resilient holding force necessary to retain the rail and which, keeping in mind the length of the support plate measured in the longitudinal direction of the rail to be joined , it is configured in such a way that at least one of its retention arms can cover maximum spring deflections. The end portion of the retention arm is angled outward to point away from the torsional portion such that in the assembled position, it is directed towards the rod of the rail to be joined.

Thanks to this measure, on the one hand the narrowly defined support region which is formed on the free end of the respective end portion in which the retaining arm exerts the necessary downward retaining force at the foot of the rail by its Extreme portion during use is displaced from the edge of the foot of the rail in the direction of the stem of the rail to be joined. This ensures that the necessary holding force is always transmitted efficiently from the respective holding arm to. the foot of the rail even when, as a result of the transverse forces that originate when a rail vehicle travels over the rail and as a result of a possibly not accurate lateral support on the support plate, the foot. The ri moves to an excessive degree transverse to its longitudinal direction. Furthermore, the displacement of the support region in the direction of the rail shank produces a higher resistance to an undesirable twisting action, thereby facilitating in particular the positionally correct assembly of the rail clamp.

Practical experience using the system mentioned above shows that the angled configuration of the end portions of the retaining arms of the rail clamp ensures secure retention of the rail even in the case of a relatively wide transverse displacement. In a supported manner, the specific configuration of the rail clamp used in the known system described above proves to be adequate with respect to a maximum spring elasticity. However, there is a demand for rail clamps that are not only capable of applying substantial downward retention forces, but which also have an optimized duration limit. These requirements exist for example in the case of railroads in which extremely heavy transport trains travel in a high number of cycles.

Against the background of the prior art described above, the aim of the invention was to provide a rail clamp and a system for joining a rail which, with a high limit of duration, are capable of applying high downward retention forces and also ensures the At the same time that the adequately high retention forces continue to act on the rail even during a progressive wear of the rail fastening media.

With respect to a rail clamp, this object is achieved in accordance with the invention since this rail clamp has the features indicated in claim 1.

With respect to a system for joining a rail, the object is achieved according to the invention in that this system comprises a rail clamp that is configured according to the invention.

Suitable configurations of the invention are set forth in the dependent claims and will be described in detail below, as well as the general inventive concept.

According to the prior art described in the introduction, a rail clamp according to the invention for joining a rail comprises a central portion, at least one torsional portion that is branches out laterally from the central portion, at least one transitional portion joining the torsional portion and at least one retaining arm connected to the transitional portion. At the free end of the respective retaining arm, an end portion is formed by means of which the rail clamp is supported on the rail pi which will be joined in each case during use.

According to the invention, the retaining arm of the rail clamp is continuously curved at least in a curved portion that extends up to the free end of its end portion in such a way that, seen in a plan view of the rail clamp, the extreme portion will go to the central portion and the length in the torsional portion associated with the respective holding arm.

In this way, in the case of a rail clamp. according to the invention, the end portion which is present in the respective retaining arm is curved in the installation position, being directed away from the rail stem to be joined towards the longitudinal axis of the torsional portion, associated with the respective retaining arm , of the rail clamp. In this regard, the curvature of the curved portion with the end portion of the retention arm is preferably not restricted to only one curvature in one plane. Instead, the curvature is appropriately configured in three spatial directions. In this way, it is possible to configure in the respective end portion a support surface in approximately a narrowly defined tip shape, by means of which the end portion is supported on the foot of the rail that will be joined during use.

Thus, in a rail clamp according to the invention, the support surface preferably defined narrowly is in the region of the curved end portion according to the invention and by which a rail clamp according to The invention is supported on the surface of the rail foot during use, it travels in a location that is at a distance measured transversely to the longitudinal extent of the rail from the torsional portion associated with the respective retaining arm, a distance which, when viewed in a planar view from above the clamp of the kidney, it is shorter than the larger stance, also measured transversally to the longitudinal extension of the rail. Accordingly, the retaining arm, curved up to its free end, of a rail clamp according to the invention, has an increased overall length compared to conventional rail clamps thanks to its curvature, projecting with respect to the surface of support in the direction of the rod of the rail to be joined, from the torsional portion upwards to the supporting surface of its end portion during use. Thanks to this increased length and the curved shape, the retention arms are capable of absorbing high alternating loads without the risk of being damaged. Thus, with a rail clamp according to the invention, it is possible that high forces of descending retention with optimized duration resistance of the rail clamp.

An equally positive effect is achieved with the configuration of. according to the invention of a rail clamp when, as a result of wear, the rail is displaced transversely to its longitudinal extension and relative to the guide plate on which the rail clamp is supported. The curved shape, provided by the invention, of the curved portion of the retaining arm leading to the end portion, and of the end portion itself which, in the position of use is directed away from the stem of the rail to be joined, ensures that there is a secure contact between the rail foot and the rail clamp and suitable downward retention forces acting on the rail foot even when a space has formed between the guide plate and the rail foot during wear, which space is so large that the end portion that acts on the rail foot projects onto this space over part of its length. In this case, although the rail clamp no longer presses the rail foot with the support surface, loaded in the new condition, of the respective end portion, the shape of the end portion that is curved in the direction of the torsional portion of the rail clamp or its imaginary extension or longitudinal axis ensures that the rail clamp still acts safely on the rail even in this situation. Thus, the rail clamp "wheel" with its end portion curved on the rail foot when the rail is displaced, with the result that according to the displacement of the rail due to wear, the support surface by means of which the end portion acting on the rail is also displaced. This effect occurs in particular when the end portion is curved in three spatial directions, that is, when it is seated on the rail foot only by a roughly defined tip-shaped support surface during use.

Due to this shape, guided in a comparatively wide curve, of its curved portion, the retaining arm of a rail clamp according to the invention has an increased length. This results in a stronger elasticity of the retention arm and thus in a lower load, and in this way its durability is increased. In this regard, the shortest distance between the end portion configured in accordance with the invention and the associated torsional portion can be used as an indication of the minimum length of the retention arm. In the new state of an assembled system ready in accordance with the invention, this distance must be greater than the shortest distance between the torsional portion and the edge of the rail foot associated with a contact surface of the guide plate. In this way, it is ensured that even when there is a non-precise alignment of the rail foot and guide plate that occurs as a result of wear or assembly errors, the end portion always sits on the rail foot over a sufficient length. in order to apply the necessary downward retention force.

The advantages, summarized above, of an alignment and configuration of the end portion of a rail clamp according to the invention are particularly evident when the length of the curved end portion of the retention arm corresponds to at least 20% of the length of the torsional portion.

According to a variant of the retaining arm according to the invention, only the curved portion of the end face comprising the respective end portion is continuously curved, while the retaining arm is straight at least in another portion to thereby bridge long distances, for example.

According to another variant, since the complete retention arm is configured as a continuously curved portion, the stresses acting on the retention arm can be reduced in such a way that a resistance of maximum duration is achieved. At the same time, with this configuration, it is easy to produce the rail clamp.

The retention arm can be formed in such a way that during the course of the hug, it only minimally deforms. This makes it possible to align the end portion of the retention arm from the start with respect to its remaining part so that it is already sitting on the surface of the rail foot when the rail clamp is relaxed. For this purpose, the configuration and alignment of the retention arm are selected in such a way that the retention arm acts as much as possible exclusively as a lever with an inherent lowering of elasticity, such that the spring force exerted by the clamp Rail in the embraced state is generated substantially only by torsion of the torsional portion. This can be achieved since the retaining arm is aligned with respect to the torsional portion such that the torsional portion and the retaining arm, seen in a top plan view of the rail clamp, include an angle of 80. ° to 1 1 0 °, in particular 85 ° to 95 °, when an included angle that approaches 90 ° within the manufacturing possibilities provides optimum results.

The stiffness of the retention arm can be optimized since a curved part of the retention arm runs in a plane through which the entire portion passes at an angle of 80 ° to 1 00 °. In practice, this orientation of the curved part of the retaining arm can be achieved since the transitional portion between the retaining arm and the torsional portion describes a curve that is directed upwards when the rail clamp is on a horizontal surface and includes an angular region of 80 ° to 1 1 0 °. When the respective part of the retaining arm of a rail clamp according to the invention is curved, the retention arm is bent or dome-shaped in the region of this part in a side view, which ensures that the The shape of the retaining arm remains substantially unchanged even under high resilient holding forces or if the rail is transversely displaced. In consequence, in the embraced state, its extreme portion is always in an optimal position on the rail foot.

The concentration of the generation of the downward torsional force in the torsional portion can be further promoted since, seen in a plan view, the central portion includes with the torsional portion an angle of 80 ° to 1 1 0 °. In this configuration, the central portion also acts substantially exclusively as a lever for twisting the torsional portion, without itself being elastically flexible.

Rail clamps according to the invention, like the known rail clamps of the prior art, can be produced in one place from a spring steel wire forming a continuously curved line.

The storage and handling of a rail clamp according to the invention can be simplified in a manner known per se already. that the spacing between the free end of the curved end portion and the central portion is smaller than the smaller thickness of the central portion, the torsional portion, the transitional portion, the retaining arm and the end portion. This measure reliably prevents loosely stored rail clamps from becoming entangled with each other.

Of course, it is possible for a rail clamp according to the invention to be configured symmetrically identical to the known rail clamps since the central portion is configured; in the manner of a loop with two opposite torsional portions branching outward therefrom, to which a respective retaining arm with a curved end portion is connected by a transitional portion respective. The rail clamp according to the invention then has the shape of W or the shape of?.

The concentration, by means of which the inventive struggle is fought according to the invention, of the generation of the downward retaining force of the plastic in the torsional portion permits a particularly space-saving saving configuration of a rail clamp according to the invention. Therefore, according to a suitable embodiment of the invention, the length of the torsional arm is calculated in each case to be short enough so that at least portions of the respective retaining arm are guided on the guide plate.

The invention will now be described in more detail with reference to schematic drawings illustrating an exemplary embodiment.

Figure 1 shows a fixation point, shown in Figure 4, along the sectional line X-X marked in Figure 4.

Figure 2 is a front view of a rail clamp used in the system shown in Figure 4 and 5.

Figure 3 is a top plan view of the rail clamp according to Figure 2.

Figure 4 is a plan view of a fixing point formed by two systems for joining a rail.

Figure 5 is a partially sectioned and side view of the fixation point according to Figure 4.

The rail clamp 1 formed in one piece from a steel wire spring in a continuously curved line to join a rail S supported on a base U that is formed and, for example, by a concrete sleeper is configured in a manner symmetrically identical in relation to a plane NI aligned normal to the contact surface of the base U. It has a central portion in the form of a loop 3 having the shape of U in a plan view (figure 4), with two extremities 4, 5 separated and mutually parallel and a semicircular connecting portion 6 joining the ends 4, 5 together and associated with the foot F of the rail S to be joined.

A respective torsional portion 9, 10 which branches out laterally is connected to each end 4, 5 of the central portion 3 by a respective transitional portion 7, 8 which is curved by 90 °. In this regard, the torsional portions 9, 10 are directed in opposite directions away from the central portion 3 and, seen in a plan view, include with the extremities 4, 5, associated respectively with them, of the central portion an angle respective to approximately 90 °. ' Connected to the ends, away from the central portion 3, of the torsional portions 9, 1 0 is a respective transitional portion 11, 12 leading upwards in a circular arc that includes an angle of approximately 90 ° when the rail clamp 1 is placed on its underside (figures 1, 2).

Each of the transitional portions 11, 12 is fused in a retaining arm 13, 14 continuously bent at its far end of the respective torsional portion 9, 10. Thanks to the shape that is continuously curved in the three spatial directions X, Y, Z, the retaining arms 13, 14 in this way, in each case are a single portion of a curve. Viewed in a plan view, the parts 15, 16 of the retention arms connected to the respective transitional portion 11, 12 include in each case with the torsional portion 9, 10 associated with an angle β of approximately 90 °, in such a way that , seen in a plan view, they are aligned substantially parallel to the extremities 4, 5 of the central portion 3.

Consequently, the central axis M of the respective part 15, 16 of the retaining arms 13, 14 runs in a plane N2 through which the common longitudinal axis L passes from the torsional portions 9, 10 in each case at an angle of approximately 90 ° +/- 5 °. In this respect, the parts 15, 16 of the retention arms 13, 14 are bent in the manner of a dome strut and comprise an angular region of approximately 180 °.

At its far end of the respective torsional portion 9, 10, the parts 15, 16 of the retaining arms 13, 14 are fused in a respective transitional portion 17, 18 leading downwards about 90 ° towards the central portion 3 to a respective end portion 1, 9, 20. Viewed in a plan view (figure 3), these end portions 1, 9, 20 are both curved in the three spatial directions X, Y, Z as a continuation of the transitional portions 1 7, 1 8 in addition in the direction of the example. longitudinal L of the torsional portions 9, 10 and in the direction of the central portion 3 such that when placed on a flat surface, both are supported on the respective surface by a support surface approximately in the form of tip 21, 22 defined narrowly. Having in mind the length of the parts 1, 5, 16 of the retention arms 1 4, 14 extending substantially for the extremities 4, 5 of the central portion 3, the length and curvature of the end portions 19 20 are selected in each case in such a way that the end portions 19, 20 end in a gap a towards the connector portion 6 of the central portion 3, spaced apart to be smaller than the smallest thickness d of the spring steel, a from which the rail clamp 1 is curved. The tolerance of the spacing between the central portion 3 and the end portions 19, 20 is consequently so small that no other rail clamp 1 can pass through this spacing.

To join the rail S to the base U, two identically configured S I, S2 systems are used which are assembled on opposite sides of the rail S and each comprise a rail clamp 1, a plate guide 23 and a tensioning screw 24 required as a means for tensioning the rail clamp 1.

In the example embodiment described herein, the guide plate 23 is configured as a conventional type of angular guide plate and has on its lower side associated with the base U a shoulder extending over its width B measured in the longitudinal direction of the rail S and which sits in a correspondingly formed groove provided in the base U when the guide plate 23 is in the assembled position. Furthermore, in the assembly position, the guide plate 23 is supported in each case by its being supported in each case by its remote rear part of the rail S on a shoulder which is also configured on the base U. The guide rail 23 has a respective contact surface against which the leg of the F is supported by its longitudinal edge, in the front part of the guide plate 23 which is enlarged with respect to the rear part and is associated with the rail foot F. Transverse forces originating from the rail S when an iron vehicle (not shown here) traveling on the rail are then absorbed by the guide plate 23 and diverted to the base U.

Adjacent to its rear part, the guide plate 23 has on its upper side a respective groove extending parallel to the contact surface of the guide plate 23 as well as additional molded elements, not shown here in detail, for guiding the clamp of rail 1 mounted in each case in the guide plate 23 and a through hole, not visible here either, which leads from the upper side to the base U and through which the tensioning screw 24 is inserted. The tensioning screw 24 is screwed in each case into a claw (not visible here) that is inserted into the base U.

The rail clamp 1 disposed on the respective guide plate 23 is seated with its torsional portions 9, 1 0 in the groove in the guide plate 23. The length Lt of the torsional portions 9, 10 is calculated in each case as so that the retaining arms 1 3, 1 4 are each guided on the guide plate 23 and at least on the enlarged front region of the guide plate associated with the rail foot F. Thus, the width occupied respectively by the The clamp of R1 is only larger than the width B of the guide plates.

At the same time, the length of the ends 4, 5 of the central portion 3 is calculated in such a way that when the tensioning screw has been screwed in but not completely tightened, the rail clamp 1 can be seated in a pre-positioned position. assembly in which its torsional portions 9, 1 0 are disposed off-center in the direction of the rear part of the guide plate 23 to an extent outside the slot, associated therewith, in the guide plate 23 which curved end portions 1, 9, 20 of the rail clamp 1 are no longer projected into the region provided for the rail S. Once the rail S has been placed in the space provided for it between the guide plates 23 of the systems S I, S2, the rail clamps 1 can then be pushed out of their preassembly position into the assembly position end where they rest on the upper side OR of the rail foot F with its end portions 1 9, 20 which are curved away from the shank G of the rail S. The respective tensioning screw 24 is then tightened. In doing so, the central portion 3 of the rail clamps 1 is moved in each case in the direction of the base U. Since the retaining arms 13, 14 are simultaneously supported in a substantially rigid manner on the rail foot F , when the rail clamps 1 are embraced, only the torsional portions 9, 10 thereof are substantially twisted. As a result, high elastic forces are provided to elastically retain the rail S. These elastic forces are applied to the rail foot F on a comparably large contact surface, so that despite the increased retention forces, the risk of abrasive wear is minimized in the region of contact between rail clamp 1 and the rail foot F. To ensure the necessary cooperation of the rail support S also in the direction of the base U, an elastic layer E can be provided in a manner known per se between the rail foot F and base.

The length Lh, measured transversely to the longitudinal extent of the rail S and to the longitudinal arm L, of the retaining arms 1 3, 14 is calculated in such a way that in a new condition with a newly assembled system SI, S2, the distance shorter w between the respective torsional portion 9, 1 0 running axially parallel to the longitudinal ej L and the respectively associated end portion 9, 20 is greater than the distance B between the edge of the rail foot F associated with the respective guide plate 23 and the respective torsional portion 9, 1 0. This configuration of the retention arms 1 3, 1 4 ensures that the end portions 1, 9, 20 are always supported reliably on the rail foot F. Yes, due to wear, the rail S is displaced relative to the guide plate 23, as a result of which the bearing surfaces 2 1, 22 originally loaded from the end portions project into a space forming between the plate 1 and 2. guide 23 and the rail foot F, the end portions 1, 9, 20 nevertheless continue to rest on the rail track F by means of support portions that are at a corresponding distance from the free end face of the end portions 19 , twenty.

List of reference numbers 1 rail clamp 2 base contact surface U 3 central portion of rail clamp 1 respective 4, 5 rail clamp tips 1 respective 6 central portion connector portion 3 7, 8 transitional portions of rail clamp 1 respective 9, 10 torsional portions of rail clamp 1 respectively 1 1, 12 transitional portions of rail clamp 1 respectively 1 3, 14 clamp retention arms of ri 1 respective 1 5, 16 parts of the retaining arms of rail clamp 1 respective 1 7, 1 8 transitional portions of rail clamp 1 19, 20 end portions of rail clamp 1 respective 2 1, 22 rail clamp support surface 1 respective 23 guide plates 24 tensioning screws to separation b width of guide plates 23 d steel thickness rail clamp spring 1 respective E elastic layer F rail foot S G rail shank S L longitudinal axis of torsional portions 9, 10 The length of end portions 19, 20 Lt length of torsional portions 9, 10 Lh length of retention arms 13, 14 M central shaft of parts 15, 16 NI plane N2 plane Or top side of rail foot F S rail YES, S2 systems for joining a rail S U base w shorter distance between torsional arms 9, 10 of rail clamp 1 and the end of the end portion 19, 20 associated therewith in each case. v distance between torsion arms 9, 10 of rail clamp 50 and the rail foot edge F associated therewith in each case at an angle ß angle X, Y, Z spatial directions.

Claims

1. Rail clamp for joining a rail (S) comprising a central portion (3), at least one torsional portion (9, 10) that branches out laterally from the central portion (3), at least a transitional portion (7) , 8) joining the torsional portion (9, 10) and at least one retaining arm (13, 14) that is connected to the transitional portion (7, 8) and at the free end of which an end portion is configured ( 19, 20), whereby the rail clamp is supported on the foot (F) of the rail (S) which will be joined in each case during use, further characterized in that the retention arm (13, 14) is continuously curved. at least in a curved portion extending up to the free end of its end portion (19, 20) such that, seen in a plan view of the rail clamp (1), the end portion (19, 20) is directed towards the central portion (3) and the longitudinal axis of the torsional portion (9, 10) associated with the arm of respective retention (13; 14).

2. Rail clamp according to claim 1, further characterized in that the curved portion of the retention arm (13, 14) and its end portion (19, 20) is curved in three spatial directions.

3. Rail clamp according to any of the preceding claims, further characterized in that the arm of retention (13, 14) and the torsional portion (9, 10) include an angle (a) from 80 ° to 110 °, seen in a plan view.

4. Rail clamp according to claim 3, further characterized in that the angle included by the retention arm (13, 14) and the torsional portion (9, 10), seen in a plan view, is 85 ° to 95 °.

5. Rail clamp according to any of the preceding claims, further characterized in that a curved part 15, 16 of the retaining arm (13, 14) extends in a plane through which the torsional portion (9, 10) passes at an angle of 80 ° to 100 °.

6. Rail clamp according to any of the preceding claims, further characterized in that, viewed in plan view, the central portion (3) includes an angle of 80 ° to 110 ° with the torsional portion (9, 10).

7. Rail clamp according to any of the preceding claims, further characterized in that it forms a substantially curved line.

8. Rail clamp according to any of the preceding claims, further characterized in that the spacing (a) between the free end of the end portion (1, 9, 20) and the central portion (3) is smaller than the smallest thickness ( D) of the central portion (3), the torsional portion (9, 1 0), the transitional portion (1 1, 1 2), the holding arm (1 3, 14) and the end portion (19, 20) .

9. Rail clamp according to any of the preceding claims, further characterized in that it is configured symmetrically in identical form since the central portion (3) is in the form of a loop and two torsional portions (9, 10) aligned in opposite fashion branches are branched out therefrom and connected to the torsional portions (9, 10) by means of a respective transitional portion (11, 12) is a respective retaining arm (1 3, 14) with an end portion (19, 20).

1 0. System for joining a rail (S) that has a rail foot (F), a shank placed on it and a rail head, the system comprises a guide plate, a rail clamp held on the plate guide and a tensioning means to embrace the rail clamp against a base that supports the rail, further characterized in that the clamp of ri is configured according to any of claims 1 to 9 and also because the shortest distance (w) between the torsional portion (9, 10) and the end portion (19, 20) associated with it is greater than the shortest distance (v) between the torsional portion (9, 10) and the edge of the rail foot (F). ) associated with a contact surface (21, 22) of the guide plate (23).

11. The system according to claim 10, further characterized in that the length (Lt) of the torsional portion (9, 10) is calculated in each case in such a way that, in the assembly position, at least portions of the retaining arm ( 13, 14) are guided on the guide plate (23).