EA038873B1 - Metal-polymer fishplate for assembled insulating rail joint - Google Patents

Description

The invention relates to the superstructure of a railway track, in particular to devices used in electrical track circuits, and can be used in the construction of insulating rail joints as insulating linings.

Rail joints are the joints between the rails. When the rolling stock passes along the joint, due to the gap between the rails, the shock-dynamic effect on the track increases, so the joint is considered the most stressful place on the track. To connect the ends of the rails and to perceive the bending moment and shear force at the junction, which are perceived by the rail outside the junction, butt strips of various designs are traditionally used.

It is known in the art that the combination of resilient base settlement, impacts of passing wheels, wave motion, compression and expansion of rails causes severe stresses in rail joints in general and in butt plates in particular. With regard to the development of maximum stresses in a rail joint, the conditions for supporting the rail at the joint and near it are important. In order to obtain sufficient bearing strength of the joint, wear of the bearing surfaces should not be excessive. In this case, the main part of the wear of the bearing surface falls on the middle of the upper surface of the lining and closer to the ends on its lower surface. When the bearing surfaces are worn, the rail ends drop and form a depression at the joint. Consequently, timely replacement of worn out linings is essential to a large extent to obtain joint strength. In this case, the insulating joint usually requires a little more attention than the usual one, since it must not only act as a fastener of the rail ends, but must also retain the electric current in the rails. In this regard, the issues of reliability and durability of insulating joints of various designs are becoming increasingly important.

Insulating joints must completely exclude the possibility of current flow from one of the connected rails to another, for which they provide electrical insulating gaskets, linings and bushings. Traditionally, two types of insulating joints are used: with metal enveloping linings and glue-bolted [1]. Both types of insulating joints require a rather laborious installation at the place of installation at the junction of the rails, and the insulating linings in them are also subject to active wear, which leads to the need to replace the linings, i.e. to perform labor-intensive processes of dismantling and subsequent installation of new insulating linings.

On the roads of Russia, the most widespread are insulating joints with metal enclosing plates [2]. Insulation of rails is ensured by placing special gaskets under the linings and linings, as well as bushings on bolts made of fiber, PCB or polyethylene. In the equalization spans of a continuous welded track, glue-bolt insulating joints with two-headed linings are widely used. In such joints, standard double-headed six-hole pads are used, stitched along the upper and lower edges, and special pads that fit the rail bosom (full-profile pads). Insulation is provided by glass fabric impregnated with epoxy adhesive. Various compositions are used as adhesives, most often based on epoxy resins. To reduce the shrinkage of adhesives and reduce their fragility, plasticizers are introduced, and to improve the mechanical and electrical insulating properties, fillers (quartz, shale flour, asbestos fibers, etc.) are introduced. Adhesives should be moisture-, heat- and frost-resistant, durable, and cheap. The adhesive seams have a tensile strength along the seam of up to 25-35 MPa, however, the forces acting perpendicular to the plane of the overlays, the adhesive layer resists worse. This is one reason why the butt bolts are usually retained when the linings are glued to the rails.

In addition, the bolts prevent the joint from breaking in the event of aging or damage to the adhesive layer. To install glue-bolt insulating joints of a reinforced structure on a continuous track, pads are used that fit the rail bosom. A snug fit of the linings to the rails is ensured, despite possible deviations from the nominal dimensions of these elements, due to the different degrees of compression of glass fabric (consisting of nine to ten layers), impregnated with glue and having a total thickness of 3-3.5 mm. Butt bolts from the headrest to the start of the thread are also glued with glass cloth in three to four layers. The assembly of the prefabricated insulating rail joint is carried out on the existing railway track during a break in the movement of trains for 2.5 hours. to be glued. After installing the butt gasket in the butt gap, it is compressed by sliding the rails. The glued surfaces of rails and linings are degreased and dried for 10-15 minutes. During the drying of the degreased surfaces, an adhesive composition is prepared. The adhesive mixture for each side of the insulated joint is packed in individual containers. The adhesive composition is applied and evenly leveled with a spatula over the surface of the linings and primed with a thin layer of glue on the rail surfaces to be glued. Then the insulating joint is assembled. As follows from the above, the process of mounting the pads at the place of their installation is quite laborious and requires movement restrictions for a certain time.

Since the end of the 20th century, composite insulating strips have been widely used as part of insulating rail joints, which are, as a rule, fiberglass plates based on epoxy binders [3-5] or other composite materials [6]. The installation of such insulating strips is greatly simplified in comparison with those described above. But the cost of such insulating linings is higher than traditional metal ones, and their use does not solve the problem of the reliability of track operation in the butt zone from the point of view of increasing the resistance to damage of such joints under the influence of train loads.

The solutions known from the prior art for insulating linings are mainly aimed at solving the problem of increasing the operational reliability of rail butt electrical insulating joints in terms of electrical insulation characteristics. The issues of increasing the mechanical reliability of insulating linings are practically not considered, since simplified assembly / disassembly of composite insulating liners is assumed to allow easy replacement if damaged. So, even the recently widely used composite linings also did not solve the problem of the reliability of the operation of insulating joints. The track breakdown in the joint zone is mainly expressed in the sagging of the sleeper under the receiving end of the rail due to insufficient stiffness of the composite linings and the formation of a step on the rolling surface of the rail head, which can lead to its fracture. Another negative consequence of the use of composite linings was the periodic electrical closure of the joints, leading to the appearance of the false track occupancy effect due to the high magnetization of the rail ends in the joint.

At present, metal-polymer insulating linings are widely used, which consist of a metal longitudinally oriented element - a core and a polymer insulating outer coating. This type of insulating linings solves the problems of both increasing the stiffness of the liner and the reliability of its insulating properties.

Thus, an insulating strip is known from the composition of a rail butt electrical insulating joint [7], in which an elongated metal element is made in the longitudinal direction with a step and a dielectric coating on the surface of its first section, which has a greater length but a smaller cross-sectional area. In this case, in the places of contact of each butt strip with abutting rails, the dielectric coating is made flush with the lateral surface of the second section of the metal element having a large cross-sectional area. On both sides of each joint rail, there are respectively a first piece of a metal element of one butt strip and a second section of a metal element of another butt strip. The cover has a rather complex geometric shape, which complicates the technology of its production, and also, taking into account the asymmetry of its shape, requires correct positioning during installation.

According to the results of the analysis of the prior art, as a prototype for the inventive metal-polymer lining, according to a set of general technical features, a metal-polymer insulating lining was selected, consisting of a metal core having a surface facing the rails and facing away from the rails, as well as end and upper and lower surfaces, and a polymer insulating outer cover, and equipped with through holes for the installation of fasteners [8]. The problems solved by the design of such a lining immediately after its installation as part of an insulated joint eventually appear due to the violation of the integrity (destruction) of the polymer coating layer in the joint zone. This leads to a significant deterioration in both the mechanical and insulating properties of the pad, which requires its replacement as a whole.

The objective of the invention is to develop a metal-polymer patch, the design of which would provide the possibility of simple restoration of the damaged layer of the polymer coating in the most problematic areas. As the technical results provided by the inventive metal-polymer lining, one should mention a significant increase in the service life of the lining as a whole, simplification and cheapening of the manufacturing technology of both individual structural elements and the lining as a whole.

The problem is solved and the above technical results are achieved by the claimed metal-polymer strip for a prefabricated insulating rail joint, consisting of a metal core having a surface facing the rails and facing away from the rails, as well as end and upper and lower supporting surfaces, and a polymer insulating outer coating, and equipped with through holes for the installation of fasteners. The problem is solved and the above technical results are achieved due to the fact that the insulating outer coating is made separately from the metal core and consists of separate elements, including two main overhead elements, each of which is made with the possibility of tight abutment to the core, at least with the side of its corresponding end surface, from the side of the surface facing the rails, and from the side of the upper and lower supporting surfaces, an intermediate removable patch element made with the possibility of installation between two main patch elements with a tight abutment to the surface of the core facing the rails in the area of the rail joint and from the side of the upper and lower support surfaces with the formation of a continuous insulating coating of the core from the side of the surface facing the rails and from the side of the upper (5) and lower (6) support surfaces and at least one additional patch

- 2 038873 element made with the possibility of tight abutment to the core surface facing away from the rails, at least in the area of the through holes, while the total length of the joined two main overhead elements and the intermediate removable overlay element corresponds to the length of the metal core, and, along at least, the main and intermediate removable attachments are connected to the core in the abutment zones by means of an adhesive layer.

In the inventive metal-polymer strip for a prefabricated insulating rail joint due to the fact that the insulating outer covering is made separately from the metal core and consists of separate elements, including two main overhead elements, an intermediate removable overlay element and additional overhead elements, the metal core is insulated with respect to rails in all necessary areas. Due to the fact that the main and intermediate removable overlay elements, and, if necessary, additional overlay elements are connected to the core in the abutment zones by means of a layer of glue, it is possible to assemble a one-piece overlay in production conditions, which greatly simplifies the installation of the overlay at the junction of the rails. In addition, the presence of an intermediate removable overlay element and its connection with the core by means of a layer of glue make it possible to replace it quite easily when worn out, while maintaining the integrity of the rest of the structure.

In preferred forms of implementation of the inventive metal-polymer lining for a prefabricated insulating rail joint, the intermediate patch element is configured to be installed end-to-end with each of the main patch elements while maintaining a continuous insulating coating with a temperature change in the length of the metal core. This arrangement allows the most simple separation from the core and the main attachments for subsequent replacement of only the intermediate attachment, as mentioned above. In addition, in such forms of implementation, the safety of the insulating function of the patch as a whole is ensured over a wide temperature range, i.e. with significant changes in the length of the metal core caused by changes, incl. sharp, temperatures.

In also preferred forms of implementation of the inventive metal-polymer lining for a prefabricated insulating joint of rails, the insulating outer coating includes two additional overlay elements, each of which has a length corresponding to the length of the main overlay element and is made with the possibility of jointly fixing a tight abutment to the core surface facing away from the rails along at least in the area where the corresponding through holes are made. Such forms of implementation simplify the installation of additional attachments with quick alignment of the corresponding holes on the additional attachments and the core.

In the inventive metal-polymer patch for a prefabricated insulating joint of rails to provide insulation in the area of the walls of the through holes made in the core, each main patch element on the side of its surface facing the core can preferably be equipped with at least one, preferably made in one piece with the main patch element with a sleeve-like protrusion, the location and dimensions of which are selected in accordance with the location and dimensions of the corresponding through hole made in the core.

In preferred forms of implementation of the inventive metal-polymer lining for a prefabricated insulating rail joint, at least an intermediate removable patch element can be connected to the core in the abutment zones, preferably by means of a layer of glue that is destroyed under the directional action of a high temperature not exceeding the melting point of the material of the application element. In such forms of implementation, the destruction of the adhesive joint under the influence of high temperature occurs without destruction of the overlay element, which makes it quite easy to remove it and replace it with a new one.

In the inventive metal-polymer patch for a prefabricated insulating rail joint for differentiated disconnection of an intermediate removable patch with a core, the adhesive layer for fixing the intermediate removable patch preferably has a fracture temperature lower than the adhesive layer for fixing the main patch. In such forms of implementation, it is possible to remove and then replace only the intermediate removable patch without destroying the connections between the core and the main patch.

To extend the service life of the metal-polymer patch as a whole without significantly increasing its cost, the intermediate patch element can preferably be made of a polymer having higher physical and mechanical properties compared to the material of the main patch elements. In particular, this may concern the deformation, strength and friction properties of the polymer.

In a number of preferred forms of implementation of the inventive metal-polymer lining to reduce the magnetization of the prefabricated insulating rail joint, the intermediate patch element can be made of a magnetically conductive polymer.

The above and other advantages and advantages of the claimed metal-polymer lining for a prefabricated insulating rail joint will be discussed in more detail in the following description and illustrated with the help of the drawings, which schematically shows one of the possible, but non-limiting form of implementation of the metal-polymer lining. The drawings, in particular, show:

fig. 1 is a general exploded view (disassembled) of a metal-polymer lining;

fig. 2 is a general view of the assembled metal-polymer patch of FIG. 1;

fig. 3 is a view of the metal-polymer patch of FIG. 1 from the side of the surface facing away from the rails;

fig. 4 is a section along line A-A of the metal-polymer patch of FIG. 3;

fig. 5 is a general view of the right main overhead element;

fig. 6 is a plan view of an intermediate patch;

fig. 7 is a side view of the intermediate attachment of FIG. 6;

fig. 8 is a general view of the metal-polymer patch according to FIG. 1 with the spacer piece removed.

FIG. 1-4 schematically shows the claimed metal-polymer strip for a prefabricated insulating rail joint in an exploded general view, in an assembled general view, in front view and in section along the line A-A, respectively. A metal-polymer patch for a prefabricated insulating rail joint consists of a metal core 1 having, in the embodiment shown in the drawings, a surface 2 facing the rails, a surface 3 facing away from the rails, end surfaces 4 and upper 5 and lower 6 support surfaces, and a polymer insulating outer coating 7. The metal-polymer pad is provided with through holes 8 for the installation of fasteners, for example, travel bolts with nuts and washers (not shown in the drawings and not indicated by positions). The insulating outer cover 7 is made separately from the metal core 1 and consists of separate elements, in the form of implementation shown in the drawings, including two main overlay elements - right 9 and left 10, an intermediate removable overlay element 11 installed between the two main overlay elements 9, 10, and two additional overlay elements 12. In the mounted metal-polymer overlay (Fig. 2), each of the two main overlay elements 9, 10 adjoins the core 1 from the side corresponding to its end surface 4, from the side of the surface 2 facing the rails, and from sides of the upper 5 and lower 6 support surfaces. An intermediate removable overlay element 11 is installed between two main overhead elements 9,10 with a tight abutment to the surface 2 of the core 1 facing the rails in the area of the rail joint and from the side of the upper 5 and lower 6 support surfaces with the formation of a continuous insulating coating 13 of the core 1 from the surface side 2, facing the rails, and from the side of the upper (5) and lower (6) support surfaces. Each of the two additional overlay elements 12 is located with a tight abutment to the core surface 3 facing away from the rails in the corresponding area of the through holes 8. The length of each of the two additional overlay elements 12 has a length corresponding to the length of the opposite main overlay element 9, 10. In additional The through-holes 14 are made in the overlay elements 12, aligned with the through-holes made in the core 1, with the formation of through holes 8 in the metal-polymer patch, and providing joint fixation of a tight abutment to the surfaces of the core 1.

The total length of the joined two main overhead elements 9, 10 and the intermediate removable overlay element 11 corresponds to the length of the metal core 1. In the embodiment shown in the drawings as an example, the main 9,10 and additional 12 overlays are connected to the core 1 in the abutment zones by means of glue, whose layer in the drawings is conventionally designated by the number 15.

FIG. 5 schematically shows a general view of the main patch - conditionally, the main right patch 9 from the composition of the metal-polymer patch in the form of implementation according to FIG. 1-4. In the presented form of implementation, the main right overhead element 9 (as well as the main left overlay element 10 made symmetrically to it) from the side of its surface 16 facing the core 1 is provided in the presented form of implementation with three made in one piece with the main overhead element 9 (10) sleeve-like protrusions 17, the location and dimensions of which are selected in accordance with the location and dimensions of the corresponding through holes 8 made in the core 1. The sleeve-like protrusions 17 define the through holes 18, which are made in the main application element 9 (10).

FIG. 6 and 7 schematically show an intermediate patch element 11 - a plan view and a side view, respectively, from the composition of a metal-polymer patch in the embodiment according to FIG. 1-4, the intermediate overhead element 11 is installed end-to-end (with the formation of joints 19) with each of the main overhead elements 9, 10 while maintaining a continuous insulating coating 13 when the length of the metal core 1 changes with temperature. the intermediate removable patch 11 is connected to the core 1 in the abutment zones by means of a layer of glue that is destroyed under the directional action of a high temperature not exceeding the melting point of the material of the intermediate removable patch 11. The layer of this glue is conventionally designated by 20.

- 4 038873

In this case, the adhesive in the layer 20 for fixing the intermediate application element 11 has a fracture temperature lower than the adhesive in the layer 15 for fixing the main application elements.

The intermediate overlay 11 is made, for example, of solid polyurethane, which has higher physical and mechanical properties in comparison, for example, with polyamide, from which the main 9, 10 and additional 12 overlay elements are made. In the matrix of solid polyurethane, from which the intermediate overhead element 11 is made, a nanopowder of a magnetically conductive material was added during the manufacturing process, as a result of which the solid polyurethane acquires magnetically conductive properties, while remaining an insulator.

FIG. 8 is a schematic perspective view of the metal-polymer patch according to FIG. 1 with removed intermediate trim 11.

The installation and operation of the inventive metal-polymer lining for a prefabricated insulating rail joint will be further discussed using the example shown in FIG. 1-8 form of implementation.

According to traditional materials and products for this type of material, for example, from steel grade M54, a metal core 1 is made, which has a surface facing the rails 2 and facing away from the rails 3, as well as end 4 and upper 5 and lower 6 support surfaces. Through holes are made in the core 1, which, when combined with the through holes 19, 14 made in the main 9, 10 and additional 12 overhead elements, respectively, form through holes 8 for the installation of fasteners, for example, travel bolts with nuts and washers (in the drawings not shown and not indicated by numbers).

Also, according to materials and products traditional for this type of materials and products (for example, injection molding), the main right 9 and left 10 overhead elements with sleeve-shaped protrusions 17 and additional overhead elements 12 are made from polyamide of a suitable grade, and an intermediate removable overlay 11.

The polymeric insulating outer coating 7 on the core 1 is formed under manufacturing conditions. To do this, on the metal core 1 from the side of the surface 2, which will face the rails, the main - right 9 and left 10 overlay elements are installed on the layer 15 of glue, and between them, with the formation of joints 19, an intermediate removable overlay element 11 is installed on the layer 20 of glue. At the same time, when installing the main overhead elements 9, 10, their sleeve-like protrusions 17, made from the side of the surface 16 facing the core 1, are placed in the corresponding through holes of the core 1, while simultaneously forming common through holes 8-18 and insulating the walls of the through holes 8. Due to the geometric shape of the main - right 9 and left 10 overlay elements and an intermediate removable overlay element 11, as well as their mutual placement butt to end, a continuous insulating coating 13 is formed on the core 1 on the surface 2 facing the rails, on the end surfaces 4 and on the top 5 and the bottom 6 support surfaces. The tight abutment of the main 9, 10 and intermediate removable 11 overlay elements to the metal core 1 along all the indicated surfaces is also ensured due to the fact that the total length of the joined two main overhead elements 9, 10 and the intermediate removable overlay element 11 corresponds to the length of the metal core 1.

Further, also in production conditions on the metal core 1 from the side of the flat surface 3, which will face away from the rails, additional overlay elements 12 are installed on the glue layer 15, aligning the through holes 14 made in them with the corresponding through holes 8.

Thus, under production conditions, a metal-polymer strip is completely ready for installation at the junction of the rails, the installation of which at the installation site is carried out by fixing with traditional fasteners (travel bolts with nuts and washers) installed in completely insulated through holes 18-8-14.

As already mentioned above, the metal-polymer strip experiences the greatest destructive effect precisely in the zone of the vertical boundary of the rail joint. The use in the claimed metal-polymer patch as a material of an intermediate removable patch 11 of a polymer having higher physical and mechanical properties (respectively, more expensive) in comparison with the material of the main patch 9, 10, allows you to extend the service life of the intermediate removable patch 11 without significant increase in the cost of the metal-polymer lining. It should also be noted that the technology described above for the manufacture of the inventive metal-polymer lining, in particular its polymer insulating outer coating 7, is much less energy-intensive and less expensive compared to the technology used in this field of technology to form a permanent outer polymer coating on the metal core over the entire surface metal core.

The intermediate overlay element 11 is installed end-to-end with each of the main overhead elements 9, 10 while maintaining a continuous insulating coating 13 with a temperature change in the length of the metal core 1, including due to the presence of layers 15, 20 of glue.

In the event of damage to the intermediate removable overlay 11, the metal-5 038873 polymer overlay is dismantled in the usual way. To replace the intermediate removable patch 11 in production conditions, the area of the metal-polymer patch, in which the intermediate removable patch 11 is installed, is heated to the temperature of destruction of the adhesive layer 20. In this case, the layer 15 of the glue, which has a higher fracture temperature, remains intact, and the main overhead elements 9, 10 remain fixed on the core 1. The damaged intermediate removable overlay element 11, thanks to butt-fitting with the main overhead elements 9, 10, can be easily dismantled. If necessary, the surface 2 of the core 1 is cleaned (mechanically and chemically) at the installation site of the intermediate removable patch 11 and a new intermediate removable patch 11 is fixed by means of a new layer 20 of glue 11. After the replacement of the intermediate removable patch 11 is made, the metal-polymer patch is ready for installation as part of prefabricated insulating rail joint.

It will be clear to those skilled in the art that other forms of implementation of the claimed metal-polymer lining are possible, both in terms of the number and geometry of structural elements and the materials from which they can be made.

Sources of information.

1. Rail joints and butt joints. Educational and educational portal All lectures. [Electronic resource] - June 18, 2020 - Access mode: http://vse-lekcii.ru/zheleznodorozhnyitransport/zheleznodorozhnyj-put-i-putevoe-hozyajstvo/relsovye-styki-i-stvkovye-skreplenjya.

2. Topic No. 6. Rail joints and butt joints. [Electronic resource] -18 June 2020. Access mode: http://static.scbist.Com/scb/uploaded/l 1386424221.pdf.

3. Patent CN No. 2371220 (Y), publ. March 29, 2000

4. Patent RU No. 2289646C1, publ. 20.12.2006

5. Patent RU No. 2694423 C1, publ. 07/12/2019

6. Patent RU No. 2398797 C2, publ. 09/10/2010

7. Patent RU2 295 603 C1, publ. 03/20/2007

8. Metal-polymer pads MPE 65. Website of the company LLC Belsvyazkomplekt-K [Electronic resource] - June 22, 2020 - Access mode:

https://www.belconnect.by/catalog/verkhnee_stroenie__puti/nakladki_metallopolimer nye_mpe_65 /

Claims (8)

CLAIM 1. A metal-polymer lining for a prefabricated insulating rail joint, consisting of a metal core (1) having surfaces facing the rails (2) and facing away from the rails (3), as well as end (4) and upper (5) and lower (6) surfaces supporting surfaces, and a polymer insulating outer coating (7), and equipped with through holes (8) for the installation of fasteners, characterized in that the insulating outer coating (7) is made separately from the metal core (1) and consists of separate elements, including two main overhead elements (9, 10), each of which is made with the possibility of tight abutment to the core (1), at least from the side of its corresponding end surface (4), from the side of the surface (2) facing the rails, and from sides of the upper (5) and lower (6) supporting surfaces, an intermediate removable patch element (11), made with the possibility of installation between the two main patch elements (9, 10) with a tight abutment to the the surface (2) of the core facing the rails in the area of the rail joint and from the side of the upper (5) and lower (6) support surfaces, with the formation of a continuous insulating coating (13) of the core (1) from the side of the surface (2) facing the rails, and from the side of the upper (5) and lower (6) support surfaces and at least one additional overlay element (12) made with the possibility of tight abutment to the surface (3) of the core (1) facing from the rails at least in the area of the through holes (8), while the total length of the joined two main overhead elements (9, 10) and the intermediate removable overlay element (11) corresponds to the length of the metal core (1), and at least the main ones (9, 10) and an intermediate removable (11) overlay elements are connected to the core (1) in the abutment zones by means of a layer (15, 20) of glue. 2. The patch according to claim 1, characterized in that the intermediate patch element (11) is made with the possibility of butt-fitting with each of the main patch elements (9, 10) while maintaining a continuous insulating coating (13) with a temperature change in the length of the metal core. 3. The patch according to claim 1, characterized in that the insulating outer cover (7) includes two additional patch elements (12), each of which has a length corresponding to the length of the main patch (9, 10), and is made with the possibility of joint fixation tight abutment to the surface (3) of the core (1) facing away from the rails, at least in the area of the corresponding through holes (8). 4. A patch according to any one of claims 1 to 3, characterized in that each main patch element (9, 10) is provided on the side of its surface (16) facing the core (1) with at least one - 6 038873, preferably made integrally with the main attachment (9, 10), a sleeve-like protrusion (17), the location and dimensions of which are selected in accordance with the location and dimensions of the corresponding through hole (8) made in the core (1). 5. The patch according to claim 1, characterized in that at least an intermediate removable patch element (11) is connected to the core (1) in the abutment zones by means of a layer (20) of adhesive, which is destroyed under the directional action of a high temperature not exceeding the temperature melting the material of the intermediate removable overlay. 6. The patch according to claim 5, characterized in that the adhesive of the layer (20) for fixing the intermediate removable patch (11) has a fracture temperature lower than the adhesive of the layer (15) for fixing the main patch (9,10). 7. The patch according to claim 1, characterized in that the intermediate patch (11) is made of a polymer having higher physical and mechanical properties compared to the material of the main patch (9, 10). 8. Cover according to claim 1, characterized in that the intermediate cover element (11) is made of a magnetically conductive polymer.