WO2008077617A1

WO2008077617A1 - Electrically insulating rail joint and method to produce such a rail joint

Info

Publication number: WO2008077617A1
Application number: PCT/EP2007/011357
Authority: WO
Inventors: Sido Sinnema; Siep J.H. Koedijk; Diederik J. Verheul
Original assignee: Corus Technology Bv; Movares Nederland B.V.
Priority date: 2006-12-22
Filing date: 2007-12-21
Publication date: 2008-07-03
Also published as: EP2097585A1

Abstract

An electrically insulating rail joint for isolating two successive rails or rail portions (1, 2) with' a ceramic insulating element (17) between the end faces of the rail's or rail portions (1, 2), wherein connecting means, (6, 7) provided to connect the rails or rail portins, are adapted to retain a compressive force applied to the electrically insulating element (17) betwee the end faces of the rails or rail portions (1, 2). A method to produce such a rail joint and to a rail part comprises the steps of providing a gap between two successive rail portions (1, 2) connecting the rail portions to each other, exerting a tensile force on the rail portions, inserting an electrically insulating element (17) in the gap between the end faces of the rail portions (1, 2) and releasing the tensile force exerted on the rail porltions at both sides of the gap.

Description

ELECTRICALLY INSULATING RAIL JOINT AND METHOD TO PRODUCE SUCH A RAIL JOINT

The invention relates to an electrically insulating rail joint for insulating two rails such that the railjoint is placed between the ends of the rails, comprising an electrically insulating sheet.

Such insulating rail joints are known and are used to subdivide railways in consecutive sections electrically insulated from one another to be able to use these sections in signalling, security and controlling systems, such as for instance automatically controlled guarded level crossings and automatic train control.

In EP 1 693 515 a railway element with an insulating rail joint is disclosed wherein a gap in the railway element to receive an electrically insulating element and the insulating element are both shaped such that the insulating element is supported in the gap. The electrically insulating element is preferably comprises a ceramic material.

Besides its insulating properties the ceramic material is in particular chosen because of its hardness and resistance to abrasion. However, with the rail joint known from the cited prior art the width of the gap between the end faces of the rails will vary with variation of temperature, as a result of which the insulating element will be subject to different loads. This means that the ceramic material will also be subjected to shear and tensile forces against which ceramic material is hardly resistant. As a result the stand time of such insulating element will only be very short.

It is an object of the present invention to provide a insulating rail joint with an electrically insulating element of a ceramic material in which optimal use can be made of hardness and resistance to abrasion of the ceramic material.

It is another object of the present invention to provide an insulating railjoint which can be manufactured relatively easy and at relatively low costs.

It is another object of the present invention to provide a railway part provided with an insulating railjoint as a prefabricated unit. It is another object of the present invention to provide a railway part with an insulating railjoint wherein the railjoint provides the same or comparable support as the rails do. It is another object of the present invention to provide a railway part that fits within the security profile of a ballast tamping machine for tamping ballast underneath the sleepers of the railway.

It is still another object of the present invention to provide a railway part with an insulating railjoint wherein the railway part at the location of the railjoint does not have to be supported.

According to a first aspect of the invention one or more of the above objects is realized by providing an electrically insulating rail joint for isolating two successive rails or rail portions with an electrically insulating element comprising a ceramic plate placed between the end faces of the rails or rail portions which rails or rail portions are connected by means of connecting means, wherein the connecting means retain a compressive force applied to the electrically insulating element between the end faces of the rails or rail portions.

In the railjoint according to the invention the insulating element is retained under a compressive force by means of the connecting means connecting the rails or rail portions on both sides of the insulating element. The connecting means are adapted to retain a compressive force that is sufficient to take up the tensile forces due to contraction of rails because of low temperatures as for instance during the night or in winter time. This is particularly important with continuous welded rails. According to a further embodiment the electrically insulating element consists of a ceramic plate. By only using a ceramic plate as an electrically insulating element it is possible to exert a compressive force on the insulating element that is sufficiently large to take up contraction forces due to temperature changes. Since the compression strength of ceramic material is better than 300MPa and for most ceramic material even far better than that, the insulating element according to this embodiment has a compression strength that is more than sufficient to withstand the compressive force exerted on it. The compression strength is also more than sufficient to take up any additional compressive load due to expansion of the rails. Furthermore, ceramic material has a low linear extension coefficient, which is typically lower than 13*10^"6 / ⁰C and for a number of commercially available ceramic materials will be in the range of 7*10^"6 and 13*10^"6 / ⁰C. Because of this low linear extension coefficient changes in temperature will have minimal effect on the compressive force exerted on the insulating sheet.

Commercially available ceramic materials that are suitable to be used as insulating element in the rail joint according to the invention are for instance Zirconia or Alumina and also glass ceramic material, such as Macor (registered trademark of Corning Inc.). These glass ceramics and more in particular Macor have a hardness of about 400 Vickers corresponding to the hardness of rails which will ensure equal abrasion of rail and rail joint. The hardness of Zirconia is about 1100 Vickers and that of Alumina 1500 Vickers. According to a further embodiment it is provided that the electrically insulating element has a thickness between 1 and 20 mm, preferably a thickness of at least 3 mm, and preferably a thickness of at most 10 mm. With such a thickness of the electrically insulating element the rail ends are kept at sufficient distance to prevent short circuiting of the railjoint by for instance accumulation of abrasion powder or the like. The specific electrical resistance of the above ceramic materials lie in a range of

10⁶ - 10¹⁵Ωm, which values are far higher then the required minimum value for the specific electrical resistance of the insulating sheet for the rail joint. The electrical resistance for a rail joint in for instance the well known UIC60 rail with one insulating sheet of for instance Zirconia with a thickness of 1 mm would be about 1 x 10⁶Ω. With a glass ceramic material as for instance Macor with a thickness of 3 mm the electrical resistance of the railjoint in the same rail would be about 50 x 10¹²Ω. These resistance values are much higher then the required minimal values of the electrical resistance of the railjoint. Even with a specific electrical resistance of 20Ωm of the insulating element the resulting resistance of the rail joint is such that the rail joint will still function properly. However the resistance of the rail joint is preferably considerable higher to prevent that due to contamination the rail joint would need to be serviced more often or that the rail joint has to be replaced after a relatively short time.

Preferably the form of the electrically insulating sheet follows the profile of at least the head part of the rails, the head part of the rail being the part that comes into direct contact with the wheels of the train. The remaining part of the profile of the rails does not have to be followed exactly, as long as the insulating sheet completely covers - A -

said profile. This gives optimal insulation while allowing an outer shape of the insulating sheet that can be manufactured easily.

According to a further embodiment the electrically insulating element has a tapered shape. With this embodiment the gap between the end faces of the rails or rail portions is adapted to accommodate the tapered insulating element.

The invention also provides for a method for producing a rail joint in which a compressive force is exerted on an electrically insulating element placed between the end faces of two successive rails or rail portions, the method comprising the steps of:

- providing a gap of a predetermined width between successive rails or rail portions,

- connecting the successive rails or rail portions at both sides of the gap to each other,

- exerting a tensile force on the rails or rail portions or on the connecting means at both sides of the gap to enlarge the width of the gap, - inserting the electrically insulating element in the gap between the end faces of the rails or rail portions, and

- releasing the tensile force exerted on the rails or rail portions at both sides of the gap. Essential to the method according to the invention is that first the rails or rail portions are connected by means of connecting means such as fish plates, after which by elastic deformation of at least part of the connecting means the gap between the end faces of the rails or rail portions is widened enough to insert the insulation element into the gap. After insertion of the insulating element the tensile force on the rails or rail portions is released and the insulating element is clamped between the end faces of the rails or rail portions. The resulting compressive force exerted on the insulating element depends on a number of variables such as the properties of the connecting means, the length of the connecting means that is submitted to elastic deformation and the amount of elastic deformation, hi dependency of these variables the resulting compressive force can be set within a certain range. According to a further embodiment the method further comprises the step of exerting a bending load force on the rails or rail portions at both sides of the gap simultaneously with the exertion of the tensile force on the rails or rail portions, in order to give the gap a tapered shape. The tapered shape is such that the resulting gap between the end faces of the rails or rail portions widens in upward direction from the foot portion to the head portion of the rail. The electrically insulating element, preferably a ceramic plate, used with the method has a tapered shape that corresponds to the tapered shape of the tapered gap between the end faces of the rails or rail portions. The advantage of this embodiment is that the rail can be cut perpendicular to the axis of the rail after which by bending the rail the tapered gap between the end faces of the rails or rail portions will result. The tapered insulating element has the advantage that because of its shape it can be inserted easily in the gap between the rail ends without the need of having to open the gap to a considerable width to be able to insert the insulating element.

As a result of the compressive force, the bending load and the tapered shape of the insulating element the rail joint is fractionally elevated. This is favourable because therewith the dynamic impact of the wheels of a passing train on the rail joint is lowered.

To have sufficient material for the elastic deformation of the connecting means it is further provided that the successive rails or rail portions at both sides of the gap are connected to each other by connecting means of which the outer portions are fixedly connected to the respective rails or rail portions and wherein an intermediate portion between the outer portions is not connected to the rails. The intermediate portion of the connecting means extends at both sides of the gap and symmetrically with respect to the gap- According to a further embodiment the connecting means comprise fish plates at both sides of the rails or rail portions the outer portions of which are bolted to each other therewith establishing the connection to the rails or rail portions. Before tightening the bolts glue is applied between at least the outer portions of the connecting means and the corresponding parts of the rails and given enough time to harden. The bolts are insulated from the rails or rail portions and/or the fish plates.

After the glue on the outer parts has hardened and the bolts are tightened, a tensile force and a bending load force is exerted on the rails or rail portions to form the gap of the desired width and shape. According to a further elaboration it is provided that, before the insulating element is inserted in the gap, glue is applied between the intermediate portion of the connecting means and the rails and to the end faces of the rails or rail portions.

According to another embodiment the glue is applied not only to the outer portions of the fish plates and the corresponding part of the rails, prior to the elastic deformation of the part of the fish plates between the bolted outer portions, but also over the intermediate portion of the fish plates and the corresponding parts of the rails. With the elastic deformation of the intermediate part of the fish plates also the glue is elastically deformed.

In order to have maximal adherence of the glue to the different parts of the connecting means and the rails or rail portions the surfaces thereof are roughened prior to the application of the glue.

According to a further embodiment, instead of pre-stressing the connecting means, the connecting means are stressed after insertion of the insulation element between the end faces of the rails or rail portions, hi this embodiment the connecting means comprise parts at both sides of the gap between the rails or rail portions which are connected by tensioning means. The connecting means comprise a shoulder at each side of the gap and at both sides of the rails or rail portions, which shoulders form for instance part of fish plates connected to the rails or rail portions, and the shoulders are connected by a tension rod. After insertion of the insulating sheet the tension rods provided on both sides of the rails or rail portions are tightened up to the desired compressive force exerted on the insulating sheet.

The fish plates are connected to the rail portions by means of an adhesive layer between fish plates and rail portions and/or by means of bolts and nuts. According to a further embodiment the fishplates are connected to the rail portions by means of an insulating adhesive interlayer. Each tension rod is connected to the respective shoulders of the connecting means using an insulating bush between the tension rod and each shoulder. By using an insulating adhesive a double security against short circuiting through the tensioning means is obtained. However, in most cases insulating the tension rods from the fishplates will give sufficient insulation. The rail joint according to the invention can be mounted in an existing railway, however according to a further elaboration of the invention a railway part is provided comprising two rail portions with a railjoint according to the invention between the rail portions. Such a railway part is mounted as a prefabricated unit in an existing railway by removing a corresponding part from the railway and replacing it by the railway part according to the invention. The railway part is connected to the existing railway by means of for instance welding techniques as commonly used in railway construction and maintenance. The advantage of using a prefabricated railway part is that the railjoint can be mounted between rail portions under the best possible conditions in a workshop ensuring an optimal fit of the railjoint between the rail portions. A further advantage of prefabricating the railway part is that it is possible to manufacture the railway part in serial or batch production therewith lowering the costs per unit. The railway parts according to the invention may be inserted in an existing railway by taking out a corresponding length of the original railway and replacing it by the railway part. The railway part is preferably connected to the existing rail such as to form a continuous welded rails. According a preferred embodiment railway parts are placed in the railway such that the rail joint in the railway parts is positioned between two sleepers of the railway. Since the space required for the fastening and/or positioning means with which a rail is mounted on the sleepers will leave only very little space for the connecting means for the rail joint, it is preferred to have the rail joint between sleepers.

According to still a further embodiment the dimensions of the connecting means are chosen such that there remains enough space to fit within the security profile of a ballast tamping machine for tamping ballast underneath the sleepers of the railway, hi the maintenance of a railway tamping ballast underneath the sleepers is done from time to time to keep good support and stability for the rails. This is particularly important for sleepers that support the railway part according the invention to ensure prevention of mechanical failure of the rail joint.

The rail joint and railway part according the invention are further elucidated on hand of the example given in the drawing in which: fig.1 shows a side view of two rail portions provided with a rail joint, and fig.2 shows a configuration to apply a bending load force to the rail joint. hi fig.l two rail portions 1,2 are shown with a foot, neck and head portion 3,4,5 respectively. The rail portions 1 ,2 are connected by means of fish plates 6 on both sides of the rail portions 1,2 and bolts 7. Between the rail portions 1,2 a gap 8 of a predetermined width is kept, which preferably is in a range of 3-10 mm, for instance 5 mm. It is of utmost importance that the gap 8 has minimal deviations, especially in the railhead to avoid misalignment in the horizontal plane.

The fish plates 6 and rail portions 1,2 are first provided with corresponding boreholes after which the bolts 7 are put through fishplates 6 and rail portions 1,2. Before tightening bolts 7 the fish plates 6 are glued to the rail portions 1,2. The glue layer has a thickness of for instance 4 mm, for which plastic shims of the same thickness are used between the rail portions 1,2 and the fish plates 6. Glue is applied at the outer portions 9,10 of the fish plates 6, which are the portions provided with bolts 7. The intermediate area 11 between the outer portions 9,10 is not glued, at least not in this example prior to the elastic deformation of this intermediate area. After hardening of the glue, the bolts are pre-stressed by tightening the bolts.

To guarantee good adhesion of the glue to the portions of the rails 1 ,2 and the fish plates 6, these portions are roughened by for instance grid blasting. Immediately afterwards these portions are preferably coated with a thin layer of glue in order to prevent oxidation.

After curing of the glue and tightening of bolts 7 a tensile load is applied to the rail portions 1,2. To this end holes 12 may be provided in the rail portions 1,2 to affix the means with which the tensile load is applied. The load is applied in a single step or in a number of successive steps to a predetermined maximum load. This tensile load is preferably in a range of 500 - 2500 kN and more preferably in a range of 1000 - 2000. The load is preferably raised in steps of 300 - 700 kN, more preferably in steps of 500 kN.

After applying the tensile load the rail joint is subjected to a bending load. In fig.2 a three point bending device 13 is shown with a beam 18, a central support 14 under gap 8 and on both outer ends of beam 18 connecting members 15,16 which connect the outer ends of beam 18 at points 19,20 with the rail portions 1 and 2 at equal distances from gap 8. In the shown example the distances between points 19,20 and gap 8 is 500 mm. The vertical load is applied by moving the central support 14 in upward direction. The gap 8 is bend to a predetermined tapered shape, with the larger width at the head of the rail, which corresponds to the tapered shape of ceramic element 17 . According to one test example a gap of 5 mm was taken as starting point after which first a tensile load was applied on the joint and then a bending load wherewith the centre of the joint was bended up to a value of 0.625 mm measured on a one meter base. This corresponds with an inclination of 1:400 over 500 mm. The difference in width of gap 8 between rail head and rail foot is about 0.4 mm after bending. Before inserting ceramic element 17 in gap 8 the space between the fish plates 6 and the rail portions 1,2 is filled with liquid glue with a low viscosity. Just before insertion, glue will be put on the end faces of the rail portions 1,2 as well. The glue used has the same mechanical properties as the glue used to glue the outer portions 9,10 to the rail portions 1,2. Immediately after inserting the ceramic element 17 the external force and moment on the joint is released in order to pretension ceramic element 17.

For the skilled person it will be evident that the invention is not limited to the embodiments described above, rather numerous alternative embodiments may be envisaged without departing from the scope of the present invention.

Claims

1. Electrically insulating rail joint for isolating two successive rails or rail portions with an electrically insulating element comprising a ceramic plate placed between the end faces of the rails or rail portions which rails or rail portions are connected by means of connecting means, wherein the connecting means retain a compressive force applied to the electrically insulating element between the end faces of the rails or rail portions.

2. Rail joint according to claim 1, wherein the electrically insulating element consists of a ceramic plate.

3. Rail joint according to claim 1 or 2, wherein the ceramic plate is made from zirconia or alumina.

4. Rail joint according to one or more of claims 1-3, wherein the ceramic plate is made from a glass ceramic, such as Macor.

5. Rail joint according to one or more of claims 1-4, wherein the electrically insulating element has a thickness between 1 and 20 mm, preferably a thickness of at least 3 mm, and preferably a thickness of at most 10 mm.

6. Rail joint according to one or more of claims 1-5, wherein the form of the electrically insulating element follows the profile of at least the head part of the rails.

7. Rail joint according to one or more of claims 1-6, wherein the electrically insulating element has a tapered shape.

8. Rail joint according to one or more of claims 1-7, wherein the connecting means comprise fish plates connecting the rail parts at both sides of the electrically insulating element.

9. Method for producing a rail joint in which a compressive force is exerted on an electrically insulating element placed between the end faces of two successive rails or rail portions, the method comprising the steps of:

- connecting the successive rails or rail portions at both sides of the gap to each other, - exerting a tensile force on the rails or rail portions or on the connecting means at both sides of the gap to enlarge the width of the gap,

- inserting the electrically insulating element in the gap between the end faces of the rails or rail portions, and

- releasing the tensile force exerted on the rails or rail portions at both sides of the gap.

10. Method according to claim 9, wherein a bending load force is exerted on the rails or rail portions at both sides of the gap simultaneously with the exertion of the tensile force on the rails or rail portions, in order to give the gap a tapered shape.

11. Method according to claims 8 or 9, wherein the successive rails or rail portions at both sides of the gap are connected to each other by connecting means of which the outer portions are fixedly connected to the respective rails or rail portions and wherein an intermediate portion between the outer portions is not connected to the rails.

12. Method according to claim 11, wherein glue is applied between the outer portions of the connecting means and the corresponding parts of the rails.

13. Method according to claim 11 or 12, wherein the connecting means comprise fish plates at both sides of the rails or rail portions the outer portions of which are bolted to each other therewith establishing the connection to the rails or rail portions.

14. Method according to one or more of claims 11-13, wherein the intermediate portion of the connecting means extends at both sides of the gap and symmetrically with respect to the gap.

15. Method according to one or more of claims 11 or 14, wherein glue is applied between the intermediate portion of the connecting means and to the end faces of the rails or rail portions prior to the insertion of the electrically insulating element in the gap.

16. Method according to one or more of claims 11-15, wherein parts of the connecting means and the rails or rail portions to which glue is to be applied are roughened prior to the application of the glue.

17. Method according to one or more of claims 9-16, wherein the electrically insulating element is a ceramic plate.

18. Method according to claim 17, wherein the ceramic plate has a tapered shape.

19. Railway part comprising two rail portions with a railjoint according to one or more of claims 1-8 between the rail portions and manufactured according to one or more of claims 9-18.

20. Railway comprising rails and one or more railway parts according to claim 19, wherein the one or more railway parts are connected to the rails using metallic joints.

21. Railway according to claim 20, wherein one or more railway parts are placed in the railway such that the railjoint in the railway parts is positioned between two sleepers of the railway.

22. Method for producing a railway according to claim 20 or 21 comprising rail portions and at least one railjoint according to any one of the claims 1-8, using a prefabricated rail part according claim 19.