Bonded electrically insulated joint system for railway rails, method for fabricating such, method of modifying at least one starting type switch rail and use of two switch rails modified in accordance with said modifying method

The present invention relates to the technical field of insulating bonded joints of railway rails (generally trains, subways and the like).

In particular, the invention refers to a particular joint structured in such a way as to have a longer operating life and a lower acoustic and vibrational impact, offering a higher safety level than existing joints, preventing breakages and potential railway accidents, while also allowing for simple installation and easy maintenance of the railway track.

Railway rails are historically jointed by mechanical joints (‘couplings’) and, more recently, by welds.

A very common type of joint is the ‘bonded insulated joint’ (G.I.I.) whose purpose is to mechanically connect the rails while keeping them electrically insulated.

In this case, there is no continuity offered by welding since there is a discontinuity between the two joints due to the insertion of electrically insulating material.

It is a well-known fact that, in order to ensure the necessary spacing between trains on the line and avoid collisions at the station, railway tracks are divided into sections of varying lengths, known as ‘automatic block sections’. The rails at the ends of these automatic block sections are mechanically connected (jointed) in order to allow trains to pass, but they are also electrically insulated so that a so-called ‘track circuit’ (or CdB) can be implemented. The two rails of a section are powered at one end by a low-voltage source; this voltage normally drives a relay at the other end of the track. When a train rolls on the section, its (steel) axles short-circuit the rails causing the relay to drop and thus changing the status of the CdB from ‘free’ to ‘occupied’.

With this system, which has been known for years, information is acquired about the passage of the train at predetermined sections where such information is needed to manage railway traffic.

That said, G.I.I.'s are widespread throughout the world and find their application in security systems and convoy spacing on the line and at stations.

In the remainder of this document, G.I.I.'s will also be identified by the internationally known acronym IRJ, from the English “Insulated Rail Joint”.

Although there are numerous types of IRJs, except for the specific cases below, they all fall within the morphology described hereinafter.

show an example of a typical IRJ.

It consists of two identical rail lengths (,), sandblasted and cut at right angles (90° relative to the rail axis) to form a ‘butt joint’. The rail lengths are drilled, usually with four or six holes, on the web. The rail lengths are placed end-to-end, thus generating the IRJ's transverse symmetry plane, separating them through a rail-shaped template in electrically insulated nylon () of typically 5 mm thickness (end post). The thickness of this template is a compromise between maximum shock reduction (which would require the smallest possible distance) and need to prevent that plastic deformation of the rails, due to the continuous ‘hammering’ of the wheels, cause mechanical and electrical contact between rail lengths (), in fact generating an IRJ failure.

The rail mechanical continuity is restored, at least partially, by means of two lateral jaws (′,″) referenced on the rails themselves by means of sloped planes (i.e., ‘splint planes’), which ensure their correct positioning.

Said jaws are secured by means of a screw () or irreversible locking nail.

In order to avoid that the jaws short-circuit the rail lengths (,), additional electrically insulating material (′,″), commonly made from shaped and perforated fibreglass sheets, is placed between jaws and rail.

The jaws are then joined to the rails by means of screws or irreversible locking nails (), provided with washers (′,″), by a sleeve made of insulating material () and a nut or deformable collar () depending on the application.

The joint is fabricated using high-strength structural adhesives, which play a fundamental function in IRJs, since mere friction would not be sufficient to transmit the vertical forces dependent on the load of the passing vehicles and, above all, the longitudinal forces that arise due to thermal effects (expansion) of the rails.

shows a top view of the same joint, in which the insulating template () as well as the other above-mentioned elements are visible.

On the plane of vertical symmetry, easily identifiable in the centre of said nylon insulating template (), the section resistant to vertical loads, which generate bending in the joint, is exclusively provided by the jaws. This results in a flexural stiffness that, in ordinary IRJs, is about one-third of the stiffness of the standard rails with which the IRJ is fabricated. In contrast, the adjacent areas, where the jaws are active, have a stiffness that is about ⅓ higher than that of the rails themselves. The two combined effects make the cross-section of symmetry critical, as a passing wheel encounters first a very rigid section (the one with the jaws alongside the rail) followed by a very flexible section (the one with only the jaws and the plastic template), with a stiffness ratio of up to four in ordinary IRJs.

The cross-section of transverse symmetry, with its abrupt stiffness variation, constitutes, in traditional IRJs, a discontinuity which, given the characteristics of the materials (typically steel), generates impulsive stresses (shocks) whose effects are amplified in the screw passage holes which represent, as is well known, cut-outs capable of generating stress concentrations and therefore fatigue cracks.

Such cracks, which are quite frequent, are indicated in the catalogue of rail cracks of the Union Internationale des Chemins de Fer (Fiche UIC 712) under the designation ‘cracks originating from holes’ with code 135 (star cracks). They develop at 45° from the edges of the holes drilled on the web, at the plane of maximum cut. Known art systems such as reaming, chucking, etc. can be used to reduce the possibility of crack emergence and growth.

The probability of failures increases when, as shown in, the IRJ is mounted in the ‘suspended’ configuration, i.e., in the centre of the span identified by crossbeams () and corresponding rail-traverse couplings ().

A very large scientific production is known on performance calculations, numerical and experimental analysis of stresses and strains, and typical damage in IRJs. Suffice it to cite the article by N. K. Mandal e B. Peach,International Journal of Engineering Science and Technology ISSN: 0975-5462 3964, Vol. 2(8), 2010, 3964-3988 summarizing the whole issue of IRJs of the various types. As a result, IRJs are in fact an unsolved problem for railway line management and safety.

In order to mitigate the technical problems, a ‘smoother’ transition between two rail lengths was attempted to reduce the impacts present in the current IRJs by sloping the rail junction line by means of an oblique cut.

An example of known art is shown in, to be found in at least one commercially available IRJ. The small web size of the rails currently used, however, does not allow the rail head to be cut at a significantly small angle (to be understood as the angle between the direction of the cut and the longitudinal axis direction of the rail), with the result that the transition zone is not sufficiently stretched, leading to limited benefits.

This is demonstrated in, which shows an IRJ obtained by machining two standard rails in such a way as to have a sufficiently long transition. This results in an angle of 4.25°, which, however, leads to portions of the rail head unsupported by the web as well as sharp surfaces. This solution, totally technically unacceptable, has in fact never been implemented.

This problem has been overcome by the known art shown inin which two special rails, with an oversized web, usually used in expansion joints especially at bridges, are shown, which are machined according to this principle.

This solution is described in the scientific article by R. H. Plaut, H. Lohse-Busch, A. Eckstein, S. Lambrecht and D. A. Dillard,Journal of Rail and Rapid Transit 2007 221:195, DOI: 10.1243/0954409JRRT107. This solution, as mentioned in the article, requires the rolling of special rails and the creation of special transitions between said special rails and the standard rails, with significant production costs.

Prototypes of these joints, described in patents U.S. Pat. Nos. 7,975,933, 8,113,441, 8,302,878, 9,328,464 have been tested in the US but have had no commercial follow-up due to the significant production costs.

It is therefore an aim of the present invention to provide a new type of bonded insulated rail joint (IRJ) assembly that solves the aforementioned technical drawbacks.

In particular, it is the aim of the present invention to provide a new IRJ solution that is reliable, low cost and easy to manufacture and install.

More specifically, it is the aim of the present invention to provide a new type of IRJ that solves the aforementioned technical drawbacks, offers greater safety, less environmental impact (noise and vibrations), is easy to install and allows for simple track maintenance.

These and other aims are achieved with this bonded insulated rail joint (IRJ) assembly according to claim.

Such an insulated rail joint (IRJ) (or simply joint as it may be) comprises:

Preferably, advantageously, the two conjugate surfaces, in virtue of their relevant length, hence, form a transition of high longitudinal length.

In accordance with this solution, all the aforementioned technical drawbacks are solved.

The use of a starting switch rail allows for the creation of a conjugate coupling surface that is robust since the lowered, unforged part of the starting switch rail has a very thick web section (40 mm). This allows the conjugate coupling surfaces to be obtained while leaving the structure of the switch rail on the opposite side unchanged and with a good amount of material.

The thus modified switch rail is robust and when coupled with its twin creates a stable and strong solution.

In addition, the bottom plate having a bolted cover plate function (i.e., the splices) further optimises strengths.

In fact, said bolted cover plate provides large surfaces for the application of adhesive material and thus substantially contributes to the flexural stiffness and to the longitudinal and structural flexural strength of the IRJ, while providing suitable surfaces for a simple and correct assembly of the IRJ in the current track.

The adhesive material is inserted in the contact area obviously between bolted cover plate and switch blade foot or restored rail that connects to it.

The adhesive material used can be any of the known ones and already in use in the industry.

The use of a switch rail, given the large thickness of the web in the lowered unforged part, therefore, allows the side to be removed, creating a conjugate coupling surface that forms in fact a face that follows a longitudinal development direction at a small angle to the longitudinal axis of the starting switch rail.

Preferably, but not necessarily, the conjugate coupling surface can be flat.

However, in further variants, as also clarified below, the conjugate coupling surface structure can take shapes other than simply flat (see examples in), thus also allowing for shape coupling and not just friction coupling.

In all cases, the two surfaces (S) are conjugate in that they mirror each other and are therefore such that they join together to complete the form (i.e., they match each other in mirror-image manner).

In this way, once the coupling is complete, the head of the restored rail or blade will show a junction curve (L) (also known as a transition line or curve) with high development along the longitudinal axis, solving all the aforementioned technical problems without affecting the structural strength of the obtained assembly or system as it may be.

In particular, advantageously, the coupling surface is of considerable length compared to known-art solutions, and therefore considerably longer than known-art transitions.

For example, it is possible to have longitudinal lengths and thus transitions of 500 mm or more.

Advantageously, as a result of the coupling of said two arbitrary conjugate coupling surfaces (S), a transition curve (L) is generated that forms, for at least one section of its length or for several sections of its entire length, a predetermined angle with respect to the longitudinal axis of the switch rail on which it is provided.