Abstract:
The present invention concerns the fabrication of a longitudinal rail for supplying electrical power to a mobile, the rail including a mounting body for mounting the rail on a support and a wear plate which is worn by the mobile. The mounting body has a rigid base and a head divided into two halves which are prestressed in elastic flexing between rims of the wear plate. Applications include the production of electrical power supply rails for rail vehicles or materials handling plant.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method of fabricating a longitudinal rail for supplying a mobile with electrical power. 
     2. Description of the Prior Art 
     Said rail includes two electrically conductive longitudinal components which are fastened together and have respective substantially constant cross sections and a common median longitudinal plane of symmetry, namely a mounting body adapted to be mounted on a support and a wear plate which is worn by said mobile, 
     said mounting body including, in mutually opposed positions in a transverse direction in said plane, a rigid longitudinal base for mounting it on said support and a longitudinal head for receiving said wear plate, which head is delimited in the direction away from said base in said transverse direction by an electrically conductive face straddling said plane and having a rebate in the direction away from said plane on respective opposite sides of said electrically conductive face, 
     said plate including a flat central strip for transmitting electrical power to said mobile, straddling said plane, having opposite said base in said transverse direction a contact face for said mobile and facing toward said base in said transverse direction an electrically conductive face bearing flat on said electrically conductive face of said body and two lateral rims on respective opposite sides of said plane and forming a projection toward said base in said transverse direction relative to said central strip, each of said rims having, facing toward said plane, an attachment face for attaching it to said body, which attachment face converges with said plane in the direction away from said central strip in said transverse direction to define a hook shape interengaged with a respective rebate so that said wear plate is fastened to said head of said mounting body by a mutual nesting effect. 
     Non-limiting examples of mobiles that can be supplied with electrical power include certain rail vehicles, such as metros, and some lifting or materials handling plant, such as travelling overhead cranes, moving along a particular trajectory along which are placed one or more lengths of a rail of the type indicated in the preamble, on the wear plate of which presses an electrical pick-up member such as a shoe carried by the mobile. 
     In this regard, a rail of the type to which the present invention relates can equally well be rectilinear or curved, and in the latter case, as will be obvious to a person skilled in the art, a median fiber of the rail is taken as the longitudinal reference and a surface defined by respective axes of symmetry of different sections of the rail perpendicular to its median fiber are taken as the median plane of symmetry. 
     Various designs of electrical power supply rails consisting of the association of a mounting body and a wear plate fastened together are well known in the art and widely used. 
     The mounting body is generally used to mount the rail on supports such as insulators and can itself be used to mount electrically insulative caps to protect against accidental contact with the power supply rail. Its cross section is generally much greater than that of the other component, and is determined on the one hand by the stiffness to be imparted to the rail and on the other hand by the current that is to flow in it. To reduce its weight, for a given cross section, the mounting body is generally made of aluminum or aluminum alloy. 
     The wear plate, which is adapted to cooperate with the electrical pick-up member carried by the mobile, is therefore made from stainless steel, for example, which is more resistant to wear than aluminum or aluminum alloy, although more dense, or of copper or brass. Its cross section is limited to that necessary to insure a particular minimum time of operation, at the end of which it is completely worn down, and its shape can vary according to the manner in which it is fastened to the mounting body. 
     One fastening method relying on clipping of the rims of the wear plate into rebates on the head of the mounting body, as indicated in the preamble, is used by the company BRECKNELL WILLIS, which employs an aluminum mounting body which is rigid, especially in the area of its head, and two stainless steel members, each of which corresponds to one half of the wear plate, i.e. to one of the parts thereof defined by the median plane of longitudinal symmetry. The electrically conductive faces of the mounting body, the central strip of the wear plate, and the contact face for the mobile are plane and perpendicular to the median longitudinal plane of symmetry. To assemble the wear plate to the mounting body, the two parts of the wear plate, which are initially independent of each other, are heated to a temperature higher than that of the mounting body and applied to the head thereof so that the corresponding respective half of the central strip is applied to a respective half of the electrically conductive face of the head and their rims are pressed against the corresponding respective rebates; when the two parts are perfectly face-to-face in this way, in the median longitudinal plane of symmetry, they are welded together and the assembly is then allowed to cool, whereby, because of the different coefficients of thermal expansion of stainless steel and aluminum, the wear plate grips the head of the mounting body and is fastened to it by this gripping effect alone. 
     However, the pressure applied by the stainless steel wear plate to the aluminum mounting body is afterwards closely dependent on temperature, and in the event of extremely low temperatures the pressure can be insufficient to retain the wear plate against movement in longitudinal translation on the mounting body and to insure an adequate quality of electrical conduction between the two components of the rail. 
     French patent FR-A-2 227 148 discloses a variant of the method indicated in the preamble including a succession of steps, the first of which consists of separately prefabricating: 
     said mounting body, conforming it so that said head is divided in said plane into two halves joined together by said base and delimiting between them a longitudinal slot open in the direction away from said base in said transverse direction, each of said two halves having opposite said base in said transverse direction a free end including a respective half of said electrically conductive face of said body and a respective rebate and being adapted to flex elastically relative to said base, in particular toward each other from a rest configuration in which said mounting body is prefabricated and as far as a maximum elastic flexing configuration, said two halves of said electrically conductive face of said body having an orientation relative to said plane such that they diverge from said base in said transverse direction toward said plane in said rest configuration, and 
     said wear plate, conforming it so that its rims define between them, perpendicularly to said plane, in an area of closest approach thereto in the direction away from the central strip in said transverse direction, a width less than the maximum width of said head perpendicularly to said plane between said halves of said electrically conductive face of said body and said rebates, in said rest configuration, 
     The wear plate and the mounting body are therefore made in one piece, and the next step consists of forcibly nesting the wear plate over the head of the mounting body, by virtue of elastic flexing of the wear plate such that its rims move apart and elastic flexing of the two halves of the head such that they move toward each other until they abut against each other, which defines a maximum elastic flexing configuration that the two halves of the head retain at the end of fabrication of the rail and in which the slot is closed. 
     A final step consists of permanently fastening the wear plate to the mounting body by spiking, riveting or welding the rims of the wear plate to the head of the mounting body. 
     The above document teaches respectively concave and convex V-shaped cross sections for the electrically conductive faces of the wear plate and the mounting body, so that any tendency for the mounting body to resume its rest configuration by virtue of its elasticity is reflected in a tendency of the wear plate to press its electrically conductive face firmly flat against the electrically conductive face of the mounting body. 
     However, obtaining the above effect inevitably gives rise to major problems in that the wear plate is nested over the head of the mounting body with elastic prestressing such that it overcomes the elastic tendency of the two halves of the head to move apart from the relative position that they occupy at the end of fabrication of the rail, i.e. a relative position in which they abut one against the other and in which the slot that they define is closed, and the fact that the rims of the wear plate are firmly spiked, riveted or welded to the head of the mounting body after nesting, would seem more likely to oppose it. 
     Accordingly, given the coefficients of thermal expansion of the materials of the wear plate and the mounting body, namely stainless steel and aluminum or aluminum alloy, respectively, the electrically conductive face of the wear plate tends rather to move away from that of the mounting body if the temperature falls below the fabrication temperature, in which case the mutual contact pressure can be significantly reduced. 
     The spikes, rivets or welds joining the wear plate to the mounting body then undoubtedly oppose relative longitudinal sliding, but the quality of the electrical conduction between the wear plate and the mounting body is not insured. 
     What is more, the necessity for the wear plate to flex elastically in order for it to nest over the head of the mounting body and then to hold it elastically prestressed thereon imposes the choice for the wear plate of a semi-hard spring stainless steel, which is particularly fragile and costly, and necessarily limits the choice of geometrical characteristics that can be imparted to the wear plate; in particular, it must be relatively thin, which limits its service life. 
     What is more, the convex cross section that the face of the wear plate in contact with the electrical pick-up member carried by the mobile necessarily has in this case means that the pick-up member must have a concave shape, with a cross section complementary to the convex cross section, which complicates the manufacture of the pick-up member and rules out any transverse offset between it and the rail, i.e. mounting the pick-up member on the mobile, whose effective trajectory is rarely rigorously parallel to the rail, is made more complicated. 
     The object of the present invention is to remedy the above drawbacks of the prior art and, to this end, the present invention proposes a method of fabricating a longitudinal rail for supplying a mobile with electrical power, said rail including two electrically conductive longitudinal components which are fastened together and have respective substantially constant cross sections and a common median longitudinal plane of symmetry, namely a mounting body adapted to be mounted on a support and a wear plate which is worn by said mobile, 
     said mounting body including, in mutually opposed positions in a transverse direction in said plane, a rigid longitudinal base for mounting it on said support and a longitudinal head for receiving said wear plate, which head is delimited in the direction away from said base in said transverse direction by an electrically conductive face straddling said plane and having a rebate in the direction away from said plane on respective opposite sides of said electrically conductive face, 
     said plate including a flat central strip for transmitting electrical power to said mobile, straddling said plane, having opposite said base in said transverse direction a contact face for said mobile and facing toward said base in said transverse direction an electrically conductive face bearing flat on said electrically conductive face of said body and two lateral rims on respective opposite sides of said plane and forming a projection toward said base in said transverse direction relative to said central strip, each of said rims having, facing toward said plane, an attachment face for attaching it to said body, which attachment face converges with said plane in the direction away from said central strip in said transverse direction to define a hook shape interengaged with a respective rebate so that said wear plate is fastened to said head of said mounting body by a mutual nesting effect, 
     said method including a succession of steps, the first of which consists of: 
     a) prefabricating separately: 
     said mounting body, conforming it so that said head is divided in said plane into two halves joined together by said base and delimiting between them a longitudinal slot open in the direction away from said base in said transverse direction, each of said two halves having opposite said base in said transverse direction a free end including a respective half of said electrically conductive face of said body and a respective rebate and being adapted to flex elastically relative to said base, in particular toward each other from a rest configuration in which said mounting body is prefabricated and as far as a maximum elastic flexing configuration, said two halves of said electrically conductive face of said body having an orientation relative to said plane such that they diverge from said base in said transverse direction toward said plane in said rest configuration, and 
     said wear plate, conforming it so that its rims define between them, perpendicularly to said plane, in an area of closest approach thereto in the direction away from the central strip in said transverse direction, a width less than the maximum width of said head perpendicularly to said plane between said halves of said electrically conductive face of said body and said rebates, in said rest configuration, 
     in which method, in step a), there are also prefabricated: 
     said mounting body, conforming it so that said two halves of said electrically conductive face of said body have an orientation relative to said plane such that they converge toward said base in the direction toward said plane in said maximum elastic flexing configuration and in a particular intermediate elastic flexing configuration, in which said slot is still open in the direction away from the base in said transverse direction, they are mutually coplanar and perpendicular to said plane and then constitute said electrically conductive face of said body, which is plane and perpendicular to said plane, and 
     said wear plate, permanently conforming it so that said contact face for the mobile and said electrically conductive face of said central strip are plane and perpendicular to said plane and its rims define between them, perpendicularly to said plane, in an area of closest approach thereto in the direction away from said central strip in said transverse direction, a width less than the maximum width of said head, perpendicularly to said plane, between said halves of said electrically conductive face of said body and said rebates, not only in said rest configuration but also in said particular intermediate configuration, but at least equal to, and in particular greater than, the maximum width of said head perpendicular to said plane between said halves of said electrically conductive face of said body and said rebates, in said maximum elastic flexing configuration, and at least equal to, and in particular greater than, the minimum width of said head, perpendicularly to said plane, at the level of said rebates in said particular intermediate configuration, and so that said attachment faces define with said electrically conductive face of said wear plate a shape complementary to the shape that said rebates define with said electrically conductive face of said body in said particular intermediate configuration, 
     and which method includes, after step a), the following succession of steps: 
     b) applying to said two halves of said head opposite thrusts to move them toward each other, perpendicular to said plane, from said rest configuration to said maximum elastic flexing configuration, 
     c) maintaining said thrusts to retain said two halves of said head in said maximum elastic flexing configuration, nesting said wear plate over said head to place said electrically conductive face of said wear plate in bearing engagement with said halves of said electrically conductive face of said body and to place said rims on respective opposite sides of said head, facing said rebates, and 
     d) releasing said thrusts while holding said electrically conductive face of said wear plate in bearing engagement with said halves of said electrically conductive face of said body so that said two halves of said head flex elastically toward each other, perpendicularly to said plane, and said rebates abut in this direction against said attachment faces of said rims of said wear plate, which hold said two halves of said head prestressed in elastic flexing in said particular configuration in which said two halves of said electrically conductive face of said body are also mutually coplanar and said electrically conductive face of said wear plate is therefore pressed flat against it. 
     It will be obvious to the person skilled in the art that, in this case, the pressure applied by the two halves of the head of the mounting body, which is advantageously prefabricated in one piece during step a) from a material chosen from the group comprising aluminum and aluminum alloys, on the wear plate, which is also advantageously made in one piece during step a) from a material chosen from the group comprising stainless steel, copper and copper alloys, depends almost exclusively on the elastic properties of the material of the mounting body and the flexing applied to the halves of the head in said intermediate flexing configuration, in comparison with the rest configuration. That pressure is therefore practically constant and independent of temperature, or can in any event be high enough for any variations that may result from differential thermal expansion to remain sufficiently low, in comparison, for it to be sure that the pressure remains sufficiently high in all circumstances to prevent movement in translation of the wear plate relative to the mounting body and to preserve good electrical conduction between the mounting body and the wear plate. 
     What is more, compared to the prior art technique previously mentioned, it is faster, less costly and more reliable to produce a rail by the method according to the invention. 
     In particular, compared to the BRECKNELL WILLIS technique, it is not necessary to weld several initially separate parts of the wear plate, which means that the equipment necessary for such welding can be dispensed with, as can the reworking steps necessary to obtaining an appropriate flatness and surface state of the face of the wear plate in contact with the mobile. What is more, although machining the weld, in practice milling it, generally causes a median longitudinal depression in the contact face, accelerating wear of the electrical pick-up member carried by the mobile, when the BRECKNELL WILLIS technique is used, the possibility of making the wear plate in one piece when the method according to the invention is used means that its face in contact with the mobile can be flat without discontinuities in the transverse direction, reducing wear of the electrical pick-up member carried by the mobile. 
     Compared to the technique described in FR-A-2 227 148, it is not necessary to rely on the elasticity of the wear plate, and to the contrary its cross section can be considered to be non-deformable in comparison with the mounting body, which gives a greater choice as to the steel used, which can be less fragile and less costly than spring steel, and a greater choice as to the thickness of the plate, which can therefore be sufficiently thick to have a satisfactory service life. 
     What is more, the wear plate is retained on the head entirely by the elasticity of the mounting body and the respective conformations of its head and the wear plate, which makes it possible to dispense with any other form of fastening them together by spiking, riveting or welding, together with the reworking operations and equipment needed for this. 
     What is more, compared to the technique described in FR-A-2 227 148, the method of the invention provides the benefit of a flat face of the wear plate in contact with the mobile, which simplifies the manufacture and the mounting of the electrical pick-up member carried by the mobile, even if longitudinal movement of the mobile is accompanied by some transverse movement relative to the rail. 
     As is known in the art, the electrical conduction between the head of the mounting body and the wear plate can naturally be improved and all risk of penetration of an electrolyte between them avoided by applying a contact grease to at least one of said electrically conductive faces, and preferably to the rebates and/or the attachment faces, prior to step c). Such application is preferably immediately preceded or accompanied by brushing them clean; in particular, when the mounting body is made of aluminum or aluminum alloy, brushing the electrically conductive face of the body, and preferably also of the rebates, eliminates from them the alumina that would compromise electrical conduction with the wear plate, which alumina is prevented from forming again by applying a neutral contact grease immediately afterwards. 
     The fabrication method in accordance with the invention can be carried out simultaneously throughout the longitudinal dimension of the mounting body and the wear plate or successively in longitudinally localized areas of the mounting body and the wear plate in longitudinal succession in a given longitudinal direction. What is more, it can be carried out entirely in the shop or partly in the shop and partly on a site on which the rail is used. 
     Accordingly, in accordance with one embodiment of the method of the invention, the mounting body is fixed to the support in a particular position of use, on a site where the rail is used, between steps a) and b), and steps b), c) and d) are carried out on site with the mounting body fixed to the support in said particular position. 
     When a string of rails is made by this embodiment of the method according to the invention, each joint between the wear plates corresponding to two longitudinally adjoining rails can be made to coincide with the joint between the corresponding mounting bodies, but it is preferable to use the wear plates to insure mechanical continuity between the rails and the mounting bodies to ensure alignment of the wear plates. To this end, one particular embodiment of the method according to the invention is characterized in that several lengths of said mounting body are fixed to said support in said particular position on said site, between steps a) and b), by placing said lengths in alignment with each other in a longitudinal direction, and wherein steps b), c) and d) are carried out with said lengths fixed to said support in said particular position on said site using several lengths of said wear plate, aligned with each other in a longitudinal direction with the joints between them offset longitudinally relative to the joints between said lengths of said mounting body. 
     Given that the method of the invention implies prefabricating a mounting body and a wear plate with respective specific conformations, the present invention also includes a mounting body and a wear plate as respectively obtained by implementing step a). 
     In this regard, in an electrically conductive longitudinal body in accordance with the invention, having a substantially constant cross section and a median longitudinal plane of symmetry and including in mutually opposite positions in a transverse direction in said plane, a rigid longitudinal base for mounting it on said support and a longitudinal head for receiving a wear plate, which head has a rebate in the direction away from said plane, on respective opposite sites thereof, and is divided in said plane into two halves joined together by said base and delimiting between them a longitudinal slot open in the direction away from said base in said transverse direction, each of said two halves having opposite said base in said transverse direction a free edge including a plane edge face and a respective rebate and being adapted to flex elastically relative to said base, in particular in the direction toward each other, from a rest configuration in which said mounting body is prefabricated and as far as a maximum elastic flexing configuration, as proposed in FR-A-2 227 148, said two edge faces have an orientation relative to said plane such that they diverge from said base in the direction toward said plane in said rest configuration, and, in a particular intermediate elastic flexing configuration, in which said slot is still open in the direction away from said base in said transverse direction, they are mutually coplanar and perpendicular to said plane and together form a plane face delimiting said head in the direction away from said base in said transverse direction between said rebates. 
     The body can be made by assembling separate components but is preferably made in one piece from a material chosen from the group comprising aluminum and aluminum alloys. 
     Apart from the advantages of saving weight, good electrical conduction and good thermal conduction that they already offer in prior art rails of the type indicated in the preamble, compared to all-steel rails, aluminum and aluminum alloys offer advantages specific to the use of the present invention by offering increased possibilities in terms of the choice of the shape and the dimensions of the cross section of the mounting body, for the best possible combination of the elastic flexibility required by the present invention with a satisfactory contact pressure between the two halves of the head of the mounting body and the wear plate, in terms of mutual mechanical connection and electrical conduction between them, and the choice of the composition of the alloy, with the same aim, for a given shape and given dimensions of the cross section of the mounting body, i.e. retaining the same die for extruding the mounting body. 
     The body can also have various optional features intended to facilitate steps b), c) and d) of the method or to improve the result thereof. 
     Accordingly, in one preferred embodiment, each half of said head includes, in the direction away from said base in said transverse direction, a rigid edge part comprising in particular the respective edge face and the respective rebate, and, between said rigid edge part and said base, an intermediate part for connecting said edge part to said base, said intermediate part defining in comparison with said base and said edge part a weakened area encouraging elastic flexing of the respective half of said head between said rest configuration and said maximum elastic flexing configuration. 
     It is therefore certain that, in said predetermined intermediate configuration, the head has a perfectly defined external geometry, closely complementary to the inside geometry of the wear plate, which obtains the strongest possible and most uniform possible mutual application, combined with the facility to choose the elasticity of each half of the head in flexing, which conditions the pressure that each half of the head applies to the respective associated rim of the wear plate in said particular intermediate elastically flexed configuration, i.e. after fabrication of the rail, in particular by the method of the invention. 
     To this end, also, each rebate is preferably farther from said base in said transverse direction than the connection between the respective rigid edge part and the respective elastically flexible intermediate part. 
     To increase in particular the cross section of the mounting body, despite the provision of weakened areas of preferred elastic flexing, which are necessarily thin, i.e. in order to respond to the requirements for carrying current, each rigid edge part has an extension toward said base in said direction, alongside the respective elastically flexible intermediate part in the direction away from said plane and forming with it a respective longitudinal slot open toward said base in said transverse direction, in particular so as not to impede flexing of the halves of the head. 
     The extension of each rigid edge part is preferably conformed to enable an insulative cap of traditional shape to be attached to said base. 
     What is more if, as is preferred to facilitate steps b) and c) of the method, each half of said head has, in the direction away from said plane, closer to said base than the respective rebate, a respective flat approximately parallel to said plane for applying a respective thrust toward the latter to move said half from said rest configuration to said maximum elastic flexing configuration, said flat is advantageously on the respective extension and closer to said base in said direction than the connection between the respective rigid edge part and the respective elastically flexible intermediate part. 
     The aforementioned flat advantageously projects in the direction away from said plane relative to the respective adjoining areas of said body, which prevents the risk of the means employed to apply said thrust interfering with those areas. 
     It is naturally important for the thrust applied to the two halves of the head in the direction toward each other in steps b) and c) does not cause plastic deformation of the halves of the head and to this end each half of said head preferably has, in the area of said slot farthest from said base in said transverse direction, an area of abutment against the other half of said head in said maximum elastic flexing configuration. 
     To offer a distributed support to the attachment faces of the rims of the wear plate and to reflect the elastic flexing of the halves of the head back toward the rest configuration, in practice only as far as the particular intermediate configuration, during step d) of the method, by firm application of the electrically conductive face of the central strip of the wear plate to the electrically conductive face of the head, each rebate is advantageously formed by a flat facing in the direction away from said plane and progressively converging with it in the direction toward the base in said transverse direction, at least in said particular intermediate configuration. The two rebates thereby apply to the rims of the wear plate a sort of cam effect, the consequence of which is that, as the head is widened by the elastic flexing of its two halves in the direction away from each other perpendicular to the median plane, and symmetrically relative to that plane because of their symmetry, the rebates apply to the rims of the wear plate traction toward the base in said transverse direction so that the two electrically conductive faces are pressed together as uniformly and as flat as possible to minimize the risk of “pinholing” of those faces by the effects of arcs struck between them. 
     This cam effect is preserved by virtue of the elastic prestressing of the head of the mounting body and the opening of the slot thereof at the end of fabrication of the rail, regardless of dimensional variations of the wear plate and the mounting body as a result of thermal expansion when the rail is in service, with the result that the two electrically conductive faces remain firmly pressed together at all times, as uniformly and as flat as possible, and with optimum conditions of electrical conduction between them. 
     In step a), the rebates and the rims of the wear plate are preferably dimensioned in said transverse direction so that the part of each rebate farthest from the electrically conductive face of the body in said transverse direction remains disengaged from the respective corresponding rim at the end of step d), so that no obstacle impedes this effect. 
     What is more, to facilitate fitting the wear plate to the head of the mounting body in step c), each half of the head preferably has, between the respective outside face and the respective rebate, an end facet facing away from said plane, Joining the respective end face and the respective rebate and progressively converging with said plane in the direction away from the base in said transverse direction, in particular in the maximum flexing configuration. In this configuration, these facets constitute a bevel on respective opposite sides of the combination of the end faces of the halves of the head, to guide the rims of the wear plate as the latter is engaged on the head, in the direction toward the base of the body in said transverse direction. 
     To constitute the wear plate of the rail, in particular when it is made by the method according to the invention, the invention proposes an electrically conductive longitudinal plate having a substantially constant cross section and a median longitudinal plane of symmetry and including a flat central strip straddling said plane, having two mutually opposite faces, and two lateral rims on respective opposite sides of said plane and projecting from the same one of said faces, having a face directed toward said plane that converges therewith in the direction away from said central strip in a transverse direction of said plane to define a hook shape, in which wear plate said faces of its central strip are plane and perpendicular to said plane. 
     Said plate can obviously be assembled from several components but it is preferably made in one piece from a material chosen from the group comprising stainless steel, copper and copper alloys. 
     To cooperate with the rebates of the head when they are plane, said faces of the rims, constituting the attachment faces, are preferably plane, enabling them to be applied flat to the rebates in the head in said particular intermediate elastically flexed configuration, i.e. when the wear plate has been assembled to the mounting body, which encourages electrical conduction at this level. 
     To this end, in a preferred embodiment of step a) of the method according to the invention, the mounting body and the wear plate are prefabricated so that the rebates and the attachment faces are plane and at the same angle to the corresponding half of the electrically conducting face of the body and the electrically conducting face of the central strip, so that at the end of step d) the rebates and the attachment faces are pressed flat together. 
     In a particularly simple configuration, each rim advantageously has a rectilinear longitudinal free edge delimiting said respective face or attachment face in the direction away from the central strip in said transverse direction and each rim is preferably flat and connected to the central strip by a respective longitudinal bend. 
     Given that the method according to the invention imparts to the rail obtained, of the type indicated in the preamble, a structure which is novel in itself, the present invention also provides a longitudinal electrical power supply rail of that type, which can be made by the method according to the invention, or by some other method, if necessary, said rail including two electrically conductive longitudinal components fastened together having respective substantially constant cross sections and a common median longitudinal plane of symmetry, namely a mounting body for mounting said rail on a support and a wear plate which is worn by said mobile, 
     said mounting body including, in mutually opposed positions in a transverse direction in said plane, a rigid longitudinal base for mounting it on said support and a longitudinal head for receiving said wear plate, which head is delimited in the direction away from said base in said transverse direction by an electrically conductive face straddling said plane and having a rebate in the direction away from said plane on respective opposite sides of said electrically conductive face, said head is divided in said plane into two halves joined together by said base and delimiting between them a longitudinal slot open in the direction away from said base in said transverse direction, each of said two halves having opposite said base in said transverse direction a free end including a respective half of said electrically conductive face of said body and a respective rebate, and 
     said wear plate including a flat central strip for transmitting electrical power to said mobile, straddling said plane, having opposite said base in said transverse direction a contact face for said mobile and facing toward said base in said transverse direction an electrically conductive face bearing flat on said electrically conductive face of said body and two lateral rims on respective opposite sides of said plane and forming a projection toward said base in said transverse direction relative to said central strip, each of said rims having, facing toward said plane, an attachment face for attaching it to said body, which attachment face converges with said plane in the direction away from said central strip in said transverse direction to define a hook shape interengaged with a respective rebate so that said wear plate is fastened to said head of said mounting body by a mutual nesting effect, and said halves of said head are held in a particular configuration prestressed in elastic flexing by said rebates bearing against said attachment faces of said wear plate in the direction away from said plane, as proposed in FR-A-2 227 148, in which rail said electrically conductive face of said mounting body and said electrically conductive face of said wear plate are plane and perpendicular to said plane and said longitudinal slot is open in the direction away from said base in said transverse direction in said particular elastic flexing prestressing configuration in which said halves of said head are retained by bearing engagement of said rebates against said attachment faces of said wear plate in the direction away from said plane. 
     When the rail is fabricated by the method according to the invention, the particular elastically flexed prestressed configuration is naturally the aforementioned particular intermediate elastically flexed configuration. 
     The rail can also have all of the features resulting either from the different variants of the method according to the invention or the configuration of the mounting body and the wear plate in accordance with the invention, according to the above embodiments thereof. 
     In particular, a contact grease is advantageously disposed at least between said electrically conductive faces and preferably between said rebates and said attachment faces, and said rebates and said attachment faces are advantageously plane, converge toward said plane in the direction toward said base in said transverse direction, and are pressed flat together. 
     As a consequence of fabrication by the method according to the invention, on the one hand, and in a manner that is particularly advantageous in allowing a worn or damaged wear plate to be replaced without it being necessary also to change the body, on the other hand, each half of said head is advantageously adapted to flex elastically relative to said base in the direction toward said plane as far as a maximum elastic flexing configuration in which the maximum dimension of said head perpendicular to said plane between said halves of said electrically conductive face of said body and said rebates is at most equal to the width defined between said rims perpendicularly to said plane in an area of maximum closeness thereto in the direction away from said central strip in said transverse direction. 
     Accordingly, by returning the head to its maximum elastically flexed configuration, the wear plate can be demounted from it, a new one fitted and the head allowed to return to its rest configuration, in practice until its two halves abut against the rims of the new wear plate, again in the particular intermediate configuration. 
     This operation can be carried out in the shop, after demounting the rail from its support on its site of use and before remounting the rail on its support, but is preferably carried out on site. 
     To this end, the present invention proposes a method of renovating a rail when its wear plate is worn out or damaged, in which method said mounting body of said rail, said halves of said head of which can flex elastically relative to its base, is fixed to a support in a particular position of use on a site on which said rail is used, said method being carried out on said site with said mounting body fixed to said support in said particular position and including the following succession of steps: 
     e) applying to said two halves of said head opposite thrusts to move them toward each other, perpendicular to said plane, from said rest configuration to said maximum elastic flexing configuration, 
     f) maintaining said thrust to retain said two halves of said head in said maximum elastic flexing configuration, separating said wear plate from said head to separate it from said mounting body, 
     g) maintaining said thrust to retain said two halves of said head in said maximum elastic flexing configuration, nesting said wear plate over said head to place said electrically conductive face of said wear plate in bearing engagement with said halves of said electrically conductive face of said body and to place said rims on respective opposite sides of said head, facing said rebates, and 
     h) releasing said thrusts while holding said electrically conductive face of said wear plate in bearing engagement with said halves of said electrically conductive face of said body so that said two halves of said head flex elastically toward each other, perpendicularly to said plane, and said rebates abut in this direction against said attachment faces of said rims of said wear plate, which hold said two halves of said head prestressed in elastic flexing in said particular configuration in which said two halves of said electrically conductive face of said body are also mutually coplanar and said electrically conductive face of said wear plate is therefore pressed flat against it. 
     In a variant, the following succession of steps can be effected between steps f) and g): 
     i) releasing said thrusts so that said two halves of said head flex elastically in the direction away from each other perpendicularly to said plane and assume a rest configuration, and 
     j) applying said thrusts again to said two halves of said head to move them from said rest configuration to said maximum elastic flexing configuration. 
     To avoid at least partly irreversible plastic deformation of the mounting body on applying the thrust intended to return it to its maximum elastically flexed configuration, each half of the head naturally preferably comprises, in the area of said slot farthest from the base in said transverse direction, an area which abuts against the other half of the head in the maximum elastically flexed configuration. 
     What is more, to facilitate the application of said thrust, each half of the head preferably has, in the direction away from said plane, nearer the base than the corresponding rim of the wear plate, a respective flat, approximately parallel to said plane, for applying a respective thrust toward the latter in order to move said half into the maximum elastically flexed configuration, each flat advantageously projecting in the direction away from said plane relative to the respective adjoining areas of the rail so that the means used to apply said thrust do not interfere either with the wear plate to be changed or with the new wear plate. 
     The renewal method according to the invention can be carried out in the shop, after demounting the rail from its support on the site of use and returning it to the shop, which then necessitates returning the rail to its site of use to mount it again on its support, or more usually replacing it immediately with a new or renovated rail, and storing it after renovation for installation on a new site. It is consequently preferable to carry it out on the site on which the rail is used, with the mounting body fixed to its support in its particular position of use, and with the mounting body fixed to the support. 
     What is more, the renewal method according to the invention can be carried out simultaneously throughout the longitudinal dimension of the rail but, for reasons of the overall size of the equipment used for this purpose when the method is carried out on site, in particular, it is preferable to carry it out successively in longitudinally localized areas of the rail in longitudinal succession in a given longitudinal direction. 
     The method is therefore advantageously carried out on site on several lengths of rail longitudinally aligned with each other, with the joints between the new lengths of wear plate offset longitudinally relative to the joints between the lengths of mounting body, which enables use of the wear plates to insure mechanical continuity between the successive rails and to align the wear plates optimally, despite possible alignment defects between the mounting bodies, to limit the abrasion suffered by the pick-up member, such as a shoe, on passing from one wear plate to another. 
     To facilitate steps e), f), g), h) and where applicable steps i) and j) of the renewal method according to the invention, in particular on site, and likewise steps b), c), d) of the fabrication method according to the invention, in particular on site, the present invention proposes a carriage adapted to travel along the rail or the mounting body and carrying out those steps as it moves forward. 
     To this end, the carriage is characterized in that it includes: 
     a rigid chassis having a median longitudinal plane of symmetry, 
     removable mechanical connecting means between said chassis and said mounting body in an orientation in which said median longitudinal plane of symmetry coincides with the median longitudinal plane of symmetry of said mounting body, said means supporting said chassis via said mounting body and guiding longitudinal movement of said chassis in translation relative to it, 
     lateral thrust means on respective opposite sides of said longitudinal plane and symmetrical to each other with respect to said plane, at a level corresponding to an area of said head of said mounting body not covered by said wear plate when said rail is fabricated, 
     means for controlled forcible movement of said lateral thrust members toward and away from said plane, perpendicularly to it, retaining their mutual symmetry, 
     a central thrust member disposed in said plane, and 
     means for controlled forcible movement of said central thrust member both ways in a transverse direction in said plane. 
     To facilitate the forward movement of the carriage, said mechanical connecting means are preferably rolling means. 
     Similarly, to this end, said lateral thrust members advantageously include at least one pair of rollers freely rotatable about a respective axis parallel to said transverse direction in said plane on a respective slider and said means for moving said lateral thrust members include slideways on said carriage for guiding said sliders in a direction perpendicular to said plane with no other possibility of relative movement and adjustable means for positioning said sliders along said slideways. In a particularly simple manner, said means for adjustably positioning said sliders include a screw mounted to rotate on said chassis about an axis perpendicular to said plane, immobilized against any other movement relative to said chassis, and meshing with respective opposite threads of said sliders. 
     Said lateral thrust members preferably include two sets of said pairs, symmetrical to each other with respect to a particular transverse plane of said carriage, constituting a plane of symmetry for said central thrust member, and said means for moving said lateral thrust members constitute two respective corresponding sets which are mutually independent. 
     In a particularly simple and effective manner said rolling means are said rollers. In particular, if the mounting body of the rail includes flats projecting relative to the adjoining areas in order to receive the thrust adapted to move it to the maximum elastically flexed configuration, each roller advantageously has an annular groove adapted to bear on a respective flat of said mounting body in areas on respective opposite sides thereof, which means that the carriage is supported by the mounting body in the required position and that the carriage is guided, in this position, along the mounting body or the rail. 
     Similarly, said central thrust member is preferably a roller freely rotatable about a transverse axis on a slider and said means for moving said central thrust member include a slideway on said carriage for guiding said slider in said transverse direction with no other possibility of relative movement and means for positioning said slider adjustably along said slideway. Said means for adjustably positioning said slider can include a screw mounted on said slider to rotate about a transverse axis of said plane, immobilized against any other movement relative to said slider, and meshing with a thread of said chassis. 
     Other features and advantages of the various aspects of the present invention will emerge from the following description, which relates to a non-limiting embodiment of the invention, and the accompanying drawings, which constitute an integral part of the description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a wear plate prefabricated in accordance with the present invention in cross section taken along the line I—I in FIG.  2 . 
     FIG. 2 shows the prefabricated wear plate in section taken along its median longitudinal plane of symmetry II—II in FIG.  1 . 
     FIG. 3 shows a mounting body in accordance with the invention, as fabricated, i.e. in its rest configuration, in cross section taken along the line III—III in FIG.  4 . 
     FIG. 4 is a lateral elevation view of the mounting body as seen in the direction of the arrow IV in FIG.  4 . 
     FIGS. 5,  6  and  7  are respectively views in section taken along the line I—I in FIG.  2  and the line III—III in FIG. 4 with the transverse profile of the prefabricated wear plate as shown in FIG. 1 superposed on the transverse profile of the mounting body in its rest configuration as shown in FIG. 3, the comparative transverse profiles of the wear strip and the mounting body in its maximum elastically flexed configuration, in a transient relative position of fitting the wear plate to the mounting body, and the rail according to the invention incorporating the wear plate retained in place on the mounting body and in its particular intermediate configuration between its rest configuration and its maximum elastically flexed configuration. 
     FIG. 8 is a plan view of an installation for assembling the wear plate and the mounting body of a rail according to the invention. 
     FIGS. 9 to  14  are views in section respectively taken along the lines IX—IX, X—X, XI—XI, XII—XII, XIII—XIII, XIV—XIV in FIG. 8 of various workstations of the above installation at various stages in the fabrication of a rail according to the invention performed therein. 
     FIGS. 15 and 16 are views corresponding to those of FIG.  14  and showing two other successive steps of the fabrication of the rail according to the invention. 
     FIGS. 17 and 18 are lateral elevation views of the rail during fabrication, showing two examples of relative positioning of the wear plate and the mounting body in the longitudinal direction. 
     FIG. 19 and 20 show two further successive steps of the fabrication of the rail. 
     FIG. 21 shows a view of the finished rail, ready for storage and packaging. 
     FIG. 22 is a view of several rails in accordance with the invention in the packaging position and shown in cross section taken along the line XXII—XXII in FIG.  8 . 
     FIGS. 23 and 24 show a carriage for assembling the wear plate to the mounting body already mounted on its support on the site of use of the rail or replacing the wear plate without demounting the body relative to the support on said site, the carriage being shown in the position of use and, like the rail, respectively in section taken along the line XXIII—XXIII in FIG.  24  and in lateral elevation perpendicularly to the common median longitudinal plane of symmetry of the rail and the carriage in a transverse direction indicated by an arrow XXIV in FIG.  23 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In a general manner, the reference numeral  1  designates a rail in accordance with the invention in the finished state,  2  designates its wear plate, considered as rigid during the fabrication of the rail as well as after it is finished, and  3  designates the mounting body which is elastically flexible, in a controlled manner, as will become apparent hereinafter. The reference numerals  4  and  5  respectively designate a longitudinal direction and a median longitudinal plane of symmetry of the rail  1 , and therefore also of the wear plate  2  and the mounting body  3  when they are assembled together to constitute the rail  1 ; for convenience, the same reference numerals  4  and  5  respectively designate a longitudinal direction and a median longitudinal plane of symmetry of the wear plate  2  and the mounting body  3  even when they are separated from each other, and in particular in the state in which they are prefabricated before they are assembled together to constitute the rail  1 . The aforementioned rigidity of the wear plate  2  and elastic flexibility of the mounting body are to be understood with reference to the comparative behaviors of their cross sections during and after the fabrication of the rail  1 , given that both of them can flex elastically in their median longitudinal plane of symmetry  5 . 
     For simplicity, the rail  1 , the wear plate  2  and the mounting body  3  are described as rectilinear, but the skilled person will deem it obvious that the present invention also applies to curved rails and can easily make the necessary adaptations to the dispositions and procedures to be described without difficulty and without departing from the scope of the invention. 
     Reference is made first to FIGS. 1 and 2, which show the wear plate as fabricated, and during its assembly to the mounting body  3  and when the rail  1  according to the invention is finished. 
     The wear plate  2  is advantageously made by shaping a strip which is preferably made of stainless steel, copper or brass, or by any appropriate method from any appropriate electrically conductive material, and has a constant cross section defined by a flat central strip  6  which straddles symmetrically the plane  5  to which it is perpendicular and two flat lateral longitudinal rims  7  on the same side of the plate  6  and on respective opposite sides of the plane  5 , relative to which they are mutually symmetrical. Each of the rims  7  is flat and connected to the central strip  6  by a respective longitudinal bend  8  which is rounded in the form of a circular arc. 
     To be more precise, the central strip  6  has two mutually parallel and mutually opposed plane faces  9 ,  10  both of which are perpendicular to the plane  5 , with respect to which they are respectively symmetrical, and the two faces  9  and  10  have a rectangular shape with a longitudinal dimension very much greater than the transverse dimension. The face  9  that faces away from the rims  7  is adapted to transmit electricity by electrical conduction from the rail  1  which is fixed to the ground, not shown, via electrically insulative supports, also not shown but familiar to the skilled person, to a mobile which moves longitudinally, i.e. parallel to the rail  1 , and which is shown schematically in FIG. 7 by a shoe  11  pressed flat onto the face  9 , along which the shoe  11  slides longitudinally as the mobile moves. The face  10  is adapted to rest flat against a plane electrically conductive face  13  of the body  3  when the rail  1  is finished, to assume a relationship of electrical conduction with that face  13 , under conditions that emerge hereinafter. 
     The rims  7  project relative to the face  10  of the central strip  6  and converge in the direction away from the face  10  in a transverse direction  16  in the plane  5 . Each of them has a respective plane face  14 ,  15 , respectively facing away from and toward the plane  5 , respectively connected to the face  9  or the face  10  by a circular arc-shaped rounded portion (no reference number), at the level of the corresponding bend  8 , and the two faces  14 , and likewise the two faces  15 , converge in the direction away from the central strip  6  in the direction  16 . At the greatest distance from the central strip  6  in the direction  16  the two plane faces  14  and  15  of each rim  7  are connected together by a respective plane longitudinal edge  18  substantially perpendicular to the two faces  14 ,  15  of the respective corresponding rim  7 . The edges  18  therefore define for each of the rims  7  a respective longitudinal rectilinear free edge delimiting the faces  14  and  15  of the rim  7 , and more generally the rim as a whole, on the side opposite its connection to the central strip  6 , and the edge where they connect to the respective face  15  constitutes the area of the corresponding rim  7  nearest the plane  5 . 
     As emerges hereinafter, the faces  15  that face toward the plane  5  define a respective attachment face for attaching the wear plate  2  to the mounting body  3  and it should be noted that each of them defines a hook-shape in conjunction with the face  10  of the central strip  6 . 
     The wear plate  2  has the transverse profile defined by the central strip  6  and the rims  7  as just described throughout its longitudinal dimension and between two plane transverse end faces  19 , except that in the embodiment shown, and in a manner that is not related to the present invention, the face  9  is connected to each of the faces  19  by a respective end transverse bevel or chamfer  20 . 
     L 1  designates the longitudinal dimension or length of the wear plate  2  between its transverse end faces  19 , α 1  designates the angle defined by each of the attachment faces  15  with the electrically conductive face  10  of the wear plate  2 , p 1  designates the distance or depth in the direction  16  between the face  10  and a longitudinal edge (no reference number) where each face  15  is connected to the edge  18  of the corresponding rim  7 , p 2  designates the distance or depth in the direction  16  between the face  10  and a longitudinal edge (no reference number) where each face  14  is connected to the edge  18  of the rim  7 , the depth p 2  being greater than the depth p 1 , e 1  designates the thickness of the wear plate  2 , which thickness e 1  is identical for the central strip  6 , the rims  7  and the bends  8  connecting the rims  7  to the central strip  6 , and l 1  designates the minimum inside width of the central strip  6 , i.e. the dimension perpendicular to the plane  5  between the longitudinal edges connecting each face  15  to the edge  18  of the respective corresponding rim  7 . The angle α 1  is less than 90°, for example of the order of 70°, but other values could be chosen without departing from the scope of the present invention. 
     Reference is now made to FIGS. 3 and 4 in particular, which show the mounting body  3  in a rest configuration, i.e. as fabricated, in particular by extrusion, in one piece, from aluminum or aluminum alloy, or by any appropriate method known in the art from any appropriate electrically conductive material. 
     In particular when it occupies this rest configuration, the mounting body  3  has a constant cross section between two plane transverse end faces  21  between which it has a longitudinal direction or length L 2  which is preferably slightly greater than the length L 1 , although the difference between these two lengths is negligible compared to their respective values; by way of non-limiting example, the length L 2  can be 12 000 mm and the length L 1  can be 11 990 mm. 
     The cross section is conformed to define in the mounting body  3  two parts which are mutually opposed in the direction  16 , namely a longitudinal mounting base  22  for mounting it on a support such as a group of insulators attached to the ground, in a manner that is not shown but which is identical in the case of the present invention and in the case of a prior art electrical power supply rail, and a longitudinal head  23  which receives the wear plate  6 , which head is elastically compressible perpendicularly to the plane  5  by flexing elastically relative to the base  22 . 
     The conformation of the base  22  is immaterial insofar as the present invention is concerned, provided that the base  22  is rigid. In the non-limiting example shown, it has opposite the head  23 , in the direction  16 , a rectangular plane longitudinal face  24  perpendicular to the plane  5 , which it straddles symmetrically, and the face  24  is delimited in the direction away from the plane  5  by connections with two plane edges  25  parallel to the plane  5  and symmetrical to each other with respect to it. The two edges  25 , facing away from the plane  5 , connect the face  24 , on the same side as the head  23 , to a respective plane face  26  which, from the point at which it is connected to the corresponding edge  25 , diverges progressively from the face  24  in the direction toward the plane  5 , relative to which the two faces  26  are symmetrical to each other. The faces  26  define in conjunction with the face  24  and the edges  25  a holding profile for holding members, not shown, for connecting the rail to the insulative supports, also not shown. 
     In the direction toward the plane  5 , which it does not reach, each face  26  is connected to a longitudinal flank  27  of a respective longitudinal groove  28  whose flank  27  is plane, parallel to and faces the plane  5 . Each flank  27  has a respective bottom  29 , which advantageously has a semi-circular cross section, which closes the groove  28  in the direction toward the face  24  in the direction  16 , and each flank  27  is connected to another flank  30  of the same groove  28 , which flank  30  is also plane, parallel to the plane  5  in the rest configuration of the mounting body  3  and extends beyond the flank  27  in the direction away from the face  24  in the direction  16 , until it connects to a longitudinal bottom  31  of another respective longitudinal groove or slot  32  directly facing the corresponding groove  28  in the direction  16 , in the sense that the bottoms  29 ,  31  of a groove  28  and a groove or slot  32  on the same side of the plane  5  as the latter directly face each other in the direction  16 . 
     Each bottom  31  advantageously has a circular arcshaped cross section subtending an angle of slightly less than 180° and connects the flank  30  of the corresponding groove or slot  32  to another longitudinal flank  33  thereof, which flank  33  is plane, faces toward the plane and diverges progressively from that plane in the direction toward the face  24  in the direction  16 , so that the groove or slot  32  is open toward the base  22  in the direction  16 . 
     Each flank  33  also extends toward the face  24  in the direction  16  as far as a longitudinal rectilinear edge  34 ; the edge  34  faces the face  26  on the same side of the plane  5 , without coming into contact with that face  26 , regardless of the configuration of the mounting body  3 , the configurations of which are described later, in order to leave a continuous space  135  between the edge  34  and the corresponding face  26 , regardless of the configuration. 
     Each edge  34  connects the corresponding flank  33  to a respective longitudinal plane beveled face  35  at approximately 45° to the plane  5 , from which it diverges in the direction away from the face  24  in the direction  16 , until it is connected to a flat  36  approximately parallel to and facing away from the plane  5 . 
     In the direction away from the face  24  in the direction  16  each flat  36  is connected to a longitudinal flat  37  approximately perpendicular to the plane  5 , facing away from the face  24  in the direction  16  and located at approximately the same level in that direction as the bottom  31  of the grooves or slots  32 . 
     Accordingly, relative to the areas of the body  3  which directly adjoin it both in the direction toward the face  24  and in the direction away from it, in the direction  16 , i.e. relative to the corresponding beveled face  35  and relative to the corresponding flat  37 , each flat  36  forms a projection in the direction away from the plane  5 . The dimension e 5  of each flat  36  between the points (no reference number) where it is connected to the beveled face  35  and the respective corresponding flat  37 , as measured in the direction  16 , can be varied according to the configuration of the mounting body  3 , the configurations of which are described later, but the variations allowed are sufficiently small to be ignored in the context of the present description. 
     Each flat  37  connects the corresponding flat  36 , in the direction toward the plane  5 , to a longitudinal flat  38  which faces away from the plane  5 , from which the flat  38  diverges from the point at which it is connected to the flat  37 , in the direction away from the face  24  in the direction  16 , until it is connected by a longitudinal rectilinear edge  49  to a plane longitudinal facet  39  which also faces away from the plane  5  but whose oblique relationship to the latter is the reverse of that of the flat  38 , with the result that the facet  39  converges toward the plane  5  in the direction away from the face  24  in the direction  16  and the flat  38  is set back relative to the facet  39  in order to attach one of the rims  7  of the wear plate  2  by means of the corresponding attachment face  15 , as becomes apparent later; note that the flat  38  which is set back is also set back toward the plane  5  relative to the corresponding flat  36  because of the presence of the flat  37 . 
     In the direction away from the face  24  in the direction  16 , each facet  39  connects the flat  38  to a longitudinal plane end face  40  which is approximately perpendicular to the plane  5  and faces away from the face  24  in the direction  16 . However, in the rest configuration shown in FIG. 3, the face  40  diverges progressively from the face  24  toward the plane  5  in the direction  16 , forming relative to a longitudinal geometrical plane  12  perpendicular to the plane  5  an angle α 2  close to zero, for example of the order of 1°. The facet  39  is connected to the end face  40  along a longitudinal rectilinear edge  50 . 
     In the direction toward the plane  5 , the face  40  is connected by a longitudinal rectilinear edge  41  to a plane longitudinal face  42  that faces toward the plane  5  and diverges from it toward the face  24  in the direction  16 . The face  42  extends as far in the direction  16  as an intermediate level between the levels where the flat  38  is connected to the flat  37  and to the facet  39 , respectively, i.e. to a distance from the face  25  slightly greater than that between it and the bottom  31  of the groove or slot  32  in the direction  16 . 
     In the direction toward the face  24  in the direction  16 , each face  42  is connected to a plane longitudinal face  43  which converges with the plane  5  in the direction toward the face  24  in the direction  16  and is connected at a distance from the face  24  in the direction  16  which substantially corresponds to the distance between the face  24  and the bottom  29  of each groove  28 , by a circular arc-shape transition, to a plane longitudinal face  44  perpendicular to the plane  5 , which the face  44  straddles in order to connect together the two faces  43  so that the faces  42 ,  43  and  44  define a longitudinal slot  45  in the mounting body  3 . The face  44  defines the bottom of the slot  45 , which is open in the direction away from the face  24  in the direction  16 , between the edges  41 , and extends from one to the other of the end faces  21  of the mounting body  3 . The slot  45  divides the head  23  in the plane  5  into two halves  46  which are symmetrical to each other with respect to the plane  5  and each of which is defined, on a respective side of that plane, by the flank  30 , the bottom  31  and the flank  33  of the groove or slot  32 , open toward the base  22  in the direction  16 , by the face  35 , the flat  36 , the flat  37 , the recessed flat  38 , the facet  39 , the end face  40  and the faces  42  and  43 , the two half-heads  46  defined in this way being connected together by the rigid base  22  which is in turn defined by the face  24 , the edges  25 , the faces  26 , the flanks  27  and the bottoms  29  of the grooves  28 . 
     For each half-head  46  the flank  33 , the face  35 , the flat  36 , the flat  37 , the recessed flat  38 , the facet  39 , the face  40  and the face  42  define a free end part or rigid end part  47  on the same terms as the base  22  and the flank  30  and the face  43  define between the rigid end part  47  and the rigid base  22  an intermediate part  48  connecting them together and defining a weakened area, compared to them, of privileged elastic flexing of the respective half  46  of the head from the rest configuration shown in FIGS. 3 and 5, in particular toward the plane  5  and toward the other half-head  46 , to a maximum elastically flexed configuration shown in FIG. 6, in which the two half-heads come into mutual abutment in the plane  5  at the edges  41 . 
     In this maximum elastically flexed configuration, in which the symmetry of the half-heads  46  relative to the plane  5  is preserved, the slot  45 , which is then closed in the direction away from the base  22  because of the mutual contact of the edges  41 , is comparatively shrunk and the faces  43  are approximately parallel to the plane  5 , whereas the faces  42  converge in a more pronounced manner toward the plane  5  in the direction away from the base  22  in the direction  16 . What is more, in this maximum elastically flexed configuration, the orientation of the end faces  40  of the half-heads  46  is reversed compared to their orientation in the rest configuration, in the sense that the faces  40  are inclined so that they converge toward the base  22  in the direction toward the plane  5  in the direction  16 ; however, their orientation relative to the face  42  of the same half-head, the facet  39 , the recessed flat  38 , the flat  37 , the flat  36 , the face  35  and the flank  33  of the same half-head  46  remains unchanged, because of the rigidity of the end part  47 . 
     Note that, in this preferred embodiment, each intermediate part  48  becomes progressively thinner perpendicularly to the plane  5  from the point at which it is connected to the base  22  to the point at which it is connected to the respective end part  47 , so that elastic flexing is privileged in the immediate vicinity of the connection of each intermediate part  48  to the corresponding end part  47 . 
     The skilled person will readily understand that the change from the rest configuration shown in FIGS. 3 and 5 to the maximum elastically flexed configuration in the direction of movement toward each other of the two half-heads  46 , shown in FIG. 6, and conversely by elasticity of the intermediate parts  48  in particular, is accompanied by a passage through a particular intermediate configuration of the body  3 , shown in FIG. 7, in which configuration the mutual symmetry of the two half-heads  46  relative to the plane  5  is preserved and the edges  41  are still separated, although they are nearer the plane  5  than in the rest configuration. In this intermediate configuration, the two end faces  40  are mutually coplanar, perpendicular to the plane  5 , and form respective halves, separated by the slot  45 , of a common plane face which is the electrically conductive face  13  of the body  6  facing toward the wear plate  2 , i.e. the face  13  onto which the electrically conducting face  10  of its central strip  6  of the wear plate  2  is pressed flat, when the rail  1  is completed by assembling together the wear plate  2  and the mounting body  3 . The profile of each end part  47  naturally remains unchanged in this intermediate configuration, compared to the rest configuration and the maximum elastically flexed configuration. 
     In this intermediate configuration, when the rail  1  is finished, the rebates  38  on respective opposite sides of the face  13  fasten the rims  7  of the wear plate  2  and to this end the attachment face  15  of each rim  7  is pressed flat against a respective flat  38 , i.e. an area of the flat  38  directly adjacent its connection to the facet  39 ; the part of the flat  38  directly adjacent the flat  37  preferably remains free, to prevent contact between the edge  18  of each rim  7  and the flat  37 , in particular when fitting the wear plate  2  to the mounting body  3 , with the mounting body  3  in its maximum elastically flexed configuration in which the flats  37  diverge progressively from the face  24  in the direction away from the plane  5  in the direction  16  (see below). Accordingly, when the rail  1  is finished, there exists between each edge  18  and the corresponding flat  37  a clearance in the direction  16  which is permanent, i.e. which is present regardless of dimensional tolerances and dimensional variations caused by thermal expansion of the wear plate  2  and the mounting body  3 , which achieves a permanent cam effect between the attachment faces  15  and the flats  38  because of their orientation relative to the plane  5  and the tendency of the mounting body  3 , which at this stage is held in said intermediate configuration exclusively by the half-heads  46  bearing against the rim  7  of the wear plate  2  in the direction away from the plane  5 , to resume its rest configuration because of its elasticity, the result of which is to press the electrically conductive face  10  of the central strip  6  of the wear plate  2  against the coplanar end faces  40  of the half-heads  46 , regardless of the dimensional tolerances and the dimensional variations caused by thermal expansion of the wear plate  2  and the mounting body  3 . 
     To enable the wear plate  2  to be attached to the mounting body  3  under such conditions, the angle α 1  between each recessed flat  38  and the end face  40  of the same half-head  46  naturally applies, regardless of the configuration of the body  3  by elastic flexing, the edge  49  connecting each flat  38  and the corresponding facet  39  is at a distance d 1  less than the depth p 1  from the face  40  of the same half-head  46 , to which it is perpendicular, and the flat  37  is at a distance d 2  from the face  40 , as measured perpendicularly to that face, greater than the depth p 2 . The distances d 1  and d 2  naturally do not vary when the body  3  flexes elastically. 
     In contrast, the separation of the edges  49  connecting each facet  39  to the flat  38  of the same halfhead  46 , perpendicularly to the plane  5 , varies with the configuration that the body  3  assumes by flexing elastically. 
     Accordingly, in the rest configuration shown in FIGS. 3 and 5, that separation has a value l 2 &gt;l 1  although, in the maximum elastically flexed configuration shown in FIG. 6, that separation has a value l 3  at most equal to l 1  and preferably slightly less than l 1 , by 1 to 2 mm, for example. In contrast, in the particular intermediate configuration shown in FIG. 7, the value l 4  of the separation, which is between the values l 2  and l 3 , is again greater than l 1  and in practice equal to the unmarked distance between the attachment faces  15 , as measured perpendicularly to the plane  5 , at a distance from the face  10  of the central strip  6  of the wear strip  2 , as measured perpendicularly to the face  10 , equal to the distance d 1  between each edge  49  of the end face  40  of the same half-head  46 , because each flat  38  is pressed flat against a respective attachment face  15  in this configuration once the rail  1  is finished. In this configuration, the respective connections (no reference number) of the recessed flats  38  to the corresponding flats  37  are mutually spaced perpendicularly to the plane  5  by a distance l 11  less than l 1 . 
     Thus if the respective transverse profiles of the body  3  in its rest configuration and the wear plate  2  are superposed, as shown in FIG. 5, overlapping is observed of an area of each half-head  46  located in the vicinity of the edge  49  and along the area of the corresponding flat  38  adjacent the edge  49  by a respective rim  7 , and more precisely by a portion of the edge  18  thereof and by an area thereof situated along the attachment face  15 , adjacent the edge  18 , given that the body  3  and the wear plate  2  are assumed to have the same median longitudinal plane of symmetry  5 . The mean value of this overlap, as measured perpendicularly to the flat  38  or the face  15 , is marked e 2  in FIG. 5; by way of non-limiting example, it can be from 1 to 2 mm, given that it is cancelled out when the mounting body has the predetermined configuration shown in FIG. 7, and that the overlap is replaced by a clearance when the mounting body  3  is in the maximum elastically flexed configuration shown in FIG.  6 . 
     Note that the value e 3  of the mutual separation of the edges  41  perpendicular to the plane  5  in the rest configuration can be predetermined, the value  13  being approximately equal to the value l 2  minus e 3 ; in the particular intermediate configuration of the body  3 , shown in FIG. 7, their mutual separation has a value e 4  less than the finite value e 3 . 
     Similarly, the distance perpendicular to the plane  5  between the edges  50  connecting each facet  39  to the face  40  of the same half-head  46  varies according to the configuration of the body  3  so that, in the rest configuration shown in FIG. 7, it has a value l 5  at most equal, and preferably substantially equal, to the width l 6  of the face  10  of the central strip  6  of the wear plate  2  perpendicularly to the plane  5  between the bends  8 , i.e. between its respective arcuate connections to the attachment faces  15 . In practice, the value of l 6  can be substantially identical to the value of l 1 . For l 5  to have a value of this kind, the edges  50  are mutually spaced perpendicularly to the plane  5  in the rest configuration shown in FIG. 3 by a distance l 7  whose value is greater than the value of l 5  in the same proportions as the value of e 3  is greater than the value of e 4  and the value of l 2  is greater than the value of l 4 . What is more, the distance d 1  between each edge  49  and the end face  40  of the same half-head  46  is made greater than the distance d 3  between the face  10  of the central strip  6  of the wear plate  2  and each of the attachment faces  15  at the level of the corresponding bend  8 , i.e. at the level of its arcuate connection to the face  10 . Thus in the configuration shown in FIG. 7 the facets  39  do not interfere with the arcuate connections of the connecting faces  15  to the face  10 . 
     Under these conditions, the rail  1  shown in FIG. 7 can be fabricated in the manner now to be described with reference to FIGS. 8 to  22 . 
     Firstly, the mounting body  3  is prefabricated in its rest configuration, for example by extruding it in one piece from aluminum or aluminum alloy, and the wear plate  2  is prefabricated in its final configuration, for example by profiling a stainless steel strip or a strip of copper or a copper alloy such as brass. 
     The mounting bodies  3  and the wear plates  2  prefabricated in this way are brought separately to an installation  51  for assembling them together to form the rails  1 . FIG. 8 shows one non-limiting example of an installation  51  that can be provided in a production shop. FIG. 8 shows the longitudinal direction  4 , which is now horizontal, that will continue to be used as a reference given that the mounting bodies  3 , the wear plates  2 , and the finished rails  1  retain this longitudinal direction  4  before, during and after assembly. 
     The installation  51  shown diagrammatically in FIG. 8 includes, in longitudinal succession in the direction  4 : 
     a table  52  for individually feeding mounting bodies  3  in the rest configuration and with an orientation such that the face  24  of the base  22  of each mounting body  3  faces downwards and rests on horizontal transport idler rollers  153  for conveying them in the direction  4  and in which the head  50  faces upward, the feed table  52  being flanked laterally by a table  53  for storing waiting mounting bodies  3 , which are already correctly oriented; 
     a station  54  for assembling together each mounting body  3 , introduced successively via the feed table  52 , and a respective wear plate  2 , the wear plates  2  awaiting assembly being stored on a storage table  55  disposed laterally relative to the station  54 , with an orientation such that the edges  18  of the rims  7  rest on the table  55  and the face  9  of the central strip  6  faces upward; and 
     a station  56  for packaging the finished rails  1  fed one by one from the station  54  in the direction  4 , preferably in a head-to-tail arrangement. 
     The successive mounting bodies  3  are individually conveyed from the station  52  to the station  54  by two groups  57 ,  58  each of two rollers  59 ,  60  in succession in the direction  4  between the stations  52  and  54 . The rollers are driven in rotation about a respective vertical axis  61 ,  62  by a motor  63  and press against respective edges  25  of the base  22 . An identical group  64  of two rollers is disposed between the stations  54  and  56  in the direction  4  to convey the finished rails  1  from the station  54  to the station  56 , also by virtue of bearing against the edges  25  of the base  22 . The three groups  57 ,  58 ,  64  are identical, and for this reason only one of them is shown in FIG. 10, it being understood that the rollers of the two groups  57  and  58  are driven by a common motor  63 . 
     A device  65  for brushing and greasing the faces  40 , the facets  39  and the recessed flats  38  of the body  3  in its rest configuration is disposed between the two groups  57  and  58  in the direction  4 , greasing being effected with a contact grease adapted to encourage subsequent electrical conduction at least between the faces  40  of the face  10  of the wear plate  2  and preferably also between the recessed flats  38  and the attachment faces  15 . 
     To this end, the device  65  includes three rotary brushes  66 ,  67 ,  68 . The brush  66  is disposed above the trajectory of the faces  40 , over the width  17  and with equal lengths on respective opposite sides of the trajectory of the plane  5 , and has a horizontal axis  69  around which it is driven in rotation so that its part in contact with the faces  40  moves in the opposite direction to them. The other two brushes  67 ,  68  are on respective opposite sides of the trajectory of the mounting body  3  at the level of the facets  39  and the recessed flats  38  and have a respective vertical axis  70 ,  71  about which they are driven in rotation so that they come into contact with the facet  39  and the recessed flat  38  of a respective half-head  46  on moving in opposite directions. The construction of the station  65  is not described in more detail and will be obvious to the skilled person anyway. 
     On reaching the station  54 , after having the faces  40 , facets  39  and recessed flats  38  brushed and greased in this way, each successive mounting body  3  rests with the downturned face  24  of its base  22  on a horizontal table  72  on which it is longitudinally and transversely immobilized in a particular position by virtue of one of the edges  25  of the base  22  bearing against stops  73  fixed to the table  72  and distributed longitudinally along the edge  25 , and by mobile stops  74  facing the fixed stops  73  in the horizontal and transverse directions and pressed against the other edge  25  by respective actuators  75  adapted to move the stops  74  horizontally toward the stops  73  to immobilize an attachment body  3  by clamping its base  22  or in the direction away-from the stops  73  to release the mounting body  3 , in particular so that it can move in translation in the direction  4 . 
     The table  72  can be plane, but it will be obvious to the skilled person that it can also have a longitudinal curvature which it communicates to the mounting body  3  when it is immobilized on it between the stop  73  and  74 , that curvature being such that when the base  22  of the rail  1  has been mounted on insulative supports, generally in an orientation in which the base  22  faces upward and its face  24  is horizontal, the curvature that the rail  1  naturally assumes between the mounting supports, because of its weight, cancels the initial curvature so that the initially curved rail  1  becomes straight. The curvature to be imparted to the basic body  3  for this purpose at the station  54 , and consequently also to the wear plate  2  after they are assembled together, can easily be determined by the skilled person, in particular according to the distance between two mounting supports of the rail  1 . 
     Only in two sets of the fixed stops  73  associated with a mobile stop  74  are preferably provided, disposed to operate in the vicinity of the end faces  21  of the mounting body  3 ; however, given the longitudinal dimensions of the mounting body, which is of the order of  12  meters, for example, other fixed stops  76  are arranged longitudinally at the station  54 . The same edge  25  bears against them as bears against the stops  73 , as can be seen in FIG.  13 . 
     Once it has been immobilized in this way at the station  54 , each mounting body  3  undergoes a number of successive operations that are described now with reference to FIGS. 12 and 14 to  20 . 
     As shown in FIG. 12, at predetermined locations in the vicinity of each of the faces  21  in the longitudinal direction  4 , boring devices  77  are mounted under the table  72  and comprise, for example, two groups each of two drills  78  which are symmetrical to each other with respect to the trajectory of the plane  5  and mounted to rotate about a respective vertical axis  79  relative to a common carriage  80  adapted to move upward and downward under the table  72 , in a controlled manner, to bore into the base  22  two groups of two vertical axis threaded holes symmetrical to each other with respect to the plane  5 , to enable subsequent fishplate joints between the mounting bodies  3  of two longitudinally juxtaposed rails  1 , on the site of use, to ensure mechanical and electrical continuity between them. The construction of each device  77  will be evident to the skilled person and is not described further. The boring operation is not characteristic of the present invention. 
     In contrast, FIGS. 14 to  20  show the assembly of the wear plate  2  to the mounting body  3  at the station  54 , which is characteristic of the present invention. 
     The station  54  has, throughout the longitudinal dimension L 2  of the mounting body  3 , a respective rectilinear bar  81 , or a respective succession of longitudinal bars  81 , each of which corresponds to a portion of the longitudinal dimension L 2 , but which can be considered as a respective unique bar, facing the trajectory of each of the flats  36  of the mounting body  3  in the rest configuration, on respective opposite sides of the trajectory of the plane  5  and symmetrically with respect to that trajectory. Each of the bars  81  or like successions of bars is supported by a respective group of actuators  82  distributed along the longitudinal dimension L 2  and adapted to move the two bars  81  or like successions of bars synchronously in a transverse horizontal direction toward or away from the trajectory of the plane  5 , in either case preserving the mutual symmetry of the bars  81  or like successions of bars with respect to that trajectory. The bars  81  or successions of bars are advantageously flexible in the horizontal plane and their connections to the actuators  82  allow limited clearance in the longitudinal direction to allow the actuators  82  to flex the bars  81  or successions of bars in said horizontal plane. 
     The bars  81  or like successions of bars can therefore evolve between a position of maximum mutual spacing perpendicular to the trajectory of the plane  5 , in which the distance l 12  between them is greater than the distance l 14  between the flats  36 , perpendicular to the plane  5 , when the mounting body  3  is in its rest configuration, as shown in FIG. 20, and a position of maximum closeness perpendicularly to the trajectory of the median plane  5 , in which position the value l 13  of the distance between them perpendicularly to that trajectory is less than the value l 9  of the distance between the flats  36  perpendicularly to the plane  5  in the predetermined intermediate configuration shown in FIG.  7 , and corresponds to the value  110  which must be imparted to this distance between of the flats  36  perpendicularly to the plane  5  to place the mounting body  3  in the maximum elastically flexed configuration shown in FIG. 6, i.e. so that the two half-heads  46  just abut against each other in the plane  5  at their edges  41  without pushing the half-heads  46  any farther toward each other. 
     The bars  81  or like successions of bars occupy their farthest apart position, shown in FIG. 20, during the feeding of a mounting body  3  in its rest configuration to the station  54  from the feed table  52 , and are returned to their closest together position only after the base  22  of the mounting body  3  has been immobilized by means of the stops  73  and  74 . 
     Once the base  22  has been immobilized and bored, as shown in FIG. 12, the actuators  82  are operated to move the bars  81  or like successions of bars progressively from the farthest apart position to the closest together position, which applies to each of the half-heads  46 , through the respective corresponding flat  36 , a thrust in the direction toward the plane  5 . That thrust causes progressive elastic flexing of each of the half-heads  46 , at the level of the corresponding intermediate part  48 , until the edges  41  bear against each other in the plane  5 , i.e. until the body  3  has the maximum elastically flexed configuration shown in FIG.  6 . 
     The movement toward each other of the bars  81  or like successions of bars is then stopped, but the pressure is maintained in the actuators  82  so that they continue to apply the thrust to the flats  36  in order to retain the body  3  in its maximum elastically flexed configuration, as shown in FIG.  14 . 
     Then, as also shown in FIG. 14, an appropriately controlled lifting device, not shown, picks up a wear plate  2  from the storage table  55 , for example by means of an electromagnet  83  applied to the face  9  of the central strip  6  if the wear plate  2  is made of stainless steel, and places the wear plate  2  it has picked up on top of the mounting body  3 , in an orientation in which the rims  7  face downward and the respective median planes of the wear plate  2  and the mounting body  3  coincide, and at a level such that the edges  18  of the rims  7 , which are facing downward, are at a higher level than the end faces  40  of the half-heads  46  of the body  3 . Then, maintaining this orientation of the wear plate  2  relative to the mounting body  3 , if necessary with the aid of appropriate guide devices, not shown, the design of which will be obvious to the skilled person, the lifting device progressively lowers the wear plate  2  toward the mounting body  3  and, because the mounting body is in its maximum elastically flexed configuration, shown in FIG. 6, in which the edges  49  are spaced by a distance l 3  less than the distance l 1  between the edges  18  of the rims  7 , the rims pass beyond the edges  49  during this downward movement of the wear plate  2 , after which the wear plate rests with the face  10  of its central strip  6  on the faces  40 , or to be more precise on the edges  50  connecting the faces  40  to the facets  39 , given the orientation of the faces  40  at this time. FIG. 15 shows this final stop of lowering the wear plate  2  onto the mounting body  3 . Note that the facets  39 , which are inclined so that they converge toward the plane  5  in the direction away from the face  24  in the direction  16 , which convergence is accentuated in this configuration of maximum elastic flexing compared to the rest state of the body  3 , facilitates interengagement of the rims  7  with respective opposite sides of the head  50  and then movement beyond the edges  49  during the downward movement just described. 
     The bars  81  preferably have a height or thickness (no reference number) at most equal to the dimension e 5  of the flats  36 , so that they can be pressed against them without projecting above them, i.e. with no risk of impeding the downward movement through untimely contact with the rims  7 . 
     Then, as shown in FIG. 16, after the electromagnet  83  has been deactivated, the lifting device raises the electromagnet but the wear plate  2  remains on the mounting body  3  which continues to be held by the actuators  82  and the bars  81  in its maximum elastically flexed configuration. 
     FIGS. 17 and 18 show two longitudinal positions of the wear plate  2  relative to the mounting body  3  at the end of this step of depositing the wear plate  2  on the mounting body  3 . In FIG. 17 it has been deposited so that the wear plate  2  is longitudinally centered relative to the mounting body  3 , i.e. each end face  19  of the wear plate  2  is set back longitudinally by the same distance, equal to half the difference between the dimensions L 1  and L 2 , relative to a respective end face  21  of the mounting body  3 . FIG. 18 shows a position in which one of the faces  19  is coplanar with one of the faces  21  and the other face  19  is set back relative to the other face  21  by a longitudinal distance corresponding to the entire difference between the dimensions L 1  and L 2 . In both cases, the dimension L 2 , which is greater than the dimension L 1 , is the length of the finished rail  1 . 
     During a subsequent step, shown in FIG. 19, the wear plate  2  is pressed against the edges  50  connecting the faces  40  and the facets  39  while the body  3  is held in its maximum elastically flexed configuration. To this end a carriage, not shown, of the station  54  moves longitudinally in a first direction  84  over the combination of the mounting body  3  and the wear plate  2 . The carriage carries a roller  86  which can rotate freely about a horizontal transverse axis  85  and whose bottom generatrix is pressed against the face  9  of the central strip  6  of the wear plate  2 , for example by spring means, not shown, or by virtue of its own weight. The roller  86  then travels in the direction  84  along the face  9  of the central strip  6  of the wear plate  2 , from one of the bevels  20  to the other one. 
     Then, as shown in FIG. 20, the roller  86  is moved back in the direction  87  opposite the direction  84  from one of the bevels  20  to the other one and, as it performs this movement, the pairs of actuators  82  it successively passes are activated to return the bars  81  progressively to their farthest apart position, subject to flexing of the bars  81  or successions of bars in a horizontal plane, allowing the mounting body  3  to return progressively to its rest configuration. 
     However, during this return movement, the recessed flats  38  abut against the attachment faces  15  of the rim  7 , in the direction away from the plane  5 , until they are pressed flat against the attachment faces  15 ; because of the angle α 1 , the face  10  of the central strip  6  of the wear plate  2  is pressed flat against the end faces  40 , which are coplanar at this time, to form the electrically conducting face  13  of the body  3  facing toward the electrically conducting face  10  of the wear plate  2 . In other words, the wear plate  2  stops the mounting body  3  in the particular intermediate configuration shown in FIG. 7 during the return movement of the mounting body  3  toward its rest configuration, so that the mounting body  3  is held prestressed in elastic flexing between the rims  7  of the wear plate  2 . 
     By way of non-limiting example, for an angle α 1  of the order of 70°, good results have been obtained in tests with an aluminum mounting body  1  and a stainless steel wear plate  2  with the dimensions of the mounting body  1  chosen so that it applies to each rim  7 , via the corresponding recessed flat  38 , a force of 150 Newtons producing a pressure of 2.5 MPa. 
     This completes a rail  1 , as shown in FIG. 21, and after its mounting body  3  has been released by appropriate movement of the mobile stops  74 , the rail is taken up by the group  64  of drive rollers, which feed it to the packaging station  56  at which the successively finished rails  1  are preferably packaged head-to-tail as shown in FIG.  22 . To this end, alternate rails  1  reaching the station  56  are turned over so that the rails  1  are stored on a plane horizontal table  88  of the station  56  in an orientation in which the face  24  of the base  22  rests on the table  88  and an orientation in which the face  9  of the central strip  6  of the wear plate  2  rests on the table  88 , so that the successively fabricated rails  1  are juxtaposed on the table  88 , parallel to each other, before they are packaged and then taken to a storage area or to the place of use. 
     Note that the wear plate  2  leaves completely uncovered an area of each end part  47  delimited by the flat  37 , the flat  36 , the face  35 , the edge  34  and the flank  33  of the groove  32 , which area takes the form of an extension  89  of the end part  47  along the intermediate part  48 , toward the base  22  in the direction  16 . The respective extension  89  does not come into contact either with the base  22  or with the intermediate part  48 , enabling an insulative cover similar to those fitted to prior art electrical power supply rails to be attached to the base  22 . This is not shown but will be evident to the skilled person. 
     Note also that despite the firm elastic attachment between the wear plate  2  and the mounting body  3 , it remains possible afterwards to remove a worn or damaged wear plate  2  by again applying to the flats  36  of the mounting body  3  a thrust moving the two half-heads  46  into the position of maximum elastic flexing shown in FIG. 6, before fitting a new wear plate  2 , which is fixed to the mounting body  3  by releasing the aforementioned thrust, although replacing a damaged or worn wear plate is generally impossible with the prior art electrical power supply rails, which must be replaced entirely if their wear plate is worn or damaged. 
     In this regard, it is particularly advantageous for each flat  36  to project relative to the respective adjoining areas of the rail  1  as a whole in the direction away from the plane  5  after fabricating the rail, i.e. after assembling and fastening together the wear plate  2  and the mounting body  3 , as this enables accurate positioning of the means employed to apply the thrust, namely the bars  81  in the case of the installation  51  described with reference to FIGS. 8 to  22 . 
     A worn or damaged wear plate can be replaced after demounting the rail  1  from its support on site and returning it to the shop, and to be more precise to the station  54  of the installation  51  where, after immobilizing the body  3  of the rail  1  in the manner described with reference to FIGS. 12 and 13, the thrust is applied to the two halves  46  of the head  23  to move them to the maximum elastically flexed configuration, as described with reference to FIG. 14, which releases the wear plate  2  from the mounting body  3 . The worn or damaged wear plate  2  is then taken off and removed, for example by means of the electromagnet  83 , after which, with the two halves  46  of the head  23  held in their maximum elastically flexed flexing position, a new wear plate  2  is nested over the head  23  of the body  3 , in the manner described with reference to FIGS. 14 to  19 . The thrust applied to the halves  46  of the head  23  is then progressively released to allow the head to return elastically to the rest configuration, during which movement it is stopped in its intermediate configuration prestressed in elastic flexing between the rims  7  of the wear plate  2 , the return movement being performed under the conditions described with reference to FIG.  20  and reconstituting the rail  1  as shown in FIGS. 7 and 21 in particular. The renovated rail  1  is then released and brought back to its site of use to be replaced on its support via the mounting body  3 , or taken to a storage area, awaiting allocation, if certain imperatives led to it being replaced with a new or renovated rail immediately after it was removed. 
     The need to remove from the rail from its support, to return it to the shop to renovate it, and then to return it to the site of use to replace it on the support constitutes a constraint that can be dispensed with by working on the site of use of the rail, with the body  3  of the rail fixed to its support. 
     To this end, a rigid beam can be mounted on a rail vehicle, on positioning means that will be evident to the skilled person, the beam essentially corresponding to the station  54  of the fixed installation  51  described with reference to FIG. 8 in particular and having means for immobilizing it in a precise position relative to the rigid base  22  of the mounting body  3 , namely the equivalent of the table  72 , the fixed stop  73  and  76  and the actuators  75  carrying the mobile stops  74 , or any other suitable device, and bearing on the support of the rail, for example, as well as the actuators  82  carrying the thrust bars  81  facing the flats  36  when the beam is immobilized in said precise position relative to the base  22  of the mounting body  3  by the aforementioned means. The renovation method in accordance with the invention is then carried out simultaneously throughout the longitudinal dimension L 2  of the rail  1 , namely throughout the respective lengths L 1  and L 2  of the wear plate and the mounting body  3 , in the same way as the installation  51  described with reference to FIG. 8 applies the method of fabricating the rail  1  simultaneously throughout the longitudinal dimensions L 1  and L 2 . 
     However, because of the overall size of the equipment employed, it is more convenient to carry out the renovation method in accordance with the invention on the site of use of the rail  1 , whose mounting body  3  remains fixed to its support in its particular position of use, by carrying it out successively in longitudinally localized areas of the rail  1  in longitudinal succession in a given longitudinal direction, it being understood that this approach can also be adopted for fabricating the rail  1  in the first place, using the fabrication method previously described successively in longitudinally localized areas of the mounting body and the wear plate in longitudinal succession in a particular longitudinal direction. 
     This progressive working along the rail  1 , or along its mounting body  3  and the wear plate  2 , can easily be carried out using a carriage adapted to travel along the rail  1 , or along its mounting body  3  and the wear plate  2 , and to carry out locally some of the operations carried out simultaneously throughout the length of the rail  1 , the mounting body  3  and the wear plate  2  at the station  54  of the installation  51 . 
     FIGS. 23 and 24 show one embodiment of a carriage for renovating a rail  1  on its site of use, with the mounting body  3  of the rail  1  immobilized relative to the ground by supporting brackets distributed along its longitudinal dimension, FIG. 23 showing one bracket  89  in its installation position on site. 
     The bracket  89  has a shape that is well known in itself in the art and is not described in detail. Suffice to say that it is generally angle-iron-shaped, is disposed in a median transverse plane relative to the rail  1  and has a vertical flange  90  which is disposed laterally relative to the rail  1  and is used to fix the bracket  89  to a post, not shown, fixed to the ground, also not shown, and a horizontal flange  91  which straddles the base  22  of the mounting body  3  and is disposed so that the plane  5  is approximately vertical and the head  23  and the wear plate  2  face downward; the base  22  is immobilized relative to the support  89  by virtue of being gripped between a jaw  92  permanently attached to the flanges  90  and  91  and a jaw  93  removably fastened to the jaw  92 , the two jaws  92  and  93  co-operating with the base  22  of the mounting body  3  in a manner comparable to that of the fixed and mobile stops  73 ,  74  described with reference to FIG.  12 . Note that the extension  89  of the rigid end parts  47  of the two halves  46  of the head  23  of the body  3  toward its base  22  is conformed and dimensioned, in particular with regard to its beveled face  35 , so as not to come into contact with the jaws  92  and  93 , which further leave uncovered at least the area of each beveled face  35  nearest the corresponding flat  46 , as well as the flats  46  and all the areas of the rail  1  which are under them, given the position of the rail  1  when it is mounted at its site of use on brackets such as the bracket  89 . 
     Given this position of use of the rail  1 , the carriage  94  is disposed under the rail, from the mounting body  3  of which it is suspended by means also enabling it to move longitudinally, preferably by rolling, in a particular position of use which is shown in FIGS. 23 and 24 and is used as a reference in the remainder of the description of the carriage  94 . The description also presupposes that the rail  1  is complete, in other words that the wear plate  2  is fixed to the mounting body  3 , which corresponds to the condition of the rail  1  before renovation by changing its wear plate  2 , for example. 
     The carriage  94  has a rigid chassis  95  the whole of which is at a lower level than the wear plate  2  of the rail  1  and takes the general form of a rectangular parallelepiped which is symmetrical with respect to a longitudinal plane coincident with the median longitudinal plane  5  of symmetry of the rail  1  and which is therefore also denoted by the reference numeral  5 . The chassis  95  also has a transverse plane of symmetry  196 , the expressions “longitudinal” and “transverse” relating to the longitudinal direction  4  of the rail  1 . 
     To be more precise, in the embodiment shown, the chassis  95  is formed of an assembly of five flat rectangular metal plates, namely: 
     a longitudinal lateral wall  96 , parallel to the plane  5  and directly under the flange  90 , which is itself parallel to the plane  5 , the wall  96  being dimensioned so as not to come into contact either with the flange  90  or with the post, not shown, carrying the bracket  89 , and having a top longitudinal edge, a bottom longitudinal edge and two transverse edges (no reference number), 
     a longitudinal bottom  97 , perpendicular to the plane  5 , which it straddles at a particular distance below the wear plate  2 , the bottom  97  having a longitudinal edge bolted to the lateral wall  96  in the immediate vicinity of its bottom longitudinal edge, a longitudinal edge symmetrical to the first one with respect to the plane  5 , and two transverse edges, none of these edges being designated by a reference number, 
     a longitudinal lateral wall  103  identical to the lateral wall  96 , with which it is symmetrical with respect to the plane  5 , the wall  103  being bolted to the longitudinal edge of the bottom  97  opposite its edge bolted to the lateral wall  96  and having a top longitudinal edge and a bottom longitudinal edge (no reference number) at the same level as the top longitudinal edge and the bottom longitudinal edge, respectively, of the lateral wall  96  and two transverse edges (no reference number) in the same transverse plane, not shown, as the transverse edges of the lateral wall  96 , and 
     two transverse front walls  98 ,  99 , each of which has four transverse edges (no reference number), namely two lateral edges freely joined to the respective lateral walls  96  and  103  along a respective transverse edge thereof, a top edge at a lower level than the top longitudinal edge of the lateral walls  96  and  103  and that of the wear plate  2  of the rail  1  when the carriage  94  is in use, but above that of the bottom  97 , and a bottom edge in whose immediate vicinity the front wall  98 ,  99  is welded to the bottom  97  and which, with regard to the front wall  98 , is at the same level as the bottom longitudinal edge of the lateral walls  96  and  103  and, where the front wall  99  is concerned, forms a downward projection relative to the bottom longitudinal edge of the lateral walls  96  and  103  so that the front wall  99  forms a transverse lug  100  under the bottom  97  for attaching a traction member  101 , for example by means of a hole  102  formed in the lug  100  in the plane  5 . 
     The lateral wall  96 , the bottom  97  and the lateral wall  103  are respectively symmetrical with respect to the plane  196 , with respect to which the front walls  98  and  99  occupy mutually symmetrical positions. 
     Toward the top, in positions that are mutually symmetrical with respect to the plane  196 , the bottom  97  has two slideways  104  fastened to it, each of which is between a respective one of the front walls  98 ,  99  and the plane  196 . The slideways  104  have at the top respective dovetail grooves  105  oriented in the same transverse direction  106  perpendicular to the plane  5  and each of the grooves  105  receives a respective dovetail tenon  107  of two sliders  108  which slide in the direction  106  and are disposed on respective opposite sides of the plane  5 , toward or away from which the two sliders  108  can move in the direction  106 , although they are not able to move in any other direction relative to the chassis  95  of the carriage  94 . 
     Other embodiments of the chassis  95  of the carriage  94  could be chosen without departing from the scope of the invention, of course, and other means of guiding the sliders  108  when they slide in the direction  106 , perpendicular to the plane  5 , relative to the chassis  95  of the carriage  94  could be chosen without departing from the scope of the invention. 
     At an intermediate level between that of the bottom  97  of the chassis  95  and that of the top longitudinal edges of the lateral walls  96  and  103 , the two sliders  108  corresponding to the same slideway  104  have respective threaded holes  110  along an axis  109  perpendicular to the plane  5 , i.e. oriented in the direction  106 , the two threads having the same pitch but opposite hands. Respective threads  111  of a common screw  112  along the axis  109  are engaged in the two threaded holes  110  of the sliders  108  corresponding to the same slideway  104 , the two threads of the same screw  112  having the same pitch but opposite hands. 
     Each of the screws  112  is journaled in a respective bearing  135  coaxial with the lateral walls  96  and  103  in two end areas so as to be able to rotate freely about its axis  109  relative to the chassis  95 , although it is prevented from moving relative to the chassis in any other direction, and in particular parallel to its axis  109 , in the direction  106 , through abutting engagement of a respective coaxial flange  136  of the screw  112  between and against the two lateral walls  96  and  103 , so that the position of the sliders  108  corresponding to the same slideway  104  can be adjusted, in the direction toward or away from the plane  5  in the direction  106 , by rotating the screw  112  one way or the other, but remain at all times mutually symmetrical with respect to the plane  5 . In this regard, the screws  112  corresponding to the pairs of sliders  108  respectively associated with the slideways  104  are independent of each other, so that the sliders  108  corresponding to one of the slideways  104  can occupy a position relative to the plane  5  in which they are spaced differently to the sliders  108  corresponding to the other slideway  104 . 
     The pitches of the threads  111  and the threaded holes  110  are preferably irreversible under normal conditions of use, to be described later, so that the position of the sliders  108  relative to the plane  5  is stable and can be modified only by intentional rotation of the respective screw  112 , applied manually, for example, by means of a wrench  113  interengaged with a square end  114  of the screw  112  projecting from the lateral wall  103  along the respective axis  109  in the direction away from the plane  5 . Note that the screws  112  do not project relative to the lateral wall  96  in the direction away from the plane  5 , however. 
     A shaft  116  fastened to each of the sliders  108  near the top, along a respective transverse axis  115  parallel to the planes  5  and  196  and perpendicular to the corresponding axis  109 , forms an upward projection along the axis  115  relative to the top longitudinal edges of the lateral walls  96  and  103 , and the dimensions of the shafts  116  along the respective axis  115  and perpendicular to that axis are such that, by appropriately positioning the sliders  108  of each pair in the direction  106  relative to the corresponding slideway  104 , they are moved on respective opposite sides of the rail  1 , i.e. of the wear plate  2  and the body  3 , without coming into contact with either the wear plate or the body, in the position of use of the carriage  94  shown in FIGS. 23 and 24, and so that they then have a top end at a higher level than the flats  36  but lower than that of the jaws  92  and  93 , so that no part of the carriage  94  can come into contact with the supporting bracket  89  when the carriage  94  is in use. 
     At the same level as the axes  95 , the four shafts  116  carry respective circular rollers  117  which can rotate freely about the respective axis  115 , with which they are concentric, but are prevented from moving in any other way. More particularly, in the direction away from the respective axis  115 , each roller has a continuous annular groove  118  concentric with the axis  115  and delimited by a circular cylindrical bottom  119  concentric with the axis  115  and by two flanks  120 ,  121  which diverge from the bottom  119  in the direction away from the axis  115 , respectively upward and downward, with a circular frustoconical shape concentric with that axis, to a point at which they merge with a plane edge face (no reference number) of the roller  117  perpendicular to that axis. The bottom  119  of the groove  118  has a dimension parallel to the respective axis  115  substantially equal to the dimension e 5  of the flats  36  of the body  3  so that they can be pressed together and the flank  120  is oblique to the respective axis  115  at the same angle as that at which each beveled face  35  of the body  3  is oblique to the plane  5 , for example, in the rest configuration, i.e. an angle of the order of 45° in this example, the slope of the beveled faces  35  varying only negligibly from one of the aforementioned configurations of the body  3  to the other. The slope of the flank  121  relative to the respective axis  115  can also be of the order of 45°. 
     Accordingly, by turning the screws  109  in the direction which moves the corresponding sliders  108  toward the plane  5 , the rollers  117  can be moved into the position of use shown in FIG. 3, in which the bottoms  119  of the respective grooves  118  in the rollers of the same pair of sliders  108 , which are on respective opposite sides of the plane  5  and symmetrical with each other with respect to that plane, are pressed onto a respective flat  36  of the body  3 , with the flanks  120  bearing on the area of the respective beveled faces  35  directly adjacent each flat  36 , at a level lower than that of the jaws  92 ,  93  to prevent any contact of the rollers  117  with them, so as to prevent dropping the rollers  117 , and consequently the whole the carriage  94 , and so that the flanks  121  bear on the body  3  at the junction between each flat  36  and the respective corresponding flat  37 , so as to retain the rollers  117 , and consequently the carriage  94 , against any movement relative to the mounting body  3  and the rail  1  as a whole other than longitudinal movement by virtue of the rollers  117  rolling along the body  3 . 
     The dimensions of the slideways  104 , the sliders  108  and the rollers  118  are such that the sliders  108  can also be moved sufficiently far apart from the above position for the flanks  120  of the rollers  117  of the sliders  108  corresponding to the same slideway  104  to be moved apart perpendicularly to the plane  5  by a distance greater than the distance l 14  between the two flats  36 , perpendicularly to the plane  5 , in the rest configuration, so that the carriage  94  can be disengaged from the body  3  or interengaged with it even with the body  3  in the rest configuration, for reasons that become apparent later. Their dimensions are also such that the two sliders  108  corresponding to the same slideway  104  can be moved sufficiently far toward the plane  5  for the distance between the bottoms  119  of the corresponding grooves  118  to be at most equal to the distance l 10  between the flats  36  perpendicularly to the plane  5  in the configuration of maximum elastic flexing, in order to enable this configuration to be imparted to the body  3  by applying thrust in the direction toward the plane  5  by means of the rollers  118 , by appropriately positioning the sliders  108  of each pair along the respective slideway  104  relative to the plane  5 . 
     Note that the co-operation of the rollers  117  with the mounting body  3 , regardless of the configuration of the latter in terms of the positioning of the rollers  117 , i.e. the corresponding sliders  108 , in the direction  106 , fixes the level of the chassis  95  relative to the mounting body  3  in the direction  16  in the plane  5  and insures that the median longitudinal planes of symmetry of the carriage  94  and the mounting body  3 , both of which are designated by the reference numeral  5 , coincide at all times. 
     What is more, the bottom  97  has a threaded hole  123  through it along a transverse axis  122  defined by the intersection of the planes  5  and  196 , i.e. perpendicularly to and centered relative to the bottom  97 , which hole engages with a thread  124  of a coaxial screw  125  which has below the bottom  97  a square end  126  for turning it using a wrench similar to the wrench  113 . The screw  125  has a top end above the bottom  97  but at a level lower than the top longitudinal edges of the lateral walls  96  and  103  and which able to rotate freely about the axis  122  but is constrained to move in translation along the axis  122  with a yoke  127  having two parallel cheeks  128  in mutually symmetrical positions with respect to the axis  122 . Each cheek  128  has a rigid finger  130  attached to it, projecting away from and along a common axis  129  perpendicular to the axis  122 , the finger having a respective terminal lug  131  engaged in a respective rectilinear slot  132  in the plane  196  formed in each of the lateral walls  96  and  103  and with its length in the direction  16 , so that engaging the lugs  131  in the slots  132  holds the two cheeks  128  in a mutually symmetrical position with respect to the plane  5 . Thus rotation of the yoke  127 , and consequently of the axis  129  with it, about the axis  122  relative to the chassis  95 , in particular when the screw  125  rotates relative to the chassis  95  about the axis  122 , is prevented and such rotation, depending on its direction, results in movement of the yoke  127 , and consequently of the axis  129  with it, relative to the rail  1  away from or toward the bottom  97  of the chassis  95  in the direction  16 , and vice-versa. The pitches of the thread  124  of the screw  125  and the threaded hole  123  are preferably irreversible so that, under the normal conditions of use described later, the yoke  127  remains in the position relative to the chassis  95  of the carriage  94  and relative to the rail  1  intentionally imparted to it by rotating the screw  125  relative to the bottom  97  of the chassis  95  about the axis  122 . 
     A roller  133  between the two cheeks  128  of the yoke  127  is journaled to both of them for rotation about the axis  129  and can rotate freely relative to the yoke  127  about the axis  129 , but with no other possibility of relative movement. The roller  133  is therefore centrally located relative to the axes  115  of the rollers  117  and has in the direction away from the axis  129  a circular cylindrical outside peripheral face  134  which is concentric with the axis  129  and has a dimension in the direction perpendicular to the plane  5 , and equally divided between the respective opposite sides thereof, which corresponds substantially to the width l 6  of the strip  6  of the wear plate  2 . 
     Accordingly, when the carriage  94  is attached to the mounting body  3  of the rail  1 , as shown in FIGS. 23 and 24, adjusting the level of the yoke  127  relative to the bottom  97  of the chassis  95  moves the roller  133  into a position in which a top generatrix perpendicular to the plane  5  of its outside peripheral face  134  bears against the strip  6  of the wear plate  2 , which itself bears against the electrically conductive face  13  of the mounting body  3 , without opposing longitudinal rolling of the carriage  94  along the rail  1 . 
     However, by appropriately dimensioning the roller, the yoke  127  and the screw  125 , and by adjusting the position of the roller  133  relative to the bottom  97  of the chassis  95  in the direction  16 , the roller  133  can also be moved sufficiently close to the bottom  97  for the top generatrix of the outside peripheral face  134  of the roller  133  to be moved away from the face  9  of the strip  6  of the wear plate  2  in the direction  16  a distance at least equal to the depth p 2  of the wear plate  2 . This is not shown but will be evident to the skilled person. 
     Of course, the mounting of the roller  133  just described is merely one non-limiting example, and other means could be chosen, in particular for guiding the yoke  127  which carries it, in the manner of a slider, relative to any form of slideway oriented in the direction  16  and attached to the chassis  95 , the slideway consisting of the slots  132  in this example. 
     The carriage  94  can therefore be used in the following manner to renovate a rail  1  by changing its wear plate  2  without demounting the rail, and to be more precise its mounting body  3 , from the support  89  first. 
     Initially, the rail  1  is in the state described with reference to FIGS. 7 and 21, i.e. the wear plate  2  holds the mounting body  3  in its particular intermediate elastically flexed configuration. This state of the rail  1  and this configuration of the mounting body  3  are shown in full line in FIG.  23 . 
     A first operation consists of installing the carriage  94  on the rail  1  so that the shafts  116  are on respective opposite sides of the wear plate  2  to be changed, immediately downstream of the junction  135  of the wear plate with another wear plate  2  which is to remain in place on the mounting body  3 , referred to a longitudinal direction  136  relative to which the front wall  99  carrying the attachment lug  100  for a traction member  101  of the carriage  94  and the front wall  98  are respectively at the front and at the rear. 
     To this end, the sliders  108  corresponding to the two slideways  104  are initially as far apart as possible and the roller  134  is lowered as far as possible toward the bottom  97  of the chassis  95 . This is not shown but will be evident to the skilled person. 
     Accordingly, after bringing the median longitudinal plane of symmetry of the chassis  95  into coincidence with that of the rail  1 , these two planes being denoted by the same reference numeral  5 , by placing the whole of the carriage  94  at a level lower than that of the rail  1 , and by means of an upward movement of the carriage  94 , the rollers  118  can be raised in the direction  16  on respective opposite sides of the wear plate  2  and then of the body  3 , until they reach the level described with reference to FIG. 23, in which the bottom  119  of the grooves  118  is directly facing one or other of the flats  36  in the direction  106 . Given its initial position, the roller  134  is then separated from the wear plate  2  by a downward distance in the direction  16  at least equal to the aforementioned depth p 2 , and preferably greater than that depth p 2 . 
     Then, by turning the two screws  112  the appropriate way about the respective axis  109  relative to the chassis  95 , the bottoms  119  of the respective grooves  118  of the two rollers  117  of each pair are brought into contact with the respective corresponding flats  36  and the flanks  120  of the respective grooves  118  are brought into contact with the corresponding respective beveled faces  35 , so that the chassis  95  is suspended from the mounting body  3 , which at this time is in its particular intermediate elastically flexed configuration, in which it retains the wear plate  2 . However, the two screws  112  are turned further in the direction that causes the two sliders  108  and the respective corresponding rollers  117  to move toward each other until the body  3  reaches its maximum elastically flexed configuration, shown in dashed line in FIG. 23, which progressively releases the rims  7  of the wear plate  2  from the rebates  38  of the mounting body  3 . When the body reaches its maximum elastically flexed configuration, the turning of the screws  112  is stopped. The wear plate  2  is then totally released at the location of the carriage  94  and all that is required is to apply slight traction to it in the downward direction to overcome the sticking effect of the contact grease and a tendency of the wear plate  2 , which is still retained elsewhere by the mounting body  3 , to remain in a generally rectilinear configuration; because of the position of the roller  134  at this time, the wear plate  2  can be locally lowered a sufficient distance, by flexing it, to disengage it entirely from the mounting body  3 , at least directly to the rear of the carriage  94  in the direction  136 . 
     Then, by pulling on the carriage  94  in the direction  136  by means of the member  101 , it is moved progressively over the whole of the longitudinal dimension L 1  of the wear plate to move longitudinally localized areas of the mounting body  3  successively into the maximum elastically flexed configuration, which enables the corresponding longitudinally localized areas to be disengaged successively from the wear plate  2 . The mounting body  3  naturally tends to revert progressively to its rest configuration to the rear of the carriage  94  referred to the direction  136 , but reattachment of the wear plate  2  because of this tendency is prevented by continuing to apply sufficient traction to the wear plate in the downward direction, and to the rear of the carriage  94  referred to the direction  136 , for example manually, for it to remain at a level lower than that of the mounting body  3 . 
     The carriage  94  is caused to travel the whole of the dimension L 1 , which corresponds more or less to the longitudinal dimension L 2  of a rail  1  fabricated by the method described with reference to FIGS. 1 to  22 , i.e. when the faces  19  of the joints  135  between the wear plates  2  coincide with the joints  137  between the front faces  21  of the mounting bodies, progressively releasing the wear plate  2 ; in this connection, FIG. 4 shows rails  1  corresponding to the disposition of the wear plate  2  relative to the mounting body  3  shown in FIG. 17, it being understood that such coincidence would be obtained by adopting the relative position shown in FIG.  18 . 
     At the end of this travel, the wear plate  2  is totally freed from the mounting body  3  of the rail  1  and the carriage  94  can be moved in the direction opposite the direction  136  to its initial position relative to the mounting body  3 , for example by rolling on the latter, which returns the anchoring body  3  to its maximum elastically flexed configuration in the immediate vicinity of the aforementioned joint  135 . 
     If necessary, the faces  40  and the rebates  38  of the mounting body  3  can then be brushed and regreased. 
     A longitudinal end area of a new wear plate  2  can then be inserted between the rollers  134  and the head  23  of the mounting body  3 , in the direction opposite the direction  136 , with its median longitudinal plane of symmetry made to coincide with that of the mounting body  3 , after which the screw  125  is turned to raise the roller  133  until it returns to the position shown in FIGS. 23 and 24, in which the end area of the new wear plate can be nested over the head  23 , which is retained locally by the rollers  117  in the maximum elastically flexed configuration, until the wear plate  2  occupies, locally relative to the mounting body  3 , the position described with reference to FIGS. 15 to  16 , i.e. with the face  10  of the central strip  6  pressed locally against the edges  50  at which each facet  39  is connected to the face  40  of the same half-head  46 . This is accompanied by flexing of the wear plate  2  immediately in front of the carriage  94 , referred to the direction  136 , but the wear plate  2  is sufficiently flexible for this flexing not to cause plastic deformation. 
     After positioning the front face  19  of the new wear plate correctly in the longitudinal direction relative to the immediately following wear plate  2  on the upstream side, referred to the direction  136 , in order to make the joint  135 , the traction member  101  is again used to move the carriage  94  in translation in the direction  136  relative to the mounting body  3 , with the rollers  117  remaining in the position in which they apply thrust to the flats  36  for moving the body  3  to its maximum elastically flexed configuration and with the roller  133  remaining in the position in which the top generatrix of its outside peripheral face  134  is at a distance at least approximately equal to the thickness e 1  of the central strip  6  of the wear plate  2  from the edges  50  of the half-heads  46 , under the mounting body  3 , which causes the face  10  of the strip  6  to be pressed against the edges  50 . 
     As the carriage  94  moves along the mounting body  3  the rollers  117  move longitudinally localized areas of the mounting body  3  in succession in the direction  136  successively into the maximum elastically flexed configuration and the roller  134  presses localized areas of the new wear plate  2 , also in succession in the direction  136 , successively against the edges  50  of the half-head  46  of the mounting body  3 , subject to elastic flexing of the wear plate  2  immediately in front of the carriage  94 , referred to the direction  136 ; to the rear of the carriage  94 , referred to the direction  136 , the areas of the mounting body  3  that the carriage  94  successively moves away from tend to revert to the rest configuration but are retained in the predetermined intermediate configuration of maximum flexing by application of the rebates  38  to the faces  15  of the rims  7  of the wear plate  2 , which presses the face  10  of the central area  6  of the latter flat against the faces  40  of the two half-heads  46 , which faces  40  are then coplanar to constitute the face  13 , as described with reference to FIGS. 20 and 21. 
     When the carriage  94  has reached the immediate vicinity of the other front face  19  of the new wear plate  2 , which is not shown but will be obvious to the skilled person, the screws  112  are turned to move the rollers  117  of each pair away from each other and away from the plane  5 , with the roller  133  remaining in the position which returns the mounting body  3  in this end area to its particular intermediate elastically flexed configuration, in which it retains the wear plate  2  by abutment of the two half-heads  46  against the rims  7  thereof, with the face  10  of the central area  6  of the wear plate  2  pressed flat against the face  13  of the mounting body. 
     When the rollers  117  of each pair are sufficiently far apart the carriage  94  can be separated from the mounting body  3 , i.e. from the rail  1  reconstituted in this way. 
     In a variant, to change a plurality of successive wear plates, the rollers  117  can remain in the position which applies to the flats  36  of the mounting body  3  a thrust which imparts to it its maximum elastically flexed configuration when the carriage  94  reaches the immediate vicinity of the other front face  19  of the wear plate  2 , and the roller  133  lowered by turning the screw  125 , before further movement of the carriage  94  in the direction  136  along the immediately consecutive rail  1  in the direction  136  to separate the wear plate  2  from it in the manner previously described, prior to fitting a new wear plate  2 . 
     Note that the carriage  94  just described, or any other equivalent device, can be used not only to renovate a rail  1  by replacing its wear plate  2 , but also to fabricate a rail  1  directly on its site of use, after the various mounting bodies  3  have been fixed to their supporting brackets  89  in their final position, i.e. in a longitudinal row, and without fitting the wear plates  2  to the mounting bodies  3  beforehand. 
     The longitudinal sequence of wear plates  2  can easily be fitted to the longitudinal sequence of mounting bodies  3  using the carriage  94  as described hereinabove in connection with fitting a new wear plate  2  to a mounting body  3  after brushing and greasing its faces  40  and rebates  38 , especially if it is made of aluminum or aluminum alloy. 
     In contrast to fabricating each rail  1  completely in the shop, it is possible to offset the joints  135  between two successive wear plates  2  longitudinally relative to the joints  137  between two successive mounting bodies  3 , for example as shown in FIG. 24, which shows in dashed line a second position of the joint  137 , so that each wear plate  2  contributes to the mechanical continuity between two successive mounting bodies  3  and any lack of alignment between the latter has no effect on the alignment of the wear plates  2 , in particular in terms of the coplanar relationship of the faces  9  adapted to be in contact with the shoe  11 , which reduces the wear of the latter by abrasion on passing from one wear plate  2  to the next. 
     Finally, the skilled person will find it obvious that the carriage  94 , or an equivalent device, working on only a longitudinally localized area of the mounting body  3  and each wear plate  2  or each rail  1 , can be used not only on site but also in the shop, in place of the bars  81  and their actuators  82 , whose role is provided locally by the rollers  117  and the screws  112 , respectively, and in place of the roller  86 , whose role is provided locally by the roller  133 . 
     The skilled person will also find it obvious that although preferred embodiments of the various aspects of the invention has been described, those embodiments can be modified in many ways without departing from the scope of the invention.