Abstract:
The extruded rubber boot is wrapped around the rail before the rail is placed in the ground. The boot provides electrical and mechanical isolation of the metal rail from the concrete of the pavement. The boot profile is configured with a double-wall column, which, when hammered in, becomes tightly wedged between the head and the base of the rail. Nothing else (such as adhesive tape wrapped around the boot) is needed in order to hold the boot to the rail during assembly and installation of the rail and pavement.

Description:
[0001]     Typically, streetcar tracks are embedded down below the surface of the road material (concrete, asphalt, etc), over a long distance. As compared with a road/rail crossing, where the track is embedded in the road for a distance of no more than, say, ten metres, streetcar tracks can be embedded in the road for distances of hundreds of metres, and more.  
         [0002]     The requirement often arises, with streetcar tracks, for the metal rail to be insulated electrically from the road material in which it is embedded. Although the rail and the road are nominally both at the same (ground) voltage, it is all too common for stray voltages and currents to be present, which can lead to (electrolytic) corrosion and other problems over a long period of service. The problem is exacerbated in cold-winter areas, where salt is likely to be present.  
         [0003]     In addition to providing electrical insulation, a boot of an elastomeric material can also provide some mechanical isolation from vibrations and shock loading. This can be beneficial both to streetcar traffic, and to the tracks and roadway.  
         [0004]     It is known to provide an insulating rubber or plastic boot or shroud, which envelops the rail, in order to address this rail corrosion problem. To be effective, the insulating boot must be complete, in that it should fully envelop the rail, with no gaps—except, of course, that the top surface of the head of the rail must be clear, and one side-face of the head of the rail (i.e the gauge-side of the rail, which receives the wheel-flanges of the passing streetcars) must also be clear.  
         [0005]     The boot passes underneath the rail profile, i.e between the rail and the cross-tie. Where the rail is secured to the cross-ties by means of clips, e.g pandrol clips, the components are arranged to ensure that the boot is not interrupted or broken at the clip locations.  
         [0006]     Being all-enveloping, the boot is applied to the rail before the rail is lowered down onto the cross-ties; then the booted rail is placed on the ties; then the clips are applied; and then concrete or other road filler material is poured in, and made up to the level of the road.  
         [0007]     Boots are not only applied to rails in cases where the rails rest on conventional cross-ties. Various procedures exist where a concrete bed is poured, then the rails are lightly supported, and concrete is poured around the rails, up to the road level; or the rails may be laid upon a pre-made concrete pad or deck, and only the final layer of concrete is poured after the rails are in place.  
         [0008]     Often, the rails are continuous-welded, for streetcar applications. In some cases, the rails are finished as to length, fitment, etc, and the rails are lifted to enable the boots to be assembled, before being finally lowered into position. Typically, the boots are extruded in e.g five-meter lengths. At the joints between adjacent boot-lengths, the joints may be sealed using a sealing cuff.  
         [0009]     A difficulty that can arise is that the boot is not secured firmly to the rail. Thus, during installation, the sides of the boot can flop down, and become displaced. One common approach is to use adhesive tape, which is applied to the upper portions of the sides of the boot, the tape passing over the top of the rail to hold those portions together until the concrete is poured in. The idea has been that, after installation, the concrete finally holds the boot against becoming displaced. However, concrete often shrinks as it sets, which can cause a gap to appear. The gap might be between the boot and the rail, or between the boot and the concrete. Either can be troublesome.  
         [0010]     The invention provides a boot that fits around the profile of the rail, except for the top and gauge-side of the rail head. The invention is aimed at providing a boot that is self-supporting, once fitted around the rail, with respect to the rail, whereby the boot holds itself in position on the rail with enough tenacity to ensure that the boot remains in its proper place during placement of the rail, and during pouring and setting of the concrete. Furthermore, it is an aim of the invention that the boot can maintain a seal against the rail, not only during assembly and concreting, but throughout the service life of the road/rail installation.  
       THE PRIOR ART  
       [0011]     U.S. Pat. No. 5,899,379 (Bruyn et al, May 1999) discloses an interface strip for a road/rail crossing, in which the (extruded rubber) strip is designed to hold itself in place against the side of the rail. The profile of the rubber strip is designed such that, when the strip is hammered into contact with the side of the rail, the profile wedges itself between the underface of the head and the overface of the base of the rail.  
       DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
    
    
       [0012]     By way of further explanation of the invention, exemplary embodiments of the invention will now be described with reference to the accompanying drawings, in which:  
         [0013]      FIG. 1  is cross-sectional profile of an extruded rubber boot that embodies the invention.  
         [0014]      FIG. 2  is a cross-sectional profile of a rail.  
         [0015]      FIG. 3  shows the boot of  FIG. 1  in an intermediate stage of assembly to the rail of  FIG. 2 .  
         [0016]      FIG. 4  shows the boot of  FIG. 1  finally assembled around the rail of  FIG. 2 .  
         [0017]      FIG. 5  shows a finished streetcar installation, with rails and boots, in cross-section at a cross-tie.  
         [0018]      FIG. 6  shows the streetcar installation of  FIG. 5 , in cross-section between cross-ties.  
         [0019]      FIG. 7  shows a modification to a portion of the boot of  FIG. 1 .  
         [0020]      FIG. 8  is a cross-sectional profile, corresponding to that of  FIG. 4 , of an alternative boot. 
     
    
       [0021]     The apparatuses shown in the accompanying drawings and described below are examples which embody the invention. It should be noted that the scope of the invention is defined by the accompanying claims, and not necessarily by specific features of exemplary embodiments.  
         [0022]      FIG. 1  shows the profile of the boot  20 , by itself, in its as-extruded condition.  FIG. 2  shows the profile of the rail  23  around which the boot  20  is to be fitted. The boot  20  comprises an extrusion in rubber. The rubber of the profile is of uniform thickness, except that there are thickened pads  24  along the under-rail-portion  25  of the profile of the boot.  
         [0023]     The boot  20  is flexible, to the extent that the portions  26 , 28  can be spread apart sufficiently for the boot to be fitted around the base of the rail. Being made of relatively thin rubber, the boot is flexible enough to do this.  
         [0024]     It will be understood that it would not be practical to build enough residual springiness into the boot such as would enable the sides of the boot to press tightly against the sides of the rail, to the extent that the sides of the boot would inherently hold themselves against the sides of the rail. It will be understood that, in a practical boot, the tendency, rather, is for the side portions  26 , 28  of the boot to flop sideways, away from the sides of the rail, after the boot has been fitted around the rail. The sides of the boot have no inherent tendency to press against the sides of the rail. It would not be practical to provide a boot of such profile that the sides of the boot would be self-supporting by building an inherent springiness into the boot.  
         [0025]     The distance  32  as measured over the gauge portion  26  of the boot, is made slightly larger than the corresponding distance  34  as measured on the rail  23 . Thus, the gauge portion  26  of the boot can be made to wedge itself between the underface  35  of the head  29  of the rail and the overface  36  of the base  30  of the rail. The same is true as regards the field portion  28  of the boot, with respect to the other side of the rail.  
         [0026]     The portions  26 , 28  of the boot are double-walled, as shown, with spacer-bars  37  at appropriate intervals. The walls are thin, being preferably between three millimetres and six millimetres in thickness. The sides of the boot need to be stiff, in the sense that an upright column is stiff, in order for the sides to become tightly jammed or wedged between the head and the base of the rail. On the other hand, the sides should not be so stiff, as columns, that it would be hard to drive them into the rail.  
         [0027]     It is recognised that this condition is met when the wall thickness of the extruded rubber is within the above limits. It is hardly practical that the walls could be less than three mm and still have the stiffness needed to hold tightly when wedged into the rail. On the other hand, thicknesses more than six mm might be favoured with the softer formulations of rubber. A wall-thickness limit might be set at ten mm. It is not so much that a thicker wall would be too stiff, but rather: the boot profile is one single unitary extrusion, and it is good extruding practise for the wall thickness of the profile to be reasonably uniform over the whole extruded section; therefore, given that the profile of the boot has to be flexible enough to be wrapped around the rail, thick chunky sections on the extruded profile are contra-indicated.  
         [0028]      FIG. 3  shows a stage during assembly, in which the boots  20  have been wrapped around the rails  23 . The sides of the boots are touching lightly against the sides of the head of the rail. Now, the sides of the boot are ready to be hammered or kicked into place, whereby the sides become wedged tightly between the head and the base of the rail in the position as shown in  FIG. 4 .  
         [0029]     It will be understood that the boot is assembled or wrapped around the rail prior to the rail being embedded in the ground. Once the boot is in place, the wrapped rail is placed on the chairs  31  on the cross-ties ( FIG. 5 ), and pandrol clips  38  are assembled in the usual way. It may be noted that plastic pads  39  are located between the clip  38  and the rubber boot material. The pads  39  provide mechanical protection for the boot, by preventing direct contact with the metal of the clip  38 . The portion  26 , 28  of the boot remain wedged against the sides of the rail during fitment of the clips  38 .  FIG. 6  is a section of the track structure, taken between cross-ties.  
         [0030]     In  FIGS. 5,6 , the roadway has been filled with concrete, or asphalt etc. The concrete contacts the cross-ties  40 , the clips  38 , the ballast  43 , and presses against the boots  20 . The concrete does not touch the metal rails  23 . As shown at  45  in  FIG. 6 , it is to be expected that the concrete will not penetrate into the space underneath the (wrapped) rails, between the cross-ties. A suitably-profiled moulding bar is used to form the cut-out  46  for the wheel flanges, on the gauge sides of the rails.  
         [0031]     The manner of embedding the rails in the roadway as shown in  FIGS. 5,6  is common for streetcars. However, many installations use means other than spaced cross-ties for mounting the rails. The applicability of the invention is not limited to the spaced cross-ties type of installation.  
         [0032]      FIGS. 5,6  show the finished installation, in which the installation is now ready for cars, trucks, bicycles, and other road vehicles to pass both along and across the tracks, and for streetcars to pass along the tracks.  
         [0033]     With the boot having the extruded form as shown in  FIG. 1 , it has been found, when the boot is pressed against the sides of the rail with the kind of force easily applied by a worker kicking or hammering the boot, that the boot will remain wedged firmly enough against the sides of the rail as to remain in place during assembly, installation, concreting, etc. It has been found that, often, a tool is required in order to remove the boot from the rail, once it has been pressed against the rail. As will be explained, the configuration of the boot is such that it is as if the boot were barbed; that is to say, the force needed to pull the boot out is greater than the force needed to press it in. This barb-like effect is not guaranteed in every case, but it is the aimed-for generality.  
         [0034]     It should be noted that the task of installing streetcar rails is carried out with the emphasis, not on careful attention to detail, but on speed and simplicity. Not only do the components have to be robust enough to stand up to the inevitable abuses, but the components should be of such design that an inspector can readily determine, at a glance, that the components are indeed properly placed, and can do this at a time when remediation, if required, can and will be carried out. It may be noted that, with a batch of concrete ready and waiting to be poured, the tendency is to proceed with pouring anyway, and cover up the mistakes. Therefore, it is important that the boot be of such design that it has very little tendency not to become misaligned during these operations. The boot as shown may be expected to be successful in this regard.  
         [0035]     It has been found that the boot of  FIG. 1  fits tightly enough against the side of the rail to make a watertight seal. It may be expected that the seal will remain over a long service life. In this regard, the designer should tailor-fit the boot to the rail. The boot should not fit so tightly between the base and the head that the thin walls might tend to buckle, as that might affect the boot-rail sealability; rather, the aim should be that the thin walls lie under a slight compression, after fitting.  
         [0036]     In  FIG. 4 , the face  47  of the boot is designed to lie flush with the flange-side  48  of the head of the rail. This makes it easy for the inspector to check that the gauge portion of the boot has been assembled properly, in that the inspector can simply sight lengthwise along the rail, and can very quickly see if and where the boot is bulging out from the rail. If it is, a worker can very quickly place a board against the face  47  of the boot, and tap it with a hammer, until the face  47  of the boot lies flush with the face  48  of the head of the rail.  
         [0037]     It may be noted that in those installations where the sides of the boot have been secured during assembly by adhesive tape wrapped around the boot (and running across the top of the rail), the inspector cannot take a comparable quick sighting to determine that the boot was correctly in place, nor can a worker quickly and simply correct any misalignments that might be present.  
         [0038]      FIG. 7  shows a variation of the boot of  FIG. 1 , in which a lip  27  is provided on the gauge-portion of the boot. Such a lip may be preferred in some cases, to assist in properly locating the boot on the rail, and in ensuring that the gauge side of the boot is not driven too far under the rail head, in case that might cause the thin material to buckle.  
         [0039]     The top surface of the head of a streetcar rail of course is subject to wear, over time. The rest of the rail, and the boot, are not subject to wear. However, even the buried components can be subject to odd movements due to the passage of road and rail traffic over a long period of time. The boot as illustrated, assuming it is tight against the rail at installation, can be expected to remain tight against the rail over a long service period, despite such odd movements of the rail.  
         [0040]     As to the material of the boot, the elastomeric material should have good electrical insulative properties, whereby it is preferred to use non-conductive materials for reinforcement and filling, in place of the usual carbon. Also, the material should have good weathering characteristics, as to e.g temperature and UN resistance, resistance to becoming brittle, etc. EPDM may be expected to perform well. The rubber should preferably be in the region of 75-80 durometer shore-A hardness, for the required degree of flexibility. Also, the compression set of the material should be such as to ensure that the material will retain enough resilience to remain firmly wedged into the rail throughout its service life.  
         [0041]     Some of the terms used in defining and explaining the invention will now be examined in more detail. Referring to  FIG. 2 , an upper-mid-point is determined, which is the mid-point between the head-gauge-extremity of the head of the rail, and the web-gauge-extremity of the web of the rail; that is to say, the upper-mid-point is halfway between those two points in vertical projection. The lower-mid-point is the point on the rail-base-gauge-overface that lies vertically below the upper-mid-point. The rail-gauge-vertical-line  34  is the line joining the upper-mid-point to the lower-mid-point.  
         [0042]     The boot-gauge-vertical-line  32  ( FIG. 1 ) is the same line as the rail-gauge-vertical-line  34  ( FIG. 2 ), but is measured over the wedged-in gauge-portion of the boot. That is.to say, if the boot were removed from the rail, whereby the boot were no longer compressed, the boot-gauge-vertical-line  32  would expand. (The rail-gauge-vertical-line  34  remains the same length, of course.) The designer should arrange that this amount of expansion, which of course is equated to the amount of compression that has been forced into the wedged-in column of the boot, is preferably around four or five millimetres. If the amount of compression were less than about two or three mm, the boot would not be wedged in tightly enough; if the compression were more than about six or seven mm, the boot would be close to euler-buckling under the compressive loading.  
         [0043]     It is important, in order for the boot to become wedged into the rail, that the vertical column of rubber be engineered properly. In  FIG. 4 , the column  49  comprises the outer strut  50 , together with the web-side wall  52  and the upper portion  53 . The outer strut  50  and the web-side wall  52  are convex with respect to the web of the rail. As a result, i.e because of the convex curvature, when the centre of the column, in the region of the spacer-bar  37 , is pressed inwards towards the web, that action inherently draws the upper  54  and lower  56  ends of the column  49  together. Thus, the action of pushing the convexly-curved centre of the column inwards, towards the web, draws the ends of the column together, and makes it easier to drive the column further inwards towards the web, into the wedge angle. By contrast, if the column had a concave curvature with respect to the web, pressing the centre of the column towards the web would make the column expand.  
         [0044]     The upper end of the column includes a lateral wall  57 , whereby the upper-portion  53  has the form of a cell or pocket. This form is important in the design, in that the form enables the column loading to be spread over the underface  35  more evenly and resiliently than it would be if the column extended, as a compressive strut, over the whole distance  32 . One effect of the cell or pocket form of the upper-portion  53  between the top of the outer strut  50  and the underface  35  is that the wedging force is relatively unaffected by manufacturing errors in the dimension  32  of the boot (and errors in the dimension  34  of the rail).  
         [0045]     The cell-like upper-portion  53  as described on the gauge-side may be present also on the field-side. In fact, the designer may prefer to include a vertical bar in the extruded profile, on the field-side, which would be symmetrical to the wall  47  on the gauge-side  
         [0046]     It has been found, with the column arrangement as illustrated in  FIG. 4 , that it takes very little skill and care on the part of the worker to hammer or kick the boot into its correct place, wedged into the side of the rail. Once the boot is in place, as mentioned, it has been found that usually a tool is required to pry it out of the rail. This applies equally to both the gauge side and the field side of the rail; the field side differs from the gauge side by the provision, on the field side, of the portion  58  of the boot that extends up the field side of the rail head. However, the column portion of the boot, being the portion under the rail head, can be the same both sides.  
         [0047]     In  FIG. 8 , the column  59  is of a single-wall construction. Again, as in  FIG. 4 , the column is convex with respect to the web of the rail. Therefore, the action of pressing the centre of the column  59  inwards towards the web again eases the upper and lower ends of the column more deeply into the wedge angle. To install the boot, the gauge and field portions of the boot are pressed (kicked, hammered) inwards against the web, until the nose  60  touches the web of the rail. Then, when the pressing force is withdrawn, the column  59  tries to straighten itself, wedging itself tightly between the base and the head of the rail.  
         [0048]     Rail profiles are set by official standards. However, the standards do permit some variations; for example, while the wedge angle is usually constant through different manufacturers&#39; versions of the standard rail, the radius between the underface of the head and the web, for instance, can vary with different manufacturers. The present design concentrates the contact areas at the upper and lower ends of the column, where the rubber settles against the predictably-flat head-underface and the predictably-flat base-overface of the rail, and away from the not-so-predictable radiused areas.  
         [0049]     In the designs as illustrated, it can be expected that the amount of springback, i.e in  FIG. 8  the distance separating the nose  60  from the web of the rail after the installation force has been removed, will be of the order of about three millimetres or so. There is no corresponding springback movement at the upper and lower ends of the column, of course. The upper and lower ends of the column lock to the underface and overface of the rail more tightly as the centre of the column springs back and the column straightens out. The springback movement of the centre of the column however does cause a rotation to take place at the ends of the columns. Thus, in  FIG. 8 , the rotation of the upper end of the gauge side of the boot profile causes the outer area  62  to press a little more tightly against the underface  35  of the head. This extra pressure serves to enhance the seal of the boot against the rail, which is advantageous because it aids in preventing moisture from seeping down between the rail and the boot.  
         [0050]     On the other hand, when the concrete or other road material is poured against the sides of the boot, and consolidated, it is likely that the web portions of the boot will then be pressed inwards, and possibly back into actual contact with the web. So the designer should-not place too much reliance on the spring-back effect to actually make the seal.  
         [0051]     The  FIG. 8  design is less preferred, however. Although the extrusion die for  FIG. 8  is easier to make, having no cavities, again these boots are hammered or kicked into place, and the  FIG. 8  profile is more likely to be abusively distorted than is the  FIG. 4  profile under the same treatment. The double wall shape of  FIG. 4  also means that the euler load of the  FIG. 4  column is greater, i.e the compressive force needed to cause the column to actually buckle is greater in  FIG. 4  than in  FIG. 8 .  
         [0052]     Attention is drawn to the following further points regarding the convexity of the column. The column should be almost straight, upon installation. That is to say, although the column should be convex in shape rather than concave, the column should not be too convex. The boot should not be so profiled that the upper and lower ends of the column become engaged with the rail while the centre of the column is still a long way from touching the web. If it were too convex, the column would be less able to support compressive forces acting vertically along its length. The designer should see to it that the wedged-in column is stressed in compression, not in bending or buckling. The column should not be so convex that, upon relaxation or springback, after the press-in force has been removed, should return the column to an almost-straight condition, rather than to a still-very-convex condition. The almost-straight condition preferably should not include an actually straight condition, since that would carry with it the possibility that the column might go slightly concave. Concavity of the column is contraindicated, as that would reverse the barb-like effect, i.e the effect (of convexity) that the boot is easier to push in than to pull out.  
         [0053]     The convexity may also be defined as follows. Upon installation, note the IEU point  64 , being the point of innermost extremity of the contact between the upper end of the column  59  and the underface  35  of the rail head; also, note the IEL point  65 , being the point of innermost extremity of the contact between the lower end of the column  59  and the overface  36  of the rail base; then, draw a line between the IEU point and the IEL point. Preferably, the whole length of this line should pass through rubber: or rather, preferably there should be rubber on both sides of the line, being rubber that is stressed by the compressive forces in the column. The column is convex if, in the vertical centre region of the column, there is compression-stressed rubber on the inside (i.e on the rail side) of the IEU-IEL line.  
         [0054]     It also follows that the column is convex if the vertical compressive stresses in the column tend to bend the centre of the column towards the web of the rail; and the column is concave if the vertical compressive stresses in the column tend to bend the centre of the column away from the web of the rail. The amount of convexity would be too much if there were no stressed rubber on the outside of the IEU-IEL line, in the centre regions of the column, i.e if all the stressed rubber were inside the IEU-IEL line. The IEU-IEL line may be on the web side of the rail-vertical-line ( FIG. 2 ), or may be outside the rail-vertical-line.  
         [0055]     The boot may be designed to the same profile as the rail in the overface, underface, and web areas. However, because the rail profile might vary, the boot should be so profiled that, whatever the actual shape of the actual rail, the boot cannot touch against the rail in any manner that might interfere with the wedging action. Thus, for example, the web-to-underface or web-to-overface radius should not be smaller in the boot than in the rail. The designer should make sure the ends of the column are free to touch, and engage tightly with, the underface and overface of the rail, which means making sure no other parts of the boot profile touch the rail, including the radiuses between the web and the underface and between the web and the overface.  
         [0056]     It is common for railway rails to be angled slightly inwards: thus the chairs  31  in  FIG. 5  have sloping upper faces. The term vertical as used herein refers to the axis of symmetry of the rail (assuming the rail is symmetrical—which sometimes they are not), and this axis lies at a slight angle to the absolute vertical if the rail is tilted.  
         [0057]     There is a rail standard in which the profile includes a rolled-in flangeway. Such a rail (often termed a girder rail) is hugely non-symmetrical. The invention can still be used with such rail profiles; the invention can be used so long as the rail profile is such that the profile includes both a rail-field-wedge-angle and a rail-gauge-wedge-angle.