RAIL INSULATOR
The present invention relates to a rail insulator comprising an electrically insulative body having a flank portion to be interposed between a shoulder member and an edge of a rail flange and wherein at least a laterally inner side of the flank portion has applied thereto an abrasion resistant covering, for example of metal . In a preferred form, the insulator has a load reception portion integral with the flank portion for extending on an upper side of the rail flange for receiving a downward force of a clip portion thereon, and an underside of the load reception portion has an abrasive resistant covering. The arrangement of the invention prevents premature failure of the insulator as a result of a combination of high compressive force and shear or abrasion applied thereto.
Some examples off structures in accordance with the invention will be illustrated with reference to the accompanying drawings .
Figure 1 is a partially perspective view showing a rail fastening incorporating an insulator having an abrasion resistant covering in accordance with the invention.
Figure 2 is an isometric view of the rail insulator employed in the rail fastening of Figure 1.
Figures 3a, 3b and 3c show components of the insulator of Figure 2. Figure 4 is an isometric view of a further form of rail insulator having an abrasion resistant covering in accordance with the invention.
Figure 4 a, 4b and 4c show components of the insulator of Figure 4. Figure 5 is a partially perspective view showing a further form of rail fastening incorporating the insulator of Figure 4.
Figures 6 and 7 are isometric views showing a side
view and a rear view, respectively, of a further form of rail insulator having an abrasion resistant covering in accordance with the invention.
Figures 8 a, 8 b and 8c show components of the insulator of Figures 6 and 7.
Figures 9 and 10 are partial side views of a rail fastener incorporating an insulator and illustrating the compressive abrasion of the insulator resulting from rail rocking. In railway track, electrical currents or signals are passed through the rails and are used to locate the trains and to activate guarded road crossings . They also serve to warn the track maintenance crew of rail breaks such as a pullapart that occurs in cold regions . In areas where concrete or steel ties or direct fixation or similar installations are used, it is necessary to isolate the rail to prevent a shorting out of the current in both rails. Traditionally, pads and insulators made from electrically insulative material such as polymers are used between the rail and the tie and between the rail and the shoulders to isolate the rail from signal leakage. This invention relates to insulators used between the rail and shoulders of steel, concrete, direct fixation or other similar installations.
Referring to the drawings, wherein like reference numerals indicate like parts, Figure 1 shows a fastening arrangement employing a steel tie 20, electrically insulating cant pad 21 and a hook-in-field and gauge shoulder members 22 and 23, together with resilient clips 24, these element being generally as and installed as described in, applicants International application PCT/CA 99/00966 which should be referred to for further details and the disclosure of which is incorporated herein by reference.
The arrangement as shown retains a rail 26 having a flange 27 providing outer edges 28. Before
installation of the clips 24, insulator members 31 as shown in more detail in Figure 2, are inserted between each shoulder member 22 and 23 and the adjacent rail flange edge 28. As best seen in Figures 3a, 3b and 3c, each insulator member 31 comprises an electrically insulative central or core member 32 formed of conventional polymer material, and laterally outer and inner abrasion resistant coverings 33 and 34 applied on opposite sides of the core member 32. Preferably, the coverings 33 and 34 are metal plates, preferably having laterally extending side surfaces that engage with the core member 32 so as to resist longitudinal displacement of the elements of the insulator relative to one another. In the example shown, the central or core member 32 has longitudinally inclining laterally extending inner and outer side surfaces 36 and 37 extending dove tail fashion. The inner and outer coverings have surfaces complementary to and engaging with the inclining surfaces of the central or core member. The laterally inner covering 34 has a dove tailed groove 38 with inclining surfaces 39 that receive the edges 36 in the assembled condition and likewise the outer covering 33 has inclining side surfaces 41 that are received in the assembled condition in an upper groove 42 in the central or core member 32 having the side surfaces 37.
The upper side of the outer covering 33 has a channel section groove 43 in an upper side having laterally extending sides 44. An inner portion 46 of the clip 24 is received in the groove 43 and engagement of the inner portion 46 with the channel sides 44 prevents lateral creep of the insulator 31 relative to the shoulder 23 and clip 24.
In the example shown, a flank portion 47 of the insulative core 32 that extends between the shoulder 23 and rail flange edge 28 in the installed condition has inwardly extending cheek portions 48 at each end. The
end surfaces 49 of a plate like flank portion 51 of the inner metal covering 34 are received between the cheek portions 48 in the assembled condition, preventing a longitudinal creep of the inner covering 34 relative to the insulative core 32.
Figure 9 is a side view, partially in section, showing the rail fastening arrangement including an insulator 31 in its normal, unstressed condition.
It has been found that, in service, the rail 26 rocks as a result of the lateral forces applied to the side of the head of the rail 26 by the passing wheels. This rocking is illustrated in Figure 10, wherein the rail 26 has rotated about a fulcrum at the point of engagement of the lower side of the rail flange edge 28 on the cant pad 21. The upper side of the rail flange 27 forces the insulator 31 upwardly relative to the shoulder 23, as seen in Figure 10. The upper edge of the rail flange edge 28 engages compressively on the inner flank of the insulator 31. Since the contact between the rail flange edge 28 and the insulator 31 is essentially a line contact, a very high compressive stress is applied to the insulator 31. At the same time, there is a strong abrasion or shear forces applied to the inner flank portion of the insulator 31 as a result of the rubbing contact with the rail flange edge 28. In the present invention, the inner plate like portion 51 of the abrasion resistant covering 34 absorbs and distributes the compressive and shear load over substantially the entire area of contact between the plate portion 51 and the flank portion 47 of the insulative core member 32. Hence, the invention avoids the application of high compressive forces and abrasion or shear to the insulative core member 32 and avoids premature failure of the structure of the insulating member 32.
In the preferred form, the flank portion 51 of the abrasion resistant covering is formed integrally with
an abrasion resistant covering portion 52 that in the assembled condition extends on the underside of the portion 42 of the insulative core member 32 that receives the load of the inner portion 46 of the clip 24 and bears on the upper side of the rail flange 27, so as to absorb and distribute the compressive and shear or abrasion forces applied to the underside of the insulator 31 by the upper side of the rail flange 27. Further, preferably an outer abrasion resistant covering 33 is provided that has an upper portion 53 extending between the insulative core 32 and the inner portion 46 of the clip in the installed condition and that absorbs and distributes abrasion or shear and compressive forces exerted by the clip 24 on the insulator 31. Further, preferably a plate like outer flank portion 54 is formed integrally with the upper portion 53 and, in the installed condition, extends between the insulator 31 and inner face of the shoulder 23 and absorbs and distributes compressive and shear forces to which the insulator 31 may be subjected. It may be noted that throughout the assembled structure, the outer metal covering 33 is spaced from the inner metal covering 34 by the thickness of the insulative core 32, so that there is no conductive path between the elements 33 and 34.
Figures 4, 4a, 4b and 4c show a further form of insulator 61 for use with a known form of PANDROL (trade mark) clip and fastening arrangement. Figure 5 shows the known form of clip 62 engaging a shoulder 63 and engaging the upper side of the insulator 61.
As seen in more detail in Figures 4a to 4c, the insulator 61 comprises an electrically insulative core member 64 and abrasion resistant outer and inner coverings 66 and 67 preferably of plate form metal. The core member 64 comprises a plate like flank portion 68 and an upper load receiving portion 69.
The outer covering 66 comprises a generally planar flank portion 71 that extends on the outer side of the flank portion 68 of the core 64, and an upper portion 72 formed integrally with portion 71 that in the assembled condition extends on the upper side of the portion 69.
An inner covering 67 similarly comprises a plate like flank portion 73 that extends in the assembled condition on the inner side of the flank portion 68 and an upper load receiving portion 74 that extends on the under side of the portion 69. The elements of the insulator 61 are assembled together and function broadly similarly to the insulator 31 described above in detail in connection with Figures 1 to 3, 9 and 10. It may be noted the outer abrasion resistant portion 66 has longitudinally spaced laterally outwardly extending ear portions 76 adjacent each end of the flank portion 71. These ear portions 76 engage opposite ends of the shoulder 63 in the installed position, as seen in Figure 5, to locate the insulator relative to the shoulder 63 and prevent longitudinal creep.
Figure 6, 7 and 8a to 8c show an insulator member 76 comprising an insulative core 77 an outer metal abrasion resistant covering 78 and an inner metal abrasion resistant covering 79. The member 76 is somewhat similar to the insulator 61 described above with reference to Figures 4 and 5, except the outer covering 78 terminates upwardly from the planar flank portion 81 of the core member 77, so that the inner side of the shoulder 63 engages directly on the insulative core 81. The compressive and shear forces exerted between the shoulder 63 and the insulator are relatively small, and therefore the coverings 78 and 79 provide adequate resistance to failure of the insulative core structure 81.