US3699275A

US3699275A - Composite electrical conductor

Info

Publication number: US3699275A
Application number: US90701A
Authority: US
Inventors: Cecil J Mayo; Ronald J Kilburg
Original assignee: Insul 8 Corp
Current assignee: Insul 8 Corp
Priority date: 1970-11-18
Filing date: 1970-11-18
Publication date: 1972-10-17
Anticipated expiration: 1989-10-17

Abstract

A pair of aluminum bars are bolted to the web of a steel rail having a generally I-shaped cross-section. The bars are contoured to fit within the recesses formed on each side of the rail to provide good electrical contact between the aluminum and the steel and a layer of conductive grease is positioned between the bar and the rail. The bars can be provided with deformable means for sealing the interface between the bar and the aluminum as the bars are drawn into engagement with the rail.

Description

United States Patent Mayo et al. I p

[ 51 Oct. 17, 1972 COMPOSITE ELECTRICAL CONDUCTOR [72] Inventors: Cecil J. Mayo, l-lillsborough; Ronald J. Kilburg, 1 San Carlos, both of Calif.

[73] Assignee: lnsul-8-Corp., San Carlos, Calif.

[22] Filed: Nov. 18, 1970 [21] Appl. No.: 90,701

[52] U.S. Cl ..191/29, 238/255 [51] Int. Cl. ..B60m 1/30 [58] Field of Search ..174/94 R, 94.5, 126 CP;

238/243, 255,191/1, 22, 29 DM, 23 R Primary Examiner-Gerald M. Forlenza Assistant Examiner-D. W. Keen Attorney-Fowler, Knobbe & Martens ['57 ABSTRACT,

A pair of aluminum bars are bolted to the web of a steel rail having a generally l-shaped cross-section. The bars are contoured to fit within the recesses formed on each side of the rail to provide good electricalcontact between the aluminum and the steel and a layer of conductive grease is positioned between the [56] References Cited bar and the rail. The bars can be provided with UNITED STATES PATENTS deformable means for sealing the interface between 3 461 250 8H969 D h l9l/23 R the bar and the-aluminumas the bars are drawn into e 11 a ement ith h' iL 1,693,359 11/1928 Wichert ..l9l/22R g g 1,401,827 12/1921 Stillwell ..238/255 6 Claims, 5 Drawing Figures 2?.4 ZZZ Ill I' L V Z! 76 30d COMPOSITE ELECTRICAL CONDUCTOR This invention relates to trolley electrification systems having a fixed electrical conductor and'a moving take-off collector or shoe"; and more particularly, to an improved composite conductor especially suited for being the so-called third rail" for an electrically energized transportation system. A perennial problem of trolley electrification systems is that the fixed conductor must be structurally strong and long wearing to sliding contact while still being an excellent electrical conductor. Steel has excellent strength and wearability, and is a reasonably good conductor. However, it is a poorer conductor than a material such as aluminum which wears faster than steel when subjected to sliding contact. As a result of this situation, many different composite conductors have been developed wherein steel forms the wearing surface to be engaged by the moving electrical collector and copper or aluminum carry most of the electrical load. The various conductors present different kinds of problems in connecting sectionsjof conductors in that normally a conductor of considerable lengthis required in trolley electrification systems; This also brings attendant installation problems and procedures. While the various systems developed have some advantages, further improvements in cost and reliability are always needed.

Thepresent invention provides a relatively simple and inexpensive system whichnevertheless has the essential characteristics of good wearability, reliability and excellent electrical characteristics. In accordance with the invention a conventional crane rail having a generally l-shaped or double T cross-section is utilized to provide the structural strength for the conductor and the wearing surface for the collector. A pair of aluminum bars contoured to fit within the recesses formed on opposite sides of the rail are positioned within these recesses to carry most of the electrical load. The bars are attached to the rail by simple nut and bolt combinations, including a Belleville washer for maintaining tension on the bolt to provide forceful engagement between the bars and the rail. A layer of electrically conductive grease is positioned between the interface between the aluminum bars and the rail to improve the electrical connection. Since the bars are contoured to fit within the recesses of the rail, the upper face of the bar is in electrical contact with the rail head, the inner face of the bar is in electrical contact with the rail web, and the lower face of the bar is in contact with the base of the rail, thus increasing the area of the interface.

In a preferred embodiment of the invention, the bar is constructed so that it can be partially inserted within a rail recessbut will then interfere with the head and the base of the rail. The bar is further formed so that the interfering portion can be deformed as the bar is drawn into engagement with the rail web. Forcing the bar into engagement with the rail web in this fashion provides a seal for the interface between the bar and the rail. This helps prevent the surrounding atmosphere from causing deterioration of the conductive grease and oxidation of the aluminum surfaces in contact with the rail, which effects would increase the electrical resistance between the aluminum and the steel. In the arrangement illustrated herein, the portions of the bar which form the seal are constructed as a pair of ribs which can be readily deformed by the force applied by the fastening means.

For a more thorough understanding of the invention, reference may be had to the following specification and drawings'in which:

FIG. 1 is a side elevational view of .the composite conductor system as it would appear in operation; 5

FIG. 2 is a cross-sectional view of the composite conductor taken on line 2-2 of FIG. 1;

FIG. 3 is a cross-sectional view of the composite conductor ofFlG. 2;

FIG. 4 is a cross-sectional view of a modified form of the composite conductor; and I FIG. 5 is a cross-sectional view of another modified form of composite conductor.

Referring first to FIG. 1, there is shown a composite conductor 10 as it might appear in operation as a socalled third rail of an electrically energized transportation system. The conductor is shown mounted on a series of insulator supports 12 which in turn are mounted on railroad ties 14 or similar elements. The composite conductor is formed by a series of separate steel rail sections 16 which are welded end to end, as the system is installed, forming joints 20. Referring to FIG. 3, it may be seen that the cross-section of the rail 16 has substantially an I-shape or double T shape including a head 22, a base 24 connected to the head 22 by a web 26. The rail is made of steel, thus having the desirable qualities of being a reasonably good electrical conductor while having great strength and the ability to withstand the sliding contact of an electrical collector shoe (not shown) for long and continuous use. The electrical collector shoe engages the upper surface 22a of the head 22.

An example of a suitable rail'has an alloy designation of ASTM Al which has an SAE designation between 1048 and 1051. This material which has been used for many years on cranes and third rail conductors is highly resistant to electrical wear due to arcing and to abrasive wear due tocollector shoes or ice scrapers.

The lower surface 24a of the base 24 rests on the insulated supports 12, and suitable clamping assemblies generally shown at 28 in FIG. 1 engage the wide flanges of the base 24 to clamp the rail to the supports;

The lower surfaces 22b of the rail head 22 together with the surfaces of the web 26 and the upper surfaces 24b of the base 24 define a pair of outwardly opening recesses on opposite sides of the web 26. Within each recess is an aluminum bar 30 extruded with a contour to fit the recess, i.e., the inner surface 30a of the bar 30 is curved to conform to the curvature of the web 26; the upper bar surface 30b conforms to the shape of the lower surface 22b of the rail head 22; and the lower surface 30c conforms to the shape of the upper surface 24b of the rail base 24. As can be seen the dimension between the surfaces 30b and 30c gradually increases outwardly from the inner surface 30a as do the mating surfaces 22b and 24b, of the rail. This enables the bar to be easily initially inserted into the recess, and the bar is dimensioned to fit within the smallest recess that might occur within the typical rail tolerances.

Prior to installing the rail and the bars, holes 32 are cut through the rail web 26' and through the bars 30 at spaced locations along the lengthof the bars and the rails. Preferred spacing between the holes along the midsections of the bars and rails is about 18 inches. A bolt 34 having a flat washer 36 on the head end of the bolt extends through the holes in the bars and the web, and a washer 38capable of providing axial spring tension, such as a Belleville washer, is positioned on the other end of the bolt and held in place by a nut 40. As the nut 40 is tightened on the bolt 34, the bars 30 are drawn inwardly into the recesses so that the inner surface 30 of the bar is brought into tight engagement with the web 26 of the rail, thus providing good mechanical and electrical connection in that area. Preferably a torque value'of approximately 200 to 250 foot pounds is applied to the nut when used with a three-fourth inch ASTMA325 high tensile bolt. The Belleville washer 38 maintains sufficient tension on the bolt to hold the bars in tight engagement with the rail whileaccommodating expansion and'contraction of the metals due to temperature changes.

Prior to attaching the bars to the rail, a layer 42 of conductive grease is applied at the interface between the steel rail and aluminum bars. The layer 42 is shown exaggerated in the drawings for purposes of illustration, and the thickness, of course, willvary depending on the tolerances and imperfections in the rail and the bars. In addition to being a good electrical conductor, this material is relatively impervious to. adverse weather conditions and shows no adverse effects on the steel and aluminum. The material is fairly heavy bodied and becomes less viscous only under extreme heat. Utilizing this material improves the electrical connection between the interface between the bar and the rail, particularly the conductivity between the surface 30b of the bar and the surface 22b of the rail head and the surface 30c,.of the barand the surface 24b of the rail base, which surfaces are not mechanically held in tight contact throughout their length due to the tolerances of the bars and them. In addition to improvingelectri'cal conductivity, the grease layer 42 protects the interface between the bar and the rail from the surrounding atmosphere which would hasten oxidation of the aluminum. The grease also protects the innerface from other corrosive effects which could over a period of time deteriorate the quality of the electrical connection.

As mentionedabove, the steel rail 16 is formed of a series of rail sections which are welded on site when being installed, a typical rail length being about 30 to 60 feet. The aluminum bars are preferably made in similar lengths. To avoid the necessity of welding the aluminum in the field, the bars 30 are axially staggered with respect to the rail 22 and with respect to each other. This may be best seen by referring to FIG. 2 wherein the welded joint between two rails 16a and 16b is indicated by line 20, and the bar 30a which extends primarily along the rail 16a protrudes beyond the endof the bar 16a preferably about inches, where it abuts another bar 300. On the opposite side of the rail, a bar 30b which primarily extends along the rail 16b protrudes beyond the end of the rail 16b and engages a portion of the rail 16a, and abuts another bar 30d. This avoids welding of the aluminum bars because if the electrical transfer at the joint 44 between the bars 30a and 300 does not provide a good electrical path, the current can cross through the steel web of the rail 16b and into the aluminum bar 30b on the other side of the rail. A similar electric path can occur across the joint 46 between the bars 30b and 30d.

In the spliced areas at the end of the rails and the bars, it is preferable that additional bolts be utilized as shown in FIG. 2, the preferred spacing beingapproximately 5 inches between bolts. As can be seen, this provides two bolts through the portion of each bar protruding beyond the end of the rail to which it is primarily attached; that is, referring to FIG. 2, two bolts 34a and 34b are shown attaching the protruding end of the bar 300 to the rail 16b, and two bolts 34:: and 34d connecting the bar 30b to therail16a. Each of these .four bolts connect the ends of the overlapping aluare modified from that of FIG. 3. Each is provided with an upper rib 50d extendingv longitudinally adjacent the outer portion of the upper surface 50b of the bar. Extending along side of the rib.50d is a continuous groove 52which defines the rib and creates a portion 502 of reduced cross-section connecting the, rib 50d to the remainder of the bar. The rib 50d and the adjacent groove 52 are conveniently formed in the bar. during the extrusion process.

A similar rib 50f is formed on the outer lower portion of the bar 50 along its lower surface 500 which is in close proximity to the surface 24c of the rail base. A continuous groove 54 extending along the length of the rail is formed adjacent the rib 50f creating a portion 50g of reduced cross-section connecting the rib to the remainder tothe bar. The dimension between the tips of the

ribs

50d and 50f is slightly larger than the largest dimension that would exist between the rail surfaces 22b and 24b at the position the ribs should occupy when the bar 50 engages the web 26 of the rail. As can be seen from FIG. 4, this point for the rib 50d is at the outer corner 220 along the lower surface 22b of the rail head. The bar is symmetrical and the rib 50f engages the base 24 at the same distance outwardly from the vertical axis of the rail that the rib 50d engages the rail head 22. a

As a result of this dimensional arrangement, the ribs interfere with the rail before the bars are fully drawn into engagement with the web. This interference, however, can be overcome by tightening the nuts40 on the bolts 56. As the barsare drawn into engagement with the web, the

ribs

50d and 50f or the portions of reduced cross-section 502 and 50g of the bars distort slightly as the

ribs

50d and 50f are wedged into engagement with the rail head and rail base. Hence, the ribs seal the interface between the bars 50 and the rail 22 from the surrounding atmosphere. Also, a layer of conductive grease 58 applied to the bar and the rail prior to installation is sealed between the rail and the bars by the

ribs

50d and 50f, the grooves 52 and 54 being filled with the grease.

Such an arrangement improves the durability of the electrical connection between the rail and the bar.

The nut, bolt and fastener combinations in FIG. 4 are identical to that in FIG. 3 with the exception that the bolts 56 are shorter than those in FIG. 3 in view of the reduced thickness of the bars 50.

Referring to FIG. 5, the aluminum bars 60 shown therein-have a thicker cross-section than those shown in FIG. 4 but have ribs 60d and 60f positioned adjacent grooves 62 and 64 similar to those shown in FIG. 4.

These ribs, as in the arrangement of FIG. 4, provide a seal for the interface and the grease 66 between the bars 60 and the rail 16. The ribs have a cross-section such that they can be deformed slightly to accommodate tolerance variations as the bars are drawn into engagement with the rail web 26. I

What is claimed is:

l. A composite electrical conductor comprising:

a steel rail having a generally l-shaped cross-section including a head forming a contact surface for a movable electrical collector, a base for supporting the rail and a web extending between the head and the base, the head, base and web defining an outwardly opening recess on each side of the web;

a pair of rigid bars made of material which is a better electrical conductor than the rail and contoured to fit within said recesses, one on each side of the bar;

fastener means longitudinally spaced along the bars for holding the bars in contact with the rail;

a layer of conductive grease on the surfaces of the bar exposed to the rail to provide good electrical contact between the bars and the rail; and

means extending longitudinally on said bars for engaging the head and the base of the rail as the bars are drawn into engagement with the web, portions of the bars being deformable so that as the bars are drawn further into the recess in engagement with the rail a seal is formed between the rail and the bar to protect the conductive grease and interface between the bar and the. rail from the atmosphere; 30

said seal means comprises a first sealing rib extending longitudinally along the upper edge of the bar and a second sealing rib extending longitudinally along the lower edge of the bar, the dimension between the tips of said ribs being such as to interfere with the head and the base of the rail before the bar is drawn into full engagement with the rail web so that the ribs are forced into sealing engagement with the rail as the bars are drawn into full contact with the rail web.

2. The rail of claim 1 wherein said sealing ribs are positioned adjacent the side of a bar remote from the rail web.

3. The rail of claim 2 wherein said fastener means comprises threaded members extending through the bars with a threaded nut clamping a bar to the rail web.

4. The rail of claim 2 wherein a longitudinal groove is formed in each bar adjacent each rib, the inner side of each rib forming a wall of each groove, the bar being formed such that the grooves define weakened portions joining each rib to the remainder of the bar, which portions deform as the bars are drawn into engagement with the rail web.

5. The rib of claim 2, wherein in only a single rib is formed along the upper and lower edge of each bar.

6. The rail of claim 2 wherein the bar portions which deform as the bar is forced into engagement with the rail web are the portions joining the ribs to the bar.

Claims

1. A composite electrical conductor comprising: a steel rail having a generally I-shaped cross-section including a head forming a contact surface for a movable electrical collector, a base for supporting the rail and a web extending between the heAd and the base, the head, base and web defining an outwardly opening recess on each side of the web; a pair of rigid bars made of material which is a better electrical conductor than the rail and contoured to fit within said recesses, one on each side of the bar; fastener means longitudinally spaced along the bars for holding the bars in contact with the rail; a layer of conductive grease on the surfaces of the bar exposed to the rail to provide good electrical contact between the bars and the rail; and means extending longitudinally on said bars for engaging the head and the base of the rail as the bars are drawn into engagement with the web, portions of the bars being deformable so that as the bars are drawn further into the recess in engagement with the rail a seal is formed between the rail and the bar to protect the conductive grease and interface between the bar and the rail from the atmosphere; said seal means comprises a first sealing rib extending longitudinally along the upper edge of the bar and a second sealing rib extending longitudinally along the lower edge of the bar, the dimension between the tips of said ribs being such as to interfere with the head and the base of the rail before the bar is drawn into full engagement with the rail web so that the ribs are forced into sealing engagement with the rail as the bars are drawn into full contact with the rail web.