Abstract:
A method of making an electrical connection to a railroad rail includes fastening a wire bonding assembly to a railroad rail, the wire bonding assembly including first and second spaced apart washer plates contacting the rail and a metal bar supported by the washer plates. The metal bar is electrically connected with the rail with a first conductive lead contacting a selected point on the rail and a selected point on the metal bar. A second conductive lead is connected to another selected point on the metal bar for establishing an electrical connection to the rail from an electrical device.

Description:
FIELD OF INVENTION 
     The present invention relates in general to railroad equipment, and in particular, to methods and apparatus for establishing electrical connections to a railroad rail. 
     BACKGROUND OF INVENTION 
     Track circuits have been used by the railroads for many years. Generally, each of a pair of rails of a block of track is connected to terminals of opposite polarity of an electrical power source. These connections are normally made on the respective rails near the insulated joints separating one end of the track block with the end of the neighboring track block. The rails are also respectively connected, near the insulated joints at the other end of the block, to opposing terminals of the coil of a relay. Signal flow through the relay, under the control of the relay coil, is monitored by associated monitoring equipment, which in turn sets signal aspects, transmits messages to dispatchers, and so on. 
     In a typical track circuit, when the block of track is clear (i.e., no locomotive or railcars are contacting the rails within the block), current through relay coil is sufficient to keep the relay closed and allow signal flow to the monitoring equipment, which processes the signal flow as a clear condition. On the other hand, when a locomotive and/or railcar is within the track block, the metal wheels and axels create an electrical shunt between the rails, which reduces the current flow though the relay coil and breaks the relay signal path. The break in the signal path indicates an occupied block to the monitoring equipment. A similar situation occurs in the case of a break in a rail, which breaks current flow through the relay coil and opens the relay. 
     While track circuits have been known in the railroad sector for many years, their implementation still presents significant challenges. One particular challenge is making, removing, and replacing solid electrical connections to the rails without causing potentially hazardous damage to the rails themselves. 
     SUMMARY OF INVENTION 
     According to one embodiment of the principles of the present invention, a method of making an electrical connection to a railroad rail is disclosed including fastening a wire bonding assembly to a railroad rail, the wire bonding assembly including first and second spaced apart washer plates contacting the rail and a metal bar supported by the washer plates. The metal bar is electrically connected with the rail with a first conductive lead contacting a selected point on the rail and a selected point on the metal bar. A second conductive lead is connected between another selected point on the metal bar for establishing an electrical connection to the rail and a selected electrical device. 
     Embodiments of the present principles provide significant advantages over the prior art practice of welding or brazing electrical connections directly to the web of railroad rails. Specifically, because most of the work of making electrical connections is now performed on a wire bonding assembly, damage to the rails themselves is substantially reduced, particularly when cables and wires must be disconnected and reconnected at a given site. Among other things, conventional welding and brazing, along with the associated surface preparation, can be performed directly on the bonding wire assembly, without having to avoid areas on the rail encompassing prior welding or brazing points, holes, or brands. Connections can be broken from the wire bonding assembly using a hammer or chisel. When damaged, the wire bonding assembly is significantly safer, easier and less expensive to replace than rail and rail joints. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is high-level diagram illustrating a small portion of a block of railroad track and associated track circuitry suitable for describing a typical application of the principles of the present invention; 
         FIG. 2  is an exploded view showing a wire bonding plate assembly, along with a corresponding portion of a rail, according to one embodiment of the principles of the present invention; and 
         FIG. 3  is a diagram showing a representative configuration of the wire bonding plate assembly shown in  FIG. 2  for establishing on or more electrical connections to a rail. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The principles of the present invention and their advantages are best understood by referring to the illustrated embodiment depicted in  FIGS. 1-3  of the drawings, in which like numbers designate like parts. 
       FIG. 1  is a diagram of small portion of a block  100  of railroad track including a pair of conventional parallel steel railroad rails  101   a  and  101   b . Block  100  is associated with conventional track circuit equipment including an electrical energy source  103  connected to rails  101   a  and  101   b  through a corresponding pair of track wires  102   a  and  102   b . Track wires  102   a  and  102   b  are connected to terminals of opposite polarity on electrical energy source  103  to create current flow through rails  101   a  and  101   b  when a closed circuit is maintained. While electrical energy source  103  is shown as a conventional direct current (DC) electrical source suitable for track circuit applications, electrical energy source  103  can also be a conventional alternating (AC) electrical source, as known in the art. 
     The circuit is monitored at the other end of track block  100  by a conventional track monitoring system  105  connected to rails  101   a  and  101   b  through a corresponding set of track wires  104   a  and  104   b . For illustrative purposes, track wires  104   a  and  104   b  are shown coupled to opposing terminals of the coil of a relay that controls a signal, although in actual practice, monitoring equipment  105  can be any one of a number of different track monitoring systems known in the art. 
     In conventional track circuit systems, track wires  102   a - 102   b  and  104   a - 104   b  are connected directly to the corresponding rails  101   a - 104   a  at the corresponding insulated joints  106   a - 106   d , which separate track block  100  from the neighboring track blocks. The electrical connections to rails  101   a - 101   b  are typically kept as close as possible to the insulated joints  106   a - 106   d  (e.g., 3 inches), given that a break in a rail between the insulated joint and an associated electrical connection will not break the closed electrical circuit and therefore will not be detected. While only track wires  102   a - 102   b  and  104   a - 104   b  for a track circuit are shown in  FIG. 1  as an example, other types of electrical connections such as PSO, crossing, or shunt/coupling wires, are also commonly made to rails  101   a - 101   b.    
     Track circuit electrical connections are conventionally implemented by exothermic welding or pin-brazing track wires  102   a - 102   b  and  104   a - 104   b  directly to the rail using specified procedures. For example, the rail surfaces to be welded are cleaned of contamination that might interfere with an effective weld. Surface cleaning may include wiping away dirt or grease with mineral spirits, warming the area with a propane torch to drive out residual moisture, and grinding to remove contaminants such as rust. When grinding is required, care must be taken to ensure that no more metal than necessary is removed and that the surface is not scratched, which can initiate a rail crack. 
     The track wire is then typically exothermically welded or pin-brazed to the web of the rail within the limits of insulated joints  106   a - 106   d . When multiple electrical track connections are being made close to an insulated joint, the first connection must be made with a maximum clearance (e.g., 3 inches) from the joint bar, after which the remaining connections are made with certain a clearance between them (e.g., 2 inches). Typically, track wires  102   a - 102   b  and  104   a - 104   b  for the track circuit are connected closest to the associated insulated joint  106   a - 106   d , with other types of connections, such as PSO, crossing, or shunt/coupling wires being made furthest from the corresponding insulated joint  106   a - 106   d . Connections can be made to both sides of the rail, in which case they are staggered. 
     While the areas of the rails where electrical connections can be made are limited, new connections also cannot be made over a location that contained an earlier connection, since the heat created by welding or brazing may cause micro-cracks in the martensic shell in the steel at the location where the earlier connection was made. (Martenization is generally a process where a hard crystalline structure is created in the steel by the application of high external heat to a local area, e.g., during welding or high-temperature brazing, followed by rapid cooling as mass of the rail sinks heat. This hard crystalline structure can lead to fatigue cracking and rail fracture.) 
     Similarly, bonds to the web of the rail must avoid areas around track connection holes, which are already considered “stress risers” and may have imperfections that could propagate due to the application of welding or brazing heat. Additionally, connections to the web of the rail must also avoid the area of the rail brand, on either side of the rail. 
     Care must also be taken when removing a bond or track connection weld from the web of a rail. For example, breaking off a weld using a hammer or chisel could tear out rail material and initiate a crack in the rail structure. Generally, the use of any tool that might score or notch the rail cannot be used to avoid future rail fractures. 
       FIG. 2  is an exploded view showing a wire bonding plate assembly  200 , and an associated portion of a rail  101 , according to one embodiment of the principles of the present invention. Wire bonding plate assembly  200  includes a metal bar or strap  201 , which is formed, for example, from steel. A pair of washer plates  202  and  203  support bar  201  on the web between the base and the head of rail  101 . In the embodiment shown in  FIG. 2 , metal bar  201  and washer plates  202  and  203  are fastened to rail  101  using a bolt under the trademark HUCKBOLT, although in alternate embodiments other forms of fastening can be used, such as welding or brazing. 
     In  FIG. 3 , wire bonding plate assembly  200  is shown in a representative application. Typically, one (1) bonding plate assembly  200  is attached to each side of the web of each rail  101   a  and  101   b  close to insulated joints  106   a - 106   d . In other words, four (4) bonding plate assemblies  200  are preferably used at each end of each track block, such as track block  100 . 
     A first tab at one end of a conductive bonding wire  204  is fastened to the corresponding rail  101 , preferably using a technique such as the STANLEY SAFEBOND process (i.e., pin brazing), which minimizes damage to the rail, although welding, brazing, or bolting can also be used, as appropriate. Preferably, this connection is made very close to associated insulated joint  106 , for example within three (3) inches. Bonding wire  204  is of any suitable construction and gauge sufficient to carry the required electrical current. 
     A second tab at the opposing end of bonding wire  204  is fastened to a nearby surface of metal bar  201   a , which in the example shown in  FIG. 3 , is the outer (major) surface of metal bar  201 . The connection between the second end of bonding wire  204  and metal bar  201  is preferably made using the STANLEY SAFEBOND pin brazing process, although welding, brazing, or bolts may also be used, given that damage to the rail itself is not at stake. 
     Although a single connection between the rail web and metal bar  201  through a single bonding wire  204  has the advantage of minimizing potential damage to the rail, the principles of the present invention do not foreclose on multiple rail to wire bonding assembly connections. Additionally, by minimizing the gap between the end of metal bar  201  and the insulation joint  106 , the exposure of bonding lead  204  is minimized. Furthermore, a connection of bonding lead  204  to the backside of metal bar  201  affords further protection. 
     For illustration purposes, four (4) track wire to bonding assembly connections  205   a - 205   d  are shown, although the actual number may vary from application to application. Connections  205   a - 205   d  are made to, for example, one of the track wires  102   a - 102   b  and  104   a - 104   b  shown in  FIG. 1  for track circuits, PSO wires, crossing wires, shunt/coupling wires, and other electrical connections to rails  101   a  and  101   b . Connections  205   a - 205   d  can be made using conventional techniques, including the STANLEY SAFEBOND pin brazing process, welding, brazing, or bolts. 
     In the illustrated embodiment, washer plate  202  is preferably insulated, although washer plate  203  may be either insulated or conductive. Advantageously, when washer plate  202  is insulated and metal bar  201  breaks between bonding wire  204  and a connection  205   a - 205   d , an open electrical circuit results, which can be detected by track monitoring circuitry  105  of  FIG. 1  and a signal put into a most safe condition. 
     Bonding plate assembly  200  realizes significant advantageous over the existing practice of welding or brazing electrical connections directly to the rails. Generally, work can be performed directly on metal bar  201  of wire bonding assembly  200  without concerns about damage to the rails themselves. If the metal bar  201  is damaged or fractured due to repeated connections or disconnections, metal bar  201  is simply replaced. Among other things, the efforts required to avoid welding or brazing over holes, brands, and the locations of a previous welding or brazing, is eliminated. Potentially damaging preparation of the welding surface, especially grinding, is also no longer a significant factor. Connections can also be broken, for example with a hammer or chisel, without the risk of damaging the rail web. 
     Overall, the need to replace damaged rail and rail joints is substantially reduced, which in turn reduces train delays, product costs, and man hours, and increases both track and maintenance personnel safety. 
     It should be recognized that establishing track wire connections near insulated joints  106   a - 106   d  of a track block  100  are only one possible application of wire bonding plate  200 . Similar advantages can be realized by employing wire bonding plate  200  where other types of electrical connections are required by a railroad, including those at switch points, stock rails, ridged frogs, swing nose frogs, and fuel facility grounds. 
     Although the invention has been described with reference to specific embodiments, these descriptions are not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed might be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 
     It is therefore contemplated that the claims will cover any such modifications or embodiments that fall within the true scope of the invention.