1. Technical Field of the Invention
The invention relates to systems and methods for bonding cables or wires to rails.
2. Description of the Related Art
Electrical connections are made to rail for both signal (rail break detection, signal actuation, and detection of train presence) and power applications (high current). A longstanding type of rail connection uses exothermic welding to join a copper conductor to the rail steel. The connection must provide continuous low electrical resistance over a long service life (25+ years). To maintain a long service life, the connection must maintain adequate mechanical strength at the weld interface. One advantage of exothermic welding over other types of connections, including brazing and mechanical drilled-hole-and-pins, is the superior electrical interface between the rail steel and the conductor due to welding.
It will be appreciated that improvements in rail bonds would be desirable.
According to an aspect of the invention, a method of making a weld material rail bond includes placing a copper sheet between a mold chamber where weld material is to be formed, and a rail or other object to be bonded to.
According to another aspect of the invention, a copper sheet, placed between a weld metal chamber and an object to be bonded to, has a variable thickness, being thicker at a portion that is more directly inline with the impinging molten weld metal material from the chamber.
According to yet another aspect of the invention, a method of forming a welded rail bond includes placing a meltable interposer material between the rail and the weld metal material, to reduce the amount of material in the rail that is affected by the heat of the bonding process.
According to still another aspect of the invention, a rail bond includes: weld metal; and a metal sheet attached to the conductor cable.
According to a further aspect of the invention, a method of bonding on a rail includes the steps of: placing a metal sheet against the rail; and bringing molten weld metal material into contact with the metal sheet, thereby causing the metal sheet to melt and bond with the rail.
According to a still further aspect of the invention, a method of bonding on a rail includes the steps of: placing a cable, wire, or rod into a chamber of a mold; placing a metal sheet in an opening in the mold, adjacent to the chamber; placing the mold against the rail, with the metal sheet between the rail and the cable, wire, or rod; and directing molten metal material into the chamber, thereby causing the metal sheet to melt and bond with the rail.
To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
In the annexed drawings, which are not necessarily to scale:
A rail bond for bonding a wire, rod, or cable to a surface of rail includes a metal sheet, such as a copper sheet, and weld metal material solidified from molten metal material. A copper or other metal sheet is placed against the surface of the rail where the bond is to be located, and against an opening of a chamber of a graphite mold where the molten weld metal material is formed. Molten material is produced into liquid form and flows to the copper sheet material. This causes the copper sheet material to melt and bond against the steel rail. The presence of the copper sheet material between the molten weld metal and the rail surface reduces the amount of heating in the steel rail, and reduces the size of the heat affected zone (HAZ) in the steel rail. By reducing heating in the steel rail, a region of structure changes in the steel rail material may be at least reduced in extent. The resulting rail bond is a high strength bond having a smaller HAZ than weld metal bonds where the weld metal is placed in direct contact with the surface of the steel rail.
Referring initially to
The rail bond 12 includes a metal sheet 24, such as a copper sheet, in contact with the web surface 18. The rail bond 12 also includes solidified weld metal material 26. The weld metal material 26 may be formed by an exothermic reaction of a reductant metal and a suitable reactant, such as a transition metal oxide. Examples are reactions of aluminum powder and copper oxide powder. Once a mixture of these powders is ignited, an exothermic reaction proceeds that produces a molten metal. In the instance of a mixture of aluminum powder and copper oxide powder, the exothermic reaction produces molten copper. Suitable powders for producing weld metal materials may be obtained from ERICO International Corporation of Solon, Ohio, USA. Further information on such powder materials may be obtained at www.erico.com.
With reference now in addition to
The copper sheet 24 may be made from a suitable piece of sheet copper. The sheet 24 may have a non-uniform thickness. The rectangular upper part 32 and a top half of the circular lower part 34 may constitute a relatively thick portion 50 of the copper or metal sheet 24. The remainder of the sheet 24 (the other half of the circular lower part 34, the radial extension 38, and the wings 40 and 42) constitutes a relatively thin portion 52 of the copper sheet 24. The variable thickness copper sheet 24 may be formed by a suitable process, such as stamping. In an example embodiment the relatively thick portion 50 may have the thickness of 0.080 inches, and the relatively thin portion 52 may have a thickness of 0.062 inches. For a 25-gram exothermic weld bond, a copper thickness of 0.062 inches has been determined to be a suitable compromise between the desirable reduction in the size and depth of a heat affected zone in the steel rail material, and the advantageous maintaining of adequate mechanical strength of the resulting rail bond 12. It will be appreciated that other suitable thicknesses may be employed.
The thick portion 50 and the thin portion 52 are configured such that the thick portion 50 corresponds to areas of direct, primary, or initial contact by the liquid copper weld metal material. In such areas a greater thickness of the copper sheet 24 is required to control the heat affected zone (HAZ) in the underlying steel of the rail 16.
It will be appreciated that the configurations of the relatively thick portion 50 and the relatively thin portion 52 may be varied, for instance depending upon the shape of the copper sheet 24 and where the liquid weld material is to impinge. As a further alternative, it will be appreciated that the copper sheet 24 may have a uniform thickness.
The overall dimensions of the main body 30 may be approximately 0.88×1.28 inches. The radial extension 38 may have a length of about 0.56 inches, and the extensions 40 and 42 may each have a length of about 1 inch. It will be appreciated that the above dimensions are only those for a single specific example embodiment, and that many variations are possible in the size and the shape of the copper sheet 24.
The wings 40 and 42 are used to clamp the copper sheet 24 to the wire 14. As seen best in
An alternative to using the wings 40 and 42 is to provide the copper sheet 24 is to insert the wire or cable 14 into a copper sleeve or tube 43, as shown in
In use the copper sheet 24 provides a barrier between the molten weld metal material and the rail to be bonded to. The copper sheet 24 absorbs heat energy from the molten weld metal, ultimately melting the copper sheet 24. Thus the copper sheet 24 operates as a heat sink with regard to heat from the molten weld metal. The copper sheet 24 then re-solidifies with the rest of the liquid copper (from the reaction of the granular weld metal material). This reduces the amount of heating occurring in the portion of the steel rail 16 underlying the copper sheet 24.
As illustrated schematically in
Variable thickness for the copper sheet 24 may be used to make the heat affected zone 60 more uniform. The thicker portion 50 of the sheet 24 is placed at the location where greater thermal effects would occur if the thicker sheet were not interposed.
The molten weld metal flows through the chute 76 and into a ball-shape chamber 80 in a bottom portion 82 of the mold 70. An opening 84 at one side of the ball-shape chamber 80 allows insertion of the wire 14 (
The chamber 80 is open along a bond surface 88 of the mold 70. The bond surface 88 is the surface that is pressed up against the rail 16 at the location where the rail bond 12 is formed. The bond surface 88 has a chamfer 90 that is around a chamber opening 92 in communication with the chamber 80. The chamfer 90 has a shape corresponding to the shape of the main body 30 of the copper sheet 24. The chamfer 90 may be sized so that when the copper sheet 24 is inserted into the chamfer 90, the main body 30 and the bond surface 88 together form a substantially flat surface for pressing up against the rail 16.
The mold 70 may be made of a suitable refractory material, for example graphite. Graphite used in making the mold 70 may be extruded graphite.
The mold 70 that is shown is a right-hand mold. It will be appreciated that left-hand mold may also be employed to create rail bonds with an opposite orientation. The geometry of the copper sheet 24 (
In step 108 the particulate weld metal material is placed into the mold 70. As discussed above, the particulate weld metal material is placed through the top opening 72 after a metal disk has been put at the bottom of the metal-forming chamber in the top portion 74 of the mold 70. As an alternative to using loose particulate weld metal material, it will be appreciated that the granular weld metal material may be placed in loose form, or may be enclosed in a suitable container or cartridge.
In step 110 the bond surface 88 and the copper sheet 24 are placed against the rail 16 at the location where the rail bond 12 is to be formed. Then, in step 112, the particulate weld metal material is ignited. Ignition may be by a spark, by an electrical igniter, or by any other suitable igniting device. The ignition causes the exothermic reaction in the particulate weld metal materials to proceed, forming the liquid copper weld metal. As discussed above, the weld metal breaks through the metal disk at the bottom of the top portion chamber and the mold 70, and proceeds through the chute 76 into the ball-shaped chamber 80. The heat from the liquid copper weld material causes melting of the copper sheet 24, which in turn causes heating in the heat affected zone 60 of the rail 16. The copper material then re-solidifies to form the rail bond 12, securely bonding the wire or cable 14 to the rail 16. After re-solidification, the mold 70 may be removed in step 116. The result is a secure long lasting rail bond 12 that reduces thermal effects on the material of the rail being bonded to.
It will be appreciated that the system and method described above may be more widely employed to couple items to metal objects other than rail bonds. The principle of using a metal sheet material to interpose between a liquid metal and an object to be bonded to may be used in bonding onto other types of objects.
Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.
This application claims priority under 35 USC 119 to U.S. Provisional Application No. 60/892,970, filed Mar. 5, 2007, which is incorporated herein by reference in its entirety.