GB2281449A - Electrical bond - Google Patents

Abstract

A rectangular elongated block 16 is brazed to a metal structure such as a rail. During brazing the block fits in an external 18 recess in a crucible 28, which recess bottoms in a heat transmitting wall 38. Exothermic material contained in the crucible produces the required heat, which is transmitted through the wall and through the block as the crucible is urged against the block to braze the block to the structure. The crucible is removed and the exothermic reaction products in the crucible discarded. After cooling, a fastener in a tapped hole in the block is used to secure a lead to the block. <IMAGE>

Description

"ELECTRICAL BOND" This invention relates generally as indicated to an electrical conductor bond, and more particularly to an electrical connection for a rail or other metal structure.

There is disclosed in European published patent application No. 526,362 a method and apparatus for brazing a flattened cross section conductor to a rail base or pipe. The process utilizes opposed large flat surfaces of the conductor.

Brazing materials are provided between the rail or pipe and one of such surfaces while the opposite surface is pressed against the rail or pipe by a heat permeable wall of an exothermic reaction crucible. When the reaction takes place, heat generated within the crucible permeates through the wall, through the flattened conductor to the brazing material. The reaction products never leave the crucible and the crucible containing the reaction products may be discarded, or the crucible may be cleaned out and reused.

While the above described process makes an excellent brazed connection and bond, there are some limitations. The relatively thin cross section of the conductor doesn't act as well as it might as a good heat sink. Heat gradients are related to distance. Accordingly, a larger block conductor will heat more uniformly or evenly. It will also cool in the same fashion. This makes the brazing process more precise and somewhat easier to control. A larger block also places the heat source further from the rail or pipe making it easier to avoid overheating or thermal shocks near the bond. With quality rails, this should be avoided for metallurgical reasons.

It would also be desirable to have a properly electrically brazed conducting block secured to the rail to which one or more electrical jumpers or leads could be quickly and conveniently secured mechanically, such as by fasteners. This would avoid drilling a hole in the rail. If the jumper or signal bond can be quickly and conveniently added or removed by a simple tool such as a screw or bolt driver, field installation and maintenance can greatly be facilitated.

Accordingly, it is desirable to provide a good torque resistant electrical connection which does not disturb the rail by either drilling, or with excess heat as in direct welding, which could cause thermal shock.

Some optional and essential features of the invention are summarised below.

An electrical bond such as rail bond or cathodic protection bond, and the like utilizes a relatively large rectangular elongated block. The block may be provided with one or more blind tapped holes, and preferably a single centered tapped hole. The block is electrically secured to rail or other metal structure by brazing the one surface of the block opposite the tapped hole to such structure.

Heat for the brazing is obtained from an exothermic reaction in a refractory mold or crucible which contains a relatively thin heat transmitting wall forming the blind end of a block receiving external recess in the crucible.

The recess is not as deep as the block so that the block projects from the recess and the mold or crucible is spaced from the rail or metal structure. The other outer surface of the block containing the hole is juxtaposed to the heat transmitting wall. With the surface of the metal structure prepared for brazing, brazing material between the one surface of the block and the structure, the block in the recess and the heat transmitting wall of the crucible juxtaposed to and pressed against the other surface, an exothermic reaction is initiated in the crucible. The reaction products are fully contained within the crucible. The heat from the reaction passes through the heat transmitting wall and heats the block uniformly which in turn heats the brazing material to brazing temperature.

After the brazing operation, the crucible may be cleaned out and reused or the entire crucible and contents may be discarded. Other than through the brazing material, neither the heated block nor the crucible contacts the metal structure.

The mass of the block provides uniform heat to the braze, and when the crucible is removed following the reaction, the block cools uniformly providing an excellent brazed connection without drilling or applying high heat or welding to the rail or other metal structure.

The rectangular conductive block has a substantially square transverse section and is preferably elongated twice or more its height or depth. The tapped hole is preferably in the center of the block dividing equally any resistance to torque as a lug fastener is tightened in the hole. In one form the block may have a longitudinal centered hole intersecting and normal to the tapped hole. In this manner, a wire or stranded jumper end may be threaded into the longitudinal hole and locked in place by a fastener threaded into the tapped hole. In this form the fastener may be used either to secure a lug to the other outer surface or lock a wire, cable or jumper end in the longitudinal hole. The process and apparatus of the present invention enables the block to be electrically secured to the rail or other structure at one time such a initial installation, while the electrical jumpers or conductors may be attached more easily at a later time.

To the accomplishment of the foregoing and related ends the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of the invention may be employed.

There now follows a description of preferred embodiments of the invention, by way of example, with reference being made to the accompanying drawings in which: Figure 1 is a transverse rail section illustrating a block being brazed to the rail base or foot; Figure 2 is a similar section illustrating a block being brazed to a rail web; Figure 3 is a similar section with the fastener components exploded illustrating two different types of fasteners by which the conductor or jumper lug may be attached; Figure 4 is an enlarged side elevation of a block partially broken away and in section; Figure 5 is an end elevator of the block of Figure 4; and Figure 6 is an isometric exploded view of another form of block in accordance with the present invention illustrating the connection of two different conductors with the same block and fastener.

Referring initially to Figure 1, there is illustrated a rail 10 in transverse section which comprises a base 11, a web 12 at a head 13. While the present invention is illustrated as applied to a rail, it will be appreciated that other metal structures such as pipes or other buried structures may have occasion to have electrical connections attached thereto, either when installed or well after installation. Cathodic protection connections are a good example. In railways, the electrical connections may be for signalling, grounding or power purposes.

The apparatus disclosed in Figure 1 is in position to attach, by brazing, a conductive rectangular block 15 to the top of rail base 11. Brazing fluxes and materials are positioned at 16 between the inner face 17 of the block 15 and the top of the rail base. The other outer face 18 is captured by a recess 19 in the exterior of a refractory crucible or mold shown generally at 20.

The refractory crucible is typically formed of graphite blocks 22 and 23 which are pressed together by a toggle clamp, not shown, such toggle clamp fitting in the holes seen at 25 and 26. A lid 27 having an opening 28 is usually hinged to one of the mold parts. The mold parts form a crucible chamber 30 adapted to contain an exothermic reaction mixture 32 with a starting powder 33 sprinkled on top. Normally, some of the starting powder will be positioned at opening 28 as indicated at 35 so that an ignitor, such as a spark gun may be employed to ignite the mixture.

It is noted that the bottom wall 38 of the chamber 30 is relatively thin, and is parallel to the bottom of the recess 19 and, of course, also parallel to the outer face 18 and the inner face 17 of the block 15.

The mold is embraced by bracket 40 which forms an angled extension of arm 41 of spring clamp 42. The other arm 43 terminates inwardly in hook 44 which fits beneath the rail. The arms are pivoted together at 45 and a relatively large coil spring 46 urges the arms toward a closed position. An adjustable stop 47 limits the closing of the arms. The spring 46 thus exerts a downward pressure on the crucible which in turn forces the block 15 against the rail base.

With the parts shown in the Figure 1 position, the starting powder is ignited and the exothermic reaction takes place within the chamber 30 of the crucible. A typical reaction forms a molten metal which runs to the bottom of the chamber while slag generally moves to the top. During the reaction sparks may be emitted from the opening 28 and the rail adjacent the apparatus illustrated may be protected by a suitable small sheet or sheets of refractory cloth.

Since there is no tap hole or other means by which the reaction products of the exothermic mixture may exit the crucible, they are contained therein and solidify as the reaction is completed and cools. However, the high heat characteristic of exothermic reactions is transmitted through the wall 38 and through the depth or height of the block 15 to the exothermic materials 16 causing the block to be brazed to the rail in the position illustrated.

After cooling the crucible is removed. The crucible continues to contain the reaction products from the exothermic reaction and such products may be discarded and the crucible used again, or both the reaction products and the crucible may be discarded.

In Figure 2 there is illustrated a block 15 in position to be brazed to the side of the web 12 of the rail 10. The refractory mold or crucible may be formed from two mold parts 50 and 51 which may be held together by the usual toggle clamps. A lid 52 is mounted on top of the crucible and provides a lateral opening 53. The crucible thus formed provides a vertically oriented crucible chamber 54 which includes a lower inward offset. In this manner the crucible clears the rail head 13. The vertically oriented chamber 54 includes a vertical heat transmitting wall 56 which is parallel to and offset from the bottom 57 of horizontally outwardly opening external recess 58. The recess has a depth slightly more than half the depth of the block 15. Thus the recess supports the block vertically even when the block is not against the brazing compounds indicated at 60 on the rail web. The vertical wall 56 is relatively thin and is designed to transmit heat from the reaction within the crucible chamber. The wall 56 is parallel to the bottom of the recess and also parallel to the outer face 18 and inner face 17 of the block 15.

The crucible is held in position by wing nut bracket 62 on the end of right angle toggle arm 63 which is secured to toggle pivot plate 64. An adjustable support 65 operative to engage the top of the rail head 13 may be mounted on the arm 63. The opposite arm 67 includes a tapped hole 68 in which is threaded stud 69. A channel shape clamp 70 is mounted on the inner end of the stud and is adapted to engage the opposite side of the rail web. A wing lock nut 72 also threaded on the stud, may be employed to lock the clamp in the desired position of adjustment. The upper end of the arm 67 includes toggle plate 73 pivoted at 74 to toggle plate 64. Toggle arms 76 and 77 are pivoted at 78 and 79, respectively, and to each other at 80. Handles 82 and 83, respectively, project from such toggle arms.

Accordingly, by swinging the toggle handles toward each other, the plates 73 and 64 pivot in opposite directions about the pivot 74 moving the arms 67 and 53 toward each other urging the crucible against the block and in turn, the block against the rail web. As soon as the pivot 80 moves over center between the pivots 79 and 78, the clamp is locked in position.

The exothermic material 85 has a starting powder 86 on the top thereof and is ignited through the opening 53 in the same manner by a spark gun, for example. When the exothermic reaction takes place, the heat generated within the crucible is transmitted through the wall 56, through the block 15, and such heat is effective to cause the brazing material to braze the block 15 to the web of the rail. Again, portions of the rail may be protected by refractory drop cloths from any sparks being emitted from the opening 53. The reaction products of the exothermic reaction will be contained within the crucible since it has no tap hole or exit. As in the Figure 1 embodiment, the reaction products may be discarded and the refractory crucible used again. Alternatively, both the crucible and the reaction products may be discarded.

Referring now to Figures 3, there is illustrated two different fastening systems for fastening a lug 90 forming the end of a conductor 91 to the outer face 18 of the block 15.

On the left-hand side of Figure 3, there is illustrated the block 15 secured to the top of the base 11 by the brazing 16. The block includes a central blind tapped hole 93 which has threads meshing with the threads 94 of cap screw or bolt 95. The bolt extends through washer 96 and hole 97 in the lug 90 to clamp and secure the lug to the face 18. The length of the threaded portion of the bolt depends upon the thickness of the lug 97. The conductor may be a wire, braid, cable, or other form of electrical conductor.

For the block 15 secured to the web, as illustrated on the right-hand side of Figure 3, a threaded stud indicated at 98 is employed. The stud is provided with threads matching the threads of the blind tapped hole. Again the length of the threaded stud will depend upon the thickness of the lug being attached to the face 18. The stud may be threaded into the blind tapped hole shortly after the block is attached to the rail. Then, when the lug is attached, the hole of the lug is simply positioned over the projecting stud and the washer is then threaded over the projecting stud with the nut 100 clamping the washer against the lug and the lug in turn against the face 18.

A typical block is illustrated in Figures 4 and 5. The tapped hole 93 is located centrally between the longitudinal ends 102 and 103. The size of the tapped hole may vary depending upon the fasteners employed. As a typical block, the block illustrated in Figures 4 and 5, may be approximately 50 mm long, 25 mm wide, and 20 mm deep. These dimensions may, however, vary.

The block illustrated in Figures 4 and 5 has a brazed layer 16 applied thereto, which may be approximately 0.5 mm thick. This brazed layer may be pre-applied or factory applied to the block to facilitate installation.

The block is made of a conductive material and many conductive materials may be employed. Preferred materials would, for example, be copper, aluminum or steel.

It is noted that the tapped hole 93 is in the longitudinal center of the block and accordingly, when torque is applied to the fastener for the conductor, the resistance to torque is divided equally longitudinally of the block. Tests have indicated that the block has excellent torsional resistance.

Referring now to Figure 6, there is illustrated an alternative form of the invention. The block 105 has an outer face 106 provided with a central tapped hole 107 which intersects untapped longitudinal center hole 108. With the block seen in Figure 6, a lug indicated at 110 may be fastened to the face 106 by fastener 112, passing through the hole 113 in the lug and tightened in hole 107.

Alternatively, or in addition, the fastener 112 may be utilized to secure a wire or cable conductor or lead indicated at 114 and threaded in the hole 108. The fastener 112 then acts as a set screw locking the conductor 114 in the hole 108.

The various forms of mechanical connection as described above, all provide good low resistance electrical connections to the block.

The method of the present invention is practiced initially by preparing an area of the rail 10 to receive the brazed block. This is done by removing any rust or scale which may be present. This may done, for example, by a scratch brush, or grinding tool, or a combination of both. The next step is to apply brazing materials to the area. The brazing materials may be applied directly to the rail or metal structure or may be applied to the inner surface of the block, or both. As indicated, the block may already have a layer of brazing material thereon.

With the block in position, the crucible or mold preheated to ensure dryness is seated on the outer opposite face with the block projecting into the recess and flush against the heat transfer wall of the crucible. With the crucible and block in the Figure 1 position, the crucible is charged with the exothermic material 32 and starting compound 33, and the lid closed. It is noted that the clamping and positioning tools in both embodiments urge the crucible against the block which is in turn urged against the rail. This forcing of the crucible against the block, is obtained by the spring 46 in the Figure 1 embodiment, and by the toggle clamping action of the Figure 2 embodiment.

Portions of the rail adjacent to the crucible may be protected by refractory drop cloths simply to keep any sparks which may exit the opening 28 from contacting the rail. When the exothermic material is ignited, the reaction will take place within the vessel of the crucible and all of the reaction products are contained within the crucible. The heat formed by the reaction will be transmitted through the wall 38, and through the thickness of the block to the brazing material 16.

After approximately 3 minutes, the mold or crucible is removed and the block 15 is brazed to the rail. When the molten crucible is removed, the reaction products remain inside the crucible and may be discarded. Alternatively, both the crucible and the reaction products may be discarded. As indicated above, either threaded stud seen in Figure 3 may be positioned in the tapped hole with the electrical lead or conductor attached later.

The process of Figure 2 is similar to the process of Figure 1. The block 15 is inserted in the deeper recess of the crucible and in effect becomes preassembled with the crucible so that it won't fall out unless the crucible is turned too far on its side. This facilitates the manipulation of the toggle clamp to obtain the locked and clamped position illustrated. Again, the brazing material may be applied directly to the rail, the interior surface of the block, or may be pre-applied to the block as seen in Figure 4. Parts of the rail may be protected with a refractory drop cloth so that any sparks emitted from the opening 53 will not contact the rail.

As indicated in the prior European publication, the heat generated in the crucible may be varied by varying the constituents of the exothermic mixture.

Since the mixture is contained within the vessel of the crucible and is not used for welding or other purposes, but is to be discarded, a low cost exothermic material is desirable. The heat generated by the reaction may be controlled by changing the thickness of the heat transmitting wall in both embodiments, or the material of the crucible or of that wall. As indicated, it is preferred to form the crucible of graphite mold parts, but other materials resistant to the exothermic reaction may also be employed.

Although the invention has been shown and described with respect to certain preferred 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. The present invention includes all such equivalent alterations and modifications.

Claims (28)

1. A method of forming an electrical connection to a metal structure comprising the steps of forming a tapped hole in a conductive block, brazing such block to the metal structure, and then using a fastener in the hole to attach an electrical lead to the block.

2. A method as set forth in claim 1 including the step of pressing the surface of the block with the hole with a heat transmitting wall of an exothermic crucible to braze the opposite surface of the block to the metal structure.

3. A method as set forth in claim 2 including the steps of seating the block in an external recess in the crucible with one surface exposed, coating such one surface and/or the metal structure with brazing materials, and then pressing the entire crucible against the block, and the block in turn against the metal structure.

4. A method as set forth in claim 3 including the step of charging the crucible with exothermic material, and igniting such material to transmit heat through the wall and the block to braze the block to the structure.

5. A method as set forth in claim 4 including the step of removing the crucible with the exothermic reaction products therein, and then discarding such products.

6. A method as set forth in any of claims 1 to 5 wherein such structure is a rail, and the block is secured to the base and/or web of the rail.

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7. A method of providing an electrical connection to a metal structure comprising the steps of providing a conductive rectangular block having opposed planar surfaces, placing an inner one of said surfaces against the metal structure with brazing material therebetween, placing a heat transmitting wall of a refractory crucible against the other outer structure, and urging the crucible against the block and the block in turn against the metal surface with the heat transmitting wall juxtaposed to said other outer surface, placing a charge of exothermic material in the crucible, and igniting such material with the heat of the reaction being transmitted through the heat transmitting wall and uniformly through the block from said other outer surface to said inner one surface to braze the block to the metal structure, the products of the reaction being contained within the crucible, removing the crucible, and then attaching an electrical lead to the block.

8. A method as set forth in claim 7 including the step of providing the other outer surface of said block with a tapped hole, and using a fastener in said hole to clamp a lug to such other outer surface.

9. A method as set forth in claim 7 including the step of providing the block with a longitudinal internal hole and the outer surface with a tapped hole intersecting the longitudinal internal hole, and using a fastener in said tapped hole selectively to clamp a lug to such other outer surface, or lock an electrical lead inserted into said longitudinal hole.

10. A brazing apparatus comprising in combination a crucible for exothermic materials for generating brazing heat while containing the exothermic reaction products, an external recess in said crucible adapted to receive and support a rectangular block to be brazed to a metal structure with one surface of the block projecting from the recess to engage the metal structure, said recess inwardly terminating in a heat transmitting wall through which the heat of the reaction is transmitted to heat the block and thus brazing material positioned between the block and metal structure to braze the block to the metal structure.

11. Brazing apparatus as set forth in claim 10 wherein said recess opens horizontally and said heat transmitting wall is vertical.

12. Brazing apparatus as set forth in claim 11 wherein said crucible includes a chamber for the exothermic materials opening at the top of the crucible, said vertical heat transmitting wall forming part of said chamber.

13. Brazing apparatus as set forth in claim 12 including means to urge said crucible horizontally to press the crucible against said block in turn against said metal structure.

14. Brazing apparatus as set forth in any of claims 10 to 13 wherein said recess surrounds the block, and the depth of the recess is at least half the depth of the block.

15. Brazing apparatus for brazing a conductive element to a vertical surface of a metal structure comprising a crucible having a horizontally opening external recess adapted to receive and support the conductive element with one surface of the element projecting from the recess to engage the vertical surface of the metal structure with brazing material between the element and structure, said recess inwardly terminating in a heat transmitting crucible wall whereby an exothermic reaction within the crucible will transmit heat through the wall and through the element to braze the element to the vertical surface of the metal structure.

16. Brazing apparatus as set forth in claim 15 wherein said heat transmitting wall extends vertically and forms part of a vertically oriented chamber into which heat producing material is charged.

17. Brazing apparatus as set forth in claim 15 or claim 16 wherein the depth of the recess is at least half the depth of the block.

18. An electrical connection for a metal structure comprising an elongated rectangular conductive block having one surface brazed to the structure, the opposite outer surface being provided with a tapped hole, and a threaded fastener in such hole securing an electrical lead to the block.

19. An electrical connection as set forth in claim 18 wherein said fastener clamps an electrical lead lug to said opposite outer surface.

20. An electrical connection as set forth in claim 19 wherein said fastener comprises a threaded stud and nut.

21. An electrical connection as set forth in claim 19 wherein said fastener comprises a capped bolt.

22. An electrical connection as set forth in any of claims 18 to 21 wherein said metal structure is a rail.

23. An electrical connection as set forth in claim 22 wherein the connection is at the base or web of the rail.

24. An electrical connection as set forth in any of claims 18 to 23 wherein said hole is at the midpoint of the elongated conductive block.

25. An electrical connection as set forth in any of claims 18 to 23 including a longitudinal hole extending through said block and intersecting said tapped hole whereby an electrical lead inserted in said longitudinal hole may be locked in place by a fastener in said tapped hole.

26. A method generally as herein desribed, with reference to or as illustrated in the accompanying drawings.

27. Apparatus generally as herein desribed, with reference to or as illustrated in the accompanying drawings.

28. An electrical connection generally as herein desribed, with reference to or as illustrated in the accompanying drawings.