WO2003028944A1

WO2003028944A1 - Welded steel/aluminum electrical connection and method

Info

Publication number: WO2003028944A1
Application number: PCT/US2002/029248
Authority: WO
Inventors: Harrie Van Den Nieuwelaar; Ashriel Mohammed; Paul J. Hollingsworth
Original assignee: Erico International Corp
Current assignee: Erico International Corp
Priority date: 2001-09-14
Filing date: 2002-09-13
Publication date: 2003-04-10
Anticipated expiration: 2004-03-14

Abstract

A method and apparatus for forming a welded fused electrical connection between a steel conductor part (20) and an aluminum conductor part (21) such as a solid, braid, cable, laminate or other flexible. The method primarily uses an iron oxide, aluminum and flux exothermic composition which when ignited forms primarily a molten iron metal which fuses to the steel part (20) but melts the aluminum part (21) which then, when the weld cools, fuses to the aluminum part (21) and recrystallizes and anneals the unmelted aluminum to form an electrical connection of sufficient strength. The weld nugget (140) comprises primarily iron fused to the steel and a layer (142) of Fe-Al intermetallics, and aluminum remelted from the aluminum part (21) and fused to the annealed aluminum.

Description

WELDED STEEL/ALUMINUM ELECTRICAL CONNECTION

AND METHOD

DISCLOSURE

This invention relates generally as indicated to a welded steel/aluminum electrical connection and method, and more particularly to an exothermic welding apparatus and method for welding a variety of steel and aluminum electrical conductors, which steel parts may be in the form of steel collector bars or yokes, rectangular-in-section or round, and which aluminum parts may be solids, braids, flexible bar, laminations, strip, cable and the like.

BACKGROUND OF THE INVENTION

Exothermic welding has become recognized as a preferred way to form top quality high ampacity, low resistance electrical connections. Exothermic welded connections are generally immune to thermal conditions which can cause mechanical and compression joints to become loose or corrode. They are recognized for their durability and longevity. The process fuses together the parts or conductors to provide a molecular bond, with a current carrying capacity usually equal to that of the conductor. Such connections are widely used in grounding systems enabling the system to operate as a continuous conductor with lower resistivity.

Exothermic welding has been widely used to join metals such as steel- to-steel and copper-to-steel, and more recently aluminum-to-aluminum. Examples of these connections are well known and widely sold throughout the world under the trademark CADWELD^Θ by ERICO International

Corporation of Solon, Ohio, U.S.A. The CADWELD^® exothermic weld compositions and the high ampacity electrical connections utilize reusable molds such as those made of graphite or high temperature refractory materials and also sold under the trademark CADWELD^®. The aluminum compositions and power connections are sold under the trademarks A-22™ and A-99™, also trademarks of ERICO.

The reusable molds are two or more part molds usually opened and closed and held together by toggle clamps. The mold parts have faces which abut at a parting plane in which are formed recesses forming the various cavities and passages when the parts are clamped together. Typically, the mold parts form a weld chamber, which usually includes a riser which may be the enlarged lower end of a tap hole passage which extends from the top of the mold to the weld chamber.

The parts to be welded enter the weld chamber through passages which extend from outside the mold to the chamber. Such passages usually extend horizontally.

A crucible normally sits on top of the assembled mold parts. The crucible includes a chamber holding the exothermic material on top of a fusible disk. A sprue or tap hole below the disk communicates with the top of the mold through the riser. When a measured and controlled quantity of exothermic material is ignited, it forms molten metal which after reacting melts the disk permitting the molten metal to run downwardly into the weld chamber to fuse and weld any parts exposed to the chamber. Any slag forms on top of the weld metal and normally accumulates in the riser. After the weld cools, the mold is disassembled and any slag removed. The molds and crucible are cleaned for reuse.

The exothermic reaction may be comprised of a reaction between aluminum (Al) and a metal oxide wherein the metal oxide is reduced providing a filler metal, i.e., the source of the filler metal is the oxide on reduction. The "Goldschmidt" reaction is the basis of the application of the process described in U.S. Patent No. 2,229,045 to Charles A. Caldwell, The reaction is as follows: Aluminum (Al) + Iron Oxide (Fe₂0₃) = heat + Aluminum Oxide (Al₂0₃) + Iron (filler metal)

(Fe) or Aluminum (Al) + Copper Oxide (CuO) = heat + Aluminum Oxide (Al₂0₃) + Copper (filler metal) (Cu) The "Goldschmidt" reaction has been successfully utilized over the years to weld or join metals such as iron (Fe) to iron, and iron or steel to copper (Cu). More recently, the process has been adapted for use in joining together a pair of nonferrous metal pieces, such as, two pieces of aluminum (Al) to one another. A successful process for this purpose is described in co-pending U.S. application Serial No. 09/283,939 filed April 4, 1 999, entitled Aluminum Welding Process and Composition for use in same.

U.S. Patent No. 3, 020,61 0 to Rejdak diskloses a method of welding aluminum (Al) and other metals, such as steel and provides a listing of various reactions which can be utilized to provide reaction products which may be utilized to provide a weldment. This Rejdak patent, along with prior patents 2,870,498 and 2,831 ,760, diskloses the bonding of steel and stainless steel to aluminum using an exothermic material having substantial amounts of tin oxide. However, the parts are dipped in molten tin so the cast weld metal will braze thereto. Other aluminum welding compositions and processes may be seen in prior U.S. patents 5,062,903 to Brosnan, et al., 5, 1 71 ,378 to Kovarik, et al., and 5,490,888 to Assel, et al.

As indicated above, ferric oxide mixtures have been used to join steel- to-steel, rail welding being a common application. In addition, such mixture is disklosed in Leuthy, et al. U.S. patents 3,234,603 and 3,255,498, both relating to the formation of the high tensile strength rebar splices using molten metal cast into a sleeve. The splice and process is also sold under the CADWELD^® trademark. CADWELD^® is a registered trademark of ERICO International Corporation. The mixture however, is not designed to fuse the bar ends but simply create a cast in place locking key.

Ferric oxide mixtures are also seen in prior U.S. patent 4, 104,093. The composition is used with a refractory filler for repairing ingot mold base plates. However, the fusion welding of steel to aluminum, which parts are widely found in electric furnaces, smelters, anode connections and other electrolytic processes, to form a high tensile strength low resistance electrical connection has not been economically successful, resulting in more expensive or more complex and costly techniques and mostly less practical techniques, such as mechanical connections, friction welding, or explosive or roll cladding, usually in combination with MIG or TIG welding. These are expensive techniques, and do not have the low cost or reliability of exothermic welding.

It would accordingly be desirable if exothermic welding could be used to form a high tensile strength low resistance electrical connection between steel and aluminum, and which connection would have a service life substantially equal to that of the equipment in which it functions.

SUMMARY OF THE INVENTION A method and apparatus for forming in-situ a welded fused electrical connection between a steel bar conductor part and an aluminum conductor part such as a solid, a braid, cable, laminate, or other flexible, uses a ferric oxide, aluminum and flux composition which when ignited, forms a molten metal which fuses to the steel part but melts the aluminum part which then, when the weld cools, recrystallizes and anneals the adjacent unmelted aluminum to form an adequately strong molecularly bonded electrical connection. The connection is an improvement over other forms of connections.

The weld metal forming the weld nugget by the process is primarily molten iron which welds to the steel but which melts the aluminum so that the nugget is on one side iron and on the other side aluminum with a substantial and very irregular Fe-AI intermetallics zone therebetween. The aluminum part as it enters the mold may be sleeved in steel to prevent excess melting of the aluminum and provide containment for the molten aluminum. The nugget is welded to about 60 - 80% or more of the steel face exposed while the entire end of the aluminum part is fused, recrystallized and annealed adjacent the melted part. The process requires no external energy, and may be accomplished in short order without shutting down the line.

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.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a fragmentary side elevation of apparatus for forming a steel-aluminum weld connection welding a round steel collector bar to an aluminum laminated flexible;

Figure 2 is a vertical section through the flexible as seen from the line 2-2 of Figure 1 ;

Figure 3 is a vertical section through the collector bar as seen from the line 3-3 of Figure 1 ;

Figure 4 is fragmentary view of a steel sleeve positioned around the aluminum flexible as it enters the mold.

Figure 5 is a vertical section taken from the line 5-5 of Figure 4 showing the L-shape components of the sleeve;

Figure 6 is a vertical section of the mold assembly of Figure 1 ;

Figure 7 is a view of the assembly from the left hand side of Figure 6; Figure 8 is a section of the apparatus assembled with the parts to be welded in place and showing the crucible;

Figure 9 is an isometric view of similar apparatus for use with a rectangular steel collector bar;

Figure 10 is an isometric view of a vertically split mold assembly as seen in Figure 9; and

Figure 1 1 is a typical weld nugget section showing in somewhat idealized fashion the steel and aluminum parts; the Fe-AI intermetallics zone, the aluminum remelted zone, and the aluminum recrystallized and annealed zone.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring initially to Figures 1 -3, there is illustrated a steel collector bar shown generally at 20 and an aluminum laminated flexible shown generally at 21 which are exothermically welded by the apparatus shown generally at 22. The exothermic weld between the steel collector bar 20 and the aluminum flexible 21 produces a good electrical connection having sufficient mechanical strength.

The electrical connection between the steel and the aluminum is typical of many industrial applications involving electrolytic or electrolysis cells, electric furnaces, pot lines, smelters, such as aluminum smelters, and like heavy electrical equipment. The various parts may comprise steel collector bars or yokes, anode yokes and stems, or cathode bars, for example. Such connections require heavy duty, low resistence and high tensile strength electrical connections and should have a useful service life equal to that of the equipment involved.

As can be seen, the steel collector bar 20 is generally circular in cross- section although it may have a small flat 24 on the bottom as seen in Figure 3. A clamp shown generally at 26 is secured around the projecting end of the collector bar. The clamp comprises two generally semi-circular clamp elements 27 and 28, each of which includes almost diametrically extending ears or flanges shown at 29 and 30 for the clamp 27, and 31 , and 32 for the clamp 28. The paired projecting ears or flanges are clamped together by respective nut and bolt assemblies shown generally at 33 and 34. The clamp 27 includes radially projecting flanges or tabs 36 and 37, while clamp 28 includes similar tabs 38 and 39. Each flange or tab is provided with a tapped hole to receive a threaded clamp rod as shown at 40, 41 , 42, and 43, respectively. The lower clamp member 28 is provided with an L-shape bracket or base 45 which projects downwardly and then outwardly to support a horizontally split mold assembly shown generally at 46. The mold assembly without the clamping, supporting, and other paraphernalia is shown more clearly in Figures 6, 7 and 8. Referring now additionally to such figures, it will be seen that the mold assembly 46 includes an upper mold part 48 and a lower mold part 49. The refractory blocks forming the mold may be machined from graphite, or other suitable refractory material. The mold parts join at a horizontal parting plane indicated at 50. Each mold part has machined grooves or openings therein designed to mate with openings in the other mold part to form a sleeving passage indicated at 51 for the aluminum part, and a mold chamber shown generally at 52 communicating therewith. A sprue passage shown generally at 54 is formed in the upper mold part and includes an angled slope sheet 55 terminating at the bottom in a lip or edge 56 at the upper end of the mold chamber 52. The mold chamber undercuts the lip 56 to form a riser chamber 57 above the aluminum part. If slag is drawn into the mold chamber during the latter stages of exothermic process, it will form on top of the mold within the riser chamber and the lower end of the sprue passage, and may be removed after the weld is formed. The weld chamber also extends below the projecting aluminum to ensure that any unreacted exothermic material which might be drawn into the weld chamber early in the welding process will flow past the end of the aluminum conductor so that at the interface between the aluminum conductor and the steel, only the desired hot metal of the correct formulation will form the principal part of the weld nugget between the aluminum and the face of the projecting steel. Situated on top of the mold assembly 46 is a crucible shown generally at 60. The crucible, like the mold assembly may be formed of mating machined refractory blocks, and when joined they form a crucible chamber shown generally at 61 containing the exothermic material 62. The lower end of the chamber is provided with a tap hole or passage 63 which communicates with the sprue passage 54 of the mold assembly. The unreacted exothermic material 62 is supported on a fusable metal disk shown at 64 seated at the top of the tap hole and the bottom of the crucible chamber. A layer of starting powder composition may be provided on top of the exothermic material as indicated at 65. The crucible may be provided with a lid or top, not shown, and the exothermic material may be ignited with a spark gun, for example, through the open top 66. Alternatively, the exothermic material may be ignited electrically.

Reverting to Figures 1 -3, it will be seen that the mold blocks forming the mold assembly 46 are held against a stainless steel plate 70, backed up by the clamp which supports a relatively thin gasket 71 formed of high temperature refractory, plastic, steel or the like (seen in Figure 8) by the threaded rods 40, 41 , 42, and 43 on which are threaded clamp nut and washer assemblies seen at 72, 73, 74 and 75 in Figure 2. Both the stainless steel plate and the relatively thin gasket have openings corresponding to the projecting face of the steel collector bar 20 so that the face of the steel collector bar shown at 77 in Figure 8 forms a vertical wall of the mold chamber.

In addition, the upper and lower mold parts are provided with jackets indicated at 78 and 79 and are clamped vertically together by side tie-rods 80 and 81 . Each of the rods are pivoted to the upper mold jacket as indicated at 82 and 83, respectively. The distal or lower tips however are threaded and provided with nut and washer assemblies indicated at 84 and 85, each tightened against the underside of a projecting U-shape clevis as shown at 86 and 87, projecting from the lower mold part jacket. The upper mold part may then quickly be clamped on the lower mold part by simply swinging the tie-rods into the receiving clevis and tightening the respective nut and washer assemblies.

The mold assembly also includes an L-shape bar indicated at 90 just below the entrance of the aluminum sleeving passage. A clamp bracket bar 91 above the aluminum sleeving passage may be used to clamp the aluminum part in place by tightening the nut and bolt assemblies 92 and 93 clamping the aluminum part against the horizontally projecting shelf provided by the L-shape bracket 90. This assures that the end face 94 of the aluminum part is properly positioned in the mold chamber 52.

Referring now more particularly to Figures 4 and 5 in addition to Figure 8, it will be seen that it is preferred to enclose the end of the aluminum part in a steel sleeve shown generally at 96. It has been found that without the steel sleeve, excessive melting on the aluminum may occur. The steel sleeve acts to absorb some of the heat generated by the exothermic reaction and the molten metal, contain the molten aluminum and provides an overall stronger joint. When the aluminum part is rectangular in section, as seen in Figure 5, the sleeve may be formed from two L-shaped members indicated at 97 and 98. The sleeve may be held in place by tape wrapped around the proximal end of the sleeve indicated at 99 and the adjacent aluminum part. The sleeving passage 51 is of course dimensioned closely to accommodate the sleeve 96.

Referring now to Figures 9 and 1 0, there is illustrated a mold assembly mounted on a rectangular steel collector bar indicated at 1 10. The mold assembly shown generally at 1 1 2 is held in place by a clamp assembly comprised of upper and lower clamps 1 13 and 1 14 which clamp around the projecting end of the collector bar. The clamps fit the rectangular configuration of the bar and are clamped together by nut and bolt assemblies extending through the aligned openings in the laterally projecting ears seen at 1 1 5 and 1 1 6. The clamps are also provided with vertically protecting tabs indicated at 1 1 7 and 1 18 accommodating threaded tie-rods which clamp the mold assembly 1 1 2 in place on the end of the collector bar. As illustrated, a two part crucible indicated at 1 20 sits on top of the mold assembly and provides a chamber 1 21 for containing the exothermic material as illustrated more clearly in Figure 8. Like the mold assembly, the two parts of the crucible may be held together by suitable clamps, and like the mold assembly, the parts may be disassembled for cleaning and reuse. Referring now to Figure 1 0, it will be seen that the mold assembly shown at 1 1 2, unlike the mold assembly 46, is vertically split so that the side-by-side mold parts 1 23 and 1 24 have a vertical center parting plane indicated at 1 25. Otherwise the mold chamber and passages formed by the mold assembly are substantially as illustrated in Figures 6, 7, and 8. The side-by-side molds form a sprue passage indicated at 1 26 which is formed of a slope sheet 1 27 which extends to the mold chamber 1 28. The slope sheet directs the molten metal away from the aluminum and toward the steel. Entering the mold chamber from the opposite side as the viewer in Figures 9 and 1 0 is the sleeving passage 1 29 for the aluminum part closely accommodating the part and its steel sleeve. The rectangular face of the protecting steel collector bar closes the side of the mold chamber facing the viewer in Figures 9 and 1 0.

The mold assembly 1 1 2 is held to the clamp assembly by suitable tie- rods or clamp rods passing through the holes indicated at 1 30 in the projections 1 31 and 1 32 extending laterally from the side-by-side mold parts.

In any event, the mold assemblies illustrated may quickly be clamped to and assembled upon the projecting end face of the steel collector bar and they hold the aluminum part with its steel sleeve in proper position vis a vis the mold chamber and the end face of the steel collector bar. When the exothermic material is ignited within the crucible, it reacts and melts the metal disk 64 to run downwardly through the sprue passage and is directed by the slope sheet toward the face of the steel to form a weld nugget bonding the steel and aluminum parts. Any slag forms on top and is later removed when the weld cools, the parts are disassembled and cleaned for reuse to form the next weld. The weld takes about thirty minutes to accomplish since the parts may be quickly assembled and disassembled with a ratchet wrench, for example, and the power for the entire system does not have to be shut off as it would for MIG or TIG welding.

Referring now to Figure 1 1 , there is illustrated the weld nugget formed by the present invention. The weld nugget indicated generally at 1 40 is formed of molten iron fused as indicated at 141 to approximately sixty to ninety percent or more of the face 77 of the steel alloy collector bar. Preferably the fusion area is at least 75 or 80% of the face 77. The iron weld nugget 140 is also fused to the steel sleeve as indicated at 142 and 143. The weld nugget forms an intermetallic zone indicated generally at 1 44 while the zone 145 is primarily aluminum melted from the aluminum part and resolidified. The zone 146 represents the part of the aluminum conductor which has been recrystallized and annealed by the weld heat.

With reference to the intermetallic zone, it will be appreciated that the preferred intermetallic aluminum-iron alloy is FeAI and that such intermetallic zone may extend only for a distance from less than fifty (50) to about one hundred and twenty (1 20) microns between the iron and the aluminum section. However, the intermetallic zone is extremely erose or irregular and literally meanders through the weld nugget in the zone 144 shown by the dotted lines which may be up to two millimeters wide. The intermetallic zone is like a meandering river running through a relatively broad valley and the actual extent of the intermetallic zone is perhaps five to ten times or more the length of such zone. For the size weld shown, the remelted zone 1 45 may be about eight (8) to twelve (1 2) millimeters wide, while the recrystallized and annealed zone 146 may be twelve (1 2) to fifteen (1 5) millimeters wide.

As indicated, the nugget extends below the sleeve as seen at 148 and above the sleeve as seen at 149. The slag on the top of the weld nugget may be removed. A preferred exothermic composition for forming the weld metal is a composition which will produce ninety-eight to ninety-nine percent (98-99%) or more of iron (Fe). A preferred composition is iron oxide scale (primarily Fe₃O₄) seventy-three point six percent (73.6%), aluminum powder twenty- two point nine percent (22.9%), and a flourspar (CaF₂) flux at about three point five percent (3.5%). It is important that additional materials such as silica not be included. It has been found that other alloys of iron and aluminum in the intermetallics zone, which are generally more brittle than Fe- AI can largely be avoided by closely adhering to the composition set forth above and the resulting temperature. Accordingly, the composition should comprise about seventy to seventy-five percent (70-75%) by weight of iron oxide scale, about twenty-five to thirty percent (25-30%) aluminum, and a flux. The proportions of the aluminum as the reducing agent and flux are designed to complete the reaction and form the resulting slag. Thus, essentially none of the aluminum in the weld nugget derives from the exothermic composition but rather from the melted or fused aluminum part.

The size of the parts and the weld connections may vary. For example, the aluminum flexible may be thirty millimeters (30mm) or more thick and one hundred twenty millimeters (120mm) or more wide, while the collector bar may be one hundred thirty millimeters (130mm) or more in diameter or in rectangular dimension. For such size bars and flexibles the amount of weld metal may vary, for example, from about two thousand grams (2000g) to about three thousand five hundred grams (3500g) .

Tests of electrical connections made in accordance with the present invention indicate a good low resistivity connection and, importantly, connections with sufficient tensile strength. The electrical connection can be made quickly without shutting down the system and the electrical connection has a service life substantially equal to that of the components being joined.

To the accomplishment of the foregoing and related ends, the invention then comprises the features particularly pointed out in the claims, these being indicative, however, of but a few of the various ways in which the principles of the invention may be employed.

Claims

CLAIMSWhat is claimed is:

1 . A method of forming a steel-aluminum electrical connection comprising the steps of mounting a clamp on the steel, placing a mold on the clamp, providing said mold with a weld chamber, and sealing said chamber against the steel, providing an opening in the mold into said weld chamber to receive the aluminum, inserting the aluminum in the opening, and sealing it with respect to said weld chamber, introducing molten metal into said weld chamber to form a weld nugget containing an interface of Al- Fe intermetallics fused to the steel and to the aluminum.

2. A method as set forth in claim 1 including the step of controlled annealing and recrystallation of the unmelted portion of the aluminum adjacent the nugget.

3. A method as set forth in claim 1 including the step of maintaining the temperature of the molten metal low enough to prevent excess fusion of the aluminum.

4. A method as set forth in claim 1 including the step enclosing the aluminum with a steel sleeve as it enters the mold.

5. A method as set forth in claim 4 wherein said aluminum is rectangular-in- section and said sleeve is formed by two L-shape sections.

6. A method as set forth in claim 1 wherein said molten metal is formed by an exothermic material composition.

7. A method as set forth in claim 6 wherein said exothermic material composition is contained in a crucible on top of said mold.

8. A method as set forth in claim 6 wherein said exothermic material composition consists essentially of Fe₃0₄ , Al and a flux.

9. A method as set forth in claim 6 wherein said composition comprises about 70 - 75% by weight of Iron Oxide scale, about 25 - 30% aluminum, and a flux.

10. A method as set forth in claim 6 wherein said composition comprises about 73.6% by weight Iron Oxide scale, and about 22.9% by weight aluminum fines, the balance being a flux.

1 1 . A method as set forth in claim 1 including the step of providing the mold with a slope sheet to direct the molten metal toward the steel.

1 2. A method as set forth in claim 1 wherein the weld nugget is fused to from about 60 to about 80% the exposed steel.

1 3. A method of welding a steel-aluminum electrical connection comprising the steps of supporting a mold having a weld chamber sealed against the steel and the aluminum, exothermically forming a weld metal from exothermic material to enter the weld chamber and form a weld nugget with an iron-aluminum alloy intermetallic zone bonded both to the steel and aluminum to form a low resistance electrical connection.

14. A method as set forth in claim 1 3 wherein the weld nugget is formed at least in part by remelted aluminum.

1 5. A method as set forth in claim 1 3 including the step of maintaining the temperature of the molten metal low enough to prevent excess fusion of the aluminum.

16. A method as set forth in claim 1 3 including the step enclosing the aluminum with a steel sleeve as it enters the mold.

17. A method as set forth in claim 1 6 wherein said aluminum is rectangular- in-section and said sleeve is formed by two L-shape sections.

1 8. A method as set forth in claim 1 3 wherein said exothermic material composition is contained in a crucible on top of said mold.

1 9. A method as set forth in claim 1 3 wherein said exothermic material consists essentially of Fe₃0₄ , Al and a flux.

20. A method as set forth in claim 1 3 wherein said exothermic composition comprises about 70 - 75% by weight of Iron Oxide scale, about 25 - 30% aluminum, and a flux.

21 . A method as set forth in claim 1 3 wherein said exothermic composition comprises about 73.6% by weight Iron Oxide scale, and about 22.9% by weight aluminum fines, the balance being a flux.

22. A method as set forth in 1 3 including the step of providing the mold with a slope sheet directing the molten metal away from the aluminum.

23. A method as set forth in claim 1 3 wherein the weld nugget is welded to from about 65 to about 90% of the steel exposed to the weld chamber

24. A steel-aluminum or aluminum alloy weld connection comprising a weld nugget formed of primarily iron fused to the steel, an irregular layer of Al-Fe intermetallics, and primarily aluminum, remelted from, and fused with the aluminum.

25. A weld connection as set forth in claim 24 wherein the aluminum is enclosed in a steel sleeve, and the weld nugget is fused to the sleeve.

26. A weld connection as set forth in claim 25 wherein said aluminum is rectangular in cross section.

27. A weld connection as set forth in claim 24 wherein the weld nugget is

fused to at least about 65 to about 80% of the cross section of the steel.

28. A weld connection as set forth in claim 24 wherein said weld nugget is formed by an exothermic material comprising primarily iron oxide, aluminum as a reducing agent, and a flux.

29. A weld connection as set forth in claim 24 wherein said steel is a collector bar and said aluminum or aluminum alloy is a flexible, braid, laminate, solid, or cable.

30. A weld connection as set forth in claim 24, wherein the aluminum adjacent the weld nugget is annealed.

31 . A weld connection as set forth in claim 24 wherein the weld nugget is formed principally of iron formed exothermically, and aluminum melted from the aluminum.

32. Apparatus for welding aluminum to steel to form an electrical connection including clamp means for securing a mold to said steel, said mold having a mold chamber to which said steel is exposed, a passage in said mold for introducing said aluminum into said mold chamber opposite the steel, said passage being sufficiently large to accommodate said aluminum and a steel sleeve surrounding said aluminum, and means for introducing molten iron into said mold chamber to weld the aluminum to the steel to form an electrical connection.

33. Apparatus as set forth in claim 32 wherein said mold is a two part mold assembly.

34. Apparatus as set forth in claim 33, wherein said two part mold assembly is vertically split.

35. Apparatus as set forth in claim 33, wherein said two part mold assembly is horizontally split.