Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1999-08-17
2001-11-20
Arbes, Carl J. (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
Reexamination Certificate
active
06317971
ABSTRACT:
BACKGROUND OF THE INVENTION
It has been the practice in, for example, aluminum electro-smelting operations to utilize aluminum bus bars which have affixed thereto copper contacts to which copper anode or furnace electrode hangers are clamped. The contact may take the form of a square or diamond-shape plate which is simply Mig welded along two or all four edges of the contact plate to the vertical major face of the aluminum bus.
This attachment system has a number of drawbacks. The first is that the connection does not provide a very good electrical connection between the bus and contact plate. The welding may cause a slight distortion of the plate, and, in any event, the current flows almost completely through the edge welds and not through the major flat surfaces even though they are supposedly abutting. This problem is made worse by wear and tear in the bus itself. Aluminum is a relatively soft metal and over years of use is subject to denting and scratching. The exposed face of the bus can become rather beat up. Without clamping pressure over the entire major surface and good area-to-area contact, the abutting surfaces with any irregularities or distortions create a small air gap, so that the major area of the plate facing the face of the bar acts like the plate of a capacitor. The connection has much higher resistance than it should.
Another major problem is that Mig welding requires the power to the system to be shut down. This can be costly and disturbing to the entire process. Power to electrometallurgical or smelting systems is designed to be continuous and literally run for months or even years. Power shutdowns can be very costly. Even where the power shutdowns are scheduled in advance, the extent of the shutdown for maintenance, repairs or replacements is, wherever possible, minimized. For many large scale electrical consumers, such as an electrical smelting operation, power is paid for, whether used or not. Also with scheduled power shutdowns and maintenance windows, it is then inherent that repairs or replacements may not be made when they should be made, making the system in that way inefficient.
Accordingly, the Mig welding connection process provides neither a good electrical nor necessarily a good mechanical connection between the two dissimilar metals.
It would be desirable to provide a connection between the two dissimilar metals which would be both a good electrical connection and a good long-lasting mechanical connection. It would also be desirable if the connection could be made without shutting off the power.
SUMMARY OF THE INVENTION
A connection and a method and apparatus for making the connection is provided between two dissimilar elements, such as an aluminum bus and a copper contact. One application is as an anode electrode hanger in an electric smelting furnace. The connection provides a lower resistance electrical connection which can be made while the power to the system is on. In a preferred form the contact is inserted and clamped in a chamber in a refractory mold assembly. The chamber opening to the face of the mold assembly is somewhat deeper than the contact. The face of the mold assembly is clamped against the bus, and exothermic weld material is ignited to form a molten metal which drops into the chamber between the contact and bus. The weld metal forms a molecular weld bond with the bus, but only a mechanical interlock with the contact. To enhance the mechanical interlock and to improve the electrical conductivity, the surface area of the contact exposed to the weld metal is significantly increased, and the interlock formed increases both the strength of the connection and its electrical conductivity. The surface area increase is obtained by forming a series of parallel vertical undercut slots in the surface of the contact exposed to the weld metal, and such surface may also be tinned to form a brazed mechanical connection. The connection of the dissimilar metals can be made without shutting off the power and provides improved electrical conductivity.
The increase in surface area may be in the ratio of about 1.5 to about 2.5 times or more, and is obtained by such undercut channels. The channels may be dovetailed and conveniently formed in circular section with a reduced chordal opening to the weld metal chamber. The channels extend in the direction of flow of the metal. In a preferred form, the contact is provided with flats for better alignment and gripping in the mold assembly.
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.
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CADWELD Bus Bar Connections catalog dated 1979.
Colarusso Louis J.
Kadlowec Jeff
Olle Ray
Arbes Carl J.
Erico International Corporation
Renner, Otto, Boiselle & Sklar LLP
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