GB2028700A

GB2028700A - Electrically connecting by compression welding

Info

Publication number: GB2028700A
Application number: GB7834880A
Authority: GB
Original assignee: Central Electricity Generating Board
Current assignee: Central Electricity Generating Board
Priority date: 1978-08-29
Filing date: 1978-08-29
Publication date: 1980-03-12

Abstract

An electrical connection is formed between an aluminium ferrule (10) and an aluminium conductor (11) by compression welding after electroless or anodic deposition of a brittle coating on the ferrule. The compression welding is effected using an indenting die giving indentations (15) of a depth and width of 1.5 to 2.0 times the wall thickness of the ferrule to give cold welding with pure metallic bridging over a substantial area. <IMAGE>

Description

SPECIFICATION Improvements in or relating to methods of effecting electrical connections by compression welding This invention relates to the effecting of electrical connections by compression welding.

Aluminium is widely used as an electrical conductor, for example in electrical power supply cables.

The word "aluminium" is used in this specification to include alloys in which aluminium is a major constituent. One of the problems however with the use of aluminium is the difficulty of making good electrical connections; the primary problem is the oxide coating which rapidly forms on any aluminium surface exposed to air and which is electrically insulating. For this reason, it is difficult to achieve consistently reliable compression joints between aluminium conductors.

According to this invention, a method of effecting an electrical connection between an aluminium ferrule and a solid aluminium element fitting within the ferrule comprises the steps of depositing a brittle layer on the surface of the ferrule by electroless or anodic deposition, and then compressing the ferrule onto the element using an indenting die giving indentations to a depth and width of 1.5 to 2.0 times the wall thickness of the ferrule.

The brittle layer may conveniently be produced by electroless deposition using a nickel phosphate solution or by an integral anodising process.

By this technique, the treated surface is provided with a brittle coating, so that the surface is rendered suitable for cold welding without the need for subsequent cleaning. In practice, it is sufficient to treat only the surface in this way; the inner surface of the ferrule will thus have an internal surface ready for putting over the end of a conductor, e.g. a core of a solid aluminium conductor cable for cold welding by a simple compression technique using indenting dies. The conductor may be abraded on the surface where the cold welding takes place.

The ferrule may have an integral palm so that the ferrule with its palm constitutes a terminal which can be secured by compression welding onto the end of a conductor. The treatment of the whole terminal comprising the palm and ferrule by the electroless process provides a good contact face on the aluminium palm for bolting to an aluminium or copper or copper plated conductor, e.g. a busbar. In the case of anodic treatment, the ferrule portion only need be treated; the integral lug is preferably masked to inhibit anodising.

As another example the ferrule may be used for joining the ends of two conductors; these are put into the ferrule from opposite ends to butt one another and the ferrule is then compressed onto the two conductors to form the electrical connection.

The use of an indenting die or dies results in deformation of the ferrule-to-conductor interfaces such that pure metallic bridging or cold welding occurs over large areas between the surfaces in contact to ensure electrical integrity. The adhesion is constant and unaffected by creep.

Conveniently the electroless deposition is effected by depositing an initial zinc strike using a zinc oxide/caustic soda solution followed by an acid nickel phosphate solution. A heat treatment, conveniently at a temperature in the range of 2000C to 250 C, may be used to improve the stability of the deposit and to increase the hardness of the deposit.

If an anodic treatment is employed, this is conve nientlyofthe integral colour type with a highly coherent hard deposit of low porosity.

In the following description, reference will be made to the accompanying drawings in which: Figure 1 illustrates a joint made between two solid aluminium conductors; and Figure 2 is an exploded view of part of an aluminium conductor and a terminal for securing thereon using the technique of the present invention.

Referring to Figure 1,there is shown a ferrule 10 of aluminium which has been secured on the ends of two aluminium conductors 11,12 constituting cores of cables 13, 14 respectively, the ferrule effecting electrical connection between the conductors. The ferrule, before making the joint, comprises an aluminium tube having shaped inner and outer surfaces, the ferrule being of internal dimensions to fit over the conductor cores. The ferrule may be cylindrical but, in Figure 1, a sectoral ferrule is illustrated for joining sector shaped cores of a cable having three sector shaped conductors for a three phase power supply. More generally the ferrule may have a cross-sectional shape corresponding to that of the cores to be joined.

The ferrule, before the joint is made, is given an electroless or anodic coating, conveniently of a thickness in the range of 5 to 10 microns, as previously described. Either treatment provides a coherent brittle layer over the whole of the ferrule thereby making it suitable for cold welding without any need for cleaning before welding.

The cold welding is effected by indenting the ferrule into the conductor using an indenting die and a backing support die. A simple hand-operated or foot-operated tool may be used for this purpose. In the example of Figure 1, the indenting die has been applied four times to produce four indentations 15.

The number of indentations in general will be determined by the mechanical strength desired for the completed joint. The die projection has a height and a width of 1.5 to 2.0 times the thickness of the ferrule wall. This gives the ncessary pressure and surface stretching of the aluminium in the region of the conductor/ferrule interface to achieve cold welding over a substantial area.

Figure 2 illustrates the application of this technique to cold welding of an aluminium terminal on the end of an aluminium conductor. In this figure, which is an exploded view showing the conductor and terminal before joining, the conductor 20 is shown as protruding from the end of a cable 21. The ferrule 22 is formed with an integral palm 23 which typically has bolt holes 24 for bolting to, for example, a busbar. The terminal comprising ferrule 22 and palm 23 is treated, as described above, to have a brittle coating. Most conveniently the electroless treatment is employed as this gives the palm surface a suitable contact face for securing by bolting to a conductor such as a busbar. If anodic treatment is employed, it is prudent to mask the palm to avoid oxide build-up and the palm surface must be prepared in the conventional way for bolting to the conductor. The ferrule 22 is put over the conductor 20 after the latter has been abraded with a coarse rasp or similar abrader on the upper surface where welding will take place. This welding is effected using an inde noting die as previously described.

Claims

1. A method of effecting an electrical connection between an aluminium ferrule and a solid aluminium element fitting within the ferrule and comprising the steps of depositing a brittle layer on the surface of the ferrule by electroless or anodic deposition, abrading the conductor, on the surface where connection is to be effected, using a coarse rasp, and then compressing the ferrule onto said element to effect a cold compression weld between the ferrule and the element using an indenting die giving indentations to a depth and width of 1.5 to

2.0 times the wall thickness of the ferrule.

1. A method of effecting an electrical connection between an aluminium ferrule and a solid aluminium element fitting within the ferrule comprising the steps of depositing a brittle layer on the surface of the ferrule by electrodes or anodic deposition, and then compressing the ferrule onto said element using an indenting die giving indentations to a depth and width of 1.5 to 2.0 times the wall thickness of the ferrule.

2. A method as claimed in claim 1 wherein electroless deposition is employed and wherein the deposited layer is stabilised and rendered more brittle by heating to a temperature in the range 2000C to 250 C.

3. A method as claimed in claim 1 wherein anodic deposition of the integral colour type is employed.

4. A method as claimed in any of the preceding claims wherein the deposited layer has a thickness in the range of 5 to 10 microns.

5. A method as claimed in any of the preceding claims wherein the electroless deposition is effected using an acid nickel phosphate solution.

6. A method as claimed in any of the preceding claims wherein the ferrule has an integral palm to form a terminal for electrical connection to a conductor constituting said element.

7. A method as claimed in any of claims 1 to 5 and having a second element, each of said elements being an electrical conductor formed of aluminium, wherein the ferrule is compressed onto the two separate conductors after they have been inserted into the ferrule from opposite ends.

8. A method of effecting an electrical connection between an aluminium ferrule and an aluminium element substantially as hereinbefore described with reference to the accompanying drawings.

9. An electrical connection made by the method of any of the preceding claims.

New claims or amendments to claims filed on 18th October 1979 Superseded claims one New or amended claims: