1. Field of the Invention
For aluminium as an electrical conductor material it is normally specified that the conductivity should exceed a certain minimum value. Usually, it is required that the conductivity should amount to at least 61 percent of the conductivity of annealed copper according to international standard (International Annealed Copper Standard). This means that small quantities of other elements in the aluminium, such as, for example iron and silicon, can be permitted. Sometimes a conductivity somewhat below the specified value can be accepted. This is particularly the case if other advantages are obtained, such as for example improved mechanical properties.
Aluminium as an electrical conductor material can be used, among other things, in cables, in wire for electrical machines and apparatus and in bars for, example, switchgears.
2. The Prior Art
When using aluminium as a material in electrical conductors, there are considerable difficulties in achieving an efficient, lasting contact between the conductor and connection devices, such as for example clamps and cable sockets. These difficulties are particularly pronounced if the contact between the aluminium conductor and the connection device is purely mechanical, for example when using a screw and clamp joint. Even if a good contact, that is one with low transition resistance, between the aluminium conductor and the connection device can be achieved in the attachment, it has been proved that the transition resistance increases in course of time, especially if the contact is exposed to heat and/or moisture. Efforts have been made to avoid the difficulties in different ways. Among other things, it is a well-known method to provide the aluminium surface with a coating of another metal, such as silver, tin, nickel, copper or zinc, which gives a low contact resistance to the connection device even when operated for a long period of time under varying conditions. This can be achieved for example by electroplating these metals on the aluminium surface. Also used is the method to connect a copper conductor to the aluminium conductor by means of cold-pressure welding where the conductor is to be brought into contact with the connection device. Another well-known way to try to prevent the contact resistance from increasing is to ensure that a required contact pressure is maintained all the time between the aluminium conductor and the connection device. This can be achieved by using a resilient connection device. The previously known methods either entail extra and expensive work operations or give in the long run an unsatisfactory contact with too high contact resistance between the aluminium conductor and the connection device.
Another problem with conductors of aluminium is to achieve predetermined properties in the produced product as a whole when the conductor is manufactured on a production scale. This is connected with the fact that especially the mechanical properties, such as tensile strength and elongation, are strongly dependent on the conditions during the metal working procedures.