Significance of surface preparation for bolted aluminium joints

For satisfactory performance of bolted joints using aluminium busbar, particular attention must be paid to preparation of the mating surfaces. The paper describes abrasion tests on aluminium to establish an efficient method. For site use a special wire brush is proposed whereas for factory prepared items, aluminium oxide shot blasting is recommended. The benefit of greasing surfaces prior to clamping has been confirmed. Load-spreading washers are advantageous in ensuring stable joints when allied to good surface-preparation techniques but more specialised clamping arrangements may be necessary if adequate surface treatment cannot be assured. A study of the degradation of alunfinium contacts indicates that the phenomenon of metal-metal adhesion is responsible for maintaining low-resistance joints despite considerable reductions in the clamping load due to creep and differential expansion. The reduction in load does, however, render the joint more susceptible to the effects of temperature cycling and external mechanical forces and this is particularly evident with poorly prepared surfaces