ROAD AND WORKSHOP by Handyman
Page 49
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Arc Welding Hints— Copper and Bronze
THE advantage of good conductivity permits many welding applications with copper or bronze, both in hot and cold working. Nevertheless, there are problems to overcome with the various grades; one such problem is gas and the danger of porosity as the work cools. This is caused by the gas" becoming trapped and held during cooling.
Again, as thickness increases, preparation is called for and this is on lines similar to other metals, single or double bevels needing an angle between 60' and 90'. Plate should be strongly tack welded, and the gap should allow for high expansion, therefore butting plates between in. and tin, should have a gap of not less than -k in. In dealing with sheet between 16 to 22 s.w.g., a good tip is to turn up the edge about..twice the sheet thickness, and "burn down" during the weld. This plus the added deposit, guarantees a good weld.
In fillet welds, normal fillet preparation is called for, and clamping is advisable. Bronze is an alloy of copper and tin, and can be welded satisfactorily with recommended phosphor-bronze electrodes— however, it should be borne in Mind that any trace of lead or solder on the work is almost certain to cause porosity. Therefore, if dealing with, say, heavy contacts or conductors in a starter motor. very through cleaning is necessary.
The electrode angle recommended is 90', but in practice it will be found advantageous to ease this a degree or so, even down to 85', as gas can be trapped. The slight easing of the angle, however, will avoid this happening. Heavy sec.tions should be preheated, or a higher current used to provide good general beat, as heat travels very quickly in bronze or copper, and it is just as quickly lost. Here a slower rate of travel may be necessary, to hold the heat in the weld area. And it is important that this operation is watched rather closely to avoid porosity.
Originally, copper-silicon alloys were mainly welded with a carbon arc, but lately this alloy has had special attention from the electrode manufacturers, and good results are now obtainable with metallic arc and the coated electrodes. Very favourable reports have been made in connection with a rod by Stubs Welding Ltd. This electrode is suitable for bronze, copper and copper alloys; the Stubs number is 32 and its colour is natural copper. This rod has easy slag removal, and work up to in. thick does not require preheating.
There is one important point here that must, be mentioned: the rod described should be used on d.c. positive pole current, Which means, of Course, that the ordinary welding transformer is unsuitable, and the machine needed is a welding rectifier or motor-driven generator. The Stubs 32 electrode is available from 12 to 4 s.w.g., current for 12 s.w.g. being 70 amp., increasing to 220 amp. for the heavy 4 s.w.g.