An investigation of some health hazards in an inert-gas tungsten-arc welding shop.

Inert-gas Arc Welding of Aluminium Aluminium is used widely in metal fabrication processes, chiefly on account of its lightness, the ease with which it may be cast, and its extreme ductility. It is also highly resistant to corrosion, owing to the formation of a protective film of oxide on the surface of the metal. This latter property, however, becomes a disadvantage when it is desired to weld the metal, as the oxide film hinders consolidation of the metal on fusion, and even when broken down it re-forms almost instantaneously in air. Aluminium may be welded by either gas or arc processes, but arc welding is more satisfactory as the area over which the heat is generated is smaller and the speed of welding can thus be increased. The thermal conductivity of aluminium is high, being five times greater than that of steel, and hence with arc welding distortion and any tendency to crack are reduced. With both gas and arc welding the oxide may be dispersed by means of fluxes, but the disadvantage of this procedure is that the [ flux residues are corrosive, and after completion of the weld thorough cleaning of the metal is essential. Joints have thus to be so designed ! as to avoid trapping flux. \ These problems have led / 'i to the development of forms of arc welding which utilize an inert-gas arc (a) shield, usually of argon or helium. This gas shield allows the arc to disperse the oxide film, and by the exclusion of oxygen prevents it from being reformed. The use of these welding methods gives greater freedom in design, and the welding torch may even be used to form a weld inside a partly sealed container. As these welding methods are capable of automatic operation higher welding speeds may be achieved, and this feature, together with the use of higher welding currents than are employed in manual welding, enables welding to be carried out on thicker metal than would otherwise be the case. Two main types of inert-gas shielded welding are used, and are shown diagrammatically in Figs. la and lb. The inert-gas tungsten-arc method (Fig. Ia) uses a non-consumable tungsten electrode for producing the arc, and the welding is normally carried out by the use of a filler rod of aluminium.