Where practicable, one popular approach is to cover the mating and adjacent areas of the sections to be welded with weld metal prior to joining together. These pads laid down with minimum restraint ensure a good bond over a wider area than the final joint thus making up for the lower tensile strength of the metal beneath. Pads sometimes include mild steel studs at intervals in drilled and tapped holes to incorporate a mechanical linkage beneath the welded surface.

Low hydrogen electrodes are sometimes used to advantage on dirty cast irons and here padding is usually essential. Cracks in the pads must be expected due to the hardening by pickup of carbon and such welds are generally reserved for compression loading areas.

The most common non ferrous metals in general industrial usage are copper and its major alloys, bronze (with tin) and brass (with zinc) and a range of aluminium alloys in casting and wrought shapes.

These metals are not as readily weldable as ferrous metals due particularly to their high heat conductivity (making local heat buildup to melting point difficult) and also to the fluxing actions required for good bonding and reduction of oxide inclusions.

Copper is used extensively for plumbing and electrical conductors. Unless fully deoxidized, fusion welds may prove porous. The most usual methods of joining are by brazing using oxyacetylene or carbon torch, and silver solder. It can be carton arc welded or for some heavy jobs a bronze arc electrode gives a satisfactory joint.

Bronzes and brasses are best tackled with the brazing or oxyacetylene fusion welding processes but the tin bronze electrode may also be employed usually with a substantial preheat to ensure better metal flow. High zinc brasses lose zinc under arc action producing copious white fumes so good ventilation is required. Fusion welding should not be attempted on leaded bronzes or brasses. The lead which is added for machining makes the weld hot short and is also a health hazard. It may be detected by its boiling action on spot melting a section of the joint under the gas torch.

Aluminium is being used increasingly in general fabrication because of its strength, lightness and durability usually in alloyed form. A popular casting alloy contains 5‑10% silicon and similar arc welding electrodes are available for use on DC. A good preheat is generally required. Oxyacetylene welding with similar filler rods and fluxes is also a handy maintenance workshop approach but care must be taken to remove the corrosive flux residues in each instance.

Argon shielded electric welding using non consumable tungsten electrode torches and hand added filler wires or automatically fed continuous coiled aluminium alloy electrode wires are the major industrial methods of welding this group.

WHAT IS THE METAL?

In the very early days of welding, when "fools rushed in", people were amazed when some welded articles "stuck together' ‑ and rightly so!

Today, with improved welding techniques,

electrodes and steels, the case of failure is usually the one for amazement. Industry in general is expecting and obtaining more out of welding than before, but with some cases of welded fabrication the original fabricator is well aware of the special materials employed and the electrodes and procedures required.

Unfortunately when the same equipment enters the jobbing shop for maintenance, modification or repair, this information is rarely available to the welder. It is hoped that the following may provide some lead to the materials used and some pointers on welding them. On many such occasions, it is the time and inconvenience which is important ‑ a conservative approach may in such cases be the quickest and cheapest in the long run.

Metals have been classified by industry into two broad groups: ferrous and non‑ferrous. The ferrous groups are those which contain iron as their basic constituent, such as steels and irons, and form the major field in which we are interested. The non‑ferrous metals and alloys ‑ the brasses, copper, aluminium etc., are used more for specialized applications and in general are not as readily weldable by the arc process, special techniques being required.

Some quick workshop checks are available which, while not infallible or as comprehensive as could be wished, can give a reasonable indication of most common metals in use and their subsequent welding needs. These include such aspects as common usage (e.g. automotive crankcases generally cast iron, some aluminium), process characteristics (cast, forged, die cast, rolled etc.) colour (silver, red, steel, grey), magnetism (non magnetic, strongly magnetic, etc) fracture (coarse or fine) and the spark test.

This latter test involves holding a section of the metal lightly against a grinding wheel (or vice versa) and observing the spark stream. All nonferrous metals do not produce any sparks with the exception of nickel which produces a minute indication of deep red sparks. The iron base alloys produce a stream of sparks of various intensities and characteristics determined by the alloying elements present, particularly carbon. We suggest a magnet, grinding wheel and some known samples are a worthy adjunct to any farm or jobbing workshop. With these scientific instruments and a list of characteristics such as indicated on pages 14 and 15, a little detective work can soon nominate a type of material sufficiently to repair weld it intelligently.

For example, as a suggested case, a piece of heavy equipment received from a quarry. If it is magnetic and big equipment it is most assuredly a steel or iron as a high nickel alloy is eliminated for economic reasons. If obviously of cast appearance, probably cast iron or cast steel. If subject to shock tension (ripper tyne) rather than compressive abrasive wear (such as a roll) then probably a cast steel. If relatively soft and tough and rolled section, probably little better than mild steel. Spark test assists in final determination. If, however, it is non magnetic or faintly magnetic in worked areas, a new range of possible alloys open up. On colour alone the non‑ferrous alloys are easily distinguishable and unlikely contenders in other than bearings or superficial components. Stainless steel is expensive and not very likely to be used and so austenitic manganese steel is the likely alternative. As a final check, if any doubt exists between the latter two, austenitic Mn steel will oxy‑cut and stainless steel will not.

Having determined the metal type, the selection of the electrode and welding procedure can now be made in the light of available materials and processes. When welding dissimilar metals it is a good general rule to choose an electrode most compatible with the more alloyed metal. When in doubt your WIA sales branch offers a free advisory service make use of this facility.