Oxy-acetylene welding manual

by Lorn Campbell

Part One.—ALUMINUM WELDING

(117) So far as the actual fusion of aluminum is concerned, it is probably more easily learned than any other metal, but on account of the rapid conductivity of heat and the loss of most of its strength when heated, aluminum has caused much concern among oxy-acetylene welders.

(118) There are two methods used in welding aluminum, the flux method and the puddle method. The puddle system gets its name from the use of a puddle stick or spoon-like rod which is used to stir the metal together, and is very satisfactorily used on all cast aluminum. The flux method is applied to both cast and sheet aluminum and it is so-called because a flux is used to break up the oxide along the line of weld. The discussion to follow applies only to cast aluminum. It is in this metal that most interest is centered, as the welding of sheet aluminum, such as is found in automobile bodies and some cooking utensils, is not encountered in the ordinary run of work.

(Courtesy of the Torchweld Equipment Co.)

Fig. 76.—Showing Aluminum Crank Cases Before and After Welding.

(119) When working with the flux method about the same sized tip is used as when working on cast iron. This is applied to the line of weld and held there until the oxide on the surface commences to wrinkle and small globules of a mercury-like appearance form on the surface. When heat is introduced in aluminum it is transmitted throughout the piece in the same manner as occurs in copper and brass, therefore it will require much more time to heat the work than the same sized piece of cast iron or steel. As soon as the weld assumes the condition mentioned, fast work is necessary or the metal will collapse, for it loses most of its strength when heated to this condition. The end of the filler-rod bearing the flux is brought down on the metal and immediately the surfaces will clear up and run together, like so much mercury. The torch is instantly jerked away and applied farther along the weld. The theory of this reaction is that the heavy aluminum oxide is the only thing which prevents the metal flowing together when heated, and as soon as the flux is introduced this oxide will be destroyed along the line of weld and a fusion of the metal effected. This actually takes place, providing enough heat has been introduced to permit this reaction to penetrate the depth of the weld. The flux contains the chemicals necessary to cause this reaction if the metal is in the right condition. There are many welders who do not use sufficient heat and blame the faulty results upon the flux. On the other hand, there are many fluxes which are absolutely useless in performing a function of this kind. The chemicals necessary in compounding a good flux for this class of work are expensive and therefore this flux cannot be procured at a low price. When the weld is finished and cooled the surface should be scrubbed with soap and water to remove all traces of the flux, otherwise a corrosion may occur a month or so afterwards, and while it may not affect the weld in any degree, the owner of the piece may not be pleased at the sight. It is therefore advisable to remove all traces of flux used on aluminum work.

(120) The puddle system differs from that of the flux, insomuch that when the metal has been brought to the same heat, where the flux has been applied it will be found that the metal is really in a pasty condition. It can be stirred together and the break entirely eliminated by the use of a puddle stick, either of a pointed or a flat spoon-shape design, as shown in [Fig. 77]. During this puddling stage, the torch is usually held in the left hand with the flame some distance away from the work, only introducing enough heat to keep the puddle pasty. The puddle stick is handled by the right hand and when extra metal is needed the puddle stick is laid aside and the aluminum filler-rod is picked up and worked into the weld. When sufficient metal has been added the puddle stick again comes into play and can be used in stirring the metal together and finishing it off in the desired manner. Reinforcing the weld will apply to aluminum the same as every other metal, and a very neat job can be made after a little practice with the puddle stick. At times some of the aluminum may adhere to the stick, which is made from a quarter-inch piece of steel filler-rod, but this can be removed by scraping it upon the fire bricks which should be in the vicinity of the weld.

Fig. 77.—“Puddle-sticks” for Welding Aluminum.

(121) There are two kinds of filler-rods used in aluminum welding. Both are aluminum, but one is cast and the other is a drawn rod. This same difference will also be noticed in bronze filler-rods, and there has been much discussion as to which is the desirable one to use. Neither of them is supposed to be 100 per cent pure aluminum, as such a filler-rod does not give the desired results under the action of the flame. A matter of from 90 to 95 per cent aluminum, with 5 per cent to 10 per cent of copper present as an alloy, is found to make a stronger and more successful weld. It is recommended, if possible, to use the drawn rods whenever available; for a weld at best is only a casting, and if this casting can be made from virgin metal, rather than recast from metal which has been cast many times and the contents not known, it is thought that the results will be far more satisfactory. A weld made with such a filler-rod, care being taken to work out the oxides, will compare very favorably with the strength of the original metal and in many instances a reinforcement will make it much stronger.

(122) To combine the two methods of welding aluminum is not recommended. If the flux were stirred up inside the weld with a puddle stick an unsatisfactory weld would result, so they are to be kept entirely separate. It is not necessary to “V” out aluminum for the same reason as other metals are “V-ed” out. When it is in workable condition it can be puddled and stirred about as desired. It is well, however, to “V” out slightly for the sake of marking the line of weld. When aluminum is heated up, the expansion which occurs may close up the crack, which was previously quite visible, in such a manner that it cannot be located without much loss of time. Ordinary chalk or soapstone, if available, may be used to mark any preheated work, but the use of a chisel along the line of weld is the most reliable method.