(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.
Part Two.—ALUMINUM WELDING
(123) It will be noticed, when welding aluminum, that bright surfaces will oxidize immediately when exposed to the air. This action occurs perhaps faster on aluminum than on any other metal. With this oxide or scale present the metal will not run together nor fuse, no matter how much heat is applied. The metal may be molten on each side of an oxidized crack and at times will cause the line of fracture to even float, but if the oxide is not destroyed the metal will not fuse. As has been noted previously, two methods are used to destroy this oxide, namely, the flux method and the puddle system. On account of this exceedingly rapid oxidation, it will be found to the operator’s advantage to complete his aluminum welds as quickly as possible in order that he will have less of this oxide to combat. It will be found in using the puddle system that greater haste can be made by using the torch in the left hand, leaving the right free to do the puddling and to add whatever metal is necessary. In this method most of the success depends upon the operator’s skill in handling his puddle stick and puddling in additional metal. Generally the right hand can do this more rapidly than the left.
(124) It is well to learn how to make a successful weld from one side of the metal only, and while this will apply to all metals, it is especially advantageous in working aluminum. Where a small layer of metal has been added to one side of an aluminum job, such as a crank case, and it does not penetrate the entire thickness of the metal, when the other side is turned, and the flame applied to it, a difference in temperature and the loss of strength in this metal when heated will cause the first side welded to crack unless the operator is extremely cautious. Therefore it is always well to learn how to penetrate the entire thickness of the metal from one side and make a satisfactory weld in this manner.
(125) As previously stated, aluminum when melted loses most of its strength, and if not supported by some means or other the metal will collapse. On account of this it is advisable to back up aluminum work, when possible, whether the job is to be done cold or in preheated condition. The most successful manner of backing up is shown in [Fig. 78], wherein A represents a thin sheet of copper which has been fitted to the work, and daubs of asbestos cement shown at B will aid to some extent in holding the plate in position, but this alone should not be depended upon. A prop or fire brick, upon the top of which has been placed a cushion of cement, will serve as a good backing, but where this cannot be accomplished filler-rods may be bent in the manner shown in [Fig. 78]. These filler-rods are not of the springy type, but are of soft wire and the loop as shown is not for a spring effect, but merely to take care of the contraction and expansion of the wire. Copper is given a preference over most of the other sheet metals, because it can be peened with a hammer to any shape desired, and many odd shaped additions can be formed by its use.
