CHAPTER IX

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.

[Illustration:

(_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.

[Illustration: 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.

[Illustration: FIG. 78.--One Method Used to “Back Up” Aluminum Work, when Welding. _A_ Represents a Sheet of Copper; _B_, Asbestos Cement.]

(=126=) The use of clamps, when working on aluminum, is not recommended on account of the great conductivity of heat and the weakening of the metal as it approaches the melting-point. Pressure of any kind is not desired and the operators who attempt to use clamps will regret it sooner or later.

(=127=) In aluminum work contraction and expansion take place the same as in other metals, only to a much greater extent, and greater allowances must be made. However, the same rules can be applied when determining whether work should be preheated or not, for if the ends are free to move, the work can usually be accomplished without preheating, whereas if confined, it will be necessary. When preheating is necessary the whole piece must be treated in the same way, regardless of the size. If only part of the work were preheated and the balance left exposed, it would be almost impossible to avoid warpage and shrinkage strains, which would render the work useless. Always preheat the entire piece if any portion requires it.

(=128=) Great care must be exercised when setting up aluminum work for preheating. Its weight should be distributed equally on whatever support is used, so that there will be no danger of any one part sagging, thereby throwing the whole piece out of alignment. A good way of accomplishing this is to lay fire bricks on their flat side, in such a manner that the weight of the work will be fairly well distributed. Then put a daub of clay or asbestos cement on each brick and press the aluminum piece down on this cushion. This will overcome the use of shims and other methods used for jacking up the work, which are unreliable.

(=129=) If charcoal is to be used as a preheating fuel, an oven of fire brick should be built up with draft holes in the bottom layer of brick, as described in the chapter on Preheating. A layer or two of charcoal is then ignited. The oven is then covered with asbestos paper or a piece of sheet metal. Asbestos paper is preferable as the metal becomes very hot and is apt to burn the operator. After the fire has received a good start, additional charcoal is added until sufficient heat is obtained. This can be determined by sprinkling a little sawdust on the surface of the aluminum, and if it chars readily, the work is ready to weld. Other methods have been outlined previously, any or all of which may be used in learning this heat. In executing the weld as little of the work is exposed to the air as possible, in order to hold a uniform heat and not permit any part to become chilled. At the completion of the weld the oven is covered over, the openings in the bottom row of bricks are stopped up, and the piece allowed to cool with the dying fire. The charcoal process is the slow but sure method of handling preheated aluminum work, and is always recommended.

(=130=) When preheating aluminum with torches burning kerosene or gas a different kind of oven is built, as previously described in the lecture on Preheating. No openings are left in the lower row of bricks and the oven is built very much closer to the work being preheated. As the object is to confine as much heat as possible and have a uniform temperature throughout, it is not desirable to have such ovens loosely constructed. If the bricks are irregular, a double wall can be built with a layer of asbestos between them. Such a procedure is always recommended if time and bricks permit. A hole is left in one end of the oven for the preheating torch flame to enter. On aluminum work the flame is never played directly upon the metal. A baffling plate of metal or fire brick is used to distribute the flame around the sides of the piece and very satisfactory results may be obtained by preheating in this manner.

PART THREE.--ALUMINUM WELDING

(=131=) Many times aluminum crank cases which have large holes punched in them and parts missing are brought to a welder for repairs. A question arises as to whether it is best to back up these holes and fill in the missing parts with a filler-rod as the welding progresses, or whether these parts should be cast separately or cut out of another crank case. It will generally depend upon the size of the hole, as to the desirable procedure in a case of this kind. It must be remembered that if the casting and welding are to be done at one and the same time each additional layer of metal must be fused to the last layer and that in reality a great deal of welding is necessary. In addition this added metal must be fused to the crank case. On small holes, perhaps two or three inches in diameter, this method is recommended, but if the hole is much larger, it is best to cast a piece and then weld it in, for in this instance there is only one line of weld to look after.

(=132=) On aluminum work it is proper to weld from the closed end of a crack toward the open, whether the piece has or has not been preheated. This is true also of all other metals, for if the weld were to be started at the open end and worked backwards there would certainly be internal strains set up, which would be undesirable. If it is not clear which end is the open one, the operator should stop a moment and figure it out.

(=133=) Were a suspension arm of the U type on an aluminum crank case to break about three or four inches from the body of the case, it could be welded in place without dismantling the motor, if handled properly. Free access must be had to the line of break, so that the operator can manipulate his flame at whatever angle he thinks best. Due to the contraction and expansion, which may throw the piece being welded out of alignment slightly, it is best to blank the bolt hole at the end of this suspension arm and face it off, before the piece is welded in position. Later a new hole can be drilled which will line up accurately with the frame, and the welder will not then have to worry or attempt to return it exactly to its former position. In order to keep the case itself as cool as possible, wet asbestos should be packed around it, near the broken arm, so that too much heat will not be absorbed by it. The broken end is then tacked in position at two or three places and the weld started. On such a problem the puddle system will be found best, for both horizontal and vertical welding are to be done, as well as some overhead. As flux causes the metal to flow, it is rather difficult for the beginner to apply it to vertical and overhead work. The puddle stick should work through the metal its full thickness and eliminate every possible trace of the break, digging out the old metal where dirt is found, and adding new metal for reinforcing. When one side has been welded and reinforced it should not be allowed to cool while the other side is being worked. The torch should be played upon it every now and then, in order that the whole line of weld will be at approximately the same temperature; otherwise, the weld may break in cooling. The ease with which aluminum is puddled together, which many welders have likened to the children’s method of making mud pies, seems so simple to the beginner that he cannot see where the strength comes from when cooled. On account of this, he invariably works his aluminum too long. After welding a few test bars of this metal and breaking them in the line of weld, many old welders will gain confidence upon seeing the results of their own efforts.