Oxy-acetylene welding manual

by Lorn Campbell

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.