(108) A “corrugated” patch has been brought out more recently than the “dished” patch, and as its name would indicate, it has corrugations around at least three of its sides. While a “dished” patch is limited in its scope and cannot be applied to square holes unless the square holes be cut round, the “corrugated” patch knows absolutely no limits as to size or shape. While its preparation is probably more difficult, yet its purpose is the same, that is, to take care of the contraction which takes place in sheets of metal where heat has been introduced. To prepare a “corrugated” patch, a piece of metal which is somewhat larger than the hole is taken and the corrugation is made by placing two rods on one side and somewhat separated and between them on the other side another rod. With this section of the patch heated to a red heat, a drop hammer is played upon it and a corrugation effected. Or an easier method is by the use of specially prepared dies, which will turn out a patch in quick order. It must be remembered that while the patch shown in [Fig. 74] is only for a very simple job, which is rectangular in shape, yet “L” shaped patches can be prepared and handled in the same manner. When the corrugation has been introduced into the patch, the latter is cut so that it will fit the hole, and it is tacked in position with the bellied sides out. The method used in applying a patch of this kind is to weld the uncorrugated side, then start up the corrugated side and weld for two or three inches, then play the torch upon the corrugation, adjoining the part welded, and slightly hammer to assist in the expansion of the same; then return to the weld, continuing it until the corrugation can again be played upon. By doing this, when finished the patch will be flat and no signs of the corrugations will be shown. While many patches of this nature are in use giving the very best service, the welder who looks upon the finished job cannot tell how it has been accomplished.
(109) While the methods here given seem only to apply to boiler work, they are not so restricted and can be applied to tanks and various vessels with success. However, when welding on tanks which have contained inflammable gases or gasoline the welder is cautioned to take every measure to safeguard himself, and while it is known that much work is being done on such jobs, it is not recommended and in fact quite the contrary. It is true that there are such methods as filling the containers with water; cleansing with live steam, and so forth, but the cautious man will refrain from working on these vessels even though such measures have been taken. Gasoline has a faculty of penetrating the pores of metallic surfaces, and although these vessels have been emptied and have remained so a matter of a year, the gasoline is still present to some extent, as is evidenced by the fact that as soon as heat is applied and the molecules of the metal are expanded, the gas is released in sufficient quantities to cause an explosion. This is not in one instance only, but in many, so it has been thought best to discourage any welding work on vessels which have contained gasoline at any time.
Fig. 75.—Working a Vertical Weld on Steel, from the Top Down.
(110) While it is possible to weld cast iron on the vertical, by the use of carbon blocks and so forth, the same kind of work can be accomplished on steel with much ease, without the use of any blocks, or materials other than the filler-rod and the welding torch. There are two methods of handling vertical welds; welding from the top down, or starting from the bottom and working up. The former seems to be condemned by those who have never tried it, on account of the carelessness which is apt to be used on work of this kind. However, for the beginner, it is thought advisable to teach this method, as there are many places where it can be used advantageously. The metal at the top of the seam, such as a broken automobile frame, or the like, is brought to a molten state and held there, not only by the velocity of the flame, but also by the filler-rod, as is shown in [Fig. 75]. With the choosing of a tip of the correct size, the melted metal can be held under control with much ease, after a little practice, and it is allowed to descend as soon as the metal below it is in the proper shape for fusion. The filler-rod is added continually, for it is never lifted out of the molten metal, merely stirred a little from side to side as it descends. None of the melted metal is allowed to precede the flame, and at all times the operator can see whether the edges to be fused are at the right heat. As soon as the bottom is reached, the weld can again be gone over if it is not thought strong enough, and reinforced as much as desired. As soon as the operator is familiar with this method, he will find that much more speed can be developed, less filler-rod lost and less lapping done than by building up from the bottom.
(111) In welding over head there is a tendency on the part of most welders to avoid the use of enough heat to bring their metal to a molten state, for fear that it will drop upon them. It must be remembered that lack of heat means poor welds and that the metal must be in a molten condition whenever the weld is to be made. As soon as a little practice is given to this kind of work, the welder will see that the melted metal can assume some proportions without dropping off, despite its weight. It has probably been noticed that on “sweating” water tanks drops of water accumulate on the bottom of the tank and do not fall off. It is the same sort of problem in the case of melted steel. The adhesion of the molecules and the surface tension are the forces that keep the metal from dropping.
CHAPTER VIII
BRASS WELDING
(112) It is difficult for the beginner to accustom himself to brass welding, especially on large work. While he has been taught to believe that brass has a much lower melting-point than iron or steel, yet when he comes face to face with the actual problem of melting it, he will find that it is necessary to hold his flame in contact with his piece much longer, on brass work than on either of the other two, before the melting point is reached. This can be accounted for by the great conductivity of brass. On cast iron and steel the heat was rather local, but on brass work it is transmitted to all parts of the piece as rapidly as it is introduced, and this absorbing process continues until practically the entire piece is near the melting point.
(113) Brass has for its base, copper to which an alloy of zinc has been added. Now the most difficult part of fusing brass work, is to add more metal from the filler-rod to the parts which are to be fused, without burning up any more of the alloy, than is absolutely necessary. Seeing that the copper and zinc have different melting points, it is a very difficult feat and requires considerable practice. Much of this trouble can be eliminated by the use of a filler-rod which has the correct proportion of alloy added, so that it may take care of and replace any that has been destroyed by the flame.
(114) Brass work is “V-ed” out when welding is to be done, in practically the same way as cast iron. Only under no circumstances should the ends of the parts be burned off, when “V-ing,” as the heavy oxide which is deposited on the remaining metal is very hard to combat with the welding flame. The ends of the work are brought to a red heat with the flame that is slightly carbonizing. This is held directly in contact with the work during the preheating stages, in much the same manner as on cast iron, and a small layer of carbon may be seen to accumulate around the weld. Now, in theory, this would seem the worst thing possible to have present, but in practice a small quantity of this soot acts as an aid in making the weld, besides making the flame less intense, which saves much of the alloy, from being burned when the fusion occurs. When the ends have become red hot, the same procedure is used as in working steel, except that the torch is given a slightly greater angle and a brass flux is used.