Oxy-acetylene welding manual

by Lorn Campbell

Part Three.—WELDING OF CAST IRON

(78) Problems in expansion and contraction should not be difficult, if it is remembered that heat causes expansion and the withdrawal of heat, or cooling causes contraction. As previously stated, when the ends of the pieces which are being welded are free to move, there is not much danger of having contraction strains set up. Where the ends are confined, measures must be taken to overcome this. In welding large pulley wheels, for example, it may be advisable to do the job without taking time to preheat. Breaks may be in evidence at any part of the wheel and generally the ends are confined, such as in the case of a spoke. If it is borne in mind that the expansion will take care of itself, the contraction is the only consideration, in a case of this kind. The welder will see that if he can spring the edges apart a sufficient amount to provide for the spoke coming back to normal when welded, he will have no difficulty. The way to proceed in a case of this kind would be to open the rim by sawing it and then introduce a jack or some sort of a wedge between the hub and the rim. This will open the crack in the spoke the amount desired. As soon as the weld is executed and while still hot, the jack is removed to permit the rim being drawn in. Later the rim can be welded, by introducing jacks between the spokes and the same procedure followed. It always must be remembered that provision must be made for the contraction, even though it be only one thirty-second or one-sixteenth of an inch. The distance will depend entirely upon the welder, as some operators use small tips and cover a small area, while others employ larger tips and cover twice the area. It is therefore impossible to set any specific distance and each welder should try to figure this out for himself.

(Courtesy of Torchweld Equipment Co.)

Fig. 50.—Large Cast-iron Gear Wheels. Although the Face on These Gears Measured 10 Inches, New Teeth were Added by Blanking In, as Shown in the Right-hand View, and Later Machined.

(79) There are many jobs not of a preheating nature that at times cause perplexity on the part of the welder. A good example of this is a cast-iron gear wheel. A number of its teeth have been broken out. Now there are three very common ways of building up or repairing such castings. First by aid of carbon blocks, cut to form and the teeth cast in by the use of the torch; second, by blanking in the space between the teeth and then sawing out the individual tooth or cutting it out with a milling machine or shaper; third, by building up each tooth with the welding rod and torch, and later dressing it down with a file. One very important point must be uppermost, when dental work on gears is being done, a good foundation is necessary, for regardless of how well the tooth may be shaped, if it is not firmly secured to the wheel itself, it will be of very little value. Another very important point is in the finishing of such gears, to see that the teeth which have been added correspond in the pitch and mesh exactly as the others do. The importance of seeing that things of this nature are machined correctly should not require mention, but it has often been found that machinists are very careless about finishing this kind of work and if anything goes wrong, the welder is naturally at fault. Therefore it is always well to put the gears which have been welded back into place and turn them over slowly by hand to see that they are in good condition before the power is turned on. In allowing this kind of work to cool after it has been welded, some operators permit it to be hurried, with the result that there may be hard spots to confront the machinist when finishing. If he ruins one or two of his cutters he will naturally frown upon all welding work. It is therefore desirable for this and many other reasons to have the weld come out as soft as possible, and great care should be exercised in cooling. Any weld that is subjected to machining, allow it to cool slowly in slack lime, in ashes, or cover it securely with asbestos paper. Occasionally it may be found difficult to find sections of carbon blocks which will take care of a job of this kind. Many welders who have had to run around the country, and do jobs in isolated places, have found that the carbon centers, from the ordinary dry cell batteries, which may be found practically everywhere in a discarded condition, can be shaped on an emery wheel and patched together in a manner that will permit their use. However, when such are used, it is quite necessary that they be heated a little with a torch beforehand, in order to drive out any chemicals or acids that may be contained in them. Unless these chemicals are removed, the molten metal coming in direct contact with them might be injured to a considerable extent.

(Courtesy of the Oxweld Acetylene Co.)

Fig. 51.—This View Shows new Teeth being Welded in an 8¹⁄₂-ft. Cast-iron Gear, Weighing over 5 Tons. Note the Improvised Preheating Oven.

(80) Ofttimes there are castings upon which parts wear off in a very short time. There may be very little strain upon these parts, yet the constant wear will weaken them in time. It is well to remember the action of a carbonizing flame when executing work of this kind. Introduce an excess of acetylene when finishing up the work. It will be found that with a strongly carbonizing flame, carbon will be taken up by the molten metal and the finished weld will be considerably harder and will wear longer than if it were executed by a neutral flame. An abrupt cooling will chill the metal on the surface and make it wear longer than it would otherwise.