Oxy-acetylene welding manual

by Lorn Campbell

Part Two.—WELDING OF CAST IRON

(76) Before commencing to weld, or even turning on the gas, it is well to see that all preparations have been made and all materials on hand to bring the weld or whatever job it may be, to a finished state.

(Courtesy of Ben K. Smith, U. S. Welding Co.)

Fig. 49.—This Locomotive Cylinder was Welded at the Saddle, near the Frame.

(77) As a specific example of a simple welding operation let us consider that two cast-iron bars, measuring one by six inches and twenty-four inches long are to be welded end to end. To start with it would be necessary to “V” off the ends that were to be joined at an angle of about 45 degrees, leaving about one-eighth inch along the bottom edge to line the metals up with and to see whether they are in proper position. If the bar were to measure exactly forty-eight inches when finished it would be necessary to move these bars apart about one-sixteenth of an inch in order to provide for their contraction. It is assumed that the weight of the bars would be sufficient to prevent their pushing apart when the line of the weld is brought to a molten state and that the expansion will be taken care of within the weld. The bars after being lined up are ready for welding, but there are such things as filler-rods, flux and goggles that are necessary to have on hand before starting to work. It is well to have a few fire bricks, a little asbestos paper and a bucket of water convenient, in case these things are needed. The acetylene gas should then be turned on and ignited. A sufficient pressure should be passing through the regulator, when using a medium, or high-pressure apparatus, to cause the flame to leave the torch tip about twice the distance of the diameter of the orifice of that particular tip. Then turn on the oxygen until a neutral flame is obtained. On some torches it is necessary to make a second adjustment by turning on a little more acetylene gas and still more oxygen, until a goodly sized neutral flame results. Apply the flame to the pieces, so that the neutral flame will just lick the surface of the metal. Move the torch slowly forward and backward on each side of the “V” until the two edges are a dull red color, or better still a bright cherry red, then hold the torch stationary until the metal in the “V” nearest to the operator commences to melt. Then bring the filler-rod end in contact with the flame to get it heated and plunge it into the flux which should be near at hand. Enough flux will adhere to break up the oxides and by placing the rod between the flame and the metal, enough flux will be introduced to allow fusing of the metal. Proceed in this manner until the metal in the bottom of the “V” is properly fused throughout its length. Do not add the filler-rod, up to this point unless necessary. In holding the flame, see that the preheating flame will heat the parts yet to be welded. The weld should be made away from the operator. After the metals along the bottom have united and a good foundation has been obtained, then start the weld at the beginning once more, working the flame across the piece, in the same manner as before; bringing the metal to the molten state and stirring the filler-rod in it. As the filler-rod melts, the amount of molten metal naturally increases and the flame is moved along the weld as fast as the metal is added. It is important that the metal is in a molten condition. It is almost impossible to get too much heat on this type of work. Build up the weld slightly higher than the original piece. It may be found in finishing up the corners that the velocity of the gases or the force of the flame will be sufficient to blow the melted metal away. This may be overcome by directing the flame at a different angle, and will cause no difficulty after a little practice. Trouble, too, may be experienced on thin cast-iron sections by having the metal collapse through the force of the flame, but this can be remedied in the same manner. While the weld is still in a heated condition, it is possible to finish it by scraping the surplus metal off with the side of the filler-rod, the chill of which has been taken off before it is allowed to come in contact with the molten metal. Another popular method that will produce even better results is to use a very heavy rasp file to bring the weld down to the measurements desired. During all of the previous operations the flame never leaves the line of weld. When the weld is completed, the torch is shut down by turning off the oxygen first, and then the acetylene, and the welded bar is covered up to prevent its cooling too rapidly.

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.)