Quantcast BACKHAND WELDING

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Figure 15-32.—Forehand welding. Figure 15-33.—Backhand welding. welding rod back and forth in opposite semicircular paths, you balance the heat to melt the end of the rod and the side walls of the joint into a uniformly distributed molten puddle. As the flame passes the rod, it melts off a short length of the rod and adds it to the puddle. The motion of the torch distributes the molten metal evenly to both edges of the joint and to the molten puddle. This method is used in welding most of the lighter tubing and sheet metals up to 1/8 inch thick because it permits better control of a small puddle and results in a smoother weld. The forehand technique is not the best method for welding heavy metals. BACKHAND WELDING.—In this method the torch tip precedes the rod in the direction of welding, and the flame is pointed back at the molten puddle and the completed weld. The end of the rod is placed between the torch tip and the molten puddle. The welding tip should make an angle of about 45° to 60° with the plates or joint being welded (fig. 15-33). Less motion is required in than in the forehand method. the backhand method If you use a straight Figure 15-34.—Four basic welding positions. welding rod, it should be rotated so that the end will roll from side to side and melt off evenly. You may also bend the rod and, when welding, move the rod and torch back and forth at a rapid rate. If you are making a large weld, you should move the rod so as to make complete circles in the molten puddle. The torch is moved back and forth across the weld while it is advanced slowly and uniformly in the direction of the weld. You’ll find the backhand method best for welding material more than 1/8 inch thick. You can use a narrower “V” at the joint than is possible in forehand welding. An included angle of 60° is a sufficient angle of bevel to get a good joint. It doesn’t take as much welding rod or puddling for the backhand method as it does for the forehand method. By using the backhand technique on heavier material, it is possible to obtain increased welding speeds, better control of the larger puddle, and more complete fusion at the root of the weld. Further, by using a reducing flame with the backhand technique, a smaller amount of base metal is melted while welding a joint. Backhand welding is seldom used on sheet metal because the increased heat generated in this method is likely to cause overheating and burning. When welding steel with a backhand technique and a reducing flame, the absorption of carbon by a thin surface layer of metal reduces the melting point of the steel. This speeds up the welding operation. WELDING POSITIONS.—The four basic welding positions are shown in figure 15-34. Also shown are four 15-25



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