weld and the rod toward the finishing end. Use a forehand technique for most oxyacetylene welding, but in some situations, a backhand technique is useful. (Figure adapted from ESAB’s Oxyacetylene Handbook with sketch by Walter Hood)
Project: Welding Pipe Practice
Although this series of welds shows welding larger-diameter pipe, it can be used for welding small-diameter tubes. The oxyacetylene welding process is still used to weld 4130 tubing for aircraft. My old friend Butch Sosnin taught sprinkler pipe weldors that oxyacetylene welding was ideal for small-diameter pipe welding, so it certainly should be considered.
Fig. 3.19. Welding a pipe is another useful exercise. The oxyacetylene welding process is still used to weld 4130 tubing for aircraft. An application of welding 1/2-inch-diameter 4130 tubing is discussed in Chapter 7. (Figure adapted from ESAB’s Oxyacetylene Handbook with sketch by Walter Hood)
EXERCISE 1: MAKE BOTTOM-TO-TOP WELD
Place tacks in the joint, as shown in Figure 3.20. With material thickness less than 1/8 inch, you can make the weld in one pass. Point the torch flame approximately toward the centerline on the pipe. Hold the filler rod tangentially to the joint. Make the weld from bottom to top, adding filler to the leading edge of the puddle. Completing the weld requires welding in the flat, vertical, and overhead positions. Stop the weld, repositioning your hand and start a puddle for each position.
Fig. 3.20. With pipe material thickness less than 1/8 inch, make the weld in one pass. Point the torch flame toward the centerline on the pipe. Hold the filler rod tangentially to the joint. The weld is made from bottom to top, adding filler to the leading edge of the puddle. (Figure adapted from ESAB’s Oxyacetylene Handbook with sketch by Walter Hood)
EXERCISE 2: MAKE TOP-TO-BOTTOM WELD
In Figure 3.21, the weldor is using a backhand technique, and the weld is made from top to bottom. There are certain situations in which welding out of position is necessary. In some welding circumstances, the flame is used to hold up the weld puddle. The aim is to keep the puddle from running onto metal that has not melted. As noted when backhand welding flat plate, the relative movements of the rod and flame are different from forehand welding. The rod and flame move in an oval path with one forward when the other is backward and vice versa.
Fig. 3.21. Use a backhand technique as the weld is made from top to bottom. There are times when welding out of position is necessary. Use the flame to hold up the weld puddle. Move the rod and flame in an oval path with one going forward and the other going backward. (Figure adapted from ESAB’s Oxyacetylene Handbook with sketch by Walter Hood)
EXERCISE 3: PERFORM OVERHEAD WELD
Welding overhead is not much different from welding vertically. Surface tension holds the molten metal up, as does the force of the flame. If forehand and backhand techniques are an option, a backhand technique can be used to start the weld at the top and move downhill. When the bottom is reached, a forehand technique is used to weld to the top. If you weld with only a forehand technique, start at the bottom and work up one side, change position, and work up the other side.
Fig. 3.22. Welding overhead is similar to welding vertically. Surface tension and the force of the flame hold up the molten metal. If forehand and backhand techniques are used, the weld can be started at the top and welded downhill with a backhand technique. When the bottom is reached, use a forehand technique to weld to the top. (Figure adapted from ESAB’s Oxyacetylene Handbook with sketch by Walter Hood)
Application: Oxyacetylene Welding Cast Iron
Oxyacetylene welding is very effective for repairing cracks in cast-iron parts. Some types of cast iron can be fusion welded, although with difficulty and the potential for cracking, while others cannot. However, they all can be braze welded. With this approach, the filler material melts and wets the cast iron, but that occurs well below the melting point of the cast iron.
Fig. 3.23. Oxyacetylene welding is very effective for repairing cracks in cast-iron parts. Some types of cast iron can be fusion welded, although with difficulty and the potential for cracking, while others cannot. However, they can all be braze welded.
Fig. 3.24. The finished brazed joint is sound and well wet into the cast iron. The brazing material is also very ductile. When the cast iron expands and cools as the part is heated and cooled, the brazing alloy can expand and contact as needed and does not excessively stress the cast iron.
Repairing an exhaust manifold is a typical example of this.
To simulate a crack repair job, a groove representing a crack was placed in the manifold. The weldor ground through the full thickness of the manifold and a V-joint was placed in it. In addition to the advantage of braze welding not melting the cast iron, it also requires heating the material to a high temperature. This essentially preheats the assembly and avoids high cooling rates. This high heating reduces the stress on the braze weld area when completed, so the brittle cast iron is less likely to crack.
AWS RBCuZn-C (58-percent copper and 41-percent zinc), a common brazing alloy, is used to braze weld this simulated crack. The white outside coating on the rod is a brazing flux, which provides good wetting of the cast iron. To further promote wetting of the cast iron, brazing alloy can butter the surfaces to be joined and this bridges the joint. In addition, it allows the wetting to be seen more clearly. The flux is applied to remove oxides from the cast-iron surface and promote wetting. There is sufficient coating on the rod so there’s no need for adding more. The brazing flux is available in a metal can. It’s applied to the joint or by dipping the bare rod into the flux as the braze welding progresses.
Fig. 3.25. Braze welding does not melt the cast iron, and also requires heating the material to a high temperature. This essentially preheats the assembly and avoids high cooling rates. Stress on the joined area is reduced as a result, so the brittle cast iron is less likely to crack.
The finished brazed joint is sound and wet into the cast iron. The brazing material is also very ductile. When the cast iron expands and cools as the part is heated and cooled, the brazing alloy can expand and contract as needed and does not excessively stress the cast iron. To be safe, the part is slow cooled after brazing.
Fig. 3.26. AWS RBCuZn-C, a common flux-coated brazing alloy, was used to braze weld this simulated crack. A flux is needed to ensure good wetting of the cast iron. It removes
