PUDDLE
For the next practice welds, hold a 1/16-inch rod as shown in Figure 3.12. Insert the rod into the leading edge of the weld puddle until a few drops flow into the deposit. Then pull the rod back slightly and advance the torch a small amount, allow a puddle to form, and repeat the process of inserting the rod.
Fig. 3.13. To fill gaps you need two pieces of steel 9 inches long and 1/8 inch thick. Place them 1/16 inch apart at one end and 3/16 inch apart at the other end. Make a tack weld at the narrower end first and then tack weld the larger gap. Advance the torch tip as the weld progresses. (Figure adapted from ESAB’s Oxyacetylene Handbook with sketch by Walter Hood)
EXERCISE 3: ADD FILLER WELD BETWEEN TWO PLATES
Filling gaps is the next thing to learn. Place two pieces of steel approximately 9 inches long, 3/32 to 1/8 inch thick, 1/16 inch apart at one end and 3/16 inch at the other. Make a tack weld at the tighter end and tack weld the end with the 3/16-inch gap. The next tack weld is somewhat more difficult because of the greater gap. Move the flame slowly from one edge to the other. As the edges melt, place a small amount of filler metal on the edge and allow it to cool slightly. This is usually best performed when the flame is on the opposite side of where the metal is added. Increase the size of the tack by adding more filler rod.
After tack welding the piece, start at the tighter end and add filler as you did for the tack; move the flame in a small arc from side to side. Advance the torch tip as the weld progresses.
Figure 3.14 is a view of the middle of the joint. The technique becomes obvious as the weld progresses. More time is spent at the edges as the torch is moved side to side. Too much time spent in the middle of the joint causes the metal to burn through. The end objective is to have the weld bead drop through slightly at the bottom while being reinforced about 1/16 inch on top.
Test the weld quality by cutting a section about 3 inches long and placing one plate in a vice and striking the other with a hammer. You should be able to bend it at a 90-degree angle without breaking it.
Fig. 3.14. This is the perspective in the middle of the joint. The technique becomes obvious as the weld progresses. More time is spent at the edges as the torch is moved side to side. Too much time spent in the middle of the joint causes the metal to burn through. (Figure adapted from ESAB’s Oxyacetylene Handbook with sketch by Walter Hood)
Fig. 3.15. To weld heavier sections use two pieces of 1/4-inch-thick steel. Bevele each plate at a 45-degree angle with a 1/16-inch nose. Concentrate the flame on melting the square-edge nose and forming the underbead. (Figure adapted from ESAB’s Oxyacetylene Handbook with sketch by Walter Hood)
EXERCISE 4: ESTABLISH ROOT WELD
Heavier sections can be welded using a similar technique (but with the appropriate tip size and filler rod). Use two pieces of steel 1/4-inch thick. Bevel each plate at a 45-degree angle. Use a grinder to make a flat nose at the bottom about 1/16 inch in width. This leaves a 90-degree bevel 3/16 inch deep. Assuming the test plates are about 9 inches long, gap them 1/8 inch at one end and 3/16 inch on the other.
Make tack welds on both edges as was done for the thinner sheet metal. Once the tack welds have been made, make a weld as before, but it should only fill up about half the thickness. This is the first of two weld passes. Focus on making a good underbead. The top edges of the plate should not have melted. The flame is concentrated on melting the square-edge nose and forming the underbead.
As the root pass approaches completion, the top corners of both pieces should still be sharp and unmelted. This first pass achieves complete root penetration and little else. The appearance of the top of the weld is not very important because it will be melted and covered by the finish pass. The puddle can be kept relatively small, which is also a help if the gap varies.
Make sure the bottom-squared nose is brought up to melting temperature before the weld puddle advances across them. Be sure not to add too much filler metal at one time.
Move the filler rod in and out of the weld puddle to control the rate of filler addition.
Move the flame across the joint, spending more time on the sides of the V, being sure they are melted up to about halfway up to the top edge of the plate.
Fig. 3.16. The objective of the first pass is to complete root penetration (here, the root pass is approaching completion). Keep in mind the appearance of the top weld is not very important. Move the flame across the joint, spending more time on the sides of the V so they are melted up to about halfway. (Figure adapted from ESAB’s Oxyacetylene Handbook with sketch by Walter Hood)
Fig. 3.17. With the second pass, keep the end of the rod in the puddle at all times. Rub the end against the solid metal below the puddle, maintaining a constant back-and-forth motion across the joint. When the flame is melting one side of the joint, the rod is pushing on the puddle on the opposite side. (Figure adapted from ESAB’s Oxyacetylene Handbook with sketch by Walter Hood)
EXERCISE 5: COMPLETE FINISH WELD
Make a second pass over the first one. A larger 1/8-inch-diameter rod can be used as the weld progresses slowly and more filler rod is needed. Start at the beginning and form a weld puddle and proceed to fill the joint completely.
Much more filler is required in this pass. Keep the end of the rod in the puddle at all times, actually rubbing the end against the solid metal below the puddle and keeping it in a constant back-and-forth motion across the joint. The flame should move in longer arcs than was needed for the root pass. It should dwell at the sides of the V so they are melted before the puddle moves forward. Use a sideways motion of the filler rod to move the puddle back.
When making this pass, heat from the weld puddle, not the flame, melts the filler rod. The flame and rod motion must be controlled because the flame is melting one side of the joint and the rod is pushing on the puddle on the opposite side. The width of the flame movement need not be as large as the rod movement. If the rod is not moved a sufficient amount, a weld undercut occurs. There may also be places where the weld bead did not reach the top surface of the plate, creating an underfill defect.
In Figure 3.18, a backhand technique (also called drag) is used for the second pass. The flame is angled toward the completed weld, and the rod is angled toward the finishing end. Although most oxyacetylene welding is done with a forehand or push technique (as shown in all previous illustrations) in some situations, a backhand technique may be desired. The rod and flame move in an oval pattern along the weld line. The rod moves backward as the flame moves forward. The finished weld has heavier ripples than a good forehand weld deposit.
Fig. 3.18. Make the second pass with a drag, or backhand, technique. Angle the flame toward
