How do you select filler metal (welding rod)?
Usually the filler metal is a close match to the base metal. Sometimes the filler metal will have deoxidizers added which will improve the weldmore than just a base metal match. Rod diameters vary from 1/16 to 3/8 inch diameter. The prefix R in the description of the oxy-acetylene welding wire means rod which is followed by two or three numbers designating the ultimate tensile strength of the as welded filler material in thousands of pounds per square inch (ksi). See Table 3-3.
Table 3-3 Oxyacetylene steel welding rods
Procedures and Material Selections
Before welding, remove all surface dirt, scale, oxide, grease, and paint. Refer to Table 3-4 for suggestions on welding common metals. See Figure 3-25.
Figure 3-25 Before welding, clean metal thoroughly to remove grime and mill scale.
Table 3-4 Information for welding various metals
SR = Slightly Reducing SO = Slightly Oxidizing N = Neutral
Figure 3-26 Be sure you have the right type flame for the job at hand. For additional information on torch flames see pages 55 and 56.
Here are the steps for beginning the OAW process.
•Put on your welding safety equipment: tinted safety goggles (or tinted face shield), cotton or wool shirt and pants, high-top shoes, and welding gloves at a minimum.
•Make sure the valves on previously used or empty cylinders are fully closed and their valve protection covers are securely screwed in place. Then remove the empty cylinders from the work area and secure them against tipping during the wait for a refill shipment. Secure the newly replaced or full cylinders to a welding cart, building column, or other solid anchor to prevent the cylinders from tipping over during storage or use.
•Momentarily open each cylinder valve to the atmosphere and reclose the valve quickly purging the valve; this is known as cracking a valve. Cracking serves to blow out dust and grit from the valve port and to prevent debris from entering the regulators and torch.
•With a clean, oil-free cloth, wipe off the cylinder valve-to-regulator fittings on both cylinders to remove dirt and grit from the fittings’ connection faces and from the fittings’ threads. Do the same to both regulators’ threads and faces. Remember, never use oil on high-pressure gas fittings. Oxygen at high pressures can accelerate combustion of oil into an explosion.
•Make sure reverse-flow check valves are installed on the torch or the regulators.
•Check to see that both the oxygen and acetylene regulator pressure adjustment screws are unscrewed, followed by threading each regulator to its respective cylinder. Snug up the connections with a wrench. Caution: Oxygen cylinder-to-regulator threads are right-handed; so are oxygen hose to-torch screw fittings. Acetylene cylinder-to-regulator fittings and acetylene hose-to-torch fittings threads are left-handed.
•Stand so the cylinders are between you and the regulators, S-L-O-W-L-Y open the oxygen cylinder valves. Open the oxygen cylinder valve until it hits the upper valve stop and will turn no further. Also standing so the cylinders are between you and the regulator, open the acetylene cylinder valve gradually and not more than 1 1/2 turns. If there is an old-style removable wrench on the acetylene cylinder, keep it on the valve in case you must close it in an emergency. Standing so that the cylinders are between you and the regulators offers some protection should the regulator fail and the housing and gauges explode.
Figure 3-27 With the tank valves closed, back out the pressure adjusting screws on the regulators. When opening the tank valves, stand to the side or behind the tank in case the regulator malfunctions and explodes.
•Look at the high-pressure—cylinder side—pressure gauges to indicate about 225 psi (15.5 bar) in the acetylene cylinder and 2,250 psi (155 bar) in the oxygen cylinder. Note: 1 bar = 1 atmosphere = 14.5 psi = 0.1 MPa. Cylinder pressures vary with ambient temperature. The pressures given above are for full cylinders at 70°F (21 °C).
•Purge each torch hose of air separately: Open the oxygen valve on the torch about three-quarters of a turn, then screw in the pressure control screw on the oxygen regulator to your initial pressure setting—about 6 psi (0.4 bar). After several seconds, close the torch valve. Do the same for the acetylene hose. Comment: We do this for two reasons, (1) to make sure we are lighting the torch on just oxygen and acetylene, not air, and (2) to set the regulators for the correct pressure while the gas is flowing through them.
Caution: never adjust the acetylene regulator pressure above 15 psi (1 bar) as an explosive disassociation of the acetylene could occur.
•Recheck the low-pressure gauge pressures to make sure the working pressures are not rising. If the working pressure rises, it means the regulator is leaking. Immediately shut down the cylinders at the cylinder valves as continued leaking could lead to a regulator diaphragm rupture and a serious accident. Replace and repair the defective regulator.
•Test the system for leaks at the cylinder-to-regulator fittings and all hose fittings with special leak detection solutions; bubbles indicate leaks.
TOOL TIP
Adjusting the Torch to a Neutral Flame
Open the acetylene valve no more than 1/16 turn and use a spark lighter to ignite the gas coming out of the tip. A smoky orange flame will be the result, Figure 3-28 (A).
Continue to open the acetylene valve until the flame stops smoking (releasing soot). Another way to judge the proper amount of acetylene is to open the acetylene valve until the flame jumps away from the torch tip, leaving about 1/16 inch gap (1.6 mm), Figure 3-28 (B). Then close the valve until flame touches the torch tip.
Open the oxygen valve slowly. As the oxygen is increased, the orange acetylene flame turns purple and a smaller, white inner cone will begin to form. With the further addition of oxygen, the inner cone goes from having ragged edges, Figure 3-28 (C), to sharp, clearly defined ones. The flame is now neutral and adding oxygen will make an oxidizing flame, Figure 3-28 (D).
If a larger flame is needed while keeping the same tip size, the acetylene may be increased and the oxygen further