How does oxyacetylene equipment perform the welding process?

It is a clear gas having a specific gravity slightly lighter than air at 0.906 (air = 1.000). Acetylene’s chemical formula, C2H2, indicates that each molecule of this hydrocarbon compound contains two carbon atoms and two hydrogen atoms.
Oxygen and acetylene gases when combined, in the proper proportions, in the torch handle’s mixing chamber, produce an approximately 5600°F (3100°C) flame at the torch tip. This flame melts the edges of the base metals to be joined into a common pool. Sometimes additional filler metal is added to the molten pool from a welding rod. When this common pool cools and the metal freezes solid, the joined metals are fused together and the weld complete.

What is Oxyacetylene Welding?
Oxyacetylene welding also known as Oxy-fuel Welding (OFW), includes any welding operation that uses combustion with oxygen as a heating medium. With this family of processes, the base metal and a filler rod are melted using a flame produced at the tip of a welding torch. Fuel gas and oxygen are combined in the proper proportions inside a mixing chamber in the torch. Molten metal from the plate edges and filler metal, if used, intermix in a common molten pool and join when cooling. Commonly-used fuel gases include acetylene, propylene, propane and natural gas.

The equipment used in oxyacetylene welding is low in cost, usually portable, and versatile enough to be used for a variety of related operations such as bending and straightening, preheating, post-heating, surfacing, brazing, and braze welding. Among commercially available fuel gases, acetylene most closely meets the requirements for all these applications. Cutting attachments, multi-flame heating nozzles and a variety of special application accessories add greatly to the overall versatility of the basic oxyacetylene welding equipment. With relatively simple equipment changes, manual and mechanized oxygen cutting operations can be performed. Metals normally welded include carbon and low alloy steels and most nonferrous metals.

What are some advantages of the OAW process?

  • Low cost
  • Readily portable
  • Excellent control of heat input and puddle viscosity
  • No external power required
  • Good control of bead size and shape
  • Fuel mixture is hot enough to melt steel.

List the steps for installation of oxygen and acetylene pressure regulators on full cylinders. Be sure to include all safety precautions :-

  • 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. This arrangement prevents putting the wrong gas into a regulator or torch connection.
  • 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.
  • Look at the high-pressure—cylinder side—pressure gauges to indicate about 225 psi (15.5 bar) in the acetylene cylinder and 2250 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.

What are the proper steps to shut down an oxyacetylene torch and its cylinders?

  • First turn off the oxygen and then the acetylene with the torch handle valves. Turning off the acetylene first can cause a flashback.
  • Turn off the oxygen and acetylene cylinder valves at the upstream side of the regulators.
  • Separately, open and re-close the oxygen and acetylene valves on the torch handle to bleed the remaining gas in the hoses and regulator into the atmosphere. Verify that both the high-pressure and low-pressure gauges on both regulators indicate zero.
  • Unscrew the regulator pressure adjustment screws on both cylinders in preparation for the next use of the equipment. The regulator screws should be loose but not about to fall from their threads.

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