Disadvantages
•Not economical to weld thick pieces of metal compared with other processes
•Slowest of the welding processes
What metals can the OAW process readily weld?
•Copper
•Low alloy steels
•Bronze
•Wrought Iron
•Lead
•Cast steel
Aluminum and Stainless Steel
These metals are usually not welded using the OAW process, but they may be welded provided one or more of the following steps are taken: preheat, postheat, use of fluxes, or special welding techniques. The reason is that aluminum does not change color prior to melting, so it requires extra welder skill to control heat input. It lacks strength at high temperatures. And exposed aluminum has a very thin oxide layer that requires the use of flux and also the oxide surface does not let the welder see a wet-looking molten weld pool.
What are some basic safety procedures?
All construction projects require a group of safe practices, and welding is no exception. Chapter 1 covered general safety measures for welding, but there are additional practices and equipment that are specific to OAW processes.
Essential Pieces of Safety Equipment
•Non-synthetic fabric (cotton or wool) long-sleeved shirt buttoned to the top to prevent sparks from entering.
•Tinted welding goggles with minimum of number 5 shade lenses.
•Leather gloves.
•Spark igniter.
•Pliers for moving hot metal.
Figure 3-2 Leather gloves.
Photo courtesy of Hobart Welders.
Figure 3-3 Cotton welding shirt.
Photo courtesy of Hobart Welders.
Figure 3-4 Tinted welding goggles.
Photo courtesy of Hobart Welders.
Figure 3-5 Spark igniter for lighting welding torch.
Photo courtesy of Hobart Welders.
Preventing Accidents
•External eye injuries from welding or grinding sparks are prevented by using welding goggles, safety glasses, or safety shields.
•Internal (retinal) eye damage from viewing hot metal and the radiation being emitted during welding and while cooling (until the metal is no longer red), prevented by using a number 5 tinted lens.
•Burns from weld sparks and hot metal prevented by leather or heavy cotton welding gloves, fire retardant clothing, leathers or specially treated welding jacket or cape-sleeves and bibs when working overhead, cuffless pants, high-top leather shoes.
•Fume hazards from the vapors of metals and flux must be avoided by proper ventilation, fume filters, and welder air supplies to the welding hood.
•Fires from the welding process prevented by moving flammables away from the weld zone and having water or fire extinguishers close at hand.
16-Step Safety Plan
•Never use oxygen in place of compressed air.
•Never use oxygen for starting engines or cleaning clothing.
•Store and use acetylene and propane cylinders valve end up.
•Secure cylinders to prevent them from being knocked over in use.
•Use valve protection caps on cylinders while moving them.
•Use a striker to light an oxyfuel torch. Never use a match or cigarette lighter because these can can cause a large fire or explosion with the potential power of a half-stick of dynamite.
•Never leave a lighted torch unattended.
•When a cylinder is empty, close the valve and mark it EMPTY (MT).
•Do not attempt repair of cylinder valves or regulators; send them to a qualified repair shop.
•Never use compressed gas cylinders as rollers.
•Never attempt welding on a compressed gas cylinder.
•Keep power and welding cables away from compressed gas cylinders.
•Prevent sparks from falling on other persons, combustible materials, or falling through cracks in the floor.
•On old-style acetylene cylinders with a removable valve wrench, always leave the wrench in place when using the equipment so that it can be shut off quickly in an emergency.
•When transporting compressed gas cylinders by vehicle have the cylinder caps in place and secure the cylinders so they will not move around as the vehicle starts and stops. Never transport cylinders with the regulators in place.
•Never carry compressed gas cylinders inside a car or car trunk.
Welding Sealed Cylinders or Other Containers
Never weld on a sealed container regardless of its size. Even if the vessel is clean and empty, penetration of the shell could release hot gases from the interior. They could also drive the torch flame back towards the welder. If the cylinder is empty and contains no residual vapors, vent it to atmosphere by opening a valve, hatch, bung, or by drilling a hole. An even more dangerous situation results when the cylinder contains residual flammable vapors whether it is vented to atmosphere or not. This will almost certainly result in an explosion. Clean or purge the cylinder with an inert gas, then have it checked for explosive vapors by a qualified person. Vent it to the atmosphere and begin welding. In some cases filling the vessel with water or other liquid and welding below the liquid is acceptable, but this is an area for experienced, knowledgeable welders.
Ventilation
Make sure the welding area is well ventilated to draw the weld fumes away from the welder. Many fumes from the welding process are poisonous and must be avoided. Welding fumes from cadmium plating, galvanized sheet metal, lead, brass (which contains zinc), and many fluxes (especially those containing fluorine) are poisonous. They can have both immediate and long-term adverse health effects. Welding supply companies, welding equipment manufacturers, and materials suppliers will provide MSDSs (Material Safety Data Sheets) on request. Often they are available for downloading via the Internet from the manufacturer. They detail the hazards of materials and equipment and show how