Also known as:
-Oxy/Acetylene
-Gas Welding
-Oxy/Fuel Welding
Oxyfuel Gas Welding (OFW) is generic term for any type of welding performed with gaseous combination of oxygen and fuel. The most common such fuel is acetylene. Oxygen Acetylene is the only gas combination that burns hot enough to weld steel. It is also versatile, with applications that include welding (of many types of metals including steel, stainless steel, and aluminum), brazing, cutting (cutting of plain carbon steel only) and heating.
The setup for OAW involves two cylinders: one for acetylene and one for oxygen. The oxygen cylinder is taller and thinner than the acetylene cylinder, indicating storage of oxygen at higher pressure.
Acetylene gas is a highly unstable hydrocarbon with the chemical formula C2H2. The two carbon atoms are triple-bonded to each other, with each also having a single bond to a hydrogen:
Once oxygen is added, the flame changes color from orange to blue and is called a carburizing flame or reducing flame, which is a flame with three distinctly visible parts: the cone (aka inner cone), the acetylene feather (aka outer cone) and the envelope (aka outer envelope). The peak temperature of a carburizing flame is about 5700 degrees F.
Carburizing flames have a high percentage of acetylene, and therefore also carbon. The carbon has a tendency to enter the weld metal and cause brittleness and pitting (which is visible on the cooled metal surface). This is therefore not the most desirable flame to use.
Adding more oxygen to the flame results in the disappearance of the feather, leaving only the cone and envelope visible. At this point, the flame is a "neutral flame" and has a peak temperature of 5900-6000 degrees F.
The neutral flame's gasses are proportioned such oxygen and acetylene burn off at an equal rate, completely burning all of each. This type of flame results in molten weld metal that is clean. It is desirable to use a neutral flame in most gas welding and cutting applications.
Adding yet more (i.e. too much) oxygen to the flame creates an "oxidizing flame," which has a peak temperature of about 6300 degrees F. Oxidizing flames are characterized by purple hue, sparks, and the leaving of white foam or scum on the surface of the metal. This flame is not ideal for most applications.
In conclusion, use a neutral flame.
The next item to consider is the filler rod. The most common types of rods (R) for gas welding (G) are RG45 (45ksi strength and copper coated to prevent rust), RG 60 (60 ksi strength and not copper coated) and ER 70S-2 (see GTAW). Filler rods should have equal or better mechanical properties than the base metal, and their diameters should be equal to or less than the base metal thickness. It's also a good idea to use filler rods with AWS designations.
When performing Oxygen Acetylene Welding, it is typical to hold the welding torch in one's dominant hand (right hand for most people) and to hold the filler rod in one's non-dominant hand.
