Flame or Gas(Oxyacetylene) Welding

The fusion of the base metal and filler is achieved by employing a blowtorch as shown in below figure. The torch utilizes a flammable gas (acetylene generally,  hydrogen,  propane etc.) along with oxygen to produce the required amount of heat.

The flame comprises of following two zones

1. Cone  : It is at the immediate exit of blow torch. In case of acetylene gas being used, this zone releases hydrogen and carbon monoxide. Temperature at cone tip is about 3000C in case of oxyacetylene flame and the atmosphere is reducing.
2. Plume: It is the zone where combustion is completed. This zone can be oxidizing, neutral or reducing based on the oxygen to acetylene ratio with neutral ration lying somewhere in 1 to 1.2.

Flow of gases can be regulated. The range of flow possible depends upon the size of nozzle. Nozzles are available that can give acetylene flow ranging from 10 by 63 l/h to 1000 by 4000 l/h. The flow is adjusted depending upon metal being welded, its thickness, type of joint and position of welding.
Filler metal is available in the form of rods ranging from 1.6m to 5mm in diameter.

For less reactive metals, the envelope hot gasses created from the torch is sufficient to avoid contamination of weldment from surrounding air. In case of metals that are sensitive to oxidation e.g. aluminum, stainless steel, copper alloys flux is necessary to be used (spread out over the edges requiring welding or incorporated with the rod) to eliminate oxides formed on the surface.