Oxyacetylene welding allows to weld parts together by fusion, with or without filler metal. The field of application of this type of welding is wide: garages, heating companies, agriculture, boiler making, locksmith and metalwork companies, etc. The adjustment of the pressure of the two gases, acetylene and oxygen, must be precise so that the blowtorch works optimally.
How does an oxyacetylene welding machine work?
The oxyacetylene torch uses two gases – oxygen and acetylene – to generate a controllable flame with a temperature of up to 3,200 degrees Celsius. Oxygen acts as the oxidizer, acetylene as the fuel: The first one aspirates the second one in the blowpipe.
To obtain a good quality flame, the pressure of oxygen must be greater than that of acetylene in the blowtorch.
The welding station post is composed of:
- 1 cylinder of oxygen compressed to 200 bar ;
- 1 bottle of acetylene dissolved at 15 bar in acetone;
- two regulators to adjust the pressure of the cylinders;
- safety features ;
- a blowtorch
The station can be mounted on a cart for easy movement. The oxygen cylinder is marked “Oxy”. It stands out with a white landmark and a blue pipe. The acetylene cylinder is marked with a brown “tan” marker and its hose is red.
The formation of the oxyacetylene flame
The oxyacetylene flame is produced by the simultaneous combustion of oxygen and acetylene when the blowtorch is lit. To ensure the complete combustion of acetylene, a proportion of 2.5 volumes of oxygen for 1 volume of acetylene must be combined. The blowtorch provides the entire volume of acetylene, but only provides 1.2 volumes of oxygen, while the remaining volume, or 1.3, is drawn from the ambient air.
These proportions must be scrupulously respected to generate a quality flame. If the oxygen dosage is insufficient, the torch produces a flame less hot, called carburizing. An excessive dosage of oxygen produces an oxidizing flame. This is characterized by the insertion of oxides (or chlorides, nitrides, sulfides) of a given metal, if heated and confronted with this flame. Only the right proportion generates a reducing flame that can be used for welding.
The flame is composed of 3 zones: the sting, the reducing zone and the plume. Each zone has a different temperature. The reducing zone constitutes the active part that can reach a temperature of up to 3,200 degrees Celsius. This allows the self-welding of the metal that joins the parts to be welded by means of the oxyacetylene flame, with or without metal addition.
Pressure control for oxyacetylene welding
The pressure of the two gas cylinders is adjusted by turning the regulator screw on each cylinder clockwise. You must first open the gas bottle taps by turning them anticlockwise by a quarter turn.
The adjustment of the pressure of the oxygen bottle must be set between 0.8 and 1.5 bar. The one for the acetylene bottle needs to be between 0.3 and 0.5 bar. You will then open the valves of your blowtorch. This adjustment will lower the pressure that you will need to readjust before welding.
Open the blue oxygen valve on the torch first, until you have a light flow, then open the red acetylene valve fully.
Always light your flame with a specially designed express ignitot and never with a lighter.