Wrought iron work, especially on bridges and gates, is testament to the fact that welding is an art practised for centuries in many countries. However, today's techniques are considerably different to the forges used by the village smiths. The oxyacetylene flame was first used in 1895, by a French chemist called Henri Louis Le Chatelier.
Commonly known as gas welding, the oxyacetylene process involves a flame burning a mixture of two gasses: oxygen and acetylene. These are contained in separate cylinders, each cylinder having a regulator and two gauges. The regulator governs the working pressure, which is shown on one gauge. The other gauge shows how much gas is in the cylinder. The regulators are screwed into the tops of the cylinders, having opposite threads to prevent them being inadvertently screwed to the wrong cylinders. From the regulators, the gas travels through canvas rubber hoses (black for oxygen and red for acetylene) to the blowpipe. Into the blowpipe is fitted a nozzle, of which there are many different sizes for different applications. On the side of the blowpipe are two valves which are colour coded black and red to signify which gas they control.
The correct mixture of oxygen and acetylene must be used to provide what is called a neutral flame. This is important because too much oxygen causes steel to oxidise, whereas too much acetylene causes it to turn hard and brittle (known as carburisation). Once the correct flame has been achieved the two pieces to be welded are placed together and heated until molten (the temperature of the flame is approximately 3000 degrees C) and a welding rod is dipped into the molten metal. The welding rod is soft iron wire often coated with copper to absorb excess oxygen.
Over recent years the gas welding process has been on the decline, being gradually superseded by other methods such as electric arc and MIG. Today only around 30% of all welding is done with oxyacetylene.
