The ultimate aim of any type of welding is to produce strong, clean welds. Though there are several types of welding, from Metal Inert Gas (MIG), Tungsten inert Gas (TIG) and Shielded Metal Arc (SMAW or ‘stick’) welding, one of the oldest forms of welding still practised today Is Oxy-Acetylene. Also known as gas welding, this uses the very high heat (around 3200°C) of the combusted oxygen and acetylene gases to heat and then fuse the metal workpiece.
Why Welders Choose Oxy-Acetylene Welding?
When compared to other welding techniques, Oxy-acetylene has some obvious benefits. It can be used to join both ferrous and non-ferrous metals, including carbon steels, alloy steels, and cast iron as well as aluminium and various aluminium alloys, copper and copper alloys, magnesium and nickel. It can also create welds in metals that require slow rates of heating and cooling.
Besides this, gas welding is used for cutting, as well as soldering and brazing metals at lower temperatures, albeit with slightly different equipment and gases (LPG and hydrogen) than what is used for welding. This kind of versatility is paired with simplicity. Gas welding is popular due to the low cost, relatively few pieces of gear (compared to other welding types, anyway) and that it’s quite easy to learn. If you’re thinking of a career in welding, a good starting point is getting an oxy-acetylene kit with all the necessary items. The equipment is lightweight, portable and cheap to buy, and doesn’t require expensive welding machines, or electricity. The welds are of decent strength, and this means widespread use.
Where is Oxy-Acetylene Welding Used?
Oxy-acetylene is widely used for repair work, especially in workpieces made of mild steel and aluminium. The automotive industry (and smash repairs) is one area where gas welding is typically useful for a range of applications, like welding frames and chassis. Aviation parts are also welded using high heat from combusted oxygen and acetylene. As well as the fabrication of thin to medium sheet metals. Other uses are for welding pipe sections, heating metals for forming and bending purposes, brazing and soldering electronics, jewellery pieces and in any welding environment where electricity is lacking.
Gas Welding Gear
Oxygen and Acetylene Cylinders
You’re guessing right that gases are supplied from separate oxygen and acetylene cylinders. Gases are pressurised and cylinders are made of thick-gauge steel. Acetylene cylinders are coloured red or maroon and have a regulator valve at the top. The flow of the fuel is monitored through pressure gauges. Acetylene cylinders come in three sizes, D, E and G, with a 10, 24 and 50 water-litre capacity.
Oxygen cylinders are similar, but coloured black, obviously for safety reasons. These too have regulator valves and pressure gauges. Common sizes are E2 and G2 cylinders, with the same water capacity, but are generally taller and thinner than acetylene cylinders.
All cylinders need to be labelled as to the contents, with the name of the gas, gas classification and grade, fill pressure, size and safety info.
Regulators and Gauges
Gas regulators are used to control the gas pressure, that is, the high pressure of the gas stored in the cylinders, and the low pressure reaching the torch. Each regulator has two separate gauges. The remaining gas in the cylinder can be determined by the high-pressure gauge.
Hoses for each gas are colour-coded to increase safety – red for acetylene, and blue for oxygen. Each hose needs to be made to high tolerances to withstand the high pressures exiting the cylinders. Fittings are also differently threaded. Oxygen hoses have right-hand threads and acetylene hoses have left-hand threads.
Hoses are fitted with a flashback arrestor at either end. These prevent the flow of gas back toward the cylinders in what is known as a flashback and a ripe recipe for an explosion. The most probable causes for flashbacks are inappropriate or low gas pressures, hose leaks or punctures, and loose connections.
Torches and Mixing Chambers
Torches and their main component, blowpipe handles, have connections for both the oxygen and acetylene hoses, as well as the flashback arrestor valves. A mixer attaches to the blowpipe handle and this is where the gases combine. Welders can adjust the flame by varying the ratio of the gases. For welding purposes, usually, a neutral flame (1:1 oxygen to acetylene mix) is used.
Torch Tips and Attachments
Tips or nozzles are chosen according to the thickness of the metals being welded. They’ll differ in length and diameter and are selected for different types of metals. There are also separate cutting, brazing and soldering tips that go with the appropriate cutting, brazing or soldering attachment connected to mixers and blowpipes.
If you’re just starting out, look for an oxy-acetylene kit with all the necessary goodies. Basic kits are geared towards welding, while combo kits will also include attachments and tips for both brazing and soldering. Oxygen and acetylene cylinders and bottles, as well as essential welding safety gear, are sold separately.