Oxy-acetylene welding (also known as oxy welding or gas welding) is a basic type of welding generally used for metal repair work, shaping and forming, cutting and joining. While oxy welding is generally no longer used for large-scale commercial welding purposes, having been superseded by arc welding, it is still widely used for commercial metal forming, steel fabrication, small-scale or backyard metalwork, home handywork and metal artwork. Because of its ease of use and low cost nature, oxy welding remains an extremely common and versatile way of working metal.
Oxy welding involves the combustion of oxygen and acetylene through a hand-held torch. When mixed in the right proportions a hot flame is produced with a temperature of about 3,500℃. Since steel melts at about 1,500℃, the mixture of oxygen and acetylene is the only gas combination that generates enough heat to melt steel.
Oxy welding can produce three types of flame setting: neutral, oxidising and carburising. The neutral flame has equal quantities of oxygen and acetylene. The oxidising flame is achieved by increasing the oxygen flow rate, while the carburising flame is achieved by increasing acetylene flow. Each flame can be used for different cutting, heating or welding techniques.
Oxy welding is used for a variety of purposes and applications. It’s a very versatile process that can be used for brazing, braze-welding, metal heating (for annealing or tempering, bending or forming), rust or scale removal, the loosening of corroded nuts and bolts and cutting and joining ferrous metals. It can also be used for depositing metal to strengthen or build up a surface, like in the hardfacing process.
Since it doesn’t require a source of electricity, it’s often used for welding on worksites or locations where there is limited access to electricity.
Common applications include steel fabrication, general metal repair work, aircraft and automotive industries and joining high-carbon steel. Oxy flames can also be used in stone processing, glass making, jewellery making and working with platinum.
Oxy welding equipment is portable, easy to use and doesn’t require electrical power. Equipment generally consists of oxygen and acetylene stored in separate pressured steel cylinders. These cylinders are each fitted with pressure regulators and hoses that lead to a blowtorch. The cylinders are usually fitted to a wheeled trolley.
The pressure regulators are used to ensure that the gas pressure from the tanks matches the required pressure in the hose. The flow rate can then be adjusted using needle valves on the torch.
Acetylene is not just flammable, it’s explosive. So it’s vital that any acetylene welding setup includes non-return valves or flashback arrestors. These are located between the regulator and the hose and the hose and the blowtorch on both the oxygen and acetylene lines. They are designed to prevent a flame or the oxygen-fuel mixture being pushed back into either cylinder and causing an explosion.
An oxy rig will also be equipped with different torches depending on the type of work you need to do. Different torches include the welding torch, cutting torch, rosebud torch and injector torch. In general, the torch contains a mixing chamber where the gases are combined and a nozzle where the fuel-oxygen mixture is burnt together.
Advantages of oxy welding
- Can weld ferrous and non-ferrous metals together
- Doesn’t require an electrical power source
- Cheap and simple equipment
- Low training requirements and doesn’t require specialised labour
- Portable equipment
Disadvantages of oxy welding
- Not suitable for thick metal sections
- Doesn’t result in high steel strength (compared to other welding methods)
- Slow rate of heating
- Lower temperature than arc welding
- Cannot make precise, neat cuts
- Large heat application area
Safety and PPE
Like any welding process, oxy welding requires a number of safety precautions and specific protective personal equipment (PPE). Since you’re working with an open flame, you need to avoid work on or near any combustible surfaces or materials. A firebrick top
workbench is recommended for cutting on.
Suitable clothing and footwear should be worn at all times when operating oxy welding equipment. This includes suitable leather work boots and heavy cotton or woollen clothing. Synthetic materials, shorts and non-leather or open-toed footwear should not be worn.
While oxy welding flames are less intense than arc welding, it’s still important to wear appropriately tinted welding goggles at all times. Leather welding gloves and a leather apron are also recommended.
While the oxygen and acetylene used are non-toxic, the welding process can give off harmful fumes. So oxy welding should always happen in a well-ventilated area. If this is not possible, appropriate fume extraction should be implemented or respiratory protection should be worn.
The welding equipment also needs to be regularly inspected and properly maintained. This includes properly storing and securing gas cylinders, regularly checking valves and hoses, and following all manufacturer guidelines and operating procedures.