Introduction to Gas Cutting and Welding
‘Oxy’ Cutting is a process which has been around for a long time but has become less frequently used as welding technology has evolved.
While more modern welding processes and techniques have been developed, there still remains a place for Oxy cutting & welding for various applications.
But what exactly is Oxy Cutting/Welding? And what is it used for? We’ve put together this quick summary to help explain.
OXY CUTTING/WELDING SUMMARY
Cutting metals is a regular application in many welding jobs and the two most common methods to execute this are Oxy-Cutting and Plasma Cutting.
While each method has advantages and challenges, the cheaper up-front costs and higher portability make Oxy-Cutting an attractive option for many.
The huge benefit to Oxy-Cutting is the ability to cut thick metals while also being versatile enough to weld, braze, solder, heat and gouge.
And many Oxy-Cutting units have both cutting and welding capabilities, with a multi-purpose blowpipe allowing the operator to switch between using a cutting attachment and welding tips.
While Plasma Cutting requires a power source and compressed air to function, Oxy-Cutting uses gas (Oxygen and Acetylene or Oxygen and LPG/Propane) which makes it easier to navigate for many job applications.
Oxy-Cutting is normally used for cutting Ferrous Metals (Iron-based) while it’s generally not applied for materials such as aluminium, stainless steel and cast iron.
With oxy-cutting, an oxygen/fuel gas flame preheats the steel to its ignition temperature. A high-powered oxygen jet is then directed at the metal, creating a chemical reaction between the oxygen and the metal to form iron oxide, also known as slag. The high-powered oxygen jet removes the slag from the kerf.
When using oxy-cutting torches, cut quality, preheating times and metal thicknesses all may be influenced by the type of fuel gas used. There are four basic fuel gases used most frequently in combination with oxygen for this process: acetylene, propane, propylene and natural gas.
Fuel gases are typically chosen according to the cutting application, cost, heat output and oxygen consumption.
At a basic level, Oxy Cutting requires a gas supply with oxygen and acetylene (or LPG/Propane) cylinders, regulators for both gases, flashback arrestors, cutting nozzles, blowpipe and a cutting attachment.
The Oxygen and Acetylene pressure levels required are ultimately determined by the thickness of the material being cut, as is the appropriate nozzle size.
The combination of Oxygen and Acetylene in almost identical amounts produces a flame which heats up to 3000C – capable of melting most materials.
The mix of Oxygen and Acetylene is the only oxygen/fuel gas combination that burns completely to produce a non-reactive secondary flame which is suitable for fusion welds.
This secondary flame acts as a natural shield for the weld and prevents atmospheric contamination. If two compatible metals are melted side-by-side than the edges can be fused together – though a filler material may be required.
Other fuel gases such as LPG or Propane are not suitable for gas welding as they produce a flame which interferes with the molten metal.
Oxy Welding requires Oxygen & Acetylene cylinders, gas regulators, flashback arrestors, correct blowpipe, hoses and welding tips.
It is commonly used for welding plain carbon steel (without flux), fusion welds of pure aluminium and copper & copper-based alloys (requires flux).
BENEFITS OF OXY-CUTTING/WELDING
- Cheaper Set-Up Costs.
- High Portability and Easier to Maneuver.
- Wide Range of Uses & Applications.
- Highly effective for cutting thicker material.
LIMITATIONS OF OXY-CUTTING/WELDING
- More Modern Welding Methods Available.
- Far slower process.
- Difficult to master & produces distortion.
- Safety Issues – using dangerous gases.