What Is Oxy-Acetylene Welding?
Oxy-acetylene welding commonly referred to as gas welding, is a process that relies on the combustion of oxygen and acetylene.
When mixed together in correct proportions within a hand-held torch or blowpipe, a relatively hot flame is produced with a temperature of about 3,200 deg.C.
In Oxy-acetylene welding, a welding torch is used to weld metals. Welding metal results when two pieces are heated to a temperature that produces a shared pool of molten metal.
The molten pool is generally supplied with additional metal called a filler. Filler material selection depends upon the metals to be welded.
The chemical action of the oxyacetylene flame can be adjusted by changing the ratio of the volume of oxygen to acetylene.
Another type of welding is oxy-acetylene welding. Also known as oxy-fuel welding, oxy-acetylene welding is a process that relies on the combustion of oxygen and a fuel gas, typically acetylene. You might hear this type of welding referred to as “gas welding.”
Gas welding is used almost exclusively for welding thin metal sections. You can also use oxy-fuel welding for heating tasks, like releasing frozen bolts and nuts, heating heavy stock for bending and soft soldering tasks.
Oxy-acetylene welding is a flexible and forgivable welding process, making it a great choice for amateur and part-time welders. Oxy-acetylene welding equipment is also portable and easy to use.
How Does Oxy-Acetylene Welding Work?
Oxy-acetylene welding uses a high-heat, high-temperature flame that is produced by burning a fuel gas (most commonly acetylene) mixed with pure oxygen.
The base material is melted with the filler rod using a flame from the combination of oxy-fuel gas through the tip of the welding torch.
The fuel gas and oxygen gas are stored in pressurized steel cylinders. Regulators in the cylinder reduce gas pressure.
Gas flows through flexible hoses, with the welder controlling the flow via the torch. The filler rod is then melted with the base material. However, melting two pieces of metals is also possible without the need for a filler rod.
Types of Flames in Oxy-Acetylene Welding
Three distinct flame settings are used, neutral, oxidizing, and carburizing.
Welding is generally carried out using the neutral flame setting which has equal quantities of oxygen and acetylene.
The oxidizing flame is obtained by increasing just the oxygen flow rate while the carburizing flame is achieved by increasing acetylene flow in relation to oxygen flow.
Because steel melts at a temperature above 1,500 deg. C, the mixture of oxygen and acetylene is used as it is the only gas combination with enough heat to weld steel.
However, other gases such as propane, hydrogen, and coal gas can be used for joining lower melting point non-ferrous metals, and for brazing and silver soldering.
As mentioned above, the flame has to be adjusted to appear a certain way before you can proceed with the Oxy-Acetylene weld. Different types of flames are used to weld different types of metals.
1. Carburizing Flame
Carburizing flame contains an excess of acetylene gas. This type of flame is suitable for applications where a low-heat flame is required. It is used for welding nickel, Monel metal, high-carbon steel, and a number of non-ferrous metals. This flame is not used to weld regular steel.
Related: What is Carburizing?
2. Neutral Flame
Neutral flame contains equal proportions of oxygen and acetylene gases. This type of flame is used in most welding operations since the chemical effect of this flame on heated metal is the least.
3. Oxidizing Flame
As you can tell by the name, an oxidizing flame has a high content of oxygen (the oxygen and acetylene ratio being 1.5:1). This type of flame is used when welding copper and alloys of copper, such as bronze and brass. It cannot be used to weld steel as it will oxidize it.
Equipment use in Oxy-Acetylene Welding
Oxyacetylene devices are portable and easy to use. It includes oxygen and acetylene gases stored under pressure in steel cylinders. The cylinders are equipped with regulators and flexible hoses that lead to the blowpipe.
Specially designed safety devices such as flame traps are placed between the hoses and the cylinder regulators. The flame trap prevents flames generated by a flashback from reaching the cylinders. The main causes of flashbacks are failure to purge the hoses and overheating of the blowpipe nozzle.
When welding, the operator must wear protective clothing and tinted colored protective goggles. Since the flame is less intense than an electric arc and very little UV radiation is emitted, tinted all-purpose glasses offer adequate protection.
Operating characteristics
The effect of the oxyacetylene flame on the surface of the material to be welded can be adjusted to produce a soft, hard, or violent reaction by varying the gas flows. There are of course practical limits to the type of flame that can be used for welding.
A hard, strong flame will cause the molten weld pool to be blown away, while a flame that is too soft will not be stable near the point of application.
The blowpipe is therefore designed to accommodate different sizes of ‘swan neck copper nozzle, allowing the correct flame intensity to be used.
The relationship between material thickness, blowpipe nozzle size, and welding speed is shown in the table. In fusion welding, filler material in the form of a rod can be added if necessary.
The main techniques in oxy-fuel welding are left, right and all positions right. The former is used almost exclusively and is ideally suited for welding butt, fillet, and lap joints in sheet metal thicknesses of up to approx. 5 mm.
The technique to the right is used for plate thicknesses over 5 mm for welding in the flat and horizontal-vertical position.
The all-position right-hand method is a modification of the right-hand technique and is ideally suited for welding steel plates and especially pipelines that require position welding (vertical and overhead).
The right and right techniques allow the welder to obtain a uniform penetration bead with additional control over the molten weld pool and weld deposit.
In addition, the welder has a clear view of the weld pool and can work with complete freedom of movement. These techniques are very highly skilled and are used less often than the traditional left technique.
Why Use Acetylene For Welding?
Welding is an important fabrication process in various manufacturing industries. There are different types of welding procedures. One important type is gas welding.
In this type of welding, the heat necessary for the process is produced by the combustion of oxygen and acetylene. Sometimes, hydrogen, butane, and propane are also used as replacements for acetylene.
The combination of oxygen and acetylene to cut metals has been in use since approximately 1906. Over the years, acetylene has earned recognition as one of the safest, yet strongest welding gas.
But, there is a rising misconception that propane is a better welding gas than acetylene. This post shares differences between these gases and discusses the benefits offered by acetylene gas in detail.
Gas Welding- 4 Degrees of Difference between Propane and Acetylene
The following are major differences between propane and acetylene:
- Flame Temperature: Propane produces a flame temperature of ~2800 degree Celsius when burned in oxygen. Acetylene produces a flame temperature of ~3100 degree Celsius along with oxygen. This high flame temperature makes acetylene a suitable choice for gas welding steel.
- Welding: When burned in oxygen, acetylene produces a reducing zone, which easily cleans the metal surface. However, propane doesn’t have a reducing zone. This property makes it unsuitable for welding. Today, oxy-acetylene welding is employed for high strength steels.
- Safety: The efficiency of acetylene when used with oxygen is very high. This means that the gasses, especially the oxygen, lasts longer. Thus, this results in less cylinder handling.
- Economic Benefits: Acetylene has less stoichiometric oxygen requirements when compared to propane. The ratio of the volume of propane is 4.3 to 1, whereas for acetylene it is 1.2 to 1. This means more oxygen gets consumed while using propane than acetylene.
All the above-mentioned differences suggest why acetylene is preferred over propane. Do you want to know more about the benefits of using oxy-acetylene for gas welding? The next section discusses it in detail.
3 Reasons Why Acetylene is Ideal for Welding
The following points will help you understand why acetylene is preferred for welding, since 1906.
- A Safe Fuel: Safety is an important priority in most process industries. As acetylene is lighter than air, there are rare chances of them accumulating at low levels. This property makes it safe to use in any processing facility or in underground applications.
- Excellent Welding Quality: Acetylene is the hottest fuel gas when combined with oxygen. In the right applications, this makes acetylene ideal for welding different steel materials.
- Money Saver: Oxy-acetylene is well-known for its flexibility, and is suited for various machining operations other welding, such as brazing, cutting, etc.
In acetylene gas filling plants and other applications, acetylene cylinders for welding are available in various sizes. This flexibility makes them easy to source and transport when compared to other fuel gases.
Rexach is one of the leading manufacturers of equipment for filling acetylene cylinders for welding. The team at Rexarc will help you understand the specifications and additional advantages of using acetylene for gas welding.
What is oxyfuel welding used for?
Oxy-fuel welding is a process to weld types of metals, including carbon steel, alloy steels, cast iron, aluminum, and magnesium using pure oxygen and fuel/gas.
In oxy-fuel welding, a torch is used to heat two pieces of metal at a temperature that produces a molten pool.
How to properly work with an oxy-acetylene torch
Lighting, adjusting, and shutting down an oxygen-acetylene torch is easy – especially when following the proper procedures.
In addition to these easy-to-follow instructions, you must always be sure to follow the torch manufacturer’s operating procedures.
How to properly light, to adjust, and shut down an oxy-acetylene torch:
First – before you attempt to light the torch follow these checks:
- Make sure regulator pressure adjustment screws are backed out!
- Make sure torch valves are closed!
- Stand away from front of regulator
- Separately and slowly open the oxygen and acetylene cylinder valves
- Adjust regulator p/a screws to tip pressure settings
- Open/close torch valves separately and fine tune pressure settings on regulators
- Depress cutting lever and adjust pressure if necessary
Lighting and adjusting the torch (with a positive/equal pressure mixer):
- Separately purge both oxygen and fuel gas lines
- Open fuel gas valve 1/2 turn
- Ignite flame with striker
- Increase fuel gas flow until flame leaves end of tip and no smoke is present
- Decrease until flame goes back to tip
- Open oxygen valve and adjust to neutral flame
- Depress oxygen lever and make necessary adjustments
Shutting down the torch (with a positive/equal pressure mixer):
- Close oxygen torch valve
- Close fuel gas torch valve
If the torch/regulators and gases are done being used for a while, follow these procedures:
- Close oxygen and fuel gas cylinder valves
- Separately purge oxygen and fuel gas lines
- Make sure all regulator gauges read 0
- Back out regulator pressure adjustment screws!
- If you are using in a commercial environment, report any damage, etc. to your supervisor
Remember to always follow basic safety rules when working with oxy-fuel equipment.