A gas cutting (called also oxy-fuel cutting) is, next to plasma cutting, one of the most common methods of cutting metals as it is primarily applicable to low-carbon steel and low-alloy steel.
In the past, we have written an article on the differences between gas and plasma cutting. Now we will remind you of the most important advantages of oxy-fuel cutting as well as its limitations.
Oxy-fuel cutting is based on heating the material to so-called ignition temperature. The torch blows out the stream of oxygen under high pressure having been mixed with a flammable gas (acetylene or propane) in the relevant proportion. Being exposed to heat, metal is melted and then blown away in the form of liquid metallic oxide by the gas stream.
There are two types of gas cutting: oxy-propane and oxy-acetylene, which we will write about more later.
The most significant advantage of gas cutting over plasma cutting is the capability of cutting through very thick materials preserving high cutting quality. Gas cutting can be performed both manually and mechanically. Another advantage of gas cutting is the low cost of consumables and needed equipment.
The most important disadvantages of oxy-fuel cutting are long piercing time, low cutting speed, and limitations regarding types of processing material. When cutting material thinner than 3 mm or other than low-alloy steel, it is recommended to apply plasma cutting.
As we mentioned before, the choice of the torch influences what type of steel we will be able to cut. Moreover, if we decide to apply oxy-fuel cutting, we must think beforehand if we are interested in using an oxy-propane or an oxy-acetylene torch as the choice between oxy-propane or oxy-acetylene depends on the cutting material and the type of production we have.
When applying oxy-propane cutting it is recommended to use the mix of propane-butane gasses along with oxygen. The market value of these gasses is lower in contrast to acetylene – and this lower price can be convincing in many cases. Furthermore, the consumables applicable to this method are cheaper and take more time to wear thanks to which the working temperature is lower when cutting with propane.
The disadvantage of propane is the fact that it gets heated approximately three times slower than when using acetylene. In case of breaks during work time, this solution might not be economic. Therefore, propane applies to long pieces of material along with undisrupted work time. This method is great with mechanized cutting (CNC).
It is worth mentioning that propane, in general, is better when cutting thicker sheets – using acetylene is more recommended when cutting thinner materials.
Acetylene is a more expansive gas than propane but it has more potential in use. It ensures that the metal is heated very fast, reaching high temperatures in a relatively short time. It allows saving the gas, especially when there are long periods between cuttings. As a result, oxy-acetylene cutting is more reasonable when there are downtimes.
The great advantage of oxy-acetylene torches is their mobility as they allow cutting under various angles. As we mentioned earlier, acetylene is recommended to cut thinner sheets; this method allows cutting materials even up to 3 mm thick. Nevertheless, acetylene is also applicable to thick materials.
To sum up, acetylene provides a lot of possibilities as it increases the range of cutting sheets and it is recommended more for manual cutting at workshops where cutting occurs occasionally. The most significant disadvantage is the high cost that is followed by low cost-efficiency in mechanized production.
It is worth noticing that not every metal can be cut using oxygen. The ignition of metal must take place at a temperature lower than its melting point and the melting of the oxides formed must take place at a temperature lower than the ignition. Metals that meet these two conditions are iron, titanium and tungsten. Oxy-fuel cutting is practically the most common application for low-alloy and low-carbon steel as increased amounts of additives in steel make cutting difficult, so high-alloy and high-carbon materials are usually cut using other methods.
Moreover, gas, in general, is not suitable for cutting very thin materials. Due to the large area of the heat-affected zone, it is merely impossible to cut materials thinner than 3 mm. Nevertheless, the range of cutting thicknesses is very wide. Gas cutting is a relatively cheap method of cutting sheet metal in contrast to plasma cutting as when cutting low-alloy and low-carbon steel, it is certainly the best solution.