In the second part of this series, we take a look at nitrogen and argon/hydrogen as plasma gases.
Most of the plasma torches earlier used nitrogen and even today nitrogen remains to be a popular choice if you need to cut plenty of stainless steel and aluminium. The use of nitrogen results in very good cut quality and prolongs the life of the consumables considerably. However, for thick materials that are over ½” in thickness, using a mixture of nitrogen and argon is more effective. Usually, when using nitrogen as the plasma gas, air as the secondary gas is the best choice.
Carbon dioxide is a better option than air and gives better cutting speed, surface finish and part life; however, carbon dioxide is more expensive than air and needs a complex system for delivery. Water is also a good secondary element to be used along with nitrogen gas. Water is usually used when cutting using a water table. By using water as the secondary element on aluminium and stainless steel, you can get shiny and smooth cut surfaces.
A mixture of argon and hydrogen is a very good choice when it comes to cutting aluminium and stainless steel that is very thick. Typically, a mixture of 65 percent argon and 35 percent hydrogen is used. The argon/hydrogen mixture has the maximum cutting capacity as it is the hottest plasma gas. This mixture is also commonly used in water injection plasma torches for cutting stainless steel that is 6 inches thick.
In the case of torches using multiple gases, you can get a smooth, polished surface and a very straight cut on stainless steel by using the argon/nitrogen mixture. However, you may also get some dross when cutting using this mixture. Typically, when using the argon/hydrogen combination, the shield gas used is nitrogen. However, this combination is quite expensive.
Thus, we can see that the best gas for use in a plasma cutting system depends on three factors i.e. productivity, cut quality and the cost.
- Oxygen as the plasma and air as the shield gas is the best for cutting mild steel. This gives the best quality cut and highest productivity because of the highest cutting speeds. It also produces least amount of dross, does not require too much rework or finishing and facilitates excellent weldability.
- Nitrogen as the plasma gas and air as the secondary gas is the best option for getting excellent cut quality on aluminium and stainless steel that is less than ½ an inch thick. This not only produces a good cut but is also quite affordable. For a faster and better cut quality, you can use CO2 as the secondary gas. The best quality of edge is produced when using a water shield.
- In the case of cutting very thick aluminium and stainless steel, to get the best quality cut, using hydrogen/argon gas with nitrogen as the shield gas is the best option.
- Using shop air that is dry and clean is the most economical and is the best for cutting aluminium, stainless steel and mild steel.
Hence, choosing the right gas for your plasma cutter can be a very vital decision. Choosing the right plasma gas and correct shield gas can help you achieve superior and precise quality cuts, improved productivity, and large cost savings.