What Gas do Plasma Cutters Use?
Plasma cutting is one of the fastest cutting processes on aluminum, carbon steel, and stainless steel. The process uses hot electrodes to cut through electrically conductive materials. Invented back in 1955 by ESAB, this method can be used for cutting on materials of up to 6 inches thick.
To achieve the best quality, productivity, parts life, and reduced cost of operation, different gas types are used on different types of material. Each gas has its own advantages and disadvantages. Simply put, selecting the right gas depends on the metal being cut, the equipment used, and the desired performance.
Here, we have provided a brief overview of each gas and the quality of the cut based on the three conductive materials mentioned above (aluminum, carbon steel, and stainless steel.)
Plasma Gases/ Materials
Good cut quality and speed. Very cost effective
Cost effective and provides a precise cut with adequate speed
Good cut quality. Moderate cutting speed
Excellent cut quality and speed. Little to no dross
Excellent parts life and cut quality. Highly recommended
Great parts life, fair cut quality
Good cut quality. Great parts life
Great cut quality. Excellent parts life
Excellent parts life. Good cut quality, some dross
Excellent cut quality and parts life
Excellent cut quality. Works great on thick materials
Excellent cut quality. Works great on thick materials
Air is one of the most adaptable forms of gas available. Introduced in the early 1960s for improved slice quality, air gas produces good cut quality while offering good speed for cutting aluminum, stainless steel, and carbon steel. Since you do not necessarily have to purchase this form of gas, the cost of operation is drastically lowered. However, shop air is a great option as it is cleaned beforehand. This cleaning process eliminates any contaminants such as moisture, oil mist, and other particulates.
Air is the widely accepted and used gas for the purpose of slicing sheets of unalloyed, low alloyed, and high alloyed stainless steel. When using air plasma, air shield gas offers the best option since it contains a mixture of approximately 80 percent nitrogen and 20 percent oxygen. The oxygen found in the air provides additional energy which increases the speed by around 25 percent over cutting with nitrogen.
A major drawback derived from using air gas is that the cut surface on stainless steel and aluminum materials might get heavily oxidized, which is unacceptable for most applications that do not require secondary operations such as grinding.
This gas is best used to obtain fast cutting speeds at lower power levels. Oxygen is ideal for cutting structural low-carbon and low alloy steel. It is capable of processing a wide range of conductive material thicknesses.
When used to cut carbon steel, oxygen increases the cut speed and helps remove all molten materials to create a clean and smooth edge. To cut through thicker steel, it’s recommended to mix some nitrogen in the shielding – this can either be an Oxygen-Nitrogen mixture or Air-Nitrogen mixture.
The major disadvantage of oxygen is the decreased parts of life and the cost of purchase. Note that plasma cutting stainless plate or aluminum plate with oxygen gas is not recommended.
Nitrogen is a great option for anyone planning to cut tons of aluminum and stainless steel. This plasma gas offers excellent parts life and great quality on the cut.
Nitrogen, however, is not as effective when used on thick materials. For best results, it’s best to substitute it with Argon-Hydrogen. Nitrogen can be applied together with air or h2o as an alternative gas to become shield fuel.
This application helps cut smooth edges, particularly on stainless steel and aluminum. If you are planning to use h2o, as the alternative fuel, using it within a water platform will make the action more effective.
Hydrogen has a high concentration level of thermal conductivity which allows for higher power denseness. Hydrogen plasma gas is environmentally friendly as it reduces the emission of CO2. The gas produces high quality of cut surface and helps reduce the labour required for finishing after cutting materials. This gas contributes to high productivity thanks to its high-speed cutting which also results in a reduction of running cost.
When Hydrogen gas is used, the base metal receives lower heat input. The process reduces thermal distortion significantly thereby producing high precision cuts. In addition, the cut surface is smooth and the corners are sharp, bringing about an excellent cut quality.
One of the main advantages of using hydrogen gas is the easy separation of dross (slag). Similar to other gases, Hydrogen cutting does generate slag. However, the slag can be easily removed which results in fewer man-hours required to finish off the cut-out products.
Hydrogen plasma gas has a higher cutting speed of 10 to 30 percent when compared to other gas cutting. In addition, since the cutting time is reduced due to the exceptional heat concentration, the overall productivity is improved.
For thick aluminum and stainless greater than ½,’’ argon is a suitable choice of gas to use. Keep in mind that argon is not recommended for use with carbon steel products. Argon does not react with materials during cutting and is therefore classified as an inert gas.
It cannot be used as a single cutting gas because it has a low thermal capacity. Plasma cutting is only used on the above-mentioned materials, primarily; carbon steel, aluminum, and stainless steel. However, there are tons of other alloys and metals that are conductive including brass, Inconel, copper, cast iron, titanium, etc. The major problem with using this method of cutting is that the melting degrees of some of these materials make it hard to receive a precise cut with clean cut edges.
Also referred to as PG, it refers to all gas mixtures which are used to generate the plasma beam and help cut through conductive materials. There are five main plasma gases namely:
Plasma gases can further be classified under three main phases including:
Ignition gas (ZG) – This is the gas used to light up the arc and help start the metal cutting process.
Cutting gas (SG) – Cutting gas determines the cutting speed and the cutting results. First, the energy derived from the arc helps soften and melt the metal. The melted metal is then pushed out of the cutting gas. Keep in mind that the cutting gases used differ based on the thickness and material type.
Marking gas (MG) – This is the gas used for plasma marking.
Swirl gas covers the plasma beam and helps increase the cutting quality. This method increases cooling and assists cutting in several different ways. It also helps protect the product during underwater cutting and piercing.
Sealing gas (SPG)
Sealing gas is similar to swirl gas but it has reduced volume flow rate, especially when used for underwater cutting. The gas prevents any water from entering the torch head when being operated underwater.
Also referred to KG, it controls the protection cap. Control gas ensures that the torch is properly installed at all times. This is important because an improperly installed torch might lead to zero performance.
Identification gas (IG)
IG gas is used to locate different torch heads.
What does Gas Swirling Do?
As mentioned above, swirling helps increase cooling and enable a user to cut their materials in several different ways. This method helps improve cut quality and provide exceptional parts life. The heat from the beam is then evenly distributed along the side of the cut.
How do Plasma Cutters Work?
A plasma cutter uses electromagnetic gases to transfer energy from a power supply to a conductive material for a clean and fast cutting process. A plasma system is inclusive of these components:
Power supply – It converts an AC line voltage into a constant DC voltage which can range from 200 up to 400 DV. The DC voltage is then used to generate enough energy to cut through a certain material.
Arc starting console – The circuit found inside an ASC produces AC voltage of up to 5,000 VAC at approximately 2 MHz. This voltage ignites the plasma torch to create the plasma arc.
Plasma torch – There are three major components (also referred to as consumables), inside a plasma torch body. These components will require replacement overtime as they tend to get consumed during a plasma cutting process. They are:
∙ Gas baffle (swirl baffle)
A plasma torch might come inclusive of a shielding cap to further enhance the cutting quality. The two common methods of cutting include:
This procedure works by sending an electric arc through a gas that is then passed through a small constricted opening. This small opening helps elevate the temperatures of the gas from solid to liquid to gas, and finally to plasma (also known as the 4th state of matter).
The small nozzle allows the gas to squeeze through at a high speed. The high speed gas emitted is directed around the perimeter of the cutting area to shield the cut and provide a precise cut.
Modern plasma cutters come inclusive of a pilot arc that is wedged between the cutter’s snout and the electrode. This arc is used to iodize the gas and generate the plasma before it’s transferred to the metal.
Another method that is being used in many of today’s plasma cutters is a plasma torch. This method uses a copper snout to compress the iodized gas and focus it to a small section of the conductive material being cut. It works in a similar way to how one uses a magnifying glass and the sun’s rays to create a beam of heat.
Note: Pilot arc and Plasma torch methods are not compatible with CNC (automated) cutting.
Important Variations Involved in Plasma Cutters
For maximum quality and production of your materials, you need to ensure that all components involved in the process maintain a healthy balance.
The cleanness of the gas is of great importance if you want to achieve excellent parts life and great cut quality. The requirements for oxygen are 99.5 percent whereas the minimum clean levels for nitrogen are at 99.995 percent.
The following could happen if the cleanness levels are lower than the above stated:
- Extremely short parts life
- Variation in cut quality
- Inability to cut through materials no matter how thin they are
- You might experience some debris in the nozzle
Aside from gas purity, the gas pressure plays a major role in plasma cutting. Each nozzle has a set current based on the maximum amount of pressure to instill. Increasing gas pressure might result in a notable decrease in the overall performance and electrode’s life whereas decreasing the pressure will undoubtedly result in a double arc failure.
Other variations to keep an eye on include:
Use filtered water as some minerals can affect nozzle life and the plasma cutting process. Also, excess water pressure might cause the arc to produce poor results
This refers to the width parallel to the torch and cut axis.
This variation is dependent on the standoff, cutting speed, current (Amps), nozzle size, gas and water flow rate.
Plasma cutting has enabled us to perform precise and quality cuts on many types of conductive metals. Different gases can be used to perform plasma cutting. All you need to do is determine the thickness and material type beforehand. This type of cutting up steel, aluminum, carbon steel, and other alloys is easy to master and faster than other types of cutting such as oxyfuel cutting.
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