Plasma Arc Cutting - with the Right Gases
Pure Gases and Gas Mixtures Tailored to the Needs of Plasma Arc Cutting
What is Plasma Arc Cutting?
Plasma cutting uses the heat and pressure generated by a constricted electric arc and a high-velocity jet of high-temperature ionized gas to cut through metal. This cutting method relies on electrical power units and requires high open circuit voltage. The cutting action is produced in the cutting torch and a number of different torch systems are available.
Plasma cutting is generally operated in the 'transferred arc' mode, where the arc is maintained between the electrode and the material to be cut. A pilot arc is struck between the electrode and the constricting orifice. This cutting process uses gas flows consisting of active or inert gases or gas mixtures. Blowing in a secondary gas, which flows around the plasma arc as a gas sheath, further constricts the arc, causing the energy flow density and the temperature of the plasma jet to rise even further.
What Torches are Used for Plasma Cutting?
Although torch designs vary depending on the gases used for the plasma and the shielding medium, there are two main types. Single gas torch designs use air or nitrogen for plasma-only operation. Dual-flow designs provide for two separate gas supplies, one for the plasma arc and the other for the shielding gas that improves torch cooling and cut quality.
What Materials Are Suited to Plasma Arc Cutting?
The plasma arc cutting process is associated with a high-energy-density heat source as this is required to melt and eject molten material in the high-velocity plasma jet. Arc temperatures can reach 25000°C (45000°F), easily hot enough to melt all metals and metal oxides, and the high-pressure plasma gas blows the molten metal from the kerf - the gap produced as the cut progresses.
This cutting method can thus be used for a wide range of ferrous and non-ferrous alloys and on a wide range of material thicknesses. It is a fast, economical cutting solution for carbon steels, low-allow steels, stainless steel, aluminum and copper - especially for cutting tasks that cannot be performed with the oxygen cutting process.
The Importance of Gases for Plasma Cutting
Key to the success of the plasma cutting process is the right plasma gas or gas mixture. Argon is easy to ionize and is thus often used as the pilot gas to initiate the arc. It also has a high atomic weight and so readily removes material from the kerf. However, its poor thermal conductivity makes it generally unsuitable for use as a single plasma gas. Consequently, it is often combined with hydrogen. The high thermal conductivity of hydrogen in the plasma gas constricts the arc and increases thermal density. Nitrogen is also frequently used in dual gas torches for different metal types - sometimes combined with hydrogen and/or argon. Air or oxygen may be suitable plasma gases for certain cutting applications.
Dual gas cutting machines also use a secondary - or shielding - gas flowing between the copper cutting nozzle and the ceramic shield to provide a cooling layer to reduce damage and wear to the electrode and nozzle. Different combinations of plasma and secondary gases are recommended depending on the metal to be cut and the quality of cut required. Secondary gases include carbon dioxide, nitrogen and air. Some process types use water as the secondary medium rather than gas.
Gases, Equipment, Services and Expertise You Need
We can support your cutting process with a range of pure gases and gas mixtures tailored to the needs of plasma arc cutting. In addition, our application experts can advise you on the mixture ideally suited to your needs. They can also help you select the correct operating parameters for optimum results and support you with the equipment and gas management services you need.
Linde for Arc Plasma Cutting: Benefits at a Glance
- High-purity process gases
- High cutting speed
- High cutting quality
- Customized supply solutions