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Thermal cutting processes separate materials by applying heat, with or without a stream of cutting oxygen. The three dominant processes are oxy-fuel, plasma and laser cutting.
The principle behind oxy-fuel (flame) cutting is simple: When hydrocarbons are oxidized, they generate heat. As with other flame processes, oxy-fuel cutting does not require expensive equipment, the energy source is easily transported, and most processes do not require electricity or cooling water. A torch and a fuel-gas cylinder are typically sufficient.
Oxy-fuel cutting is the predominant process for cutting heavy-gauge mild and low-alloy steel. After the oxy-fuel flame brings the material to ignition temperature the oxygen jet is turned on and burns through the material. How quickly ignition temperature is reached is a function of the fuel gas. Once the cut is established, the cutting speed depends on the purity of the oxygen and the velocity of the oxygen gas jet. High purity oxygen, optimized nozzle design and correct fuel gas mean high productivity and minimized overall process cost.
Plasma (arc) cutting was developed in the 1950s, to cut metals that could not be flame-cut (e.g., stainless steels, aluminum and copper). With plasma cutting, gas is ionized in the nozzle and focused through the nozzle’s special design. This hot plasma stream alone can be used to cut materials such as plastics (non-transferred arc). In metal cutting, an electrical arc is also ignited between the electrode and the work piece, to increase the energy transfer. A very narrow nozzle orifice focuses the arc and the plasma stream. Additional lacing of the discharge path can be achieved by a secondary gas (shroud gas). Selecting the correct plasma – shroud gas combination can significantly reduce overall process cost.
Laser cutting is the youngest thermal cutting technology and Linde’s LASERLINE® product offering serves the unique needs of laser users. Three areas are of interest here:
The laser beam is produced in the resonator cavity of the laser cutting system. While consumption of the resonator gas is low it’s purity and correct composition are critical. Linde’s LASERMIX resonator gases are quality controlled to protect the expensive equipment and optimize cutting performance. Linde offers high purity supply equipment to maintain the purity of the resonator gas from the cylinder all the way into the resonator cavity.
In order to cut the laser beam has to travel from the resonator to the cutting head through the beam path system. This system needs to be kept free of solvents, particles and fumes. Especially on high power systems (>4kW) nitrogen from a liquid source is recommended.
In laser cutting oxygen or nitrogen can serve as cutting gas. Oxygen is used for mild and low alloyed steel and the process is similar to oxy-fuel cutting. The purity of the oxygen is again important. Nitrogen is used for stainless steel, aluminum and nickel alloys to achieve a clean edge and maintain the critical properties of the base material. Here the purity of the nitrogen is important and the elevated pressure requirements require adequate booster technology.