Let the Weld Guru guide you through the world of PAC, Plasma Cutting, Plasma Arc
The PAC, Plasma Cutting, Plasma Arc cutting process cuts metal by melting a section of metal with a constricted arc.
A high velocity jet flow of hot ionized gas melts the metal and then removes the molten material to form a kerf.
The basic arrangement for a Plasma Cutting torch, similar to the plasma arc welding torch, is shown in figure 10-71.
PAC, Plasma Cutting, Plasma Arc
Three variations of the process exist: low current plasma cutting, high current plasma cutting, and cutting with water added.
Low current arc cutting, which produces high-quality cuts of thin materials, uses a maximum of 100 amperes and a much smaller torch than the high current version.
Modifications of processes and equipment have been developed to permit use of oxygen in the orifice gas to allow efficient cutting of steel.
All plasma torches constrict the arc by passing it through an orifice as it travels away from the electrode toward the workpiece.
As the orifice gas passes through the arc, it is heated rapidly to a high temperature, expands and accelerates as it passes through the constricting orifice.
The intensity and velocity of the arc plasma gas are determined by such variables as the type of orifice gas and its entrance pressure, constricting orifice shape and diameter, and the plasma energy density on the work.
PAC, Plasma Cutting, Plasma Arc
For high current cutting, the torch is mounted on a mechanical carriage.
Automatic shape cutting can be done with the same equipment used for oxygen cutting, if sufficiently high travel speed is attainable.
A water spray is used surrounding the plasma to reduce smoke and noise.
Work tables containing water which is in contact with the underside of the metal being cut will also reduce noise and smoke.
The plasma arc cutting torch can be used in all positions.
It can also be used for piercing holes and for gouging.
The cutting torch is of special design for cutting and is not used for welding.
(6) The metals usually cut with this process are the aluminums and stainless steels.
The process can also be used for cutting carbon steels, copper alloys, and nickel alloys.
(7) Special controls are required to adjust both plasma and secondary gas flow.
Torch-cooling water is required and is monitored by pressure or flow switches for torch protection.
The cooling system should be self-contained, which includes a circulating pump and a heat exchanger.
(8) Plasma cutting torches will fit torch holders in automatic flame cutting machines.
(9) The amount of gases and tines generated requires the use of local exhaust for proper ventilation.
Cutting should be done over a water reservoir so that the particles removed from the cut will fall in the water.
This will help reduce the amount of fumes released into the air.
Plasma arc cutting can be used to cut any metal.
Most applications are for carbon steel, aluminum, and stainless steel.
It can be used for stack cutting, plate beveling, shape cutting, and piercing.
Ear protection must be worn when working with high-powered equipment.
(1) The noise level generated by the high-powered equipment is uncomfortable.
The cutter must wear ear protection.
The normal protective clothing to protect the cutter from the arc must also be worn.
This involves protective clothing, gloves, and helmet.
The helmet should be equipped with a shade no. 9 filter glass lens.
(2) There are many applications for low-current plasma arc cutting, including the cutting of stainless and aluminum for production and maintenance.
Plasma cutting can also be used for stack cutting and it is more efficient than stack cutting with the oxyacetylene torch.
Low current plasma gouging can also be used for upgrading castings.