Plasma cutters are plasma torches which are used to cut steel and other electrically conductive metals in various fields. These devices come in a range of shapes and sizes. While the smallest cutter is a compact, hand-held unit, the largest happens to be a state-of-the-art CNC plasma cutter which uses robotic arms to facilitate the process. Irrespective of which of these you take into consideration, the basic principle on which its working mechanism is based remains the same.
Back in the World War II, an advanced method of welding was developed, wherein a protective barrier of inert gas was used around the plasma arc to protect the weld from oxidation. In course of time, the engineers working on this welding device realized that it was possible to boost its temperature by speeding up the flow of gas and restricting the opening through which it passed.
With this concept, the engineers successfully developed a device which could generate enormous amount of heat, which could be used to cut a metal instead of welding it. This enormous amount of power produced by this machine made it possible for the engineers to cut through the hardest of metal with immense ease and - more importantly, with great precision over a considerably short span of time.
Plasma Cutters: How do They Work
Basic science states that heat (or energy) tends to excite molecules to an extent wherein they break free and their activity speeds up. In solids, the amount of heat that these molecules are subjected to is least, and hence all the molecules are tightly bound together to form this solid matter. As the same matter is subjected to heat, the molecules begin escaping the rigid bonds that hold them together, and thus you get liquid. When you continue heating the same, the molecules begin escaping the loose bonds, and you reach the gas state.
If you continue to subject the matter to heat even after this point, you get a fourth state which is referred to as 'plasma'. When matter in gaseous state is subjected to extremely high temperature, it speeds up the molecular activity wherein fast-moving electrons collide with other electrons as well as ions (positively charged nuclei). This in turn releases large amount of energy, which empowers these cutters to cut through metals like a hot knife would cut through butter.
In plasma cutters, an electric arc, i.e. an electric discharge, is sent through a gas - such as nitrogen or argon, which is made to pass through a small channel with a restricted opening. At the center of this channel lies a negatively charged electrode. When power is supplied to this electrode and its tip is brought in contact with the metal that has to be cut, a circuit is created which eventually results in a spark.
The spark tends to heat the gas as it makes its way through the small channel, and this heating in turn converts the gas into a plasma state. A stream of plasma is created as a result of this reaction. With a temperature of 30,000°F, this stream of plasma cuts through the metal with immense ease while moving at the speed of 6,096 m/sec.
Plasma cutters have numerous advantages over their traditional counterparts - the foremost being the fact that they are five times faster than the traditional torches used for the same task. More importantly, they are not dependent on highly-flammable gases like their predecessors, which reduces the chances of accidents by a significant extent. While these advantages do hold ground, the biggest advantage of plasma cutters is that they don't damage the surface of the metal that is being cut - and that, in turn, helps keep problems like warping and paint damage at bay.