PLASMA CUTTERS

EVERYTHING YOU NEED TO KNOW Fuzz Townshend explains how to cut straight through metal at lightning speed

Plasma cutters are inspired by nature in a way. To watch lightning tear through the skies is to experience plasma in action and the harnessing of this natural process has provided the means to accurately cut metal, to great advantage in the workshop.

Plasma is often described as the fourth state of matter, the others being solid, liquid and gas.

By the addition of heat to a material, solids can be transformed into liquids. Apply more heat and the material becomes a gas. Apply yet more heat, in this case from an electrical current being passed through the gas, and the energy input and gas molecules will rip apart, beginning the process of splitting the atoms.

At this point, the negatively charged electrons surrounding the atoms separate from each atom’s nucleus and thus they begin to move rapidly. The remaining nuclei, known as ions, are positively charged.

As the rapidly moving electrons collide with other electrons and the separated ions, a huge amount of energy is released, which is from where the phenomenal plasma cutting power is derived.

In a workshop-type plasma cutter, a gas – most commonly compressed air – is directed at high speed through a channel, within which there is a negatively-charged electrode. Power is applied to the electrode and thus through the gas, creating the plasma state.

The metal to be cut is wired into the circuit via a return clamp and so an arc is created between it and the plasma. With the gas being forced through at high pressure and the charge applied, the very fine plasma jet created by the applied electrical current reaches temperatures in excess of 40,000 degrees Farenheit, which thus easily pierces through the metal.

With a hand-held plasma cutter, with the trigger off, the electrode and nozzle parts are held in contact with each other. As soon as the trigger is pressed, the compressed gas is first directed through a swirl ring, before being forced past the electrode, separating the latter and nozzle parts from contact and creating the spark which initiates the plasma state of the gas.

The current flow is thus transferred to the nozzle, through which the fas-flowing, swirling gas is passing, creating the plasma jet, which arcs to the metal being worked, thus cutting through it with consummate ease, rather like a precision hand-held bolt of lightning.

The cut is made precise by a further shielding flow of gas, directed around the plasma jet nozzle, which assists in keeping the cut exact.