What Is a Plasma Arc?

In arc cutting, plasma is an electrically heated gas stream. By heating the gas to high temperatures, it becomes ionized, allowing it to freely exchange electrons between atoms which gives the gas its cutting amperage. By constricting the ionized gas stream with a nozzle, it concentrates all the energy to a small cross section.

Understanding Gas Swirling

Before we dive into the components of the plasma arc, we need to discuss the concept of gas swirling and the benefits it provides.

The biggest advantage is that swirling the gas increases cooling. By swirling the gas, the cooler, heavier, un-ionized gas atoms are thrown to the outside of the gas stream, providing a cooler protective barrier for the copper nozzle.

Swirling the gas also improves cut quality by evenly distributing the arc along one side of the cut – this is due to the electrical arc attaching itself to the leading edge of the cut. Without swirling, there would be a bevel on both sides of the cut.

Starting the Arc

In a plasma torch, there are three main components working together: the electrode, the gas/swirl baffle, and the nozzle. The electrode is connected to the negative side of a DC plasma power supply while the nozzle is connected to the positive side (note: the nozzle remains electrically isolated through a normal open relay).

At the beginning of the phase, the power supply places a high negative voltage on the electrode and gas begins to flow to the torch (while being swirled by the baffle). This leads to the contacts in the nozzle circuit to close which provides a path to the positive side of the power supply.

Once this point is reached, a high-frequency generator provides the high-frequency, high-voltage potential between the electrode and the nozzle, creating a small spark that ionizes a path through the gas. Through this path, a larger DC arc begins to flow between the electrode and nozzle to create the pilot arc, which is then blown out of the nozzle by the gas flow to contact the work piece.

The main arc is created when the pilot arc transfers to the work material when the torch is close enough. This is where the nozzle relay is opened and removes the nozzle from the circuit, establishing a transferred arc condition and increasing the main arc to the required cutting amperage needed for the job.

There are many variables to consider when plasma cutting, but these are the absolute basics needed to understand how plasma cutting works. For more information, feel free to contact Action Stainless with your questions and follow us on LinkedIn!