Plasma Cutter Time and Temperature: Detailed Guide

Going to use a plasma cutter for the first time? Then it’s always helpful to be acquainted with the answers of some basic questions related to it. For example, what is plasma, the mechanism behind the high-temperature of plasma, etc.

The definition of plasma can be given in simplest term. Plasma is the next state of gas after you heat it up to a certain level. It is the fourth state of matter. At this state, the gas particles (atoms) become ionized and electrically conductive.

Plasma cutter uses this plasma to conduct energy from a power source to the metal you wish to cut. It’s faster and even cleaner than oxyfuel cutting process.

But this heating process isn’t something to describe in simplest term. To understand it clearly, you have to go through a detailed description.

Fundamental parts

Power supply

The power source must have a high voltage and a drooping characteristic. The operating voltage is typically 50 to 60V while the open circuit voltage can be up to 400 V.

This level of voltage is obvious to initiate the arc.

Arc starting console

This is an ASC circuit which produces 5000 VAC AC voltage at 2 MHz.

It creates the spark inside the torch which again creates the plasma arc.

Plasma torch

Plasma arc generates here. It provides a proper alignment of the consumable parts. Such as the electrode, nozzle and swirl ring. A shielding cap and inner and outer retaining cap are additional components. They are for improving cutting quality and holding all the parts.

Gas composition

In the conventional system, usually, the electrode is of tungsten. Either nitrogen or argon or argon-H2 creates the plasma. However, ‘process variants,' use oxidizing gases like oxygen or air, as described here. But the electrode must be of copper combined with hafnium.

Mechanism: how the temperature reaches high

A fine bore of copper nozzle constricts the chamber. The swirl ring isolates the electrode and nozzle. This ring spins the air around the electrode. The small vent holes transform the plasma into swirling vortex. When you switch on the power supply, it initiates the plasma gas. The nozzle connects with the positive potential while the electrode is negative.

Next, the arc starting console generates a high-frequency arc that ionizes the gas. It results in a current path from the anode to the cathode. Thus it creates the pilot arc.

When this pilot arc comes in contact with the work piece, the current path shifts to there. When the arc shifts to the work piece for cutting, the name also changes to ‘transferred arc’ mode. That opens the pilot arc circuits and turns off the high frequency.

The power supply then replaces the plasma gas with the optimum gas to cut the material.

As you can see, the heating process occurs in the chamber lies between the electrode and tip of the torch. Further heating causes the expansion of plasma gas both in volume and pressure. The torch tip opening which is narrow and small at the same time, so it constricts the plasma.

Thus it accelerates the plasma toward the work piece at speed nearly 20,000 ft. /s which is very high indeed. When plasma emanates from the nozzle, the temperature goes excess of 20,000°C.

And the velocity reaches near the velocity of sound. While cutting, the speed increases more for the deep penetration through the material. Approximately two-third of the arc energy is used for cutting.

This intensity jet melts a localized area on the metal. The pressure of the gas stream pushes through the work piece. Thus it removes the molten material in the efflux plasma.

The plasma flow is critical. Therefore, the setting of the speed depends upon the current level. Also, depends on the diameter of the nozzle bore. If they mismatch each other, it’ll result in ‘double arcing.'

One from the electrode to the nozzle and another from the nozzle to work piece. This double arcing usually affect the nozzle by melting it.

This process differs from the oxyfuel process. The plasma cutter uses the arc to melt the metal sheet. But in the oxyfuel process, the oxygen oxidizes the metal. The exothermic reaction produces heat that melts the metal.

The jet of plasma cuts through both metals with poor and excellent conductivity. Oxy-fuel torch cuts them comparatively poorly. So professionals consider plasma process as standard.

Final Verdict

See, the cleaner cut a plasma cutter produces requires physical and chemical mechanisms. Though they are a bit complicated, I tried to explain it as simply as possible in this article. The study of temperature is the study of how a plasma cutter works. I hope this article gave you the preliminary idea how the plasma in you plasma cutter produces. It will surely help you in future.

Joshua J. Salisbury
 

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