Plasma cutters work by sending a pressurized “gas” (in our case compressed air), through a small channel. In the center of this channel, you’ll find a negatively charged electrode. When you apply power to the negative electrode, and you touch the tip of the nozzle to the grounded metal (or a pilot arc touches), the connection creates a circuit. A powerful spark is generated between the electrode and the metal. As the inert gas passes through the channel, the spark heats the gas until it reaches the fourth state of matter. This reaction creates a stream of directed plasma, approximately 30,000 F and moving at 20,000 feet per second that reduces metal to molten slag. The plasma itself conducts electrical current. The cycle of creating the arc is continuous as long as power is supplied to the electrode and the plasma stays in contact with the metal that is being cut. The cutter nozzle has a second set of channels. These channels release a constant flow of shielding gas around the cutting area. The pressure of this gas flow effectively controls the radius of the plasma beam.
What does this mean to you? That small, intense plasma beam is extremely powerful and can cut through metal with ease. This also means it can wear out consumables. We get calls from time to time about customers that have had issues with their plasma cutters. The symptoms are often that the plasma cutter won’t initiate an arc on the metal, or the arc will start and stop erratically while you’re cutting. I decided to put together a few causes for those sort of issues. Hopefully one of them can save you time when diagnosing an issue with your plasma cutter.
1.Initiating an arc with no or too little air pressure- Without the air to cool the consumables the arc alone can super-heat the electrode and burn up the tungsten found in the center of the electrode almost instantly. It can happen easily and in an instant. Say you forgot to flip the pressure valve to feed your airline and hit the trigger once or twice before realizing what the issue is, you probably damaged your electrode.
2. Too slow of travel speed when cutting- Moving excessively slow when cutting (especially at higher amps) overheats the torch consumables and can cause the parts to wear out prematurely. It can also cause the arc to terminate.
3. Dragging the Torch Nozzle on work piece- This is a common mistake beginners make. It can overheat the nozzle and it also exposes the nozzle to an abundance of slag which can wear it out extremely quick.
4. Inadequate Water separator or air dryer on compressor or internal separator full. Water in the air stream will “put the fire out” in the torch. It can cause the arc to be erratic and unstable and may seem like the plasma cutter isn’t working correctly. Make sure at the least you are running a small disposable in-line water separator or upgrade to a desiccant system on your compressor. The internal plasma cutter’s separator should be checked or drained periodically.
5. Too long or small of an extension cord being used on the machine- If you have a low quality, thin gauge extension cord or too long of a cord the machine could have trouble initiating an arc or it won’t cut metal as thick as rated or the settings on machine don’t match what it can cut.
Below are some samples of bad consumables. If your nozzle has an elnlarged, oblong, or otherwise gouged out center it will cause the plasma beam to wander and will lose it’s punch. If you allow it to get too worn like seen below, it will burn a divot into the center of the electrode, thus burning out the conductive tungsten that’s creates the arc in the electrode. Lastly if you get the torch too hot or you light up the torch with no air pressure it can overheat and melt the swirl cup/diffusor and it may look something like below. This will cause the air to fail to mix in the torch and will make an unstable arc. The moral of the story is to be sure to inspect your torch parts regularly and make sure that none are worn out.