Yes, moisture in the air is one of the most common causes of plasma electrodes and nozzles wearing out fast. Water disturbs the arc and speeds up wear of the electrode insert. It is not the only cause, though: before changing your air treatment, also check the pressure while cutting, the current setting and the way you start the arc.
Signs of wet air
- The arc crackles, changes colour or spits now and then.
- Cut quality drops with no change in settings: dross, an uneven kerf.
- The electrode insert pits after only a few starts.
- The filter bowl on the power source fills with water.
- Wear changes with the weather: it gets worse on hot, humid days.
If several of these signs add up, the air is to blame. Our page on the compressor for plasma cutting explains the role of air in the cut and the basic treatment.
A simple test in the workshop
After a long cutting session, when the compressor has been running for a while, drain the filter bowl on the power source. Then disconnect the air supply at the power source inlet and blow for a few seconds onto a clean, dry cloth or a cold mirror. Traces of moisture or oil show that the air treatment is not enough. Test at the power source inlet, not at the compressor outlet: what counts is the air that reaches the torch.
Where does the water come from? The calculation
Water comes in with the air the compressor draws in. The values below are physical orders of magnitude.
- Ambient air at 25 °C can hold at most about 23 g of water per m³.
- At 60% relative humidity: 23 × 0.6 = about 14 g of water per m³.
- A compressor delivering 0.5 m³/min for one hour draws in 0.5 × 60 = 30 m³ of air.
- Water drawn in: 30 × 14 = 420 g, close to half a litre per hour.
Once compressed, the air can no longer hold all that water. It condenses as the air cools: in the receiver, in the pipework and, if nothing stops it, in the hose and the torch. A refrigerated dryer cools the air to a few degrees and removes the water before the network. The hotter and more humid the intake air, the more water there is to remove, so a cool, ventilated room helps. See compressor room installation.
Other causes to rule out
- Wrong pressure while cutting. Too low and the arc becomes unstable; too high and it starts poorly. Read the power source gauge during a cut.
- Not enough flow. A compressor that is too small, a hose that is too long or too narrow, undersized quick couplings.
- Wrong current or consumables. Running above the rating of the consumable, or mixing parts from another range, wears the electrode quickly.
- Frequent starts. Every arc start wears the electrode. Cutting lots of small parts wears it more than long cuts.
- Oil in the air. A lubricator on the line, or a hose that has carried oiled air.
Stop the water before the torch
- A refrigerated dryer after the compressor. It is built into the K 75 (1.1 m³/min at 8 bar) and the K 110 (1.7 m³/min at 8 bar). With a standalone compressor such as the S 75, choose a dryer sized for its flow: see which air dryer to choose.
- Filtration of particles and oil aerosols. Our compressors are oil-lubricated: filtration after the compressor holds back the oil carried over.
- Automatic draining on the receiver and at the low points of the network, with an automatic condensate drain.
- Take-offs from the top of the main pipe, so that leftover water does not run down to the power source.
- A filter at the power source, in addition to its built-in filter, if the maker recommends it.
If the torch maker states an air quality class, our technicians will work out with you the treatment that reaches it, using our ISO 8573-1 guide. For a check of your installation, send us your power source data sheet with a quote request.
For your trade: Compressor for plasma cutting.