The Role of Plasma Torch Coolant
By their very nature, torches for CNC plasma cutting tables, generate a lot of heat. It clearly takes high temperatures to melt and cut metals cleanly and accurately.
The problem is that the heat that cuts thick pieces of metal can also melt the plasma torch’s electrode, nozzle, and even the torch itself, if left unchecked. That’s where the plasma cooling system goes to work and coolant is a crucial part of the system.
Managing Heat Build-up
Power Leads: Ironically, it isn’t the torch itself that generates the most heat in a plasma cutting system. That honor goes to the power leads, which pull a huge amount of electrical current and generate a substantial amount of heat in a relatively small physical space. That heat is absorbed by the coolant that flows around the copper cable on it’s trip through the hoses.
In the photo, at right, we cut through a set of leads near the torch. The blue lead is the chilled coolant (water-in) and red lead is coolant exiting the torch (water-out) flowing back to the radiator/chiller.
The water-in lead is often marked with a green band at the fitting; and water-out lead with a red band.
Electrode: Another source of heat is the electrode. A lot of current is required as the plasma arc blooms on the face of the electrode and that heat is carried off by coolant circulating through the backside of the electrode. Without coolant, the electrode itself would quickly melt.
The space around the back of the electrode where the coolant flows is very tight and forces the coolant to move at very high pressure through a small gap.
Depending on the design, the coolant may also circulate around the nozzle or the body.
The Cool-Down Process
The cooling system is closed, meaning the coolant continually circulates through the system pulling heat from the affected components.
To remain within a specified temperature range, the coolant, after passing through the torch, passes through a chiller. The chiller is essentially a radiator that uses refrigerant and a compressor to quickly reduce the temperature of the liquid.
After passing through the radiator the plasma torch coolant is returned to its starting point, the reservoir, ready for another journey through the system.
The plasma system manufacturers offer their own brand of coolant, although there are also plenty third-party brands available, that generally consists of distilled (or de-ionized) water mixed with ethylene glycol or in some cases, propylene glycol.
The distilling and filtering processes remove heavy metals from the water effectively making it less conductive.
The mix ratio of most coolant blends is approximately 3 parts water to 1 part glycol. Freeze protection can vary depending on the blend of ingredients, but can go as low as -25º F. The reason for the having the glycol in the mix is to reduce the freezing point of the water.
- Do not mix coolant types.
- Use only the plasma torch coolant specified by your equipment manufacturer.
- Don’t repeatedly “top off” the coolant without ever draining and re-filling the system. Draining and refilling the system is the only way to reduce the conductivity of the coolant. This important maintenance should be done at regularly scheduled intervals, as required by your equipment’s preventative maintenance program.
Is More Glycol better?
No. While it’s true that glycol reduces the freezing point in water, making freeze-ups less likely, it turns out that glycol reduces consumable life. In fact, reducing the percentage of glycol can increase consumable life, according to some equipment manufacturers, up to 30%.
We’ve heard that, to increase consumable life, some plasma cutting equipment operators (those in warmer climates) use a lower percentage of glycol. While it’s true that pure water is a great coolant, check the manual and always follow the equipment manufacturer’s recommendation.
Check the 5 areas listed above to keep your PHD®, Hypertherm®, Esab® or Thermal Dynamics® plasma cutting torch running smoothly.