Plain answers on the parts around a water-cooled AC/DC TIG welder: the cooling unit, torch necks, adaptors and fittings.
Why does an AC/DC TIG welder need AC for aluminium?
Aluminium carries a tough oxide film on its surface that melts at a much higher temperature than the metal underneath. AC power must be used on aluminium because the electrode-positive part of each cycle lasts long enough to break up the oxide and clean the surface, while the electrode-negative part gives the heat and penetration.
That is why a machine that can switch between AC and DC suits mixed work, and why the torch, tungsten and gas parts you choose need to suit both modes.
Can I run a water-cooled torch without coolant, even briefly?
No. Never operate a water-cooled TIG torch without coolant, as the torch can be damaged within moments. At every start-up, check the water connections for leaks and check the coolant level in the tank, and bleed air from the cooling unit if the manual says to.
While you weld, confirm that coolant is circulating. On many cooling units you can see a regular return flow in the tank. If you cannot, stop welding and find out why before you carry on.
Which tungsten electrodes suit AC welding of aluminium?
Lanthanated and ceriated electrodes are common choices for AC welding of aluminium on inverter machines, but the best type depends on the machine, the current and the work, so follow the electrode maker's and machine maker's guidance. The tip shape you use also matters, and a slightly blunted tip is often preferred to a needle point.
Always match the tungsten diameter to the current and to the collet and collet body you use. If you are unsure which electrode suits your machine, ask our team or check the manual.
Why use a water-cooled torch instead of an air-cooled one?
Water-cooled TIG torches carry coolant through the torch and cable, so they cope better with sustained high-current work. They suit regular shop use, while air-cooled torches rely on shielding gas and the surrounding air, which limits how hard they can be worked. Because the coolant removes the heat, the front-end parts of a water-cooled torch can also be smaller.
It does need a cooling unit, hoses and regular checks of the coolant. Torch ratings are normally given as a current at a stated duty cycle, so read the two together.
What coolant should I use in a TIG cooling unit?
Use the coolant the cooling unit and torch maker specify, usually a commercial welding coolant made for TIG torches. Do not use car or RV antifreeze, alcohol or home-made mixes, and do not mix brands or types, because the wrong fluid can damage the pump, torch and hoses. Ordinary tap water is best avoided, as its dissolved minerals make it conductive and leave scale in the torch and cooler.
Distilled or deionised water on its own gives no frost or algae protection. Check the manual for the type, the mix and the capacity, and for freezing protection if the unit is used in the cold.
How often should I check and change the coolant?
Check the coolant level and its appearance before welding, and look for leaks around hoses and fittings. How often to change the coolant depends on the cooling unit, the coolant type and how heavily it is used, so follow the figure in your cooling unit manual.
Topping up is not the same as replacing, because old coolant can lose its protection, reduce flow and let the torch run hotter. If the coolant looks cloudy, brown or dirty, or has particles in it, drain, flush and refill sooner, then bleed any air from the circuit as the manual describes.