What really limits a station
A 400 A machine with a 60 percent duty cycle will not give you 400 A for 6 minutes if the torch is rated for 250 A. What limits a station is always the weakest element in the current path, and at high currents that is the torch.
A gas cooled torch carries heat away through the power cable and the flow of shielding gas. A water-cooled torch has a separate coolant circuit that takes the heat out of the neck and the lead. At 400 A the difference is not a matter of comfort but of whether the neck survives a full shift.
Torch duty cycles
Below are indicative values for MIG/MAG torches in an M21 mixture, at 60 percent duty cycle for gas cooled torches and 100 percent for water-cooled ones. A particular model may differ, and in pure CO2 manufacturers usually quote slightly higher values.
| Torch class | Cooling | Current in a mixture | Duty cycle | Typical use |
|---|---|---|---|---|
| Light, up to 180 A | gas | 150 to 180 A | 60 percent | sheet 1 to 4 mm, assembly work |
| Medium, up to 250 A | gas | 200 to 250 A | 60 percent | metalwork shop, structures up to 8 mm |
| Heavy, up to 320 A | gas | 280 to 320 A | 60 percent | structures 8 to 15 mm, short runs |
| Water-cooled, 400 A | water | 350 to 400 A | 100 percent | continuous welding, long runs |
| Water-cooled, 500 A | water | 450 to 500 A | 100 percent | heavy sections, mechanised welding |
Look at the last two columns together. A 320 A gas cooled torch at 60 percent gives 6 minutes of arc in every 10. A 400 A water-cooled torch at 100 percent has no break at all, so on the same shift you will lay down half as many metres again.
Three cases from the workshop
250 A on gas: a gas cooled torch is enough
A metalwork shop welding frames from 40x40x3 section and sheet up to 6 mm works at 160 to 220 A. The runs are short, 100 to 300 mm, with breaks to reposition the part. The actual arc time is 1.5 to 2.5 hours a shift.
Here a gas cooled torch of the 250 A class is the right choice. It is lighter, cheaper, it has no coolant hoses and there is nothing to spring a leak. A cooler would be one more piece of equipment to service with no gain.
300 A on gas: the limit at which it still works
A workshop welding channel sections and plate of 8 to 12 mm works at 260 to 300 A. If the runs are 300 to 600 mm with a break between them to clean and set up, a 320 A gas cooled torch will cope. There is one condition: the torch has to be chosen with a margin, not right on the edge.
A 320 A gas cooled torch used at 300 A gets hot in the neck. After an hour the handle becomes unpleasant and the contact tip wears out faster. The work is possible, but every extra metre of weld pushes the sums towards water cooling.
400 A on water: there is no alternative
A plant welding beams and brackets from plate of 15 to 25 mm works at 320 to 400 A, in runs of 1 to 3 metres, several passes per joint. Arc time reaches 5 hours a shift. A gas cooled torch in those conditions will not last until the morning break.
Here water cooling is not an economic choice but a condition of the work. Added to that is the welder's comfort, because at the same current a water-cooled torch is cooler and slimmer in the hand than its gas cooled equivalent.
What it costs to start with
| Item | Indicative net price |
|---|---|
| Gas cooled torch 3 m, 250 A class | 200 to 450 zloty |
| Gas cooled torch 3 m, 320 A class | 300 to 650 zloty |
| Water-cooled torch 4 m, 400 to 500 A class | 800 to 1 800 zloty |
| External cooler with a trolley | 2 500 to 5 000 zloty |
| Coolant, pack of about 10 l | 120 to 250 zloty |
On premium machines of the 400 A class and above, the cooler is part of the set or a module that slides under the power source, so its cost is often already included. Check that in the list of what is included with every machine, because it is an item worth several thousand zloty. We list the contents of the set on every unit in the used MIG/MAG category.
Running costs, where the matter is settled
Take a workshop working 4 arc hours a day at 350 A, 20 days a month, that is 80 arc hours a month. Below is the same workshop on a gas cooled torch pushed to its limit and on a water-cooled torch.
| Monthly item | Gas cooled torch at the limit | Water-cooled torch |
|---|---|---|
| Contact tips | 60 pieces, 240 zloty | 10 pieces, 50 zloty |
| Gas nozzles | 4 pieces, 160 zloty | 1 piece, 45 zloty |
| Necks and liners | 100 zloty | 25 zloty |
| Complete torch, spread over months | 100 zloty | 60 zloty |
| Coolant | 0 zloty | 15 zloty |
| Consumables in total | 600 zloty | 195 zloty |
| Downtime changing tips | 3 hours, 450 zloty | 0.5 hours, 75 zloty |
| Total | 1 050 zloty | 270 zloty |
The difference comes to 780 zloty net a month. The investment is a cooler at 3 500 zloty plus a water-cooled torch at 1 200 zloty minus the 500 zloty you do not spend on a gas cooled torch, that is 4 200 zloty. The payback works out at about 5 to 6 months.
The figures are an example and depend on how many tips you actually burn through. Put your own in: count how many packs of tips you buy in a month and how many times a day the welder walks away from the station for a new nozzle. That second item is often larger than the first.
With TIG the limit sits lower
Gas cooled TIG torches run out at roughly 150 to 200 A on direct current. On alternating current for aluminium take off about 30 percent of that, because half of each cycle falls on the polarity that heats the electrode and the torch harder.
Water-cooled TIG torches work at roughly 200 to 400 A and are noticeably slimmer with it. That matters when welding in tight spots, where a thick gas cooled torch will not go in at an angle. If you weld aluminium above 5 mm or stainless steel thicker than 6 mm, water cooling on TIG is effectively a requirement.
Looking after the circuit so that it works
A cooler has three things to watch: the coolant level, its condition and the clearance of the heat exchanger. Change the coolant roughly once every 12 months, or sooner if it darkens and leaves sludge. Spent coolant loses its anti-corrosion properties and starts to silt up the channels in the torch neck.
Do not top up with plain water or with automotive coolant. Welding coolants have reduced electrical conductivity, which matters on a torch carrying voltage. Once a quarter, blow out the fins of the heat exchanger and check that the cooler fan turns freely.
When not to buy water cooling
- Arc time below 2 hours a day and currents up to 250 A: the running costs are too small for anything to pay back.
- Work away from base and installation jobs: a cooler is one more piece of kit to carry, and the coolant hose is easily damaged.
- An unheated workshop in winter: the coolant has to have frost protection, and during shutdowns the circuit has to be protected.
- A tack welding station: short arc strikes do not heat the torch enough for the coolant to have anything to take away.
In those four situations a strong gas cooled torch with a current margin is cheaper to run and simpler to handle. The current margin matters more here than the type of cooling.
What to do before you spend the money
Check whether your machine has a cooler connector and cooler control, because not every design supports it. Machines with a cooler socket also have a flow sensor, which blocks welding when there is no coolant and protects the torch. If the machine cannot be extended, replacing the power source is sometimes cheaper than adding an external cooler.
Machines prepared for water cooling are in the new MIG/MAG and Migatronic categories, and for Migatronic we are the authorised distributor and service centre. If you want to do the sums on your own job first, take a set with a cooler on rental for a month and compare how many tips you use.
We will work out the payback on your figures
Give us your working current, your daily arc time and your monthly consumption of contact tips, and we will prepare a comparison for your station together with a torch and cooler selection. Call or write, and if the machine needs its circuit checked first, book it into our service centre for a cooling system inspection.