Fronius MTG320i & MTB320i Parts FAQs
Straight answers on choosing, fitting and looking after the wearing parts of a gas-cooled MIG torch from one maker's range.
Which parts wear out first, and what does a worn part look like?
The contact tip, gas nozzle, insulating parts, nozzle fittings and spatter guard are the usual wearing parts, because they face heat, spatter and the constant rubbing of the wire.
The maker's instructions describe the signs to look for. On a contact tip, the wire entry and exit holes wear oval or the tip is heavily covered in spatter. On a gas nozzle, the edges are burned off, notched or clogged with spatter. Check the wearing parts every time you start work and replace any that are damaged rather than waiting for the weld to suffer.
How do I choose between gas nozzle shapes and sizes?
A nozzle trades gas coverage against access. A straight (cylindrical) nozzle gives the best gas flow and is common at higher currents, but it limits access. Conical nozzles spread gas well and keep a good view of the weld. Bottle-shaped or tapered nozzles reach into tight joints but give tighter coverage and gather spatter faster.
In general, use the largest bore that still lets you reach the joint, because a small nozzle clogs sooner and can starve the weld of gas. Heavy-duty versions are made for longer life in demanding use. Nozzles are made for a particular torch, so check the fit.
What do the insulating parts and nozzle fittings do?
They keep the live front end of the torch electrically separate from the gas nozzle, and they seat the nozzle in the right position. Without sound insulation, current can arc to the nozzle, which can damage the parts and upset the weld.
The maker's instructions list insulating parts and nozzle fittings among the parts to check for damage. Look for cracks, charring, heavy spatter or a nozzle that sits loose, and replace the part rather than cleaning a damaged one. If you use anti-spatter compound, apply it sparingly and as its maker directs.
Why does my contact tip wear out quickly?
The usual causes are overheating and a poor connection. A tip that is loose in its holder or diffuser heats up, wears faster and can burn back. The maker's troubleshooting guidance gives a loose contact tip as a cause of fast wear and says to tighten it.
Other causes include welding above what the torch is rated for, a worn or wrong-size bore, and a dirty or kinked liner that makes the wire drag. Check the tip is fitted snugly to the maker's instructions, that the size suits your wire, and that your current and duty cycle are within the torch rating.