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.
What are contact tips made from, and does the material matter?
Yes, it can. Plain copper tips have good electrical conductivity and are the usual choice for general work on steel, stainless steel and aluminium. Harder copper alloys, such as copper-chromium-zirconium, resist heat and wear better, so they suit heavy use, long arc-on times and abrasive wires such as some cored or uncoppered wires, though their conductivity is slightly lower.
The right choice depends on your wire material, your welding current and how long you weld at a time, so follow the torch maker's recommendation. Some tips are made specifically for aluminium wire. Whatever the material, the bore must match your wire size.
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.