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Practical answers on choosing and looking after the front-end parts, neck and liner of a gas-cooled MIG torch.
It can. Tips are usually made from electrolytic copper or from a harder copper alloy. Electrolytic copper conducts very well but softens at lower temperatures, so it suits lower currents. A harder alloy tip usually lasts longer at medium to high current and with rough or abrasive wire. Tips made for aluminium wire normally have a slightly larger bore, because aluminium wire expands more when heated, so use a tip made for the wire you run.The wire diameter and the thread are the first things to match. Check the torch manual or the markings on your old tip for the thread and bore before choosing the material.
Cored wires and some uncoated wires have a rougher surface than a smooth copper-coated solid wire, so they scour the bore of the tip as they pass through. The bore then opens up, the arc becomes unstable and wire may wander or burn back.If you switch to a cored wire, expect to inspect and change tips more often, and consider a harder alloy tip. Keep the liner clean and the tip tight, because worn or loose parts add to the heat load. Your wire supplier's guidance and the torch manual will say which tip suits the wire you use.
Common signs are a handle that vibrates with the arc length changing quickly, heat that you can feel travelling back through the neck and handle into the cable, and a blue or oxidised look at the end of the liner. Running for too long at high current is the usual cause. Other causes include consumables sitting too close to the weld pool (short stickout or a flush tip), mixed shielding gas, which tends to run hotter than carbon dioxide, and a poor or distant work clamp.Try shorter weld periods, a better placed clamp, a longer stickout or heavier-duty front-end parts. If it keeps happening, the job may need a torch with a higher rating. Always follow the maker's ratings and your risk assessment.
Follow the instructions supplied with the liner and the torch manual. A liner that is too short or badly seated is a known cause of wire burnback and feed problems, and cutting too short is the most common cause of early liner wear. Lay the torch cable out straight before measuring and cutting, rather than copying the old liner, which may have been cut wrongly. Cut square and remove any burr from the end.The front end of a steel liner is usually finished at an angle so that it sits centrally in the seat at the back of the contact tip. A liner that looks fused or shows melted ringlets at the end has overheated, so look for the cause as well as changing it.
The tip adaptor holds the contact tip and passes current to it. It also protects the neck thread from wear when tips are changed often. The gas diffuser spreads the shielding gas round the tip so it flows smoothly into the nozzle. On some torches one part does both jobs.Check them whenever you change a tip. Replace a diffuser if its edges look burnt, it is cracked, or its gas ports are blocked with spatter. Replace an adaptor that is loose, overheated or damaged. Different torches use different designs and threads, so match the part to the manual or to the old part.
Too much shielding gas is a common surprise. High flow can cause turbulence that pulls air into the weld zone, giving porosity and spatter. Spatter built up inside the nozzle or blocked diffuser ports also upsets the gas flow, as do draughts.Check the flow set on the regulator against the welding procedure or the wire and gas maker's guidance, remove spatter from the nozzle with suitable pliers, make sure the diffuser ports are clear, and check hose connections for leaks. Excess flow relative to the nozzle diameter is a particular cause of turbulence, so a larger nozzle is not an excuse to turn the flow up.