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Contact tips, nozzles, diffusers and liners for a mid-size MIG torch: how to pick the right ones and keep them working.
Work from the quickest checks to the longest. If the drive rolls turn but the wire does not move, look at the drive rolls first: they should be the right type for the wire, not worn, and set to the right tension, because too little pressure can stop the wire feeding. Then check the contact tip for a blockage or debris and replace it if needed.Check the liner last, as it takes longer to inspect and replace. Look for kinks, wear, debris, the wrong size, or gaps where it was poorly trimmed. Also make sure the wire is clean and not tangled on the spool. If the drive rolls do not turn at all, follow the troubleshooting section of your machine manual.
Choose the nozzle shape and bore that your torch is designed for, and check the manual for the ones that fit. In general a larger bore gives better gas cover and suits higher current, while a tapered or shorter shape gives better access in tight joints.Spatter that blocks the nozzle or diffuser can restrict the shielding gas flow and lead to spatter and porosity, so clean or replace a nozzle that is clogged, damaged or out of round. Clean it with a brush or tool made for the job rather than pliers, files or hammering, which can damage the nozzle and the parts inside.
The diffuser sits at the front of the torch neck. The contact tip screws into it, and it spreads the shielding gas around the tip so that it forms an even shield over the weld pool. It also helps pass current to the tip.Clogged gas holes restrict the gas flow and can lead to spatter and porosity, so clean or replace the diffuser if they are blocked. Replace it too if the threads are damaged, if the tip will not seat firmly, or if it is worn or damaged by heat. Worn diffusers and seals can also spoil gas cover. Fit only the type specified for your torch.
Not necessarily. Too little shielding gas leaves the weld exposed to air and can cause porosity and spatter. But very high flow can also be a problem, because it can create turbulence that draws air into the shield and causes porosity of its own.Check the flow against the guidance for your wire and gas, then look for blocked nozzles or diffuser holes, damaged O-rings or hoses, and draughts. If the problem remains, ask your gas supplier or the maker for advice.
