Some of the main problems people can have are all related to welding wire feed issues. It is crucial when you are wire feed welding that the wire feeds along the gun very smoothly. Any obstruction or blockage will cause the arc to become erratic and inconsistent. When this occurs it is very hard or next to impossible to keep a constant arc voltage. Your welding arc voltage is a very critical piece of the puzzle in terms of welding spatter reduction.
Usually in most cases the cause of erratically feeding wire in your mig welding gun simply comes down to wear, tear, and dirt. Coming from a country and rural area I have seen a lot of different welding workshops of which I can compare to workshops in the city. A lot of these workshops out in the country quite often don't have a concrete floor. With all the wind out there a lot of this fine dust is picked up and blown throughout the whole workshop, and those places that don't have a sealed floor all their welding equipment gets totally covered in dust.
You can take a look at the wire feeding mechanism where the drive rollers are, and you will see them covered in dirt and metallic particles from grinding and stuff like that. All this rubbish will eventually work its way down the gun cable inside the liner. As the welding wire fees along it's going to pick up these bits of dirt and grinding dust and slowly over time the internal resistance is going to increase. This means that sooner or later the welding wire will start playing up and eventually fail by not feeding through the gun.
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