mig polarity

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Been around a while but never heard this before. At work we are setting up a procedure to weld to different steels LCS to a 4130 shaft don't ask it's top secret for that company that make jet engines.So we get sample material and the spec'ed wire .045 flux core in and it runs like crap (spatter, cold welds) tryed for several hours finally start making calls and the wire people say reverse the polarity so we did it is smooth as warm butter.Anyone ever heard this before? We actually put the ground to the wire feeder and the power from the machine to the part.i dunno!!!!!!!!!!!!! Guess it's true you can learn something new everyday if you ask questions.Miller 330 A/BP Bernard SS coolerMiller cst 250Miller Big Blue 251DCentury 210 Mig (first welder I bought)Hypertherm PowerMax 800Victor torch setRu Fong 31 MilAtlas lathe
Reply:gas shield fluxcore wire is normally ran like that DC+, self shielded is usually DC- but there are exceptions to both.Have we all gone mad?
Reply:IIRC the switch in polarity is because of the cross sectional area of the wire.hollow wire of the same gauge as solid wire is much thinner metal wise.  There's an upper and lower limit on how much current you can put through a given area of wire without either it vaporizing and burning back. Or being too cold and stubbing into the work piece.in a similar note if you reverse your polarity in DC tig welding, most of the heat stays on the electrode and we did it to TIG braze sometimes without melting the base material.
Reply:Originally Posted by MetarinkaIIRC the switch in polarity is because of the cross sectional area of the wire.hollow wire of the same gauge as solid wire is much thinner metal wise.  There's an upper and lower limit on how much current you can put through a given area of wire without either it vaporizing and burning back. Or being too cold and stubbing into the work piece.in a similar note if you reverse your polarity in DC tig welding, most of the heat stays on the electrode and we did it to TIG braze sometimes without melting the base material.
Reply:Yep thats how it's usually run. I actually dont know why its done that way. I almost never use fcaw. I'm sure someone will chime and enlighten us.
Reply:there is a self shielded wire used for galvanized applications that runs this way not sure of the number but it is great for building gates etc from pre galvanized materialwww.burdettenetworks.com