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The E7XT-X number should be written on the roll of wire somewhere. This number will tell you if you need shielding gas or not(particularly the last digit(s) after the hyphen). There are several fluxcore wires that don't require external shielding. If your wire needs shielding gas and you don't supply it, you will know in a hurry. Porosity will take over.
Slag will "normally" chip easier on the wires that require an external supply of shielding gas. However if you get your settings where they should be, the slag will "almost" fall off on it's own as it cools, unlike solid wires where the silicon has to be chipped off. We run E70T-1 and E71T-1 on our machines here. They require 100% CO2 shielding in addition to the flux in the wire. With these wires the slag will peel up like a E7018 SMAW rod when you get the machine dialed in.
Find that number on your wire and post back, someone can tell you what type wire you have by the number.
HTH,
John Wright