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Hi Mike, I bought a cylinder of tri-mix cover gas, 75%HE 23%AR 2%o2, so I could use one cover gas for Tig, Mig or a purge gas. Although more expensive I only have to have one gas cylinder for all my welding needs so it's cheaper in the long run. I haven't bought a cylinder lately (10yrs) so it's got to be around $75? Here's something I wrote about cover gases last month. Helium adds high thermal conductivity with-in the arc reducing it's density. Read this as a cheap(free) amperage increase. Increases penetration and flatens the weld bead contour. Argon adds arc stability with shallow penetration, lowers weld spatter and removes oxides at the weld surface. Qxygen in amounts upto 5% can be added for broading the penetration in the center of the weld bead, controls undercutting and helps improve arc stability. Co2 can be added but has a spatter problem on most thin gauge metals and defeats my useage. O2 on the other hand enhances the tri-mix. You will see more splatter changing to the Co2 with less penetration. If your not welding on maxmium voltage you will be. You will need a female flare to Co2 adapter about $10 ?. You will use your current flow meter. Each Co2 cylinder comes with a new gasket on a rubber band around the neck. In the shop I can usually get away with using 15cfh flow Mig, so I don't use much. T_Bone
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