i'm a novice tig welder, and have been having a lot of problems welding mild steel. i took a class about 10 years ago, using an older miller syncrowave, and tig was basically a snap then -- nice & slow, clean & methodical. i've since bought a used miller econotig, and while the unit seems to work ok, the welding is much more troublesome. i'm generally practicing on anywhere from 1/16" to 3/16" steel plate & angle, using argon at 20 cfm (or cfh -- i forget how it's calibrated) and dc w/ electrode negative at around 80-100 amps, and switching back & forth between 3/32" & 1/8" ceriated tungstens. i started with thoriated, but got scared off by the radioactivity of the thorium dust from grinding the tips (wasn't aware of it when i bought my first tungstens). i'm grinding the tungstens longitudinally to a30 degree +/- point on an aluminum oxide wheel used only for tungstens. i'm also trying to get the base metal in the weld areas as clean as reasonably possible. i'm also preflowing the argon & using the hi-freq-type start (i don't know if econotigs have true hi-freq or some capacitor discharge starter).
i have no idea what i'm doing wrong!! i'd appreciate it if any of you could offer any advice with the following issues (or anything else that seems relevant):
- my tungstens get contaminated incredibly fast. i can weld for maybe 2 to 4 linear inches & have it come out ok. then everything gets screwed up. even when i don't mess up & touch the puddle or filler rod, the electrode seems to get nasty-looking and poorly-performing quickly. it's almost like the weld puddle spews a spray of molten steel onto the tungsten. and sometimes the puddle does spit. if i try to back off the foot pedal to lower the puddle temp slightly so that the puddle doesn't spit, then the arc is less stable. after things start going bad, often the arc starts wandering & comes out the side of the electrode tip. i find that, if i crank the amperage up, i can kinda "blow" the arc back out thru the electrode tip -- forcing it, i guess, but it still performs poorly, and everything, obviously, gets too hot. i'm ending up with welds that have these porous spots that look kinda like the mineral pumice (that light lava rock), although the voids tend to be angular-looking & kinda follow the lines of the weld puddle ripples.
- i'm using copper-coated filler rod -- have some in 1/16" and some in 3/32". my welder will hardly even melt the thicker rod during the kind of practice weld's i've been doing -- i either have to melt the rod off with the arc directly, rather than melting it off while dipping into the puddle (i know this is a no-no) or crank the amperage up so high that i start melting thru the base metal. is it normal for 3/32" rod to be too thick for the material/amperage i'm working with?
- is it true that mill scale on rolled steel shapes will impede tig welding?
- is one kind of tungsten better than another for mild steel?
- when you contaminate a tungsten, is it true that you have to break off the tip & grind a completely new point? a welding manual i read said to do this, but a local welding supply place said no -- just grind off the contamination & reshape the tip. i've tried it both ways, and the break-off seems to maybe be better, but even so, it's always only a short time before the problems mentioned in #1 above recur.
- i live in michigan -- pretty cold now (mid 20's-30's), and my welding setup is in an unheated garage. i'd like to keep practicing thru the cold weather, but will the steel act up when welded cold (excessive thermal shock, cracking, etc.)? preheating may be possible, but is kinda dificult for my arrangement. and i don't understand how you could preheat stuff with an oxyacetylene torch & then not have to clean up the base metal from the torch soot/oxidation after preheating. while you're cleaning it up, it seems like you'd lose your preheat.
- my interest in tig stems from my boyhood interest in bmx bikes. the high-end frames have the most beautiful tig welds i've ever seen. the thing i can't understand is how the welders get the ripples so far apart. a lot of those welds have maybe 1/16" or even 1/8" between ripples (on welds that are about 1/8" to 5/32" +/- wide. even when i didn't have the troubles i'm having now, i've never been able to get my beads to be so (for lack of a better way to describe it) laid-out & leisurely-looking. mine tend to have the ripples a lot more closely-spaced & busy-looking. does this nice kind of weld bead result from some type of pulsed welding?
- are econotigs known to be troublesome machines? i don't know if the problem's me or the welder.
sorry for such a long message. thanks for any help you can offer.