having trouble where i didnt before

by scott
(indiana)

i am a self taught tig welder, and have had pretty good results in the past, but i am trying to build an intake manifold for a customer.
he has supplied his own materials (t-6) plates and extruded tubing.

at first, all of the welds looked great, but the longer i worked, the worse they got. eventually, it got so bad that when i would try to heat the parent metals before adding the filler, the parent metals would "creep" away from each other, adding filler at this point would make things drastically worse. almost burning the filler away and making terrible welds. i am using a hobart 185 tigmate and straight argon.

is my shielding gas bad maybe?, could my tungsten
electrode be bad? can the tungsten get contaminated?
i have had great results until just lately.

but now i just am getting a big mess and have a lot of grinding to do.

i dont think preheating with a torch would help because the problem seems to arise after i have been working on the piece for a while and its allready hot.

it does seem to happen more frequently when i have been welding long enough for the duty cycle to run out on my welder and the thermostatic switch will shut me down for a few minutes.

does this reduce or effect the way the welder performs?
any help is appreciated.

i am using a plain aluminum filler rod that my welding supply shop set me up with, and as i said earlier, i have had good results up until now.

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The key here might be "the thermostatic switch will shut me down for a few minutes"...
When that happens, your shielding gas might be shutting off before your tungsten cools and then it turns grey because it absorbed oxygen.

when you light back up, you get instant crap...and it takes a minute for things to clean up.

if this is not the exact problem, it still sounds like a shielding gas issue either way.

anyone else got a comment?

hope this helps,
jody