TIG and contaminants

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I'm an armchair TIG student... someday maybe I'll actually put my hands on a machine. I've been reading a pile of stuff about it here and elsewhere, thanks for a great source of info.Anyway, I'm curious about porosity/contamination. I've been trying to figure out if it's an inherently bigger problem with TIG for some reason, or if it's just that TIG is often used to make welds that are more sensitive to contamination (like Aluminum) than other welds. Or maybe I'm confused on both points.If TIG is inherently more sensitive to contamination than other welding approaches, I can't figure out why that would be. Substrate cleaning is emphasized to such an extreme degree, but given that you have a shielding gas, I don't see why TIG would be more vulnerable than, say, another shielding gas process, like MIG.It may be something obvious... but thanks for any thoughts in any case. This site is a terrific resource.Keith
Reply:reading and doing is a lot different...when i read about tig i felt i was in for this big project. but in reality when you get the torch in your hand and your planning on welding something its not much different. get your piece clean.. just as you would with a mig gun. you will know when a piece isnt as clean as it should be. aluminum is alittle more difficult to clean but it will clean up. i wouldnt say that tig is more sensitive.. its just a more fine tuned weld, and with that you need to fine tune your work alittle bit moreMiller ab/p 330Hobart champ 16Miller 140Lincoln Power Mig 255Lincoln SA-250
Reply:Hi Keith, I have had the experience working with metals that if you overheat them especially with any form of arc, which is at 6,000 C...(steel melts at about 1,300 deg C), so if you heat metals for a prolonged period you change the nature of the metal, especially ally and stainless, ordinary steel too but not so much.I did a lot of stainless steel components with silver soldering by Oxy Acc, and if you overheat the metal it turns black and no matter what you do it is scrap, just can't be cleaned up.I did some frames using 20mm X 1.5mm wall square tubing and Tigged the joints......one thing I did learn if you overheat the joints you get a black claggy mess that needs angle grinding to recover.Alluminium melts at a much lower temperature than steel, but the tendency to overheat the metal with 6,000 deg C from the Tig arc is quite common, and I think could be the reason why so many have problems with this metal.Your thoughts would be interesting, even if only as a theory.Ian.
Reply:A a generalization, processes that rely on inert arc shielding are less tolerant to contaminants than processes that use flux (which seems to have more of an ability to remove contaminants.)Regarding inert gas aluminum welding specifically, various substances, such as water, oils, greases, and petroleum type products contain hydrogen.  A large amount of hydrogen can be absorbed in a molten aluminum puddle which can't remain homogenous when solidified.  So the excess hydrogen in the molten aluminum puddle forms pockets of hydrogen gas bubbles ("porosity") in the solifified weld bead.
Reply:My experience with contamination would be LACK of shielding gas.....Too small of a cup too fast welding speeds and drafts that disrupt the shielding gas.......That's why you see huge gas lens for aircraft welding.........  Miller Dynasty 350Twenty Six HammersThree Crow BarsBig Rock
Reply:I found my greatest enemy is when residual amounts of oils or ,horrors, paint will vapourize and become part of the shielding gas cloud with disasterous results.  When you GMAW the same area you can get away with it and get a decent weld.   SMAW and GMAW are much more tolerant of contamination.
Reply:Thanks for the insights everyone. And no, I don't imagine that reading about TIG is the same as doing it!Interesting about hydrogen in the puddle, I'll look into that further.
Reply:Just from my experience, TIG does seem to become contaminated much easier than MIG does. Just for example, on mild steel. Sure you can get a better weld by grinding the mill scale off, but it really isn't "necessary" with a MIG weld, you can weld right through the mill scale. But try that with a TIG, and it's just an exercise in frustration. The weld doesn't seem to flow right at all, sparks fly, you get porosity etc...I admit I don't know "why" that happens though, perhaps someone will enlighten me  My best guess is that MIG is more tolerant due to the fact that you often use an active gas in the mix (CO2), coupled with 70S6 filler with more deoxidizers compared to the 70S2 typically used for TIG, and you generally use more filler metal with a MIG weld thereby further increasing the volume of deoxidizers?Give me fuel, give me fire, give me that which I desire.
Reply:Primetime: very interesting thoughts.I also wonder if the puddle temperature is higher with TIG, which might allow smaller quantities of contaminants to affect things.I also like the point about flux vs. gas: It is believable that a flux would be more reactive than gas. Interesting food for thought.
Reply:Hmmmm, hydrogen in the puddle?....I would have thought that hydrogen being very inflamable would burn off instantly, so how can it exist in a molten weld pool?I have the feeling that porosity in an alluminium weld pool could be caused by the alloy constituents, ( trace metals in the alloy), in the ally boiling off at elevated temperatures........metals such as copper which melt at a lower temperature but can vaporize when the Tig arc at 6,000 C is in prolonged cantact.Here's another theory....when you have the tig on the ally weld puddle you also have the Argon gas cooling it somewhat, and as soon as you remove the "cooling" gas the weld pool getting heat from the adjacent metal just boils up and so you get porosity.......holding the gas there as in post weld gas should eliminate this......I got this effect with steel Tigging when I inadvertently removed the torch too quick and the weld pool bubbled up.Ian.
Reply:Originally Posted by puddytatHere's another theory....when you have the tig on the ally weld puddle you also have the Argon gas cooling it somewhat, and as soon as you remove the "cooling" gas the weld pool getting heat from the adjacent metal just boils up and so you get porosity.......holding the gas there as in post weld gas should eliminate this......I got this effect with steel Tigging when I inadvertently removed the torch too quick and the weld pool bubbled up.Ian.
Reply:if you are afraid of contamination go with OAW,  you can weld over paint if you feel so inclined.  Though granted you're not really welding over it.  Just burning it away before you get there.  with any process preparation is most of the work and far too often new students want to just get to the fun part and wind up with awful welds.  It's made worse when people practice on old metal that's been painted, greasy, rusty or commonly all three!Also, as you guessed it's alot about the final product, very rarely are people tigging backyard bbq pits or the like.  Usually critical stuff they don't want failing.
Reply:Sometimes if you get the steel too hot with TIG, you can boil off trace elements (for example sulfur) that may be present in the steel in trace quantities, leading to porosity.
Reply:Hi, here's a conundrum for you to ponder on.....I saw a video, I think it was on Utube, about an Oxy Hydrogen torch, the type that runs on gas generated by the electrolysis of water.Now we have Oxygen, the biggest oxidiser known combined with Hydrogen the cause of Hydrogen embrittlement in steel welding, yet it welded the steel job without a problem......How?How can you weld steel with Oxygen and Acetylene without a shielding gas to prevent the Oxygen from getting into the weld pool?I weld steel with a plasma welder and do not get porosity, even though the plasma is formed by a mix of water and alcohol in abundance.....I have a photo to prove it.Ian.
Reply:Originally Posted by puddytatHi, here's a conundrum for you to ponder on.....I saw a video, I think it was on Utube, about an Oxy Hydrogen torch, the type that runs on gas generated by the electrolysis of water.Now we have Oxygen, the biggest oxidiser known combined with Hydrogen the cause of Hydrogen embrittlement in steel welding, yet it welded the steel job without a problem......How?How can you weld steel with Oxygen and Acetylene without a shielding gas to prevent the Oxygen from getting into the weld pool?I weld steel with a plasma welder and do not get porosity, even though the plasma is formed by a mix of water and alcohol in abundance.....I have a photo to prove it.Ian.
Reply:Originally Posted by shovelonYou have to understand that the OA flame burns off in a neutral mixture producing neither  oxides or carbides when OA welding. I am not familiar with water welding, but i would assume the same thing results in a neutral burnoff.
Reply:Originally Posted by puddytatHmmmm, hydrogen in the puddle?....I would have thought that hydrogen being very inflamable would burn off instantly, so how can it exist in a molten weld pool?
Reply:Originally Posted by jakeruRegarding oxidation, steel is generally much more tolerant of oxidation (and contamination that causes oxidation) when welding than aluminum is, because the melting point of the steel oxides are below that of the parent metal, so the steel oxides will tend to harmlessly float to the surface of the weld puddle.  Underneath the oxidized surface of a steel weld there can easily be deep penetration and a very strong weld.
Reply:Originally Posted by keithwins... you're getting things plenty hot with TIG, so why doesn't it just "burn off" the paint.