Gas for tig welding

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What mixture of gas do I need to tig weld steel?All i have right now is straight Argon for the mig gun for welding aluminium,I thought it was C02/Argon for welding stainless with the tig.But I aint sure about just welding steel.Thanks        Jeff
Reply:Straight argon will do for any tig welding, to get more heat, there are mixes with either helium and argon, or nitrogen and argon, I think.Owner of Welding Wiki,The free wiki based resource for weldor's around the world.http://www.weldingwiki.comWe have cookies!
Reply:Thanks,Atleast now i can start my self taught cours of tig welding.I have a full bottle of argon and i just was not sure if i could use it for steel,but now i know.Thanks again                   Jeff
Reply:Jeff,For TIG of steel, stainless steel, copper, aluminum, and any other weldable metal or alloy such as Inconel, Hasteloy, whatever, is done with straight Argon shielding gas.Argon/Helium mix or Helium may be used for any weldable metal/alloy as well.  For thicker aluminum, over 1/4", 100% helium with direct current electrode negative (DCEN) may be used without any need to preheat as may be needed with alternating current (AC) and argon.  Helium is commonly said to "weld hotter" than argon.  The science behind this is actually that helium is a far better thermal conductor than argon and the arc power transfered to the pool may be increased from about 75% for argon, to about 85% for helium.  Additionally, for a given current, the arc voltage (thus arc power) for helium is about 2-3 volts higher.Another mix for TIG is argon-5% hydrogen, comonly used for precision autogeneous (no filler metal) welding of austenitic (300 series) stainless steels and high nickel alloys.  Hydrogen is also "hotter" than agon, in this case diatomic hydrogen, two molecules, H2 absorb arc energy in being disassociated to monatomic form in the arc, then when consequently recombining at the weld pool it very effectivey transfering this energy to the pool.  This may be called a "reactive thermal conductivity".  Additionally, hydrogen has the effect of "reducing" metal oxides from the weld.  In this case "reducing" means the chemical reaction breaking down metal oxide in the arc and combining the oxygen and hydrogen to form water vapor.  This may be benificial in critical nickel alloy welds.  Also, apparently the Ar-5%H arc tend to be more constricted than pure Ar."Reactive" gases such as oxygen and CO2 are never used with TIG since they oxidize the tungsten electrode and the weld.Lastly, nitrogen may be used as an economical "purge" gas to protect the backside or inside of some types of stainless steel tubing or containers.  Nitrogen can react with molten metals forming detrimental nitrides (hard and brittle compounds) so it is not used as a primary TIG shield gas around the arc.Hope this helps.
Reply:I've never heard of using Ar-5%H for aluminum.  I'd like to give that a try.  My TIG supply won't do AC, and I don't really have a need, but I'd like to play with DCEN on aluminum.-Heath
Reply:Just to clarify the gas choices.Argon-5%Hydrogen is not used for aluminum, it is used for stainless and nickel alloys that are austenitic, non-heat treatable, such as 300 series stainless, Inconel, and Monel.I suspect if 5%Hydrogen were used on aluminum you would end up with swiss cheese, lots of porosity.  Aluminum is very very suceptable to porosity from any form of hydrogen, such as moisture, oils, any hydrocarbons, even oil from your fingers.  Molten aluminum can dissolve (hold in solution) hydrogen, but solid aluminum cannot, so as the weld solidifies any hydrogen forms porosity.Again, just for clarification, do not us 5%Hydrogen on carbon steels.  I suspect porosity could again be an issue, but also hydrogen cracking (also called cold cracking, delayed cracking, underbead cracking) can be a real problem, particularly on higher carbon, higher strength, more hardenable steels.  Hardenable steels are austenitic at high temperature and can hold large quanties of hydrogen, but upon cooling the structure changes to ferrite and martensite, which cannot hold hydrogen to the same degree, so the hydrogen actually causes an stress within the metal and can produce brittle failures (cracks) in the hardened heat affected zone next to the weld.
Reply:Howdy Howdy!   I would like to thank you for your commentary and interesting reasons for gas choices   It goes along with my Lincoln welders bible.  But your explanations are easier to understand then the lincoln books are.  I see your a newer member pulser, welcome!  Do you think I could realistically use 2 gases for my mig and tig uses?  I have a 250 cu ft tank of 100% argon for all my tig neads, and alluminum mig,  and then an 80 cu ft tank of C-25 for mig steel.  The 80 cu ft tank will be traded up to a 250 when it's empty.  With these two tanks, I HOPE I can weld all common metals in either the mig, tig, or both processes.  My machine is an Invertec V-350 multi-process CC/CV DC inverter unit.  It has 8-425 amps of output.  350 amps at 60% duty cycle.   ( I nead to pay it all off before I can get the actuall wire feeder unit) So currently I am using it in stick mode, with amazing results!  I love the hot start and arc force control features the advanced process panel gives me! working on building my metals shop. Thanks for the input!  Brian Lee  Sparkeee24Last edited by Sparkeee24; 11-14-2005 at 10:38 PM.
Reply:IMO we could probably keep it simple by just saying run  pure argon for all your metals except aluminum, and either run a pure argon, or a 75/25 ar/he for the alum.  The avg home user is not welding the Hastelloy, Inconell, Monell, Titanium,  or these types of exotic alloys commonly found in the aerospace industry This is the general rule of thumb I use at work, and I have been welding these exotic alloys for 20+ years. And referencing my commonly used welding specs BAC5975, MIL -STD 2219, AMS1595, AWSD1.1  would support the aboveI am sure there  are exceptions to the "rule" based on certain industry standards, but for the avg individual the 100% argon will work just fineedit: this is of course for the TIG process, for Mig use your pure argon on Alum, I prefer 75/25 ar/c02 for the  steel alloy mig and you need the tri mix for the SS migLast edited by elderthewelder; 11-14-2005 at 11:03 PM.
Reply:Reply to Sparkeee24,checked the Lincoln site, your V-350 is a very nice machine.Your two bottle idea sounds good.Argon for steel/stainless TIG and aluminum MIG.CO2 for short arc steel MIG.With two flow meters and a "Y" you can mix your own 75Argon/25CO2 for reduced spatter short arc MIG on steel.For spray or pulsed spray MIG of steel 92Argon/8CO2.For spray or pulsed spray MIG of stainless steel - 95Argon/5CO2.  This may be ok for short arc stainless as well, haven't tried it, though as mentioned by Elderthewelder, tri-mix with some helium is generally recommended.So, all your V-350 is missing is AC for moderate thickness aluminum with Argon.  I have used DCEN TIG with helium for 3/8 to 1/2" aluminum, works well with excellent preweld cleaning.  Have not tried DCEN TIG on thin aluminum with Argon, theoretically it should work ok with excellent preweld cleaning.Comment on AC TIG of aluminum - during electrode positive portion of AC, surface oxides are removed from the base metal, adjusting the "balance setting" on some power supplies allows the width of the "frosted" cleaned area to be adjusted, and also affects the degree of balling on the tungsten.  During the electrode negative portion of AC, weld penetration is achieved.
Reply:Howdy Howdy!  This is a very informative thread folks!    OK!  next comment/question.   So 100% Argon, I have.  I have 2 nice flowmeters, no Y as of yet.  Would it be good to go with 100% CO2, and try and mix my own?  How realistically feasable is this?  Can I actually get my percentages accurate enough?  or would it be better to go with 75-25 mix  in pre-mixed form?  I have looked at mixer things, and they're horribly expensive especially since they're such a specialty item.    second comment:  I plan to go with mig for alluminum, since it has the cool programs and such for pulse on pulse, and various waveforms.   I would like to get an MK-Lincoln pushpull cabinet for alluminum. Maybee a cheep spoolgun. but before that would be an LF-72 wire feeder unit.  for 750$ new including cables and 400 amp mig gun, that's hard to beat I think.  Well, I am a weekend warrior of sorts.  For welding, camping, building, whatever I am doing.  So my neads are in those directions.  I have 4X4's I like to work on,  (thick parts too, like cut and turning axle tubes)  I also work with farm machinery, repairing and improving them.     Thanks for all the great info folks!  Brian Lee  Sparkeee24!
Reply:Speaking of mixing gases, has anyone seen a relatively low flow welding flowmeter for CO2?  If I'm running 30CFH of C25 that's 7.5CFH of CO2 and if I want to run 30CFH of C5 that's 1.5CFH.  I can't really get that kind of precision out of a standard flowmeter.-Heath
Reply:I think halbritt is correct in his calculations and makes a good point about the problem of measuring small flow rates.  The way I understand it, gas mixes are done as % by volume.  So as halbritt says, 30CFH of C25 could be mixed as follows:30 CFH x 75% Ar = 22.5 CFH Ar30 CFH x 25% CO2 = 7.5 ArNote 1:  If you are using a flow meter with three different scales, Ar, CO2, and He, make sure you are reading the correct scale.Note 2:  Flow meters are built and calibrated to operate a particular pressure setting.  The inside of the tube has a specific taper and different material/density float balls are used for different density gases, flow ranges, and operating pressures.  If you have an adjustable high pressure regulator and a precision ball type flow meter attached, you must know what pressure that flow meter was designed to operate at.One flow meter company I know of, McCrometer, provides precision meters built for a particular gas, operating pressure and flow range, but they are not cheap.  http://www.mccrometer.comIf someone comes up with an inexpensive solution, please lets us all know.
Reply:I have seen some medical grade flowmeters, but not for shielding gasses.  They are supposed to be high precision, low flow, because of their application.  I have even seen digital flow meters in hospitals, but the medical staff got upset when they saw me trying to unhook it from my uncle to examine it .  I have seen some of the regular ones come up occasionally on ebay.  Do you think there is a chance these medical grade meters can be used along with the solution to a math problem to make a mixer work?  Seems like a mixing chamber would help also...something like a fuel injection rail/manifold, but backwards.Smithboy...if it ain't broke, you ain't tryin'.