Inert Gas Cylinder Questions

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I'm finally looking at getting a gas cylinder for my lil MIG. I have a few questions before I go to the LWS. 1. How long will a 40 cf cylinder last if run constantly? (I know it won't be run constant but this is for reference)2. What is the best gas mix for welding steel?3. Is there a gas mix that will allow you to weld aluminum, stainless and mild steel with a filler wire change?4. What do I need to check to make sure I get a cylinder that I can get serviced in a different state? (I'm retiring from the USAF in 6 months)5. How hard is it to get a cylinder re certified and cost?I read a lot on this forum, and I've learned a lot. Thanks
Reply:1:  The cylinder will last (approximately) according to the formulavolume of cylinder / flow rate of gas = how long the gas will flowA typical flow rate for a small MIG is 20 cfh, give or take.  So that means your 40 ft3 cylinder will let you flow 20 cfh for about 2 hours.  That's 2 hours of arc or trigger time, not 2 hours of project time.2:  It depends on the specific type of steel (stainless steel generally uses a different gas for MIG than plain low-carbon steel does).  That said, for a small MIG unit and welding on mild steel, the general purpose gas is C25 (75% argon and 25% CO2).3:  Not with the MIG process.  With TIG you would use pure argon for all three materials (or at least you generally could use just plain argon).  With a small MIG unit and limited to short-circuit transfer only, you'd need a tank of gas for the mild steel (C25), a tank of gas for the stainless steel (tri-mix), and a tank of plain argon for the aluminum.4:  Keep the sales receipt as proof of ownership.  5:  Most of the time you just drop off 'your' cylinder and pick up an already filled cylinder in exchange.  You rarely actually keep just the one cylinder.  The constant exchanging means you usually always have a 'valid' cylinder.  Most of the time that cost of having cylinders recertified is all part of the business cost of paying to get the cylinder refilled.YMMV.
Reply:What Moonrise said. If you buy used tanks and a LWS near you will exchange them they will charge apx $25 for a new date stamp if needed. SO, re-testing isn't expensive. If you get a good deal on some used tanks just make sure there's NO physical damage to them, dings and small scrapes are allowable. Being on base you might very well be able to find some killer deals from guys shipping out !!Good Luck and Happy Retirement !!Anything worth doing is worth doing RIGHT
Reply:I own all six of my tanks outright. I drop off one and pick one up. If they will swap this is always best but were im at that is just not an option. I know people are going to talk about what im going to say but I feel me welding record will back me up here. I use 100% argon for everything. Last week for example I welded a stainless intake for a motorcycle, A bucket for a large track hoe, A broken aluminum trailer, and provided a welding sample to a potential client on stainless and cabon steel. So in doing that I MIG welded steel, stainless steel, and Aluminum all with my MIG (aluminum was done in pulse) and I TIG welded stainless steel and steel. No trouble at all with any welds or penitration I have even done penitration test with iodine and get great penitration on steel with pure argon. Steel Thunder Welding LLC. St. Thomas VI USAMM350PBOBCAT 3MAXSTAR 150 STH375 EXTREME PLASMA6.5 HP COMPRESORDEWALT 18, 24, AND 36 VOLTO/A TORCH SETAND SO MUCH MORE I DONT REMEMBERALL IN MY 2005 2500HD EXTENDED CAB L/B
Reply:so what is your question????G3miller... 225g, s32p, 250x, 304, 12vs, MSW41     victor o/a thermal dynamics cutmaster 50 lenco panel spotter        hobart hf-boxG3 Farms.....raising cattle, hay, kids and hell, ...oh yeah I'm a fire sprinkler contractor by trade.
Reply:you can also use Co2 pure.  It welds a little different, but is sure is cheaper.  ONLY works for short circuit and globular transfer on low carbon steel.DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:Originally Posted by MrRodeoCCI'm finally looking at getting a gas cylinder for my lil MIG. I have a few questions before I go to the LWS. 1. How long will a 40 cf cylinder last if run constantly? (I know it won't be run constant but this is for reference)2. What is the best gas mix for welding steel?3. Is there a gas mix that will allow you to weld aluminum, stainless and mild steel with a filler wire change?4. What do I need to check to make sure I get a cylinder that I can get serviced in a different state? (I'm retiring from the USAF in 6 months)5. How hard is it to get a cylinder re certified and cost?I read a lot on this forum, and I've learned a lot. Thanks
Reply:pssst,  get two cylinders.  This way when the first one runs out late on a weekend after the LWS is closed, you can continue working using the second one.40's are relatively handy from a size standpoint, but they really don't last all that long.  80's are still mostly portable, last twice as long as a 40, and cost maybe an extra 5-10 dollars to refill.  Of course the original purchase of the tank is almost twice as much ...
Reply:I am with Dave on the CO2, I have a few"Pepsi" 20 pounders, and they last for ever, and are cheap to fill. When I run solid wire it is good, when I run Tri-Mark 777 it is great.Disclaimer; "I am just an a$$hole welder, don't take it personally ."
Reply:Originally Posted by David Ryou can also use Co2 pure.  It welds a little different, but is sure is cheaper.  ONLY works for short circuit and globular transfer on low carbon steel.David
Reply:Originally Posted by offrdfun73I use 100% argon for everything. Last week for example I welded a stainless intake for a motorcycle, A bucket for a large track hoe, A broken aluminum trailer, and provided a welding sample to a potential client on stainless and cabon steel. So in doing that I MIG welded steel, stainless steel, and Aluminum all with my MIG (aluminum was done in pulse) and I TIG welded stainless steel and steel. No trouble at all with any welds or penitration I have even done penitration test with iodine and get great penitration on steel with pure argon.
Reply:Originally Posted by 3 weelin geezerDo you have any pix done on aluminum with pure argon?
Reply:I understand you need a mix of argon/co2 for aluminum and straight argon for mild steel.  I expect to do mostly mild steel so I didn't get the mix.  I have heard that it just doesn't melt the puddle but just blobs it on.  Very little penetration.  I haven't had a chance to try it with just the argon.
Reply:You have it in reverse.  Argon for aluminum and mix 75/25 for mild steel.        John      SMAW,GMAW,FCAW,GTAW,SAW,PAC/PAW/OFCand Shielding Gases.  There all here. :
Reply:Really?  Cool!  Argon does a really good job on steel already.  This is at the base of my new welding cart.  I am quite pleased with how it looks.  Does anyone have pics of aluminum with straight argon and with a co2 mix?
Reply:Aluminum with a CO2 mix just don't work... Pure argon or argon/heliumMiller EconotigCutmaster 38Yes ma'am, that IS a screwdriver in my pocket!
Reply:If you use co2 on aluminum it wont weld for crap trust me. I was in a pinch one weekend and all I had was 75/25 and I tried to TIG aluminum and I would not even weld at all just spaterd and turned black. I had to grind it out and grab a bottle of argon and it was fine. Steel Thunder Welding LLC. St. Thomas VI USAMM350PBOBCAT 3MAXSTAR 150 STH375 EXTREME PLASMA6.5 HP COMPRESORDEWALT 18, 24, AND 36 VOLTO/A TORCH SETAND SO MUCH MORE I DONT REMEMBERALL IN MY 2005 2500HD EXTENDED CAB L/B
Reply:pssst,  as a sort-of follow up to the original poster's question about small tanks of shielding gas for GMAW aka MIG, my LWS is phasing out all the 40 ft3 tanks of C25.  Minimum size they now have for C25 is a 60 ft3.  Too much hassle for their refill to deal with the 40's when they have to blend the gas.  40's of pure argon is still available, but for the blended gas they've moved the minimum to 60's.  So they upgraded my little ole 40 to a 60 for a slight charge.YMMV.
Reply:For short-arc i use  C02 straight, or sometimes mix in a little Argon with mostly C02.For  T I G  - THIN aluminum pure argon is used , but, thick aluminum ,(3/16" or more ) i use a mix of helium -about 80-90% and argon (argon just for cleaning effect. ) I personally NEVER use tig for carbon steel, why bother ? I use mig (short-arc) or, on heavier steel, good old stick welding with low hydrogen , it can't be beat . All my gas bottles are big -280cu.feet, but that size holds about 480cu.ft  of Co2. The gas cost TOO much (per cu.ft.) in small sizes. Oh, my acetylene bottle is about 112 cu ft.[SIZE="5"Yardbird"