mig gas tank

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ive never used gas yet im useing a HF 151 mig i want gas but i dont know anything about the gas to use or size of tank to get. im more thin a hobby welder less thin a pro and i also can use flux wire good but want cleaner welds or better looking welds. what i would like to know is how long does a 20 cubic feet last and is their a place to get used tanks cheap if not free.
Reply:In a pistachio shell ...The gas you use depends upon what you are MIG welding and the process you choose. For short circuit transfer, pure CO2 is cheap and works well for common steel but C25 (25% CO2 in argon) creates less spatter. For spray transfer, higher argon concentrations are need. Every material (aluminum, stainless, etc) has a "preferred" gas or mix which works "best".As to how long your cylinder of gas "will last", that really depends upon how fast you use its contents. A typical flow rate used at school (fairly drafty conditions) was 35 cubic feet per hour. In my garage I can get away with a flow rate of 20 CFH.  If your flow rate is either too low or too high, you will know it by the burnt-cheese look of your fresh weld's extreme porosity. So ... a 20 CF tank might last me for an hour of arc time. I've never welded continuously for an hour. Neither my machine nor my body could survive laying 1500 feet of wire all at once! My wrists would be hamburger and the poor machine a pile of smouldering junk.Best source of used OWNER tanks is craigslist. It is also a good source of all kinds of tanks but some places will not fill a commercial tank with an embossed collar. Some will.Good luck!Last edited by wirehead; 02-17-2012 at 08:19 AM.XMT304 (school)SP125+ (home)HF 4x6 BandsawGood judgement comes from experience and much of that comes from bad judgement.