Gas Mixnig for MIG

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hi all. new here but not new to welding. i have TIG/Stick, MIG, and small gas torch, mostly for hobby work.i am using my Miller 251 heavily these days and i need to move up wire size to 035 and start to use argon/co2 mix. however, i have co2 tank and a argon tank that i dont want to give up for a mixed tank. thus i am venturing into my own DIY for a gas mixer. surely not the professional way to do it but i'd like to share what i have and some Q's.my regulators accept the 5/8" RH B-size inert gas fitting. i confirmed that my argon reg does not have built-in check valve so i got two Western WESQDB-33 check valves and will attach to my regulators. i then got a 3-way brass 1/4" NPT fitting from harbor freight (very inexpensive with a 20% coupon, but any brass or aluminum air manifold would suffice and are easy to find). i will use Western 1/4"male-to-inert female in the 3-way to connect hoses to. its a T fitting so i plan to input the gases at the top of the T so that the gas flows hit each other to mix. thus far very basic/crude setup that should work for my needs, also allows me to mix helium with argon for when i do AL TIG, etc.ok, some Q's.i plan to seal the T fittings using epoxy. any reason not to?the T fitting has some room to stuff some steel wool in there, or perhaps one of those small brass aerators you see in fish tanks or chemical pickups for power washers. this would be to help mix the gases. good or bad idea?Last edited by welding_kid; 05-31-2013 at 12:55 PM.
Reply:There is no way you are going to accurately mix gas without a gas mixer, it is just going to be a crap shoot. The reason being, is that in order to get a 75/25 mix you need to run one reg at a higher pressure than the other reg, which will cause the lower pressure reg to become satisfied and shut down. You could potentially run both regs at the same pressure and change the orifices to the correct mix, but you are going to need a really good set of gauges to set it up. The regs themselves are really not accurate enough to accomplish this either. Your MM251 will run CO2 just fine, so just use CO2. No reason to go to 75/25 unless you are having trouble running CO2. Co2 is a LOT cheaper. I have 4 welders set up in the shop right now. They all run CO2, except for my little mIG (MM140), that I use for thin sheet metal with .023 wire. That one I have a small bottle of 75/25. So save your time and frustration and just spend the 100 buck on a small bottle, or swap your CO2 bottle when it is empty for a mixed gas bottle and try it. If you really want to mix your own gas, you HAVE to have a proportional gas mixer. Try ebay for a search for a Smith Proportional Gas MIxer. They are not cheap either.
Reply:i am finding posts online from both sides. those who say it works fine, and those who say it wont work. my needs are not inspection types of welds, but i am looking to make good welds.when the gas valve in the 251 opens the line is open to 1ATM, both regs will flow. i'll set argon to say 15cfh and my co2 to 5cfh (or whatever mix i want).i believe inside my 251 side cover it has a matrix chart with wire size, metal sizes, and type of gas to use. i'd have to go look again, but i believe 1/4" mild steel is looking for 030 or 035 wire, with different machine settings depending on gas type used. argon/co2 mix gives a different weld than just co2. w/o diving into metallurgy, inert gas is always better for the weld.
Reply:Been covered pretty heavily on this site. Here's my thread on a mixer and another thread where I write about the problems with trying to do it this way. http://weldingweb.com/vbb/showthread.php?t=41659http://weldingweb.com/vbb/showthread.php?t=257211 There's a lot more posts on this forum about this if you do a search.Millermatic 252XMT 304'sDynasty 280DXHypertherm PowerMax 1250Miller Trailblazer 302 EFIOptima PulserXR feeder and XR Edge gun and more athttp://members.dslextreme.com/users/waynecook/index.htm
Reply:How much cheaper are we talking here? I pay 40$ with my corp discount for an 80cf of mix at my LWS. That seems reasonable to me for how long it lasts. I guess I could get liquid CO2 and that would last a lot longer right?(Home)Miller Maxstar 152 (sold)MM211/spool gunLincoln AC 225C(Work)Dynasty 350Powcon 300STLincoln SP-175TWeldlodgic AWS150sWeldlodgic AWS300Custom Resistance seam weldersCambridge Vacuum EB weldersI smell something burning.
Reply:its not the price of gas mix, its that i dont want to buy another tank, and, i am wanting to keep my co2 and argon tanks. i guess the diff in my setup is that i am looking to add some sort of diffuser block or material to the T fitting which will cause vortex flow helping to mix the gases together. perhaps a few of those stainless screens used in faucet nozzles?
Reply:Originally Posted by atariHow much cheaper are we talking here? I pay 40$ with my corp discount for an 80cf of mix at my LWS. That seems reasonable to me for how long it lasts. I guess I could get liquid CO2 and that would last a lot longer right?
Reply:so, does the crude method as i describe work differently depending on the gases being mixed? since i know some about chemistry and fluid dynamics, the short answer is yes and its why a real gas mixer is for the pros, but for my needs (non-professional non-inspection work) these Y tricks seem to be commonsee this videoi will attempt to make the simple Y setup a tad better by installing a diffuser inside the fitting. i'll get some pics up.Last edited by welding_kid; 06-01-2013 at 11:10 AM.
Reply:I don't think the diffuser is going the help much if any. If the gas is not mixed by the time it goes through the hose, solenoid valve, and welding lead then it's not going to get mixed.   As I stated in the one thread the single biggest issue is keeping the two source supplies at exactly the same pressure. If they're not at the same pressure then the higher pressure one will flow for longer after the solenoid valve closes giving to much of that gas. As long as it's flowing the mix works well but the initial start up can be messy until the lines are purged of that wrong mix caused by that over supply of the higher pressure gas.   That's where the commercial mixer come into play. They have a balance regulator that keeps all the source supplies at exactly the same pressure all the time.   Based on my experience trying this in several different incarnations the best advise I can give is to get good gauges on the regulators to read and keep the pressure the same and put the Y fitting right on the solenoid valve with check valves on both sides of the input. Keeping the volume between the check valves and the solenoid valves low is the single best method of keeping the mix stable at all times. Otherwise as the source pressures drift (which they will as bottle pressure changes) you'll end up with improper mix.Millermatic 252XMT 304'sDynasty 280DXHypertherm PowerMax 1250Miller Trailblazer 302 EFIOptima PulserXR feeder and XR Edge gun and more athttp://members.dslextreme.com/users/waynecook/index.htm
Reply:thanks for the feedback. let me try some analysis and you can tell me if i am wrong.my regulators measure output flow in CFH (a volume). lets looks at the flows vs trigger state.1) when machine valve opens both regs will flow the set amount, in this example say 10CFH each. regardless of pressure the gauges are only allowing 10CFH of each to flow into the Y fitting and then 20CFH total into the machine. how the gas mixes at the Y to the machine seems to be about on par with two gases sitting in a single tank.2) ok, lets look at the possible issue of when you go from trigger-on to trigger-off. the machine valve closes and you think there will be post flow into the lines, and if the flow rate (time it takes to dwindle off to zero flow) of each is not exactly the same then one gas might have more post flow than the other into the lines therefore creating an unexpected balance of gases in the lines. this incorrect gas mix/balance is then used at the MIG tip for a short time when you start welding again.#2 seems plausible, guess i will have to test this to see how the regs dwindle to zero flow after machine valve closes.for #1, having a better diffuser in the Y fitting certainly helps to mix the two gases.
Reply:That's pretty much it. As long as it's flowing full out the mix is pretty stable to what you set it. In that case the hardest part is being accurate on setting the flow of each. Most welding flow meters aren't the most accurate ones ever made.   The after flow is there for a fact. There's always pressure drop along the lines and it takes a little time for the the lines to fully equalize. Keeping that pressure drop and volume low will go a long ways to solving the problems with this setup. In my case it's lot more complicated in the fact that I'm trying to stay very flexible in my options. I never know what's going to come in the door next and I need to be able to change setups easily. The problem comes in from the fact that I have 50' of hose after my mixer. Even though I used a small hose to reduce the volume it's still there. I can see between 10 and 15 seconds of flow after the valve shuts off. Though towards the end there's not a lot of flow it's still there.   As long as I keep the pressures on all the feeds the same then I don't have a lot of problem (other than a larger than normal rush of gas at the start). But if the pressures are different you can definitely tell a difference in the weld after a few seconds of gas flow.   It's nowhere near as bad as my former mixer setup which was much less sophisticated than my current. My first setup wouldn't weld worth a flip for 4-5" before the gas settled down and then things where fine till I stopped. I improved that one by moving the flow meters and valves as close to the feeder and solenoid as possible but it was still not very accurate and had a large rush of gas when first started.   My current setup is better than that one by a long shot with accurate flow meters and a lower overall pressure in the hoses ( I'm calibrated to 20psi currently). But I feel it would be better still if the flow meters where mounted right at the welder. That's a little harder to do for me though I may change my setup one day to try it out.  I'm just putting out my own observations from my experience of trying to make this work. YMMVLast edited by irish fixit; 06-01-2013 at 03:36 PM.Millermatic 252XMT 304'sDynasty 280DXHypertherm PowerMax 1250Miller Trailblazer 302 EFIOptima PulserXR feeder and XR Edge gun and more athttp://members.dslextreme.com/users/waynecook/index.htm
Reply:i appreciate the info. in my case my line from tanks to the Y is 3ft. from Y to Miller is 3ft. so i will have much less time with unbalanced mix in the line than you at 50ft. i understand the flow meters on the gauges i have on my tanks are not precision, but if the needle or ball says 10CFH then i will accept that as 10CFH and not worry about the error it has.my MIG welds should be nicer going from 100%co2 to 50/50. and since my TIG is not that beefy i might try some helium to see how it improves my AL welding.
Reply:That's going to be better alright but I'd still try and reduce it more if possible. In my case I'd make up a short hose if I had to though the right adapters would allow direct mounting of the Y to the welder.Millermatic 252XMT 304'sDynasty 280DXHypertherm PowerMax 1250Miller Trailblazer 302 EFIOptima PulserXR feeder and XR Edge gun and more athttp://members.dslextreme.com/users/waynecook/index.htm
Reply:yeah, i thought about that, T right on the machine. in my case though i will use this T for my MIG and TIG machines, thus i thought i'd just leave a hose connected to each machine and then just move the T over. and sorry, i called it a Y earlier, i am using T.today i found some SS and brass screens. SS ones have weave with holes a tad larger than human hair. the brass ones about size of human hair. using rod in my drill press to press in, i stuffed two SS screens into each port of the T, and then the two brass screen into outlet of T. i then gently soldered the edges of brass screens to the T. these screens should allow for some break-up of the flows helping to mix the gases as they pass through the T. i am using harbor freight item #68197. this items works better than the std NPT plumbing item you find at plumbing stores because it has longer cylindrical ports making it easier to stuff screens into.
Reply:so here's my mixer. was only $14 for the check valves. the check valves have a ball on rubber seat and is spring loaded. i dont know how long the check valves will last, but i guess i shall see. about $45 all said & done with this setup (fittings, hoses, etc). with 6 screens inside the T and with the gases hitting each other as they enter the T, i hope to get some decent mixing. hose to machine is 2ft, hoses from tank to check valves is 3ft.  i will test post flow and do some weld testing to see if this helps.
Reply:so the only not-sure is the fittings from hose to check valve. valve is 1/4 NPT with tapered seat, but i think the hose guy used 9/16" fitting. threads on hose side seem loose on the NPT, but it has taper on the inside so it does seal. i might switch to NPT-to-AN fittings.
Reply:seems to work fine. post flow into the hoses seem to be about same time for each reg. for my needs this is just fine.
Reply:75/25 is plenty cheap why go through all the exercise?Helium mixtures? I wouldn't have thought you'd need it but what do I know I never welded aluminum.As to the specific Questions:    i plan to seal the T fittings using epoxy. any reason not to?
Reply:i wanted to keep my co2 and argon tanks, didnt want to buy another tank. i can mix, and now i can mix helium for my TIG.as for out-gassing, i used just enough on the male threads to seal the connection, i dont see this as being an issue for my use. not recommended for professionals, etc. i used SS & brass screens and not steel wool.