Welding Tips and Tricks

I would like to try mixing my own gases. I use 75 argon/25 helium to weld castings. The pre mixes are getting pricey. I seem to remember a vid that Jody did where he made a mixer, but can't find it. I remember 2 bottles, 2 regulators, and a Y valve. How would I get the ratio I'm looking for. Also, if 1 tank has more pressure than the other, won't I backfill the lower pressure?
Thanks, Mike

As long as you are mixing on the low pressure side of the regulators, there's no danger of backfilling a tank.
Calculating the mix ratio could be done with flow meters. Some experimenting may be required to get a proper ratio.

Alumike wrote:I would like to try mixing my own gases. I use 75 argon/25 helium to weld castings. The pre mixes are getting pricey. I seem to remember a vid that Jody did where he made a mixer, but can't find it. I remember 2 bottles, 2 regulators, and a Y valve. How would I get the ratio I'm looking for. Also, if 1 tank has more pressure than the other, won't I backfill the lower pressure?
Thanks, Mike

Werkspace is right, and I've done this myself.

I'll probably be doing it tomorrow, for a 50/50 Ar/He mix for some 1/2" aluminum overhead.

Two bottles, two flowmeters, both feeding a tee (a wye is nice, but the gas doesn't care), and the tee feeding the machine/torch.

I have an advantage in that I have flowmeters marked for Helium, but an Argon flowmeter will work fine with Helium... The rule of thumb for an Argon flowmeter flowing Helium is, when the ball just begins to dance and spin, you're at about 5 cfh. As soon as the ball stops dancing and stays at it's (very small) height, you're at about 10 cfh. (The low density of Helium won't lift the ball near as much for the same flow as a heavier gas.)

If you bring the ball on the Helium side to that "dancing" point (look close, it's not much movement) and set your Argon to 15 CHF, you'll be in the ballpark, then gently bump up the He until it performs like you expect. A couple seconds of pre-flow assures mixing before the torch.

Make sure the Helium bottle in particular is opened all the way, tight against the stop, and soap-test the valve and all your lines. Helium ain't cheap, and will escape the narrowest imaginable path. I use helium to detect leaks that pass x-ray.

Steve S

I'm pretty certain that everyone involved with this so far has a fair understanding of gases, flowmeters and regulators, but for those of you who don't, you need to know that you should only try and mix gases on the low pressure side of a regulator. Never try and mix gases on the high pressure side unless you have the training to do so. Dealing with pressures in the 2000+ lbs. range is a litle more than slightly dangerous. Most tee's, nipples, and wye's are not rated for that kind of pressure.

And to all parties, any mixes that involve O2 or Hydrogen should be left to a reputable cylinder fill plant.

A mixer is always the best way to get the blend in the right proportions. But the worst thing that can happen while mixing helium and argon is that your proportions will be off, nothing a little trial and error can't fix. Seems like Steve's been down this road of t. & e. and offered some good starting points.
Len