Tri-Mix - Stainless - Helium/Argon/CO2

By Lawrence (*****)

Date 01-07-2015 23:21

Ryan,

Yes, 3 part gas mixers are available. Your local Praxair or Airgas distributer can give you data.

However, since you are doing GMAW, you may want to look into a two part mix of 98/2 Argon/Co2 This gas mixture is being used more and more for GMAW Spray Transfer and Pulsed Spray with austenitic Stainless steels. It works well in many cases.

If you are using the tri-mix to GMAW short circuit your stainless that is thinner, the helium mix is understandable... But many people have discovered that GMAWP with 98/2 Argon/C02 can weld .040 fillets with zero burn thru and with better fusion and travel speed than short circuiting and tri-mix with helium.

Anything you can do to remove the helium may be worth your while... Many people do it with a net improvement in both quality and productivity.

Just a thought.

By Metarinka (****)

Date 01-28-2015 06:11

I keep coming to this board to answer questions and I find you have them all answered wonderfully! Keep up the amazing work. I personally wouldn't recommend mixing your own gas unless your usage rate was high enough to justify Installed cryo dewars.

By fschweighardt (***)

Date 01-08-2015 05:54

http://mcdantim.com/product-lines/

http://www.wittgas.com/EN/mixers_metering_panels_downloads.html

http://www.thermco.com/ss118.php

lots of 3 gas mixers out there, smith, thermco, Witt, mcdantim. If I wasn't on my tablet, I could do better links, but here are a few

You doing spray or short arc

By Rparz Date 01-20-2015 16:32

Thanks for the help guys. I've been scouring this forum for tips on making the switch from tri-mix to 98/2. Some of my guys don't like to have anything change so I'm trying to figure out what differences they'll see and what possible fixes are. We're doing mostly stainless pipe, sch 40 and sometimes 10.

Thanks,
Ryan

By Lawrence (*****)

Date 01-20-2015 17:14

Hold on to your hat sir !

http://www.weldreality.com/MIG_welding_gases.htm

By Lewis87 (*)

Date 01-24-2015 05:29

That's an interesting read Lawrence.

By fschweighardt (***)

Date 01-22-2015 04:57

2% CO2 or 2% O2
Either way, they welders will not like it.
I am unaware of any gas that will beat the tri-mix in a combined score of surface appearance and wetting and operator appeal, at least on traditional CV non-pulsed power supplies in short-circuit transfer

By Metarinka (****)

Date 01-28-2015 06:09

The tri mixes tend to help out on thin wall applications where increasing heat heat input to get better wetting of the weld tends to blow through, in any other application you can match it with a dual mix, by increasing your heat input and travel rate. From a physics standpoint there really isn't much if any benefit from using a tri-mix all the factors that control thing like arc width, arc gap etc are based on on the net resistance of the gases and mixing 3 can't give you any theoretical number that mixing 2 gases would. While Ed still has the craziest website design he does always have very good information in regards to MIG gas mixes http://www.weldreality.com/MIG_welding_gases.htm

By fschweighardt (***)

Date 01-28-2015 14:06

Ed has a number of interesting points, as well as some odd comments. One of my favorites is below:

"... In the welding industry, there has never been a need for any MIG gas mix that contains oxygen, however their has always been a great need for industrial gas companies to sell their abundant, low cost supply of oxygen..."

As many may know, there is virtually no way for anyone to make a business case for "selling oxygen" by adding it to shielding gas. If we assume all welding mixes could contain 5% oxygen, and a typical bottle holds 300 SCF, the the oxygen per cylinder is 15 SCF. Then lets say 5 million bottles of this mix are sold every year, which is probably a huge exaggeration. Now you have 75,000,000 SCF of oxygen. At 24,160 SCF per ton, you end up with 3104 tons of oxygen per year. A single air separation plant of reasonable size will make 250 tons of O2 per day, which would indicate that this ridiculous number of cylinders would only require 12.4 DAYS of oxygen production from a single plant. There are probably well over 100 plants in the US, and many are larger than 250 tons oxygen capacity.

Regarding SS tri-mix,
There seem to be certain applications where good wetting, low heat input, and bead appearance (minimum post-weld cleanup) where nothing will perform just like the 90%He mixes. Are there many applications where the 2% CO2 work just fine? Of course there are. Are some shops using tri-mix when 2% is all they need? Absolutely. Are there power supplies that can make the 2%CO2 work very much like the 90% He? No question.

Does every single welding operation involving SS and short-circuit transfer have the ability to use the 2% or more advanced power supplies to get the best overall results? Probably not.

By Lawrence (*****)

Date 01-28-2015 15:10 Edited 01-28-2015 15:15

You really do need to eat the meat and spit out the bones with Ed.

But I respect him greatly... He will actually pick up the phone and call me from time to time just to debate stuff like this.

If you look at his "body" of recommendations, there is quite a lot there that would be beneficial to most manufacturers. I've really never seen so much deep technical information given away for free. (No offence to Jody Collier)

Edit: As far as that whole oxygen thing goes... I walked into some work with Spray GMAW and steel with 5% Oxygen/ Argon balance.... In all my searching I have never been given any type of explanation of why 5% oxygen has a benefit above 2% for structural steel...... Nobody... has an answer... Yet there are MANY U.S. manufacturers who adopted that mix in the 1980's and are still using it. The people who made the decisions dead and buried.

By fschweighardt (***)

Date 01-29-2015 12:57

I have quite a few customers that run 5% O2, and it does have both pros and cons. It wets out better than 2% (a bit), and it is sometimes available as premixed liquid product. It can also undercut easier than 2%, depending on the operator.

Like most things with shielding gas, you really have to look hard to see the differences in real performance when you make small changes in the mix.

By Metarinka (****)

Date 02-09-2015 23:35

My experience is almost solely in automated welding of stainless and exotics, I nix any o2 mix due to the increase in oxidation, it's basically a no-go if you are doing multi pass welding. With the higher travel speeds you tend to get more solid-state surface oxidation on the root pass which subsequently affects any pass put on top of it. I would never recommend it for any stainless work, maybe it's more acceptable with low alloy carbon steels?

By fschweighardt (***)

Date 02-10-2015 02:40

I am not a fan of the Ar/O2 mix for SS welding, its just that a bunch of folks are. Typically I see it in thinner single pass sort of stuff, but I have seen it in multi-pass work. You get such a hard tightly adhering oxide stringer (running down the center of the bead, usually). Even if it is removed, often you can see the outline of the nasty old Cr2O3 crust when this gas is used. On multi-pass, it gets bad quick, and even a 3 pass weld has vast chances of inclusions, LOF, etc.

Theres plenty of recommendations on the web for 1-2% O2 mixes. Im not gonna name names, but its not my idea of a good idea.

By Metarinka (****)

Date 02-10-2015 23:02

I'm surprised to hear that, SS does run sluggish which is why people are willing to try anything that helps with wetting. But the excessive oxidation does it in on any setup I've tried, or it makes the process margins razor thin.

In my tiny dips into arc physics, any ionization potential (within the upper and lower bounds) can be made by a two gas mix, so there's no benefit on tri mixes being "hotter" than He/Ar mixes, O2 does help with wetting, but it's not worth it.

By fschweighardt (***)

Date 02-11-2015 13:25 Edited 02-11-2015 13:36

So here are some pix i made up a long time ago, 81/18/1 (Ar/He/CO2) vs. 98/2 (Ar/O2). If the damn pictures uploaded in the right order, there should be 5 of each weld (tri-mix series first), with an overall, closeup, wiped with a leather glove, SS wire brushed, and finally pickled with some pretty lame pickling juice. The 98/2 is a good bit uglier in my opinion, you can see the rough crusty crap all over the weld.

Date 01-29-2015 13:42

[topic branch moved]