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Up Topic Welding Industry / Technical Discussions / Advantage of Composite GMAW Filler?
- - By tom cooper (**) Date 03-17-2008 13:12
Hello again-
As we gear up for our big re-bar job, we decided to PQR a MIG procedure along with our FCAW procedure.

For GMAW, we are thinking about spray arc with 95/5 Argon/Oxygen mix. Because we are joining rebar to mild steel, we can use a 70S or a 70C wire (according to AWS D1.4).  I've been advised that the application will have impact requirements so as I compare AWS A5.18  ER70S-6 to E70C-6, they both appear to offer the same as welded Charpy number.  The only difference seems to be that E70C wire is a composite and 70S is solid.

What pupose/advantage does a composite wire offer?

Also our senior welder is insisting on the 95/5 Argon/O2 mix, yet the manufactures cut sheets and AWS A5.18 lean towards 75/25 Argon/CO2 mix.   Can you advise on advatages either way ?

Thanks.
Parent - By js55 (*****) Date 03-17-2008 13:48
The advantage to composite wires is deposition rate. The disadvantage is cost.
So I doubt, if your doing rebar, that the dep rate advantage is going to mean much to you. The other issue of gas is that with Charpy regimes you can get impact testing already thruogh the spec with 75/25 gas. You can't with 95/5. 95/5 is not part of the standard classification system of A5.18. Your going to have to have special testing with that gas. And depending upon your code you will have to do it with every heat of wire you use.
Parent - By 803056 (*****) Date 03-17-2008 21:21
Hello Tom;

The letter "C" stands for "cored" electrode which is similar to flux cored electrode.

Composite electrode was a forerunner of flux cored electrode where the wire was woven or braided and the flux material was "trapped" between the braids. As you can imagine, composite electrodes were not all that successful because the flux materials would flake off jamming the liner of the welding gun.

The cored electrode material has deoxidizer materials inside the hollow tubular electrode, but it doesn't have the flux constituents that interact with the molten weld puddle to form the slag layer as is the case with flux cored electrode. There are some oxides that form on the surface of the weld bead similar to that observed with bare GMAW electrode.

Most welding standards group the cored electrodes with the solid GMAW electrodes (AWS A5.18 for example) and consider the welder as qualified for either solid or cored electrodes where as the true flux cored electrodes (AWS A5.20) are considered to be a separate welder qualification.

You will find out soon enough whether the SG-AO-X%X% is as good or better than SG-AC-25% when you qualify your welding procedure and check the Charpy test results.

Best regards - Al 
Parent - - By DaveBoyer (*****) Date 03-18-2008 04:13
I think You will have problems getting a spray transfer with the 75/25 gas using solid or metal cored wire, most likely You will have short circut or globular transfer. If You use a flux core wire, the shielding gas mix [of the alowable choices] usually has an effect on impact properties.
Parent - - By tom cooper (**) Date 03-18-2008 13:19
JS, Al & Dave-
Thanks for your helpful insights.
Last night I was reviewing Lincolns data on tensile and Charpy Values for their SuperArc 70S-6 wire when welded with various mixes of Ar/CO2 and AR/Oxy.

Unless I am reading the data wrong, there is a remarkable difference in strength between Ar/CO2 mix and AR/Oxy mixes - the Ar/CO2  90/10 mix being the highest (85ksi UTS and 140 ft-lbf Charpy@-20F) and the Ar/Oxy 98/2 mix being the least (70ksi UTS and 20 lb-f Charpy@-20F).  Even straight CO2 was better than the At/Oxy mix (81 UTS and 40 ft-lbf Charpy@-20F).

What is happening here? How does a gas mix so drastically affect strength and toughness and why does the Oxy component seem be detrimental to strength and tougness? This seems very strange because will not the CO2 in any Ar/CO2 mix supply a greater amount of oxygen to the weld pool than a Ar/Oxy 98/2 mix? 
Need help with theory here!
Thankyou again.
Parent - - By js55 (*****) Date 03-18-2008 14:06
Its the carbon. Without it you're oxygen ends up as oxides it the weld deposit as opposed to carbon monoxide and remnant carbon dioxide in the fume gas) which does not help the weld perform well under low temp impact testing.
That helps explain the Charpy's. The carbon also helps explain the the strength, as some of it will end up in the deposit as well.
But keep in mind, and this is often lost on many who agonize over strength differences with different gases, it doesn't really matter that much if your tensiles change to any great extent (given certain specific exceptions) if the min strength is still greater than the base metal. Even though your strength went from 85ksi to 70ksi, the 70ksi is still 10ksi stronger than carbon steel base metal mins.
So if you're gas gives you enough strength you look for other variables to optimize your application. Charpy's, cost, ductility, weldability, tensile to yield ratios, productivity, materials, etc. Its called engineering.
Parent - By tom cooper (**) Date 03-18-2008 18:56
js55-
"Agonize" was a good word to use - I fell in to that trap of thinking more had to be better and consequently, not as much must be really, really bad!  Thanks for putting things in perspective.
Parent - - By hogan (****) Date 03-18-2008 14:58
Dave, I'm using metal core with 75/25 in a spray transfer with no problems. everything is UT'd. What type of issues are you seeing?
Parent - By js55 (*****) Date 03-18-2008 19:51
The metal core spray relationship is different than solid wire because the arc density is increased. The same reason the deposition rate goes up. That and I2R heating. Its almost like reducing wire diameter. Which, obviously means that if you increase wire diameter with CO2 mixes you have to increase current to achieve spray.
Parent - - By DaveBoyer (*****) Date 03-19-2008 02:56
Hogan, I know that while spray transfer can be achieved with solid wire using 75/25 it is hard to do reliably. I was under the impression that it would be dificult with metal cored wire as well. What is the minimum argon percentage for reliable spray transfer with metal cored wire? Does it varry with different wires, or is it a "line in the sand"
Parent - - By hogan (****) Date 03-19-2008 14:54
Dave, spray is not as difficult with cored vs solid. we are using 75/25, and we run at manufactures recommendations (I'll attach) for .045 and 1/16. 300@31 and 350@31. the main difference is the higher gas flow and heat. It's not used for thinner material or small fillets, we still use fcaw or solid wire. Fluctuations in gun angle, stick out, and electrical seem to have a less detrimental effect on the weld. We have used this wire for about 6 months and i have not seen the side wall fusion issue that is common with solid wire. great penetration.
Attachment: gas_shielded_metal_core_wire_e70c-6.pdf (496k)
Parent - - By DaveBoyer (*****) Date 03-20-2008 05:03
Hogan, Thanks for the information.I looked at Your link & some other metal core data, it seems that 75% argon is the minimum. You must really be putting down some metal @ 350A.
Parent - - By hogan (****) Date 03-20-2008 13:51
we do a lot of 3/4" A36 using joint detail B-U2a-GF. These are 20' to 50' longseams. It works great for a root pass prior to SAW, almost no prep needed.
Parent - - By DaveBoyer (*****) Date 03-21-2008 04:25
Hogan, can You post a drawing of that joint detail or a link to someplace it is shown so this amature can see what it looks like?
Parent - - By hogan (****) Date 03-21-2008 17:58
here is a wps. is this what you were looking for?
Attachment: core.pdf (180k)
Parent - By DaveBoyer (*****) Date 03-22-2008 03:16
Thanks, a picture is worth a thousand words.
Up Topic Welding Industry / Technical Discussions / Advantage of Composite GMAW Filler?

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