Spray transfer root pass question

[Delgado]

Hi guys, have been working back in workshop of late, mainly frying together thin stuff with the squirty (god I miss Tig welding), 10-20mm plates, beams etc..

Today I was joining two lengths of 20 x 180mm mild steel flat bar, chamfered to about 35 degrees on both sides with a 2mm gap and land.. when I sprayed the root in it had a kind of brown soot all over the surface of the weld bead, it penetrated fine, had no signs of porosity, I back ground it from the other side to make sure, as it will be forming part of a valve set and will most likely be NDTed in some form or another. Then, when I welded it from the other side (again with spray) it did the same thing (I put two more passes on each side afterwards, grinding the surface back slightly between each one, and they came out fine).

The settings...

1.2mm non coated wire

28v + or -

7.5 mpm Wire speed

Argon/co2/o2 trimix gas (praxair stargon gs83)

Any thoughts, or is this a normal thing that just happens sometimes with Spray?

Oh, and by the way I was pulling the gun, with a 10mm ish stickout.

Thanks in advance! (Hoping I wont have to grind it all out and do it again tomorrow)

 

[RapidResponse]

Wire speed sounds a little slow. Did you have an intermittant crackle?

 

[Omniata]

What % composition was the gas mix?
An "Argoshield Universal" type mix is better for spray transfer I believe

You may be better with a "push" technique

 

[Delgado]

Wire speed sounds a little slow. Did you have an intermittant crackle?

Yes, well, more like a constant slight crackle, but it was definitely spraying(could see the "pinch" effect on the wire). I normally have the WFS up on about 8/8.5mpm but it was burning straight through, so I had to slow it down a bit. It's a synergic set, so the voltage also went down from about 28.5/29v.
Regarding the set, it has a program for everything under the sun except trimix gas (I guess there are too many compositions), when I use it on the argon co2 program it goes straight into globular mode, and the technician told us to use it on the flux core program although it does exactly the same thing.(I usually turn the voltage knob up 1 or 2 notches on the suitcase to compensate)

What % composition was the gas mix?
An "Argoshield Universal" type mix is better for spray transfer I believe

You may be better with a "push" technique

Not sure about the composition of the gas as I don't buy it and it doesn't say on the label, although I do know that it is suitable for spray transfer.

 

[weldingscotty803]

brown soot????? sounds like gas needs turning up, what lpm you set the regulator. only other thing may be oxidation on the metal. maybe clean the nozzle and tip and have the tip a bit closer. any crap inside the tip can cause the gas to create a kind of mini tornado if it doesnt flow freely.(so i was told by my old tutor anyway)

 

[Delgado]

brown soot????? sounds like gas needs turning up, what lpm you set the regulator. only other thing may be oxidation on the metal. maybe clean the nozzle and tip and have the tip a bit closer. any crap inside the tip can cause the gas to create a kind of mini tornado if it doesnt flow freely.(so i was told by my old tutor anyway)

Interesting, I normally clean the tip and nozzle thoroughly and regularly (almost like I have OCD) although I didn't know about the turbulence, mainly just do it to get a nice even wire feed and prevent short outs. I have to admit that today I just glanced at it (it looked ok) and welded away, you know how it is when the boss is cracking the whip. I had the gas on about 18lpm, using 500amp gun.

 

[shenion]

I get brown soot if my torch angle is not close enough to vertical. Get black soot on aluminum/5356 wire if the same happens.

Here, we don't use O2 and a CO2 less than 20%. I use 82/8 on the bit I have done.

 

[Delgado]

When I get time I'll have a bit of a play with gas pressures, torch angle and such. Many thanks for the replies fellas!!

 

[backpurge]

You can get this brown soot when dragging in spray transfer, try increasing gas flow a bit and maybe fit a straight gas nozzle (if not already using one) to improve gas coverage. Lifting your angle so you are not "dragging" as much may also help

Personally would have thought you may have been better keyholing the root in dip transfer

 

[old rollei]

THe Brown soot as you call it is iron oxide, BURNT STEEL. cause, lack of gas cover over weld pool. Check the gas distributor in the torch end. The insulator holes should match the distributor holes. this affects the laminar flow, a mismatch will deflect the shield gas causing entrainment of air into the shielding. Gas nozzle angle to work should not be greater than 10' to the vertical. Straight gas nozzles are very prone to entrainment, tapered nozzles are more efficent. Gas type Ar- 5% Co2 for pulse welding. Weld prep. on spray transfer feather edge prep /close butt, pushing reduces penetration pulling the torch increases penetration. To check the Gas cover/ deoxidisers in wire look at the colour of the silica ponds on the finished weld. when all is correct the colour should be an olive and glassy smooth. History of research/ design of equipment.