help...miller's stt (rmd) on stainless

then3wguy · Sep 17, 2014

tonight I'm just messing around with miller's version of stt process... rmd... on stainless but it's not going so well

I'm using the pipeworx 350 with smart feeder
.035 wire
1/8 - 5/32 gap
tapered nozzle
stainless pipe all cleaned (heavy wall)
no back purge on the inside
100% argon gas (wrong gas I know)

the smart feeder don't have a setting for 100% argon .. so this might be my problem

I've set the machine to 1.7 for volts/arc length and 149 on wire speed

it's give me a mig like weld, with the short circuit process and not a clean spray kind of like a proper stt

the root isn't heavy and might be OK except that it's totally sugared.... I'm using 100% argon and not the argon/co2 or helium trip mixture

does anyone have any suggestions on the machine settings?

or technique suggestions for in postion welding on pipe? not rolling

ty in advance

shovelon · Sep 17, 2014

Well you have your answer right in front of you. Wrong gas and no purge. You need a reactive gas mixed with your argon to get into spray. Try adding 2℅ co2, commonly called stain-mix. Any more than 5% and you can get intergranuler corrosion. Or you can go with tri mix, but that is costly.

then3wguy · Sep 17, 2014

we figured it might have been the gas and got a bottle of tri mix

ty for your post, greatly appreciated

ttoks · Sep 18, 2014

Im thinking you may have STT confused, STT is meant to be a short circuit process, not a spray process.

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ttoks · Sep 18, 2014

The job im currently on we weld 304 with 316 wire, using lincoln STT 2's, argon helium gas with no purge, on open root pipe, no need for purge

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then3wguy · Sep 18, 2014

we got the machine dumped off for us to try with the tri mix gas but the roots are totally sugared and heavy roots...

not sure which settings to try for... only got a 'arc length' setting from -3 to 3 and a wirespeed setting. .. been trying 1.7 and 149 ws. ... no such luck

HT2-4956 · Sep 18, 2014

then3wguy said:
tonight I'm just messing around with miller's version of stt process... rmd... on stainless but it's not going so well

I'm using the pipeworx 350 with smart feeder
.035 wire
1/8 - 5/32 gap
tapered nozzle
stainless pipe all cleaned (heavy wall)
no back purge on the inside
100% argon gas (wrong gas I know)

the smart feeder don't have a setting for 100% argon .. so this might be my problem

I've set the machine to 1.7 for volts/arc length and 149 on wire speed

it's give me a mig like weld, with the short circuit process and not a clean spray kind of like a proper stt

the root isn't heavy and might be OK except that it's totally sugared.... I'm using 100% argon and not the argon/co2 or helium trip mixture

does anyone have any suggestions on the machine settings?

or technique suggestions for in postion welding on pipe? not rolling

ty in advance

then3wguy,

Here's some of what I know about this from my experience with using Miller's PipePro 450 RFC machine....

What Lincoln calls the STT (surface tension transfer) process is actually just a modified form of short circuit transfer and not a clean spray like what it seems you think it might be from what you've written above. Miller's equivalent of that is called RMD (regulated metal deposition). Again it's a short circuit type transfer. Both STT and RMD are just for putting the root in. For the fill and cap you switch over to the "pulse" mode which is a pulsed spray transfer.

If you don't have the manual for that machine and smart feeder I highly recommend you get them and read it.

As far as being able to put a stainless root in with out having to purge well, while I heard it said that it "might" be possible under certain conditions I've yet to see it done or talk to any one that's claimed to be able to do it. I myself haven't tried to do it yet. At this point it's my opinion that being able to do that might be more marketing hype than any thing else. So for now it's my professional opinion that if you're going to realistically expect to get consistently clean acceptable stainless roots with the RMD process you're going to have to purge just like you would if you were using TIG.

100% argon is never going to give you good results. You're going to have to use one of the 4 gas options available on the machines menu (C2, 98Ar/2O2, Tri-H or Tri-A) and then you have to have it selected on the menu so the machine knows.

Having a good ground path back to the machine is really important. Keep the sensing lead clipped as close to the weld as possible.

For .035 wire with one of the listed gas mixes I would try around 200 ipm on the wire feed with the arc length set to 0. Before turning the arc length up above 0 I'd try turning it a little below 0.

Weld progression is down hill.

then3wguy · Sep 18, 2014

thanks... I might try another joint tomorrow with the tri mix going to the gun

and I might put a Y on the tri mix to purge the pipe with that also or try a 100% argon purge or maybe both at separate times to see what happens

the rooting with no back purge so far has been awful.. total

I'll try your settings too for the machine and see what happens

thanks again for taking the time to post

any suggestion on gap size?

shovelon · Sep 18, 2014

Simply putting a y fitting on your bottle to purge will not work . As you will not be able to confirm the proper flow to your torch. A tee for another flow gauge will.

HT2-4956 · Sep 18, 2014

then3wguy said:
thanks... I might try another joint tomorrow with the tri mix going to the gun

and I might put a Y on the tri mix to purge the pipe with that also or try a 100% argon purge or maybe both at separate times to see what happens

the rooting with no back purge so far has been awful.. total

I'll try your settings too for the machine and see what happens

thanks again for taking the time to post

any suggestion on gap size?

I wouldn't waste Tri-mix on a back purge. And even if it was free I wouldn't recommend using it (or any thing but 100% Argon) for a back purge. As far as the back purge goes the same rules apply as if you were Tig welding it.

The reason 100% argon doesn't work on the gun (even on carbon steel) has to do with the basic nature of MIG vs. TIG. It's just the nature of the beast that when Mig welding carbon or stainless steels you have to have a little bit of free oxygen present in the arc zone in order to get the metal to wet out.

1/8 to 5/32 sounds like a good gap size to me.

You need a little bit of drag angle on the top. As you come down the sides you can increase your drag angle some. By the time you get to the very bottom you need to be straight in at it (no drag angle). If you've got a positioner and can have it rolling while you weld the real sweet spot for welding is around 2 o'clock.

What shovelon told you about not using a wye but getting a separate flow meter for your back purge is good advice. Besides what he said about confirming (ensuring) proper flow to both the gun and back purge in this situation you aren't going to be (or shouldn't be) using the same gas for both things.

help...miller's stt (rmd) on stainless

then3wguy

shovelon

then3wguy

ttoks

ttoks

then3wguy

HT2-4956

then3wguy

shovelon

HT2-4956

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