[dunkster]

Been doing a lot of sheet metal (.030/.035 mild steel) butt welds and soon found out that back purging is your friend, especially if you're finishing the back side. If not B/P'd, the scale and suck back can leave a real mess.

I should mention this isn't the typical scenario where a closed off chamber (like exhaust) or tank is filled with argon. These are all short 1 to maybe 6 dab at a time welds on flat sheet.

So far, my setup has been a dual regulator and this:

DSCN1267.JPG (4.15 MiB) Viewed 24039 times

While this has worked great, I am noticing the waste in gas from the time valve goes on until arc is lit. So this got me thinking why not just add another solenoid valve for the purge line. This would not only rid the waste at start up but also have zero chance of forgetting to shut the (manual) valve off, like I've done a few times now.

But not being real hip on electronics, the ?'s started adding up.
(btw, machine is a Miller syncrowave 350lx)

1) Can I just pull power from the first solenoid, basically teeing off it?

2) If not, what are my options?

3) Should they be wired in series or parallel?

4) What voltage valve do I need? (I think they are 24VDC, but not 100% certain)


If anyone can chime in on any of the above ?'s or anything else I should be aware of, it'd be much appreciated.

[cj737]

I’ve never purged mild steel. I’ve also not encountered “scale” on the backside of a weld to be an issue, stainless, CroMo, Ti, you bet I’d purge those. Are you cleaning the material properly on both sides? Are you running too much heat? I’m just asking because I don’t understand the circumstances necessitating your purge setup…

I don’t have any advice on the setup because I’ve made a handful of fixtures with venting and use a quick connect coupler to run the purge line. I only run 3-6 PSI so it doesn’t use a whole lot of gas anyway…

[tweake]

i would not do a solenoid valve. simply because you want it to run before you start to weld and a bit after.
the other thing to look at is if a chill block would achieve the same thing. i use it now and then if i can get a nice tight fit. very handy for doing flat sheet.

[dunkster]

I’ve never purged mild steel. I’ve also not encountered “scale” on the backside of a weld to be an issue, stainless, CroMo, Ti, you bet I’d purge those. Are you cleaning the material properly on both sides? Are you running too much heat? I’m just asking because I don’t understand the circumstances necessitating your purge setup…

I don’t have any advice on the setup because I’ve made a handful of fixtures with venting and use a quick connect coupler to run the purge line. I only run 3-6 PSI so it doesn’t use a whole lot of gas anyway…

Yes, material is clean on both sides.

Amp setting for .035" is 24 to 26A. For .030" about 18 to 20.

I've tried just about everything I can think of (pulse, super low amps, super fast travel speed) to prevent scale from forming on the backside and have come to the conclusion that it's impossible, at least for me, to do w/o a backpurge on such thin material.

Backside, w/o backpurge

DSCN0933crop.jpg (738.89 KiB) Viewed 24009 times

By this point, a lot of this has been cleaned up to some degree, but you can still see scaling around the tacks which would most likely (and did) boil into the final weld, making for all kinds of havoc.

Backside, with backpurge

DSCN1396.JPG (4.14 MiB) Viewed 24009 times

This is much more friendly when it comes to both final welding and finishing.

For ref, this 2nd patch measures 7/16" x 2.5", .035" thick.

[dunkster]

i would not do a solenoid valve. simply because you want it to run before you start to weld and a bit after.
the other thing to look at is if a chill block would achieve the same thing. i use it now and then if i can get a nice tight fit. very handy for doing flat sheet.

My thinking is that if power is pulled from the same source that goes to the torch solenoid, then the 2nd 'noid would be subject to same pre and post flow settings as set to on the front panel...wouldn't it?

I did try some chill blocks...3/8" thick copper, clamped on the backside while trying to weld up some pitting from rust.
While it did leave the backside scale-free, it did leave what I'd best describe as worm tracks where full penetration did eek thru. And cleaning these up with a Roloc would take the material too thin for my liking.

[tweake]

i would not do a solenoid valve. simply because you want it to run before you start to weld and a bit after.
the other thing to look at is if a chill block would achieve the same thing. i use it now and then if i can get a nice tight fit. very handy for doing flat sheet.

My thinking is that if power is pulled from the same source that goes to the torch solenoid, then the 2nd 'noid would be subject to same pre and post flow settings as set to on the front panel...wouldn't it?

catch is you lengthen the pre and post flow (not all machines can adjust preflow) and you will use more gas, so your not really any better off.
also your in the usa where gas is cheap. gas downunder is expensive so i'm usually keen on any gas saving.

[tweake]

I’ve never purged mild steel. I’ve also not encountered “scale” on the backside of a weld to be an issue, stainless, CroMo, Ti, you bet I’d purge those. Are you cleaning the material properly on both sides? Are you running too much heat? I’m just asking because I don’t understand the circumstances necessitating your purge setup…

I don’t have any advice on the setup because I’ve made a handful of fixtures with venting and use a quick connect coupler to run the purge line. I only run 3-6 PSI so it doesn’t use a whole lot of gas anyway…

Yes, material is clean on both sides.

Amp setting for .035" is 24 to 26A. For .030" about 18 to 20.

I've tried just about everything I can think of (pulse, super low amps, super fast travel speed) to prevent scale from forming on the backside and have come to the conclusion that it's impossible, at least for me, to do w/o a backpurge on such thin material.


DSCN0933crop.jpg

By this point, a lot of this has been cleaned up to some degree, but you can still see scaling around the tacks which would most likely (and did) boil into the final weld, making for all kinds of havoc.



DSCN1396.JPG


This is much more friendly when it comes to both final welding and finishing.

For ref, this 2nd patch measures 7/16" x 2.5", .035" thick.

is it just me or are those welds really big ??
sorry i can't remember the last time i did steel, I'm more used to stainless.

[dunkster]

My preflow is never any more than about a second and post is just long enough to cool the tungsten.

If I ever need more post on the cool down, I'll stab the pedal a time or two.


Width wise, those should be no more than an 1/8".
I do plan to experiment with tungsten grinds to see if the puddle can be narrowed up.
Think I read where a more blunt grind makes for smaller puddle?

If these were just fusions, I'd hold a tighter arc. Think I'm about as close as I dare go when adding filler.

[Arno]

1) Can I just pull power from the first solenoid, basically teeing off it?

2) If not, what are my options?

I would not drive the second solenoid directly from the first as you don't know how much 'headroom' the driving electronics have current-wise.

A workaround, if it's indeed 24V, would be to tee off and bring the internal solenoid power pins to the outside on a neat plug/connector and then make an external box with a separate powersupply and the gas solenoid you want to run and use a truck/bus automotive relay (they usually use 24V) to then trigger/drive this external solenoid. (make sure the relay has a back-current protection diode or resistor on it..)

The relay will pull quite low current compared to the gas solenoid, so it's likely fine on the driving circuit on the welder.

That way you can drive/add more stuff as you want and perhaps extend the external 'box' with things like a delay circuit to add some additional postflow for the back gas flow when the front shuts off. Include a flow meter and ball valve on the external 'box', perhaps even a distribution manifold with multiple outlets/valves and you have all the control on what you want to do in 1 spot. Can pretty much make it as fancy as you want/need.

You'll need to verify the voltage on the solenoid in the welder though to select the correct relay for the application.

Bye, Arno.

[cj737]

One thing I'd try first is to use a larger cup and some higher CFH. That material looks pretty "shagged out" to begin with, so some amount of discoloration is inevitable.

Have you considered using Silicon Bronze wire? That looks to be a rust repair patch panel. I have great success with SilBr for these applications because you areducing the heat quite a bit and you can use 0.024 wire instead of 0.035 wire (even less heat).

I'm with Tweake, your tacks are awfully large for their application which also causing you to camp out on the weld to get enough heat to melt the filler. Change to a smaller wire, drop your amps, or do both and use SilBr. And bump up your cup/gas a tad.

[tweake]

I'm with Tweake, your tacks are awfully large for their application which also causing you to camp out on the weld to get enough heat to melt the filler. Change to a smaller wire, drop your amps, or do both and use SilBr. And bump up your cup/gas a tad.

i was wondering if that may to low of amps and not enough travel speed. sitting around to long pushing filler in.

[dunkster]

i was wondering if that may to low of amps and not enough travel speed. sitting around to long pushing filler in.

Thing to remember is I'm finishing both sides off, so having any "lows", on either side, is not acceptable. I'd rather have them a touch too proud than not enough.

And smallest filler I have atm is .030". IDK about smaller filler, but with .030, for me anyway, it's very hard to get bead down to even .1" wide, let alone less. I'd do anything to be able to lay 1/16" wide beads with full pen on .035 stock (with filler, not fusion)...love to see somebody do it.

I still got to get out and experiment with electrode grind angles, which reminds me.
Right now, I'm using 1/16" thoriated. Any benefit in going to .040"?

[dunkster]

One thing I'd try first is to use a larger cup and some higher CFH. That material looks pretty "shagged out" to begin with, so some amount of discoloration is inevitable.

Have you considered using Silicon Bronze wire? That looks to be a rust repair patch panel. I have great success with SilBr for these applications because you areducing the heat quite a bit and you can use 0.024 wire instead of 0.035 wire (even less heat).

I'm with Tweake, your tacks are awfully large for their application which also causing you to camp out on the weld to get enough heat to melt the filler. Change to a smaller wire, drop your amps, or do both and use SilBr. And bump up your cup/gas a tad.

Only thing shagged out is the first pic. IIRC, that had sat a few days un-oiled and started to rust a bit around the tacks. And the scaling don't help matters none either. I can assure you at fit up time, that was every bit as clean as brand new stock.

SilBr...won't go there, as I had mentioned, these are all getting dressed down flush after welding.

I will be trying some sub 20 amp passes on .035". My fear is that will just keep me in the puddle longer...IDK, we'll see what happens.

[tweake]

i was wondering if that may to low of amps and not enough travel speed. sitting around to long pushing filler in.

Thing to remember is I'm finishing both sides off, so having any "lows", on either side, is not acceptable. I'd rather have them a touch too proud than not enough.

And smallest filler I have atm is .030". IDK about smaller filler, but with .030, for me anyway, it's very hard to get bead down to even .1" wide, let alone less. I'd do anything to be able to lay 1/16" wide beads with full pen on .035 stock (with filler, not fusion)...love to see somebody do it.

I still got to get out and experiment with electrode grind angles, which reminds me.
Right now, I'm using 1/16" thoriated. Any benefit in going to .040"?

its hard for me to comment as i do mostly stainless and rarely steel at least with tig.
its not really filler size (i've done it with 1/16" filler) but how much is added.
my go to is to use pulse at a high rate. that way you can keep the amps up high as my cheap machines don't do well at low amps. then super super tight arc with a needle point electrode. with a fish's rear end tight arc the weld size drops way down.

[dunkster]

Executed!

After talking to a Miller rep and being assured that the factory 24V circuit for the torch solenoid had plenty of oomph for a 2nd one, I ordered one in and got it installed a couple weeks ago. Just got around to using it today and I couldn't be happier with it. While it's great not dealing with having to manually turn the valve on now, it's even better knowing it's impossible for me to forget to shut the thing off when I'm done... which has happened now more than once with the manual valve. I added the toggle switch so it can be turned off when not needed. And when I need to purge an exhaust system or the like, I'll just come straight off the regulator, bypassing the solenoid.

Thought long and hard about mounting the valve inside the machine but wanted it in a monitorable location.

Couple shots of my install. (sorry for the blurred wiring shot, hence the diagram)