Tungsten burning back on AC

[tmorgan4]

After receiving lots of helpful info with my last dilemma, I'm looking for some more advice on an issue I had for the first time today.

BACKGROUND: I have done very little aluminum. Probably about 10 minutes of welding to be honest. I've got about 20 hours of arc time on my Dynasty 200dx and it's almost all on mild steel and 4130.

Today I switched my machine to AC to try and weld a 3/8" plate to a cast aluminum transfer case. The plate is not structural whatsoever...just needs to hold oil.

I had the machine set to 200 amps, default balance and frequency settings, water cooled WP-20 torch, 3/32 thoriated tungsten. As soon as I let off the pedal to extinguish the arc I can watch the tungsten point melt back into a ball. It didn't seem to matter how long the arc was held as I don't have a problem until I let off. Still have post-flow for 12 seconds.

What could cause this?

[thunder71]

on the dynasty 200 i use on aluminum i use 1/8" green 100% tungston with no problems...3/8" plate is kind of thick for 200 amps...

[popspipes]

Try keeping the torch the same distance from the work when you let off the pedal. I have seen this condition when drawing a long arc on my trailblazer. Too low a setting on the cleaning will degrade the tungsten qiickly as well.

make sure you dont have it set in the RMT2 setting, use RMT as the former doesnt shut off the machine off instantly. Check the manual as I am not familiar with it.

The Dynasty is a very nice machine!

mike sr

[cosmosuave]

The tungsten is suppose to form a ball...

[popspipes]

The tungsten is suppose to form a ball...

The tungsten does form a ball, more so on the older machines where the cleaning is not adjustable, the inverter machines are easier on the tungsten in my very limited experience if the cleaning is set to about 75 percent.........

mike sr

[FoxPerformance]

For one, your using too small a diameter of tungsten. Does the end of the tungsten "bounce" as your welding? I'd be using 1/8" at least. For something that thick.

Also I would preheat with a torch as much as possible! What your trying to weld is sucking up heat and dispersing it throughout the entire part.

[Bodybagger]

If your tungsten is burning back, it sounds like your shielding gas is cutting out as soon as you let off the pedal. Despite what the postflow is set at, how long is your postflow actually running?

[SundownIII]

thunder71,

Think if you check, you'll find that Miller (and about everyone else in the know) recommend NOT using pure tungsten in the inverter tigs.

Personally, I've had better luck with 2% Lanthanated.

I suspect the OP has several issues contributing to the problem he's experiencing.

1. Needs to use a larger tungsten for AC at 200A.
2. Check to make sure he's getting a true 10 sec. postflow of gas.
3. May have machine set for too much cleaning (ie. too high of EP)

[thunder71]

i know everyone says don't use green BUT I HAVE FOUND out with my experiance with the dynasty 350 & 200 that it works BEST, much better then red or orange...i will be getting some gold soon to try...miller also says don't use a 50' water cooled rig BUT thats what i use

thunder71,

Think if you check, you'll find that Miller (and about everyone else in the know) recommend NOT using pure tungsten in the inverter tigs.

Personally, I've had better luck with 2% Lanthanated.

I suspect the OP has several issues contributing to the problem he's experiencing.

1. Needs to use a larger tungsten for AC at 200A.
2. Check to make sure he's getting a true 10 sec. postflow of gas.
3. May have machine set for too much cleaning (ie. too high of EP)

[FusionKing]

i know everyone says don't use green BUT I HAVE FOUND out with my experiance with the dynasty 350 & 200 that it works BEST, much better then red or orange...i will be getting some gold soon to try...miller also says don't use a 50' water cooled rig BUT thats what i use

Is this is what you use on the Anodized projects you posted earlier?
Maybe that would contribute to your findings. Are you using a point?
I personally don't like Green for anything. It just disappears for me. I had much better luck with the brown and now love gold.
I would love to use blue but my LWS don't stock it and I buy mine from them.
Besides I usually touch the tungsten before it wears away.

[thunder71]

yes i use green on ALL aluminum,anodized & mill finish...no point it will not hold a point on A/C ,nice chrome looking ball on the end...i have read lots of good things about the gold HERE & would like to try it...i don't know why miller says don't use it but i have proven them wrongif it disappears on you just pull somemore out...i run hot when i weld & it seems to hold up really well...when i weld thin stuff i use 1/16" green or 3/32" green...dipping your tungsten or "touching" it is never a good thing,maybe your tungsten is to far out?

Is this is what you use on the Anodized projects you posted earlier?
Maybe that would contribute to your findings. Are you using a point?
I personally don't like Green for anything. It just disappears for me. I had much better luck with the brown and now love gold.
I would love to use blue but my LWS don't stock it and I buy mine from them.
Besides I usually touch the tungsten before it wears away.

[tmorgan4]

Thank you to everyone for the suggestions! While I do think I could use a bigger tungsten, I think my problem lies beyond that. When I had a friend of mine do some aluminum work (identical setup, he's the reason I bought mine!) he was welding 12" long beads at 200 amps without having the tungsten melt away like this. The vinyl water hoses were about to burst but the tungsten was still fine.

I better check my post-flow and make sure it's still getting gas like it's supposed to. Didn't have any problems when I put it away but it has been sitting for a month. I made sure to purge the lines well from sitting.

And if you wouldn't mind helping a young guy....I could use it.

It seems a lot of people don't point the tungsten on aluminum and just leave it a blunt end. I simply break a 7" tungsten in half (usually anyways...sometimes it shatters into 30 pieces) and it leaves a perfect, square, blunt tip. After this gets dipped, I can't seem to break off just the tip and get my square, blunt edge back. Cutting it with a grinding wheel doesn't leave a nice edge and I find myself having to point the tungsten a little to clean up the cut.

Is there a better way to go about this?

[popspipes]

I sharpen all my tungsten for stainlessd or aluminum, it helps to focus the arc on aluminum, it will ball slightly on the end depending on the current and cleaning settings. Most of my welding is on light gage materials. I grind the end when it gets contaminated and if its really bad grind off the bad end and start over.
Tungsten usually breaks after it has been heated and cooled, probably hardens it some.
I have welded with the square ended tungsten but I like the point or small ball better..

My way may not be correct either but it works for me..

mike sr

[Vicegrip]

I am no expert by any means. I have a Syncro transformer machine, use lanthanated and sharpen w/ blunt tip for AC. I have 2 blocks of steel with one having a small groove in it. I lay the tung in the grove with the bad part sticking out lay the other block on top lining them up, push down hard and strike the bad part with something metal and heavy. 99% of the time I get a single clean break with no splits regardless of it being new or used. Used seems softer to me and I have bent rather than break some tungs before. I chuck the tung in a drill and spin it while runing in my 6X48 beltsander. I know, amature hour but it works for now untill I get a real sharpener.

[Bodybagger]

For an inverter machine running running thoriated, lanthanated, ceriated, or a mixture of these rare earths, point the tungsten like a pencil then grind a flat land in the end. With experience, you'll know how wide to make the land. For aluminum, the width of the land should be about 1/3 of the diameter of the tungsten. Of course, you can vary this for best results. But this is not why your tungsten is burning, if it is indeed burning and not melting or cracking off. I wonder if it isn't splitting into little shards due to the way it's been broken in half...

No matter what kind of tungsten you are using, right or wrong tungsten, or how much heat you are putting through it while the arc is alive, there is no reason why it should burn after the arc is out unless the tungsten loses its envelope of shielding gas while the tungsten is still above a reactive temperature.

The question you have to answer to solve your problem is why is your tungsten getting oxygen while it's still hot. Here are some possibilities:

Your machine is shutting off the gas flow too early. This could be due to incorrect postflow setting or a problem with the machine. Set it to a different setting, like 25 seconds and see if it is indeed running that long after the arc goes out.

Maybe the flow rate is so low that pulling the torch away from the weld causes enough turbulence to overcome the barely adequate amount of shielding gas. The only way to know how much gas is really flowing is with a ball flowmeter. A dial guage will show the same flow rate with a 100% plugged up tube, because it does not measure flow... it actually measures back pressure behind an orifice inside the regulator.

With a ball flowmeter, you will also be able to tell if there is an interruption in the flow of gas just by looking at the ball. And consider getting a diamond cutoff wheel for a Dremel. The name brand Dremel diamond cutoff wheel is like 20 bucks, and the off brand Chinese diamond cutoff wheels are like 6 bucks. That way you can nicely point your tungstens, as well as cut them.

So consider getting a ball flowmeter and a diamond cutoff wheel.