Lanthanated Tungsten

Date 01-24-2003 21:01

I have had very little experience with this electrode, but I too have converted my training program over to Lanthanated tungsten. I treat this tungsten as I would 2% thoriated. This being that as a weldor completes a weld the torch should *not* be raised so that the tungsten is pointing upward. This keeps the argon shielding flowing in a downward position and covering the tungsten. If a post purge setting is not available on the machine, such as with a scratch start, the argon is allowed to flow until the tungsten is cool enough not to absorb oxygen and create the oxide colors. Then the torch can be moved and the valve turned off. Usually, a post purge of five to eight seconds is sufficient. So far I have not noticed any oxide film that occurs upon shutting off the arc if the argon continues to flow.

By brande

Date 01-26-2003 05:32

Oxidation on tungsten electrodes can and does happen. Base metal condition, tungsten composition, tungsten quality, shield gas quality, tightness of your gas system and operator technique all can contribute.

In any case, I find that a quick touch or scratch to the work before hitting the foot control (when the tunsten is still electrically "cold") will break the oxide to ensure better starts. A quick, light swipe is all that is needed.

Obviously this will not work if a current/contactor control is not being used.

I got into this habit and use it on every start. Really helps and if you develop the habit, you'll never miss a start. Give it a try!

Good Luck
brande

By aircraft (**)

Date 01-28-2003 09:39

That is a very, very bad habit

By brande

Date 02-01-2003 07:29

Why??

By aircraft (**)

Date 02-07-2003 04:58

Number one, if your getting oxidation on your tungsten (manual TIG) your doing something wrong.
Number two, never ever run the risk of contaminating your work or your tungsten.

By brande

Date 02-11-2003 04:14

Used this method for years-never any contamination.

We're talking a very light tap-not a hard scratch!!

The tungsten, when cold, is also much harder than anything you might be welding.

brande

By billvanderhoof (****)

Date 08-19-2003 03:33

This isn't my area of work but just curious. Would there be any objection if one attached a piece of sandpaper to some convenient object, say a block of wood, and touched that instead of the work before each start?
Bill

By smithdos (*)

Date 01-28-2003 16:12

OK. We do manual TIG and have remote foot-pedal controls for arc control. We also have post-weld purge setup on our machines.

The machine I use (for test/experimentation) is a Miller Synchrowave 200. The post-weld purge is set at 20 seconds. We use Sylvania 2% Lanthanated, 1/16" OD.

Here are my observations:

1. Grind tungsten on dedicated grinder.

2. Tack weld part (we fab sheet metal assys for aerospace - machine is set at 20 Amps). I usually do tests with 3 inch OD tubular stainless or Inconel, usually .035" wall thickness.

3. After 4th tack, cannot ingite arc. Greyish "film" has formed on tungsten.

4. Scrub tungsten with 300 grit silicon-carbide fabric-backed sandpaper or manual SS wire brush.

5. Start welding.

6. Extinguish arc after a couple of inches of weld (I'm not the best welder on the planet).

7. Attempt to re-ignite arc to continue welding. The arc will not ingite again without scrubbing with sandpaper.

I have noticed that if I continue welding before the tungsten has cooled below red-hot, I do not have any ignition problems.

There is no other discoloration of the tungsten (it does not turn blue).

Our argon checks fine (acceptable dew point readings).

I have also received similar complaints from welders after switching to Lanthanated tungsten. These welders have not previously complained about arc ignition difficulty with Thoriated tungsten, so I have assumed that there are no problems with the argon hoses, etc.

Dave

By Lawrence (*****)

Date 01-29-2003 14:12

Dave,

Coupla things,

Firstly all the hubub about thorium is in my opinion overstated. There are no cases that I know of that GTAW welders having actually had ill effects from radioactive thorium. The ground dust is the issue at hand. Tungsten itself is related to more lung irritation as far as that goes. I tell my students to treat all tungsten as if it were radioactive so that they take no risk of harm.

Next, try the same sequence you stated above with thoriated electrodes of the same dia. and prep, if no problems occurs than it might be wise to try another vendor of lanthanated.

We make lanthanated electrodes available and they are manufactured by
Louis Renner GmbH and imported by
International tungsten In Sacramento Fax. (916) 921-0751

This brand has excellent arc performance. The only drawback we have found is that it does not break as clean as Thorium electrodes (longitudinal fractures) so we just cut them with a diamond wheel when we need small ones.

We have seen the dusty film you describe on our automated line where we do buildups, our machines may run up to 5 hours on a single arc strike and at the end they will need to be redressed. But as the dust accumulates there is negligible change in arc characteristics and little change in arc voltage. For manual welding we have no problems.

Lawrence

By rodofgod (**)

Date 08-16-2003 21:16

Fact 1-Tungsten without Thorium will have a lower currant carrying capacity,and ability to maintain a point,than with Thorium.
Fact 2-When currant capacity is exceeded, 'Furring' of the point will occur
Fact 3-Move up to a larger diameter Tungsten i.e. 3.2mm instead of 2.4mm,when 'furring' occur's.This will solve your problem.

By ssbn727 (*****)

Date 08-16-2003 22:54

Hey Rodofgod!!!
Long time no read!!!

Do you mean that about courrant or is it currant??? Just kidding!!! (I hope you have a good sense of humor)
Must be that fat fingered virus again... (He meant CURRENT!!!) For all of us that do'nt comprehend the word "Furring" could you please elaborate? (I know what you mean but others do'nt, and since you mentioned it, please explain.)) other than that, I agree to a degree... Man, that ryhmes!!!
Anywho, Smithdos! A couple or maybe a bunch of questions please... You say you're using a Miller Synchrowave 200 am I correct? at around 20 amps? Is your "Work" or commonly referred to as your ground clamp in relatively close proximity to the work? Have you checked the HF (Hi Frequency) adjustment setting? Do you frequently check your gaps on your points, and the condition of the points (pitting?) themselves for your HF?
Are your connections from your GTAW torch shielded properly? Are your torch parts in good condition? Are the gas line connections from the machine to the torch in good condition and tight? Are you using a gas lens cup on your torch? Are you welding with gloves that might be contaminated which in turn might be contaminating the material or filler rod prior to welding? Is there an extremely thin layer of the material's oxide or chemical/oil residue present in between the tungsten and the metal? I ask this because, if you do'nt clean or remove that layer then, you MAY experience arc starting and restarting problems, and electrode contamination as a result of this thin layer of either oxide or chemical/oil residue from previous handling through another fabrication area in your assembly "chain"... Now I'm not saying this is the reason that you're experiencing these problems because of this, NO!!!! All I'm saying is that sometimes, when you change something that's part of the welding process you've used previously then, you should back-track your way, and every step of the way back to the root cause of the problem...
If you've already done this then, the suggestions given by the others that have already replied to you, would be recommended...
In summary, usually the root cause of the problem lies in something that you've overlooked or some sort of adjustment in the machine or size of electrode or even the mfg. of the electrode or a change of parts is required in order to correct the problem...
Well, I hope that you find out wherein the problem lies...
Look foward to your response...

Respectfully,

SSBN727 Run Silent... Run Deep!!!

By Lawrence (*****)

Date 08-18-2003 14:05

So many Facts so little time.

For those of you interested in electrode performance here are some rules of thumb.

Thorium 2% (red), Lanthanum 1.5% (Gold) & 2% (Black), Cerium (Orange)and most "Tri-mix" (Grey). Electrodes have equivalent current carrying capacity,(each melting at just under 5,500 degrees F).

Next we have Zirconium (Brown) (preferred for aluminum) which has a slightly lower current carrying capacityn than the above..

At the bottom we find Pure (green) I see no reason to use pure tungsten at all, unless your tool crib can't get rid of it. Zirconium outperforms it in every way.

Now, Tungsten electrodes are pretty hard to make, (powder mettelurgy) and different manufactures have different ways of going about it. Therefore the properties of these electrodes can differ significantly. This is especially true with Lanthanated electrodes. From different vendors I have experienced Lanthanated 0.040 and 0.063 tungstens that have had charicteristics ranging from bending like stainless to fracturing the entire length, to perfect (thoriumlike) ductility. and as for the fuzzzzzzz? just try a different vendor if you fuzz up. It may have nothing at all to do with over heating. we have had 0.063 lanthinum electrodes fuzz up on water cooled torches running under 20 amps.

Remember, the alloying (doping) elements are added to the tungsten to make it a better electrical emitter. That means that things are actually movin around at the heated tip of the electrode at the micro level and that that growth on the electrode can be an indication of an unfavorable batch of electrodes.

There ya go

Lawrence

By ssbn727 (*****)

Date 08-18-2003 21:57

Hello again Lawrence!
I believe the Powder Metallurgy mfg. process is called "Sintering"???
Bad batches can happen!!! Especially if the Mfger's (Manufacturer's) QC dept. is'nt up to "snuff"!!!

Another rule of thumb is to double-check everything before one comes to the conclusion that the root cause lies in the "Wolfram" (tungsten) alloy mix...It would be a shame to presume one probable cause only to find that the problem was lurking somewhere else, as it does quite often... Always good to read from you Lawrence!!! Your explanations are always impressive, and accurate!!! Love that Zirconium!!!

Respectfully,

SSBN727 Run Silent... Run Deep!!!