Why does AC arc favor thinner stock?

Date 12-18-2003 17:01

I would keep your torch a little bit more on the thicker material.I would also try adding your rod diffrent maybe on the toe of your weld insted of the center of the weld it would also depend on what position you are welding in.

hope that helps

By Niekie3 (***)

Date 12-18-2003 18:39

Hi Larry

This is the first time that I have heard of this problem. As you are welding AC, it SHOULD not be arc blow, but it certainly sounds like it. Are you welding with high frequency on? Are you welding with some sort of a pulse setting switched on?

I hope that someone can throw some light on this. - Very interesting.

Regards
Niekie Jooste

By LarryL

Date 12-19-2003 01:03

I forgot to mention that I've been using about 85% EN, 15% EP balance setting and AC frequency of 150 Hz. The high frequency is set for start only and pulse has been off. I always direct the arc toward the thicker stock and when that begins to show a molten pool, move the arc on to the thinner stock. However, the arc just wants to head toward the thinner member, and, I have to put the electrode's point very close to the thicker one in order to heat it up. I usually have to feed the rod on the thinner member because that's where it's melting fastest. The ground is clamped on to a large, thick sheet of aluminum and the test pieces have been clamped to it.

Initially I had the test pieces clamped directly on to my steel welding table. The arc was wandering around a lot when my pieces were on the steel table. A Thermal Arc engineer told me to try welding off the steel table - because induced magnetic fields/currents in the steel might be the cause of arc wandering. The wandering of the arc was less after I clamped the test pieces to a large piece of aluminum stock (itself clamped to the steel table).

Niekie, what is "arc blow?"

By billvanderhoof (****)

Date 12-19-2003 05:39

I'm not a TIG guy but from a purely electrical point of view if you are 85% EN and 15% EP then 60% of your current is in the EN direction and unbalanced by current in the other direction. An electronics guy would call this AC with a DC bias. Thus arc blow (redirection of the arc due to magnetic fields) is a possibility. As an experiment try setting the bias to 50/50 and see what happens.
Bill

By Niekie3 (***)

Date 12-19-2003 05:48

Hi Larry

Arc blow is the phenomenon that the welding arc is pushed around by the magnetic fields set up in the base metal due to the current flowing through the base metal and the welding leads. This is usually only a problem in DC welding, because in AC welding, the magnetic fields in the base metal keep "changing direction" so that on average, the arc still goes where you are pointing it.

In your case however, you are 85% of the time in one direction, and 15% of the time in the other direction. This means that you still have the possibility of arc blow occurring. This would be confirmed by the fact that your problem became less when you "isolated" the workpieces from the magnetic steel work bench, by clamping the work pieces to another piece of aluminium. (Which is non-magnetic.)

I suspect that you are still getting arc blow from the magnetic fields in your workbench. You can get rid of this by trying any of the following:

1) Change the position of your earth clamp.
2) Give 50% EN & 50% EP balance.
3) Wrap your earth cable around your workbench (or part of the workbench.)
4) Try moving the workpiece onto another workbench, or onto the floor. (Uncomefortable, but at least you will see if this solves the problem.)

Let us know what happens.

Regards
Niekie Jooste
Fabristruct Solutions.

By ssbn727 (*****)

Date 12-19-2003 08:00

Hi Larry!
This changes everything I had previously mentioned before because of this unbalanced alternating current which is exactly like Bill mentioned with a "DC Bias".....

"YOU MUST TELL US EVERYTHING!!!" just kidding but, as much info as possible is always better to finding the root cause of your problem...

You mentioned that the high frequency is set for START only and not continuous? Well my experience with AC Aluminum is that using your High Frequency set to "CONTINUOUS" gives you better control of your arc characteristics provided that you also have control (adjustment) over the intensity of the the high frequency... In an evenly balanced or unbalanced condition with AC (I'm not familiar with the new inverter Thermal Arc AC-DC power sources so I would'nt know if this is available with your power source)... We must never forget that aluminum and it's alloys always have an oxide layer no matter how thin and no matter how much we try to remove it by other means, it will still continue to exist so long as the surface makes contact with the atmosphere resulting in a thin layer of aluminum oxide because as soon as the unoxided surface of the aluminum metal is exposed to the atmosphere - bingo! you have more surface oxidation - that inevitably we must first break through and vaporize in order fuse to the uncontaminated metal while it's being shielded by the inert gas (Argon?) in order to prevent further contamination within the weld pool!!! How do we accomplish this in a relatively efficient manner?
By making sure the aluminum is as clean as possible prior to welding and by using AC with the High Frequency setting @ CONTINUOUS... Pure tungsten does'nt hurt either but, you can also use the newer types of Wolfram powder (of course - it's compressed to form the electrodes) metallurgical blends out there with similar results and without the need to form a ball at the tip which eventually gets worse and contaminated, especially quicker in an AC unbalanced condition (Arc Transfer)...
I heard that because of this (not having such a large ball at the exposed end of the tungsten), the operator can direct the not so wide arc stream more towards the center of the joint and I've seen it myself also. You can also increase the welding current frequency higher than 150 hz if I remember correctly - with these new power sources like yours and constrict the arc stream even further and possibly eliminate the need for background high frequency current in a continuous mode but, since I'm not familiar with your TA power source, I cannot say for sure...

I believe that by following Niekie's and Thermal Arc engineer's suggestions (about the steel table) and also by switching to CONTINUOUS for your High Freq setting and changing to a more balanced AC condition, you'll begin to see better results in the control of your arc characteristics. Is there any way you can isolate the aluminum plate from the steel table without clamping the Al plate to the steel table? Try either attaching with non ferrous fasteners or by tack welding a configuration of channels of some sort that would enable you to place in between the Al work plate and the steel table some firebrick or some other fire retardant material if possible within the channel in order to isolate the Al workplate from the steel table so that the Al does'nt come in contact with the steel table and use non-ferrous clamps to hold the test pieces on the Al plate... Just remember not to bang on or clamp the Al work plate to the steel table or you'll either quckly break up the firebrick and defeat the whole purpose of isolation from the steel table's magnetic fields... Remember to place the channels stregically under the Al work plate so that the firebricks rests on the steel table with an even load on it from the channel that's attached to the work plate (A smaller perimeter within the perimeter of the Al workplate will work so long as the firebricks sit evenly within the perimeter of the steel table -Capish?)...
Also you'll eliminate or at least minimize to an irrevelant amount any magnetic fields that could cause "Arc -blow"...
That surface oxidation also causes the arc to deflect off it until the surface oxidation is broken up and vaporized in a very short amount of time but, this can only be achieved with HF set @ CONTINUOUS...
If the intensity, current and tungsten shape is set correctly - in less than a second!!! Also try increasing your welding current frequency higher than 150hz with your background high freq set to start to see if you get even better results than with the HF set @ CONTINUOUS...
Hey what the heck, give it a try and let us know if you notice any improvement!!!
A squarewave power source if properly set does not require the use of the separately produced background High Freq setting @ continuous using AC...

Ultimately, both the surface oxidation and the magnetic fields must be eliminated in order to achieve better arc characteristics!!!

Respectfully,

SSBN727 Run silent... Run Deep!!!

By aircraft (**)

Date 12-20-2003 23:45

HF has nothing to do with cleaning the metal.

By ssbn727 (*****)

Date 12-23-2003 11:24

Hi Aircraft, Larry L!!!

You're right Aircraft when it comes to a true square wave power source such as Larry L's machine but, with a sinosudial wave type power source like for the older conventional power sources; the high frequency setting @ continuous is needed to maintain or stabilize the arc so that the cleaning action can be accomplished and maintained. For more precise control of maintaining the AC arc without a superimposed HF current, manufacturers came out with (approximate square wave form) early PCB models - followed by microprocessor based progammable square wave power sources yet some sort of ionization of the gas across the air gap was still required in order to start and stabilize the arc without making contact with the metal first... This is where capacitor discharging was first used and then later replaced with HF start and continuous as found in the more recent conventional power sources... Inverters achieve this with greater efficiency in a variety of ways that have rendered the conventional power sources "Obsolete"!!! Well maybe not yet but, it's inevitable!!!
Could you imagine if computers took as long to become obsolete???

When the first generation of inverter type power sources came out they were at first DC output only power sources which were'nt suitable for thinner aluminum until the twin inverter design which enabled polarity switching. Hence, a form of variable polarity became available...
So yes, Aircraft you are correct in mentioning that HF does'nt actually do the cleaning with either a conventional or inverter type AC/DC power source.

The cleaning action is from the current @ the positive or reverse polarity side of either the sinosudial or square wave half cycle. This half cycle current is much more stable in the "True" square wave form and @ a higher frequency (150hz max for Larry's power source) AC welding current output (not to be confused with pulse-frequency) because it takes relatively speaking, much less (almost immeasurable with Miller) time for the AC current to go from one half cycle to the other (do not include the amount of time the current stays in each 1/2 hz @ peak polarity % for this can be adjusted with sloping and or pulsing) than it does with a sinosudial wave where there is greater period of time of thermal electron emission decay as opposed to virtually no time with a "true" square wave form without sloping... As the current passes close to (arc extinction zone) and through "ZERO" (in order to complete a full cycle or hertz, this "arc extinction" zone is found on both halves of each cycle in a sinosudial wave) the arc is unstable (@50hz in other countries - 60hz over here) so in reality, when the AC current in a sinosudial wave is used without HF continuous frequency; The cleaning action is'nt consistent because the arc itself is'nt stable... Older conventional GTAW power sources that produced sinosudial wave forms needed continuous HF in order to maintain the cleaning action that was intitially achieved by the current being @ it's peak% (usually balanced or 50%) in the positive (RP) half of each cycle. Otherwise the arc would become unstable resulting in poor weld quality.

The opposite is the case with programmable true square wave output current whereby thermal electron emission decay & the so called "arc extinction" zone between each 1/2 cycle is virtually eliminated and as the case with progammable square wave forming (customizing the % of polarity in each half cycle and the amount of time the current stays in each polarity before the beginning of the next 1/2 cycle) coupled with (pulsing) control of output frequency - customized variable polarity pulsed welding current output can be achieved. This is limited by how much control the operator has with both the wave "shaping" or forming and controlling the amount of frequency that is available which varies between manufacturers of welding power sources...

NASA had concluded in their initial research that welding current with very little time in electrode positive or reverse polarity would improve the welding of aluminum. The reverse polarity or electrode positive 1/2 cycle is required for ionic cleaning, but the maximium work is performed by the straight polarity 1/2 cycle so longer time is needed in the electrode negative 1/2 cycle... This is not to be confused with the percentage of straight and reverse polarity current amounts found in balanced and unbalanced square wave forms

A special variable polarity power source with a square wave output was designed for GTAW & PAW of high strength aluminum. This power source, which provides a waveform with a short time period of electrode positive (1/2) cycle and a long time period in the electrode negative (1/2) cycle, was in effect 2 power sources - one with straight polarity and one with reverse polarity connected by means of a high speed electronic switch. This is an SCR type of power source with extremely fast switching and was used to PAW 1/2" thick aluminum alloy with "keyholing" in one pass that would produce "Water Clear" X-ray quality welds!!! This was an automated application called Variable Polarity Plasma Arc Welding with Pulsing or VPPAW-P used in the construction of the external fuel tanks for the space shuttle fleet...
I believe they're using updated equipment today...May our heroes Rest In Peace!!!

Twin type or even more sophisticated Inverters with computer controlled switching can achieve the same so long as the electronics are designed to enable the operator to control and customize the amount of time period the welding current output is in either reverse or in straight polarity coupled with programmable wave forming, adaquate storage for a large amount of customizable weld schedules and a far greater range in frequency output control than what is currently available on the market at an affordable price... Only some of the newer orbital welding equipment power sources can do this and they're far more expensive than what Larry L's got!!! That Miller Aerowave is on paper as close as it gets to a GTAW power source with all the bells and whistles and yet, I only used one welding Duplex SS so, I do'nt know what it can do with aluminum. Hey, the Dynasty 300 with pulsing (higher AC frequency limit than the Thermal Arc model) is no slouch either!!!

I guess I was thinking in a "nostalgic" frame of mind within my initial replies to Larry L without considering the power source he's using...
I apologize for any confusion there folks!!!
I ca'nt help with the type of tungsten but I'm sure you'll find what works for you best... What about a 65-70% electrode (-) and 30-35% electrode (+) wave balance setting with an increased pulse frequency not to be confused with the AC frequency and or are you using any up and down sloping??? Btw, Lawrence (not to be confused with Larry L.) - what do you mean by cathodic etch? Aircraft?

I believe that the black color coded W (lanthanated) alloy will work best with Larry L's balance setting but then, it's just my personal preference... Good Luck!!!

Respectfully,

SSBN727 Run Silent... Run Deep!!!

P.S. Happy Holidays to all!!!

By aircraft (**)

Date 12-23-2003 22:37

No offense. I just misunderstood.
And I do by-the-way like your long replies no matter what anyone else says.

By ssbn727 (*****)

Date 12-24-2003 05:26

Hi Aircraft!
None taken sir!
Thank you for your support and may you - your family - friends enjoy a wonderful, safe and peaceful holidays!!!

Respectfully,

SSBN727 Run Silent... Run Deep!!!

By TRC

Date 12-19-2003 23:42

Hey Larry, in addition to everyone's post I would crank up the frequency. I've been welding just what your talking about
(thick-thin fillets) and have my Aerowave at 300 for the frequency. Unfortunately my machine isn't where this computer is so I can't give exact numbers to you until later. I also have the EN amps turned up about 30% higher than the EP. The user's guide that came with this machine show's 2% thoriated pointed for all applications increasing in size as the material increases in thickness. It's a new machine so I haven't had a lot of experience with it.

Ted

By ssbn727 (*****)

Date 12-18-2003 19:06

Hi Larry L!
I used to think it's because the thinner material will melt faster than the thicker member... Just a thought!
The thickest member will take longer to establish a puddle especially with aluminum being such a good "Heatsink" ( Hence, electrons finding the least path of resistance so to speak) so EV has a point there regarding the use of a torch angle slightly favoring the thickest of the two members...
Question: Which member is the work cable attached to or is the work cable attached to the joint by any chance??? I do'nt know if it'll make a difference but, it would'nt hurt to try it out...

I also agree with feeding the filler towards the toe of the weld instead of the center of the puddle - leading edge of the puddle, towards the toe favoring the thickest member is preferrable...

In any event good luck and let us know how you made out!

Respectfully,

SSBN727 Run Silent... Run Deep!!!

By ArkWeld Date 12-19-2003 04:34

I've seen this quite often when welding dissimilar size metals. In my opinion the smaller size piece produces less resistance to the electrical path formed between the electrode and work, hense the arc wanting to take the path of the thinner piece. The torch should be pointed to the thicker piece regardless and "twitched" toward the smaller for best fussion. If you go to a pure tungsten you may find better control of the arc for aluminum. Arc Blow only occurs in DC welding and is a result of the magnetic field induced around the electrode. For a visual representation of this look at the grinding dust on the floor near your welding cables.
ArkWeld

By Niekie3 (***)

Date 12-19-2003 05:59

Hi ARCWELD

I do not agree entirely with your explanation, because the thinner material will actually give a higher resistance to the current flow. This is however such a small difference that it should not have any real effect.

What will however have a big effect is that the different thickness materials will "generate" different amounts of magnetic fields. As soon as you have any "uneven" magnetic fields around the welding arc, it will result in arc-blow. This would explain the arc-blow on different thickness magnetic materials.

Regards
Niekie Jooste
Fabristruct Solutions

By jwright650 (*****)

Date 12-19-2003 12:31

Once you are satisfied that everything is clean and arc blow is kept at bay, are you preheating the thicker part with the arc for a few seconds before getting down to business and forming a puddle to add filler to? This has seemed to help for me, but I don't call myself a welder by any stretch of the imagination, so take the advise of the one's who have more experience with this process.
just another thought to consider with getting the thicker part up to welding temp,
John Wright

By Lawrence (*****)

Date 12-19-2003 14:09

So much to say I don't know where to start; you have a pretty unusual situation as arc blow in AC GTAW Aluminum is a pretty rare thing.

The work cable suggestion is a good one.

Perfect surface prep is also good. (more on that below)

Your electrode selection and prep look to be good. (a long slim taper provides less rather than more directional control and penetration, so you might try a little steeper included angle in your tip prep)

AC Frequency around 150 is good for increasing directional arc control at the amps your using, you could go as high as 200 but I don’t think it will make much difference, the real advantage to frequencies above 150 up to about 220 is in materials that are thinner than what your welding.

With a gas lens (check your diffuser screen) and the amperage you need to weld quarter inch thick aluminum you might want to boost your argon flow to 25 cfh.

If your machine has a setting for continuous high frequency it should be engaged for the work your doing. However, it’s also important to discuss the function of the superimposed high frequency and what it does and does not do in AC welding of aluminum. The high frequency will run all the time when set in the “continuous” mode. The function is to help the arc reestablish itself (jump across the arc gap) when the polarity changes (EN/EP/EN). Without the superimposed high freq. sometimes the arc will refuse to reignite and arc instability and heat loss occurs, this condition is known as rectification. (Is your arc sputtering?) Arc ignition is the one and only purpose of the superimposed high frequency. The cleaning action is provided solely by ionic bombardment during the reverse polarity (EP) side of the AC cycle. Have you ever forgotton to attach your ground/work clamp and attempted to start an arc? You see little blue squiggles emitted from your tungsten looking for any ground they can find. That’s your high frequency trying to do its job. Those squiggles might touch the table or your work or even yourself, however, if nothing is grounded, an arc cannot be established. The point is that’s all the High Freq. really does. Remove the amps and there is no cleaning.

As a side note, Millers Aerowave and Dynasty are the only machines I know of that switches back and forth between EN and EP so sharply/cleanly that it requires no superimposed High Frequency, in fact, continuous high freq. is not even an option on that machine.

As for the notion that your 85% balance control is the culprit; I wonder if your getting sufficient cathodic etch at 85%. 50/50 will prolly just melt your electrode tip. But it can’t hurt to try an adjustment. I would suggest starting with 75% and then dropping down in 5% increments. When you have a nice white etch around the toe of your weld and no scum on the top of your bead you will be in the ballpark. Mechanical removal (I like an 80-120 grit aluminum oxide disc) of all oxides and contaminants immediately BEFORE striking an arc is an absolute necessity when using exaggerated balance controls such as you have suggested. That 85% dwell time on EP really decreases the cathodic etch and can cause real problems unless surface prep is pristine.

Beside the other advice you have been given I can only add that your torch angle should be pretty close to perpendicular to aid in directional control and also it might help things to keep your arc length to an absolute minimum (without touching). The heat will go where the tungsten is pointed, if this means a little exaggeration toward the thicker member that’s ok as long as the bead profile and the fusion at the root are good, this technique is very common in thin thick fillet welding.

Let us know how your trials go.

By LarryL

Date 12-20-2003 04:55

My TA Pro-Wave 300GTSW is a square wave inverter with a choice of high frequency (HF) start or lift start. According to the manual HF goes off after the arc starts; there does not seem to be a continuous HF setting like that in my old IdealArc 250 unit. I prefer HF starts because I don't like the slight sticking of the tungsten's tip to the work piece when using lift starts.

I've been quite meticulous in my cleaning of the work pieces: cleaning with a aluminum oxide deburring wheel, then wire brushing with a stainless steel brush (dedicated to aluminum) to get off aluminum oxide, including that from the deburring wheel. Finally I wipe all the surfaces with an alcohol moistened clean towel. The prep is sufficiently good so that I can adjust the balance to 90% EN - 10% EP and not get a muddy pool.

During AC welding the arc seems to be very stable, without any of the sputtering that I've experienced with older, non-squarewave TIG welders. During DC welding of steel I have not experienced any significant arc blow - the arc comes straight off the electrode's tip and I can direct it as I wish. Therefore, it seems strange to me that I should encounter arc blow when AC welding.

I tried welding at 50% EN - 50% EP and that produced a broad arc cone with a lot of wandering. It produced the worst arcs of all. Turning up the EN portion of the cycle narrows the arc and I found that a 90% EN -10% EP setting produces the narrowest arc. I wrapped the ground cable twice around the base of my steel welding table. This seems to have helped as there seemed to be less tendency of the arc to be drawn to the thinner stock. I tried higher argon flows but that didn't seem to make a difference. During all these trials I've been using a new gas lens and new ceramic cups.

With this seemingly solved, I can now mention my second arc problem: the arc comes off the tip at an angle. This forces me to tilt the torch one way or the other in order to direct the arc where I want it to go. I've noticed that with a freshly ground tip the arc initially comes straight off the tip. After a few minutes of welding, however, the arc begins to come off the tip (or off the side near the tip) at an angle, around 45 to 60 degrees. If I change to an electrode with a freshly ground tip, the arc will come straight off the tip initially but then begins to angulate after several minutes of welding.

I have tried grinding the tips to tapers of 1 X diameter, 2 X diameter, and even at a 90 degree point angle. I've tried putting small flats of various diameters on the end of the point, from what I estimate to be 0.01" to 0.03". Using a taper of 2 X dia. with a slight flattened point seems to work just as well as any other point angle for fillet welding. I've tried grinding the points with a 400 grit belt and even polishing the points on a fine diamond stone. Nothing like this seems to make a significant difference. Lawrence, you indicated in a previous post several months ago that not all brands of tungsten electrodes are of equal quality. I wonder if my arc problems might be related to the quality of the ceriated electrodes I'm using. They're a U.S. brand but may have been made overseas. Can you share with us information about the brands of tungsten electrodes that have provided the best results for you and your aircraft welders?

Finally, my inverter's top AC frequency setting is 150 Htz - unlike the Dynasty which has settings up to 250 Htz.

I can now achieve fillet welds with legs of 1/4" using a 1/8" ceriated electrode. To accomplish this, however, I have to do some contorting of my torch holding hand whenever the arc comes off the tip at an angle and also have to keep the tip very close to the molten pool - about 3/32" away - in order to direct the heat where I want it to go. If I were able to get the arc to come straight off the tip, I might be able to create fillet welds with 3/16" or smaller legs.

By ssbn727 (*****)

Date 12-23-2003 13:11

Hi Larry L!

What does the letter "G" stand for on your Thermal Arc Pro wave 300"G"TSW power source because I only read the manual for a Pro-Wave 300TSW??? Is this the same power source?

Respectfully,

SSBN727 Run Silent... Run Deep!!!

P.S. In the manual I read, the color code for 2% ceriated W is grey! Hmmm, I wonder where Lawrence got white for ceriated???

By Lawrence (*****)

Date 12-23-2003 13:55

I'm now a bit confused.

http://www.mkt-intl.com/tungsten/tig.html

Here is a link that "says" it has the color codes for AWS A5.12, ISO 6848, and JIS Z 3233, My problem is that my brain does not agree with any of these specs. Now I won't have a merry Christmas until I run back to the shop and see those silly electrodes with my own eyes.

By ssbn727 (*****)

Date 12-24-2003 05:16

Hi Lawrence!

Do'nt sweat it pal because the holidays are more important to celebrate than to ponder or whatever...
Now maybe my mind is too nostalgic for it's own good but, I cannot seem to remember what you were talking about when you mentioned "cathodic etch"? Please refresh this old fart's memory.

Respectfully,

SSBN 727 Run Silent... Run Deep!!!

By Lawrence (*****)

Date 12-24-2003 14:20

The "Cathodic Etch" or or "Ionic Bombardment" are terms used by one of my mentors to describe the etching action happening on the reverse polarity side of the AC half cycle. Electrons going up and Ions comming down, oxides being blasted, thats the stuff!

Here is somebody who also uses the term :)
http://www.thefabricator.com/xp/Fabricator/Articles/Welding/Article285/Article285_p1.xml

Dona Nobis Pachem

By ssbn727 (*****)

Date 12-25-2003 10:44

Hi Lawrence!

Excellent article!!!
Oxide surface area etched or "cleaned" via cathode (RP) = area of cathodic etch or ionic bombardment that results in the break-up and eventual vaporization and displacement of these oxides away from the weld pool...
Thanks for the memory jolt!!!

Respectfully,

SSBN727 Run Silent... Run Deep!!!

By LarryL

Date 12-23-2003 15:46

SSBN727, I don't know what the "G" in my TA Pro-Wave 300GTSW stands for. Apparently the model that I have, the 300GTSW, was discontinued (according to the Airgas salesman who sold this refurbished unit to me) and the 300TSW is the new model that replaces it. The 300TSW has digital settings and readouts like the Dynasty models whereas the 300GTSW has dials for all of its functions. The 300TSW also has its lowest AC setting at 5 amps while the 300GTSW only goes down to 10 amps AC. I haven't been able to determine (from online info) whether or not the 300TSW has a pulse feature - which I've found very useful in welding thin stock. Like Lawrence I prefer a welder with dials rather than one in which you must bring up an individual function on the welder's screen before being able to adjust it. Both types, however, seem to be marvelous welders.

Lawrence, the color coding for some of the newer electrodes doesn't conform to one standard. Several months ago I purchased a package of 3/32", 2% ceriated electrodes from one company. Their ends were painted gray. Recently I purchased a package of 1/8", 2% ceriated from another company. The ends of these electrodes are orange. Maybe the only consistent color coding is that the thoriated ones are red and the pure green.

By ssbn727 (*****)

Date 12-24-2003 05:20

Hi Larry!
Thanks for the update and may you and your family - friends enjoy a wonderful, safe and peaceful holidays!!! The same goes to everyone else in the forum also!!!

Respectfully,

SSBN727 Run Silent... Run Deep!!!

By brande

Date 12-20-2003 07:00

Could be wrong here. Been wrong before, but...

Your uneven arc could be easily caused by too long an arc.

When tig welding aluminum, the arc is very directional, for lack of a better word or phrase. You have to put the arc where you want it.

You have to keep an absolute short arc to get the results you want.
Seems to be even more important on the newer AC/DC inverters-
I run both a Syncrowave and a Dynasty on aluminum pretty regular.
A short arc is essential to putting the heat where you want it.

How long an arc is permissable??
For me, 1/32 to 3/32. 3/32 is the absolute max. Over that, the AC tig arc gets sloppy and hard to control.

Choice of arc length has a lot to do with equipment type, gas purity, and
welder ability.

When running the newer AC/DC inverters, I have found 1.5 Lanthanated
tungsten to be the best. Ceriated is a close second- but keep in mind it does not handle higher amps well. Seems the alloy ingredient in ceriated burns at higher amps, leaving you with nothing but pure tungsten in your torch.
The factory recommends 2% thoriated on these machines on AC-but it hasn't worked as well as the lanthanated. Pure and zirconiated do not work on these newer machines, if you want to take advantage of the hi tech features of these machines. (frequency, balance).

On my Syncrowave, zirconiated seems to work the best. In all honesty, I haven't used a pure tungsten in many years.

Keep in mind, too, that each tungsten electrode diameter (regardless of type) has a definite amperage range that it works well under.
From my experience, for example, 1/8 pure runs well at about 150-210 amps. 1/8 Zirconiated, 225-360 amps on conventional equipment.
Below these amperages, the arc seems to be sloppy and hard to use. Above these amperages, the tungsten produces a "q-tip" type ball and melts. In conventional, non-inverter ac welding, the ball on the end of the electrode should ideally be the same diameter as the electrode. It should never exceed 1.5 times the diameter.
On my Dynasty, I have found that 3/32 handles everthing the machine has.

Now that all this is said-

I would try a 3/32 1.5 lanthanated for this app. Remember we can run a smaller tunsten diameter on these new AC/DC inverters. Your grind seems about right, with a small flat at the tip (.040 or so).

Go to the Profusion web site. They have a lot of good info on all types of tungsten electrodes. They'll even send you a couple of samples, if you ask.

Keep in touch and let us know how you make out. There are a lot of these newer machines out there, and this info will help!!

Good Luck

brad

By Lawrence (*****)

Date 12-20-2003 14:49

I'm beginning to see that the whole tungsten choice debate as subjective/relative. There is very little consistency in performence between brands and often times not much consistency between batches within a brand. Automated work will prove the inconsistency.

Lately I've had good luck with Anchor brand. Cerium 1.5 (orange)and 2.0 (white), I prefer the 2.0 between these two.

Zirconium (brown) has been my usual choice over the years for AC aluminum, my reasoning on this is that even tho it has a slightly lower current carrying capicity the arc stays on the tip longer than others.

I've never had good performance with any sort of lanthanum on AC, 1.5 or 2.0, even tri mixes, all produce arc wander when you tail off and fuzzy tips far to quickly. On DC- Lanthanum can outperform all other.

Now if you are getting several decent sized welds out before your arc begins to wander you aren't really doing so badly. If a trip to the belt sander every 3 or 4 welds is the price you pay to get that nice small fillet profile than I think your getting a bargain. AC will always be more abusive on the tip of your tungsten than DC.

It really sounds like your on top of things, working them out logically.

Good work!

By jer

Date 12-22-2003 20:36

Hello Brande, would you have the web site address to profusion, for I would like to try my luck at another type of tungsten. I typically use thoriated and pure and would like to try the zirconiated and ceriated.

Thank you Jerry

By LarryL

Date 12-23-2003 00:59

Thanks for the lead to Pro-fusion, Brande. I read their articles about electrode selection and requested a 3/32" diameter, 2% lanthanated sample. This is the url for their website:

http://www.pro-fusiononline.com/

Lawrence, it's true that one can find quite a difference in opinion about the best type of GTAW electrodes to use for AC welding with inverters. I've started compiling a list of the best choices recommended by various manufacturers and welding supply firms and may post my findings when I've finished the survey.

By tab_1999 (**)

Date 12-24-2003 02:22

Sure makes you wonder if the arc isn't just following the path of least resistance? Is the thinner member clamped to the top or bottom. Is the ground clamp clamped directly to the pieces? / which piece or both? Isn't the tungsten typically 100% pure w/green end?
Just curious.

By ssbn727 (*****)

Date 12-25-2003 11:28

hi tab_1999!

What it comes down to is the differences in types of design of power sources being used, waveform output, manual & automated applications and personal preference.
Power source design improvements plus the improvements in the alloying of W electrodes with "friendly" elements have led to - pardon the pun, "putting the green back in the grass" when it comes to choosing the optimum W electrode for AC aluminum GTAW/PAW...

Still, pure W works just fine with the older equipment at least until the "ball gets funky and dirty" - hmmm, I wonder which electrode type & tip geometry and other variables lasts longer before a decay in overall efficiency becomes noticeable with AC GTAW/PAW of aluminum and it's alloys??? To ponder or not to???

Respectfully,

SSBN727 Run Silent... Run Deep!!!