Electrode wear

[Goulton]

For the past few weeks I have been welding up a structure in box section steel (50mm x 3mm thick) using a 1.6mm thoriated electrode on d.c. at about 80 amps. I noted that the electrode did not change or wear away except when my hand shook and I grounded it so a re-grind was necessary.

I have now tried to weld a length of 16mm by 3mm thick aluminium L section using 1.6mm zirconiated electrode on a.c. and 4043 filler. I started on a test piece and found that I needed about 90 amps to get a reasonable liquid pool but, more seriously, the electrode formed a large ball on the end and in quite a short time burnt back so that it was almost inside the shroud. I was using 50/50 duty cycle on the a.c. I tried pulsing but as I had never used this before I set at 120/70 amps with about a 30% pulse at about 12 Hz but this made no difference to the wear rate on the electrode. All the welds were across the section giving a maximum length of run of about 12mm and most were not much more than a generous tack so the torch was only active for short periods

This web site gives the range for 1.6mm electrodes as 70 -160 amps on a.c. so I should be within the safe range. I know that a.c. will put a greater heat load on the electrode than d.c. but my question is should Zirconiated electrodes burn back at this rate or am I doing something silly? Do the current charts assume water cooling at the upper end of the ranges?

Other information that may be useful. I have a R-Tech TIG201 welder, the argon flow was 8 l/minute and I was using a number 6 shroud on a WP26 torch.

The picture shows the electrode after a very short use - not exactly as described above as this had a somewhat larger ball almost entirely inside the shroud.

Thanks for any help you can give.

Chris

 

[hotrodder]

Watercooling doesn't effect the temp at the tip of the tungsten much if at all- it's white hot when welding. It's about cooling the torch head and power cable so they can be smaller etc

I was using 50/50 duty cycle on the a.c

That's your major problem. Approx 2/3 of the arcs heat occurs at the + electrode. AC balance (duty cycle) has a huuuuuge effect on the tungsten, only want enough EP (electrode positive/cleaning) to get a clean, shiney weldpool. From memory Rtech do AC balance 'backwards' to convention which means turning it up increases the amount cleaning**

Everyone (including those that make charts) has differing opinions* for the amperage range of different flavours of tungsten and prep alters things with DCEN while AC balance alters things with AC.


* At the balance and frequency settings i normally use i can run a 1.6 tungsten @ well over 100A but usually switch to a 2.4 at about 90ish with AC. Don't own tungstens smaller than 1.6mm (i just change the prep for low amp DCEN stuff) for example

** Don't take my word on that and (unless they've rewritten it) don't take the manual at face value either- it used to contradict itself

 

[Shox Dr]

Like HR, I use 2.4mm over 90ish amps, tungsten quality, also plays a part

 

[Wendelspanswick]

** Don't take my word on that and (unless they've rewritten it) don't take the manual at face value either- it used to contradict itself

It still does, as do R-Tech's online TIG welding instructions. Had me scratching my head till I worked it out.

On my R-Tech TIG:

Fully clockwise is Max cleaning = Less penetration and more balling in tip.
Full anti clockwise is Max penetration = Less cleaning but better tip shape retention.

Problem I had to start with was using too much cleaning and not enough penetration to blast the oxide layer off.

 

[edh]

Watercooling doesn't effect the temp at the tip of the tungsten much if at all- it's white hot when welding. It's about cooling the torch head and power cable so they can be smaller etc


That's your major problem. Approx 2/3 of the arcs heat occurs at the + electrode. AC balance (duty cycle) has a huuuuuge effect on the tungsten, only want enough EP (electrode positive/cleaning) to get a clean, shiney weldpool. From memory Rtech do AC balance 'backwards' to convention which means turning it up increases the amount cleaning**

Everyone (including those that make charts) has differing opinions* for the amperage range of different flavours of tungsten and prep alters things with DCEN while AC balance alters things with AC.


* At the balance and frequency settings i normally use i can run a 1.6 tungsten @ well over 100A but usually switch to a 2.4 at about 90ish with AC. Don't own tungstens smaller than 1.6mm (i just change the prep for low amp DCEN stuff) for example

** Don't take my word on that and (unless they've rewritten it) don't take the manual at face value either- it used to contradict itself

Hotrodder - last point, you are correct I have just started welding Ali with an R-0Tech 201 AC/DC and found the same problem - initially my 1.6mm electrodes were balling up inside the ceramic @ ~70amps! backing of (turning down) the balance sorted it.
/Ed

 

[Goulton]

Thanks for the guidance. I managed to finish the job in hand but will now look out some more Ali of the same size and practice the things mentioned in your replies.

I did a short welding course at the local college recently to try and point me in the right direction but they only had a very basic AC/DC TIG machine (no pulse or balance control, no foot pedal and fixed AC frequency) so I had no chance to practice using the bells and whistles that are on the R201.

I have to admit that I haven't tried the foot pedal yet. Keeping control of my left and right hands is bad enough at this stage of my learning without having to control a foot as well!

Quite agree with the comments about R-Tech literature. They quote a pulse width of 0.1 - 0.9 seconds which is incompatible with the pulse frequency range and when I queried it with them on the phone they did not quite understand the problem.

Chris