What do you know about Arc Rectification?

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I started a thread a month ago about an erratic arc I was getting when welding high amps on 3/8" and larger Aluminum. Here it is:http://weldingweb.com/vbb/showthread.php?t=75821The Lincoln tech said I am seeing Arc Rectification. I described it in detail in the thread. It only happens on non-ferrous metals. It is worse with non square-wave transformer machines like mine.What I want to know is how to minimize it or possibly eliminate it. Any Ideas? My machine is a: Lincoln Tig 300/300, code 9401 which puts it at about 1997. Transformer machine without AC balance control,CK 230 Rigid torch rated to 300 amps,1/8" zirconiated tungsten,# 8 cup with 1/8" tip out.Amp setting High,Spark continuous,Remote pedal control,AC mode.Gas is Argon and Helium. I am trying to mix about 75/25 for penetration.Flow is about 20 cfh combined.
Reply:The subject is mentioned in the Lincoln Bible, IIRC. I don't think I've seen much about it anywhere but would think increasing the HF would help reduce any rectification by initiating the arc at a lower voltage and thus sooner (closer to zero on the sine wave curve).
Reply:Go to:http://www.millerwelds.com/resources...Book_Chpt2.pdfand see the discussion of arc rectification on page 10.I'm not sure how much you can do about it on a straight sine wave machine (other than cleaning the oxide layer off REAL well with SS brush and acetone) but suggested cures include:"Don’t dwell in the weld pool""Add filler metal""Keep arc moving along weld joint"
Reply:I don't know anything about arc rectification, but I know I get a smoother arc at high amps by using a bigger tungsten. Try some 5/32 EWZr-1 and see how it acts.
Reply:Originally Posted by Oldiron2... increasing the HF ...
Reply:Originally Posted by MikeGyverWhat do you mean by this?
Reply:Originally Posted by MikeGyverWhat do you mean by this?
Reply:Originally Posted by Oldiron2Increasing the intensity of the high frequency setting.
Reply:[double post]Welding/Fab Pics: www.UtahWeld.com
Reply:I think he is referring to the Spark Intensity. It is one of the few controls the older transformers had on HF. I tried going to max with no positive result. It was like the arc would just stop on the return, EP, and start again on the EN. If I pushed harder on the amps it would just blow the puddle apart. It got if I went back over a weld to try and smooth it out. The cleaner the Alu the more likely it is  to occur.
Reply:Originally Posted by MikeGyver?"high frequency" is the spark that starts the arc (and runs continuously to stabilize AC sine wave arcs), It's either on of off, there's no adjustment. Do you mean increase the AC frequency of the arc?
Reply:So thats what that is, arc rectification. I have experienced that, not to the level you described. It would only happened at work on a syncrowave 250. I would experience it quite a bit because of "dwelling in the puddle" (I use an on/off switch so i sometimes have to wait a little to get it going). I could pause just a couple seconds and start to get an irritate arc (but nothing alarming). With my dynasty i don't get that at all. At first when i read your op i thought it was something else (gas, settings, etc.) may still be. Have you tried pure tungsten. Thats all i would use (transformer) and never had arc rectification become a problem. I didn't know there was a name for it. Are you sure your getting enough heat(amps) in it, trying to run cold causes all sorts of problems (thats part of the reason why you see so many disastrous first attempts at aluminum, they jump the gun). But thats my opinion.www.performancealuminumfabrication.com
Reply:I was pre-heating with a propane weed burner. Tried pure tungsten but it can't begin to handle the amperage needed on heavy aluminum. Your squarewave does better than my 300/300 but will still have some at times. I was using a He/Ar mix and at the higher He settings it was worse. I think we have it nailed at rectification. I would like some secret old-timer solution if there is one. Maybe a larger capacitor in the cleaning circuit. I tested mine yesterday and it was within specs. I would sure like to understand the cause better. Why only non-ferrous? Very interesting. Joe
Reply:Ironwood mentioned it.I was just going to add, can you make it with pure argon?  Argon seems to be pretty decent at establishing a stable arc.  Maybe Helium hurts this (or needs higher voltages etc.)  I have to wonder if there is something reactive that can be added to the gas.  Inert gases have all their electrons tightly bundled up in stable 'orbits'.  Other gases tend to have free-er electrons.  Maybe nitrogen? I know with TIG welding they tried all kinds of gases before settling on argon.  Maybe you can get a list of what they tried and why rejected.  There might something there.Con Fuse!Miller Dynasty 350Millermatic 350P-Spoolmatic 30AMiller Multimatic 200Hypertherm PowerMax 1000G3Miller Maxstar 200DX
Reply:Ironwood,I'm "late to the dance" and haven't read all the responses in detail, but may suggest a different approach in the future.In dealing with 3/8'-3/4" aluminum, you may be better off with a preheat to about 300F and using straight DC (DC-) with straight helium.  Several posters here will say to use "lab grade helium", but my experience says that most "high purity" helium will work.Heavy aluminum weldments are where DC welding of aluminum has major advantages.You may want to do a search on "DC welding of aluminum".Even better, you may want to PM either B_C or Pangea and describe your issues.  Both have considerable experience in DC welding of aluminum.  I see that B_C (Bill) just posted to a new thread called Shop Stuff.  Pangea has done considerable DC welding with NASA.Last edited by SundownIII; 02-03-2012 at 02:23 PM.Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.