wide etching on aluminum

[johnson697]

There is no magic setting to achieve what you want. It is a combination of techniques and wave shape that determines how that happens. It helps to know the theory behind what is happening during the weld process, as it's much faster than you can see. There are many good books on metallurgy and welding, and also a ton of white papers on the Lincoln Electric site. Just search for "cathodic etching" to learn about what is happening, and why. Once you know what all the controls of each welding machine do to the wave shape and how that impacts what you are after, you will be able to tailor the machine settings to your technique and the job, to achieve the best appearance, strength and corrosion resistance of your welds. Some people pick this up by experience, some by researching and reading, and some need to be taught. Everyone learns differently and I'm sure you know what works best for you.

This is kind of respone i was looking for ,ty.

[johnson697]

these are some of the tanks i welded this week

[jakeru]

My understanding of gasses is that different gasses have different voltage requirements to initiate and sustain an arc through them. I've sure noticed it when say, you weld through a container that outgasses something nasty and non-inert (like water vapor) that wreaks havoc with a previously stable TIG welding arc, and sends that arc suddenly blowing off to the side considerably (like an inch or more!), presumably where there is still inert gas capable of sustaining an arc at the voltage being used. So it makes sense to me, that changing the cup configuration actually could change the cathodic etch pattern.

In fact, I've thought I've noticed that using a large diameter gas lens does indeed enlarge the diameter of the cathodic etch pattern, all else being equal.

I'm not saying it's a good way to sufficiently control the width of the cathodic etch all by itself, but I do believe it can have a small difference. Changing the gas flow (and travel speed plus current output being used as previously mentins) are other variables that can influence the etch pattern. By all means, yes, I would recommend experimenting with different size cups and types of collet bodies (gas lens versus non-has lens) to try to arrive at the characteristics you desire - these components are available for a relatively low cost, so it's easy to try.

If your budget is a little higher, with all the aluminum welding you're doing, you might want to try a helium-argon mix. Mixing Helium in with the Argon *definitely* reduces the width of the cathodic etch pattern. In fact, IME, if you mix in too much Helium, you won't get enough cleaning to even keep the puddle itself clean! It changes other characteristics of the arc advantageously for welding aluminum also, IMO.

Too bad there's not an easy way to check what kind of AC balance your 250EX is actually kicking out. (e.g., to verify if it is indeed, putting out 90% EN 10% EP as advertised.)

I remember there was some posts a while back about some people's IGBT machines not putting out the specified AC balance. It took a pretty experienced and knowledgeable weldor to suspect this, and then someone confirmed it. Everlast replaced some boards or something and corrected the problem. Could be something to check out. (Making sure your machine is really putting out its advertised AC balance adjustment range...)

Edit: here we go, the thread I was thinking of:
Super wide etching on Aluminum!

[johnson697]

what kind of mix would you do?and im thinking about getting a #4 cup to use on my torch,i have a #6 gas lens on it right now.

[jakeru]

If you're looking at experimenting with a pre-mixed bottle, something in the area of 25% He / 75% Ar is probably a useful area. You're going to maintain good arc starts and get very noticeable benefits from Helium in that general range. I have a separate Helium and Argon bottle (and mix my own) and often I will just run just a very small amount of Helium, rarely over 33% He. It has really nice arc qualities for welding aluminum and is great for penetration or welding larger, thicker things.

A #4 cup is VERY small; there is a dramatic difference in its surface area compared to even a #5 cup (just to be aware of...) You'll may need to turn down you flow rate to avoid turbulence. In fact a #4 will work well with very little gas flow (like 8cfh or so Argon.) Definitely try a #5 cup also.

You should have already tried turning your EP (AC Balance knob) down to the minimum if you haven't already. You might want to compare your test beads to that those shown in the picture at the end of the thread I linked to above. If you aren't getting the same results, try and find someone with an oscilloscope test what AC balance range your machine is putting out. The 250EX is rated to put out 10% EP (90% EN) with the AC balance knob turned all the way counter-clockwise. At that setting you really shouldn't be getting much cathodic etching. Edit: here we go, this post has pictures (indicated as "NEW") of expected 250EX cathodic etching:
http://www.everlastgenerators.com/fo...=3932#post3932

Also, what tungsten are you using and how are you prepping its tip? I've found with a big, balled tungsten, seems to spread the arc out wider (and thus, the cathodic etching out wider as well.)

Happy experimenting!

[johnson697]

i am using both lanthanated 1.5% and also thoriated ,but try to stay with the lanthanated for my aluminum ,and i dont ball my tungsten up.

[performance]

Thoriated won't ball either, if it's less than 40%, which is where it should be located at anyway.

[johnson697]

these are the tanks i did recently and used a #4 cup to weld with and etching is almost completly gone

[everlastsupport]

Welds look great Nice work. Glad all the bugs seem to be gone.