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in stick current can affect the polarity of the workpiece and of the electrode, the heat that is distributed to the workpiece and the elecrode, the rate at which the electrode is deposited into the puddle, the depth of penetration and the occurance of arc blow.
ac current reversal characteristics that effect the magnetic field are almost eliminated, as a result arc blow is not a problem in ac stick.
in tig the diff of ac and dc is a little more technical, but simply put ac allows for ease of welding on lighter and non-ferrous materials. with a high-freq imposed on the current arc starts are much easier.
ac machines produce higher voltages, allowing the use of larger electrodes thus increasing the rate of deposition. power consumption is lower making the ac machines more efficient.
anyway I could go on and on but I hope this helped a little
Although I get the basic differences between the effects of AC vs DC stick, could someone give a few practical examples of when you would use each setting and why. Sometimes I feel my settings are rather abitrary. I tend to use DC when the material is thinner or fit is poor and I am trying to control blowing through but I am not sure I am really applying the settings correctly.
Maxstar 150 STL
Blue Star 185 DX
When you are welding thin material you need to be using straight polarity. This is when the electrode is negative and the work clamp is positive. You should be using a rod like 6013 which is a fast fill rod made for welding thinner material.( DC -) Use a small rod and turn the current down.
You get the most penetration with reverse polarity - electrode positive and work clamp negative. For best penetration you would be using a rod like a 6010 or 6011.( DC +)
You would use AC when welding on material that was magnetized or when welding using current in excess of 200 amps and arc blow becomes a problem.
If I had know I was going to live this long, I would have taken better care of myself.