ac dc question

admin

I am very new to welding and i want to find out the difference in ac  and dc on my stick welder.  i talked to a nice guy at my local weld shop today and was explaining to him a project i was doing and he told me i should have swithed my trailblazer to ac instead of dc.  you guys always explain these things better than the people i deal with.    i want to thank you guys up front.
Reply:There are many questions to be ask and answered before it can be determined AC or DC.  What are you welding on and what Electrode do you want to use.  JohnSMAW,GMAW,FCAW,GTAW,SAW,PAC/PAW/OFCand Shielding Gases.  There all here. :
Reply:When using AC ( 60 cycles per second in the US ) twice during each cycle the AC wave passes through zero. This means 120 times per second the AC arc on the welder goes out. For this reason the arc is not quite as stable as the arc when using DC, and maybe a little harder to learn to weld with for the beginner because the arc is less stable.In DC there are two polarities that can be chosen, positive and negative. In positive polarity the electrode is positive ( reverse polarity ) and the electron flow is from the negatively charged work to the positive electrode. Two thirds of heat when using positive polarity is liberated at the electrode and one third at the work. The intense heat liberated at the electrode causes the rod material to travel across the arc to the work at high velocity and gives the deepest penetration. DC (electrode negative) the electron travel is from the negative electrode to the work. One third of the heat is liberated at the electrode and two thirds at the work. This gives less penetration and is why DC negative is used for thinner material, using with something like a 6013 rod.AC is good to use then arc blow is a problem. This is when magnetic fields interfere with the arc path. This happens when you are welding something magnetic or welding with a current in excess of around 200 amps under certain conditions.As far as penetration is concerned the deepest is with DC positive, then AC, and then DC negative. Unless you are welding on something magnetic, or something thin, set it on DC positive and weld away.
Reply:Originally Posted by 6010When using AC ( 60 cycles per second in the US ) twice during each cycle the AC wave passes through zero. This means 120 times per second the AC arc on the welder goes out. For this reason the arc is not quite as stable as the arc when using DC, and maybe a little harder to learn to weld with for the beginner because the arc is less stable.In DC there are two polarities that can be chosen, positive and negative. In positive polarity the electrode is positive ( reverse polarity ) and the electron flow is from the negatively charged work to the positive electrode. Two thirds of heat when using positive polarity is liberated at the electrode and one third at the work. The intense heat liberated at the electrode causes the rod material to travel across the arc to the work at high velocity and gives the deepest penetration. DC (electrode negative) the electron travel is from the negative electrode to the work. One third of the heat is liberated at the electrode and two thirds at the work. This gives less penetration and is why DC negative is used for thinner material, using with something like a 6013 rod.AC is good to use then arc blow is a problem. This is when magnetic fields interfere with the arc path. This happens when you are welding something magnetic or welding with a current in excess of around 200 amps under certain conditions.As far as penetration is concerned the deepest is with DC positive, then AC, and then DC negative. Unless you are welding on something magnetic, or something thin, set it on DC positive and weld away.