Hi,
Thanks to the advice here, I just bought a Lincoln Arc Welder AC 225/ DC 125 (SMAW). I have used one like this many years ago, but I did not receive any formal training. My question is about the settings on the welder. You can weld AC, DC+, or DC-. The manual provides a chart showing how to match the correct electrode to the correct setting, however it gives no advice why you would use each setting. In other words, when do you use DC+? When do you use AC? When do you use DC-? I know, I know, you can use any of these settings after a hearty breakfast and a good cup of coffee. But seriously, what applications are each of these settings appropriate for?
Chris
i only use DC+ for all my work...on some rare occasions i might use AC if i needed some low penetration on something, or if i was having major problems w/ magnetic arc blow. DC+ works on all cellulose rods (E6010, 6011, 7010, etc.) and on most low hydrogen rods (E7018, 8018, etc.) DC+ penetrates more than AC or DC-, but not all rods are designed for use w/ all polarities. most rods use DC+ anyway. and like i said before, the only reason i'd use AC is if i was having magnetic arc blow that i couldn't control by any other means. DC- is used for some hard surfacing rods to minimize heat input to the base metal. if you got a TIG setup, you would use DC- for steel and stainless steel and AC for aluminum. if you get a flux core setup you can use DC+ or DC-, depending on the type of flux core. if you get a MIG setup you would use DC+.
I am welding mild steel SMAW. So does the different polarities only have to do with the electrode you use? Can you weld mild steel on any of the three AC, DC+, or DC-? On the box it says something about DC giving a "smooth stable arc..." I do understand you need to match electrode numbers to the correct polarity. So is DC- the best polarity for thinner materials like sheet metal since you say it puts less heat in the base metal, right?
You say you use DC+ on all your work. What type of work are you involved in? Also, you said AC has less penetration. Does that mean you use AC on thinner metals like sheet? Or would you use DC- on sheet since it heats up less?
When I am going to weld mild steel say 1/8" thk angle, when I walk up to the welder, what polarity do I use, and why?
What is magnetic arc blow?
i weld mild steel 1/8"-1" thick. i use DC+ and E6010 or E7018 most of the time. i've tried welding w/ DC- and these 2 rods, but the arc isn't stable at all and tends to stick a lot when you try to start the arc. i've found that AC makes a 7018 rod stick more than DC+ when you start the arc. but i've usually overcome that drawback by turning the amperage up a little to compensate for the "colder" arc in AC.
in your case, DC+ would be the best polarity. there are ways of controlling how hot a puddle gets on thin materials so it doesn't burn through, so you shouldn't have to use AC for anything.
magnetic arc blow is when you have electricity flowing in only one direction (DC+ or DC-) and it turns your piece of steel into an electromagnet and it forces your arc to stray toward or away from the puddle, depending on which direction the magnetism is pointed. it can really make you mad if you don't know how to control it before it happens, or while it's happening because it will blow a giant crater in your piece faster than you can fill it. but switching to AC polarity (if you're using a rod capable of AC current) is a cure because then the electricity is switching directions 60 times a second and does not give enough time for a magnetic field to form.
Suppliers of consumables want you to be satisfied with their products. Thus they supply pamphlets (free there at the welding supply store), web sites, and usually make general suggestions on the box the rods come in. Look to these sources for starting points, try, adjust from there. You won't be exactly the same as the next guy anyhow so exact recomendations are useless. For general use 1/8 rods work well most burn at 90-120 amps- high end for thick stuff- low end for thin stuff. If you blow holes try smaller rods. If it seems like the rod doesn't last long enough try bigger ones. Weld some just for practice you will develop your own preference.
Safety tip- No cuffs on your pants they catch sparks and you find yourself on fire.
Have fun
Bill
Hi , Personaly, I use dc+ (most of my welding is in the field with a welding rig ). The only time I would use ac current (in shop) would be if the machine was ac only, or if I had only ac type electrodes available. AC current can be useful to eleminate arc blow when welding with E-7024 electrodes and probably some others as well. There are some types of cast iron electrodes that specify dc - (straight polarity) also. I buy the dc+ ones so I dont have to switch to dc- in the field. The machine you have should be handy because it is easy to switch current settings if you need to. It is certainly better than the old ac only buzz-box some of us learned to weld on. Have a good day - WS
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