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Hi Glenn, Wow, you're getting a variety of answers on this one, not all of them correct. DC rods are generally considered to be easier striking but the arc is subject to arc blow. Arc blow is when the unchanging magnetic field of direct current causes the arc to wander off the intended line. AC welding is not subject to arc blow. A few electrodes can be used with only one current/polarity but most can be used with either. 6010 is the most widely used rod that runs well only one way: DC+. 7018 is often considered to be a DC only rod except when it's specifically designated as 7018AC, but even this is not strictly true. In addition to their 7018AC, Lincoln makes Jetweld LH-70 (AWS: E7018 H4R) for which the preferred polarity is DC+ for rods up to 3/16" and AC for rods 7/32" to 5/16", and Jetweld LH-73 (AWS: E7018 H8) for which the preferred polarity is AC, period. In simple transformer type welders, you almost always get more bang for your buck with AC. This is because the limiting factor is the duty cycle (the total amount of time in a ten minute period that you can weld at a given setting.) The duty cycle is determined by the amount of heat which is generated inside the welder. DC welding current is produced from AC current through the use of diodes in a rectifier which creates additional heat in the welder. Therefore the same duty cycle will be at lower current for DC than for AC in the same welder, or the same current will have a lower duty for DC than for AC, either way you want to look at it. This difference is reflected in the AC/DC ratings of light duty welders. Lincoln's AC/DC buzzbox is 225 amps AC, 125 amps DC. I have a Hobart Stickmate AC/DC which is 235 amps AC, 160 amps DC. Lincoln says that their buzzbox has a 20% duty cycle at all settings but many welders have an increasing duty cycle as the amps are lowered. My stickmate has a 100% duty cycle at 100 amps AC, but at only 65 amps DC. 6011 is often considered the AC equivalent of 6010 (DC+ only) and is almost as widely available. In practice they don't run exactly the same, but I'd be hard pressed to choose one over the other. Many brands of 7018 are very hard starting on small, low OCV (open circuit voltage) AC welders, but unless you store your 7018 a lot more carefully than most people do (you really do have to keep it at 200 degrees or more) you won't get the low hydrogen welds that this electrode is intended to provide. Then you might as well use 7014, 7024, or even 6013 if you don't need the extra tensile strength. These electrodes run beautifully on AC. If you absolutely must have the characteristics only 7018 can provide, and you'll go to the trouble to store and use the rod properly, then you can still get by with an AC only welder by using 7018AC or one of the varieties of 7018 for which AC is the preferred polarity. In my experience, there's only DC electrode that has no AC counterpart, and it's used so infrequently that I can't see how it could justify the extra expense of an AC/DC welder over a quality AC only one. 6012 electrode run DC- bridges gaps without creating slag inclusions better than any other stick electrode I have used. But if that one thing is really important to you, you ought to be saving up your money to buy a good wire feed welder and run it with shielding gas. Nothing I'm familiar with can fill gaps as well as that. All the best, Stan
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