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Tool Talk Discussion Forum

Welding theory revisited!

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135 Fan

04-09-2008 12:28:19




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I'm not wanted to get into a big debate. I'm just relaying some very interesting info I got from a welding engineer at Lincoln. I was in a welding supply and happened to pick up a Lincoln brochure on pipe welding. It said that 6010 can be used for the root pass on straight polarity for thinner wall pipe. I was always taught, and it is even specified by the AWS, that 6010 is a DC+ electrode only. At least for any code type welds or so I thought. He said 6010 is almost always used on reverse (DC+) in N. America but in Europe it is sometimes used on DC- for thin wall pipe. After some further corrospondence, I received some more interesting info. 6010 on DC- has a faster burn off rate than on DC+. AWS doesn't have specs. for 6010 on DC- but Europe does with their EN classifications. EN doesn't stand for electrode negative as I learned. He then said what was most shocking and against everything I've ever heard. He said DC- has the most penetration. If this is true, even if it is opposite what every school teaches, why would you use it for thinner wall pipe to avoid burn through? 6010 is much smoother on DC+. He did say that some 6010 work better on DC- than others. 5P works better than 5P+. I suggested that they need to make a new desigination if 6010 is acceptable on DC-. Maybe putting a 6010-1 which would indicate that it can be used on DC- in certain conditions. The same as 7018-1 has slightly better properties than standard 7018. He said TIG is different than stick. On DC+ the tungsten gets too hot. All the highest depostion rods and wires run on DC+ because with 2/3rds. of the heat on the electrode, it preheats it so it burns faster. I've, as well as every welder I know, always thought and been told that DC+, then AC and finally DC- are the order for highest penetration to lowest. Going by the guy from Lincoln, it's DC-, AC and DC+. I know current flows from negative to positive on DC and some people get that confused but being told that one of the most basic principles you were taught is backwards confuses the heck out of me. What do you welders on here think? Dave

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buickanddeere

04-09-2008 19:31:20




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 Re: Welding theory revisited! in reply to 135 Fan, 04-09-2008 12:28:19  
Electrons flow from negative to positive. They carry the heat with them.



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T_Bone

04-12-2008 08:03:57




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 Re: Welding theory revisited! in reply to buickanddeere, 04-09-2008 19:31:20  
Hi B&D,

Wouldn't that only be on DC resistive circuits flowing negative to positive where as DC electronic circuits flow positive to negative.

T_Bone



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rexhellwig

04-09-2008 18:32:38




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 Re: Welding theory revisited! in reply to 135 Fan, 04-09-2008 12:28:19  
It's been awhile since I've burned any 6010. We used to use it for the initial pass when repairing an old 320B stripping shovel. That 1920s steel was sure different from modern stuff.

If I understand Weldcote's spec sheet correctly, they claim straight or reverse is OK here:

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135 Fan

04-09-2008 21:07:41




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 Re: Welding theory revisited! in reply to rexhellwig, 04-09-2008 18:32:38  
AWS doesn't have a DC- spec. for it and even on the Lincoln website is says DC+ only. Lincoln are the most popular 6010 by a big margin. 5P and 5P+ are the preferred rods. Most other brands tend to fingernail. That's why it's confusing. Dave



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135 Fan

04-09-2008 13:03:25




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 Re: Welding theory revisited! in reply to 135 Fan, 04-09-2008 12:28:19  
I might have the 2/3rds. heat thing backwards. I can't remember but I know DC+ is supposed to have the most penetration and highest deposition rates. The guy from Lincoln also said with innershield, different fluxes are used to put more heat into the electrode. How can a flux alter where the heat from DC current goes? Still confusing. Dave



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Bud in WV

04-09-2008 17:00:10




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 Re: Welding theory revisited! in reply to 135 Fan, 04-09-2008 13:03:25  
I'll bet you just opened a great BIG can of worms! As a former welder, I'll be lurking to hopefully learn something....
I still weld at home and for my neighbors but I'm too old and crippled to consider myself a real welder now!



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135 Fan

04-09-2008 17:16:46




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 Re: Welding theory revisited! in reply to Bud in WV, 04-09-2008 17:00:10  
Hey Bud. If DC- has higher deposition and more penetration, why aren't the rod makers designing rods for DC-? I just found it very interesting. Dave



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Bud in WV

04-10-2008 04:16:55




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 Re: Welding theory revisited! in reply to 135 Fan, 04-09-2008 17:16:46  
It's like I used to tell my millwrights when they ask me a high tech question - I'm a LOT better at dumb looks than good answers!
I'm sure there's a weld engineer somewhere that can answer it but my experience welding was like driving a car. Just 'cause I can operate it doesn't mean I have a clue how to work on the transmission.
It's a good question. I've wondered about it myself. I'll be looking to see what the answer is.

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135 Fan

04-10-2008 09:27:59




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 Re: Welding theory revisited! in reply to Bud in WV, 04-10-2008 04:16:55  
The Lincoln guy said it is confusing. What's really confusing is that he said DC- has more penetration at the weld puddle and is better for preventing burn through and filling up larger gaps. How can more penetration be better for filling a gap? Interesting stuff? Dave



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135 Fan

04-10-2008 17:18:00




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 Re: Welding theory revisited! in reply to 135 Fan, 04-10-2008 09:27:59  
I'm not going crazy after all. I got another e-mail from Lincoln. When he said DC- has more pentration at the puddle, he meant more heat on the work. He also confirmed that DC+, then AC and then DC- are the most to least penetration in that order. I was confused but it's cleared up now. Dave



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