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Crawlers, Dozers, Loaders & Backhoes Discussion Forum

broken welds D6B

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U9 U9 CAT

07-24-2007 07:18:04




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Give me the low down on A/C D/C welding, do you swap the leads to get A/C, Use your ground to weld with? Any advive on over head welding would help also




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BrianA

09-04-2007 15:21:28




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 Re: broken welds D6B in reply to U9 U9 CAT, 07-24-2007 07:18:04  
Overhead welding can be too much fun sometimes!!!
If you're not that sure and realy want to fix it right the first time I'd have a welder come in and do it for you, let them get the hot steel and slag on them. I've done my share of welding, and theirs nothing worse than watchig it drop towards you with nowhere to move.



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john_bud

07-24-2007 20:52:35




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 Re: broken welds D6B in reply to U9 U9 CAT, 07-24-2007 07:18:04  
I just want to echo the comment that you need to pre-heat. Most things on a cat are pretty big and will need a lot of heat to have decent penetration. Overhead the puddle will slide off into your collar if you heat it with just the rod.

Out of position welding always gives me the urge to be a super hero - so I can flip the sucker over and weld it down!

jb



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135 Fan

07-24-2007 20:28:27




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 Re: broken welds D6B in reply to U9 U9 CAT, 07-24-2007 07:18:04  
DC is much more stable and easier to weld with, especially overhead. With DC the current flows in one direction or the other with 2/3rds of the heat on the positive terminal. This makes for faster deposition and increased penetration because the electrode is hotter (preheated). AC current flows back and forth so changing cables makes no difference. This is a basic explanation. For welding on a Cat, I wouldn't recommend anything less than 7018. It works best on DC electrode positive. To make overhead welding a little easier use a size smaller rod than you might use for flat position. It will be easier to control. Grind the area really clean and put a groove where the crack is. You can put more than one pass but make sure to clean up the previous pass really nice so everything flows together and fuses properly. If you are using smaller rods like 3/32 it would help to preheat the area as it not only makes the weld flow in better it also prevents cracking from the quenching effect of the extreme heat on the cold steel. Try to keep as close of an arc length as posssible without the rod sticking. It should be close to the same heat as flat position. If it's too cold the bead will pile up with little penetration. If it's too hot it will blow a lot and be very hard to keep a close arc for a nice weld. Have the rod angled back only a little bit to force the slag back from the puddle and also to push the molten weld metal up. It would be a good idea to practice on some pieces before you did the repair. If the repair doesn't look good, grind the weld out and start again. I've had to do this a few times on some jobs. Being that it's on a Cat and cracked in the first place, it's no use doing a bad repair that will just have to be fixed again that may be even worse. Hope this helps. Dave PS/ Wear a leather jacket and a welders cap or ear plugs to keep sparks and hot slag from burning you or getting in your ears.

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135 Fan

07-24-2007 20:36:06




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 Re: broken welds D6B in reply to 135 Fan, 07-24-2007 20:28:27  
I forgot to mention that on a Cat in particular stick welding is the best choice. MIG would be too easy to get cold lap or lack of penetration. When using 7018 use a straight drag technique with no whipping back and forth. A small side to side weave could be used to get a wider weld but don't go more than about 2 rod widths wide. Dave



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Bill in IL

07-24-2007 10:14:19




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 Re: broken welds D6B in reply to U9 U9 CAT, 07-24-2007 07:18:04  
This depends upon what type of power source you have for a welder if you have AC or DC. Some DC machines also have a AC output. Switching leads in AC will not change anything due to the fact that alternating current is alwas constantly changing from positive to negative. Switching leads in DC will change the way the electrode behaves. Direct Current Electrode Positive (DCEP)is better for deep penetration. Direct Current Electrode Negative (DCEN) is more suited for shallow penetration and some rods require use of DCEP or DCEN. It all depends upon what you are trying to achive with your welds and what electrode you use and current source. If I was to weld overhead I would use DC current if avaliable and you need to use either a 6010 6011 or 6013 electrode. The 6010 and 6011 are better cause they are fast freeze electrodes and will be better out of position.

The biggest keys to overhead welding is turning the current down to control the weld puddle better. You will not get the same weld penetration overhead as flat position so always turn your part over if possible. Use a whip technique where you will burn the electrode in the weld puddle for 1 second then "whip" out of the puddle maintaining the arc for a half second then back to the puddle for another second. This helps to keep the molten puddle smaller and more in control. It does take some practice to master but a useful technique for fast freeze rods. Third you need to keep the sparks off of you somehow by covering up or staying out of the way. This is the hardest part.

I as most people find MIG welding easier in out of position welding so I would use that if its an option for you. Good luck hope this helps.

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U9 U9 CAT

07-24-2007 20:32:08




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 Re: broken welds D6B in reply to Bill in IL, 07-24-2007 10:14:19  
I'm using a miller bobcat 225 welder I'll look tomorrow closer at it to try and figure out the A/C D/C Thanks for the help.



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135 Fan

07-24-2007 20:38:40




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 Re: broken welds D6B in reply to U9 U9 CAT, 07-24-2007 20:32:08  
The DC connections are usually red for positive and black for negative and AC yellow. At least that's how some Miller machines are. Dave



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