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Making a structural weld with a mig welder?

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Making a structural weld with a mig welder?

Postby Backyardmech » Sun Sep 10, 2017 9:32 pm

I'm an Industrial mechanic at a plastics and fiberglass plant...my welding skills are good..had training an near by collage and just on the site training..lol Anyways we make fiberglass septic tanks, and our biggest mold is a 8 ftr(diameter)..and 30 ft long made of steel...engineer at work estimated weight at 8500lbs...drive shaft that rotates this tank broke at weld that holds mounting plate to this mold..can a mig weld this properly and safely? Machine is a Miller 250..any thoughts ?
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Re: Making a structural weld with a mig welder?

Postby Coldman » Sun Sep 10, 2017 10:32 pm

Some pics would help alot to give a better answer. The more info the better, such as thickness etc.
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Re: Making a structural weld with a mig welder?

Postby Poland308 » Mon Sep 11, 2017 7:08 am

With a dual shield wire and a good preheat. Would be my choice. Or talk the engineer into buying a 300 amp tig/ stick machine. A desperate engineer will often aprove big expenses if you make a strong case.
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Re: Making a structural weld with a mig welder?

Postby cj737 » Mon Sep 11, 2017 7:44 am

A friend who farms had me come over yesterday to assess repairing a number pieces of his equipment that require welding, cutting edges, etc. The piece most relevant to your situation is a bucket on a skid steer. The 3/16" plate MIG welded to 1/2" plate sheared at the weld for 2 reasons:

Whomever MIG welded it, did so downhill and; there's not a single bit of fusion to the 1/2" plate. The entire weld is connected only to the 3/16" plate.

So, can your repair be MIG welded? Yes, but are you competent enough to do it properly is the real question. If not, hire it out, or choose a different process.
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Re: Making a structural weld with a mig welder?

Postby Bill Beauregard » Mon Sep 11, 2017 8:08 am

Bill Beauregard wrote:I just responded, it didn't work.

I used Lincoln Innershield .045" in a Millermatic 252 last night. The product burns deep like 6011. I believe it is considered to be low hydrogen if wire is properly stored. It runs vertical with incredible ease, and lays down a lot of filler in a big hurry.

My project involved filling 16 cubic inches of joint in (I'll estimate) 1 hour of trigger time. The 252 handles the load fine. On demand fan comes on, runs continuously while welding, and shuts off a few minutes after stopping. I fused all the head components together in my stock M25 gun, so I bought a 400 amp Bernard gun for Dualshield.

You need the gun, knurled rollers, roller wire guide, and .045 either Dualshield from ESAB or Lincoln's Innershield, Or is it outer shield?

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Re: Making a structural weld with a mig welder?

Postby Louie1961 » Wed Sep 13, 2017 7:01 am

Willie, Innershield may not be bad but that is FCAW-S, not FCAW-G. I think outershield (71M) is what you were referring to.
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Re: Making a structural weld with a mig welder?

Postby Bill Beauregard » Wed Sep 13, 2017 7:23 am

Louie1961 wrote:Willie, Innershield may not be bad but that is FCAW-S, not FCAW-G. I think outershield (71M) is what you were referring to.

Yeah, I realized that minutes after clicking submit. Still, I believe it's a good choice for structural welds with plenty of penetration, and dependable fusion in structural applications.

The biggest shortcoming I find is lots of spatter.

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Re: Making a structural weld with a mig welder?

Postby homeboy » Wed Sep 13, 2017 7:43 pm

Somehow I have lost most of my pictures so I cannot post any. You can weld almost spatter free with flux core. I use Lincoln .035 only and with only a dampening in the weld area with water based anti spatter spray just before welding and a quick hit with a wire wheel after and done. The only time I get much spatter is with multiple passes without much cooling and the spray boils away fairly quick. Get the thin stuff that sounds like water in the can. I tried the thick stuff, for mig tips I guess and it worked but made a heck of a mess to clean up. Of course getting your settings right is very important also. :D :geek:
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Re: Making a structural weld with a mig welder?

Postby Backyardmech » Fri Sep 15, 2017 8:12 pm

Thanks for the advice...but after talking with the plant manager and our engineer....we got a crane in to remove the steel mold, and will remove the drive shaft and mounting plate and send them out to get done by a outside company..crane operator weighed tank in at just over 10,000lbs..I trust my welding..but not putting the lieability out there..shaft is 6 inch dia. And plate is 1 inch thick by 16 inch dia.
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Re: Making a structural weld with a mig welder?

Postby weldin mike 27 » Sat Sep 16, 2017 6:45 am

There is nothing wrong with that weld. Its a base metal or stress distribution issue that will require some engineering input to make sure it doesn't happen again. Good choice to remove, but make sure the company has the appropriate brains to fix it.
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