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Crack repair failure??

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Crack repair failure??

Postby Backyardmech » Mon Aug 21, 2017 8:16 pm

I'm an Industrial mechanic at a plastics and fiberglass plant...lots of older machines and equipment. Well during one of my machine inspections today I found a badly cracked shaft...it's been repaired once. Not sure our miller 250 mig is the right welder for the repair? When I repaired it last fall I gouged the crack out and cleaned it up nice..this time it's way worse..cracked in 2 places almost all the way around..I think there were cracks on the inside I never seen? This pc of machinery makes man ways for water and septic tanks. Weighs about 1.5 tonnes.
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Re: Crack repair failure??

Postby Coldman » Mon Aug 21, 2017 8:38 pm

Any idea what the material specification is?
Also can you post a pic zoomed out a bit so we can see the whole thing?


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Re: Crack repair failure??

Postby Backyardmech » Mon Aug 21, 2017 8:46 pm

Material is just reg. Carbon steel I believe. This winding machine is very old..I will get better pics tomorrow once I have it apart.
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Re: Crack repair failure??

Postby Brettmm92 » Mon Aug 21, 2017 9:14 pm

From my experience, I would give the crack a nice, deep bevel, and spray-transfer over it. I'm no old timer but that seems to be a solid way to fix most mild carbon steel cracks. Hope all goes well!
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Re: Crack repair failure??

Postby Arno » Tue Aug 22, 2017 3:16 am

As you grind out the part, do a spark-test on the clean base material at the same time to see if it's perhaps a high(er) carbon material.

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Just so you're not fighting an uphill battle against a base material that gets hard and brittle and crack-prone after welding on it.

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Re: Crack repair failure??

Postby Poland308 » Tue Aug 22, 2017 8:40 am

Even if it's mild steel it's very likely that that is a stress point that has caused the whole area around the crack to become work hardened and brittle. I would recommend a 250deg F pre heat and try to keep it above this temp even as you weld. Preheat at least 3-6 inches away from the weld as well. After you finish welding keep the temp up for at least 15 min before you let it cool.
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Re: Crack repair failure??

Postby MarkL » Tue Aug 22, 2017 1:01 pm

Arno wrote:As you grind out the part, do a spark-test on the clean base material at the same time to see if it's perhaps a high(er) carbon material.

Arno, what book is that chart from?
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Re: Crack repair failure??

Postby Backyardmech » Tue Aug 22, 2017 6:02 pm

Here's some better pics...got part taken off today and cleaned and beveled the cracks..it worse then I though..
Thanks for the advice.
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Re: Crack repair failure??

Postby LtBadd » Tue Aug 22, 2017 7:13 pm

MarkL wrote:
Arno wrote:As you grind out the part, do a spark-test on the clean base material at the same time to see if it's perhaps a high(er) carbon material.

Arno, what book is that chart from?

Mark, google "spark test chart" or "spark test pdf" you'll have many results
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Re: Crack repair failure??

Postby Coldman » Tue Aug 22, 2017 9:09 pm

Whichever process you use, that crack is going to have to be bevelled out with root gap for full penetration weld with re-enforcement. The ends should be drilled to stop the crack.

It can be migged but you would need to be a solid mig welder to do it right with full fusion. Root pass downhill and fill/cap passes uphill.

Personally I think stick or tig would give a more reliable result.
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