Casting Stress Cracks? 4

[qnen]

I've gotten involved with a casting issue, and to be honest, castings are far from my normal subject matter,-- so please forgive me if this question is basic knowledge.

We've had a casting made that resembles a large shoebox. Overall dims are 26in long, 10in wide, and about 6in deep and the walls are about 1in thk. Material is cast ductile iron. For some reason, the original designer kept the inside corners fairly sharp (about 1/8in rad). Once the castings were made amd some surfaces machined, we noticed cracks in some of the internal corners (assumed to be stress cracks from cooling?).

The question is can this casting be used? can it be repaired? will the cracks almost be guarenteed to continue growing?

I realize a lot of this is very vague, but hopefully it is a starting point for discussion.

 

[btrueblood]

Used for what? Is this to contain pressure or other significant load? I'd not use an item with visisble surface cracks, even if the answers to the questions are no -- just because of the number of times I'd have to say "it's okay to use" every time somebody looks at it.

 

[qnen]

Hopefully I added a .jpg showing the casting in question. It is a pivot mount for an oscillating arm. The red circled areas indicate the cracks. The real question to the group is about repair options. Pros and cons of welding the cracks... or other solutions. Obviously time and money has been invested in these castings. If they are repairable, great!! However, if one stress crack is visible, does that mean many more are hiding, waiting to show up? Does anyone know of inspection techniques (service providers) that may answer these questions?

Thanks

 

[TVP]

Generally speaking, there are repair options. Take a look at these links to get an idea of what is done. I'm sure others will offer their insights as well.

http://www.aera.org/ep/downloads/ep9/EPQ110_20-27.pdf

http://www.ductile.org/magazine/2007_2/ductilewelding.htm

http://www.lincolnelectric.com/en-us/support/welding-how-to/Pages/cracks-cast-iron-detail.aspx

http://fulltorque.com/pdf/GMRC white paper.pdf

 

[arunmrao]

The cracks are formed due to poor fillets at the corners. Sharp joints are never advised. Also,the core hardness influences occurrence of cracks.

I would not suggest salvaging such cracks for DI castings.

_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

 

[micalbrch]

As longs as the part is not pressurized or subjected to any significant load I would use it. Ask yourself what will happen if it fails. Will there be any danger for people? If the answer is "yes" or even just "perhaps", you'll have to scrap it. But if not try to get it repaired and use it. Or ask your foundy to cast a new item it it was their fault.

 

[arunmrao]

Upon,taking a second look at the crack, it appears to be in the region close to a thick section. I assume the crack exists only in the red highlighted region and not else where. It can then be a hot tear or crack due to shrinkage. The casting feeder was inadequate or there was a process deviation.

_____________________________________
"It's better to die standing than live your whole life on the knees" by Peter Mayle in his book A Good Year

 

[metengr]

Before I would make any decision on weld repair, you need to first determine the quality of the casting using radiographic testing (aka x-ray). Otherwise, as you excavate defects you may find more buried flaws and ultimately it is more economical to scrap the casting.