HELI-COIL in heavy duty joint

[mhoyos]

A contractor of us broke a bit while machining a big nodular cast piece, so some M30 threads become unusable. The contractor suggest to use heli-coil to repair it, but we have some reservations about that:

- Heli-coils are usually intended for using high tensioned bolts in soft materials, but we don't have any news of their use in heavy duty cast pieces.
- The bolts to be used are high strength (10.9), high pretensioned (90%), but as far as we know usual applications of heli-coils are located in parts with low tightening requirements like covers, etc.
- The joint has a high responsability, since its failure can derive in a total destruction of a big, $500000 machine, so we don't want to take any risk...
- The joint is quite exposed to the environment, so we are not sure if the cast could be more prone to oxidize with the stainless-steel insert.

Any suggestions/advises? Any better solution to save the cast piece? Thank you in advance.

 

[diamondjim]

I think I would prefer a heavy duty keensert
if you have the room for them.

 

[arto]

Heleicoils are awesome! They usta use them all the time to fix "Whoopses" in turbine land [huge ones that looked like "slinkies", & also "by design" for highly loaded joints to favorably distribute the load/prevent stripping.
The only problem is they're not sealable [need blind holes] to be pressure tight.
Look in the design charts - they're stronger than the bolt.

http://www.emhart-vic.com/emhart/sc_app/sc_description.asp?code=default&famID=30

http://www.emhart-vic.com/emhart/pdf/Main HC-2000.pdf