Stress Cracks in Noryl

[stevenmon]

I have a problem with a part that we have been using for years. We are installing Helicoils into a machined Block of Noryl. We are constantly getting cracking around the helicoils. None of the rest of the features in the part show any stress cracking.

Note we see the cracks before any screws are fastened into the Helicoils.

Any idea what could be causing this problem? I know that Noryl should be machined with non-hydrocarbon based lubricants. I checked with our machine shop and they are using a semi-synthtic. Is brittleness in Noryl a side affect of using a hydrocarbon based cutting fuid?

Thanks

 

[orbit03]

Are the parts seeing much thermal cycling? Instead of helicoils, why not use a thermal or mechanically installed brass insert? They would probably work a bit better than threading a helicoil into the noryl.



------------
Jason Williams
K Development, Inc.

 

[swertel]

No. Noryl has a very large glass content which makes it very strong, but also brittle and subject to impact failures.

Have you contacted your local GE Plastics rep? Try this website...

http://www.geadvancedmaterials.com

--Scott

For some pleasure reading, try FAQ731-376

 

[plastx]

Most NORYL grades will crack or craze when exposed to typical machine shop solvent/fluids. If you add stress to the equation then it will only add to the problem.

NORYL is a blend of PPE and polystyrene. The polystyrene component is what the solvents attack. Some NORYL grades have glass fibers which will make the material stiffer but also more brittle.

Mike