PU Casting Warpage

[EdgeDesign]

I have a pair of matched covers for an electronics device that are now warping. I suspect thermal effects but it may be moisture related. Can anyone offer suggestions etc please?

Notes:
- The material is a general purpose polyurethane casting mix with no fillers.
- The parts are vac cast in silicone tooling
- There is a thin wall area that warps up to 10mm along a 150mm length
- the temperature difference between inside and out is approx 20deg C
- warping occurs only on parts experiencing the interior warm environment.
- warping occurs gradually over 1 - 2 weeks.

Many thanks in advance

Matt

 

[MikeHalloran]

PU is not noted for great heat resistance.

I suppose you could cool and reinforce the covers with metal doublers/ nutplates or something like that.

Or, you could heat the interfaces just a bit more at the factory and get a nice permanent bond.



Mike Halloran
Pembroke Pines, FL, USA

 

[BillPSU]

You may have incomplete crosslinking of the plastic and the heat maybe completing the crosslink in the inside of the cover. I would bake your parts to assure crosslinking is complete and see if the problem continues.