16 May 12 12:06
Thanks for the advice.
@Pud: the Delrin 500T is a copolymer as far as I understand. We tried a homopolymer which behaved worse.
1)The plastic is dried prior to molding.
2)This is a hot manifold system, running at between 380-390F at the tips, barrel temp about the same, We've tried mold temps from 155F to 200F, and have gotten slightly better results at 155F. But pressure increases at this temperature to 700 to 800 PSI.
4)What is a non-nucleated grade and how would that affect the performance?
5)The parts are not run with a mold release sprayed into the mold. We have tried an additive in the Dupont Delrin 500T before, Axel INT-38DHT at 0.5% which showed a slight improvement, but even though the molding parameters didn't change between subsequent runs, the limited success could not be repeated the next run. Higher percentages of the additive didn't improve it either. We also tried a Sabic Lubricomp* Compound KI001A and Lubriloy* Compound K2000 without success.
6)We have been running these in natural. Colorants didn't affect performance.
7) Warm out of the tool, the parts can be flexed forever, and are quite strong. After sitting for a day, they become brittle, fracture is typically an audible "crack" when it breaks. "Annealing" by soaking them at an elevated temperature (50C) for a time causes increased breakage.
The maddening part about this project is that we made a mud mold first with 4 cylinders instead of 25, to verify that the design would work, and it worked fine (except for the intermittent knit line that ended up on the hinge) which we fixed by gating every other cup on the final mold. The other difference was that the mud mold was a cold runner system.
I would appreciate any other advice that anyone can offer.
(Changing careers to cleaning portable toilets has already been considered. )
Thanks for your help.