Hardest resin/part you've ever worked on.

[rickbatey]

I was wondering what was the hardest resin or part you've ever worked on? I am curious if they fall into one of two main catagories:1-Never ran that resin before. 2-Part design and customer requirements were night and day away from one another.
Fire away folks!

[Suhas]

For me, it was a long fibre glass filled nylon. Of course at that time, I did not know that we needed a different screw design. Regardless I was at it for about 2 days.
The other one was a TPE that just refused to fill consistently. -
Suhas

[rickbatey]

First for me was a a 22 oz. stadium cup mold. Ran from a good grade of resin, in a good JSW press, but was a bear to make good p arts in about an hour after starting. We finally realized that the issue was due to very short residence time n the press, and the melt temp was dropping due to the cycle time/shot size.
Lastly was Santoprene. I had ran soft resins before, but this one killed us! Those soft resins just love to be sheared, and low hold times and pressure. Of course we only had a shot utilization of 7.6% of the barrel! Luckily I got hold of Bill Tobin before I commited ritual suicide!

[Danny R]

Hardest resin to process: Polyketone - Carilon. No part has ever been hard to mold, everything has always looked great but please don't ask me about dimensions :D

[rickbatey]

Most of the dimensional issues for me have always been tooling related. Once a wheel house liner was 5 mm too short! I couldn't get more than about 1.5 mm of the length back. We had to switch the resin for a low shrinkage one?! The we molded some antenna parts, one hole was .025" too small in diameter. Yep, the pin wasn't even as large as the minimum diameter requirement of the hole!?

[ProcessEval]

For me they have been TPEs not wanting to eject out of the mold, sprue not wanting to come out. (Will post another question, I think). Any tricks?

[rickbatey]

YES. With the soft resins, stay away from polished finishes unless that is where you WANT the part to stick! They form a vacuum to these areas. You can assist the mold with making the B-side (moving) half cooler/colder than the other mold half. But by adjusting the grain finish, you can make the part stick pretty much where you want. Adding puller rings to the ejector pins can help. I see many peolpe run too much old time and pressure, making the sticking issue worse. Cold mold temps are another mistake. These resins LOVE to be sheared: Shoot them as fast as the mold/part will allow!
Now with the sprue not pulling, drop the polished finish inside, then we left special pullers on the sprue ejector pin. There was a guy in the Italy plant that ONLY made ejector pins for pulling parts and runners/sprues. One of his tricks was to leave small fingers of resin around the outside of the ejector pin. these fingers are trapped between the pin and the pin bore of the mold base until ejected out. Then they can flex and release (removed with a robot gripper). You can make the area very aggressive then soften in the press for the balance between pulling the sprue and removing from the mold. Either that style or the one that leaves a round or square projection into the base of the sprue work best. Trying to get them with the standard styles just fall short. After all that, the only thing left is to plate the release half of the mold.
Hope this helps, Rick

[Suhas]

Good Tricks Rick. I must use these also. I occasionally have the sprure sticking issue. Looks like then to reduce the pack and hold pressures, the gate and runner sizes also need to be large. Next time I try this, I will let you know.
Suhas

[brentb]

Have run (sometimes with success):
PEI
PEEK
PBT
PMMA
PC
PPS
PE
PP
PA
PS
LCP
PU
PVC
PTFE-PVDF
TPR
UHMPE
and many more.
A nasty mold and/or part design can make any resin tough to mold, but what took the cake was an experimental TPE where tou could extrude a bit and it was so soft that you could stretch it across the room. Then there was HSG (High Specific Gravity) Nylon. Thias was heavier and denser of course than lead. If you tried to lift a 2 gallon pail of the stuff,you'd swear it was welded to the floor. I think the fill was depleted uranium!

Keep on Molding!

brent

[Danny R]

what was the shore hardness for that TPE? I just got 2 sample bags today from Lubrizol, I actually can't wait until Monday to get them going. 70A & 80A

[brentb]

I would have to look it up. I know fifty and 70 ran well compared to this stuff! What scared me was that it came in a syrup bottle.
I think it was from GLS.
Keep on molding (not stretching)!
brent