Ultem and CF Peek in an aluminum mold

[JayDub]

I used to mold a PEEK plaque that was around 2.5” x 2.5” x .375”. Mold temp 400 F and – most importantly – the cavity was sprue gated. Cooling time was very long – 60 or 90 seconds. Hold pressure just low enough to not blow the mold open. But as Nikom says, I wouldn’t have much hope of making a good part with a .625” wall section.

As for Ultem, if you’re going to machine the parts so appearance isn’t an issue: if you run the melt and mold very hot so the part cools very slowly, you just might be able to trade voids for sink.

[iamplwirtz]

Thanks Jay, yeah these are very thick parts. It makes sense why no company would give them a bid for doing it. Good for me, I have a great job. Bad for me, mission impossible. I'm going to try to add more heat to the mold and open the runner to the normal call out of 75% and spure gate the cavities. Hopefully that helps.

Thanks for the insight all. Will post if I'm successful in my efforts.

[rickbatey]

How are you heating the tool? Can you get it hotter? Perhaps the runner is freezing too soon hence the sinks or voids. Can you injection compression the parts? Maybe that would work.
Rick

[cheeseyone1]

I would try to buy some material bar stock and place it in the center of the cavity and over mold it this would help you cycle time also as it does reheat the the plastic to bond and does help to cool the part from the inside . Just try to find the same grade of resin to ensure there is no delamination . I would try place a .250 bar of plastics inside the cavity on spring loaded pins . Other wise I agree injection compression or a delayed core pin to keep the cavity pressure up during cool

Also if you balance the tonnage and injection pressure close to the point of flashing you will see the mold blow open and the as shrink occurs it will close again If you were to try this I would take a drop indicator between plattens and watch for it to move .002 -.003 during pack and hold and it should if you did not flash the tool go back down during cool . It might work but obviously this is not very robust

[iamplwirtz]

Rick:

Currently heating with oil at 400 degrees... Could potentially go hotter, but it's an aluminum mold... I'm wondering if we tried filling from multiple positions if it would help? There's very little sink, and the parts look really nice on the outside. But when we CNC the top half off, there's always a couple of small voids. The issue is that these are near-net parts. The idea behind this was to prevent having the buy blocks of PEEK and waste 80% of it. However, if there are voids, then the parts we run are waste in the same sense that they cannot use them.

[rickbatey]

How about making gate a fan style so you can get enough area to stay open during the entire pack/hold phase? Have you ran a gate freeze to see how long it stays open? Are you gated into the thickest area of the part? Maybe you’re not using enough pack/hold time. Run more time ev n if you must run low pressure and remove time from cooling portion of cycle.
Next then I’d try multiple gates but you’ll have knit lines that may be bad.
Rick

[Ten Fingers]

Have you done a 'gate' freeze study? May be that the process is freezing off at the nozzle/mold touch point limiting the length of time you can effectively pack the part out.