Proposal of Acetal in a Hot Manifold

Hello to all!

A new job has come across my desk, a proposed new mold to be built with a hot manifold, direct gated, using acetal... as I have never seen this particular combo, I wanted to see if others have seen this before, and the results as such.

I have particular concerns with the cosmetic appearance of the part, especially near the gate, .....and would the added heat time cause additional gassing, or other issues?

Thank You,
Joel

Hi Joel,

Yes, appearance is a concern. I would also be concerned about the residence time in the hot manifold. Sometimes to reduce the residence time, they will reduce the channel diameters which increases the pressure drop making processes pressure limited.

Hope this helps some.
Thanks,
Suhas

We run a couple molds like this, 48 cavity in Celcon M90. Cosmetics at the gate are poor, we also had issue with cold slugs from the gate causing parts to split at the knit line during assembly.

If the mold is down for any amount of time or we lose a cavity and get it open again the parts will be covered in splay for a few cycles.

Joel JS,
If this were my choice... From prior experience with this combination I would refrain from this at all costs. As others have mentioned, any amount of downtime can be very detrimental to product yield. Outgassing is definitely a concern when processing POM. Acetal almost always works better with cold runner.

Thanks everyone for their replies, and confirming my suspicions!.... Much appreciated.

Joel

We have a lot of automotive molds that run P.O.M. in a hot runner molds .One big thing is to make sure you have valve gates in the mold .

Well, I voiced my opinion, and the ship has sailed...... let's see how it comes out.

Thanks,
Joel