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Hello,
We are injecting a lot of differnt materials in our molding shop (EPDM, PA,ABS..), sometimes on normal production the hot runner of the molds running with EPDM get clogged with PA or PBT pellets.
What would be the best way to unclog the EPDM hot runner? increase the hot runner temeprature to 295 šC and purge it ? does this have bad effect on the hot runner system ?
Hi,
the "issue" is the difference of the temperatures used for each type of polymer.
1)
Establish the procedure of cleaning every time You have to change from Higher melt polymer (PC, PA, PBT,...) to lower (PP, EPDM, TPE).
You have to do it exactly after the production when the temperatures are high and the higher melt polymer is melted (and not degraded yet by dwelling at high temperature). Do this even if You donīt start the next production immediately.
2)
Make changes in the planning of production
Target is to have the less exchanges between high/low Tm polymers as possible.
What is clear that sometimes the difference between temperatures are so high (PC->TPE) that You canīt clean the PC by TPE so usually its better to use some step between (ABS) or to ask companies (asaclean,...) about their system to clean the certain combinations.
This can be also well planned in the production plan part from PC/ABS -> ABS -> PP -> EPDM -> PP -> ABS ->PA...etc.
With this You should be safe and the plastic coming into the tool should be always the one you need.
Donīt forget to switch off the backpreassure when purging - theres no need to mix old and new material together.
Anyway when happend that the hot runner is after this cloged by foreign plastics, You have to continue the way You describe.
High temperature to melt all what is inside, than purge to partially opened tool (keep tool opened but still on the guiding bars/pins). Cover all surface and cavities as the plastic purged out can be degraded. Wear safety glases at all the time.
Never inject part with this "mixture".
The hotrunner system is usually constructed on the temperature around 350-380°C Max Limit temp. so with 295°C Your safe (check this at HR supplier or in the docmnetation)
The target is still to perfectly clean the screw after the production.
J.