Ultem Hot Runner Mold with Cartridge Heaters

[JEHI7278]

Has anyone had and thermal expansion problems while running (attempting to) a cartridge-heater, hot runner mold with Ultem Material? We are eating interlocks like candy, and suffer part both lateral and vertical mismatch. Thermal expansion seems to be the culprit, but I am looking for advice on hot to fix the existing mold. My thought is to balance the temperature across both mold plates, but will cartridge heaters do this. The center mass of the mold's A side is hot (manifold and material coming in) as expected, and the outlying areas are cooler. Do I simply balance the heats, or get rid of cartridge heaters for some other system, i.e. hot oil or even pressurized water?

[JEHI7278]

One more thing - This mold has no cooling (water/glycol lines).

[brentb]

Have run lots of ULTEM, always used hot oil. Have tried ctg heaters in other hi tmp thermoplastic injection molds and hate them. The ctg works in thermoset, but for me, avoid in thermoplastic.
Thermal expansion in molds can be a challenge, but with cartridge heaters, it is too hard to control the mold temp!

KOM

brent

[JayDub]

The obvious problem with cartridge heaters is they can only add heat to the tool, they don’t carry it away. I’ve used them successfully in small tools (8 x 11 MUD sets) with PEEK and PFA, where the ejection temperature is high. (These were also generally low volume products or prototypes where cycle time wasn’t critical).

Bigger tools retain relatively more heat (and bigger shots add more heat) so you need thermal regulation not just heating. Look at it this way: Oil or water will take heat from hotter parts of the mold and add heat to cooler parts. Cartridges can only maintain a minimum temperature (the set-point) while hotter parts of the mold stay hotter. Sure you have conduction through the mold and into the platen, plus radiation off the mold surfaces, but you have absolutely no control over those.

The hot runner system is going to complicate things even more, because you are intentionally adding heat to one mold half, with no controlled way to dissipate it. All in all, it sounds like a recipe for a headache.

[JEHI7278]

Thanks for your responses all. I have been saying this for a while, but without traction. It is good to see useful info from the rest of the world.