Hot Selling for Injection Molding 101 - PP Copo plastic Molette pied F2 – Bolok Mold

Automatic Unscrewing by rack and hydraulic jack

Internal threads are commonly found on plastic parts that screw together, such as bottle caps, drinkware lids and plastic hardware. Due to the delicate nature of threads, molding these parts requires a slightly different approach than your average plastic part. An unscrewing core must be incorporated in the tool in order to eject them from the mold without damaging the threads.

In the past, these parts needed to be manually unscrewed from the core by hand to avoid stripping the threads. The additional labor and time it took to do this added to the part price and lead time. While many injection molding shops still follow this practice, we knew there had to be a better way.
Here’s How It Works:
First the plastic is injected into the tool. After the plastic has cooled, the threaded core starts to unscrew. The unscrewing mechanism works off of a rack and pinion and is powered by a hydraulic cylinder.
The rack turns three sets of gears which then retracts the threaded core into the ejector box.
Once the threaded core is fully unscrewed, the mold opens and the ejector system pushes a stripper plate forward to eject the part.
After the part is fully ejected, the hydraulic cylinder reverses, screwing the threaded core back into molding position and the process repeats.