During each injection molding cycle, molded parts need to be released from the cavity by ejection system, it is also called de-molding system, design of ejection system affect product quality and production efficiency.
See below figure, a complete mold ejection system include:
- ejection plate, fixation plate, mold base plate.
- screws to fix the these plates.
- ejector pin, ejector block, sleeve.
Ejection distance is normally defined at 5-10mm, or 2/3 of the length of some of the plastic parts with big draft angle.
When no special ejection problems are expected, the standard ejector pin will perform well, a sleeve ejector is used to provide uniform ejection around core pin.
A central valve ejector is frequently used combination with air ejection on cup shaped parts where vacuum might exist. The air valve is thus only a secondary ejection device. A stripper plate or ring is used when ejector pins or valves would not operate effectively. The stripper plate is often operate by means of a draw bar or chain.