Failsafe shooting pot actuator for an injection molding machine

A seizure detection system, for detecting piston and valve gate seizure in an injection molding machine having a shooting pot actuator, the shooting pot actuator having a plurality of pusher rods mounted on plate, the pusher rods abutting a respective plurality of injection pistons for injecting a molten material into a mold, the plate being driven to advance the pusher rods simultaneously against the injection pistons, the shooting pot actuator further having a pressure relief mechanism activated when a piston or valve gate seizure occurs, comprising:

• a laser transmitter and a laser receiver aligned with a row of the pusher rods;
• sighting means comprising of circumferential grooves provided on the pusher rods through which a beam transmitted by the transmitter passes to the receiver when the pressure relief mechanism has not been activated;
• and
• means for detecting if the beam is interrupted.

An multimaterial injection molding machine, comprising:

• a mold cavity;
• at least two shooting pots for providing material to the mold cavity, each shooting pot having an injection piston for expressing material into the mold cavity;
• a shooting pot actuator having a first plate and a second plate, each plate carrying pusher rods for abutting a respective injection piston, the first and second plates being sequentially driven to advance their respective pusher rods against the injection pistons;
• a pressure relief mechanism for mounting each pusher rod to its respective plate, the mounting means including a first aperture for receiving an end of the pusher rod, the aperture being aligned with a second aperture in the plate to form a channel for receiving the pusher rod, a shearing member interposed between the first and second apertures, the shearing member having a predetermined shear force which, if exceeded, causes the shearing member to shear to permit the pusher rod to retract within the channel.