Mechanism for opening the molding dies of an injection molding machine

A molding machine comprising a fixed support, a turret mounted on said support and adapted to be indexed step-by-step about an upright axis, a series of molding units carried on and spaced angularly around said turret and each adapted to be rotated into and to dwell momentarily in an opening station during indexing of said turret, each of said molding units comprising upper and lower molds, the lower mold of each unit being disposed in a closed position relative to the upper mold when the unit is rotated into said opening station and being moved downwardly to an open position and then back upwardly to said closed position when the unit dwells in said opening station, an operating member connected to and depending from the lower mold of each unit, a puller located in said opening station, a fluid-operated actuator connected to said puller and operable to reciprocate the latter upwardly and downwardly, said puller being operable to interfit automatically with the operating member of each unit when the unit is rotated into said opening station and the puller is in an intermediate position, said actuator moving said puller upwardly from said intermediate position to an upper position during the initial dwell period of each unit in said opening station, moving said puller downwardly from said upper position, past said intermediate position and to a lower position during a first intermediate dwell period of each unit in said opening station, moving said puller upwardly from said lower position to said upper position during a second intermediate dwell period of each unit in said opening station, and moving said puller downwardly from said upper position to said intermediate position during the final dwell period of each unit in said opening station, said puller acting on the operating member of each unit to move the lower mold of the unit toward said open position as said puller is moved toward said lower position and to move the lower mold toward said closed position as said puller is moved from said lower position, said actuator forcing said puller downwardly from said intermediate position toward said lower position as each unit is rotated into said opening station, a stop engageable with said puller when the latter is in said intermediate position and operable to hold said puller precisely in said intermediate position against the downward force exerted by said actuator so as to keep said puller in position to interfit with the operating member of the unit being rotated into said opening station, means for retracting said stop out of holding engagement with said puller when said unit dwells thereby to enable said puller to move toward said lower position and open said lower mold, and said last-mentioned means extending said stop back into holding engagement with said puller after the puller has moved from said lower position to said upper position and has closed said lower mold and before said actuator returns said puller downwardly to said intermediate position.