A method of operating a molding system having:
- a base;
- a fixed mold plate secured to the base;
- a fixed mold half carried on the fixed mold plate;
- a movable mold plate displaceable on the base longitudinally forward away from the fixed mold half and backward toward the fixed mold half;
- a movable mold half carried on the movable plate and fittable with the fixed mold half;
- a pair of main cylinders fixed to the fixed mold plate;
- respective main pistons subdividing the main cylinders into respective front and rear main compartments and each having a piston rod secured to the movable mold plate and formed with a longitudinally extending chamber, one of the main pistons being formed with a main longitudinal passage extending between a rear end of the respective longitudinally extending chamber and the respective rear main compartment and with a secondary radial passage extending between the rear end of the respective longitudinally extending chamber and the respective front main compartment;
- a small closing piston subdividing the chamber of the other main piston into a front opening compartment and a rear closing compartment and having a rearwardly extending piston rod fixed to the fixed mold plate, the small closing piston having a front face in the front opening compartment and a smaller annular rear face in the rear closing compartment;
- a pressure-amplifying piston subdividing the chamber of the one piston into a front control compartment and a rear pressure-amplifying compartment, being freely longitudinally movable therein, and having
- a front face in the front control compartment,
- a smaller annular rear face in the rear pressure-amplifying compartment, and
- a piston rod extending longitudinally rearward from the pressure-amplifying piston;
- a valve element longitudinally slidable on the rod of the pressure-amplifying piston and engageable sealingly in the main passage of the one main piston to block flow therethrough;
- means interconnecting the valve element and the pressure-amplifying piston for displacement of the valve element out of blocking engagement in the main passage of the one main piston on displacement of the pressure-amplifying piston into a front position and into blocking engagement in the main passage on displacement of the pressure-amplifying piston into a rear position;
- a conduit interconnecting the front main compartments;
- and
- a source of fluid having a high-pressure side and a low-pressure side, the method comprising the steps of
- in a closing position of the mold halves, connecting the closing compartment of the other piston to the high-pressure side of the source and the opening compartment to the low-pressure side and preventing fluid flow into or out of the control compartment and thereby arresting the pressure-amplifying piston in its chamber,
- in an opening position of the mold halves connecting the closing compartment to the low-pressure side and the opening compartment to the high-pressure side and connecting the control compartment to the low-pressure side;
- and
- in a pressurizing position of the mold halves connecting the control compartment to the high-pressure side and thereby displacing the pressure-amplifying piston toward its rear position.