Hydraulic speed controls for die closing unit of injection molding machine

Claim 1

A hydraulic actuator assembly adapted for use in a die closing unit of an injection molding machine as a rapid-travel drive for die opening and closing movements and as a source of elevated die closing pressure, which die closing unit includes a stationary cylinder head plate and a movable die carrier member guided for die opening and closing movements along the center axis of the die closing unit, whereby, in the die closing travel, said member moves away from the cylinder head plate in an axially forward direction; the hydraulic actuator assembly comprising in combination: a power cylinder extending rearwardly from the cylinder head plate, in alignment with the center axis of the die closing unit, the bore of the power cylinder being axially delimited by the cylinder head plate and a rear cylinder cover and enclosing a power piston seated on a piston rod which extends sealingly through the cylinder head plate and is connected to the movable die carrier member, the power piston dividing the interior space of the power cylinder into a high-pressure space on the rear side of the piston and a cross-sectionally smaller low-pressure space on the forward side of the piston; a closable power piston bypass in the form of at least one bypass channel in the power piston connecting said high-pressure and low-pressure spaces, and hydraulically operated valve means for opening and closing the power piston bypass, so that, when the piston moves rearwardly in a die opening movement and the bypass is open, a volume of fluid corresponding to the difference between the effective areas of two pressure spaces is displaced out of the power cylinder; hydraulic cylinder means for imparting to the movable die carrier member a forwardly directed force producing a closing travel; means for supplying pressurized fluid to the high-pressure space of the power piston, when the power piston bypass is closed, so as to create an elevated die closing pressure against the movable die carrier member in the closed position of the die closing unit; at least one opening travel cylinder in parallel alignment with the power cylinder, the opening travel cylinder having a cylinder bore and a matching travel piston seated on a piston rod which is connected to the piston rod of the power cylinder to move in unison with the latter, the travel piston dividing the interior space of the opening travel cylinder into a pressureless space on the rear side of the piston and an opening travel pressure space on its forward side, and the total effective area of opening travel pressure space being larger than said difference between the effective areas of the power cylinder pressure spaces by a net opening travel area; and a flow connection between the low-pressure space of the power cylinder and the pressure space of the opening travel cylinder, or cylinders, respectively, so arranged that, when the pistons move rearwardly in a die opening movement, with the power piston bypass open, fluid corresponding to said difference in power cylinder pressure spaces passes from the latter into the opening travel pressure space, and an opening travel is obtained, when pressurized fluid corresponding to said net opening travel area is supplied to said connected pressure spaces and, conversely, a die closing movement causes a volume of fluid to pass from the opening travel pressure space into the low-pressure space of the power cylinder and a volume of fluid corresponding to said net opening travel area to exit from said connected pressure spaces into a fluid return line; and wherein the net opening travel area by which the effective area of the opening travel pressure space exceeds the difference between the effective areas of said power cylinder pressure spaces is a fraction of said difference, and the volume of pressurized fluid which is required to produce an opening travel of the movable die carrier member is, correspondingly, a fraction of the volume of fluid which simultaneously passes through said flow connection between the low-pressure space of the power cylinder and the opening travel pressure space; and said flow connection includes a continuously adjustable throttle valve adapted to control the speed of opening travel and closing travel by determining the flow rate at which it allows fluid to pass through said flow connection.