Abstract

Two halves of a split mold of an injection molding machine are respectively mounted on a stationary plate and a movable plate guided on guide rods projecting from the stationary plate for movement toward and away from the latter. A guide plate, likewise guided on said guide rods, is connected to the movable plate for movement therewith, and a moving arrangement is connected to the guide plate for moving the same and the movable plate connected thereto toward and away from the stationary plate to thus move the mold halves between an open and a closed position. The guide plate includes a clamping arrangement for clamping the guide plate in fixed position on the guide rods and a hydraulically operated arrangement for holding the mold halves in closed position against the force of molding material injected under pressure into complementary cavities in the mold halves.BACKGROUND OF THE INVENTIONThe present invention relates to an injection molding machine which includes a movable plate for one half of a split mold which, together with a guide plate connected thereto, is movable on guide rods toward and away from the other mold half mounted on a stationary plate. The guide plate includes a clamping cone movable in axial direction of the guide rods relative thereto and cooperating with a plurality of clamping jaws movable in radial direction during movement of the cone in axial direction into clamping engagement with portions of the guide rods.Closure devices of this type are already known in the art and for instance disclosed in DT-PS No. 1,529,902. This known construction includes a clamping cone movable in axial direction and pressing during such movement clamping jaws cooperating therewith in radial direction against portions of stationary guide rods for the movable plate. To move the clamping cone in axial direction, this known arrangement includes a wedge-shaped key movable in a direction normal to the moving direction of the movable plate and hydraulically operated means for moving the wedge-shaped key in this normal direction. In order to reduce wear on the cooperating faces of the clamping cone and the wedge-shaped key, rollers, respectively balls, are arranged between the opposite cooperating faces. This known arrangement is rather complicated, requires considerable space, and has the additional disadvantage that it may lead to an undesirable tilting of the movable guide plate.When, after the two mold halves are moved to the closed position thereof, molding material is injected under considerable pressure into the complementary cavities of the two mold halves, the pressure at which the molding material is injected tends to move the two mold halves away from each other. Therefore, a corresponding counteracting force has to be applied to the movable plate on which one of the mold halves is mounted to prevent such an undesired opening of the split mold during the molding operation. In principle, such a counteracting force could be provided by pressing the clamping jaws against the rods; however, this would require such a large pressure on the clamping jaws, which may subsequently lead to difficulties when attempting to loosen the clamping jaws so as to be able to move the mold halves to an open position at the end of the molding operation.SUMMARY OF THE INVENTIONIt is an object of the present invention to provide a closure device for an injection molding machine which avoids the above-mentioned disadvantages of such closure devices known in the art.It is a further object of the present invention to provide a closure device in a molding machine of the aforementioned kind in which the force counteracting the force of the molding material injected under pressure into the mold cavity of the mold is independent from the force exerted by the clamping jaws on the guide rods.It is an additional object of the present invention to provide such a closure device which is adapted for split molds of different thickness without requiring additional elements for this purpose.With these and other objects in view, which will become apparent as the description proceeds, the injection molding machine according to the present invention comprises a stationary plate, a plurality of guide rods fixed at one end to the stationary plate and projecting substantially normal thereto, a movable plate mounted on the guide rods for movement toward and away from the stationary plate, a split mold having two complementary mold halves, one of which is mounted on the stationary plate and the other on the movable plate for movement therewith between an open and a closed position, guide plate means movably mounted on the guide rods and connected to the movable plate for movement therewith, moving means connected to the guide plate means and the movable plate connected thereto for moving said movable plate toward and away from the stationary plate to thereby move said mold halves between the open and the closed position, means for injecting molding material under pressure into the split mold, when the mold halves are in said closed position, means in the guide plate means for clamping the latter in fixed position on the guide rods, after the movable plate has been moved by said moving means, to bring the mold halves to the closed position, and hydraulically operated means incorporated in the guide plate and operable independently of the clamping means for providing a force maintaining the mold halves in the closed position against the force of the molding material injected under pressure thereinto.The clamping means preferably comprise a clamping cone mounted in the guide plate means movable in axial direction of the rods and a plurality of clamping jaws engaging the peripheral surface of the cone and being moved during axial movement of the cone in radially outward direction into clamping engagement with the rods.The clamping means may further include a guide frame having portions engaging outer peripheral portions of the rods, and the clamping jaws are arranged within the guide frame to respectively engage, during movement of the cone in the aforementioned axial direction, inner peripheral portions of the rod opposite to those engaged by the guide frame.The guide plate means further preferably comprises a piston having a piston rod fixed to the movable plate, a membrane plate between the piston and the large diameter end face of the cone, a pair of membranes respectively sandwiched between opposite faces of the membrane plate, the large diameter end faces of the cone and the piston and forming with opposite end faces of the membrane plate a pair of pressure spaces, and means for feeding pressure fluid into the pressure spaces. This will provide for a very compact construction in which the force for maintaining the split mold in closed position during the molding operation will be independent from the force for clamping the guide plate on the rods.The moving means connected to the guide plate means for moving the latter, and the movable plate connected thereto, toward and away from the stationary plate preferably comprises cylinder and piston means connecting the guide plate means with another stationary plate, forming together with the first mentioned stationary plate a stationary frame.The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.