Plastic article or earthenware shaping or treating: apparatus – Female mold and charger to supply fluent stock under... – With product ejector
Reexamination Certificate
1999-02-26
2001-05-29
Heitbrink, Tim (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Female mold and charger to supply fluent stock under...
With product ejector
C425S809000
Reexamination Certificate
active
06238202
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to plastic injection molding and more particularly, to stripping apparatus for plastic injection molds and even more particularly, to an unscrewing apparatus for ejecting threaded plastic closures.
BACKGROUND OF THE INVENTION
The injection molding of plastics generally involves introducing molten plastic under pressure into a space defined between a core part and a cavity part of an injection mold. The molten plastic is allowed to cool and thereby solidify to form a “part” in the space, after which the core and cavity parts are separated. The part generally shrinks a bit upon cooling and remains on the core part of the mold from where it must be “stripped”.
Simple parts having no internal protrusions may be stripped in a variety of ways, including air pressure, stripper plates or rings and ejector rods. A stripper plate is basically a plate which lies against the core part of the mold during injection and through which individual cores extend. The stripper plate, which is moved away from the core part during stripping, presses against an innermost edge of the molded part to urge the part off of the core part of the mold.
Threaded parts are more difficult to strip. Parts with shallow threads may sometimes be forced off of a core using a stripper plate. Deeper threads however would be damaged by any effort to force them off the core with a stripper plate.
The optimal mechanism for removing a threaded part from a core is a simultaneous combination of pressure away from the core and rotation or “unthreading”. Simple rotation on its own may damage the newly formed threads as parts are generally stripped while still warm to maximize output and therefore, the threads are still somewhat soft during stripping.
Mechanisms for removing threaded closures from injection molds are well known in the industry. One common method includes a rotating core to unscrew the molded closure from the core and eject the part. A major problem with this mechanism is one of water leakage due to the use of rotary seals necessary because the cores are typically water cooled. To overcome this problem, injection molds having stationary cores have been developed, for example, U.S. Pat. No. 5,383,780 (McCready et al.)
U.S. Pat. No. 5,383,780 (McCready et al.) and related U.S. Pat. Nos. 5,565,223 and 5,798,074 disclose apparatus for removing molded threaded parts using a movable, rotatable stripper ring. McCready utilizes what is referred to as a pinion to rotate a stripper ring coaxial with a mold core . The pinion is mounted for movement with the stripper ring. The pinion receives rotational input from a rack through a gear . The rack in turn receives input from a hydraulic cylinder mounted transversely to the molding machine axis.
In McCready, translational movement is provided by a pneumatic piston extending longitudinally relative to the machine axis and acting on the stripper ring support structure. Translational movement is controlled by a cam secured to and moveable with the rack. The cam does not move the stripper ring but instead prevents the degree of movement that would otherwise occur as a result of the pneumatic piston being actuated.
While McCready does provide an apparatus for synchronously, rotating and translating a stripper ring, it is mechanically quite complex requiring both hydraulic and pneumatic cylinders which must be coordinated with the molding machine cycle. This requires special machine logic which can only be incorporated in certain models of molding machines. Furthermore, hydraulic cylinders are prone to leakage which can contaminate the parts being formed and the hydraulic cylinder and its associated structure are quite bulky, requiring a considerable amount of space.
Pneumatic cylinders are also prone to leak which results in compressed air leakage. Compressed air leakage can cause contamination due to condensation. Contamination of any kind would prevent the use of a mold in a “clean room” environment. A clean room environment is often required in closure manufacturing.
Finally, the McCready arrangement is relatively expensive due to the complexity of the structures involved and the additional machine logics.
An object of the present invention is to provide an apparatus for rotating and translating a stripper ring which apparatus is driven by a machine ejector of an injection molding machine rather than a separate remote drive structure.
A further object of the present invention is to provide an apparatus for ejecting threaded injection molded parts which is suitable for a clean room environment without fear of contamination.
A still further object of the present invention is to provide an apparatus for ejecting threaded injection molded parts which may be used with a basic injection molding machine without adding special machine logic.
Yet another object of the present invention is to provide an apparatus useable with an unlimited number of cavitations, preferably in multiples of four, including a 72 cavity mold.
SUMMARY OF THE INVENTION
An unscrewing apparatus for stripping threaded injection molded articles from a mold core having a core axis generally parallel to a machine axis of an injection molding machine. The unscrewing apparatus has a rotatable stripper ring coaxial with the mold core, a stripper ring rotator for rotating the stripper ring about the core axis, a translator for moving the stripper ring relative to the core in an axial direction generally parallel to the core axis and a driver for rotating the stripper ring rotator.
The stripper ring rotator is rotatable about a rotator axis generally parallel to the machine axis and has a radially extending stripper ring drive pinion which meshes with a stripper ring driven pinion extending radially about the stripper ring. The stripper ring drive pinion causes the stripper ring to rotate about the core axis in response to rotation of the stripper ring rotator.
The driver for rotating the stripper ring has a helically splined spindle connected at one end to and axially moveable by a machine ejector rod. The spindle engages a corresponding, axially extending, helical spline in the stripper ring rotator to cause the stripper ring rotator to rotate in response to relative axial movement between the stripper ring rotator and the spindle imparted by movement of the machine ejector rod.
The stripper ring rotator has gear teeth extending radially thereabout which mesh with corresponding teeth of a transversely extending rack which forms part of the translator. The gear teeth cause transverse movement of the rack in response to rotation of the stripper ring.
The rack has at least one cam secured to it. The cam acts on a cam follower connected to the stripper ring to move the stripper ring in the axial direction at a controlled rate to synchronize the translational and rotational movement of the stripper ring to correspond to the rate at which the threaded article unthreads.
One embodiment of this invention has a plurality of stripper ring rotators each of which is mounted between and drives a plurality of stripper rings.
Another embodiment of this invention has the ejector rod connected to each spindle by an ejector plate.
REFERENCES:
patent: 3712786 (1973-01-01), Aoki
patent: 3737268 (1973-06-01), Ryder
patent: 4155698 (1979-05-01), Aichinger
patent: 4274617 (1981-06-01), Schriever
patent: 4496302 (1985-01-01), Brown
patent: 4881892 (1989-11-01), Webster et al.
patent: 5061168 (1991-10-01), Fox
patent: 5135700 (1992-08-01), Williams et al.
patent: 5230856 (1993-07-01), Schellenbach
patent: 5368469 (1994-11-01), Ekkert
patent: 5383780 (1995-01-01), McCready et al.
patent: 5421717 (1995-06-01), Hynds
patent: 5518679 (1996-05-01), Junk
patent: 5558887 (1996-09-01), Skufca et al.
patent: 5565223 (1996-10-01), McCready et al.
patent: 5609894 (1997-03-01), Rathbun
patent: 5776521 (1998-07-01), Wright et al.
patent: 5798074 (1998-08-01), McCready et al.
Heitbrink Tim
Luk Emmanuel
Ridout & Maybee LLP
Unique Mould Makers Limited
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