Abstract:
The invention generally discloses an apparatus and method for removing threaded, molded articles from an injection mold. A cam system and linear drive/following gear mechanism engages a finely resolved retraction of a threaded mold core, under substantially full mold clamp pressure, prior to rotational disengagement of the core from the molded article. The invention also describes a system for the reduction of galling that may otherwise occur when mold components experience relative rotation with respect to each other. Moreover, the invention describes an apparatus and method for substantially reducing periodic maintenance checks and interruptions in production.

Description:
FIELD OF THE INVENTION 
     This invention generally relates to the field of injection molding. More specifically, the present invention relates to the reduction of galling between mold components as they experience rotation relative to one another. In yet a further specific aspect, the present invention describes an improved method and apparatus for the manufacture of articles having internally disposed threads in which a thread-forming core is at least partially disengaged from the molded article under substantially full mold clamp pressure. 
     BACKGROUND OF THE INVENTION 
     The art of forming internally threaded plastic injection molded closures is generally well known in the industry. Injection molds of this type typically include a female mold housing which substantially surrounds at least a partially threaded core component. The mold cavity is generally defined by the void space between a female mold housing and an internally disposed core component. Molten plastic material is usually injected into the mold cavity to form the threaded article. After injection and molding of the plastic, coolant may then be introduced to circulate through channels in various mold components in order to accelerate cooling of the product article. Once the article has cooled, a general feature of injection mold systems is the application of an ejection mechanism for removal of the article. Because a plastic injection mold generally has a plurality of mold cavities, it is often generally the case that the ejection mechanism operates to dislodge the articles in a group for each product cycle of the mold. 
     In the case of prior art methods of forming and ejecting threaded, molded products, the female mold half and mold core half are separated to initiate removal of the article from the mold. Because of the engaging nature of the threads however, the article generally remains connected to the face of the stripper ring upon separation of the mold halves. Accordingly, an ejection mechanism is generally required for subsequent removal of the article from the outer surface of the mold core. 
     Depending on the design parameters of the thread-molded article, the product may be removed from the mold core in various ways. These parameters may vary according to the type of plastic used to form the article as well as the number and type of threads to be formed. If the molded article is flexible, and the thread type permits, the article may be removed from the threaded core by the action of a stripper ring. In this process, the plastic should be sufficiently resilient and elastic to return to its original conformation, within a specified tolerance, after the formed threads have been stretched over the threaded core during extraction. If the polymer material is not flexible, or if the thread profile is very deep, very thin or has a more cantilevered shape, stripping may damage the article. An additional complication may occur when the thread-molded product has inherently delicate features, such as a tamper evident ring, which may experience strip-ejection damage even if an otherwise suitable polymer were to be used. 
     Additional prior art methods and devices for removing internally threaded articles from a mold include, for example, separation of the mold halves prior to disengagement of the article from the threaded mold core. These methods generally involve first separating the mold halves and then rotating the threaded-core while a stripper grabber ring engages the molded article and translates axially along the core in timed relation to the rotation and pitch of the threaded core. In this regard, the stripper ring may often have structural features known as grabbers to hold the molded article and prevent it from turning with the rotation of the threaded core. Such methods generally known in the art, however, have previously been applied to mold timing cycles where rotational removal of the article is accomplished only after the article has suitably cooled and the mold halves have been separated. For example, in U.S. Pat. No. 5,421,717 to Hynds, incorporated herein by reference, a moveable ejection mechanism, including a camming mechanism, which engages a stripper ring, is used to remove the article from the mold in an open-clamp configuration after the mold halves are separated. 
     On the other hand, U.S. Pat. No. 4,130,264 to Schroer, incorporated herein by reference, discloses an apparatus in which a plurality of thread-forming components are peripherally disposed around the core which translate on tracks to cause the core to collapse so that the thread-molded article may be pushed off. However, the collapse and expansion of the core in this device adds substantially to the overall complexity and cost of the injection mold apparatus as well as the production cycle time between mold injections. Additionally, the collapse of the core is typically engaged only after the additional step of separating the mold halves. 
     In the case of the manufacture of a tamper evident ring, U.S. Pat. No. 4,155,698 to Aichinger, incorporated herein by reference, generally discloses a device in which a first female cavity component surrounds a threaded component and is removed from the molded closure while a second female component adjacent to the tamper evident ring remains in place. However, this method, while generally effective, is uniquely adapted for the production of molded caps having an integral tamper evident ring and also typically includes separation of the mold halves prior to disengagement of the article. 
     Alternatively, when using a polymer which is generally too inflexible to be ejected by the action of a stripper ring without permanent stripping damage to the article, a method disclosed in U.S. Pat. No. 4,625,227 to Hara, incorporated herein by reference, may be used. In the &#39;227 patent to Hara, a rotationally displaced chuck is engaged over the molded article after the female component of the mold cavity is removed. The chuck engages the outer edge of the closure and rotates the closure as it translates backward to allow the rotational removal of the unscrewing article. This method, however, is often applied in mold timing cycles where the mold is separated prior to rotational removal of the article. 
     Thus, a need exists in the injection molding art for a method and apparatus for the molding and ejection of threaded articles in which the injection cycle time is substantially reduced while simultaneously preserving the thread integrity of the articles. As such, the need exists for a device capable of realizing a reduced in-mold product cooling time, the commencement of resolved rotational disengagement of the article from the threaded mold core under substantially full mold clamp pressure, and the achievement of a greater number of injection production cycles between periodic inspection and maintenance checks. 
     SUMMARY OF THE INVENTION 
     The present invention generally relates to the production and removal of threaded, molded articles from a plastic injection mold device. Articles having internally disposed threads are created by a thread-forming core, which may be rotationally disengaged from the article under substantially full mold clamp pressure. A cam system and linear drive/following gear mechanism are employed to engage a finely resolved retraction of the threaded core under substantially full mold clamp pressure prior to substantially complete rotational disengagement of the threaded core from the product article and subsequent separation of the mold halves. 
     Specifically, the mold halves are brought together to a closed-mold position to create a mold cavity for receiving molten plastic with the core in the set position. As plastic is injected into the mold, the liquid plastic fills the cavity to form the product part. The product part may then be partially cooled in preparation for removal from the mold. Thereafter, a linear drive system is engaged to partially retract the threaded core away from the metal-to-metal contact areas of the shutoffs under substantially full mold clamp pressure. After the threaded core is subsequently disengaged from the product part, still under substantially full mold clamp pressure, the mold halves are opened to expose the part for ejection from the mold. The molded part is then ejected, the mold halves are returned to a closed position, the cores are re-set and the mold is readied for the next production cycle. While the timing and order of these steps may be varied, many of the steps may occur substantially simultaneously at various points in the mold cycle, to reduce or otherwise optimize the production cycle time. 
     The present invention is additionally directed to reducing galling that may otherwise occur when mold components experience rotation with respect to each other without initial retraction of the core under pressure in closed-mold configurations. Moreover, the need for periodic maintenance and incident interruption of production is substantially reduced as well. 
    
    
     BRIEF DESCRIPTION OF EXEMPLARY DRAWINGS 
     The above and other features and advantages of the present invention are hereinafter described in the following detailed description of illustrative embodiments to be read in conjunction with the accompanying drawings and figures, wherein like reference numerals are used to identify the same or similar apparatus parts and/or method steps in the similar views and: 
     FIG. 1 is an open-mold, side view of an exemplary prior art apparatus for the injection molding of internally threaded articles. 
     FIG. 2 is a closed-mold, side view of an exemplary prior art apparatus in accordance with the device depicted in FIG.  1 . 
     FIG. 3 is a closed-mold, end view of an exemplary prior art apparatus in accordance with the device depicted in FIG.  1  and FIG.  2 . 
     FIG. 4 is an open-mold, end view of an exemplary prior art apparatus in accordance with the device depicted in FIGS. 1-3 in a stripping position. 
     FIG. 5 is a closed-mold, end view of an exemplary apparatus for the injection molding of articles having internally disposed threads in accordance with one aspect of the present invention. 
     FIG. 6 is a perspective view of an exemplary mold in which the male and female halves have been engaged in their closed-mold configuration in accordance with one aspect of the present invention. 
     FIG. 7 is a forward perspective view of an exemplary linear drive mechanism for use with an exemplary mold as previously depicted in FIGS. 5 and 6 in accordance with one aspect of the present invention. 
     FIG. 8 is a rearward perspective view of an exemplary linear drive mechanism for use with an exemplary mold as previously depicted in FIGS. 5 and 6 in accordance with one aspect of the present invention. 
     FIG. 9 is a cut-away side view of the linear drive, camming and core-rotation delay mechanisms for use with an exemplary mold as previously depicted in FIGS. 5 and 6 in accordance with one aspect of the present invention. 
     FIG. 10 is a perspective depiction of an exemplary apparatus in accordance with the present invention wherein the mold halves have been separated to expose their inner surfaces of relative engagement and wherein the linear drive has been engaged with the rotary gears of the threaded core components (not shown) housed within the female mold half. 
     FIG. 11 is a perspective view of mold components generally defining an exemplary mold cavity in accordance with one aspect of the present invention. 
     FIG. 12 is a plan view of mold components generally comprising an exemplary molding apparatus in accordance with one aspect of the present invention wherein stripper ring  110  is displaced to the stripping position for the dislodgment of article  160  from main core  115 . 
     FIG. 13 is a process schematic generally depicting the sequence of method steps for an exemplary mold production cycle according to one aspect of the present invention. 
     Other aspects and features of the present invention will be more fully apparent from the detailed description that follows. 
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The following descriptions are of exemplary embodiments of the invention only, and are not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the following description is intended to provide convenient illustrations for implementing various embodiments of the invention. As will become apparent, various changes may be made in the function and arrangement of the elements described in these embodiments without departing from the spirit and scope of the invention. 
     Referring to FIGS. 1-4, an exemplary prior art molding apparatus is depicted. In an exemplary injection stage of the molding cycle, mold halves  7  and  8  are brought together in relative engagement to a closed-mold position suitably adapted to receive molten plastic (as depicted in FIGS.  2  and  3 ). A hot manifold  70  serves as a heating and distribution system for the plastic material to be injected into the mold and may be either standard or custom designed for the molding application of interest. Hot manifold  70  is generally employed to reduce runner waste and/or to deliver a more consistent melt temperature to distal portions of the mold in order to obtain better quality production of article parts  2 . Manifold  70  feeds from a central injection nozzle-locating ring  73  for engagement with injection nozzle  72  and carries the plastic to each molding cavity or secondary runner system. 
     A manifold sprue bushing  75  generally provides a seat for the injection nozzle-locating ring  73  to align with the hot manifold  70  of the mold apparatus. Hot drops  65  (also termed “hot nozzles”, “hot tips” or “hot probes”) may be used with a manifold  70  or singularly in place of a sprue bushing  75 . A hot drop  65  is generally comprised of a plastic feed hole, an electrical heating unit and a thermocouple and fits substantially flush to the hot manifold  70  in front of a mold cavity or a secondary runner system. Molten plastic material flows through the hot drop  65  to the outlet end or tip (“sharp point”) where it then enters the mold cavity or runner thereby generally leaving a small gate mark on the molded article  2 . Alternatively, a valve gate drop may be used in place of a hot drop  65  wherein a moving pin is interiorly disposed within the center of the drop whose backward and forward movement either hydraulically or pneumatically actuates the gate to open and closed positions. An exemplary reason for using a valve gate drop in place of a standard hot drop is to deliver higher plastic volume more rapidly into the mold cavity or to minimize gate vestige. 
     As molten plastic is injected into the apparatus, the liquid plastic flows to substantially fill the mold cavity thereby conforming the shape of the product article  2  to the design features of the mold. Thereafter, article  2  is cooled to allow the plastic to at least partially solidify, whereby the article  2  substantially retains the mold&#39;s design features and is suitably prepared for subsequent ejection from the mold. Coaxial bubbler tubes  50  are generally installed in the bottom clamp plate  32  to direct cooling water from the feed line  34  to the inside of core  35  to cool the article  2  prior to ejection from the mold. A water-cooled gate insert  60 , generally used on hot runner molds, provides direct cooling at the article  2  and gate interface. Cooling of the continually heated gate area is generally required in order to facilitate shorter mold cycle times, minimize gate vestige and/or realize quality production of article parts  2 . 
     After article  2  is suitably cooled, in exemplary prior art devices, mold halves  7  and  8  are separated to expose the article  2  (as depicted in FIG.  4 ). Cam followers  5  then engage and ride cam bars  1  to begin removal of the molded article  2 . Hydraulic cylinder  12 , mounted on top of the mold, actuates cam bars  1  to lift cam followers  5  and stripper (“grabber”) plate  9 . Cam followers  5  are attached to stripper plate  9  and generally provide a hard, matching, angular surface to ride on the cam bar  1  and actuate stripper plate  9  to subsequently eject the article  2 . Cam bars  1  generally are timed so that while the rotation of the unscrewing rack  25  operates to withdraw threaded core  35  from the article  2 , stripper plate  9  is actuating at a suitable rate to remain in sufficient contact with the base of molded article  2  until the threads formed inside the article  2  have been unscrewed. Rack  25  and cam bars  1  may be actuated by the same hydraulic cylinder  12  and can be attached to a common drive plate  13 . Rack  25  rotates the matching following gear  17  on threaded core  35  while the cam bars  1  lift stripper plate  9 . Rack wear plates  30  are generally mounted on the three surrounding sides of the rack  25  that are not operationally engaged with the following gear  17  of the threaded core  35  and generally define the recess  80  for receiving the rack  25 . The wear plates  30  provide a lubricated surface that may, in an exemplary preferred embodiment, be fabricated from non-ferrous material with grease-grooves machined into the plate  30  surfaces to allow rack  25  to move back and forth freely. Rack guide rails (not depicted) move independently of rack  25  to allow cams  1  to actuate core carrier plate  13  prior to rotational disengagement of threaded core  35  by action of engagement of rack drive  25  with core following gear  17 . 
     Threaded core  35  is actuated by engagement of a following gear  17  with the linear drive mechanism  25 . Threaded core  35  generally has threads exteriorly disposed on the molding end that form the interior threads of the article  2  and a matched pitch following thread on the opposing end of the threaded core and also generally incorporates a tapered shutoff seat as well as provisions for water cooling well known in the art of injection molding. Thrust-needle bearings  40  provide a smooth travel envelope for the core  35  to rotate inside. Each set of bearings  40  generally comprises two hardened thrust washers and one radial roller bearing. Generally, thrust washer thickness is critical in prior art devices for the accurate and resolved positioning of the threaded core  35 . Thrust-needle bearings  40  absorb injection pressure as pressure is applied to the top of the threaded core  35  during the closed-mold injection stage of the molding cycle. Roller bearings  45  are press fitted into the rack plate  30  and generally provide stability, smooth rotation and alignment to the threaded core  35 . While roller bearings  45  generally operate to hold the core  35  on its true centerline axis, thrust bearings  40  generally operate to stabilize the height position of the core  35  during rotation. Cam bar wear plates  55  generally surround the unengaged surfaces of the cam bars  1  to provide a lubricated surface for cam bars  1  to ride against in order to reduce metal-on-metal galling. Cam bar wear plates  55  may generally be fabricated in much the same fashion as rack wear plates  30 , wherein the wear surface is generally manufactured from a non-ferrous metal or metal alloy that may be easily replaced during periodic maintenance if required. 
     After the unscrewing operation is generally completed, cam followers  5  are subsequently engaged with the acceleration ramps  10  of the cam bars  1  to displace the stripper plate  9 , with a forward motion approximately normal to the interior face of the mold  7 , to provide the final jarring force to the molded article  2 , which dislodges the article  2  from the grabber teeth  20  (as depicted in FIG.  1 ). The grabber portion  20  of the stripper rings  15  generally form interrupted, ramping teeth annularly disposed around the perimeter, usually at the base of the molded article  2 . These teeth  20  are generally biased to provide suitable resistance to torque at the base of the article  2  to prevent the article  2  from turning with the rotation of the withdrawing threaded core  35 . The tapered portion of the grabber teeth  20  generally provides for easier final ejection of the molded article  2  after the unscrewing operation is completed. 
     After the article  2  is ejected from the mold, cam bars  1  are returned to their original position by reversing the hydraulic cylinder  12  before re-engaging the mold halves  7  and  8  into a closed-mold position, as depicted in FIG. 2, in preparation for the next injection molding cycle. For more information regarding injection molding, see “What is a Mold” (Len Graham, published by Tech Group, Inc., 2000), which is incorporated herein by reference. 
     FIGS. 5-12 depict an injection molding apparatus in accordance with one exemplary embodiment of the present invention. In the injection stage of the molding cycle, mold halves  101  and  102  are brought together in relative engagement and secured by means of latch locks  175  to a closed-mold position (see step  202  depicted in FIG. 13) suitably adapted to receive molten plastic (as depicted in FIGS. 5 and 6 ). Various exemplary methods of engaging the mold halves may include, but shall not be limited to: pneumatic means, hydraulic means, worm gear means, stepper-motor driven means, manual engagement means, camming mechanisms, electromotive means, etc. For example, a hot manifold heats and distributes molten plastic to mold cavity  99  (see step  201  depicted in FIG.  13 ). Mold cavity  99  is defined by, in an exemplary embodiment, the void volume between the threaded core  100 , the main core  115  and the mold jacket housing  105  (as depicted in FIGS. 5 and 11 ). As in prior art devices, a hot manifold may be generally employed to reduce runner waste and/or to deliver a more consistent melt temperature to distal portions of the mold in order to obtain improved quality production of article parts  160 . The manifold generally feeds from an injection nozzle (not shown) and carries the plastic to each molding cavity  99  by methods generally well known in the art of injection molding and previously described. Other methods of delivering plastic known in the art of injection molding, such as cold runner delivery systems, hot runners as well as combination methods such as cold-to-hot and hot-to-cold runner delivery systems, may also be used and shall be regarded as conceived and representative of alternative embodiments of the present invention. 
     As molten plastic is injected into the mold (see step  203  depicted in FIG.  13 ), the liquid plastic flows to substantially fill the mold cavity  99  thereby conforming the shape of the article  160  to the design features of the mold. Thereafter, the article  160  may be at least partially cooled to allow the plastic to solidify (see step  204  depicted in FIG.  13 ), whereby the article part  160  substantially retains the mold&#39;s design features and is suitably prepared for subsequent removal from the mold. Coaxial bubbler tubes  92  and  94  (as shown in FIG. 5) may be generally installed in the bottom clamp plates  106  and  107  of mold halves  101  and  102  respectively to direct cooling water from the feed lines  91  and  93  to the inside of threaded core  100  and main core  115  to cool the article  160  prior to ejection from the mold. A water-cooled gate insert may also be used on hot runner molds generally to provide direct cooling at the article  160  and gate interface. Other methods of cooling mold components and product parts known in the art of injection molding, such as thermal pins, bubbler tubes, barrels, drilled water lines, air jets, fans, heat sinks, insulation material, non-ferrous metals, etc., may also be used and shall be similarly regarded as conceived and representative of alternative embodiments of the present invention. 
     Threaded core receiver assembly  120  is mounted to threaded core carrier plate  108 . As linear drive mechanism  111  is actuated, in an exemplary embodiment, threaded core carrier plate  108  rides on cam bars  109  to retract threaded core receiver assembly  120  and threaded core  100  in a preferred exemplary range of about 0.005-0.007 inches from article  160  under closed-mold clamp pressure. In an exemplary embodiment of the present invention, the closed-mold clamp pressure may be up to about 1*10 1 -1*10 3  tons. Acceptable retraction displacement values may range anywhere from about 0.001-0.015 inches depending on the desired product article geometry. 
     In one exemplary embodiment, after article  160  is optionally cooled, cam-actuated threaded core carrier plate  108  is engaged by cam bars  109  disposed on linear drive mechanism  111  (as shown in FIGS. 7 and 8 ) to at least partially retract the threaded core  100  (see step  205  depicted in FIG. 13) from the main core  115 . Maintenance access to the threaded core carrier plate  108  may be had by removal of panels  180 . In another embodiment, core carrier plate  108  may be alternatively disposed on the opposing mold half to at least partially retract the main core  115  to substantially perform the same function and/or to substantially achieve a similar result of partial retraction of conical interlocks  145  and  171  of the threaded core  100  with the interlock recesses  150  and  142  of the main core  115  and the cavity sleeve  90 . 
     In the mold set position, threaded core  100  is engaged with main core  115  by means of an interlocking mechanism that, in an exemplary embodiment, is generally comprised of a conical interlock  145  for relative engagement with a conical interlock recess  150 ; additionally, conical interior surface  171  is relatively engaged with conical interlock recess  142 . The selection of a conical geometry for the interlocking features generally provides for suitably adapted alignment of the mold components with line-contact between the surfaces of engagement. This generally permits a free path of relative rotation of the threaded core  100  with respect to the main core  115  and cavity sleeve  90  as well as accurate and reproducible sealing of the shutoffs. In an alternative embodiment of the present invention, a spherical geometry for the interlocking features may also generally be used to provide a free path of relative rotation of the threaded core  100  with respect to the main core  115 ; however, use of a spherical geometry would generally provide for only point-contact between the surfaces of relative engagement. In yet other embodiments of the present invention, various polygonal geometries may be employed to provide surface contact between the surfaces of relative engagement, such as, for example, that of a tapered pyramidal section; however, not all polygonal geometries may provide a free path of rotation for the threaded core  100  with respect to the main core  115 . In general, the taper of a polygonal interlock feature should be correlated to the magnitude of the linear retraction of the threaded core  100  to provide a suitable free path of rotation. While line-contact may be generally regarded as inferior to surface-contact in terms of securing positive, relative engagement between mold components, line-contact has generally been shown to provide an adequate interlock between the threaded core  100 , the main core  115  and the cavity sleeve  90  while permitting linear retraction parameters to take on generally unconstrained values while providing a free path of rotation. 
     Threaded core following gear  130  engages linear rack  112  to begin unscrewing of threaded core  100  (see step  206  depicted in FIG. 13) from article  160  after the threaded core  100  has been at least partially retracted from engagement with main core  115  so as to reduce metal-on-metal galling that may otherwise result. In an alternative exemplary embodiment of the present invention, other methods of translational displacement of a core mold component under substantial closed-mold clamp pressure may also be used such as, for example: a spring actuated mechanism; a worm gear mechanism; electromotive and/or magnetically inductive means; etc. 
     Galling is generally defined as the undesirable stripping away of material, usually metal, when at least two bodies experience the application of relative force after the bodies have already come into contact with each other. In injection mold applications, galling of mold components may often be attributed to a physical property (e.g., the thermal expansion coefficient) of a metal or metal alloy used to construct the mold components. For example, the thermal expansion coefficient, which corresponds to the rate of linear growth of stainless steel λ as a function of temperature T, may generally be given as:            ∂   λ       ∂   T       ≅     0.0006        inches     Γ   ×     100   °                     F   .                                  
     . . . where Γ is the linear dimension of interest (here, in inches) for a stainless steel component. More generally stated, a stainless steel mold component could be expected to grow by about 0.0006 inches for every inch of steel that comprises the component for every 100 degrees Fahrenheit that the component is heated. In a typically hot runner molding system, mold and manifold temperatures can reach up to about 550° F., corresponding to a growth of about 0.0029 inches of the steel mold components as compared to the same components&#39; dimensions at room temperature. Conical seat shutoff  171  and conical interlock  145  will therefore expand against their surfaces of relative engagement in the mold set position. This expansion will generally result in galling of the mold components as they experience rotation relative to one another in prior art devices under full clamp pressure. In an exemplary embodiment of the present invention, galling of the conical interlock  145  of the threaded core  100  with the interlock recess  150  of the main core  115  and conical interlock  171  with cavity sleeve  90  is virtually eliminated, or otherwise dramatically reduced, with the partial retraction (i.e., 0.005-0.007 inches) of the threaded core  100  prior to rotational disengagement with the article  160 . This has the effect of substantially increasing the Mean Time Between Failure (MTBF) for these components and allows the mold apparatus to have a greater duty cycle between periodic maintenance and inspections procedures. 
     Because the threaded core  100  is partially retracted from main core  115  and cavity sleeve  90 , the internal threads formed on article  160  experience displacement as the threaded core carrier plate  108  retracts the threaded core  100 . In the case of a 0.005-0.007 inch partial retraction of the threaded core  100 , prior to rotational disengagement of the article  160 , it has been observed that suitable plastics (for example, but not limited to: nylon, polypropylene, polyethylene, polycarbonate, high-impact styrene, etc., and mixtures thereof) retain a memory of the stretched displacement of the threads and substantially re-adopt the conformation of the originally molded thread design parameters after the threaded core  100  has been unscrewed and removed from the article  106 . Additionally, partial retraction of the threaded core  100  from the article  160  under substantial full, closed-mold clamp pressure allows for simultaneous cooling of the article  160  and commencement of removal of the same from the mold, which has the effect of substantially further reducing the mold cycle time allowing for improved rates of production of article parts  160  over time. 
     The linear drive unscrewing rack  112  and cam bars  109  attached to cam guide rails  85  are actuated by hydraulic cylinder  113 . In alternative embodiments of the present invention, pneumatic means, worm gear means, stepper-motor driven means, manual engagement means, camming mechanisms, electromotive means, etc., may be generally substituted for hydraulic means  113  to perform substantially the same function and/or to achieve a substantially similar result of actuating unscrewing rack  112  and cam bars  109 . 
     FIG. 9 depicts an exemplary mechanism to provide for the delayed linear retraction of threaded core  100  from main core  115  and conical interlock  171  with cavity sleeve  90  followed by subsequent rotational disengagement of threaded core  100  from the product article  160  in accordance with one embodiment of the present invention. Hydraulic cylinder  113  is communicably connected and actuates rack drive plate  401 , which is connected to and further actuates cam drive plate  400 . Rack drive plate  401  and cam drive plate  400  are initially retained by at least one latch-lock  405 . As rack drive plate  401  moves down, rack drive  112  remains stationary while cam drive plate  400  actuates linear displacement of cam drive rails  85  and cam bars  109 . Cam bars  109 , in turn, actuate displacement of threaded core carrier plate  108  to linearly retract the threaded core  100  under substantially full mold clamp pressure. As hydraulic cylinder  113  continues to actuate downward movement, cam drive rail  85  moves to close the distance between follower-block stop  320  and rack follower-block  315 . As the distance between follower-block stop  320  and rack follower-block  315  is closed, latch-lock  405  disengages rack drive plate  401  from cam drive plate  400  and retaining block  300  engages retaining block recess  310  just prior to follower-block  315  making contact with follower-block stop  320 . As hydraulic cylinder  113  continues to actuate the further downward movement of guide rail  85 , engagement of retaining block  300  with the matched recess  310  assures that linear rack  112  does not return to its original position until the final set is made after the core re-set is complete in the upstroke. The continued downstroke of linear rack  112  actuates the rotation of following gear  130  to initiate rotational retraction of the threaded core  100  from the product article  160 . Threaded core following-threads  114  are pitch-matched to the molding threads  116 . Threaded core receiver assembly  120  is mounted to threaded core carrier plate  108  by means of mounting counter-bores  155 , which are adapted for precise adjustment of the engagement of threaded core  100  with the core set conical interlock features previously described. Threaded core receiver assembly  120  has internally disposed threads for receiving threaded core  100  and provides for mounting of the threaded core  100  to threaded core carrier plate  108 . As threaded core  100  rotates in response to the engagement of threaded core following gear  130  with linear rack  112 , the matched pitch of the molding threads  116  with the core mounting threads  114  generally permits rotational disengagement of the molding threads  116  from the product article  160  while minimizing any stripping damage that might otherwise result. At some point in the downward movement of linear rack  112 , threaded core  100  becomes substantially completely disengaged from product part  160 . Thereafter, mold halves  101  and  102  may be separated to expose product part  160  for subsequent removal from main core  115 . Either prior to reengagement of mold halves  101  and  102 , or after their relative reengagement, hydraulic cylinder  113  may be reversed to return the mold to a core-set position, suitably prepared for the next injection mold cycle, by means of substantially reversing the order of the downstroke steps described above. 
     Rack wear plates  96  are generally mounted on the three surrounding sides of the rack  112  that are not operationally engaged with the following gear  130  of the threaded core  100 . The wear plates  96  provide a lubricated surface that may be, in an exemplary embodiment, fabricated from non-ferrous material with grease-grooves machined into the plate  96  surfaces to allow rack  112  to move back and forth freely. Threaded core  100  is actuated by rotational engagement of following gear  130  with the linear rack mechanism  112 . Rotation of threaded core  100  is stabilized and lubricated by an annularly engaged, oil-impregnated bronze bearing  140  disposed within cavity sleeve  90 . Threaded core  100  generally has threads exteriorly disposed on the molding end that form the interior threads of the article  160  and also generally incorporates a tapered shutoff seat as well as provisions for water cooling well known in the art of injection molding. 
     Cam guide wear plates  97  are generally mounted on the three surrounding sides of the cam guide rails  85 , which define the cam guide rail recess  86  and generally do not comprise surface area attributable to the threaded core carrier plate  108 . The cam guide wear plates  97  also provide a lubricated surface that may be, in an exemplary embodiment, fabricated from non-ferrous material with grease-grooves machined into the plate surfaces to allow cam guide rails  85  to move back and forth substantially freely. 
     After the threaded core  100  is rotationally disengaged from the article  160 , the mold halves  101  and  102  are separated to expose the article  160  (see step  207  depicted in FIG.  13 ). A stripper ring  110  is then displaced along the axis of the main core  115  with a forward motion approximately normal to the interior face of the mold  102 , to dislodge the article  160  (see step  208  depicted in FIG. 13) from the mold (as depicted in FIG.  12 ). Other methods for ejecting a product part known in the art of injection molding, such as ejector pins, sleeve ejections, blades, air ejectors, post-mold ejectors, robotic ejectors, manual ejection means, etc., may also be used and shall be regarded as conceived and representative of alternative embodiments of the present invention. 
     In one exemplary embodiment of the present invention, after product article  160  is ejected from the mold, cam bars  109  and linear rack  112  may be optionally returned to their original positions by reversing the hydraulic cylinder  113  (see step  209  as shown in FIG. 13) before re-engaging mold halves  101  and  102  into a closed-mold position (as depicted in FIGS. 5 and 6 ) in preparation for the next injection molding cycle (returning to step  201  as depicted in FIG.  13 ). In an alternative embodiment, threaded core carrier plate  108  may be returned to the mold set position after re-engagement of mold halves  101  and  102 . 
     The present invention offers substantial advantages and improvements over existing injection mold technology. Testing of the disclosed preferred exemplary device, in accordance with one embodiment of the present invention, showed no detectable signs of pressure contact or wear of the shutoffs after more than 70,000 production cycles of the mold. 
     Various principles and applications of the present invention have been described by way of the preceding exemplary embodiments; however, other combinations and/or modifications of the above-described structures, arrangements, applications, proportions, elements, materials or components used in the practice of the present invention, in addition to those not specifically recited, may be varied or otherwise particularly adapted by those skilled in the art to specific environments, manufacturing or design parameters or other operating requirements without departing from the general principles of the same.