Abstract:
A stripper assembly is provided for stripping a mold part from a core, extending from a core part of an injection mold where the core part has core lock wedges which is disposed thereabout for engaging a corresponding mold cavity and resisting outward movement of an outer edge of the mold cavity. The core lock wedges are spaced apart to provide respective openings between adjacent ends of the adjacent wedges. A stripper plate extends about the core and has acutator attachment regions extending through the openings.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to injection molding molds. More specifically, this invention relates to the stripping of molded parts from an injection mold featuring core lock wedges on a core portion thereof. 
     BACKGROUND OF THE INVENTION 
     Injection molding basically involves the injection of a molten material, such as a plastic into a space defined between a core and a cavity of an injection mold. The core is typically an outward projection from a core portion of the mold. The cavity is typically a recess extending into a cavity portion of the mold. After injection the molten material is allowed to cool and solidify subsequent to which the core portion and cavity portion of the mold are separated in a longitudinal direction. As cooling and solidification of the part is generally accompanied by some shrinkage, the part usually shrinks onto the core from which it has to be removed or “stripped”. 
     Various methods and apparatus are used for stripping parts, the selection of which depends upon practical considerations such as the configuration of the part to be stripped and space available. A stripping assembly which is often desired for thin wall containers and other cup shaped parts is called a stripper plate. A stripper plate, as the name suggests is a plate which lies against the core portion during molding, extends about each core, and engages an outer edge or lip of the molded part. The stripper plate may in fact define a portion of a mold face of the core. This initial position is referred to herein as the “molding position”. 
     The stripper plate is axially movable relative to the core by any suitable actuator connected thereto, such as a pressurized fluid displaceable piston or a linkage arm. As the stripper plate is urged away from the core portion, it presses against the part (usually a lip of the part) and urges the part off of the core. Stripper plates are desirable because they are relatively inexpensive (compared for example to pin ejection systems), reliable (compared to air ejection systems) and require minimal height and minimal changeover times. 
     A problem encountered with thin wall containers, particularly with relatively large ones, is a tendency of the outer edge of the cavity to flex laterally outwardly in response to the pressure of the molten material being injected, thereby causing the wall of the part to be unduly thick toward its outer edges. One way to combat this flex of the cavity is with “core lock wedges”. Core lock wedges are protrusions which extend about the core and abut against an outer perimeter of the cavity to prevent radial outward movement of the outer end of the cavity. A single “wedge” may be used which extends continuously about the cavity in which case the mold is referred to as having a “ring lock core”. The present invention relates to wedge lock cores in which a plurality of spaced apart wedges are provided. 
     FIG. 1A is a perspective view of a prior art wedge lock core on a core part which is illustrated generally by reference  20 . The core part  20  has a core  22  extending from a core face  24 . Disposed about the core  22  and also extending from the core face  24  are four core lock wedges  26 . Although four are shown in this illustrative example, it will be understood by persons skilled in such structures that other numbers are possible. 
     FIG. 1B is a section on line  2 — 2  of FIG. 1A additionally showing a cavity part  30  of a mold (the cavity part  30  does not appear in FIG.  1 ). The cavity part  30  has a cavity  32  extending therefrom with an outer end  34  distal the cavity part  30 . 
     FIG. 1B illustrates the core  32  and the cavity  22  in a molding configuration in which the core lock wedges  26  engage the outer ends  34  of the core  30  to resist outward lateral movement in the direction of arrows  36 . 
     Until the present invention, a problem associated with wedge lock cores has been the inability to use a stripper plate. The presence of the core lock wedges  26  interferes with placing a stripper plate on the core face  24  and accordingly, the stripper plate is replaced with a stripper ring. FIG. 1C is a sectional view corresponding to FIG. 1B of a prior art stripper ring  40 . The stripper ring  40  extends between the core  22  and the core lock wedges  26 . As the stripper ring  40  does not extend to edges  28  of the core part  20 , its actuation cannot be from adjacent the edges  28  as with a conventional stripper plate. Accordingly, the prior art solution has been to provide an ejector box  50  behind the core part  20  and connect the stripper ring  40  to an ejector plate  52  with ejector rods  54 . The ejector plate  52  and in turn the ejector rods  54  and stripper ring  40  are moved by ejector cylinders  56  also connected to the ejector plate  52 . 
     While the use of an ejector box  50  provides a workable arrangement, it has the disadvantage that the ejector box adds significantly to the height of the mold and accordingly, reduces the number of levels that may be provided in a stack mold. 
     An object of the present invention is to provide a stripper plate assembly actuatable without an ejector box for use with a wedge lock core. 
     SUMMARY OF THE INVENTION 
     A stripper assembly is provided for stripping a mold part from a core, extending from a core part of an injection mold where the core part has core lock which is disposed thereabout for engaging a corresponding mold cavity and resisting outward movement of an outer edge of the mold cavity. The core wedges are spaced apart to provide an opening between adjacent ends of the adjacent wedges. 
     The stripper assembly includes a stripper plate extending about a base of the core to engage a part formed on the core and is longitudinally moveable relative to the core by an actuator connected to the stripper plate, between a molding configuration in which the part is formed on the core and a stripping configuration for removing the part from the core. 
     The stripper plate has actuator attachment range extending through the openings between the core lock wedges to provide for attachment of the actuator thereto. The actuator is disposed laterally outwardly of the adjacent ends of the core lock wedges to move the stripper plate between the molding and stripping configurations with the core part being mounted directly to a respective part of an injection molding machine. 
     The actuator may include a fluid pressure response of piston slidably mounted within a bore extending into the core part adjacent at least one of the actuator attachment regions, with the piston being connected to the stripper plate. 
     The actuator may include two or more such pistons, each of the pistons being associated with a different one of the actuator attachment regions. 
     The stripper plate may have one of the actuator attachment regions at each corner thereof and respective of the pistons associated therewith. The actuator attachment regions may extend laterally beyond the confines of the injection mold and the actuator may include at least one lever arm acting between the stripper plate and the core part of the injection mold to move the stripper plate away from the core part in response to the injection mold moving from its molding to a stripping configuration. 
     The actuator may include two such lever arms, each of which is associated with a different one of the actuator attachment regions. 
     The stripper plate may have one of the actuator attachment regions at each corner thereof and a respect of the lever arms associated with each of the actuator attachment regions. 
     The stripper plate may include an inner plate adjacent, the core part and an outer plate adjacent the inner plate. The stripper plate is moveable by the actuator in a first stage wherein the inner and outer plates move together and further moveable by the actuator in a second stage, wherein the outer plate is moved away from the inner plate. 
     The first and second plates may act as an outer end of the cavity associated with the core for the forming of an outer edge of the molded part between the inner and outer plates and the core. The actuator may include first stage actuator coupled to the inner plate for moving the stripper plate in a first stage and a second stage actuator coupled to the outer plate for moving the stripper plate in the second stage. 
     The inner plate may include inner plate actuator attachment regions extending laterally beyond the core of the injection mold. The first stage actuator may include respective lever arms acting between the inner plate and the core part on at least two diametrically opposed of the first actuator attachment regions to move the stripper plate away from the core part in response to the injection mold moving from its molding to a stripping configuration. The outer plate may include at least two diametrically opposed second actuator attachment regions. The second stage actuator may include a respective fluid pressure responsive pistons slidably mounted within corresponding bore extending into the core part, adjacent each of the second actuator attachment regions. 
     A method is also provided for stripping apart from a core extending from core of injection mold where the core part has core lock wedges disposed thereabout for engaging and resisting outward lateral movement of an outer and of a corresponding mold cavity. The core lock wedges are spaced apart to provide respective openings between adjacent ends of adjacent core lock wedges. The method includes the steps of: 
     1. Providing a stripper plate extending about a base of the core for engaging a part formed between the core, the cavity and the stripper plate; 
     2. Providing the stripper plate with actuator attachment regions which extend through the respective openings between the adjacent of the core lock wedges; and 
     3. Applying a stripping force to the actuator attachment regions laterally outwardly of the core to move the stripper plate longitudinally relative to the core with an actuator mounted ahead of a mounting face of the core, and disposed laterally outwardly of the core. 
     According to one embodiment of the method, the stripper plate may further include an inner plate adjacent to the base of the core and an outer plate adjacent the inner plate. The actuator attachment regions may include first actuator attachment regions for movement of the inner plate and second actuator attachment regions for movement of the outer plate. The stripping force in step 3 may be first applied to the first actuator attachment regions to cause the inner and outer plates to move together. The stripping force in step 3 may subsequently be applied to the second actuator regions to cause the outer plate to move away from the inner plate. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     Preferred embodiments of the present invention are described below with reference to the accompanying drawings in which: 
     FIG. 1A is a perspective view illustrating a typical prior art wedge lock core; 
     FIG. 1B is a section on line  2 — 2  of FIG. 1; 
     FIG. 1C is a sectional view corresponding to FIG. 1B additionally showing an ejector box and ring; 
     FIG. 2A is a plan view of the core part of a mold having a stripper plate assembly according to the present invention; 
     FIG. 2B is a section on line  2 B— 2 B of FIG.  2  and also illustrating a cavity part of the mold; 
     FIG. 3 is a section corresponding to FIG. 2B but showing the cavity part removed; 
     FIG. 4 is a section corresponding to FIG. 3 showing a first stage of movement of an ejector assembly according to the present invention; 
     FIG. 4 a  is an enlargement of the area indicated in the box labelled  4   a  in FIG. 4; 
     FIG. 5 is a section corresponding to FIGS. 3 and 4 but showing a second stage of movement of the ejector assembly; 
     FIG. 5 a  is an enlargement of the area in the box labelled  5   a  in FIG. 5; 
     FIG. 6 is a perspective view of a single stage ejector assembly according to the present invention mounted on a core part of a mold and showing an alternate embodiment of an actuator assembly; 
     FIG. 7 is a partial sectional view corresponding to FIG.  6  and showing lever arm actuators in a position corresponding to a molding configuration of the stripper plates; and, 
     FIG. 8 is a view corresponding to FIG. 7 but showing the lever arms in a stripping configuration. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     A mold assembly according to the present invention is generally indicated by reference  100 . The mold assembly includes a core part  110  and a cavity part  120 . The core part  110  includes at least one core  112  extending from a core face  114  thereof. The core part  110  is secured to a platen  150  which may be fixed or movable depending on whether a single level or a multi-level stack mold is being used. 
     The cavity part  120  includes a cavity  122  opposite the core  112 . The cavity part  120  is secured to a platen  152 . The cavity  122  and core  112  are movable by at least one of their respective platens  152  and  150  relative to each other between a molding configuration shown in FIGS. 2B,  3  and  7  and a stripping configuration shown in FIGS. 4 and 8. In the molding configuration a space  160  is defined between the core  112  and cavity  122  into which space  160  molten plastic is injected through a nozzle  170  to form a part  180 . 
     The core part  110  includes core lock wedges  190  spaced apart from the core  112  and extending from the core face  114 . The core lock wedges  190  have wear plates  192  which engage an outer end  124  of the cavity when the mold is in its molding configuration. The wear plates  192  are of a softer material than the core  112  (for example, brass) and both protect the outer end  124  of the cavity  122  from wear and provide a replaceable wear part. The core lock wedges  190  are spaced apart to provide an opening  194  therebetween. 
     A stripper plate  200  is provided which extends around a base  116  of the core  110 . The stripper plate rests on the core face  114  when the mold is in the molding position. The stripper plate is movable away from the core face  114  into a stripping configuration. The stripper plate  200  has a lip  202  which engages an edge  182  of the part  180  to move the part  120  off of the core  112  away from the core face  114 . 
     Unlike a stripper ring, the stripper plate  200  has actuator attachment regions  204  which extend through the openings  194  between the core lock wedges  190 . The attachment regions  204  allow the stripper plate  200  to be acted upon by a stripper ring actuator such as fluid pressure responsive pistons  210  mounted within the bores  212  in the core part  110  of the mold  100 . The pistons  210  and their bores  212  are disposed laterally outwardly of the ends of the core lock wedges  190 . 
     An alternate stripper ring actuator is a lever arm  220  as shown in FIGS. 6,  7  and  8 . The lever arm(s)  220  may be carried on a separate actuator carriage such taught by U.S. Pat. No. 6,086,355. In order to use a lever arm  220  as an actuator, the core part  110  would typically be relieved in its corners  118  to provide access for the lever arm  220  to engage the actuator attachment regions  204 . 
     FIGS. 6 through 8 show a single stage stripper plate in which stripping is accomplished by a single motion of the entire stripper plate  200  from its molding to its stripping configurations. FIGS. 2B through 5 a  illustrate a more complex arrangement in which the stripper plate  200  is made up of an inner plate  206  adjacent the core face  114  and an outer plate  208  on the face of the inner plate  206  opposite the core face  114 . Such an arrangement is referred to as a two-stage stripper plate as the inner plate  206  and outer plate  208  are initially moved together in a “first” stage and the outer plate  208  is moved away from the inner plate  206  in a second stage. 
     Two stage stripper plate arrangements are required for certain shapes of the part  180 . Such a shape is illustrated in the enlargement of FIGS. 4 a  and  5   a . The edge of the part  180  has an outwardly projecting lip  184  which is formed between the core and the inner plate  206 . The lip  184  causes the part to nest within the inner plate  206  and therefore, while movement of the inner plate  206  away from the core face  114  will cause the part  180  to lift away from the core, it will still remain with the inner plate  206 . 
     If an attempt were made to strip the part  180  using only the outer stripper plate  208 , the lip  184  would get sheared off as there is no room for it to pass between the inner plate  206  and the core  112  while the inner plate  206  rests against the core face  114 . 
     With two stage stripping, as illustrated in FIGS. 4 and 4 a , both the inner stripper plate  206  and outer striper plate  208  are moved simultaneously for a first stage of stripping. This lifts the part  180  along and away from the core  112 , to a region  119  wherein there is adequate space S between the core  112  and the inner stripper plate  206  to accommodate the lip  184 . At this point the inner stripper plate  206  ceases to advance while the outer stripper plate  208  is advanced as shown in FIGS. 5 and 5 a  to separate the part  180  from the inner stripper plate  206  by having the lip deflect radially inwardly into the space S and out of engagement with the inner stripper plate  206 . Once out of engagement with the inner stripper plate  206 , the part  180  is free to fall clear. 
     The above description is intended in an illustrative rather than a restrictive sense and variations may be apparent to persons skilled in the relevant art without departing from the spirit of the invention as defined by the claims set out below.