Abstract:
A molding apparatus has a pair of slide inserts which are laterally movable into and out of engagement with the other mold components. The lateral movement of the slide inserts is provided by a slide mechanism having a driving rack, a pair of drive pinions at either end of the driving rack, two pairs of driven racks and a plurality of slides connected to the driven racks. The driven racks of each pair are parallel and spaced from one another, engaging opposite sides of a pinion and thereby being driven in opposite directions by rotation of the pinion. The molding apparatus is more compact than conventional devices having slide inserts, eliminates the use of slide retainers, eliminates obstructions between the mold plates when the plates are separated, and can cycle faster than conventional devices.

Description:
FIELD OF THE INVENTION 
     The present invention relates to slide core molds for use in injection molding, and more specifically to slide mechanisms employed in such molds. 
     BACKGROUND OF THE INVENTION 
     Conventional molds for injection molding typically comprise mating parts, such as a core and a cavity, which abut each other at a parting line and are moved directly away from each other along a machine axis during opening of the mold. 
     Such molds may also include one or more mold components which form an undercut portion of the article to be molded. These mold components, also to herein as “slide inserts”, are moved laterally into and out of engagement with the other mating parts of the mold during closing and opening of the mold. Usually, a pair of such slide inserts is provided, one slide insert on each side of the mold. During mold opening, the slide inserts are moved outwardly in opposite directions from the other mating parts of the mold. Molds which include such laterally movable components are referred to herein as “slide core molds”. 
     Presently used mechanisms for opening and closing slide core molds typically include slide blocks on which the slide inserts are mounted. Usually, these slide blocks are slidably mounted on the mold plate which carries the core, with one slide block being provided on each side of the mold. Lateral movement of the slide blocks is accomplished by providing angled horn pins mounted to the mold plate which carries the cavity. The horn pins extend through angled apertures in the slide blocks. As the core is separated from the cavity, the slide blocks slide along the horn pins, resulting in outward displacement of the slide blocks and the associated slide inserts from the other mating parts of the mold. 
     Examples of this type of mechanism are described in U.S. Pat. No. 3,811,645 issued May 21, 1974 to Feist and U.S. Pat. No. 4,889,480 issued Dec. 26, 1989 to Nakamura et al. These two pat. are actually concerned with slide retainers which are required in this type of slide core mold since the horn pins and the apertures in the slide blocks may become misaligned when the mold is opened, preventing reinsertion of the horn pins into the slide blocks. 
     Conventional slide mechanisms have several disadvantages. Firstly, conventional slide mechanisms include components such as cams which must be mounted on the outside of the mold and which increase the size of the mold. Some conventional slide retainers, such as the pull rod/compression spring retainer shown in FIG. 2 of the Feist patent, also include components which project from the sides of the mold. These components have the effect of enlarging the mold, reducing the number of mold cavities which can be fitted into a molding apparatus of a given size. 
     In addition, components such as cams and/or horn pins project from the parting line face and obstruct the space between the mold plates during ejection of the molded parts from the core. Since these components are lubricated, contact with the molded parts during ejection can result in product contamination. 
     Another disadvantage of conventional slide mechanisms is that these mechanisms are actuated as the mold opens and closes. This requires that the opening and closing of the mold be slowed down In order to avoid damaging the relatively delicate slide inserts, thereby lengthening the mold cycle time. 
     Therefore, the need exists for an effective slide mechanism which eliminates or reduces the size and/or number of components projecting from the outside of the mold. It would also be desirable to provide a slide mechanism which eliminates the need for a slide retainer to reduce the size and complexity of the mechanism, which also eliminates obstructions between the mold plates, and which can be actuated independently of opening and closing the mold. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes at least some of the disadvantages of the prior art by providing a molding apparatus having a slide mechanism which is more compact than conventional slide mechanisms, does not form obstructions between the open mold plates, eliminates the need for slide retainers, and does not depend on mold opening and closing for actuation. 
     The molding apparatus according to the present invention comprises at least two mold plates which preferably carry a plurality of mold cores and mating mold cavities which form a plurality of molds. Each mold has a pair of laterally movable mold elements which are movable toward and away from each other. The mold elements of each mold are mounted on a pair of slides positioned on either side of the mold. 
     The mechanism for moving the mold elements between their inner and outer positions includes a reciprocating driving rack which drives at least one pinion. Each pinion drives a pair of driven racks which are movable in opposite directions, each of the racks being connected to one of the slides. Therefore, movement of the driving rack results in lateral movement of the slides and the associated mold components inwardly or outwardly in relation to the mold. 
     Since the apparatus of the invention does not utilize horn pins, misalignment of the slides during opening and closing is not a problem, and therefore slide retainers are not required. The slide mechanism of the present invention is compact and is recessed into the stripper plate, away from the mold parting line. This reduces the overall size of the mold and eliminates obstructions between the mold plates, thereby reducing the risk of contamination of parts being ejected from the molds. Furthermore, the slide mechanism does not rely on mold opening and closing for actuation since the driven racks are preferably actuated by a pneumatic cylinder after the mold is opened and retracted before it is closed, thereby allowing a shorter mold cycle time. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described, by way of example only, with reference to the accompanying drawings in which: 
     FIG. 1 is a cross-sectional view through one mold of an injection molding apparatus in a plane parallel to a direction in which the slides are moved, showing the mold in the closed position; 
     FIG. 2 is a cross-sectional view in the same plane as FIG. 1 showing the mold of FIG. 1 with the cavity plate separated from the stripper plate; 
     FIG. 3 is a cross-sectional view in the same plane as FIG. 1 showing the mold of FIG. 2 with the slides and the slide inserts moved laterally to their outer positions; 
     FIG. 4 is a cross-sectional view in the same plane as FIG. 1 showing the mold of FIG. 3 with the stripper plate separated from the core plate to advance the stripper ring along the machine axis and eject the molded part from the core; 
     FIG. 5 is a top plan view of a molding apparatus of the present invention, partially disassembled to show details of the slide mechanism; 
     FIG. 6 is a perspective, partially cut away view of a partially disassembled molding apparatus of the present invention, illustrating the preferred slide mechanism, showing details of one pair of slide bars and one pair of slide inserts only; 
     FIG. 7 is a perspective view similar to that of FIG. 6 illustrating the operation of the preferred slide mechanism; 
     FIG. 8 is an enlarged cross-sectional view through the molding apparatus of FIG. 1 in a plane parallel to the driving rack, showing the sliding mechanism at the proximal end of the driving rack and omitting, for clarity, some of the teeth of the driving rack; and 
     FIG. 9 is an isolated, enlarged cross-sectional view of the stripper plate and the slide mechanism of the molding apparatus of FIG. 1 in a plane perpendicular to the driving rack, showing the slide mechanism at the proximal end of the driving rack and omitting, for clarity, some of the teeth of the driven rack. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A preferred molding apparatus according to the present invention is generally indicated by reference numeral  10  in the drawings. The molding apparatus  10  comprises three mold plates, namely a mold core plate  12 , a mold cavity plate  14  and a mold stripper plate  16  between the core plate  12  and cavity plate  14 . A mold core  18  is mounted in the mold core plate  12 , a mold cavity  20  is mounted in the mold cavity plate  14 , and an annular stripper ring  22  is mounted in the mold stripper plate  16  and surrounds the mold core  18 . 
     Both the core plate  12  and stripper plate  16  are movable along a machine axis to move the mold plates between a mold closed position and a mold open position. The stripper plate  16  is movable along tie rods  24  (FIG. 5) relative to the core plate  12  in order to strip a molded part  26  from the core  18 . The stripper plate  16  is preferably actuated by machine ejector rods (not shown) which advance the stripper plate  16  along the machine axis. 
     The molded part  26  shown in the drawings comprises a threaded closure for a container having a tamper-evident skirt which is separable from the remainder of closure  26  by a line of pre-weakening  27 . The molten plastic which forms molded part  26  is injected into mold  28  through injection nozzle  38 . 
     The cavity plate  14  and stripper plate  16  abut each other at a first parting line P 1  in the mold closed position (FIG.  1 ), and the core plate  12  and the stripper plate  16  likewise abut each other along second parting line P 2  in the mold closed position. With the plates  12 , 14  and  16  in the mold closed position, a mold  28  is formed in which the molded part  26  is formed. The mold  28  is formed between the mold core  18  and the mold cavity  20 . The radially inner portion of the upper surface of the stripper ring  22  also forms part of mold  28  at the lower peripheral edge of the molded part  26 . 
     As illustrated in the drawings, the apparatus  10  also comprises a plurality of laterally-movable mold elements. A pair of such mold elements are provided for each mold  28 . In the preferred embodiment shown in the drawings, each pair of laterally-movable mold elements comprises slide inserts  30  and  32  mounted on slide bars  34  and  36 , respectively. The slide inserts  30  and  32  are each semi-circular in shape and combine to form a split insert which combines with the stripper ring  22 , the core  18  and the cavity  20  to form mold  28 . In the preferred embodiments shown in the drawings, the slide inserts  30  and  32  each have a radially inner molding surface which is provided with an undercut portion to form the line of pre-weakening  27  separating the skirt from the main body of molded part  26 . 
     The mold  28  is opened and part  26  is removed from the mold  28  by first separating the cavity plate  14  from the stripper plate  16  (FIG.  2 ), laterally moving the slide inserts  30  and  32  and their associated slide bars  34  and  36  away from core  18  (FIG.  3 ), and then separating stripper plate  16  from core plate  12  (FIG.  4 ), thereby advancing stripper ring  22  along the machine axis to strip the part  26  from the core  12 . These steps will be described in greater detail below. 
     As illustrated in the plan view of FIG. 5, the molding apparatus  10  preferably comprises a plurality of molds  28  as described above, to permit the simultaneous formation of a number of molded parts  26 . Preferably, the molds  28  are arranged in a plurality of spaced, parallel rows  40 . In the preferred apparatus  10  shown in the drawings, the mold apparatus  10  comprises four rows  40 , each comprising eight molds  28 . Thus, mold apparatus  10  is capable of simultaneously forming thirty-two molded parts  26 . 
     In the leftmost row  40  of molds  28  in FIG. 5, the slide bars  34 ,  36  have been omitted to reveal a pair of apertured wear plates  41  which are bolted to the stripper plate  16 . The edges of wear plates  41  are also visible in the other rows  40 . The wear plates  41  underlie the slide bars  34 ,  36  and are provided with apertures  43  which surround the stripper rings  22  and the mold cores  18 , this being illustrated in FIGS. 1 to  4 . 
     The molding apparatus  10  also comprises a slide mechanism for moving the slide inserts  30  and  32  between their inner positions (mold closed position) and their outer positions (FIGS. 3 and 4) in which they are separated from the molded part  26 . 
     The slide mechanism includes a driving rack  42  which is mounted in the stripper plate  16 . The driving rack  42  comprises an elongate metal bar having a rectangular cross-section, and is provided along one edge with a plurality of teeth  44 . The driving rack  42  has a proximal end  46  and a distal end  48 , the distance between the distal and proximal ends  46  and  48  being greater than the lengths of the rows  40  of molds  28 . 
     The slide mechanism includes driving means for producing reciprocating movement of the driving rack  42  along a lateral axis which is perpendicular to the machine axis and which is substantially parallel to the rows  40  of molds  28 . The driving means preferably comprises a pneumatic cylinder  50  (FIGS. 5 and 8) which is mounted to an outer surface of the stripper plate  16 . It will be appreciated that the driving means may comprise any means capable of actuating the driving rack, including hydraulic cylinders. Pneumatic cylinders are however preferred over hydraulic cylinders since leakage of fluid from hydraulic cylinders can cause contamination of the molded parts. 
     Provided near the respective. ends  46  and  48  of driving rack  42  are a pair of drive pinions  52  and  54 . The drive pinions  52  and  54  are mounted in the stripper plate  16  and are rotatable about an axis parallel to the machine axis. As shown in the drawings, the pinions  52 ,  54  are each mounted on a guide bushing  53 , with each pinion and bushing  53  being retained by a pinion retainer plate  55  secured by screws to the stripper plate. The drive pinions  52  and  54  are provided with gear teeth  56  which engage the teeth  44  on driving rack  42  such that movement of the driving rack  42  parallel to the rows  40  of molds  28  causes rotation of drive pinions  52  and  54 . Specifically, movement of the driving rack  42  in the direction of arrow A in FIG. 7 causes counter-clockwise rotation of pinions  52 ,  54  and movement of driving rack  42  in the opposite direction causes clockwise rotation of drive pinions  52  and  54 . 
     Preferably, engagement between the driving rack  42  and the drive pinions  52 ,  54  is maintained by rollers  58  provided near each of the drive pinions  52  and  54 . Rollers  58  are also mounted in the stripper plate  16  for rotation about an axis parallel to the machine axis. As shown in FIGS. 6 and 7, one or more rollers  58  may also be provided intermediate the ends  46 ,  48  of driving rack  42 . 
     The slide mechanism further comprises two pairs of driven racks  60  and  62 , each having one edge provided with teeth  61  and  63 , respectively. As shown in FIGS. 6 and 7 (in which one of the driven racks  62  is partially cut away), one pair of driven racks  60 ,  62  engages the drive pinion  52  near the proximal end  46  of driving rack  42  for reciprocating movement along an axis which is perpendicular to the machine axis and perpendicular to the rows  40  of molds  28  in response to rotation of drive pinion  52 . The driven racks  60  and  62  are spaced from one another and are substantially parallel so that they engage opposite sides of the drive pinion  52 . Therefore, rotation of drive pinion  52  results in movement of the driven racks  60  and  62  in opposite directions, as indicated by arrows B and C in FIG.  7 . Specifically, when drive pinion  52  rotates in a counter-clockwise direction, rack  60  is driven to the left along arrow B and rack  62  is driven to the right along arrow C. Conversely, when drive pinion  52  rotates in the clockwise direction, rack  60  will be driven to the right and rack  62  will be driven to the left. 
     An identical pair of driven racks  60  and  62  is provided in engagement with drive pinion  54  at the distal end  48  of driving rack  42 . It will be appreciated that the driven racks  60  at the proximal and distal ends of driving rack  42  move in the same direction in response to rotation of drive pinions  52  and  54 , and that driven racks  62  at the opposite ends of driving rack  42  also move in the same direction. 
     As illustrated in the plan view of FIG. 5, the two pairs of driven racks  60 ,  62  are separated by a distance which is greater than the lengths of the rows  40  and extend across the tops and bottoms of all of the rows  40 . 
     The slide bars  34  and  36  are mounted on the stripper plate  16  for reciprocal movement towards and away from the mold core  18 . The slide bars are movable along an axis which is perpendicular to the machine axis and which is also perpendicular to the rows  40  of molds  28  and to the longitudinal directions of the slide bars  34 ,  36 . As shown in FIGS. 6 and 7, the slide bars  34 ,  36  extend across the two pairs of driven racks  60 ,  62 , with the slide bar  34  being attached at its opposite ends to both driven racks  60 , and slide bar  36  being attached at its opposite ends to both driven racks  62 . Therefore, the slide bars  34 ,  36  simultaneously move inward and outward in relation to the mold core  18  in response to movement of driven racks  60  and  62  in opposite directions. 
     As illustrated in FIGS. 6 to  8 , the slides  34 ,  36  are retained on pins  64  which project upwardly above the upper surfaces of driven racks  60  and  62 . The ends of the slide bars  34 ,  36  are prevented from being released from driven racks  60 ,  62  by gibs  66 ,  68  which are bolted to the stripper plate  16  at opposite ends of the slide bars  34 ,  36 . Gib  68  near the distal end  48  of driving rack  42  is shown partially cut away in FIG.  5 . 
     As best illustrated in FIGS. 1 and 2, provided along the first parting line P 1  is a series of locking wedges, including wedges  70  and  72 . The single acting locking wedge  70  and double acting locking wedge  72  have sloped inner surfaces  76  and  78  (FIG. 2) respectively which engage sloped outer surfaces  80  and  82  (FIG. 2) of slide bars  34  and  36  respectively. Thus, when the cavity plate  14  and stripper plate  16  abut one another in the mold closed position of FIG. 1, the locking wedges  70  and  72  firmly retain the slide bars  34  and  36  in place to prevent outward displacement of the slide bars and the slide inserts  30  and  32 . 
     A molding operation utilizing apparatus  10  will now be described below with reference to the drawings. 
     With the mold  28  in the mold closed position as shown in FIG. 1, molten plastic is injected under pressure into mold  28  from injection nozzle  38  to form molded part  26 . The mold is subsequently opened and the part ejected by the following sequence of steps: 
     1. The cavity plate  14  and stripper plate  16  are separated along parting line P 1  as shown in FIG.  2 . As discussed above, this is preferably accomplished by mold opening along the machine axis, leaving the molded part  26  attached to the core  18 . 
     2. With the mold open along parting line P 1  and locking wedges withdrawn as in FIG. 2, the pneumatic cylinder  50  is activated to push the driving rack  42  in a direction away from cylinder  50 , thereby causing rotation of pinions  52 ,  54  and translation of driven racks  60 ,  62  as described above. 
     This results in the slide bars  34 ,  36  being moved from their inner positions to their outer positions, as illustrated in FIG.  3 . 
     3. With the slide bars  34  and  36  and associated slide inserts  30  and  32  moved to the outer positions as shown in FIG. 3, the stripper ring  22  is advanced axially upward by separation of stripper plate  16  from core plate  12 , thereby ejecting the molded part  26  from core  18  as shown in FIG. 4 
     The mold is again closed for the next molding operation by bringing core plate  12  and stripper plate  16  together along parting line P 2 , followed by activation of pneumatic cylinder  50  to move the driving rack  42  in the opposite direction to the mold opening step, resulting in movement of the slide bars  34 ,  36  and slide inserts  30 ,  32  to the inner position, and then bringing together the cavity plate  14  and stripper plate  16  along parting line P 1 , to close the mold  28 . 
     Since actuation of the slide mechanism is independent of the opening and closing of the mold, the order of the above steps can be varied somewhat. For example, the slide mechanism could be actuated during mold opening and closing to further decrease the mold cycle time. This would not, however, require slowing down of the mold opening and closing step since the slide mechanism is operated independently. 
     Although the invention has been described in connection with a molding apparatus having a certain number of molds, it will be appreciated that the invention can be applied to a molding apparatus having any number of molds, including an apparatus having only one mold. 
     Although the invention has been described in connection with a molding apparatus which utilizes a stripper plate and a stripper ring, it will be appreciated that the present invention could be applied to a molding apparatus having two mold plates which form a one or more molds, with the slide mechanism of the present invention could be mounted in either of the mold plates. 
     It is also conceivable that a molding apparatus according to the invention could be configured with only one drive pinion and one pair of driven racks, for example where the apparatus contains relatively few molds such that the slides are relatively short. 
     Although the invention has been described in connection with certain preferred embodiments, it is not to be limited thereto. Rather, the invention is intended to encompass all embodiments which may fall within the scope of the following claims.