Abstract:
The upper and lower halves of a blow mold define a blow mold cavity when the halves are closed together. A bottom plug which serves to form a dome in the bottom of the blown bottle is shifted into and out of a cooperating relationship with the two mold halves by cam mechanism that operates in response to raising and lowering of the upper die set upon which the upper mold half is mounted. The actuating mechanism comprises a pair of mutually opposed cam rods having a follower trapped therebetween that is in turn coupled with the bottom plug so that as the cam rods are shifted with the upper die set, the follower reacts to cam surfaces on the rods to impart a corresponding extension and retraction motion to the bottom plug. To handle multiple, side-by-side blow mold cavities, the bottom plugs for such cavities are ganged together on a common support bar that is in turn provided with operating shanks, each provided with a cam follower operated by a cam assembly. In an alternative embodiment, the bottom plug is split into two upper and lower halves, with each half being provided with its own actuating mechanism. Sets of upper plug halves can be ganged together for actuation in unison, as can sets of lower plug halves.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to blow molding apparatus and, more particularly, to improvements in the way bottom plugs associated with such molds are actuated between their extended and retracted positions.  
         BACKGROUND AND SUMMARY  
         [0002]    Blow molded plastic bottles are typically provided with recessed, generally dome-shaped bottoms to provide increased structural integrity. To produce such a dome in the finished bottle, a corresponding “plug” or “push-up” is provided in the bottom of the blow mold cavity so that as the small parison stretches and enlarges during the blow cycle to meet the confines of the mold cavity, the bottom of the bottle partially forms around the protruding plug to conform to its shape and present the dome. However, to then facilitate discharge of the blown bottle from the machine, the bottom plug must be retracted out of the bottom of the bottle.  
           [0003]    Typical injection blow mold machines have an upper plate-like die set that reciprocates vertically toward and away from a stationary, lower die set mounted on the machine bed. Cooperating blow mold halves are carried on the die sets to form blow mold cavities when the upper die set is in its lowered position, and to open such cavities when the upper die set is raised. A corresponding number of bottom plugs are arranged in side-by-side relationship and shifted horizontally into and out of the respective cavities for use in forming bottom domes in the blown bottles.  
           [0004]    It is known in the art to actuate the bottom plugs using interacting cam wedges and return springs. Using this technique, a first cam wedge carried on the upper mold half comes into mating engagement with a second cam wedge carried on the bottom plug associated with the lower mold half. Thus, as the upper mold half moves downward into a closed condition with the lower mold half, the top wedge moves into engagement with the bottom wedge, camming the plug horizontally inwardly into proper position within the mold cavity. Then, as the upper mold half rises at the completion of the blow cycle, a return spring associated with the lower wedge pushes the lower wedge and associated plug back out to a retracted position so that the plug is withdrawn from the dome in the bottom of the blown bottle. Each mold cavity has its own set of cam wedges, its own set of return springs, and its own set of guide rods on which the bottom wedge reciprocates with its plug during actuation.  
           [0005]    The conventional cam wedge actuating mechanism has many shortcomings. For one thing, the point of physical interaction and engagement between the wedge surfaces is vertically offset from the horizontal line of action of the plug itself so that the force of the interacting cam surfaces imparts a moment that tends to rock and cock the plug during actuation. This can lead to a multitude of problems, including failure of the plug to withdraw when the mold halves open because the bottom wedge is jammed on its guides and the return springs are simply incapable of providing enough force to break it loose. If a plug fails to withdraw, bottle quality can be compromised as the bottle is forced off the plug during the eject cycle.  
           [0006]    The known cam wedge mechanism quickly becomes a problem due to premature wear of its various mechanical parts. It is important to grease the guides on which the lower cam wedge reciprocates, yet the grease has a way of working its way up into the bottle cavity areas, causing unsightly marks on the finished bottles. This can lead to rejecting entire production runs if even just a few rejects are noticed during random sampling. Furthermore, frequent tedious maintenance is required to replace prematurely worn springs, to clean the numerous components and to regrease the slide surfaces associated with the moving lower wedge.  
           [0007]    The present invention provides a highly reliable, trouble-free actuating mechanism that supplies smooth, positive actuation of the bottom plug in both directions of actuation. No return springs of any kind are utilized. Cam surfaces interact with follower structure during both the extend and retract strokes of the bottom plug.  
           [0008]    In one preferred embodiment, one or more cam assemblies are carried by the movable die set for reciprocation therewith during movement toward and away from the stationary die set. Each cam assembly includes an extend cam surface and a retract cam surface which are located in mutually spaced relationship on opposite sides of a follower carried by the bottom plug. Thus, as the movable mold half closes against the stationary mold half, the moving extend cam surface engages the follower and causes a reaction force transverse to the direction of die set travel which pushes the plug to its extended position within the mold cavity. Then, as the movable mold half opens at the completion of the blow cycle, the reversely moving retract cam surface engages the opposite side of the follower, causing a force in the opposite, transverse direction to withdraw the plug out to its extended position.  
           [0009]    In a most preferred form of the invention, the mold halves open vertically and the upper die set is the part that reciprocates, the bottom plug having a horizontal stroke. Preferably, the cam surfaces are on separate cam rods operating within upright bores of a guide block that has a horizontal passage intersecting with the cam rod bores and slidably receiving an operating shank associated with the bottom plug. The shank has a slot that carries the cam follower, which is preferably in the nature of a roller, and the two cam rods are received within the slot on opposite sides of the roller to cause the shank to reciprocate horizontally within the passage as the cam rods are shifted up and down during raising and lowering of the upper die set.  
           [0010]    In one preferred embodiment for multiple cavities, a series or gang of the bottom plugs are secured side-by-side on a common mounting bar for actuation in unison. Multiple gangs can be handled, with each gang secured to its own bar. Two or more of the operating shanks project rearwardly from each bar adjacent opposite ends thereof and are received within a pair of corresponding guide blocks mounted on the lower die set. Each guide block has its own cam rod assembly that reciprocates vertically therein during raising and lowering of the upper die set. Thus, all plugs of each gang of cavities are operated in unison for positive extension and retraction, using only a pair of cam assemblies and a pair of followers for the entire group instead of a pair of cam wedges for each cavity as in conventional constructions.  
           [0011]    In another preferred embodiment each bottom plug is split into two halves which come together to present a complete plug when the two mold halves close. One plug half is carried on the movable die set while the other plug half remains with the stationary die set. Separate actuating mechanisms are provided for the separate plug halves, and the plug halves of each die set can be ganged together for actuation in unison. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is an isometric view of a prior art unit cavity blow mold employing cam wedge actuating mechanism for the bottom plug, the mold halves being shown in a closed condition;  
         [0013]    [0013]FIG. 2 is a side elevational thereof;  
         [0014]    [0014]FIG. 3 is a slightly enlarged, vertical cross sectional view of the prior art unit cavity blow mold;  
         [0015]    [0015]FIG. 4 is a vertical cross sectional view of the prior art unit cavity blow mold but with the mold halves in an open condition and the bottom plug in its retracted position;  
         [0016]    [0016]FIG. 5 is a rear isometric view of blow mold apparatus constructed in accordance with the principles of the present invention and showing the mold halves open and the bottom plugs retracted;  
         [0017]    [0017]FIG. 6 is a front isometric view thereof with the mold halves open and the bottom plugs retracted;  
         [0018]    [0018]FIG. 7 is a rear isometric view of blow molding apparatus constructed in accordance with the principles of the present invention showing the mold halves closed and the bottom plugs in their extended positions;  
         [0019]    [0019]FIG. 8 is a front isometric view thereof with the mold halves closed and the bottom plugs in their extended positions;  
         [0020]    [0020]FIG. 9 is an enlarged, fragmentary vertical cross sectional view through the apparatus in an open condition revealing details of construction;  
         [0021]    [0021]FIG. 10 is an enlarged, fragmentary vertical cross sectional view through the closed apparatus revealing details of construction;  
         [0022]    [0022]FIG. 11 is a isometric view of the two cam rods that comprise the major components of each cam rod assembly of the apparatus;  
         [0023]    [0023]FIG. 12 is an exploded, fragmentary isometric view with various components shown in cross section to reveal details of construction of the apparatus; and  
         [0024]    [0024]FIG. 13 is a rear isometric view of another embodiment of the invention wherein the bottom plugs are split into two halves. 
     
    
     DETAILED DESCRIPTION  
       [0025]    Prior Art  
         [0026]    FIGS.  1 - 4  show a prior art unit cavity blow mold  10  having an upper mold half  12  and a lower mold half  14 . Mold halves  12  and  14  are mounted on respective upper and lower die sets (not shown) for vertical movement of upper half  12  toward and away from lower half  14  to open and close the mold defined by halves  12 ,  14 . A plurality of external nipples such as nipples  16  on halves  12 ,  14  communicate with internal cooling passages such as passages  18  in halves  12 ,  14  for the purpose of supplying a cooling liquid such as water to the mold.  
         [0027]    When the mold halves  12 ,  14  come together as illustrated in FIG. 3, a blow mold cavity  20  becomes defined between halves  12  and  14  corresponding in shape and size to the final blown bottle. A major portion of the bottom of cavity  20  is defined by a cylindrical plug  22  having a convex or dome-shaped leading surface  24 . Plug  22  is adapted to be actuated horizontally between an extended position in FIG. 3 and a retracted position in FIG. 4 by interacting cam wedges  26  and  28 .  
         [0028]    The upper cam wedge  26  is fixed to the outer end of upper mold half  12  for vertical reciprocation therewith and has a downwardly and inwardly facing bevel  30  at its lower extremity. Upper wedge  26  also has an inverted, generally U-shaped notch  32  in its lower extremity.  
         [0029]    On the other hand, lower wedge  28  is affixed to plug  22  for horizontal reciprocation therewith and is guided in such movement by a pair of lower outwardly projecting guide pins  34  on lower mold half  14  and a pair of upper outwardly projecting guide pins  36  on lower mold half  14 . A coiled return spring  38  surrounding each upper guide pin  36  yieldably biases lower wedge  28  and thus also plug  22  outwardly to the retracted position determined by the enlarged head  34   a  of each lower guide pin  34 . Lower wedge  28  has an outwardly and upwardly facing bevel  40  on its upper end having the same inclination as bevel  30  of upper wedge  26 . A cooling tube  42  for water or the like is threaded into the outboard end of plug  22  and projects outwardly through a hole  44  in bevel  40  to support a fitting  46  at its outer end, to which is connected one of the nipples  16 .  
         [0030]    The notch  32  in upper wedge  26  is aligned with the tube  42  associated with lower wedge  28  so that as upper half  12  moves downwardly toward lower half  14  to close mold  10 , tube  14  slips into clearance notch  32 . Bevels  30  and  40  come into engagement with one another, causing a horizontal reaction force directed rightwardly viewing FIGS. 4 and 3, causing plug  22  to be shifted into its extended position of FIG. 3 as mold halves  12 ,  14  fully close. Springs  38  become compressed at this time. As mold halves  12 ,  14  are then reopened, bevel  30  rises from bevel  40  and return springs  38  push lower wedge  28  leftwardly viewing FIGS. 3 and 4 to the extent permitted by heads  34   a  of guide rods  34 . Thus, plug  22  becomes shifted outwardly to its retracted or withdrawn position.  
         [0031]    In practice, production molds typically comprise a multiplicity of side-by-side blow mold cavities, each provided with their own pair of upper and lower mold halves and their own bottom plug. Each mold is also provided with its own pair of upper and lower cam wedges for actuating the corresponding bottom plug during raising and lower of the upper die set to which the upper mold halves are commonly attached.  
       A PREFERRED EMBODIMENT OF THE PRESENT INVENTION  
       [0032]    The present invention is susceptible of embodiment in many different forms. While the drawings illustrate and the specification describes certain preferred embodiments of the invention, it is to be understood that such disclosure is by way of example only. There is no intent to limit the principles of the present invention to the particular disclosed embodiments.  
         [0033]    FIGS.  5 - 12  show various aspects of one embodiment of blow mold apparatus constructed in accordance with the principles of the present invention. Although the mold halves are adapted to open vertically, and the upper mold halves are the movable ones while the lower halves are stationary, other arrangements are possible within the scope of the present invention. As illustrated in those figures, the apparatus includes an upper die set member  48  adapted to be attached to an upper platen (not shown) of a suitable injection blow molding machine, a lower die set member  50  adapted be attached to the machine bed of the machine, and a plurality of upright guide posts  52  that guide upper die set  48  during vertical reciprocation toward and away from lower die set  50 . A series of blow molds comprising respective pairs of upper mold halves  54  and lower halves  56  are mounted on upper die set  48  and lower die set  50  respectively for opening and closing of the molds as illustrated in FIGS. 5, 6 and  7 ,  8 , for example.  
         [0034]    Each mold defines its own internal blow mold cavity  58  when mold halves  54 ,  56  are closed, and each mold is provided with its own bottom plug  60  that provides a closed bottom for the cavity  58 . The convex or domed leading surface  62  of each plug  60  provides the desired domed or recessed bottom of the blown bottle, and each set of mold halves  54 ,  56  is provided with the usual type of cooling passages such as internal passages  64  shown in FIGS. 9 and 10. Such passages  64  communicate with external nipples such as nipples  66  shown in FIGS.  5 - 8 . Although not shown in the drawings, it will be understood that plugs  60  may be provided with means for circulating cooling fluid through the interior thereof.  
         [0035]    The foregoing components of the blow molding apparatus of FIGS.  5 - 12  are substantially the same as corresponding conventional components. The difference between such apparatus and the prior art resides in the manner in which bottom plugs  60  are ganged for actuation in unison, and in the particular actuating mechanism used for carrying out such actuation. In this respect, the apparatus of FIGS.  5 - 12  further includes a transverse mounting bar  68  that extends along behind the row of bottom plugs  60  and serves as a common mounting and support bar for all of the plugs  60  of that particular gang. Additional bottom plugs may be ganged together on additional bars as desired, to accommodate additional sets of mold cavities. In a preferred embodiment, each bar  68  is rectangular in cross sectional configuration, although this may vary, and each plug  60  is secured to the front side of bar  68  by a pair of upper and lower screws  69 . Bar  68  may be provided with suitable conditioning means (not shown) for cooling or heating purposes.  
         [0036]    In the illustrated embodiment, each mounting bar  68  has a pair of cylindrical operating shanks  70  projecting rearwardly therefrom (although more than two maybe provided) at a pair of spaced locations along its length somewhat inboard from opposite ends thereof. Each shank  70  is secured to the rear face of mounting bar  68  by a mounting plate  72 . Each plate  72  traps an enlarged head  74  (see FIGS. 9 and 10) up against mounting bar  68 , while the rest of shank  70  projects rearwardly through plate  72  for interaction with other structure as subsequently described. Each mounting plate  72  is releasably attached to mounting bar  68  using suitable fasteners such as screws (not shown) which may be recessed within countersunk bores  76  in plate  72  as illustrated, for example, in FIG. 12.  
         [0037]    As illustrated particularly in FIG. 12 and also in FIGS. 9 and 10, each operating shank  70  has a vertical through slot  78  intermediate its opposite ends of the shank. Within slot  78 , disposed centrally thereof in a fore-and-aft direction, is cam follower structure in the nature of a roller  80  journaled for rotation on a transversely extending, horizontal cross pin  82 . Slot  78  is of such length and roller  80  is of such diameter that spaces are defined on opposite sides of roller  80  between the latter and the corresponding end of slot  78 . Roller  80  is slightly smaller in diameter than the diameter of shank  70  and its axis of rotation defined by cross pin  82  is located on the central axis of shank  70  so that roller  80  is symmetrical with respect to shank  70  and does not project above or below the same.  
         [0038]    The apparatus of FIGS.  5 - 12  further includes a pair of upstanding guide blocks  84  that are secured to lower die set  50  at locations spaced behind mounting bar  68  in alignment with operating shanks  70 . Each guide block  84  has a fore-and-aft extending, horizontal passage  86  that slidably receives the corresponding shank  70  of mounting bar  68 . Shank  70  may thus slidably reciprocate within passage  86  between the two extreme positions illustrated in FIGS. 9 and 10. Each guide block  84  is secured to lower die set  50  by suitable fasteners not shown which pass through vertically extending, countersunk bores at the four corners of the block as illustrated by the two countersunk bores  88  in FIG. 12, for example.  
         [0039]    Horizontal passage  86  within each guide block  84  intersects with a pair of vertical, fore-and-aft spaced guide bores  90  and  92 . Such bores  90 ,  92  are, in turn, adapted to slidably receive corresponding vertically disposed, generally cylindrical cam rods  94  and  96  of a cam assembly  98  secured to and carried by upper die set  48 . Thus, the cam assemblies  98  comprise another part of the blow mold apparatus of FIGS.  5 - 12 .  
         [0040]    The cam rods  94  and  96  of each cam assembly  98  are secured to upper die set  48  by a circular mounting plate  100  which is itself secured to die set  48  by fasteners not shown passing through bores  102  in plate  100  (FIG. 12). Each mounting plate  100  has a pair of countersunk bores  104  and  106  for receiving the corresponding cam rod  94  and  96  respectively and capturing the enlarged heads  94   a  and  96   a  thereof up against the bottom surface of upper die set  48 . As shown in FIGS. 9 and 10, lower die set  50  is provided with a pair of horizontally spaced, vertical bores  108  and  110  aligned with bores  90  and  92  of each guide block  84  for the purpose of receiving and clearing the lower ends of cam rods  94  and  96  when upper die set  48  is in its lowered position as illustrated in FIG. 10.  
         [0041]    Each cam rod  96  is an “extend” cam, while each cam rod  94  is a “retract” cam. Extend cam rod  96  is generally cylindrical, but has a forwardly facing cam surface that includes a flat, upright, follower-engaging segment  112  extending upwardly from its lowermost tip to approximately its mid-portion. At the upper termination of flat segment  112 , the effective cam surface of extend cam  96  transitions to a radiused, forwardly facing, outwardly extending, concave segment  114  so that the effective working cam surface progressively moves closer to the forward extremity of cam rod  96  during this segment. At the upper extremity of concave segment  114 , just before it would otherwise intersect with the forward most portion of the outer periphery of cam rod  96 , the cam surface changes to a short, flat, upright segment  116 . The horizontal, radial distance between flat segment  112  and flat segment  116  in one preferred embodiment is on the order of ten millimeters such that the effective stroke of the bottom plugs  60  from their retracted positions to their extended positions is likewise on the order of ten millimeters. Although in practice the upper flat segment  112  may be produced to have an uppermost arcuate portion, such uppermost arcuate portion is of no particular significance in the functioning of cam rod  96  and, in any event, that portion of cam rod  96  above upper flat segment  112  is cylindrical for the remaining length of rod  96  to its upper end.  
         [0042]    Retract cam rod  94  is likewise generally cylindrical. However, this overall cylindrical configuration is deviated from over its lower portion through the presence of the rearwardly facing retract cam surface which includes a long flat, rearwardly facing, upright segment  118 . Flat segment  118  corresponds in length to flat segment  112  of extend cam  96 , although it is somewhat narrower than segment  112 . At the upper extremity of flat segment  118 , the cam surface face of retract cam  94  transitions to a rearwardly facing concave segment  120  that deepens into retract cam  94  at essentially the same radius as the concave segment  114  of extend cam  96  curves out toward the outer periphery of extend cam  96 . Concave segments  114  and  120  are directly opposed to one another. At the upper and inner termination of concave segment  120 , a short flat upright segment  122  commences in spaced opposition to short flat segment  116  on extend cam  96 . Above short flat segment  122 , a second rearwardly facing concave segment  124  curves outwardly and intersects with the rearmost periphery of retract cam  94 .  
         [0043]    In one preferred embodiment, guide blocks  84  are constructed from aluminum that is hard-anodized, while cam rods  94 ,  96 , operating shanks  70 , and follower rollers  80  are constructed from hardened steel. Mounting bar  68  and plugs  60  are constructed from a high thermoconductive material such as aluminum.  
         [0044]    It will be appreciated that although cams  94 ,  96  have been disclosed as being associated with die sets  48 ,  50  and follower roller  80  has been disclosed as being associated with bottom plug  60 , it is within the concepts of the present invention for this relationship to be reversed. It is to be understood that, in principle, cams  94 ,  96  could be carried by bottom plug  60  while follower roller  80  is carried by the movable one of the two die sets.  
         [0045]    Operation  
         [0046]    When the upper die set  48  is in its raised position as illustrated in FIGS. 5, 6, and  9  to open the molds, plugs  60  are in their retracted positions. Cam rods  94  and  96  are fully raised such that the follower roller  80  in each guide block  84  is confined between flat segments  112  and  118  on cam rods  94  and  96 .  
         [0047]    As upper die set  48  begins to descend, upper mold halves  54  start moving toward lower mold halves  56 . However, this does not initially result in movement of bottom plugs  60  because cam rods  94 ,  96  have no effect on followers  80  even though rods  94  and  96  are moving downwardly into guide blocks  84  at this time. Because segments  112  and  118  are upright and flat, they merely travel vertically along opposite front and rear sides of rollers  80  without imparting any horizontal movement to shanks  70 .  
         [0048]    As the upper mold halves  54  are close to closing on top of lower mold halves  56 , however, concave segments  114  and  120  of cam rods  94  and  96  come into registration with follower rollers  80 . Continued downward movement of upper die set  48  thus causes concave segment  114  of each extend cam rod  96  to exert a horizontal, forwardly directed force against the corresponding roller  80 , resulting in shifting of all plugs  60  simultaneously toward their extended positions further into the mold halves. Such actuation is permitted at this time by virtue of the relief provided by concave segments  120  on the retract cam rods  94 . By the time upper mold halves  54  have fully closed on lower mold halves  56  and cam rods  94 ,  96  have fully descended into blocks  84 , follower rollers  80  have climbed up concave segments  114  of extend cam rods  96  and onto short flat segments  116 . In this position the bottom plugs  60  are fully extended as illustrated in FIG. 10 and are retained against rearward movement out of such position by short flat segments  116 . Short flat segments  122  on retract cam rods  94  preclude further inward movement of bottom plugs  60  beyond their fully extended positions at this time.  
         [0049]    Upon completion of the blow cycle, upper die set  48  begins to lift away from lower die set  50 . This immediately starts to separate upper mold halves  54  from lower mold halves  56  and also immediately starts to retract bottom plugs  60  under the positive action of retract cams  94 . As cam rods  94 ,  96  move upwardly with upper die set  48 , follower rollers  80  leave short flat segments  116  and  122  and enter the region between concave segments  114  and  120 . Thus, as cam rods  94  and  96  continue upwardly, the concave segments  120  of retract cam rods  94  lift against the front sides of follower rollers  80  and exert rearwardly directed horizontal forces thereto, causing shanks  70  to slide rearwardly within their passages  86  in guide blocks  84  and retracting bottom plugs  60 . By the time flat segments  112 ,  118  are reached by follower rollers  80 , bottom plugs  60  are fully retracted, and continued upward movement of cam rods  94 ,  96  merely results in bottom plugs  60  holding stationary as upper mold halves  54  continue to rise with upper die set  48 . When upper die set  48  is fully raised, the condition of FIG. 9 is once again established with mold halves  54 ,  56  fully opened and bottom plugs  60  fully retracted.  
         [0050]    It will thus be seen that the actuating mechanism in accordance with the present invention achieves positive actuation of the bottom plugs in both directions. No springs are relied upon to return the plugs to extended positions as in conventional, prior art arrangements. Furthermore, the thrust from the vertically moving cam rods in the present invention is directly in line with the operating shanks for the bottom plugs such that no canting or cocking of the plugs occurs during their actuating movement, which results in smooth, positive travel without risk of jams and damage to the equipment. And, by mounting all of the bottom plugs on a common mounting bar, only a pair of cam assemblies are needed to actuate the entire set of plugs, instead of having a separate wedge mechanism for each plug. This greatly increases reliability and reduces the likelihood of maintenance problems and consequential downtime. Moreover, the present design can be readily retrofitted onto existing blow molding apparatus.  
         [0051]    Alternative Embodiment  
         [0052]    [0052]FIG. 13 shows an alternative embodiment wherein the bottom plugs are split into two upper and lower halves with one half carried by the upper die set and the other half supported on the lower die set. When the mold halves close, the plug halves also come together to present a complete plug, but each half (or series of halves) is moved through its extension and retraction strokes by its own actuating mechanism. Details of construction of each actuating mechanism remain the same as in the embodiment of FIGS.  5 - 12  and will not be described again at this juncture. However, due to the split nature of the bottom plugs, the actuating mechanisms are arranged differently than in the earlier embodiment, and more of such mechanisms are necessary.  
         [0053]    Specifically, it will be seen that each plug  60  in the embodiment of FIG. 13 now comprises a top half  60   a  and a bottom half  60   b . The top plug halves  60   a  are secured to a common top mounting bar  68   a , while the bottom plug halves  60   b  are secured to a common bottom mounting bar  68   b . In the illustrated embodiment, the top mounting bar  68   a  has three operating shanks  70   a  projecting rearwardly therefrom, which are identical to shanks  70 , although that number may vary. Likewise, bottom mounting bar  68   b  has three operating shanks  70   b . Top shanks  70   a  are reciprocably received by three top guide blocks  84   a  secured to and depending downwardly from upper die set  48 , while bottom shanks  70   b  are reciprocably received by three bottom guide blocks  84   b  secured to and projecting upwardly from lower die set  50 .  
         [0054]    The top plug halves  60   a  are actuated by three bottom cam assemblies  98   b  that are secured to and project upwardly from lower die set  50  (only two of such assemblies  98   b  being visible in FIG. 3). Cam assemblies  98   b  are identical to cam assemblies  98  and are reciprocably received within the three corresponding top guide blocks  84   a  to interact with the followers (not shown, but identical to followers  80 ) of the corresponding top shanks  70   a . Likewise, the bottom plug halves  60   b  are actuated by three top cam assemblies  98   a  that are secured to and depend downwardly from upper die set  48 . Cam assemblies  98   a  are identical to cam assemblies  98  and are reciprocably received within the three corresponding bottom guide blocks  84   b  to interact with the followers of the corresponding bottom shanks  70   b.    
         [0055]    As the top mold halves  54  approach the bottom mold halves  56  and top plug halves  60   a  approach bottom plug halves  60   b , the upper shanks  70   a  are actuated by the bottom cam assemblies  98   b  and the bottom shanks  70   b  are actuated by the top cam assemblies  98   a . By the time mold halves  54  and  56  have completely closed, and plug halves  60   a  and  60   b  have come together, cam assemblies  98   a  and  98   b  will also have fully extended plug halves  60   a  and  60   b  into the mold. After the blow cycle, the mold halves  54 ,  56  and plug halves  60   a ,  60   b  start to separate, and the cam assemblies  98   a ,  98   b  withdraw plug halves  60   a ,  60   b  to their retracted positions. Upper die set  48  continues its upward movement until reaching its fully raised position of FIG. 13.  
         [0056]    The inventor(s) hereby state(s) his/their intent to rely on the Doctrine of Equivalents to determine and assess the reasonably fair scope of his/their invention as pertains to any apparatus not materially departing from but outside the literal scope of the invention as set out in the following claims.