Abstract:
A mold insert retaining structure including a retainer plate connectable, in use, to a mold plate with a spring-clamp, a complementary bayonet structure defined on the retainer plate and a mold insert for providing a twistable interconnection therebetween, a portion of the mold insert clamped between the retainer plate and the mold plate.

Description:
BACKGROUND OF INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates, generally, to retaining a mold insert on a mold plate of an injection mold and more particularly, but not exclusively, the invention relates to a mold insert retaining structure having a spring-clamp for clamping the mold insert to the mold plate. 
         [0003]    2. Background Information 
         [0004]    The state of the art includes U.S. Pat. Nos. 4,911,632 issued Mar. 27, 1990 to Dana Corporation, 3,871,611 issued Mar. 18, 1975 to Phyllis Taketa, 4,556,377 issued Dec. 3, 1985 to Husky Injection Molding Systems Ltd., and 5,750,161 issued May 12, 1998 to Electra Form, Inc. 
         [0005]    U.S. Pat. No. 4,911,632 describes a structure for releasably securing a plurality of mold inserts to a mold plate attached to a power press machine. A mold insert is inserted within an aperture by aligning the tabs with the spaces between the protrusions and moving the mold insert axially therein. Then, by rotating the mold insert relative to the mold plate, the tabs are moved over the protrusions. As a result, the mold insert is retained within the aperture. Locking bars prevent rotation of the mold inserts at undesired times to prevent them from being removed from the mold plate. 
         [0006]    U.S. Pat. No. 3,871,611 describes an improved mold having removable and replaceable cores and cavities, so that the need of providing a new mold base for every new part or product is eliminated. The cores and cavities are tightly nested within pockets of each mold half, they are further secured therein by means of set screws. 
         [0007]    U.S. Pat. No. 4,556,377 describes an injection mold with a female mold portion and a male mold portion has a locking ring which closely surrounds one mold portion and has a beveled inner centering surface coacting in a mold-closed position with a complementarily beveled outer centering surface of the other mold portion for properly aligning the two mold portions with each other. 
         [0008]    U.S. Pat. No. 5,750,161 describes a mold core assembly for removable installation in a molding machine and includes a first lock element attached to a core and a second lock element movably attached to a core retainer. The second lock element is movable between a locked position fitted in locking connection with the first lock element and an unlocked position separated from the first lock element. A slip ring surrounds the first lock element of the core, engaging and holding the second lock element in its locked position. A spring is connected between the core retainer and the slip ring, with the spring biased to oppose movement of the slip ring away from its locked position so that the core is normally held in its locked position in the core retainer. 
         [0009]      FIG. 1  is a cross-sectional view of a portion of an injection mold that depicts a section through a mold insert assembly that defines a molding cavity for the production of preforms of the type that are blow molded into bottles and the like. The injection mold is illustrated in a mold closed position. The mold insert assembly includes a core insert  12 , a cavity insert  14 , a gate insert  20 , a split mold insert  16 , and a lock ring insert  30  that cooperate to define the molding cavity. 
         [0010]    The cavity insert  14  and gate insert  20  each include molding surfaces that define portions of the molding cavity that correspond to an outer body portion and an end portion of the preform  2 , respectively. The gate insert  20  defines an interface  23  for cooperation with a nozzle assembly (not shown) of a melt distribution system (not shown), the gate insert  20  also defines a melt channel to allow, in use, molten plastic to be injected from the nozzle assembly and into the molding cavity. The cavity insert  14  and the gate insert  20  are arranged in a cavity plate  15 . Cooling channels  21  are defined in the cavity plate  15  that cooperate with cooling channels defined on the cavity insert  14  and the gate insert  20  for circulation, in use, of a coolant. 
         [0011]    The core insert  12  and the lock ring insert  30  each include molding surfaces that define portions of the molding cavity that correspond to an inner body portion and a top portion, in part, of the preform  2 , respectively. The core insert  12  and lock ring insert  30  are mounted to a face of a core plate  13 . More particularly, the lock ring insert  30  is bolted to the face of the core plate  13  by bolts  17  (only one shown), the lock ring insert  30  surrounding the core insert  12  with a taper interface  31  defined therebetween for clamping the core insert  12  to the core plate  13 . A cooling tube  22  extends from the core plate  13  and into a bore  26  defined within the core insert  12 . The cooling tube  22  and the channel  26  cooperate to define a channel that extends between cooling channels  24 ,  25  defined in the core plate  13  for circulation, in use, of a coolant. 
         [0012]    The split mold insert  16  includes a molding surface that defines a portion of the molding cavity that correspond to a neck finish portion of the preform  2 . The split mold insert  16  includes a complementary pair of split mold halves  16   a  and  16   b  that can be positioned laterally between an engaged and a disengaged position with respect to the other mold inserts of the mold insert assembly, and in any case perpendicular to a longitudinal axis of the core insert  12 . The split mold halves  16   a  and  16   b  are mounted to a connecting structure for the repositioning thereof between the engage and disengaged positions. The connecting structure includes a pair of slides  36   a  and  36   b  that are supported on a stripper plate  32  by a wear plate  34 . Each neck ring half  16   a  and  16   b  is secured to a respective one of the slides  36   a  and  36   b . The connecting structure also includes an actuator (not shown), typically a cam and cam follower arrangement, for repositioning, in use, the slides  36   a  and  36   b , and with them the split mold halves  16   a  and  16   b . Cooling channels  39  are defined in the slides  36   a  and  36   b  that cooperate with cooling channels defined in the split mold halves  16   a  and  16   b  for circulation, in use, of a coolant. 
         [0013]    In operation of the injection mold the replacement of one or more of the mold inserts of the mold insert assembly is common place. In the foregoing example, the replacement of the core insert  12  on the core plate  13 , for example, requires undoing the bolts  17  and removing the lock ring  30 . This is time consuming and labor intensive activity. 
       SUMMARY OF INVENTION 
       [0014]    In accordance with a first aspect of the present invention a mold insert retaining structure is provided for quick removal and replacement of a mold insert on a mold plate of an injection mold. The mold insert retaining structure includes a retainer plate connectable, in use, to a mold plate with a spring-clamp, a first bayonet structure defined on the retainer plate and a second bayonet structure associated with the mold insert, the first bayonet structure and the second bayonet structure configured to cooperate for providing, in use, a twistable interconnection therebetween, the first bayonet structure and the second bayonet structure may be arranged between a clamped position wherein the second bayonet structure is clamped between the first bayonet structure and the mold plate, and an unclamped position wherein the first bayonet structure is disengaged from the second bayonet structure. 
         [0015]    In accordance with a second aspect of the present invention a mold insert is provided for quick removal and replacement on a mold plate of an injection mold having a mold insert retaining structure. The mold insert includes a body having a molding surface that defines a portion of a molding cavity in cooperation with other mold inserts of a mold insert assembly. A second bayonet structure associated with the body, the second bayonet structure configured to cooperate with a first bayonet structure defined on a first retainer plate of the mold insert retaining structure for providing a twistable interconnection therebetween. The retainer plate connected, in use, to the mold plate with a spring-clamp. The first bayonet structure and the second bayonet structure may be arranged between a clamped position wherein the second bayonet structure is clamped between the first bayonet structure and the mold plate, and an unclamped position wherein the first bayonet structure is disengaged from the second bayonet structure. 
         [0016]    In accordance with a third aspect of the present invention an injection mold is provided that includes the mold insert retaining structure and mold insert in accordance with the first and second aspects of the present invention, respectively. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0017]    A better understanding of the embodiments of the present invention (including alternatives and/or variations thereof) may be obtained with reference to the detailed description of the embodiments along with the following drawings, in which: 
           [0018]      FIG. 1  is a cross-sectional view of a portion of a known injection mold taken through a mold insert assembly that defines a molding cavity for forming preforms; 
           [0019]      FIG. 2  is a plan view of a portion of a mold plate assembly of an injection mold in accordance with a non-limiting embodiment of the present invention. 
           [0020]      FIG. 3  is a cross-sectional view taken along the section line  3 - 3  in  FIG. 2 ; 
           [0021]      FIG. 4  is an enlarged sectional view of an encircled portion designated at  4 - 4  identified in  FIG. 3  that depicts a mold insert retaining structure retaining a mold insert to a mold plate of the mold plate assembly; 
           [0022]      FIG. 5  is an exploded view of the mold insert retaining structure and mold insert of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0023]    Referring to  FIG. 2 , a portion of a mold plate assembly  60  in accordance with a non-limiting embodiment of the present invention is shown. The mold plate assembly  60  may be used with the injection mold  18  described previously and shown with reference to  FIG. 1 . The portion of the mold plate assembly  60  includes a mold plate  41  with eight mold inserts  42  retained thereon by a corresponding plurality of mold insert retaining structures  40 . Other configurations of the mold plate assembly are, of course, possible such as, for example, different quantities of the mold inserts  42  and corresponding mold insert retaining structures  40 . Each of the mold insert retaining structures  40  is shown as including a retainer plate  43  holding a corresponding one of the mold inserts  42  to the mold plate  41 . The retention of the mold inserts  42  on the mold plate  41  will be described in more detail hereinafter with reference to  FIGS. 3 ,  4  and  5 . 
         [0024]    In the non-limiting embodiment the mold insert  42  is configured similarly to the core insert  12  described previously for the purpose of molding the inner body portion of the preform  2 . Alternatively, the mold insert  42  may be configured similarly to other mold inserts of the mold insert assembly to mold other portions of the preform  2 , such as, for example, cavity insert  14  for molding the outer body portion of the preform  2 . 
         [0025]      FIG. 3  is a sectional view of the mold plate assembly  60  taken along the sectional line  3 - 3  of  FIG. 2 . The mold inserts  42  are positioned on a face  63  of the mold plate  41  with a spigot portion  57  thereof received in a complementary bore  62  formed in the mold plate  41 . The interface between the spigot portion  57  and the complementary bore  62  may be close fitting such that the mold insert  42  is closely positioned for alignment with the other mold inserts of the mold insert assembly. Each mold insert  42  is retained on the mold plate  41  with the assistance of a clamping pressure exerted by the retainer plate  43  of the mold insert retaining structure  40 . More particularly, each of the mold insert retaining structures  40  further includes a plurality of spring-clamps  64  coupling the retainer plate  43  to the mold plate  41  and urges the retainer plate  43  towards the face  63  of the mold plate  41 . In the non-limiting embodiment three of the spring-clamps  64  are equi-angularly arranged around each mold insert  42 , however, any reasonable number of mold insert retaining structures  40  could be used. A non-limiting embodiment of the spring-clamp  64  is shown in more detail in  FIGS. 4 and 5 . Each spring-clamp  64  of the non-limiting embodiment is an assembly that includes a pin  44 , a spring  50 , a first fastener  46 , a second fastener  48 , and a washer  49 . The pin  44  is a cylindrical member having a outwardly projecting head  45  at an end thereof. Each pin  44  is slidably received in a pin bore  65  that passes through the mold plate  41 . The pin bore  65  includes a first counter-bore portion  65   a  at an end thereof for receiving the head  45  of the pin  44 . Each pin  44  includes a first coupler  66  formed in the head  45  thereof and a second coupler  67  formed at the opposite end of the pin  44  from the head  45 . The first coupler  66  and the second coupler  67  cooperate, in use, with the first and second fasteners  46 ,  48 , respectively. Each retainer plate  43  includes three fastener bores  58 ,  69 , and  60  formed therethrough that cooperate with the corresponding first fastener  46  of the three spring-clamps  64  associated with each mold insert  42 . Each pin bore  65  also includes a second counter-bore  65   b  at another end thereof (opposite end of the pin bore  65  from the first counter-bore portion  65   a ). The spring  50  is arranged in the second counter-bore portion  65   b  sandwiched between a face  54  of the second counter-bore portion  65   b  and the washer  49 , the washer  49  fastened to the end of the pin  44  between the second fastener  48  and the second coupler  67 . The springs  50  are placed into a pre-compressed condition by engaging the second fastener  48  with the second coupler, such as, for example, the tightening of a screw fastener into a complementary threaded bore, respectively. In the pre-compressed condition the compressed spring  50  retains sufficient remaining resiliency that the retainer plate  43  may be lifted slightly for sake of effecting a removal and/or installation of the mold insert  42 . It has been found that with only a minimal flexibility remaining in the spring  50  in the pre-compressed condition that the mold insert  42  remains better aligned with the cavity insert  14  than was previously possible with the more rigid core insert  12  mounting shown in the prior art design illustrated in  FIG. 1 . 
         [0026]    Each retainer plate  43  is a substantially rectangular plate with the fastener bores  58 ,  59  and  60  equi-angularly arranged and a central bore  68 . The central bore  68  extends through a top and bottom face of the retainer plate  43 . The central bore includes an upper portion  68   a  having an inner surface that surrounds, in use, a portion of the mold insert  42 , the inner surface having a diameter that is the same as, or slightly larger than, the diameter of the portion of the mold insert  42  adjacent thereto. The upper portion  68   a  of the central bore  68  having a first irregular outline defining three arcuate cut-out portions  51 ,  52  and  53  formed in an equi-angularly spaced relation through the inner surface of the upper portion  68   a  through which fingers  55  and  56  of the mold insert  42  may be passed. A plurality of webs  70  span between the cut-out portions  51 ,  52 , and  53 . The central bore includes a lower portion  68   b  beneath the webs  70  having a diameter that is at least as wide as a maximum diameter of the fingers  55  and  56  of the mold insert  42 . 
         [0027]    Each mold insert  42  includes a body with three arcuate fingers  55  and  56  (shown with one hidden in  FIG. 5 ) projecting from a base portion thereof. The fingers  55  and  56  of the mold insert  42  are complementary to the cut-out portions  51 ,  52  and  53  of the retainer plate  43  in shape and angular position. To install the mold insert  42  onto the mold plate  41 , the fingers  55  and  56  are to be aligned and passed through the cut-out portions  51 ,  52 , and  53  of the retainer plate  43  and into the space defined by the lower portion  68   b  of the central bore  68 . Thereafter, the mold insert  42  is rotated to pass the fingers  55  and  56  beneath webs  70  of the retainer plate  43  that span between the cut-out portions  51 ,  52 , and  53  whereupon the fingers  55  and  56  of the mold insert  42  are clamped between corresponding bottom surfaces  71  of the webs  70  and the face  63  of the mold plate  41 . To ease the engagement of the fingers  55  and  56  beneath the webs  70  of the retainer plate  43 , a relief on a portion of a top surface of the fingers  55  and  56  and/or on the bottom surfaces  71  of the webs  70  may be provided. Alternatively, a pry slot or other lifting means may be provided to momentarily lift the retainer plate  43  from the face  63  of the mold plate  41  to effect the rotation of the mold insert  42 . To remove the mold insert  42  from the mold plate  41  is the reverse of the steps of installation thereof. 
         [0028]    Hence, the mold insert retaining structure  40  permits the mold insert  42  to rotate between an unclamped position wherein the fingers  55  and  56  and the cut-out portions  51 ,  52 , and  53  are aligned and the mold insert  42  is not retained to the mold plate  41 , and a clamped position where the fingers  55  and  56  are arranged in the lower portion  68   b  of the central bore  68  and are aligned with the plurality of webs  70  wherein the fingers  55  and  56  of the mold insert  42  are clamped between a plurality of bottom surfaces  71  of the plurality of webs  70  and the face  63  of the mold plate  41 . When it is necessary to change a mold insert  42 , hand pressure on the mold insert  42  against the pressure of springs  50  is generally sufficient to permit rotation of the mold insert  42  to a position where the fingers  55  and  56  and the one hidden are aligned with the cut-out portions  51 ,  52  and  53  in the retainer plate. The mold insert  42  can then be withdrawn from the mold plate  41 . In like manner, a replacement mold insert  42  can be readily mounted on the mold plate  41  by simply aligning its fingers  55  and  56  with the cut-out portions  51 ,  52  and  53  on the retainer plate  43  and inserting and rotating the replacement mold insert  42  into the position vacated by the earlier mold insert  42 . 
         [0029]    More particularly, the spring  50  permits the retainer plate  43  to be lifted by twisting action of the mold insert  42 . As a practical matter, when the mold insert  42  is removed, the spring  50  draws the retainer plate  43  into contact with the mold plate  41 . However, when the mold insert  42  is in place, the retainer plate  43  is slightly lifted by the action of engaging the mold insert  42  and a small gap exists between the retainer plate  43  and the mold plate  41 . 
         [0030]    In the embodiment shown in  FIG. 5 , the cut-out portions  51 ,  52  and  53  and the fingers  55  and  56  are complementary and of equal arcuate length and form a bayonet structure that can, through twisting of the mold insert  42  alone, permit insertion and removal of the mold insert  42 . 
         [0031]    For example, the fingers  55  and  56  could be of very short arcuate length and the cut-out portions  51 ,  52  and  53  could be any arcuate length greater than the arcuate length of the fingers  55  and  56 . Also, the fingers  55  and  56  and cut-out portions  51 ,  52 , and  53  could be of different shapes, the only requirement being that the fingers  55  and  56  on the mold insert  42  be able to pass through the cut-out portions  51 ,  52 , and  53  on the retainer plate  43 . Also the number of cut-outs and fingers could something other than three as shown in our preferred embodiment. The shape, size, number and location of the fingers  55  and  56  and cut-out portions  51 ,  52 , and  53  may be largely determined by such factors as cost and ease of manufacture and the part strength necessary to withstand the rigors of injection molding. 
         [0032]    It will, of course, be understood that the above description has been given by way of example only and that modifications in detail may be made within the scope of the present invention.