Abstract:
A universal mountable and demountable rack-and-pinion structure for a stack mold includes mounting plates affixed to the mold parts and rack-and-pinion mounting elements which are mountable to and demountable from the mounting plates. This arrangement permits the rack and pinion elements first to be mounted in an approximately correct position for the appropriate proportionation of movement within a molding machine. The device includes an adjustment feature which permits the relative distances between the mold parts to be finely adjusted to ensure correct proportionation of movement. The rack-and-pinion structure is interchangeable for various stack molds.

Description:
FIELD OF THE INVENTION 
     The present invention relates to injection molding machines and, in particular, to stack molds employed therein. 
     BACKGROUND TO THE INVENTION 
     In the molding of plastic parts by injection molding, mold parts are brought together to define a mold cavity, polymeric material is injected into the mold cavity and, after allowing time for the polymer to solidify, the mold parts are drawn apart and the molded part removed. 
     The moveable elements or plattens of the molding machine are arranged to move in a horizontal direction and slide on stationary bars to transport the moveable mold parts into and out of mating relationship with a stationary mold part. 
     Such molds may be single face, with a single moveable mold part and a stationary mold part or may be a stack mold where two or more moveable mold parts move towards and away from a stationary mold part. 
     In the latter molding machines, a rack-and-pinion structure often is used to achieve synthronized self-positioning of the moveable mold parts. In such devices, rack elements are attached to the stationary mold part and the outer moveable mold part, while a pinion is mounted to the inner moveable mold part. Depending on the size of the stack mold, one or more such rack-and-pinion structures may be provided on each side of the stack mold. 
     In general, the rack-and-pinion structure is custom-made for a specific stack mold and it is necessary to precisely position the device on the mold parts of the stack mold to ensure correct mold operation in the molding machine. When access to the mold parts is required for removal from the molding machine and replacement by another stack mold, the rack-and-pinion structure often needs to be first removed and then subsequently reassembled, a time consuming operation. 
     SUMMARY OF INVENTION 
     The present invention represents an improvement on the prior art, permitting a degree of flexibility and ease of operation which has not previously been achieved. The present invention provides a universal rack-and-pinion structure for use with stack molds, which is readily and rapidly demounted and mounted and permits rapid adjustment for proper proportioning of movement of the moveable mold parts in a stack mold in a molding machine. 
     Accordingly, in one aspect of the present invention, there is provided in a stack mold of the type wherein at least a pair of moveable molding parts move into and away from mold-cavity forming relationship with each other and a stationary mold part, the improvement comprising rack-and-pinion structure mounting plates affixed one to each of the moveable mold parts and stationary mold part; a pinion housing structure containing a pinion mountable to and demountable from the mounting plate affixed to the inner moveable mold part; a rack mounting element mountable to and demountable from the mounting plate affixed to the outer moveable mold part and to the stationary mold part; a first rack element extending between one said rack mounting elements and into gear-meshing relationship with the pinion in the pinion housing when said molding parts are out of mold cavity forming relationship; a second rack element extending between the other of said rack mounting element and into gear-meshing relationship with the pinion in the pinion housing when said molding parts are out of mold cavity forming relationship; and adjustment means associated with each of the rack mounting elements and the respective end of the rack element to adjust the distance between the moveable mold part from each other and from the stationary mold part to ensure that a mold cavity is formed between the outer and inner moveable mold parts at the same time as a mold cavity is formed between the inner moveable mold part and the stationary mold parts. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a elevational view of a stack mold of otherwise conventional structure but modified in accordance with one embodiment of the invention, in a closed position; 
     FIG. 2 is a elevational view of the stack mold of FIG. 1, in an open position; 
     FIG. 3 is a close up, perspective view of rack-and-pinion device provided in accordance with one embodiment of the invention and utilized with the stack mold of FIGS. 1 and 2; 
     FIG. 4 is a close up front elevational view of a detail of the rack-and-pinion device of FIG. 3; 
     FIG. 5 is a sectional view of the rack-and-pinion device taken on line A—A of FIG. 4; 
     FIG. 6 is a perspective partly broken-away view of the rack-and-pinion device of FIG. 4; 
     FIG. 7 is a perspective partly broken-away view of a mounting assembly for mounting the rack-and-pinion device of FIG. 3 to the moveable mold parts; and 
     FIGS. 8 and 9 are elevational views illustrating the mounting of the rack-and-pinion device to the moveable mold parts. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     Referring first to FIGS. 1 and 2, a stack mold  10  comprises an end stationary mold part  12  and a pair of moveable mold parts  14 ,  16  moveable into and out of mold-cavity forming relationships between the inner moveable mold part  14  and the stationary mold part  12  and between the outer moveable mold part  16  and the inner moveable mold part  14 . 
     The moveable mold parts  14 ,  16  are arranged in sliding relationship with the stationary mold part  12  by guide pins  18 ,  20 . The guide pins  18 ,  20  protrude respectively from the stationary mold part  12  and outer moveable mold part  16 , through openings  22  in the central moveable mold part  14  and into recesses  24  formed in the stationary mold part  12  and the moveable mold part  14  when in the closed position (FIG.  1 ). 
     In order for the stack mold to function correctly within a molding machine, it is necessary for the mold cavities to be formed between the stationary mold part  12  and the inner moveable mold part  14  and the mold cavity to be formed between inner ( 14 ) and outer ( 16 ) moveable mold parts to be formed at the same moment and hence the movements of the moveable mold parts  14  and  16  are required to be coordinated to achieve this effect. 
     As mentioned previously, one known manner of achieving the required coordinated movement is to employ a rack-and-pinion device. Accordingly to one embodiment of the invention, a novel rack-and-pinion device  26  comprises a set of mounting plate elements  28 ,  30 ,  32 . The mounting plate  28  enables the pinion element to be mounted to the inner moveable mold part  14 , while the mounting plates  30  and  32  enable the rack elements to be mounted to the mounting to the stationary mold part  12  and the moveable mold part  16 . 
     The mounting plate element  28  is intended to be permanently mounted in a suitable recess  29  in the face of the inner moveable mold part  14  using mounting pins  31  while the mounting plate elements  30  and  32  are intended to be permanently mounted in the suitable recesses  34  (FIG. 7) in the face of the outer moveable mold part  16  and the stationary mold part  12  respectively using mounting pins  33  and  35 . 
     A pinion housing  36  and rack mounting elements  38 ,  40  are structured, as detailed below, to permit rapid mounting and demounting of the rack-and-pinion structure from the respective mounting plates  28 ,  30  and  32 , thereby rapidly mounting and demounting the rack-and-pinion structure from the stack mold. 
     In addition, by selecting a length of rack element  42 ,  44 , a rough adjustment of a relative positioning of the mold parts is achieved and a respective adjustment element  46 ,  48  associated with the respective rack mounting elements  38 ,  40  permits rapid fine adjustment of the relative position of the mold parts for precise operation. 
     The mounting plate element  28  has a shaft  50  mounted in an opening  52  in the mounting plate and protruding therefrom and over which is mounted the pinion housing  36 . A gear wheel  54  is mounted on the shaft  50  for rotation in a recess  56  formed in a guide plate  58  sandwiched between an inner plate  60  and an outer face plate  62  into which the shaft  50  also extends. Locating pins  63  on the outer plate  62  and corresponding recesses  64  in the guide plate  58  ensure proper alignment of the elements. The overall pinion housing assembly  36  is mounted to the mounting plate  28  by threaded bolts  66  extending through openings in the elements  58 ,  60 ,  62  and into screw-threaded engagement with threaded recesses in the mounting plate  28 . 
     Upper and lower rack guide elements  68 ,  70  comprise a roller  72  rotatably mounted on a shaft  75 , which extends from a mounting element  76 , which has a further shaft  74  extending into the mounting plate  28 . The rack guide elements  68 ,  70  are mounted to the mounting plate  28  by screw-threaded bolts  78  extending through the element  76  and into screw-threaded engagement with threaded recesses in the mounting plate  28 . 
     A pair of elongate gear-toothed rack elements  42  and  44  extend in gear meshing relationship with the gear wheel  54  and in engagement with the roller elements  72 , in a channel  80  formed by the opposed faces of the elements  60  and  62  and a shoulder  82  on element  58 . A pair of centering bars  84  is provided on opposite sides of the channel  80  to ensure proper positioning of the rack elements  42  and  44 . 
     It will be seen that the whole pinion and rack support assembly  36  is readily and rapidly mounted to and demounted from the mounting plate  28  by removing and replacing the mounting bolts  78 . 
     The opposite ends of the rack elements  42  and  44  from the support assembly  36  are mounted respectively to ones of the rack mounting elements  38 ,  40 . The rack mounting elements  38 ,  40  each comprises a yoke element  85  which can be mounted to the mounting plate  32  by suitable screw-threaded bolts  86  extending into screw-threaded recesses in the mounting plate  32  with the aid of locating pin  87  received in recess  88  in plate  32 . A screw-threaded element  89  extends from the end of the rack element  42  through an opening  90  in the yoke element  85  while the square cross-sectioned end of rack element  42  is received in a C-shaped element  91  of the yoke  85 , which is closed by plate  92  to define a rectangular cavity in which the rack element  42  is received in sliding fit relationship. A pair of screw-threaded bolts  93  extend through openings  94  in the plate  92  into screw-threaded recesses  96  in the C-shaped element  91 . 
     A first pair of locking nuts  100  is mounted on the screw-threaded element  89  between the arms of the yoke  85  while a second pair of locking nuts  102  is mounted to the screw threaded element  89  at the free end of the element  89  extending through the opening  90 . 
     In general, the rack elements  42 ,  44  have a length which enables the rack and pinion structure to be mounted to a number of different stack molds, thereby providing a universal structure applicable to a number of stack molds to be employed in a particular molding machine. Fine adjustment of the relative positions of the mold parts  12 ,  14 ,  16  to provide for accurate proportionation during molding by the stack mold within the molding machine may be achieved by manipulation of the pairs of locking nuts  100 ,  102 , such as is seen in FIGS. 8 and 9. 
     While the illustrated embodiment of FIGS. 1 and 2 shows a single rack-and-pinion device  26  mounted to the mold parts, it is desirable to provide at least two such devices on each side of the mold, one adjacent the upper position of the mold parts and the other adjacent the lower portion of the mold parts. Such an arrangement avoids the stress on a single element. 
     In addition, while the illustrated embodiment of FIGS. 1 and 2 shows a stack mold having two moveable mold parts, it is possible to have three, four or more moveable mold parts. In such case, further rack-and-pinion devices are used to achieve the required proportionality of mold part movement. 
     In operation, as the moveable mold parts  14 ,  16  move towards and away from the stationary mold part  12  in molding operations, the elements  42  and  44  move relative to the rotatable ring gear  54  located in its housing structure  36 . 
     The recess  80  in which the rack members  42 ,  44  move guided by the rollers  72  and the mounting of the free ends of the rack members  42 ,  44  to the mounting plates  30 ,  32  ensures proper operation of the stack mold within a molding machine. 
     As seen from the above discussion, by providing mounting elements which are permanently affixed to stack mold parts and by providing elements which are rapidly mounted or demounted from the mounting elements, the rack-and-pinion structure illustrated herein is very flexible and universally applicable to all stack molds. 
     In addition, by providing for fine adjustment of the position of the mold parts relative to each other, accurate molding operations are possible. Further, the device of the invention is useful with different stack molds, in view of the flexibility of operation. 
     SUMMARY OF DISCLOSURE 
     In summary of this disclosure, the present invention provides a universal rack-and-pinion structure for use with stack molds which is readily mounted thereto and demounted therefrom. Modifications are possible within the scope of this invention.