Abstract:
A valve pin actuating device for a hot runner apparatus includes a yoke plate coupled to actuators. The actuators are generally disposed at the ends of the yoke plate and are configured to move the yoke plate in a direction parallel to a longitudinal axis of the valve pins. A deflection distributor apparatus is coupled to the yoke plate. The deflection distributor apparatus is connected to a first force distributor plate, to which the valve pins are connected. The deflection distributor apparatus includes a second force distributor plate and a third force distributor plate. Rods are disposed between the yoke plate and the third force distributor plate, between the third force distributor plate and the second force distributor plate, and between the second force distributor plate and the first force distributor plate holding the valve pins.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. provisional patent application No. 60/814,548 filed Jun. 19, 2006, which is hereby incorporated by reference in its entirety herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention is relates to an injection molding hot runner nozzle valve pin actuating apparatus, more particularly an actuating apparatus which simultaneously actuates a plurality of valve pins. 
     2. Related Art 
     In injection molding, when melt material is delivered to one or more mold cavities, it is sometimes desired to simultaneously actuate the valves of a plurality of nozzles that regulate the flow of the melt. This can be the case when there are many nozzles each serving its own cavity or when many nozzles serve one cavity. 
     An injection molding apparatus can include an array of nozzles that have valves that are simultaneously actuated via a yoke plate that is connected to one or more actuators; this is particularly useful in small pitch applications where there is not enough room between nozzles to accommodate individual actuators for each nozzle. One problem that can occur with this type of apparatus is yoke plate deflection caused by pressurized melt in the mold cavity pushing back on valve pins. This can result in larger than acceptable witness marks on the finished product or back-leakage of melt material from the cavity. This problem can affect any kind of injection molding where yoke plates are used. 
     Conventional solutions to yoke plate deflection include thickening the yoke plate. However, thickening the yoke plate adds to the stack height of the injection molding apparatus and adds significant cost to the injection molding apparatus. 
     SUMMARY OF THE INVENTION 
     In an embodiment of the present invention, a valve pin actuating device for a hot runner apparatus includes a yoke plate coupled to actuators. The actuators are generally disposed at the ends of the yoke plate and are configured to move the yoke plate in a direction parallel to a longitudinal axis of the valve pins. The valve pins are coupled to a first force distributor plate. A deflection distributor apparatus is coupled to the yoke plate and disposed between the yoke plate and the first force distributor plate. The deflection distributor apparatus includes a second force distributor plate and a third force distributor plate. Rods are disposed between the yoke plate and the third force distributor plate, between the third force distributor plate and the second force distributor plate, and between the second force distributor plate and the first force distributor plate holding the valve pins. 
     In another embodiment of the present invention, a valve pin actuating device includes a yoke plate connected to actuators and movable with respect to a mold clamp plate by the actuators. A plurality of force distributor plates are connected to the yoke plate and a plurality of valve pins are connected to the force distributor plates. Rods form a bearing connection between the yoke plate and the force distributor plates. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Embodiments of the present invention will now be described more fully with reference to the accompanying drawings where like reference numbers indicate similar structure. 
         FIG. 1  is a perspective cross-sectional view of a mold assembly according to a first embodiment of the invention. 
         FIG. 2  shows a close-up partial sectional view  200  of the deflection distributor apparatus of the mold assembly of  FIG. 1 . 
         FIG. 3  is a top view of the mold assembly of  FIG. 1  without hidden lines shown. 
         FIG. 4  is a top view of the mold assembly of  FIG. 1  with hidden lines shown. 
         FIG. 5  is simplified side cross-sectional view of the mold assembly of  FIG. 1 . 
         FIG. 6  is a close-up cross-sectional view  600  of four of the valve pin adjustment devices of  FIG. 1 . 
         FIG. 7  is simplified side cross-sectional view of another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a mold assembly  10  according to a first embodiment of the invention. The mold assembly  10  comprises a mold clamp plate or back plate  102 , below which a conventional mold plate can be disposed, such mold plate holding a manifold  103  fixed with respect to the back plate  102  and an array of nozzles  104  (only one shown for clarity) connected to the manifold  103  to deliver melt to a mold cavity or cavities  105 . As would be apparent to one of ordinary skill in the art, such a manifold  103  conventionally includes a manifold channel that delivers melt from a sprue to nozzle channels in the nozzles  104 , through mold gates, and into the mold cavity or cavities  105 . In addition,  FIG. 1  omits other, well-known components such as additional mold pates, alignment pins, bolts, etc for clarity. At each end of the mold clamp plate  102  is an actuator assembly  106  that can comprise a linear electric actuator, a hydraulic actuator, a pneumatic actuator, or any other actuator known in the art. The actuator assemblies  106  are connected to and adapted to move a yoke plate  108  up and down along an axis X. Connected to the yoke plate  108  is a deflection distributor apparatus  112 , which is connected to a first force distributor plate  114 . The first force distributor plate  114  has valve pins  116  connected thereto, such valve pins  116  running through holes  117  in the mold clamp plate  102  and controlling the flow of melt from the tips of the nozzles  104  to the mold cavity or cavities  105 . The first embodiment has eight valve pins  116 , yet any amount is acceptable. The deflection distributor apparatus  112  transfers force from the yoke plate  108  to the first force distributor plate  114  such that when the actuator assemblies  106  move the yoke plate  108  up along the axis X the first force distributor plate  114  moves the valve pins  116  up likewise, and when the actuator assemblies  106  move the yoke plate  108  down along the axis X the first force distributor plate  114  moves the valve pins  116  down likewise. In this way, the actuator assemblies  106  can be used to control the flow of melt through the nozzles  104  into the cavity or cavities  105 , and can do so in a synchronized manner. When hydraulic or pneumatic actuator assemblies are selected, the first force distributor plate  114  can act as a stop against the mold clamp plate  102 . This may be unnecessary when the actuator assemblies  106  are selected to comprise linear electric actuators. 
       FIG. 2  shows a close-up view  200  of a portion (as indicated in  FIG. 1 ) of the deflection distributor apparatus  112 . The deflection distributor apparatus  112  includes a second force distributor plate  204 , a third force distributor plate  202 , an upper rod  206 , two middle rods  208 , and four lower rods  210 . The third force distributor plate  202  can serve to compensate for any tilt of the yoke plate  108  between the actuator assemblies  106 , and as such the third force distributor plate  202  can be omitted, if such tilt does not exist or can be neglected. The upper rod  206  provides a bearing connection between the yoke plate  108  and the third force distributor plate  202 . The middle rods  208  provide a bearing connection between the third force distributor plate  202  and the second force distributor plate  204 . Likewise, the lower rods  210  provide a bearing connection between the second force distributor plate  204  and the first force distributor plate  114 . The rods are positioned in rod locating grooves  210   a  and  210   b  located on the plates  202 ,  204 ,  114 . The rod locating grooves  210   a  and  210   b  can have rounded, rectangular, or other cross-sections. 
     A bolt  212  or other means for connecting is further provided to keep the plates  108 ,  202 ,  204 ,  114  sandwiched together. The bolt  212  is threaded on a narrowed portion  213   a  at the tip to mate with the force distributor plate  114 . The remainder of the bolt  212  comprises an unthreaded wider portion  213   b . This allows for easier assembly and disassembly of the bolt  212  and plates  108 ,  202 ,  204 ,  114 . It should be noted that the bolts  212  mainly act to keep the plates  108 ,  202 ,  204 ,  114  sandwiched together (e.g., during assembly or when the yoke plate  108  moves up), and are not required to carry any appreciable load when the yoke plate  108  moves down. Any number of bolts  212  can be used. 
     Further shown in  FIG. 2  is one of the valve pins  116 . It can be seen that the head of the valve pin  116  is flattened. The head of the valve pin  116  is coupled to the valve pin adjustment device  214 , which can be used to adjust the height of the valve pin  116 . The end (not shown) of the valve pin  116  opposite the flattened end is for regulating the flow of melt in the respective nozzle  104 , as known in the art. 
     To provide access to the valve pin adjustment device  214 , the yoke plate  108 , the third force distributor plate  202 , and the second force distributor plate  204  have holes that form access openings  216 . An operator can use an access opening  216  to adjust the valve pin adjustment devices  214  so as to adjust the heights (along axis X) of the valve pins  116  without disassembly of the mold assembly  10 . 
       FIG. 2  also shows a guide rod  218  connected to the bottom of the first force distributor plate  114  and a guide hole  220  disposed in the mold clamp plate  102 . The guide rod  218  mates with the guide hole  220  and is for preventing the first force distributor plate  114  from shifting with respect to the mold clamp plate  102 . In this embodiment four mating sets of guide rods  218  and guide holes  220  are provided, although more or fewer are acceptable. 
       FIG. 3  and  FIG. 4  show top views of the mold assembly  10  without hidden lines and with hidden lines, respectively. As shown in  FIG. 4 , rods  208 ,  210  are disposed on either side of the access openings  216 . Were the access openings to be eliminated, the rods  208 ,  210  could be single continuous rods like the rod  206 . In addition,  FIG. 4  shows two second force distributor plates  204 . Alternatively, one longer plate can be used. 
     Referring to  FIG. 5 , a simplified side cross-sectional view of the mold assembly  10  is illustrated. When the valve pins  116  are positioned to close the valves, back-pressure from the mold cavity  105  pushes the valve pins  116  in a direction  502 . Forces on the yoke plate  108  from the actuator assemblies are shown by arrows  512 . The forces from the back pressure on the valve pins act against the forces  512 . In a conventional configuration, wherein the valve pins are coupled to the yoke plate, bending of the yoke plate due to the forces acting on the ends of the yoke plate and forces from the valve pins causes yoke plate  108  to deflect into an arc type shape, thereby causing the valve pins of equal length to extend to different heights and to be other than vertical. In the embodiment shown in  FIG. 5 , the forces from the valve pins are transferred to the second force distributor plates  204  through the lower rods  210  and to the third force distributor plate  202  through the middle rods  208 . Similarly, these forces are transferred to the yoke plate  108  via the upper rod  206 . The arrangement of rods  206 ,  208 ,  210  and plates  108 ,  202 ,  204 ,  114  and valve pins  116  prevents deflection of the first force distributor plate  114 , which ensures that the desired closure of all the valves can be attained. Whether or not the yoke plate  108  or second and third force distributor plates  204 ,  202  flex is unimportant since the first force distributor plate  114  remains substantially flat. When the valve pin adjustment device  214  of each valve pin  116  is properly adjusted, witness marks on the end product(s) can be minimized and/or made uniform, i.e., no abnormally large witness marks due to deflection of the yoke plate  108  or other plates. As can be seen by the arrows  514 , the forces on the first force distributor plate  114  are substantially equal over the length of the first force distributor plate  114 , and the corresponding forces on the valve pins  116  are acceptably uniform (i.e., are not so different as to cause a problem). 
       FIG. 6  illustrates a close-up view  600  of a portion (as indicated in  FIG. 1 ) of four of the valve pin adjustment devices  214 . Each valve pin adjustment device  214  comprises a valve pin holder  602 , two dowel pins  604 , and a lock nut  606 . The valve pin holder  602  has a recess for receiving the flattened head portion of the valve pin  116 . The valve pin  116  is secured in the valve pin holder  602  by dowel pins  604 . The valve pin holder  602  has an external thread that mates with a thread in the force distributor plate  114 . The height of the valve pin holder  602  and thus the height of the valve pin  116  and the closing position at the nozzle tip end can be adjusted by turning the valve pin holder  602  in the thread. When a desired height is achieved, the lock nut  606  can be threaded onto the thread of the valve pin holder  602 . At any time, an operator can, via an access opening  216 , adjust heights of the valve pins  116  by way of the lock nuts  606  and threaded valve pin holders  602 . 
     The yoke plate  108 , third force distributor plate  202 , second force distributor plate  204 , first force distributor plate  114 , and rods  206 ,  208 ,  210  may be made from any material suitable for use in an injection molding apparatus environment, for example, tool steel. 
     In other embodiments, more or fewer actuator assemblies  106  can be used. The number of force distributor plates  202 ,  204  and the respective pins can also be increased or decreased depending on requirements. Likewise, the number of valve pins  116  can be changed to suit any type of molding application. 
       FIG. 7  illustrates another embodiment of the present invention in simplified form, which may be used in a mold assembly, such as the mold assembly  10  previously described. Components, aspects, and advantages of the other embodiments also apply to this embodiment. 
     A yoke plate  708  and force distributor plates  714  are coupled by rods  710  that sit in rod locating grooves  710   a ,  710   b . The rods  710  provide a bearing connection between the yoke plate  708  and the force distributor plates  714 . Bolts  712  or other means for connecting are provided to keep the force distribution plates  714  coupled to the yoke plate  708 . To this end, the bolts  712  are threaded into threaded bores of the force distribution plates  714 , but pass through wider, unthreaded bores in the yoke plate  108 . Therefore, the bolts  712  mainly act to keep the force distribution plates  714  coupled to the yoke plate  108  (e.g., during assembly or when the yoke plate  108  moves up), and are not required to carry any appreciable load when the yoke plate  108  moves down. Valve pins  116  are connected to the force distributor plates  714  and can be moved up and down via actuators (e.g., actuator assemblies  106 ) connected to the yoke plate  708 . Any number of bolts  712  can be used. 
     It can be seen from  FIG. 7  that the valve pins  116  will likely not all have the same force because of their different locations on the force distributor plates  714 . However, the rods  710  and force distributor plates  714  do make the forces in the valve pins  116  more uniform than they would be with only a yoke plate, as in the prior art. This is because the geometry makes the forces in the rods  710  approximately equal. As a result, the forces on the valve pins  116  are acceptably uniform (i.e., are not so different as to be problematic). If such level of uniformity is acceptable for a given application, then this embodiment has the advantage of a reduced number of parts. 
     The many features and advantages of the invention are apparent from the detailed specification and, thus, it is intended by the appended claims to cover all such features and advantages of the invention that fall within the true spirit and scope of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.