Abstract:
A hot runner injection molding apparatus includes a manifold for transferring molten plastic into a channel to a mold gate. A valve pin extends at least partially through the channel and is reciprocally movable from a retracted position to an extended position to close the mold gate when the valve pin is in the extended position, and to open the mold gate when the valve pin is in the retracted position. A valve pin moving mechanism is coupled with the valve pin to directly move the valve pin to the extended position; and a resilient coupling is located between the valve pin and the valve pin moving mechanism for normally moving the valve pin to the retracted position.

Description:
BACKGROUND 
   This invention relates to hot runner injection molding apparatus, and in particular, to the operating mechanism for a valve pin in such a molding apparatus. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a partially cut-away front perspective view of an embodiment of the invention; 
       FIG. 2  is a cross-sectional view of a portion of the embodiment shown in  FIG. 1  in a first position of operaton; 
       FIG. 3  is a cross-sectional view of a portion of the embodiment shown in  FIGS. 1 and 2  in a second position of operation; and 
       FIG. 4  is a cross-sectional view of a portion of the embodiment shown in  FIG. 1  illustrating another feature of the operation of the embodiment of  FIG. 1 . 
   

   DETAILED DESCRIPTION 
   Reference now should be made to drawings, in which the same reference numbers are used throughout the different figures to designate the same or similar components. The embodiment of the invention which is shown in  FIGS. 1 through 4  is incorporated into an injection molding apparatus for a multi-cavity mold employing a hot runner manifold with gated nozzles. Such multi-cavity molds typically are used to produce large quantities of molded plastic parts with a relatively high repetition cycle. The molds may have a large number of cavities, for example sixteen to fifty, to simultaneously produce parts from each of the cavities in each cycle of operation of the molding machine. In order to produce parts with minimal gate remnants on them, a valve gate often is employed for each of the different cavities. 
   Valve gates consist, essentially, of an orifice or small hole through which the molten plastic is introduced into the cavity for producing the desired part. These orifices are closed by means of a precision fitted valve pin, which is moved forward into the orifice to close off the gate and retracted to open the gate for the next cycle of operation. 
   The opening and closing of the valve gates occurs at very high rates of speed, with operating cycles of several hundred times per hour in a typical multi-cavity mold. Generally, all of the valve gates in a multi-cavity mold are simultaneously activated by a single activation plate which is hydraulically, pneumatically, or mechanically. All of the gates are opened or closed at every cycle. If for some reason it is desirable to disable a particular cavity (which may be producing defective parts, for example), it generally is necessary to close down the entire system and physically remove or alter the pistons which activate the valve pin for the gate associated with the cavity to be disabled. 
   In many hot runner injection molding devices, separate heating coils are employed in conjunction with each of the channels in the hot runner manifold associated with each different valve gate. This maintains the fluidity of the plastic during the operation of the mold, and the hot plastic typically flows around the valve pin in the region where the valve pin moves into and out of engagement with the gate or orifice for introducing molten plastic into the associated cavity. 
   The general description which has been given above is typical for many hot runner injection molding machines; and the embodiment of the invention which is disclosed in conjunction with  FIGS. 1 through 4  is directed to that portion of a hot runner molding machine which involves the operation of the reciprocal movement of the valve pins for the valve gates in such a machine. Since other components of the machine with which the embodiment of  FIGS. 1 through 4  are used are conventional, those components have not been disclosed in order to avoid unnecessary cluttering of the drawings. It is to be understood, however, that the operation of such a machine including the supply of plastic to the machine, the dividing of the melt and the individual heating coils for each of the channels for supplying plastic to the valve gate are standard. The hydraulic, pneumatic or mechanical operation of the reciprocal movement of an activation plate for opening and closing the valve gates also is standard. The right-hand portion of  FIG. 4  diagrammatically illustrates a hydraulic or pneumatic control for such an activation plate  18 ; but the manner in which the activation plate  18  is reciprocally moved within the mold apparatus  10  is conventional and may be of any suitable type desired by a particular machine manufacturer. 
     FIG. 1  illustrates a partially cut-away perspective view of a portion of four channels of a hot runner injection molding apparatus illustrating the operation of such an apparatus to supply molten plastic to valve gate orifices  13  under the control of the reciprocal operation of valve pins  14  moving through individual channels  12  associated with each of the valve pins  14  to supply molten plastic to mold cavities (not shown) located beneath the orifices or openings  13  associated with each of the cavities of the mold. It should be noted that while  FIG. 1  shows four channels of a multi-cavity mold, the number of channels and cavities may be less than four, or greater than four (for example, sixteen to fifty as described above). The operation of each individual valve pin  14 , however, is the same throughout the entire multi-cavity mold. 
     FIG. 1  shows parts associated with four cavities, while  FIGS. 2 and 4  show parts associated with two cavities; and  FIG. 3  shows parts associated with only a single cavity. The operation is the same for each cavity, however many cavities are employed in a particular molding apparatus. 
   In  FIGS. 1 through 4 , an activation plate  18  is located in the molding apparatus for reciprocal movement (vertically, as shown in  FIGS. 1 through 4 ), upward and downward, to open and close the valve gates or orifices  13  by means of the retraction and extension of the valve pins  14  passing through the individual channels  12  associated with each of the valve gates  13 . The mechanism for moving this activation plate  18  between its uppermost and lowermost positions is diagrammatically shown in the right-hand portion of  FIG. 4 ; but no specific reference is made to that portion, since that operation is standard in whatever molding apparatus the embodiment of  FIGS. 1 through 4  may be used. As mentioned previously, such reciprocal movement of an activation plate in multi-cavity hot runner molds may be accomplished in a variety of different ways. 
     FIGS. 1 and 2  illustrate the interconnections between the activation plate  18  and the shafts  14   a  of the valve pins  14  to control the reciprocal retraction and extension of the valve pins into the valve gate orifices  13 . A sleeve  28 , having a cylindrical configuration and having a hollow interior cylindrical shape, is threaded into the activation plate  18  for each of the valve pin shafts  14  to reciprocally move within an associated cylindrical aperture  16  in the block of the mold  10 . The bottom of each sleeve  28  comprises a shoulder which rests on top of a corresponding connector  22 , also preferably of a cylindrical configuration. Each connector  22  has a slot in it for carrying the T-shaped top  20  of a corresponding valve pin  14 , as shown most clearly in  FIG. 1 , and also shown clearly in  FIGS. 2 through 4 . 
   The bottoms of each of the sleeves  28  are open and have a valve pin extension member  24  passing through them and threaded into a recess  23  in the corresponding connector  22  to partially compress a coil spring  32  between a shoulder  30  on the inside of each of the sleeves  28 , and a corresponding shoulder  26  located at the top of each of the members  24 . The spring  32  is illustrated as a compression coil spring which surrounds the corresponding cylindrical extension member  24 . 
   Each spring  32  is under some compression when it is in its relaxed or normal state of operation, with the component parts having the relative positions shown in  FIG. 2 . In this position of operation, the top surface of each connector  22  is in direct contact with the bottom of the corresponding sleeve  28  to form a metal-to-metal contact. Similarly, there is metal-to-metal contact between the T-shaped top  20  of the valve pin  14  and the connector  22 ; so that when the activation plate  18  is moved to its downward position to drive the valve pin  14  into the valve gate orifice  13 , a direct or solid steel-on-steel contact is made throughout the entire assembly. This is readily apparent from an examination of  FIG. 3 . 
   When the activation plate  18  is moved upward in the direction of the arrows shown in  FIG. 2  to lift the valve pins  14  upward to open the valve gates at the orifices  13 , the normal operation is with the parts in the relative positions shown in  FIG. 2 . All of the metal-to-metal contact mentioned above remains. The compression force of the spring  32  is selected to be such that it is greater than the frictional forces between the pins  14  and the molten plastic in the pin guides or channels  12 . In this position of operation, the pins  14  are pulled upward to the retracted position, leaving a space  40  between the bottom of the connectors  22  and the top of the mold machine assembly located immediately below the activation plate. The upper limits of movement for the activation plate  18  are established by blocks  36 ; and its lower limits of movement are established by blocks  34 , as illustrated in  FIGS. 2 and 3 . 
   When the injection of molten plastic into the cavities has been completed, the activation plate  18  again is moved downwardly in the direction of the arrows shown in  FIG. 3  to drive the valve gate pins  14  in a tight metal-to-metal direct movement, with all of the parts in contact as shown in  FIG. 3 , to close the various orifices  13 . The cycle of moving the activation plate  18  back and forth between the position shown in  FIG. 2  and the position shown in  FIG. 3  is continuously repeated. So long as all of the molded articles are of a quality to pass inspection and so long as no leakage or dripping of molten plastic from a closed valve gate  13  takes place, this is the operation which continuously occurs. 
   Occasionally, however, a defective part is produced in one or more of the cavities of a large multi-cavity mold. In such a case, it is desirable to be able to discontinue making parts from such a cavity until some later time when the mold machine is turned off for repair or is otherwise idle to allow the repair or replacement of parts necessary to operate the machine with all of the cavities producing parts. For large multi-cavity machines, it is highly desirable to be able to turn off a defective cavity “on the fly” requiring little or no down time of the machine, while still allowing it to produce parts from those cavities which are properly functioning. For example, if one cavity out of a 20 cavity machine should somehow become defective for any reason, it is desirable to be able to turn off only that cavity and prevent defective parts from being made therein from one cycle to another, or within a very few cycles of the machine, without stopping the operation of the machine to accomplish this purpose. 
   As mentioned previously, many multi-cavity hot runner machines employ separate heating coils for the sleeves or channels which surround the valve pins in order to effectively control the temperature of the plastic at the point where it is delivered into the cavity. This is a standard procedure in many machines, and for that reason, the details of the heating coils and the controls for these heating controls are not illustrated in the drawings. The machine which is illustrated, however, is employed in conjunction with such individually controlled heating coils around each of the pin guide channels  12 . 
   Reference now should be made back to  FIG. 1 , where the right-hand channel  12  is shown filled with solidified plastic  48 . This is representative of a pin guide channel where the heating coil has been turned off to allow the plastic in the sleeve or pin guide  12  to harden around the shaft of the corresponding valve pin identified as valve pin shaft  14 A in  FIG. 1 . If a defective cavity is determined upon inspection of parts produced by a machine, the heating coil for the channel  12  for that cavity is turned off; and the plastic  48  is allowed to solidify, as diagrammatically illustrated in  FIG. 1 . This plastic then freezes around the shaft  14 A of the valve pin associated with it to produce high friction to hold the valve pin  14  in its downward or closed position of operation. 
   On the next cycle of operation of the activation plate  18  to its upward position, as illustrated in  FIG. 4 , the connector  22  which is secured to the T-shaped top  20  of the assocaited valve pin  14 A is held in its downward position by the friction of the solidified plastic  48  (shown in  FIG. 1 ). The activation plate  18 , however, continues to move in the upward direction shown in  FIG. 4 , to its uppermost position comparable to the position shown in  FIG. 2 . The sleeve  28  for the pin or pins  14 A, however, moves upwardly, compressing the spring  32  between the shoulder  30  on the inside of the sleeve  26  and the shoulder  26 . This produces a gap  50  which is equal to the gap  40  described previously. Continued operation of the activation plate in its reciprocal movement, as illustrated in  FIGS. 1 and 2 , takes place for the remainder of the cavities associated with normal or non-frozen valve pins  14 , while at the same time the spring force of the springs  32  for the captivated or frozen valve pins  14  is less than the frictional force between the hardened plastic and the valve pin shafts  14 A. Thus, the springs  32  associated with a captivated or closed valve pin  14  alternately compress in the retracted position and extend when the activation plate  18  moves to the extended position without requiring any physical shutdown or intervention whatsoever in conjunction with the operation of the machine. The only difference is that the heating coil power is removed from the cavity where the valve pin  14  is to remain in its extended position to close the gate orifice  13  of the associated valve gate. 
   The foregoing description of an embodiment of the invention is to be considered as illustrative and not as limiting. For example, while a coil spring  32  has been illustrated as the resilient coupling between the valve pin and the activation plate for moving the valve pin to its retracted position, other resilient interconnections could be provided as well. Various other changes and modifications will occur to those skilled in the art for performing substantially the same function, in substantially the same way, to achieve substantially the same result, without departing from the true scope of the invention as defined in the appended claims.