Abstract:
The invention relates to an adjustment device for a valve pin on an injection molding machine, and particularly on a multi-cavity machine, having a plurality of valve pins mounted on a common yoke plate which is actuated by a common actuator. The adjustment device includes a pin holder for holding the valve pin, and a locking member. The pin holder has two threaded portions. The first threaded portion is adjustable within a threaded receiving hole in the yoke plate. The second threaded portion is received by the locking member. The locking member has a bottom shoulder which butts against the yoke plate, and retains the pin holder in place.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/402,957, filed on Aug. 14, 2002. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to injection molding and more particularly to valve gated injection molding hot runner nozzles. 
     BACKGROUND OF THE INVENTION 
     Valve pins are well known in the art for use in controlling the flow of a molten material (melt) in an injection molding hot runner mold towards a mold cavity through a mold gate into a mold cavity. The valve pins are often controlled by an actuator, which advances or retracts the valve pin, either to vary the flow to a mold cavity or to open or close the mold gate. 
     In a multi-cavity mold, a plurality of valve pins are, in some instances, controlled using a common actuator, which advances and retracts the valve pins simultaneously. Due to differences in the molding conditions and machining tolerances at each mold cavity, however, it can occur that a valve pin for a particular cavity requires an adjustment so that it will properly seat in the mold gate to prevent plastic from leaking when the valve pin is moved to shut off the flow from the melt channel leading from the nozzle into the mold cavity. The ability to adjust the valve pin position for each individual nozzle is particularly useful when the pins are commonly actuated. To adjust a valve pin, an operator is typically required to remove the valve pin assembly, machine the valve pin to adjust the length, and re-insert the valve pin assembly into the machine. If the pin is the incorrect length, the procedure must be repeated again. This procedure is cumbersome, time consuming, and results in lost production time for the manufacturer. 
     Alternatively, the operator can insert one or more spacers to adjust the position or the length of the valve pin. While inserting spacers is easier than machining the valve pin, it is inaccurate, in that the fineness of the adjustment is limited to the thinness of the spacer. 
     There is a need for a device and method that permits fast, and accurate adjustment of valve pins. 
     SUMMARY OF THE INVENTION 
     In a first aspect, the present invention is directed to an adjustment device for a movable gating element on an injection molding hot runner mold apparatus. The device includes a holder for the gating element and a gripping portion for adjustment. The holder has a first threaded portion that is adjustably connectable to a corresponding threaded portion on a movable member connected to an actuator on the injection molding hot runner mold apparatus. In an embodiment of the first aspect, the movable gating element is a valve pin. In another embodiment of the first aspect, the holder has a second threaded portion and the device further includes a locking member, which has a corresponding threaded portion for receiving the second threaded portion. The locking member further includes a locking shoulder for contacting the movable member. In yet another embodiment of the first aspect, the second threaded portion has a larger diameter than the first threaded portion. In a further embodiment the hot runner mold apparatus has more then one movable platen and can be used to stack or tandem molding applications. 
     In a second aspect, the present invention is directed to a gating element assembly for an injection molding hot runner mold. The assembly includes a gating element, a holder for the gating element, and a gripping portion for adjustment. The gating element is movable within a melt channel in a nozzle on the injection molding hot runner mold. The holder has a first threaded portion that is adjustably connectable to a corresponding threaded portion on a movable member connected to an actuator. In an embodiment of the second aspect, the gating element is a valve pin, having a head and a pin portion and the device also has a pin cap to prevent the pin from being pushed up in the holder. 
     In a third aspect, the present invention is directed to a gating assembly for controlling melt flow through a mold gate at the discharge of a melt channel in an injection molding hot runner mold. The gating assembly includes a gating element, an adjustment device, a movable member and an actuator. The gating element is located within the melt channel and is movable to control melt flow through the gate. The adjustment device has a holder for the gating element, and has a first threaded portion. The movable member has a corresponding threaded portion for receiving the first threaded portion. The actuator is connected between the movable member and a stationary member on the injection molding hot runner mold. 
     In a fourth aspect, the present invention is directed to an injection molding hot runner mold. The hot runner mold includes at least one nozzle, a gating element, an actuator and an adjustment device. The nozzle conveys melt through a melt channel from a melt source. The nozzle communicates with a mold gate convey melt from a nozzle melt channel into a mold cavity. The gating element is movable in the melt channel, for controlling melt flow in the melt channel. The actuator is connected to the gating element for moving the gating element within the melt channel. The adjustment device is connected to the gating element and to the actuator, for adjusting the gating element relative to the mold gate. In an embodiment of the fourth aspect, the adjustment device includes a holder for the gating element. The holder has a first threaded portion, and the injection molding hot runner mold further includes a movable member having a corresponding threaded portion for receiving the first threaded portion. The movable member is connected to said actuator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made by way of example to the accompanying drawings. The drawings show various embodiments of the present invention, in which: 
         FIG. 1  is a sectional side view of a portion of an injection molding hot runner mold incorporating a valve pin adjustment device in accordance with a first embodiment of the present invention; 
         FIG. 2  is a sectional side view of one of the nozzles shown in  FIG. 1 , showing a valve pin moved to a ‘closed’ position; 
         FIG. 3  is a sectional side view of the nozzle shown in  FIG. 2 , showing the valve pin moved to an ‘open’ position; 
         FIG. 4  is a magnified view of a gating adjustment device for the nozzle shown in  FIG. 2 ; 
         FIG. 5  is an exploded side view of the gating adjustment device of  FIG. 4 ; 
         FIG. 6  is a magnified sectional side view of an alternate embodiment of a gating adjustment device in accordance with another embodiment of the present invention; 
         FIG. 7  is an exploded side view of the gating adjustment device of  FIG. 6 ; and 
         FIG. 8  is a side view of a pin holder in accordance with an alternate embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference is made to  FIG. 1 , which illustrates a sectional side view of a portion of an injection molding hot runner mold  10 , which will be used for the purposes of describing the operational aspects of the invention. 
     Mold  10  has multiple cavities, and therefore fills a plurality of mold cavities simultaneously with molten plastic for the production of injection molded articles. Mold  10  has a mold assembly  12  comprising a molding machine plate  14 , a back mold plate  16 , a movable member, which is hereinafter referred to as yoke plate  18 , a support mold plate  20 , an intermediate mold plate  22 , a nozzle mold plate  24  and a mold cavity plate  26 . Melt travels from a melt source (not shown), through mold assembly  12  through a central melt channel  28 , a manifold melt channel  31  in a manifold  30 , a plurality of melt channels  32  in nozzles  34  and finally through mold gates  35  into mold cavities (not shown). 
     Valve pin actuating assembly  36  is used to control melt flow through mold gates  35  into the mold cavities. Valve pin actuating assembly  36  comprises a plurality of valve pin assemblies  37 , yoke plate  18 , and actuators  28 . Each valve pin assembly  37  includes a movable element or valve pin  40 , and an adjustment device  42 . Valve pins  40  each comprise a pin portion  44 , which extends into melt channel  32 , and a head  46 , which is used for connecting valve pin  40  to adjustment device  42 . Actuators  38  are used to control melt flow by moving yoke plate  18 , and, in turn, valve pins  40  towards or away from mold gates  35 .  FIG. 2  shows and individual nozzle  34  with valve pin  40  in the ‘closed’ position.  FIG. 3  shows an individual nozzle  34  with valve pin  40  in the ‘open’ position. 
     Referring back to  FIG. 1 , each valve pin  40  is mounted to an adjustment device  42 , which is, in turn, mounted to yoke plate  18 , so that each valve pin  40  can be individually adjusted relative to yoke plate  18 . Adjustment device  42  permits the adjustment of valve pin  40  towards or away from gate  35  without the need for removing valve pin  40  from machine  10 . Adjustment device  42  incorporates a threaded adjustment for valve pin  40 , so that fine adjustments can be made to the position of valve pin  40  easily. Bores  47 , located in plate  16  permit access to adjustment device  42 . 
     Reference is now made to  FIG. 4 , which shows a magnifies view of adjustment device  42 . Device  42  comprise a pin holder  48  and a locking member  50 . Pin holder  48  comprises a body  52  and a pin cap  54 . Body  52  has a first threaded potion  56 , a second threaded portion  58  and a gripping portion  60 , which is preferably a hex head. First portion  56  mates with a threaded receiving portion in yoke plate  18 , which is, in this embodiment a receiving hole  62 . Second portion  58  mates with locking member  50 . Second portion  58  may have a larger diameter than first portion  56 . 
     A pin holding portion  64  inside pin holder  48 , comprises a first hole portion  66 , and a second hole portion  68 , which ends at a shoulder  70 . First hole portion  66  is adapted to hold pin portion  44  of valve pin  40 . Head  46  of pin  40  seats against shoulder  70 . A pin cap receiving portion  72  in body  52  ends at a second shoulder  74  and is threaded for receiving pin cap  54 . 
     Pin cap  54  has a gripping portion  76 , which is preferably a hex head, and a threaded portion  78  for mounting into receiving portion  72 . On the bottom of pin cap  54  is a pin retaining surface  80 , which butts against second shoulder  74  and captures pin  40  in body  52 . 
     Locking member  50  comprises a body  82  and a gripping portion  84 . Body  82  has a threaded receiving portion, which is, in this embodiment, a receiving hole  86 , for mating with portion  58  on pin holder  48 . A bottom shoulder  88  on body  82  mates with the outside surface of yoke plate  18 . 
     Reference is now made to  FIG. 5 , which shows an exploded view of the components of adjustment device  42 . To assemble and mount the device, valve pin  40  is inserted through hole  66  in body  52  of pin holder  48 . Pin cap  54  is then fastened into hole  68  on body  52 . The assembly is then installed into receiving hole  62  in yoke plate  18 , as shown in  FIG. 4 . The assembly is then adjusted within threaded hole  62  until it is positioned to the desired depth. Lastly, locking member  50  is threaded onto portion  58  of body  52  until shoulder  88  seats against yoke plate  18 . Locking member  50  acts as a locking nut, preventing pin holder body  52  from unthreading within receiving hole  62 . 
     If an adjustment is required, plate  14  is separated from plate  16 , and device  42  is accessed through bore  47  in plate  16 . Locking member  50  is unthreaded and removed, pin holder  48  is adjusted as necessary within receiving hole  62  and locking member  50  is reinstalled on portion  58 , until locking member  50  seats against yoke plate  18 . Thus, device  42  does not have to be removed from yoke plate  18  for adjustment, and the adjustment is made relatively easily and quickly. Furthermore, no machining is required in order to carry out an adjustment. 
     Reference is now made to  FIGS. 6 and 7 , which show an adjustment device  90  in accordance with another embodiment of the present invention. Device  90  is similar to device  42  in function, but is preferable for use with tapered valve pins, such as valve pin  92 . Valve pin  92  has a head  94  and a pin portion  96  having a tapered bottom. If a tapered valve pin, such as pin  92  is adjusted too far into a melt channel, the bottom of pin portion  96  can contact the melt channel during closing of the gate and can therefore be subject to shock. Device  90  incorporates a spring therein to reduce the shock if valve pin  92  contacts the melt channel. 
     Device  90  comprises a pin holder  98  and a locking member  100 . Pin holder  98  comprises a body  102 , a spring retainer  104 , a spring  106  and a pin cap  108 . Body  102  is similar to body  52  on pin holder  48  and has first and second portions  110  and  112 , which are both threaded, and a gripping portion  114 , which is preferably a hex head. A first hole portion  116  receives pin portion  96  of valve pin  92 , and a second hole portion  118 , which ends at shoulder  120 , receives head portion  94  of valve pin  92 . A third hole portion  122  ends at a shoulder  124 . Hole portion  122  receives spring retainer  104 . A fourth hole portion  126  ends at a shoulder  128  and is threaded for receiving pin cap  108 . 
     Spring retainer  104  seats against shoulder  124 , and holds spring  106 . Spring  106  is preferably a stack spring, but which may alternately be a coil spring or another suitable type of spring. Spring  106  is held on retainer  104  by a snap ring  130  which mates with a groove in retainer  104 . 
     Pin cap  108  is similar to pin cap  54  and has an outside threaded portion  132  which mates with hole portion  126 . A bottom shoulder  134  on pin cap  108  butts against shoulder  128  in hole  126 . As well, shoulder  134  butts against spring  106 . A hole  136  inside pin cap  108  provides clearance for the top of retainer  104 . 
     Locking member  100  is similar to locking member  50  and includes a body  138  and a gripping portion  140 . Body  138  has a threaded receiving hole  142  and a bottom shoulder  144 . Gripping portion  140 , body  138 , receiving hole  142 , and bottom shoulder  144  are all similar to gripping portion  84 , body  82 , receiving hole  86 , and bottom shoulder  88  on locking member  50 . 
     In the event that valve pin  92  contacts the melt channel, valve pin head  94  pushes against the bottom of spring retainer  104 , pushing spring retainer  104  upwards, thus compressing spring  106 . Thus, spring  106  relieves the shock incurred by pin  92 . 
     Reference is now made to  FIG. 8 , which shows a pin holder in accordance with another embodiment of the present invention. Pin holder  150  is similar to pin holder  98 , but has a single threaded portion  152 , which is divided into first and second portions  154  and  156 . Thus, portions  154  and  156  have the same diameter and are integral with each other. Portion  154  threads into the yoke plate, leaving portion  156  exposed for the mounting of a locking member. 
     By using a threaded pin holder, relatively fine adjustments may be achieved quickly and easily for valve pins in an injection molding machine. Furthermore, using a locking member to prevent the movement of the pin holder prevents the valve pin adjustment from wandering from its previously set position. Adjustments can be carried out quickly and easily without the need for removal and machining of the valve pin, and without the need for spacers. 
     While the embodiments of the present invention include have been disclosed to operate with molding machines incorporating valve pins to open and close mold cavity gates, the present invention can operate with molding machine wherein the gates are open and closed by other types of gating element. 
     While the present invention has been described with respect to a multi-cavity injection molding hot runner mold, the invention applies to a single cavity hot runner mold as well. 
     As will be apparent to persons skilled in the art, various modifications and adaptations of the apparatus described above are possible without departure from the present invention, the scope of which is defined in the appended claims.