Abstract:
A valve pin actuator is disclosed that includes a cylinder mounted to the clamping plate, a piston slidably mounted in the cylinder, and a valve pin assembly carried by the piston. A hydraulic or pneumatic circuit is provided for controlling the movement of the piston, and in turn translation of the valve pin between the seated and unseated positions. The valve pin assembly includes a first part removably secured to the piston so as to translate therewith, and a second part for receiving the valve pin and secured to said manifold. The actuator assembly enables removal of the clamping plate without removal of the valve pin assembly, and also adjusting of the valve pin without removal of the clamping plate. The assembly further provides a clearance between the piston and valve pin assembly, to accommodate expansion and movement of the manifold that would otherwise cause a side load to be exerted on the valve pin.

Description:
This application is a divisional of application Ser. No. 08/874,962, filed Jun. 13, 1997, entitled VALVE PIN ACTUATOR, now U.S. Pat. No. 5,894,025. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates in general to improvements in valve gate actuators used in injection molding systems. Although not limited to any particular field of use, the actuator of the present invention is in particular useful for the fabrication of large molded parts such as, for example, automotive bumper fascia. 
     2. Description of the Related Art 
     In hot runner systems used in injection molding, valve pins are used to open and close the gate to a cavity in the mold in which the molded part is formed. Typically, the valve pin is opened prior to the start of injection allowing plastic to flow into the cavity of the mold. The valve pin is maintained in the open position while the melt material is being packed in the cavity to form the molded part. At the end of packing, the pin is closed to eliminate any drooling from the hot runner nozzle and eliminate any vestige that would be left on the molded part by forming a smooth surface with the inner surface of the mold cavity. 
     The valve pin is typically located in the center of the bore of the hot runner nozzle. In a multiple gate system that uses a plurality of nozzles, the nozzles typically will be connected to a heated manifold, which in turn receives the machine nozzle from the injection molding machine. The tip of the valve pin extends to the gate of the mold. From its tip, the valve pin extends through the hot runner nozzle, through a bore in the manifold, and is connected at one end to an actuator located above the manifold and attached to a top clamp plate. A valve pin cylinder in the actuator is usually actuated using either hydraulic or pneumatic pressure. 
     In hot runner systems, that there are two basic techniques for providing valve pin actuators. The first technique is to build the hydraulic actuator assembly into the top clamp plate. With this product, when performing maintenance on, or disassembling, the system, it is necessary to allow the manifold to cool, then remove the valve pin from the hot runner manifold prior to removal of the top clamp plate. This can require a significant amount of time. Since the valve pin is precision machined to fit at the gate, great care must be taken when replacing the valve pin. Molds for large automotive parts are very large, thus, ease of assembly and disassembly for maintenance of the hot runner is an important issue. 
     A further drawback of prior systems is the fact that the valve pin itself is typically mounted in the actuator in a relatively fixed position and is free to move only in one direction. The manifold will expand relative to the top clamp plate when heated. Thus, the valve pin actuator has to be positioned so that the pin can slip relative to the actuator in the expansion direction. If the alignment or predicted expansion direction is off, the pin sees a side load resulting from the expansion of the manifold, possibly resulting in binding of the pin in the valve pin bushing, or even pin breakage. Thus, prediction of the line of expansion is necessary along with precise alignment of the valve pin. 
     Another type of actuator has the entire hydraulic actuator assembly bolted to the hot runner manifold. This system includes through holes in the top clamp plate to provide clearance for the actuator assembly. There are several drawbacks associated with this system. For example, because the actuator cylinder is directly bolted to the heated manifold, the actuator cylinder needs water channels formed therein for cooling. Further, because it is bolted directly to the manifold, flexible water and hydraulic lines must be run to each valve gate actuator between the manifold and the top clamp plate. It can be cumbersome to position these lines, and they can get hot due to proximity to the manifold causing deterioration of hoses and fittings. Leakage can result. If hydraulic fluid contacts the hot manifold, hazards may result. 
     Accordingly, it is an object of the present invention to provide an improved valve pin actuator, particularly wherein the actuator itself can be at least partially disassembled without requiring removal of the valve pin. 
     Another object of the present invention is to provide a valve pin actuator in which the cylinder and piston along with the hydraulic fluid lines are retained within the top clamp plate, while the valve pin assembly itself stays with the hot runner system. 
     Still another object of the present invention is to provide an improved valve pin actuator wherein the actuator can be at least partially disassembled without the need to drain the hydraulic fluid lines, and without the need to remove the valve pin from the hot runner manifold. 
     A further object of the present invention is to provide an improved valve pin actuator that provides for a clearance between the actuator piston and actuator cap. This clearance allows for relative expansion between the hot runner manifold and the top clamp plate in any direction, without putting a significant side load force on the valve pin. 
     Still another object of the present invention is to provide an improved valve pin actuator that provides for a more simplified operating hydraulic circuit. 
     SUMMARY OF THE INVENTION 
     In one illustrative embodiment of the invention, an injection molding system is provided that includes a valve pin actuator adapted for mounting between a plastic distribution manifold and an overlying clamping plate. The valve pin is adapted to extend through an injection nozzle and positioned to seat and unseat at a mold gate. 
     The valve pin actuator includes a cylinder mounted to the clamping plate; a piston slidably mounted in the cylinder; a valve pin assembly carried by the piston and for holding a top end of the valve pin; and a circuit coupled to said piston to control sliding movement thereof and in turn translation of said valve pin between the seated and unseated positions. 
     The valve pin assembly includes a first part removably secured to the piston so as to translate therewith, and a second part for receiving said valve pin and secured to said manifold. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Numerous other objects, features and advantages of the present invention will be apparent based upon the following description of drawings. 
     FIG. 1 is a cross-sectional side view of a preferred embodiment of the valve pin actuator as employed in an injection molding system; 
     FIG. 2 is a top plan view of the valve pin actuator as taken along line  2 — 2  of FIG. 1; 
     FIG. 3 is an enlarged fragmentary cross-sectional side view of the assembly of FIGS. 1 and 2 as taken along line  3 — 3  of FIG. 2; 
     FIG. 4 is a somewhat schematic cross-sectional side view of the valve pin actuator similar to that illustrated in FIG. 3, but illustrating both fluid ports simultaneously and the piston in its “up” position; 
     FIG. 5 is also a somewhat schematic cross-sectional side view of the valve pin actuator as illustrated in FIG. 4, but with the piston shown in its “down” position; 
     FIG. 6 is an enlarged fragmentary cross-sectional side view of the valve pin actuator detailing the valve pin actuator as taken along line  6 — 6  of FIG. 4; 
     FIG. 7 is a cross-sectional plan view taken along line  7 — 7  of FIG. 5; 
     FIG. 8 is a somewhat schematic exploded cross-sectional side view showing removal of the clamping plate and actuator body without requiring the disconnection of any hydraulic hoses or the valve pin; and 
     FIG. 9 is an exploded perspective view of the valve pin actuator showing the various components thereof. 
    
    
     DETAILED DESCRIPTION 
     Reference is now made to a preferred embodiment of the present invention as illustrated in FIGS. 1-9 herein. In particular, FIGS. 1-3 illustrate an injection molding system  10  used to mold a plastic part. As illustrated, there is a mold part  12 , typically called a core block, and a mold part  14 , typically called a cavity block. Disposed over the upper mold part  14  is the hot runner manifold  16 . As illustrated in, for example, FIGS. 1 and 3, the hot runner manifold  16  supports nozzles  18 , which are threadably screwed therein. About each nozzle  18  there is provided a heater  20 , for maintaining the melt material passing through the nozzle at its process temperature. Also, heat pipes may be employed in the nozzle  18 , alone, or in conjunction with the band heaters  20 , such as illustrated in U. S. Pat. No. 4,389,002. 
     As illustrated in FIGS. 1 and 3, between mold parts  12  and  14 , there is a cavity  22  that determines the contour of the molded part being produced. Also, as noted in particular in FIG. 3, at the end of the nozzle  18 , there is provided a nozzle tip  24 , disposed about a nozzle insert  26 . 
     FIG. 3 also illustrates the valve pin  28  in its closed position. The valve pin  28  extends through a central bore in the nozzle  18 , and, in the embodiment illustrated, has a tapered end  30  that mates with a like tapered gate  32  in the mold. It should be noted that the invention is not limited to a particular type of nozzle arrangement, as different tip and insert configurations are possible. For example, the gate could be formed in the tip, with the valve pin mating with the tapered surface of the tip. Furthermore, as shown in FIGS. 1 and 3, when gating directly onto an angled part surface, the valve pin can be contoured to match the part. 
     FIG. 1 also illustrates the machine nozzle  34  of the injection molding machine that feeds the molten plastic material through a porting arrangement that extends through the top clamping plate  36 . This porting arrangement also feeds through a bore  38  in the hot runner manifold  16 . The bore  38  feeds each of the nozzles  18 . 
     FIG. 1 also illustrates spacers  42  for properly positioning the clamping plate  36  relative to the mold part  14 . The clamping plate  36  is cooled as illustrated by the water channels  44 . To position the manifold  16  there is provided a locating pin  46  disposed between the manifold and the mold part. FIG. 1 also illustrates a series of support pads  48  for providing proper distancing and positioning between the mold part  14 , the manifold  16 , and the cooled clamping plate  36 . 
     In the drawings, there is illustrated, associated with the valve pin  28 , the actuator assembly  52 . For the basic components of the actuator assembly  52 , reference may be made to the exploded perspective view of FIG. 9, and FIG. 8, which show the various components. The actuator assembly  52  includes a cylinder  54  which is mounted in an accommodating aperture  55  in the clamping plate  36 . As illustrated, for example, in FIG. 3, this aperture is of a stepped configuration. The actuator assembly also includes a piston  56  supported within the cylinder  54  and held in place by a retainer  58 . 
     FIGS. 8 and 9 also illustrate other components which make up the valve pin assembly  70 , such as the actuator cap  60 , the pin head  62 , the actuator support  64 , and the locking screw  66 . As seen in FIG. 8, the ring  68  and associated snap ring  69  facilitate interconnection between the valve pin assembly  70  and the piston  56 . 
     The valve actuator cylinder  54  has two hydraulic lines  72  that connect thereto, as illustrated in FIG.  2 . These hydraulic lines provide pressurized fluid between the piston  56  and the cylinder  54  to facilitate movement of the piston within the cylinder. In this regard, refer to FIGS. 4 and 5. In FIGS. 4 and 5 it is noted that the hydraulic lines  72  are schematically shown on opposite sides of the cylinder  54 . In actuality, these lines are disposed as illustrated in FIG. 2, but for the sake of schematic explanation, they are illustrated on opposite sides of the cylinder in FIGS. 4 and 5 to more clearly describe the operation of the hydraulic circuit as it relates to operation of the actuator assembly  52  and valve pin assembly  70 . 
     In FIGS. 4 and 5, the pressure is applied as indicated by arrows “a”. In FIG. 4, the pressure is input at the hydraulic line  72   a  and in FIG. 5 an opposing pressure is illustrated at hydraulic line  72   b . These pressures correspond to the positioning of the valve pin. 
     When hydraulic line  72   b  is pressurized, as in FIG. 5, the valve pin  28  is held in its down position (as shown). The piston  56  is moved to its down position by means of hydraulic fluid entering the annular port  75 , and exerting pressure on annular flange  81 . In that position, the check pin  76  is in its lowermost position and seals off fluid flow to the lower part of the hydraulic circuit. 
     When the other hydraulic line  72   a  is pressurized, as in FIG. 4, the valve pin moves to the up position with hydraulic pressure being imposed at the port  77  against annular flange  83  of piston  56  to move the piston  56  in an upward direction. In this instance, the check pin  76  is in the “up” position and permits some fluid flow from the lower hydraulic circuit to the upper hydraulic circuit, as explained in greater detail hereinafter. 
     As indicated previously, the cylinder  54  is positioned in a recess or aperture  55  that is machined in the top clamp plate  36  and is held in position by four mounting screws  79 , such as illustrated in FIGS. 2 and 3. The top of the cylinder  54  is provided with two lift holds  84 . These lift holds enable the cylinder to be easily removed from the top clamp plate, when the screws  79  and the ring  69  are removed. The hydraulic lines  72  are located within machined channels in the top clamp plate. These channels are typically terminated on one side of the top clamp plate (nonoperator side) using quick disconnect fittings. 
     The cylinder  54  is in thermal contact with the top clamp plate as illustrated in FIG.  3 . This thermal contact is important so that the cylinder remains relatively cool. On the other hand, the temperature of the manifold  16  is controlled to be at the plastic processing temperature (450° F.-550° F. typically). If the hydraulic cylinder gets too hot (greater than 400° F.) due to the manifold, there can be a degradation or damage of the O-rings  82 . 
     Accordingly, as illustrated in FIGS. 1 and 3, the top clamp plate is provided with water cooling lines  44  machined through the top clamp plate. In this way, thermal contact between the valve cylinder  54  and the top clamp plate  36  is important in preventing the valve cylinder from getting too hot. 
     With regard to the description hereinbefore, reference has been made to hydraulic lines  72 . However, the same principles also apply to the use of pneumatics instead of hydraulics. Typically, higher pressures are used in hydraulics such as 300-1500 p.s.i. Pneumatics are limited to plant supplied air pressure which is typically 85-100 p.s.i. Accordingly, a pneumatic actuator tends to be larger with increased piston area needed to generate forces equivalent to a hydraulic actuator. 
     As described above, movement of the valve pin  28  is caused by the piston  56  moving vertically within the valve cylinder  54  when pressurized. As indicated previously, there are three O-rings  82  that are provided. These O-rings may be constructed of Viton. The O-rings  82  provide hydraulic fluid seals between the piston  56  and the cylinder  54 , as well as between the piston  56  and the retainer  58 . Furthermore, other seals such as cup seals may be used. 
     The retainer  58  is used to support the piston  56  within the cylinder  54 . The retainer  58  also limits the travel of the piston in the downward direction such as is illustrated in FIG.  5 . The retainer is provided with a series of through holes and counter bores to receive the retainer screws  59 , as illustrated, for example, in FIGS. 3,  8  and  9 . As further illustrated, for example, in FIGS. 4 and 5, one of the larger O-rings  82  is disposed between the retainer  58  and the piston  56 . This provides a hydraulic seal with the piston. A second smaller O-ring  94  is used to provide a hydraulic seal between the retainer  58  and the cylinder  54 . 
     The valve pin assembly  70  secures the valve pin  28  to the actuator and includes actuator cap  60 , actuator support  64 , pin head  62 , and locking screw  66 . The valve pin assembly  70  is secured to the piston  56  primarily by means of the ring  68  and the associated snap ring  69 , as illustrated in FIG.  8 . The ring  68  and the snap ring  69  provide a clamping action to secure the valve pin assembly  70  to the piston  56 . 
     The actuator cap  60  has a counter bore and a through hole to receive the locking screw  66 . The actuator cap  60  is also internally threaded, such as illustrated in FIGS. 4-6, to receive the externally threaded pin head  62 . 
     The actuator support  64  has a base flange  65  that is used to mount the actuator support directly to the hot runner manifold  16 . For providing this mounting, there are provided mounting screws  67 . The actuator support  64  is preferably constructed of a material of low thermal conductivity such as titanium or stainless steel to increase the thermal gradient between the manifold  16  and the actuator assembly  52 . 
     As illustrated in FIGS. 6-9, the actuator support  64  has a horizontal through hole to receive a relatively large dowel  85 . Also, additional through holes  86  are provided to allow any plastic that may leak from the valve pin bushing  102  into the actuator support to flow out of the part without creating a high pressure. 
     The pin head  62  is used to retain the valve pin  28 . As indicated previously, the pin head  62  is provided with external threads to hold the pin head to the actuator cap  60 . Also, the pin head  62  has a central bore that is threaded to receive the end of the locking screw  66 . See, for example, FIGS. 6 and 8. The pin head  62  is also provided with a transverse slot  87  to receive the large dowel  85 , as illustrated in FIG.  9 . The vertical slot  87  allows the valve pin assembly  70  to move vertically relative to the dowel. The vertical slot  87  and the dowel  85  serve to prevent rotation of the valve pin assembly and maintain angular alignment of the valve pin relative to the gate  32 . 
     The pin head  62  has a central hole for receiving the top of the valve pin and also has two horizontal holes as illustrated in FIG. 9, for receiving the pair of dowel pins  90 . FIG. 9 also shows corresponding slots  92  at the top of the valve pin  28  for receiving the dowel pins  90 . The two dowel pins  90  are used to hold the valve pin  28  with respect to the pin head  62  while preventing rotation of the valve pin. The larger dowel  85  is used to prevent rotation of the valve pin assembly  70 . The lock screw  66 , when tightened, insures that the pin head  62  does not rotate with respect to the actuator cap  60 . 
     Associated with the hot runner manifold  16  is a bushing nut  100 , as illustrated, for example, in FIG.  8 . The bushing nut has external threads as illustrated for engagement into the hot runner manifold  16 . The bushing nut serves to retain the valve pin bushing  102  in position without exerting any axial stresses that can cause binding of the valve pin  28 . The valve pin bushing  102  provides a guide for the valve pin  28 . Using tight tolerances, a plastic seal is created between the valve pin  28  and the valve pin bushing  102 . The bottom surface of the valve pin bushing  102  provides a seal between the manifold  16  and the bushing  102  to prevent plastic leakage. 
     With regard to the operation of the hydraulic circuit of the actuator assembly  52 , the check pin  76  is positioned, such as illustrated in FIGS. 4 and 5, in a bore in the cylinder  54 . The bore is dimensioned so as to provide for a small amount of hydraulic fluid flow between the two hydraulic ports. A small gap between the check pin and the bore will limit the flow substantially. The flow is unidirectional. When the check pin is in the “up” position, as in FIG. 4, a flow about the pin is allowed. When the check pin is in the “down” position as illustrated in FIG. 5, the check pin seals against a taper at the bottom of the bore. The purpose of the flow is to allow any air that may otherwise be trapped in the hydraulic lines to be bled out of the lines. 
     In addition to the check pin  76 , there is also provided a pin stop  104  that limits the travel of the check pin  76  in the vertical direction. The hydraulic circuit of the actuator assembly  52  also includes metal expansion plugs  108  that are used to cap the ends of the bores in the cylinder used for hydraulic fluid flow, such plugs as Lee or CV plugs may be used. 
     There are several benefits with the construction of the present invention, particularly in comparison with the prior art previously described. For example, the assembly and disassembly of the top clamp plate  36 , and of the entire injection molding system  10 , are greatly simplified. The disassembly of the hydraulic actuator assembly  52  from the hot manifold is accomplished by simply removing the ring  68  and associated snap ring  69  as shown in FIG.  8 . The cylinder  54  and piston  56  along with the hydraulic fluid lines are essentially retained within the top clamp plate  36 , while the valve pin assembly  70  remains with the hot runner manifold  16 . With the system of the present invention, there is no need to drain the hydraulic fluid for disassembly, and there is no need to remove the valve pin from the hot runner manifold. 
     Another clear advantage of the actuator of the present invention is the manner in which there is essentially a self-alignment between the actuator assembly  52  and the valve pin assembly  70 . In this regard, reference can be made to such drawings as FIGS. 4-6 which show that the valve pin assembly  70  is supported in a manner that would allow some limited side-to-side motion in any direction thereof as the hot runner manifold undergoes certain expansion such as might be indicated by the arrow B in FIG.  3 . This is facilitated by the interaction of the ring  68 , actuator cap  60  and the annular flange  110  extending inwardly of the piston  56 . When the manifold, and valve pin assembly  70  mounted thereto, moves, the flange and piston can move side to side within the clearance  103  that is formed between the actuator cap  60  and the flange  110 . 
     In one embodiment of the present invention, there is about a 0.25″ clearance radially between the actuator cap  60  and the piston  56 . This clearance allows for relative expansion between the hot runner manifold  16  and the top clamp plate  36  essentially in any direction without putting a significant side load force on the valve pin  28 . It is also preferred that the piston  56  includes a plating thereon, such as chrome. This plating adds lubricity and insures slippage between the piston  56  and the actuator cap  60  during heat up or cool down of the manifold. 
     Another important benefit of the present invention is the particular check pin design as illustrated herein. This design provides for a small flow of hydraulic fluid about the check pin  76 . In contrast, prior designs required two additional hydraulic ports for bleed lines. That doubled the number of lines needed to be run in the top clamp plate. 
     A further benefit of the present invention is the ease with which the valve pin can be adjusted. Valve pin adjustment is necessary so that the pin can be positioned to seat at a precise location in the gate, to eliminate vestige on the molded part. With the snap ring  69 , ring  68  and locking screw  66  removed, rotation of the actuator cap  60 , which is threaded onto the pin head  62 , will raise or lower the valve pin  28  with respect to the hot runner manifold and the gate. Replacement of the locking screw  66  then locks the new position of the valve pin in place. This adjustment can be done with or without the top clamp plate  36  in place. 
     Having now described a limited number of embodiments of the present invention, it should now be apparent to those skilled in the art that numerous other embodiments and modifications thereof are contemplated as falling within the scope of the present invention as defined by the appended claims.