Abstract:
Disclosed is a high pressure injection molding system employing one or more plastic injection molding workstations including split molds, a single plastic extruder coupled to a heated manifold capable of delivering fluid plastic to multiple workstations, and wherein final lockup of the split mold halves results in application of compressive forces effective to maintain the split mold halves in nominal position during high pressure injection molding conditions. Operational movement is performed by use of a single remote pumping station utilizing pressure compensated pumps, accumulators and manifolds. The independent mold workstations allow independent operation while providing efficency of operation for the hydraulic system and extruder system.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. Ser. No. 08/879,107, filed Jun. 19, 1997, abandoned, the contents of which is herein incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention is related to the field of plastic molding, particularly to a high pressure injection molding machine which requires no externally applied clamping pressure, and additionally to a multiple mold workstation module comprising a single extrusion machine and hydraulic pumping station coupled to individual mold workstations each having an independent injection unit and mold clamp. 
     BACKGROUND OF THE INVENTION 
     High pressure injection molding devices, e.g. those devices operating at injection pressures of greater than 1000 psi, are well-known in the art for their use in producing plastic components. In a conventional injection molding machine, a mold sized for the machine must be properly positioned in order to receive plastic through a high temperature/pressure injection process. In this manner, the mold is placed within the machine by first opening a mold clamp section wherein the mold can be mounted to a front platen of the machine. This mounting is usually performed by the use of clamps bolted to some, of the many, threaded holes in the platen. The back half of the clamp section must also be set, which is a complicated adjustment, for the clamp section must be firm but not too tight if proper plastic flow is expected. Knock-out bars, referred to as ejectors, must also be adjusted for ejection of the finished parts. The ejectors are positioned for proper length of travel to eject the finished parts. It is critical that the ejectors do not over travel, or mold damage will occur. When the adjustment is complete, the clamp section is closed to secure the back half of the mold to the rear platen, again typically with clamps. The mold may then be cycled open and closed to permit ejector and clamp pressure adjustment. Upon positioning of the movable portion of the mold to its mating position with the stationary mold half, sufficient clamping pressure must be externally applied and maintained during high pressure injection to prevent flashing of molten plastic from the mold interface, and to prevent warpage during the cool-down and shrinkage phase, prior to ejection of the parts. Maintenance of the required clamping pressure is normally maintained by applying sufficient external force, e.g. via the use of a hydraulically powered ram, so as to oppose the internal pressures developed within the mold cavity during injection. Mold speed is set to occur within a cycle specified. 
     Heater zones must be turned on, usually three to six, depending on the machine size. Temperatures must be set according to the plastic material being used wherein variations run from 300 degrees Fahrenheit to 700 degrees Fahrenheit. If the temperature is too hot, the plastic will burn, and if it is too cold, damage to the machine will likely occur. The controllers on the machine regulate and maintain set temperatures within a very close range at a very considerable cost. While a machine is heated up, water lines on the mold are installed and tested for leaks. 
     Once all heat zones are stabilized, the injection unit is retracted from the mold area and materials added to the hopper. Molten plastic is then extruded from the nozzle to remove contaminated plastic that was used previously in the machine. This can be time consuming and materially wasteful, the amount of wasted material varies dependent upon the specific type of plastic and color of plastic selected. For example, if the machine previously had black color, and the new material is clear, it is not uncommon to use up to 100 pounds of plastic prior to making the first acceptable molding. 
     In operation, a shot size is determined and set, usually by moving limit switches located on the rear of the injection unit. Too much plastic will make the mold flash open, and too little will cause ejection problems. Estimates can be problematic, owing to the discrepancies caused by other variables such as pressure, temperature of the plastic, and back pressure. If the weight of the part to be formed is known, air shots can be made and weighed, otherwise the operation is guesswork. Once the settings are made manually, the machine timers must be set for a semi-automatic or automatic cycle. This requires trial and error but in either event, a trained set-up man can still spend several hours getting a machine on cycle, making acceptable parts, and still the operator can change any number of controls in seconds to make inferior parts that are not immediately identified. 
     The above complications are multiplied when additional molds are used. For instance, if ten molding machines are employed, the above set-up must be repeated ten times. In addition, when one mold machine is being set-up or serviced, the plastic is allowed to stagnate, if not cool, causing the malfunction of the plastic feeder and/or injector system. This non-operation can cause problems in and of itself. 
     What is lacking in the art is a compact high pressure injection molding device of simplified design, which maintains nominal pressure upon the mold cavity, prior to and during high pressure injection molding, while eliminating the need for additional means for generating and/or maintaining externally applied clamping pressure forces, e.g. hydraulic rams and the like; and wherein all process functions are commonly controlled from a single source. 
     SUMMARY OF THE INVENTION 
     The instant invention teaches a single or multi-mold high pressure injection molding device including a single extrusion machine and a single hydraulic system coupled to one or more independent mold workstations. Each mold workstation consists of an injection means including a resin accumulator for receipt of a particular volume of molten softened plastic, and which employs a source of hydraulic pressure to increase the pressure of the transferred softened plastic derived from the extrusion machine for subsequent high pressure injection into the workstation mold, which is of a split mold design. The injection units are coupled to the extrusion machine by a heated manifold having heated coupling lines. The hydraulic system provides fluid to each workstation via a single pumping station preset to a given pressure and controlled by variable displacement pumps and hydraulic accumulators. 
     The resin accumulator which supplies molten plastic to the injection unit employs a hydraulically driven piston having a step-down reduction chamber to increase the injection pressure of the molten plastic. The injection unit provides for high pressure passage of the plastic which allows the plastic to be transferred at lower temperatures. The injection unit has thermocouples to monitor the plastic temperature and a nozzle shut-off to regulate plastic flow. A series of heated check valves prevent the back-flow of plastic through the injection unit, manifold and extrusion machine. 
     Each mold workstation includes a split mold positioned between two plates, one movable and one stationary, which are mechanically linked via cylindrical tiebars. In a particular embodiment, a moving plate having half of the mold coupled to it, is in slidable engagement with the tiebars and is mechanically coupled to one or more relatively small hydraulic cylinders for effecting opening and closing of the mold. Upon initial closing, one or more piston actuators secured to the rear side surface of the moving plate operate slidable wedge shaped securement devices which are forced between reciprocally angled wear plates located on the rear side surface of the moving plate and the distal end of the tiebars, to provide final lockup. The slidable wedge shaped securement devices are particularly designed so as to partially encircle the tiebars when in the final lockup position, so as to provide over-center positioning of the wedge shaped securement device with respect to the longitudinal axis of the tiebar. The tiebars each have a threaded portion and a keyway allowing an adjustment nut to position the slidable wedges into an appropriate spatial locking position, while preventing rotation of said wedges about the tiebar. Movement of the securement devices causes the moving plate to lock against the fixed plate, whereby compressive forces are generated upon the mold halves, in an amount effective to maintain said mold halves within nominal position, during high pressure injection molding conditions, so as to prevent flashing from the mold, and without incurring warpage as the plastic cools. The necessary compressive forces for maintaining this nominal positioning of the mold halves, under high pressure injection molding conditions, derives from appropriately sizing the tiebars, such that the length, thickness and type of steel result in an elastic modulus which maintains the stretch or creep of the tiebar within a range effective to insure successful molding conditions. The adjustment nut further allows the use of various sized molds and accommodates ongoing wear of the wear plates. 
     In a second embodiment, a moving plate having half of the mold coupled to it is operated by a hydraulic piston coupled to an over-center hinge member. The hinge member maintains the mold in a closed position by positioning the hinge arms in a parallel, or near parallel position. The piston provides a high pressure actuator to maintain the mold in a fixed position. Mold separation is made possible by movement of the hinge arms. 
     The mold workstation further employs ejectors that protrude into the forming chamber when the mold is opened. The ejectors cause the finished product to be expelled from the mold and can be either operated by a hydraulic piston, or operated in the form of ejector fingers that extend through the mold when the mold is opened. 
     The initial cost, and operating costs, of a multi-mold workstation “module” becomes a fraction of the cost of multiple free operating adjustable machines. One extrusion machine can supply molted plastic to multiple injection units, e.g. ten or more, by use of a heated manifold whereby an economy of scale is achieved. Each injection unit employs a hydraulic actuated piston having a step down chamber reduction to increase the plastic pressure. The injection unit is cycled to accept a preset amount of plastic through the manifold system. The piston is then actuated to force the plastic at a high pressure into the mold. The injection unit has thermocouples to monitor the plastic temperature and a nozzle shut-off to regulate plastic flow. A series of heated check valves prevents the back-flow of plastic through the injection unit, manifold and extrusion machine. 
     Controls for the multi-mold workstation are centrally located allowing operation of each injector unit and mold machine from a single location. However, since the individual workstations utilize valves that perform all of the various functions, a plug-in connector could be in series with the wiring allowing the mold set-up person to plug in a portable control box and manually run any function prior to switching on automatic control. 
     The single extruder minimizes energy costs, as only two to three motors run constantly at independent load versus 20 to 60 motors on conventional machines of the same size. In addition, one raw material feeder, versus e.g. 10 raw material feeders, reduces spillage of pellets and lessens the chance of contaminating the material. 
     Accordingly it is an objective of the instant invention to teach an improved high pressure injection molding machine having a unique mold locking assembly which eliminates the necessity for application of clamping pressure during high pressure injection. 
     It is another objective of the invention to reduce the controls of a mold machine by 80 to 90 percent over typical production machines. The lack of adjustable controls decreases cost and increases reliability of operation. 
     Still a further objective of the invention is to teach a system wherein the power requirements are reduced by more than half of typical production machines. 
     Yet another objective of the invention is to teach the reduction of the workstation size and footprint so as to be less than half that of a typical production machine. 
     Yet a further objective of the instant invention is to provide the quality and product repeatability heretofore only obtainable in a single injection unit in a multi-mold system. 
     An additional objective of the invention is to teach the use of a mold workstation having slidable securement locks that are adjustable to the size of a mold and to accommodate wear. 
     Still an additional objective is to reduce the noise levels of a mold system by providing a system wherein motors and pumps are remote and reduced in size. 
     Additionally, a further objective is to reduce localized wiring to low voltage and eliminate high voltage motors at the individual workstations for increasing personnel safety. 
     Still another objective is to provide a single hydraulic system to feed multiple workstations which eliminates the need for multiple oil reservoirs thereby reducing costs, accidental spills, leaks and floor space. 
     Further still, an objective of the instant invention is to teach the use of a single extrusion machine for coupling to multiple mold workstations by use of a heated manifold system. 
     Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a pictorial view of the multi-mold workstation with single extrusion machine and manifold of the instant invention; 
     FIG. 2 is a cross sectional view of the injector unit; 
     FIG. 2A is an enlarged cross sectional view of a heated check valve; 
     FIG. 3 is a top plane view of a mold machine having an alternative clamp design in a closed position; 
     FIG. 4 is a top plane view of a mold machine in an open position; 
     FIG. 5 is a top plane view of a mold machine having a preferred clamp design in a closed position; 
     FIG. 6 is a rear plane view of a mold machine having the preferred clamp design; 
     FIG. 7 is a partial side view of a mold machine having the piston actuated wedge clamp; 
     FIG. 8 is a flow diagram of the hydraulic system; and 
     FIG. 9 is a pictorial view of a particular embodiment of a continuous extrusion injection molding system. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Although the invention will be described in terms of a specific embodiment, it will be readily apparent to those skilled in this art that various modifications, rearrangements and substitutions can be made without departing from the spirit of the invention. The scope of the invention is defined by the claims appended hereto. 
     Referring now to FIG. 1, set forth is a pictorial of the multiple mold workstation module of the instant invention. The module employs an extrusion unit  10  for use in feeding softened plastic through pipe  12  into a heated distribution manifold  14 . The heated distribution manifold  14  includes a collating hub  16  that allows for the even distribution of softened plastic to multiple mold workstations as depicted by numerals  18 - 27 . The illustrated and preferred quantity of mold workstations being between two and ten workstations with individual injection units forming the workstation module. 
     The distribution manifold  14  carries the plastic to the mold workstations through coupling pipe  30  having heater bands  20  positioned along the length of the pipe  30  for maintaining the plastic in a softened state during transfer. The coupling pipe  30  is secured to injector unit  100 , described in detail later in this specification, with directional flow check valve  108  to prohibit back flow of plastic into the manifold  14 . A valve  154  provides a shut-off between the mold workstation  184  and the manifold  14  and further allows for injection unit  100  detachment should the system require servicing. The removal of the mold workstation  18  does not inhibit operation of the extrusion machine  10  or injector unit  100  on other workstations. 
     For purposes of drawing clarity, the remaining coupling pipes are illustrated, but not numerated. Each coupling pipe operates in the above captioned manner to transfer softened plastic to the individual injector units and attached mold workstations. 
     Mold workstation  18  depicts one embodiment of the clamping mechanism. In this illustration the injection unit  100  provides for a pressurized flow of plastic into mold workstation  18 . Mold sections are forced together by piston  192  which operates in conjunction with hinge members  194  to securely lock the plate mold in a closed position upon placement of the hinge members in a parallel plane forming a direct wedge between a rear plate  204  and the mold support plate  186 . The locking arrangement permits the mold  180  and  182  to receive the pressurized plastic. 
     Mold workstation  22  depicts the clamp mechanism in an open position. In this illustration the injection unit  100 ′ again provides for a pressurized flow of plastic into the mold workstation  22 . Mold sections are forced open by piston  192  which operates in conjunction with hinge members  194  to open the plate mold upon placement of the hinge members in a non-parallel plane to eliminate the wedge between rear plate  204  and the mold support plate  186 . The open arrangement permits access to contents of molds  180  and  182 . 
     Mold workstation  26 , FIGS. 1 and 5 depict the preferred embodiment of the clamping mechanism in a closed position for receipt of pressurized plastic. In this illustration the injection unit provides for a pressurized flow of plastic into mold workstation  26 . Mold sections are forced together by illustrated piston  322  which operates in conjunction with wedge shaped securement device  324  to securely lock the mold in a closed position by forming a direct wedge between rear plate  330  and the end of the tiebars. Cylinders  340  and  342  are used to position the mold in a closed position before the wedge shaped securement devices lock the mold. 
     Mold workstation  27  depicts the preferred embodiment of the clamping mechanism in an open position for removal of a completed component. Mold sections are unlocked by the retraction of illustrated piston  322 ′ which operates in conjunction with wedge shaped securement device  324 ′ to securely lock the mold in a closed position. Cylinders  340 ′ and  342 ′ are then used to place the mold in an open position. 
     FIG. 2 depicts the injection unit  100  having a lower housing  102  forming chamber  104 . Softened plastic from the extrusion machine is fed through the manifold and into the coupling lines  30  for placement into chamber  104 . Check valve  108  prohibits the back flow of plastic into the manifold. 
     The lower housing  102  is secured to upper housing  112  by mounting bolts  114 . The upper housing  112  contains a plastic driving piston  116  having a distal end  118  for engaging the plastic within chamber  104  that enters in the direction of arrow  107 . The piston  116  has sealing rings  122  to prevent bypass around the piston. 
     The piston is part of a step up pressure multiplier. In this manner, piston  116  is preferably constructed of 4130 steel hardened to RC 45-55 with an outer diameter surface ground and polished for minimal fluid bypass. The piston  116  has a diameter of approximately 6 inches and provides an area of 28.27 square inches. The upper end  120  of piston  116  is coupled to a 10 inch diameter cylinder  124 , having an area of 78.54 square inches, and is secured to the piston  116  by mounting bolt  121 . The cylinder  124  is sealed to the piston by use of seal  123 . 
     Hydraulic fluid for operation of the piston is controlled by a solenoid valve  128  having a pressurized inlet  129  for delivery of fluid at discharge pressure through coupling pipe  130  and an outlet  127  for return of fluid to a reservoir  400 . The solenoid has an actuator  131  to control the speed of fluid and pressure delivered through the solenoid. The hydraulic fluid is inserted in the space  126  above cylinder  124  at a pressure of 2000 psi providing a force of 157,080 lbs, thus, the resulting force on the plastic within the chamber is 5,556 psi. The cylinder  124  employs steel rings  132  and  134  with a Teflon ring  136  positioned beneath the steel rings for sealing of the fluid. End cap  138  is bolted  140  to the upper housing allowing for ease of maintenance to the cylinder  124  and piston  116 . End cap  138  is sealed by o-ring seal  139  placed around the outer diameter of the end cap  138  with the bolts  140  holding the end cap securely in position. 
     In operation, plastic is inserted through inlet  106  which forces the piston  116  upward allowing the chamber  104  to be filled with a predetermined amount of plastic. The band heaters  146  and heated injection unit  110  maintain the plastic in a softened state. Upon demand, the plastic is delivered through outlet  142  into the workstation mold. The coupling pipe includes band heaters  146  for maintaining of the plastic in a softened state for placement through nozzle opening  148 . Thermocouple  150  and  152  verify plastic temperature and control shut off valve  154  to prevent plastic flow if necessary. 
     FIG. 2A sets forth a cross sectional side view of the check valve  108 . Seat  111  includes spacial openings to allow the flow of plastic during the filling process, at low pressure. However, the ball  109  engages seal  113  during a back flow position to prevent the return flow of plastic. The mass of high pressure plastic is capable of displacing the ball  109  to form the seal to prevent the backflow condition. If a backflow condition exists, such as when the chamber is pressurized, the ball  109  is pushed against seal  113  to prevent plastic from escaping the chamber. Band heaters  115  are located around the check valve to maintain the plastic in a fluid state. It is noted that the check valve depicted is used through the module for control of plastic flow where needed. 
     FIG. 3 depicts the mold workstation  18  coupled to the manifold injection unit  100  by coupling pipe  106 A. The injection unit  100  provides the high pressure flow of plastic into the mold workstation  18 ; having a split mold defined by first section  180  securable to fixed plate  184  and a second section  182  movably securable to plate  186 . The plates and molds are maintained in alignment by tiebars as depicted by numerals  188  and  190 . It is noted that the tiebars form the super structure for support of the plates and molds. 
     The means for moving plate  186 , and second section of spit mold, also referred to as mold  182 , into a position for accepting plastic injection is performed by use of piston actuator  192  which operates in conjunction with hinge members to lock the plate  186  in a fixed position. A first hinge  194  consists of hinge arm  198  having a proximal end  196  secured to the first plate  186  and hinge arm  202  having a proximal end  200  coupled to end plate  204  with each said hinge arms having a proximal end coupled together and secured to the piston actuator  192  at pinion point  206 . A second hinge member  207  has a distal end  208  of a first hinge arm  210  secured to the first plate  186  and a distal end  212  of a second hinge arm  214  secured to end plate  204  with said first  210  and second  214  hinge arms having a proximal end coupled together and secured to the piston actuator  192  by tying bracket  218 . The spaced apart positioning of the proximal ends places the hinge members in a parallel position to maintain the mold in a closed position. In this position, the mold is ready to accept the injection of plastic from the injection unit  100 . 
     FIG. 4 depicts the mold workstation  18  in an opened position. the mold workstation is again manipulated by a first section  180  secured to fixed plate  184  and a second section  182  securable to plate  186 . In this manner the first hinge member is dislocated wherein the first hinge arm  198  and second hinge arm  202  are moved which causes an over center hinge coupling thereby moving the plate  186  toward end plate  204 . The second hinge member employing hinge arm  210  and  214  to provide uniform movement of plate  186 . 
     The second portion  182  of the split mold has a plurality of apertures allowing for the protrusion of ejectors  234  through surface  236  for expelling of the molded piece of plastic when the molds are separated. The ejectors can be secured to bracket  230  causing protrusion of the ejectors upon retraction of plate  186 , preferably the ejectors are coupled to a hydraulic piston  232  to allow for movement of the ejectors as needed. 
     Referring to FIG. 4, the mold workstation  18  is shown coupled to the manifold injection unit  100  by coupling pipe  106 A. The injection unit  100  provides the high pressure flow of plastic into the mold workstation  18 ; having a split mold defined by first section  180  securable to fixed plate  184  and a second section  182  movably securable to plate  186 . The plates and molds are maintained in alignment by tiebars as depicted by numerals  188  and  190 . It is noted that tiebars form the super structure for support of the plates and molds. 
     The means for moving plate  186 , and mold  182 , into a position for accepting plastic injection is performed by use of piston actuator  192  which operates in conjunction with hinge members to lock the plate  186  in a fixed position. A first hinge  194  consists of hinge arm  198  having a proximal end  196  secured to the first plate  186  and hinge arm  202  having a proximal end  200  coupled to end plate  204  with each said hinge arms having a proximal end coupled together and secured to the piston actuator  192  at pinion point  206 . A second hinge member  207  has a distal end  208  of a first hinge arm  210  secured to the first plate  186  and a distal end  212  of a second hinge arm  214  secured to end plate  204  with said first  210  and second  214  hinge arms having a proximal end coupled together and secured to the piston actuator  192  by tying bracket  218 . The spaced apart positioning of the proximal ends place the hinge members in a parallel position to maintain the mold in a closed position. In this position, the mold is ready to accept the injection of plastic from the injection unit  100 . 
     Now referring in general to FIGS. 5 and 6, set forth is the preferred embodiment of the mold workstation depicted by numeral  26 . The mold workstation  26  is coupled to the injector unit  100 ′ by coupling pipe  106 A′. As with the previously described alternative embodiment of the mold workstation, the injection unit  100 ′ is coupled to the heated manifold by pipe  30 ′ with backflow prevented by use of check valve  108 ′. 
     In the preferred embodiment, the mold workstation  26  consists of a fixed support plate  300  having tiebars  302 ,  304 ,  306 , and  308 . The tiebars are secured to support plate  300  by use of a coupling nut  310  located on a first side surface of the support plate  300  and a second coupling nut  312  located on the opposite side surface of the support plate  300 . Each shaft, as depicted by shaft  302 , includes a threaded end portion  314  having a key slot  316  which allows for directional receipt of slotted wear washer  318  held in position by adjustable securement nut  320 . Unique to this embodiment is the use of four piston actuators, as illustrated in FIG.  6 . Each actuator, as depicted by numeral  322 , is coupled to a slidable wedge shaped securement device  324  for use in spacial spreading the distance between wear washer  318  and wear plate  326 . 
     The slidable wedge shaped securement device includes an angle shape and is operatively associated with wear plate  326  to maintain an engagement alignment when not used for said spacial spreading. Preferably the wedge shaped securement device  324  is approximately twelve inches in length which allows sufficient room for removal of finished products and allows for servicing of the molds. In operation, the wedge shaped securement device  324  causes the first portion of split mold  332  to lock against the second portion of split mold  334  thereby allowing for receipt of the highly pressurized plastic from injection unit  100 ′. The mold plate  330  is securely locked in position upon the positioning of the wedge members  324  between the wear plate and wear washer. Upon retraction of the wedge member, the mold plate  330  may be opened by pistons  340  and  342 A used to provide a spatial distance between support plate  300  and movable mold plate  330  allowing access to the mold chamber. The wear plate  326  is replaceable and formed at a reciprocal angle to the angled wedge shaped securement device  324 . Each angle increasing the spacial separation to create a positive seal between the mold sections. Securement nut  320  is used to accommodate for wear of the plate  326  or washer  318  as well as allow for various size molds to be placed within the mold workstation. The threaded nut may also be used to accommodate various size molds. 
     FIG. 6 depicts an end view of the preferred mold workstation embodiment having the piston actuators shown engaging the tiebar shafts. As previously described, movable plate  330  is first positioned by use of cylinders  340  and  342 . The wedge-shaped securement devices are retracted from engagement with the alignment shafts to allow an opening of the mold of approximately twelve inches. It will be obvious to one skilled in the art that the size of the wedge shaped securement device may be altered as well as that of the spatial wear washers without defeating the intent of this invention. Piston actuator  322  is shown engaging shaft  302 . Similarly, piston actuator  342  engages shaft  306 , piston  344  actuator is used for engaging shaft  308 , and piston actuator  346  is used for engaging shaft  304 . The wear plate  326  includes a lip for maintaining the wedge shaped securement device  324  in alignment while in a retracted position. 
     Referring now to FIG. 7, shown in an enlarged side view of the movable mold plate  330  having piston actuator  322  inserting wedge shaped securement device  324  between the wear plate  326  and wear washer  318  juxtapositioned to the securement nut  320 . The wear washer includes a tab, not shown, operatively associated with key way  316  for use in preventing rotation of the wear washer during engagement. A portion of the shaft  314  is threaded allowing for use of various size molds as well as to accommodate excessive wear of the wear plate and wear washer. 
     FIG. 8 is a flow pictorial diagram of the hydraulic system for the instant invention which allows operation of multiple mold work stations from a single pump. In this manner, a hydraulic reservoir is fluidly coupled to a circulating pump  402  which pressurizes hydraulic oil maintained at a high operating pressure by use of a hydraulic accumulator  404 . The hydraulic accumulator  404  is capable of storing the pressurized oil and allowing for an immediate disbursement as necessary. The hydraulic fluid is then available to operate the hydraulic system in the module namely the extruder machine, the injector units  100  including the operating solenoid valves  128 , the piston actuators  131  for engagement of the wear plate, as depicted by number  300  , the piston cylinders as depicted by numeral  340 , and the ejectors as depicted by numeral  232 . Hydraulic volume is returned at low pressure to return pipe  406  back to reservoir  400 . 
     Referring now to FIG. 9, a pictorial view of a particular embodiment of a continuous extrusion, multiple mold station, injection molding system is shown. A central extrusion machine  10  provides a source of molten plastic. The extrusion rate (lbs/hr.) and speed of the extruder screw (rpm&#39;s) necessary to maintain the molten plastic at a specified pressure is determined by pressure transducer  910 , through which the molten plastic passes as it travels from the extrusion machine  10  to the heated manifold  14  wherein it fills the accumulator/injection units  100 , for pressure multiplication and ultimate filling of the high pressure injection molding stations, herein illustrated as double clamp molding stations  912 . These molding stations utilize one common stationary central plate  914  for two independent and distinct movable plates  916  to define two separate molding stations which comprise the double clamp molding station  912 . In operation, each of the movable plates  916 , can be retracted for extraction of finished parts from the molds, then the movable plates can be independently slid back into locking engagement and the wedge shaped securement devices  324  are forced into locking engagement via actuators  322 , so as to positively position the mold halves for the next injection of high pressure molten plastic. 
     It is to be understood that while we have illustrated and described certain forms of our invention, it is not to be limited to the specific forms or arrangement of parts herein described and shown. It will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is shown in the drawings and described in the specification.