MXPA99002981A - Operating container actuator for a molding machine by inyecc - Google Patents

Abstract

The present invention relates to an injection molding machine comprising: a mold having at least two mold cavities, each mold cavity having a respective operation vessel for loading an injectable material into a respective mold cavity, Each injection operation vessel has an injection piston for expressing the material from the operation vessel in its respective mold cavity, a clamping unit for holding the mold, the clamping unit includes a fixed platen and a moving platen positioned on opposite sides of the mold, an injection unit for supplying the material to the operation vessels, an operation container actuator, outside the clamping unit and extending through one of the platens, the operation vessel includes an impeller for each operating vessel, each impeller has (i) a reverse movement limiting the retracted position of the injector piston ion as the operation vessel is loaded, and (ii) moves to a second position to advance the injection piston and expresses a measured amount of material from the operation vessel; a linear position sensor operably linked to a control system, for detecting the position of the actuator, and drive means responsive to the control system and operable to move the actuator drives separately between the retracted and second positions, wherein the injection molding machine includes at least four operating vessels grouped in at least the first and second groups of at least two operation vessels each, and wherein the driven includes first and second corresponding groups of impellers for each group and the driving means are operable to move independently each group between the retracted positions and according to

Description

OPERATING CONTAINER ACTUATOR FOR A MOLDING MACHINE BY INJECTION FIELD OF THE INVENTION The present invention relates to injection molding machines. More particularly, the present invention relates to a common control of multiple operation vessels in an injection molding machine.

BACKGROUND OF THE INVENTION The use of control units, such as operating vessels, for introducing thermoplastic resins or other materials into a mold cavity in an injection molding machine is well known. Generally, a primary resin source feeds the material into an operation container reservoir which, in turn, is operated to feed a measured or dosed amount of the material into the cavity. The patents of E.U.A. No. 3,516,123, entitled "Injection Molding Machine", by Lang; and No. 3,231,656, entitled "Apparatus and Method of Plastic Molding", by Ninneman both disclose the use of operating vessels to provide exactly measured batches of resin to a mold cavity. The dosing allows an exact amount of material to be injected into a mold to ensure that an appropriately formed part is created and to avoid wasting of the material in the form of "flash", etc., due to overfilled molds. The dosing is generally carried out by controlling the distance through which an injection plunger in the operation vessel is retracted and advanced for each batch. Other dosing techniques are also well known. For example, the patent of E.U.A. No. 4,966,545, entitled "Staged Shooting Pot for Injection Molding," by Brown, shows how an individual operation vessel can be operated to make two sequential metered injections of the same resin go into the same mold cavity. The patent of E.U.A. 4,460,324, by Van Appledorn, entitled "Shot Cylinder Controller for Die Casting Machines and the Like", shows how the piston injection speed of the operation vessel can be controlled, thus controlling the injection speed of the resin into the mold cavity . It is also well known to supply the thermoplastic material to a multi-cavity mold through a hot operator system. The hot operator system may include a plurality of operation containers, with at least one operation container associated with each mold cavity. Hot operator systems can also be used for multi-material or co-injection injection molding. Typically, two or more resins are injected, either simultaneously or sequentially, into each mold cavity to produce multi-layer molded structures. For example, a common application of multiple material molding is the production of food grade containers of recirculated plastic. Government regulations require that any surfaces that come into contact with food be made of new, virgin plastic. To take advantage of the lower cost recirculated plastic, manufacturers use co-injection techniques to encapsulate the recirculated material in a new plastic sheath. The patent of E.U.A. No. 5,098,274 to Krishnakumar, entitled "Apparatus for Injection Molding of Multilayer Preforms", and US Patent No. 4,717,324 to Schad, entitled "Coinjection of Hollow Articles and Preforms", both describe injection molding machines for multiple material applications . Generally, individual control of the runs of the operation vessel is provided in these prior art injection molding machines. Separate hydraulic drive cylinders for each operation vessel injection piston are mounted inside the fixed plate of the machine. These hydraulic cylinders must be individually set for the stroke to control the individual dosage of the resins towards the mold cavities. The fixing of the cylinders can be a dangerous operation, which is done manually and requires the personnel to reach the machine between the hot injection nozzles, near the hot surfaces and hot injection materials. In addition, the molding process has to be interrupted for this adjustment, which can cause a significant loss of production time, especially in larger machines that have up to 96 injection pistons. The patent of E.U.A. No. 4,632,653 to Plocher, entitled "Press with a Plurality of Injection Plungers" discloses a common actuator for injection pistons in a transfer molding machine. The injection pistons are driven by a hydraulic impeller acting on an individual crosspiece. However, the operation vessel actuator described by Plocher has several limitations and disadvantages, which make it inapplicable for metered injection molding machines. First, the operation vessels in a compression molding machine do not provide batched batches. Rather, each operation vessel is filled with an approximate amount of resin, and the injection pistons are driven through the crosspiece to compress the resin into the mold cavity. Plocher describes pressure compensation pistons and overflow channels to relieve mold qualities in the case of overfilling, which results in a non-uniform product and flash formation. Also, there is no mechanism provided for adjusting the stroke of the injection pistons, since precise control of the amount of resin injected into the mold is not critical in said transfer molding process. Secondly, the Plocher cross-piece actuator is located inside the mold, which increases the cost of mold design and manufacture. Also, such a design is not practical in machines with high fastening forces as the volume occupied by the crossing piece reduces the strength of the mold component where it is located, thus increasing the probability of deformation of the mold components when hold. In addition, the mold must be completely disassembled to have access for maintenance, adjustment or replacement.

COMPENDIUM OF THE INVENTION It is an object of the present invention to provide a novel operation vessel actuator for a multi-cavity injection molding machine, which avoids or mitigates at least one of the disadvantages of the prior art. In a first embodiment of the present invention, there is provided an injection molding machine comprising: a clamping unit for clamping a mold having at least two operating containers, each having an injection piston, said clamping unit including a fixed platen and a mobile platen disposed on the opposite sides of said mold; an injection unit for providing the operating vessels with the material to be injected; an operation container actuator, outside the clamping unit and extending through one of the platens; and actuating means operating to move the actuator between a first position and a second position, wherein the first position of the injection pistons limits the volume of material that each operation container can receive from the injection unit, and where the material is expressed from the operation vessels as the actuator moves to the second position. In a further aspect of the present invention, there is provided a multiple material injection molding machine comprising: a mold having at least two mold cavities, each of these two mold cavities having at least one first and a second operation vessel communicating therewith, the first and second operation vessels having first and second respective injection pistons; a clamping unit including a fixed platen and a moving platen disposed on the opposite sides of the mold; an injection unit for providing the operating vessels with the material to be injected; an operation container actuator, outside the clamping unit and extending through one of the platens; said actuator having a first group of impellers for bumping with the first injection pistons, and a second group of impellers for bumping the second injection pistons; and driving means operating to move the first and second groups of impellers between a first position and a second position, wherein the first position of the injection pistons limits the volume of material that each operation vessel can receive from the unit of injection, and wherein the material is expressed from the operating vessels as the actuator moves to the second position. In another aspect of the present invention, there is provided an operation vessel drive assembly for an injection molding machine having a clamping unit for clamping a mold having at least two operation vessels each having a piston of injection, said clamping unit including a fixed platen and a mobile platen disposed on opposite sides of the mold, and an injection unit for providing the operating containers with the material to be injected, comprising: a frame that can be securing to the outside of one of the plates and having a separate portion of said plate; an operation vessel actuator, supported for linear movement within the frame, for extension through the plate to abut the injection pistons; and an impeller mounted on the portion, said driving means can be operated to move the actuator between a first position and a second position, wherein the first position determines the volume of material that each operation vessel can receive from the injection unit. , and wherein the volume is expressed from the operation vessels as the actuator moves to the second position. In a further embodiment of the present invention, an operation container actuator is provided for a multiple material injection molding machine having a clamping unit including a fixed platen and a moving platen disposed on opposite sides of a mold having at least two mold cavities and at least first and second operation vessels for each mold cavity, the operation vessels having first and second corresponding injection pistons, and an injection unit for providing the operation vessels with the material to be injected, comprising: at least two first impellers, each first impeller operable to come up against a first respective injection plunger; and at least two second impellers through which the first impellers extend, each second impeller operable to abut a second respective injection piston; the first and second impellers operable to move independently between a first and a second position, wherein the first position determines the volume of material of each respective operation vessel can receive from the injection unit, and wherein the volume is expressed from the As operation vessels move the impellers to the second position.

BRIEF DESCRIPTION OF THE DRAWINGS Preferred embodiments of the present injection will now be described by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic illustration of a hot multi-material operator system for a four-cavity mold; Figure 2 shows a cross-section of a hot multi-material operating system near a nozzle assembly; Figure 3 shows a cross-section of a portion of the multiple material injection molding machine, including a common operating vessel drive assembly with all the impellers in the retracted position; Figure 4 shows a rear view of the machine of Figure 3 in the direction of line D; Figure 5 shows a cross-section of the machine of Figure 3 along line A-A; Figure 6 shows a cross-section of the machine of Figure 3 along the line B-B; Figure 7 shows a cross section of the machine of Figure 3 along the line C-C; Figure 8 shows the machine of Figure 3 with the first group of advanced impellers; and Figure 9 shows the machine of Figure 3 with both the first and the second group of advanced impellers.

DETAILED DESCRIPTION For purposes of illustration, the present invention will be described with reference to a double hot operator injection molding machine as shown in the drawings. As will be apparent to those skilled in the art, the present invention can be generally employed in injection molding machines having multiple operating vessels for which a common control is desired. One embodiment of the present invention is shown in Figures 1 and 2, wherein Figure 1 shows a schematic view and Figure 2 shows a cross section of a portion of a hot operating system for an injection molding machine, which adapts two thermoplastic resins, or other material to be molded, generally indicated with the reference number 20. A resin is provided from a source identified as extruder A, the other resin is provided with a source identified as extruder D. Although the mode illustrated shows two sources of resin A and B, is completely within the scope of the invention uses one, two or more sources. The portion of the hot operating system 20 exiting the extruder A is shown in solid lines, and the portion of the system exiting the extruder B is shown in faded lines. As shown in Figure 1, the materials supplied by the extruders A and B are fed into the mold cavities 22, 24, 26 and 28 through corresponding individual co-injection nozzles 32, 34, 36 and 38. extruder A supplies a hot manifold Ma which, in turn, communicates with each nozzle 32, 34, 36 and 38 through operators or hot channels 42, 44, 46 and 48, respectively. The rotary valves 52, 54, 56 and 58 operate to control the loading of the operating vessels, or injection cylinders, 62, 64, 66 and 68. Correspondingly, the hot manifold Ma directs, from the extruder B, to each nozzle 32. , 34, 36 and 38 through the hot operators 72, 74, 76 and 78. The rotary valves 82, 84, 86 and 88 control the loading of the operation vessels 92, 94, 96 and 98. Although the schematic view of Figure 1 shows a hot operating system 20 driven from two sources, extruders A and B, conveying conditioned thermoplastic resins to a four-cavity mold, it is completely within the scope of the present invention to serve 48 or more mold cavities that are originate from one, two or more sources. As shown in Figure 2, a central manifold block 102 is maintained at an appropriate temperature scale through the heating elements 104. For example, if the resin is polyethylene terephthalate (PET)., the central manifold block can be maintained at a temperature ranging from about 260 to 287.7 ° C. The channels 106 and 108 receive plasticized resin from the extruder A. The rotary valve 112, in circuit with the channel 108 and operated through a linker mechanism 114, controls the charge of the reservoir 116 of the operation vessel, or injection cylinder, 118 , each of which is equipped with an injection plunger 122. The rotary valve 112 is formed with a transverse past hole 124 and is shown in Figure 1 in a closed position. The reservoir 116 communicates with the channel 126, which in turn, is directed towards the nozzle assembly 32. The nozzle assembly 32 functions to inject the resin into a mold cavity (not shown). Similarly, for the path directed from the extruder B, a manifold block 130, which may be a segment separate from the manifold 102 or a portion thereof, is maintained at an appropriate temperature scale through the heating elements 132. For example, if the resin is an ethylene-vinyl alcohol copolymer (EVOH), the central manifold block can be maintained at a temperature ranging from about 204.4 to 226.6 ° C by the heaters 132. The channels 134 receive plastified resin from the extruder B. The rotary valve 144, in the circuit with the channel 134 and operated through the link mechanism 133, controls the charge of the reservoir 136 of the operation vessel, or injection cylinder, 138, each of which is equipped with an injection piston 142. The rotary valve 144 is formed with a transverse past hole 146 and is shown in Figure 2 in the closed position. The reservoir 136 communicates with the channel 140 which, in turn, is directed towards the nozzle assembly 32. The nozzle assembly 32 includes a central pin 146 in thermal contact with the multiple block 102. The pin 146 is formed with a past channel 148, through which the resin can flow into a composite nozzle 152. As shown, a valve rod 166 moved by a piston 164 controls the opening and closing of the gate 152. Another gate forming system , as well known to those skilled in the art can be used to control the injection of resin through the nozzle assembly 32. The spike 146 is supported by minimum bearing surfaces 154-156 in a housing 158, which is separate of the spike 146 substantially through its length through an insulating air gap 162 to maintain the resin of the extruder B at its optimum processing temperature as it progresses towards the compuer ta 152 through a channel 160. Generally, to inject the two resins of the extruders A and B to each mold cavity, the group of injection plungers 122 for the resin supplied by the extruder A is first advanced to move a measured amount of the first resin into the mold cavity, partially filling it. This is followed by advancing the injection plunger 142 to displace a measured amount of the second resin supplied by the extruder B, or through only partially filling the mold cavity. Finally, a second feeding of the first resin directly through the channel 126, by diverting the operation vessel 118, fills the mold cavity and packages the molded articles. As is well understood, the particular sequence selected to produce the molded articles will depend on the desired final structure, and may include simultaneous injection, as well as sequence, into the mold cavity. Figures 3-9 show side and rear views of an injection molding machine incorporating one embodiment of the present invention. In Figure 3, a mold 180, shown in faded lines and including a hot operating system 20, is mounted between a clamping unit 184. The clamping unit 184 generally comprises a fixed platen 190 and a moving platen 192. Mounted on the external part of the fixed platen 190 is a common operation container drive assembly 196. Although in the embodiment illustrated, and the following description of the present invention, the operation container drive assembly 196 is mounted on the fixed platen 190, and it is completely within the inventors' addendum that the assembly 196 can be mounted to the moving platen 192. The operation container drive assembly 196 generally comprises a frame 198, an operation container actuator 200 and means for drive 202. The frame 198 has four columns 204, 206, 208 and 210 secured to the fixed stage 190 in a pattern generally r Ectilinear, as best seen in Figure 4, through bolts 212. A drive bracket 214, spaced from the rear of the fixed stage 190 through the exposed length of the columns 204, 206, 208 and 210 is mounted on the ends of the columns and secured through bolts 216. To the drive bracket 214 are attached first and second impellers 218 and 220, the operation of which will be described later. The impellers 218 and 220 may be hydraulic rams, linear electric motors or any other suitable impeller. The operation vessel actuator 200 is mounted on the columns 204, 206, 208 and 210 for sliding movement between the drive bracket 214 and the rear part of the fixed platen 190. In the illustrated embodiment, the actuator 200 has two platens parallel and separately mobile 222 and 224. A first group of impellers 226 is secured to a first plate 222. The impellers 226 are arranged to correspond to the position of each of the injection pistons 142 in their respective group in the mold 180. Similarly, a second group of impellers 228 are secured to the second plate 224 and are arranged to correspond to the position of the injection pistons 122 in their respective group. Impellers 226 and 228 may be screwed into plates 222 and 224, or may be secured with "bayonet" assemblies, or in any other appropriate form. Ideally, the mounting method ensures that each mounted impeller 226, 228 extends from its respective plate 22, 224 to a substantially identical degree. The impellers 226 and 228 extend through the holes 230 and 232, respectively, in the fixed platen 190 and abut the injection pistons 142 and 122. The arrangement of impellers 226 and 228 depends on the placement of the operation containers. 138 and 118, and their respective injection pistons 142 and 122, in the hot operating system 20. Figure 7 shows a suitable arrangement for a cavity coinjection molding machine with 48 molds for making preform. To adapt a number of different operating container arrangements, the impellers 226 and 228 can be separated and repositioned as desired on the plates 222 and 224, or separate plate-impeller assemblies can be provided for different molds 180. It is contemplated that standard injection plunger separations can be employed. to allow the molds to be interchangeable, as described below in detail. The plate 222 can be reciprocally driven along the columns 204, 206, 208 and 210 through a corresponding actuator 218. As best seen in Figures 5 and 6, the actuator 218 comprises two hydraulic cylinder pistons 234. The plate 224 is similarly driven by the actuator 220, which comprises two hydraulic cylinder pistons 236. Since the plate 222 is disposed opposite the plate 224, piston holes 238 are provided in the plate 222 to adapt the passage of pistons. 236 and allowing free movement of the plate 222 with respect to the plate 224. Similarly, holes 239 are provided in the plate 22 to allow the free passage of impellers 228 therethrough. Depending on the configuration of the pistons 236, the holes 238 and 239 may be replaced by cuts, or be omitted if the impellers do not interfere. The position and linear velocity of the plates 222 and 224 can be sensed through the linear position sensing means 240. The sensor 240 can be a magnetic, opto-electronic or other suitable sensor, such as those manufactured by Temposonic Inc. The sensor 240 is fixed to the frame 198, or otherwise fixed relative to the plates 222 and 224. The sensor 240 may be attached to a suitable control system (not shown) for conventional electronic and / or programmable control. of the actuator 200, as is well known to those skilled in the art. Referring to Figures 3, 8 and 9, the operation of the actuator 200 with respect to a multiple material injection sequence will be described. Prior to the injection sequence described below, the clamping unit 184 is activated to hold the mold 180 together, in a manner well known to those skilled in the art. The injection sequence begins with the impellers 226 and 228, and plates 222 and 224, in a retracted position, as shown in Figure 3. In the retracted position, the free ends of the impellers 226 and 228, which meet with the injection pistons 142 and 122 in the hot operating system 20, limit the backward movement of the injection pistons 142 and 122 and, therefore, the volume of the material that can be received in the tanks of operation vessel 136 and 116. The adjustment of the retracted positions of plates 222 and 224, by adjusting the rearward stroke of their respective cylinder pistons 234 and 236, thus effectively doses the amount of material that can be accepted by each operation vessel 138 and 118 of the extruders B and A. Once the operation vessels 138 and 118 are filled with the desired amount of material in the manner described below, the plate 222 and its impellers 228 are advanced to acc The injection piston group 122 is then injected, thereby injecting the measured batch of material from each reservoir 116 into its respective mold cavity. The impellers 228 are advanced through a forward stroke of the cylinder pistons 236 acting on the plate 224 in the direction of the arrow F, as shown in Figure 8. The holes 238 and 239 allow the plate 222 move forward without affecting the position of the plate 222. The position and speed of the plate 224 during the forward stroke are sensed by the sensor 240. The sensor 240 retransmits the information to the control system which, at its once, it controls the speed and distance traveled by the impellers 228. Then, as shown in Figure 9, the plate 222 and its impellers 226 are advanced to drive the injection pistons 142., thus injecting the measured batch of material from each reservoir 136 into its respective mold cavity. The impellers 226 are advanced through a forward stroke of the cylinder pistons 234 acting on the plate 222 in the direction of the arrow G. The position and speed of the plate 222 are sensed by the sensor 240 to control the speed and the distance traveled by the impellers 226, as described above. An injection of the material of the extruder A is then fed directly to the nozzle 32 to pack the mold, and the gate 152 closes. Then, the operation of co-injection molding continues as in conventional machines. The material injected into the mold cavities is allowed to cool, the clamping unit 184 is released and the finished product is ejected from the mold. As will be apparent to those skilled in the art, the present invention is not limited to two plates, but may be extended to three or more impeller plates and corresponding groups of operating vessels, as desired. No actuator of the present invention is limited to the sequence injection of the multiple resins. Combinations of sequential and / or simultaneous movement of the push rods are possible to cause similar injections of the respective resins. The actuator assembly 196 of the present invention can also be incorporated into a transfer molding system, as described in the provisional application of E.U.A. No. 60 / 078,587 filed March 19, 1998. As described therein, the injection pistons are pulled back from their forward stroke position at the same speed as the operation vessels are being filled to reduce the acetaldehyde content of the finished articles. In this case, to incorporate the actuator assembly 196, the push rods 226, 228 are fixed to the injection pistons to allow controlled retraction of the injection pistons, and a control system verifies and controls the speed at which the pistons are pulled back. The provision of an individual drive assembly 196 for a plurality of operation containers, outside the mold 180 and the clamping unit 194, has clear advantages over the prior art. The operation of a group of operating vessels in a mold can be effected by an individual adjustment of the speed and distance traveled by its related plate and its respective impellers. This adjustment can be achieved "on the fly" and / or can be automatically controlled through the control system in response to the information detected by the linear position sensor. This eliminates individual, dangerous manual adjustments, and long production delays and interruptions, while ensuring the supply of accurately dosed materials. The stroke of each plate, and the arrangement of the impellers on each plate can also be independently adjusted. The fact that the actuator is out of the mold can reduce the cost of construction of the injection molding machine by providing a much simpler structure and reducing the number of more expensive hydraulic components and the circuit system required for driving the injection vessel. individual operation. For example, the significant reduction in number of hydraulic cylinders and 96 valves to a 48-cavity co-injection molding machine, to just four cylinders and their corresponding valve formation can result in significant cost reductions. The cost of operation and maintenance can also be reduced due to the simpler construction. In particular, the hydraulic cylinders and the pipe inside the fixed stage can be eliminated, and few more robust cylinders can be used and access to the cylinders for maintenance and adjustment is simplified. The present invention also provides the increased design flexibility to the mold and production line designers. Extra plates can easily be added to the actuator to handle additional resin injections. The push rods can also be relocated to match the different dispositions of the operation vessel and this is easily done. The drilling of a different hole pattern in the plates and the fixed stage is much less expensive than having to relocate the multiple actuation cylinders within the fixed stage of the prior art. Mold design is also greatly simplified eliminating the need for multiple cylinders inside the fixed stage, and the cost of the molds in this way is reduced. The ability to add / separate impellers and rearrange them on their respective plates can also reduce the time and cost associated with the equipment of new tools in an injection molding machine. Generally, the separable nature of the impellers allows new impeller arrangements to be easily effected for any given mold design. Impellers of different lengths, shapes and sizes can be exchanged on the same plate, as appropriate for each particular mold design. It is contemplated that molds can be designed with standard operating vessel spaces. For example, if a mold has 24 mold cavities at a distance of 20.32 cm it can be replaced by a mold having 12 cavities at 40.64 cm spacings, each second impeller can be removed to reach the proper arrangement.

The actuator of the present invention can also greatly reduce the time required to set, or reprogram, the stroke cycle for a particular mold or product. The current cycle only has to be set for each group of similar operating vessels, not for each separate operating vessel. The information regarding the control of the stroke for a particular mold can be stored, through electronic means or other means, which allow the rapid change of mold. This can be especially useful for "short operation" molds. The location of the actuator outside the mold also allows the operating vessels in the hot operator to be repositioned to optimize the resin flow channels and shorten the flow lengths. The prior art actuators imposed limitations on the design of the operation vessel by virtue of the space required in the fixed platen to adapt the hydraulic drive cylinders and their associated valves and tubes. By removing this limitation, more efficient hot operator designs are possible and the handling of the resin can be optimized, thus reducing the existence of resin inside the machine. The above described embodiments of the invention are intended to be examples of the present invention and alterations and modifications may be made thereto by those skilled in the art, without departing from the scope of the invention, which is defined only by the claims annexes.

Claims (28)

1. - An injection molding machine comprising: a clamping unit for holding a mold having at least two operating vessels, each having an injection piston, the clamping unit including a fixed stage and a mobile stage arranged on the opposite sides of the mold; an injection unit for providing the operating vessels with the material to be injected; an operation container actuator, outside the clamping unit and extending through one of the platens; and actuating means operating to move the actuator between a first position and a second position, wherein in the first position said injection pistons limit the volume of material that each operation container can receive from the injection unit, and where the material is expressed from the operation vessels as said actuator moves to the second position.

2. An injection molding machine according to claim 1, wherein the operation vessel actuator comprises at least two impellers, each operable to abut a respective injection piston.

3. An injection molding machine according to claim 1, wherein the drive means is a hydraulic ram.

4. - An injection molding machine according to claim 1, characterized in that it includes a linear position sensor operably connected to the driving means.

5. An injection molding machine according to claim 4, wherein the sensor detects the position of the actuator.

6. An injection molding machine according to claim 4, wherein the sensor is an optical sensor.

7 .- An injection molding machine according to claim 1, wherein the actuator can be moved to a third intermediate position to the first and second positions.

8. An injection molding machine according to claim 1, characterized in that it includes at least four operating containers grouped in at least first and second groups of at least two operation vessels, each, and wherein the The actuator includes first and second corresponding groups of impellers for each group and said driving means are operable to independently move each group between the first and second positions.

9. An injection molding machine according to claim 8, wherein the first and second groups are connected to the first and second supports, wherein the first group extends through the second support.

10. An injection molding machine according to claim 9, wherein the supports are flat plates.

11. - An injection molding machine according to claim 9, wherein the impellers can be disconnected from the supports.

12. An injection molding machine according to claim 8, wherein the impellers are arranged symmetrically.

13. An injection molding machine according to claim 8, wherein the impellers in each group are equally separated.

14. An injection molding machine according to claim 8, wherein said groups receive different materials.

15. A multi-material injection molding machine comprising: a mold having at least two mold cavities, each of the two mold cavities having at least a first and a second operation vessel communicating with the molds. same, the first and the second operation vessel having and first and second respective injection pistons; a clamping unit including a fixed platen and a moving platen disposed on the opposite sides of the mold; an injection unit for providing the operation vessels with the material to be injected; an operation vessel actuator, outside the clamping unit and extending through one of the plates; the actuator having a first group of impellers for bumping with the first injection pistons, and a second group of impellers for bumping with the second injection pistons; and driving means operating to move the first and second groups of impellers between a first position and a second position, wherein the first position of the injection pistons limits the volume of material that each operation vessel can receive from the unit of operation. injection, and wherein the material is expressed from the operation vessels as the actuator moves to the second position.

16. A multiple material injection molding machine according to claim 15, wherein the second group extends through the first group.

17. A multiple material injection molding machine according to claim 15, wherein the first and second groups are joined to respective first and second plates.

18. A multiple material injection molding machine according to claim 15, wherein the first operating vessel receives a first material and the second operating vessel receives a second material.

19. A multiple material injection molding machine according to claim 15, wherein the first and second groups operate independently.

20. An operation vessel drive assembly for an injection molding machine having a clamping unit for clamping a mold having at least two operation vessels, each having an injection piston, the clamping unit including a fixed platen and a mobile platen disposed on opposite sides of the mold and an injection unit for providing the operation containers with the material to be injected, comprising: a frame which is secured to the outside of the fixed platen and having a separate portion of the fixed stage; an operating vessel actuator, supported for linear movement within the frame for extension through one of the plates to abut the injection pistons; and an actuator driven on said portion, the actuating means being operable to move the actuator between a first position and a second position, wherein the first position determines the volume of material that each operation container can receive from the injection unit, and wherein the volume is expressed from the operation vessels as the actuator moves to the second position.

21. An operation vessel drive assembly according to claim 20, wherein the operation vessel actuator comprises at least two impellers, each operable to abut a respective injection piston.

22. An operation vessel drive assembly according to claim 20, wherein the drive means is a hydraulic ram.

23. An operation container drive assembly according to claim 20, characterized in that it includes a linear position sensor operably connected to the drive means.

24. An operating container drive assembly according to claim 23, wherein the sensor detects the position of the actuator.

25. An operation vessel drive assembly according to claim 23, wherein the sensor is an optical sensor.

26. An operation vessel operating assembly according to claim 20, wherein the actuator can be moved to a third intermediate position to the first and second positions.

27. An actuator for an operation vessel for a multiple material injection molding machine having a clamping unit including a fixed stage and a moving stage arranged on opposite sides of a mold having at least two mold cavities and at least first and second operation vessels for each mold cavity, the operation vessels having first and second corresponding injection pistons, and an injection unit for providing the operation vessels with the material to be injected, comprising: at least two first impellers, each first impeller operable to come up against a first respective injection plunger; and at least two second impellers through which the first impellers extend, each second impeller operable to abut a second respective injection piston; said first and second pusher operable to move independently between a first and a second position, wherein the first position determines the volume of material that each respective operation vessel can receive from the injection unit, and wherein the volume is expressed from the operating vessels as the impellers move to the second position.

28. An operation vessel actuator according to claim 27, wherein the first and second impellers can be moved to intermediate positions to the first and second positions.