Device for stretch blow molding and method for producing preforms

A device for the stretch blowing of plastic containers in a continuous single-stage process, having at least one injection rotor, with injection molds for preforms, which are fed via controlled valves from an extruder head and by way of a melt distributor from a central extruder, wherein the axis of the extruder is placed at least essentially in the axis of the injection pipe, and at least the extruder head and the melt distributor can be permanently and synchronously rotationally driven by the injection rotor. A method where, during the manufacture of each preform in the injection mold, injection molding phases and a compression molding or dwell pressure phase are combined and superimposed.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of priority of International Patent Application No. PCT/EP2008/008651, filed Oct. 13, 2008, which application claims priority of German Application No. 10 2007 049 689.5, filed Oct. 17, 2007. The entire text of the priority application is incorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

The disclosure relates to a device and a method for stretch blowing of plastic containers in a continuous single stage process, such as for beverage bottling operations.

BACKGROUND

A known device according to DE 197 37 697 A for implementing a single-stage process has a central stationary extruder which alternately feeds two injection rotors via a two-way controlled valve. During injection molding one injection rotor is stationary while the other injection rotor is rotationally driven and transfers the preforms to a transfer carousel with cooling devices. A rotary distributor is arranged in each injection rotor which sequentially feeds the injection molds via controlled injection valves. The respective injection valve is only actuated when the injection mold has been first closed by the inner arbor, which has moved to the end position, and has been fixed.

With a device known from DE 31 24 523 A a central extruder is arranged stationary. Sequentially controlled needle valves fill the cavities of each of four injection molds which are combined, forming a unit. The injection rotor is stationary. Four rotationally driven blowing rotors are arranged on the circumference of the injection rotor. Transfer grippers grip the openings of the preforms to transfer them in groups.

With the device known from U.S. Pat. No. 3,357,046 A two extruders are provided, which operate continuously and are mounted diametrically opposite on a disk-shaped carrier. The carrier rotates about its axis until in a respective discharge position, it remains stationary in the discharge position or it is at least largely retarded before a billet emitted from the extruder is parted off and transferred to a stretch-blowing mold located stationary beneath it.

With the device known from DE 195 28 695 for realizing a single-stage process expanding arbors, which engage in the opening of the respective preform, are used for transferring the preforms manufactured by injection molding. A stationary central extruder alternately feeds two injection molds which can move to and fro along an arc-shaped guide.

SUMMARY OF THE DISCLOSURE

One aspect of the disclosure is to optimize a device of the type mentioned in the introduction for an efficient single-stage process with a high output capacity. Part of the aspect is to provide an improved method of manufacturing the preforms.

With the device to be realized one aspect is to obtain a continuously running single-stage process without delays or intervening stops, which facilitates a small extruder size, with optimum use of the number of cavities, wherein the device should be characterized by low mold costs and a modular construction for easy servicing. According to the method one aspect is to shorten the injection time and possibly the dead times, to achieve a high preform quality due to careful handling of the melt and to increase the performance per cavity and to save energy through an optimized process sequence.

With this device, through the at least mutually rotating extruder head and the rotary distributor, a high realizable injection pressure is produced with a shorter process time, reinforced if necessary by a melt pump, wherein a small extruder size is sufficient and, where necessary, the large number of cavities in the injection molds can be optimally used. These advantages are paired with low mold costs, because the needle valves can be integrated into the machine module, and with high service friendliness due to the modular construction of the device.

According to the method, shortening the injection time and the dead times can be achieved, because the injection mold does not need to be completely closed at the start of the process, i.e. the nozzle mold can be open or raised. The melt, flowing initially under low pressure, is not immediately cooled by the cold inner arbor, but can rather spread out evenly at least in the bottom section of the subsequent preform. A metering unit is not needed and problems with portioning accuracy are eliminated, as are specific dwell pressure problems. Low pressing forces are sufficient for the adjustment of the inner arbor, because during the compression molding phase no final shaping of the preform has occurred yet. In this way the melt is handled carefully and a high quality is produced in the preform. The performance per cavity can be increased. Energy is saved by the optimized process sequence. The dwell pressure phase, superimposed if necessary, prevents shrinkage.

In a practicable embodiment the complete extruder can be rotationally driven together with the injection rotor. The extruder can be fitted from above or below, preferably separable, on the injection rotor.

In a practicable embodiment the extruder, practicably arranged vertically above, has a rotationally drivable pressure section surrounding the extruder nozzle and a stationary charging section. The charging section is preferably fixed relative to the injection rotor via a torque support and facilitates a convenient granule feed, for example via one or more stationarily arranged feed devices. Between the pressure section and the charging section a sealed rotary joint is provided so that the extruder nozzle rotates with the pressure section while the charging section remains stationary. Since the melt fed in from the extruder is brought on the shortest path to the injection molds so that no constrictions or significant deviation sections exist, a relatively small extruder size is sufficient, because the process runs continuously and not in cycles as in prior art.

Expediently, the rotary distributor, which rotates with the extruder nozzle and the injection rotor, has a multi-channel disk connected to the extruder head, preferably able to be uncoupled, which is connected via, preferably heated, pipes or hot channels to controlled needle valves installed in the injection rotor mold holders. Thus, only equally long transfer paths are present and a permanent, continuous flow of melt is ensured.

Since various media, e.g. a cooling medium, compressed air, hydraulic medium, electrical power for control and supply, a cleaning medium, etc. are required, and the supply must also be ensured during the operation of the injection rotor, another rotary distributor for these working media is practicably arranged on the side of the rotary distributor facing away from the extruder head.

An especially important feature of the disclosure is that each injection mold has a bottom and body mold, an openable, preferably cooled, nozzle mold and inner arbor which is axially adjustable through the nozzle mold, movable and preferably internally cooled. In this way an exactly controllable temperature distribution is possible in the preform.

In a preferred embodiment each injection mold has a bottom and body mold and a nozzle mold, which is movable relative to the bottom and body mold together with an internally cooled and internally hollow inner arbor, and which can be opened. The melt injection valve is a metering needle valve, which can be connected to the inner arbor to feed the cavity through the hollow inner arbor. The metering needle valve supplies an exactly predetermined charge of melt, wherein the charge is dimensioned such that shrinkage in the preform is avoided. Since the melt is fed through the hollow inner arbor, the bottom and body mold can be formed more simply. As with the bottom and body mold, the hollow inner arbor is cooled internally in order to optimize the temperature distribution in the preform.

With this embodiment the inner arbor has an inner through channel which opens into the region of the free end of the arbor and into which the melt charge can be brought into the cavity via the metering needle valve. In the inner channel a needle is arranged, which can be moved between a withdrawn feed position through a melt dwell pressure stroke to a closed position which closes the opening of the inner channel. The complete melt charge is introduced into the cavity through the controlled metering needle valve and in fact in three consecutive or contiguous steps. Initially, with the inner arbor raised out of the cavity, a first part of the charge is introduced into the cavity through the inner channel of the inner arbor with a low pressure until a filling level is obtained here below the location of the nozzle mold. Then the inner arbor together with the nozzle mold is lowered, wherein the initial melt filling is compressed at a low pressure by the insertion of the inner arbor in the direction of the location of the nozzle mold. Once the nozzle mold is blocked with the bottom and body mold, and the inner arbor has reached its lower end position and has been fixed, i.e. the cavity is tightly closed, the second part of the melt charge is injected by the metering needle valve through the inner channel until the region of the nozzle mold is filled. In this phase a residue of melt volume remains in the inner channel. This remaining melt volume is finally pressed into the cavity in a dwell pressure phase by inserting the needle through the inner channel of the inner arbor in order to prevent shrinkage. The needle is pressed so far in until finally the opening of the inner channel of the inner arbor closes.

Expediently, at its free end the needle has a dwell pressure stamp with the diameter of the opening of the inner channel. This stamp presses the remaining melt volume out of the inner channel into the cavity and finally closes the opening. After production of the preform the nozzle mold is lifted out of the cavity together with the inner arbor, wherein the preform remains on the inner arbor. Then the nozzle mold is opened and the preform removed from the inner arbor and transferred to the conditioning section. In this phase the needle with the stamp is again withdrawn so far that the inner channel of the inner arbor is free again for feeding the next melt charge. In doing this the stamp closes the inner channel at the top.

Expediently, transfer expanding arbors, which can be actuated for the removal of the preforms in each case from the opened nozzle mold, are assigned to the injection molds in the conditioning section, preferably rotatable in the conditioning section. Each preform is grasped inside in the nozzle and precisely conditioned in the conditioning section in order to have the correct temperature profile for stretch blowing, in particular in the regions in which the most severe deformation occurs during stretching and blowing, while the nozzle remains cool with the final shape in the injection mold and along the conditioning section.

In order to simplify the transfer of the preforms along the shortest path and matched to the rotational speed of the blowing rotor, an entry carousel with transfer elements for preforms removed from the transfer expanding arbors is provided between the blowing rotor and the conditioning section.

With another, particularly important embodiment, each injection mold has in each case openable bottom and body molds and a preferably cooled nozzle mold as well as an inner arbor which can be moved through the nozzle mold and removed from the injection mold. During the complete injection process and in the conditioning section, the inner arbor serves as a carrier for the preform and is, for example, not cooled. However, on the return path along the conditioning section into the injection rotor each inner arbor can be cooled so far that it exerts no unwanted temperature effect on the preform produced.

Expediently, the removable inner arbor is provided with an adapter part on which transfer grippers, arranged on a link chain in the conditioning section, grasp to remove or accept the inner arbor with the preform and to transport it along the conditioning section.

Since the preforms are relatively firmly seated on the inner arbors, with one practicable embodiment a preform removal and transfer device is provided in or along the conditioning section, for example a cam-controlled lowering device with which the preforms can be removed from the inner arbors and transferred to a transfer carousel which interacts with an entry carousel of the blowing rotor.

With a further, alternative and important embodiment an openable and removable nozzle mold is included in each injection mold. The inner arbor remaining in the injection mold is practicably cooled internally. The nozzle mold is removed together with the finished preform by means of transfer elements and at least transported along the conditioning section, preferably even into the blow-molds of the blowing rotor so that in this case each nozzle mold serves as a transfer element remaining on the preform and used again in the blow-mold.

With regard to quick and precise opening and closing movements of the nozzle mold, in a practicable embodiment of the nozzle mold a pneumatic cylinder is assigned to an articulated lever mechanism. The closing force of the nozzle mold is however realized by blocking with the body mold and/or with the inner arbor.

Here, the inner arbor is effectively adjusted by a hydraulic cylinder which applies a high closing force, e.g. a hydraulic cylinder with a power capacity of about 8 tons.

For conveying the melt and for a uniform effect of the melt flow, a buffer zone can be practicably formed in the extruder in the region of the rotary joint.

In an alternative embodiment the conditioning section is even variable in length. This can be realized either by adjustment or by replacement of the link chain and an offset in the diversion mechanism.

With regard to compact dimensions of the device, the conditioning section can be a rotor-shaped conditioning section, which carries a link chain with transfer expanding arbors on its circumference. Alternatively, the conditioning section can however be formed as a longitudinally extended conditioning loop with a circumferential link chain and e.g. inner-arbor transfer grippers arranged on it.

For thermally conditioning the preforms at least one preform cooling station is assigned between the injection rotor and the entry carousel to the conditioning section which is practicably formed as a conditioning circuit.

With another embodiment at least one cooling station with which the inner arbor is cooled on the return path is provided on the conditioning section formed as a conditioning loop in the return trunk between the transfer carousel and the injection rotor.

Finally, in order to be able to overcome problems due to separation delay it is practicable to especially form the conditioning section formed as conditioning circuit as a separation delay section in which the preform rotates.

According to the method, during the manufacture of high quality preforms initially only a part of the cavity is filled under low pressure with melt from the needle valve in the absence of the inner arbor and in fact up to a filling level below the nozzle mold. Thereafter this melt filling is displaced under low pressure in the direction towards the nozzle mold by adjusting the inner arbor in the direction towards the end position. Only then is the inner arbor fixed in the end position before the remaining melt volume is injected under increased pressure.

This occurs for example in that, with the inner arbor not yet inserted into the cavity and into the end position, the needle valve is opened and, metered under low pressure, melt is introduced into the bottom and body mold. In the absence of the cool inner arbor the melt can be conveniently distributed before the inner arbor is then moved into the end position under the displacement of melt in the direction of the nozzle mold and blocked with the nozzle mold with the required closing force. The cavity is then closed and the remaining melt volume is injected under high pressure, metered out of the needle valve, until the preform is produced.

With a practicable variant of the method a dwell pressure phase is superimposed on the injection molding of the preform to prevent shrinkage. The cavity is initially partially filled by the inner arbor under low pressure with the inner arbor still withdrawn and the nozzle mold lifted. Then the inner arbor with the nozzle mold is lowered and blocking occurs, wherein the initial melt filling is displaced under low pressure by the inserted inner arbor. After blocking, the remainder of the melt charge, except the remaining melt volume in the inner channel of the inner arbor, is introduced into the cavity. Once the metering needle valve has been closed, a needle is pushed through the inner channel to press the rest of the melt volume into the cavity in the dwell pressure phase, thus preventing shrinkage.

Furthermore, according to the method even the nozzle mold can be closed first or placed upon the body mold and/or the inner arbor first introduced once sufficient melt has been introduced in one part of the cavity without contact with the inner arbor. This saves process time and facilitates an initially low pressure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1shows in a plan view a device V for the stretch blowing of plastic containers, in particular PET bottles, in a single-stage process. The individual components of the device V are arranged in a modular design compactly with respect to one another and comprise an injection rotor1, which is combined with an extruder2, which at least partially rotates with it, and which interacts with an adjacent conditioning section3, formed here as a conditioning circuit, to which several cooling and/or heating stations4are assigned. The conditioning section3cooperates with a feed carousel5, which for its part operates together with a blowing rotor6for stretch blowing the containers, from which finished containers are transported away by a discharge carousel7in the arrow direction8. Several injection molds10are arranged on the injection rotor, e.g. in the circumferential region. In the conditioning section3transfer expanding arbors40are provided as transfer elements on movable arms of a separation delay carousel43. The entry carousel5also has transport or transfer elements which transfer the preforms P coming from the injection rotor1to blow-molds50of the blowing rotor6.

According toFIG. 2the injection rotor1is arranged for rotational drive on a carrier9situated on the underside and fitted with the injection molds10arranged in the carriers located in the tension rod28. In the center of the injection rotor1a rotary distributor11is arranged, which comprises a multi-channel disk12and pipes13(heating channels with heaters) leading to controlled needle valves14on the injection molds10. Furthermore, with the illustrated embodiment a media rotary distributor15for working media of the injection rotor1is arranged centrally underneath (cooling medium, cleaning medium, heating medium, compressed air, hydraulic medium, control or supply current, etc.).

Each injection mold10contains an inner arbor16, which can be linearly adjusted by means of a hydraulic cylinder or a servo-operated closing spindle (designated as servo in the following)20, a single-part or divided bottom and body mold17and a divided or openable nozzle mold19. Each nozzle mold19is opened or closed by means of a pneumatic cylinder21and an articulated lever mechanism30illustrated inFIG. 3and blocked in the closed position through conical mold closure by means of the hydraulic cylinder or servo20via the inner arbor16. Expediently, the inner arbor16is internally cooled and the nozzle mold19is also cooled.

The central extruder2is essentially in the X axis of the injection rotor1and at the top (alternatively at the bottom), wherein at least the extruder nozzle rotates synchronously with the injection rotor1. Expediently, the extruder housing is divided into a high-pressure part23with the extruder nozzle and a charging part24. The high-pressure part23interacts with the charging part24via a sealed rotary joint22such that the charging part24is stationary when the high-pressure part23rotates, for example is held via a torque support25relative to the injection rotor1. Inside the housing of the extruder2there is at least one extruder screw26, which is not highlighted in further detail and which rotates with a movement relative to the high-pressure part (23). The extruder is supplied with plastic granules, for example, via at least one stationary granule feed screw27.

FIG. 3illustrates the opened injection mold10, to which access is possible on four sides through the columns28and a carrier plate29of a mold holder. The pneumatic cylinder21has already opened the nozzle mold19via the articulated lever mechanism30. On the upper side of the nozzle mold19a closing cone31can be seen which interacts with a counter cone in a carrier of the inner arbor16in order to establish the required closing pressure in the closed position of the nozzle mold19. The finished preform P is pulled out of a cavity32of the body and bottom mold17by a height-adjusting movement of the nozzle mold19and already coupled to a transfer expanding arbor40, which is not highlighted in further detail (or a sidewards moving gripper), which conveys the preform P into the conditioning section3. In this embodiment the body and bottom mold17does not need to be separable nor openable.

The transfer expanding arbor40grasps inside into the opening of the preform P, which in this operating phase is stable and has a low temperature. The transfer expanding arbor40is then transferred with the preform on a separation delay carousel43into the conditioning section3, wherein the transfer expanding arbor40rotates and the preform is conveyed past the cooling stations4until the correct temperature profile is obtained. Then grippers41on the entry carousel5accept the respective preform and transfer it to a blow mold50of the blowing rotor6. The usual stretch-blowing process occurs with further rotation of the blowing rotor6.

FIGS. 4A to 4Fillustrate a possible movement sequence in the injection mold10.

InFIG. 4Athe injection mold is still closed after the completion of an injection process. The needle valve14closes off. A carrier33of the inner arbor16blocks the closed nozzle mold19. The articulated lever mechanism30is closed.

InFIG. 4Bthe inner arbor16is moved upwards with its carrier33. Now the nozzle mold19is moved upwards together with the articulated lever mechanism13and the pneumatic cylinder21into the position inFIG. 4Ctogether with the preform. In this way the blocking between the nozzle mold19and the body and bottom mold17is released. The transfer expanding arbor is moved up and the preform with the nozzle mold mechanism34is moved into the transfer expanding arbor40of the conditioning section3.

InFIG. 4Dthe nozzle mold19has been opened and the preform P is already seated on the transfer expanding arbor40, which swivels it out of the injection carousel.

InFIG. 4Ethe nozzle mold mechanism34is again retracted and lowered and the nozzle mold19is closed. The inner arbor16is lowered.

InFIG. 4Fthe inner arbor16has reached its lower end position and is blocked with the nozzle mold19, which for its part is also blocked with the body and bottom mold17. The needle valve14opens and begins a new injection process.

The movement sequence inFIGS. 4A to 4Fcan be practicably modified somewhat in order to realize a method according toFIGS. 5A to 5Cin which an injection molding process is combined with or superimposed by a compression molding process. This means that according toFIG. 5A, in contrast toFIGS. 4E and 4F, the inner arbor16has not yet moved downwards into the end position and, if necessary, even the nozzle mold19is also not yet placed in position and closed when, with the opening of the needle valve14, which is displacement/time controlled as required, melt35flows metered under slight pressure initially into the cavity32of the bottom and body mold17. In contrast to the illustration inFIG. 4F, now first with a still open needle valve inFIG. 5B, the inner arbor16is inserted into the melt35in the direction of the end position, wherein it displaces melt35in the direction towards the nozzle mold19. The nozzle mold19has, where necessary, only now or still not been blocked with the body and bottom mold17and closed. In the sequence according toFIG. 5Cthe inner arbor16is moved up into the end position and blocked by means of the carrier33with, as applicable, the cone31of the now lowered, closed nozzle mold19, so that the cavity32is closed. The required closing force is produced via the servo20. The remaining melt volume is then injected under high pressure according to a conventional injection molding process.

The advantages of the method outlined based onFIGS. 5A to 5Care as follows:

The melt35flowing in under low pressure is not immediately cooled by the cold inner arbor16, because it is still raised. Uniform spreading of the melt occurs, wherein shortening of the injection time can be achieved. Also, with this method shortening of the dead time arises, because the injection mold at the start of the process does not need to be completely closed. A metering unit is not needed and also no problems occur with regard to the portioning accuracy during compression molding. Similarly, a specific dwell pressure problem for the compression molding does not arise. Since no final molding occurs during the compression molding phase, only slight press forces are required for the inner arbor16. Overall the melt is handled very carefully, resulting in a high quality preform. Overall an increase in the capacity per injection mold or cavity arises and energy can be saved due to the optimized process. This method is practicable for the device V according toFIG. 1(or according toFIG. 8), but is also practicable for other stretch-blowing devices or preform injection molding devices.

InFIG. 6the injection mold10is formed with a bottom and body mold17from a separate bottom mold17band a separate body mold17cand the carrier33of the inner arbor16is seated in a carrier48, which is connected to a piston rod47of the hydraulic cylinder or alternatively to the servo20. InFIG. 6the injection mold10is closed.

InFIG. 7the injection mold10is illustrated in the disassembled state. The inner arbor16with its carrier33is withdrawn from the carrier48. The inner arbor has cooling channels53which communicate with the cooling channels52in the carrier48when the carrier33is deployed. Also, a locking cone54below in the carrier33is shaped for cooperating with the locking cone31of the nozzle mold19and a locking cone55is also formed in the body mold17c. The bottom mold17band the body mold17care consecutively introduced into a bush49which is mounted in the mold holder28,29adjoining the needle valve14and includes channels51for cooling and/or heating, which communicate with channels56formed in the body mold17cand bottom mold17b. InFIG. 7the articulated lever mechanism30is released from the nozzle mold19.

In the further embodiment of the device illustrated inFIG. 8in a schematic plan view for stretch blowing plastic containers, in particular PET bottles, in a single-stage process the respective inner arbor16serves as a carrier for the preform P during the injection process and along the conditioning section. In this case the inner arbor16is not internally cooled.

InFIG. 8on the injection rotor1with the mutually rotating extruder2a conditioning section3ais connected, which is formed as a conditioning loop with the link chain43, which also extends around the injection rotor1. The conditioning section3acan, as indicated with37, be variable in length. On the link chain43grippers39are arranged, which for example are rotatable in the direction of the arrow46along the conditioning section3aand are used to grasp adapter parts44of the inner arbors16illustrated inFIG. 9.

InFIG. 8a transfer carousel42, which for example is fitted with grippers40(e.g. expanding arbors), is arranged between the conditioning section3aand the entry carousel5. The grippers40accept the preforms P from a removal and transfer device38in the conditioning section3a. The removal and transfer device38is for example a lowering device for the preforms transported from the inner arbors16. A cooling station4between the transfer carousel42and the injection rotor1can be used for cooling the inner arbors16on the return path into the injection rotor1. Further heating and/or cooling stations, which are not illustrated, can be used for conditioning preforms on the inner arbors16. If necessary, preform cooling stations are assigned to the transfer carousel42. Also, the device V illustrated inFIG. 8is a modular design composed of single modules optionally combined together in a compact arrangement.

FIG. 9shows that in each injection mold10the bottom and body mold17ais separable and openable and also already includes the nozzle mold19in an openable version. The inner arbor16carries on top the adapter part44on which the gripper39on the link chain34grasps to remove the inner arbor16carrying the preform P from the opened injection mold10and to transfer it to the conditioning section3a. If necessary, each inner arbor16is moved laterally after lifting to the waiting gripper39on the link chain34. In this case the inner arbor16can be held like a bottom mold. The bottom and body mold17can be opened and closed together with the nozzle mold19by a pneumatic cylinder21(not illustrated) and an articulated lever mechanism30. The blocking by the inner arbor16occurs via the hydraulic cylinder20, which provides the required closing pressure and mold closure via appropriate cones and, where necessary, locking pins. The grippers39on the link chain43are designed such that they release the inner arbor16in the injection rotor1and rotate it along the conditioning section. The removal and transfer device38removes the preform P, which is brought to the required temperature profile, from the inner arbor16by pulling it off downwards and transfers the preform to the transfer carousel42. Then the empty inner arbors16are cooled during the return transport into the injection molds10.

According to the embodiment ofFIG. 2, the mutually rotating extruder2is arranged for example suspended on the injection rotor1centrally and above using a torque support, with the rotary distributor11arranged below the extruder nozzle, from which the individual needle valves14below the injection mold10are supplied. The needle valves14here belong to the machine module. The modular design is service-friendly.

In an alternative embodiment, which is not shown in detail and which is explained based onFIGS. 8 and 9, the inner arbors16are not used as carriers for the preforms P on the path to the blowing rotor6, but instead the openable nozzle molds19, which can be removed from the injection molds10, are used for this. Each nozzle mold19can have an adapter part, which is grasped by a gripper39and taken out of the injection mold10with the closed nozzle mold19with the preform P located in it. The nozzle mold19remains closed and is first opened in the removal and transfer device38in the conditioning section3a, before for example an expanding arbor of the transfer carousel42accepts the preform P.

In a further alternative the closed nozzle molds19are even directly transferred into the blow-molds50of the blowing rotor6so that they also act as mold parts during the stretch-blowing process. However, a return device, which is not illustrated, is then needed for the nozzle molds19.

For the optimum loading of the stretch blowing molds50in the blowing rotor6(the cycle time for the stretch blowing can be shorter than the cycle time for the injection molding of a preform) it is practicable with respect to the number of blow-molds50to provide a larger number of injection molds10so that the single-stage process operates under optimized conditions.

InFIGS. 10A to 10Dfour process phases are illustrated in a further embodiment of the injection mold10. The injection mold10has a bottom and body mold17(single or two-part) in which part of the cavity32is defined. The nozzle mold19can be moved together with the inner arbor16relative to the bottom and body mold17. In this embodiment the inner arbor16has an inner through channel61which terminates at an opening59at the free end of the inner arbor16. On a carrier part58of the nozzle mold19and the inner arbor16cooling channels52are connected to be able to cool the internally cooled inner arbor16and, where applicable, also the nozzle mold19. The bottom and body mold17also has cooling channels which are not illustrated. At the upper end of the inner arbor16a nozzle56is provided to which the melt injection valve is connected, which in this embodiment is formed as a metering needle valve14and in each case introduces under control an exactly measured charge. In the inner channel61of the inner arbor16a needle57is movably guided, which at the free end is formed as a stamp60which fits relatively tightly into the inner channel61. A heating channel for the melt, which is not highlighted in further detail, leads to the metering needle valve14.

In the process phase illustrated inFIG. 10Awith the inner arbor16raised and the nozzle mold19closed melt from the metering needle valve14is introduced via the inner channel61into the cavity32under slight pressure, filling the lower part of the cavity32. The needle57is in its upper feed position in which it closes the inner channel61at the top and releases the flow connection from the metering needle valve into the inner channel61.

Then between the process phases inFIG. 10AandFIG. 10Bthe stamp16is lowered together with the nozzle mold19until the nozzle mold19is blocked with the bottom and body mold and the inner arbor16has been fixed in its lower end position. In doing this, the inserted inner arbor16displaces the melt35initially up to the top end of the cavity32in the bottom and body mold17. Until this point the complete melt charge has not yet been introduced.

In the process phase inFIG. 10Bthe nozzle mold19is blocked with the bottom and body mold17. As before, the needle57is in the feed position. The remainder of the melt charge is introduced from the metering needle valve14so that the region of the nozzle mold19is also filled.

In the next process phase inFIG. 10Cthe metering needle valve14is controlled for closure and the needle57displaced in a lower dwell pressure position, wherein the needle57with the stamp60then presses the remaining as it were temporarily stored melt volume in the inner channel61out of the inner channel61into the cavity until finally the stamp60closes the opening59of the inner channel61.

In the process phase inFIG. 10Dafter the production of the preform P, the inner arbor16has been raised relative to the bottom and body mold17together with the nozzle mold19, wherein the preform P remains on the inner arbor16and in the nozzle mold19and is withdrawn out of the cavity32. Then the nozzle mold19is opened and the preform P removed and transferred to the conditioning section. Simultaneously or soon after, the needle57is drawn again into its upper feed position to release the connection between the metering needle valve14and the inner channel61. Then follows the process step according toFIG. 10A.

In an embodiment ofFIGS. 10A to 10Dwhich is not illustrated the nozzle mold19could also remain on the bottom and body mold17while the inner arbor16is moved. To remove the preform P the nozzle mold19must however be first opened so that the preform can be withdrawn from the cavity32with the inner arbor16.