Abstract:
A device and a method for manufacturing plastic containers, where a preform is manufactured in a casting mold and finished in a blow mold, and to ensure a constructively simple realization and an improved temperature control, the casting mold and the blow mold are lined up to form a mold complex.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of priority of German Application No. 102010001096.0, filed Jan. 21, 2010. 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 manufacturing plastic containers. 
     BACKGROUND 
     A device of this type is known from DE 197 37 697 A1. The prior device comprises a casting mold in the form of an injection mold, in which a plastic blank, a so-called preform, is manufactured. In the blow mold this preform is blown to form the finished container. There are provided a plurality of casting molds, which are disposed on preferably two injection mold rotors, which move past an extruder one after the other, which fills the injection molds with liquid plastic. Next, the preforms formed in the injection molds are transferred to a transfer rotor, The transfer rotor then transfers the preforms to a blow molding rotor, which is provided with a plurality of circumferential blow molds. Each preform is inserted into a blow mold and blown to form the finished container. 
     The blowing is preferably accomplished by means of a stretching rod, which stretches the preform in an axial direction, while the introduced compressed gas (usually air) entails a radial stretching of the preform. Stretching rods are commonly used for the manufacture of plastic containers and are described, for instance, in U.S. Pat. No. 4,039,641. 
     One problem involved by the transfer of the injection molded preform to the blow mold is the temperature control, which is never exactly definable because the preforms, when being transferred, are exposed to exterior conditions that vary according to the ambient conditions (outside temperature). Therefore, it is safer to let the preforms cool down and provide a heater for heating the preforms to a predetermined temperature for the blowing process. In addition, the prior device is very complex with regard to its construction and requires plenty of floor space. 
     SUMMARY OF THE DISCLOSURE 
     The disclosure is based on the object to provide a device and a method for manufacturing plastic containers, which has a constructively simply design and permits a controlled temperature control. 
     Due to the embodiment according to the disclosure the preform can be transferred directly between the two molds, that is, between the casting mold and the blow mold, without being exposed to ambient conditions in the meantime. Thus, the predetermined blowing temperature can be exactly maintained, without the need for an interim heating. Moreover, the mold complex according to the disclosure can be disposed on a single transport device, preferably on a rotor, so that the required floor space is at least half the size. 
     Another constructive advantage resides in the fact that the inner mold or the outer mold required for manufacturing the preform can assume a plurality of functions both in the casting mold and particularly also in the blow mold. For instance, the inner mold may assume the function of an ejector or the transfer device between the molds. Additionally, or alternatively, the inner mold may also be employed as a stretching mandrel and/or as a blowing lance in the blow mold. Finally, it is even possible to use the inner mold or the outer mold for feeding a product to be filled into the container after the blowing process, so that both the manufacture of the containers and the filling thereof can be accomplished on the same transport device (rotor). Also, a return air pipe for the filling process may be located either in the inner mold or the outer mold. 
     By arranging a temperature control device in the casting mold, the same can be heated additionally or cooled more strongly at the appropriate places, so that the preform can be provided with a predetermined temperature profile. 
     Furthermore, the inner mold may be provided with a cooling device, by means of which, for instance, the places to be stretched to a smaller extent during the blowing process can be cooled. This applies, for instance, to the orifice region of the preform, where dimensional stability is required. 
     The disclosure can be realized with any type of casting mold, especially with the two most conventional casting molds, i.e. an injection mold or a pressing mold. 
    
    
     
       Embodiments of the disclosure shall be explained in more detail below by means of the drawings. In the drawings: 
         FIG. 1  shows a schematic top view of the disclosed device, 
         FIG. 2  shows a mold complex of the device. 
         FIG. 3  shows the mold complex of  FIG. 2  in another method step, 
         FIG. 4  shows the mold complex of  FIG. 2  in another method step, 
         FIG. 5  shows the mold complex of  FIG. 2  in another method step, 
         FIG. 6  shows the mold complex of  FIG. 2  in another method step, 
         FIG. 7  shows the mold complex of  FIG. 2  in another method step, 
         FIG. 8  shows the mold complex of  FIG. 2  in another method step, 
         FIG. 9  shows the mold complex of  FIG. 2  in another method step, 
         FIG. 10  shows the mold complex of  FIG. 2  in another method step, and 
         FIG. 11  shows an alternative mold complex. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows an extremely schematic representation and top view of a device  1  for manufacturing containers  2  of plastic, in the embodiment shown bottles, especially of PET, The device  1  comprises a continuous conveyor system, specifically a carrousel or rotor  3 , respectively, which is rotatably driven around an axis  3 ′ in the conveying direction F and initially rotates past a feeding device  4  for liquid plastic, specifically an extruder, and then to a conveyor  5 , by means of which finished containers  2  are withdrawn from the rotor  3  and are transported away. Moreover, the rotor  3  is assigned a filling device comprising, for instance, a revolving distributor  6  and a feed line  7 . The components described above are of a conventional type. However, the assignment of a feeding device for liquid plastic and component parts of a filling device have so far not yet been combined in a single rotor. 
     The rotor  3  is provided with a plurality of mold complexes  8  on its circumference, which are explained in more detail in the accompanying drawings. 
       FIG. 2  shows a partial representation of such a mold complex  8 , comprising a casting mold  9  and a blow mold  10 . The casting mold  9  and the blow mold  10  are lined up coaxially with respect to each other along a common center line M and in vertical direction. The casting mold  9  and the blow mold  10  directly abut against each other, that is, there is no transfer or conveying distance with a prevailing ambient atmosphere between the two molds  9 ,  10 . With respect to the respective center lines the lining up could also be realized in an angular manner or offset from each other. 
     The casting mold  9  serves the manufacture of a preform  11  ( FIG. 4 ) as is commonly used for the manufacture of plastic containers. A “preform” is a massive hollow body which only has an orifice and no welding seams (e.g. for welding the opposite side) and of which preferably those parts that have to correspond to each other on the finished containers  2  as dimensionally stable as possible are already fully preformed. These dimensionally stable parts are, for instance, a neck portion  11   b  for receiving a closure (e.g. a screw neck, a closing collar or a flange edge) and a so-called collar  11   c , with which the finished container is to be fitted into and transported in holding devices or conveyors or the like later. 
     As is shown in  FIG. 2  the casting mold  9  is formed as an injection mold and comprises a first mold half  9   a  and a second mold half  9   b , which can be moved apart from each other in the direction of the double arrow O for opening the casting mold  9  and which can be reassembled. The casting mold  9  is divided along a plane that includes the center line M. The mold halves  9   a ,  9   b  each enclose half of a hollow space  12  and form the outer mold, which defines the outer shape of the preform  11 . 
     The inner shape of the preform is defined by an inner mold  13 , which can immerse into the hollow space  12  in the direction of the arrow I along the center line M and can be drawn out of it. If the inner mold  13  is positioned in the hollow space  12  it has an all-around distance to the hollow space  12 , thereby defining the wall thickness of the preform  11 , as can be seen in more detail in  FIG. 3 . 
     The blow mold  10  likewise comprises at least two blow mold parts  10   a ,  10   b , which are separated in the plane of the center line M and enclose a hollow space  14  that defines the outer shape of the finished container  2 . The mold parts  10   a ,  10   b  of the blow mold  10 , too, can be opened and closed in the direction of the arrow O. 
     If a mold complex  8  is located in the region of the plastic feeder  4 , liquid plastic is pressed into the casting mold  9  through a filling section  15 , as is shown in  FIG. 4 , until the hollow space  12  defined by the outer mold  9   a ,  9   b  and the inner mold  13  is completely filled. The introduction of the plastic is accomplished by an injection. 
     As is shown in  FIG. 5 , the injection mold  9  is provided with a temperature control device  16 , by means of which the preform  11  now located in the casting mold  9  can be provided with a desired temperature profile. For instance, by means of a cooling device  16   a , which is provided in certain sections, the regions on the neck  11   b  and the collar  11   c , which have to remain dimensionally stable, can be cooled to a temperature at which the plastic material used cannot be stretched or extended, or only by applying a substantially increased force. In other regions, e.g. in region  16   b , the preform  11  may be heated or maintained at a temperature. 
     Subsequently, the mold halves  9   a  and  9   b  are moved apart, as can be seen in  FIG. 6 , and release the preform  11  sitting on the inner mold  13 . 
     The inner mold  13  of the casting mold  9  is designed for a plurality of other functions. After the casting mold  9  is opened, the inner mold  13  moves as transfer device from the region of the casting mold  9  downwards into the region of the blow mold, which can be seen in a comparison of  FIG. 6  with  7 . In the embodiment shown, the hollow space  14  defined by the blow mold  10  is dimensioned such that the preform  11  can be inserted (through the later feed opening  14   a  of the container  2 ) into the hollow space  14  without opening the blow mold  10 . In other embodiments, however, the blow mold  10 , too, can be opened to receive the preform  11 . 
     The inner mold  13  moves into the hollow space  14  of the blow mold  10  until the preform  11  can be positioned in the correct blowing position in the manner described below. 
     The inner mold  13  comprises a stretching rod  17  commonly used for blow molding, which, in the embodiment shown, is received in an outer sleeve  18 . The stretching rod  17  is disposed in the outer sleeve  18 , coaxially with respect to the center line M, and can be moved relative to it. The outer side of the outer sleeve serves the formation of the inner side of the preform  11  and, in the embodiment shown (see  FIG. 7  or  8 ), is moved into the hollow space  14  of the blow mold  10  at least as far as the neck portion. The stretching rod  17  is then axially displaced relative to the sleeve  18  in the direction of the double arrow R along the center line M, emerges from an opening  18   a  in the head  18   b  of the sleeve in a sealing manner and strips the preform  11  from the inner mold  13  into the hollow space  14 . Outside the head  18   b  a hollow space  18   c  is provided between the stretching rod  17  and the sleeve  18 , through which, for instance, a coolant can be introduced, which cools the head  18   b  of the sleeve  18  and, thus, the parts  11   b ,  11   c  that are adjacent thereto and have to remain dimensionally stable. 
     The stretching rod  17  is provided in a manner known per se with a head  17   a  adapted to the bottom  11   a  of the preform  11 , by means of which the bottom  11   a  can be stretched by further extending the stretching rod  17  in the axial direction with respect to the center line M, which is shown in  FIG. 8 . 
     Another function of the inner mold  13  is its embodiment as a blowing lance, whereby it is the stretching rod  17  that is provided with air outlet openings  19  in its head  17   a , which come out transversely with respect to the center line M and are supplied with blow gas, either compressed air or another pressurized gas, in the usual manner through a supply line  20 . Compressed gas is introduced through these outlet openings  19  into the interior of the preform  11  until, with the support of the stretching rod  17 , all sides of the preform  11  lie against the inner walls of the hollow space  14  of the blow mold halves  10   a ,  10   b  and the container  2  has thus received its final shape. 
     Apart from a stronger portion  17   b , which comprises the head  17   a  and is capable of sealing the opening  18   a  of head  18   b  of the sleeve  18 , the stretching rod  17  has a narrower portion  17   c  in the axial direction, whose outer width is smaller than the opening  18   a  of head  18   b  of the sleeve  18 . When the container  2  has received its final shape the stretching rod  17  is retracted into the sleeve  18  until the narrow portion  17   c  comes to rest inside the opening  18   a  of the sleeve head  18   b . The narrower portion  17   c  merges via an oblique surface  17   d  into the stronger portion  17   b  of the stretching rod  17 , so that, depending on the position of the oblique surface  17   d , there remains an annular gap  21  between the narrow portion  17   c  and the opening  18 , which annular gap  21  serves as a filling valve and has an adjustable flow cross-section. If a product is now filled into the hollow space  18   c  inside the sleeve  18 , it emerges through the annular gap  21  and fills the container  2 . Thus, the inner mold  13  can also be used as a filling device. 
     Preferably, the casting mold  9  is movable relative to the blow mold  10 , so that it can clear the space above the blow mold  10 . By this it is possible to close the container  2  with an appropriate closing means while it is still located in the blow mold  10 . The container is released from the blow mold  10  by opening the blow mold halves  10   a ,  10   b  after the inner mold  13  has completely retired into the casting mold  9 . The containers  2  are picked up by the conveying rotor  5  and are transported away, while the casting mold  9  is closed again around the inner mold  13  and is ready for another injection molding process. 
     Instead of the injection mold, the casting mold  9  may also be designed as a pressing mold for press molding, as is shown in  FIG. 11 . To this end, the inner mold  13 , which is incidentally designed in the same way as in the first embodiment, is completely withdrawn from the hollow space  12  prior to filling in liquid plastic, and an exactly proportioned quantity of liquid plastic is introduced into the hollow space  12 . If the inner mold  13  is then lowered into the hollow space  12  until is has a uniform distance from the hollow space  12  on all sides, the liquid plastic is distributed uniformly, and the preform  11  shown in  FIG. 4  is obtained. 
     Thus, the described mold complex  8  according to the disclosure permits the direct transfer of the preform from the heat of the casting mold to the blow mold, so that a defined temperature can be maintained. Moreover, also the predetermined temperature profile is maintained. 
     According to a modification of the embodiment as described and drawn the disclosure can also be employed if the container need not or cannot directly be filled in the blow mold. If a filling is not necessary, also a horizontal, side-by-side arrangement could be possible instead of the described arrangement of casting mold and blow mold on top of each other, provided that both molds are arranged coaxially with respect to each other so that a direct transfer from the casting mold into the blow mold is possible. The function of the inner mold, the stretching rod and the blowing lance may also be accomplished by one single component. The filling of the container may also be accomplished through other portions of the mold complex. In a preferred embodiment the preform or container, respectively, is continuously transported by the blow mold and/or the casting mold. Specifically, the blow mold and/or the casting mold are disposed on a rotating carrousel. In another preferred embodiment the preform or container, respectively, is handled by a stationary blow mold and/or casting mold.