Abstract:
A blowing apparatus for expanding containers with a gaseous medium has a blowing piston and a blowing nozzle, through which the container is expanded with the gaseous medium. The blowing piston is movable in a longitudinal direction (L) of the blowing nozzle, the blowing nozzle is movable in the longitudinal direction (L) relative to the blowing piston, and a guide device is provided which guides the movement of the blowing nozzle in the longitudinal direction (L) relative to the blowing piston.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to an apparatus for treating containers and in particular to a blowing apparatus for expanding containers. In addition, the invention also relates to a method for expanding containers. 
     From the prior art, it is known in the context of producing various vessels to expand the latter using a blowing nozzle. To this end, suitable blanks are heated and then are acted upon by compressed air at a pressure in the region of approximately 40 bar through a blowing nozzle. By virtue of this pressure, the container is expanded. It is known from the prior art that a sealing between the blowing apparatus and the container takes place during the actual expansion process, i.e. the process during which the container is expanded with the compressed air, so that the container can be properly expanded. It is known to perform such sealing for example at the upper rim of the mouth of the container or also below the mouth rim. 
     A mouth will hereinafter be understood to mean a region of the preform which has a collar and a region extending beyond this collar in the direction of the pouring opening. According to one preferred further development, the mouth has a thread. A collar is understood to mean a radially protruding, at least partially circumferential accumulation of material which is preferably configured as a ring. In this case, the collar may be configured as a carrying ring, but also as a securing ring. However, the invention is not limited to the use of the above mouths. 
     In order to achieve this sealing, in the prior art the blowing piston is lowered onto the vessel and is usually pressed against the latter. In doing so, the contact pressure can be controlled only with relative difficulty. An excessively high pressure on the mouth of the preform may lead to deformations, and an excessively low pressure may result in insufficient sealing between the blowing apparatus and the container. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is therefore to improve a blowing process for plastic containers and in particular to improve the sealing between the blowing apparatus and the container, without at the same time risking deformation of the preform. 
     The blowing apparatus according to the invention for expanding containers with a gaseous medium comprises a blowing piston and a blowing nozzle, wherein the container is expanded with the gaseous medium through the blowing nozzle. According to the invention, the blowing piston is movable in a longitudinal direction of the blowing nozzle and the blowing nozzle is likewise movable in the longitudinal direction relative to the blowing piston, and furthermore a guide device is provided which guides the movement of the blowing nozzle in the longitudinal direction relative to the blowing piston. 
     According to the invention, therefore, two different degrees of freedom of movement are provided, namely on the one hand a degree of freedom of movement of the blowing piston in a longitudinal direction, wherein this longitudinal direction is usually also the longitudinal direction of the container to be expanded, and also a degree of freedom of movement of the blowing nozzle relative to the blowing piston in the longitudinal direction. By virtue of this further degree of freedom of movement in the longitudinal direction, finer control of the contact pressure of the blowing apparatus relative to the container is possible. 
     In a further advantageous embodiment, the blowing nozzle is configured in such a way that it is urged towards the container by the gaseous medium as the container is acted upon by the gaseous medium. This means that the air flow which brings about an expansion of the container at the same time also urges the blowing nozzle and possibly also the guide device towards the container and thus brings about a sealing effect between the container and the guide device. 
     In a further advantageous embodiment, the blowing nozzle is arranged radially inside the guide device and is in this way guided by the guide device. 
     In a further preferred embodiment, the blowing apparatus comprises a pretensioning device which urges the blowing nozzle towards the container in the longitudinal direction relative to the blowing piston and possibly also relative to the guide device. In this embodiment, with particular preference, the blowing nozzle is movably guided in parallel with the blowing piston axis and is pretensioned by means of a spring, preferably a coil spring. In this case, the guide is likewise mounted on the blowing piston. A certain pretensioning of the nozzle relative to the container is thus brought about by the spring. 
     In a further advantageous embodiment, the blowing nozzle comprises a first section (nozzle section) with a first internal cross-section and a second section (nozzle piston) with a second internal cross-section. In this case, the first internal cross-section differs from the second internal cross-section. With particular preference, there is provided a lower cross-section of the blowing nozzle and an upper cross-section which is larger in comparison thereto. In other words, the nozzle preferably has a nozzle diameter adapted to the associated preform diameter and also a resulting surface area adapted to the desired contact pressure between the nozzle and the preform. 
     The gaseous medium flowing through the nozzle in order to expand the container in this way exerts a pressure on the resulting surface area which results from the difference between the two internal cross-sections, and in this way causes the nozzle and/or the guide device to press against the container. More specifically, preferably the nozzle itself has a sealing means which brings about the sealing relative to the upper rim of the mouth for example or also other regions of the mouth. The sealing means may be both an elastomer and also the nozzle itself, so that then a seal between metal (blowing nozzle) and plastic (container). 
     In a further preferred embodiment, the internal cross-section of the blowing nozzle tapers in the longitudinal direction from top to bottom. This tapering may preferably be continuous. In this case, the tapering internal cross-section means that the medium passing through the blowing nozzle urges the blowing nozzle towards the container. 
     In a further advantageous embodiment, the guide device has an inner wall which surrounds the mouth of the container at least partially but around the entire circumference during the blowing process in the longitudinal direction of the container. In this way, it is possible to achieve an improved centring of the blowing apparatus relative to the container to be expanded. 
     A guide device is understood to mean any device which guides a movement of one element relative to another element. Preferably, the guide device is arranged on the blowing piston and immovably in the longitudinal direction relative to a blowing piston. Preferably, the guide device is also detachably arranged on the blowing piston. In this way, for example in the context of changing a fitting, the guide device can be replaced together with the blowing nozzle in order quickly to achieve a changeover to other mouth properties. However, it would also be possible for the guide device to be arranged fixedly on the blowing nozzle and movably relative to the blowing piston. In other words, the concept according to the invention means that there is no need to change the blowing piston when changing a fitting; it is sufficient to replace only the blowing nozzle with its guide device. 
     In a further advantageous embodiment, the blowing apparatus comprises a sealing device which is in contact with a region of the wall of the container during the blowing process and seals off a space between the blowing nozzle and a wall of the container. As mentioned above, this sealing device is preferably arranged on the blowing nozzle and means that the container can be expanded without the gaseous medium, such as blown air for example, being able to escape to the outside. Preferably, the region of the wall is an upper mouth rim of the container and thus the blowing apparatus is preferably a top-sealing blowing apparatus. This sealing device is preferably made from an elastomer or comprises such an elastomer. However, the sealing device may also be metallic, so that then a sealing takes place between a plastic (container) and a metal (blowing nozzle). 
     In a further embodiment, the region of the mouth is a region of the outer circumference of the mouth of the container and preferably the carrying ring of the container, and thus the blowing apparatus is an outside-sealing blowing apparatus. 
     During operation, the blowing piston is moved into a lower end position and the nozzle is pressed onto the preform by the pretensioning device. The preform is then expanded or the bottle is blown. By virtue of the resulting surface area of the nozzle or the abovementioned difference in the internal cross-section, an additional contact pressure besides the spring force is generated via the pressure already exerted by the pretensioning device, which seals off the nozzle relative to the carrying ring or also relative to a region of the mouth. 
     In a further advantageous embodiment, a sealing ring is provided between the guide device and the blowing nozzle. 
     In a further advantageous embodiment, the blowing nozzle is secured relative to the guide device by means of a screw body which surrounds the blowing nozzle in the circumferential direction. Preferably, the guide device in this case has a thread. By loosening the screw body, in this way the blowing nozzle itself can be detached from the guide device. The guide device is also detachable from the blowing piston for example by loosening one or more screws. 
     The present invention also relates to an arrangement for expanding containers, comprising a blowing apparatus of the type described above. 
     Preferably, the present invention is used in the production of bottles made from plastic, and preferably made from PET. 
     The invention thus relates in particular to a stretch-blowing machine and in particular to a rotary stretch-blowing machine. Located in a stretch-blowing machine are a plurality of blowing apparatuses according to the invention which in each case comprise at least one blow mould, an apparatus for producing bottles and also preferably at least three valves for switching and controlling the blown air. In this case, these valves control the supply of blown air for expanding the containers. It is pointed out that, in one particularly preferred embodiment, the air which serves for expanding the containers at the same time also serves for achieving an increased contact pressure of the blowing nozzle against the container. 
     The present invention also relates to a method for filling and expanding containers with a gaseous medium. In a first method step a blowing piston, which comprises a blowing nozzle arranged on this blowing piston such that it can move in the longitudinal direction of the container, is lowered in the longitudinal direction of the container as far as a predefined end position of the blowing piston relative to the container. In a further method step, the container is filled with the gaseous medium through the blowing nozzle. 
     According to the invention, the gaseous medium flowing through the blowing nozzle during the filling and expansion process causes the blowing nozzle to be urged towards the container in the longitudinal direction of the container and causes the blowing nozzle to exert a pressure on the container in the longitudinal direction. 
     More specifically, the abovementioned different cross-sections of the blowing nozzle cause the blowing piston to be moved towards the mouth. 
     However, it would also be possible that the additional pressure of the blowing nozzle on the container is brought about by a pretensioning device such as a coil spring instead of by the air flow. In this case, it is also possible to configure the coil spring or the arrangement thereof in such a way that the spring force on the blowing nozzle can be varied by the user. With particular preference, however, the pressure on the container is brought about both by the coil spring and also by the air flowing through during the expansion process. 
     In this preferred embodiment, therefore, the blowing nozzle is pretensioned relative to the container by means of a pretensioning device or spring device. In a further advantageous method, the blowing nozzle is guided movably in the longitudinal direction relative to the blowing piston by means of a guide device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages and embodiments will emerge from the appended drawings. 
       In the drawings: 
         FIG. 1  shows a blowing apparatus according to the invention with a container to be expanded; 
         FIG. 2  shows the blowing apparatus of  FIG. 1  in a first operating position; 
         FIG. 3  shows the blowing apparatus of  FIG. 1  in a second operating position; 
         FIG. 4  shows the blowing apparatus of  FIG. 1  in a third operating position; and 
         FIG. 5  shows a further blowing apparatus according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a blowing apparatus  1  according to the invention in a first embodiment. This blowing apparatus  1  comprises a blowing piston  2 . The blowing piston  2  is moved into a certain (end) position by means of a guide cam (not shown) in order in this (end) position to supply compressed air to a container  10 , here a preform, so as to expand the latter. The container  10  is arranged in a blow mould (not shown) with the aid of a centring plate  30 . Reference  32  denotes a protrusion of the centring plate  30 , on which a carrying ring  10   b  of the container is supported. Reference  10   a  denotes in its entirety a mouth of the container  10 . Provided on this mouth  10   a  are a thread  10   c  and also a further ring  10   d.    
     A guide device  4  is detachably mounted on the blowing piston  2 . A blowing nozzle  6  is arranged such that it can move in a longitudinal direction L relative to this guide device  4 . The blowing nozzle  6  is moved towards the container  10  by means of a spring. Reference  24  denotes a screw body, by means of which the blowing nozzle  6  is screwed into the guide device  4 . More specifically, this screw body  24  has a screw thread  24   a  which cooperates with a corresponding internal thread of the guide device  4 . 
     The blowing nozzle  6  has an internal cross-section A nozzle-internal . In addition, the blowing nozzle  6  has a nozzle piston  16  which is movable in the longitudinal direction L relative to the guide device  4 . This nozzle piston  16  has an internal cross-section A piston-nozzle . Reference A preform,internal  denotes the internal cross-section of the preform or container  10 , in particular of the mouth  10   a  thereof. 
     Through an opening  3  of the blowing piston  2 , the nozzle  6  and thus the container  10  is acted upon with compressed air having the pressure P blown air . This compressed air results in the force F blowing nozzle  acting on the blowing nozzle, as follows:
 
 F   blowing nozzle   =P   blown air ·( A   piston-nozzle   − )−( A   preform,internal   −A   nozzle,internal )
 
 F   blowing nozzle   =P   blowing nozzle ·( A   piston-nozzle   −A   preform,internal )
 
     This means that the force F blowing nozzle  acting on the blowing nozzle F depends only on the internal cross-section A piston-nozzle  of the piston  16  and on the internal cross-section A preform,internal  of the container  10 . Therefore, according to the invention, the blowing nozzle  6  has a nozzle diameter adapted to the associated preform diameter and also a resulting surface area adapted to the desired contact pressure between the blowing nozzle  6  and the container  10 . This adaptation takes place by a suitable choice of guide diameter or guide radius R guide , since the resulting surface area A res  is obtained as follows:
 
 A   res =(( R   guide ) 2 −( R   nozzle ) 2 )·π
 
     The radius of the blowing nozzle R nozzle  (or of the nozzle section  14 ) is in this case already determined by the type of preform. 
       FIG. 2  shows a blowing apparatus of  FIG. 1  in a first operating position, i.e. before the blowing apparatus  1  is placed onto the mouth  10   a  of the container  10  (or preferably the outer wall of this mouth  10   a ). The guide device  4  is securely but detachably mounted on the blowing piston  2  via a screw connection  26 ,  27 . The compressed air passes through the blowing piston  2  in the direction L towards the blowing nozzle  6 . This blowing nozzle  6  has a nozzle section  14  and the nozzle piston  16  already mentioned above. This nozzle piston  16  and the nozzle section  14  are formed in one piece with one another and are joined via a radially running ring  15 . Reference  28  denotes a sealing device, by means of which the blowing piston  6  is sealed off relative to the guide device  4 . 
     In the embodiment shown in  FIG. 2 , the blowing piston  2  has a sealing device  22  on its underside, which can be pressed against a mouth rim  10   e  of the container  10 . 
     Reference  13  denotes a guide ring for guiding the blowing nozzle  6  relative to the guide device  4 . The screw body  24  or the limiting nut  24  at the same time limits the movement of the blowing nozzle  6  relative to the guide device  4  in the longitudinal direction L. 
       FIG. 3  shows a position of the blowing apparatus  1  in which it is in contact with the mouth  10   a  of the container  10 . More specifically, the abovementioned mouth rim  10   e  now bears against the sealing device  22  of the blowing nozzle  6 , so that the space located between the blowing nozzle  6 , more specifically the nozzle section  14  thereof, and the container  10  is sealed off. 
     In the diagram shown in  FIG. 4 , the blowing piston  2  has again been moved downwards slightly and, since the blowing nozzle already bore against the upper rim  10   e  of the container  10  in the situation shown in  FIG. 3 , in this way brings about a pretensioning of a pretensioning device or spring  12 . More specifically, the blowing nozzle  6  is biased relative to the guide device  4  in the downward direction, i.e. onto the container  10 , by the spring  12 . 
     Starting from the situation shown in  FIG. 4 , the blowing piston  2  and thus also the blowing nozzle  6  is acted upon by compressed air, which leads to a further pressure acting in the direction B being exerted on the blowing nozzle  6  according to the above equation. By virtue of this pressure, the sealing effect between the container  10  and the blowing nozzle  6  is increased. Since the force acting on the container from the blowing nozzle also depends directly on the pressure of the blown air, the contact pressure of the blowing nozzle  6  on the upper rim  10   e  of the container  10  is also increased as the pressure of the blown air increases, and thus the sealing effect is at the same time increased when the pressure of the blown air is increased. 
       FIG. 5  shows a further embodiment of a blowing apparatus  1  according to the invention. Unlike the blowing apparatus  1  shown in the preceding figures, here a sealing of the container  10  from the outside takes place, more specifically via the carrying ring  10   b  of the container  10 . In this embodiment, the guide device  4  is fixedly arranged on the blowing nozzle  6  in the longitudinal direction L. More specifically, the guide device  4  is arrested in the longitudinal direction by a lower lug  46  and a first securing ring  44 . On the other hand, however, the guide device  4  is movable in the longitudinal direction L relative to the blowing piston  2  or an intermediate piece fixedly arranged on this blowing piston  2 . In addition to the aforementioned first securing ring  44 , a second securing ring  42  is provided on the inner circumference of the guide device  4 . The range by which the guide device  4  can be displaced in the longitudinal direction L relative to the intermediate piece  37  and thus also the blowing piston  2  is determined by the distance between these two securing rings and optionally also the width of the recess  35 . 
     Reference  36  denotes a sealing device which is provided between the guide device  4  and the intermediate piece  37 , more specifically an inner wall  18  of the guide device  4  and the intermediate piece  37 . Reference  41  denotes a guide ring. 
     The intermediate piece  37  is arranged here on the blowing piston  2  with the aid of a quick-action fastener, wherein reference  38  denotes balls of this quick-action fastener. However, other possibilities are also conceivable for arranging the intermediate piece  37  on the blowing piston, such as screw threads for example. 
     Reference  12  once again denotes here a coil spring which is provided between the blowing nozzle  6  and the blowing piston  2 , more specifically the intermediate piece  37  fixedly arranged on the blowing piston  2 . 
     In the embodiment shown in  FIG. 5 , the force F blowing nozzle  acting on the blowing nozzle by the compressed air is as follows:
 
 F   blowing nozzle   =P   blown air ·( A   piston-nozzle   −A   nozzle,internal )−( A   active surface area   −A   nozzle,internal )
 
 F   blowing nozzle   =P   blown air ·( A   piston-nozzle   −A   active surface area )
 
     The force acting on the blowing nozzle thus also depends only on the cross-section A piston-nozzle  of the nozzle piston  16  and on the active surface area A active surface area . 
     It is pointed out that the respective subtrahend in the above equations is obtained by the counter-pressure which is in turn directed upwards from the container, i.e. in the direction of the blowing nozzle. To a good approximation, this pressure corresponds to the abovementioned pressure of the blown air P blown air . 
     All of the features disclosed in the application documents are claimed as essential to the invention in so far as they are novel individually or in combination with respect to the prior art.