Plastic article or earthenware shaping or treating: apparatus – Means utilizing force from explosive or thermic composition
Reexamination Certificate
2002-06-04
2004-09-28
Davis, Robert B. (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Means utilizing force from explosive or thermic composition
C264S084000, C425S529000, C425S535000
Reexamination Certificate
active
06796780
ABSTRACT:
The invention relates to a device for manufacturing containers from a plastics material which can be formed by stretch-blowing, with a mould, the internal space of which corresponds to the finished container, which is held by its open end by a receiving portion, wherein lines connected to a metering unit are provided on the receiving portion, a moveable stretching die is guided through the receiving portion, and an ignition means is arranged in order to ignite an explosive gas mixture inside the container, and wherein heating and cooling means are provided.
A device of the type described hereinabove for manufacturing plastics containers, for example bottles from polyethylene terephthalate (PET) is known from international published document number WO98/06559. These PET bottles are manufactured in that firstly a blank is heated to a temperature suitable for stretch blowing, of approximately 100-120° C. This blank is inserted into a tooling mould corresponding to the shape of the container, and a stretching pressure of at least 2 bar, normally of 5-10 bar, is produced. With the aid of an axially, and in general vertically, moveable stretching die, the blank is stretched axially. Then, a blowing pressure is produced in the blank, which is in the region of 40 bar. In this way the wall of the blank is pressed against the inside wall of the mould, and in this way the container is formed. While the stretching pressure is created by blowing an explosive gas mixture into the blank, for example a mixture of oxyhydrogen gas and an inert gas, the blowing pressure is created by igniting the explosive gas mixture, and this blowing pressure presses the wall of the intermediate form, or respectively the partly pre-formed container, completely against the inside wall of the mould. In this way the PET bottle is produced. The ignition of the explosive gas mixture is done by a spark generator or an emission, and the explosive gas mixture is a mixture of an oxidising agent and a component which can be oxidised such as, for example, hydrogen, methane or the like. In the same process of stretching and blowing, by achieving a brief increase in temperature, sterilisation of the container to be manufactured is possible, so this technique is considered very advantageous.
It has been shown, however, that when converted to technology, the containers manufactured with the known device could not be used industrially. They could not be manufactured and were not reproducible with sufficient quality with respect to shape and volume, and also with respect to their optical appearance. It was for example, not possible to manufacture PET bottles with clearly transparent walls. To the extent that it was not caused intentionally or could be accounted for specific reasons, it was thought that this sometimes unattractive appearance was due to unavoidable effects of temperature.
The object of the invention is thus to provide a device of the type described in the introduction, with the aid of which plastics containers with a better appearance, for example with largely clearly transparent walls, can be manufactured without large additional expenditure.
This object is solved in accordance with the invention in that, on its end facing the container, the receiving portion can be engaged in a flowable medium-tight manner with a distribution module, through which module the stretching die is moveably guided in the axial direction, extending the receiving portion, and on which at least one connector for flowable media is fitted, in that the at least one connector for flowable media can be closed for sealing the device-side interior space, and in that ignition means is fitted in the device-side interior space. During the manufacturing process, the receiver is, in one stage, in sealed engagement with the distributor module, and in the other stage is disengaged from the distributor module. In the stretching stage, the stretching die is moveably guided through the distributor module and thereby also axially through the receiving portion.
In the case of one embodiment of the invention, a device-side interior space is formed by the parts of the device fitted together, these being the distributor module, receiving portion and the container located in the mould. With this embodiment, a flowable medium is conducted through the at least one connector for flowable media into the distributor module, and through this into the receiving portion and the container.
With another embodiment, the device-side interior space is formed by the same parts of the device, wherein, however, in addition flowable medium can also be supplied through the stretching die to the inside of the container.
In the case of a further embodiment, the device-side interior space is formed only by the container and the receiving portion arranged upon it, when, for example, the distributor module is separated from the receiving portion and the receiving portion is closed. The stretching die is conducted axially through the receiving portion, and said stretching die can include a supply line. It can, however, also be configured to be solid.
Each of the different device-side interior spaces (according to the embodiment) can be closed off in the area of the single connector for flowable media or the plurality of connectors for flowable media. Only in a closed device-side interior space does the explosion caused by the ignition means arranged externally thereto produce the desired parameters of a brief high pressure and increased temperature. Clearly, this interior space can be opened up again after the termination of the manufacturing process.
The advantage of the limited device-side interior space is its small volume. The volume in the container to be manufactured is then less critical. The container, and also preferably the receiving portion supporting it, are namely removed from the device after the respective manufacturing process, in order to be subjected to further processing. The device-side volume which was involved in enclosing the space for the explosion is, by means of the measures according to the invention, so small in relationship to the known device that reaction products, for example water when oxyhydrogen gas is used, remain in significantly smaller quantities. It has been established that the clouding of the container walls occurs because when oxyhydrogen gas is used, water formed in droplets is propelled with considerable kinetic energy from the inside onto the walls and there causes changes to the surface which in the end lead to clouding. With the first explosion, and also in the case of a continuous process for manufacturing only three to six containers, sufficient reaction product was still not formed in the device-side interior space, for example the supply and drainage lines, so there were hardly any water droplets present to cloud the internal walls of the container. With a longer continuous manufacturing process, because of the large number of successive explosions over time, there was, however, a large enough amount of reaction product (water) such that with each following explosion clouding of the container walls was unavoidable.
The closing off of a small device-side interior space, which is formed only from the interior space of the distributor module, the receiving portion and the container itself, in particular does not allow any accumulation of the unwanted reaction product (water), in that at least container itself, and preferably from the container and receiving portion is removed after the explosion, and thereby the accumulated reaction product as well. Insignificant amounts of reaction product therefore remain in the remaining device-side interior space which, even in a continuous manufacturing process, can still be ignored after a long period.
By means of this change in the construction technique of the device, it is unexpectedly possible to manufacture, without a large cost increase, plastics containers with a better appearance, in the case of PET bottles having largely clearly transparent walls.
The invention is further advantageous
Chatard Dominique
Fuchs Jens
Kindinger Hans
Kuhn Rolf
Riedel Thomas
Davis Robert B.
Dunn Michael L.
Tetra Laval Holdings & Finance S.A.
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