Package making – Methods – Forming or partial forming a receptacle and subsequent filling
Patent
1987-05-08
1990-01-23
Culver, Horace M.
Package making
Methods
Forming or partial forming a receptacle and subsequent filling
53 51, 53559, B65B 5702, B65B 4710
Patent
active
048949779
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method and a device for length rectification of a shrinkable foil strip such as thermoplastic synthetic material, in machines for the production and separation of packages.
THE RELATED ART
Heated foil strips which are formed through deep drawing cool down and shrink as they move in a longitudinal direction of a package producing/separation machine through a forming station, a further work station (e.g. a sealing station) and a separating station of the machine and, optionally, are cut after filling sealing. Modifications in the package size and the intervals between packages can be automatically absorbed and/or compensated, up to a built-in maximal tolerance range, without impairing the work process.
In such machines, the foil strip, on its way from the forming station to the separating station, experiences a cooling and thereby a longitudinal shrinkage. In the sealing and separating work stations, this shrinkage leads to package intervals and package sizes which remain basically constant in the direction of travel and determines the transport path whereon the foil strip moves in a timed manner through the separating station. This transport path remains constant through the machine cycles. The possibility of minor changes in the package size and intervals between packages, as a result of correspondingly minor changes in the shrinkage characteristics of the foil strip, is taken into consideration by providing a built-in free tolerance play in the following work station, between the package mold and the work tools (e.g. sealing tools). Such length modifications can therefore be easily absorbed or compensated for without impairing the work process during, for instance, the sealing of the package, as long as these modifications remain smaller than the preestablished maximal tolerance resulting from the free tolerance play in the work station. The cooling of the foil strip between the forming station and the separating station is smaller in the case of uninterrupted transport of the foil strip, than in the case of a transport interruption, during which the foil portion between the forming and the separating stations has the opportunity to cool down more or even to reach room temperature. This way, the cooling taking place during the transport interruption is in any case accentuated, leading to a correspondingly stronger longitudinal shrinkage of the strip portion, which is thereby even more shortened. There results in turn even shorter distances between adjacent packages in the travel direction than is the case during uninterrupted operation. This shortening is maintained when the machine is restarted. As a result, a particularly large distance is created between the last package formed before interruption and the first package formed after the machine is restarted. At restart of the machine, when the packages in the strip portion with the higher shrinkage are sealed, increasing packaging failures occur between the package and the sealing tools. These failures correspond to the stronger longitudinal shrinkage occurring during work interruptions and cannot be eliminated. At a path length of approximately two meters between the forming station and the separating station, length differentials can add up to several millimeters. This surpasses by far the aforementioned tolerance range, so that the sealing process can be impaired by the packing failures, the seals can be excessively strained and even the packages can be damaged, until the first package formed after restart of the machine finally reaches the work or sealing station and this way the packing failures come to an end.
In order to reduce the packing failures, it is known to guide the foil strip in a loop between the forming station and the separating station and to vary the length of the loop for the purpose of equalizing the various longitudinal shrinkages of the foil strip. However, in practice considerable problems are encountered in establishing precisely and setting the respectively correct length
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Auer Peter
Janek Dieter
Rittinger Herbert
Scheffold Rudolf
Culver Horace M.
Dubno Herbert
Josef Uhlmann Maschinenfabrik GbmH & Co. KG
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