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Calibrated cooling

In course of working on the new cooling system the main aim was to increase the heat transfer factor. The big amount of warmed up air in the bubble significally impairs the cooling efficiency. The previous construction already incorporated internal cooling, but the big volume of silent, warmed up air could only be replaced with difficulties. In order to eliminate this problem, we placed a closing element at the conical section of the bubble that otherwise would not participate in the air flow and the cooling.
Inside the conical, orientation section of the bubble we placed an element filling up the film-cone and only a thin gap remains for the cooling air-flow between this element and the film. This way much less cooling air is enough to reach the same cooling effect, because this cooling air is lead directly to the film. The amount of air closed in the bubble is reduced and therefore it does not deteriorate the efficiency of the cooling and the airflow. This closing element (cone) needs to be hold in the bubble and the cooling air also needs to be blown in either from under or above. In case of conducting from under, the die construction must have a sufficient channel in its core. The die with a rotating core can associate this. In case of implementing the cone to a traditional rotating die, the cone needs to be hang from above and therefore the bubble has to be opened on the top. The closing cone funtions as a plug in the bubble and therefore the opened bubble causes no problem, as between the film and the cone only the amount of air leaves the system which is replaced by the cooling air blown in. Inside the cylindric section of the bubble we placed horizontal discs to avoid the air’s sudden run off as it leaves the conical section. An additonal advantage of the open bubble is that the warmed up air can leave upwards freely and and it does not need to be sucked out.

The value of the heat transfer factor is determined mostly by the relative speed difference betwen the cooling agent and the surface which needs to be cooled. As a next step we have rotated the upper, cylindric shaped part of the cooling cone where the film frozes and we supplied it with an air recooling system. The air upwarding along the cone warms up and at the point where the cooling intensity mostly needed, we recool it with a cylinder rotated on a high peripherical speed and we lead out the continuously occuring heat. The spinning part highly increases the speed difference and therefore advances the heat transfer factor. Parallel to it, it derives the heat from the film helping its total refrosting. Because of the high speed the flow boundary layer is reduced that further improves the heat transfer. This equipment cooles the film very intensively at the end of the orientation section, defrosting it in a relatively narrow peripherical section. Therefore it allowes the production of a completely homogenious film at high speed.

In the gap between the film and the cooling ring there is another accompaniment: the air flowing at high speed in the gap sucks the film onto the surface. This effect assures the constant diameter of the bubble and it is only a few mms bigger that the diameter of the upper cylindric part of the cooling cone. This way the inner cooling cone plays the role of the caliber. With this solution it is possible to produce a very precise film, not only in thickness but also in diameter (width). The size of the calibrating ring is determined based on the size of the end product and therefore we are able to realize the production of blown cling film without trim edge waste.