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12-19-2008

Better Internal Cooling

By using water, cooling is improved without actually having the water in contact with the film. The texture on the surface of the cooling body promotes stabilization of the bubble

By using water, cooling is improved without actually having the water in contact with the film. The texture on the surface of the cooling body promotes stabilization of the bubble

To increase cooling of the bubble during extrusion of blown film, so-called IBC systems (Inner Bubble Cooling) are used. These systems circulate air inside the bubble and thus facilitate heat removal. Nevertheless, the amount of heat that can be removed from the inner surface of the bubble is limited: only 10 to 25% of the total heat content can be extracted in this way. This is attributable in part to the relatively minor and largely undirected flow of cooling air inside the bubble. At the same time, the outward-flowing air is being heated and provides less cooling action.

In view of this situation, Kiefel Extrusion GmbH has developed the ECP (Enhanced Cooling Package) and Perfect Cool internal cooling systems. These are based on installation of a cooling body inside the bubble. The surface of this cooling body is chilled by an internal closed cooling water circuit. The geometry of the cooling body and its surface have been designed such that attracting and repelling forces between the film and cooling body are balanced, ensuring that the bubble remains stable even at high output rates. Turbulent air flow that assures good heat transfer between the air and cooling surface is created between the bubble and surface of the cooling body. As a result, the air is kept at a low temperature all the way to the frost line, providing extended internal cooling of the bubble. The system ensures that the film never comes in contact with the cooling medium (water) or the surface of the cooling body.

In conventional systems, the air inside the bubble warms relatively quickly upon contact with the hot bubble. In contrast, the air is cooled continuously in the bubble formation zone over its entire path in the direction of extrusion in systems that have an internal cooling body, since the air is continually transferring its heat to the water inside the cooling body. Furthermore, the stream of air inside the bubble is directed along the film, once again ensuring good heat removal from the film. The more uniform cooling permits higher outputs and has a positive effect on product characteristics.

Dr.-Ing. Harald Sambale
sambale <AT> kunststoffe.de

contact
Kiefel Extrusion GmbH
Cornelius-Heyl-Str. 49
DE 67547 Worms
Tel: +49 6241 902-0
Fax: +49 6241 902-100

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