How to choose extruder when extruding blown film?

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blown film generally uses a single screw extruder, and the screw diameter is mostly 45 ~ 150, the aspect ratio is usually (Natural 20 ~ 30) : 1, but the length-diameter ratio of the extruder for extruding pvc film should not be large, generally 20:1. In order to improve the mixing efficiency, sometimes a mixing device is added to the head of the Screw, and the length-diameter ratio of the screw should be relatively large, above 25:1.

in order to produce blown film, the extruder with suitable specifications should be selected according to the width and thickness of the film so as to obtain good economic benefits. The productivity of extruder is generally controlled by cooling and traction. For example, using a large extruder to produce a thin and narrow plastic film makes it difficult to achieve cooling under rapid traction; On the contrary, using a small extruder for thick and wide films will make the plastic stay at high temperature for too long, causing great damage to the quality of the films, and at the same time the productivity cannot meet the requirements. Therefore, an extruder can only be suitable for extruding plastic products of a few specifications. Table 6- 1 lists the relationship between extruder specifications and film sizes. Thin-film of extruder screw diameter and film blowing machine head diameter of relationship see Table 6-2.

In addition, the selection of the extruder should also consider the physical properties of the processed materials, mainly considering the structural type of the extruder screw. For example, when processing heat-sensitive pvc plastic, it is necessary to avoid the material staying in the barrel for too long. In order to avoid the accumulation of material between the screw head and the perforated plate, the screw head should be designed as pointed; However, the screw cannot be of barrier type to avoid material decomposition due to excessive shear force. For polyolefin materials, high-efficiency screws can be used to improve quality and output without decomposition problems.