Blown film extrusion

An advantage of blown film extrusion over traditional film extrusion is that in the latter there are edges where there can be quality (thickness) variations.
Blown film extruders require limited amounts of compressed air for two operations:
1) To increase the film width by adding air inside the bubble. Once the bubble is inflated, no additional air is required. The air is trapped inside, and with the help of the top nip rolls and cooling air, shapes the plastic tube to the desired width and film thickness. The volume of air required initially depends highly on the size of the machine and width to be extruded. This can be anywhere from 50l to 400l of uncompressed air. As this is only required at the start of a production run, flow rate is to be considered as insignificant. A compressor with a tank size of about 200l at a working pressure of 8 Bar can store more than 1000l of uncompressed air.For instance:

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2) To apply pressure on the nip rolls, these need to be held together so that the film can be pulled up. It is important that even and regulated pressure is used to ensure proper thickness control. The pressure required can be adjusted by an air pressure regulator attached to the machine. The incoming pressure needs to be more than 6 Bar. Ideally a compressor, with more than 8 Bar but less than 11 Bar, is used in conjunction with a regulator to maintain the pressure. As the application is only to apply pressure, any air loss is only through leakage. As per ISO standards, 0.1l/connection/hr is the maximum allowable leakage for pneumatics. There are about 36 connections in an average blown film extruder. So a leakage rate of 3.6l/hour (0.06l/min) could be expected. This is also very low for any industrial compressor.