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What are common PET Extrusion Defects?


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mherz

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Posted 16 July 2009 - 04:57 AM

Hello Everyone!!!


Can somebody here in the forum who is also engage in PET sheets manufacturing share the kinds/types of defects you encountered and what are the probable causes



Simon

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Posted 17 July 2009 - 07:34 AM

Hello Everyone!!!


Can somebody here in the forum who is also engage in PET sheets manufacturing share the kinds/types of defects you encountered and what are the probable causes


Not into PET extrusion myself but I found this practical article that may help you.


Defects of Plastic Film Ought to be Caught

Plastic Film defects ought to be detected and eliminated by the extruder operator before the rolls get shipped to the customer.

First is the appearance and a good looking finished plastic roll of film this aspect can be half of the battle. Keep in mind is that first impression what you see is what you get! A superficially ugly looking roll which may convert on the filling machine or bag machine can have the operator looking at the roll much closer for the entire lot for real or imaginary defects.

A roll that has a machine cylinder look means no scuff marks, damaged edges, and fuzzy ends, protruding or buried core ends, or crushed cores. The solutions to these problems are self evident. There are other finer detailed defects that can be buried in the roll, and may be if the production line is never approached by the operator except during a roll change. There is no excuse for the customer being the first to see these.

I have a couple of areas for helping prevent roll defects:

How to Tackle Blocking of the Plastic Film - a common reason for blocking is too much winding tension. There is an area over looked and it is the tension which is set so great as to crush the core as the film is being wound on the roll. This makes it impossible for the operator to remove the roll from the winder shaft. With a case of crushed cores, the rolls may be hard to get off of the shaft, only to have the customer find them impossible to remount on a un-wind stand. Just as bad of a problem can arise if the winding tension is too light, no blocking but the film may telescope from one end of the roll, making it impossible to convert into finished product. Hot weather can bring its share of blocking problems. Plastic Film is insufficiently cooled and the inner surface blocks as they pass through the nip rolls. For a cure you must reduce the output, raise the tower height or nip rolls, or use refrigerated air or other means of improving cooling efficiency. It also can be an inefficient air ring. The cause of blocking can be using too much additive when producing 1 mil that has slip and anti-block additive level designed for heavier guages like 3 mil. Sometimes there isn't enough additive to do the proper job. Over-treatment and or high gloss can aggravate if not cause blocking with any of the above conditions.

Continued; Here

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mherz

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Posted 19 July 2009 - 04:33 AM

thanx for the great info simon!!! :thumbup:






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