"Below each step is explained.
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Preheat:
The first Preheat roll (P1), also acts as a nip for tension control of the web coming into the MDO
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Drawing:
These are the rolls between PH-2 and A-1.
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...
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Nipping the Film in the Draw Section:
There are two standard ways to nip film. One is with the film being pressed between a
rubber roll and a steel roll while it travels straight through the nip point with little or no
wrap in either roll. This like the Primary nip on Blown Film lines. This type of nip
arrangement is adequate for the Draw rolls for many films.

A second nip arrangement is the “S-wrap”. In this case the web wraps the rubber roll 180
degrees or more, before reaching the nip point. This permits the film to be laid down flat
against the steel roll. This can be helpful in preventing wrinkles, and is sometimes
necessary when the nip rolls begin to wear".

https://www.tappi.org/content/events/07place/papers/hatfield...