Winding nips, such as a layon roller, do many things depending on the circumstances. The primary functions are to meter air into the roll, improve stack, increase wound-roll tightness and to support the winding roll. Nips can also be destructive, however, by causing wrinkles, corrugations and other defects. Nip rollers help keep some air out of the winding roll. This lets us reach higher speeds and/or wind tighter. The air-handling function is negligible on materials that are not smooth. On smooth film, however, a nip is usually necessary at speeds more than a few hundred ft/min. Without enough nip, the roll will be soft, the edges will be rough and the roll may buckle when the air weeps out.
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