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November 18, 2005
Nips are the double-edged swords of web processing.
Pro: Nips and the high pressure they create are required for many web processes. The high pressure or controlled gap of two nips rollers is used for coating, extrusion, calendaring, laminating, and embossing. Shear knives are a unique form of nips. Nip rollers at winding help controlled entrained air and increase roll tightness.
Con #1: Nips can create wrinkles from either uneven feeding of the web length or steering the web into shear or tracking wrinkles.
Con #2: Nips can't be perfect. The pressure within the footprint of the nip is not uniform and will vary with on web variations (crossweb thickness, wrinkles) and roller variations (diameter, hardness, alignment, deflection).
How to avoid these problems?
Nip roller systems are quite complex, but by following a list of nip system design 'rules of thumb' (ROT), many problems can be avoided.
Throughout today's live blog, I'll try to work up a long list of these ROTs, and get your comments.
Posted by Tim Walker at November 18, 2005 08:20 AM
