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February 24, 2006
What Are Nips For?
Filed under: Rollers, Traction --- Tim Walker @ 07:15 AM
I've had a few different client consults lately that all center around nip rollers, usually for laminating, but also embossing or printing.
What are nips for? Or what are the important properties to understand webs in nips.
1. Nip are for high pressure.
If you don't need pressure, why nip? Nip pressure can easily be 10-100x higher than the pressure of a tensioned web over a roller.
Many processes use nip pressure, usually to move something. Pressure moves a coating or extrusion fluid into the valleys of web surface roughness and exclude excess liquid (control coat weight). High enough pressure moves solid material around, such as in embossing, die cutting, crush or shear slitting. Low pressure moves air or liquid around, excluing bubbles in a laminate or squeegeeing liquid off a web as it leaves a submerged process.
2. Air elimination
This is part of high pressure, but in some cases, this is the primary function of the nip. Air is never completely eliminated (unless you have a vacuum process), but it can be reduced 15x or more with nip pressure. How much needs to be eliminated to stop bubbles? It depends on how much air your product can hide. Air bubbles at some size are usually invisible to the naked eye. Many solids and liquids can absorbs a limited amount of air. Reducing air is used to keep wound rolls tight and at the entrance of heating rollers to improve conduction.
Other nip effects:
3. Web elongation and speed control (web metering)
4. Web-roller slip (burnishing or calendaring)
5. Web compression
6. High friction
I'll have to write more thoughts on these last 4 later.
February 07, 2006
International Coating Conference: ISCST '06
Filed under: Coating, Laminating, and Printing --- Tim Walker @ 10:51 AM
ICSTS: International Coating Science and Technology Symposium.
I'm not a coating guy, more of a beam-head (MEs), but I know the who's who of advance coating wet-heads (ChemEs) go to this conference every two years.
The next one is this year, September 9-13 in Denver, CO.
Beside coating experts, these guys are great at acronym confusion. The symposium is the ICSTS. The organization that runs it is the ISCST (Int'l Soc. of CST). ISCST's ICSTS? Whew.