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April 13, 2005
When should winding nips be rubber covered?
Rubber covered rollers are common in almost any nipped process. Without a compliant covering on one or both rollers, the nip pressure will vary greatly from roller misalignment, diameter variations, uneven loading, roller deflection, and web thickness variations. Steel just doesn't deform much, so even variations as small as 2-10 mils can create larger nip pressure variations.
The compliance of a rubber covered roller is forgiving. The rubber (or elastomer) will deform from the nip load, often as much as 30-100 mils. If the rubber covering is deflection 50 mils, a 5 mils error from product variation or deflection will create a 10% pressure variations. The same 5 mils error in a steel nip will likely cause a gap in the nip. In some cases, a 5 mil thick lane in the product could end up carrying 100% of the nip load, creating what could be a 100-1000% pressure change. Whew.
So what about winding nips. Should they be elastomer-covered or hard?
If the winding roll is compliant, such as winding toilet paper, many nonwovens, and the like, the nip compliance is built into the product, so the winding nip need not be.
If the winding roll is relative rigid, such at foils, many films, coated papers, and the like, the nip roller must provide the compliance and forgiveness. For rigid materials, you may be able to avoid a compliant nip if the roll is narrow and has relative little alignment and other errors that need compliance.
So if you need a winding nip, what is the best material or hardness? Another great question. The first followup question is "What did you use before and did it work?" If you can't answer this question, look for someone who can.
This is where I usually turn to the rubber-covered roller experts. This topic moves away from my mechanical aptitude into chemistry, processing, and a need for extensive experience with rubber-covered rollers. Anyone care to comment on how to choose the best winding nip elastomer coverings? -tjw
Posted by Tim Walker at April 13, 2005 10:05 AM
Comments
1) Does this logic also apply to layon rollers?
2) Is there a certain durometer or thickness of covering that works for a variety of substrates? I have not tried covering any of my nip or layon rollers with an elastomer material as of yet.
Posted by: Patrick at July 29, 2005 02:27 PM
