Nip Care News
Troubleshooting Press Rolls with Pressurex7/Fuji Prescale7 Films October 27, 1998
Keeping a Stiff Upper Nip
AA nip, as described by the dictionary, is a be processed evenly as well. Variations in
pinching force between two surfaces. However, process roller nips can cause product variations,
in converting, the term refers more specifically to even if the web is transported successfully.
rollers that are forced together. Stresses can be
created within the nip and can vary with loading, If a uniform product is desired, the pressure or
modulus and geometry. The objective is to keep stresses imposed by the nip rollers onto the web
these stresses uniform so that calendering, must be controlled in both the CD and MD to
laminating, printing, and other nipped roll some tolerances. It is these tolerances that define
processing is uniform. acceptable loading systems, roller geometrical
precisions, roller stiffnesses and material
For transport roller nips, the nominal nip load variations.@
must lie within a specific range. If it is too low,
traction can be lost on the rollers; wound rolls Excerpted from The Mechanics of Rollers by David R.
Roissum, Ph.D. Reprinted with permission from TAPPI
may telescope because too much air is brought in, PRESS. 81996.
and so on. If the nip load is too high, the web, roll
or roller could be damaged due to Z direction To obtain a dynamic or static profile of pressure
overstress. A separate and more difficult across the nip, Pressurex/Fuji Prescale film can be
constraint is to keep the nip uniform with respect placed between contacting rollers. An instant and
to the machine direction position or time, and permanent ultra-high resolution visual record of
especially with respect to cross direction position. pressure distribution and magnitude can be
If the linear nip load varies with the CD, the web captured. The film changes varying shades of
may not be drawn into the nip evenly. This is the magenta according to the amount of force exerted
major cause of wrinkling and other web damage by the contacting rollers. Pressurex/Fuji Prescale
in the nipped roller or the nipped wound roll films can be interpreted visually by comparing
systems, especially for thin materials. the resultant film color intensity to a color
calibration chart or by employing optical pressure
Process rollers also share the same nip uniformity analysis systems available from Sensor Products.
considerations as do transport rollers. Not only For more information about Pressurex/Fuji
must the web be drawn into the nip evenly, it must Prescale nip impression films, please call Sensor
Products at 800.755.2201 and ask for Bill Ebn
Call now or anytime in the months of
Sept/Oct. to purchase our nip 188 RTE. 10, SUITE 307
EAST HANOVER, NJ 07936 USA
impression films and receive a FREE PHONE 973-884-1755
imaging analysis of any nip length. FAX 973-884-1699
www.sensorprod.com
Your operation can=t afford to miss e-mail: sales@sensorprod.com
even the slightest roller imperfection!
