CD Uniformity of Tissue
Reduce Wear on Felt
Unless it is corrected, the trade line (seam) in a felt will run
with a "smile". In order to straighten this smile, a negative (concave)
crown is ground onto a
strategically selected felt roll. This will
- Minimize shear deformation in the felt to prevent
porosity variation in CD. This helps in sheet formation, pick-up,
pressing and drying.
- Reduce shear stresses in the felt/fabric to minimize
slip across the felt. This will ensure uniform felt wear in CD.
- Forming section wires: sheet formation, pick-up.
- Pressing and drying sections.
- Fabric in TAD machines.
The distance traveled by the felt in the middle is not the
same as that at the edges due to:
A felt roll which will provide the best correction for the least
amount of crown is selected for the purpose of crowning. A set of
equations is now developed and solved iteratively to compute the
- Roll deflections on account of the roll weight, felt
tension and vacuum, which reduces the path length travelled by the felt
in the middle.
- The crowning of the pressure roll drives the felt
in the middle than at the edges.
- Schematic drawing of the felt section showing x, y
coords of the rolls.
- Drawing of the rolls showing i.d., o.d., face,
bearing span. journals.
- Roll material, and any crowning.
- Vacuum on any roll, and its geometry,
- Felt material (sample or specification) and felt
- Identification of the roll selected for negative
- Amount of negative crown, and degree of cosine curve.
- In a 200+" wide LDC paper machine running at 5500
fpm. the negative crown dropped the smile of the trade line in the
felt from 14" to almost zero; and
the felt life increased by weeks.
- Negative crown was prescribed for a number of other
machines (TAD, HWC) ; but no feedback from the papermakers, except that
they were happy.