Comparison of plate and conical fillings in refining of bleached softwood and hardwood pulps

The purpose of this study was to compare
plate and conical refiner fillings in laboratory
refining of softwood and hardwood pulp
fibers. A better dewatering-tensile strength
combination was achieved when SWK was
refined with conical fillings, and the development
of strength was found to be insensitive
to variations in refining intensity in
the range of 1.3-4.0 J/m. A bar microprofile
was measured with the aid of a profilometer.
The leading edges of conical filling bars were
found to be rounder. A possible reason for
the better tensile strength of pulp refined
with conical fillings is that the round edge
helps large SW fiber flocs to enter the space
between the bars, resulting in less heterogeneous
or more efficient treatment of fibers.
The recorded gap closure values supported
the above interpretation. The gap between
conical fillings was found to become wider
when pulp consistency and thus the tendency
for fiber flocculation increased, whereas
increased pulp consistency decreased the
gap between plate fillings, which was further
reflected as increased fiber cutting. The reduction
in fiber length appears proportional
to the increase in gap closure, supporting
the earlier theory that fibers are squeezed
and crushed between the bars. More attention
should be paid to the wear of filling
materials when refining long-fiber pulp. A
filling material which wears so that the bar
edges are rounded would seem to promote
high tensile strength and high average fiber
length.