Kawanoe Zoki's BestFormer Tissue Machine- BF, which
produces toilet paper,
facial paper, and
towel paper has been
highly evaluated
as a high-speed, high-efficiency,
and highquality tissue
machine. In total,
160 BestFormer units
have been delivered
not only in Japan
but all over the
world. In China,
42 machines are in
operation and an
additional eight
machines are scheduled to startup within one year. A development
of the BF machine is the BF-EX series.
STRUCTURE AND FUNCTION
Stock inlet (Figure 1): Stock flows through pipes
into the tapered square header in order to get good formation
on cross direction. To keep constant pressure on cross direction
and to avoid piling-up of stock, 10% is recirculated from the
opposite side. Then stock goes into the dispersion room through
a perforated plate. This plate is made of specially-shaped stainless
steel to get a uniform jet stream even when the flow speed goes
up. The plate is also carefully finished to prevent fibre clogging
or dirt. A dispersion bar and guide plate are installed in the
dispersion room so that the proper stock dispersion and good formation
on cross direction are achieved, ie the narrow channel blocked
by the dispersion bar is effective to break turbulence caused
by hard collision of stock as well as shear force from both walls
of the guide plates. Stock is pushed out of the throat part between
the cylinder and the top lip and dewatered through the channel
from the throat position to the top lip.
The speed ratio between the cylinder and the stock
in the throat part is very important. It determines the orientation
of fibre, the level of the MD/CD strength and the formation. The
throat part is movable so that flow speed can be easily adjusted
during operation by changing its opening. Stock dewatering starts
after passing through the throat part, being pushed out at a certain
angle between the cylinder and the top lip. Mass dewatering is
possible with both suction dewatering by cylinder and pressurization
dewatering achieved by variation of the narrow wedge-shaped space
between the cylinder and the top lip. The lip opening in the cross
direction is adjusted by the adjuster installed on the lip.
Suction cylinder (Figure 2): The shell surface of
the stainless steel cylinder is perforated with specially shaped
holes so that sufficient water can be stored. The faster the machine
runs, the less water flows into the suction box through the shell,
leaving water in the shell temporarily. Finally water is released
from the shell surface after the paper web is picked up at the
couch roll. The shell is made of stainless steel and is assembled
on its surface with top and bottom wire. A diagonal wire is standard.
Approach flow (Figure 3): This is a standard approach
flow of BestFormer. Stock is fed into the suction side of the
fan pump from the stuff box, then goes into the stock inlet through
a screen. After air is resolved from white water by a separator,
the white water is circulated from the white water pit to a fan
pump and further to the stock inlet. Flow volume is controlled
by adjusting the fan pump rotation. Overflow at the white water
pit is always necessary so that the flow from the fan pump does
not change. A cleaner might be installed before the screen depending
on furnish.
OPERATION OF BESTFORMER
Household tissue paper must be light, soft and bulky.
The BF is designed to offer these qualities.
The normal machine speed is up to 1400 m/min, depending
on drying capability. The newest model runs at up to 1500 m/min.
Some machines which make special paper at high substance are running
at 15 m/min. As the range of the machine speed is wide, it is
possible to choose proper speed according to the paper grade and
substance.
Normally, at lower consistency, better formation
of fibres can be obtained, while pumps and screens of higher capacity
as well as powerful drives are needed. However, BestFormer can
make tissue paper of good formation even at higher consistency.
For BestFormer, consistency is 0.15- 0.25% and retention is 75-80%.
Changes of consistency and freeness have less effect on formation
since both suction and pressure dewatering is so strong.
Endless wire is the standard KZ specification for
top and bottom wire. Under normal operation, the wire needs changing
once in 1-2 years. The yankee dryer's shell is made of special
cast iron, which is strong enough to resist damage from the crepe
doctor. Correct choice of drain exhaust is important to take full
advantage of the yankee dryer. At more than 600 m/min, blow through
is standard. Steam drawn from the blow through and flash is used
to heat the air beforehand when steam is used to heat the hood.
When gas or oil is used, the heat is withdrawn from this steam
by a thermo-compressor. Then, this heat is used to heat the dryer.
CBC crepe doctor (Figure 6): The doctor is a crucial
part affecting quality and productivity. The yankee dryer changes
under the influence of pressure and heat. The doctor blade has
to adapt to these changes or there will be paper breaks or uneven
creping. The KZ machine mounts CBC crepe doctor to counter this
risk. The separate and independent adjustment of blade load and
creping pocket angle is achieved by the blade holder pivoting
around the blade contact point on the yankee surface, and by the
pressure on the creping blade being applied very close to the
creping blade tip. The blade automatically follows the profile
of the cylinder surface and the actuators ensure even linear load
all along the blade length. The creping blade tip position coincides
with the blade holder pivot point and there is a continuous adjustment
for different blade heights.
The working angle adjustment is achieved by pivoting
the whole blade holder around the contact point between the yankee
and the creping blade. Blade changes are easy because the beam
rotates well away from the yankee.
Unlike conventional blade holders, there is no blade
deflection as the
load is applied close
to the blade tip,
giving better control
and more even load distribution. The wear of the creping blade
is slower and perfectly uniform, resulting in longer blade life.
Thus, if this holder is used, the life of conventional
blades becomes longer and even long-life ceramic blades can be
used.
Reel-up is a surface type consisting of a single
pneumatically pressurized drum.
The diameter of jumbo rolls has grown in order to
improve paper/converting machine efficiencyand it now generally
1800-3000 mm.
