weight, however, the headbox becomes even more important and is regarded as an
extremely critical part of the paper machine. And many technological renovations have
been made to improve its capability. For instance, the deterioration of fiber orientation
that occurs when controlling CD basis weight by adjusting the slice gap has been
resolved with the emergence of a dilution headbox.
5)
And improved deflocculation of
fiber flocs in the headbox were made possible with the development of step diffusors or
perforated plate.
6-7)
These developments of cutting edge technologies have been made
mostly by paper machinery builders in advanced countries, which remains the domestic
paper machinery industry lacks far behind in technology. To overcome this technological
deficiency extensive research efforts in theoretical as well as experimental aspects should
be made.
In this study, a special attention has been paid to examine the influence of the
geometry of the turbulence generator and slice on velocity and pressure uniformity in
the headbox. These are of great importance in obtaining good formation, even basis
weight profile and fiber orientation. To investigate the effect of the design parameters of
the turbulence generator and slice on hydrodynamic behavior, analytical as well as
experimental approaches have been made.
Experimental
Construction of pilot headbox
A
pilot
headbox
consisted
of
turbulence generators
and
slice
was
designed
and
constructed to study the flow behavior in the headbox. The schematic diagram of the
pilot headbox is shown in Fig. 1. Water stored in a 2 m
3
tank was pumped by a
centrifugal pump to the distributor and passed through the flexible hoses to step
diffusors, and ejected through the slice and recirculated. The detailed specifications of
the tank and pump are shown Table 1 and 2. The flow rate from the distributor to the
headbox was controlled by adjusting the opening of the return gate valve, and the flow
rate from the water tank to attenuator was monitored using an ultrasonic flowmeter.
Distributor rather than tapered manifold was adopted to distribute stock evenly to the
full width of the slice as shown in Fig. 2. A hole plate was installed inside the
distributor to even up the flow instability. Air pad that exists at the upper part of the
distributor functions as a pulse attenuator. Air pressure in the distributor was adjusted
with an air compressor and monitored with a pressure gauge mounted at the top of the
distributor. Liquid level in the distributor was measured with a transparent tube mounted
on the outside of the distributor. Four flexible hoses were used to connect the flow
distributor and headbox. This design was found to be very effective in maintaining the
constant pressure inside the headbox and eliminating the secondary flow produced when