Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF THE INVENTION
1 The present invention relates to an improved
headbox in a paper machine, and more particularly to a
headbox in a paper machine which is adapted to make
paper of improved quality.
Fibers in a raw paper liquid become entangled
due to turbulence in the flow thereof generated at
projections and recesses on the inner surface or
bending portions of the piping in the midway of the
flow path for feeding the raw paper liquid to a
headbox, resulting in agglemeration into flocks of
fibers. If such raw paper liquid is ejected as it is
from the headbox to make paper, then the finished paper
sheet will have a clear pattern consisting of light
portions and dark portions as viewed with penetrating
light.
Since such a paper sheet having
unsatisfactory formation due to poor distribution of
fibers is generally inferior in quality, such as
mechanical strength, to a paper sheet having
satisfactory formation due to good distribution of
fibers, a headbox is required to eject a raw paper
liquid after the flocks in the raw paper liquid have
been dispersed a much as possible. In addition, if the
surface of the ejected eject becomes irregular, then
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iL.'f2~SZ7
1 dewatering of the raw paper liquid on a wire becomes
irregular, resulting in unsatisfactory formation due to
poor distribution of fibers, and hence it is necessary
to eject a jet having a smooth surface.
In the headbox of a paper machine in the
prior art, dispersion of the flocks generally has been
achieved by imparting turbulence to a flow. According
Jo this prior art method, as a practical procedure for
imparting turbulence to a flow, separation of the flow
is induced by providing protrusions of various
configurations on a wall surface or by changing the
direction of the flow. Thus the flocks are
disintegrated and mixed together by stirring oE the raw
paper liquid generated at this time, and thereby fibers
are distributed macroscopically uniformly.
However, fiber dispersion caused by stirring
has the following shortcomings:
(1) Since turbulence is present in the flow, if
the flow is ejected as it is, then the jet becomes
irregular, Chile if it is attempted to obtain a smooth
jet, then a section for attenuating the turbulence is
necessary.
(2) When the flow is being stirred, even if the
flocks have been disintegrated into small flocks by the
turbulence of small size, in the event that a section
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3 lZ435Z~
1 for attenuating the turbulence is provided in order to
obtain a smooth jet in the downstream flow path,
turbulence of small size Jill be attenuated more
quickly. Hence, turbulence o large size will become
more predominant, and the so-called reflocking in which
flocks of large size are newly produced will occur.
(3) If separation of the flow is induced for the
purpose of imparting turbulence to the flow, vortexes
will be generated, and a difference in concentration
will be produced due to the fact that the fibers are
moved outwardly by centrifugal forces, and thereby new
flocks are produced.
(4) In addition, if vortexes are generated,
twisting of fibers is liable to occur due to rotation
of the fibers, and this causes production of flocks
which are difficult to disintegrate.
(5) Furthermore, there is a tendency that a
paper sheet having a large variation of the degree of
brightness between a portion containing flocks and a
portion not containing flocks as viewed with
penetrating light is apt to be produced.
On the other hand, in Laid-Open Japanese
Patent Specification No 57-35092 there is disclosed a
method in which dispersion is achieved by repeatedly
; 25 subjecting a raw paper liquid to acceleration and
4 5~
1 deceleration without giving turbulence to the flow of
the raw paper liquid, According to this method, the
raw paper liquid is subjected to acceleration and
deceleration by gradually decreasing and increasing
along the direction of the flow the cross-sectional
area of the flow path which is uniform in the widthwise
direction so that turbulence may not be generated due
to separation of the flow. Thus, flocks are divided
finely by exerting a force adapted to pull and tear off
the flocks when they are in the accelerating region,
while exerting a force adapted to push and extend the
flocks when they are in the decelerating region, and
thereby dispersion of the fibers can be achieved.
Moreover, upon dispersion caused by
acceleration and deceleration, as will be described in
more detail later, since the concentration of the
fibers is different between a central portion of a
flock and a peripheral portion thereof, the forces
exerted upon the respective portions by water are
different, and hence the fibers will diffuse. In such
a dispersion process, a dispersing force will act upon
every flock in the raw paper liquid. Hence, fibers in
the peripheral portion of the flock itself will diffuse
into the surrounding raw paper liquid, and thus the
flock will be dispersed. Therefore, there is provided
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1 a paper sheet having excellent formation and fiber
distribution such that variation in brightness between
a portion containing flocks and a portion not
containing flocks as viewed with penetrating light is
small compared to a paper sheet obtained by
disintegrating flocks merely by stirring the raw paper
liquid.
SUMMARY OF THE INVENTION
The object of the present invention is as an
object, to achieve improvements in quality such as
formation or fiber distribution, mechanical strength,
etc. of a paper sheet which has been produced by
dispersing flocks in a raw paper liquid within a
headbox, in distinction from the prior art as described
above, thereafter ejecting this raw paper liquid and
dewatering.
In view of the Eact that, while stirring has
the efEect of disintegrating flocks in a raw paper
liquid and mixing the raw paper liquid to make fibers
distribute macroscopically uniformly, it also has the
effect of producing new flocks, in the headbox in a
paper machine according to the present invention,-
although there is provided a flow path in which at
first separation is caused in a flow to generate
turbulence in the flow and thereby a raw paper liquid
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1 is stirred for the purpose of effectively utilizing the
former effect, in order that the turbulence of the flow
generated by stirring will not become large, an
accelerating and decelerating flow path is provided
continuously to the first-mentioned flow path to
repeatedly subject the raw paper liquid to acceleration
and deceleration without giving turbulence to the flow
at all. Thereby, the turbulence of the flow generated
in the stirring flow path section is made to disappear r
and it is intended to achieve dispersion of fibers due
to acceleration and deceleration.
In other words, the present invention is
characterized by the fact that there are provided a
first flow path having a uniform cross-section in the
widthwise dlrection to cause separation in a flow
therethrough to impart turbulence to the flow and
thereby stir a raw paper liquid, and a second flow path
having a uniform cross-section in the widthwise
direction and disposed contiguously to and downstream
of the first flow path for repeatedly subjecting the
raw paper liquid to acceleration and deceleration
without giving turbulence to the flow at all.
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The above-mentioned and other objects,
features and advantages of the present invention will
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1 become more apparent by reference to the following
description of preferred embodiments of the invention
taken in conjunction with the accompanying drawings,
wherein
Fig. 1 is a longitudinal cross-section side
view of a headbox in a paper machine according to one
preferred embodiment of the present invention,
Fig. 2 is a longitudinal cross-section side
view of a headbox in a paper machine according to
another preferred embodiment of the present invention,
and
Fig. 3 is a longitudinal cross-section side
view of a headbox in a paper machine according to still
another preferred embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
_
In the following, the present invention will
be described in greater detail in connection with the
preferred embodiments illustrated in the accompanying
drawings. At fist referring to Fig. 1, a raw paper
liquid flows through a rectangular header 1 which is
narrowed towards its tip end in the widthwise
direction, then it is diverted by 90 and passes
through holes in a perforated plate 2, and the raw
paper liquid enters into a flow path having a uniform
cross-section in the widthwise direction which is
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1 defined by an upper plate 3 and a lower plate 4. A
depth of the flow path at the inlet of this portion is
smaller that the holes in the diameter of the
perforated plate.
The depth of the flow path just before
entering into a stirring chamber 5 is made small, and
the depth of the flow path is abruptly enlarged in the
stirring chamber 5. The dimensions of the stirring
chamber 5 are appropriately determined depending upon
the properties of the raw paper liquid. Immediately
after the raw paper liquid has been stirred in the
stirring chamber 5, the cross-sectional area of the
flow path is reduced to accelerate the flow, and the
stirring chamber 5 is thus connected to an accelerating
and decelerating flow path 6 in which the cross-
sectional area of the flow path is smoothly decreased
and increased without giving turbulence to the flow at
all.
A nozzle lip 7 is flexible, such that the
opening of an ejecting port partially defined thereby
can be adjusted by displacing the tip end of the nozzle
lip.with the aid of an adjusting rod, not shown.
With reference to Fig. 1, the depth of the
flow path just before entering into the stirring
chamber 5, which flow path has a uniform cross-section
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1 in the widthwise direction, is made small. In this
portion of the flow path, the raw paper liquid is
accelerated into a uniform velocity along the widthwise
direction, and is made to have a flow velocity that is
necessary for stirring.
In addition, since the depth of the flow path
is abruptly enlarged at the inlet of the stirring
chamber, the flow will separate simultaneously along
the widthwise direction, the main flow and the
separated flow will mix together, and thus fibers in
the raw paper liquid will distribute macroscopically
uniformly. Also, while the raw paper liquid is being
stirred, flocks will be disintegrated.
Moreover, the dimensions of the stirring
chamber are appropriately determined depending upon the
properties of the raw paper liquid. With the flow path
having a uniform cross-section in the widthwise
direction the flow will separate simultaneously, and
uniform stirring is effected in the widthwise direction
as well as in the direction o the depth of the flow
path. In addition immediately after stirring, the
flow is subjected to acceleration, and turbulence
contained in the flow will be attenuated rapidly, so
that regeneration of flocks will be suppressed.
l Also, there is provided an accelerating and
decelerating flow path 6 in which acceleration and
deceleration are repeated without giving turbulence to
the flow, contiguously to and downstream of the
stirring chamber 5. Since there exists the property
that if a flow is accelerated, then turbulence
contained in the flow would be attenuated rapidly, in
the accelerating section the turbulence in the flow
would be attenuated rapidly, while in the decelerating
section since the flow is decelerated so as not to
generate turbulence in the flow, the turbulence
contained in the flow will be attenuated as the raw
paper liquid flows. As such acceleration and
deceleration are repeated, the turbulence generated in
the stirring chamber will disappear quickly.
Accordingly, it will never occur that the size of the
turbulence grows and flocks again are produced, or that
the surface of the jet becomes irregular due to
turbulence in the flow.
With regard to dispersion of fibers in the
accelerating and decelerating flow path, by varying the
cross-section area of the flow path acceleration and
deceleration are caused in the flow of the raw paper
liquid flowing through the flow path. When a flock in
the raw paper liquid is in an accelerating region,
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1 since the flow velocity on the upstream side is low and
the flow velocity on the downstream side is high, the
flock will be pulled and torn off, and thereby fibers
will be dispersed. Whereas in a decelerating region,
since the relation of the high and low flow velocities
is reversed, a flock will be pushed and extended in the
directions at right angles to the average traveling
direction, that is, in the widthwise and thicknesswise
directions. By repeating such processes, the flocks
will be divided finely, and the fibers will be
dispersed uniformly in the raw paper liquid.
In addition, when acceleration and
deceleration are caused in a flow of a raw paper liquid
flowing through a flow path by varying the cross-
sectional area of the flow path, flocks in the raw
paper liquid will be accelerated and decelerated as
exerted forces from the flow of water. However, since
the concentration of the fibers is high at a central
portion of the flock and low at a peripheral portion of
the flock, the forces exerted upon the fibers from the
flow of water will be different depending upon the
portions of the flock. At the central portion the
force exerted upon fibers from the water upon
acceleration and deceleration is weak because the
fibers become overlapped with one another, whereas at
the peripheral portion the same force is strong.
12 ~;~4~527
1 Therefore, when a flock is in an accelerating
region the peripheral portion of the flock will expand
in the traveling direction of the flow, whereas when a
flock is in a deceleration region, the peripheral
portion of the flock will expand in the upstream
direction of the flow. As such acceleration and
deceleration are repeated, a flock will diffuse from
its peripheral portion, and fibers will be dispersed
uniformly in the raw paper liquid. Even at the central
portion of the flock, if there is a difference in
concentration of the flock or where a network of fibers
is weak, then dividing of the flock will start also
from that portion for the above-mentioned reasons.
While the fibers are directed in the average
traveling direction in the accelerating region, in the
decelerating region the directions of the fibers will
become random because the fibers are pushed from the
rear. Accordingly, the dispersed fibers will become
non-directionalS and even undispersed flocks will be
directed randomly unless the flocks have a spherical
configuration with respect to flow resistance.
Accordingly, undispersed flocks will be subjected to
dispersing forces directed in various directions.
In a modified embodiment of the present
invention illustrated in Fig. 2, in a flow path having
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1 a uniform cross-section in the widthwise direction that
is defined by an upper plate 8 and a lower plate 9, the
configuration of the longitudinal cross-section of the
stirring flow path is different from that of the first
embodiment shown in Fig. l. Also, the number of
stirring processes is larger in this modified
embodiment. More particularly, in the stirring flow
path there are provided asymmetric proiections and
recesses on the upper and lower walls so that
separation Jay be caused in a flow therethrough to give
turbulence to the flow and thereby the raw paper liquid
is stirred. However, with regard to practical means
for causing such stirring, various methods for stirring
in the prior art such that various shapes of
projections are provided on the wall surfaces or the
direction of the flow is changed, can be employed in
the portion of the stirring flow path shown in Fig. 2,
in place of the illustrated flow path structure.
In a further modified embodiment of the
present invention illustrated in Fig. 3, one end of a
flow restraining element 12 is held in a groove of a
holder ll that is fixedly secured to a perforated plate
10. Thus, two upper and lower flow paths having
- uniform cross-sections in the widthwise direction are
formed by the holder ll, flow restraining element 12,
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1 upper plate 13 and lower plate 14, and each of the flow
paths is formed of a flow path portion for effecting
stirring and a flow path portion for carrying out
acceleration and deceleration. Although the structural
configurations are different, neither of the modified
embodiments shown in Figs. 2 and 3 is different in
operation and advantages from the embodiment shown in
Fig. 1.
The headbox in a paper machine according to
the present invention is constructed in the above-
described manner, and in this improved headbox, flocks
are disintegrated and mixed together by stirring, and
after the fibers have been distributed macroscopically
uniformly, the flocks are further divided finely by
acceleration and deceleration. Moreover, fibers in the
peripheral portions of the flocks will diffuse into the
raw paper liquid around the flocks due to the
acceleration and deceleration! so that the flocks are
dispersed. Therefore, both macroscopically and
microscopically, a raw paper liquid in which fibers are
dispersed far more throughly than in the prior art can
be produced in a headbox having a short flow path.
In addition, turbulence generated in the
stirring flow path will disappear quickly in the
accelerating and decelerating flow path, so that the
1 S ~;~,L~5Z~
1 resultant fiber dispersion in the raw paper liquid will
not be deteriorated, and a smooth jet can be
obtained. Accordingly, a paper sheet obtained by
ejecting this raw paper liquid on a wire is of high
quality in that formation or distribution of the fibers
is good and the mechanical strength thereof is high.
Since many changes and modifications can be
made to the above-described construction without
departing from the spirit of the present invention, it
is intended that all matter contained in the above
description and illustrated in the accompanying
drawings shall be interpreted to be illustrative and
not limiting.
