Note: Descriptions are shown in the official language in which they were submitted.
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FI~LD OF THE INVENTION
The present invention relates to the general
field of paper-making equipment and more particularly,
to a novel headbox with a diffuser to improve the
dispersion of fibers throughout the suspension.
BACXG~OUND OF THE INVENTION
In the manufacture of paper, it has been
recognized that the quality of the final product
largely depends on the uniformity of the jet of fiber
suspension delivered from the headbox to the paper-
making machine. Prior attempts to establish a uniform
distribution of fibers have involved using a diffuser
installed between the inlet and the outlet chambers of
the headbox and comprising a cluster of conduits wlth
stepped widenings to promote a turbulent flow. Thls
concept makes the subject of the U.S. Patent H. Dahl e
al., number 3,725,197 which has been granted on Apr
3, 1973.
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Although this concept constitutes a
substantial improvement over the prior art, throughout
testing and experimentation, it has been found tha~
this headbox design is not capable of providing optimum
results in terms of uniformity of fiber distribution.
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Therefore, an object of this invention is an
improved headbox with superior fiber distribution
charactexistics and yet which is simple and inexpensive
to manufacture.
: The headbox, according to a preferred
embodiment of this invention, comprises a diffuser
mounted between the inlet and the outlet chambers of
the headbox. The diffuser includes a cluster of
conduits, each being divided into at least two
successive portions of larger cross-sectional area,
namely a first portion and a second portion, the second
portion being located downstream respectively to the
flrst portion. ~ : `
In the first portion of the conduit is
mounted an elongated stem that: defines with an inner
wall of the conduit a passage for conveying fiber
suspension, the passage, in cross-section, having the
shape of a multiply connected domain, such as an
annulus.
Pr:eferably, the transition between the first
and second portions ls abrupt to create vortices in the
flow of the fiber suspension.
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The above described conduit structure is
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advantageous for two reasons. Firstly, the multiply
connected domain passage allows to obtain an increased
contact surface between the fiber suspension and the
conduit comparatively to a cylindrical passage, thus
increasing the shear forces in the fiber suspension.
Secondly, the abrupt transition permits to establish
and maintain a controlled level of turbulence. Both
factors contribute to break and disperse flocs present
in the fiber suspension.
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;~ In a preferred embodlment, a stem is provided
only in the first portion of the conduit, however, it
may be envisaged to construct the stem as a stepped
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structure of diminishing cross-sectional area in the
direction of the fiber suspension flow to define in the
conduit a plurality of multiply connected domain
passages of increasing dimension.
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It has been found advantageous, although not
essential, to provide the stem of each conduit of the
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diffuser with a channel including an inlet portion in
fluid communication with the inlet chamber of the
headbox, the channel further comprising tw~ or more
branches leading from the inlet portion to the fiber
suspension passage in the conduit. This arrangement
further promotes a turbulent flow because the flow of
fiber suspension is split in two or more, and forced to
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effect a series of sharp bends before entering the
fiber suspension passage in the conduit.
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Therefore, the present invention comprises,
in general terms, a headbox including~
- an inlet chamber communicating with a
supply of fiber suspension;
- an outlet chamber located downstream of the
inlet chamber and comprising a discharge opening; and :
- a diffuser mounted between the inlet and : ~:
the outlet chambers to establish a fluid path f~rom the
inlet chamber to the outlet chamber, the diffuser
including a plurality of conduits in fluid
communication with the inlet and outlet chambers, each
conduit being divided in at least two successive
poxtions, establishing respective passages to convey
fiber suspension of increasing cross-sectional area in
the direction of flow of fiber suspension through the
conduits, an elongated stem received in the conduit,
one of the passages being defined between the stem and ~: ~
an inner wall of the conduit, the passage defining in :
cross-section a multiply connected domain. :~
The invention also extends to a headbox
comprising:
- an inlet chamber communicating with a
supply of fiber suspension;
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- an outlet chamber downstream of the inlet chamber
and comprising a discharge opening; and
- a diffuser mounted between the inlet and the outlet
chambers to establish a fluid path from the inlet chambex
to the outlet chamber, the diffuser including a cluster of
conduits in fluid communication with the inlet and outlet
chambers, each conduit being divided in at least two
successive portion , establishing respective fiber
suspension passages of increasing cross-sectional area in
the direction of ~iber suspension flow through the
conduit, at least one of the passages defining in cross-
section a multiply connected domain.
~ s embodied and broadly described herein, the
invention relates to a headbox comprising:
~ an inlet chamber communi.cating with a source of
fiber suspension, said fiber suspension having a direction
o~ flow through the headbox;
- an outlet chamber downstream of said inlet chamber,
said outlet chamber comprising a discharge opening;
- a diffuser mounted between said inlet chamber and
said outlet chamber to establish a ~luid path from said
inlet chamber to said outlet chamber, said di~fuser
including a plurality of conduits in fluid communication
with said inlet and outlet chambers, each conduit keing
divided in at least two successive portions, referenced as
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a first portion and a second portion establishing first
and second fiber suspension passages respectively, said
first passaqe having a smaller cross-sectional area than
said seGond passage, each of said conduits including an
elongated stem mounted therein such that said second
portion is free of said stem, said first passage being
de~ined between said stem and an inner wall o~ said
conduit, said first passage defining in cross-section a
multiply connected domain; and
- said elongated stem constituting means to create an
abrupt enlargement of the cross-sectional area of the
conduit at a juncture between said passages in the
direction of flow tbrough the headbox, for producing a
vortex in the flow of ~iber suspension through the
conduit.
As embodied and broadly described herein, the
invention further relates to a headbox comprising:
- an inlet chamber communicating with a source o~
fiber suspension, said fiber suspension having a direction
o~ flow through the headbox;
- an outlet chamber downstream of said inlet chamber,
said outlet chamber comprising a discharge opening;
-- a dif~user mounted between said inlet and outlet
chambers to establish a fluid path therebetween, said
diffuser including a plurality of conduits in fluid
communication with said inlet and outlet chambers, each
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conduit ha~iny a beginning and including at least first
and second successive portions establishing respective
fiber suspension passages of larger cxoss-sect~onal area
in the direction of fiber suspension flow through said
conduit, the first portion being located at the beginning
of said conduit, a stem mounted in ea~h of said conduits,
one of said passages being defined between said stem and
an inner wall of said conduit, said one of said passage~
defining in cross-section a multiply connected domain;
each said conduit having a generally constant cross-
sectional area in the absence of said stem; and
- said elongatPd stem constituting means to create an
abrupt enlaryement of the cross-sectional area of the
conduit at a juncture between said passages in the
direction of flow through the headbox; for producing a
vortex in the flow of fiber suspension through the
conduit.
As embodied and broadly described herein, the
invention further relates to a headbox comprising:
- an inlet chamber communicating with a ~ource of
fiber suspension, said fiber suspension having a direction
of flow through said headbox;
- an outlet chamber downstream of said inlet chamber,
said outlet chamber comprising a discharge opening;
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- a diffuser ~ounted between said inlet and outlet
chambers to establish a fluid path tharebetween, said
diffusçr including a plurality of conduits in fluid
communication with said inlet and outlet chambers, each
conduit having a predetermined internal volume and
including an elongated member received in an initial
portion of said conduit, said elongated member ~illing
partially said internal volume to establish in said
conduit an initial pass~ge and at least one additional
passage downstrea~ of said initial passage, said initial
passage having a smaller cross-sectional area than said ~;~
additional passage, said elongated member including a
channel means therein to establish a fluid communication
between said inlet chamber and said initial passage, said
elongated member constituting means to create an abrupt
enlargement of the cross-sectional area of the conduit at
a juncture between said passages in the direction of flow
through the headbox, for producing a vortex in the flow of
fiber suspension through said conduit, said initial
passage being defined between said elongated member and an ~:
inner wall of ~aid conduit, said initial passage defining
in cross-section a multiply connected domain.
As embodied and broadly described herein, the
invention further relates to a headbox comprising: ~ :
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- an inlet chamber communîcating with a source of
fiber suspension, said fiber suspension having a direction
of flow through said headbox;
- an outlet chamber downstream of said inlet chamber
comprising a di~charge opening;
- a diffuser mounted between said inlet and outlet
chambers to establish a fluid path therebetween, said
diffuser having a plurality of conduits in fluid
CGmmunicatiOn with said inlet and outlet chambers, each
conduit having a predetermined internal volume and
comprising: :
i) an elongat2d member mounted in said conduit
for filling partially æaid internal volume to define in
said conduit two successive passages of different cross-
sectional areas, r~ferenced as a first passage and a
~econd passage, said first passage being defined between
said elongated member and an inner wall of said conduit
and having a smaller cross-sectional area than said second
passage;
ii) be~ween said passages a zone of abrupt
transition fro~ one cross-sectional area value to another,
said zone of abrupt transition constituting means to
create a vortex in the flow of fiber suspension through
said conduit;
iii) channel means in said elongated member to
establish a fluid communication between said passages and
said inlet chamber.
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As em~odied and broadly described herein, the
invention further relates to a headbox comprising:
- an inlet chamber communicating with a source o~
fiber suspension, said fiber suspension having a direction
of 10w through said head~ox;
- an outlet chamber downstream of said inlet chamber,
said outlet chamber comprising a discharge opening;
- a dif~user mounted between said inlet chamber and
outlet chamber to establish a fluid path from said inlet
chamber to said su~l~t chamber, ~aid diffuser including a
plurality of conduits in fluid communication with said
inlet and outlet chambers, each conduit having a beginning
and being divided in at lest two successive portions,
referenced as a first portion and a second portion
establishing ~irst and second fiber suspension passages
respectively, said first passage being located at the
beginning of the conduit and having a smaller cross-
sectional area than said seaond passage, each of said
conduits including an elongated stem mounted therein, said
first passage being defined between said stem and an inner
wall of said conduit, said first passage defining in
cross-section a multiply connected domain, said conduit
coextensive with said stem having a generally constant
cross-sectional area throughout its length in a~sence o~
said stem; and
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- an abrupt transition bP.twe2n said passages, said
abrupt transition constituting meanq to create a vortex in
the flow of fiber suspenslon through said conduit.
BRIEF D1~5CRIPq!I0~ 0~ TlIE DRAWING~3
- Figure 1 is a schematical vertical cross-sectional ~:
view of a headbox constructed in accordance with this :~
invention;
- Figure 2 is an enlarged cross-sectional view of the
headbox diffuser showing a single fiber suspension
conduit;
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- Figure 3 is an elevational view of a variant of a
stem adapted to be mounted within the fiber suspension
conduit shown in Figure 2;
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- Figure 4 is a perspective view of the stem
shown in Figure 2 schematically illustrating the fiber
~uspension fl.ow,
- Figure 5 i3 a variant of the st~m shown in :;
Fligure 2;
- Figure 6 is another variant of the stem
shown in Figure 2;
- Figure 7 is a view taken along lines 7-7 in
Figure 6;
- F`igure 8 ill.ustrates a simply connected
domain; and
- Figures 9a ancl !3b illustrate multip.l~
connected domains, more particularly, Figure 9a show~ a
doubly connected domain and Figure ~b an ntupl;~ ~ ~
connected domain. .. :
Throughout the drawings, similar elements are
designated by the same reference numerals.
DESCRIPTION OF A PREFERRED EMBODIMæNT
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R~ferrin~ now to Figure 1, the reference
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numeral 10 designates in general a headbox shown in
cross-section that is used to continuously supply fiber
suspension to a foraminous carrier of a paper machine.
The headbox 10 comprises a pair of converging top and
bottom walls 12 and 14 respectively, constructed from
metallic plates. At one end, the plates 12 and 14
define an inlet chamber 16 closed by a wall 18. The
inlet chamber 16 is connected to a suitable supply of
fiber suspension.
Opposite the inlet chamber 16, the plates 12
and 14 define an outlet chamber 18 which is generally
triangular in cross-section. The outlet chamber 18 is
provided with a slice opening 20 for discharging fiber
suspension, extending the entire width of the headbox
10 and being defined between the extremities of the
plates 12 and 14.
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Between the inlet and the outlet chambers 16
and 18 respectively, is mounted a diffuser 22 to
establish a fluid path between these chambers. The
diffuser 22 comprises a pair of parallel metallic
plates 24 and 26 extending the entire width of the
headbox 10 and being secured to the plates 12 and 14 by
welding or by any other appropriate means. The plates
24 and 26 constitute a support for a cluster of tubes
28 which may or may not be parallel, defining fiber
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suspension passages between the inlet and the outlet
chambers 16 and 18 respectively.
As best shown in Figure 2, each tube 28 is of
a generally constant cross-section throughout the
length thereof except at the extremity thereof
extending in the outlet chamber 18 which is slightly
enlarged. The tube 28 is made of metallic material and
it is secured in respective bores provided in the
plates 24 and 26 by welding or by any other appropriate
means. The extremity of the tube 28 received in the
plate 24 is slightly recessed to define a seat 30.
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In the tube 28 is received a metallic stem 32 ; :
having at one end an annular ridge 34 secured in the ;.
seat 30. Downstream of the annular ridge 34, the :~
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radius of the stem 32 is reduced by an amount
corresponding generally to the wall thickness of the
tube 28 to provide a circular portion 36 received
within the conduit 28 and sealingly engaging the inner
wall thereof.
Downstream of the circular portion 36, the
stem d1ameter is reduced once again to define between
the outer surface of the stem 32 and the inner wall of
the conduit 28, in cross-section, a passage 38 for
conveying fiber suspension, shaped as an annulus or,
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more generally stated, defining a multiply connected
domain.
In plain terms, a domain is simply connected
if it has no "holes". More precisely, a domain is
simply connected if, for every simple closed curve in
tne domain, the region encompassed by the curve lies
wholly in the domain. A simply connected domain is
shown in Figure 8.
Examples of simply connected domains are the
following: the interior of a circle, the interior of a
square, a sector, a quadrant, the whole xy plane. The
annular region between two circles is not simply
connected, nor is the interior of a circle minus the
center point.
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One can distinguish between types of multiply
connected domains as follows: a domain with just one
hole is doubly connec~ed (see Figure 9a), one with two
holes is triply connected; one with n-l holes is ntuply
connected (see Figure 9b).
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The passage 38 communicates with the inlet
chamber 16 through a channel structure 39 including an
inlet portion constituted by a straight centrally
located and longitudinally extending bore 40 opening in
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the inlet chamber 16 and extending slightly beyond the
circular portion 36 to unite with a cross bore 42
communicating wi.th the passage 38. The channel
structure 39, which is somewhat T shaped as best shown
in Figure 4, has the effect of splitting in two the
flow of fiber suspension and subjecting the flow to two
90 bends to augment the turbulence for better
uniformity of the fiber distribution in the suspension.
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In a first variant, illustrated in Figure 5,
the centrally located bore 40 communicates with the
passage 38 by two generally oppositely extending
passages 100, each passage 100 defining an obtuse angle
with the axis of the stem 32. Stated otherwise, the
passages 100 force the flow of fiber suspension to
effect a bend in excess of 90 when leaving the central
conduit 40.
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In another variant, illustrated in Figures 6
and 7, the centrally located bore 40 leads to a chamber
200 communicating with the passage 38 through ~our
passages 202 parallel with the central conduit 40. The
central conduit 40, the chamber 200 and the passages
202 force the flow of fiber suspension to effect two
180 degrees bends before reaching the passage 38.
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The embodiment illustrated in Figures 5, 6
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and 7 are suitable for applications where it is
desirable to substantially augment the turbulence in
the flow of fiber suspension before it enters the
annular passage 38.
Referring back to Figure 2, the length of the
stem 32 is somewhat shorter than the overall length of
the tube 28 to divide the tube in two portions, namely
a first portion 44 and a second portion 46 which are
separated by an imaginary plane tangent to the free end
of the stem 32 and being identified by the dotted line
48. The second portion 46 defines a cylindrical fiber
suspension passage of larger cross-sectional area than
the ring shaped passage 38 of the first portion 44, the
first and second passages being separated by an abrupt
transition produced by the sudden termination of the
stem 32. The abrupt transition contributes to create
vortexes in the fiber suspension flow to establish and
maintain a controlled level of turbulence.
In a variant of the invention shown in Figure
3, the stem 32 has a stepped structure creating in the
tube 28 three successive passages of lar~er
cross-sectional area separated by abrupt transitions,
namely two adjacent ring-shaped passages followed by a
cylindrical passage.
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It may be envisaged to construct the stem of
three or more serially connected sections providing the
desired number of ring-shaped passages in the tube 28.
The dimensions of the various elements of the
tube 28 and of the stem 32 are selected according to
the desired flow characteristics.
The above description of a preferred
embodiment of this invention has been given only as an
example and it should not be interpreted in any
limiting manner because it may be refined and modified
in various ways without departing from the spirit of
the invention. The scope of the invention will be
defined in the apended claims.
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