ELEMENTS DIRECTEURS D'ECOULEMENT DANS LA CAISSE DE TETE D'UNE MACHINE A PAPIER

FLOW RESTRAINING ELEMENTS IN THE HEADBOX OF A PAPER MACHINE

Abrégé anglais

ABSTRACT OF THE DISCLOSURE
A headbox for a paper machine comprising a top plate
and a bottom plate defining a chamber therebetween and a
plurality of flow restraining elements disposed one above
another in the chamber to define a plurality of paths spaced
one above another therein. The top and bottom plates are
connected to one end to a perforated plate defining an inlet
for the chamber and approach each other as they approach an
outlet for the chamber. Each element is removably connected
at one end to the perforated plate, and the paths extend from
the inlet to the outlet. Each element has a mildly corrugated
upper surface and a mildly corrugated lower surface which
approach each other until they terminate in a free end remote
from the perforated plate. Those surfaces are substantially
symmetrical to each other with respect to a center line of
said element. Each element has a free end portion formed
from an easily deformable material, such as rubber or plastics.
The surfaces of each element define an angle of 1° to 15°
therebetween.

Revendications

The embodiments of the invention in which an
exclusive property or privilege is claimed are defined as
follows:
1. In a headbox for a paper making machine, the
headbox having a top plate and a bottom plate defining a
chamber therebetween, a perforated plate connected. to an
inlet end of said top plate and an inlet end of said bottom
plate to form an inlet of said chamber, said top plate and
said bottom plate approaching each other at an outlet end
spaced from said inlet end to form an outlet of said
chamber, and a plurality of flow restraining elements
disposed one above another in said chamber to define a
plurality of flow paths spaced one above another in said
chamber, said flow restraining elements extending from said
inlet to said outlet, having free ends at said outlet, and
being removably connected at one end thereof to said
perforated plats, the improvement wherein;
each of said flow restraining elements has an upper
surface and a lower surface which approach each other until
they meet at said free end in a downstream direction away
from said perforated plate toward said outlet end,
said upper and lower surfaces each having a surface
portion having corrugated patterns which are symmetrical
with respect to each other and formed by a cross section
perpendicular to said downstream direction, which
alternately gradually increases and decrease along the
length of said flow restraining elements to said free end so

Claim 1 continued....
as to define alternating portions of increased and reduced
cross section, such that the increased cross sections
gradually decrease in said downstream direction and the
decreased cross sections gradually decrease in said
downstream direction, said cross sections varying
sufficiently gradually between successive portions of
increased and reduced cross section so as to resist warping
during variable temperature use,
said upper surface and said lower surface
defining an angle of 1° to 15° therebetween,
said free ends of said flow restraining elements
being formed from a flexible material selected from the
group of flexible material consisting of rubber and plastic,
said material having a low modulus of elasticity and a
specific gravity of about 1.0 so as to be easily deformable,
each of said flow restraining elements being
provided with an upper recessed portion on said upper
surface and a lower recessed portion on said lower surface,
said upper and lower recessed portions being respectively
defined by an upper wall on said upper surface and a lower
wall on said lower surface which are substantially
perpendicular to said downstream direction, said flow
restraining element being arranged in said chamber with said
recessed portions adjacent one another to create an abruptly
enlarged area in each of said paths between adjacent flow

Claim 1 continued....
restraining elements, said recessed portions being located
between said perforated plate and said surface portions of
said flow restraining elements having said corrugated
patterns, and
said flow restraining elements being positioned in
said chamber with said corrugated patterns symmetrical with
respect to each other, whereby the flow paths between
adjacent flow restraining elements have cross-sectional
configurations which gradually increase and gradually
decrease, thus causing liquid which flows between said flow
restraining elements in said downstream direction to have a
speed which decreases and increases to create a stirring
effect on the liquid.
2. The improved headbox of claim 1, wherein each of
said flow restraining elements consist entirely of plastic.
3. The improved headbox of claim 1, wherein said angle
between said upper surface and said lower surface is 4°.
4. The improved headbox of claim 1, wherein said
perforated plate has a surface forming an inside wall of
said chamber, said surface of said perforated plate being
convex in shape towards said flow restraining elements.
5. The improved headbox of claim 1, wherein the most
upstream one of said reduced cross section portions has a

Claim 5 continued....
cross section greater than that of the most downstream one
of said increased cross section portions.
6. The improved headbox of claim 1, wherein said upper
and lower surfaces diverge from each other in a downstream
direction respectively from said upper and lower walls.
7. The improved headbox of claim 1, wherein said upper
and lower walls are spaced from said perforated plate at
locations downstream of said perforated plate.
8. The improved headbox as in claim 1, wherein said
top plate has a corrugated inner surface which is
substantially symmetrical to said upper surface of the
uppermost element, while said bottom plate has a corrugated
inner surface which is substantially symmetrical to said
lower surface of the lowermost element with respect to a
substantially horizontal plane.

Description

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FLOW RESTRAINING ELEMENTS IN THE HEADBOX
OF A PAPER MA~HINE
BACKGROUND OF THE INVENTION
,
1~ Field of the Invention~
.
This invention rel~tes to a headbox in a paper machine.
More particularly, i~ relates to flow restraining Plements in
the ~l~adboxO
BRIEF DESC RI PTION OF THE ~RAWINGS
FIGURE t is a longitudinal and vertical sectional view
1~ of a paper machine headbox known in the art, and
FIGURE 2 is a longitudinal and vertical sectional view
o~E a headbox embodying ~his inventionO
2. D3scription of the Prior Art:
..~ conventional headbox for a paper machine is shown by
1~ ~ay o:E example in FIGURE lo It comprises a top plate 2 and
a botrom plata 3 defining therebetween ~ chamber in which a
plurality of flow restraining element~ 1 are provided one
above another. æach elsment 1 is held at one end by one of
a plurality of grooves formed in a perforated plate 4 disposed
2~ upstream of the elements lo The f low of a raw paper li~uid
in the chamber maintains the elements 1 in their positions
shown in FIGURE 1. The slements 1 define a plurality of
paths 5. Those portions of the paper material which flow
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1 through the paths 5 meet downstream of the elements 1, and
it is ejected onto a wire not shown after its degree of open-
ing has been controlled by a slice lip 6.
A plurality of paths defined by a plurality of ~low
restraining elements enable the effective dispersion of
fibers in the liquid with a small head loss and thereby the
prod~lction of paper of high qualityO
The known flow restraining elements as shown a~ 1 in
~IGURE 1, however, has a number of drawbacks. They are dif-
ficult to make because of their large variation in thic~nessO
; They easily get warped along their width. Correctly sizedpaths are, ~herefore, difficult to define. The elements
break easily a~ any portion of reduced thic]cnessO Those por-
tlons of the elements at which they are connected to the
15 perforated plate are so small in thickness t:hat they easily
get deformed and are difficult to attach to, or de~ach from,
the perforated plate.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an improved
20 headbox for ~ paper machine including improved flow restrain-
ing elements which are easy to make and define correctly
sized paths.
This invention provides an improvement in a paper machine
headb~x comprising a top plate and a bottom plate connected
at one end to a perforated plate, defining a chamber there-
between and approaching each other toward a slice lip, and
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1 a plurality of flow restraining elements disposed in the
chamber to define a plurality of paths therein and each re-
movably connected at one end to the perforated plate through
which a liquid paper material is introduced into the pathsO
~ ccording to a saLiant feature of this invention, each
flow restraining element has a thickness which gradually
~ecreases as i-t becomes farther from the perforated plateO
This gradually decreasing thickness is defined by an upper
surface and a lower surface which approach each other until
Lq the~ join each other a~ the free end of the e~ementO The up-
per and lower surfaces have a substantially e~ual mildly cor-
rugated pattern and the corruga~ions on each surface. extend
p~ a downstream d~rectio~ . `
At least that portion o~ each e~ement which ~ermina~es in its
free end is formed from an easily deformable material, such
as rubber or plastics, so that t;hat portion may be easily
deformable along the width of the elementO
The upper and lower surfaces of each slement pr~ferably
define an angle of 1 to 15 ~herebetweenO
~0 Each element has a gradually decreasing ~hickness and
its upper and lower surfaces are miidly corrugated. In other
words, its thickness varies only to a small extentO Its upper
and lower surfaces are substantially symmetrical to each other
with respect to a ce~er li.ne of sa~d element.
Therefors, the elements are not appreciably warped when they
are made. They are not appreciably warped despite variation
in temperature during the operation of the paper machineO
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1 Insofar as they are not ea~ily warped, they are easy to
make and ensure that correctly siz~d paths be maintained.
= -Tha~ portion of Pach element which ~erminates in its free
end is formed from an sasily deformable material, such as
rubber or plastics, and has a very small thicknessO Therefore9
the warpage of the elemen~, if any, is easily rectified by
its deformation w~en the liguid ~aper material is caused to
flow through the pa~hs, this feature contributes ~o ensuring
the correct dimens:ions of the pathsO
The elements have a gradually decreasing thickness and
its sur~aces are m:Lldly corrugated and do not define any por-
tion that is extremely thick or thinO Therefors, they are
not easily broken, while they are light in weight and easy
to handle. That erld of each element at which it i5 connected
15 to the perforated ~>late has a sufficiently large thic~ness
not to be easily bent~ and is9 therefore, easy to connect to,
or disconnect from, the perforated pla~e,
Other features and advantages of this invention will
become apparent from the following description and the ac
companying drawings.
DETAILED DESCRIPTION OF THE INVENTION
A headbox embodying this invention is shown by way of
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example in FIGURE 2. It comprises a plurality of flow re-
straining elements 7 disposed one above another in a chamber
defined between a top plate 8 and a bottom plate 9. Each
element 7 is connected at one end to a perforated plate 10
defining an inlet for the chamber.
Each element 7 has a mildly corrugated upper surface and
a substantially equally mildly corrugated lower surface.
The upper and lower surfaces approach each other gradually
until they terminate in a free end located remotely from the
perforated plate 10 and in the vicinity of an outlet for the
chamber. The surfaces preferably define an angle of 1 to
15 therebetween. If this angle is smaller than 1, it is
difficult to form each element 7 and particularly its free
end portion with satisfactorily corrugated surfaces which
create a satisfactory stirring effect on the liquid which is
caused to flow through the paths defined by the elements 7.
I~ the angle is larger than 15, that end of each element 7
at which it is connected to the perforated plate 10 is too
large in thickness and makes the element heavy and difficult
to handle. The upper and lower surfaces of each element 7
shown in FIGURE 2 have an angle of about 4 therebetween by
way of example.
The corrugated surfaces are defined by corrugations which
extend to a downstream direction. The corrugated serfaces serve to

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create a turbulent flow in the liquid. They define paths hav-
ing a cross sectional configuration which gradually increases
or decreases along the elements 7 and thereby causes the
liquid to flow at a speed which decreases and increases along
the paths. The dimensions of the corrugations are so selected
as to ensure that the thickness of each element 7 vary mildly.
The corrugatad upper and lower surfaces are substantially
symmetrical to each other with respect to a longitudinal axis
of said element.
The free end portion of each element 7, which has a very
small thickness, is formed from a material having a low
modulus of elasticity and a specific gravity close to 1, such
as rubber or plastics, so that it may be easily deformable.
The other portion may be formed from the same material, or
any other material.
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