Note: Descriptions are shown in the official language in which they were submitted.
~~~~~~~
WO 91/01408 PCT/US90/04144
-1- .
IMPROVED .SYSTEM AND .METHOD..FOR FORMING..AND
DEWATERING A W'EE ON 'A FOURDRINIER FABRIC
TECHNfCAL FIELD
This invention relates to the technical field
of the pulp and paper industry, especially to. the Fourdrinier
process of laying an aqueous suspension of fibers on a
Fourdrinier fabric and dewatering and drying it to a
sheet of paper.
8'ACKGROUND OF 'THE INVENTION
Modern paper making grocesses and machinery follow
the Fourdrinier method wherein an aqueous dispersion of
paper making~fibers is poured onto a high_.speed travelling
woven fabric through which water from the dispersion drains
leaving a thin web of wet fibers which is dried and finished
to a sheet of paper. The key step in this method is that of
forming the web from the fiber/aqueous dispersion. This
must be done very quickly and uniformly across. the width
of the endless fabric. Normally, the transition of de-
watering commences by gravity, followed by other means
such as foil blades, continuing with a plurality of con-
trolled low uacuum boxes and then by a plurality of high
vacuum boxes. There are many causes for mishaps to occur
that prevent the final sheet of paper from being perfect.
One of the principal causes is that air may penetrate
the web of paper and the fabric causing nonuniformities~
;,
in the paper: Such 'disturbances may be caused by nonuniform
drainage at every square inch of the fabric surface, and
entrainment of air in the fiber/aqueous dispersion, followed
by forcing air through the dispersion and fabric whereby
air,wi:.'_. find the path of least resistance and fixing
the flocculation of such dispersion unevenly over the fabric.
The demand for higher and higher speed makes it increasingl;J
difficult to produce a paper sheet that is isotropic.
d
suBStsH~r
,:~.~..:... -...:..:.r . , :...;:: . ...:,;,,., ...;,,..: ,.;.::;:~, - ':: .
;~. ..:,,..:.. .~ >.."..;~; .;.:.~.;... , -. , .,,. '
CA 02040439 1997-08-13
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The critical step of this process is the water removal,
which must be done quickly and uniformly in order to obtain a
layer of fibers on the fabric that can be finished to a high
quality paper. The principal difficulty in producing a fast,
uniform drainage has been that when the drainage is speeded up
by applying a vacuum there are numerous instances at random
locations across the fabric where air will be pulled through
the layer of wet fibers. At each location a small vortex
appears to break the continuity of the film of water and fiber
on the fabric, and to permit the passage of air through the
entire film and thereby disrupting the uniform settling of the
fibers into a web of uniform thickness and strength. Every
time such an instance occurs, a meniscus is formed at the
interface of the water and air and this is an obstruction to
the free uniform flow of water away from the fibers forming
the web. The formation of such air holes through the mass of
fibers forming the web must be minimized if any improvement in
sheet formation at high speed is to be achieved.
It is an object of this invention to provide improved
sheet formation in the Fourdrinier paper making process. It
is another object of this invention to provide an improved
procedure for maintaining a continuous drainage of water with
substantially no air flow discontinuities occurring in the
forming web. It is an object of this invention to provide a
drainage process wherein all of the web forming fibers are
essentially submerged in water until the last moment when the
last portion of water is drained away from all parts of the
web simultaneously. A further object is to improve the
drainage while maintaining a higher retention of fines and
fillers in the web than heretobefore accomplished. For
example, the prior art mills may have a first pass retention
of between 40-60 percent whereas this invention provides first
pass retention of up to 900. Another object is to decrease
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CA 02040439 1997-08-13
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the amount of friction between the fabric and the dewatering
components to increase the fabric life. A further object is
to substantially reduce the length of the forming area of the
Fourdrinier fabric, thereby reducing the number of dewatering
components required. For example, one submerged drainage box
in accordance with this invention may replace 20-25 foils of
the prior art and in substantially less space along the length
of the fabric. An additional object is to improve the sheet
formation by decreasing its porosity and substantially
eliminating pin holes through the sheet. Another object is to
decrease the power consumption of the Fourdrinier machine in
both driving the fabric and by eliminating high vacuum pumps
to supply suction to the dry end flat boxes thereof.
Yet other objects include:
A. retention of more chemical additives and fines
due to the more gentle dewatering and uniformity of
dewatering;
B. easier release of web from the fabric due to
the web not being forced into the interstices of the fabric by
high vacuum whereby a web pick-up vacuum roll or high pressure
air from below the fabric not needed;
C. amount of defoamer is reduced;
D. enhanced sheet strength; and
E. enhanced drying at the drier end of the fabric
(couch roll) thus reducing the power used in the press and/or
the drying sections. Still other objects will appear from the
more detailed description which follows.
BRIEF SUMMARY OF THE INVENTION
These definitions may be used in understanding this
invention:
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A. Meniscus is the surface area of a water volume
which is in contact with unlike surfaces . The unlike surfaces
being either the container holding the water or the gases in
contact with a surface of the water or surrounding the water,
such as air when a drop of water is falling through it.
Webster's New International Dictionary, 2nd Edition
Unabridged, 1934 defines Meniscus as ---the curved upper
surface of a liquid column that is concave when the containing
walls are wetted by the liquid and convex when not. However,
the meniscus also is present at the interface between the
liquid and the vessel in which it is contained.
B. Surface Tension is a condition that exists at
the free surface film of a liquid by reason of intermolecular
forces about the individual surface molecules and is
manifested by properties resembling those of an elastic skin
under tension. Surface Tension is a characteristic of the
water meniscus which can be modified by chemical means. The
meniscus changes its geometric (concave) shape depending on
the size of the vessel containing the fluid. In capillary
tubes the meniscus reaches extremely high levels of energy in
the form of pressure. The resistance of the meniscus to
rupture, compared to its thickness is very high as is well
known.
C. Draining by eliminating the meniscus, or
submerged drainage, is a water removal operation whereby water
is removed from the aqueous dispersion or wet web by means of
a reduction of pressure originating from, and transmitted by
the water itself and not by the prior art vacuum as may be
provided in the wet and drier end of a Fourdrinier fabric. In
particular, the meniscus is eliminated in the surface of the
fabric opposite to the pulp or web so that drainage is
unimpeded.
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CA 02040439 1997-08-13
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This invention relates to a submerged drainage system for
removing water from a moving Fourdrinier fabric having a drier
end downstream of a wetter end, an outer surface, and an inner
surface in a paper making process. The improved system
includes a first plurality of spaced elongated stationary
dewatering meniscus tension units or meniscus separator units
each having a bottom and an upper drainage surface in
continuous sliding contact with the inner surface and an
aqueous dispersion of paper making fibers supported on the
outer surface. The dewatering meniscus tension units or
meniscus separator units are spaced along the wetter end of
the fabric and each has an internal space for containing a
volume of water extending to and in contact with the inner
surface of the fabric . A plurality of passageway are provided
from the drainage surface to the internal space of the unit to
conduct water from the outer to the inner surface of the
fabric to the internal space of the unit. A first passageway
conducts water from the space by gravity outwardly of the
unit. A means for applying a low vacuum by means of a fan to
the volume of water within the internal space induces the
control of enhanced drainage of water from the aqueous
dispersion.
An important aspect of this invention includes means for
maintaining the level of water of the internal space of the
drainage unit constantly in contact with the inner surface of
the fabric to inhibit the formation of an air water meniscus
from being between said inner surface of the fabric and the
upper drainage surface of the unit.
Another important aspect the system further includes is
a second plurality of spaced elongated stationary multicell
meniscus separator drainage unit or boxes along the drier end
of the fabric and having a drainage surface in continuous
contact with the inner surface. A web is formed prior to the
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drier end from the aqueous dispersion of paper making fibers
supported on the outer surface above the boxes, each drainage
box including a plurality of cells each having an internal
space placed under subatmospheric pressure by a fan means for
each cell extending to and in contact with the inner surface
of the fabric. A first passageway conducts air from outside
the box to the drainage surface of the box and the inner
surface of the box to the internal space of the box and the
first passageway through the interstices of the fabric. A
second means applies a small vacuum to the internal space to
modify the natural tension of the meniscus of the water in the
fabric to induce drainage of water from the web to the fabric
and the box. Also, a means is provided to discharge the water
from the internal space of the unit.
In other aspects, there is provided a means for applying
a vacuum which may include a vertical head of water having an
upper surface with air under subatmospheric pressure above
such surface of the head of water. A means to control and
maintain constant the level of water in the internal spaces of
the first dewatering meniscus tension units is provided. The
first passageway of each unit includes an exit conduit for
water to flow out of such dewatering meniscus tension unit,
and a movable valve to open and close the conduit. A float
may be placed on the surface of the vertical head of water,
and means to sense the position
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WO 91/01408 PCT/US90/04144
2~~~43~
-6-
of the float or the pressure of the volume of water in the
box, and correspondingly to move the valve to open or close
same in accordance with its position so sensed, may be lo-
cated adjacent the float. This is accomplished in one
embodiment by a source of electrical and fluid power and in
another preferred embodiment by mechanical and fluid power.
In specific and preferred embodiments of this inven-
tion the upper surface of a volume of water is in contact
with the Fourdrinier fabric as it passes by, and water is
removed from the aqueous dispersion of paper making fibers
resting on the fabric by controlling the outflow of water
from that volume so as to produce a differential pressure,
as by it flowing into a tray at the box bottom and outwardly
- therefrom. In- another embodiment of a vacuuiia-over a vertical
column of water is controlled so as to cause a suction to be
applied to the volume of water to place the meniscus of water
in a pretension condition to cause contact with and with-
drawal of water from the aqueous dispersion. In still~another
embodiment water removal is effected in two directions from
the dispersion by employing two Fourdrinier fabrics, one
above and one below the dispersion, and causing water to flow
out through both fabrics.
In further aspects each box includes a plurality of
spaced parallel blades with a forward area in contact with
the fabric and a rearward area being relieved to enhance de-
watering of the dispersion on the fabric thereabove. Air
suction tubes may be spaced along the length of the box to
remove air and water entrained in the water in the fabric and
therebelow. Such tubes are connected to an exhaust fan and a
water discharge leg is connected therebetween to discharge
water into the outflow of water from the boxes.
Additional aspects are provided by each cell having a
nose with a horizontal planar surface over which the inner
surface of the fabric slides. The first passageway is at an
acute angle with the planar surface to conduct air into the
inner surface of the fabric in the same direction as the
movement of the fabric. The second passageway is at an acute
SUBSTITUTE SHEET',
W4 91/01408 PCT/US90/04144
-j-
angle with the planar surface to conduct air and water away
from the inner surface of the fabric into the internal space
thereby minimizing any air being passed through the web. A
source of steam preferably is used to heat the air passing
through the first passageway to enhance water drainage from
the web.
The invention herein is also seen to include a method
of removing water from an aqueous fiber dispersion supported
on the fabric including sequentially passing the.fabric and
the dispersion over and in contact with an ugper level of a
volume of water enclosed on all sides except for the side in
contact with the fabric; removing water from the volume of
water at a level below the upper level to produce a differ-
ential pressure.effect on the volume of water;. controlling
the removal of water and the differential pressure effect to
achieve an optimum dewatering of the dispersion uniformly
over the fabric as it passes over the volume of water; and
recovering a wet web of paper on the fabric suitable for
pressing, drying and finishing to a sheet of paper. The
above controlling may be automatic and include sensing the
rise and fall of the pressure of the water in the box; and
increasing and decreasing respectively the removal of water
according to the sensed rise and fall of the pressure in the
water volume in the box. Also, the method preferably in-
cludes removing water and entrained air from the dispersion
and/or from the fabric followed by separating the air and the
water so removed for separate treatment of each.
The invention also includes a method of removing
water from an aqueous fiber dispersion formed into a wet
web including passing the fabric and wet web of fibers
over and in contact with a submerged drainage r=moval
means; applying a small vacuum to the removal m:-:ns to
extract water and air from the fabric and modifying con-
sequently the natural tension of the meniscus of the water
in the fabric to extract water from the wet fabric; and
permitting air from the atmosphere to be applied to the
removal means and thence to the fabric from below the
SU1~3~TITUTE SHEET
WO 91/01408 pCT/US90/04144 -
2~4~~~~
-8-
fabric to enhance the removal of water from the fabric
and water from the web. The air is introduced upstream
from the vacuum whereby the air travels in the same
direction as and in the interstices of the fabric and en-
hances the removal of water from the web. Steam.also may
be applied to further enhance water removal from the web.
This method may also include supplying another-fabric on
the wet web moving in the same direction as the fabric.
The aforementioned steps of passing, applying, and permitt-
ing are applied above the other fabric with the same
effective results to produce a paper web and sheet there-
from having substantially the same characteristics on each
_._ _ planar surface thereof.
BRIEF DESCRIPTTON OF THE DRAWINGS
The novel features believed to be characteristic
of this invention are set forth with particularity in the
appended claims. The invention itself, however, both as
to its, organization and method of operation, together with
further objects and advantages thereof, may best be under-
stood by reference to the following description taken in
connection with the accompanying drawings in which:
FIG. 1 is an overall schematic side elevational
view of the system of this invention using two Fourdrinier
r fabrics;
FIG.,2 is a front elevational view of a drainage box
in a Fourdrinier process modified in accordance with one
embodiment of this invention;
FIG. 3 is a cross sectional view taken at 3--3 of
FIG. 2;
FIG. 4 is a front elevational view of a drainage box
in a Fourdrinier process modified in accordance with a
second embodiment of this invention, employing an automatic
control;
FIG. 5 is a cross sectional view taken at 5--5 of
WO 91/01408 PCT/US90/04144
~~~~~i~ 3
FIG. 6 is a front elevational view of a drainage box
in a Fourdrinier process including a means for removing
entrained air in accordance with a third embodiment of this
invention;
FIG. 7 is a cross-sectional view taken at 7--7 of
FIG. 6;
FIG. 8 is an enlarged cross-sectional view taken of
a drainage box, similar to that taken at 8--8 of FIG. 4,
but in considerably greater detail and with some modifications.
thereto;
FIG. 9 is a cross sectional view taken at 9--9 of
FIG. 8;
FIG. 10 is a cross sectional view taken at 10--10 of
_. _. __ FIG. 8 ; . _ _ _ _
FIG. 11 is a cross sectional view of the improved
drainage box cover, taken transversely to the running blades,
arid usable on each of the drainage boxes illustrated in FIGS.
3 , 5 and 7 ;
FIG. 12 is an enlarged cross-sectional view of the
drainage box taken at 12--12 of FIG. 1;
FIG. 13 is an enlarged cross-sectional view of a
portion of the drainage box of that shown in FIG. 12; and
FIG. 14 is identical to FIG. 13, except to include an
improvement in the air inlet portion.
DETAILED DESCRIPTION 'OF THE 'INVENTION
On the surface of the Fourdrinier fabric the meniscus
infiltrates the interstices or, meshes and produces several
phenomena, one being that while a dry fabric is easily .
penetrated by air, the same fabric, when wet, will be
difficult to penetrate by air and yet easily penetrated by
the water. Since the film of the meniscus attaches to the
fabric, it allows the passage of water, the meniscus itself
being water. However, before air pan pass through the
fabric the meniscus layer must first be ruptured by a certain
level of air pressure considered here as tension of the
meniscus of water.
$lJ~$TITtJTE $i-IEET
WO 91/01408 PGT/US90/04144
~, . .. -10-
The features of this invention are best understood
by reference to the attached drawings.
A Fourdrinier paper making machine of the prior art
is somewhat similar to the lower half of the apparatus of
FIG. 1 wherein a woven fabric 20 travels horizontally in
the direction of arrow 40 and passing over the top of
several devices in locations such as those shown at 41, 42,
43, 32, 33, 34 and 35 to remove water from a layer of a
fiber/aqueous dispersion 44 fed to the top of fabric 20
by a head box 115 and to leave a self supporting web of
wet fiber at 109 which can be taken from the fabric 20
and processed through drying, pressing, and finishing
operations to become a sheet of paper. The water removal
devices-of the prior art are normally boxes with a top cover
of approximately 40-50~ open area over which fabric 20
passes and with the interior of the box at subatmospheric
pressure so as to suck water and/or air through the fabric
20 into the box for additional water removal. Generally,
such boxes are fashioned with a plurality of parallel
slots and/or holes and blades or foils, which. are inclined
against the direction of movement 40 of fabric 20 so as to
cause water beneath the fabric to flow more readily through
and away from the fabric 20. The purpose of such action is
to essentially wipe away any bubble or any drops or hanging
water below the bottom of fabric 20 and thereby seeking to
maintain a flow of water draining out of the dispersion on
the top of fabric 20 against the resistance formed by the
meniscus of water attached along the interstices of the
fabric .
It is an important feature of this invention to
eliminate, to the maximum extent possible, the opportunities
for the water to form bubbles or menisci, and thereby to
keep the Water drainage flowing as rapidly and uninterrupt-
edly as possible. The guiding principle for the improved
system of this invention is maintaining an uninterrupted
continuous volume of water from fabric 20 to a place of
SUf3STiTUTE SHEET
WO 91/01408 PCT/US90/04144
-11-
discharge of the water drained from the fabric 20 while
maintaining a negative pressure differential, i.e., a small
vacuum, on the water at the fabric 20. This general system
is now known as "submerged drainage " because the objective
is to prevent any interfaces of water and air or other sur-
faces which form a meniscus and which seriously impede the
rapid drainage of water. Of course, it is not possible to
be perfect in preventing the formation of menisci and so the
system must also provide means for destroying any meniscus as
soon as it is formed so as to resume "submerged drainage".
FIGS. 2-3 show one system whereby the prior art ap-
paratus is modified to employ components of this invention.
The improved drainage box 52 having an internal volume 58 and
a--pl-urality of parallel blades 53 in an assembly frame 57,-
with an open area of at least about 90~, on top of the box is
modified by the addition of~a bottom drainage means including
drainage opening 110, a drainage tray 54, and a valve in-
cluding a gate 55 pivoting about pin 56 to open or close
drainage opening 110. In this situation, when the improved
drainage box 52 is used as a retrofit, the valve remains
closed. The internal space 58 is not filled with water. A
vertical standpipe 61 is placed at the end of conduit 111
through flange connection 62 to receive the air and water
passed thereinto. At the upper end of standpipe 61 is a
suction fan 59 blowing air outwardly in the direction of
arrow 60 so as to create a vacuum in internal space 58. The
lower portion of standpipe 61 serves as a hydraulic 1=.g to
seal the vacuum with water at level 66 draining throu..::, pipe
65 to a discharge below the water level 64 in a pond or col-
lection vessel 63: This system of FIGS. 2-3 snows both the
standpipe 61 and fan 59 as well as tray 54 and valve gate 55
which is not used to assist in providing a vacuum, via dif-
ferential pressure action, on a volume of water in box 52
that extends in a continuous manner to the water in disper-
sion 44 on fabric 20.
SUf35TITUTE SHEET
wo 9ieo~aos Pcrius9oeoa~aa
2~4~~3~ -12-
One preferred embodiment, in accord with this inven-
tion, is shown in FIGS. 4-5, and includes means to automati-
cally control the water level in the drainage box 52 which in
all respects are identical to that described above, as well as
its internal space 58, blades 53, blade assembly frame 57,
with an open area of at least about 900, tray 54, valve gate
55, and pivot pin 56. However, an improved subassembly is
attached to conduit 111 at flanges 62. A control tower 67
extends upwardly from conduit 111 and is filled with water to
a level 71 which is slightly above the elevation of the inner
or lower surface 38 of fabric 20. Above level 71 is a vacuum
manifold 68 leading to a source of small vacuum, e.g., a fan,
such as fan 59 in FIG. 2, With air flowing in the direction
of arrow 69. In the Fourdrinier the tension of meniscus
varies from about 15 to 20 cm of water column and a small
vacuum on the volume of Water below the fabric in accord with
this invention will be in pretension of about 10 cm of water
column so that dewatering is induced more readily. Cover
plate 112 is provided as an access for cleaning conduit 111
and/or tower 67.
' The float 70 is designed to be maintained at level 71,
but it will move up and down, and the movement of float 70 is
sensed by transducer 102 to control via electric line 104 an
electric motor and fluid pump 78 which pumps the fluid
through fluid lines 79 and 80 to and from actuator 74 causing
connecting rod 75 to move. The linear movement of rod 75 is
transmitted through clevis.76 and arm 77 to cause shaft 72 to
rotate about its longitudinal axis, which in turn, causes
valve gate 55 to open or close. Thus, the level of water at
lower surface 38 is controlled so as to maintain it at that
elevation while sucking as much.water as rapidly as possible
away through box 52 and into tray 54 and out therefrom to pro-
duce a differential pressure effect, together with the modi-
fication of the natural tension of the meniscus of water
attached to the interstices of the fabric 20.
Another embodiment of the invention is shown in FIGS.
6-7. Because of the imperfections involved in forming the ,
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fiber aqueous dispersion 44, glacing it on fabric 20, and
moving it through the process, there are pockets of entrained
air found in dispersion 44 as it moves across drainage box
52. As noted above the presence of air is undesirable and
the air should be removed as soon as possible so as to elim-
inate the formation of any air/water meniscus beneath fabric
20. In FIGS. 6-7, a means is provided to eliminate such for-
mation and is seen to include a plurality of suction tubes 81
spaced apart from each other across the lateral width of
fabric 20. The upper free ends 83 of tubes 31 are placed be-
tween adjacent blades 53, preferably at least the most down-
stream blades, and positioned at, or very near, to the bottom
surface 38 of fabric 20. Tubes 81 are connected to a mani-
fold 82-wtiich leads to a source of low vacuum through-conduit
68 in which air flows in the direction of arrow 69. Tubes 81
will cause water as well as air to pass from adjacent the
bottom of the fabric 20 with the water being separated to flow
downward in hydraulic leg 61 to a discharge level such as the
level of water in tray 54.
In FIGS. 8-10 there is shown a mechanical apparatus
for controlling the system such as that shown in FIGS. 4-5
and described generally hereabove. Control tower 67 is con-
nected~to internal space 58 in a drainage box 52 and is
filled with water with a float 70 resting on the surface of
the water and a vacuum line 68 leading off to a vacuum source
(not shown), such as fan 59 of P'IG. 2. As float 70 moves up
and down because of water level 71 changing, lever linkages
113 connected to float 70 by connector 116, cause shaft 88 to
rotate in the direction of arrow 114. At the lower end of
shaft 88 is a valve plate_84 with openings 86 extending ver-
tically through plate 84. Valve seat 85 also has complemental
openings 87 therein, which generally match openings 86. When
valve plate 84 is rotated, the openings 86 and 87 will par-
tially.or fully align to permit water in tower 67 to flow into
drop leg 61 and when fully unaligned will not permit water to
so flow. ~Oater in drop leg 61 fills up to a level at 66 and
may be drained away in either of two ways; namely, through
SUBSTITUTE SHEET
WO 91/01408 PCT/US90/04144
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side arm exit 90 or through valve 89 into pipe 65 and thence
to pond or vessel 63 having a water level at 64. Valve 89 is
a fine adjustment to divert the necessary water to side arm
exit 90 and allow the remainder to fall into pond or vessel
63. Water from side arm exit 90 flows in the direction of
arrow 91 into diaphragm valve 93 causing arm 96 to move up
and down as the diaphragm 117 of valve 93 flexes. The dia-
phragm guide is. illustrated by numeral 11~. Spring 97 is
biased to hold levers 94 and 98 down until water in diaphragm
valve 93 causes it to move upward. The movement of arm 96 is
transmitted through pivot 95 and lever 94 to leg 98 to lever
100 through pivot 99 to connector 101 which operates a lever
119, that is used to control the.opening and closing of valve
gate 55 in drainage tray 54 by pivoting about pin 56. Thus
. the movement of float 70 is, transformed into a compensating
opening or closing movement of valve gate 55. As the float
70 moves upward beyond the desired level, valve gate 55 auto-
matically opens and vice versa so as to control and maintain
constant the water level in the drainage box 52 at the fabric
20 which passes over the box 52.
The covers 122 for the submerged drainage boxes 52 of
FIGS. 2-7 are shown in FIG. 11 and are generally disclosed in
the U.S,. Patent Application Serial No. 07/326,384 filed :larch
21, 1989 corresponding to Italian Patent Application No.
83354/A/88, filed P3arch 29, 1988 by Glauco Corbellini, and
the subject matter thereof is incorporated herein by ref-
erence. Basically, the submerged drainage box cover assembly
125 includes a lead blade 126 and trailing blade 127 which
are preferably ceramic and fixed to respective rigid parallel
bases 128 and 129 and assembled aver lateral beams 130. A
rigid box beaiti support or plate 131 joins the lateral beams
130 into a unitary assembly 125. The assembly 125 provides
a series of blade holders 132 whereby individual ceramic de
flector blades 53 can be installed. Each blade 53 fits into
a slot 133 and is glued together. The holder 132 is prefer
i
ably a laminated fiberglass unit constructed of multiple
layers of fiberglass cloth bonded with epoxy resin. The
suss-r~-ru-cE sHE~r
WO 91/01408 PCT/US90/04144
_15_ ~~~0~~~
bonding material 134 is preferably ceramic to metal and such
material attaches lead blade 126 and trailing blade 127 to
respective bases 128 and 129 and reinforced with screws. Box
support plates 131 are connected to lateral beams 130 via a
threaded key 135 located in keyway 136 and bolt 137. The
holders 132 are affixed in the stainless steel members 138 by
the key I24. As seen, the cover assembly 125 is supported on
frame 139 forming the side walls of the suction boxes 52.
The deflector mounting angle 140 preferably is between
35-60 degrees and this can be adjusted to ,obtain the desired
drainage conditions for each of the drainage boxes 52. The
contact nose surface 145 of each of blades 53 is normally
between about 2-3 mm wide and gives an open area of about
90%. The divergence angle 146 is designed to be adjustable -
from about 5-15 degrees, depending on drainage conditions
desired, even for the particular location of the drainage
boxes 52 in the wetter end of the Fourdrinier. The blade
holder slot thickness 141 can vary between about 3-4 mm and
the blade spacing 142 can vary according to blade thickness
143, which is maintained between 6-9 mm, the desired open
area and other physical dimensions of the assembly I25. The
nose surface 145 of the blades 53, over which the fabric
slides, includes an acute divergence angle 146, which has
heretobefore not been disclosed in the above mentioned patent
application nor the above open area or other preferred dimen-
sions for. the particLlar purposes of the herein disclosed
system, and these are important in subrierged drainage to min-
imize the contact with the fabric and to cause more water to
be drained from the.fabric as it is passing over the blades
53 offering an open area of at least about 90% with a de-
flector angle 140 of approximately 45°.
FIGS. 12-14 show an improved design for a drainage box
for the drier end of the Fourdrinier machine to be used in
place of the high vacuum flat suction boxes of the prior art,
and FIG. 1 shows a preferred arrangement for their use. As
mentioned above the lower part of FIG. 1 is somewhat similar
in many respects to the prior art Fourdrinier paper making
SUBSTITUTE SHEET,
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system, but without the improved submerged drainage boxes,
etc., set forth herein. FIG.. 1 has conbined an auxiliary
Fourdrinier system in the drier end of the drainage area,
which is somewhat generally known in the prior art, as shown
for example, by U.S. Patent No. 4,306,934, dated Deceriber 22,
1981 invented by Erkki 0. Seppanen. An upper Fourdrinier
fabric 21 has an outer surface 31 in contact with the upper
surface of, the web 44', which has now formed by the prior
dewatering operation acting on aqueous dispersion 44, so as
. to have fabric 20 below the web 44' and fabric 21 above the
web 44'. Both fabrics 20 and 21 are horizontal with the dis-
persion 44 and web 44' supported on lower fabric 20 and both
fabrics 20 and 21 are nade to run in the same direction 40
where they az'e closely parallel to each other. Since each
fabric 20 and 21 is separate and distinct and is an. endless
length, they must each be driven, guided, and tensioned by
separate sets of rollers. Upper fabric 21 is driven through
its course with its inner surface 30 in contact with drive
roller 23, return roller 22, tension roller 24, and guide
roller 25, and its outer surface 31 in contact with web 44'.
A similar set of rollers is needed far fabric 20 although only
drive couch roller 36, breast roller 120, and tension roller
f7 are shown in contact with inner surface 38, while outer
surface 39 is in contact with web 44'. In the wet end first
portion of the process, only one fabric, namely lower fabric
20, is needed while the fiber/aqueous dispersion 44 is passed
over a dewatering,forming box 41, a dewatering fiber locking
box 42, and a final drainage box 43, all being submerged
' drainage boxes in accord with the invention hereinabove set
forth. In the remainder of the web formation portion of the
process there are upper submerged drainage boxes 26, 27, 28
and 29 and lower submerged drainage boxes 32, 33, 34 and 35.
Upper fabric 21 is in contact With upper drainage boxes 26, 27,
28 and 29, while lower fabric 20 is in contact with lower
drainage boxes 32, 33, 34 and 35. Thus, a paper web is dis-
charged from between the Fourdrinier fabrics 20 and 21 in
which the sides of the paper are substantially identical.
SUBSTITUTE SHEIET
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SJ
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Both upper and lower submerged drainage boxes are made
of a plurality of drainage cells 121 as shown in FIGS. 12-14.
Each cell is constructed generally as shown in FIG. 13 having
a central vacuum chamber 50 maintained at subatmospheric
pressure, a nose 51 in sliding contact with the inside sur-
face (38 of fabric 20 or 30 of fabric 2I) with inclined
passageways 48 and 49 leading toward and away from nose 51.
Three such cells are shown in FIG. 12 extending laterally
across fabrics 20 and 21 in generally the same fashion as
blades S3 in FIGS. 2-7, and 11. One end of each vacuum
chamber SO is opened into an individual conduit like conduit
111 of FIG. 2 or into a manifold (not .shown) which is then
attached to a conduit, like conduit 111, where the air and
Water is separated by reason .of -water falling into the water
in standpipe 61 and being drained away into pond or vessel 63
while the air is blown away. through fan 59. The other end of
vacuum chamber 50 is closed so as to force all air and water
into conduit I11. As air and water is sucked through pas-
sageway 49 into chariber 50, air from the surrounding atmo-
sphere flows into passageway 48 to pass over nose 51 and
through the fabric 20 below or the fabric 21 above. So long.
as water is being sucked from the fabric 20 and 21 the men-
iscus of water of the surface; of the web 44' in contact with
each fabric 20 and 21 transfers the water therefrom to the
respective fabric 20 and 21, repeating the action until the
energy of meniscus in the fabric is unable to extract residual
water from the web. The vacuum that is needed for this oper-
ation is low and only about 3 inches of Hg. generally for most
fabric speeds, but this is sufficient to pernit drainage boxes
26, 27, 28 and 29 to even function upside down on upper fabric
21. This is in sharp contrast to the high vacuum of the prior
art which may be at about 5-12 inches of Hg. Also, an appro-
priate discharge from one end of .each of the boxes or cells
121 is provided to discharge the water therefrom in any well-
known manner such as illustrated in FIG. 2. The combination
of three rows of cells as shown in FIG. 12 includes a lead
deflector surface 4S, intermediate deflectors 46, and trailing
S~JBSTITUTE SHEET
WO 91/01408 PCf/US90/04144
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deflector surface 47, all being stationary surfaces over which
the moving fabric 20 or fabric 21 travels. Such suxfaces are
needed to support the fabric 20 and 21 in a smooth stable
manner. In one improved embodiment as shown in FIG. 10 a
pipe 105 carrying stea.~~ to spray downwardly out at 106 into
passageway 48 enhances the operation by heating the air
passing through passageway 48 and thereby heating the water
in web 44 causing its viscosity to be lowered and thereby
making it flow more rapidly through fabric 20 os 21. An in-
sulated reflector 108 is shown to protect against loss of the
heat before it is sprayed at 106. The entrance of air into
passageway 48 is permitted by opening 107 through reflector
108.
As shown-in.-FIG.--12, the upper drainage boxes or cells -
are horizontally offset from the lower drainage boxes so that
a vacuurl is not applied to each side of the paper web at the
same time at a particular location. If this were not so, it
is likely that air may occasionally pass through and damage
the paper web. Also, the spacing or tolerance between the
upper and lower fabrics might cause damage thereto on account
of entrained debris in the web and to inhibit such damage the
water is not withdrawn from the web simultaneously vertically
at any particular location spaced along the two fabrics.
While the invention has been described with respect to
certain~specific embodiments, it will be appreciated that many
modifications and changes may be made by those skilled in the
art without departing from the spirit of the invention. It is
intended, therefore, by the appended claims to cover all such
modifications and changes as fall within the true spirit and
scope of the invention.
SUSS i iTUTE SHEET
