Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to a process and apparatus
for improving the formation of a paper web on a paper making
machine.
In the operation of a typical paper making rnachine,
the pulp stock which is a thin suspension of fibers and
fillers, containing generally ahout 99.5% water, is flowed
from a headbox slice onto the upstream surface of a rnoving
endless screen belt (forming fabric) which is made of woven
¦ metal or plastic filaments. The fabric passes over a breast
¦ 10 roll at one end of the forrning section of the machine and a
¦ couch roll at the other end and between these two rolls the
fabric travels in contact with spaced apart transverse
dewatering foils and then over suction boxes where water is
withdrawn from the pulp stock leaving a thin, self-support-
ing formation of matted fibers on the surface of the fabric.
This sheet of formed fibers is lifted off the fabric at the
couch roll at the downstream end of the forming section and
is transferred to a press section and then to a dryer section
to complete the dewatering. After travelling around the
couch roll, the fabric belt is returned through a series of
return rolls to the upstream end of the forming section
where it travels around the breast roll and again passes
under the slice to complete the cycle.
In spite of attempts ~o thoroughly mix the pulp
stock in the headbox of the paper machine so that the fibers
thereof will be uniformly dispersed, the fibers tend to
agglomerate as they emerge from the slice and deposit on the
fabric in clumps or flocs. If these flocs remai.n undis-
persed -the finished paper will no-t be of uniform density.
Also, there is a tendency for stock fibers to become
aligned in the machine direction which is de-trimental to
S cross machine s-trength of the paper.
Severa] methods have been proposed and used to
redistribute fibers in the pulp stock after it has been
transferred to the forming wi:re and during the early stages
of dewatering. A common method that has been used for many
years to reduce flocculation is to provide a rapid shaking
motion to the upstrearn end of the forming section of the
machine. In other methods air and/or water -jets are sprayed
on the wet stock either from above or below to rewet and
agitate the stock and so redistribute the fibers. These
methods have not proven entirely satisfactory particularly
in the case of large, high speed machines where machinery
required to shake the forming section is expensive and
power consuming or when jets of air and/or water tend to
force excessive amounts of the fibers and solids through
the forming fabric and increases the amount of water which
ultimately has to be withdrawn from the stock therefore
requiring additional dewatering equipment which is usually
power consuming.
It is known that flocculation occurs almost
continuously in the formation zone while the pulp fibers
are still in suspension and that deflocculation of the
fibers is most effectively accomplished on slow running
machines in which the wet pulp stock is subjected to almost
continuous cross-machine shear by a shake mechanism during
the forming cycle. On large machines running at high speed
it is impossible -to attain adequate continuous cros.s-machine
sheax due -to rapid passage of the wet pulp through the
forming zone and -to di.ffi.culty in overcoming -the inertia
of the large mass of machinery to provide sufficiently
rapid cross-machine oscillation.
I It has been observed also that when ridges and
¦ gullies form in the sheet of stock discharged from the
I slice and produce thick and thin sections alternately in
the cross-machine direction, the ridges tend to dissipate
when the stock lands on the forming fabric and, as they do,
create a flow of stock in the cross-machine direction which
, produces shear action within the layer of stock at the
' dissipating ridge also in this direction. This condition
¦ is most apparent in cases where intermittent ridges are
produced by the action of a rectifier roll in the headbox
immediately preceding the slice.
Further, and possibly due to the greater energy
contained in the ridges, a wave action is promoted and
there occurs an interchange where a ridge becomes a gully
and vice versa as the wet pulp moves down the forming table
of the machine. This interchange of phase is enhanced as
the stock on the fabric passes over a dewatering element
such as a table roll or a foil blade where the stock is
subjected to the vacuum created thereon and even a more
vigorous shearing action is promoted within the layer of
stock. While this action is almost instantaneous in a high
speed machine it does tend to counteract the continual
flocculation of pulp fibers with the result that in the
vicinity where variations in stock thickness have occurred,
and particularly where there has been a longitudinal
%
(machine direction) change oE phase as described above,
agglomeration of pulp fibers i5 reduced and the formation
oE the paper becomes more uniform.
Ano-ther known method of redistributing fibers
in the pulp stock attempts to utilize the shearing action
promoted by ridges by providing a serrated slice lip to
induce a regular flow of ridges in -the headbox discharge.
This measure has not been entire:Ly effective because the
ridges tend to dissipate too soon.
It is a feature of this invention to utilize
the above mentioned phenomenon and induce controlled varia-
tions in -thickness in the wet sheet of pulp stock on the
forming fabric throughout the forming zone of a paper
making machine to create cross-machine shear in the wet
, 15 sheet for the purpose of deflocculating agglomerated fibers
'i of stock.
According to one aspect of the invention there
is provided one or a plurality of dewatering foil blades
that are specifically designed to provide cross-machine
variations in dewatering of the pulp stock to promote like
variations in the thickness of the sheet of wet pulp stock
on the forming fabric.
The blade of the invention is generally similar
to those normally installed in a fixed position to extend
crosswise under and in contact with the forming fabric in
the dewatering zone. The blade has a leading edge, a flat
fabric supporting surface and a foiling surface set at a
small divergent angle from the supporting surface. The
foiling surface of the blade of the invention, however, is
provided with repeti-t:ive machine direction non-foiling
portions at intervals cross-wise of the machine direction
so that uniform drainage induced by the foiling angle is
interrupted and sections of wet pulp on the fabric
passing over a non-foiling portion will not be dewatered
~o the same extent as sections passing over a foiling
portion. The resulting interrupted drainage produces
thick and thin sections in the wet pulp in the cross-
machine direction and promote.s cross-direction shear ko
beneficially influence fiber distribution. The foiling
and non-foiling surfaces are formed integral in the
downstream portion of the blade.
The foiling surface of a foil blade is defined
as a surface diverging from the forming fabric by an
angle of less than approximately 5 degrees.
The blade of the invention may be constructed
of any suitable material that is chemically inert and
which provides a wear resistant, low friction surface.
A preferred materi.al is high density polyethylene which
is easily machinable. The preferred way of mounting the
blade is generally referred to as a T-bar attachment and
is described in detail in U.S. Patent No. 3,337,394.
Standard drainage foils may be replaced by
blades of the invention at any location in the forming
section to improve deflocculation thus providing an
efficient, inexpensive and flexible method of improving
formation on the paper making machine.
According to another broad aspect of the
present invention, there is provided a fabric supporting
blade for use in a wet section of a paper making machine
., and being positionable in suppor-ting relationship to a
forming fabric in the wet end of the paper making machine.
- 6 -
The blade extends across the machine transversely of
fabric travel and comprises a body having an upstream
side and a downstream side. A leading edge is provided
at the upstream side. A transverse continuous flat
fabric contacting and supporting surface of constant
width extends downstream from the leading edge. A
discontinuous foiling surface ex-tends downstream from
the continuous flat surface~ The foiling surface in-
cludes a plurality of foiling portions lying in a common
plane which slopes downwardly and rearwardly from the
plane of the continuous flat surface in divergi.ng re-
lationO The foiling portions are separated from each
other by intermediate slots extending parallel to one
another and defining non-foiling portions and providing
intermittent dewatering in a cross-machine direction
to induce longitudinal ridges and gullies in a layer of
wet stock as it is being dewatered for the purpose of
causing lateral shear in the stock to effect a more
thorough interlacing of the stock fibers to thereby
improve formation.
According to another broad aspect of the pre-
sent invention, there is provided a method of forming
a web of paper on a forming fabric of a paper making
machine. The method comprises positioning at least one
fabric supporting blade under and in contact.with the
forming fabric in a wet section thereof. The blade has
a leading edge, a transverse flat fabric supporting sur-
face of constant width, a downstream surface, and in
the downstream surface, a plurality of uniform foiling
surfaces interspersed by non-foiling surface in the
cross-machine direction. The foiling surfaces e~tend
from and converge with the downstream edge of the trans-
.~ -- 7
verse flat Eabric su~porting surEace and diverge there-
from at an angle less than 5 degrees. The foiling and
non-foiling surfaces are formed integral in the down-
stream surface oE the blade by slots extending parallel
to one another transversely of the blade and extending
from the contact and supporting surface and angulated
downwardly to the downstream side of the blade relative
to the foiling surfaces. The method also comprises
depositing a layer of wet paper stock on the forming
fabric upstream of the blade. The method further com-
prises inducing, in the layer of wet stock, longitudinal
alternate ridges and gullies as the pulp on the fabric
is conveyed over the blade for causing lateral shear
in the wet stock to effect a more thorough interlacing
of fibers in the wet stock to thereby improve formation.
The invention will be better understood by the
following description and the accompanying drawings which
illustrate preferred embodiments and in which:
FIGUR~ 1 is a perspective view, illustrating
schematically the forming section of a conventional paper
making machine equipped with foil blades, some of which
are modified according to the invention'
FIGURE 2 shows end and side elevations of a
portion of a foil blade modified according to one embo-
diment of the invention,
FIGURE 3 shows end and side elevations of a
foil blade portion modified according to another embodi-
ment of the invention' and
figure ~ shows encl and side elevations of a
foil blade por-tion modified according to yet another
embodiment of the invention.
Referring to Figure 1, 10 is the side rail of
the machine, 11 is the breast roll over which the forming
fabric 12 passes, 13 is the headbox and 14 is the slice.
Numeral 15 designates a forming board and 16, 17 and 18
are detachable foil blades of the invention which ex-tend
the width of the machine. Numerals 19 and 20 are
conventional detachable Eoil blades shown here as they
might be placed in a secondary dewatering stage. Nurneral
~ 21 denotes a conventional T-shaped rail upon which the
; individual blades may be mounted. At 22 is shown,
generally, the layer of wet pulp stock on the fabric and
ridges in the stock produced by the foil blades of the
invention are shown as strokes running in the direction
of the fabric which is shown by arrow 23. An attempt has
been made to indicate phase changes in the ridges as they
decay and reappear as gullies with adjacent new ridges on
either side. A phase change is most likely to be seen at
or just after a blade where a slight vacuum is produced
which promotes the interchange as explained previously.
For example, as the stock 22 issues from the slice, small
ridges are usually formed which soon dissipate. As the
wet pulp passes over blade 16 which is slotted according
to the invention, variations in dewatering are promoted
and, as a result, ridges and gullies form in the stoc~.
The location of ridges will generally correspond to the
location of non-foiling portions in the blade~ As the
._ g _
, . ~ . .. .
ridged pulp approaches the next b]ade in line, numeral
17, the interchange of r.idges and gullies (phase change)
has commenced and is accelerated by the dewatering
action as it passes over -this blade. Blade 17 may be
a conventional blade or, as is shown in the drawing,
another blade of the i.nvention, in which case, it would
be preferable to offset the foiling portions in the
cross-machine direction from those of the preceding
blade to enhance -the above mentioned phase changeO
Other blades at locations 18, 19 and 20 may be blades
of the invention or they may be conventional foil blades.
The preferred T-rail method of attachment
all.ows considerable flexibility to be exercised in the
deployment of blades to achieve optimum dewatering effi-
ciency and fiber formation for any given stock and
operating condition.
~ Referring to Figure 2, nurneral 20 is a blade of
i the invention which has an upstream side 23, a leading
edge 21, a flat fabric supporting surface 22 and, commenc-
ing at the downstream edge 25 of the fabric supporting
surface, a plurality of uniform foiling surfaces 26
interspersed in the cxoss-machine direction with a
plurality of uniform non-foiling surfaces 27. The foiling
surfaces 26 diverge downward from the downstream edge of
the fabric supporting surface at an angle not exceeding
5 degrees to meet the downstream side of the blade body
24. The noll-foiling portions 27 in this embodiment are
slots which have been cut at even spacing in the cross-
machine direction in such a way that their bottom surfaces
28 diverge downwardly from the downstream edge of the
- 10 --
Eabric support:ing surface a-t an angle exceeding the
divergent angle of the foiling surfaces. The non-foiling
slots open into the downstream side 24 of the blade.
Numeral 29 is a T-shaped recess in the bottom of the
blade having opposed flanges for slidable attachment to
a T-bar mounted on the frame of the machine. Numeral
30 is a section of the forming fabrlc which runs in
contact with the support surface 22 in the direction of
arrow 31. ~umeral 32 depicts the layer of wet pulp on
the fabric and 33 a ridge forming in the pulp over a
non-foiling slot in the blade.
Preferably, but not exclusively, the cross-
machine width of the land areas of the foiling surfaces
26 may range from l/8 of an inch to 2 inches and the
cross-machine width of the slots may range from l/8 of an
inch to 3/4 of an inch. The overall width of the blade,
in the machine direction, will be the same as any conven-
tional foil blade and the blade will extend in the cross-
machine direction a few inches beyond each edge of the
forming fabric.
In Figure 3 the flat fabric supporting surface
42 extends to the downstream side of the blade and a
plurality of identical foiling slots 47 is cut in the
fabric supporting surEace, each slot having a flat sloping
bottom 48 which diverges from the supporting surface at
a common alignment shown at 49 which is parallel to and
some distance downstream of the leading edge. The
extensions of the fabric supporting surface provide
intermitten1: non-foiling portions. The slope of the
bottoms 48 of the foiling slots will be less than 5 degrees
in order to produce the oi1ing action required -to induce
intermittent dewatering in the cross-machine direction.
Preferably, but not exclusively, the cross-machine width
of the land areas of the non-foiling portions may range
from 1/~ of an inch to 2 inches and the cross-machine
width of the foiling slo-ts may range from 1/8 of an inch
to 3/4 of an inch.
In Figure 4 the downstream portion oE the
fabric supporting surface 52 of blade 50 is slotted with
a plurality of identical flat, slanting foiling sur~aces
57 which slope in the cross-machine direction and extend
from a short distance downstream from the leading edge
51 to the downstream side 54 where the slots present a
' saw tooth appearance. The slanting slots provide for
intermittent dewatering in uniformly varying degrees in
the cross-machine direction. In this particular embodi-
ment of the invention the maximum slope in the machine
direction of each of the slanted slots would be less
than 5 degrees and preferably, but not exclusively, the
width of the slots in the cross-machine direction at the
downstream side of the blade could range from about 1/2
of an inch to 2 inches.
In the preferred concept of this embodiment
alternate blades may have slots which slope in the
opposite direction.
It is not intended to limit the invention to
foiling slots having rectangularly or triangularly
oriented flat surfaces. The slots in the downstream
surface of the foil of the invention may have curved
surfaces to provide for varying degrees of dewatering
crosswise of each slot.
- 12
In order to minimize uneven wear at the
downstream portion of -the transverse fabric supporting
surface which is continuous, it is recommended that the
foil blades of the invention be provided with wear
resistant inserts as described in detail in U.S. patent
; No. 3,446,702.
It is within the ambit of the presen-t invention
to cover any obvious modifications of the examples of the
preferred embodirnent described herein, provided .such
modifications fall within the scope of -the appended clairns.
As a typical example of modifications, it is conceivable
that the cross-section of the slots may take other confi-
gurations than those shown in the drawings. For example,
the foiling or non-foiling slots may be of triangular
cross-section, semi-circular cross-section, or any o-ther
suitable shape and they may be angled with respect to the
machine direction. Also, these blades rnay be intermixed
with conventional foil b]ades, throughout the wet section
and the slot configuration of these blades may also vary
one from the other.
