U.S. patent number 3,876,498 [Application Number 05/397,400] was granted by the patent office on 1975-04-08 for controlled forming wire separation on impervious roll of twin-wire papermaking machine.
This patent grant is currently assigned to Beloit Corporation. Invention is credited to Edgar J. Justus.
United States Patent |
3,876,498 |
Justus |
April 8, 1975 |
Controlled forming wire separation on impervious roll of twin-wire
papermaking machine
Abstract
A method and mechanism for continuously forming a fibrous web
from a slurry of stock including first and second looped permeable
woven forming wires positioned to travel over a solid impermeable
roll and converge in a throat to travel through a forming run over
the roll. A headbox chamber has trailing self-positionable elements
therein and delivers stock to the forming throat. At the end of the
forming run, the outer wire is separated from the inner wire at a
separation point by a small angle .alpha. with the inner wire
continuing on the roll for a short distance beyond said separation
point. The outer wire will be cleaned at the separation point, and
the web will uniquely follow the inner wire despite centrifugal
force.
Inventors: |
Justus; Edgar J. (Beloit,
WI) |
Assignee: |
Beloit Corporation (Beloit,
WI)
|
Family
ID: |
23571042 |
Appl.
No.: |
05/397,400 |
Filed: |
September 14, 1973 |
Current U.S.
Class: |
162/199; 162/203;
162/301; 162/274; 162/343 |
Current CPC
Class: |
D21F
9/003 (20130101) |
Current International
Class: |
D21F
9/00 (20060101); D21f 001/00 () |
Field of
Search: |
;162/203,301,303,306,317,318,214,199,274,343 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Bashore; S. Leon
Assistant Examiner: Tushin; Richard H.
Attorney, Agent or Firm: Hill, Gross, Simpson, Van Santen,
Steadman, Chiara & Simpson
Claims
1. A mechanism for continuously forming a fibrous web from a slurry
of stock comprising in combination:
a first looped permeable woven outer forming wire;
a second looped permeable woven inner forming wire; said wires
positioned to form a converging throat leading to a forming run
wherein the wires press against a web being formed
therebetween;
a headbox having an opening positioned to direct a stream of stock
into said throat;
guide rolls within each of the wire loops holding the loops in
tension so that the outer wire applies a pressing force to press
the stock between the wires in said forming run;
a convexly curved surface within the second wire with the first and
second wires wrapping said surface along said forming run;
a first off running guide means for said first wire positioned
following the forming run and separating the first wire from the
second wire at a first separation point on said curved surface;
and a second off running guide means for said second wire following
said forming zone and separating the second wire from said surface
at a second separation point immediately following the first
separation point with the web following the second wire;
2. A mechanism for continuously forming a fibrous web from a slurry
of stock constructed in accordance with claim 1:
wherein said curved surface is the outer surface of a rotatable
imperforate
3. A mechanism for continuously forming a fibrous web from a slurry
of stock constructed in accordance with claim 1:
and including a saveall means positioned within the first wire
adjacent the forming zone receiving water expressed from the web in
the forming zone
4. A mechanism for continuously forming a fibrous web from a slurry
of stock constructed in accordance with claim 1:
wherein said second offrunning guide means is positioned so that
the angle between the wires at the second separation point is in
the range of
5. A mechanism for continuously forming a fibrous web from a slurry
of stock constructed in accordance with claim 1:
6. A mechanism for continuously forming a fibrous web from a slurry
of stock constructed in accordance with claim 1:
including within the head box immediately upstream of the opening a
tapered slice chamber with a plurality of flexible trailing members
anchored only at their upstream ends and being self-positionable
responsive to the
7. A mechanism for continuously forming a fibrous web from a slurry
of stock constructed in accordance with claim 1:
including a traveling pick-up felt and a pick-up roll within the
felt positioned to carry the felt in contact with the web on the
second wire
8. A mechanism for continuously forming a fibrous web from a slurry
of stock constructed in accordance with claim 1:
including means for adjusting the angle between the first and
second wire
9. A mechanism for continuously forming a fibrous web from a slurry
of stock comprising in combination:
a first looped permeable woven outer forming wire;
a second looped permeable woven inner forming wire with said wires
positioned to form a converging throat leading to a forming run
wherein a web formed between the wires is pressed and
dewatered;
a slice means having an opening positioned to direct a stream of
stock into said throat;
a roll having an imperforate outer surface over which the wire
loops are wrapped through said forming run;
first guide means for the outer wire bending the outer wire over
said roll throughout the forming run and lifting the outer wire off
of the roll,
and second guide means for the inner wire training the inner wire
on the roll for the forming run and lifting the inner wire off the
roll immediately after the outer wire is separated therefrom so
that the web
10. The method of continuously forming a fibrous web from a slurry
of stock which comprises:
passing a pair of looped perforate woven tensioned forming wires
through an arcuate forming run over an arcuate surface to apply a
force normal to a web being formed therebetween to dewater the
web;
delivering a stream of fibrous stock to the upstream end of said
forming run;
separating the outer wire from the inner wire at a first separation
point while traveling through said arcuate run and separating the
inner wire from said run at a second separation point immediately
after said first point;
and blocking the inner surface of the inner wire so that fluid is
prevented from flowing outwardly at said separation points so that
the web follows
11. The method of continuously forming a fibrous web from a slurry
of stock in accordance with the steps of claim 10:
maintaining the wires at an angle of separation between greater
than
12. The method of continuously forming a fibrous web from a slurry
of stock in accordance with the steps of claim 10:
wherein said blocking of the inner surface of the wire is performed
by
13. The method of continuously forming a fibrous web from a slurry
of stock in accordance with the steps of claim 10:
including the step of subsequently picking the web off of the inner
wire after it has traveled a distance on the inner wire of said
separation
14. The method of continuously forming a fibrous web from a slurry
of stock which comprises:
guiding a pair of looped perforate woven forming wires under
tension through an arcuate forming run over an imperforate rotating
roll to apply a force normal to the web being formed therebetween
to press water from the web into the space between the inner wire
and the roll within interstices of the wire and through the outer
wire so that water is thrown therefrom;
delivering a stream of fibrous stock slurry to the upstream end of
the forming run;
and separating the outer wire from the inner wire lifting it off of
the curved arcuate path on the roll while maintaining the inner
wire on the roll so that the web remains pasted thereto and
immediately thereafter lifting the inner wire off the roll so that
the separation of the wires from each other and the inner wire from
the roll generates an inward surge of air through the outer wire to
clean fibers from the outer wire left thereon from dewatering
through the outer wire.
Description
BACKGROUND OF THE INVENTION
The present invention relates to improvements in fibrous web
formation wherein an aqueous fiber suspension is dewatered on a
porous forming surface. More particularly, the invention relates to
improvements in web forming mechanisms of the type which have
become to be known to the art as twin wire formers wherein a slurry
of fibrous stock is delivered from a headbox slice opening to a
forming throat between a pair of looped traveling forming wires
with the web dewatered by being squeezed between the forming
wires.
In relatively recent developments the art of papermaking has
undergone a number of significant advances in the field of paper
web formation using two opposed forming wire runs for web formation
therebetween as contrasted to the heretofore more conventional
Fourdrinier type papermaking machine employing only a single
forming wire. Such twin wire forming machines have met with
commercial success offering advantages of requiring less space and
improved dewatering at high speeds. As the speed of the papermaking
machines are increased, it becomes increasingly difficult to handle
and control a high speed traveling fibrous web and to determine
with a certainty the continued position of the web and to insure
that it will continue to follow a forming wire without leaving the
forming wire surface or following an opposing wire. In the
manufacture of light weight paper webs, such as tissue, it is
increasingly difficult to insure that the paper is not damaged at
the point of wire separation due to splitting of the web at that
point and the problem is one of insuring that most of the fiber
follows one or the other of the two forming wires. These problems
are particularly presented in a twin wire forming machine wherein
the wires must be separated in order to pick off the web, and the
web must follow the exact wire which will carry it to a pickoff
device.
Efforts to solve this problem have resulted in teachings of the art
that a suction mechanism such as a suction box must be positioned
within the wire which the web is to follow to insure that it is
stapled or adhered to the wire just before or as the wires are
separating. Where the twin wires pass over a roll in an upwardly
extending forming run, the roll has been provided with a suction
box to staple the web to the inner wire. The necessity of providing
a suction gland and a hollow roll is undesirable in increasing
initial construction cost and increasing power consumption. Another
method which has been employed is to keep the wires together, but
to pass one of the wires over a suction box to insure transfer of
the web to that wire. An important disadvantage associated with
structures of the type described above is that on light weight
sanitary grades, such as tissue, the suction box surface damages
the sheet even though such suction box is designed with great care.
Also, the requirement for the provision of suction boxes or suction
rolls requires additional cost and space for pumps and other
ancillary parts that wear and require maintenance.
An example of teachings of the prior art is shown in U.S. Pat. No.
3,056,719, Webster, wherein the patentee solves the problems of the
operation by either employing only a single forming wire with an
additional open roll and a suction gland at the end of the forming
run to transfer the web to the wire, or, where two wires are used,
providing an additional open roll with a suction box therein to
assure adherence of the web to one of the wires.
Another teaching of the art is exemplified in U.S. Pat. No.
3,400,045, Graham, wherein the patentee requires that one of the
flexible belts between which the web is sandwiched when it is
formed be a felt, utilizing the commonly accepted teaching of the
art that when two belts separate, the web will follow the belt of
greater density, i.e., the felt.
A feature of the invention is applicant's discovery of a
combination of elements so constructed and so arranged that it is
possible to combine the advantages of a twin wire former with the
economics of a plain roll, and the use of two woven mesh wires
permitting operation at maximum speed so that the unit is capable
of operation at speeds approaching 7,000 feet per minute which is
unusually high in the operation of present-day machines. High
speeds are accomplishable by utilizing woven wires for both the
formation members along the forming run and passing them over a
plain solid cylindrical roll which has an absence of suction glands
and where the wires do not have to run over suction boxes. Contrary
to previous teachings, applicant has discovered that by separation
of the outer wire from the inner wire by a small angle .alpha.
while the inside wire is still supported on the plain roll, the web
will unerringly follow the inner wire regardless of centrifugal
force and contrary to expectation if one follows the teachings of
the prior art and as would be expected from observing the obviously
high centrifugal forces. The phenomena of physical forces will
position the web on the outer surface of the inner wire without it
being stapled thereto for each pickoff and the mechanism discovered
causes a cleaning of the outer wire removing fibers entrained or
intermeshed with the outer wire due to the dewatering being
effected through the outer wire during the forming run. At the end
of the forming run, the outer wire is first led away from the inner
wire at a very small angle, and the physical force of the vacuum
created as the upper wire is separated from the solid roll, at
speed, will cause a flow of air through the outer wire sweeping any
water remaining in the outer wire inwardly to help clean the outer
wire of fiber and water. The web is held to the inner wire by the
dynamically created differential pressure across the web, created
by the separation, at speed, of the outer wire from the roll while
the inner wire is still wrapped on the roll. This separation, at
speed, tends to create a void or vacuum between the two wires which
can only be filled from outside the outer wire and cannot be filled
from inside the inner wire because of the solid impervious surface
of the roll. It is the filling of this void from the outside which
creates the differential pressure which flushes the web and water
from the outside surface of the inside wire. The vacuum or suction
formed beneath the inner wire causes an inward flow of air and
water through the outer wire so as to clean the outer wire and to
help hold the web onto the inner wire. The surface tension of the
water filling the interstices of the inner wire also causes the web
to adhere to the inner wire, and in effect, the web is pasted onto
the inner wire with a force which will completely overcome the
centrifugal force on the web which tends to cause the web to lift
off the inner wire. Using a woven inner wire and by pressing the
web between the wires during the dewatering forming run, the
removal of water will be substantially all through the outer wire.
However, a small amount of water will travel inwardly to be held in
the interstices of the inner wire to perform the sealing function
which aids the phenomena of vacuum and surface tension thus
insuring that the web will follow the inner wire. Since dewatering
has occurred through the outer wire, the web will not be stapled to
the inner wire, but will be resting lightly thereon so that it can
readily be picked off the inner wire at the pickoff point and
reducing the possibility of damage or splitting of the web.
An object of the present invention is to provide an improved and
more economical twin wire forming mechanism and method using two
woven wires with positive web control and the capability of having
the web follow the inner wire without requiring suction boxes or
suction rolls within the wire to effect the transfer of the
web.
A further object of the invention is to provide an improved twin
wire forming mechanism which is particularly well adapted to
forming tissue or toweling and which utilizes simple high speed
imperforate solid rolls for support of the twin wires.
A still further object of the invention is to provide a unique
method and mechanism for the positive control of the web traveling
in an arcuate path between a pair of forming wires insuring that
the web follows the inner forming wire.
A further object is to provide a high speed paper forming system
utilizing the dynamics of the woven forming wires and supports and
without the use of externally powered vacuum devices such as
suction rolls or suction boxes.
A further object of the invention is to provide a twin wire forming
mechanism wherein the wires travel over a curved surface to dewater
a web therebetween and dewatering is effected entirely through the
outer wire and the outer wire is cleaned of fibers as the wires are
separated and the web follows the inner wire.
The method and mechanism fine particular advantages in the
formation of a paper web from cellulose fibers, but it will be
understood that the features may be used to advantage in forming a
web from other types of fibers. Also, the mechanism as disclosed is
best suited for the handling of a slurry formed of an aqueous
suspension but other forms of fluids may be employed.
Other objects, advantages and features, as well as equivalent
structures and methods which are intended to be covered hereby will
become more apparent with the disclosure of the preferred
embodiment in the specification, claims and drawings in which:
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevational view shown in somewhat schematic form
of a machanism constructed and operating in accordance with the
principles of the present invention;
FIG. 2 is an enlarged fragmentary schematic view of a portion of
the mechanism of FIG. 1 shown for the purposes of illustrating
certain principles as will become clear from the description;
and
FIG. 3 is another enlarged fragmentary schematic view illustrating
an alternate form of operation of a mechanism embodying the
principles of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As shown in FIG. 1, the mechanism includes first and second looped
woven permeable forming wires 10 and 12. The wires are trained over
rolls so as to approach each other and form a tapered throat 13
into which a jet of stock is delivered, followed by an arcuate
forming zone 14. For defining the arc of the forming zone, the
wires are wrapped over the arcuate outer surface of a plain
cylindrical roll 15. The roll has a smooth outer imperforate
supporting surface for the wires, and the wires are tensioned so
that they apply squeezing force normal to the web being formed
therebetween to force the water out through the first or outer wire
10. It is important that the second or inner wire 14 be a pervious
woven wire so as to provide a web backing or support, which can
receive but does not absorb or retain excess water and which does
not require elaborate dewatering mechanisms itself for removal of
its water, such as would be required for a felts.
It is also important to provide a wire for the inner support for
the web so that its interstices hold water for sealing the
underside of the web and pasting it onto the wire at the separation
point with the wire providing a substantially noncompressible and
nonexpansible web support.
Further, the wires 12 and 10 being substantially similar in
openness or weave are particularly well adapted for the formation
required for a given web such as tissue and toweling. The solid
imperforate roll 15 is particularly well adapted to very high speed
operation and eliminates the need for suction glands or suction
means and eliminates necessity of rubbing surfaces. The mechanism
as is shown which eliminates the need for the wire passing over
suction boxes and eliminates the need for suction glands is capable
of operating at uniquely high speeds on the order of up to 7,000
ft. per minute with satisfactory long wire life.
The elimination of suction glands and the elimination of the
necessity for a hollow roll shell is significant in the ability of
the mechanism to achieve unusually high operating speeds. The noise
factor would create substantial problems at high speeds if a
perforate suction roll were used and problems would vary likely
exist providing sealing surfaces that could operate for any length
of time at these high speeds. The problems of inertia and pressure
waves exist when high speeds are encountered in that the periods of
time to which the web or wire is subjected to pressure becomes
unusually small. Also, as will be immediately recognized by those
versed in the art, the initial cost of a plain roll is considerably
lower and the driving power needed for operation is lower. Wire
abrasion and wear are reduced and the pressure between wires and
roll surface do not create the problems that are present when a
perforate roll is used.
The first looped outer wire 10 is supported on rolls located within
the wire shown at 16, 17, 18, 19, 20, 21 and 22. At least one of
the rolls, such as the roll 18 is capable of being moved to an
adjusted position to place a predetermined linear tension in the
wire to apply the desired squeezing force to the web in the forming
zone 14.
The second looped inner forming wire 12 is supported on rolls 23,
24 and 25. The wires are both woven and preferably of the same size
mesh.
As the water is squeezed from the web W which is being formed along
the forming zone 14, the water is thrown outwardly from the surface
of the outer wire 10 to be caught by a saveall 33. An additional
saveall 33a is located when the outer wire is separated from the
inner wire.
For delivering stock to the throat 13, a headbox 26 is provided.
Stock is delivered to the headbox under pressure to flow through
the tapered slice chamber 26a of the headbox formed between the
converging slice walls 27 and 28. Slice wall 28 is preferably
pivotally adjustable so as to controllably regulate the size of the
slice opening 29 from which issues a stock jet 30. The movable wall
of the headbox is pivoted at 28a, and a power means shown
schematically at 28b controls the pivotal position of the wall and
hence the size of the slice opening 29. The headbox 26 is supported
on a pivot 26a and power means shown schematically at 26b and is
attached to the headbox to establish its pivotal position. The
pivotal position is chosen so that the stock jet 30 will
substantially bisect the throat 13, but adjustments can be made so
that the jet 30 passes into the throat more or less tangential to
either the inner wire 12 or the outer wire 10.
A preferred form of headbox construction particularly well adapted
to the formation of the web between wires, wherein the deflecting
support for the wires is a solid roll, includes a plurality of
trailing elements 31 positioned in the tapered slice chamber 30. A
fine scale turbulence is generated maintaining uniform fiber
dispersion for dewatering through the outer wire. These trailing
elements are anchored only at their upstream ends at a perforate
wall 32 in the headbox and are positionable responsive solely to
forces of the stock flowing through the slice chamber. The trailing
elements 31 may be in the form on individual flexible strands of
material such as plastic, or may be in the form of continuous or
interrupted sheets extending across the headbox. These trailing
elements divide the stock flow into a plurality of independent
flows having small scale turbulence for intermixing and
distribution of the fibers which form the web in the forming
run.
The web W is formed in the forming zone 14. As the wires are
separated from the roll 15 and are separated from each other
despite the fact that the outer wire is lifted first from the roll,
the web follows the inner second wire 12. The outer wire 10 is
separated from the inner wire 12 at a separation point 34, shown in
FIGS. 1 and 2.
The web W follows the wire 12 and is picked off the upper surface
of the wire by pickoff felt 36 brought into close adjacency with
the web by pickoff felt roll 37. The web because it is dewatered
through the outer wire, is not stapled to the inner wire but is
easily removable.
The solid arcuate support for the wires in the forming zone is
provided preferably by a cylindrical smooth surface roll 15, but
because of high attainable speeds and lack of wire to roll
friction, it will be understood that other forms of supports may be
used such as a curved shoe. It is important in the mechanism and
method of the structure that the support be imperforate at the
first separation point 34 where the outer wire 10 is separated from
the inner wire 12 and at the second separation point 35 where the
inner wire is separated from the roll.
By providing an imperforate smooth support for the inner wire at
the first and second separation points 34 and 35, the web is
effectively sealed to the inner wire. It is also essential that the
voids of the inner wire be filled with water so that the web will
be sealed or pasted onto the inner wire. This is a result of the
roll being imperforate and the web being squeezed during the
forming run so that water which flows inwardly from the web fills
the interstices of the inner wire. This will occur fairly easily in
the forming zone and the rest of the water squeezed out of the web
will be forced outwardly through the outer wire. Also, since the
inner wire is filled with water, fibers will not be forced inwardly
to staple themselves to the inner wire. Instead the web will be
pasted to the inner wire and when the inner wire is lifted off the
roll and the seal which holds the web to the inner wire is broken,
the web can easily be lifted off the inner wire. When the inner
wire reaches the separation points 34 and 35, the surface tension
of the water within the inner wire and the sealing effect of the
solid roll pastes or holds the web to the inner wire. At the second
separation point 35 when the inner wire is lifted off the roll, a
vacuum tends to form beneath the inner wire drawing the web down
against the inner wire and tending to draw the water out from the
inner wire. This vacuum plus the surface tension between the water
and the roll surface, will tend to cause the water in the
interstices of the inner wire to follow the surface of the roll 15
when this water is thrown off the roll, it is caught by a saveall
15a. A separating doctor may be provided, not shown, to help the
water separate from the outer surface of the roll 15 to pass into
the saveall 15a.
Preferably, the outer wire 10 is separated on a very small distance
from the inner wire 15 forming an acute angle .alpha. therebetween,
as shown in FIG. 2. The angle .alpha. should be kept as small as
possible so that the distance D is small.
The dewatering run along the surface of the roll is of a length so
that the web will be dewatered therealong and by the time the web
reaches the top of the roll 15, no substantial remaining amount of
water is being squeezed therefrom. The amount of water squeezed
from the web during the dwatering run is a function of the size of
the roll as shown by the radius R of the roll 15 in FIG. 2, and the
linear tension of the outer wire 10.
As illustrated in FIG. 1, the supporting roll 16 for the outer wire
10 is adjustable in location so as to be able to selectively
control the angle .alpha. between the outer and inner wires 10 and
12. As illustrated somewhat schematically, the roll 16 is supported
on a pivotal arm 16a pivotally supported at 16b and controllable in
its position by a power means shown schematically at 16c. This
permits moving the roll 16 through a range of positions to select
an angle shown at .alpha. in FIG. 2 and at .alpha. ' in FIG. 3. A
saveall 33a is positioned above the wire separation points 34 and
35.
The angle .alpha. is preferably chosen to be at a minimum size such
as in the range of greater than 0.degree. and preferably not
greater than 5.degree.. With this arrangement, the vacuum formed at
location 40, FIG. 2, and the surface tension between the water and
roll surface will tend to draw the water from the inner wire 12 and
paste the web W onto the wire so that centrifugal force will not
lift it. The separation of the web from the outer wire will cause
an inrush of air down through the outer wire 10 cleaning the wire.
Because during forming dewatering has occurred only through the
outer wire 10, the wire has tended to become dirty because the
fibers adhering to the wire. The inward flow of air and remaining
adhering particles of water through the outer wire 10 cleans the
wire. This cleaning is augmented by the inward surge of air tending
to push forwardly any water present to cause a surge at location 41
to wash and help clean the upper wire removing the fibers stapled
to the strands thereof. This surge of air through the outer wire is
due to a large part to the inner wire being lifted off the roll
with the inward pull on the web at that point. The operation shown
in FIG. 3 lends support for this theory of outer wire cleaning
because when the mechanism is operated in accordance with the
relationship shown in FIG. 3 where the angle .alpha. is large, the
outer wire 10 is not as well cleaned.
In the operation of FIG. 3, the inner wire 12 is lifted off the
roll a substantially greater distance D' after the point of first
separation A'. Thus, the vacuum formed at point 40' does not
augment or act substantially simultaneously with, the vacuum formed
at location 41' so as to cause the inrush of air. It has been
discovered, however, that some advantages of the invention are
still obtainable with the operation of the arrangement of FIG. 3.
That is, the web will still be pasted to the inner wire 12. As the
outer wire 10 is lifted off of the roll, the web remains adhered to
the inner wire due to the surface tension of the water in the
interstices of the wire and due to the vacuum caused as the web
tends to lift. As the wire 12 is lifted off of the roll from
centrifugal force, the surface tension of the water causes the
water in the wire to follow the roll. Because dewatering was
substantially completely through the outer wire 10, the web is not
stapled to the inner wire 12 and rides lightly thereon making it
relatively easy for a pickoff felt to pick the web off the
wire.
Thus, in operation a stock from the headbox 26 is directed in a jet
30 into the throat 13 between the forming wires 10 and 12. Along
the forming run 14, the web is dewatered through the outer wire 10
into the saveall 33. At the end of the forming run, the outer wire
10 is first lifted off the roll and the inner wire 12 is almost
immediately thereafter lifted off the roll 15, and the physical
effects of surface tension and vacuum create the phenomena of
overcoming the centrifugal force on the web and cause it to adhere
to the inner woven wire with a concurrent cleaning of the outer
wire. The web resting on the inner wire is readily picked off the
wire by a pickup felt.
* * * * *