Note: Descriptions are shown in the official language in which they were submitted.
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PATENT APPLICATION
MULTI-PLY WEB FORMER
FIELD OF THE INVENTION
This invention relates to papermaking machines. More particularly, this
invention relates to papermaking machines for the manufacture of multi-ply
linerboard.
BACKGROUND OF THE INVENTION
Achieving an effective bond between the plies on multi-ply board formers
has commonly presented a problem. One known method employs multi-web
forming stock jets directed through a slice from a single headbox into a formingzone between two converging forming surfaces in a papermaking machine. In
this process, a multi-ply board is co-formed and limited intermixing between thelayers forms a good bond between the layers. However, as the board thickness
increases, dewatering and excessive mixing between the layers can be a
problem.
In other linerboard machines heretofore available, mini-fourdriniers and
other twin-wire top formers form the top ply first and then bond it to the base
sheet with a starch shower which bonds or glues the plies together. The use of
costly starch showers and their inherent adverse effects on cleanliness,
runnability and operating costs presents a less than ideal solution.
Another approach to forming a multi-ply web on a Fourdrinier machine is
the use of secondary or tertiary headboxes which deposit successive layers onto
the forming wire as shown in U.S. Patent No. 5,064,502.
Multicylinder board machines use wire-covered cylinders in cylinder
forming vats. A single bottom felt picks up multiple layers of paper from the wire
cylinders making up the multicylinder board machine.
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A Kobayashi Ultra Former utilizes headboxes which form fiber mats on
wire cylinders which are then deposited as paper layers on top of a single felt.
One type of multi-ply former utilizes a blade former which injects paper
forming stock between two wires. A web is formed between an upper wire and
a lower wire and is dewatered in the forming zone by applying vacuum solely
beneath the lower wire. Water is removed from the upper wire solely by wire
tension, gravity and centrifugal force by passing the co-running forming wires
over a convex upwardly curved path of travel. This permits a greater
concentrate of pulp stock fines to remain in the upper surface of the web formedbetween the co-running wires. The greater concentration of pulp stock fines
facilitates the bonding of the web to a base ply when the web and the base ply
are brought together. This type of former is shown in U.S. patent No. 5,468,348
to Blackledge et al. which is incorporated herein by reference.
Blackledge et al. disclose an exemplary former capable of forming and
bonding a layer of high grade fibers to a base layer of lower grade fibers.
However, additional ways of accomplishing the same function would
advantageously provide needed flexibility in the design of a former for a
particular application.
SUMMARY OF THE INVENTION
The method and apparatus of this invention forms a multi-ply linerboard
from a top ply or outer ply (sometimes referred to as "white top liner" generally
formed of a higher grade of fiber) and a base ply web. The base ply is generallyformed from one or more plies of lower grade fibers, typically recycled fiber. Atwin wire former has a lower wire extending between an open mesh forming roll
and a turning roll which engages a base forming wire. An upper wire joins the
lower wire over the forming roll and the upper and lower wires follow a curved
generally downwardly extending path. The top ply is formed between the upper
and the lower wires. A headbox supplies a stream of stock onto the lower wire
as the lower wire wraps around the open mesh forming roll. As the lower wire
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approaches the apex of the forming roll it is joined by the top wire which is
supported by a lead in roll. The upper and lower wires pass over the forming roll
apex and pass beneath a first auto-slice which removes water from the top of
the upper wire. Water is caused to flow upwardly through the upper wire by
centrifugal force and wire tension. The upper wire has a surface interior to theloop formed by the upper wire which extends along a forming zone between the
upper and lower wires as they follow a joint path.
The upper wire interior surface is convex upwardly so that the upper wire
generates centrifugal forces as it moves along the joint path of the upper and
lower wires. Two additional auto-slices are positioned along the interior surface
of the upper wire to receive and remove water expressed from the web by wire
tension and centrifugal forces. The web is dewatered through the lower wire by
blades forming a curved blade shoe. The blade through hydrodynamic forces
creates regions of low pressure which draw water from the forming web. The
curved shoe may be augmented with vacuum. Following the shoe two vacuum
boxes are positioned below the lower wire which define the path of lower wire.
The second vacuum box extends beneath the line where the upper wire is led
away from the lower wire. Thus the second vacuum box keeps the web on the
lower wire.
The upper side of the web is dewatered solely by wire tension and
centrifugal forces which prevents fines and filler materials from being removed in
the dewatering process. Thus the web formed by the twin wire top former has
an upper surface comparatively rich in fines and fillers which improves the
bonding characteristics of the web formed. Water drawn through the bottom of
the web by the shoe and vacuum boxes must pass through the bulk of the web
which acts to filter out the fines and fillers leaving them in the upper portion of
the web. The turning roll brings the web with the upper side facing the base plyinto engagement with the base ply on the base wire.
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It is a feature of the present invention to provide an apparatus for forming
a multi-layer web and cojoining it to another web without a binder.
It is another feature of the present invention to provide a method and
apparatus for producing the outer ply of a multi-ply paper sheet wherein the
surface to be ply-bonded is dewatered solely by centrifugal force, wire tension
and gravity.
It is a further feature of the present invention to provide an apparatus and
method for forming linerboard with a white top liner with improved ply-bonding
characteristics and a commercially desirable outer surface.
It is yet another feature of the present invention to provide a method and
apparatus for forming multi-ply linerboard at higher web speeds.
Further objects, features, and advantages of the invention will be
apparent from the following detailed description when taken in conjunction with
the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
The figure is a schematic elevational view of the twin wire former of this
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring more particularly to the figure wherein similar parts have like
numbers a twin wire former 20 is shown. The twin wire former 20 is mounted
above a traveling foraminous base forming wire 22 which moves in an endless
loop. The base wire has a base web 24 formed by a forming apparatus (not
shown). The base web 24 may be composed of several ply and will normally be
formed of lower grade paper fibers, for example recycled fiber or ground wood
fibers. In order to have an improved printing surface with a white background a
"white top liner" web 26 is formed on the twin wire former 20 and bonded to the
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base web 24. Because the furnishes used to make the base web 24 and the top
web 26 are different, bonding between the webs 24, 26 can be problematic.
The former 20 provides dewatering of the top web so as to increase the
amount of fines and fillers present on the upper side 28 of the top web 26.
Paper forming stock is normally made of paper fibers having a range of sizes
and containing various additives such as starch and clay. The formation of a
web of paper on a forming wire depends on the longer fibers forming a mat on
the forming wire. This mat of fibers then retains the smaller fiber fragments and
fillers. The retained fibers, fines, and fillers, if retained or concentrated near one
surface of the top ply, increase the ability of that surface to make intimate
contact with the base web. It is intimate contract which allows hydrogen bonds
to form between the upper web and the base web which in turn hold the webs
together.
The former 20 achieves a desired concentration of fiber fines and fillers in
the upper surface 28 of the top web 26 by applying vacuum dewatering only to
the lower surface 30 of the web 26. The upper surface is dewatered solely
through wire tension and centrifugal forces.
Formation of the web 26 starts with a headbox 32 with a slice opening 34
positioned over a first or lower forming wire 36 where the lower forming wire 36wraps around an open mesh forming roll 38. The slice opening 34 is positioned
approximately sixty degrees ahead of the forming roll 38 apex 40. An aqueous
top ply stock stream is projected from the slice opening 34 onto the lower looped
forming wire 36 as the wire passes over the open mesh forming roll 38 to form a
top ply web.
A lead in roll 42 brings a second or upper forming wire 44 into co-running
engagement with the lower wire 36 approximately thirty degrees ahead of the
forming roll apex 40. The top web 26 is formed on the lower wire 36 as it is
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supported on the forming roll 38. Thus the web 26 is initially dewatered by
drainage downwardly through the forming roll into a saveall 41.
After the lower wire 36 joins the upper wire 44 and the two wires pass
over the apex 40 of the forming roll 38, an auto-slice 46 with a leading lip 47
removes water from above the upper wire 44. The auto-slice 46 may use
vacuum to remove free water on the wire 44 upper surface and deposit the free
water in a saveall 49. The vacuum is not applied to the web 26 itself and does
not draw water from the web 26. The water removed by the auto-slice 46 is
expressed from the web 26 by centrifugal force and wire tension. Wire tension
causes compression between the upper wire and the lower wire thus forcing
water from the web 26.
After leaving the forming roll 38 the wires 36, 44 with the web 26
therebetween pass over a forming shoe 48. The shoe is made up of blades 50
which are arranged to form the curved shoe 48. The blades 50 create a
hydrodynamic action beneath the lower wire 44 which draws water out of the
web 26 by the vacuum produced by the hydrodynamic forces. Water removed
from the lower side 30 of the web 26 by the shoe 48 flows down into a drain 52.
A second auto-slice 53 with saveall 54 is positioned immediately
downstream of the forming shoe 48 to remove additional water from the upper
side 28 of the web 26. The twin wires 36, 44 continue to move in a generally
downward direction with the web 26 clamped therebetween. The twin wires
pass over a first vacuum box 56 and a second vacuum box 58 which control the
path of the twin wires. A third auto-slice 60 is positioned between the first
vacuum box 56 and the second vacuum box 58 for drawing water expressed
from the web 26 upwardly through the upper wire 44 by centrifugal and wire
tension forces. The auto-slice 60 also transfers water to a third saveall 61.
An upper wire lead out roll 62 leads the upper wire 44 away from the web
26 at the trailing end 64 of the second vacuum box 58. Because vacuum is still
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being applied to the web 26 when the upper wire is pulled away from the web 26
the vacuum holds the web 26 on the lower wire 36.
Following the separation of the upper wire 44 from the lower wire 36 the
lower wire and web 26 traverse a turning roll 66 which inverts the web 26 so theupper side 28 is brought into opposition to the upper side 68 of the base web 24and as the web 26 continues around the turning roll 66 the top liner web 26 is
brought into engagement with and bonds with the base web 24.
Both the upper wire 44 and the lower wire 36 form complete loops. The
upper wire 44 after leaving the forming path travels around the lead out roll 62and then travels around a tension adjusting guide roll 70. A second guide roll 72
directs the upper wire back to the lead in roll 42. The lead in roll 42 and the first
auto-slice 46 and saveall 49 are mounted to a pivoting arm 74 controlled by a
hydraulic actuator 76 or the like. The former 20 may be opened up for replacing
wires etc. by pivoting the arm 74 upwardly and pivoting the vacuum boxes 56,
58 down to move the upper wire 44 and lower wire 36 apart.
The lower wire 36 is removed from engagement with the base wire 22 by
a guide roll 78. From the guide roll 78 the lower wire 36 passes over a tension
adjusting roll 80 and further guide rolls 81, 82 which direct the wire onto the
forming roll 38. Tension in the upper and lower wires can thus be adjusted by
controlling the tension guide rolls 70, 80. The turning roll 66 is mounted on a
pivotable arm 84 which controls the amount of pressure and wrap of the base
wire 22 with the turning roll 66.
Forming the web 26 over the forming roll 38 means an initial mat of fibers
is formed on the lower wire 36. This mat then traps the fibers, fines and fiber
fillers above the mat. Because the fiber mat is already in place and tends to
prevent the fines and fillers from passing through the bottom of the web 26,
additional vacuum dewatering from below the web 26 does not remove fines and
fillers from the upper portion of the web 26. On the other hand the initial
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formation of the mat does deplete fines and fillers from the lower side 30 of the
web 26. By utilizing only web tension and centrifugal force to remove water
upwardly from the upper side 28, the fines and fillers which have been retained
in the upper portion of the web 26 may in large part be kept in the web 26. The
presence of the fibers, fines, and web fillers improves the quality and strength of
the web 26 and most importantly improves the bonding characteristics of the
upper surface 28 of the web 26.
The upper wire interior surface is convex upwardly so that the upper wire
generates centrifugal forces as it moves along the joint path. The upper wire 44has a surface 90 interior to the loop formed by the upper wire 44. The surface
90 extends along a forming zone 94 between the upper and lower wires as they
follow a joint path. Similarly the loop formed by the lower wire 36 has a surface
92 interior to the loop formed by the lower wire 36. This inner surface 92 is
concave downwardly which matches the curvature of the upper wire 44 along
the forming zone 94.
It should be understood that although the web is described and claimed
as being dewatered solely by centrifugal force and wire tension, included withincentrifugal force and wire tension will be some component of gravity acting
together with the aforementioned forces, inasmuch as the downwardly extending
path of the wire reduces the apparent force of gravity.
It is understood that the invention is not limited to the particular
construction and arrangement of parts herein illustrated and described, but
embraces such modified forms thereof as come within the scope of the following
claims.
