Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO ~/09~ (1) PCT/US90/00213
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PATENT APPLICATION
A FORMING APPARATUS FOR FORMING A WEB FROM STOCK
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
This invention relates to a forming apparatus for
forming a web from stock. More particularly, the present
invention relates to a forming apparatus for forming a web
from stock ejected through a slice lip of a headbox into a
forming section defined between a first and a second wire.
INFORMATION DISCLOSURE STATEMENT
In some of the earlier paper-forming machines, a
headbox was disposed at the upstream end of a moving
fourdrinier wire and stock was ejected from the slice lip of
the headbox onto the forming wire such that water drained
through the wire leaving a formed web on the top surface of
the wire.
Subse~uent proposals included the provision of a top
wire disposed downstream relative to the headbox such that
water was drained from the stock not only downwardly through
the fourdrinier wire but also upwardly through the top wire
thereby improving the two-sidedness of the resultant web.
With the aforementioned twin-wire formers, certain
problems existed in that the web was already partially
formed prior to extending through the twin-wire formation
section. Furthermore, the top surface of the stock
supported on the fourdrinier wire was subjected to vibration
which caused nonuniform characteristics to the upper surface
of the resultant web.
More recently, proposals have been made particularly in
US Patent No. 4,830,709 in which the headbox is disposed
;mm~; ately adjacent to the upstream end of the forming
section defined between cooperating twin wires. Such true
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gap formers ave improved the two-sidedness of the resul t
web because the slice lip ejects stock almost immediately
between the gap formed between the cooperating forming
wires.
However, although the aforementioned gap formers have
proved very successful in the formation of lightweight
grades such as newsprint, problems have been experienced
using such forming apparatus for forming heavier grades.
In the formation of heavier grades, the speed of the
former is considerably less than the speed of the former
when forming lightweight grades because more time is
required in draining the water from the larger quantity of
stock used in the production of heavier grade webs.
Because of the lower wire speed and the correspondingly
slower rate of ejection of stock through the slice lip, it
is essential that the slice lip be disposed as close as
possible to the upstream end of the forming section. If the
headbox is disposed at a relatively considerable distance
from the upstream end of the forming section, there exists a
tendency for the trajectory of the jet of stock to be
excessively curved and the angle of impingement of the stock
relative to the lower wire to be increased to an
unacceptable angle.
Ideally, the impingement angle relative to the lower
wire should be as small as possible so that as the jet
impinges on the wire, m;n;mum disturbance to the stock
occurs and the stock impinges on the lower wire at a speed
which is the same as that of the lower wire.
The present invention attains the aforementioned
objective by substituting turning bars for the breast rolls
disclosed in the aforementioned proposal as taught in US
Patent No. 4,830,709.
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Therefore, it is a primary object of the present
invention to provide a high capacity forming apparatus which
overcomes the aforementioned inade~uacies of the prior art
proposals and which provides a significant contribution to
the art of forming a web from stock.
Another object of the present invention is the
provision of a twin-wire forming apparatus including a first
and a second turning bar which permit the headbox slice lip
to be disposed in close proximity to the first or upstream
end of the forming section defined by the wires.
Another object of the present invention is the
provision of a forming apparatus which includes at least two
auto slices with means for adjusting the vacuum slots of the
auto slices relative to the second wire for varying the
amount of water removed from the second wire.
Another object of the present invention is the
prov:ision of a forming apparatus in which the forming
sect:ion is disposed substantially horizontally.
Another object of the present invention is the
provision of a forming apparatus in which the forming
section follows a generally sinusoidal path from the first
to the second end thereof.
Another object of the present invention is the
provlsion of a vacuum box disposed between the first and the
second vacuum slots and on the opposite side of the wires
relal:ive to the vacuum slots, the vacuum box having a curved
surface which permits removal of water downwardly through
the first wire and upward removal of water centrifugally
throllgh the second wire.
Another object of the present invention is the
prov~sion of a forming apparatus which includes at least one
further vacuum slot disposed between the first and the
WO90/09~1 (4) PCT/US90/00213
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second vac~ for upward removal of water through the
second wire.
Other objects and advantages of the present invention
will be apparent from a consideration of the detailed
description of various embodiments of the invention as
described hereinafter and as shown in the annexed drawings.
SUMMARY OF THE INVENTION
The present invention relates to a forming apparatus
and method for forming a web from stock. More particularly,
the present invention relates to a forming apparatus and
method for forming a web from stock ejected through a slice
lip of a headbox. The apparatus includes a first wire which
extends in an endless loop past the slice lip such that the
stock is ejected through the slice lip onto the first wire.
A second wire extends in a further endless loop with the
second wire cooperating with the first wire for defining
therebetween a forming section having a first and a second
end such that the web is formed during passage of the stock
through the forming section. A first turning bar is
disposed within the endless loop and adjacent to the first
end of the forming section such that the first wire is
sandwiched between the stock and the first turning bar. A
second turning bar is disposed within the further endless
loop and adjacent to the first end of the forming section
such that the stock is disposed between the wires, the wires
being disposed between the turning bars permitting the slice
lip to be disposed in close proximity to the first end of
the forming section. A curved drainage means is disposed
within the endless loop immediately downstream relative to
the first turning bar for removing a first portion of water
from the stock through the first wire and for removing a
second portion of water centrifugally through the second
wire during passage of the stock through the forming section
and past the curved draining means. A first vacuum slot is
disposed within the further endless loop and extends in a
cross-machine direction ; mmeA; ately downstream relative to
the curved drainage means for removing a third portion of
WO ~/09~1 (5) 20~65~8 ~ ~ ~
water from the stock through the second wlre. A vacuum box
is disposed within the endless loop ;mme~;ately downstream
relative to the vacuum slot with the vacuum box defining a
curved surface for removing a fourth portion of water from
the stock through the first wire. A second vacuum slot is
disposed within the further endless loop and extends in a
cross-machine direction downstream relative to the vacuum
box for removing further water from the stock through the
second wire. Additionally, a further curved drainage means
is disposed within the further endless loop and immediately
downstream relative to the second vacuum slot for removing
water from the stock through the second wire. The curvature
of the curved drainage means and the vacuum box is opposite
to the curvature of the further curved drainage means such
that the stock is progressively drained through both wires
during passage through the forming section from the first
towards the second end thereof.
More specifically, the first wire is disposed relative
to the slice lip such that the stock impinges on the first
wire before contacting the second wire.
In a preferred embodiment of the present invention, the
forming section is disposed substantially horizontally and
the forming section follows a generally sinusoidal path.
In one embodiment of the present invention, the turning
bars are of ceramic material and the curved drainage means
also includes a plurality of drainage slots which are
connected to a source of partial vacuum.
The curved drainage ~e~n~ defines a face having a
radius of curvature which is greater than the radius of
curvature of the curved surface of the vacuum box.
In the preferred embodiment of the present invention,
the first vacuum slot is a first auto slice which includes
adjusting means for adjusting the vertical and/or the
angular position of the first vacuum slot relative to the
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second wire. The adjusting means also permits movement o~
the first vacuum slot between the curved drainage means and
the vacuum box.
In one embodiment of the present invention, the curved
surface of the vacuum box permits centrifugal removal of a
fifth portion of water from the stock through the second
wire.
In another embodiment of the present invention, the
forming apparatus includes an adjustable foil which is
disposed within the endless loop between the vacuum box and
the second vacuum slot for assisting removal of further
water through the second vacuum slot.
In an alternative embodiment to the present invention,
the forming apparatus also includes a further vacuum slot
which is disposed within the further endless loop and
disposed between the first and second vacuum slots for
removing water from the stock through the second wire.
In another embodiment of the present invention, the
second vacuum slot is a second auto slice which includes
further adjusting means for adjusting the second vacuum slot
relative to the second wire for sk;mm; ng the further water
removed from the stock through the second wire.
In the preferred embodiment of the present invention,
the further curved drainage means also includes a plurality
of cross-machine direction shoes defining therebetween a
plurality of openings connected to a source of partial
vacuum for removing water from the stock through the second
wire.
The present invention also includes a method of forming
a web from stock ejected through a slice lip of a headbox.
The method comprises the steps of moving a first wire, which
extends in an endless loop, past the slice lip and then
ejecting the stock through the slice lip onto the first
WO ~/09~1 (7) 20465~8
wire. The arrangement is such that the stock contacts the
firt;t wire at a m;nim~l angle of impingement due to the
first wire extending around a first turning bar disposed
adjacent to the point of impingement of the stock onto the
first wire.
Additionally, the method includes the step of moving a
second wire, which extends in a further endless loop, around
a second turning bar such that the second turning bar is
disposed adjacent to the first turning bar so that the slice
lip is disposed in close proximity to a first end of the
forming section defined between the wires.
Also, the method includes the step of forming the web
from the stock during passage of the stock through the
forming section by progressively removing water from the
stoc:k through both wires.
More specifically, the step of forming the web from
stock during passage of the stock through the forming
section includes removing a portion of water from the stock
through a curved vacuum box disposed downstream and on the
opposite side of the wires relative to a vacuum slot.
Although specific embodiments of the present invention
are described hereinafter in the detailed description and
are shown in the annexed drawings, it will be apparent to
those skilled in the art that many variations and
modifications of the present invention may be made without
departing from the spirit and scope of the present invention
as defined by the appended claims.
Included among such modifications and variants would be
the provision of a gap former having a forming section
disposed substantially vertically.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a side-elevational view of a forming
apparatus according to the present invention;
WO90/09~1 - (8) PCT/US90/00213
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Figure 2 is an enlarged fragmentary view of the
drainage means;
Figure 3 is an enlarged fragmentary view of the curved
inverted vacuum box; and
Figure 4 is a side-elevational view of an alternative
embodiment of the present invention showing a further vacuum
slot disposed between the first and the second vacuum slots.
Similar reference characters refer to similar parts
throughout the various embodiments of the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
Figure 1 is a side-elevational view of a forming
apparatus generally designated 10 according to a preferred
embodiment of the present invention.
The forming apparatus 10 forms a web W from stock S
ejected through a slice lip 12 of a headbox generally
designated 14.
The apparatus 10 includes a first wire 16 which extends
in an endless loop generally designated 18 past the slice
lip 12 such that the stock S is ejected through the slice
lip 12 onto the first wire 16.
A second wire 20 extends in a further endless loop
generally designated 22. The second wire 20 cooperates with
the first wire 16 for defining therebetween a forming
section generally designated 24 having a first and a second
end 26 and 28, respectively, such that the web W is formed
during passage of the stock S through the forming section
24.
A first turning bar 30 is disposed within the endless
loop 18 and adjacent to the first end 26 of the forming
WO 90/09~1 ( 9 ~ 8 ~PCT/US90/00213
sect.ion 24 such that the first wire 16 is sandwiched between
the stock S and the first turning bar 30.
A second turning bar 32 is disposed within the further
endless loop 22 and adjacent to the first end 26 of the
forming section 24 such that the stock S is disposed between
the wires 16 and 20. The wires 16 and 20 respectively are
disposed between the turning bars 30 and 32 respectively
thereby permitting the slice lip 12 to be disposed in close
proximity to the first end 26 of the forming section 24.
A curved drainage means generally designated 34 is
disposed within the endless loop 18 immediately downstream
relative to the first turning bar 30. The drainage means 34
removes a first portion of water from the stock S through
the first wire 16 and removes a second portion of water
centrifugally through the second wire 20 during passage of
the stock S through the forming section 24 and past the
curved drainage means 34.
A first vacuum slot generally designated 36 is disposed
within the further endless loop 22 and extends in a
cross-machine direction immediately downstream relative to
the curved drainage means 34 for removing a third portion of
water from the stock S through the second wire 20.
A vacuum box 38 is disposed within the endless loop 18
immediately downstream relative to the vacuum slot 36. The
vacuum box 38 defines a curved surface 40 for removing a
fourth portion of water from the stock S through the first
wire 16 and removes another portion of water centrifugally
through the second wire 20 during passage of the stock S
through the forming section.
A second vacuum slot generally designated 42 is
disposed within the further endless loop 22 and extends in a
cros.s-machine direction downstream relative to the vacuum
box 38 for removing further water from the stock S through
the second wire 20.
WO90/09~1 ~ (10) PCT/US90/00213
A further curved drainage means generally designated 44
is disposed within the further endless loop and immediately
downstream relative to the second vacuum slot 42 for
removing water from the stock S through the second wire 20.
The curvature of the curved drainage means 34 and the vacuum
box 38 are opposite to the curvature of the further curved
drainage means 44 such that the stock S is progressively
drained through both wires 16 and 20 respectively during
passage through the forming section 24 from the first end 26
towards the second end 28 thereof.
More specifically, as shown in figure 1, the forming
apparatus 10 is arranged such that the first wire 16 is
disposed relative to the slice lip 12 so that the stock S
impinges on the first wire 16 before contacting the second
wire 22.
As shown in figure 1, the forming section 10 is
disposed substantially horizontally and the forming section
24 follows a generally sinusoidal path.
In one embodiment of the present invention, the turning
bars 30 and 32 are of ceramic material. Figure 2 is an
enlarged fragmentary view of the drainage means 34 in which
the curved drainage means 34 further includes a plurality of
support foils 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56,
57, 58, 59, 60, 61, 62 and 63 which define therebetween a
plurality of drainage slots 64, 65, 66, 67, 68, 69, 70, 71,
72, 73, 74, 75, 76, 77, 78, 79, 80 and 81.
The plurality of drainage slots 64 to 81 are connected
to a source of partial vacuum 82.
The curved drainage means 34 defines a face 84 having a
radius of curvature which is greater than the radius of
curvature of the curved surface 40 of the vacuum box 38.
~4~58~
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~ As shown in figure 2, the first vacuum slot 36 is a
first auto slice 86 which includes adjusting means 88 for
adjusting the angular and vertical position of the first
vacuum slot 36 relative to the second wire 20.
Additionally, the adjusting means 88 permits movement
of the first vacuum slot 36 between the curved drainage
means 34 and the vacuum box 38.
The curved surface 40 of the vacuum box 38 also permits
cent:rifugal removal of a fifth portion of water from the
stock S through the second wire 20.
Figure 3 is an enlarged fragmentary view showing the
further curved drainage means or curved inverted vacuum
boxes 44. As shown in figure 3, the forming apparatus 10
also includes an adjustable vacuum foil 90 which is disposed
within the endless loop 18 between the vacuum box 38 and the
second vacuum slot 42 for assisting removal of the further
water through the second vacuum slot 42.
Figure 3 also shows the second vacuum slot 42 as a
second auto slice 92 with the second auto slice 92 further
including further adjusting means 94 for adjusting the
second vacuum slot 42 relative to the second wire 20 for
sk; mm; ng the further water removed from the stock S through
the second wire 20.
Figure 3 shows the further curved drainage means 44 as
incl.uding a plurality of cross-machine direction shoes 96,
97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108,
109, 110, 111, 112, 113 and 114 which define therebetween a
plurality of openings 115, 116, 117, 118, 119, 120, 121,
122, 123, 124, 125, 126, 127, 128, 129, 130, 131 and 132
connected to a source of partial vacuum (not shown) for
removing water from the stock through the second wire 20.
In an alternative embodiment to the present invention
as shown in figure 4, a forming apparatus generally
WO90/09~1 ~ (12) PCT/US90/00213
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designated lOA further includes a further vacuum slot 13
which is disposed wïthin a further endless loop 18A and
disposed between the first and the second vacuum slots 36A
and 42A respectively for removing water from the stock
through the second wire 2OA.
In operation of the apparatus according to the
preferred embodiment of the present invention, high
consistency stock S is ejected from the headbox 14 through
the slice lip 12 such that the angle of impingement of the
jet of stock relative to the first wire 16 is very small.
Furthermore, the slice lip 12 is able to be disposed in very
close proximity to the first end 26 of the forming section
24 due to the provision of the turning bars 30 and 32
respectively. Therefore, according to the present
invention, when ejecting high consistency stock at
relatively low machine speeds, the stock is deposited on the
lower wire 16 with mi n; m~ 1 disturbance of the stock.
Subsequently, a first portion of water is removed
downwardly through the curved drainage means 34 and a second
portion of water is removed upwardly through the second wire
20 due to the centrifugal force applied to the stock during
passage of the stock through the forming section 24 around
the curved drainage means 34.
Thereafter, a third portion of water is removed by
means of the first vacuum slot 36, and a fourth portion of
water is removed downwardly through the vacuum box 38.
The vacuum box 38 having a curved surface 40 results in
a fifth portion of water being removed upwardly through the
second wire 20. The first wire 16 then passes over the foil
90 which assists the removal of a further portion of water
through the second vacuum slot 42.
The wires then proceed to extend around at least one
curved inverted vacuum box or further curved drainage means
44 for removing water through the second wire 20.
WO90/09~1 (13) ,PCT/US90/00213
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20465~8
The curved drainage means 34 and vacuum box 38 have a
radius of curvature which is opposite to the radius of
curvature of the further curved drainage means 44 so that
the forming section 24 follows a generally sinusoidal
configuration from the first end 26 to the second end 28 of
the forming section 24.
The operation of the apparatus shown in figure 4 is
similar to the operation of the apparatus shown in figures
1-3 except in that a further auto slice 134 is used for
assisting withdrawal of water upwardly through the wire 20A.
The aforementioned arrangement not only permits
prog~essive drainage through both wires during passage
through the forming section but also permits the high
consistency stock to be ejected into the forming section
with a m;n;mum trajectory thereby improving formation and
the two-sidedness of the resultant web.
