Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD OF MOISTENING PAPER WEB AND PAPER WEB MOISTENING DE-
VICE
BACKGROUND OF THE INVENTION
[0001] The invention relates to a method of moistening a paper web
comprising moistening the paper web by a moistening device by spraying wa-
ter mist onto the paper web surface and by removing excess water mist from
the moistening device.
[0002] The invention further relates to a paper web moistening de-
vice comprising a body, moistening nozzles and at least one means for remov-
ing water, water mist or air from the moistening device.
[0003] The paper web is moistened to control the paper web mois-
ture profile, for instance. Moistening can also be used for managing the
curling
of the paper web in the paper machine. Furthermore, in online calendering, for
example, the controlling of certain quality measures requires high-grade mois-
tening with water.
[0004] The moistening device is provided with several moistening
nozzles in the cross direction of the paper web for blowing water mist contai
n-
ing air and water onto the paper web surface. One moistening apparatus of
this kind is disclosed in DE 952 765.
[0005] Moistening devices exist where the above-mentioned mois-
tening nozzles are arranged in several successive rows. The nozzles in suc-
cessive rows may overlap with one another. A problem associated with mois-
tening devices is how to achieve a sufficiently even moistening result. A mov-
ing paper web carries air and air is also blown by the moistening nozzle. The
air currents generated make the controlling of the moistening nozzle response
difficult, i.e. the fact which point of the paper web is in reality moistened
by
moistening nozzle. In the moistening device, the current may cause the noz-
zles at different points in the lateral direction to moisten the same point of
the
paper web, which results in too moist and too dry points in the paper web. Fur-
thermore, the controlling of the moistening nozzle response is so difficult
that
the adjustment of the moistening nozzles becomes very complicated.
BRIEF DESCRIPTION OF THE INVENTION
[0006] The object of the present invention is to provide a new and
improved method of moistening a paper web and a paper web moistening de-
vice.
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[0007] The method according to the invention is characterized in
that the removal of water mist and/or air occurs closer to the paper web sur-
face than the spraying of water mist.
[0008] The paper web moistening device according to the invention
is further characterized in that the moistening device comprises a means that
extends closer to the paper web surface than the moistening nozzles for re-
moving water mist and/or air from the vicinity of the paper web surface.
[0009] The basic idea of the invention is that several moistening
nozzles are arranged in the body of the paper web moistening device. At least
one means for removing water mist and/or air from the vicinity of the paper
web surface is arranged between the moistening nozzles so that the means
extends closer to the paper web than the moistening nozzle. By means of the
invention, the desired moisture profile can be achieved with a very high accu-
racy. Furthermore, the detrimental effect of air currents on moisture nozzle
re-
sponses can be prevented, which facilitates the controlling of the moistening
device. The idea of an embodiment is that the means for removing water mist
and/or air from the vicinity of the paper web surface is a discharge nozzle.
The
idea of another embodiment is that before the moistening nozzles, the
moistening device comprises a slit nozzle having substantially the same width
as the paper web for blowing air against the machine direction of the paper
web to decrease the laminar air current travelling along with the paper web.
The purpose of this is also to improve the moisture profile produced by the
moistening device. The idea of a third embodiment is that the nip side of the
moistening device is provided with a slit nozzle having substantially the same
width as the paper web for blowing air in the direction opposite to the
machine
direction of the paper web to prevent water mist from spreading into the
environment from the moistening device.
[0010] This description discloses the use of air and water in mois-
tening but other gases and liquids may also be employed. Thus, in this
description, the term "air" refers to any gas or gas mixture usable in
moistening
the paper web and the term "water' refers to any liquid or liquid mixture suit-
able for moistening the paper web.
BRIEF DESCRIPTION OF THE FIGURES
[0011] The invention will be described in greater detail in the aG
companying drawing, where
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Figure 1 is a schematic and cross-sectional side view of a paper
web moistening device, and
Figure 2 is a schematic top view of the moistening device according
to Figure 1.
[0012] For the sake of clarity, the figures illustrate the invention in a
simplified manner. Like reference numbers refer to like parts in the figures.
DETAILED DESCRIPTION OF THE INVENTION
[0013] Figure 1 illustrates a paper web moistening device where the
body 1 is provided with moistening nozzles 2. The body 1 is a beam arranged
in the cross direction of the paper web 3. The moistening device is arranged
below the paper web 3. The paper web 3 moves in the direction of arrow A.
The paper web 3 may be a paper or cardboard web already manufactured in a
paper machine or a fibrous web in a paper machine or cardboard machine, still
containing moisture that is to be removed in the paper machine. The moisten-
ing device is typically arranged below the paper web 3, but if desired, it may
also be mounted above the paper web 3 or both above and below the paper
web. The particular purpose of the moistening device is to increase the mois-
ture content of the paper web 3.
[0014] Water mist is blown or sprayed by moistening nozzles 2 to-
wards the paper web 3 surface, the water mist being typically a mixture of air
and water. The cone-shaped water mist spray achieved by means of the mois-
tening nozzle 2 is illustrated by arrows B in the accompanying drawing.
[0015] The body 1 of the moistening device is provided with water
discharge outlets 4, through which excess water mist or condensed water can
exit from the space between the moistening device and the paper web 3. The
water discharge outlets 4 are connected to discharge pipes, which are not
shown in the figures. The discharge of water mist and water can be intensified
by low pressure. The water discharge outlets 4 are located farther from the
paper web 3 surface than the moistening nozzles 2.
[0016] The moistening nozzles 2 are arranged in rows in the cross
direction of the paper web 3. The moistening nozzles 2 in successive rows
overlap, i.e. they are at different points in the lateral direction, as
appears from
Figure 2.
[0017] A discharge nozzle 5 having substantially the same width as
the paper web 3 is arranged between the second and the third row of moisten-
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ing nozzles. The discharge nozzle 5 is used for air suction as illustrated by
ar-
row C. The discharge nozzle 5 is connected to a discharge pipe, which is not
shown in the figures. The generation of suction does not require a very great
low pressure or low pressure is not necessarily needed at all, provided that
air
can be removed through the discharge nozzle 5, i.e. that the current is high
enough for keeping the discharge nozzle 5 open. At the same time, the dis-
charge nozzle 5 removes excess water mist.
[0018] The distance h1 of the moistening nozzles 2 from the paper
web 3 surface is typically 50 to 150 mm. The discharge nozzle is arranged
closer to the paper web 3 surface than the moistening nozzles 2, in which case
the distance h2 of the discharge nozzle 5 from the paper web 3 is smaller than
the distance h1 of the moistening nozzles 2 from the paper web 3. In that
case,
air currents caused by the movement of the paper web 3 and by the first and
second rows of moistening nozzles can be absorbed by the discharge nozzle 5
without the air currents interfering with the operation of the moistening
nozzles
in the third and fourth rows of moistening nozzles. In that case, the
responses
of the moistening nozzles in successive rows do not turn or overlap but each
moistening nozzle moistens only its own point in the paper web 3, which pro-
vides a very even moistening result. Furthermore, the desired moistening pro-
file can be achieved very accurately and relatively easily.
[0019] The distance h2 of the discharge nozzle 5 from the paper
web 3 is typically 10 to 15 mm. Preferably, this distance h2 is at most 50 mm.
In any case, the distance h2 of the discharge nozzle 5 is smaller than the dis-
tance h1 of the moistening nozzles 2 from the paper web 3. Preferably, the
distance h2 of the discharge nozzle 5 from the paper web 3 is at least 20 mm
smaller than the distance h1 of the moistening nozzles 2 from the paper web 3.
Particularly preferably, the distance h2 of the discharge nozzle 5 from the pa-
per web 3 is at least 50 mm smaller than the distance h1 of the moistening
nozzle 2 from the paper web 3.
[0020] The dimension of the moistening device in the machine di-
rection A of the paper web 3 may be 1 m, for example, when the moistening
device comprises four successive nozzle rows as in the appended figures. The
dimension of the moistening device in the machine direction A of the paper
web may vary between 0.5 and 1.5 m, for example, and the number of succes-
sive moistening nozzle rows may vary from two to ten, for instance. The mois-
tening device naturally has the same width as the paper web 3 and the number
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of moistening nozzles depends on the paper web width 3, the shape of
moistening nozzle responses and on the desired moistening efficiency.
[0021] The front edge of the moistening device comprises a first slit
nozzle 6 having the same width as the paper web 3. The first slit nozzle 6
5 blows air against the machine direction A of the paper web 3 in accordance
with arrow D. The purpose of this blow is to remove the laminar air current
car-
ried along with the paper web 3 that interferes with the evenness of the mois-
tening nozzle 2 sprays. The slit nozzle 6 has a planar surface that guides the
air current D. The planar surface may be slightly curved so that the air
current
D curves in the direction of the curved surface.
[0022] The nip side of the moistening device comprises a second
slit nozzle 7. Also, the second slit nozzle 7 has substantially the same width
as
the paper web 3. The second slit nozzle 7 also blows air against the machine
direction of the paper web 3 in accordance with arrow E. The structure and
operation of the slit nozzle 7 correspond to those of the first slit nozzle 6.
The
air current E blown by the second slit nozzle 7 is used to prevent the water
mist from spreading into the environment from the moistening device.
[0023] For the sake of clarity, the appended figures do not show
pipes, connectors or other arrangements for bringing air and water into the
moistening device and for carrying air and water away from the moistening
device.
[0024] The machine line for fibrous web may comprise several suc-
cessive moistening devices in the machine direction. At least one moistening
device is provided with the structure according to the solution described
here.
The described solution can also be arranged in two successive moistening de-
vices or, if desired, in more than two moistening devices and even in all mois-
tening devices. The described moistening device is preferably utilized in mois-
tening mechanical uncoated papers, such as SC paper. One preferred solution
is to arrange the described moistening device in connection with a multi-roll
calender or a multi-roll calender having two stacks of rolls.
[0025] The drawing and the related description are only intended to
illustrate the inventive concept. The details of the invention may vary within
the
scope of the claims. Thus, for example, the moistening nozzles need not be
arranged in rows in the cross direction of the paper web but they may be ar-
ranged otherwise in the moistening device. On the other hand, the distance
between the rows of the moistening nozzles arranged in rows may vary be-
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tween successive rows. Tests have shown that in the solution according to the
appended figures, the two first moistening nozzle rows interfere with each
other relatively little, and the result can be improved considerably by
removing
the air current from between the second and the third moistening nozzle row
by the discharge nozzle 5. If desired, discharge nozzles 5 may be arranged
between each moistening nozzle row or, if moistening nozzles are not ar-
ranged in rows, discharge nozzles may be mounted between all moistening
nozzles. The discharge nozzle 5 needs not necessarily have the same width
as the paper web 3 but there may be several discharge nozzles 5 one after
another in the lateral direction of the paper web 3. On the other hand, the
dis-
charge nozzle 5 may be a single pipe, in which case discharge nozzles can be
arranged everywhere in the moistening device between the desired moistening
nozzles 2. In that case, a row may be formed of the discharge nozzles 5 in the
cross direction of the paper web 3, in which case there are discharge nozzles
next to or at a distance from one another in a row, whose function corresponds
to that of the discharge nozzle 5 provided with a slit, which has the same
width
as the paper web 3 and is illustrated in Figures 1 and 2.
[0026] Instead of the discharge nozzle 5, the means for removing
water mist and/or air from the vicinity of the paper web 3 surface may be any
structure arranged to extend closer to the paper web than the moistening noz-
zle 2 and to remove air and/or water mist from the vicinity of the paper web 3
surface. As such, this structure does not require a discharge pipe or suction,
but the structure may be formed by a partition wall, beam, spoiler, air doctor
or
another similar structure. Also a tap or taps arranged next to one another or
a
plate or plates may function as the means for removing water mist and/or air.
In a manner corresponding to the one described in connection with the dis-
charge nozzle 5, this structure enables removal of the interfering effect of
air
currents caused by the moistening nozzles and the movement of the paper
web on the function of the other moistening nozzles. This function may be
based, for example, on the fact that the current in the direction of the paper
web 3 surface can be cut at a desired point and/or a current can be formed at
a desired point in the direction away from the paper web surface for guiding
excess air and/or water mist. If means of this kind for removing water mist
and/or air is not itself provided with discharge pipes or suction, the excess
air
and/or water mist or condensed water removed by them from the vicinity of the
paper web can be first collected onto the surface of the moistening device,
i.e.
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onto a "floor level" formed by it, and removed through water discharge outlets
4 arranged in the body 1 of the moistening device, for example.
