U.S. patent application number 10/919762 was filed with the patent office on 2008-07-31 for arrangement in connection with the press and dryer section of a web forming machine.
This patent application is currently assigned to Metso Paper, Inc.. Invention is credited to Antti Komulainen, Matti Kurki, Juhani Vestola.
Application Number | 20080178487 10/919762 |
Document ID | / |
Family ID | 27839077 |
Filed Date | 2008-07-31 |
United States Patent
Application |
20080178487 |
Kind Code |
A1 |
Komulainen; Antti ; et
al. |
July 31, 2008 |
Arrangement in connection with the press and dryer section of a web
forming machine
Abstract
An arrangement in connection with the press and dryer section of
a web-forming machine includes first and second devices for
transporting the web. The second device includes a dryer wire and a
roll arranged to support it. In the arrangement there is an open
gap between the first and second devices, across which the web is
arranged to be transferred, so that the web and the dryer wire form
a closing throat. The arrangement further includes a deflector
before the open gap in the direction of travel of the dryer wire,
which is arranged close to the dryer wire, in order to restrict the
air layer travelling with the dryer wire, and thus to prevent the
formation of an excess pressure in the closing throat.
Inventors: |
Komulainen; Antti; (Keuruu,
FI) ; Kurki; Matti; (Jyvaskyla, FI) ; Vestola;
Juhani; (Jyvaskyla, FI) |
Correspondence
Address: |
Christopher J. Fildes;Fildes & Outland, P.C.
Suite 2
20916 Mack Avenue
Grosse Pointe Woods
MI
48236
US
|
Assignee: |
Metso Paper, Inc.
|
Family ID: |
27839077 |
Appl. No.: |
10/919762 |
Filed: |
August 17, 2004 |
Current U.S.
Class: |
34/117 |
Current CPC
Class: |
D21F 2/00 20130101; D21F
3/04 20130101; D21F 5/00 20130101; F26B 13/16 20130101; F26B 13/101
20130101 |
Class at
Publication: |
034/117 |
International
Class: |
D06F 58/00 20060101
D06F058/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 20, 2003 |
FI |
20035134 |
Claims
1. An arrangement in connection with the press and dryer section of
a web-forming machine, which arrangement includes first means in
the press section for transporting the web manufactured on a
web-forming machine, second means in the dryer section for the
onward transportation of the web manufactured on a web-forming
machine, which second means include a dryer wire and a roll
arranged to support it, inside which a vacuum is arranged, in which
arrangement there is an open gap between the first and second
means, across which the web is arranged to be transferred from the
first means to the dryer wire in the vacuum area of the roll, in
which the web and the dryer wire form a closing throat, and the
arrangement further includes deflector means on the side of loop
formed from the dryer wire opposite to the roll and before the open
gap in the direction of travel of the dryer wire, which are
arranged close to the dryer wire, in order to restrict the air
layer travelling with the dryer wire, and thus to prevent the
formation of an excess pressure in the said closing throat, and the
arrangement further includes runnability components arranged in
connection with the roll inside the loop formed from the dryer
wire, which are arranged to restrict the air layer travelling with
the inner surface of the dryer wire and thus to prevent the
formation of an excess pressure in the closing throat formed by the
dryer wire and the roll, characterized in that the distance of the
deflector means from the dryer wire is 1-12 mm, and the runnability
components include at least one blow box.
2. An arrangement according to claim 1, characterized in that the
distance of the blow box from the part of the dryer wire on the
side of the deflector means is at most 50 mm.
3. An arrangement according to claim 1, characterized in that the
distance of the deflector means from the point of contact of the
roll and the dryer wire is less than 3000 mm.
4. An arrangement according to claim 1, characterized in that the
deflector means are arranged to be active or passive.
5. An arrangement according to claim 4, characterized in that the
active deflector means are formed of elements arranged to move or
rotate, or of airflow devices.
6. An arrangement according to claim 4, characterized in that the
passive deflector means are formed of an air baffle or a
doctor.
7. An arrangement according to claim 4, characterized in that the
distance of the active deflector means from the dryer wire is 3-12
mm.
8. An arrangement according to claim 4, characterized in that the
distance of the passive deflector means from the dryer wire is 1-6
mm.
9. An arrangement according to claim 1, characterized in that in
the blow box there is at least one blast, both before the roll and
after the roll.
10. An arrangement according to claim 1, characterized in that
vacuum devices are arranged in connection with the roll, in order
to create a vacuum over at least part of the distance of the area
of the perforated jacket belonging to the roll.
Description
[0001] The present invention relates to an arrangement in
connection with the press and dryer section of a web-forming
machine, which arrangement includes [0002] first means in the press
section for transporting the web manufactured on a web-forming
machine, [0003] second means in the dryer section for the onward
transportation of the web manufactured on a web-forming machine,
which second means include a dryer wire and a roll arranged to
support it, inside which a vacuum is arranged, in which arrangement
there is an open gap between the first and second means, across
which the web is arranged to be transferred from the first means to
the dryer wire in the vacuum area of the roll, in which the web and
the dryer wire form a closing throat, and the arrangement further
includes deflector means on the side of the loop formed from the
dryer wire opposite to the roll and before the open gap in the
direction of travel of the dryer wire, which are arranged close to
the dryer wire, in order to restrict the air layer travelling with
the dryer wire, and thus to prevent the formation of an excess
pressure in the said closing throat, and the arrangement further
includes runnability components arranged in connection with the
roll inside the loop formed from the dryer wire, which are arranged
to restrict the air layer travelling with the inner surface of the
dryer wire and thus to prevent the formation of an excess pressure
in the closing throat formed by the dryer wire and the roll.
[0004] Even in modern web-forming machines, locations remain, in
which the web is carried over an open gap. Such a location occurs,
for example, between the web-forming machine's press section and
dryer section. In one known problem location, the web is guided,
from the surface of a press roll belonging to the press section, to
the dryer wire belonging to the dryer section. The dryer wire is
arranged in a loop supported by rolls, one of which is arranged
near to the press roll. In practice, the web is guided onto the
dryer wire at this point. In addition, a closing throat is formed
between the web and the dryer wire on the surface of the roll. The
web travels on to the dryer section, supported on the dryer
wire.
[0005] At the other end of the endless loop of the first dryer
wire, the web is transferred to the following dryer wire. In its
return cycle, the dryer wire is empty and finally again travels
past the roll arranged near to the press roll. Particularly during
the return cycle, the dryer wire transports an air layer with it,
which finally reaches the closing throat formed by the web and the
dryer wire. Some of the air exits upwards from the throat and
through the dryer wire into the vacuum roll. However, the amount of
air is so great that a considerable excess pressure arises in the
throat and causes bagginess in the web, especially in the edges,
which are looser than the rest of the web. In the cross-direction
of the web-forming machine, the bagginess is indeterminate, which
hinders the travel of the web. The excess pressure also causes
cross-direction currents, which cause web flutter. The bagginess
and the indeterminate movement of the web stretch the web and
reduce its quality. Attempts have been made to avoid this problem
by rotating the dryer section at a higher speed than the press
section, in order to tension the web. However, in modern high-speed
web-forming machines, it is difficult to increase the speed
differential. In addition, at high speeds, even a small relative
difference in speed will create a large absolute change, which
leads to varying forces in the machine direction. The motion of the
web then becomes jerky and the bagging problem appears at least
occasionally. The possibility of web breaks in the web-forming
machine also increases, thus reducing the total output.
[0006] U.S. Pat. No. 545,593 discloses a device, which includes a
deflector fitted before the throat and a vacuum box set inside the
loop. Wear occurs in both the seals of the vacuum box and in the
dryer wire. In addition, the deflector is far from the throat.
[0007] The invention is intended to create a new type of
arrangement, by means of which flutter and bagging in the web can
be avoided. The characteristic features of this invention are
stated in the accompanying Claims. The use of the arrangement
according to the invention prevents air layer from travelling into
the closing throat. Thus, the pressure is essentially the same on
both sides of the web, thus stabilizing the travel of the web. The
arrangement can be assembled from various components, so that the
problem can be avoided at each position. In addition, the number
and dimensioning of the components provide a simple way to regulate
the amount of air being removed.
[0008] In the following, the invention is examined in detail with
reference to the accompanying drawings showing some embodiments of
the invention, in which
[0009] FIG. 1 shows a schematic drawing of a side view of the
arrangement according to the invention,
[0010] FIG. 2a shows a schematic drawing of a side view of a second
embodiment of the arrangement according to the invention,
[0011] FIG. 2b shows a schematic drawing of a side view of a third
embodiment of the arrangement according to the invention.
[0012] FIG. 1 shows an arrangement according to the invention, in
connection with the press section and the dryer section of a
web-forming machine. In this case, the arrangement includes first
means 10 in the press section, for transporting the web 11 being
made on the web-forming machine. In FIG. 1, only parts of the press
section and the dryer section are shown. In the press section, the
web 11 is transported on a press felt 12, which is led through a
press nip formed by two press rolls 13 and 14. The press felt 12 is
an endless loop and is supported from the structure of the
web-forming machine, on turnover rolls 15. Correspondingly, there
are second means 16 in the dryer section, for transporting the web
11 being made on the web-forming machine onwards. In this case, the
second means 16 include a dryer wire 17 and a roll 18 arranged to
support it. A vacuum is also arranged inside the roll 18, which is
used to hold the web 11 on the dryer wire 17. In the arrangement,
there is an open gap 19 between the first and second means 10 and
16, across which the web is arranged to be transferred. FIG. 1
shows the web 11, which travels from the surface of the press roll
14 to the dryer wire 17, in the open gap 19. From the press roll
14, the web 11 is thus guided to the area of the vacuum roll 18, in
which the web 11 and the dryer wire 17 form a closing throat
20.
[0013] Before the open gap, in the direction of travel of the dryer
wire 19, the arrangement according to the invention further
includes deflector means 21, which are arranged on the side of the
loop formed from the dryer wire 17 opposite to the roll 18 (FIGS.
1, 2a, and 2b). In addition, the deflector means are arranged close
to the dryer wire, in order to restrict the air layer travelling
with the dryer wire, and thus to prevent an excess pressure forming
in the said closing throat. The deflector means are thus used to
remove, or other wise deflect a significant part of the air layer
travelling with the dryer wire. Particularly on the outer surface
of the loop, the air layer increases significantly in the
aforementioned position and causes problems in the open gap.
[0014] The amount of air transported by the dryer wire is affecting
by several factors, of which the most important are the speed of
the dryer wire and the open formation length. The air near the
surface of the dryer wire travels at the speed of the dryer wire
and the boundary layer tends to increase continually. To create a
sufficient preventive effect, the deflector means are arranged at
1-12 mm from the dryer wire. However, it is preferable to locate
the deflector means as close to the dryer wire as possible, so that
an increasing part of the boundary layer and particularly its
rapidly travelling portion can be removed. The location of the
deflector means relative to the closing throat also affects their
operation. Generally, it is preferable to install the deflector
means as close to the throat as possible, so that the formation of
a new boundary layer of air will be prevented. In other words, the
formation length will remain advantageously short. The distance of
the deflector means according to the invention from the point of
contact between the roll and dryer wire is less than 3000 mm,
preferably 50-1500 mm. The boundary layer of air restricted by the
deflector means will then no longer be able to increase again
before the throat.
[0015] The air layer can be restricted in various ways. Generally,
according to the invention, the deflector means are arranged to be
passive or active. Active deflector means are formed of elements
arranged to move or rotate, or of airflow devices. In FIG. 1, the
deflector means 21 is the aforementioned press felt 12, which
travels in the opposite direction to the dryer wire 17. The press
felt travels at a speed nearly as great as, but in the opposite
direction to that of the dryer wire, making the removal of the air
layer extremely effective. FIG. 2b too shows an active deflector
means 21, which in this case is an auxiliary roll 22 arranged to
rotate. The auxiliary roll is preferably rotated against the
direction of travel of the dryer wire. The effect of active
deflector means has, in practice, a specific reach. Nevertheless,
the aim is to locate the deflector means as close to the dryer wire
as possible. According to the invention, the distance of the active
deflector means from the dryer wire is 3-12 mm. The effect of the
deflector means will then extend as far as the dryer wire, thus
removing a substantial part of the air layer.
[0016] Correspondingly, passive deflector means are formed of air
baffles or doctors. As passive deflector means lack the reach
effect, they must be set closer to the dryer wire than active
deflector means. According to the invention, the distance of
passive deflector means from the dryer wire is 1-6 mm. Doctors, for
example, can even be set to touch the dryer wire. However,
deflector means that touch the wire require maintenance and may
wear the dryer wire, even if they are manufactured to conform to
the shape of the surface they touch. FIG. 2a shows an air baffle
23, which is used to guide a significant part of the air layer away
from the surface of the dryer wire. Particularly passive air
baffles can be easily installed with several one after the other.
This will remove the air layer in stages. The air baffle can also
be combined with a vacuum, by means of which air can be removed
from the position. Active and passive deflector means can also be
combined, or fitted after each other, thus preventing the greatest
possible part of the boundary air layer from travelling into the
closing throat.
[0017] The dryer wire also transports a certain amount of air on
its inner surface. The air in question travels into the closing
throat formed by the dryer wire and the roll and from there through
the dryer wire to the outside of the loop. As all excess air causes
problems in the open gap, that the arrangement further includes
runnability components arranged inside the loop formed from the
dryer wire. The runnability components are preferably fitted in
connection with the roll and are arranged to restrict the air layer
travelling with the inner surface of the dryer wire. This will
prevent both an excess pressure forming in the closing throat
formed by the dyer wire and the roll, and air permeating through
the dryer wire. In FIG. 2a, the runnability component 24 is a blow
box 25, which is used to create a blast 29 that restricts the
boundary air layer on the inside of the loop. At the lower corner
of the blow box, there is also a second blast 29, which is used to
create a vacuum inside the loop, which pulls the web being
transported on the under surface of the dryer wire onto the dryer
wire. Beside pulling the web, both blasts also remove air that may
have moved inside the loop. The same components as outside the loop
can be used inside the loop, though there is little installation
space. On the other hand, passive air baffles require only a small
installation space.
[0018] The blow box is fitted close to the dryer wire, in order to
achieve the most effective possible deflection effect. According to
the invention, the distance of the blow box 25 from the part of the
dryer wire 17 on the side of the deflector means is at most 50 mm,
preferably 5-20 mm. In addition, the operation and positioning of
the air baffle 23 also depend on the properties of the dryer wire
17. The air baffle is used to deflect the boundary layer on the
surface of the dryer wire to a desired place, to prevent the
penetration of the detrimental boundary layer between the roll 18
and the blow box 25. This will also prevent the web from detaching
from the under surface of the dryer wire. In the embodiment of FIG.
2a, the air baffle 23 acts essentially on top of the blow box 25.
In the situation in question, the air permeability of the dryer
wire is normal, i.e. about 1000-2000 m.sup.3/h/m.sup.2. At greater
permeabilities, the optimal location for the air baffle 23 will be
in the area between the roll 18 and the blow box 25.
[0019] FIGS. 1 and 2a show the roll 18 as being a vacuum roll that
is, as such, conventional, with a vacuum zone limited by seals 26
formed inside it. The vacuum effect acting through the perforated
jacket of the vacuum roll is directed through the dryer wire to the
web, which is thus made to follow the dryer wire. In FIG. 2b, the
vacuum zone is limited by a special vacuum box 27, which is sealed
to the surface of the vacuum roll 18. Thus a greater part of the
jacket of the vacuum roll than before will be subject to a vacuum
effect. At the same time, the blow box 25 restricting the boundary
air layer can be easily connected to the vacuum box 27.
[0020] In principle, the boundary air layer could be removed by
increasing the capacity of the vacuum roll. In practice, however,
this situation is impossible. The vacuum must be held at a certain
level determined by the properties of the web. The openness of the
jacket has already been optimized correspondingly while, on the
other hand, a lack of space often makes it impossible to increase
the diameter of the jacket. Making the vacuum roll larger will also
increase costs. Thus, according to the invention, the air layer, or
at least a significant part of it is removed before the open gap.
The vacuum roll can then be adjusted to suit the control of the web
while capacity will still remain for removing the rest of the
excess air. The arrangement is preferably set up in such a way as
to remove the air in a controlled manner and to eliminate air
currents that disturb the travel of the web. The number of
deflector means and their distance from the dryer wire and throat
are arranged case-specifically. In practice, the amount of air to
be removed using the vacuum roll depends on these factors. Thus, an
effective device set close to the dryer wire and the closing throat
will remove nearly all of the boundary air layer, thus preventing
the formation of an excess pressure in the throat.
[0021] In FIGS. 2a and 2b, the direction and magnitude of the
boundary air layer outside the loop are shown by arrows drawn with
a solid line. Correspondingly, the direction and magnitude of the
boundary air layer inside the loop are shown by arrows drawn with a
broken line. The dryer wire is shown with a broken line and the web
with a line of dots and dashes. In reality, the web lies on the
dryer wire, but for greater clarity the web is shown in the figures
as separate from the dryer wire.
[0022] Particularly the positioning of active deflector means close
to the dryer wire demands special care. Especially the meeting of
the press felt and the dryer wire should preferably take place at a
large angle, so that the fabrics will travel for a short distance
in opposite directions to each other. In addition, the rolls
supporting the fabrics are preferably set as close to each other as
possible, to minimize stretch in the fabrics. The deflector means
can then be brought advantageously close to the dryer wire, to
effectively remove the boundary air layer. Though they are very
close to the wire, deflector means that do not touch the wire will
not wear and, if they are taken into account beforehand in the
design, can even be implemented without additional costs.
[0023] The arrangement according to the invention can be applied to
all forms of production and to different positions. The boundary
air layer can be removed in different ways and in each case a
sufficient removal capacity will be achieved. The arrangement is
also economical to implement and it is simple to increase its
capacity as the production speed rises, for example. In addition,
the arrangement will operate with known vacuum rolls, as the
movement of the boundary air layer is limited before the throat, or
is removed entirely. The travel of the web is thus undisturbed and
production and quality problems are avoided.
* * * * *