Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND DEVICE FOR DRYING A FIBER WEB
The present invention relates to a method
for drying a fiber web using a two wire and two row
drying cylinder arrangement. The invention has
S particular use in a papermaking machine. The
invention concerns supplying air flows at, through or
near different parts of the loop path of the dryer
wire in the path between adjacent drying cylinders in
one row for effective web control. The invention
concerns a method and an apparatus for the carrying
out such a method related to the air flows.
The prior art includes U.S. Patent No.
5,379,526 (Fig. 2) and Federal Republic of Germany
44 04 726 (Fig. 6).
Constructions in the above cited prior art
have the following features in common:
1. Upon the web to be dried leaving a
"first" drying cylinder, the web first travels a
distance together with and is therefore supported by a
first wire generally up to a wire guide roll that is
off the row of the first drying cylinder wire and is
toward the other row of drying cylinders. After
leaving this guide roll, the web separates from the
wire and travels unsupported to the following "second"
drying cylinder which is part of the other row of
cylinders. Thus, the ~free web paths" or open draws,
i.e., the web travel paths over which the web is not
supported, are relatively short. This prevents the
danger of fluttering of the web and tearing of the
web. In regions where the paper web and/or the drying
wire do not rest on a closed surface, for instance, a
cylinder surface or a guide roll surface, they can dry
more or less undisturbed.
2. The drying wire coming from the first
drying cylinder in the first row wraps around the wire
guide roll. There the web separates from the wire.
Then the wire travels from the guide roll back to the
next "third" drying cylinder in the first row of
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cylinders, thereby forming a loop of the wire or a
pocket. This loop contains a so called air guide box.
3. A sealing element supported by the air
guide box prevents a layer of boundary air from being
drawn into the loop. That layer of boundary air is
carried along by the wire traveling over the first
cylinder.
4. A second region of the wire loop
extends from the guide roll to the third drying
cylinder. In the second region, the drying wire is
not covered by the web. A second flow of air is
required in the second region to ventilate the so
called "pocket", i.e., the region between the drying
wire and the web of paper that is spaced away from the
wire and that is traveling onto the next, i.e., third
cylinder. The second flow of air blows through the
drying wire. This so called pocket ventilation is
effected in Fig. 6 of Federal Republic of Germany '726
by means of a blower which is arranged in the "run-off
gussetH between the wire guide roll and the departing
wire.
In many cases, it has been found that the
known method of producing a vacuum along the first
part of the wire loop, between the first cylinder and
the guide roll and/or the known method of ventilating
the pocket are not sufficient.
The operating speeds of modern papermaking
machines have greatly increased in recent years. Some
are now operating at a speed of 1800 m/min. and more.
This makes it necessary to increase the drying
performance of each drying cylinder and thus to
increase the amount of drying air necessary for
removing the vapors that come off the web as it is
dried. To do this, more air must be forced into the
pocket through the uncovered drying wire. At the same
time, despite the greater web travel speed, the web
travel must be as stable and quiet as possible.
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The object of the present invention is to
obviate or mitigate the above disadvantages of the
prior art.
A web drying apparatus, e.g., for a paper
web, includes several heatable drying cylinders
arranged in at least one row over which passes at
least one endless loop drying wire, and the drying
cylinders may be arranged in two rows of cylinders,
each row with a respective drying wire. A wire guide
roll is located between and offset from two of the
adjacent cylinders in the one row. The one endless
loop dryer wire carries the web thereon on a first
part of the loop path from the first cylinder to the
wire guide roll. There the web separates from the
wire, and the web travels to a second cylinder in the
second row. The wire does not travel to the second
row but instead wraps around the wire guide roll and
returns on a second part of the loop path to the next,
third cylinder in the first row, without supporting a
web along the second part. On the path between the
first and third cylinders and around the wire guide
roll, the wire defines a loop.
An air guide box and a blower are arranged
within the wire loop. The air guide box produces a
vacuum at the first part of the wire loop path for
drawing the web against the wire. An air channel
extends between the air guide box and the blower. At
least one drive nozzle outlets into the air channel.
The air channel draws air out of the first part of the
loop path to create the vacuum there. The blower
directs a stream of air through the wire at the second
part of the wire loop path, and the air blows into a
pocket outside the second part of the wire loop path.
The drive nozzle and the blower are supplied by
independently controlled flows of blown air.
A stream of air under pressure is fed solely
to the blower in order to intensify the ventilation of
the pocket in accordance with prevailing requirements.
Independently, a second stream of air makes the vacuum
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present in the first part of the loop path adjustable
by means of a drive nozzle, again in accordance with
the prevailing requirements. For this purpose, an air
channel extends from the first part of the wire loop
between the air guide box and the blower. This air
channel is known from the aforementioned publications.
In the known arrangements, however, the same air
channel not only draws air out of the first part of
the loop path but also ventilates the pocket.
However, this may not ventilate the pocket to a
sufficient extent. In contrast, the method and the
apparatus of the invention provide the advantage that
the blower can be acted upon by an air throughput
which is as high as desired in order to intensify the
ventilation of the pocket as much as desired. The
division of the system into two individual systems is
also advantageous because their individual functions
can now be controlled individually.
BRIEF DESCRIPTION OF THE DRAWING
Other objects and features of the invention
will be apparent from the following description and
the accompanying drawing in which:
Fig. 1 is a diagrammatic longitudinal
section through a two wire drying cylinder
arrangement, showing one wire and two associated
cylinders and a roll.
The paper web 7 to be dried and the drying
wire 8 travel together off a first cylinder 4 in a
first row of cylinders. On the side of the drying
wire facing away from the drying cylinder 4, a layer
of boundary air 9 is entrained. It is deflected by a
seal 10 at the top of the air guide box 11 which is in
the pocket defined by the adjacent top row cylinders
4, 5 and by the wire guide roll 6 which is off the
first row of cylinders and toward the second row
thereof. The drying wire and the paper web now travel
together in the direction from the first cylinder 4
toward the drying wire guide roll 6.
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The paper web 7 travels unsupported from the
drying wire guide roll 6 to the next in the web path,
second drying cylinder of the second row of cylinders,
which is not shown, but is known from the conventional
two row design. See the above references incorporated
by reference.
The air guide box 11 feeds the drive nozzle
17 with air via line 18 and channel 13a. The flow of
air subsequently into the channel 23 creates and
exerts vacuum on the wire loop first region 1. In
this way, in the region 1, the paper web 7 is
supported on the path between cylinder 4 and drying
wire guide roll 6 by the drying wire 8. Furthermore,
vapors which escape from the drying wire 8 in this
region are transported away. These masses of air pass
through the channel 23 into the region 3, where they
can flow off undisturbed. A part thereof may possibly
also enter the pocket T through the second part of the
wire loop path.
A further part of the apparatus, namely the
blower 15, has a separate air path from the part
described above. The blower 15 is arranged at the
"bottom" of the loop and therefore in the direct
vicinity of the wire guide roll 6. It has a plurality
of blow openings which are directed through the wire 8
into the pocket T. The blower 15 is provided with
compressed air via a line 19 and channels 13 and 14.
However, it is also possible for the blower 15 to have
a lateral compressed air connection of its own. In
that case, no connecting channels 14 are required
between the support tube 11 and the blower 15.
As another alternative, there may be a
common source of compressed air connected to the lines
18 and 19 and their respective channels, and for
control then, there would be an adjustable choke for
the channel from the drive nozzle.
The gusset shaped region 2 of the loop
(defined between blower 15, wire guide roll 6 and wire
8) is limited by sealing elements 16 and 17a. The one
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seal 16 extends along the path of travel of the wire 8
and the other seal 17a extends along the wall of the
wire guide roll 6.
The Figure shows a few other preferred, but
not absolutely necessary, features. The air guide box
11 has a pipe 12 as a supporting element. The inside
of the pipe is divided by a partition 22 into two
halves which form the channels 13 and 13a. The
channel 14 rigidly connects the blower 15 with the
pipe 12.
Although the present invention has been
described in relation to a particular embodiment
thereof, many other variations and modifications and
other uses will become apparent to those skilled in
the art. It is preferred, therefore, that the present
invention be limited not by the specific disclosure
herein, but only by the appended claims.
