Note: Descriptions are shown in the official language in which they were submitted.
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MBT~OD AND APPAR~TU8 FOR DRYING
A PAPBR ~B IN A COATING ~AC~INB
BAC~GROUND OF THB I~nRNTION
The invention concerns a method for drying a paper web in a
~; coating machine, in Which method a paper web that has been coated on --
one side or on both sides iS run through the drying gap in a dryer
unit or units, wherein the web iS supported and drièd by means of air ~;
jets without being contacted by the dryers producing the air jets. ~ -
The invention further concerns a coating-drying device
intended for carrying out the method, comprising one or several
coating stations, a dryer or dryers placed after the coating station
and/or between subsequent Coating stations, these dryer/dryers being
éither plural gas nozzle web dryors and/or combined infrared and
plur41~gas nozzle web dryers through whose drying gap the web is
passed~supported by air and free`of contact With the dryers.
As~is~known in the prior a~rt,~problems have occurred in the
threading~oP the~papèr web in a~coating machine. In partlcuIar,
` ~ lem~s~have~occurred ln "on-machlne"~coat1ng machines, where1n the
~thre~dl~ng takes place at full speed, 1.e. the speed~may be up to 1500
~;` ~ min.`~ In~ways known in the prior art, a number of different modes
have been émployed for threading~of~ the web. In "on-machine"
ppara~u8es, the threading of the web~has been accomplished by means
~of guiding;~ rope8.~ A180, ln prior~art apparatuses, flat belts
~;similar`to~ropes~or~a~ pUsh-button" blow plate have been used.
~: Moreover,~ as is known in the pr10r~art, it has been possible to carry
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out the threading manually by using a low running speed, especially
in "off-machine" coating machines. A little used structure for
threading of the web is based on flying reel exchanges.
In the prior art, in "on-machine" apparatuses, the threading
of the web by means of threading ropes has been accomplished as
follows: At the edge of the paper web at the operating side, double
ropes placed one above the other and guided by pulleys revolve, the
cut leader of the web being guided into the inlet nip between these
ropes. The ropes lock the leader between them and carry it through
the machine. In a paper making machine the apparatus of threading of
the web based on threading ropes operates well when the adjustments
are correct. However, the structure based on threading ropes does
not operate adequately in a coating machine. For example, problems
of the following types occur in the prior art: The threading ropes
are worn and stretched and may thereby cause operating problems and
standstills. The use of threading ropes for threading of the web
requires experienced operating personnel, for the threading by means
of threading ropes is, in itself, not easy to accomplish. Threading
of a web by means of threading ropes operates well when the speed of
the paper web is lower than 1000 m/min. At higher speeds problems
occur, as a result of which the times taken by breaks become longer.
During threading, the leader becomes dry, whereby the susceptibility
to breaks become higher. Moreover, in threading taking place by
means of threading ropes, rapidly revolving parts are employed, which
may cause problems of safety during work. A system of ropes also has
a complicated construction and is expensive to carry out.
; As is known in the prior art, for guiding the paper web on a
coating machine and in particular for leading the web, tension rolls
have been used. These tension rolls have been cooled teflon-coated
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chromium leading rolls or cylinders, which are expensive both with
respect to their material and with respect to their cost of
manufacture. Moreover, in leading of the web carried out by means of
tension rolls, problems caused by formation of spots have occurred
because of the moistness of the paper web. Moreover, when coating is
carried out, the web must not contact the rolls, because in such a
case flaws might arise in the coating.
8UMHARY OF T~ INV~TION
Objects of the invention are to provide both a method and an
apparatus for guiding the paper web in a coating machine wherein the
above detrimental factors present in prior art methods and
apparatuses do not occur. Moreover, another object is to make the
invention suitable for other applications of a coating machine as
well as threading.
The prior art apparatuses based on contact-free handling of
the web consist of a number of nozzle boxes, out of whose nozzles a
gas flow that supports and/or dries the web is applied to the web.
The nozzle in these devices can be divided into two groups:
nozzles with positive pressure (float nozzles) and nozzles with
negative pressure (foil nozzles). The operation of the nozzle with
positive pressure is based on the air cushion principle. The nozzles
with negative pressure attract the web and stabilize the run of the
web, whereby the tensile force applied to the web is based, as is
well known, on a gas flow field parallel to the web, this flow field
forming a static negative pressure between the web and the carrier
face of the nozzle.
Both in nozzles with positive pressure and in nozzles with
negative pressure, the coanda effect is employed in order to guide
air in the desired direction.
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With a view to achieving the objects stated above and those
that will be explained hereinafter, the method in accordance with the
invention mainly comprises both the threading of the leader of the
web and the supporting and guiding of the full width web being
carried out by means of contact-free gas nozzle web supporting and
drying devices, wherein, at least in the area of the leader, most
appropriately over the entire width of the web, blowings directed
along the direction of runn~ng of the web are employed.
Moreover, the apparatus in accordance with the invention
comprises dryer units and, in connection with the dryer units, a
contact-free guide device or guide devices based on air support,
which device(s) operate~s) both as means for threading the leader of
the web and as support and guide means for a full-width web.
By means of the guide device in accordance with the present
nvention, the present day threading ropes are replaced. The device
in accordance with the invention is not sensitive to wear, as are the
threading ropes, and, moreover, the device in accordance with the
invention is also useful in other applications, besides during the
threading of the web. By means of the device in accordance with the
invention, the leading and spreading rolls present in the prior art
apparatuses are substituted for.
Air is blown during threading of the web in accordance with
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the invention, and thereby evaporation is promoted. If necessary, it
is also possible to use warm air. According to the invention, it is
also possible to accomplish threading of the web starting from the ;
middle thereof, and by regulating the moisture of the air it is
possible to prevent drying of the web and the resulting increased
susceptibility to breaks during threading of the web.
In the guiding of the paper web in accordance with the
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invention, the paper web does not contact the leading members,
whereby no problem of formation of spots occurs. Thus, the apparatus
in accordance with the invention is well suitable for use in two
sided coating. Moreover, when an apparatus in accordance with the
invention is used, separate cylinders needinq cooling and related
complicated structures are not needed.
Nor has the device in accordance with the invention any
limitations with respect to machine speed and, moreover, when the
device is used, components that constitute safety risks are
eliminated from the coating machine.
BRIBF DF8CRIPTION OF T~ DRAWING8
In the following, the invention will be described in detail
with reference to a preferred exemplifying embodiment of the
invention illustrated in the Figures in the accompanying drawings,
the invention being, however, by no means strictly confined to the
details of these embodiments.
Figure 1 is a schematical illustration of a preferred
embodiment of the threading system in accordance with the invention.
Figure 2 is a schematical illustration of a guide device in
accordance with the invention.
Figure 3 is a schematical illustration of the threading
apparatus in accordance with the invention.
Figure 4 is a schematical illustration of the air flow of
the plural nozzle foil units of the invention.
Figure 5 i5 a schematical illustration of the air flow of a
guide device in accordance with the invention.
Figure 6 is a schematical illustration of a second preferred
embodiment of the threading apparatus in accordance with the
invention.
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Figure 7 is a schematical illustration of a preferred
embodiment of the device in accordance with the invention as applied
in a multicylinder dryer.
Dl~igi~RIPl!ION OF q~Ei PRI~FBRR13D ~MBODINI~NTEi
Fig. 1 shows a paper web guide apparatus in accordance with
the invention as app:~ied in a coating machine of the SYM-SIZER R
type (Applicant's trademark). The paper web W runs around but does
not contact the guide device 10 provided with negative pressure
nozzles and then runs toward the support nozzle 20, 20a. In the
Figure the IR (infrared) dryers are denoted with the reference
numerals 21, 21a. The paper web then runs between the plural nozzle
foil units 22, 22a whose nozzles concurrently blow on the web. The
direction of the air flow is denoted with the arrows F. The plural
nozzle foil unit 22a is provided with a curved guide end 23, which
guides the web, free of contact therewith, further along. Hereupon
the web has a short draw Wp without support blowings, the length L
of this draw being maximally 2 meters, most appropriately 0.5 to 1.5
m. Thereupon the paper web W meets another plural nozzle foil unit
25a provided with a curved guide end 24, as well as the plural nozzle
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foil unit 25. From there the paper web goes further to a multi -~
cylinder dryer, whose cylinders are denoted with the reference ~ ;~
numerals 50. According to the invention, the concurrent blowings F
guide the run of the web. As is shown in the Figure, the air flow F
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catches the end of the paper web from the guide device 23 and ejects
it to the next guide device 24, whose concurrent blowings F guide the
~; web further. In this way the paper web W is guided across the free~
draw Wp
The apparatus in accordance with the invention is uniform
across the entire width of the paper web W, and the apparatus can
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have nozzle adjustment to achieve a particular threading position, in
which only the blow width required by the lesser width leader is
employed, whereupon, when the web reaches its full width, the
apparatus is set into the guide position. The threading position may
be, for example, between the open closed positions of the nozzles.
Fig. 2 is a schematical illustration of a guide device which
is provided with negative pressure. The direction of the air flow is
denoted with the reference arrows F. Such a guide device 10 provided
with nozzles 11 of negative pressure attracts the paper web that runs
into its proximity. The negative pressure nozzles 11 with concurrent
blowings F are installed in compliance with the desired run of the
web, whereby the end of the paper web can be passed through the
coating machine without threading ropes. In a coating machine with a
threading and guide system in accordance with the invention, the
other guide devices and ends thereof 19, 23, 24, 26 have similar
structures.
The guide device 10 in accordance with Figure 2 extends
across the entire width of the web, and after threading it is used
for guiding the whole paper web W. The intensity of the blowings F
, . .
from the guide device 10 may be adjusted to be less when threading
the leader of the web than when guiding the width of the entire web.
Figure 3 is a schematical illustration of the concurrent
foil alrborne units 25 and 25a, both of which are provided with
guiding ends, the guide end 24 for the plural nozzle foil unit 25a
and the guide end 26 for the plural nozzle foil unit 25. In the
Figure, the negative pressure nozzles are denoted with the reference
numeral 11.
Figure 4 shows an air flow diagram of the plural nozzle
units in the paper web guide system in accordance with the
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invention. In the diagram the reference numerals 66 and 67 representthe air intake ducts for the compressed-air system. The reference
numerals 60 represent the blowers through which the air passes into
the heat exchanger 61. Through the intake duct 64 the compressed air
is passed to the inlet 62a of the plural nozzle foil unit 22a; 25a
and to the inlet 62 of the foil unit 22:25. Through the outlet 63a
and 63 of compressed air the air is passed out of the foil units
22;25 and 22a;25a, respectively. Through the outlet duct 65, the
compressed air is passed either through the exhaust duct 68 out of
the compressed air system or into the duct 67 in a partially closed
system circulation. By means of the cylinder 69, when necessary, the
plural nozzle flow unit 22a;25a can be shifted respectively to the
positions open-threading-closed.
Fig. 5 shows an air flow diagram of a guide device in
accordance with the invention. The compressed air is passed along
the intake duct 71 into the blower 70, from which it is passed
further through the duct 72 to the guide device or guide end
10;19:23;24;26.
Fig. 6 shows an application of the thread~ng system in
accordance with the invention in a blade-position arrangement of the
AUTOBLADE R type (Applicant's trademark). Being pulled by the
guide device 19 provided with a negative pressure nozzle, the paper
web W runs further between the IR dryers 21, 21a, being supported
further by the air flow F of the foil units 22, 22a, by passing the -;
curved guiding end of the foil unit 22a. After the free run Wp the
run of the paper web W is supported by the foil unit 25 provided with
a guiding end 24 as well as by foil unit 24a, which is also provided
with a curved guiding end 26 to guide the web. In this exemplifying ;;~
embodiment of the invention, the multicylinder dryer 40 is also
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provided with an airborne based paper web support device 41 for
guiding and threading as well as for threading of the paper web. The
lower wire in the multicylinder dryer 40 is denoted with the
reference numeral 51.
Fig. 7 shows a paper web support device 41 for a
multicylinder dryer 40, this support device being provided with a web
detaching jet nozzle 42 and with foil nozzles 43. The chamber for
equalization of excessive pressure is denoted with the reference
numeral 44, and the nozzle used for conditioning of the nip is
denoted with the reference numeral 45.
In the paper web guide system in accordance with the
invention, the plural nozzle foil units with concurrent blowing pulls
the paper web W and feeds it forwards. Owing to their nozzles with
negative pressure, the guide devices also attract the paper web
placed in their proximity. The threading in the cylinder part
requires twin wire draw if it is desirable to use the paper web
threading and guide device 41 in accordance with the invention in a
multicylinder dryer. The device in accordance with the invention is
as such not suitable for solutions with single wire draw.
In the following, the patent claims will be given, and the
various details of the invention may show variations within the scope
of the inventive idea defined in these claims.
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