Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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P/563-7
DEVICE FOR DRYING A RUNNING WEB
BACKGROUND OF THE INVENTION
The present invention relates to a device for
drying a running web, for example, the drying section of
a paper manufacturing machine. A drying section is
disclosed in DE 43 28 554 A1 and is divided into a
plurality of successive cylinder groups. Each of these
: cylinder groups comprises, as a rule, a plurality of
heatable drying cylinders which come into contact with
the web and which are coupled, for example, via
gearwheels and/or an endless supporting belt ("felt"), to
a common drive which determines the operating speed of
the cylinder group.
The above German patent document DE 43 28 554
A1 discloses that, as also in the subject matter of the
present invention, in the initial region of a drying
section, preferably a plurality of single-felt cylinder
groups are provided, which can be of quite different
design. In the end region of the drying section, on the
other hand, at least one two-felt cylinder group is
provided. For the most part, two (or three) of this type
of two-felt cylinder groups are preferred, of which each
has an upper and a lower row of cy~inders, the web
running alternately over the upper and the lower
cylinders. From cylinder to cylinder, a free,
unsupported web path is provided. Each two-felt cylinder
group has in turn a drive of its own. The term "felt"
also includes the porous (endless) drying fabrics mostly
customary today.
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The present invention is concerned with the
problem of the threading of the paper web into a paper
manufacturing or paper processing machine (for example at
start-up of the machine or after an unintentional break
of the paper web). This threading of the paper web is
carried out mostly, as is known, at full operating speed.
When, during threading, the paper web has reached a
determined position, for example, the end of the drying
section, it is first led, as is known, as broke down into
_ 10 a broke pulping system. At the same time, at one of the
' two web edges, an initially narrow web part ("edge
strip") is severed from the web by means of a tail-
cutter. Initially, only said edge strip is transferred
to the following units (for example, calendar and winder
or coating units). The tail-cutter then runs to the
other web edge, so that the transferred web part finally
has the full web width. Normally, the tail-cutter is
arranged in the end region of the two-felt cylinder group
or of the last two-felt cylinder group; see Figure 1, 12
or 13 of the above-referred to DE '554.
The above-described method is practiced in
numerous paper machines, mostly with good success, even
in manufacturing machines with relatively high operating
speeds. However, it is desirable to be able to carry out
the transfer of the paper web from the drying section
into the following units with even greater reliability
than previously. In this case, it is to be taken into
account that, in many cases, the operating speed is
intended to be increased even further, approximately to
the order of magnitude of from 1600 to 2400 m/min. In so
doing, the risk that the paper web breaks during tail-
cutting is increased. In such an event, an additional
difficulty is that the large quantities of broke
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accumulating in a short time do not always reliably
automatically reach down into the broke pulping system,
but instead scraps of broke from time to time remain
unchecked in the drying section.
SUMMARY OF THE INVENTION
The invention is based on the object of further
developing and improving a drying device for drying a
running web, for example, the drying section of a paper
_. manufacturing or processing machine, with the effect that
~ 10 the risk of web breakage during tail-cutting is
eliminated as far as possible, even at the ever increas-
ing operating speeds. This is primarily true for the
drying section of paper manufacturing machines, but also
for drying devices of paper processing machines, for
example, coating machines.
The above and other objects are achieved by a
device for drying a running web, in particular, a drying
section of a paper manufacturing or paper processing
machine, comprising: a plurality of successive cylinder
groups, each cylinder group having an individual drive,
at least one cylinder in each group being heatable and
comprising a drying cylinder and coming into contact with
the running web; at least one of the cylinder groups
comprising a two-felt cylinder group, wherein the web
runs in serpentine fashion alternately over upper
cylinders, felted above, and lower cylinders, felted
below; at least one additional cylinder group adjacent
the two-felted cylinder group and provided with an
additional drive; a free web path unsupported by a felt
provided between the two-felt cylinder group and the
additional group; and a tail-cutter disposed at the free
web path.
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Preferably, in the device of the invention, the
drive of the two-felt cylinder group and the drive of the
additional cylinder group following the two-felt cylinder
group are connected to a common control unit which allows
a ratio between an operating speed of the additional
cylinder group and an operating speed of the two-felt
cylinder group to be set to a specific value. Preferably
the ratio for normal long-term operation is a different
value than the ratio when tail cutting.
Further, in the device of the invention, the
common control until preferably comprises means for:
a) in normal production operation, allowing
the setting of an operating speed in the
additional cylinder group which is equal
lS to or slightly smaller than the operatingspeed of the two-felt cylinder group; and
b) during operation of the tail-cutter,
allowing the setting of an operating speed
in the additional cylinder group which is
slightly higher than during the normal
production operation, thereby setting a
web longitudinal tension necessary for
tail-cutting.
It is essential that a free web path, which is
in the region of the end of the drying section and
wherein the longitudinal tension of the web can be set
for the requirements of the tail-cutting, be present for
the positioning of tail-cutter.
It is common to the different variants of a
first group of exemplary embodiments of the invention
that the free web path be provided for the tail-cutter
always at the end of a two-felt cylinder group. By this
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means, important advantages of the drying sections
disclosed in the above described DE '554 are maintained,
specifically:
1. Uniform paper quality, especially
identical or almost identical surface
properties on both sides of the paper.
2. Even when a very high final dryness
content is sought (of the order of 98 ~),
'~ there is no risk of paper web breaks,
since longitudinal tensions can be
dissipated in the two-felt cylinder group.
3. Compared with drying sections which
exclusively have single-felt cylinder
groups, the wear on the felts (drying
fabrics) is significantly less.
The free web path for the tail-cutter can (but
need not) be a so-called felt separation point; in this
case, the felts of the two-felt cylinder group run back
from this point to the beginning of the respective group.
This means that the following additional cylinder group
has at least one additional felt of its own, which guides
the paper web further after the felt separation point.
In a further variant of the first group of
exemplary embodiments of the invention, the free web draw
for the tail-cutter lies at the point where at least one
of the two felts of the two-felt cylinder group bridges a
separation point between two drive groups. In other
words: the felt (or the felts) bridges (or bridge) the
"boundary" between the two-felt cylinder group and the
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following additional cylinder group. Preferably, the
"boundary" is bridged by only one of the two felts. This
means that at this "boundary", one of the two felts of
the two-felt cylinder group runs back to the beginning of
the same. In these cases, the other of the two felts is
ex'ended and runs additionally over the cylinders of the
additional cylinder group, which is here a single-felt
cylinder group (having its own drive). In this case,
this extended felt is somewhat stretched at the
"boundary" by the drive of the additional cylinder group,
~~ if the paper web is intended to be tensioned during tail-
cutting. This stretching of the felt disappears again,
however, at the latest when the felt runs back to the
beginning of the two-felt cylinder group.
The additional cylinder group following the
tail-cutter can comprise quite a different number of
cylinders. In many cases, one to three cylinders are
sufficient. However, this number can be raised from four
to, for example, eight cylinders in the event that the
final dryness content of the web is intended to be
extremely high, for example 98%.
The above-described summary of the invention,
relating to the variant in which one felt bridges the
separation point between two drive groups, can also be
applied in a second group of exemplary embodiments. In
these embodiments, two neighboring cylinder groups may be
provided, of which each has a drive of its own; each of
these cylinder groups can have a plurality of cylinders,
in the extreme case, however, only a single cylinder may
be provided in each group. All cylinders of the two
groups come into contact with the same side of the web;
this is because only a single endless felt is associated
with them. This felt must also bridge the boundary
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between the two cylinder groups. It can also be said
that what is described is one single-felt cylinder group,
which is divided into two drive groups. The exact
nomenclature is unimportant, since the same device is
being described with different terminology. At the
boundary between the two drive groups, the felt runs from
one of the cylinders over a felt guiding roll, directly
to the next cylinder, while the paper web makes a detour
over an additional unfelted roll (or cylinder) before it
reaches the next cylinder. Consequently, in the region
of the boundary, a free web path is present for a tail-
cutter, wherein the web longitudinal tension can be set
to an optimal value for the tail-cutting, due to the two
separately controllable drives.
Drying devices of this type according to the
invention can be applied primarily (but not exclusively)
in paper processing machines, for example, coating
machines.
Other features and advantages of the
present invention will become apparent from the following
description of the invention which refers to the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWING(S)
Figures 1-3 show schematic side views of a
plurality of different drying sections of paper
manufacturing machines according to the invention;
Figure 4 shows the end region of the drying
section according to Figure 3 on an enlarged scale, with
some additional details relating to the control of the
individual drives;
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Figures 5-8 are schematic side views of the end
region of further different drying sections according to
the invention;
Figure 5' shows an embodiment in a schematic
side view of the end region of a drying section which is
a variant of that shown in Fig. 5;
Figure 9 shows a paper coating machine with the
associated drying cylinder groups according to the
invention; and
_q Figure 10 shows a further embodiment of the
~ '7 invention.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
With reference now to the drawings, the drying
section shown in Figure 1 first has six single-felt
cylinder groups (11-16) arranged one behind the other.
Each of these cylinder groups has a respective single
endless felt F. As an example, in the first cylinder
group (11), the felt F runs together with the web (9)
alternately over drying cylinders (51) and over
deflection rolls (51'), which are preferably designed as
suction rolls. In the first two cylinder groups (11) and
(12), and in the fourth and in the sixth cylinder group
(14, 16), the underside of the web comes into contact
with the cylinders. Correspondingly, the drying
cylinders (51, 52, 54, 56) are here above the associated
deflection suction rolls (51', 52', 54' and 56'); the
cylinders are here described as "felted above". It is
otherwise, however, in the third cylinder group (13) and
in the fifth cylinder group (15): here the cylinders (53,
55) come into contact with the upper side of the web;
they are therefore "felted below" and are beneath the
associated deflection suction rolls (53', 55').
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Consequently, the separation points present between the
cylinder groups (12) to (16) are designed as so-called
turning separation points. With reference to the details
of these turning separation points, specific reference
may be made to German Patent Application P 43 11 351.
It can be seen from Figure 1 that, at each of
these turning separation points, the paper web (9) forms
a short open draw; that is to say it is temporarily not
supported by a felt. It runs in the region of a small
suction zone of a transfer roll (58) onto the next
respective felt. In Figure 1 these transfer rolls (58)
are individual suction rolls with internal stationary
suction boxes. The deflection suction rolls (51'-56')
are, in contrast, free from inner stationary built-in
fittings and from direct suction connections. Instead,
an external suction box (59) is provided on each of these
deflection suction rolls. This suction box (59) lies in
the so-called pocket between two neighboring drying
cylinders and has, at the point where felt F and web (9)
together leave the first of these two cylinders, a strip
(not visible in the drawing), which strips off and
deflects the air boundary layer transported along by the
felt.
After the last single-felt cylinder group (16),
there follows a two-felt cylinder group (17) with several
lower cylinders (57) and several upper cylinders (57'),
and with a lower felt UF and an upper felt OF. Here the
web (9) runs in serpentine fashion alternately over the
lower and upper cylinders. Thereafter, the web runs over
a free web path, on which a tail-cutter S is arranged, to
an additional cylinder group (18). This comprises two
commonly driven but individually felted cylinders (58,
58').
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inclined forwardly. Between the lowest cylinders of
these two cylinder groups (33, 34) a gap can be opened,
for the purpose of removing broke downwardly, by means of
a pivotable felt guiding roll (87).
The fifth cylinder group (35) has, again,
drying cylinders (85) felted exclusively above, which
again form a V-shaped double row. After the last
cylinder of this cylinder group (35), the web is led
obliquely downwardly to the first lower cylinder (86) of
the following two-felt cylinder group (36). Following
this cylinder group there is once again an additional
cylinder group (37) and a tail-cutter S. The free web
path for the tail-cutter S runs from below upwardly.
Consequently, the cylinder group (37), which preferably
has two cylinders (87) and a deflection roll (87')
between them, is felted above. This simplifies the
guiding of broke away from the cylinders (87) in a
downwardly direction.
In contrast to the above-described DE '493, all
the deflection suction rolls (81'-85'), which are
arranged in the respective cylinder group between two
cylinders, are arranged at an increased distance from
these cylinders and are e~uipped with external suction
boxes. This constructional method Gan be manufactured
not only at lower cost; it is, moreover, also energy-
saving; this is because an extended free evaporation path
is present between each two cylinders, so that the drying
is more economical. The latter comments are also valid
for the arrangement according to Figure 1.
Deviating from Figure 3, instead of the fifth
single-felt cylinder group (35) present there, a (two-
row) two-felt cylinder group (similar to the group 36)
can be provided.
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Fig. 4 shows details of the cylinder groups 36
and 37 of Fig. 3. In Fig. 4, it is schematically
indicated that, in the two-felt cylinder group (36), the
two last cylinders (an upper and a lower cylinder) have a
common drive (38) having a motor M. The other cylinders
of the two-felt cylinder group (36) are, for example,
driven via the felts (OF, UF) or by means of an
additional drive, not shown. The additional cylinder
group (37) has likewise a drive (39) of its own having a
motor M'; it could also comprise more than only two
cylinders 87, as is indicated with two dotted circles
87". The diameter of the cylinders 87 can be smaller
than or equally large as or preferably larger than the
diameter of the cylinders 86/86'.
Both motors are connected independently of each
other to a control unit 40. By this means, according to
requirements, the operating speed ~f the additional
cylinder group 37 and the operating speed of the two-felt
cylinder group 36 can be set in a specific ratio to each
other, so that a web longitudinal tension favorable for
tail-cutting is produced in the free web path. A
reliable operation of the tail-cutter S is thus achieved.
In particular, web breaks during operation of the tail-
cutter can be avoided. During normal production
operation, however, a somewhat different ratio between
the motor operating speeds can be set than during the
tail-cutting, if desired, for the purpose of dissipating
longitudinal tensions in the web (9).
According to the embodiment of Figure 5, a two-
felt (depicted partially) cylinder group 90 and an
additional single-felt (depicted partially) cylinder
group 91, felted above, are provided. The last cylinder
92 of the two-felt cylinder group 90 is in the upper row
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of cylinders and is therefore felted above. So that the
paper web 9 to be dried changes over from the two-felt
cylinder group 90 to the single-felt cylinder group 91,
the felt 93 of the single-felt cylinder group contacts a
small part of the periphery of the cylinder 92. Shortly
before this, felt 93 runs over an adjustable guiding roll
94. For tail-cutting, this roll 94 is brought into the
position represented with a chain-dotted line, so that
the felt runs directly from the roll 94 to the first
deflection roll 9S (which can be a suction roll). By
this means, the paper web 9 runs without support of the
felt 93 from the cylinder 92 to the deflection roll 95.
Therefore, the tail-cutter S can be arranged in this free
web draw. This type of tail-cutter arrangement has
similarities with that according to US Patent 5,248,390.
A further advantageous tail-cutter arrangement
is shown in Figure 5'. Figure 5' differs essentially
from Figure 5 by the following features: the paper web 9
runs from the last cylinder 92 of the two-felt cylinder
group 90 permanently over a free web path to a suction
guiding roll 95 and is there sucked onto the felt 93 of
the following single-felt cylinder group 91 by means of
vacuum. This felt 93 then guides the paper web in a
known way through the group 91. The tail-cutter S is
once more arranged in the region o~f the free web path.
The embodiment of Figure 6 differs from
Figure 4 essentially only in that the two-felt cylinder
group 36' and the additional cylinder group 37' (which is
a single-felt cylinder group, felted above) have a common
upper felt OF'. The drives 38 and 39 are, nevertheless,
designed as shown in Figure 4.
The embodiment according to Figure 7 has
similarities with the end region of the drying section
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according to Figure 1. While in Figure 1 each of the
cylinders 58, 58' of the additional cylinder group 18 has
a felt of its own, the following is provided in Figure 7:
both cylinder groups 17' and 18' each have a common upper
felt OF' and a common lower felt UF'. Nevertheless, each
of the cylinder groups 17' and 18', as in Figure 4, has
its own drive 38' and 39'. The tail-cutter S is once
more arranged where the paper web 9 changes over from the
last cylinder of the cylinder group 17', on a free web
path, to the first cylinder of the cylinder group 18'.
' The embodiment of Figure 8 has similarities
with that of Figure 6. Once more a two-felt cylinder
group 36'' and an additional cylinder group 37'', felted
above, are provided and both cylinder groups have a
common upper felt OF'. The additional cylinder group
37'' includes as an example, three drying cylinders and a
grooved deflection roll between each two cylinders. In
the two-felt cylinder group 36'', the felt guiding rolls
are arranged in such a way that the free web paths from
cylinder to cylinder are shortened. So that the free web
path for the tail-cutter S is also as short as possible,
there is, between the last upper cylinder of the cylinder
group 36'' and the first cylinder of the additional
cylinder group 37'', a felt guiding-roll 99, of
relatively large diameter, over which the upper felt runs
and to which both web paths are tangential.
Figure 9 shows a paper coating machine with the
associated drying cylinder groups according to the
invention. As is illustrated in Figure 9, a material web
101, for example, a paper web from a plurality of drying
cylinders groups as shown in Figures 1-3, runs over web
guiding rolls 102 to 107 into a first coating station
108. The coating station 108 comprises an application
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roll 110, a counter-roll 111 lying opposite the latter
and forming a press nip with it, and an applicator 113.
Downstream of the first coating station 108
there is a web guiding roll 112 which deflects the
material web running out of the press nip from its
direction running obliquely upwardly into an essentially
vertical direction upwardly. In this way it reaches an
infrared dryer 115 and is then guided over two further
web guiding rolls 116 and 117 through a hot-air dryer
118. The material web is subsequently delivered to a
first contact drying cylinder arrangement 121 via web
guiding rolls 119 and 120.
Associated with the arrangement 12i is a row of
at least two drying cylinders 122, 124, felted below,
which have drives controllable independently of each
other, but a common lower felt 123. The felt runs, inter
alia, over a felt guiding roll 125 arranged between the
two cylinders. The paper web leaves the lower felt at
the felt guiding roll 125 and runs freely to a paper
guiding roll 126 additionally provided and from the roll
126, past the position of the tail-cutter S, to the
cylinder 124. If necessary, the paper guiding roll 126
can have its own drive. In the exemplary embodiment
shown, the two motors M of the cylinder 122 and of the
paper guiding roll 126 are coupled to a central control
unit 40 via a common control lead i27. However, these
two motors can also be controllable independently of each
other.
It is important that the second cylinder 124
has a drive of its own with a motor M' which is coupled
to the central control unit 40 via a separate control
lead 128. If necessary, yet another following felt
guiding roll 129 can be provided with a drive M'.
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The web 101 runs from the cylinder 124 to a
further cylinder 130, felted above, and thereafter to a
second coating station 108', which is designed
essentially as a mirror-image of the first coating
station 108. The components corresponding to each other
are provided with the same designations in the drawing
figure.
After leaving the coating station 108', the
material web 101 again passes an infrared dryer 115. It
is subsequently fed into a hot-air dryer 131 via a
deflection device 139, operating without contact with the
web. From here, the material web 101 runs over a
spreading roll 138 into a second contact drying cylinder
arrangement 140.
The latter comprises once again two drying
cylinders 132, 134, which can be driven independently of
each other, having a single felt 133. This runs between
the cylinders over a felt guiding roll 135, on which the
paper web 101 once again leaves the felt, in order to run
freely to the paper guiding roll 136 and from there to
cylinder 134. Once again, by means of the mutually
independent drives of the two cylinders 132 and 134, the
web longitudinal tension can be set appropriately at the
position of the tail-cutter S.
Figure 9 shows yet anoth;er alternative tail-
cutter position S' between the spreading roll 138 and the
drying cylinder 132.
It is to be understood that each of the tail-
cutters S can become effective only when the paper web
101 at full web width has reached the position of the
tail-cutter. Before this, the paper web also runs here
initially only in the form of a narrow edge strip through
the coating machine. In order to thread this narrow edge
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strip properly, a rope feed known per se is present (as
usual on coating machines). This comprises two endless
ropes, for example shown symbolically at 141 and 142 in
Figure 9, which run along the route of the web 101 over
the cylinders and guiding rolls (for example over 122,
125, 126, 124 and 130) and, in so doing, draw the
arriving point of the edge strip into the machine. Also
dispensed with are special, for example pneumatic,
auxiliary devices, which would be necessary for rope-less
_; threading of the edge strip.
; It is further noted that in the additional
cylinder groups, e.g. 18, 26, 37, 91, etc., at least one
cylinder can optionally be heated, e.g. by steam, or
cooled, e.g., by a suitable cooling medium. Furthermore,
at least one cylinder can alternatively be heated or
cooled, depending on the specifications of the different
paper grades to be manufactured.
In Figures 9 and 10, a pocket in the web formed
by the guiding rolls 126, 136 is provided where the tail-
cutter S is arranged. The advantage of the configuration
shown in Figures 9 and 10 is that the free web path
(where the tail-cutter will cut into the web) is
relatively short. Nevertheless, the pocket is large
enough to arrange the tail-cutter at the pocket. A
relatively short web path improves the reliability of the
tail cutting process, i.e., the risk of web breaks during
tail cutting is minimized. This configuration can also
be used without requiring that all the cylinders have
individual drives.
Although the present invention has been
described in relation to particular embodiments thereof,
many other variations and modifications and other uses
will become apparent to those skilled in the art.
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Accordingly, the present invention should be limited not
by the specific disclosure herein, but only by the
appended claims.
Addition to the description o~ Fig. 9
At Sa, a ~urther alternative tailcutter position is shown,
namely between the last one 124 o~ the bottom ~elted cylin-
ders and the single top felted cylinder 130. In that case,
~elt guide roll 125 would be omitted; ~elt 123 and web 101
would commonly travel across roll 126.
I~ paper guide roll 136 has its own drive, the two motors (not
shown) o~ ~irst cylinder 132 and paper guide roll 136 may be
commonly coupled to a central control unit ~also not shown) so
that they are commonly controllable but indëpendently o~ the
motor o~ the second cylinder 134.
