U.S. patent number 3,868,780 [Application Number 05/412,463] was granted by the patent office on 1975-03-04 for group of drying cylinders in a multiple cylinder dryer for a material web, in particular for paper.
This patent grant is currently assigned to Valmet Oy. Invention is credited to Vesa Holopainen, Martti Koponen, Mauri Soininen.
United States Patent |
3,868,780 |
Soininen , et al. |
March 4, 1975 |
GROUP OF DRYING CYLINDERS IN A MULTIPLE CYLINDER DRYER FOR A
MATERIAL WEB, IN PARTICULAR FOR PAPER
Abstract
In a group of drying cylinders constituting of a multiple
cylinder dryer for drying a paper web or another equivalent
product, having a drying felt or drying wire which is common for
all drying cylinders of the particular group, arrangements serving
to eliminate the need of the web to travel unsupported between
drying cylinders and also to eliminate the objectionable feature of
arrangements of prior art, where a single drying felt or drying
wire has been provided for all cylinders of the group, namely, that
on every second drying cylinder the web is not interposed between
the cylinder surface and the felt or wire but, instead, the felt or
wire intervenes between the web and cylinder. The invention is
particularly, characterized in that by the aid of guiding rollers
or equivalent the drying felt or wire, together with the web, has
been guided to travel from one drying cylinder to the next cylinder
in the same group so that the drying cylinders all lie outside the
drying felt or wire loop, thus causing the web to travel between
the surface of the drying cylinder and the drying felt or wire in
every instance. The drying cylinders may be disposed in one or
several rows, preferably substantially parallel, the web being
conducted from the last cylinder in one row to the next drying
cylinder row. Various preferable placements of the guiding rollers
with reference to the drying cylinders are specified. It is further
suggested that the space formed within the felt or wire loop is
enclosed by means of side walls and a vacuum is maintained in this
space, in which case it is advantageous to make the guiding rollers
foraminous, whereby they are able to operate as traverse flow
dryers, and possibly to provide them with blowing hoods, which may
contain a heat source.
Inventors: |
Soininen; Mauri (Naantali,
SF), Koponen; Martti (Jyvaskyla, SF),
Holopainen; Vesa (Jyvaskyla, SF) |
Assignee: |
Valmet Oy (Helsinki,
SF)
|
Family
ID: |
8508103 |
Appl.
No.: |
05/412,463 |
Filed: |
November 2, 1973 |
Current U.S.
Class: |
34/116; 34/117;
34/123 |
Current CPC
Class: |
F26B
13/16 (20130101); F26B 13/08 (20130101); D21F
5/02 (20130101) |
Current International
Class: |
D21F
5/02 (20060101); F26B 13/16 (20060101); F26B
13/10 (20060101); F26B 13/00 (20060101); D21F
5/00 (20060101); F26B 13/08 (20060101); F26b
013/08 () |
Field of
Search: |
;34/116,117,111,123 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
158,236 |
|
Mar 1940 |
|
DD |
|
930,673 |
|
Feb 1948 |
|
FR |
|
Primary Examiner: Antonakas; Manuel A.
Assistant Examiner: Devinsky; Paul
Attorney, Agent or Firm: Richards & Geier
Claims
We claim:
1. In a multiple cylinder dryer for web material, a drying cylinder
group, comprising in combination
a plurality of heatable drying cylinders arranged to be rotatable
about their horizontal axis.
guiding rolls between consecutive drying cylinders,
an endless drying belt permeable to air, which is common to all
drying cylinders of the group, zigzagging from one drying cylinder
to the next drying cylinder in the group over the guiding roll,
for the drying belt, guiding means which together with said guiding
rolls direct the drying belt to travel so that all drying cylinders
of the group lie outside the loop formed by the endless belt and
said guiding rolls lie inside said loop,
means by which the web to be dried is directed into the drying
cylinder group so that on the drying cylinders the web will travel
between a sector surface of considerable extent of the drying
cylinders and the drying belt, and outisde of the drying belt when
traversing said guilding rolls,
and wherein the open sides of the drying belt are closed by walls
in order to produce a closed space inside of the drying belt, and
that in said closed space a vacuum has been arranged to act in
order that the web when traversing upon the drying belt is attached
to the same by suction,
the entire combination being so arranged that the drying belt
together with the web travels, with mutual contact between the two,
the whole distance from one drying cylinder to the next drying
cylinder group.
2. Drying cylinder group according to claim 1, characterized in
that the drying cylinders are disposed in at least one row, and
that the drying belt (8) and the web are guided to travel from one
end to the other of the row of drying cylinders from one drying
cylinder to the adjacent cylinder in the row.
3. Drying cylinder group according to claim 2, characterized in
that the group comprises two, substantially parallel, rows of
drying cylinders, the web being conducted from the last drying
cylinder in the row which is first in the direction of travel of
the web to the second drying cylinder row.
4. Drying cylinder group according to claim 2, characterized in
that said guiding rollers are disposed interjacent between two
adjacent drying cylinders in the row.
5. Drying cylinder group according to claim 3, characterized in
that the guiding rollers are disposed to be interjacent with the
drying cylinders disposed in a row, so that the planes passing
through their axes lie outside the planes passing through the axes
of the drying cylinders placed in a row.
6. Drying cylinder group according to claim 3 characterized in that
said guiding rollers lie so far outside the planes passing through
the axes of the drying cylinders that the planes passing through
the axes of the guiding rollers will lie outside the tangential
planes of the drying cylinders.
7. Drying cylinder group according to claim 2 having only one row
of drying cylinders, characterized in that the web has been
conducted from one drying cylinder group to the next, supported by
the drying belt of the first-mentioned drying cylinder group.
Description
The present invention concerns a group of drying cylinders in a
multiple cylinder dryer for a web, in particular for paper, having
a drying felt or wire which is common for all drying cylinders.
The cylinders in the dryer which dry the web are frequently placed
in two rows one above the other, and the web travels along a zigzag
path alternately under the lower cylinders and over the upper
cylinders. In the longitudinal direction of the machine the
cylinders are usually grouped to form a few drive groups, the
peripheral velocities of each cylinder being constant within one
such group. It is common practice to provide in each drive group
both for the upper cylinders and for the lower cylinders a felt or
wire loop of their own, which loops urge the web against the
surface of the cylinders. It is thus understood that the web has to
travel from one cylinder row to the other completely without
support. It may be specified as a characteristic feature of the
arrangement just described that as a rule the drive group comprises
two felt or wire loops, outside which the drying cylinders are
located and which, both separately, urge the web in the direction
of travel of the web against every second cylinder, that is, the
lower felt or wire urges it against the lower cylinders and the
upper felt or wire urges it against the upper cylinders.
Particularly in the course of the recent continuous increase of the
output of multiple cylinder dryers, that is of their breadth and
running speed, certain drawbacks of the construction just described
have become ever more appreciable.
1. The web passing over from one cylinder to another, which has no
mechanical support, is susceptible to suffer breaks particularly in
the wet condition. This susceptibility increases with increasing
speed, in which connection the tendency of the web margins to
flutter under effect of various disturbing factors quite often
increases. It has been found that this tendency is often in
machines provided with drying wires if the permeability of the
wires is too high and the placement of the rollers is unfavourable,
and the air currents produced by the wires in the interstices
between cylinders are strong, so as to increase the fluttering of
the edges.
2. In a multiple cylinder dryer a so-called "drying pocket" is
formed adjacent to each cylinder, which is a space open only at its
ends and confined by the bare cylinder surface, by the drying felt
or wire passing around the adjacent roller and by the web arriving
at and departing from the cylinder. It is a rather difficult task
to ventilate this space, and as a result of deficient ventilation
the drying process is often non-uniform and the ultimate product
has an objectionable moisture content profile. In order to rectify
this situation, auxiliary equipment for ventilating the pockets of
the dryer is frequently mounted within the pockets themselves in
machines having drying felts, or on their outside when drying wires
are employed. Such equipment is invariably impractical to a certain
extent and even tends to cause additional breaks or other kinds of
trouble, nor is its use successful in all instances, because it is
difficult to correct major moisture content errors.
3. In the event of a web break, waste material tends to remain in
the space between the drying felt loops, where the drying cylinders
are located, and its removal is not always easy, certainly not in
the case of machines having a great width. The fact that this space
in particular has to be watchable during operation and that,
especially in a machine with felts, air flows are present at the
ends of the drying pockets, forbids the practice of constructing
both longitudinal sides of the dryer as closed partitions. This
implies the necessity of using machine frame structures assembled
of beams and columns. These are permeable to air flows, for which
reason it is furthermore common practice to enclose the entire
multiple cylinder dryer in a hood--either an open or an enclosed
hood.
It is known in prior art to support the web between cylinders in
the manner disclosed by the U.S. Pat. No. 3,503,139. Instead of
providing for the upper as well as the lower drying cylinders of a
given drive group each their own drying felt or wire loop, outside
which the drying cylinders are positioned, as in the conventional
design solution, which was considered in the foregoing, any given
set (group) of drying cylinders in the multiple cylinder dryer
according to said patent has only one single felt loop, with one of
the two cylinder rows within this loop and the other cylinder row
remaining outside this loop. The web will then travel from one
cylinder row to the other under guidance by the felt. It is a
drawback, however, that on every second cylinder the web lies on
top of the felt, not between the felt and the cylinder. As a
consequence, in association with these cylinders the felt
constitutes an insulating layer between the cylinder and the web,
which impedes the heat transfer from the cylinder to the web. In an
attempt to compensate for this, it is suggested that in the
respective cylinders a higher steam pressure should be maintained.
This may possibly damage the drying felt lapping these drying
cylinders, yet without being able to increase the specific
evaporation (evaporation/cylinder surface area) to be on a level
with that of the drying cylinders whose surface is immediately
lapped by the web.
The aim of the present invention is to eliminate in multiple
cylinder web dryers the above-drawbacks, which have been
encountered in them. The invention is characterized in that, with
the aid of guiding rollers or equivalent, the drying felt or wire
together with the web has been guided to travel from one drying
cylinder to the next drying cylinder in the drying cylinder group
in such manner that the drying cylinders will lie outside the
drying felt or wire loop, in order that the web to be dried might
always be compelled to travel between the surface of the drying
cylinder and the drying felt or wire.
The drying cylinder group may comprise two substantially parallel
rows of drying cylinders, the web being directed from the last
cylinder in the row which is first in the direction of travel of
the web to the second drying cylinder row. The guiding rollers
belonging to the drying cylinder group may be placed between each
two adjacent drying cylinders in the rows. It is advantageous if
the guiding rollers are so disposed between the drying cylinders in
the rows that the planes passing through their axes lie outside the
planes passing through the axes of the drying cylinders, and most
appropriately so that the planes passing through the axes of the
guiding rollers lie outside the tangential planes of the drying
cylinders. It is advantageous if the open sides of the felt or wire
loop have been closed with walls in order to produce an enclosed
space within the felt or wire loop and if in said enclosed space a
vacuum has been arranged to prevail in order that the web, while
travelling upon the drying felt or wire, will be attached to it by
suction. Said guiding rollers are most appropriately foraminous so
that the vacuum within the drying felt or wire loop causes the web
to be attached by suction to the drying felt or wire passing over
the guiding rollers. In said enclosed space a vacuum of such height
may be arranged to act that the guiding rollers may operate as
traverse flow dryers. It is then advantageous if the guiding
rollers have been provided with a blow hood containing a heat
source. The drying cylinder group may also comprise a drying
cylinder intended for the drying of the drying felt and which may
be located inside or outside the felt loop.
The invention is described in closer detail in the following with
reference to the embodiment examples presented in the attached
drawings.
In the drawing,
FIG. 1 presents as a longitudinal sectional view a cylinder group
of a multiple cylinder dryer according to the invention.
FIG. 2 shows, in longitudinal section, a cylinder group of a
multiple cylinder dryer according to another embodiment of the
invention.
FIG. 3 shows, as a longitudinal section, a cylinder group of a
multiple cylinder dryer according to a third embodiment of the
invention.
FIG. 4 shows the section along line IV--IV in FIG. 3. FIGS. 5, 6,
7, 8 and 9 present examples of the longitudinal sections of
multiple cylinder dryers according to the present invention.
FIG. 1 represents the invention in its simplest form. The reference
numerals 1, 2, 3, 4, 5 and 6 indicate drying cylinders disposed in
two rows. The drawing has been so executed that 1, 2 and 3 are
lower cylinders and 4, 5 and 6 are upper cylinders, but in actual
fact the positioning of the rows with regard to gravity may be
arbitrary and the rows might therefore equally be vertical. It
should be noted that the drying cylinders need not even necessarily
lie in rows. The numerals 7 refer to drying felt (or wire) guiding
rollers belonging to the group, 8 indicates the drying felt (or
wire), 9 its tensioning means, 10 a conveyor which conveys the web
11 from the wet end from the press section, or from the preceding
group, to the group under consideration. It is observed that the
web 11 is transferred from the conveyor 10 onto the drying felt (or
wire) 8 with fully closed conduction without even a single moment
at which it would not receive support from one or the other
conveyor. It is a characteristic feature of the arrangement that
the group comprises only one drying felt (or wire) 8 and that the
drying cylinders 1, 2, 3, 4, 5 and 6 of the group all are located
outside the felt (or wire) loop. It is thus understood that the web
11 is supported by the drying felt (or wire) throughout its travel
within the group and that at all drying cylinders it is interposed
between the drying felt (or wire) and the cylinder surface, whereby
an efficient drying action is ensured at all cylinders. Within one
group the web is in contact with all cylinders with one and the
same side. If it is desired, for instance in view of the gloss of
the web, to change the side which is in contact with the cylinder,
the dryer may be constructed to have a pluralitiy of groups in
succession, the side of the web changing at transition from one
group to another. Examples of various possible arrangements are
seen in FIGS. 5-8. It may be noted that in the exemplary case of
FIG. 1 the number of cylinders may naturally be another than six;
it may in principle by any number from two upwards.
The following advantages are now gained by the arrangement.
1. The web is supported throughout its travel.
2. There are no drying pockets. The uniformity of ventilation
within the felt (or wire) loop (in the space 12, FIG. 1) is not
essential because the web is covered by the drying felt (or wire)
and therefore is not sensitive to variations within this space.
Those regions where the web is exposed during its travel (the runs
8' and upon the guiding rollers 7, FIG. 1) are readily approachable
from the outside. In order to improve the drying profile, blowing
tubes 13 adjustable in the breadth direction of the web, or blowing
hoods 14, may be constructed in association with some of the
guiding rollers 7 or perhaps with all of them.
3. The removal of waste becomes easier because now, owing to the
closed felt (or wire) loop, waste cannot easily get into the
interstices of the drying cylinders. It is particularly
advantageous in view of the waste to make the rows vertical, as for
instance in FIG. 2, in which case there are no horizontal surfaces
on which waste could accumulate.
FIG. 2 presents a variation developed from the preceding one.
Equivalent parts have been indentified by the same reference
numerals. In addition to the fact that the rows of drying cylinders
now are vertical, it is essential that the guiding rollers 7 have
now been made with a foraminous mantle. When the ends of the wire
loop formed by the wire 8 are closed with partitions (not depicted
in the drawing), in its interior space 12 a vacuum may be
maintained with reference to the surroundings. For the purpose of
maintaining the vacuum, FIG. 2 shows schematically a suction tube
15 departing from the space 12 and a blower 16, by the aid of which
said vacuum is generated. This vacuum now causes the web to be
drawn by suction to adhere both to the felt (or wire) 8 at the runs
8' and to the surface of the foraminous guiding rollers 7, which
enables fully automatic threading of the leading web end to be
accomplished and ensures the travel of the web during operation,
which is necessary particularly in the case of high machine speeds,
in which instance otherwise the centrifugal force on the surface of
the guiding rollers 7 may be disturbing. In the figure also doctors
17 have been shown, which during the web introduction operation
also ensure the travel of the web 11 together with the felt (or
wire) 8.
FIG. 3 shows a still more advanced modification of the preceding
embodiment. Equivalent parts have been indicated by the same
reference numerals. The difference is that now the partitions on
either side of the felt (or wire) loop 8 are sturdy enough and the
seals have been well enough constructed to enable in the space 12
with the aid of the flower 16 a vacuum of such magnitude to be
maintained that a traverse flow through the web 11 is produced. In
that case at least part of the guiding rollers 7 may be replaced by
traverse flow drying cylinders 18, in themselves known in prior
art, with blowing hoods 19', 19". The drying air or gas flows from
the hoods in the direction of arrows a through the web and the
mantle of the drying cylinder, and the spent gases flow in the
direction of arrows b into the space 12 and thence into the suction
pipe 15. For several traverse flow dryers either individual hoods
19' or a common hood 19" may be provided. Furthermore, in FIG. 3
dotted lines indicate the positions of the hoods 19', 19" during a
web break, giving access to those parts of the mchine where waste
may accumulate. It may be observed that it is to be expected that
the dryer now described has a favourable specific evaporation,
because the specific evaportion of each drying cylinder 1, 2, 3, 4,
5 and 6 increases owing to the lowered total pressure in the space
12 and the specific evaporation of the transverse flow dryers 18
can be made a multiple of that of a common cylinder. The
ventilation and heat recovery equipment for the machines described
differ completely from conventional design solutions. It may be
observed, among other things, that since the described dryer may be
constructed with impermeable side walls and since at the
evaporating surfaces of the web 11 facing towards the room there is
a flow directed into the space 12, as a result of the suction
effect, it follows that a drying hood proper, in particular a
closed one, is unnecessary. To that space outside the drying felts
or wires of a conventional dryer around which a hood has been
constructed from which the exhaust suction of a dryer of this type
is effected, corresponds in the dryer according to FIG. 3 the space
12 inside the drying felt or wire loop, whence the withdrawal of
exhaust air can be accomplished through the pipe 15, without need
of a separate hood for collecting the exhaust air.
FIG. 4 shows the section through a cylinder group according to FIG.
3 along the line IV--IV. Equivalent parts have been indicated by
the same reference numerals. In addition to the components shown in
the longitudinal section (FIG. 3) this figure also shows the walls
20 enclosing the space 12 and which have apertures for the mantles
of the drying cylinders 1, 2, 3, 4, 5 and 6 and of the traverse
flow dryer cylinders 18 and covers 21 and 22 closing these
apertures, in which covers the shafts 23 and 24 of the cylinders
are carried. If the dryer is provided, in particular, with drying
felts, in each group of consecutive drying cylinders, which
according to the present invention have one common drying felt, one
or several such cylinders may be incorporated for the purpose of
drying the drying felt, which are not lapped by the web.
FIG. 5 shows a dryer according to the invention having two cylinder
groups A and B each with its own drying felt 8. In the group A the
drying cylinders are disposed in two vertical rows, which are side
by side, and the number of drying cylinders is five. Group B has
four drying cylinders, which lie in two rows, one above the other.
The groups have their own drying felts 8. The direction of travel
of the web 11 is indicated by arrows C. Each cylinder group has one
drying cylinder 25,26 for the drying felt 8. Of these, the drying
felt (8) drying cylinder 25 in group A lies outside the felt loop,
whereas the drying cylinder 26 for the drying felt 8 in group B is
within the felt loop. Although it is expedient, as in FIG. 5, to
place the felt drying cylinder 25, 26 between the first and last
drying cylinders of the web 11, it may in principle also be placed
between another pair of cylinders. If the felt permits, it is
possible alternatively for its drying to use a traverse flow drying
cylinder having a foraminous mantle.
FIG. 6 also shows a multiple cylinder dryer according to the
invention. This, too, has two drying cylinder groups A and B, both
with their own drying felt 8 and guiding rollers 7. Said guiding
rollers are so positioned that the drying cylinders lie outside the
drying felt loops. The arrow C indicates the direction of travel of
the web 11. Each drying cylinder group A and B has six drying
cylinders, which lie in two rows, one above the other. The dried
web 11 is conducted through a calender 27 to the reeling device
28.
FIG. 7 also shows a multiple cylinder dryer according to the
invention. It, too, has two drying cylinder groups A and B,
similarly as the multiple cylinder dryer of FIG. 6. The multiple
cylinder dryer of FIG. 7 differs from that of FIG. 6 mainly only in
that both drying cylinder groups A and B have six drying cylinders
each, which are disposed in two vertical rows side by side, and
that the guiding rollers are traverse flow drying rollers 18
provided with a hood 19', 19". The web 11 travels in the direction
of the arrow C and upon having dried, goes through the calender 27
to the reeling device 28.
FIG. 8 shows a multiple cylinder dryer similar to that of FIG. 7,
and equivalent parts have been indicated by the same reference
numerals. The multiple cylinder dryer depicted in this figure
differs from that of FIG. 7 mainly in that in the groups the drying
cylinders in two rows side by side are interjacent. It follows that
both groups have six traverse flow dryers 18 with hood 19', 19",
serving as guiding rollers. The conduction of the wire 11 from one
cylinder group to the other is also different from the conduction
of the web 11 shown in FIG. 7.
FIG. 9 shows a multiple cylinder dryer according to the invention
having in an oblique position, consecutively, a plurality of drying
cylinder groups A, B, C, D, E, F and G. Each one of these comprises
one row of drying cylinders, each such row having its own drying
felt 8 and the drying cylinders lying outside the felt loop formed
by it. The felt loop is guided by guiding rollers 7. The web 11 is
conducted from one group to another, supported by the drying wire
or felt.
The invention is by no means confined to the embodiment examples
presented in the foregoing, and it can be modified in numerous ways
within the scope of the invention.
* * * * *