Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2~1 ~9~0
HEATED HOLLOW ROLL
The invention relate~ to hollow roll~ for use
as smoothing rolls, press rolls or drying cylinders in
the manufacture of a web of material, and in particular
to heated hollow rolls.
Hollow rolls, used as smoothing rolls, press
rolls or drying cylinders utilized in paper-making
machines may be equipped with various means to heat
regions thereof. In the manufacture of an endless web
of material (e.g. paperj, the material web is conveyed
in more or less meandering fashion over such heated
hollow roll~ in order to perform various successive
processes or treatments on the web. Depending on the
type of rolls utilized and the particular processes
being performed, the web of material contacts different
rolls at different angles. The contact between the web
of material and a roll may also be direct or indirect,
for example, a screen or other covering may be ~
interposed between the web and the roll. ~-
Process conditions are typically such that
the material web, viewed axially, does not contact the
heated roll over the entire width of the roll (i.e.,
roll length), which results in thermal fluctuations
over the length of the roll. The reason for such
fluctuations i~ that in the region where the material
web overlaps the roll, it removes heat therefrom,
whereas only a relatively small amount of heat is drawn
off the roll on either side of the web near the roll
pins upon which the roll is mounted (via the air and in
the form of radiation).
Edge regions of the roll are therefore
overheated relative to the region of the roll in
contact with or overlapping the web. This causes the
diameter of the roll to increase at the edge regions
thereof (known as an "ox-bow" effect). As a
consequence, the web is over-dried at its edge regions
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-- 2
and undesirable web tears may develop. A further
hazard i9 that the linear force distribution over the
width of the web may become uneven because of the roll
diameter increase. Such an unequal web compression may
lead to unequal web material compaction at the edge
regions thereof.
To summarize, webs being produced or treated
utilizing a heated hollow roll can experience a
reduction in quality because of a non-homogeneous
temperature profile along the roll. Such quality
problems may include thinning in the edge regions of
the web, over-drying of the edge regions of the web
with the possibility of material rupture, and
thickening in the edge regions of the web due to
excessive transverse shrinkage thereof. Moreover,
increased wear of a screen or smooth coatings
contacting a heated roll may occur because of the
increased diameter of the roll edges due to the "ox-
bow" effect.
It is an object of the invention to overcome
one or more of the problems described above.
A hollow roll according to the invention for
use with a web of material includes apparatus for the
controlled heating of edge regions of the roll. The
heating apparatus comprises an internal andtor an
! èxternal heating device or devices. The internal
heating device is disposed within the roll and is inset
with respect to a width of a web passing over the roll.
The external heating device is disposed in the vicinity
of the edge regions thereof.
Other objects and advantages of the invention
will be apparent to those skilled in the art from the
following detailed description taken in conjunction
with the drawings and the appended claims in which:
Fig. 1 is a partially schematic longitudinal
sectional view of a device accordin~ to the invention.
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Fig. 2a is a graph showing heat (Qp and QL)
withdrawn from a roll section internally heated across
an entire length thereof (not in accordance with the
invention).
Fig. 2b i9 a graph showing heat (Qj')
internally provided to a portion of the roll section of
Fig. 2a (not in accordance with the invention).
Fig. 2c i9 a graph showing a temperature
profile (T) along the surface of the roll heated as
shown in Fig. 2b.
Fig. 2d is a graph showing a preferred or
ideal selective heat supply (QA' ) along the surface of
a roll.
Fig. 2e is a graph showing a preferred or
ideal temperature profile (T) along the surface of the
roll shown in Fig. 2d.
Fig. 3a is a graph showing heat withdrawn
from a portion of a heated roll of the device shown in
Fig. 1.
Fig. 3b is a graph showing heat (Q;)
internally provided to the portion of the roll shown in -~
Fig. 3a.
Fig. 3c is a graph showing a temperature
profile (T) along the surface of the roll heated as
shown in Fig. 3b.
Fig. 3d is a graph showing heat (QA)
externally provided to the portion of the roll shown in
Fig. 3a.
Fig. 3e ia a graph showing a temperature
profile (T) along the surface of the roll heated as
shown in Figs. 3b and 3d.
Fig. 4 is a graph showing heat (Qj and QA)
provided over a section ~ of the device shown in Fig.
1.
An apparatus according to the i~vention is
described below with reference to Figs. 1, 3, and 4.
Such an apparatus provides selective heat control of an
edge zone of the roll disposed between a material web
~ 211~9~o
transported about the roll and an end of the roll. The
heat control is provided by an internal heating device
which is narrower than a width of a material web
passing over the roll and/or by an external heating
device or devices disposed in the vicinity of both edge
regions of a material web (and the ends of the roll).
Furthermore, heat control may be synergistically
reinforced at the web edge regions by utilizing both
the internal and external heating devices described
herein.
An apparatus according to the invention
comprises a roll equipped with means to provide
controlled heat to the roll to compensate for or
eliminate the heat-related problems described above by
selectively heating end or edge regions of the roll in
order to obtain a substantially constant temperature
profile across a sur~ace of the roll, including the
heating of the end regions of the roll up to roll pins
upon which the roll is mounted.
Fig. 1 shows an apparatus according to the
invention in longitudinal section. The apparatus
includes a hollow roll, generally designated 1, having
an axis A. The roll 1 i9 mounted on roll pins 10.
Supply lines or connections depicted by an arrow x,
extend into an interior of the roll and pass through
the roll pins 10 to supply energy to an internal
heating device 20 disposed coaxially with a roll
surface of the roll 1. The intern
c z ~ cal h~l iDs _ The
device 20 can also be designed so that separate sectors
(illustrated by arrows s) are formed in the axial
direction that can be activated selectively in response
to actual operating conditions.
The individual sections or sectors of the
internal heating device 20 are connected and
disconnected with reference to a width w of the web 2
fed over the roll surface 90 that the internal heating
device 20 does not act over the entire width w of the
web 2. Edge regions of the web 2 are therefore not
directly heated by the internal heating device 20.
This i9 illustrated in Fig. 1 which shows that the web
~.
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2 passing over the roll surface has an edge R that is
disposed beyond a boundary G of the direct heating zone
of the internal heating device 20. The spacial
relationship between the web 2 and the device 20 shown
in Fig. 1 advantageously minimizes problems typically
encountered when heating material webs, such as over-
drying, undesirable compacting and tearing of the web
material, to name a few.
The internal heating device 20 is disposed in
a region where the web 2 contacts and/or overlaps the
roll 1. However, it is also possible to utilize a
device 20 to provide heat control over an entire
internal wall of the roll 1. Heat control of the edge
regions of roll barrel 1 may also be influenced by ~-
utilizing insulating material and/or integrated
cooling.
With reference to Fig. 1, because the
interior heating device 20 is inset relative to the
width of the web 2 (i.e. the edges of the web 2 extend
beyond the heating device 20 at either end thereof), a
substantially homogeneous temperature prof~le is
achieved along the surface of the roll ~. However, if
the device 20 is utilized alone, a reduction of
temperature may develop in the edge regions of the roll
1 (i.e. at a length of the roll 1 disposed between the
boundary G and the edge R designated in Fig. 1 as
which, under certain circumstances could result in
undesirable web material properties.
The temperature reduction may be eliminated
by utilizing an external heating device included in the
apparatus according to the invention shown in Fig. 1.
With reference thereto, external heating is provided by
two external heating devices 30 and 30'. The devices
30 and 30' are each located in the vicinity of an edge
region of the roll 1 and edge regions ~ of the web 2
passing over the roll 1. The amount of heat provided
by the devices 30 and 30' may be selectively matched to
cooperate with the heat provided by the internal
heating device 20 ~o that the external heating of the
roll 1 overlaps with the internal heating thereof on
both sides of the roll 1.
21 ~
- 6
The degree of external heating preferably
increases in an axially outward direction toward the
roll pins 10. Depending on the specific operating
conditions, the external heating devices 30 and 30'
terminate at the outer edges of the web 2. However,
the heating devices 30 and 30' may also extend
substantially linearly outwardly beyond the width of
the outer edge of the web 2, either continuously or
discontinuously.
The external heating devices shown in Fig. 1
are disposed substantially parallel to the axis A of
the roll 1 (i.e. parallel to a direction depicted by a
double arrow Y which is parallel to the axi~ A of the
roll 1). The embodiment of the device according to the
invention hown in Fig. 1 illustrates external heating
devices 30 and 30' disposed beneath the roll 1.
However, the devices 30 and 30' can be disposed at any
other location along the roll surface of the roll 1,
including above it. This flexibility in choosing the
location of the devices 30 and 30' is particularly
advantageous when the roll 1 is disposed in a multiple-
roll arrangement through which the web 2 is fed in
meandering fashion. The external heating devices 30
and 30' therefore can be integrated into an overall
layout, such as an air feed unit, with the devices 30
and 30' cooperating with the roll 1 as shown in Fig. 1.
With respect to Fig. 1, the increasing length
of arrows s' depicting heating sectors of the devices
30 and 30' illustrate the fact that, with respect to an
30 axial direction toward the roll pins 10, the heating ``
devices 30 and 30' provide an incipient, then
increasing, and finally constant heating effect on the
roll 1. The external heating devices 30 and 30' -
produce about half of their heating output at inner end
35 regions thereof which overlap the internal heating~
device 20. The heat output then increases linearly in ~ :
the direction of the roll pins 10 and then at full -~
power at outward ends thereof disposed in the vicinity
of the roll pins 10. The heat supplied near the roll -
pins 10 remains substantially constant 50 that a
constant temperature is guaranteed at the roll pins 10. `
Similar to sectors s discussed herein with respect to
the internal heating device 20, the heating devices 30
and 30' may also include heating sectors s' which may
be activated individually.
The external heating devices 30 and 30~ are
preferably inductive, infrared, or eddy current
heaters. The devices 30 and 30' may also utilize
steam, hot air, or oil heating. The internal heating
device 20 and the external heating devices 30, 30' can
be of the same or different type.
With reference to Figs. 2a - 2e and 3a - 3e,
comparisons may be made between the heating provided by
a device according to the invention and that of other
heated rolls. Figs. 2a - 2c show thermal conditions
which are established in edge regions of a roll R' if
the roll is heated in a manner other than that
described with respect to the devices 20 and 30, 30'
shown in Fig. 1 (the roll R' shown in Figs. 2a - 2d is
otherwise identical to the roll 1 shown in Fig. 1).
Figs. 2d and 2e illustrate preferred or ideal thermal
edge conditions and Figs. 3a - 3e show the thermal edge
conditions when a web 2 passes over a device according
to the invention.
Fig. 2a shows thermal conditions of a section
of a roll R' wherein the entire surface of the roll R'
is heated internally and illustrate~ heat Qp withdrawn
along a portion of a hollow roll 1' above which the web
2 (shown in phantom) advances. The portion of the roll
1' shown is in the vicinity of an edge zone R' (shown
in phantom) of the web 2. The portion of the roll 1'
to the right of the edge R' is therefore not in contact
with or in any other way overlapping the web 2. From
Fig. 2a it can be seen that a relatively large amount
of heat Qp is withdrawn from the roll 1' in a region of
overlap U between the web 2 and the roll 1'. However,
only a relatively small amoun~ of heat QL is withdrawn
from the portion of the roll 1' which does not overlap
with the web 2. This heat loss occurs via the
surrounding air and heat radiation. The result is that
211~9~
the temperature profile ln the edge region of the web 2
fluctuates widely.
Fig. 2b, on the other hand shows the heat
output (Q;) of the roll R' if it is heated only along
S ~he width of the web 2. In such an embodiment, the
temperature profile is somewhat equalized on each side
of the edge zone R (see Fig. 2c which depicts the
changes in temperature T along the same section of the
roll 1' depicted ln Fig. 2b~. ~owever, when the roll
1' is heated along the entire width of the web 2,
temperature irregularities develop in the web edge
region, which influence the roll 1, and thus ultimately
the material properties of the web.
An objective of the invention is depicted
with respect to Figs. 2d and 2e inasmuch as it is
desirable to achieve a constant temperature Tol along
the surface of the roll 1' (Fig. 2e) by providing a
selective heat supply QAI in or near the edge region R'
(Fig. 2d). ~ ~
The problem discussed herein with reference ~ ~-
to Figs. 2a - 2e is resolved by a device aecording to
the invention described herein with reference to Fig. 1
and further described below with respect to Figs. 3a -
3e and 4.
Figs. 3a - 3e each show graphs depicting
thermal conditions of an apparatus according to the
invention with reference to the section ~ of the roll
1. Fig. 3a is similar to Fig. 2a in that it shows the
amount of heat withdrawn by the web 2 from the roll 1.
However, because the apparatus according to the
invention utilizes an internal heating device 20 which
is disposed opposite the web 2 but directs heat toward
the roll 1 in a vicinity bounded by the reference
letter G, the heating effect produced by the device 20
ends before (i.e. within) the edge R of web 2, when
viewed in the axial direction. The roll surface of the
roll 1 is thus supplied with thermal energy from the
inside which results in a heating curve that diminishes
toward the web edge R (see Fig. 3b). The corresponding
temperature profile for the roll 1 surface temperature
2-~9940
is shown in Fig. 3c. A temperature drop results
between the boundary G of the internal heating device
20 and the edge R of the web 2. If an amount of heat Q
exactly complementary to this temperature drop is
supplied via the external heating devices 30 and 30'
(Fig. 3d), a desired constant temperature profile To
results (Fig. 3e).
An example of the synergistic interaction of
the internal and external heating devices of the roll
depicted in Fig. 1, is shown in Fig. 4. The amount of
heat Qj provided to the roll 1 by the internal heating
device 20 up to the boundary G thereof and the amount
of heat QA provided by the external heating device 30
or 30' within the region where the internal heating
device 20 i9 effective and thus overlaps it are shown
in Fig. 4. The amount of external heat QA roughly
reaches half its capacity at the boundary G and
continues to ri~e until it reaches its full capacity
about halfway across the edge region ~. The heat
output QA then remains constant at the edge R of the
web 2.
Other embodiments of a roll according to the
invention are possible. For example, depending on the
web material properties and the roll operating
parameters, including its mechanical characteristics,
it i9 possible to establish a sort of thermal
calibration curve to which the internal and external
heating devices may be adjusted. In particular, it is
possible to dynamically adjust the working conditions
of the internal and external heating devices at the
beginning of an operation, during a change in external
temperatures, or with respect to a change in web width.
External heating can also be controlled, for example,
by monitoring the properties of the web at its edges
and adjusting the internal and external heating devices
accordingly.
The foregoing detailed description is given
for clearness of understanding only, and no unnecessary
limitations should be understood therefrom, as
~1199~0
- 10 -
modifications within the scope of the invention will be
apparent to those skilled in the art.
