Note: Descriptions are shown in the official language in which they were submitted.
CA 02272205 1999-OS-19
P17767.S02
CALENDER ROLL AND PROCESS OF OPERATING THE SAME
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. ~ 119 of German
Patent Application No. 198 22 531.8, filed on May 19, 1999, the disclosure of
which is expressly incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns a calender roll that includes a core having
an elastic coating that extends over an operating width and a process for
operating
the calender roll.
2. Discussion of Background Information
A calender roll of the type generally discussed above is usually used as a
center roll in a stack of rolls of a calender. It is also referred to as a
soft or elastic
calender roll, since the coating creates a roll surface which is flexible to a
certain
degree. These calender rolls usually work along with a "hard" roll to glaze a
paper
web or another material web. The hard roll is usually heated such that the
paper
web can be subjected to an elevated pressure and an elevated temperature in
the
nip or roll gap formed between the soft and hard rolls. The elastic coating
serves
to smooth the surface of the paper web.
The operating width of the above-noted calender roll generally corresponds
to a width of the web of material to be treated. Outside the operating width,
the
coating can taper conically, which generally extends over an axial length in
the
range of approximately 20 to 100 mm. This tapering is intended to prevent the
coating not covered by a paper web from coming into contact with the opposing
roll and being damaged. In the present application, the term "operating width"
refers to the working region of the coating.
It has been found that some rolls are damaged during operation due to
coating tears or breaks. This damage occurs even with coatings that have
-1-
CA 02272205 1999-OS-19
P17767.S02
temperature stability or temperature resistance, which should actually
withstand
the temperatures during operation.
SUMMARY OF THE INVENTION
The present invention provides a calender roll in which stress on the coating
S is reduced.
Thus, according to the present invention, a calender roll of the type
generally described above includes an internal heat equalization system which
at
least approximately matches the temperature of the axial ends to the
temperature
of the axial center of the roll.
As is known in the art, heating can come about in an elastic roll in various
ways. For example, the rolling friction of the coating in the roll nip or gap
produces heat, heat is transferred to the elastic roll through the paper web
heated
by the opposing roll, and heat is added by the flexing of the coating. As a
result,
heat is delivered primarily in the region of the axial center of the roll,
i.e., in the
barrel region, such that a higher temperature is reached there, which causes
varying radial expansion behavior of the roll over its length. The roll
generally
has a smaller diameter on its axial ends than toward its axial center.
Accordingly,
nonuniform pressing action of the roll over its length results. Those places
where
the roll then has the greatest diameter experience the greatest stress. The
coating
can in many cases no longer withstand this stress. It then breaks.
When an internal heat equalization system in accordance with the present
invention is provided, temperature equalization may be performed between the
barrel region and the axial ends of the roll without the addition of auxiliary
energy.
The term "auxiliary energy" may be understood to refer both to energy for
heating
and for cooling, e.g., heat transfer liquids added from outside the roll or
discharged
therefrom, electrical current for heating, magnetic fields, or the like.
Instead, only
the above-described heat occurring during operation is delivered. The heat
equalization takes place internally.
-2-
CA 02272205 1999-OS-19
P 17767. S02
It is known, e.g., from DE 44 10 675 A1 (and U.S. Patent No. 5,571,066)
to heat the roll journals separately in a heat roll in order to reach
operating
temperature more quickly. However, for this, it is necessary to deliver
auxiliary
energy from the outside.
In an exemplary embodiment of the present invention, thermal insulation
may be positioned axially outside the operating width. With this insulation,
heat
outflow can be reduced and temperature equalization is thus effected.
Surprisingly, it turns out that the coatings have a longer service life or no
longer
break or are not damaged as often with the applied thermal insulation. This
measure is in and of itself paradoxical since, with the insulation, heat is
prevented
from being able to flow out and the temperature of the coating thereby
increases.
This has for a long time been considered the major reason for the destruction
of
the coating. Because of the insulation, the heat can no longer escape as well
through the end region of the roll. It was previously assumed that, in the end
region of the rolls, only a comparatively low addition of heat occurred, e.g.,
by
radiation heat from the opposing roll and by friction of the roll bearing.
Further,
increased heat dissipation was previously possible in the end regions of the
roll
since the greatest free surface was available there. Accordingly, a lower
temperature occurred in the end regions than in the barrel region, i.e., in
the axial
roll center. Now, if care is taken via the insulation so that the heat can no
longer
escape so simply, a substantially uniform temperature profile over the axial
length
of the roll results such that a correspondingly uniform roll diameter also
results.
The roll diameter can be kept constant over the operating width within
predefined
limits. Overall, a higher temperature of the roll results since the heat can
no longer
flow out so readily. However, this higher temperature is less damaging than
mechanically overstressing of the coating.
Preferably, the insulation covers both a section on the circumference of the
roll and at least part of the end face of the roll. Thus, the outflow of heat
can be
-3-
CA 02272205 1999-OS-19
P 17767.502
prevented not only through the circumference but through the end face. An
exception here under certain circumstances is the shaft end, by which the roll
is
rotatably mounted. However, the shaft end is exposed to rolling friction in
the
bearing such that heat losses developing here are nevertheless small, and
under
certain circumstances heat can even be added.
Alternatively or additionally, the roll can have journal heating. With the
insulation, it is possible to make heat outflow more difficult, but not to
completely
prevent it. Accordingly, it is still possible that, under unfavorable
conditions,
temperature differences of such a magnitude may occur which result in
noteworthy
differences in diameter over the axial length of the roll. As noted above,
this can
possibly result in excessive mechanical stress of the coating. However, if the
axial
end of the roll is heated by j ournal heating, it is possible to keep the
axial ends)
and the axial center, i.e., the barrel region, of the roll at substantially
the same
temperature. With appropriate design and efficiency of the journal heating, it
may
also be possible under certain circumstances to even eliminate the insulation.
Via
journal heating, the axial ends of the roll may be brought to the temperature
of the
barrel region. With the same temperature over the axial length, uniform
expansion
occurs such that the roll has the desired constant or approximately constant
diameter distribution over the entire axial length in operation with heat
added.
It may be preferable that the journal heating uses heat from an axially
inwardly region of the roll for heating This design has two advantages: No
separate addition of heat from the outside is necessary, and the roll end
cannot
become hotter than the axial center of the roll. Accordingly, connections with
couplings, through which a heat transfer medium can be fed from the outside
into
the interior of the roll, can be omitted. Accordingly, the same temperature
can be
reached as a maximum. With a higher temperature, a heat transfer from the
axial
center of the roll to the ends would no longer be possible. Thus, the present
invention also results in a self protective and self regulating effect. Thus,
a heat
-4-
CA 02272205 1999-OS-19
P17767.502
transport system that acts in the axial direction, which transports the heat
to the
"cooler" points to heat them, while it cools the hotter points, is provided in
the roll.
There are several possibilities for the design of the journal heating.
In a particular embodiment, the roll may be formed as a tubular roll that
surrounds a closed cavity in which a vaporizable liquid is disposed. The vapor
pressure of the liquid may be set to the operating or working temperature of
the
roll, i.e., the liquid vaporizes when it comes into contact with a part of the
roll
which has a higher temperature. The vapor distributes itself uniformly in the
cavity. Thus, it inevitably comes into contact with those places having a
lower
temperature than the vaporization temperature. It condenses there and heats
this
place by releasing its condensation heat. During operation, when the roll is
rotating, the condensate is again transported radially outwardly via
centrifugal
force and distributes itself uniformly on the boundary wall of the cavity,
where it
again vaporizes at warmer points and thus continues the cycle. This effect is
known as a "heat pipe" effect. In the present roll, it results primarily in
conjunction with the insulation of the end regions in a very uniform
temperature
distribution. This yields a correspondingly constant diameter of the core.
Preferably, the cavity may be closed on each end with a roll journal, which
has a heat exchanging surface on its internal surface. Thus, not only are the
axial
ends of the core heated with the heat originating in the barrel region of the
roll, but
so are the roll journals. Thus, a capability is simultaneously provided to
discharge
some heat from the roll. It can reach the outside via the roll journals and
the shaft
ends thereon. The outflow of heat here is, to be sure, not very great.
However,
under certain circumstances, it prevents overheating of the coatings.
Preferably, the heat exchanging surface may be quantitatively larger than
the area of the cross-section of the cavity in a plane perpendicular to the
axis of
rotation. Thus, it is possible to provide the heat exchanging surface with
cooling
ribs or grooves such that the vaporizable liquid disposed in the cavity has a
greater
-5-
CA 02272205 1999-OS-19
P17767.S02
precipitation surface. This accelerates the heating of the roll j ournal and
thus the
roll end, which is advantageous, for example, at the beginning of operation.
Advantageously, the roll may include a heat conducting arrangement. This
heat conducting arrangement can also be provided when the temperature
equalization takes place between the axial center and the axial ends of the
roll via
the vaporizable liquid or otherwise. Instead of, or in addition to, the heat
transport
via a moving medium, heat transport may also occur simply through heat
conduction, i.e., through static elements.
Preferably, the heat conducting arrangement may be composed of inserts
of material having good thermal conductivity. For example, aluminum or copper
may be used for this. The inserts many be designed as rods or plates which
extend
the length of the core. They can also be incorporated into the core, or, in
the case
of a hollow roll, can cover the boundary wall of the cavity. With adequate
dimensioning, it is possible to achieve adequate heat transport such that the
temperature remains virtually constant over the axial length of the roll and
the
diameter remains virtually constant.
An additional possibility for temperature equalization also results if a pump
is fixedly or stationarily located in the roll and is drivable from the
outside to
circulate a heat transfer liquid. This heat transfer liquid, e.g., water, can
be
conducted through an appropriate channel arrangement, e.g., through a system
of
peripheral boreholes or channels beneath the surface of the core. If a pump is
stationarily located inside the roll, the pump rotates with the roll, such
that no
inflow or outflow connections with the outside have to be provided. All that
is
necessary is to drive the pump from the outside. This may occur, e.g., in that
a
drive element of the pump engages a stationary opposing surface by friction or
by
teeth such that the pump automatically operates when the roll rotates. The
higher
the rotational speed of the roll, the greater the output of the pump. However,
this
is the desired effect since, in this case, a greater amount of heat must also
be
-6-
CA 02272205 1999-OS-19
P17767.S02
transported from the inside out (viewed axially).
In another embodiment, the insulation can transition into the coating. In
this manner, the coating and the insulation can then be applied in one
process.
Preferably, the insulation outside the operating width has a greater
thickness than the maximum thickness of the coating within the operating
width.
This takes into account the fact that within the operating width heat is
delivered,
i.e., insulation via the coating in and of itself is not necessary, whereas
outside the
operating width, heat dissipation should be prevented to greater extent.
It may also be advantageous if the heat conductivity of the insulation is less
by at least a factor of 5 than that of the coating. Effective insulation is
thus
achieved. The material of the coating conducts heat, for example, at 0.5 W/m-
K,
whereas the insulation has a value of only 0.03 W/m-K.
The present invention is directed to a calender roll that includes a core, an
elastic coating which extends over an operating width of the core, and an
internal
heat equalization system arranged to match the temperature of the axial ends
to at
least approximately a temperature of an axial center of the roll.
In accordance with the features of the present invention, thermal insulation
is located axially outside of the operating width. Further, end faces are
positionable at axial ends of the core, and the insulation is arranged to
cover a
circumferential section of the core and at least part of the end faces.
According to another feature of the present invention, the roll may include
journal heating. Further, the journal heating may use heat from an axially
inward
region of the roll for the heating.
According to still another feature of the present invention, the core may
include a tubular roll that surrounds a closed cavity. A vaporizable liquid
may be
located within the closed cavity. Roll journals may be provided that include a
heat
exchanger surface, and each axial end of the closed cavity may be closed by
the
roll j ournals. Further, the heat exchanger may have a surface area
quantitatively
CA 02272205 1999-OS-19
P17767.S02
larger than a cross-sectional area of the cavity in a plane perpendicular to
an axis
of rotation of the roll.
In accordance with another feature of the present invention, a heat
conducting arrangement may be included. Further, the heat conducting
arrangement may include inserts composed of a material having good thermal
conductivity.
In accordance with a further feature of the present invention, a pump may
be fixedly positioned on the roll and drivable from outside of the roll. The
pump
may be adapted to circulate a heat transfer liquid.
According to a still further feature of the present invention, the insulation
is arranged to transition into the coating.
According to further features of the present invention, a thickness of the
insulation outside of the operating width is greater than a maximum thickness
of
the coating within the operating width.
In accordance with another feature of the present invention, a heat
conductivity of the insulation may be less than a heat conductivity of the
coating
by a factor of least about 5.
In accordance with still another feature of the present invention, the core
may include a plurality of axial bores extending through the core. A heat
transfer
medium may be circulated through the bores. Further, pumps may be positioned
adj acent to the plurality of axial bores. Still further, the roll may include
at least
two toothed gears, in which one of the toothed gears is coupled to the pumps
and
another of the toothed gears is coupled to a bearing arrangement.
According to another feature of the present invention, roll journals
including a heat exchanger surface that includes cooling ribs extending into
an
interior of the core may be provided, and axial ends of the core may be closed
by
the roll journals.
The present invention is also directed to a process for operating the calender
_g_
CA 02272205 1999-OS-19
P17767.S02
roll in an apparatus that further includes a mating roll positionable against
the
calender roll. The process includes forming a press nip between the calender
roll
and the mating roll, guiding a web through the press nip and within the
operating
width of the coating, and rotating the calender roll. In this manner, the
internal
heat equalization system substantially matches a temperature of the axial ends
to
a temperature of the axial center of the roll.
According to another feature of the present invention, during operation, a
temperature increase occurs within the calender roll, and a temperature at the
axial
ends of the roll is less than a temperature in the axial middle of the roll.
According to still another feature of the present invention, during operation,
a temperature increase occurs within the calender roll, and a temperature
within
the calender roll is uniformly distributed over the axial length of the
calender roll.
In accordance with yet another feature of the present invention, during
operation, a temperature increase occurs within the calender roll, and a
temperature at the axial ends of the roll is less than a temperature in the
axial
middle of the roll by less than approximately 20°C.
The present invention is directed to a process for operating an apparatus
that includes a core, an elastic coating that extends over an operating width
of the
core, and an internal heat equalization system. The process includes rotating
the
calender roll and equalizing a temperature within the calender roll between
axial
ends of the calender roll and an axial middle of the calender roll.
In accordance with a feature of the present invention, the apparatus may
further include thermal insulation that covers a circumferential section of
the core
and at least part of the end faces, the process may further include preventing
heat
loss through the axial ends of the calender roll. In this manner, the
temperature in
the axial ends may increase to substantially match the temperature in the
axial
middle.
According to another feature of the present invention, the process may
-9-
CA 02272205 1999-OS-19
P17767.S02
further include heating the axial ends to substantially match the temperature
in the
axial middle.
According to a further feature of the present invention, the apparatus may
further include axial bores within the core, and the process may further
include
pumping a heat transfer medium through the bores.
In accordance with yet another feature of the present invention, the
apparatus may further include a heat exchanger surface positioned on the axial
ends of the calender roll, and a vaporizable liquid located within an interior
of the
calender roll, and the process may further include pressurizing the calender
roll so
that the vaporizable liquid vaporizes at a predetermined temperature and
condenses at below the predetermined temperature.
Other exemplary embodiments and advantages of the present invention may
be ascertained by reviewing the present disclosure and the accompanying
drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is further described in the detailed description which
follows, in reference to the noted plurality of drawings by way of non-
limiting
examples of exemplary embodiments of the present invention, in which like
reference numerals represent similar parts throughout the several views of the
drawings, and wherein:
Figure 1 illustrates an axial end section of a first embodiment of a calender
roll of the present invention; and
Figure 2 illustrates an end section of a second embodiment of a calender
roll of the present invention.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
The particulars shown herein are by way of example and for purposes of
illustrative discussion of the embodiments of the present invention only and
are
presented in the cause of providing what is believed to be the most useful and
readily understood description of the principles and conceptual aspects of the
-10-
CA 02272205 1999-OS-19
P17767.502
present invention. In this regard, no attempt is made to show structural
details of
the present invention in more detail than is necessary for the fundamental
understanding of the present invention, the description taken with the
drawings
making apparent to those skilled in the art how the several forms of the
present
invention may be embodied in practice.
As illustrated in Figure 1, calender roll 1 is formed as a tubular roll that
includes a core 2 with a coating 3. An exterior surface of coating 3 forms a
working region or width 4. On the ends of working region 4, an end zone 5 is
provided in which coating 3 tapers conically. Working region 4 can be adapted
to a width of a material web to be glazed in a nip or roll gap between
calender roll
1 and an opposing roll (not shown). The opposing roll may be formed, e.g., as
a
hard, heated roll.
Axially outside coating 3, core 2 is covered by thermal insulation 6.
Thermal insulation 6 is provided to surround a polished shoulder 7 of core 2,
i.e.,
circumferentially around an end portion of calender roll 1, and to extend over
a
portion of end face 8 of calender roll 1. Thermal insulation 6, in the region
of end
face 8, can have a greater thickness than thermal insulation 6 at polished
shoulder
7. Overall, thermal insulation 6 has a greater thickness than the thickness of
coating 3 in working region 4.
A region of end face 8 in which a shaft end 9 protrudes from end face 8 is
not covered with thermal insulation 6. Calender roll 1 is rotatably mounted
via
shaft end 9 in a schematically depicted bearing 10.
Shaft end 9 is part of a roll journal 11, which has a section 12 that extends
into core 2 and which has a section 13 that abuts the end face of core 2. Roll
journal 11 may be coupled to core 2, e.g., with bolts 14 through section 13.
Calender roll 1 is depicted only partially in its upper half in cross-section.
In the
lower half, the outer view is depicted, whereby only insulation 6 is depicted
in
cross-section.
-11-
CA 02272205 1999-OS-19
P 17767.502
Core 2 and roll journal 11 bound a cavity 15, in which a liquid 16 is
contained to be pressed against the boundary wall of cavity 15 due to
centrifugal
force upon rotation of calender roll 1. Within cavity 15, a pressure prevails,
which
is adapted to a working temperature of calender roll 1 and liquid 16 such that
liquid 16 vaporizes at the working temperature. In this manner, the vapor is
distributed uniformly in cavity 15 and precipitates on parts of calender roll
1
which have a temperature below the vaporization temperature. These parts are
primarily the sections 12 of roll journal 11 at each end of the core 2. To
provide
an even greater heat transfer surface, cooling ribs 17 which extend or
protrude into
cavity 15 may be provided. In this manner, the heat exchanging surface is
increased such that the heat exchanging surface of section 12 is greater than
a
cross-sectional area of cavity 15 in a plane perpendicular to an axis of
rotation 18.
In accordance with the features of the present invention, insulation 6
prevents a greater heat flow from leaving calender roll 1 in the region of its
axial
ends. It is noted here that the other end of calender roll 1 is similarly
designed to
the end depicted in the exemplary illustration. Thus, the temperature becomes
quite uniform over the axial length of calender roll 1. Without insulation 6,
temperature differences of, e.g., more than approximately 20 ° C can
arise between
the region in which coating 3 with operating region 4 is located and the axial
ends
of calender roll 1. With insulation 6, the temperature difference can be
reduced
by more than half.
A still more uniform temperature distribution can result by utilizing
vaporizable liquid 16 to transport heat out of the barrel region of calender
roll 1,
i.e., out of operating region 4, and transport the heat to the axial ends of
calender
roll 1. Roll journals 11 may be heated in this manner. Under certain
circumstances, it may even be possible to do without insulation 6 here. As is
known, liquid 16 vaporizes at points having a temperature greater than the
vaporization temperature of liquid 16. In this manner, the liquid removes heat
-12-
CA 02272205 1999-OS-19
P 17767. S02
from these hotter points and cools them. The vapor, which is uniformly
distributed in cavity 15, then arrives at cooler parts, e.g., cooling ribs 17
of roll
j ournal 11 and condenses, which releases heat, thereby heating roll j ournal
11.
However, it is noted that roll journal 11 cannot become hotter than the
hottest
point in the barrel region of calender roll 1.
With this measure of heating journal 11 and possibly even insulation 6, the
temperature over the axial length of calender roll 1 can be equalized such
that
noteworthy diameter changes, due to temperature changes, no longer occur.
Thus,
the pressure acting on coating 3 can be equalized and the mechanical load
drops
below tolerable values.
Figure 2 depicts an alternative embodiment to that depicted in Figure l,
however, identical parts are provided with the same reference characters.
Further,
it is noted that the measures discussed in relation to the exemplary figures
for
journal heating, i.e., for transporting heat out of the barrel region of
calender roll
1 and to roll journals 11, maybe combined, however, it is not necessary to use
all
measures depicted in a single exemplary figure together. For example, cooling
ribs 17 may be omitted from the exemplary embodiment depicted in Figure 1
without departing from the scope of the present invention.
In the exemplary embodiment according to Figure 2, insulation 6 remains
substantially the same, however, it may be applied somewhat thinner in the
region
of polished shoulder 7. Of course, the thickness of insulation 6 is governed
by the
specific material used.
Additional measures have been taken for the j ournal heating. For example,
an arrangement of inserts 19 made of, e.g., aluminum, copper, or another good
heat conducting material may be provided. Inserts 19 may be heat conductingly
connected with core 2 and with roll journal 11. Inserts 19 may also be
connected
to each other. Via inserts 19, heat may flow out of the barrel region of
calender
roll 1 into the axial ends of calender roll 1.
-13-
CA 02272205 1999-OS-19
P17767.502
Another journal heating possibility can be provided by virtue of core 2
including a large number of axis-parallel boreholes 20 distributed in the
circumferential direction. Boreholes 20 may be connected with pumps 21 (only
one of which is schematically depicted). Pumps 21 may have a drive gear 22,
which engages with a stationary annular gear 23 that is mounted on a lever 24
coupled to bearing 10. Annular gear 23 may surround the entire shaft end 9,
however, for the sake of clarity, only the upper half has been depicted in
Figure
2. Pump 21 may circulate a heat transfer liquid which flows in the axial
direction
through the boreholes 20, as indicated by arrows 25 and 26. Arrow 26 is shown
in a bore depicted in dashed lines, which is intended to express that this
bore is
disposed behind borehole 20. In this manner, the heat transfer liquid can be
pumped out and back using pump 21. Moreover, this can result in uniform heat
distribution over the axial length of calender roll 1.
It is noted that the foregoing examples have been provided merely for the
purpose of explanation and are in no way to be construed as limiting of the
present
invention. While the present invention has been described with reference to an
exemplary embodiment, it is understood that the words which have been used
herein are words of description and illustration, rather than words of
limitation.
Changes may be made, within the purview of the appended claims, as presently
stated and as amended, without departing from the scope and spirit of the
present
invention in its aspects. Although the present invention has been described
herein
with reference to particular means, materials and embodiments, the present
invention is not intended to be limited to the particulars disclosed herein;
rather,
the present invention extends to all functionally equivalent structures,
methods and
uses, such as are within the scope of the appended claims.
- 14-
