CA2119940A1

CA2119940A1 - Heated hollow roll

Info

Publication number: CA2119940A1
Application number: CA 2119940
Authority: CA
Inventors: Karl Steiner; Albrecht Meinecke
Original assignee: JM Voith GmbH
Current assignee: JM Voith GmbH
Priority date: 1993-03-31
Filing date: 1994-03-25
Publication date: 1994-10-01
Also published as: FI941494A0; JPH0771443A; FI941494A; DE4310404A1

Abstract

HEATED HOLLOW ROLL

ABSTRACT OF THE DISCLOSURE
A hollow roll, especially for use as a smoothing roll, press roll, or drying cylinder in the manufacture of a web of material, such as paper, includes apparatus for the controlled heating of edge regions of the roll. The heating apparatus comprises an internal and/or an external heating device or devices. The internal heating device is disposed within the roll and is inset relative to a width of a web passing over the roll. The external heating device is disposed outside of the roll and in the vicinity of the edge regions thereof.

Description

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 211~40 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.

~1 3940 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 ~.

211~40 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 ~

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 modifications within the scope of the invention will be apparent to those skilled in the art.

Claims

1. In a hollow roll for use with a web of material, said roll including means for controlled heating of edge regions thereof, the improvement comprising at least one of (a) means for heating an internal wall of the roll disposed within the roll and inset relative to a width of a web passing over an external roll surface, and (b) means for heating the external roll surface disposed substantially in the vicinity of the edge regions thereof.

2. The improvement of claim 1 wherein the edge regions of the roll are simultaneously heat-controlled by the internal heating means and the external heating means.

3. The improvement of claim 2 wherein the internal and external heating means are disposed relative to the edge regions of the roll SQ that zones of heating of the internal and external heating means at least partially overlap.

4. The improvement of claim 1 wherein the internal heating means comprises individually activated sectors.

5. The improvement of claim 1 wherein the external heating means comprises individually activated sectors.

6. The improvement of claim 1 wherein the external heating means is disposed parallel to an axis of the roll.