WO2001063045A1

WO2001063045A1 - Method and apparatus for cooling the edge zone of a roll

Info

Publication number: WO2001063045A1
Application number: PCT/FI2001/000138
Authority: WO
Inventors: Timo Torvi; Kari Hasanen; Matti Lares; Pekka Koivukunnas; Eero Nupponen
Original assignee: Metso Paper, Inc.
Priority date: 2000-02-21
Filing date: 2001-02-14
Publication date: 2001-08-30
Also published as: FI20000391A0; AU2001237463A1; FI106732B

Abstract

The invention relates to a method and an apparatus for cooling the edge zone of a polymer-coated roll or a long-nip roll (1) forming a nip (N) with a heated roll (2) in a paper/board machine, said nip having a temperature within the range of about 200 °C to about 400 °C. The method comprises bringing a cooling medium within the edge zone of the roll (1) into a contact with the roll surface at an inlet immediately downstream of the nip (N) by means of cooling elements (3) which are in contact with the surface of the roll (1). The cooling elements (3), and thereby the surface of the roll (1), are supplied with doses of cooling medium in drops or pulses such that the amount of cooling medium delivered to the surface of the roll (1) is sufficiently small for the same to build a discontinuous film across the section between the cooling medium inlet and its nip-preceding outlet, thereby denying the cooling medium an access to the nip (N).

Description

Method and apparatus for cooling the edge zone of a roll

The present invention relates to a method for cooling the edge zone of a polymer-coated roll or a long-nip roll forming a nip with a heated roll in a paper/board machine, said nip having a temperature within the range of about 200° C to about 400° C. The invention relates further to an apparatus for cooling the edge zone of a polymer-coated roll or a long-nip roll forming a nip with a heated roll in a paper/board machine, said nip having a temperature within the range of about 200°C to about 400°C.

In calendering, a web of paper is pressed between a hot thermo roll and a counter roll, whereby the paper, as a result of mechanical work and heat, undergoes a deformation both in a lateral direction and in a perpendicular direction. The web being calendered may have its width fluctuate over several hundred millimeters. Thus, when the counter roll comprises a polymer-coated roll or a long-nip roll, the roll surface comes to a direct contact with the thermo roll at full surface pressure as the paper web sinks within the polymer coating or the belt of a long-nip roll and the counter-roll surface and the paper surface are more or less flush with each other. In this situation, air alone is not enough for cooling the counter-roll surface in its edge zone but, at least in testing, it has been supplemented with water spray. One major problem with such water spray is its inability to readily penetrate the air layer carried by the roll surface and, furthermore, the rebounding of water from the roll surface causes unnecessary splashing. The production machine requires a powerful exhauster for removing these water drops.

It is an object of the present invention to provide enhanced cooling for the edge zone of a roll forming a nip with a heated thermo roll, thereby avoiding the problems associated with the use of water spray. In order to accomplish this objective, a method of the invention is characterized in that the method comprises bringing a cooling medium within the edge zone of a roll into a contact with the roll surface at an inlet immediately downstream of the nip by means of cooling elements which are in contact with the roll surface, said cooling elements, and thereby the roll surface, being supplied with doses of cooling medium in drops or pulses such that the amount of cooling medium delivered to the roll surface is sufficiently small for the cooling medium to build a discontinuous film across the section between the cooling medium inlet and its nip-preceding outlet, thereby denying the cooling medium an access to the nip. On the other hand, an apparatus of the invention is characterized in that the apparatus comprises cooling elements which are in contact with a roll surface in the edge zone of a roll, said cooling elements being provided with means for delivering a cooling medium to the cooling elements and by means of the cooling elements in drops or pulses further to the roll surface in the edge zone of the roll. The cooling medium comprises preferably water.

The invention will now be described in more detail with reference to the accompanying drawings, in which

figs. 1-4 show schematically in end views a few aspects in principle for an apparatus applicable to a method of the invention,

fig. 5 shows one embodiment for an apparatus of the invention in a plan view, and

fig. 6 shows yet another embodiment for an apparatus of the invention.

The figures are provided with identical reference numerals for the same or matching elements. In the illustrated embodiments, reference numeral 2 refers to a thermo roll and reference numeral 1 to a counter roll forming a nip N therewith. The thermo roll 2 is preferably heated to a temperature range of about 200°C to 400°C. The counter roll 1 comprises a soft-surfaced polymer-coated roll or a long-nip roll (belt roll), which is provided with a belt adapted to be rotatable around a stationary roll journal. Reference numeral W indicates a paper web and reference numerals 11a, 11 b in fig. 5 refer to an edge of the paper web W, said edges being located in the axial direction of a roll inwards from the roll ends. Thus, a section or zone of the counter roll 1 left outside the web W is forced to a direct contact with the heated thermo roll 2 as a result of the paper web sinking within the polymer coating or the belt of the counter roll, whereby the counter roll surface and the paper surface are approximately flush with each other. In view of cooling this edge zone, the method and apparatus of the invention involve the use of cooling elements 3, which are installable against the surface of a counter roll or near the surface and which are supplied with a cooling medium, preferably water, dispensed in drops or pulses from a container 5, e.g. by means of a regulating valve 6, such that the amount of cooling medium delivered to the edge zone surface of the roll 1 is sufficiently small for building a discontinuous film across the section between a cooling-medium inlet and its nip-preceding outlet, thus denying the cooling medium an access to the nip N. According to figs. 1 and 2, the cooling element 3; 3a, 3b is preferably located over a quadrant of the roll 1 first downstream of the nip N. In fig. 1 the cooling element 3 is depicted being mounted over a section of about 30° to about 60° downstream of the nip N, in fig. 2 the cooling element consists of two separate components 3a, 3b, the locations of which are about 30° to about 60° and about 70° to about 90° downstream of the nip. According to fig. 3, the cooling element may extend also to the area of a quadrant second downstream of the nip N, for example over the section of about 30° to about 150°. The cooling element may comprise for example a woven structure, a spongy structure or a stranded, brush-type cooling element. When the employed cooling element comprises a ribbon-like element, it is possible to reel off a fresh clean ribbon and to reel up the soiled ribbon on a reject roller.

The inventive method and apparatus may further involve the use of dryer elements 4 for making sure that no cooling medium finds its way to the nip N and thus, possibly, to moisten the paper web. In figs. 1-3 the dryer elements are located counter-clockwise as seen from the nip N in positions substantially the same as the cooling elements 3. In principle, the dryer elements may comprise structures similar to those of the cooling elements.

Fig. 4 depicts a solution, wherein the cooling elements and the dryer elements are designed as a continuous ribbon-like element 3, 4, the forward end thereof being supplied with a cooling medium in drops or pulses from a container 5 by means of a regulating valve 6 or a similar control device and the tail end of said ribbon 3, 4 drying the roll surface. For enhanced drying, it is possible to employ an exhauster unit within the drying zone or the dryer element can be maintained in contact with the roll surface for the resulting heat due to friction to encourage evaporation.

In order to prevent splashing, which is problematic e.g. at a running speed of more than 500 m/min, the cooling and dryer elements are adapted to cover as large a portion as possible of the exposed roll surface.

The amount of cooling medium used in a method and an apparatus of the invention is most conveniently within the range of about 2 l/h to about 20 l/h, preferably less than about 10 l/h, whereby it evaporates partly or completely prior to reaching the outlet (site of the dryer elements).

The evaporation of a cooling medium delivered to the roll surface can also be enhanced by means of air blowing, and reclaiming of the evaporating cooling medium can be performed by means of currently available exhausters but, the amount of cooling medium being substantially smaller than before, the capacity required by exhausters will also be smaller.

Fig. 6 depicts still another embodiment for the cooling element 3. The cooling element comprises a wheel 12 of some soft material, which is all the time maintained in contact with the edge-zone surface of the roll 1. From the container 5 a cooling medium is delivered by way of the regulating valve 6 to a centre axle 14 of the wheel 12, wherefrom it is driven by a centrifugal force to wheel rim sections, and further to the roll surface. Around the wheel is mounted a guard element 13. The wheel 12 is made of a material which is porous, e.g. polyester or polyamide, which is comparatively easy for a cooling medium to penetrate. Thus, the cooling medium is received on the roll surface in a controlled fashion and the amount thereof can be regulated as required by the surface temperature. The amount of a cooling medium is preferably adjusted in pulses in order to give it time to evaporate before the inlet comes back to the nip again. Evaporation can be enhanced by means of air blowing and, if necessary, further assistance can be provided by the dryer elements 4.

Claims

1. A method for cooling the edge zone of a polymer-coated roll or a long-nip roll (1 ) forming a nip (N) with a heated roll (2) in a paper/board machine, said nip having a temperature within the range of about 200°C to about 400°C, characterized in that the method comprises bringing a cooling medium within the edge zone of the roll (1 ) into a contact with the roll surface at an inlet immediately downstream of the nip (N) by means of cooling elements (3) which are in contact with the surface of the roll (1 ), said cooling elements (3), and thereby the surface of the roll (1 ), being supplied with doses of cooling medium in drops or pulses such that the amount of cooling medium delivered to the surface of the roll (1 ) is sufficiently small for the cooling medium to build a discontinuous film across the section between the cooling medium inlet and its nip-preceding outlet, thereby denying the cooling medium an access to the nip (N).

2. A method as set forth in claim 1 , characterized in that the cooling medium is delivered to the roll (1 ) at an inlet located within the range of about 5° to about 150°, preferably about 30° to about 60°, downstream of the nip.

3. A method as set forth in claim 1 or 2, characterized in that the cooling medium is delivered in an amount within the range of about 2l/h to about 20 l/h, preferably less than about 10 l/h, whereby the cooling medium evaporates partly or completely prior to reaching an outlet located upstream of the nip (N).

4. A method as set forth in any of claims 1 -3, characterized in that the cooling element (3; 3a, 3b) comprises a ribbon-like element, extending circumferentially of the edge zone to be cooled.

5. A method as set forth in any of the preceding claims, characterized in that the method further comprises the use of a dryer element (4; 4a, 4b) located at the outlet for removing, prior to entering the nip, any cooling medium possibly remaining on the roll surface.

6. A method as set forth in any of the preceding claims, characterized in that the cooling medium comprises water.

7. An apparatus for cooling the edge zone of a polymer-coated roll or a long- nip roll (1 ) forming a nip (N) with a heated roll (2) in a paper/board machine, said nip (N) having a temperature within the range of about 200°C to about 400°C, characterized in that the apparatus comprises cooling elements (3) which are in contact with the surface of the roll (1 ) in the edge zone of the roll, said cooling elements (3) being provided with means for delivering a cooling medium to the cooling elements and by means of the cooling elements in drops or pulses further to the surface of the roll (1 ) in the edge zone of the roll.

8. An apparatus as set forth in claim 7, characterized in that the cooling elements (3; 3a, 3b) comprise a ribbon-like element.

9. An apparatus as set forth in claim 7 or 8, characterized in that the apparatus further includes dryer elements (4), which are located upstream of the nip for ensuring a substantially complete removal of the cooling medium from the roll surface before it enters the nip.

10. An apparatus as set forth in claim 7, characterized in that the cooling elements (3) comprise a wheel-shaped element (12), which is adapted to be rotatable around an axle (14) and which is in contact with the edge zone surface of the roll (1 ).

11. An apparatus as set forth in claim 10, characterized in that the wheel- shaped element (12) is made of a soft material which is permeable to the cooling medium.