WO2001073306A1

WO2001073306A1 - Method for decreasing the temperature difference between the edge section and the middle section margin of a polymer coating on a cylinder and equipment used in the method

Info

Publication number: WO2001073306A1
Application number: PCT/FI2001/000312
Authority: WO
Inventors: Kari Hasanen; Pekka Koivukunnas; Juha Lipponen; Mika Viljanmaa; Henri Vaittinen
Original assignee: Metso Paper, Inc.
Priority date: 2000-03-31
Filing date: 2001-03-30
Publication date: 2001-10-04
Also published as: DE10195955T1; FI108072B; AU2001250450A1; FI20000742A0

Abstract

The invention relates to a method for reducing the temperature difference (ΔT) between the border portion (8; 8b) of the polymer surface on a roll and the border area (8; 8a) of its central portion by blowing gas onto the roll surface during the calendering of the fibre web (5) by feeding the fibre web into the calender nip (7) between at least one pair of rolls. The pair of rolls comprises a heated thermo-roll (3) and an opposite roll (2), covered by the polymer surface. In the method, the fibre web is disposed to contact the polymer surface (8) in the vicinity of the nip at a first location, after which the fibre web is disposed to circulate about the polymer surface to a second location, where the fibre web diverges from the polymer surface. Cooling gas is blown on the polymer surface on the roll between the first and second location, in the vicinity of the nip, so that the cooling gas is directed partly to the border portion (8; 8b) of the polymer surface (8) that is not coated with paper or board web, and partly to the border area (8; 8a) of its central portion that is coated with paper or board web and is located adjacent to the border portion. The invention also relates to the apparatus used in the method. The apparatus comprises means (4) for controlling the fibre web and a cooling apparatus (1) including a blowing means.

Description

Method for decreasing the temperature difference between the edge section and the middle section margin of a polymer coating on a cylinder and equipment used in the method

The invention relates to a method for instance such as defined in the preamble of claim 1 for reducing the temperature difference between the border portion and the central portion border area of a polymer coating on a roll.

The invention also relates to an apparatus for instance such as defined in the preamble of claim 8 for reducing the temperature difference between the border portion and the central portion border area of a polymer coating on a roll.

The paper or board web in "soft and/or super calendering" in paper machines passes through at least one calendering nip, one of the rolls forming the nip being flexible and soft on the surface, and the other roll being a heated metal roll, called a "thermo-roll". In this context, a nip stands for the contact area between a pair of rolls, with the longitudinal axes PI and P2 of the rolls (cf. figure 2) disposed substantially in alignment. In the "soft calendering" in paper machines, polymer- coated rolls have been increasingly adopted for use as flexible rolls. The coating of polymer-coated rolls does not withstand temperatures above approx. 80-120 degrees without damage, and on the other hand, for each polymer quality, the specific maximum temperature difference between different areas of the coating is ΔTmax, which the coating endures without damage. For the most frequently used polymer coatings, ΔTmax is approx. 20-30 degrees.

In soft calendering, the surface temperature of a heated metal roll, i.e. a "thermo- roll", may rise up to about 250 degrees. When a paper or board web is run in soft calendering through the nip between a polymer-coated roll and a thermo-roll, there are often problems caused by the width of the paper and board web varying in the. direction of the longitudinal axis PI of the polymer-coated roll. If the width d of the web is smaller than the length L of the nip (the nip length equalling the length P of the cylindrical portion of a polymer-coated roll in the direction of the longitudinal axis of the roll), the thermo-roll 3 and the polymer-coated roll 2 will be allowed to get in mutual contact or to close to each other at the nip edges. In this case, the border area of the polymer-coated roll surface will be notably more heated by the thermo-roll than the central portion border area of the surface coated with the paper or board web 5. This phenomenon is illustrated in figures 3 A and 3C. Figure 3 A is a side view of a portion of the end of a roll pair, viewed perpendicularly to the nip, with the direction of movement of the fibre web 5 towards the viewer. The roll pair comprises a polymer-coated roll 2; 2' and a thermo-roll 3. A nip 7 is provided between the rolls, and a paper or board web passes through the nip. The width d of the paper or board web is smaller than the length L of the nip in the direction of the longitudinal axis of the polymer-coated roll. In figure 3C, the curve Kl shows the development of the temperature difference ΔT1 between the border portion 8b' of the surface 8; 8' of the cylindrical portion of the polymer roll and the border area 8a' of the central portion of the surface of the same roll. As shown in the figure, a distinct temperature difference peak arises between the border portion and the border area of the central portion of the polymer-coated roll surface. Should the temperature difference ΔT1 grow too much, it could cause damage to the polymer coating and thus deteriorate the roll properties, thus requiring the roll or its coating to be replaced at shorter intervals.

There have been attempts to solve this problem by running the paper or board web with excess width, i.e. with a width larger than the length P of the cylindrical portion of the polymer-coated roll, and by cutting off the excess width of the fibre web before rolling. This method involves the problem of paper or board loss, which entails higher calendering costs.

There have also been attempts to cool the border portions of a polymer-coated roll by means of an accurately directed water jet. DE Patent Application 40 37 166 describes an example of such a cooling method, in which the edges of a polymer- coated roll are cooled by means of a water jet. For exact positioning of the water jet, the method of this reference resorts to a complex control system. US patent specification 5,266,167 also describes a solution in which the border areas of the polymer-coated roll extending beyond the paper and board web are cooled with a water jet directed to the edges. Despite the efforts to direct the cooling water jet accurately, the edges of the paper or board web easily get wet. In fact, in this method, air blowing is required after the water cooling in order to evaporate the water from the edges of the paper and board web, and this operation makes the apparatus and the water jet control method even more complex.

There have also been attempts to solve the resistance problem of the polymer coating of a roll, as mentioned above, by determining the temperatures at the edges of the roll surface with an IR camera and by cooling the border portions of the roI surface extending beyond the paper or board web with an air jet, which is directed to the area of the border portions of the roll surface which is not covered by the fibre web in the nip. However, it is difficult to direct an air jet to the desired location on a polymer-coated roll because of air turbulence. Automatic air jet directing systems, in turn, are complicated and expensive in terms of control engineering, and in the practice, the air jet is thus usually directed by hand by following the width of the paper and board web. In the practice, a manually directed air jet will cool not only the border portions of the polymer-coated roll surface, but also as a rule the border area of the cylindrical roll portion, which gets under the paper or board web in the nip, and then the temperature difference between the border portion and the border area of the central portion of the polymer coated roll surface is not reduced as desired. This phenomenon is illustrated in figures 3A and 3C. Figure 3A shows the blowing means 6 with a broken line. The blowing means is located partly on the border area 8a' of the central portion of the roll 2 surface and partly on the border portion 8b' of the roll surface. Under the action of the cool air jet blown by the blowing means, the temperature of the border portion 8b, 8b' of the surface indeed drops to a temperature Tl' (curve K2 in figure 3C), however, at the same time, the temperature of the border area 8a, 8a' of the central portion of this roll surface drops to a value T2', which is lower than T2, because part of the air flow tends to be directed under air turbulence also to the border area of the central portion of the roll surface, which gets under the paper or board web 5 in the nip. Then the temperature difference Tl' - T2' = ΔT2 between the border portion 8b' and border area 8a' of the central portion of the roll surface is not sufficiently reduced. Should the temperature difference ΔT2 grow too much, the nip will have to be opened and the calendering of the paper or board web interrupted.

The description above is confined to damage and deterioration of the quality of polymer-coated roll surfaces caused by high temperatures used in calendering. However, long-nip calendering involves the same problem. When long-nip calendering is performed with a shoe calender, a static shoe roll on which an endless belt rotates is disposed opposite the thermo-roll. By contrast, when long-nip calendering is performed with a belt calender, an endless belt is disposed in the nip between the thermo-roll and the opposite counter-roll, the belt being adapted to rotate on the counter-roll by means of control/pull rolls. If polymer is used as the coating material of the belt in the shoe calender or the belt calender, similar problems will arise as those described above in connection with a polymer-coated roll, if the thermo-roll is allowed to heat the polymer surface of the belt excessively.

The object of the invention is to eliminate the prior art drawbacks mentioned above. Thus, the first object of the invention is to provide a method for cooling the border portions of a polymer surface on a roll, which will extend beyond the edges of the paper or board web in the calendering nip. The purpose of the invention is to perform the cooling so as to reduce the temperature difference between the border portions of the polymer coating and the border areas of the central portion of the roll surface, which gets under the paper or board web in the nip.

A second object of the invention is to provide a method for reducing the temperature difference that is straightforward in terms of control engineering.

A third object of the invention is to provide a cooling method that does not wet the border areas of the paper or board web.

The invention relates to a method for instance such as defined in claim 1 fo reducing the temperature difference (ΔT) between the border portion of the polymer coating on a roll and the border area of the central portion of the polymer coating by blowing gas onto the polymer coating.

The invention also relates for instance to an apparatus such as defined in claim 8 for reducing the temperature difference between the border portion and the border area of the central portion of the polymer coating during the calendering of a paper or board web in a calendering nip comprising at least one pair of rolls.

The basic idea of the invention is the cooling of the border portions of the polymer coating on the roll, in the vicinity of the calendering nip, by means of a gas flow, which is directed partly to the border portion of the polymer surface which is not coated with a fibre web, i.e. a paper or board web, and partly to the border area of the central portion coated with a fibre web, which is adjacent to the border portion.

When the pair of rolls is viewed from the end as in figures 1A and IB, the fibre web is usually located in the nip only on the polymer surface 8 on the roll 2 (cf. figures'

3A and 4C, showing the conventional way of feeding fibre web into the nip and of removing it from the nip), however, in the method of the invention, the fibre web has been disposed to run on the polymer surface over a distance equalling at least 5 degrees, preferably more than 15 degrees calculated on the circumferential angle of the cross-sectional circle of the roll under the polymer surface.

In the method of the invention, the temperature difference (ΔT) between the border portion of the polymer coating on a roll and the border area of the central portion of the polymer coating is reduced by blowing gas onto the polymer coating during the calendering of the fibre web. The gas is preferably air. The fibre web is calendered by feeding the fibre web into the calendering nip between at least one pair of rolls, the pair of rolls comprising a heated thermo-roll and an opposite roll coated with polymer coating. The polymer coating covers the roll either in the vicinity of the nip alone or over its entire periphery (soft and shoe calenders). In this method, the fibre web is disposed to meet the polymer surface in the vicinity of the nip at a first location, and after this the fibre web is disposed to circulate around the polymer surface to a second location, where the fibre web diverges from the polymer surface. Cooling gas is blown onto the polymer surface between the first and second location, in the vicinity of the nip, so that the cooling gas is partly directed to the border portion of the polymer surface that is not coated with fibre web and partly to the border area of the central portion coated with fibre web, adjacent to the border portion.

The fibre web contacts the polymer surface at a first location, before the nip, in the vicinity of the nip or in the nip proper. Similarly, the second location is in the nip, after the nip or in the vicinity of the nip.

The apparatus used in the method comprises means for controlling the fibre web¹ and a cooling device including a (gas) blowing means. The first control means is located relative to the roll under the polymer surface so as to guide the fibre web onto the polymer surface at a first location and the second control means is located relative to this same roll so as to guide the fibre web off the polymer roll surface at a second location. The gas jet from the blowing means is directed to the vicinity of the nip, partly onto the border portion of the polymer surface that is not coated with fibre web, and partly onto the border area of the central portion that is coated with fibre web, adjacent to the border portion.

When the calendering nip is viewed perpendicularly from the direction of the cooling device, the cooling means of the cooling device are partly on top of the border portion of the polymer surface that is not coated with paper or board web and partly on top of the border area of the central portion coated with paper and board web, adjacent to the border portion.

Compared to conventional methods using a water jet to cool the edges, the use of gas jet for cooling the border portions of the polymer surface on top of the roll achieves the advantage of avoiding wetting of the edges of the paper and board web and consequently deteriorated paper quality. In the method of the invention, the cooling gas jet is directed partly onto the border portion of the polymer surface on the roll that is not coated with paper or board web, and partly onto the border area of the central portion that is coated with paper or board web, adjacent to the border portion of the polymer surface. Thus the paper or board web prevents the underlying polymer surface from being cooled. This arrangement reduces the temperature difference between the edges of the polymer surface extending beyond the paper or board web and the part of the polymer surface covered by the paper and board web in the nip. With the method of the invention, the temperature difference between the different parts of the polymer surface is reduced to an extent such that the maximum temperature difference between the different parts of the polymer surface is not exceeded. Compared to conventional methods, this achieves the advantage of the calendering nip not having to be opened for cooling the polymer surface on the roll, thus allowing increased average rate of calendering of the paper or board web.

Among the additional benefits gained by the method of the invention, we mention that it is very straightforward in terms of control engineering, because the direction of the gas jet does not require high-precision control in alignment with the longitudinal axis of the roll under the polymer surface, given the use of the fibre web to protect the polymer surface against excessive cooling. Nor is the control method susceptible to shifted positions of the paper or board web in the direction of the longitudinal axis of the roll under the polymer surface. i The invention is described in greater detail below with reference to the accompanying figures.

Figure 1A is a schematic view of the arrangement of transferring a paper or board web onto a polymer-coated roll and of the device for cooling the roll polymer surface, viewed from the end of the pair of rolls.

Figure IB is a schematic view of the arrangement of transferring a paper or board web and of the device for cooling the roll polymer surface on a shoe roll, about which a polymer-coated endless belt circulates, viewed from the end of the pair of rolls. The shoe roll is shown in partly cross-sectional view.

Figure 2 shows the transfer arrangement and the cooling device of figure 1A viewed in direction II of figure 1A. Figure 3 A shows a prior art air-cooling method, in which the second border portion of the calender nip formed by the roll pair is viewed perpendicularly from the side of the roll pair.

Figure 3B shows the gas cooling method of the invention, in which the second border portion of the calender nip formed by the roll pair is viewed perpendicularly from the side of the roll pair.

Figure 3C shows the development of the temperature difference between the border portion of the polymer roll surface and the border area of its central portion in the nip, both in conventional cooling methods and in the cooling method of the invention.

Figure 4A shows an embodiment of the cooling method of the invention, with the nip viewed perpendicularly from the end of the calender nip formed by the roll pair.;

Figure 4B shows a second embodiment of the cooling method of the invention. The reference numerals and the representation in the figure are identical to those of figure 4A.

Figure 4C shows a prior art cooling method. The reference numerals and the representation in the figure are identical to those of figures 4A and 4B.

In the system for cooling a polymer-coated roll surface shown in figure 1A, the fibre web 5 is calendered in the calender nip 7; 7' between the polymer-coated roll 2; 2' formed by a rotating roll pair and an opposite thermo-roll 3. The rolls rotate in opposed directions: the polymer-coated roll rotates counter-clockwise and the thermo-roll rotates clockwise. The fibre web 5 contacts the polymer-coated roll surface 8; 8' at A; A and diverges from the polymer-coated roll surface at B; B'.

Figure IB shows a shoe calender, in which opposite the thermo-roll 3 is placed a static shoe roll 2; 2", around which an endless polymer-coated belt 8; 8" circulates. The fibre web 5 is disposed to contact the polymer-coated belt 8" rotating about the shoe roll surface at A; A" and diverges from the surface of the polymer-coated belt at B; B". The fibre web is pressed against the thermo-roll in the nip 7; 7" under the pressure exerted by the shoe 9 of the shoe roll against the polymer-coated belt. In the shoe calender, the length of the nip parallel to the longitudinal axis of the shoe roll is equal to the width of the endless belt in the direction of the longitudinal axis of the shoe roll. Figure 2 shows the cooling system of figure 1A viewed from the side of the roll pair. Cooling gas is blown with the cooling device 1 to the border portions 8b' of the polymer-coated roll surface 8; 8' and border areas 8a' of the central portion. The figure shows that the longitudinal axes PI and P2 of the polymer-coated roll and the thermo-roll are substantially aligned. The blowing means 6 of the cooling device 1 is located partly on top 8', 8b' of the border portion of the polymer-coated roll surface and partly on top 8'; 8a' of the border area 8'; 8a' of its central portion.

Figures 3A-3B show one border portion of a calender nip formed by a pair of rolls, with the nip viewed perpendicularly from the side of the pair of rolls. Figure 3 A shows a prior art air cooling method, in which the width of the fibre web, i.e. paper and board web, is d, which is smaller than the length P of the cylindrical portion of the polymer-coated roll, in the direction of the longitudinal axis of the roll, which is simultaneously the length L of the longitudinal axis PI of the polymer-coated roll 2; 2' of the nip 7; 7'. The paper web 5 only covers the polymer roll surface in the nip. The fibre web is cooled with a blowing means 6. Figure 3B, and also figure 3A, show the other border portion of the calender nip formed by a roll pair. The width of the fibre web is d, the length of the coated portion of the polymer-coated roll is P_s and the nip length is L. The fibre web 5 covers the polymer roll surface 8; 8' also after the nip. The fibre web is cooled with the blowing means 6. In both cases, the blowing means 6 is located partly on top of the border portion 8b' of the polymer- coated roll and partly on top of the border area 8a' of its central portion.

Figure 3C shows the development of the temperature difference (ΔT) between the border portions 8'; 8b' of the polymer coated roll 2 surface and the border areas 8'; 8a' of its central portion in the nip. The curve Kl illustrates the development of the temperature difference Tl - T2=ΔT1 unless the border portions of the roll surface are cooled. Curves K2 and K3 illustrate the development of the temperature difference when the border portions of the roll surface are cooled by different methods. Curve K2 illustrates the development of the temperature difference Tl' - T2'= ΔT2 with the prior art cooling method and the curve K3 the development of the temperature difference Tl" - T2"= ΔT3 with the method of the invention. T2 T2' and T2" denote the temperature (T2 being about 60 degrees) of the border area 8'; 8a' of the central portion of the cylindrical area of the polymer-coated roll and Tl, Tl' and Tl" denote the temperature (Tl being about 80 degrees) of the border portion 8'; 8b' of the cylindrical area of the same roll.

Figure 4A shows one embodiment of the cooling method, in which a cooling gas such as cooling air is blown in the vicinity of the nip 7; 7', when the fibre web 5 has been adapted to cover a given distance on the outer surface 8; 8' of the roll. The fibre web runs from the left to the right and it contacts the polymer roll surface at location C. The fibre web diverges from the roll surface immediately after the calender nip at location D. The fibre web is led to the polymer roll surface 8; 8' and away from this by control rolls 4a and 4b. Cooling gas is blown by blowing means 6, which is located on the input side of the fibre web viewed from the nip. The angle between locations C and A is α calculated on the peripheral angle of the roll 2'.

Figure 4B shows a second embodiment of the cooling method, in which cooling gas such as cooling air is blown in the vicinity of the nip 7; 7'. The fibre web 5 contacts the polymer-coated roll surface in the nip, i.e. at A; A and the fibre web diverges from the roll surface at B; B". The fibre web is directed to the polymer-coated roll surface 8; 8' and off this surface by control rolls 4c and 4d. Cooling gas is blown by blowing means 6, which is located on the output side of the web relative to the nip.

For the sake of comparison, figure 4C shows the air cooling method currently used for polymer-coated rolls 2; 2'. Air is blown by blowing means 6, which is located on the output side of the web relative to the nip, the fibre web 5 runs from the left to the right through the nip 7; 7', and its contacts the polymer-coated roll surface 8; 8' only in the nip.

As noted above, regarding several paper and board grades, the temperature of the, heated thermo-roll must be raised to a point such that the thermo-roll tends to heat the border portion 8b of the polymer surface - especially in a nip where the thermo- roll surface is next to the polymer-coating on the opposite roll - notably more than the border area 8a of its central portion coated with fibre web. Without cooling of the border portions of the polymer surface, the temperature of the border portion of the polymer surface tends to rise to the temperature Tl while the temperature of the border area of the central portion of the surface remains at a lower temperature T2, the temperature difference between the parts being ΔT1 (cf. figure 3C curve Kl).

In the method of the invention, the fibre web, i.e. the paper or board web, is conducted in the vicinity of the nip 7 to run on the polymer surface 8 by means of the control rolls 4. The fibre web 5 can be disposed to run on the polymer surface on the roll, either before or after the nip, the latter provision being easier to carry out in technical terms. The fibre web 5 is brought via the control roll 4; 4a; 4e, 4c t the calender nip 7; 7', 7" between the rotating roll pair. The fibre web contacts the polymer surface 8; 8', 8" on the roll 2; 2', 2" in the vicinity of the nip, i.e. at C or A; A', A", depending on the fact whether the fibre web 5 meets the surface of the roll 2 before the nip (C) or in the nip (A). At both ends of the polymer surface, a border portion 8b is formed, whose surface is not covered by fibre web, in case the width d of the paper web is smaller than the nip length L. After this, the fibre web is guided by the control roll 4; 4b, 4d, 4f to diverge from the polymer surface. The fibre web thus circulates around the polymer surface 8 so that the angle between the location C or A at which the fibre web contacts the polymer surface and the location D or B at which it diverges from the surface is α calculated on the peripheral angle of the roll 2. Depending on the fact whether the fibre web 5 runs on the polymer surface before or after the calender nip 7, the blowing of cooling gas, such as cooling air, is provided in the vicinity of the nip, from the web input or output direction viewed from the nip. Cooling air is blown with the blowing means 6 in the vicinity of the calender nip 7 partly to the border portions 8b of the polymer surface and partly to the border area 8a of the central portion of the surface, between the surface locations C and D or A, and B, depending on the fact whether the fibre web has been disposed to run on the polymer surface before or after the nip. Because there is a continuous fibre web 5 on the border area 8a of the central portion of the polymer surface between location C and D and A and B, the air jet is not here allowed to cool the border area of the central portion of the polymer surface notably. Thus the temperature difference Tl" - T2"= ΔT3 between the border portion of the polymer surface and the border area of its central portion decreases, without the quality of the polymer coating surface being deteriorated by an excessive temperature difference.

One single embodiment of the inventive idea has been described above. It is obvious to those skilled in the art that the invention can be implemented in manv_j other ways without departing from the scope of the invention defined in the claims. Consequently, the cooling device 1 shown in figures 1 and 2 can be replaced with another cooling device, which has been provided with edge sensors, for instance. The polymer-coated roll may also be a roll made completely of polymer.

Claims

1. A method for reducing the temperature difference (ΔT) between the border portion (8; 8b) of the polymer surface (8) on a roll and the border area (8;, 8a) of the central portion of the polymer surface by blowing gas onto the polymer surface on the roll during the calendering of the fibre web (5) by feeding the fibre web into the calender nip (7) between at least one pair of rolls, the pair of rolls comprising a heated thermo-roll (3) and an opposite roll (2), covered by the polymer surface, characterised in that

- the fibre web is disposed to contact the polymer surface (8) in the vicinity of the nip at a first location, after which the fibre web is disposed to circulate about the polymer surface to a second location, where the fibre web diverges from the polymer surface, and

- cooling gas is blown on the polymer surface between the first and second location; in the vicinity of the nip, so that the cooling gas is directed partly to the border portion (8; 8b) of the polymer surface (8) that is not coated with fibre web, and partly to the border area (8; 8a) of the central portion that is coated with fibre web and is located adjacent to the border portion.

2. A method as defined in claim 1, characterised in that air is blown on the polymer surface and that the cooling gas is cooling air.

3. A method as defined in claims 1-2, characterised in that the angular distance between the first and the second locations is above 5 degrees, preferably above about 15 degrees, calculated on the peripheral angle of the cross-sectional circle of the roll.

4. A method as defined in claim 3, characterised in that the first location is in the vicinity of the nip (7) before the nip or in the nip, and the second location is in the nip or in its vicinity after the nip.

5. A method as defined in claims 1-4, characterised in that the fibre web is a paper web or a board web.

6. A method as defined in any of claims 1-5, characterised in that the polymer surface (8; 8') is solidly fixed to the rotating roll (2; 2').

7. A method as defined in any of claims 1-5, characterised in that the polymer surface (8; 8") rotates about a stationary shoe roll (2; 2").

8. An apparatus for reducing the temperature difference between the border portion (8; 8b) of a polymer surface (8) on a roll (2) and the border area (8; 8a) of its central portion during the calendering of a fibre web (5) in the calender nip (7) formed of at least one pair of rolls, each pair of rolls comprising a heated thermo-; roll (3), having an opposite roll covered by a polymer surface, the apparatus comprising means (4) for controlling the fibre web and a cooling apparatus including a blowing means (6), characterised in that

- the first control means is located relative to the roll covered by polymer coating so as to guide the fibre web (5) onto the polymer surface (8) at a first location, and the second control means is located relative to the same roll so as to guide the fibre web off the polymer surface on the roll at a second location and

- the gas jet from the blowing means is directed to the vicinity of the nip (7), partly onto the border portion (8; 8b) of the polymer surface that is not coated with fibre web, and partly onto the border area of its central portion (8; 8a) that is coated with fibre web.

9. An apparatus as defined in claim 8, characterised in that the control means

(4) are placed relative to the roll (2) under the polymer surface so that the fibre web

(5) rotates about the outer periphery of the roll covered by polymer coating, before or after the calender nip (7), at least about 15 degrees calculated on the peripheral angle of the cross-sectional circle of the roll.

10. An apparatus as defined in claim 8 or 9, characterised in that, with the calender nip viewed perpendicularly from the direction of the cooling apparatus, the blowing means (6) of the cooling apparatus (1) are partly on top of the border portion (8; 8b) of the polymer surface (8) that is not coated with fibre web, and partly on the border area of its central portion (8; 8a) coated with fibre web, adjacent to ihe border portion.

11. An apparatus as defined in any of claims 8-10, characterised in that the control means (4) are placed relative to the roll (2) under the polymer surface so as

- to guide the fibre web into contact with the polymer surface at a first location (A) or (C) and

- to guide the fibre web out of contact with the polymer surface at a second location (B) or (D), the angular distance between the second location and the first location being more than about 15 degrees calculated on the peripheral angle of the cross-' sectional circle of the roll (2) under the surface.