EP2295632B1 - Calendar - Google Patents

Description

The invention relates to a calender with a web running path for a running paper or board web through a first and a second, each having a first and a second circumferential contact surfaces having nip, wherein the web in the contact zones of each nip under pressure and / or temperature is treatable and the first contact zone of the first nip has a length in the web running direction of at least 100 mm and the second contact zone of the second nip has a length in the web running direction of at most 50 mm, wherein a first contact surface of the first and a first contact surface of the second nip are identical and closed a central roller and the second contact surface of the second nip is formed by a second roller.

In recent years, various methods have been developed with which a web of paper or cardboard can be smoothed by means of a so-called Breitnipkalanders. In this case, the contact zone in which the web is smoothed, not generated by two pressed against each other solid rollers, but it is an aggregate installed, which allows, in the running direction of the web, the so-called machine direction or MD (= machine direction), an extended Nip, for example, greater than 100 mm to produce. All of the processes aim to achieve the positive effect of improving the surface quality of the web, while at the same time minimizing the undesirable thickness loss that occurs, to a value that is smaller than a conventional roll calender.

The extended nip can be achieved on a roller by using an additional elastic band which partially wraps around the roller to extend the contact zone. The band may be made of a plastic or a metal. Or you can create the extended nip by a so-called shoe roll, in which a static, concave shaped and wrapped by a soft, rotating jacket element is pressed against the roller.

A short contact zone in a roll calender acts in contrast to the long contact zone in a Breitnipkalander significantly different on the web.

Basically, there are four main influencing factors on the calendering of a material web. These are the compressive stress in the nip, the heat transferred, the surface quality of the contact surfaces with the web and the trapped moisture in the web. In this case, shorter nips are characterized by a positive influence on the macro-roughness (long-wave thickness fluctuations), which mainly refers to the measuring method Bendtsen. In contrast, long nips have a greater effect in improving micro-roughness, which is described by the smoothness measurement PPS s10.

It is easy to understand that you can bring a larger amount of heat through a wide nip due to the longer residence time in the web. However, this also increases the risk of sudden and destructive evaporation of the web after the nip. It is also understandable that greater compressive forces can be introduced in a shorter contact zone, which in turn usually give the web a higher gloss and better smoothness, but in principle also cause undesirable thickness losses. Especially in Mehrwalzenkalandern a paper or board web is significantly compressed.

The invention has a calender to the content, at the central roller both a wide and a narrow nip are arranged. Such an arrangement is for example from the DE102007024581 A1 , and here in particular from the FIGS. 1 and 3 known. To produce the longer nip, a metal belt partially wrapped around the roller is used. The short nip is formed by a counter roll. The disadvantage of the illustrated arrangement is that two longer nips are used, of which the second is to cause as little as possible heat input into the web by cooling the band forming the second contact surface of the third nip. Thus, it should not come to a so-called flash evaporation. However, since the web still rests against the hot central roll, this desire can only be realized with an energy-technically unfavorably high cooling capacity on the belt.

Already in the EP 0 141 614 A2 a method for increasing the smoothness of a web is presented in which this is pressed by means of a woven metal or plastic tape over a larger wrap angle against a heating cylinder In addition, inside and outside the band press rollers can press the web against the heating cylinder.

From the WO 2009/077643 A1 For example, a metal strip calender is known which, with its metal strip, forms a longer nip on a central roll. At the central roller opposite to the tape and a second roller at both rollers together form another nip for the web. The second roll is a non-temperable roll with an elastic Surface. In this constellation, an influence of the pressure of the second nip forming the shorter nid on the pressure distribution in the longer nip formed by the band is unavoidable. Conversely, even slight changes in the thickness profile of the belt and the resulting pressure pulses on the center roll disperse a negative impact on the pressure cross-section in the shorter nip.

It is the object of the invention to improve a calender, which has a long and a short nip on a central roll over the prior art so that an exploitation of the calendering parameters pressure and temperature in both nips are independent from each other as before and the Rail can be treated more versatile.

The task is fulfilled by the combination of two characteristics.

First - the first characteristic - runs the web running path such that the web at least over a wrapping angle of 50 °, preferably at least 70 °, on the second roller, which is designed to be tempered. It creates in this way the possibility before or after the second nip and in the second nip to cool the track on one side at will or heat. Common methods for heating the roll are known to the person skilled in the art and include the internal flow through with hot tempering fluids and the external heating by induction or hot air. Also, cooling methods of the roll are known which include flowing the roll through cooled fluids and blowing with cooled air. The second characteristic provides that the planes of action of the two nips, which are respectively defined by the contact zone center in the web running direction and the central axis of the central roll, are at an angle of 75 ° to 105 ° to each other. Thus, almost any influence of a pressure change in the first or second nip on the other can be excluded.

This gives a calender with a wide first nip and a short second nip in a particularly compact design. Nevertheless, they are Pressure and temperature in the two nips largely independently adjustable.

It is particularly preferred if the active planes are at an angle of 90 ° to one another. The printing direction in a nip is then no longer important for the adjustment of the pressure cross-section in the other nip. Under pressure profile is here to understand the pressure profile, which is set perpendicular to the web running direction.

Preferably, the central roll is also tempered. In this way, the possibility is created to also heat or cool the other side of the web. The tempering of the web side, which rests against the central roller, can increase the Satinageleistung.

It is advantageous if the second contact surface of the first nip is formed by a circulating band. Such a band may for example be made of a plastic or steel. It rotates in the simplest case, three guide rollers and abuts over a peripheral portion of the central roller, so that a long contact zone and thus a long nip for the web is formed. About an adjustability of the guide rollers, the length of the contact zone and the contact pressure of the band can be made changeable.

Advantageously, it is ensured that the second contact surface of the first nip is formed by a heatable metal strip. This creates a third possibility of influencing the temperature of the web. A metal strip is significantly easier tempered than a typically provided with low thermal conductivity and also insulating plastic tape. Again, there are induction devices and blowing devices in question. Depending on whether the train is on or off be smoothed on both sides, in addition to the heating of the second roller either the metal strip or the central roll can be brought to elevated temperature. In the first case, consider whether to provide the central roller with an elastic coating, so that the second nip is a soft nip. This improves the uniform compaction of the web. In the second case, it may be possible to dispense with the advantage of heatability of the tape and replace the tape with a shoe roll with an elastic jacket.

There are two ways to go through the calender. Alternatively, the web running path can be designed so that the central roller is arranged in the web running direction in front of or behind the second roller. Here, the expert must decide case by case, depending on which paper or cardboard type is to be satined.

If the band touches the central roller at a wrap angle of more than 50 °, preferably at least 70 °, and the heat transfer to the second roller is to be as high as possible, then it is favorable if the web running path fits the central roller and the second roller is S-shaped wraps. It remains to lay the design of the calender, the axes of the central roller and second roller in a horizontal, vertical or inclined at any other angle plane.

It is advantageous if the web running path is traversable in both directions. This allows a freer selection in the paper quality to be treated. There are types of paper and cardboard, which preferably initially abut over a large angle of wrap on the heated second roll to be well soaked, then passed through a soft or hard nip for calibration and finally to be finished on a heated metal strip. There is also on the other side paper and board grades, which should be smoothed on both sides in the long first nip, then compacted in a short nip and finally cooled on the second roll. Overall, the calender according to the invention offers numerous possibilities for web treatment here.

The calender has a particular advantage if it has a humidifying device in the inlet of the web. A moistened paper or board web can be satined to a higher quality. Both nozzle moisteners, which are distinguished by very small droplet sizes which can penetrate the web quickly, and vapor dampers, which can condense much larger amounts of water on the web, and the Moisture Gradient Calendering known to the person skilled in the art, are very well known in the prior art are.

• Figur 1 eine schematische Darstellung eines erfindungsgemäßen Kalanders mit einem Bahnlaufpfad von der Zentralwalze zur zweiten Walze und
• Figur 2 eine schematische Darstellung des gleichen erfindungsgemäßen Kalanders mit einem Bahnlaufpfad von der zweiten Walze zur Zentralwalze.

The invention is explained in more detail below with reference to exemplary embodiments with reference to the drawings. In these shows

• FIG. 1 a schematic representation of a calender according to the invention with a web running path from the central roller to the second roller and
• FIG. 2 a schematic representation of the same calender according to the invention with a web running path from the second roller to the central roller.

Both figures show a calender 1 according to the invention with a central roll 11, the surface of which constitutes a peripheral contact surface 4.1, 5.1. In a first nip 4, a first contact zone is formed with a further circumferential contact surface 4.2.

Offset by 90 ° on the circumference of the central roller, a second contact zone 7 is formed by means of the contact surface 5.2 of a second roller 12, which constitutes a second nip 5.

The first contact zone 6 is over 100 mm long (in the circumferential direction), the second contact zone 7 is less than 50 mm long.

A web travel path 3 determines the path on which a paper or board web 2 is passed through the calender 1, in particular through the contact zones 6, 7. In the contact zones 6, 7, the web 2 is subjected to pressure and / or temperature.

In the first nip 4, the second contact surface 4.2 is predetermined by the surface of a circumferential metal strip 13 according to the embodiment. Instead, however, it is also possible to use plastic strips or a shoe roll likewise known in the prior art, since they too can produce a contact zone length of more than 100 mm. The system pressure in this first long nip is usually between 0.05 and 5 N / mm ² .

The metal strip is guided over band guide rollers 14. These have an adjusting device (indicated at two band guide rollers by the arrow with the reference numeral 20). Depending on which of the belt guide rollers 14 have such an adjustment device 20, the contact zone length can be changed via this and the contact pressure of the metal strip 13 on the central roller 11 can be determined.

In order to pressurize the web 2 in the long first contact zone 6 on both sides with heat, both the central roller 11, for example of inside via a heating fluid, and the metal strip 13, for example via an induction heater 18.1, be heated.

Also, the second roller 12 can supply or dissipate heat energy; So it is designed to be tempered. In the FIG. 1 is shown by the box 18.2, for example, an induction heater or a cooling fan. Just as well, the roller 12 can be tempered from the inside via a heat transfer fluid. For the treatment of the web, many possibilities of influence remain here because the web 2 wraps around the second roller at least 50 °, preferably at least 70 °. Over such a large peripheral portion of the web can be added or removed a lot of heat. In the FIG. 1 the wrap angle is indicated by the arrow 16.

Often it makes sense if one of the rollers 11, 12 has a coating 17. For technological reasons, for example, an elastic coating comes into question here. Thus, the second nip 5 could become a soft nip when the second roll has an elastic coating 17. Optionally, however, it is also possible to provide the roller 12 with a coating 17 which conducts heat particularly well. It is advantageous if the compressive stress in the second nip 5 is significantly higher than that in the first nip 4, particularly preferably in the range of 10 to 30 N / mm ² .

Almost all paper and board grades are easier to smooth if the calender 1 is preceded by a moistening device 19. The known effect of temperature gradient calendering is then joined by the well-known effect of Moisture Gradient Calendering. This causes only the wet surface is leveled, while the inner volume of the web 2 is largely retained.

For both nips a so-called active plane 8, 9 is defined. The planes are respectively laid through the center of the nip in the circumferential direction and the central axis of the central roller 11. So that the contact pressures in the contact zones 6, 7 affect each other as little as possible adversely affecting the respective pressure profile, the angle 21 between the two active planes is not less than 75 ° and not greater than 105 °. Preferably, it is understandably 90 °.

The big difference between the two FIGS. 1 and 2 lies in the web running direction 10. In FIG. 1 The web runs first through the long first contact zone 6, then through the short second contact zone 7 and then is still in a total S-shaped web running path 3 on the second roller 12 at. In FIG. 2 the same calender 1 is used. However, web 2 is first brought into contact with second roller 12 via web deflection rollers 15, again S-shaped, then passes through short second contact zone 7 and is finally finished in a long first contact zone 6. It should be noted that an air squeezing device provided in a manner not shown, which ensures that no air boundary layer between web 2 and the surface of the second roller 12 is drawn in, can be very advantageous in order to increase the heat transfer value between web 2 and roller 12 , The driving style is heavily dependent on the paper or board type.

Of course, it is also possible to arrange several of the calenders one behind the other in order in this way to have, for example, both sides of the web once against a central roll. So the satin work can be intensified.

LIST OF REFERENCE NUMBERS

1

calender

2

Paper or board web (short: web)

3

Web running path

4

first nip

4.1, 4.2

Contact surfaces of the first nip

5

second nip

5.1, 5.2

Contact surfaces of the second nip

6

first contact zone

7

second contact zone

8th

Working plane first nip

9

Working plane second nip

10

Web direction

11

central roll

12

second roller

13

Ribbon, metal band

14

Guide roll band

15

Guide roller track

16

Wrap angle

17

coating

18.1, 18.2

Induction heating or cooling fan

19

humidifying

20

adjustment

21

Angle between the working planes

Claims (10)

1. Calender having a web running path (3) for a moving paper or board web (2) through a first and a second nip (4, 5) each having a first and a second revolving contact surface (4.1, 4.2, 5.1, 5.2), it being possible for the web (2) to be treated with the application of pressure and/or temperature in the contact zones (6, 7) of each nip (4, 5), and the first contact zone (6) of the first nip (4) having a length of at least 100 mm in the web running direction (10), and the second contact zone (7) of the second nip (5) having a length of at most 50 mm in the web running direction (10), a first contact surface (4.1) of the first nip (4) and a first contact surface (5.1) of the second nip (5) being identical and belonging to a central roll (11), and the second contact surface (5.2) of the second nip (5) being formed by a second roll (12),
   and

   a) the web running path (3) running in such a way that the web (2) rests on the second roll (12), which is designed such that its temperature can be controlled, at least over a wrap angle (16) of 50°, preferably at least 70°, and

   b) the planes of action (8, 9) of the two nips (4, 5), which are each defined by the centre of the contact zone in the web running direction (10) and the mid-axis of the central roll (11), being at an angle (21) of 75 to 105° with respect to each other.
2. Calender according to Claim 1,
   characterized in that
   the planes of action (8, 9) are at an angle (21) of 90° with respect to each other.
3. Calender according to one of Claims 1 or 2,
   characterized in that
   the temperature of the central roll (11) can be controlled.
4. Calender according to one of Claims 1 to 3,
   characterized in that
   the second contact surface (4.2) of the first nip (4) is formed by a circulating belt (13).
5. Calender according to Claim 4,
   characterized in that
   the second contact surface (4.2) of the first nip (4) is formed by a metal belt (13) of which the temperature can be controlled.
6. Calender according to one of Claims 1 to 5,
   characterized in that
   the central roll (11) is arranged before the second roll (12) in the web running direction (10).
7. Calender according to one of Claims 1 to 5,
   characterized in that
   the second roll (12) is arranged before the central roll (11) in the web running direction.
8. Calender according to one of Claims 1 to 7,
   characterized in that
   the web running path (3) wraps around the central roll (11) and the second roll (12) in an S shape.
9. Calender according to one of Claims 1 to 8,
   characterized in that
   it is possible to pass through the web running path (3) in both directions.
10. Calender according to one of Claims 1 to 9,
    characterized in that
    a moistening device (19) is arranged before the calender (1) in the web running direction (10).

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