DE102011004730A1 - calender - Google Patents

Abstract

The invention relates to a calender with a web path (3) for a running paper or cardboard web (2) through a first and a second nip (4, each having a first and a second circumferential contact surface (4.1, 4.2, 5.1, 5.2) 5), whereby the web (2) in the contact zones (6, 7) of each nip (4, 5) can be treated under pressure and / or temperature and the first contact zone (6) of the first nip (4) has a length in the direction of travel of the web (10) of at least 100 mm and the second contact zone (7) of the second nip (5) has a length in the web running direction (10) of at most 50 mm, a first contact surface (4.1) of the first nip (4) and a first The contact surface (5.1) of the second nip (5) are identical and belong to a central roller (11) and the second contact surface (5.2) of the second nip (5) is formed by a second roller (12), and the web travel path (3) runs in such a way that the web (2) either first through the first nip (4) and then through the second nip (5) or first through the second nip and then through the first nip. In order to improve a calender, which has a long and a short nip on a central roll, over the prior art so that the risk of creasing in the web is avoided, it is provided that the web travel path between the first and the second contact zone (6, 7) runs around an additional guide means (15).

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 surface 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 nip and a first contact surface of the second nip are identical and belong to a central roller and the second contact surface of the second nip is formed by a second roller, and wherein the web running path such that the web either first through the first nip and then through the second nip or first through the second nip and then through the first nip is led.

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 these processes have the purpose of achieving the positive effect of improving the surface quality of the web, while at the same time minimizing the undesirable loss of thickness which occurs, to a value which is smaller than that of 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 DE 10 2007 024 581 A1 , and here in particular from the 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.

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 web guide between both nips takes place on the surface of the central roller. 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 nip on the pressure distribution in the longer nip formed by the band is unavoidable. Conversely, even small changes in the thickness profile of the belt and the resulting pressure impart impulses on the central roll a negative influence on the pressure cross-profile in the shorter nip.

From the EP 0 141 614 A2 a device is known which serves to treat a paper or board web. The train goes through, for example, in 2 a roll nip and then, guided on the surface of a heating roller, a pressed against this heat roller by deflecting rollers band. This tape is described as a metal or plastic fiber fabric, so it is completely unsuitable for a tape calender because of its roughness.

The youngest is also the WO11000529 A1 which has certainly been the closest prior art to the present invention. Experiments with such a belt calender described there have, however, shown that the web guide is fraught with great deficiencies for some types of paper. So it has been recognized that forms a webless between the first nip and the second nip. That is, probably due to the length and width changes of the web in the first nip, loops can form in the web between the nips, which in turn can turn into folds. Apart from the fact that such wrinkles are of course detrimental to the calendering result, they also offer the risk of destruction of roll coverings.

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 the risk of wrinkling in the web is avoided.

The object is achieved in that the web running path between the first and the second contact zone extends around an additional guide means. The web is thus guided away from the central roll between the first nip and the second nip and wraps around a conducting means, usually a guide roll. It has not yet been finally clarified why this conductive agent prevents the web from wrinkling. It is believed that a train can build up on the way from the first contact zone to the conducting means and from the conducting means to the second contact zone in the web. This formation of a web tension is accordingly prevented when the web is in contact with the central roll from the first to the second nip all the time. Presumably, the situation is comparable to that of a multi-roll calender, for example Applicant's Janus calender, where the web also has to be fed first from nip to nip around a guide roll.

It is advantageous if the second contact surface of the first nip is formed by a circulating band. Such a band can be made for example of a plastic or steel. The invention is particularly supportive when the tape is a smooth plastic tape. The band rotates in the optimal 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.

It is particularly preferable that the tape has a maximum surface roughness Ra of 4 μm. By such a consistently smooth band side to the web, either when the band mitbildet the first nip in the web running direction, the web for Walzennip already pre-smoothed, or if the band forms the second nip in the web running direction, the already smoothed web page not back in deteriorates their gloss and smoothness level.

Preferably, the guide means comprises a tension measuring device. Such Zugmesseinrichtung are known per se. For this particular type of calender, the tension measuring device can ensure, via a suitable drive control of the central roller, second roller and belt guide rollers, that a sag of the web is avoided. In addition, it is possible to design the guide roller so that it can perform a movement in a fluctuating web tension to counteract the fluctuations.

It is advantageous if the web at least over a wrapping angle of 50 °, preferably at least 70 °, on the second roller, which is designed to be tempered, is applied. 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.

It is also advantageous that the active planes 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, pressure and temperature in the two nips are largely independent of each other 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.

Advantageously, it is ensured that the second contact surface of the first nip is formed by a heatable band. This creates a third possibility of influencing the temperature of the web. Again, there are induction devices and blowing devices in question. Depending on whether the web is to be smoothed on one or two sides, in addition to the heating of the second roller either the belt or the central roller 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 the heatability of the tape. Under certain circumstances, it may also be simply advantageous if the band consists of a material with a thermal conductivity of less than 1 W / mK as a thermal insulator. This ensures a uniform and safe heating of the web.

If the strip touches the central roll at a wrap angle of more than 50 °, preferably at least 70 °, and the heat transfer to the second roll is to be as high as possible, then it is favorable if the web running path fits the central roll and the second roll 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 applied 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 strip. On the other hand, there are also paper and board grades which, for example, 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.

In order to avoid heat or moisture losses by the passage of the web to the guide means, it is of great advantage if the guide means has at least a quarter of the circumference of an insulating hood. Convection and radiation of the web are satisfactorily contained.

The invention will be explained in more detail below with reference to exemplary embodiments with reference to the drawing. In these, the single figure shows a schematic representation of a calender according to the invention with a web running path from the central roll to the second roll.

The figure shows a calender according to the invention 1 with a central roller 11 whose surface has a circumferential contact surface 4.1 . 5.1 represents. In a first nip 4 comes with another circumferential contact surface 4.2 formed a first contact zone.

By 90 ° offset on the circumference of the central roll is by means of the contact surface 5.2 a second roller 12 a second contact zone 7 formed a second nip 5 represents.

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 track 3 determines the path on which a paper or board web 2 through the calender 1 , in particular through the contact zones 6 . 7 to be led. In the contact zones 6 . 7 will be the train 2 subjected to pressure and / or temperature.

In the first nip 4 becomes according to the embodiment, the second contact surface 4.2 through the surface of a revolving band 13 , preferably a plastic strip with a surface roughness Ra below 4 microns, given. The system pressure in this first long nip is usually between 0.05 and 5 N / mm ² .

The tape is over tape guide rollers 14 guided. 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 such an adjustment 20 can change the contact zone length over this and the contact pressure of the metal strip 13 at the central roller 11 be determined.

To the train 2 in the long first contact zone 6 Apply heat to both sides, both the central roll 11 , For example, from the inside via a heating fluid, as well as the band 13 , for example via an induction heater 18.1 , heated when the plastic tape has, for example, metallic fillers. Instead, the band can also be isolating. It is also advantageous if the band has a hardness as conventional plastic-based counter-rollers in calenders.

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

Between the contact zones 6 . 7 the web is guided away from the central roll in its web travel path and wraps around a conducting agent 15 in the form of a guide roller. As a result, the train is able to build a train and stay taut. To prevent the threat of heat and moisture loss, is the guide roller 15 on a part of its circumference of an insulating hood 22 covered.

Often it makes sense when one of the rollers 11 . 12 a coating 17 having. For technological reasons, for example, an elastic coating comes into question here. So could the second nip 5 to become a soft nip when the second roller has an elastic coating 17 having. But it is also possible, the roller 12 with a particularly good heat conductive coating 17 to provide. It is advantageous if the compressive stress in the second nip 5 significantly above the first nip 4 is particularly preferred in the field 3 to 30 N / mm ² .

Almost all paper and board grades are easier to smooth out when the calender 1 a humidifier 19 upstream. 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 to be leveled while the inner volume of the web 2 largely preserved.

For both nips is a so-called working plane 8th . 9 Are defined. The planes are defined respectively by the center of the nip in the circumferential direction and the central axis of the central roll 11 placed. So that the plant pressures in the contact zones 6 . 7 Affect each other as little as possible affecting the respective pressure profile, the angle 21 between the two working planes not smaller than 75 ° and not larger than 105 °. Preferably, it is understandably 90 °.

With an arrow is in the web direction of travel 10 indicated. The web first passes through the long first contact zone 6 , then through the short second contact zone 7 and is then still in a total S-shaped web track 3 on the second roller 12 at. However, the web direction can also be exactly the other way around. The train 2 is then first, again S-shaped, in contact with the second roller 12 brought, then passes through the short second contact zone 7 and finally comes in a long first contact zone 6 final treatment. It should be noted that an unillustrated manner provided Luftabquetschvorrichtung, which ensures that no air boundary layer between the web 2 and the surface of the second roller 12 being drawn in can be very beneficial to the heat transfer value between web 2 and roller 12 to increase. 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

tape

14

Guide roll band

15

Conductor, guide roll web

16

Wrap angle

17

coating

18.1, 18.2

Induction heating or cooling fan

19

humidifying

20

adjustment

21

Angle between the working planes

22

insulating hood

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102007024581 A1 [0007]
• WO 2009/077643 A1 [0008]
• EP 0141614 A2 [0009]
• WO 11000529 A1 [0010]

Claims (14)

Calender with a web track ( 3 ) for a running paper or board web ( 2 ) by a first and a second, in each case a first and a second circumferential contact surface ( 4.1 . 4.2 . 5.1 . 5.2 ) having nip ( 4 . 5 ), whereby the web ( 2 ) in the contact zones ( 6 . 7 ) every nip ( 4 . 5 ) is treatable under pressure and / or temperature and the first contact zone ( 6 ) of the first nip ( 4 ) a length in the web running direction ( 10 ) of at least 100 mm and the second contact zone ( 7 ) of the second nip ( 5 ) a length in the web running direction ( 10 ) of at most 50 mm, wherein a first contact surface ( 4.1 ) of the first nip ( 4 ) and a first contact surface ( 5.1 ) of the second nip ( 5 ) are identical and to a central roller ( 11 ) and the second contact surface ( 5.2 ) of the second nip ( 5 ) by a second roller ( 12 ) is formed, and wherein the web running path ( 3 ) is such that the web ( 2 ) either first through the first nip ( 4 ) and then through the second nip ( 5 ) or is guided first through the second nip and then through the first nip, characterized in that the web running path between the first and the second contact zone ( 6 . 7 ) by an additional conducting agent ( 15 ) runs. Calender according to claim 1, characterized in that the second contact surface ( 4.2 ) of the first nip ( 4 ) by a circulating belt ( 13 ) is formed. Calender according to Claim 2, characterized in that the strip has a maximum surface roughness Ra of 4 μm. Calender according to one of claims 1 to 3, characterized in that the conductive agent ( 15 ) has a tension measuring device. Calender according to one of claims 1 to 4, characterized in that the web on the second nip at least over a wrap angle ( 16 ) of 50 °, preferably at least 70 °, on the second roller ( 12 ) and the second roller ( 12 ) is temperature controlled. Calender according to one of claims 1 to 5, characterized in that the working planes ( 8th . 9 ) of the two nips ( 4 . 5 ), each through the contact zone center in the web running direction ( 10 ) and the central axis of the central roller ( 11 ) are defined at an angle ( 21 ) from 75 ° to 105 ° to each other. Calender according to claim 6, characterized in that the working planes ( 8th . 9 ) at an angle ( 21 ) of 90 ° to each other. Calender according to one of claims 1 to 7, characterized in that the central roller ( 11 ) is temperature controlled. Calender according to one of claims 1 to 8, characterized in that the second contact surface of the first nip is formed by a heatable band. Calender according to one of claims 1 to 9, characterized in that the second roller ( 12 ) in web running direction ( 10 ) in front of the central roller ( 11 ) is arranged. Calender according to one of claims 1 to 10, characterized in that the web running path ( 3 ) the central roll ( 11 ) and the second roller ( 12 ) Wraps around in an S-shape. Calender according to one of claims 1 to 11, characterized in that the web running path ( 3 ) is durchfahrbar in both directions. Calender according to one of claims 1 to 12, characterized in that in the web running direction ( 10 ) in front of the calender ( 1 ) a humidifying device ( 19 ) is arranged. Calender according to one of claims 1 to 13, characterized in that the conductive agent ( 15 ) at least a quarter of the circumference of an insulating hood ( 22 ) having.

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