EP1156155B1 - Dryer section of a machine for manufacturing a paper or board web - Google Patents

Description

The invention relates to a machine for producing a paper or board web with a press section and arranged after the press section dryer section, which has a plurality of drying cylinders with smooth contact surface and in which at least one designed as a floating dryer gas-operated web guide means is provided by the web together with a Sieve is passed.

In the hitherto customary multi-cylinder drying sections, the paper web is guided for drying over steam-heated cylinders or over steam-heated cylinders and suction suction rolls. Especially at the beginning of drying, where the wet paper web still does not have sufficient strength, but now occur with respect to the web guide often problems that are particularly due to the fact that the still wet and poorly ventilated web stick to the smooth contact surfaces, for a sufficient heat transfer are absolutely necessary. In order to be able to pull the web from the cylinders, sufficient web tension is necessary, which can only be generated by train, ie corresponding differential speeds, before or directly after the first smooth contact surface. However, this often leads to web breaks and overstretching of the web edges. Accordingly, it must be ensured as a rule that the drying takes place more slowly, ie, for example, prevails at the beginning of a lower vapor pressure, which also means that the required drying section is longer overall. The The aforementioned problems occur increasingly at higher web speeds.

In order to influence the curl inclination, DE 196 05 195 proposes to guide the web around a non-contact drying device. The web is supported on the one hand on the air cushion of the drying device and on the other hand on the sieve.

FR 2 439 959 discloses the use of a suspended bed dryer for drying fabrics.

The aim of the invention is to provide a machine of the type mentioned, in which at the same time both a very optimal drying rate at the beginning of the drying and a secure web guide is ensured at high machine speed.

This object is achieved by the characterizing features of claim 1.

Due to this training, the still relatively wet web must not be prematurely withdrawn from a smooth surface. Due to the avoidance of smooth contact surfaces at the beginning of drying the risk of web breaks and overstretching of the web edges is virtually eliminated. In particular, higher drying rates are now possible, as a result of which the overall length of the dryer section is shortened accordingly. The load on the web after the press section is minimized after the web has to be subjected to higher, peel-applied release tensions only at higher dry levels.

Finally, correspondingly higher machine speeds are possible.

In a preferred practical embodiment of the invention, at least one compressed-gas-operated web guiding device designed as a floating dryer can be provided directly after the press section and before the first drying cylinder. As a result of the combination of a fluidized bed dryer with a dryer fabric, a web of low strength (e.g., at high humidity such as prior to cylinder drying) may also be dried.

While the web can be deflected in a wave-like manner by a corresponding gas pressure distribution in the respective web guiding device and stabilized, for example, in a sine wave, the screen in the respective compressed-gas-operated web guiding device generally has an at least substantially rectilinear course.

The web guiding device expediently comprises a plurality of nozzles arranged one behind the other in the web running direction for pressurizing gas of the web, such nozzles preferably being provided on both sides of the web. In particular, a plurality of nozzle bars each extending in the direction of the web width may be provided.

In particular, air can be provided as compressed gas.

It is also advantageous if at least one impingement-flow dryer provided with at least one dryer hood is provided, through which the web can be subjected to a hot-air and / or hot-steam impact flow. In this case, the web is preferably guided over at least one particular larger support roller with associated impingement dryer.

Such an impingement flow dryer is also preferably arranged again in front of the first drying cylinder.

Before the web is first pulled off a smooth heated surface, it can therefore be pre-dried by at least one floating dryer and optionally at least one impingement dryer. The gas or air drying is advantageously carried out until a sufficient dry content is reached at which the required web tension can be applied easily.

In a preferred practical embodiment, the web already has a dry content higher than about 58 to about 65 ° when drained from the first dryer cylinder or when first drawn from a smooth heated surface. In this case, as already mentioned, a part of the gas or air drying can also take place by means of an impingement-flow dryer or an impingement hood.

Advantageously, following the last press nip of the press section, at least one pressurized-gas-operated web guiding device is initially provided.

In certain cases, it is expedient if the web, following the last press nip of the press section, is first guided through at least one compressed-gas-operated web guiding device and subsequently via at least one, in particular, larger support roll with associated impingement dryer, before it is fed to the first drying cylinder.

The drying speed in the region of a respective web guiding device designed as a floating dryer or of a respective impingement flow dryer is advantageously adjustable via the pressure gas temperature, speed and / or moisture.

(300 cfm). und vorzugsweise größer als etwa $2,54\frac{m^3}{m^{2}s}$

(500 cfm).The air permeability of a screen associated with a respective compressed-gas-operated web guiding device is preferably chosen as high as possible. Thus, in a preferred embodiment, this air permeability of the respective sieve is greater than about $1.52\frac{m^3}{m^{2}s}$

(300 cfm ). and preferably greater than about $2.54\frac{m^3}{m^{2}s}$

(500 cfm ).

It is also advantageous if the web, starting from the last press nip of the press section, is fed to the first drying cylinder in a closed train.

In certain cases it is expedient if the web from the press section directly to that of a compressed-gas-operated web guiding device assigned sieve is passed. However, the transfer of the web from the press section to the screen assigned to a compressed-gas-operated guide device can also take place via at least one transfer belt or the like.

The web can be removed from a run through the last Preßnip the press section felt (upper or lower felt). But it is also a decrease directly from a last Preßnip the press section associated press roll conceivable.

In order to achieve the desired dry content, it is also possible to provide a plurality of floating dryers and / or a plurality of impingement flow dryers.

A respective compressed-gas-operated web guiding device can be arranged horizontally, vertically or obliquely. In the latter case, the web may be generally obliquely upwards or generally obliquely downwards in the inclined gas-operated web guiding device.

If a plurality of compressed-gas-operated web guiding devices are provided, at least a part of these web guiding devices can each be assigned a separate sieve.

In certain cases, it is also advantageous if at least one screen guided by a plurality of compressed-gas-operated web guiding devices is provided.

For holding the web on the screen, suction rolls, transfer foils and / or suction boxes can be provided before and / or after the associated compressed-gas-operated web guiding device and / or between successive web guiding devices.

The roll (suction roll or cylinder) following the last float dryer may be partially wrapped around the screen associated with the float dryer, or the web may be transferred from a suction roll to a subsequent dryer fabric.

For transferring the web through a respective compressed-gas-operated web guiding device, the web is expediently pressed against the wire and / or sucked. This is possible, for example, in that the web to be transferred is subjected to negative pressure in a respective compressed-gas-operated web guiding device only on its side facing away from the wire and in the web running direction with compressed gas and / or from the wire side.

In the latter case, vacuum boxes may be arranged between the nozzle bars provided on the screen side facing away from the web.

The transfer through the gas or air dryer is preferably carried out web width through the air dryer. However, the transfer can also be done partially or completely with Überführbändel and appropriate transfer zones in suction and blow boxes. In the case of a Überführbändels must be taken to ensure that the rest of the web can be driven before the corresponding gas or air dryer from the felt or wire with an additional removal device in the pulper or basement.

In certain cases, it may also be advantageous if at least one web guide device is provided, through which the web can be acted upon by compressed gas at low temperature in the range of preferably approximately 20 to approximately 150 °. Thus, in particular, it is also possible to use such a compressed-gas-operated web guiding device as a pure transfer element.

In order to allow as unobstructed shrinkage as possible in the cross machine direction and thus to achieve small differences in the transverse shrinkage between the edge and the center, at least one floating dryer without a sieve can be provided between the last press nip of the press section and the first drying cylinder and / or within a pre-drying section.

The inventive, operated as a float dryer gas-operated Schwebeführungseinrichtung (possibly in conjunction with at least one impingement dryer) is at the beginning of the drying between the press and the first drying cylinder, preferably in combination with a tandem NipcoFlex press or DuoCentri press with band around the central roll or other press configurations, at where the web is not pulled off a smooth roll used.

Figur 1

eine schematische Teildarstellung einer als Schwebetrockner ausgeführten druckgasbetriebenen Bahnführungseinrichtung mit zugeordnetem Sieb,

Figur 2

eine schematische Darstellung einer Ausführungsform einer Trockenpartie mit zwei als Schwebetrockner ausgeführten druckgasbetriebenen Bahnführungseinrichtungen und einem Prallströmungstrockner, wobei durch die beiden Bahnführungseinrichtungen ein gemeinsames Sieb geführt ist, und

Figur 3

eine schematische Darstellung einer anderen Ausführungsform einer Trockenpartie mit zwei als Schwebetrockner ausgeführten druckgasbetriebenen Bahnführungseinrichtungen, wobei jeder dieser beiden Bahnführungseinrichtungen ein eigenes Sieb zugeordnet ist.

The invention is explained in more detail below with reference to embodiments with reference to the drawing; in this show:

FIG. 1

FIG. 2 a schematic partial representation of a pressurized gas-operated web guiding device designed as a floating dryer with associated sieve, FIG.

FIG. 2

a schematic representation of an embodiment of a dryer section with two running as a flotation dryer gas-operated web guide means and an impingement dryer, wherein by the two web guide means a common wire is guided, and

FIG. 3

a schematic representation of another embodiment of a dryer section with two running as a flotation dryer gas-operated web guide means, each of these two web guide means is associated with its own screen.

FIG. 1 shows, in a schematic partial representation, a web guiding device 10 which is operated with compressed gas, in this case compressed air, and which is designed as a floating dryer.

The web guide device 10 is assigned to a web 12 serving the web support, which is passed together with the web 14 through the web guide device 10. The material web 14 is a paper or board web.

In the web guide device 10, the material web 14 is acted upon by compressed air so that it is lifted in the web running direction L alternately from the wire 12 and rests against this. Due to the air permeability, the screen 12 has an at least substantially straight course within the web guiding device.

For corresponding loading of the material web 14, the web guide device 10 comprises a plurality of nozzles 16 arranged one behind the other in the web running direction L. In this case, nozzles 16 are provided on both sides of the wire 12 and corresponding to the material web. In the present case, a plurality of each extending in the direction of the web width nozzle beam 16 are provided on both sides.

(300cfm) und vorzugsweise größer als etwa $2,54\frac{m^3}{m^{2}s}$

(500cfm).The air permeability of the screen 12 is suitably greater than about $1.52\frac{m^3}{m^{2}s}$

(300 cfm ) and preferably greater than about $2.54\frac{m^3}{m^{2}s}$

(500 cfm ).

Moreover, the nozzles 16 can be designed and / or controlled such that, for transferring the material web 14, the web 14 in the web guiding device 10 only on its side facing away from the wire 12 and in Web running direction L with pressurized gas, here compressed air, is acted upon. For the transfer of the material web 14, the material web 14 but also from the screen side through the wire 12 through are subjected to negative pressure. For this purpose, vacuum boxes (not shown) can be arranged between the nozzle bars provided on the lower screen side 16.

Figures 2 and 3 show in a purely schematic representation in each case a drying section 18 of a machine for producing a material web, which is a paper or board web.

In both embodiments of FIGS. 2 and 3, two web guiding devices 10, 10 'of the type described in FIG. 1 are provided in each case. These two web guiding devices 10, 10 'are respectively arranged after the last press nip 20 of the press section 22 and before the first drying cylinder 24 of the dryer section 18.

In the embodiment according to FIG. 2, an impingement dryer 28 provided with a dryer or impingement hood 26 is provided between the two web guiding devices 10, 10 ', through which the material web 14 can be subjected to a hot air and / or superheated steam impingement flow. In this case, the material web 14 with a special the screen 30 associated with the impingement dryer 28 is guided over a larger support roller 32 provided with the dryer hood 26.

The drying speed in the region of a respective web guiding device 10, 10 'designed as a floating dryer or of the impingement flow dryer 28 still provided in the embodiment according to FIG. 2 can be regulated via the compressed air temperature, speed and / or humidity. In the various embodiments, the drying may take place, for example, in such a way that the material web 14 (see also FIG. 1) already has a dry content when draining from the first drying cylinder 18 or during the first removal from a smooth heated surface, which is preferably higher than approximately 60 to about 65%.
As can be seen from Figures 2 and 3, the web 14 is supplied in both cases, starting from the last Preßnip 20 of the press section 22 to the first drying cylinder 18 in a closed train. In this case, the material web 14 is removed in each case from the bottom felt 34 guided through the last press nip 20 of the press section 22.

In the embodiment according to FIG. 2, a common sieve 12 is guided by the two web guiding devices 10, 10 '. The material web 14 is removed in the area of a suction roll 36 from the bottom felt 34 guided through the last press nip 20 of the press section 22.

Between the two web guide devices 10, 10 ', the wire 12 is guided over a further suction roller 38. In the web running direction L behind the web guide device 10 ', a suction roll 40 is provided, over which the wire 12 is guided. Following this, the material web 14 is taken over by the sieve 30 assigned to the impingement flow dryer 28.

For example, a transfer foil 44, a suction box 46 or the like may be provided at the transfer location. In the area of a further suction roll 48, the material web 14 is transferred from the wire 30 to a drying wire 44, through which the web is finally fed to the first drying cylinder 18.

In the embodiments shown in FIGS. 2 and 3, the material web 14 is guided generally obliquely downward in the first web guiding device 10 and generally obliquely upward in the second web guiding device 10 '.

In the embodiment according to FIG. 3, only two compressed-gas-operated web guiding devices 10, 10 'are used. An impingement flow dryer is therefore not provided here. The two web guiding devices 10, 10 'are each assigned their own sieve 12, 12'. The transfer of the material web 14 from the lower wire 34 of the press section 22 to the guided through the first web guide means 10 screen 12 takes place here via a transfer belt 50. In this case, the decrease of the lower wire 34 in the region of a suction roller 52, over which the transfer belt 50 is guided. The transfer of the web to the wire 12 takes place again in the region of a wire 12 associated with the suction roller 36. The transfer of the web 14 from the wire 12 to the through the second web guide means 10 'guided screen 12' takes place in the region of another, the screen 12 'associated with the suction roll 54. The sieve 12 'simultaneously serves as a drying sieve, through which the material web 14 is fed to the first drying cylinder 18 via a further suction roll 56 following the second web guiding device 10'.

As already mentioned, at least one of the compressed-gas-operated web guiding device 10, 10 'is designed as a floating dryer. In principle, however, it is also conceivable to operate one of these web guiding devices 10, 10 'with compressed gas or compressed air at low temperature and, for example, to use it at least predominantly as a transfer element.

In principle, it is also possible to provide at least one floating dryer without a sieve between the last press nip 20 of the press section 22 and the first drying cylinder 18 and / or within a pre-drying section.

LIST OF REFERENCE NUMBERS

10

Web guiding device, floating dryer

10 '

Web guiding device, floating dryer

12

scree

12 '

scree

14

web

16

Nozzles, nozzle bars

18

drying section

20

last press nip

22

press section

24

first drying cylinder

26

dryer hood

28

Impingement dryer

30

scree

32

supporting roll

34

felt

36

suction roll

38

suction roll

40

suction roll

42

suction roll

44

transfer foil

46

suction box

48

suction roll

50

transfer tape

52

suction roll

54

suction roll

56

suction roll

L

Web direction

Claims (32)

1. Machine for producing a paper or board web, having a press section and a drying section (18) which is arranged after the press section (22), has a plurality of drying cylinders with a smooth contact surface and in which at least one compressed-gas-operated web guiding device (10, 10') implemented as a float dryer is provided, through which the web (14) is led together with a fabric (12, 12'),
   characterized in that the at least one compressed-gas-operated web guiding device (10, 10') implemented as a float dryer is arranged before the first drying cylinder (18), and in that, in the at least one compressed-gas-operated web guiding device (10, 10') implemented as a float dryer, compressed gas can be applied to the web (14) in such a way that it is alternately lifted off the fabric (12, 12') and rests on the latter in the web running direction (L).
2. Machine according to Claim 1, characterized in that the fabric (12, 12') is guided rectilinearly by the compressed-gas-operated web guiding device (10, 10').
3. Machine according to one of the preceding claims, characterized in that the web guiding device (10, 10') for applying compressed gas to the web (14) comprises a plurality of nozzles (16) arranged one after another in the web running direction (L).
4. Machine according to Claim 3, characterized in that nozzles (16) are provided on both sides of the fabric (12, 12').
5. Machine according to Claim 3 or 4, characterized in that a plurality of nozzle beams (16) each extending in the direction of the web width are provided.
6. Machine according to one of the preceding claims, characterized in that the compressed gas provided is air.
7. Machine according to one of the preceding claims, characterized in that at least one impingement dryer (28) provided with at least one drying hood (26) is provided, by means of which a hot air and/or hot steam impingement flow can be applied to the web (14).
8. Machine according to Claim 7, characterized in that the web (14) is led over at least one supporting or suction roll (32) with associated impingement dryer (28).
9. Machine according to Claim 7 or 8, characterized in that at least one impingement dryer (28) is arranged before the first drying cylinder (18).
10. Machine according to one of Claims 7 to 9, characterized in that, in the web running direction (L), the impingement dryer (28) is arranged after at least one compressed-gas-operated web guiding device (10, 10').
11. Machine according to one of the preceding claims, characterized in that, as it runs off the first drying cylinder (18) or as it is pulled off a smooth heated surface for the first time, the web (14) already has a dryness which is higher than about 58 to about 65%.
12. Machine according to one of the preceding claims, characterized in that, following the last press nip (20) of the press section (22), at least one compressed-gas-operated web guiding device (10, 10') is provided first.
13. Machine according to one of the preceding claims, characterized in that, following the last press nip (20) of the press section (22), the web is led first through at least one compressed-gas-operated web guiding device (10, 10') and, following that, over at least one supporting or suction roll (32) with associated impingement dryer (28) before it is fed to the first drying cylinder (18).
14. Machine according to one of the preceding claims, characterized in that, in the region of a respective web guiding device (10, 10') implemented as a float dryer or of a respective impingement dryer (28), the drying rate can be regulated via the compressed gas temperature, velocity and/or humidity.
15. Machine according to one of the preceding claims, characterized in that the air permeability of the fabric (12, 12') assigned to the compressed-gas-operated web guiding device (10, 10') is greater than about $1.52\frac{m^3}{m^{2}s}$

    

    (300 cfm) and preferably greater than about $2.54\frac{m^3}{m^{2}s}$

    

    (500 cfm).
16. Machine according to one of the preceding claims, characterized in that, starting from the last press nip (20) of the press section (22), the web (14) is fed to the first drying cylinder (18) in a closed draw.
17. Machine according to one of the preceding claims, characterized in that the web (14) is transferred from the press section (22) directly to the fabric (12) assigned to the compressed-gas-operated web guiding device (10, 10').
18. Machine according to one of Claims 1 to 16, characterized in that the transfer of the web (14) from the press section (22) to the fabric (12) assigned to a compressed-gas-operated web guiding device (10, 10') is carried out via at least one transfer belt.
19. Machine according to one of the preceding claims, characterized in that the web (14) is picked up by a felt (34) led through the last press nip (20) of the press section (22).
20. Machine according to one of Claims 1 to 18, characterized in that the web (14) is picked up directly by a press roll assigned to the last press nip (20) of the press section (22).
21. Machine according to one of the preceding claims, characterized in that a plurality of web guiding devices (10, 10'), preferably each implemented as a float dryer, and/or a plurality of impingement dryers (28) are provided.
22. Machine according to one of the preceding claims, characterized in that at least one horizontally arranged compressed-gas-operated web guiding device (10, 10') is provided.
23. Machine according to one of the preceding claims, characterized in that at least one vertically arranged compressed-gas-operated web guiding device (10, 10') is provided.
24. Machine according to one of the preceding claims, characterized in that at least one compressed-gas-operated web guiding device (10, 10') is provided, in which the web (14) is led generally obliquely upwards.
25. Machine according to one of the preceding claims, characterized in that at least one compressed-gas-operated web guiding device (10, 10') is provided, in which the web (14) is led generally obliquely downwards.
26. Machine according to one of the preceding claims, characterized in that a plurality of compressed-gas-operated web guiding devices are provided, and in that at least some of these web guiding devices (10, 10') are each assigned an individual fabric (12, 12').
27. Machine according to one of the preceding claims, characterized in that at least one fabric (12) led through a plurality of compressed-gas-operated web guiding devices (10, 10') is provided.
28. Machine according to one of the preceding claims, characterized in that, in order to hold the web (14) on the fabric (12, 12') before and/or after the associated compressed-gas-operated web guiding devices (10, 10') and/or between successive web guiding devices (10, 10'), suction rolls (36-40, 54, 56), transfer foils (44) and/or suction boxes (46) are provided.
29. Machine according to one of the preceding claims, characterized in that, in order to transfer the web (14), in a respective compressed-gas-operated web guiding device (10, 10'), compressed gas can be applied to the web (14) only on its side facing away from the fabric (12, 12') and in the web running direction (L) and/or vacuum can be applied from the fabric side.
30. Machine according to one of the preceding claims, characterized in that vacuum boxes are arranged between nozzle beams (16) provided on the fabric side facing away from the web (14).
31. Machine according to one of the preceding claims, characterized in that at least one web guiding device (10, 10') is provided, by means of which compressed gas at low temperature in the range from preferably about 20 to about 150° can be applied to the web (14).
32. Machine according to one of the preceding claims, characterized in that at least one float dryer without fabric is provided between the last press nip (20) of the press section (22) and the first drying cylinder (18) and/or within a pre-drying section.

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