EP1186702B2 - Process for controlling a paperbreak and machine for making a web material - Google Patents

Abstract

Process and apparatus for monitoring web breaks in a machine for producing a material web includes at least one impingement dryer. The process includes guiding the material web through the at least one impingement dryer, and monitoring the material web for web breaks in at least one of a region, viewed in a web travel direction, before an intake into the at least one impingement dryer, after an exit from the at least one impingement dryer and within the at least one impingement dryer. The process further includes at least partially deactivating the at least one impingement dryer when a web break is detected.

Description

The invention relates to a method for web break monitoring in one of the production of a material web, in particular paper or board web, serving machine. It further relates to a machine for producing a material web, in particular paper or board web, in which such a web break monitoring is realized.

While in the previously used multi-cylinder dryer sections, the paper web is led to dry over several steam-heated cylinder or an array of several steam-heated cylinders and Siebsaugwalzen, also the use of at least one impingement or impingement dryer has been proposed by the material web with a Hot air and / or superheated steam flow can be acted upon (see, for example DE-A-198 41 768 and DE-A-199 35 138 ,

Typically, in paper machines, a tear detection on the leader and the drive side takes place at several positions in the machine direction within the cylinder drying section. Such a break detection serves to avoid an uncontrolled paper accumulation in the dryer section as well as a so-called packing of cylinders. A respective break detection triggers a discount of the paper web (see, for example WO-A-9412724 and DE 9206844 U ) or lifting the pickup roller.

A problem with the use of impingement dryers is that damage to the dryer fabrics can occur in the event of a break-off.

The aim of the invention is now to further develop the method and the machine of the type mentioned so that despite the use of one or more impingement dryer, the risk of such damage to the dryer fabrics is virtually eliminated.

To solve this problem, a method with the features of claim 1 is proposed according to the invention.

In this case, the material web is viewed in the web running direction preferably monitored prior to entry into the impingement dryer and / or between multiple impingement dryers to a break out.

In a preferred practical embodiment of the method according to the invention, the material web is monitored for tear-off at least substantially over its entire width. Such web-wide monitoring detects even if only parts of the web are missing, so that even a partial overheating of the dryer fabrics is avoided.

In certain cases, however, it may be sufficient if the material web is monitored for tear-off only at one or both lateral web edges. It is thus basically also a monitoring of only the web edges on the driver and drive side conceivable.

As a rule, a respective impingement dryer is provided with at least one impingement hood. When the web break is detected, preferably at least one impingement hood assigned to the respective impingement dryer is thus deactivated.

In order to deactivate a respective impingement hood, it is preferably changed over from a normal operating state in which the material web is subjected to a hot air and / or superheated steam blast flow into a tear-off operating state in which only an internal hot air circulation or a superheated steam circulation occurs.

For a respective deactivation of the impingement hood, alternatively or additionally, one of these associated burners can be switched to minimum power.

Alternatively or additionally, it is also possible for a respective deactivation of the Impimgementhaube to move this away from the normal web running path in a transfer path.

The deactivation of the impingement dryer should take place within 20 seconds, preferably within 10 seconds after a web break, so that even at air temperatures of 300-500 ° C. no overheating of the dryer fabrics occurs.

According to an expedient practical embodiment of the method according to the invention, the opening of the pickup should take place within 5 s, preferably less than 2 s after a web break.

In certain cases, it is also expedient if, in the event of web breakage being detected, not only the at least partial deactivation of the impingement dryer but also a material web or paper deduction is triggered at the same time.

According to a preferred practical embodiment, the material web is monitored at least at one point by means of at least one sensor for a tear out. The use of sensors of different types is conceivable. Advantageously, at least one optical sensor is used. A respective web break can in particular by a color detection or detected when using a camera by image evaluation.

In certain cases, it is advantageous if at least one sensor is preferably directed onto the material web directly after a respective impingement hood.

In this case, the sensor can be directed, for example, in an area on the material web in which it still lies on a guided through the respective impingement dryer dryer.

However, it is also possible, for example, to direct the sensor onto the material web in a region in which it lies on a drying wire of an evacuated roll provided following the impingement dryer. This suctioned roll may be, for example, a suction roll or a so-called "DuoStabi roll".

The dryer fabrics are preferably made of plastic, wherein the maximum allowable temperature is between 100 and 300 ° C. However, temperatures between 300 and 500 ° C during deactivation of the impingement dryer should not cause any damage to the dryer fabric.

However, it is also conceivable to direct the sensor in the region of a first drying cylinder following the impingement dryer onto the material web, in which the material web is exposed after the expiration of a preceding sieve and before the emergence of a new sieve, the sensor being exposed to the Railway station is directed. The sensor can thus be directed to the first cylinder after the impingement dryer, if there is a group change on this cylinder, through which a point results, at which the paper web is exposed.

In certain cases, it may also be advantageous to monitor the web of material in the area of an evacuated roll following the impingement dryer or one of the large evacuated rolls of the impingement dryer by monitoring the vacuum of that evacuated roll. The negative pressure drops sharply as soon as the roller is no longer covered by the material web, in particular the paper web. The evacuated roll may, for example, again be a suction roll or a so-called "DuoStabi roll". In this case, this evacuated roll is preferably provided within the first cylinder group following the impingement dryer. It can be viewed in the web running direction, in particular provided in front of a pickup scraper. In particular, it may be the first suctioned roll following the impingement dryer.

The evacuated rolls being monitored may also be the large suction rolls on which the impingement hoods are mounted.

In certain cases, it may also be advantageous if the material web is monitored in the region of an impingement dryer for a tear, which is arranged within a cylinder drying section of the production of the web serving machine.

The material web can be monitored, for example, in the region of an impingement dryer for a tear, in which the material web is guided at least partially along at least one straight or slightly curved and / or at least one, in particular larger, preferably evacuated support roll.

According to the invention, a machine for producing a material web, in particular paper or board web with the features of claim 24, also proposed.

The tear-off monitoring means preferably comprise at least one sensor in order to monitor the material web at least at one point by means of at least one such sensor for a tear-off.

In an expedient practical embodiment of the machine according to the invention, the tear-off monitoring means and / or the deactivating means comprise at least one electronic control.

Particularly suitable is the use in machines in which the web is guided in the press section together with both sides each have a band in the form of a press felt or a transfer belt through the press nips or the.

Even at high machine speeds of more than 1100 m / min, the use is recommended.

In the subclaims further advantageous embodiments of the machine according to the invention are given.

Figur 1

eine schematische Darstellung einer ersten Ausführungsform einer Trockenpartie mit nur einem Impingement-Trockner,

Figur 2

eine schematische Darstellung einer weiteren Ausführungsform einer Trockenpartie mit zwei Impingement-Trocknern und

Figur 3

eine schematische Darstellung einer weiteren Ausführungsform einer Trockenpartie mit einer geraden oder leicht gekrümmten Impingementtrocknungs-Strecke und einer unteren größeren Stützwalze mit zugeordnetem Impingement-Trockner.

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

FIG. 1

a schematic representation of a first embodiment of a drying section with only one impingement dryer,

FIG. 2

a schematic representation of another embodiment of a drying section with two impingement dryers and

FIG. 3

a schematic representation of another Embodiment of a drying section with a straight or slightly curved impingement drying section and a lower, larger support roller with associated impingement dryer.

FIG. 1 shows in a purely schematic representation of a drying section 10 of a machine for producing a material web 12, which may be in particular a paper or board web.

Between the last press nip 14 of a press section 16 and a subsequent impingement or impingement dryer 18, a larger pickup suction roll 20 is provided, which transfers the web 12 of a guided through the last Preßnip 14 press felt 22 directly to the impingement dryer 18.

In the present case, the pickup suction roll 20 is wrapped by a sieve 24.

The impingement dryer 18 includes a larger support roller 26 associated, in the present case one-piece Impingementhaube 28. The web 12 is passed through the pickup suction roll 20 on the support roller 26 of this impingement drying unit.

In the present case, the support roller 26 is surrounded by a wire 30 and formed by a suction roll, which is here associated with an outer suction box 32.

The acquisition of the material web 12 by the large support roller 26 is supported by a in the web running direction L at a distance behind the pickup suction roll 20, provided within the loop of the screen 24 deflecting roller 34. After this deflecting roller 34 bears against the support roller 26, the screen 24 and thus the material web 12 is applied to the support roller 26 in the region between the pickup suction roller 20 and the deflecting roller 34.

Subsequent to the support roller 26, the material web 12 is taken over in the region of a suction roller 36 from the screen 38 of a first multi-cylinder group 40 of a plurality of drying cylinders 42. In this case, the acquisition takes place so that the paper can fall in the case of a break between the screens 30 and 38 in the basement 44.

In this drying section 10, the web 12 is viewed in the web running direction L in the area in front of the inlet 41 in the impingement dryer 18 and / or in the area after the outlet 42 from the impingement dryer 18 monitored for a tear out to the web when it is detected Impingement dryer 18 at least partially disable.

In this case, the material web 12 viewed in the web running direction L can be monitored directly in front of the inlet 41 in the impingement dryer 18 and / or directly after the outlet 42 from the impingement dryer 18 to a tear out. In FIG. 1 the relevant monitoring stations are designated S1 and S2, respectively.

As based on the FIG. 1 can be seen, in addition or alternatively, in the area of the following on the impingement dryer 18 first sucked roller, here the suction roller 36, carried out a corresponding web break monitoring. The monitoring site concerned is designated S3.

At a respective monitoring point S1-S3, the material web 12 can be monitored for a tear-off at least substantially over the entire width. In principle, however, a demolition monitoring only at one or at the two lateral web edges is possible.

If a web break is detected, the impingement hood 28 assigned to the impingement dryer 18 is deactivated in the present case. For this purpose, this can in particular be reversed from a normal operating state, in which the material web 12 is subjected to a hot air and / or hot steam impact flow, into a tear-off operating state in which only a hood-internal hot air or hot steam circulation occurs.

Alternatively or additionally, to deactivate the impingement hood 28, a burner associated therewith can be switched to minimum power. For example, this burner can also be switched off completely.

Alternatively or additionally, the impingement hood 28 may be for deactivating the normal web travel, i. Here are moved away from the support roller 26 in a web transfer position.

In the case of a web break detected, in addition to the at least partial deactivation of the impingement dryer, a material web or paper deduction may also be triggered at the same time. In principle, it is also possible to open at least one pickup point provided in the web running direction L in front of the impingement dryer 18 at the same time as the at least partial deactivation of the impingement dryer 18.

At at least one point S1-S3, the material web 12 can be monitored for at least one sensor 46 by means of at least one tear-off. In this case, for example, at least one optical sensor can be used.

In this case, it is particularly possible that a respective web break is detected, for example, by a color detection.

Both at the monitoring point S1 provided in front of the impingement hood 28 and at the monitoring point S2 directly adjoining the impingement hood 28, a respective sensor can be directed, for example, directly onto the material web 12. In this case, the respective sensor 46 is directed in an area on the material web 12, in which this is already or still on the guided through the impingement dryer 18 drying wire 30.

Also at the monitoring point S3, a respective sensor 46 may again be directed to the Matetrialbahn 12. In this case, the material web 12 lies on the drying wire 38 of the provided after the impingement dryer 18 first sucked roller, here the suction roller 36th

In principle, it is also possible to monitor the material web 12 at the monitoring point S3 by monitoring the negative pressure of the evacuated roll, here the suction roll 36.

The demolition monitoring means comprising the sensors 46 or the vacuum monitoring means and / or the deactivating means comprise at least one electronic control 48 in the present case.

In the present case, the material web 12 is monitored in the region of an impingement dryer 18 for a tear, which is arranged between the press section 16 and the multi-cylinder group or cylinder drying section 40 of the production of the web 12 serving machine.

In principle, however, a respective demolition monitoring can also take place at an evacuated roller provided within the first cylinder group 40 following the impingement dryer 18. Thus, for example, a corresponding demolition monitoring on the example provided as besaugte roller roller 48 is possible.

The respective suctioned roller may be provided in the web running direction L in front of a pickup scraper.

Moreover, it is in principle also possible to monitor the material web 12 in the region of an impingement dryer for a tear which is arranged inside the cylinder drying section 40 of the machine used for producing the material web 12.

The embodiment according to FIG. 2 differs from the embodiment described above essentially by the fact that the impingement dryer 18 provided following the last press nip 14 is followed by another impingement dryer 18 '.
This second impingement dryer 18 'includes a two-piece impingement hood 28' associated with a larger back-up roll 26 '. Also in this case, the support roller 26 'is again formed by a suction roll, which is assigned, for example, an outer suction box 32'. In the present case, the diameters of the two support rollers 26, 26 'at least substantially the same size. The second support roller 26 'is looped by a first screen 38 of the cylinder drying section 40.

As based on the FIG. 2 can be seen, the web 12 is transferred from the wire 30 of the first impingement dryer 18 directly to the looped by the wire 38 large support roller 26 'of the subsequent second impingement dryer 18'.

The large back-up roll 26 'is disposed obliquely below the large back-up roll 26. While the impingement hood 28 of the first impingement dryer 18 is provided generally above the associated back-up roll 26, the two-piece impingement hood 28 'of the subsequent second impingement dryer 18' is generally disposed beneath the associated large back-up roll 26. As a result, different web sides are acted upon by the two impingement hoods 28, 28 '.

As based on the Figures 2 can be seen, a demolition monitoring, for example, at a point S1 'immediately after the first impingement hood 18 is possible. Alternatively or additionally, a tear-off monitoring at a point S2 'immediately following the impingement hood 28' of the two-part impingement dryer 18 'is possible. The respective demolition monitoring takes place here between the two of the support roller 26 associated impingement hood 28 '.
Alternatively or additionally, a tear-off monitoring at a point S3 'in the region of the outlet 52 of the screen 38 from the support roller 26' is conceivable.

At the monitoring point S2 ', a respective sensor 46 may be directed onto the material web 12 guided together with the wire 38 via the support roller 26'.

At the monitoring point S3 ', a respective sensor 46 can be directed onto the web of material 26 still lying on the screen 38 running away from the support roller 26.

At the monitoring point S4 ', a respective sensor in the manner shown in the range of a first on the impingement dryer 18' following drying cylinder 54 may be directed to the web 12, wherein the web after the expiration of the previous screen 38 and before the casserole of a new screen 56 is exposed, with the sensor 46 directed to the exposed web site 58.

Moreover, the embodiment according to FIG. 2 at least essentially the same structure as the one of the FIG. 1 , wherein like reference numerals are assigned to corresponding parts. The respective demolition monitoring at the relevant points can otherwise again take place as previously described, for example, with reference to the embodiment according to FIG FIG. 1 has been described.

In the embodiment according to the FIG. 3 the web of material 12, starting from the last press nip 14 of the press section 16 over at least one straight or slightly curved path 60 in closed train to a particular larger support roller 62 with associated impingement dryer 64 out through which guided over the support roller 62 web 12 with a Hot air and / or hot steam impact flow can be acted upon, wherein the straight or slightly curved path 60 is provided as Impallströmungstrocknungs- and / or as Transferfoil route with associated impingement dryer 61. The impingement dryer 61 may, for example, again be provided with at least one impingement hood 61 '. The impingement dryer 64 again has a two-piece impingement hood 64 '.

FIG. 3 shows an embodiment with a following the straight or slightly curved path 60 provided lower larger support roller 62 with associated impingement dryer 64. In this case, the support roller 62 is arranged in front of a drying group 66 with at least one drying cylinder 68.

In the straight or slightly curved path 60, the material web 12 is guided between two screens 70, 72. In this case, the material web 12 is acted upon, for example, from the top by means of the impingement dryer 61 through the relevant sieve 72 through an impingement flow. This impingement dryer 61, which may be provided with at least one impingement hood 61 'again, can be correspondingly deactivated again when the web break is recognized.

The material web 12 is taken over by a pick-up roller 74 from the bottom guided by the press nip 14 press felt 22 on the wire 72. In the area of an additional pickup roller 76, the material web 12 can be moved into the cellar 44, by means of which the material web 12 can be removed from the press felt or press belt 22.

The screen 70 of the Impallströmungstrocknungs- or Transferfoil section 60 is guided in front of the larger support roller 62 via a smaller suction roller 78. A part of such a smaller suction roll may be formed as a pressure zone, or it is installed in the space overpressure box to press the web 12 from the previous sieve, here the sieve 70.

The web 12 is transferred from the wire 70 of the straight or slightly curved Impallströmungstrocknungs- or Transferfoil section 60 on a guided over the following larger support roller 62 screen 80, wherein the transfer area is besaugbar example by means provided before or on the support roller 62 suction box ,

In this case, the web break monitoring can take place, for example, at a point S1 "'in the region of the suction roll 78. In this region, the material web 12 is exposed after lifting off the wire 72 and before running the wire 80. A respective sensor 46 can thus be used directly again be directed to the web 12.

Alternatively or additionally, a web break monitoring can also take place at a point S2 "'in the region of the run 82 of the wire 80 from the support roller 62. Also in this area, the web 12 carried by the wire 80 is exposed, so that a respective sensor 49 again directly on the web 12 may be directed.
As in the embodiment according to FIG. 2 can here, for example, the Bahnrißüberwachung done again, for example, as in connection with the embodiment according to FIG. 1 has been described. Again, the demolition monitoring means 46 and / or the deactivating means may again comprise at least one electronic control 48. In addition to the deactivation of the impingement dryer 64, the pickup roller 74 can be lifted off the press felt 22 at the same time, in particular, when the web break is detected.

In all embodiments, it is thus ensured that, despite the use of one or more impingement dryers, damage to the dryer fabrics in the event of a break is virtually ruled out.

As shown, for example, a tear-off monitoring of the paper web is possible directly after the impingement drying. Such, preferably web-wide tear detection not only triggers the lifting of the pickup roller or the paper deduction, it also controls the impingement hood on tear-off, which may in particular mean that switched to an internal circulation of the hot air, the burner to minimum power converted and / or the hood is moved to a transfer position. With a web-wide monitoring is also recognized if only parts of the web are missing, so that a localized overheating of the dryer fabrics is avoided.

But it is also a monitoring of only the edges of the track on the driver and / or the power side conceivable.

The monitoring can be done by means of various sensors, in particular optical sensors can be used to perform, for example, a monitoring by color detection. A possible position for the monitoring results in particular directly after the impingement hood, where a respective sensor is directed directly at the paper web, which is still on the drying wire, for example while the web on the drying wire of the subsequent suction roll or "DuoStabi roll" lies. But it is also conceivable that the sensor is directed to the first cylinder after the impingement dryer, and in particular when a group change takes place at this cylinder. Namely, with such a change of group, a position where the paper web is exposed after the preceding wire has been lifted and before the new wire runs on the cylinder results.

However, a particular demolition detection is also possible in that the negative pressure of the first evacuated roller is monitored after the impingement dryer. The negative pressure drops sharply as soon as the roller is no longer paper-covered. The monitored evacuated roll may be a suction roll or a so-called "DuoStabi roll" and should conveniently be provided within the first cylinder group after the impingement dryer, preferably before the take-off scraper.

The monitored roll may also be one of the large evacuated rolls of the impingement dryer, wherein, for example, several of these rolls may be appropriately monitored for large evacuated rolls.

The tear detection can be done with an impingement dryer between the press section and a cylinder dryer section or with an impingement dryer be combined within the dryer section.

The impingement dryer may rather be arranged in a straight line or on a large, preferably evacuated roll. In principle, any combinations of several of the one and / or other variant are conceivable.

LIST OF REFERENCE NUMBERS

10

drying section

12

web

14

press nip

16

press section

18

Impingement dryer

18 '

Impingement dryer

20

Pickup suction roll

22

press felt

24

scree

26

larger support roller

26 '

larger support roller

28

impingement hood

28 '

two-piece impingement hood

30

scree

32

suction box

32 '

suction box

34

deflecting

36

suction roll

38

scree

40

Multi-cylinder group, cylinder drying section

41

enema

42

outlet

44

basement, cellar

46

sensor

48

roller

52

procedure

54

drying cylinders

56

scree

58

exposed railway station

60

straight or slightly curved impingement track

61

Impingement dryer

61 '

impingement hood

62

larger support roller

64

Impingement dryer

64 '

two-piece impingement hood

66

drying group

68

drying cylinders

70

scree

72

scree

74

Pickup roll

76

Pickup roll

78

suction roll

80

scree

82

procedure

L

Web direction

S1 - S3

monitoring body

S1 '- S4'

monitoring body

S1 "'- S2"'

monitoring body

Claims (46)

1. Method for monitoring a web break in a machine used for producing a material web (12), in particular paper or board web, in which the material web (12) is led through at least one impingement dryer (18, 18', 61, 64), the material web (12), as viewed in the web running direction (L), being monitored for a break in the region after the exit (42) from the impingement dryer and/or within the impingement dryer, and the impingement dryer being at least partly deactivated if a web break is detected, characterized in that the material web (12) is monitored for a break in the region of an impingement dryer (18, 18', 61, 64) which is arranged between a press section (16) and a cylinder drying section (40) of the machine used for producing the material web, wherein, if a web break is detected, in addition to the at least partial deactivation of the impingement dryer (18, 18', 61, 64), at least one pickup point provided before the press section (16) in the web running direction (L) is also opened at the same time.
2. Method according to Claim 1, characterized in that the material web (12), as viewed in the web running direction (L), is monitored for a break before the entry (41) into the impingement dryer (18, 18', 61, 64) and/or between a plurality of impingement dryers.
3. Method according to Claim 1 or 2, characterized in that the material web (12) is monitored for a break at least substantially over its entire width.
4. Method according to Claim 1 or 2, characterized in that the material web (12) is monitored for a break only on one or the lateral web edges.
5. Method according to one of the preceding claims, characterized in that, if a web break is detected, at least one impingement hood (28, 28', 64') assigned to the impingement dryer (18, 18', 61, 64) is deactivated.
6. Method according to Claim 5, characterized in that, in order to deactivate the impingement hood (28, 28', 61', 64'), the latter is changed over from a normal operating state, in which the material web (12) has a hot-air and/or hot-steam impingement flow applied to it, to a break operating state, in which only a hot-air or hot-steam circulation within the hood occurs.
7. Method according to Claim 5 or 6, characterized in that, in order to deactivate the impingement hood (28, 28', 61', 64'), a burner assigned to the latter is changed over to minimum output.
8. Method according to one of Claims 5 to 7, characterized in that, in order to deactivate the impingement hood (28, 28', 61', 64'), the latter is moved away from the normal web running path into a web transfer position.
9. Method according to one of the preceding claims, characterized in that the deactivation of the impingement dryer is carried out within 20 s, preferably within 10 s, after a web break.
10. Method according to one of the preceding claims, characterized in that, if a web break is detected, in addition to the at least partial deactivation of the impingement dryer (18, 18', 61, 64), at least one pickup point (74) provided before the impingement dryer in the web running direction (L) is also opened at the same time.
11. Method according to one of the preceding claims, characterized in that, if a web break is detected, in addition to the at least partial deactivation of the impingement dryer (18, 18', 61, 64), a material web or paper knock-off is also triggered at the same time.
12. Method according to one of the preceding claims, characterized in that the material web (12) is monitored for a break at at least one point (S1-S3 ; S1' -S4' ; S''', S2''') by means of at least one sensor (46).
13. Method according to Claim 12, characterized in that at least one optical sensor (46) or a camera is used.
14. Method according to Claim 13, characterized in that a respective web break is registered by means of a colour detection.
15. Method according to Claim 14, characterized in that a respective web break is registered by means of an image evaluation.
16. Method according to one of the preceding claims, characterized in that at least one sensor (46) is preferably aimed at the material web (12) directly after a respective impingement hood (28, 28', 64').
17. Method according to Claim 16, characterized in that the sensor (46) is aimed at the material web (12) in a region in which the latter is still lying on a dryer fabric (30, 38, 70, 80) led through the relevant impingement dryer (18, 18', 61, 64).
18. Method according to Claim 16, characterized in that the sensor (46) is aimed at the material web (12) in a region in which the latter is lying on a dryer fabric (38) of an evacuated roll (36) provided after the impingement dryer.
19. Method according to Claim 16, characterized in that the sensor (46) is aimed at the material web (12) in the region of a first drying cylinder (54) following the impingement dryer (18'), in which region the material web (12) is free after running off a preceding fabric (38) and before running onto a new fabric (56), the sensor (46) being aimed at the free web point (58).
20. Method according to one of the preceding claims, characterized in that the material web (12) is monitored in the region of an evacuated roll (36, 78, 48) following the impingement dryer (18, 61) or of one of the large evacuated rolls of the impingement dryer, by monitoring the vacuum of this evacuated roll (36, 78, 48).
21. Method according to Claim 20, characterized in that the evacuated roll (48) is provided within the first cylinder group (40) following the impingement dryer (18).
22. Method according to Claim 21, characterized in that the evacuated roll (36, 78) is provided before a removal doctor in the web running direction (L).
23. Method according to one of the preceding claims, characterized in that the material web (12) is monitored for a break in the region of an impingement dryer (18, 18', 61, 64) in which the material web (12) is, at least to some extent, led along at least one straight or slightly curved path (60) and/or on at least one in particular relatively large, preferably evacuated, supporting roll (26, 26', 62).
24. Machine for producing a material web (12), in particular paper or board web, in which the material web (12) is led through at least one impingement dryer (18, 18', 61, 64) and means (46) are provided in order to monitor the material web (12) for a break, as viewed in the web running direction (L), in the region after the exit (42) from the impingement dryer, and also means (48) are provided in order to deactivate the impingement dryer, at least partly, if a web break is detected, characterized in that the material web (12) can be monitored for a break in the region of an impingement dryer (18, 18', 61, 64) which is arranged between a press section (16) and a cylinder drying section (40) of the machine, wherein, if a web break is detected, in addition to the at least partial deactivation of the impingement dryer, at least one pickup point (74) provided before the press section (16) in the web running direction (L) is also opened at the same time.
25. Machine according to Claim 24, characterized in that the material web (12), as viewed in the web running direction (L), can be monitored for a break directly before the entry (41) into the impingement dryer (18, 18', 61, 64) and/or directly after the exit (42) from the impingement dryer and/or between a plurality of impingement dryers.
26. Machine according to Claim 24 or 25, characterized in that the material web (12) can be monitored for a break at least substantially over its entire width.
27. Machine according to Claim 24 or 25, characterized in that the material web (12) is monitored for a break only on one or the lateral web edges.
28. Machine according to one of Claims 24 to 27, characterized in that, if a web break is detected, at least one impingement hood (28, 28', 61', 64') assigned to the impingement dryer (18, 18', 61, 64) can be deactivated.
29. Machine according to Claim 28, characterized in that, in order to deactivate the impingement hood (28, 28', 61', 64'), the latter can be changed over from a normal operating state, in which the material web (12) has a hot-air and/or hot-steam impingement flow applied to it, to a break operating state, in which only a hot-air or hot-steam circulation within the hood occurs.
30. Machine according to Claim 28 or 29, characterized in that, in order to deactivate the impingement hood (28, 28', 61', 64'), a burner assigned to the latter can be changed over to minimum output.
31. Machine according to one of Claims 28 to 30, characterized in that, in order to deactivate the impingement hood (28, 28', 61', 64'), the latter can be moved away from the normal web running path into a web transfer position.
32. Machine according to one of Claims 24 to 31, characterized in that, if a web break is detected, in addition to the at least partial deactivation of the impingement dryer (18, 18', 61, 64), a material web or paper knock-off can also be triggered at the same time.
33. Machine according to one of Claims 24 to 32, characterized in that the break monitoring means comprise at least one sensor (46) in order to monitor the material web (12) for a break at at least one point by means of at least one such sensor (46).
34. Machine according to Claim 33, characterized in that the break monitoring means comprise at least one optical sensor (46) or a camera.
35. Machine according to Claim 34, characterized in that a respective web break can be registered by means of a colour detection and/or an image evaluation.
36. Machine according to one of Claims 24 to 35, characterized in that at least one sensor (46) is preferably aimed at the material web (12) directly after a respective impingement hood (28, 28', 61', 64').
37. Machine according to Claim 35, characterized in that the sensor (46) is aimed at the material web (12) in a region in which the latter is still lying on a dryer fabric (30, 38, 70, 80) led through the relevant impingement dryer (18, 18', 61, 64).
38. Machine according to Claim 35, characterized in that the sensor (46) is aimed at the material web (12) in a region in which the latter is lying on a dryer fabric (38) of an evacuated roll (36) provided after the impingement dryer.
39. Machine according to Claim 37 or 38, characterized in that the dryer fabric (30, 28, 70, 80) consists of plastic, the maximum permissible temperature preferably lying between 100°C and 200°C.
40. Machine according to Claim 25, characterized in that the sensor (46) is aimed at the material web (12) in the region of a first drying cylinder (54) following the impingement dryer (18'), in which region the material web (12) is free after running off a preceding fabric (38) and before running onto a new fabric (56), the sensor (46) being aimed at the free web point (58).
41. Machine according to one of Claims 24 to 40, characterized in that the material web (12) can be monitored in the region of an evacuated roll (36, 78, 48) following the impingement dryer (18, 61) by monitoring the vacuum of this evacuated roll (36, 78, 48).
42. Machine according to Claim 41, characterized in that the evacuated roll (48) is provided within the first cylinder group (40) following the impingement dryer (18).
43. Machine according to Claim 42, characterized in that the evacuated roll (36, 78) is provided before a removal doctor in the web running direction (L).
44. Machine according to one of Claims 24 to 43, characterized in that the material web (12) can be monitored for a break in the region of an impingement dryer (18, 18', 61, 64) in which the material web (12) is, at least to some extent, led along at least one straight or slightly curved path (60) and/or on at least one in particular relatively large, preferably evacuated, supporting roll (26, 26', 62).
45. Machine according to one of Claims 24 to 44, characterized in that the break monitoring means (46) and/or the deactivation means comprise at least one electronic controller (48).
46. Machine according to one of Claims 24 to 45, characterized in that, in the press section (16), the material web is led through the press nip or press nips (14) together with a belt on both sides in each case in the form of a press felt (22) or a transfer belt.

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