EP1484442B1 - Method for treating a web, in particular a paper web - Google Patents

Abstract

In a paper manufacturing process a web (11) of paper or carton feeds between a lower shoe drum (2) with a flexible mantle (5) and a heated overhead drum (3). The two drums form a broad nip (4) between their two faces. The mantle (5) is continually monitored for signs of damage that would indicate the onset of fire. If fire is detected the drums are separated and the web continues through the nip as a fire blanket. Mantle damage is detected by monitoring a change in pressure within a void (8) surrounded by the mantle. The shoe drum is monitored by an optical device e.g. a camera. In the event of a web break the web winds itself around either the top or bottom drum behind the wide nip. The rolled-up web is detached from the drum when the accumulated paper reaches a pre-determined thickness on the drum.

Description

The invention relates to a method for treating a web, in particular a paper or board web, in which the web is passed through a nip formed between a shoe roll with a circumferential jacket and a heated counter roll, as for example from the document US 2002/0059872 A1 is known.

The treatment of a web in a nip serves to smooth the web volume-saving. The shell of the shoe roll is pressed by means of a pressure shoe in a peripheral region of the counter roll, which is longer in the web running direction than the width of a nip formed between two cylindrical rollers, even if one of these two rollers can have an elastic surface coating.

The coat of the shoe roll must be performed on its circulation over the pressure shoe. To reduce friction and to cool the jacket, it is known to introduce oil into the cavity surrounded by the jacket. In many cases, this oil is introduced by a hydrostatic lubrication in the pressure surface between the pressure shoe and the jacket. At the front, the cavity is sealed by seals, e.g. Slices, limited. Thus, the oil can not easily emerge from the cavity during normal operation. However, facilities are provided with which the oil can be removed.

The coat of the shoe roll is relatively heavily stressed. He becomes out of its cylindrical shape at each revolution deformed out. During operation, it can not be ruled out that the jacket will be damaged. In this case, the circumferential speed with web speed coat and also with the web speed circulating counter roll must be slowed down, but this course requires a certain amount of time. Usually one can achieve a speed reduction of 10 m / min per second. This means that the braking process can reach an order of minutes in time. During this time, oil is very likely to escape from the damaged shell. This leakage can be exacerbated by centrifugal forces of the still circulating shell. This creates a dangerous situation. On the one hand, the oil spraying out of the damaged jacket can cause mechanical damage in the environment. On the other hand, this oil can also reach the heated counter-roller. Here temperatures of well over 100 ° C are common. If this temperature is above the flash point of the oil used in the shoe roll, the oil can ignite, which severely limits the reliability.

The invention has for its object to reduce the risk of fire.

This object is achieved in the method of the type mentioned above in that the coat is monitored for damage, opens the wide nip on the occurrence of damage and the web continues to feed and used as a protective device.

So you do not beat, as was usual, the web after the occurrence of damage before the nip but leads them further through the wide nip to use it as a protective device. This can prevent the oil spouting out of the jacket from directly reaching the counter-roller. The danger that this oil will ignite is drastically reduced.

Preferably, to detect damage to the shell, pressure is monitored in a cavity surrounding the shell. In the jacket there is usually a pressure of at least 25 mbar to stabilize the shape of the shell. Advantageously, this pressure is even higher, for example in the range of 35-90 mbar. With higher pressure, the stability of the shoe roll increases. However, the seals must still seal the jacket effectively against a higher pressure difference to the outside. A shell damage can now be detected by making one or more pressure measurements during operation. If, for example, the overpressure in the cavity surrounding the jacket drops to a value below 20 mbar, this is interpreted as a crack or damage to the jacket. The exact values that indicate a crack in the coat, of course, depending on the shoe shoe.

Preferably, one monitors a pressure change in the cavity. It is often easier to monitor a pressure change than an absolute pressure. If the pressure changes by more than a predetermined amount in a predetermined time, this is an indication of damage to the jacket.

Additionally or alternatively, monitoring of the pressure or the pressure change, the shoe roll can also be optically monitored, for example with the aid of a camera. The camera then takes a picture of the surface of the shoe roll. If this image changes, this is also an indication of damage to the roller. Optionally, an oil spill itself can be seen.

Preferably, if damage occurs, the web is wrapped behind the nip and wrapped around one of the two rolls. So you let the web still run, but uses the web to "pack" one of the two rolls. In addition to means that are used to knock off the web, then, if necessary, additional conducting agents are required, which give the web the desired direction. When the web is wrapped around the backing roll, the oil is prevented from coming into contact with the hot roll surface. When the shoe roll is wrapped, the shoe roll is trapped so that the web is used to prevent the escape of oil from the jacket. In addition, the coat is stabilized. The winding forming on the jacket in both cases represents a thermal insulation to the respective other roller.

Preferably, the web is deflected in front of the nip when wrapped around the roll at a predetermined thickness. In general, it is sufficient if the protective layer has reached a predetermined thickness on the roller. Additional layers of the web then provide no additional protection. In this case, the track becomes separated from the broad nip, so that the "wrapped" roller can then leak.

In this case, it is preferable that the web is wound around the roll with a thickness which corresponds to a maximum of 90% of the distance of the rolls in the open state of the wide nip. This prevents the reel from becoming too thick and damaging the rolls forming the widening nip.

It is also advantageous if the web is wrapped around the roll with a thickness of at least 1 mm. The diameter of the roller then increases by 2 mm. If you pack the shoe roll, then the winding can also have a thickness of at least 1.5 mm in order to stabilize the coat can additionally. You can also choose a different design: For example, you can ensure that the web is wound around the roller with at least six layers, preferably in higher basis weight grades.

Preferably, a sensor is used which determines the thickness of the web wound around the roll. This sensor can then generate a signal on which the web is knocked off before the nip.

Alternatively or additionally, one can calculate a time for the knocking off of the web in front of the nip taking into account the circumference of the roll, the speed profile of the roll and the distance of the teeing-off device in front of the nip. If necessary, one can also incorporate the thickness of the web in the calculation.

It is preferred here that the calculation is carried out after the occurrence of the damage. In this case, the current data are available, especially the web speed and the braking speed when braking the rollers.

It is preferable to lift aggregates which are adjacent to or closely adjacent to the roll to be wound in the event of damage from the roll. This has two advantages. On the one hand, it prevents that the web, which is to wrap around the roll, is damaged. On the other hand, it also prevents the web from damaging the aggregates with the forming roll.

In an alternative embodiment, it is provided that leads the web through the opened wide nip to a position behind the broad nip. There, the web can be returned, for example, in the pulper or wound up. If the web is continued, it merely prevents oil from being sprayed from the damaged shell of the shoe roll to the heated counter roll. In many cases, this approach is also sufficient to prevent a fire hazard.

It is preferred that one marks the web. For example, one can spray paint onto the edge of the web so that one can readily recognize later on the finished roll which part of the web is to be considered scrap.

In all cases, it is advantageous that when a damage occurs a Bahnbeschnitt before the nip disabled. Thus, the width of the web is increased, so that the web seen in the axial direction of the rolls covering a larger area. This further reduces the risk that oil from the damaged shell on the surface of the hot roller injected and ignited there.

Preferably, the web is offset transversely to its direction of travel when the damage of the jacket occurs outside the web width. For example, if the damage occurs in an axial end or edge region of the shell, then the oil could splash out laterally adjacent to the web. This failure is easily defused by moving the web so far that it can cover the damage again. Such a shift can be effected, for example, by tilting a guide roller arranged in front of the broad nip somewhat.

Preferably, one determines the axial position of the damage. In this case, one not only determines if damage has occurred, but also where. Based on the axial position can then be determined whether the web must be offset or not.

Fig. 1

eine schematische Darstellung zur Erläuterung einer ersten Ausführungsform des Verfahrens,

Fig. 2

eine schematische Darstellung zur Erläuterung einer zweiten Ausführungsform des Verfahrens und

Fig. 3

eine schematische Darstellung zur Erläuterung einer dritten Ausführungsform des Verfahrens.

The invention will be described below with reference to preferred embodiments in conjunction with the drawings. Herein show:

Fig. 1

1 is a schematic representation for explaining a first embodiment of the method,

Fig. 2

a schematic representation for explaining a second embodiment of the method and

Fig. 3

a schematic representation for explaining a third embodiment of the method.

Fig. 1 shows a wide-nip calender 1 with a shoe roll 2 and a counter-roller 3, which form a nip 4 between them. In Fig. 1 the wide nip 4 is opened, ie the shoe roll 2 and the counter roll 3 have been removed from each other.

The shoe roll 2 has a circumferential jacket 5, which is loaded by means of a pressure shoe 6 in the direction of the counter roll 3. The pressure shoe 6 has a pressure surface 7 which is concavely curved so that the jacket 5 can be pressed against the circumference of the counter roller 3 in the region of the pressure shoe 6. This is shown schematically by the corresponding curvature of the jacket 5.

In order to reduce the friction between the jacket 5 and the pressure shoe 6, a not shown in detail hydrostatic lubrication is provided in the pressure surface, ie it is continuously pressed an oil between the jacket 5 and the pressure shoe 6. This oil accumulates in a cavity 8, which is surrounded by the jacket 5. From the cavity 8, the oil is carried away with discharge means, not shown. The cavity 8 is closed at its end faces, for example by end plates.

The counter roll 3 is heated. For this purpose, it has, for example, peripheral bores 9, through which a heating medium, for example steam or heated oil, can be passed in order to heat the surface of the counter-roller 3. In the case of a wide-nip calender, the temperature of the surface of the counter-roller 3 can certainly assume values of the order of 180 ° C. or more.

Each time the jacket 5 passes through the nip 4, it is transformed to a considerable extent. This prolonged loading of the jacket leads to the risk that the jacket will be damaged. If such damage results in an opening, then oil may be expelled from the cavity 8. There is a risk that the oil comes to the hot counter-roller 3 and ignited there.

Usually, in a fault, a knock-off device 10 is activated, which cuts through a web 11 which passes through the wide nip. The chopping device 10 is arranged in the web running direction, which is represented by an arrow 12, in front of the nip 4, i. Attempts to remove the web 11 from the nip 4. This procedure is not used in this case. Rather, the following happens:

One first monitors whether the jacket 5 is damaged. For this purpose, one can for example use a pressure sensor 13, which is arranged in the cavity 8. The pressure sensor 13 can either detect an absolute pressure in the cavity. The pressure in the cavity 8 is normally on the order of 25 to 95 mbar higher than the ambient pressure. If this pressure on one Value falls below 20 mbar, this is interpreted as a crack of the mantle 5.

One can also let the pressure sensor 13 detect a pressure difference over time. If, for example, the overpressure in the cavity 8 drops by 10 mbar in one second, this is also interpreted as damage to the jacket 5.

In addition to or instead of the pressure sensor 13, it is possible to use optical monitoring, for example in the form of a camera 14, which is directed onto the surface of the jacket 5. If there is a change, then it is also decided on a damage of the shell 5.

If such damage is found, then the shoe roll 2 and the counter roll 3 are driven apart as soon as possible to open the nip 4. At the same time, the oil supply to the shoe roll 2 is interrupted. The oil containing and circulating at web speed shoe roll 2 must then be slowed down, but this requires a certain amount of time due to the inertia. Usually, the speed can be reduced by 100 m / min in 10 s. At production speeds of over 600 m / min, it would therefore take over one minute until the shoe roll 2 has come to a standstill. At higher web speeds, this time takes even longer.

In this time, oil is likely to come out of the shoe roll 2, which can be reinforced by the centrifugal forces of the moving shell 5. Operational creates a risk not only directly by the spurting oil, but also in that this oil can reach the opposite mating roll 3. There, the oil can ignite.

So you drive not only the counter roll 3 and the shoe roll 2 apart, but severed the web in the direction 12 behind the nip 4 by means of a chopping 15. A part 16 in the web running direction 12 behind the chipper 15 is further wound or removed. The part of the web 11 adjacent to the broad nip 4 is guided around the shoe roll 2 with the aid of guide means shown only schematically as arrows 17, so that a winding 18 forms on the shoe roll 2 from the web 11. This wrap 18 "packs" the shoe roll 2 and prevents 5 oil is pushed out of the jacket.

After a certain time, the web 11 is severed by the chopping device 10 in front of the broad nip. The time is determined by the thickness of the web 11 and thus the thickness of the "packaging" of the shell 5, so the coil 18, the strength of the web 11 and the distance between the two rollers 2, 3 in the open state of the broad nip 4. Der Winding 18 may be at most as thick as the distance between the rollers 2, 3. Preferably, the thickness should be less than 90% of the distance.

The strength of the "package" depends on the strength of the web used. The winding should consist of at least 6 layers of the web or at least 1.5 mm thick. This results in a diameter increase of at least 3 mm.

By means of the speed of the web 11, the deceleration with which the shoe roll 2 is decelerated, the circumference of the shoe roll 2 and the distance of the stripping device 10 located in front of the nip 4, the time at which the web 11 is knocked off for the second time can be calculated , namely in front of the nip 4. The calculation of this time can take place while the process described is running.

Alternatively, a sensor 19 may be used which measures the thickness of the coil 18 and determines therefrom and from the distance of the knock-off device 10 the time for knocking off the wide nip 4.

In many cases, a device for trimming the edges of the web is still provided in front of the nip 4. These aggregates for web trimming can be deactivated for the duration of the disturbance, that is to say when the reel 18 is produced around the shoe roll 2. This increases the width of the web 11 on the shoe roll 2, which offers even better protection.

In addition, it may be useful to other, not shown components that were previously attached to the jacket 5 or were attached very close thereto, such as scrapers or humidifiers, for the duration of the disturbance.

Fig. 2 shows a modified embodiment. The same elements are provided with the same reference numerals.

In this case, the web 11 is guided after knocking off with the aid of the knock-off device 15 around the counter-roller 3. Schematically represented by arrows 20 are guiding means which, after being knocked off, behind the broad nip 4 guide the web 11 around the counter-roller 3 in order to form the winding 18 there.

In this case, the hot surface of the backing roll 3 is covered and thus prevents oil from getting onto the hot surface of the backing roll 3.

The roll 18 should also consist in this case of at least six layers or be at least 1 mm thick, so that the diameter of the backing roll 3 grows by at least 2 mm.

Otherwise, the procedure is as related to Fig. 1 described.

Fig. 3 shows a further modified embodiment. Same elements are denoted by the same reference numerals as in FIG Fig. 1 and 2 described.

At the in Fig. 3 As shown, the web 11 is not severed when an error occurs. Rather, it continues to run and is wound into a winding roll 21 or passed into a pulper, not shown. However, the web 11 still acts as a barrier between the shoe roll 2 and the counter roll 3, so that oil can not reach the hot surface of the counter roll 3.

Appropriately, one marks the web 11, for example, characterized in that sprayed with the aid of a spraying device 22 color on the edge of the web 11, so that one can recognize on the finished roll 21, where is Committee.

Also in the designs according to the Figures 2 and 3 It may be appropriate to increase the width of the web 11 by disabling aggregates for web trimming, as long as you have to handle the error. This increases the width of the web 11 on the roller 3 or between the rollers 2 and 3.

In the embodiment according to Fig. 3 the web 11 is then knocked off by means of the chopper 10 in front of the nip 4 when the mantle 5 only has a low speed. The speed should preferably be less than 100 m / min, better less than 50 m / min and more preferably less than 5 m / min.

To accelerate the deceleration of the shell, it can be ensured when opening the nip that the jacket of the shoe roll continues to rest against the pressure shoe. In this case, when separating the rolls, the axes of the rolls are removed from each other.

If the damage occurs in an area that is not covered by the web, then the oil would be able to escape from the mantle without being obstructed by the web. In this case, an upstream of the wide nip guide roller is tilted slightly. This has the consequence that the web is offset laterally. The lateral offset causes the web to cover the damage.

Also in this case, the web can be used as a protective device.

Claims (17)

1. Method for treating a web (11), in particular a paper or board web, in which the web (11) is led through an extended nip (4) which is formed between a shoe roll (2) having a revolving shell (5) and a heated mating roll (3), characterized in that the shell (5) is monitored for damage, in the event that damage occurs the extended nip (4) is opened and the web (11) continues to be supplied and is used as a protective device.
2. Method according to Claim 1, characterized in that, in order to register damage to the shell (5), a pressure in a hollow space (8) enclosed by the shell (5) is monitored.
3. Method according to Claim 2, characterized in that a pressure change in the hollow space (8) is monitored.
4. Method according to one of Claims 1 to 3, characterized in that the shoe roll (2) is monitored optically.
5. Method according to one of Claims 1 to 4, characterized in that, upon the occurrence of damage, the web (11) is knocked off after the extended nip (4) and is wound around one of the two rolls (2, 3).
6. Method according to Claim 5, characterized in that the web (11) is knocked off before the extended nip (4) when it has been wound around the roll (2, 3) with a predetermined thickness.
7. Method according to Claim 6, characterized in that the web (11) is wound around the roll (2, 3) with a thickness which corresponds to a maximum of 90% of the spacing of the rolls (2, 3) when the extended nip (4) is opened.
8. Method according to Claim 6 or 7, characterized in that the web (11) is wound around the roll (2, 3) with a thickness of at least 1 mm.
9. Method according to one of Claims 6 to 8, characterized in that use is made of a sensor (19) which determines the thickness of the web (11) wound around the roll (2, 3).
10. Method according to one Claims 6 to 9, characterized in that a time for knocking off the web (11) before the extended nip (4) is calculated while taking into account the circumference of the roll (2, 3), the speed profile of the roll and the distance of the knock-off device (10) before the extended nip (4).
11. Method according to Claim 10, characterized in that the calculation is performed after the occurrence of the damage.
12. Method according to one of Claims 5 to 11, characterized in that units which bear on the roll (2, 3) which is to be wrapped or are directly adjacent thereto are lifted off the roll upon the occurrence of the damage.
13. Method according to one of Claims 1 to 4, characterized in that the web is led through the opened extended nip (4) to a position (21) after the extended nip (4).
14. Method according to Claim 13, characterized in that the web (11) is marked.
15. Method according to one of Claims 1 to 14, characterized in that, upon the occurrence of damage, web trimming before the extended nip (4) is deactivated.
16. Method according to one of Claims 1 to 15, characterized in that the web (11) is offset transversely with respect to its running direction if the damage to the shell (5) occurs outside the web width.
17. Method according to Claim 16, characterized in that the axial position of the damage is determined.

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