EP1484442A1 - 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 cardboard web, where the web is led through a wide nip, the one between a shoe roller with a rotating one Sheath and a heated counter roll is formed.

The treatment of a web in a wide nip serves to smooth the web in a volume-saving manner. The coat of the Shoe roller is in with the help of a pressure shoe a circumferential area pressed against the counter roller, which in Web direction is longer than the width of a nip, which is formed between two cylindrical rollers, even if one of these two rollers has an elastic one Can have surface covering.

The jacket of the shoe roller must over in its circulation the pressure shoe are guided. To reduce Friction and for cooling the jacket is known in bring in the cavity surrounded by oil. In many cases, this oil is replaced by a hydrostatic Lubrication in the contact surface between the contact shoe and introduced the coat. The cavity is on the face by seals, e.g. Disks, limited. The Oil cannot escape from the cavity during normal operation step out easily. However, they are facilities provided with which the oil are removed can.

The jacket of the shoe roller is relatively heavily used. It turns out of its cylindrical shape with every revolution deformed out. In operation, it cannot be ruled out that the coat is damaged. In this Fall must the jacket revolving at the speed of the web and also the counter roll rotating at web speed be slowed down, but of course a certain Takes time. Usually one can be done every second achieve a speed reduction of 10 m / min. This means that the braking process is timed can reach an order of magnitude of minutes. It is very likely that this will occur Oil from the damaged coat. This exit can still be caused by centrifugal forces Coat to be reinforced. This creates one dangerous situation. On the one hand, this can result from the damaged Coat spurting oil around cause mechanical damage. On the other hand this oil also get on the heated counter roll. Temperatures of well over 100 ° C are common here. If this temperature is above the flash point in the Oil is used, the oil can ignite, which severely limits operational safety.

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

This task is in the process of the aforementioned Kind of solved by placing the coat on one Damage monitored, if damage occurs the Breitnip opens and the web continues and used as a protective device.

So you don't hit, as has been customary up to now Path after the occurrence of damage before the Breitnip but leads them through the wide nip to them to be used as a protective device. This can prevent that the oil spurting out of the coat immediately gets onto the counter roller. The danger that this oil then ignites is drastically reduced.

It is preferable to monitor to detect damage of the coat a print in a surrounding of the coat Cavity. There is usually overpressure in the coat of at least 25 mbar to stabilize the shape of the jacket. This pressure is even advantageous even higher, for example in the range of 35-90 mbar. With higher pressure, the stability of the shoe roller decreases to. However, the seals must cover the jacket too against a higher pressure difference still effective to the outside caulk. A coat damage can now be recognized be that one in operation one or more Takes pressure measurements. For example, the overpressure drops to a value in the cavity surrounded by the jacket below 20 mbar, this is called a crack or damage of the coat interpreted. The exact values that are on to indicate a tear in the coat are of course from the depending on the respective shoe roller.

A pressure change in the cavity is preferably monitored. A change in pressure is much easier monitor as an absolute pressure. If the Pressure by more than one in a predetermined time changes predetermined amount, this is an indication of the Damage to the jacket.

Additionally or alternatively, monitoring the pressure or the pressure change can also be seen optically monitor, for example with the help of a camera. The The camera then takes a picture of the surface of the shoe roller on. If this picture changes, so is it an indication of damage to the roller. Possibly oil leakage can also be recognized.

It is preferable to hit when damage occurs the web behind the wide nip and wraps it around one of the two rollers around. So you leave the train still run, but uses the train to "wrap up" one of the two rollers. In addition to funds, that are used to knock off the web are then additional guidance may be required, which give the train the desired direction. If the web is wrapped around the counter roll is prevented that the oil is in contact with the hot roller surface comes. If the shoe roll is wrapped, then the shoe roller is enclosed so that the web used to prevent oil from escaping from the mantle prevent. The coat is also stabilized. The wrap that forms on the jacket is placed in both cases thermal insulation for each other roller.

Preferably you cut off the web in front of the Breitnip, when they are around the roller with a predetermined thickness has wrapped. As a rule, it is sufficient if the Protective layer on the roller reaches a predetermined thickness Has. There are no other locations of the railway additional protection more. In this case, the web separated in front of the wide nip so that the "wrapped" Roller can then leak.

It is preferred that the web be of a thickness wraps around the roller, the maximum 90% of the distance of the Rolls in the open state of the wide nip corresponds. This prevents the wrap from becoming too thick and the rollers forming the wide nip are damaged.

It is also an advantage if you have the web with a thickness of at least 1 mm around the roller. The diameter the roller then increases by 2 mm. If you have the Packs the shoe roller, then the wrap can also be a Have a thickness of at least 1.5 mm to add to the coat to be able to stabilize. You can also get one choose a different design: for example, you can use it ensure that the web has at least six layers around the Roll is wound, preferred for varieties with higher Basis weights.

Preferably a sensor is used that measures the thickness of the web wound around the roller. This The sensor can then generate a signal to which the Web is knocked off before the Breitnip.

Alternatively or additionally you can set a time for taking the course off before the Breitnip into account the circumference of the roller, the course of the speed the roller and the distance of the knock-off device calculate before the wide nip. Possibly you can also calculate the thickness of the web let in with.

It is preferred that the calculation according to Occurrence of the damage. In this case stand the current data is available, especially the web speed and the braking speed when braking the rollers.

Preferably, one lifts aggregates that are to be wrapped up Roller or are close to it, when the damage occurs from the roller. this has two advantages. First, you prevent the train from which is supposed to wrap around the roller is damaged. On the other hand, one also prevents the train from using the the aggregates are damaged.

In an alternative embodiment it is provided that the web through the open wide nip to a position leads behind the Breitnip. There the train can for example, be returned to the pulper or be wound up. If the train continues, then it only prevents oil from the damaged one Jacket of the shoe roller to the heated counter roller is injected. In many cases this procedure is sufficient but also to prevent a fire hazard.

It is preferred that the path is marked. For example you can spray paint on the edge of the web, so that later on the finished wrap without can also see which part of the web as a committee is to be considered.

In all cases it is an advantage that when you occur damage a web trim before the Breitnip disabled. This increases the width of the web, so that the web seen one in the axial direction of the rollers covers larger area. So the danger continues reduces oil from the damaged coat to the The surface of the hot roller splashes and ignites there.

The web is preferably offset transversely to its direction of travel, if the damage to the jacket is outside the Web width occurs. For example, if the damage in an axial end or edge region of the jacket occurs, then the oil could spurt out to the side of the web. This error case is simple mitigated by shifting the train so far, that she can cover the damage again. Such one Relocation can be caused, for example, by that you have a guide roller arranged in front of the wide nip something tends.

The axial position of the Damage. In this case, you don't just determine whether damage has occurred, but also where. Based the axial position can then be determined whether the Path must be moved 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 is described below on the basis of preferred exemplary embodiments in conjunction with the drawing. Show here:

Fig. 1

1 shows a schematic illustration to explain a first embodiment of the method,

Fig. 2

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

Fig. 3

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

Fig. 1 shows a wide nip calender 1 with a shoe roller 2 and a counter roller 3, one between them Form Breitnip 4. In Fig. 1, the wide nip 4 is open, i.e. the shoe roller 2 and the counter roller 3 been separated from each other.

The shoe roller 2 has a circumferential jacket 5, who with the help of a pressure shoe 6 towards the Counter roll 3 is loaded. The pressure shoe 6 has one Pressure surface 7, which is concavely curved, so that the jacket 5 in the area of the pressure shoe 6 to the circumference the counter roller 3 can be pressed. This is schematically through the corresponding curvature of the jacket 5 shown.

To the friction between the jacket 5 and the pressure shoe 6 is to be reduced in the pressure area not shown hydrostatic lubrication device provided, i.e. there will be an oil in between the coat 5 and the pressure shoe 6 pressed. This Oil accumulates in a cavity 8, which is from Coat 5 is surrounded. From the cavity 8, the oil transported with removal means not shown. The cavity 8 is closed on its end faces, for example through end plates.

The counter roll 3 is heated. For example, she points to this peripheral holes 9 through which a Heating medium, such as steam or heated oil, passed can be applied to the surface of the counter roller 3 to heat. With a wide nip calender, the temperature can values of the surface of the counter roller 3 assume in the order of 180 ° C and more.

Every time the jacket 5 passes through the wide nip 4, it is significantly reshaped. This ongoing Loading the coat leads to the risk that the coat is damaged. If such damage leads to an opening, then oil from the cavity 8th are thrown out. There is a risk that the oil comes to the hot counter roll 3 and itself ignited there.

A teeing-off device is usually used in the event of a fault 10 activated, the one web 11, the Breitnip goes through, cuts. The tee 10 is in the direction of web travel by a Arrow 12 is shown, arranged in front of the wide nip 4, i.e. one tries to get the web 11 from the Breitnip 4 to remove. This procedure is described in the present Case not used. Rather, it does the following:

One first monitors whether the jacket 5 is damaged. For example, a pressure sensor 13 can be used for this purpose use which is arranged in the cavity 8. The pressure sensor 13 can either be an absolute pressure in the cavity determine. 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 you If the value drops below 20 mbar, this is called the tear of the jacket 5 interpreted.

The pressure sensor 13 can also have a pressure difference over time. For example, if the Overpressure in cavity 8 drops by 10 mbar in one second, this is also considered damage to the jacket 5 interpreted.

In addition or instead of the pressure sensor 13, one can use optical monitoring, for example in Form a camera 14 on the surface of the jacket 5 is directed. If there is a change results, then damage to the Coat 5 decided.

If such damage is found, then the shoe roller 2 and the counter roller 3 are as possible immediately moved apart to the Breitnip 4 to open. At the same time, the oil supply to the shoe roller 2 interrupted. The oil containing and at web speed The circumferential shoe roller 2 must then be braked become, but what due to the inertia takes time. Usually the speed can be reduced by 100 m / min in 10 s. At production speeds of over 600 m / min it would take over a minute for the shoe roller 2 has come to a standstill. At higher web speeds this time takes even longer.

It is very likely that oil will occur during this time out of the shoe roll 2, which by the centrifugal forces of moving jacket 5 can be reinforced. Operational a danger not only arises directly the oil spurting out, but also because this Oil on the opposite counter roller 3 can. The oil can ignite there.

So you don't just drive the mating roller 3 and Shoe roller 2 apart, but cuts the web in the direction 12 behind the Breitnip 4 with the help of a Teeing device 15. A part 16 in the direction of web travel 12 behind the tee 15 continues wound up or removed. The one adjacent to the Breitnip 4 Part of the web 11 is only schematic using guidance means shown as arrows 17 around the Shoe roller 2 passed around, so that on the shoe roller 2 forms a roll 18 from the web 11. This Wrap 18 "packs" the shoe roller 2 and prevents that 5 oil is pressed out of the jacket.

After a certain time, the web 11 is through the tee 10 severed before the wide nip. The Time is determined from the thickness of the web 11 and thus the thickness of the "packaging" of the jacket 5, ie of the winding 18, from the strength of the web 11 and the Distance between the two rollers 2, 3 in the open state of the wide nip 4. The winding 18 may at most so become thick as the distance between the rollers 2, 3. Preferably the thickness should be less than 90% of the distance be.

The strength of the "packaging" depends on the strength the path used. The wrap should be out at least 6 layers of the web exist respectively be at least 1.5 mm thick. This results in a Diameter increase of at least 3 mm.

About the speed of web 11, the delay, with which the shoe roller 2 is braked, the extent the shoe roller 2 and the distance in front of the Breitnip 4th arranged tee device 10 may be the time can be calculated at which the web 11 for the second time is knocked off, namely before the Breitnip 4. The calculation this point in time can take place during the described process is running.

Alternatively, a sensor 19 can also be used, which measures the thickness of the roll 18 and out and out the distance of the tee 10 the time intended for teeing off in front of the Breitnip 4.

In many cases there is still a device before the Breitnip 4 intended to trim the edges of the web. These web trimming units can be used for Duration of the fault, that is when the winding 18 around the Shoe roller 2 is generated, deactivated. Thereby the width of the web 11 increases on the shoe roll 2, which offers even better protection.

It can also be useful to others, not closer Components shown that previously applied to the jacket 5 or were very close to it, for example Scraper or humidifier, for the duration to turn away the disturbance.

Fig. 2 shows a modified embodiment. Same Elements are provided with the same reference symbols.

In this case, the web 11 after the tee off with With the help of the knock-off device 15 around the counter roller 3 directed. Are schematically represented by arrows 20 Leitmittel that after the tee behind the Breitnip 4 guide the web 11 around the mating roller 3 to there the Form winding 18.

In this case the hot surface of the counter roll 3 covered and thus prevents oil on the hot surface of the counter roll 3 arrives.

The wrap 18 should also consist of at least in this case there are six layers or at least 1 mm be thick so that the diameter of the counter roll 3 µm grows at least 2 mm.

Otherwise, the procedure is the same as in the context described with Fig. 1.

Fig. 3 shows a further modified embodiment. The same elements have the same reference symbols as described in Figs. 1 and 2.

In the procedure shown in Fig. 3, the Lane 11 is not severed if an error occurs. Rather, it continues to run and becomes a winding roll 21 wound or in a not shown Pulper headed. However, the web 11 still acts as a lock between the shoe roller 2 and the counter roller 3, so that oil does not hit the hot surface of the backing roll 3 can reach.

Appropriately you mark the web 11, for example characterized in that with the help of a spray device 22nd Color is sprayed onto the edge of the web 11, so that you can see on the finished wrap 21, where committee is.

This also applies to the configurations according to FIGS. 2 and 3 it may be appropriate to increase the width of the web 11, by deactivating aggregates for web trimming as long as you have to handle the mistake. Thereby increases the width of the web 11 on the roller 3 or between rollers 2 and 3.

3, the web 11 is with Help of the tee 10 in front of the Breitnip 4th then knocked off when the jacket 5 is only a little Has speed. The speed should be are preferably below 100 m / min, better below 50 m / min and advantageously below 5 m / min.

To accelerate the braking of the jacket, can When opening the nip, make sure that the coat the shoe roller is still in contact with the pressure shoe. In this The axes of the rollers fall when the rollers are separated separated from each other.

If the damage occurs in an area that is not is covered by the web, then the oil would come out of the Coat can step out without being hindered by the web to become. In this case, one is placed upstream of the Breitnip Guide roller slightly inclined. As a consequence, that the web is offset laterally. The lateral offset causes the web to cover the damage.

In this case too, the web can be used as a protective device be used.

Claims (17)

Method for treating a web (11), in particular a paper or cardboard web, in which the web (11) is passed through a wide nip (4) which is between a shoe roller (2) with a circumferential jacket (5) and a heated counter roller (3) is formed, characterized in that the jacket (5) is monitored for damage, the wide nip (4) is opened in the event of damage and the web (11) is fed in further and used as a protective device. A method according to claim 1, characterized in that a pressure in a cavity (8) surrounding the jacket (5) is monitored to detect damage to the jacket (5). A method according to claim 2, characterized in that a pressure change in the cavity (8) is monitored. Method according to one of claims 1 to 3, characterized in that the shoe roller (2) is monitored optically. Method according to one of claims 1 to 4, characterized in that when damage occurs, the web (11) behind the wide nip (4) is knocked off and wound around one of the two rollers (2, 3). Method according to Claim 5, characterized in that the web (11) is knocked off in front of the wide nip (4) when it has wound around the roller (2, 3) with a predetermined thickness. Method according to Claim 6, characterized in that the web (11) is wound around the roller (2, 3) with a thickness which corresponds to a maximum of 90% of the distance between the rollers (2, 3) when the wide nip (4) is open , Process according to claim 6 or 7, characterized in that the web (11) is wound around the roller (2, 3) with a thickness of at least 1 mm. Method according to one of claims 6 to 8, characterized in that a sensor (19) is used which determines the thickness of the web (11) wound around the roller (2, 3). Method according to one of Claims 6 to 9, characterized in that a point in time for knocking off the web (11) in front of the wide nip (4) is taken into account, taking into account the circumference of the roller (2, 3), the speed profile of the roller and the distance between the rollers Teeing device (10) calculated before the wide nip (4). Method according to Claim 10, characterized in that the calculation is carried out after the damage has occurred. Method according to one of Claims 5 to 11, characterized in that aggregates which bear against the roller (2, 3) to be wrapped or are directly adjacent to it are lifted off the roller when the damage occurs. Method according to one of claims 1 to 4, characterized in that the web is guided through the opened wide nip (4) to a position (21) behind the wide nip (4). A method according to claim 13, characterized in that the web (11) is marked. Method according to one of claims 1 to 14, characterized in that a web trim in front of the wide nip (4) is deactivated when damage occurs. Method according to one of Claims 1 to 15, characterized in that the web (11) is offset transversely to its running direction if the damage to the jacket (5) occurs outside the web width. A method according to claim 16, characterized in that one determines the axial position of the damage.

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