EP0780513B1 - Process for making a fibrous web - Google Patents

Description

The invention relates to a method for producing a fibrous web, e.g. Paper web, especially in a paper making machine.

The starting point of the invention is a known method or a known device according to DE 42 18 595 A1; in particular reference is made to FIG. 3. It gets a wet one Paper web - for the further removal of water - by at least led a press nip of a press section, from where they in a dryer section arrives. The dryer section includes - at least in its initial area - some from the train one after the other passed dry felted groups above. The said Figure 3 shows, without being explained in more detail, that the Number of cylinders increases from dryer group to dryer group.

From the cited document it is also known that the drives of the successive aggregates (namely the last Press and the subsequent drying groups) to minor Speed differences. You want to achieve that the still wet track with every transition from one Aggregate on the subsequent aggregate in the direction of web travel is tensioned to ensure the most stable running possible Reaching the web through the paper machine.

In this regard, however, further improvements should be made become; because modern papermaking machines should with ever increasing working speeds operate. At the same time, the so-called running efficiency can be increased by reducing the risk of web breaks. Finally, paper consumers continue to do so increasing demands on the quality of the finished Paper.

The invention has for its object the above known paper manufacturing processes accordingly the requirements of different types of paper continue to develop that the above requirements as best possible can be fulfilled.

The invention is based on the knowledge that it is optimal Treatment of a still wet web in the press section and in the first dryer groups of the dryer section to take into account the so-called initial wet strength (INF).

The INF is a value for the strength of the still wet paper web. Among other things, this depends on the amount of Ash content (filler content). The higher the ash content the lower the wet strength, the more difficult So the handling of a still wet paper web is in the Papermaking machine.

The following was recognized in detail: the lower the INF the larger the number should be at the beginning of the dryer section be as small as possible dry groups, whereby under one small dry group is understood to be one that is relative has a few drying cylinders. It can also be beneficial be, in addition, the dry content of the paper web when running in into the dryer section to take into account that one tends to have a low dry matter content also as small as possible and many drying groups at the beginning the dryer section provides.

In extreme cases, i.e. when a low INF and a low Inlet dry matter will meet, according to the invention in the first one to three drying groups per drying group only two or three cylinders are provided. Maybe the very first dryer group should only comprise a single cylinder.

The number of cylinders in the dryer group can be advantageous to dry group (as known per se) preferably around to raise a drying cylinder.

It is essential that - as in the known method - the drives of the last press and the first dryer groups so adjusted for slight speed differences, that the still wet track a little at each separation point is tensioned in the direction of web travel. According to the invention this tensioning more often than before and in smaller steps.

Thanks to these small steps it is possible that you can still damp web essentially without any free web train over all Separation points leads, not only (as known from DE '595) over the separation points within the dryer section, but in particular also (by means of suction guide roller 13) via the Separation point between the last press and the first Drying group, possibly also via the separation point between two presses within the press section. Thereby the web will be gentler than before thanks to the paper machine performed so that the risk of web breaks is significantly reduced is.

Gentle web guiding can be done to a considerable extent also be contributed by having at least one the press points, preferably all press points of the press section, trained as long-gap presses. This is best done through this realizes that shoe presses are used.

An example is a paper making machine in the drawing, those for performing the method according to the invention is shown in a schematic side view.

In addition, it should be mentioned that at constant machine speed and increasing ash content the elongation of the Paper increases sharply.

In order to take this phenomenon into account, it is therefore necessary the most appropriate possible distribution of dry groups to choose the appropriate differential speeds.

This need arises to an increasing extent increasing machine speed.

Furthermore, it should also be shown in this context be that at constant dryness web tension increases Behave proportionally. The same applies the ratio of web tension to machine speed.

For the number of short drying groups at the beginning of the It is an advantage if the dryer section is dependent of the dry matter with an initial wet strength (INF) of less than 60 - 65 kN / m 3 short dry groups, at an INF of less than 75 - 85 kN / m 2 short drying groups and also only has a short drying group at the beginning.

The main sections of the paper machine are a headbox S, a twin wire former F, a press section P and a dryer section T. The various other sections, such as B. Smoothing unit and / or optionally a coating machine as well a retractor are omitted in the drawing.

The units essential for the process according to the invention are at least one long nip press (in the present example two long gap presses 11, 12 are provided) and in the initial area the dryer section two or three relatively short Drying groups 21, 22, 23.

If the paper web in the dryer section a certain Dry matter content (e.g. 60%), then each of them can subsequent drying groups 24, 25 a relatively large number of cylinders (e.g. five to eight cylinders). there can refer to some felted single felt dry groups 21 - 24 connect one or preferably two two-felt dryer groups 25.

In the example shown here, the first dryer group has 21 two cylinders and the second dryer group 22 three Cylinder. It is indicated schematically that every press and every Dryer group 21 - 25 in a known manner their own drive having. The drives are connected to a line system Speed controller 30 connected. With their Aid can be provided in a known manner between successive ones Set aggregates any speed differences. For the process according to the invention it is important that these speed differences to relatively small values are adjustable so that the still wet web at each separation point carefully by a small amount in the direction of web travel is excited.

Claims (3)

1. Method of producing a fibrous web, in particular a paper web in a papermaking machine, in which the web formed from a fibrous suspension but still wet - for the purpose of extracting further water - is led through a plurality of individually drivable units in the form of a press section (P) and a plurality of drying groups (21 - 25), the drives of the successive units being set with slight speed differences in such a way that the still wet or moist web is tensioned in the web running direction at each transition from one unit to the following unit, characterized in that the number of individually drivable units necessary to achieve an average web dryness is made a function of the initial wet strength (IWS), as it is known, in such a way that, in the case of a lower IWS, a higher number of individually drivable units is provided than in the case of a higher IWS.
2. Method according to Claim 1, characterized in that the still moist web is led from each of the units to the following unit substantially without a free web draw, that is to say the web is guided always, that is to say even when changing over from one unit to the next, by means of a running surface such as roll cover, cylinder cover, felt or fabric.
3. Method according to Claim 1 or 2, characterized in that the web, immediately following a press section (P), is guided through the drying section (T) - at least through its initial part - in such a way that only the underside of the web comes into contact with the drying cylinders.

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