WO1996017126A1

WO1996017126A1 - Wire section for a paper machine

Info

Publication number: WO1996017126A1
Application number: PCT/EP1995/004737
Authority: WO
Inventors: Günter HALMSCHLAGER
Original assignee: Voith Sulzer Papiermaschinen Gmbh
Priority date: 1994-12-01
Filing date: 1995-12-01
Publication date: 1996-06-06
Also published as: FI963027A; EP0742856A1; DE4442756A1; FI963027A0; BR9506961A; CA2182569A1; JPH09508947A

Abstract

The invention concerns a wire section for a paper machine with a forming cylinder (1), with a felt band (2) and a wire band (3) which both loop around the forming cylinder (1), the inner felt band (2) being on the inside and the wire band (3) being on the outside, and define a receiving slot (4) for a machine-wide pulp jet or a paper web which has undergone preliminary de-watering. The forming cylinder has a perforated outer casing which is mounted in such a way that it can rotate. The invention is characterised by the following features: at least part of the looping zone of the forming cylinder can be pressurized from inside.

Description

5/04737

Screen section for a paper machine

The invention relates to a wire section for a paper machine according to the preamble of claim 1.

Twin-wire sections are known in a large number of variants. Reference is made to the magazine "Das Papier", issue 10 A, year 1991, pages V 100 ff.

Accordingly, there are so-called roll formers, in which only rolls or rollers are used as drainage elements. There are also blade formers in which strips which are arranged transversely to the machine direction are used as drainage elements.

In the case of machines with a horizontal sheet formation section, the

Top roll input roller, i.e. that roller which brings the top wire to the bottom wire, be arranged at a certain horizontal distance from the input roller of the bottom wire. This creates a pre-drainage section (so-called "hybrid former"). Basically, there is such a shift between the input rollers of the two

Screening belts also possible on a machine with a vertical sheet formation section. In most cases, however, the two input rollers in the latter type of machine are approximately in the same horizontal plane. These machines are also called "gap formers" (gap formers).

Instead of two sieves, it is also known (US Pat. No. 3,378,435) to use a sieve belt and a felt belt. Both bands wrap around the forming cylinder. The felt tape lies on the inside of the loop, i.e. directly on the outer surface of the forming cylinder, while the

Screen belt wraps around the forming cylinder on the outside. Between these two there is again the paper web, sandwiched by felt belt and wire belt. In this case, ie when using a felt, the forming cylinder has a closed outer surface.

In order to achieve good sheet formation when using a so-called former, the felt must not run onto the forming cylinder too dry. In many cases, the felt is even saturated with water. However, such a high water content in the felt has a negative effect on the moisture content of the paper web. The felt tape runs - together with the paper web lying on or attached to it - after leaving the

Forming cylinder further. The two are passed through a roller press. There they arrive with a relatively high water content. It goes without saying that the higher the input water content of the felt and paper web, the higher the input water content when it enters the press nip of the press. The presence of water in the felt before the

Wrapping around the forming cylinder is therefore necessary on the one hand for the forming cylinder to work properly, and on the other hand it is disadvantageous when it is a matter of achieving the highest possible dry content of the paper web as it passes through the press nip of a press.

The invention has for its object to design a wire section according to the preamble of claim 1 such that the felt has enough water when it rotates around the forming cylinder on the one hand to be able to cope with the forming work, but on the other hand it has as little water in With a view to the lowest possible

Water content after running out of the subsequent press or presses.

This object is solved by the characterizing features of claim 1. The inventor has taken a path that runs completely counter to the classic view. Instead of exposing the felt on its way of wrapping the forming cylinder to a vacuum, so that water is removed from the felt and introduced into the interior of the forming cylinder and discharged, it is provided that the felt band in the area of the wrapping zone

Exposing the forming cylinder (or at least part of this wrapping area) to overpressure. At the same time, the forming cylinder is perforated. This ensures that the overpressure presses the water contained in the felt to its radially outer surface during wrapping and thus to the interface with the paper web.

This ensures that there is sufficient water in the area of this interface. This also means that the felt as a whole - after leaving the forming cylinder - has a relatively low water content. Relatively little water can thus be removed from the felt by the press or the presses. The

The initial dry content of the felt when it runs out of the press section is therefore relatively high, compared to embodiments according to the prior art. However, the dry content of the paper web also becomes quite high, since the relatively dry felt in the press section can absorb much more water from the paper web than a moist felt according to the prior art.

In addition to the advantages mentioned, which are achieved by the invention, it is quite conceivable that the pressurization according to the invention produces slight movements of the fibers in the nonwoven, and thus that

Fiber orientation perpendicular to the paper surface is affected. The orientation of a single fiber can thus be influenced in the direction from one side of the paper to the other. For example, the softness of a tissue paper can be advantageously influenced in this way. The pressure must not necessarily be applied with air. Other media are also possible, for example steam. When using different temperatures, the viscosity of the water contained in the nonwoven fabric can be changed and thus influence the drainage behavior.

It is also conceivable to use media containing chemicals, for example for felt treatment.

If the pressure zone is divided transversely to the machine direction, you have the option of applying different values to the resulting individual zones. The moisture cross profile of the resulting paper web can thus be controlled or regulated.

The invention is explained in more detail with reference to the drawing.

Figure 1 shows a twin wire former, comprising a forming cylinder 1, a felt belt 2, which wraps around the forming cylinder 1 and thereby lies directly on its outer surface, and with a wire belt 3, which also wraps around the forming cylinder 1, but is located on the outside during the wrapping. Felt belt 2 and wire belt 3 form a wedge-shaped inlet slit 4. This inlet slit 4 receives a machine-wide stream of material which emerges from a headbox. Of this, only its outlet nozzle 5 is shown.

Felt belt 2 and wire belt 3 then run through further forming lines, formed from resiliently mounted strips and rigidly arranged strips. Finally, the paper web 8 now formed (dashed) is removed with the felt belt and passed through a press 11 (FIG. 2) or 11A (FIG. 3) and transferred to a drying cylinder 12. The above

Lasts are not shown. It is crucial that the forming cylinder 1 according to the invention has a pressure zone 1.1, connected, for example, to a compressed air source 10 and preferably delimited by a stationary seal carrier 9. In addition, the jacket of the forming cylinder 1 is provided with a large number of holes 1.4 (FIG. 4). Thus, the above-mentioned overpressure reaches the felt belt 2, the resulting paper web 8 and the wire belt 3. Water contained in the felt belt 2 is thus pressed radially outwards. Part of the water passes through the paper web 8 and together with water from the supplied stream of material through the sieve belt 3 into a collecting box 7 which surrounds the looping zone (FIG. 3).

Further possible variants are shown in FIGS. 2 and 3. In any case, the forming cylinder has, on the one hand, an overpressure zone, specifically in the wrapping area of felt belt 2 and wire belt 3, and the jacket of the forming cylinder is also perforated.

Figure 4 schematically illustrates things in high magnification. The forming cylinder 1 can again be seen, the jacket of which has a multiplicity of bores 1.4. Its interior is under pressure, illustrated by (+). It revolves in the direction of arrow 1.2. The nozzle 5 of a headbox throws a machine-wide jet into the wedge-shaped gap 4, which is formed from felt belt 2 and sieve belt 3. The resulting paper web 8 is thus sandwiched between felt belt 2 and wire belt 3.

Felt tape 2 contains a certain amount of water necessary. Due to the overpressure, this water located in the felt belt 2 is transported radially outwards and thus accumulates on the radially outer surface, and thus on the interface between the felt belt 2 and the resulting paper web 8. Because of the accumulation of the water in the felt belt 2, it is only necessary a relatively small amount of water in the felt belt 2. In other words, the felt tape 2 is relatively dry. Therefore, the initial dry content of the felt belt 2 when leaving a press section - not shown here - is relatively low. For this reason, only a slight rewetting of the paper web 8 takes place, so that the paper web 8 also reaches a relatively high dry content after it has left the press section. Further advantages: The risk of the paper web being twisted in the press section is lower than before; likewise less energy is required for drying (by means of the drying cylinder 12).

The example according to FIG. 4 is less expensive to produce because the stationary seal carrier (9 in FIG. 1) is dispensed with.

In FIG. 2, a seal carrier 9A is provided which delimits two pressure zones (+) which can be acted upon at different heights in the direction of rotation, followed by a zone in which atmospheric pressure or negative pressure (-) can prevail.

Fig. 5 shows a seal carrier 9B (seen in the direction of arrow 5 of Fig. 3), which can form several adjacent pressure zones 13A, 13B and 13C by means of additional sealing washers 13, which can be acted upon with pressures of different heights.

Claims

Expectations

1. wire section for a paper machine 1.1 with a forming cylinder (1);

1.2 with a felt belt (2) and a sieve belt (3), both of which loop around the forming cylinder (1), with the inside felt belt (2) and the outside sieve belt (3), and which have a receiving gap (4) for receiving a machine-wide stream of material or form pre-dewatered paper web;

1.3 the forming cylinder (1) has a rotatably mounted, perforated jacket; characterized by the following features:

1.4 at least part of the wrap zone of the forming cylinder (1) can be pressurized from the inside.

2. Screen section according to claim 1, characterized in that a pressure zone (1.1) is separated from the interior of the forming cylinder (1) by means of a stationary seal carrier (9).

3. Sieve section according to claim 2, characterized in that seen in the direction of rotation, several successive zones with different pressures are present (Fig. 2).

4. Screen section according to claim 1 or 2, characterized in that seen transversely to the web running direction, side by side several zones with different pressures (13A, 13B, 13C) are present (Fig. 4). Screen section according to claim 1, characterized in that the entire interior of the forming cylinder (1) is under positive pressure (Fig. 4).