EP0967323B1 - Twin-wire former - Google Patents

Abstract

The double-fourdrinier section of a papermaking machine, has a lateral support bar (9) which applies an underpressure to the outer fourdrinier (11). The support bar (9) has a sliding surface (9a) in contact with the outer fourdrinier (11), followed by a foil surface (9b) in the direction of fourdrinier travel, which diverges from the fourdrinier surface to create an underpressure. The sliding surface (9a) is pressed against the outer fourdrinier (11) with a pliable pressure. As seen in cross section through the bar (9), the downstream section is supported by a swivel (7), while the upstream zone is held by a pliable setting unit such as a pneumatic hose (6). The gap can be varied between the swivel (7) and the outer fourdrinier (11), and the angle between the foil surface (9b) and the outer fourdrinier (11) can be set to give the required level of underpressure. The position of the support system can be varied parallel to the direction of fourdrinier travel, as a support shoe or suction box and the like which is pressed pliably against the outer fourdrinier. The support unit (9) is in the loop of the lower fourdrinier (11) and the roller (14) to form the wet pulp web within the loop of the upper fourdrinier (12). The two fourdriniers (11,12) can run upwards, from below, between the web forming roller (14) and the support (9), or downwards from above.

Description

The invention relates to a twin wire former for forming a fibrous web according to the preamble of claim 1.

The invention is based on the subject of German published patent application DE 196 52 485 A1. Accordingly, a twin wire former has two endless, rotating wire belts which together form a twin wire zone. In the area of this twin-wire zone, the fibrous web forms between the two wire belts. Within the twin-wire zone or at the beginning thereof, the two wire belts run together over a forming roller, one wire belt, namely the “inner” wire belt, coming into direct contact with the forming roller. At the discharge point of the two wire belts from the forming roller, the other wire belt, namely the "outer" wire belt, comes into contact with at least one support device extending transversely over the wire belt, here with a bar. In special cases, this bar can be rigidly fixed in the machine frame. However, it can preferably be resiliently pressed onto the outer sieve belt (for example by means of a pneumatic hose). In all cases, a temporary divergence of the two sieve belts (sieve separation) should be prevented by means of the bar at the drain point mentioned. Such a divergence of the two sieve belts can occasionally be observed, although the sieve belts are stretched in the running direction. The result is that proper formation of the fibrous web is disturbed. The resilient pressing of the bar provides the advantage that the position of the bar automatically adapts to the current layer thickness of the fiber suspension located between the two sieve belts. In a similar form, this is also disclosed in WO 95/34713.
However, the prior art arrangements described above have not yet proven to be sufficiently effective. Occasionally one still observes disturbances of an orderly path formation.

This manifests itself e.g. B. that the desired uniform in the finished paper web Fiber distribution is disturbed. So it can e.g. B. to an uneven basis weight cross section coming, or making the paper web (when looking at one Light source) a cloudy impression, the cloudiness sometimes strong and / or in other words, the quality of the "formation" is not satisfactory.

The invention is therefore based on the object of a twin wire former described design to improve that the disturbances mentioned be avoided in the quality of the finished paper.

This object is essentially according to the characterizing part of claim 1 solved by that the support device is a bar, the one the sliding surface touching the outer sieve belt and a sliding surface in thereon Screen direction seen-adjoining foil surface, for the purpose of generating Vacuum diverges from the outer screen belt.

It can now be expected that the previously mentioned negative pressure zone will be in the sense of a Increases the quality of the finished paper web. I.e. one can disturbances in the Avoid basis weight cross section at least to a large extent; the same applies to them cloudiness observed so far; in other words, the latter means: you get one significantly improved quality of the "formation".

Presumably, the effect of the inventive design of the negative pressure zone is based on the fact that a similar negative pressure develops in the gusset, which always is present between the running inner screen belt and the jacket of the Forming roll.

Because presumably this is the result (under the so-called register roller effect) Negative pressure - if atmospheric pressure on the side of the outer screen belt there is - the cause of the mentioned disorders.

According to the invention, that now acts by means of a foil strip generated negative pressure on the forming roller itself counteracting negative pressure, so that the negative effect of the latter is canceled or at least reduced.

According to claim 2, the sliding surface of the foil strip touching the outer screen belt, as known per se, resiliently pressed onto the outer screen belt. Thereby the advantage remains that the Foilleiste automatically at different suspension heights adapts. For this purpose, one is preferably (according to claim 3) the foil strip (seen in a cross section through the foil strip) in its downstream Area by means of a joint on a fixed or on an adjustable Support component and in its upstream area by means of a flexible Press the adjusting device (e.g. pneumatic hose) onto the outer sieve belt.

Die Figur 1 zeigt den an der Formierwalze liegenden Bereich eines Doppelsiebformers in einer schematischen Seitenansicht.

Die Figur 2 zeigt eine Variant zur Figur 1.

Jede der Figuren 3 - 6 zeigt eine erfindungsgemäße Anordnung in Doppelsiebformern unterschiedlicher Bauart.

Embodiments of the invention are described below with reference to the drawing.

FIG. 1 shows the area of a twin wire former lying on the forming roll in a schematic side view.

FIG. 2 shows a variant of FIG. 1.

Each of Figures 3 - 6 shows an arrangement according to the invention in twin wire formers of different designs.

In Figure 1 a breast roller 13 and a forming roller can be seen from a twin wire former 14 and two screen belts 11 and 12, which - starting on the forming roller 14 - form a twin wire zone with each other.

The one screen belt 12 is the so-called inner screen belt, which is in direct contact comes with the forming roller 14. The other sieve belt 11 is the so-called outer one screen belt; it comes into direct contact with the breast roller 13 and runs from it to the forming roller 14.

A headbox 10 guides a fiber suspension jet into the (from the two sieve belts 11 and 12 formed) inlet gusset. Loop around the two sieve belts 11 and 12 now together a relatively small area of the jacket of the forming roller 14; A suction zone 14a can be located in this area.

A large part of the supplied suspension water flows through the mesh of the outer sieve belt 11, a smaller part in the interior of the forming roller 14. This the fibrous web begins to form between the two sieve belts. On the discharge point of the two fabric belts 11 and 12 from the forming roller 14 that comes outer screen belt in contact with a support device 9, which is shown in Figure 1 as a so-called Foil bar is formed. This has an outer screen belt 12 touching Slide surface 9a and a foil surface 9b adjoining it in the direction of wire travel. The the latter diverges at a small angle of, for example, 1 to 5 ° from the outside Sieve belt 12. This results from the movement of the sieve belts between the Foil area 9b and the outer screen belt 11 a negative pressure zone.

The foil bar 9 is part of a drainage box 8, for example Guide the sieve belts has further strips 8a. To support the foil bar on the drainage box 8, a bearing block 7a, the downstream Supported area of the foil bar 9 by means of a joint 7. The upstream area the foil strip 9 with the sliding surface 9a, however, is by means of a pneumatic hose 6 (with finely adjustable power) resiliently pressed onto the outer sieve belt 11.

In Figure 1, the sliding surface 9a of the foil bar 9 is in the immediate vicinity of the drain point of the two screen belts 11 and 12 from the forming roller 14.

However, it can also be expedient, according to FIG. 2, that the outer sieve belt 11 Contacting sliding surface 9a by a small amount x downstream from (ie behind) the Arrange drain point A. An arrangement of the sliding surface 9a in front of the drain point A is also possible. By moving the drainage box 8 along the double arrow P any intermediate position can be brought about. So you can the position (and the beginning) of the negative pressure zone (between foil strip 9 and sieve belt 11) set as desired.

In this way it is possible to create the gusset F (between the forming roller 14 and the wire belt 12 Counteract negative pressure in an optimal way, so that the emergence of Fibrous web between the two screens 11 and 12 is no longer disturbed. Figure 3 shows a schematic Side view of a complete twin wire former, again with a headbox 10, two endless sieve belts 11 and 12, breast roll 13 and forming roll 14, from the two sieve belts to a small sector a (with an angle between 10 and 40 °) is entwined. The two fabric belts run from the forming roller 14 (together with the fibrous web that forms in between) via a first Suction roller 18 and then a second suction roller 19. Here the inner part separates Screen belt 12 from the fibrous web and runs back over guide rolls 22 to the forming roll 14. The outer screen belt 11 continues the fibrous web until the fibrous web removed from the sieve belt by means of a take-off felt 23 and a take-off roller 24 becomes. The outer screen belt 11 runs over guide rollers 21 back to the breast roller 13. In the loop of the (lower) outer sieve belt 11 there is one pivotable support device 15 '. On this is a trained in detail according to Figure 1 Foilleiste 9 arranged, also two compliant to the Umschlingunszone the forming roller 14 pressable formation strips 15. The arrangement is made such that the outer sieve belt 11 is a lower sieve and that the inner sieve belt 12th is a top sieve. Thus, the foil bar 9 is from bottom to top in the direction of the forming roller 14 pressed against the lower sieve 11.

In the construction shown in FIG. 4, the two sieve belts run from the forming roller 14, obliquely upwards. Immediately at the outlet of the two Screening belts from the forming roll, the outer screen belt 11 in turn comes with a Foil strip 9 in contact, which (as described above) with the outer sieve belt 11 Vacuum zone forms.

3, the outer sieve belt 11 is a top sieve and the inner sieve belt 12 a bottom sieve, so that the foil strip 9 from top to bottom to the top sieve 11 is pressed. The foil strip 9 is in turn fixed by means of a joint 7 Component supported, which in the present case as an upper drainage box 38 is formed. This is bulged down slightly (with one large radius of curvature R). Located on the bottom of the drainage box 38 a series of strips 28 which are fixedly connected to the box 38 and over which the outer screen belt 11 slides. To discharge the urgent Suspension water 38 vacuum chambers 32 are formed in the box. Within the loop of the inner screen belt 12 is a lower drainage box 37 provided. This carries several so-called formation strips 27, which are from below are resiliently pressed onto the inner sieve belt 12, preferably by means of individually controllable pneumatic hoses. In the further course of the twin-wire zone is a suction pad 33 is arranged; on this separates the outer screen belt 11 from the inner screen belt 12, which transports the fibrous web formed, first via a screen suction roll 30. Deviating from this, the outer Only separate the sieve belt 11 from the inner sieve belt at the circumference of the sieve suction roll, as indicated in FIG. 4 with dash-dotted lines. In another variant too Figure 4 can the two sieve belts, starting from the breast roll 13 and Forming roller 14, substantially vertically from bottom to top through the twin wire zone to run.

FIG. 5 shows a more compact design compared to FIG. 4, in which the separating suction device 33 does not apply. The drain box 38 'has an additional vacuum chamber 32 '; the screen suction roller 30 is arranged immediately behind this.

The twin wire former shown in FIG. 6 again comprises two wire belts 11 and 12. In the arrangement shown, the inner sieve belt 12 forms a lower sieve and the outer sieve belt 11 is a top sieve. Before the top wire 11 on the circumference of the forming roller 14 comes into contact with the lower sieve 12, it runs over a breast roller 13. Between the two rollers 13 and 14, the two screen belts 11 and 12 form together a wedge-shaped inlet gap, which is directly from a headbox 10 Fibrous suspension absorbs.

The headbox is only indicated schematically. It is preferably a Headbox, which in a known manner with a sectionally controllable dilution water addition is equipped for the purpose of setting a desired basis weight cross section the finished paper web.

The twin-wire former has within the loop of the upper wire 11 in the area of Forming roller 14, a water collecting device 36. It first arrives there large part of the suspension water, which at the beginning of the twin sieve zone Upper sieve 11 penetrates. This is done essentially in the upper descending quadrant the forming roll 14. Approximately at the level of the film roll axis of rotation the two sieves 11 and 12 run with the fibrous web formed between them down from the forming roller. They then run over one in the loop of the Upper sieve 12 arranged, and formed from strips 8a convex curved forming shoe. Further suspension water penetrates into the collecting trough between the strips 8a 36. Another part of the suspension water flows through the lower sieve 11 in a drip pan 40. Here, molding strips can be provided, which are known in the art Can be resiliently pressed onto the lower sieve 12 (not shown in FIG. 6). Instead of these forming strips, the bottom wire 12 can be in the area of the strips 8a at least one deflector can be assigned.

The jacket of the forming roller 14 has recesses for temporary use in a known manner Storing water, e.g. in the form of a honeycomb cover and one on it attached sieve stocking.

In addition, if necessary, the forming roller 14 can be designed as a suction roller, with vacuum source 29. Also arranged in the loop of the top wire 11 Water collecting device 36 can be connected to a vacuum source 29 'if necessary his. According to the invention at the outlet of the sieve belts 11, 12 of the forming roll 14 arranged a vacuum bar 9, with the help of of the features described in FIG. 1.

It is also essential in the embodiment according to FIG. 6 that in the twin-wire zone the two screens 11 and 12, starting directly from the forming roller 14, run down steeply.

In this area, the twin-wire zone forms one with an imaginary vertical plane Angle a, which is between 10 and 50 degrees, in this section the top sieve 11 is always located above the lower sieve 12. The angle a is preferably less than 45 degrees. In the steeply descending section of the twin-wire zone further drainage elements can be provided, e.g. the lower sieve 12 touching suction boxes 47.

At the end of the steeply descending section of the twin-wire zone is one Deflection roller 42 is provided, which essentially transforms the two screen belts 11, 12 into one horizontal direction deflected. Here is in the loop of the bottom wire 12 Separating suction device 33 is provided, on which the upper sieve 11 is separated from the lower sieve 12 and the paper web on it lifts off. The top wire 11 runs from here over guide rollers 46 back to the breast roll 13. The bottom wire 12 runs after the separating suction device 33 - If necessary via at least one further suction box 37 '- to a screen suction roll 30, then via guide rollers 41 back to the forming roller 14. Immediately behind the screen suction roller 30 is the paper web formed in a known manner by means of a Felt 23 and a take-off roller 24 removed from the lower wire 11.

The foil strip 9 according to the invention in connection with steep sieve belts running below (similar to FIG. 6) can also be used in a twin-wire former according to the German published application DE / A1 19651493; this is for education a multilayer paper web arranged on a long screen.

Claims (9)

1. Twin-wire former for forming a fibrous web, for example a paper web, from a fibrous suspension, in particular as part of a papermaking machine, having the following features:

   a) two endless, circulating mesh belts (11, 12) form with each other a twin-wire zone, in which the fibrous web is formed between the two mesh belts (11, 12);

   b) in the twin-wire zone, the two mesh belts (11, 12) run jointly over a forming roll (14), one mesh belt, namely the "inner" mesh belt (12), coming into direct contact with the forming roll (14);

   c) in the area of the point at which the two mesh belts (11, 12) run off the forming roll (14), the other mesh belt, namely the "outer" mesh belt (11), comes into contact with at least one supporting device (9) which extends transversely over the mesh belt, the supporting device (9) exerting a negative pressure on the outer mesh belt (11);

   characterized in that the supporting device is a bar (9), which has a sliding face (9a) that contacts the outer mesh belt (11) and a foil face (9b) which follows said sliding face (9a) - as viewed in the wire running direction - and diverges from the outer mesh belt (11) for the purpose of generating a negative pressure.
2. Twin-wire former according to Claim 1, characterized in that the bar (9) can be pressed compliantly with its sliding face (9a) against the outer mesh belt (11).
3. Twin-wire former according to Claim 2, characterized in that - as viewed in a cross section through the bar (9) - the downstream area of the bar (9) is supported by means of a joint (7), but the upstream area of the bar (9), on the other hand, is supported by means of a compliant actuating device, for example by means of a pneumatic hose (6).
4. Twin-wire former according to Claim 3, characterized in that the distance between the joint (7) and the outer mesh belt (11) can be varied in order to be able to adapt the angle of inclination between the foil face (9b) and the outer mesh belt (11) and therefore the level of the negative pressure which is produced.
5. Twin-wire former according to one of Claims 1 to 4, characterized in that the position of the supporting device (9) can be varied substantially parallel to the wire running direction (arrow P).
6. Twin-wire former according to one of Claims 1 to 5, characterized in that the supporting device (9) is arranged in the loop of a lower wire (11) and the forming roll (14) is arranged in the loop of an upper wire (12).
7. Twin-wire former according to one of Claims 1 to 5, characterized in that the supporting device (9) is arranged in the loop of an upper wire (12) and the forming roll (14) is arranged in the loop of a lower wire (11).
8. Twin-wire former according to Claim 7, characterized in that the wires (11, 12) run from bottom to top between the forming roll (14) and supporting device (9).
9. Twin-wire former according to Claim 7, characterized in that the wires (11, 12) run from top to bottom between the forming roll (14) and supporting device (9).

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