EP0967323A2 - 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, for. B. Paper web, from a fiber suspension, in particular as part of a paper manufacturing machine.

The invention is based on the subject of the unpublished patent application 196 52 485.7 of December 17, 1996 (PA 10459). 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 is formed 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 comes into contact with the "outer" wire belt, in contact with at least one support device extending across 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 gives the advantage that the position of the bar automatically adapts to the instantaneous layer thickness of the fiber suspension located between the two sieve belts. In a similar form, this is also disclosed in WO 95/34713 (FR 20365).
However, the prior art arrangements described above have not yet been shown to be sufficiently effective. Occasionally, disturbances of an orderly path formation are still observed.

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 come, or makes 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 in that in the area of the discharge point of the fabric belts from the forming roller a vacuum zone is formed on the side of the outer screen belt, e.g. using a so-called foil bar. Such a foil bar, known from itself DE 91 05 328 = US 5262009 (PA 04835), has a sliding surface touching the screen belt and a subsequent so-called foil surface, which against the Sieve running direction is inclined, where it diverges from the wire belt in the wire running direction. Thereby is in the opening gusset between the outer screen belt and the Foil area created by the movement of the screen belt a vacuum zone.

It is now to be expected that the previously mentioned negative pressure zone is in the sense of a Increases the quality of the finished paper web. That is, one can see 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 roller.

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

According to the invention, it now acts by means of a foil strip or by means of a suction shoe, Suction box or the like generated vacuum 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 3, 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 adjusts. For this purpose, one is preferably (according to claim 4) 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.

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

Die Figuren 2 und 3 zeigen Varianten zur Figur 1.

Jede der Figuren 4 - 7 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.

FIGS. 2 and 3 show variants of FIG. 1.

Each of FIGS. 4-7 shows an arrangement according to the invention in twin wire formers of different designs.

A breast roll 13 and a forming roll can be seen in a twin wire former in FIG 14 and two screen belts 11 and 12, which - starting at 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 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 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 sieve belt in contact with a support device 9, which is shown in FIG. 1 as a so-called Foil bar is formed. This has an outer screen belt 12 touching Sliding surface 9a and a foil surface 9b adjoining it in the direction of wire travel. The the latter diverges from the outside at a small angle of, for example, 1 to 5 ° 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 strip 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 screen 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 before 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 start) of the negative pressure zone (between foil strip 9 and sieve 11) set as desired.

This enables the resultant in the gusset F (between the forming roller 14 and the screen 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. According to Figure 3 is at the outlet of the two wire belts 11 and 12 from the forming roller 14 a suction zone is formed by means of a suction shoe 9 ', which in turn is on a joint 7 rests and with the help of a pneumatic hose 6 to the outer sieve belt 11 is resiliently pressable. The interior of the suction shoe open to the filter belt 11 9 'is connected to a vacuum source 29. Figure 4 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 screen belt by means of a take-off felt 23 and a take-off roller 24 becomes. The outer screen belt 11 runs back over guide rollers 21 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 bars 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. 5, 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.

4, the outer sieve belt 11 is a top sieve and the inner sieve belt 12 a lower sieve, so that the foil strip 9 from the top down to the upper 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 weakly bulged downwards (with a 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 separating suction device 33 arranged; at this the outer sieve belt 11 separates 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. 5 with dash-dotted lines. In another variant too Figure 5 can the two sieve belts, starting from the breast roll 13 and the Forming roller 14, substantially vertically from bottom to top through the twin wire zone to run.

FIG. 6 shows a more compact design compared to FIG. 5, 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. 7 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 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 forming 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 last 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 pressed resiliently onto the lower sieve 12 (not shown in FIG. 7). 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 collection device 36 can be connected to a vacuum source 29 'if necessary be. 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. 7 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 wire 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 redirects horizontal running direction. 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 foam strip 9 (or suction shoe 9 ') according to the invention in connection with steep sieve belts running below (similar to FIG. 7) can also be used in a twin-wire former according to patent application 19651493.2 (PA 10449); this is for education a multilayer paper web arranged on a fourdrinier wire.

Claims (12)

Twin wire former for forming a fibrous web, e.g. B. paper web, from a fiber suspension, in particular as part of a paper making machine, with the following features: a) Two endless, rotating sieve belts (11, 12) together form a twin-wire zone in which the fibrous web is formed between the two sieve belts; b) In the twin-wire zone, the two wire belts (11, 12) run together over a forming roller (14), the one wire belt (the "inner" wire belt 12) coming into direct contact with the forming roller; c) In the area of the discharge point of the two sieve belts (11, 12) from the forming roller (14), the other sieve belt (namely the "outer" sieve belt 11) comes into contact with at least one support device extending transversely across the sieve belt (eg bar 9) ; d) characterized in that the support device (9) exerts negative pressure on the outer screen belt (11). Twin-wire former according to claim 1, characterized in that the Support device is a bar (9), which touches the outer sieve belt Slide surface (9a) and a foil surface adjoining it (in the direction of wire travel) (9b) which, in order to generate negative pressure from the outer screen belt (11) diverges. Twin-wire former according to claim 2, characterized in that said Bar (9) on its sliding surface (9a) resiliently to the outer sieve belt (11) is pressable. Twin-wire former according to claim 3, characterized in that - in one Cross section seen through the bar (9) - the downstream area of the bar is supported by means of a joint (7), the upstream region against it by means of a resilient adjusting device, e.g. B. by means of a pneumatic hose (6). Twin-wire former according to claim 4, characterized in that the distance of the mentioned joint (7) from the outer sieve belt (11) is variable to the Tilt angle between the foil surface and the outer sieve belt (and thus the Height of the resulting negative pressure). Twin-wire former according to one of claims 1 to 5, characterized in that the position of the support device (a) substantially parallel to the direction of wire travel (Arrow P) is variable. Twin-wire former according to claim 1, characterized in that the Support device is designed as a suction shoe (9 '), suction box or the like. Twin-wire former according to claim 7, characterized in that the suction shoe, Suction box or the like. Is resiliently pressed onto the outer support band. Twin-wire former according to one of claims 1 to 8, characterized in that the support device (9) in the loop of a lower sieve (11) and Forming roller (14) are arranged in the loop of a top wire (12) (Fig. 4). Twin-wire former according to one of claims 1 to 8, characterized in that the support device (9) in the loop of a top wire (11) and the forming roller (14) are arranged in the loop of a lower sieve (12) (Fig. 5, 6). Twin-wire former according to claim 10, characterized in that the screens (11, 12) between the forming roller (14) and the support device (9) from bottom to top run (Fig. 5 or 6). Twin-wire former according to claim 10, characterized in that the screens (11, 12) between the forming roller (14) and the support device (9) from top to bottom run (Fig. 7).

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