EP2630293B1 - Sheet-forming unit for producing a material web, and method for operating the sheet-forming unit - Google Patents

Description

The invention relates to a sheet forming unit of a paper machine, in particular a tissue machine, for producing a fibrous web, with a headbox emitting a suspension jet and with a respective inner loop and outer screen forming a loop. Within the loop of the inner wire is a forming element and within the loop of the outer wire are guide rollers and a wire pit for receiving the incurred in the region of the forming element white water, arranged. The inner screen and the outer screen form a gap for receiving the suspension jet and at least partially wrap around the forming element in a looping area.

Furthermore, the invention relates to a method for operating a sheet forming unit.

In generic sheet forming units in the prior art solutions for efficient Siebwasserabführung are known. The document describes this WO 82/02910 Solutions for double-wire sections as well as for double-wire sections with a pre-connected fourdrinier wire section. The white water thrown from the forming cylinder is directed via guide walls into collecting container. The thrown off white water suffers only a small loss of speed, so that only small flow cross sections for the removal of the white water are necessary. Mixing this from hurled white water with other proportions of water is avoided for this reason.

The document WO 00/73581 A1 discloses a crescent former for making a tissue web with a dewatering air press and a Yankee drying cylinder for drying the tissue web. It is provided a headbox for introducing a suspension jet between two fabrics. The fabrics enclose together a breast roll. In the loop of the outer clothing deflecting elements and a white water container for receiving the centrifuged white water are provided in the region of the breast roll.

In the document EP 1424437 A1 is a twin-wire former of a machine for producing a fibrous web, in particular a paper or board web, described. It comprises a continuous endless upper sieve and a circulating endless lower sieve, which converge in the region of a forming element, and at least one white water collecting container. In this case, at least one guide element is provided via the white water obtained in the former to the white water collecting container so that there is an at least substantially smooth white water surface in this. In addition, a guide device is present in the region of a guide element of the outer screen outside the outer screen. The publication EP 1382740 A1 shows a wire section for producing a multi-ply fibrous web, from at least one pulp suspension with a belt on which runs at least a first pulp layer, with a twin-wire section with a forming roller and with a first and a second sieve (upper sieve, lower sieve), the one another in sections Forming a twin-wire zone in which a second fibrous layer is produced, and having a lower vertex-joining section merging the first and second fibrous layers to form a multi-layer fibrous web. The two screens are in the area of the twin-wire zone over a peripheral region of at least one Wrinkle device led. The forming roller is followed by a dewatering section in the form of a D-part.

In the known sheet forming units, increasingly high velocities, in particular in the area of the outer sieves, result in increasingly polluting water mist containing fines. In order to avoid an impairment of the production and the quality of the produced paper web, the water mist is drained via pipes and hoods by an active suction by means of blowers. This solution is expensive in terms of the required devices and energy consumption.

It is therefore an object of the invention to provide a cost effective solution to avoid the disturbing effects of contamination in the sheet forming unit.

The object is solved by the features of claim 1. It is provided a sheet forming unit of a paper machine, in particular a Tissuemaschine, for producing a fibrous web, with a suspension jet emitting headbox and with a respective loop forming inner wire and outer wire, wherein within the loop of the inner wire a forming element and within the loop of the outer wire guide rollers and a Siebwasserkasten for receiving the incurred in the region of the forming element white water, are arranged, wherein the inner wire and the outer wire form a gap for receiving the suspension jet and at least partially wrap around the forming element in a wrap. It is essential to the invention that a machine-wide guide element is arranged in the looping area within the loop of the outer screen such that the white water is formed into a jet and directed into the wire pit such that a contact surface between the jet and the space formed by the loop of the outer screen arises for receiving water mist, wherein between the guide element and the forming element, a gap is formed and the course of the guide element substantially follows the contour of the forming element and so ewähit is that the gap seen in the running direction has a divergent course, and / or that in At least one of the guide rollers of the outer screen at least one machine-wide guide device is provided outside of the space formed by the loop of the outer screen, wherein the guide device (17, 18) in erection forms a convergent gap to Aussensiebs (6).

Advantageous in this solution is the use of the existing kinetic energy of machine components or fluid jets, such as sieves, white water jets, headbox jet in conjunction with the arrangement and geometric design of vanes for removing water mist from the area of the outer wire of a sheet forming apparatus. Thus, both the water mist in the space within the loop of the outer screen and the entrained by the outside of the outer screen water mist can be dissipated. The guide elements are made for example of simple and inexpensive sheets and mounted accordingly. The cost of hoods and blowers is thereby greatly reduced or even avoided.

The outer screen and the inner screen are designed, for example, as Formiersiebe.

In an alternative embodiment, the outer screen is as Formiersieb, preferably with zonal different permeability, and the inner wire out as a felt out. The outer screen may have patterns for forming images and ornaments in the fibrous web.

In an alternative embodiment, the outer sieve is designed as a forming fabric, preferably with zonal different permeability, and the inner sieve as a structured sieve. Structured sieves are known from the production of voluminous tissue papers, for example in so-called through-air tissue machines. In this variant too, the outer sieve can have patterns which are suitable for producing images and ornaments in the fibrous web.

In a practical embodiment, the machine-wide guide element, seen in the beam direction, ends before the wire pit. This creates a sufficiently long jet of white water, which in turn allows a sufficiently long contact surface to the space formed by the loop of Aussensiebes to suck by the Treibstrahleffekt the water mist from this space to absorb and dissipate.

The contact surface is preferably in direct contact with the space formed by the loop of the outer screen.

It is also conceivable that the guide element protrudes into the wire pit only so far that the required contact surface for sucking the water mist is ensured from the space formed by the loop of the outer screen. The length of the wire pit, seen transversely to the machine width, only so long that the water mist are sucked out of the space formed by the loop of the outer screen.

The length of the opening of the wire pit is in a practical case less than 1m, preferably less than 0.6m. This avoids that the water mist absorbed by the white water jet due to vortex formation can partially return back into the space formed by the loop of the outer screen.

Advantageously, the length of the contact surface, seen in the running direction or in the flow direction of the beam, more than 100mm, preferably more than 150mm, in particular more than 200mm.

It is advantageous if the guide element is designed so that the formed white water jet is not deflected substantially.

The forming element preferably has an open surface to promote dewatering of the fibrous web.

In some cases, the forming element may be evacuated.

In a practical embodiment, the forming element is formed by a roller.

Between the guide element and the forming element, a gap is formed. The screen water leaving the outer sieve collects in the intermediate space and flows along the guide element in the direction of the white water box.

In the embodiment, the course of the guide element is chosen so that the intermediate space, seen in the running direction of the outer screen, has a divergent course. As a result, a reflection of the white water is avoided on the outer wire of increasing in the direction of the sieves Siebwassermenge and thus prevents interference with the quality of the fibrous web.

In an expedient embodiment, the course of the guide element is chosen so that the initial distance to the forming element at the beginning of the gap between 10mm and 60 mm, preferably between 20 and 40mm. As a result, a good collection effect is achieved with respect to the emerging white water.
The divergence of the gap extends from the initial distance to a distance of greater than 30mm, preferably greater than 40mm, in particular greater than 50mm after a distance corresponding to an angle of about 90 ° of the wrap.

The beginning of the guide element is arranged so that the passing through the outer wire white water of the headbox jet is received. Preferably the beginning of the guide element is arranged substantially on the imaginary extension of the headbox jet.

In a further embodiment of the invention, the Siebwasserkasten on deflection devices for the lateral deflection of the supplied white water and entrained water mist on. The lateral deflection takes place transversely to the direction of the paper machine, preferably to the drive side. The deflection devices consist of bent or preferably bevelled sheets.

In a practical embodiment, in each case two adjacent deflecting devices form a channel, that is to say a flow channel for the white water, wherein the spacing of the deflecting devices is so small that the flow vortex extending into the space formed by the loop of the outer sieve is avoided.

Furthermore, the deflection devices have surfaces which are inclined relative to one another by a deflection angle, the deflection angle in the flow direction between adjacent surfaces being less than 20 °. This avoids vortexes and backflows.

In the embodiment, the at least one arranged in the region of the guide rollers of the outer screen outside the space formed by the loop of the outer sieve guide in the running direction forms a convergent gap with the outer screen. As a result, the boundary layer of water mist entrained by the outer screen is captured in the region of the curvature of the outer screen and returned to the outer screen in the form of a water layer, and then removed in a controlled manner, for example via the headbox jet.

It is advantageous if the gap has an initial height of less than 150 mm, preferably less than 100mm, in particular less than 80 mm and a final height of less than 50 mm, preferably less than 30 mm, in particular less than 10mm.

Conveniently, the guide head adjacent to the headbox is associated with a guide device such that the space formed by the guide device and by the outer wire can be sucked by the driving jet effect of the suspension jet. As a result, the accumulating in this room water mist is discharged through the headbox jet in the white water box.

The invention is particularly advantageous to apply at screen speeds of more than 1400m / min, preferably more than 1500m / min, especially at more than 1600m / min.

Another aspect of the invention for achieving the object relates to a method for operating a sheet forming unit of a paper machine according to claim 9. Further features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the drawings.

Figur 1

eine schematische Darstellung einer erfindungsgemäßen Ausführungsform einer Blattbildungseinrichtung im Längsschnitt;

Figur 2

eine schematische Darstellung des Siebwasserkastens aus Figur 1 im Querschnitt

It shows

FIG. 1

a schematic representation of an embodiment of a sheet forming device according to the invention in longitudinal section;

FIG. 2

a schematic representation of the white water box FIG. 1 in cross section

In FIG. 1 is a schematic representation of an embodiment of a sheet forming device 1 of a tissue machine according to the invention shown in longitudinal section. The inner wire 5 wraps around the forming element 7, which is formed by a forming roller, and carries the formed fibrous web 2 to a transfer point for transferring the fibrous web 2 to a subsequent clothing or directly to the next, not shown, process section. This may alternatively or in combination comprise a stand-alone press, a press formed from a press roll and a drying cylinder, a drying, creping and winding device. The outer wire 6 wraps together with the inner wire 5, the forming roller 7 on a wrap 14. This is preferably more than 90 °. The inner wire 5 and the outer wire 6 form an inlet gap for receiving the suspension jet 4 delivered by a headbox 3. The suspension is dewatered in the region of the forming roller 7 and the fibrous web 2 is formed. The drainage takes place mainly through the outer sieve 6. The screened water 13 tangentially emerging through the outer screen 6 is collected by the guide element 15 and deflected so that a white water jet 13 is formed. The beginning of the guide element 15 is located in the region of an imaginary extension of the headbox jet 4, so that the entrained by the outer sieve 6 white water 13 is collected.

The starting distance of the guide element 15 to the inside of the outer screen 6 is 30 mm at the beginning of the guide element 15 in this example. In the further course of the guide element, the distance, after a distance which corresponds approximately to an angle of 90 ° of the wrap, increases to 45 mm, so that there is a divergent gap. Thereafter, the curvature of the guide element decreases, whereby the divergence increases further. As seen in the direction of flow of the white water, a screen water box 12 is arranged downstream of the guide element 15, into which the white water jet 13 discharges. It is essential that the guide element is not immersed too deep in the white water box 12, but that a free jet length of the white water jet 13 is ensured to produce a sufficient contact surface at least one side of the white water jet 13 to the space formed by the loop of the outer screen 16. The contact area in this example is more than 150mm. This contact surface generates a suction effect according to the propellant jet principle, whereby the water mist is removed in the space 16 and discharged together with the white water 13 via the white water box 12. As a result, complex pipelines, hoods and blowers for water mist extraction can be omitted in comparison to the prior art. The cross section of the white water tank for receiving the white water 13 is dimensioned so that no vortex formation is possible. The length of the opening of the white water box 12 is in this practical case, preferably less than 0.6m. This avoids that the water mist absorbed by the white water jet due to vortex formation can partially return back into the space formed by the loop of the outer screen. The recorded white water 13 with water mist is deflected within the white water box 12 to the side, preferably to the drive side, and dissipated. The deflection takes place by deflecting devices 24, which are installed in the wire pit 12. Adjacent deflection devices 24 each form a flow channel. After the forming element 7, the outer wire 6 is separated from the inner wire 5, wherein the formed fibrous web 2 is led away together with the inner wire 5. The Outer sieve 6 is returned via guide rollers 8, 9, 10, 11 back to forming element 7. Below and the side facing away from the forming element of the loop of the outer sieve 6, a white water boat 23 is provided for receiving Siebwassers and water mist entrained by the outer sieve 6 in the fabric and on its surface. The white water ship 23 surrounds the lower part of the loop of the outer sieve 6, whereby this part is encapsulated. The dragged on the Sieboberfläche with liquid is stripped by curved guide devices 19, 20, 21, 22 wirbelarm, deflected and fed to the white water ship 23. In the region of the guide rollers 10, 11 guide devices 17, 18 are arranged outside of the space formed by the loop of the outer screen 6. As a result, the boundary layer of water mist entrained by the outer screen 6 is caught in the region of the curvature of the outer screen 6 and returned to the outer screen 6 in the form of a water layer and then controlled, for example via the headbox jet 4, dissipated. The gap has an initial height of less than 100mm and a final height of less than 30mm. The gap in front of the head box 3 is sucked through the headbox jet 4 by the propulsion jet principle and thus the water mist entrained by the outer sieve 6 is removed via the forming area into the white water box 12. The forming roller 7 has a closed jacket. The drainage is thus carried out exclusively by the outer sieve.

The FIG. 2 shows a schematic representation of the white water box 12 FIG. 1 in cross section. The white water box 12 is machine-wide executed. The white water jet 13 flows from above into the opening of the white water box 12. In this deflection devices 24 are provided, wherein two adjacent deflection devices 24 form a channel, that is a flow channel for the white water 13, wherein the distance of Umlenkvor-directions 24th is so small that the training of in the space formed by the loop of Aussensiebes inside extending flow vortex is avoided. Furthermore, the deflecting devices 24 have surfaces which are inclined relative to one another by a deflection angle, the deflection angle in the flow direction between adjacent surfaces being less than 20 °. This avoids vortexes and backflows. The screen water is returned to the drive side of the paper machine via the lateral white water removal 25 in the manufacturing process. The lateral sieve-water discharge 25 can be directly drained via a vacuum device or via a downpipe. This allows the discharge capacity to be adapted to the amount of white water.

LIST OF REFERENCE NUMBERS

1

Sheet forming unit

2

Fibrous web

3

headbox

4

suspension jet

5

inside screen

6

outer wire

7

forming element

8th

guide roll

9

guide roll

10

guide roll

11

guide roll

12

wire pit

13

White water, white water jet

14

wrap region

15

vane

16

Space outdoor sieve

17

guide

18

guide

19

guide

20

guide

21

guide

22

guide

23

Siebwasserschiff

24

Baffles

25

lateral white water drainage

26

water spray

Claims (9)

1. Sheet-forming unit (1) of a paper machine, in particular a tissue machine, for producing a fibrous web (2), comprising a headbox (3) discharging a suspension jet (4) and comprising an inner fabric (5) and outer fabric (6) each forming a loop, a forming element (7) being arranged within the loop of the inner fabric (5), and guide rolls (8, 9, 10, 11) and a white-water box (12) for receiving the white water accumulating in the region of the forming element (7) being arranged within the loop of the outer fabric (6), the inner fabric (5) and the outer fabric (6) forming a gap for receiving the suspension jet (4) and jointly wrapping at least partly around the forming element (7) in a wrap region (14),
   characterized in that
   a machine-width guide element is arranged within the loop of the outer fabric (6) in the wrap region (14) and ends before the white-water box or projects only to such an extent into the white-water box and is arranged in such a way that the white water (13) is formed into a jet and is deflected into the white-water box (12) in such a way that a contact area is produced between the jet and the space (16) formed by the loop of the outer fabric (6) to receive water mist, an interspace being formed between the guide element (15) and the forming element (7), and the course of the guide element (15) substantially following the contour of the forming element (7) and being chosen such that, viewed in the running direction, the interspace has a divergent course, and/or in that, in the region of at least one of the guide rolls (8, 9, 10, 11) of the outer fabric (6), a machine-width guide device (17, 18) is provided outside the space (16) formed by the loop of the outer fabric (6), the guide device (17, 18) forming a convergent gap with respect to the outer fabric (6) in the running direction.
2. Sheet-forming unit (1) according to Claim 1,
   characterized in that
   the forming element (7) is formed by a roll.
3. Sheet-forming unit (1) according to Claim 1,
   characterized in that
   the course of the guide element (15) is chosen such that the distance from the forming element at the start of the interspace is between 10 mm and 60 mm, preferably between 20 and 40 mm.
4. Sheet-forming unit (1) according to one of the preceding claims,
   characterized in that
   the white-water box (12) has deflection devices (24) for the lateral deflection of the white water (13) fed in and the entrained water mist (26).
5. Sheet-forming unit (1) according to Claim 4,
   characterized in that
   in each case two adjacent deflection devices (24) form a channel, the distance of the deflection devices (24) being dimensioned to be so small that the formation of flow vortices extending into the space (16) formed by the loop of the outer fabric (6) is avoided.
6. Sheet-forming unit (1) according to Claim 4 or 5,
   characterized in that
   the deflection devices (24) have surfaces inclined at a deflection angle relative to each other, the deflection angle between adjacent surfaces in the flow direction being less than 20°.
7. Sheet-forming unit (1) according to Claim 1,
   characterized in that
   the gap has an initial height of less than 150 mm, preferably less than 100 mm, in particular of less than 80 mm, and a final height of less than 50 mm, preferably less than 30 mm, in particular less than 10 mm.
8. Sheet-forming unit (1) according to Claim 1 or 7,
   characterized in that
   the guide roll (11) adjacent to the headbox (3) is assigned a guide device (18) in such a way that the space formed by the guide device (18) and by the outer fabric (6) can be evacuated by the propulsion jet effect of the suspension jet (4).
9. Method for operating a sheet-forming unit (1) according to Claim 1, comprising a headbox (3) discharging a suspension jet (4) and comprising an inner fabric (5) and outer fabric (6) each forming a loop, a forming element (7) being arranged within the loop of the inner fabric (5), and guide rolls (8, 9, 10, 11) and a white-water box (12) for receiving the white water accumulating in the region of the forming element (7) being arranged within the loop of the outer fabric (6), the inner fabric (5) and the outer fabric (6) forming a gap for receiving the suspension jet (4) and jointly wrapping at least partly around the forming element (7) in a wrap region (14),
   characterized in that
   a machine-width guide element (15) is arranged within the loop of the outer fabric (6) in the wrap region (14) and ends before the white-water box (12) or projects only to such an extent into the white-water box (12) and is arranged in such a way that the white water (13) is formed into a jet and is deflected into the white-water box (12) in such a way that a contact area is produced between the jet and the space (16) formed by the loop of the outer fabric (6) to receive water mist, an interspace being formed between the guide element (15) and the forming element (7), and the course of the guide element (15) substantially following the contour of the forming element (7) and being chosen such that, viewed in the running direction, the interspace has a divergent course, and/or in that, in the region of at least one of the guide rolls (8, 9, 10, 11) of the outer fabric (6), a machine-width guide device (17, 18) is provided outside the space (16) formed by the loop of the outer fabric (6), the guide device (17, 18) forming a convergent gap with respect to the outer fabric (6) in the running direction, so that the kinetic energy of the suspension jet (4) and/or of the white-water thrown off and/or of the outer fabric (6) is used for the controlled extraction of water mist.

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