EP1586702B1 - Twin-wire former for a machine for manufacturing a fibrous web - Google Patents

Abstract

A papermaking assembly has a blade gap former with two endless sieve belts (3, 4) which are both deflected by the circumference (5, 6) of a breast roller (7.1, 8.1). The sieves then form a wedge-like inlet gap (10) into which a fibrous suspension (13) is discharged as a jet (12). The jet impinges (14(3, 14(4) at a number of points on the two sieves (3, 4). The sieves subsequently form a sandwich either side of the fibres and feed through a sequence of forming and dewatering stations. The impingement station (9) is a shoe (9.1) with a coating (28) with a series of strips (29.1-29.6) in-line with the direction of sieve travel (S). The gaps between the strips incorporated water drain holes (30.1-30.5), each in contact with the circulating sieve belt (3) within a housing (32). The housing base panel (33) is in contact with the breast roller.

Description

The invention relates to a twin-wire former of a machine for producing a fibrous web, in particular a paper or board web, according to the preamble of claim 1.

Such a twin-wire former is known, for example, from German Offenlegungsschriften DE 41 41 607 A1 . DE 42 08 681 A1 and DE 198 03 451 A1 It is commonly referred to as a "blade gap former".

On known ingot gap formers, the drainage of the introduced pulp suspension begins on a box equipped with ceramic strips, over the curved surface of which the two screens converge and the first dewatering takes place. The box may, depending on the embodiment, be designed to be open or closed to the environment. In a closed box, the use of vacuum is possible. It may also be individual ceramic strips, which are preferably mounted on support ribs.

At high speeds, bright spots often occur in the fibrous web produced on this type of former, since the air entrained into the stock inlet slit during the jet injection of the fibrous suspension, both in the fibrous suspension jet and in the sieves, can not be sufficiently removed by the two sieves.

So that the entrained air is removed in an improved way, in the past so-called foil grooves have been incorporated into individual ceramic strips on open boxes having individual ceramic strips, which are intended to suck the entrained air through the foil vacuum created in operation. Such an embodiment is for example from the German patent application DE 100 84 722 T1 known. The embodiment has a plurality of grooves formed in the central part, the grooves running along the front width to a discharge opening in the rear part.

A disadvantage of this design is that the applied vacuum is not adjustable and thus is not adjustable independently of the sieve speed. Furthermore, even under normal operating conditions, the grooves may become more or less soiled and heavily soiled. On closed boxes you have already created a vacuum, but it must either be installed behind the ceramic strips, a weir or an open water sump. Otherwise, the vacuum zone begins so late that the white water taken from the pulp suspension can drain freely in the box over the breast roll crown. The weir and the open water sump also have the disadvantage that they hinder the removal of air from the screen. Furthermore, the free fall of the box usually sits so far above that the entrained air is already enclosed by the produced fibrous web (fiber mat).

It is therefore an object of the invention to provide a twin-wire former of a machine for producing a stain-free fibrous web as a result of a trouble-free removal of both entrained air and drawn from the pulp suspension white water in the initial drainage area.

This object is achieved in that the box bottom has a - seen in the vertical direction - highest point by a vertical height in the range of 10 to 700 mm, preferably from 100 to 400 mm, above the beginning of the first free drainage opening in the wire direction is located, and that the impingement shoe by means of at least one vacuum source with a vacuum ≥ 0.5 kPa, preferably ≥ 2 kPa, in particular ≥ 5 kPa, is regulary / controllable sucked.

This affects the trouble-free removal of removed from the pulp suspension white water in the initial drainage area in a particularly favorable extent, without causing an open water sump. The white water can drain freely in the box over the breast roll crest.

Moreover, the air contained in the pulp suspension is effectively taken out, and the discharge of the air-white water mixture is also effectively promoted.

This solution allows the operation of the twin-wire former even at high wire speeds ≥ 1,500 m / min, preferably ≥ 1,700 m / min, and at low basis weights, without water streaks and / or bright spots occur in the fibrous web produced.

Furthermore, a very good formation and very good cross-sections, in particular basis weight and ash transverse profile, result in the fibrous web produced.

Furthermore, the twin-wire former according to the invention can also be used in conversions of existing systems, such as in the case of conversions of BelBaie-formers.

Furthermore, the strips preferably have run-off-side scraping edges, wherein the second strip in the wire direction and the subsequent strip thereof has a respective guide surface whose geometrically linear extension does not touch the bottom of the box on the inside. This ensures that the white water discharged from the scraping edges is thrown freely over the highest point of the box bottom and in turn the emergence of an open water sump is completely avoided.

It is particularly advantageous if the respective guide surface is arranged at an angle ≦ 80 °, preferably ≦ 60 °, to the respective wire direction.

In order to ensure adequate guidance and stabilization of the twin-wire section in the area of the impingement shoe, the strips have a width ≦ 150 mm, preferably ≦ 100 mm, in particular ≦ 60 mm.

In this case, the open surface of the impingement shoe can also have interrupted, machine-wide and transverse to Sieblaufrichtung aligned slits, aligned in Sieblaufrichtung herringbone slots, holes and / or differently shaped openings, these embodiments have only exemplary character. Further design options are of course possible.

The impingement shoe should or must have a strong curvature, that exert a high pressure on the pulp suspension in order to squeeze out the entrained air on the opposite side by means of the wire tension from the pulp suspension. For this purpose, the impingement shoe preferably has at least one, preferably two or more curved regions, preferably with different lengths, whose radii each have a greater value in the wire direction. The radius of the first region preferably has a value in the range from 0.6 to 4 m, preferably from 1 to 2 m, and the radius of the second region preferably has a value in the range from 2 to 5 m, preferably 3 m, whereas the length of the The first region preferably has a value in the range of 15 to 150 mm, preferably 70 to 120 mm, and the length of the second region preferably has a value in the range of 90 to 250 mm. These dimensions are particularly advantageous at high speeds.

In order that the forming fibrous web is continually gently dewatered in the course of its drainage, the free drainage openings have different sizes, which decrease in magnitude, preferably in the direction of the wire run.

On the opposite side of the impingement shoe Doppelsiebstrecke several strips are advantageously arranged, which are flexibly pressed against the adjacent sieve and at least partially opposite the free drainage openings can be arranged. This promotes an increased removal of accumulating white water in the impingement shoe.

The twin-wire former according to the invention is suitable for all possible embodiments, so that the twin-wire section can be arranged at an angle of 0 ° to 90 ° to the horizontal. The twin-wire former can therefore be designed as a horizontal, as a vertical or as a skew former.

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 Seitenteilansicht eines Doppelsiebformers gemäß dem bekannten Stand der Technik;

Figur 2:

eine weitere schematische Seitenteilansicht eines Doppelsiebformers gemäß dem bekannten Stand der Technik; und

Figur 3:

eine schematische Seitenteilansicht einer Ausführungsform des erfindungsgemäßen Doppelsiebformers.

Show it

FIG. 1:

a schematic partial side view of a twin-wire former according to the known prior art;

FIG. 2:

a further schematic partial side view of a twin-wire former according to the known prior art; and

FIG. 3:

a schematic side view of an embodiment of the Doppelsiebformers invention.

The FIG. 1 shows a schematic partial side view of a twin wire former 1 according to the known prior art.

The known twin-wire former 1 of a machine for producing a fibrous web 2, in particular a paper or board web, with two continuous endless screens 3, 4, both over a peripheral region 5, 6 of a respective deflecting element 7, 8, in particular a breast roller 7.1, 8.1, run thereafter at least until reaching an impingement device 9 to form a wedge-shaped material inlet gap 10, which immediately receives at least one of a headbox 11 as a pulp suspension jet 12 pulp suspension 13 at training respective Strahlauftreffpunkte 14 ₃ , 14 ₄ on the two wires 3, 4 receives , converge and subsequently form a twin-wire section 15, in which the two wires 3, 4 and the at least one fibrous stock suspension 13 located therebetween are guided over a plurality of forming and drainage elements 16.

The drainage of the introduced pulp suspension 13 begins on a box 17 equipped with ceramic strips 17.1 to 17.4 box 18, on the curved surface 19, the two wires 3, 4 converge and the first dewatering takes place. The box 18 has at the outset a casserole 20 for the protection of the beam after the impact points 14 ₃ , 14 ₄ . The box 18 may, depending on the embodiment, open or close to the environment, as in FIG FIG. 1 shown executed. In a closed box 18, the application of vacuum possible. It may also be in unillustrated embodiment also to individual ceramic strips, which are preferably mounted on support ribs.

At high wire speeds v (arrow) in the range of ≥ 900 m / min, preferably ≥ 1,200 m / min, in particular ≥ 1,700 m / min occur in this embodiment increasingly bright spots in the fibrous web 2 produced, since the at the jet injection of the pulp suspension 13 entrained into the material inlet gap 10 air 21, both in the pulp suspension jet 12 and in the wires 3, 4, not sufficiently by the two wires 3, 4 can be removed. The reason for this is that the air 21 must be removed through the accumulated in the box 18 water sump 22. The production of these bright spots in the produced material web 2 occurs mainly in the initial dewatering area with a mean solids concentration c of the pulp suspension 13 of ≦ 4%, preferably ≦ 2.5%.

The FIG. 2 shows a further schematic partial side view of a twin wire former 1 according to the known prior art.

With regard to the basic structure of this Doppelsiebformers 1 is on the description of the Doppelsiebformers 1 of FIG. 1 directed.

The impingement device 9 comprises several in Sieblaufrichtung S (arrow) arranged after the breast roller 7.1 wide ceramic strips 23 with so-called Foilrillen 24, as for example from the already mentioned German Offenlegungsschrift DE 100 84 722 T1 are known. The white water expelled by means of the ceramic strips 23 from the pulp suspension 13 is removed by means of a guide device 25, in particular a guide plate 25.1, via the breast roller 7.1. In Sieblaufrichtung S (arrow) after the wide ceramic strips 23 a pressurized with a vacuum box 26 is arranged, which in turn contains several ceramic strips 27.1 to 27.3 in the manner already described.

This in FIG. 2 Although illustrated embodiment works without sump, but the air-white water mixture is dissipated insufficiently in the initial drainage area. On the one hand, the wide ceramic strips block the occurrence of air and white water from the pulp suspension over a considerable distance in the initial drainage area. On the other hand, the air discharge is not efficient in the non-blocked, ie open, sections. Furthermore, the foil grooves 24 of the ceramic strips 23 may become more or less quickly and heavily contaminated even under normal operating conditions. The production of bright spots in the produced material web 2 is favored by this design as a rule.

The FIG. 3 now shows a schematic partial side view of an embodiment of the twin-wire former 1 according to the invention.

With regard to the basic structure of this Doppelsiebformers 1 is in turn to the description of the Doppelsiebformers 1 of FIG. 1 directed.

The impingement device 9 is formed as an impingement shoe 9.1, which has a covering 28 with several in the wire direction S (arrow) successively and preferably mutually parallel bars 29.1 to 29.6 with intermediate free drainage holes 30.1 to 30.5, each with a stationary and open surface 31.1 to 31.6 touch the rotating sieve 3, and has a comprehensive box 32, the box bottom 33 is arranged so close to the direction in the wire direction S (arrow) upstream breast roller 7.1, that the box bottom 33 is at least partially guided around the breast roller 7.1. The in the FIG. 1 shown number of strips has only exemplary character; Of course, more or fewer strips can find their use. The first strip 29.1 in the direction of the direction of movement S (arrow) is also shown as a known casserole for supporting the screen 3 after the beam impingement point 14 ₃ .

The box bottom 33 has a - seen in the vertical direction - the highest point B, by a vertical height Hv in the range of 10 to 700 mm, preferably from 100 to 400 mm, above the beginning of the S in the direction of filament S (arrow) first free drainage opening 30.1 is located.

The strips 29.1 to 29.6 have run-off side scraping edges 34.1 to 34.6, wherein in the direction of wire direction S (arrow) second strip 29.2 and their subsequent strip 29.3 to 29.6 a respective guide surface 35.2 to 35.6, the geometrically linear extension V _29.2 to V _29.6 the box bottom 33 not touched on the inside.

The respective guide surface 35.2 to 35.6 is preferably arranged at an angle α ≤ 80 °, preferably ≤ 60 °, to the respective wire direction S (arrow) and the strips 29.1 to 29.6 have a width B _29.1 to B _29.6 (only giving the width B _29.4 ) ≤ 150 mm, preferably ≤ 100 mm, in particular ≤ 60 mm.

In addition to and / or as an alternative, the open surface 31 of the Impingementschuhs 9.1 also interrupted, machine width and transverse to the wire direction S (arrow) aligned slits, in Sieblaufrichtung S (arrow) aligned herringbone slots, holes and / or differently shaped openings, in particular breakthroughs, exhibit.

Furthermore, the impingement shoe 9.1 has two curved regions B ₁ , B ₂ , preferably with different lengths L ₁ , L ₂ , whose radii R ₁ , R ₂ each have a greater value in the direction of wire run S (arrow). The radius R _{1 of} the first region B ₁ has a value in the range of 0.6 to 4 m, preferably 1 to 2 m, and the radius R _{2 of} the second region B ₂ has a value in the range of 2 to 5 m, 3 m, whereas the length L _{1 of} the first region B _{1 has} a value in the range of 15 to 150 mm, preferably 70 to 120 mm, and the length L _{2 of} the second region B _{2 has} a value in the region of 90 up to 250 mm. Of course, several areas with these properties may be present.

The free drainage openings 30.1 to 30.5 also have different sizes, which preferably decrease in amount in the direction of wire run S (arrow).

Moreover, the impingement shoe 9.1 is regularly / controllably evacuated by means of at least one vacuum source not shown in detail but known to the person skilled in the art with a vacuum V ≥ 0.5 kPa, preferably ≥ 2 kPa, in particular ≥ 5 kPa, and on the side opposite the impingement shoe 9.1 the Doppelsiebstrecke 15 a plurality of strips 36 are arranged, which are in a known manner flexible to the adjacent sieve 4 can be pressed. The flexible contact strips 36 are at least partially opposite the free drainage holes 30.1 to 30.5 arranged.

The two wires 3, 4 have a respective wire speed v ≥ 1,500 m / min, preferably ≥ 1,700 m / min, and the Doppelsiebstrecke 15 is disposed at an angle β of 0 ° to 90 ° to the horizontal H. The twin-wire former 1 according to the invention can therefore be designed as a horizontal, vertical or skew former.

In summary, it should be noted that the invention provides a sheet forming system of a machine for producing a stain-free fibrous web having a very good formation even at high speeds.

LIST OF REFERENCE NUMBERS

1

twin

2

Fibrous web

3, 4

scree

5, 6

peripheral region

7, 8

deflecting

7.1, 8.1

breast roll

9

Impingementeinrichtung

10

Stock inlet gap

11

headbox

12

Fibrous suspension beam

13

Fibrous suspension

14 ₃ , 14 ₄

beam spot

15

twin-wire

16

Forming and drainage elements

17.1 to 17.4

ceramic bar

18

box

19

surface

20

baking tray

21

air

22

water swamp

23

ceramic bar

24

Foilrille

25

guide

25.1

baffle

26

box

27.1 to 27.3

ceramic bar

28

covering

29.1 to 29.6

strip

29.1

First bar

30.1 to 30.5

drainage opening

30.1

First drainage opening

31, 31.1 to 31.6

surface

32

box

33

box bottom

34.1 to 34.6

stripping

35.2 to 35.6

baffle

36

strip

B

Point

B ₁ , B ₂

Area

B _29.1 to B _29.6

width

c

Average solids concentration

H _v

Vertical height

L ₁ , L ₂

length

R ₁ , R ₂

radius

S

Sieblaufrichtung (arrow)

V

vacuum

v

Sieving speed (arrow)

V _29.2 to V _29.6

renewal

α

Angle (guide surface)

β

Angle (twin-wire)

Claims (13)

1. Twin-wire former (1) for a machine for manufacturing a fibrous web (2), in particular a paper or board web, having two circulating endless wires (3, 4), which both run over a circumferential region (5, 6) of a respective deflection element (7, 8) in the form of a breast roll (7.1, 8.1) and which thereafter run together, at least until they reach an impingement device (9, 9.1) forming a wedge-shaped stock inlet gap (10), which directly picks up the at least one fibrous suspension (13) applied by a headbox (11) as a fibrous suspension jet (12), forming respective impingement points (14₃, 14₄) on the two wires, and which then form a twin-wire section (15), in which the two wires (3, 4) and the at least one fibrous suspension (13) located between them is led over a plurality of forming and dewatering elements (16), the impingement device (9) being formed as an impingement shoe (9.1), which has a cover (28) having a plurality of bars (29. 1 to 29.6), arranged one after another in the wire running direction (S), with free dewatering openings (30.1 to 30.5) located between them, which touch the circulating wire (3) with a respectively stationary and open surface (31.1 to 31.6), and which has an encompassing box (32), the base (33) of which box is arranged close to the breast roll (7.1) arranged upstream in the wire running direction (S), in such a way that the base (33) of the box is led around the breast roll (7.1), at least in some sections,
   characterized
   in that the base (33) of the box - seen in the vertical direction - has a highest point (B) which is located by a vertical height (H_v) in the range from 10 to 700 mm, preferably from 100 to 400 mm, above the start of the first free dewatering opening (30.1) in the wire running direction (S), and
   in that the impingement shoe (9.1) is evacuated by means of at least one vacuum source such that it can be controlled/regulated with a vacuum (V) ≥ 0.5 kPa, preferably ≥ 2 kPa, in particular ≥ 5 kPa.
2. Twin-wire former (1) according to Claim 1,
   characterized in that
   the bars (29.1 to 29.6) have wiping edges (34.1 to 34.6) on the run-on side, the second and its following bar in the wire running direction (S) having a respective guide surface (35.2 to 35.6) whose geometrically linear extension (V_29.2 to V_29.6) does not touch the base (33) of the box on the inside.
3. Twin-wire former (1) according to Claim 2, characterized in that the respective guide surface (35.2 to 35.6) is arranged at an angle (α) ≤ 80°, preferably ≤ 60°, with respect to the respective wire running direction (S).
4. Twin-wire former (1) according to one of the preceding claims,
   characterized in that
   the bars (29.1 to 29.6) have a width (B_29.1 to B_29.6) ≤ 150 mm, preferably ≤ 100 mm, in particular less than ≤ 60 mm.
5. Twin-wire former (1) according to Claim 1,
   characterized in that
   the open surface (31) of the impingement shoe (9.1) additionally has broken, machine-width slots oriented transversely with respect to the wire running direction (S), herringbone slots oriented in the wire running direction (S), drilled holes and/or openings shaped in other ways.
6. Twin-wire former (1) according to one of the preceding claims,
   characterized in that
   the impingement shoe (9.1) has at least one, preferably two or more, curved regions (B₁, B₂) with preferably different lengths (L₁, L₂), whose radii (R₁, R₂) in the wire running direction (S) have a greater value in each case.
7. Twin-wire former (1) according to Claim 6,
   characterized in that
   the radius (R₁) of the first region (B₁) has a value in the range from 0.6 to 4 m, preferably from 1 to 2 m, and the radius (R₂) of the second region (B₂) has a value in the range from 2 to 5 m, preferably of 3 m.
8. Twin-wire former (1) according to Claim 6 or 7,
   characterized in that
   the length (L₁) of the first region (B₁) has a value in the range from 15 to 150 mm, preferably from 70 to 120 mm, and the length (L₂) of the second region (B₂) has a value in the range from 90 to 250 mm.
9. Twin-wire former (1) according to one of the preceding claims,
   characterized in that
   the free dewatering openings (30.1 to 30.5) have different sizes, whose magnitudes preferably decrease in the wire running direction (S).
10. Twin-wire former (1) according to one of the preceding claims,
    characterized in that
    on the side of the twin-wire section (15) opposite the impingement shoe (9.1) there are arranged a plurality of bars (36), which can be pressed flexibly against the adjacent wire (4).
11. Twin-wire former (1) according to Claim 10,
    characterized in that
    the bars (36) that can be pressed on flexibly are at least partly arranged opposite the free dewatering openings (30.1 to 30.5).
12. Twin-wire former (1) according to one of the preceding claims,
    characterized in that
    the two wires (3, 4) have a respective wire speed (v) ≥ 1500 m/min, preferably ≥ 1700 m/min.
13. Twin-wire former (1) according to one of the preceding claims,
    characterized in that
    the twin-wire section (15) is arranged at an angle (β) of 0° to 90° with respect to the horizontal (H).

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