DE19951928A1 - Web formation station at a multi-layer papermaking/cardboard prodn machine has an initial water extraction zone at a fourdrinier with a structured gap between the stock inlet and the suction box - Google Patents

Abstract

The web formation zone (1) where pulp is converted into a multi-layer web by extraction of the water content, at a papermaking or cardboard prodn. machine, has a double-fourdrinier structure (D) where the lower fourdrinier (16) has a longitudinal initial water extraction zone (VEW1) as a long fourdrinier. The length (L1) of the gap between the jet of the stock inlet (22) and the water extraction suction box (32) is 0.75-2.5 m and pref. 1.25-2.0 m. The initial water extraction zone (VEW1) has entry and exit bars (17a,17b), across the direction (R) of travel by the first layer of the paper/cardboard web. At least one parallel support bar (17c) and at least one vacuum box (17d) is between the other bars (17a,17b). The vacuum box (17d) is operated with an overpressure against the atmospheric pressure, with holes to the side of the initial water extraction zone (VEW1), or slits with a slit width of <= 20 mm and pref. <= 15 mm. The water extraction rate in the double-fourdrinier zone is \-50%. The time span between the outflow of the pulp suspension from the jet of the stock inlet (22) and the entry into the double-fourdrinier zone (D) is <= 0.1 secs. An assembly of bars (L), to form the web, develops the first web layer in front of the web shaping roller (24) of the double-fourdrinier zone (D), in the direction (R) of web travel, fitted with pressure bars (30). The double-fourdrinier zone (D) has a secondary stock inlet, aligned into the gap between the secondary fourdriniers (16,18) as they come together. The primary fourdrinier (10) of a web shaping unit, with a former, has an initial water extraction zone with a gap between the stock inlet (14) and the suction box (32) in a length of 0.75-2.5 m and pref. 1.25-2.0 m. A second web forming unit is at the first, which forms a web layer to be laid on the first layer from the double-fourdrinier zone (D), in an identical structure, and followed by additional and identical units to overlay additional web layers for the final multi-layer web.

Description

The invention relates to a sheet forming device for producing a more ply paper or cardboard web with a sheet forming unit consisting of a primary longitudinal screen and two secondary designed as twin wire formers seven (bottom wire, top wire), which is a first layer of multi-ply paper or Place the cardboard web on a second layer of the primary longitudinal screen, the Twin wire former a forming roller as a deflection roller for the course of the seconds darts sieves and wherein a suction box in the area of the upper sieve Twin wire former is arranged.

The closest prior art to the present invention is in US Pat German published patent application DE 40 31 038 A1 (PB06624 DE). she discloses an apparatus for making a multi-ply paper or card tons with a primary longitudinal screen and a secondary length arranged above Sieve as a twin wire former, which is an upper layer of multilayer paper or Put boxes on a lower layer, whereby the twin-wire former forms one roller as a deflecting roller for the course of the twin wire. In the direction of travel of the twin wire in front of the forming roller, a pressure bar former is arranged and the so-called water line of the fiber suspension lies in the area of the For greasing roller.

A disadvantage of this disclosed device is that it is a secondary longitudinal screen Double-wire former designed both produces an insufficient formation and even a limited amount of water with the result of a bad fez action removed.  

In practice, attempts have been made to use the secondary longitudinal screen guided twin wire former as close as possible to the headbox or as close as possible to be placed on the press section. The first placement has the advantage of one improved formation, but the disadvantage of limited removal Amount of water (poorer strength). The second placement, however, owns the advantage of producing a low tear length ratio L / Q, however the disadvantage of a less than optimal formation. As a result of these attempts which generally hold that the possible placements have respective advantages bring with them, but they cannot be realized at the same time, which in turn results in receiving disadvantages.

It is therefore an object of the invention to create a device of the type mentioned with which a very good formation when removing high water quantity is achieved with the result of good strength, and this if possible a reduction in the screen length and the overall length of this paper or cardboard machine section.

According to the invention, this object is achieved in a device of the aforementioned type solved in that the bottom wire of the twin wire former has a slow wire type Pre-drainage section with a length (= distance between the nozzle of the Headbox and the suction box) between 0.75 and 2.5 m, preferably between 1.25 and 2 m. This length of the pre-drainage section he brings a reduction in both the screen length and the overall length of the blade educational device, and this when the properties mentioned.

In a preferred embodiment of the invention it is provided that the slow like pre-drainage section has a drain bar and an overflow bar, the transverse to the direction of the first layer of the multilayer paper or cardboard web are arranged. Between the drain bar and the drain bar can have at least one support bar running parallel to them as well at least one vacuum box may be arranged. In a further embodiment  can the vacuum box, optionally also designed as a vacuum foil, with Overpressure, for example 1 to 40 mm water column, in relation to the atmosphere phere pressure operated, the compressed air for the positive pressure example can be removed from a blow-out duct or a fan. The vacuum box is preferably to the side of the pre-drainage stretch out with holes or slots with a slot width of less than 20 mm, preferably less than 15 mm. The mentioned drainage elements elements and their designs all have the advantage of being controllable positive support for the drainage process that is emerging multi-layer paper or cardboard web.

In order to allow the main sheet formation to take place in the twin wire former, it is advantageous if the drainage in the twin wire former is greater than 50% (100% Headbox quantity).

In a further preferred embodiment of the invention, the Time between jet exit from the headbox nozzle and the Entry into the twin wire former is less than 0.1 seconds. This time period results derive from the necessity of going through a calming section for the fiber suspension emerging from the headbox nozzle, and this until to reach the immobilization point of the fibers. The turbulence is coming preferably after reaching the immobilization point in the twin-wire zone initiated.

Furthermore, it is advantageous according to the invention if a last mold is running Direction of the resulting first layer of the multi-layer paper or cardboard web is arranged in front of the forming roller of the twin wire former. This will Generating turbulence and introducing the same into the pulp board promotes. In another version, the last is formed with pressure strips, some of which are resiliently supported, thereby preventing the generation of turbulence can be controlled or regulated in some cases.  

In a further special embodiment of the invention it is provided that the twin wire former is provided with a secondary headbox and the Se secondary material casserole in the gusset of the converging secondary screens is aimed. This makes the sheet forming device for making one more layered paper or cardboard web still the possibility of multi-layer technology opened, which in turn has qualitative and technological advantages for the ent standing paper or cardboard web arise.

In a continuation of the inventive concept, it is also proposed that the primary longitudinal screen of the first sheet forming unit is a former known per se (Hybridformer) is assigned, the primary longitudinal screen being a slow-screen type drainage section with a length (= distance between the nozzle of the fabric casserole and the suction box) between 0.75 and 2.5 m, preferably between 1.25 and 2 m. This type of former and this length of the previous one Watering section provide the aforementioned, for the bottom sieve of the double Siebformers outlined advantages, such as a reduction in both the screen length and the overall length of the sheet forming device, and this at Achievement of the mentioned properties and improved symmetry of the more layer structure.

In a continuation of the inventive concept, it is also proposed that the a further sheet formation unit is assigned to the first sheet formation unit, wherein the further sheet forming unit is a layer of the multilayer paper or cardboard path to the first, from the twin wire former of the first sheet forming unit witnessed position and the bottom wire of the twin wire former both mentioned Layers on the second, generated by the primary longitudinal screen of the first sheet forming unit Location. This additional sheet formation unit opens up the possibility net, a multi-layer paper or cardboard web with more than two layers under to produce different layer qualities. Is the further sheet formation unit as Primary longitudinal screen with associated shaper (hybrid former), whereby the Primary longitudinal sieve a slow sieve-like pre-drainage section with a length (=  Distance between the headbox nozzle and the suction box) between 0.75 and 2.5 m, preferably between 1.25 and 2 m, so result the benefits outlined in the previous section.

In a further advantageous embodiment of the invention it is provided that the first sheet formation unit is assigned to a further sheet formation unit, wherein the further sheet formation unit is a layer of the multi-layer paper or Cardboard web on at least those generated by the first sheet forming unit Layers layers, with the further sheet forming unit being advantageous is designed as a primary longitudinal screen. This results in the two advantages outlined in previous sections.

It is understood that the above and to be explained below not only in the combination given tion, but can also be used in other combinations or alone are without departing from the scope of the invention.

Further features and advantages of the invention result from the Unteran say and the following description of preferred embodiments with reference to the drawing in which the sheet according to the invention educational devices for making a multi-ply paper or cardboard web are shown in schematic side views.

It shows:

Fig. 1 shows a first sheet forming device according to the invention for manufacturing a multilayered paper or paperboard web;

Fig. 2 shows another embodiment of a sheet forming device according to the invention;

Fig. 3 shows an embodiment according to Figure 1 with another For mer, whereby a so-called hybrid former is formed.

FIG. 4 shows a twin wire former according to FIG. 1, but without so-called SP pressure bars;

FIG. 5 shows a twin wire former according to FIG. 2, but with a secondary casserole; and

Fig. 6 is a sheet forming device according to the invention with three sheet forming units.

The figures show a primary longitudinal screen 10 which moves from right to left in accordance with arrow A in the respective figure. In the area of a deflection roller (breast roller) 12 for the primary longitudinal screen 10 there is a headbox 14 for a lower (second) layer of the multilayer paper or cardboard web. The primary longitudinal sieve 10 can also, as shown in FIG. 3, be formed as a hybrid former H.

Above the primary longitudinal screen 10 there is a twin-wire former D as a secondary screen arrangement with a lower screen 16 and an upper screen 18 . The screens 16 and 18 move according to the arrow B in the respective figure from left to right, that is, the bottom wire 16 around a deflection roller 20 in the area of the headbox 22 , a forming roller 24 (here an open forming roller) with a trough 31 for removal of water and other rollers 26 . The upper screen 18 moves around a series of deflecting rollers 28 and together with the lower screen 16 around the forming roller 24 . Thus, the lower wire 16 and the upper wire 18 move in front of the forming roller 24 partially together essentially in the horizontal direction and after the forming roller (in the direction of travel R) behind the forming roller 24 at least partially together essentially in the vertical direction. However, it is also possible in a not shown embodiment, the bottom wire 16 and the top wire 18 that extend at least partially together at an angle of about 45 degrees downward behind the forming roll 24th

In the direction of travel R in front of the forming roller 24 , in the region of the twin wire former D below the lower wire 16, according to the invention there is a strip former L with pressure strips 30 acting on the lower wire 16 . Opposed to these pressure bars 30 is a suction box 32 above the upper sieve 18 .

The bottom wire 16 of the twin wire former D now has, according to the invention, a pre-dewatering section VEW1 with a length L1 (= distance between the nozzle of the headbox 22 and the suction box 32 ) between 0.75 and 2.5 m, preferably between 1.25 and 2 m , on. The slow-drain pre-dewatering section VEW1 also has a drain bar 17 a and a run-up bar 17 b, which are arranged transversely to the running direction R of the first layer of the multilayered paper or cardboard web that is created. In the area of slow-moving pre-drainage route VEW1 are also arranged between the drain bar 17 a and the ramp bar 17 b at least one support bar 17 c and at least one vacuum box 17 d. It is understood that the number of support strips 17 c and 17 d of vacuum boxes during operation of the paper or board machine are not limited to the number shown.

The embodiment according to FIG. 2 differs from that according to FIG. 1 only by the different assignment of the twin wire former D to the primary long wire 10 in that the headbox for both layers takes place on the same side of the system. In the embodiment of FIG. 1, the headbox for both systems takes place on opposite sides.

The sheet forming apparatus 1 shown in Fig. 3, in addition to the Blattbil-making device 1 of Fig. 1 in the region of the Primärlangsiebs 10 equipped with a further shaper 29, thereby forming a so-called hybrid former H. The additional former 29 has both a screen 19 , which is guided around deflection rollers 27 , and a suction box 32 . The primary longitudinal screen 10 of the first sheet formation unit 5 now has, according to the invention, a pre-dewatering section VEW2 with a length L2 (= distance between the nozzle of the headbox 14 and the suction box 32 ) between 0.75 and 2.5 m, preferably between 1.25 and 2 m, on.

FIG. 4 shows a twin wire former D according to FIG. 1, but without so-called SP pressure bars 30 . Furthermore, the suction box 32 is equipped on its side facing the upper sieve 18 with a curvature, so that this results in advantageous convex guidance of the twin sieve when the pressure bars 30 are arranged in an arcuate manner. The Fig. 5, however, shows a twin wire former D as shown in FIG. 2, but with a secondary headbox 23rd

The sheet forming apparatus 1 shown in FIG. 6 consists of three sheet forming units 5 , 6 and 7 . The middle sheet formation unit 5 has the construction of the sheet formation device 1 in FIG. 1; with regard to the description of the sheet formation unit 5 , reference is therefore made to FIG. 1. The only difference of the sheet forming device 1 with respect to the embodiment according to FIG. 1 is that the lower wire 16 and the upper wire 18 behind the forming roller 24 at least partially together do not essentially run in a vertical direction, but at an angle of approximately 60 degrees downwards.

The sheet-forming unit 5 is assigned a further sheet-forming unit 6 , the further sheet-forming unit 6 depositing one layer (insert) of the multilayer paper or cardboard web onto the first layer (insert) generated by the twin-wire former D of the sheet-forming unit 5 and the bottom wire 16 of the Twin wire formers D deposits both layers (deposits) on the second layer (back) generated by primary longitudinal wire 10 of sheet forming unit 5 . The sheet forming unit 6 is designed as a primary longitudinal screen 10 'with an associated former 29 , where in the primary longitudinal screen 10 ' a slow screen pre-dewatering section VEW3 with a length L3 (= distance between the nozzle of the headbox 14 'and the suction box 32 ') between 0.75 and 2.5 m, preferably between 1.25 and 2 m.

Further, the sheet forming unit 5 is associated with a further second sheet forming unit 7, wherein the further sheet forming unit 7, a position (ceiling) of the multi-ply paper or board web, onto at least of the leafing device 5 layers produced (deposits and back) deposits. The sheet forming unit 7 is designed as a primary longitudinal screen 10 ″.

In summary, it should be noted that the device of the invention is created with which a very good formation when removing a large amount of water, resulting in good strength is achieved, and if possible with a reduction in the screen length and. Overall length of this paper or board machine section.  

Reference list

1

Sheet forming device

5

,

6

,

7

Sheet formation unit

10th

,

10th

',

10th

"Primary longitudinal screen

12th

,

20th

Deflection roller

14

,

14

',

22

Headbox

16

Lower sieve (secondary sieve)

17th

a drain bar

17th

b Casserole bar

17th

c support strip

17th

d vacuum box

18th

Top sieve (secondary sieve)

19th

scree

23

Secondary headbox

24th

Forming roller

26

Rollers

27

,

28

Deflection rollers

29

,

29

'Shaper

30th

Pressure bars

31

Tub

32

,

32

'' Suction box
A, B arrow
D twin wire former
H hybrid former
L last mold
L1, L2, L3 length
R running direction
t duration
VEW 1-3 pre-drainage section

Claims (18)

1. A forming apparatus (1) for producing a multilayered paper or paperboard web having a sheet forming unit (5) consisting of a primary wire (10) and two as twin (D) formed secondary seven (bottom wire 16, the top wire 18), a first Lay the layer of the multi-layer paper or cardboard web on a second layer of the primary longitudinal screen ( 10 ) afj, the twin-wire former (D) having a forming roller ( 24 ) as a deflection roller for the course of the secondary screens ( 16 , 18 ) and a suction box ( 32 ) is arranged in the area of the upper sieve ( 18 ) of the twin wire former (D), characterized in that the lower wire ( 16 ) of the twin wire former (D) is a slow sieve-like pre-dewatering section (VEW1) with a length (L1) (= distance between the nozzle of the Headbox ( 22 ) and the suction box ( 32 )) between 0.75 and 2.5 m, preferably between 1.25 and 2 m. 2. Sheet forming device ( 1 ) according to claim 1, characterized in that the slow-like pre-dewatering section (VEW1) has a drain bar ( 17 a) and a run-up bar ( 17 b) which is transverse to the direction of travel (R) of the resulting first layer of the multi-layer paper or cardboard web are arranged. 3. Sheet forming device ( 1 ) according to claim 2, characterized in that at least one parallel support strip ( 17 c) is arranged between the drain bar ( 17 a) and the run-up bar ( 17 b). 4. Sheet forming device ( 1 ) according to claim 2 or 3, characterized in that at least one vacuum box ( 17 d) is arranged between the drain bar ( 17 a) and the run-up bar ( 17 b). 5. Sheet forming device ( 1 ) according to claim 4, characterized in that the vacuum box ( 17 d) can be operated with overpressure relative to the atmospheric pressure. 6. Sheet forming device ( 1 ) according to claim 4 or 5, characterized in that the vacuum box ( 17 d) to the side of the pre-dewatering section (VEW1) is provided with holes. 7. sheet forming device ( 1 ) according to claim 4 or 5, characterized in that the vacuum box ( 17 d) to the side of the pre-dewatering section (VEW1) with slots with a slot width of less than 20 mm, preferably less than 15 mm, is provided. 8. Sheet forming device ( 1 ) according to one of the preceding claims, characterized in that the dewatering in the twin wire former (D) is greater than 50%. 9. Sheet forming device ( 1 ) according to one of the preceding claims, characterized in that the time period (t) between the jet exit from the nozzle of the headbox ( 22 ) and the entry in the twin wire former (D) is less than 0.1 Se customer. 10. Sheet forming device ( 1 ) according to one of the preceding claims, characterized in that a strip former (L) is arranged in the running direction (R) of the first layer of the multilayered paper or cardboard web being formed in front of the forming roller ( 24 ) of the twin-wire former (D). 11. Sheet forming device ( 1 ) according to claim 10, characterized in that the strip former (L) is equipped with pressure strips ( 30 ) which are partially elastically supported. 12. Sheet forming device ( 1 ) according to one of the preceding claims, characterized in that the twin wire former (D) with a secondary headbox ( 23 ) is seen ver. 13. Sheet forming device ( 1 ) according to claim 12, characterized in that the secondary stock head ( 23 ) is directed into the gusset of the converging secondary screens ( 16 , 18 ). 14. Sheet forming device ( 1 ) according to one of the preceding claims, characterized in that the primary longitudinal screen ( 10 ) of the sheet forming unit ( 5 ) is associated with a known formers ( 29 ), the primary longitudinal screen ( 10 ) a slow-like pre-dewatering section (VEW2) with a length (L2) (= distance between the nozzle of the headbox ( 14 ) and the suction box ( 32 )) between 0.75 and 2.5 m, preferably between 1.25 and 2 m. 15. Sheet-forming device ( 1 ) according to one of the preceding claims, characterized in that the first sheet-forming unit ( 5 ) is assigned a further sheet-forming unit ( 6 ), the further sheet-forming unit ( 6 ) being a layer of the multilayer paper or cardboard web on the first, the layer created by the twin wire former (D) of the first sheet forming unit ( 5 ) and the lower wire ( 16 ) of the twin wire former (D) deposits both of these layers onto the second layer generated by the primary longitudinal wire ( 10 ) of the first sheet forming unit ( 5 ). 16. Sheet forming device ( 1 ) according to claim 15, characterized in that the further sheet forming unit ( 6 ) is designed as a primary longitudinal screen ( 10 ') with an associated former ( 29 '), the primary longitudinal screen ( 10 ') being a slow-screen pre-dewatering section (VEW3) with a length (L3) (= distance between the nozzle of the headbox ( 14 ') and the suction box ( 32 ')) between 0.75 and 2.5 m, preferably between 1.25 and 2 m. 17. Sheet-forming device ( 1 ) according to one of the preceding claims, characterized in that the first sheet-forming unit ( 5 ) is assigned a further sheet-forming unit ( 7 ), the further sheet-forming unit ( 7 ) having a position of the multilayer paper or cardboard web on at least that of the first sheet-forming unit ( 5 ) deposits layers. 18. Sheet forming device ( 1 ) according to claim 18, characterized in that the further sheet forming unit ( 7 ) is designed as a primary longitudinal screen ( 10 ").