EP0496073B1 - Twin wire former - Google Patents

Abstract

The invention relates to a twin-wire former in which the forming turbulence of a first forming region (F1) is abated by a main forming roll (26). A further forming process in a second forming region (F2) follows behind the main forming roll. Optimum forming with little dilution water is possible with this arrangement. In addition, flocculations which can arise in the region of the main forming roll can be eliminated from both the suspension and the web by intense shear forces in the second forming region, so that the web structure is made uniform. <IMAGE>

Description

The invention relates to a twin wire former according to the preamble of claim 1.

Such a twin wire former is known from US Pat. No. 4,925,531, which has a forming roll with further forming sections in front of and behind it, but does not achieve the highest dewatering effect in all cases with a relatively long length.

In a further twin wire former according to DE-38 15 470 A1, forming shoes, forming rollers and support surfaces are installed which are intended to guide a first or second wire. The shear stress between the sieves on the suspension is weak and therefore the former has to be operated with a lot of dilution water. With packaging papers from 280 to 100g / m², this leads to large overall heights of the former, which can be greater than 8 m, and requires a longer sheet formation length. With this twin wire former, when forming the web, i.e. the formation ends at a point E of the looping length of the forming roll. However, this is followed by dewatering on a support surface and a suction roll.

On the other hand, with so-called Intensa presses, ever higher machine speeds of more than 1000 m / min can be achieved with packaging paper. Here, as can be seen from EP-028 933 A1, the water removal, in particular against gravity, presents considerable difficulties. The white water cannot be led away directly vertically from the screen at the point of origin, but must first be collected via baffles and sucked away with vacuum support. This creates contamination or an undesirable formation of material mist.

Other twin-wire formers known from DE-OS 20 00 661 and DE-OS 21 02 717 show a large deflection on the forming cylinders located in the middle area, but have neither strips arranged on both sides in the forming sections lying in front of or behind them. The drainage performance is therefore often not sufficient.

In the solution according to US Pat. No. 4,790,909, symmetrical drainage is sought. However, since the formation shoes are staggered, the drainage to the outside differs in time and intensity, which results in an uneven formation structure on both sides of the paper. In addition, the overall height is very large, which leads to vibrations for machine parts and thus affects the paper quality. In particular, at particularly high machine speeds, the turbulence is inadmissibly increased by the stationary drainage elements and the sheet formation deteriorates.

It is an object of the invention to provide a twin-wire former of the type mentioned at the outset, with which an optimal and uniform formation structure of the paper can be achieved with a lower overall height and the use of reduced dilution water.

According to the invention, this object is achieved by the characterizing features of claim 1.

This solution makes it possible to run with a little dilution water, ie it can be run with little water in the headbox, which in turn saves space, since less water has to be removed through the screens. The angular arrangement of the two forming sections also leads to a lower overall height, which in turn leads to lower machine vibrations. A turbulence increase of the suspension caused over the forming bars of the first forming section (F1) is caused by the forming roll lying between the mentioned forming sections interrupted. A gentle sheet formation with good formation and high retention of fillers is achieved. The second forming section after the forming roller, which reduces or disrupts turbulence, exerts particularly intensive shear forces on the suspension and the nonwoven. As a result, flocculations which have arisen at least partially in the region of the (main) forming roller can be eliminated and the web structure can be made more uniform.

The system according to the invention thus prevents soiling and so-called substance-fog formation. In addition, good water drainage is also possible against gravity, without the need to first collect the white water via guide surfaces.

With regard to a lower overall height in connection with an optimal formation, the forming sections are arranged essentially at an angle of 90 ° to one another. One of the two forming sections can be arranged essentially horizontally.

The first forming section can expediently be oriented vertically in connection with a vertically directed or also inclined headbox.

The use of the intermediate forming roll eliminates the need for a special suction roll. Nevertheless, the second forming section achieves a higher dry content than in the twin-wire former of DE 38 15 470 A1 using the suction roll, and also a better formation, with a relatively low deflection in combination with a low profile, especially with a small deflection over the forming roll Shear occurs, in contrast to the relatively large shear on the formed web due to the 180 ° deflection on the suction roll of DE 38 15 470 A1.

The forming roller lying between the stationary forming elements has a very strong influence on the drainage. In addition, the redirection leads to the Forming roller so that the former can be built very compactly and at the same time the dewatering is improved by centrifugal centrifugal force.

In the case of a vertical first forming section, the stock inlet gap can expediently be arranged above or below the first forming section.

The stationary forming elements can be formed by a so-called forming shoe or at least one forming pressure bar. There is the possibility that the resilient, adjustable forming pressure bars (SP bars) are arranged either on the left or right or above or below.

In particular, below the first, vertical forming section, there may be another forming roller in the vicinity of the headbox, either on the left or right side. However, two further forming rollers can also be provided.

The forming rollers in the area of the headbox have a calming (turbulence-reducing) effect on the stock suspensions. This may be desirable, but is not always desirable. If there are no forming rollers in this area, the material with the turbulence leading from the headbox is guided into the turbulence-maintaining or reinforcing zone, which is characterized by stationary strips that touch the screen.

After the first forming section with stationary forming elements has passed through, the main forming roll follows, which leads to a substantial calming of the turbulent suspension, and then another turbulence generation occurs again through the second forming section with at least one stationary forming element. This second turbulence generation in particular prevents flocculation in the suspension layer. The presence of a turbulence-increasing forming section after the deflection or forming roll is an important characteristic of this invention.

A drainage effect of approx. 20% occurs in the first, in particular vertical, forming section with the stationary forming elements. A dewatering effect of approx. 40% takes place in the intermediate forming roll itself. Finally, in the subsequent, in particular horizontal, forming section with stationary forming elements, there is a drainage effect of approximately 20% (for example). These percentages mean the volumetric values of the suspension quantities originally present in the headbox.

The particularly advantageous embodiment of the invention with the two forming sections and the intermediate main forming roll includes an essentially vertical alignment of the first forming section, an approximately 90 ° deflection in the area of the main forming roll and an essentially horizontally oriented subsequent second forming section.

The length of the second forming section is expediently at least 80% of the wrap length of the forming roll lying between the forming sections. But it can also be the same or larger.

When using the stationary forming pressure bars, four to five forming bars can preferably be arranged one behind the other at a forming point.

For a uniform formation and for a simultaneous dewatering to be carried out on both sides, at least two stationary forming elements can be arranged in essentially opposite directions in the first forming section and also in the second forming section, although they do not have to overlap one another in their full length. You can also form a forming section, which thus acts on both sides of the twin wire. This forming section is preferably shorter than the wrap length of the main forming roll lying between the forming sections.

To further improve the formation and thus the sheet or web formation, one of the opposing forming elements can be designed as a forming shoe with a curved or straight contact surface and the other forming element as at least one forming pressure bar.

The stationary forming element located at the top can in particular be designed as a forming shoe with suction drainage.

In the second forming section, the stationary forming element, in particular a molded shoe, can be followed by a separating element, which is designed, for example, as a separating roller or as a separating suction device.

Furthermore, a pre-suction device can be connected upstream of the stationary forming element, in particular a forming shoe, and in particular an upper forming shoe, in the second forming section.

Finally, in the second forming section, a curved forming shoe, which lies in particular on the transport screen located below, can be directly connected upstream of a stationary forming element, which is in particular at the top and in particular in the form of a shoe. The screen length of the first forming section (F1) touched by the forming shoe is preferably shorter than the looping length of the downstream forming roll.

The forming roller between the forming sections can be an open forming roller, either one whose surface is opened up by a honeycomb structure or a suction roller.

The active surface of the stationary shaped element can lie in the area between the upper and lower apex of the forming roller located between the forming sections.

Fig. 1

eine schematische Ansicht eines Doppelsiebformers gemäß einer ersten Ausführungsform,

Fig. 2

eine schematische Ansicht eines Doppelsiebformers gemäß einer zweiten Ausführungsform,

Fig. 3

eine schematische Ansicht eines Doppelsiebformers gemäß einer dritten Ausführungsform, und

Fig. 4

eine schematische Ansicht eines Doppelsiebformers gemäß einer vierten Ausführungsform.

The invention is explained in more detail below with the aid of a few exemplary embodiments. Show it:

Fig. 1

2 shows a schematic view of a twin wire former according to a first embodiment,

Fig. 2

2 shows a schematic view of a twin wire former according to a second embodiment,

Fig. 3

is a schematic view of a twin wire former according to a third embodiment, and

Fig. 4

is a schematic view of a twin wire former according to a fourth embodiment.

The twin-wire former of the various exemplary embodiments has a first wire 10 as the transport wire and, moreover, a second wire 12. The sieves move in the direction of the arrows indicated and converge in a stock inlet gap 14. There, the sieves 10 and 12 are guided over breast rollers 16, 18, these breast rollers in FIGS. 2 and 3 being designed as open forming rollers 16 ', around which both sieves are brought together at a certain angle, including the fiber suspension.

In front of the stock inlet gap is a headbox nozzle 20. In FIG. 1, the headbox takes place vertically downwards via this nozzle 20, in FIG. 2 from left to top right, likewise in FIG. 3 and in FIG. 4 essentially vertically from bottom to top .

Furthermore, the screens 10 and 12 are guided as endless screens over deflecting rollers 22 and 24, respectively. The second sieve 12 is only partially shown in FIGS. 2 and 3.

The entire forming zone is divided into two forming sections, namely a first forming section F1 and a second forming section F2, in which the two screens are moved together with the fiber suspension interposed. Between the forming sections F1 and F2 there is a preferably open forming roller 26, which can also be referred to as the main forming roller. There is a redirection of the twin sieve. The deflection angle in the exemplary embodiments according to FIG. 1, 2, 3, 4 is approximately 90 °. This requires a corresponding wrap angle alpha of the main forming roller 26.

In the forming sections mentioned, in Fig. 1, Fig. 2, Fig. 3 there are on both sides of the twin wire, i.e. on the side of each sieve 10 and 12, a stationary forming element in the form of a so-called forming shoe 28 or formation pressure bars 30, which rest under pressure on adjustable elements, preferably on the twin wire or a wire of this twin wire. As can be seen from the drawings, a forming shoe 28 is preferably opposite a row of forming pressure bars 30 (for example four to five). The respective water withdrawal systems are adapted to whether the water is drawn off with or against gravity.

It should be noted that in the examples one forming section runs essentially horizontally and the other runs essentially vertically. In these exemplary embodiments, the first forming section F1 is in a vertical orientation and the forming section F2 in a horizontal orientation, which in principle can also be the other way round, although the exemplary embodiments shown are of particular advantage.

2, a forming shoe 27 is arranged in the forming pressure bars 30 in the second forming section F2 in the area of the first sieve 10 (transport sieve) and does not necessarily have to be provided with suction drainage. 1 and 2, a so-called "top suction device 28" is arranged in front of the forming shoe 28 arranged in the second forming section F2 and resting on the counter-sieve 12.

In FIG. 1, FIG. 2 and FIG. 4, a separating suction device 23, which is designed as a separating roller 21 in FIG. 3, is preferably arranged on the transport screen 10 behind the forming section F2.

The formation shoes can be provided with a curved, but also with a straight surface. They can be operated with or without vacuum.

The main forming roller can be designed as an open roller, for example such a roller with a grill structure (honeycomb structure) or as a suction roller.

Claims (18)

1. Twin-wire former for paper manufacture, with two circulating continuous wires (10, 12) which meet while forming a stock inlet gap (14) and are guided together in this state along a forming zone, one of the wires being a conveyor wire (10) and the other a counter-wire, with at least one forming roll, over at least a part of the circumference of which the two continuous wires are guided together, at least one stationary forming element (28) bearing against at least one of the wires on at least one side in a first forming section (F1) lying before the forming roll (26) in the wire movement direction, and a second forming section (F2) being provided after the forming roll (26) in the wire movement direction, in which section at least one further stationary forming element (28; 30) bears against at least one of the wires on at least one side and at least two stationary forming elements (28, 30) are arranged essentially opposite one another, characterised in that the second forming section (F2) is arranged at an angle of essentially 90° to the first forming section (F1), and that at least two stationary forming elements (28', 30') are disposed essentially opposite one another in the first forming section (F1).
2. Twin-wire former according to claim 1, characterised in that the stock inlet gap (14) is arranged above the first forming section (F1).
3. Twin-wire former according to claim 1, characterised in that the stock inlet gap (14) is arranged below the first forming section.
4. Twin-wire former according to one of claims 1 to 3, characterised in that the stationary forming elements consist of a so-called forming shoe (28) or at least one forming pressure bar (30).
5. Twin-wire former according to one of claims 1 to 4, characterised in that a further forming roll (16') is arranged at the stock inlet gap (14).
6. Twin-wire former according to claim 1, characterised in that the second forming section is at least 80% of the length of contact of the forming roll (26) lying between the forming sections (F1, F2), the same as the latter and, in particular, greater than this.
7. Twin-wire former according to claim 4, characterised in that at least four to five forming pressure bars are arranged one behind the other.
8. Twin-wire former according to claim 1, characterised in that one of the forming elements disposed opposite one another is constructed as a forming shoe (28'; 28) with a curved or straight contact surface and the other forming element as at least one forming pressure bar (30'; 30).
9. Twin-wire former according to one of claims 1 to 8, characterised in that the respective top stationary forming element (28) is constructed as a forming shoe with a suction dewatering action.
10. Twin-wire former according to claim 1, characterised in that a separating element constructed, for example, as a separating roll (21) or as a separating suction device (23) is disposed after the stationary forming element (28), in particular a forming shoe, in the second forming section (F2).
11. Twin-wire former according to claim 1, characterised in that a preliminary suction device (28'') is disposed before the stationary forming element (28), in particular a forming shoe, and especially a top forming shoe, in the second forming section (F2).
12. Twin-wire former according to claim 1, characterized in that a curved forming shoe (28'') is disposed before a stationary forming element (28), which is in particular a top forming element and constructed in particular as a forming shoe, in the second forming section (F2), which curved shoe bears in particular against the counter-wire (12).
13. Twin-wire former according to claim 1, characterized in that the active surface of the stationary forming element lies in the region between the top and the bottom crown point of the forming roll (26) disposed between the forming sections (F1, F2).
14. Twin-wire former according to claim 8, characterised in that the sub-forming section (F3), which is acted upon on both sides, is shorter than the length of contact of the main forming roll (26) lying between the forming sections (F1, F2).
15. Twin-wire former according to claim 1, characterised in that the wire length of the first forming section (F1) which is contacted by the forming shoe is shorter than the length of contact of the forming roll (26) disposed between the two forming sections (F1, F2).
16. Twin-wire former according to one of claims 1 to 15, characterised in that the forming roll (26) disposed between the two forming sections (F1, F2) is constructed as an open roll.
17. Twin-wire former according to claim 16, characterised in that the open forming roll (26) is one which is opened up by a grill or honeycomb structure.
18. Twin-wire former according to claim 17, characterised in that the open forming roll is a suction roll.

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