EP0454989B1 - Vertical former - Google Patents

Abstract

The invention relates to a vertical former with a vertical double sieve (DS). In the formation section (12), mutually opposite different forming elements (18, 19, 20, 21) are arranged, in order to achieve an improved formation in association with an improved web strength and in particular a more uniform web structure. <IMAGE>

Description

The invention relates to a vertical former of a paper machine according to the preamble of claim 1.

Such a vertical former is known from US Pat. No. 4,790,909. Here, curved suction boxes are arranged one after the other in the running direction after a forming roller, with one suction box on one side and the other suction box offset in the running direction on the other side of the twin wire in order to achieve symmetrical dewatering and thus a symmetrical sheet structure. However, the drainage takes place at different times, so that the two side areas without a forming element produce a different formation structure. In addition, the screens are not guided over long distances, which leads to a wave formation of the screens across the web width and to streaky paper.

Fl-PS 843 081 shows a vertical former in which a suction former is arranged directly over a vacuum shoe with a certain radium and opposite pressure bars. Another suction box is arranged behind the first-mentioned suction box in the running direction. This results in an uneven distribution of the drainage quantities and an asymmetrical path structure is achieved. Due to the radius of the vacuum shoe and the engagement of the rigid strips directly on top of each other, a very strong initial drainage is achieved, which leads to deformations in the web leads.

The invention has for its object to provide a vertical former of the type mentioned, in which an improved formation in connection with an improved web strength and in particular a more uniform web structure can be achieved without streaking.

This object is achieved by the features of the characterizing part of claim 1.

An open forming roll is expediently connected upstream of the formation section. However, an open forming roller can also be connected downstream of the formation section. These forming rollers are preferably designed as suction rollers.

However, there is also the possibility of providing a vacuum suction device before the first forming element.

With the solution according to the invention, an improved formation in connection with an improved web strength and in connection with a more uniform web structure and smoothness on the surface can be achieved. The formation according to the invention is particularly suitable, also for web weights 80 g / m². The device according to the invention can also be used in conjunction with a multi-layer headbox with targeted detection of the white water. Finally, better retention of the fibers is possible during the dewatering process.

The suction boxes can expediently have one, two or more suction zones. In an advantageous embodiment (FIG. 5), the water builds up in the suction box parts and the vacuum is present above the water surface. The vacuum in the different suction zones can be different. If one looks at the negative pressure curve within a part of the suction box along a section transverse to the drainage strips, the vacuum is greatest at the top due to the accumulated water and decreases from the top to the bottom as viewed in the direction of rotation of the twin wire. This effect is very favorable because it allows the dewatering effect to be dosed so that at the beginning, where the substance drains more easily, the negative pressure applied is lower. This affects the formation favorably. A continuous development of the vacuum can also be achieved with a finite subdivision of the suction box.

The rear formation zone in the running direction of the twin wire can expediently be longer than the front formation zone. This leads to a particularly gentle formation, in particular when the formation shoe of the suction box at the front in the running direction of the twin wire is expediently not curved, i.e. is essentially straight. As a result, the track is treated carefully in the first phase of formation and drainage.

A further possibility for optimization results from the fact that the forming strips can be pressed elastically onto the twin wire.

The mutual arrangement of different forming elements in several stages makes it possible to avoid asymmetrical blank pages, which has a positive influence on a uniform and gently effective formation.

Further advantageous embodiments result from the subclaims.

Fig. 1

eine schematische Gesamt-Seitenansicht eines Vertikalformers mit einer im wesentlichen geraden Formationsstrecke,

Fig. 2

den Formationsabschnitt alleine,

Fig. 3

ebenfalls den Formationsabschnitt alleine, jedoch mit einer gekrümmten Formationsstrecke,

Fig. 4

ebenfalls den Formationsabschnitt alleine mit einer gegenüber Fig. 3 entgegengesetzt gekrümmten Formationsstrecke, bei der in der ersten Formationszone die Formationsstrecke gerade ist,

Fig. 5

schematisch einen zweistufigen Saugkasten,

Fig. 6

schematisch einen dreistufigen Saugkasten mit einer anderen Wasserabführung und

The invention is explained in more detail below on the basis of a few exemplary embodiments which are illustrated purely schematically in the drawings. It shows:

Fig. 1

1 shows a schematic overall side view of a vertical former with an essentially straight formation section,

Fig. 2

the formation section alone,

Fig. 3

also the formation section alone, but with a curved formation section,

Fig. 4

likewise the formation section alone with an oppositely curved formation section compared to FIG. 3, in which the formation section is straight in the first formation zone,

Fig. 5

schematically a two-stage suction box,

Fig. 6

schematically a three-stage suction box with a different water drainage and

The vertical former, as is shown schematically in FIG. 1, comprises two screens S1 and S2, which converge to form a twin screen in the area of a nozzle 10 which feeds the suspension. This twin wire passes through a formation section or a formation gate 12. At the exit of this formation section, the twin wire DS is guided around a forming roller 14. After this forming roller 14, the screen S1 is guided around deflecting rollers 16 or at the inlet around a closed breast roller 14 '. This forming roller 14 is designed as an open forming roller.

After the forming roller 14, the screen S2 is guided around deflection rollers 16 'or 16'', wherein between the breast roll 14 'and the deflection roll 16'', the screens S1 and S2 converge to form the double screen DS. The nozzle 10 is directed into this merging nip in order to introduce the aqueous suspension into the nip where a first dewatering takes place.

The formation section 12 or the formation section 12 is here divided into two zones, namely a first forming zone Z1 and a second forming zone Z2, the course of the twin wire DS taking place essentially vertically, with a maximum inclination of 30 ° to the vertical. The first formation zone Z1 is preferably shorter than the second formation zone Z2. Of course, several zones can also be provided in succession. It is important that a forming element is arranged opposite each other on the opposite ends of the twin wire DS in each zone, specifically in the first formation zone Z1 on the right-hand side pressure bars 18, which are preferably elastic and, if appropriate, adjustable, elastic to the twin wire or to the Sieve S2 in the area of the double sieve DS are pressed to discharge the extracted water via a discharge box 18 '. On the opposite side, adjacent to the screen S1, there is a suction box 19 with a formation shoe 19 ', which consists of a lattice-like structure with strips and slits extending across the width, as is known in principle.

In the second formation zone Z2 on the same side as the suction box 19, there are pressure strips 20 with a water discharge box 20 '. On the opposite side, a suction box 21 with a formation shoe 21 'bears against the screen S2. This means that in each formation level Z1 and Z2 a forming element is arranged on both sides of the twin wire DS, the opposite forming elements as pressure strips on the one hand and as suction boxes on the other hand being different forming elements, which are however arranged alternately in the direction of movement of the twin wire DS. Here the formation shoes 19 ', 21' are straight in FIG. 1. The formation section 12 also takes a straight course between the forming rollers 14 'and 14.

2, the forming section or the formation section 12 is drawn out in detail. One difference is that the nozzle 10 slants the suspension from bottom left to top right into the space between the rollers 14 and 16 ", which affects the initial dewatering process in a modified form. The suction box 19 is designed here in one stage with a deflection element 19 ″ and the suction box 21 in two stages with the deflection elements 21 ″. A clearer representation of this two-stage suction box 21 with the water accumulation 22 can be seen more clearly in FIG. 5, attached drawing.

3 and 4 each show a double-wire belt curve curved to the left and to the right in the formation section 12, although the formation shoe 19 'is preferably straight in the first formation stage Z1 in order to be able to carry out a more gentle drainage in the first stage. However, there is also the possibility of also executing the formation shoe 21 'straight in the second zone Z2, the two formation stages Z1 and Z2 then being arranged at a slight angle to one another. In both cases, the nozzle 10 is oriented so that it directs the suspension from bottom right to top left into the gap where the screens S1 and S2 converge to form the twin screen DS. In this case, the screen S2 is guided around the open forming roller 14 '.

6, a three-stage suction box 26 is shown, with a formation shoe 26 ', which is just formed here. The twin wire belt course is indicated by an arrow 27. From the water levels in the drainage water outlet 28 it can be seen that the uppermost section 29 has a higher negative pressure than in the section 30 below and the section 31 still underneath. This means that the suction pressure in the suction box sections corresponds to the direction of movement 27 from bottom to top increases, which also has a positive influence on gentle drainage with regard to an improved formation taking into account the desired web strength and in particular a uniform web structure.

It should also be noted that, as shown in FIGS. 2, 3 and 4, troughs can be provided for collecting the water extracted from the forming breast rollers 14 '.

4, a suction box for sub-separation can be provided under the screen S2 after the open forming roll 14.

Claims (11)

1. Vertical former of a paper machine for producing wood-free printing paper and liner-board or test-liners with a double mesh (DS), both meshes (S1, S2) of which are moved through a substantially vertical formation section together with a suspension, whereby a said formation section (12) comprises at least two formation zones (Z1, Z2), in each of which a forming member (19, 21) is disposed, which are disposed one after another in a direction of movement of a double mesh, which moves upwards from below, and which act on one or another mesh, and whereby forming elements (19, 21) are suction boxes with a forming shoe (19', 21') which lies, with grids formed by forming bars, on a said double mesh (DS) wherein
   other forming members (18, 20) are disposed one after another in a direction of movement, respectively opposite forming members (19, 21) on opposite sides of a double mesh (DS), whereby two forming members (18, 20) are contact bars.
2. Vertical former in accordance with claim 1, wherein a suction box (21) has at least two suction zones.
3. Vertical former in accordance with claim 2, wherein there are different large negative pressures, which diminish downwards, in suction zones (29, 30, 31) concerned.
4. Vertical former in accordance with claim 1, wherein a rear forming zone (Z2), in a direction of movement of a double mesh concerned, is developed such that it is longer that a front forming zone (Z1).
5. Vertical former in accordance with claim 1, wherein a forming shoe of a front suction box (19), as seen in a direction of movement of a double mesh, is substantially straight.
6. Vertical former in accordance with claim 1, wherein contact bars (18, 20) are flexibly applied.
7. Vertical former in accordance with claim 1, wherein an open forming breast roll (14') is connected in before a forming stretch (12).
8. Vertical former in accordance with claim 1, wherein an open forming roller is connected in after a forming stretch (12).
9. Vertical former in accordance with claim 7, wherein an open forming breast roll (14') is developed as a suction roller.
10. Vertical former in accordance with claim 8, wherein an open forming roller (14) is developed as a suction roller.
11. Vertical former in accordance with claim 1, wherein a slit-suction means, which has a vacuum applied to it, is applied in front of a first forming member (18).

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