WO1990015899A1

WO1990015899A1 - Process and unit for drying wet nonwovens on a fourdrinier machine

Info

Publication number: WO1990015899A1
Application number: PCT/DE1990/000474
Authority: WO
Inventors: Heinz Braun; Wilfried Theermann
Original assignee: Gustav Reinhard Gmbh & Co. Kg
Priority date: 1989-06-21
Filing date: 1990-06-21
Publication date: 1990-12-27
Also published as: CS274937B2; EP0429621A1; CS310590A2

Abstract

A process for drying wet nonwovens on a Fourdrinier machine improves both the drying and the quality of the finished paper. The nonwoven is fed over a first wire screen belt section to the drying unit, from where it is conveyed on another wire screen belt section. In the region between the two wire screen sections the nonwoven, covered by an upper revolving screen, is brought into contact with a downward facing drying surface of a drying box arranged inside the upper revolving screen, by means of an intermediate wire screen belt section, and conveyed along said drying surface by an intermediate wire screen belt section. In the region of the intermediate wire screen belt section, the nonwoven is carried past a further drying surface of a further drying box, i.e., with the face facing away from the first drying surface. This results in alternate drying which promotes the uniformity of the paper. The drying boxes used are suction drying boxes.

Description

Process for dewatering a water-containing nonwoven fabric on Fourdrinier paper machines and associated dewatering unit

The invention relates to a method for dewatering a water-containing nonwoven fabric on Fourdrinier paper machines according to the preamble of claim 1 and to a dewatering unit according to the preamble of claim 6.

The method or the dewatering unit for each of the types described above is known, for example, from DE-OS 27 20 046. In the dewatering unit used to carry out this method, the base plate of the dewatering box is designed as a rigid shoe that bulges downward. The distance between the Fourdrinier wire and the upper circulating wire in the area of the middle Fourdrinier wire section is therefore not variable or, in other words, constant in the running direction of the Fourdrinier wire. Since the water-containing nonwoven fabric on the fourdrinier wire is continuously dewatered upwards during the passage in the area of the middle fourdrinier wire section, the layer thickness of the nonwoven fabric decreases continuously. With a constant distance between the middle Fourdrinier section and the upper circulating sieve, the dewatering effect then decreases at the same time. For process-economical paper production, however, the greatest possible drainage is to be striven for in all phases of the drainage in order to be able to manage with the lowest possible energy requirement in the subsequent drying phase.

A basically similar situation with regard to both the detailed design and the effect can be found in the method and the associated dewatering unit for four-wire paper machines according to DE-PS 29 51 183.

To improve the drainage in the area of the middle Fourdrinier section, in connection with the use of a drainage disposed within the upper circulation screen already used as abutment elements which support the central Fourdrinier section from below, in particular in order to prevent the Fourdrinier from deflecting and sagging in this area. For example, a drainage unit is known from DE-PS 31 53 305, in which support elements running transversely to the direction of travel of the Fourdrinier wire are provided on the underside of the middle Fourdrinier section, which can even be adjusted in the vertical direction. By means of these support elements, the middle long wire section and the upper circulating wire as well as an additionally provided lower circulating wire are arched upwards, so that the two circulating screens in the middle long wire section experience a deflection which is opposite to their deflection on the associated deflecting rollers is directed and thus affects both screens in their lifespan. The elements acting from below on the middle Fourdrinier section are pure support or abutment elements without any own drainage function.

From DE-PS 34 06 217 a dewatering method is known in which the nonwoven fabric is guided past a dewatering box by means of a twin-wire section, on the other side of which the sieve has a guideway which consists of strips lying close together. These strips sit with their side facing away from the screen on an elastic base layer and can follow deflections of the screen individually and / or in groups and thereby form an abutment. In a special embodiment, it is provided that the strips are equipped with a cavity which has a suction slot open towards the sieve side. By connecting the cavity of the individual strips on the other hand to a device generating negative pressure, the abutment formed by the strips can also be used for dewatering. Drainage by means of the strips is only possible at the same time as drainage of the drainage box located on the other side of the screen. Because, in particular due to the elastic base layer underneath the strips, the abutment formed by the strips is then not suitable for Drainage of the nonwoven if no drainage box is provided on the opposite side of the twin-wire section.

The invention is based on the object of designing the dewatering method of the type mentioned at the beginning and the dewatering unit likewise of the type initially mentioned such that, in addition to intensifying the dewatering of the nonwoven fabric, a fundamentally improved quality and, in particular, improved homogeneity and strength of the dewatered nonwoven or the later completely dried paper web.

According to the invention, this object is achieved in terms of process technology or device technology by the features specified in the characterizing part of patent claim 1 or 6.

Advantageous further developments in terms of process technology or device technology can be seen from subclaims 2 to 5 and 7 to 10.

By guiding the fiber fleece to be dewatered according to the invention past at least one further dewatering surface of a further dewatering box, namely with the side of the fiber fleece facing away from the first dewatering surface of the first dewatering box, the possibility is now created of both of the fiber fleece to be dewatered Sides to drain. This primarily shortens the path of the water particles to be removed during dewatering within the nonwoven fabric and speeds up dewatering. Another major advantage is that this acceleration of the drainage basically allows a constructive shortening of the drainage section of a paper machine. In addition, the quality of the paper to be produced is improved because the "two-sidedness" of the paper is reduced by the two-sided drainage, ie the structure of the top and bottom of the finished paper is more identical to each other than with one-sided drainage. This also applies to the fine and filler content of the paper seen from the top and bottom. It cannot be overlooked, moreover, that a better connection (gassing) can be achieved with multi-layer papers, so that they have a considerably improved gap strength.

If the fiber fleece is to be guided past more than a total of two drainage areas, this route should be carried out in such a way that the fiber web is successively passed alternately with its upper and lower sides past a drainage area. This further improves the quality of the advantages achieved above.

To further increase the quality or increase the effectiveness of the dewatering, it is advisable to carry out the fiber fleece on the dewatering surfaces in the running direction of the Fourdrinier wire with increasing mutual approximation of the middle Fourdrinier section and the upper circulating wire. For this purpose, the above-mentioned sieves only have to be guided in such a way that, viewed in the running direction of the wire, taking into account the "thinning" of the fiber fleece achieved by a preliminary dewatering phase, they can approach each other accordingly, which is easily achievable in terms of device technology in that the Dewatering surfaces are arranged with respect to the pass-through path of the central fourdrinier section and the section of the upper circulating sieve located there in such a way that the above-mentioned mutual approximation of the sieves occurs, which can easily be achieved in that the successive dewatering surfaces of the successive dewatering boxes can each be arranged closer to the center line of the addressed continuous path.

As there is always a natural tendency towards downward drainage during the horizontal routing of the nonwoven fabric through the drainage section of a paper machine, ie the downward drainage is practically "easier" is feasible, in view of the advantages basically achieved above, it is advisable to bring the fiber fleece with its upper side to a drainage surface more than with its underside. With regard to the alternating top and bottom dewatering of the nonwoven fabric, this in turn means that the nonwoven fabric is dewatered at the beginning and at the end of the dewatering section. However, an even more extensive equalization of the finished paper web can be achieved.

On the other hand, there is also the possibility of passing the nonwoven fabric on the top and bottom sides of the same number of drainage surfaces, which is particularly appropriate if the paper to be produced is a relatively thin paper.

Finally, it is noteworthy that the dewatering process according to the invention, even if only paper was mentioned above, can of course also be used in the production of cardboard. Furthermore, it does not matter whether the nonwoven fabric to be dewatered is one with or without plastic particles or fibers.

The method according to the invention is further illustrated below with the aid of an associated dewatering unit, which is shown schematically in the single attached figure.

The single figure shows a schematic side view of the dewatering section of a Fourdrinier paper machine.

The nonwoven fabric to be dewatered is guided through the dewatering section by means of a central wire screen section 1 and at the same time is covered on the upper side by an upper circulating screen 2. The direction of transport of the nonwoven fabric is indicated by an arrow 3.

The parts of the associated paper machine lying in front of and behind the drainage section shown are conventional, for this reason not shown and also here not described further.

In the embodiment shown, a total of six drainage boxes, namely three upper drainage boxes 4a, 4b, 4c and three lower drainage boxes 5a, 5b, 5c, are provided within the drainage section.

While the lower drainage boxes 5a - 5c are arranged at a uniform height within the frame 6 of the drainage section, the upper drainage boxes 4a - 4c are arranged to be adjustable in the vertical direction. With this adjustable arrangement, an approximation of the upper circulating sieve 2 and the middle Fourdrinier section 1 can be achieved on the device side, viewed in the running direction 3 of the nonwoven fabric.

For the drainage boxes 4 and 5, a design as previously known is possible, which is why there is no detail view from the single figure. It is only necessary that water can be removed from the fiber fleece through the base plates 7 of the drainage boxes 4 and 5 and that the drainage boxes are those for vacuum drainage.

REPLACEMENT LEAF

Claims

1. Process for dewatering a water-containing nonwoven fabric on Fourdrinier paper machines, the nonwoven fabric being fed to the dewatering unit on an essentially horizontal first Fourdrinier section and being carried on from there to an essentially horizontal second Fourdrinier section while the nonwoven is in the area between the first and the second four-wire section by means of a middle four-wire section with simultaneous coverage by an upper circulating screen against a downward drainage surface of a drainage box arranged within the circulating screen and guided past this drainage surface in contact, characterized in that the nonwoven fabric is guided past at least one further dewatering surface of another dewatering box in the area of the middle long wire section and at the same time in the area of the upper circulating wire, namely with its from the side facing away from the first drainage surface, all drainage boxes being those for vacuum drainage.

2. The method according to claim 1, characterized in that when the non-woven fabric is guided past more than a total of two drainage surfaces, the non-woven fabric is passed alternately with its upper and lower sides in each case in contact with a drainage surface.

3. The method according to claim 1 or 2, characterized in that the nonwoven fabric is seen moving in the direction of the Fourdrinier sieve progressively with increasing mutual approximation of the middle Fourdrinier section and upper circulating sieve touching the successive drainage surfaces of the drainage box.

4. The method according to at least one of claims 1 to 3, da¬ characterized in that the nonwoven fabric is guided over the top and bottom of the same amount of drainage surfaces touching.

5. The method according to at least one of claims 1 to 3, characterized by the fact that the nonwoven fabric is guided past a drainage surface in a more touching manner than on the underside.

6. Dewatering unit for Fourdrinier paper machines for dewatering a water-containing nonwoven fabric, which is fed to the dewatering unit on a substantially horizontal first Fourdrinier section and is continued from there on an essentially horizontal second Fourdrinier section, with an upper circulation guided over guide rollers - Sieve, which is brought together between the two Fourdrinier wire sections together with a middle Fourdrinier wire section onto a downward-directed drainage surface of a drainage box arranged within the upper circulation sieve and touching the drainage surface which is curved downward in the running direction of the Fourdrinier screen. can be passed, characterized in that at least one further dewatering box (5a, 5b, 5c) with an upward dewatering surface (7) is arranged below the central fourdrinier section (1) and at the same time in the area of the upper circulating sieve, all dewatering boxes those for vacuum drainage are.

7. Drainage unit according to claim 6, characterized gekennzeich¬ net that provided a total of more than two drainage boxes these are arranged so that seen in the direction of travel (3) of the wire on a drainage box (5a, 5b, 5c) with down Directed drainage surface (7) is followed by a drainage box (4a, 4b, 4c) with an upward drainage surface (7) and vice versa.

8. Drainage unit according to claim 6 or 7, characterized in that the drainage boxes (4a, 5a, 4b, 5b, 4c, 5c) with their drainage surfaces (7) as seen in the running direction (3) of the Fourdrinier sieve ¬ Lich the continuous path of the middle Fourdrinier section (1) and the section of the upper circulating sieve located there (2) are arranged in such a way that the middle Fourdrinier section (1) and the section of the upper circulating sieve (2) located there are progressively closer to one another from drainage box to drainage box.

9. Drainage unit according to at least one of claims 6 to 8, characterized in that above and below the central Fourdrinier section (1) the same number of drainage boxes (4a, 4b, 4c, 5a, 5b, 5c) are arranged.

10. Drainage unit according to at least one of claims 6 to 8, characterized in that above the central Fourdrinier section (1) a drainage box is more angeord¬ net than below the central Fourdrinier section (1).

ER _SA TZBLATT