EP0346519B1 - Dewatering unit for fourdrinier machines - Google Patents

Abstract

In a drainage unit for Fourdrinier machines for upward-directed drainage of a paper mat (7), which is fed on an endless-wire section to the drainage unit and is passed along from there on a further endless-wire section, having an upper circulated wire (4) which is guided over guide rollers and which is brought together between the two endless-wire sections with a middle endless-wire section onto a downward-pointing drainage surface (3) of a drainage box (1) arranged inside the upper circulating wire (4) and can be moved past the drainage surface (3) bulging downwards in the running direction (8) of the endless wire (6), and in contact therewith, the bottom plate (2), having the drainage surface (3), of the drainage box (1) can be variably bent for changing the downward-pointing bulge of its drainage surface (3), and the upper side of the bottom plate (2) of the drainage box (1) is associated with at least one pressure element (17, 18), by means of which the bottom plate (2) can be variably bent and which, on the other side, is supported on a rigid and immovable part of the drainage box (1). <IMAGE>

Description

The invention relates to a dewatering unit for Fourdrinier paper machines for the upward dewatering of a water-containing paper fleece, according to the preamble of claim 1.

In the drainage unit of the type described above, which is known from DE-OS 27 20 046, the base plate of the drainage box is already designed as a shoe that bulges downward; however, the bulge is unchangeable, so the shoe base plate is rigid in itself. The distance between the fourdrinier wire and the upper circulating wire in the area of the middle fourdrinier wire section is therefore not variable when viewed in the running direction of the fourdrinier wire. Since the water-containing paper fleece located on the fourdrinier wire is continuously dewatered upwards and at the same time dewatered downward as it passes through the middle wire sieve section, the layer thickness of the paper fleece decreases continuously. If the distance between the fourdrinier sieve and the upper circulating sieve remains the same, the drainage effect then decreases at the same time. For process-economical paper production, however, in all phases of the dewatering, a dewatering as far as possible is to be aimed for, in the subsequent drying phase to be able to make do with as little energy as possible.

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

To improve the drainage in the area of the central Fourdrinier section, units serving as abutments have already been used in conjunction with the use of a drainage box arranged within the upper circulating sieve, which support the above-mentioned Middle Fourdrinier section from below, in particular to prevent the sagging and sagging of the Fourdrinier in this area to prevent. For example, a drainage unit is known from DE-PS 31 53 305, in which support elements extending transversely to the direction of travel of the fourdrinier wire are provided on the underside of the central fourdrinier wire section, which are adjustable in the height direction. By means of these support elements, the middle Fourdrinier section and the upper circulating sieve and the additionally provided lower circulating sieve are even bulged upward, so that the two circulating sieves experience a deflection in the affected middle Fourdrinier section, which is directed opposite to their deflection on the associated deflection rollers and thus both sieves impaired in their lifespan. For the rest, in this drainage unit, the drainage box located at the top is only designed as a housing which is open at the bottom, that is to say as a drainage box without a base plate, so that the upper circulation screen is without a guide on the top.

From DE-PS 34 06 217 known the use of a support table over which the sieves run. On the other side of the sieve there is a guideway opposite the support table is formed closely adjacent strips. These 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. The support table represents a drainage box arranged within the upper circulating sieve, and the plurality of strips arranged transversely to the running direction of the Fourdrinier sieve forms an abutment. It is true that the adjustability of the individual slats in the height direction can already achieve a certain degree of adjustability of the distance between the upper circulating sieve and the Fourdrinier sieve; the effort required for this, however, can hardly be justified in view of the result achieved, especially since the downward drainage in the affected middle Fourdrinier section is impaired.

The invention has for its object to design the dewatering unit of the type mentioned in such a way that the distance between the fourdrinier wire and the upper circulating wire on the section of the middle fourdrinier wire section can be adjusted from the direction of the upper dewatering box, to achieve different distances in the running direction of the fourdrinier wire in order to improve the efficiency of the upward drainage and at the same time to be able to take into account the decreasing fleece thickness with continuous drainage.

This object is achieved by the measures specified in the characterizing part of claim 1.

Advantageous further developments can be seen from the subclaims.

Due to the variably deflectable design of the base plate, the distance between the fourdrinier sieve and the upper circulating sieve can be seen in the running direction of the fourdrinier sieve according to the respective Needs can be set. For example, by reducing the distance between the two screens, in particular in the area of the attachment of the pressure element acting on the top of the base plate, a progressively greater approximation of the two screens can be achieved, which takes into account the reduction in the fleece height caused by the drainage. This is of considerable advantage in particular in the production of special papers and, in particular, thin papers, since overall improved drainage can be achieved in the area of the middle Fourdrinier section. The intended deflectability can be easily achieved by the pressure element provided at the top of the base plate. In addition, a stepless arching of the drainage surface is achieved by means of the variably deflectable design of the base plate, which is of considerable importance for the smooth running of the screens and their service life.

By providing several pressure elements, one behind the other as seen in the running direction of the Fourdrinier wire, practically any desired curve of the drainage surface can be achieved.

A hydraulic or pneumatic piston / cylinder unit and a hydraulically or pneumatically pressurized hose are considered to be the most effective form of a pressure element in every respect. In contrast to worm drives or similar mechanical devices, these types of printing elements have a certain elasticity, which has an advantageous effect at least with regard to the screens at the high running speeds of modern four-wire paper machines.

Because of the variable deflection of the base plate is recommended for its attachment to the end walls of the Drainage box a pivoting arrangement. This pivotable arrangement can be achieved, for example, by the provision of a hinge joint in the affected area between the base plate and the end wall of the drainage box, but also in that, with a rigid assignment of the base plate and the front wall, the base plate in the affected area is executed in such a wall thickness that it can be pivoted under deformation. It is noteworthy in this connection that it is only a relatively small pivoting angle and that the base plate is not exposed to any rapid swiveling back and forth. A swiveling in the affected area only ever takes place when the deflection of the base plate changes.

In practice, the deflection of the base plate is particularly easy to implement if it is made in one piece and consists of plastic. The deflection can then easily be achieved as a deformation under the action of the at least one pressure element.

On the other hand, there is also the possibility of designing the base plate in a divided manner and arranging a hinge joint between adjacent parts. In this case, the first-mentioned variant will probably be preferred because it guarantees a gentler run of the upper circulation screen over the drainage area.

Fig. 1

einen vertikalen Längsschnitt durch eine bevorzugte Ausführungsform einer erfindungsgemäßen Entwässerungseinheit mit zweiteiliger Bodenplatte und Schlauch als Druckelement;

Fig. 2

eine Einzelheit einer zweiten Ausführungsform ebenfalls im Längsschnitt mit einteiliger Bodenplatte und Kolben/Zylinder-Einheit als Druckelement;

Fig. 3

eine starre Befestigungder Bodenplatte an einer Stirnwand des Entwässerungskastens;

Fig. 4

eine gelenkige Anordnung der Bodenplatte an einer Stirnwanddes Entwässerungskastens;

Fig. 5

eine Bodenplatte in zweiteiliger Ausführung mit Scharniergelenk zwischen den beiden Teilen.

The invention is described in more detail below with reference to embodiments shown in the drawings; in the drawings show:

Fig. 1

a vertical longitudinal section through a preferred embodiment of a drainage unit according to the invention with two-part base plate and hose as a pressure element;

Fig. 2

a detail of a second embodiment also in longitudinal section with one-piece base plate and piston / cylinder unit as a pressure element;

Fig. 3

a rigid attachment of the bottom plate to an end wall of the drainage box;

Fig. 4

an articulated arrangement of the base plate on an end wall of the drainage box;

Fig. 5

a two-part base plate with a hinge joint between the two parts.

The drainage box 1 shown in longitudinal section in FIG. 1 is closed at the bottom by a base plate 2, the lower surface 3 of which is the drainage surface and at the same time the guide surface for the upper circulating sieve 4. In the base plate 2, a plurality of passage channels 5 are provided for the drainage of the drainage water.

A wire 4 can be seen at a certain distance below an upper circulating screen 4, a water-containing paper fleece 7 to be dewatered being shown between the two screens 4 and 6.

The guidance of the two screens 4 and 6 in front of and behind the drainage box 1 is the usual type and is therefore not shown.

The running direction of the paper fleece 7 and the two screens 4 and 6 is indicated by an arrow 8.

Inside the drainage box 1 are usually in three collecting basins 9, 10 and 11 are provided, the basin 9 being intended for the water which is immediately in front of the drainage box 1 for removal; the associated supply of this drainage water into the basin 9 is of a conventional type and is not shown. The basin 10 serves to receive the drainage water, which is in front of a wall 12 transverse to the inside of the drainage box 1 for removal, while the basin 11 is intended for the drainage water behind the transverse wall 12.

The base plate 2 is fastened to the end walls 13 of the drainage box which are transverse in the running direction 8 of the wire 4. This attachment can be of virtually any type, for example articulated, as shown schematically in FIG. 1, or rigid, as can be seen from FIG. 3. 4, where the free end of the end wall 13 and the associated end of the base plate 2 are jointly designed as a hinge joint 14. For a rigid connection between the end wall 13 and the base plate 2, in particular a design of the associated end of the base plate 2 according to FIG. 3 is also possible, where the portion 15 of the base plate 2 located immediately behind the fastening area of the base plate 2 is considerably reduced in wall thickness in order to be there to be able to achieve a pivoting mobility under deformation.

The base plate 2 can be formed in one part or in several parts. A one-part design can be seen from FIG. 2, while FIGS. 1 and 5 show a two-part design, a joint then having to be provided between the two parts 2a and 2b, as indicated schematically in FIG. 1. A special embodiment of such a joint 16 can be seen from FIG. 5; it is in turn a hinge joint similar to the design of the hinge joint 14 between end wall 13 and base plate 2 according to FIG. 4.

As a pressure element for the targeted bending of the base plate 2, a hose element 17 is provided in the embodiment of FIG the drainage box 1 is in rigid connection. By increasing the pressure inside the hose element 17, the latter widens and thereby presses on the base plate 2 from above, whereby it deflects downward and experiences the desired deflection.

Instead of the hose element 17, a piston / cylinder unit 18 can be used, for example according to FIG. 2.

The transverse wall 12, which divides the interior of the drainage box 1 into a front and a rear section, to which the collecting basins 10 and 11 are assigned, must be guided over the entire height of the interior of the drainage box 1. When using a hose element 17, which rests sealingly on the top of the base plate 2, the transverse wall 12 can already end at a certain distance from the top of the base plate 2, since the tube element 17, according to FIG. 1, also at the same time supports transverse wall 12 and an opposite, downward extension 19, so that the tube element 17 forms part of the transverse wall 12 in terms of effectiveness.

If a wall that is actually continuous from the top of the base plate 2 to the upper end wall of the drainage box 1 is provided, the transverse wall must be extendable in itself because of the deflection of the base plate 2 under the action of the pressure element 17 or 18. This can be achieved for example by a telescopic design or the provision of a bellows element.

Dabei bedeuten:

P

die auf die Oberseite der Bodenplatte 2 einwirkende Kraft je Längeneinheit gemessen in Querrichtung der Bodenplatte;

L

den Abstand zwischen den beiden einander gegenüber liegenden Stirnwänden 13 des Entwässerungskastens 1 bzw. zwischen den zugehörigen endseitigen Befestigungen der Bodenplatte 2;

V₁

den Unterdruck in der einen Innenkammer des Entwässerungskastens 1;

V₂

den Unterdruck in der anderen Innenkammer des Entwässerungskastens 1;

S₁

den Siebzug im oberen Umlaufsieb 4;

S₂

den Siebzug im Langsieb 6.

The inventive design, namely the deflectability of the floor slat 2 is in fact achieved that the same pressure is always exerted on the paper fleece 7, which is clamped between the screens 4 and 6. This pressure is determined by the size of the vacuum in the two areas of the interior of the drainage box 1 separated from one another by the transverse wall 12 and the size of the tensile forces in the screens 4 and 6. The pressure elements 17 and 18 on the top of the base plate 2 Exerted force, for example in the form of the internal pressure in the hose element 17, always causes a deflection of the base plate 2 The following relationship applies to this deflection:

$\text{D = [4P - L (V₁ + V₂)] / [8 (S₁ + S₂)]}$

Mean:

P

the force acting on the top of the base plate 2 per unit length measured in the transverse direction of the base plate;

L

the distance between the two opposing end walls 13 of the drainage box 1 or between the associated end fastenings of the base plate 2;

V₁

the negative pressure in one inner chamber of the drainage box 1;

V₂

the negative pressure in the other inner chamber of the drainage box 1;

S₁

the wire draw in the upper circulation wire 4;

S₂

the wire in the wire 4.

The equation given above shows that the entire system is in equilibrium, i.e. the pressure on the paper web remains the same even if one of the various components changes, whether intentional or unintentional.

Claims (11)

1. A dewatering unit for Fourdrinier machines for the upwardly directed dewatering of a water-containing paper mat, which is guided on a substantially horizontal endless wire section of the dewatering unit and is guided from there on a further substantially horizontal endless wire section comprising an upper circulating wire guided over guide rollers, which is brought together between the two endless wire sections with a central endless wire section on a downwardly directed dewatering surface of a dewatering box disposed within the upper circulating wire and is capable of being guided past the dewatering surface which is downwardly arched in the running direction of the endless wire, contacting it, characterized in that the bottom plate (2) of the dewatering box (1) which comprises the dewatering surface (3) can be variably bent to change the downwardly directed arching of its dewatering surface (3) and that at least one pressure element (17, 18) is allocated to the upper side of the bottom plate (2) of the dewatering box (1), by means of which the bottom plate (2) can be variably bent and which is supported on a rigid and stationary part of the dewatering box (1) on the other side.
2. A dewatering unit according to claim 1, characterized in that the pressure element consists of a hydraulic or pneumatic piston/cylinder unit (18).
3. A dewatering unit according to claim 1, characterized in that the pressure element consists of a tube element (17) being hydraulically or pneumatically under internal pressure and capable of being expanded by increased pressurizing.
4. A dewatering unit according to at least any of the preceding claims, characterized in that the bottom plate (2) of the dewatering box (1) is disposed swingingly at the two front walls (13) of the dewatering box (1) located transversely to the running direction (8) of the endless wire (6).
5. A dewatering unit according to claim 5, characterized in that a hinged joint (14) is provided at the front walls (13) of the dewatering box (1) between bottom plate (2) and front wall (13) for the swinging arrangement of the bottom plate (2) of the dewatering box (1).
6. A dewatering unit according to claim 6, characterized in that the bottom plate (2) is certainly rigidly allocated to the front walls (13) for the swinging arrangement of the bottom plate (2) at the front walls (13) of the dewatering box (1), however has such a wall thickness in the allocation area (15), which allows a pivoting under deformation.
7. A dewatering unit according to at least any of the preceding claims, characterized in that the bottom plate (2) is designed in one piece and consists of plastic material.
8. A dewatering unit according to at least any of the preceding claims, characterized in that the bottom plate is designed in divided fashion transversely to the running direction (8) of the endless wire in the area of the arrangement of the at least one pressure element (17, 18).
9. A dewatering unit according to at least any of the preceding claims, characterized in that a wall (12) extending transversely to the running direction (8) of the endless wire (7) projects upwardly from the bottom plate (2), to which a collecting basin (10) for the water penetrating through the bottom plate (2) in the running direction (8) of the endless wire (7) before the wall (12) is allocated.
10. A dewatering unit according to claim 9, characterized in that the wall (12) extending transversely is designed longitudinally variably in the height direction.
11. A dewatering unit according to claim 9, characterized in that the lower part of the transversely extending wall (12) is formed by the tube element (1) serving as a pressure element.

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