WO2020193003A1

WO2020193003A1 - Pressure screen, screen element and method for manufacturing a screen element

Info

Publication number: WO2020193003A1
Application number: PCT/EP2020/053864
Authority: WO
Inventors: Werner Brettschneider; Ingo Kauer; Melanie Schädler; Ralf Burger
Original assignee: Voith Patent Gmbh
Priority date: 2019-03-26
Filing date: 2020-02-14
Publication date: 2020-10-01
Also published as: DE102019107693A1

Abstract

The invention relates to a pressure screen for cleaning a fibrous stock suspension (1), comprising a screen element (3) which is of rotationally symmetrical configuration about a screen axis (2) and divides the pressure screen into an inlet chamber (4) and an accepted stock chamber (11). The inlet chamber (4) is connected at one axial end to a suspension inlet (8) and at the opposite axial end to a reject outlet (9), and the accepted stock chamber (11) is connected to an accepted stock outlet (10), and a rotor (5) with rotor vanes (12) is situated in the inlet chamber (4), the rotational axis (13) of which rotor (8) corresponds to the screen axis (2), and which rotor (8) rotates relative to the screen element (3). In order to improve sorting, the screen element (3) is conical.

Description

PRESSURE SORTER, SCREEN ELEMENT AND METHOD OF MANUFACTURING

OF A SCREEN ELEMENT

The invention relates to a pressure sorter for cleaning a pulp suspension with a sieve element which is rotationally symmetrical about a sieve axis and which divides the pressure sorter into an inlet space and an accepts space, the inlet space at one axial end with a suspension inlet and at the opposite axial end with a reject outlet and the accepts space is in connection with an accept drain and there is a rotor with rotor blades in the inlet chamber, the axis of rotation of which corresponds to the sieve axis and which rotates relative to the sieve element.

The invention also relates to a rotationally symmetrical screen element with a large number of profile bars, in which a plurality of ring-shaped bar holders, which run perpendicular to the screen axis and are spaced apart, are provided on the inside or outside with open-edged recesses, the shape of which corresponds essentially to the bar feet of the profile bars and which are slightly larger than the rod feet and in which the profile rods are inserted into the recesses essentially parallel to one another and essentially parallel to the sieve axis, as well as their lowering position.

Pressure sorters are used in the preparation of paper pulp suspensions, specifically to process the pulp suspension in wet screening. For this purpose, such a pressure sorter contains a screen element which is provided with a large number of openings. The fibers contained in the suspension should pass through the openings as accept, while the unwanted solid components are rejected and passed out of the sorter as rejects.

It is also conceivable to use it to separate different fiber components, i.e. the shorter from the longer fibers.

As a rule, round holes or slots are used as sorting openings. In most cases, pressure sorters of the type under consideration here are provided with screen clearers which have clearing surfaces that move past the screen. This prevents clogging of the sieve openings in a manner known per se. From WO 98/53135 a sieve clearer has become known which is provided with wing elements for clearing the sieve. These wing elements have a hydrodynamic profile which extends over the entire length of the sieve element, a sieve basket. Due to the relative movement to the surrounding suspension, the wing element emits a pressure impulse at the front and a suction impulse behind it on the sieve to be cleared. As a result, part of the suspension that was rejected by the sieve or has already passed the sieve as accepted material is sucked back, whereby the sieve openings are kept or cleared.

In contrast to this, the rotor blades are formed by elevations, for example in DE-OS 3701669.

A well-known example of the use of rotationally symmetrical, previously cylindrical screen elements, which can be produced in particular by the method also claimed, is the sorting of pulp suspensions, as is carried out in pressure sorters in the paper-making industry.

The fibers contained in the suspension should pass through the sieve element, while the unwanted solid constituents are rejected at the gap and passed out of the sieve device again.

Because the openings have an essentially elongated shape, that is, slits or gaps, fibrous, elongated particles are more easily let through than the cubic, undesired impurities, even if both types should be present in a similar order of magnitude.

With such a sorting technology, a very good elimination effect of non-fibrous impurities from fibrous material suspensions is therefore possible.

It is also conceivable to use it to separate different fiber components, so-called fiber fractionation into long and short fiber fractions.

DE 10 2006 007 660 A1 shows a possible method of producing such strainer baskets, in which the profile bars are clamped in by plastic deformation of the c-shaped retaining rings provided with recesses for the bars. For this

Particularly suitable profile bars are used for such manufacturing processes. With the help of this process it was possible to make the production considerably cheaper. The This method is used for sieve baskets in which the rods are inserted on the inner edge of the retaining rings. Such an arrangement of the rods is chosen if the suspension is to pass through the slots from the inside to the outside (centrifugal operation). To reshape the retaining rings, bending forces are introduced from the outside at the joint ends, with the joint ends being supported on the inside on support rollers.

DE 44 35 538 A1 shows an alternative method for producing such baskets. This method is used with strainer baskets where the rods are inserted on the outer edge of the retaining rings. Such an arrangement of the rods is chosen if the suspension is to pass the slots from the outside to the inside (centripetal operation).

To fix the profile rods, the radius of curvature of the retaining rings is increased.

In contrast to this, EP 31 43 198 A1 describes a sieve device in which the retaining rings are each formed by a rod holder package made up of several rod holders. When the rod holder packages are bent into rings, the profile rods are clamped in the recesses due to the different position of the neutral fibers of the rod holders of a rod holder package.

It is generally important that the dimensions of the sieve openings are maintained with very low tolerances. In order to keep them free from clogging, scrapers are usually required, which are moved closer to the screen surface and which generate hydraulic impulses. Screening devices for use in pressure sorters must therefore be manufactured very precisely and withstand high loads.

The object of the invention is to improve the sorting.

According to the invention, the object was achieved in that the sieve element is conical.

The conical shape provides additional design options in a simple manner with regard to the annular gap between the rotor and the screen element on the one hand and the screen openings on the other hand. Because of the thickening occurring in the annular gap towards the reject outlet, it can be advantageous that the width of the annular gap between the rotor and the sieve element decreases continuously from the suspension inlet to the reject outlet. Accordingly, the wider sieve end of the conical sieve element is then located in the area of the inlet.

However, because of the increasing number of contaminants in the annular gap in the direction of the reject outlet and the associated risk of clogging and / or increased wear, it can be advantageous if the width of the annular gap between the rotor and the sieve element increases continuously from the suspension inlet to the reject outlet. For this purpose, the wider sieve end of the conical sieve element is located in the area of the reject outlet.

Rotors that are designed as cylindrical drums are easy to manufacture. The change in the annular gap then takes place exclusively via the conical screen element.

If the change in width of the annular gap is to be supported by the rotor, it must be designed as a conical drum.

To adapt to a special design of the rotor and / or its rotor blades and / or the sieve openings, it can also be advantageous if the width of the annular gap between the rotor and the sieve element remains constant from the suspension inlet to the reject outlet. In this case, the rotor would have to be designed as a conical drum, the wider end of the rotor being at the wider end of the sieve element.

For the purpose of simple construction, the rotor blades should have the same shape and / or the same radial extent.

The axis of rotation should advantageously be inclined or perpendicular to the machine plane.

Advantages with regard to the design and function of the pressure sorter also result when the rotor is located within the screen element. The suspension inlet should be arranged above the reject outlet.

To achieve the advantages mentioned, it is sufficient if the inclination of the conical screen element jacket to the screen axis is less than 2 °, preferably between 0.1 and 1 °, and / or the diameter of the conical screen element differs by a maximum of 10 mm.

This slight inclination in turn has a positive effect on the production of the screen element.

To influence the throughput and / or sorting effect along the annular gap between the rotor and the sieve element, it can be advantageous if the open area and / or the size of the sieve openings of the sieve element increases slightly in the direction of the widening conical end of the sieve element.

Also with regard to the rotationally symmetrical sieve element with a multitude of profile bars, in which several ring-shaped bar holders running perpendicular to the sieve axis and spaced apart from one another are provided with open-edged recesses on the inside or outside, the shape of which corresponds essentially to the bar feet of the profile bars and which are slightly larger than the rod feet and in which the profile rods are inserted into the recesses essentially parallel to each other and essentially parallel to the sieve axis, the essence of the invention is that the sieve element is conical.

In order to realize the advantages and possibilities already described, only a very slight conicity is sufficient, which facilitates simple production of the sieve element. This also has the consequence that the profile bars deviate only slightly from their parallelism with one another and with respect to the sieve axis.

It has been found that for this purpose the inclination of the profile rods to the screen axis should be less than 2 °, in particular less than 1 ° and / or the diameter of the conical screen element should differ by a maximum of 10 mm.

In order to do justice to the inclination of the profile bars, the bar holders should be designed differently. To compensate for the conicity, the rod holders can differ from one another in terms of inner or outer diameter or the depth of their recesses. In addition, with a constant cross-section of the profile bars, via the conicity of the screen element, the distance between the profile bars of the screen element increases slightly in the direction of the widening conical end of the screen element. This can be used to influence the throughput and / or the sorting effect and reduce wear.

Such a rotationally symmetrical sieve element is advantageously produced in that a permanent form fit is generated between the profile bars and the recesses via forces acting radially from the outside.

These radial forces lead to a plastic deformation of the rod holders in the area of the recess and, via the narrowing of the recesses, ultimately to the clamping of the profile bars in the same.

If the recesses are only present on the inside of the rod holder, the radial force is applied directly to the rod holder.

In the other case, where the recesses are only present on the outside of the rod holders, the radial force is exerted on the profile rods and, via these, indirectly on the rod holders.

To protect the rod holder, the inside of the same should not be exposed to any supporting or bending forces during the radial application of force.

Manufacture is particularly simple if the radial force is applied via a plurality of punches acting radially from the outside.

These stamps should preferably be distributed equally spaced around the circumference of the screen cylinder. Furthermore, the pressing surface of the punch pointing in the pressing direction, ie towards the center axis of the sieve device, should be concave, this pressing surface advantageously being formed perpendicular to the cylinder axis by a circular segment, the radius of which corresponds to the outer radius of the finished, cylindrical sieving device. This makes it possible to distribute the forces increasingly evenly to the radial outside of the rod holder during pressing. In addition to a uniform change in shape, this protects the rod holder. In the interests of precise guidance, the punches should be guided in a radially movable manner and / or axially fixed to the cylinder axis at least during the radial action of force.

The invention is to be explained in more detail below using several exemplary embodiments.

In the attached drawing show:

FIGS. 1 a + b: a schematic perspective view of various rotationally symmetrical screen elements 3;

FIGS. 2a + b: a schematic cross section through the screen elements 3 according to FIGS. 1 a + b with punches 15;

FIGS. 3a + b: the recess 14 with the profile bar 6 before and after the radial action of force;

FIG. 4: a schematic longitudinal section through a pressure sorter and

Figures 5a + b + c: an extremely schematic longitudinal section through different

Pressure sorter.

In FIG. 4 one recognizes a pressure sorter according to the invention with a sieve element 3 in the form of an essentially cylindrical sieve basket with a very small conicity, which cannot be seen here, and a vertical sieve axis 2.

This sieve element 3 divides the interior of the pressure sorter into an inlet space 4 and an accepted material space 11.

The fiber suspension 1 is fed into the feed space 4 via a suspension feed 8.

As a result of the pressure gradient present between the suspension inlet 8 drawn above and the reject outlet 9 of the inlet chamber 4 located below, however, a transport flow is generated.

On the path of this transport flow, a large part of the pulp suspension 1 is diverted as intended through the sieve element 3 as accepted material into the accepted material space 11 and from there discharged via the accepted material outlet 10. At the same time, at least a large part of the fibers contained in the fiber suspension 1 also pass into the accepts space 11.

The part of the pulp suspension 1 rejected by the sieve element 3 is conveyed as reject via the reject outlet 9 from the inlet chamber 4. If necessary, the suspension inlet 8 can also be located at the lower end and the reject outlet 9 at the upper end of the screen basket.

In order to prevent the openings of the sieve element 3 from being clogged, there is a sieve clearer which is known per se and which moves relative to the sieve element 3.

This screen scraper is formed by a rotor 5 rotating in the screen element 3 with rotor blades 12 attached thereto. The rotor 5 here has the shape of a cylindrical drum, the axis of rotation 13 coinciding with the sieve axis 2.

All rotor blades 12 here have the same shape and the same radial extent, which leads to a uniform effect on the pulp suspension 1 and the sieve element 3.

In FIG. 4, the rotor blades 12 are designed as elevations on the rotor 5, which accordingly have no radial spacing from the rotor 5. The cross-sectional area of the rotor blades running in the direction of rotation of the rotor 5 is designed as a rectangle.

The rotor blades 12 can, however, also be configured differently, for example with an airfoil profile.

Via the slightly conical sieve element 3, the open area and / or the size of the sieve openings of the sieve element 3 can be enlarged in the direction of the widening conical end of the sieve element 3.

In addition, the slightly conical sieve element 3 can also be used to change the course of the annular gap between the rotor 5 and the sieve element 3.

This is to be shown in FIGS. 5a-c as an example and with a greatly exaggerated conicity.

In FIG. 5 a, the rotor 5 is designed as a cylindrical drum, so that the width of the annular gap between the rotor 5 and the sieve element 3 increases exclusively in accordance with the conical widening of the sieve element 3.

In contrast to this, the rotor 5 in FIGS. 5b and 5c is designed as an essentially cylindrical drum with a slight conicity.

According to Figure 5b, the conical screen element 3 and the conical rotor 5 widen in the same axial direction, so that the width of the annular gap between rotor 5 and Sieve element 3 remains constant in the axial direction, ie from the suspension inlet 8 to the reject outlet 9. In this case, the conicity of the sieve element 3 is used for the described influencing of the open area or the size of the sieve openings, without this being associated with a widening of the annular gap.

Alternatively, in FIG. 5c, the conical screen element 3 and the conical rotor 5 widen in opposite, axial directions, so that the widening of the annular gap is further increased compared to the embodiment according to FIG. 5a.

The conicity of the sieve element 3 is very small, which has a simplifying effect on its clearance position. The inclination of the lateral surface of the sieve element 3 to the sieve axis 2 is less than 1 °.

As a rule, with the usual expansions of the conical screen element 3, the diameter widens by a maximum of 10 mm.

If the width of the annular gap between the rotor 5 and the sieve element 3 decreases continuously from the suspension inlet 8 to the reject outlet 9, this can be advantageous because of the thickening of the fiber suspension 1 along the annular gap in the direction of the reject outlet 9.

However, if it is to be expected that contaminants will increasingly accumulate along the annular gap in the direction of reject outlet 9, which can lead to increased wear and / or clogging in this area, it is advantageous if the width of the annular gap between rotor 5 and the sieve element 3 from the suspension inlet 8 to the reject outlet 9 increases continuously.

The rotationally symmetrical, here essentially cylindrical but slightly conical screen elements 3 preferably consist of essentially parallel, i.e. likewise slightly conical to the cylinder and sieve axis 2 running profile bars 6, which are held by a plurality of axially spaced apart and perpendicular to the sieve axis 2 bar holders 7.

The rod holders 7 are produced here as one-piece rings, for example by means of laser cutting, the diameter being slightly larger than that of the final screen basket. This is the basis for a high degree of dimensional accuracy of the sieve element 3. In Figure 1a and 2a, the bar holder 7 on the inside and in Figure 1b and 2b on the outside a plurality of evenly distributed recesses 14 for the profile bars 6. The recesses 14 offer sufficient play according to Figure 3a, so that the profile bars 6 can easily be pushed axially through this.

The sieve openings of the sieve basket, i.e. of the screen element 3 are formed by the slots in adjacent profile bars 6. In practice, such slots often have a width between 0.05 and 2 mm.

In order to fix the profile bars 6 in the recesses 14, a permanent form fit between the profile bars 6 and the recesses 14 is generated via forces F acting radially from the outside.

If the recesses 14, as in FIG. 2a, are on the inside of the rod holders 7, then the radial force acts directly on the rod holders 7.

FIG. 2 b shows the other case in which the recesses 14 are present on the outside of the rod holders 7 and the radial force is exerted on the profile rods 6 and thus only indirectly on the rod holders 7.

In both cases, since the inside of the rod holders 7 is not exposed to any supporting or bending forces during the radial force, there is a reduction in the diameter of the rod holder 7, albeit a small one, and a plastic deformation of the rod holder 7 in the area of the recesses 14, in the consequence of which the space between the profile bar 6 and the bar holder 7, as shown in FIG. 3b, is closed.

Because of the profiling of the profile bars 6 and the complementary shape, a strong clamping of the bar feet in the respective recess 14 is achieved.

The radial force is implemented according to FIGS. 2a + b via several punches 15, which are arranged radially evenly distributed over the cylinder circumference and which are directed radially from the outside onto the bar holder 7 or profile bars 6 and in particular onto the sieve axis 2 of the sieve basket. For this purpose, the pressing surface of all punches 15 pointing in the pressing direction is each formed by a segment of a circle, its radius corresponds to the outer radius of the screening device after the pressing process. Since the outer radius of the screening device formed by the rod holders 7 or profile rods 6 is slightly larger before the pressing process than afterwards, there is a little play at the beginning of the pressing process between the rod holders 7 or profile rods 6 and the pressing surface in the middle part of the punch 15. This play can be accepted at the beginning of pressing and the associated lower pressing forces and decreases as the pressing progresses.

This deformation takes place very gently and evenly, so that there is no overstressing of the rod holders 7.

During the radial application of force, the punches 15 are guided axially and radially in guide grooves.

Alternatively, the rod holders 7 can also be composed of several partial rod holders, which have different heights in the radial direction R, so that their neutral fibers differ from one another.

To achieve the desired effect, a very small conicity of the sieve element 3 is sufficient. Therefore, the inclination of the profile bars 6 to the sieve axis 2 is less than 1 ° or, in general, the expansion of the diameter of the conical sieve element 3 is a maximum of 10 mm.

Nevertheless, the rod holders 7 are designed differently to compensate for the conicity. In addition to varying the inside and / or outside diameter of the rod holders 7, changing the radial depth of the recesses 14 is also possible.

Because of the very small deviation from the cylindrical shape, the end rings can be attached to the two ends of the sieve element 3 in a plane-parallel-cylindrical manner.

Since the profile bars 6 have a constant cross-section in the interests of simple manufacture, the distance between the profile bars 6 of the sieve element 3 increases slightly in the direction of the widening conical end of the sieve element 3. This expansion is usually not critical for the sorting. On the contrary, it can be used consciously to influence throughput and sorting effect along the annular gap. In most cases, larger sieve openings in the direction of the reject outlet 9 will be preferred.

Claims

1. Pressure sorter for cleaning a pulp suspension (1) with a sieve element (3) which is rotationally symmetrical about a sieve axis (2) and divides the pressure sorter into an inlet space (4) and an accepts space (11), the inlet space (4) at one axial end with a suspension inlet (8) and at the opposite axial end with a reject outlet (9) and the accepts space (11) is connected to an accepts outlet (10) and a rotor (5) with rotor blades (12) is located in the inlet space (4) ) whose axis of rotation (13) corresponds to the sieve axis (2) and which rotates relative to the sieve element (3), characterized in that the sieve element (3) is conical.

2. Pressure sorter according to claim 1, characterized in that the width of the

Annular gap between the rotor (5) and the sieve element (3) from

Suspension inlet (8) to reject outlet (9) decreases continuously.

3. Pressure sorter according to claim 1, characterized in that the width of the

Annular gap between the rotor (5) and the sieve element (3) from

Suspension feed (8) to reject outlet (9) increases continuously.

4. Pressure sorter according to claim 1, characterized in that the width of the

Annular gap between the rotor (5) and the sieve element (3) from

Suspension inlet (8) to reject outlet (9) remains constant.

5. Pressure sorter according to one of claims 1 to 3, characterized in that the rotor (5) is designed as a cylindrical drum.

6. Pressure sorter according to one of claims 1 to 4, characterized in that the rotor (5) is designed as a conical drum.

7. Pressure sorter according to one of the preceding claims, characterized in that the rotor blades (12) have the same shape and / or the same radial extent.

8. Pressure sorter according to one of the preceding claims, characterized

characterized in that the axis of rotation (13) is perpendicular.

9. Pressure sorter according to one of the preceding claims, characterized

characterized in that the rotor (5) is located within the sieve element (3).

10. Pressure sorter according to one of the preceding claims, characterized in that the suspension inlet (8) is arranged above the reject outlet (9).

11.Drucksortierer according to one of the preceding claims, characterized in that the inclination of the sieve element (3) to the sieve axis (2) is less than 1 °.

12. Pressure sorter according to one of the preceding claims, characterized in that the diameter of the conical screen element (3) differs by a maximum of 10 mm.

13. Pressure sorter according to one of the preceding claims, characterized in that the open area and / or the size of the sieve openings of the sieve element (3) increases slightly in the direction of the widening conical end of the sieve element (3).

14. Rotationally symmetrical sieve element (3) with a plurality of profile bars (6), in which several annular bar holders (7) which are spaced apart from one another and run perpendicular to the sieve axis (2) are provided with open-edged recesses (14) on the inside or outside, whose shape corresponds essentially to the rod feet of the profile rods (6) and which are slightly larger than the rod feet and in which the profile rods (6) are inserted into the recesses (14) essentially parallel to one another and essentially parallel to the sieve axis (2) , in particular for a pressure sorter according to one of the preceding claims, characterized in that the screen element (3) is conical.

15. Rotationally symmetrical sieve element (3) according to claim 14, characterized in that the inclination of the profile bars (6) to the sieve axis (2) is less than 1 °.

16. Rotationally symmetrical sieve element (3) according to claim 14 or 15, characterized in that the rod holders (7) differ from one another.

17. Rotationally symmetrical sieve element (3) according to one of claims 14 to 16, characterized in that the distance between the profile bars (6) of the sieve element (3) increases slightly in the direction of the widening conical end of the sieve element (3).

18. A method for producing a rotationally symmetrical sieve element (3) according to one of claims 14 to 17, characterized in that a permanent form fit between the profile rods (6) and the recesses (14) is generated via forces acting radially from the outside.

19. The method according to claim 18, characterized in that the inside of the rod holder (7) is not exposed to any supporting or bending forces during the radial force.

20. The method according to claim 18 or 19, characterized in that the radial force is applied via a plurality of rams (15) acting radially from the outside.

21. The method according to any one of claims 18 to 20, characterized in that the recesses (14) are only present on the inside of the rod holder (7) and the radial force is exerted on the rod holder (7).

22. The method according to any one of claims 18 to 20, characterized in that the recesses (14) are only present on the outside of the rod holder (7) and the radial force is applied to the profile rods (6).