WO2013072174A1

WO2013072174A1 - Screen

Info

Publication number: WO2013072174A1
Application number: PCT/EP2012/071140
Authority: WO
Inventors: Werner Brettschneider
Original assignee: Voith Patent Gmbh
Priority date: 2011-11-16
Filing date: 2012-10-25
Publication date: 2013-05-23
Also published as: DE102011086428A1; CN103930617B; ES2751461T3; EP2780505B1; CN103930617A; DE202011108856U1; PT2780505T; EP2780505A1

Abstract

The invention relates to a screen (2) having a plurality of slit-shaped screen openings (3) and intended for treating a suspension (1). The sorting effect and/or the throughput are to be improved, while guaranteeing the required screen stability, in that at least one section of the screen (2) comprising a plurality of slit-shaped screen openings (3) is integrally formed, has an open screen area between 12 and 30%, and has a profiled screen front side (4).

Description

scree

The invention relates to a sieve for treating a suspension having a multiplicity of slot-shaped sieve openings.

The invention also relates to a method for producing a screen with slot-shaped screen openings. Such screens are used for example for wet screening of pulp suspensions to remove impurities present therein. As a rule, they are rigid and differ from flexible endless screens used in screen presses and paper machines.

The characteristic of such a sieve results essentially from the size, shape and number of sieve openings therein. These are usually kept smaller than the auszusiebenden substances.

Are used such sieves with advantage z. As in pulpers, Sekundärstofflösern and sorters for the treatment of paper fiber suspensions, where they have the task of retaining impurities.

Of course, one endeavors to enable the highest possible throughput in such screens, d. H. The largest possible amount of non-rejected substances should pass through the openings. This can be promoted by having as many openings as possible. Taken as a whole, efforts are made to have the largest possible open screen area, based on the entire surface of the screen

Screen element.

Another requirement is a relatively high resistance to hydraulic pressure. Such strainers are used in a production plant in which it too Once disturbances occur, which leads to different and considerable pressure load of the screens. Since a blockage can not always be ruled out, it is possible for high pressures to act on the surface of such screens and, for the correspondingly large areas, also high forces. These increased forces must be able to be absorbed by the sieve without damaging it.

The object of the invention is therefore to improve the sorting effect and / or throughput while ensuring the required screen stability.

According to the invention, this object is achieved in that at least one, a plurality of slot-shaped screen openings comprehensive section of the screen in one piece

is formed, has an open screen area between 12 and 33% and has a profiled Siebvorderseite.

The one-piece design because of the lack of dividing lines within the respective section of the screen surface ensures the required strength of the section or of the screen at all. This high strength in turn allows the increase of the open screen area and thus the throughput.

Typically, such slots are formed with and between parallel screen bars. On the one hand, this is relatively expensive to manufacture and, on the other hand, limits the achievable open screen area while ensuring high strength.

The profiled screen front creates turbulence in the suspension and thus significantly improves the sorting effect and the throughput, which has a positive effect on the

Energy requirement.

As Siebvorderseite here the side of the sieve is considered, from which the suspension flows through the sieve. For most applications, it has proven to be advantageous if the open screen area of the section is between 15 and 25%.

Furthermore, the positive effects of the invention can then be used extensively if the entire sieve, in particular the entire perforated sieve surface is integrally formed.

With regard to sufficient turbulence formation on the front side of the screen, it is advantageous if the profile depth of the front side of the screen is between 0.5 and 3 mm,

preferably between 0.7 and 1.2 mm.

To achieve a high density of screen openings, it is advantageous if at least a substantial part of, preferably all slot-shaped screen openings are arranged parallel to each other. In order to achieve a high strength of the screen despite the large open screen area, the thickness of the screen between 2 and 8 mm, preferably between 4 and 6 mm and / or the web width between adjacent slot-shaped screen openings should be greater than 0.3 mm, and preferably between 1 and 5 mm. Depending on the type of treatment and / or the nature of the suspension and / or the contaminants, it may be advantageous if the cross section of the slot-shaped screen openings lying perpendicular to the flow direction has at least one round section or only straight sections. The throughput can also be increased by the fact that at least a portion of the slot-shaped screen openings at least a section opens into a survey of the profile of the Siebvorderseite and / or at least in part of the slot-shaped screen openings, the height of the mouth on the Siebvorderseite in the longitudinal direction of the slot changed. This not only creates further turbulence in the suspension but also improves the absorption capacity of the mouths. Depending on the application, the screen may be flat or designed as a cylinder, wherein the slot-shaped screen openings preferably approximately parallel to

Cylinder axis run.

Because of the special requirements, in particular with regard to stability and wear, the use of the invention is particularly suitable for the treatment of one, for the production of a paper, board, tissue or another

Fiber web suitable pulp suspension. In this case, at least the one-piece section of the screen, preferably the entire screen should be made of metal. Furthermore, the slot-shaped screen openings should have a width between 0.1 and 1.0 mm, preferably between 0.1 and 0.45 mm.

Cost advantages in the manufacture of the screen arise when the slot-shaped screen openings of at least one section and preferably also the profile of the front side of the screens are produced by means of water jet cutting. For this purpose, the thickness of the screen should be less than 20 mm.

If in the production of sieve openings, the Siebvorderseite a

Water jet treatment is exposed, then results in the production of the slot-shaped screen openings and an irregular profiling of the

Mouth area, which can already be enough for many cases.

In many applications, it is also advantageous that expand the screen openings in the flow direction of the suspension to be screened, preferably conically or trumpet-like widen, which in water jet cutting of the

Siebrückseite ago can be easily realized. In this case, the angle between a straight line through the sieve front-side beginning and the siebrückseitige end of the wall of the sieve opening and the flow direction between 1 and 8 °, preferably between 3 and 5 °. The expansion of the sieve opening counteracts blockage, but is so small that the strength of the sieve is not significantly affected.

The invention will be explained in more detail below with reference to several exemplary embodiments.

In the attached drawing shows:

FIG. 1 shows a schematic cross section through a pressure sorter;

FIG. 2 shows a schematic cross section through a pulper;

Figure 3 and 4: a partial cross section through different screens 2 and

Figure 5 a-d: screen openings with different cross-section.

FIG. 1 shows a pressure sorter according to the invention with a one-piece, metallic screen 2, here in the form of a cylindrical screen basket with a vertical cylinder axis 10, which divides the interior of the pressure sorter into an inlet space 8 and an accepts space 9.

In the inlet space 8 1 1, the pulp suspension 1 is fed via a suspension feed.

In the pressure sorter used here, the pulp suspension 1 receives an angular momentum which causes it to move circumferentially. In addition to this, due to the applied pressure gradient between the above drawn

Suspension feed 1 1 and the underlying Rejektauslauf 12 of the inlet chamber 8 generates a transport flow.

On the way of this transport flow, a large part of the

Pulp suspension 1 as intended derived by the sieve 2 as accepts 17 in the accepts space 9 and discharged from there via the accepts drain 13. At the same time, at least a large part of the fibers contained in the pulp suspension 1 also passes into the accept chamber 9. The rejected from the screen 2 part of the pulp suspension 1 is conveyed as a reject 18 via the Rejektauslauf 12 from the feed chamber 8. In order to prevent the openings of the screen 2 are clogged, a known Siebräumer is used, which moves relative to the wire 2.

By way of example, this sieve scraper is formed by a rotor 6 rotating in the screen 2 with rotor blades 15 attached thereto. In this case, the rotor 6 has the shape of a cylindrical drum, wherein the axis of rotation 7 coincides with the cylinder axis 10.

All rotor blades 15 in this case have the same shape, which leads to a uniform effect on the pulp suspension 1 and the wire 2.

In addition, the rotor blades 15 are arranged distributed over a plurality of perpendicular to the axis of rotation 7 extending circumferential planes of the rotor 6.

In Figure 1, the rotor blades 15 are exemplified as elevations on the rotor 6 is formed.

In this case, the sieve surface comprises a multiplicity of sieve openings 3 arranged as uniformly as possible with the same minimum cross-sectional area in the direction of flow 5 to ensure the same sorting effect. For a high throughput, the open screen area of the screen 2 is between 15 and 25%. In this case, the sum of the smallest flow cross-sections through the sieve 2 relative to the respective perforated sieve surface is considered as open sieve surface.

In contrast, a pulper is shown in Figure 2, in the container 16, a suspension 1 of pulp and water is formed. For this purpose, the suspension is 1 from a front of a sieve 2 at the bottom of the container 16 rotating rotor 6 mixed. The rotor 6 generates in front of the screen 2 a rotational flow, which improves the sorting effect and the passage.

The screen 2, which is an example here, is flowed through by the pulp suspension 1 from the front of the sieve 4. Larger impurities are thereby

retained and can be cleared away from the rotor 6 on the Siebvorderseite 4. After flowing through the sieve 2, the suspension 1 can be collected and removed under the sieve 2.

As can be seen in FIG. 3, the longest extent of the slots in the sieve 2 is approximately perpendicular to the rotational flow 14 of the suspension 1 generated by the rotor 6 in front of the sieve 2.

While the thickness of the screen 2 is between 4 and 6 mm, the

slot-shaped screen openings 3 a width of 0.1 to 0.45 mm and a length between 10 and 100 mm.

To increase the throughput, the screen front side 4 of the screen 2

according to Figures 3 and 4, an irregular micro-profile whose depth is in the range between 0.5 and 1, 2 mm. This profile has the consequence that the height of the mouth on the Siebvorderseite 4 changed in the longitudinal direction of the slot and ensures microturbulence in the suspension. 1

In addition to this micro-profile, the screen 2, as shown in Figure 4, or Makroprofile in the form of grooves o.ä. having a tread depth between 1, 2 and 3 mm or more. In this case, the screen openings 3 on the Siebvorderseite 4th partially or wholly in the sinks or even in the surveys of the macro-profile. This variety of mouth design also extends the sorting characteristics of the screen openings 3 and also has more turbulence in the suspension 1 result.

As can be seen in FIGS. 5 a-d, all adjacent screen openings 3 on the long sides of the slots have the same distance from one another, which ensures effective utilization of the screen surface with high stability.

In this case, the screen openings 3 are arranged in parallel rows, wherein the web width between the, on the long sides adjacent slot-shaped screen openings 3 is approximately between 1 and 5 mm.

FIGS. 5a-d show possibilities of slit design of the screen openings 3. In Figure 5a, the slots are formed by only a single straight section.

In contrast, the slots in Figure 5b each have two straight

Sections, wherein the sections form an obtuse angle. In Figure 5d, these obtuse-angled slots are arranged offset from each other.

The slots in FIG. 5c are formed exclusively by round sections.

The production of the screen openings 3 of the screen 2 by means of

Waterjet cutting.

When water jet cutting, the material to be processed by a

High-pressure water jet separated, wherein to increase the cutting power of the water, a cutting agent, a so-called abrasive, is added.

The water jet cutting allows the introduction of narrow slits even in such a thick, metallic screens 2. As a result, a large open screen surface generated and also counted because of the one-piece with a high strength of the screen 2 become.

Furthermore, in a water-jet treatment of Siebvorderseite 4 micro- but also macro profiles can be generated on this, which the

Manufacturing process further simplified.

A conical or trumpet-shaped widening of the screen openings 3 in the flow direction 5, as shown in Figure 4, can be with the

Produce waterjet cutting from the back of the screen without problems. In this case, the angle 19 between a straight line through the sieve front-side beginning and the siebrückseitige end of the wall of the sieve opening 3 and the flow direction 5 is between 3 and 5 °.

Claims

Claims 1. Sieve (2) for treating a suspension (1) having a plurality of

slit-shaped screen openings (3), characterized in that at least one, a plurality of slot-shaped screen openings (3) comprehensive section of the screen (2) is integrally formed, has an open screen area between 12 and 33% and has a profiled screen front side (4).

2. Screen (2) according to claim 1, characterized in that the open screen area of the section is between 15 and 25%.

3. sieve (2) according to claim 1 or 2, characterized in that the entire sieve (2), in particular the entire perforated sieve surface is integrally formed.

4. sieve (2) according to any one of the preceding claims, characterized in that the thickness of the screen (2) is smaller than 20 mm and preferably between 2 and 8 mm.

5. sieve (2) according to any one of the preceding claims, characterized in that the profile depth of the Siebvorderseite (4) is smaller than 3 mm and preferably between 0.7 and 1, 2 mm.

6. sieve (2) according to any one of the preceding claims, characterized in that at least a substantial part of, preferably all slot-shaped screen openings (3) are arranged parallel to each other.

7. sieve (2) according to claim 6, characterized in that the web width between adjacent, slot-shaped screen openings (3) is greater than 0.3 mm and preferably between 1 and 5 mm.

8. Screen (2) according to one of the preceding claims, characterized in that the slot-shaped screen openings (3) have a width between 0.1 and 1, preferably between 0.1 and 0.45 mm.

9. sieve (2) according to one of the preceding claims, characterized in that the perpendicular to the flow direction (5) lying cross-section of the slot-shaped screen openings (3) has at least one round section.

10. sieve (2) according to one of claims 1 to 9, characterized in that the perpendicular to the flow direction (5) lying cross-section of the slot-shaped screen openings (3) has only straight sections.

1 1. Sieve (2) according to one of the preceding claims, characterized in that at least at a part of the slot-shaped screen openings (3) at least a portion in a survey of the profile of the Siebvorderseite (4) opens.

12. sieve (2) according to any one of the preceding claims, characterized in that at least in part of the slot-shaped screen openings (3), the height of the mouth on the Siebvorderseite (4) changed in the longitudinal direction of the slot.

13. sieve (2) according to any one of the preceding claims, characterized in that the sieve openings (3) in the flow direction (5) expand, in particular conically or trumpet-like widening, wherein the angle (19) between a straight line through the sieve front side and the back end of the Wall of the sieve opening (3) and the flow direction (5) between 1 and 8 °, preferably between 3 and 5 °.

14. sieve (2) according to any one of the preceding claims, characterized in that the sieve (2) is flat.

15.Sieb (2) according to one of claims 1 to 13, characterized in that the

Screen (2) is designed as a cylinder and the slot-shaped screen openings (3) preferably approximately parallel to the cylinder axis (10).

16.Sieb (2) according to any one of the preceding claims for the treatment of a, for the production of a paper, board, tissue or another fibrous web suitable pulp suspension (1), characterized in that at least the one-piece portion of the sieve (2), Preferably, the entire sieve (2) consists of metal.

17.Verfahren for producing a screen (2) with slot-shaped screen openings (3), in particular according to one of the preceding claims, characterized

in that the slot-shaped screen openings (3) of at least one section and preferably also the profile of the screen front side (4) are produced by means of water jet cutting.