Profiled bar for a screen basket for fibre processing

Abstract

The invention relates to a screening device, to a screen basket and to profiled bars for a screen basket for wet screening fibrous suspensions. The screen basket has slots formed by parallel profiled bars. The accepted part of the fibrous suspension passes through the slots during the wet screening. The cross section of the profiled bars has an elongate profile. The profile, which is elongate in cross section, is designed with a rear end region for fastening in a screen basket and with a V-shaped profiled-head cross section as a front end region with a profiled-head profile which is raised on one side. The cross section has a first planar lateral boundary surface on the raised side and a second planar lateral boundary surface for forming the V-shaped profiled-head-shape cross section. The first lateral boundary surface encloses an angle of inclination α with respect to a profile main axis of the profiled bar, and the second boundary surface encloses an angle of inclination β with respect to the profile main axis, the angle α being greater than the angle β.

Description

[0001] Profile bar for a screen basket for fiber processing

[0002] The invention relates to a profile bar for a screen basket and to a screen basket comprising such profile bars, and to the use of such a screen basket. Such screen baskets are used in screening devices for wet screening, in particular of fibrous suspensions. Sorting slots are formed by the axially aligned profile bars of the screen basket. The sorting slots are each formed by two adjacently arranged profile bars. The profile bar has an elongated cross-section with two opposite end regions, a profile head and a profile foot. The profile heads of the profile bars form the screening surface. The profile feet of the profile bars are fixed in at least one support element of the screen basket. The arrangement and cross-sectional shape of the profile bars influence the geometry of the slots and thus also the screening behavior of a screen basket.During wet screening, a part of the fiber suspension known as accept or good material passes through the sorting slots.

[0003] DE 39 27 748 discloses a screen basket and a profile bar, wherein the profile bar has a profile head with a V-shaped cross-section. A first lateral boundary surface on a raised side of the profile head has a negative angle of inclination α to a profile center plane, and a second boundary surface has a positive angle of inclination β to the profile center plane. The profile center plane extends from the profile head to the profile base within the profile bar, and the angle α is greater than the angle β.

[0004] An important application for such baskets formed from profile bars is in screening devices for sorting fiber suspensions. The fibers contained in the suspension are designed to pass through the screening device, while the undesired solid components are rejected at the gap and guided out of a special opening in the pressure screen. Because the openings are elongated, i.e., slits or gaps, fibrous particles are more easily passed through than flat particles, even if both types are of a similar size. This type of screening technology enables a very effective separation of non-fibrous contaminants from fiber suspensions. However, a prerequisite is a high degree of precision in the slot shape of the entire screening device. Another important application is the separation of different fibers, particularly fractionation, e.g.due to fiber thickness, fiber length or flexibility.

[0005] From published patent application DE 33 27 422 A1, screens or screen baskets are known in which the sorting slots are formed by parallel, identical profiles connected by transverse retaining ribs. The profile bars have a triangular cross-section. The profile bars are arranged such that the surfaces of the profile bars exposed to the flow during operation of the screening device have an inclined contour and a separation edge behind them. This deflects the passing suspension flow, diverting the suspension flow from the sorting slot, thus creating vortices that promote the clearing of the sorting slots and the passage of the fibers through the screen.

[0006] EP 1 954 874 B1 discloses a screen cylinder with screen bars. This screen cylinder also features screen bars with a radially inward-facing triangular profile relative to the circumferential radius of the screen basket. A 90° angle is arranged relative to the tangent of the screen basket, and the angle of the thus formed triangle of the profile bar, which faces the flow, is in the range of 45 to 135°. These profile bars with inclined, flow-on triangular profiles provide steps for creating downstream turbulence zones. A curved acceptance channel adjoins the turbulence zone.

[0007] DE 10 2010 030 084 A1 discloses a screening device for wet screening fiber. The screen basket comprises profile bars to form screening slots. The profile bars are curved, creating a wide flow channel that widens out after the profile head and tapers toward the profile base of the profile bar. In almost all cases, the process described here uses a scraper, also known as a rotor, that moves closely past one side of the screen.

[0008] The object of the invention is to provide a profile bar for a screen basket of a screening device for wet screening of fiber suspension, with which an increased throughput can be achieved with at least a constant sorting efficiency of a screen basket equipped with the profile bars.

[0009] According to the invention, the object was achieved in that the profile bars used are designed with a V-shaped profile head cross-section. A first lateral boundary surface is formed on a raised side of the profile head and encloses a negative inclination angle α with a profile center plane. A second boundary surface encloses a positive inclination angle β with the profile center plane. The absolute value of angle α is greater than angle β. The ratio of a profile head width b to a profile base width 2*a applies that the profile head width b is at least 1.8 times wider than the profile base width 2*a.

[0010] Due to their design, screen baskets equipped with such profile bars can achieve increased accuracy in slot widths despite manufacturing inaccuracies. Higher accuracy in slot widths results in higher accuracy in screening efficiency. In addition, the widening after the slot in the direction of flow of the accept material can improve the flow, which has a positive impact on throughput.

[0011] In one embodiment, the ratio of profile head width b to profile foot width is as follows: Profile head width (b) <Profilfußbreite (2*a)*1 ,95. Würde man das Verhältnis zu groß wählen, so hätte es einen negativen Einfluss auf die Stabilität eines mit derartigen Siebstäben gebildeten Siebkorbes. In einer bevorzugten Ausführungsform ist vorgesehen, dass der Winkel a vom Betrag mindestens das 1 ,4-fache des Winkels ß beträgt. Dadurch wird auf der Seite des Winkels a eine vergrößerte Öffnung bereitgestellt. Dadurch kann insbesondere eine erhöhte Sortiereffizienz bei einem mit den Profilstäben bestückten Siebkorb einer Siebvorrichtung erreicht werden. Hinzu kommt, ausgehend von dem Verhältnis, eine hohe Stabilität des Profilstabes.

[0012] The angle ß is preferably between 8° and 13° to create the widest possible channel for the accept. The larger the angle ß, the faster the channel expands behind the side of the profile head facing away from the screen surface. This has a positive effect on throughput.

[0013] In one embodiment, the profile head has a flat profile head surface inclined relative to the vertical of the profile center plane. The inclination of the profile head surface provides a profile depth c of the screening surface. The profile depth c influences the formation of turbulent flow and thus contributes to sorting efficiency and throughput.

[0014] In one embodiment, the profile head surface has an inclination angle y to the perpendicular to the profile center plane, where y is a maximum of 30°, preferably a maximum of 26°. Such an inclination angle leads to increased microturbulence, which reduces reflocculation in front of the slot and thus increases throughput. Reflocculation refers to the regression of fiber flakes and the associated fiber enrichment. The slot, or slot width w, is further defined as the narrowest point between two profile bars.

[0015] In a preferred embodiment, the cross-section of the profile bar has a maximum length of 9 mm, preferably 8 mm, from the raised profile head to the end of the profile base. The short length of the profile bars has a beneficial effect on flow resistance and thus on increased throughput. In one embodiment, the flat lateral boundary surfaces adjoin the profile head surface on both sides. This simple geometric design has a positive effect on manufacturing costs.

[0016] In one embodiment, the lateral boundary surfaces in the area of ​​the profile base run parallel to each other, preferably also to the profile center plane, at least over a section. This promotes good airflow, which leads to an increase in throughput. It can also increase the stiffness of the profile bar.

[0017] In one embodiment, one of the first and / or second boundary surfaces is formed with at least one groove on one or both sides of the profile head in the region of height h, wherein the groove preferably has a depth of at least 0.15 mm and preferably a maximum depth of 0.3 mm. This allows for an additional widening of the channel downstream of the slot, which has a beneficial influence on the flow behavior when used in a strainer basket and thus on the throughput through the strainer basket.

[0018] It has proven advantageous for a screen basket equipped with the previously described screen profile bars that the channel formed by two adjacent profile bars increases in the circumferential direction to a channel width d after a narrowest point w referred to as the slot, and that this channel width is related to the profile head width b, where: 0.35 < (dw) / b < 0.45 preferably 0.41 < (dw) / b< 0.45. This in particular promotes good outflow, which has a positive effect on throughput. The channel width minus the slot width is the widening after the narrowest point. This relationship therefore refers to the ratio of the widening of the channel after the slot and the profile head width.

[0019] In a preferred embodiment, the channel width is reached at a distance of 1*b to 1.5*b behind the narrowest point, where b is the profile head width. Maintaining this ratio promotes good throughput. By maintaining at least the achieved channel width, good outflow behavior can be achieved, which in turn has a positive effect on throughput.

[0020] A wide channel is desirable to ensure efficient removal of the material from the slot and thus high throughput through a screen basket. The dependence on the head width also ensures high rigidity of the profile bar.

[0021] In a preferred embodiment, the profile depth c is in the range of 0.3 to 1.5. The profile depth c depends on the inclination of the surface of the profile head as well as on the inclination of the profile bar relative to the radial of the screen basket. Thus, the profile height is largely provided by the inclined profile head surface b of the profile head. The inclination has a beneficial effect on the flow guidance downstream of the slot.

[0022] Cylindrical screens of the type considered here are subject to either centrifugal or centripetal flow. The commonly used terms mean centrifugal = radial flow from the inside out, and centripetal = radial flow from the outside in. This does not always determine the position of the screen scrapers. As is well known, there is screen scraping on the accept side and screen scraping on the inlet side. The invention is advantageously used when a scraper is present on the inlet side.

[0023] The invention will be explained in more detail below using several exemplary embodiments. The accompanying drawing shows:

[0024] Figure 1 : Profile bars in parallel arrangement with cross-section shown

[0025] profile bars

[0026] Figure 2: Section of a screen basket Figure 3: Enlarged view of the flow profile of adjacent screen bars in the area of ​​the slot

[0027] Fig. 4: Profile bar with groove in cross section

[0028] Fig. 5: Sieve basket

[0029] Fig. 6 Screening device

[0030] Figure 6 shows a screening device 1, also referred to as a pressure screen, with a cylindrical screen basket 3. The screen basket 3 has a vertical screening axis 13. The screen basket divides the pressure screen into an inlet chamber 15 and an accept chamber 17. Here, the inlet chamber 15 is located radially inside the screen basket 3, and the accept chamber 17 is located radially outside. The screening surface is formed by the profile heads 27 of the screen bars 5. If the inlet chamber were arranged radially outside of the screen basket 3, the accept chamber would be radially inside the screen basket.

[0031] The medium to be treated, ie the fiber suspension 19, is fed into the inlet chamber 15 via a suspension inlet 16.

[0032] In the pressure screen 1 used here, the fiber suspension 19 receives a rotational momentum that causes the fiber suspension 19 to move circumferentially. In addition, a transport flow is generated as a result of the pressure gradient between the suspension inlet 16 shown above and a lower reject outlet 20 of the inlet chamber 15.

[0033] On the path of this transport flow, a large part of the fiber suspension 19 is discharged as intended through the screen surface 9 of the screen basket 3 as accepts into the accepts space 17 and from there discharged via the accepts outlet 18.

[0034] The part of the fiber suspension 19 rejected by the screen basket 3 is conveyed as reject via the reject outlet 20 from the inlet chamber 15.

[0035] To prevent the screen openings from becoming clogged, a conventional rotor 11, also known as a screen cleaner, is used. The rotor 11 moves relative to the screen surface 9. The rotor 11 can be provided with attached rotor blades. The rotor 11 has the shape of a cylindrical drum, with its rotational axis coinciding with the screen axis 13.

[0036] According to Figures 4 and 5, the cylindrical screen basket 3 consists of a plurality of profile bars 5 running parallel to the cylinder axis 13, which are held by a plurality of holding elements 7 which are axially spaced from one another and run perpendicular to the cylinder axis 13.

[0037] The sieve openings of the sieve basket 3 are sorting slots 8. The sorting slots 8 are formed by adjacently arranged profile bars 5, Fig. 1 - 3. The sorting slots 8 are flowed against clockwise or counterclockwise depending on the flow direction of the suspension.

[0038] In the example shown in Figure 6, the fiber suspension 19 flows essentially along the radial centrifugally, ie from the inside to the outside through the sorting slots 8 of the screen basket 3. Accordingly, the profile bars 5 are supported on the inside of the holding element 7.

[0039] In the case of a centripetal flow through the sieve basket 3, the profile bars 5 are arranged and held on the radial outer side of the holding elements 7.

[0040] For the same sorting quality, the slot width w between the profile bars 5 is the same and constant in the axial direction.

[0041] As can be seen in Figures 1 to 4, the profile bars 5 have an elongated cross-sectional profile 21 with a front end region 23 referred to as profile head 27 and a rear profile foot 25. The profile head 27 has the boundary surfaces 31, 33 on both sides and the lateral boundary surfaces 41, 43 in the region of the profile foot 25. While the profile foot 25 is provided for fixation in the holding element 7, the profile head 27 is provided for forming the sieve surface 9 of the sieve basket 3. The front end region has a profile head 27 with a V-shaped cross-section. On the side of the first boundary surface 31, the profile head 27 is formed with a raised profile 29. The profile head surface 32 is formed between the lateral boundary surfaces 31, 33 of the profile head 27. This surface is inclined to the perpendicular to the profile center plane. The angle of inclination to the vertical is denoted by y, see Figure 4.

[0042] The rotor 11 not only removes the rejected part, but also guides the fiber suspension 19 in the direction of a first lateral boundary surface 31 of the profile head 27 and thus to the slots 8.

[0043] 1 to 4, it is important that a channel 53 for the passage of accept material is formed through each of the adjacently arranged profile bars 5. To widen the channel downstream of the slot 8, the boundary surfaces 31, 33 are arranged at an incline in the region of the profile head 27. The first boundary surface 31 is arranged at an incline by an angle α in the region of the profile head, and the second boundary surface 33 is arranged at an incline by an angle β in the region of the profile head 27. The angle is always measured as a positive angle starting from a profile center plane 37 of the profile bar 5. The profile center plane is a central plane of symmetry of the profile bar 5 in the rear end region 25. The different inclinations of the boundary surfaces 31, 33 in the region of the profile head 27 provide a widening of the channel 53 downstream of the slot 8.The flow behavior of the accepted material is influenced by the expansion. The angle α relative to the raised profile head 27 is at least 1.4 times greater than the angle β relative to the lower profile head 27. The angle β is positive when viewed clockwise (Fig. 1) and lies on the opposite side of the angle α of the profile center plane 37.

[0044] The first boundary surface 31 is arranged on the side of the profile bar 5 facing away from the flow direction and the second boundary surface 33 is arranged facing the flow direction. The channel 53 created by two adjacent profile bars 5 has a channel width d at a height h behind the slot 8. The channel width d is according to the following relationship (dw) > 0.35 * b. Here, the height h measures the distance from the constriction of the slot w to the enlargement of the channel 53 subsequently formed by the profile bars 5 to the channel width d. Here, 1 * b < h < 1.5 * b applies. This relationship describes how quickly the channel 53 opens up after the constriction of the slot w in order to reduce pressure losses and to be able to discharge the substance more effectively.

[0045] A shorter bar length, with lower flow resistance and thus lower pressure loss, has a supporting effect. Profile bars 5 with a cross-sectional length in the range of 6.5 to 8 mm are particularly advantageous.

[0046] Such a channel 53 allows pressure loss in the channel 53 to be kept to a minimum. As a result, backflow can be prevented or at least reduced. The accept 18 passing through the slot is more effectively removed. Thus, a larger accept mass flow can be achieved.

[0047] In the profile bars 5 of Figures 1 and 4, the distance between the lateral boundary surfaces 41, 43 in the area of ​​the profile base 25 is approximately constant throughout, which simplifies production and facilitates the realization of different flexural rigidities. The width of the profile bar 5 in the rear end region is twice the width a, where a is the distance from the lateral boundary surfaces 41, 43 to the profile center plane 37.

[0048] Figures 2 and 3 show an enlarged view of the arrangement of the profile bars 5 in Figure 5. The flow is also shown. Figure 3 in particular shows the flow behavior in the area of ​​the profile head 27 of two adjacently arranged profile bars 5. A turbulent flow transports the fibers through the slot 8 and reaches the channel 53. In the embodiment shown in Figure 2, the profile bars 5 have notches in the area of ​​the profile foot 25 for fastening in the holding elements 7. Figure 4 shows an alternative embodiment with a profile head 27 with a groove 55. This additional groove 55 represents a further widening in the flow path behind the slot 8. The groove 55 is formed in the area h in the first lateral boundary surface 31.

[0049]

Claims

Patent claims:

1. Profile bar (5) for a screen basket (3) of a screening device (1) for wet screening fiber suspension (19), wherein the profile bar (5) is formed in cross-section (21) as an elongated profile with a rear end region (25) referred to as the profile foot for fastening in a screen basket (3) and with a front end region (23) referred to as the profile head (27) with a V-shaped cross-section, wherein the profile head (27) has a first flat, lateral boundary surface (31) on a raised side (29) of the profile head (27) and a second flat, lateral boundary surface (33), wherein the first lateral boundary surface (31) encloses a negative angle of inclination α to a profile center plane (37) and the second boundary surface (33) encloses a positive angle of inclination β to the profile center plane (37) in the region of the profile head (27),wherein the profile center plane (37) runs from the profile head to the profile foot within the profile bar and wherein the angle a is greater than the angle ß, characterized in that the following applies to a ratio of a profile head width (b) and a profile foot width (2*a): Profile head width (b) > 1.8*profile foot width (2*a) 2. Profile bar (5) according to claim 1, characterized in that the ratio of profile head width b to profile foot width is: Profile head width (b) <Profilfußbreite (2*a)*1 ,95.

3. Profile bar according to one of the preceding claims, characterized in that the angle a is at least 1.4 times the angle ß.

4. Profile bar (5) according to one of the preceding claims, characterized in that the angle ß is a maximum of 13° and preferably a value from the range 8° - 13°.

5. Profile bar (5) according to one of the preceding claims, characterized in that the profile head (27) has a flat profile head surface (32) inclined to the perpendicular to the profile center plane (37).

6. Profile bar (5) according to claim 5, characterized in that the profile head surface (32) has an angle of inclination y to the perpendicular of the profile center plane (37), wherein Y is a maximum of 30°, preferably a maximum of 26°.

7. Profile bar according to one of the preceding claims, characterized in that the profile foot (25) has two lateral boundary planes (41, 43) which can be arranged at an angle to one another, preferably running parallel.

8. Profile bar (5) according to one of the preceding claims, characterized in that the cross section (21) of the profile bar (5) has a maximum length of 9 mm, preferably 8 mm, from the raised profile head (27) to the end of the profile foot (25).

9. Profile bar (5) according to one of the preceding claims, characterized in that the flat, lateral boundary surface (31, 33) adjoins the profile head surface (32) on both sides.

10. Profile bar (5) according to one of the preceding claims, characterized in that the distance between the boundary surfaces (41, 43) in the region of the profile foot (25) runs parallel to one another at least over one section, preferably also to the profile center plane.

11. Profile bar (5) according to one of the preceding claims, characterized in that in the first and / or second boundary surfaces (31, 33) a groove (55) is formed on one side or both sides of the profile head (27), wherein the groove preferably has a depth of at least 0.15 mm and a maximum of 0.3 mm.

12. Screen basket (3) for a screening device (1) for wet screening fiber suspension with a plurality of parallel aligned profile bars (5) according to one of the preceding claims 1 to 11, wherein sorting slots (8) are formed by the parallel profile bars (5), wherein the front end region (23) forms the screening surface (9) and the rear end region (25) is fixed in at least one holding element (7), characterized in that a channel (53) is formed by two adjacently arranged profile bars (5) through the lateral boundary surfaces of the profile bars (5), wherein the channel (53) increases to a channel width (d) in the circumferential direction after a narrowest point (w) designated as slot (8), and this width (d) of the channel (53) is in relation to the profile head width b, where: 0.35 < (dw) / b < 0.45 ; preferably 0.41 < (dw) / b< 0.45 applies.

13. Screen basket (3) according to claim 12, characterized in that the channel width (d) is reached at a distance of 1 *b to 1.5 *b behind the narrowest point (8).

14. Screen basket (3) according to claim 13, characterized in that the channel width (d) reached at a distance of 1 *b to 1.5 *b behind the narrowest point (8) does not decrease any further up to the foot end of the profile bar (5).

15. Screen basket (3) according to one of the preceding claims 12 to 14, characterized in that the profile depth c of the profile head (27) is in the range from 0.3 to 1.5 mm.

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