FORMER FOR PRODUCING A FIBER TRAY IN A PAPER MACHINE

Description

[0001] The invention relates to a former for a paper machine for producing a fibrous web, in particular a paper, cardboard, tissue, or packaging paper web. The former comprises a forming wire forming a loop, on which the fibrous web lies and is guided together via a deflection roller located within the loop to a pickup point, where the fibrous web is taken over from the forming wire by a screen. Immediately upstream of the pickup point and immediately downstream of the deflection roller, a suction element with openings facing the forming wire is arranged within the loop.

[0002] Devices of this type are known. Document WO2013026597 A1 describes a double screen former with a first screen that, together with the fiber web, is guided over a grooved, drilled, or otherwise structured guide roll that is not directly suctioned through the roll shell. Such structures on the guide roll surface are intended to prevent the fiber web from floating. Such a former is also disclosed in WO 00 / 09804 A1.

[0003] Despite these measures, floatation cannot be completely prevented in known devices. Furthermore, the dry content of the fiber web at the pickup point is too low compared to known formers with expensive and costly suction rollers. This results in a higher load on the downstream press section with regard to dewatering capacity. Documents US 4243482 A and US 3576714 A disclose roller designs for a forming section and for rollers as pickup rollers, respectively, with improved roller surfaces.

[0004] The object of the invention is therefore to improve the known formers with regard to better running behavior of the fiber web and a lower load on the press section.

[0005] The problem is solved by features of claim 1. A former for a paper machine for producing a fibrous web, in particular a paper, cardboard, tissue, or packaging paper web, is proposed. It comprises a forming wire forming a loop, on which the fibrous web lies and is guided together via a deflecting roller located within the loop to a pickup point, where the fibrous web is taken over from the forming wire by a tensioning device. A suction element with openings facing the forming wire is arranged within the loop immediately before the pickup point and immediately after the deflecting roller. According to the invention, the deflecting roller is non-vacuum-controlled and has at least one spirally extending groove on its surface in the circumferential direction, and preferably the suction element is designed as a high-vacuum suction device.

[0006] To avoid inefficient energy consumption, the deflection roller is unvacuumed, meaning it is neither vacuumed from the inside nor from the outside.

[0007] The spiral shape of the at least one groove improves the absorption and removal of air that is introduced into the run-up gap between the forming screen and the deflection roller by the air boundary layer formed on the inside of the forming screen.

[0008] The grooved area of ​​the surface of the deflection roller preferably corresponds at least to the width of the fiber web, in particular to the entire width of the deflection roller.

[0009] The at least one spiral groove extends between the drive side and the guide side of the former. The beginning and end of the groove are open, allowing air trapped between the forming screen and the deflection roller surface to flow within the groove. This also improves air intake into the groove. This prevents the fiber web from floating and improves its running properties. Furthermore, the groove prevents marking in the fiber web, unlike a groove arranged concentrically to the deflection roller's cross-section. This avoids any impairment of the fiber web's quality.

[0010] The advantages are particularly evident at high speeds and high basis weights of the fibrous web. Preferably, the speeds are above 800 m / min, particularly above 1000 m / min, and preferably above 1100 m / min. The basis weight is greater than 70 g / m².

[0011] In one possible design, the former is designed as a hybrid former or as a gap former.

[0012] In an advantageous further development, the deflecting roller has at least two spirally extending grooves on its surface in the circumferential direction.

[0013] The two grooves can begin at one edge of the deflection roller.

[0014] Alternatively, you can start in the middle of the deflection roller. In this case, the orientation of the spirals is opposite to each other.

[0015] It is also conceivable, in principle, to arrange more than two spirally running grooves.

[0016] Even in cases with multiple spiral grooves, these can extend between the drive and guide sides of the former. The beginning and end of the grooves are open, allowing air trapped between the forming screen and the deflection roller surface to flow within the groove. This also applies if the grooves begin in the center of the deflection roller. Air intake into the grooves is improved in these cases as well. This prevents the fiber web from floating and improves its running characteristics. Furthermore, the grooves counteract marking in the fiber web, compared to a groove arranged concentrically to the deflection roller's cross-section. Thus, even in this possible embodiment, any impairment of the fiber web's quality is avoided.

[0017] It is particularly advantageous if the groove depth is at least 1 mm, preferably at least 3 mm. This promotes the intake of air into the grooves.

[0018] Preferably, the open surface area of ​​the deflection roller is greater than 10% and less than 75%. Consequently, the land area of ​​the deflection roller's surface between the grooves is preferably less than 90% and greater than 25%. The sum of the land area and the open surface area yields the surface area of ​​the deflection roller's outer surface.

[0019] In a possible practical further development, another suction element with openings facing the forming sieve is arranged immediately in front of the deflection roller within the loop.

[0020] Furthermore, the suction element and / or the additional suction element can be designed as a high-vacuum suction device and dimensioned such that a negative pressure of greater than or equal to 40 kPa, in particular greater than or equal to 52 kPa, preferably greater than 60 kPa, can be applied. This promotes a high dryness content of the fiber web before the pickup point.

[0021] Preferably, the openings are designed as suction slots.

[0022] Furthermore, the slot widths of the suction slots can be less than or equal to 25 mm, preferably less than or equal to 20 mm, and particularly less than or equal to 17 mm. In conjunction with the high vacuum, this reduces wear on the forming screen and also reduces the drive power of the former.

[0023] The openings can also be designed as suction bores. The diameters of the suction bores can be less than or equal to 27 mm, preferably less than or equal to 22 mm, particularly less than or equal to 18 mm, and most especially less than or equal to 16 mm.

[0024] The invention expressly extends to embodiments which are not given by combinations of features from explicit cross-references of the claims, whereby the disclosed features of the invention can be combined arbitrarily with one another - insofar as this is technically sensible.

[0025] Further features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the drawings.

[0026] They show Figure 1 shows a section of a former in cross-section in a schematic, simplified representation; Figure 2 shows an embodiment of a grooved surface of a deflection roller in a schematic, simplified representation; Figure 3 shows another embodiment of a grooved surface of a deflection roller in a schematic, simplified representation; Figure 4a shows a section of the shell of the deflection roller with one possible embodiment of the groove in a schematic, simplified, cutaway view; Figure 4b shows a section of the shell of the deflection roller with another possible embodiment of the groove in a schematic, simplified, cutaway view;

[0027] The Figure 1Figure 1 shows a simplified cross-sectional view of a former according to the invention for a paper machine for producing a fibrous web, in particular a paper, cardboard, tissue, or packaging paper web. In this example, the former is designed as a hybrid former. It comprises a forming screen 2 forming a loop, on which the fibrous web 1 lies and is guided together in the direction of travel 14 over a deflecting roller 3 located within the loop to a pickup point, where the fibrous web 1 is transferred from the forming screen 2 by a screen 6. Immediately upstream of the pickup point 4 and immediately downstream of the deflecting roller 3, a suction element 7 with openings 9 facing the forming screen 2 is arranged within the loop. The deflecting roller 3 is non-suctioned and has at least one spirally extending groove 10 on its surface in the circumferential direction. The suction element 7 is designed as a high-vacuum suction element.The grooved area of ​​the surface of the deflection roller 3 corresponds at least to the width of the fiber web 1. The grooved area can also extend across the entire width of the deflection roller 3 in the axial direction. In this example, a spiral groove 10 is provided on the surface of the deflection roller 3. It extends between the drive side and guide side of the former, i.e., transversely to the direction of travel 14 of the fiber web. The beginning and end of the groove 10 are open, allowing air trapped between the forming screen 2 and the deflection roller surface to flow within the groove 10. This also improves the intake of air into the groove 10. This prevents the fiber web 1 from floating and improves its running characteristics. Furthermore, the groove 10 counteracts the formation of marks in the fiber web 1, compared to a groove arranged concentrically to the cross-section of the deflection roller.This prevents any impairment of the quality of the fiber web 1. The groove depth 11 is 1.5 mm. It can also be at least 3 mm. This promotes air intake into the grooves 10. The open surface area of ​​the deflection roller 3 is, for example, 42%, and the land area of ​​the surface of the deflection roller 3 between the grooves 10 is 58%. Immediately upstream of the deflection roller 3 within the loop, another suction element 8 with openings 9 facing the forming screen 2 is arranged. This additional suction element 8 is also designed as a high-vacuum suction device and is dimensioned to allow a negative pressure of 40 kPa or greater. This promotes a high dryness content of the fiber web before the pickup point. The openings 9 are designed as suction slots and have slot widths of less than 25 mm. The suction element 7 and the further suction element 8 are connected to a suction device 13 to generate the vacuum.

[0028] The Figure 2 Figure 1 shows a simplified embodiment of a grooved surface of a deflection roller 3. In this example, two spirally extending grooves 10 are incorporated into the surface of the deflection roller 3. They each begin in the center of the deflection roller 3 and extend to the respective edge of the deflection roller 3, i.e., towards the drive side and the operator side, respectively. The orientation of the spirals is opposite to each other. The land area 12 is 58% in this example.

[0029] The Figure 3Figure 1 shows a further embodiment of a grooved surface of a deflection roller 3 with only one groove 10 in a simplified representation. The grooved area of ​​the deflection roller 3's surface extends over the entire width of the deflection roller 3. The surface area 12 is also 58% in this example. The single spiral groove 10 extends between the drive side and the guide side of the former. The beginning and end of the groove 10 are open, allowing air trapped between the forming screen 2 and the deflection roller surface to flow within the groove 10. This also improves air intake into the groove 10.

[0030] The Figures 4a and 4b Each figure shows a section of the casing of the deflection roller 3 with a possible embodiment of the groove 10 in a simplified, cutaway view. The cross-section of the groove 10 in Figure 4aIt is rectangular and has a groove depth of 1.5 mm. The land area 12 is also 58% in this example. Figure 4b In contrast, groove 10 shows a round cross-sectional shape and has a groove depth 11 of 1.3 mm. The land area 12 is also 58% in this example.

[0031] The various features described in the exemplary embodiments are not limited to the respective embodiments, but can expressly be combined or interchanged with one another, provided no contradictions arise. Likewise, the exemplary embodiments do not limit the scope of the invention. Any possible combination or partial combination of the described features of the invention shall be considered within the scope of the invention. Reference symbol list

[0032] 1 Fiber web 2 Forming screen 3 Deflection roller 4 Pickup point 5 Take-off roller 6 Covering 7 Suction element 8 Additional suction element 9 Openings 10 Groove 10.1 Second groove 11 Groove depth 12 Land area 13 Suction device 14 Direction of travel

Claims

1. Former for a paper machine for producing a fibre web (1), in particular a paper, cardboard, tissue or packaging paper web, comprising a forming screen (2) forming a loop, on which the fibre web (1) lies and is guided together via a deflection roller (3) located within the loop to a pickup point (4) at which the fibre web (1) is transferred from the forming screen (2) by a fabric (6), wherein immediately before the pickup point (4) and immediately after the deflection roll (3) within the loop, a suction element (7) with openings (9) facing the forming wire (2) is arranged, characterised in that the deflection roller (3) is not suctioned and has at least one spiral groove (10) on its surface in the circumferential direction, and preferably the suction element (7) is designed as a high-vacuum suction device.

2. Former according to claim 1, characterised in that the deflection roller (3) has at least two spiral grooves (10) on its surface in the circumferential direction.

3. Former according to claim 2, characterised in that both grooves (10) start at one edge of the deflection roller (3) or that both grooves start in the centre of the deflection roller (3).

4. Former according to one of the preceding claims, characterised in that the groove depth (11) is at least 1 mm, preferably at least 3 mm.

5. Former according to one of the preceding claims, characterised in that the open surface area of the deflection roller (3) is greater than 10% and less than 75% ( ).

6. Former according to one of the preceding claims, characterised in that immediately before the deflection roller (3), a further suction element (8) with openings (9) facing the forming screen (2) is arranged within the loop.

7. Former according to one of the preceding claims, characterised in that the suction element (7) and / or the further suction element (8) are designed as squat vacuum suction cups and are dimensioned such that a negative pressure greater than or equal to 40 kPa, in particular greater than or equal to 52 kPa, preferably greater than 60 kPa, can be applied.

8. Former according to one of the preceding claims, characterised in that the openings (9) are designed as suction slots.

9. Former according to claim 8, characterised in that the slot widths of the suction slots are less than or equal to 25 mm, preferably less than or equal to 20 mm, in particular less than or equal to 17 mm.

10. Former according to one of the preceding claims, characterised in that the openings (9) are designed as suction holes.

11. Former according to claim 10, characterised in that the diameters of the suction holes are less than or equal to 27 mm, preferably less than or equal to 22 mm, in particular less than or equal to 18 mm, and especially less than or equal to 16 mm.