Machine and method for producing a fibrous web

Abstract

A machine for producing a fibrous web, such as a tissue web, has pressing device with a pressing element and a counter-element with a closed surface for forming a pressure nip. A water-absorbing belt with a web side and an opposite pressing element side is guided together with the fibrous web through the pressure nip and the fibrous web is separated at the end of the pressure nip from the web side of the water-absorbing belt and runs further with the counter-element. The water-absorbing belt has at least a first ply and a second ply, and, as viewed in the thickness direction of the water-absorbing belt, a layer in or on the belt half which faces the pressing element, which layer has a higher specific throughflow resistance than the first ply and/or the second ply.

Claims

1. A machine for producing a fibrous web, the machine comprising: at least one pressing device having a press nip formed by a pressing element and an opposing element being a drying cylinder with a closed surface; a water-absorbing belt having a web side and an opposite pressing element side; wherein, during an operation of the machine, said water-absorbing belt is guided together with the fibrous web through said press nip and the fibrous web is separated from said web side of said water-absorbing belt upon issuing from said press nip, and the fibrous web runs further on the closed surface of said drying cylinder; said water-absorbing belt having at least a first ply and a second ply, and, viewed in a thickness direction of said water-absorbing belt, a layer on a half of said water-absorbing belt that faces said pressing element; said layer having a specific throughflow resistance that is higher than a specific throughflow resistance of at least one of said first ply or said second ply.

2. The machine according to claim 1, wherein said first ply forms the web side of said water-absorbing belt.

3. The machine according to claim 1, wherein said second ply is a woven ply and said first ply is connected to said second ply.

4. The machine according to claim 3, wherein said first ply is a non-woven formed of plastic fibers and said first ply is needled to said second ply.

5. The machine according to claim 1, wherein said layer is connected to said second ply.

6. The machine according to claim 1, wherein said layer forms the pressing element side of said water-absorbing belt.

7. The machine according to claim 1, which comprises a further ply on a half of said water-absorbing belt which faces said pressing element.

8. The machine according to claim 7, wherein said further ply is a non-woven formed of plastic fibers.

9. The machine according to claim 7, wherein said layer is arranged between said second ply and said further ply.

10. The machine according to claim 7, wherein said layer is arranged within said further ply.

11. The machine according to claim 7, wherein said layer is arranged adjacent said further ply and forms the pressing element side of said water-absorbing belt.

12. The machine according to claim 1, wherein said layer is a membrane with openings formed therein.

13. The machine according to claim 1, wherein said layer is a laid fiber fabric made of fibers having a fiber fineness of less than 3 dtex.

14. The machine according to claim 1, wherein said layer at least partly comprises thermoplastic polyurethane elastomer.

15. The machine according to claim 1, further comprising a suction device for dewatering said water-absorbing belt disposed in an area of said water-absorbing belt that is free of the fibrous web, said suction device being disposed on the pressing element side of said water-absorbing belt.

16. The machine according to claim 1, wherein the drying cylinder is a Yankee Cylinder.

17. A water-absorbing belt for use in a machine for producing a fibrous web, the machine having a pressing device with a press nip formed by a pressing element and an opposing drying cylinder with a closed surface, the water-absorbing belt comprising: at least a first ply and a second ply, and, as viewed in a thickness direction of the water-absorbing belt, a layer on a half of the water-absorbing belt which faces the pressing element; said layer having a specific throughflow resistance that is higher than a specific throughflow resistance of at least one of said first ply or said second ply.

18. A method for producing a fibrous web, the method comprising: providing at least one pressing device with a press nip formed between a pressing element and an opposing drying cylinder having a closed surface; providing a water-absorbing belt with at least a first ply, a second ply, and, as viewed in a thickness direction of the water-absorbing belt, a layer on a half of the water-absorbing belt which faces toward the pressing element, and wherein the layer has a higher specific throughflow resistance than a specific throughflow resistance of the first ply and/or the second ply; and guiding the water-absorbing belt together with the fibrous web through the press nip such that the fibrous web is separated from a web side of the water-absorbing belt at the end of the press nip and runs further on the closed surface of the drying cylinder.

19. The method according to claim 18, which comprises producing a tissue web.

20. The method according to claim 18, wherein the drying cylinder is a Yankee Cylinder.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 shows an embodiment of a machine according to the invention for producing a fibrous web in a schematic illustration;

(2) FIG. 2 shows an embodiment of a pressing device of the machine according to the invention in a schematic illustration;

(3) FIG. 3 shows an embodiment of a water-absorbing belt of a machine according to the invention for producing a fibrous web in a schematic illustration;

(4) FIG. 4 shows a further embodiment of a water-absorbing belt of a machine according to the invention for producing a fibrous web in a schematic illustration.

DETAILED DESCRIPTION OF THE INVENTION

(5) FIG. 1 shows an embodiment of a machine 1 according to the invention for producing a fibrous web 2 in a schematic illustration. In the forming area, a water-absorbing belt 3 together with an outer fabric 25 is guided partly around a forming roll 24, forming an inlet gap. Via a headbox 23, a fibrous material suspension, from which the fibrous web 2 is formed, is fed into the inlet gap. After the forming roll 24, the outer fabric 25 is guided away and the fibrous web 2, lying on the web side 4 of the water-absorbing belt 3, is guided to a pressing device 6 having a press nip 9, which is formed between a pressing element 7 and a Yankee drying cylinder 8. In this example, the pressing element 7 is formed by a shoe roll 7. The cylindrical surface of the Yankee drying cylinder 8 is smooth. After the press nip 9, the fibrous web 2 runs further with the Yankee drying cylinder 8 through a hood 21 for further drying by means of impact drying and is creped by a creping doctor and taken off and guided to a further machine section. Inside the loop formed by the water-absorbing belt 3, before the press nip 9, an evacuated suction roll—not illustrated here—or a suction element 22 for evacuating the water-absorbing belt 3 and the entrained fibrous web 2 can be provided. To increase the dewatering performance, a steam- or hot-air blower hood can be arranged opposite the suction element 22. Between the press nip 9 and the forming area, a suction device 12 for conditioning the water-absorbing belt 3 is arranged inside the loop formed by the water-absorbing belt 3. The suction device 12 has a covering with openings through which the water is sucked into the suction element and which are preferably embodied as holes and/or slots. The suction device 12 is arranged in an area in which the water-absorbing belt 3 is free of a fibrous web 2. As a result, the conditioning is made easier and improved. By means of the suction device 12, the water from the water-absorbing belt 3 is guided away toward the inner side, i.e. toward the pressing element side 5. The shoe roll 7 comprises a press shoe 10, which can be pressed against the Yankee drying cylinder 8 to produce a pressing pressure in the press nip. Between the press shoe 10 and the fibrous web 2, the cover 11 surrounding the press shoe 10 runs through the press nip 9. To increase the dewatering of the fibrous web 2 in the press nip 9, the side of the cover 11 that comes into contact with the pressing element side 5 of the water-absorbing belt 3 has grooves. The water pressed out of the fibrous web 2 in the area of the press nip 9 passes partly through the water-absorbing belt 3 into the grooves of the cover 11 and, after the press nip 9, is partly thrown against the pressing element side 5 of the water-absorbing belt 3 as a result of the centrifugal force. Thus, the water-absorbing belt 3 is re-wetted. This water thrown off can be removed efficiently and with little expenditure of energy as a result of the arrangement according to the invention of the suction device 12, without having to be sucked through the entire thickness of the water-absorbing belt 3. In addition, as viewed in the running direction 26 of the water-absorbing belt 3, a suction element 20 can be arranged downstream of the suction device 12 if necessary.

(6) FIG. 2 shows an embodiment of a pressing device 6 of the machine 1 according to the invention in a schematic illustration. The fibrous web 2, lying on the web side 4 of the water-absorbing belt 3, is guided to a pressing device 6 having a press nip 9, which is formed between a pressing element 7 and a Yankee drying cylinder 8. In this example, the pressing element 7 is formed by a shoe roll 7. The cylindrical surface of the Yankee drying cylinder 8 is smooth. The shoe roll 7 comprises a press shoe 10, which can be pressed against the Yankee drying cylinder 8 to produce a pressing pressure in the press nip 9.

(7) Between the press shoe 10 and the fibrous web 2, the cover 11 surrounding the press shoe 10 runs through the press nip 9. To increase the dewatering of the fibrous web 2 in the press nip 9, the side of the cover 11 that comes into contact with the pressing element side 5 of the water-absorbing belt 3 has an open surface, in this example grooves. The water pressed out of the fibrous web 2 in the area of the press nip 9 passes partly through the water-absorbing belt 3 into the grooves of the cover 11.

(8) After the end of the press nip 9, the water-absorbing belt 3 is guided on a section through the pressing element 7. The length of the section is chosen such that the direction of the water-absorbing belt 3 guided away assumes an angle 14 of more than 10°, in particular more than 15°, preferably in the region of 20°, to a tangent 12 to the opposing element 8 at the end of the press nip. As a result, re-wetting of the fibrous web 2 by the water-absorbing belt 3 is counteracted. The conditioning of the water-absorbing belt 3 is assisted by the negative pressure produced in the pocket between the water-absorbing belt 3 and the pressing element 7.

(9) In FIG. 3, an embodiment of a water-absorbing belt 3 of a machine 1 according to the invention for producing a fibrous web 2 is shown in a schematic illustration. The water-absorbing belt 3 comprises a first ply 15, a second ply 16, a further ply 17 and a layer 18, which has a higher specific throughflow resistance than the first ply 15 and/or the second ply 16 and/or the further ply 17. The web side 4 is formed by the first ply 15 and the pressing element side 5 by the further ply 17. As viewed in the thickness direction of the water-absorbing belt 3, the layer 18 is arranged on the half which faces the pressing element 7. The higher throughflow resistance of the layer 18 prevents or minimizes the water contained in the pressing-element-side half of the water-absorbing belt 3 flowing back in the direction of the web side 4. The water can thus be removed more easily by the suction device 12 arranged on the pressing element side 5. The first ply 15 forming the web side 4 comprises a felt-like laid fiber fabric and is needled with the second ply 16. The second ply 16 is a woven ply. In this example, the layer 18 is incorporated into the further ply 17 between the second ply 16 and the pressing element side 5 and is thus located within the further ply 17. The layer 18 can also adjoin the second ply 16 directly and be connected thereto, for example by needling. The further ply 17 forming the pressing element side likewise comprises a felt-like laid fiber fabric and is needled with the second ply 16. The layer 18 is embodied as a membrane with openings. This can be, for example, a plastic film with needled or punched or laser-drilled holes. Within the context of the invention, it is also possible to embody the layer 18 as a laid fiber fabric made of fine fibers. The fiber fineness can preferably be less than or equal to 3 dtex. The layer 18 at least partly contains components of thermoplastic polyurethane elastomer (TPU). This increases the elasticity of the belt 3.

(10) In FIG. 4, a further embodiment of a water-absorbing belt 3 of a machine 1 according to the invention for producing a fibrous web 2 is shown in a schematic illustration. It differs from the embodiment in FIG. 4 only in the arrangement of the layer 18 in the thickness direction of the water-absorbing belt 3. The layer 18 is connected to the further ply 17 and forms the pressing element side 5 of the water-absorbing belt 3. In the machine 1, the layer 18 comes into contact with the pressing element 7. The layer 18 is optimized with regard to low wear as a result of mechanical abrasion and at the same time with regard to the throughflow resistance.

(11) Corresponding elements of the exemplary embodiments are provided with the same designations in the figures. The functions of such elements in the individual figures correspond to one another, if not otherwise described and it does not lead to contradictions. A repeated description is therefore omitted. It is also pointed out that different features of the exemplary embodiments shown can be interchanged with one another and combined with one another. The invention is therefore not restricted to the feature combinations shown of the exemplary embodiments shown.

LIST OF REFERENCE SYMBOLS

(12) 1 Machine 2 Fibrous web 3 Water-absorbing belt 4 Web side 5 Pressing element side 6 Pressing device 7 Pressing element 8 Opposing element, drying cylinder 9 Press nip 10 Press shoe 11 Cover 12 Suction device 13 Tangent 14 Angle 15 First ply 16 Second ply 17 Further ply 18 Layer 19 Press felt 20 Sucker 21 Hood 22 Suction element 23 Headbox 24 Forming roll 25 Outer fabric, forming fabric 26 Running direction