SEAMED FELT AND USE OF THE SEAMED FELT IN A TISSUE MACHINE

Abstract

A seamed felt for use in a machine for producing a tissue web has a single-layer or multilayer base structure and at least one layer of non-woven fibers. The base structure has a textile structure with MD threads which form seam loops at the two front edges of the base structure. The fabric can be made endless by connecting its front edges by way of a seam. The seam can be formed by interlocking the seam loops of the two front edges and introducing a push-in element. The MD threads wholly or predominantly have a diameter between 0.25 mm and 0.45 mm, in particular between 0.3 mm and 0.35 mm, and the thread density of the MD threads is more than 37%, in particular between 37% and 45%. There is also described a corresponding machine and a method for producing a tissue web.

Claims

1-15. (canceled)

16. A seamed felt for use in a machine for producing a tissue web, the seamed felt comprising: at least one layer of nonwoven fibers; a base structure being a woven material having machine direction (MD) threads and cross-machine direction (CD) threads, said base structure having two front edges with seam loops; a seam rendering the seamed felt endless by connecting said front edges, said seam interlocking said seam loops of said front edges with a push-in element inserted therein; at least 90% or all of said MD threads having a diameter of between 0.25 mm and 0.45 mm, and said MD threads having a thread density of more than 37%, wherein the thread density of said MD threads is determined by multiplying a number of threads per unit length by a diameter of said MD threads and setting a multiplication result in relation to the unit length.

17. The seamed felt according to claim 16, wherein the diameter of said MD threads lies between 0.3 mm and 0.35 mm, and the thread density of said MD threads lies between 37% and 45%.

18. The seamed felt according to claim 16, wherein a weight of the seamed felt lies between 750 g/m.sup.2 and 1250 g/m.sup.2.

19. The seamed felt according to claim 18, wherein the weight of the seamed felt lies between 900 g/m.sup.2 and 1100 g/m.sup.2.

20. The seamed felt according to claim 16, wherein a proportion by weight of said at least one layer of nonwoven fibers corresponds at most to a proportion by weight of said base structure.

21. The seamed felt according to claim 20, wherein the proportion by weight of said at least one layer of nonwoven fibers corresponds at most to ⅔ of the proportion by weight of said base structure.

22. The seamed felt according to claim 16, wherein said at least one layer of nonwoven fibers forms an overlay layer having a weight of less than 600 g/m.sup.2.

23. The seamed felt according to claim 22, wherein said overlay layer has a weight of less than 450 g/m.sup.2.

24. The seamed felt according to claim 16, wherein said woven material is a flatweave, said MD threads of the seamed felt are warp threads of a loom and said flatweave is made endless by connecting front ends thereof to form a two-layer structure by laying said flatweave on itself.

25. The seamed felt according to claim 24, wherein seam loops are formed at the front edges of the two-layer structure by removing one or more CD threads.

26. The seamed felt according to claim 16, wherein at least some of said CD threads are twisted threads.

27. The seamed felt according to claim 26, wherein at least 50% of said CD threads are twisted threads.

28. The seamed felt according to claim 16, wherein the seamed felt has a thickness of 3.5 mm or less.

29. A machine for producing a tissue web, the machine comprising: a former; and at least one seamed felt according to claim 16 configured to run through said former during an operation of the machine.

30. The machine according to claim 29, wherein said former is a Crescent Former.

31. The machine according to claim 29, further comprising a press device with at least one press nip, and wherein the seamed felt is disposed to run through said at least one press nip during an operation of said press device.

32. The machine according to claim 31, wherein said at least one press nip of said press device is an extended nip.

33. The machine according to claim 32, wherein said at least one press nip of said press device is a shoe nip.

34. The machine according to claim 31, wherein said press device has a wastewater trap configured to collect water which has been removed from the tissue web in said at least one press nip, wherein said wastewater trap is arranged to collect and conduct away splash water.

35. A method for producing a tissue web, the method which comprises operating the machine according to claim 29 for producing the tissue web.

36. The method according to claim 35, which comprises carrying out dewatering in the press device of more than 10% by nip dewatering, as opposed to Uhle box dewatering, and removing the water removed by the nip dewatering after collection by a wastewater trap.

Description

[0067] The invention will be explained in more detail below with reference to schematic figures, not to scale.

[0068] FIG. 1 shows a tissue machine according to one aspect of the invention.

[0069] FIG. 2 shows the seam area of a seamed felt according to one aspect of the invention.

[0070] FIG. 1 shows a tissue machine 1 according to one aspect of the invention. Using the example of this typical design of a tissue machine 1, exemplary aspects of the idea described here are to be explained. The invention is not restricted to this embodiment. A fibrous material suspension is applied via a headbox to a fabric 2 or between a fabric 2 and an outer wire 22. The fabric 2 is designed as a forming felt 2 in the form of a seamed felt 2. In a former 20, initial dewatering takes placed with the aid of an evacuated forming roll 21, around which the forming felt 2 partly wraps. The former 20 in FIG. 1 is designed as a Crescent Former 20, but other former types are also possible. The fibrous material web that has been produced is then transported into the press device 30, supported by the forming felt 2. In FIG. 1, the press device 30 is designed as a shoe press 30. The press nip 31 is between the shoe roll 34 and a Yankee cylinder 41. The forming felt 2 passes through the press nip 31 together with the tissue web 3. After the press nip, the web 3 runs onward on the upper surface of the Yankee cylinder 41. Here, a dryer hood 42 is arranged on the Yankee cylinder 41. By means of a creping doctor 43, the web 3 is detached from the Yankee cylinder 41 and transported onward to a reel-up 60. As shown in FIG. 1, a scanner 50 or another suitable measuring device 50, with which important parameters of the fibrous web 3 such as, for example, the thickness, moisture or mass per unit area are detected, can also be provided before the reel-up 60. If the scanner 50 is designed to be traversing, transverse profiles of these parameters can also be determined.

[0071] The fabric 2 of the machine 1 shown in FIG. 1 is advantageously a seamed felt 2 according to one aspect of the invention. Advantageously, it can comprise a base structure 100 made of a flatweave 110, in particular a plain weave, which is made endless by connecting—e.g. welding—the front ends and a two-layer structure 100 is formed by laying it on itself.

[0072] The MD threads of this base structure 100 in the embodiment all have a diameter between 0.25 mm and 0.45 mm, in particular between 0.3 mm and 0.35 mm. The thread density of the MD threads is more than 37%, preferably between 37% and 45%, particularly preferably between 39% and 43%. With a preferred weight of the felt 2 between 750 g/m.sup.2 and 1250 g/m.sup.2, in particular between 900 g/m.sup.2 and 1100 g/m.sup.2, the nonwoven overlay 200 can be reduced such that it makes up only half or less of the weight of the felt 2. In particular, the weight of the nonwoven overlay 200 on the paper side of the seamed felt 2 or even of the entire seamed felt 2 can be less than 600 g/m.sup.2, in particular less than 500 g/m.sup.2, especially 450 g/m.sup.2 or less.

[0073] Since, in a fabric 2 according to one aspect of the invention, the base structure 100 performs part of the function of the nonwoven layers 200, this fabric 2 can be designed to be very thin. As a result, the seam location 150 or butt joint 210 offers a smaller area of attack for the stock jet. In addition, the particularly susceptible nonwoven fibers of the nonwoven layers far removed from the base structure 100 are omitted, and the service life of the forming felt 2 in the tissue machine 1 is significantly prolonged!

[0074] Furthermore, as opposed to the tissue machines 1 known from the prior art, when such a seamed felt 2 is used in the press nip 31, in particular in a shoe press nip 31, nip dewatering can be achieved. Hereby, splash water or spray mist is produced, which normally occurs after the press nip 31, but can sometimes also occur before the nip 31. In order to prevent soiling of the press 30 or uncontrolled wetting of the surroundings, it is advantageous to provide one or more wastewater traps 33 in the press device 30. In FIG. 1, a wastewater trap 33 is arranged after the press nip 31. Alternatively or additionally, a wastewater trap 33 can also be provided before the press nip 31. The wastewater trap or traps 33 pick up the proportion of the water which has been removed from the web 3 by nip dewatering. The remaining part is stored in the fabric 2 and transported away from the press nip 31. In order to remove this water from the fabric 2, in the installation shown in FIG. 1, a suction box 32, what is known as a Uhle box, is provided between press nip 31 and the headbox 10. In a method according to one aspect of the invention, the proportion of nip dewatering is more than 10%, preferably between 20% and 50%, of the total dewatering of the press 30.

[0075] FIG. 2 shows a detail from a seamed felt 2 according to one aspect of the invention. The felt 2 shown here consists of a base structure 100 and a nonwoven layer 200 on the paper side of the felt 2. The nonwoven layer 200 can comprise one or more layers of nonwoven fibers. Likewise, a further nonwoven layer, which is not illustrated in FIG. 2, can be provided on the running side of the felt 2. The base structure 100 in FIG. 2 is a woven base structure 100. A flatweave 100 can be laid on itself by folding such that the result is the two-layer base structure shown. The ends of the flatweave 110 are advantageously connected to each other, for example by a welded connection. Seam loops 120 are formed at the front edges of the two-layer base structure 100 thus produced. For this purpose, one or more CD threads can be removed from the woven material. To close the seam, the seam loops 120 are interlocked and can be connected to each other by an element such as a pintle wire 130.

[0076] For the nonwoven layer 200, in seamed felts 2 of this type, there is the problem that this nonwoven layer 200 can be non-continuous at the seam 150 but have a butt joint 210 (possibly in the form of an overlap 210). This butt joint 210 is very critical in particular in the use as a forming felt 2. The stock jet from the headbox 10 can widen the butt joint or detach the nonwoven fibers since the anchoring, primarily of the outer nonwoven fibers, is reduced in the seam area 150. In a seamed felt according to one aspect of the invention, the base structure 100 can then perform parts of the function of the nonwoven layer 200, such as evening out the pressure. The result of this, amongst other things, is that the nonwoven layer 200 can be designed to be thinner. As a result, it becomes more difficult for the stock jet to penetrate the butt joint 210. In addition, on average the nonwoven fibers are located less far away from the woven material of the base structure 100, which improves the anchoring. As a result, a use of a seamed felt 2 with a considerably improved service life as a forming felt 2 of a tissue machine 1 is made possible.

LIST OF DESIGNATIONS

[0077] 1 Tissue machine [0078] 2 Fabric, seamed felt [0079] 3 Tissue web [0080] 10 Headbox [0081] 20 Former [0082] 21 Forming roll [0083] 22 Outer wire [0084] 30 Press device [0085] 31 Press nip [0086] 32 Suction box, “Uhle Box” [0087] 33 Wastewater trap [0088] 34 Shoe roll [0089] 40 Drying apparatus [0090] 41 Yankee cylinder [0091] 42 Hood [0092] 43 Creping doctor [0093] 50 Scanner [0094] 60 Reel-up [0095] 100 Base structure [0096] 110 Flatweave [0097] 120 Seam loop [0098] 130 Pintle wire [0099] 150 Seam [0100] 200 Nonwoven layer