FABRIC AND USE OF THE FABRIC IN A TISSUE MACHINE

Abstract

A fabric, in particular a felt, for use in a machine for producing a tissue web, has a base structure, which has a textile structure with MD threads, and at least one layer of nonwoven fibers. The MD threads predominantly or as a whole have a diameter ranging 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 machine and a method for producing a tissue web using such a fabric.

Claims

1-13. (canceled)

14. A fabric for use in a machine for producing a tissue web, the fabric comprising: a base structure being a woven textile structure with machine direction (MD) threads and cross-machine direction (CD) threads; said MD threads wholly or predominantly having a diameter of between 0.25 mm and 0.45 mm and said MD threads having a thread density of more than 37%; and at least one layer of nonwoven fibers.

15. The fabric according to claim 14, wherein at least one of the following is true: said MD threads have a diameter of between 0.3 mm and 0.35 mm; or said MD threads have a thread density of between 37% and 45%.

16. The fabric according to claim 14, wherein: said base structure is composed of two endless woven layers or of two woven layers that have been made endless; each of said two woven layers has said MD threads which, wholly or predominantly, have a diameter of between 0.25 mm and 0.45 mm; and each of said two woven layers has said MD threads with a thread density of more than 37%.

17. The fabric according to claim 14, wherein said textile structure is a flatweave, wherein warp threads of a loom provide said MD threads of the fabric and said flatweave is made endless by connecting front ends thereof.

18. The fabric according to claim 17, wherein the front ends are welded to form a welded connection.

19. The fabric according to claim 14, wherein at least some of said CD threads are twisted threads.

20. The fabric according to claim 19, wherein 50% or more of said CD threads are twisted threads.

21. The fabric according to claim 14, wherein the fabric has a thickness of 3.5 mm or less.

22. The fabric according to claim 21, wherein the fabric has a thickness of between 2.5 mm and 3 mm.

23. The fabric according to claim 14, wherein a weight of the fabric lies between 750 g/m.sup.2 and 1250 g/m.sup.2.

24. The fabric according to claim 23, wherein the weight of the fabric lies between 900 g/m.sup.2 and 1100 g/m.sup.2.

25. The fabric according to claim 14, wherein a proportion by weight of said nonwoven layers corresponds at most to a proportion by weight of said base structure.

26. The fabric according to claim 25, wherein the proportion by weight of said nonwoven layers is at most ⅔ of the proportion by weight of said base structure.

27. A machine for producing a tissue web, comprising; a press device with at least one press nip; and at least one fabric according to claim 14 disposed to run through said at least one press nip during an operation of said press device.

28. The machine according to claim 27, wherein said at least one press nip is an extended nip.

29. The machine according to claim 27, 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.

30. A method for producing a tissue web, the method comprising: providing a machine according to claim 22 and producing the tissue web in said machine.

31. The method according to claim 30, which comprises dewatering the tissue web in the press device by nip dewatering, and wholly or partly collecting water thus removed by a wastewater trap.

32. The method according to claim 31, wherein the nip dewatering makes up more than 10% of a total dewatering quantity of the press device.

33. The method according to claim 32, which comprises dewatering the tissue web in the at least one nip by between 20% and 50%.

Description

[0053] The invention will be explained in more detail below with reference to schematic figures, not to scale.

[0054] FIG. 1 shows a tissue machine according to one aspect of the invention.

[0055] 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. In a former 20, initial dewatering takes placed with the aid of an evacuated forming roll 21, around which the fabric 2 partly wraps. The former 20 in FIG. 1 is designed as a Crescent Former, 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 fabric 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 fabric 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.

[0056] The fabric 2 of the machine 1 shown in FIG. 1 is advantageously a fabric according to one aspect of the invention. Advantageously, it can comprise a base structure made of a flatweave, in particular a plain weave, which is made endless by connecting—e.g. welding—the front ends. The MD threads of this base structure 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 fabric 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 can be reduced such that it makes up only half or less of the weight of the fabric. Since, in a fabric 2 according to one aspect of the invention, the base structure performs part of the function of the nonwoven layers, this fabric can be designed to be very thin. As opposed to the tissue machines 1 known from the prior art, when such a fabric 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.

LIST OF DESIGNATIONS

[0057] 1 Tissue machine [0058] 2 Fabric [0059] 3 Tissue web [0060] 10 Headbox [0061] 20 Former [0062] 21 Forming roll [0063] 22 Outer wire [0064] 30 Press device [0065] 31 Press nip [0066] 32 Suction box, “Uhle Box” [0067] 33 Wastewater trap [0068] 34 Shoe roll [0069] 40 Drying apparatus [0070] 41 Yankee cylinder [0071] 42 Hood [0072] 43 Creping doctor [0073] 50 Scanner [0074] 60 Reel-up