METHOD FOR OPERATING A SHOE PRESS, SHOE PRESS, MACHINE COMPRISING A SHOE PRESS, AND USE OF AN INK IN A LUBRICANT FOR A SHOE PRESS

Abstract

A shoe press has a shoe on which a radial inner surface of a press jacket slides. In a method of operating the shoe press, lubricating fluid is introduced between the shoe and the press jacket for lubricating purposes. The press jacket has at least one polymer layer into which a reinforcing structure is integrated, the reinforcing structure including at least one reinforcing thread. The lubricating fluid, the at least one polymer layer, and/or the at least one reinforcing thread is/are designed such that the lubricating fluid reaches the at least one reinforcing thread of the reinforcing structure and produces a color change in same in the event the polymer layer breaks. There is also described a shoe press, the inclusion of a press jacket in such a shoe press, and a machine with such a shoe press.

Claims

1-15. (canceled)

16. A method for operating a shoe press, the method comprising providing a press cover with at least one polymer layer having a reinforcing structure embedded therein, the reinforcing structure including at least one reinforcing thread, and the press cover having a radially inner surface for gliding on a shoe of the shoe press; introducing a lubricating fluid between the shoe and the press cover for lubrication; providing the lubricating fluid, the at least one polymer layer, and/or the at least one reinforcing thread such that, in the event of a breakage of the polymer layer, the lubricating fluid reaches the at least one reinforcing thread of the reinforcing structure and brings about a color change of the reinforcing thread.

17. The method according to claim 16, which comprises adding a dye to the lubricating fluid, wherein the dye changes a color of the reinforcing threads of the reinforcing structure in the event of a breakage of the polymer layer.

18. The method according to claim 17, which comprises choosing the dye from the group of luminescent dyes selected from the group consisting of a fluorescent dye and a phosphorescent dye and configured to emit light as a result of energy supplied from outside.

19. The method according to claim 17, which comprises adding a luminescent dye responding to ultraviolet light.

20. A shoe press, comprising: a press cover having at least one polymer layer and a reinforcing structure embedded therein, said reinforcing structure including at least one reinforcing thread, and said press cover having a radially inner surface; a shoe disposed to have the radially inner surface of said press cover glide thereon; a lubricant reservoir with lubricating fluid for introducing the lubricating fluid between said shoe and said press cover; wherein at least one of said lubricating fluid or said at least one reinforcing thread is configured such that, in the event of a breakage of said polymer layer, said lubricating fluid reaches said at least one reinforcing thread of said reinforcing structure and brings about a color change of said at least one reinforcing thread.

21. The shoe press according to claim 20, which comprises dye added to said lubricating fluid, said dye being configured to change a color of the reinforcing threads of said reinforcing structure in the event of a breakage of said polymer layer.

22. The shoe press according to claim 21, wherein the dye is a luminescent dye chosen from the group consisting of fluorescent dye and phosphorescent dye and configured to emit light as a result of energy supplied from outside.

23. The shoe press according to claim 21, wherein the dye is a luminescent dye responding to ultraviolet light.

24. The shoe press according to claim 20, wherein the lubricating fluid is an oil.

25. The shoe press according to claim 20, wherein said at least one polymer layer is produced from polyurethane or comprises a polyurethane, and said at least one reinforcing thread is produced from a polymer or comprises a polymer, and said polymer is selected from the group consisting of polyester, polyethylene naphthalate, and polyamide.

26. The shoe press according to claim 20, wherein said polymer is aramid.

27. The shoe press according to claim 20, wherein a material of said reinforcing structure and a material of said at least one polymer layer have mutually different levels of transmittance for visible light.

28. The shoe press according to claim 27, wherein the transmittance of the material of said at least one polymer layer is higher than the transmittance of said reinforcing structure by more than 1.1-1.5 times.

29. The shoe press according to claim 20, wherein a material of said reinforcing structure and a material of said at least one polymer layer are chosen such that a transmittance of the entire press cover for visible light lies between 5% and 100%.

30. The shoe press according to claim 29, wherein the transmittance of the press cover lies between 15% and 35%.

31. The shoe press according to claim 29, wherein the transmittance of the press cover corresponds to a total transmission according to ASTM D 1003-00 and is measured in a radial direction of the press cover.

32. The shoe press according to claim 20, wherein said at least one polymer layer is undyed.

33. The shoe press according to claim 20, wherein said at least one reinforcing thread is one of a plurality of longitudinal reinforcing threads extending in a longitudinal direction of the press cover, over a circumference of the press cover, and at a spacing distance and parallel to one another.

34. The shoe press according to claim 33, wherein at least one further reinforcing thread is provided as a circumferential thread that extends helically in the circumferential direction of the press cover within said polymer layer, and wherein said longitudinal reinforcing threads and said at least one further reinforcing thread that is formed as a circumferential thread together form a laid fabric, with said longitudinal reinforcing threads being arranged radially within said at least one circumferential thread, viewed in relation to the longitudinal axis of the press cover.

35. The shoe press according to claim 20, wherein said at least one polymer layer is one of a plurality of polymer layers and said at least one polymer layer, viewed in relation to the longitudinal axis of the press cover, is a radially inner or innermost polymer layer and said plurality of polymer layers includes a radially outermost polymer layer.

36. The shoe press according to claim 35, wherein the plurality of polymer layers are exactly two polymer layers with the radially inner polymer layer simultaneously being the radially innermost polymer layer of the press cover.

37. A machine, comprising a shoe press according to claim 20.

38. In a shoe press having a shoe, a press cover with a radially inner surface disposed to glide on the shoe, and a lubricant reservoir for introducing a lubricating fluid between the shoe and the press cover, the improvement which comprises: the press cover having at least one polymer layer and a reinforcing structure embedded in the polymer layer, with the reinforcing structure including at least one reinforcing thread; the lubricating fluid containing a dye; and the lubricating fluid and/or the at least one reinforcing thread being configured such that, on occasion of a breakage of the polymer layer, lubricating fluid and the dye reach the at least one reinforcing thread of the reinforcing structure and bring about a color change of the at least one reinforcing thread.

39. The improvement according to claim 38, wherein the dye is a luminescent dye chosen from the group consisting of fluorescent dye and phosphorescent dye and configured to emit light as a result of energy supplied from outside.

40. The improvement according to claim 38, wherein the dye is a luminescent dye responding to ultraviolet light.

41. The improvement according to claim 38, wherein the lubricating fluid is an oil.

Description

[0038] The invention will be explained in more detail below with reference to the drawings without restricting the generality. In the drawings:

[0039] FIG. 1 shows a partly sectioned schematic side view of a shoe press having a press cover according to an exemplary embodiment of the present invention;

[0040] FIGS. 2a and 2b show embodiments of a press cover, in each case viewed in a section through its longitudinal axis;

[0041] FIG. 3 shows a highly schematic illustration of a device for producing the press cover in a side view.

[0042] FIG. 1 illustrates a partly sectioned schematic side view of a shoe press 10 which, in the present case, comprises a press roll according to the invention such as a shoe press roll 12, and an opposing roll 14. The shoe press roll 12 and the opposing roll 14 are arranged parallel to each other with respect to their longitudinal axes. Together, they form a nip 22 or delimit such a nip.

[0043] While the opposing roll 14 here comprises a cylindrically configured roll rotating about its longitudinal axis, the shoe press roll 12 is composed of a shoe 16, a stationary yoke 18 carrying the latter and a press cover 20. The shoe 16 and yoke 18 are arranged to be stationary in relation to the opposing roll 14 and the press cover 20. This means that they do not rotate. The shoe 16 is supported by the yoke 18 and pressed by hydraulic pressing elements, not illustrated, onto the radially innermost surface of the press cover 20 revolving relative thereto. The press cover 20 surrounds the shoe 16 and yoke 18 in the circumferential direction and rotates about its longitudinal axis in the opposite direction of rotation to the opposing roll 14. Because of the concave configuration of the shoe 16 on its side facing the opposing roll 14, the result is a comparatively long nip 22.

[0044] The shoe press 10 is suitable in particular for dewatering fibrous webs 24. During the operation of the shoe press, a fibrous web 24 having one or two press felts 26, 26′ is guided through the press nip 22. In the present case, there are exactly two press felts 26, 26′, which pick up the fibrous web 24 between them in the manner of a sandwich. During the passage through the nip 22, a pressure is exerted indirectly on the fibrous web 24 in the nip 22 by the press felts 26, 26′. This is done by the radially outermost surface of the opposing roll 14, on the one hand, and the radially outermost surface of the press cover 20 coming directly into contact with the corresponding press felts 26, 26′. The liquid emerging from the fibrous web 24 is picked up temporarily by the press felt or felts 26, 26′ and any depressions (not illustrated) provided in the press cover surface. After leaving the nip 22, the liquid picked up by the depressions of the press cover 20 is thrown off before the press cover 20 enters the press nip 22 again. In addition, the water picked up by the press felt 26, 26′ can be removed by suction elements after leaving the press nip 22.

[0045] In a further embodiment of the invention, not illustrated in the figures, it is possible to dispense with the press felts 26, 26′. In such a case, the fibrous web 24 is directly in contact on one side with the press cover 20 and on the other side with the opposing roll 14, which together form a press nip. The opposing roll can then be designed as a heated drying cylinder.

[0046] Irrespective of the embodiment illustrated, the radially inner surface the press cover 20 slides on the shoe 16. The shoe 16 has a fluidic connection to a lubricant reservoir 28 to supply lubricating fluid. This is indicated by the dashed line. Although not illustrated, appropriate means can be provided to deliver the lubricant from the lubricant reservoir 28 to the shoe 16, e.g. pumps.

[0047] The press cover illustrated in FIG. 1 can be designed according to the invention, as illustrated in the following figures.

[0048] FIGS. 2a and 2b illustrate different embodiments of the invention in a cross section, not to scale and illustrated partially, through the longitudinal axis 20′ of the finished press cover 20. The distance of the longitudinal axis 20′ to the radially innermost surface of the corresponding polymer layer of the press cover 20 is likewise not illustrated to scale.

[0049] According to FIG. 2a, exactly two polymer layers are provided, namely a first 20.1 and a second 20.2. In the present case, the first polymer layer 20.1 is simultaneously the radially outermost polymer layer of the press cover 20. On the other hand, the second polymer layer 20.2 is simultaneously the radially innermost polymer layer of the press cover 20. The two polymer layers 20.1, 20.2 adjoin each other directly as seen in the radial direction, i.e. there is no intermediate layer between these two.

[0050] As illustrated, a reinforcing structure 20″ can be provided in the second polymer layer 20.2. In the present case, this is embedded completely in the polymer layer 20.2. This is indicated by the hatched circles, which can be textile surface structures or linear structures such as fibers. This means that the reinforcing structure 20″ does not extend beyond the limits of the polymer layer 20.2.

[0051] The reinforcing structure 20″ here comprises a plurality of reinforcing threads 21 serving as longitudinal threads 21.1. These are arranged in the longitudinal direction of the press cover 20, extending over its circumference at a distance from and parallel to one another. In addition, here at least one further reinforcing thread 21 is provided as a circumferential thread 21.2, which extends helically in the circumferential direction of the press cover, preferably within the same polymer layer 20.1, 20.2, 20.3 in which the longitudinal threads 21.1 are also arranged. The longitudinal threads 21.1 and the circumferential thread 21.2 form a laid fabric with one another, namely in such a way that the longitudinal threads 21.1 are arranged radially within the at least one circumferential thread 21.1—viewed in relation to the longitudinal axis 20′ of the press cover 20.

[0052] In the present case, the first and a second polymer layer 20.1, 20.2 are produced from a polyurethane. This is obtainable, for example, from a pre-polymer and a cross-linker. The respective pre-polymer itself is obtainable by reaction of an isocyanate with a polyol.

[0053] FIG. 2b shows a three-layer press cover in a modification relative to FIG. 2a. This comprises a—here radially outermost—first polymer layer 20.1, a radially innermost, third polymer layer 20.3 and a second polymer layer 20.2 arranged in the manner of a sandwich between these two. The arrangement—as also in the illustration of FIG. 2a—is related starting from the longitudinal axis 20′ of the press cover 20 as seen in its radial direction. In the present case, a (single) reinforcing structure 20″ is provided only in the second polymer layer 20.2. Of course, this could also be different so that, alternatively or additionally, such a reinforcing structure 20″ could also be arranged in the first polymer layer 20.1 and/or the third polymer layer 20.3. That explained in relation to the reinforcing structure 20″ in FIG. 2a applies analogously.

[0054] If, in FIG. 1, a lump then gets into the press nip, then this can lead to local loadings and break up the polymer layer in which the reinforcing structure is embedded. Breaking up therefore means that case in which the polymer layer is separated mechanically with the result that lubricant reaches the latter or the reinforcing structure. Then, lubricant can get into the reinforcing threads. According to the invention, in such a case, a color change, for example a local color change, then takes place in the reinforcing threads of the reinforcing structure. As a result, such a lump passage can now be detected sooner than previously, detected in good time with the means mentioned at the beginning. To be specific, still before leakage of the lubricant through the press cover to the outside in the direction of the fibrous web 24 occurs. In particular, in this way the stoppage times of a press device equipped with such a press cover can be reduced considerably.

[0055] It has been shown that the advantages according to the invention are implemented particularly well if the polyurethane of the at least one polymer layer 20.1, 20.2, 20.3 or all the polymer layers, as mentioned at the beginning, is chosen in such a way that it is more transparent than the material of the reinforcing structure 20″.

[0056] FIG. 3 shows a highly schematic side view of a device for producing a press cover 20 according to the invention. The device has exactly one cylindrical winding mandrel 4 in the present case, wherein, for example, a starting material 20′″ is applied helically to its radially outermost lateral surface here. After being embedded in the polymer, the starting material 20″″ forms the reinforcing structure 20″ of the finished press cover 20 according to the invention.

[0057] The illustration shows an initial stage of the production method. In the present case, to this end the one end of the starting material 20′″ is fixed to a polymer which is arranged on the outer circumference of the winding mandrel 4. Apart from the schematic illustration shown, the one end of the starting material 20′″ could also rest on or be applied directly to the winding mandrel 4 without a polymer initially being provided between the starting material 20′″ and the winding mandrel 4. The starting material 20′″ can be a textile surface structure or linear structure.

[0058] The winding mandrel 4 is rotatably mounted about its longitudinal axis 20′, which corresponds to the longitudinal axis of the press cover to be produced. Here, the longitudinal axis 20′ extends perpendicularly into the drawing plane. Via a line 5, a casting material, such as a castable, curable elastomeric polymer, e.g. polyurethane, is put from above through a casting nozzle 6 onto the radially outermost lateral surface of the winding mandrel 4 and onto the starting material 20′″. Such a casting material can be chosen in such a way, for example with regard to its pot time and viscosity, such that it does not drip off the winding mandrel 4 during the casting. During this, the winding mandrel 4 is rotated about its longitudinal axis in the direction of the arrow. At the same time as this rotation, the casting nozzle 6 is guided via a suitable guide, not further illustrated in FIG. 3, parallel to the longitudinal axis 20′ and along the latter relative to the winding mandrel 4. At the same time as the casting material is poured on, the starting material 20′″ is rolled and wound onto the rotating winding mandrel 4 to form helices. The casting material can get through the starting material 20′″ as far as the winding mandrel 4. In this example, after the curing step, the polymer forms a radially innermost and preferably elastomeric polymer layer, which corresponds to the polymer layer 20.2 of the press cover from FIG. 2a, of which only part is shown in FIG. 3.

[0059] The casting material emerging from the casting nozzle 6 in the present case is a mixture of a pre-polymer and a cross-linker. The first is provided from a pre-polymer container, not shown, in which it is stored or stirred. The pre-polymer is the reaction product of an isocyanate according to the invention and a polyol. It can be present in the pre-polymer container, for example, in the form of a pre-polymer made of the materials just mentioned.

[0060] The cross-linker can be provided in a cross-linker container.

[0061] The pre-polymer container and cross-linker container are associated with the device for producing a press cover 20. They have a fluidic connection via lines, likewise not illustrated, to a mixing chamber (not illustrated) connected upstream of the casting nozzle 6 in the flow direction. The pre-polymer-cross-linker mixture is therefore produced upstream and outside of the casting nozzle 6, that is to say mixed in the mixing chamber. Irrespective of the production of the mixture, this is then applied to the surface of the winding mandrel 4 to form the at least one polymer layer of the press cover 20.

[0062] In principle, it would be conceivable that two or more casting nozzles 6 could be provided. These could be connected via appropriate lines to separate pre-polymer and cross-linker containers, in order also to supply different polymers to the plurality of casting nozzles 6, independently of one another. The casting nozzles 6 could be then arranged at a distance from one another along the longitudinal axis of the press cover 20 in order to produce a plurality of polymer layers 20.1, 20.2, 20.3 simultaneously by simultaneous application of the polymer from the casting nozzles 6 in one pour.

[0063] By means of such a continuous casting process, which is also known as rotation casting, an endless cylindrically tubular press cover 20 intrinsically closed about its longitudinal axis 20′ is thus produced step-by-step over the width of the winding mandrel 4, the inner circumference of the press cover 20 corresponding substantially to the outer circumference of the winding mandrel 4.

[0064] In principle, it would be conceivable to wind the starting material 20′″ onto more than the one winding mandrel 4 shown in FIG. 3. For example, two winding mandrels could be provided, which could be arranged in parallel with regard to their longitudinal axes at a distance from one another. Alternatively, it would also be conceivable to also apply the polymer to the radially inner lateral surface of the winding model 4, for example in a spinning manner. Irrespective of the embodiment mentioned, the finished press cover 20 is finally taken off the at least one winding mandrel 4.

[0065] As illustrated in FIG. 3, the press cover 20 is designed according to the invention.

[0066] Although this is not illustrated in the figures, the reinforcing structure 20″ of the at least one polymer layer 20.1, 20.2 could also be built up from a plurality of starting materials 20′″ laid over one another in the radial direction and each extending in the longitudinal axial direction and in the circumferential direction of the press cover 20.