Press cover, use thereof, and press roll and shoe press

Abstract

A press cover has at least one polymer layer in which a reinforcing structure is embedded. The reinforcing structure has at least one reinforcing thread as a longitudinal thread which runs in the longitudinal direction of the press cover. The at least one reinforcing thread itself is produced by interlacing a plurality of fibers or fiber bundles with one another. There is also described the use of such a press cover, as well as a press roll and a shoe press.

Claims

1. A press cover, comprising: at least one polymer layer having a reinforcing structure embedded therein; said reinforcing structure including at least one reinforcing thread being a longitudinal thread extending in a longitudinal direction of the press cover; said at least one reinforcing thread being formed of a plurality of fibers or fiber bundles interlaced with one another, a number of fibers or fiber bundles from which an individual said reinforcing thread is produced being an odd number greater than one, and said reinforcing thread representing being a flat braid.

2. The press cover according to claim 1, wherein said at least one reinforcing thread is one of a plurality of reinforcing threads each being longitudinal threads, which, extending in the longitudinal direction of the press cover, are arranged at a distance from and parallel to one another over a circumference of the press cover.

3. The press cover according to claim 1, comprising at least one further reinforcing thread being a circumferential thread.

4. The press cover according to claim 3, wherein said at least one further reinforcing thread extends within said polymer layer in form of a helix in a circumferential direction of the press cover.

5. The press cover according to claim 3, wherein a plurality of said reinforcing threads being said longitudinal threads and said at least one further reinforcing thread being a circumferential thread form a laid fabric with one another.

6. The press cover according to claim 5, wherein said longitudinal threads are arranged radially within said at least one circumferential thread, as viewed relative to a longitudinal axis of the press cover.

7. The press cover according to claim 5, wherein, as viewed in the radial direction of the press cover, said longitudinal threads are spaced apart in the radial direction from said at least one circumferential thread at crossing points.

8. The press cover according to claim 1, comprising at least one radially outermost polymer layer, being radially outermost in relation to the longitudinal axis of the press cover, and a radially inner polymer layer, being a radially inner layer in relation to the longitudinal axis of the press cover.

9. The press cover according to claim 8, wherein said radially inner polymer layer has a reinforcing structure embedded therein, said reinforcing structure including at least one reinforcing thread being a longitudinal thread extending in the longitudinal direction of the press cover, and said at least one reinforcing thread being formed of a plurality of fibers or fiber bundles interlaced with one another.

10. The press cover according to claim 8, wherein said outermost and inner polymer layers are exactly two polymer layers of the press cover, and said radially inner polymer layer is a radially innermost polymer layer of the press cover.

11. A press roll for a shoe press for treating a fibrous material web, the press roll comprising at least one press cover according to claim 1.

12. The press roll according to claim 11, being a shoe press roll.

13. A shoe press for treating a fibrous material web, the shoe press comprising: a press roll and an opposing roll together delimiting a nip; and a rotating press cover being a press cover according to claim 1.

14. A method of treating a fibrous material web, the method comprising: providing a press cover according to claim 1; integrating the press cover into a shoe press and treating the fibrous material web in the shoe press.

15. The method according to claim 14, which comprising treating paper, board, tissue, or pulp web.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) 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;

(2) FIGS. 2a and 2b show embodiments of a press cover, as seen in each case in a section through its longitudinal axis;

(3) FIG. 3 shows a highly schematic illustration of a device for producing the press cover in a side view;

(4) FIGS. 4a and 4b show a highly simplified illustration, not to scale, of an end of a reinforcing thread according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(5) 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. With regard to their longitudinal axes, the shoe press roll 12 and opposing roll 14 are arranged parallel to each other. Together, they form a nip 22 or delimit such a nip.

(6) While the opposing roll 14 here consists of a cylindrically configured roll rotating about its longitudinal axis, the shoe press roll 12 is assembled from a shoe 16, a stationary yoke 18 carrying the latter and a press cover 20. In relation to the opposing roll 14 and the press cover 20, the shoe 16 and yoke 18 are arranged to be stationary. This means that they do not rotate. The shoe 16 is supported herein by the yoke 18 and, via hydraulic press elements, not illustrated, is pressed onto the radially innermost surface of the press cover 20 rotating relative thereto. The press cover 20, which surrounds the shoe 16 and the yoke 18 in the circumferential direction, in the process 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, a comparatively long nip 22 results.

(7) The shoe press 10 is suitable in particular for dewatering fibrous material webs 24. During the operation of the shoe press, a fibrous material web 24 is guided through the press gap 22 with one or two press felts 26, 26′. In the present case, there are exactly two press felts 26, 26′, which accommodate the fibrous material 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 material web 24 in the nip 22 through 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 material web 24 is temporarily picked up 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 gap 22 again. In addition, the water picked up by the press felt 26, 26′ can be removed by suction elements after leaving the press gap 22.

(8) In a further embodiment of the invention, not illustrated in the figures, it is possible to omit the press felts 26, 26′. In such a case, the fibrous material web 24 is directly in contact with the press cover 20 on the one hand and on the other hand with the opposing roll 14 which, together, form a press nip. Said opposing roll 14 can then be designed as a heated drying cylinder.

(9) The press cover illustrated in FIG. 1 can be designed according to the invention, as illustrated in the following figures.

(10) In FIGS. 2a and 2b, different embodiments of the invention are illustrated in a partially illustrated cross section, not to scale, 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.

(11) The illustration of FIG. 2a shows a press cover 20 having a single polymer layer 20.1. A reinforcing structure 20″ is embedded therein. In the present case, the polymer layer 20.1 is produced from a polyurethane. This can be obtained from a prepolymer and a crosslinker.

(12) According to the illustration of FIG. 2b, exactly two polymer layers are provided in unbroken lines, 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. The arrangement relates—as also in the illustration of FIG. 2a—as viewed starting from the longitudinal axis 20′ of the press cover 20 in the radial direction thereof. 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 viewed in the radial direction, i.e. there is no intermediate layer between these two. A third polymer layer 20.3 is also indicated in dashed lines. The last-named is arranged radially within the second polymer layer 20.2. 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. Here, too, the first and the second polymer layer 20.1, 20.2 are each produced from a polyurethane or contain one such. That stated also applies analogously to FIG. 2a.

(13) The reinforcing structure 20″ in the two embodiments of FIG. 2 is respectively embedded completely into the corresponding polymer layer 20.1 or 20.2. This means that the reinforcing structure 20″ does not extend beyond the limits of the polymer layer 20.1, 20.2. In principle, it would be conceivable for the reinforcing structure 20″ to extend beyond the limit of two, immediately adjacent polymer layers 20.1, 20.2, 20.3. In other words, the reinforcing structure 20″ would be simultaneously embedded into two adjacent polymer layers 20.1, 20.2, 20.3.

(14) The reinforcing structure 20″ can herein consist of a plurality of reinforcing threads 21 formed as longitudinal threads 21.1. These extend parallel to the longitudinal axis 20′ of the press cover 20 and are arranged relative to one another so as to be distributed at a distance over the circumference thereof. This can best be seen in FIG. 3.

(15) In addition, one or more reinforcing threads 21 each extending spirally over the circumference of the corresponding polymer layer 20.1, 20.2 and designed as circumferential threads 21.2 can also be provided, once more see FIG. 2. The last-named are indicated by broken circles drawn in FIGS. 2a and 2b. In the illustration of FIG. 2, the plurality of longitudinal threads 21.1 and the at least one circumferential thread 21.2 form a laid fabric with one another. Here, the circumferential threads 21.2 are arranged in such a way that they surround the longitudinal threads 21.1, that is to say are arranged radially further out than the longitudinal threads 21.1. Longitudinal threads 21.1 and the at least one circumferential thread 21.2 cross one another as viewed in the radial direction as a result of the spiral winding of the at least one circumferential thread 21.2. As viewed in the radial direction (that is the say in the sectional illustration of FIGS. 2a and b), they do not touch at these crossing points, however, but are arranged at a distance from one another. This has the advantage that an improved force distribution from local overloads acting radially on the press cover 20 from the outside is transferred in the radially inward direction onto the longitudinal threads 21.1 via the at least one circumferential thread 21.2.

(16) As indicated in FIG. 2, the radially outermost surface of the press cover 20 or the corresponding polymer layer 20.1 can have grooves or blind holes.

(17) FIGS. 4a and 4b show a highly simplified illustration, not to scale, of an end of a reinforcing thread 21 according to the invention, which can be designed as a longitudinal thread 21.1 and/or a circumferential thread 21.2. The illustration shows for clarity how such a reinforcing thread 21 is produced, i.e. the distances of the individual fibers or fiber bundles 22 from one another are illustrated exaggeratedly large.

(18) In the illustration of FIGS. 4a and b, both reinforcing threads 21 are produced by braiding a plurality of fibers or fiber bundles 22. In FIG. 4a, an odd number of fibers or fiber bundles 22 (here: three) is herein provided, so that a reinforcing thread 21 which is a flat braid results therefrom. In FIG. 4b, on the other hand, an even number of fibers or fiber bundles 22 (here: four) is provided, so that a round braid results as a reinforcing thread 21. In both cases, the fibers or fiber bundles 22 of each reinforcing thread 21 are intertwined in the manner of a plait.

(19) The reinforcing thread 21 illustrated in FIGS. 4a and b can be used as a longitudinal or circumferential thread 21.1, 21.2 in the reinforcing structure 20″ of the press cover 20, as explained in the preceding figures.

(20) FIG. 3 shows a device for producing a press cover 20 according to the invention in a highly schematic side view. The device in the present case has exactly one cylindrical winding mandrel 4. On the circumference, a plurality of reinforcing fibers 21 formed as longitudinal threads 21.1 are provided at a distance from one another. A polymer is applied to the radially outermost circumferential surface of the winding mandrel 4 in order to apply a polymer layer 20.1, 20.2, 20.3—as described in the preceding figures. In addition, for example, a circumferential thread 21.2 is introduced spirally into the polymer of the polymer layer 20.1, 20.2, 20.3. The circumferential thread 21.2, after being embedded into the polymer together with the longitudinal threads 21.1, forms the reinforcing structure 20″ of the finished press cover 20 according to the invention.

(21) 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. The longitudinal axis 20′ here extends perpendicularly into the drawing plane. Via a line 5, the casting material, such as a castable, curable elastomeric polymer, for example polyurethane, is discharged from above through a casting nozzle 6 onto the radially outermost circumferential surface of the winding mandrel 4 and onto the longitudinal threads 21.1. Such a casting material can, for example, be chosen with regard to its pot-time and viscosity in such a way that it does not drip off the winding mandrel 4 during the casting. During this process, 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 along in a relative manner on the winding mandrel 4, parallel to and along the longitudinal axis 20′, via a suitable guide which is not further illustrated in FIG. 3. At the same time as the casting material is poured on, the at least one circumferential thread 21.2 is unwound and wound spirally onto the rotating winding mandrel 4 to form helices. The casting material can herein pass through the longitudinal threads 21.1 as far as the winding mandrel 4. In this example, following the curing step, the polymer forms a radially innermost and preferably elastomeric polymer layer which, for example, corresponds to the polymer layer 20.1 of the press cover from FIG. 2a, of which only a part is shown in FIG. 3.

(22) The casting material emerging from the casting nozzle 6 is a mixture of a prepolymer and a crosslinker. The former is provided from a prepolymer container, not shown, in which it is stored or stirred. The prepolymer can comprise an isocyanate according to the invention and a polyol. It can be present in the prepolymer container, for example, in the form of a prepolymer made of the materials just mentioned. The crosslinker can be provided in a crosslinker container. The prepolymer container and the crosslinker container are assigned to the device for producing a press cover 20. They have a flow-carrying connection via lines, likewise not shown, to a mixing chamber (not illustrated) connected upstream of the casting nozzle 6 in the flow direction. The prepolymer-crosslinker mixture is thus produced upstream and outside of the casting nozzle 6, i.e. mixed in the mixing chamber. Irrespective of the production of the mixture, the latter is then applied to the surface of the winding mandrel 4 to form the at least one polymer layer of the press cover 20.

(23) By means of such a continuous casting process, which is also known as rotational casting, an endless, cylindrically tubular press cover 20, which is intrinsically closed about its longitudinal axis 20′ and the inner circumference of which corresponds substantially to the outer circumference of the winding mandrel 4, is therefore gradually produced over the width of the winding mandrel 4.

(24) In principle, it would be conceivable to wind the reinforcing threads 21 onto more than the one winding mandrel 4 shown in FIG. 3. For example, two winding mandrels could be provided, which could be arranged at a distance from one another parallel relative to their longitudinal axes. Alternatively, it would also be conceivable to apply the polymer also to the radially inner circumferential surface of the winding mandrel 4, for example in a centrifugal manner. Irrespective of the embodiment mentioned, the finished press cover 20 is finally taken off the at least one winding mandrel 4.

(25) As illustrated in FIG. 3, the press cover 20 is designed according to the invention.

(26) 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 laid fabrics of longitudinal and circumferential threads 21.1, 21.2, each extending in the longitudinal axial direction and in the circumferential direction of the press cover 20 and laid above one another in the radial direction.