Press arrangement

Abstract

A press arrangement for a machine for producing and/or processing a fibrous web, in particular a paper, board or tissue web. The arrangement has at least a central roll and a first and a second mating pressing unit. The first mating pressing unit forms a first press nip with the central roll, and the second mating pressing unit forms a second press nip with the central roll. The central roll has a plurality of pressure sensors embedded in the central roll and arranged beside one another in the cross-machine direction, by way of which the pressure profile in the cross-machine direction can be determined in the first and in the second press nip. There is also disclosed a method for operating such a press arrangement.

Claims

1. A press arrangement for a machine for producing and/or processing a fibrous web, comprising: a central roll; a first mating pressing unit disposed to form a first press nip with said central roll; a second mating pressing unit disposed to form a second press nip with said central roll; a plurality of pressure sensors embedded in said central roll and arranged beside one another in a cross-machine direction, said pressure sensors being configured to determine a pressure profile in the cross-machine direction in said first press nip and in said second press nip; and a Hall sensor disposed to issue a trigger signal during a rotation of said central roll for determining a rotational position of said pressure sensors during rotational movement of said central roll.

2. The press arrangement according to claim 1, wherein said pressure sensors are fiber-optic pressure sensors.

3. The press arrangement according to claim 2, wherein said fiber-optic pressure sensors are Bragg grating sensors.

4. The press arrangement according to claim 3, wherein all said Bragg grating sensors have a mutually different Bragg wavelengths.

5. The press arrangement according to claim 2, wherein at least one optical fiber is provided, wherein the at least one optical fiber comprises sections without Bragg grating sensors and sections formed as Bragg grating sensors, and in each case between two adjacent sections without Bragg grating sensors there is arranged a section formed as a Bragg grating sensor, and vice versa, and wherein each section with a Bragg grating sensor provides a pressure sensor and each section without a Bragg grating sensor provides part of at least one signal line connecting said pressure sensors to a signal excitation unit and/or to a signal evaluation unit.

6. The press arrangement according to claim 1, wherein said plurality of pressure sensors are connected by way of at least one signal line to a signal excitation unit and/or to a signal evaluation unit.

7. The press arrangement according to claim 1, wherein said central roll comprises a roll core and a cover substantially covering a circumferential surface of said roll core.

8. The press arrangement according to claim 7, wherein said cover has a functional layer located radially on the outside, to be brought into contact with the fibrous web or with a fabric of the machine for producing and/or processing the fibrous web.

9. The press arrangement according to claim 8, wherein said functional layer is selected from the group consisting of a polymer functional layer, a ceramic functional layer, and a metallic functional layer.

10. The press arrangement according to claim 7, wherein said pressure sensors are embedded in said cover or between said cover and said roll core.

11. The press arrangement according to claim 1, wherein said plurality of sensors comprise a first number of said pressure sensors arranged in a first region extending in the cross-machine direction over substantially a working width of said central roll, and an extent of said region in the circumferential direction is less than 30 cm.

12. The press arrangement according to claim 11, wherein said region in the circumferential direction is less than 15 cm.

13. The press arrangement according to claim 11, wherein said region in the circumferential direction is less than 5 cm.

14. The press arrangement according to claim 1, wherein at least one of said first and second mating pressing units is a press roll or a shoe press roll.

15. The press arrangement according to claim 14, wherein at least one of said press rolls is a deflection compensated press roll.

16. The press arrangement according to claim 1, wherein each of said first and second mating pressing units is a press roll and wherein one of said press rolls is a deflection compensated press roll and the other of said press rolls is not a deflection compensated press roll.

17. The press arrangement according to claim 1, wherein said first mating pressing unit is a press roll and said second mating pressing unit is a shoe press roll.

18. A method of measuring a pressure profile in a cross-machine direction in a press arrangement having at least two press nips, wherein a first press nip is formed between a first mating pressing unit and a central roll and a second press nip is formed between a second mating pressing unit and the central roll, and at least one of the two mating pressing units is a controlled deflection press roll or shoe press roll, and the central roll carries a plurality of pressure sensors arranged in the cross-machine direction, wherein the method comprises the following steps: rotating the central roll so that the pressure sensors pass the first and second press nip; issuing a trigger signal with a Hall sensor during a rotation of the central roll for determining a rotational position of the pressure sensors during a rotational movement of the central roll; measuring a pressure profile in the first press nip and in the second press nip with the pressure sensors; and determining a hydraulic pressure of the holding arms of the mounting of the bearing journals and/or supporting rams for supporting a roll shell with respect to a supporting yoke of a mounting of the controlled deflection press roll or shoe press roll.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) The invention will be explained further below by using schematic drawings, in which

(2) FIG. 1 shows a first embodiment of a press arrangement according to the invention,

(3) FIG. 2 shows a second embodiment of a press arrangement according to the invention, and

(4) FIG. 3 shows a detailed illustration of the central roll from FIG. 1.

DESCRIPTION OF THE INVENTION

(5) FIG. 1 shows a first embodiment of a press arrangement 6 according to the invention from a paper machine 1.

(6) A fibrous web 2 is transferred from a forming section 5 into the press arrangement 6 at a prick-up point 4 comprising a pick-up roll 3. The press arrangement 6 has a press nip 9 formed by two press rolls 7, 8, through which the fibrous web 2 runs first, before the latter is led through a first press nip 10 and a second press nip 11 of a central roll arrangement, in which a central roll 12 forms the first press nip 10 with a first mating pressing element formed as a press roll 13 and forms the second press nip 11 with a second mating pressing element formed as a press roll 14.

(7) In the present case, the press rolls 7, 8, 13 and 14 are driven, whereas the central roll 12 is not driven. The press roll 13 is also a controlled deflection press roll. The central roll 12 has a roll cover 15 with a polymer functional layer 16 made of glass fiber-reinforced epoxy resin and an adhesive layer 18 arranged radially between the roll core 17 and the functional layer 16.

(8) The material of the other roll covers of the other rolls can, for example, comprise polyurethane and/or natural rubber as a substantial constituent.

(9) According to the invention, the central roll 12 has a plurality of pressure sensors 19 embedded in the central roll 12 and arranged beside one another in the cross-machine direction, by means of which the pressure profile in the cross-machine direction can be determined in the first and in the second press nip 10, 11.

(10) As can be seen from the detailed illustration of FIG. 3, the pressure sensors 19 are arranged between the functional layer 16 and the adhesive layer 18 of the cover 15.

(11) In the present case, the pressure sensors 19 are Bragg-grating sensors which all have a mutually different Bragg wavelength.

(12) After the passage of the fibrous web 2 through the first and second press nip 10, 11 of the central roll arrangement, the fibrous web 2 is transferred into a drying section 20.

(13) The embodiment of FIG. 2 differs substantially from the embodiment of FIG. 1, in that the second press nip 11 of the central roll arrangement is formed by a shoe press roll 21 and the central roll 12, and by the fact that the central roll 12 a cover with a ceramic functional layer 16 of chromium oxide, which has been produced by a thermal spraying process.