METHOD AND DEVICE FOR THE DETERMINATION OF THE CONTAMINATION OF A SUCTION ROLL OF A MACHINE FOR PRODUCING A FIBROUS WEB

Abstract

A method and a suitable device determine the contamination of a suction roller of a machine for producing a fibrous web, in particular a paper, cardboard, tissue or pulp web. The method includes the steps of: a. flowing a fluid through a measurement area of a roller shell, wherein either the pressure or the throughflow speed of the fluid is kept constant; b. determining a characteristic variable, wherein the characteristic variable includes the resulting throughflow speed in the case of a throughflow at a constant pressure and of the resulting pressure drop in the case of the measurement at a constant throughflow speed; c. providing one or more reference variables; and d. determining a degree of contamination of the suction roller by way of comparison of the characteristic variable with the reference variable or variables.

Claims

1-13. (canceled)

14. A method for determining contamination of a suction roller of a machine for producing a fibrous web, which comprises the following steps of: a) causing a fluid to flow through a measuring area A of a roller shell, either a pressure or a flow rate of the fluid being kept constant; b) determining a characteristic variable K, the characteristic variable K including the flow rate with a flow at a constant pressure and of a resultant pressure drop during a measurement with a constant flow rate; c) providing at least one reference variable; and d) determining a level of the contamination of the suction roller by comparing the characteristic variable K with the at least one reference variable.

15. The method according to claim 14, which further comprises repeating the steps a) and b) n times on measuring areas A.sub.i(i=1, . . . n), by which means variables K.sub.i are determined and the characteristic variable K is formed as an average of the variables K.sub.i.

16. The method according to claim 14, which further comprises providing a gas as the fluid.

17. The method according to claim 14, which further comprises maintaining the flow at the constant pressure, and the constant pressure is chosen between 20 Pa and 200 Pa.

18. The method according to claim 14, which further comprises maintaining the flow at the constant flow rate, wherein the constant flow rate is chosen between 250 mm.sup.3/mm.sup.2/s and 2000 mm.sup.3/mm.sup.2/s.

19. The method according to claim 15, wherein the measuring area A or at least one of the measuring areas Ai has an area content of less than 4000 mm.sup.2.

20. The method according to claim 14, wherein the determining of the level of the contamination is carried out by a remaining running time R of the suction roller being carried out by comparing the characteristic variable K with the at least one reference variable.

21. The method according to claim 14, which further comprises selecting the fibrous web from the group consisting of paper, a board, tissue or a pulp web.

22. The method according to claim 15, wherein then times is selected from the group consisting of at least 4 times and at least 8 times.

23. The method according to claim 16, which further comprises providing air as the gas.

24. The method according to claim 14, which further comprises maintaining the flow at the constant pressure, and the constant pressure is chosen between 50 Pa and 150 Pa.

25. The method according to claim 14, which further comprises maintaining the flow at the constant flow rate, wherein the constant flow rate is chosen between 500 mm.sup.3/mm.sup.2/s and 1000 mm.sup.3/mm.sup.2/s.

26. The method according to claim 15, wherein the measuring area A or at least one of the measuring areas Ai has an area content of between 2000 mm.sup.2 and 3000 mm.sup.2.

27. A device for determining a contamination of a suction roller of a machine for producing a fibrous web, the device comprising: a fluid source set up to provide a fluid at a constant pressure or a constant flow rate; measuring means for determining a flow rate and/or a pressure drop of the fluid; and a computer, the device being set up to carry out a method for determining the contamination of the suction roller, which comprises the following steps of: a) causing the fluid to flow through a measuring area of a roller shell, either a pressure or the flow rate of the fluid being kept constant; b) determining a characteristic variable K, the characteristic variable K including the flow rate with the flow at the constant pressure and of a resultant pressure drop during a measurement with the constant flow rate; c) providing at least one reference variable; and d) determining a level of the contamination of the suction roller by comparing the characteristic variable K with the at least one reference variable.

28. The device according to claim 27, further comprising a first connecting piece having a first inlet and a first outlet, through which the fluid can flow from said first inlet to said first outlet, wherein said first inlet is or can be connected to said fluid source, and said first outlet is shaped such that it can be placed on the roller shell being a first cylindrical roller shell and encloses a measuring area there.

29. The device according to claim 28, further comprising a sealing means provided on said first outlet in order to seal off an interior of said first connecting piece with respect to surroundings.

30. The device according to claim 28, wherein said first connecting piece is detachably connected to said fluid source.

31. The device according to claim 28, further comprising a flow-obstructing element disposed in an interior of said first connecting piece.

32. The device according to claim 28, further comprising a second connecting piece having a second inlet and a second outlet, said second inlet is or can be connected to said fluid source additionally or alternatively to said first inlet, and said second outlet is shaped such that it can be placed on a second cylindrical roller shell and encloses the measuring area A there, wherein the second cylindrical roller shell has a different diameter from the first cylindrical roller shell.

33. The device according to claim 31, wherein said flow-obstructing element is a grille or a filter element.

Description

[0053] In the following, the invention will be explained further by using schematic figures, not to scale.

[0054] FIG. 1 shows, schematically, a device according to one aspect of the invention.

[0055] FIGS. 2a and 2b show trial results for different aspects of the invention.

[0056] The device shown in FIG. 1 for the determination of the contamination of a suction roll has a fluid source 1, which provides a fluid, in particular air, at a pressure p and a flow rate {dot over (V)}. By means of the device, the fluid is led through the openings 3a of the roll shell 3 in the form of holes 3a. The pressure can be kept constant, and the resultant flow rate can be determined by measuring means, not illustrated here. Alternatively, with a constant flow rate, the resultant pressure drop can also be determined. The characteristic variable K thus determined can then be compared with a reference variable K0 for the uncontaminated roll, and a level of contamination can be determined therefrom.

[0057] Furthermore, the device has a connecting piece 2, in particular a first connecting piece 2. This has an inlet 10 and an outlet 20. This connecting piece 2 is connected to the fluid source 1 by its inlet 10. Fluid can flow through the connecting piece 2. The outlet 20 is shaped such that it can be placed on the cylindrical roll shell 3. It encloses the measuring area A and prevents the medium escaping into the surroundings. It is thus possible to ensure that the fluid flows exclusively through the openings 3a of the roll shell 3. In addition, sealing means can be provided at the edge of the outlet 20 in order to seal off the interior of the connecting piece 2 with respect to the surroundings. In particularly preferred embodiments, the edge of the outlet 20 itself can serve as a sealing means. Thus, for example, the edge of the outlet can consist of a soft material, in particular a rubber. Alternatively or additionally, it may also be advantageous if the edge itself has a certain thickness, which is at least 75%, advantageously at least 100%, in particular more than 150%, of the diameter of the largest suction hole 3a. With the usual hole diameters of about 5 mm, a wall thickness of more than 5 mm, in particular more than 7 mm, is advantageous. However, wall thicknesses of 10 mm and more are also possible.

[0058] FIGS. 2a and 2b show trial results from two series of measurements. For the results from FIG. 2a, the fluid was provided at a constant pressure of 100 Pa, and the resultant flow rate was determined. For the results from FIG. 2b, the fluid was provided with a constant flow rate of 0.5 m.sup.3/m.sup.2/2 (corresponding to 500 mm.sup.3/mm.sup.2/s), and the resultant pressure drop was measured. Both series of trials were each carried out for rolls with holes of different depths (97 mm and 26 mm). In addition, the method described at the beginning was used, that in addition to measurements on the uncontaminated roll (0%), measurements were carried out on the same roll in which 15%/50%/75% of the holes were closed.

[0059] The graphics show that the differences in the measured values as a result of the different contamination in the two cases were sufficiently higher than the standard deviation of the measured values.

[0060] By means of interpolation of these respective four measured values, an interpolation function can then be created which produces a functional relationship between level of contamination (‘obstruction’) and the measured characteristic variable. This functional relationship can, for example, be stored in a computing unit, which then determines a level of contamination from the currently measured value of the characteristic variable.