Method and device for determining contamination of a suction roller of a machine for producing a fibrous web

Abstract

A method and a suitable device for determining the contamination of a suction roll of a machine for producing a fibrous web, in particular a paper, board, tissue or pulp web, the method comprising the following steps: a. A fluid is passed through a measuring surface A of the roll jacket, wherein the pressure or the flow velocity of the fluid is kept constant. b. A characteristic variable K is determined, wherein the characteristic variable K is formed by the flow velocity that occurs when the fluid flows through at a constant pressure, and the characteristic variable K is formed by the pressure drop that occurs when measuring at a constant flow velocity. c. One or more reference variables are provided. d. The degree of contamination of the suction roll is determined by comparing the characteristic variable K with the one or more reference variables.

Description

[0001] The invention relates to a method and a device for determining the contamination of a suction roller of a machine for producing a fibrous web.

[0002] When producing fibrous webs, in particular paper webs, suction rollers are used at various locations.

[0003] They usually include a roller shell that is at least partially perforated and rotatable about its longitudinal axis, as well as a device for applying a pressure difference between the environment and the interior of the roller. On the one hand, the suction roller can hold the fibrous web on a certain wire cloth or transfer it to the wire cloth. Among other applications, the suction roller is also used for dewatering the web. Here, water is sucked from the web through the wire cloth into the roller interior. However, a large amount of impurities are also sucked away with the water. These impurities can be, for example, pulp fibers, but also fillers and fine materials. As the suction roller runs longer, the holes in the roller shell are completely or partially blocked. Due to this contamination of the suction opening, the performance of the suction roller continues to decline until trouble-free operation of the roller is no longer possible.

[0004] Therefore, in the prior art, especially document DE 10 2008 002 259, it is suggested to equip the suction roller with a cleaning device. The cleaning device is provided for cleaning the suction holes of the roller by a cleaning medium under high pressure. However, as described in the same document, such cleaning is not possible when the installation is in operation. Therefore, cleaning is only performed when the machine is stopped.

[0005] A disadvantage of the prior art is that the operator has no information about whether or when the suction roller needs to be cleaned. Cleaning is therefore carried out at regular intervals, more precisely usually during downtimes that are required anyway. In order to reliably avoid disruptions due to contamination, the operator must therefore clean earlier and more frequently than is actually necessary due to actual contamination. This leads to higher costs and personnel expenditures as well as increased consumption of cleaning media.

[0006] Therefore, the technical problem to be solved by the present invention is to further improve the prior art so as to extend the cleaning interval of the suction roller and avoid unnecessary cleaning.

[0007] A further object of the invention is to be able to reliably determine the contamination of the suction roller.

[0008] The above technical problem is completely solved by the method and the device according to the present invention:

[0009] A method for determining the contamination of a suction roll of a machine for producing a fibrous web, in particular a paper, board, tissue or pulp web, comprising the following steps:

[0010] a. in a stopped state of the machine, without removing the suction roller from the machine, the fluid outputted from the fluid source arranged outside the suction roller flows through the measuring surface A of the roller shell from the outer side of the roller shell of the suction roller to the inner side of the roller shell, wherein the pressure or flow velocity of the fluid is kept constant;

[0011] b. determining a characteristic quantity K, wherein the characteristic quantity K is composed of the flow velocity generated when the flow is at a constant pressure, and the characteristic quantity K is composed of the pressure drop generated when the flow is measured at a constant flow velocity;

[0012] c. provide one or more reference quantities;

[0013] d. determining the degree of contamination of the suction roller by comparing the characteristic quantity K with the one or more reference quantities,

[0014] In this case, the fluid source arranged outside the suction roller has an outlet which is shaped such that it can be arranged on the cylindrical roller shell and surrounds the measuring surface A on the cylindrical roller shell.

[0015] A device for determining the contamination of a suction roller of a machine for producing a fibrous web, in particular a paper, board, tissue or pulp web, comprising a fluid source, which is arranged to provide a fluid with a constant pressure or a constant flow velocity, the device also comprising a measuring device and a computing unit for determining the flow velocity and / or the pressure drop of the fluid, the device being arranged to carry out the method according to the invention.

[0016] Advantageously, the design solution has at least one of the following technical features:

[0017] On sub-measurement surface A i Repeat steps a and b n times, in particular at least 4 times, preferably at least 8 times on (i=1,..n), thereby determining the quantum characteristic quantity K i , and with sub-feature quantity K i The average value of forms the characteristic quantity K;

[0018] The fluid is a gas, especially air;

[0019] The flow is carried out under constant pressure, and the pressure is selected between 20 [Pa] and 200 [Pa], in particular between 50 [Pa] and 150 [Pa];

[0020] The flow is carried out under the condition of constant flow velocity, wherein the velocity is 250 [mm 3 / mm 2 / s] to 2000[mm 3 / mm 2 / s], especially between 500[mm 3 / mm 2 / s] to 1000[mm 3 / mm 2 / s];

[0021] The measuring surface A or the sub-measuring surface A i At least one of them has a diameter less than 4000mm 2 , especially at 2000mm 2 Up to 3000mm 2 The area between

[0022] By comparing the characteristic quantity K with one or more reference quantities, the remaining operating time R of the suction roller is calculated, thereby determining the degree of contamination;

[0023] The device comprises a first connecting piece with a first inlet and a first outlet, through which a fluid can flow from the first inlet to the first outlet, wherein the first inlet is connected or can be connected to the fluid source and the first outlet is shaped such that it can be placed on a cylindrical first roller shell and surrounds a measuring surface A there;

[0024] A sealing member is provided at the outlet to seal the interior of the first connecting member relative to the environment;

[0025] The first connecting member is detachably connected to the fluid source;

[0026] A flow-blocking element, in particular a mesh or a filter element, is arranged inside the first connecting member;

[0027] A second connecting piece is provided with a second inlet and a second outlet, wherein, in addition to or as an alternative to the first inlet, the second inlet is connected to the fluid source or can be connected to the fluid source, and wherein the second outlet is shaped in such a way that it can be placed on a cylindrical second roller shell and surround the measuring surface A there, wherein the cylindrical second roller shell has in particular a diameter that is different from the cylindrical first roller shell.

[0028] With regard to the method, the above technical problem is solved by a method for determining the contamination of a suction roll of a machine for producing a fibrous web, in particular a paper, board, tissue or pulp web, comprising the following steps.

[0029] a.) A fluid flows through the measuring surface A of the roller shell, wherein the pressure or the flow velocity of the fluid is kept constant.

[0030] b.) Determining a characteristic variable K, wherein the characteristic variable K is formed by the resulting throughflow velocity in the case of a throughflow with a constant pressure, and the characteristic variable K is formed by the resulting pressure drop in the case of a measurement with a constant throughflow velocity.

[0031] c.) Providing one or more reference quantities.

[0032] d.) Determining the degree of contamination of the suction roller by comparing the characteristic variable K with one or more reference variables.

[0033] In the context of the present application, the measuring surface A or the sub-measuring surfaces A constituting the measuring surface A are i The area is to be understood as meaning in each case the curved surface of the cylindrical wall of the roller shell.

[0034] The flow velocity is the volume flowing through the measuring surface per unit time, for example in mm 3 / mm 2 / s.

[0035] The exact manner in which the degree of contamination is determined can be adapted to the needs of the respective user.

[0036] The degree of contamination can advantageously be determined in such a way that the value of the degree of contamination lies between 0 and 1, wherein, for example, “0” represents no contamination and “1” represents complete contamination.

[0037] A feasible design scheme of steps c) and d) may be:

[0038] c1.) Providing a reference variable K0 which specifies the value of the characteristic variable for an uncontaminated suction roller.

[0039] d1.) Determining the degree of contamination of the suction roller using the difference between the values ​​of the characteristic variable K-K0 or the quotient K / K0.

[0040] An example of this is the determination of the contamination level V as follows:

[0041]

[0042] Here, K0 is the flow velocity of the uncontaminated roller and K is the actually measured value of the flow velocity.

[0043] Another possible example is to determine the contamination level V as follows:

[0044]

[0045] Compared to the first example, for this calculation the slight decrease in flow velocity has a relatively small effect on the calculated contamination level.

[0046] Another advantageous alternative may be to measure the reference quantity by measuring at holes that are contaminated in a targeted manner. Thus, a hole pattern can be generated that completely or largely corresponds to the hole pattern of the roller to be measured. To generate a reference quantity, for example, for a 50% contamination, 50% of the holes of the measuring surface can be blocked, and then measurements can be performed on this surface and the reference quantity K can be obtained. 50％If the measurement is repeated for different pollution levels, a set of reference quantities (such as K 15％ , K 25％ , K 50％ ). By comparing the characteristic quantity K with reference quantities or with suitable interpolations / extrapolations of these reference quantities, the degree of contamination can be determined. For a qualitatively good determination of the degree of contamination, it is advantageous to use 2, 3, 4 or more reference quantities.

[0047] The example shown can also be used for the pressure drop and does not constitute a restriction of the invention but merely illustrates various possibilities for determining the degree of contamination from the measured values.

[0048] A great advantage of the method is that it allows the contamination of the suction roller to be assessed without removing it from the machine. This flow measurement takes only a few minutes and can therefore be carried out with very little effort, regardless of how short the machine downtime is. The operator can thus regularly monitor the development of contamination of the suction roller. The roller is thus only cleaned when the degree of contamination of the roller reaches a critical value. This critical value can vary depending on the type of paper produced and the quality of the raw material. Alternatively, continuous cleaning is also possible, so that the dirt does not harden and cannot be practically cleaned without removing the roller.

[0049] Today, contamination can at best be estimated visually when the machine is stopped and the roll is installed in the machine. Here, however, the measuring personnel are an important factor that can lead to incorrect estimates and often do not provide stable estimates, but are influenced by the conditions of the day. Likewise, several personnel have different subjective perceptions and can therefore provide results or estimates that can be very different.

[0050] Compared to a mere visual inspection of the suction roller by the operating personnel, the method according to one aspect of the invention has the further great advantage that it detects an actual reduction in the flow capacity of the suction openings. Merely observing the upper or lower side of the suction openings does not give any information about contamination in the central region of the openings of the roller shell, which are sometimes up to 100 mm deep.

[0051] Since the suction roller is not necessarily uniformly soiled, it is advantageous to carry out steps a) and b) a plurality of times (n times). The steps can be repeated, for example, at least 4 times, at least 8 times or at least 16 times. The measurements are respectively made on the partial measuring planes A and B. i (i=1,...n) is performed, thereby determining the sub-feature quantity K i The sub-measurement surface A i Here, they may all be disjoint, or they may at least partially overlap. iThe average value of forms the characteristic variable K. The arithmetic mean is expedient here, but other means can also be formed, for example a weighted mean, where certain measuring positions are weighted more heavily than other measuring positions.

[0052] The fluid is preferably a gas, in particular air.

[0053] In an advantageous embodiment of the method, provision can be made for the throughflow to take place at a constant pressure and for the pressure to be selected between 20 [Pa] and 200 [Pa], in particular between 50 [Pa] and 150 [Pa].

[0054] In a further advantageous embodiment of the method, it can be provided that the flow through takes place at a constant flow velocity, wherein the velocity is 250 [mm 3 / mm 2 / s] to 2000[mm 3 / mm 2 / s], especially between 500[mm 3 / mm 2 / s] to 1000[mm 3 / mm 2 / s] to choose between.

[0055] Preferably, it can be provided that the measuring surface A or, in the case of multiple measurements, at least one partial measuring surface A i , especially all sub-surfaces A i With less than 4000mm 2 , especially at 2000mm 2 Up to 3000mm 2 The area between.

[0056] The disadvantage of a measuring surface that is too large is that, in particular when the roller is not too dirty, a relatively large amount of fluid flows through it. This means that the measuring device must cover a very wide measuring range from "almost no flow" in heavily dirty rollers to very large flow rates. This makes the measuring device more complex and therefore more expensive.

[0057] But on the other hand, the size of the measuring surface should not be less than 1000mm 2 , even 2000mm 2 , so that the measuring surface, especially at a larger hole diameter of, for example, 5 mm, still includes a sufficient number of suction holes. In this regard, the applicant's experiments have proven that the best is 2000 mm. 2 Up to 3000mm 2 The range between.

[0058] Furthermore, it is advantageous if the remaining operating time R of the suction roller is calculated by comparing the characteristic variable K with one or more reference variables, in order to determine the degree of contamination.

[0059] The remaining operating time R, i.e. the period of time during which the suction roller can still be operated without risk before it has to be replaced due to excessive contamination, can be an advantageous way of presenting the degree of contamination of the suction roller. Knowledge of the reliable remaining operating time R is very important for the operator, since he can decide with little effort whether the suction roller must be dismantled and maintained during the current shutdown of the plant, for example, or whether it can still be maintained during the next planned maintenance shutdown of the plant.

[0060] In particular, when determining the remaining operating time, it is advantageous to determine the relevant reference quantity or quantities without special measurements, for example by calculation and / or simulation. For example, this allows very fast statements about the remaining operating time of a suction roller without previously determining reference quantities as described above.

[0061] For this purpose, a possible solution is to determine the reference quantity K0% for the flow through an uncontaminated suction roller by flow simulation for the known roller geometry and its hole pattern. Such simulation can be realized with relatively little effort using current technology and can be carried out directly on site by maintenance personnel who carry out contamination measurements, if necessary.

[0062] It is also possible to determine a further reference quantity Kmax which indicates up to which flow velocity or pressure drop the roller can still be operated. It is possible to use limits defined by the customer which are defined or measured based on experience with the machine operating capacity and the resulting removal of the rollers.

[0063] Then, by comparing the measured characteristic quantity K with K0% and Kmax, the remaining operating time R can be calculated. For example, a linear contamination degree curve can be used as a basis. If "n" days have passed since the suction roller was installed or cleaned, the remaining operating time R can be calculated as follows:

[0064]

[0065]

[0066] This calculation of R is merely an example of how the method can be carried out. However, the present invention is not limited to this way of determining R.

[0067] In terms of the device, the above technical problem is solved by a device for determining the contamination of a suction roller of a machine for producing a fibrous material web, in particular a paper, cardboard, tissue or pulp web, the device comprising a fluid source, which is configured to provide a fluid with a constant pressure or a constant flow rate, and the device also comprises a measuring device and a calculation unit for determining the flow rate and / or pressure drop of the fluid, wherein the device is configured to perform the method according to the invention.

[0068] In a preferred design of the device, it can be provided that the device comprises a first connecting piece having a first inlet and a first outlet, through which a fluid can flow from the first inlet to the first outlet, wherein the first inlet is connected or can be connected to a fluid source, and the first outlet is shaped such that the first outlet can be placed on a cylindrical first roller sleeve and surround the measuring surface A there.

[0069] Such a connection piece can ensure, by the curved shape of the outlet, that the fluid from the pressure source is guided exclusively through the holes of the roller sleeve. For this purpose, it is particularly advantageous to provide a seal at the outlet to seal the interior of the connection piece relative to the environment. If the connection piece is made of a soft material, such as rubber, the edge of the outlet itself can provide a seal. However, other suitable sealing devices can also be installed. Alternatively or additionally, it is advantageous that the edge itself has a certain thickness, which is at least 75%, advantageously at least 100%, and in particular more than 150% of the diameter of the maximum suction hole, in order to prevent air from penetrating. In the case of a typical hole diameter of about 5 mm, a wall thickness of more than 5 mm, in particular more than 7 mm, is advantageous. But a wall thickness of 10 mm or more is also feasible.

[0070] The curved shape of the outlet also allows standard devices that already exist for other purposes to be used as pressure source and measuring device. Such a device can be, for example, the permeability tester FX 3345 from the Swiss company "textest", which was developed for measuring contaminated filter materials.

[0071] In order to simplify the use of standard devices, it is expedient if the first connecting piece is detachably connectable to the fluid source.

[0072] Such a connection piece can be produced easily and cost-effectively, for example, by means of an additive process. Since the connection piece is not subject to any additional loads other than the fluid flowing through it, no particularly high requirements are imposed on the material used. It can be made of plastic. In principle, a simple and inexpensive 3D printer can also be used for production.

[0073] In some applications, it is advantageous to arrange a flow-blocking element, in particular a grid or a filter element, inside the first connecting piece. For example, if the selected fluid source is dimensioned so that it provides a fluid with too high a pressure, this can be appropriately adjusted by an appropriately selected filter element. An example for this is the above-mentioned measuring device for filter paper. It provides a fluid (air) with pressure, and when the filter paper is clogged, the pressure leads to a flow rate in the measuring range of the installed measuring device. When the suction roller has a significantly smaller flow resistance, this pressure can lead to a significantly larger flow rate that may exceed the measuring range. By arranging a flow-blocking element in the connecting piece, the flow resistance can be increased and the flow rate can be reduced thereby. It is advantageous here to note that the element appears as evenly as possible on the surface in terms of its structure, so that there is no possibility that possible turbulence or the like distorts or weakens the measurement result.

[0074] It is particularly advantageous that the choke element can be easily removed from the connecting piece and reinstalled when necessary, or an alternative choke element can be substituted. This also expands the application range of the proposed device.

[0075] Alternatively or additionally advantageously, a second connecting piece with a second inlet and a second outlet is provided, wherein, in addition to or as an alternative to the first inlet, the second inlet is connected or can be connected to a fluid source, and wherein the second outlet is shaped in such a way that it can be placed on a cylindrical second roller shell and surround the measuring surface A there, wherein the cylindrical second roller shell in particular has a diameter that is different from the cylindrical first roller shell.

[0076] The invention is explained in more detail below with reference to schematic diagrams which are not drawn to scale.

[0077] Figure 1 Schematically illustrating an apparatus according to one aspect of the present invention,

[0078] Figure 2a and Figure 2b Experimental results for different aspects of the present invention are shown.

[0079] Figure 1 The device for determining the contamination of a suction roller shown in FIG. 1 has a fluid source 1 which provides a fluid having a pressure p and a flow velocity The fluid, in particular air, is guided by the device through openings 3a in the form of holes 3a in the roller shell 3. The pressure can be kept constant and the resulting flow velocity can be determined by a measuring device (not shown here). Alternatively, the resulting pressure drop can also be determined at a constant flow velocity. The characteristic quantity K determined in this way can then be compared with a reference quantity K0 for an uncontaminated roller, and the degree of contamination can be determined from this.

[0080] In addition, the device has a connecting piece 2, especially a first connecting piece 2. It has an inlet 10 and an outlet 20. The connecting piece 2 is connected to the fluid source 1 through its inlet 10. The connecting piece 2 can be flowed through by the fluid. The outlet 20 is shaped so that it can be placed on the cylindrical roller sleeve 3. The outlet 20 surrounds the measuring surface A and prevents the medium from entering the environment. This ensures that the fluid flows only through the opening 3a of the roller sleeve 3. In addition, a seal can be set at the edge of the outlet 20 to seal the interior of the connecting piece 2 relative to the environment. In a particularly preferred design, the edge of the outlet 20 itself can be used as a seal. The edge of the outlet can be made of a soft material, especially rubber, for example. Alternatively or additionally, it is also advantageous that the edge itself has a certain thickness, which is at least 75% of the diameter of the maximum suction hole, advantageously at least 100%, and especially more than 150% of the diameter of the maximum suction hole. In the case of a common hole diameter of about 5mm, a wall thickness greater than 5mm, especially greater than 7mm is advantageous. But a wall thickness of 10mm or more is also feasible.

[0081] Figure 2a and Figure 2b The experimental results of two series of measurements are shown. Figure 2a The results in , provide a fluid with a constant pressure of 100Pa and determine the resulting flow velocity. Figure 2b The results are provided with 0.5m 3 / m 2 / s(equivalent to 500mm 3 / mm 2 / s) and the resulting pressure drop was measured. Two test series were conducted on rollers with holes of different depths (97 mm and 26 mm). In addition, the method described at the beginning was used, and in addition to the measurements on an uncontaminated roller (0%), measurements were also carried out on the same roller in which the holes were closed by 15% / 50% / 75%.

[0082] The diagram shows that in both cases the different contaminations lead to differences in the measured values ​​which are significantly greater than the standard deviation of the measured values.

[0083] By interpolating the four measured values, an interpolation function can now be created, which establishes a functional relationship between the degree of contamination ("clogging") and the measured characteristic quantity. This functional relationship can be stored, for example, in a computing unit, which then determines the degree of contamination from the currently measured value of the characteristic quantity.

Claims

1. A method for determining contamination of a suction roll of a machine for producing a fibrous web, the method comprising the following steps: a. in a stopped state of the machine, without removing the suction roller from the machine, the fluid outputted from the fluid source arranged outside the suction roller flows through the measuring surface A of the roller shell from the outer side of the roller shell of the suction roller to the inner side of the roller shell, wherein the pressure or flow velocity of the fluid is kept constant; b. determining a characteristic quantity K, wherein the characteristic quantity K is composed of the flow velocity generated when the flow is at a constant pressure, and the characteristic quantity K is composed of the pressure drop generated when the flow is measured at a constant flow velocity; c. provide one or more reference quantities; d. determining the degree of contamination of the suction roller by comparing the characteristic quantity K with the one or more reference quantities, The fluid source arranged outside the suction roller has an outlet (20) which is shaped so as to be arranged on the cylindrical roller shell (3) and surrounds the measuring surface A on the cylindrical roller shell (3).

2. The method according to claim 1, characterized in that The measuring surface A is composed of sub-measuring surfaces A i (i=1,..n) and in the sub-measurement plane A i Repeat steps a and b n times on (i=1,..n) to determine the sub-feature quantity K i , and with sub-feature quantity K i The average value of forms the feature quantity K.

3. The method according to claim 1 or 2, characterized in that The fluid is a gas.

4. The method according to claim 1 or 2, characterized in that: The throughflow takes place at a constant pressure, and the pressure is selected between 20 Pa and 200 Pa.

5. The method according to claim 1 or 2, characterized in that: The flow is carried out under the condition of constant flow velocity, wherein the flow velocity is 250 mm 3 / mm 2 / s to 2000mm 3 / mm 2 / sChoose between.

6. The method according to claim 2, characterized in that The sub-measurement surface A i At least one of them has a diameter less than 4000mm 2 area.

7. The method according to claim 1 or 2, characterized in that: By comparing the characteristic variable K with one or more reference variables, the remaining operating time R of the suction roller is calculated and thus the degree of contamination is determined.

8. The method according to claim 1, characterized in that The fibrous web is a paper web, a cardboard web or a tissue web.

9. The method according to claim 2, characterized in that The n is at least 4.

10. The method according to claim 2, characterized in that The n is at least 8.

11. The method according to claim 3, characterized in that The fluid is air.

12. The method according to claim 4, characterized in that The pressure is selected between 50Pa and 150Pa.

13. The method according to claim 5, characterized in that The flow velocity is 500 mm 3 / mm 2 / s to 1000mm 3 / mm 2 Choose between / s.

14. The method according to claim 6, characterized in that The sub-measurement surface A i At least one of them has a diameter of 2000 mm 2 Up to 3000mm 2 The area between.

15. A device for determining the contamination of a suction roller of a machine for producing a fibrous web, comprising a fluid source (1) which is arranged to provide a fluid with a constant pressure or a constant flow velocity, the device also comprising measuring means and a calculation unit for determining the flow velocity and / or the pressure drop of the fluid, characterized in that The device is configured to carry out a method according to one of the preceding claims.

16. The device according to claim 15, characterized in that The device comprises a first connecting piece (2) having a first inlet (10) and a first outlet (20), through which a fluid can flow from the first inlet (10) to the first outlet (20), wherein the first inlet (10) is connected to the fluid source (1) and the first outlet (20) is shaped such that it can be placed on a cylindrical first roller shell (3) and surround a measuring surface A there.

17. The device according to claim 16, characterized in that A sealing member is provided at the outlet (20) to seal the interior of the first connecting member (2) from the environment.

18. The device according to claim 16 or 17, characterized in that The first connecting member (2) is detachably connected to the fluid source (1).

19. The device according to claim 16 or 17, characterized in that A flow-blocking element (4) is arranged inside the first connecting member (2).

20. The device according to claim 16 or 17, characterized in that A second connecting piece with a second inlet and a second outlet is provided, wherein the second inlet is connected to the fluid source in addition to or as an alternative to the first inlet, and wherein the second outlet is shaped such that it can be placed on a cylindrical second roller shell (3) and surround the measuring surface A there.

21. The device according to claim 15, characterized in that The fibrous web is a paper web, a cardboard web or a tissue web.

22. The device according to claim 19, characterized in that The flow-blocking element (4) is a mesh or a filter element.

23. The device according to claim 20, characterized in that The cylindrical second roller sleeve has a diameter different from that of the cylindrical first roller sleeve (3).

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