Method for operating a machine for producing a fibrous web and machine for producing a fibrous web

Abstract

A method of operating a machine for producing a fibrous web. The machine has a de-watering device with a plurality of pivotally embodied de-watering strips. In the method, an inclination angle of at least one of the de-watering strips is modified as a function of at least one parameter. The modification is effected by way of the pivoting installation which is activated by a control installation. The actual inclination angle of the at least one de-watering strip to be pivoted is detected and transmitted to the control installation. The control installation activates the pivoting installation as a function of the transmitted inclination angle.

Claims

1. A method of operating a machine for producing a fibrous web, the machine having a de-watering device with a plurality of pivotally mounted de-watering strips, the method comprising: providing a pivoting installation configured to pivot the de-watering strips; activating the pivoting installation by a control installation to thereby modify an inclination angle of at least one of the de-watering strips as a function of at least one parameter; directly detecting, with an inclination sensor, an actual inclination angle of the at least one de-watering strip to be pivoted and transmitting the actual inclination angle to the control installation; and activating the pivoting installation with the control installation as a function of the actual inclination angle transmitted to the control installation.

2. The method according to claim 1, wherein the step of modifying the inclination angle comprises: determining a setpoint value for the inclination angle by the control installation as a function of the parameter, the detected actual inclination angle corresponding to an actual value of the inclination angle; determining a system deviation by the control installation from the setpoint value and the actual value of the inclination angle; and transmitting the system deviation as an input variable to the pivoting installation.

3. The method according to claim 1, wherein the at least one parameter is a constant value which describes a property of the fibrous web to be produced or a property of the machine per se, and the constant value is stored in the control installation or a memory assigned to the control installation.

4. The method according to claim 3, wherein the property of the fibrous web to be produced is a raw material or a type of the fibrous web, and the property of the machine is a construction mode of the machine or a calculated theoretical machine speed of the machine which is required for producing the fibrous web.

5. The method according to claim 3, which comprises determining the setpoint value of the inclination angle of the de-watering strip at a start of the operation as a function of the constant value.

6. The method according to claim 3, which comprises determining the setpoint value of the inclination angle of the de-watering strip during a further operation of the machine as a function of the process parameter.

7. The method according to claim 3, which comprises defining a nominal value of the inclination angle that at the start of the operation has been determined as a function of the constant value as a reference value for a further operation of the machine for further closed-loop controlling, and modifying the nominal value to a nominal value that is determined as a function of the process parameter.

8. The method according to claim 7, which comprises assigning the reference value a range with a minimum value and a maximum value, and modifying the nominal value that is determined as a function of the method parameter, proceeding from the reference value, only within the maximum value and the minimum value.

9. The method according to claim 8, wherein the maximum value is at most 150% and the minimum value is at most 50% of the reference value.

10. The method according to claim 1, wherein the at least one parameter is a process parameter that is measured or determined during an operation of the machine and that describes a current property of the fibrous suspension, of the fibrous web being produced, or an actually established variable of the machine.

11. The method according to claim 10, wherein the process parameter that describes the current property of the fibrous web being produced is an actually established fabric density of the fibrous web or a current dry content of the fibrous web, and the actually established variable of the machine is an actual machine speed of the machine at which the fibrous web is currently being produced.

12. The method according to claim 1, wherein the inclination angle of the de-watering strips is in relation to a horizontal plane and the actual inclination sensor detects a combination of inclination angles about a plurality of x, y, or z axes.

13. A machine for producing a fibrous web, the machine comprising: a de-watering device having a plurality of pivotally mounted de-watering strips; at least one pivoting installation assigned to de-watering device for pivoting at least one of said de-watering strips; and a control installation connected to said pivoting installation and configured to carry out the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) The invention is to be explained now in an exemplary manner by means of the figures in which:

(2) FIG. 1 shows a schematic, partially sectional, longitudinal illustration of a screen section of a machine for producing a fibrous web, said machine being illustrated only in fragments;

(3) FIG. 2 shows a detailed view of the de-watering device from FIG. 1;

(4) FIGS. 3a and 3b show a partially sectional illustration of an embodiment of the de-watering strip;

(5) FIG. 3c shows a plan view of an embodiment of a de-watering strip;

(6) FIG. 4 shows a schematic illustration of a control diagram for a machine; and

(7) FIG. 5 shows a closed-loop control circuit for the closed-loop control of the inclination angle of at least one de-watering strip.

DESCRIPTION OF THE INVENTION

(8) FIG. 1 shows a schematic, partially sectional, longitudinal illustration of a screen section 200 of a machine 100 illustrated only in fragments for producing a fibrous web 2 from at least one fibrous suspension. The machine direction L here runs from left to right. The fibrous web 2 can in particular be a paper, cardboard, or packaging paper web. The fibrous suspension makes its way from a headbox onto a screen which is embodied as a continuous belt and which revolves relative to the de-watering device 1. The fibers deposited on the upper side of the screen are transported onward conjointly with said screen. The excess water of the fibrous suspension makes its way into the de-watering device 1 by way of the lower side of the screen. The fibrous web 2 thus formed on the upper side of the screen is transported onward to the next processing station by way of said screen.

(9) A detailed view of the de-watering device 1 from FIG. 1 is shown in FIG. 2. The de-watering device 1 can be a component part of the screen section 200 illustrated in FIG. 1 of the machine 100.

(10) The de-watering device 1 comprises a box-shaped main body 4 which is optionally impingeable by a vacuum source 3 which is indicated in dashed lines and is preferably capable of being controlled in an open-loop/closed-loop manner. Said vacuum source 3 serves for improving the de-watering of the fibrous suspension, is assigned to the screen section 200, and is presently disposed within the main body 4.

(11) A plurality of spaced-apart de-watering strips 5 which extend transversely to the machine direction L (arrow in FIG. 1) are disposed on the main body 4 on the upper side of the main body 4 that faces the lower side of the screen.

(12) The de-watering strips 5 are mutually spaced apart when viewed in the machine direction L which corresponds to the running direction of the fibrous web to be produced in the machine. In the present case, said de-watering strips 5 are disposed so as to be mutually parallel in terms of the longitudinal axes thereof which transversely to the machine direction L run into the image plane.

(13) Two directly neighboring de-watering strips 5, on the end sides thereof that face one another, conjointly delimit in each case one de-watering slot 6. When the de-watering strips 5 are disposed as illustrated in FIG. 2, said de-watering strips 5 in this instance conjointly preferably configure a flat de-watering face 5 which has a plurality of de-watering slots 6. Said de-watering face 5 runs so as to be substantially parallel to the screen revolving thereto, or so as to be substantially parallel to the fibrous web 2 to be produced thereon, respectively.

(14) Each of the individual de-watering strips 5 comprises an upper part 7 that faces the screen, and a lower part 8 that faces the main body 4. Said lower part 8 is connected in a stationary manner to the main body 4.

(15) A cross section through the de-watering strip 5, perpendicular to the longitudinal axis of the latter, is in each case illustrated in FIGS. 3a and 3b. The upper part 7 is presently embodied in two parts. Said upper part 7 comprises a U-shaped first part on which a second part (also referred to as a wearing part) which faces the fibrous web is disposed. The second part can be releasably connectable to the first part so as to be replaceable in a destruction-free manner. The lower part 8 engages in the free opening which is delimited by the U of the upper part 7, as is indicated here by the dashed illustration.

(16) Some or all of the de-watering strips 5 illustrated in the figures of the de-watering device 1 can be embodied so as to be pivotable. Said de-watering strips 5 can in this instance be in each case assigned one pivoting installation 9 so as to pivot the de-watering strip 5 relative to the main body 4 on which said de-watering strip 5 is assembled.

(17) For example, such a pivoting installation 9 can be disposed within the de-watering strip 5, between the lower part 8 and the upper part 7. Said pivoting installation 9 can be completely encapsulated in relation to the ingress of media from the outside. The movable upper part 7 can thus be rotated or pivoted, respectively, relative to the fixed lower part 8 and thus relative to the main body 4 which is likewise connected in a stationary manner to the machine. The rotation axis about which the upper part 7 can be pivoted by means of the pivoting installation 9 is presently parallel to the longitudinal axis of the de-watering element 5 and thus transverse to the machine running direction. Said rotation axis as illustrated runs into the drawing plane and is indicated by a dot in the figures.

(18) An inclination sensor 10 is disposed in that portion of the U that connects the two lateral legs of the upper part 7.

(19) As is illustrated in FIG. 3b, the current inclination angle of the upper part 7, actually present on the respective de-watering strip(s) 5, in relation to a horizontal plane (illustrated in dashed lines) or the main body 4 can be detected directly by means of the inclination sensor 10. The inclination sensor 10 herein can be disposed within the upper part 7 in such a manner that said inclination sensor 10 detects the inclination angle of the upper part 7, preferably of the outer side of the upper part 7 that faces the lower side of the screen or the fibrous web, in relation to the horizontal plane.

(20) Independently of the embodiment illustrated, the inclination sensor 10 can be embodied so as to be integral to the de-watering strip, here the upper part 7, or can be provided so as to be separate therefrom. In the last-mentioned case, said inclination sensor 10 is connected in a materially integral manner, a force-fitting manner and/or a form-fitting manner to the de-watering strip or the upper part 7, respectively.

(21) A de-watering strip 5 across the entire length thereof is illustrated in a plan view perpendicular onto the fibrous web to be produced (not shown) in FIG. 3c.

(22) The pivotally embodied de-watering strip 5, when viewed here across the length thereof, is even assigned a plurality of inclination sensors 10. It would be conceivable that the de-watering strip 5 along the length thereof (corresponds to the width direction of the fibrous web to be produced) is subdivided into a plurality of portions. This is indicated by the chain-dotted lines. Each portion could thus be assigned a separate pivoting installation 9 as well as a separate inclination sensor 10. On account thereof, the individual portions of a single de-watering strip 5 can assume another inclination angle in a mutually independent manner.

(23) Independently of the embodiment illustrated, the inclination sensors 10 can be disposed within the respective de-watering strip 5, for example within the space delimited by the upper part 7 and the lower part 8. Said inclination sensors 10 can likewise be sealed or encapsulated, respectively, in relation to the ingress of media from the outside.

(24) A circuit diagram for the closed-loop control of the inclination angle of the de-watering device 1 according to the invention, which is part of the machine 100 according to the invention, is shown in FIG. 4. Only one de-watering strip 5 is illustrated. However, this circuit diagram is also applicable to the remaining de-watering strips 5 of the de-watering device 1.

(25) The inclination sensor 10 of a respective de-watering strip 5 is connected to a control installation 12 by way of a first communication channel 11, so as to transmit the actual inclination angle of the de-watching strip 5 to the control installation 12. Furthermore, the control installation 12, for setting the inclination of the de-watching strip 5, is connected to the pivoting installation 9 of the de-watering strip 5 by way of a second communication channel 13. The control installation 12 can thus address the pivoting installation 9 by way of the second communication channel 13 so as to set a specific inclination angle. The control installation is presently connected to a display installation 15 by way of a third communication channel 14, so as to graphically display the inclination angle/angles of one or a plurality of dewatering strips 5, for example.

(26) The control installation 12 can be connected to the control system of the machine 100 by way of a fourth communication channel 16. Current method parameters of the machine such as, for example the energy requirement of the latter or the machine speed as well as properties of the fibrous suspension or of the fibrous web produced therefrom, such as the raw materials or the fabric density of said fibrous web, are transmitted as a predetermined variable to the control installation 12 by way of said fourth communication channel 16.

(27) The control installation 12 can furthermore be assigned a memory 17 in which constant values, for example the types of fibrous webs that are producible on the machine, are stored in the form of a database, for example.

(28) Only a single control installation 12 can be provided herein for all pivotably embodied dewatering strips 5. Respective communication channels 11, 13 are provided for each de-watering strip 5 connected to said control installation 12.

(29) The closed-loop control of the inclination angle is now to be explained in more detail by means of the closed-loop control circuit illustrated in FIG. 5.

(30) The inclination angle as a function of at least one parameter is now to be set in a corresponding manner, specifically as a function of the currently fed back inclination angle of the respective de-watching strip 5.

(31) To this end, a nominal value w for the inclination angle to be set is first predefined by the control installation 12. The nominal value w can be predetermined as a function of a constant value at the beginning of the production process of the fibrous web, for example. To this end, the control installation 12 in the present case checks the memory 17 as to which fibrous web type is to be currently produced, for example. By way of this item of information, the control installation 12 determines the initial inclination angle (also referred to as the reference value) which the respective de-watching strip 5 is to assume at the beginning of the fibrous web production. This corresponds to a rough closed-loop control of the inclination angle.

(32) Furthermore, the current, actually set inclination angle of the de-watering strip 5 is detected by means of the inclination sensor 10 and as the actual value y is likewise transmitted to the control installation 12. The latter forms a system deviation e from the nominal value w and the actual value y of the inclination angle. The control installation 12 from said system deviation e determines a corresponding input variable u by way of which said control installation 12 addresses the pivoting installation 9 so as to set the inclination angle so as to correspond to the system deviation e.

(33) Once the machine 100 is operationally ready, said machine can be set in operation and de-water the fibrous web by means of the de-watering device, the de-watering strips of the latter being inclined to the pre-set reference value.

(34) The rough closed-loop control can also be followed or superimposed by a fine closed-loop control of the inclination angle. To this end, the closed-loop control circuit is performed once again, as has been described at the outset. However, another parameter, specifically a method parameter for the closed-loop control which is typically modified in the operation is now resorted to for the fine closed-loop control. Such a method parameter can be the current screen speed of the screen of the screen section 200.

(35) The pre-set nominal value of the inclination angle used in the rough closed-loop control can be a valid reference value in the fine closed-loop control. Proceeding from said reference value, the nominal value can then be modified (increased or decreased) in the fine closed-loop control so as to correspond to the method parameter.

(36) In the operation, the reference value is then resorted to as the base value for the further closed-loop control, thus for the fine closed-loop control. The nominal value (based on the method parameter) determined for the fine closed-loop control herein is compared with the reference value by the control installation 12. The determined nominal value is set when the determined nominal value of the fine closed-loop control deviates from the reference value. However, this applies only as long as the determined nominal value of the fine closed-loop control does not exceed a range about the reference value. The range about the reference value is the limited by a maximum value which is larger than the reference value, on the one hand, and by a minimum value which is smaller than the reference value, on the other hand. As long as the nominal value as a function of the method parameter thus lies within said range, said nominal value is thus set to the actually calculated nominal value. However, as soon as said nominal value lies outside the range defined by the minimum value and the maximum value, the respective minimum value or maximum value, respectively, is set. For example, it is conceivable that the maximum value is at most 150% and the minimum value is at most 50% of the reference value.

(37) In principle, it would be conceivable for the rough closed-loop control to be dispensed with and only the fine closed-loop control to be used for the closed-loop control. Conversely, it would also be possible for only the rough closed-loop control to be carried out at the start of the operation, and the fine closed-loop control to be dispensed with, such that the set inclination angle would remain correspondingly fixedly set in the operation.

(38) In principle, the closed-loop control can continue until the effective setting of the inclination angle, thus the actually present inclination angle of the respective de-watering strip 5, is established by the control installation 12 by way of the first communication channel 11.

(39) Independently of the embodiments illustrated, it would in principle be conceivable that the respective pivoting installation 9 of the pivotably embodied de-watering strips 5 could also be specified in such a manner that said pivoting installation 9 in addition to the pivoting movement also enables an axial movement of the upper part 7 relative to the lower part 8 in a direction of a vertical onto the fibrous web. Besides the inclination angle, the height of the upper part 7 in relation to the lower part 8, or to the main body 4, respectively could thus also be set.

(40) The invention offers the advantage that in machines in which the operating conditions often change, a respective modification of the mentioned inclination angle at the de-watering strips is implementable in a simple and rapid manner in the running operation of the machine. Moreover, the efficiency of the de-watering can be increased as a function of the prevailing circumstances of the machine or of the fibrous web to be produced.