DEVICE AND METHOD FOR MOISTENING A MATERIAL TRACK

Description

[0001] The invention relates to a method for regulating and / or controlling at least one moistening device, comprising a valve with at least one electromagnetic force sensor and a restoring force sensor, a valve body, a control unit, and an application nozzle, suitable for moistening a material web, in particular a paper, cardboard or fiber web.

[0002] Furthermore, the invention relates to a moistening device and the use of a moistening device for the defined moistening of a paper, cardboard, tissue or other material web in a machine for producing and / or finishing the same.

[0003] The material web is moistened to adjust the defined final dry content or to change quality properties such as dimensional stability ("curl"). The material web can also be moistened to compensate for local moisture differences. In particular, a large number of moistening devices distributed across the width of the material web can achieve a uniform moisture content across the paper web. The terms "profiling" or "cross-profiling" are also used in the literature to describe moisture control across the width of the material web, as in DE 102007025611 A1, for example.

[0004] Furthermore, a humidification device is known from the prior art from DE 42 33 992 A1.

[0005] Humidification occurs via nozzles that apply a medium such as water or a water / steam mixture to the paper web. The water can be of various qualities, such as fresh water, condensate, clear filtrate, or higher-quality process water. Since dirt, solids, or fibers can also enter the nozzle and valve body via the application medium, ensuring consistent operation and precise control of the humidification device often arises.

[0006] Therefore, the state of the art pays particular attention to the control valve and the application nozzles. EP1088594B1 describes the control of the application quantity via a pulsation valve. The pulsation valve is controlled binary via a pulsation, meaning it operates only in the open and closed states. This means that the application quantity is controlled by pulsations based on the temporal sequence of open and closed valve states. The pulsations are then compensated for by a damping element to maintain a uniform volume flow of the application medium.

[0007] The advantage of pulsation valves is that the movement moves the valve body to a stop, which can typically be done with high speed and force. This makes it very rare for the valve to jam, especially due to deposits or contamination. Pulsation valves are also usually moved regularly and quickly.

[0008] The disadvantage of pulsation valves, also known as pulsed valves, has so far been the additional effort required to compensate for the resulting fluctuations in the application rate. This can be achieved by using downstream damping elements or by using a large number of valves arranged in parallel or series, thus achieving a balanced volume flow.

[0009] Proportional valves are not currently used for moistening webs due to the low application quantities required for web moistening and constant operation modes, due to their tendency to clog due to deposits or contamination. Furthermore, conventional proportional valves are often unable to ensure the required rapid control of the moistening quantity. Slow control can result in incorrect local moisture values ​​in the web, which no longer equalize over time and lead to quality problems in the web.

[0010] The object of the invention is to combine the advantages of proportional valves for the precise control of the application quantity for moistening a material web with the advantages of fast pulsation valves in order to reduce the disadvantages mentioned according to the invention.

[0011] The object is achieved according to the invention by a method according to the independent claim and by a device or the use of a device according to the subclaims. Further advantageous embodiments of the present invention can be found in the subclaims.

[0012] According to the invention, the object is achieved by a method, wherein the humidification device can carry out a cleaning cycle, wherein the valve is designed as a proportional valve, wherein the proportional valve pulsates around the set target value, wherein the deviation from the set target value occurs by means of a clocking such that a positive and / or a negative deviation from the target value occurs.

[0013] The brief pulsation during the cleaning cycle has the beneficial effect of loosening deposits and contaminants that may adhere to the valve body or application nozzle, preventing clogging of the application nozzle. The application nozzle can also be designed as an application opening. Furthermore, application nozzles or application openings can also include a ceramic insert to further minimize wear and / or contamination.

[0014] Advantageously, at least one humidification device comprising a valve with at least one electromagnetic force transducer and a restoring force transducer, a valve body and a control unit as well as an application nozzle or application opening, suitable for humidifying a material web, in particular a paper, cardboard or fibrous web, wherein the valve is a proportional valve and has a control range which can be set to a target value in at least 25 steps, preferably at least 100 steps.

[0015] The proportional valve differs from a pulsation valve in that it allows for different target values ​​in the range between the closed and open states of the valve body. In comparison, a pulsation valve only allows two states: open and closed. The target value refers to a variable, defined volume flow that can pass through the valve when partially opened. Since valve opening and flow rate or volume flow are directly dependent variables, it is irrelevant whether the target value is defined as the valve position or the application quantity.

[0016] The desired target value can be set by changing the force that can be exerted on the valve body by the electromagnetic force sensor.

[0017] The control unit for the humidification device can receive a command or a signal to change the valve position, for example as an electrical signal from a higher-level controller, process control, closed-loop control, or as a direct manual user input. Depending on the command, the control unit can then change the electrical current or voltage for the electromagnetic force sensor so that the desired target value can be set. To achieve rapid control, the control unit operates at a high operating frequency at which signals can be processed and modified. This is typically done at an operating frequency greater than 100 Hz, preferably greater than 1 kHz, and in particular greater than 1 MHz.

[0018] The humidification device according to a claim is further advantageous if the proportional valve has a valve body, wherein the valve body travels a distance of less than 5 mm from closed to open, preferably less than 2 mm.

[0019] The described path is the control loop through which the valve body can travel, whereby the volume flow passing through the valve is changed proportionally to the control loop. A short control loop is advantageous here, as only a short distance needs to be covered between different target values. Therefore, the short path enables a correspondingly fast response of the valve. In laboratory tests, valves with a path of less than 2 mm and even with a path of less than 1 mm have been tested. It is important that a high resolution of intermediate steps remains possible to enable precise control of the application quantity.

[0020] Furthermore, a humidification device according to one of the claims is advantageous, wherein the electromagnetic force sensor(s) is / are suitable for completely opening or closing the proportional valve from any target value in a time of less than 0.3 seconds, preferably less than 0.1 seconds.

[0021] A fast reaction of the proportional valve enables even moistening of the material web, since short changes in the application quantity can be compensated for later in the paper if only minor differences need to be compensated for.

[0022] Furthermore, a humidification device according to one of the claims is advantageous, wherein the electromagnetic force transmitter is suitable for setting the proportional valve to each target value in a time of less than 0.3 seconds, preferably less than 0.1 seconds.

[0023] Even when production conditions change, it's important that the humidification unit can react quickly to compensate for local moisture differences. Appropriate moisture control based on measured final moisture can also contribute to improving paper quality and moisture content through rapid valve response.

[0024] Furthermore, a humidification device is a humidification device according to one of the preceding claims, wherein the nozzle or the application opening follows directly from the proportional valve, and no further functional elements, in particular for pulsation damping, are used.

[0025] An advantageous embodiment of the invention is achieved if the expensive and failure-prone pulsation dampers, which are used in the prior art after pulsation valves or clocked valves, can be dispensed with.

[0026] A functional element in this case is, for example, a pulsation damper that uses an elastomer, spring element, or a compressible gas to equalize pressure. Pipelines and (manual) shut-off valves, which are used, for example, for maintenance work, are not considered functional elements within the meaning of the invention.

[0027] Furthermore, a humidification device according to one of the claims is advantageous, wherein the restoring force sensor in the proportional valve can have a mechanical spring element, a magnetic or electromagnetic force sensor or a pneumatic force sensor.

[0028] A spring element can be any type of mechanical spring, such as a metal spring, a spring washer or an elastomer or similar material that can exert a spring force due to its material properties.

[0029] Also advantageous is a method for regulating and / or controlling at least one humidifying device according to one of the claims for humidifying a material web, in particular a paper, cardboard, or fiber web. The humidifying device can perform a cleaning cycle in which the proportional valve pulses around the set target value, with the deviation from the set target value being clocked such that a positive and / or a negative deviation occurs. The deviations are advantageously at least of a similar length, preferably the same length.

[0030] The aim of the process is to keep the quantity of applied medium constant at the target value, as far as possible, over time. Pulsation is understood as a brief movement of the valve body along the controlled system, which first deviates positively and then negatively from the target value, or first negatively and then positively.

[0031] If the target value is a completely or largely open valve (~ 100%), the cleaning cycle can only be carried out by a partial short closure; a short-term slight decrease in the amount of application medium over time cannot then be avoided, but is also part of the invention.

[0032] This also applies if the valve is completely closed (~0%). Here, too, the cleaning cycle can only be completed by briefly opening the valve, resulting in a brief, slight increase in the amount of application medium. In both of these cases (closed or open), the pulsation should therefore be understood as a brief deviation from the target value in only one direction.

[0033] A method according to claim 1 is also advantageous, wherein the humidification device contains a proportional valve that can be opened or closed at least partially in a pulsating manner around the set target value, wherein the deviation from the set target value lasts less than 0.3 seconds, preferably less than 0.1 seconds, and the pulsing can be repeated.

[0034] Furthermore, a method according to a claim is advantageous, comprising at least two, preferably more than three humidification devices, wherein a humidification device which pulsates in a cleaning cycle is arranged next to at least one other humidification device which can carry out an opposite pulsation.

[0035] A moistening device in this design has a large number of application nozzles arranged across the width of the paper web. This compensates for differences in moistening across the width of the paper web. The cleaning cycle is then not carried out on all moistening devices simultaneously, but only on individual ones, whereby the neighboring nozzles can pulsate in opposite directions. Since each application nozzle applies moisture to the material web with a spray cone, and the spray cones are usually arranged in such a way that the neighboring nozzles overlap, enabling even moistening. Short-term differences in the moistening of the material web can thus be effectively compensated for by neighboring nozzles.

[0036] Furthermore, a method according to one of the claims with at least two, preferably more than three humidification devices according to one of the claims is advantageous, wherein the opposite pulsation can have only half the amplitude or the duration of the deviation from the set target value.

[0037] The cleaning cycle can thus be performed on individual nozzles from the multitude of nozzles arranged across the web width. The goal of the opposing pulsation of the adjacent moistening devices at half the amplitude is to ensure uniform moistening of the material web. This allows the moistening device to be balanced during the cleaning cycle by the neighboring moistening devices.

[0038] A method is also advantageous in which the cleaning cycle and / or the pulsation deviates from the target value only in one direction, whereby the cleaning cycle (12) and / or the pulsation can be started even when the valve is completely closed or completely open.

[0039] In order to perform a cleaning cycle and / or pulsation even when the humidification device valve is closed, it must be opened briefly. Oscillation around the target value is not possible here; only a pulsation to the open state is provided. Similarly, with a fully open valve, only a pulsation to an at least partially closed state can occur.

[0040] Further advantageous is a method according to one of the claims, wherein the pulsing or the cleaning cycle is preferably carried out at a time when a material web of reduced quality is being produced, or a machine for producing this material web is in a particular operating state.

[0041] The frequency of the cleaning cycle and pulsing required to prevent the valve body from jamming can vary greatly, as various factors can lead to jamming, for example: Water quality, especially dissolved and undissolved solids and contaminants. Flow rates and the associated nozzle and valve geometry (larger valves and nozzles are less prone to clogging in practice). Thermal changes in the humidification device and application medium.

[0042] Accordingly, depending on the embodiment of this invention, it may be necessary for the valve body to be constantly or nearly constantly in motion through pulsation or a cleaning cycle, or in another embodiment, to be moved only a few times per day. In this embodiment, it is advantageous to perform the pulsation or cleaning cycle, for example, during a break, a grade change, a cleaning stoppage, or when starting up after a stoppage, as this prevents moisture differences from entering the saleable material web.

[0043] Another advantageous feature is the use of at least two humidification devices, with a plurality of them arranged across the width of the material web, suitable for moistening different zones differently. This arrangement is also known in the paper industry as a jet moistener. The moisture content of the paper web's cross-sectional profile can be controlled via the plurality of humidification devices. Typically, 20 to 200 humidification devices can be arranged across the material web. This allows a zone width of 5 cm to 50 cm to be achieved; a zone width of 5 cm to 20 cm for a single humidification device is particularly advantageous.

[0044] Further advantageous embodiments of the invention are explained using exemplary embodiments with reference to the drawings. The features mentioned can be advantageously implemented not only in the illustrated combination, but also individually combined with one another. The figures show in detail: Figure 1 shows a schematic partial representation of a possible embodiment of a moistening device for moistening a material web in a sectional view. Figure 2 shows a schematic characteristic curve to explain the control range for the application quantity in the method according to a claim of the invention. Figure 3 shows a schematic partial representation of a possible embodiment of a method and a device of the invention.

[0045] The figures are described in more detail below.

[0046] Figure 1shows a schematic partial representation of a possible embodiment of a humidification device 1. The humidification device 1 comprises a proportional valve 2 with an electromagnetic force sensor 3 and a restoring force sensor 4, which are capable of moving a valve body 10 in a control range 9. The valve body is controlled or regulated to the target value by the control unit 5. The controlled volume flow of the application medium is then sprayed onto a material web 8 using an application nozzle 6 or application opening 7. The application nozzle here has a nozzle shape with a tapered cross-section. Due to the high shear forces at the application opening 7, the escaping liquid is atomized into small droplets, which enable uniform humidification of the material web 8.

[0047] Figure 2shows a schematic characteristic curve to explain the control range for the application quantity in the method according to a claim of the invention. The control range is shown on the vertical axis as a percentage of the valve opening or application quantity. The horizontal axis refers to time [t]. A pulsation movement is shown with a cleaning cycle 12. The opposite pulsation 13 shows the inversely proportional opening of the adjacent valves from a claim of the invention, which in this application example each deviate from the target value 11 by only half the amplitude of the cleaning cycle 12. The target value 11 is shown in this example as 50% of the possible valve opening or application quantity.

[0048] Figure 3shows a schematic partial representation in a plan view of a possible embodiment of a method of the invention. Shown are several application nozzles 6 with corresponding application openings 7 which are arranged next to one another across the width of the material web 8. The sprayed application medium is represented schematically by dotted lines. The middle nozzle is currently undergoing a cleaning cycle 12, while the two neighboring nozzles carry out an opposite pulsation 13. In this way, on average, the material web 8 is moistened largely constantly. If the cleaning cycle 12 and opposite pulsations 13 are carried out accordingly quickly, the moisture in the paper can equalize locally more easily, and the quality of the moistening remains acceptable. In the illustration, the material web 8 runs perpendicular to the illustration along a Z-axis (not shown).The application nozzles 6 are each part of a humidification device 1, which includes a proportional valve 2 (not shown). In the method shown, the cleaning cycle 12 is carried out by one humidification device 1, with the adjacent humidification devices 1 executing an opposite pulsation 13. List of reference symbols

[0049] 1 Humidification device 2 Proportional valve 3 Electromagnetic force sensor 4 Return force sensor 5 Control unit 6 Application nozzle 7 Application opening 8 Material web 9 Control range 10 Valve body 11 Target value 12 Cleaning cycle 13 Opposite pulsation

Claims

1. Method for the closed-loop control and / or open-loop control of at least one dampening device (1), comprising a valve (2) having at least one electromagnetic force transmitter (3) and a return force transmitter (4), a valve body (10), a control unit (5) and an applicator nozzle (6), suitable for dampening a material web (8), in particular a paper, card or fibrous web, characterized in that the dampening device (1) can perform a cleaning cycle (12), wherein the valve (2) is designed as a proportional valve (2), wherein the proportional valve (2) is pulsed around a set target value (11), wherein the deviation from the set target value (11) takes place by means of clocking such that there is a positive and / or negative deviation from the target value (11).

2. Method according to Claim 1, characterized in that the proportional valve (2) is rapidly at least partially opened and / or closed in a manner pulsing around the set target value (11), wherein the deviation from the set target value lasts for less than 0.3 seconds, preferably less than 0.1 seconds, and the pulsing can be repeated.

3. Method according to Claim 1 or Claim 2, characterized in that, for the method, at least two, preferably more than three, dampening devices (1) are subjected to open-loop control and / or closed-loop control, wherein one dampening device (1), which pulses in a cleaning cycle (12), is arranged next to at least one other dampening device (1) which executes opposite pulsation (13).

4. Method according to Claim 3, characterized in that the opposite pulsation (13) has only half the amplitude or half the duration of the deviation from the set target value (11).

5. Method according to any of the preceding claims, characterized in that the cleaning cycle (12) and / or the pulsation is preferably executed at a time in which a material web of reduced quality is produced or a machine for producing this material web is in a particular operating state.

6. Method according to any of the preceding claims, characterized in that the cleaning cycle (12) and / or the pulsation deviates from the target value (11) only in one direction, wherein in this way the cleaning cycle (12) and / or the pulsation can be started even when the valve (2) is completely closed or completely open.

7. Dampening device (1), comprising a valve (2) having at least one electromagnetic force transmitter (3) and a return force transmitter (4), a valve body (10) and a control unit (5), and an applicator nozzle (6) or application opening (7), suitable for dampening a material web (8), wherein the valve is a proportional valve (2) and has a control region (9) which can be set to a target value (10) in at least 16 steps, preferably at least 100 steps, characterized in that the dampening device (1) is suitable for executing a cleaning cycle (12) and / or a pulsation by means of the control unit (5), as result from a method according to any of Claims 1 to 6.

8. Dampening device (1) according to Claim 7, characterized in that the proportional valve (2) has a valve body (10), wherein the valve body covers a distance of less than 5 mm, preferably less than 2 mm, when moving from closed to open.

9. Dampening device (1) according to Claim 7 or Claim 8, characterized in that the electromagnetic force transmitter or transmitters (3) is / are suitable for completely opening or closing the proportional valve (2) from each target value (11) in a time of less than 0.3 seconds, preferably less than 0.1 seconds.

10. Dampening device according to any of the preceding Claims 7 to 9, characterized in that the electromagnetic force transmitter (3) is suitable for setting the proportional valve (2) to any target value (11) in a time of less than 0.3 seconds, preferably less than 0.1 seconds.

11. Dampening device (1) according to any of the preceding Claims 7 to 10, characterized in that the proportional valve (2) is directly followed by the nozzle (6) or the application opening (7), and no further functional elements are used, in particular for pulsation damping.

12. Dampening device (1) according to any of the preceding Claims 7 to 11, characterized in that the return force transmitter in the proportional valve may have a mechanical spring element, a magnetic or electromagnetic force transmitter or a pneumatic force transmitter.

13. Use of at least two dampening devices (1) according to any of the preceding Claims 7 to 12 in a method according to Claims 1 to 6, characterized in that a large number of dampening devices (1), suitable for dampening different zones differently, are arranged over the width of the material web (8).