DE102013208808A1 - Film press and method for operating a film press - Google Patents

Abstract

A film press for finishing a fibrous web (4), in particular a paper or cardboard web, comprises a roller (1) and a counter-roller (2) forming a nip (3) with the roller (1) and at least one on the roller (1) and / or the doctor bar (5, 6) that can be brought into contact with the counter-roll (2) for applying a liquid or pasty medium to the roll (1) and / or the counter-roll (2) for transferring the medium to the fibrous web (4). The roller (1) and the counter roller (2) each have a roller core and a roller cover (7, 8) surrounding the roller core. At least in the roll cover (7) of the roll (1) and / or between the roll core and roll cover (7) of the roll (1) and / or in the roll cover (8) of the counter roll (2) and / or between the roll core and roll cover (8 ) the counter roller (2) has a sensor system (9) which has at least one glass fiber (10) into which Bragg gratings (11) are inscribed. By means of the sensor system (9), a web detachment point of the fibrous web (4) from the roller (1) and / or the counter roller (2) can be determined after passing through the nip (3) and transfer of the medium and the web detachment point can be regulated using the measured values.

Description

The invention relates to a film press for applying a liquid or pasty medium on a fibrous web such as a paper or board web according to the preamble of claim 1 and a method for operating such a film press according to the preamble of claim. 7

The film press is used in paper machines to apply starch and pigments. The common technique is well known.

From a nozzle liquid medium - coating color or starch suspension - sprayed onto the applicator roll and brought by means of a rotating metering rod to a defined thickness. The film thus produced is transferred to the moving paper web in a pressure-loaded nip of application roller and counter-roller.

It is in the interest of the papermaker to achieve a complete and uniform transfer of the medium in order to obtain a uniform surface quality. The quality of the distribution depends on many factors, including, for example, the inclination of the rolls to each other, the elasticity of the roll covers, the paper thickness, properties of the coating medium, working speed, etc.

An excellent place here takes the pressure distribution in the nip. This can generally be roughly determined only from calculations or estimates from constraints, which does not allow satisfactory monitoring.

When so-called sheet stealing, which occurs with simultaneous application of medium on both sides of the paper web, there is also an extension of the contact time between roller and paper web with the problem of uneven liquid application, Papierzweiseitigkeit and Misting.

It is therefore in the interest of the papermaker to obtain information about the pressure distribution in the nip in the film press in order to be able to address the above-mentioned problems.

It has long been known to equip rollers with sensors in order to obtain information about the operating parameters when the machine is stationary or running. The type and number of sensors varies greatly, ranging from impressions with films with pressure-sensitive coating to sophisticated sensor systems, which can determine and display a high level of information with fiber-optic sensors with evaluation units and evaluation algorithms.

Such a fiber optic sensor system, which works with a fiber optic sensor with inscribed Bragg gratings is, for example, from WO2010 / 034321A1 known. Here, the Bragg gratings are inscribed in different or equal distances in the glass fiber and designed so that they reflect the injected light of different frequencies, which are shifted under pressure different degrees in their frequency, which draw conclusions about the pressure distribution in the respective sensor position the roller allows. A suitably designed trigger system allows the assignment to a specific location on the surface of the roll cover.

So far, such sensor systems have been used mainly in paper machines in the press section or during winding. The situation is considerably more complex in a film press, since it is important to note other components, such as the metering rod, which also affect the operating state of the film press.

The object of the invention is therefore to provide a roller with sensor system, which allows to determine the pressure signal, the separation points, the effective length of the nip and its change during operation and use procedurally.

The object is achieved by a film press with the characterizing features of the main claim in conjunction with the generic features.

It is provided that by means of the sensor system, a web release point of the fibrous web of the roller and / or the counter roll after passing through the nip and transfer of the medium can be determined and the web release point is controlled using the measured values determined.

The knowledge of this size during operation can accordingly be used to control the application rate and adjustment of rheological properties. Paper two-sidedness and grade change can be better controlled. In addition, it is possible to react to different operating states faster and more accurately.

Since the signal of the sensor is triggered to the rotational frequency of the film press roll, also a control and adjustment of the pressure in the nip is possible. This has the advantage that by controlling the pressure profile in the nip, the pressure in the nip and thus the Penetration depth is controllable. Calibration with water as a coating medium makes it possible to significantly reduce the number of influencing parameters.

Further advantageous developments and refinements of the invention are specified in the subclaims.

Advantageously, the at least one glass fiber can be arranged straight, curved, meandering or spirally on the roll and / or the counter roll.

The Bragg gratings may be formed in accordance with advantageous embodiments at regular or irregular intervals to each other. It is thus possible to take into account any desired roll geometries, for example with camber or in different hardness ranges.

Preferably, an evaluation unit can be provided, by which the measurement signals from the sensor system ( 9 ) are detectable and evaluable.

The evaluation unit may be in communication with the sensor system. According to an advantageous aspect of the invention, the evaluation unit may be connected to a control and regulation unit via a cable connection or wirelessly communicating. This makes it possible to easily adapt the entire sensor system to the conditions prevailing in the respective roller position.

To control the web release point of the roller or the counter roll can be used according to the invention, the pressure pulse of the roller or the backing roller leaving the fiber web as a signal.

The invention will be explained in more detail below with reference to the drawings without limiting the generality. In the figures show:

1 a schematic side view of prevailing in a film press of the type mentioned operating condition,

2 a graphic representation of the pressure curve in the nip in a film press,

3 a schematic representation of an inventively designed roller for a film press.

In 1 is shown in a highly schematic view of a film press in its essential components. It is a roller 1 provided, which with a counter-roller 2 to a nip 3 interacts. Through the nip 3 becomes a fibrous web, in particular a paper or board web 4 guided.

The roller 1 and the counter roll 2 be in the embodiment in each case by a squeegee 5 . 6 occupied in a known and therefore not shown manner with a film of a liquid or pasty coating medium, which to the paper web 4 during its passage through the nip 3 is transmitted. There are also known film presses for one-sided brushing, in which according to the counter roll 2 not provided with medium.

The transfer of the film from the roller 1 or from the roller 1 and the counter roll 2 takes place by contact of the liquid film with the paper web 4 , The aim is a complete and uniform transfer of the medium over the entire width of the nip 3 ,

The transfer of the medium begins at the first contact in the positions A and C, which is characterized by an increase in pressure on the roll surface, and ends with a corresponding pressure drop across the roll surface at positions B and D. It is easy to see that it not punctiform, but about linear positions, which due to the non-perspective representation in 1 appear punctiform.

The quality of the distribution of the liquid film depends on the timing and intensity of the pressure distribution during the transfer.

The "effective length" in the nip 3 The distance covered is influenced by the geometric, dynamic and rheological properties of all the aggregates and substances involved at the time of the order. These include, for example, the inclination of the roller 1 and the counter roll 2 to each other, the elasticity of the roller covers described in more detail below 7 . 8th the roller 1 and the counter roll 2 , the flow behavior as well as the elasticity of the liquid or pasty medium, the web speed, thickness and quality of the paper web 4 and the speed of the roller 1 and the counter roll 2 ,

The at the time of delivery across the length and width of the nip 3 currently prevailing pressure distribution is currently largely unknown, as explained above. Information on pressure profiles in the nip 3 based on idealized calculations and from the selective power consumption from the roller drives. The exact separation point of the paper web 4 from the roll surface after passing through the nip 3 is observable only by high-speed photography.

With simultaneous application of liquid to the top and bottom of the paper web 4 it comes by running the paper web 4 on the roller 1 or on the counter roll 2 at different peel points from the roll surface, which is called "sheet stealing". As in 1 As can be seen, the separation zone migrates on the roller 1 from position D to position E.

The sheet stealing occurs on one side, in this case on the roller 1 facing side of the paper web 4 , to extend the contact time between application medium and paper web 4 , Due to the applied web tension is still too low pressure on the roll surface of the paper web 4 and the liquid medium. The effective length of the nip 3 extends accordingly on this page compared to the already contactless paper page.

The resulting asymmetry in the liquid application can be observed as Papierzweiseitigkeit on the finished paper surfaces. It is the result of a longer exposure time (pressure penetration, pressure drainage) of the application medium on the affected side. In addition, the progress of the drainage not infrequently in the form of an undesirable, increased misting when removing the paper web from the affected side. Balancing paper two-sidedness and minimizing misting usually requires the papermaker to asymmetrically engage in the application formulation and application amount for the two paper sides, as well as alternatively or additionally by changing the roll positions, particularly by displacing the backing roll 2 , To avoid or reduce the misting, the web release point should also be as close as possible to the exit of the nip 3 lie.

The pressure distribution in the nip 3 and on the squeegee bars 5 . 6 The film press is crucial for the application of the coating color or the starch solution. At constant speed of the film press and at the same blade gap, the pressure profile should be dependent only on the viscosity of the medium (coating color or starch solution). The advantage of controlling the doctor blade pressure over the pressure profile of the roller 1 and the counter roll 2 and not on the measurement of the contact pressure is that instead of the pressure of the pressure pulse can be used as a signal. For a more accurate and faster dosage is possible. Likewise, instead of the pure control of the contact pressure of the metering rods 5 . 6 now a regulation possible.

Changes the pressure profile in the nip 3 , For example, by a changed penetration of the paper or a different nature (density, solids content ...) of the application medium, this is used as a control signal for tracking the rollers. Takes the paper at the given width of the nip 3 and given speed less coating color or starch, this leads to an increase of the pressure in the nip 3 , Here, too, a control and regulating circuit can be set up, since setpoint values can be predetermined and compared with measured actual values.

In 2 the graph of sheet stealing described above is shown graphically. It can be seen that at the roller 1 the separation zone is shifted and the pressure drop after passage through the nip is delayed over a longer range.

In 3 is an exemplary one roller 1 or a counter roll 2 which are suitable for use in a film press at the positions described above with doctoring 5 . 6 is suitable and in a roll cover 7 . 8th a sensor system 9 has, which receives the pressure and tension parameters. The sensor system 9 can either be in one of the two components 1 . 2 or in both components 1 . 2 be provided.

The roller 1 or counter roll 2 has at least one glass fiber 10 on which in the roll cover 7 . 8th or at an interface between roll cover 7 . 8th and roll core is arranged. In the fiberglass 10 are Bragg grids 11 inscribed at regular or irregular intervals in the fiberglass 10 can be distributed. The Bragg grating 11 can roll in any patterns across the surface of the roller 1 or counter roll 2 be arranged regularly or irregularly distributed, wherein the at least one glass fiber 10 may be laid substantially straight, meandering, in spirals or other suitable forms.

The measuring principle is essentially known and is therefore only briefly outlined for the sake of completeness. Will light of a certain wavelength distribution in the at least one glass fiber 10 Coupled, this is at the Bragg grids 11 reflected. The Bragg grating 11 can when writing into the glass fiber 10 be tuned to any wavelengths. Will pass through the nip 3 the glass fiber 10 in the area of the Bragg grid 11 deformed, shifts the wavelength of the at the respective Bragg grating 11 reflected light. The degree of displacement can be used as a measure of deformation and thus as a measure of the nip 3 acting forces are understood.

To evaluate the measurement signals, an evaluation unit may be provided which is connected to one of the rollers 1 . 2 or near it is housed and with the sensor system 9 communicates. The evaluation unit can be connected to a control and regulation unit wirelessly or via cable communicating.

Just as the effect of a pressure or a local pressure increase can be detected by measurement, the decrease in pressure can also be measured. Due to the fact that the sensitivity of the measuring system 9 is very high, can so, inter alia, the Bahnablösepunkt D / E or B in 2 by means of suitably designed roller 1 or counter roll 2 be recorded. This allows the control and regulation of the roller position, the pressing force of the rollers 1 . 2 on each other and the pressing force of the metering rod 5 . 6 ,

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2010034321 A1 [0009]

Claims (7)

Film press for refining a fibrous web ( 4 ), in particular a paper or board web, comprising a roller ( 1 ) and one with the roller ( 1 ) a nip ( 3 ) forming mating roll ( 2 ), and with at least one on the roller ( 1 ) and / or on the counter-roller ( 2 ) can be brought into contact metering rod ( 5 . 6 ) for applying a liquid or pasty medium to the roller ( 1 ) and / or the counter-roller ( 2 ) for transferring the medium to the fibrous web ( 4 ), wherein the roller ( 1 ) and the counter roll ( 2 ) each have a roll core and a roller cover surrounding the roll core ( 7 . 8th ) and wherein at least in the roll cover ( 7 ) of the roller ( 1 ) and / or between roll core and roll cover ( 7 ) of the roller ( 1 ) and / or in the roll cover ( 8th ) of the counter roll ( 2 ) and / or between roll core and roll cover ( 8th ) of the counter roll ( 2 ) a sensor system ( 9 ) is arranged, which at least one glass fiber ( 10 ) into which Bragg gratings ( 11 ) are inscribed, characterized in that by means of the sensor system ( 9 ) a web release point of the fibrous web ( 4 ) from the roller ( 1 ) and / or the counter roll ( 2 ) after passing through the nip ( 3 ) and carry of the medium can be determined and the web release point can be controlled using the determined measured values. Film press according to claim 1, characterized in that the at least one glass fiber ( 10 ) straight, curved, meandering or spiraling on the roller ( 1 ) and / or the counter roll ( 2 ) is arranged. Film press according to claim 1 or 2, characterized in that the Bragg gratings ( 11 ) are formed at regular or irregular intervals to each other. Film press according to one of claims 1 to 3, characterized in that an evaluation unit is provided, through which the measurement signals from the sensor system ( 9 ) are detectable and evaluable. Film press according to claim 3, characterized in that the evaluation unit with the sensor system ( 9 ). Film press according to claim 5, characterized in that the evaluation unit is connected to a control and regulating unit via a cable connection or wirelessly communicating. Method for operating a film press according to one of the preceding claims, characterized in that for controlling the web release point of the roller ( 1 ) or the counter-roll ( 2 ) the pressure pulse of the roller ( 1 ) or the counter-roller ( 2 ) leaving fiber web ( 3 ) is used as a signal.

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