U.S. patent application number 14/891488 was filed with the patent office on 2016-05-05 for film press and method for operating a film press.
The applicant listed for this patent is VOITH PATENT GMBH. Invention is credited to CHRISTIAN NAYDOWSKI, MATTHIAS SCHMITT.
Application Number | 20160122948 14/891488 |
Document ID | / |
Family ID | 50639553 |
Filed Date | 2016-05-05 |
United States Patent
Application |
20160122948 |
Kind Code |
A1 |
NAYDOWSKI; CHRISTIAN ; et
al. |
May 5, 2016 |
FILM PRESS AND METHOD FOR OPERATING A FILM PRESS
Abstract
A film press for finishing a fibrous web, in particular a paper
or board web, includes a roll and a backing roll forming a nip
therebetween, and at least one metering rod for contacting at least
one of the rolls for applying a liquid or pasty medium thereto to
transfer the medium to the fibrous web. The rolls each have a roll
core and a roll cover surrounding the roll core. A sensor system
having at least one glass fiber into which Bragg gratings are
inscribed is disposed in the roll cover and/or between the roll
core and roll cover of at least one of the rolls. The sensor system
determines a web separation point of the fibrous web from at least
one of the rolls after passage through the nip and transfer of the
application medium. The web separation point can be controlled by
using determined measured values.
Inventors: |
NAYDOWSKI; CHRISTIAN;
(WIKON, CH) ; SCHMITT; MATTHIAS; (MUENCHEN,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
VOITH PATENT GMBH |
Heidenheim |
|
DE |
|
|
Family ID: |
50639553 |
Appl. No.: |
14/891488 |
Filed: |
May 6, 2014 |
PCT Filed: |
May 6, 2014 |
PCT NO: |
PCT/EP2014/059179 |
371 Date: |
November 16, 2015 |
Current U.S.
Class: |
427/8 ;
118/708 |
Current CPC
Class: |
D21H 23/58 20130101;
D21H 23/78 20130101; D21H 23/56 20130101 |
International
Class: |
D21H 23/58 20060101
D21H023/58; D21H 23/78 20060101 D21H023/78 |
Foreign Application Data
Date |
Code |
Application Number |
May 14, 2013 |
DE |
10 2013 208 808.6 |
Claims
1-7 (canceled)
8. . A film press for finishing a fibrous web or a paper or board
web, the film press comprising: a roll and a backing roll forming a
nip therebetween, said roll and said backing roll each having a
respective roll core and a respective roll cover surrounding said
respective roll core; at least one metering rod to be brought into
contact with at least one of said rolls for applying a liquid or
pasty medium to at least one of said rolls in order to transfer the
medium to the fibrous web; and a sensor system having at least one
glass fiber with Bragg gratings inscribed therein, said sensor
system being disposed at least in said roll cover of at least one
of said rolls or between said roll core and roll cover of at least
one of said rolls; said sensor system being configured to determine
a web separation point of the fibrous web from at least one said
rolls after a passage through said nip and a transfer of the
applied medium and being configured to determine measured values,
permitting the web separation point to be controlled by using the
determined measured values.
9. The film press according to claim 8, wherein said at least one
glass fiber is disposed on at least one of said rolls in a
straight, curved, meandering or spiral manner.
10. The film press according to claim 8, wherein said Bragg
gratings are formed at regular or irregular intervals relative to
one another.
11. The film press according to claim 8, which further comprises an
evaluation unit configured to detect and evaluate measured signals
from said sensor system.
12. The film press according to claim 11, wherein said evaluation
unit is connected to said sensor system.
13. The film press according to claim 12, which further comprises
an open-loop and closed-loop control unit communicating with said
evaluation unit through a cable connection or without cables.
14. A method for operating a film press for finishing a fibrous web
or a paper or board web, the method comprising the following steps:
providing a film press including: a roll and a backing roll forming
a nip therebetween, the roll and the backing roll each having a
respective roll core and a respective roll cover surrounding the
respective roll core; at least one metering rod to be brought into
contact with at least one of the rolls for applying a liquid or
pasty medium to at least one of the rolls in order to transfer the
medium to the fibrous web; and a sensor system having at least one
glass fiber with Bragg gratings inscribed therein, the sensor
system being disposed at least in the roll cover of at least one of
the rolls or between the roll core and roll cover of at least one
of the rolls; the sensor system being configured to determine a web
separation point of the fibrous web from at least one the rolls
after a passage through the nip and a transfer of the applied
medium and being configured to determine measured values,
permitting the web separation point to be controlled by using the
determined measured values; and using a pressure pulse of the
fibrous web leaving the roll or the backing roll as a signal in
order to control the web separation point from the roll or the
backing roll.
Description
[0001] The invention is based on a film press for applying a liquid
or pasty medium to a fibrous web such as a paper or board web
according to the preamble of claim 1 and on a method for operating
such a film press according to the preamble of claim 7.
[0002] The film press is used in paper machines to apply starch and
pigments. The usual technique has been known for a long time.
[0003] From a nozzle, liquid medium--coating color or starch
suspension--is sprayed onto the application roll and brought to a
defined thickness by means of a rotating metering rod. The film
thus produced is transferred to the moving paper web in a
pressure-loaded nip comprising application roll and backing
roll.
[0004] It is in the interest of the papermaker to achieve a
transfer of the medium which is as complete and uniform as
possible, in order to obtain a uniform surface quality. The quality
of the distribution depends on many factors, which include, for
example, the inclination of the rolls in relation to each other,
the elasticity of the roll covers, the paper thickness, properties
of the coating medium, working speed, etc.
[0005] Here, the pressure distribution in the nip assumes a
prominent position. This can generally be determined only roughly
from calculations or estimates of boundary conditions, which does
not permit satisfactory monitoring.
[0006] In what is known as sheet stealing, which occurs during the
simultaneous application of medium to both sides of the paper web,
there is additionally a prolongation of the contact time between
roll and paper web, with the problem of non-uniform liquid
application, paper two-sidedness and misting.
[0007] It is thus 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 combat the aforementioned
problems.
[0008] It has already been known for a long time to equip rolls
with sensors in order to obtain information about the operating
parameters in a stationary or running machine. The type and number
of sensors is very different and reaches from impressions with
films with a pressure-sensitive coating as far as highly developed
sensor systems which, by using fiber optic sensors with evaluation
units and evaluation algorithms, are able to determine and display
a high level of information.
[0009] Such a fiber optic sensor system, which operates with a
fiber optic sensor with inscribed Bragg gratings, is known from
WO2010/034321 A1, for example. Here, the Bragg gratings are
inscribed into the glass fiber at different or equal intervals and
are designed in such a way that they reflect the injected light of
different frequencies, the frequencies of which are shifted to a
different intensity under the action of pressure, which permits
conclusions to be drawn about the pressure distribution in the
respective sensor position on the roll. A suitably equipped trigger
system permits the assignment to a specific location on the surface
of the roll cover.
[0010] Hitherto, such sensor systems have primarily been used in
paper machines in the press section or during winding. The
situation in a film press is considerably more complex, since it is
necessary to take account of further components such as the
metering rod, which likewise have effects on the operating state of
the film press.
[0011] It is thus an object of the invention to specify a roll with
sensor system which permits the pressure signal, the separation
points, the effective length of the nip and the change thereof
during continuous operation to be determined and used in a
process-effective manner.
[0012] According to the invention, the object is achieved by a film
press having the characterizing features of the main claim in
conjunction with the generic features.
[0013] Here, provision is made that, by means of the sensor system,
a web separation point of the fibrous web from the roll and/or the
backing roll after the passage through the nip and the transfer of
the application medium can be determined, and the web separation
point can be controlled by using the measured values
determined.
[0014] The knowledge of this variable in continuous operation can
accordingly be used to control the application quantity and to set
rheological properties. Paper two-sidedness and grade change can
thus be managed better. In addition, it is possible to react more
quickly and in an accurately targeted manner to different operating
conditions.
[0015] Since the signal from the sensors is triggered at the
frequency of revolution of the film press roll, monitoring and
setting the pressure in the nip are also possible. This has the
advantage that, as a result of the monitoring of the pressure
profile in the nip, the pressure in the nip and therefore also the
penetration depth can be monitored. The calibration with water as
application medium makes it possible to considerably reduce the
number of parameters that act.
[0016] Further advantageous developments and configuration variants
of the invention are specified in the sub-claims.
[0017] Advantageously, the at least one glass fiber can be arranged
on the roll and/or the backing roll in a straight, curved,
meandering or spiral manner.
[0018] According to an advantageous design variant, the Bragg
gratings can be formed at regular or irregular intervals in
relation to one another. It is thus possible to take account of any
desired roll geometries, for example with cambering or in different
hardness regions.
[0019] Advantageously, an evaluation unit, by means of which the
measured signals from the sensor system (9) can be detected and
evaluated, can be provided.
[0020] The evaluation unit can be connected to the sensor
system.
[0021] According to an advantageous aspect of the invention, the
evaluation unit can be connected to an open-loop and closed-loop
control unit via a cable connection or in a manner communicating
without cables. As a result, simple adaptation of the whole of the
sensor system to the conditions prevailing in the respective roll
position is possible.
[0022] In order to control the web separation point from the roll
or the backing roll, according to the invention the pressure pulse
of the fibrous web leaving the roll or the backing roll can be used
as a signal.
[0023] The invention will be explained in more detail below with
reference to the drawings, without restricting the generality. In
the figures:
[0024] FIG. 1 shows a schematic lateral illustration of the
operating conditions prevailing in the film press of the type
mentioned at the beginning,
[0025] FIG. 2 shows a graphical illustration of the pressure
variation in the nip in a film press,
[0026] FIG. 3 shows a schematic illustration of a roll constructed
in accordance with the invention for a film press.
[0027] FIG. 1 illustrates a highly schematic view of a film press
in its essential components. A roll 1 is provided, which interacts
with a backing roll 2 to form a nip 3. The fibrous web, in
particular a paper or board web 4, is led through the nip 3.
[0028] The roll 1 and the backing roll 2 in the exemplary
embodiment are each covered by a doctor 5, 6, in a manner that is
known and therefore not specifically illustrated, with a film of a
liquid or pasty coating medium, which is transferred to the paper
web 4 during the passage of the latter through the nip 3.
Furthermore, film presses for single-sided coating are also known,
in which the backing roll 2 is accordingly not provided with
medium.
[0029] The transfer of the film from the roll 1 or from the roll 1
and the backing roll 2 is carried out as a result of contact of the
liquid film with the paper web 4. The intention is a complete and
uniform transfer of the medium over the entire width of the nip
3.
[0030] The transfer of the medium begins during the first contact
in the positions A and C, which contact is characterized by a
pressure rise on the roll surface, and ends with a corresponding
pressure drop on the roll surface at the positions B and D. It can
easily be understood that here these are not point-like but
line-like positions, which appear to be correspondingly point-like
because of the non-perspective illustration in FIG. 1.
[0031] The quality of the distribution of the liquid film depends
on the chronological sequence and the intensity of the pressure
distribution during the transfer.
[0032] The distance covered as "effective length" in the nip 3 is
influenced by the geometric, dynamic and rheological properties of
all the units and substances involved at the time of the
application. These include, for example, the inclination of the
roll 1 and the backing roll 2 in relation to each other, the
elasticity of the roll covers 7, 8, described in more detail below,
of the roll 1 and of the backing roll 2, the flow behavior and the
elasticity of the liquid or pasty medium, the web speed, thickness
and quality of the paper web 4 and the speed of the roll 1 and the
backing roll 2.
[0033] The pressure distribution currently prevailing over the
length and width of the nip 3 at the time of the transfer is
largely unknown at present, as already explained above. Statements
relating to pressure profiles in the nip 3 are based on idealized
calculations and on the point force absorption from the roll
drives. The exact separation point of the paper web 4 from the roll
surface after the passage through the nip 3 can be observed only by
means of high-speed photography.
[0034] Given simultaneous application of liquid to the top side and
the underside of the paper web 4, as a result of the paper web 4
running along on the roll 1 or on the backing roll 2, different
separation points from the roll surface occur, which is designated
"sheet stealing". As can be seen in FIG. 1, the separation zone
wanders on the roll 1 from position D to position E.
[0035] As a result of the sheet stealing, on one side, in this case
on the side of the paper web 4 facing the roll 1, prolongation of
the contact time between application medium and paper web 4 occurs.
As a result of the applied web tension, furthermore an excessively
low pressure is exerted on the roll surface by the paper web 4 and
the liquid medium. The effective length of the nip 3 is accordingly
lengthened on this side as compared with the already contactless
paper side.
[0036] The asymmetry in liquid application arising from this can be
observed as paper two-sidedness on the finished paper surfaces. It
is a result of a longer action time (pressure penetration, pressure
dewatering) of the application medium on the affected side.
Furthermore, the dewatering progress not infrequently acts in the
form of undesired, intensified misting during separation of the
paper web from the affected side. Compensating for the paper
two-sidedness and minimizing the misting usually require of the
papermaker asymmetrical intervention in the application formulation
and application quantity for the two paper sides and, alternatively
or else additionally, by changing the roll positions, in particular
by displacing the backing roll 2. For the purpose of avoiding or
reducing misting, the web separation point should additionally be
located as closely as possible to the exit from the nip 3.
[0037] The pressure distribution in the nip 3 and at the metering
rods 5, 6 of the film press is critical for the application of the
coating color or the starch solution. With a constant speed of the
film press and with a constant metering gap, the pressure profile
that is established should depend only on the viscosity of the
medium (coating color or starch solution). The advantage of
controlling the doctor contact pressure via the pressure profile of
the roll 1 and the backing roll 2 and not via measuring the contact
pressure is that, instead of the pressure, the pressure pulse can
be used as a signal. More accurate and quicker metering is
therefore possible. Likewise, instead of the pure open-loop control
of the contact pressure of the metering rods 5, 6, closed-loop
control is now possible.
[0038] If the pressure profile in the nip 3 changes, for example as
a result of changed penetration of the paper or a different
consistency (density, solids content . . . ) of the application
medium, this is used as a control signal for readjusting the rolls.
If the paper takes up less coating color or starch with a given
width of the nip 3 and a given speed, this leads to an increase in
the pressure in the nip 3. Here, too, it is possible to build up an
open-loop and closed-loop control loop, since set points can be
predefined and compared with measured actual values.
[0039] In FIG. 2, the sheet stealing situation described above is
illustrated graphically. It can be seen that, in the case of the
roll 1, the separation zone is displaced and the pressure drop
after the passage through the nip takes place with a delay over a
relatively long area.
[0040] FIG. 3 illustrates, by way of example, a roll 1 or a backing
roll 2 which is suitable for use in a film press at the positions
described above with doctors 5, 6 and, in a roll cover 7, 8, has a
sensor system 9 which picks up the pressure and tension parameters.
The sensor system 9 can be provided either in one of the two
components 1, 2 or in both components 1, 2.
[0041] Here, the roll 1 or backing roll 2 has at least one glass
fiber 10, which is arranged in the roll cover 7, 8 or at an
interface between roll cover 7, 8 and roll core. Inscribed in the
glass fiber 10 are Bragg gratings 11, which can be distributed at
regular or irregular intervals in the glass fiber 10. The Bragg
gratings 11 can be arranged to be distributed regularly or
irregularly in any desired patterns over the surface of the roll 1
or backing roll 2, wherein the at least one glass fiber 10 can be
laid in a substantially straight, meandering form, in spirals or
other suitable shapes.
[0042] The measuring principle is substantially known and will
therefore be outlined only briefly, more for completeness. If light
with a certain wavelength distribution is injected into the at
least one glass fiber 10, said light is reflected at the Bragg
gratings 11. The Bragg gratings 11 can be matched to any desired
wavelengths as they are inscribed into the glass fiber 10. If,
during the passage through the nip 3, the glass fiber 10 is
deformed in the area of the Bragg gratings 11, the wavelength of
the light reflected at the respective Bragg grating 11 is
displaced. The extent of the displacement can be understood as a
measure of the deformation and therefore as a measure of the forces
acting in the nip 3.
[0043] To evaluate the measured signals, it is possible to provide
an evaluation unit, which is accommodated suitably on one of the
rolls 1, 2 or in the vicinity thereof and is connected to the
sensor system 9. The evaluation unit can be connected to an
open-loop and closed-loop control unit without cables or in a
manner communicating via cables.
[0044] Just as the action of a pressure or a local pressure
increase can be detected by measurement, the decrease in the
pressure can also be measured. As a result of the fact that the
sensitivity of the measuring system 9 is very high, it is thus
possible, amongst other things, for the web separation point D/E or
B in FIG. 2 to be detected by means of suitably equipped roll 1 or
backing roll 2. This permits the open-loop and closed-loop control
of the roll position, the contact force of the rolls 1, 2 on each
other and the contact force of the metering rod 5, 6.
* * * * *