U.S. patent application number 13/713128 was filed with the patent office on 2013-04-25 for method for operating a sheet-forming unit, and sheet forming unit.
This patent application is currently assigned to VOITH PATENT GMBH. The applicant listed for this patent is VOITH PATENT GMBH. Invention is credited to Markus Haussler, Hans Loser, Thomas Ruehl, Wolfgang Ruf, Volker Schmidt-Rohr.
Application Number | 20130098573 13/713128 |
Document ID | / |
Family ID | 42760342 |
Filed Date | 2013-04-25 |
United States Patent
Application |
20130098573 |
Kind Code |
A1 |
Haussler; Markus ; et
al. |
April 25, 2013 |
METHOD FOR OPERATING A SHEET-FORMING UNIT, AND SHEET FORMING
UNIT
Abstract
A sheet forming unit including a headbox with at least one feed
device, a turbulence generating device having a plurality of
turbulence generating channels and a nozzle. The nozzle includes an
outlet gap located downstream from the headbox forming a line of
impingement in a flow direction. Immediately upstream from the
nozzle is the turbulence generating device in which during
operation of the headbox a fibrous stock suspension passes through
the plurality of turbulence generating channels in partial flows.
Inside a turbulence generating channel there is a final
fluidization region in which a pressure loss is produced in the
partial flow of fibrous stock suspension in the turbulence
generating channel. The headbox and the forming unit are arranged
so that a dwell time of the fibrous stock suspension from the final
fluidization region to the line of impingement on the clothing is
.gtoreq.30 ms to .ltoreq.300 ms.
Inventors: |
Haussler; Markus;
(Herbrechtingen, DE) ; Loser; Hans; (Langenau,
DE) ; Schmidt-Rohr; Volker; (Heidenheim, DE) ;
Ruf; Wolfgang; (Herbrechtingen, DE) ; Ruehl;
Thomas; (Wernau, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
VOITH PATENT GMBH; |
Heidenheim |
|
DE |
|
|
Assignee: |
VOITH PATENT GMBH
Heidenheim
DE
|
Family ID: |
42760342 |
Appl. No.: |
13/713128 |
Filed: |
December 13, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13370697 |
Feb 10, 2012 |
8382955 |
|
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13713128 |
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PCT/EP2010/056308 |
May 10, 2010 |
|
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13370697 |
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Current U.S.
Class: |
162/341 |
Current CPC
Class: |
D21F 1/02 20130101; D21F
1/028 20130101; D21F 11/00 20130101; D21F 1/026 20130101; D21F 9/02
20130101; D21F 9/003 20130101 |
Class at
Publication: |
162/341 |
International
Class: |
D21F 11/00 20060101
D21F011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 10, 2009 |
DE |
10 2009 028 385.4 |
Claims
1. A sheet forming unit (3) for a machine to produce fibrous webs,
in particular paper, cardboard or tissue webs, the sheet forming
unit comprising: a headbox with at least one feed device feeding at
least one fibrous stock suspension thereto; a turbulence generating
device having a plurality of turbulence generating channels; and a
nozzle including an outlet gap for dispensing said at least one
fibrous stock suspension in the form of a free jet onto a clothing
of a forming unit (2) located downstream from said headbox forming
a line of impingement as viewed in a flow direction, located
immediately upstream from said nozzle is said turbulence generating
device in which during operation of said headbox the at least one
fibrous stock suspension is led through said plurality of
turbulence generating channels in partial flows, whereby inside at
least one of said turbulence generating channels there is a final
fluidization region in which a pressure loss (.DELTA.p) is produced
in the partial flow of fibrous stock suspension in said at least
one turbulence generating channel, said headbox and said forming
unit (2) are arranged so that a dwell time (T.sub.V) of said
fibrous stock suspension from said final fluidization region to
said line of impingement on said clothing is .gtoreq.30 ms to
.ltoreq.300 ms.
2. The sheet forming unit (3) of claim 1, wherein said dwell time
(T.sub.V) is in a range of at least one of .gtoreq.50 ms to
.ltoreq.200 ms and .gtoreq.80 ms to .ltoreq.200 ms.
3. The sheet forming unit (3) of claim 1, wherein said nozzle has a
length l.sub.D in the range of 100 mm.ltoreq.l.sub.D.ltoreq.500 mm,
and a distance (l.sub.1) between said final fluidization region
within an individual of said turbulence generating channels of said
turbulence generating device and an inlet into said nozzle of
.ltoreq.180 mm.
4. The sheet forming unit (3) of claim 3, wherein said length
l.sub.D is in a range of at least one of 100
mm.ltoreq.l.sub.D.ltoreq.400 mm and 200
mm.ltoreq.l.sub.D.ltoreq.400 mm.
5. The sheet forming unit (3) of claim 4, wherein said distance
(l.sub.1) is one of at least one of .ltoreq.150 and .ltoreq.120
mm.
6. The sheet forming unit (3) of claim 1, wherein said nozzle has a
length (l.sub.D) which under consideration of a stock consistency
of said fibrous stock suspension which is led through said nozzle
during operation meets the following requirement:
l.sub.D.times.SK.ltoreq.1000 whereby l.sub.D=length of the nozzle,
measured in mm; and SK=stock consistency in %.
7. The sheet forming unit (3) of claim 6, wherein said nozzle
length (l.sub.D) meets at least one of the following requirements:
l.sub.D.times.SK.ltoreq.700 and l.sub.D.times.SK.ltoreq.800.
8. The sheet forming unit (3) of claim 1, wherein said nozzle
further includes a nozzle chamber and an outlet gap, said nozzle
chamber being defined by two individual nozzle walls converging in
the flow direction and thereby forming an outlet gap, an angle of
convergence (.alpha.) between said two individual nozzle walls in
an area of the outlet gap is between 5.degree. and 45.degree..
9. The sheet forming unit (3) of claim 8, wherein said angle of
convergence (.alpha.) is between 10.degree. and 20.degree..
10. The sheet forming unit (3) of claim 1, wherein said turbulence
generating device has a length (l.sub.TE) viewed in the flow
direction in the range of 100 mm.ltoreq.l.sub.TE.ltoreq.500 mm.
11. The sheet forming unit (3) of claim 10, wherein said length
(l.sub.TE) is in a range of at least one of 100
mm.ltoreq.l.sub.TE.ltoreq.400 mm and 150
mm.ltoreq.l.sub.TE.ltoreq.300 mm.
12. The sheet forming unit (3) of claim 1, wherein said final
fluidization region before an inlet into said nozzle is formed by a
local graduated change of the cross sectional area of at least one
of said plurality of turbulence generating channel viewed in the
flow direction.
13. The sheet forming unit (3) of claim 1, wherein said final
fluidization region before an inlet into said nozzle is formed by a
local constant change of the cross sectional area of at least one
of said plurality of turbulence generating channels viewed in the
flow direction.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a division of U.S. patent application Ser. No.
13/370,697 entitled "METHOD FOR OPERATING A SHEET-FORMING UNIT, AND
SHEET FORMING UNIT", filed Feb. 10, 2012, which is incorporated
herein by reference. U.S. patent application Ser. No. 13/370,697
was a continuation of PCT application No. PCT/EP2010/056308,
entitled "METHOD FOR OPERATING A SHEET-FORMING UNIT, AND
SHEET-FORMING UNIT", filed May 10, 2010, which is incorporated
herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to a method for operating a sheet
forming unit for a machine for producing fibrous webs, in
particular paper, cardboard or tissue webs from at least one
fibrous stock suspension.
[0004] 2. Description of the Related Art
[0005] The production process of fibrous webs is substantially
dependent on the stock consistency of the fibrous stock suspension
being used. With increasing stock consistency of the used fibrous
stock suspension a deteriorating formation of the fibrous web at
the end of the process which can be described through the
macroscopic and microscopic distribution of fibers and fillers can
be observed. In order to achieve satisfactory results in regard to
the quality of the fibrous web, fibrous stock suspensions having
stock consistencies in the range of 0.8-1.2% are brought into the
downstream forming units in the current conventional headboxes. If
stock consistencies with higher values are used, a coarsely clouded
formation inside the fibrous stock suspension is to be expected,
already at the outlet of the jet from the headbox, due to heavy
fiber flocculation. Measures are therefore to be taken to
facilitate destruction of these flakes and timely fixing of the
flow. In particular, an as flake-free fibrous stock suspension jet
as possible is to be provided through the headbox at its outlet.
Inside the turbulence generating device which is arranged before
the nozzle, regions serving the de-flocculation and better
fluidization for the fibrous stock suspension are therefore
provided by different means in turbulence generating channels. Many
times these are however not sufficient. The reason is the greatly
reduced re-flocculation time with increased stock consistency.
However, in order to achieve satisfactory formation parameters for
the developing fibrous web, re-flocculation of the fibrous stock
suspension is to be completely avoided if possible in the headbox
after the most recent fluidization. This however, assumes
appropriately short construction of units, which again are adverse
to other requirements, in particular rigidity and reduction of the
vibration tendency, as well as avoidance of hydraulic
disturbances.
[0006] The problem of flake formation and its effect upon the
quality of the developing fibrous web is described in publication
EP 1 313 912 B1. As a solution, one design of a headbox with a
modified turbulence generating device is suggested, whereby inside
the turbulence generating device a fluidization is undertaken only
once in one step in each turbulence generating channel of the
turbulence generating device, thereby causing an acceleration of
the flow and short dwell time of the fibrous stock suspension in
the headbox. The level of fluidization can be maintained through
the special design of the lamellas of the nozzle. For the
fluidization, graduated changes of the cross sectional area of the
individual turbulence generating channel of the turbulence
generating device and lengths of the individual partial regions of
the flow channels of the turbulence generating device forming the
fluidization region are suggested which result in a length of the
turbulence generating device in a range of 400 mm.
[0007] To improve the formation and the tear length properties of
the developing fibrous web, a multitude of additional measures are
already known which are characterized through a modification of the
nozzle or the turbulence generating device.
[0008] Publication DE 101 06 684 A1 discloses one embodiment of a
headbox with a specially designed lamella end for avoiding
instabilities in the flow inside the nozzle and thereby a
stimulation of vibration, whereby the lamella end is slanted on the
side facing the nozzle wall and which, on the side facing away from
the nozzle wall is provided with a structure. To influence the
formation it is also known from publication DE 199 02 621 A1 to
design the nozzle with different geometric regions to produce
different flow cross sections inside the nozzle.
[0009] Publication WO 2008/077585 A1 discloses the promotion of the
development of symmetric properties in a Z-direction over
symmetrically designed headbox nozzles and the embodiment and
dimensioning of same.
[0010] Measures for improving the transverse rigidity through
alignment of the fibers in the region of the outlet from the nozzle
are described in publication EP 1 022 378 A2. Design of the nozzle
includes a region having a constant cross sectional reduction and
an adjacent shorter region of constant cross sectional
expansion.
[0011] In order to avoid bursting of the free jet during its exit
from the nozzle, document DE 297 13 433 U1 discloses one embodiment
of a headbox having a nozzle formed by machine-wide limiting areas
of contact whereby at least one of the limiting surfaces is
characterized by at least three segments of different angles of
convergence.
[0012] Document DE 102 34 559 A1 discloses one embodiment of a
headbox in a sheet forming system, wherein the nozzle is
characterized by a length of .gtoreq.400 mm, whereby the turbulence
block, which is formed by the turbulence generating device and
which is located upstream from the nozzle, preferably is also
within this length range.
[0013] All already known measures are however not suitable for
bringing the dwell time of the individual fibrous stock suspension
below its re-flocculation time, in particular at a higher stock
consistency.
SUMMARY OF THE INVENTION
[0014] The current invention includes a method for operation of a
sheet forming unit for a machine for producing fibrous webs, in
particular paper, cardboard or tissue webs from at least one
fibrous stock suspension, comprising a headbox and a forming unit
arranged downstream from the headbox, whereby the at least one
fibrous stock suspension is fed to the headbox over the machine
width and by forming partial flows is led in a plurality of
turbulence generating channels and to a nozzle from which the at
least one fibrous stock suspension is applied or respectively
delivered in the form of a free jet into the forming unit, in
particular onto a clothing or between two clothings of the forming
unit under definition of a line of impingement, whereby within an
individual turbulence generating channel a pressure loss is set in
the fibrous stock suspension.
[0015] The invention also relates to a sheet forming unit for a
machine for producing fibrous webs, in particular paper, cardboard
or tissue webs, comprising a headbox and a forming unit arranged
downstream thereof, into which the fibrous stock suspension is
supplied from the outlet gap of the headbox in the form of a free
jet into a forming unit, in particular onto at least one clothing a
the machine produces fibrous webs, in particular paper, cardboard
or tissue webs so that the aforesaid disadvantages are avoided. In
particular, re-flocculation of the fibrous suspension is avoided
after the last fluidization inside the turbulence generating device
prior to the nozzle until the outlet from the nozzle, and also
after the nozzle and a fibrous stock suspension jet having high
uniformity is supplied into the forming unit while avoiding
strongly defined flake areas.
[0016] The present inventive method for operating a sheet forming
unit for a machine for producing fibrous webs, in particular paper,
cardboard or tissue webs from at least one fibrous stock
suspension, includes a headbox and a forming unit located
downstream from the headbox. The at least one fibrous stock
suspension is fed across the machine width to the headbox, which is
directed by the forming of partial flows through a plurality of
turbulence generating channels of the turbulence generating device
and is fed to a nozzle from where the at least one fibrous stock
suspension is delivered in a free jet into the forming unit,
particularly onto the clothing of the forming unit under definition
of a line of impingement. Inside at least one individual turbulence
generating channel a pressure loss is set in the fibrous stock
suspension which is characterized by a final fluidization region of
an individual turbulence generating channel upstream from the inlet
into the nozzle, a pressure loss inside the fibrous stock
suspension of .gtoreq.50 mbar, preferably .gtoreq.75 mbar,
especially .gtoreq.100 mbar, most especially .gtoreq.150 mbar is
produced. The fibrous stock suspension is led from this final
fluidization region to the line of impingement so that its dwell
time in the region defined from the final fluidization region as
far as the line of impingement is .gtoreq.30 ms to .ltoreq.300 ms,
preferably .gtoreq.50 ms to .ltoreq.200 ms, especially .gtoreq.80
ms to .ltoreq.200 ms.
[0017] A fluidization region is to be understood to be a region
where the fibrous stock suspension, in particular the respective
partial flow, is actively or passively influenced so that almost no
fiber network is formed. The influence can hereby occur actively in
regard to its effect through controllable elements, for example,
static mixing devices, or passively through the geometric design of
the flow path. The thereby determined generation of turbulences on
the fibrous stock suspension result in disintegration of
accumulations, in particular flakes. Viewed in a flow direction,
the region may be limited locally on a line in cross machine
direction, or can be designed progressing in flow direction.
[0018] The inventive solution offers the advantage of an expansion
of the range of application of headboxes to fibrous stock
suspensions with increased stock consistencies (fibers and
fillers), preferably of approximately 1%, in particular in the
range of .gtoreq.0.5% to .ltoreq.4%, preferably .gtoreq.1% to
.ltoreq.3%, in particular .gtoreq.1% to .ltoreq.2.5% and at the
same time optimized fiber and filler distribution or respectively
formation at the discharge of them in a free jet into the forming
unit by avoiding fiber and filler agglomeration. New development of
flakes in the flow direction, as far as to the line of impingement
of the fibrous stock suspension jet in the forming unit, which were
disintegrated by the minimum pressure loss in the last fluidization
region, can be safely avoided. The mobility of the fibers and
thereby the level of fluidization is maintained due to the short
dwell time until impingement onto the clothing of the downstream
forming unit and in particular right through to the starting
immobilization of the fibrous stock suspension.
[0019] Control of the fibrous stock suspension inside the
turbulence generating device occurs preferably so that its dwell
time between the last fluidization region of an individual
turbulence generating channel and the outlet of the turbulence
generating device is .gtoreq.10 ms to .ltoreq.100 ms. This mode of
operation determines a short and compact design of a headbox,
suitable for fibrous stock suspensions having a wide consistency
range, as well as avoidance of re-flocculation based on the minimum
distance from the final fluidization region and outlet from the
nozzle and based on the minimum dwell time due on the acceleration
resulting from the pressure loss.
[0020] The individual turbulence generating channel is designed and
dimensioned so that, in the final fluidization region prior to the
inlet into the nozzle, the pressure loss inside the partial flow
guided in the region is .gtoreq.50 mbar, preferably .gtoreq.75
mbar, especially .gtoreq.100 mbar, most especially .gtoreq.150
mbar. The magnitude of the pressure loss offers the advantage of
certain assurance of a high deflocculation level and high fiber
mobility even at high consistencies which can be maintained over
the aforementioned longitudinal regions in the flow direction as
far as the outlet from the nozzle and further.
[0021] Regarding realization of the pressure loss inside the final
fluidization region upstream from the nozzle in the flow direction
a multitude of possibilities exist. Here, the final fluidization
region viewed in the flow direction may be strongly limited locally
or may be designed over a partial region of the turbulence
generating channel of the turbulence generating device, extending
in the flow direction. According to a first variation, the pressure
loss may be generated passively, in the most simple case as a
function of the geometry and/or dimensioning of the flow path in
the individual turbulence generating channel of the turbulence
generating device, or actively through the provision of additional
devices and/or for supplies energy into the fibrous stock
suspension inside the turbulence generating channel.
[0022] According to an especially preferred first variation of the
present invention the pressure loss, in the final fluidization
region of an individual turbulence generating channel before inlet
into the nozzle, is produced by a graduated cross sectional change
inside the turbulence generating channel. The cross sectional area
of the individual turbulence generating channel of the turbulence
generating device is described by a geometric form and dimension.
The graduated change offers the advantage of easier generation of
higher pressure losses in a locally, strictly limited area, inside
the flow path by generating a very strong turbulence to break up
flakes, whereby overall the fluidization is improved. The thereby
adjusted high fiber mobility is then maintained through the short
dwell time, according to the invention, as well as the short
distance of the fluidization region from the outlet of the
nozzle.
[0023] In an additional variation, the pressure loss prior to inlet
into the nozzle is produced by a constant change of the cross
sectional area of the individual turbulence generating channel,
viewed in the flow direction.
[0024] The magnitude of the change of the cross sectional area,
either the graduated or constant change from the minimum cross
sectional area to the maximum cross sectional area, which can be
described as the difference of the hydraulic diameters
characterizing the cross sectional areas, is selected suitable for
generating the required minimum pressure loss. Depending upon the
characteristics of the fibrous stock suspension, which is to be
used, the change of the cross sectional area in the fluidization
region is selected and designed so that the change, in particular
the level of progression characterizing the cross sectional change
suits at least the medium fiber length of the utilized fibrous
stock suspension. The fluidization level required for the short
dwell time is thereby ensured.
[0025] According to an additional advantageous variation of the
present invention the pressure loss can be brought about
additionally or alternatively through a static mixing device
provided in the fluidization region or by means of furnishing
energy by producing the desired pressure loss in the fibrous stock
suspension. These options offer the advantage of an easily
realizable free adjustability of the pressure loss, independent of
the geometry in the turbulence generating channel.
[0026] According to an especially advantageous embodiment of the
present invention the fibrous stock suspension is led in the nozzle
over a length in the range of 100 mm.ltoreq.l.sub.D.ltoreq.500 mm,
preferably 100 mm.ltoreq.l.sub.D.ltoreq.400 mm, in particular 200
mm.ltoreq.l.sub.D.ltoreq.400 mm, and from the final fluidization
region inside the individual turbulence generating channel of the
turbulence generating device upstream from the nozzle and the
outlet from the turbulence generating device over a length of
.ltoreq.180 mm, preferably .ltoreq.150 mm, especially .ltoreq.120
mm, more especially .ltoreq.100 mm. These measures permit a short
and compact design of a headbox, suitable for fibrous stock
suspensions having a wide consistency range, as well as avoidance
of re-flocculation due to the minimum dwell time based on the
minimum distance from the final fluidization region and outlet from
the nozzle and from the acceleration resulting from the pressure
loss.
[0027] To always assuredly avoid a segregation of fibers and fluid
inside the final turbulence generating device before the nozzle,
length l.sub.TE of the turbulence generating device for guidance of
the fibrous stock suspension therein and of the individual
turbulence generating channel is selected preferably to be in the
range of 100 mm.ltoreq.l.sub.TE.ltoreq.500 mm, preferably 100
mm.ltoreq.l.sub.TE.ltoreq.400 mm, especially 150
mm.ltoreq.l.sub.TE.ltoreq.300 mm.
[0028] Guidance of the respective partial flow of the fibrous stock
suspension from the final fluidization region before the inlet into
the nozzle occurs in an advantageous design through an additional
region with a constant cross sectional change in the range of 50 mm
to 100 mm.
[0029] Regarding the construction and design of the turbulence
generating device of the present invention there are several
options for which the above described conditions apply. The
turbulence generating device can consist of a plurality of
machine-wide turbulence generating channels which are arranged
vertical to the flow direction above one another, or of a plurality
of individually designed turbulence generating channels arranged in
rows in cross machine direction and in columns arranged vertical to
the cross machine direction. In one advantageous embodiment the
number of rows of flow channels in the turbulence generating device
is selected, such that the flow speed of the partial flow traveling
in the narrowest cross section of such a turbulence generating
channel of the turbulence generating device is between 5 m/s and 20
m/s, preferably between 7 m/s and 15 m/s. This design offers the
advantage, together with the constructive characteristics, of a
sensitive and effective fluidization.
[0030] The forming unit may be in the embodiment of a hybrid
former, a gap former having two wire belts which form an inlet gap
for the fibrous stock suspension, or a Fourdrinier wire former,
having a wire belt onto whose surface the fibrous stock suspension
is delivered by the headbox.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] The above-mentioned and other features and advantages of
this invention, and the manner of attaining them, will become more
apparent and the invention will be better understood by reference
to the following description of embodiments of the invention taken
in conjunction with the accompanying drawings, wherein:
[0032] FIG. 1A illustrates a section of a machine for producing a
material web having an embodiment of a sheet forming unit of the
present invention;
[0033] FIG. 1B is a process flow chart illustrating the sequence of
the method for the inventive operation of the sheet forming unit of
FIG. 1A;
[0034] FIG. 2 illustrates with the assistance of a diagram the
connection between stock consistency and formation;
[0035] FIG. 3 shows a detailed section from an embodiment of a
headbox of the present invention according to FIG. 1A;
[0036] FIGS. 4A1 and 4A2 show one arrangement of the turbulence
generating channels for guidance of the partial flows;
[0037] FIGS. 4B1 and 4B2 show another arrangement of the turbulence
generating channels for guidance of the partial flows; and
[0038] FIG. 5 shows an embodiment of a turbulence generating
channel of the present invention.
[0039] Corresponding reference characters indicate corresponding
parts throughout the several views. The exemplifications set out
herein illustrate embodiments of the invention and such
exemplifications are not to be construed as limiting the scope of
the invention in any manner.
DETAILED DESCRIPTION OF THE INVENTION
[0040] Referring now to the drawings, and more particularly to FIG.
2 there is shown a schematically simplified illustration of a
diagram of the influence of the level of stock consistency SK
inside a fibrous stock suspension FS upon the formation. For this
purpose the development of formation FO characterized by the
Ambertec-value relative to consistency K of the fibrous suspension
FS which is to be delivered by the headbox is plotted. From this
the connection can be seen between high stock consistency SK and an
uneven and coarsely clouded formation FO in regard to the
arrangement of the fibers and fillers based on increased fiber
flocculation, that is the tendency in conventional known headboxes
toward larger flakes in the free jet F of fibrous stock FS
suspension being delivered from the outlet gap of a headbox. It can
also be seen that with fibrous stock suspensions with lower stock
consistency the formation parameters are clearly improved. FIG. 2
only illustrates the basic connection between consistency of a
fibrous stock suspension FS and the formation FO.
[0041] Now additionally referring to FIG. 1A, in order to reduce,
and if possible avoid, reflocculation, that is re-occurrence of
flakes within the fibrous stock suspension FS before or during
discharge from headbox 1, a method according to the present
invention is utilized. This is illustrated in FIG. 1B in the form
of a flow chart for the method of operation of a sheet forming unit
3 according to FIG. 1A suitable to implementation of the method. In
explanation of the method, the design of a sheet forming unit 3
with suitability to implement the inventive method is first
discussed.
[0042] Here, headbox 1 is located upstream from a forming unit 2,
which together form sheet forming unit 3 for a machine for
producing a material web, in particular a fibrous web in the form
of a paper, cardboard or tissue web. Headbox 1 serves the
machine-wide feeding of at least one fibrous stock suspension FS
into forming unit 2. For clarification of the individual directions
a coordination system is placed on sheet forming unit 3, whereby
X-direction describes the longitudinal direction which is also
referred to as machine direction MD and which coincides with the
direction of travel of fibrous web F. Y-direction describes the
direction transverse to the direction of travel of the fibrous web,
in particular the width direction of the machine which is therefore
also referred to as the cross machine direction CD, whereas
Z-direction characterizes the height direction.
[0043] Headbox 1 includes a feeding device 4 through which the at
least one fibrous stock suspension FS can be distributed across the
entire width of headbox 1. In the most simple case this is in the
embodiment of an element representing a distribution channel, in
particular a distribution pipe extending in cross machine direction
CD and which tapers in flow-through direction in cross machine
direction. In the illustrated example fibrous stock suspension FS
comes from feed device 4, for example, into a first turbulence
generating device 5, having a plurality of turbulence generating
elements. Turbulence generating device 5 may be of varying
construction and in the simplest scenario is in the embodiment of
flow channels, in particular turbulence generating channels 6
describing through-flow openings with an orifice plate or bundle of
pipes. Viewed in a flow-through direction a space 13 is located
adjacent to the first turbulence generating device 5 which is
followed by an additional second turbulence generating device 7,
having turbulence generating elements forming turbulence generating
channels 8. Following second turbulence generating device 7,
located at its outlet 7A is a nozzle 9, whereby a nozzle chamber 10
is formed which is capable of substantially accelerating the flow
of fibrous stock suspension FS during operation and whereby fibrous
stock suspension FS is delivered by way of an aperture 11 and
through outlet gap 12 to forming unit 2 for the machine for
producing a material web. Nozzle chamber 10 is limited by nozzle
wall 16.1, and 16.2 in a directional plane vertical to machine
direction MD and cross machine direction CD. Inside individual
turbulence generating devices 5 and 7 the fibrous stock suspension
FS is apportioned according to a pre-defined separation and travels
on, distributed into partial flows. Turbulence generating devices 5
or respectively 7 include a plurality of turbulence generating
channels 6, 8 extending in longitudinal direction of the machine,
that is in machine direction MD and which are either machine-wide
or are arranged parallel to each other in cross machine direction
CD in rows and in vertical direction in columns, in other words
vertical to a plane which can be described by the flow-through
direction and cross machine direction CD.
[0044] Inside individual turbulence generating channel 8 at least
one region representing a fluidization region 15 is provided, where
a pressure loss is produced in the individual partial flow of
fibrous stock suspension FS being guided in this region.
[0045] The second turbulence generating device 7, which is located
upstream from nozzle 9 viewed in the direction of flow of fibrous
stock suspension FS, and nozzle 9 are designed and dimensioned and
located opposite forming unit 2 so that the dwell time T.sub.V of
fibrous stock suspension FS when running through second turbulence
generating device 7 until impingement onto a clothing 20.1 of
forming unit 2 is .gtoreq.30 ms to .ltoreq.300 ms, preferably
.gtoreq.50 ms to .ltoreq.200 ms, in particular .gtoreq.80 ms to
.ltoreq.200 ms. This is achieved through appropriate matching of
the geometry of second turbulence generating device 7, that is the
element of headbox 1, which is located immediately prior to nozzle
9, and the design of nozzle 9. Second turbulence generating device
7 is arranged and dimensioned so that by way of it at least a
pressure loss of .gtoreq.50 mbar, preferably .gtoreq.75 mbar,
especially .gtoreq.100 mbar, most especially .gtoreq.150 mbar is
produced in last fluidization region 15 before nozzle 9 within the
partial flow guided in this region. Several options are conceivable
here, whereby one differentiates between active and passive
measures, in other words between a permanent adjustment of the
achievable pressure loss or an open adjustability. As further
explained below, the pressure loss can be achieved through the
geometric design of individual turbulence generating channel 6, 8,
in particular through local change of the cross sectional areas
and/or arrangement of additional devices such as static mixing
devices or an additional supply of energy into the individual
partial flow.
[0046] The length of final turbulence generating device 7 upstream
from nozzle 9, viewed in machine direction MD is indicated as
l.sub.TE and is characterized by a length in the range of 100
mm.ltoreq.l.sub.TE.ltoreq.500 mm, preferably 100 mm to
.ltoreq.l.sub.TE.ltoreq.400 mm, especially 150
mm.ltoreq.l.sub.TE.ltoreq.300 mm. Length l.sub.D of nozzle 9,
measured from outlet 7A from turbulence generating device 7 to
outlet gap 12 in machine direction MD is 100
mm.ltoreq.lD.ltoreq.500 mm, preferably 100
mm.ltoreq.l.sub.D.ltoreq.400 mm, especially 200
mm.ltoreq.l.sub.D.ltoreq.400 mm. The stability of the jet can
hereby only be maintained if the damping effect of the fibers
increases and length l.sub.D of nozzle 9 meets the following
condition
l.sub.D.times.SK.ltoreq.1000, preferably.ltoreq.800,
especially.ltoreq.700,
whereby l.sub.D is consistent with the length of the nozzle in mm,
and SK with the stock consistency in %.
[0047] An additional substantial geometric characteristic is length
l.sub.1 which describes the distance between final fluidization
region 15 in turbulence generating device 7 located immediately
before nozzle 9 and outlet 7A from turbulence generating device 7,
which coincides with an inlet 14 into nozzle 9 and which is
.ltoreq.180 mm, preferably .ltoreq.150 mm, especially .ltoreq.120
mm, more especially .ltoreq.100 mm.
[0048] An angle of convergence a is provided in the area of outlet
gap 12 between individual nozzle walls 16.1, 16.2 which define
nozzle chamber 10 and describes the angle between these in the area
of the outlet gap 12 is selected within a range of 5.degree. and
45.degree., preferably between 10.degree. and 20.degree.. With this
geometric design of the combination of the characteristics, whereby
essentially the length of nozzle l.sub.D and distance l.sub.1
determine the dwell time T.sub.V and can be adjusted to a duration
within a predetermined range and in particular to below the
reflocculation time of fibrous stock suspension FS with higher
stock consistency SK.
[0049] According to FIG. 1B delivery of fibrous stock suspension FS
and machine-wide distribution in headbox 1 occurs in a first
process step A0. In process step A1.1 fibrous stock suspension FS
is fed, separated into partial flows into, for example, a first
turbulence generating device 5 where it is subjected to a pressure
loss according to A1.2 and is brought together again in a
subsequent space 13 in A1.3. Prior to inlet into nozzle 9, fibrous
suspension FS is potentially fed to an additional, in this instant
a second turbulence generating device 7 by adding fluid and by
separating into partial flows according to A2.1 and after these
individually developed partial flows of fibrous stock suspension
have traveled through the adjacent nozzle chamber 10 in A3.1 they
are brought together again. A region 15 is provided inside second
turbulence generating device 7 where in process step A2.2 a locally
strong pressure reduction is produced inside turbulence generating
channels 8 in the individual partial flow of fibrous stock
suspension across the entire width of channel 8 in cross machine
direction CD. The pressure reduction in machine direction MD occurs
preferably graduated and the thereby set pressure loss is
.gtoreq.50 mbar, preferably .gtoreq.75 mbar, especially .gtoreq.100
mbar, more especially .gtoreq.150 mbar. The individual partial flow
experiences acceleration. In A2.3 the partial flow flows through
turbulence generating channel 8, then further on to outlet 8A which
coincides with inlet 14 into nozzle 9. The dwell time inside this
region which is characterized by the final fluidization range 15
before nozzle 9 and inlet 14 into same is identified with
T.sub.V-TE. After the inlet according to A3.1 into nozzle 9 it is
carried through to outlet gap 12 in A3.2 and is discharged at
outlet gap 12 in process step A3.2. The dwell time between inlet 14
into nozzle 9 in A3.1 and discharge from outlet gap 12 in A3.3 is
identified with T.sub.V-D. Discharge occurs in the form of a free
jet in A4 until impingement in forming unit 2 in A5. The dwell time
between discharge of free jet F from outlet gap 12 of nozzle 9 and
setting of the immobility point is identified with T.sub.V-F.
[0050] The geometry of turbulence generating device 7 and nozzle 9
as well as the arrangement relative to forming unit 2 is such that
the dwell time of fibrous stock suspension T.sub.V between final
deflocculation in fluidization region 15 and line of impingement 21
after discharge of free jet F from outlet gap 12, which can be
described as the sum of individual time durations T.sub.V-TE,
T.sub.V-D and T.sub.V-F, is in the range of 30 ms to .ltoreq.300
ms, preferably 50 ms to 200 ms, especially preferably 80 ms to 200
ms.
[0051] FIG. 3 illustrates a detailed section of headbox 1 the
components which are essential for producing the necessary
geometric conditions on headbox 1 to implement the inventive
process. Illustrated is nozzle 9 and the last region actively
influencing the fibrous stock suspension FS which is located
upstream, viewed in flow direction and which is formed by a
turbulence generating device 7 and includes a fluidization region
15. Illustrated are the basic geometric dimensions l.sub.D in form
of the length of nozzle, 11 as distance of the final fluidization
region 15 within turbulence generating device 7 prior to inlet 14
into nozzle 9. The distance is hereby measured at the end of
fluidization region 15. Fluidization region 15 may be planar,
extending over a partial region of the flow path or may be linear
in cross machine direction CD, that is locally strictly limited.
Also illustrated is the angle of convergence .alpha. of nozzle 9 in
the region of outlet gap 12 and length l.sub.TE of turbulence
generating device 7, as well as length l.sub.1 for identification
of the distance between fluidization region 15 and inlet 14 into
nozzle 9 in flow direction.
[0052] FIGS. 4A1, 4A2 and 4B1, 4B2 show a schematically greatly
simplified illustration of advantageous designs of turbulence
generating devices 7 for guidance of the partial flows. Turbulence
generating device 7 which is utilized for the fluidization of
fibrous stock suspension FS may take different forms. According to
FIGS. 4A1 and 4A2 this can consist of a plurality of channels 8 in
the embodiment of individual channels which are arranged in rows in
cross machine direction CD and in columns in height direction.
Individual channels 8, in this example 8.11 to 8.nn, can be in the
form of pipes, square or rectangular profiles, etc. Moreover,
integration of them into orifice plates is conceivable. FIG. 4A2
illustrates the arrangement in rows without offset relative to each
other in cross machine direction CD. It is understood that also
alternating offset of individual channels 8 between two rows
relative to each other arranged vertically on top of one another is
possible.
[0053] According to FIG. 4B2 it is moreover conceivable to design
flow channels 8 as channels 8.1 to 8.n extending over the width in
cross machine direction CD which are arranged on top of one another
in height direction. These channels are identified here for example
with 8.1 to 8.n and are illustrated in two views in FIGS. 4B1,
4B.2. The coordinate system according to FIG. 1 was transferred for
the purpose of directional allocation.
[0054] All embodiments have a channel geometry property in common
which provides an area characterized by a graduated cross sectional
change 17, in particular by progression. An example of such a
turbulence generating channel 8 is illustrated in FIG. 5. This view
shows the extension in longitudinal direction that is in
flow-through direction when installed in a machine for producing
material webs. FIG. 5 clarifies the design of individual turbulence
generating channel 8 in schematically greatly simplified depiction.
In this example turbulence generating channel 8 is separated into a
plurality of different partial regions 18.1 to 18.4. Inlet side 8E
of turbulence generating channel 8 describes together with
additional such channels inlet 7E into turbulence generating device
7. Outlet 8A corresponds to inlet 14 into nozzle 9. Between these,
several partial regions 18.1 to 18.4 having different cross
sectional areas Q1 to Q3 are arranged. The region of the final
fluidization prior to the outlet into nozzle 9 is hereby realized
through a graduated cross sectional change 17, in particular
through a progression between two cross sectional areas Q1 and Q2.
Here, turbulence generating channel 8 has a first partial region
18.1 which is characterized by a constant cross sectional area Q1
over its extension range in the flow-through direction, which is
described by a hydraulic diameter d.sub.hydr, in the illustrated
example by a circular cross section through a diameter D1. Second
partial region 18.2 which is located adjacent in flow-through
direction between inlet 8E to outlet 8A is also characterized over
the extension of the partial region 18.2 in flow direction, through
a constant cross section which can be described by a diameter D2.
The second partial region is followed by a transition area 18.3
which permits a constant, that is continuous transition to a third
partial region 18.4 which is characterized by a cross sectional
area Q3 which can be described by a diameter D3.
[0055] The design of the progression that is the cross sectional
change 17 between cross sectional areas Q1 to Q2 which is
characterized advantageously by a diameter change D2/D1 of the
geometry describing the partial regions of turbulence generating
channel 8 occurs so that a pressure loss between the first partial
region 18.1 and the second partial region 18.2 of greater than 50
mbar, preferably 75 mbar, especially preferred greater than 100
mbar is produced. It is decisive however, that length l.sub.1 of
second partial region 18.2 and third partial region 18.4 under
consideration of transitional region 18.3 which characterizes the
distance from fluidization region 15 formed by progression region
18.3 to outlet 8A from turbulence generating channel 8 or
respectively from turbulence generating device 7, must be at least
.ltoreq.180 mm, preferably .ltoreq.150 mm, especially .ltoreq.120
mm, more especially .ltoreq.100 mm in the preferred design. Length
l.sub.TE of individual turbulence generating channel 8 is between
100 mm.ltoreq.l.sub.TE.ltoreq.500 mm, preferably 100
mm.ltoreq.l.sub.TE.ltoreq.400 mm, especially between 150
mm.ltoreq.l.sub.TE.ltoreq.300 mm.
[0056] If cross sectional areas Q1, Q2 and Q3 cannot be described
by a diameter D1, D2 and D3, in other words, in the case of other
cross sectional geometries, then the hydraulic diameter
D.sub.hydr=4Q/U, with Q=cross sectional area and U=circumference is
used.
[0057] According to a particularly advantageous design the final
progression which is necessary for fluidization and which is
located before nozzle 9 should be at least in the range of the
medium fiber length of the utilized fibrous stock suspension FS,
that is (D2-D1)/2.gtoreq.l.sub.Fmittel whereby here the diameter
with a circular cross section is formulated, otherwise the
respective hydraulic diameter d.sub.hydr.
[0058] Since after fluidization, that is after the last progression
viewed in the flow direction the formed flake size inside fibrous
stock suspension FS depends on the available space, or in other
words, on the cross sectional area Q. The largest hydraulic
diameter d.sub.hydr-8 inside turbulence generating channel 8 should
be in the range of 5 mm.ltoreq.d.sub.hydr.ltoreq.25 mm, preferably
5 mm.ltoreq.d.sub.hydr.ltoreq.20 mm, especially preferred 10
mm.ltoreq.d.sub.hydr.ltoreq.20 mm, and because of the fiber wipe
formation the hydraulic diameter d.sub.hydr-8E in the area of inlet
8E on turbulence generating channel 8 should be selected preferably
in the range of 8 mm.ltoreq.d.sub.hydr-8E.ltoreq.20 mm, preferably
10 mm.ltoreq.d.sub.hydr-8E.ltoreq.20 mm, especially preferably 10
mm.ltoreq.d.sub.hydr-8E.ltoreq.15 mm.
[0059] The number of rows, in other words, the number of flow
channels 8 within one column should be selected so that the flow
speed in the narrowest cross section is between 5 m/s and 20 m/s,
preferably between 7 m/s and 15 m/s.
[0060] A headbox 1 of this type can be further modified as desired.
There may be headboxes equipped with lamellas and/or with dilution
fiber technology, meaning with at least one metering device for
adding a fluid into flow channels 8.
[0061] The inventive method can moreover be used in combination
with randomly designed forming units 2, in particular a Fourdrinier
wire, a Hybrid Former and a Twin Wire Former. The example
illustrated in FIG. 1A represents an advantageous design in
combination with a Gap Former whereby the free jet F is directed
into a gap 19 between clothing 20.1, 20.2 which is supported by two
rollers. It is however not limited to this.
[0062] While this invention has been described with respect to at
least one embodiment, the present invention can be further modified
within the spirit and scope of this disclosure. This application is
therefore intended to cover any variations, uses, or adaptations of
the invention using its general principles. Further, this
application is intended to cover such departures from the present
disclosure as come within known or customary practice in the art to
which this invention pertains and which fall within the limits of
the appended claims.
COMPONENT IDENTIFICATION LIST
[0063] 1 Headbox
[0064] 2 Forming unit
[0065] 3 Sheet forming unit
[0066] 4 Feed device
[0067] 5 Turbulence generating device
[0068] 6 Turbulence generating channel
[0069] 7 Turbulence generating device
[0070] 7E Inlet into turbulence generating device
[0071] 7A Outlet from turbulence generating device
[0072] 8 Turbulence generating channel
[0073] 8.1-8.2, 8.11-8.n Turbulence generating channel
[0074] 8E Inlet into turbulence generating channel
[0075] 8A Outlet from turbulence generating channel
[0076] 9 Nozzle
[0077] 10 Nozzle chamber
[0078] 11 Aperture
[0079] 12 Outlet gap
[0080] 13 Space
[0081] 14 Inlet
[0082] 15 Region
[0083] 16.1 Nozzle wall
[0084] 16.2 Nozzle wall
[0085] 17 Cross sectional change
[0086] 18.1 First partial region
[0087] 18.2 Second partial region
[0088] 18.3 Transitional region
[0089] 18.4 Third partial region
[0090] 19 Gap
[0091] 20.1, 20.2 Wire belt
[0092] 21 Line of impingement
[0093] A0-A5 Process steps
[0094] CD Cross machine direction
[0095] D1 Diameter of first partial region
[0096] D2 Diameter of second partial region
[0097] D3 Diameter of third partial region
[0098] d.sub.hydr Hydraulic diameter
[0099] d.sub.hydr-8 Hydraulic diameter of turbulence generating
channel
[0100] d.sub.hydr-8E Hydraulic diameter at inlet into turbulence
generating channel
[0101] F Free jet
[0102] FS Fibrous stock suspension
[0103] l.sub.D Length of nozzle
[0104] l.sub.Fmittel Medium fiber length
[0105] l.sub.TE Length of turbulence generating device
[0106] l.sub.1 Length of distance between progression and inlet
into nozzle
[0107] MD Machine direction
[0108] FO Formation parameter
[0109] K Consistency
[0110] T.sub.V Dwell time
[0111] T.sub.V-TE Dwell time, turbulence generating device after
fluidization
[0112] T.sub.V-D Dwell time, nozzle
[0113] T.sub.V-F Dwell time, free jet
[0114] Q1 Cross sectional area of first partial region
[0115] Q2 Cross sectional area of second partial region
[0116] Q3 Cross sectional area of third partial region
[0117] .DELTA.p Pressure loss
[0118] .alpha. Nozzle angle of convergence
* * * * *