DE102009028389A1 - Headbox, sheet forming unit with a headbox and method of operating a sheet forming unit - Google Patents

Abstract

The invention relates to a headbox (1) for a machine for the production of fibrous webs, in particular paper, cardboard or tissue webs from at least one fibrous suspension (FS), with at least one feeding device (4) that feeds at least one fibrous suspension (FS), one an outlet gap (12) having a nozzle (9) for discharging the pulp suspension (FS) in a free steel (F) and a turbulence generating device (7) arranged immediately upstream in the flow direction of the nozzle (9) in which the at least a pulp suspension (FS) is passed through a multiplicity of turbulence-generating channels (8; 8.1-8.n; 8.11-8.nn) in partial flows, wherein within the individual turbulence-generating channel (8; 8.1-8.n; 8.11-8. nn) the turbulence generating device (7) has at least one area which forms a fluidization area (15) and in which there is a pressure loss (Δp) in the partial flow de guided through it r pulp suspension (FS) can be generated. The headbox (1) according to the invention is characterized in that the nozzle (9) and the turbulence generating device (7) arranged directly upstream of the nozzle (9) are designed and dimensioned in such a way that they are suitable for a dwell time (TV) of the pulp suspension ( FS) from a last fluidization area (15) of a single turbulence-generating channel (8; 8.1-8.n; 8.11-8.nn) of ...

Description

The The invention relates to a headbox for a machine for the production of fibrous webs, in particular paper, cardboard or tissue webs of at least one pulp suspension, with at least one which delivers at least one pulp suspension Feeding device, one having an outlet gap Nozzle for dispensing the pulp suspension in a free jet and one directly in the flow direction of the nozzle upstream turbulence generating device, in which during operation of the headbox, the at least one pulp suspension through a plurality of turbulence generating channels in sub-streams is guided, being within the individual turbulence generating Channel of the turbulence generating device at least one, a fluidization region forming area is provided, in which a pressure loss in the guided through this partial flow of the pulp suspension can be generated.

The The invention further relates to a sheet forming unit for a machine for producing fibrous webs, in particular Paper, board or tissue webs, comprising a headbox and a subordinate shaping unit, in which the pulp suspension from the exit slit of the headbox in the free jet on at least a fabric is applied and a method of operation such a sheet forming unit.

Of the The manufacturing process of fibrous webs is decisive of the consistency of the underlying pulp suspension dependent. It is with increasing consistency of the pulp suspension used deteriorated through the macroscopic and microscopic distribution of fibers and Fillers describable formation within the end to observe the process of the present fibrous web. To still Satisfactory results in terms of quality To reach fibrous web are currently common Headboxes Pulp suspensions with fabric consistency in the range of 0.8-1.2% introduced into the downstream forming units. If substance consistencies of higher values are used, must with a coarse cloudy formation within the pulp suspension already at the exit of the jet from the headbox by strong Fiber flocculation can be expected. Therefore, measures are too meet the destruction of these flakes and the timely Fixation of the flow serve, in particular is over the headbox a flakeless pulp suspension jet as possible to provide the exit from this. Inside the front of the nozzle arranged turbulence device are therefore in turbulence generating Channels of turbulence generating device of deflocculation and better fluidization serving areas for the pulp suspension formed by different measures. Indeed these are often insufficient. The cause lies in the greatly reduced reflocking time at elevated levels Stock consistency. However, satisfactory formation characteristics for To achieve the resulting fibrous web is the reflocculation the pulp suspension after the last fluidization in the headbox as completely as possible to avoid. However, this requires correspondingly short-built units, which in turn to other requirements, in particular to the strength and reduction the tendency to oscillate and the avoidance of hydraulic disturbances are contrary.

The problem of flocculation and its effect on the quality of the resulting fibrous web is in the document EP 1 313 912 B1 described. To solve this problem, an embodiment of a headbox with modification of the turbulence generating device is proposed with which fluidization is performed only once in one stage in each turbulence generating channel of the turbulence generating device within the turbulence generating device, whereby an acceleration of the flow and short residence time of the pulp suspension in the headbox is achieved. The degree of fluidization can then be maintained by the special design of the blades of the nozzle. For fluidization, stepwise changes in the cross-sectional areas of the individual turbulence-generating channel of the turbulence-generating device and lengths of the individual sections of the flow channels of the turbulence-generating device which produce a length of the turbulence-generating device in the region of 400 mm are proposed.

to Improvement of the formation and the breaking length ratio The resulting fibrous web is a variety of other measures Previously known by a modification of the nozzle or the Turbulence generating device are characterized.

The publication DE 101 06 684 A1 discloses an embodiment of a headbox having a fin end specifically designed to prevent flow instabilities within the nozzle, and thus vibratory excitation, which has a slope on the side facing the nozzle wall and is patterned on the side away therefrom. For influencing the formation is according to the document DE 199 02 621 A1 Furthermore, it is previously known to form the nozzle with different geometric regions for generating different flow cross sections within the nozzle.

The publication WO 2008/077585 A1 discloses the promotion of the formation of symmetrical properties in the Z direction via symmetrically formed headbox nozzles and the design and dimensioning of these.

Measures to improve the transverse stiffness by aligning the fibers in the area of exit from the nozzle are in the document EP 1 022 378 A2 described. The formation of the nozzle takes place with a region with continuous reduction in cross-section and adjoining shorter region with continuous cross-sectional widening.

In order to prevent the bursting of the free jet from the nozzle, the document discloses DE 297 13 433 U1 an embodiment of a headbox with a nozzle formed from machine-extending boundary surfaces, wherein at least one of the boundary surfaces is characterized by at least three sections of different Konvergenzwinkel.

The publication DE 102 34 559 A1 discloses an embodiment of a headbox in a sheet forming system in which the nozzle is characterized by a length of ≥ 400 mm, wherein the upstream turbulence block, which is formed by the turbulence generating means, preferably also lies in this length range.

All However, known measures are not suitable, the Residence time of the individual pulp suspension below its reflocculation time, in particular at a higher consistency, to press.

Of the Invention is therefore based on the object, a headbox of initially mentioned type for a machine for production of fibrous webs, in particular paper, board or tissue webs to further develop such that the mentioned disadvantages avoided become. In particular, the reflocculation of the pulp suspension should after the last fluidization within the turbulence generator in front of the nozzle until it leaves the nozzle and if possible also avoided after the nozzle become.

The solution according to the invention is characterized by the features of independent claims 1, 12 and 14 characterized. Advantageous embodiments are in the dependent claims described.

One Headbox for a machine for producing fibrous webs, in particular paper, board or tissue webs of at least one Pulp suspension, with at least one, the at least one Pulp suspension feeding feeder, a discharge gap having nozzle for delivery the pulp suspension in a free jet and in the flow direction of the Nozzle directly upstream turbulence generating device, in which during operation of the headbox, the at least one pulp suspension through a plurality of, preferably in series, turbulence generating Channels are guided in sub-streams, wherein within the single turbulence generating channel of the turbulence generating means at least one area forming a fluidization area is, in which a pressure loss in the guided by this Partial flow of the pulp suspension is produced according to the invention by characterized in that the nozzle and the nozzle directly upstream turbulence generating device designed in such a way and are dimensioned to be suitable, a residence time the flowing through this pulp suspension of a last fluidization region of a single turbulence generating Channel of the turbulence generating device before entering the Nozzle up to the exit slit of the nozzle of ≤ 200 ms, preferably ≦ 175 ms, in particular ≦ 150 ms, and a pressure loss in the last fluidization area before entering the nozzle of ≥ 50 mbar, preferably of ≥ 75 mbar, in particular ≥ 100 mbar, whole in particular of ≥ 150 mbar.

Under A fluidization region is understood to mean a region in which such on the pulp suspension, in particular the respective Partial flow of the pulp suspension actively or passively affected is that almost no fiber network is formed. The impact can be active through elements which are controllable in their effect, such as static mixers or passively the geometric design of the flow path and the consequent generation of turbulence on the pulp suspension under Dissolution of accumulations, especially flakes occur. The area can be viewed locally in the direction of flow limited to a line in the cross machine direction or but be carried out extending in the direction of flow.

The solution according to the invention offers the advantage of expanding the field of use of headboxes onto pulp suspensions with increased fabric consistencies (fibers and fillers), preferably ≥ 1%, in particular in the range of ≥ 0.5% to ≤ 4%, preferably ≥ 1% to ≤ 3%, in particular from ≥ 1% to ≤ 2.5%, with simultaneously optimized fiber and filler distribution or formation at the outlet of these in the free-stream into the forming unit by avoiding fiber and Füllstoffballungen. Thus, the formation of new flakes in the direction of flow up to the exit from the nozzle, which by the Mindestverver lust in the last Fluidisierungsbereich was resolved safely avoided. The mobility of the fibers and thus fluidization height is maintained by the short residence time to the exit in the free jet.

The Forming the individual turbulence-generating channel of the turbulence generating device is preferably such that the residence time of the pulp suspension between the last fluidization region of a single turbulence generating Channel of the turbulence generating device to the exit from the turbulence generating device from ≥ 10 ms to ≤ 100 ms is.

A particularly advantageous embodiment of the headbox is characterized in that the nozzle has a length l _D in the range of 100 mm ≦ l _D ≦ 500 mm, preferably 100 mm ≦ l _D ≦ 400 mm, in particular 200 mm ≦ l _D ≦ 400 mm, and that the distance between the last fluidization area within a single turbulence-generating channel of the turbulence generating device in front of the nozzle and the outlet from the turbulence generating device ≤ 180 mm, preferably ≤ 150 mm, in particular ≤ 120 mm, very particularly ≤ 100 mm. This combination of measures allows for a short and compact design of headbox suitable for pulp suspensions having a wide consistency range and avoiding re-flocculation due to the minimum residence time resulting from the minimum distance from last fluidizing area and exit from the nozzle and the acceleration due to pressure loss.

l_D

= Länge der Düse, gemessen in mm; und

SK

= Stoffkonsistenz in %.

Depending on the type and composition of the pulp suspensions to be applied, in particular the consistency of the fabric, the length of the nozzle, which is characterized by the distance between the outlet from the upstream turbulence generating device and the outlet, is advantageous for ensuring the stability of the pulp suspension jet emerging from the outlet of the nozzle is limited by the following specification, which takes into account the damping effect of the fibers: l _D × SK ≦ 1000, preferably ≦ 800, in particular ≦ 700, With

l _D

= Length of the nozzle, measured in mm; and

SK

= Fabric consistency in%.

Of the Nozzle space of the nozzle is of two in the flow direction forming nozzle walls converging to form the exit gate, an upper and a lower nozzle wall, limited, wherein it is advantageous under fluidic aspects, if the convergence angle between these at least in the area of Exit Gates between 5 ° and 45 °, preferably 10 ° and 20 °, is.

In order to always reliably avoid segregation of fibers and fluid within the last turbulence generating device in front of the nozzle in an advantageous embodiment, the length l _{TE of} the turbulence generating device and thus of the individual turbulence generating channel of the turbulence generating device is preferably in the range of 100 mm ≦ l _TE ≦ 500 mm , preferably 100 mm ≦ l _TE ≦ 400 mm, in particular 150 mm ≦ l _TE ≦ 300 mm.

In a particularly advantageous further development is the individual turbulence generating channel of the turbulence generating device such executed and dimensioned that in the last Fluidisierungsbereich before entering the nozzle the pressure loss within of the partial flow of ≥ 50 mbar, preferably ≥ 75 mbar, in particular ≥ 100 mbar, in particular ≥ 150 mbar is generated. The size The pressure loss offers the advantage of a secure warranty a high degree of deflocculation and high fiber mobility even at high consistencies, which over the mentioned length ranges in the direction of flow until it leaves the nozzle and beyond.

In terms of the realization of the pressure loss within the flow direction last fluidization area in front of the nozzle is a Plurality of possibilities. In this case, the last fluidization area locally strong in the direction of flow limited or over a portion of the turbulence generating Channel of the turbulence generating device in the flow direction be formed extending. The pressure loss can according to a first variant passive, in the simplest case as a function of geometry and / or sizing the flow path in the individual turbulence generating channel of the turbulence generator or active by providing additional facilities and / or Possibilities for the energy input into the pulp suspension within the turbulence generating channel of the turbulence generator be generated.

According to a particularly preferred embodiment of a first variant for generating a pressure loss, the last fluidization region before entry into the nozzle is formed by a local, step-like change in the cross-sectional area of the individual turbulence-generating channel of the turbulence generator in the direction of flow. The cross-sectional area of the individual turbulence generating channel of turbulence Generation device is described by a geometric shape and dimension. The step change offers the advantage of easily creating higher pressure drops in a highly localized area within the flow path, producing very high turbulence to break up flocs, thereby improving overall fluidization. The thus set high fiber mobility is then maintained by the short residence time according to the invention and the small distance of Fluidisierungsbereichs to the exit from the nozzle.

In In another embodiment, the last fluidization area before entering the nozzle of a steady change the cross-sectional area of the individual turbulence generating Channel of the turbulence generating device in the flow direction be formed considered.

The Size of change in cross-sectional area with incremental or continuous change from the minimum Cross-sectional area to the maximum cross-sectional area, which as a difference of the cross-sectional areas characterizing Hydraulic diameter is writable, it is used to generate chosen the required minimum pressure loss suitable. Depending on the properties of the pulp suspension to be used will change the cross-sectional area in the Fluidisierungsbereich selected and designed such that the change, especially the height of the cross-section change characterizing increment at least the mean fiber length corresponds to the pulp suspension used. This will be the required for the short residence time Fluidisierungshöhe guaranteed.

According to one additional design, the pressure loss in addition or alternatively by at least one in the fluidization region to be provided static mixing device or at least one means for energy input to produce the desired duck loss be caused in the pulp suspension. These possibilities offer the advantage of an easy-to-implement free adjustability the pressure loss, regardless of the geometry in the turbulence generating channel of the turbulence generating device.

In an advantageous embodiment, the individual turbulence-generating channel of the turbulence _{generating device is} designed and dimensioned such that its maximum cross-sectional area by a hydraulic diameter d _hydr in the range of 5 mm ≤ d _hydr ≤ 25 mm, preferably 5 mm ≤ d _hydr ≤ 20 mm, in particular 10 mm ≤ d _hydr ≤ 20 mm, is characterized. As a result, the flake size which is obtained after fluidization can be kept to a minimum in order to avoid fiber wiping, the hydraulic diameter d _{hydr-8E is} preferably in the range of 8 mm _≦ d _{hydr-8E ≦} 20 mm, preferably in the individual turbulence _-generating channel of the turbulence- _{generating device} 10 mm ≤ d _hydr-8E ≤ 20 mm, in particular 10 mm ≤ d _hydr-8E ≤ 15 mm.

The Guiding the respective partial flow of the pulp suspension from the last fluidizing area before entering the nozzle takes place in an advantageous embodiment another area with a constant change in the cross section in the range of 50 mm to 100 mm.

In terms of the construction and the formation of the turbulence generating device There are basically several options for which, however, the above conditions apply. The Turbulence generating means may be of a plurality of machine widths consist of running turbulence generating channels, which are perpendicular to the flow direction one above the other are arranged or from a plurality of in the cross machine direction in rows and perpendicular to the cross-machine direction in columns arranged to each other, designed as individual channels, turbulence generating channels are formed. In an advantageous embodiment is however the number of lines of the flow channels the turbulence generating device selected such that the flow rate of the in the narrowest cross section such a turbulence generating channel of the turbulence generating device guided partial flow between 5 m / s and 20 m / s, preferably between 7 m / s and 15 m / s. This version offers in combination with the design features the advantage of a sensitive and effective fluidization.

An inventively designed head box is preferably in a sheet forming unit for a machine for producing fibrous webs, in particular paper, board or tissue webs, further comprising a downstream forming unit, in which the pulp suspension from the exit slit of the headbox into the forming unit, in particular on a Covering or between two fabrics under definition of a line of impact is applied in the free jet, are used. The execution and arrangement of headbox and forming unit is such that the residence time of the pulp suspension from the last Fluidisierungsbereich up to the impact line from ≥ 30 ms to ≤ 300 ms, preferably from ≥ 50 ms to ≤ 200 ms, in particular from ≥ 80 ms to ≤ 200 ms, is. The inventive arrangement of a headbox according to the invention and a forming unit offers the advantage that, up to the impact on the fabric with respect to the to be achieved formation of the fibrous web with respect to the fiber distribution and orientation optimized pulp suspension is introduced into the forming unit.

The Forming unit can as a hybrid former, gap former, comprising two an inlet gap for the pulp suspension forming Screen belts or wire screen former be executed, comprising a screen belt, on the surface of the pulp suspension is applied by means of the headbox.

The inventive method for operating a Sheet forming unit, wherein the at least one pulp suspension supplied to the headbox over the machine width is, with the formation of partial streams in a plurality turbulence generating channels of the turbulence generating device directed and guided to a nozzle, from which the at least one pulp suspension in the free jet in the Forming unit introduced, in particular to a fabric of the Forming unit applied under definition of a line of impact being within a single turbulence generating channel the turbulence generating device, a pressure drop in the pulp suspension is set, is characterized in that in a last Fluidization region of a single turbulence generating channel the turbulence generating device before the inlet to the nozzle a pressure drop within the pulp suspension of ≥ 50 mbar, preferably of ≥ 75 mbar, in particular of ≥ 100 mbar, in particular of ≥ 150 mbar, is generated and that the pulp suspension from this last fluidization area led to the exit slit from the nozzle so is that whose residence time in that of the last Fluidisierungsbereich up to the exit slit descriptive range ≤ 200 ms, preferably ≦ 175 ms, in particular ≦ 150 ms, and / or the dwell time in which is from the last fluidization area up to the impact line extending range of ≥ 30 ms to ≤ 300 ms, preferably from ≥ 50 ms to ≤ 200 ms, in particular from ≥ 80 ms to ≤ 200 ms.

The solution according to the invention is hereinafter explained with reference to figures. In detail is the following shown:

1 illustrated by a section of an axial section of a sheet forming unit for a machine for producing a material web, the structure of a head box according to the invention;

2 illustrated by a diagram the relationship between fabric consistency and formation of the flake structure in the free jet;

3 shows again in detail a section of a headbox according to the invention according to 1 ;

4a1 and 4a2 show a first arrangement of the turbulence generating channels of the turbulence generator;

4b1 and 4b2 show a second arrangement of the turbulence generating channels of the turbulence generator; and

5 shows a particularly advantageous embodiment of a turbulence generating channel of the turbulence generating device.

The 2 illustrates in a schematic simplified representation on the basis of a diagram, the influence of the height of the fabric consistency SK within a pulp suspension FS on the formation. For this purpose, the formation of the flake structure FL in the free jet with regard to the dimension of the flakes forming is applied over the fabric consistency SK. This shows the relationship between the high consistency of the fabric SK and an uneven and coarse-grained formation of fibers and fillers due to increased fiber flocculation, that is to say the tendency for larger flocs to form in the known freewheel F of pulp suspension emerging from the exit slit of a headbox headboxes. It is also clear that in pulp suspensions with lower consistency, here below a consistency consistency index SK _x of 1.2%, the flocculation is lower, that is, only smaller flakes are observed in the free jet at the exit from the exit slit of the headbox. The 2 illustrates only the basic relationship between the consistency of a pulp suspension FS and the flock slope. This is also dependent on the pulp itself.

To reduce and if possible avoid a reflocculation, ie back flocculation within the pulp suspension FS before or at the exit from the headbox 1 becomes a headbox designed according to the invention 1 as shown in the 1 for use in a sheet forming unit 3 proposed. The headbox 1 is here a forming unit 2 upstream and forms with this the sheet forming unit 3 for a machine for producing a material web, in particular fibrous web in the form of a paper, board or tissue web. The headbox 1 serves the machine-wide introduction of at least one pulp suspension FS in the forming unit 2 , To clarify the individual directions is to the sheet forming unit 3 a coordinate system is applied, wherein the X direction describes the longitudinal direction, which is also referred to as the machine direction MD which coincides with the passage direction of the fibrous web F. The Y direction describes the direction transverse to the direction of passage the fibrous web, in particular the width direction of the machine, which is therefore also referred to as the cross-machine direction CD, while the Z-direction characterizes the height direction.

The headbox 1 includes a feeder 4 , via which the at least one pulp suspension FS on the entire width of the headbox 1 can be distributed. In the simplest case, this is designed as an element, in particular a distributor tube, which extends in the cross-machine direction CD and forms a distribution channel, which element is designed to taper in the cross-machine direction in the through-flow direction. From the feeder 4 In the case illustrated, the pulp suspension FS passes by way of example into a first turbulence generating device 5 comprising a plurality of turbulence generating elements. The turbulence generator 5 can be carried out in various ways and is in the simplest case as flow channels, in particular turbulence-generating channels 6 descriptive and through holes formed perforated plate or tube bundle formed. In the direction of flow, the first turbulence generating device closes 5 a gap 13 to which a further second turbulence generating device 7 comprising turbulence generating elements to form turbulence generating channels 8th follows. To the second turbulence generating device 7 joins the exit 7A out of this one nozzle 9 under formation of a nozzle chamber 10 , which is capable of substantially accelerating the flow of the pulp suspension FS during operation and the pulp suspension FS by one, here by way of example by means of a diaphragm 11 and the, the nozzle space 10 in the direction perpendicular to a plane defined by the machine direction MD and cross machine direction CD plane bounding the nozzle wall 16.1 . 16.2 indicated exit slit 12 , to the forming unit 2 for the machine for producing a material web, at. Within each turbulence generator 5 and 7 the fibrous suspension FS is divided according to a predefined division and distributed distributed in partial streams. The turbulence generating devices 5 respectively 7 for this purpose comprise a multiplicity of turbulence-generating channels extending in the longitudinal direction of the machine, that is to say in the machine direction MD 6 . 8th , which are either machine-width or in the cross-machine direction CD in rows and in the vertical direction, that is perpendicular to a through the flow direction and the cross-machine direction. CD writable level in columns are arranged parallel to each other.

Within the single turbulence generating channel 8th the turbulence generating device 7 is at least one, a fluidization area 15 forming region, provided in which a pressure loss in the guided in this individual partial flow of the pulp suspension FS can be generated.

According to the invention are the second turbulence generating device 7 , which of the nozzle 9 arranged in the flow direction of the pulp suspension FS upstream, and the nozzle 9 executed and dimensioned such that the residence time T _{V of} the pulp suspension FS when passing through the second turbulence generating device 7 until the exit from the exit slit 12 the nozzle 9 ≤ 200 ms, preferably ≤ 175 ms, in particular ≤ 150 ms. This is done in a particularly advantageous embodiment by the appropriate coordination of the geometry of the second turbulence generating device 7 that is, in front of the nozzle 9 directly arranged element of the headbox 1 and the design of the nozzle 9 achieved. The second turbulence generating device 7 is designed, arranged and dimensioned such that by means of this in the last Fluidisierungsbereich 15 in front of the nozzle 9 at least one pressure loss is generated within the partial flow of ≥ 50 mbar, preferably ≥ 75 mbar, in particular ≥ 100 mbar, very particularly ≥ 150 mbar. For this purpose, several possibilities are conceivable, in which case a distinction is made between active and passive measures, that is to say a fixed setting of the achievable pressure loss or a free adjustability. The pressure loss can, as discussed below, by the geometric design of the individual turbulence generating channel 6 . 8th , In particular, the local change of these descriptive cross-sectional areas and / or the arrangement of additional facilities, such as static mixers or an additional energy input into the individual partial flow can be achieved.

The length of the last turbulence generating device 7 in front of the nozzle 9 When viewed in machine direction MD is denoted by l _TE and characterized by a length in the range of ≥ 100 mm to ≤ 500 mm, preferably from ≥ 100 mm to ≤ 400 mm, in particular from ≥ 150 mm to ≤ 300 mm. The length l _{D of} the nozzle 9 , measured from the exit 7A from the turbulence generating device 7 up to the exit slit 12 in the machine direction MD, is from ≥ 100 mm to ≤ 500 mm, preferably from ≥ 100 mm to ≤ 400 mm, in particular from ≥ 200 mm to ≤ 400 mm ,. The beam stability can only be maintained if the damping effect of the fibers increases and the length l _{D of} the nozzle 9 the condition l _D × SK ≦ 1000, preferably ≦ 800, in particular ≦ 700, where l _D corresponds to the length of the nozzle in mm and SK to the consistency of the material in%.

Another essential geometric feature is the length l ₁ , which is the distance between the last fluidization region 15 in the front of the nozzle 9 immediately upstream turbulence generating device 7 and the exit 7A from the turbulence generating device 7 that with an entry 14 in the nozzle 9 coincides, describes and which is ≤ 180 mm, preferably ≤ 150 mm, in particular ≤ 120 mm, very particularly ≤ 100 mm.

The between the individual, the nozzle space 10 delimiting nozzle walls 16.1 . 16.2 in the area of the exit gate 12 provided convergence angle α, which the angle between them in the region of the exit gap 12 is selected in the range between 5 ° and 45 °, preferably between 10 ° and 20 °. With this geometric embodiment of the combination of the features, wherein essentially the length of the nozzle l _D and the distance l _{1 are} decisive, the residence time T _V to a period of time within a predefined range and in particular below the Reflockulationszeit the pulp suspension FS at higher fabric consistencies SK be set.

The 3 clarified once again by means of a section of the headbox 1 the components essential to the invention for the generation of the required geometric conditions on the headbox 1 , Shown is the nozzle 9 and the upstream in the flow direction last on the pulp suspension FS actively acting area, which of a turbulence generating means 7 is formed and a fluidization area 15 having. Shown again are the basic geometric quantities l _D in the form of the length of the nozzle, l ₁ as the distance of the last Fluidisierungsbereichs 15 within the turbulence generator 7 before the entrance 14 in the nozzle 9 , At this time, the distance becomes the end of the fluidizing area 15 measured. The fluidization area 15 may be planar over a portion of the flow path extending or in the cross machine direction CD linear, that is locally very limited, be formed. Also shown are the convergence angle α of the nozzle 9 in the region of the exit gap 12 and the length l _{TE of} the turbulence generator 7 and the length l ₁ to the indication of the distance between Fluidisierungsbereich 15 and admission 14 in the nozzle 9 in the flow direction. The residence time in l ₁ is between 10 ms and 100 ms.

The 4a1 . 4a2 and 4b1 . 4b2 illustrate in schematic highly simplified representation advantageous embodiments of turbulence generating devices 7 , The turbulence generating device used for fluidizing the pulp suspension FS 7 can be designed in various ways. This can according to 4a1 . 4a2 from a plurality of channels formed as individual channels 8th which are arranged transversely to the machine direction CD in rows and in height direction in columns. The individual channels 8th the turbulence generating device 7 , here 8.11 to 8.nn , may be in the form of tubes, square or rectangular profiles, etc. in a known manner. Also conceivable is the integration of these in perforated plates. The 4a2 illustrates the arrangement in rows free of offset in the cross-machine direction CD to each other. It is understood that also the alternate offset of each channel 8th the turbulence generating device 7 to each other between two vertically arranged one above the other rows is possible.

According to 4b2 it is also conceivable, the flow channels 8th as extending across the width in the cross-machine direction CD channels 8.1 to 8.n. the turbulence generating device 7 execute, which are arranged one above the other in the height direction. These channels of the turbulence generator 7 are exemplary here with 8.1 to 8.n. designated and in two views in the 4b1 . 4b2 shown. For the direction assignment, the coordinate system is according to 1 Have been transferred.

All versions have in common is the formation of the channel geometry, which allows a range by a step-like cross-sectional change 17 , in particular increment is characterized. Is exemplary in the 5 such a turbulence generating channel 8th the turbulence generating device 7 shown. The view corresponds to the extension in the longitudinal direction, that is to say through-flow direction when installed in a machine for producing material webs. The 5 illustrates the formation of the individual turbulence generating channel 8th the turbulence generating device 7 in schematized strongly simplified representation. The turbulence generating channel 8th the turbulence generating device 7 is here in a plurality of different sections 18.1 to 18.4 divided. The entrance side 8E of the turbulence generating channel 8th the turbulence generating device 7 describes in cooperation with other such channels of the turbulence generating device 7 the entrance 7E into the turbulence generating device 7 , The exit 8A corresponds to the entrance 14 in the nozzle 9 , Between these are several subareas 18.1 to 18.4 arranged different cross-sectional areas Q1 to Q3. The area of the last fluidization before exiting into the nozzle 9 is characterized by a step-like cross-sectional change 17 , realized in particular a step jump between two cross-sectional areas Q1 and Q2. For this purpose, the turbulence-generating channel 8th the turbulence generating device 7 a first subarea 18.1 on, passing through one over its extension area in the flow _direction constant cross-sectional area Q1 is characterized, which can be described by a hydraulic diameter d _hydr , in the illustrated case with a circular cross-section through a diameter D1. The flow direction between the input 8E to the exit 8A subsequent second section 18.2 is about the extent of the subarea 18.2 in the flow direction also characterized by a constant cross section, which can be described by a diameter D2. The second subarea is followed by a transition area 18.3 on, which is a steady, that is, continuous transition to a third subarea 18.4 which is characterized by a cross-sectional area Q3 which is writable by a diameter D3.

The formation of the increment, that is the change in cross section 17 between the cross-sectional areas Q1 on Q2, which advantageously by a change in diameter D2 / D1 of the subregions of the turbulence-generating channel 8th the turbulence generating device 7 descriptive geometry is carried out such that a pressure loss between the first portion 18.1 and the second subarea 18.2 greater than 50 mbar is generated. It is crucial that the length l ₁ of the second subarea 18.2 and the third section 18.4 taking into account the transitional area 18.3 , which is the distance from the incremental fluidization area 15 to the exit 8A from the turbulence generating channel 8th or the turbulence generating device 7 characterized, at least ≤ 180 mm, preferably ≤ 150 mm, in particular ≤ 120 mm, very particular ≤ 100 mm, must be. The length l _{TE of} the individual turbulence generating channel 8th is in the range between 100 mm and 500 mm, preferably 100 mm to 500 mm, in particular between 150 mm and 300 mm.

If the cross-sectional areas Q1, Q2 and Q3 can not be described by a diameter D1, D2 and D3, ie in the case of other cross-sectional _geometries , the hydraulic diameter d _hydr = 4 · Q / U, with Q = cross-sectional area and U =, respectively, is used instead of the diameter Set scope.

According to a particularly advantageous embodiment, the last increment required for fluidization should be in front of the nozzle 9 at least in the range of the mean fiber length of the pulp suspension FS used, that is (D2 - D1) / 2. l _Fmittel , in which case the diameter is set at circular cross section, otherwise the respective hydraulic diameter d _hydr .

Since the flake size within the pulp suspension FS after fluidizing, ie the last increment in the flow direction FS, depends on the available space, ie the cross-sectional area Q, the largest hydraulic diameter d _{hydr-8 should be} within the turbulence _-generating channel 8th the turbulence generating device 7 in the range of 5 mm ≤ d _hydr ≤ 25 mm, preferably 5 mm ≤ d _hydr ≤ 20 mm, in particular 10 mm ≤ d _hydr ≤ 20 mm, because of the fiber wiping, the hydraulic diameter d _hydr-8E in the region of entry 8E at the turbulence generating channel 8th the turbulence generating device 7 in the range of 8 mm _≦ d _{hydr-8E ≦} 20 mm, preferably 10 mm _≦ d _{hydr-8E ≦} 20 mm, in particular 10 mm _≦ d _{hydr-8E ≦} 15 mm.

The number of lines, that is the number of flow channels 8th Within a column, it should be chosen such that the flow velocity in the narrowest cross section is between 5 m / s and 20 m / s, preferably between 7 m / s and 15 m / s.

Such a designed headbox 1 can be further modified in any way. These may be headboxes equipped with lamellas and / or with dilution fiber technology, ie at least one metering device for metering a fluid into the flow channels 8th are characterized.

The headbox according to the invention can also be used in combination with arbitrarily designed forming units 2 , in particular wire, hybrid former and twin-wire former are used. The in the 1 illustrated embodiment represents an advantageous embodiment in combination with a Gapformer, wherein the free jet F in a supporting between two rolls of clothing 20.1 . 20.2 formed gap 19 is introduced, but is not limited to these.

LIST OF REFERENCE NUMBERS

1

headbox

2

forming unit

3

Sheet forming unit

4

feeder

5

Turbulence-generating device

6

Turbulence generating the channel

7

Turbulence-generating device

7E

entry into the turbulence generating device

7A

exit from the turbulence generating device

8th

Turbulence generating the channel

8.1-8.n, 8.11-8.nn

Turbulence generating the channel

8E

entry into the turbulence-producing channel

8A

exit from the turbulence generating channel

9

jet

10

nozzle chamber

11

cover

12

exit slit

13

gap

14

entry

15

Area

16.1

nozzle wall

16.2

nozzle wall

17

Cross-sectional change

18.1

first subregion

18.2

second subregion

18.3

Transition area

18.4

third subregion

19

gap

20.1, 20.2

screen belt

21

impinging

CD

CMD

D1

diameter of the first subarea

D2

diameter of the second subarea

D3

diameter of the third subarea

dhydr

hydraulic diameter

dhydr-8

hydraulic Diameter of the turbulence generating channel

dhydr-8E

hydraulic Diameter at the entrance to the turbulence generating channel

8E

entrance

8A

output

FL

flake structure

FS

Fibrous suspension Length of the distance between increment and entry into the nozzle

lD

length the nozzle

lFmittel

middle fiber length

LTE

length the turbulence generating device

MD

machine direction

Q1

Cross sectional area of the first subarea

Q2

Cross sectional area of the second subarea

Q3

Cross sectional area of the third subarea

SK, SKx

stock consistency

TV

length of stay

α

Nozzle angle of convergence

Ap

pressure drop

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - EP 1313912 B1 [0004]
• - DE 10106684 A1 [0006]
• - DE 19902621 A1 [0006]
• WO 2008/077585 A1 [0007]
• - EP 1022378 A2 [0008]
• - DE 29713433 U1 [0009]
• - DE 10234559 A1 [0010]

Claims (14)

Headbox ( 1 ) for a machine for the production of fibrous webs, in particular paper, board or tissue webs of at least one pulp suspension (FS), with at least one, the at least one pulp suspension (FS) feeding feeder ( 4 ), an exit slit ( 12 ) having nozzle ( 9 ) for the delivery of the pulp suspension (FS) in a free jet (F) and in the flow direction of the nozzle ( 9 ) immediately upstream turbulence generating device ( 7 ), in which during operation of the headbox ( 1 ) the at least one pulp suspension (FS) through a plurality of turbulence-generating channels ( 8th ; 8.1 - 8.n. ; 8.11 - 8.nn ) is conducted in sub-streams, wherein within the individual turbulence-generating channel ( 8th ; 8.1 - 8.n. ; 8.11 - 8.nn ) of the turbulence generating device ( 7 ) at least one, a fluidization region ( 15 ) is provided in which a pressure loss (Δp) in the guided through this partial flow of the pulp suspension (FS) can be generated, characterized in that the nozzle ( 9 ) and the nozzle ( 9 ) directly upstream turbulence generating device ( 7 ) are designed and dimensioned such that they are suitable for a residence time (T _V ) of the fibrous suspension (FS) flowing through them from a last fluidization region ( 15 ) of a single turbulence generating channel ( 8th ; 8.1 - 8.n. ; 8.11 - 8.nn ) of the turbulence generating device ( 7 ) before entry ( 14 ) in the nozzle ( 9 ) up to the exit slit ( 12 ) of the nozzle ( 9 ) of ≦ 200 ms, preferably of ≦ 175 ms, in particular of ≦ 150 ms, and a pressure loss (Δp) in the last fluidization region ( 15 ) before entry ( 14 ) in the nozzle ( 9 ) of ≥ 50 mbar, preferably ≥ 75 mbar, in particular ≥ 100 mbar, very particularly ≥ 150 mbar. Headbox ( 1 ) according to claim 1, characterized in that the nozzle ( 9 ) has a length (l _D ) in the range of 100 mm ≤ l _D ≤ 500 mm, preferably 100 mm ≤ I _D ≤ 400 mm, in particular 200 mm ≤ l _D ≤ 400 mm, and that the distance (l ₁ ) between the last fluidization area ( 15 ) within a single turbulence generating channel ( 8th ; 8.1 - 8.n. ; 8.11 - 8.nn ) of the turbulence generating device ( 7 ) and admission ( 14 ) in the nozzle ( 9 ) ≤ 180 mm, preferably ≤ 150 mm, in particular ≤ 120 mm, very particularly ≤ 100 mm. Headbox ( 1 ) according to claim 1 or 2, characterized in that the nozzle ( 9 ) has a length (l _D ) which, taking into account the consistency of the material (SK) of the pulp suspension (FS) to be fed through it during operation, satisfies the following condition: l _D × SK ≦ 1000, preferably ≦ 800, in particular ≦ 700, with l _D = length of the nozzle ( 9 in mm; and SK = fabric consistency in%. Headbox ( 1 ) according to claim 1, 2 or 3, characterized in that the nozzle space ( 10 ) of the nozzle ( 9 ) of two in the flow direction with formation of the outlet ( 12 ) converging nozzle walls ( 16.1 . 16.2 ) and that the angle of convergence (α) between them in the region of the exit ( 12 ) is between 5 ° and 45 °, preferably between 10 ° and 20 °. Headbox ( 1 ) according to one of the preceding claims, characterized in that the turbulence generating device ( 7 ) has a length (l _TE ) in the flow direction in the range of 100 mm ≦ l _TE ≦ 500 mm, preferably 100 mm ≦ l _TE ≦ 400 mm, especially 150 mm ≦ l _TE ≦ 300 mm. Headbox ( 1 ) according to one of the preceding claims, characterized in that the last fluidization region ( 15 ) before entry ( 14 ) in the nozzle ( 9 ) of a local, incremental change ( 17 ) of the cross-sectional area of the individual turbulence-generating channel ( 8th ; 8.1 - 8.n. ; 8.11 - 8.nn ) of the turbulence generating device ( 7 ) is formed viewed in the flow direction. Headbox ( 1 ) according to one of the preceding claims, characterized in that the last fluidization region ( 15 ) before entry ( 14 ) in the nozzle ( 9 ) of a constant change ( 17 ) of the cross-sectional area of the individual turbulence-generating channel ( 8th ; 8.1 - 8.n. ; 8.11 - 8.nn ) of the turbulence generating device ( 7 ) is formed viewed in the flow direction. Headbox ( 1 ) according to claim 6 or 7, characterized in that the change ( 17 ) of the cross-sectional area in the fluidization area (FIG. 15 ), in particular the height of the step change characterizing the change in the cross-section corresponds at least to the average fiber length (l _Fmittel ) of the pulp _suspension (FS) used. Headbox ( 1 ) according to one of the preceding claims, characterized in that the individual turbulence-generating channel ( 8th ; 8.1 - 8.n. ; 8.11 - 8.nn ) of the turbulence generating device ( 7 ) is designed and dimensioned such that the maximum hydraulic diameter (d _hydr ) describing a cross-sectional area in the range of 5 mm _≦ d _{hydr ≦} 25 mm, preferably 5 mm _≦ d _{hydr ≦} 20 mm, in particular 10 mm _≦ d _{hydr ≦} 20 mm, is. Headbox ( 1 ) after one of the previous ones the claims, characterized in that the cross-sectional area at the entrance ( 8E ) into the individual turbulence generating channel ( 8th ; 8.1 - 8.n. ; 8.11 - 8.nn ) of the turbulence generating device ( 7 ) descriptive hydraulic diameter (d _hydr-8E ) in the range of 8 mm ≤ d _hydr-8E ≤ 20 mm, preferably 10 mm ≤ d _hydr-8E ≤ 20 mm, in particular 10 mm ≤ d _hydr-8E ≤ 15 mm. Headbox ( 1 ) according to one of the preceding claims, characterized in that the number of lines of the turbulence-generating channels ( 8th ; 8.1 - 8.n. ; 8.11 - 8.nn ) of the turbulence generating device ( 7 ) is selected such that the flow velocity in the narrowest cross-section of a single turbulence-generating channel ( 8th ; 8.1 - 8.n. ; 8.11 - 8.nn ) of the turbulence generating device ( 7 ) between 5 m / s and 20 m / s, preferably between 7 m / s and 15 m / s. Sheet forming unit ( 3 ) for a machine for producing fibrous webs, in particular paper, board or tissue webs, comprising a headbox ( 1 ) according to one of claims 1 to 11 and a subordinate thereto forming unit ( 2 ), in which the pulp suspension (FS) from the exit slit ( 12 ) of the headbox ( 1 ) is applied or introduced in the free jet (F). Sheet forming unit ( 3 ) according to claim 12, in which the pulp suspension (FS) in the free jet (F) is applied to a covering ( 20.1 . 20.2 ) of the forming unit ( 2 ) forming an impact line ( 21 ), characterized in that the headbox ( 1 ) and the forming unit ( 2 ) are formed and. arranged that the residence time (T _V ) of the pulp suspension (FS) from the last fluidization area ( 15 ) to the impact line ( 21 ) on the clothing ( 20.1 . 20.2 ) from ≥ 30 ms to ≤ 300 ms, preferably from ≥ 50 ms to ≤ 200 ms, in particular from ≥ 80 ms to ≤ 200 ms. Method for operating a sheet forming unit ( 3 ) according to one of claims 12 or 13, in which the at least one pulp suspension (FS) of the headbox ( 1 ) is supplied across the machine width, forming partial streams in a plurality of turbulence-generating channels ( 8th ; 8.1 - 8.n. ; 8.11 - 8.nn ) of the turbulence generating device ( 7 ) and to a nozzle ( 9 ) is guided, from which the at least one pulp suspension (FS) in the free jet (F) in the forming unit ( 2 ), in particular on a string ( 20.1 . 20.2 ) of the forming unit ( 2 ) under definition of an impact line ( 21 ) is applied or introduced, whereby within a single turbulence-generating channel ( 8th ; 8.1 - 8.n. ; 8.11 - 8.nn ) of the turbulence generating device ( 7 ) a pressure drop (Δp) in the pulp suspension (FS) is set, characterized in that in a last fluidization region ( 15 ) of a single turbulence generating channel ( 8th ; 8.1 - 8.n. ; 8.11 - 8.nn ) of the turbulence generating device ( 7 ) before entry ( 14 ) in the nozzle ( 9 ) a pressure loss (Δp) within the pulp suspension (FS) ≥ 50 mbar, preferably ≥ 75 mbar, in particular ≥ 100 mbar, very particular ≥ 150, mbar is generated and that the pulp suspension (FS) of this last fluidization region (FS) 15 ) up to the exit slit ( 12 ) of the nozzle ( 9 ) is guided in such a way that its residence time (T _V ) in which the last fluidization area ( 15 ) up to the exit slit ( 12 ) extending range ≤ 200 ms, preferably ≤ 175 ms, in particular ≤ 150 ms, and / or that the dwell time (T _V ) in which from the last fluidization area ( 15 ) to the impact line ( 21 ) extending from ≥ 30 ms to ≤ 300 ms, preferably from ≥ 50 ms to ≤ 200 ms, in particular from ≥ 80 ms to ≤ 200 ms.

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