EP0892108B1 - Headbox - Google Patents

Description

The invention relates to a headbox Paper machine or board machine according to the Preamble of claim 1.

A headbox according to the preamble of the claim 1 is from the patent application DE 44 37 180 of the Applicant known. This headbox has a machine-wide cross distributor, one turbulence generating area and a subsequent one Headbox. The turbulence generating area contains a grid, a subsequent compensation chamber and a tube bundle that extends in the direction of flow gradually expanded and at the end of the tube bundle largest pipe diameter.

Have the tubes of the tube bundle turbulence generator thus significantly smaller inlet than outlet cross sections. One reason for this is that there is minimal land area the inflow side must be maintained to the formation to prevent fiber wiping and contamination. Sudden cross-sectional enlargements in the pipe generate the desired turbulence and ensure making sure that the fiber flakes in the suspension be broken up. This has a positive impact on the later leaf formation.

To annoying wake effects in the following To avoid nozzle, it is necessary to land on the Keep the outlet of the tube bundle low. Because of these Demand for small land areas at the end of the turbulence generating area are the Outlet cross sections of the tube bundle at none Headbox circular but have a shape which enables the highest possible packing density. Due to the non-circular tubes in the End area of the turbulence generator form in the Tubes of secondary flows that lead to disturbances lead up to the nozzle outlet gap of the can blow through the subsequent nozzle. This Breakdown of interference ultimately leads to a negative influence on the formation and thus Final paper quality deterioration.

It is an object of the invention to the headbox to the preamble of claim 1 improve that it creates a jet of material that the Requirement for a paper or cardboard with provides improved formation.

The solution to the problem is through a headbox achieved with the features of claim 1.

1. In Folge der Sekundärströmungen im divergenten Auslaßbereich der Rohre entstehen Querströmungen, die in der Düse nicht vollständig abgebaut werden können. Diese Querströmungen werden durch die Strömungsumlenkung vor der Blende am Düseneintritt wieder verstärkt und sind im Strahl als regelmäßige Furchen sichtbar. Ein gestörter Strahl führt zu einer streifenförmigen Formation des Blattes.

2. In Folge von Entmischungen in den Rohrecken kann ebenfalls eine streifige Formation entstehen.

3. Falls dem Turbulenzrohr Lamellen nachgeschaltet sind, müssen sich diese über einen wesentlichen Teil des Strömungsweges erstrecken, um die oben beschriebenen Turbulenzrohrstörungen reduzieren zu können. An der Lamellenoberfläche werden durch Reibung zwischen Fluid und Wand Mikroturbulenzen erzeugt, die die beschriebenen Störungen teilweise beseitigen können. Eine vollständige Beseitigung der Störungen ist wegen der geringen Wellenlänge der Mikroturbulenzen und dem vergleichsweise geringen Energieinhalt dieser turbulenten Querbewegungen nicht möglich. Mit zunehmender Lamellenlänge werden die beschriebenen Störungen zwar weiter abgebaut, jedoch ist nachteilig, daß aufgrund der dann zunehmenden Mikroturbulenz ebenfalls eine unerwünscht harte, feinkörnige Formation der Papierbahn entsteht.In der Praxis stellt die Wahl der Lamellenlänge somit stets einen Kompromiß zwischen ausreichender Beseitigung von Störungen auf der einen und möglichst geringer negativer Beeinflussung der Formation auf der anderen Seite dar. Eine ausreichende Beseitigung von Störungen, die durch die heute üblichen Turbulenzerzeuger hervorgerufen werden, durch nachgeschaltete Lamellen, ist somit nicht möglich. Alle heute gebauten Stoffaufläufe erzeugen daher bei kritischen Betriebsbedingungen streifenförmige Störungen der Formation.

4. Im Falle von Lochwalzen-Stoffaufläufen, mit Lochwalzen als Turbulenzerzeuger, muß aus statischen Gründen der Anteil der Landfläche der Lochwalze größer als ca. 55 % sein. Die dadurch entstehenden großen Stege verursachen grobe Turbulenzen beim Durchtritt der Strömung, die häufig in der Stoffauflaufdüse nicht ausreichend abklingen können und in der Folge ebenfalls Formationsstörungen verursachen.

The inventors have recognized the following: The known turbulence generation concepts cause the following typical disturbances:

1. As a result of the secondary flows in the divergent outlet area of the pipes, cross flows arise which cannot be completely broken down in the nozzle. These cross currents are intensified again by the flow deflection in front of the orifice at the nozzle inlet and are visible in the jet as regular furrows. A disturbed beam leads to a streak-like formation of the leaf.

2. As a result of segregation in the pipe corners, a streaked formation can also arise.

3. If fins are connected downstream of the turbulence tube, they must extend over a substantial part of the flow path in order to be able to reduce the turbulence tube disturbances described above. Microturbulence is generated on the lamella surface by friction between the fluid and the wall, which can partially eliminate the disturbances described. A complete elimination of the disturbances is not possible due to the small wavelength of the microturbulence and the comparatively low energy content of these turbulent transverse movements. With increasing lamella length, the disturbances described are further reduced, but it is disadvantageous that, due to the then increasing microturbulence, an undesirably hard, fine-grained formation of the paper web also arises one and the least possible negative influence on the formation on the other side. A sufficient elimination of disturbances caused by the turbulence generators common today by downstream fins is therefore not possible. All headboxes built today therefore create strip-like disturbances in the formation under critical operating conditions.

4. In the case of perforated roller headboxes, with perforated rollers as turbulence generators, the proportion of the land area of the perforated roller must be greater than approx. 55% for static reasons. The resulting large webs cause rough turbulence when passing through the flow, which often cannot decay sufficiently in the headbox nozzle and consequently also cause formation disorders.

It has single and multilayer headboxes shown that the disturbances in headboxes with Pipe bundle turbulence generators, which by the Increments and / or extensions of Turbulence pipes are generated, as well as faults on Exit of the perforated roller in headboxes with as Perforated roller trained turbulence generators caused by the usual today Geometries of the following elements in the headbox cannot be reduced to a sufficient extent. Even minor convergent extensions in one level, especially at the Operating limits of the headbox, too Cross flows that can no longer be eliminated are. So this means that the turbulence generating Unit in front of the nozzle must be dimensioned so that by this turbulence-generating element far less Disturbances, in the form of stationary irregularities, caused.

Since the influences of disturbances generated by the turbulence generator are largely determined by the dimensioning of the turbulence-generating passages, it makes sense to relate the design of a headbox essentially to the hydraulic diameter of the turbulence-generating area. The hydraulic diameter d _hydr is defined as four times the total cross-sectional area through which the liquid flows, divided by the length of all occurring edge regions. In the case of an ideal circular cross-section, this corresponds exactly to the geometric diameter of the circular area. In the case of an infinitely long gap, twice the height of the gap results for the hydraulic diameter.

It is to avoid formation disturbances necessary according to the concept of the invention hydraulic diameter, respectively individual hydraulic diameter of the turbulence generating area, at its transition to To design the headbox nozzle so that no coarse Currents can occur up to the point of exit blow through the headbox nozzle. This means at Headboxes of known dimensions must be maximum hydraulic diameter at the end of the Turbulence generator smaller than 17 mm, preferably less than 14 mm, preferably in the range between 14 and 7 mm.

According to a special embodiment of the invention, the hydraulic diameter of the turbulence-generating region at its transition to the headbox nozzle to the gap height of the nozzle outlet gap d _D behaves as follows for any headboxes: 6 mm ≤ d hydr [mm] ≤ -0.52 · d D [mm] + 30 With d D = Nozzle height [mm] with half nozzle length [mm] · 0.5.

A further development according to the invention leads to the land area ratio at the end of the turbulence generator being taken into account in addition to determining the maximum hydraulic diameter in the end region of the turbulence generator, which has at least two machine-wide ducts and lamellae are arranged between the ducts. The land area ratio is defined _total divided by the suspension flowed through surface F _open at the end of the turbulence generator F than the total cross-sectional area. Accordingly, the land area ratio should have a value in the range of 1 <F total / F open <- 0.0094d L + 2.16 exhibit. Here d _{L is} the largest fin spacing in the nozzle at the end of the turbulence generator.

Furthermore, a further development according to the invention leads, in addition to determining the maximum hydraulic diameter in the end region of the turbulence generator, which has at least two machine-wide channels, to taking into account the land area ratio at the end of the turbulence generator. The land area ratio is defined _total divided by the suspension flowed through surface F _open at the end of the turbulence generator F than the total cross-sectional area. Accordingly, the land area ratio should have a value in the range of 1 <F total / F open <- 0.0094d D + 2.16 exhibit. Here, d _{D is} the largest nozzle height at the end of the turbulence generator.

On the basis of the explanations presented above, a headbox for a paper machine or board machine is proposed, with at least one means for supplying stock suspension distributed over the machine width, at least one means for generating turbulence, which is the means or which means for supplying stock suspension in the direction of flow is / are arranged and at least one means for machine-wide application of the stock suspension to a sieve or introduction of the stock suspension between two sieves, which is connected downstream of the means for generating turbulence in the flow direction, at least one of the means or the means for generating turbulence being hydraulic Diameter d _hydr has less than 17 mm. This hydraulic diameter is preferably less than 14 mm, preferably 14 to 9 mm.

The design of the headbox, especially the turbulence generating area, corresponding to the above ideas according to the invention, caused advantageous that the growth of turbulent Cross movements due to the smaller wall distance is hindered, which is already a clear advantage by reducing the wall clearance in just one Level can be determined.

It is also advantageous if the relation of ratio of turbulence energy due to wall friction to the flow cross-section of a turbulence-generating Unit itself in reducing the hydraulic Diameter increased. In this way the specific fine turbulence proportion significantly increased and disruptive turbulent transverse movements of a large extent effectively broken down. Due to the fact that the Fine turbulence compared to the use of fins in a larger distance from the outlet nozzle the cooldown is significantly longer. this applies especially because on the flow path between the slat end and the nozzle outlet Speed is greater by at least a factor of 3 than at the beginning of the nozzle. Under decay is here Association of many turbulence balls with high-frequency transverse movement to a small extent such a low frequency with a slightly larger amplitude Roger that. Below are some examples Embodiments of the headbox, in particular the turbulence generating area of the headbox, called.

One way of designing the Turbulence generator is this only from a variety of panels that are horizontal, are arranged vertically or at an angle. Here, at least two current-carrying run Walls - in one cut across the machine direction considered - parallel to each other. The inlet side The distance between the plates is in accordance with the invention smaller than 16 mm. The plate surface can be wholly or partially structured to the Improve turbulence generation. The Cross-sectional profile along the flow path can be stepped. It can too different plate formers and / or distances in Alternate regularly. Likewise, the Plates at different distances from Nozzle outlet gap ends.

In a further embodiment of the Turbulence insert with a variety of channels have this hydraulic diameter in the outlet area of the channels of a maximum of 17 mm, preferably 14 mm. This can be done, for example, by appropriately small Single pipes, channels with a large length / width ratio or even through larger pipes achieved with internals, at least in the outlet area become. The tube walls are broken. You can for example, slotted parallel to the pipe axis. These slots can be over part or too extend the entire length of the pipe. In the latter case the turbulence generator thus consists of a large number parallel webs without connection to each other. The tube walls can also be in the flow direction seen, have different lengths. To the For example, the vertical walls can continue into the subsequent nozzle may be drawn in as the Horizontal. This way a reduction in Land areas reached in the respective level. Likewise can the ratio of the longer to the shorter pipe side of a rectangular turbulence pipe at the pipe outlet larger than 1.8. With these tubes with an aspect ratio greater than 1.8, the longer distance runs horizontally. In in this case is the division of the tube bundle preferably less than 200 mm. Likewise, the pipes with a large aspect ratio by several Holes or through a slot on the be fed to the material suspension feed side. is the aspect ratio is less than 1.8, so is the Pipe pitch less than 20 mm. With one out Rectangular tubes are the existing turbulence generator vertical pipe sides offset against each other. Also can have different tube shapes in regular Alternate episode.

The characteristics of the two versions described above the turbulence generator can also be in with each other Combination can be used.

Another advantageous form of turbulence generator is the turbulence pipes in the form of a static mixer. The hydraulic Here, too, diameters are preferably smaller than 17 mm. In this regard, the registration DE 42 11 291 of the applicant and is intended to be part the disclosure content of the present description his.

Another embodiment according to the invention exists in that the turbulence generator in C-clamp construction, so with a C-shaped strut around the Reaches around to carry out material suspension distribution. This gives the advantage that the on Internal pressure acting through the nozzle wall Turbulence insert is conducted. A big advantage this design principle is the short lever arm. This results in very small deformations of the Nozzle outlet gap under operating conditions what known for a flat fiber orientation angle profile is of central importance. The C construction can also be used in turbulence generators, for example realize that from vertical panels or individual Channels are established. With these two Use cases are the nozzle forces for the purpose of Traction through all or part of the vertical Plates or the vertical walls of the Channels. It is also essential that the hydraulic diameter of these plates at the The outlet side of the turbulence generator is less than 17 mm.

When designing the turbulence generator with plates or channels, these can be complete or partial be provided with structures, especially smooth turbulent transverse movements through the corrugated plates can be achieved. Preferably run the waves of one side are parallel, however Waves of opposite sides parallel or run at an angle not equal to 0 ° to each other. In in this connection, reference is made to patent application DE 44 33 445 of the applicant, the content this application forms part of the disclosure of the present Description should be.

It is also advantageous if the flow guidance in the turbulence inserts is designed so that a one- or multi-dimensional divergent flow is avoided.

It is also advantageous if in the area of Turbulence insert a single flow cross-section extension is made and this preferably in Entry area of the turbulence insert is.

It is also advantageous, following cross bars, Increments and other disrupting uniformity or internally coarse internals in the turbulence level Turbulence insert in the nozzle hydraulic diameter to generate, which are definitely less than 17 mm.

Another advantageous embodiment of the Turbulence insert is that for Turbulence generation used slats in their length designed to be changeable.

The above characteristics of the headbox can also advantageous for a multi-layer headbox be used.

Further embodiments of the invention are in the Subclaims to claim 1 and in the following Figure descriptions shown.

It is understood that the above and Features of the invention to be explained below not only in the specified combination, but also in other combinations or in USP can be used without the scope of Leaving invention.

Figur 1:

Längsschnitt durch einen Rohrbündel-Turbulenzerzeuger mit Einsätzen zur Reduktion des hydraulischen Durchmessers';

Figur 2:

Schnitt B-B aus Figur 1;

Figur 3:

Längsschnitt durch Stoffauflauf mit einem Turbulenzerzeuger mit Ausgleichskammer und Mitteln zur Reduktion des hydraulischen Durchmessers;

Figur 4:

Schnitt B-B aus Figur 3.

Further features and advantages of the invention result from the following description of preferred exemplary embodiments with reference to the drawing.

Figure 1:

Longitudinal section through a tube bundle turbulence generator with inserts for reducing the hydraulic diameter ';

Figure 2:

Section BB from Figure 1;

Figure 3:

Longitudinal section through the headbox with a turbulence generator with compensation chamber and means for reducing the hydraulic diameter;

Figure 4:

Section BB from FIG. 3.

Figure 1 shows a headbox 1 with his Cross distributor 2, which the stock suspension in the turbulence generating area 3 feeds. from Turbulence-generating area 3 becomes the stock suspension passed into the nozzle 4. The nozzle 4 has a Upper lip 4.1 and a lower lip 4.2, the Upper lip 4.1 is equipped with an aperture 4.3.

F_hydr =

gesamte flüssigkeitsdurchströmte Querschnittsfläche

L_hydr =

Länge aller vorkommenden, suspensionsberührten Randbereiche.

The turbulence generator 3 consists, in a known manner, of a multiplicity of tubes 5 which widen in steps from their entry area to the exit area. According to the invention, additional crosses consisting of horizontal and vertical surfaces 6 are introduced in the end region of the turbulence pipes, which ensure that the hydraulic diameter of the turbulence generator is significantly reduced in the end region. This is achieved by increasing the length of the edge regions in contact with the suspension at the end of the turbulence generator. The hydraulic diameter d _{hydr is} calculated as follows: d hydr = 4 · F hydr / L hydr With:

F _hydr =

total cross-sectional area through which liquid flows

L _hydr =

Length of all occurring marginal areas in contact with the suspension.

The section BB from FIG. 1 is shown in FIG. The rectangular contours of the individual tubes 5 are shown, which are arranged offset in several rows. In the rectangular tubes there are surfaces 6 which form crosses and are arranged centrally in the rectangular tube 5 of the turbulence generator. In this way, the total length of the edge regions in _{contact with} the suspension is increased while the area through which the liquid flows is virtually constant, so that this also _results in a corresponding reduction in the hydraulic diameter d _hydr in the end region of the turbulence _generator .

The version shown in the tubes Crosses with the faces 6 can also be realized in this way be that the surfaces 6 not the walls of the tubes touch and / or in their crossing area Have recess. An exemplary representation is shown in the oval labeled 10.

There is also the possibility of the surfaces 6 in their end area with a slight bend provided so that the flow an additional Rotational component is supplied.

FIG. 3 shows a headbox 1 according to the invention with a cross distributor 2. From the cross distributor 2, the stock suspension is guided via a pipe distribution grating 3.1 into an intermediate channel 3.2. After the intermediate channel 3.2, the stock suspension passes through a further pipe distribution grating 3.3 with a large number of openings 5 into a further turbulence-generating area. This area consists of a multiplicity of walls 8 and 7 arranged perpendicular to one another. The walls 8, which are perpendicular with respect to the machine width, are shorter than the horizontally arranged walls 7. An embodiment in reverse length arrangement, or with walls 7 and 8 in the same Length, is also possible. In all versions, it is essential that the hydraulic cross-section in the end area of the turbulence generator is <17 mm, or in the area of the formula: 6 mm ≤ d hydr [mm] ≤-0.52 · d D [mm] + 30 With d D = Nozzle height [mm] is half the nozzle length [mm] · 0.5.

4 is section B-B of FIG. 3 represented by the vertical and horizontal Walls 8 and 7 leads. As seen in Figure 4 is, the walls 8 and 7 touch in this Embodiment does not. However, it is in the area of Invention, also a mutual crossing of the walls 7 and 8, over the entire length or only partially, permit.

d_L =

größter Lamellenabstand in der Düse am Ende des Turbulenzerzeugers;

F_gesamt =

Gesamtquerschnittsfläche am Ende des Turbulenzerzeugers;

F_offen =

offene Durchtrittsfläche am Ende des Turbulenzerzeugers.

It is particularly advantageous in this embodiment that the land area ratio at the end of the turbulence generator can be kept very low, or is in the range of the following formula: 1 <F total / F open <-0.0094d L + 2.16 With:

d _L =

greatest distance between fins in the nozzle at the end of the turbulence generator;

F _total =

Total cross-sectional area at the end of the turbulence generator;

F _open =

open passage area at the end of the turbulence generator.

d_D =

größte Düsenhöhe am Ende des Turbulenzerzeugers;

F_gesamt =

Gesamtquerschnittsfläche am Ende des Turbulenzerzeugers;

F_offen =

offene Durchtrittsfläche am Ende des Turbulenzerzeugers.

If the headbox (1) has no lamellae in a further embodiment of the invention (not shown), the land area ratio at the end of the turbulence generator should also be kept very low or should be in the range of the following formula: 1 <F total / F open <-0.0094d D + 2.16 With:

d _D =

greatest nozzle height at the end of the turbulence generator;

F _total =

Total cross-sectional area at the end of the turbulence generator;

F _open =

open passage area at the end of the turbulence generator.

LIST OF REFERENCE NUMBERS

1

headbox

2

Querverteiler

3

turbulence generating area

3.1

first pipe distribution grid

3.2

intermediate channel

3.3

second pipe distribution grid

4

jet

4.1

upper lip

4.2

bottom lip

4.3

cover

5

Tube

6

area

7

wall

8th

wall

9

channel

10

recess

Claims (6)

1. Flowbox (1) for a paper machine or a board machine, having:

   1.1 at least one means (2) of supplying stock suspension distributed over the machine width,

   1.2 at least one means (3) of generating turbulence,

   1.3 at least one means (4) for the machine-width application of the stock suspension to a wire or for the introduction of the stock suspension between two wires,
   characterized

   1.4 in that at least one of the means or the means (3) for producing turbulence has a hydraulic diameter d_hydr in the end region which is less than 17 mm.
2. Flowbox according to Claim 1, characterized in that the hydraulic diameter d_hydr is less than 14 mm, preferably in the range of 14 mm to 5 mm, preferably lying in the range of 14 mm to 9 mm.
3. Flowbox according to Claim 1 or 2, characterized in that the means (4) for the machine-wide application of the stock suspension is designed as a nozzle,
   in that the greatest hydraulic diameter of the means (3) of producing turbulence has a value for which it is true that: 6 mm ≤ dhydr [mm] ≤ -0.52 · dD [mm] + 30 where dD = nozzle height [mm] at half the nozzle length [mm] · 0.5.
4. Flowbox according to one of Claims 1 to 3, characterized in that the means (4) for the machine-wide application of the stock suspension is designed as a nozzle,
   in that the means (3) of producing turbulence has at least two machine-wide ducts (9),
   in that between the ducts (9), slats are arranged downstream, and
   in that the land area relationship at the end of the means (3) of producing turbulence lies in the range 1 < Ftotal/Fopen < -0.0094 · dL + 2.16 where:

   d_L =

   greatest slat spacing in the nozzle at the end of the turbulence generator (3);

   F_total =

   total cross-sectional area at the end of the turbulence generator (3);

   F_open =

   open passage area at the end of the turbulence generator (3).

5. Flowbox according to one of Claims 1 to 3, characterized in that the means (4) for the machine-wide application of the stock suspension is designed as a nozzle,
   in that the means (3) of producing turbulence has at least two machine-wide ducts (9), and
   in that the land area relationship at the end of the means (3) of producing turbulence lies in the range 1 < F_total/F_open < -0.0094 ·d_D + 2.16
   where:

   d_D =

   greatest slat spacing in the nozzle at the end of the turbulence generator (3);

   F_total =

   total cross-sectional area at the end of the turbulence generator (3);

   F_open =

   open passage area at the end of the turbulence generator (3).

6. Flowbox according to one of Claims 1 to 5, characterized in that the means (3) of generating turbulence has a large number of ducts (9) arranged beside one another and above one another.

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