EP0992625B1 - Headbox system and method for improving the transverse consistency profile of a fiber web - Google Patents

Abstract

In the control of the lateral consistency profile of a paper or cardboard web, the stock inlet has a fiber suspension flow of high consistency and a fiber suspension flow of low consistency together with a third fiber suspension flow of a different fiber composition or clear water. In the control of the lateral consistency profile of a paper or cardboard web, the stock inlet has a fiber suspension flow (QH) of high consistency and a fiber suspension flow (QL) of low consistency together with a third fiber suspension flow (QC) of a different fiber composition or clear water. The third suspension (QC) is mixed with the other two suspension flows (QH,QL) by sections across the machine width. The third suspension flow (QC) has a different proportion of solid matter in its composition from the other two fiber suspensions (QH,QL). The first fiber suspension has a normal composition, the second suspension is water from the fourdrinier section of the machine, and the third suspension is a clarified filtrate or clear water or diluted retention material. The suspensions contain different proportions of filling materials, fibers and fiber lengths and shrinkage characteristics. The second suspension is mainly of fibers, and the third suspension is mainly of filling materials. The fiber content of the second suspension is mainly of fibers with a high shrinkage, and the fiber content of the third suspension is mainly of fibers with a low shrinkage, together with a fourth suspension flow with a mainly filling material content. A fifth suspension flow can be introduced, mainly of retention materials. The sectional volume flow of the separate suspensions is controlled at least partially, and preferably wholly. An Independent claim is included for a stock inlet with a suspension flow (3) upstream of the turbulence generator (5) and a flow control (7) for the third suspension flow into the stock inlet, which has a different suspension composition from the other two suspension flows.

Description

The invention relates to a method and a Headbox system to improve the consistency cross profile a fibrous web, in particular a paper or cardboard web, in the wet process according to the preamble of the first Process claim, or according to the preamble of the device claim.

From patent US 5,560,807 it is basically known in an aperture controlled headbox in the area of the cross distributor, sectionally and regulated a suspension with additives, chemical additives or fillers to supply that based on the z direction of the emerging Paper, the concentration of additives can be adjusted and the addition of the additives as close as possible to the outlet of the Headbox takes place to change the additives due to a too long dwell time in the stock suspension avoid.

From the German Offenlegungsschrift DE 40 19 593 A1, a sectionally regulated headbox with two machine-wide distributed sets of individual feeds for two stock suspensions with different solids content is known. Whole material and white water are preferably used here. If the basis weight profile of the paper web deviates at a certain point in the web width, the concentration C _{M of} the section stream in question is corrected by changing the quantitative ratio of the control streams fed to a mixer with different solids content Q _H / Q _L. This type of basis weight cross profile control is very advantageous with respect to a good fiber orientation cross profile and brings very good results with respect to the basis weight cross profile. However, with ever increasing demands on the paper quality, it can be seen that the papers produced in this way, despite uniform fiber orientation and uniform basis weight, can have streaky irregularities with regard to their printability. More detailed investigations showed that this uneven printability is due to an uneven composition of the paper.

The applicant's European patent application EP 0 824 157 A2 discloses a headbox and a method of distribution a fiber suspension in the headbox Paper machine. It is provided that the Fibrous suspension on at least two different ones Different aggregate levels in the z direction be metered in, the individual metering in Area of the entire headbox, that is from the Headbox feed up to the headbox nozzle. This configuration is a targeted influencing the paper properties even with highly filled papers of the leaf surface or in the marginal zones as far as possible enables simple way. Additionally or alternatively also a targeted influencing of the Printability properties for graphic papers allows.

From European Patent EP 0 600 251 B1 (∼ US 5,401,363) is known to remedy a uneven cross-consistency profile of a paper web - caused by varying degrees of screen wear - the Headbox sectioned across the machine width supply different amounts of retention aid. On however, such a procedure will not be successful if the original consistency of the stock suspension already over the Machine width is unequal.

So there is a task and a task Describe headbox system which the Cross consistency profile of a fibrous web, especially one Paper or cardboard web, improved.

The object of the invention is characterized by the features of both first procedural claim and the first Device claim solved.

Accordingly, the inventors propose the known process for the production of a fibrous web, in particular a paper or cardboard web, in the wet process, in which the fiber suspension is distributed over the width of the machine onto a sieve or between two sieves with the aid of a headbox, and the basis weight cross-section is at least partially is influenced by a sectionally variable mixture of a first suspension Q ₁ with a given solids content and a given percentage composition of different solids contents and a second suspension Q ₂ with a lower or higher solids content, the percentage composition of the solids contents of the second suspension being different from the composition the first suspension differs to improve in that at least a third suspension Q ₃ with a lower or higher solids content is mixed in sections across the machine width, the percentage Z composition of the solids content of the third suspension differs from the composition of the first and / or second suspension.

This improved process now enables it through corresponding variation of the mixture of the at least three Suspensions of different compositions resulting sectional total volume flow influence that despite reducing or increasing the total The percentage of solids in the section Composition of the individual solid components constant remains. However, the influence of one can now changing specific retention - based on the individual solids due to the different Total solids content in the suspension - through targeted Influencing the initial composition of the abandoned Stock suspension can be compensated.

Advantageous refinements of the invention lie in the fact that the first suspension Q _{1 is} normal stock suspension (whole stock) and / or the second suspension Q _{2 is} white water and / or the third suspension Q _{3 is} clear filtrate and / or clear water and / or dilute retention agent and / or white water other sections of the wire section and / or Q ₁ is used.

Furthermore, the suspensions can differ in terms of their proportion Filler and / or by their share of fibers differ. There is also the possibility that the Suspensions differ due to their fiber content of different lengths and / or by their proportion of fibers with different shrinkage influences on the fiber web differentiate in the further manufacturing process. In this Context, reference is made to the explanations of the applicant's published German patent application DE 198 43 729 A1.

A special and advantageous embodiment of the method also consists in that the second suspension Q ₂ is designed so that it contains predominantly or exclusively fiber components, and that the third suspension Q ₃ is designed so that it contains predominantly or exclusively filler components. In this way it can be achieved that with a certain mixing ratio Q ₂ / Q _{3 of} the second and third suspensions a solid composition is achieved which corresponds to the solid composition of the first suspension but has a different concentration of solids. Thus, by simply maintaining this mixing ratio, the solids composition can remain constant, even if different quantitative ratios to the first suspension are set. A targeted shift in the mixing ratio Q ₂ / Q _{3 of} the second and third suspensions then causes a shift in the solids composition in the direction of fillers or fibers.

If, in addition, the mass fraction of the solids of the first and second suspensions is chosen to be the same, a shift in the mixing ratio Q ₂ / Q _{3 of} the second and third suspensions with a constant total volumetric flow of Q ₂ + Q ₃ does not change the total solids fraction of the total volumetric flow of the first, second and third suspension and therefore - assuming constant retention and shrinkage behavior - no change in the basis weight of the corresponding section of the finished fiber web. Such a configuration has a particular effect on the complexity of the regulating / control behavior and permits simple or simply programmable regulations, since the mutual interactions are limited by changes in individual volume flow ratios.

Another special embodiment of the method according to the invention is that the second suspension Q ₂ predominantly contains fiber components with a high tendency to shrink, the third suspension Q ₃ predominantly contains fiber components with a low tendency to shrink, and a fourth suspension Q ₄ mainly contains filler components and, if appropriate, a fifth suspension Q ₅ retention agent , The above-mentioned explanations apply accordingly.

To perform the above procedure, the Inventor before, a headbox system of a paper or Carton machine with sectioned fabric density control over the Machine width through variable mix of a first and a second suspension with different Solids concentrations, which are preferably a first machine wide feeder or a first set of Single feeds for the first suspension, a second Set of individual inlets with flow-influencing Means for the second suspension, a turbulence-generating Section and includes a nozzle section to that effect to further develop that upstream of the turbulence generating section and each section in the z direction at least a third has the same effect as the fibrous web Set of individual inlets with flow-influencing Means for a third suspension is provided, the Solid composition according to the above Executions of the method according to the invention differs.

Further features and advantages of the invention result from the following description more preferred Embodiments with reference to the drawings.

Fig. 1a-1c:

Schematische Darstellungen erfindungsgemäßer Suspensionszuführung zum Stoffauflauf mit drei Sätzen von Einspeisungen vor dem Stoffauflauf;

Fig. 2a-2c:

Schematische Darstellungen erfindungsgemäßer Suspensionszuführung zum Stoffauflauf mit zwei Sätzen von Einspeisungen vor dem Stoffauflauf und einem Satz Einspeisung in eine dem Turbulenzerzeuger vorgelagerten Kammer.

The invention will be explained in more detail below with reference to the drawings. They represent:

1a-1c:

Schematic representations of the suspension feed according to the invention to the headbox with three sets of feeds before the headbox;

2a-2c:

Schematic representations of the suspension feed to the headbox according to the invention with two sets of feeds before the headbox and one set of feeds into a chamber upstream of the turbulence generator.

Figures 1a-1c show schematic representations of suspension feed according to the invention to a headbox with three sets of suspension feeds 1, 2 and 3 and their sectional merging before the headbox. In this example, three stock suspensions Q _H , Q _L and Q _C are mixed with different filler proportions and compositions. Specifically, whole material with a high proportion of fillers is led in the sectioned main stream Q _H and in turn two sectioned suspension streams with white water Q _L and clear water Q _{C are} introduced into the section lines.

The white water and clear water flows are controlled or regulated with dosing valves 7,8 per section with regard to their volume flow. In addition, a sectional volume flow control or volume flow control of the sectional total volume flows Q _G = Q _H + Q _L + Q _{C (} not shown here) can also be carried out by additional valves upstream or downstream of the sectional feeds of the total flows from white water Q _L and clear water Q _C.

With regard to the individual metering of partial flows Q _L , Q _C into a main flow Q _H while maintaining a total volume flow Q _G , reference is made to the German patent specifications of the applicant DE 42 11 291 C2 and DE 42 11 290 C2.

Another embodiment of the invention The method and the device is shown in FIGS. 2a-2c shown schematically. These show the supply of three different headbox suspensions with two Sets of suspension feeds 1,2 before the headbox and a set of Suspension feed 3 in a turbulence generator 5 upstream Headbox 4 of the headbox.

First, a known stock density-controlled headbox with two sets of sectional feeds 1, 2 of whole stock and white water is shown before the actual headbox. In addition, a third set of sectional suspension flows 3 with clear water Q _{C is} mixed into a chamber 4 upstream of the turbulence generator 5. So that the admixture in this area of the headbox does not result in any undesirable changes in the sectional total volume flows Q _G , either metering must be carried out at a certain angle which does not influence the total volume flow, or the supplied sectional total volume flow Q _S must be provided by additional valves Q _H + Q _{L can be} varied.

Since the composition of the solids content with respect to fibers and fillers in white water and clear water is different, the above-mentioned headbox systems can be used to regulate the dilution of the basis weight cross-section, which allows a desired and specific, section-wise change in the composition of the total volume flow Q _{G applied to a} headbox ,

It should be noted that the in the figures sections of the suspension feeds shown in three sections should only represent the principle, in practical execution, however, mostly an essential one smaller subdivision into much more sections takes place. Likewise, the width of the individual sections vary across the machine width. So may have a smaller subdivision in the edge area, for example should be chosen as in the middle range, since usually the largest Error gradient occurs in the edge areas, while in middle area with smaller error sizes per width too to calculate.

LIST OF REFERENCE NUMBERS

1

first set of suspension feeds

2

second set of suspension feeds

3

third set of suspension feeds

4

Pre-chamber in the headbox

5

Turbulence generator in the headbox

6

headbox

7

Metering valves

8th

Metering valves

9

scree

10

dewatering devices

11

breast roll

12

Clear water tank

Q _H

Suspension stream with high concentration / stock

Q _L

Suspension stream with low concentration / white water

Q _C

Suspension flow with different Composition / clear water

Q _G

total flow

Q _S

Total volume flow

Q ₁

first suspension stream

Q ₂

second suspension stream

Q ₃

third suspension stream

Claims (15)

1. Method of improving the cross-machine consistency profile of a fibrous web, in particular a paper or board web, in the wet process,

   1.1 the fibrous suspension being distributed over the width of the machine onto a wire or between two wires with the aid of a headbox and

   1.2 the cross-machine grammage profile being influenced, at least to some extent, by variable mixing, section by section over the machine width, of a first suspension Q₁ with a given solids content and a given percentage composition of different solids components, and a second suspension Q₂ with a lower or higher solids content, the percentage composition of the solids components of the second suspension differing from the composition of the first suspension,
   characterized

   1.3 in that at least a third suspension Q₃ with a lower or higher solids content is admixed in sectionalized form over the machine width, the percentage composition of the solids components of the third suspension differing from the composition of the first and second suspension,

   1.4 in that, in spite of a reduction or increase in the total solids component in one section, the percentage composition of the individual solids components in the total sectional volume flow remains constant, and

   1.5 in that the at least three suspensions Q₁, Q₂ and Q₃ are admixed upstream of the turbulence generator.
2. Method according to Claim 1, characterized in that normal stock suspension is used as the first suspension Q₁.
3. Method according to one of the preceding claims, characterized in that whitewater is used as the second suspension Q₂.
4. Method according to one of the preceding claims, characterized in that clarified filtrate is used as the third suspension Q₃.
5. Method according to one of Claims 1 - 3, characterized in that clarified water is used as the third suspension Q₃.
6. Method according to one of Claims 1 - 3, characterized in that diluted retention aid is used as the third suspension Q₃.
7. Method according to one of the preceding claims, characterized in that the suspensions differ in their proportion of fillers.
8. Method according to one of the preceding claims, characterized in that the suspensions differ in their proportion of fibres.
9. Method according to one of the preceding claims, characterized in that the suspensions differ in their proportion of fibres of different length.
10. Method according to one of the preceding claims, characterized in that the suspensions differ in their proportion of fibres with a different shrinkage influence on the fibrous web in the further production process.
11. Method according to one of Claims 1 - 3, characterized in that the second suspension Q₂ predominantly contains fibrous components and the third suspension Q₃ predominantly contains filler components.
12. Method according to one of Claims 1 - 3, characterized in that the second suspension Q₂ predominantly contains fibrous components with a high shrinkage tendency, the third suspension Q₃ predominantly contains fibrous components with a low shrinkage tendency, and a fourth suspension Q₄ predominantly contains filler components.
13. Method according to Claim 12, characterized in that a fifth suspension Q₅ contains retention aids.
14. Method according to one of the preceding claims, characterized in that the sectional volume flow of the individual suspensions is at least partly, preferably completely, regulated/controlled.
15. Headbox system of a papermaking or board marking machine having sectionalized consistency regulation over the machine width by means of the variable mixing of a first and a second suspension (Q₁, Q₂) with different solids concentrations, preferably containing a first machine-width supply or a first set of individual supplies for the first suspension (1), a second set of individual supplies (2) with flow-influencing means (8) for the second suspension, a turbulence generator (5) and a headbox nozzle (6), characterized in that, upstream of the turbulence generator (5) and acting in the same way in the z direction of the fibrous web in each section, at least a third set of individual supplies (3) with flow-influencing means (7) is provided for a third suspension, whose solids composition differs from the first and second suspension.

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