DE19906062A1 - Method and device for producing a material web - Google Patents

Abstract

In a method and a device for producing a material web, such as in particular a paper or cardboard web, a stock suspension used to produce the material web is fed to a web formation zone comprising at least one wire belt by means of a headbox distributed over the machine width. In order to influence the web composition across the machine width, at least one metering substance stream containing at least one component of the stock suspension is fed to the headbox in sections, the volume flow of which can be adjusted accordingly.

Description

The invention relates to a method for producing a material web such as in particular a paper or cardboard web, in which one is used to generate the material suspension used by means of a material application at least one sieve belt is distributed over the machine width comprehensive web formation zone is supplied. It also concerns one Device of the type specified in the preamble of claim 9.

In papermaking one is u. a. strives to be as uniform as possible or desired cross and longitudinal profiles of quality features hold, for example the basis weight, fiber orientation, Count ash, fines, gloss, etc. There are already procedures and pre known directions in which the basis weight cross profile at the end of Paper machine is measured and when an occurring target / actual Deviation in the area of the headbox provided actuators in the sin ne to compensate for the deviation. One can Control or regulation take place.

There are two methods for setting the basis weight cross profile knows. In one of these two known methods, the spout gap of the headbox by locally bending an aperture over the Profiled machine width in such a way that the aforementioned target / actual Deviation of the basis weight cross profile is compensated  (Displacement rule). In contrast, the other known Ver drive the outlet gap of the headbox over the width essentially constant. The basis weight cross profile is influenced here by the fact that the local solids concentrations of the Stock suspension can be set sectionally. This happens because in the headbox two suspensions of different concentrations in the desired ratio. The concentra tion of the mixed volume flow of the section in question set so that the desired area dimensions assigned to this section in the produced Paper is reached. This principle of dilution water regulation is in described in DE 40 19 593 C2.

Cross between the location of setting the desired basis weight profiles in the area of the headbox and the location of the measurement at the end the paper machine, disturbances affect the paper manufacturing process on. For example, only a part of the mass is deposited on the fabric run on a dewatering sieve, continue on the sieve transported. A certain part of the mass falls in the drainage pro cut through the sieve or, in the case of a gap former, the sieves. How much mass is lost and how much remains on the sieve (retention) depends to a large extent on the composition of the suspension in the headbox, from the design of the drainage area, strips and sieves etc. In addition to the pulp or Depending on the type of paper, wood pulp fibers can contain larger or smaller quantities fillers (e.g. ash), fine substances, brighteners. This Aggregates can differ in size and shape from one another the.  

This is the case for paper types with short fibers and high ash or fill proportion of solids more solid mass through the drainage sieve than with Pa Types of paper with long fibers and a low ash or filler proportion of. The behavior of the drainage sieve behaves correspondingly the other way round retained solid mass. The percentage of retained by the sieve mass to the total mass applied to the drainage screen is called retention. It is known that the retention of the feast Mass of material not uniform across the width of the drainage area is. These irregularities lead to a poor area dimension sequerprofil and become Flä cross-sectional profile control compensated.

With the known methods and devices one achieves this good basis cross-sections, but uneven are a disadvantage Paper properties in the sheet plane.

The aim of the invention is the method and the device of a gangs mentioned to improve in that a higher Uniformity of the material web or paper properties in the sheet level, in particular better property and composition cross profiles, and thus a higher material or paper quality can be achieved are. The aim is to improve the material or paper web together transverse and longitudinal direction can be achieved.

With regard to the method, this object is achieved according to the invention solved that the headbox to influence the web composition section across the machine width, little in each case least one containing at least one component of the stock suspension  Dosing material flow is supplied, the volume flow accordingly is adjustable.

This takes into account in particular the fact that the Re tention of the fixed and surcharge included in the fiber suspension fabric components in terms of time and location across the machine width are different. Due to the training of the invention this has an adverse impact on the quality of it witnessed material web are at least substantially compensated. The desired quality of the material web produced is in particular even at higher web speeds (e.g. V <1500 m / min. esp special V <1800 m / min) still ensured. So it's special also possible the composition of the material web across the width adjust.

In a preferred practical embodiment of the invention The process is the headbox to influence the web area weight over the machine width, the stock suspension in sections supplied, the different section streams each by mixing a suspension stream of higher consistency and a suspension current lower consistency can be set accordingly. It is so with in particular a combined setting of the local area weight and the concentration or proportions of the components in the material web possible.

The sectional metered substance flows are preferably the respective mixed with section streams.  

In a preferred expedient embodiment, at least a section of a suspension stream with a higher consistency in stream direction one behind the other a suspension stream ge lower consistency and at least one metering stream mixed. Here can result in particular a kind of series connection.

In certain cases it is an advantage if in at least one section a suspension stream with a higher bulk density lower consistency and the suspension flow of lower consistency at least one dosing agent stream is mixed. This is especially egg ne cascade arrangement possible. The Suspensi onsstrom of lower consistency cascade-like also two or more Dosing streams are added.

In principle, such an arrangement is also conceivable in which the Sus Pension stream of lower consistency in the flow direction behind elsewhere at least two dosing streams mixed become. In particular, there are also any mixed forms of rice circuit and cascade-like arrangement possible.

When using a multi-layer headbox or a single layer Headbox with different layers can be made by an appropriate Sectioning the web composition also in the direction of the web density can be influenced. The invention is therefore particularly based on a multi-layer headbox or a single-layer headbox with ver different layers applicable, whereby the distribution of the com components not only in the transverse direction, but also in the z direction, i.e. H. in Can adjust the direction of the material thickness. It can in particular  also the cross profiles of such quality features of the Ma produced terialbahn such. B. the opacity, brightness, firmness, gloss, color, Moisture, etc. can be influenced in the desired manner.

With regard to the device, the object is achieved according to the invention solved that for an additional supply of the headbox section by section at least one metering line for supplying at least one Component of the dosing stream containing the substance suspension hen, the volume flow is adjustable to the web composition influence over the machine width accordingly.

Advantageous embodiments of the device according to the invention are specified in the subclaims.

The invention is un based on exemplary embodiments ter explained in more detail with reference to the drawing; in this show:

Fig. 1 is a schematic plan view of a possible exporting approximate shape of a headbox according to the invention,

Fig. 2 is an exemplary diagram in which the diarrhea of Par tikeln is plotted against the particle size,

Fig. 3 is an exemplary diagram for wood-containing papers, in which the ash retention is plotted against the fiber retention,

Fig. 4 shows a possible arrangement of the invention of Dosierlei obligations in a corresponding section, series circuit is formed by the one type,

Fig. 5 shows another possible arrangement of metering in a corresponding section according to the invention, by the total results in a cascade-like structure,

Fig. 6 shows another possible arrangement of metering in a corresponding section according to the invention, resulting from a combination of the orders At shown in Figs. 5 and 6,

Fig. 7 shows another possible arrangement of metering lines according to the invention in a relevant section, which results from a combination of the arrangements shown in FIGS . 5 and 6, and

Fig. 8 shows an example for a local change of the retention.

Fig. 1 shows a possible embodiment of an apparatus for producing a material web 12, it is in the present case a paper or board web shows a schematic plan view of the headbox 10 degrees.

By means of the headbox 10 , a stock suspension used to produce the material web 12 is distributed over the machine width to a web forming zone 16 comprising at least one screen belt 14 . In the present case, the stock suspension is fed to the sieve belt 14 . The web formation zone 16 can in principle include one or more sieve belts and in particular also a twin wire former or gap former.

As can be seen from FIG. 1, the stock suspension is fed to a sectioned section 18 of the headbox 10 in different section streams Q _S1 -Q _Sn . A turbulence insert 22 is provided between the section 18 and a nozzle-like outlet 20 , for example.

Fig. 2 shows an example of a diagram in which the diarrhea of particles, for example through the sieve belt 14 or, for example, by two opposite sieve belts of a gap former over the particle size is shown. After that, the loss increases disproportionately as the particles become smaller during filtration. Ash and fine particles are in a size range with a lower limit of, for example, about 1-2 µm. In contrast, fibers can sit lengths in the mm range.

Fig. 3 shows an example of a diagram for wood-containing papers, in which the ash retention is plotted against the fiber retention (both in%). The difference between the ash retention and the fiber retention for wood-containing papers with different basis weights is shown on. These relationships are dependent on the nature of the drainage screen (s), the drainage speed, the solid mass deposited on the screen, the pressure surges of the drainage elements, etc. This purely exemplary list illustrates the large number of disruptive factors that may affect the sheet formation process. These disruptive factors do not have a uniform effect across the width of the paper machine. For example, the screen quality may vary across the width, or the drainage bars may have different radii along the front edges across the width, which are decisive for the level of the impulse of the drainage pressure.

In order to achieve a higher uniformity of the paper properties in the sheet level ne, ie in particular better properties and composition pro file, and thus a higher paper quality, according to FIGS. 4 to 7 for an additional feeding of the headbox 10 section by section at least one metering line l ₁ -l _{i is provided} for supplying a dosing stream D ₁ -D _i containing at least one component of the stock suspension, the volume flow of which is adjustable in each case by a controlled and / or regulated valve V ₁ -V _i . Accordingly, the web composition can be influenced across the machine width.

To influence the web basis weight across the machine width, the different section streams Q _{S can} each be adjusted accordingly by mixing a suspension stream H _{C with} higher consistency C _H and a suspension stream LC with lower consistency C _L. The sectional dosing streams D ₁ -D _i are mixed into the respective section streams Q _S.

Fig. 4 shows a possible arrangement of metering lines l ₁ -l _i in a relevant section, through which a type of series connection is formed.

In each section, the section line l _{S in question} (cf. also FIG. 1) is fed with the suspension stream HC of higher consistency C _H , the mixing points M ₁ , M ₂ , M _{i of} the section line 1 lying one behind the other in the flow direction L. _S the suspension stream LC of lower consistency C _L and the metering agent streams D ₁ -D _{i can be} mixed in via a respective mixer. The suspension stream LC of lower consistency C _L is supplied via line 10 with an associated valve V ₀ . The Do sierstoffströme D ₁ -D _i are supplied via lines l ₁ -l _i , in each of which a valve V ₁ -V _{i is} arranged again. The respective volume flows can be set accordingly via the valves V ₀ -V _i .

Fig. 5 shows a possible arrangement of metering lines in a concerned section, through which there is an overall cascade-like structure. The section line l _{S in question is} again fed with the suspension current HC of higher consistency C _H. This suspension stream HC of higher consistency C _H is fed to a mixing point M _1, a partial flow Q _LD , which was formed by mixing the suspension stream LC of lower consistency C _L with a dosing agent flow D _{1, i} at the mixing point M ₂ . The dosing stream D _{1, i} is again formed by mixing the dosing streams D ₁ , D _i at the mixing point M _i . The suspension stream LC of lower consistency C _L is fed again via a line 10 provided with a valve V ₀ . The metering agent flows D ₁ , D _i are supplied via metering lines l ₁ , l _i each provided with a valve V ₁ , V _i .

As can be seen from FIG. 5, the valve V ₀ lies in the flow direction L behind the mixing point M ₂ and the valve V ₁ behind the mixing point M _i . In the present case, this results in a cascade-like arrangement.

The further arrangement of metering lines shown in FIG. 6 in a relevant section results from a combination of the arrangements shown in FIGS . 5 and 6. Here, the line l ₀ on the fed suspension flow LC lesser material density C _L at the mixing point _M1 again the suspension flow HC greater material density C _H admixed. In the flow direction L of the line l ₀ associated valve V ₀ are the flow of suspension LC lesser material density C _L hinte reinan the supplied via the metering lines l _1, l _{i is} the Dosierstoffströme D ₁ -D _i. Also in the metering lines l ₁ -l _i a valve V ₁ , V _i is seen again.

The further possible arrangement of metering lines shown in FIG. 7 in a relevant section also results from a combination of the arrangements shown in FIGS . 5 and 6. In this case, via a line l ₀ supplied LC suspension stream is lesser material density C _L at a mixing point M ₁ again to the suspension flow HC higher material density C _H admixed. In the flow direction L upstream of the valve V ₀ , the suspension stream LC of lower consistency C _{L is} fed to the mixing point M ₂ via the metering line l _{1 of} the metering agent stream D ₁ , the volume flow of which can again be adjusted via a valve V ₁ . In the direction of flow L behind the mixing point M ₁ , the suspension stream HC of higher material density C _{H is} fed to the mixing point M _i via the metering line L _i, a further metering stream D _i , the volume flow of which can be adjusted again via a valve V _i .

In addition, any combinations z. B. the arrangements shown in FIGS. 4 to 7 possible. In all embodiments, the valves V ₀ -V _{i can} again have such a structure as described in DE-A-44 02 516.

The suspension stream LC of lower consistency C _L can contain, for example, white water and / or water. The different dosing streams can have a different concentration. A respective dosing substance D _i can contain, for example, ash, organic fine substance, fiber material, retention aid, starch, brightener, chemicals and / or the like. A mixer can be provided at a respective mixing point M _i .

With the arrangements described, it is possible to assemble the width of the paper web. The invention is also on a multi-layer headbox or a single-layer headbox different layers applicable. This allows the distribution of the Components not only in the transverse direction, but also in the z direction, d. H. in the direction of the paper thickness, which also creates the cross profiles such quality features of the paper web produced such as se opacity, brightness, firmness, gloss, color, moisture, etc. be can be influenced.

The valves V _{i of} the metering lines can be set, for example, via control units. For this purpose, an actual value of the concentration or the proportion of the components of a relevant metering agent flow D _i or the quality characteristic of the paper or representative of the suspension is measured in the section in question. This actual value is compared in the control unit with a target value. In the event of a discrepancy between the target and the actual value, the associated valve V _i in the metering line D _i is adjusted by a pre-calculated value such that the target / actual discrepancy is again reduced or even compensated.

In some cases, it is sufficient to manually operate the valves, for example to control. Such a procedure makes sense for such components, de their share only slowly or during the manufacturing process little changes.

Another aspect of the invention relates to the combined setting of the local basis weight and the concentration of the components of the compo nents in the paper.

If the basis weight cross profile of the paper web produced is impaired, for example, by retention-related disturbances, then the basis weight deviations at the corresponding points are corrected, for example according to FIG. 5 (without component D _i ), by adjusting valve V ₀ . This changes the partial flow or volume flow Q _LD . The ratio of the volume flows Q _LD and D _{1, i} and D ₁ can be kept constant before and after the control intervention (ratio control).

Has the basis weight cross-section across the width, for example, no constant value because z. B. a certain target cross profile was specified and / or the paper web has shrunk to different degrees in the transverse direction during the drying process (according to FIG. 5 without component D _i ), the relationship between Q _LD changes over a width for a constant composition of the paper web and D ₁ in the local correction of the basis weight. The valves V ₀ and V ₁ are thus set independently of one another. For this purpose, in addition to the local basis weight or the consistency, the local concentration or the local proportion of component D _{1 must also be} measured and fed to a control unit as the actual value.

The last two exemplary considerations apply to constant concentrations C _{Di of} the dosing agent flows.

The principle for an exemplary local change in the retention is shown purely schematically in FIG. 8. The retention is shown above the basis weight. The solid curve shows the course with normal retention. With the dashed curve, the course is indicated with disturbed retention ge. "1" indicates the target value, "2" indicates a disturbed position and "3" the corresponding correction. In the following table, some representative quantities for such a local change in retention are summarized purely by way of example:

Assume the following:

• 1. The relative change in ash retention is 1.5 to 2 times greater than that relative change in total retention.
• 2. To simplify matters, let the total mixture from the headbox be kept constant. This corresponds to Module Jet with clear filtrate, or Blen denregulation.

As a result, it follows that in addition to correcting lighter spots Ash must be doped.  

Reference list

10th

Headbox

12th

Material web

14

Screen belt

16

Path formation zone

18th

sectioned section

20th

Spout

22

Turbulence insert
l ₀

management
l ₁

Dosing line
l _i

Dosing line
l _p

Section leader
D ₁

-D _i

Dosing agent flows
D _{1, i}

Dosing agent flow
HC suspension stream of higher consistency CH
L flow direction
LC suspension flow of lower consistency C _L

Q _LD

Partial flow
Q _S

Section stream
V ₀

-V _i

Valves

Claims (18)

1. A method for producing a material web ( 12 ) such as in particular a paper or cardboard web, in which a stock suspension used to produce the material web ( 12 ) by means of a headbox ( 10 ) distributed over the machine width of an at least one wire belt ( 14 ) comprising web formation zone ( 16 ) is supplied, characterized in that the headbox ( 10 ) for influencing the web composition across the machine width additionally section by section at least one at least one component of the stock suspension containing feed stream (D ₁ -D _i ) is fed, the volume flow of which can be adjusted accordingly is. 2. The method according to claim 1, characterized in that the headbox ( 10 ) for influencing the Bahnflächenge weight across the machine width, the stock suspension is fed section by section and the different section streams (Q _S ) each by mixing a suspension stream (HC) higher consistency (C _H ) and a suspension stream (LC) of lower consistency (C _L ) can be set accordingly. 3. The method according to claim 1 or 2, characterized in that the sectional dosing streams (D ₁ -D _i ) to the respective Sekti ons streams (Q _S ) are mixed. 4. The method according to any one of the preceding claims, characterized in that in at least one section a suspension stream (HC) higher consistency (C _H ) at points in the flow direction (L) one behind the other (M ₁ -M _i ) a suspension stream (LC) lower consistency (C _H ) and at least one dosing stream (D ₁ -D _i ) is added. 5. The method according to any one of the preceding claims, characterized in that in at least one section a suspension stream (HC) higher consistency (C _H ) a suspension stream (LC) lower consistency (C _L ) and the suspension stream (LC) lower consistency ( C _L ) at least one dosing stream (D ₁ -D _i ) is added. 6. The method according to claim 5, characterized in that the suspension stream (LC) of lower consistency (C _L ) kaska-like at least two dosing streams (D ₁ -D _i ) admixed who the. 7. The method according to claim 5, characterized in that the suspension stream (LC) lower consistency (C _L ) in the flow direction (L) one behind the other (M ₂ , M _i ) we at least two dosing streams (D ₁ -D _i ) are mixed . 8. The method according to any one of the preceding claims, characterized, that when using a multi-layer headbox or an Laminate headbox with different layers through an ent speaking sectioning the web composition also in Direction of the web thickness is affected. 9. Device for producing a material web ( 12 ) such as in particular a paper or cardboard web, in which a material suspension used to produce the material web ( 12 ) by means of a headbox ( 10 ) distributed over the machine width of an at least one screen belt ( 14 ) Formation zone ( 16 ) is supplied, in particular for carrying out the method according to one of the preceding claims, characterized in that for an additional supply of the headbox ( 10 ) section by section at least one metering line (l ₁ -l _i ) for supplying at least one Component of the stock suspension-containing metering material stream (D ₁ -D _i ) is provided, the volume flow of which is adjustable in order to influence the web composition over the machine width accordingly. 10. The device according to claim 9, characterized in that for influencing the web surface weight over the Ma machine width, the stock suspension to the headbox ( 10 ) sektionswei se via section lines (l _S ) can be fed, and that means are vorgese hen to the different section streams ( Q _S ) accordingly by mixing a suspension stream (HC) higher consistency (C _H ) and a suspension stream (LC) lower consistency (C _L ) accordingly. 11. The device according to claim 9 or 10, characterized in that means are provided to mix the sectional metered substance flows (D ₁ -D _i ) to the respective section flows (Q _S ). 12. Device according to one of the preceding claims, characterized in that in at least one section the section line (l _S ) in question is fed with a suspension stream (HC) of higher consistency (C _H ), which at the mixing points (M) one behind the other in the flow direction (L) _1, M _2, M _i) of the section line (l _S) a suspension current (LC) of lower consistency (C _L) and at least one dosing stream (D ₁ -D _i) is admixed. 13. Device according to one of the preceding claims, characterized in that in at least one section the section line in question (l _S ) is fed with a suspension stream (HC) of higher consistency (C _H ), which at a mixing point (M ₁ ) of the section line ( l _S ) a suspension stream (LC) of lower consistency (C _L ) can be admixed, this suspension stream (LC) of lower consistency (C _L ) at least one metering agent (D _1- D _i ) can be admixed. 14. The apparatus according to claim 13, characterized in that the suspension stream (LC) lower consistency (C _L ) kaska-like at least two dosing streams (D ₁ -D _i ) can be admixed. 15. The apparatus according to claim 13, characterized in that the suspension stream (LC) lower consistency (C _L ) in the flow direction (L) one behind the other (M ₂ , M _i ) egg ner this suspension stream (LC) leading supply line (l ₀ ) at least two dosing streams (D ₁ -D _i ) can be mixed. 16. Device according to one of the preceding claims, characterized in that the volume flow of at least one via a metering line (l ₁ -l _i ) metered substance flow (D ₁ -D _i ) through a controlled and / or regulated valve (V ₁ -V _i ) is adjustable. 17. Device according to one of the preceding claims, characterized in that the volume flow of the suspension flow (HC) higher consistency (C _H ) admixable suspension flow (LC) lower consistency (C _L ) through a controlled and / or regulated valve (V ₀ ) is adjustable. 18. Device according to one of the preceding claims, characterized, that in the case of a multi-layer headbox or a single layer headbox with different layers by a corresponding one Sectioning the web composition also in the direction of Web thickness can be influenced.