FI122113B - A method and a headbox for improving the transverse property profile of a fibrous web - Google Patents

Description

A method and a headbox to improve fiber web of the transverse property profile of the 5 invention relates to a method for improving the fiber web of the transverse property profile, in which method a dilution headbox, which comprises dividing the mass of the manifold based on the mass of the headbox over the entire width, dividing laimennusvesitukin dilution water based on the mass of the ranks so that the dilution water supply locally controlling the influencing of the fibrous web bo-10 machine direction, the grammage profile , and to distribute the additional mass support to the base mass at least a portion of the width of the headbox so that the transverse property profile of the fibrous web being optimized is affected by locally controlling the additional mass feed.

The invention also relates to a headbox of a fiber web machine comprising a mass distribution log through which the base mass is distributed over the entire width of the headbox, a dilution water support through which the dilution water is distributed .

The invention further relates to a feed system for a headbox of a fiber web machine with dilution profiling and additional T-mass feed.

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As a result of the edge shrinkage, the transverse strengths of the non-woven web (paper, board) produced by conventional cylinder drying are significantly lower at the edges of the web than in the region of the central web, which virtually necessitates driving the fiber web machine. In this way, the edge strengths are made to meet the minimum values of the quality beats, while the strengths at the center of the 30nm are up to 15-20% higher than required.

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For cost reasons, for example, board is generally made from the cheapest raw material that provides the required strength and other properties. Due to the high basis weight, for example, the tensile strength of paperboard is not as critical as with many thinner paper grades. Of the plane mechanical properties of carton products, the compressive strength is generally more important than the tensile strength. For example, in liner, the most important strength properties are puncture resistance and transverse compression strength, which can be measured, for example, with the Short Span Compression Test (SCT CD) or the Ring Crush Test (RCT CD). An important feature of Fluting, in addition to the transverse compression strength 10, is the compression strength, which can be measured by the Concora Medium Test (CMT).

Most commonly, the fibrous web is made from a single, homogeneous spray jet of pulp, which is uniformly extended over the entire width of the fibrous web machine. FI 72550 C discloses a method for certifying paper web threading and reducing the susceptibility to breakage by applying to the paper web edge areas a special or additional pulp having a raw material composition, consistency, or feed rate such that the edge areas have substantially greater strength than the middle region. of which the web is mainly formed. DE 3715551 A1 discloses a method for reducing flattening of the edges of a web, in which a pulp suspension having a higher strength potential than the pulp suspension used at the other width of the web is fed to the web edge areas. Higher strength potential is achieved, for example, by adding strength enhancing chemicals i and binders, by grinding the fiber material, or by adding fibers with substantially higher strength. In these two publications,

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cp 25 extra weight is applied only to the edges of the web.

I '- £ Dilution headboxes are also known in the art where, in order to adjust the square footage of the web to the mass flow rate from the headbox mass distribution supports, the dilution water flow from the headbox supports is mixed at several points. The proportion of dilution water flow at each position along the headbox width is controlled by valves 3 several in parallel across the headbox. Dilution water can be either pure water or fibrous tap water from short circuits.

FI 100345 B discloses a method for adjusting the transverse property profile of a paper web, wherein at least two feed streams containing the raw materials of the paper to be manufactured as an aqueous suspension are fed into the headbox. The headbox is divided transversely into feed zones, each of which is fed by a combination flow of feed streams. The characteristic property of the paper web is measured and the measurement signal is fed to the headbox control system. The property of one or more raw materials of the feed streams, such as concentration, density, brightness, color, or the like, is measured and the resulting measurement signal is fed to a control system. Based on the paper web property profile, the feed flow property, and set values, control signals are formed to control the actuator in each feed zone of the headbox, affecting the composite portions of the various feed streams to be fed to that feed zone.

EP 992625 B1 discloses a method for improving the transverse profile of a fiber web consistency. The square mass profile is influenced by locally varying the first, second, and third suspensions, each with a different solids content and different solids percentage composition, up to about 20 parts of the machine width. Although the total solids concentration i changes locally, the percentage composition of the individual solids components in the local total volume flow is kept constant.

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EP 995834 B1 discloses a method for smoothing a fiber web property profile E, wherein the transverse profile o of the shrinkage of the material web is smoothed during the web formation process by locally affecting the local composition of the pulp suspension by varying the proportion of shrinkage components g 30. In one embodiment, long fibers are used as fibers having increased tendency to shrink, and short fibers are used as fibers having reduced shrinkage behavior. This easily results in more short fibers being fed to the edges and correspondingly more long fibers in the center to reduce the edge shrinkage.

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When, in prior art solutions, three different feed streams are fed to the same headbox, a separate feed cycle with pumps and return cycles is required for each feed stream. Part of the flow introduced into each manifold is generally returned to the beginning of the feed cycle in a so-called pa-10 bone cycle. The return cycle aims to equalize the flow pressure throughout the manifold so that the flow profile is uniform.

The object of the invention is to facilitate the transverse profiling of the properties of the fibrous web and at the same time to reduce the cost of manufacturing the fibrous web. It is a further object of the invention to provide a fibrous web having a uniform cross-sectional profile of the same fiber raw material.

Another object of the invention is to provide a simpler device structure for adjusting the transverse property profile of a fiber web in a dilution headbox.

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The method according to the invention is characterized in what is stated in the characterizing part of claim 1.

cm The headbox according to the invention is characterized in what is stated in the characterizing part of claim 6 of claim 25.

The supply system according to the invention is characterized by what is disclosed in the characterizing part of claim 9.

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In a manner known per se, the headbox is divided in width into feed zones, each of which is supplied with a base mass through a pulp manifold and a dilution water, which is controlled locally by controlling the transverse basis mass profile of the fibrous web. At least a portion of the width of the headbox is fed to the feed zones via additional mass support, which is controlled locally by affecting the transverse property profile of the fibrous web. The supply of dilution water and additional mass in each feed zone is controlled by actuators, which may be for example valves. In this way, the fibrous web is made from the base mass and the additional mass which are doped in different proportions at different positions along the width of the headbox so as to obtain the desired transverse profile for the properties of the fibrous web. In this way, for example, due to 10 drying shrinkages, lower edge strengths can be compensated for by supplying a mass of better strength potential to the edges of the web than to the middle of the web, thus making it possible to make a web of sufficient strength.

In the method according to the invention, the additional mass is diluted from the dilution water support with the return dilution water flow from the dilution support before passing the additional mass through the additional mass support to the base mass.

The additional pulp used to improve the transverse property profile of the fibrous web may be a pulp of greater strength than the base pulp, such as long fiber fraction separated from the base pulp, or may be the same pulp fed to the headbox pulp logs. The additional mass may also be -i completely different from the base mass. The incremental pulp may also have a lower strength cv potential pulp than the base pulp, whereby it is fed more to the center of the web than to the edges.

g When the additional mass is mixed with the dilution water from the dilution support, the flow pressure in the additional support is substantially the same as the pressure of the dilution support. It follows that it is possible to feed additional mass flows to the headbox o 30 together with the dilution water flows used for dilution profiling.

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Alternatively, additional mass flows may be fed to the headbox separately from dilution water flows.

The apparatus for introducing additional mass into the base mass may, in principle, be of the same type as that used in current dilution-controlled headboxes, but the design of flow channels and valves must take into account the requirements of higher consistency of the additional mass. Continuous automatic adjustment of the auxiliary mass valves may not be necessary for the supply of additional mass, but the adjustment of the valves may also be performed manually.

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If the long pulp fiber fractionated from the base pulp is used as an additional pulp, the pulp fractionation is preferably done on the pulp compartment side and the fractions are led separately to the short circulation of the fiber web machine. The fractionation may be effected by means of a pressure screen or any other suitable fractionating device. Ritual sorting accuracy can be achieved by performing fractionation in only one step. Because fractionation generally increases the consistency of the reject, it is usually good to dilute the long fiber before it is added to the base mass. The strength potential of the long fiber pulp can be further increased, if necessary, by means of grinding and dispersing.

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For example, the pulp may be fractionated to give a short fiber fraction of 60-70% and a long fiber fraction of 30-40% of the original fiber mass. The fibrous web to be manufactured contains substantially the same proportions of short fiber and long fiber, but these fractions are disposed in the web so that the proportion of the long fiber fraction in the region of the web edges is different from that in the middle portion of the web.

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The headbox according to the invention comprises a mass distribution log through which the base mass is applied over the entire width of the headbox, a dilution water log through which o 30 dilution water is locally controlled to the base mass for adjusting the to improve the transverse property profile of the fibrous web. The auxiliary mass support is disposed after the dilution water support and a mixing point is provided between the dilution water support and the additional mass support, whereby the additional mass is mixed with the dilution water support return stream.

In a preferred embodiment of the invention, the additional mass distribution channels are connected to the dilution water distribution channels, wherein at least a portion of the headbox width is diluted water and the additional mass is conducted in a stream connected to the headbox through the dilution water distribution channels.

Alternatively, the additional mass distribution channels may be connected to the headbox separately from the dilution water distribution channels.

Preferably, the mixing point for the dilution water and the additive mass is provided with a tube mixer comprising an inlet tube axially guided to the center of the dilution water tube by a tube portion between the dilution water support and the additional mass support. One such tube mixer 20 manufactured by the applicant is known as the LobeMix Stock Mixer.

The invention provides many advantages. It is possible to achieve savings in raw material costs, since it is not necessary to feed one cm of good mass over the entire width of the web in order to obtain sufficient strength at the edges of the web. The square of the mass of the web i

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o 25 can be lowered when the edges are sufficiently strong with less mass.

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> - A uniform transverse strength profile can be achieved by applying an average stronger mass to the edges of the web than to the middle region of the web.

o o g Other properties of the fiber web can be optimized instead of strength. For example, if it is desired to optimize the surface roughness of the web, an average shorter fiber mass can be fed to the edges than to the center portion, thereby reducing the roughness of the edge areas. This reduces the need for calendering to achieve a certain smoothness.

Since the additional mass used to adjust the fiber web property profile is supplied to the headbox at substantially the dilution water pressure, it is possible to connect the additional mass flows directly to the dilution plate alongside the dilution water supply channels. This is a relatively simple structure that does not cause any changes to the actual headbox structure. A separate additional mass feed cycle from the wire well to the headbox is not required when the additional mass feed cycle is combined with the bottom 10 recycle water return cycle. Because the additive mass supply cycle slavishly follows the dilution water cycle and the manual adjustment of the additive mass distribution channels in the valves is sufficient, there is no need to significantly increase automation to control the system.

The solution of the invention for improving the transverse property profile of a fibrous web can be used in new dilution headboxes and can also be retrofitted to existing dilution headboxes.

The invention will now be described with reference to the examples shown in the figures of the drawings, in which the invention is not, however, to be narrowly limited.

Figure 1 is a graphical representation of the r-transverse profile of the machine direction tensile index of a fibrous web.

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Figure 2 is a graphical representation of the transverse profile of the transverse tensile stiffness index of the fibrous web.

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Fig. 3 is a schematic drawing of a short rotation of a papermaking machine in which the headbox is provided with g basis weight control and web transverse feature profile optimization.

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Fig. 4 is a plan view of the headbox of Fig. 3, viewed in cross-machine direction.

Figure 1 shows a machine direction tensile index (Tensile 5 Stiffness Index or TSI MD) of a fibrous web, measured at various points in the cross machine direction. The profile of the machine direction tensile index would appear to be relatively uniform over the entire width of the web. It is generally known that the puncture resistance and transverse profiles of the CMT correlate with the machine tensile index.

Fig. 2 shows, respectively, the Tensile Strength Index (TSI CD) of the fibrous web, measured at various points in the cross machine direction. The transverse tensile strength index at the edges of the web is about 18% lower than at the center of the web. It is generally known that the transverse profile of compressive strength (SCT CD or RCT CD) is similar to the transverse tensile index.

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Figures 1 and 2 illustrate an object represented by a solid line T which can be achieved by the solution according to the invention. The aim is to raise the CD tensile index at the edges of the web to the level at which it is in the center of the web (Figure 2). As a result, the MD tensile stiffness index 20 at the edges of the web increases to a greater extent than in the middle region of the web (Figure 1).

By using the method according to the invention, it is possible to supply a mass of average strength to the region of the headbox ·> - edge portions than to the center of the headbox region, which results in both machine direction and

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o 25 directional strengths in the edge area increase. As the profile of the transverse compression lash, * - hair becomes even more even, it is possible to reduce the compression strength in the middle of the web £. This results in savings in fiber raw material costs and / or in the use of starch to improve web strength. Also, the basis weight of the web may be reduced.

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The pulp of higher strength potential fed to the region of the headbox portions may be long fiber produced by fractionation of the fiber raw material and correspondingly the base pulp of lower strength potential may be the fraction of short fiber produced by fractionation of fiber material. Thus, the entire fibrous web can be made from the same fiber raw material, which is distributed in different proportions at desired positions along the width of the headbox. The fibrous raw material can be recycled fiber, mechanical pulp, chemical pulp or a mixture thereof.

Figures 3 and 4 together illustrate an embodiment of the invention. The pulp Mo used in the manufacture of fiber-10 web is diluted with the tap water 1 to the desired consistency with the tap water. The diluted pulp is fed by pump 2 to the vortex purification plant 3 and further to the deaerator 4, from which the pulp is pumped to the screen 6. The accepter of the screen 6 forms the base mass Mi, which is fed to the headbox 7 mass distributor 10. across the width. Part of the fiber suspension flow through the pulp distributor 10 is returned to the wire well 1 as a return circuit R1.

The dilution water D used for adjusting the basis weight profile of the fibrous web is led from 20 wire wells 1 via pump 8 and through screen 9 to the dilution water logs 20. The dilution water logs 20 are provided with multiple parallel distribution channels 22 The dilution water log 20 is further provided with a return circulation, which means that part of the dilution water flow is removed by the so-called end of the dilution water log 20. as the return stream Dr, which is normally returned to the wire well. The return cycle aims to equalize the flow pressure over the entire length of the dilution water log 20 so as to obtain a smooth flow profile.

Oog Dilution Water Distribution Channels 22 are spaced apart at appropriate intervals 30 across the entire width of the headbox 7 and each distribution channel 22 is provided individually or in groups with an adjustable dilution water valve 24. With the help of the square-mass profile.

An additional mass log 30 is disposed above it at the dilution water log 20. The additional mass log 30 is provided with a plurality of additional mass distribution channels 32 through which additional mass is distributed to headbox 7 for at least a portion of the headbox width. Part of the auxiliary mass flow is discharged as a return flow R2 from the auxiliary mass support 30 to balance the pressure of the flow throughout the additional mass support 30.

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The pipe section 26 between the outlet of the dilution water logger 20 and the inlet of the additional mass support 30 has a mixing point 28 where additional mass M2 is mixed with the dilution water leaving the additional mass support 30 as a return stream Dr. The additive M2 can be mixed with a suitable mixer, e.g. With the Lobe-15 Mix pulp mixer. LobeMix is a tubular static mixer that efficiently mixes two different streams with different consistency. It is commonly used for, among other things, diluting a thick pulp in a short rotation of a papermaking machine, and is also well suited for diluting additional pulp before feeding additional pulp to the headbox.

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A plurality of manifolds 32 emit from the auxiliary mass supports 30, each of which is provided with an adjustable valve 34. In this case, each auxiliary mass manifold 32 is ί- connected in a corresponding position to a dilution water manifold 22 in the width direction of headbox 7. the dilution water log 20 and the additional mass log 30 are at the same pressure.

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o Additional mass feeds may be provided over the entire width of the headbox 7, or alternatively, g may be present only in the areas of the headbox edges. Preferably, the auxiliary mass supply valves 34 associated with each additional mass o 30 distribution channel 32 are manually set to the desired position prior to driving. It is not necessary in most cases 12 to automatically adjust them while driving. Instead, the dilution water valves 24 may need to be adjusted while driving and are generally automated.

Preferably, the additional mass M2 used to optimize the transverse property profile of the fibrous web is a mass which has a better strength potential than the base mass Mi supplied over the entire width of the stern. It may be a long fiber fraction separated from the pulp Mo by fractionation or a completely different pulp. Alternatively, the same base mass Mi 10, which is fed to the headbox mass distribution log 10, may be used to optimize the property profile.

The transverse profile of a property of a fiber web can be optimized, for example, by fractionating the pulp used as a raw material into two pulp components having different fiber properties and mixing these fiber pulp components differently at different points along the headbox width. The paperboard's optimized property may be, for example, transverse compression strength (liner, fluting) or transverse bending stiffness (other board). It is also possible with the method according to the invention to influence, for example, the roughness profile of the fibrous web. By supplying to the web edges less than 20 shorter fibers of average fiber, it is possible to compensate for the roughening of the edges due to shrinkage shrinkage, thereby achieving a more uniform roughness or smoothness profile with less calendering. Further, the process of the invention can adjust the filler profile in the transverse direction of the fibrous web or any addition of a chemical or additive such as starch to the paper or board to be dispensed with the pulp component.

g The process of the invention can be used to make paperboard (e.g. liner, o fluting, liquid packaging board) or paper (e.g. newsprint).

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Many variations of the invention are possible within the scope defined by the following claims.

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Claims (9)

A method of improving the transverse property profile of a fiber web, in which method a dilution inlet carriage (7) is used, comprising a pulp distribution stock (10) for distributing a matrix (Mi) over the entire width of the inlet carriage. dilution water stock (20) for distributing dilution water (D) in the matrix in such a way that the transverse surface weight profile of the fiber web is affected by regulating the dilution water supply locally, and a stock (30) for supplementary mass distribution (M2) ) in the matrix over at least a portion of the width of the inlet carriage (7) in such a way that the transverse property profile of the fiber web subject to optimization is affected by controlling the feed of supplementary mass locally, characterized by the addition mass (M2). ) is diluted with a dilution water flow acting as a return circulation (Dr) until dilution water flow the yoke (20) before the auxiliary mass (M2) is led into the matrix (Mi) through the auxiliary mass (30). Process according to claim 1, characterized in that the additive mass (M2) is a mass with better pour strength potential than the matrix (Mi). 20 Method according to claim 2, characterized in that the additional mass (M2) is a long fiber fraction produced by fractionation of fiber pulp and the base mass (Mi) is a short-fraction fraction produced by fractionation of the same fiber mass. o 25 Method according to Claim 1, characterized in that the additive mass is g the same mass as the matrix. o o g 5. A method according to any of the preceding claims, characterized in that the additive mass flows are measured in the inlet carriage together with the 17 dilution water streams used for dilution profiling or separate from them. An inlet carriage (7) in a fiber web machine, the inlet carriage comprising a pulp distribution stock (10), through which a matrix (Mi) is distributed over the entire width of the inlet carriage (7), a stock (20) for dilution water, through which dilution water (D) is distributed locally controllably in the matrix for controlling the surface weight profile of the fiber web, and a stock (30) for supplementary mass, through which an additional mass (M2) is distributed locally adjustably over at least a portion of the width of the inlet carriage to improve the transverse direction. the characteristic profile of the fiber web, characterized in that the auxiliary stock (30) is arranged after the dilution water stock (20) and that a mixing site (28) is arranged on a pipe section (26) between the dilution water stock (20) and the supplementary stock (30). the additive mass (M2) is mixed with a return flow (Dr) of the dilution water. 7. An inlet carriage according to claim 6, characterized in that the auxiliary distribution distribution channels (32) are connected to the dilution water distribution channels (22), the dilution water and the additional mass being fed to the inlet carriage (the flowing water) as a combined flow through the distribution tank (22). part of the width of the inlet carriage (7). 8. An inlet carriage according to claim 6, characterized in that the channels (32) for distributing additional mass are led to the inlet carriage separated from the channels (22) for distribution of dilution water. Jr. 9. Feed system for an inlet carriage (7) in a fiber web machine provided with dilution profiling and feeding of supplementary pulp, characterized in that the feed circulation of dilution water (D) and the feed circulation of o additional pulp (M2) are joined together of a return flow (Dr) of the dilution water circulation to the dilution of the additional mass (M2), 18 from which the combined feed circulation of the dilution water and additional mass is conducted only one return flow (R2) to a viral well (1) or equivalent. 5 δ (M tn o h- · x and CL O o δ o δ {M