Sheet forming device and method for sheet forming

Abstract

Plies that are formed by respective formers are couched together in a sheet forming device, specifically a machine for the production of a multi-ply fiber web, particularly a paper or cardboard web, or a packaging paper web. At least one of the formers for forming a multi-ply web includes a multi-layer headbox, to which at least two different stocks, or stock partial streams of different composition for different plies are furnished.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet forming method and device, specifically a machine for the production of a multi-ply fiber web, such as a paper, or cardboard web, or a packaging paper web in which layers formed by a respective former are couched together.

2. Description of the Related Art

When installing a new paper machine, the machine must be designed so that the prevailing qualitative demands in the market place are met as soon as possible following the start up (see FIG. 1). Once optimized, the qualitative demands are usually easily met by a new paper machine, thereby allowing the paper manufacturer to increase production and to reduce the total costs per net registered ton. However, this often results in a reduction of the quality level.

In addition the general trend must be considered with regard to the utilized furnish, based on which the cycle time, to achieve the desired market quality, may change. This poses the question as to how the machine speed may be increased and at the same time maintain the quality level. In the event that machine production is limited by the wet section, there are generally two options, produce an additional ply or go to the next former generation.

Adding one or more plies, not only increases the production, but also improves the quality. FIG. 2 illustrates the theoretically possible improvement of the basis weight (law of error propagation) in dependency on the number of plies. The improvement is around 30% if two layers are utilized instead of one layer. It can also be seen from FIG. 2 that the gain in the improvement diminishes with an increasing number of plies. In order to gain an additional 25% improvement, three additional plies ar required. Such formulations are based on the theoretical assumption that the quality of the individual paper webs remains constant and independent from the basis weight. In reality however, the numbers will vary.

In cylinder mold machines, multi-layer forming was necessary due to the greatly limited production of a single former. FIG. 3 illustrates the operating window of a newer cylinder mold former. When increasing the speed of this type of machine, the number of plies is increased until the maximum operating speed becomes a limiting factor. In order to overcome this limitation, one has to go to the next former generation. A considerable production level for a particular cardboard quality is achieved with concepts of this type.

Multi-ply endless wire machines (Foudrinier machines) combine the advantages offered by single endless wire machines with those of multi-ply cylinder mold machines. As seen in FIG. 4, the operating window of multi-ply endless wire machines is wider than that of cylinder molds. The motivation for using multi-ply endless wire machines for the production of cardboard is the speed, resulting in increased production, and increased quality attributes, such as the creation of smoothness and flexural strength in the sheet or paper web.

The trend toward lower basis weight and higher production makes the Gapformer the desired concept, in accordance with the state of the art for packaging paper qualities in new machines and conversions. In similar fashion, as previously discussed, with regard to the cylinder molds, it is the speed limitation, in this instance that of the endless wire machines, that provide the main motivation for moving on to the next generation of formers (see FIG. 5).

Voith Paper introduced the Gapformer technology in 1992. Since that time 14 styles of Gapformers for cardboard and packaging paper are in production, including the first Double-Gapformer machine in the world. An additional “Top-Ply” Gapformer has now been shipped. These types of Gapformers were developed specifically for multi-ply cardboard and multi-ply packaging papers. The strong two-sided dewatering, of the “Duo-Former Base” (compare i.e. DE 198 03 591 A1) and “DuoFormer Top” (compare i.e. DE 196 51 493 A1) results in high quality webs, even at high production speeds.

FIG. 5 compares the operating window of multi-ply endless wire machines (zone “A”) with a single-ply Gapformer and a two-ply Gapformer. As can be seen from FIG. 5, single-ply Gapformers are highly competitive in the average speed range. A sheet, or a web of 150 g/m² can, for example, be produced with only one Gapformer at a speed of 950 m/min, resulting in a production of approximately 205 t/(d-m). This is considerable for one former. Nevertheless, a second ply is essential for a high output. Curve “C” illustrates the operating range for a two-ply Gapforming concept. Such a concept enables the production of a high sheet-square meter weight, even at high speeds.

In addition to the production aspect, there are also other reasons for a multi-ply Gapforming concept. Consistency is one of the determining factors for the production of corrugated board and base paper. Producing two plies instead of one results in a significant improvement in consistency. Even though the consistency may differ with different forming concepts, the multi-ply technology offers a clear advantage.

SUMMARY OF THE INVENTION

FIG. 6 shows the tear-length of a web of a 100% Old Corrugated Container (OCC) web for various basis weights, utilizing one or two Gapformers. As can be seen, the two-ply concept results in a clearly higher consistency at higher basis weights. The sheet formation is improved with a better formation and with a reduced z-orientation of the fibers. Both of these factors assist in optimum utilization of fiber potential and a reduction in fiber material costs.

A multi-ply Gapformer, such as shown in FIG. 7, ensures optimum formation and consistency at the highest production speeds, thereby a compensation and averaging effect is utilized.

The present invention develops and optimizes the aforementioned concepts for complete paper machines, specifically packaging paper machines and more particularly creates a paper machine, which offers additional advantages in at least a part of the aforementioned areas.

The present invention is a sheet forming device, and specifically a machine for the production of a multi-ply fiber stock web, and more particularly a paper or cardboard web, or a packaging paper web. The plies that are formed by respective formers are couched together and at least one of the formers, for forming a multi-ply web, includes a multi-ply headbox, which is furnished with at least two different stocks, or partial stock streams of different compositions for each ply. With additional layering in the headbox additional advantages, specifically with regard to even further improved machine efficiency are achieved.

In one embodiment of the machine according to the present invention the multi-ply headbox is furnished with at least two of the following stock fractions:

• • Long fiber fraction
  • Long fiber/short fiber fraction
  • Short fiber fraction
  • Fines poor fraction
  • Fines poor/fines rich fraction
  • Fines rich fraction

The long fiber fraction and/or the fraction having a low fines content are furnished to a first former; and the long fiber/short fiber fraction and/or the fines poor/fines rich fraction, as well as the short fiber fraction and/or the fines rich fraction are furnished to a multi-layer headbox of a second former. Preferably, the long fiber fraction and/or the fines poor fraction that is furnished to the first former a liner layer.

The long fiber/short fiber fraction and/or the fines poor/fines rich fraction as well as the short fiber fraction and/or the fines rich fraction are furnished to a former including an outer and inner wire, in which the long fiber/short fiber fraction and/or the fines poor/fines rich fraction are dewatered by the outer wire and the short fiber fraction and/or the fines rich fraction are dewatered by the inner wire.

Advantageously, the long fiber fraction and/or the fines poor fraction, particularly on the base wire, form a liner layer. A backing layer is formed by the long fiber/short fiber fraction and/or the fines poor/fines rich fraction, and a center layer is formed by the short fiber fraction and/or the fines rich fraction between the liner layer and the backing layer.

In a preferred, practical embodiment of the machine in accordance with the present invention at least one of the formers is a Gapformer, including a forming element that is specifically in the embodiment of a forming roll. The long fiber/short fiber fraction and/or the fines poor/fines rich fraction, as well as the short fiber fraction and/or the fines poor fraction are fed advantageously to a Gapformer in which the sheet is formed with the short fiber and/or the fines rich fraction on the forming element. The machine may be specifically designated for the packing segment.

In addition to the formers, having the headboxes designated to them, the machine includes a press section, a dryer section, at least one coating or applicator device and/or a rewinder. At least one of the headboxes may be designed as described in DE 40 19 593 A1. The press section may be designed as described in DE 40 26 021 A1. An example of a dryer section is described in DE 42 18 595 A1. A coating or applicator device may be designed as described in DE 34 17 487 A1. A rewinder may used, as described in WO 98/52858.

In all these segments the multi-ply/multi-layer combination offers relevant advantages.

In the method for sheet forming, in accordance with the current invention, specifically for the production of a multi-ply fiber web, particularly a paper or cardboard web, or a packaging paper web the plies that were formed by a corresponding former are couched together. At least one of the formers for forming a multi-ply web includes a multi-layer headbox which is furnished with at least two different stocks, or partial stock streams of different compositions for each ply.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and advantages of this invention., and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a diagram illustrating the effects of an increase of performance of a paper machine;

FIG. 2 is a diagram illustrating the averaging effect of multi-ply paper webs;

FIG. 3 is a diagram where the basis weight is shown versus the speed of the paper web;

FIG. 4 is a diagram illustrating forming concepts and design limits for cardboard machines;

FIG. 5 is a diagram illustrating forming concepts and design limits for packaging paper machines;

FIG. 6 is a diagram illustrating the effects of multi-ply Gapforming upon the consistency of the paper web;

FIG. 7 is a schematic illustration of an example of one embodiment of the machine for the production of a multi-ply fiber web, according to the present invention;

FIG. 8 is a diagram illustrating the two-ply Gapforming of the paper web by the machine shown in FIG. 7;

FIG. 9 is a diagram illustrating the web structure, following couching on the machine showy in FIGS. 7 and 8;

FIG. 10 is a diagram illustrating the effects of a layered web in the press function, having been processed on the machine shown in FIGS. 7-9;

FIG. 11 is a diagram illustrating the effects of a layered web in the pre-dryer section of the machine shown in FIGS. 7-9; and

FIG. 12 is an illustration of the effects of a layered web in the size press/Speedsizer of the present invention.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one preferred embodiment of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, and more particularly to FIGS. 8-11, only the terms “long”, “short” and “long/short” are used. These terms are essentially to be equated with the respective terms “fines poor”, “fines rich” and “fines poor/fines rich”.

Now, additionally referring to FIG. 7 there is illustrated an embodiment of machine 10 for the production of multi-ply fiber web 12, in which the plies that were formed by a former are couched together. Multi-ply web 12 may specifically be a paper or cardboard web 12. In the present instance two plies A and B are each produced by a respective former.

At least one of plies A and B is produced by a Gapformer, including forming element 14 in the embodiment of forming roll 14. Each Gapformer includes two endless dewatering wires that run together, forming stock infeed nip 30 and which are routed over respective forming element 14, in this instance a forming roll 14, in the area of stock infeed nip 30. The outer dewatering wire is brought to forming element 14 over breast roll 28. Stock infeed nip 30 is furnished with fiber stock suspension via a headbox.

In the embodiment illustrated in FIG. 7, first Gapformer 16 is provided for the forming of first ply A, and second Gapformer 18 is provided for the forming of second ply B. First ply A is delivered by the lower or base wire 22 of first Gapformer 16, which is separated from top wire 20, to couch section 24 in which plies A and B are couched together. The direction of rotation of forming element 14 of second Gapformer 18 is the same as the direction of rotation of forming element 14 of first Gapformer 16. Basically, the layout can be arranged so, that opposite directions of rotation result.

First Gapformer 16 may, for example, be a “DuoFormer Base”-former and second Gapformer 18 may be a “DuoFormer Top”-former. Headbox 30 of second Gapformer 18 is designed to be a multi-ply headbox, which is furnished with at least two different stocks or stock partial streams of varying composition for the different plies.

Multi-layer headbox 30 can be furnished with at least two of the following stock fractions:

• • Long fiber fraction
  • Long fiber/short fiber fraction
  • Short fiber fraction
  • Fines poor content fraction
  • Fines poor/fines rich fraction
  • Fines rich fraction

The long fiber fraction and/or the fraction having a fines poor fraction may specifically be furnished to first former 16. And the long fiber/short fiber fraction and/or the fines poor/fines rich fraction, as well as the short fiber fraction and/or the fines rich fraction may be furnished to multi-layer headbox 30 of second former 18. A liner layer is formed on base wire 22 by the long fiber fraction and/or the fines poor fraction that is furnished to first former 16.

In second Gapformer 18, the sheet formation may occur specifically with the short fiber fraction and/or the fines poor fraction on the former element side. Consequently, the long fiber/short fiber fraction and/or the fines poor/fines rich fraction is dewatered by outer wire 20 and the short fiber fraction and/or the fines rich fraction is dewatered by inside care 32. A liner layer is formed by the long fiber fraction and/or the fines poor fraction on base wire 22. A backing layer is formed by the long fiber/short fiber fraction and/or the fines poor fines rich fraction and a center layer is formed by the short fiber fraction and/or the fines rich fraction between the liner layer and the backing layer. Machine 10 may be specifically designated for the packaging segment.

FIG. 8 shows the relative location of the fractions during the dewatering process. The long fiber/short fiber fraction and/or the fines poor/fines rich fraction is dewatered by outside wire 20 of second Gapformer 18. The short fiber fraction and/or the fines rich fraction, containing the largest amount of fines, is dewatered by inner wire 32 of Gapformer 18. A gentle dewatering by way of corresponding forming element 14 allows the fines in the short fiber fraction and/or the fines rich fraction to be retained in the web. This is desirable for various reasons, particularly for good ply bonding. The long fiber/short fiber fraction and or the fines poor/fines rich fraction on the side of outside wire 20 brings about a reduction in the wash-out effects.

Now, additionally referring to FIG. 9, the web leaving the forming zone is layered as follows:

LS Long fiber fraction and/or fines poor
   fraction as a liner layer on wire 20.
S  Short fiber fraction and/or fines rich fraction
   having a high fines content inside the web.
L  Long fiber/short fiber fraction and/or fines
   poor/fines rich fraction as a backing 1
   layer on the top outside.

Additionally, referring to FIG. 10 there is shown a schematic of press nip 34. It is known that a long fiber web and/or a fines poor fraction is significantly more open and easier to dewater than a short fiber web and/or a fines rich fraction. Since the long fiber fraction and/or the fines poor fraction and the long fiber/short fiber fraction and/or the fines poor/fines rich fraction are located on the outsides of the web, the water can be drawn off more easily. This counters web crushing in the press section, which is particularly important for a high production output. Better dewatering correspondingly increases the wet-densification, which is advantageous for the consistency development.

There are also advantages in the dryer section with the multi-ply/multi-layer technology. Now, additionally referring to FIG. 11 there is illustrated long fiber fraction and/or the fines poor fraction opposite the dryer cylinders. Due to the better bonding of the longer fibers in the web, the development of dust in the dryer section is reduced. Reduced dust leads to increased runability and improved conversion characteristics.

Another advantage consists in that the long fiber/short fiber fraction and/or the fines poor/fines rich fraction comes into contact with the dryer wire. This fraction is very clean, with only a small portion of “stickies”. This leads to reduced contamination of the dryer wires, which is a positive factor for runability, as well as for cleanliness and maintenance.

The increased surface porosity of a layered web permits a faster escape of the steam, which is an added advantage. Since the web becomes open to a greater extend toward both surfaces, the risk of bubble formation and delamination is reduced.

High consistency values require full starch-penetration. At high speeds the dwell time in the nip is shortened and it becomes more difficult to maintain full starch penetration of the web in the press section. The layered web structure of the present method facilitates dewatering. The open surface of the layered web permits an increased starch penetration and the fines have a higher affinity for starch. Now, additionally referring to FIG. 12, the high fines content, in direction of the web center, supports the penetration process in that the starch is sucked toward the inside. This effect is particularly advantageous for high basis weights and high production.

The long fiber fraction and/or the fines poor fraction on the surface preserves a certain roughness, necessary in order to maintain the desired gliding angle. In addition, the hot glue characteristics are improved in that the glue is better able to penetrate the surface, causing a mechanical anchoring with the web.

The major motivations for the multi-ply/multi-layer technology, in accordance with the present invention, are speed, production and quality. This applies also to the newest cardboard- and packaging-Gapformer concepts.

Even though it is difficult to quantify all of the additional advantages of a layered web, the present invention improves the efficiency of the machine, and the runability, as well as the web characteristics that are necessary for further conversion and the final application. Consequently, natural resources are utilized more efficiently, thereby serving the environment. The total costs per net registered ton of paper are reduced, thereby correspondingly increasing profits.

While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.

Claims

1. A sheet forming device for the production of a multi-ply fiber web, specifically one of paper, cardboard and packaging paper in which at least two plies, formed by corresponding formers, are couched together comprising:

a plurality of formers, at least one of said plurality of formers comprising a multi-layer headbox for receiving at least two of stocks and stock partial streams of different compositions for different plies.

2. The device of claim 1, wherein said at least two of different stocks and stock partial streams include at least two of long fiber fraction, long fiber/short fiber fraction, short fiber fraction, fines poor fraction, fines poor/fines rich fraction and fines rich fraction.

3. The device of claim 2, wherein said plurality of formers include a first former and a second former, said second former having said multi-layer headbox, at least one of said long fiber fraction and said fines poor fraction being supplied to said first former, at least one of said long fiber/short fiber fraction, said short fiber fraction, said fines poor/fines rich fraction and said fines rich fraction being furnished to said multi-layer headbox.

4. The device of claim 3, wherein said first former forms a liner layer.

5. The device of claim 2, wherein at least one of said plurality of formers includes at least one former having an outer wire and an inner wire, at least one of said long fiber/short fiber fraction, said short fiber fraction, said fines poor/fines rich fraction and said fines rich fraction being furnished to said at least one former, said outer wire dewatering at least one of said long fiber/short fiber fraction and said fines poor/fines rich fraction, said inner wire dewatering at least one of said short fiber fraction and said fines rich fraction.

6. The device of claim 2, further comprising a base wire, whereupon a liner layer is formed by at least one of said long fiber fraction and said fines poor fraction, a backing layer is formed by at least one of said long fiber/short fiber fraction and said fines poor/fines rich fraction and a center layer is formed by at least one of said short fiber fraction and said fines rich fraction between said liner layer and said backing layer.

7. The device of claim 2, wherein said plurality of formers include at least one Gapformer, said Gapformer including a forming element, said forming element being a forming roll.

8. The device of claim 7, wherein at least one of said long fiber/short fiber fraction, said short fiber fraction, said fines poor/fines rich fraction and said fines poor fraction are fed to said Gapformer thereby forming a sheet, said sheet having at least one of said short fiber and said fines rich fraction forming proximate said forming element.

9. The device of claim 1, wherein the device is configured for the packing segment.

10. The device of 1, further comprising:

a press section;

a dryer section; and

at least one of a coating device, an applicator device and a rewinder.

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