Method and machine for producing a dry-laid fibrous web

Abstract

The invention relates to a machine (1) and to a corresponding method for producing a dry-laid fibrous web (309). The machine (1) comprises: a solidifying device (8) for solidifying the flat fiber fabric (300) by applying pressure in a press nip (84) which is formed by two press rolls (86, 88); a connecting belt (102) for transporting the flat fiber fabric (300) to just before the press nip (84); and a transfer belt (103) for receiving the fiber fabric (305) solidified by the press nip (84) just after the press nip (84) so that the flat fiber fabric (300) is guided through the press nip (84) without support. At least one of the two press rolls (86, 88) and / or the connecting belt (102) and / or the transfer belt (103) can be adjusted with respect to the position thereof such that the angle at which the fiber fabric (300) enters the press nip (84) and / or the angle at which the solidified fiber fabric (305) leaves the press nip (84) can be controlledly adjusted.

Description

[0001] Method and machine for producing a dry-cured fibrous web

[0002] The invention relates to a method for producing a fibrous web, preferably a tissue, paper or cardboard web or a nonwoven web, in particular a tissue web with a basis weight of 28g / m². 2 up to 42g / m² 2 , comprising the following steps: a) low-water raw material preparation of cellulose-containing fibers into individual fibers and / or fiber bundles; b) forming the individual fibers and / or fiber bundles in an air stream into a flat fiber fabric on a forming belt by a dry forming process; c) application of a fluid, preferably water and / or a water-additive mixture, onto the fiber fabric; d) consolidation of the flat fiber fabric by applying pressure in a press gap formed by two press rollers.

[0003] Many fibrous webs, especially paper, cardboard, or tissue, were and still are produced almost exclusively using the wet process on an industrial scale. For this process, unless recycled paper is used, baled pulp is typically dissolved in large quantities of water in a vat, resulting in a fiber suspension consisting of approximately 99% water by weight and only about 1% fiber by weight. This fiber suspension is then applied to a forming wire via a headbox to form the sheets. The resulting fibrous web is subsequently dewatered or dried by pressure and heat until it can be wound up or otherwise processed. The wet process has the advantage that hydrogen bonds form between the individual fibers during dewatering or drying, giving the fibrous web the necessary strength.However, a disadvantage of this process is that drying the fiber web requires large amounts of energy. Especially in light of current climate change, there is therefore an intensive search for alternatives to this traditional wet process.

[0004] As an alternative to the wet process, the dry air-laying process is already known, in which fibers are laid down to form a fiber web in a largely dry state. To give the fiber web a certain degree of strength, small amounts of water (to form hydrogen bonds) and / or other binders are added. This results in significantly less energy being required for drying.

[0005] The embodiment shown in Figure 3 in publication WO 2019 / 137667 A1 already discloses a generic method, described above, for producing a dry-formed fiber web. In this process, fibers are first laid onto a forming belt to form a flat fiber mat using a dry forming process. The fiber mat is then transferred from the forming belt to a press belt. The press belt transports the fiber mat to a press gap formed by two rollers, through which the press belt and the fiber mat pass. The fiber mat is compressed in the press gap, thereby increasing its strength.

[0006] In the manufacturing process known from the prior art, achieving a sufficiently high strength has not yet been satisfactorily resolved. It would be advantageous if the strength of the fiber web could be increased even further without applying a significantly larger amount of fluid. Alternatively, it would be desirable if less fluid had to be applied to achieve the same strength. The amount of fluid correlates with the energy consumption and / or the production costs. For example, an increase in the amount of fluid leads to an increase in the energy required for drying. Furthermore, the applied fluid, unless it is pure water, also has a noticeable impact on production costs. In addition, the recyclability of the final product may also suffer, especially if chemical binders are used to achieve the desired strength.

[0007] It is therefore an object of the present invention to provide a method and a machine for producing a dehydrated fibrous web, in particular a tissue web, with which the problems described above can be solved or at least reduced. In particular, it should be possible to produce fibrous webs with higher strength compared to known manufacturing methods without using significantly more, preferably no more, fluid, and / or to produce fibrous webs without a reduction in their strength while using less fluid.

[0008] The problem described above is solved by the features of the independent claims. The dependent claims relate to advantageous embodiments of the present invention.

[0009] In particular, the problem is solved by the generic manufacturing process described above, which is characterized in particular by the fact that the planar fiber fabric is guided unsupported through the press gap, wherein the planar fiber fabric is transported by a connecting belt to just before the press gap and wherein the fiber fabric, compacted by the press gap, is picked up by a transfer belt just behind the press gap, wherein at least one of the two press rollers and / or the connecting belt and / or the transfer belt is adjustable with respect to its position in such a way that the angle at which the fiber fabric enters the press gap and / or the angle at which the compacted fiber fabric leaves the press gap can be specifically adjusted.

[0010] In the context of the present invention, "shortly before" or "shortly after" preferably means that the free pull, i.e. the distance which the fiber fabric must bridge unsupported to the press gap or away from the press gap, is less than 1 m, preferably less than 0.5 m, and more preferably less than 0.3 m.

[0011] In this context, the term "angle" refers to the angle to a plane that passes through the press gap and is oriented orthogonally to another plane, which other plane encompasses the axes of rotation of the two press rollers.

[0012] In the context of the present invention, the phrase "adjustable with respect to its position" means that the absolute position in space and / or the angular orientation in space should be changeable in a manner that does not require any fundamental modifications, but is relatively quick and easy to carry out, preferably automatically.

[0013] The inventors recognized that the strength of the fiber web depends not only on the quantity and / or type of applied fluid, but also significantly on the pressure applied to the fiber web. It has been shown that higher pressure tends to lead to higher strength. However, with the machine known from the prior art described above, there are limits to increasing the pressure in the press gap, as the press belt transporting the fiber web, which is usually made of plastic threads, can only withstand a limited amount of pressure. If excessive pressure is applied in the press gap, plastic deformation and thus permanent damage to the press belt can occur. Significantly higher pressure can be applied to the fiber web if it is guided through a press gap unsupported, i.e., without a tensioning device like the press belt.However, a problem arises here: especially at the high speeds required for the industrial-scale production of a dry-cured fiber web, the fiber layup does not always detach well from the surface of the press rolls. To improve the detachment behavior, or rather to avoid the problem of adhesion, it is important, as the inventors have recognized, that the angle at which the fiber layup enters the press gap and / or the angle at which it exits the press gap can be precisely adjusted. This can be achieved by precisely adjusting the position of the transfer belt and / or the connecting belt and / or at least one press roll. It has been observed that it is often advantageous with regard to the detachment behavior if the respective angle is not exactly 0°. In such a case, at least one of the two press rolls is wrapped around the fiber layup at an angle greater than 0°.The precise setting for optimal and stable release of the fiber layup from the two press rollers, even at high production speeds, should be dynamically adjustable during operation. This setting depends, for example, on the specific basis weight of the fiber layup, the quantity and type of previously applied liquid, and the fiber properties. Sometimes even small changes in the wrap angle of the press rollers have a significant impact on the release behavior.

[0014] To give the fiber fabric the necessary strength for passing through the press gap under free tension, it is proposed that the fiber fabric, supported by a press belt, be guided through a pre-pressing gap before passing through the press gap. While pressures as high as those in the actual press gap cannot yet be applied to the fiber fabric in this pre-pressing gap without damaging the press belt supporting the fiber fabric, sufficiently high pressures can be applied in the pre-pressing gap to achieve adequate strength in the pre-pressed fiber web for guiding it under free tension through the actual press gap.

[0015] Preferably, the fiber fabric in the press gap is subjected to a pressure greater than the pressure applied to it previously in the pre-press gap. The pressure in the press gap can be, in particular, 1.5 to 4 times greater than the pressure in the pre-press gap. The surface materials of the two press rollers forming the press gap should be designed to withstand correspondingly high compressive forces on the fiber fabric. For this purpose, the material can be, in particular, a metallic material such as steel and / or a ceramic material.

[0016] To achieve high strength in the fiber web without negatively affecting the bulk, absorbency, and / or feel, it is particularly advantageous if at least one of the two press rollers is designed to provide the fiber layup in the press gap with a multitude of high-pressure and low-pressure zones, thereby increasing the fiber layup's strength. Preferably, the high-pressure and low-pressure zones are dimensioned such that they form a structure visible to the naked eye within the fiber layup. In such a case, the high pressures are applied to the fiber layup only in the high-pressure zones, whereas the fiber layup is compressed significantly less or not at all in the low-pressure zones.

[0017] For the same reasons, the aforementioned press belt can also be designed to provide the fiber fabric in the pre-pressing gap with a plurality of high-pressure and low-pressure zones, thereby increasing the strength of the fiber fabric, wherein the high-pressure and low-pressure zones are preferably dimensioned in such a way that they form a structure visible to the naked eye in the fiber fabric.

[0018] It is preferred if both one of the two press rollers forming the press gap and the press belt are suitable for creating corresponding high-pressure and low-pressure zones in the fiber layup. This allows the strength to be increased even further. Furthermore, in this case, it is particularly preferred if the high-pressure and low-pressure zones introduced into the fiber layup in the pre-pressing gap are not identical to the high-pressure and low-pressure zones introduced in the press gap. In this way, a so-called moiré effect can be created in the finished fiber web, which gives the product a particularly high-quality appearance.In order to reliably transfer the individual fibers and / or fiber bundles laid down on the forming belt to form a planar fiber fabric from the forming belt to the aforementioned press belt without loss of quality, particularly with regard to formation and / or fiber distribution, even at industrial-scale production speeds, an advantageous embodiment of the present invention proposes that the fiber fabric be transferred from the forming belt to the press belt in a transfer area, wherein a fiber fabric-transporting section of the forming belt is guided at its end over a final forming belt deflection roller and a fiber fabric-transporting section of the press belt is guided at its beginning over a first press belt deflection roller, wherein in the transfer area the forming belt and the press belt both move substantially parallel to a displacement direction over a length of at least 50 mm and at most 1.000mm, preferably at least 100mm and at most 800mm, are guided, wherein the length is defined as the distance, measured in the displacement direction, between the axis of rotation of the first press belt deflection roller and the axis of rotation of the last forming belt deflection roller.

[0019] It should be noted here that in mechanical engineering, the term "Trum" regularly refers to a part or branch of a rotating component. In particular, the terms "loaded run" and "slack run" for belts that transmit tensile forces are common in mechanical engineering. For the purposes of the present invention, the term "Trum" is used specifically to describe the section of a covering or belt that transports the fiber fabric.

[0020] "At an industrial level" means a high, continuous production speed of 150 m / min or greater, in particular 250 m / min or greater, and preferably 400 m / min or greater. Furthermore, at an industrial level, the width of the continuously produced fibrous web is preferably 0.5 m or greater, more preferably 1 m or greater, in particular 2.3 m or greater, but generally 10 m or less.

[0021] It was recognized that quality problems observed when production speeds were increased could be reduced by making the transfer area sufficiently long and ensuring that the forming belt and the pressing belt within the transfer area were essentially parallel to each other and to the direction of transfer. "Essentially parallel" here means that any angular deviation, if measurable at all, should be very small, in particular less than 5°, preferably less than 3°, and even more preferably less than 1°. The inventors explain this as follows: The fiber fabric transported on the forming belt has very low tensile strength. To prevent any deterioration in the quality of the fiber fabric, a "gentle" transfer appears to be important, allowing the fiber fabric sufficient time to detach from the forming belt and adhere to the pressing belt.This means that the transfer area should be longer if production speed is increased. However, extending it beyond 1,000 mm has not shown any further advantages. The increased space requirement results in only disadvantages with a further extension of the transfer area.

[0022] The advantages of a "gentle transfer" are particularly evident when the speed at which the fiber fabric is conveyed through the transfer area is greater than or equal to 150 m / min, especially greater than or equal to 250 m / min, and preferably greater than or equal to 400 m / min. The advantages of a "gentle transfer" are also particularly pronounced when the moisture content of the fiber fabric being transferred in the transfer area is less than 20%. In such cases, transfer is especially critical. Furthermore, to further counteract any deterioration in the quality of the fiber fabric at high production speeds, it has proven particularly advantageous if, in the transfer area, the forming belt and the pressure belt are spaced no further apart than the thickness of the fiber fabric immediately before the transfer area.The distance between the two belts can be at least 80% of the thickness of the fiber layup immediately before the transfer area. The thickness of the fiber layup immediately before the transfer area can, for example, be between 0.3 mm and 10 mm. In this way, the fiber layup is supported by both belts simultaneously along the entire length of the transfer area. The fiber layup experiences no significant change in its direction of movement throughout the entire transfer area, and it has enough time to gently detach from the forming belt and adhere to the pressing belt. However, if the distance between the two belts is less than 80% of the thickness of the fiber layup immediately before the transfer area, this is disadvantageous because the fiber layup loses too much bulk, which negatively affects the absorbency and feel of the finished fiber web.The aim is instead to introduce high density into the fiber fabric exclusively in certain high-pressure zones through pressure and / or heat, whereas the fiber fabric is only slightly densified in the low-pressure zones.

[0023] To facilitate the detachment from the forming belt and the attachment to the pressing belt, it is advantageous for the first pressing belt deflection roller to be vacuum-operated and / or for the last forming belt deflection roller to be non-vacuum-operated. For this purpose, the forming belt and the pressing belt should be air-permeable. Additional vacuum devices, such as suction boxes, can also be provided behind the first pressing belt deflection roller in the screen loop of the pressing belt to attach and hold the fiber fabric to the pressing belt. Preferably, the intensity of the vacuum in the transfer area increases in the direction of displacement. The applied vacuum from the vacuum devices is preferably between 1 mbar and 10 mbar.In an advantageous embodiment of the present invention, the fiber fabric, after leaving the transfer area, is preferably suspended overhead, and is guided to the pre-pressing gap, in particular by means of vacuum means provided in the loop of the press belt, in order to then be guided through the pre-pressing gap together with the press belt.

[0024] The fluid from step c) can be applied to the fiber fabric after it leaves the transfer area and before reaching the press gap. If this fluid is applied to the fiber fabric shortly before reaching the press gap, the water has less time to penetrate the interior of the fibers, so that more free water is available to form hydrogen bonds between the fibers in the press gap.

[0025] The concept of a "gentle" transfer is not only applicable to the transfer area between the forming belt and the pressing belt, even though it is particularly important there due to the low tensile strength of the fiber fabric, but can also be advantageously applied at other points where the fiber fabric is transferred from one belt to another. In particular, the fiber fabric can be transferred from the pressing belt to the connecting belt in a further transfer area, which transports the fiber fabric to just before the press gap. It is advantageous not to transfer the fiber fabric directly from the pressing belt into the press gap in free tension, but instead to provide the connecting belt in between, as it is easier to guide the fiber fabric to just before the press gap with the connecting belt. Specifically, the connecting belt and / or the deflection rollers in the screen loop of the connecting belt can be designed accordingly.If, for example, the last connecting belt deflection roller, located at the end of the conveying section of the connecting belt, has a relatively small diameter, preferably no more than 0.5 m, more preferably no more than 0.4 m, and even more preferably no more than 0.3 m, then the last connecting belt deflection roller can be positioned correspondingly close to the press gap. The diameter of the last connecting belt deflection roller should preferably be less than half the diameter of at least one of the two press rollers that together form the press gap. Furthermore, the connecting belt can have a smaller thickness and / or lower bending stiffness than the press belt in order to be guided or deflected over the last connecting belt deflection roller, provided the latter has a correspondingly small diameter.

[0026] In an advantageous further development of this idea, it is proposed that the fiber-carrying section of the press belt is guided at its end over a final press belt deflection roller, and a fiber-carrying section of the connecting belt is guided at its beginning over a first connecting belt deflection roller, wherein in the further transfer area the press belt and the connecting belt are both guided substantially parallel to a further displacement direction over a length of at least 50 mm and at most 1,000 mm, preferably at least 100 mm and at most 800 mm, and wherein the length is defined as the distance, measured in the further displacement direction, between the axis of rotation of the first connecting belt deflection roller and the axis of rotation of the last press belt deflection roller.

[0027] Furthermore, the consolidated fiber fabric can be picked up by the transfer conveyor just behind the press gap. This conveyor then transfers the consolidated fiber fabric to a further processing unit, in particular to a drying screen, where the consolidated fiber fabric is subsequently dried, especially in a drying unit. Here, too, it is advantageous not to transfer the fiber fabric directly from the press gap in free motion to the further processing unit, especially to the drying screen, but instead to provide the transfer conveyor in between, since it is easier to pick up the fiber fabric just behind the press gap with the transfer conveyor. In particular, the transfer conveyor and / or the deflection rollers in the screen loop of the transfer conveyor can be designed accordingly.If, for example, the first transfer belt deflection roller, located at the beginning of the conveying section of the transfer belt, has a relatively small diameter, preferably no more than 0.5 m, more preferably no more than 0.4 m, and even more preferably no more than 0.3 m, then the first transfer belt deflection roller can be positioned correspondingly close to the press gap. The diameter of the first transfer belt deflection roller should preferably be less than half the diameter of at least one of the two press rollers that together form the press gap. Furthermore, the transfer belt can have a smaller thickness and / or lower bending stiffness than the drying screen in order to be guided or deflected over the first transfer belt deflection roller if the latter has a correspondingly small diameter.

[0028] Furthermore, the transfer belt can also be used to apply a fluid to the side of the fiber fabric facing away from the transfer belt while the fiber fabric is being transferred.

[0029] A particularly advantageous way of adjusting the entry and / or exit angles of the fiber layup into and out of the press gap is to allow both press rollers, preferably together, to be displaceable in a substantially vertical direction. In this case, the connecting belt and / or the transfer belt can be fixed in place, i.e., not adjustable. Alternatively or additionally, it would also be conceivable, for example, that at least one of the two press rollers, preferably only one of the two press rollers, is pivotably arranged, namely such that its axis of rotation can be pivoted along a circular arc around the axis of rotation of the other press roller.

[0030] An advantageous embodiment of the present invention provides that only water and / or dry-strength agents are applied to the fiber layup before the press gap, whereas wet-strength agents are applied to the consolidated fiber layup after the press gap. Wet-strength agents serve to impart a degree of mechanical strength—albeit limited—to the fiber web, particularly tissue webs, even in the wet state. Without wet-strength agents, the fiber web would otherwise lose its internal cohesion due to the breaking of hydrogen bonds upon exposure to water. In their processed state, wet-strength agents are generally water-soluble polymers, primarily produced from polyamines and epichlorohydrin derivatives, which react with the fibers. This reaction forms water-insoluble cross-links between the fibers, stabilizing the fiber web.Dry strength agents, on the other hand, primarily serve to further increase the strength of the fiber web, especially tissue webs, in their dry state. A well-known and relatively inexpensive dry strength agent is starch, particularly cationic starch. However, there are also chemical dry strength agents, such as sodium carboxymethylcellulose (CMC). Wet strength agents, especially those that are not yet dry, and to some extent even dry strength agents, tend to contaminate or adhere to the surfaces of machine parts with which they come into contact. For this reason, wet strength agents should only be applied to the fiber web downstream of the press gap, which is preferably also the last press gap in the manufacturing process or machine, in order to protect the elements, especially the rollers that form the press gap, from contamination.

[0031] Another aspect of the present invention relates to a machine for producing a fibrous web, preferably a tissue, paper or cardboard web or a nonwoven web, in particular a tissue web with a basis weight of 28g / m². 2 up to 42g / m² 2, comprising: a) a raw material processing plant for the low-water processing of cellulose-containing fibers into individual fibers and / or fiber bundles; b) a dry forming device for the dry forming of the individual fibers and / or fiber bundles in an air stream into a flat fiber layup on a forming belt; c) an application device for applying a fluid, preferably water and / or a water-additive mixture, to the fiber layup; d) a consolidation device for consolidating the flat fiber layup by applying pressure in a press gap formed by two press rollers;wherein the machine further comprises a connecting belt to transport the flat fiber fabric to just before the press gap, and a transfer belt to receive the fiber fabric compacted by the press gap just behind the press gap, so that the flat fiber fabric is guided unsupported through the press gap, wherein at least one of the two press rollers and / or the connecting belt and / or the transfer belt is adjustable with respect to its position such that the angle at which the fiber fabric enters the press gap and / or the angle at which the compacted fiber fabric leaves the press gap is / are specifically adjustable.

[0032] The advantageous further developments previously described for the method according to the invention also apply analogously to the machine according to the invention.

[0033] For the purposes of the present invention, the term "low-water" raw material processing also includes the processing of the raw material entirely without the targeted addition of water and / or other liquids.

[0034] The invention expressly extends to embodiments which are not given by combinations of features from explicit cross-references of the claims, whereby the disclosed features of the invention can be combined arbitrarily with one another - insofar as this is technically sensible.

[0035] To differentiate between the manufactured fiber webs, for example a tissue, paper or cardboard web on the one hand and a nonwoven web on the other, the following distinction is made, which is based on fiber length, density and fiber bonding type: A tissue, paper or cardboard web is defined as a fiber web with predominantly medium fiber lengths, which are shorter than the fiber lengths of nonwoven webs, of less than or equal to 5 mm, in particular less than or equal to 4 mm, preferably less than or equal to 3 mm, predominantly bonded by hydrogen bonds and with a bulk density of greater than or equal to 0.4 g / cm³. 3 Understood. The fibers used in a tissue, paper or cardboard web are additionally characterized by having a slenderness ratio of fiber length to fiber diameter of less than or equal to 200, in particular less than or equal to 150, preferably less than or equal to 100.

[0036] A nonwoven web, which also consists primarily of fibers, is defined—as a key distinction from tissue, paper, or cardboard webs—by having a fiber content of at least 30% consisting of very long fibers with an average fiber length of more than 5 mm, or continuous fibers, which determine the nonwoven characteristics. Furthermore, a fiber-to-diameter ratio of greater than or equal to 300 is targeted for a nonwoven web. The remaining fiber content of a nonwoven web can be of a different composition, and the bulk density should be below 0.40 g / cm³. 3 to classify a fibrous web as a nonwoven fabric.

[0037] Further features and advantages of the invention will become apparent from the following description of a preferred embodiment with reference to the drawing.

[0038] The invention will be explained below with reference to the following figures.

[0039] Fig. 1 shows a schematic representation of a raw material processing plant 2 for the low-water processing of cellulose-containing fibers 200;

[0040] Fig. 2 shows a schematic representation of a fiber web plant 3 for the production of a dry-formed fiber web 309; Figs. 3a-3c show schematically various possibilities for selectively adjusting the entry and exit angle of the fiber layup 300, 305 into and out of the press gap 84.

[0041] Fig. 4 shows the arrangement according to Fig. 3c with additional elements.

[0042] To clarify the individual directions, a higher-level Cartesian coordinate system is used in the figures. The x-direction corresponds to a longitudinal extent, also known as the machine direction (MD). The y-direction corresponds to a direction orthogonal to the machine direction (MD) and is also known as the cross-direction (CD). The z-direction corresponds to the vertical direction.

[0043] Figures 1, 2 and 3a-3c show a schematic representation of a possible embodiment of the manufacturing process or the manufacturing machine 1 according to the invention.

[0044] Figure 1 schematically depicts a possible embodiment of a low-water processing plant, or a low-water raw material processing plant 2, in which the individual fibers and / or fiber bundles 209 are produced, for example, from fiber-containing recycled material and / or from virgin fiber pulp as bales 200, by comminution devices 221, 222, 223 and / or fiberizing devices 222, 223. After successful comminution or fiberizing, the individual fibers and / or fiber bundles 209 are transported in an airflow. Specifically, the air / fiber mixture is fed via a distribution channel or several distribution channels to at least one of the dry forming devices 4A, 4B, 4C shown in Figure 2 of a fiber web plant 3 for the production of a dry-formed fiber web 309.

[0045] It is also conceivable to have several raw material preparation plants 2 in parallel, which can supply a single fiber web plant 3. This is advantageous if a raw material preparation plant 2 alone cannot produce the required quantity of individual fibers and / or fiber bundles 209, or if different types of cellulose-containing fibers 200 are used as raw material, for example for a multi-layer fiber web 309.

[0046] The low-water processing method significantly contributes to the quality and properties of the produced dry-formed fiber web 309, as well as to the overall economic and energy efficiency of the manufacturing process. One challenge, for example, is transforming a discontinuous process into a continuous one, aiming for very high production volumes of several thousand tons of finished fiber web 309 per year. These high production volumes mean that the available raw material should ideally be stored as compactly as possible to minimize storage requirements. An important aspect of low-water raw material processing is that the required volume of processed raw material increases steadily until final processing in the fiber web plant 3.The increase in volume can typically range from a factor of 30,000 to 50,000 between that of virgin pulp in bales 200 and that of individual fibers and / or fiber bundles 209 dissolved in the airflow. This allows storage or intermediate storage in a storage facility 240 in the raw material processing plant 2 to be kept to a minimum and / or only required at the crucial processing steps.

[0047] Another aspect for the overall balance is to keep the availability of the supplied raw materials high and the costs low. For example, virgin fiber pulp can be delivered not only in bales but also in the more expensive and voluminous form of rolls. A bale typically consists of several sheets or strips of virgin fiber pulp. Due to the widespread use of virgin fiber pulp in roll form for end products, the term "fluff pulp" (or "cellulose wadding") has become synonymous with virgin fiber pulp in roll form. However, this is incorrect, as fluff pulp can only be obtained by shredding the rolls.

[0048] Typically, with virgin pulp in roll form, a large part of the raw material preparation for the manufactured fiber web is already integrated into the virgin pulp production process. This makes production more complex and costly. Generally, the mass distribution in rolls is subject to lower tolerances compared to bales. This is advantageous for the known, simplified fiber web production process, ensuring a continuous mass flow.

[0049] Furthermore, the composition of the pulp in the roll stock can already be tailored to the final fiber web to be produced, using additives. For example, additives such as debonding agents are typically already mixed into the roll stock. These facilitate the separation of the fibers and counteract fiber recombination during the subsequent manufacturing process. This is usually not the case with baled pulp, or is reduced to a minimum.

[0050] Fresh pulp in bale and roll form typically has similar material density values ​​of around 600 - 960 kg / m³. 3However, due to its cylindrical shape, a roll typically requires up to 30% more storage space for the same quantity of virgin pulp compared to a bale, which is essentially cubic. Virgin pulp in bale form is therefore characterized by a smaller storage volume and a higher fiber concentration per cubic meter of storage space compared to roll form. The lower volume of bales allows for optimized transport and storage. This is particularly important when processing large quantities, especially several tons per day, to ensure competitive production.

[0051] A coupling of the two manufacturing processes of the low-water raw material preparation 2 and the fiber web plant 3 is an important component for the production of high-quality fiber webs 309, both of which can be coordinated, controlled and / or regulated via a higher-level control and / or regulation device 60.

[0052] The low-water raw material preparation process or raw material preparation plant 2 is characterized by a multi-stage comminution of the discontinuously fed raw material, whereby at the end of the low-water raw material preparation process 2, an airflow containing dispersed individual fibers and / or fiber bundles 209, tailored to the subsequent fiber web plant 3, can be continuously provided. The low-water raw material preparation process or raw material preparation plant 2 and the subsequent fiber web plant 3 are preferably free of an intermediate storage of the individual fibers 209 between plants 2 and 3 and are thus provided to the fiber web plant 3 "on demand".

[0053] The general term "raw material" is used for cellulose-containing fibers 200, preferably virgin fiber pulp in bales 200 and / or recycled fibers. The recycled fibers can originate from the fiber web plant 3 itself as high-quality recycled virgin fiber pulp and / or it can be provided that recycled material from waste paper is used to further improve the overall efficiency of the manufacturing process.

[0054] The discontinuously supplied raw material is usually fed as bales 200 via a conveyor belt 220 to a first shredding device 221. The first shredding device 221, preferably a first shredder 221, is designed such that it can perform a first shredding of the bales 200 into coarse chips, shreds or chips 201.

[0055] For example, a bale of 200 mm virgin fiber pulp can consist of numerous stacked 200 mm pulp sheets. This pulp is NBSK pulp, typically used for wet-process paper, board, or tissue production. The starting material can have a density of approximately 920 kg / m³. 3 The individual cellulose sheets have a thickness of approximately 1.5 mm. One to five of these cellulose sheets are always fed simultaneously in a substantially horizontal direction to a first comminution device 221, preferably a shredder 221.

[0056] The chips 201 are then fed into a cleaning device 230, where any unwanted components, so-called "rejects," such as metals, contaminants, and / or packaging residues, that may still be contained in the chips 201 can be filtered out. After passing through the cleaning device 230, which may be, for example, a cyclone separator, the chips 201 are available as cleaned chips 202.

[0057] These cleaned chips 202 are ideally temporarily stored in a larger storage unit 240, preferably in the form of a silo. Advantageously, this is the only larger storage unit 240 in the entire raw material processing plant 2. The term "single larger storage unit 240" refers to the fact that, due to the design of the individual components of the raw material processing plant 2, there may be smaller micro-storage units, which, however, are not suitable for supplying the process for several minutes. Advantageously, the storage unit 240 is located immediately after the cleaning of the chips 201, thus minimizing the increase in volume.The storage unit 240 can have a maximum capacity of 30 minutes or more, in particular 60 minutes or more, preferably 90 minutes or more, and 120 minutes or less than, of the production time of the fiber web system 3. The size of the storage unit 240 depends on the desired basis weight and width of the fiber web 309, as well as on the production speed of the fiber web system 3. The design of the storage unit 240 is preferably geometrically optimized to enable compact, low-air, volume-optimized storage of the cleaned chips 202.

[0058] Optionally, a conditioning device 260 or a conditioning process can be provided for the cleaned chips 202 after the cleaning of the chips 201 and before the memory 240. During conditioning, a small amount of moisture can be added to the cleaned chips 202, for example, to minimize or prevent dust formation and / or electrostatic charging. However, the amount of moisture applied should be kept as low as possible to avoid negatively impacting the overall energy balance. Additives can also be added during conditioning.

[0059] The storage unit 240 is preferably designed as a vertical storage silo 240, wherein the cleaned chips 202 can be easily compressed by their own weight. Furthermore, at least one discharge device 241 is provided in the storage unit 240, which enables continuous discharge of the cleaned chips 202.

[0060] To facilitate the discharge of the cleaned chips 202 from the storage unit 240, a first airflow 90 is introduced directly at the outlet of the storage unit 240, allowing the cleaned chips 202 to disperse and mix within the first airflow 90 and thus be easily transported to the second shredding device 222. In one embodiment, preferably, reject material from the fiber web system 3 can be added to the cleaned chips 202. This reject material can, for example, be edge trimming 50 or edge extraction 50, in which fibers from a fiber web 300 are extracted at the edge after at least one of the dry forming devices 4A, 4B, 4C. Furthermore, uncollected individual fibers and / or fiber bundles 209 filtered from the ambient air can also be added back in as recycled material before the second shredding device 222.It is particularly advantageous if the recycled material does not yet contain any additives and therefore meets the quality requirements without further processing steps.

[0061] The second comminution device 222, or first fiberizing device 222, is preferably designed as a first hammer mill 222, in which the cleaned chips 202 are comminuted or fiberized until individual fibers with isolated nodes 205 are formed. These fibers can then pass through a filter device included in the second comminution device 222. The discharge of the individual fibers 205 from the second comminution device 222 is supported by the supply of an airflow 90 downstream of the second comminution device 222, and their transport to the next processing station is carried out. The individual fibers with isolated nodes 205B are highly dispersed in the supplied airflow 90.

[0062] The individual fibers with isolated nodes 205B can be further processed in a fiber processing device 250 to form a continuous mass flow of fibers 206, to which a further air flow 90 is subsequently added and the continuous mass flow of fibers 206 becomes a high-resolution, continuous mass flow of a fiber-air mixture 207.

[0063] The high-resolution, continuous mass flow of a fiber-air mixture 207 is fed directly to the third comminution device 223 or second fiberizing device 223, which is preferably designed as a second hammer mill 223. The third comminution device 223 comminsues or fiberizes the high-resolution, continuous mass flow of a fiber-air mixture 207 until essentially only individual fibers 208 remain, preferably free of knots or with only a small proportion of knots, which can then pass through a filter device included in the third comminution device 223.

[0064] To further reduce the single-fiber concentration, another airflow 90 can then be added. Alternatively or additionally, for example, exhaust air from the vacuum boxes 32 included in the fiber web system 3 can be added for web stabilization (see also Fig. 2) before the high-resolution single fibers 209, essentially free of knots, are precisely metered and continuously fed to the fiber web system 3 via a distribution system or distribution channels.

[0065] In the embodiment shown in Figure 2, three dry forming devices 4A, 4B, 4C are arranged one behind the other to produce three superimposed layers of the finished fiber web 309. However, this is not mandatory. The fiber web system 3 could also include fewer than three dry forming devices, in particular only a single dry forming device, or it could include more than three dry forming devices.

[0066] The individual fibers and / or fiber bundles 209 transported by the airflow are guided to at least one of the dry forming devices 4A, 4B, 4C of the fiber web system 3 and distributed as evenly as possible transversely to the machine direction MD or in the transverse direction CD of the fiber web system 3. If the capacity of the raw material preparation system 2 is sufficiently large and all three layers of the finished fiber web 309 are to consist of the same fiber material, the raw material preparation system 2 preferably feeds all three dry forming devices 4A, 4B, 4C. Otherwise, at least one of the dry forming devices 4A, 4B, 4C is fed by another method. This can be achieved, in particular, by a further raw material preparation system, not shown here, which may be similar to or substantially identical to the raw material preparation system 2 described above.The provision of at least three dry forming devices 4A, 4B, 4C has the advantage that the two outer cover layers of the finished fiber web 309 can be formed from a different, in particular higher quality, fiber material than the at least one layer in between.

[0067] Following the dry forming devices 4A, 4B, 4C, preferably at least two application devices 7 are provided, which apply a fluid, preferably water or a water-additive mixture, to the fiber fabric 300 or the consolidated fiber fabric 305. The at least two application devices 7 are configured as a first application device 71 and at least one further application device 72, 73. Preferably, one of the further application devices 72, 73 is also the last application device in the fiber web system 3. In the embodiment shown in Fig. 2, three application devices 7 are provided, with a second application device 72 arranged between the first application device 71 and the third application device, which is also the last application device.

[0068] Following the dry forming devices 4A, 4B, 4C, at least one consolidation device 8 is provided which can consolidate the fiber fabric 300. In the embodiment shown in Fig. 2, three consolidation devices 8 are arranged. Preferably, at least one consolidation device 8 is designed such that, in addition to consolidating the fiber fabric, it can also structure and / or heat it. Structuring by the consolidation device 8 is particularly useful for producing a tissue web with low- and high-pressure zones, preferably a tissue web with a basis weight of 28 g / m². 2 up to 42g / m² 2 , important. To complete the continuously produced fiber web 309, a web-width winding unit 12 is arranged at the end of the fiber web system 3.

[0069] Preferably, at least one drying device 10 is further included in the fiber web system 3. It is advantageous if the at least one drying device 10 is arranged downstream of the application devices 7 in order to dry the fiber web 309 onto which the fluid has been applied. Preferably, the at least one drying device 10 is arranged upstream of the winding unit 12 of the finished fiber web 309, which is also included in the fiber web system 3.

[0070] The dry forming step in at least one of the dry forming devices 4A, 4B, 4C can be controlled and / or regulated by at least one included control and / or regulating means, wherein the individual fibers and / or fiber bundles 209 in the dry forming devices 4A, 4B, 4C are laid down, preferably partially by the force of gravity, onto a rotating, preferably permeable, forming belt 40 and form a fiber fabric 300, preferably still substantially unconsolidated.

[0071] Furthermore, the dry forming devices 4A, 4B, 4C can each include a suction device 30 which supports the depositing of the individual fibers 209 on the permeable forming belt 40, and can also influence this process as a control and / or regulating means.

[0072] Preferably, the fiber layup 300 is measured with respect to its mass distribution by at least one enclosed measuring device 61, preferably a mass measuring device extending in the transverse direction CD of the machine, wherein the measuring signal can act as a control variable, preferably via the higher-level control and / or regulating device 60, on the feed of the individual fibers without knots 209 from the raw material preparation plant 2 and / or on the suction device 30. The air 39A, 39B, 39C extracted by the respective suction device 30 can contain a certain quantity of individual fibers 209. Therefore, it is advantageous if a large proportion, preferably up to 95%, of the volume of air extracted by the respective suction device 30 is returned directly to the respective dry forming device 4A, 4B, 4C as a recirculation circuit.This makes it possible to dissolve the continuously added individual fibers 209 even better in order to achieve a good formation on the forming belt 40, whereby the extracted individual fibers can be immediately fed back to the corresponding production step.

[0073] In one embodiment, an extraction device extending in the transverse direction CD of the machine can extract excess fibers in the z-direction (thickness) from the surface of the first fiber layup 300 after it has left the at least one dry forming device 4A, 4B, 4C, so that a homogeneous thickness distribution of the fiber layup 300 is achieved in both the CD and MD directions. This process can be selectively influenced by the at least one measuring device 61, preferably supported by the higher-level control and / or regulating device 60.

[0074] Alternatively, the extraction device can also be designed as an edge trimming device 50 or edge extraction device 50, wherein fibers are preferably selectively extracted from the edge regions of the fiber web 300 emerging from the at least one dry forming device 4A, 4B, 4C and which is not yet consolidated. It is evident that the edge regions often exhibit very strong variations in thickness compared to the main or central region of the fiber web 300. Advantageously, by means of the edge strip extraction, fresh fibers, free of chemicals, can be fed directly back into the raw material preparation plant 2 immediately after the last of the at least one dry forming device 4A, 4B, 4C, which has a positive effect on the overall efficiency of the manufacturing process. Likewise, a clean edge of the fiber web 309 can be produced in this way. As shown in Fig.As shown in Figure 2, the fiber fabric 300 deposited in at least one dry forming device 4A, 4B, 4C can pass through a pre-solidification device 83 before the first application device 71, in which the still unsolidified fiber fabric 300 receives a first, full-surface pre-solidification or pre-compacting over the entire transverse direction CD.

[0075] The application devices 71, 72, 73 are preferably designed as nozzle applicators which can spray a fluid in the form of a spray jet consisting of individual small fluid droplets onto the fiber fabric 300, 305. Alternatively, the application devices can also be designed such that the fluid is applied in the form of foam, mist or vapor.

[0076] Alternatively, a curtain applicator or a roller applicator can be provided, wherein the roller applicator is advantageously integrated into one of the consolidation devices 8 and is coated with a fluid via an applicator, e.g. one of the two press rollers 81, 82, which is then transferred to the fiber fabric 300 in a subsequent pre-pressing gap 80.

[0077] Immediately before being wound 12, the fiber web 309 is guided through a dryer 10, preferably electrically operated. A non-contact dryer 10 advantageously preserves the properties of the fiber web 309 with regard to its thickness, feel, and absorbency. The non-contact dryer 10 can be designed, for example, as a hot air dryer, a flow-through drying hood, or a TAD dryer. Alternatively or additionally, the dryer 10 can also be equipped with infrared elements. Due to the small amounts of moisture used in the manufacturing process, the length of the dryer 10 can be kept very compact compared to the usual drying sections in wet lay-up processes. This allows the overall length of the fiber web plant 3 and infrastructure costs to be kept low.

[0078] Furthermore, at least one additional heating step of the laid fiber web 300 can also be provided upstream of the dryer 10. This additional heating step can, for example, be integrated into a consolidation device 8 by heating, for instance, a press roller 81 provided for pre-consolidation and / or a press element 82 arranged opposite it. Heating below 250°C, in particular less than or equal to 100°C, preferably less than or equal to 80°C, is advantageous because the heating supports the penetration depth and distribution of a fluid, preferably water, applied in a first application step 71 within the fiber web 300, leading to more efficient pre-consolidation and / or structuring. The temperature specifications refer to the temperature of the heating elements used. The temperature of the fiber web or...The temperature introduced into the fiber fabric can be lower.

[0079] The first application device 71 is preferably arranged directly upstream of the solidification device 8, which follows the pre-solidification device 83. Furthermore, the first application device 71 applies a fluid, preferably ordinary water, i.e., water that is free of artificial or chemical additives.

[0080] Alternatively, the first application device 71 can be configured to apply a different fluid, preferably a water-additive mixture. If a water-additive mixture is applied to the fiber web 300 before consolidation 8, the additive is preferably selected from the group of dry-strength agents, for example starch, to increase the strength of the produced fiber web 309 in a dry state. Dry-strength agents are suitable for application prior to consolidation because they often exhibit a lower tendency to stick compared to adhesives or wet-strength agents.

[0081] The application devices 71, 72, 73 are designed such that the fiber fabric 300 can be wetted over its entire surface with the fluid. "Over its entire surface" means that the fluid is applied substantially uniformly over the entire width or over the entire transverse direction CD of the fiber fabric. In the first, second, and third application devices 71, 72, 73, a vacuum box 31 can be arranged on the side of the fiber fabric 300 opposite the side to be wetted. This vacuum box draws ambient air through the fiber fabric 300 and through a permeable support element that supports the fiber fabric 300, preferably a pressure belt 41 and / or a transfer belt 103 and / or a drying screen 42, by means of a vacuum applied, preferably during application.This advantageously allows, for example, influencing the penetration depth of the applied fluid into the fiber fabric 300 and / or the quantity distribution in the machine direction MD or machine transverse direction CD during the application of a fluid. It should be noted that the reference numeral 22 indicates the respective running direction of the press belt 41 and other coverings in Fig. 2.

[0082] Optionally, at least one moisture measuring device 63 and / or a measuring device for monitoring the fluid application may be provided. Preferably, the at least one moisture measuring device 63 is arranged such that it can measure before and / or after the heating device 10.

[0083] It is also conceivable to provide a moisture measuring device 63 immediately after each application device 71, 72, 73. The moisture measuring device 63 can be stationary or traversing in the machine transverse direction CD. Furthermore, the moisture measuring device 63 can also be suitable for measuring other fiber web properties, such as mass, thickness, formation, opacity, or the like.

[0084] After passing through the pre-consolidation unit 83, the fiber fabric 300 is transported on the conveying section of the forming belt 40 to a transfer section 100. The transfer section 100 serves to transfer the fiber fabric 300 from the forming belt 40 to the pressing belt 41. Preferably, this transfer is particularly gentle, so that even at high production speeds and with low moisture content of the fiber fabric 300, no qualitative impairment of the fiber fabric 300 occurs. For this purpose, the forming belt 40 and the pressing belt 41 are both guided essentially parallel to a displacement direction. In the embodiment shown in Figure 2, the displacement direction corresponds to the machine direction MD. The transfer section 100 preferably has a certain length, namely a length of at least 50 mm and at most 1,000 mm, preferably at least 100 mm and at most 800 mm.The length of the transfer area 100 is defined as the distance, measured in the displacement direction or machine direction MD, between the axis of rotation of a first press belt deflection roller and the axis of rotation of a last forming belt deflection roller. The first press belt deflection roller is the deflection roller in the screen loop of the press belt 41, which is located at the beginning of the conveying section of the press belt 41. The last forming belt deflection roller, on the other hand, is the deflection roller in the screen loop of the forming belt 40, which is located at the end of the conveying section of the forming belt 40.By guiding the two belts 40, 41 parallel over the corresponding length, the still very delicate fiber fabric 300 is given sufficient time, even at high production speeds, particularly at production speeds of 150 m / min or more, preferably 250 m / min or more, and more preferably 400 m / min or more, and at low moisture contents, particularly less than 20%, to gently detach from the forming belt 40 and adhere to the pressing belt 41. It is also advantageous if the forming belt 40 has a distance from the pressing belt 41 in the transfer area 100 that is no greater than the thickness of the fiber fabric 300, measured immediately before the transfer area 100. The distance between the two belts 40, 41 can be controlled by a device perpendicular to the direction of displacement.The distance between the axis of rotation of the first press belt deflection roller and the axis of rotation of the last forming belt deflection roller, measured in the z-direction, is determined or set. The distance between the two belts 40, 41 in the transfer area 100 essentially corresponds to the distance between the axis of rotation of the first press belt deflection roller and the axis of rotation of the last forming belt deflection roller, minus the radius of the first press belt deflection roller, the radius of the last forming belt deflection roller, the thickness of the forming belt 40, and the thickness of the press belt 41.The press belt 41 is preferably designed to provide the fiber fabric 300 in the subsequent pre-pressing gap 80 between the press roller 81 and the press element 82 with a plurality of high-pressure and low-pressure zones, thereby increasing the strength of the fiber fabric 300. The high-pressure and low-pressure zones should be dimensioned such that they form a structure visible to the naked eye in the fiber fabric 300. In such a case, the press belt 41 includes protrusions on its upper surface facing the fiber fabric 300 to form the high-pressure zones. However, the height of these protrusions should be disregarded when determining the "thickness of the press belt 41".

[0085] This distance between the two belts 40, 41 in the transfer area 100 prevents the fiber web 300 from undergoing any significant change in its direction of movement, which corresponds to the displacement direction or the machine direction MD. This also helps to ensure that the quality of the fiber web 300 is not impaired at high production speeds. However, the distance between the two belts 40, 41 in the transfer area 100 should not be too small to avoid excessive bulk loss. A sufficiently high degree of compaction should ultimately be present only in the high-pressure zones of the finished fiber web 309, while the low-pressure zones are only lightly compacted, so that the fiber web 309 has the desired bulk and / or absorbency.Therefore, the distance between the two belts 40, 41 in the transfer area 100 can, for example, be at least 80% of the thickness of the fiber fabric 300 immediately in front of the transfer area 100.

[0086] The first press belt deflection roller can optionally be designed with suction to enable the "gentle" transfer of the fiber fabric 300 to begin immediately at the start of the transfer section 100. Several vacuum boxes 32 or other vacuum devices can be arranged in the screen loop of the press belt 41 behind the first press belt deflection roller to continue the transfer of the fiber fabric 300 over the entire length of the transfer section 100 and to hold the fiber fabric upside down on the conveying section of the press belt 41 even after the transfer section 100.

[0087] In contrast to the first press belt deflection roller, the last forming belt deflection roller is preferably non-vacuum-free, and there are also no vacuum boxes or other vacuum means in the sieve loop of the forming belt 40, at least in the transfer area 100, in order to prevent the fiber fabric 300, which is to detach from the forming belt 40 in the transfer area 100, from being held on it.

[0088] At the end of the conveying section of the press belt 41, the fiber fabric 300, which has meanwhile been compacted by the pre-pressing gap 80, is transferred from the press belt 41 to a connecting belt 102 in a further transfer section. The second transfer section is preferably designed analogously to the transfer section 100. Although the fiber fabric 300 exhibits a significantly greater strength after the pre-pressing gap 80 than before the pre-pressing gap 80, the principle of "gentle transfer" has also proven advantageous for the quality of the final fiber web 309 at this point.

[0089] After passing through the pre-pressing gap 80, the fiber fabric 300 is transported overhead on the conveying section of the press belt 41 to the further transfer area. This further transfer area serves to transfer the fiber fabric 300 from the press belt 41 to the connecting belt 102. For this purpose, the press belt 41 and the connecting belt 102 are preferably both guided essentially parallel to a further transfer direction. In the embodiment shown in Fig. 2, this further transfer direction also corresponds to the machine direction MD. The further transfer area preferably also has a certain length, namely a length of at least 50 mm and at most 1,000 mm, preferably at least 100 mm and at most 800 mm. The length of the further transfer area is defined as the distance measured in the further transfer direction.in the machine direction, between the axis of rotation of a first connecting belt deflection roller 125 and a last press belt deflection roller 126. The first connecting belt deflection roller 125 is the deflection roller in the screen loop of the connecting belt 102, which is located at the beginning of the conveying section of the connecting belt 102. The last press belt deflection roller 126, on the other hand, is the deflection roller in the screen loop of the press belt 41, which is located at the end of the conveying section of the press belt 41. Due to the parallel guidance of the two belts 41 and 102 over the corresponding length, the fiber fabric 300 is given sufficient time, even at high production speeds, to detach "gently" from the press belt 41 and attach itself to the connecting belt 102.

[0090] The connecting belt 102 serves to guide the fiber fabric 300 from the press belt 41 to just before a press gap 84, through which the fiber fabric 300 is then guided unsupported. In the press gap 84, the fiber fabric 300 is further compacted by pressure before being guided as a compacted fiber fabric 305 to the dryer 10. The press gap 84 can be provided by a gap between two press rollers 86, 88. However, because the fiber fabric 300 is guided unsupported through the press gap 84, unlike in the previous pre-press gap 80, no consideration needs to be given to the stability of a supporting fabric for the fiber fabric 300 at this point. Thus, it is possible to apply significantly higher pressures to the fiber fabric 300 in the press gap 84 than is the case in the pre-press gap 80. The higher pressures allow for a significantly greater strength of the finished fiber web 309.The press rollers 86, 88 should be designed to be correspondingly robust. For example, the rollers can be made primarily of steel.

[0091] In addition, preferably at least one of the two press rollers 86, 88, which form the press gap 84 between them, is designed to also provide the fiber fabric 300 with a plurality of high-pressure and low-pressure zones. The previously mentioned high pressures in this case refer only to the high-pressure zones. This further increases the strength of the fiber fabric 300. Just as the high-pressure and low-pressure zones introduced into the fiber fabric 300 in the pre-pressing gap 80 are dimensioned, so too are the high-pressure and low-pressure zones introduced into the fiber fabric 300 in the press gap 84 preferably dimensioned such that they form a structure in the fiber fabric 300 that is visible to the naked eye.For an aesthetically pleasing appearance of the finished fiber web 309, it is particularly advantageous if the high-pressure and low-pressure zones introduced into the fiber fabric 300 in the pre-pressing gap 80 are not identical to the high-pressure and low-pressure zones introduced in the pressing gap 84, so that a moiré effect preferably appears.

[0092] The connecting belt 102 is designed to guide the fiber fabric 300 as close as possible to the press gap 84 in order to keep the free pull, i.e., the distance that the fiber fabric 300 must travel unsupported between the connecting belt 102 and the press gap 84, as short as possible. For this purpose, a final connecting belt deflection roller, i.e., the deflection roller at the end of the conveying section of the connecting belt 102, can have a relatively small diameter, and the connecting belt 102 itself can be designed to be sufficiently flexible to follow the correspondingly strong surface curvature of the final connecting belt deflection roller.

[0093] After leaving the press gap 84, the consolidated fiber fabric 305 is picked up by a transfer belt 103, which transfers the consolidated fiber fabric 305 to the drying screen 42. For similar reasons as before, the transfer belt 103 can be designed similarly to or identically with the connecting belt 102. In particular, the transfer belt 103 can be designed to pick up the fiber fabric 305 as close as possible behind the press gap 84 in order to keep the free pull, i.e., the distance that the consolidated fiber fabric 305 has to travel unsupported between the press gap 84 and the transfer belt 103, as short as possible. For this purpose, a first transfer belt deflection roller, i.e. the deflection roller at the beginning of the conveying section of the transfer belt 103, can have a relatively small diameter and the transfer belt 103 itself can be designed to be flexible enough to follow the correspondingly strong surface curvature of the first transfer belt deflection roller.

[0094] To enable the fiber fabric 300 to be processed as smoothly as possible, even at industrial production speeds, the present invention provides that at least one of the two press rollers 86, 88, which form the press gap 84, and / or the connecting belt 102 and / or the transfer belt 103 are adjustable in their position such that the angle at which the fiber fabric 300 enters the press gap 84 and / or the angle at which the compacted fiber fabric 305 exits the press gap 84 can be precisely adjusted. As schematically illustrated in Figure 3a, it is possible, for example, to design the two press rollers 86, 88, which form the press gap 84 between them, to be adjustable in the z-direction, preferably together. As indicated in Figure 3b, however, alternatively or additionally, one of the two press rollers 86, 88 could also be designed to be tiltable about an axis extending in the transverse direction CD of the machine.In particular, one of the two press rollers 86, 88 can be displaced on a circular path whose center point lies on the axis of rotation of the other of the two press rollers 86, 88. Furthermore, as schematically illustrated in Figure 3c, the connecting belt 102 and / or the transfer belt 103 can also be pivotable in order to selectively adjust the entry and / or exit angle of the fiber layup into the press gap 84 or from the press gap 84. In particular, the deflection roller of the connecting belt 102 and / or the transfer belt 103 facing away from the press gap 84 can be pivotably mounted about the axis of rotation of the deflection roller of the connecting belt 102 and / or the transfer belt 103 facing towards the press gap 84.

[0095] Stabilizing elements can be arranged between the connecting belt 102 and the two press rollers 86, 88. The same applies to the transfer belt 103 and the two press rollers 86, 88. Figure 4 shows the arrangement of Figure 3c, with a stabilizing element (foil) arranged in each of the aforementioned spaces as an example. The arrangement shown in Figure 4 is particularly advantageous if one of the press rollers 86 or 88 has a structured surface to provide the fiber layup with a multitude of high-pressure and low-pressure zones, and the other press roller 88 or 86 has a smooth surface.

[0096] Each stabilizing element has one side facing the fiber fabric. This side is smooth and its surface is preferably flat or, more preferably, slightly concave. The stabilizing elements are slightly recessed into the path of the fiber fabric. The surface of the stabilizing element facing the fiber fabric runs essentially parallel to the plane in which the fiber fabric would be located if the stabilizing element were not present.

[0097] In the arrangement shown in Figure 4, a first stabilizing element is arranged between the connecting belt 102 and the press rollers 86, 88 and is connected with

[0098] The first stabilizing element is designated 401. A second stabilizing element is arranged between the press rollers 86, 88 and the transfer belt 103 and is designated 402. Stabilizing elements 401 and 402 serve, on the one hand, to reduce the length of the free tension of the fiber web. On the other hand, the wrapping angles of the fiber web around the press rollers 86 and 88 can also be influenced by the stabilizing elements. The first stabilizing element is arranged so that it can increase the wrapping angle around the press roller 88. The further the stabilizing element is inserted into the web of the fiber web, the larger the wrapping angle of the web around the press roller 88 becomes. The second stabilizing element 402 is arranged so that it can also increase the wrapping angle around the press roller 86. The arrangement of the first stabilizing element 401 improves the insertion of the fiber fabric into the press gap 84, while the arrangement of the second stabilizing element

[0099] 402 facilitates the removal of the fiber fabric from the press roller 88.

[0100] Vacuum devices, not shown in Fig. 2, may be provided in the sieve loop of the connecting belt 102 and / or in the sieve loop of the transfer belt 103. This applies in particular to the transfer belt 103, on which the bonded fiber fabric 305 is preferably transported hanging upside down. Here, the vacuum devices can help to hold the bonded fiber fabric 305 against gravity on the transfer belt 103. Furthermore, vacuum devices in the sieve loop of the transfer belt 103 are advantageous if a fluid is to be applied to the side of the bonded fiber fabric 103 facing away from the transfer belt 103. This is indicated in Fig. 2 by the second application device 72. After the solidified fiber fabric 305 is transferred to the drying screen 42, fluid is again applied to the side of the solidified fiber fabric 305 facing away from the drying screen 42 by the third application device 73.Thus, the consolidated fiber fabric 305 can be moistened from both sides by the second application device 72 and the third application device 73 before being dried in the drying device 10 and then rolled up on the winding unit 12.

[0101] To protect the press rollers 86, 88, which form the press gap 84 between them, from contamination and to minimize their cleaning effort, it is advantageous to apply only water and / or dry-strength agents to the fiber fabric 300 upstream of the press gap 84. These lead to no or only minimal contamination of the press rollers 86, 88. Downstream of the press gap 84, wet-strength agents can be applied to the compacted fiber fabric 305 by the second application device 72 and / or the third application device 73 to give the finished fiber web 309 a certain degree of wet strength. Common wet-strength agents, in particular, tend to contaminate surfaces, at least until they have dried.

[0102] 1 machine

[0103] 2 Raw material processing plant

[0104] 3 Fiber web plant

[0105] 4A, 4B, 4C Dry forming device

[0106] 7 Application device

[0107] 8 Solidification device

[0108] 10 T dryver construction

[0109] 12. Rolling direction

[0110] Suction device of the dry forming device vacuum box - application device

[0111] Vacuum boxes A, 39B, 39C extracted air

[0112] Support element, forming belt

[0113] Support element, press band

[0114] Support element, drying sieve

[0115] Edge trimming (edge ​​extraction) Control and / or regulating device Measuring device

[0116] Moisture measuring device, first application device, second application device, third application device, pre-compression gap

[0117] Press roller

[0118] Press element

[0119] Pre-solidification device

[0120] Press gap

[0121] Press roller

[0122] Press roller

[0123] Airflow 0 Transfer area 2 Connecting belt 3 Transfer belt 5 First connecting belt deflection roller 6 Last press belt deflection roller 0 Pulp-containing fibers (bales) 1 Shredded bales, chips 2 Cleaned chips 205 Individual fibers with isolated knots or shredded chips

[0124] 205B single fibers with isolated nodes or fiberized chips, high resolution in a fiber-air mixture

[0125] 206 continuous mass flow of fibers

[0126] 207 continuous mass flow of fibers, high resolution in a fiber-air mixture

[0127] 208 individual fibers essentially free of knots

[0128] 209 single fibers and / or fiber bundles

[0129] 220 Conveyor belt

[0130] 221 first shredding device (shredder)

[0131] 222 second shredding device, preferably

[0132] Fibrecing device, in particular first hammer mill

[0133] 223 third comminution device, preferably a fiberizing device, in particular a second hammer mill

[0134] 230 Cleaning device

[0135] 240 storage

[0136] 241 Discharge device

[0137] 250 fiber processing device

[0138] 260 Conditioning device

[0139] 300 fiber layups after dry forming device

[0140] 305 reinforced fiber fabric

[0141] 309 Fibre web

[0142] 401 Stabilizing element

[0143] 402 Stabilizing element

[0144] MD Machine direction

[0145] CD machine transverse direction z vertical direction

Claims

1. Method for producing a fibrous web (309), preferably a tissue, paper or cardboard web or a nonwoven web, in particular a tissue web with a basis weight of 28g / m² 2 up to 42g / m² 2, comprising the following steps: a) low-water raw material preparation of cellulose-containing fibers (200) to individual fibers and / or fiber bundles (209); b) forming the individual fibers and / or fiber bundles (209) in an air stream to form a planar fiber fabric (300) on a forming belt (40) by a dry forming process; c) application of a fluid, preferably water and / or a water-additive mixture, to the fiber fabric (300); d) Consolidation of the planar fiber fabric (300) by applying pressure in a press gap (84) formed by two press rollers (86, 88), characterized in that the planar fiber fabric (300) is guided unsupported through the press gap (84), wherein the planar fiber fabric (300) is transported by a connecting belt (102) to just before the press gap (84) and wherein the fiber fabric (305) consolidated by the press gap (84) is picked up by a transfer belt (103) just behind the press gap (84),where "shortly before the press gap (84)" means that the distance which the planar fiber fabric (300) must bridge unsupported to the press gap (84) is less than 1 m, and where "shortly after the press gap (84)" means that the distance which the consolidated fiber fabric (305) must bridge unsupported away from the press gap (84) is less than 1 m, and where at least one of the two press rollers (86, 88) and / or the connecting belt (102) and / or the transfer belt (103) is adjustable with respect to its position such that the angle at which the fiber fabric (300) enters the, The press gap (84) is entered, and / or the angle at which the consolidated fiber fabric (305) leaves the press gap (84) is / are specifically adjustable.

2. Method according to claim 1, characterized in that the fiber fabric (300) is guided through a pre-pressing gap (80) supported by a press belt (41) before passing through the press gap (84).

3. Method according to claim 2, characterized in that the fiber fabric (300) in the press gap (84) is subjected to a pressure which is greater than the pressure to which the fiber fabric (300) was previously subjected in the pre-press gap (80), preferably between 1.1 and 4 times, particularly preferably 1.2 to 1.6 times as large.

4. Method according to one of the preceding claims, characterized in that at least one of the two press rollers (86, 88) is designed to provide the fiber fabric (300) in the press gap (84) with a plurality of high-pressure and low-pressure zones and thus increase the strength of the fiber fabric (300), wherein preferably the high-pressure and low-pressure zones are dimensioned such that they form a structure visible to the naked eye in the fiber fabric (300).

5. Method according to one of the preceding claims, at least according to claim 2, characterized in that the press belt (41 ) is designed to provide the fiber fabric (300) in the pre-pressing gap (80) with a plurality of high-pressure and low-pressure zones and thus increase the strength of the fiber fabric (300), wherein preferably the high-pressure and low-pressure zones are dimensioned such that they form a structure visible to the naked eye in the fiber fabric (300).

6. Method according to claims 5 and 4, characterized in that the high-pressure and low-pressure zones introduced into the fiber fabric (300) in the pre-pressing gap (80) are not identical to the high-pressure and low-pressure zones introduced into the pressing gap (84), so that a moiré effect preferably appears.

7. A method according to one of the preceding claims, at least according to claim 2, characterized in that the fiber fabric (300) is transferred from the forming belt (40) to the pressing belt (41) in a transfer area (100), wherein a section of the forming belt (40) transporting the fiber fabric (300) is guided at its end over a final forming belt deflection roller and a section of the pressing belt (41) transporting the fiber fabric (300) is guided at its beginning over a first pressing belt deflection roller, wherein in the transfer area (100) the forming belt (40) and the pressing belt (41) are both guided substantially parallel to a displacement direction over a length of at least 50 mm and at most 1,000 mm, preferably at least 100 mm and at most 800 mm, wherein the length is the distance, measured in the displacement direction, between the axis of rotation of the first pressing belt deflection roller and is defined by the axis of rotation of the last forming belt deflection roller.

8. Method according to claim 7, characterized in that in the transfer area (100) the forming belt (40) has a distance to the pressing belt (41) which is not greater than the thickness of the fiber fabric (300) immediately in front of the transfer area (100).

9. Method according to one of the preceding claims, at least according to claim 2, characterized in that the fiber fabric (300) is transferred from the press belt (41) to the connecting belt (102) in a further transfer area.

10. Method according to claim 9, characterized in that the fiber fabric (305) transporting section of the press belt (41) is guided at its end over a final press belt deflection roller (126), and a fiber fabric (305) transporting section of the connecting belt (102) is guided at its beginning over a first connecting belt deflection roller (125), wherein in the further transfer area the press belt (41) and the connecting belt (102) are both guided substantially parallel to a further displacement direction over a length of at least 50 mm and at most 1,000 mm, preferably at least 100 mm and at most 800 mm, wherein the length is defined as the distance, measured in the further displacement direction, between the axis of rotation of the first connecting belt deflection roller (125) and the axis of rotation of the last press belt deflection roller (126).

11. Method according to one of the preceding claims, characterized in that the transfer belt (103) transfers the solidified fiber fabric (305) to a further treatment unit, in particular to a drying screen (42), on which the solidified fiber fabric (305) is subsequently dried, in particular in a drying device (10).

12. Method according to claim 11, characterized in that a fluid is applied to the side of the solidified fiber fabric (305) facing away from the transfer belt (103) while the solidified fiber fabric (305) is transferred.

13. Method according to one of the preceding claims, characterized in that both press rollers (86, 88), preferably together, are displaceable in a substantially vertical direction (z).

14. Method according to one of the preceding claims, characterized in that only water and / or dry strength agents are applied to the fiber fabric (300) before the press gap (84), whereas wet strength agents are applied to the solidified fiber fabric (305) after the press gap (84).

15. Machine (1 ) for producing a fibrous web (309), preferably a tissue, paper or cardboard web or a nonwoven web, in particular a tissue web with a basis weight of 28g / m² 2 up to 42g / m² 2, comprising: a) a raw material preparation plant (2) for the low-water processing of cellulose-containing fibers (200) into individual fibers and / or fiber bundles (209); b) a dry forming device (4) for the dry forming of the individual fibers and / or fiber bundles (209) in an air stream into a planar fiber fabric (300) on a forming belt (40); c) an application device (71) for applying a fluid, preferably water and / or a water-additive mixture, to the fiber fabric (300); d) a consolidation device (8) for consolidating the planar fiber fabric (300) by applying pressure in a press gap (84) formed by two press rollers (86, 88); characterized in that machine (1) further comprises a connecting belt (102) for transporting the planar fiber fabric (300) to just before the press gap (84), and a transfer belt (103) for receiving the fiber fabric (305) compacted by the press gap (84) just behind the press gap (84), so that the planar fiber fabric (300) is guided unsupported through the press gap (84), wherein just before the press gap (84) means that the distance which the planar fiber fabric (300) must bridge unsupported to the press gap (84) is less than 1 m, and wherein just behind the press gap (84) means that the distance which the compacted fiber fabric (305) must bridge unsupported away from the press gap (84) is less than 1 m, and wherein at least one of the two press rollers (86, 88) and / or the connecting belt (102) and / or the transfer belt (103) are adjustable with respect to their position such that the angle,with which the fiber fabric (300) enters the press gap (84), and / or the angle at which the consolidated fiber fabric (305) leaves the press gap (84) is / are specifically adjustable.

16. Machine (1 ) according to claim 15, characterized in that the machine (1 ) comprises at least one stabilizing element (401 , 402) with a surface, and wherein the at least one stabilizing element (401 , 402) is arranged between the connecting belt (102) and the transfer belt (103) such that the at least one stabilizing element (401 , 402) can immerse its surface into the fiber fabric (300, 305) in order to guide the fiber fabric (300, 305) and to adjust a wrapping angle of the fiber fabric (300, 305) around one of the two press rollers (86, 88).

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