EP4187013B1 - Method and machine for producing a bag-type kraft paper web having increased elongation properties - Google Patents

Description

The invention relates to a method for producing a fibrous web, in particular a sack kraft paper web, with increased stretch in the machine direction and/or in the transverse direction in a paper machine, comprising a forming section for forming and dewatering the fibrous web, a press section and a drying section with a pre-drying section and an after-drying section for further dewatering the fibrous web, as well as a reel, and a compression device arranged between the pre-drying section and the after-drying section for compressing the fibrous web.

The invention also relates to a paper machine suitable for producing a fibrous web, in particular a sack kraft paper web.

The invention is explained below in connection with the treatment of a sack kraft paper web. However, it can also be used with other fibrous webs that can be handled in a similar way. These include, for example, but not exclusively, fibrous webs made of paper, cardboard, cardboard or tissue.

Devices of this type are known. The documents WO2016/083170 A1 and EP 3 835 482 A1 disclose a paper machine for producing sack kraft paper, as a niche product of packaging paper. The investment and operating costs for production should be minimized while maintaining high quality. This is achieved, among other things, by subjecting the fiber suspension used in stock preparation to high-consistency grinding and low-consistency grinding and by stimulating the sheet formation area to shake movements using a shaking device. The stretchability of the sack kraft paper is improved by a compression device. The disclosed paper machine and process are tailored to the production of the niche product “sack kraft paper”.

Sack kraft paper contains fresh fiber pulp, which is preferably obtained from softwood and is also known as long fiber pulp. Sack kraft paper therefore has a much higher strength potential than other paper webs.

The strength potential of a sack kraft paper web, for example, can usually be further increased by using high-consistency refining in the stock preparation and the use of a compression device. The use of a compression device usually has a positive effect on the strength potential by compressing or shrinking the paper web in the machine direction and thus increasing the possible elongation of the paper web.

A "higher strength potential" means a higher energy absorption (TEA = Tensile Strength Absorption) of the paper web. The energy absorption (TEA) is defined in the TAPPI standard T494 - om 1, as of 2006-06, as the integral of the load or force curve over the elongation of the paper web until it breaks.

“Elongation” is understood to mean the elongation at break of the paper web, which can usually be determined from a tensile strength test according to DIN EN ISO 1924-2, as of 2021-08, and from the resulting force using an elongation diagram from a paper web.

The elongation can also be described equivalently by the shrinkage of the paper web. “Shrinkage” is understood here to mean the change in the width of the paper web/partial paper web in relation to the width of the paper web/partial paper web in a preceding machine section in the machine direction MD. This can be determined by simply measuring the width using commonly used measuring methods.

The disadvantage of the above-mentioned measures is that there is still little influence on the expansion, especially in the transverse direction.

The object of the invention is to improve the strength potential of a sack kraft paper web, in particular the elongation in the transverse direction, of the sack kraft paper web.

The object is achieved according to the invention by an embodiment according to the independent claims. Further advantageous embodiments of the present invention can be found in the subclaims.

In the method according to the invention, after the pre-drying section and before rolling up, the sack kraft paper web is cut or divided by at least one cutting group in the machine direction or longitudinal direction, so that the original, uncut or undivided sack kraft paper web is cut after the first cutting group into at least two sack kraft paper partial webs lying side by side in the transverse direction or is divided and the cut or the division leads to at least a minimum stretch value in the transverse direction of the at least two sack kraft paper webs being influenced before the roll-up is reached in such a way that the minimum elongation value before the roll-up is greater than a minimum elongation value of the uncut or undivided sack kraft paper web.

The paper machine is designed so that the dry content of the sack kraft paper web at the entry into the first cutting group is in the range of 60% to 65%. In order to achieve good porosity values for the sack kraft paper web, it is only dewatered a lot in the press section so that a dry content in the range of 38% to 44% is achieved after the last press nip. This can be achieved with small line forces in the press section. The sack kraft paper web is then further dried in several drying sections, the paper machine having a pre-drying section and a post-drying section, which are characterized by an upsetting device arranged between them. After the compression device, the sack kraft paper web is completely dried in the post-drying section, preferably to a dryness content of between 92% and 98%, in particular between 95% and 98%. The sack kraft paper web is then rolled up in the roll-up.

Another optional possibility of achieving the required dry content in the sack kraft paper web at the end of the pre-drying section is for the steam and condensate system of the pre-drying section to include at least one heating group, preferably 2 or more, with thermocompressors for heating the drying cylinders assigned to the heating group. In this way, in contrast to a cascade system, the drying performance of the drying cylinders in the heating group can be adjusted independently of the drying performance of the other heating groups. This is not the case with the cascade system and there is a dependency between the heating groups. When producing a sack kraft paper web, the drying performance of the drying cylinders can be adjusted.

The sack kraft paper webs are known to be produced using a so-called "extensible unit", for example known as a Clupak unit, as a compression device with an elastic band, through which the still wet sack kraft paper web is creped in order to improve its stretch properties in the machine direction.

In an advantageous practical embodiment, the compression device in the paper machine can be suitable for compressing the sack kraft paper web in the machine direction and/or in the transverse direction.

In an advantageous practical embodiment, the sack kraft paper web is cut a first time at a first cutting group and a second time by at least one further second cutting group. The first cutting group preferably cuts the sack kraft paper web into at least two sack kraft paper partial webs lying next to one another in the transverse direction and the second cutting group in particular preferably cuts the sack kraft paper web or the sack kraft paper partial webs at the web edge for a web edge trim and/or for cutting out at least one transfer strip.

Advantageously, both, preferably the first and second, cutting groups can be controlled independently of each other and enable several operating states in which only one cutting group cuts the sack kraft paper web or sack kraft paper partial webs or the cutting groups cut alternately or both cutting groups cut simultaneously.

Advantageously, this has the advantage of having a positive effect, i.e. reducing, on the dust load caused by the different positions of the division of the paper webs or the web edges. The dust load depends on the dry content of the paper web, with increasing dry content leading to increased dust formation. Furthermore, the location of the dust formation can advantageously be located in areas that allow controlled ventilation and extraction, preferably extraction. An appropriate selection of the type of cutting element also influences the dust load caused, as well as usually the quality of the separating edges.

In another advantageous practical design variant, the first cutting group cuts the sack kraft paper web before the compression device.

In a further advantageous practical embodiment, the first cutting group cuts the sack kraft paper web after the compression device, in particular and before substantially half of the length in the machine direction of the after-drying section, preferably for dividing the sack kraft paper web into fibrous partial webs, in particular sack kraft paper partial webs.

This can be advantageous in cramped structural conditions.

In a further advantageous practical embodiment, the second cutting group cuts the sack kraft paper web or the sack kraft paper partial webs after essentially half the length in the machine direction of the after-drying section and before winding, preferably at a web edge and/or to cut out a transfer strip.

In a further advantageous practical embodiment, it can be provided that a transfer device is arranged after the pre-drying section and is designed to be suitable for transferring the paper web into the compression device or into the cutting group. The transfer device can be automated or manually operated. It can be designed with a cable guide for transferring the paper web. The transfer device can comprise steering and/or transport elements for steering and transporting the paper web into the respective cable guide. The steering and/or transport elements can be designed to be pivotable.

In a further alternative embodiment, the sack kraft paper web is cut into at least two, in particular three, in particular preferably four, sack kraft paper partial webs at the at least one first cutting group. The at least one cut is carried out at the at least one cutting element arranged in the transverse direction and included in the cutting group.

Advantageously, for example, several, in particular adjustable cutting elements for different cuts can be attached in a cutting group.

The "cutting elements" are the cutting elements or cutting means usually used in paper machines and can be, for example, solid cutting elements, in particular knives and/or rotating circular knife disks. The cutting elements can also come from the group of liquids and/or gases and/or solids, which usually include water, air or dry ice. Furthermore, cutting elements in the form of lasers can cut the sack kraft paper web and/or sack kraft paper partial webs.

In a further alternative embodiment, the sack kraft paper web is cut simultaneously by at least two cutting groups.

Advantageously, the division into sack kraft paper webs can be carried out by the first cutting group and the second cutting group can cut a Cut edge trimmings or a transfer strip from the sack kraft paper webs.

In a further alternative embodiment, the at least one first cutting group cuts the sack kraft paper web, into sack kraft paper partial webs, with a dry content of the fibrous web, in particular the sack kraft paper web, of at least 60%, in particular at least 63%, particularly preferably at least 65%.

Advantageously, from the dry content values onwards, there is already a sufficiently stable sack kraft paper web for a cut and it is only in this area that the greatest possible effect of the cut made on the elongation values of the sack kraft paper partial webs becomes apparent.

Dry contents of the fibrous web of at least 60% are achieved by a longer drying section in the pre-drying section than in the post-drying section.

The definition of "dry matter content" commonly used in paper machines is the ratio of dry matter to wet matter.

In a further alternative embodiment, the at least two sack kraft paper partial webs have a minimum elongation in the machine direction and/or transverse direction of greater than 3%, in particular greater than 5%, particularly preferably greater than 7%.

Advantageously, the minimum elongation value achieved by the cut sack kraft paper partial webs when reaching the roll-up is above this elongation value and the strength potential of the cut or split sack kraft paper partial web is above the elongation value of the uncut sack kraft paper web.

In a further alternative embodiment, the number of cuts is selected such that the at least one minimum elongation value of the at least two partial sack kraft paper webs on the roll-up has a multiple of at least 1.2, in particular at least 2.0, in particular preferably 3.0, of the minimum elongation value of the undivided sack kraft paper web.

Advantageously, the minimum stretch value of the sack kraft paper webs increases with an increasing number of cuts in the machine direction. The desired stretch value of the sack kraft paper web can thus be set by the number of cuts.

In a further alternative embodiment, the at least two divided sack kraft paper webs are wound onto a winding core that is continuous in the transverse direction.

Advantageously, by using only one winding core, the winding can be retained in its usual, undivided design.

In a further alternative embodiment, the at least two divided sack kraft paper webs are wound onto several winding cores, in particular those divided from one another in the transverse direction. A separate winding core is assigned to each corresponding paper web and these are wound up into so-called finished shipping rolls.

Preferably, ready-made shipping rolls can be wound up in the desired end widths and a downstream roll cutting machine and thus a further work step can be dispensed with. The quality of the finished shipping rolls can be further increased by trimming the edges in the second cutting group. At least one defined transfer strip can also be cut out, which ensures a safe, positionally stable and reliable transfer.

1. a) die erste Schneidegruppe in eine Warteposition gefahren wird und die Sackkraftpapierbahn, nicht mehr in Sackkraftpapierbahnen, schneidet,
2. b) die zweite Schneidegruppe in eine Schneideposition gefahren wird, und
3. c) die zweite Schneidegruppe mit mindestens einem Schneideelement mindestens einen Überführstreifen aus einem Randbereich der Sackkraftpapierbahn herausschneidet

A method for transferring the sack kraft paper web or partial sack kraft paper webs produced according to the invention from the after-drying section to being rolled up is characterized in that:

1. a) the first cutting group is moved to a waiting position and cuts the sack kraft paper web, no longer in sack kraft paper webs,
2. b) the second cutting group is moved into a cutting position, and
3. c) the second cutting group with at least one cutting element cuts out a transfer strip from an edge area of the sack kraft paper web

In a further alternative embodiment, step c) is alternatively replaced by step d) and the second cutting group with at least two cutting elements cuts at least one transfer strip out of the sack kraft paper web. Advantageously, one transfer strip is cut out with two cuts and thus with at least two cutting elements. The transfer strip has a fixed width and a precisely determined position. The width and position of the transfer strip can be taken from the machine control and corresponds to the respective position of the cutting elements. This can enable safe and reliable transfer of the sack kraft paper web in all operating states. Another advantage is that the transfer strip can be cut out in the edge area of the paper web and/or the middle. This allows a high degree of flexibility in the process.

• e) die zweite Schneidegruppe in Warteposition gefahren wird und die Sackkraftpapierbahn nicht mehr schneidet, und
• f) die erste Schneidegruppe in Schneideposition gefahren und
• g) die erste Schneidegruppe mit dem mindestens einem Schneideelement die Sackkraftpapierbahn in Maschinenlaufrichtung schneidet und zu mindestens zwei, in Querrichtung nebeneinander liegende Sackkraftpapierteilbahnen teilt.

In a further alternative embodiment, after the at least one transfer strip of the sack kraft paper web has been transferred from the after-drying section to the roll-up, it is characterized in that

• e) the second cutting group is moved to the waiting position and the sack kraft paper web no longer cuts, and
• f) the first cutting group moved into the cutting position and
• g) the first cutting group with the at least one cutting element cuts the sack kraft paper web in the machine direction and divides it into at least two sack kraft paper partial webs lying next to one another in the transverse direction.

• h) die zweite Schneidegruppe in Schneideposition gefahren, und
• i) die zweite Schneidegruppeschneidet mit den mindestens zwei Schneideelementen an mindestens zwei Papierrandkanten der mindestens zwei Sackkraftpapierteilbahnen mindestens eine Randkante in Maschinenlaufrichtung ab.

In a further alternative embodiment, at the same time as the first cutting group

• h) the second cutting group moved into the cutting position, and
• i) the second cutting group cuts with the at least two cutting elements at least one edge edge in the machine direction on at least two paper edge edges of the at least two sack kraft paper partial webs.

The paper machine according to the invention for producing a sack kraft paper web is characterized in that the paper machine is suitable for carrying out the method according to the independent method claim and the preceding subclaims.

In a further alternative embodiment, the paper machine is characterized in that after the pre-drying section and before substantially half of the after-drying section in the machine direction, at least one first cutting group for cutting in the machine direction or longitudinally cutting the sack kraft paper web is arranged.

In a further alternative embodiment, the paper machine is characterized in that the first cutting group is arranged after the compression device and before essentially half of the length in the machine direction of the after-drying section. In other words, the first cutting group in the drying section, which is made up of the pre-drying section and the after-drying section, is arranged after the compression device and thus in the context of the entire drying section from a length greater than 50% of the drying section, preferably greater than 55%, in particular greater than 60% and before half of the after-drying section, and thus less than or equal to 80% of a length of the drying section, preferably less than 77.5%, in particular less than or equal to 75%.

Advantageously, in this arrangement the fibrous web is cut at a dry content of at least 60%.

In a further alternative embodiment, the paper machine is characterized in that after the pre-drying section and before the reeling, at least one first cutting group and at least one second cutting group are arranged in the machine direction.

In a further alternative embodiment, the paper machine is characterized in that the second cutting group is arranged in the machine running direction, after essentially half the length of the after-drying section and before the winding up.

In a further alternative embodiment, the paper machine is characterized in that the at least one cutting group comprises at least one cutting element in the transverse direction.

In a further alternative embodiment, the paper machine is characterized in that the at least one cutting group comprises at least one cutting element that is adjustable in the transverse direction.

In a further alternative embodiment, the paper machine is characterized in that the compression device is suitable for compressing the sack kraft paper web in the machine direction and/or in the transverse direction.

Advantageously, the compression device is suitable for increasing the elongation in the machine direction and/or the minimum elongation value in the transverse direction by suitable means included in the compression device.

The invention also expressly extends to those embodiments which are not given by combinations of features from explicit references to the claims, with which the disclosed features of the invention can be combined with one another - to the extent that this makes technical sense.

Corresponding elements of the exemplary embodiments in the figures are provided with the same reference numbers. The functions of such elements in the individual figures correspond to one another unless otherwise described and this does not lead to contradictions. A repeated description is therefore omitted.

It is also pointed out that the differing features of the embodiments shown can be exchanged for one another and combined with one another. The invention is therefore not limited to the combinations of features shown in the embodiments shown.

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

Fig.1

Seitenansicht einer erfindungsgemäßen Papiermaschine in vereinfachter Darstellung

Fig.2

Vergrößerte Seitenansicht der Figur 1 ab der Überführvorrichtung aus der Vortrockenpartie bis zur Aufrollung in vereinfachter Darstellung

Fig.3a-c

Schematische Diagramme von Dehnungsverläufen über der Querrichtung der Sackkraftpapierbahn und/oder der Sackkraftpapierteilbahnen für verschiedene alternative Ausführungsformen

Fig.4a-d

Vereinfachte Draufsicht auf eine Sackkraftpapierbahn in der Darstellung der Papiermaschine aus Figur 2 und den Schneidegruppen in verschiedenen Betriebszuständen und alternativen Ausführungsformen

The invention is explained below with reference to figures. The figures show in detail:

Fig.1

Side view of a paper machine according to the invention in a simplified representation

Fig.2

Enlarged side view of the Figure 1 from the transfer device from the pre-drying section to the roll-up in a simplified representation

Fig.3a-c

Schematic diagrams of expansion curves over the transverse direction of the sack kraft paper web and/or the sack kraft paper partial webs for various alternative embodiments

Fig.4a-d

Simplified top view of a sack kraft paper web in the illustration of the paper machine Figure 2 and the cutting groups in various operating states and alternative embodiments

Figure 1 to 4 refer to a common coordinate system, where MD indicates the machine direction or the main direction of movement of the sack kraft paper partial webs 2 and the sack kraft paper partial webs 2.1, 2.2, 2.3, CD indicates the transverse direction of the paper web, the paper partial webs or the paper machine 1 and z is the third axis in a right-handed coordinate system.

Figure 1 shows an exemplary embodiment of a paper machine 1 according to the invention in a simplified representation. The paper machine 1 shown is suitable for producing a sack kraft paper partial web 2 and/or at least two strength-increased sack kraft paper partial webs 2.1, 2.2, 2.3, in particular marked with an increased minimum elongation value in the machine direction MD and/or in the transverse direction CD.

A fibrous suspension is introduced through a headbox into the forming section 3, which is designed as a fourdrinier wire, where it is drained and a sack kraft paper partial web 2 is formed. The forming section is used to form and dewater the paper web, which is preferably designed as a fourdrinier wire, and in which a fiber suspension is added through a headbox, which is dewatered there and a sack kraft paper web is formed. The headbox is fed by a fibrous suspension which has essentially the same consistency and therefore the same properties in the transverse direction. The headbox applies the fibrous suspension as a single-layer paper web.

A press section 4 then follows in the machine running direction MD. In this example, it comprises two individual press nips, both of which are designed as press nips with an extended press gap, in this case two shoe press nips. The paper web 2 is then dried in the pre-drying section 5.1 of the drying section 5. In this exemplary embodiment, it has at least one single-row drying group at the beginning, in which the paper web 2 is guided alternately around drying cylinders 6 and guide rollers 7. This is followed by two rows of drying groups, with the paper web 2 being guided alternately around drying cylinders. The paper web 2 runs in a meandering shape around steam-heated drying cylinders 6 and around guide rollers 7 and comes into direct contact with the drying cylinders 6. The pre-drying section 5.1 is enclosed with a hood 8. Other configurations of the drying groups can also be used.

After the pre-drying section 5.1, a compression device 10 is arranged for compressing the sack kraft paper web. In this example, the compression device 10 is arranged above the basement 15 of the paper machine 1. The compression device 10 can advantageously be compressed in the machine direction MD and/or in the transverse direction CD, increase the elongation D of the sack kraft paper sections 2 or the sack kraft paper sections 2.1, 2.2, 2.3. Seen in the machine direction MD, a transfer device 12 is provided in front of the compression device 10, with which it is possible to guide the sack kraft paper partial webs 2 through the compression device 10. For this purpose, the transfer device 12 includes steering and/or transport elements for steering and transporting the paper web into the respective cable guide. According to the invention, after the pre-drying section 5.1, at least one first cutting group 20.1, 20.2 is arranged for cutting in the machine direction MD, in particular longitudinal cutting, of the sack kraft paper partial webs 2 into sack kraft paper partial webs 2.1, 2.2, 2.3 that are divided from one another. This is followed by a post-drying section 5.2 in which the sack kraft paper partial webs 2 extending over the entire transverse direction CD and/or the cut sack kraft paper partial webs 2.1, 2.2, 2.3 lying next to one another in the transverse direction are dried to the desired final dryness content.

The after-drying section is also enclosed with a hood 8. In this example, the after-drying section 5.2 only includes two-row drying groups, but can only include single-row drying groups or one- and two-row drying groups. The first four upper drying cylinders 6 of the after-drying section 5.2 are not wrapped around a drying fabric. This means that the paper web 2 is not covered. This enables the use of impingement flow dryers 17 to further increase the expansion in the transverse direction CD in the production of sack kraft paper webs 2 and/or sack kraft paper partial webs 2.1, 2.2, 2.3.

The entire length of the dryer section 5 is in Fig.1 divided into a pre-drying section 5.1 and a post-drying section 5.2, the larger part of the length is included in the pre-drying section 5.1.

For example, as in the Fig.1 shown, the pre-drying section 5.1 comprises approximately 60% of the total length of the drying section 5 and the post-drying section 5.2 approximately 40%.

Successful cutting of the sack kraft paper webs 2 with an advantageous increase in the minimum elongation values Dmin of the sack kraft paper webs 2.1, 2.2, 2.3 only takes place when the sack kraft paper web 2 undergoes a first cut a dry content of at least 60% is cut or divided, or in other words, the sack kraft paper web 2 is dried in the drying section 5 over a drying section of more than 50%, preferably more than 55%, preferably more than 60%, of the total drying section length of the machine 1 becomes. The sack kraft paper partial webs 2 or the sack kraft paper partial webs 2.1, 2.2, 2.3 are then rolled up onto a, in particular continuous, winding core 22.

In an alternative embodiment, which in Figure 1 is not shown, it is also conceivable that alternatively there are several winding cores divided in the transverse direction CD, in particular separate ones, with the same axis of rotation. Ideally, in this alternative embodiment, the number of divided winding cores corresponds to the number of sack kraft paper partial webs 2.1, 2.2, 2.3 produced. It is therefore advantageously conceivable that the paper partial webs 2.1, 2.2, 2.3 are wound directly in the desired final widths on so-called finished shipping rolls and thus do not require any further processing by one or more roll cutting devices (not shown).

In an alternative embodiment, the paper machine comprises a further, second cutting group 20.2 for cutting in the machine direction MD, in particular longitudinally, the sack kraft paper partial webs 2 and/or the sack kraft paper partial webs 2.1, 2.2, 2.3. The second cutting group 20.2 is arranged between the second half of the after-drying section and in front of the reel 9. The second cutting group 20.2 is advantageously used for cutting out at least one transfer strip 24 from and/or for trimming the web edge or edge trimming the web edge 23 of the respective sack kraft paper partial webs 2 or the respective sack kraft paper partial webs 2.1, 2.2, 2.3.

Figure 1 further shows various alternative embodiments of the arrangement or position of the first cutting group 20.1 and the second cutting group 20.2. In a first position, the first cutting group 20.1 carries out the cut in the machine direction for division into sack kraft paper webs advantageously after the upsetting device and before the post-drying section.

In a further alternative embodiment, the at least one first cutting group 20.1 is advantageously positioned in front of the upsetting device 10 in order to advantageous to further increase the elongation D in the transverse direction CD by means of the compression device in CD.

In a further alternative embodiment, the at least one first cutting group 20.1 is arranged in the first half of the length of the after-drying section 5.2. The arrangement is advantageously adapted to the paper web 2 based on the existing dry content of the sack kraft paper web of at least 60%, in particular 63%, in particular preferably 65%, for an advantageous effect of the cut carried out on the transverse expansion CD of the sack kraft paper partial webs.

The second cutting group 20.2 can advantageously be arranged between essentially half the length in machine direction MD of the after-drying section 5.2 and the reel 9, since here only a small change in the web width of the paper web or sack kraft paper partial web occurs due to the dry contents achieved.

Figure 2 shows an enlarged view of the Figure 1 from the transfer device 12, which follows the pre-drying section 5.1 in the machine direction MD, up to the reel 9.

Figure 3a-c show in schematic, qualitative diagrams expansion curves D over the transverse direction CD of the paper web 2 and/or the partial paper webs 2.1, 2.2, 2.3. The expansion curve D0 for an uncut sack kraft paper partial web 2 is shown qualitatively from one web edge 23 to the other web edge 23. This is characterized by the fact that the course resembles a "bathtub curve", which usually has maximum expansion values Dmax at the edges and in the central area in the transverse direction CD reaches a flat level, in particular a substantially constant level, with a minimum strain value Dmin. This is achieved by the drying sections 5 usually used and the web stabilization elements usually contained therein, such as suction boxes, drying screens or belts, which "hold" the not yet completely dried sack kraft paper webs 2 and only move in the transverse direction CD in the areas near the paper web edges or web edges, an increased elongation D is set up to a maximum elongation value D _max . As explained at the beginning, the expansion value D can also be influenced in its maximum height Dmax by influencing the stock preparation and the compression device 10. The strain profile D over the transverse direction CD is also characterized by its minimum strain value Dmin. Alternatively, other characteristic values such as the mean value of the elongation, which is formed as an integral of the elongation curve over the transverse direction CD divided by the width of the paper web, or the arithmetic mean value, can also be used for the determination. The maximum achievable elongation value Dmax is usually in the edge areas of the paper web 2 or. the paper sections 2.1, 2.2, 2.3.

Figure 3a further shows another, dotted, schematic, qualitative stretching curve D1, D2. It is assumed, for example, that the sack kraft paper partial webs 2 are cut or divided by a first cut on the cutting element 21.1, which is included in at least one cutting group 20.1, 20.2, and two sack kraft paper partial webs 2.1, 2.2 are formed. The cut or division into two paper partial webs 2.1, 2.2 and the associated reduced holding force of the paper partial web in the post-drying section 5.2 results in an increased stretching curve D1, D2 compared to D0. The minimum elongation value Dimin and/or D2min of the two partial paper webs, when cut with a cutting element 21.1 into two partial paper webs 2.1, 2.2, has a multiple A1, A2 compared to the initial value of the minimum elongation value D0min of the undivided sack kraft paper partial webs 2.

The maximum elongation value Dmax of the elongation curve D0 achieved in the edge area can be exceeded by the maximum elongation value D1max and/or D2max of the elongation curves D1, D2, especially if further settings in the compression device 10 or in the fiber suspension in the headbox are changed. Not shown here, alternatively the elongation value of the paper webs 2.1, 2.2 at the cut 21.1 may not reach the maximum elongation value D1max and D2max of the outer web edges 23 and thus cause a develop an asymmetrical course, this is mainly due to the advanced drying in the machine sections before the first cutting group 20.1.

As in Figure 3b However, it is also conceivable that the maximum elongation value D1max and/or D2max of the elongation curve D1, D2 of the paper partial web 2.1, 2.2 is essentially equivalent to the initial value Dmax. It is also conceivable, but not shown, that in the area of the cut 21.1 and/or the outer web edge 23 of the sack kraft paper partial webs 2, the achieved maximum elongation value D1max, D2max of the elongation curve D1, D2 of the sack kraft paper partial web 2.1, 2.2 remains below the original maximum elongation value Dmax. The division into sack kraft paper partial webs does not influence the gradient in the edge area of the sack kraft paper partial webs or only influences it slightly by the multiple A1, A2 of the minimum elongation value.

Figure 3c shows analogously to Figure 3a and 3b another, schematic, qualitative expansion curve D1, D2, D3 shown in dotted lines. It is assumed, for example, that the sack kraft paper partial webs 2 are cut or divided by two cutting elements 21.1, 21.2, which are included in at least one cutting group 20.1, 20.2, and three sack kraft paper partial webs 2.1, 2.2, 2.3 are formed. The holding force is compared to the cuts or divisions into three partial paper webs 2.1, 2.2, 2.3 Figure 3a and 3b further reduced and a larger multiple A1, A3 of the minimum elongation D1min, D3min occurs compared to D2min. It is conceivable that the achieved multiples A1, A2, A3 of the partial paper webs are different, in particular if the cutting elements cut the partial paper webs in different widths in the transverse direction CD. As in Figure 3c shown, the multiple A2 of the paper web 2.2 is less than the multiple A1, A3 of the paper webs 2.1, 2.3. The multiple A1, A2, A3 with two cutting elements usually exceeds the multiple A1, A2 with only one cutting element 21.1 (shown in Figure 3b ). It can be said that as the number of cutting elements 21.1, 21.2, 21.3, 21.4, 21.5, 21.6 increases Minimum elongation value Dmin of the paper webs 2.1, 2.2, 2.3 increases until a limit value, in particular the maximum elongation value Dmax, is reached. It can be deduced from this that with a reduced width in the transverse direction CD of the paper webs and an increased number of cuts, the minimum elongation Dmin in the paper webs increases. The prerequisite here is that the settings and boundary conditions of the previous machine sections of the paper machine 1 remain the same.

Figure 4a-d show a schematic, simplified top view of a sack kraft paper partial web 2 in the representation of the paper machine Figure 2 . The figures show various alternative embodiments of the paper machine in different operating states. The illustration includes a first cutting group 20.1 and a second cutting group 20.2 and the cutting elements 21.1, 21.2, 21.3, 21.4, 21.5, 21.6, each comprised by a cutting group, for cutting the paper web in the longitudinal direction or in the machine direction MD.

In all cases Figures 4a-d the sack kraft paper webs 2 coming from the pre-drying section 5.1 (not shown) and transfer device 12 (not shown) in the machine direction MD are shown. In the exemplary embodiments in Fig. 4a-d the paper web 2 runs through the compression device 10 and then passes the first cutting group 20.1; which here, for example, is located after the compression device 10 and before the after-drying section 5.2. The paper web 2 and/or partial paper web 2.1, 2.2, 2.3 is then dried in the after-drying section 5.2, which is shown here in abbreviated form. The after-drying section 5.2 is followed by the second cutting group 20.2. The second cutting group 20.2 is followed by the winding up 9, whereby the paper web 2, 2.1, 2.2, 2.3 is rolled up or wound onto at least one winding core 22. The reduction in the paper web width in the machine direction MD is caused by the progressive increase in the dry content of the paper web in the after-drying section 5.2 and is represented by the schematically sketched course of the web edge 23 of the paper web 2, 2.1, 2.2, 2.3. For example, as explained below, Figures 4a , the change of the output width in Cross direction CD of the paper web 2 at the inlet of the after-dryer section 5.2 up to the exit of the paper web 2 in machine direction MD.

Figure 4a shows an example configuration during the operating state of transferring the sack kraft paper partial webs 2 from the after-drying section 5.2 to the reel 9 onto a new, empty winding core 22. The paper machine is usually already at full production speed and the preceding winding core has been wound up or rolled up to the desired winding diameter with a sack kraft paper partial web 2 or sack kraft paper partial webs 2.1, 2.2, 2.3 and the new, empty winding core 22 has been prepared. The first cutting group 20.1 is moved to the "waiting position" and does not cut the sack kraft paper partial webs 2. The second cutting group 20.2 is moved to the "cutting position" and uses the cutting elements 21.1, 21.2 to cut a transfer strip 24 with a defined width from the sack kraft paper web 2. This is particularly advantageous each time the new, empty winding core 22 is changed, since the two cutting elements can keep a fixed, defined width and position constant and thus the transfer conditions remain constant. The transfer strip 24 is transferred to the new winding core in a transfer device provided for this purpose (not shown), and the remaining part of the sack kraft paper web 2 that is not currently required is recirculated and fed back into the material preparation.

The divided transfer strip 24 is advantageously located in the edge region of the sack kraft paper sections 2 or the edge regions of the sack kraft paper sections. In a further advantageous embodiment, the transfer strip 24 can also be advantageously separated from the center of the web of sack kraft paper or the partial webs of sack kraft paper.

In an alternative embodiment, it is also conceivable that only one cutting element 21.1 divides the transfer strip 24 out of the paper web 2, preferably in the edge region of the paper web 2.

Figure 4b shows a possible configuration in the operating state for the production of sack kraft paper webs. After successful transfer, the second Cutting group 20.2 is moved to the "waiting position" and the paper web 2 is not cut. The first cutting group 20.1 is moved to the "cutting position" and the two cutting elements 21.1, 21.2 shown as examples cut the sack kraft paper webs 2 into three, preferably equally wide, sack kraft paper webs 2.1, 2.2, 2.3. It is also conceivable that the cutting elements divide the paper web into unequal or different width paper webs at different intervals. In particular, it is advantageous if the cutting elements 21.1, 21.2, 21.3, 21.4, 21.5, 21.6 are mounted within the cutting groups 20.1, 20.2 so that they can be adjusted in the transverse direction CD, in particular in axially movable guide rails. It is also advantageous to automatically adjust the cutting elements using linear actuators.

The Figure 4b In an alternative embodiment, the one-piece, continuous winding core 22 shown can have three, in particular several, winding cores divided in the transverse direction with the same axis of rotation. Ideally, in this alternative embodiment, the number of divided winding cores corresponds to the number of sack kraft paper partial webs 2.1, 2.2, 2.3 produced. This advantageously makes it conceivable that the paper partial webs 2.1, 2.2, 2.3 are wound directly in the desired final widths on so-called finished shipping rolls and thus do not require any further processing by one or more roll cutting devices (not shown).

Figure 4c also shows a possible alternative configuration in the edge trimming operating state. After the successful transfer, the second cutting group 20.2 remains in the "waiting position" for a short time, preferably less than 10 seconds; this is required to adjust the cutting elements 21.1, 21.2 to a new position in the transverse direction CD. In the exemplary embodiment, the second cutting group 20.2 comprises six cutting elements 21.1, 21.2, 21.3, 21.4, 21.5, 21.6, which, after the position in the transverse direction CD has been correctly set, cut the sack kraft paper partial webs 2.1, 2.2, 2.3 at the same time as the first cutting group 20.1 with the cutting elements 21.1, 21.2, which is already in the "cutting position".

This advantageously enables the edge edges 23 of the partial paper webs 2.1, 2.2, 2.3 to be trimmed before they are wound up in the reel 9.

Figure 4d also shows a possible alternative configuration in the transfer operating state. Based on the operating state of the Figure 4c a transfer strip 24 is cut or divided out of each paper web part 2.1, 2.2, 2.3 and transferred to or onto the new, empty winding core. This is particularly advantageous in an alternative embodiment when the paper web parts are wound onto several winding cores divided in the transverse direction with the same axis of rotation.

The term “waiting position” means that the cutting groups 20.1, 20.2 do not cut the sack kraft paper web and/or sack kraft paper sub-webs. This can be done by extending, in particular, moving and/or pivoting the cutting groups 20.1, 20.2 and/or the included cutting elements 21.1, 21.2, 21.3, 21.4, 21.5, 21.6 or alternatively by deactivating or switching off the cutting elements.

“Cutting position” is understood to mean a position opposite to the waiting position, which cuts the paper web and/or partial paper webs through the cutting group 20.1, 20.2 on the included cutting elements 21.1, 21.2, 21.3, 21.4, 21.5, 21.6.

List of reference symbols

1

Paper machine

2

Sack kraft paper web

2.1, 2.2, 2.3

Sack kraft paper web(s)

3

forming section

4

Press section

5

Dry section

5.1

Pre-drying section

5.2

Night drying section

6

Drying cylinder

7

Guide rollers

8th

Hood

9

Rolling up

10

Upsetting device

12

Transfer device

13

Operating level

14

foundation

15

basement, cellar

16

Machine direction

17

Impingement dryer

20.1

First cutting group

20.2

Second cutting group

21.1, 21.2, 21.3, 21.4, 21.5, 21.6

Cutting elements in the transverse direction within a cutting group

22

winding core

23

Sack kraft paper web edge

24

Transfer strip

A1, A2, A3

Multiple of the strain value D0min

D

Stretching of the sack kraft paper web

D0, D1, D2, D3

Strain progression in transverse direction

Dmin

Minimum stretch level in the transverse direction of the paper web

Dmax

Maximum level of stretch in the transverse direction of the paper web

MD

Machine direction

CD

Transverse direction

z

z direction

Claims (15)

1. Method for producing a bag-type kraft paper web (2) using a paper machine (1) comprising a forming section (3) for forming and dewatering the paper web (2), a pressing section (4) and a drying section (5) having a pre-drying section (5.1) and a post-drying section (5.2) for further dewatering the bag-type kraft paper web (2), and a reel (9), wherein a compression device (10) for compressing the bag-type kraft paper web (2) is disposed between the pre-drying section (5.1) and the post-drying section (5.2), characterized in that
   the bag-type kraft paper web (2) after the pre-drying section (5.1) and before the reel (9) is imparted at least one cut in the machine running direction (MD) by at least one first cutting unit (20.1, 20.2), and is divided into at least two bag-type kraft paper partial webs (2.1, 2.2, 2.3) which lie next to one another in the cross direction (CD), so that at least one minimum elongation value (D1min, D2min, D3min) in the cross direction (CD) of the at least two bag-type kraft paper partial webs (2.1, 2.2, 2.3) before reaching the reel (9) is influenced by the cut in such a way that the minimum elongation value (D1min, D2min, D3min) is higher than a minimum elongation value (DOmin) of the undivided bag-type kraft paper web (2).
2. Method according to Claim 1,
   characterized in that
   the at least one first cutting unit (20.1) cuts the bag-type kraft paper web (2) a first time, preferably for dividing into bag-type kraft paper partial webs (2.1, 2.2, 2.3), and at least one further, second cutting unit (20.2) cuts the bag-type kraft paper web (2) or the bag-type kraft paper partial webs (2.1, 2.2, 2.3) a second time, preferably for trimming at least one web peripheral edge (23) and/or for cutting out a transfer tail (24) .
3. Method according to Claim 1,
   characterized in that
   the first cutting unit (20.1) cuts the bag-type kraft paper web (2) before the compression device (10) .
4. Method according to Claim 1,
   characterized in that
   the first cutting unit (20.1) cuts the bag-type kraft paper web (2) after the compression device (10) and before substantially half the length in the machine running direction (MD) of the post-drying section (5.2).
5. Method according to Claim 2,
   characterized in that
   the second cutting unit (20.2) cuts the bag-type kraft paper web (2), or the bag-type kraft paper partial webs (2.1, 2.2, 2.3) after substantially half the length in the machine running direction (MD) of the post-drying section (5.2) and before the reel (9).
6. Method according to one of the preceding claims, characterized in that
   the at least one first cutting unit (20.1, 20.2), by way of at least one cutting element (21.1, 21.2, 21.3, 21.4, 21.5, 21.6) disposed in the cross direction (CD), cuts the bag-type kraft paper web (2) into at least two, in particular three, in particular preferably four, bag-type kraft paper partial webs (2.1, 2.2, 2.3).
7. Method according to Claim 2,
   characterized in that
   the first cutting unit (20.1) and the second cutting unit (20.2) simultaneously cut the bag-type kraft paper web (2).
8. Method according to one of the preceding claims, characterized in that
   the bag-type kraft paper web (2) is cut by the at least one first cutting unit (20.1, 20.2) at a dry content of the bag-type kraft paper web (2) of at least 60%, in particular at least 63%, particularly preferably at least 65%.
9. Method according to one of the preceding claims, characterized in that
   the number of cuts is chosen in such a way that the at least one minimum elongation value (D1min, D2min, D3min) in the machine running direction (MD) and/or in the cross direction (CD) of the at least two bag-type kraft paper partial webs (2.1, 2.2, 2.3) at the reel (9) has a value of more than 3%, in particular of more than 5%, particularly preferably of more than 7%.
10. Method according to one of the preceding claims, characterized in that
    the number of cuts is chosen in such a way that the at least one minimum elongation value (D1min, D2min, D3min) in the machine running direction (MD) and/or in the cross direction (CD) of the at least two bag-type kraft paper partial webs (2.1, 2.2, 2.3) at the reel (9) is a multiple of at least 1.06, in particular at least 1.1, particularly preferably 1.5, times the minimum elongation value (DOmin) of the undivided bag-type kraft paper web (2).
11. Method according to one of the preceding claims, characterized in that
    the at least two bag-type kraft paper partial webs (2.1, 2.2, 2.3) are wound onto a winding core (22) which is continuous in the cross direction (CD), or wound onto a plurality of winding cores which are in particular separated from one another in the cross direction (CD).
12. Method according to Claim 2,
    characterized in that

    a) the first cutting unit (20.1) is moved to a standby position and does not cut the bag-type kraft paper web (2);

    b) the second cutting unit (20.2) is moved to a cutting position; and

    c) the second cutting unit (20.2) by way of at least one cutting element (21.1, 21.2, 21.3, 21.4, 21.5, 21.6) cuts at least one transfer tail (24) out of a peripheral region of the bag-type kraft paper web (2); or

    d) the second cutting unit (20.2) by way of at least two cutting elements (21.1, 21.2, 21.3, 21.4, 21.5, 21.6) cuts at least one transfer tail (24) out of the bag-type kraft paper web (2); and
    after transferring the at least one transfer tail (24) of the bag-type kraft paper web (2) from the post-drying section (5.2) to the reel (9)

    e) the second cutting unit (20.2) is moved to the standby position and no longer cuts transfer tails (24) out of the bag-type kraft paper web (2); and

    f) the first cutting unit (20.1) is moved to the cutting position; and

    g) the first cutting unit (20.1) by way of the at least one cutting element (21.1, 21.2, 21.3, 21.4, 21.5, 21.6) cuts the bag-type kraft paper web (2) in the machine running direction (MD) and divides said bag-type kraft paper web (2) into at least two bag-type kraft paper partial webs (2.1, 2.2, 2.3) which lie next to one another in the cross direction (CD); and

    h) the second cutting unit (20.2) is again moved to the cutting position; and

    i) the second cutting unit (20.2) by way of the at least two cutting elements (21.1, 21.2, 21.3, 21.4, 21.5, 21.6) on at least two paper peripheral edges (23) of the at least two bag-type kraft paper partial webs (2.1, 2.2, 2.3) cuts off at least one peripheral edge in the machine running direction (MD) .
13. Paper machine (1) for producing a bag-type kraft paper web (2),
    characterized in that
    the paper machine (1) is configured to carry out the method according to one of the preceding claims.
14. Paper machine (1) according to Claim 13, characterized in that
    at least one first cutting unit (20.1) for cutting the bag-type kraft paper web (2) in the machine running direction (MD) is disposed after the pre-drying section (5.1), in particular after the compression device (10) and before substantially half the post-drying section (5.2) in the machine running direction (MD).
15. Paper machine (1) according to Claim 14, characterized in that
    a first cutting unit (20.1) and at least one second cutting unit (20.2) are disposed in the machine running direction (MD) after the pre-drying section (5.1) and before the reel (9).

Images