EP1016754B1 - Machine and method for the manufacture of a fibrous web - Google Patents

Abstract

Between a shoe-pressing unit (14) and a dry/tissue cylinder (16) there is a pressed gap (12), the length (L) of which, when considered in the direction (I) a ribbon runs, is greater than a value of about 80 mm and, preferably, smaller than 200 mm, and 150 mm at most. A pressure profiled section in the pressed gap that results from the length of the pressed gap has a maximum pressing pressure less than or equal to, a value of about 2 MPa. An independent claim is also included for a method producing strips of fibrous material, especially strips of tissue and sanitary paper.

Description

The invention relates to a machine for producing a fibrous web, in particular tissue or tissue paper web, with at least one press nip formed between a shoe press unit and a dryer or tissue cylinder, through which a water-absorbing carrier tape, a water-impermeable press belt and the fibrous web are passed.

In the DE-A-42 24 730 Several embodiments of a machine of the type mentioned are described. In each case at least two press gaps are provided in all embodiments. The main press, as viewed in the direction of web travel, comprises a drying cylinder and an associated pressing element. As such a pressing element may be provided a suction press roll or a shoe press roll.

Even with one from the DE-A-196 54 197 known machine of the type mentioned again two press nips are provided. The rear main press is formed by a shoe press unit and a drying cylinder.

From the EP 0 289 477 Furthermore, a paper machine is known in which two or more press nips are formed on a heated cylinder, wherein one of the at least two press nips is formed by a shoe press.

In the known machines thus always two or more press nips are provided. This is considered essential here on the one hand to achieve a gentle drainage, in particular in the manufacture of a tissue or tissue paper web, without displacement, and, on the other hand, to achieve improved production efficiency through an increased dry content after the press. It is achieved with the complete or partial replacement of the nip presses by shoe presses due to the corresponding gap extension or increase the pressing time gentle drainage of the web without displacements.

However, a major disadvantage of these known embodiments is now in terms of the achieved improvements relatively high investment and operating costs. Given the hitherto customary limitation of the maximum line force to a value in the range of 90 kN, e.g. For Yankee cylinders, it was always necessary in the known press concepts to provide at least two press nips.

The aim of the invention is to provide a machine of the type mentioned above, with which the highest possible dry content and / or specific volume can be achieved while avoiding the aforementioned disadvantages and while largely maintaining the quality characteristics required for the produced web.

At one in the EP-A2-0 852 273 described dewatering press one of the production of a paper and / or board web serving machine is the residence time of the web in an extended press nip less than 12 ms.

This object is achieved with respect to the machine according to the invention in that at least one between a Schuhpreßeinheit and the Dry or Tissue cylinder formed press nip is provided, considered in the web running direction length of My or equal to a value of about 60 mm and whose over the press nip length resulting pressure profile has a maximum pressing pressure which is greater than or equal to a value of about 3.3 MPa is.

With such a design, a substantial increase in both the dry content and the specific volume of the fibrous web is achieved completely unexpectedly. This is all the more surprising, as is left with the proposed solution of the previously embarked in the press development path whose objective was to effect the replacement of the nip presses by shoe presses with extended nip gentle, slow dewatering as a prerequisite for optimal results. Due to the construction according to the invention, for example, many tissue paper machines can now be realized with only a single shoe press nip.

In a preferred practical embodiment of the machine according to the invention, the press nip length is equal to or equal to a value of about 50 mm and the maximum press pressure is greater than or equal to a value of about 4.3 MPa. The press nip length is defined as the contact length between the drying cylinder and associated pressing element and continuous new carrier tape.

Here, the specific volume is also slightly increased. Such an increase may be for example about 5%. There is a significant increase in terms of dry content, which is particularly true in comparison to a press nip, by means of a Saugpreßwalze or is formed by a shoe press with a gap length of, for example, 120 mm. In this case, for example, an increase in dry content of about 2.5 to 3% is possible, assuming a constant line force of about 90 kN / m. Such a value must not be exceeded in the usual Yankee cylinders in view of a maximum allowable mechanical stress. The invention can therefore be used with particular advantage especially in conversions of existing presses. Thus, in spite of a respective linear force limitation, dry content increases as well as constant or higher values of the specific volume (bulk) can be achieved in comparison to conventional presses.

In a further expedient embodiment, the press nip length is in a range of about 37 mm and the maximum pressing pressure in a range of about 4.8 MPa.

In the case of short shoes, it has been found that the angle between the tangent applied to the drying or tissue cylinder at the end of the press nip and the carrier web leaving the press nip has a significant influence on the dry content of the tissue web. An advantageous embodiment is characterized in that, in particular for the production of a tissue web, this angle between the tangent applied to the drying or tissue cylinder at the end of the press nip and the carrier tape leaving the press nip is ≥ 10 °, in particular ≥ 18 ° and preferably ≥ 20 ° is. This results in comparison with applications with Saugpreßwalzen a dry content increase of about 1 to 3%. Here, the press belt is preferably grooved and / or blind drilled.

It may be advantageous if the residence time of the fibrous web in the press nip is greater than or equal to a value of, for example, about 3.5 ms and in particular greater than or equal to 4 ms. In this case, the residence time can be defined in particular by the ratio of gap or shoe length to the web speed.

For example, the maximum line force generated by the press nip may be in the range of about 90 to about 120 kN / m.

In an expedient practical embodiment of the inventive machine, the shoe press unit comprises a press shoe, which can be pressed against the drying cylinder via a plurality of contact elements arranged side by side transversely to the web running direction. Thus, a respective desired pressing force transverse profile can be adjusted to even out the web properties, in particular at the web edges.

As a drying cylinder, a creping cylinder, i. a so-called Yankee cylinder may be provided.

The pressure profile resulting over the press nip length is preferably asymmetrical.

The maximum pressing pressure is expediently in the rear half of the press nip length considered in the web running direction.

It is advantageous if the average pressure rise gradient in the section of the pressure profile extending from the gap beginning to the maximum pressing pressure at a new carrier tape is greater than or equal to a value of about 40 kPa / mm, in particular greater than or equal to about 60 kPa / mm and preferably greater or is equal to about 120 kPa / mm.

The average pressure drop gradient in the end region of the pressure profile is preferably greater than or equal to a value of about 300 kPa / mm, in particular greater than or equal to about 500, in the case of a new carrier tape kPa / mm and preferably greater than or equal to about 800 kPa / mm. The mean pressure drop gradient in the end region increases with increasing operating time of the felt. As a result, values of more than 1000 to more than 1600 kPa / m are achieved in a press nip of the invention.

In a preferred practical embodiment, the water-absorbing carrier tape is in the press nip between the water-impermeable press belt and the fibrous web, wherein the fibrous web contacts the drying cylinder.

As a water-absorbing carrier tape may be provided in particular a felt. Such a felt may have, for example, a weight per unit area equal to or equal to a value of about 1450 g / m ² . It is, for example, a specially structured felt in the manner of a bumped embossing screen or felt, ie a so-called "imprinting fabric" or "imprinting felt" (see, for example, US Pat WO98 / 00604 )) or a "patterning fabric" or "patterning felt" having a rough textured surface.

The water-absorbing carrier tape may have a different nature in the thickness direction. Thus, the fibrous web facing side of the carrier tape, for example, have a finer structure than its side facing away from the fibrous web page.

In an expedient practical embodiment, the press belt has a grooved and / or provided with blind holes surface, as for example in the DE-A-196 54 198 is described.

In principle, a further press nip can also be formed on the drying cylinder. It may be useful in certain applications, if at least two press gaps formed by a respective shoe press unit are provided on the drying cylinder. In principle, it is also conceivable to provide an additional press nip in the web running direction in front of the drying cylinder.

In an expedient practical embodiment of the inventive machine, the carrier tape and the fibrous web are guided in the web running direction in front of the drying cylinder via at least one suction device through which then a corresponding pre-dewatering takes place. In this case, expediently at least one suction device or suction box may be provided, which comprises a suction roll and / or a suction shoe.

In a preferred practical embodiment of the machine according to the invention, a shoe press roll is provided as the shoe press unit.

It is also advantageous if the shoe press unit comprises at least one exchangeable press shoe.

The substance input for the production of, for example, a tissue web can consist, for example, of "refined pulp". Here, the inventive press nip can be used particularly advantageous for dry content increase.

However, such a fabric feed serving, for example, for producing a tissue web may also consist of unground material. In this case, the inventive long press nip can be used particularly advantageously for increasing the specific volume.

The invention is also applicable for example for so-called "curled fibers". The stock suspension in this case contains a proportion of fibers which have been subjected to a special treatment. Here, the substantially linear or curved in a plane pulp fibers are curved so that a spatial fiber shape, for example, arises in the manner of a spiral.

The invention is particularly applicable to a tissue paper machine with at least one so-called "through-air-drying" drying process, wherein the press nip according to the invention is used in particular before a corresponding "through-air-drying" device. Such a combination is particularly advantageous in terms of a high dry content and a high specific volume. By virtue of the press nip of the invention, on the one hand, a high dry content is achieved, as a result of which the operating costs of the energy-intensive drying phase are reduced. On the other hand, the web is at most slightly compacted, which means that the specific volume of the web is increased or remains unaffected at higher pressures, which in particular, the "through-air-drying" drying process is more efficient and economical.

In particular, the invention is also applicable to the manufacture of multilayer webs using a single headbox or the manufacture of multilayer webs using multiple headboxes.

Figur 1

eine rein schematische Teildarstellung einer erfindungsgemäßen Schuhpresse mit einem zwischen einer Schuhpreßeinheit

Figur 2

presseinheit und einem Trockenzylinder gebildeten Pressspalt, den Pressdruckverlauf einer herkömmlichen Schuhpresse,

Figur 3

den Pressdruckverlauf einer beispielhaften Ausführungsform der erfindungsgemässen Schuhpresse mit relativ kurzem Pressschuh,

Figur 4

einen Vergleich des Pressdruckverlaufs einer beispielhaften Ausführungsform der erfindungsgemässen Schuhpresse mit relativ kurzem Pressschuh mit dem Pressdruckverlauf einer mit einer Saugpresswalze versehenen herkömmlichen Presse,

Figur 5

das spezifische Volumen gegenüber dem Trockengehalt, wobei die für eine beispielhafte Ausführungsform der erfindungsgemässen Schuhpresse mit relativ kurzem Pressschuh erhaltenen Ergebnisse mit denen für eine mit einer Saugpresswalze versehenen herkömmlichen Presse verglichen werden,

Figur 6

eine rein schematische Teildarstellung einer weiteren Ausführungsform der erfindungsgemässen Schuhpresse mit einem zwischen einer Schuhpresseinheit und einem Tissuezylinder gebildeten Pressspalt.

The invention will be described below with reference to embodiments with reference to the drawing; in this show:

FIG. 1

a purely schematic partial view of a shoe press according to the invention with a between a Schuhpreßeinheit

FIG. 2

pressing unit and a drying cylinder formed press nip, the compression pressure curve of a conventional shoe press,

FIG. 3

the compression pressure curve of an exemplary embodiment of the shoe press according to the invention with a relatively short press shoe,

FIG. 4

a comparison of the pressure pressure curve of an exemplary embodiment of the shoe press according to the invention with a relatively short press shoe with the pressure profile of a conventional press provided with a suction press roll,

FIG. 5

the specific volume compared to the dry content, comparing the results obtained for an exemplary embodiment of the shoe press with a relatively short press shoe according to the invention with those for a conventional press provided with a suction press roll,

FIG. 6

a purely schematic partial view of another embodiment of the inventive shoe press with a formed between a shoe press unit and a tissue cylinder press nip.

FIG. 1 shows a purely schematic partial representation of an embodiment of an inventive shoe press 10, which can be used for example in a machine for producing a fibrous web such as in particular a tissue or tissue paper web.

The press nip 12 of this shoe press 10 is formed between a shoe press unit, in the present case a shoe press roll 14, and a drying cylinder 16 through which except the fibrous web, a water-absorbing carrier tape 18 and a water-impermeable press belt is passed, which in the present case to the press cover 20 of the shoe press roll 14 is. The water-absorbing carrier tape 18 may be formed in particular by a felt. In the present case, the water-absorbing carrier tape 18 is guided between the press cover 20 and the fibrous web through the press nip 12, wherein the fibrous web contacts the drying cylinder 16.

As based on the FIG. 1 can be seen, the shoe press roller 14 has a two-piece press shoe 22, between the two parts of a thermal insulating layer 24 is inserted.

The press shoe 22 can be pressed against the drying cylinder 16 via a plurality of juxtaposed pressing elements 26 arranged transversely to the web running direction 1.

The drying cylinder 16 may be, for example, a Yankee cylinder.

The water-absorbing carrier tape 18 formed for example by a felt may have a different texture in the thickness direction. In this case, for example, the fibrous web facing side of the carrier tape 18 have a finer structure than its side facing away from the fibrous web page. The Preßmantel 20 may have a smooth, grooved and / or provided with blind holes surface. At least one further, not shown here press nip can be formed on the drying cylinder 16. In the web running direction 1 in front of the drying cylinder 16, an additional press nip can be provided. In principle, the carrier tape 18 and the fibrous web in the web running direction 1 in front of the drying cylinder 16 can also be guided via at least one suction device. The shoe press unit 14 may comprise at least one replaceable press shoe 22.

In the FIG. 2 the pressure profile or the pressing pressure curve p (L) of a conventional shoe press is shown. In this case, the pressing pressure p over the length L of the press nip 12 and the press shoe 22 is applied.

In such a conventional extended nip initially results in a very gentle increase in pressure up to a relatively low maximum pressure p _max . Following the maximum pressing pressure p _{max of} this pressure curve p (L) then takes place a rapid pressure drop.

The shoe press 10 according to the invention can now be designed in particular such that the length L of the press nip 12 considered in the web running direction l (cf. FIG. 1 ) is less than or equal to a value of about 60 mm and whose over the press nip length L resulting pressure profile p (L) has a maximum pressing pressure p _max , which is greater than or equal to a value of about 3.3 MPa.

In the FIG. 3 Now the Preßdruckverlauf p (L) of an exemplary embodiment of such a shoe press 10 according to the invention with a relatively short press shoe 22 is shown. In this case, starting from the gap beginning initially results in an extreme increase of the pressing pressure up to a relatively high maximum pressing pressure p _max . Following this maximum pressing pressure p _max , the pressing pressure then drops very rapidly in the end region.

Based on FIG. 3 In addition, it can be seen that the pressure profile p (L) resulting over the press nip length L is asymmetrical. In this case, the maximum pressing pressure p _{max is} in the web running direction l considered back half of the press nip length L.

The FIG. 4 shows a comparison of the Preßdruckverlaufs p ₁₀ (L) of an exemplary embodiment of the shoe press 10 according to the invention with a relatively short press shoe 12 with the Preßdruckverlauf p _S (L) provided with a Saugpresswalze conventional press. Compared to the conventional press results in particular a shorter press nip and a higher maximum pressure pmax. In the present case, the maximum line force generated in the press nip was 90 kN / m in each case.

The FIG. 5 shows the specific volume versus the dry content, comparing the results V ₁₀ obtained for an exemplary embodiment of the shoe press 10 according to the invention with a relatively short press shoe 22 again with the results V _S for a conventional press provided with a suction press roll. If, in both cases, the starting point is a constant maximum line force of 90 kN / m, then an increase in dry content of 2.5% and an increase in specific volume of 5% can be achieved compared to the conventional press. With a higher maximum line force of, for example, 270 kN / m, for example, a further increase of the dry content by 4.5% can be achieved, ie a total of 2.5% + 4.5% = 7% more than with the conventional suction press roll, wherein in this Case of only 10% of specific volume.

FIG. 6 shows in a schematic partial representation of another embodiment of an inventive shoe press 10th

For short shoes 22 it has been found that the angle alpha between the tangent 30 applied to the drying or tissue cylinder 16 at the end of the press nip 12 and the carrier web 18 leaving the press nip 12 has a significant influence on the dry content of the tissue web 28. The present embodiment is characterized in that, in particular for producing a tissue web 28, this angle .alpha. Between the tangent 30 applied to the drying or tissue cylinder 16 at the end of the press nip 12 and the carrier web 18 expiring from the press nip 12 is .gtoreq.10.degree .. in particular ≥ 18 ° and preferably ≥ 20 °. This results in a dry content increase of about 1 to 3% compared to applications with suction press rolls. The press belt 18 is preferably grooved and / or blind drilled.

Moreover, the present shoe press 10, for example, again the same structure as that according to FIG. 1 , Corresponding elements are provided with the same reference numerals.

LIST OF REFERENCE NUMBERS

10

shoe press

12

nip

14

shoe press

16

drying cylinders

18

carrier tape

20

Press belt, press cover

22

press shoe

24

thermal insulation layer

26

pressing element

28

tissue web

30

tangent

L

nip length

l

Web direction

p (L)

Preßdruckverlauf, pressure profile

p _max

maximum pressing pressure

α

angle

Claims (12)

1. Machine for the manufacture of a fibrous web, in particular a tissue or hygienic paper web, having at least one press nip (12) which is formed between a shoe press unit (14) and a drying or tissue cylinder (16) and through which a water-absorbing carrier belt (18), a water-impermeable press belt (20) and the fibrous web are led, characterized in that at least one press nip (12) formed between a shoe press unit (14) and the drying or tissue cylinder (16) is provided, of which the length (L), viewed in the web running direction (I), is less than or equal to a value of 60 mm and of which the pressure profile (p(L)) resulting over the press nip length (L) has a maximum pressing pressure (p_max) which is greater than or equal to a value of 3.3 MPa.
2. Machine according to Claim 1, characterized in that the press nip length (L) is less than or equal to a value of 50 mm and the maximum pressing pressure (p_max) is greater than or equal to a value of 4.3 MPa, the press nip length (L) preferably lying in the region of 37 mm and the maximum pressing pressure (p_max) preferably lying in the region of 4.8 MPa.
3. Machine according to one of the preceding claims, characterized in that, in particular for the manufacture of a tissue web (28), the angle (alpha) between the tangent (30) drawn to the drying cylinder (16) at the end of the press nip (12) and the carrier belt (18) running out of the press nip (12) is ≥ 10°, in particular ≥ 18° and preferably ≥ 20°, the press belt (20) preferably being grooved and/or blind drilled.
4. Machine according to one of the preceding claims, characterized in that the maximum line force produced in the press nip (12) lies in a range from 90 to 110 kN/m, and/or in that the shoe press unit (14) comprises a press shoe (22) which can be pressed against the drying cylinder by a plurality of pressing elements (26) which are arranged beside one another transversely with respect to the web running direction (I) and can preferably be actuated independently of one another.
5. Machine according to one of the preceding claims, characterized in that the drying cylinder (16) provided is a Yankee cylinder, and/or in that the pressure profile (p(L)) resulting over the press nip length (L) is asymmetrical.
6. Machine according to one of the preceding claims, characterized in that the maximum pressing pressure (p_max) is located in the rear half of the press nip length (L), as viewed in the web running direction (I).
7. Machine according to one of the preceding claims, characterized in that the average pressure rise gradient in the section of the pressure profile (p(L)) reaching from the start of the nip as far as the maximum pressing pressure (p_max) in the case of a new carrier belt is greater than or equal to a value of 40 kPa/mm, in particular greater than or equal to 60 kPa/mm and preferably greater than or equal to 120 kPa/mm, and/or in that the average pressure drop gradient in the end region of the pressure profile (p(L)) in the case of a new carrier belt is greater than or equal to a value of 300 kPa/mm, in particular greater than or equal to 500 kPa/mm, expediently greater than or equal to 800 kPa/mm, and is preferably greater than or equal to 960 kPa/mm, and/or in that the water-absorbing carrier belt (18) in the press nip (12) is located between the water-impermeable press belt (20) and the fibrous web and the fibrous web touches the drying cylinder (16), and/or in that the water-absorbing carrier belt (18) provided is a felt.
8. Machine according to one of the preceding claims, characterized in that the water-absorbing carrier belt (18) has a different composition in the thickness direction, and in that the side of the carrier belt (18) facing the fibrous web preferably has a finer structure than its side facing away from the fibrous web.
9. Machine according to one of the preceding claims, characterized in that the press belt (20) has a surface that is smooth, grooved and/or provided with blind drilled holes, and/or in that at least one further press nip (12) is formed on the drying cylinder (16), at least two press nips (12) formed by means of a respective shoe press unit (14) preferably being provided on the drying cylinder (16).
10. Machine according to one of the preceding claims, characterized in that, in the web running direction (I), an additional press nip (12) is provided before the drying cylinder (16), and/or in that the carrier belt (18) and the fibrous web are led over at least one suction device before the drying cylinder (16) in the web running direction (I), at least one suction device preferably being provided which comprises a suction roll and/or a suction shoe, and/or in that the shoe press unit provided is a shoe press roll (14), the press belt preferably being formed by the press shell (20) of the shoe press roll (14).
11. Machine according to one of the preceding claims, characterized in that the shoe press unit (14) comprises at least one replaceable press shoe (22), and/or in that the carrier belt (18) provided is a structured felt of the type of an embossing fabric or felt provided with elevations, that is to say what is known as an "imprinting fabric" or "imprinting felt" or a "patterning fabric" or "patterning felt" having a coarsely structured surface.
12. Use of the machine according to one of the preceding claims for the manufacture of a fibrous web by using what are known as "curled fibres".

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