APPARATUS FOR PRODUCING A MATERIAL WEB

Abstract

An apparatus for producing a fibrous web, in particular a tissue, paper or cardboard web, has a forming section and a dryer section, whereby the dryer section includes a pressure nip formed by a suction roll and a press roll, a drying cylinder and a transfer pressure nip which is positioned downstream from the pressure nip for transferring the fibrous web to the drying cylinder, whereby the fibrous web together with a clothing wraps around the suction roll in a wraparound region in such a way that the clothing is positioned between the suction roll and the fibrous web.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an apparatus for producing a fibrous web, in particular a tissue, paper or cardboard web, having a forming section and a dryer section, whereby the dryer section comprises a pressure nip formed by a suction roll and a press roll, a drying cylinder and a transfer pressure nip which is positioned downstream from the pressure nip for transferring the fibrous web to the drying cylinder, whereby the fibrous web together with a clothing wraps around the suction roll in a wraparound region in such a way that the clothing is positioned between the suction roll and the fibrous web.

2. Description of the Related Art

Apparatuses of this type are known. Document EP2090691 A1 discloses a device for the production of tissue webs. Here, the tissue web is carried on a textured fabric through a pressure nip which is formed by a suction roll and a press roll; the web is dewatered and directed to the transfer nip to be transferred to the Yankee drying cylinder. This provides a compact press arrangement.

What is needed in the art is a solution for the production of a fibrous web with a view to economical energy utilization at the same or improved quality.

SUMMARY OF THE INVENTION

The present invention provides an apparatus for producing a fibrous web, in particular a tissue, paper or cardboard web, having a forming section and a dryer section, whereby the dryer section includes a pressure nip formed by a suction roll and a press roll, a drying cylinder and a transfer pressure nip which is positioned downstream from the pressure nip for transferring the fibrous web to the drying cylinder, whereby the fibrous web together with a clothing wraps around the suction roll in a wraparound region in such a way that the clothing is positioned between the suction roll and the fibrous web, characterized in that the wraparound region is located upstream of the pressure nip and a heating device is assigned directly to the fibrous web in the wraparound region.

According to the invention, the wraparound region is located upstream of the pressure nip and a heating device is assigned directly to the fibrous web in the wraparound region.

The advantage of this arrangement is in that the fibrous web is heated already before the pressure nip in the region of the suction roll, thereby achieving easier dewaterability. The fibrous web which still has a high water content is hereby already gently—that is at low dewatering pressure—dewatered by the vacuum of the suction roll. As a result important quality parameters, for example the specific volume which is also referred to as bulk and the texture of the fibrous web are not impaired. The heated fibrous web can also be more easily dewatered mechanically in the subsequent pressure nip. This results in a higher dry content before the heated drying cylinder, which is preferably in the embodiment of a Yankee cylinder. Less energy is hereby required for the less efficient thermal drying than is required with otherwise the same conditions.

The clothing is routed preferably through the forming section and through the drying section. The fibrous web is carried on said clothing until it is transferred to the drying cylinder. This renders the apparatus very simple and cost effective in its design. In addition it is advantageous if the fibrous web is formed already on the textured fabric. This provides it with a stable spatial structure.

In one design variation the Yankee drying cylinder is the only drying cylinder. After having been transferred to the Yankee drying cylinder the fibrous web is dried. It is subsequently removed by means of a creping doctor and wound onto a reel.

In one preferred design example the clothing is provided by a permeable textured fabric. Textured fabrics are already known. They are frequently used in through air drying (TAD) tissue machines. The texture of the textured fabric utilized for the invention is arranged so that a texturing effect occurs in regard to the fibrous web. The specific volume is thereby increased and the functional characteristics of the produced fibrous web—for example the water absorption capacity, the water absorption speed and hand feel—are improved.

In an additional design variation of the invention the suction roll is partially wrapped by an inside felt which is positioned between the clothing and the suction roll. This produces a soft, volume-protective press nip. Moreover, the water which is removed from the fibrous web is being evenly distributed to the suction bores in the roll shell.

In an additional variation it is possible that the inside felt is also routed through the transfer nip.

Moreover it is advantageous if the inside felt is more compressible than the clothing. Thus the inside felt changes its thickness at a certain pressure load more than the clothing. This has a compensative effect, particularly in the pressure nip and possibly also in the transfer nip. Pressure spikes which could compromise the fibrous web can thereby be reduced or even avoided. It is also advantageous if the inside felt has a greater capillarity than the clothing. This counters remoistening of the fibrous web.

According to an additional practical advancement the clothing is provided by a water-absorbing felt. This is advantageous, particularly in the production of tissue webs having a low specific volume and high rate of production. In this case, the inside felt can be forgone, so that the fibrous web runs through the pressure nip between the felt which embodies the clothing and an outside felt which wraps partially around the press roll.

In an additional advantageous design variation the heating device is provided by a steam blow box, hot air pressure hood or a hot air blower hood. This has the advantage that the steam or the hot air flows through the fibrous web due to the vacuum in the suction roll, thereby being able to achieve effective heating of the fibrous web. The heating device preferably has a direct, in other words immediate influence upon the fibrous web. The surface of the fibrous web is exposed in the region of the heating device and not covered by a clothing.

It is also conceivable that the heating device is in the embodiment of an infrared or microwave emitter. In this case the fibrous web is primarily heated. Only heated ambient air flows through the fibrous web.

According to a preferred design variation the suction roll features a suction box in the region of the wraparound region and/or in the region of the pressure nip and/or after the pressure nip, providing suction zones. The suction box can thus be divided into three suction zones which can be controlled or adjusted independently in regard to the pressure. The first suction zone is essentially allocated to the wraparound region of the suction roll before the pressure nip, whereas the second suction zone is located in the region of the pressure nip. The third suction zone is located following the pressure nip and serves the conditioning or dewatering of the inside felt.

In an additional advantageous design form the distance between the forming section and the drying section is greater than the transfer distance formed by the distance between the pressure nip and the transfer nip. Because of the short transfer distance severe cooling of the fibrous web which was heated by the heating device is avoided and the thermal energy of the downstream drying cylinder can be used almost completely for drying without having to first heat the fibrous web.

In one practical design version the transfer distance is shorter than 3 m, in particular shorter than 2 m, preferably shorter than 1.5 m.

The press roll is advantageously partially wrapped by an outside felt. The outside felt is also softer than the textured fabric. The fibrous web is thereby pressed uniformly and independently of the transferred structure.

In one practical preferred design variation the clothing and the fibrous web are routed together through the transfer nip.

According to an additional embodiment the wraparound region extends in an angular range of 45° to 120°, preferably between 80° and 100°.

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG. 1 is a possible design form of an inventive apparatus; and

FIG. 2 is a sectional view of the drying section of the apparatus.

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

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates apparatus 1 in the embodiment of a tissue machine, with the exception of the winder. In forming section 24 the fibrous suspension is fed through a headbox 3 into the nip which is formed by the outside fabric 4 and clothing 5. Outside fabric 4 and clothing 5 together partially wrap around a forming roll 6. The fibrous stock suspension is thereby dewatered and fibrous web 2 is formed and following the forming section 24 is carried on clothing 5 to and through a segment of the dryer section 25. This comprises a wraparound region 19 around a suction roll 10, a pressure nip 14, a transfer pressure nip 15 and a drying cylinder 9 which is in the embodiment of a Yankee drying cylinder with a large diameter, for example in the range of 3 to 6 m. In this example, clothing 5 is in the embodiment of a textured fabric. In this case suction roll 10 is additionally wrapped by an inside felt 8, 8′ which is positioned inside the loop of textured fabric 5. This inside felt 8 is fed preferably only through pressure nip 14. It is however also optionally possible to feed inside felt 8′ through transfer pressure nip 15. Through pressure nip 14 which is formed by suction roll 14 and press roll 11 an outside felt 7 is led around press roll 11, whereby it is in contact with fibrous web 2. After pressure nip 14, fibrous web 2 is led to transfer pressure nip 15 and is separated from the textured fabric and transferred to the hot surface of the heated Yankee drying cylinder 9. There, a further increase of the dry content in fibrous web 2 occurs through contact drying. Subsequently it is removed by a crepe doctor 26 from Yankee drying cylinder 9 and is fed to a winder station. Yankee drying cylinder 9, press roll 11 and transfer pressure roll 12 respectively are equipped with their own drive (21, 22, 23). The arrangement of drying section 25 distinguishes itself by its compactness. Pressure nip 14, suction roll 10, press roll 11 and transfer pressure roll 12 are located below Yankee drying cylinder 9. This provides for a very short structural length. This is especially advantageous when converting existing tissue machines to an energy efficient concept. In a second design version of the tissue machine, the textured fabric 5 is replaced by a felt. In this case the inside felt 8, 8′ is omitted.

FIG. 2 illustrates an enlarged segment of a section of drying region 25 in FIG. 1. At the beginning of drying region 25 the wraparound region 19 is provided in the region of a suction roll 10, followed by pressure nip 14 which is formed by suction roll 19 and a press roll 11. Textured fabric 5 is led together with fibrous web 2 over wraparound region 19 so that clothing 5 is positioned between suction roll 10 and fibrous web 2. The outer side of fibrous web 2 is thereby exposed and not covered. A heating device 17 which directly influences and heats fibrous web 2 is provided in this region. The current example shows a steam blow box 17 which directly supplies the surface of fibrous web 2 with steam. Due to the prevailing vacuum of suction roll 19 steam is drawn through fibrous web 2 into the suction roll. The fibrous web 2 is thereby heated, not only on its surface but also in its mass. Wraparound region 19 represents a heating and flow-through zone in which fibrous web 2 is already being dewatered and heated, thereby improving dewatering in press nip 14. Transfer section 18 between pressure nip 14 and transfer pressure nip 15 is very short. Severe cooling of fibrous web 2 before the transfer pressure nip is thereby avoided. Transfer section 18 in this example is 2 m long. Wraparound region 19 of suction roll 10 is between 45° and 120°. In the existing example it is approximately 90°. Pressure nip 14 is preferably arranged so that the direction of travel of the fibrous web progresses essentially vertically in upward direction. A first suction zone 16.1 of the suction box of suction roll 10 is assigned to transfer region 19 and a second suction zone 16.2 is assigned to pressure nip 14. In this example, inside felt 8 is separated from textured fabric 5 after passing through pressure nip 14 in the region of a third suction zone 16.3 and fed to a conditioning device which is not illustrated here. In a second design variation of the invention a felt, for example a press felt is used in place of the textured fabric 5. In this case the inside felt 8, 8′ and the third suction zone 16.3 are omitted, and felt 5′ is removed from fibrous web 2 after transfer pressure nip 15 so that the Yankee drying cylinder is no longer wrapped. This is however the case when using a textured fabric 5. Press roll 11 and transfer pressure roll 12 are preferably identical in construction. This saves stocking of a spare roll. They are designed preferably with a grooved and/or blind drilled U-cover. They may also be in the embodiment of a solid shell press roll, deflection roll with flexible cover or as a shoe roll for formation of an extended pressure nip. A conditioning device with tube suction device and shower is assigned to each fabric and felt respectively.

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

COMPONENT IDENTIFICATION LIST

• • 1 Apparatus
  • 2 Fibrous web
  • 3 Headbox
  • 4 Outside fabric
  • 5 Textured fabric, felt
  • 5′ Felt
  • 6 Forming roll
  • 7 Outside felt
  • 8 Inside felt
  • 8′ Inside felt
  • 9 Yankee drying cylinder
  • 10 Suction roll
  • 11 Press roll
  • 12 Transfer pressure roll
  • 13 Guide roll
  • 14 Pressure nip
  • 15 Transfer pressure nip
  • 16 Suction box
  • 16.1 First suction zone
  • 16.2 Second suction zone
  • 16.3 Third suction zone
  • 17 Heating device, blow box
  • 18 Transfer section
  • 19 Wraparound region, wraparound angle
  • 20 Catch pan
  • 21 Drive
  • 22 Drive
  • 23 Drive
  • 24 Forming section
  • 25 Drying section
  • 26 Creping doctor

Claims

1. An apparatus for producing a web of fibrous material, said apparatus comprising: a forming section;a clothing;a dryer section including a suction roll, a press roll, a drying cylinder, a transfer pressure nip, and a heating device, said suction roll and said press roll forming a pressure nip, said transfer pressure nip being positioned downstream from said pressure nip and being configured for transferring the web to said drying cylinder, the web together with said clothing wrapping around said suction roll in a wraparound region in such a way that said clothing is positioned between said suction roll and the web, said wraparound region being located upstream of said pressure nip, said heating device being assigned directly to the web in said wraparound region.

2. The apparatus according to claim 1, wherein the web is one of a tissue web, a paper web, and a cardboard web.

3. The apparatus according to claim 1, wherein said clothing is a textured fabric.

4. The apparatus according to claim 1, further including an inside felt, said suction roll being partially wrapped by said inside felt which is positioned between said clothing and said suction roll.

5. The apparatus according to claim 4, wherein said inside felt is routed through said transfer pressure nip.

6. The apparatus according to claim 4, wherein said inside felt is more compressible than said clothing.

7. The apparatus according to claim 1, wherein said clothing is a water-absorbing felt.

8. The apparatus according to claim 1, wherein said heating device is one of a steam blow box and a hot air blower hood.

9. The apparatus according to claim 1, wherein the apparatus includes a region of said wraparound region and a region of said pressure nip, said suction roll including a suction box at least one of (a) in said region of said wraparound region, (b) in said region of said pressure nip, and (c) after said pressure nip, providing at least one suction zone.

10. The apparatus according to claim 1, wherein the apparatus includes a region of said wraparound region and a region of said pressure nip, said suction roll including a suction box at least one of (a) in said region of said wraparound region, (b) in said region of said pressure nip, and (c) after said pressure nip, providing a plurality of suction zones.

11. The apparatus according to claim 1, wherein a distance between said forming section and said dryer section is greater than a transfer distance created by a distance between said pressure nip and said transfer pressure nip.

12. The apparatus according to claim 11, wherein said transfer distance is shorter than 3 meters.

13. The apparatus according to claim 11, wherein said transfer distance is shorter than 2 meters.

14. The apparatus according to claim 11, wherein said transfer distance is shorter than 1.5 meters.

15. The apparatus according to claim 1, further including an outside felt, said outside felt being partially wrapped around said press roll.

16. The apparatus according to claim 1, wherein said clothing and the web are routed through said transfer pressure nip.

17. The apparatus according to claim 1, wherein said wraparound region extends in an angular range of 45° to 120°.

18. The apparatus according to claim 1, wherein said wraparound region extends in an angular range of between 80° and 100°.