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(11) | EP 1 544 350 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Paper making machine |
| (57) The invention relates to a paper making machine and especially a tissue-paper making
machine comprising a formation section (F) including a jet-headbox (10). The wires
are cleaned by cleaning water. In the return stroke just upstream the headbox (10)
there is provided a dewatering means has a suction box (14) for making the wire dry
before entering the nip (9) between the wires in order to avoid that entrained water
is directed into the fiber suspension jet. Thus, an improved and more homogeneous
sheet formation is possible. |
Technical Field
[0001] The invention relates to a paper making machine, especially tissue-paper making machine, comprising a formation section including a jet-headbox directed to a nip formed by an endless twin-wire configuration or an endless wire and an endless felt where the wires or the wire and the felt run over rollers, wherein in the area of the wire-return stroke upstream of the nip at least one-water cleaning means is provided.
[0002] The production of tissue is distinguished from paper production by the its extremely low basis weight and its much higher tensile energy absorption index (see DIN EN 12625-4 and DIN EN 12625-5). Paper and tissue paper also differ in general with regard to the modulus of elasticity that characterizes the stress-strain properties of these planar products as a material parameter.
[0003] A tissue's high tensile energy absorption index results from the outer or inner creping. The former is produced by compression of the paper web adhering to a dry cylinder as a result of the action of a crepe doctor blade or in the latter instance as a result of a difference in speed between two wires ("fabrics" or belts). This causes the still moist, plastically deformable paper web to be internally broken up by compression, shearing and tension, thereby rendering it more stretchable under load than an uncreped paper.
[0004] If tissue paper is to be made out of pulp, the process essentially comprises
a forming an embryonic web that includes the head box and the forming wire section,
b the drying section (TAD (through air drying)) or conventional drying on the Yankee-cylinder) that also usually includes the crepe process essential for tissues,
c typically the monitoring and winding area.
[0005] The embryonic paper web can be formed by placing the fibers, in an oriented or random manner, on one or between two continuously revolving wires ("fabrics" or belts) of a paper making machine while simultaneously removing the main quantity of water of dilution until dry-solids contents of usually between 12 and 35 % are obtained.
[0006] Drying the formed primary fibrous web occurs in one or more steps by mechanical and thermal means until a final dry-solids content of usually about 93 to 98 %. In the case of tissue making, this stage is followed by the crepe process which crucially influences the properties of the finished tissue product in conventional processes. The conventional dry crepe process involves creping on a usually 3.6 to 6 m diameter drying cylinder, the so-called Yankee cylinder, by means of a crepe doctor with the aforementioned final dry-solids content of the raw tissue paper (wet creping can be used if lower demands are made of the tissue quality). The creped, finally dried raw single ply tissue paper (raw tissue) is then available for further processing into the paper product or tissue paper product according to the invention.
Background art
[0007] In such tissue-paper making machines, especially on the return stroke the wires ("fabrics" or belts) are cleaned with water jets at least at one position and not preferably at two positions differentiated such that at first using a high amount of water cleaning of the wire ("fabric" or belt) is accomplished and at a more downstream position water cleaning of the wire in accomplished using high pressure. Thereafter the wire returns to the headbox forming a nip into which the pulp is jetted in. Such conditions often lead to poor formation and especially to areas of different basis weight over the surface of the manufactured paper, especially in the machine direction and in the cross-machine direction.
Disclosure of invention
[0008] It is a problem of the invention to improve the forming section of a paper making machine and especially a tissue-paper making machine in order to achieve a more homogeneously formed paper.
[0009] This problem is solved by a paper making machine described above, in which downstream of the last water cleaning means and upstream of the nip at least one cleaning water-dewatering means is provided at at least one of the wires or the wire if combined with a felt.
[0010] By such dewatering means the forming wire ("fabric" or belt) is essentially dry when running in the return stroke back to the headbox so that no water is entrained, which could detoriate the formation process in connection with dewatering in the forming section, especially at a position where the first dewatering is made in the forming section. Furthermore, it is not possible that entrained water has an influence on the homogeneity of the fiber suspension jet within the head box. Therefore, according to the invention especially with respect to the basis weight a more homogeneous paper is achieved.
[0011] Preferably, the cleaning water-dewatering means is provided inside of the wire ("fabric" or belt) with a result that the cleaning water-dewatering means can not damage the paper side of the wire by friction and wear, especially when as cleaning water-dewatering means a suction box or vacuum box is used contacting the wire by a sliding shoe. Nevertheless, it is possible to provide the cleaning water-dewatering means outside the wire, especially when a suction roller is used rolling on the wire in a more wear avoiding manner.
[0012] The cleaning water-dewatering means preferably is provided at the outer wire of the twin-wire configuration, especially when the outer wire is present as a multi-layer wire, which has a higher water entraining capacity. Nevertheless, it can be advantageous to provide the cleaning water-dewatering means at the inner wire of a twin-wire configuration.
[0013] The cleaning-water-dewatering means may be a suction or vacuum box or a suction roller or a suction shoe contacting the wire.
[0014] Especially, when a breast roller is used for instance in connection with a forming roller for providing the nip in which the water diluted pulp is jetted by the headbox the suction box or the suction roller or the suction shoe is movable relative to the wire and specially perpendicularly to the wire in order to avoid any negative influence on the formation process by the suction box or suction roller or the suction shoe contacting the wire when the formation and nip configuration is set inter alia by the breast roller.
[0015] In order to avoid that the suction box runs dry and therewith to avoid wear of the wire in the vicinity of the suction box an applicator device is provided applying lubrication material to the place where the suction box contacts the wire. Lubrication material may be for instance a small amount of water, which may be applied as a film of water. The invention described can also be applied to a crescent former type of a (tissue) paper machine.
Brief description of drawings
[0016] In the accompanied drawings embodiments of the invention are illustrated in a schematic manner.
Fig.1 shows in a diagrammatic manner a cross section to a C-wrap tissue-paper making machine.
Fig.2 shows a similar illustration of a crescent-former tissue-paper machine.
Fig.3 shows a similar illustration of a S-wrap former.
[0017] The present invention is described on the basis of the embodiments illustrated in Fig.1 and Fig.2 and now especially according to Fig.1 mentioning only the essential parts of the machine, especially with respect to the invention.
[0018] Fig.1 shows on the left hand the forming section F and on the right hand the drying section D and therebetween the paper transporting section ("press felt section") T. The drying section D comprises as a main part a so called Yankee-Cylinder 1. The transporting section T comprises an endless felt 2 taking over the wet web from an inner wire 3 by a pick-up shoe 4 (or pick-up roll). By press rollers 5 and 6 the paper web is pressed against the Yankee-Cylinder and is transferred from the felt 2 onto the Yankee-Cylinder.where.it is adhered to the Yankee-Cylinder surface by means of pressure and adhesives from which the paper web W runs by creping means from the Yankee-Cylinder to the winding-up station of the finished paper.
[0019] The forming section F comprises a twin-wire configuration including an outer wire 8 and the inner wire 3. Usually the outer wire as a backing and paper forming wire is a multi-layer wire. The inner wire usually is as a conveying forming wire a single-layer wire, although it might also be a multi-layer wire. Both wires are endless wires running around a plurality of rollers. The outer wire 8 runs around rollers a1 - a6 and according the C-wrap configuration around a forming roller b1. The inner wire 3 runs also according to the C-wrap configuration around the forming roller b1 and rollers b2 and b3. In this embodiment the roller b1 around which both wires are running is a forming roller and forms with the two wires 3 and 8 and the roller a6 a nip 9. The roller a6 is a so called breast roller being movable and fixable in different positions in order to set the nip and the jet-in configuration. A jet-head box 10 directs over the widths of the wires (up to 12m) the pulp of fiber suspension into the nip 9. Preferably, the rollers a1 and b2 are tension rollers pretensioning the wires and the roller b3 is movable as a control roller in order to control the edge position of the wire.
[0020] On the return stroke the wires 3 and 8 are cleaned by water spraying. For cleaning the outer wire 8 there are provided for instance with two cleaning devices 11, 12. In this example the cleaning device 11 is a low pressure cleaning device for instance applying an amount of 1500 1/min for a 7m wide machine. The other cleaning device 12 is an oscillating high pressure cleaning device (8-35 bar; 0 0.7-1.2mm jet tubes) using lower amount of water. For the inner wire 3 a similar water cleaning devices 13 and 13' is provided behind the roller b2. Furthermore, it is possible to position high pressure cleaning jets 20 directive to the paperside of the wires.
[0021] In the outer wire 8 downstream the last water cleaning device 12 a suction box 14 is provided upstream the nip 9 and the head box 10. This suction device as a suction box (or suction shoe) is provided at the inner side of the outer wire 8 because the suction box contacts the wire such that it slides on a sliding surface of the suction box (or suction shoe) in which over the widths of the wire a slot is provided. As such those suction boxes (or suction shoes) are known in this technical field. Therefore, it is not necessary to describe those in detail. Thus, the suction box does not contact the wire on the paper forming side with the result that some wear of the wire is not disadvantageous for paper forming. Furthermore, less rest fibers intend to be collected upstream the suction box. This happens more when the suction box is located on the opposite side of the wire.
[0022] The suction box (or suction shoe) can be replaced by a suction roller with the result that less wear on the wire happens so that the location on the paper side is less disadvantageous. ,
[0023] Upstream the suction box 14 is provided an applicator 15 for applying lubricating material as for instance water to the sliding surface of the suction box in order to avoid dry running of the suction box.
[0024] A similar suction box or suction roller 16 is provided inside the inner wire 3 downstream the control roller b3. The control roller b3 is movable and fixable in different positions along the double arrow indicated there and it is preferred that the suction box 16 is movable together with the control roller b3. Downstream the roller b2 water cleaning device 13 is provided for the inner wire 3.
[0025] By the suction boxes (or suction shoes) 14, 16 which can may be replaced by suction rollers the wires returning into the nip 9 are essentially dry so that no entrained water can in negative manner influence the fiber suspension jet and the dewatering in the formation zone in the area of the forming roller b1.
[0026] If the suction box 14 or the suction roller for the outer roller 8 is provided outside the wire then the suction box 14 or suction roller should be placed close to the roller a5. Otherwise, the suction box 14 should not be placed to close to the head box because then the suction box 14 is less visible. Furthermore, then exists in front of the head box a calming-zone for the wire.
[0027] According to Fig.2 the forming wire 8 is combined with a felt 2'. The drying suction box 14, which can also be a roller is provided there at another place. Otherwise, the paper making machine as far as the invention is concerned works similar to the paper making machine illustrated in Fig.1.
[0028] When the word "dewatering" of the wire is used for making the return stroke of the wire 3 dry this includes also a dewatering action by pressing or blowing air through the wire or by a combination of both. However, this causes more energy consumption and is not such effective. From a principal standpoint using heat would also be effective for dewatering actions.
[0029] More than one suction box (or suction shoe) or suction roller can be placed one behind the other. However, this could lead to the effect that the most downstream suction box intends to run dry. Then at least there lubricating material (such as siloxane compounds) for instance as water should by applied. Finally, suction boxes can be provided alternately on the inner side and the outer side of the wire.
[0031] Such paper making machines as tissue-paper making machines are running at a speed of up to 5000 m/min. The cleaning water-dewatering is especially effective for machine running speed between 1200 m/min. and 2000 m/min. and especially above 1500 m/min. Under such high speed with a forming zone as short as 1 m the dewatering time is up to 0,03 sec. Fig.3 shows a S-wrap former. For means being similar to the embodiment according to Fig.1 are used the same reference numbers.
1. Paper making machine, especially tissue-paper making machine comprising a formation
section (F) including a jet-head box (10) directed to a nip (9) formed by an endless
twin-wire configuration (3,8) or an endless wire (8) and an endless felt (2') where
the wires (3,8) or the wire (8) and the felt (2') run over rollers, wherein in the
area of the wire-return-stroke upstream of the nip (9) at least one water cleaning
means (11,12;13) is provided, characterized in that downstream of the most downstream water cleaning means (12;13) and upstream of the
nip (9) at/least one cleaning water-dewatering means (14) is provided at at least
one of the wires (3;8) or the wire (8) if combined with a felt (2;2').
2. Paper making machine according to claim 1, characterized in that the cleaning water-dewatering means (14;16) is provided inside of the wire (3;8).
3. Paper making machine according to claim 1, characterized in that the cleaning water-dewatering means (14;16) is provided on the outside of the wire.
4. Paper making machine according to claim 1, characterized in that the cleaning water-dewatering means (14;16) is provided at an outer and/or inner
wire of the twin-wire configuration.
5. Paper making machine according to claim 1, characterized in that the cleaning water-dewatering means (14;16) is a suction box (14) or a suction shoe
or a suction roller contacting the wire (8).
6. Paper making machine according to claim 5, characterized in that the suction box (14) or the suction shoe or the suction roller is installed as a
movable means which can be fixed in various positions.
7. Paper making machine according to claim 6, characterized in that the suction box (14) or the suction shoe or the suction roller is movable perpendicularly
to the surface of the wire (8).
8. Paper making machine according to claim 5, characterized in that the suction box (14) is provided with a lubrication material-applicator device (15).