Device for forming multi-layer paper

Abstract: The present invention is to manufacture paper layer with high grammage and good, formation even in lower speed by making direction of hydration of a fixed type dehydrator having a curvature at least partly downward so as not to reverse to the gravity and making dehydrating capacity larger with small vacuum value. The device includes a looped endless felt 5 and at least two short wire units provided thereunder and having a fixed type dehydrator 2 with a curvature at least partly and the short wire 4. The endless felt 5 touches the short wire 4 on the curvature of each fixed type dehydrator 2, and the paper layers are formed and combined by hydrating stock while the stock from the head box 1 and spouted on the short wire 4 is held and moved between the endless felt and the short wire. Each of forming roll 10, couch roll 11 and a felt roll 12 have a construction movable vertically. By raising the endless felt 5 by the felt roll 12, touch between the short wire unit at the upstream of the felt roll 12 and the endless felt 5 is released and also replacement of short wire 4 in such short wire unit can be made easily under operation.

Description: The present invention relates to a device for forming multilayer paper in a paper machine according to the preamble portion of claim 1. Fig. 3 shows an example of a prior device for forming multilayer paper. The device shown in Fig. 3 is a wet end of a typical paper machine to make paper layers adhere between short wire units, and Fig. 3 shows a front view near a short wire part especially. The paper stock spouted from the head box 20, after being dehydrated by a table unit 22 arranged in the loop of short wire 21, forms a paper layer on a short wire 21 by being dehydrated to the forming cylinder 24 side furthermore by a pressing force of a felt 19 wrapped around the forming cylinder 24. A paper layer formed on the felt 19 by an upstream units and a paper layer formed on the short wire of the above units are bonded each other on the forming cylinder 24 by being pressed with a touch roll 25. And the white water, spouted from the cylinder when the short wire 21 is separated from the forming cylinder 24, is absorbed by the suction slider 26. On the other hand, the paper layers bonded on the forming cylinder 24 is shifted on the felt 19 by a suction pick-up 29 in the course of traveling by catching them between the short wire 21 and the felt 19, and fed to the next unit. Fig. 4 shows an another example of a prior device for forming multilayer paper. The device in this example is a typical wire part in a paper machine to combine paper layers by using a short wire and a Fourdrinier wire. In Fig. 4, paper stock spouted from a head box 30 forms a paper layer by being dehydrated with a table unit 33 arranged in the loop of a Fourdrinier wire 32. On the other hand, paper stock spouted from a head box 31 touches on the paper layer formed already, and enters into a gap formed by touching a short wire 34 with the Fourdrinier wire on a lead-in box 40. In the short wire part, the paper layer is formed and combined at the same time, being dehydrated upward by a tension of the short wire on a lead-in box 40 and by vacuum mainly at a vacuum dehydrator 39. After that, the combined paper layers are transferred to the next short wire after shifting on the Fourdrinier wire 32 by vacuum applied to a transfer box 41. In-order to raise density of combined paper layers, a vacuum box 42 is arranged in the Fourdrinier wire loop. A paper comprising the paper layers thus combined are picked up by a suction pick-up roll 44 through a suction couch roll 43 and transferred to the next process (press part). In the device for forming multilayer paper shown in Fig. 3 above, the formation was not sufficient because the paper layer formation and dehydration were carried out by the table unit 22 such as forming board, foil, table roll and a wet suction box (detail description thereof are omitted since those are used for the Fourdrinier wire and cylinder mould type paper machine for a long time and familiar) and the forming cylinder 24 and shearing force applied to the stock became less. In addition, in this prior device, there is a problem of wet paper breakage resulting from the difficulty of taking-in on the forming cylinder occurred by lowering of wet paper density entering into the combination part at increasing an amount of the attached stock per one layer on the short wire and at high speed, so that the attached stock amount per one unit in the short wire part could not be increased. Further, the device shown in Fig. 3 is to intend to simplify the white water treatment, but there are problems of mist spattering as well as difficulty on the white water treatment in the cylinder mould because the forming cylinder 24 is on the felt. Replacement of the endless felt in this prior device became difficult because the loop is complicated due to the felt length elongated by wrapping the felt 19 on the surface of short wire 21. Accordingly, sometimes the seam felt (the seam method of felt is similar to that of dryer canvas) is used, and the seam mark by the touch roll might occur. In addition, since the felt is wrapped on the short wire part, the replacement of short wire was also difficult. Besides, in the device for forming multilayer paper shown in Fig. 3, there was such a weak point where the wet paper formation approaches the dry on dry adhesion and the bonding strength lowers, because when the dehydrating capacity on short wire table becomes larger the wet paper density becomes higher. In the prior device for forming multilayer paper shown in Fig. 4, vacuum capacity is required necessarily for lifting up the white water against the gravity as mentioned above, which is dehydrated upward on the lead in box 40, and discharging it from the auto slice provided in the vacuum dehydrator. And since the white water is pulled up in the vacuum dehydrator 39 all the time, more vacuum capacity was required for discharging the white water and dehydrating the stock in the two wires through the white water. In addition, because the short wire 34 is pressed forcefully on the forming shoes (not shown) of the vacuum dehydrator 39 by the high level vacuum, large driving power was required. Besides in order to improve taking-in and possibility of lowering speed and to make grammage high, the taking-in in case of Fig. 4 is easier than in case of Fig. 3, because the radius of curvature at taking-in part shown in Fig. 4 is larger than that shown in Fig. 3, but sometimes there is still a problem in taking-in at very low speed. Therefore it was necessary to increase the attached amount per one layer more. Further, in the short wire part in the prior art explained above, treatment of cleaning water for short wire 34 was difficult and the measures for preventing the mist generated from spattering was also required, because the short wire part is provided on the Fourdrinier wire. A prior art device forming multilayer paper comprising the features of the preamble portion of claim 1 is disclosed in DE-OS 1 808 403. In this device, the endless felt touches the fixed dehydrator on a straight line portion downstream of a curvature portion. The front or upstream curved section of the dehydrator serves for a smooth transition of the running short wire. The endless felt and the short wire of each of the short wire units contact at the rearward end of each dehydrator as seen in the running direction. It is the object of the present invention to provide a device for forming multilayer paper which is improved with respect to the fiber dispersion of the paper stock. According to the present invention there is provided a device for forming multilayer paper, including one looped endless felt, plural short wire units provided under the endless felt, each having a short wire and a fixed type dehydrator having at least partly a curvature portion, wherein a paper layer is formed by dehydrating stock spouted on each of the short wires while said stock moves being held between said endless felt and said short wire, and paper layers thus formed in the short wire units are combined together, characterized in that the endless felt touches with each of the short wires on the curvature portion of each fixed type dehydrator. In a preferred embodiment of this device said fixed type dehydrator in the short wire unit has a construction which is able to accelerate the dehydration by vacuum. In a further preferred embodiment the device further comprises a forming roll for making a support so that a touching position of the endless felt and the short wire is adjustable, a couch roll for pressing the endless felt to a wet paper, said forming roll and said couch roll being each supported to be releasable from the endless felt, and a felt roll supported between adjacent short wires units such that its position is changeable vertically to thereby raise the endless felt by the felt roll and to release the touching between the short wire unit upstream of the felt roll and the endless felt. The stock spouted from the head box enters into a gap in touching between the endless felt and the short wire after being dehydrated by a foil effect of the forming blade at releasing part in the first half of the fixed type dehydrator. The stock entered and held between the short wire and the endless felt is dehydrated in the condition that the fiber dispersion is accelerated by a pulse pressure induced by the forming shoe blades. By raising the felt roll as well as changing the positions of the forming roll and the couch roll, touch between the short wire at the upstream of felt roll and the endless felt can be released. Accordingly the use of only necessary units in accordance with grammage to be manufactured becomes possible and the replacement of short wire in stopped unit can be carried out easily under operation. Brief Description of the Drawings Fig. 1 is a front view of paper machine wet end equipped with the device for forming multilayer paper according to an embodiment of the present invention. Fig. 2 is a detailed section of major part in Fig. 1. Fig. 3 is a front view showing an example of the prior device for forming multilayer paper. Fig. 4 is a front view of a prior device for forming multilayer paper different from the prior device shown in Fig. 3. One embodiment of the present invention will be explained hereunder. In Fig. 1 and Fig. 2, 1 is a head box, 2 is a fixed type dehydrator, 3 is a forming shoe blade, 4 is a short wire, 5 is an endless felt, 6 is a breast roll, 7 is a drive roll, 8 is a stretch roll, 9 is a guide roll, 10 is a forming roll, 11 is a couch roll, 11' is a suction couch roll, 12 is a felt roll, 13 is a flow back device and 14 is a suction pick-up roll. A short wire unit has the short wire 4 and the fixed type dehydrator 2 with plural forming blades 3, the short wire 4 moves on the fixed type dehydrator 2 in contact with its surface. The dehydrator 2 is under the loop of endless felt 5 and its first half part is free from the endless felt 5, the surface of dehydrator 2 touches the endless felt 5 by the forming roll 10 in the midway. For the fixed type dehydrator 2, though it is allowable to splice into plural pieces, the touching part with the endless felt 5 on the surface has larger radius of curvature compared with the past one. It is possible to raise up the dehydrating pressure with an increase of wet paper density by reducing the radius of curvature along the direction of the movement of the endless felt 5. Said forming shoe blades may be of fixed type and also they may be supported so as to be able to extract or insert. In addition, the inside of fixed type dehydrator 2 is made vacuum, the forming roll and the couch roll are supported releasable from the endless felt 5, and the felt roll 12 is so provided as to be able to raise the endless felt between the short wire units. The head box 1 is provided so as to eject the stock on the short wire 4 between the breast roll 6 and the forming roll 10 of the short wire unit as constructed above, and plural head boxes and short wire units are provided along the direction of the endless felt 5. The forming shoe blade 3 of the fixed type dehydrator 2 is consisting of plural pieces, and the formation is improved by dispersing again the fibre in the stock by a shearing force which is induced by a pulse pressure generated at each blade 3. The fixed type of blade 3 is acceptable, but it is also acceptable to alter into the insert type (not show in the figure) by changing the blade shape and the number of pieces to be used as necessary so that the level of pulse pressure aforesaid and number of times can be adjusted and the fine adjustment of formation can be made. If making the radius of curvature of the fixed type dehydrator 2 smaller gradually, it is possible to increase the dehydrating pressure with an increase of the mat density. In addition, the white water treatment is also easy because the short wire unit is under the loop of endless felt 5. Since the fixed type dehydrator 2 has same construction as that of ordinary suction box, it is feasible to enhance the dehydration by applying low negative pressure as required to intend to improve the dehydrating capacity. Furthermore as all the dehydrating direction of fixed type dehydrator 2 is downward, reverse against that of vacuum dehydrator 39 in the prior device for forming multilayer paper (Fig. 4) and without antigravity, the required air quantity for vacuum is small and the driving power is also little. In addition, a part of the dehydrator 2 near the head box 1 may be flat without curvature and the other part may be curved as above. In this embodiment, the stock spouted from the head box 1 enters into a gap in touching between the endless felt 5 and the short wire 4 after being dehydrated by a foil effect in the forming shoe blade 3 at the free part in the first half of fixed type dehydrator 2. Since the radius of curvature R in the curved part of fixed type dehydrator is large, the pushing pressure by the endless felt 5 is small and the stock is caught in the gap without trouble. It is needless to say that the position of catching-in can be set in optimum conditions by adjusting the forming roll 10 provided in the loop of the endless felt 5 vertically as shown by an arrow mark, depending on the thickness of material to be entered. In touching between the endless felt 5 in the second half of fixed type dehydrator 2 of the short wire unit and the short wire 4, the stock caught in between the short wire and the endless felt 5 is dehydrated while the fibre dispersion is being accelerated by a pulse pressure induced by the forming shoe blade 3. And it is possible to enhance the dehydration by applying a negative pressure to the fixed type dehydrator 2 as required. On the other hand, the paper layer formed on the short wire 4 is bonded to the wet paper on the felt side by pressing the couch roll 11 to the drive roll 7 and attached to the under face of endless felt 5 to transfer to the next unit. In order to ensure the transfer to the felt side, it is also feasible to use the suction couch roll 11' instead of the couch roll. Fig. 1 shows an example of wet end to transfer the wet paper to the press part as a next step after repeating the above combination (adhesion) of paper layers, and shows the case in which all of each paper layer are formed at the short wire part 4 in the plural units. The multilayer paper turned after combining by the suction couch roll 11' following to the last short wire unit shown in Fig. 1 is put on the endless felt 5 and transferred to the next step. The wet paper is raised in density by being dehydrated more by the flow back device 13 of known type and provided in the loop of endless felt 5 on the way, and picked up by the suction pick-up roll 14 to transfer to the next step (press part), By changing the positions of the forming roll 10, the couch roll 11 and the felt roll 12 upward, as shown by a chain line in Fig. 1, the touch between the short wire 4 and the felt 5 can be released, and necessary number of units can be operated by stopping such short wire unit, and the short wire in the stopped unit can be replaced easily. As described in detail, in the present invention, the formation of each layer is good because it is performed by a pulse pressure induced by the forming shoe blade. And this dispersion effect raises the bonding strength between layers in paper board together with the wet on dry combination (adhesion) method. Since the fixed type dehydrator has a construction for vacuum, the attaching grammage per one unit becomes large due to a fixed type vacuum dehydration not affected by the manufacturing speed, and it is possible to reduce the installation area and to lower the cost as well as the number of units can be reduced even in high speed operation. Further, the vacuum level applied to the fixed type dehydrator can be made less than the past level, and the air quantity for vacuum can be reduced. In addition, the driving power can be saved because the frictional force in the fixed type dehydrator becomes small,. Accordingly, these contribute for lowering not only the initial cost of equipment but the running cost too. Furthermore since the present invention is so designed as the touch between the short wire unit at the upstream of felt roll and the endless felt can be released by lifting the felt roll as well as changing the positions of forming roll and couch roll, it is possible to use only necessary units in accordance with the grammage to be manufactured and to perform easily the replacement of the short wire in a stopped unit under operation. On the other hand, as the felt is endless, there is no fear of occurring the mark due to the seam part on the seam felt.

Claims: A device for forming multilayer paper, including one looped endless felt (5), plural short wire units provided under the endless felt (5), each having a short wire (4) and a fixed type dehydrator (2) having at least partly a curvature portion, wherein a paper layer is formed by dehydrating stock spouted on each of the short wires (4) while said stock moves being held between said endless felt (5) and said short wire (4), and paper layers thus formed in the short wire units are combined together, characterized in that the endless felt (5) touches with each of the short wires (4) on the curvature portion of each fixed type dehydrator (2). The device for forming multilayer paper according to claim 1, characterized in that said fixed type dehydrator (2) in the short wire unit has a construction whwich is able to accelerate the dehydration by vacuum. The device for forming multilayer paper according to claim 1 or 2, characterized by further comprising a forming roll (10) for making a support so that a touching position of the endless felt (5) and the short wire (4) is adjustable, a couch roll (11) for pressing the endless felt (5) to a wet paper, said forming roll (10) and said couch roll (11) being each supported to be releasable from the endless felt (5), and a felt roll (12) supported between adjacent short wires units such that its position is changeable vertically to thereby raise the endless felt (5) by the felt roll (12) and to release the touching between the short wire unit upstream of the felt roll (12) and the endless felt (5).

Inventors: BANDO TAKASHI, KUNIHISA KAZUO, SHIMAZU HIROTO, TOKUNO MASATERU, BANDO, TAKASHI, KUNIHISA, KAZUO, SHIMAZU, HIROTO, TOKUNO, MASATERU, BANDO, TAKASHI, C/O MIHARA MACHINERY WORKS OF, KUNIHISA, KAZUO, C/O MIHARA MACHINERY WORKS OF, SHIMAZU, HIROTO, C/O MIHARA MACHINERY WORKS OF, TOKUNO, MASATERU, C/O SK ENGINEERING, LTD.
Applicants: MITSUBISHI HEAVY IND LTD, SK ENG CO LTD, MITSUBISHI JUKOGYO KABUSHIKI KAISHA, SK ENGINEERING LTD
Application year: 1993
Main classification: D21F9
IPC codes: D21F1, D21F9, D21F11