FI121184B - Paper machine dual-wire reformer - Google Patents

Description

Paper machine dual-wire reformer

The present invention relates to a paper or board machine twin-wire reformer comprising a bottom wire loop and a top wire loop, the bottom wire loop forming a single-wire initial dewatering section to which the fiber slurry is fed from the headbox. The single-wire initial dewatering portion is followed by a dual-wire portion having a curved dewatering box at the beginning, fitted inside the upper wire loop so as to direct the upper wire into contact with the bottom wire. The dewatering box comprises 10 suction chambers with a non-pulsation dewatering area.

Hybrid formers have traditionally been formed by positioning the top wire unit on a horizontal flat wire, whereby the front roll at the beginning of the wire and the suction roll at the end of the wire are at substantially the same height. In such a solution, the pick-up roll of the press section has to be located very close to the suction roll of the flat wire section, whereby it is no longer possible to fit dewatering fixtures behind the suction roll. Solutions of the Applicant's SymFormer ™ hybrid formers are also known where the suction roll is located below the breast roll. When the suction roll is lower than normal, the lower wire passes only a short distance on the surface of the suction roll, leaving the suction zone ly-20 hy.

Figure 7 of WO Application Publication No. 2004018768 shows a hybridformer of the type described above. In it, the twin-wire portion is initiated by a curved dewatering box on the side of the upper wire loop, which comprises three successive suction chambers with different vacuum pressures. The first suction chamber is non-pulsed, which means that the chamber is provided with an open lid structure which provides a substantially non-pulsed dewatering pressure. This results in a symmetrical z-directional structure. The second suction chamber is pulsating, meaning that it is provided with a cover structure which provides a pulsating dewatering pressure. The cover consists of transverse dewatering strips opposed by loading strips on the side of the bottom wire loop. Dewatering and loading strips generate pressure pulses in the web which improve web formation and enhance dewatering. The third suction chamber is also pulsating, but the underside is unloaded at the molded cover. Such a dewatering box comprising several successive suction chambers is relatively expensive both in terms of investment and operating costs.

The object of the invention is to solve the problems of the prior art.

The two-wire reformer according to the invention is characterized in what is set forth in the characterizing part of claim 1.

In the former according to the invention, the twin-wire portion begins with a dewatering box known per se, which provides for non-pulsatile dewatering, whereupon the web passage is directed obliquely upwards until a suction roll is received on the side of the bottom wire loop. Preferably, the web passage is directed upward at an angle of at least 5 ° to the horizontal. The upper wire is guided apart from the web before the suction roll, so that the web passes over the suction roll only supported by the lower wire. The lower wire curves over the suction roll at the end of the wire section in a sector of greater than 60 °, preferably greater than 75 °.

By positioning the suction roll at the end of the wire section at a higher level than the initial flat wire section, it is possible to obtain a larger lower wire coverage angle for the suction roll. The dewatering of the suction roll can be enhanced by increasing the length of the suction zone 25. The new geometry of the wire section allows the dewatering elements to be located behind the suction roll before the pick-up roll, thereby increasing the dry solids content of the web before it leaves the wire section. It is also possible to place the edge cut behind the suction roller, which keeps the cutting groove even more open. The solution provides space for the suction box on the edge band. The new wire end structure 30 also provides advantages in joining various press concepts in the pick-up area.

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Various dewatering elements, such as suction boxes, curved forming shoe or dewatering molds, may be disposed between the dewatering box and the subsequent roller located higher than the dewatering box level, which may interact with dewatering molds 5 on the lid of the dewatering box.

In the following, the invention will be described with reference to the figure in the accompanying drawings, but the details are not intended to be narrowly limited.

Figure 1 is a side view of a two-wire reformer according to the invention.

The braided wireformer shown in Fig. 1 comprises a bottom wire 10 which, under the control of the breast roll 11a, dewatering elements 13a, 13b, 13c, 13d, suction roll 1bb and guide rolls 11, forms an endless loop, and over the bottom wire 10 Guided by 22b, 22 and 22a, forms another endless loop.

The fibrous slurry is fed from the head box 12 to the level of the wire section formed by the bottom wire 10, where the fibrous slurry is dewatered by means of dewatering elements 13a. A fiber layer, or web W, is applied to the surface of the bottom wire 10, which is applied to the double wire portion defined by the parallel run of the bottom wire loop 10 and the top wire loop 20. At this point, the bottom surface of the web already forms a continuous fiber web, while the top surface of the web may still have a fluid slurry in the fluid state.

At the beginning of the twin wire section, there is a dewatering box 21 on the side of the upper wire loop 20 whose curved lid guides the upper wire 20 from the breast roll 22a to contact the web W on the underside 10. The dewatering box 21 is used to drain water from the web upwards through the upper wire 20. The dewatering box 21 comprises four successive suction chambers 23, 24, 25, 26, each of which has a different male-30 grate structure facing the wire 20. In addition, a different vacuum can be provided in each suction chamber 23, 24, 25, 26. Preferably, the vacuum increases in the direction of web travel.

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The lid of the first suction chamber 23 is shaped such that a pulsatile dewatering pressure can be applied therethrough to the web W. The substantially dewatering pressure is achieved by providing the lid of the dewatering box 21 with a perforation that does not produce a pressure pulse. One such cover structure is described, for example, in EIS patent 6372091 and WO application 2004018768.

The lid of the second suction chamber 24 is formed by transverse dewatering strips 10 with gaps between which the water can be discharged upward due to the vacuum in the second suction chamber 24. In a corresponding position on the side of the bottom wire loop 10 there is a strip loading unit 13b comprising a plurality of dewatering strips 16 to be loaded against the bottom wire 10, each disposed between the dewatering strips on the cover of the suction chamber 24. The dewatering strips below and above the web, together with the vacuum, provide a powerful pulsation which enhances dewatering and improves web formation. The strip loading unit 13b may, if desired, be provided with a vacuum.

The lids of the third and fourth suction chambers 25, 26 consist of transverse dewatering strips, thereby providing a pulsating dewatering pressure.

After the dewatering box 21, the passage of the lower wire 10 is directed obliquely up to the suction roll 1b. This inclined portion has stiffened suction boxes 13c and 13d on the side of the bottom wire loop 10, which drain water from web W downwardly through the bottom wire 10. Another function of the suction boxes 13c, 13d is to ensure that the web W remains on the surface of the lower wire 10 when the upper wire 20 is guided apart by the roll 22b from the web W. The suction roll 1b1 is positioned so that the forming an angle α, preferably of 5-15 °, with the horizontal initial portion of the bottom wire 10. The bottom wire 10 curves over the suction roll 1 Ib in a sector β of at least 60 °. Preferably, the sector β has a length greater than 75 °. After the suction roll 1 Ib, the web W is detached from the lower wire 10 by means of a pick-up roll 32 and transferred to the underside of the release felt 30, which transfers the web W from the forming section to the press section. Between the suction roll 11b and the pick-up roll 32, it is possible to place dewatering elements or an edge cutter (not shown).

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Many variations of the invention are possible within the scope defined by the following claims.

Claims (3)

6 A paper or board machine twin-wireformer comprising a bottom wire loop (10) and an upper wire loop (20), the bottom wire loop (10) forming an initial portion of a single wire 5, followed by a double wire section beginning with a curved dewatering box (21) for directing the upper fabric (20) into contact with the web (W) on the lower fabric (10), the dewatering box (21) comprising a suction chamber (23) in the area of which the dewatering is impulsive, characterized in that the dewatering box (21) (W) is guided obliquely upwards until a suction roll (1 Ib) is received on the side of the bottom wire loop (10), which reverses the direction of travel of the web (W) from obliquely upwardly to downward, and the top wire (20) is guided apart before the suction roll (11b) inside the bottom wire loop (10). A two-wire forming machine according to claim 1, characterized in that the direction of travel of the web (W) after the dewatering box (21) forms an angle (a) of at least 5 ° with respect to the horizontal. A two-wire forming machine according to claim 1, characterized in that the lower wire 20 (10) is curved over the suction roll (11b) in a sector (β) of more than 60 °, preferably more than 75 °. 7