DE2413421A1 - TWO-PIPE FORMER IN A PAPER MACHINE - Google Patents

Description

PATENT AGENCY OFFICE? A 1 ΊΑ? 1 TlEDTKE - BOHL-ING "KlNNE

TEL. (0B9) 539653-56 TELEX: 524845 tlpat CABLE ADDRESS: Germaniapatent Munich

8000 Munich 2

Bavariaring 4

P.O. Box 20 24Oa 2O ₄ March 1974

B 5912

Valmet Oy
Helsinki, Finland

Two-wire former in a paper machine

The invention relates to a two-wire former of a paper machine, in which the removal of water from the paper web being formed is carried out simultaneously by the supporting wire and by the covering wire '^; and which has two suction rolls within the loop of the supporting wire, of which the first suction roll in the running direction of the web is a web-forming roll and the second is a chewing roll, the web-forming roll having a dewatering zone consisting of at least two suction compartments, which is a sector, which is covered by both sieves and in which the drainage primarily by pressing the sieves together

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is achieved and the length of which is most suitably 90 to 120 °, the supporting screen and covering screen in the Sew one web forming roll in front of its dewatering zone Form throat in which the headbox fiber suspension gives in.

In recent years there have been a number of so-called twin wire former designs have been developed in which the drainage of the resulting paper web in two directions at the same time takes place. This working principle speeds up drainage quite considerably. Furthermore, the paper web formed in this way has a more homogeneous structure than that achieved with a conventional Fourdrinier screen.

In the original, aim for symmetrical drainage In the two-wire former, the sieves ran vertically and the mass was introduced between the sieves from above. The present The two-wire formers in use differ from the original design and from each other primarily Line with regard to the direction of mass feed and in what way the common run of the sieves in that section is done, in which the formation and consolidation of the web takes place between these wires.

It has been found to be beneficial in most cases- 409843/0270

put to effect the dewatering with the help of centrifugal force by making such a two-wire combination designed that the wires must run along a curved path, especially in the one immediately after the headbox following initial section, where the main Drainage takes place.

One such solution is the construction according to GB-PS 993 837, in which the sieves wrap around two rollers Describe the S-shaped path. The weak point with this type of construction and its modifications is that the sieve that around the first roller was running around as the inner screen, the next roller is on the outside. The sieves must be here move with respect to each other, which can damage the already formed fiber web carried between them, with either their fiber orientation is disturbed or their strength is reduced.

Constructions in which both the wires on their common runway and the fiber web formed in this way curve only in one direction are previously known, for example, from Finnish patent applications Nos. 3319/68 and 2580/65. These have the disadvantage, among other things, that the path of the sieve following a curved path by means of different types against the Screen of scraping members (suction shoe with curved surface

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and the like.) Is achieved, which has a strong wear effect exercise on the sieve. A disadvantage can also be seen in the relatively large space these constructions in the Claim machine direction.

The object of the invention is to create an effective dewatering unit that is in relation to the production capacity Has the smallest possible size and is therefore inexpensive to build and saves space in the paper machine room. Therefore the dewatering of the fiber web should take place as symmetrically as possible, i.e. equally through both surfaces of the Fiber web through, but in such a way that the above-mentioned disadvantages occurring in the known constructions are avoided.

This object is achieved in that the supporting wire and the covering wire from the beginning of the suction zone of the web-forming roller from together towards the center of the loop formed by the supporting screen obliquely upwards at least run to the point where the supporting screen touches the chewing roller.

The invention is explained in more detail below with reference to schematic drawings.

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1 shows a schematic side view of an embodiment of the invention;

Fig. La shows, on an enlarged scale, a partial section through the web forming roller in sector β;

FIG. 2 shows a second exemplary embodiment which differs somewhat from the former.

Belong to the construction shown in the figures two dewatering rollers lying within one and the same wire loop 4 and 5 connected to a suction system. The load-bearing sieve is understood to mean that sieve on which the paper web remains after the forming process and from which it is in the usual way for forwarding to the Press part is removed. The first of these suction rolls in the running direction of the web is the web forming roll 4. The one around the The supporting wire 1 running around the web-forming roller H and the covering wire 2 brought together therewith form a throat 12, into which the fiber suspension from the headbox 11 is added. In order to prevent flooding, i.e. filling of the throat 12 and transverse currents, the circumferential speed of the web forming roller U must be higher than the speed of the mass jet. The angle, i.e. the size, and the direction of the throat gap 12 can be adjusted by adjusting

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of the breast rolls 8a and 7b. Same way is the pressing force acting on the mass between the sieves 1, 2 can also be regulated. The drainage begins effectively and symmetrically in the throat 12 itself and then continues on the forming roller 4 by centrifugal force. That from the The mass of squeezed out water escapes to the outside through influence the centrifugal force and into the web-forming roller 4 into the holes in the roller shell. Suction supports them Emptying the holes, but is not absolutely necessary.

If the dewatering caused by centrifugal force tends to cause one-sidedness at high speeds, one can choose a sufficiently dense fabric for the covering screen 2; above all, however, this is done with use of suction on the web forming roller 4. The web forming roller U has at least two suction compartments in its sector ß, in which the prevailing negative pressure depending on the drainage conditions can be regulated.

Following the web forming roller 4, the wires 1, 2 are passed together to the chewing roller 5 along an either straight or slightly curved path. A curvature of the path is necessary so that the sieves 1, 2 remain together over the entire route without this being excessive Tightness of the screen 2 is required.

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The holding together of the sieves 1 and 2 can be supported by means of a sipe strip on the side of the covering Siebs lies and which both presses on the sieve and also serves as a drainage element.

So that the path traversed jointly by the sieves is curved, a few can be placed between the suction rolls H and 5 Insert sieve members 10, 14 (Fig. 2). Either rotating rollers 10 or one or one serve as sieve members 10, 11 . Several fixed and narrow strips 14, whose'schabende Effect on the sieve 1 is as low as possible.

The chewing roller 5 also most suitably has at least two suction fans in its sector γ.

For removing the on the section between the web forming roll U and the chewing roller 5 pressed out of the paper web 3 are located on both sides of the Suitable drainage devices such as deflectors, scrapers, etc. (foils) IH or the like. Which are arranged so that they Present as few edges as possible that scrape and wear the sieves 1, 2. These limbs do not press strongly against the Sieves 1, 2. The small number of dewatering elements also makes it possible to adjust the distance between the web forming roller U and to keep the chewing roller 5 relatively short; the one in question

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Distance is most suitable 1.5 to 2 times, but at most 3 times the diameter 2R. of the roller U. The screen length thus saved can be used on the section where the tensioning and guide rollers 8 and 7 of the screens 1, 2 are located, whereby one can take care of the guidance of the sieves 1, 2 in a reliable manner. The loop of the load-bearing screen 1 is formed as an elongated in the horizontal plane, the web 3 forward-conveying part, of which the web 3 with the help of a Suction roll 9 is removed.

In Fig. 1 a used inside the loop of the screen 1 suction shoe 6 is shown, which to a small extent (with Radius of curvature R_) is curved in the same direction as The sieves 1 and 2 curve on the rollers 4 and 5.

The water that has leaked on the web forming roller M- is Collected in specially provided troughs 15a and fed to the suction side of the mixing pump feeding the material outlet box 11 Used as dilution water.

That from the drainage organs 6, 13, IU and from the The chewing roll 5 is running water, the fiber content of which is usually lower than that obtained from the forming roll Water is collected in its own troughs 15b and carried to a point in the water system where there is a lower fiber content is assumed.

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It is also important in the invention that the straighter lonely traveled by the wires 1, 2 range continuously in one direction (R curves _1, R ₂ '^ 3 ^ · The following size differences of the radii R, R', R _3, also meaningful:

As for the guidance of the covering screen 2, this takes place here. Aid drßrustwalze 7b in the vicinity of the web-forming roller ¹ ^ i this breast roller 7b is displaceable in such a way that the angle of the throat 12 and the length of the throat 12 can be regulated as required. On the chewing roller 5, the covering wire 2 runs around the pressure roller 7a, by means of which the fiber web 3 is simultaneously pressed against the suction zone y of the chewing roller 5 in order to bring about dewatering. The position of the pressure roller 7a and its pressure against the chewing roller 5 can be regulated, and in its one end position (FIG. 2) the suction zone -γ of the chewing roller 5 can be brought into congruence with the covering screen 2 in its entirety.

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Claims (7)

- ίο - Claims Two-wire former in a paper machine, in which the dewatering of the resulting paper web (3) is carried out at the same time takes place through the supporting sieve (1) and through the covering sieve (2) and within the supporting sieve (1) two suction rolls (4,5) are located, of which the one at the front in the running direction of the web (3) is a web forming roll (4) and the second is a chewing roll (5), the web-forming roll (4) being one consisting of at least two suction fans Dewatering zone (ß) which includes that roller sector which is covered by both screens (1, 2) and in which the drainage is primarily achieved by pressing the screens (1,2) together is achieved and the length of which is most suitably 90 to 120, and wherein the supporting sieve (1) and covering sieve (2) in the vicinity of the web-forming roller (4) in front of its dewatering zone (β) form a throat (12) into which the head outlet box (11) adds fiber suspension, characterized in that the supporting sieve (1) and the covering sieve (2) from the beginning the suction zone (β) of the web-forming roller (4) together in the direction of the center point of the loop formed by the supporting wire (1) run diagonally upwards (OC) at least to the point where the supporting screen (1) touches the chewing roller (5). 409843 / 027U - li - 2. Two-wire former according to claim 1, characterized in that the supporting sieve (l) and the covering sieve (2) together via the one beginning at the point of contact of the chewing roller (5) with the supporting sieve (1) or in its vicinity The suction zone (Ύ ~) is running (Fig. 2). 3. Two-wire former according to claim 1 or 2, characterized characterized in that the common portion of the supporting and covering wires (1, 2) is between the web forming roll (4) and the chewing roller (5) curves in the same direction as the screens (1,2) on the suction rollers (4,5), the The center of curvature (P) of this section is in the vicinity of the center of the loop formed by the supporting sieve (1). 4. Two-wire former according to claim 3, characterized in that that the aforesaid curvature (Rq) of the common section is achieved by the action of the curved surface of a suction shoe (6) or the guidance by guide rollers (10). 5. Two-wire former according to one or more of the preceding Claims 1 to 4, characterized in that the length of the common section of the supporting and the covering Sieves at most 3 times and most suitably 1.5 to 2 times as large as the diameter (2P ^) of the web forming roller (4) 409843/0270 is and that the loop of the supporting screen (1) as a in the Horizontal plane more elongated, the web (3) conveying forward Part is formed. 6. Two-wire former according to one or more of the preceding Claims 1 to 5, characterized in that the common portion of the supporting screen (1) and the covering Siebs (2) or its main direction an angle (OO from 30 to 60 ° to the vertical plane. • - 7. Two-wire former according to one or more of the preceding Claims 1 to 6, characterized in that on the common portion of the supporting screen (1) and the covering Siebs C2) the drainage by means of deflectors (13) and / or Wipers (foils) (14) takes place. 409843 / Ö27Ü Blank page