FI77702C - BANFORMNINGSPARTI I PAPPERSMASKIN. - Google Patents

Description

77702 1 Paper forming web forming part Banformningsparti i pappersmaskin 5

The invention relates to a web forming section of a paper machine comprising first and second wire loops, wherein the dewatering of the web-forming fiber suspension takes place in two directions by a common flow of said wires, the forming section having first and second forming rolls inside the first 10 wire loops and a third forming member inside the second wire loop the intermediate ring and the second spinning ring, mainly determined by the first forming roll, form a converging groove into which the paper machine headbox feeds the pulp barrier and in which in the web-forming section which wires form a two-wire web-forming zone comprising, starting from the forming die, the following, 20 es (a) a first forming zone in the region of said first forming roll, located substantially or entirely in the lower quarter of the roll 25, wherein dewatering occurs substantially simultaneously through the first wire and the second wire in the first groove and (b) a second forming zone defined by the curved office of the stationary forming shoe, curved in the same direction as said sector on said first forming roll, and wherein the forming support shoe has slats separated by slits; a guide cover which exerts a pulsating water-35 discharge pressure in the pulp layer passing by it and the interior of the forming shoe of which is connected to a source of vacuum, if necessary, and whose forming shoe guide cover is wrapped the radius is in the range of 1 m to 10 m, preferably in the range of 3 m to 5 m, 2 77702 1 (c) a third forming zone controlled by a forming element within the second bead, and (d) a fourth forming zone controlled by said second forming roll, which in the region, the second wire is separated from the web formed between the wires.

Over the last 20 years, a number of two-wave web-forming components have been implemented by various manufacturers, an overview of which 10 has been published, for example, in Pulp & Paper, September 1982. In addition to or in connection with this review, reference is made to the following patents: CA 960.496, DE 2.105.613, US 3,438,854, 3,846,232, 3,941,651, 3,997,390, 4,113,556, 4,154,645 and 3,996,098. The latter U.S. patent corresponds to pending Applicant 15 FI Application 751774.

Paper is known to be made from cellulosic retention fibers, most commonly derived from wood material. In the papermaking process, the suitably pretreated fibers are usually slurried in about 100 to 300 times the amount of water to form a fiber suspension to which various additives, e.g., mineral fillers, etc., can be added and then fed to a paper machine to provide a uniform, desired width of these fibers. The paper web. When the final dry matter content of the finished paper is about 95%, this means that the removal of water from the fiber suspension is an essential part of the operation of the paper machine. The bulk of this dewatering takes place as a kind of filtration process, the so-called through the wire fabric by the web-forming section of the paper machine, which may be either a single-wire fourdrinier or taeovilof section, or the dewatering of a substantial portion takes place simultaneously through two wires, the common passage of which is then generally curved.

In the mutual comparison of the different types of double-forming web-forming parts, i.e. formers, they should be divided into a few main groups, for example on the basis of how and at what stages dewatering takes place in them. Using this criterion, it is possible to distinguish between "pure" double-layer former and the so-called hybrid formers.

3 77702 1 Cyber-formers are defined as truss-forming sections in which a considerable part of the dewatering takes place with a relatively long section of primer through only one wire, followed by the actual double-wire section.

5 In pure twin wool formers, the pulp is fed directly into the gap between the two wires, i.e. the throat, in order to "freeze" from the very beginning the even gold distribution provided by the headbox to the nonwoven mat or warp formed between the two wires. These ralna formation branches are called kltaformerelksl as shown below. In addition, as an intermediate form between these and the hybrid formers, there are ralna-forming coils in which the pulp is not fed directly into the inter-wire gutter, but into the rather short, often fluff-supported eslvee removal section immediately preceding the gutter.

In connection with the present invention and in comparison with the prior art, attention should be drawn to the paper terms 'formation' and 'retention' which appear both in the description of the invention and in the above-mentioned patents.

20 The term formation has two meanings in paper technology. It can mean, in the papermaking process, a broad concept that includes both the formation of a nonwoven, i.e., the placement of cults on the forming portion of the wire, and the simultaneous dewatering of this clay mat. In this case, the formation of web forming.

25

The designation also means not a property of the finished paper that can be ascertained by looking at a sheet or sample of paper against light. Paper formation is said to be poor if the fibrous material is unevenly distributed in the paper so that there are many larger or smaller cloudy formations. Similarly, the formation is good if the distribution of the fibrous material through the surface of the paper is uniform.

In the following, a forming member or forming surface means a structural member which, in one way or another, participates in the formation of the structure, e.g.

35 by influencing the Dewatering Intensity or how the fibers settle relative to each other. In the forming zone, the roll flanking or guiding the wire can act as a format member.

4 77702 1 The format plate may be a mere plate, but is preferably a box-shaped office opposite the wire. The shaped sheet may be solid, non-perforated, but most commonly has slits that are generally substantially transverse to the direction of travel of the wire. The slits can also be oblique to the course of the ralna, e.g. When the mold is a cover in a box-like structure, this may be under atmospheric pressure, but it may also be connected to a sub-source and thus operate under vacuum.

The term 'retention *' means the ability of a paper web in the wire section to form during the dewatering process to retain in its structure the fine fibers and filler particles in the fiber suspension. Retentlo is affected not only by the fibrous material itself and its e.g. physicochemical properties, but also by many external factors such as the density of the wire fabric, the type of organ-forming member, the speed of the paper machine, etc. Because said fines are important paper raw material components. improve the finishing properties of the finished paper, in various ways, for example in the production of newsprint and printing paper, the aim is to keep the retention as high as possible.

20

As the speeds of paper machines increase, several problems in the formation of ralna have become even more pronounced. In the forming part of the paper machine, the phenomena affecting the fiber network and the still free water in connection therewith, e.g. centrifugal forces, are generally intensified in proportion to the square of the speed of the 25 webs. The maximum web speeds of current newsprint machines are in the order of 1200 m / min. However, there are plans for a newspaper machine with a track speed of up to about 1,500 m / million. Said increase in speed causes several problems, which are discussed below.

30

The problem with hybrid formers as well as flat wire formers at high working speeds is that splashes occur on the free surface of the pulp on the single wire section. These splashes are generated when a jet of pulp from the headboard collides at a small angle with the wire of the chest support-35 ground, whereby the pulp jet partially disintegrates. The load-bearing capacity of said splashes in the direction of travel is quite high and these splashes cause marks on the web formed and thus degrade the quality of the paper to be produced. On the other hand, the impulses caused by the foils used for dewatering in the flat part increase at such high speeds that this also causes splashing which impairs the formation of the ralna. The follicle pulse is known to increase in the square of the velocity. In order for the pulse plate 5 to remain below the spatter limit at high speed, the foil angles must be reduced so small (approaching the 0 ° angle) that sufficient water firing power is not achieved.

Another disadvantage of the flat wire section is that the transverse profile defects in the lip seal may still be accentuated on the flat wire, e.g. due to the flow components of the pulp slurry (so-called plows on the wire) or due to the strengthening of the longitudinal vanes.

In general, it has been found that with guitar formers the variations in basis weight are smaller than with planar warp or hybrid formers, which may be due in part to the fact that the jet feeds the jet directly into the chute where the pulp jet is immediately "cooled" between the two wires. .

20

As the speed of paper machines, especially newspaper machines, has increased, it has become clear that web smoothness is not only an important feature of paper quality but also increasingly a factor in paper machine runnability, as the weakest points in the web are usually the cause of breakage.

25

Against the background set forth above, it is an object of the present invention to provide a method and apparatus for forming a paper web suitable for high web speeds up to 1500 m / min and even higher.

30

It is an object of the invention to provide a method and a former which is particularly well suited for the production of lightweight paper papers such as newsprint and LWC paper, in particular with a paper square of between 2 2 30 g / m 2 and 60 g / m 2. Developments are constantly moving to a smaller 35 square meters (now 45 g / m is common in the newspaper, but in the near future 2 will go 40 g / m and below), which will make the paper uniformity requirements even stricter.

It is a particular object of the present invention to provide a web forming method and a former which achieves even better formation and sheet formation while at the same time achieving at least the same level of retention as is achieved with known retention formers.

Other objects of the invention are to provide a method of forming a web and a former which achieves an even distribution of fines and fillers so that the opposite surfaces of the web are as similar as possible, with low porosity of the paper produced (not so-called pinholes), with which the offset of the paper -printing properties are good and achieve a sufficiently high dry matter content after the wire section.

In order to achieve the said objects, the present invention is based on the so-called a kit former, as it is generally understood and as described above to be best suited for high velocities due to the uniformity of the square mass and the elimination of splashes. On the other hand, the invention seeks to avoid the weaknesses of several previously known kitaformers 20, namely poor formation and poor retention.

The object of the invention is to further develop the web-forming part disclosed in F1 Patent Application No. 751774 (U.S. Patent No. 3,996,098) on the basis of user experience of this structure both for its few commercial applications and especially as a result of extensive test runs on the applicant's test paper machine. , in which case the effect of different structural variants of the basic structure and its components on the operation of the rally forming part has been studied.

30

As stated in the explanatory part of FI application No. 751774, the advantage of the various two-wire web-forming parts is that dewatering takes place considerably more efficiently and faster than with conventional fourdrinier flat wire fabrics and that the former formed paper web 35 has a homogeneous structure than the latter. In this context, the homogeneity of the web structure means that the fibrous material contained in the paper and the so-called the fillers have been uniformly felt in the thickness direction of the web and that both surfaces of the web are, for example, as similar as possible in slile properties. For example, paper intended for newspapers, magazines, etc. must generally contain as many fine fibers and fillers as possible, which give good printing properties to such types of paper.

The experience gained in the web forming section according to FI 751774 in industrial papermaking and the results of test runs performed on a similar structure by the applicant's test machine show that this former avoids one-sidedness and can achieve good pulp retention, but that other formulation is not always satisfactory. The high retention rate is the result of a pulse-free water firing method.

15 Efforts have been made to analyze the factors influencing formatting and some old paper skills need to be recalled in this context. With old low-speed (100-300 m / min) fourdrinier machines, the formation was influenced by shaking the wire back and forth in its plane transverse to the direction of travel of the wire. As the velocities increased, the shaking became ho-te-20 and it was replaced by various fixed flat wire drag-la so-called. forming board structures or similar dewatering and / or forming members having as an integral part a llsta / slit / llsta-type deck structure, one example of which is the structure of Applicant's U.S. Patent No. 4,154,645. The principle of operation of the various arrangements for improving the formation is to apply a controllable and adjustable pulse effect or series of pulses to the nonwoven mat or web to be formed, as a result of which the fibers in the cultivar move relative to each other in a suitable manner to achieve the desired result.

30

Stationary so-called. The disadvantage of using wire rods is their wire-consuming effect, which has been a major drawback, especially when using metal wires. Plastic wires are less delicate in this respect, but the use of stationary members has generally been kept to a minimum. However, as good format has become an increasingly important paper quality criterion in modern high-speed high-power paper machines and thus requires some kind of fixed formation elements, their operation and operating conditions in connection with the present invention have been extensively studied by the applicant.

It has long been known empirically and also as a result of consistent thinking that the uniform positioning of the fibers relative to each other in the nascent mat requires a certain freedom of movement, which is possible only if the non-fibrous water content is high enough to allow the fibers to move. This means that dewatering must not take place quickly. Thus, with the old planer, the aim was to slow down the drainage by using solid-edged forming boards at the beginning of the wire run.

In order to be able to mechanically affect the formation, it has been found that a suitable non-fibrous water content is about 30- to 100-fold the amount of fiber. Such a large amount of water is also useful in that the water leaving the nonwoven during the forming step acts as an effective lubricant between the stationary forming elements and the wire, thus reducing the risk of wear on the wire.

20

As explained in the application F1 751774, dewatering in the web-forming section according to this concept takes place mainly on the first web-forming roll in a sector of about 90 °, although this represents only a small part of the total flow between the first wire and the second wire available for dewatering and generally stripping. for nanoforming. The dewatering thus takes place very efficiently, with the result that the nonwoven mat between the wires has time to reach a dry matter content of 8-10 Z already after the first web-forming roll. In such a consistency, the mutual position of the cults with respect to each other 30, i.e. the formation of the resulting web, solidifies so that it is no longer possible to be influenced sufficiently effectively by the stationary members placed after the forming roll.

The headbox-35 belonging to the web-forming part which is the subject of the present invention feeds a jet of pulp directly into the gap between the two wires as they are sideways in a relatively small sector of the first forming roll. The fiber consistency of the pulp, i.e. the weight amount of paper grains per corresponding unit of suspension volume - 77702 9 1 can at this stage be 0.3-0.5%, which means that the pulp contains 200-300 times the amount of water compared to the fibers. Kultusus pension, or pulp, also contains fillers when making paper for printing. The amount of filler can be equal to the amount of fibrous material, in which case the total consistency of the pulp suspension will be of the order of 0.5-1.5 X.

The web-forming part according to the invention aims at relatively careful dewatering, which is intended to be distributed in controlled successive stages in an optimal and generally relatively even manner in terms of the quality of the paper produced by the different forming members. The aim is to control the dewatering event by initially allowing thinner primary gold layers to form on the surface of each wire, which act like filter cloths. Thanks to these pre-felted fibrous layers, it is possible to substantially improve the retention for the main part of the web forming mass, despite the relatively efficient formation-improving pulsation being applied to the cultivated mat.

In order to achieve the above and later objects, the invention is mainly characterized in that the third forming zone is defined by an arcuate auxiliary forming member, under the control of which the third forming zone curves in the opposite direction to the previous cohesive forming zones. 50 °, preferably between 20 ° -30 °.

Thanks to the invention, it is possible first to felt the surface layers of the ralna with a good retention and then to cause a pulsation-improving pulsation in the forming shoe and, in addition, to exploit the shear force effects acting on the cultivating means on the forming members. The flat water polystopal on the forming roll promotes retention and the shear forces generated in the web when the web is subjected to the wire tension pressure smooth the web formation. The retention of the ralna under pulsation, on the other hand, is improved by the cultured layers already first felted on the ralna surfaces, which act like filter cloth.

ίο 77702 1 It is recommended that these successive forming zones be located substantially vertically with respect to each other, since this makes the treatment and drainage of the suspension water leaving the web relatively simple.

5

A part of the improvement of the formation according to the present invention is achieved by arranging the common coverage angle of the first and second wires on the first forming roll considerably smaller than it is in the web forming part according to the applicant's previous concept (FI 751774).

In addition, the first forming roll el must not necessarily be a suction roll, but in many cases it can be replaced by a suitable hollow surface roll, e.g. a grooved roll.

15

The magnitude of said coverage angle can be only a few degrees at its lowest and even about 50 ° at its maximum. This coverage angle can be adjusted within the desired limits according to the type of paper to be produced with the former by adjusting the position of the wire guide rollers. It should be noted that in order to achieve the desired objectives, it must also be possible to adjust the position of the headbox so that the direction of the mass jet discharged from the headbox relative to the gap formed by the wires together is desired.

Experience gained in various ways with this type of rack formation parts 25 has shown that in order to achieve good or at least satisfactory formation in the dewatering zone following the first forming roll, at least one fixed pulsating formation member must be placed with a sufficiently long range of action.

The arrangement and arrangement of the forming element and forming rolls according to the invention makes it possible that the formation and dewatering of the web can be directed to take place in several lies in the desired manner with a view to the highest possible retention level and good formatting at the same time.

The first lie on the web-forming support takes place in the region of the first forming roll, in which thin fiber layers from the headbox 35 77702 11 1 are pre-felted on the surface of both wires of the former, using a slight water-burning force. The duration of this phase is determined e.g. the extent of the sector in which the wires cover the forming roll. As mentioned above, in the former of application 751774, the wires cover 5 forming rolls in a sector of about 90 °. According to the present invention, a sector of about 5 ° -50 ° and a correspondingly shorter exposure time are satisfied. The water polystopalne drives the suspension water partly into the on-surface vigilant structure of the forming roll, partly away from the roll, in which direction the centrifugal force also acts. Careful dewatering per se has a beneficial effect on the retent, which effect is further accentuated by the pre-felting event.

The closest subsequent dewatering step takes place in the region of the forming shoe, the lid of which is formed by strips substantially transverse to the passage of the wire separated from each other by the slots, thus causing a pulse between the wires on the nonwoven fabric adjacent to the cover. This nonwoven mat forms a kind of sandwich structure, the central part of which is considerably more watery (its consistency close to that of a headbox) than the fiber layers facing the wires. The average fiber density of this non-fibrous material may be in the range of 20 to 1-4 Z as it enters the region of said forming shoe. The non-fibrous water content is thus about 25-100 times that of the fibers, and this makes it possible at this stage to control the formation of the resulting web in the desired manner by means of this pulsation caused by the cover of the forming shoe.

25

The function of the web-forming shoe is not only to influence the formation but also to act as a dewatering element. The lid of the forming shoe is curved and the drainage in its area takes place partly in the direction of centrifugal force bleaching, but also inside the box-like structure of the forming shoe, especially if this box is connected to a vacuum source.

Together, the two dewatering steps described mainly solve the quality of the paper to be produced by the web-forming part according to the invention, in particular with regard to retention and formation.

For example, a forming shoe disclosed in Applicant's F1 Application No. 771364 (corresponding to U.S. Patent No. 35 12 77702 1 4.154.645) can be used in the invention. Ko. the forming shoe is positioned in the ralnan forming section for the common running of the wires so that the wires and the nonwoven between them adjoin the cover of this shoe, which consists of a plurality of strips substantially transverse to the direction of travel of the wire. Each edge of the slat 5 causes a certain hydraulic pulse on the adjacent cult mat, which causes a certain rearrangement of the fibers in the fiber network forming the final web, which usually leads to an optimal formation. Naturally, in the region of such a forming shoe, not only does the fibers move relative to each other, but also the water dewatering, the intensity of which depends on the radius of curvature of the wire guide shoe surface and whether the hollow surface of the shoe is under pressure or vacuum.

In order for the forming surface formed by the lid of such a shoe or box and its possible slats to function to improve the formatting, the non-fibrous water content between the wires in the area of this surface must be high enough so that the fibers can still move relatively freely. In the web forming section according to the present invention, this statlonary forming surface is placed at a suitable distance therefrom after the first forming roll. In this case, it is important that the previous dewatering on the first forming roll has not been too efficient.

The dewatering in the area of the format shoe is influenced by certain structural features of the formation surface, such as its length in the direction of web travel, its radius of curvature, the number of strips therein and the size of gaps between them, etc. The fabric density and type of wires have a considerable effect on dewatering, as does the tension of the wires, which determines the compressive force applied to the nonwoven mat 30 between the wires and which also contributes to dewatering the web.

The invention will now be described in detail with reference to an embodiment of the invention shown in the figures of the accompanying drawing, to which the invention is not limited.

Figure 1 shows a schematic side view of an embodiment of the forming part according to the invention.

Fig. 2 shows a side view in more detail of a forming part according to the invention with its frame structures.

The forming member shown in Figures 1 and 2 comprises a loop 5 of the first wire 20 and a loop 10 of the second wire. The wires 10,20 have a common run between lines A and B, which delimit the binary formation zone of the forming part. The wire 10 is a so-called covering wire and wire 20 ns. load-bearing wire followed by ralna W after the double-wool formation zone. The lip portion 30 of the headbox feeds the pulp jet to the limiting ground K of the wires 10 and 20, which is formed by the relative position of the guide roll 11 and the forming roll 21. The gap D formed on one side of the main wire 10 from the roll 11 to the line A, where the wire 10 meets the first wire 20 (the pulp layer is placed in between), and on the other side of the muodostuskl-TAA D limit of the first muodostuetelan 21 passing over the first 15 of the wire 20.

According to Figures 1 and 2, the first formation roll 21 is a suction roll 21 with a torn sheath 21 'and a suction zone 21a. After the forming roll 21 in the double-forming zone A-B, a forming shoe 22 with a recess 23 consisting of strips 23 follows inside the loop of the ensil-20-like wire 20. There are gaps between the strips 23 of the shoe 22. The radius of curvature 23 of the recess 22 of the shoe 22 is marked with R.

The radius of curvature R of the shoulder of the shoe 22 does not have to be constant over the entire length of the shoe 25, although a constant radius 23 of the shoe is an implementation option. Another preferred embodiment is such that the radius of curvature of the cover part 23 decreases continuously or by suitable steps in the direction of travel of the wires 10 and 20.

In the region of the forming roll 21 and the shoe 22, the common running of the wires curves in the same direction. After these, an auxiliary forming member 13 formed by a roll is placed inside the loop of the second wire 10, in the sector b of which the common run of the wires 10 and 20 is turned to curve in the opposite direction.

This is followed by a second forming roll 35 24 inside the loop of the wire 20, in the region of which in sector c the running of the wires is again turned curved, now in the opposite direction to that of roll b in sector b.

U 77702 1 The second forming roll 24 is a suction roll having two successive suction zones 24a and 24b, in the region of which the web W differs from the covering wire 10 and follows the load-bearing wire 20. The web U then advances to a point P where it is detached from the wire 20 and 26 between the pick-up roll 40 and its suction zone 40a. And is transferred to the pick-up fabric 41 which further carries the web W to the press section of the paper machine (shown).

At the forming shoe 22, inside the second wire loop 10, there are water collecting nozzles 12 that direct the water exiting through the wire 10 to the side of the paper machine. After the auxiliary forming roll 13, there is a water collecting device 26 inside the first wire loop 20, which directs the water leaving the roll 13 to the side of the paper machine. - The guide rollers of the first wire are indicated by reference numerals 25 and the guide rollers of the second wire by reference numerals 15.

15

The following discusses the operation of the former described above and its various variations.

Dewatering from the pulp jet J is started in the groove K through both wires 10 20 and 20. At this point, the sector a of the first forming roll 21 provides for the pre-felting of the cultures on the surface of both wires 10,20 with substantially the same amount of dewatering through both wires. The dewatering is carried out through the first wire 20 with the aid of the inter-wire compression 10,20 and the vacuum 21 in the optional suction zone 25a of the roll 21 and through the second wire 10 mainly under the influence of the wire tension pressure and acceleration forces. In sector a, the dewatering is limited so that the pulp suspension el is completely felted, but it is passed for further dewatering to the cover part of the forming shoe 22, the strips 23 of which cause a pulsation at the water combustion pressure. In this case, water is removed mainly due to the acceleration forces and the tightening of the wires through the second wire 10 and also through the first wire 20, especially if the interior of the box-like shoe 22 and the gaps between the slats 23 are connected by the block 27 shown schematically in Fig. 1.

The auxiliary forming member 13 is a roll provided with a smooth surface 13 'and in its sector b the dewatering takes place mainly through the first wire 20.

II

l5 77702 1 under the effect of tightening and acceleration forces. The auxiliary forming roll can in some cases be replaced by a forming shoe. In sector c of the second forming roll 24, dewatering still takes place to some extent, in particular in the suction zone 24a of the roll 24 under reduced pressure, the suction zone 24b 5 being mainly a release zone, ensuring that the web W follows the first wire 20 after detaching from the second wire 10 (line B).

In the following, the structural alternatives of the former members of the former according to the invention and the suitable ranges and limits of variation of the various parameters will be described.

10

For the reasons set out above, the two-wire drainage zone is preferably substantially vertical, which is not the only embodiment of the invention, but in some cases even a substantially horizontal double section can be used, naturally making the necessary modifications located in its first or second upper quarter.

It is essential in the invention that the field sector-20 of the first forming roll 21 is not purple for the reasons described above, mainly related to formation. The size of sector a is a few degrees upwards and at its maximum sector a within the scope of the invention can be about 50 °. In general, for most preferred purposes of the invention, sector a is about 5-30 ° when the diameter of the roll 21 is of the order of 1.5 m. After sector a, the fiber density of the pulp layer is less than about 3-4 X, generally about 1 X - 3 Z. The radius of curvature R of the guide cover 23 of the shoe 22 is generally in the range of 1 m to 10 m and most preferably in the range of R »3 m to 5 m. After the shoe 22, the fiber density is generally at least about 4 X.

The auxiliary forming member is, according to the figure, a rotating flat roll 13 having a sector b of 5 ° -50 °, preferably between 20 ° -30 °. However, in some cases the auxiliary forming cell may also have a stationary curved surface shoe, the extent of the format of which corresponds to the above-mentioned sector b. The use of the shoe core allows the choice of an arbitrary radius of curvature. The size of the sector c of the roll 24 is of the order of about 60 ° -120 ° and the size of the coverage sector d of the wire 20 is about 120 ° -180 °. After the roll 13, the fiber density of the formed web is generally between 6 X and 7 X.

16 77702 1 As described above, the web-forming part according to the invention makes it possible, thanks to the different types of forming members shown and their arrangement, to achieve a much more even distribution of dewatering in the formation zone than e.g. FI-hak. No. 751774.

5

The amount of water discharged at different stages naturally depends on several different factors, e.g. the type and properties of the pulp used (which partly affect retention), former working speed, type and density of wires, length of forming members (· sectors on forming rolls), etc. the following values can be given for the distribution of dewatering portions of the former according to the invention: zone I 75% - 50 2 15 II 20% - 25 2 III "5 2 - 15% IV" 22-72

Roll 11 is a smooth surface normal guide roll, roll 21 is a snow roll or a hollow surface roll without a suction zone 20. The roll 21 must necessarily have a hollow or open surface so that in sector a the dewatering can take place in two directions, preferably substantially equally through both wires 10 and 20. The auxiliary forming member 13 may in special cases be a hollow surface roller.

Roller 24 is a suction roller. The vacuum 25 in the first suction zone 24a of the roll 24 is generally in the range of 10-30 kPa and the vacuum in the second zone 24 is generally higher and in the range of 40-70 kPa, with which increasing vacuum ensures final drainage so that the fiber density of the formed web W after market d, is in the manufacture of newsprint of class 15 to 20 2.

30

The diameter of the roll 13 is of the order of 1 m. The smaller the curvature or radius of the auxiliary forming member 13, the greater the dewatering pressure in zone b. If the auxiliary forming member 13 is a roll, it is generally possible to go at least much less than 1 m in diameter. due to. The diameter of the roll 24 is almost 1.5 m.

The total length of the two-wire zone is generally of the order of 3-5 m, of which about 77702 17 1 about 1 n becomes part of the cover 23 of the forming shoe 22. The straight runs of the wires 10 and 20 between said active forming zones a, R, b and c are generally kept as short as possible, taking into account space issues and design considerations.

5

A preferred feature in the overall geometry of the former according to the invention is that on the first forming roll 21 the coverage zone a of the wires 10,20 is located in the lower quarter of the roll 21.

A structural example of a former body according to the invention will now be described with reference to Figure 2. The loop of the second wire 10 is arranged as a closed loop on the chest roll 11, the auxiliary forming member 13, the turning roll 14 and the guide rollers 15. The body part 50 comprises vertical beams 51 from which a beam 52 protrudes upwards, to the upper end of which the medicine carriers of the turning roller 14 15 are attached. The frame part 50 is arranged as a carriage to be moved on the rails 55 and 56 in the machine direction, for example for wire change and other maintenance work. This carriage has wheels 53 and 54 which move on said rails 55 and 57. The extreme position of the outer wheels 53 on the rails 56 is indicated by the reference 53 *. The body portion of the first wire 10 comprises 20 vertical beams 61 and 65 and horizontal beams 66 therebetween. The bearing supports of the first forming roll 21 are attached to the vertical beam 61 by means of brackets 62. Correspondingly, the bearing supports of the second forming roll 24 are fixed to the upper end of the vertical beam 51 by means of the body parts 63. The forming shoe 22 is attached to the body 60 via a bracket 25 63. The ends of the beams marked with the reference number 67 in the frame part are in the so-called pedal direction extending along the entire width of the machine. edge release beams by means of which the body part of the first wire is supported on the use side (rear side) in wire change. In this case, the snacks marked with the reference number 68 have been removed from the treatment side (front side). In Figure 2, the floor level of the paper machine room is indicated by reference numeral 70 and the pulp tube entering the headbox 30 by reference numeral 31.

The following claims set forth within the scope of the inventive idea defined by the various details of the invention may vary and differ from those set forth above.

Claims (4)

A paper machine web forming portion comprising first and second intermediate loops (20, 10), wherein in the forming portion dewatering of the cult suspension forming the web (W) takes place in two directions by a common run (AB) of said wires (10, 20), wherein the forming portion 20) there are first and second forming rolls (21, 24) inside and a third forming member (13) inside the second grain loop (10), wherein in the forming part the first wire loop (20) and the second wire loop (10) substantially form the first forming roll (21) a converging groove (K) into which the paper machine headbox (30) feeds the pulp jet (J) and in which the first wire loop (20) and the second wire loop (10) from the first forming roll (21) run a common path to the second forming roll (24); using a suction roll and which, when resuscitated, separate from the loops (10,20) and which form the wires (10,20) a double-forming web forming zone (AB) comprising, in the order shown, the following special and separate forming and dewatering zones 20 (a), the first forming zone in the region of said first forming roll (21) located mainly or entirely in the lower quarter of the roll (21), and wherein the dewatering takes place substantially simultaneously through the first wire (20) and the second wire (10) 25 first in the groove and then in a common sector (a) covering the forming roll (21) of the wires (10,20) is at most about 50 °, (b) a second forming zone defined by the curved (R) office (23) of the stationary forming shoe (22), which curves in the same direction as said sector (a) on said first forming roll (21), and wherein the forming shoe (22) ) is a guide cover formed by slats (23) separated by slots, which causes it to run past but a dewatering pressure pulsating in the pulp bed and the interior of the forming shoe is connected to a vacuum source (27) if necessary, and the radius (R) of curvature of the guide cover (23) of the forming shoe (22) is in the range 1 m to 10 m, preferably in the range 3 m to 5 m, II 77702 19 1 (c) a third forming zone (sector b) controlled by a forming element (13) within the second wire loop, and (d) a fourth forming belt zone (24a, 24b) controlled by said second forming roll (24), in the region of which the second wire (10) is separated of the ralna (W) formed between the wires (] 0.20), characterized in that the third forming zone (sector b) is defined by an auxiliary forming member (13) of the curved surface, under the control of which the third forming zone (sector b) curves in the opposite direction to the previous bipolar forming zones (10). a, 23) and that the extent of the dewatering zone sector (b) controlled by said auxiliary forming member (13) is between about 5 ° -50 °, preferably between 20 ° -30 °. 1 Claims Forming part according to claim 1, characterized in that the surface (13 ') of said auxiliary forming member (13), preferably a roll, is substantially smooth. A web forming section according to claim 1 or 2, wherein the diameter of the first forming roll (21) is of the order of 1.5 m, the length of the guide cover (23) of the forming shoe (22) in the direction of travel of the wires (10,20) is about 1 m, the second forming roll (24) ) is of the order of 1.5 m, characterized in that the radius of curvature of the auxiliary forming member (13) is of the order of 0.5 m and the total length (AB) of the entire double-forming zone is of the order of 4-7 m. A web-forming section according to any one of claims 1 to 3, wherein the different forming zones (a, R, b, c, d) and the members therein are arranged such that the gold consistency of the fibrous layer or web formed by the bipolar portion (AB) develops as follows: - after zone (a) less than about 3-4%, preferably about 1-2%; at least about 4% after the second forming zone (R) defined by the stationary shoe, characterized in that the gold consistency is about 6-7% after the auxiliary forming member (b) and about 15-20% after the second forming roll (24) and possibly the subsequent water treatment elements. 35 20 77702