DE19706923A1 - Double fourdrinier section - Google Patents

Abstract

The fourdrinier section, of a papermaking machine, has a leading paper forming roller (32) at the leading end of the upper fourdrinier in a double fourdrinier assembly. The upper (12) and lower (14) fourdriniers pass together round the roller (32) by an angle of at least 10 deg . Also claimed is an assembly process to build the fourdrinier section using a paper forming roller (32). The upper fourdrinier (12) is placed over the lower fourdrinier (14), with a separation suction unit (34) at the under side of the lower fourdrinier (14) behind the forming roller (32), where the fourdriniers (12,14) pass round the roller (32) by at least 10 deg . An initial zone (18) to extract water from the pulp is between the stock inlet (26) and the roller (32), with a double fourdrinier zone (20) between the roller (32) and the suction separation unit (34).

Description

The present invention relates to a wire section of a Paper machine, with an upper sieve and a lower sieve, one pre-dewatering zone formed by the bottom wire, one twin-wire zone formed by the top wire and the bottom wire, which is downstream of the pre-dewatering zone and at the other The beginning of a roller is provided, and a separating suction device which separates the top sieve from the bottom sieve.  

The invention further relates to a method for producing a Screen section of a paper machine, with the steps of a roller to provide an endless top screen that wraps around the roller and provide a separating suction.

Finally, the invention relates to a method for sheet formation in a wire section of a paper machine, with the steps, a pulp suspension from a headbox on a first Sieve in a pre-dewatering zone to dewater the pulp suspension in a downstream of the pre-dewatering zone Double sieve zone with an upper sieve and a lower sieve to drain, the bottom sieve through the sieve of the previous one Watering zone is formed and the top wire around a roller is looped.

Such a wire section, such a method of manufacture a wire section and such a method for sheet formation a wire section is known from EP-A-0 688 900.

Generally, screen sections can be divided into the following main types divide. The first type is a so-called four-wire former, at the one on a substantially horizontal sieve Fibrous suspension is applied. Below the sieve if necessary, drainage elements are available for drainage as well as to support the even leaf formation. The second The main type is a so-called twin-wire former, in which two endless sieves (one lower sieve and one upper sieve) over one certain section (twin-wire zone) guided parallel to each other will. With the twin wire former, both the top wire as well as drainage elements on the lower sieve. A hybrid former is the third main type generally combinations of wire formers and twin wire formers, as a rule, the twin-wire zone is the four-wire former  is connected downstream and the sieve of the Fourdrinier former Bottom wire of the downstream twin wire former forms.

In EP-A-0 688 900 mentioned at the outset is a hybrid former arrangement with an endless top sieve and an endless Lower sieve formed, the lower sieve being an initial simple pre-drainage zone with a stationary drainage Forming element. Connects to the pre-drainage zone a twin-wire zone. At the beginning of the twin wire zone is a roller is provided, which is followed by a D-part. In the D-part are drainage elements for pulsating ent watering provided.

The roller at the beginning of the twin wire zone is a breast roll that has an active surface area with an open Has surface area of approximately 50 to 80% and with a cover can be provided. The roller can be provided with a suction zone be partially to the fibrous web through perforations suck. The roller is arranged so that the contact surface this roller just lightly into an upper section of the pulp suspension is immersed without significantly bending the lower sieve. In this way, drainage through the upper sieve is intended a thin fiber should be on the upper sieve form layer of fabric. Through this thin layer of fibrous material good retention on the subsequent drainage strips reached and a thrust of desired size in the fiber fabric layer are generated, whereby flakes are dissolved and the formation should be improved.

The further drainage is carried out in the direction of web travel sufficiently spaced D-part with flexible molding strips pressed onto the sieves. In EP-A-0 688 900 is also addressed by such a wire section Conversion work on existing screen sections.  

The known hybrid former has a relatively complex construction tion on. Firstly, the breast roll must be positioned very precisely so that the bottom wire is not deflected significantly. On the other hand, the D-part downstream of the breast roll is one complex assembly that not only requires a lot of assembly but also implies a high maintenance effort.

Another section of wire is known from DE-A-44 20 801. This known section of the screen is a Hybridformer. A D-part is upstream of a forming roller. Following the forming roll, the screens are inside the Twin wire zone redirected a few more times. This section of sieve too has a relatively complex structure.

Finally, a screening section is known from DE 43 01 103 C1, in which a hybrid former for the production of a two-layer Fibrous web is used. For this purpose there is a first headbox at the inlet of the Fourdrinier zone. A second Headbox is located at the inlet of the twin wire zone. In the twin-wire zone is a dewatering element with secondary stored drainage strips provided.

Against this background, the basis of the invention exists Problem in being a comparatively simple and therefore cost inexpensive screen section to form a single-layer fibrous web specify.

This is achieved in the above-mentioned wire section solved that the roller is a forming roller, which is at an angle of at least 10 ° wrapped around the top sieve and the bottom sieve is.  

In the method for producing a Sieve section the problem is solved in that the roller Forming roller is that the upper wire wrapping around the forming roller arranged on the top of a wire of a Fourdrinier former and that the separating suction at the bottom of the sieve of the Fourdrinier former in the running direction of the sieve behind the former roller is arranged such that the forming roller of the Upper sieve and the sieve of the now forming a lower sieve Four-wire former wrapped at an angle of at least 10 ° and that between a headbox of the Fourdrinier and the forming roll a pre-dewatering zone and between a twin-wire zone formed the forming roller and the separating suction will.

In the above-mentioned process for sheet formation in one Sieve section the problem is solved in that the roller Forming roller is and that the top wire and the bottom wire by one An angle of at least 10 ° together around the forming roller be performed.

The problem underlying the invention becomes in this way completely solved.

Because the wire section according to the invention is based on an except neatly simple and therefore inexpensive and yet effective construction. By the measure that the between the pre-dewatering zone and the separating suction Forming roller from the bottom wire and the top wire by at least 10 ° is entwined, at least for the production of ver equally simple fiber web qualities with high Adequate drainage is achieved at speeds.  

In contrast to the solution proposed in EP-A-688 900 takes place due to the wrapping of the forming roller and the this results in the fiber suspension between the two screens pressure exerted a strong drainage instead.

With regard to the method for producing such The following section should be noted. The procedure concerns the conversion of a fourdrinier former into a hybrid former. Approaches of the kind described, for example, in EP-A-0 688 900 are hinted at the prejudice that the Sieve level of the Fourdrinier former must be largely preserved and that the top sieve placed on it is only supportive contributes to drainage. In contrast, according to the invention suggested the forming roller either as far as the screen level of the Fourdrinier former that a sufficient order angle is achieved. Alternatively, it is also possible a downstream separating vacuum so far over the sieve level of the Fourdrinier "raise" that the invention Wrap angle is reached. This makes it a hybrid former, whose twin-wire zone is not only supportive contributes to the four-wire drainage. Rather forms now the twin-wire zone is the main drainage component of the Wire section. In other words, one could say that through the Conversion of the four wire former formed a twin wire former which is preceded by a four-wire section. Through this radical type of conversion surprisingly becomes one significantly increased compared to the original Fourdrinier former Dewatering effect achieved, so that fibrous webs with a much higher running speed can be produced.

The method according to the invention for sheet formation in such Sieve section offers essentials compared to conventional solutions Speed advantages without complex constructions to have to provide.  

According to a preferred embodiment, the two screens are by at least one forming bar against the forming roller acted upon.

This measure can reduce the drainage effect in the area the forming roller can be further increased. Because of this is on the pulp running past the forming roller suspension between the two screens not just a pressure in Direction to the forming roller but also a back pressure exercised so that the drainage takes place through both sieves. The forming strips are preferably resiliently mounted Last so that on the fiber suspension running past it Pressure pulses are triggered, which has a positive drainage effect influence and at the same time for an even formation the fiber suspension.

It is further preferred if the forming roll is vacuumed.

The drainage pressure and thus the Drainage performance further increased.

According to a further preferred embodiment, between no further dewatering from the forming roller and the separating suction Maintenance elements provided.

Surprisingly, it has been shown that the invention according to the sieve section is not absolutely necessary, drainage elements in the twin wire zone between the forming roller and to provide the vacuum cleaner. In particular, it is not necessary to arrange a D-part in this area. So far the experts generally assumed that such additional drainage elements in the twin-wire zone are essential to ensure adequate drainage performance  to achieve. In contrast, it has been shown that it is a product sufficient at least simple fiber web qualities is when in a hybrid former as the main drainage element only a forming roller is provided, which is from the bottom wire and wrapped around the top wire at an angle of at least 10 ° is. Precisely the absence of such additional drainage elements brings considerable constructive simplifications and with it cost advantages.

It is further preferred if in the pre-dewatering zone on the underside a shoe with fixed drainage strips is provided.

Such a shoe or press shoe, which is preferably a curved one Can have top, leads to an improvement in Drainage performance in the pre-drainage zone. Hereby it may be possible, for example, to vacuum the forming roll to renounce.

Another preferred development of the invention provides that the distance from the center of a first roll of the wire section to the center of the forming roller approximately equal to the sum of the radii the first roller and the forming roller and the length of the shoe is.

This measure ensures adequate drainage created a particularly compact pre-dewatering zone.

According to an alternative embodiment, the forming roller directly after a first roller of the wire section.  

In this alternative, a shoe is dispensed with. In this Case, it is particularly preferred if the forming roller ver equally close to the first roller (breast roller) of the Fourdrinier wire zone is arranged.

It is understood that the above and the next Features to be explained not only in the respective specified combination, but also in other combinations or can be used alone, without the scope of to leave the present invention.

Further features and advantages of the invention result from the following description of preferred exemplary embodiments with reference to the drawing. In it show:

Figure 1 is a schematic side view of a first imple mentation form of a wire section according to the invention. and

Fig. 2 is a schematic side view of another embodiment of the wire section according to the invention.

A first embodiment of a wire section of a paper machine according to the invention is generally designated by the reference number 10 in FIG. 1.

The wire section has an endless top wire 12 and an endless bottom wire 14 .

The lower sieve 14 forms a pre-dewatering zone 18 . A double sieve zone 20 adjoins the pre-dewatering zone 18 , in which the sieves 12 , 14 are guided approximately parallel to one another. The twin-wire zone is followed by an outlet zone 22 , from which a fibrous web formed by the wire section 10 is transferred to a (not shown) press section of the paper machine.

At the inlet of the pre-dewatering zone 18 , a headbox 26 is provided, by means of which a fiber suspension is placed on the lower wire 14 . In this area, the lower wire 14 is guided around a first roller 28 of the wire section 10 , which is designed as a so-called breast roller 28 .

At the breast roller 28 on the underside, a statio nary drainage element in the form of a curved shoe 30 is provided, which is provided with fixed drainage strips which press against the lower wire 14 and thereby cause suctioning of the applied fiber suspension.

At the outlet of the press shoe 30 is located immediately to the inlet of the twin-20th Here is a suction forming roller 32 is provided, around which the top wire 12 is looped and which is wrapped together by the top wire 12 and the bottom wire 14 at an angle of about 20 °. The suction zone of the forming roller 32 extends in front of and behind the area of the common wrap through the top wire 12 and the bottom wire 14 . The outlet of the twin-wire zone 20 is located at a separating suction device 34 which is arranged on the underside and in the area of which the top wire 12 is lifted off the fibrous web formed. A plurality of so-called support foils 38 are provided between the separating suction device 34 and a screen guide roller 36 which is vacuumed and wrapped by the lower screen 14 . In the outlet area of the suctioned wire guide roller 36 , the fibrous web formed is taken over in a known manner by a pickup roller 40 and transferred to the downstream press section.

A series of wire guide rollers 42 are provided to form the endless loops of the top wire 12 and the bottom wire 14 .

The wire section 10 is a so-called hybrid former with a simple pre-dewatering zone 18 and a twin wire zone 20 . Although it is conceivable to produce this screen section 10 as a whole, a preferred way of producing such a screen section 10 is to convert or upgrade an existing wire former. This is explained as follows.

In a four-wire former, the fiber suspension is guided approximately horizontally on a sieve. In the present case, this could be the lower wire 14 , which is guided between the breast roll 28 and the suctioned wire guide roll 36 in a plane 46 , as shown in FIG. 1. The retrofitting of such a four-wire former to a hybrid former according to the invention is carried out in such a way that the top wire 12 and the forming roller 32 with the associated wire guide rollers 42 are arranged so that the forming roller 32 "plunges" into the plane 46 . This ensures that the top wire 12 and the bottom wire 14 loop around the forming roller 32 together over an angular range of at least 10 °. It is understood that larger wrap angles can be achieved if the forming roller 32 is "plunged" further into the plane 46 . From Fig. 1 it can also be seen that the wrap angle is also largely determined by the arrangement of the separating suction 34 . Such a separating suction device 34 must necessarily be provided when converting the fourdrinier former to a hybrid former, so that the upper sieve 12 can be lifted off the fibrous web formed on the lower sieve 14 . Depending on the arrangement of the separating suction device 34 , a more or less large wrap angle of the two screens 12 , 14 around the forming roller 32 is achieved. In the illustration of FIG. 1, the top of the separating suction device 34 lies approximately on the level 46 (the former sieving level of the Fourdrinier former). However, it is also conceivable to arrange the separating suction device 34 lower, as a result of which the wrap angle is reduced. In a higher arrangement of the suction pad 34 , the wrap angle 32 is increased.

Thus, the position of the forming roller 32 with respect to the plane 46 and the relative position of the separating suction device 34 results in a more or less large wrap angle of the two screens 12 , 14 around the forming roller 32 . It is therefore understood that the arrangement of the forming roller 32 and the separating suction 34 shown in FIG. 1 is only to be understood as an example. Their relative position is rather to be adapted to the boundary conditions in the sheet formation. These boundary conditions include the type and moisture content of the fiber suspension, the fiber web quality to be achieved, and the desired running speed.

As shown in Fig. 1, the wire section 10 according to the invention in the twin wire zone 20 between the forming roller 32 and the separating suction 34 preferably no further drainage elements. Although there has been a prejudice in the professional world that dewatering elements, in particular flexible forming strips, must be present in hybrid formers in the twin-wire zone, it has surprisingly been found that respectable fiber web qualities can also be achieved in the twin-wire zone 20 without further dewatering elements. In particular, it is critical that there is no D-part in this preferred embodiment. Such D-parts consist of an arrangement of resiliently mounted forming strips on a sieve and generally fixed forming strips on the other side of the sieve, which are arranged alternately to the resiliently mounted forming strips. It is recognized that such D-parts have an extremely positive influence on the drainage performance and the fiber formation. However, they also add significantly to the cost of a wire section. Thus can be converted through the inven tion-appropriate sieve section 10 , which manages without such a D-part, an existing four wire former particularly inexpensively to a hybrid former with improved dewatering performance and thus higher running speed.

In the pre-dewatering zone 18 , the press shoe 30 is designed with a curved surface on which the lower wire 14 is guided. Due to the curved surface, the lower wire 14 can be deflected within certain limits with respect to a straight connection between the breast roll 28 and the forming roll 33 , so that the pressure on the lower wire 14 and thus on the fiber suspension is increased. In particular, by combining such a curved press shoe 30 with a downstream forming roller, between which the lower wire 14 is guided in an "S-shaped" manner, high drainage performance can be achieved both through the lower wire 14 and through the upper wire 12 .

Another embodiment of a wire section 10 'according to the invention is shown in FIG. 2. The representation of the wire section 10 'extends essentially to those parts which differ from the wire section 10 . Regarding the common, reference is made to Fig. 1.

In the wire section 10 , the lower wire 14 is guided between the breast roll 28 and the forming roll 32 'approximately horizontally on the plane 46 . A looping of the forming roller 32 'through the upper wire 12 and the lower wire 14 of at least 10 ° is achieved in that the top of one of the forming roller 32 ' downstream separating suction 34 'above the level 46 is arranged. As a result, the fibrous web formed runs obliquely downward between the separating suction device 34 'and the wire guide roller 36 in the outlet zone 22 ' on the lower wire 14 .

With the special arrangement of the forming roller 32 'and the separating suction 34 ' of the wire section 10 'it is illustrated once again that, in order to achieve a certain wrap angle of the two wires 12 , 14 around the forming roller 32 ', it is not just the arrangement of the forming roller 32 'itself , but also depends on the arrangement of the downstream vacuum cleaner 34 '.

In contrast to the wire section 10 of FIG. 1, in the wire section 10 'of FIG. 2 in the pre-dewatering zone 18 ' there is no dewatering element like the press shoe 30 of the wire section 10 . As a result, a lower dewatering performance is achieved in the pre-dewatering zone 18 '. However, this can be compensated for, for example, by the fact that the wrap angle of the two screens 12 , 14 around the forming roller 32 'is chosen to be larger than in the wire section 10 of FIG. 1. While in the wire section 10 of FIG. 1, a wrap angle of approximately 20 ° is provided, the wrap angle in the wire section 10 'is approximately 50 °.

Preferably, the wrap angle is in the inventive wire section 10 ; 10 'in the range of 10 ° and 70 °, particularly preferably in a range of 20 ° to 50 °.

Another difference between the wire section 10 'and the wire section 10 of FIG. 1 is that the forming roller 32 ' is not vacuumed. This also results in a lower dewatering performance than by the forming roller 32 of the wire section 10 of FIG. 1. However, this is also compensated for by the larger order looping angle.

In addition, it is also possible to design the surface of the separating suction device 34 'to be comparatively strongly curved, so that a higher drainage capacity can also be achieved by the separating suction device 34 ' due to the higher contact pressure.

The two embodiments of screen sections 10 , 10 'of FIGS. 1 and 2 have in common that the screens 12 , 14 are guided in an approximately S-shape in the region of the twin screen zones 20 and 20 '. The S-curvature is much larger in the wire section 10 'than in the wire section 10 .

Claims (11)

1. Sieve party ( 10 ; 10 ') of a paper machine, with
an upper sieve ( 12 ) and a lower sieve ( 14 ),
a pre-dewatering zone ( 18 ; 18 ') formed by means of the bottom wire ( 14 ),
a twin-wire zone ( 20 ; 20 ') formed by the upper wire ( 12 ) and the lower wire ( 14 ), which is connected downstream of the pre-dewatering zone and at the beginning of which a roller ( 32 ; 32 ') is provided, and
a separating suction device ( 34 ; 34 ') on which the upper sieve ( 12 ) is separated from the lower sieve ( 14 ), characterized in that
the roller (32; 32 ') a forming roll (32; 32') which is embraced by an angle of at least 10 ° from the top wire (12) and the bottom wire (14). 2. Screen section according to claim 1, characterized in that the two screens ( 12 , 14 ) by at least one forming bar ( 33 ; 33 ') against the forming roller ( 32 ; 32 ') are beaten. 3. Screen section according to claim 1 or 2, characterized in that the forming roller ( 32 ) is suctioned. 4. Screen section according to one of claims 1-3, characterized in that no further dewatering elements are provided between the forming roller ( 32 ; 32 ') and the separating suction device ( 34 ; 34 '). 5. Sieve section according to one of claims 1-4, characterized in that in the pre-dewatering zone ( 18 ) on the underside a shoe ( 30 ) is provided with fixed drainage strips. 6. Screen section according to claim 5, characterized in that the distance from the center of a first roller ( 28 ) of the screen section ( 10 ) to the center of the forming roller ( 32 ) is approximately equal to the sum of the radii of the first roller ( 28 ) and the forming roller ( 32 ) and the length of the shoe ( 30 ). 7. Screen section according to one of claims 1-4, characterized in that the forming roller ( 32 ') is arranged directly after the first roller ( 28 ) of the screen section ( 10 ). 8. A method for producing a wire section ( 10 ) of a paper machine, comprising the steps:
Providing a roller ( 32 ; 32 '),
Providing an endless top wire ( 12 ) which wraps around the roller ( 32 ; 32 '),
Providing a separating suction device ( 34 , 34 '),
marked by:
the fact that the roller ( 32 ; 32 ') is a forming roller and by the further steps:
Arranging the top wire ( 12 ) wrapping around the forming roller ( 32 ; 32 ') on the top side of a screen ( 14 ) of a wire former and arranging the separating suction device ( 34 , 34 ') on the bottom side of the wire ( 14 ) of the wire former in the running direction of the wire ( 14 ) behind the forming roller ( 32 , 32 ') in such a way that the forming roller ( 32 , 32 ') is wrapped around the top wire ( 12 ) and the wire of the wire forming machine, which now forms a bottom wire ( 14 ), by an angle of at least 10 ° , and that between a headbox ( 26 ) of the Fourdrinier former and the forming roller ( 32 , 32 ') a pre-dewatering zone ( 18 , 18 ') and between the forming roller ( 32 , 32 ') and the separating suction device ( 34 , 34 ') a twin-wire zone ( 20 , 20 ') are formed. 9. The method according to claim 8, characterized in that the forming roller ( 32 ) is arranged so that its lower apex is below the screen plane ( 46 ) of the former Fourdrinier former. 10. The method according to claim 8, characterized in that the forming roller ( 32 ') is arranged so that its lower vertex is on or above the screen plane ( 46 ) of the former Fourdrinier former, and that the top of the separating suction ( 34 ') over the sieve level ( 46 ) of the former Fourdrinier former. 11. A method for sheet formation in a wire section ( 10 ) of a paper machine, comprising the steps:
Pre-dewatering a fiber suspension from a headbox ( 26 ) on a first sieve ( 14 ) in a pre-dewatering zone ( 18 ; 18 '),
further dewatering the pulp suspension in one of the pre-dewatering (18; 18 ') downstream of double screening zone (20; 20') with a top wire (12) and a bottom wire (14), wherein the bottom wire (14) through the screen (14) of the predewatering is formed and the top wire ( 12 ) is wound around a roller ( 32 ; 32 '),
characterized in that
the roller ( 32 ; 32 ') is a forming roller ( 32 ; 32 ') and that the upper wire ( 12 ) and the lower wire ( 14 ) are guided together around the forming roller ( 32 ; 32 ') by an angle of at least 10 ° .