EP0831172B1 - Wire section and process for dewatering of a fibrous web in a wire section - Google Patents

Description

The invention relates to a method for dewatering a Fiber web in a wire section of a paper machine, at which a fiber suspension from a headbox on Sieve is spread and dewatered.

The invention further relates to a wire section of a paper machine.

When forming sheets in a wire section in a paper machine numerous influencing factors have to be taken into account in order to uniform cross-web density profile, a uniform cross-fiber orientation cross-profile or formation cross profile too and achieve a uniform quality of the paper surface to ensure.

In a conventional headbox, the width of the Outlet gap, through which the material jet exits, via the Specifically influenced web width in order to be as uniform as possible Adjust the fabric density cross profile (aperture control). however is the setting of a uniform formation cross profile problematic.

Recently, it has made significant progress achieves that the headbox is controlled by density a fiber concentration of higher concentration a second Low concentration pulp suspension, e.g. white water, is mixed in the desired amount, the total volume flow regardless of the size of the admixed Partial volume flow remains constant. This led to a significant one Improvement since now the cross-sectional density of the material became controllable without the fiber orientation cross profile was adversely affected.

The disadvantage, however, remained that despite the fact that it remained constant of the volume flow seen over the web width one uneven formation.

EP-A-0 629 740 and DE-A-43 30 546 disclose Twin-wire former with formation strips that overlap extend the web width and one on the sieves Apply varying contact pressure across the web width.

The invention has for its object a screen section and a method for dewatering a fibrous web in a To specify the wire section of a paper machine, with which one if possible uniform formation cross profile can be achieved.

The object of the invention is in a method according to the achieved at the outset in that the drainage rate seen across the web running direction Reaching the immobility point in the lateral edge areas in the Relationship to the center of the fibrous web by means of a suction device, which extends across the web width the paper machine extends and the one across the web width Has varied suction, in particular a forming roller, is changed such that the formation cross-section is as uniform as possible.

The object of the invention is completely achieved in this way.

It was recognized by the invention that the fact that a paper web after its manufacture in the side Edge areas a higher basis weight than in the middle has to be explained in that when drying the The fibrous web shrinks more in the edge areas than in the middle. It was also recognized that the at material density-controlled headboxes lower solid mass flow the drainage resistance at the edge areas the fiber mat in the edge areas compared to the middle of the web reduced. It was also recognized that the edge of the Fibrous web lower suspension layer heights before reaching the immobility point, i.e. the point from which the fibers no longer change their relative position to each other, a disadvantage Influence the formation cross profile.

Now, according to the invention, the drainage rate seen transversely to the web running direction in the edge areas in Ratio to the center of the fibrous web changed, preferably is slowed down before the immobility point is reached becomes a uniformity of the cross-sectional density reached even before the formation cross profile was finally determined is.

In this way, a uniform formation cross profile largely unchangeable after reaching the immobility point fixed.

Preferably takes place in a stronger suction in the edge areas than in the middle.

This is an easy way to make an adjustment the drainage of the fibrous web in the edge areas cause what the cross-sectional density before reaching the Immobility point is evened out.

In the case of a wire section according to the type mentioned at the beginning, the Object of the invention by a arranged in front of the immobility point Suction device that extends across the web width of the paper machine extends and a suction effect varied over the web width in order to achieve a formation cross-section that is as uniform as possible has, solved.

In this way, as already explained, an equalization becomes of the cross-sectional density before the Immobility point is reached and thus the formation is final is set.

It is understood that the invention regardless of the type of headbox and former used, e.g. Hybrid former, rank sieve former or duoformer, advantageous can be used.

The drainage device can be a stationary one or rotating element, such as a suction roll.

The drainage element is an advantageous further development formed as a suction roll, in particular as a forming roll, the divided into at least two lateral and a central zone which can be acted upon with different negative pressures.

In this way it is possible in the side zones to set a different vacuum than in the middle zone, so that the drainage rate of the Fiber web influenced in the edge areas, in particular can be slowed down.

In an additional development of the invention, the width of the Zones designed to be changeable.

This allows a better adjustment of the drainage rate Reach across the web direction.

For this purpose, the zones can be separated from one another by partitions be displaceable in the axial direction.

This is a particularly easy way to get adjustability the width of the zones.

In additional development of the invention are in the individual Zones different suction angles are provided.

This way too, the drainage rate can be adjusted the edge areas in relation to the drainage speed be changed in the middle. Here are in the marginal areas lower suction angle than intended in the middle area, a faster drainage in the middle area to enable.

In an additional development of the invention, the vacuum is adjustable at least in the peripheral areas.

In this way, an optimal adjustment of the drainage speed can be reached across the width of the paper web.

Fig. 1

eine erfindungsgemäße Siebpartie in schematischer Darstellung;

Fig. 2

ein Aufsicht auf die Faserstoffbahn im Formerbereich, wobei Linien gleicher Stoffdichte eingezeichnet sind;

Fig. 3

einen Längsschnitt durch eine erfindungsgemäße Saugwalze und

Fig. 4

einen schematischen Querschnitt durch die Saugwalze gemäß Fig. 3 in vereinfachter, verkleinerter Darstellung zur Erläuterung des Besaugungswinkels.

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

Fig. 1

a screen section according to the invention in a schematic representation;

Fig. 2

a top view of the fibrous web in the former area, lines of the same consistency being drawn;

Fig. 3

a longitudinal section through a suction roller according to the invention and

Fig. 4

a schematic cross section through the suction roll according to FIG. 3 in a simplified, reduced representation to explain the suction angle.

In Fig. 1 is a screen section with the number 10 designated.

The wire section 10 comprises a so-called duoformer CFD, such as this in the "Wochenblatt für Papierfabrikation" 119, 1992, no. 11/12, page 455-460 is described in detail.

The pulp suspension is between a headbox 12 between a forming roll 20 arranged below and one laterally screen guide roller 20 or breast roller arranged obliquely above it diagonally upwards between an upper sieve 16 and a lower sieve 14 shot. The stream of fabric passes diagonally upwards the upper sieve 16 and is discharged via a jet channel (not shown). After the jet channel, the rest water passing through the upper sieve 16 together with the leading edge drainage removed on a vacuum skimmer (likewise not shown) .

At the forming area 19 through the forming roller 20 and the first subsequent section is formed, is followed by a so-called D-part 24, in which the fibrous web through pulsating forming elements in shape of forming strips 27, 28, which are on both sides of the screens 14, 16 are arranged, is dewatered.

Within the D-part 24 there is also the so-called immobility point reached, i.e. the point at which a final fixation the fibers between the sieves 14, 16.

A suction area connects to the D-part, which is separated by a Wet vacuum cleaner 30 and a combination suction box 32, which is a vacuum cleaner for separating the upper sieve 16 and two flat suction zones, before the lower wire 14 is designed as a suction roll Screen guide roller 34 is guided.

In a conventional manner, this normally takes place in the wire section a uniform drainage of the fibrous web across Web running direction 11.

According to the invention, measures are now provided around the drying of the fibrous web 18 in the edge areas to influence in relation to the central area, preferably to slow down. The reason for this is explained with reference to FIG. 2. Even with a headbox that is regulated by density 12 usually results in a faster at the edge areas Drying of the fibrous web 18, since in the edge areas lower solid mass flow into the fibrous web 18 is introduced, which is the drainage resistance of the fiber mat reduced at the edge areas compared to the center of the web.

In Fig. 2 lines 36 are drawn, each one given time points of the same consistency on the Mark fibrous web 18. These lines could therefore also are referred to as so-called iso-density lines. there of course the fabric density increases from left to right, because yes the fibrous web 18 drained on its way to the D-part 24 becomes. From the ISO fabric density lines 36 it can be seen that the Fibrous web 18 normally faster at its edge areas dries than in the middle, as already explained above. This leads to a corresponding increase in the consistency of the Edges. By the measures now provided according to the invention will reduce the rate of drainage in the Edge areas reached in order to homogenize the cross-sectional density to reach before the immobility point the fibrous web 18 is reached within the D-part 24.

Ideally, the ISO fabric density lines 36 would be transverse to 11 running lines before the immobility point is achieved. An ISO fabric density line that can be achieved in practice 36, which shows only minor deviations shown between the two dash-dotted lines 37.

By reducing the drainage rate according to the invention the fibrous web 18 at its edge areas becomes a significant homogenization of the formation profile achieved compared to the prior art.

In principle, however, are also special cases Types of paper conceivable for which a Increasing the drainage rate is desirable.

A particularly preferred way to control the drainage rate the fibrous web 18 at its edge areas to slow down is to use a forming roller 20, according to FIG. 3, at least in two lateral zones 76, 80 and a central zone 78 divided with different ones Suppress can be applied.

The particular advantage of using such a forming roller 20 is that by this special design the forming roller only the dewatering speed the fibrous web 18 is affected in this area, while the drainage rate after leaving the D-part 24 can be largely constant seen over the web width.

The forming roller 20 comprises a perforated roller jacket 39 with two roller covers 40, 42, which with tubular extensions and by means of a roller bearing 48, 50 in stationary bearing housings 44, 46 are supported. The latter also wear a stationary suction box, designated 38 in total is. The suction box 38 is composed of e.g. tubular seal support body 41, end plates 58, 60, and Support tubes 52, 54, which rest in the bearing housings 54, 56 and which serve as suction lines on both roller ends.

The length of the suction box 38 is in the three suction zones 76, 78, 80 divided, the two lateral zones 76, 80 from the central zone 78 through two partitions 62, 64 are divided. The two edge zones 76, 80 are marked by a Connecting tube 56 connected to each other, so that both of the right side over the support tube 54 with the same negative pressure can be acted upon via a suction line 72 connected fan 74 is generated. In contrast, the middle zone 78 through the left support tube 52 via a suction line 68 applied with a different vacuum, which over a connected blower 70 is generated.

The suction zones 76, 78, 80 are through in relation to the perforated jacket Sealing strips 66 sealed, both in the axial direction as well as in the circumferential direction, as can be seen from FIG. 4.

The two partitions 62, 64 are in the direction of arrows 82, 84 adjustable towards the center, so the size of the edge zones 76, 80 in relation to the central zone 78.

In addition, the suction angle α, i.e. the center angle, over which the suction zones extend, in the Edge zones 76, 80 are smaller than in the central zone 78 be to a lower drainage performance in the peripheral areas than allow in the middle.

It is understood that the forming roller 20 also in a larger Number of suction zones can be divided to better Fine adjustment of the drainage speed in the axial direction to enable. Furthermore, one or more of the blowers 70, 74 be designed to be adjustable to the respective suction zones applied vacuum to the respective requirements optimal to be able to vote.

Claims (9)

1. Method of dewatering a fibrous stock suspension in a wet end (10) of a papermaking machine, in which the fibrous stock suspension is applied to a wire (14) from a head box (12) and is dewatered, characterized in that, as early as before reaching the immobilization point, the dewatering rate viewed transversely with respect to the web running direction (11) is varied in the lateral edge regions in relation to the centre of the fibrous web (18), by means of a suction device which extends over the web width of the papermaking machine and which has a suction action that varies over the web width, in particular a forming roll (20), in such a way that the most uniform cross-machine formation profile possible is achieved.
2. Method according to Claim 1, characterized in that the fibrous web (18) has a vacuum applied to it less intensely in the lateral edge regions than in the centre.
3. Wet end (10) for a papermaking machine, characterized by a suction device which is arranged before the immobilization point, extends over the web width of the papermaking machine and has a suction action that varies over the web width for the purpose of achieving the most uniform cross-machine formation profile possible.
4. Wet end (10) for a paper machine according to Claim 3, characterized in that the suction device is constructed as a suction roll, in particular a forming roll (20), and in that the suction roll is divided up at least into two lateral zones (76, 80) and a central zone (78), to which different vacuums can be applied.
5. Wet end (10) for a paper machine according to Claim 4, characterized in that the width of the zones (76, 78, 80) can be varied.
6. Wet end (10) for a papermaking machine according to Claim 4 or 5, characterized in that the zones (76, 78, 80) are separated from one another by dividing walls (62, 64), which can be displaced in the axial direction.
7. Wet end (10) for a papermaking machine according to one or more of Claims 4 to 6, characterized in that various suction application angles (α) are provided in the individual zones.
8. Wet end (10) for a papermaking machine according to one or more of Claims 4 to 7, characterized in that the vacuum can be adjusted, at least in the lateral edge zones (76, 80).
9. Wet end (10) for a papermaking machine according to one or more of Claims 4 to 8, characterized by a cover (39) whose flow resistance is varied over the roll width.

Images