EP0831172A2 - Wire section and process for dewatering of a fibrous web in a wire section - Google Patents

Abstract

In a process for dewatering a suspension of fibrous material delivered onto the wire (14) of a paper machine by a head box (12), the rate of dewatering is changed in the crossmachine direction before the immobility point is reached so that the rate at the edges differs from that in the centre of the web. Also claimed are (a) a paper machine wire section which incorporates a means of changing the dewatering rate in the forming section at the edge of the web with respect to that at the centre, and (b) a suction device (especially a forming roll) in which the suction can be varied across the machine width.

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 with at least one headbox, one former area and a suction area.

When forming sheets in a wire section in a paper machine there are numerous influencing factors to be considered in order to uniform cross fabric density profile, a uniform cross fiber orientation cross profile or formation cross profile too achieve and 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 Target width influenced in order to achieve the most uniform 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 achieved that the headbox is controlled by density a fiber suspension 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 became controllable without the fiber orientation cross profile was adversely affected.

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

The invention is therefore based on the object, a wire 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. Further a drainage device that extends across the width of the web, in particular a forming roller, which are suitable for improving the formation in a wire section is.

The object of the invention is in a method according to the achieved in that the dewatering rate seen across the web running direction Reaching the immobility point in the peripheral areas in the Ratio to the center of the fibrous web is changed.

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 by the fact that when drying the The fibrous web shrinks more in the edge areas than in the middle. It was also recognized that the 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.

According to an advantageous development of the invention, this becomes achieved in that the fibrous web in the edge areas is vacuumed differently than in the middle. 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 a wire section according to the type mentioned at the beginning Object of the invention solved in that means in the former to change the drainage speed in the side Marginal areas in relation to the drainage speed are provided in the middle.

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 formers, rank formers or duoformer, advantageous can be used.

In an advantageous development of the invention, at least a sieve in the edge areas another, preferably one higher drainage resistance than in the middle.

This is one of the ways to control the drainage rate opposite the fibrous web in the edge areas to affect the middle area.

This can be achieved in a simple manner in that the Sieve in the edge areas a different mesh size than in the middle, preferably a reduced mesh size.

In an additional development of the invention, the wire section has a D part contained in the former area, in which Formation strips extend transversely to the web running direction are adjustable to the sieves, at least some of the Formation strips in the edge areas weaker than in the Are pressed in the middle or one that varies across the width of the web Have geometry.

This also allows the D-part, in which the fibrous web reaches their immobility point, a leveling off of the formation cross profile.

According to a further embodiment of the invention, at least some of the formation strips are designed to be adjustable in deflection.

According to a further embodiment of the invention, at least some formation strips are provided, which are over a extend the central area transversely to the web running direction.

These measures also reduce the drainage rate in the middle of the fibrous web compared to the edge areas elevated.

The object of the invention is further achieved by a suction device, solved in particular by a forming roller for a wire section, which has a suction effect that varies over the web width.

This will affect the drainage rate across the width of the web, so one To achieve uniformity of the formation cross profile.

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 side and a middle 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 is 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.

In this way too, the drainage rate can 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, the 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.

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

Fig. 1

eine erfindungsgemäße Siebpartie in schematischer Darstellung;

Fig. 2

ein Aufsicht auf die Faserstoffbann 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 fiber spell in the former area, lines of the same material density being drawn;

Fig. 3

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

Fig. 4

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

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

The wire section 10 comprises a so-called duoformer CFD, such as this in "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 jet of material 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, which is formed by 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 screens 14, 16.

A suction area connects to the D-part, which is separated by a Wet vacuum 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 formed by a suction roll Screen guide roller 34 is guided.

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

According to the invention, a number of 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 controlled 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 also are referred to as so-called iso-density lines. Here 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. Through 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.

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

A number of measures are in place to influence the drainage rate possible over the web width:

On the one hand, screens 14, 16 can be used, which in the Edge areas, for example, a higher drainage resistance than in the middle, which e.g. by a lesser Mesh size in the border areas than reached in the middle can be.

Another option is to use formation bars in the D-section 27, 28 to use the weaker in the peripheral areas than are pronounced in the middle or the deflection adjustable are trained.

Another option is to add certain ones Provide formation strips that are only about extend a central area, but not to the Border areas are sufficient.

All of these measures can be taken individually or in combination Influencing the drainage speed of the fibrous web 18 can be used at their edge areas.

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 middle 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 drainage 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 (16)

Process for dewatering a fiber suspension in a wire section (10) of a paper machine, in which the Fibrous suspension from a headbox (12) on a Sieve (14) is applied and dewatered, characterized in that that before reaching the immobility point the drainage speed transverse to the direction of web travel (11) seen in the edge areas in relation to the center the fibrous web (18) is changed. A method according to claim 1, characterized in that the fibrous web (18) is less strong in the edge areas is sucked as in the middle. Screen section of a paper machine with at least one Headbox (12), a former area (19) and a suction area (30, 32), characterized in that in the former area (19) Means of influencing drainage rate in the side marginal areas in relation to the drainage speed in the middle are provided. Screen section according to claim 3, characterized in that at least one sieve (14, 16) in the edge regions has a different drainage resistance than in the middle. Sieve section according to claim 3 or 4, characterized in that that the sieve (14, 16) in the edge areas is different Mesh size than in the middle. Sieve section according to one or more of claims 3 to 5, characterized by a in the former area (19) contained D-part (24), in which there are formation strips (27, 28) extend transversely to the web running direction (11), the on the sieves (14, 16) can be adjusted, at least some of the formation strips (27, 28) in the edge areas are weaker than the middle. Sieve section according to one or more of claims 3 to 6, characterized in that by a in the former (19) contained D-part (24), in which there are formation strips (27, 28) extend transversely to the web running direction (11), the on the sieves (14, 16) and their geometry is varied across the web width. Sieve section according to one or more of claims 3 to 7, characterized by an attached to the former area (19) adjoining D-part (24), in which there are formation strips (27, 28) extend transversely to the web running direction (11), which can be set on the screens (14, 16), at least some of the formation bars (27, 28) adjustable in deflection are trained. Sieve section according to one or more of claims 3 to 8, characterized by an attached to the former area (19) adjoining D-part (24), in which there are formation strips (27, 28) extend transversely to the web running direction (11), which can be set on the screens (14, 16), at least some formation strips (27, 28) are provided, which is only across a central area transverse to the direction of web travel (11) extend. Suction device, which is the width of a web Extends paper machine, in particular forming roller (20) for a wire section according to one or more of the claims 3 to 9, characterized by a across the web width varied suction. Suction roll according to claim 10, characterized in that the suction roller in at least two lateral zones (76, 80) and a middle zone (78) divided with different pressures can be applied. Suction roll according to claim 11, characterized in that the width of the zones (76, 78, 80) can be changed. Suction roll according to claim 10, 11 or 12, characterized in that that the zones (76, 78, 80) by partitions (62, 64) are separated from each other in the axial direction are movable. Suction roll according to one or more of claims 10 to 13, characterized in that in the individual zones Different suction angles (α) are provided. Suction roll according to one or more of claims 10 to 14, characterized in that the negative pressure at least is adjustable in the peripheral zones (76, 80). Suction roll according to one or more of claims 10 to 15, characterized by a jacket (39), the Flow resistance across the roll width is varied.

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