DE29615057U1 - Headbox for adjusting the formation of a paper web - Google Patents

Description

P 05481 / 29&bgr; 15 057.8 / Voith Sulzer Papiermaschinen GmbH i _t DrSJsp0fQB1 /£g. November 1B9Q

Invent U. Begemann ,**··** « » ·· · ··

Headbox for adjustment

the formation of a paper web

The invention relates to a headbox with the features of the preamble of claim 1,

Headboxes that comprise turbulence tube bundles to generate turbulence in the headbox are well known from the state of the art. In particular, for example, DE 33 21 406 shows turbulence inserts in a headbox that comprise a large number of stepped turbulence tubes, so-called step diffusers. The turbulence spectrum is adjusted in such turbulence generators using exchangeable sleeves, also called inserts, with which the gradation and the inlet cross-sections in the turbulence generator can be changed. A special feature of such headboxes is that no slats are arranged in the nozzle channel, which is formed by the upper and lower lips.

A second embodiment of headboxes known from the prior art relates to those with slats arranged in the nozzle, which are attached horizontally between the individual rows of turbulence tubes. In such headboxes, both the number of slats and the slat geometry can be varied to produce a specific turbulence spectrum. In this context, reference is made, for example, to DE 43 07 143, which shows a headbox with slats in the nozzle channel, whereby the slat shape can be designed differently to adjust the speed in the individual slat channels.

If a certain formation in the sheet or a particularly low breaking length ratio is desired, the formations or breaking lengths that can be achieved with a headbox that only comprises turbulence tubes are

P 054&bgr;1 ( 29&bgr;&Lgr;5057.&bgr; / Voith Sulzer Papiermaschinen qmbH /„DrS/spOP831 /£S. J Inventor: U. Begemann .".." ·· ·· ; JJ,.

November 19S8

severely limited. A turbulence spectrum generated solely with the help of a turbulence tube bundle is too coarsely turbulent for a sufficiently good formation with a low breaking length ratio. In order to achieve a low breaking length ratio in such a case, considerable pulsations are generated in the sheet with the help of strips in the wire section in order to obtain a finely distributed fiber network. On the other hand, however, this can lead to fines and fillers being washed out of the sheet. Furthermore, with such headboxes it must be noted that if a sufficiently even distribution of the fibers in the jet is to be generated solely by the turbulence in the headbox, such a strong turbulence generation is required that in such a case jet instabilities are the result.

The disadvantages of the first-mentioned headbox are essentially avoided by headboxes with lamellas in the nozzle channel. However, such headboxes only work optimally in a very narrow throughput range.

If the throughput is too high, the stability of the jets emerging from the individual turbulence tubes increases. The result of this is stable individual jets, which can be seen in the form of formation disturbances in the blade. If, on the other hand, the specific throughput is too low, segregation phenomena can occur. The result of this is again formation disturbances.

The task therefore arises of improving headboxes in accordance with the state of the art so that a consistently good formation in the sheet is achieved largely independently of the specific throughput of the headbox and, at the same time, the lowest possible tear length ratio is achieved. In particular, it should be possible to handle throughput fluctuations that are greater than 1:1.3, i.e. of more than 30%, with consistently good formation without major structural expenditure.

P 05461 / 29&bgr; 15 037.8 / Voith Sulzer Papiermaschinen GmbH / DrS/spOOO81 /2$. Inventor U. Begemann ·· ·· .! .1 .**··

V 5 ''JO

November 19&bgr;&bgr;

This object is achieved by a device according to claim 1.

By combining a turbulence tube bundle, in which the turbulence spectrum can be determined by selecting the turbulence tube inserts, and turbulence lamellae, which can specifically influence the turbulence spectrum generated with the help of the turbulence tube bundle by varying the number, length and surface shape, it is possible to achieve a consistently good formation of the sheet for a wide throughput range. In particular, with the device according to the invention and the method according to the invention, it is possible for the first time to optimize the headbox in the shortest possible time in the event of changes in throughput without structural interventions that would require the paper machine to be shut down for a long period of time in relation to the quality of the fibrous web formed. As a rule, the rough adjustment of the turbulence spectrum required for good sheet quality is carried out by replacing the turbulence insert(s) and the fine adjustment or adjustment is then carried out using the lamellae arranged in the headbox. In particular, according to the method according to the invention, it is possible for the first time to adjust the turbulence spectrum generated by the turbulence tube to the operating mode of the turbulence lamellae. This results in a further advantage over the prior art in a precisely adjustable or controllable turbulence spectrum.

In a particularly advantageous embodiment, it is provided that the turbulence inserts have devices for changing the inlet geometry of the turbulence tubes. This can be achieved by means of inserts with differently sized inlet cross-sections.

It has been found that the inlet cross-sections must be increased with increasing specific flow rate. The aim here is to ensure that the minimum ratio of the flow velocity before the

P 05461 / 288 15 057.6 / Voith Sulzer Papiermaschinen GmbH / DrS/sp00081 / November 22, 1996 Inventor U. Begemann ,,»· · · ....

turbulence inlet and in the initial area of the turbulence inlet is 1:2.

By designing the turbulence insert with a stepped turbulence tube, it is possible to influence the intensity and frequency spectrum of the turbulence by changing the number and position of the steps in the turbulence tubes.

In a further developed embodiment, it is provided that the lamellae, whose length can be changed in the nozzle channel in order to adapt to the turbulence spectrum of the turbulence insert, are detachably connected to the turbulence insert. This enables the exchange and replacement of a certain type of lamellae with a predetermined length for another with, for example, a shorter or even longer length in the nozzle channel. In particular, it is provided that the lamellae extend beyond the center of the nozzle channel in the axial direction if a particularly low tear length ratio is to be achieved. On the other hand, for the setting of a soft formation in contrast to a hard, fine-grained formation, it is provided to reduce the lamellae length, i.e. to make the lamellae shorter so that they do not extend beyond the center of the nozzle channel in the axial direction.

In a special embodiment, it is provided that the slat length can be changed during operation by means of adjustment devices, for example by making the slat telescopic, which enables different slat sections to be pushed into one another.

In a particularly preferred embodiment, it can be provided that the lamellae have a surface structure, for example a periodic one, as is known from DE 44 33 445. Such a

P 05461 / see -V5 057.6 / Voith Sulzer Papiermaschinen GmbH / DrS/sp000S1 l£$.

Invent U. Begemann .**«.** ·· ·· · ··

November 1st

Surface structure leads to a constant acceleration or deceleration in the individual channels of the headbox, so that a sectional regulation of the degree of turbulence is achieved with the help of such a surface structure,
5

Particularly noteworthy in this context is a special design in which the surface structure towards the headbox outlet

decreases.

In a further developed embodiment, it can be advantageous to provide the individual turbulence tubes with exchangeable step inserts. In this way, it is possible to change the step changes in the turbulence tube. It is particularly advantageous to shift the degree of flocculation by shifting the step change of the inlet area towards the turbulence insert outlet and away from it.

Furthermore, it can be provided that in a headbox that has both a turbulence insert with turbulence tubes and slats in the area of the headbox between the upper and lower lip, the formation in the paper is adjusted by first generating a certain turbulence spectrum using the turbulence insert according to the specific throughput by adjusting the inlet geometry, and then, depending on this turbulence spectrum, using the slats introduced into the headbox, this is changed or adjusted so that the predetermined formation or the predetermined tear length ratio is obtained.

In a special embodiment, it is possible that with decreasing tear length ratio the lamellae are displaced beyond the center of the nozzle channel in the axial direction.
30

P 05461 / 296 15 057.6 / Voith Sulzer Papiermaschinen GmbH / DrS/spQ0081 / November 22, 1896 Invented by U, Begemann. ■ · · · · ' ' · · · ·

To achieve a soft formation, a further developed embodiment of the method provides for the lengths of the lamellae in the nozzle channel to be reduced accordingly. To achieve a hard, fine-grained formation, in a special embodiment the length of the lamellae in the nozzle channel is extended beyond the middle of the channel in the axial direction.

As the tendency of the material to flocculate increases, the invention proposes, in a special embodiment, to shift the last step of the turbulence insert towards the outlet of the same.

The invention will now be described by way of example with reference to the figures.

Show it:

Fig. 1 shows an embodiment of the invention with a total of three turbulence tube bundles with stepped turbulence tubes and two lamellae arranged in the nozzle channel, which extend over the entire length of the nozzle channel.

Fig. 2 shows another embodiment of the headbox according to Fig. 1, in which the lamellae extend approximately to the middle of the nozzle channel in the axial direction.

Fig. 3 shows an embodiment of the invention in which a lamella is designed in such a way that a narrowing of the nozzle channel and thus a change in the turbulence spectrum in this channel is produced.

Fig. 4 shows an embodiment of the invention, wherein the slats have a surface structure.

P 05461 / 296 15 057.6 / Voith Sulzer Papiermaschinen GmbH / DrS/sp00081 / November 22 , 1996 Inventor U. Begemann ·· ·· · .J »"*··""

The headbox according to the invention shown in Fig. 1 has an upper lip 1.1 and a lower lip 1.2 in cross section. In the following embodiment, the turbulence inserts 2.1, 2.2 and 2.3 are arranged symmetrically between the upper and lower lips. The suspension is fed to the turbulence inserts via feed channels 4.1, 4.2 and 4.3, whereby these feed channels or feed lines can be fed from a common main feed line (not shown).

In the embodiment shown, the turbulence inserts 2.1, 2.2 and 2.3 each have three turbulence tubes 6.1, 6.2 and 6.3 in cross section.

The turbulence tubes in turn are made up of three sections in the axial direction, with the flow cross-section increasing from section to section. The turbulence tube can be designed as a unit comprising the three aforementioned sections.

However, it is also possible to arrange three inserts with different flow cross-sections one behind the other, each of which can be individually exchanged. In this way, the invention ensures that the inlet opening of the first turbulence tube section of the turbulence insert can be exchanged in an extremely simple manner in the axial direction. This makes it possible to change the inlet cross-section of the turbulence insert in an easy manner depending on the throughput. For example, it has been found that at high throughputs, in order to achieve a sufficiently good formation in the blade, it is necessary to enlarge the inlet cross-section of the turbulence tubes. This can be done by simply changing, for example, the first section of the turbulence tube. A turbulence insert with such a flexible structure also enables the steps resulting from the different diameters of the individual tube sections in the axial direction to be shifted in their axial position by exchanging them. For example, it is advantageous if, with increasing flow rate,

P 05461 / 2S6 15 057.6 / Voith Sulzer Papiermaschinen GmbH / DrSfep00081 / November 22, 1888 Invented by U. Begemann ·· ·· · · «**··**

Flocculation tendency of the material or with the increase in its flocculation strength the last step of the inlet area of the turbulence insert is shifted towards its outlet.

The turbulence insert shown in Fig. 1 allows a specific turbulence spectrum to be set by varying the diameters of the individual pipe sections depending on the material consistency and the throughput.

Two rigid slats 10.1 and 10.2, which taper evenly towards the outlet, are attached between the upper lip 1.1 and lower lip 1.2 with an essentially moment-free bearing 8.1 and 8.2, which terminate at the front ends with upper and lower lips of equal length in the present embodiment.

The slats, together with the upper and lower lips, form flow or nozzle channels 12.1, 12.2 and 12.3.

It is now possible to change the mostly very coarsely turbulent turbulence spectrum, which results after the suspension leaves the turbulence insert, by means of the lamellae in such a way that the most uniform formation possible is achieved in the blade or the tear length ratio is reduced.

If strong turbulences were generated in the turbulence tube in order to ensure the even distribution of the fibers in the jet, a high jet instability very often results. Due to this jet instability, very long lamellae are used as shown in Fig. 1 in order to reduce the jet instabilities through wall friction effects. If this is not taken care of, segregation phenomena can occur, which result in poor formation in the blade. Furthermore, a too coarsely turbulent frequency spectrum leads to the omission of the inventive

P 05461 / 29&bgr; 15 057.6 /Voith Sulzer Papiermaschinen GmbH / DrS/sp00081 / 22 November 1B96
Invent U. Begemann ·· ·· · J ,**»·"*

Vl" ·"

Lamellas mean that no finely distributed fiber network is achieved in the leaf, which has a negative impact on the formation. The lack of a
sufficiently high fine-turbulence portion of the

The suspension turbulence spectrum also results in the sheet having a very high breaking length ratio.

By introducing the lamellae, the turbulence spectrum that results at the exit of the turbulence insert can be influenced in such a way that these influences, which are perceived as disturbing, are eliminated.

Fig. 2 again shows a headbox according to the invention, which

compared to that shown in Fig. 1 only by the axial extension of the
Lamellae 100.1 and 100.2 within the space formed by the upper and lower lips
formed nozzle channel 110. Again, a total of three
Turbulence inserts 6.1, 6.2 and 6.3 are provided, which comprise turbulence tubes whose diameter changes section by section.

The slats 100.1 and 100.2 only reach to about the middle of the
Nozzle channel 110. By means of detachable connections which are attached to the
moment-free bearings or suspensions 8.1 and 8.2, it is possible to replace the lamellae known from Fig. 1, which extend over the entire channel in axial length, with the shorter lamellae shown in Fig. 2.

Especially if you have a soft formation at the same

If turbulence is to be introduced into the blade, the blade length must be reduced from that shown in Fig. 1 to that shown in Fig. 2.

If the turbulence is maintained at the same level, the
If the tear length ratio in the blade is reduced, it has been found that the lamellae are axially

direction of expansion. This can

P 05461 / 29&bgr; 15 &Ogr;57.&bgr; / Voith Sulzer Papiermaschinen GmbH / DrS/sp00081 / November 22, 1886 Inventor: U. Begemann ·· ·· J J »**··**

for example, as already mentioned, by replacing the slats or by providing an adjustment device to adjust the axial length of the slat. For this purpose, the slat can be designed like a telescope, for example. A slat designed in this way would also make it possible to change the slat length during operation without downtime. For example, the turbulence spectrum that is generated at the outlet of the nozzle channel 110 could always be kept the same or adjusted regardless of the throughput quantity supplied.

Of course, in addition to the embodiments shown with three turbulence inserts and two slats arranged between them, it is possible to provide more turbulence inserts and a large number of slats, depending on the number of supply channels. For example, with four supply channels with four turbulence inserts, three slats would be required.

The embodiment according to Rg. 3 differs from the embodiments shown in Fig. 1 and Fig. 2 in particular in that one of the slats has a shape that leads to a narrowing of one of the three flow channels formed between the slats and the upper or lower lip.

Here, the lamella 120.1 has a convex surface, which leads to the channel 122.1 being narrowed. This makes it possible, as described in detail in DE 43 07 143, to change the jet speed in this suspension jet, whereby the relative flow speeds of the flows of the individual material suspensions can be adjusted to one another. Assuming the same turbulence inserts 6.1, 6.2 and 6.3, this results in the coarsely turbulent spectrum at the outlet of the turbulence insert being different in the individual channels. This is due to the fact that the

P 05461 / 296 15 057.8 / Voith Sulzer Papiermaschinen GmbH / DrS/spOjJOSI 1££. November 18S8 Inventor U. Begemann **,,*" ·· ·· ·"*··.

The difference in speed between the individual jets of material ensures the formation of a different turbulence structure in the channels 122.1, 122.2 and 122.3. This allows a changing turbulence spectrum to be generated across the blade height, which in turn results in an improvement in formation under certain operating conditions.

In a final embodiment shown in Fig. 4, the lamellae 130.1 and 130.2, which are inserted into the headbox between the upper and lower lips and are arranged downstream of the turbulence inserts 6.1, 6.2 and 6.3, have a surface structure which in the present case is a periodic, wave-shaped surface structure.

As in Fig. 2, the two lamellae do not extend to the end of the upper and lower lips, respectively, but rather end within the nozzle channel 110 formed by the upper and lower lips. The periodic surface structure in the present case means that the stock suspension in the channels 140.1, 140.2 and 140.3 is alternately accelerated and decelerated by the widening and narrowing, as disclosed for example in DE 44 33 445, so that a turbulence spectrum that can be changed in a very simple manner is produced due to these accelerations and decelerations of the stock suspension. Since, as already mentioned several times before, the turbulence spectrum is crucial for the formation of the paper web, even with such a design of the lamellae, it is possible to decisively influence or improve the formation.

In a particularly advantageous embodiment, it is provided that the surface structure decreases towards the outlet end of the headbox, i.e. the acceleration or deceleration generated by means of the constrictions or widenings decrease, whereby a particularly good formation can be achieved.

P 054&bgr;&Lgr;�iacgr;23&bgr; 15 &Ogr;57.&bgr; / Voith Sulzer Papiermaschinen GmbH /JDrS/spOgQet /£g. Inventor U. Begemann .**··** ·· ·· J i !..

November 1998

With the device according to the invention it is thus possible for the first time to achieve a constant turbulence spectrum and thus a constant formation with changing throughput quantities in a simple manner.

Claims (8)

P 05481 / 29&bgr; 15 057.8 /Voith Sulzer Papiermaschinen GmbH / DrS/sp00081 J 22.1 Invention U. Begemann ·· ·· .· .1 ,**··" November 189&THgr; Claims 1. Headbox with the following features: 1.1 The upper lip (1.1) and lower lip (1.2) together with the side parts form the nozzle channel 1.2 Between the upper lip (1.1) and the lower lip (1.2) there are slats (10.1, 10.2) which are hinged to a joint running transversely to the flow direction in the direction of the machine width 1.3 the lamellae (10.1, 10.2) divide the headbox into at least two flow channels (12.1, 12.2, 12.3) 1.4 Each flow channel is assigned a turbulence tube bundle (2.1, 2.2, 2.3) comprising at least one turbulence tube (6.1, 6.2, 6.3), wherein the headbox is characterized in that 1.5 at least one turbulence tube (6.1, 6.2, 6.3) of the turbulence tube bundle (2.1, 2.2, 2.3) comprises a device for changing the inlet geometry and
1.6 the at least one lamella (10.1, 10.2) comprises devices which enable the lamella length to be changed depending on the inlet geometry. 2. Headbox according to claim 1, characterized in that the devices for changing the inlet geometry comprise inserts for the turbulence tubes, the inserts having different inlet cross-sections. 3. Headbox according to one of claims 1 or 2, characterized in that the means for changing the slat length comprise a fastening device for releasably connecting a slat of predetermined length to the joint. P 05481 / 298 15 057.&bgr; / Voith Sulzer Papiermaschinen GmbH / DrS/sp00081 / 2|. November 1&thgr;&bgr;&bgr; Inventor. U. Begamann »·*··** ·· ·· ***··" 4. Headbox according to one of claims 1 or 2, characterized in that the device for changing the slat length includes devices for changing during operation. 5 5. Headbox according to one of claims 1 to 4, characterized in that the lamella has a surface structure. 6. Headbox according to claim 5, characterized in that the surface structure is a periodic surface structure, 7. Headbox according to one of claims 5 or 6, characterized in that the surface structure decreases towards the headbox outlet. 8. Headbox according to one of claims 1 to 7, characterized in that the at least one lamella has such a length that it is located in the front part of the nozzle channel formed by the upper and lower lips.