EP0683266B1 - Headbox for papermaking machine with local fluid admixture - Google Patents

Abstract

A head box for a paper machine has an inlet chamber (1) for the stock, a flow section (2) with internal passages and a nozzle chamber (8) which terminates in an outlet slot (5) for the stock. Upstream of the flow section (2) is a chamber (4) across which are arranged devices (6) for introducing a liq. which has different properties to the stock. The devices, which extend into the chamber at right angles to the direction of stock flow, are in the form of several pipes which each have a number of outlets (7) lying above one another along a line perpendicular to the direction of flow of the stock. <IMAGE>

Description

The invention relates to a headbox for a paper machine according to the preamble of claim 1.

As is well known, recent developments in the headbox of some paper machines mean that in addition to the actual stock suspension flow required for paper production, an additional controlled admixture of fluid, e.g. Water or suspension with low consistency occurs. This admixture takes place at several locations distributed over the width of the headbox. The amount and / or properties of the fluid can be adjusted. With this measure e.g. the basis weight cross profile is regulated or the occurrence of cross flows in the headbox can be prevented.

The German patent specification 40 19 593 C2 shows such a headbox. The fluid is mixed in through inlet openings in the wall of the mixing chamber or directly into the turbulence generator. In order to locally limit the effect of the admixed fluid, partition walls are either installed in the mixing chamber or hydraulic means (not specified in more detail) for forming section flows are proposed.

The invention has for its object to provide a headbox of the type specified, in which the local admixture of a fluid, for example dilution water, can be carried out to the main flow of the stock suspension in such a way that the admixing is as simple as possible over the entire height of the with simple means Suspension layer can take place and at the same time is easily influenced.

This object is fully achieved by the characterizing part of claim 1. The subsequent subclaims describe particularly advantageous embodiments of the invention.

The measures described in the characterizing part of claim 1 make it possible for the first time to enter the fluid to be supplied uniformly in the desired manner over the height of the headbox. This makes it possible to influence the entire sheet subsequently produced on the paper machine, i.e. evenly across the thickness of the sheet. Since the feed devices are located in the mixing chamber, their outer contour can be used to influence the suspension flow flowing in the mixing chamber.

With a special design of the feed devices in the form of a non-circular tube, e.g. an oval profile, the flow state can be changed by simply twisting, which leads to an influence on the total throughput at this point of the headbox. This means e.g. the simultaneous influencing of the basis weight and the fiber orientation possible. The possibility of influencing the amount of fluid added with respect to the height in the headbox described in further refinements can further improve the quality of the sheet produced, since e.g. Unevenness caused by other sources can be compensated. Another advantage that should not be underestimated is the ease of converting existing headboxes, since they usually have a chamber in front of the last turbulence generator.

In the mixing chamber lying between two guide devices, the pipes in special designs can be attached with their admixing openings in such a way that the fluid streams emerging from them can get directly into a mouth of the downstream guide device. Furthermore, the individual partial suspension jets can thus enter the intermediate chamber be divided up so that when they exit from the intermediate chamber, that is to say when they enter the second guide device, they mix with adjacent partial jets. Such measures create a controlled, locally limited swirl. The fluid to be mixed can advantageously be introduced into the vortex zones thus created. Furthermore, at multiple speeds of the fluid compared to the flowing suspension flow, additional locally narrowly limited mixing effects can be generated. The relative speeds between the supplied fluid and the surrounding suspension can be adjusted to a large extent, which results in a good influence on the turbulence and the mixing effect. Under certain circumstances, the need for partitions can be eliminated.

The mixing action and the turbulence can be additionally controlled by moving the admixing devices in the direction of the confluence with the turbulence generator.

Figur 1

schematische geschnittene Seitenansicht eines erfindungsgemäßen Stoffauflaufes;

Figur 2

schematische geschnittene Draufsicht eines erfindungsgemäßen Stoffauflaufes;

Figur 3

eine weitere Ausführungsform des Stoffauflaufes;

Fig. 4 und 6-9

diverse Ausführungsformen von Zuführungseinrichtungen;

Fig. 10

im Detail: Bestimmte Strömungsverhältnisse in Aufsicht;

Fig. 11

eine schrägstehende Zwischenkammer in Seitenansicht;

Fig. 12

eine schrägstehende Zuführeinrichtung in Seitenansicht.

The subject matter of the invention is described and its advantages are further explained with reference to drawings which show:

Figure 1

schematic sectional side view of a headbox according to the invention;

Figure 2

schematic sectional plan view of a headbox according to the invention;

Figure 3

another embodiment of the headbox;

4 and 6-9

various embodiments of feed devices;

Fig. 10

in detail: certain flow conditions under supervision;

Fig. 11

a sloping intermediate chamber in side view;

Fig. 12

a sloping feed device in side view.

1 shows a side view of the section through a headbox according to the invention with a distribution device 1, a first guide device 3, an adjoining mixing chamber 4, and another adjoining it Guide device 2, which opens into a nozzle chamber 8, which forms an outlet gap 5 for the stock suspension. In the operation of the headbox, the suspension necessary for paper production will flow through it in the order described. One can see in the mixing chamber 4 one of the feed devices 6, which extends essentially perpendicularly into the mixing chamber. Advantageously, the tube can also have a slight inclination, for example about 10 degrees, against the vertical in order to avoid the occurrence of stagnation points for the suspension flow. In the example shown here, the feed device has three admixing openings 7. This feed device 6, which is only indicated schematically here, is supplied with the fluid to be mixed from above via a line 10 and a control valve 11, so that the fluid can be introduced through the three admixing openings 7 into the stock suspension located in the mixing chamber 4.

As FIG. 2 shows in a similar example in a top view, there are several feed devices 6 across the width of the mixing chamber 4. Their number depends on the requirements of a more or less finely divided influence on the property of the stock suspension. On the other hand, FIG. 2 shows a different shape of the guide devices 2 and 3 compared to FIG. 1. In this example, the guide device is provided with step diffusers in one case and a simple perforated plate in the other. The possible variations in this regard are very diverse and depend on the conditions for paper production. Application of the invention is not limited to the forms of guide devices shown here. Although it has been found that highly effective turbulence-generating guiding devices are the preferred field of the invention, the application of the invention is not restricted to the forms of the guiding devices shown here.

The distribution devices 1 shown in FIGS. 1 to 3 are cross-flow distributors. However, other possibilities of mass distribution, not shown, are also conceivable, for example a plurality of feed lines which connect the headbox with one Connect the damping container.

Another possibility shown in FIG. 2 for locally influencing the flow conditions is to shift the feed device in or against the flow direction.

The headbox according to the invention can also be a multi-layer headbox.

Fig. 3, again in plan view, shows feed devices which essentially consist of tubes 6 ', the cross-section of which is not circular but oval. Such devices can be rotated, so that a further influence on the prevailing flow is possible, for example to correct unwanted cross flows. The statements made with regard to FIGS. 1 and 2 apply to the illustrated guide devices.

Fig. 4 shows schematically and in perspective a feed device 6 with a tube 6 'and three admixing openings 7. The tube 6' in this figure has a circular cross-section, a rotary movement according to a curved arrow, the flow cross-section generated by the outer contour in the mixing chamber would only be a little or not at all change, but the direction of flow of the mixed fluid. This also enables a local influence on the flow properties.

In order to regulate the amount of fluid transferred by a feed device 6, the size of the admixing opening 7 - as shown in FIG. 6 - can be determined by two concentric, nested tubes 6 'and 6''which are mutually movable and each contain openings, are changed. This results in larger or smaller overlaps of the openings. With elongated holes (not shown) in the inner tube 6 ', the location of the inflow can also be adjusted via the height of the headbox.

The embodiment according to FIG. 7 allows different flow rates to be set for the different admixing openings in one and the same feed device 6. The central tube 6 'is surrounded by a plurality of concentric tubes 6' 'which can be moved, as a result of which the open opening 7 can be changed in each case. With an inclined or step-shaped edge, a rotary movement can also be used to change the cover instead of the sliding movement, which is normally easier to accomplish in terms of construction.

According to FIG. 8, similar to that shown in FIG. 6, the openings can be changed by varying the degree of coverage when the tubes 6 ', 6' 'which are coaxially inserted into one another are rotated relative to one another. The vertically elongated shape of the openings allows the required angle of rotation to be kept low in order to minimize an undesirable change in the exit direction.

The variant of the feed device 6 shown in FIG. 9 also contains a plurality of coaxial tubes which can be moved relative to one another. However, the openings are only in the innermost tube 6 ', so that the outflow size can be adjusted without changing the position or angle of the admixing openings 7.

10 specifically shows the flow conditions which result when the outflow from the tubes 6 'inserted into the mixing chamber 4 is oriented such that it is aligned with the middle of an opening 12 in the downstream guide device 2.

From Fig. 11 it can be seen that the invention is not only applicable to an intermediate chamber 4 with a horizontal skin flow direction, but that the main flow can also run obliquely to the horizontal. This alternative depends on the overall structure of the headbox.

Fig. 12 indicates that the feed devices 6 can not be arranged perpendicular to the main flow direction in every case, but also in an appropriate inclined position, in particular to prevent the hanging of suspended fibers. This angle of inclination alpha will generally be between 0 and 30 degrees and a maximum of 45 degrees.

Claims (17)

1. Headbox for a paper machine, comprising a distributor device (1) for the material suspension, a guide means (2) having a plurality of channels, a mixing chamber (4) lying upstream of the guide means (2) and having a plurality of supply devices (6) distributed transversely across the headbox for a fluid to be admixed which differs in its characteristics from the material suspension, and a nozzle space (8) following the guide means (2) and forming an outlet gap (5) for the material suspension, characterised in that the supply devices (6) are formed as tubes (6') inserted into the mixing chamber (4) and having a plurality of admixing openings (7) lying above one another substantially perpendicular to the main flow direction.
2. Headbox in accordance with claim 1, characterised in that the tube (6') in the mixing chamber (4) extends substantially perpendicular to the main flow direction.
3. Headbox in accordance with claim 1, characterised in that the centreline of the tube (6') has an inclined positioning angle (alpha) between 0 and 45°, starting from the right angle to the main flow direction.
4. Headbox in accordance with claim 1, 2 or 3, characterised in that the tube (6') has a cross-section differing from the circle, in particular an oval cross-section.
5. Headbox in accordance with claim 1, 2, 3 or 4, characterised in that the tube (6') is rotatable about its axis.
6. Headbox in accordance with claim 1, 2, 3, 4 or 5, characterised in that the tube (6') is displaceable relative to the downstream guide means (2).
7. Headbox in accordance with one of the preceding claims, characterised in that means are provided in order to change the size of the admixing openings (7).
8. Headbox in accordance with claim 7, characterised in that the supply device (6) consists of at least two coaxial tubes (6', 6"), which are movable relative to one another and which are provided with openings (7', 7"), the overlap of which can be changed by rotation or displacement of the two tubes relative to one another.
9. Headbox in accordance with claim 8, characterised in that the number of the tubes (6', 6") arranged concentrically to one another and moving relative to one another corresponds to the number of the admixing openings (7) of a supply device (6); and in that tubes lying radially further inwardly contain openings which free the passage of the fluid to the openings in tubes disposed further outwardly.
10. Headbox in accordance with one of the preceding claims, characterised in that it has, upstream of the mixing chamber (4), a further guide means (3) provided with a plurality of channels.
11. Headbox in accordance with claim 10, characterised in that the predominant number of the channels of the guide means (2, 3) are so positioned and dimensioned that the outlet openings (13) from the upstream first guide means (3) are not aligned with the entry openings (12) into the second downstream guide means (2), and in that the admixing openings (7) for the fluid to be admixed are so aligned that they are each substantially aligned with the centre of an inlet (12) into the downstream guide means (2).
12. Headbox in accordance with claim 11, characterised in that the admixing openings (7) of the supply devices (6) are so aligned that the central normal to the projection surface of the admixing opening (7) generated in the outflow direction is each substantially aligned with the centre of an inlet (12) into the downstream guide means (2).
13. Headbox in accordance with claim 11 or claim 12, characterised in that the predominant part of the outlet openings (13) of the upstream guide means (2) is aligned with a location of the downstream guide means (3) lying between adjacent inlets (12).
14. Headbox in accordance with one of the preceding claims, characterised in that the supply device (6) has at least three admixing openings (7) lying above one another substantially perpendicular to the main flow direction.
15. Headbox in accordance with one of the preceding claims, characterised in that one or both of the guide means (2, 3) contain channels in the form of stepped diffusers with free cross-sections which broaden in a step-like manner in the flow direction provided.
16. Headbox in accordance with one of the preceding claims, characterised in that the mixing chamber (4) is split up by partition walls which extend substantially in the flow direction.
17. Headbox in accordance with claim 16, characterised in that the number of partition walls corresponds to the number of supply devices (6) minus one.

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