FI98385C - Inlet box in a paper or cardboard machine - Google Patents

Description

5 98385

Paper or board machine headbox Inloppsläda i en pappers- eller kartonmaskin

The invention relates to a headbox of a paper or board machine in which the feed points for the additional fluid flow in the upstream direction of the main mass flow are located to control the entire transverse surface weight profile of the web. for the controlled supply of pulp with a non-consistency to the main mass flow into the main mass flow, the supply points being additional liquid or mass supply channels provided with control means such as control valves for controlling additional flows, and the headbox comprising a manifold connected to consisting of separate manifolds which reverse the flow of 20 manifolds in the direction of the wire .

In a paper or board machine, an aqueous suspension containing the final product-forming fibrous materials, hereinafter referred to as pulp, is fed from the headbox lip at the orifice to a feed substrate moving in the feed direction 25, i.e. a wire where dewatering and pulp felting into the final product begins.

As the wide lip jet coming from the lip opening of the headbox discharges onto the forming base, it spreads from its edges. The spreading causes a flow component in the pulp 30 that is transverse to the direction of travel of the forming substrate, which affects the fiber orientation and the surface shape of the finished product. Since the basis weight profile in the cross-machine direction must be kept as even as possible, the lip opening must be enlarged from the edge area. This, in turn, causes a transverse flow component in the flow space of the headbox immediately preceding the lip opening, in the lip channel, which affects the orientation in the same way as the spread of the lip jet on the wire.

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The basis weight profile of the final product is also affected by the subsequent narrowing of the web formed from the mass fed from the headbox to the wire as a result of tension and drying shrinkage. This narrowing is more likely to occur at the edges of the web. This results in an increase in basis weight in the edge region. Very close to the edge, this phenomenon compensates for the decrease in basis weight caused by the edge effect mentioned in the previous paragraph, but when moving from the edge to the center, the basis weight reaches its maximum, after which it decreases towards the center. Again, an attempt has been made to compensate for this phenomenon by lip placement, which again results in orientation errors.

Efforts have been made to control the spread of the mass towards the edges after the lip opening with special edge rulers, which, however, have more disadvantage than benefit due to the edge wave they cause.

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With regard to the state of the art most closely related to the invention, reference is made to FI patent application 885684 (J.M. Voith GmbH, cf. DE-3741603).

This application discloses a paper machine headbox as set out in the preamble of claim 1, in which the diluent is fed to 20 pulp channels immediately before the throttling point of the turbulence generator. However, this known device has the disadvantage of harmful flow disturbances, inaccurate and unstable adjustment of the basis weight profile, and in particular the fact that an increase in the supply of diluent increases the total flow and causes harmful cross-flows. The disadvantage is also the poor mixing of the main-25 flow and the additional flow, which is very detrimental especially if the consistency differences of the flows are large.

The object of the invention is to provide a headbox which does not have the above-mentioned drawbacks. To accomplish this, the headbox 30 according to the invention is mainly characterized in that said feed points are additional feed channels opening adjacent to the orifices of the manifolds, which open into the manifold wall in the flow direction before the part of the mass flow in the manifolds flows transversely and transversely thereto.

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Additional fluid flows are fed through separated flow paths,. as in the case of manifolds, so that each of them mixes with the effect of the currents in the flow paths on the main mass flow at the junction of the flow paths at the latest. The basis weight profile can thus be controlled without disturbing the behavior of the mass as it flows out of the lip opening. The combination of the additional fluid flow with the main mass flow then takes place at a sufficiently early stage to allow any transverse flows in the main mass flow to equalize, but still close enough to the orifice so that arranging the additional fluid flow at a certain transverse position affects surface weight at the same point in the web. In addition, by means of separated flow paths, such as manifolds, the additional fluid flow can be caused to mix with the main mass flow so that at each point the additional fluid flow directed to the main mass flow acts in a predeterminable area in the headbox width direction.

The additional fluid flow is preferably of such a quality that the consistency of the main mass flow decreases. In this case, it can be either water alone or a suspension with a lower fiber content than the suspension forming the main mass flow.

The invention will now be described in more detail with reference to the accompanying drawings, in which Fig. 1 illustrates the behavior of a pulp jet from a lip opening on a subsequent web-forming substrate, Fig. 2 schematically shows a prior art solution for correcting this phenomenon. as a result of various phenomena, Fig. 4 schematically shows a lip opening profile used in prior art headboxes, Fig. 5 shows a longitudinal section of a headbox in which the invention can be applied, Fig. 6 shows a detail according to an alternative embodiment of the invention, and Fig. 7 shows another a detail according to an alternative embodiment.

Figure 1 shows a headbox 1 which, in the direction of flow of the pulp, terminates in a transverse lip opening 2, from which a jet of pulp discharges onto a movable forming base, i.e. a wire 4, passing through a breast roll 3 at the lip opening of the headbox. As the pulp discharges from the lip opening, it spreads at the edges as described by the lateral arrows 15, whereby both the basis weight decreases in the edge region of the web formed from the pulp and the orientation of the fibers in this region changes.

Figure 2 shows the way to influence these phenomena. Here, the width of the opening 2 of the lip-20, i.e. its dimension in a direction perpendicular to the plane of the wire 4, is arranged larger in the edge region. This is done by lifting the upper lip 2a at the respective edges of the lip opening. In this case, however, a transverse velocity component is already formed in the lip channel before the lip opening 2 and after the lip opening in the wire 4. This phenomenon is also illustrated by the lateral arrows in Fig. 2.

Figure 3 shows the basis weight profile of the formed web in its transverse direction, strongly exaggerated. The effect of the drying shrinkage on the basis weight is illustrated by dashed lines and the actual basis weight profile of the final web 30 is depicted by a solid line showing the edge effect, i.e. the decrease in basis weight in the edge region caused by the spread of the above lip jet.

Fig. 4 shows schematically and strongly exaggerated the shape of the lip opening 2 of the headboard 35, which is intended to counteract the distortions shown in Fig. 3. In this case, the width of the lip opening in the central region of the web is arranged to be a minimum in those areas between the central region and the edge regions where the maximum surface weight and shrinkage of the finished web is expected due to the maximum. In this case, the transverse currents described by the lateral arrows 5 again arise, which cause orientation errors. In addition, it is clear from Figure 4 how the lip structure, in particular its upper lip, is required to have a special structure and the adjustment devices connected to it.

Figure 5 is a longitudinal section of a headbox 10 of a paper and board machine in which the invention can be applied. The headbox 1 comprises a lip channel 5 in the flow direction immediately before the lip opening 2, which tapers in the mass flow direction ending in the lip opening 2. In connection with the lip opening there are devices for adjusting the total width here its in more detail. The pulp, which is an aqueous suspension containing cellulosic fibers and possibly other substances, is introduced into the headbox 1 by a pump-fed pulp supply pipe 6, from which the pulp flows in the wire direction 20 due to the of separate pipes 7. The manifolds can also be provided, for example, in two or more overlapping rows extending in the transverse direction of flow, and the invention is particularly well implemented in this type of headbox. However, for the purpose of the invention, it is essential that at this point the flow of the pulp has flow paths separated from each other in the transverse direction. Through the distribution pipes 7, the mass flows from the distribution supports 6 to the equalization chamber 8, i.e. to the intermediate chamber, where the flows from the different pipes again coalesce under the effect of the flows 30 discharging from the pipe openings opening from the rear wall of the equalization chamber 8. In connection with the equalization chamber 8 there is an air chamber 9 equalizing the pressure variations of the flow, which opens into the upper wall of the equalization chamber 8 via a duct, the upper part on the air chamber side has an overflow to dissipate the extra mass. After the equalization chamber 8 follows a turbulence-35 generator 10 consisting of separated tubes or openings through which the mass flow passes from the equalization chamber 8 to the channel 5, the upper wall and the lower wall of which approach each other in the direction of the lip opening 2.

According to the invention, a channel 11 is connected in the vicinity of the manifold 7, which 5 is connected to a device for supplying an additional liquid flow to the main mass flow flowing in the manifold. The channel 11 is introduced from the inlet side of the main mass flow by a portion of the manifold which is in the mass flow direction before the stepped expansion 7a, as a result of which the additional liquid flow mixes well with the main mass flow.

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The additional liquid may be the consistency of the mainstream stream, i.e., a fiber that lowers the fiber content, such as dilute water alone or water, or an aqueous suspension having a fiber content less than the fiber content of the mainstream stream. The question may include e.g. various waters of the circulating water system of 15 paper machines. Naturally, as dilute water as possible is advantageous, because then even very small changes in the flow rate of this water can affect the consistency of the mass flow after channel 11 in the manifold 7. Devices for supplying additional liquid flow can be located e.g. above or below the rows of manifolds 7.

According to the invention, it is essential that the supply of the additional liquid in question is arranged in a sufficiently large number, preferably in each of the distribution pipes at different points in the transverse direction of the mass flow. In addition, it is important for the control of the basis weight-25 profile that at least the flow rate of the additional liquid flow to the manifolds 7 or the like is adjustable for each such manifold.

The auxiliary fluid supply channels and manifolds or the like can also be arranged so that the auxiliary fluid flow replaces the main mass flow from the manifold to the manifold, with the combined flow of main mass flow and auxiliary fluid flow from the manifold to the damping chamber always being the desired size for each manifold. In any case, the additional fluid flow supply channels 11 are provided with control means 35, such as valves, by means of which the additional fluid flow is regulated, and they can then be connected to a suitable control automation.

Figure 6 shows in more detail an arrangement according to an embodiment of the invention for supplying additional liquid so that the surface weight profile of the paper web can be influenced. The additional liquid flow is introduced so that the channel 11 opens into the wall of the manifold 6 from which the manifolds leave. Figure 6 shows a top view of this wall and the manifold of the manifold in longitudinal section. As can be seen, the channel 11 10 joins said wall at an acute angle, the acute angle being located on the inlet side of the manifold flow (indicated by the arrow A). The channel 11 opens into said wall just before the point where part of the flow in the manifolds starts to flow transversely along the manifold 7, i.e. the channel 11 opens just upstream of the mouth of the manifold 7. The additional fluid flow is preferably introduced from above into the wall of the manifold 6. As a result of the flow forces of the manifold and the manifold mass flow, the additional fluid flow supplied at the manifold mouth enters the manifold with the main mass flow. With this construction, the adjustment of the basis weight profile can be realized with all the possibilities already mentioned above.

Figure 7 shows another possibility to arrange the additional fluid flow so that it can control the track weight profile of the track. The figure shows the wall of the equalization chamber on the side of the manifolds as seen against the flow direction of the main mass flow 25, and shows the openings opening in the wall of two overlapping manifold rows. Between the orifices of the manifolds 7 of one manifold row, there are orifices of the additional liquid supply channels 11 opening into the wall of the equalization chamber 8. Also in this case, the channels 11 are brought from above. The additional fluid flows discharge into the equalization chamber 30, each between the discharge points of two adjacent main mass flows, and at this point affect the basis weight of the web in the finished web. The possibilities of adjusting the basis weight profile with this practical arrangement are similar to those already described above.

As already mentioned above, in order to carry out the invention, there must be a sufficient number of additional liquid flow supply points in the transverse direction of the headbox. Since the manifolds 7 are often in two or more overlapping rows, it is sometimes sufficient to practice the invention to provide one such row with supplemental fluid flow supply channels 11. If there are three or more such rows, said rows with additional fluid flows 5 are most preferably one or some of the middle fluid rows. . For example, these rows may be the second highest and second lowest rows, for which the channels 11 can be brought from above and below, respectively.

10 The control of the basis weight profile can be further improved by feeding a thicker mass to the transversely extreme manifolds so that the flow from the manifold to the equalization chamber is narrower than the flow from the other manifolds in the middle. This pulp is thicker than the other pulp and has a maximum consistency of 3%. This causes the thick mass to form protective walls on each edge region of the web, which prevent the mass from spreading after the lip opening. To achieve this purpose, it is sufficient to arrange one outlet pipe at the extreme edge in each overlapping row as such a special manifold, and these manifolds can also be completely separated from the rest of the mass flow so that the mass flow in them comes entirely from their own thick pulp feeder.

The edge area of the web on which the edge formed by the thicker mass is located is trimmed in the normal way by means of the edge whistles into the cam cone.

An important advantage of the invention is that the width of the lip opening can be kept constant in the transverse direction of the machine, i.e. the lip opening can be made completely straight, so that transverse currents causing orientation errors cannot be generated.

The invention is particularly suitable for the production of fine papers, where high quality is required of the final product, but it is clear that it can be used in all paper or board machines to improve the quality of the product produced with them.

Claims (8)

An inlet carriage for a paper or cardboard machine, wherein for controlling the entire transverse surface weight profile of the male and at the same time for controlling the fiber orientation profile, there are feeding sites for an additional fluid stream located before the lip opening (2) in the direction of flow of the main mass stream, flow paths separated from each other in the transverse direction of the inlet carriage, and which feeding sites interfere with means 10 for controlled feeding of water or to the thickness of the main mass stream deviating mass into the main mass stream, which feeding sites comprise extra channels (11) of feed channels (11) , which are provided with control means such as control valves, by means of which the auxiliary currents are regulated, and which inlet carriage comprises a distribution bar (6), to which is connected a mass feed pipe and from which distribution bar (6) discloses a distribution pipe system consisting of separate distribution pipes (7) which pivots the distribution boom current in the direction of the wire, characterized in that said feeding points are formed by the additional feeding channels (7) adjacent to the orifices of the distribution pipes (7). 11), which opens in the wall of the distribution boom (6) in the flow direction before the place where part of the mass flow in the distribution boom (6) starts to flow transversely in relation thereto along the distribution tubes (7). 25 2. An inlet carriage according to claim 1, characterized in that said auxiliary supply channels (11) open just next to the opening of the distribution pipes (7). . 30 3. An inlet carriage according to claim 1 or 2, characterized in that said auxiliary supply channels (11) open at an acute angle from the wall of said distribution boom (6), the acute angle being located on the side of the input direction of the current (pi A). in the distribution boom (6). 35 98385 12 4. An inlet carriage according to any one of claims 1-3, characterized in that the chamber where the flow paths are combined is constituted by the inlet carriage chamber (8), followed by a turbulence generator (10) before the space (5) which narrows to a lip opening. 5 5. An inlet carriage according to any one of claims 1-4, characterized in that the extra liquid to be introduced into said feed ducts (11) is a liquid which lowers the thickness of the main mass flow, such as pure dilution water or water or aqueous suspension, the fiber content of which is less than the content of fiber in the main mass stream, e.g. water from the paper machine's circulation water system. 6. An inlet carriage according to any one of claims 1-5, characterized in that a sufficient number of supply pipes (11) for the auxiliary currents have been arranged in the transverse direction of the inlet carriage and that the inlet carriage, where there are several adjacent said streams, is arranged. supply paths separated from each other provide supply tubes (11) for the extra current in one or more of said rows, most preferably in one or more of the middle rows. 7. An inlet carriage according to any one of claims 1-6, characterized in that in connection with the flow path at at least one edge which is the outermost there are means for feeding pulp which is thicker than the main mass flow. An inlet carriage according to any one of claims 1-7, characterized in that the width of the lip opening of the inlet carriage is constantly poured in the transverse direction of the machine so that no orientation errors causing transverse currents will be formed.