FI84736B - Turbulence generator in the headbox of a paper machine - Google Patents

Description

84736

The invention relates to a turbulence generator for a paper machine headbox, the turbulence generator providing a pulp suspension turbulence, the turbulence generator, the turbulence generator, the turbulence generator on the side of a substantially circular cross-section, gradually and smoothly changing in the flow direction into a planar cell structure, the flow cross-sections of each cell, except for possible edge channels, being substantially equal and of the same shape, and the cell structure is turbo-15

It is known to use turbulence generators in various paper machine headboxes, in which the pulp suspension flow is divided into turbulence tubes into partial flows which discharge into a wedge-shaped converging lip channel on the outlet side of the turbulence-20 generator.

From the lip of the lip channel, the pulp suspension jet is discharged onto the forming wire or two forming wires bounded by the forming wire.

It is already known and commonly used to have a headbox 25 in which the turbulence generator has a perforated plate first in the flow direction of the pulp suspension. This perforated plate has a large number of flow holes in overlapping rows which open into turbulence tubes wider than the diameter of the holes. These turbulence tubes start in a circular cross-section coaxially with the flow holes of said perforated plates and pivot slightly vertically towards each other. Upon entering the outlet side of the turbulence generator, the turbulence tubes have become smoothly transverse so that they have, for example, vertical and horizontal walls. The vertically overlapping tubes are staggered to each other so that the vertical walls of the overlapping tubes are 35 laterally with a certain phase shift relative to each other.

With regard to the state of the art most closely related to the invention, reference is made, by way of example, to U.S. Patent 3,528,882, FI Patent 51,229 and Applicant's 2,84736 FI Patent Application 892709 (filed June 2, 1989).

The disadvantage of the previously known, e.g. above-described and other headboxes, has been that they can form 5 striped papers with machine direction stripes, generally in the transverse direction for the same period as the tubular section of the turbulence generator. Measurements have also shown that there is variation in the turbulence intensity and velocity profiles in the headbox lip duct at the same pipe spacing. Said variation occurs in all overlapping layers of the headbox flow 10. The greatest of this variation is at and near the surface of the lower and upper walls of the lip canal.

When using previously known turbulence generators, there have been problems in adjusting the headbox, especially in obtaining a sufficiently stable headbox. When using previously known flow technology solutions, the stability of the operation of the headbox and the avoidance of flow streaking have been opposite objectives.

The main object of the present invention is to further develop the turbulence generator used by the applicant described above and its turbulence piping.

It is an object of the present invention to provide a novel turbulence generator and its turbulence tubing structure which can at least partially eliminate the above-mentioned problems which could not be effectively addressed by previously known methods and flow engineering solutions. It is also an object of the invention to improve the edge areas of the flow by shortening the vertical walls and improving the mixing of the 30 layers with each other with a new type of pipe pattern.

It is a further object of the invention to provide a paper machine headbox turbulence generator at the outlet side of which the partial flows discharged from the turbulence tubes into the lip channel are distributed regularly relative to each other but so interleaved so that said stiffness problem is largely avoided.

3,84736

It is therefore a further object of the present invention to provide a new solution for avoiding headbox flow and paper streaks while maintaining good headbox stability.

It is a further object of the invention to provide a honeycomb structure for a headbox turbulence generator which is more advantageous in terms of manufacturing cost and technique.

In order to achieve the above and later objects, the invention is mainly characterized in that in the initial plane of the turbulence generator the honeycomb structure of the turbulence piping is formed of its equilateral cell triangles. and that the bases of said cell triangles are horizontal to form the top wall, the bottom wall and the partitions of the cell rows.

In the invention, the outlet sides of the turbulence tubes of the turbulence generator are triangular in shape and said overlapping tubes are staggered vertically at different points from the outlet side so that any flow disturbance caused by the corners of the tubes is not felt in the jet.

The flows discharged from the turbulence tubes placed according to the invention into the lip channel are made to overlap regularly but still with each other so that the streaking of the headbox flow in its different layers and the corresponding machine direction streaking of the headbox paper can be largely avoided.

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According to the invention, a new turbulence generator is provided, which is furthermore advantageous in terms of manufacturing technology and cost, since the turbulence tubes can be formed from a round cross-section tube with a mold and mandrel tool into exactly the right shape in a simple and fast operation. In addition, the turbulence tubes can be fastened together on the starting side, e.g. by welding, into a full-bodied honeycomb structure which discharges the mass to the inlet side of the lip channel in an advantageous manner.

The invention will now be described in detail with reference to some preferred embodiments of the invention shown in the figures of the accompanying drawing, to the details of which the invention is not narrowly limited.

Figure 1 shows a machine direction vertical section of a headbox-10 structure, in connection with which it is advantageous to apply the turbulence generator according to the invention.

Fig. 2 shows the turbulence generator of the headbox according to Fig. 1 seen from the direction A marked in Fig. 1.

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Figure 3 shows an axonometric view of the shape of one turbulence tube of a turbulence pipe system according to the invention and its smooth transition from a circular cross-section to a triangular cross-section.

The headbox structure shown in Figure 1 is mainly known from the prior art and will only be described as a background of the invention and an application environment. The headbox pulp suspension jet J is fed to a forming wire 11 passing over the breast roll 10. The headbox comprises a base structure 12 with a lower frame beam 13. Attached to the front wall 25 of the beam 13 is a lower lip beam 14. The lip channel 29 is bounded from above by the upper lip wall 14b, to which the protective structures 28 are connected. Through the lip opening 30, the pulp suspension jet J is fed to the wire 11 or to the gap between the wires. Above the lip opening 30 30 is limited and adjusted by the tip strip 26.

The pulp suspension is introduced into the headbox by means of a transverse manifold 15 which flows are divided into a plurality of machine-directional distribution pipes 16. The distribution pipes 16 the pulp suspension will equalizing chamber 17, 35 on which the output side is a conduit 18 which opens above the equalizing chamber 19. The equalizing chamber 19 is an air space V, which is the pressure 5 84 736 fluctuation damper. The upper end of one 18 terminates in a dam 18a, followed by an overflow 19a. The dam 18a sets the height C of the pulp suspension.

After the equalization chamber 17, a turbulence generator 20 according to the invention follows, first in the flow direction, a perforated plate 21 with five overlapping horizontal rows (Fig. 2) of flow holes 21a. Each hole 21a opens into the turbulence tube 22 of the turbulence generator 20, which begins coaxially with its hole 21a. The diameter D2 of the tubes 22 is 10 larger than the diameter Dx of the holes 21a. Ratio of said diameters D2 / D]. is preferably in the range Dz / D! - 1 ... 2. Thus, there is a 90 ° step between the holes 21a and the tubes 22, which widens the flow channel in the flow direction F of the pulp suspension.

After the initial initial portions, the turbulence tubes 22 pivot slightly towards each other in the vertical plane and their flow cross-section changes smoothly and gradually from a circular cross-section to a triangular cross-section (Fig. 3) to form a turbulent generator 20 at the outlet plane 23.

At the outlet plane 23 of the turbulence generator 20, the entire flow cross-section, excluding the wall thicknesses of the turbulence tubes 22, is a flow cell.

- · turbulence generator 20 the output level of the tubes 23 of the sub-flows pur pent kolmiokennostorakenteesta the slice channel 29, which continues to flow in the direction of the arrow F the slice opening 30.

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Figure 2 shows a honeycomb structure according to the invention of the turbulence piping outlet end 23, in which the turbulence generator 20 outlet end consists of five horizontal rows of triangular tubes RltR2, R3, R4 and R5. The triangular tubes form horizontal top walls 30 24a and 24b and double horizontal partitions 24 in the exit level 23 of the honeycomb.

The tubes 22 of the turbulence generator 20 are in the shape of an equilateral triangle in the starting plane 23, as shown in Fig. 2, the outer dimensions of the sides of the triangle being denoted by s. The wall thickness of the pipes is marked with b. The mouths of the triangular tubes are in their overlapping horizontal rows Rj-Rs staggered with each other so that they are displaced laterally by dimension s / 8. In this way, the lower tip 5 of the cell triangle of the upper row of pipes R1 becomes in the same vertical plane as the upper tip of the triangle of the lower row of pipes R5 at the corresponding point, i.e. in four rows the lateral displacement totals s / 2.

In the edge areas of the turbulence generator 20, in connection with the vertical side walls 10 of the headbox, suitable edge channels are used, the shape of which may be triangular. Additional mass from the adjustable supply connections can be fed to these edge channels in a known manner.

Figure 3 shows the deformation of the turbulence tube 22 from the circular cross-sectional tube shape 22a through the intermediate portion 22b to the triangular transverse tube portion 22c in a smooth manner. The triangular cross-section of the portion 22c has rounded tips that change to a sharp triangular cross-sectional shape with a short portion 22d of the tube end.

The total length L of the turbulence tubes 22 is of the order of L ~ 500 mm, the length of the intermediate part 22b 1¾ <30-100 mm and the length L3 «50-150 mm of the triangular part 22c, preferably about 100 mm. As an example of the dimensioning of the cell shown in Fig. 2, it can be stated that the dimension of the side of the triangle is s - 20-40 mm and the wall thickness b - 1-3 mm.

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The equilateral triangular cell described above and shown in Figure 2 is generally the most preferred embodiment of the invention, but in some cases a rectangular cell can also be used, of which two adjacent cells together form a parallelogram. Again, the bases of the triangular angles are horizontal in the initial plane 23 of the turbulence generator and form the end walls 24a, 24b and the partitions 24 of the cell rows.

The discharge end of the honeycomb formed by the tubes 22 is formed into a rigid honeycomb structure 35, e.g. by welding the opposing walls of adjacent cells to each other and grinding the welding seams in the starting plane 23.

The turbulence tubes 22 shown in Figure 3 are preferably made of round cross-section tubes 5 by shaping the exterior portion 22c, 22d substantially triangular with an external mold tool and accurately drawing the inner dimension of the tubes 22 to final dimensions with a suitable inner mandrel tool. In addition, the tubes 22 are polished from the inside to a high gloss.

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The following claims set forth within the scope of the inventive idea defined by the invention may vary and differ from those set forth above by way of example only.

Claims (7)

1. Inlet turbulence generator (20) of a paper machine which provides internal microturbulence in the pulp suspension stream 5 (F), thereby improving the homogeneity of the stream, the turbulence generator (20) comprising a turbulence tube system having several pA alternates parallel turbulence tubes (22), wherein the cross-section of the turbulence tubes (20) initially at the input side of the turbulence generator (20) is substantially round and changes in the direction of flow 10 gradually and evenly to a flat-side cell structure where a cell - except any edge channels - is substantially equal in size and of the same shape and which cell structure Ar is substantially complete at the output plane (23) of the turbulence generator (20), characterized in that the cell structure of the turbulence tube system 23 at the output plane (23) (20) are formed by cell triangles with equal sides, being next to each other the sides of each other are immediately adjacent to each other, that the cell triangles of said cell structure Ar in offset in the transverse direction relative to each other in the adjacent cell rows (R R -. R ^), and that the bases of said cell triangles Ar be straightened, thereby forming the upper wall (24a) and lower wall (24b) of the cell system and the middle walls (24) of the cell rows (R1-. Rn). Turbulence generator according to Claim 1, characterized in that the cell triangles of said cell structure have flat sides at the output plane (23) of the turbulence generator (20) (Figure 2). Turbulence generator according to claim 1 or 2, characterized in that said laterally offset of the cell triangles Ar, so that the lower tip of the cell triangles of the upper cell row (Rj) Ar in the same vertical plane as the upper tip of the lower cell row (R5) (Figure 2). 4. A turbulence generator according to any one of claims 1-3, characterized in that said laterally offset of the pA each of the 84736 second cell triangles is about s / 8, where s is the outer dimension of the base of the triangle cell. 5. A turbulence generator according to any one of claims 1-4, characterized in that the length (L) of the turbulence tubes (22) is of the class L «500 mm and that the length of the portion (22c) of it which has triangular cross-section Lj is L3 »50-150 mm, most preferably L3« 100 mm. Turbulence generator according to any one of claims 1-5, characterized in that said turbulence pipe (20) is formed of a circular cross-section pipe by forming the side of one end thereof with a molding and mandrel tool for a portion (22c). with a triangular cross section and an intermediate section (22b), where the triangular cross section is joined to the circular cross section (22a). 15 Turbulence generator according to any one of claims 1-6, characterized in that the cell triangles of the turbulence tubes (22) are stacked tightly against each other and welded with their ends at each other at the output plane (23) of the turbulence generator (20). 20