EP1217122B1 - Process for making screens for cleaning of paper pulp - Google Patents

Abstract

In paper manufacture a suspension of paper fibre is wet sieved through a perforated (7) sheet metal panel (1) which is held in position by profiled metal fixtures (3). The panel has holes (2) into which the fixtures are pressed. The fixtures especially project above the sieve surface. The profiled metal fixtures are of octagonal cross section and project between 2 and pref. 15 mm above the sieve surface. The fixtures are fabricated of a high wear-resistant alloy e.g. sintered tungsten carbide powder. The cross sectional area of each fixture is between 50 and 200 mm.

Description

The invention relates to a method according to the preamble of claim 1.

In the pulp processing screens are used, for. In sorters of the pulp and paper industry to treat the fiber-containing suspension in a wet sieving. In this case, in most cases, non-fiber impurities should be retained on a sieve due to their size and then deposited. The fibers can pass through the sorting openings together with part of the water. Also, pulpers are often provided with sieves, which restrain the unresolved paper content and coarse impurities. There are also other applications, e.g. to fractionate fiber-containing suspensions according to the fiber length. Basically, such sieves can be flat or curved. They are usually made of metal, e.g. alloyed high quality steel. They are called baskets if they are rotationally symmetric, e.g. cylindrical, are constructed.

In order to prevent clogging of the sorting openings, scrapers that are moved past them are usually used. Their effect can be significantly improved by projecting strips, as they lead to turbulence, which prevent the solidification of solids.

In many applications such screens are subject to considerable wear. This is due primarily to the fact that, for example, in the case of the already mentioned use in paper fiber suspensions, a certain contamination load likewise reaches the area of the sieves. This pollution may consist of metal parts, broken glass, sand or stones. Since it is the task of these screens to hold back such dirt load, they produce considerable wear in conjunction with the sweeper passed by. Therefore, there have long been elongated armor by wear-resistant materials, eg by build-up welding. In other cases, finished wear strips are mounted on the screen plate. Such strips or armor can therefore protect the screen from wear in addition to the aforementioned turbulence increase. Patch strips are known for example from DE-A-195 06 084. The production and installation requires greater effort, especially since they often consist of wear-resistant, but brittle material.

Even if the sieves already fulfill their purpose, there is always the requirement to reduce or improve the sieves, which are also to be regarded as wear parts. In fact, these parts are rather expensive items that are often replaced at certain intervals. Therefore, the special endeavor of the manufacturers of such screens is aimed at being able to produce these as inexpensively as possible.

The invention is based on the object to provide a method for producing screens, with either the cost can be reduced without the quality, in particular their robustness suffers, or with the wear resistance and thus the life of the screen is increased ,

This object is achieved by the features mentioned in the characterizing part of claim 1.

The profile pieces used in the invention are relatively simple to produce as standard parts, even if they are made of very hard, highly wear-resistant material, such as sintered carbide. In a holding hole in the screen plate, which is usually made of a tough, high-strength metal alloy, they can be easily fastened by pressing. In this case, preferably deforms the material of the screen plate and adapts to the shape of the profile piece. Welding is not required. Worn profile pieces can be knocked out and replaced by new ones.

Flat sieves are particularly well suited for the production by this method. They are also used mostly where rough operation leads to a high wear load. The pressing of the profile pieces can be easily performed in flat screens. In most cases, the sieve apparatus, in the flat sieves are to be installed, provided with a support structure that prevents the sagging of the sieves. As a result, a possible weakening of the screen plate through the holding openings is generally without detriment.

However, if the screen plate would be weakened too much by closely adjacent holding openings, the profile pieces can also be set at a distance. Another possibility would be to provide the profile pieces with a paragraph, so that the projecting beyond the screen surface part is wider than that pressed into the holding opening. That would be more expensive, but the holding openings could have a greater distance. If the screen plate is sufficiently thick, the holding openings can be blind holes, so that the tensile area of the screen plate does not need to be pierced or only very finely penetrated (venting during pressing in).

Fig. 1

Teilansicht eines erfindungsgemäß hergestellten Siebes;

Fig. 2 und 3

je einen Schnitt durch den Teil eines Siebes;

Fig. 4

etwas detaillertere Aufsicht auf das Sieb;

Fig. 5

Teilschnitt durch ein Sieb mit variiertem Profilstück;

Fig. 6 und 7

je eine variierte Anordnung der erfindungsgemäß eingesetzten Profilstücke.

The invention and its advantages will be explained with reference to drawings. Showing:

Fig. 1

Partial view of a sieve made according to the invention;

FIGS. 2 and 3

a section through the part of a sieve;

Fig. 4

a little more detailed supervision of the sieve;

Fig. 5

Partial section through a sieve with varied profile piece;

6 and 7

each a varied arrangement of the invention used profile pieces.

Fig. 1 shows the part of a screen in which in the screen plate 1 according to the invention a plurality of profile pieces 3 is inserted. These are grouped together in such a way that each group forms a bar. The sieve is flat and has a circular outer diameter. In addition to the profile pieces, the sieve is also provided with screwed strips 8. The mounting holes, which usually a such sieve are not shown here. The sorting openings 7 are shown in this figure only to a small extent. The direction of view of this figure is directed to the side of the screen on which the suspension to be screened tapers and on which the screen dreamer is located.

In the section shown in Fig. 2 through the screen plate 1 can be seen by way of example a sorting opening 7 and the lower part of the holding hole 2. This is preferably circular and has a slightly smaller diameter d than the Eckmaß e of the profile piece 3. The latter consists here an octagonal profile with regular cross section. The illustration shows the moment of the manufacturing process in which the profile piece 3 is pressed about halfway into the screen plate 1. The side surfaces 4 of the profile piece 3 are at the surface of the screen at a right angle α. The sorting opening 7 has on its inlet side a circular cylindrical shape, which then merges into a conical enlargement (viewed in the direction of passage). Such sorting holes are typical of screens to be used for sorting pulp of paper pulp suspensions. At the bottom of Fig. 2, the clamping seat between the round retaining opening and octagonal profile piece is shown in plan view.

In Fig. 3, the press-fitting operation is completed, i. the profile piece 3 is completely inserted through the screen plate 1. It can be seen that the profile piece 3 protrudes above the screen plate 1 due to its length. The supernatant 5 has the height h, which is usually a few millimeters. It is also another supernatant visible 5, partially covered by lying in front profile piece 3, which belongs to a further inserted into the screen plate 1 profile piece.

Fig. 4 shows in somewhat more detail the arrangement of several mutually belonging profile pieces 3. It recognizes a part of a group of profile pieces 3, which are lined up here in a zigzag line 6. At the bottom of this screen plate cutout is a holding opening 2 with diameter d, in which the associated profile piece is not yet used. Furthermore, this illustration shows the Sorting openings 7.

As already mentioned, it is also possible to manufacture the profile pieces such that, as shown in FIG. 5, they have a projection 5 'which has a greater width in the direction of the adjacent profile piece than the lower inserted part of the profile piece 3'. As a result, the holding openings can also be arranged at a greater distance if the projections 5 'touch or should have a very small distance. As an example, this Fig. 5 shows a varied sorting opening 7 'with inlet side bevel. This form is particularly favorable for high throughput and can also be used in other cases.

While Fig. 1 shows the combination of profile pieces 3 with attached strips 8, there is, as the Fig. 6 shows by way of example, also the ability to produce all the required surveys on the screen plate in the form of the profile pieces 3 already described. The groups of profile pieces can be designed so that form either linearly aligned rows or that adjacent profile pieces are offset from each other. In all these cases, strip-shaped elevations are produced on the inlet side of the screen, which have the known turbulence-increasing effect. They are either strictly radially oriented, as shown here, or have a skew angle to promote solids slippage. They can also be arcuate.

But it is also conceivable to use the profile pieces insulated in the screen plate. Such a version is shown in FIG. 7. With it, in particular contaminants can be moderately crushed, and this effect can be controlled by the distance from the rotor.

Claims (20)

1. Method for making screens used in the wet screening of paper fibre suspensions, consisting of at least one screen plate (1) that has a large number of grading holes (7, 7'),
   characterised in that
   the screen plate (1) is provided with a number of retaining holes (2), in that profiled parts (3, 3') are subsequently inserted into these retaining holes (2) in such a manner that they protrude above the surface of the screen.
2. Method as in claim 1,
   characterised in that
   the side surfaces (4) of the profiled parts (3, 3') stand essentially perpendicular to the surface of the screen.
3. Method as in claim 1 or 2,
   characterised in that
   the profiled parts (3, 3') are inserted in such a manner that the projection above the surface of the screen is at least two millimetres and at most 30 millimetres.
4. Method as in claim 1, 2 or 3,
   characterised in that
   the profiled parts (3, 3') have a regular polygonal profile.
5. Method as in claim 4,
   characterised in that
   the Polygonal profile is an octagon.
6. Method as in one of the preceding claims,
   characterised in that
   the profiled parts (3, 3') are made from a highly wear-resistant material.
7. Method as in claim 6,
   characterised in that
   the profiled parts (3, 3') are made from a sintered metal alloy.
8. Method as in claim 7,
   characterised in that
   a tungsten carbide powder is sintered to form the finished profiled parts (3, 3').
9. Method as in one of the preceding claims,
   characterised in that
   the cross-sectional area of a profiled part (3, 3') is between 50 and 200 mm².
10. Method as in one of the preceding claims,
    characterised in that
    the height (h) of the projection (5, 5') of the profiled parts (3, 3') above the screen plate (1) is between 2 and 15 mm.
11. Method as In one of the preceding claims,
    characterised in that
    the retaining holes (2) are circular and that their diameter (d) is smaller than the width across the corners (e) of the profiled parts (3, 3'), and in that when the profiled parts (3, 3') are inserted into the retaining holes (2), a press fit is produced.
12. Method as in one of the preceding daims,
    characterised in that
    the retaining holes (2) pass right through and have a larger cross-section at the side at which the profiled parts are inserted than at the opposite side.
13. Method as in one of the preceding claims,
    characterised in that
    the retaining holes (2, 2') are arranged in each case in groups, and in that the retaining holes of each group lie along a line, the edges of adjacent retaining holes (2, 2') that lie along a line having only small spaces between them.
14. Method as in claim 13,
    characterised in that
    the lines of retaining holes (2, 2') are straight.
15. Method as in claim 13,
    characterised in that
    the lines are curved.
16. Method as in claim 13,
    characterised in that
    the lines (6) are in a zig-zag shape.
17. Method as in one of claims 1 to 12,
    characterised in that
    the retaining holes (2, 2') are positioned singly on the screen plate (1), there being a space of at least 50 mm between them.
18. Method as in one of the preceding claims,
    characterised in that
    profiled parts (3, 3') are inserted into, and strips (8) are placed on to, the screen plate (1).
19. Method as in one of the preceding claims,
    characterised in that
    the grading holes (7, 7') are circular in cross-section, with a diameter (d) of between 1 and 30 mm.
20. Method as in one of the preceding claims,
    characterised in that
    the screen plate (1) is made of a high-strength metal alloy.

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