EP0236843A2 - Sorting screen - Google Patents

Abstract

The sorting screen has depressions 5, on the bottom of which there are fine slots 4 or screen holes. The depressions are generally elongated in shape, with their longitudinal extent parallel or slightly inclined to the axis of rotation of a rotor, the sorting wing 2 passes close to the screen. The front edge of the recesses 5 - seen in the direction of rotation of the sorting wings 2 - is arranged inclined to the enveloping outer surface of the screen basket, specifically at an angle between 15, preferably 30 and 60 °. The sieve slots or rows of sieve holes run parallel to the front edge of the depressions 5 mentioned. For the use of the sieve baskets when sorting fiber suspensions, a better sorting effect and a stronger sieve clearance are achieved.

Description

The invention relates to a sorting screen according to the preamble of claim 1. Sorting screens are used both as flat screens and as rotationally symmetrical screen baskets in many embodiments, in particular in the paper industry, for the different sorting tasks, e.g. ultimately to obtain the fibers or a pure fiber suspension from waste paper. Sorting tasks have become quite demanding lately, so that e.g. the slot widths are already below 0.3 mm. There is either a high risk of clogging of the screens or there is a low sorting performance.

The object of the invention is to provide a sorting screen which has a good sorting performance, ie a good sorting efficiency with good throughput without the risk of clogging, and in which the highest possible percentage of good fibers can pass through the screen.

This object is achieved in a sorting screen of the type mentioned by the features of the characterizing part of claim 1. Particularly advantageous embodiments for sorting baskets result from subclaims 2 to 4 and 7, 8.

From US-PS 45 29 520 an arrangement according to the preamble of claim 1 is known, but only one slot or row of holes is provided per recess. This is intended to prevent matting of the fiber layer located on the outer surface of the screen, in particular by fixing longer fibers, and thus a strong increase in the resistance to penetration of the screen. In this version, the recess can only be very flat. This has the disadvantage that it can only be used at low suspension material densities and that the depressions quickly become ineffective when the edges are worn.

According to the invention, however, the risk of blockage of the sieve is reduced to a particularly great extent even at higher suspension consistencies, because there is greater freedom in the recesses for in particular the larger components, such as dirt and specks. In addition, the effectiveness is not impaired if the edges of the depressions are worn.

EP 00 79 811 explains a similar arrangement to the known arrangement described above, but it is a single row of holes per groove, the holes of a groove wall being to be arranged directly adjacent or abutting the fibers in a direct way by reflection to facilitate passage through the holes on the groove wall.

• Fig. l eine Ansicht auf einen aufgebrochenen Siebkorb;
• Fig. 2 einen Schnitt durch einen Siebkorb quer zu den Schlitzen in vergrößerter Darstellung;
• Fig. 3 eine weitere Ansicht eines Siebkorbes und
• Fig. 4 eine Siebausführung mit Lochreihen

The invention is explained below using an exemplary embodiment shown in the figures. It shows:

• Fig. L is a view of a broken screen basket;
• Figure 2 shows a section through a screen basket transverse to the slots in an enlarged view.
• Fig. 3 is another view of a strainer and
• Fig. 4 shows a sieve design with rows of holes

On the inflow side of the strainer basket 1, the sorting wings 2 held by support arms 6 run at a short distance from the surface of the strainer basket in the direction of the arrow. The sorting wings 2 have an airfoil profile and generate pressure pulsations in the vicinity of the screen basket surface, which propagate into the depressions 5 and into the screen openings 4. The recesses 5 give the screen basket 1 practically an interrupted, no longer smooth surface. The depressions 5 create a vortex field in the flow, which prevents the sieve openings from becoming clogged. It is also achieved that relatively long fibers can also squeeze through the sieve slots 4. Heavy or larger particles of dirt that get into these wide depressions can thus be more easily excreted and do not cause constipation. Overall, this results in a relatively large throughput of accepted material. The sieve slots 4 preferably run parallel to the axis of rotation and the generatrix of the generatrix of the sieve basket 1. The depressions in the axial direction of the rotor blades 2 are interrupted by cross webs l3 in order to give the screen basket greater strength. Two to four parallel sieve slots or corresponding rows 9 of sieve holes are preferably provided for each recess 5. The width of the sieve slots can be less than 0.45 mm, in particular less than 0.30 mm. In order to best utilize the effect of the turbulence generated by the depressions, only two (at most three) slots per depression are the cheapest.

The angle a, which the front side surface 11 forms with respect to the direction of rotation of the sorting wing 2 or the suspension flow on the sieve surface (see thick arrows) with the vertical on the lateral surface or flow direction (thick arrow) is between 15 ° and 60 ° , preferably 35 ° and 50 °. The rear surface l2 hardly deviates from this vertical line, since this makes the slot pitch t the smallest and the free screen passage area the largest.

The use of a flat screen is preferred for vibration sorters. For sieve baskets with sorting wings according to Fig. 1 that run closely along the surface, sieve slots or rows of holes 9 running parallel to or slightly inclined at angles between 0 and 35 ° to the axis of rotation. In this embodiment, the sorting effect according to the invention is the most favorable for the corresponding sorting devices with fine slots or narrow sieve holes, which are generally known as vertical classifiers.

Claims (7)

1.Sorting sieve, in particular rotationally symmetrical as a sieve basket, with slots (4) or rows of holes for sorting, in particular, fiber suspensions, the sieve (l) on its inflow side having depressions (5) at short intervals, on the basis of which the slots (4 ) or holes are worked in, the depressions (5) are essentially formed as elongated rectangles, the slots (4) or rows of holes (9) run parallel to the longitudinal edge of the depressions and parallel or inclined at an angle of up to 35 ° to the generating line of the strainer jacket and the side surface of the depressions (5) lying at the front in the flow direction of the suspension is inclined to the vertical there on the screen basket jacket by an angle (a) between 15 ° and 60 °, thus from the bottom of the depression (5) and from the respective slot (4) to form an extension of the recess, characterized in that several parallel slots or rows of holes are provided per recess s ind. 2. Sorting sieve according to claim l, characterized in that the depressions have a width b of at least 10 times the slot or 5 times the hole width. 3. Sorting sieve according to claim l or 2, characterized in that two to four sieve slots (4) or corresponding rows of holes (9) are provided per recess (5). 4. Sorting sieve according to claim 3, characterized in that two recess slots (4) or corresponding rows of holes (9) are provided for each recess (5). 5. Sorting sieve according to one of claims 3 and 4, characterized in that the side surface of the recesses (5) lying in front in the direction of flow of the suspension is inclined at an angle (a) between 35 ° and 50 ° to the vertical there on the sieve basket jacket. 6. Use of a sorting sieve according to one of claims 1 to 5 in a sorting device, in which on the inflow side of the strainer basket sorting wings (2) sweep past the surface of the strainer basket at a short distance. 7. Sorting sieve according to one of claims l to 6, characterized in that the recesses (5) extending perpendicularly or slightly inclined to the main flow direction in the direction of the height of the sieve (sieve basket l), i.e. are also interrupted one or more times transversely to the direction of flow by transverse webs (l3).

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