EP0067895A1 - Centrifugal sifter - Google Patents

Abstract

1. A centrifugal air classifier comprising a substantially cylindrical housing (1), which is provided with an approximately tangential inlet (2) for classifying air and which contains an annular series of guide vanes (9), which is concentric with and radially spaced from the shell of the housing, and a classifying rotor (10), which is radially inwardly spaced from said guide vanes and comprises an annular series of blades (11) defining radial passages, wherein an inlet (72) for a mixture of particles to be classified opens into the classifying space disposed between the guide vanes (9) and the classifying rotor (10), an outlet (8) for coarse particles extends out of the classifying space at the lower end thereof, an outlet (3, 4) for fines-entraining classifying air is provided at the end of the rotor and has a diameter which is approximately as large as the inside diameter of the classifying rotor (10), and the inlet (2) for classifying air and the guide vanes (9) extend approximately over the same axial length as the classifying rotor (10), characterized in that the entire air classifier is pivotally movable about a horizontal axis.

Description

The invention relates to a centrifugal force classifier according to the preamble of patent claim 1.

Such a classifier, as is already known from DT-OS 1 607 631, is used for classifying; H. for separating a mixture or batch of grains of different sizes and / or shapes and / or different specific weights in coarse material 3zw. Coarse grain (grain size above a certain limit grain diameter) and in fine material (grain size below the limit grain size). The grain mixture to be sifted is entered from above into the viewing area (annular space between the guide vane ring and the viewing rotor); At the same time, visible air flows from the outside through the guide vane ring into the visible space, so that the visible air describes a spiral movement and entrains the particles in the corresponding movement paths. In the viewing space, the particles are exposed to the radially directed, opposing resistance and centrifugal forces. For a certain radial and axial air speed, there is a limit grain size for which the two forces are equal.

The coarser particles (larger than boundary grain) get to the coarse grain outlet at the lower end of the viewing space sooner or later. The fine grain, on the other hand, is entrained by the classifying air which flows in through the channels of the classifying wheel and is sucked off by the fine material classifying air outlet by an axially connecting to the interior of the classifying wheel. The fine grain is finally separated or separated from the classifying air, whereupon the classifying air is re-entered into the classifying air inlet, that is, can be circulated. Such classifiers are primarily used to obtain fine material with the smallest possible grain size in a narrow grain size distribution; An upper grain size (limit grain size) of 2 to 4 _/ um is desired. This very fine grain is required in many ways, e.g. B. as a filler for plastics and car tires. The coarse grain is used for other purposes or fine material is removed again after a further grinding process.

It is therefore very important for economical work that as much as possible all the fine material contained in the batch of grain is separated out when it passes through the classifier, with a relatively high throughput.

The invention is therefore based on the object of creating a classifier of this type with a higher fine material output, the fine material output being to be adjustable. (The “fine material output” is the proportion of the fine material that has been discharged, that is to say extracted, of the total fine material contained in the mixed material that has been fed in.) According to the invention, the solution to this problem is that the classifier can be pivoted overall about a horizontal axis. In this way - depending on the inclined position - the dwell time of the particle mixture in the viewing area can be adjusted according to the respective grain size and density and other influencing factors. If the dwell time is longer, a higher percentage of the fine material contained in the grain mixture is subtracted. Furthermore fall in particular coarser particles following gravity onto the inclined view rotor, are thrown away by it and hit the guide vanes. As a result, in addition to a comminution effect, a deagglomeration is achieved, ie fine grain adhering to coarse grain is separated from the coarse grain; this fine grain is thus drawn off through the classifying rotor and is not "lost" with the coarse grain. In a further embodiment, the classifying rotor is surrounded on both ends by a deflector ring. These bumpers rings make the flow more even and thus increase the selectivity. Another training is that the individual guide vanes are displaceable in the radial direction for universal use of the classifier. For this purpose, the guide vanes are guided in the radial direction at their two ends in the housing covers and are adjustable in the guides. In this way, the radial depth of the viewing space can be optimally adjusted such that the separation zone is quite close to the outer diameter of the viewing rotor. This ensures that all fine grain gets into the area close to the rotor and is sucked in through the classifying air. If the separation zone is too far away from the classifying rotor, fine material could get into the coarse material outlet together with the coarse material. In particular, the respective width or radial extent of the viewing space can hereby be optimally adapted to the respectively set inclination and thus to the dwell time.

The classifier according to the invention can be provided with only a single fine material class air outlet, but a special embodiment consists in that a fine material class air outlet connects to both end faces of the classifying rotor. As a result, the throughput is increased when the fine material output is increased.

Thanks to the double-sided fine material sight air outlets, the outlet cross-section is approximately doubled, so that despite increased Throughput performance results in a smaller flow rate. At the previous higher flow velocities, on the other hand, the fine material is thrown against the walls so violently that it adheres there, especially once a first fine material layer has built up. As a result, the flow conditions deteriorate continuously, which also results in a reduction in throughput.

Above all, however, parts of these layered approaches (so-called "egg shells") burst from time to time and get into the fines, which makes them unusable or which in any case leads to great difficulties. To avoid these approaches (eggshells), the flow velocity has therefore been limited, but this also limits the throughput.

According to the invention, such a setting of fine material is prevented in that the two fine material sight air outlets are each surrounded by a cooling chamber in the area near the rotor. Cooler particles adhere less easily to a cooled surface. In this case, the bearings of the classifying rotor shaft mounted on both sides are advantageously arranged in one cooling chamber each; the bearings are cooled at the same time, which benefits operational safety and a long service life of the machine.

Another embodiment is that on the forehead A labyrinth seal is provided at each end of the classifying rotor, which is connected to one of the cooling chambers by a channel. This flushing prevents coarse material from entering the sighting air fine material outlets (or into the outlet).

• Fig. 1 zeigt einen erfindungsgemäßen Sichter im Längsschnitt;
• Fig. 2 zeigt den Sichter von oben, links im Querschnitt und rechts in Draufsicht;
• Fig. 3 zeigt die Einzelheit III in Fig. 1, nämlich die Labyrinthdichtung mit Spülluftzufuhr, aus der Kühlkammer.

For a more detailed explanation, an embodiment is described below with reference to the drawing:

• Fig. 1 shows a classifier according to the invention in longitudinal section;
• Fig. 2 shows the classifier from above, on the left in cross section and on the right in plan view;
• Fig. 3 shows the detail III in Fig. 1, namely the labyrinth seal with purge air supply from the cooling chamber.

The classifier has a concentric, essentially cylindrical housing 1 with a tangential classifier air inlet 2, into which the classifier air enters uniformly in the direction of the arrows 20 over the entire axial height.

A guide vane ring 9 is provided in the housing at a radial distance from the housing jacket. Again, at a radial distance from the guide vane 9 of the lamellar ring ₁ 1 is of the classifying rotor 10. In the viewing space 23 between the vane ring 9 and the rotor lamella ring 11 is to be separated from above de grain batch entered. In fact, an annular channel 22 is provided in the upper housing wall for blowing in the grain mixture, into which a connecting piece 7 opens. A funnel-shaped coarse-grain outlet 8 is provided on the opposite, that is to say the lower end of the housing.

On both ends of the classifying rotor, a fine material classifying air outlet 3, 4 is provided in the form of a curved tube piece, the diameter of which corresponds approximately to the rotor inside diameter. According to the invention, the classifier can be pivoted overall about a horizontal axis. In the present exemplary embodiment, the pivot axis 30 extends transversely to the plane determined by the outlets 3, 4, approximately at the center between the outlets 3, 4. In particular, the position of this pivot axis 30 can be carried out in a manner known per se. The sifting air fine material outlets 3, 4 are each surrounded by a cooling air chamber 17, 18, to which cooling air is supplied in each case via a connection 19, as a result of which fine material is prevented from being deposited in the outlets. In the cooling air chambers 17, 18, the rotor shaft 10a, which is guided through the curved outlets 3, 4, is also supported on both sides in bearing brackets 5, 6. The bearings are also cooled. Due to an overpressure in the cooling air chambers 17, ₁ 8, no fine material can penetrate them (see arrows on the shaft bushings). It is driven by means of a V-belt pulley 12.

The classifying rotor 10 is open on both end faces 13, 14 so that it tightly connects the outlets 3 4. Between the Sighting rotor and the housing are each a seal 15, 16, which is designed like a disk or labyrinth. A purge air duct 27 in each case introduces purge air from the cooling air chambers ₁ 7, ₁ 8 for sealing between the viewing space 23 and the outlets 3, 4 (arrow ₁ 9 in FIG. 3).

Support disks 24 provided with radial passage openings are shrunk on the shaft 10a of the classifying rotor. The rotor ends are each surrounded by a deflector ring 25, 26 on their outer circumference.

Claims (6)

_1st Centrifugal classifier with a substantially cylindrical, provided with an approximately tangential sight air inlet, in which a fixed vane ring with a radial distance from and centered to the housing shell and with a radial distance inward from this a sifting rotor with a radial channels forming lamellar ring are arranged, in the viewing space located between the guide vane ring and the viewing rotor opens at the top an inlet for the grain mixture to be sifted and an outlet for coarse grain opens out from the bottom of the viewing area and an outlet for the fine air loaded with fine material, the diameter of which corresponds approximately to the inside diameter of the rotor, and wherein the sight air inlet and the guide vane ring extend over approximately the same axial length as the rotor, characterized in that that the classifier can be pivoted overall about a horizontal axis. 2. classifier according to claim 1,
characterized,
that the rotor (10) is surrounded at both ends by a deflector ring (25, 26). 3. classifier according to claim 1 or 2;
characterized, -
that the guide vanes of the guide vane ring (9) are adjustable in their radial distance from the sight tube (10). 4. Sifter according to one of claims 1 to 3,
characterized,
that at each end of the classifying rotor there is a fine material class air outlet (3, 4). 5. Sifter according to one of claims 1 to 4,
characterized,
that the fine material visual air outlet or both fine material visual air outlets (3, 4) is or are surrounded by a cooling chamber (17, 18) in the vicinity of the rotor. 6. classifier according to claim 5,
characterized,
that a labyrinth seal at each end of the classifying rotor is provided, which is connected by a channel (27) to each of the cooling air chambers (17, 18).

Images