EP0067894B1 - Centrifugal sifter - Google Patents

Description

The invention relates to a centrifugal 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, i.e. for separating a mixture or batch of grains of different sizes and / or shapes and / or different specific weights in coarse material or 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 area, 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) sooner or later reach the coarse grain outlet at the lower end of the viewing area. 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 a fine material classifying air outlet which axially adjoins the interior of the classifying wheel. The fine grain is finally separated or separated from the classifying air, whereupon the classifying air is re-introduced into the classifying air inlet, that is to say it 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 μm is desired. This very fine grain is needed in many ways, e.g. 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.

Relatively large quantities at the lowest possible prices are required for the named purposes. In the previously known classifiers of this type, which have only a single fine material class air outlet, the throughput is relatively low. The throughput depends, among other things, on the size of the classifier, in particular on the length and diameter of the classifying rotor, that is to say its peripheral surface on which the classifying takes place. However, the diameter is limited due to the increasing centrifugal force, and the limiting grain size also depends on the diameter and the speed, and thus on the centrifugal force. The length of the classifying rotor is also limited, in particular because of different radial flow velocities along the classifying rotor between two fins. This radial flow velocity is dependent on the suction, ie the negative pressure with which suction is drawn off at the outlet. This suction is greatest at the outlet and decreases towards the opposite end.

The invention has for its object to provide a classifier of this type with a much higher throughput, and Gret-tzkom- ― sizes preferably between 10 microns down to 2 microns. This object is achieved by the features of the characterizing part of claim 1.

The two fine material class air outlets allow a far longer class wheel than before and therefore a correspondingly higher throughput. There are practically two classifiers with the permissible axial pressure drop connected in series. The large length of the classifying rotor gives a correspondingly long zone of relatively even, stable flow, which is not disturbed by irregularities at the ends of the classifying rotor, and thus a correspondingly effective, uniform classifying.

Thanks to the double-sided fine material-visible air outlets, the outlet cross-section is approximately doubled, so that despite the increased throughput there is a lower 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 one embodiment, such a setting of fine material is prevented in that the two fine material classifying air outlets are each surrounded by a cooling chamber in the area near the rotor.

Cooler particles adhere less easily to a cooled surface. Here, the bearings of the double-sided rotor shaft are advantageously arranged in a cooling chamber; the bearings are cooled at the same time, which benefits operational safety and a long service life of the machine. This is particularly important given the increased throughput.

A further embodiment consists in that a labyrinth seal is provided at each end of the classifying rotor, which is connected to one of the cooling air chambers by a channel. The cooling air thus serves at the same time for flushing the labyrinth seals, so that the labyrinth seals are cooled, and there is also no special flushing air Source required. A rinsed labyrinth seal in a classifier is already known from DE-AS 1 757 582.

Finally, it is also provided that an annular channel is provided on the end face of the housing opposite the coarse material outlet for blowing the batch of material to be sifted into the viewing space. In this way, an increased throughput is evenly given up.

• 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 111 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 111 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 classifying air inlet 2, into which the classifying air enters uniformly in the direction of 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 ring 9, the lamella ring 11 of the classifying rotor 10 is provided. The grain mixture to be separated is entered from above into the viewing space 23 between the guide vane ring 9 and the rotor disk ring 11. In fact, an annular channel 22 for blowing in the grain mixture is provided in the upper housing wall, into which a connecting piece 7 serving as an inlet for coarse grain opens. A funnel-shaped coarse-grain outlet 8 is provided on the opposite, ie lower, front side 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.

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, 18, 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 opened on both end faces 13, 14 in such a way that it connects tightly to the outlets 3, 4. Between the classifying rotor and the housing there is in each case a seal 15, 16 which is designed like a face plate or a labyrinth. A purge air channel 27 in each case introduces purge air from the cooling air chambers 17, 18 for sealing between the viewing space 23 and the outlets 3, 4 (arrow 19 in FIG. 3).

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

Claims (5)

1. A centrifugal air separator comprising a substantially cylindrical, upright housing, which is provided with an approximately tangential inlet (2) for separating air and which contains guide vanes (9) forming an annular array (9), which is radially spaced from and concentric to the housing shell and stationary relative to the housing, and a separating rotor (10), which is radially inwardly spaced from said array and provided with an annular array (11) of blades, which define radial passages, wherein an inlet (7) for a mixture of particles to be separated opens into the separating space (23) disposed between the annular array (9) of guide vanes and the separating rotor (10), an outlet (8) for coarse particles opens out of the separating space at the bottom, an outlet (3 or 4) for separating air which is laden with fine particles adjoins the separating rotor (10) on the end thereof and has a diameter which is approximately as large as the inside diameter of the separating rotor (10), and the inlet (7) for separating air and the annular array (9) of guide vanes extend over approximately the same axial length as the separating rotor, characterized in that two outlets (3, 4) for fine particles and separating air adjoin the two ends of the separating rotor (10), respectively, the diameter to length ratio of the separating rotor amounts to 1:1.5 to 1:4, and supporting discs (24) having axial passage openings and serving to mount thp blades (11) of the separating rotor (10) are shrunk on the shaft (10a).

2. An air separator according to claim 1, characterized. in that the two outlets (3, 4) for fine particles and separating air are surrounded by respective cooling air chambers (17, 18) close to the rotor.

3. An air separator according to claim 2, characterized in that the bearings (5, 6) of the separating rotor shaft (10a) are disposed in respective ones of the cooling air chambers (17, 18).

4. An air separator according to any of claims 1 to 3, characterized in that a labyrinth gland (15, 16) is provided at each end of the separating rotor (10) and communicates through a passage (27) with an associated one of the cooling air chambers (17, 18).

5. An air separator according to any of claims 1 to 4, characterized in that an annular passage (22) for blowing the mixture to be separated into the separating space (23) is provided on that end face of the housing which is opposite to the outlet (8) for coarse particles.

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