EP0250747B1 - Method of and device for air sifting - Google Patents

Method of and device for air sifting Download PDF

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Publication number
EP0250747B1
EP0250747B1 EP87105736A EP87105736A EP0250747B1 EP 0250747 B1 EP0250747 B1 EP 0250747B1 EP 87105736 A EP87105736 A EP 87105736A EP 87105736 A EP87105736 A EP 87105736A EP 0250747 B1 EP0250747 B1 EP 0250747B1
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EP
European Patent Office
Prior art keywords
air
air classifier
classifying
stage
centrifuge basket
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EP87105736A
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German (de)
French (fr)
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EP0250747A2 (en
EP0250747A3 (en
Inventor
Ernst W. Dr.-Ing. Hanke
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CHRISTIAN PFEIFFER MASCHINENFABRIK GMBH & CO. KOMM
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Christian Pfeiffer Maschinenfabrik GmbH and Co KG
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Priority to AT87105736T priority Critical patent/ATE82876T1/en
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B07—SEPARATING SOLIDS FROM SOLIDS; SORTING
    • B07B—SEPARATING SOLIDS FROM SOLIDS BY SIEVING, SCREENING, SIFTING OR BY USING GAS CURRENTS; SEPARATING BY OTHER DRY METHODS APPLICABLE TO BULK MATERIAL, e.g. LOOSE ARTICLES FIT TO BE HANDLED LIKE BULK MATERIAL
    • B07B7/00—Selective separation of solid materials carried by, or dispersed in, gas currents
    • B07B7/08—Selective separation of solid materials carried by, or dispersed in, gas currents using centrifugal force
    • B07B7/083—Selective separation of solid materials carried by, or dispersed in, gas currents using centrifugal force generated by rotating vanes, discs, drums, or brushes

Definitions

  • the invention relates to a method for air separation of a grain mixture with indulgence according to the preamble of claim 1 and an air classifier according to the preamble of claim 2.
  • Such a method and a corresponding air classifier are known from EP-B-23 320.
  • This known air classifier generally requires dust separators, e.g. in the form of cyclones and filters.
  • the fine material throughput of such a known air classifier depends in particular on the vertical height and the diameter of its centrifugal basket, that is to say on its circumferential surface or the cylindrical annular space in which the screening is carried out.
  • the other essential parameter of a sifting namely the grain size limit, which distinguishes the fine material from the coarse material, is determined on the one hand by the diameter and the speed of the centrifugal basket and on the other hand depends on the outer diameter of the visible space and the inflow speed of the visible air into the visible space.
  • the grain size limit depends on the acceleration forces acting on the material to be viewed.
  • the vertical dimensioning of the centrifuge basket is also limited due to the mechanical load on its peripheral strips. Above all, however, the enlargement of the centrifugal basket in the vertical direction is restricted by the occurrence of different flow velocities along the strips of the centrifugal basket when visible air and fine material pass between these strips.
  • the flow velocities along the jacket-like peripheral surface of the centrifugal basket are essentially directly dependent on the suction within the centrifugal basket. This suction is greatest at the visible material outlet of the centrifuge basket for the fine material and decreases in the direction of the opposite, closed end face of the centrifugal basket.
  • the rotary drive takes place via this closed or at least largely closed end face by means of the vertical drive axis.
  • the windsifter according to EP-B-23 320 also has the fact that, viewed circumferentially, different flow velocities should prevail on the centrifugal basket. This is because there are variously designed spiral feed channels in an approximately tangential arrangement to the centrifugal basket, blowing air of various types, e.g. dust-containing, hot mill exhaust air and opposite, for example, colder but dust-free atmospheric air into the air classifier.
  • various types e.g. dust-containing, hot mill exhaust air and opposite, for example, colder but dust-free atmospheric air into the air classifier.
  • another known air classifier according to DE-C-29 51 819 is the way to design visual air outlets on both ends of the centrifugal basket.
  • this latter known air classifier however, the problem arises that the strips of the centrifugal basket are provided by a large number of radially due to the large vertical extension compared to the diameter of the centrifugal basket Spokes must be supported and braced. This is necessary in order to be able to counter the centrifugal forces that occur during operation and the other mechanical stresses such as vibrations with a sufficiently high degree of certainty.
  • the last-mentioned known air classifier therefore appears to be unsuitable for highly abrasive visible material, such as sintered aluminum oxide, quartz sand or cement clinker at solid concentrations of, for example, 800 g / m3 to 1200 g / m3 in the classifier exhaust air.
  • highly abrasive visible material such as sintered aluminum oxide, quartz sand or cement clinker at solid concentrations of, for example, 800 g / m3 to 1200 g / m3 in the classifier exhaust air.
  • highly abrasive visible material such as sintered aluminum oxide, quartz sand or cement clinker at solid concentrations of, for example, 800 g / m3 to 1200 g / m3 in the classifier exhaust air.
  • a rotary air centrifugal scatter classifier known from DE-A-30 38 625
  • the centrally placed visible material enters the viewing area via the spreading disc and is exposed to the upward flow of circulating air.
  • the separation efficiency of the classifier is to be improved overall by the greater cleaning of the concentrically derived circulating air from fine particles which is thereby achieved.
  • the circulating air is fed into the viewing area via the deflection surface of a mechanical separator, which is arranged concentrically below the coarse material discharge.
  • This air classifier is also not very suitable for particularly abrasive material due to its baffle-like fittings.
  • the invention has for its object to design a method and an air classifier for performing the method so that the aforementioned disadvantages are avoided and a long operating time is achieved even with relatively abrasive visible material, with high throughput and improved selectivity, this possibly being able to be achieved with a relatively small footprint for the air classifier.
  • This object is achieved in a method according to the preamble of claim 1 by the features of the characterizing part of claim 1 and in an air classifier according to the preamble of claim 2 by the features of the characterizing part of claim 2.
  • a corresponding air classifier is designed with at least two air classifier stages, wherein the air separator stage used for indulgence has a separate or a spreading disc integrated with the downstream, second centrifugal basket, via which the coarse material can be fed to the first stage.
  • this air classifier stage is equipped with a centrifugal basket, corresponding centrifugal basket rails and one or more coaxial rings of guide vanes, although the dimensions of the second air classifier stage are usually different from those of the first air classifier stage for better viewing.
  • the sifting parameters of the second air classifier stage can be adjusted even more suitably to the desired grain sizes and limiting grain sizes.
  • the method according to the invention and the corresponding device are therefore particularly suitable for upper grain sizes below 10 ⁇ m. Since appropriate dust separators, such as cyclones or filters, are required for the separation of the fine material from the classifying air, the small installation area achieved by the vertical multi-stage in the air classifier according to the invention suits use with cyclones accordingly.
  • the multi-stage of the air classifier makes it possible to keep the classifier diameter relatively small, so that the wind classifier according to the invention is very well adapted to the cyclone use due to the small space requirement and, moreover, the relatively large overall height of the cyclones can be fully utilized.
  • the wind sifter according to the invention is also suitable due to its multi-stage nature that different sifting air quantities of different fluidic properties can be used, the controlled introduction into the sifting space through the adjustable guide vane rings and the optimization of the sighting in With regard to improved selectivity by means of different dimensions of the downstream air classifier stage is guaranteed.
  • the air classifier advantageously has at least two centrifugal baskets of different axial heights and with different diameters. Different strips can be provided with different angles of inclination.
  • the individual centrifugal baskets of the various air classifier stages are advantageously driven separately, e.g. via corresponding hollow shafts that run into each other. This possibility opens up the fine tuning of the mechanical centrifugal rejection of the coarse grain to be sifted.
  • a further advantage for indulgence is achieved with the formation of the end face of the downstream centrifugal basket facing the upstream air classifier stage as a closed surface, which takes over the function of a spreading disc.
  • the spreading plate for the coarse material coming from the upstream air classifier stage can also be provided separately from the centrifugal basket. Above all, the spreading plate function is essential, which enables further dispersion of the coarse material that has already been viewed at least once, so that it can be introduced into the subsequent viewing area in a well-distributed manner.
  • the centrifugal basket of the second air classifier stage expediently has a somewhat larger diameter with reduced axial extension than the centrifugal basket of the first wind classifier stage.
  • both end faces of the centrifugal basket of the first air classifier stage are largely designed as through-openings, the centrifugal basket itself being in drive connection with the axle via a few radial stiffening webs.
  • the air classifier is designed with a closed lower end face of the first centrifugal basket and an open end surface for the second centrifugal basket, which is connected to a corresponding suction line, the advantage of better classification is achieved, since in this case three areas of different grain sizes can be viewed and separated .
  • the air channels are expediently designed as two- or multi-flight spiral housings, which allow a largely tangential air inlet to the guide vane rings.
  • the individual inlets are arranged equidistantly around the circumference in order to achieve flow conditions that are as uniform as possible over the entire circumference of the viewing space.
  • the vertical separation of the different air channels for a centrifugal basket can, for example, in one Air duct on one horizontal level is used to inject hot mill exhaust air and on another, for example horizontal level below, cooler, possibly dust-free, atmospheric visual air is blown in.
  • the colder viewing air is preferably supplied in a lower air duct in order to already cool the material being viewed. There is therefore the possibility of allowing visible air with process-related different flow velocities to flow in only in a certain plane of the centrifugal basket, so that, viewed over the entire circumference of the centrifugal basket, there are uniform operating conditions.
  • the wind classifier according to the invention is not limited to the version with two wind classifier stages.
  • the use of a further, downstream third air classifier stage may be necessary and expedient.
  • the removal of the sifting air loaded with fine material from the third air classifier stage is expediently carried out independently of the discharge of the sifting air of the upstream stages and downwards.
  • the possibility of a subsequent multiple sifting in a wind sifter means that it is possible to work with less sifting air via predispersing air sifter stages, so that the air sifter can in principle be constructed with a smaller diameter. Due to the multi-stage sifting, in connection with the design of the centrifugal baskets largely without radial stiffening spokes, the processing of relatively wear-resistant visible material is also possible.
  • the only drawing shows a vertical section through an air classifier 3 with two air classifier stages 1, 2.
  • the material to be placed in the air classifier 3 is fed via a largely centrally arranged upper material inlet 25.
  • the visible material predispersed by this spreading plate 26 reaches a further, second spreading plate 27 via two tapering steps of the housing of the air classifier 3.
  • the material to be sighted reaches the first sighting chamber 4 of the first wind sifter stage 1 in a well-dispersed manner.
  • the sighting chamber 4 is circular, cylindrical, being delimited radially outwards by separately adjustable guide vane rings 6 and 7, which are arranged vertically one above the other. Radially inward, the boundary of the visible space 4 is formed by the outer edges of the blow bars 10 of the centrifugal basket 9.
  • the classifying air for the first air classifier stage 1 reaches the classifying room 4 via the air channels 5, which are designed, for example, in a horizontal section as a two-flight spiral housing inside the viewing space 4 flowing Air flow accelerate the particles falling into the visual space on a spiral track. As a result, coarse material particles are carried out of the spiral track as a result of the higher centrifugal forces acting on them and fall due to gravity onto the first coarse material funnel 8 arranged at the lower region of the first air classifier stage 1.
  • the fine material particles remaining in the spiral air flow on the first air classifier stage 1 are taken to the outer circumference of the rotating centrifugal basket 9.
  • the rotation of the centrifugal basket 9 with its blow bars 10 arranged radially on the outside in the vertical direction accelerates the particles reaching between the blow bars again, entrained particles of the coarse material being thrown back into the viewing space 4.
  • the fine material guided into the interior of the centrifugal basket 9 through the classifying air is suctioned off to the subsequent dust separators via the front opening 11 provided in the upper region of the centrifugal basket 9 and via a two-course discharge spiral 12 connected therewith.
  • the centrifugal basket 9 is driven via a drive shaft 28 designed as a hollow tube, in which a further drive shaft 29 for the centrifugal basket 14 of the second air classifier stage 2 is guided.
  • the centrifugal basket 9 has a closed end wall 31 in the lower region which, for better stabilization, is guided and stiffened approximately in the middle with struts 30 running obliquely to the drive shaft 28 or a wear-protected cone jacket.
  • the coarse material leaving the first coarse material hopper 8 reaches the upper, closed end wall 13 of the second centrifugal basket 14 intended for indulgence.
  • the centrifugal basket 14 of the second air classifier stage 2 is provided with a smaller vertical extension than the first centrifugal basket 9. However, it has a larger diameter than the first centrifugal basket 9.
  • the second centrifugal basket 14 is driven via a second drive shaft 29, which is guided coaxially in the first drive shaft 28, intermediate bearings and struts with the housing of the air classifier 3 being provided via the vertical extension.
  • the separate drive shaft 29 also allows the lower air classifier stage 2 to be operated at a different number of revolutions.
  • the centrifugal basket 14 has blow bars 21 arranged radially on the outside, which are distributed equidistantly over its circumference.
  • the annular visual space 15 of the second air classifier stage 2 is delimited radially outwards by guide vane rings 16 and 17 which can be adjusted independently of one another about their vertical axis.
  • the guide vane ring 16 is assigned to a separate air duct 18, 18 ⁇ , which in horizontal section e.g. is designed multi-course.
  • the lower guide vane ring 17, guides the visible air flowing in via the air duct 19 and 19 ⁇ into the visible space 15 with swirl.
  • the air ducts are approximately rectangular in vertical section.
  • the air channels 18 and 18 ⁇ are vertically separated from one another with respect to the air channels 19 and 19 ⁇ . This makes it possible to feed these air ducts with different visual air.
  • the air duct 18, 18 ⁇ which is designed to be more wear-resistant, can be used for the supply of hot, particle-laden mill exhaust air, while the air ducts 19 and 19 ein introduce cool fresh atmospheric air into the viewing space in order to cool the visible material again at this level.
  • An inspection of the coarse material takes place in the viewing area 15 in the manner already explained for the air classifier stage 1.
  • the coarse material cleaned from undesired fine material falls out of the viewing space 15 into the coarse material funnel 20 and is discharged downward.
  • the mixed air from the air channels 18, 18 ⁇ , 19 and 19 ⁇ flows with the desired, remaining fine particles through the blow bars 21 of the second centrifuge basket 14. These remaining fine particles are together with the mixed air via a collecting container connected to the lower open end face 32 of the centrifugal basket 14 22 aspirated.
  • the extraction takes place via two air outlets 23 which are connected laterally to the collecting container 22 and which feed the visual air laden with fine material to further dust separators.
  • a fine material with a completely different grain structure can be achieved via the air outlets 12 compared to the fine material which is obtained via the air outlets 23.
  • This procedural production of different grain distributions for the fine material is particularly advantageous for the production of cement flour, in order in this way to improve the concrete's technical properties, such as the increase in strength over time when hardening, to improve.
  • Improved screening and better selectivity for fines as well as for coarse goods can also be achieved with the air classifier according to the invention by intentionally varying the air quantities supplied to the two classifying rooms 4 and 15 and by applying different flow velocities.
  • the invention therefore has the advantage that the optionally multi-stage indulgence achieves a higher setting accuracy for desired limit grain sizes, the mechanical cleaning by means of the function of the centrifugal baskets in particular improving this.

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  • Combined Means For Separation Of Solids (AREA)
  • Separation By Low-Temperature Treatments (AREA)
  • Magnetic Resonance Imaging Apparatus (AREA)
  • Centrifugal Separators (AREA)

Abstract

The invention relates to a process and to an air classifier for the separation of classifying material into coarse material and fine material. Known air classifiers suffer from considerable deficiencies with regards to the throughput and the separation efficiency. To avoid this, the invention provides for the performance of a separate reclassification, which takes place in the same way as the pre-classification, whilst incorporating mechanical centrifugal rejection of coarse material particles, particularly through the impact ledges of a centrifuge basket.

Description

Die Erfindung betrifft ein Verfahren zur Windsichtung eines Korngemenges mit Nachsichtung gemäß Oberbegriff des Anspruches 1 sowie einen Windsichter gemäß Oberbegriff des Anspruches 2.The invention relates to a method for air separation of a grain mixture with indulgence according to the preamble of claim 1 and an air classifier according to the preamble of claim 2.

Ein derartiges Verfahren und ein entsprechender Windsichter sind aus der Druckschrift EP-B-23 320 bekannt. Dieser bekannte Windsichter benötigt zur Aussonderung der Feingutteilchen aus der Sichtluft im allgemeinen Staubabscheider, z.B. in Form von Zyklonen und Filtern. Der Feingutdurchsatz eines derartigen, bekannten Windsichters hängt insbesondere von der vertikalen Höhe und dem Durchmesser seines Schleuderkorbes ab, also von seiner Umfangsfläche bzw. dem zylindrischen Ringraum, in dem die Sichtung durchgeführt wird. Der andere wesentliche Parameter einer Sichtung, nämlich die Grenzkorngröße, die das Feingut vom Grobgut unterscheidet, wird einerseits durch den Durchmesser und die Drehzahl des Schleuderkorbes mit bestimmt und hängt zum anderen vom äußeren Durchmesser des Sichtraumes und der Einströmgeschwindigkeit der Sichtluft in den Sichtraum ab.Such a method and a corresponding air classifier are known from EP-B-23 320. This known air classifier generally requires dust separators, e.g. in the form of cyclones and filters. The fine material throughput of such a known air classifier depends in particular on the vertical height and the diameter of its centrifugal basket, that is to say on its circumferential surface or the cylindrical annular space in which the screening is carried out. The other essential parameter of a sifting, namely the grain size limit, which distinguishes the fine material from the coarse material, is determined on the one hand by the diameter and the speed of the centrifugal basket and on the other hand depends on the outer diameter of the visible space and the inflow speed of the visible air into the visible space.

In beiden Fällen kann man daher davon sprechen, daß die Grenzkorngröße von den auf das Sichtgut einwirkenden Beschleunigungskräften abhängt.In both cases it can therefore be said that the grain size limit depends on the acceleration forces acting on the material to be viewed.

Eine Durchmesservergrößerung des Schleuderkorbes läßt sich zwar theoretisch durchführen. In der Praxis jedoch ist man wegen der quadratisch zunehmenden Fliehkräfte und der großen Druckkräfte, die auf die Leisten des Schleuderkorbes einwirken, eingeschränkt. Ein weiterer Aspekt, der einer Vergrößerung des Durchmessers des Schleuderkorbes entgegensteht, ist die geringer werdende Krümmung der Sichtluftbahnen mit größer werdendem Durchmesser. Dies kann zwar durch höhere Ausströmgeschwindigkeit bzw. größere Luftmengen der Sichtluft ausgeglichen werden, wobei dies und die auch größer werdenden Widerstandsverluste jedoch einen höheren Energieaufwand erforderlich machen würden.An increase in the diameter of the centrifugal basket can theoretically be carried out. In practice, however, one is restricted due to the quadratic increasing centrifugal forces and the large pressure forces that act on the bars of the centrifugal basket. Another aspect of enlargement the diameter of the centrifuge basket is opposed, is the decreasing curvature of the visible air paths with increasing diameter. Although this can be compensated for by higher outflow velocity or larger amounts of air in the classifying air, this and the increasing resistance losses would, however, require a higher expenditure of energy.

Bei der vertikalen Dimensionierung des Schleuderkorbes ist man aufgrund der mechanischen Belastung seiner peripheren Leisten ebenfalls begrenzt. Vor allen Dingen jedoch ist die Vergrößerung des Schleuderkorbes in vertikaler Richtung durch das Auftreten unterschiedlicher Strömungsgeschwindigkeiten längs der Leisten des Schleuderkorbes beim Durchtritt von Sichtluft und Feingut zwischen diese Leisten eingeschränkt.The vertical dimensioning of the centrifuge basket is also limited due to the mechanical load on its peripheral strips. Above all, however, the enlargement of the centrifugal basket in the vertical direction is restricted by the occurrence of different flow velocities along the strips of the centrifugal basket when visible air and fine material pass between these strips.

So sind auch bei dem bekannten Windsichter die Strömungsgeschwindigkeiten längs der mantelähnlichen Umfangsfläche des Schleuderkorbes im wesentlichen direkt abhängig vom Sog innerhalb des Schleuderkorbes. Dieser Sog ist am Sichtgutauslaß des Schleuderkorbes für das Feingut am größten und nimmt in Richtung der gegenüberliegenden, geschlossenen Stirnfläche des Schleuderkorbes hin ab. Über diese geschlossene bzw. zumindest weitgehend geschlossene Stirnfläche erfolgt bei dem bekannten Windsichter der Rotationsantrieb mittels der vertikalen Antriebsachse.In the known air classifier, the flow velocities along the jacket-like peripheral surface of the centrifugal basket are essentially directly dependent on the suction within the centrifugal basket. This suction is greatest at the visible material outlet of the centrifuge basket for the fine material and decreases in the direction of the opposite, closed end face of the centrifugal basket. In the known air classifier, the rotary drive takes place via this closed or at least largely closed end face by means of the vertical drive axis.

Diese unterschiedlichen Strömungsgeschwindigkeiten beim Eintritt des Feingutes in den Schleuderkorb auf unterschiedlichen vertikalen Höhen des Schleuderkorbes, bringen es mit sich, daß unterschiedliche Gütegrade für die Trennschärfe erreicht werden. Es dürfte hinreichend plausibel sein, daß in der Nähe des Sichtluftauslasses, wo die größte Sogwirkung anzutreffen ist, Überkorn in das Feingut gelangt und im Bereich des größten Abstandes vom Sichtluftauslaß Unterkorn im Grobgut verbleibt. Diese gravierenden Nachteile bei der Trennschärfe erhöhen sich um so mehr, je größer die vertikale Erstreckung des Schleuderkorbes wird. Diese vorgenannten Nachteile erscheinen jedoch bei windsichtern mit großer Durchsatzleistung unabwendbar zu sein. Zu diesem vorgenannten Nachteil kommt bei dem windsichter gemäß der EP-B-23 320 noch hinzu, daß umfangsmäßig betrachtet, am Schleuderkorb unterschiedliche Strömungsgeschwindigkeiten vorherrschen dürften. Dies deshalb, da man dort über unterschiedlich ausgelegte spiralförmige Zuführkanäle in etwa tangentialer Anordnung zum Schleuderkorb Sichtluftmengen unterschiedlichster Art, z.B. staubhaltige, heiße Mühlenabluft und gegenüberliegend z.B. kältere, aber staubfreie atmosphärische Luft in den Windsichter einbläst.These different flow velocities when the fine material enters the centrifugal basket at different vertical heights of the centrifugal basket mean that that different grades of selectivity can be achieved. It should be reasonably plausible that near the sight air outlet, where the greatest suction is to be found, oversize gets into the fine material and remains in the coarse material in the area of the greatest distance from the sight air outlet. These serious disadvantages in terms of selectivity increase the greater the vertical extension of the centrifuge basket. However, these aforementioned disadvantages appear to be unavoidable in wind classifiers with a high throughput. In addition to the above-mentioned disadvantage, the windsifter according to EP-B-23 320 also has the fact that, viewed circumferentially, different flow velocities should prevail on the centrifugal basket. This is because there are variously designed spiral feed channels in an approximately tangential arrangement to the centrifugal basket, blowing air of various types, e.g. dust-containing, hot mill exhaust air and opposite, for example, colder but dust-free atmospheric air into the air classifier.

Speziell zur Überwindung der letztgenannten Nachteile, der unterschiedliche Strömungsgeschwindigkeiten in vertikaler Richtung längs des Schleuderkorbes, geht man bei einem weiteren bekannten Windsichter nach der DE-C-29 51 819 den Weg, an beiden Stirnseiten des Schleuderkorbes Sichtluftauslässe zu konzipieren. Bei diesem letztgenannten bekannten Windsichter tritt jedoch das Problem auf, daß die Leisten des Schleuderkorbes aufgrund der großen vertikalen Erstreckung im Vergleich zum Durchmesser des Schleuderkorbes durch eine Vielzahl von etwa radial vorgesehenen Speichen abgestützt und abgesteift werden müssen. Dies ist erforderlich, um den im Betrieb auftretenden Fliehkräften und den sonstigen mechanischen Beanspruchungen wie Schwingungen mit ausreichend hoher Sicherheit begegnen zu können. Diese zur Versteifung vorgesehenen Speichen kommen jedoch mit den in der Sichtabluft enthaltenen Feingutteilchen in Berührung und unterliegen dadurch einer relativ hohen Verschleißbeanspruchung. Zur Vermeidung einer derartigen Beanspruchung darf, wie es auch aus der für diesen Windsichter angegebenen oberen Korngröße von 2 bis 4 µm entnehmbar ist, angenommen werden, daß dieser bekannte Windsichter für weniger abrasives Sichtgut und Material entwickelt worden ist. Aufgrund der letztgenannten Korngrößen herrschen in der abgeführten Sichtluft auch bedeutend geringere Feststoffkonzentrationen, denen die radialen Speichen ausgesetzt sind.Specifically to overcome the latter disadvantages, the different flow velocities in the vertical direction along the centrifugal basket, another known air classifier according to DE-C-29 51 819 is the way to design visual air outlets on both ends of the centrifugal basket. In this latter known air classifier, however, the problem arises that the strips of the centrifugal basket are provided by a large number of radially due to the large vertical extension compared to the diameter of the centrifugal basket Spokes must be supported and braced. This is necessary in order to be able to counter the centrifugal forces that occur during operation and the other mechanical stresses such as vibrations with a sufficiently high degree of certainty. However, these spokes provided for stiffening come into contact with the fine particles contained in the exhaust air and are therefore subject to relatively high wear. In order to avoid such stress, it can be assumed, as can also be seen from the upper grain size of 2 to 4 μm specified for this air classifier, that this known air classifier was developed for less abrasive material and material. Due to the latter grain sizes, there is also significantly lower solid concentrations to which the radial spokes are exposed.

Der letztgenannte bekannte Windsichter erscheint daher für ein stark abrasives Sichtgut, wie gesintertes Aluminiumoxid, Quarzsand oder Zementklinker bei Feststoffkonzentrationen von z.B. 800 g/m³ bis 1200 g/m³ in der Sichterabluft ungeeignet zu sein. Vor allem ist bei einem stark verschleißenden Korngemenge als Sichtgut ein Dauerbetrieb über mehrere Wochen oder Monate ohne längere Betriebsstillstandzeiten für Reparaturen oder einer Erneuerung des Schleuderkorbes kaum denkbar.The last-mentioned known air classifier therefore appears to be unsuitable for highly abrasive visible material, such as sintered aluminum oxide, quartz sand or cement clinker at solid concentrations of, for example, 800 g / m³ to 1200 g / m³ in the classifier exhaust air. Above all, in the case of heavily wearing grain batches as visible material, continuous operation over several weeks or months without longer downtimes for repairs or renewing the centrifugal basket is hardly conceivable.

Bei einem aus der DE-A-30 38 625 bekannten Drehluft-Fliehkraft-Streusichter sind im oberen Teil eines konisch ausgebildeten Sichtraums mindestens zwei konzentrisch untereinander angeordnete Streuteller mit separaten Antrieben, sich von oben nach unten vergrößernden Durchmessern und mit konischen Anwurfringen, Flügeln, Rührwerken und dergleichen zur Feststoffbeschleunigung bzw. zur Zwangsführung für die im unteren Teil des Sichtraums zugeführte Umluft angeordnet. Das zentral aufgegebene Sichtgut gelangt über die Streuteller in den Sichtraum und ist dabei dem aufwärts gerichteten Umluftstrom ausgesetzt. Über die dadurch erzielte größere Abreinigung der konzentrisch abgeleiteten Umluft von Feingutpartikeln soll die Trennschärfe des Sichters insgesamt verbessert werden. Zu diesem Zweck wird die Umluft über die Umlenkfläche eines mechanischen Abscheiders, der konzentrisch unter dem Grobgutaustrag angeordnet ist, dem Sichtraum zugeführt. Auch dieser Umluftsichter ist wegen seiner schikaneartigen Einbauten wenig geeignet für besonders abrasives Sichtgut.In a rotary air centrifugal scatter classifier known from DE-A-30 38 625, there are at least two concentrically arranged spreading discs with separate drives, diameters increasing from top to bottom and with conical projection rings, blades, agitators in the upper part of a conically shaped viewing area and the like arranged for accelerating solids or for positive guidance for the circulating air supplied in the lower part of the viewing space. The centrally placed visible material enters the viewing area via the spreading disc and is exposed to the upward flow of circulating air. The separation efficiency of the classifier is to be improved overall by the greater cleaning of the concentrically derived circulating air from fine particles which is thereby achieved. For this purpose, the circulating air is fed into the viewing area via the deflection surface of a mechanical separator, which is arranged concentrically below the coarse material discharge. This air classifier is also not very suitable for particularly abrasive material due to its baffle-like fittings.

Ausgehend von diesem Stand der Technik liegt der Erfindung die Aufgabe zugrunde, ein Verfahren und einen Windsichter zur Durchführung des Verfahrens so zu konzipieren, daß die vorgenannten Nachteile vermieden werden und auch bei relativ abrasivem Sichtgut eine lange Betriebszeit, bei hoher Durchsatzleistung und verbesserter Trennschärfe erreicht wird, wobei gegebenenfalls dies mit relativ geringer Aufstellfläche für den Windsichter realisierbar sein soll.Based on this prior art, the invention has for its object to design a method and an air classifier for performing the method so that the aforementioned disadvantages are avoided and a long operating time is achieved even with relatively abrasive visible material, with high throughput and improved selectivity, this possibly being able to be achieved with a relatively small footprint for the air classifier.

Diese Aufgabe wird erfindungsgemäß bei einem Verfahren nach dem Oberbegriff des Anspruches 1 durch die Merkmale des kennzeichnenden Teils des Anspruches 1 und bei einem Windsichter gemäß Oberbegriff des Anspruches 2 durch die Merkmale des kennzeichnenden Teils des Anspruches 2 gelöst.This object is achieved in a method according to the preamble of claim 1 by the features of the characterizing part of claim 1 and in an air classifier according to the preamble of claim 2 by the features of the characterizing part of claim 2.

Ein essentieller Grundgedanke der Erfindung, sowohl verfahrensmäßig die vorrichtungsmäßig, kann darin gesehen werden, die Sichtung und die Trennschärfe dadurch zu verbessern, daß eine mehrstufige Sichtung durchgeführt wird, wobei die Sichtungsparameter auf jeder Stufe nach Möglichkeit umfassend einstellbar sind. Verfahrensmäßig erreicht man dieses Ziel, daß ergänzend zu einer Dispergierung des aus der ersten Verfahrensstufe resultierenden Grobgutes eine mittels weitgehend spiralförmig einströmender Sichtluft und Zentrifugalabweisung erfolgende zweite Sichtung vorgesehen wird. Diese Zentrifugalabweisung wird jedoch nicht rein strömungstechnisch durch eine Einleitung von Sichtluft oder anderer gasförmiger Medien erreicht, sondern im Zusammenwirken mit einer gleichzeitig erfolgenden mechanischen Zentrifugalabweisung, wie sie z.B. durch den Einsatz eines Schleuderkorbes erfolgt.An essential basic idea of the invention, both procedurally and device-wise, can be seen in improving the sighting and the selectivity by carrying out a multi-stage sighting, with the sighting parameters being extensively adjustable on each step as far as possible. In terms of the process, this goal is achieved that, in addition to dispersing the coarse material resulting from the first process step, a second sighting, which is carried out by means of largely spiral inflowing sight air and centrifugal rejection, is provided. However, this centrifugal rejection is not achieved purely in terms of flow technology by introducing visible air or other gaseous media, but in cooperation with a mechanical centrifugal rejection that takes place at the same time, as is e.g. by using a centrifugal basket.

Vorrichtungsmäßig wird ein entsprechender erfindungsgemäßer Windsichter mit mindestens zwei Windsichterstufen ausgelegt, wobei die zur Nachsichtung dienende Windsichterstufe einen separaten oder einen mit dem nachgeschalteten, zweiten Schleuderkorb integrierten Streuteller aufweist, über den das Grobgut der ersten Stufe zuführbar ist. Diese Windsichterstufe ist in einer analogen Ausstattung mit einem Schleuderkorb, entsprechenden Schleuderkorbleisten und einem oder mehreren koaxialen Kränzen von Leitschaufeln ausgestattet, wobei jedoch zu einer optimaleren Nachsichtung in der Regel die Abmessungen der zweiten Windsichterstufe unterschiedlich zu denen der ersten Windsichterstufe sind.In terms of the device, a corresponding air classifier according to the invention is designed with at least two air classifier stages, wherein the air separator stage used for indulgence has a separate or a spreading disc integrated with the downstream, second centrifugal basket, via which the coarse material can be fed to the first stage. In an analog configuration, this air classifier stage is equipped with a centrifugal basket, corresponding centrifugal basket rails and one or more coaxial rings of guide vanes, although the dimensions of the second air classifier stage are usually different from those of the first air classifier stage for better viewing.

Hierdurch lassen sich die Sichtungsparameter der zweiten Windsichterstufe ergänzend zu der Verstellbarkeit der Leitschaufeln und der Einströmgeschwindigkeit der Sichtluft noch geeigneter auf die gewünschten Korngrößen und Grenzkorngrößen einstellen.In this way, in addition to the adjustability of the guide vanes and the inflow speed of the sifting air, the sifting parameters of the second air classifier stage can be adjusted even more suitably to the desired grain sizes and limiting grain sizes.

Das erfindungsgemäße Verfahren und die entsprechende Vorrichtung eignen sich daher besonders auch für obere Korngrößen unter 10 µm. Da für die Aussonderung des Feingutes aus der Sichtluft entsprechende Staubabscheider, wie Zyklone oder Filter benötigt werden, kommt die durch die vertikale Mehrstufigkeit beim erfindungsgemäßen Windsichter erreichte geringe Aufstellungsfläche einer Verwendung mit Zyklonen entsprechend entgegen. Die Mehrstufigkeit des Windsichters ermöglicht es, den Sichterdurchmesser relativ klein zu halten, so daß der erfindungsgemäße Windsichter durch den geringen Flächenbedarf sehr gut der Zyklonverwendung angepaßt ist und zudem die relativ große Bauhöhe der Zyklone voll genutzt werden kann. Der erfindungsgemäße Windsichter eignet sich auch aufgrund seiner Mehrstufigkeit dazu, daß verschiedene Sichtluftmengen unterschiedlicher strömungstechnischer Eigenschaft eingesetzt werden können, wobei die kontrollierte Einführung in den Sichtraum durch die verstellbaren Leitschaufelkränze und die Optimierung der Sichtung im Hinblick auf verbesserte Trennschärfe mittels unterschiedlicher Dimensionierung der nachgeschalteten Windsichterstufe gewährleistet ist.The method according to the invention and the corresponding device are therefore particularly suitable for upper grain sizes below 10 μm. Since appropriate dust separators, such as cyclones or filters, are required for the separation of the fine material from the classifying air, the small installation area achieved by the vertical multi-stage in the air classifier according to the invention suits use with cyclones accordingly. The multi-stage of the air classifier makes it possible to keep the classifier diameter relatively small, so that the wind classifier according to the invention is very well adapted to the cyclone use due to the small space requirement and, moreover, the relatively large overall height of the cyclones can be fully utilized. The wind sifter according to the invention is also suitable due to its multi-stage nature that different sifting air quantities of different fluidic properties can be used, the controlled introduction into the sifting space through the adjustable guide vane rings and the optimization of the sighting in With regard to improved selectivity by means of different dimensions of the downstream air classifier stage is guaranteed.

Vorteilhafterweise weist der Windsichter mindestens zwei Schleuderkörbe unterschiedlicher axialer Höhe und mit unterschiedlichen Durchmesser auf. Es kann dabei eine unterschiedliche Leistenbestückung mit unterschiedlichen Neigungswinkeln vorgesehen sein. Der Antrieb der einzelnen Schleuderkörbe der verschiedenen Windsichterstufen erfolgt zweckmäßigerweise getrennt, z.B. über entsprechende ineinander geführte Hohlwellen. Diese Möglichkeit eröffnet die Feinabstimmung der mechanischen Zentrifugalabweisung des zu sichtenden Grobkornes.The air classifier advantageously has at least two centrifugal baskets of different axial heights and with different diameters. Different strips can be provided with different angles of inclination. The individual centrifugal baskets of the various air classifier stages are advantageously driven separately, e.g. via corresponding hollow shafts that run into each other. This possibility opens up the fine tuning of the mechanical centrifugal rejection of the coarse grain to be sifted.

Ein weiterer Vorteil für die Nachsichtung wird mit der Ausbildung der der vorgeordneten Windsichterstufe zugewandten Stirnfläche des nachgeschalteten Schleuderkorbes als geschlossene Fläche erreicht, die die Funktion eines Streutellers übernimmt. Der Streuteller für das aus der vorgeschalteten Windsichterstufe kommende Grobgut kann auch separat zum Schleuderkorb vorgesehen sein. Wesentlich ist vor allen Dingen die Streutellerfunktion, die eine weitere Dispergierung des bereits mindestens einmal gesichteten Grobgutes ermöglicht, so daß dieses gut verteilt in den nachfolgenden Sichtraum eingeführt werden kann. Der Schleuderkorb der zweiten Windsichterstufe weist zweckmäßigerweise einen etwas größeren Durchmesser bei verringerter axialer Erstreckung wie der Schleuderkorb der ersten Windsichterstufe auf. Hierdurch ist bei gleicher Drehzahl der Schleuderkörbe auch eine mechanische Sichtung feinerer Partikel des Grobgutes aufgrund der höheren Beschleunigungskräfte im Außenbereich des Schleuderkorbes möglich. Andererseits ermöglicht gerade die reduzierte axiale Erstreckung des zweiten Schleuderkorbes auch eine gemeinsame Absaugung und Abführung der mit Feingut beladenen Sichtluft, z.B. nach oben im Bereich der Antriebsachse. In der letztgenannten Ausführungsform sind beide Stirnseiten des Schleuderkorbes der ersten Windsichterstufe weitestgehend als Durchlaßöffnungen ausgebildet, wobei der Schleuderkorb selbst über wenige radiale Versteifungsstege mit der Achse in Antriebsverbindung steht.A further advantage for indulgence is achieved with the formation of the end face of the downstream centrifugal basket facing the upstream air classifier stage as a closed surface, which takes over the function of a spreading disc. The spreading plate for the coarse material coming from the upstream air classifier stage can also be provided separately from the centrifugal basket. Above all, the spreading plate function is essential, which enables further dispersion of the coarse material that has already been viewed at least once, so that it can be introduced into the subsequent viewing area in a well-distributed manner. The centrifugal basket of the second air classifier stage expediently has a somewhat larger diameter with reduced axial extension than the centrifugal basket of the first wind classifier stage. As a result, mechanical centrifugation of finer particles is possible at the same speed of the centrifugal baskets of the coarse material possible due to the higher acceleration forces in the outer area of the centrifuge basket. On the other hand, the reduced axial extension of the second centrifugal basket also enables the extraction and removal of the fine air laden with fine material, for example upwards in the area of the drive axis. In the last-mentioned embodiment, both end faces of the centrifugal basket of the first air classifier stage are largely designed as through-openings, the centrifugal basket itself being in drive connection with the axle via a few radial stiffening webs.

Bei Ausbildung des Windsichters mit einer geschlossenen unteren Stirnfläche des ersten Schleuderkorbes und einer offenen Stirnfläche beim zweiten Schleuderkorb, die mit einer entsprechenden Absaugleitung in Verbindung steht, erreicht man den Vorteil einer besseren Klassierung, da in diesem Fall drei Bereiche unterschiedlicher Korngrößen gesichtet und separiert werden können.If the air classifier is designed with a closed lower end face of the first centrifugal basket and an open end surface for the second centrifugal basket, which is connected to a corresponding suction line, the advantage of better classification is achieved, since in this case three areas of different grain sizes can be viewed and separated .

Ein weiterer Vorteil kann durch vertikal voneinander getrennte Luftkanäle für die Sichtluft erreicht werden. De Luftkanäle sind dabei zweckmäßigerweise als zwei- oder mehrgängige Spiralgehäuse ausgebildet, die einen weitgehend tangentialen Lufteintritt zu den Leitschaufelkränzen ermöglichen. Bei mehrgängigen Spiralgehäusen in einer horizontalen Ebene sind die einzelnen Einlässe äquidistant am Umfang verteilt angeordnet, um über den gesamten Umfang des Sichtraumes verteilt möglichst gleichmäßige Strömungsverhältnisse zu erreichen. Durch die vertikale Trennung der unterschiedlichen Luftkanäle für einen Schleuderkorb, kann z.B. in einem Luftkanal einer horizontalen Ebene heiße Mühlenabluft und auf einer anderen, z.B. darunter liegenden horizontalen Ebene, kältere, eventuell staubfreie atmosphärische Sichtluft eingeblasen werden. Bevorzugterweise wird die kältere Sichtluft in einem unteren Luftkanal zugeführt, um dadurch bereits eine Abkühlung des gesichteten Gutes zu erreichen. Es besteht daher die Möglichkeit, Sichtluft mit verfahrenstechnisch bedingten unterschiedlichen Strömungsgeschwindigkeiten jeweils nur in einer bestimmten Ebene des Schleuderkorbes einströmen zu lassen, so daß über den gesamten Umfang des Schleuderkorbes betrachtet, gleichmäßige Betriebsverhältnisse vorliegen.Another advantage can be achieved by vertically separated air channels for the classifying air. The air channels are expediently designed as two- or multi-flight spiral housings, which allow a largely tangential air inlet to the guide vane rings. In the case of multi-flight spiral housings in a horizontal plane, the individual inlets are arranged equidistantly around the circumference in order to achieve flow conditions that are as uniform as possible over the entire circumference of the viewing space. The vertical separation of the different air channels for a centrifugal basket can, for example, in one Air duct on one horizontal level is used to inject hot mill exhaust air and on another, for example horizontal level below, cooler, possibly dust-free, atmospheric visual air is blown in. The colder viewing air is preferably supplied in a lower air duct in order to already cool the material being viewed. There is therefore the possibility of allowing visible air with process-related different flow velocities to flow in only in a certain plane of the centrifugal basket, so that, viewed over the entire circumference of the centrifugal basket, there are uniform operating conditions.

Der erfindungsgemäße Windsichter ist dabei nicht auf die Ausführung mit zwei Windsichterstufen beschränkt. Je nach Einsatzzweck, z.B. für einen hohen Abreinigungsgrad eines Grobgutes mit bestimmter Grenzkorngröße, kann der Einsatz einer weiteren, nachgeschalteten dritten Windsichterstufe erforderlich und zweckmäßig sein. Die Ableitung der mit Feingut beladenen Sichtluft aus der dritten Windsichterstufe erfolgt zweckmäßigerweise unabhängig von der Ableitung der Sichtluft der vorgeordneten Stufen und nach unten.The wind classifier according to the invention is not limited to the version with two wind classifier stages. Depending on the application, e.g. For a high degree of cleaning of a coarse material with a certain size limit, the use of a further, downstream third air classifier stage may be necessary and expedient. The removal of the sifting air loaded with fine material from the third air classifier stage is expediently carried out independently of the discharge of the sifting air of the upstream stages and downwards.

Insgesamt gesehen, kann daher durch die Möglichkeit einer nachgeschalteten Mehrfachsichtung in einem Windsichter über vordispergierende Windsichterstufen mit weniger Sichtluft gearbeitet werden, so daß ein Aufbau des Windsichters mit prinzipiell kleinerem Durchmesser möglich wird. Durch die mehrstufige Sichtung, in Verbindung mit der Gestaltung der Schleuderkörbe weitgehend ohne radiale Versteifungsspeichen, ist auch die Verarbeitung relativ verschleißungünstigen Sichtgutes möglich.Seen as a whole, the possibility of a subsequent multiple sifting in a wind sifter means that it is possible to work with less sifting air via predispersing air sifter stages, so that the air sifter can in principle be constructed with a smaller diameter. Due to the multi-stage sifting, in connection with the design of the centrifugal baskets largely without radial stiffening spokes, the processing of relatively wear-resistant visible material is also possible.

Die Erfindung wird nachstehend anhand eines schematischen Ausführungsbeispieles noch näher erläutert.The invention is explained in more detail below with the aid of a schematic exemplary embodiment.

Die einzige Zeichnung zeigt einen vertikalen Schnitt durch einen Windsichter 3 mit zwei Windsichterstufen 1,2.The only drawing shows a vertical section through an air classifier 3 with two air classifier stages 1, 2.

Die Aufgabe des Sichtgutes in den Windsichter 3 erfolgt über einen weitgehend zentral angeordneten oberen Sichtguteinlaß 25. Der Sichtguteinlaß 25, der schräg durch den oberen Gehäuseabschluß hindurchragt, führt das Sichtgut weitgehend im Achsbereich des Windsichters 3 auf einen ersten Streuteller 26, der konisch nach oben geöffnet ist. Das durch diesen Streuteller 26 vordispergierte Sichtgut gelangt über zwei nach unten verjüngend zulaufende Stufen des Gehäuses des Windsichters 3 auf einen weiteren, zweiten Streuteller 27.The material to be placed in the air classifier 3 is fed via a largely centrally arranged upper material inlet 25. The material inlet 25, which projects obliquely through the upper housing end, guides the material to be sighted largely in the axial area of the air classifier 3 to a first spreading plate 26, which opens conically upwards is. The visible material predispersed by this spreading plate 26 reaches a further, second spreading plate 27 via two tapering steps of the housing of the air classifier 3.

Über diesen Streuteller 27 gelangt das Sichtgut gut vordispergiert in einen ersten Sichtraum 4 der ersten Windsichterstufe 1. Der Sichtraum 4 ist kreisringförmig, zylindrisch ausgebildet, wobei er nach radial außen durch separat einstellbare Leitschaufelkränze 6 und 7, die vertikal übereinander angeordnet sind, begrenzt wird. Nach radial innen wird die Begrenzung des Sichtraumes 4 durch die Außenkanten der Schlagleisten 10 des Schleuderkorbes 9 gebildet.Via this spreading plate 27, the material to be sighted reaches the first sighting chamber 4 of the first wind sifter stage 1 in a well-dispersed manner. The sighting chamber 4 is circular, cylindrical, being delimited radially outwards by separately adjustable guide vane rings 6 and 7, which are arranged vertically one above the other. Radially inward, the boundary of the visible space 4 is formed by the outer edges of the blow bars 10 of the centrifugal basket 9.

Die Sichtluft für die erste Windsichterstufe 1 gelangt über die Luftkanäle 5, die im Horizontalschnitt beispielsweise als zweigängiges Spiralgehäuse ausgebildet sind, in den Sichtraum 4. Durch die mit Drall in den Sichtraum 4 einströmende Sichtluft findet eine Vortrennung des Sichtgutes statt, wobei die von außen nach innen den Sichtraum 4 durchströmende Luftströmung die in den Sichtraum einfallenden Teilchen auf einer Spiralbahn beschleunigen. Hierdurch werden Grobgutpartikel infolge der auf sie einwirkenden höheren Fliehkräfte aus der Spiralbahn getragen und aufgrund der Schwerkraft auf den ersten am unteren Bereich der ersten Windsichterstufe 1 angeordneten Grobguttrichter 8 ausfallen.The classifying air for the first air classifier stage 1 reaches the classifying room 4 via the air channels 5, which are designed, for example, in a horizontal section as a two-flight spiral housing inside the viewing space 4 flowing Air flow accelerate the particles falling into the visual space on a spiral track. As a result, coarse material particles are carried out of the spiral track as a result of the higher centrifugal forces acting on them and fall due to gravity onto the first coarse material funnel 8 arranged at the lower region of the first air classifier stage 1.

Die in der spiralförmigen Luftströmung verbleibenden Feingutpartikel auf der ersten Windsichterstufe 1 werden zum Außenumfang des rotierenden Schleuderkorbes 9 mitgenommen. Durch die Rotation des Schleuderkorbes 9 mit seinen radial außen in vertikaler Richtung angeordneten Schlagleisten 10 werden die zwischen die Schlagleisten gelangenden Teilchen nochmals beschleunigt, wobei mitgerissene Teilchen des Grobgutes in den Sichtraum 4 zurückgeschleudert werden. Das durch die Sichtluft ins Innere des Schleuderkorbes 9 geführte Feingut wird hingegen über die im oberen Bereich des Schleuderkorbes 9 vorgesehene stirnseitige Öffnung 11 und über eine damit in Verbindung stehende zweigängige Austragsspirale 12 zu den nachfolgenden Staubabscheidern abgesaugt.The fine material particles remaining in the spiral air flow on the first air classifier stage 1 are taken to the outer circumference of the rotating centrifugal basket 9. The rotation of the centrifugal basket 9 with its blow bars 10 arranged radially on the outside in the vertical direction accelerates the particles reaching between the blow bars again, entrained particles of the coarse material being thrown back into the viewing space 4. The fine material guided into the interior of the centrifugal basket 9 through the classifying air, however, is suctioned off to the subsequent dust separators via the front opening 11 provided in the upper region of the centrifugal basket 9 and via a two-course discharge spiral 12 connected therewith.

Der Antrieb des Schleuderkorbes 9 erfolgt über eine als Hohlrohr ausgebildete Antriebswelle 28, in der eine weitere Antriebswelle 29 für den Schleuderkorb 14 der zweiten Windsichterstufe 2 geführt ist. Im Ausführungsbeispiel weist der Schleuderkorb 9 im unteren Bereich eine geschlossene Stirnwand 31 auf, die zur besseren Stabilisierung etwa in der Mitte mit schräg zur Antriebswelle 28 verlaufenden Verstrebungen 30 oder einem verschleißgeschützten Kegelmantel geführt und versteift ist.The centrifugal basket 9 is driven via a drive shaft 28 designed as a hollow tube, in which a further drive shaft 29 for the centrifugal basket 14 of the second air classifier stage 2 is guided. In the exemplary embodiment, the centrifugal basket 9 has a closed end wall 31 in the lower region which, for better stabilization, is guided and stiffened approximately in the middle with struts 30 running obliquely to the drive shaft 28 or a wear-protected cone jacket.

Das den ersten Grobguttrichter 8 verlassende Grobgut gelangt auf die obere,geschlossene Stirnwand 13 des für die Nachsichtung vorgesehenen zweiten Schleuderkorbes 14. Im Beispiel ist der Schleuderkorb 14 der zweiten Windsichterstufe 2 mit geringerer vertikaler Erstreckung als der erste Schleuderkorb 9 ausgestattet. Er weist jedoch einen größeren Durchmesser auf als der erste Schleuderkorb 9. Der Antrieb des zweiten Schleuderkorbes 14 erfolgt über eine koaxial in der ersten Antriebswelle 28 geführte zweite Antriebswelle 29, wobei über die vertikale Erstreckung Zwischenlagerungen und Verstrebungen mit dem Gehäuse des Windsichters 3 vorgesehen sind.The coarse material leaving the first coarse material hopper 8 reaches the upper, closed end wall 13 of the second centrifugal basket 14 intended for indulgence. In the example, the centrifugal basket 14 of the second air classifier stage 2 is provided with a smaller vertical extension than the first centrifugal basket 9. However, it has a larger diameter than the first centrifugal basket 9. The second centrifugal basket 14 is driven via a second drive shaft 29, which is guided coaxially in the first drive shaft 28, intermediate bearings and struts with the housing of the air classifier 3 being provided via the vertical extension.

Die separate Antriebswelle 29 gestattet es, die untere Windsichterstufe 2 auch mit unterschiedlicher Umdrehungszahl zu betreiben. Der Schleuderkorb 14 weist radial außen vertikal angeordnete Schlagleisten 21 auf, die äquidistant über seinen Umfang verteilt sind. Der kreisringförmige Sichtraum 15 der zweiten Windsichterstufe 2 wird nach radial außen durch unabhängig voneinander um ihre vertikale Achse einstellbare Leitschaufelkränze 16 und 17 begrenzt. Der Leitschaufelkranz 16 ist dabei einem separaten Luftkanal 18, 18ʹ zugeordnet, der im Horizontalschnitt z.B. mehrgängig ausgelegt ist. Der untere Leitschaufelkranz 17 führt dagegen die über den Luftkanal 19 und 19ʹ einströmende Sichtluft mit Drall in den Sichtraum 15. Die Luftkanäle haben im Ausführungsbeispiel im Vertikalschnitt etwa Rechteckform.The separate drive shaft 29 also allows the lower air classifier stage 2 to be operated at a different number of revolutions. The centrifugal basket 14 has blow bars 21 arranged radially on the outside, which are distributed equidistantly over its circumference. The annular visual space 15 of the second air classifier stage 2 is delimited radially outwards by guide vane rings 16 and 17 which can be adjusted independently of one another about their vertical axis. The guide vane ring 16 is assigned to a separate air duct 18, 18ʹ, which in horizontal section e.g. is designed multi-course. The lower guide vane ring 17, on the other hand, guides the visible air flowing in via the air duct 19 and 19ʹ into the visible space 15 with swirl. In the exemplary embodiment, the air ducts are approximately rectangular in vertical section.

Die Luftkanäle 18 und 18ʹ sind gegenüber den Luftkanälen 19 und 19ʹ vertikal voneinander getrennt. Hierdurch ist es möglich, diese Luftkanäle mit unterschiedlicher Sichtluft zu beschicken. So kann beispielsweise der gegen Verschleiß verstärkt ausgelegte Luftkanal 18, 18ʹ für die Zuführung heißer, partikelbeladener Mühlenabluft dienen, während die Luftkanäle 19 und 19ʹ kühle atmosphärische Frischluft in den Sichtraum einführen, um auf dieser Ebene das Sichtgut wieder zu kühlen.The air channels 18 and 18ʹ are vertically separated from one another with respect to the air channels 19 and 19ʹ. This makes it possible to feed these air ducts with different visual air. For example, the air duct 18, 18ʹ, which is designed to be more wear-resistant, can be used for the supply of hot, particle-laden mill exhaust air, while the air ducts 19 and 19 ein introduce cool fresh atmospheric air into the viewing space in order to cool the visible material again at this level.

Im Sichtraum 15 erfolgt eine Nachsichtung des Grobgutes, in der bereits vorausgehend zur Windsichterstufe 1 erläuterten Weise. Das von unerwünschtem Feingut abgereinigte Grobgut fällt aus dem Sichtraum 15 in den Grobguttrichter 20 und wird nach unten abgeführt. Die Mischluft aus den Luftkanälen 18, 18ʹ, 19 und 19ʹ strömt mit den gewünschten, restlichen Feingutpartikeln durch die Schlagleisten 21 des zweiten Schleuderkorbes 14. Diese restlichen Feingutpartikel werden zusammen mit der Mischluft über einen, an der unteren offenen Stirnseite 32 des Schleuderkorbes 14 anschließenden Auffangbehälter 22 abgesaugt. Die Absaugung erfolgt im Beispiel über zwei seitlich an dem Auffangbehälter 22 angeschlossene Luftauslässe 23, die die mit Feingut beladene Sichtluft weiteren Staubabscheidern zuführen.An inspection of the coarse material takes place in the viewing area 15 in the manner already explained for the air classifier stage 1. The coarse material cleaned from undesired fine material falls out of the viewing space 15 into the coarse material funnel 20 and is discharged downward. The mixed air from the air channels 18, 18ʹ, 19 and 19ʹ flows with the desired, remaining fine particles through the blow bars 21 of the second centrifuge basket 14. These remaining fine particles are together with the mixed air via a collecting container connected to the lower open end face 32 of the centrifugal basket 14 22 aspirated. In the example, the extraction takes place via two air outlets 23 which are connected laterally to the collecting container 22 and which feed the visual air laden with fine material to further dust separators.

In der vorstehenden Konzipierung des Windsichters 3 kann über die Luftauslässe 12 ein Feingut mit völlig verschiedenem Kornaufbau im Vergleich zu dem Feingut erreicht werden, welches über die Luftauslässe 23 gewonnen wird. Diese verfahrensmäßige Herstellung unterschiedlicher Kornverteilungen für das Feingut ist insbesondere für die Herstellung von Zementmehl von Vorteil, um auf diese Weise die betontechnischen Eigenschaften des Zementes, wie den zeitlichen Festigkeitsanstieg beim Erhärten, zu verbessern. Eine verbesserte Sichtung und bessere Trennschärfe beim Feingut wie beim Grobgut kann mit dem erfindungsgemäßen Windsichter auch dadurch erreicht werden, daß die den beiden Sichträumen 4 und 15 zugeführten Luftmengen gewollt variiert werden und mit unterschiedlichen Strömungsgeschwindigkeiten beaufschlagt werden.In the above design of the air classifier 3, a fine material with a completely different grain structure can be achieved via the air outlets 12 compared to the fine material which is obtained via the air outlets 23. This procedural production of different grain distributions for the fine material is particularly advantageous for the production of cement flour, in order in this way to improve the concrete's technical properties, such as the increase in strength over time when hardening, to improve. Improved screening and better selectivity for fines as well as for coarse goods can also be achieved with the air classifier according to the invention by intentionally varying the air quantities supplied to the two classifying rooms 4 and 15 and by applying different flow velocities.

Die Erfindung bringt daher den Vorteil, daß durch die gegebenenfalls mehrstufige Nachsichtung eine höhere Einstellgenauigkeit für gewünschte Grenzkorngrößen erreicht wird, wobei die mechanische Abreinigung mittels der Funktion der Schleuderkörbe dies insbesondere verbessert.The invention therefore has the advantage that the optionally multi-stage indulgence achieves a higher setting accuracy for desired limit grain sizes, the mechanical cleaning by means of the function of the centrifugal baskets in particular improving this.

Claims (11)

  1. Process for the air classification of a particle mixture with reclassification, in which a particle mixture is supplied in dispersion to a first classification, in which the fines from the first classifying process are sucked out substantially coaxially and in which the coarse material of the first classifying process is led away downwards and subject to an at least one-step-reclassification, characterized in that separate to and after the first classifying process and before reclassification there is a dispersion of the coarse material led off downwards and reclassification of the dispersed coarse material takes place by means of largely spirally flowing in classifying air and rotor-mechanical centrifugal rejection of the coarse material particles.
  2. Air classifier (3) with at least one air classifier stage (1) having a centrifuge basket (9) drivable about a substantially vertical rotation axis and having radially outwardly positioned ledges and through which the classifying air flows from the outside to the inside, with a circular classifying chamber (4) surrounding the centrifuge basket (9) and on which there is a coaxial ring of guide vanes on the radial outside, the classifying air past the guide vanes being spirally introducable into the classifying chamber (4), with a classifying material inlet (25) and a whizzer (26) above the classifying chamber (4) and an outlet for the classified coarse material below the classifying chamber (4) and with substantially coaxial suction removal for the finesladen classifying air from the centrifuge basket (9), particularly for carrying out the process according to claim 1, characterized in that said upper first air classifier stage (1) is followed by at least one further, second air classifier stage (2) with a centrifuge basket (14) having different dimensions to the upper, first centrifuge basket (9) for the reclassification of the coarse material from the first air classifier stage and in that there is a separate whizzer (13) or a whizzer integrated with the following second centrifuge basket (14) by means of which the coarse material of the first air classifier stage (1) is supplied to the circular classifying chamber (15) of the second air classifier stage (2).
  3. Air classifier according to claim 2, characterized in that the centrifuge basket (14) or the centrifuge baskets following the centrifuge basket (9) of the first air classifier stage (1) can be driven at the same speed or a different speed as the first centrifuge basket (9).
  4. Air classifier according to claim 2 or 3, characterzied in that the second centrifuge basket (14) has a smaller vertical extension and/or a larger diameter than the first centrifuge basket (9).
  5. Air classifier according to one of claims 2 to 4, characterized in that classifying air from different, vertically separating air ducts (18, 18', 19, 19') is supplied to the second centrifuge basket (14).
  6. Air classifier according to one of claims 2 to 5, characterized in that the air ducts (5, 18, 19) for supplying classifying air to a classifying chamber (4, 15) are constructed spirally with a single or multiple thread design and tangential inflow direction and in that the air ducts when having a multiple thread design are equidistantly arranged round the circumference of air classifier casing (33) in a horizontal plane.
  7. Air classifier according to one of claims 2 to 6, characterized in that the guide vane rings (6, 7; 16, 17) associated with the vertically separated ducts (5, 18, 19) can be separately adjusted with respect to their inclination angles.
  8. Air classifier according to one of claims 2 to 7, characterized in that the first and second air classifier stages (1, 2) have a common or a separate substantially coaxial suction removal for the fines.
  9. Air classifier according to one of claims 2 to 8, characterized in that the centrifuge basket (14) of the following second air classifier stage (2) has a central downwards suction removal of the fines with a plurality of lateral suction lines (23).
  10. Air classifier according to one of claims 2 to 9, characterized in that a further, third air classifier stage for a further reclassification is provided following to the second air classifier stage (2), said third air classifier stage particularly having different dimensions compared with said second stage.
  11. Air classfier according to one of claims 5 to 10, characterized in that in the case of vertically separate air ducts (5, 18, 19) for a following air classifier stage, cooler classifying air is supplied in the lower air duct (19) than in the upper air duct (5, 18) or inversely the upper air duct leads the cooler classifying air.
EP87105736A 1986-06-25 1987-04-16 Method of and device for air sifting Expired - Lifetime EP0250747B1 (en)

Priority Applications (1)

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AT87105736T ATE82876T1 (en) 1986-06-25 1987-04-16 PROCESSES FOR AIRCLASSIFICATION AND AIRCLASSIFIERS.

Applications Claiming Priority (2)

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DE3621221 1986-06-25
DE19863621221 DE3621221A1 (en) 1986-06-25 1986-06-25 METHOD FOR WINDPROOFING AND WINIFIFIER

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EP0250747A2 EP0250747A2 (en) 1988-01-07
EP0250747A3 EP0250747A3 (en) 1989-05-24
EP0250747B1 true EP0250747B1 (en) 1992-12-02

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EP (1) EP0250747B1 (en)
AT (1) ATE82876T1 (en)
DE (2) DE3621221A1 (en)
ES (1) ES2036541T3 (en)

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Also Published As

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US4869786A (en) 1989-09-26
EP0250747A2 (en) 1988-01-07
DE3621221C2 (en) 1988-09-22
DE3621221A1 (en) 1988-01-14
DE3782859D1 (en) 1993-01-14
ES2036541T3 (en) 1993-06-01
ATE82876T1 (en) 1992-12-15
EP0250747A3 (en) 1989-05-24

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