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EP0265707B1 - Method of and device for thermo-mechanical regeneration of bulk goods especially foundry returned sand - Google Patents

Method of and device for thermo-mechanical regeneration of bulk goods especially foundry returned sand Download PDF

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Publication number
EP0265707B1
EP0265707B1 EP87114398A EP87114398A EP0265707B1 EP 0265707 B1 EP0265707 B1 EP 0265707B1 EP 87114398 A EP87114398 A EP 87114398A EP 87114398 A EP87114398 A EP 87114398A EP 0265707 B1 EP0265707 B1 EP 0265707B1
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EP
European Patent Office
Prior art keywords
fluidized bed
bed furnace
sand
arrangement according
silo
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP87114398A
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German (de)
French (fr)
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EP0265707A2 (en
EP0265707A3 (en
Inventor
Norbert Becker
Michael Dipl.-Ing. Gross
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Forder- und Anlagentechnik GmbH
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Forder- und Anlagentechnik GmbH
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Priority to AT87114398T priority Critical patent/ATE76794T1/en
Publication of EP0265707A2 publication Critical patent/EP0265707A2/en
Publication of EP0265707A3 publication Critical patent/EP0265707A3/en
Application granted granted Critical
Publication of EP0265707B1 publication Critical patent/EP0265707B1/en
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22C—FOUNDRY MOULDING
    • B22C5/00—Machines or devices specially designed for dressing or handling the mould material so far as specially adapted for that purpose
    • B22C5/18—Plants for preparing mould materials
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22C—FOUNDRY MOULDING
    • B22C5/00—Machines or devices specially designed for dressing or handling the mould material so far as specially adapted for that purpose
    • B22C5/08—Machines or devices specially designed for dressing or handling the mould material so far as specially adapted for that purpose by sprinkling, cooling, or drying
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S241/00—Solid material comminution or disintegration
    • Y10S241/10—Foundry sand treatment

Definitions

  • the invention relates to an arrangement for the thermo-mechanical regeneration of bulk materials, in particular of foundry sands, in which the used sand to be regenerated is heated in a fluidized bed furnace to a temperature exceeding 750 ° C.
  • the molding sand used in foundries is used to process it with the additives that secure it.
  • a molding sand used in this way can, however, only be partially reused at best.
  • Both the procurement of new sand and the disposal of old sand in landfills prove to be disadvantageously costly. Especially since the disposal of the old sand, for example by depositing it in landfills, is becoming more difficult and more expensive due to increasing environmental awareness.
  • thermal and mechanical as well as wet-chemical and thermo-mechanical processes for the regeneration of used sand are therefore known.
  • the thermal, mechanical and wet-chemical processes are not economically justifiable here
  • DE-C1-3 516 191 recommends that bulk materials of this type to be decoated slide over floors in a metered thin layer, which allows the sliding bulk material to be heated by infrared rays.
  • Such arrangements are praised as inexpensive, small and compact, and particularly flexible in terms of throughput, but the heating and throughput that can be achieved have proven to be both inadequate and uneconomical.
  • Thermal stripping with the aid of fluidized bed furnaces with a relatively large content is also listed.
  • Such fluidized bed furnaces are explained and illustrated, for example, in Gmelin-Durrer, Metallurgy of Iron, 1964 Weinheim, 4th edition, volume 1a, page 62a and volume 1b, page 62b, Fig. 252, and also the foundry practice, Issue No. 17, 1984, Berlin, shows on pages 293 to 297 on page 295 a process flow diagram of a regeneration process using a fluidized bed furnace 8.
  • these fluidized bed furnaces are fed centrally, so that for the thermal stripping of the sand, fluidized bed furnaces with a relatively large content are used, which prove to be disadvantageously costly and can only be used for large throughput quantities.
  • the central feed results in different dwell times of the sand in the furnace, which further reduce the throughput actually achieved and thus the economy. Furthermore, such fluidized bed furnaces do not ensure continuous, trouble-free operation, since heavy foreign bodies, for example cast spatter, settle on the furnace bed with increasing operating time and thus further reduce the furnace output.
  • the invention aims at a powerful, continuously operable and in particular profitable arrangement of the described To create genus, the starting product can be used without restrictions like new sand.
  • the fluidized bed furnace used is equipped with a forced discharge device, which transports the bulk material in a layer of a predetermined, relatively lower level, the complete whirling of which ensures the level is completely horizontal through the hearth chamber of the fluidized bed furnace over its entire length to a transfer device which does this Throws bulk material into a discharge silo, and in that the bottom of the fluidized bed furnace is porous and / or is provided with openings or nozzles through which combustion air and heating gases and / or a heating gas / air mixture are fed to the hearth of the fluidized bed furnace.
  • the bulk material guided in a direct, largely constant current through the hearth of the fluidized bed furnace is heated to such a high temperature, with constant swirling, that both the crystalline binders are removed from the crystal water and the organic binder materials are burnt completely, so that the grains of the bulk material connect and envelop Binder residues are completely destroyed.
  • the swirling in connection with the forced discharge is not only able to completely remove binding residues adhering to grains of the bulk material by mutual friction, but also heavier admixtures, such as, for example, casting splashes, sprue parts or the like, are safely removed from the hearth of the fluidized bed furnace, so that interference effects can be avoided by congestion in the stove area.
  • a silo 1 for receiving old sand to be processed, which is designed to be closable by means of a closure 2 after the loading of a batch if the closure alone is not considered sufficient by the good column.
  • a metering device 3 At its lower end there is a metering device 3, which has two metering plates 5 and 6, one above the other, with openings, at least one of which can be set in vibration by means of a vibrator 4.
  • This metering device allows metered removal from the silo 1.
  • the material released by the metering device 3 is fed into the hearth of a fluidized bed furnace 8 via a closing funnel 7 in such a way that it covers the bottom 9 thereof in a good layer 10 of a predetermined height.
  • the bottom 9 is vibrated by vibrators 11 in such a way that the material undergoes a loosening vertical acceleration and on the other hand in the conveying direction, i.e. to the right in the figure, is slowly moved towards a transfer device 12.
  • the layer height is stabilized by one or more retaining webs 13.
  • the sand falls into a transfer silo 14, in which the sand is cooled down to a favorable processing temperature.
  • the sasnd is fed into a penumatic conveyor 16 via a trigger 15 and fed to a classifier 19 via a delivery line 17.
  • the delivery line 17 is provided with an acceleration nozzle 18, and the accelerated sand is blown into an impact bell 20 so that any impact of the burned binder is released from the grains of sand by the impact.
  • the sand entered into the silo 1 is metered into the hearth of the fluidized bed furnace (8) by the mutual movements of the metering plates 5 and 6.
  • Sand tubers and larger core pieces are placed in the feed hopper 28, which is suitably equipped with a good lock in order to prevent the escape of smoke gases.
  • Released tubers slide down a chute 26 or a corresponding grate and lie in front of the grate 27 until thermal decay has occurred to such an extent that the released sand is able to pass through the narrow grates. Any metal parts that may accumulate can be removed from the furnace via the chamber door 29.
  • the air required for combustion is sucked in by means of a blower 30 and pressed through the heat exchangers 31 provided in the upper part of the discharge silo 14, so that the regenerated sand which is emitted from the fluidized bed furnace (8) at, for example, 750.degree. C. while heating the combustion air to, for example Is cooled to 200 to 300 ° C.
  • the gas intended for combustion is transferred to the fluidized bed furnace Pipes 33 supplied while the preheated supply air is removed from the heat exchangers 31 of the discharge silo 14. Gas and combustion air are fed into the chambers 32 provided under the porous base 9 and mix there to form a combustible gas mixture.
  • the combustion takes place effectively within the whirled-up material layer 10 or directly above it, so that effective heating with high efficiency is achieved.
  • the flue gases formed in the fluidized bed furnace 8 are fed via a flue gas line 34 to a series of heat exchangers 35 operated in series, which are arranged in the lower regions, in the exemplary embodiment in the lower two thirds of the silo 1.
  • the flue gases are then fed via an exhaust pipe 37 via a collector in the direction of arrow 25, expediently via a filter, a chimney, a fireplace or the like.
  • the flue gases give off the essential part of their heat content practically in countercurrent when they flow through the heat exchangers 35 and heat the old sand in the silo 1 to be regenerated to, for example, 300 ° C., so that the fluidized bed furnace is already loaded with material that is at that temperature is preheated to which conventional thermal processes heat the goods as a whole.
  • the silo 1 By closing the silo 1 through its closure 2, but in the absence of such a closure, however, due to sand masses present above the heat exchangers, the waste gases arising during this preheating are conducted via the funnel 7 into the hearth of the fluidized bed furnace 8, in which they burn completely and , extracting with the exhaust air, can no longer be regarded as environmentally hazardous.
  • the optimum processing temperature for molding sand is around 25 ° C.
  • further heat exchangers 39 which, interspersed with cooling water, cool the regenerated sand down to the temperature recognized as appropriate.
  • a heat exchanger 31, 35 and 39 is shown in section.
  • Several parallel tubes (41) are connected to a common heat transfer plate 42, so that there are large contact surfaces to the sand.
  • the heat exchanger can also have an elliptical cross-section with tubes onto which the heat-conducting plates 42 are pressed and / or with this are welded. The longer axis of the tube is expediently vertical.
  • the heat exchangers 31 and 39 can be designed in the same way, but in particular the heat exchangers 39 through which cooling water flows can have pipes of smaller cross-section.
  • the heat-conducting sheets which mediate contact with the bulk material can be drawn onto the pipe; but there is also the possibility, in a manner known per se, of winding sheet metal strip onto the pipes in a helical manner and, if appropriate, welding them at the base.
  • one or more retaining webs 13 in the hearth of the fluidized bed furnace 8 on the base 9 thereof can have recesses 44 on their upper side. But essential are on their underside facing the bottom 9 recesses 43, which allow the passage of non-fluidizable material, such as cast splatter, ceramic parts, etc., so that clogging of the stove by such foreign objects is reliably prevented. It has been found that, for example, 25 ° C. can be considered the most favorable processing temperature for the regenerated sand, since at this temperature the binder sets neither too quickly nor too slowly and has proven to be particularly effective. The cooling in the transfer silo 14 is therefore expediently regulated.
  • a temperature sensor provided at the output detects the actual value of the output temperature, and a solenoid valve 38 is provided as an actuator of the control device, which allows the control to be carried out relatively simply and inexpensively as a so-called two-point control; the cooling water is then discharged via the waste water line 40.
  • the cooling streams of the heat exchangers are not shown in FIG. 1.
  • the heat exchangers 31 and 35 through which air flows it has proven useful to carry out the diversion from one heat exchanger to the higher one via deflection chambers 36 and 45, respectively.
  • These, their outer walls or in each case over the faces of the mouths of the heat exchangers can be designed to be removable, so that in particular the heat exchangers 35 through which the flue gases flow can be easily cleaned.
  • the invention can be varied; However, it has been shown that binder layers are reliably destroyed when heated to correspondingly high temperatures. On the other hand, heating to such high temperatures ensures that the flue gases released in this process are free of environmentally harmful constituents and essentially of nitrogen, There is water vapor and carbon dioxide so that the flue gas can be safely discharged through chimneys, food or the like, after filtering.
  • the heat exchangers 31 and 35 ensure a desired high efficiency of the arrangement, so that the fuel consumption remains pleasantly low and high efficiency can be achieved.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Molds, Cores, And Manufacturing Methods Thereof (AREA)
  • Fluidized-Bed Combustion And Resonant Combustion (AREA)
  • Feeding, Discharge, Calcimining, Fusing, And Gas-Generation Devices (AREA)

Abstract

In order to rationalize the operation of foundries and to avoid environmental stresses, it is endeavored so to rework used molding sand accruing as black sand and to free it from binder residue, so that this sand can be used without restriction like new sand. To achieve this aim through thermo-mechanical regeneration the black sand is heated in predetermined, relative low height layer in a fluidized bed furnace to a temperature exceeding 500 DEG C., preferably 750 DEG C. Through the swirling motions of the heated black sand, preferably supported through strong vibrations of the supporting base, the thermal destruction of the enveloping binder particles and a mechanical liberation of the sand grains form their enveloping binder remains is achieved. By means of a forced throughout (e.g. through appropriate vibrations or by means of a scraper conveyor) a uniform throughput with constant layer height is achieved which can be stabilized by means of additionally installed webs so that the desired mode of operation is ensured. By means of pre and post-treatment heat exchangers, the energy requirement can be kept low, while an appropriately high combustion temperature ensures at the same time the creation of environmentally safe oxidation products.

Description

Die Erfindung betrifft eine Anordnung zur thermo-mechanischen Regenerierung von Schüttgütern, insbesonderevon Gießerei-Altsanden, bei welcher der zu regenerierende Altsand in einem Wirbelschichtofen auf eine 750°C überschreitende Temperatur aufgeheizt wird.The invention relates to an arrangement for the thermo-mechanical regeneration of bulk materials, in particular of foundry sands, in which the used sand to be regenerated is heated in a fluidized bed furnace to a temperature exceeding 750 ° C.

Der in Gießereien benutzte Formsand wird zu seiner Verarbeitung mit die ihm gegebene Form sichernden Zusätzen benutzt. Ein derart verwendeter Formsand läßt sich jedoch nur bestenfalls anteilig erneut verwenden. Sowohl die Beschaffung von neuem Sand als auch die Ablagerung von Altsand in Deponien erweisen sich als unvorteilhaft kostspielig. Zumal die Beseitigung des Altsandes, bspw. durch Ablagerung auf Deponien, wird durch das steigende Umweltbewußtsein sowohl erschwert als auch verteuert.The molding sand used in foundries is used to process it with the additives that secure it. A molding sand used in this way can, however, only be partially reused at best. Both the procurement of new sand and the disposal of old sand in landfills prove to be disadvantageously costly. Especially since the disposal of the old sand, for example by depositing it in landfills, is becoming more difficult and more expensive due to increasing environmental awareness.

Aus dem Industrieanzeiger Hr. 26 vom 29. 3. 1985, Seite 32, sind daher sowohl thermische als auch mechanische sowie naß-chemische und thermo-mechanische Verfahren zur Regenerierung von Altsand bekannt. Allerdings werden hier sowohl die thermischen als auch die mechanischen sowie die naß-chemischen Verfahren als nicht wirtschaftlich vertretbar Die DE-C1-3 516 191 empfiehlt, derartige zu entschichtende Schüttgüter in einer dosierten dünnen Schicht über Böden gleiten zu lassen, welche eine Aufheizung des gleitenden Schüttgutes durch Infrarotstrahlen gestattet. Derartige Anordnungen werden als preisgünstig, klein und kompakt sowie insbesondere bezüglich des Durchsatzes als flexibel gepriesen, die erzielbare Erwärmung sowie Durchsatzleistung haben sich jedoch sowohl als unzureichend klein als auch als unwirtschaftlich erwiesen. Es wird auch die thermische Entschichtung mit Hilfe von Wirbelschichtöfen mit relativ großem Inhalt aufgeführt. Solche Wirbelschichtöfen sind bspw. in Gmelin-Durrer, Metallurgie des Eisens, 1964 Weinheim, 4. Auflage, Band 1a, Seite 62 a und Band 1b, Seite 62 b, Fig. 252, erläutert und dargestellt, und auch die Gießerei-Praxis, Heft Nr. 17, 1984, Berlin,zeigt auf Seiten 293 bis 297 auf Seite 295 ein Verfahrensfließbild eines Regenerierverfahrens, das einen Wirbelschichtofen 8 verwendet. Diese Wirbelschichtöfen werden jedoch zentral gespeist, so daß für die thermische Entschichtung des Sandes Wirbelschichtöfen mit relativ großem Inhalt benutzt werden, die sich als unvorteilhaft kostenaufwendig erweisen und nur für große Durchsatzmengen brauchbar sind. Durch die, z.B. zentrale, Speisung ergeben sich unterschiedliche Verweilzeiten des Sandes im Ofen, welche die tatsächlich erzielte Durchsatzleistung und damit die Wirtschaftlichkeit weiterhin vermindern. Weiterhin ist mit derartigen Wirbelschichtöfen kein kontinuierlicher, störungsfreier Betrieb gesichert, da sich mit zunehmender Betriebsdauer schwere Fremdkörper, bspw. Gußspritzer, auf dem Ofenbett absetzen und damit die Leistung des Ofens weiter reduzieren.From the industrial display Mr. 26 of March 29, 1985, page 32, thermal and mechanical as well as wet-chemical and thermo-mechanical processes for the regeneration of used sand are therefore known. However, the thermal, mechanical and wet-chemical processes are not economically justifiable here DE-C1-3 516 191 recommends that bulk materials of this type to be decoated slide over floors in a metered thin layer, which allows the sliding bulk material to be heated by infrared rays. Such arrangements are praised as inexpensive, small and compact, and particularly flexible in terms of throughput, but the heating and throughput that can be achieved have proven to be both inadequate and uneconomical. Thermal stripping with the aid of fluidized bed furnaces with a relatively large content is also listed. Such fluidized bed furnaces are explained and illustrated, for example, in Gmelin-Durrer, Metallurgy of Iron, 1964 Weinheim, 4th edition, volume 1a, page 62a and volume 1b, page 62b, Fig. 252, and also the foundry practice, Issue No. 17, 1984, Berlin, shows on pages 293 to 297 on page 295 a process flow diagram of a regeneration process using a fluidized bed furnace 8. However, these fluidized bed furnaces are fed centrally, so that for the thermal stripping of the sand, fluidized bed furnaces with a relatively large content are used, which prove to be disadvantageously costly and can only be used for large throughput quantities. The central feed, for example, results in different dwell times of the sand in the furnace, which further reduce the throughput actually achieved and thus the economy. Furthermore, such fluidized bed furnaces do not ensure continuous, trouble-free operation, since heavy foreign bodies, for example cast spatter, settle on the furnace bed with increasing operating time and thus further reduce the furnace output.

Die Erfindung bezweckt, eine leistungsfähige, kontinuierlich betreibbare und insbesondere rentable Anordnung der beschriebenen Gattung zu schaffen, deren Ausgangsprodukt sich ohne Einschränkungen wie Neusand verwenden läßt.The invention aims at a powerful, continuously operable and in particular profitable arrangement of the described To create genus, the starting product can be used without restrictions like new sand.

Gelöst wird diese Aufgabe, indem der verwendete Wirbelschichtofen mit einer Zwangs-Austragsvorrichtung ausgestattet ist, welche das Schüttgut in einer Schicht vorgegebener, relativ geringer, deren vollständige Durchwirbelung sichernder Höhe horizontal durch den Herdraum des Wirbelschichtofens über dessen gesamte Länge auf eine Übergabevorrichtung transportiert, welche das Schüttgut in ein Abgabesilo abwirft, und indem der Boden des Wirbelschichtofens porös ausgebildet und/oder mit Öffnungen bzw. Düsen versehen ist, durch welche Verbrennungsluft sowie Heizgase und/oder ein Heizgas-Luftgemisch dem Herdraum des Wirbelschichtofens zugeführt werden. Hierdurch wird das in direktem, weitgehend konstanten Strom durch den Herdraum des Wirbelschichtofens geführte Schüttgut unter ständiger Durchwirbelung auf eine so hohe Temperatur aufgeheizt, daß sowohl kristallinen Bindern das Kristallwasser entzogen wird als auch organische Binderstoffe restlos verbrennen, so daß die Körner des Schüttgutes verbindende und umhüllende Binderreste völlig zerstört werden. Die Durchwirbelung in Verbindung mit der Zwangsaustragung vermag hierbei nicht nur, an Körnern des Schüttgutes haftende Binderreste durch gegenseitige Reibung restlos zu entfernen, auch schwerere Beimengungen, wie bspw. Gußspritzer, Angußteile oder dergleichen, werden sicher aus dem Herd des Wirbelschichtofens herausgeführt, so daß Störeffekte durch Stauungen im Herdraum vermieden werden.This task is solved in that the fluidized bed furnace used is equipped with a forced discharge device, which transports the bulk material in a layer of a predetermined, relatively lower level, the complete whirling of which ensures the level is completely horizontal through the hearth chamber of the fluidized bed furnace over its entire length to a transfer device which does this Throws bulk material into a discharge silo, and in that the bottom of the fluidized bed furnace is porous and / or is provided with openings or nozzles through which combustion air and heating gases and / or a heating gas / air mixture are fed to the hearth of the fluidized bed furnace. As a result, the bulk material guided in a direct, largely constant current through the hearth of the fluidized bed furnace is heated to such a high temperature, with constant swirling, that both the crystalline binders are removed from the crystal water and the organic binder materials are burnt completely, so that the grains of the bulk material connect and envelop Binder residues are completely destroyed. The swirling in connection with the forced discharge is not only able to completely remove binding residues adhering to grains of the bulk material by mutual friction, but also heavier admixtures, such as, for example, casting splashes, sprue parts or the like, are safely removed from the hearth of the fluidized bed furnace, so that interference effects can be avoided by congestion in the stove area.

Vorteilhafte und zweckmäßige Weiterbildungen der Erfindung sind in den Unteransprüchen gekennzeichnet.Advantageous and expedient developments of the invention are characterized in the subclaims.

Im einzelnen sind die Merkmale der Erfindung anhand der folgenden Beschreibung eines Ausführungsbeispieles in Verbindung mit dieses darstellenden Zeichnungen erläutert. Es zeigen hierbei:

Figur 1
schematische eine Anordnung zur Regenerierung von Gießereisand,
Figur 2
im Querschnitt einen der verwendeten Wärmetauscher, und
Figur 3
die Ansicht eines Rückhaltesteges.
In detail, the features of the invention are based on the following description of an embodiment in connection with this illustrative drawings explained. They show:
Figure 1
schematic an arrangement for the regeneration of foundry sand,
Figure 2
in cross section one of the heat exchangers used, and
Figure 3
the view of a retaining web.

In der Fig. 1 ist ein Silo 1 zur Aufnahme aufzuarbeitenden Altsandes gezeigt, der nach der Aufgabe einer Charge mittels eines Verschlusses 2 schließbar gestaltet ist, falls der Abschluß allein durch die Gut-Säule nicht als ausreichend erachtet wird. An seinem unteren Ende befindet sich eine Dosiervorrichtung 3, die zwei übereinander gelegene, Durchbrüche aufweisende Dosierplatten 5 und 6 aufweist, von denen mindestens eine mittels eines Vibrators 4 in Schwingungen versetzbar ist. Diese Dosiervorrichtung erlaubt das dosierte Abziehen aus dem Silo 1. Das von der Dosiervorrichtung 3 freigegebene Material wird über einen abschließenden Trichter 7 in den Herdraum eines Wirbelschichtofens 8 so aufgegeben, daß es dessen Boden 9 in einer Gut-Schicht 10 vorgegebener Höhe bedeckt. Der Boden 9 wird durch Vibratoren 11 derart in Schwingungen versetzt, daß das Gut eine es auflockernde vertikale Beschleunigung erfährt und andererseits in Förderrichtung, d.h. in der Figur nach rechts, langsam in Richtung auf eine Übergabevorrichtung 12 vorwärts bewegt wird. Die Schichthöhe wird durch eine oder mehrere Rückhaltestege 13 stabilisiert.1 shows a silo 1 for receiving old sand to be processed, which is designed to be closable by means of a closure 2 after the loading of a batch if the closure alone is not considered sufficient by the good column. At its lower end there is a metering device 3, which has two metering plates 5 and 6, one above the other, with openings, at least one of which can be set in vibration by means of a vibrator 4. This metering device allows metered removal from the silo 1. The material released by the metering device 3 is fed into the hearth of a fluidized bed furnace 8 via a closing funnel 7 in such a way that it covers the bottom 9 thereof in a good layer 10 of a predetermined height. The bottom 9 is vibrated by vibrators 11 in such a way that the material undergoes a loosening vertical acceleration and on the other hand in the conveying direction, i.e. to the right in the figure, is slowly moved towards a transfer device 12. The layer height is stabilized by one or more retaining webs 13.

In der Übergabevorrichtung 12 fällt der Sand in einen Übergabesilo 14 ab, in dem der Sand auf eine günstige Verarbeitungstemperatur herabgekühlt wird. Über einen Abzug 15 wird der Sasnd in einen penumatischen Förderer 16 gegeben und über eine Förderleitung 17 einem Sichter 19 zugeführt. Dier Förderleitung 17 ist mit einer Beschleunigungsdüse 18 versehen, und der beschleunigte Sand wird in eine Prallglocke 20 geblasen, so daß durch den Aufprall eventuelle Rest des verbrannten Binders von den Sandkörnern gelöst werden.In the transfer device 12, the sand falls into a transfer silo 14, in which the sand is cooled down to a favorable processing temperature. The sasnd is fed into a penumatic conveyor 16 via a trigger 15 and fed to a classifier 19 via a delivery line 17. The delivery line 17 is provided with an acceleration nozzle 18, and the accelerated sand is blown into an impact bell 20 so that any impact of the burned binder is released from the grains of sand by the impact.

Im Sichter sind schräg verlaufende Böden 21 vorgesehen, über die der Sand abgwärts geführt wird. Vermittels eines Gebläses 22 und eines verteilenden Luftkastens 23 wird, durch Pfeile angedeutet, Luft quer durch den Sichter 19 geblasen, so daß zwar der spezifisch schwere und in seinen Körnern kompakte Sand herabfällt, Binderreste, Staub und weitere leichte Verunreinigungen jedoch über einen Sammler für die Abluft und eine Abluftleitung abgeführt und in Richtung des Pfeiles 25 einem Filter zugeführt werden.In the classifier, inclined floors 21 are provided, over which the sand is led downwards. By means of a blower 22 and a distributing air box 23, indicated by arrows, air is blown across the classifier 19, so that although the specifically heavy and compact sand falls down, binder residues, dust and other light impurities, however, via a collector for the Exhaust air and an exhaust air line are discharged and fed in the direction of arrow 25 to a filter.

Der in den Silo 1 eingegebene Sand wird durch die gegenseitigen Bewegungen der Dosierplatten 5 und 6 dosiert in den Herdraum des Wirbelschichtofens (8) aufgegeben. Sandknollen und größere Kernstücke werden in den Aufgabetrichter 28 gegeben, der zweckmäßig mit einer Gut-Schleuse ausgestattet ist, um das Entweichen von Rauchgasen zu unterbinden. Aufgegebene Knollen gleiten über eine Rutsche 26 oder einen entsprechenden Rost herab und liegen vor dem Rost 27, bis der thermische Zerfall so weit eingetreten ist, daß der freigegebene Sand die engen Roste zu passieren vermag. Gegebenenfalls sich ansammelnde Metallteile können über die Kammertür 29 dem Ofen entnommen werden.The sand entered into the silo 1 is metered into the hearth of the fluidized bed furnace (8) by the mutual movements of the metering plates 5 and 6. Sand tubers and larger core pieces are placed in the feed hopper 28, which is suitably equipped with a good lock in order to prevent the escape of smoke gases. Released tubers slide down a chute 26 or a corresponding grate and lie in front of the grate 27 until thermal decay has occurred to such an extent that the released sand is able to pass through the narrow grates. Any metal parts that may accumulate can be removed from the furnace via the chamber door 29.

Um den Betrieb günstig zu gestalten, sind in einem unteren Bereich des Silos 1 sowie im oberen und im unteren Bereiche des Abgabesilos 14 Wärmetauscher 31, 35 und 39 vorgesehen.In order to make the operation inexpensive, 14 heat exchangers 31, 35 and 39 are provided in a lower area of the silo 1 and in the upper and lower areas of the discharge silo.

Die zur Verbrennung benötigte Luft wird mittels eines Gebläses 30 angesaugt und durch die im oberen Teil des Abgabesilos 14 vorgesehenen Wärmetauscher 31 gepreßt, so daß der mit bspw. 750°C vom Wirbelschichtofen (8) abgegebene, regenerierte Sand unter gleichzeitiger Erhitzung der Verbrennungsluft auf bspw. 200 bis 300°C abgekühlt wird. Das zur Feuerung vorgesehene Gas wird dem Wirbelschichtofen über Rohre 33 zugeführt, während die vorgeheizte Zuluft den Wärmetauschern 31 des Abgabesilos 14 entnommen wird. Gas und Verbrennungsluft werden in unter dem porösen Boden 9 vorgesehene Kammern 32 eingespeist und vermischen sich dort zu einem brennbaren Gasgemisch. Diesespassiert Porenkanäle des Bodens 9 des Wirbelschichtofens 8, der entweder porös ausgebildet sein kann oder mit Öffnungen bzw. Düsen versehen ist. So erfolgt die Verbrennung wirkungsvoll innerhalb der aufgewirbelten Gut-Schicht 10 bzw. direkt über dieser, so daß eine wirkungsvolle Aufheizung mit hohem Wirkungsgrad erreicht wird.The air required for combustion is sucked in by means of a blower 30 and pressed through the heat exchangers 31 provided in the upper part of the discharge silo 14, so that the regenerated sand which is emitted from the fluidized bed furnace (8) at, for example, 750.degree. C. while heating the combustion air to, for example Is cooled to 200 to 300 ° C. The gas intended for combustion is transferred to the fluidized bed furnace Pipes 33 supplied while the preheated supply air is removed from the heat exchangers 31 of the discharge silo 14. Gas and combustion air are fed into the chambers 32 provided under the porous base 9 and mix there to form a combustible gas mixture. This passes through pore channels of the bottom 9 of the fluidized bed furnace 8, which can either be porous or is provided with openings or nozzles. The combustion takes place effectively within the whirled-up material layer 10 or directly above it, so that effective heating with high efficiency is achieved.

Die im Wirbelschichtofen 8 gebildeten Rauchgase werden über eine Rauchgasleitung 34 einer Reihe in Serie betriebener Wärmertauscher 35 zugeführt, die im unteren Bereiche, im Ausführungsbeispiel in den unteren zwei Dritteln des Silos 1, angeordnet sind. Über eine Abgasleitung 37 werden die Rauchgase dann über einen Sammler in Richtung des Pfeiles 25, zweckmäßig über einen Filter, einer Esse, einem Kamin oder dergleichen zugeführt. Die Rauchgase geben beim Durchströmen der Wärmetauscher 35 den wesentlichen Teil ihres Wärmeinhaltes praktisch im Gegenstrom ab und erhitzen hierbei den im Silo 1 befindlichen, zu regenerierenden Altsand auf bspw. 300°C, so daß der Wirbelschichtofen bereits mit Gut beschickt wird, das auf jene Temperatur vorerhitzt ist, auf welche übliche thermische Verfahren das Gut insgesamt erhitzen. Durch das Abschließen des Silos 1 durch seinen Verschluß 2, beim Fehlen eines solchen Verschlusses jedoch bereits durch über den Wärmetauschern anstehende Sandmassen, werden die bei dieser Vorerhitzung entstehenden Abgase über den Trichter 7 in den Herdraum des Wirbelbettofens 8 geleitet, in dem sie vollständig verbrennen und, mit der Abluft abziehend, als nicht mehr umweltgefährdend betrachtet werden können.The flue gases formed in the fluidized bed furnace 8 are fed via a flue gas line 34 to a series of heat exchangers 35 operated in series, which are arranged in the lower regions, in the exemplary embodiment in the lower two thirds of the silo 1. The flue gases are then fed via an exhaust pipe 37 via a collector in the direction of arrow 25, expediently via a filter, a chimney, a fireplace or the like. The flue gases give off the essential part of their heat content practically in countercurrent when they flow through the heat exchangers 35 and heat the old sand in the silo 1 to be regenerated to, for example, 300 ° C., so that the fluidized bed furnace is already loaded with material that is at that temperature is preheated to which conventional thermal processes heat the goods as a whole. By closing the silo 1 through its closure 2, but in the absence of such a closure, however, due to sand masses present above the heat exchangers, the waste gases arising during this preheating are conducted via the funnel 7 into the hearth of the fluidized bed furnace 8, in which they burn completely and , extracting with the exhaust air, can no longer be regarded as environmentally hazardous.

Die optimale Verarbeitungstemperatur von Formsand liegt, je nach Art des verwendeten Binders, etwa bei 25°C. Im unteren Bereiche des Abgabesilos 14 sind daher die weiteren Wärmetauscher 39 vorgesehen, die, von Kühlwasser durchsetzt, den regenerierten Sand auf jene als zweckmäßig erkannte Temperatur herabkühlen.Depending on the type of binder used, the optimum processing temperature for molding sand is around 25 ° C. In the lower area of the discharge silo 14 there are therefore provided further heat exchangers 39 which, interspersed with cooling water, cool the regenerated sand down to the temperature recognized as appropriate.

In der Fig. 2 ist ein Wärmetauscher 31, 35 bzw. 39 geschnitten dargestellt. Mehrere parallele Rohre (41) sind mit einem gemeinschaftlichen Wärmeübertragungsblech 42 verbunden, so daß sich große Kontaktflächen zum Sand hin ergeben. Um einerseits eine große Oberfläche sowie einen das ungehinderte Abziehen der Rauchgase sichernden Querschnitt zu erhalten und andererseits das vertikale Weiterwandern des Schüttgutes im Silo 1 nicht zu beeinträchtigen, kann der Wärmetauscher auch einen elliptischen Querschnitt aufweisende Rohre aufweisen, auf die Wärmeleitbleche 42 aufgepreßt und/oder mit diesem verschweißt sind. Zweckmäßig steht die längere Achse des Rohres vertikal. Gleichartig können die Wärmetauscher 31 und 39 ausgeführt sein, insbesondere die von Kühlwasser durchflossenen Wärmetauscher 39 können jedoch Rohre geringeren Querschnittes aufweisen. Die den Kontakt mit dem Schüttgut vermittelnden Wärmeleitbleche können auf das Rohr aufgezogen sein; es besteht aber auch die Möglichkeit, in an sich bekannter Weise Blechband auf die Rohre schraubenlinienartig aufzuwickeln und gegebenenfalls im Fußpunkt zu verschweißen.2, a heat exchanger 31, 35 and 39 is shown in section. Several parallel tubes (41) are connected to a common heat transfer plate 42, so that there are large contact surfaces to the sand. In order on the one hand to obtain a large surface area and a cross-section which ensures the unhindered removal of the flue gases and on the other hand not to impair the vertical movement of the bulk material in the silo 1, the heat exchanger can also have an elliptical cross-section with tubes onto which the heat-conducting plates 42 are pressed and / or with this are welded. The longer axis of the tube is expediently vertical. The heat exchangers 31 and 39 can be designed in the same way, but in particular the heat exchangers 39 through which cooling water flows can have pipes of smaller cross-section. The heat-conducting sheets which mediate contact with the bulk material can be drawn onto the pipe; but there is also the possibility, in a manner known per se, of winding sheet metal strip onto the pipes in a helical manner and, if appropriate, welding them at the base.

Zur Erleichterung des Einhaltens der vorgegebenen Stärke der Gutschicht 11 kann es sich als zweckmäßig erweisen, im Herd des Wirbelschichtofens 8 auf dessen Boden 9 einen oder mehrere Rückhaltestege 13 vorzusehen. Diese können auf ihrer Oberseite Ausnehmungen 44 aufweisen. Wesentlich aber sind auf ihrer dem Boden 9 zugewandten Unterseite Ausnehmungen 43, welche das Durchtreten von nicht fluidisierbarem Material, z.B. Gußspritzern, Keramikteilen usw., erlauben so daß ein Zusetzen des Ofenherdes durch derartige Fremdkörper sicher unterbunden wird. Es wurde gefunden, daß bspw. 25°C als günstigste Verarbeitungstemperatur des regenerierten Sandes gelten kann, da bei dieser Temperatur der Binder weder zu schnell noch zu langsam abbindet und sich als besonders wirksam erweist. Zweckmäßig wird dsaher die Kühlung im Übergabesilo 14 geregelt. Ein am Ausgang vorgesehener Temperaturfühler faßt den Ist-Wert der Ausgangstemperatur auf, und als Stellgied der Regelvorrichtung wird ein Magnetventil 38 vorgesehen, welches es erlaubt, die Regelung relativ einfach und wenig aufwendig als sogenannte Zwei-Punkt-Regelung durchzuführen; das Kühlwasser wird dann über die Abwasserleitung 40 abgeführt.To facilitate compliance with the predetermined thickness of the material layer 11, it may prove expedient to provide one or more retaining webs 13 in the hearth of the fluidized bed furnace 8 on the base 9 thereof. These can have recesses 44 on their upper side. But essential are on their underside facing the bottom 9 recesses 43, which allow the passage of non-fluidizable material, such as cast splatter, ceramic parts, etc., so that clogging of the stove by such foreign objects is reliably prevented. It has been found that, for example, 25 ° C. can be considered the most favorable processing temperature for the regenerated sand, since at this temperature the binder sets neither too quickly nor too slowly and has proven to be particularly effective. The cooling in the transfer silo 14 is therefore expediently regulated. A temperature sensor provided at the output detects the actual value of the output temperature, and a solenoid valve 38 is provided as an actuator of the control device, which allows the control to be carried out relatively simply and inexpensively as a so-called two-point control; the cooling water is then discharged via the waste water line 40.

Um die Darstellung nicht zu überlasten sind in der Fig. 1 die Kühlbäche der Wärmetauscher nicht dargestellt. Insbesondere bei den von Luft durchströmten Wärmetauschern 31 und 35 hat es sich bewährt, die Umleitung von einem Wärmetauscher zum höhergelegenene jeweils über Umlenkkammern 36 bzw. 45 durchzuführen. Diese, ihre Außenwandungen bzw. jeweils über den Mündungen der Wärmetauscher anstehenden Flächen können abnehmbar ausgebildet sein, so daß insbesondere die von den Rauchgasen durchströmten Wärmetauscher 35 leicht reinigen lassen.In order not to overload the illustration, the cooling streams of the heat exchangers are not shown in FIG. 1. In particular in the case of the heat exchangers 31 and 35 through which air flows, it has proven useful to carry out the diversion from one heat exchanger to the higher one via deflection chambers 36 and 45, respectively. These, their outer walls or in each case over the faces of the mouths of the heat exchangers can be designed to be removable, so that in particular the heat exchangers 35 through which the flue gases flow can be easily cleaned.

Die Erfindung läßt sich variieren; es hat sich jedoch gezeigt, daß beim Aufheizen auf entsprechend hohe Temperaturen Binderschichten sicher zerstört werden. Die Aufheizung auf derartig hohe Temperaturen sichert andererseits, daß die hierbei abgegebenen Rauchgase frei von umweltschädlichen Bestandteilen sind und im wesentlichen aus Stickstoff, Wasserdampf und Kohlendioxid bestehen, so daß das Rauchgas, zweckmäßig nach einer Filterung, unbedenklich über Kamine, Essen oder dergleichen abgegeben werden kann. Die Wärmetauscher 31 und 35 sichern einen erwünscht hohen Wirkungsgrad der Anordnung, so daß auch der Brennstoffverbrauch erfreulich gering bleibt und ein hoher Wirkungsgrad erzielbar ist.The invention can be varied; However, it has been shown that binder layers are reliably destroyed when heated to correspondingly high temperatures. On the other hand, heating to such high temperatures ensures that the flue gases released in this process are free of environmentally harmful constituents and essentially of nitrogen, There is water vapor and carbon dioxide so that the flue gas can be safely discharged through chimneys, food or the like, after filtering. The heat exchangers 31 and 35 ensure a desired high efficiency of the arrangement, so that the fuel consumption remains pleasantly low and high efficiency can be achieved.

Claims (13)

  1. An arrangement for the thermomechanical regeneration of bulk goods, especially of used foundry sand, in which the used sand to be regenerated is heated in a fluidized bed furnace to a temperature in excess of 750°C,
    characterised in that the fluidized bed furnace (8) is equipped with a controlled delivery device, which transports the bulk goods in a layer at a preset, relatively low height, which ensures its complete turbulence, horizontally through the hearth of the fluidized bed furnace over its entire length to a transfer device (12), which tips the bulk goods into a delivery silo (14),
    and in that the base (9) of the fluidized bed furnace (8) has a porous construction and/or is provided with apertures or nozzles respectively, through which combustion air and also heating gases and/or a mixture of heating gas and air is supplied to the hearth of the fluidized bed furnace.
  2. An arrangement according to Claim 1,
    characterised in that to the fluidized bed furnace (8) there is associated at least one vibrator (11) acting on its base (9), which breaks up the bulk goods and guides them in the longitudinal direction through the fluidized bed furnace.
  3. An arrangement according to Claim 1 or 2,
    characterised in that the transfer device (12) comprises separators or sieves respectively, which keep foreign bodies out of the delivery silo (14).
  4. An arrangement according to one of Claims 1 to 3,
    characterised in that the combustion air supplied to the fluidized bed furnace (8) is guided via heat exchangers (31) provided in the delivery silo (14),
    and in that the flue gases formed in the fluidized bed furnace are supplied to a chimney via heat exchangers (35) disposed in the silo (1), if necessary via a filter device.
  5. An arrangement according to one of Claims 1 to 4,
    characterised in that the silo (1) sealed at the top by a seal (2) or at least by a column of material is also connected to the hearth of the fluidized bed furnace (8) for its ventilation.
  6. An arrangement according to one of Claims 1 to 5,
    characterised in that in the lower region of the delivery silo (14) heat exchangers (39) through which cooling water flows are provided.
  7. An arrangement according to Claim 6,
    characterised in that to the heat exchanger (39) there is allocated a control device which preferably operated according to the two-point principle and after which a magnet valve (38) is inserted as a control element.
  8. An arrangement according to at least one of Claims 4, 6 and 7,
    characterised in that heat exchangers (31, 35, 39) are constructed as pipes (41) connected on their circumference to heat transfer plates (42) and comprising an elliptical cross section, the larger cross sectional axes of which are directed vertically.
  9. An arrangement according to one of Claims 1 to 8,
    characterised in that after the silo (1) there is inserted a metering device (3) which determines the supply to the fluidized bed furnace (8).
  10. An arrangement according to one of Claims 1 to 9,
    characterised in that the base (9) of the fluidized bed furnace (8) comprises at least one retaining piece (13), which is equipped in its base region with apertures (43) to allow the passage of foreign bodies.
  11. An arrangement according to one of Claims 1 to 10,
    characterised in that for lumpy material a separate, additional distributing device (28) is provided, which is preferably equipped with a material lock.
  12. An arrangement according to one of Claims 1 to 11,
    characterised in that a separator (19) is inserted after the delivery silo (14).
  13. An arrangement according to Claim 12,
    characterised in that between the delivery silo (14) and the separator (19) there is provided a pneumatic conveyor (16), preferably with an accelerating nozzle (18) inserted after it, and the delivery pipe (17) inserted after the pneumatic conveyor is directed towards a deflector bell (20) of the separator (19).
EP87114398A 1986-10-27 1987-10-02 Method of and device for thermo-mechanical regeneration of bulk goods especially foundry returned sand Expired - Lifetime EP0265707B1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AT87114398T ATE76794T1 (en) 1986-10-27 1987-10-02 METHOD AND ARRANGEMENT FOR THE THERMO-MECHANICAL REGENERATION OF BULK MATERIALS, IN PARTICULAR FROM GIESSEREI-ALTSANDT.

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE3636479 1986-10-27
DE19863636479 DE3636479A1 (en) 1986-10-27 1986-10-27 METHOD AND ARRANGEMENT FOR THE THERMO-MECHANICAL REGENERATION OF SCHUETTGUETE, ESPECIALLY OF FOUNDRY OLD SAND

Publications (3)

Publication Number Publication Date
EP0265707A2 EP0265707A2 (en) 1988-05-04
EP0265707A3 EP0265707A3 (en) 1988-08-17
EP0265707B1 true EP0265707B1 (en) 1992-06-03

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EP (1) EP0265707B1 (en)
AT (1) ATE76794T1 (en)
DE (2) DE3636479A1 (en)

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EP0343272A1 (en) * 1988-05-26 1989-11-29 Pohl Giessereitechnik Method of and installation for regeneration of returned sand of foundry
EP0465778A2 (en) * 1990-06-28 1992-01-15 Fried. Krupp AG Hoesch-Krupp Process for reclaiming used foundry sand
EP0505722A1 (en) * 1991-03-27 1992-09-30 Alb. Klein GmbH & Co. KG Process for reclaiming bulk material containing coated grains, in particular used foundry sand
EP0512236A1 (en) * 1991-04-10 1992-11-11 KGT GIESSEREITECHNIK GmbH Process for mechanical reclaiming of used foundry sand
WO2003061873A1 (en) * 2002-01-23 2003-07-31 Pec Technologies Limited A method of treating sand

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DE4015031A1 (en) * 1990-05-10 1991-11-14 Kgt Giessereitechnik Gmbh METHOD FOR THE THERMAL REGENERATION OF OLD SANDS CONTAINING IN FOUNDRIES, AND FOR TREATING THE DUST RESULTING IN THE SAND CIRCUIT
US5027721A (en) * 1990-09-21 1991-07-02 Enviro-Klean Soils, Inc. Method and apparatus for cleaning contaminated soil
US5111756A (en) * 1990-09-21 1992-05-12 Enviro-Klean Soils, Inc. Apparatus for cleaning contaminated soil
US5251565A (en) * 1990-12-13 1993-10-12 Shell Oil Company Process and apparatus for removal of carbonaceous materials from particles containing such materials
DE4102168C2 (en) * 1991-01-25 1994-10-20 Klein Alb Gmbh Co Kg Method and device for burning dust
DE4126976C1 (en) * 1991-08-14 1993-01-07 Kuenkel-Wagner Gmbh & Co Kg, 3220 Alfeld, De
US5127343A (en) * 1991-10-16 1992-07-07 Terrachem Environmental Services, Inc. Hydrocarbon extractor
DE4215867A1 (en) * 1992-05-14 1993-11-18 Kgt Giessereitechnik Gmbh Method and device for regulating the sand discharge during the thermal regeneration of old foundry sand in fluidized bed furnaces
DE4316610A1 (en) * 1993-05-18 1994-11-24 Gut Gieserei Umwelt Technik Gm Ecologically sound mechanical/pneumatic sand regeneration in batchwise operation
FR2730653B1 (en) * 1995-02-16 1997-05-09 Fm Ind PROCESS FOR REGENERATION BY THERMAL DISCHARGE OF USED FOUNDRY SANDS
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JP3355325B2 (en) * 2000-05-18 2002-12-09 旭有機材工業株式会社 Temperature control unit for raw molding sand or resin-coated sand for shell mold and temperature control device using the same
KR101161779B1 (en) * 2010-09-09 2012-07-03 한전원자력연료 주식회사 Producing equipment for u3o8 powder
US9109531B2 (en) * 2012-01-09 2015-08-18 Honda Motor Co., Ltd. Method for testing casting quality and apparatus therefor
CN104043772A (en) * 2014-06-20 2014-09-17 中机中联工程有限公司 Casting used sand thermal reclamation system
CN109093065A (en) * 2018-10-11 2018-12-28 深圳清大同科生态环境有限公司 A kind of precoated sand production system of UTILIZATION OF VESIDUAL HEAT IN

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Publication number Priority date Publication date Assignee Title
EP0343272A1 (en) * 1988-05-26 1989-11-29 Pohl Giessereitechnik Method of and installation for regeneration of returned sand of foundry
US5045090A (en) * 1988-05-26 1991-09-03 Pohl Giesserreitechnik Process and device for reclaiming used foundry sands
EP0465778A2 (en) * 1990-06-28 1992-01-15 Fried. Krupp AG Hoesch-Krupp Process for reclaiming used foundry sand
EP0465778A3 (en) * 1990-06-28 1993-04-14 Kuenkel-Wagner Gmbh & Co.Kg Process for reclaiming used foundry sand
EP0505722A1 (en) * 1991-03-27 1992-09-30 Alb. Klein GmbH & Co. KG Process for reclaiming bulk material containing coated grains, in particular used foundry sand
EP0512236A1 (en) * 1991-04-10 1992-11-11 KGT GIESSEREITECHNIK GmbH Process for mechanical reclaiming of used foundry sand
WO2003061873A1 (en) * 2002-01-23 2003-07-31 Pec Technologies Limited A method of treating sand
GB2399528A (en) * 2002-01-23 2004-09-22 Pec Technologies Ltd A method of treating sand

Also Published As

Publication number Publication date
US4821654A (en) 1989-04-18
EP0265707A2 (en) 1988-05-04
DE3779560D1 (en) 1992-07-09
DE3636479C2 (en) 1990-09-13
EP0265707A3 (en) 1988-08-17
ATE76794T1 (en) 1992-06-15
DE3636479A1 (en) 1988-05-05

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