DK157740B - Method and apparatus for recycling of moulding sand - Google Patents

Description

DK 157740 B

in

The present invention relates to a process for regenerating cast sand containing mixtures of spent sand with organic and inorganic binders such as active and dead burnt bentonite and synthetic resin, and optionally additional slurries such as coal dust, polystyrene, fine quartz dust, etc., wherein the comminuted and optionally sieved cast sand is subjected to thermal regeneration to remove organic binders by heating and a subsequent post-cleaning, by which the binder residues adhering to the sand grains are mechanically removed from the grain surfaces.

The castings made in foundries are often made in so-called green sand molds, where "green sand" is understood to mean a quartz sand with inorganic binders such as e.g. bentonite (clay). After the addition of water, the green sand is solidified by mechanical shaking until the required mold strength is obtained.

To form cavities in the castings, core pieces are inserted into the green sand molds. These core pieces are formed from quartz sand with the addition of organic binders such as furan resins or phenolic resins. The core gains its strength by chemically curing the binder.

25 After solidification of the casting, this is removed from the mold.

As a rule, the core pieces are broken because the thermal load during the casting so as to obtain a mixture of green sand and core sand, hereinafter referred to as "cast sand", which must be prepared before being reused.

It is known to prepare green sand by mechanical treatment after it has been used in casting.

In this way the sand is thrown with a fast flow of air 2

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r towards -en. per plate, whereby bentonite is detonated from the quartz grains, cf. DE Patent Specification No. 11 46 226

Furthermore, it is known to do thermal preparation of core sand with organic binders. At the thermal preparation, all organic constituents in the binder are incinerated so that the quartz sand can be recycled, according to DE disclosure specification no.

22 52 217, DE Publication No. 22 52 259 and CH Patent No. 560 081.

10 In an article by H.W. Zimnau / oda "Verfahren zur Sand-ruckgeu / innung" in "Gieøerei" 59. JG. (1979), booklet 20, page 593 et seq. other methods for regenerating cast sand are described. Here is described pneumatic regeneration, wet regeneration ("water purification") and 15 thermal sand regeneration, the latter, however, can only be used for organically bonded cast sand, since clay-containing binders in the thermal treatment (annealing) sinter onto the sand grains, so that they practically do not can be further removed, even-20 before H. Jansen "Die Regenerierung von Formstoffen, especially von Kunstharzgebundenen Altsanden" in "Gieperei" 59. JG '. (1972), booklet 20, pages 599 et seq., Especially page 604, left column, DE disclosure no.

29 09 408, page 6, second subparagraph and DE Submission 25 Writing No. 24 29 169, column 2, lines 41-45. Furthermore, combined methods are described. HW Zimnau / oda and H. Jansen refer to the possibility of regenerating cast sand by a two-step process in which the majority of clay material must be removed by wet cleaning in a first pre-purification step, after which the organic binder components in a subsequent thermal step must be completely removed by annealing. (750-820 ° C), see Zimnau / oda's article, page 597 and Janssen's article, page 604. However, Zimnau / oda mentions that the 3

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wet regeneration ("water purification") is costly, whereas Jansen doubts the practical utility of the combined regeneration process.

5 For all of the reasons mentioned here, the recovery of reclaimed used sand is essentially restricted to mold manufacturing. For the core preparation, new sand must be used predominantly to ensure the necessary core strength using given amounts of binder. So far, only 30-40% regenerated spent sand could be mixed in core production, cf. Zimna-νι / oda's article, page 594, right column.

Preparation of used sand comprising the mixtures of core and green sand, which usually occur due to 15 of the cores broken during the casting process, is extremely problematic. These sand mixtures are called cast sand or waste sand as they usually cannot be properly regenerated and therefore must be disposed of by landfill.

In a known process for regenerating cast sand, all organic binders are incinerated in a first phase at approx. 800 ° C, while the active inorganic bentonite in the green sand is burnt dead and transferred into a passive, dead phase. Active bentonite is meant bentonite with swelling ability, while deadburned bentonite is meant bentonite without swelling ability. Then, the cast sand is mechanically post-treated by impact as described above. The main disadvantage of this two-step regeneration process is that the dead-burned bentonite is sintered to the quartz grains in the thermal phase, so these bentonite shells can only be removed from the quartz grains in an extremely difficult and incomplete manner.

Furthermore, this known two-step method is only applicable

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satisfactory when the content of the so-called slurries in the casting sand is less than 435. Slime substances are the constituents of active bentonite (swellable bentonite), dead-burnt bentonite (non-swellable bentonite), coal dust or so-called polystyrene parts, resins and fine quartz dust.

At a slurry content of more than 535, especially at a content of 10-1235, the two-stage 10-regeneration described is incomplete, especially because of the bentonite sintered, so that these regenerates can only be reused to a very limited extent. because the usual additions of binders can only provide considerably inferior strengths than the strengths obtained using new sand. Therefore, reclaimed cast sand of this kind is virtually useless in core fabrication and can only be used in smaller quantities in the production of green sand molds.

Therefore, used cast sand, especially used cast sand 20 with a slime content of approx. 1035 and more, usually in depots. Due to the ever-increasing lack of suitable depots and the large quantities of cast sand, considerable space problems occur in this landfill. Due to the rising transport costs 25 and landfill fees, but also because of the limited amount of available, expensive new sand, this raw material consumption is economically unacceptable. In addition, environmental problems occur because the chemical constituents in the casting sand as these constituents can be washed out by rain during 30 weather events and thus pose a risk of contamination of the groundwater.

The object of the invention is to provide a method which allows a complete

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eWv continually regenerates cast sand with high content of slurry to a quality level corresponding to new sand, so that the regenerate can be processed by core production as new sand.

5 This object is solved according to the invention by a method of the kind initially described, characterized in that the casting sand before the thermal regeneration is subjected to a dry pre-cleaning, in which the mucus adhesives, especially inorganic binders, are removed from the sand grains by rubbing grains against grains provided by mixing and rerouting the cast sand about a preferably horizontal axis and / or by radial acceleration of the sand grains, which are then thrown against a stationary annular baffle, after which the removed slurries are separated from the thus-cleaned cast sand; preferably by means of a gas / air stream.

The dry pre-cleaning of the casting sand is carried out, for example, by rubbing grain against grain obtained by re-mixing and rerouting the casting sand about a transversely horizontal axis and / or by radial acceleration of the sand grains, which are then thrown against a stationary annular baffle plate.

The present three-step process comprising mechanical pre-cleaning, thermal treatment and mechanical post-cleaning provides surprisingly high-quality, regenerated quartz sand that can be used without restriction in any core fabrication process. Thanks to this recovery of regenerated cast sand, also with high sludge content, it is achieved that the previously described landfill of this material in large heaps and the resulting environmental impact is greatly reduced. The present process allows a recovery of up to 6

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75¾ of good quality regenerated quartz sand. This also provides a considerable cost savings in mold making, since the quartz sand regenerated by the process in question is less expensive than new sand, while also saving on landfill and freight costs.

As the purification is carried out in a dry state, the problems and costs described in the literature are avoided in using significant quantities of water.10 during the wet regeneration, without the problems of sintered clay particles during the thermal regeneration.

The slurry content of the regenerated casting sand is preferably reduced to 2-4% by weight in the pre-cleaning phase 15 by the intensive mechanical pre-cleaning. This is preferably done by an intensive rubbing of grains against grains and / or pre-acting of the grains of sand, so that the impurities adhering to the quartz sand grains are rubbed off, abraded and / or ruptured.

Without an advantageous embodiment of the invention, the cast sand is dried and preheated without the hot exhaust gas purification resulting from the thermal regeneration.

By using the furnace's exhaust gas as a gas stream to remove the mucus, the cast sand 25 is simultaneously dried and preheated during the pre-cleaning phase. This results in less energy consumption in carrying out the process. Hereby, the casting sand is preferably dried to a water content of 0.5¾.

The invention further relates to an apparatus for the thermal generation of cast sand containing mixtures of spent sand by organic and inorganic binders such as active and dead-burned bentonite and synthetic resin, and possibly additional slurries such as coal dust, poly 7

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styrene, fine quartz dust and the like, with a furnace, preferably a fluidized bed furnace in which the casting sand is heated to hot cooking and a mechanical cleaning plant arranged after the furnace, preferably configured as a rotary drum with generally horizontal axis and / or like a sling wheel cleaner.

The object of the invention is also to develop such an apparatus so that it can also regenerate in it high sand slurry mold material 10 for a material with a quality level corresponding to new sand, especially using the method of the present invention, thus that the regenerate can also be processed as new sand by nuclear production.

15 The present apparatus for regenerating cast sand must, as far as possible, be composed of finished modules or aggregates, be easy to transport and possess the ability to be put into operation easily and in a short time at the place of use.

This object is solved according to the invention by an apparatus of the above-mentioned nature, characterized in that it comprises an anhydrous, mechanical purification plant, placed before the furnace and designed as a drum rotatable about a substantially horizontal axis. 25 le and / or as a sling wheel cleaner, wherein the rotating drum preferably contains built-in brake elements and / or grinding bodies, such as balls or the like, and that the unit's assemblies are arranged in several transportable containers which can be placed one above the other and which are provided with connecting flanges, spacers, couplings or pins connected around the floor and / or ceiling level to connect the individual units in the apparatus.

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Advantageously, the dry-working pre-cleaning system consists of a sling wheel cleaner and / or a rotating cylindrical drum, which is preferably provided with brake housings in the form of plates or grinding bodies, such as balls or the like. In this way, an intensive comminution of the casting sand is provided during the pre-purification, which enables a very high efficiency of the thermal regeneration in the after-coupled furnace. This mechanical cleansing, which can also be carried out on clean green sand, has the advantage compared to appliances operating with an air flow that the wear effect of the machine is poorer while the sand's own influence in the rotating drum does not lead to increased proportions of fine dust or destruction of 15 the grain structure.

As. the whole apparatus is placed in transportable containers, not only provides a considerable simplification of the transport, as one has to simply pack and load the individual elements of the apparatus, but also the installation of the apparatus at the point of use is simplified for the erection of the containers and for the necessary connections between the containers. . Thus, it is possible to complete the apparatus at the production site and carry out test run, so that the test run after installation 25 at the point of use is considerably simplified.

The necessary connections between the containers may consist of spacers, quick couplings, tap connections and / or connection flanges with correspondingly arranged connections. When placed in the containers, a mobile system is provided which can be easily moved from place to place and installed and again easily dismantled. This has made it possible, for the first time, to affordably regenerate cast sand resulting from casting elsewhere than on permanent foundries.

35 Such a plant is also particularly suitable for implementation 9

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of experiments, as the appropriate regeneration conditions usually have to be determined in advance in a pilot plant.

According to a preferred embodiment of the present apparatus, the system is provided with a conduit containing a blower which extends axially, preferably coaxially, into the rotating drum. This conduit is connected to the furnace and serves to supply hot exhaust gas from it. An advantage of this embodiment is that substantially less energy 10 is required to provide the gas flow through the rotary drum used for the pre-cleaning into baffle apparatus.

For further energy saving and simplification of the construction of the apparatus herein, the air supply line to the fluidized bed furnace may be connected to the rotary drum used for post-cleaning so that the air is supplied through this rotating drum.

The dimensions of the containers preferably correspond to the dimensions of shipping containers, since it will be possible to use the containers and means of transport common to containers.

The arrangement and operation of the apparatus herein is greatly simplified when the apparatus contained in the containers operates independently of external energy supply, other than the electrical energy supply.

According to a particularly preferred embodiment of the assemblies, in particular the machines in the containers in question mounted anti-vibration dampers. This avoids further loading of the foundation and a more noise-free operation.

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The division of the individual aggregates in the present apparatus between the containers, of which three are usually used, can be carried out in various ways. For example, silos, a filtration system 5 and a fluidized bed furnace can be placed in the upper container, while the middle container contains the rotary drums for pre- and post-cleaning and a sieving system, while the lower container contains a gas system, a compressed air system , a central control system as well as a dosing apparatus with subsequent mixing screw. However, an arrangement is provided wherein the upper container contains the rotary drum for the mechanical dry cleaning, the middle container contains the furnace for the thermal treatment, while the bottom container contains the rotary drum for the mechanical post-cleaning of the casting sand.

This embodiment requires particularly little energy for transporting the regenerated casting sand during processing in the apparatus, and is particularly suitable for pilot-sized and / or large-size plant 20.

Ued. embodiments of the apparatus herein may include, in addition to the superimposed containers, an elevator for supplying the casting sand to be regenerated to the upper containers provided with a feeding site.

This device can be built into (used) shipping containers. However, it is also possible to place the aggregates in container-like containers.

In this connection, it is advisable that at least some of the assemblies arranged in the containers, in particular the containers, the carrier structures for the running rollers and the rotary drum and / or fluid bed furnace drive means, are at least partially integrated into the frame, wall, the floor and / or ceiling structure of the respective containers.

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11 In the following, the invention is further illustrated with reference to the drawing, in which FIG. 1 schematically shows the construction of a first embodiment of an apparatus for regenerating cast sand; FIG. 2 shows another embodiment; FIG. 3 shows a third embodiment; FIG. 4 shows a section along the line IV-IV in FIG. 3, and FIG. 5 shows a section along the line V-V in FIG. Third

The FIG. 1, the apparatus shown in the first paragraph is arranged in three transportable containers I-III which stand on top of each other. In the connection plans between the containers, easy-to-use connecting means and connecting flanges are arranged for interconnection of the assemblies contained in the individual containers.

Hereby, the connections are preferably immediately opposite one another.

The container used in the exemplary embodiment has the dimensions prescribed for ship containers. The exterior dimensions are e.g. length: 12.19 m, width 2.44 m and height 20 2.59 m.

The upper container III is provided with a supply silo II with a vibrating ring 3 located therein. In addition, a filtration system 22 is filtered which filters the exhaust air from the apparatus before it is discharged 25 into the open air. In addition, containers III are provided with a fluid bed furnace 9 in which the thermal treatment (second step of the present process) of the casting sand is carried out. In addition, container III contains an intermediate silo 12 and a supply silo 18.

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The middle container II contains a magnetic separator 4, two cylindrical rotating drums 5 and 12, both with horizontal axis of rotation 24, and a mechanical sieving system 13, placed side by side.

5 Each of the rotating drums 5 and 10 is provided with a fan 6 and 23 respectively.

Before the casting sand is regenerated by annealing in the fluid bed furnace 9, it is pretreated by pre-cleaning in the rotating drum 5.

The longitudinal direction of the rotating drum 5 provided by the rotary drum 5 serves to purify the casting sand flowing from the fluidized bed furnace 9.

The lower container I contains a gas system 20, a compressed air system 21, a buffer feeder 7 with a pneumatic conveyor 8 disposed therein, a control 19, 15 a second pneumatic conveyor 11 and several quartz sand containers 14 of different grain sizes, arranged side by side. and side where the sand contained in the containers 14 is taken out via metering means 15 and applied to a post-coupled mixing screw 16 which leads the mixture to another 2q a pneumatic conveyor 17.

The feed silo 2 in the upper container III is filled with material via a conveyor I, e.g. an elevator whose feed hopper 25 is positioned at the level of the lower container I, i. at ground level.

The product silo 18 is provided with a drop pipe 26 which opens at a level corresponding to the lower part of the middle container II, where additional transport means may be connected to transfer regenerate to the place of use.

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Since the gas system 20 and the compressed air system 21 are located in the lower container I, the apparatus located in the three containers I, II and III merely requires an electrical energy connection to be operational. After opening up the fast-opening connections between the containers, the containers can be transported separately so that they can easily be transported to winding places of use. An advantage of this is e.g. in that the regeneration of various cast sand can be tested at site 10 under the special conditions prevailing at that site.

The containers may be provided with noise attenuation, but for further attenuation of the noise, it may be advantageous that the individual assemblies, in particular the machines 15 (the vibrator gutter 3, the magnetic separator 4, the fans, the pneumatic conveyors, the sieve system 13, the dosing system 14, etc.) are mounted attenuated. in the individual containers.

The FIG. 1, the embodiment of the present apparatus operates as follows: used cast sand containing organic and inorganic binders is supplied to the elevator 1 via the feed hopper 25 pg is transferred into the feed silo 2. Via the vibrator gutter 3, the cast sand is continuously fed through the magnetic 25 'separator'. 4, located in the middle container II, for the first cylindrical rotating drum 5.

During the transport on the vibrator trench 3, a preliminary comminution of the casting sand into grain sizes of approx. 5 ml.

In magnet separator 4, any remaining pieces of molding material are separated from the casting sand and these residues are removed via a drop pipe 27.

14

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In the first rotating drum 5, the first regeneration phase takes place in the form of a dry pre-purification. The rotary. drum 5 is provided with conventional brake housings in the form of plates which determine the passage path 5 of the inflowing casting sand and provide a further comminution. Instead of, or in addition to, the brake incorporators, the rotating drum 5 may be provided with grinding bodies in the form of balls or the like, thereby providing a good comminution of the casting sand.

The rotational movement of the drum 5 about its horizontal axis 24 not only results in comminution but also a rubbing grain against grain in the casting sand as this is shaken and mixed intensively. Due to this mutual rubbing between the quartz grains, a mechanical removal or abrasion of binder residues is provided. This grain-to-grain rubbing is further enhanced by the brake housings and / or the grinding bodies of the rotating drum 5.

During this mechanical and dry pre-cleaning of the casting sand, this is simultaneously dried and heated with blown hot air into the rotating drum 5.

The exhaust gas delivered by the fluid-bed furnace 9 is cleaned of dust particles and the like in the filter system 22, after which it is supplied to the hot air blower 6 via the 25 symbolized conduit 29, after which the hot exhaust gases are blown horizontally into the rotating drum 5, preferably coaxially with The axis of rotation 24. Thus, one can utilize the hot exhaust gases from the fluid bed furnace 9 and keep the overall energy consumption at a low level.

The horizontally incoming gas stream dries the casting sand, e.g. to a water content of 0.5? ό and enters worn-out material and suspended particles separated by filter 15

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the plant 22 in the upper container III before the gas stream is sent out into the open.

In the pre-cleaning of the casting sand, its mucus content is reduced, e.g. to 2-4? ό, in particular, binder in 5 green sands, namely benzonite, is separated and removed by the rubbing of the quartz grains grain against grain.

After passing through the rotary end drum 5, the finely divided, pre-cleaned and preheated casting sand crashes into the buffer silo 7 of the lower container I, from which 10 it is taken out via a pneumatic conveyor 8 and a pipeline 28 through which it is fed to the fluid bed furnace 9. the container III.

In the fluid-bed furnace 9, the casting sand is heated to a temperature of approx. 800 ° C, whereby the organic additives such as hardeners and binders in the core sand are burned. Yet active bentonites are burnt to death and lose their swelling ability. The combustion products are carried out with the air supplied via a blower 30 and filtered off in the filter system 22. The substantially purified exhaust gas from the fluidized bed furnace 9 is then supplied via the line 29 to the suction nozzle of the hot air blower 6 associated with the rotating drum 5 in the middle container II.

Following the fluid bed furnace 9, the sand is fed via a conduit 25 35 into the cylindrical rotary drum 10 in the middle container II. The rotating drum 10 is similar in construction to the drum 5, it also rotates about a horizontal axis 24 and is also preferably provided with brake inlets and / or needle bodies 30 such as balls or the like.

Via a fan 23, the rotating drum 10 is supplied horizontally and preferably coaxially with the axis of rotation.

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16 24 supplied cooling air which cools the sand contained in the drum 10 and at the same time removes the residual and abrasive combustion residues of the hardener and binder by rubbing between the grains. At the same time, rotating drum 10 is provided with a post-cleaning and cooling of regenerate, so that space-consuming cooling units for the regenerate are eliminated.

After the aftermath of the rotary drum 10, all binder and hardener residues as well as 10 other chemical additives have been removed to a considerable extent. Regenerate! falls through a drop pipe 31 into the pneumatic conveyor 11, after which it is led via a pipe 32 into a storage silo 12 in the upper container III.

15 The regenerate is then classified by grain size into the sieve system 13 and the grain fractions are transferred to the containers 14 in the lower container I.

The finest grains (quartz sand dust, etc.) are immediately removed via a drop tube 33 and transferred to 20 containers not shown or other collection or transport apparatus.

Quartz sand is extracted from the containers 14 via the metering means 15 by means of sliding valves in a ratio corresponding to the desired grain composition of the regenerate.

The material taken out is mixed in the mixing auger 16 and transported via the pneumatic conveyor 17 and a conduit 34 to the product silo 18 in the upper container III.

The resulting regenerate, the quality of which corresponds to the quality of new sand, can be extracted from the product silo 18 via a drop pipe 26.

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The cast sand thus regenerated in three stages corresponds in all respects to new sand, so that the regenerate can be used for all conventional core manufacturing processes. In particular, it should be emphasized that the original β-quartz in the new sand p.g.a. the thermal treatment in the fluid-bed furnace 9 has been converted to α-quartz, which is accompanied by a volume increase of 0.86-1.30 / ¾. This means that there is no danger of a volume increase during the molding process due to the conversion of β-quartz to α-quartz, so that no stresses or cracks can occur in the sand surfaces of the mold and core sections.

In contrast, such conversion can occur using new sand, so that the occurring stresses and cracks in the sand surfaces of the mold and core portions are imaged in the casting surface and require a greater trimming.

The binders separated from the quartz sand grains are substantially separated by the flowing air or gas 20 in several places in the apparatus, namely by the magnetic separator 4, the rotary drums 5 and 10, the fluidized bed furnace 9, the sieve system 13 and the product silo 18. The exhaust air or exhaust gas from the individual aggregates which cause the binder particles are passed through a gas line 36 designated as a puncture ring to the filter system 22, where the air and gas are filtered so that they are essentially a dust-free exhaust gas leaving the apparatus.

For carrying out regeneration experiments with cast sand or mixtures of cast sand, the ones in 30 fig. 2 pilot plant. This facility is mobile so that it can be transported to centrally selected supply points. In terms of workflow and process technique, it corresponds to a large plant according to the present invention. In addition, in FIG. 2, the pilot-33 system showed sufficient process technical safety so that 10

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it can be used to treat a wide variety of cast sand mixtures. Finally, the pilot plant allows optimization of the design of large plants by providing various tests.

5 The embodiment of FIG. 2 pilot plants are mounted in three containers with the internal dimensions 12020 x 2350 x 2390 mm. All pipelines and electrical supply and control cables are fixedly located within the individual container, so that the interconnection between the containers takes place by means of removable spacers, quick-connect and disconnect couplings or pins. As shown in FIG. 1, the system shown in FIG. 2 shows a power supply only, since the system itself is provided with gas and compressed air supply.

15 Except for the lift, all the parts of the plant are placed in the containers. The reason the elevator is located outside the containers is because the installation of an elevator inside the containers would lead to a particularly complicated installation.

20 During the operation of the plant, all its units are readily available, so that the various plans in the plant are accessible via fixed mounted ladders.

The elevator 41 located on the side of the containers IV, V and VI has an inlet hopper 42 and an inlet pipe 43 arranged above, which leads down into the upper container VI.

The upper container VI contains an old sand container 44, a worm conveyor 45, a horizontal axis rotating drum 46 and 4 sand containers 47, 30 of which only 2 are visible.

The middle container V contains a fan 48, a cyclone separator 49, a second fan 50, a 19

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fluid bed furnace 51 with a side-mounted inlet tube 52, a fan 53, a grain grading apparatus 54 (Mogensensizer), a sling wheel cleaner 55 with an outlet tube 56, and a ladder 57.

The lower container IV contains a gas tank 90, a transport screw 58 connected to the lower end of the cyclone 49, a rotating drum 59, pneumatic conveyors 60, 61 and 62, a storage container 63 for the various grain fractions whose drains are connected. 20 a transport screw 64, as well as another sand container 65.

The FIG. The pilot plant shown in paragraph 2 works as follows: the casting sand to be regenerated is placed e.g.

25 is manually inserted into the supply hopper 42 of the elevator and is fed via the inlet pipe 43 into the storage container 44, which e.g. can hold 1000 kg. The transport auger 45 carries a dosed amount of sand into the rotating drum 46, where the sand chunks are comminuted while the sand is dried, pre-washed 9 ° preheated.

The rotary drum 46 is subdivided into 3 sections with housings perpendicular to the drum axis. In the first section, first and foremost, the sand clumps are comminuted, which is supported by the use of rod-shaped grinding bodies. This section is separated from the subsequent section of the rotating drum 46 by a hole plate so that only just flowable sand can enter the next section of the drum. In the middle section of the drum 46, the sand is cleaned by rubbing 30 grains against grains supported by a variable amount of grinding bodies. The third section of the rotary drum 46 operates without paint bodies and serves mainly for dusting the sand.

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The sand contained in the rotary drum 46 is dried, dusted and preheated with the countercurrent exhaust gas from the fluid bed furnace 51. The gas is transferred via a conduit 66 provided with a throttle flap 67.

5 The sand preheated to a temperature of approx. 300 ° C and freed of most of the ground fine parts by wind sieving in the rotary drum 46, has a slurry content of 3-4%, and via a tube 69 this is introduced at a transition piece 52 in the fluidized bed furnace 51, 10 where a sand temperature of 700-800 ° C is maintained.

In the fluid bed furnace 51, the organic binder residues are completely incinerated, after which the sand is transferred via an outlet tube 70 to a rotating drum 59 in the lower container IV.

The rotating drum 59 having the same structure as the rotating drum 46 in the upper container IV causes cooling of the sand to approx. 120 ° C, cleaning of combustion residues and the deactivated bentonite, and dusting of the sand.

Both the rotary drum 46 and the rotating drum 59 are sized such that the sand has a residence time of approx. 0.50 t / h. 60 minutes.

Most of the required regeneration work has already been carried out via the vertical line described so far. The sand extracted from the rotating drum 59 is already sufficiently regenerated for many purposes.

The FIG. 2, however, allows further post-cleaning of the sand extracted from the rotating drum 59.

To this end is removed from the rotating drum 59 removing 21

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sand via the pneumatic conveyor 60 and a conduit 71 into a four-chamber sand container 47. By optionally activating the pneumatic valves 72 provided for the container 47, it is possible to select the chamber or chambers in the container 47 from which the sand supplied via the conduit 71 must be taken out. Thus, it is possible to fill one of the chambers in the container 47 while simultaneously removing sand from one of the other chambers via one of the sliding valves 73 and the drain pipe 74 and passing this sand 10 to the sling wheel cleaner 55. This is designed so that the cleaning process may be repeated four times during the time required to fulfill one of the chambers in container 47. The sand is passed through container 65 and pneumatic conveyor 62 and on sand conveyor line 75 to another of chambers in container 47 or after final purification. to a third of the chambers in the container 47.

The purified sand is now in the third chamber of the container 47, the previously filled chamber 20 is now empty, and the first chamber is filled with sand.

The post-purified sand in the sling wheel cleaner 55 and in one of the chambers in the container 47 is passed through a line to the classifier 54. Here regenerate is divided! in the three most important cereal fractions, the division being chosen such that mam can produce all common grain distributions. Via the dotted lines indicated by broken lines 76, the individual grain fractions in the three-part container 63 are transferred. The desired quantities of the individual grain fractions in this container are extracted 50 by means of an adjustable discharge sliding valve 77, after which the fractions are mixed and transported to the fourth chamber in the container 47 via worm conveyor 64, pneumatic conveyor 61 and conduit 78.

35 The regenerates 22 prepared with the desired grain distribution

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may be withdrawn from the container 47 via an un-shown outlet pipe.

The vortex air required for the operation of the fluidized bed furnace 51 is supplied by a fresh-air suction fan 53. In the fluidized bed furnace 51, a exhaust gas having a temperature of 700-80 ° C is provided, which is passed through the exhaust gas line 66 to the rotary drum 46, from which it is extracted into a manifold 79 via a conduit 78.

Another air flow coming from the sling wheel cleaner 55 or classifier 54 as cooling air to the rotating drum 59 via a conduit 10 80, and also this air is eventually fed to the conduit line 79.

From this manifold 79, the exhaust gas is fed via the fan 50 into a cyclone separator 49 and via a conduit 81 to a purified gas fan 48, and 15 from there finally into the open via a conduit 82.

The plant's gas supply consists, for example. in a 900 kg liquid gas tank fitted with all necessary control and safety fittings. Filling the tank 90 extends to an operating time of 20 approx. 80 hours.

The lower container IV is further provided with a (not shown) compressor, e.g. located to the right of the container 65. This compressor serves to supply conveying air to the pneumatic conveyors 25 60, 61 and 62 and to control air for the pneumatic sliding valves 73 and 77.

The dust fraction separated in the cyclone 49 (optionally the plant can also contain two or more cyclones) is fed via the transport screw 58 to a gear loop through which it is removed from time to time.

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The FIG. 3-5, the embodiment of the present apparatus is also arranged in three superposed containers VII, VIII and IX and is dimensioned for a production performance of 7.5 t / h. In this embodiment, the silos for the casting material used as the starting material as well as the regenerate and grading unit are placed outside the containers, which is advantageous, since the capacity of the plant e.g. can be increased to 15 t / h by setting up another regeneration unit (containers VII, VIII and IX).

In the construction of the embodiment of FIG. 3-5, the individual assemblies have not been mounted in containers as in the figures shown in FIG. 1 and 2, but on the other hand, containers and aggregates are designed as a structural unit. Thus, for example, the sand containers 101 and 112 are formed using the frame construction of the container IX as a wall structure.

At the same time, the support structure for running rollers and drive means for the two rotating drums 107 and 109 constitute the bottom structure of containers VII and XI.

The fluid bed furnace 108 is integrated into the containers VII and IX.

The fluid bed furnace 108 is integrated into the containers VIII and also has no independent carrier and wall structure.

The three superposed containers VII, VIII and IX constitute a complete regeneration unit, only the two elevators 105 and 145 and the pneumatic conveyor 150 are externally arranged.

30 In FIG. 3-5 are shown in the following way: 24

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With a non-v / ist, e.g. pneumatic conveyor, the casting sand to be regenerated is introduced into the sand container 101 of the upper container IX. Powered by gravity, the sand is fed to an underlying sling reel cleaner 102 and thence via a vibration conveyor porter 103 to the supply funnel on elevator 105. The sand container 101 and sling reel 102 are connected to a conduit 146 provided with a pneumatically actuated slide valve 147 .

An adjustable subset (e.g., 20-30¾) of the sand transported through line 103 is transferred with pneumatic conveyor 148 into the lower container VII to a sand container 106 located on the upper side of the upper container IX, while elevator 105 transfers to the rest, i.e. e.g. 70-80? Af, of the sand flow to the sand container 101. In this arrangement, the sand is passed through the sling wheel cleaner 102 three to five times before reaching further processing in the rotating drum 107. The rotating drum and its function correspond to the rotary drum 46 in the embodiment of FIG. 2.

After the rotary drum 107, the pre-cleaned casting sand passes through a fluid bed furnace 108 where the organic binder residues are burnt, after which it is fed to a post-cleaning drum in a rotating drum 109.

A second pneumatic conveyor 150 located after the rotating drum 109 and below the lower container VII in the foundation 149 transfers the regenerated sand to the sand container 112 in the upper container IX. From this sand container 112, the sand is fed into a second sling of Christmas cleaner 151, where a final cleaning process is carried out. Then, the final regenerated sand is fed via a vibration tube 152 to a pneumatic conveyor 25

DK 157740B

104, e.g. transports the regenerate to a mixing silo set up next to containers VII, VIII and IX.

In connection with this mixing silo or immediately 5 in connection with the pneumatic conveyor 104, the plant may be provided with an apparatus for classifying and mixing the individual grain fractions in the desired ratio, which may be designed analogously to that of FIG.

2.

10 In the lower container VII, a fan III is arranged for the fluidized bed furnace 108. The other air supply lines are only partially shown in FIG. 3-5 for the sake of clarity. The air flow and the exhaust gas flow as in FIG. 5, in principle 15 corresponds to that of FIG. 2.

Using the method of the present invention and / or the present regeneration plant, it is possible to remove binder and curing residue, quartz dust (sub-grains) and other harmful substances from widely used cast sand. This can also be done on cast sand composed of green sand and chemically bonded core sand.

For the most important characteristics, such as grain shape, grain distribution, average grain size and uniformity, the regenerated sand practically corresponds to new sand, and it is also possible to adjust these quality characteristics as required by sieving and grading.

The nature of the regenerate obtained by the present process is such that it used for core production gives the same strengths as new sand at

DK 157740B

26 same binder addition. Here, it should be considered that regenerate yields of 75% of the amount of old sand applied are obtained, so that a mixture of regenerate and new sand in a mixing ratio of 75:25 can also be compared with pure new sand.

Since the cast sand to be regenerated is predominantly composed of green sand and chemically bonded core sand, the following parameters are critical for determining the degree of regeneration: 10 Bentonite-bound sand

Chemically Bonded Sand Glow Loss The table below lists the input of these parameters during regeneration, and these are compared to the corresponding values for new sand.

Cast sand Regenerated Fresh sand

_mtm_ZE 82 N

Slæmmestofindhold_11,00_0,28_0,40

Glødetab_5,78_0,00_0,30

A very important feature of the present process consists in providing a regenerate whose use with the same amount of added binder no significant strength loss 20 of the core (measured as flexural strength in N / cm) can be detected. The strengths were determined using the binder furan resin,

Hot Box and Cold Box, see US Pat.

3,409,579, and it was found that a mixture of regenerated and fresh sand in the ratio of 75:25 under otherwise 25 similar conditions practically led to the same results as pure mixtures of new sand.

27

DK 157740B

Both the values of the essential product parameters of the regenerate produced by the present process as well as the practical results have shown that the total regenerate (15% of the cast sand quantity) can be processed seamlessly in core production. It should also be noted that experiments were carried out with binder types that are extremely sensitive to the quality of sand.

The most important measurement data are summarized in the following table: 2 Bending strength (N / cm)

Furan Resin, Hot Box Cold Box, Curing 24h Processing 30 min.

Fresh sand F 32 388 750 335 15% Regenerated 25 * NSPFtPJ2XJ '369 700 323 - -.- x) Fresh sand from the sand pit in Frechen (Federal Republic of Germany)

The following table contains a list of the most important harmful substances to be removed by sand-regeneration. At the same time, the degree of removal provided in the individual regeneration steps is indicated.

Here, the "mechanical I" step corresponds to the treatment in the rotating drums 5, 46 and 107: the "thermal" process step corresponds to the treatment in fluid bed systems 9, 51 and 108 and the process step "mechanical II" to the treatment in the rotating drums 10, 59 and 109.

DK 157740 B

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29

DK 157740 B

In the embodiments described, the dry pre-cleaning is carried out in a rotating drum (see Figs. 1 and 2) or in a sling wheel cleaner and a rotating drum (see Figs. 3-5).

However, depending on the nature of the treated sand, it is also possible to carry out the dry pre-cleaning alone in a sling wheel cleaner. In this case, therefore, the use of the rotary drum for the pre-cleaning can be dispensed with. In addition, to utilize the energy of the hot exhaust gas from the fluidized bed furnace for preheating and drying the casting sand, the sling wheel cleaner may be provided with a fluidized bed preheater.

These three options for pre-cleaning (rotary drum, sling wheel cleaner with post-coupled rotary drum and optionally fluid-bed preheater sling reel cleaner) can also all be used for the post-cleaning. If the post-cleaning is carried out solely in a sling wheel cleaner, the air-bed furnace used for the thermal regeneration can be preheated in a fluid-bed cooler used for cooling the sand.

Finally, it is also possible to carry out the purification and post-purification of a plant in different appliances or combinations of apparatus, e.g. rotary drum and / or sling wheel cleaner, if any, with fluid bed preheater 25 and cooler.

A slingwheel cleaner applicable to the practice of the present invention has a radially slotted rotary slingwheel with a radial strip, through which it is subjected to radial acceleration via a coaxial tube supplied with the rotary axis from above 30. The sling reel cleaner is further provided with a fixed bell ring coaxial with the sling wheel and exhibiting a V-shaped recess per electric plate, so that

DK 157740B

The sling wheel radially accelerated sand is thrown onto the bottom half of the bell ring and thence again towards the upper ring half and thereafter substantially radially inwards, whereupon it descends and exits from the bottom of the sling wheel cleaner after crossing the sand stream moving towards prel-ring. In this slingwheel purifier, the sand purification is carried out by beading and mutual rubbing between the sand grains, the latter especially taking place in the area where the sand currents are crossed.

Claims (20)

A process for regenerating cast sand containing mixtures of spent sand with organic and inorganic binders, such as active and dead-burned bentonite and synthetic resin, and any. additional slurries, such as 5 coal dust, polystyrene, fine quartz dust, etc., in which the comminuted and possibly sieved cast sand is subjected to thermal regeneration to remove organic binders by heating and a subsequent post-purification, whereby the 10 binder residues adhering to the sand grains are mechanically removed from the grain surfaces, characterized in that the cast sand is subjected to a dry cleansing prior to thermal regeneration. Slurry adhesives to the sand grains, especially inorganic binders, are removed from the sand grains, after which the removed slurries are separated from the thus-cleaned casting sand, preferably by a gas stream. A method according to claim 1, characterized in that the dry pre-cleaning of the casting sand is carried out by rubbing grain against grain provided by mixing and rerouting the casting sand about a preferably horizontal axis. Method according to claim 1 or 2, characterized in that the grains of sand, in the dry pre-purification, are radially accelerated and thrown m-to a stationary baffle plate. Process according to any one of claims 1-3, characterized in that the content of the casting sand of sludge is reduced to 2-4¾ by the pre-cleaning. Process according to any one of claims 1-4, characterized in that during the pre-purification the casting sand is dried and preheated with hot gas in the form of waste gas from the thermal regeneration. DK 157740B Process according to claim 5, characterized in that the casting sand is dried to a water content of 0.5¾. 7. Apparatus for thermal regeneration of cast sand containing mixtures such as active and dead-burned bentonite and synthetic resin, as well as any. additional slurries, such as coal dust, polystyrene, fine quartz dust, etc., with a furnace (9, 51, 108), preferably a fluidized bed furnace in which the casting sand is heated to anneal, and one after the furnace (9, 51, 108) disposed cleaning apparatus for mechanical cleaning of the casting sand, preferably formed as a rotating drum (10, 59, 109) with a generally horizontal axis (24) and / or as a sling wheel cleaner (151), characterized in that it comprises an anhydrous, mechanical pre-cleaning system disposed prior to the furnace (9, 51, 108) and configured as a rotary drum (5, 46, 20 107) rotatable (5, 46, 20 107), preferably containing built-in brake elements, and / or grinding bodies, such as balls or the like, and / or as a sling wheel cleaner (102), and that the unit's assemblies are arranged in several transportable containers (I, II, III, IV, V, VI, VII, VIII, IX) which can be placed on top of each other and provided with about floor o g / or ceiling level, connecting flanges, spacers, couplings or tap connections are provided to connect the individual units in the apparatus. Apparatus according to claim 7, characterized in that the rotating drum (5, 46, 107) is provided with a conduit (29, 66) provided with a blower (6), which extends axially, preferably coaxially, into the drum. is connected to the furnace (9, 51, 108) and serves to supply hot exhaust gas from it. Apparatus according to claim 7 or 8, characterized in that it is provided with an air supply line (70) leading to the furnace (9, 51, 108) connected to the rotating drum (10, 59, 109) for the purification through which the supplied air is passed. Apparatus according to any one of claims 7-9, characterized in that the containers (I-IX) have dimensions 10 corresponding to shipping containers. Apparatus according to any one of claims 7-10, characterized in that the assemblies arranged in the containers (I-IX) are independent of external energy supply, other than the electrical energy supply. Apparatus according to any one of claims 7-11, characterized in that the aggregates, in particular the machines, in the relevant containers (I-IX) are mutually damped. Apparatus according to any one of claims 7-12, characterized in that the upper container (III) contains silos (2, 12, 18), a filtration system (22) and a furnace (9) with a fluidized bearing, that the middle container (II) contains the rotary drums (5, .10) for pre- and post-cleaning as well as a sieving system (13), and that the lower container (I) contains a gas system (20), a compressed air system (21), a central control (19) and a metering device (15) with subsequent mixing screw (16). Apparatus according to any one of claims 7-12, characterized in that the upper container (VI, IX) contains the rotating drum (46, 107) for mechanical dry cleaning, the middle container (V, VIII). Inside, the furnace (51, 108) holds for thermal treatment, and the lower container (IV, VII) contains the rotating drum (59, 109) for mechanical post-cleaning of the casting sand. Apparatus according to claim 14, characterized in that, in addition to the containers (I - IX) arranged above, there is an elevator (1, 41, 105) for supplying the casting sand to be regenerated to supply positions (containers 2 , 44, 101) in the upper con- 10 tainer (III, VI, IX). Apparatus according to any one of claims 7-15, characterized in that a sling wheel cleaner (102) is arranged between the supply container (101) and the rotating drum (107). Apparatus according to any one of claims 7-16, characterized in that a sling wheel cleaner (55, 131) is arranged between the rotating drum (10, 59 109) for the post-cleaning and a classifier (13, 54). Apparatus according to any one of claims 7-17, characterized in that some of the assemblies disposed in the containers (VII-IV), in particular the containers (101, 112), the supporting structures for the running rollers and the rotary drum drive means (107 , 109) and / or the furnace (108) is at least partially integrated into the frame, wall, floor and / or ceiling structure of the containers (VII-IX) - Apparatus according to any one of claims 7-18, characterized in that the sling wheel cleaner (103, 151) has a vertical axis rotating sling wheel, the upper side of which is provided with moldings, and a stationary bell ring, which faces towards the sling wheel. DK 157740B has a V-beveled recess, the sling wheel being positioned at a level next to the lower half of the barrel. Apparatus according to any one of claims 7-19, characterized in that the sling wheel cleaner for cleaning the casting sand is arranged after a fluidization bed heat exchanger connected to a discharge gas line on the furnace used for the thermal regeneration.