EP0149595B1 - Process and machine for regenerating used foundry sand - Google Patents

Description

The invention relates to a process for the regeneration of foundry rubble sands which contain old sand mixtures with organic and inorganic binders, such as active and still burned bentonite and synthetic resins and optionally further sludge materials, such as hard coal dust, polystyrene, quartz fine dust, etc., in which process the crushed and optionally sieved foundry sand is used Removal of organic binders is subjected to thermal regeneration by heating and then to post-cleaning, in which binder residues adhering to the sand grains are mechanically removed from the grain surfaces, and a device therefor.

The castings manufactured in foundries are predominantly made in so-called green sand molds, with green sand being a quartz sand with inorganic binders such as e.g. B. bentonite (clay) is understood. The green sand is mechanically solidified with the addition of water by shaking to the required dimensional stability.

In order to form the inner contours of the casting, core pieces are inserted into the green sand molds, which are formed from quartz sand with the addition of organic binders, such as furan resins or phenolic resins. The core gets its strength through chemical hardening of the binders.

After the casting has solidified, it is separated from the mold. As a rule, the core pieces disintegrate due to the thermal load during the casting process, resulting in a mixture of green sand and core sand (“rubble sand”), which has to be processed if it is to be used again.

It is known to treat green sand obtained after the casting process by mechanical treatment. For this purpose, the sand is thrown against an impact bell at high speed by means of an air stream, bentonite being blasted off from the quartz grains (DE-C-11 46 226).

It is also known to thermally process core sands with organic binders. During the thermal treatment, all organic constituents of the binders are burned, so that the quartz sand can be reused (DE-A-22 52 217, DE-A-22 52 259, CH-A 560081).

In the essay by H.W. Zimnawoda "Process for sand recovery" in "Foundry 59. JG (1972), No. 20; Other regeneration processes for foundry sands are described on page 593 ff. Zimnawoda describes pneumatic regeneration, wet regeneration («water purification •) and thermal sand regeneration, which, however, can only be used for exclusively organically bound foundry sands, since clay-containing binders sinter onto the sand bodies during the thermal treatment (annealing) and practically not more can be removed (cf. H. Jansen "The regeneration of molding materials, especially of synthetic resin-bonded old sands" in "Foundry 59.JG. (1972), No. 20; page 599 ff., esp. page 604, left column; DE- A-29 09 408, page 6, 2nd paragraph and DE-B-24 29 169, column 2, lines 41-45). Combined processes are also described. H.W. Zimnawoda and H. Jansen point out the possibility of regenerating foundry sands in a two-stage process, in which the main part of the clay residues is to be removed by wet regeneration in a first stage and in a subsequent thermal stage the organic parts of the bend agent are to be removed by annealing (750-820 ° C) should be completely removed (Zimnawoda loc. Cit. Page 597 and Jansen loc. Cit. Page 604). However, Zimnawoda points out that wet regeneration («water purification •) is expensive, whereas Jansen doubts the practical application of the combined regeneration process.

For all of the above reasons, the reuse of regenerated old sands is essentially limited to the production of molds. For the core production, new sand must be used predominantly to ensure the required core strength with given amounts of binder. So far, only 30 to 40% of regenerated old sand could be mixed in for core production (see H.W. Zimnawoda, op. Cit., Page 594, right column).

The processing of old sand mixtures aux core and green sand, as is usually the case with cores that disintegrate during the casting process, is extremely problematic. This old sand mixture is also called rubble sand, since it cannot generally be regenerated satisfactorily and has to be disposed of in landfills.

In a known process for the regeneration of such rubble sands, all organic binders are burned in a first phase at approx. 800 ° C., while the active inorganic bentonite of the green sand is converted into a passive, dead phase (dead burning). Swellable bentonite is understood as active bentonite, bentonite without burnability is understood as burnt-dead bentonite. The rubble sand is then mechanically post-treated in the manner already described above by means of an impact effect. The main part of this two-stage regeneration process is that the dead burned bentonite is sintered onto the quartz grain due to the thermal phase, which makes this bentonite shell extremely difficult and incomplete to remove from the quartz grain. In addition, this known two-stage process can only be used satisfactorily if the so-called sludge content of the rubble sand is less than 4%. Among slurries are the components of active bentonite (swellable bentonite), still burned bentonite (non-swellable bentonite), hard coal dust or so-called carbonaceous materials such as polystyrene, resins and Qu fine dust, understood.

With a sludge content of more than 5%, but especially at 10 to 12%, the two-stage regeneration described is incomplete, in particular due to the sintered-on bentonites, so that these regenerates can be reused only to a very limited extent, because with the prescribed additions of binder amounts, only considerably lower strengths can be achieved are like with new sand. Such regenerated rubble sands are therefore practically unusable in core production and are mainly used as a percentage of green sand mold production.

Rubble sands, but especially those with a sludge content of approx. 10% and more, are therefore regularly deposited in landfills. Due to the ever decreasing number of suitable landfills and the large amount of rubble sands, there are considerable space problems. This waste of raw materials is economically unacceptable due to the transport costs and landfill fees incurred and the expensive new sand that is only available to a limited extent. In addition, environmental problems arise due to the chemical components in the rubble sands, since these components can be washed out under the influence of the weather when it rains and there is a risk of groundwater contamination.

From US-A-4144 088 a method for regenerating rubble sands is known according to the preamble of claim 1. In this known method, the rubble sand to be regenerated is crushed, then subjected to a magnetic separation process for the separation of metal components and finally subjected to wind screening to remove dust components before it is thermally treated in an oven. Since in the steps preceding the thermal treatment in US-A-4144 088 (comminution, separation of metal and sintering), adhering to the grains of the sand is not removed, the known process has the disadvantages described above.

The invention has for its object to provide a method with which a complete regeneration of foundry rubble sands with a high sludge content is possible down to the quality level of new sand, so that the regenerate can be processed like new sand during core production.

This object is achieved in that the foundry sand is subjected to a dry pre-regeneration before the thermal regeneration, in which sludge adhering to the sand grains, in particular inorganic binders, are removed from the sand grains, and in that the removed sludge is then preferably removed by the foundry sand thus pre-regenerated a gas stream to be separated.

The three-stage regeneration process according to the invention - mechanical pre-cleaning, thermal treatment, mechanical post-cleaning - surprisingly achieves a high-quality regenerated quartz sand that can be used indefinitely for all of the core manufacturing processes that occur. The possibility of also reusing high-sludge-containing rubble sands after the regeneration according to the invention means that the dumping of these old sands on heaps described above and the consequent impairment of the environment is considerably reduced. With the three-stage process according to the invention, up to 75% recovery of high-quality regenerated quartz sand is possible. This enables considerable cost savings in the production of molds, since quartz sand regenerated by the method according to the invention is less expensive than new sand and, moreover, the landfill costs and freight costs can be saved.

The fact that the pre-cleaning is carried out dry eliminates the problems and costs described in the literature for the use of considerable amounts of water in the course of the wet regeneration, without sintered clay casings being formed in the thermal regeneration stage.

In the pre-cleaning phase, the intensive mechanical pre-cleaning advantageously reduces the sludge content of the debris sand to be regenerated to 2 to 4%. This is preferably done by intensive grain-to-grain friction and / or by allowing the sand grains to impact, so that contaminants adhering to the quartz sand grain are rubbed off, ground off and / or blasted off.

In an advantageous development of the invention, the foundry sand is dried and preheated during the pre-cleaning by warm exhaust gas originating from the thermal regeneration. This ensures low energy consumption when carrying out the method. According to the invention, the foundry sand is preferably dried to a water content of 0.5% in the pre-regeneration stage.

The invention also relates to a device for the regeneration of foundry rubble sands containing old sand mixtures with organic and inorganic binder parts, active and still burned bentonite and synthetic resins, and optionally further sludge materials, such as hard coal dust, polystyrene, quartz fine dust, etc., with an oven, preferably a fluidized bed oven which the foundry sand is heated for the purpose of annealing and a cleaning device downstream of the furnace for mechanical cleaning of the foundry sand, which is preferably designed as a rotating drum with an essentially horizontal axis and / or as a centrifugal wheel cleaner.

Such a device is known from DE-A-22 52 259.

The invention is further based on the object of developing a device of this type in such a way that, particularly using the method according to the invention, rubble sands with high sludge contents can be regenerated down to the quality level of new sand, so that the regenerate, like new sand, can also be processed in the core production .

Furthermore, the device according to the invention for the regeneration of foundry rubble sands should be largely prefabricated and easily transportable and should be able to be put into operation easily and in a short time at the place of use.

This object is achieved in that the furnace is preceded by a waterless mechanical pre-regeneration device, which is rotatable about a substantially horizontal axis rotating drum, in which baffle internals are preferably arranged and / or grinding media, such as balls, and / or as a centrifugal wheel cleaner is formed and that the units of the device are arranged in several transportable containers, connection flanges, intermediate pieces, couplings or plug connections for connecting the individual units of the device being provided in the area of the ceilings and / or the floors of the containers which can be placed congruently with one another.

It is advantageous that the dry-working pre-cleaning device is a centrifugal wheel cleaner and / or a cylindrical drum rotating about a horizontal axis, in which baffle internals in the form of sheets or grinding media, such as balls or the like, are preferably arranged or accommodated. In this way, intensive rubble sand comminution is achieved in the course of the pre-regeneration, which enables high efficiency in the thermal regeneration in the downstream furnace. This mechanical pre-regeneration, which is also possible for pure green sand, has the advantage over the devices that work with an air stream that the wear on the machine is lower and the self-stressing of the sand in the rotating drum does not lead to increased fine dust contents or to the destruction of the sand grain structure.

The fact that the individual units of the device are arranged in transportable containers not only results in a considerable simplification of transport - there is no need to pack and load the individual elements of the device - but also the assembly of the device at the place of use is restricted on parking the containers and making the connections between the containers. It is thus possible to assemble the device at the manufacturer and test drive it, the test run after installation on site is considerably simplified.

The necessary connections between the containers can be formed by intermediate pieces, quick couplings, plug connections and / or connecting flanges, the connections of which are congruent with one another. The arrangement in containers creates a mobile system that can be easily brought on site and that can be installed and removed with little effort. In this way, it is possible for the first time to regenerate rubble sand cost-effectively using the service process. Such a system is also particularly suitable for carrying out experiments, since as a rule the suitable conditions for a regeneration process must be examined on site for practical testing in a pilot process.

It can advantageously be provided within the scope of the invention that a line containing a blower opens axially, preferably coaxially, in the rotary drum and is connected to the furnace for supplying hot exhaust gas from the latter. This embodiment has the advantage that considerably less energy is required to generate the gas flow through the rotary drum for the pre-cleaning than for devices with impact bodies.

To further save energy and simplify the structure of the device according to the invention, it can also be provided that the line for the supply air for the fluid bed furnace is connected to the rotary drum for subsequent cleaning, the supply air being supplied through this rotary drum.

In order to be able to use the loading and transport means customary for the containers, it is provided according to the invention that the containers sea containers have corresponding dimensions.

Setting up and starting up the device according to the invention is considerably simplified if, as proposed according to the invention, the device arranged in the containers is, apart from the electrical energy supply, independent of external energy supply.

In order not to overload the foundation on which the device according to the invention is placed and to further reduce the noise pollution, it can be provided according to the invention that the units, in particular the machines in the respective container, are mounted in a vibration-damped manner.

There are various options for dividing the individual units of the device according to the invention into the containers, of which three are generally provided. It can be provided that silos, a filter system and a fluidized bed furnace are arranged in the upper container, that the rotary drums for pre- and post-cleaning as well as a screening system are arranged in the middle container and that a gas system, a compressed air system, a central control and a Dosing device with a downstream mixing screw are arranged. However, an arrangement is preferred which is characterized in that the rotating drum for mechanical, dry pre-cleaning is arranged in the upper container, the furnace for thermal treatment in the middle container and the rotating drum for mechanical subsequent cleaning of the foundry sand in the lower container. This embodiment requires for conveying the debris sand to be regenerated within the Device particularly low energy and is preferably suitable for pilot and / or large systems.

In all embodiments of the invention it can be provided that an elevator for feeding the rubble sand to be regenerated to the loading point provided in the upper container is arranged next to the stacked containers.

The device according to the invention can be accommodated in (used) sea containers. However, it is also possible to arrange the units in container-like containers. It is recommended according to the invention to provide that some of the units arranged in the containers, in particular the containers, the support structure for the rollers and the drives of the rotary drums and / or the fluidized bed furnace, at least partially in the frame, wall, floor and / or Ceiling construction of the affected containers are integrated.

• Figur 1 schematisch den Aufbau einer ersten Ausführungsform einer Vorrichtung zur Regenerierung von Gießereischuttsanden,
• Figur 2 eine zweite Ausführungsform,
• Figur 3 eine dritte Ausführungsform,
• Figur 4 einen Schnitt längs der Linie IV-IV in Figur 3 und
• Figur 5 einen Schnitt längs der Linie V-V in Figur 3.

Further features of the invention result from the following description and the drawings. It shows

• FIG. 1 shows schematically the structure of a first embodiment of a device for the regeneration of foundry rubble sands,
• FIG. 2 shows a second embodiment,
• FIG. 3 shows a third embodiment,
• Figure 4 is a section along the line IV-IV in Figure 3 and
• FIG. 5 shows a section along the line VV in FIG. 3.

The device according to FIG. 1 is arranged in three transportable containers up to III, which are congruent with one another. Quick connections and connecting flanges are provided in the connection levels between the containers in order to connect the units provided in the individual containers to one another. The connections are preferably congruent.

The containers used in the exemplary embodiment have the dimensions standardized for sea containers. For example, they are 12.19 m long, 2.44 m wide and 2.59 m high on the outside.

In the upper container 111 there is a feed silo 2 with a vibrator trough 3 arranged underneath. In addition, a filter system 22 is installed, which filters the exhaust air of the device before being discharged into the open. In addition, a fluidized bed furnace 9 is provided in container III, in which the thermal treatment (second stage of the method according to the invention) of the rubble sand is carried out. Furthermore, a buffer 12 and an output silo 18 are provided in container III.

In the middle container II, a magnetic separator 4, two cylindrical rotary drums 5 and 10, each with a horizontal turning axis 24, and a mechanical screening system 13 are arranged side by side.

Each rotary drum 5 and 10 is assigned a blower 6 or 23.

In the rotary drum 5, the rubble sand is pretreated for pre-regeneration before being placed in the fluidized bed furnace 9, in which the rubble sand is annealed for thermal regeneration.

The rotating drum 10 arranged in the longitudinal direction behind the rotating drum 5 serves for the subsequent cleaning of the rubble sand flowing out of the fluidized bed furnace 9.

In the lower container I, a gas system 20, a compressed air system 21, a buffer store 7 with a pneumatic conveyor 8 arranged underneath, a controller 19, a further pneumatic conveyor 11 and several containers 14 for quartz sand, each with a grain size, are arranged next to one another Containers 14 located sand is withdrawn via a metering system 15 and a downstream mixing screw 16 is fed, which feeds the mixture to a further pneumatic conveyor 17.

The feed silo 2 in the upper container III is a conveyor 1, z. B. feeds an elevator, the hopper 25 is provided at the level of the lower container I near the ground.

A down pipe 26 leads downwards from the discharge silo 18, which ends approximately in the area of the bottom of the middle container II and to which further transport devices can be connected in order to be able to create the regenerate at the place of use.

Since the gas system 20 and the compressed air system 21 are arranged in the lower container I, the device accommodated in the three containers I, II and III only requires an electrical power connection in order to be ready for operation. After loosening the quick-release connections provided between the containers, the containers - each individually - are portable and can be brought to any location. This has the advantage, for example, that the regeneration of different rubble sands can be tested on site under practical conditions.

For noise reduction, in addition to noise insulation, the container itself can advantageously be provided such that the individual units, in particular the machines (vibrator channel 3, magnetic separator 4, the blowers, the pneumatic conveyors, the screening system 13, the metering system 14, etc.) are vibration-damped within the respective container be stored.

• Gießereischuttsand, enthaltend organische und anorganische Bindemittel, wird über den Aufgabetrichter 25 dem Elevator 1 aufgegeben, der den Schuttsand in den Aufgabesilo 2 befördert. Über die Vibratorrinne 3 wird der Schuttsand kontinuierlich über den im mittleren Container II befindlichen Magnetabscheider 4 in die erste zylindrische Drehtrommel 5 gefördert. Während des Förderns auf der Vibratorrinne 3 wird der Schuttsand auf Korngrößen von etwa 5 mm vorzerkleinert.

The embodiment of the device shown in FIG. 1 works as follows:

• Foundry rubble sand containing organic and inorganic binders is fed via the hopper 25 to the elevator 1, which conveys the rubble sand into the feed silo 2. The rubble sand is continuously conveyed via the vibrator trough 3 via the magnetic separator 4 located in the middle container II into the first cylindrical rotary drum 5. During the conveying on the vibrator trough 3, the rubble sand is pre-crushed to grain sizes of approximately 5 mm.

By means of the magnetic separator 4, any remaining pieces of the Cast iron separated and discharged via a down pipe 27.

The first phase of the regeneration takes place in the form of a dry pre-cleaning in the first rotating drum 5. In the rotary drum 5, conventional baffles are provided in the form of sheets, which determine the path of the incoming rubble sand and ensure further comminution. Instead of or in addition to the chicane internals, 5 grinding elements in the form of balls or the like can be provided in the rotary drum, whereby a good comminution of the rubble sand is achieved.

As a result of the rotary movement of the rotary drum 5 about its horizontal axis 24, a grain-to-grain friction in the rubble sand is achieved in addition to the comminution, since the rubble sand is intensively circulated and mixed. As a result, due to the friction of the quartz grains against one another, mechanical residues are removed or ground off. This grain-to-grain friction is further increased by the chicane internals and / or the grinding elements in the rotary drum 5.

During this mechanical and dry pre-cleaning of the rubble sand, it is simultaneously dried and heated in the rotating drum 5 by means of hot air blown in.

The exhaust gas emitted by the fluidized bed furnace 9 is cleaned of dust particles etc. by the filter system 22 and fed to the hot air blower 6 in the line 29 symbolized by arrows, which blows the hot exhaust gases horizontally into the rotary drum 5, preferably coaxially with the axis of rotation 24. In this way, the heat content of the exhaust gas from the fluidized bed furnace 9 can be used and the energy requirement of the overall system can be kept low.

The horizontally entering gas stream dries the rubble sand, for example, up to a water content of 0.5% and takes abrasion and floating particles with it, which are separated by the filter system 22 in the upper container 111 before the gas stream exits.

Through the pre-regeneration of the rubble sand, the sludge content z. B. reduced to 2 to 4%, in particular the binders in the green sand, namely the bentonites are separated and discharged from the quartz grain by grain-to-grain friction.

After passing through the rotary drum 5, the shredded, pre-regenerated and preheated rubble sand falls into the buffer store 7 in the lower container 1, from which it is drawn off via the pneumatic conveyor 8 via a pipeline 28 and fed to the fluidized bed furnace 9 in the container 111.

In the fluidized bed furnace 9, the rubble sand is heated to a temperature of approximately 800 ° C., as a result of which the organic additives such as hardener and binder of the core sand burn. Bentonites that are still active are burned to death and lose their ability to swell. The combustion residues are discharged by air supplied by the fan 30 and filtered out in the filter system 22. The preferably cleaned exhaust gas from the fluidized bed furnace 9 is then fed via line 29 to the intake port of the hot air blower 6 assigned to the rotary drum 5 in the middle container II.

After the fluidized bed furnace 9, the sand reaches the cylindrical rotary drum 10 in the middle container II via a pipeline 35. The rotary drum 10 corresponds in structure to the drum 5, also rotates about the horizontal axis 24 and preferably also has baffles and / or grinding media in the interior such as balls or the like.

Cooling air is fed to the rotary drum 10 horizontally and preferably coaxially to the axis of rotation 24 via a blower 23, which cools the sand in the drum 10 and at the same time discharges the combustion residues of the hardener and binder which have been abraded and ground by grain-to-grain friction. In the rotary drum 10, the post-cleaning and the cooling of the regenerate take place simultaneously, so that voluminous cooling units for the regenerate can be dispensed with.

After the post-cleaning, which is carried out in the rotary drum 10, all residues of binder and hardener such as chemical additives are largely separated. The regenerate falls through a down pipe 31 into the pneumatic conveyor 11 and is conveyed through a pipe 32 into the intermediate storage silo 12 in the upper container 111.

The regrind is then classified by the sieve system 13 according to grain sizes and the grain fractions are temporarily stored in containers 14 in the lower container I.

The undersize (quartz sand dust etc.) is discharged directly via a down pipe 13 into containers (not shown) or other collecting or transport devices.

Quartz sand is drawn off from the containers 14 via the metering system 15 by means of sliders in the ratio corresponding to the desired grain composition of the regrind, mixed in the mixing screw 16 and conveyed by the pneumatic conveyor 17 via a line 34 into the discharge silo 18 in the upper container 111.

The regrind corresponding to the quality of new sand can be withdrawn from the discharge silo 18 via a down pipe 26.

The rubble sand processed in this three-stage regeneration device corresponds to new sand in all quality characteristics, so that the regenerate can be used for all common core manufacturing processes. It should be particularly emphasized that the original beta quartz of the new sand has been converted into alpha quartz due to the thermal treatment in the fluidized bed furnace 9, which is associated with an increase in volume of 0.86 to 1.30%. There is therefore no risk of an increase in volume during the casting process by converting beta quartz into alpha quartz, so that no tensions and cracks can occur in the sand surfaces of the mold and core areas. In contrast, such a conversion will occur when using new sand, so that the occurring Tensions and cracks in the sand surfaces of the mold and core areas are depicted in the cast surface and require an increased amount of cleaning.

The binding agents separated from the quartz sand granules are mainly excreted by flowing air or gas at several points of the device, namely at the magnetic separator 4, the rotary drums 5 and 10, the fluid bed furnace 9, the screening plant 13 and at the discharge silo 18. The exhaust air entraining the binder particles or the exhaust gas of the individual units is conducted to the filter system 22 via a line-dotted line 36 and filtered there, so that largely dust-free exhaust air leaves the device.

The pilot plant shown in FIG. 2 can be used to carry out regeneration tests with old sands or old sand mixtures. This system is mobile so that it can be transported to the centers of selected supply areas. In terms of workflow and process engineering, it corresponds to a large system according to the invention. Furthermore, the pilot plant shown in FIG. 2 has sufficient procedural safeties so that the diversity of the existing old sand mixtures can be managed. Finally, the pilot plant offers the possibility of further optimizing the design of large plants.

The pilot plant shown in Figure 2 is mounted in three containers with internal dimensions of 12020 x 2350 x 2390 mm. All pipelines and electrical supply and control cables are permanently installed within the individual containers, with the containers being connected to one another by means of removable intermediate pieces, quick couplings or plugs. Like the system shown in FIG. 1, the system according to FIG. 2 only requires a power connection, since a gas and compressed air supply is installed in the system itself.

Except for the elevator, all components of the system are housed within the container. The reason that the elevator is located outside the container is that when the elevator is installed inside the container, assembly becomes very complicated.

When the system is in operation, all of its units are easily accessible, and the various levels of the system can be reached by fixed ladders.

The elevator 41 attached to the side of the containers IV, V and Vi has a feed hopper 42 and at its upper end an inlet pipe 43 leading into the upper container VI from above.

In the upper container VI an old sand container 44, a screw conveyor 45, a rotating drum 46 with a horizontal axis and four sand containers 47 (only two are visible) are accommodated.

In the middle container V, a fan 48, a cyclone separator 49, a further fan 50.a fluidized bed furnace 51 with an inlet pipe 52 attached to the side, a fan 53, a grain classifier 54 (Mogensensor), a blast wheel cleaner 55 with an outlet pipe 56 and a riser 57 are accommodated.

In the lower container IV there is a gas tank 90, a screw conveyor 58 connected to the lower end of the cyclone 49, a rotary drum 59, pneumatic conveyors 60, 61 and 62, storage containers 63 for the various grain fractions, which are connected to a screw conveyor 64 on the outlet side, and another sand tank 65.

• Zu regenerierender Altsand wird beispielsweise händisch in den Aufgabetrichter 42 des Elevators 41 aufgegeben und gelangt über das Einlaufrohr43 in den beispielsweise 1 000 kg fassenden Altsandvorratsbehälter 44. Die Förderschnecke 45 fördert Sand dosiert in die Drehtrommel 46, in der Sandknollen zerkleinert, der Sand getrocknet und vorgereinigt sowie vorgewärmt wird.

The pilot plant shown in FIG. 2 operates as follows:

• Used sand to be regenerated is, for example, manually fed into the feed hopper 42 of the elevator 41 and reaches the used sand storage container 44, which can hold 1,000 kg, for example, via the inlet pipe 43. The conveyor screw 45 conveys sand in a metered manner into the rotating drum 46, in which sand tubers are crushed, the sand is dried and pre-cleaned as well as being preheated.

The rotary drum 46 is divided into three sections by internals arranged perpendicular to the drum axis. In the first section, the sand tubers are primarily crushed, which is supported by the use of rod-shaped grinding media. This section is separated from the following section of the rotary drum 46 by a perforated plate, so that only free-flowing sand can get into the next section of the drum. In the middle section of the drum 46, the old sand to be regenerated (rubble sand) is pre-regenerated by grain-to-grain friction, which is supported by a variable proportion of grinding media. The third section of the rotary drum 46 works without grinding media and is mainly used to remove dust from the sand.

The sand contained in the rotary drum 46 is dried, dedusted and preheated by exhaust air from the fluidized bed furnace 51 which is conducted in countercurrent. For this purpose, the fluidized bed furnace 51 is connected via a line 66 with a throttle valve 67.

The sand in the rotary drum 46, which is freed from the abraded fine particles by air sifting and preheated to a temperature of approx. 300 ° C. and has a sludge content of 3-4%, is fed through a pipe 69 at 52 into the fluidized bed oven 51, in with a sand temperature of 700-800 ° C is given up. In the fluidized bed furnace 51, organic binder residues are completely burned and the sand is then fed through an outlet pipe 70 to the rotating drum 59 arranged in the lower container IV.

The rotating drum 59 has the same structure as the rotating drum 46 in the upper container VI and causes the sand to cool to approximately 120 ° C. the cleaning of the combustion residues and the deactivated bentonite as well as the dedusting of the sand.

Both the rotating drum 46 and the rotating drum 59 are designed so that the sand has a residence time of approx. 60 min at a capacity of 0.50 t / h. Has.

Much of the regeneration work required is through the vertical described above Line already done. The sand emerging from the rotary drum 59 has already been sufficiently regenerated in many cases.

The system shown in FIG. 2, however, permits additional post-cleaning of the sand emerging from the rotating drum 59.

For this purpose, the sand emerging from the rotary drum 59 is brought by the pneumatic conveyor 60 via a line 71 into the sand container 47 having four chambers. By optionally actuating the pneumatic quest valves 72 arranged on the container 47, it can be selected in which of the chambers of the container 47 the sand supplied via the line 71 is released. This makes it possible to fill one of the chambers of the container 47, while sand is fed to the centrifugal wheel cleaner 55 from another of the chambers via one of the sliders 73 and the downpipe 74. The centrifugal wheel cleaner 55 is designed so that the cleaning process can be repeated four times during the filling time of one of the chambers of the container .47. The sand passes through the container 65 and the pneumatic conveyor 62 and a sand conveying line 75 into another of the chambers of the container 47 or, after the after-cleaning has been completed, into a third of the chambers of the container 47.

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

The sand cleaned by the centrifugal wheel cleaner 55 and contained in one of the chambers of the container 47 is brought into the classifier 54 via a line. The regrind is broken down into the three most important grain fractions, the separating cuts being selected in such a way that all the usual grain distributions can be produced. The individual grain fractions enter the three-part container 63 through downpipes 76 indicated by dash-dotted lines. The desired quantities of grain fractions are removed from the container 63 via adjustable discharge metering slides 77 and mixed with the screw conveyor 64, the pneumatic conveyor 61 and a line 78 into the fourth Chamber of the container 47 promoted.

The regenerate with the desired particle size distribution can be drawn off from the container 47 via an outlet pipe (not shown).

The fluidizing air required for the fluid bed furnace 51 is supplied by the fan 53 which draws in fresh air. The exhaust gas, which heats up to 700 to 800 ° C. in the fluidized bed furnace 51, is fed to the rotary drum 46 via the exhaust gas line 66 and sucked out of it via a line 78 into a collecting line 79.

A second air flow originating from the centrifugal wheel cleaner 55 or from the classifier 54 is fed as cooling air to the rotary drum 59 via a line 80 and finally also reaches the collecting line 79.

From the collecting line 79, the exhaust air passes through the fan 50 into the cyclone separator 49 and further via a line 81 to the clean gas fan 48 and finally via a line 82 to the outside.

The system is supplied with gas via, for example, a 900 kg tank 90 for liquid gas, which is equipped with all the necessary control and safety fittings. One filling of the tank 90 is sufficient for an operating time of approximately 80 hours.

Furthermore, a compressor (not shown) is provided in the lower container IV, for example to the right of the container 65, which supplies conveying air for the pneumatic conveyors 60, 61 and 62 and furthermore the control air for the pneumatic slide valves 73 and 77.

The dust fraction separated in the cyclone 49 (if desired, two or more cyclones can also be provided) is conveyed via the screw conveyor 58 to a cellular wheel sluice and discharged through it from time to time.

The embodiment of the plant according to the invention shown in FIGS. 3 to 5 is also accommodated in three containers VII, VIII and IX arranged one above the other and is designed for a throughput of 7.5 t / h. In this embodiment, the silos for the rubble sand, the regenerate and the classifying unit are accommodated outside the container, which offers the advantage that the capacity of the plant is expanded to 15 t / h, for example, by installing a second regeneration unit (containers VII, VIII and IX) can be.

In the construction of the embodiment shown in FIGS. 3 to 5, it was assumed not to assemble the individual units in containers as in the embodiments shown in FIGS. 1 and 2, but to design containers and units as a structural unit. For example, the sand containers 101 and 112 are constructed as a wall construction using the frame construction of the container IX. The supporting structure for the accommodation of the rollers and the drives for the two rotary drums 107 and 109 are also the base construction of the containers VII and IX.

The fluid bed furnace 108 is integrated in the container VIII and likewise does not have its own support and wall construction.

The three containers VII, VIII and IX standing one above the other represent a complete regeneration unit, only the two elevators 105 and 145 and the pneumatic conveyor 150 are arranged externally.

• Von einem nicht gezeigten, beispielsweise pneumatischen Förderer wird der zu regenerierende Schuttsand in den sandbehälter 101 im oberen Container IX gefördert. Durch Schwerkraft gelangt der Sand in einem darunter liegenden 5chleuderradreiniger 102 und aus diesem uber ein Vibrationen ausgesetztes Rohr 103 in den Aufgabetrichter des Elevators 105. Zwischen dem Sandbehälter 101 und dem Schleuderradreiniger 102 ist in der diese Aggregate verbindenden Leitung 146 ein Schieber 147, der pneumatisch betätigt werden kann, vorgesehen.

The system shown in Figures 3 to 5 works as follows:

• The rubble sand to be regenerated is conveyed into the sand container 101 in the upper container IX by a pneumatic conveyor, not shown, for example. By gravity Sand in a centrifugal wheel cleaner 102 underneath and from this via a vibration-exposed pipe 103 into the feed hopper of the elevator 105. Between the sand container 101 and the centrifugal wheel cleaner 102, a slide 147, which can be actuated pneumatically, is provided in the line 146 connecting these units .

An adjustable portion (for example 20 to 20%) of the sand conveyed through the line 103 is conveyed by a pneumatic conveyor 148, which is arranged in the lower container VII, into a sand container 106 at the top of the upper container IX, whereas the elevator 105 The rest, for example 70 to 80% of the sand stream, is conveyed back into the sand container 101. This arrangement ensures that the sand passes through the centrifugal wheel cleaner 102 three to five times before it reaches the rotary drum 107 for further treatment. The rotary drum and its function correspond to the rotary drum 46 of the embodiment shown in FIG. 2.

After the rotating drum 107, the pre-regenerated rubble sand passes through a fluidized bed furnace 108 to burn off organic binder residues and then through a rotating drum 109 for subsequent cleaning.

Another pneumatic conveyor 150 arranged in the foundation 149 after the rotary drum 109 and below the lower container VII conveys the regenerated sand into the sand container 112 in the upper container IX. From this sand container 112, the sand reaches a second centrifugal wheel cleaner 151, in which a final cleaning process is carried out. From the centrifugal wheel cleaner 151, the completely regenerated sand passes through a vibro pipe 152 into a pneumatic conveyor 104 which conveys the regenerate, for example, to a mixture silo set up next to the containers VII, VIII, IX.

A device for classifying and mixing the individual grain fractions in the desired ratio, which can have a structure similar to the corresponding device of the plant shown in FIG.

A fan 111 for the fluidized bed furnace 108 is also shown in the lower container VII. The remaining air duct lines are only partially shown in Figures 3 to 5 for clarity. The air flow or exhaust gas flow in the system shown in FIG. 5 corresponds in principle to that of FIG. 2.

Using the method according to the invention and / or using the regeneration system according to the invention, it is possible to largely remove binders and hardener residues, quartz dust (undersize) and other harmful substances from the old sands. This also works with rubble sands composed of green sand and chemically bound core sands.

Regarding the most important quality characteristics, such as grain shape, grain distribution, average grain size and degree of uniformity, the regenerated sand practically corresponds to new sand and it is possible to adapt these quality characteristics to the respective requirements by classifying and classifying them.

The regenerate obtained in accordance with the invention is such that the same strengths as with new sand are possible when used in core making with the same binder additions. It is taken into account that regenerate yields of 75% of the amount of old sand are achieved, so that a mixture of regenerate and new sand of 75:25 can be compared with pure new sand.

Since the rubble sands to be regenerated mainly consist of green sand and chemically bound core sands, the following parameters are decisive for determining the degree of regeneration:

In the following overview, the changes in these parameters due to regeneration are shown and compared with those of new sand.

• 25 unter sonst gleichen Bedingungen praktisch die gleichen Ergebnisse wie reine Neusandmischungen bringt.

It is of considerable importance for the process according to the invention that a regrind is achieved. when used with the same amounts of binder, there is no significant decrease in strength (bending strength in N / cm ² ) of the cores. The strengths were carried out for the binders furan resin, hot box and cold box (US-A-3 409 579) and it was found that a mixture of regenerate / new sand 75:

• 25 produces practically the same results as pure new sand mixtures under otherwise identical conditions.

Both the decisive parameters of the regrind obtained according to the invention and the practical tests have shown that the entire regrind (75% of the amount of rubble sand) can be processed without problems in the core making shop. It should also be noted that the tests were carried out with those types of binders that are particularly sensitive to sand quality.

The most important parameters are shown below:

The following overview summarizes the most important pollutants to be removed during sand regeneration. At the same time it is indicated which degradation is achieved in the individual regeneration stages. The "mechanical 1" level corresponds to the treatment in the rotary drums 5, 46 and 107, the "thermal" process level corresponds to the treatment in the fluidized bed furnace 9, 51 and 108 and the "mechanical II" level corresponds to the treatment in the rotary drums 10, 59 and 109.
(See table on page 11 f.)

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

However, it is also possible (depending on the nature of the rubble rubble) to carry out the dry pre-cleaning in a centrifugal wheel cleaner alone. In this case, the rotary drum is not necessary for pre-cleaning. In order to utilize the heat content of the exhaust gases from the fluidized bed furnace for preheating and drying the rubble sand, a fluidized bed preheater can be provided in addition to the centrifugal wheel cleaner.

These three options for pre-cleaning (rotating drum, centrifugal wheel cleaner with downstream rotating drum and centrifugal wheel cleaner, if necessary with fluid bed preheater) can also be used for post-cleaning, whereby in the case of post-cleaning, the supply air for the fluid bed oven alone is used for post-cleaning in a centrifugal wheel cleaner. in which the thermal regeneration takes place, can be preheated by a fluid bed cooler that cools the sand.

Finally, it is still possible to carry out the pre-cleaning and post-cleaning in one system in different apparatuses or apparatus combinations (rotary drum and / or centrifugal wheel cleaner, if necessary with a hard-bed preheater or cooler).

A centrifugal wheel cleaner which can be used in the context of the invention has a centrifugal wheel rotating about a vertical axis with radial strips, by means of which the sand supplied from above via a pipe coaxial with the axis of rotation is radially accelerated. A fixed baffle ring with a V-shaped recessed baffle surface is arranged coaxially with the centrifugal wheel, whereby the sand radially accelerated by the centrifugal wheel strikes the lower half of the baffle ring, where it is deflected upwards to the upper half of the ring and is essentially deflected radially inwards, whereupon it the sand stream moving to the impact ring falls out of the centrifugal wheel cleaner downwards. The sand is cleaned in this centrifugal wheel cleaner by impacting and rubbing the sand bodies against each other, the latter taking place in particular in the area where the sand stream crosses.

Claims (20)

1. Process for reclaiming foundry scrap sands containing used sand mixtures with organic and inorganic binders, such as active and dead-burned bentonite and synthetic resins and optionally additional slurry materials such as coal dust, polystyrene, fine quartz dust, etc., in which process the comminuted and optionally screened foundry sand is subjected, for removal of organic binders, to a thermal regeneration by heating and subsequently to a final cleaning wherein binder redidues adhering to the sand grains are mechanically removed from the grain surfaces, characterized in that the foundry sand, prior to thermal regeneration, is subjected to a dry precleaning step wherein slurry materials adhering to the sand grains, particularly inorganic binders, are removed from the sand grains, and in that the removed slurry materials are subsequently separated from the thus-precleaned foundry sand, preferably by a gas stream.

2. Process according to claim 1, characterized in that a grain-against-grain friction is effected in the foundry sand during the dry precleaning by intermixing and circulation of the latter about a preferably horizontal axis.

3. Process according to claim 1 or 2, characterized in that the sand grains, during the dry precleaning, are radially accelerated and flung against a fixed impact surface.

4. Process according to one of claims 1-3, characterized in that the content of slurry materials in the foundry sand is reduced during the precleaning step down to 2 % to 4 %.

5. Process according to one of claims 1-4, characterized in that the foundry sand, during the precleaning step, is dried and preheated by warm waste gas resulting from the thermal regeneration.

6. Process according to claim 5, characterized in that the foundry sand is dried down to a water content of 0.5 %.

7. Apparatus for the regeneration of foundry scrap sands, which contain used sand mixtures with organic and inorganic binder components, such as active and dead-burned bentonite and synthetic resins, and optionally additional slurry materials, such as coal dust, polystyrene, fine quartz dust, etc., comprising a furnace (9, 51, 108), preferably a fluidized-bed furnace, wherein the foundry sand is heated for the purpose of processing by annealing, and with a cleaning device arranged downstream of the furnace (9, 51, 108) for the mechanical cleaning of the foundry sand, which device is preferably designed as a rotary drum (10, 59, 109) with an essentially horizontal axis (24) and/or as a centrifugal cleaner (151), characterised in that there is arranged upstream of the furnace (9, 51, 108) a mechanical precleaning device operating without water and designed as a rotary drum (5, 46, 107) rotatable about a substantially horizontal axis (24), in which there are arranged preferably baffle installations and/or grinding elements, such as balls, and/or as a centrifugal cleaner (102) and in that the units of the device are arranged in several portable containers (I, II, 111, IV, V, VI, VII, VIII, IX), there being provided connecting flanges, adapters, coupling means or plug-in connections in the zone of the top and/or the bottoms of the congruently stackable containers (I, II, III, IV, V, VI, VII, VIII, IX) for connecting the individual units of the apparatus.

8. Apparatus according to claim 7, characterized in that there terminates in the rotary drum (5, 46, 107) axially, preferably coaxially, a conduit (29, 66) containing a fan (6), this conduit being connected to the furnace (9, 51, 108) for supplying hot waste gases from the latter.

9. Apparatus according to claim 7 or 8, characterized in that the conduit (70) for the feed air for the fluidized-bed furnace (9, 51, 108) is connected to the rotary drum (10, 59,109) for the final cleaning step, the feed air being supplied through this rotary drum (10, 59, 109).

10. Apparatus according to one of claims 7-9, characterized in that the containers (I to IX) have dimensions corresponding to sea containers.

11. Apparatus according to one of claims 7-10, characterized in that the apparatus arranged in the containers (I to IX) is independent of external energy supply except for the electrical energy supply.

12. Apparatus according to one of claims 7-11, characterized in that the units, especially the machines, in the respective container (I through IX) are mounted with vibration damping.

13. Apparatus according to one of claims 7-12, characterized in that the top container (III) houses silos (2, 12, 18), a filtering installation (22), and a fluidized-bed furnace (9) ; that the middle container (11) houses the rotary drums (5, 10) for the precleaning and final cleaning steps as well as a screening installation (13) ; and that the bottom container (I) houses a gas installation (20), a compressed-air installation (21), a central control unit (19), as well as a metering device (15) with a mixing screw (16) arranged downstream thereof.

14. Apparatus according to one of claims 7-12, characterized in that the top container (VI ; IX) houses the rotary drum (46 ; 107) for the mechanical, dry precleaning step ; the middle container (V ; VIII) houses the furnace (51 ; 108) for thermal treatment ; and the bottom container (IV ; VII) houses the rotary drum (59 ; 109) for the mechanical final cleaning of the foundry sand.

15. Apparatus according to claim 14, characterized in that an elevator (1, 41, 105) for feeding the scrap sand to be reclaimed to the feed point (tank 2 ; 44 ; 101) provided in the top container (III, VI, IX) is arranged beside the containers (I to IX) stacked in superimposed relationship.

16. Apparatus according to one of claims 7-15, characterized in that a centrifugal cleaner (102) is provided between the charging tank (101) and the rotary drum (107).

17. Apparatus according to one of claims 7-16, characterized in that a centrifugal cleaner (55, 131 ) is provided between the rotary drum (10, 59, 109) for the final cleaning step and a classifier unit (13, 54).

18. Apparatus according to one of claims 7-17, characterized in that several of the units arranged in the containers (VII to IX), especially the tanks (101, 102), the supporting structure for the casters and the drive mechanisms of the rotary drums (107, 109) and/or the fluidized-bed furnace (108) are at least partially integrated into the frame, wall, floor and/or ceiling construction of the respective containers (VII to IX).

19. Apparatus according to one of claims 7-18, characterized in that the centrifugal cleaner (102,151) comprises a centrifugal wheel, rotationally driven about a vertical axis of rotation, with strips arranged on its topside, and a fixed impact ring, the inside of this ring that faces the centrifugal wheel being indented in a V-shape ; and that the centrifugal wheel is arranged in the zone of the lower half of the impact ring.

20. Apparatus according to one of claims 7-19, characterized in that the centrifugal cleaner for precleaning the foundry sand is followed by a fluidized-bed heat exchanger connected to the waste gas conduit of the fluidized-bed furnace for thermal regeneration.

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