EP0125384A1 - Method of regenerating used foundry sand and device for carrying out the method - Google Patents

Abstract

Process for the regeneration of foundry sand by thermal and mechanical processing with separation of the fine fraction. Device with a comminution tool (4) rotating in a container (3) at high speed and with devices (1) for the supply of heat. preferably burner, and for separating the fines, preferably blowers. The thermal and mechanical processing takes place simultaneously in one and the same container (3). while at least one burner (1) or a gas line is provided for the device on the same container (3), in which at least one comminution tool (4) is also arranged.

Description

The invention relates to a method for the regeneration of foundry sand by thermal and mechanical processing with separation of the very fine fraction and also relates to an apparatus for performing such a method.

There are various molding sand systems in the foundry, namely those in which inorganic binders e.g. Clay, the others in which organic binders, e.g. Synthetic resin, including those using a volatile solvent-containing binder. The latter sand system mainly serves the mask molding process; that with synthetic resin as a binder mainly serves for core molding; and for the areas outside the core, prefabricated sand with clay is mainly used as a binding agent.

A molding sand system with clay is the cycle in which the finished sand is put into the mold, does its actual molding work during casting, is emitted as old sand after emptying and is at least partially mixed with new sand, bentonite, water and coal dust, so that at correct dosing and mixing the finished sand is created again.

With such a molding sand system with clay, which is used in many places in today's technology, there is an ongoing need for new sand. Among other things, this is to compensate for losses, replace sand, and is also used to manufacture cores that contain synthetic resin as a binder. The losses arise when the molds are emptied after casting, for example when cleaning, knocking out, etc. The sand quality for the production of the cores is generally higher than that for the production of the other finished sand in the outer moldings, so that often after casting the decay of the inserted cores is already a good compensation for the loss of sand in the molding sand system with clay.

In the known molding sand systems with clay, therefore, the need for new sand is increasingly concentrated on the sand for the cores, i.e. New sand with high quality.

Experience has shown that large quantities of old sand are taken to the dumps as waste after the molds have been emptied, on the one hand to compensate for the excess through the core feed and on the other hand to keep the average quality of the circulating old sand at a constant value.

The aim of the experts and also of the present invention is to process the waste sand as well as possible in order to obtain a new sand with such good quality that the core can also be formed therewith, and there is obviously great economic interest in the treatment of the waste sand because of this Transport and storage incur additional costs.

As a result of the known reprocessing plant for used sand and in particular the ongoing core feed in the molding sand system, the sand quality required for this is continuously sufficiently achieved, so that, for example, an improvement or enlargement of reprocessing plants for sand with the lower quality is no longer required. But there is certainly a need for new sand or processed old sand with the higher quality for the creation of the cores. In order to achieve this sand with the higher quality, neither the mechanical nor the thermal regeneration of used sand is sufficient in itself, but a combination of thermal and mechanical processing of used sand is required.

Such methods for the regeneration of used sand by thermal and mechanical processing are known per se. For example, DE-OS 31 03 030 describes such a method in which used sand is metered into a fluidized bed furnace and is thermally treated and heated by hot gases in such a way that the fine grain can already be separated. All of the old sand is dried in this fluidized bed furnace, and the clay and bentonite are stripped of their binding capacity and plasticity. The embrittled bentonite crusts lying around the quartz grains are fed to an impact mill with a downstream sifter after cooling the thermally treated sand mixture in accordance with the known method. The solid binder residues or crusts are removed in this impact mill and the quartz grains are, so to speak, rubbed bright, whereby the rubbed-off fine material is separated from the heavier quartz grains in the classifier.

With sufficiently intensive thermal and subsequent mechanical treatment of the old sand, this known method can actually give a 'higher quality similar to that of the new sand.

The disadvantage, however, is the high energy expenditure of the known system, which essentially results from investigations in that the entire amount of sand in the fluidized bed furnace has to be heated to about 870 ° C. In other words, each quartz grain is heated up to the core. This is understandable because the thermal conductivity of the quartz is higher than that of the bentonite shell. In order to ensure that all binder constituents or bentonite casings around the quartz grains have the required temperature even during the mechanical processing, it is necessary in the separate, previous heating stage with its entire mass (through and through) to the required final temperature bring. But this means the supply of a disadvantageously large amount of heat.

The object of the invention is therefore to improve a method for regenerating foundry sand of the known and initially described type so that less energy is required Tigt and a lower investment is sufficient to create a device for performing the method.

This object is achieved in that the thermal and mechanical processing takes place simultaneously in one and the same container. In contrast to the known methods, a separate thermal and separate mechanical treatment is not carried out, which was previously considered indispensable, but is simultaneously divided and rubbed off while the material to be treated is heated. In another view, the comminution takes place during the heating, so that the heating of a strongly moving mass is carried out with all the advantages that result from this.

From a microscopic point of view, the energy saving with the method according to the invention can be explained by the fact that not the entire grain of sand, including the binder casing, but only the casing is heated, so that obviously a smaller amount of heat is sufficient for the required minimum treatment of the used sand.

The mechanical processing or reprocessing of the used sand is preferably carried out in the event of a stormy movement while achieving friction and impact effects. In any case of mechanical treatment, freshly embrittled shell parts or binder parts are chipped off by the heating and are ready for removal. Even before the heat can penetrate the grain of sand, as it were during the supply of heat, the abrasion effect occurs through the simultaneous shredding.

If one proceeds according to the teaching of the invention according to the above features, experience has shown that the sand end product only has a temperature of 100 ° to 400 ° C., preferably 250 ° to 300 ° C. Obviously, it is on average a much smaller amount of heat, which for thermal loading action within the meaning of the invention must be supplied in comparison to that of the known method.

In order to further increase the efficiency of the method according to the invention, it is expedient if the fines are sucked off during the thermal and mechanical processing. Since only the remaining parts have to be processed and thermally treated during this simultaneous suction of the fines, the mass to be heated is becoming less and less while increasing the efficiency. The sludge, the grain diameter of which is generally less than 20µm, is considered to be a very fine fraction.

In an advantageous further embodiment of the invention, the temperature and / or the degree of purity of the sand mixture being processed is or are measured during the thermal and mechanical treatment, and the measurement result is used as a control signal for setting the intensity of the thermal and / or mechanical action on the Used in Sarean mix. The moisture and temperature measurement can be carried out contactlessly or by sensors, and conclusions can be drawn from the measurement signal for the creation of control signals which are used, for example, to increase the performance of the firing or increase the speed of the comminution tool, but on the other hand a change in the dwell time can also be expedient .

It advantageous even if the purity of the preparation in befi.dlichen _S andgemisches is measured by applying a Teilme ge entnomme of the sand mixture present in purification and tested separately during the Urd _A ufbereitungsvorganges. When taking samples, for example, the topping age can be determined with great accuracy in a very short time. If one converts these measurement or test results into control signals, one can change the performance of the heat supply devices or the mechanical processing tools as well as the dwell time or processing time of the goods to be treated. Such sampling can be carried out at short intervals so that optimal preparation is achieved.

The efficiency of the regeneration process according to the invention can be further improved when processing old sand containing lumps by pre-grinding prior to the thermal and mechanical processing for crushing large lumps in the sand mixture at a lower temperature than the temperature reached in the thermal processing. Then you get better access to the heat supply to the individual bentonite shells of the grains of sand, to which a thermal shock is supplied by the process according to the invention, so that the sheath jumps off and is immediately sucked off as a fine fraction, preferably during processing.

It is also expedient according to the invention if the sand mixture is mixed with a volatile solvent or a low-melting binder in the final stage of the thermal treatment. This type of coating of the grains of sand is already known, for example for the mask molding process. In the known methods, however, after the binder containing the volatile solvent has been applied, the solvent must be added subsequently; introduced hot air or heated by hot gases and caused to evaporate. Through the measures according to the invention, the heat still available from the regeneration can be used immediately to evaporate the solvent in an accelerated manner. In addition to binders with solvents, binders in powder form with a low melting point, preferably below 400 ° C., are also used. In conventional processes, these binders also supply heat for melting, for example in the form of hot air, while according to the invention the heat required for melting is already contained in the sand to be coated. Both methods ensure particularly good utilization of the available energy. In contrast to conventional systems, where heating, rubbing and wrapping take place in separate machines according to the invention, these machining operations are carried out in one and the same machine, as a result of which temperature and time losses, for example due to transport routes, are avoided. The thermal efficiency of the process is additionally improved by under these conditions that the heat not only from the outside with the be _k to _n - must be initiated th loss of heat transfer in the grain of sand, but is included in this.

The device for carrying out the method according to the invention has a comminution tool rotating in a container at high speed and devices for supplying heat, preferably a burner or gas line, and for separating the very fine particles, preferably a blower, and is characterized in that at least one burner or a gas line is provided on the same container in which the comminution tool is also arranged. The above-described economical regeneration process according to the invention can be done in this way with a. perform very simple device. As a result, capital expenditure and maintenance are advantageously ensured, even when the process is carried out with high efficiency. The use of the high-speed or high-speed comminution tool allows great turbulence to be created in the material to be treated, which is not only advantageous for suction after the embrittled binder casings have been knocked off. The burner gas flame or the biting gases generated by an oil burner can act on a turbulently moving material to be processed, so that it can be guaranteed with great certainty that the heat used acts primarily on the binder casing and causes embrittlement, so that the heat of the sand grain which has been thermally prepared shortly thereafter opens up the comminution tool allows the desired mechanical processing, after which the very fine fraction is separated and is expediently removed immediately.

The thermal shock mentioned above occurs where the sand comes in the burner flame or the hot gases pass by, and the embrittled clay shell can be knocked off shortly afterwards in the desired manner.

When using a container which can be more or less sealed on all sides and in which the old sand is acted on for a certain time, the regeneration process can be carried out continuously or in batches. When using the known impact mills, the processing or dwell time is only very short and is usually only a few seconds. When using the device according to the invention, the dwell time can be set much higher; it is a few minutes even in continuous operation if this is desired. Batch operation can be particularly cheap because machines with high turbulence generation can then be used, high mechanical energy can be introduced with intensity and the residence time can nevertheless be set more precisely. For example, the quality (degree of purity) of the end product in the manner described above allows the possibility of control and precise adjustability of the residence time.

It is also advantageous according to the invention if the burner and / or the comminution tool are attached such that they can be folded out of the container. Despite the simultaneous thermal and mechanical processing in one and the same container, simple, easy-to-use and maintainable machines can be used.

It is particularly advantageous if, according to the invention, the axis of the tube introducing the fuel gas or hot gas into the container is parallel to the axis of rotation of the comminution tool and the gas introduction tube is fastened to the closure cap of the container at a distance from the comminution tool. When using a burner, it is expedient if the axial direction of the burner flame is parallel to the axis of rotation of the comminution tool. It is favorable to use cylindrical containers in which the preparation takes place, the container axis then also lying parallel to the axis of rotation of the shredding tool and to the burner flame. Instead of the axial direction of the burner flame, one can also consider the axial direction of the flowing hot gases, because it is expedient to carry out the thermal treatment of the old sand at one point in the container and the mechanical treatment at a certain distance from it at the other point in the container.

It is particularly advantageous if, according to the invention, the gas introduction tube is fastened in the lower edge region of the container in the case of a container rotatably driven about an axis set at an angle to the perpendicular. Such cylindrical, rotatably driven containers are already known in processing and mixing machines. Your axis of rotation is set at an angle to the perpendicular, for example 10 ° to 60; preferably 20 to 50 °. 30 ° is an advantage that has been tried and tested on many machines, which results in a lower area and an upper area when the container is viewed from above. If wall scrapers are used, these are usually arranged in the upper region, while according to the invention the burner or a biting gas pipe are fastened in the lower edge region of the container. Of course, the _B ends rennergasausströmrohr or oil burner hot gas tube at a distance from the container base and the container has feed and discharge openings, preferably in the lid and bottom.

It is expedient according to the invention if the burner or the gas line is arranged in front of the comminution tool as seen in the direction of rotation of the container. This ensures that the rubbing of _S takes place andkornes before the heat in the interior of _S can penetrate andkornes, because after heating the grain of sand along the shortest path arrives in no time in engaging portion of the crushing tool. This also improves efficiency further.

The shredding tool can be driven at an adjustable speed, so that it can be adapted to the respective task (e.g. recovery of different old sands or recovery for different reuse). The suction can take place through at least one tube which projects into the container of the comminution machine. The tube can be designed to be pivotable and the immersion depth can be adjusted in order to carry out the suction at the most favorable point with the desired turbulence.

• Figur 1 teilweise schematisiert und im Schnitt die Seitenansicht einer Aufbereitungsmaschine gemäß der Erfindung mit angesetztem Brenner,
• Figur 2 eine Draufsicht auf die Maschine der Figur 1 in ' Richtung der Drehachse des Zerkleinerungswerkzeuges,
• Figur 3 eine ähnliche Ansicht wie Figur 1, jedoch mit der Ausführungsform mit herausklappbarem Brenner und Zerkleinerungswerkzeug und
• Figur 4 in ähnlicher Darstellung wie Figur 1 eine weitere ; andere Ausführungsform für die Verwendung eines ölbrenners.

Further advantages, features and possible uses of the present invention result from the following description in conjunction with the drawings. Show it:

• FIG. 1 is a partially schematic and sectional side view of a processing machine according to the invention with the burner attached,
• FIG. 2 shows a plan view of the machine of FIG. 1 in the direction of the axis of rotation of the comminution tool,
• Figure 3 is a view similar to Figure 1, but with the embodiment with a fold-out burner and crushing tool and
• Figure 4 in a similar representation as Figure 1 another; another embodiment for the use of an oil burner.

The device for regenerating or reprocessing foundry sand has a machine frame 6 fastened to a base frame 15, which carries a rotatable container 3, the axis of rotation 16 of which is set against the solder 17 at an angle of 25 °. This container is cylindrical with a cylindrical jacket-shaped side wall, which is closed at the bottom by a fixed base 18 and at the top by a cover 19 fixed to the machine frame 6. The container 3 is driven by a motor 13, which is only partially visible in FIGS. 1, 3 and 4.

The angular inclination of the container axis of rotation 16 results in an upper region inside the container 3, which is located on the right in the figures, and an opposite lower region. In the upper area, a wall scraper with a deflector 14 is fastened to the cover 19, the guide plate of which can be arranged in an L _- shape (and extending in an arc shape over the container bottom 18) along the walls. Eccentric to the axis of rotation 16 of the container 3 is the axis of rotation 20 of the comminution tool 4, which is as parallel to the axis 16 as the axis 21 of the burner flame 2 or axis 21 'of the hot gases 2'. These axes 21 and 21 'are also those of the gas introduction pipes 22 and 22' of the burner 1 on the one hand and the hot gas line 12 on the other hand.

The bottom 18 of the container 3 can be closed by a closure lid 5 or can be opened by pivoting the bottom closure lid 5 about the axis of rotation 23 in the direction of the dash-dotted, curved line 24. The comminution tool 4 is driven by the electric motor 7. The bottom closure cover 5 is driven by a hydraulic unit 8.

In FIG. 2, the closure flap 25 of the input opening located below and not shown can be seen from above, the curved, dashed line 14 illustrating the wall wiper and material deflector. A fines extraction device can be connected to the flange 27.

It can be seen for the embodiment according to FIGS. 1 to 3 that the axis 21 of the burner hot gas introduction tube 22 is arranged in the lower edge region of the container 3 at a distance from the comminution tool 4.

In the case of the embodiment in FIG. 4, a hot gas line 12 with the hot gas introduction tube 22 ′ is provided instead of the burner, the hot gases being generated by the combustion chamber 11. This in turn is the oil burner 10 nachge switches. This leads to a more complete combustion of the oil.

If the machine is to be moved from the functional position in FIGS. 1 and 2 to the maintenance position, the pivoting takes place around the pivot bearing 9. In the embodiment in FIG. 4, the hot gas line 12 must be removed from the cover 19 beforehand.

Claims (11)

1. A method for regenerating foundry sand by thermal and mechanical processing with separation of the fines, characterized in that the thermal and mechanical processing takes place simultaneously in one and the same container (3). 2. The method according to claim 1, characterized in that the fines are sucked off during the thermal and mechanical processing. 3. The method according to claim 1 or 2, characterized in that during the thermal and mechanical processing the temperature and / or the degree of purity of the sand mixture being processed is / are measured and the measurement result as a control signal for adjusting the intensity of the thermal and / or mechanical Acting on the sand mixture is used. 4. The method according to claim 3, characterized in that the degree of purity of the sand mixture being processed is measured by removing a portion of the sand mixture being processed and testing it separately during the processing operation. 5. The method according to any one of claims 1 to 4, characterized in that prior to the thermal and mechanical processing for crushing large lumps in the sand mixture at a lower than the temperature reached in the thermal treatment, a pre-crushing takes place. 6. The method according to any one of claims 1 to 5, characterized in that the sand mixture in the final stage of the thermal treatment with a volatile solvent tendency or a low-melting binder is added. 7. Device for performing the method according to one of claims 1 to 6, with a in a container (3) rotating at high speed comminution tool (4) and with devices (1; 12) for the supply of heat, preferably burner (1) or gas line (12), and for separating the very fine particles, preferably blowers, characterized in that at least one burner (1) or a gas line (12) is provided on the same container (3), in which at least one comminution tool (4) is also arranged is. 8. The device according to claim 7, characterized in that the burner (1) and / or the crushing tool (4) from the container (3) are attached foldable (Fig 3). 9. Apparatus according to claim 7 or 8, characterized in that the axis (21, 21 ') of the fuel (2) or hot gas (2') in the container (3) introducing tube (22, 22 ') parallel to the axis of rotation (20) of the comminution tool (4) and the gas introduction tube (22, 22 ') at a distance from the comminution tool (4) is fastened to the closure lid, (19) of the container. 10. Device according to one of claims 7 - 9, characterized in that in a container (3) rotatably driven about an axis (16) set at an angle to the perpendicular (17), the gas introduction tube (22, 22 ') in the lower edge region of the container ( 3) is attached. 11. Device according to one of claims 1 to 10, characterized in that the burner (1) or the gas line (12) is arranged in the direction of rotation of the container (3) in front of the comminution tool (4).

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