Method and apparatus for regenerating green sand

Abstract

A method and apparatus for regenerating green sand are provided. In this method and apparatus, during the regeneration of green sand, a first mechanical treatment is applied to the green sand, a thermomechanical treatment is applied to at least a portion of the green sand fraction that has undergone the first mechanical treatment, and a second mechanical treatment is applied to at least a portion of the green sand fraction that has undergone both the first mechanical treatment and the thermomechanical treatment.

Description

Technical Field

[0001] The present invention relates to the recycling of green sand (sand containing a clay-based binder).

Background Art

[0002] Green sand is sand (raw sand) containing a clay-based binder and is used in a casting factory for mold manufacturing (i.e., manufacturing of molds and cores required during metal casting). The casting sand used in a casting factory is typically sand processed from green sand. In this case, a sand fraction with a particle size suitable for the intended use is selected from the green sand, and for example, a clay-based binder is further added to the sand. The clay-based binder includes clay (typically bentonite) and one or more additives (typically at least carbon) added to the clay. With this clay-based binder, the sand can be molded to form a desired mold or core.

[0003] One of the greatest challenges and problems in a casting factory is the final disposal of the used casting sand remaining from the molds. The casting sand used during the production of castings typically generates the same amount as the finished castings on average. Previously, the used casting sand was typically transported to a landfill. However, today, as the reserves of natural sand decrease and environmental regulations become stricter, the recycling of used casting sand for reuse as casting sand or for other purposes is increasing.

[0004] However, for the recycling of used casting sand for reuse as casting sand or for other purposes, typically, the regeneration of the used casting sand is required. The regeneration of the used casting sand is performed so that the regenerated casting sand has properties that can be reused as casting sand or for other purposes.

[0005] For example, mechanical or thermal treatments have been used to recycle used foundry sand. These treatments have aimed to remove impurities from used foundry sand or binders, including clay and additives, that would have interfered with the sand's function in its previous use. More efficient recycling of used foundry sand is needed to enable more effective use of natural resources. This would allow a large portion of the sand, at least once used, to be recycled, thereby reducing the use of natural sand. [Overview of the project]

[0006] The object of the present invention is to provide a novel method and apparatus for regenerating green sand.

[0007] The solution according to the present invention is characterized by the content disclosed in the independent claims.

[0008] The present invention is based on regenerating green sand by applying a plurality of different treatments to green sand in a specific order. Each treatment acts on the green sand at the stage in which the previous treatment has been applied to the green sand, and the action of each treatment assists (supports) the regeneration of the green sand during the subsequent treatment. In the solution according to the present invention, a first mechanical treatment is applied to the green sand, then a thermomechanical treatment is applied to at least a portion of the green sand fraction that has undergone the first mechanical treatment, and subsequently a second mechanical treatment is applied to at least a portion of the green sand fraction that has undergone both the first mechanical treatment and the thermomechanical treatment.

[0009] The first mechanical treatment, thermomechanical treatment, and second mechanical treatment are carried out in this order, efficiently recycling the foundry sand containing the clay binder. Furthermore, after the first mechanical treatment, the spent binder (i.e., spent clay) and additives separated from the binder (particularly carbon) can be recovered, increasing the total amount of various materials that can be recovered and reused.

[0010] The dependent claims illustrate several embodiments of the present invention. [Brief explanation of the drawing]

[0011] The present invention will be described in more detail in relation to preferred embodiments with reference to the following attached drawings.

[0012] [Figure 1] This outlines how to restore green sand. [Figure 2] A schematic diagram of the equipment used to regenerate green sand is shown.

[0013] For clarity, some embodiments of the present invention are shown in simplified form in the figures. In the figures, similar parts are indicated by the same reference numerals. [Modes for carrying out the invention]

[0014] Figure 1 schematically illustrates the main method according to this embodiment for regenerating green sand. Green sand is sand containing a clay binder. The clay binder comprises clay (typically bentonite) and one or more additives (e.g., carbon) added to the clay. Renewable green sand consists of sand grains having a layer of clay binder on their surface. Renewable green sand may include, for example, sand containing clay binder derived from a metal foundry and used in casting. Renewable green sand may also include unused sand containing clay binder left over from the manufacture of casting molds or cores. Typically, the clay binder contains bentonite, but other clay binders can also be used for green sand.

[0015] Referring to Figure 1, the method according to this embodiment includes at least the following steps (1) to (3). (1) Step of applying the first mechanical treatment (first mechanical process) to the green sand. (2) A step of applying a thermomechanical treatment (thermomechanical process) to at least a portion of the green sand fraction that has undergone the first mechanical treatment. (3) The step of applying the second mechanical treatment (second mechanical process) to at least a portion of the green sand fraction that has undergone both the first mechanical treatment and the thermomechanical treatment.

[0016] The purpose of the first mechanical treatment applied to green sand is to mechanically remove clay-based binders and the carbon typically contained in those binders from renewable green sand.

[0017] The purpose of the thermomechanical treatment applied to at least a portion of the green sand fraction that has undergone the first mechanical treatment is to subject the green sand fraction to both a mechanical treatment for separating carbon from the binder remaining in the green sand fraction and a thermal treatment for burning the carbon and evaporating the crystalline water in the binder that still remains in the green sand fraction.

[0018] The purpose of the second mechanical treatment, applied to at least a portion of the green sand fraction that has undergone both the first mechanical treatment and the thermomechanical treatment, is to mechanically separate any binder still remaining in the green sand fraction from it, thereby providing recycled sand.

[0019] Figure 2 schematically shows a device 10 for regenerating green sand. The device 10 in Figure 2 includes an element for performing a green sand pretreatment step 100 (hereinafter also simply referred to as "pretreatment step 100"). In the pretreatment step 100, a first mechanical treatment is applied to the regenerative green sand in addition to several other treatments. The device 10 in Figure 2 further includes an element for performing a green sand thermomechanical treatment step 200 (hereinafter also simply referred to as "thermomechanical treatment step 200"). In the thermomechanical treatment step 200, a further thermomechanical treatment is applied to at least a portion of the green sand fraction that has undergone the first mechanical treatment. Furthermore, the device 10 in Figure 2 includes an element for performing a green sand posttreatment step 300 (hereinafter also simply referred to as "posttreatment step 300"). In the posttreatment step 300, a second mechanical treatment is applied to at least a portion of the green sand fraction that has undergone both the first mechanical treatment and the thermomechanical treatment, in addition to several other treatments. Figure 2 is intended solely to provide a schematic illustration of the structure and operation of the device 10. Depending on the various embodiments of the device 10, the configuration of the device 10 may differ from that shown in Figure 2.

[0020] To perform the green sand pretreatment step 100, the apparatus 10 includes at least one supply device 110. The supply device 110 is configured to receive recyclable green sand and to supply the green sand forward in the regeneration process performed by the apparatus 10. The supply device 110 may include, for example, a supply container (supply box, supply container) and a conveyor positioned in connection with the supply container. The supply container (supply box, supply container) is configured to receive recyclable green sand and to supply the green sand forward by the conveyor in the regeneration process.

[0021] The green sand supplied to the green sand pretreatment step 100 (i.e., the supply device 110) is preferably mostly single-grain sand (i.e., sand with as few lumps as possible and with as few impurities as possible, such as dust). Therefore, at least one crushing device 1 may be provided upstream of the actual device 10 for regenerating the green sand. The crushing device 1 is configured to crush, for example, molds and cores removed from casting applications. This ensures that the sand supplied to the supply device 110 contains as few lumps as possible. Furthermore, at least one separation device 2 may be provided downstream of the crushing device 1 and upstream of the actual device 10 for regenerating the green sand. The separation device 2 is configured to separate dust or other impurities lighter than sand grains from the green sand supplied to the supply device 110 (green sand supplied for regeneration). This separation may be performed, for example, by air classification (dry classification). Thus, the separation device 2 may be, for example, a cyclone. The supply of green sand to the green sand pretreatment step 100 is indicated by arrow F in Figure 2. PT-IN This is outlined by [the relevant source].

[0022] To perform the green sand pretreatment step 100, the apparatus 10 includes at least one first processing device 130. The first processing device 130 is configured to generate a mechanical impact on the green sand supplied to the regeneration process in order to apply a first mechanical treatment to the green sand. The first processing device 130 may be, for example, a grinder. The grinder as the first processing device 130 is configured to crush or prepare the green sand in order to separate the clay-based binder and the carbon that may be contained therein from the mechanically regenerated green sand. The grinder may be, for example, a substantially vertical column grinder (columnar grinder). The column grinder may include, for example, a spiral rotating blade or one or more vanes for applying the mechanical impact to the green sand to be processed. In this case, due to the impact directly acting on the green sand by the blade or vane and the mutual friction of the sand grains generated within the green sand, the binder and the carbon that may be contained therein are removed from the surface of the sand grains. Alternatively, the grinder as the first processing device 130 may be, for example, a substantially horizontal grinder mill. The grinder mill may include two drums rotating relative to each other inside. In this case, the two drums apply a mechanical impact to the green sand supplied between the drums. Thereby, both the impact directly acting on the green sand by the drums and the mutual friction of the sand grains generated within the crushed green sand remove the clay-based binder and the carbon that may be contained therein from the surface of the sand grains.

[0023] The first mechanical treatment generated by the at least one first processing device 130 preferably acts on dry green sand (i.e., green sand that contains no moisture or has at least a very low moisture content) (preferably green sand with a moisture content of less than 1%). Since the moisture content of the green sand supplied from the casting process for regeneration typically exceeds 1% and has conventionally been 1 - 2%, moisture may be removed from the green sand supplied to the first processing device 130 by at least one moisture removal device 120. Thereby, the green sand supplied to the first processing device 130 contains no moisture or very little moisture, and preferably its moisture content is less than 1%.

[0024] In the moisture removal device 120, moisture (i.e., water or a mixture of water and some additive) is removed from the green sand. The moisture removal device 120 may include, for example, at least one solid - liquid separator. The solid - liquid separator separates the liquid (i.e., water or a mixture of water and some additive) mixed in the green sand from the green sand. The separated liquid is schematically indicated by arrow SLQ in FIG. 2. The liquid (arrow SLQ) separated by the moisture removal device 120 may be supplied for further processing, for example, to recover chromite mixed in the liquid (arrow SLQ). The moisture removal device 120 may include, in addition to or instead of at least one solid - liquid separator, at least one heater for evaporating moisture from the green sand supplied to the first processing device 130. The heater may utilize the heat recovered in the thermo - mechanical treatment step 200, for example, as schematically indicated by arrow RHE in FIG. 2. Thus, the moisture removal device 12 has the purpose of removing the moisture of the green sand supplied to the first processing device 130. The moisture content of the green sand fraction proceeding from the moisture removal device 120 to the regeneration process (i.e., the green sand fraction supplied to the first mechanical treatment) is preferably less than 1%. If the green sand supplied to the regeneration process contains no moisture, the moisture removal device 120 is unnecessary.

[0025] According to one embodiment, the first processing device 130 may be integrated with the supply device 110. In this case, the moisture removal device 120, which may be provided in the device 10, is positioned upstream of the combination of the supply device 110 and the first processing device 130 in the flow direction of the regenerative green sand.

[0026] The green sand fraction that has undergone the first mechanical treatment is led from the first processing apparatus 130 to at least one separation apparatus 140. The separation apparatus 140 is configured to separate the clay binder and the carbon removed from the clay binder from the green sand fraction that has undergone the first mechanical treatment. The clay binder removed from the green sand and the carbon removed from the clay binder may be recovered for further processing and / or utilization, as schematically shown by the arrow FPU in Figure 2. The separation of the clay binder removed from the green sand and the carbon removed from the clay binder from the green sand that has undergone the first mechanical treatment may be performed, for example, by air classification. In this case, the separation apparatus 140 may be, for example, a cyclone.

[0027] The green sand fraction discharged from the separation device 140 (the green sand fraction that has undergone the first mechanical treatment, in which the clay binder and the carbon removed from the clay binder have been removed to the maximum extent possible) is led to at least one vibrator 150. In the vibrator 150, vibrational motion is introduced to the green sand for the purpose of breaking up any lumps still present in the sand at this stage, thereby reducing the number or size of the lumps.

[0028] From the vibrator 150, the green sand that has undergone the first mechanical treatment is led to at least one magnetic separator 160. The magnetic separator 160 is configured to separate any ferromagnetic material (e.g., chromite or steel) that may remain in the green sand recovered from the foundry from the green sand fraction that has undergone the first mechanical treatment. Depending on the flow rate of the material being processed or the required separation capacity, the magnetic separator 160 may be equipped with one or more permanent magnets or electromagnets. According to one embodiment, the magnetic separation performed by the magnetic separator 160 may be performed in connection with the vibrator 150.

[0029] From the magnetic separator 160, the green sand fraction that has undergone the first mechanical treatment is supplied to at least one mixing device 170. In the mixing device 170, an additive is added to the green sand fraction that has undergone the first mechanical treatment and mixed. The purpose of this is to promote the removal of alkali metals or alkali compounds (e.g., potassium) remaining in the clay binder from the regenerated green sand. The additive may be a substance containing, for example, aluminum silicate (Al2SiO5, Al2O3·SiO2) or aluminum hydroxide silicate (hydrated aluminum silicate) ((OH)4(Al2O3·2SiO2·2H2O)). The purpose of the additive is to increase the melting temperature of the alkali metal oxides or alkali compounds in the clay binder remaining in the regenerated green sand. This can prevent the alkali metals and alkali compounds from reacting with silicon dioxide on the surface of the sand grains or adhering to the surface of the sand grains. Thus, the additive reacts with alkali metals or alkali compounds in the clay-based binder remaining in the regenerated green sand to form alkali salts that at least partially melt at the temperature used in the thermomechanical treatment. These at least partially melted alkali salts facilitate the removal of impurities, including the alkali metals or alkali compounds, from the regenerated green sand during the thermomechanical treatment step 200. The mixing device 170 may be, for example, a screw feeder. The additive may be added directly to the mixing device 170, or it may be added to the green sand fraction supplied to the mixing device 170 by at least one feeder 180, as schematically shown by arrow BC in Figure 2. The content of the additive in the composition formed by the regenerated green sand and the additive may be, for example, 0.5 to 3 weight percent. The higher the content of the additive in the green sand and additive composition, the lower the pH and electrical conductivity of the regenerated sand. Since a considerable amount of binder has already been removed from the green sand during the first mechanical treatment applied to the regenerated green sand, the amount of additive added to the green sand supplied for thermomechanical regeneration can be kept very small relative to the amount of green sand.

[0030] The composition of the green sand fraction that has undergone the first mechanical treatment and the additives mixed with the green sand fraction is supplied to the thermomechanical treatment step 200. In the thermomechanical treatment step 200, the green sand fraction is further regenerated by simultaneously applying both thermal and mechanical treatments to it. In the apparatus 10 of Figure 2, the thermomechanical treatment step 200 is performed by a heatable rotary kiln 210 (hereinafter also simply referred to as "kiln 210"). The heatable rotary kiln 210 may also be called a heatable and rotatable rotary kiln. The heatable rotary kiln 210 may also be called a heated rotary kiln.

[0031] The heated rotary kiln 210 in Figure 2 is substantially cylindrical and has a first end 210a and a second end 210b (the end substantially opposite to the first end 210a) along the longitudinal direction of the kiln 210. The green sand supplied from the pretreatment step 100 to the thermomechanical treatment step 200 is indicated by arrow F in Figure 2. TM-IN As schematically shown, the green sand is supplied to the first end 210a of the kiln 210. The green sand that has passed through the kiln 210 (i.e., the green sand that has passed through the thermomechanical treatment step 200) is directed to the first end 210a of the kiln 210, as shown by arrow F in Figure 2. TM-OUT As schematically shown, it is removed from the second end 210b of the kiln 210.

[0032] The inner wall of the kiln 210 is typically provided with one or more lifters 212. The lifters 212 extend at least partially in the diametrical direction from the inner wall of the kiln 210 toward the center of the kiln 210, and substantially in the longitudinal direction toward the second end 210b of the kiln 210. The lifters 212 are very schematically shown by dashed lines in Figure 2. Each lifter 212 is configured to capture at least a portion of the green sand supplied to the kiln 210 as the kiln 210 rotates around its axis of rotation. This causes the captured portion of green sand to move along the inner surface of the kiln 210 until it falls to the bottom of the kiln 210. The kiln 210 is rotated by a variable-speed motor (motor 214). The rotational speed of kiln 210 is typically about 5 to 20 revolutions per minute, depending on, for example, the diameter and / or filling rate of kiln 210.

[0033] The lifter 212 may be positioned at an inclined location schematically shown in Figure 2. This allows the lifter 212 to guide and increase the passage of green sand from the first end 210a to the second end 210b of the kiln 210. A similar effect can be provided or enhanced by positioning the kiln 210 at an inclined location such that the first end 210a of the kiln 210 is higher than the second end 210b of the kiln 210, as schematically shown in the embodiment of Figure 2. The total inclination (angle of inclination) from the first end 210a to the second end 210b of the kiln 210, provided by the lifter 212 and / or the position of the kiln 210, may be, for example, 0.5 to 5 degrees.

[0034] The kiln 210 in Figure 2 further comprises at least one heating device 216. The heating device 216 is configured to heat the internal space of the kiln 210 and the green sand fraction supplied to the kiln 210. In Figure 2, the heating device 216 is located at the first end 210a of the kiln 210. Alternatively, the heating device 216 may be located in the internal space of the kiln 210 (for example, in the vicinity of the first end 210a of the kiln 210). The heating device 216 may be, for example, a gas burner, a plasma gas burner, a liquid gas burner, or other burner. Other devices may be used instead of, or in addition to, the burner to heat the internal space of the kiln 210 and the green sand fraction supplied to the kiln 210. The first end 210a may also be referred to as the supply end.

[0035] The kiln 210 in Figure 2 further comprises at least one exhaust device 218. The exhaust device 218 is, for example, an exhaust fan or an exhaust blower. The exhaust device 218 is configured to remove exhaust gas and particulate matter (e.g., fumes) generated from the internal space of the kiln 210 during the processing of the green sand fraction. In Figure 2, the exhaust device 218 is located at the second end 210b of the kiln 210. Alternatively, the exhaust device 218 may be located in the internal space of the kiln 210, for example, in the vicinity of the second end 210b of the kiln 210. In relation to the exhaust device 218 or its exhaust gas channel, at least one heat recovery device 220 may be provided. The heat recovery device 220 is configured to recover heat from the exhaust gas from the kiln 210. The recovered heat can be used, for example, to remove moisture from the green sand to be processed in the manner described above in relation to the green sand pretreatment step 100, and / or to preheat the green sand fraction supplied to the thermomechanical treatment step 200. The power of the exhaust system 218 is adjusted, for example, based on the filling rate of the kiln 210, so that the amount of air flowing through the kiln 210 is, for example, about 1000 to 3000 normal cubic meters per hour. This air can flow through the kiln 210, for example, through the same channel through which the green sand fraction supplied to the thermomechanical treatment is supplied to the kiln 210, or through one or more air supply channels 240 separately located in the kiln 210.

[0036] In the apparatus 10 of Figure 2, the green sand fraction, which has undergone a first mechanical treatment and to which the aforementioned additives have been added, is supplied to the first end 210a of the kiln 210. This causes the green sand fraction to pass through the flame of a burner used as a heating device 216, preferably toward the bottom of the kiln 210. This effectively initiates heating of the green sand fraction inside the kiln 210. Simultaneously, the kiln 210 is rotated by a rotary motor (motor 214). As a result, each lifter 212 captures at least a portion of the green sand fraction supplied to the kiln 210. This causes the captured green sand fraction to move along the inner circumference of the kiln 210 until it returns to the bottom of the kiln 210. This causes the sand grains to form a kind of sand cloud inside the kiln 210. The formation of this sand cloud makes it possible to heat the green sand fraction substantially uniformly within the internal space of the kiln 210. The temperature of the green sand fraction being processed in kiln 210 can be measured by a temperature sensor. This measured temperature can be used, for example, to adjust the power of the heating device 216 and / or the rotational speed of kiln 210. This ensures that the temperature and residence time of the green sand fraction reach appropriate levels for regeneration within kiln 210. The temperature of the green sand fraction in kiln 210 during thermomechanical processing is preferably about 500 to 850°C, and the residence time of the green sand fraction is about 10 to 60 minutes.

[0037] As the regenerated green sand fraction rotates along the kiln 210 and falls to the bottom of the kiln 210, mechanical shocks (i.e., mechanical treatments acting on the green sand fraction being processed in the kiln 210) are generated on the regenerated green sand fraction. As a result, the clay binder is removed from the surface of the sand grains, and carbon-containing dust is removed from the clay binder. The carbon removed from the clay binder is burned inside the kiln 210. This reduces the amount of dust generated in the process. The exhaust gas and unburned particulate matter generated by the combustion are discharged from the kiln 210 via the exhaust device 218.

[0038] The heating of the green sand being regenerated in kiln 210 affects the heat treatment of the green sand fraction being processed in kiln 210. As a result, the crystalline water in the clay-based binder remaining on the surface of the sand grains evaporates from the binder. Once the crystalline water evaporates from the binder, it becomes easier to remove the binder from the surface of the sand grains in the post-treatment step 300 following the thermomechanical treatment step. In the post-treatment step 300, a second mechanical treatment is applied to at least a portion of the green sand fraction that has passed through the thermomechanical treatment step 200.

[0039] As previously described, an aluminum silicate additive is mixed into the green sand fraction supplied to kiln 210. The purpose of this is to facilitate the removal of alkali metals or alkali compounds (e.g., potassium) remaining in the clay binder from the green sand fraction being regenerated. The additive reacts with the alkali metal oxides or alkali compounds in the binder remaining in the green sand fraction supplied to kiln 210, forming alkali salts that at least partially melt at the sand processing temperature in kiln 210, for example, 500-850°C. At least partially melted alkali salts are generated in the green sand fraction being processed in kiln 210. As a result, impurities from the binder in the green sand being regenerated adhere to the partially or completely melted alkali salts, forming aggregates that adhere to each other. These aggregates further collect both sand grains and impurity particles still remaining in the green sand fraction being regenerated. This results in the formation of aggregates resembling grains, for example, about 5-10 millimeters in diameter. Such aggregates can be separated from the green sand discharged from kiln 210 by known methods, such as sieving.

[0040] Thus, in the thermomechanical treatment, additives containing aluminum silicate are added to the recycled green sand, causing impurities in the sand to aggregate and form aggregates resembling grains, for example, about 5-10 millimeters in diameter, depending on the equipment used and / or the method of application of the thermomechanical treatment. These aggregates move along the recycled green sand, carrying together alkali metals or alkali compounds and other impurities attached to the aggregates until they are separated from the green sand. The use of a rotary kiln 210 in the thermomechanical treatment of the green sand fraction promotes contact between different particles. This allows these particles to be subjected to an impact sufficient to form the aforementioned grains.

[0041] The green sand discharged from the second end 210b of the kiln 210, along with any remaining agglutinations in the green sand, is fed to at least one separator 230. The separator 230 is configured to separate the agglutinations generated by the green sand thermomechanical treatment from the green sand fraction discharged from the kiln 210 (i.e., the green sand fraction that has undergone both the first mechanical treatment and the thermomechanical treatment). The separation of agglutinations by the separator 230 is performed before the second mechanical treatment is applied to the green sand fraction discharged from the kiln 210. The separator 230 may, for example, comprise one or more sieves. The mesh of the sieves is sized so that the agglutinations do not pass through the sieve set. The green sand fraction that has passed through the separator 230 forms the green sand fraction that has undergone both the first mechanical treatment and the thermomechanical treatment, and is fed to a post-processing step 300 which includes the second mechanical treatment. This green sand fraction is indicated by arrow F in Figure 2. ATーIN As schematically shown in Figure 2, the material is fed forward into the regeneration process and led to the post-processing step 300. The aggregates separated by the separation device 230 are removed from the regeneration process as waste for further processing, as schematically shown by the arrow WT in Figure 2.

[0042] Thus, the green sand fraction that has undergone both the first mechanical treatment and the thermomechanical treatment is supplied to the post-treatment step 300. In the post-treatment step 300, the green sand fraction is further regenerated by applying a second mechanical treatment to it. In the apparatus 10 of Figure 2, the second mechanical treatment is performed in the rotary kiln 310 (hereinafter also simply referred to as "kiln 310"). The rotary kiln 310 simultaneously constitutes a cooling device (i.e., a cooling kiln) for cooling the green sand fraction heated by the thermomechanical treatment. In other words, the second mechanical treatment is performed in the cooling kiln (kiln 310) to cool the green sand fraction heated by the thermomechanical treatment.

[0043] The rotary kiln 310 in Figure 2 is substantially cylindrical. The kiln 310 has a first end 310a and a second end 310b substantially opposite to the first end 310a in the longitudinal direction of the kiln 310. The green sand supplied from the green sand thermomechanical treatment step 200 to the green sand post-treatment step 300 is indicated by arrow F in Figure 2. ATーIN As schematically shown, it is supplied to the first end 310a of the kiln 310. The clean sand that has been regenerated by passing through the kiln 310 (i.e., the green sand that has also passed through the second mechanical processing step) is directed to arrow F in Figure 2. ATーOUT As schematically shown, the material is removed from the second end 310b of the kiln 310. The kiln 310 is rotated by a variable-speed motor 314. The rotational speed of the kiln 310 is typically about 5 to 20 revolutions per minute. The residence time (time spent passing through the kiln 310) of the green sand processed in the kiln 310 is about 5 to 30 minutes, depending, for example, on the diameter and / or filling rate of the kiln 310.

[0044] The kiln 310 in Figure 2 includes at least one second processing apparatus 320 in a first portion of the kiln 310 near the first end 310a of the kiln 310. The second processing apparatus 320 is configured to generate mechanical impact on the green sand supplied to the kiln 310, thereby acting a second mechanical treatment on the green sand. The second processing apparatus 320 may be, for example, a grinder configured to crush the green sand supplied to the kiln 310. The crushing by the grinder is performed to mechanically remove any clay-based binder that may still remain in the regenerated green sand from the green sand fraction supplied to the kiln 310. The grinder may be a ball mill, as schematically and partially shown in Figure 2. The ball mill comprises a plurality of balls 322 arranged inside the kiln 310. As the kiln 310 rotates, the balls 322 move inside the kiln 310, and as they move, they mechanically impact the green sand, acting a second mechanical treatment on the green sand. During the thermomechanical treatment, crystal water has already been removed from any clay-based binders that may still be present in the green sand fraction supplied to kiln 310. Therefore, this second mechanical treatment, acting on the green sand through impact and friction between the sand grains, makes it easier to remove the binder from the surface of the sand grains.

[0045] In the apparatus shown in Figure 2, at least one second processing device 320 is integrated with the kiln 310 to apply the second mechanical treatment to at least a portion of the green sand fraction that has undergone both the first mechanical treatment and the thermomechanical treatment. However, this at least one second processing device 320 may be a separate device from the kiln 310 and may be positioned in front of (upstream of) the kiln 310 in the flow direction of the regenerated green sand.

[0046] The inner wall of the kiln 310 is typically provided with one or more lifters 312. The lifters 312 extend in the diametrical direction from the inner wall of the kiln 310 toward the center of the kiln, and in the longitudinal direction substantially toward the second end 310b of the kiln 310. The lifters 312 are very schematically shown by dashed lines in Figure 2. Each lifter 312 is configured to capture at least a portion of the green sand supplied to the kiln 310 from the bottom of the kiln 310 as the kiln 310 rotates around its axis of rotation. This causes the captured green sand to move along the inner circumference of the kiln 310. This movement continues until the captured portion of green sand, the binder removed from the green sand, and any other fine particles that may be present in the green sand return to the bottom of the kiln 310. The binder, along with other particles lighter than the green sand, forms a dust cloud within kiln 310. This dust cloud is removed from kiln 310 in a manner that will be described in detail later.

[0047] The lifter 312 may be positioned at an inclined location schematically shown in Figure 2. This allows the lifter 312 to guide and increase the passage of green sand from the first end 310a to the second end 310b of the kiln 310. A similar effect may be provided or enhanced by positioning the kiln 310 at an inclined location such that the first end 310a of the kiln 310 is higher than the second end 310b of the kiln 310, as schematically shown in the embodiment of Figure 2. The total inclination (angle of inclination) from the first end 310a to the second end 310b of the kiln 310, provided by the above-described positioning of the lifter 312 and / or the kiln 310, may be, for example, 0.5 to 5 degrees. This total inclination (angle of inclination) is an angle compared to the horizontal level.

[0048] The kiln 310 in Figure 2 further comprises at least one exhaust device 330. The exhaust device 330 is located outside the kiln 310 at the first end 310a of the kiln 310. Alternatively, if possible, the exhaust device 330 may be located at least partially inside the kiln 310 at the first end 310a of the kiln 310. The exhaust device 330 may be, for example, an exhaust fan or an exhaust blower. An air supply channel 340 is located at the second end of the kiln 310, leading from outside the kiln 310 to the inside of the kiln 310. The exhaust device 330, together with the air supply channel 340, is configured to generate an airflow that flows from the second end 310b of the kiln 310 toward the first end 310a of the kiln 310 and is discharged from the kiln 310 via the exhaust device 330. The airflow contains air drawn in from the external environment of the kiln 310 (typically air at the ambient temperature of the kiln 310) and forms a cooling airflow within the kiln 310. The cooling airflow flows from the second end 310b of the kiln 310 toward the first end 310a of the kiln to cool the green sand fraction within the kiln 310, and is then discharged from the kiln 310 via the exhaust device 330. At the same time, the airflow removes from the kiln 310 the binder removed from the green sand, as well as other particulate matter that is lighter than the green sand and may still remain in the green sand.

[0049] The power of the exhaust system 17 is controlled so that only the binder removed from the green sand and any other particulate matter that may still be present in the green sand are discharged from the kiln 310 along the cooling airflow, and the green sand that has been purified from the binder and other impurities is not carried away. The binder and particulate matter may be separated in the airflow by a filter or the like and led to further processing. If cooled air at a temperature lower than the ambient temperature around the kiln 310 is available, this cooled air may be used to cool the green sand fraction being processed in the kiln 310. The power of the exhaust system 330 is adjusted so that the amount of air flowing through the kiln 310 is, for example, about 1000 to 3000 normal cubic meters per hour, based on the kiln 310's filling rate, for example.

[0050] The clean green sand regenerated by passing through kiln 310 (i.e., the sand that has gone through the first mechanical treatment, thermomechanical treatment, and second mechanical treatment) is indicated by arrow F in Figure 2. ATーOUT As schematically shown, it is removed from the second end 310b of the kiln 310.

[0051] The apparatus 10 in Figure 2 further comprises at least one classifier 350. The classifier 350 is configured to receive the green sand fraction that has passed through the kiln 310 and classify it into at least two recycled sand fractions of different particle sizes. The recycled sand fractions thus classified are schematically shown in Figure 2 by arrows RS1 and RS2. The classifier 350 may, for example, comprise one or more sieves. According to one embodiment, the mesh size of the sieve may be, for example, 2 millimeters. This directs the first recycled sand fraction that has passed through the sieve (arrow RS1) to be used for a specific first application (e.g., reuse as foundry sand), and the second recycled sand fraction that has not passed through the sieve (i.e., a coarse-grained recycled sand fraction) (arrow RS2) to be used for other applications.

[0052] A solution involving a first mechanical treatment, a thermomechanical treatment, and a second mechanical treatment in that order effectively regenerates foundry sand containing a clay-based binder. Furthermore, the addition of an aluminum silicate additive to the green sand fraction supplied for thermomechanical regeneration can effectively remove alkali metals or alkali compounds from the regenerated green sand. If alkali metals or alkali compounds remain on the surface of the sand grains, they can hinder the binder's function when the regenerated green sand is used, potentially impairing or at least weakening the usability of the regenerated green sand, for example, as foundry sand. Additionally, the recovery of the binder and the carbon removed from the binder in the pretreatment step of the green sand to be regenerated increases the total amount of various materials recovered and reused from the process.

[0053] In the apparatus 10 of Figure 2, at the end of the pretreatment step 100, an additive is added and mixed to the green sand fraction supplied to the thermomechanical treatment step 200. This can facilitate the removal of alkali metals or alkali compounds from the clay binder still present in the recycled green sand from the recycled green sand in the thermomechanical treatment step. However, the solution of the present invention is also applicable to methods and apparatuses in which the thermomechanical treatment acts on green sand that has undergone the first mechanical treatment, in such a manner that the clay binder and carbon removed in the first mechanical treatment (preferably ferromagnetic materials as well) are removed from the green sand as much as possible, even without the addition of the aforementioned additive to the green sand supplied to the thermomechanical treatment step 200. If the aforementioned additive is not added to the green sand supplied to the thermomechanical treatment step 200, alkali metals or alkali compounds in the green sand are not efficiently removed from the recycled green sand. This type of recycled sand is still very suitable for reuse in many different applications, such as aggregate in various products in the construction industry (e.g., concrete).

[0054] It will be apparent to those skilled in the art that the fundamental concept of the present invention can be implemented in many different ways as the art progresses. Therefore, the present invention and its embodiments are not limited to the examples given above and can be modified as appropriate within the scope of the claims.

Claims

1. A method for restoring green sand, Before applying the first mechanical treatment to the green sand, the steps include removing moisture from the green sand, A step of applying the first mechanical treatment described above to green sand, wherein the first mechanical treatment involves grinding the green sand with at least one grinder in order to separate the clay-based binder and the carbon in the binder from the green sand, The steps include separating the binder and carbon removed from the green sand by at least one separation device from the pulverized green sand to form the green sand fraction that has undergone the first mechanical treatment, The steps include applying a thermomechanical treatment to at least a portion of the green sand fraction that has undergone the first mechanical treatment, The steps include applying a second mechanical treatment to at least a portion of the green sand fraction that has undergone both the first mechanical treatment and the thermomechanical treatment, A method for providing this.

2. In the thermomechanical treatment of the green sand, the green sand fraction that has undergone the first mechanical treatment is supplied to a heated rotary kiln (210), A mechanical treatment for separating carbon from the clay-based binder remaining in the green sand fraction after the first mechanical treatment, The carbon is burned, and a thermal treatment is performed to evaporate the crystal water from the clay-based binder remaining in the green sand fraction after the first mechanical treatment. The method according to claim 1, characterized by applying both of the following:

3. By adding and mixing at least one additive to a thermomechanically treated green sand fraction, the melting temperature of alkali metals or alkali compounds in the green sand is increased. In the thermomechanical treatment, the reaction of at least one additive with the alkali metal or alkali compound generates a partially or completely molten alkali salt, and during the thermomechanical treatment, the alkali salt collects green sand and impurity particles, thereby forming a separable aggregate from the green sand fraction after the thermomechanical treatment. The method according to claim 1 or 2, characterized by the features described herein.

4. Before applying the second mechanical treatment to the green sand fraction that has undergone both the first mechanical treatment and the thermomechanical treatment, at least one separation device is used to separate the aggregates generated in the thermomechanical treatment from the green sand fraction that has undergone the thermomechanical treatment. The method according to feature 3.

5. The aforementioned additive includes at least aluminum silicate. The method according to claim 3 or 4, characterized by the features described herein.

6. In the second mechanical treatment, in order to remove the clay-based binder remaining in the green sand fraction that has undergone both the first mechanical treatment and the thermomechanical treatment from the green sand fraction, at least a portion of the green sand fraction is crushed to form regenerated green sand that has undergone the first mechanical treatment, the thermomechanical treatment and the second mechanical treatment. The method according to any one of claims 1 to 5, characterized by...

7. The steps include supplying the green sand fraction that has undergone both the first mechanical treatment and the thermomechanical treatment to at least one grinder, In order to remove the clay-based binder remaining in the green sand fraction after both the first mechanical treatment and the thermomechanical treatment from the green sand, the green sand fraction is crushed. To form recycled green sand after the first mechanical treatment, the thermomechanical treatment, and the second mechanical treatment, the steps include removing the binder removed in the crushing step from the grinder, The method according to 6, characterized by comprising:

8. The second mechanical treatment is performed in a cooling kiln (310) for cooling the green sand fraction heated by the aforementioned thermomechanical treatment. The method according to claim 6 or 7, characterized by the features described herein.

9. A device (10) for regenerating green sand, At least one moisture removal device (120) for removing moisture from the green sand supplied to the first processing device (130), A first processing apparatus (130) configured to provide a mechanical impact to be applied to the green sand in order to subject the green sand to a first mechanical treatment, the first processing apparatus (130) comprising a grinder configured to crush the green sand in order to remove a clay-based binder from the green sand, To form the green sand fraction that has undergone the first mechanical treatment described above, at least one separation device (140) for separating the binder and the carbon removed from the binder from the crushed green sand, A rotary kiln (210) that can be rotated and heated is used to apply a thermomechanical treatment to at least a portion of the green sand fraction that has undergone the first mechanical treatment, A second processing apparatus (320) configured to provide a mechanical impact to be applied to the green sand in order to apply a second mechanical treatment to at least a portion of the green sand fraction that has undergone both the first mechanical treatment and the thermomechanical treatment, A device equipped with the following features.

10. The rotatable and heatable rotary kiln (210) is configured to subject the green sand fraction that has undergone the first mechanical treatment to both a mechanical treatment for separating carbon from the clay-based binder remaining in the green sand fraction and a thermal treatment for burning the carbon and evaporating the crystal water from the clay-based binder remaining in the green sand fraction. The apparatus according to feature 9.

11. A supply device (180) for adding at least one additive to the green sand fraction treated by the thermomechanical treatment in order to raise the melting point temperature of alkali metals or alkali compounds in the green sand, A mixing device (170) for forming a mixture of the green sand fraction and an additive to be treated by the thermomechanical treatment, wherein the formation of the mixture generates at least partially or completely melted alkali salts by the reaction of the at least one additive with the alkali metal or alkali compound in the thermomechanical treatment, and the alkali salts collect green sand and impurity particles during the thermomechanical treatment, thereby forming separable aggregates from the green sand fraction after the thermomechanical treatment, The apparatus according to claim 9 or 10, characterized by comprising:

12. The system includes at least one separation device (230) configured to separate the aggregates generated by the thermomechanical treatment from the green sand fraction that has undergone the thermomechanical treatment, before applying the second mechanical treatment to the green sand fraction that has undergone the thermomechanical treatment. The apparatus according to feature 11.

13. The second processing apparatus (320) is a grinder, The grinder is configured to form recycled green sand after undergoing the first mechanical treatment, the thermomechanical treatment, and the second mechanical treatment, by crushing at least a portion of the green sand fraction that has undergone both the first mechanical treatment and the thermomechanical treatment in the second mechanical treatment to remove the clay-based binder contained in the green sand fraction. The apparatus according to any one of claims 9 to 12.

14. It is further equipped with a cooling kiln (310), The grinder is a ball mill having a ball (322) placed inside the cooling kiln (310), The ball (322) moves within the cooling kiln (310) as the cooling kiln (310) rotates, and during this movement, it applies a mechanical impact to the green sand so as to apply the second mechanical treatment to the green sand. The apparatus according to feature 13.

Images