JP6445334B2 - Recycling of recovered foundry sand - Google Patents

Description

  The present invention relates to a method for reclaiming recovered foundry sand, and more particularly to a method for advantageously reclaiming recovered foundry sand recovered from a mold formed by a foundry sand composition using a water-soluble binder. .

  Conventionally, after molding a mold using a foundry sand composition in which an organic compound such as a phenol resin is mainly kneaded as a binder with a foundry sand, and casting with the obtained mold, The recovered foundry sand obtained by crushing the mold after use (demolding) has the binder used, so the recovered foundry sand is recycled and reused. Sometimes. Various methods such as a wet regeneration method, a heating regeneration method, and a dry regeneration method have been proposed and practiced for a long time as a method for regenerating such recovered foundry sand.

  Thus, if the binder to be kneaded into the foundry sand is an organic compound, the recovery of the recovered foundry sand is relatively easy due to the heat history and firing at the time of casting. When an inorganic binder is used, the recovered casting sand cannot be regenerated as in the case of organic compounds, and an effective regenerating method has not been established.

  In addition, as a method of reclaiming the recovered foundry sand from the mold using water glass as the binder, conventionally, as disclosed in Patent Document 1, the particles of foundry sand are 590 μm or less. After aligning the size, it is inserted into a high temperature furnace, the sand particles are heated while slowly stirring, and fired at a temperature of about 900 to 1100 ° C. to burn and sublime the sodium silicate, A regeneration and recovery method is known in which sand particles are added with water and filtered, and then neutralized so that the pH value of the sand particles is about 7, and then the sand particles are dried.

  However, the sand obtained by such a regeneration treatment method, from which sodium silicate used as a binder has been removed from its surface, can be used again as recycled foundry sand, In addition to the need for particle size adjustment operations such as mold crushing and classification before the binder removal treatment, the subsequent binder removal treatment is also performed at high temperature heating, cooling, washing, Drying and many processes are required. For this reason, the amount of energy consumed is very large, and it takes time to regenerate. Therefore, there are problems that the regeneration cost increases, and that a large regeneration plant is required.

  Furthermore, as another regeneration method, there is also a regeneration method by polishing as disclosed in Patent Document 2, in which 0.5 to 20 parts by mass of water is added to 100 parts by mass of recovered sand. Then, after performing the hydrogenated polishing process for performing the polishing process, a technique of regenerating the foundry sand by further performing a dry polishing process is employed. This method is intended to make it possible to remove the residual resin easily by adding a small amount of water to the collected sand so that it can be efficiently removed.

  However, a method for reclaiming foundry sand by combining such hydrogenated polishing treatment and dry polishing treatment is a mold that is molded by using a water-soluble phenol resin as a binder and curing it with an organic ester compound. Therefore, when an inorganic adhesive such as water glass is used, it is difficult to adopt it as it is. However, since such inorganic binders are inherently water-soluble, they become difficult to dissolve in water and hard to peel off due to the heat history and firing action during casting. Then, the binder on the sand surface could not be sufficiently polished and removed by polishing, which was insufficient for the regeneration of the recovered foundry sand.

JP-A-6-344076 JP 2008-30120 A

  Here, the present invention has been made in the background of such circumstances, and the problem to be solved is that the removal rate of binder and impurities is high, and casting quality and mold strength are advantageous. An object of the present invention is to provide a simpler method for reclaiming recovered foundry sand that can be improved.

  Then, as a result of intensive studies on the recovery method of recovered foundry sand, the present inventors have found that the above-described problems can be solved in various ways as listed below, and complete the present invention. It came to. Each aspect described below can be adopted in any combination. In addition, aspects or technical features of the present invention are not limited to those described below, and can be recognized based on the inventive concept that can be grasped from the description of the entire specification. Should be understood.

(1) A method for reclaiming recovered foundry sand to which a water-soluble binder has adhered, wherein the recovered foundry sand and water are accommodated in a container and pressurized to a pressure of 0.1 MPa or more, and 100 ° C. A method of reclaiming recovered foundry sand, comprising performing a polishing step of polishing the recovered foundry sand in a state heated to the above temperature.
(2) The method for reclaiming recovered foundry sand according to the aspect (1), wherein the amount of water used is 30 to 200 parts by weight with respect to 100 parts by weight of the recovered foundry sand.
(3) The method for reclaiming recovered foundry sand according to the aspect (1) or the aspect (2), wherein the heating temperature is in a range of 100 to 300 ° C.
(4) The method for reclaiming recovered foundry sand according to any one of aspects (1) to (3), wherein the pressure is in a range of 0.1 to 10 MPa.
(5) The method for reclaiming recovered foundry sand according to any one of aspects (1) to (4), wherein the binder is mainly composed of a water-soluble inorganic binder.
(6) The method for reclaiming recovered foundry sand according to the aspect (5), wherein the inorganic binder is a silicate compound.
(7) The polishing step further includes storing a polishing stone in a container, and the recovered foundry sand is polished by the polishing stone by rotating the container or stirring the contents in the container. The method for reclaiming recovered foundry sand according to any one of the above aspects (1) to (6), characterized in that:
(8) The regeneration method according to the aspect (7), wherein the amount of the grinding stone used is a ratio of 30 to 300 parts by mass with respect to 100 parts by mass of the recovered foundry sand.
(9) In the polishing step, a polishing layer formed of an abrasive is provided on the inner surface of the container, and the recovered foundry sand removes the polishing layer by rotating the container or by stirring the contents in the container. The method for reclaiming recovered foundry sand according to any one of modes (1) to (6), wherein the method is a step of polishing with a polishing material to be formed.
(10) The recovery according to any one of the modes (7) to (9), wherein the stirring is performed using a stirring blade or a drum blade that is rotatable in a container. Casting sand recycling method.
(11) The polishing step is a step in which a pair of polishing rollers are arranged in the container, and the recovered foundry sand is polished by the polishing roller by rotation of the polishing roller. The method for reclaiming recovered foundry sand according to any one of modes (1) to (6).
(12) Any of the above aspects (1) to (11), wherein the recovered foundry sand is recovered foundry sand recovered from a mold formed using a sodium silicate-based binder. A method for reclaiming the recovered foundry sand according to claim 1.
(13) The aspect (1), further comprising, after the polishing step, a neutralization step of neutralizing the contents in the container and a drying step of drying the reclaimed foundry sand. Thru | or the reproduction | regeneration method of the recovery foundry sand as described in any one of the said aspects (12).
(14) After the polishing step, the method further includes a moisture removal step of removing moisture by filtration or centrifugation under normal pressure or reduced pressure, and a drying step of drying the reclaimed foundry sand. The method for reclaiming recovered casting sand according to any one of the aspects (1) to (12), characterized in that:
(15) The above aspect (13) or the above aspect, further comprising a fine powder removing step of removing the fine powder of the binder separated from the recovered foundry sand with a dust collector after the drying step. 14) The recovery processing method of the recovery foundry sand described in 14).
(16) The method for reclaiming recovered foundry sand according to any one of aspects (1) to (15), wherein the heating and pressurization are performed by blowing water vapor.

  In such a method for reclaiming recovered foundry sand according to the present invention, when the recovered foundry sand is brought into contact with water under specific heating and pressurizing conditions, the binding agent adhering to the foundry sand is dissolved in water. The effect is that it is easy to be peeled off, and the binder can be easily removed by polishing in that state, so that efficient regeneration can be performed. Is played.

It is longitudinal cross-sectional explanatory drawing which shows the state of 1 process in 1st Embodiment of the reproduction | regeneration method of the recovery foundry sand according to this invention. It is longitudinal cross-sectional explanatory drawing which shows the state of 1 process in 2nd Embodiment of the reproduction | regeneration method of the recovery foundry sand according to this invention. It is principal part cross-sectional explanatory drawing of the drum part of the apparatus used for 2nd Embodiment shown by FIG. It is principal part cross-sectional explanatory drawing corresponding to FIG. 3 which shows the other form of the drum part of the apparatus used for 2nd Embodiment shown by FIG. It is longitudinal cross-sectional explanatory drawing which shows the state of 1 process in 3rd Embodiment of the reproduction | regeneration method of the recovery foundry sand according to this invention. It is AA cross-section explanatory drawing in FIG.

  First, the recovered foundry sand used in the method for reclaiming recovered foundry sand according to the present invention is a method of crushing a mold formed using a foundry sand composition in which a water-soluble binder is kneaded with a foundry sand (mold Used casting sand obtained by separating, and having a binding agent attached to the surface thereof. The recovered foundry sand is obtained from a used mold obtained by casting a cast metal by pouring a molten metal, and is cast at the stage of the molded mold without being used for casting. In addition, it is possible to target a solidified or hardened material in the state of a foundry sand composition without being used, and any of them may be mixed. Here, the above-mentioned used foundry sand is desirably present in a ratio of 5% by mass or more, more preferably 10% by mass or more, and further preferably 20% by mass or more of the recovered foundry sand.

  The polishing employed in the present invention is an operation in which the binding agent adhering to the sand surface is scraped and peeled off from the recovered foundry sand by collision or friction with the abrasive. The material of the abrasive is preferably a material that is harder than the aggregate and binder constituting the recovered foundry sand, and the abrasive itself is not scraped off by polishing, and particularly has a Mohs hardness of 7 The above will be used suitably. Specific examples include inorganic materials such as quartz, alumina, zirconia, silicon nitride, and silicon carbide. Further, the form of the abrasive is not particularly limited as long as the recovered foundry sand can be polished, and a known form can be appropriately employed. The formed solid stones having a predetermined solid shape, a polishing layer in which the inner surface of the container is formed of an abrasive, a polishing roller in which a cylindrical outer peripheral surface is formed of an abrasive, and the like are preferably used.

  By the way, the binder adhering to the recovered foundry sand targeted in the regeneration treatment method according to the present invention contains a water-soluble binder as a main component, and is used in the form of an aqueous solution. Even in such a water-soluble binder, a water-soluble inorganic binder, particularly a water-soluble silicic acid compound typified by water glass or the like, is preferably used in the present invention. Examples of the silicate compound include sodium silicate, potassium silicate, sodium metasilicate, potassium metasilicate, lithium silicate, ammonium silicate, colloidal silica, and alkyl silicate. With respect to the recovered foundry sand obtained by using sodium silicate (sodium silicate) as a binder, the coated sand obtained is difficult to block, difficult to absorb moisture, and more difficult to mold after molding. Thus, the present invention is advantageously applied.

Then, such a sodium silicate, usually by the molar ratio of SiO ₂ / Na ₂ O, are classified into types 1 No. 5 No. are used. Specifically, sodium silicate No. 1 has a SiO ₂ / Na ₂ O molar ratio of 2.0 to 2.3, and sodium silicate No. 2 is SiO ₂ / Na ₂ O The molar ratio is 2.4 to 2.5, and the sodium silicate No. 3 has a SiO ₂ / Na ₂ O molar ratio of 3.1 to 3.3. In addition, sodium silicate No. 4 has a SiO ₂ / Na ₂ O molar ratio of 3.3 to 3.5, and sodium silicate No. 5 has a SiO ₂ / Na ₂ O molar ratio. Is 3.6 to 3.8. Among these, sodium silicate Nos. 1 to 3 are also defined in JIS K1408. These sodium silicates may be used in combination as well as used alone, or by mixing or adding additives such as sodium hydroxide, SiO ₂ / Na ₂ It is also possible to adjust the molar ratio of O.

In addition, the sodium silicate used as a binder changes the solubility in water depending on the molar ratio of SiO ₂ / Na ₂ O. Specifically, if the molar ratio is 2.6 or less, It is easy to dissolve in water, and from around 2.6, the solubility in water will decrease, so it is used at a molar ratio in the range of 2.0 to 2.6. Although it is more desirable, the regeneration method according to the present invention allows regeneration even at a molar ratio in the range exceeding 2.6 where the solubility in water is low.

  Further, as the refractory aggregate (casting sand) constituting the recovered foundry sand targeted in the present invention, it is a refractory substance that functions as a base material of a mold, and has been conventionally used for molds. Any of the above refractory granular materials can be used. Specifically, general sand such as silica sand and recycled silica sand, special sand such as alumina sand, olivine sand, zircon sand, chromite sand, and ferrochrome-based slag can be used. Slag particles such as ferronickel slag and converter slag, spherical or porous particles such as alumina particles and mullite particles, and regenerated particles thereof; alumina balls, magnesia clinker and the like. These refractory aggregates may be fresh sand, or reclaimed sand or recovered sand that has been used once or a plurality of times as casting sand for casting molds. Even mixed sand made by adding new sand to sand or recovered sand and mixing them can be used. Such a refractory aggregate is generally used as a particle having an AFS index of about 30 to 110, preferably about 60 to 80 or less.

  By the way, when molding a mold, the conventional binders containing water-soluble inorganic compounds and the like as essential components may contain various known additives as required. Specifically, Solid metal oxides, salts, carbohydrates, surfactants, coupling agents, lubricants, mold release agents, etc. will be added as appropriate, but when these additives are added, in the recovery of recovered foundry sand Because it becomes difficult for the binder adhering to the foundry sand to dissolve in water and the binder becomes difficult to peel off from the foundry sand, the addition of such an additive makes it difficult to regenerate the recovered foundry sand. However, according to the recycling method according to the present invention, even the recovered foundry sand to which such an additive is added has a feature that it can be regenerated without problems.

  Further, in the present invention, the foundry sand composition obtained by kneading the binder and the aggregate is not limited to a dry one, and any casting sand composition may be used. The recovered foundry sand obtained from the mold using the product can also be regenerated by the regenerating method of the present invention. In addition, according to the amount of water contained in the foundry sand composition, it is assumed here that it is in a dry state when it is less than 0.5% by weight, and is wet when the amount of water is 0.5% by weight or more. We classify as thing of state. In the case of a dry state, the foundry sand composition is used as a coated sand in which a binding agent covers a refractory aggregate (casting sand). Although this dry molding sand composition itself is not sticky, the coating layer on the surface of the aggregate is dissolved by aeration of water vapor or the like, and dried as a wet casting sand composition. Can be solidified or cured. Further, the wet casting sand composition is in the form of sticky sand containing moisture, and the wet casting sand composition in such a state is molded and heated to dry, thereby solidifying. Or it can be cured.

  Hereinafter, in order to clarify the first embodiment of the method for recycling recovered foundry sand according to the present invention more specifically, the form of a representative process will be described in detail with reference to FIG. I decided to. It should be understood that the illustrated steps are examples and are not limited thereto.

  First, in FIG. 1, the container 1 is pressure-resistant, and when the lid 1a is closed, the inside of the container 1 can be sealed. The container 1 is provided with a ventilation path 2 and an exhaust path 3 communicating with the inside of the container so as to penetrate the lid 1a. Therefore, the air passage 2 is connected to a pump 4 that supplies pressurized air, while the exhaust passage 3 is open to the atmosphere, and the opening and closing valve 5 can open and close the passage. In addition, a motor 6 is disposed at the lower part of the container 1, and a rotating shaft 6a of the motor 6 is penetrated into the container 1 in a sealed state, and a stirring blade 7 is attached to the rotating shaft 6a. By driving the motor 6, the inside of the container 1 can be stirred. The container 1 is provided with a heater (not shown) capable of heating the inside, the internal temperature can be adjusted, and a thermometer (not shown) or a pressure gauge (not shown) for measuring the internal temperature. (Not shown) is provided so that the temperature and pressure inside the container can be measured. In addition, in this embodiment, although the ventilation path 2 and the exhaust path 3 are provided separately, it is also possible to provide them collectively.

  And the reproduction | regeneration procedure of the recovery foundry sand according to this invention using this container shown in FIG. 1 is the order of a preparation process, a heating / pressurizing process, a polishing process, a cooling / depressurizing process, a moisture removing process, and a drying process. It will be done in.

  Therefore, in the first preparation step, a predetermined amount of recovered foundry sand 8 and water are accommodated in the container 1, and further, alumina balls as the grinding stone 9 are accommodated, and the lid 1 a of the container 1 is provided. , Closed. At this time, the on-off valve 5 of the exhaust passage 3 is left open. Here, the amount of the recovered foundry sand 8 and water contained in the container 1 is preferably about 20 to 50% of the capacity of the container 1.

  Next, in the heating / pressurizing step, the inside of the container 1 is heated to a predetermined temperature with a heater (not shown), while the on-off valve 5 is closed and the pump 4 is operated, so that the pressurized air is contained in the container 1. To be sent to. And when the inside of the container 1 is heated with a heater, the pressure inside the container 1 will be further raised. While checking the pressure gauge and thermometer attached to the container 1, the inside of the container 1 is adjusted to a set temperature: 100 ° C. or higher, pressure (gauge pressure): 0.1 MPa or higher, and the motor 6 is driven. The contents are stirred and kneaded by rotating the stirring blade 7.

  In the polishing process caused by stirring and kneading the contents, the polishing process is continued for a predetermined time (for example, 30 minutes) at a set temperature and pressure. In this embodiment, the temperature and pressure are constant at, for example, 180 ° C. and 1.0 MPa. However, by controlling heating and pressurization, the temperature and pressure are gradually increased in a region above the set value, It is also possible to raise or fluctuate in steps.

  In such a polishing process, when the recovered foundry sand 8 is brought into contact with water under the heating and pressurizing conditions under the above-described setting conditions, the binding agent adhering to the recovered foundry sand 8 becomes water. It becomes easy to melt | dissolve and will be in the state which peels easily. In this state, the recovered foundry sand 8 and the grinding stone 9 are agitated and kneaded by the rotation of the stirring blade 7, and the recovered foundry sand 8 and the abrasive stone 9 repeat mechanical collision and rubbing. Effective polishing of the recovered foundry sand 8 can be performed by the collision energy and friction of friction at this time. As described above, the binder of the recovered foundry sand 8 is easily peeled off and polished, whereby the binder adhering to the recovered foundry sand 8 is easily peeled off, and further, under a predetermined heating / pressurized state. When the binder becomes soluble in water, the binder is effectively removed from the recovered foundry sand 8. At this time, when the binder is dissolved in water under a predetermined heating and pressurizing condition, when receiving a high-temperature heat history by casting, or when it is difficult to dissolve in water by the addition of additives Further, even when a high molar ratio sodium silicate that is not soluble in water at normal temperature and normal pressure is used, the binder can be easily removed, so that the surface of the recovered casting sand 8 can be removed. Recycled foundry sand from which the binder was removed was advantageously obtained.

  In the subsequent cooling / decompression step, heating by the heater is stopped, and the on-off valve 5 is gradually opened to cool and depressurize the inside of the container 1. The cooling may be performed using the same cooling means as in the prior art. For example, the cooling flow path is provided in the container 1 and the cooling is performed by circulating an appropriate cooling medium such as cooling water. There is nothing wrong with going.

  Further, in the water removal step subsequent to the cooling / decompression step, the contents taken out from the container 1 are separated into reclaimed foundry sand and treatment liquid by filtration. In addition, as a method of filtration, in particular, when the amount of water is small with respect to recycled casting sand in the contents, specifically, the ratio of water is 30 to 100 parts by mass of recycled casting sand. When the amount is 80 parts by mass, suction filtration using a decompression action may be performed, and by adopting this suction filtration operation, even if there is little moisture, it can be easily separated by filtration. Of course, even when the amount of water is large, it is possible to remove the moisture by the suction filtration operation using the pressure reducing action as described above. Further, in this moisture removal step, centrifugation is cited as a preferable method in addition to filtration, but the means is not particularly limited as long as it can be separated into recycled foundry sand and treatment liquid. . In addition, although the process liquid obtained at this moisture removal process will be processed as a waste liquid, it can also be reused after performing an appropriate measure.

  And in the last drying process, drying operation is given using dry air, heating dry air, etc. with respect to the reproduction | regeneration casting sand obtained by removing operation as mentioned above and removing a binder. Although this drying method is not particularly limited, the transpiration of water needs to be performed quickly.For example, a method in which heated dry air is blown simultaneously with regenerated foundry sand and kneading is employed. It is desirable that the water content be removed within 5 minutes, preferably within 3 minutes. In addition, in this drying process, it is desirable that drying is performed until water becomes a ratio of 0.5 parts by mass or less with respect to 100 parts by mass of the foundry sand. Through the above steps, reclaimed foundry sand obtained by reclaiming recovered foundry sand is obtained.

  By the way, the shape of the grinding stone 9 used in the first embodiment as described above is not particularly limited as long as it is a stone having a particle diameter larger than that of the recovered foundry sand 8 formed of a polishable material. A spherical shape is desirable so as not to be chipped or damaged by impact during stirring and kneading. Moreover, as the magnitude | size, it is desirable that it is a size of the range of diameter about 1 mm-50 mm larger than the collection | recovery foundry sand 8. Specifically, ceramic balls, quartz balls, alumina balls, zirconia balls, silicon nitride balls, silicon carbide balls, and the like are preferable.

  Further, if the amount of the grinding stone 9 used is too small, it becomes difficult to perform the polishing sufficiently. If it is too large, the grinding stone is damaged due to the collision between the grinding stones. A ratio of 30 to 300 parts by mass, preferably 50 to 200 parts by mass, and more preferably 80 to 150 parts by mass is employed with respect to 100 parts by mass of the above. The amount of the grinding stone 9 used varies depending on the speed of rotation and stirring of the container, and is preferably a small amount if the speed is fast, and a large amount if the speed is slow.

  Furthermore, the heating temperature in the container 1 employed in the polishing step according to the present invention is 100 ° C. or higher, generally 100 to 300 ° C., preferably 120 to 200 ° C., more preferably 150 to 180 ° C. In this way, the binder adhering to the recovered foundry sand 8 is easily dissolved in water by being heated to 100 ° C. or higher. In addition, when this heating temperature becomes too high, energy cost will be required and heat resistance will be required for the packing etc. for maintaining a sealed state, Therefore 300 degrees C or less is preferable. The heating method is not particularly limited as long as the inside of the container 1 can be heated, other than installing a heater in the container 1, and heating by an oil bath or microwave may be performed.

  In addition, the pressure applied in the container 1 employed in the polishing process according to the present invention is a gauge pressure of 0.1 MPa or more, generally 0.1 to 10 MPa, preferably 0.3 to 5 MPa, more preferably Is 0.5-3 MPa. In this way, by pressurizing the inside of the container 1 to 0.1 MPa or more, the binder adhering to the recovered foundry sand 8 is not dissolved in water under normal pressure, even if it is not dissolved in water. It becomes easy to dissolve in water by the pressurizing action. The pressure is expressed by both an increase in internal pressure due to heating in a sealed state and pressurization by the pump 4.

  Here, as the time of the polishing process as described above, the longer the time that is kept under heating and pressurization, the better the regeneration efficiency. However, if the polishing time is too long, the aggregate may be damaged. Therefore, generally, it is about 1 to 10 minutes, preferably about 4 to 8 minutes.

  In addition, regarding the amount of water added (used amount) to the recovered foundry sand 8 in the present invention, an amount of water that wets the surface of the recovered foundry sand 8 is necessary, but if the amount of water is too large, The amount of water is generally about 30 to 200 parts by mass with respect to 100 parts by mass of the recovered foundry sand 8, and 50 to 150 parts by mass is particularly preferable. -100 mass parts is more preferable. The water added first may be room temperature water, but the use of warm water is more preferable.

  Furthermore, it is also possible to add an alkaline aqueous solution together with the addition of water in the preparation step described above. In particular, when the binder is a sodium silicate-based binder, the addition of an alkaline aqueous solution facilitates the dissolution of the same alkali sodium silicate. Although it does not specifically limit as an alkali compound used for this alkaline aqueous solution, For example, alkali metal hydroxides, such as sodium hydroxide and potassium hydroxide, are preferable. Furthermore, various additives may be added in the preparation process in order to make it easy to peel off the binder adhering to the recovered foundry sand 8 or to make the binder easily dissolve in water. Addition of an agent is mentioned. By adding this surfactant, the binder can be easily peeled off, and the antistatic effect can prevent the fine powder of the binder from being adsorbed. Examples of the surfactant include fatty acid sodium and fatty acid potassium.

  Next, the second embodiment of the method for reclaiming recovered foundry sand according to the present invention will be described in more detail with reference to FIGS. This will be described in detail.

  First, in FIG. 2, the outer frame 11 is constituted by support frames 12 and 12 for holding the drum 20 at both axial ends thereof, and horizontal frames 13 and 13 that connect both the support frames 12. ing. In addition, a rotation shaft 14 disposed through each of the support frames 12 is rotatably provided in the center portion of both support frames 12 with a bearing 15 interposed therebetween. A driven pulley 19 connected to a driving pulley 17 attached to the motor 16 by a belt 18 is fixed to one end of the rotating shaft 14, and the rotating shaft 14 is rotated by driving the motor 16. It is supposed to be. The drive pulley 17 and the driven pulley 19 may use variable speed pulleys so that the rotation speed of the rotary shaft 14 can be changed. The motor 16 can be a servo motor and the rotation speed can be varied. It is also possible to do.

  A cylindrical drum 20 is installed inside the outer frame 11, and a polishing layer 21 made of an abrasive is provided on the inner peripheral surface of the drum 20 with a predetermined thickness. . The rotating shaft 14 penetrates through the central portion of both end portions in the axial direction of the drum 20. The rotating shaft 14 and the drum 20 are fixed, and the drum 20 is rotated by the rotation of the rotating shaft 14. It can be rotated. Further, an openable / closable inlet / outlet (not shown) is provided near the edge of one end face of the drum 20 so that the recovered foundry sand 8 and water are supplied and discharged from the inlet / outlet. It has become. Furthermore, the drum 20 is provided with a heater (not shown) capable of heating the inside thereof, and the internal temperature can be adjusted, and a thermometer (not shown) for measuring the internal temperature is provided. A pressure gauge (not shown) is also provided to measure the internal temperature and pressure.

  A ventilation hole 22 extending from one end to the vicinity of the center of the rotation shaft 14 is provided inside the rotation shaft 14, and a communication hole 23 that opens from the rear end of the ventilation hole 22 to the surface of the rotation shaft 14. Is provided so that air can be sucked into and exhausted from the inside of the drum 20 through the vent hole 22. A connecting pipe 24 is connected to the end of the rotating shaft 14 where the vent hole 22 is opened, with the vent hole 22 sealed from the outside, and the connecting pipe 24 is further branched into two. One is open to the atmosphere and the other is connected to the pump 25. Further, a three-way valve 26 is provided at a branch portion of the communication pipe 24 so that the passage can be switched between the atmosphere opening side and the pump 25 side.

  By the way, the polishing process of the second embodiment using the apparatus having such a structure is advanced as follows.

  That is, in the polishing step, the recovered foundry sand 8 is brought into contact with water under a predetermined heating / pressurizing condition, so that the binder is easily dissolved and peeled off as described above. In this state, as shown in FIG. 3, when the drum 20 is rotated, the recovered foundry sand 8 collides with the polishing layer 21 on the inner peripheral wall of the drum 20 and adheres by the collision energy at this time. A part of the binder is polished and removed from the recovered foundry sand 8. Further, the recovered foundry sand 8 is caused by its own weight to simultaneously cause a force to drop to the lower part of the drum 20 and a centrifugal force to rotate on the inner peripheral surface of the rotation of the drum 20. The recovered foundry sand 8 gradually slides down while being agitated along the inner peripheral surface of the drum 20 from a high position on the inner peripheral surface of the drum 20. In the process of sliding down while being agitated, the recovered foundry sand 8 rolls on the polishing layer 21 on the inner peripheral surface of the drum 20, so that the recovered foundry sand 8 is rubbed against the polished layer 21 to be polished. It will be done. In this way, the binding agent attached to the recovered foundry sand 8 can be easily peeled by making the binder of the recovered foundry sand 8 easy to peel and polishing. Furthermore, the binder is effectively removed from the recovered foundry sand 8 by dissolving the binder in water under heating and pressure.

  Since other procedures are the same as those in the first embodiment described above, the description thereof will be omitted. The inside of the drum 20 is pressurized from the communication hole 22, and at the time of decompression, the decompression is performed by switching the three-way valve 26 to the atmosphere release side.

  The polishing layer 21 formed on the inner peripheral surface of the drum 20 used in the second embodiment is formed of an abrasive material made of an inorganic material with little wear, and the polishing layer 21 is formed of a drum. It may be formed on all of the 20 inner peripheral surfaces, or may be formed on a part. It is also possible to form the entire drum 20 with an abrasive. Furthermore, it is desirable that the surface of the polishing layer 21 is formed in a rough state or a state in which irregularities are provided in order to improve impact and friction with the recovered foundry sand.

  In the second embodiment, a configuration in which the polishing layer 21 is provided on the inner peripheral surface of the drum 20 and the recovered foundry sand is polished by the polishing layer 21 by the rotation of the drum 20 is employed. The polishing stone used in the first embodiment may be further added to the drum 20 to perform polishing in a form in which two polishing means are used in combination. Thus, the polishing effect can be further improved by using a plurality of polishing means in combination. On the contrary, it is also possible to perform polishing by forming a polishing layer on the inner peripheral surface of the container 1 during the stirring in the first embodiment.

  Further, in the second embodiment, as shown in FIG. 4, the drum blade 27 may be provided inside the drum 20 so as to be rotatable. The drum blade 27 is a water wheel in which a plurality of partition plates 28 radially arranged at a required central angle are fixed to donut-shaped rotating discs 30 positioned at both ends in the axial direction of the rotating shaft 14 at both ends thereof. It is comprised by the shape-shaped member. The drum blade 27 is rotatable in the reverse direction with respect to the drum 20. A cylindrical rotary abrasive 29 attached to the rotary shaft 14 is mounted so as to be rotatable in the reverse direction with respect to the drum blade 27 so as to be positioned at the center of the drum blade 27. By rotating the drum blade 27, the contents in the drum 20 can be stirred while being lifted. Therefore, polishing by the drum blade 27 and the polishing layer 21 and polishing by the rotating abrasive 29 further increase the polishing effect. It can be further improved.

  Furthermore, in order to clarify the third embodiment of the method for reclaiming recovered foundry sand according to the present invention more specifically, the form of a representative process will be described in detail with reference to FIG. I decided to.

  First, in FIG. 5, the container 31 has a pressure-resistant structure, and the inside of the container 31 can be sealed by closing the lid 31a. The container 31 is provided with a ventilation path 32 and an exhaust path 33 communicating with the inside of the container. Therefore, the air passage 32 is connected to the pump 34, and the exhaust passage 33 is opened to the atmosphere and can be opened and closed by the opening / closing valve 35. Inside the container 31, there are provided a pair of polishing rollers 36a and 36b whose outer peripheral surfaces are formed of an abrasive, and roller driving portions 37a and 37b connected to the rotation shafts of the polishing rollers 36a and 36b. The roller driving portions 37a and 37b are fixed by the support arm 38, respectively, so that the polishing rollers 36a and 36b can be rotated in opposite directions in parallel in the container 31. In addition, a motor 39 is disposed at the center of the lid 31a of the container 31, and the rotary shaft 40 of the motor 39 is inserted into the container 31 in a sealed state. Is fixed, and the support arm 38 is rotatable while holding the pair of polishing rollers 36a and 36b. Furthermore, the container 31 is provided with a heater (not shown) capable of heating the inside thereof, and the internal temperature can be adjusted, and a thermometer (not shown) or a pressure gauge (not shown) for measuring the internal temperature. (Not shown) is provided, and the internal temperature and pressure can be measured.

  Then, the polishing step according to the third embodiment using the apparatus having such a configuration is performed as follows.

  That is, also in the polishing step according to the third embodiment, when the recovered foundry sand 8 comes into contact with water under a predetermined heating / pressurized state, the binder adhering to the recovered foundry sand 8 is water. It is in a state where it is easily dissolved and peeled off. In this state, the pair of polishing rollers 36 a and 36 b are rotated in opposite directions, and the support arm 38 is further rotated to revolve the polishing rollers 36 a and 36 b in the container 31. . Thus, when the pair of polishing rollers 36a and 36b rotate, the recovered foundry sand 8 passes through the gap between the polishing rollers 36a and 36b and the gap between the polishing rollers 36a and 36b and the inner peripheral surface of the container 31. In other words, polishing is performed by friction generated by pressing between the polishing rollers 36a and 36b and the inner peripheral surface of the container 31. Further, when the polishing rollers 36a and 36b revolve, the contents in the container 31 are agitated, and polishing is performed by the impact of centrifugal force generated by the rotation of the polishing rollers 36a and 36b, and thus the polishing rollers 36a and 36b. The polishing by is repeated. In this way, the binder of the recovered foundry sand 8 can be easily peeled off and polished, so that the binder adhering to the recovered foundry sand 8 can be easily peeled off, and further the adhesive can be bonded under heating and pressure. By the binder being dissolved in water, the binder is effectively removed from the recovered foundry sand 8. Since other procedures are the same as those in the first embodiment, description thereof will be omitted.

  The polishing rollers 36a and 36b used in the third embodiment are made of an abrasive material made of an inorganic material with little wear. These polishing rollers 36a and 36b are arranged in a state where they are inclined at a fixed angle with each other in order to increase the stirring efficiency in the container 31, or stirring blades are attached to the side surfaces of the polishing rollers 36a and 36b. There is no problem even if 36a and 36b are provided so as to be movable up and down. The polishing rollers 36a and 36b are respectively rotated by roller driving portions 37a and 37b. However, the roller driving portions 37a and 37b are not provided, but are fixed by the support arm 38, and the polishing rollers are rotated. It is good also as just rotating with the motor 39, without making it. Further, the container 31 may be provided with a polishing layer on the inner peripheral surface as in the second embodiment described above, and the polishing effect is further improved by using a plurality of polishing means in combination. I can do it. In the present embodiment, it is desirable to avoid the combined use with the polishing stone in the first embodiment.

  By the way, in the first to third embodiments according to the present invention described above, the rotational speed of the stirring blade 7, the drum 20, and the polishing rollers 36a and 36b is generally about 100 to 3000 rpm, preferably about 500 to 1500 rpm. It is desirable. If this rotational speed is lower than 100 rpm, energy due to collision or friction by the grinding stone, polishing layer, or polishing roller will be reduced, and it will be difficult to perform polishing sufficiently, and if the rotational speed will be higher than 3000 rpm. Due to the momentum of rotation, there is a risk that the recovered foundry sand will be damaged due to excessive impact and frictional loads applied by the polishing stone, polishing layer, or polishing roller.

  In addition, after the polishing step employed in the present invention, in addition to the first embodiment in the order of the cooling / decompression step, the water removal step, and the drying step, the concentration step, the neutralization step, and the drying step were performed. There is no problem even if it is a procedure. Any of these procedures may be used, but the procedure is selected mainly depending on the amount of moisture at the time when the polishing step is completed. For example, when there is a lot of moisture, specifically, when the ratio of water is 50 to 200 parts by mass, preferably 80 to 150 parts by mass with respect to 100 parts by mass of the recovered foundry sand, It is preferable that the removal step and the drying step are performed in this order. On the other hand, when the water content is low, specifically, when the ratio of water is 30 to 80 parts by mass, preferably 30 to 50 parts by mass with respect to 100 parts by mass of the recovered foundry sand, the concentration step, neutralization It is preferable to perform in order of a process and a drying process. And when a moisture content will be 50-80 mass parts, any method will implement suitably.

  Among these steps, in the concentration step, the on-off valve 5 in FIG. 1 is gradually opened so that the internal pressure of the container 1 is gradually reduced to normal pressure and heating with the heater is continued as it is. The amount of water in the container 1 is reduced to some extent, specifically, the water is evaporated until the water becomes 50 parts by mass or less with respect to 100 parts by mass of the recovered foundry sand. Thereafter, heating by the heater is stopped, and the inside of the container 1 is cooled. In addition, if the water | moisture content in the container 1 is a certain little amount at the time of finishing a grinding | polishing process, even if it performs a neutralization process without performing a concentration process, it does not interfere at all.

  In addition, in the neutralization step, the content of the container 1 is dissolved into a binder such as sodium silicate, and when the alkalinity is strong, an acidic aqueous solution is added to become neutral. In addition, it is desirable to adjust the pH. When the dissolved sodium silicate is neutralized, the particle surface of the resulting reclaimed foundry sand becomes neutral even when the contents are dried.For example, the reclaimed foundry sand is used as a wet mold. It is possible to prevent the usable time from being shortened when used for molding, and it can be used as recycled casting sand without any problem. In addition, although it does not specifically limit as an acidic compound used as acidic aqueous solution, Inorganic acids, such as hydrochloric acid, a sulfuric acid, phosphoric acid, nitric acid, boric acid, etc. are preferable. Thereafter, as in the first embodiment, the reclaimed foundry sand is obtained by drying in the drying step.

  In these regeneration procedures, if the binder is dissolved in water and can be removed from the aggregate surface by polishing, the binder does not need to be completely dissolved in water. When the binder peeled off remains in a fine powder state, a fine powder removing step can be performed in which the fine powder is scattered by blowing air, and the scattered fine powder is sucked into a dust collector. Further, this fine powder removing step can be performed at the same time as the drying step.

  Further, in pressurization in the polishing process according to the present invention, instead of gas pressurization by a pump, pressurization may be performed using a gas cylinder, preferably water vapor. And such water vapor | steam is 100 degreeC or more, Preferably it is about 120-200 degreeC, More preferably, it is about 150-200 degreeC, and the pressure of water vapor | steam is 0.1-2.0 MPa, Preferably it is 0.2- It is effective to use one having a pressure of 1.5 MPa. In this way, by using water vapor, heating and pressurization in the container and drum are performed simultaneously, and since the internal heating efficiency is good, the time required for heating and pressurization can be performed in a short time. There is an advantage that the time required for regeneration can be shortened, for example, when a large regeneration facility is provided in the factory. As the water vapor, either saturated water vapor or superheated water vapor can be used.

  Hereinafter, the present invention will be more specifically clarified by using some examples, but the present invention is not construed as being limited in any way by the description of such examples. It should be understood. In the following examples and comparative examples, all parts and percentages are shown on a mass basis unless otherwise specified. Moreover, the measurement of the bending strength of the casting_mold | template obtained from the reproduction | regeneration molding sand and the measurement of residual Na amount which were performed by the Example and the comparative example were each implemented as follows.

−Measurement of bending strength (N / cm ² ) −
Commercially available No. 3 sodium silicate (manufactured by Suzukawa Chemical Co., Ltd., trade name: sodium silicate No. 3) is added to each recycled casting sand at a ratio of 1.5 parts to 100 parts of recycled casting sand, and zinc carbonate. (Shodo Chemical Industry Co., Ltd.) was added at a ratio of 0.1 part to 100 parts of recycled foundry sand and kneaded with a Shinagawa universal stirrer (5DM-r type) (Dalton Co., Ltd.) The test piece having a size of width: 10 mm × height: 10 mm × length: 80 mm obtained by blow-filling a mold at a temperature of 150 ° C., holding for 1 minute, and then removing the mold was subjected to its breaking load. Is measured using a measuring instrument (Takachiho Seiki Co., Ltd .: Digital foundry sand strength tester). Then, the bending strength is calculated by the following formula using the measured breaking load.
Bending strength = 1.5 × LW / ab ²
[However, L: distance between fulcrums (cm), W: breaking load (N), a: width of test piece (cm),
b: Thickness of test piece (cm)]

-Measurement of residual Na amount-
The aggregate (recycled foundry sand) after the regeneration treatment was measured by ICP emission spectroscopic analysis (ICP-AES). Since this measurement is performed in the state of a liquid sample, as a pretreatment, hydrous acid was added to the aggregate after the regeneration treatment to cause acid decomposition, and a solution sample was prepared. Thereafter, an aqueous solution with a known Na concentration was measured together with the sample, and quantified using a calibration curve method.

-Production example 1 of recovered foundry sand-
Lunamos # 50 (true ball artificial sand, trade name: manufactured by Kao Quaker Co., Ltd.) is prepared as foundry sand, and commercially available sodium silicate No. 3 (trade name: manufactured by Suzukawa Chemical Co., Ltd.) is used as a binder. ) Was diluted with water to prepare a sodium silicate aqueous solution having a nonvolatile content (a ratio obtained by removing the amount of water from the sodium silicate aqueous solution) of 27.7% by mass and a SiO ₂ / Na ₂ O molar ratio of 3.17. did. Furthermore, zinc carbonate (manufactured by Shodo Chemical Industry Co., Ltd.) was prepared as an additive.

  Next, after putting Lunamos # 50 at a temperature of 20 ° C. into a Shinagawa universal agitator (5DM-r type) (manufactured by Dalton Co., Ltd.), the above sodium silicate aqueous solution was added to 100 parts of Lunamos # 50. In addition, in terms of solid content when considered as only the non-volatile content, 1.0 part is added, and zinc carbonate is added at a rate of 10 parts with respect to 100 parts of the solid content of the sodium silicate aqueous solution. Then, the mixture was kneaded for 30 seconds, stirred and mixed, and then taken out to obtain a wet casting sand composition having free flow at room temperature.

  Thereafter, the casting sand composition at a temperature of 20 ° C. is heated in a dryer heated to 150 ° C. for 15 minutes to cure the casting sand composition, and is further assumed to receive a high-temperature thermal history by casting. Then, heating for 30 minutes was performed in a baking furnace heated to 700 ° C. Then, after the cured lump of the obtained foundry sand composition is cooled to 100 ° C. or lower, it is crushed with a Shinagawa universal stirrer (5DM-r type) (Dalton Co., Ltd.), and 20 mesh The recovered foundry sand was produced by passing through a sieve.

-Example 1 (Reclaimed foundry sand regeneration example 1)-
In the container 1 shown in FIG. 1, 100 parts of recovered foundry sand, 100 parts of water, and 100 parts of alumina balls (polishing stone) having a diameter of 20 mm are placed, the on-off valve 5 is closed, and heated by a heater. At the same time, the pressure is applied by the pump 4, and the polishing process starts when the temperature and pressure inside the container 1 become 120 ° C. and 0.2 MPa, and the contents are stirred by the stirring blade 7 at a rotation speed of 800 rpm. At the same time, heating was continued with a heater and the state was maintained for 5 minutes. The temperature was adjusted within a range of ± 5 ° C., and the pressure was adjusted within a range of ± 0.02 MPa. Thereafter, the on-off valve 5 is gradually opened, the pressure is reduced to normal pressure, the inside of the container 1 is cooled to room temperature, and the sand obtained by filtering the contents is blown with hot air of 150 ° C. to be dried. Thus, recycled casting sand was produced. The physical properties of the reclaimed foundry sand thus obtained were measured, and the results are shown in Table 1 below.

-Examples 2 to 4 (Recycled casting sand regeneration examples 2 to 4)-
In Example 1, the temperature and pressure inside the container 1 were 150 ° C. and 0.5 MPa, 180 ° C. and 1.0 MPa, or 200 ° C. and 1.5 MPa, respectively, except that the polishing process was started. Recycled foundry sand was produced in the same manner as in Example 1. And the physical property measurement result was shown in the following Table 1 about the obtained recycled foundry sand.

-Example 5 (Reclaimed foundry sand regeneration example 5)-
In Example 3, recycled cast sand was produced in the same manner as in Example 3 except that the amount of water used was 50 parts. And the physical property measurement result of the obtained recycled foundry sand is shown in the following Table 1.

-Example 6 (Reclaimed foundry sand regeneration example 6)-
100 parts of recovered foundry sand, 50 parts of water, and 100 parts of polishing stone are added, heated with a heater while the on-off valve 5 is opened, and saturated steam of 0.2 MPa is blown at 120 ° C. After the temperature has risen to or higher, the on-off valve 5 is closed, and when the temperature and pressure inside the container 1 become 120 ° C. and 0.2 MPa, the polishing process starts, and the contents are stirred with the stirring blade 7. Recycled foundry sand was produced in the same manner as in Example 1 except that heating was continued with a heater and the state was maintained for 5 minutes. Note that the blowing of water vapor was stopped when the amount of water blown into the container 1 reached 50 parts (measured by the increase in mass). The physical property measurement results of the reclaimed foundry sand thus obtained are shown in Table 1 below.

-Example 7 (Reclaimed foundry sand regeneration example 7)-
In Example 6, while saturated steam of 1.0 MPa was blown at 180 ° C., after the temperature in the container 1 became 170 ° C. or higher, the on-off valve 5 was closed, and the temperature and pressure inside the container 1 were 180 ° C. Recycled foundry sand was produced in the same manner as in Example 6 except that the polishing step was started when the pressure reached 1.0 MPa. And the physical property measurement result of the obtained recycled foundry sand is shown in the following Table 1.

-Comparative example 1 (recovered casting sand regeneration example 8)-
In Example 1, while the on-off valve 5 of the container 1 is kept open, the container 1 is heated with a heater and the inside of the container 1 is at 100 ° C. at normal pressure without being pressurized (because it is under normal pressure; Recycled foundry sand was produced in the same manner as in Example 1 except that it was not heated. The physical property measurement results of the reclaimed foundry sand thus obtained are shown in Table 1 below.

-Comparative example 2 (recovered foundry sand reclaim example 9)-
In Comparative Example 1, recycled casting sand was produced in the same manner as in Comparative Example 1 except that the polishing time was 10 minutes. And the physical property measurement result of the obtained recycled foundry sand is shown in the following Table 1.

-Comparative example 3 (recovered casting sand regeneration example 10)-
In Example 3, the polishing treatment was performed under the same conditions as in Example 3 without adding water. Since water was not added, filtration and drying were not performed, and the fine powder of the binder was removed with a dust collector to prepare recycled foundry sand. And the physical property measurement result of the obtained recycled foundry sand is shown in the following Table 1.

-Comparative example 4 (recovered foundry sand regeneration example 11)-
Recycled foundry sand was produced in the same manner as in Example 1 except that no grinding stone was added and stirring was not performed with the stirring blade 7 in Example 1. And the physical property measurement result of the obtained recycled foundry sand is shown in the following Table 1.

  As is clear from the results of Table 1, in each of Examples 1 to 5, reclaimed foundry sand with a reduced amount of residual Na was obtained, and using such reclaimed foundry sand, high mold strength was obtained. You can see that you can get it. Moreover, since the dissolution of the binder with water is promoted by polishing in a wet state under a predetermined heating / pressurized state to which water has been added, the caking from the recovered foundry sand. It is recognized that the agent is efficiently polished and removed. Further, in Examples 6 to 7, since the heating and pressurization are promoted by the blowing of water vapor, the polishing efficiency is further improved. In addition, the time for adjusting to a predetermined heating temperature and pressure can be performed in a short time.

  On the other hand, even in the case of heating only without applying pressure as in Comparative Examples 1 and 2, or in the case of polishing in a dry state without adding water as in Comparative Example 3, residual Na The amount of untreated Na is about 2100 ppm, so the amount of residual Na is not reduced so much. Polishing with water added to increase the temperature or polishing in a dry state under pressure, It is understood that the polishing could not be performed sufficiently. In particular, in Comparative Example 2, it is recognized that the polishing effect is not so much even if the polishing time is doubled. Moreover, in Comparative Example 4, although a slight effect is observed in the reduction of the residual Na amount due to dissolution of the binder in water under pressure and heating, the amount of residual Na is smaller than that in the case of polishing. There is not enough reduction.

DESCRIPTION OF SYMBOLS 1 Container 1a Cover 2 Ventilation path 3 Exhaust path 4 Pump 5 On-off valve 6 Motor 6a Rotating shaft 7 Stirring blade 8 Collected casting sand 9 Polishing stone 11 Outer frame 12 Support frame 13 Horizontal frame 14 Rotating shaft 15 Bearing 16 Motor 17 Drive pulley 18 Belt 19 Driven pulley 20 Drum 21 Polishing layer 22 Vent hole 23 Communication hole 24 Connection pipe 25 Pump 26 Three-way valve 27 Drum blade 28 Partition plate 29 Rotating abrasive 30 Rotating disk 31 Container 31a Lid 32 Ventilation path 33 Exhaust path 34 Pump 35 On-off valve 36a, 36b Polishing roller 37a, 37b Roller drive part 38 Support arm 39 Motor 40 Rotating shaft

Claims (15)

A method for reclaiming recovered foundry sand with a water-soluble binder attached thereto,
In a container, the recovered foundry sand and water are accommodated at a ratio of 30 to 200 parts by weight of water with respect to 100 parts by weight of the recovered foundry sand, and a pressure of 0.1 MPa or more. A method for reclaiming recovered foundry sand, comprising performing a polishing step of polishing the recovered foundry sand in a state where the recovered foundry sand is heated to a temperature of 100 ° C. or higher. The method for reclaiming recovered foundry sand according to claim 1, wherein the heating temperature is in the range of 100 to 300 ° C. The method for reclaiming recovered foundry sand according to claim 1 or 2 , wherein the pressurizing pressure is within a range of 0.1 to 10 MPa. The method for reclaiming recovered foundry sand according to any one of claims 1 to 3 , wherein the binder is mainly composed of a water-soluble inorganic binder. The method for reclaiming recovered foundry sand according to claim 4 , wherein the inorganic binder is a silicate compound. The polishing step is a step in which a polishing stone is further accommodated in the container, and the recovered foundry sand is polished by the polishing stone by rotating the container or stirring the contents in the container. The method for reclaiming recovered foundry sand according to any one of claims 1 to 5 , characterized in that: The method for reclaiming recovered foundry sand according to claim 6 , wherein the amount of the grinding stone used is 30 to 300 parts by weight with respect to 100 parts by weight of the recovered foundry sand . In the polishing step, a polishing layer formed of an abrasive is provided on the inner surface of the container, and the recovered foundry sand forms the polishing layer by rotating the container or by stirring the contents in the container. 6. The method for reclaiming recovered foundry sand according to any one of claims 1 to 5 , wherein the method is a step of polishing by polishing. The method for reclaiming recovered foundry sand according to any one of claims 6 to 8 , wherein the agitation is carried out using an agitating blade or a drum blade rotatable in a container. The polishing step is a step in which a pair of polishing rollers is disposed in the container, and the recovered foundry sand is polished by the polishing roller by rotation of the polishing roller. The method for reclaiming recovered foundry sand according to any one of claims 1 to 5 . The collection molding sand is recovered according to any one of claims 1 to 10, characterized in that it is recovered foundry sand recovered from molding to mold by using a sodium silicate based binder A method for reclaiming foundry sand. After the polishing step, a neutralizing step for neutralizing the contents of the said container, and a drying step of drying the foundry sand that is reproduction process of claims 1 to 11, characterized by further comprising A method for reclaiming recovered foundry sand according to any one of the preceding claims. 2. The method according to claim 1, further comprising: a moisture removing step for removing moisture by filtration or centrifugal separation at a normal pressure or a reduced pressure after the polishing step; and a drying step for drying the reclaimed foundry sand. The method for reclaiming recovered foundry sand according to any one of claims 1 to 11 . After said drying step, fines peeled binder from the collection molding sand fines removal step of removing at dust collectors, the recovery foundry sand according to claim 12 or claim 13, characterized by further comprising re-UBUKATA method. The method for reclaiming recovered foundry sand according to any one of claims 1 to 14 , wherein the heating and pressurization are performed by blowing water vapor.

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