JP2018140425A - Method for producing reconditioned sand and method for producing casting sand - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel method for producing reconditioned sand that is operated without heat treatment, and to provide a method for producing casting sand.SOLUTION: A method for producing reconditioned sand conducts only machine work to a sand mold containing: a plurality of pieces of casting sand containing sand and a surface modification layer containing a coating resin curing material for coating the sand; and a binder resin curing material for bonding the plurality of pieces of casting sand mutually.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for producing reclaimed sand and a method for producing foundry sand.

  As foundry sand for shaping a sand mold (mold), known foundry sand (so-called resin-coated sand) having sand as an aggregate and phenolic resin for coating the sand is known. Such casting sand is filled in a heated mold, for example, so that the phenol resin is thermally cured to form a sand mold.

  In addition, it is desired to recycle the sand as an aggregate after the casting is finished by crushing the sand mold. However, in the recovered sand obtained by crushing the sand mold, the hardened phenolic resin adheres to the sand, so in order to recycle the sand, the recovered sand is heat-treated and the phenol resin adhering to the sand is removed. It is necessary to remove the cured product.

  For example, a method for reclaiming foundry sand has been proposed in which air heated to 550 ° C. or higher is supplied to recovered sand obtained by pulverizing a mold material to remove phenolic resin from the recovered sand (for example, Patent Documents). 1).

Japanese Patent Laid-Open No. 7-314080

  However, in the method of reclaiming foundry sand described in Patent Document 1, it is necessary to supply air heated to 550 ° C. or higher to the recovered sand, so that the environmental load is large, the work process is complicated, and the equipment cost is high. There is a problem that increases. Therefore, it is difficult to reduce the cost required for sand regeneration.

  Therefore, the present invention provides a novel method for producing reclaimed sand and a method for producing foundry sand that can be carried out without heat treatment.

  The present invention [1] includes a plurality of foundry sands having sand and a surface-modified layer containing a cured coating resin covering the sand, and a binder resin cured product that adheres the plurality of foundry sands to each other. It includes a method for producing reclaimed sand, in which only machining is performed on the contained sand mold.

  However, when the binder resin cured product is directly attached to the sand in the sand mold, even if such a sand mold is machined, the binder resin cured product cannot be sufficiently peeled from the sand, and the binder resin cured product is sand. It remains on the surface. Therefore, in order to recycle sand, it is necessary to remove the cured binder resin by heat treatment.

  On the other hand, according to the above method, the foundry sand has sand and a surface modified layer containing a cured coating resin that coats the sand, and the cured binder resin adheres to the surface modified layer. doing. Therefore, the binder resin cured product can be peeled from the surface modified layer by performing machining on the sand mold in which the cured binder resin adheres to the surface modified layer of the foundry sand.

  That is, the cured binder resin adhering to the surface modified layer can be peeled and removed only by machining without heat treatment, and recycled sand can be produced from the sand mold.

  The present invention [2] includes a step of mixing the reclaimed sand produced by the method for producing reclaimed sand described in [1] above and a coating resin composition, and the regenerated sand mixed with the coating resin composition. And a step of mixing a curing agent.

  However, in casting, molten metal (melted metal) is poured into the sand mold. Therefore, among the foundry sand contained in the sand mold, in the foundry sand in contact with the molten metal and the foundry sand located in the vicinity thereof, the surface modified layer covering the sand may be burned out. In this case, the reclaimed sand produced from the sand mold includes reclaimed sand in which the surface modification layer has been burned away. If such recycled sand is recycled into a sand mold, the accuracy and strength of the sand mold may be reduced.

  On the other hand, according to the above method, after mixing the regenerated sand and the coating resin composition, the curing agent is mixed. Therefore, after the coating resin composition is coated so as to surround each particle of the regenerated sand, Cured with a curing agent to form a cured coating resin.

  Therefore, even if the reclaimed sand contains reclaimed sand whose surface modified layer has been burned away, the sand can be recoated, and the sand and the surface modified layer containing the cured coating resin covering the sand The foundry sand can be reliably manufactured (regenerated).

  According to the present invention, reclaimed sand and foundry sand can be produced from a sand mold without heat treatment.

FIG. 1 is a schematic configuration diagram of a sand mold applied to one embodiment of the present invention. FIG. 2A is a schematic configuration diagram of recycled sand produced from the sand mold shown in FIG. 1. FIG. 2B is a schematic configuration diagram of attached reclaimed sand contained in reclaimed sand manufactured from the sand mold shown in FIG. 1. FIG. 2C is a schematic configuration diagram of burned reclaimed sand contained in reclaimed sand produced from the sand mold shown in FIG. 1.

<Method for producing recycled sand>
In the method for producing reclaimed sand of the present invention, the reclaimed sand is produced by performing only machining on the sand mold. The sand mold contains a plurality of foundry sands and a cured binder resin that adheres the foundry sands to each other.

1. Sand mold First, the sand mold applied to the manufacturing method of the regenerated sand of this invention is demonstrated.

  Examples of the sand mold include a self-hardening sand mold that hardens at room temperature (0 ° C. or more and 35 ° C. or less) (for example, a furan self-hardening sand mold, a phenol urethane self-hardening sand mold, an alkali phenol self-hardening sand mold, etc.), or a thermosetting type that cures by heating. Examples include sand molds. In addition, this embodiment demonstrates the furan self-hardening sand type | mold whose binder resin composition mentioned later is a furan resin composition.

  As shown in FIG. 1, the sand mold 30 contains a plurality of foundry sands 1 and a cured binder resin 5 that adheres the foundry sands 1 to each other. Although one embodiment of a sand mold is illustrated in FIG. 1 for convenience, the shape of the sand mold is not particularly limited.

(1-1) Foundry sand The foundry sand 1 has a sand 2 and a surface-modified layer 3 containing a cured coating resin covering the sand 2.

  Examples of the sand 2 include natural silica sand and artificial sand. Further, the sands 2 provided in each of the plurality of foundry sands 1 may be the same or different from each other.

Natural silica sand is silica sand whose main component is quartz (silicon dioxide: SiO ₂ ).

  The artificial sand is produced by a known method (for example, a sintering method, a melting method, a flame melting method, etc.).

  Among such sands 2, artificial sand is preferable.

  Examples of the artificial sand include aluminum oxide sand (alumina sand), mullite sand, mullite-zircon sand, and the like. Artificial sand can be used alone or in combination of two or more. Among the artificial sand, mullite sand is preferable.

  Mullite sand is mainly composed of a mixed composition compound (aluminosilicate) of aluminum oxide (alumina) and silicon dioxide (silica).

  The content ratio of aluminum oxide is, for example, 50% by mass or more, preferably 60% by mass or more, more preferably 65% by mass or more, for example, 90% by mass or less, preferably 80% by mass with respect to the total amount of mullite sand. % Or less.

  The content ratio of silicon dioxide is, for example, 5% by mass or more, preferably 15% by mass or more, for example, 45% by mass or less, preferably 40% by mass or less, more preferably 30% by mass with respect to the total amount of mullite sand. % Or less.

  Such mullite sand can be prepared, for example, by the method described in JP-A No. 61-63333 or the method described in JP-A No. 2003-251434.

  A commercially available product of mullite sand can also be used. Examples of commercially available products of mullite sand include Spearl (manufactured by Yamakawa Sangyo Co., Ltd.), Cera Beads (manufactured by ITOCHU CERATECH Co., Ltd.) and the like.

  The artificial sand may contain feldspar. The feldspar is an aluminosilicate containing alkali metal and / or alkaline earth metal.

As feldspar, for example, potassium feldspar _{(K 2 O · Al 2 O} 3 · 6SiO 2), soda feldspar _{(Na 2 O · Al 2 O} 3 · 6SiO 2) , and the like.

  The content ratio of feldspar exceeds 0% by mass, for example, 10% by mass or less, preferably 5% by mass or less, with respect to the total amount of artificial sand.

(1-2) Surface Modification Layer The surface modification layer 3 is disposed on the entire surface of the sand 2 so as to cover the sand 2. The surface modification layer 3 contains a cured coating resin that covers the entire surface of the sand 2, and is preferably composed of a cured coating resin.

  The cured coating resin is a cured product of the coating resin composition described below, and the curing reaction has been completed. For example, even when heated, the curing reaction does not proceed further.

  Examples of the cured coating resin include a furan resin, a phenol resin, an epoxy resin, a silicone resin, and a resol type phenol resin, and a furan resin is preferable from the viewpoint of heat resistance.

  The content ratio of such a cured coating resin is, for example, 80% by mass or more, preferably 90% by mass or more, for example, 100% by mass or less, with respect to the total amount of the surface modified layer 3.

  Moreover, the coating resin cured product preferably contains a crosslinking agent such as silane.

  When the coating resin cured product contains a crosslinking agent (silane), the crosslinking agent can crosslink the coating resin cured product and the sand 2 to improve the adhesion of the surface modification layer 3 to the sand 2.

  The content of the crosslinking agent is, for example, 0.01% by mass or more, preferably 0.5% by mass or more, for example, 20% by mass or less, preferably 3% by mass or less, with respect to the total amount of the cured coating resin. is there.

  The thickness of the surface modification layer 3 is, for example, 0.01 μm or more, preferably 0.1 μm or more, for example, 10 μm or less, preferably 1 μm or less.

(1-3) Hardener Layer In the present embodiment, as described above, the sand mold 30 is a furan self-hardening sand mold. In this case, the foundry sand 1 preferably has a hardener layer 4 disposed on the peripheral surface of the surface modified layer 3 so as to cover the surface modified layer 3.

  The curing agent layer 4 is made of a curing agent that adheres to the surface of the surface modification layer 3. The curing agent contains an acid catalyst that cures (completely cures) the furan resin composition as the binder resin composition.

  Examples of the acid catalyst include aliphatic sulfonic acids (for example, methanesulfonic acid, ethanesulfonic acid, etc.), aromatic sulfonic acids (for example, benzenesulfonic acid, paratoluenesulfonic acid, xylenesulfonic acid, etc.), inorganic acids (for example, Sulfuric acid, phosphoric acid, hydrochloric acid, etc.), carboxylic acids (eg, maleic acid, oxalic acid, etc.) and the like. The acid catalyst can be used alone or in combination of two or more.

  Among such acid catalysts, an aromatic sulfonic acid is preferable, and a xylene sulfonic acid is more preferable.

  The content ratio of the acid catalyst is, for example, 90.0% by mass or more, preferably 95.0% by mass or more, for example, 100% by mass or less, with respect to the total amount of the curing agent layer 4.

(1-4) Manufacturing method of foundry sand In such foundry sand 1, for example, the above-described sand and coating resin composition are mixed, and then the coating resin composition is cured to form a surface modified layer. It is prepared by.

(1-4-1) Mixing step of sand and coating resin composition Specifically, after preheating the sand to a predetermined temperature (mixing temperature), the coating resin composition is added to the sand. Then, stirring and mixing are performed until the sand and the coating resin composition become uniform while maintaining the mixing temperature.

  The coating resin composition is a curable resin composition that becomes the above-described cured coating resin by curing.

  Examples of the coating resin composition include a furan resin composition, a phenol resin composition, an epoxy resin composition, a silicone resin composition, a resol type phenol resin composition, and preferably a furan resin composition.

  In the presence of an acid, the furan resin composition is in a completely cured state (C stage), for example, at 35 ° C. or higher and lower than 150 ° C. The furan resin composition contains a furan resin precursor.

  Examples of the furan resin precursor include furfuryl alcohol and furan resin prepolymer.

  As a furan resin prepolymer, for example, a furfuryl alcohol homopolymer, a copolymer of furfuryl alcohol and an aldehyde compound, a copolymer of furfuryl alcohol, urea and an aldehyde compound (urea-modified furan resin prepolymer), Examples thereof include a copolymer of furfuryl alcohol and furfural. Furan resin prepolymers can be used alone or in combination of two or more.

  Among such furan resin prepolymers, a copolymer of furfuryl alcohol, urea and an aldehyde compound (urea-modified furan resin prepolymer) is preferable. Examples of the aldehyde compound as the monomer of the urea-modified furan resin prepolymer include formaldehyde, acetaldehyde, glyoxal, paraformaldehyde, and preferably paraformaldehyde.

  As such a furan resin precursor, either furfuryl alcohol or furan resin prepolymer can be used alone, but preferably furfuryl alcohol and furan resin prepolymer are used in combination.

  The content ratio of the furan resin precursor is, for example, 10% by mass or more, preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 90% by mass with respect to the total amount of the furan resin composition. For example, it is 95% by mass or less.

  When the furan resin composition contains furfuryl alcohol and a furan resin prepolymer, the content ratio of the furan resin prepolymer is, for example, 1 part by mass or more, preferably 100 parts per 100 parts by mass of furfuryl alcohol. It is 150 parts by mass or more, for example, 300 parts by mass or less, preferably 150 parts by mass or more.

  In addition to the above components, the coating resin composition can contain a solvent, the above-described crosslinking agent, and the like. Examples of the solvent include water, acetone, ethyl acetate, alcohol and the like, and preferably water.

  The mixing ratio of the coating resin composition is, for example, 0.005 parts by mass or more, preferably 0.10 parts by mass or more, more preferably 0.15 parts by mass or more, particularly preferably 100 parts by mass of sand. 0.20 parts by mass or more, for example, 3 parts by mass or less, preferably 0.50 parts by mass or less, and more preferably 0.30 parts by mass or less.

  The mixing temperature is, for example, 0 ° C. or higher, preferably 35 ° C. or higher, preferably 70 ° C. or higher, such as 150 ° C. or lower, preferably 100 ° C. or lower, more preferably 90 ° C. or lower, and particularly preferably 80 ° C. or lower. It is below ℃.

  When the stirring target (mixture of sand and coating resin composition) is 1 kg, the stirring time is, for example, 1 second or more, preferably 3 seconds or more, for example, 20 seconds or less, preferably 10 seconds or less. is there. The stirring time is N times the above when the stirring target is N kg.

  Thereby, the coating resin composition is coated so as to surround each particle of the sand.

(1-4-2) Curing step of coating resin composition Next, the coating resin composition to be coated so as to surround the sand is cured.

  The method for curing the coating resin composition is appropriately selected depending on the type of the corresponding coating resin composition.

  For example, when the coating resin composition is a furan resin composition, the curing agent containing the acid catalyst described above is added to and mixed with the sand mixed with the furan resin composition. Then, stirring and mixing are performed until the sand to which the curing agent is added smoothly flows.

  The mixing ratio of the curing agent is, for example, 0.005 parts by mass or more, preferably 0.05 parts by mass or more, more preferably 0.15 parts by mass or more, and particularly preferably 0 with respect to 100 parts by mass of sand. 20 parts by mass or more, for example, 3 parts by mass or less, preferably 0.50 parts by mass or less, and more preferably 0.30 parts by mass or less.

  In the stirring of the sand and the curing agent, the range of the stirring temperature is, for example, the same as the range of the stirring temperature described above, and the range of the stirring time is, for example, the same as the range of the stirring time described above.

  As a result, the furan resin composition covering the sand comes into contact with the curing agent to form a furan resin film (cured resin resin), and a surface modified layer containing the furan resin covering the sand is formed.

  Specifically, when the furan resin composition contains furfuryl alcohol, as shown in the following formula (1), the furfuryl alcohol undergoes condensation polymerization by contacting with an acid catalyst (in the formula, HA). To form furan resin.

Formula (1)

  Further, as shown in the above formula (1), water is generated in the condensation polymerization of furfuryl alcohol.

  A part of the water produced by the reaction is leached on the surface of the surface modification layer and then removed by evaporation. At this time, the curing agent containing the acid catalyst is extruded onto the surface of the surface modification layer together with water. Thereby, a hardening | curing agent adheres to the surface of a surface modification layer, and forms a hardening | curing agent layer. That is, in this embodiment, the curing agent that cures the coating resin composition is also used as the curing agent that cures the binder resin composition.

  Moreover, the water which did not ooze out on the surface of the surface modification layer is contained in, for example, furan resin, or when artificial sand contains potassium feldspar or soda feldspar, the following formula (2) and formula As shown in (3), it is removed by reacting with potassium feldspar and soda feldspar.

Formula (2)

Formula (3)

  Thus, foundry sand is prepared that includes sand, a surface modified layer containing a cured coating resin coating the sand, and a hardener layer attached to the surface modified layer.

(1-5) Binder resin cured product As shown in FIG. 1, the binder resin cured product 5 has a plurality of foundry sands 1 bonded to each other, and the surface modified layer 3 (and / or cured) of each foundry sand 1. It adheres to the agent layer 4).

  The cured binder resin 5 is a cured product of the binder resin composition, and the curing reaction has been completed. For example, even when heated, the curing reaction does not proceed any further. In the present embodiment, the binder resin composition is a furan resin composition.

  The furan resin composition as the binder resin composition contains the above-mentioned furan resin precursor. As the furan resin precursor of the binder resin composition, preferably, furfuryl alcohol is used, and more preferably, furfuryl alcohol is used alone.

  The content ratio of the furan resin precursor is, for example, 1% by mass or more, preferably 10% by mass or more, more preferably 85% by mass or more, for example, 100% by mass or less, with respect to the total amount of the furan resin composition. Preferably, it is 95 mass% or less.

  Further, the furan resin composition can contain a curing accelerator and the like in addition to the above furan resin precursor. Examples of the curing accelerator include resorcin, cresol, hydroquinone, phloroglucinol, methylene bisphenol, bishydroxymethyl furan, and the like.

  When such a binder resin composition (furan resin composition) is added to the foundry sand in the sand mold shaping described later, the binder resin composition (furan resin composition) comes into contact with the curing agent of the foundry sand and cures to become a cured binder resin. .

(1-6) Sand Mold Modeling (Manufacturing) Method Such a sand mold is not particularly limited, and is modeled by a known modeling method. Examples of the sand mold forming method include an original model forming method using a prototype (for example, a wooden mold or a mold), a three-dimensional layered modeling method (that is, modeling by a 3D printer), and preferably 3 A three-dimensional layered manufacturing method is mentioned.

  In the three-dimensional additive manufacturing method, a binder resin composition in a layer of foundry sand is formed by adding the above-described binder resin composition (furan resin composition) to the foundry sand layer, and a step of forming the above-described foundry sand into a layer shape. A sand mold is formed by repeating the step of hardening the added portion.

2. Casting process The sand mold can be used for casting various industrial products, and is suitably used for casting automobile parts such as a cylinder head, for example.

  In casting, after a molten metal is poured into a sand mold, the molten metal is cooled and solidified into a predetermined shape. Thereby, a casting is manufactured. Examples of the material for the molten metal include aluminum alloys and cast iron. The heating temperature of the molten metal is appropriately changed according to the material. For example, when the molten metal is an aluminum alloy, the temperature is 600 ° C. or higher.

  Therefore, as shown in FIG. 1, in the sand mold, at least a part of the surface modification layer 3 covering the sand 2 is burned away in the foundry sand 1 in contact with the molten metal and the foundry sand 1 located in the vicinity thereof. On the other hand, the casting sand 1 far from the molten metal (casting) is maintained so as to cover the entire surface of the sand 2 without burning out the surface modification layer 3.

  As a result, the sand mold after casting is such that the molding sand 1 having the surface modification layer 3 covering the entire surface of the sand 2 and at least a part of the surface modification layer 3 are burned away, and the sand 2 is the surface modification layer 3. Casting sand 1 (hereinafter referred to as burnt casting sand 8).

3. Next, a machining process for the sand mold after casting will be described.

  The machining process includes a crushing process for crushing the sand mold, and preferably further includes a sizing process for sizing the recovered sand obtained by the crushing process.

(3-1) Crushing step In the crushing step, the sand mold is pulverized by a known crusher so that a plurality of foundry sands are separated from each other.

  Examples of the crusher include a hammer crusher and a roll crusher.

  The crushing conditions are not particularly limited as long as a plurality of foundry sands can be separated from each other.

  Moreover, the temperature in a crushing process is normal temperature, Comprising: For example, it is 0 degreeC or more and 40 degrees C or less.

  The crushing time is not particularly limited, and is, for example, 20 seconds or longer and 2 minutes 30 seconds or shorter when the crushing object (sand mold) is 1 kg. The crushing time is N times the above when the crushing object is Nkg.

  As a result, the sand mold is separated and the cured binder resin (furan resin) is peeled off from the foundry sand. Therefore, a plurality of foundry sands are separated from each other to obtain recovered sand.

  As shown in FIGS. 2A to 2C, the recovered sand includes reclaimed sand 10 derived from foundry sand 1 (cast sand 1 in which the surface modification layer 3 is not burned away) included in the sand mold after casting, and reclaimed sand 10. The adhesion reproduction | regeneration sand 11 to which the binder resin hardened | cured material 5 adheres to this, and the burning reproduction | regeneration sand 12 derived from the burning casting sand 8 contained in the sand mold after casting are included. That is, reclaimed sand can be produced from the cast sand mold only by the crushing step.

  The recycled sand 10 has the same configuration as the foundry sand 1, and includes a sand 2, a surface modified layer 3 that covers the entire surface of the sand 2, and a hardener layer that adheres to the surface of the surface modified layer 3. 4.

  The adhered reclaimed sand 11 has reclaimed sand 10 and a cured binder resin 5 that adheres to the surface modification layer 3 of the reclaimed sand 10.

  The burned and regenerated sand 12 includes sand 2, a surface modified layer 3 that exposes the sand 2 when at least a part of the surface modified layer 3 is burned, and a hardener layer 4 that adheres to the surface of the surface modified layer 3. And have. Further, the hardener layer 4 is burned out together with the surface modified layer 3 in the burned-out portion of the surface modified layer 3.

(3-2) Sizing Step In the sizing step, the recovered sand obtained in the crushing step is sized so that, for example, the nominal size is 212 μm or less. The sizing process is performed by, for example, a sizing apparatus having a 70 mesh screen.

  Thereby, the adhesion reproduction | regeneration sand 11 etc. whose nominal dimension exceeds 212 micrometers are removed from collection | recovery sand.

(3-3) Polishing Step The machining step preferably further includes a polishing step for polishing the recovered sand. The polishing step is not particularly limited as long as it is after the crushing step, and may be performed before the sizing step or may be performed after the sizing step, but is preferably performed after the sizing step. The

  A grinding | polishing process is implemented by a well-known grinding | polishing apparatus, for example so that the binder resin hardened | cured material 5 adhering to the adhesion reproduction | regeneration sand 11 may be peeled. The polishing apparatus includes, for example, a storage tank that stores the collected sand, and a rotatable rotating body that is disposed in the storage tank.

  Then, when the rotating rotating body comes into contact with the recovered sand, the recovered sand is polished, and the binder resin cured product 5 attached to the attached recycled sand 11 is removed. As a result, the attached reclaimed sand 11 becomes reclaimed sand 10.

  The temperature range in the polishing process is the same as the temperature range in the crushing process described above. The polishing time is not particularly limited. For example, when the polishing object (collected sand) is 1 kg, the polishing time is 20 seconds or longer and 2 minutes 30 seconds or shorter. The polishing time is N times the above when the object to be polished is N kg.

  Thereafter, the above-described sizing step is performed as necessary. The number of times the sizing process is performed is not particularly limited.

  Thus, recycled sand is produced.

<Recycled casting sand (manufacturing method)>
Further, such reclaimed sand may include burnt reclaimed sand 12 shown in FIG. 2C as described above. Therefore, preferably, the regenerated sand is recoated and regenerated (manufactured) as foundry sand.

  Such a method for regenerating casting sand (manufacturing method) includes a step of mixing the regenerated sand and the coating resin composition, and a step of mixing a hardener with the regenerated sand mixed with the coating resin composition. . In the molding sand regeneration method (manufacturing method), the coating resin composition is preferably a furan resin composition.

  In order to mix the reclaimed sand and the coating resin composition, the same method as the mixing step of the sand and the coating resin composition described above can be used.

  Specifically, after the regenerated sand is preheated to the above mixing temperature, the above-described coating resin composition is added to the regenerated sand at the above mixing ratio. Thereafter, under the above-described stirring conditions, the recycled sand and the above-described coating resin composition are stirred and mixed until they are uniform. Thereby, a coating resin composition coat | covers so that the circumference | surroundings of each particle | grains of reproduction | regeneration sand may be surrounded.

  Next, in order to mix the curing agent with the regenerated sand mixed with the coating resin composition, the same method as the mixing step of the sand and the curing agent described above can be used.

  Specifically, the above-mentioned curing agent containing the acid catalyst is added to the regenerated sand mixed with the coating resin composition at the mixing ratio described above. Thereafter, under the above-described stirring conditions, stirring and mixing are performed until the regenerated sand to which the curing agent is added smoothly flows. Thereby, the coating resin composition which coat | covers the reproduction | regeneration sand contacts with a hardening | curing agent, and is hardened.

  As described above, as shown in FIG. 2A, the regenerated sand is recoated so that the sand 2, the surface modified layer 3 containing the cured coating resin covering the entire surface of the sand 2, and the surface modified layer 3 are formed. The foundry sand 1 provided with the adhering hardener layer 4 is regenerated (manufactured).

  Each of such recycled sand and foundry sand (recoated sand obtained by recoating recovered sand) can be suitably used for the above-described sand mold forming method, in particular, the three-dimensional additive manufacturing method (that is, modeling by a 3D printer).

  It is also possible to mix and use recovered sand and re-coated sand according to various applications, and mix recovered sand and / or re-coated sand with new foundry sand that is not used for sand mold shaping. Can also be used.

4). In the sand mold used in the above-mentioned method for producing reclaimed sand, as shown in FIG. 1, the foundry sand 1 includes sand 2 and a surface modified layer 3 containing a cured coating resin covering the sand 2. The binder resin cured product 5 is attached to the surface modification layer 3.

  Therefore, the cured binder resin 5 can be peeled from the surface modified layer 3 by performing machining on the sand mold.

  That is, the binder resin cured product 5 adhering to the surface modification layer 3 can be peeled and removed only by machining. Therefore, as shown in FIG. 2A, the reclaimed sand 10 can be produced from the sand mold only by machining without heat treatment.

  In addition, when the sand 2 is artificial sand, the artificial sand has higher crush resistance than that of natural silica sand, so that the above embodiment can stably produce reclaimed sand, The sand recyclability can be improved.

  On the other hand, when the curing agent containing an acid catalyst comes into contact with artificial sand, the activity of the acid catalyst may be reduced due to components contained in the artificial sand.

  For example, when the artificial sand contains potassium feldspar, potassium feldspar and water react to generate potassium carbonate as shown in the above formula (2).

And potassium carbonate reacts with an acid catalyst (HA) as shown in the following formula (4).
Formula (4)

  Thereby, the acid catalyst (HA) in a hardening | curing agent will be converted into a weak acid (KA), and the active ability of a hardening | curing agent will fall.

In addition, the carbonic acid produced | generated by reaction of potassium carbonate and an acid catalyst is decomposed | disassembled into water and a carbon dioxide, as shown in following formula (5).
Formula (5)

  On the other hand, in the regenerated sand 10, since the surface modified layer 3 containing the cured coating resin coats the sand 2, the surface modified layer 3 can prevent the curing agent from coming into contact with the sand 2. Therefore, it can suppress that the active ability of a hardening | curing agent falls. As a result, when the binder resin composition is added to the recycled sand 10, the binder resin composition can be reliably cured, and the sand mold can be reliably shaped.

  Further, in the casting, since the molten metal is poured into the sand mold, as shown in FIG. 1, among the casting sand contained in the sand mold, the casting sand in contact with the molten metal or the casting sand located in the vicinity thereof is sand 2. At least a part of the surface modification layer 3 that coats is burned away.

  Therefore, as shown in FIG. 2C, the regenerated sand produced from the sand mold includes burnt regenerated sand 12 in which a part of the surface modification layer 3 has been burned away. In the burnt portion of the surface-modified layer 3 in the burned reclaimed sand 12, the hardener layer 4 is burned together with the surface-modified layer 3, and the sand 2 is exposed from the surface-modified layer 3. May come into contact with hardener.

  As a result, if the recycled sand containing the burned recycled sand 12 is recycled into a sand mold, the accuracy and strength of the sand mold may be reduced.

  On the other hand, in the above embodiment, after the recycled sand and the coating resin composition are mixed, the curing agent is mixed. Therefore, after coating the coating resin composition so as to surround each particle of the recycled sand, the coating resin composition is cured with a curing agent to form a cured coating resin.

  As a result, as shown in FIG. 2A, even if the regenerated sand contains burnt regenerated sand 12 (see FIG. 2C), the sand 2 can be recoated with the coating resin cured product, and the foundry sand 1 can be reliably Can be manufactured (regenerated).

5. Although the said embodiment demonstrates the case where a sand mold is a furan self-hardening sand mold, this invention is not limited to this. For example, the binder resin composition may be a phenol resin and may be a phenol urethane self-hardening sand type in which the curing agent is polyisocyanate, the binder resin composition is an alkali phenol resin, and the curing agent is an organic ester. It may be a self-hardening sand mold. Moreover, the thermosetting sand type | mold (resin coated sand) whose binder resin composition is a phenol resin may be sufficient. In this case, each of the foundry sand and the recycled sand does not have a hardener layer.

  Also by these, the same effect as said embodiment can be show | played.

  The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to them. Specific numerical values such as blending ratio (content ratio), physical property values, and parameters used in the following description are described in the above-mentioned “Mode for Carrying Out the Invention”, and the corresponding blending ratio (content ratio) ), Physical property values, parameters, etc. The upper limit value (numerical value defined as “less than” or “less than”) or lower limit value (number defined as “greater than” or “exceeded”) may be substituted. it can.

(Production Example 1: Production of foundry sand)
Artificial sand (mullite sand, trade name: ESPARL # 100DAM, manufactured by Yamakawa Sangyo Co., Ltd.) and a coating resin composition (furan resin composition) shown in Table 1 were prepared. The artificial sand contained potassium feldspar and soda feldspar. The artificial sand had an AFS (particle size index) of 106.4.

  Next, 100 parts by weight of artificial sand was preheated to 70 ° C., and then 0.25 part by weight of the coating resin composition was added and stirred and mixed until the artificial sand and the coating resin composition were uniform.

  Thereafter, 0.25 parts by mass of a curing agent containing xylene sulfonic acid (acid catalyst) is added to the artificial sand mixed with the coating resin composition, and stirred until the artificial sand to which the curing agent has been added smoothly flows. Mixed. The concentration of xylene sulfonic acid in the curing agent was 95.0 mass% or more and 97.0 mass% or less. Further, in the curing agent mixing step, the temperature range of 70 ° C. + 5 to 10 ° C. was maintained.

  As a result, there was obtained casting sand including artificial sand, a surface modified layer containing a furan resin covering the artificial sand, and a curing agent attached to the surface modified layer.

(Production Example 2: Production of sand mold)
The foundry sand obtained in Production Example 1 and the binder resin composition (furan resin composition) shown in Table 1 are set in a three-dimensional additive manufacturing apparatus (trade name: S-Print, manufactured by ExOne), and cast. Sand layer formation and addition of the binder resin composition to the casting sand layer were sequentially repeated to form a sand mold used for casting the cylinder head.

  Thereafter, a molten aluminum alloy was poured into the sand mold and then cooled to cast a cylinder head.

(Example 1: Production of recycled sand)
After completion of casting, the sand mold obtained in Production Example 2 was crushed by a crusher so that a plurality of foundry sands were separated from each other to obtain recovered sand.

  Next, the recovered sand was sized with a 70-mesh sieve so that the nominal size was 212 μm or less. Thus, recycled sand was obtained.

(Example 2: Production of recycled sand)
The recycled sand obtained in Example 1 was polished by a polishing machine. Thereafter, the polished recycled sand was sized with a 70-mesh sieve so that the nominal size was 212 μm or less. Thus, recycled sand was obtained.

(Examples 3 and 4: Production of foundry sand)
After 100 parts by weight of the reclaimed sand obtained in Examples 1 and 2 is preheated to 70 ° C., 0.25 part by weight of the coating resin composition shown in Table 1 is added to obtain the reclaimed sand and the coating resin composition. Stir and mix until uniform.

  Thereafter, 0.25 parts by mass of a curing agent containing xylene sulfonic acid (acid catalyst) is added to the regenerated sand mixed with the coating resin composition, and stirred until the regenerated sand to which the curing agent is added smoothly flows. Mixed. The concentration of xylene sulfonic acid in the curing agent was 95.0 mass% or more and 97.0 mass% or less. Further, in the curing agent mixing step, the temperature range of 70 ° C. + 5 to 10 ° C. was maintained.

As a result, casting sand (recoated sand) including artificial sand, a surface modified layer containing a furan resin covering the artificial sand, and a curing agent attached to the surface modified layer was obtained.
<Evaluation>
A sand mold used for casting the cylinder head was formed from each of the recycled sand and the recoated sand of Examples 1 to 4 in the same manner as in Production Example 2. The molten aluminum alloy was poured into these sand molds and then cooled to cast a cylinder head. Thereafter, the cylinder heads obtained were compared with the cylinder heads cast by the sand mold of Production Example 2, and it was confirmed that the cylinder heads were equivalent.

DESCRIPTION OF SYMBOLS 1 Foundry sand 2 Sand 3 Surface modification layer 10 Recycled sand 30 Sand mold

Claims (2)

  A plurality of foundry sand having sand and a surface modified layer containing a cured coating resin coating the sand, and a sand mold containing a binder resin cured product that adheres the plurality of foundry sand to each other, A method for producing reclaimed sand, characterized by performing only machining. Mixing the reclaimed sand produced by the method for producing reclaimed sand according to claim 1 and a coating resin composition;
And a step of mixing a curing agent with the regenerated sand mixed with the coating resin composition.

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