JP2009269038A - Casting mold manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a casting mold manufacturing method capable of suppressing reduction of the hardening rate when manufacturing a casting mold by using reproduced casting sand of chromite sand and a binder containing acid-hardening resin. <P>SOLUTION: When manufacturing a casting mold by using reproduced casting sand of chromite sand together with a binder containing acid-hardening resin and a hardening agent, the reproduced casting sand is used, which is obtained from a casting mold manufactured by using chromite sand, a binder containing acid-hardening resin, and a hardening agent containing methanesulfonic acid with its sulfuric acid content in the hardening agent being ≤5 wt.%. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  In order to compensate for the shortcomings of silica sand, which has been widely used for foundry sand (fire-resistant granular material) used for molding of molds, chromite sand with low thermal expansion coefficient and high fire resistance is used as foundry sand, especially in the cast steel casting field. It is done. Also in chromite sand, a furan self-hardening process, which is a mold forming process using an acid-curable furan resin, is widely used, but it is also known that there are some problems.

  In Patent Document 1, in the case of furan resin using acid as a curing agent, chromite sand adds a binder containing an acid-curable furan resin to chromite sand for the problem of low mold strength, A mold manufacturing method comprising adding a curing agent to cure an acid curable furan resin is disclosed.

  Patent Document 2 describes the use of para-toluenesulfonic acid or xylenesulfonic acid as a curing catalyst for a furan resin containing nitrogen in obtaining a furan mold using recycled foundry sand.

Patent Document 3 describes a binder-coated sand particle for a mold using a furan resin and methanesulfonic acid as an acid curing agent.
Japanese Patent Laid-Open No. 2000-102840 JP 57-58948 A Japanese Patent Laid-Open No. 9-234540

  In general, foundry sand is recycled repeatedly. Cast iron with relatively high iron and aluminum content, such as chromite sand, is produced using an acid curable resin and a curing agent. In this case, there is a problem that the curing rate of the mold is lowered. In particular, when performing a strong regeneration process in order to manage the residual resin content of the reclaimed foundry sand, or when the sand metal ratio, which is the weight ratio of the mold to the foundry [mould / molten metal (weight ratio)], is low, This problem appears prominently. This problem cannot be solved even when the same curing agent used for the mold for obtaining the reclaimed foundry sand is used for obtaining the mold from the reclaimed foundry sand. Moreover, patent document 1, 3 does not mention the problem about such chromite sand. On the other hand, Patent Document 2 describes that chromite sand can be used as recycled sand, but the strength of chromite recycled foundry sand is not sufficient even with the method of Patent Document 2.

  The present invention is to provide a production method capable of suppressing a decrease in the curing rate in producing a mold using a reclaimed foundry sand having a relatively high iron element or aluminum element content such as chromite sand. .

  The present invention is a method for producing a mold including a step of producing a mold using recycled foundry sand, wherein the recycled foundry sand comprises (1) chromite sand, and (2) a binder containing an acid-curable resin. (3) The present invention relates to a method for producing a mold, which is obtained from a mold produced using a curing agent containing methanesulfonic acid and having a sulfuric acid content of 5% by weight or less.

  The present invention also relates to a method of repeatedly using chromite sand in the production of a mold and the production of reclaimed casting sand from the mold, wherein the mold is composed of (1) chromite sand and (2) an acid curable resin. The present invention relates to a method for repeatedly using chromite sand for molds, which is produced by using a binder contained and (3) a curing agent containing methanesulfonic acid and having a sulfuric acid content of 5% by weight or less.

  According to the present invention, it is possible to suppress a decrease in the curing rate when producing a mold using recycled casting sand obtained from a mold using chromite sand, and to obtain a good mold strength, particularly an initial mold strength. Can do.

The present invention is a method for producing a mold using recycled foundry sand, a binder (I) containing an acid curable resin, and a curing agent (I),
The reclaimed foundry sand is reclaimed foundry sand obtained from a mold produced using a chromite sand (A), a binder (II) containing an acid curable resin, and a hardener (II),
The curing agent (II) contains methanesulfonic acid, and the sulfuric acid content in the curing agent is 5% by weight or less.
It can be implemented as a method for producing a mold. Therefore, the following description is based on this aspect.

The reclaimed foundry sand used in the present invention is reclaimed foundry sand obtained from a mold produced using a chromite sand (A), a binder (II) comprising an acid curable resin, and a hardener (II). . Here, the curing agent (II) contains methanesulfonic acid, and the sulfuric acid content in the curing agent is 5% by weight or less. The curing agent (II) preferably has a phosphoric acid content of 5% by weight or less. Regarding the curing agent (II), sulfuric acid refers to a substance represented by the chemical formula H ₂ SO ₄ , and phosphoric acid is a general term for acids formed by hydration of diphosphorus pentoxide, including metaphosphoric acid, pyrophosphoric acid, Examples include orthophosphoric acid, phosphoric acid, diphosphoric acid, triphosphoric acid, and tetraphosphoric acid.

  The curing agent (II) contains methanesulfonic acid. In the curing agent (II), the content of methanesulfonic acid is preferably 5 to 100% by weight, more preferably 10 to 90% by weight, and still more preferably 20 to 70% by weight.

  The curing agent (II) can contain other organic sulfonic acid in addition to methanesulfonic acid. Other organic sulfonic acids include alkanes such as ethane sulfonic acid, benzene sulfonic acid, toluene sulfonic acid, xylene sulfonic acid, aryl sulfonic acid, phenol sulfonic acid, etc., but from the viewpoint of mold strength, cost, etc., xylene At least one selected from the group consisting of sulfonic acid, toluenesulfonic acid, and ethylbenzenesulfonic acid is preferable, and at least one selected from the group consisting of xylenesulfonic acid and toluenesulfonic acid is more preferable.

  Other organic sulfonic acids may contain isomers produced during production. For example, taking xylene sulfonic acid as an example, m-xylene-4-sulfonic acid, m-xylene-2-sulfonic acid, o-xylene-4-sulfonic acid, o-xylene-2-sulfonic acid, p-xylene -2-sulfonic acid and disulfonic acid such as m-xylene-2,4-disulfonic acid and m-xylene-2,6-disulfonic acid may be contained as impurities.

  The content of other organic sulfonic acids in the curing agent (II) is preferably 0 to 95% by weight, more preferably 0 to 80% by weight, and still more preferably 0 to 75% by weight.

  The contents of sulfuric acid, sulfonic acid and phosphoric acid in the curing agent (I) and the curing agent (II) can be identified by potentiometric titration, elemental analysis and / or NMR.

  Curing agent (II) can be used in combination with methanesulfonic acid and other curing agents such as sulfuric acid and phosphoric acid other than organic sulfonic acid. From this viewpoint, the content of sulfuric acid in the curing agent (II) is 5% by weight or less, preferably 1% by weight or less, and more preferably substantially 0% by weight. From the same viewpoint, the content of phosphoric acid in the curing agent (II) is preferably 5% by weight or less, more preferably 1% by weight or less, and still more preferably 0% by weight. “Substantially” means that an impurity amount may be contained.

  Hardener (II) may contain methanesulfonic acid, sulfur (S) element derived from other organic sulfonic acid and sulfuric acid, but maintain mold hardening speed and improve strength when using reclaimed foundry sand. In view of the above, the proportion of the amount of S element derived from organic sulfonic acid in the total amount of S element contained in the curing agent (II) is preferably 80% by weight or more, more preferably 90% by weight or more, and substantially 100% by weight. % Is more preferable. Further, from the same viewpoint, the ratio of the amount of S element derived from sulfuric acid to the total amount of S element in the curing agent (II) is preferably 10% by weight or less, more preferably 6% by weight or less, and substantially 0% by weight. Is more preferable. Further, the amount of phosphorus (P) element contained in the curing agent (II) is preferably 1% by weight or less, and more preferably substantially 0% by weight. “Substantially” means that an impurity amount may be contained.

  A known acidic substance other than methanesulfonic acid and other organic sulfonic acids may be added to the curing agent (II). The acidic substance may contain, for example, one kind or a mixture of two or more kinds of organic acids such as carboxylic acids and inorganic acids such as nitric acid, but the amount of sulfuric acid, more preferably phosphoric acid is limited. .

  In addition, the curing agent (II) may contain a diluent solvent such as water or alcohol. As the solvent used for the dilution solvent, water, methanol, ethanol, and isopropyl alcohol are preferable from the viewpoint of cost and the like.

In the present invention, by using reclaimed foundry sand from a mold containing methanesulfonic acid and using a specific curing agent (II) having a reduced amount of sulfuric acid, in reclaimed foundry sand of chromite sand (A) , It is possible to suppress a decrease in the curing speed during regeneration. The reason for this is unknown, but in the case of sulfuric acid, it reacts with iron and Al ₂ O ₃ components in the chromite sand due to the heat during casting, producing some kind of hardening inhibitor, which is the next recycled casting. It is presumed that sand molding is affected. On the other hand, in the case of methanesulfonic acid, since such a curing inhibitor is hardly generated, it is presumed that a decrease in the curing rate during regeneration is prevented.

  The curing agent (II) is used together with a binder (II) containing an acid curable resin. Examples of the acid curable resin include acid curable furan resins and acid curable phenol resins. As the acid curable furan resin, conventionally known resins are used, and these are used alone or in combination as a binder. Specific examples of the acid curable furan resin include furfuryl alcohol, furfuryl alcohol polymer, and furfuryl alcohol / aldehyde polycondensate. Furthermore, mixtures or cocondensates with furfuryl alcohol such as phenols / aldehydes polycondensates, melamine / aldehydes polycondensates, urea / aldehydes polycondensates, etc. are used. Moreover, what further co-condensed 2 or more types of these polycondensates can also be used as an acid-curable furan resin. Conventionally known aldehyde compounds such as formaldehyde, glyoxal, and furfural can be used as aldehydes that are polycondensed with furfuryl alcohol or the like. Moreover, when using phenols and aldehydes polycondensate, as phenols, conventionally well-known phenol compounds, such as phenol, resorcinol, bisphenol A, bisphenol F, can be used individually or in mixture. Moreover, you may use it with a well-known modifier | denaturant.

  When the binder (II) contains an acid curable furan resin as the acid curable resin, one or more of the compounds represented by the following general formula (1) is selected from the viewpoint of further improving the mold strength. It is preferable to contain.

  Examples of the compound of the general formula (1) include 2,5-bishydroxymethylfuran, 2,5-bismethoxymethylfuran, 2,5-bisethoxymethylfuran, 2-hydroxymethyl-5-methoxymethylfuran, 2- Examples thereof include hydroxymethyl-5-ethoxymethylfuran and 2-methoxymethyl-5-ethoxymethylfuran, which are used alone or in combination. In particular, it is preferable to use 2,5-bishydroxymethylfuran.

  The content of the compound represented by the general formula (1) in the binder (II) is, for example, 0.5 to 63.0% by weight, preferably 1.8 to 50.0% by weight, more preferably 2.5. -50.0 wt%, more preferably 5.0-40.0 wt%, still more preferably 7.0-40.0 wt%. When the amount of the compound represented by the general formula (1) is 0.5% by weight or more, an effect of improving the mold strength due to the inclusion of the compound represented by the general formula (1) is easily obtained, When it is 63.0% by weight or less, it is easy to prevent the compound represented by the general formula (1) from rapidly dissolving in the acid curable resin and causing precipitation in the binder.

  Moreover, when binder (II) contains acid-curable furan resin as acid-curable resin, it is preferable to contain a polyphenol compound from the point of a hardening rate improvement. A synthetic or natural polyphenol compound can be used as the polyphenol compound. For example, synthetic products such as catechol, resorcinol, hydroquinone, pyrogallol and phloroglucinol, and synthetic polyphenol compounds having a skeleton derived therefrom, natural polyphenol compounds such as tannin, lignin and catechin, and skeletons derived therefrom Examples include synthetic polyphenol compounds. Moreover, content in binder (II) of a polyphenol compound becomes like this. Preferably it is 0.1 to 40 weight%, More preferably, it is 0.1 to 20 weight%, More preferably, it is 3 to 10 weight%. When the content of the polyphenol compound is within this range, the polyphenol compound is preferably dissolved in the acid curable resin without causing precipitation.

  Further, when a mold is produced using the binder (II), a silane coupling agent may be added for the purpose of further improving the mold strength. As the silane coupling agent, for example, γ- (2-amino) aminopropylmethyldimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane and the like are used. be able to. In order to add the silane coupling agent to the kneaded sand, the silane coupling agent is added to the binder (II) or the curing agent (II), and the binder (II) or the curing agent ( II) may be added and kneaded to chromite sand (A), or a silane coupling agent may be directly added and kneaded to chromite sand (A).

  The chromite sand (A) used in the present invention has a particle size distribution of 30 to 1500 μm. The particle size distribution is measured according to JIS foundry sand particle size distribution test method (Z 2601).

The chemical composition of chromite sand (A) is generally 45 to 50% by weight of Cr ₂ O _3, 0.3 to 1.5% by weight of SiO ₂ , 25 to 30% by weight of FeO, and 5 to 15% by weight of MgO. %, Al ₂ O ₃ is 10 to 20%. Examples of other components include CaO and TiO ₂ .

  Examples of the chromite sand (A) include trade names “chromite # A201”, “chromite # A301”, “chromite # A401” (manufactured by Yamakawa Sangyo Co., Ltd.), and trade names “tochu chromite sand” (manufactured by Tochu). Is mentioned.

  In order to mold a mold using the chromite sand (A), the binder (II) containing the acid curable resin, and the curing agent (II), according to a conventional method, for example, first, chromite Bonds containing 0.2 to 3 parts of curing agent (II) to 100 parts of sand (A) (weight basis, the same below), and then containing 0.5 to 5 parts equivalent of acid-curable furan resin The agent (II) is mixed and molded.

  The method for obtaining reclaimed foundry sand from the mold can be in accordance with a known method, and a normal mechanical wear type or roasting type reclaim method is used. Economically preferable.

  From the viewpoint of maintaining the hardening rate of the mold and improving the strength of the reclaimed casting sand, the elution amount of iron element and aluminum element per 1 g of sand is 150 μg or less, further 120 μg or less, further 60 μg or less, The aluminum element is preferably 20 μg or less, more preferably 10 μg or less.

(Measurement method of elution amount of iron element and aluminum element)
25.0 g of reclaimed foundry sand is weighed in a beaker, 50.0 ml of 0.1N HCl aqueous solution is added, and then stirred for 15 minutes with a magnetic stirrer. After standing for 5 minutes, the supernatant liquid is filtered using filter paper, and the amount of iron element and aluminum element in the filtrate is determined by ICP analysis (inductively coupled plasma emission spectrometry), and per 1 g of recycled foundry sand. Calculate the amount of elution.

  In addition, this aluminum elution amount can be adjusted by adjusting the strength of machine regeneration (number of processing stages, processing time, number of revolutions of regenerator, etc.) in the regeneration of chromite sand (A), and molding conditions (sand metal ratio, etc.) It can be adjusted by changing

  The reclaimed foundry sand preferably has a loss on ignition of 3% by weight or less, more preferably 2% by weight or less, further 1% by weight or less, and still more preferably 0.5% by weight or less. The loss on ignition is the mass change rate of the substance that thermally decomposes in addition to the adsorbed moisture and interlayer moisture remaining in the foundry sand. In the present invention, the Japan Casting Technology Association Standard: “JACT It means what was measured in accordance with “Testing method for loss on ignition of foundry sand” defined in “Test method S-2”.

  In the present invention, a mold is produced using the reclaimed foundry sand having a specific history as described above, the binder (I) containing an acid curable resin, and the curing agent (I).

  The binder (I) may be the same as or different from the binder (II), and the preferred embodiment is the same as that of the binder (II). The binder (I) preferably contains an acid curable furan resin as the acid curable resin. In that case, one or more of the compounds represented by the general formula (1) and / or a polyphenol compound is used. It is preferable to contain. Further, the curing agent (I) can be the same as or different from the curing agent (II), but from the viewpoint of repeatedly using the reclaimed foundry sand using the curing agent (II) containing methanesulfonic acid, It is preferable to use a curing agent that satisfies the preferred embodiment of the curing agent (II).

  In order to manufacture a mold using the reclaimed foundry sand, the binder (I), and the hardener (I), for example, first, 100 parts of reclaimed foundry sand (weight basis, the same applies hereinafter) to the hardener (I ) Is mixed in an amount of 0.2 to 3 parts, and then the binder (I) containing 0.5 to 5 parts of an acid-curable furan resin is mixed and molded. Moreover, the mixed sand obtained by the above may be used for all the molds, or may be used only for necessary portions. For example, it may be used as skin sand, and the back sand may be made of commonly used silica sand. Further, when molding the mixed sand (mold molding composition), a known additive such as an additive for accelerating curing may be used.

  After the kneaded sand is obtained as described above, it is filled into a mold and left at room temperature for a predetermined time, whereby the acid curable furan resin is cured and a mold body can be obtained.

  In the present invention, when the chromite sand is repeatedly used for molding and regeneration, if the regeneration conditions are the same, the mold from which the chromite sand is derived is manufactured under specific conditions. It has been found that it has a positive effect on the suppression of the decrease in the curing rate in the production of. The present invention is a method of repeatedly using chromite sand in the production of a mold and the production of reclaimed foundry sand from the mold, the mold comprising (1) chromite sand and (2) an acid curable resin. It can be implemented as a method of repeatedly using foundry sand, which is produced using a binder and (3) a curing agent containing methanesulfonic acid and having a sulfuric acid content of 5% by weight or less.

  The above description relates to a preferred method for producing a mold according to the present invention, but other methods can be employed as appropriate. For example, in the above description, the preparation of the kneaded sand, the filling of the kneaded sand, and the curing of the binder are performed at room temperature (atmospheric temperature), but may be performed while heating. The mold production method of the present invention can be used for general purposes in the production of various molds.

Example 1
To 100 parts by weight of chromite sand (chromite # A301, manufactured by Yamakawa Sangyo Co., Ltd.), 0.4 part by weight of a 33.9% by weight aqueous solution of methanesulfonic acid [curing agent (II)] was added as a curing agent, followed by furan A test mold was prepared by adding 1.0 part by weight of resin (Kaolitener EF-5401, manufactured by Kao Quaker Co., Ltd.) [Binder (II)] and kneading, and a casting having a sand metal ratio of 2 was cast. The recovered sand was crushed with a crusher to obtain recovered sand. The recovered sand was mechanically regenerated using a hybrid sand master HSM1115 manufactured by Nippon Casting Co., Ltd. at a rotational speed of 2600 rpm, a treatment time of 30 minutes, and a treatment amount of 80 kg to obtain reclaimed foundry sand. Using the obtained reclaimed foundry sand, the elution amounts of iron element and aluminum element were measured, and p-toluenesulfonic acid 61% by weight as a curing agent with respect to 100 parts by weight of sand at 25 ° C. and 55% RH. 0.4 parts by weight of an aqueous solution [curing agent (I)], and then 1.0 part by weight of a furan resin (Kao Quaker Co., Ltd., Kaolitener EF-5401) [Binder (I)] was added and kneaded. Immediately thereafter, a cylindrical test piece having a diameter of 50 mm and a height of 50 mm was prepared, and the compressive strength after 0.5 hours and 24 hours was measured. The results are shown in Table 1.

Example 2
The recovered sand of Example 1 was roasted at 500 ° C. for 1 hour to obtain recycled casting sand, and the elution amounts and compressive strengths of iron element and aluminum element were measured by the same method as described in Example 1. The results are shown in Table 1.

Comparative Example 1
Recycled foundry sand was obtained by the same method as described in Example 1 except that an aqueous solution of 32.7% by weight sulfuric acid was used as the curing agent (II), and the elution amounts and compressive strengths of iron and aluminum elements were measured. The results are shown in Table 1.

Comparative Example 2
The recovered sand of Comparative Example 1 was roasted at 500 ° C. for 1 hour to obtain recycled casting sand, and the elution amount and compressive strength of the iron element and aluminum element were measured by the same method as described in Example 1. The results are shown in Table 1.

Example 3
Recycled foundry sand was obtained in the same manner as described in Example 1 except that an aqueous solution of 9.5% by weight of methanesulfonic acid and 47.8% by weight of xylenesulfonic acid was used as the curing agent (II). The aluminum element elution amount and compressive strength were measured. The results are shown in Table 1.

Comparative Example 3
Recycled foundry sand was obtained in the same manner as described in Example 1, except that an aqueous solution of 9.4% by weight sulfuric acid and 47.8% by weight xylene sulfonic acid was used as the curing agent (II). The amount of elution and compressive strength were measured. The results are shown in Table 1.

Example 4
To 100 parts by weight of chromite sand (chromite # A301, manufactured by Yamakawa Sangyo Co., Ltd.), 0.40 part by weight of a 33.9% by weight aqueous solution of methanesulfonic acid as a curing agent (II) was added, and then a furan resin (Kao) A test mold was prepared by adding and kneading 1.0 part by weight of Caolitener EF-5401) [Binder (II)] manufactured by Quaker Co., Ltd., and castings having a sand metal ratio of 2 were cast. The recovered sand was crushed with a crusher to obtain recovered sand. The recovered sand was mechanically regenerated by using a hybrid sand master manufactured by Nippon Casting Co., Ltd. in the same manner as in Example 1 to obtain reclaimed foundry sand. Further, using the reclaimed foundry sand, the above operation was repeated 5 times, and the fifth reclaimed foundry sand was used to measure the elution amount and compressive strength of iron element and aluminum element in the same manner as described in Example 1. The results are shown in Table 1.

Comparative Example 4
Recycled cast sand was obtained by the same method as described in Example 4 except that an aqueous solution of 32.7% by weight sulfuric acid was used as the curing agent (II), and the elution amounts and compressive strengths of iron element and aluminum element were measured. The results are shown in Table 1.

Example 5
As a binder (II), 10 parts by weight of a polyphenol compound (manufactured by Koshii Wood Solutions, methanol extract of Acacia mangium GKA-100) and furan resin (manufactured by Kao Quaker Co., Ltd., Kao Lightner EF-5401) Except for using the solution consisting of 90 parts by weight, the casting sand was mechanically regenerated by the same method as described in Example 1 to obtain reclaimed casting sand, and the elution amount and hardening behavior of iron element and aluminum element were measured. The results are shown in Table 1.

Comparative Example 5
Recycled foundry sand was obtained by the same method as described in Example 5 except that an aqueous solution of 32.7% by weight sulfuric acid was used as the curing agent (II), and the elution amount and compressive strength of the iron element and aluminum element were measured. The results are shown in Table 1.

Example 6
Curing agent composed of an aqueous solution of 61% by weight of p-toluenesulfonic acid with respect to 100 parts by weight of sand under the conditions of 25 ° C. and 55% RH using the reclaimed foundry sand obtained in Example 5 [curing agent (I) ] 0.6 parts by weight, followed by 10 parts by weight of a polyphenol compound (manufactured by Koshii Wood Solutions, methanol extract of Acacia mangium GKA-100) and furan resin (manufactured by Kao Quaker Co., Ltd., Kao Lightner EF-) 5401) A cylindrical test piece having a diameter of 50 mm and a height of 50 mm was prepared by adding 1.5 parts by weight of a solution [binder (I)] consisting of 90 parts by weight and kneading immediately. Compressive strength was measured after 5 hours and 24 hours. The results are shown in Table 1.

Comparative Example 6
Except for using the reclaimed foundry sand obtained in Comparative Example 5, the elution amounts and compressive strengths of iron element and aluminum element were measured in the same manner as described in Example 6. The results are shown in Table 1.

Reference example 1
0.4 parts by weight of an aqueous solution of 61% by weight of p-toluenesulfonic acid as a curing agent with respect to 100 parts by weight of fresh sand chromite sand (chromite # A301, manufactured by Yamakawa Sangyo Co., Ltd.) at 25 ° C. and 55% RH. Then, 1.0 part by weight of a furan resin (manufactured by Kao Quaker Co., Ltd., Kaolitener EF-5401) was added and kneaded to immediately produce a cylindrical test piece having a diameter of 50 mm and a height of 50 mm. The compressive strength was measured after 5 hours and 24 hours. In addition, the elution amounts of iron element and aluminum element of the fresh sand chromite sand used in this example were also measured in the same manner as in Example 1. The results are shown in Table 1.

Reference example 2
Under conditions of 25 ° C. and 55% RH, 0.28 parts by weight of 61% by weight aqueous solution of p-toluenesulfonic acid as a curing agent with respect to 100 parts by weight of fresh sand free mantle silica sand (Fremantle, manufactured by Yamakawa Sangyo Co., Ltd.) In addition, 0.7 parts by weight of furan resin (Kao Quaker Co., Ltd., Cao Lightner EF-5401) was added and kneaded to immediately produce a cylindrical test piece having a diameter of 50 mm and a height of 50 mm. The compressive strength after 24 hours was measured. The elution amounts of iron element and aluminum element of the fresh sand free mantle silica sand used in this example were also measured in the same manner as in Example 1. The results are shown in Table 1.

Reference example 3
An aqueous solution [curing agent (II)] of 9.4% by weight sulfuric acid and 47.8% by weight xylene sulfonic acid is used as a curing agent for 100 parts by weight of fresh sand free mantle silica sand (free mantle, manufactured by Yamakawa Sangyo Co., Ltd.). Add 0.28 parts by weight, then add 0.7 parts by weight of furan resin (Kaolitener EF-5401, manufactured by Kao Quaker Co., Ltd.) [Binder (II)] and knead to prepare a test mold. Castings with a ratio of 2 were cast. The recovered sand was crushed with a crusher to obtain recovered sand. The recovered sand was mechanically regenerated using a hybrid sand master manufactured by Nippon Casting Co., Ltd. in the same manner as in Example 1 to obtain reclaimed foundry sand. Using the obtained reclaimed foundry sand, the elution amounts of iron element and aluminum element were measured, and 61% by weight of p-toluenesulfonic acid as a curing agent with respect to 100 parts by weight of sand at 25 ° C. and 55% RH. 0.28 parts by weight of an aqueous solution [curing agent (I)], and then 0.7 parts by weight of a furan resin (Kaolitener EF-5401, manufactured by Kao Quaker Co., Ltd.) [Binder (I)] was added and kneaded. Immediately after that, a cylindrical test piece having a diameter of 50 mm and a height of 50 mm was produced, and the compressive strength after 0.5 hours and 24 hours was measured. The results are shown in Table 1.

  From Reference Examples 2 to 3, when free mantle silica sand is used, the curing rate of the reclaimed foundry sand does not decrease. Therefore, it can be seen that a decrease in the curing rate in the reclaimed foundry sand is a problem peculiar to chromite sand.

  Compared with the reference example 1 using fresh sand, in Examples 1-6, although the fall of initial strength (after 0.5 hour) is suppressed, in Comparative Examples 1-6, it is falling significantly. That is, by using regenerated foundry sand of chromite sand (A) containing methanesulfonic acid and a curing agent (II) having a low sulfuric acid content as in Examples 1 to 6, the curing rate of Provided is a method for producing a mold in which the decrease is suppressed.

Claims (6)

  A method for producing a mold comprising a step of producing a mold using reclaimed foundry sand, wherein the reclaimed foundry sand comprises (1) chromite sand, (2) a binder containing an acid curable resin, and (3) A method for producing a mold, which is obtained from a mold produced using a curing agent containing methanesulfonic acid and having a sulfuric acid content of 5% by weight or less.   The method for producing a mold according to claim 1, wherein the curing agent further contains another organic sulfonic acid.   The method for producing a mold according to claim 2, wherein the other organic sulfonic acid is at least one selected from the group consisting of xylenesulfonic acid, toluenesulfonic acid, benzenesulfonic acid, and ethylbenzenesulfonic acid.   The method for producing a mold according to any one of claims 1 to 3, wherein the curing agent contains 5 to 100% by weight of methanesulfonic acid.   The method for producing a mold according to any one of claims 1 to 4, wherein the binder contains an acid curable furan resin as an acid curable resin, and further contains a polyphenol compound.   A method of repeatedly using chromite sand for the production of a mold and the production of reclaimed casting sand from the mold, wherein the mold is (1) chromite sand, and (2) a binder containing an acid-curable resin, (3) A method of repeatedly using chromite sand for molds produced using a curing agent containing methanesulfonic acid and having a sulfuric acid content of 5% by weight or less.