JP5250301B2 - Mold manufacturing method - Google Patents

Description

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

  In recent years, artificially produced foundry sand has been used to compensate for the shortcomings of silica sand, zircon sand, chromite sand, olivine sand, etc. that have been widely used for foundry sand (refractory granular material) used for mold molding. Is being considered.

  In Patent Document 1, when molding a large or complex mold, the mold strength is reduced when the mold is adjusted and molded so that the time until the kneaded sand begins to harden, that is, when the so-called pot life is long. In order to solve this problem, a mold molding composition in which phosphoric acid and organic sulfonic acid are essential components in the curing agent, the phosphoric acid content is 10 to 85% by weight, and the organic sulfonic acid content is 5 to 70% by weight. Things are disclosed.

Patent Document 2 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. 9-47840 Japanese Patent Laid-Open No. 9-234540

  In general, casting sand is reused repeatedly. Among casting sands, casting sand obtained by the granulation firing method has a lower mold curing rate when the mold is produced using an acid curable resin and a curing agent. There was a problem to do. 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 documents 1, 2 do not mention the problem about the reclaimed foundry sand obtained from the foundry sand obtained by the granulation firing method.

  This invention is providing the manufacturing method which can suppress the fall of a hardening rate in manufacturing a casting_mold | template using the recast foundry sand of the foundry sand obtained by the granulation baking method.

  The present invention relates to a method for producing a mold including a step of producing a mold using reclaimed foundry sand, wherein the reclaimed foundry sand comprises (1) foundry sand obtained by a granulation firing method, and (2) acid hardening. The present invention relates to a method for producing a mold, which is obtained from a mold produced using a binder containing a functional resin and (3) 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 the foundry sand obtained by the granulation firing method in the production of a mold and the production of reclaimed foundry sand from the mold, wherein the mold is used in (1) the granulation firing method. And (2) a binder containing an acid curable resin, and (3) a curing agent containing methanesulfonic acid and having a sulfuric acid content of 5% by weight or less. The present invention relates to a method for repeatedly using foundry sand.

  According to the present invention, it is possible to suppress a decrease in the curing speed when producing a mold using a reclaimed foundry sand obtained from a mold using a foundry sand obtained by the granulation firing method. However, the initial mold strength can be obtained.

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 regenerated foundry sand is regenerated from a mold produced using a foundry sand (A) obtained by a granulation firing method, a binder (II) containing an acid curable resin, and a hardener (II). Casting sand,
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 obtained from a mold produced using a foundry sand (A) obtained by a granulation firing method, a binder (II) comprising an acid curable resin, and a hardener (II). It is the reclaimed foundry sand obtained. 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, foundry sand obtained by a granulation firing method 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 the recycled foundry sand of (A), it is possible to suppress a decrease in the curing rate during regeneration. The reason for this is unknown, but in the case of sulfuric acid, it reacts with the Al ₂ O ₃ component in the foundry sand obtained by the granulation firing method due to the heat during casting, and some hardening inhibitor is generated. This is presumed to have an effect on the molding of the next reclaimed foundry sand. 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, melamines / aldehydes polycondensates, urea / aldehydes polycondensates 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 polycondensates, known phenol compounds such as phenol, resorcinol, bisphenol A, bisphenol F and the like can be used alone or as a 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 the foundry sand (A), or a silane coupling agent may be directly added and kneaded to the foundry sand (A).

  The average particle size (mm) of the foundry sand (A) used in the present invention is preferably 0.05 to 1.5 mm from the viewpoint of reducing the amount of binder used during molding (improving regeneration efficiency) and mold strength. It is. From the viewpoint of increasing the recycle efficiency of the foundry sand, 0.75 to 1.5 mm is preferable, and from the viewpoint of increasing the mold strength, 0.05 to 1.0 mm is preferable. From the viewpoint of increasing both the regeneration efficiency and the mold strength, 0.05 to 0.5 mm is more preferable, and 0.05 to 0.35 mm is still more preferable.

  The average particle diameter can be determined as follows. That is, the diameter (mm) is measured when the sphericity from the projected particle cross section of the foundry sand particle is 1, while the major axis diameter (mm) of the randomly oriented foundry sand particle when the sphericity <1. The major axis diameter (mm) is measured to obtain (major axis diameter + minor axis diameter) / 2, and the average particle diameter (mm) is obtained by averaging the values obtained for any 100 casting sand particles. And The major axis diameter and the minor axis diameter are defined as follows. When the particle is stabilized on a plane and the projected image of the particle on the plane is sandwiched between two parallel lines, the width of the particle that minimizes the distance between the parallel lines is called the minor axis diameter. The distance when a particle is sandwiched between two parallel lines in a direction perpendicular to the line is called the major axis diameter.

  The major axis diameter and minor axis diameter of the foundry sand particles are obtained by obtaining an image (photograph) of the particles with an optical microscope or a digital scope (for example, VH-8000 type, manufactured by Keyence Corporation), and image analysis of the obtained image is performed. Can be obtained.

The foundry sand (A) obtained by the granulation firing method is foundry sand mainly composed of Al ₂ O ₃ , and preferably contains 20 to 100% by weight, and further 40 to 100% by weight of Al ₂ O _3. From the viewpoint of increasing the effect of the present invention, it is preferably contained in an amount of 60 to 100% by weight, particularly preferably 80 to 100% by weight. Further, from the viewpoint of ease of production of sand and reduction of thermal expansion of the obtained mold, SiO ₂ is preferably contained, and SiO ₂ is preferably contained in an amount of 40 to 5% by weight, more preferably 40 to 15% by weight. .

  Examples of the foundry sand (A) obtained by the granulation firing method include those disclosed in JP-A-61-63333. Furthermore, as a commercial item, a brand name "Nyiga Cera beads 60 # 650" [made by ITOCHU CERATECH Co., Ltd.] etc. are mentioned, for example.

As a specific example of the method for producing foundry sand by the granulation firing method, slurry is blended so that Al ₂ O ₃ is 20 to 70% by weight and S≡O ₂ is 80 to 30% by weight, and the slurry is spray-dried. And dry granulation at 350 to 450 ° C., and thereafter sintering this at 1550 ° C. in a rotary kiln.

  In order to mold a mold using the foundry sand (A), the binder (II) containing the acid curable resin, and the curing agent (II), according to a conventional method, for example, first, the casting 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 mold curing speed and improving the strength, the recycled casting sand preferably has an aluminum element elution amount of 50 μg or less, more preferably 40 μg or less per 1 g of sand.

(Measurement method of aluminum element elution)
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, the amount of aluminum element in the filtrate is quantified by ICP analysis (inductively coupled plasma emission spectrometry), and the amount of elution per gram of recycled foundry sand is calculated. To do.

  In addition, this aluminum elution amount is determined by adjusting the strength of machine regeneration (number of processing stages, processing time, number of revolutions of regenerator, etc.) during regeneration of spheroidal casting sand (A), and roasting regeneration conditions (temperature, time). ) And molding conditions (sand metal ratio, amount of hardener added).

  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 molding and regeneration are used repeatedly from casting sand obtained by the granulation firing method, if the regeneration conditions are the same, the mold from which the mold is derived is manufactured under specific conditions. Has been found to have a positive effect on suppressing the decrease in the curing rate in the next new mold production. The present invention is a method of repeatedly using the foundry sand obtained by the granulation firing method for the production of a mold and the production of reclaimed foundry sand from the mold, wherein the mold is obtained by (1) the granulation firing method. Foundry sand, (2) a binder containing an acid curable resin, and (3) a hardener containing methanesulfonic acid and having a sulfuric acid content of 5% by weight or less. It can be implemented as a repeated use method.

  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
An aqueous solution of 33.9% by weight of methanesulfonic acid as a curing agent (curing agent (II)) with respect to 100 parts by weight of foundry sand (Naigaisera beads 60 # 650, manufactured by ITOCHU CERATECH Co., Ltd.) obtained by the granulation firing method 0.6 parts by weight, and then added 1.5 parts by weight of a furan resin (Kaolitener EF-5401, manufactured by Kao Quaker Co., Ltd.) [Binder (II)] and kneaded to prepare a test template. A casting with 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 aluminum element elution amount was measured, and an aqueous solution of 61% by weight of p-toluenesulfonic acid as a curing agent with respect to 100 parts by weight of sand under the conditions of 25 ° C. and 55% RH [ Curing agent (I)] 0.6 parts by weight was added, followed by addition of 1.5 parts by weight of furan resin (Kaolitener EF-5401, manufactured by Kao Quaker Co., Ltd.) [Binder (I)] Cylindrical test pieces having a height of 50 mm and a height of 50 mm were produced, and the compressive strength was measured after 0.5 hours and 24 hours. 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 aluminum element elution amount and compressive strength were measured in the same manner as described in Example 1. The results are shown in Table 1.

Comparative Example 1
Recycled cast 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 aluminum element elution amount and compressive strength 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. Using the obtained recycled foundry sand, the aluminum element elution amount and compressive strength 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). Quantity 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 compressive strength was measured. The results are shown in Table 1.

Example 4
An aqueous solution containing 33.9% by weight of methanesulfonic acid as a curing agent (II) is added to 100 parts by weight of casting sand (Nyiga Sera Beads 60 # 650, manufactured by ITOCHU CERATECH Co., Ltd.) obtained by the granulation firing method. Add 75 parts by weight, then add 1.5 parts by weight of furan resin (Kaolitener EF-5401, manufactured by Kao Quaker Co., Ltd.) [Binder (II)] to prepare a test mold, and the sand metal ratio is 2 The casting was 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 regenerated foundry sand, the above operation was repeated 5 times, and the fifth regenerated foundry sand was used to measure the aluminum element elution amount and compressive strength in the same manner as described in Example 1. The results are shown in Table 1.

Comparative Example 4
Recycled casting 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 aluminum element elution amount and compressive strength were measured. The results are shown in Table 1.

Example 5
As binder (II), a polyphenol compound (manufactured by Koshii Wood Solutions Co., Ltd., methanol extract of Acacia mangium GKA-100) and furan resin (manufactured by Kao Quaker Co., Ltd., Kao Lightner EF-5401) Except using the solution which consists of 90 weight part, the mechanical reproduction | regeneration of foundry sand was performed by the same method as the method of Example 1, the reclaimed foundry sand was obtained, and the aluminum element elution amount and hardening behavior were measured. The results are shown in Table 1.

Comparative Example 5
Recycled cast sand was obtained in the same manner 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 aluminum element elution amount and compressive strength 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
The aluminum element elution amount and compressive strength were measured by the same method as described in Example 6 except that the reclaimed foundry sand obtained in Comparative Example 5 was used. The results are shown in Table 1.

Reference example 1
P-Toluenesulfonic acid as a curing agent with respect to 100 parts by weight of foundry sand (Naigai Cera Beads 60 # 650, manufactured by ITOCHU CERATECH Co., Ltd.) obtained by granulation and firing under the conditions of 25 ° C. and 55% RH A cylinder having a diameter of 50 mm and a height of 50 mm was added after adding 0.6 parts by weight of a 61% by weight aqueous solution and then adding 1.5 parts by weight of a furan resin (Kao Quaker Co., Ltd., Kao Lightner EF-5401). Shaped test pieces were prepared and the compressive strength was measured after 0.5 and 24 hours. In addition, the aluminum element elution amount of the foundry sand used in this example was 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 aluminum element elution amount was measured, and an aqueous solution of 61% by weight of p-toluenesulfonic acid as a curing agent with respect to 100 parts by weight of sand under the conditions of 25 ° C. and 55% RH [ Curing agent (I)] 0.28 parts by weight was added, and then 0.7 parts by weight of furan resin (Kaolitener EF-5401, manufactured by Kao Quaker Co., Ltd.) [Binder (I)] was added and kneaded to obtain a diameter. Cylindrical test pieces having a height of 50 mm and a height of 50 mm were produced, and the compressive strength was measured after 0.5 hours and 24 hours. 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 turns out that the fall of the hardening rate in reproduction | regeneration molding sand is a subject peculiar to casting sand (A).

  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, as in Examples 1 to 6, by using the reclaimed foundry sand of the foundry sand (A) using the curing agent (II) containing methanesulfonic acid and having a low sulfuric acid content, the curing rate can be increased. Provided is a method for producing a mold in which the decrease is suppressed.

Claims (6)

  A method for producing a mold including a step of producing a mold using reclaimed foundry sand, wherein the reclaimed foundry sand comprises (1) foundry sand obtained by a granulation firing method, and (2) an acid-curable resin. A method for producing a mold, which is obtained from a mold produced using a binder that comprises (3) 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 xylene sulfonic acid, toluene sulfonic acid, and ethylbenzene sulfonic 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.   The casting sand obtained by the granulation firing method is used repeatedly in the production of a mold and in the production of recycled casting sand from the mold, wherein the casting mold is obtained by (1) the granulation firing method. And (2) a binder containing an acid curable resin, and (3) a curing agent containing methanesulfonic acid and having a sulfuric acid content of 5% by weight or less. .