JP2011056563A - Structure for producing casting - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a structure for producing a casting, which has sufficient hot strength during casting and can produce a casting having an excellent effect of lessening gas defects. <P>SOLUTION: The structure for producing the casting contains inorganic particles, inorganic fibers and thermosetting resin. The kurtosis of the particle size distribution of the inorganic particles is 1 to 20. It is desirable that the mode of the inorganic particle distribution is 100 to 600 μm. It is desirable that the inorganic particles are graphite such as earthy graphite and artificial graphite. It is also desirable that the inorganic particles are spheroidal activated carbon. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a casting manufacturing structure such as a mold used in manufacturing a casting.

  Casting is generally based on wooden molds or molds, and a mold with a cavity inside is formed from casting sand, and if necessary, a core is placed in the cavity and then molten metal is supplied to the cavity. Manufactured. In the sand mold using the foundry sand, a binder is added to normal sand and cured to maintain the shape. Therefore, a recycling process is essential for reusing the sand. Further, there is a problem that waste such as dust is generated during the regeneration process. When the core is manufactured in a sand mold, in addition to the above-mentioned problems, it is difficult to handle due to the mass of the core itself, and furthermore, there are conflicting performances of strength maintenance during casting and core removal after casting. Required.

  As a technique for solving such a problem, a technique for obtaining a casting manufacturing structure that is excellent in lightness, workability, and waste reduction is known (see, for example, Patent Document 1). This structure contains organic fibers, inorganic fibers, inorganic particles, and a thermosetting resin.

  Patent Document 2 describes a casting manufacturing structure containing scaly graphite having an average particle size of 70 μm or less, a thermosetting resin, and organic fibers. Patent Documents 3 and 4 describe shell mold materials made of sand coated with a thermosetting resin and hydrous magnesium silicate clay mineral. Further, Patent Document 5 describes a thermal insulator used for casting molten metal. The document mentions the air permeability of the thermal insulator.

JP 2005-349428 A JP 2007-144511 A JP 62-45446 A JP 62-156044 A Japanese Patent Publication No. 50-20545

  According to the technique described in Patent Document 1, it has excellent hot strength even at the time of casting, and is excellent in shape retention of the casting after casting, so that it is possible to manufacture a casting having excellent surface smoothness. However, when producing a casting having a complicated shape, a gas defect may occur in the casting, and further reduction of the gas defect in the casting has been desired.

  The present invention provides a structure for producing a casting, which is superior in various performances to the prior art described above.

  The present invention provides a casting manufacturing structure containing inorganic particles, inorganic fibers, and a thermosetting resin, and provides a casting manufacturing structure having a kurtosis of 1 to 20 in particle size distribution of the inorganic particles. It is.

  According to the present invention, by setting the kurtosis of the inorganic particles in a specific range, the air permeability becomes good without impairing the moldability of the structure for casting production, and it occurs during the production of the target casting. There is provided a casting manufacturing structure with improved gas discharge performance. Furthermore, by setting the mode of the particle size distribution of the inorganic particles to a specific range, the surface property of the structure for producing castings is improved, and the casting product does not adversely affect the surface properties of the target castings. A structure is provided. As a result, it is possible to obtain a casting manufacturing structure having an excellent gas defect reduction effect. The problem pointed out in the description of Patent Document 1 is solved, that is, a remarkable effect is exhibited in reducing gas defects generated under severe conditions such as manufacturing a casting having a complicated shape.

FIG. 1 is a schematic view showing an embodiment of a casting manufacturing structure of the present invention. FIG. 2 is a schematic view showing an embodiment in which the casting manufacturing structure of the present invention is housed in a mold. FIG. 3 is a schematic view showing an apparatus for measuring the air permeability of the structure for manufacturing a casting according to the present invention.

  Hereinafter, the present invention will be described based on preferred embodiments thereof. The structure for producing a casting according to the present invention contains inorganic particles, inorganic fibers, and a thermosetting resin as its constituent materials. Of these constituent materials, one of the characteristics is the particle size distribution of the inorganic particles. The structure for producing a casting having this feature has sufficient hot strength even during casting and has a good air permeability, so that the discharge of gas generated during the production of the target casting is improved. Even in the production of a casting having a complicated shape, an excellent effect of suppressing the generation of gas defects is exhibited.

  More specifically, one of the features of the present invention is the problem of casting gas defects generated when a casting having a complicated shape is manufactured using a structure for manufacturing a casting having excellent lightness and workability. As a means for solving this problem, it has been found that it is effective to set the kurtosis of the particle size distribution of the inorganic particles in a specific range. Thereby, it is presumed that fine voids having a uniform size are formed between the inorganic particles of the structure for producing castings, and the air permeability is improved without impairing the moldability. As a result, even in the production of a casting having a complicated shape, the gas generated during the production is excellent in discharging, so that the occurrence of gas defects can be suppressed.

  The air permeability of the structure for manufacturing a casting according to the present invention is preferably 1 or more, more preferably 2 or more, and more preferably 8 or more from the viewpoint of making the gas defect generation reduction effect of the casting remarkable. More preferably. In particular, it is preferably 10 or more, and particularly preferably 20 or more. Further, the upper limit value of the air permeability is preferably 500 or less, preferably 400 or less, from the viewpoint of the effect of reducing the occurrence of gas defects in the casting and the structure having sufficient hot strength even during casting. Is more preferable, and it is still more preferable that it is 300 or less. In particular, it is preferably 200 or less, particularly preferably 150 or less. From these viewpoints, the air permeability of the structure for producing castings is preferably 1 to 500, more preferably 2 to 400, and still more preferably 8 to 300. 10-200 is particularly preferable, and 20-150 is particularly preferable. The air permeability of the structure for producing castings is measured by the method described in Examples described later.

  As a result of the study by the present inventors, it is effective to adjust the particle size distribution of the inorganic particles among the materials constituting the structure in order that the structure for producing castings has the preferable air permeability. found. Specifically, it is effective to adjust the kurtosis in the particle size distribution of the inorganic particles to a range of 1 to 20, preferably 1 to 19, and more preferably 1 to 10. Kurtosis is a statistical term and is a numerical value representing the relative acute angle or flatness of a frequency distribution curve by comparing the particle size distribution of inorganic particles with a normal distribution. When the kurtosis is a positive number, it indicates that the frequency distribution curve is relatively acute, and when it is a negative number, it indicates that it is relatively flat. In the present invention, the kurtosis is an index of the sharpness of the distribution of inorganic particles. The kurtosis is expressed by the following formula (1).

  In order to adjust the kurtosis in the particle size distribution of the inorganic particles within the above range, the inorganic particles may be subjected to pretreatment such as classification by sieving. Or even if it is a case where a commercial item is used as it is, kurtosis may be in the above-mentioned range.

  The reason why the air permeability of the structure for casting production is adjusted by using inorganic particles having a kurtosis of the particle size distribution within the above range is that by using inorganic particles having a uniform particle size, the size between the inorganic particles is uniform. This is presumed to be due to the formation of fine voids. On the other hand, if inorganic particles having a wide particle size distribution are used, inorganic particles having a small particle size are likely to enter between inorganic particles having a large particle size, and thus the air permeability of the structure for casting production is likely to be hindered. Become. On the other hand, the use of inorganic particles having a uniform particle size may reduce the bonding points between the inorganic particles, making it difficult to form a structure for producing a casting, or reducing the strength even if it can be formed. . On the other hand, when inorganic particles having a wide particle size distribution are used, the number of bonding points between the inorganic particles increases, and it becomes easy to form a structure for casting production.

  When comparing inorganic particles having the same kurtosis of the particle size distribution, the air permeability tends to decrease as the particle size decreases, and conversely, molding becomes difficult as the particle size increases. From this viewpoint, on the condition that the kurtosis of the particle size distribution is within the above range, the mode of the particle size distribution of the inorganic particles is preferably 100 to 600 μm, particularly 105 to 500 μm, and particularly preferably 150 to 425 μm. . The mode is a statistical term and represents the class with the highest frequency in each class of the frequency distribution. In the present invention, when measuring the particle size of the inorganic particles, the nominal size of the sieve that maximizes the weight of the particles present on each sieve surface used in the first measurement method described below is defined as the mode value.

The particle size distribution of the inorganic particles is measured by the following first measurement method. When the cumulative particle weight on the sieve surface having a nominal size of 425 μm exceeds 10% of the total sample weight, the particle size distribution by the first measurement method is used. If this is not the case, it can be obtained by measuring with the following second measurement method.
<First method>
Measured based on the method specified in JIS Z2601 (1993) “Testing Methods for Foundry Sand”, Appendix 2. The weight accumulation is calculated by regarding the particles on each sieve surface as “average diameter Dn (μm)” shown in Table 2 of JIS Z2601 (1993).
<Second method>
It is measured using a laser diffraction particle size distribution analyzer (LA-920 manufactured by Horiba, Ltd.). The measurement conditions are as follows.
・ Measurement method: Flow method ・ Refractive index: Varies depending on inorganic particles (Refer to the manual attached to LA-920)
・ Dispersion medium: Ion exchange water + 0.1% sodium hexametaphosphate mixed ・ Dispersion method: Stirring, built-in ultrasonic wave 3 minutes ・ Sample concentration: 2 mg / 100 mL

  The structure for manufacturing a casting according to the present invention exhibits a remarkable effect in reducing gas defects generated under severe conditions such as manufacturing a casting having a complicated shape. The reason why such an effect appears is not clear, but in the field of using a casting manufacturing structure having excellent lightness and workability, a conventional casting manufacturing structure does not have sufficient air permeability, so it is particularly complicated. Under severe conditions such as manufacturing a casting having a simple shape, it is considered that a small amount of gas generated from the casting manufacturing structure entered the molten metal side constituting the casting and caused gas defects on the casting surface. On the other hand, since the casting manufacturing structure of the present invention has an appropriate air permeability, a trace amount of gas generated from the casting manufacturing structure is generated even under severe conditions such as molding a casting having a complicated shape. It is considered that the entry into the molten metal constituting the casting can be remarkably suppressed, and as a result, gas defects in the casting can be reduced particularly.

  Additional preferable conditions for the structure for producing a casting of the present invention to have the above-described air permeability include adjustment of the kind of inorganic particles, the kind of thermosetting resin, and the blending ratio of each component. Regarding the blending ratio of each component, the blending ratio (mass ratio) of inorganic particles, inorganic fibers, and thermosetting resin is inorganic particles / inorganic fibers / thermosetting resin = 40 to 90/1 to 20/1 to 30. It is preferably 50 to 85/2 to 16/2 to 25, and more preferably 50 to 85/2 to 16/2 to 20.

  An inorganic particle is a component which improves the heat resistance of the structure for casting manufacture. In the present invention, it is preferable to use at least one graphite selected from earthy graphite and artificial graphite from the viewpoint of improving the air permeability of the structure for producing castings. Graphite is also a material preferably used from the viewpoint of high seizure resistance. Of these graphites, it is preferable to use artificial graphite from the viewpoint of stable quality and easy control of the air permeability of the structure. Note that graphite is generally classified into those that are naturally produced, such as scaly graphite and earthy graphite, and artificial graphite that is artificially produced from petroleum coke, carbon black, pitch, or the like.

  Examples of inorganic particles other than graphite include activated carbon, obsidian, mica, mullite, silica, magnesia, and talc. In addition, activated carbon is generally classified into powdered activated carbon, spherical activated carbon, and fibrous activated carbon depending on its shape. Moreover, according to the raw material, it classify | categorizes into a wood type activated carbon, an insulator type activated carbon, and a coal type activated carbon. In the present invention, from the viewpoint of improving the air permeability of the structure for producing castings, the shape of the activated carbon is preferably spherical, and any raw material can be used as long as it is spherical activated carbon. These various inorganic particles including graphite can be used alone or in combination of two or more. A preferred proportion of the total amount of graphite in the total inorganic particles is 90% by mass or more, a more preferred proportion is 95% by mass or more, and a further preferred proportion is substantially 100% by mass. When two or more kinds of inorganic particles including graphite are used in combination, the kurtosis of the particle size distribution described above is measured for mixed particles.

  The mode value in the particle size distribution of the inorganic particles is as described above, and the average particle size of the inorganic particles is preferably 80 μm or more, more preferably 100 μm or more, from the viewpoint of further improving the air permeability of the structure for casting production. 120 μm or more is more preferable. Further, from the viewpoint of having sufficient hot strength even when casting is produced, the structure is preferably 3000 μm or less, more preferably 2500 μm or less, still more preferably 1000 μm or less, and particularly preferably 800 μm or less. From these viewpoints, the average particle size of the inorganic particles is preferably 80 to 3000 μm, more preferably 100 to 2500 μm, still more preferably 100 to 1000 μm, and particularly preferably 120 to 800 μm. The average particle size of the inorganic particles is measured by the same method as the particle size distribution described above, and is defined as an average particle size of 50% volume accumulation.

  The content of the inorganic particles is preferably 40 to 90% by mass in the structure from the viewpoint that the shape retention at the time of casting of the structure, the surface property of the molded product, and the release property after molding are suitable. -85 mass% is still more preferable. The numerical value of this content may be the numerical value of the blending amount when manufacturing the structure (the same applies to the materials described below).

  The inorganic fiber contained in the structure for producing a casting according to the present invention mainly forms a skeleton of the structure, and for example, one that maintains its shape without being burned by the heat of the molten metal at the time of casting. Examples of the inorganic fiber include carbon fiber, artificial mineral fiber such as rock wool, ceramic fiber, and natural mineral fiber. An inorganic fiber can be used individually or in combination of 2 or more types. Among these fibers, it is preferable to use carbon fibers which are fibers having high strength even at high temperatures from the viewpoint of effectively suppressing shrinkage associated with carbonization of the thermosetting resin. When carbon fibers are used, pitch-based or polyacrylonitrile (PAN) -based carbon fibers are preferable, and polyacrylonitrile (PAN) -based carbon fibers are particularly preferable.

  The inorganic fibers preferably have an average fiber length of 0.5 to 15 mm, particularly 1 to 8 mm, from the viewpoint of moldability and uniformity of the structure for producing castings.

  The content of the inorganic fiber is preferably 1 to 20% by mass and more preferably 2 to 16% by mass in the structure from the viewpoint of moldability of the structure for producing castings and shape retention during casting.

  The thermosetting resin contained in the structure for producing castings of the present invention maintains the normal temperature strength and hot strength of the structure, improves the surface property of the structure, and uses the structure as a mold. It is a component necessary for improving the surface roughness of the casting. Examples of the thermosetting resin include a phenol resin, an epoxy resin, and a furan resin. These resins can be used alone or in combination of two or more. Of these resins, it is particularly preferable to use a phenol resin. The reason for this is that phenol resin has a small amount of cracked gas generated during casting, has an effect of suppressing combustion, has a high residual carbon ratio of 25% or more after pyrolysis (carbonization), and the structure is used as a mold. This is because a good cast skin can be obtained by forming a carbonized film on the surface. Examples of the phenol resin include novolak phenol resins that require a curing agent and resol phenol resins that do not require a curing agent.

  Of the phenolic resins, it is more preferable to use a resole phenolic resin alone or in combination with another resin. The reason for this is that it does not require a curing agent such as acid or amine, so that it is possible to reduce the odor generated when molding the structure, and to reduce casting defects when the structure is used as a mold. Because you can.

  As a resole phenol resin, a commercial item can be used, for example. As such a commercial item, for example, the product name REGITOP PGA-2165 manufactured by Gunei Chemical Industry Co., Ltd., the product name KL-4000 manufactured by Asahi Organic Materials Co., Ltd., the product name manufactured by Air Water Co., Ltd. Belpearl S-890 etc. are mentioned.

  The content of the thermosetting resin is preferably 1 to 30% by mass in the structure from the viewpoint of moldability of the structure for casting production and shape retention during casting, and from the viewpoint of surface smoothness of the casting. 2-25 mass% is still more preferable, and 2-20 mass% is still more preferable.

  In the present invention, it is preferable to add a water-soluble polymer compound to the molding raw material for the casting production structure from the viewpoint of improving the moldability of the casting production structure. The water-soluble polymer compound is a polymer compound that adsorbs or absorbs water under normal use conditions (for example, 25 ° C.), and is preferably dissolved in, for example, 1.0% by mass or more in pure water at 25 ° C.

  Examples of water-soluble polymer compounds include thickening polysaccharides, polyvinyl alcohol, and polyethylene glycol. Of these, it is preferable to use thickening polysaccharides from the viewpoint of improving the moldability of the structure. A thickening polysaccharide is a polysaccharide that exhibits thickening in an aqueous system. Examples thereof include gum agents such as xanthan gum, tamarind gum, gellan gum, guar gum, locust bean gum and tara gum, cellulose derivatives such as carboxymethyl cellulose and hydroxyethyl cellulose, carrageenan, pullulan, pectin, alginic acid, agar and the like. Among these polysaccharides, non-natural products such as cellulose derivatives such as carboxymethyl cellulose are preferable to natural products such as agar because they can exhibit sufficient performance even if the amount used is small. The weight average molecular weight of the water-soluble polymer compound is preferably 10,000 to 3,000,000, more preferably 20,000 to 1,000,000.

  In the case where a water-soluble polymer compound is added to the molding raw material of the structure for casting production, the content of the polymer compound is preferably 0.5% by mass or more from the viewpoint of improving the moldability of the structure, 1 mass% or more is still more preferable. From the viewpoint of setting the air permeability of the structure within a suitable range, it is preferably 10% by mass or less, and more preferably 7% by mass or less. From these points, the content of the water-soluble polymer compound is preferably 0.5 to 10% by mass, and more preferably 1 to 7% by mass in the forming raw material.

  In the present invention, it is preferable to add thermally expandable particles to the forming raw material of the structure for producing castings from the viewpoint of improving the formability of the structure. The thermally expandable particles are preferably microcapsules in which an expansion agent that expands by vaporization is encapsulated in the shell wall of a thermoplastic resin. For example, when the microcapsule is heated at 80 to 200 ° C., the diameter preferably expands 3 to 5 times and the volume preferably 50 to 100 times. The average particle diameter before expansion is preferably 5 to 80 μm, more preferably 20 to 50 μm. When the expansion of the heat-expandable particles is within the range, the effect of addition is easily obtained while suppressing the adverse effect on the molding accuracy due to the expansion.

  Examples of the thermoplastic resin constituting the shell wall of the microcapsule include polystyrene, polyethylene, polypropylene, polyacrylonitrile, polyvinylidene chloride, acrylonitrile-vinylidene chloride copolymer, ethylene-vinyl acetate copolymer, or combinations thereof. . Among these resins, from the viewpoint of obtaining an appropriate expansion start temperature and a high expansion coefficient, the shell wall is preferably composed of a polymer made of acrylonitrile or vinylidene chloride, or a copolymer containing one or more of them. Examples of the expanding agent contained in the shell wall include low-boiling organic solvents such as propane, butane, pentane, hexane, isobutane, and petroleum ether.

  The content of the heat-expandable particles in the case where the heat-expandable particles are added to the molding raw material for the structure for producing castings is 0.5 to 10 mass in the molding raw material from the viewpoint of excellent moldability of the structure. % Is preferable, and 1 to 5% by mass is more preferable. Within this range, the molding raw material is filled over the details of the mold by expansion, the shape of the mold can be faithfully transferred, and the effect of addition can be sufficiently obtained.

  In addition to the components described above, other components such as a colorant, a release agent, and colloidal silica can be added to the molding raw material for the structure for producing castings in an appropriate ratio. Moreover, you may add these other components at the time of shaping | molding of the structure for casting manufacture, or after shaping | molding.

  When the structure for casting production is produced from a forming raw material containing water, the mass moisture content before use of the structure (before being used for casting) is preferably 5% or less, and preferably 2% or less. It is more preferable that The lower the moisture content, the lower the amount of gas generated due to the water vapor during casting, and the reduction of gas defects.

  The casting manufacturing structure of the present invention is applied to a main mold having a casting product-shaped cavity on the inner surface, a core used in the main mold, or a pouring member such as a runner, a filter holder, and the like. be able to. The structure for producing a casting of the present invention is excellent in surface smoothness, and a casting having a good casting surface can be obtained. Therefore, application to a main mold and a core is preferable. The structure for producing a casting according to the present invention is particularly excellent in reducing gas defects in castings. Therefore, it is preferably applied to a core that is covered with molten metal during casting and is likely to generate gas defects. Application to is more preferable.

  Next, the manufacturing method of the structure for casting production according to the present invention will be described based on preferred embodiments thereof. In this production method, a forming raw material (a composition containing a structure for casting production and a dispersion medium) containing inorganic particles, inorganic fibers, a thermosetting resin, and a dispersion medium is prepared, and the forming raw material Is poured into a mold to obtain a structure for casting production.

  The compounding ratio (mass ratio) of each component of the composition for a structural body for casting production suitable for use in this production method is the total solid content of inorganic particles, inorganic fibers, thermosetting resin and water-soluble polymer compound. In contrast, inorganic particles / inorganic fibers / thermosetting resin / water-soluble polymer compound = 40 to 90/1 to 20/1 to 30/1 to 10 is preferable, and 50 to 85/2 to 16/2 to 25 /. 1-7 are still more preferable, and 50-85 / 2-16 / 2-20 / 1-7 are still more preferable. However, the total of the numerical values of each component used for the mass ratio is 100. Further, in the composition for a structure for casting production, (i) the total content of inorganic particles, inorganic fibers and thermosetting resin, (ii) of inorganic particles, inorganic fibers, thermosetting resin and water-soluble polymer compound Total content, (iii) Total content of inorganic particles, inorganic fibers, thermosetting resins and thermally expandable particles, or (iv) Inorganic particles, inorganic fibers, thermosetting resins, water-soluble polymer compounds and thermal expansion The total content of the conductive particles is preferably 90 to 100% by mass, and more preferably 95 to 100% by mass. The content of organic fibers such as paper fibers, fibrillated synthetic fibers, and regenerated fibers in the composition for a structure for casting production is preferably 0.1% by mass or less, particularly preferably 0.05% by mass or less. . When the organic fiber is contained, the strength of the structure itself is improved, but the pyrolysis gas of the organic fiber is easily generated, which may cause a gas defect.

  When the blending of the inorganic particles is within the above range, the shape retention at the time of casting and the surface property of the molded product are good, and the mold release property after molding tends to be suitable. When the blending ratio of the inorganic fibers is within the above range, the moldability and shape retention during casting are likely to be good. When the blending ratio of the thermosetting resin is within the above range, the moldability of the structure, the shape retention after casting, and the surface smoothness are likely to be good. When the mixing ratio of the water-soluble polymer compound is within the above range, the molding material (raw material obtained by adding a dispersion medium to the composition for forming a molded body) is filled into the molding die. The dispersion medium in the raw material can be filled with good fluidity without separation, and the air permeability of the resulting structure tends to be good.

  In the preparation of the structure for a casting manufacturing structure, it is preferable to dryly mix inorganic particles, inorganic fibers, and a thermosetting resin in advance. From the viewpoint of being able to mix uniformly and improving moldability, it is preferable to further mix the water-soluble polymer compound in advance by a dry method. From the viewpoint of moldability, it is preferable to mix the heat-expandable particles in a dry manner. And it is preferable to disperse these mixtures in a dispersion medium and knead them with a kneader to prepare the forming raw material in a dough shape. Preferably, the dough-shaped forming raw material is filled in a mold, and the mold is heated to cure the thermosetting resin.

  Examples of the dispersion medium include water, a solvent such as ethanol and methanol, and an aqueous dispersion medium such as a mixed system thereof. It is particularly preferable to use water from the viewpoints of stability of the quality of the resulting structure, production costs, ease of handling, and the like.

  Preparation of the forming raw material in a dough shape means that the composition containing inorganic particles, inorganic fibers and a thermosetting resin and a dispersion medium are gently kneaded so that the inorganic particles and the inorganic fibers and the dispersion medium have fluidity. Refers to the preparation in a state where it is not easily separated. The content of the dispersion medium in the forming raw material is determined from the viewpoint of preparing the forming raw material so that the inorganic particles and the inorganic fibers and the dispersion medium are not easily separated while the forming raw material has fluidity. , Preferably 10 to 200% by mass, more preferably 25 to 180% by mass, and still more preferably 30 to 170% by mass based on the total solid mass of the inorganic fiber, thermosetting resin and water-soluble polymer compound. %.

  The molding die used in the method for manufacturing a casting manufacturing structure is configured by including, for example, a main die having a cavity corresponding to the hollow rod-shaped product shown in FIG. 1 and a core material that forms a hollow. At the time of molding the structure, the mold is heated to about 120 to 250 ° C. in consideration of evaporation of the dispersion medium, curing of the thermosetting resin, and expansion of the thermally expandable particles. Next, the molding raw material is filled in the mold by opening the gate opening / closing means provided in the mold. The filling pressure is preferably about 0.5 to 3 MPa when air is used as the filling means. When the molding raw material filled in the mold is heated, vapor derived from the dispersion medium, gas derived from the thermosetting resin, and the like are generated. The molding raw material is dried while releasing the generated gas out of the mold. And then. By performing trimming, drug application, and the like as necessary after cooling, a target casting manufacturing structure can be obtained.

  Next, the casting manufacturing method using the casting manufacturing structure of the present invention will be described. In this manufacturing method, the casting manufacturing structure obtained as described above is embedded in a predetermined position in the molding sand to perform molding. As the foundry sand, conventional ones conventionally used for producing this type of casting can be used without any particular limitation. Then, the molten metal is poured from the pouring port and cast. At this time, since the structure of the present invention maintains the hot strength and the thermal shrinkage accompanying the thermal decomposition of the structure is small, cracks in the structures for casting production and damage to the structures for casting production itself It is suppressed, and the insertion of molten metal into the casting structure and the adhesion of foundry sand are less likely to occur. After the casting is completed, the casting is cooled to a predetermined temperature, the casting frame is disassembled to remove the casting sand, and the casting manufacturing structure is removed by blasting to expose the casting. In this case, since the thermosetting resin is thermally decomposed, the removal process of the casting manufacturing structure is easy. Thereafter, post-processing such as trimming is performed on the casting as necessary to complete the manufacturing of the casting.

  A more preferred casting production method is an embodiment in which the casting production structure of the present invention is used as a hollow core. In this embodiment, the hollow core is disposed in the mold such that at least one of the openings of the hollow core is opened outside the mold, and then the molten metal is poured into the mold. Specifically, as shown in FIG. 2, the hollow core shown in FIG. 1 is arranged in the main mold and the hollow core is supported by keren, and one of the openings of the hollow core is opened outside the mold. Then, the molten metal is poured into the mold to produce a casting. In addition, as a method for arranging one of the openings of the hollow core so as to open to the outside of the mold, a method of providing an opening in the main mold so as to communicate with the hollow part of the hollow core may be employed.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples. Unless otherwise specified, “part” means “part by mass”.

[Examples 1 to 5 and Comparative Examples 1 and 2]
(1) Preparation of casting composition for structural body and preparation of molding raw material The composition and blending ratio (mass ratio) of inorganic particles, inorganic fibers, thermosetting resin, water-soluble polymer compound and thermally expandable particles are shown in Table 1. After preparing the structure for casting manufacturing structure so that it might become like this, the amount of water shown in the same table was added to this structure for casting manufacturing structure, and the dough-shaped forming raw material was prepared. Each component shown in Table 1 is as shown in Table 2.

(2) Manufacture of structure for casting production A molding raw material was filled in a heated mold having a main mold having a cavity corresponding to the hollow rod-shaped product shown in FIG. 1 and a core material forming a hollow. The air pressure for filling was 1 MPa. The temperature of the mold was 200 ° C. A hollow rod-shaped product (casting) shown in FIG. 1 having an outer diameter of 11 mm (hollow part diameter of 5 mm) and a length of 380 mm is dried while discharging the vapor derived from the dispersion medium or the gas derived from the thermosetting resin by heating. Manufacturing structure) was obtained.

(3) Evaluation The air permeability of the obtained casting production structure was measured by the following method. Moreover, the moldability and the surface property of the casting were evaluated by the following methods. These results are shown in Table 1 below.

[Air permeability]
“5. Standard test method of coating material for disappearance model” (March 1996, Kansai Branch, Japan Foundry Engineering Society) defined based on JIS Z2601 (1993) “Testing method of foundry sand”. According to the method of measuring the air permeability, the air permeability was measured using a device having the same principle as the air permeability measuring device (compressor air ventilation method) described in the publication (FIG. 5-2 on page 24). The air permeability P is expressed by “P = (h / (a × p)) × V”. In the formula, h is the specimen thickness (cm), a is the specimen cross-sectional area (cm ² ), p is the ventilation resistance (cmH ₂ O), and V is the air flow rate (cm ³ / min). The thickness of the test piece was the thickness of the hollow rod-shaped product, that is, “(outer diameter−hollow part diameter) / 2”, and the cross-sectional area of the test piece was “hollow part diameter × circumferential ratio × length”. At the time of measurement, as shown in FIG. 3, a rubber tube and a connecting jig (packing) are attached to the air permeability measuring device so that it can be connected to the hollow rod-shaped product without omission, and the connection treatment is applied to one end of the hollow portion of the hollow rod-shaped product. The tools were connected without gaps, and the other end was closed with a packing or the like to prevent air leakage.

[Formability]
The moldability of the hollow rod-like product (structure for producing castings) obtained by the above method was evaluated according to the following criteria.
A: A desired hollow rod-like structure is obtained with a probability of 90% or more.
A: A desired hollow rod-like structure is obtained with a probability of 70% or more and less than 90%.
Δ: A desired hollow rod-like structure is obtained with a probability of 50% or more and less than 70%.
X: The desired hollow rod-like structure cannot be obtained with a probability of 50% or more.

[Surface properties of structures for casting production]
The surface properties of the resulting casting production structure were evaluated visually according to the following criteria.
A: Smooth surface with no irregularities or cracks on the surface.
○: Even if there are irregularities and cracks on the surface, the size is sufficiently small and there is no possibility of adversely affecting the casting skin.
(Triangle | delta): The thing with a high possibility that an unevenness | corrugation and a crack exist in the surface and has a bad influence on casting skin.
X: A thing with remarkable unevenness | corrugation, a crack, and a missing part on the surface.

  As is apparent from the results shown in Table 1, the structure for producing castings (the product of the present invention) composed of the hollow rod-like product obtained in each example is set by setting the particle size distribution of the inorganic particles within a specific range. It can be seen that it has an appropriate air permeability and is well molded. Moreover, it turns out that the surface property of the shape | molded structure for casting manufacture is also favorable by setting the mode value of the particle size distribution of an inorganic particle in a specific range. On the other hand, the hollow rod-like product obtained in Comparative Example 1 in which the kurtosis of the particle size distribution of the inorganic particles is out of the range of the present invention and the mode value of the particle size distribution of the inorganic particles is out of the range of the present invention. It can be seen that the structure for producing a casting made of the above has a low air permeability and the surface property of the formed structure for producing a casting is not good.

Claims (6)

  A casting manufacturing structure containing inorganic particles, inorganic fibers and a thermosetting resin, wherein the kurtosis of the particle size distribution of the inorganic particles is 1 to 20.   The structure for casting production according to claim 1, wherein the mode value of the particle size distribution of the inorganic particles is 100 to 600 μm.   The structure for casting production according to claim 1 or 2, wherein the inorganic particles are graphite.   The structure for casting production according to claim 3, wherein the graphite is earthy graphite or artificial graphite.   The casting manufacturing structure according to claim 1, wherein the inorganic particles are spherical activated carbon.   6. The casting manufacturing structure according to claim 1, wherein the casting manufacturing structure is a hollow core.

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