Shell mold materials

Abstract

The present invention provides a mold material for a shell mold which makes it possible to advantageously mold a shell mold capable of effectively suppressing or preventing an occurrence of a molding defect relating to a casting surface, veining, a pin hole, or the like.　This mold material for a shell mold is prepared in such a manner as to comprise a mixture including a fire resistant aggregate, phenol resin, and a tar generating material of which a residual carbon rate acquired by a thermogravimetric analysis in a nitrogen atmosphere is less than 30 mass%, and set a tar generating amount at a time when a mold made of the mixture is heated at 600°C for 6 minutes to be equal to or more than 3 mg per gram of the mold.

Description

[Technical Field]

[0001] The present invention relates to a molding material for a shell mold, and more particularly to a molding material that can be used to advantageously mold a shell mold that can effectively suppress or prevent the occurrence of casting defects. [Background technology]

[0002] Conventionally, in a casting process using a shell mold obtained by binding refractory aggregate such as silica sand with a binder and molding the resulting mold, casting defects such as deterioration of the casting surface due to penetration or seizure of molten metal have been caused, so a mold wash containing graphite, zircon, aluminum oxide, etc. has been applied to the surface of the mold. However, this application process is troublesome and complicates the casting process, making it difficult to perform, and also has inherent problems such as making the mold less likely to collapse after casting.

[0003] For this reason, in Japanese Patent Application Laid-Open No. 2002-316237, a coating layer containing a thermosetting resin and a carbonaceous material is formed on the surface of a refractory aggregate, and the amount of gas generated when heated under predetermined conditions is 1 cm per 1 cm of the mold. 3 Resin-coated sand for shell molds with a volume of 20 mL or more per mold has been proposed, and it has been pointed out that this can protect the shell mold (casting mold) from the high temperature of the molten metal without the need for a mold wash, and can also improve the casting surface of the casting.

[0004] However, in the case of shell molds obtained by molding using such resin-coated sand, even when high-temperature molten metal is poured into the mold during casting, a large amount of carbon remains in the mold, which causes the resulting casting to be carburized, resulting in problems such as a decrease in the corrosion resistance and other properties of the casting.In addition, improvement of the casting surface is not yet sufficient, and furthermore, casting defects such as veining and pinholes cannot be sufficiently improved. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-316237 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in light of the above circumstances, and an object of the present invention is to provide a shell mold material that can be used to advantageously mold a shell mold that can effectively suppress or prevent the occurrence of casting defects related to the casting surface, veining, pinhole defects, etc. Another object of the present invention is to provide a shell mold material that can be used to advantageously mold a shell mold that can effectively improve casting operations without the need for the application of a mold wash. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, the present invention can be suitably implemented in various aspects as listed below, and the aspects described below can be adopted in any combination. It should be understood that the aspects and technical features of the present invention are not limited to those described below, but can be recognized based on the inventive idea grasped from the entire description of the specification and drawings.

[0008] Therefore, in order to solve the above-mentioned problems, the gist of the present invention is to provide a mold material for a shell mold, which comprises a mixture containing a refractory aggregate, a phenolic resin, and a resin-generating material having a residual carbon percentage of less than 30% by mass as determined by thermogravimetric analysis in a nitrogen atmosphere, and which is characterized in that when a mold made from this mixture is heated at 600°C for 6 minutes, the amount of resin generated is 3 mg or more per 1 g of mold.

[0009] In one preferred embodiment of the shell mold material according to the present invention, the tar / phenol ratio of the resin generated from the mold, as determined by gel permeation chromatography, is adjusted to 1.00 or more, more preferably 1.25 or more.

[0010] In the casting material for a shell mold according to the present invention, the resin-generating material is advantageously a powder material having an average particle size of 0.1 to 200 μm.

[0011] Furthermore, according to another preferred embodiment of the shell mold material of the present invention, the resin-generating material is contained in an amount of 1 to 50 parts by mass, more preferably 5 to 45 parts by mass, per 100 parts by mass of the phenolic resin.

[0012] Additionally, according to another desirable aspect of the present invention, the resin-generating material is a nitrogen-containing hydrocarbon or aliphatic hydrocarbon having 3 to 50 carbon atoms that can be volatilized or easily thermally decomposed at a temperature of 150°C or higher and 500°C or lower, and among these, an organic amide compound is preferably used.

[0013] In the present invention, in order to more effectively achieve the object of the present invention, the mixture advantageously further contains (a) a phosphate ester, (b) a metal oxide and / or a metal nitrate, or (c) a phenol and / or a phenolic dimer.

[0014] The present invention also encompasses a shell mold produced by molding using the shell mold material having the above-described structure and then heat-hardening the mold. [Effects of the Invention]

[0015] In a shell mold mold produced using such a shell mold material according to the present invention, for example, during a casting operation (1200 to 1600°C) for cast iron or cast steel, a specific resin-generating material is volatilized or thermally decomposed together with a phenolic resin that serves as an organic binder. The generated resin and gas form a barrier, like an air curtain, between the surface of the mold and the molten metal, and this barrier protects the mold from the high temperature of the molten metal. This not only effectively improves the casting surface of the resulting casting, but also effectively prevents veining due to the cushioning effect of the resin generated when the molten metal is poured. Furthermore, pinhole defects (hydrogen) can also be advantageously prevented. Furthermore, during aluminum casting operations (660-800°C), resin is generated by the thermal decomposition of the phenolic resin and the volatilization or thermal decomposition of the resin-generating material contained in accordance with the present invention. This resin prevents the molten aluminum from penetrating (entering) between the sand grains, thereby advantageously improving the casting surface of the resulting aluminum casting. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a chromatogram obtained by gel permeation chromatography of a resin generated from a mold made using the shell mold material obtained in Example 7. [Figure 2] 1 is a chromatogram obtained by gel permeation chromatography of tar generated from a mold made using the shell mold material obtained in Comparative Example 3. [Figure 3] FIG. 2 is an explanatory vertical cross-sectional view of a sand mold for casting tests used to produce castings used to evaluate mold characteristics in the examples. [Figure 4] FIG. 4 is an explanatory vertical cross-sectional view of an iron casting obtained using the sand mold for casting tests shown in FIG. 3. DETAILED DESCRIPTION OF THE INVENTION

[0017] First, the shell mold material according to the present invention is prepared by mixing a predetermined refractory aggregate with a phenolic resin as a binder, a resin-generating material having a residual carbon content of less than 30% by mass as determined by thermogravimetric analysis in a nitrogen atmosphere, and other additives as needed. Generally, this material is resin-coated sand (RCS) in which a coating layer composed primarily of phenolic resin is formed on the surface of the refractory aggregate particles, and this coating layer contains the resin-generating material and other additives as needed.

[0018] Furthermore, such shell mold material (RCS) must generate 3 mg or more of resin per 1 g of mold when the mold made using it is heated at 600°C for 6 minutes. This effectively suppresses or prevents the occurrence of casting defects, and advantageously improves the casting surface of the resulting casting, prevents veining, and prevents pinhole defects.

[0019] The resin generated by heating the mold is generated not only from the resin-generating materials described above, but also from the phenolic resin used as a binder and other additives added as needed. Furthermore, such resin is a mixture that is liquid or solid at room temperature and primarily composed of monomers and dimers generated by the volatilization or thermal decomposition of these resin-generating components. Specifically, it is composed of monomers with a boiling point of 400°C or less or aliphatic hydrocarbons with approximately 3 to 10 carbon atoms generated by thermal decomposition. Furthermore, because such resin contains radicals resulting from hydrogen abstraction from the resin-generating components, it is prone to recombination and resinification, and as a result, it eventually becomes a solid over time.

[0020] The tar / phenol ratio of the resin generated from such a mold, as measured by gel permeation chromatography, is preferably 1.00 or higher, more preferably 1.25 or higher. This increases the amount of resin gasified, resulting in a further improvement in the casting surface. On the other hand, if the amount of phenol in the resin components is greater than the amount of tar, it may be difficult to sufficiently gasify the resin. The upper limit of the tar / phenol ratio is generally about 10, and preferably about 8.

[0021] The tar / phenol ratio is calculated using the peak values of tar and phenol obtained from a chromatogram obtained by measuring the resin by gel permeation chromatography. Specifically, the phenol peak value: P appears at an elution time (retention time) of 16 to 17 minutes in the chromatogram, and the tar peak value: T appears at an elution time (retention time) of 17 to 19 minutes in the chromatogram. These peak values are then obtained from the chromatogram, and the ratio of their peak heights, T / P, is calculated to determine the tar / phenol ratio. Naturally, depending on the analytical equipment and analytical conditions, the elution times (retention times) at which each peak appears may differ from those described above. In such cases, there is no problem if the tar and phenol peaks are identified and the tar / phenol ratio is determined.

[0022] The refractory aggregate constituting the shell mold material according to the present invention is a refractory substance that functions as the base material of the mold. Any of the various granular or powdery refractory materials conventionally used for molds can be used. Specific examples include silica sand, recycled silica sand, specialty sands such as alumina sand, olivine sand, zircon sand, and chromite sand, slag particles such as ferrochrome slag, ferronickel slag, and converter slag, artificial particles such as alumina particles and mullite particles, and recycled particles thereof, alumina balls, magnesia clinker, etc. These refractory aggregates may be virgin sand, recycled sand or reclaimed sand that has been used once or multiple times as foundry sand for molding, or a mixed sand obtained by mixing such recycled sand or reclaimed sand with new sand. However, when such a mixed sand is used, it is preferable that the new sand ratio be 30% by mass or more. Such refractory aggregate is generally used with a particle size of about 40 to 200, preferably about 60 to 150, in terms of AFS index.

[0023] Furthermore, the phenolic resin, which is one of the components constituting the casting material for the shell mold according to the present invention, is used as a binder (binding agent). As is well known, it is a solid or liquid (including varnish or emulsion) condensation product obtained by reacting phenols with aldehydes in the presence of an acidic or basic catalyst. Depending on the type of catalyst used, it is called a novolak type or a resol type phenolic resin, and it is a phenolic resin that exhibits thermosetting properties when heated in the presence or absence of a specific curing agent or curing catalyst.

[0024] Specifically, such phenolic resins include, for example, novolac-type phenolic resins, resole-type phenolic resins, nitrogen-containing resole-type phenolic resins, and benzyl ether-type phenolic resins, all of which are made from phenol. Other examples include modified novolac-type phenolic resins made entirely or partially from modifying raw materials such as bisphenol A or bisphenol A purification residues, and naphthol-modified phenolic resins obtained by reacting phenols and naphthols with aldehydes. However, the phenolic resins are not limited to these, and various known phenolic resins can be used. Among these phenolic resins, novolac-type phenolic resins, mixtures of novolac-type phenolic resins and resole-type phenolic resins, and naphthol-modified phenolic resins are preferred. From an environmental perspective, the phenolic resins used herein are preferably prepared so that the free phenol content is 2.0% by mass or less, and more preferably 1.0% by mass or less.

[0025] The proportion of such phenolic resin in the casting material for the shell mold cannot be unequivocally defined, as it is determined appropriately taking into consideration the type of resin used, the required strength of the casting mold, and the like. However, it is generally within the range of about 0.2 to 10 parts by mass, preferably 0.5 to 8 parts by mass, and more preferably 0.5 to 5 parts by mass, per 100 parts by mass of the refractory aggregate.

[0026] Furthermore, in the present invention, the resin-generating material to be mixed with the refractory aggregate together with the phenolic resin is a material that volatilizes or thermally decomposes due to the heat during casting to generate the resin described above, and when subjected to thermogravimetric analysis in a nitrogen atmosphere, the residual carbon content must be less than 30% by mass, preferably less than 20% by mass. The lower limit of the residual carbon content may be 0 if the material does not leave residual carbon, specifically, 0.01% by mass or more. By using a resin-generating material with a residual carbon content of less than 30% by mass, pinhole formation can be effectively suppressed. In contrast, a resin-generating material with a residual carbon content of 30% by mass or more is more likely to develop pinhole defects due to its reduced volatile content. Furthermore, in the present invention, the resin-generating material is not limited to either a solid or a liquid, but is preferably used in a powder or particulate form for uniform dispersion and mixing with the refractory aggregate and phenolic resin. It is particularly preferable that the average particle size (median diameter: D 50 ) is advantageously used.

[0027] Such tar-generating materials are generally nitrogen-containing hydrocarbons or aliphatic hydrocarbons having 3 to 50 carbon atoms that can be volatilized or easily thermally decomposed at temperatures of 150°C or higher and 500°C or lower. More specific examples include organic amide compounds such as acrylamide, benzamide, ethylene bisstearamide, methylene bisstearamide, acetanilide, nicotinamide, acetamide, stearamide, ethylene bisoleamide, erucamide, and oleamide; carbon source materials such as Gilsonite, asphalt, bituminous coal, coal tar, pitch, and carbon black; and further alkylene polymers such as polyethylene; sugars such as starch; and corn starch. Of these, organic amide compounds are advantageously used from the viewpoint of the amount of tar generated.

[0028] The amount of resin-generating material used is selected appropriately, taking into consideration the amount of phenolic resin used, so as to obtain the amount of resin generated according to the present invention, but is generally used in a ratio of 1 to 50 parts by mass, preferably 5 to 45 parts by mass, more preferably 8 to 40 parts by mass, and particularly preferably 10 to 30 parts by mass, per 100 parts by mass of phenolic resin. If the amount of resin-generating material used is too small, the effect of its addition will not be fully exerted, and if the amount used is too large, the mold strength of the shell mold will decrease, and the heat resistance of the mold will also decrease.

[0029] Thus, by using a shell mold mold made from a shell mold material obtained by blending such a resin-generating material with refractory aggregate or phenolic resin, for example, in aluminum casting (660-800°C), the resin generated by thermal decomposition of the phenolic resin and resin-generating material is prevented from penetrating between the sand grains of the molten aluminum, thereby effectively improving the casting surface of the resulting aluminum casting. Also, in casting of cast iron or steel (1200-1600°C), the resin and gas generated by thermal decomposition of the resin-generating material and phenolic resin form a barrier between the surface of the shell mold and the molten metal, protecting the mold from the high temperature of the molten metal, thereby improving the casting surface of the resulting casting and advantageously suppressing or preventing the occurrence of veining.

[0030] In the present invention, it is desirable to prepare a shell mold material by adding and blending an organic phosphate ester in addition to the refractory aggregate and phenolic resin, in addition to the resin-generating material described above. This allows the object of the present invention to be achieved even more advantageously. Such an organic phosphate ester advantageously decomposes the phenolic resin and the resin-generating material, effectively increasing the amount of resin generated, thereby enhancing the barrier effect of the resin and generated gas. The amount of such an organic phosphate ester used is appropriately selected from the range of typically about 1 to 50 parts by mass, preferably about 5 to 40 parts by mass, and more preferably about 10 to 30 parts by mass per 100 parts by mass of the phenolic resin.

[0031] Examples of such organic phosphate esters include aliphatic phosphate esters such as trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, methyl diethyl phosphate, methyl dibutyl phosphate, ethyl dibutyl phosphate, and tris(β-chloropropyl)phosphate; triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, cresyl diphenyl phosphate, 2-ethylhexyl diphenyl phosphate, t-butylphenyl diphenyl phosphate, bis-(t-butylphenyl)phenyl phosphate, tris-(t-butylphenyl)phosphate, isopropyl phenyl diphenyl phosphate, bis-( Examples of suitable phosphate esters include aromatic phosphate esters such as tris-(isopropylphenyl)diphenyl phosphate and tris-(isopropylphenyl)phosphate, as well as aliphatic condensed phosphate esters and aromatic condensed phosphate esters such as oligomeric ethyl ethylene phosphate, modified oligomeric ethyl ethylene phosphate, phenylene bis(phenylcresol phosphate), 2,2-bis{4-[bis((mono- or di)methylphenoxy)phosphoryloxy]phenyl}propane, 1,3-phenylene bis(dixylenyl)phosphate, and α-diphenoxyphosphoryl-ω-phenoxypoly(n=1 to 3)[oxy-1,4-phenyleneisopropylidene-1,4-phenyleneoxy(phenoxyphosphoryl)].

[0032] Furthermore, the shell mold material according to the present invention preferably contains a metal oxide and / or a metal nitrate salt along with the resin-generating material. This promotes the gasification of resin generated by thermal decomposition, thereby advantageously enhancing the barrier effect. Furthermore, the metal oxide and / or metal nitrate salt convert the generated resin into harmless CO₂ or HO (inert) gas, preventing pinhole defects (hydrogen) and, when casting low-carbon stainless steel, advantageously contributing to the prevention of carburization. In particular, carburization defects are caused by active CO gas. For example, in stainless steel, the alloy component Cr reacts with active CO gas, reducing the Cr content. This reduces the passive film on the stainless steel surface, making the stainless steel more susceptible to corrosion. In other words, corrosion resistance is reduced. However, the inclusion of the metal oxide and / or metal nitrate salt advantageously avoids such carburization defects.

[0033] Such metal oxides are used in powder form, with an average particle size comparable to that of the resin-generating material to ensure uniform dispersion and mixing. Specific examples of metal oxides include oxides of metals such as iron, copper, nickel, cobalt, and zinc, or mixtures thereof. Metal nitrates include nitrates of alkali metals such as sodium and potassium, and alkaline earth metals such as calcium and magnesium. Either one or both of these metal oxides and nitrates are selected and used separately, typically in amounts of about 0.1 to 100 parts by weight, preferably about 3 to 50 parts by weight, more preferably about 5 to 40 parts by weight, and even more preferably about 10 to 30 parts by weight, per 100 parts by weight of the phenolic resin.

[0034] Furthermore, the shell mold material according to the present invention preferably contains phenols and / or phenolic dimers, which can improve the strength of the mold and reduce the thermal expansion coefficient of the mold. Examples of phenols include xylenol, o-cresol, p-cresol, m-cresol, naphthol, resorcinol, catechol, hydroquinone, bisphenol A, bisphenol F, bisphenol S, and biphenol. Examples of phenolic dimers include bisphenol A, bisphenol F, bisphenol S, and biphenol. These phenols may be used alone or in combination. The total amount of phenols and phenolic dimers used is generally about 1 to 50 parts by weight, preferably about 5 to 40 parts by weight, per 100 parts by weight of the phenolic resin.

[0035] Furthermore, in order to increase the amount of resin generated, an organic halogen compound may be further added. Examples of such organic halogen compounds include organic chlorine compounds such as chlorinated paraffin, chlorinated diphenyl, chlorinated ethane, chlorinated polyethylene, chlorinated polyphenyl, chlorinated diphenyl, vinyl chloride, perchlorocyclopentadecanone, tetrachlorobisphenol A, trischloroethyl phosphate, trisdichloropropyl phosphate, and tris-β-chloropropyl phosphate; brominated paraffin, brominated polyphenyl, tetrabromoethane, tetrabromobenzene, decabromodiphenyloxide, octabromodiphenyloxide, hexabromocyclododecane, bis(tribromophenoxy)ethane, ethylenebistetrabromophthalimide, hexabromobenzene, and polydibromophenylene oxide. Examples of suitable organic halogen compounds include organic bromine compounds such as brominated polystyrene, tribromoneopentyl alcohol, dibromodichloropropane, dibromotetrafluoroethane, tris(tribromophenyl)phosphate, and tris(tribromoneopentyl)phosphate; and organic fluorine compounds such as polytetrafluoroethylene, perfluoroalkoxyalkane, perfluoroethylenepropene copolymer, ethylenetetrafluoroethylene copolymer, ethylenechlorotrifluoroethylene copolymer, polyvinylidene fluoride, and polychlorotrifluoroethylene. The amount of the organic halogen compound used is typically about 1 to 50 parts by mass, preferably about 5 to 30 parts by mass, per 100 parts by mass of the phenolic resin.

[0036] The shell mold material according to the present invention can further contain various commonly used additives, as needed, to improve the physical properties of the mold material itself and the mold. For example, lubricants that contribute to improving the fluidity of the mold material (RCS) can include waxes such as paraffin wax, synthetic polyethylene wax, and montanic acid wax; stearic acid, stearyl alcohol, stearic acid monoglyceride, and stearyl stearate; metal stearates such as calcium stearate, zinc stearate, magnesium stearate, and lead stearate; and hydrogenated oils. It is also effective to add a coupling agent that strengthens the bond between the refractory aggregate and additives such as phenolic resin. Examples of such agents include silane coupling agents, zirconium coupling agents, and titanium coupling agents. Additionally, release agents that can be used include paraffin, wax, light oil, machine oil, spindle oil, insulating oil, waste oil, vegetable oil, fatty acid ester, organic acid, mica, vermiculite, fluorine-based release agents, silicone-based release agents, etc. These additives are used in an amount of about 0.1 to 10 parts by mass, preferably about 0.5 to 5 parts by mass, per 100 parts by mass of the phenolic resin.

[0037] Furthermore, when producing the shell mold material (RCS) according to the present invention using the additive components described above, various known methods can be appropriately employed without any particular limitation, including, for example, any of the conventionally known methods such as the dry hot coating method, semi-hot coating method, cold coating method, powder solvent method, etc. Among these, the so-called dry hot coating method is advantageously employed, which involves adding a phenolic resin and a resin-generating material to preheated refractory aggregate (particles) in a kneader such as a Whirl mixer or a Speed mixer, adding other additives as needed, kneading the mixture, adding a predetermined curing agent or curing accelerator such as hexamethylenetetramine, cooling the mixture with air to break down the aggregates into granules, and then adding calcium stearate (lubricant). The timing for kneading the phenolic resin, resin-generating material, other additives, and curing agent / curing accelerator with the refractory aggregate can be appropriately selected based on the knowledge of those skilled in the art, and they can be kneaded individually or sequentially, or in appropriate combinations. The resin-generating material may be mixed during the production of the phenolic resin, but because it is less susceptible to thermal history, it is preferable to add the resin-generating material separately when kneading the refractory aggregate and phenolic resin. When a large amount of resin-generating material is to be added, it may be added both during the production of the phenolic resin and when kneading the refractory aggregate and phenolic resin.

[0038] When the shell mold material obtained as described above is used to produce the desired shell mold, the mold is produced under heat to heat-cure the shell mold material (RCS). The method for producing the desired mold is not particularly limited, and any conventionally known method can be advantageously used. For example, the mold material described above can be poured into a mold heated to approximately 150-300°C, using gravity or blowing, to form the desired shape and cavity of the desired mold. The mold material is then allowed to harden, and the hardened mold is then removed from the mold to obtain the desired casting mold. The mold thus obtained can advantageously be endowed with the excellent characteristics described above. [Example]

[0039] Below, several examples of the present invention will be presented to further clarify the present invention, but it goes without saying that the present invention is not limited in any way by the description of such examples. It should be understood that in addition to the following examples and the above-mentioned specific description, various changes, modifications, improvements, etc. can be made to the present invention based on the knowledge of those skilled in the art, as long as they do not deviate from the spirit of the present invention. In the following examples and comparative examples, parts and percentages are all expressed by mass. Furthermore, measurements of the residual carbon rate, mold strength, amount of tar generation, tar / phenol ratio, and thermal expansion coefficient, as well as evaluation of casting surface, veining, and pinhole defects, were each performed as follows.

[0040] -Measurement of residual carbon rate- The mold materials obtained in the examples and comparative examples were heated to 600°C at a heating rate of 10°C / min in a nitrogen atmosphere using a Rigaku Corporation TG8230 differential thermobalance, and the mass was measured. The mass loss rate was then divided by 100% by mass to obtain the residual carbon rate.

[0041] -Measurement of mold strength- The produced shell mold material was used to prepare a JIS type test piece (width: 10 mm x thickness: 10 mm x length: 60 mm) in accordance with JIS-K-6910 (sintering conditions for specimen: 250°C for 60 seconds), and the mold strength (N / cm 2 ) was measured.

[0042] -Measurement of resin generation amount- Four mold strength measurement test pieces (width: 10 mm x thickness: 10 mm x length: 60 mm) were placed in a glass test tube (inner diameter: 27 mm x length: 200 mm), and then pre-weighed glass wool (2.5 g) was inserted near the opening of the test tube to create a tar generation amount measurement device. Next, the measurement device was placed in a tubular heating furnace whose furnace temperature was maintained at 600 ° C., and subjected to heat exposure treatment for 6 minutes, after which it was removed and allowed to cool to room temperature. The glass wool was then removed from the measurement device, and its mass was measured. The amount of tar generation (mg) was calculated by subtracting the glass wool mass (mg) before explosion heating from the glass wool mass (mg) after explosion heating.

[0043] -Measurement of tar / phenol ratio- The tar obtained in the above-mentioned tar generation amount measurement was measured using a Tosoh Corporation gel filtration chromatograph HLC-8320GPC (column: G1000Hx1 + G2000Hx1, detector: UV 254 nm, carrier: tetrahydrofuran 1 mL / min, column temperature: 38°C), and each tar was analyzed in terms of standard polystyrene. From the resulting chromatogram, the phenol peak value (P) appearing at an elution time of 16 to 17 minutes and the tar peak value (T) appearing at an elution time of 17 to 19 minutes were calculated, and the ratio of these peak heights, T / P, was calculated to obtain the tar / phenol ratio. Naturally, depending on the analytical equipment and conditions, the elution times at which each peak appears may differ from those described above. In such cases, there is no problem if the tar and phenol peaks are identified and the tar / phenol ratio is calculated.

[0044] -Measurement of thermal expansion coefficient- The rapid thermal expansion test was performed according to the JACT Test Method M-2 Thermal Expansion Test Method. A test piece (28.3 mm diameter x 51 mm length, approximately 1 / 4 of the circumference) was prepared at a firing temperature of 280°C for 120 seconds. The test piece was placed in a high-temperature foundry sand tester with a furnace temperature of 1000°C and removed after 4 minutes. The thermal expansion coefficient was calculated from the test piece length before and after exposure to heat using the following formula: Thermal expansion coefficient (%) = {(after heat exposure - before heat exposure) test piece length} / (test piece length before heat exposure) x 100

[0045] -Evaluation of casting surface- First, as shown in Figure 3, a half-split hollow main mold 6 (cavity diameter: 6 cm, height: 6 cm) was made from room-temperature self-hardening sand. The half-split hollow main mold 6 had a molten metal inlet 2 at the top and a core baseboard fixing portion 4 at the bottom. A circular hollow core 10 (diameter: 5 cm, height: 5 cm) with a baseboard portion 8 was then glued into the half-split hollow main mold 6 at the baseboard fixing portion 4. The half-split hollow main molds 6 were then glued together to form a casting test sand mold 12. To prevent leakage during casting, the glued main molds were clamped with a vice or wrapped with wire. Next, molten cast iron (FC200) (temperature: 1380°C ± 40°C) was poured through the molten metal inlet 2 of the casting test sand mold 12. After solidification, the main mold 6 and core 10 were broken, and a cylindrical casting 16, as shown in Figure 4, was removed. The resulting casting 16 is then cut in half, and the condition of the casting surface (skin of the casting) is checked visually and by touch, and evaluated on a four-point scale according to the following criteria. In the present invention, ⊚ and ◯ are considered to be acceptable. ⊚: No seizure was observed and the surface was smooth. ◯: No seizure is observed, but roughness is observed on the surface. △: Burning is observed in part of the casting surface, and the surface is also rough. ×: Burning is observed over the entire surface of the casting surface, and roughness is also observed on the surface.

[0046] -Evaluation of veining occurrence- Each RCS was used to create a mold for casting a cylinder head, and then 20 cast iron cylinder heads were produced using the sand casting method by pouring molten FC200 into them, and an evaluation of the occurrence of veining was carried out. Each of the 20 resulting castings (cylinder heads) was cut, and the interior was inspected and visually checked for the presence or absence of veining. The evaluation of the occurrence of veining was expressed as the numerator, with the 20 castings used as the denominator and the number of castings that developed veining listed as the numerator.

[0047] -Evaluation of pinhole defects- The surface of the casting (cylinder head) obtained in the above evaluation of veining occurrence is visually inspected. Furthermore, the interior of the cut piece is visually inspected. Relatively small, circular, bubble-like cavities (depressions) with a diameter of 1 mm or more are recognized as pinhole defects, and the number of pinhole defects is counted. The casting is rated as follows: no pinhole defects, △, with one pinhole defect, and ×, with two or more pinhole defects.

[0048] -Production of phenolic resin A- A reaction vessel equipped with a thermometer, a stirrer, and a condenser was charged with 940 parts of phenol, 428 parts of 47% formalin, and 2.8 parts of oxalic acid. The temperature of the reaction vessel was then gradually increased until the reflux temperature was reached, and the mixture was refluxed for 90 minutes. The mixture was then heated and concentrated under reduced pressure until the reaction temperature reached 170°C, yielding a phenolic resin A.

[0049] -Production of phenolic resin B- 200 parts of phenol, 800 parts of bisphenol A, 270 parts of 47% formalin, and 3 parts of oxalic acid were charged into a reaction vessel equipped with a thermometer, a stirrer, and a condenser. The temperature of the reaction vessel was then gradually increased, and after the reflux temperature was reached, the mixture was refluxed for 70 minutes. The mixture was then heated and concentrated under reduced pressure until the reaction liquid temperature reached 170°C, thereby obtaining a phenolic resin B.

[0050] Example 1 A 1:1 mixture of flattery sand and recycled silica sand was used as the refractory aggregate. 2.8 parts of the phenolic resin A and 0.28 parts of acrylamide powder (residual carbon content: 2%, average particle size: 150 μm) were added to 100 parts of this mixture in a laboratory Whirl mixer and mixed for 60 seconds. A solution of 0.42 parts of hexamethylenetetramine in water was then added, followed by cooling with a blower. 0.1 parts of calcium stearate was then added to obtain a shell mold material.

[0051] -Examples 2 and 3- A casting material for a shell mold was obtained in the same manner as in Example 1, except that the amount of acrylamide powder, which is a resin-generating material, added was set to 0.56 parts or 0.84 parts.

[0052] -Examples 4 to 7- Shell mold casting materials were obtained in the same manner as in Example 2, except that powdered acetanilide, ethylene bisstearic acid amide, Gilsonite, or polyethylene was used as the resin-generating material instead of acrylamide powder.

[0053] Examples 8 to 11 Shell mold materials were obtained in the same manner as in Example 2, except that 0.56 parts of powdered red iron oxide, copper oxide, potassium nitrate, or a 1 / 1 mixture of copper oxide and potassium nitrate was further added as a metal oxide.

[0054] Examples 12 and 13 A shell mold material was obtained in the same manner as in Example 2, except that 0.56 parts of tributyl phosphate or TCPP [tris(β-chloropropyl) phosphate] was further added as an organic phosphate ester.

[0055] Example 14 A shell mold material was obtained in the same manner as in Example 2, except that 0.56 parts of powdered copper oxide as a metal oxide and 0.56 parts of tributyl phosphate as an organic phosphate ester were further added and blended.

[0056] Example 15 A mold material for a shell mold was obtained in the same manner as in Example 2, except that phenolic resin B was used instead of phenolic resin A as the phenolic resin.

[0057] Example 16 A mold material for a shell mold was obtained in the same manner as in Example 14, except that phenolic resin B was used instead of phenolic resin A as the phenolic resin.

[0058] -Comparative Example 1- A mold material for a shell mold was obtained in the same manner as in Example 2, except that acrylamide powder was not added as a resin-generating material.

[0059] -Comparative Example 2- A mold material for a shell mold was obtained in the same manner as in Example 2, except that 0.56 parts of graphite powder (average particle size: 3 μm) with a carbon residue rate of 60% was used instead of acrylamide powder as the resin-generating material.

[0060] -Comparative Example 3- A mold material for a shell mold was obtained in the same manner as in Example 2, except that phenolic resin B was used instead of phenolic resin A and acrylamide powder was not added as a resin-generating material.

[0061] -Comparative Examples 4 and 5- A shell mold material was obtained in the same manner as in Example 2, except that acrylamide powder was not added as a resin-generating material, and 0.56 parts of powdered copper oxide or red iron oxide was added as a metal oxide.

[0062] -Evaluation of mold materials- The amount of resin generated, the tar / phenol ratio, the casting surface, the rate of veining, and the presence or absence of pinhole defects of the molds produced from each of the shell mold materials obtained above in Examples 1 to 16 and Comparative Examples 1 to 5 were measured or evaluated according to the measurement or evaluation methods described above. The measurement or evaluation results are shown in Tables 1 to 3 below.

[0063] [Table 1]

[0064] [Table 2]

[0065] [Table 3]

[0066] As is clear from a comparison of the results in Tables 1 to 3, the shell mold materials of Examples 1 to 16, which contain the specified resin-generating material according to the present invention, all exhibit sufficient resin generation amounts and tar / phenol ratios, thereby improving the casting surface, reducing the rate of veining, and effectively suppressing or preventing the occurrence of pinhole defects, thereby enabling the production of high-quality castings.

[0067] In contrast, the shell mold material obtained in Comparative Example 1 did not contain any of the resin-generating material according to the present invention, and therefore the resulting casting had a poor casting surface and was subject to increased veining and pinhole defects. In Comparative Example 2, in which graphite powder with a residual carbon content outside the range specified in the present invention was added as a resin-generating material, some improvement in the casting surface was observed, but the rate of veining and the occurrence of more pinhole defects were still high. Furthermore, as in Comparative Examples 3 to 5, it was revealed that, in the absence of the resin-generating material according to the present invention, the use of phenolic resin B or the addition of copper oxide or red iron oxide as a metal oxide was insufficient to improve the casting surface, suppress the occurrence of veining, or prevent the occurrence of pinhole defects.

[0068] Examples 17 and 18 Shell mold materials were prepared in the same manner as in Example 2, except that 0.56 parts or 0.84 parts of bisphenol A, which is a phenol and also corresponds to a phenolic dimer, was further added.

[0069] Next, the obtained shell mold material was measured or evaluated for the amount of resin generated, tar / phenol ratio, mold strength, thermal expansion coefficient, and casting surface according to the measurement or evaluation methods described above, and the results are shown in Table 4. For reference, the measurement and evaluation results for the shell mold material obtained in Example 2 are also shown in Table 4.

[0070] [Table 4]

[0071] As is clear from the results in Table 4, the shell mold materials of Examples 17 and 18, which contain refractory aggregate and, in addition to acrylamide as a resin-generating material, phenols or phenolic dimers, are significantly effective in improving the casting surface, have high mold strength, and exhibit low thermal expansion coefficient characteristics. [Explanation of symbols]

[0072] 2 Molten metal inlet 4 Baseboard fixing part 6 Main mold 8 Baseboard section 10 core 12 sand mold 14 Waste core discharge port 16 Casting

Claims

1. A mold material for a shell mold, comprising a mixture containing a refractory aggregate, a phenolic resin, and a resin-generating material having a residual carbon percentage of less than 30% by mass as determined by thermogravimetric analysis in a nitrogen atmosphere, wherein the resin-generating material is contained in an amount of 8 to 50 parts by mass per 100 parts by mass of the phenolic resin, and wherein when a mold made from the mixture is heated at 600°C for 6 minutes, the amount of resin generated is 3 mg or more per 1 g of the mold.

2. 2. The casting material for a shell mold according to claim 1, wherein the tar / phenol ratio determined by gel permeation chromatography of the resin generated from the casting mold is 1.00 or more.

3. 3. The molding material for a shell mold according to claim 2, wherein the tar / phenol ratio is 1.25 or more.

4. 4. The casting material for a shell mold according to claim 1, wherein the resin-generating material is a powder material having an average particle size of 0.1 to 200 μm.

5. The shell mold material according to any one of claims 1 to 4, characterized in that the resin-generating material is contained in an amount of 8 to 40 parts by mass per 100 parts by mass of the phenolic resin.

6. 6. The shell mold material according to claim 1, wherein the resin-generating material is contained in an amount of 10 to 30 parts by mass per 100 parts by mass of the phenolic resin.

7. 7. The shell mold material according to claim 1, wherein the resin-generating material is a nitrogen-containing hydrocarbon or an aliphatic hydrocarbon having 3 to 50 carbon atoms that can be volatilized or easily thermally decomposed at a temperature of 150°C or higher and 500°C or lower.

8. 8. The casting material for a shell mold according to claim 1, wherein the resin-generating material is an organic amide compound.

9. 9. The casting material for a shell mold according to claim 1, wherein the mixture further contains an organic phosphate ester.

10. 10. The molding material for a shell mold according to claim 1, wherein the mixture further contains a metal oxide and / or a metal nitrate.

11. 11. The casting material for a shell mold according to claim 1, wherein the mixture further contains phenols and / or phenolic dimers.

12. A shell mold produced by molding using the shell mold material according to any one of claims 1 to 11 and then heat-curing the mold.

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