Method for producing core

Abstract

To provide a method for producing a core, capable of producing the core under a wide range of manufacturing conditions and also excellent in productivity.SOLUTION: The method for producing a core of the present disclosure includes steps of: (i) preparing a mixture containing granular aggregate, water glass, an amphoteric surfactant, and amorphous silica having an average particle diameter of less than 1 μm; (ii) kneading the mixture prepared in the step (i) until the mixture becomes a whipped state to prepare a kneaded product; and (iii) molding the kneaded product prepared in the step (ii) to produce the core.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a core (sand mold).[Background Art]

[0002] A core molding method is known, which involves kneading molding sand (kneaded sand) with a binder, etc., in a kneading mixer, and injecting and filling the kneaded molding sand into a mold to mold a core.

[0003] The present inventor previously reported that a core with high moisture resistance and capable of preventing sand adhesion to castings can be produced by a process involving: preparing a mixture by mixing a particulate aggregate, water glass, a surfactant, and a specific proportion of amorphous SiO2 having an average particle size of 0.01 μm to 0.05 μm; preparing a kneaded material by kneading the mixture until it becomes whip-like; and molding this kneaded material to produce a core (Patent Literature 1).[Prior Art Literature][Patent Literature]

[0004] [Patent Literature 1] Japanese Unexamined Patent Application Publication No. 2023-153624[Summary of the Invention][Problem to be Solved by the Invention]

[0005] The market desires a method for producing cores that can be manufactured under a wide range of production conditions and also offers excellent productivity.

[0006] The present disclosure has been made in view of the above problem, and aims to provide a method for manufacturing a core that enables core production under a wide range of manufacturing conditions and also offers excellent productivity.[Means for Solving the Problem]

[0007] To solve the aforementioned problem and achieve the objective, the following method for manufacturing a core is provided.The method for manufacturing a core according to the present disclosure includes: a step (i) of preparing a mixture containing a particulate aggregate, water glass, a zwitterionic surfactant, and amorphous silica having an average particle size of less than 1 μm; a step (ii) of kneading the mixture prepared in step (i) until it becomes whip-like to prepare a kneaded material; and a step (iii) of molding the kneaded material prepared in step (ii) to produce a core.

[0008] According to the method for manufacturing a core of the present disclosure, fluctuations in the fluidity of the kneaded material can be suppressed even if the content ratio of water glass, which functions as a binder, varies. Also, even when using, for example, colloidal silica as the amorphous silica, the kneaded material exhibits excellent fluidity. As a result, productivity is excellent, and cores can be manufactured under a wide range of manufacturing conditions.[Effect of the Invention]

[0009] According to the present disclosure, the excellent effect of providing a method for manufacturing a core that enables core production under a wide range of manufacturing conditions and also offers excellent productivity can be achieved.[Brief Description of Drawings]

[0010] [Fig. 1] A graph showing the relationship between water glass content ratio and dynamic viscosity for the Example group and the Comparative Example group.[Mode for Carrying Out the Invention]

[0011] The present disclosure will be described in detail below. Needless to say, other embodiments are included within the scope of the present disclosure as long as they conform to the gist of the present disclosure.

[0012] The method for manufacturing a core according to the present disclosure includes: a step (i) of preparing a mixture containing a particulate aggregate, water glass, a zwitterionic surfactant, and amorphous silica having an average particle size of less than 1 μm; a step (ii) of kneading the mixture prepared in step (i) until it becomes whip-like to prepare a kneaded material; and a step (iii) of molding the kneaded material prepared in step (ii) to produce a core.

[0013] 1. MixtureThe mixture of the present disclosure (also referred to as the present mixture) contains a particulate aggregate, water glass, a zwitterionic surfactant, and amorphous silica having a nano-sized average particle size of less than 1 μm, and is prepared in step (i). Each component is detailed below.

[0014] 1-1. Particulate AggregateThe particulate aggregate is a granular material such as sand that constitutes the core. The type of particulate aggregate is not limited, and examples include silica sand, alumina sand, olivine sand, chromite sand, zircon sand, mullite sand, and various artificial aggregates. The particulate aggregate may be used alone or as a mixture of two or more types.

[0015] 1-2. Water GlassWater glass is so-called sodium silicate and functions as a binder in the mixture of the present disclosure, acting as an adhesive that agglomerates the particulate aggregates together. Water glass is a viscous alkaline liquid (Na2O·nSiO2) containing three components: silicon dioxide (SiO2), sodium oxide (Na2O), and water (H2O). Its properties can be classified by the molar ratio of SiO2 / Na2O. The molar ratio of SiO2 to Na2O (SiO2 / Na2O) is, for example, 1.2 to 3.8, preferably 2.0 to 3.3.

[0016] The amount of water glass can be designed as appropriate according to the application, but is usually 0.2 to 1.2 parts by mass, preferably 0.5 to 0.9 parts by mass, per 100 parts by mass of the particulate aggregate. Adding water glass in an amount of 0.2 to 1.2 parts by mass relative to the particulate aggregate can effectively prevent the water glass from generating odor and smoke.

[0017] 1-3. Amorphous SilicaAmorphous silica is a spherical silicon dioxide known in the technical field, and nano-sized particles having an average particle size of less than 1 μm are used. Nano-sized means an average particle size of less than 1 μm and 1 nm or more. Examples of amorphous silica include silica gel, precipitated silica, and colloidal silica. The shape of the amorphous silica is not limited, and examples include spherical, amorphous, and scaly. Among these, spherical is suitable. Using colloidal silica allows easy obtainment of spherical silica.

[0018] Adding nano-sized amorphous silica can reduce the resistance (release resistance) when releasing from the mold after molding in the mold in step (iii). Furthermore, a molded product with high moisture resistance can be obtained. These results can enhance productivity. The average particle size of the amorphous silica is preferably 10 to 500 nm, more preferably 10 to 100 nm, and even more preferably 10 to 50 nm. Note that in this specification, the average particle size is a value determined by the BET method as described later.

[0019] The amount of amorphous silica is 0.10 to 0.35 parts by mass, preferably 0.20 to 0.30 parts by mass, per 100 parts by mass of the particulate aggregate. Using the amorphous silica having said average particle size in said amount of 0.10 to 0.35 parts by mass causes the amorphous silica to aggregate during kneading in step (ii), and this aggregated amorphous silica forms irregularities on the surface of the core prepared in step (iii), inducing a lotus leaf effect. As a result, release resistance can be reduced, minimizing sticking of the core sand to the mold.

[0020] 1-4. Zwitterionic SurfactantThe zwitterionic surfactant is a surfactant having both an anionic site and a cationic site within the same molecule. Using a zwitterionic surfactant allows the mixture to be efficiently foamed into a whip-like state in step (ii).

[0021] The type of zwitterionic surfactant is not limited, and suitable examples include amino acid-type surfactants, betaine-type surfactants, sulfobetaine-type surfactants, and amine oxide-type surfactants. Specific examples include betaine-type surfactants such as fatty acid amide propyl betaine, myristamidopropyl betaine, cocamide propyl betaine, lauramidopropyl betaine, fatty acid amide propyl dimethyl amino acetate betaine, coconut fatty acid amide propyl dimethyl amino acetate betaine, lauric acid amide propyl dimethyl amino acetate betaine, stearyl dimethyl amino acetate betaine, lauryl dimethyl amino acetate betaine, lauryl dihydroxyethyl betaine, 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine; sulfobetaine-type surfactants such as alkyl hydroxysulfobetaine, cocamidopropyl hydroxysulfobetaine, lauramidopropyl hydroxysulfobetaine; amine oxide-type surfactants such as fatty acid amide propyl dimethyl amine oxide, lauramidopropyl dimethyl amine oxide, lauryl dimethyl amine oxide, coconut alkyl dimethyl amine oxide, dodecyl dimethyl amine oxide, decyl dimethyl amine oxide, tetradecyl dimethyl amine oxide; and amino acid-type surfactants such as N-lauroyl-N'-carboxymethyl-N'-hydroxyethyl ethylenediamine sodium, N-coconut oil fatty acid acyl-N'-carboxyethyl-N'-hydroxyethyl ethylenediamine sodium, β-lauryl aminopropionic acid sodium, cocaminopropionic acid sodium, alkyl carboxymethyl hydroxyethyl imidazolium betaine, lauryl dimethyl amino acetate betaine, alkyl diamino ethyl glycine hydrochloride, lauryl amino dipropionic acid sodium.

[0022] The addition amount of the zwitterionic surfactant is not particularly limited as long as the foaming property of the kneaded material is considered. From the viewpoint of maintaining better fluidity of the kneaded material, it is preferably 0.001 to 1 part by mass, more preferably 0.01 to 0.1 part by mass, and even more preferably 0.02 to 0.08 part by mass, per 100 parts by mass of the particulate aggregate. Using the zwitterionic surfactant allows the fluidity of the kneaded material to be maintained favorably.

[0023] 1-5. Other AdditivesThe mixture of the present disclosure may contain any other additives within a range not departing from the gist of the present disclosure. Specific examples include inorganic compound particles, such as carbonates (e.g., calcium carbonate or magnesium carbonate) and hydroxides (e.g., magnesium hydroxide or aluminum hydroxide). Also, synthetic resins (e.g., phenol resin, furan resin, urethane resin), cement (e.g., Portland cement), bentonite, clay, starch, sugars (e.g., polysaccharides such as cellulose, fructose; tetrasaccharides such as acarbose; trisaccharides such as raffinose, maltotriose; disaccharides such as maltose, sucrose, trehalose; monosaccharides such as glucose, fructose, and other oligosaccharides), and derivatives thereof (e.g., saponin) can be mentioned. Furthermore, cross-linking agents, catalysts, and oxidation promoters can be exemplified. Various additives may be used alone or in combination of two or more.

[0024] 2. Kneaded MaterialThe kneaded material of the present disclosure refers to the mixture of the present disclosure prepared in step (i) that has been kneaded until it becomes whip-like.By kneading the mixture prepared in step (i), the mixture efficiently incorporates (entrains) air while becoming a whip-like kneaded material. "Whip-like" means that the viscosity of the mixture prepared in step (i) becomes, for example, 0.5 Pa·s to 10 Pa·s, preferably 0.8 Pa·s to 2.0 Pa·s, through kneading.

[0025] As a result of diligent studies by the present inventor, it was found that by using a zwitterionic surfactant instead of an anionic surfactant as the surfactant, even if the concentration of water glass is increased, the fluidity of the kneaded sand does not decrease, fillingability into the mold is excellent, and productivity can be significantly enhanced. This is thought to be because using a zwitterionic surfactant instead of an anionic surfactant reduced the influence of ion concentration in the kneaded material. For example, if the concentration of water glass, which functions as a binder, increases, the concentration of cations such as Na ions derived from water glass is thought to increase. Also, in the production of colloidal silica, when produced by the ion exchange method, cations such as Na ions may be contained.

[0026] While anionic surfactants have the advantage of good foaming ability, it is thought that when the cation concentration in the kneaded material increases, the ionization of the anionic surfactant is hindered, and production conditions become limited due to foaming promotion inhibition by the surfactant. In other words, by using a zwitterionic surfactant, good fluidity can be maintained even if the concentration of cations such as Na ions becomes high in the kneaded material, ensuring the fluidity of the kneaded sand over a wide range of manufacturing conditions. As a result, fillingability into the mold can be enhanced, leading to excellent productivity.

[0027] The bubble ratio of the kneaded material is preferably about 50% to 80% immediately after preparation of the kneaded material, from the viewpoints of moldability and strength. By having said viscosity and bubble ratio, the kneaded material has improved fluidity, and the various materials in the kneaded material are mixed uniformly. Therefore, the bearing effect obtainable by various particles being spherical need not be obtained, i.e., the various particles may aggregate, and as a result, there is no need to adjust the pH of the kneaded material with a pH adjuster such as sodium hydroxide.

[0028] The bubble ratio of the kneaded material is determined as follows.Bubble ratio (%) = {(Total volume of kneaded material - Total volume of mixture (i.e., volume of mixture before foaming)) / (Total volume of kneaded material)} × 100

[0029] Through kneading, the amorphous silica aggregates. This aggregated silica then forms irregularities on the surface of the core prepared in step (iii), inducing a lotus leaf effect, and as a result, release resistance can be reduced, minimizing sticking of the core sand to the mold.

[0030] Furthermore, by having said viscosity and bubble ratio, even if the filler effect, which can be obtained by the presence of particles of various sizes and which might be lost due to the phenomenon of binder migration (where the interior becomes hollow and the surface layer becomes dense when the kneaded material is placed in a heated mold during molding in step (iii)), is not obtained, the strength of the core prepared in step (iii) can be ensured.

[0031] 3. Manufacturing MethodIn step (i), the particulate aggregate, water glass, the zwitterionic surfactant, and the amorphous silica having an average particle size of less than 1 μm are mixed to prepare a mixture. The mixing order and mixing method of each material are not limited, and known mixing means in the technical field can be used. Examples of mixing methods for each material include a homogenizer, an ultrasonic disperser, and a bead mill. When performing step (i) and step (ii) simultaneously, the kneading apparatus used in step (ii) may be used for mixing the materials.

[0032] Step (ii) is a step of kneading the mixture prepared in step (i) until it becomes whip-like to prepare a kneaded material. Kneading refers to mixing the mixture prepared in step (i) to make it uniform, for example, while applying shear force. Kneading apparatuses such as a rotation / revolution mixer, an Eirich intensive mixer, or a Sintokogio Simpson mix muller can be used for kneading.

[0033] When performing step (i) and step (ii) simultaneously, it can be carried out by, for example, sequentially adding the materials constituting the kneaded material, namely, the particulate aggregate, water glass, the surfactant, and the amorphous silica, into the kneading apparatus. The order of addition is not limited.

[0034] Step (iii) is a step of molding the kneaded material prepared in step (ii) to produce a core. The molding of the kneaded material in step (iii) can be achieved by known molding methods in the technical field. The molding of the kneaded material may be molding by a molding machine or molding by hand ramming.

[0035] The molding machine is not particularly limited, and known molding machines in the technical field can be mentioned. Examples include jolt molding machines, squeeze molding machines, jolt-squeeze molding machines, high-pressure molding machines, blow-squeeze molding machines, sand slinger molding machines, blow molding machines, plunger pressure injection molding machines, and three-dimensional molding machines.

[0036] As a suitable example of step (iii), a method can be exemplified wherein the kneaded material prepared in step (ii) is injected and filled under a pressure of, for example, 0.10 to 0.50 MPa into a core molding space (mold) heated to, for example, 120 to 300°C for core molding, and solidified by evaporating the moisture.

[0037] By step (iii) being a step of molding into a core by pressure filling into a mold heated to a high temperature that defines the core molding space, a phenomenon occurs where the bubbles dispersed in the kneaded material through kneading and the water vapor generated from the moisture in the kneaded material due to the heat of the heated mold gather in the central part of the core (sand mold). Therefore, the central part becomes a core with a low packing density (i.e., density of solid content) of sand, water glass, and amorphous silica, while conversely, the surface becomes a core with a high packing density (density of solid content) of sand, water glass, and amorphous silica.

[0038] Water glass absorbs moisture in the air, causing a decrease in strength, but the mold (core) obtained by this manufacturing method has reduced release resistance and excellent moisture resistance due to the addition of nano-sized amorphous silica. This is because, on the core surface, the amorphous silica has a large specific surface area and absorbs (adsorbs) moisture instead of the water glass.Furthermore, the core obtained by the method for manufacturing a core of the present disclosure contains nano-sized amorphous silica, so the silica is distributed on the core surface, significantly suppressing the occurrence of defects where the kneaded material strongly adheres to the mold and the core breaks when taking it out from the mold. Therefore, according to this manufacturing method, even cores (molds) with weak strength, such as thin shapes, can be easily manufactured, significantly increasing the degree of freedom in mold shape.Moreover, according to the method for manufacturing a core of the present disclosure, by using a zwitterionic surfactant as the surfactant, the fluidity of the kneaded material in step (ii) can be maintained, enabling core production under a wide range of manufacturing conditions and significantly enhancing productivity.

[0039] The core manufactured by the present disclosure is used for casting various metals or alloys. Examples of materials for the molten metal used in casting include the following. Note that the pouring temperatures below represent temperatures at which the following materials are suitably molten for pouring.Aluminum or aluminum alloy (Pouring temperature: 670°C to 700°C)Iron or iron alloy (Pouring temperature: 1300°C to 1400°C)Bronze (Pouring temperature: 1100°C to 1250°C)Brass (Pouring temperature: 950°C to 1100°C)

[0040] Casting is performed by pouring molten metal made of materials such as those listed above into the space within the core and mold, followed by cooling and removal of the core.

[0041] Note that the core manufactured by the present disclosure is easily removable from the casting due to the amorphous silica on the core surface. Therefore, core removal can be performed using low-cost and simple equipment such as vibration or air flow, and even if complete removal is not possible with such simple equipment alone, the extent of cumbersome removal methods traditionally used, such as crushing, heat treatment, blasting, and cleaning, can be reduced, enabling energy savings and cost reduction in the casting process.

[0042] Furthermore, conventionally, the lower the temperature of the poured molten metal, the worse the removability of the core tends to be; for example, in the case of aluminum castings using aluminum or aluminum alloy, the pouring temperature is relatively low as mentioned above, so removability tended to be even worse. However, according to the core manufactured by the present disclosure, due to the amorphous silica on the core surface, core removal from the casting can be easily performed even in the case of casting aluminum or aluminum alloys.[Examples]

[0043] Examples related to the present disclosure will be described below. The present disclosure is not limited to the following examples.

[0044] Core Manufacturing [Example Group]<Step (i)>Fused mullite sand as the particulate aggregate, water glass functioning as a binder (0.65 to 1.4 parts by mass per 100 parts by mass of particulate aggregate), a zwitterionic surfactant as the surfactant (0.03 parts by mass relative to the total mass of the particulate aggregate), and colloidal silica as the amorphous silica (0.35 parts by mass relative to the total mass of the particulate aggregate, average particle size (measured by BET method): 0.020 μm) were mixed for 1 minute using a homogenizer to prepare a mixture.

[0045] <Step (ii)>The mixture prepared in step (i) was kneaded for 5 minutes using a homogenizer to prepare a whip-like kneaded material.

[0046] <Step (iii)>The kneaded material prepared in step (ii) was filled by injection into a mold at 250°C and molded to produce a core.

[0047] [Comparative Example Group]Cores were manufactured in the same manner as in Example 1, except that an anionic surfactant was used instead of the zwitterionic surfactant in the preparation step (i) of the Example group.

[0048] The dynamic viscosity of the kneaded material for the Example group and Comparative Example group was measured by the following method.The mixture was placed into a cylindrical container with an inner diameter of 42 mm having a small hole with a diameter of 6 mm at the bottom. A cylindrical weight with a mass of 1 kg and a diameter of 40 mm was used to pressurize the mixture under its own weight, causing the mixture to discharge through the small hole. The time required for the weight to move 50 mm was measured, and the viscosity was calculated using the following formula.Formula μ = πD4Ppt / 128L1L2Sμ: Viscosity [Pa·s]D: Diameter of bottom small hole [m]Pp: Pressurizing force by the weight [Pa]t: Time required for the weight to move 50 mm [s]L1: Movement distance of the weight (=50 mm)L2: Thickness of the plate with the bottom small hole [m]S: Average value between the bottom area of the cylindrical weight and the cross-sectional area of the hollow region inside the cylinder (i.e., the inner diameter part) [m2]

[0049] Figure 1 shows the relationship between the water glass content ratio (parts by mass) and the dynamic viscosity in the kneaded material for the Example group and the Comparative Example group. The water glass content ratio is the content ratio relative to 100 parts by mass of the particulate aggregate. As shown in the figure, it was confirmed that in the Example group, the fluctuation range of dynamic viscosity was small even when the water glass content ratio was varied, whereas in the Comparative Example group, the viscosity increased sharply when the water glass content ratio exceeded 1 part by mass. It was confirmed that by using the zwitterionic surfactant, the fluidity of the kneaded material can be maintained well regardless of the water glass content ratio.

[0050] For the cores of the Example group, SEM observation confirmed that silica was aggregated on their surface and distributed on the surface of the sand particles serving as the particulate aggregate.

Claims

【Claim 1】 Step (i) of preparing a mixture containing particulate aggregate, water glass, an amphoteric ion surfactant, and amorphous silica having an average particle size of less than 1 μm, Step (ii) of kneading the mixture prepared in step (i) until it becomes whipped to prepare a kneaded product, and A method for manufacturing a core, comprising step (iii) of molding the kneaded product prepared in step (ii) to produce a core.

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