JP2023153624A - Method for manufacturing core - Google Patents

Abstract

To provide a method for manufacturing a core having high moisture absorption resistance, wherein flowability of core sand and mold release of cores from a mold are improved.SOLUTION: The present invention relates to a method for manufacturing a core, including the steps of: (i) preparing a mixture by mixing a particulate aggregate, water glass, a surfactant, and an amorphous SiO2 having an average particle size of 0.01 μm to 0.05 μm, wherein the amorphous SiO2 is 0.10 wt.% to 0.35 wt.% based on the weight of the particulate aggregate; (ii) kneading the mixture prepared in the step (i) until it becomes whipped to prepare a mixture; and (iii) molding the mixture prepared in the step (ii) to prepare a core.SELECTED DRAWING: Figure 3

Description

The present invention relates to a method of manufacturing a core (sand mold).

A method of forming a core is known in which core sand is kneaded with a binder etc. in a kneading pot, and the kneaded core sand (kneaded sand) is injected into a mold and filled to form the core. .

Patent Document 1 describes the steps of (a) foaming the aggregate mixture by stirring the aggregate mixture containing particulate aggregate, one or more water-soluble binders (caking agents), and water; ) Filling the foamed aggregate mixture into the mold forming space; (c) evaporating the water in the filled aggregate mixture to solidify the aggregate mixture to form a mold; and (d) molding. Disclosed is a method for making a mold, which includes the step of taking out the mold from the mold-making space.

Patent Document 2 discloses a casting mold material mixture containing molding sand, a sodium hydroxide solution, an alkali silicate binder, and an additive, wherein the molding sand particles have a size of 0.1 to 1 mm. the mold material mixture has a particle size of 0.1 to 10% by weight of the sodium hydroxide solution relative to the weight of the mold material mixture, and the sodium hydroxide solution has a concentration of 20 to 40% by weight. wherein said mold material mixture comprises said alkali silicate binder having a solids content of 20 to 70% by weight in an amount of 0.1 to 5% by weight; said molding material mixture comprises as said additive , containing a suspension of amorphous spherical SiO ₂ (hereinafter referred to as SiO ₂ ) having a solid content of 30 to 70% by weight and having two different particle sizes in an amount of 0.1 to 3% by weight, The first SiO ₂ having a particle size A is SiO ₂ (hereinafter referred to as micro SiO ₂ ) having a particle size of 1 to 5 μm, and the second SiO ₂ having a particle size B has a particle size of 0.01 to 0.05 μm. SiO ₂ (hereinafter referred to as nano-SiO ₂ ) having a particle size, and the volume ratio of particles having the particle size A and particles having the particle size B is 0.8:1.2 to 1.0:1.0. Disclosed is a mold material mixture characterized in that:

International Publication No. 2005/023457 Japanese Patent Application Publication No. 2008-307604

However, in Patent Document 1, there is a possibility that the binder absorbs moisture and causes a decrease in strength. In addition, the core may crack because the binder sticks to the surface of the mold or the molded product, and sand from the core may adhere to the mold or the molded product.

Furthermore, Patent Document 2 requires SiO ₂ having two types of particle sizes and sodium hydroxide for pH adjustment to prevent agglomeration and promote dispersion of fine particles, and requires many core manufacturing steps and materials to be prepared. As a result, material costs were high and adjustments took time, resulting in low productivity.

Therefore, the present invention aims to provide a method for manufacturing a core that improves the fluidity of core sand and the release of the core from the mold, has high moisture absorption resistance, and prevents sand from adhering to the casting. Take it as a challenge.

As a result of studying various means for solving the above problems, the present inventors have found that by kneading particulate aggregate, water glass, and a surfactant, and molding the resulting kneaded product, a core is formed. In the method for producing granular aggregate, in addition to granular aggregate, water glass, and surfactant, amorphous SiO ₂ having an average particle size of 0.01 μm to 0.05 μm is added to By adding 0.10% to 0.35% by weight to the mixture and then kneading the resulting mixture until it becomes whipped, the whipped kneaded product improves fluidity and becomes amorphous. The present invention was completed based on the discovery that SiO ₂ can improve the moisture absorption resistance of the core and reduce the mold release resistance, and that when the resulting core is used in casting, sand is less likely to adhere to the casting.

That is, the gist of the present invention is as follows.
(1) (i) A step of preparing a mixture by mixing particulate aggregate, water glass, surfactant, and amorphous SiO ₂ having an average particle size of 0.01 μm to 0.05 μm. And,
a step in which the amorphous SiO ₂ is 0.10% to 0.35% by weight based on the weight of the particulate aggregate;
(ii) A step of kneading the mixture prepared in step (i) until it becomes whipped to prepare a kneaded material, and (iii) molding the kneaded material prepared in step (ii) to form a core. A method for manufacturing a core, the method comprising the step of preparing a core.

The present invention provides a method for manufacturing a core that improves the fluidity of core sand and the release of the core from a mold, has high moisture absorption resistance, and prevents sand from adhering to castings.

It is a SEM photograph (x2000) showing the surface of the core of the example. It is a photograph showing an aluminum casting (A) produced using a core of an example and an aluminum casting produced using a core of a comparative example (B). It is a graph showing the relationship between the moisture absorption time and the bending strength in the cores of the example group and the comparative example group. FIG. 2 is a schematic diagram showing the shape of a test piece of a core used for evaluation of mold release resistance during core molding. It is a graph showing the relationship between the amount of colloidal silica added to the core and mold release resistance.

Preferred embodiments of the present invention will be described in detail below.
In this specification, features of the present invention will be explained with reference to the drawings as appropriate. In the drawings, the dimensions and shapes of various parts are exaggerated for clarity and do not accurately depict actual dimensions and shapes. Therefore, the technical scope of the present invention is not limited to the dimensions and shapes of the parts shown in these drawings. The core manufacturing method of the present invention is not limited to the following embodiments, and may be modified in various forms with modifications and improvements that can be made by those skilled in the art without departing from the gist of the present invention. It can be implemented.

The present invention includes (i) a step of preparing a mixture by mixing particulate aggregate, water glass, a surfactant, and a specific amount of amorphous SiO ₂ , (ii) the step of (i) A step of preparing a kneaded product by kneading the mixture prepared in step (ii) until it becomes whipped; and (iii) a step of molding the kneaded product prepared in step (ii) to prepare a core. Concerning a method for producing children.

Each step (i) to (iii) will be explained below.

(i) A step of preparing a mixture by mixing particulate aggregate, water glass, surfactant, and a specific amount of amorphous SiO ₂ In the step (i), particulate aggregate, A mixture is prepared by mixing water glass, surfactant, and amorphous _SiO2 .

Here, particulate aggregate is a material such as sand that constitutes a core known in the art. Particulate aggregates include, but are not limited to, silica sand, alumina sand, olivine sand, chromite sand, zircon sand, mullite sand, various artificial aggregates, and mixtures of two or more of these.

Water glass is a sodium silicate known in the art and is _a liquid (Na 2 O.nSiO 2 ) that is a mixture of SiO _{2 (} anhydrous silicic acid) and Na ₂ O (sodium oxide) in various ratios. It is. As water glass, the molar ratio of SiO ₂ to Na ₂ O (SiO ₂ /Na ₂ O) is usually 1.2 to 3.8, preferably 2.0 to 3.3.

The amount of water glass is usually 0.2% to 1.2% by weight, preferably 0.5% to 0.9% by weight, based on the weight of the particulate aggregate.

By adding the water glass in the above amount, the water glass can act as a binder to coagulate the particulate aggregates without producing odor or smoke.

Surfactants are substances known in the art that have a hydrophilic site and a lipophilic site within the molecule. Surfactants include, but are not limited to, anionic surfactants, nonionic surfactants, amphoteric surfactants, and the like. Examples of anionic surfactants include sodium fatty acids, monoalkyl sulfates, sodium linear alkylbenzenesulfonates, sodium lauryl sulfates, sodium ether sulfates, and the like. Examples of the nonionic surfactant include polyoxyethylene alkyl ether, fatty acid sorbitan ester, alkyl polyglucoside, and the like. Examples of the amphoteric surfactant include cocamidopropyl betaine, cocamidopropyl hydroxysultaine, lauryldimethylaminoacetic acid betaine, and the like.

By adding a surfactant, the mixture can be efficiently foamed into a whipped form in step (ii).

Amorphous SiO ₂ (amorphous silica) is amorphous silicon dioxide known in the art. Examples of amorphous SiO ₂ include silica gel, precipitated silica, and colloidal silica. The shape of amorphous SiO ₂ is preferably spherical.

The average particle size of amorphous SiO ₂ is 0.005 μm to 0.09 μm, preferably 0.01 μm to 0.05 μm. The average particle size of amorphous SiO ₂ can be measured by the BET method, the Sears method, or the laser diffraction method.

The amount of amorphous SiO ₂ is between 0.10% and 0.35% by weight, preferably between 0.20% and 0.30% by weight, based on the weight of the particulate aggregate.

By adding the amorphous SiO ₂ having the above average particle size in the above amount, the amorphous SiO ₂ aggregates during kneading in the step (ii), and the aggregated amorphous SiO 2 becomes the amorphous SiO ₂ in the step (iii). Roughness is formed on the surface of the core prepared in the process to cause a lotus leaf effect, which results in a decrease in demolding resistance and a reduction in the sticking of core sand to the mold.

Furthermore, even in the core prepared in step (iii), amorphous _SiO2 can secure a large specific surface area regardless of agglomeration, and can absorb moisture (moisture absorption) instead of water glass. The moisture absorption resistance of the core can be improved.

In step (i), particulate aggregate, water glass, surfactants, and other additives known in the art other than amorphous SiO ₂ can be added to the mixture.

Other additives include, but are not limited to, inorganic compound particles, such as carbonates (e.g., calcium or magnesium carbonate) and hydroxides (e.g., magnesium or aluminum hydroxide), synthetic resins (e.g., phenol resin, furan resin, etc.). , urethane resins), cement (e.g. Portland cement), bentonite, clay, starch, sugars (e.g. polysaccharides such as cellulose and fructose, tetrasaccharides such as acarbose, trisaccharides such as raffinose and maltotriose) , disaccharides such as maltose, sucratose, trehalose, monosaccharides such as glucose, fructose, and other oligosaccharides), derivatives thereof (e.g., saponin), crosslinking agents, catalysts, oxidation promoters, mixtures of two or more of these, etc. can be mentioned.

In step (i), the mixture preferably consists of particulate aggregate, water glass, surfactant, and amorphous _SiO2 .

In step (i), since the mixture does not contain other additives, the steps for manufacturing the core and the materials to be prepared can be reduced, leading to reductions in material costs and the number of steps, increasing productivity. be able to.

The mixing order and mixing method of each material are not limited, and mixing means known in the art can be used. Examples of methods for mixing each material include a homogenizer, an ultrasonic dispersion device, and a bead mill. As explained below, when the steps (i) and (ii) are performed simultaneously, the kneading device in the step (ii) may be used to mix each material.

(ii) A step of preparing a kneaded product by kneading the mixture prepared in step (i) until it becomes whipped. In step (ii), the mixture prepared in step (i) is kneaded until it becomes whipped. Knead to prepare a kneaded product.

Kneading means mixing the mixture prepared in step (i) so that it becomes uniform, for example while applying shearing force. For kneading, a kneading device such as a rotation/revolution mixer, an Eirich intensive mixer, a Shinto-Simpson Mix Muller, etc. can be used.

By kneading the mixture prepared in step (i), the mixture, especially the surfactant contained in the mixture, efficiently entrains (incorporates) air, resulting in a whip-like kneaded product.

Whipped shape means, for example, that the viscosity of the mixture prepared in step (i) becomes usually 0.5 Pa·s to 10 Pa·s, preferably 0.8 Pa·s to 2.0 Pa·s, by kneading. In other words, it becomes a kneaded product.

The viscosity of the mixture (kneaded material) is measured as follows.
-Viscosity measurement method: Pour the mixture into a cylindrical container with an inner diameter of 42 mm and a pore with a diameter of 6 mm at the bottom, and use a cylindrical weight weighing 1 kg and a diameter of 40 mm to pressurize it with the weight of the weight, and the mixture will be discharged from the pore. be done. At this time, the time required for the weight to move 50 mm is measured, and the viscosity is determined using the following formula.
Formula μ=πD ⁴ P _p t/128L ₁ L ₂ S
μ: Viscosity [Pa・s]
D: Diameter of bottom pore [m]
P _p : Pressure force of weight [Pa]
t: Time required for the weight to move 50mm [s]
L ₁ : Weight movement distance (=50mm)
L ₂ : Thickness of bottom pore [m]
S: Average value of the area of the bottom of the cylindrical weight and the cross-sectional area of the hollow area inside the cylinder (in other words, the inner diameter part) [m ² ]

Immediately after preparation of the kneaded material, the kneaded material usually has a cell content of 50% to 80% from the viewpoint of formability and strength.

The bubble rate of the kneaded material can be calculated as follows.
Foam rate (%) = {(Volume of the entire kneaded product - Volume of the entire mixture (i.e., volume of the mixture before foaming))/(Volume of the entire kneaded material)} x 100

When the kneaded material has the above-mentioned viscosity and bubble rate, fluidity is improved and various materials in the kneaded material are uniformly mixed. Therefore, the bearing effect that can be obtained due to the spherical shape of the various particles may not be obtained, that is, the various particles may aggregate, and as a result, the pH of the kneaded material may be lowered by using a pH adjusting agent, such as sodium hydroxide. There is no need to make any adjustments.

Furthermore, as mentioned above, when the amorphous SiO ₂ aggregates during kneading, the aggregated amorphous SiO ₂ forms unevenness on the surface of the core prepared in step (iii), resulting in a lotus leaf effect. As a result, the mold release resistance is reduced, and the sticking of the core sand to the mold can be reduced.

In addition, since the kneaded material has the above-mentioned viscosity and bubble rate, when the kneaded material is molded in the step (iii), when the kneaded material is put into a heated mold, the inside is hollow and the surface layer is dense. In other words, even if binder migration occurs and the filler effect that can occur due to the presence of particles of various particle sizes cannot be obtained, it is possible to ensure the strength of the core prepared in step (iii). can.

In the present invention, step (i) and step (ii) may be performed simultaneously or separately.

When carrying out the steps (i) and (ii) at the same time, for example, the materials constituting the kneaded material, i.e., particulate aggregate, water glass, surfactant, and amorphous SiO ₂ , are mixed in a kneading device. This can be carried out by sequentially adding the components to the solution. Note that the order of addition is not limited.

(iii) A step of molding the kneaded material prepared in step (ii) to prepare a core. In step (iii), molding the kneaded material prepared in step (ii) to prepare a core. do.

The molding of the kneaded product in step (iii) may be any molding known in the art. The kneaded product may be molded by a molding machine or by manual molding.

The molding machine includes, but is not limited to, molding machines known in the art, such as a jolt molding machine, a squeeze molding machine, a jolt squeeze molding machine, a high pressure molding machine, a blow squeeze molding machine, a sand stringer molding machine, and a blow molding machine. Examples include molding machines, plunger press-fit molding machines, and three-dimensional molding machines.

In the step (iii), the kneaded material prepared in the step (ii) is heated in a mold for forming a core, for example, press-fitted into a space for forming a core heated to usually 120°C to 300°C, for example, usually at a temperature of 0°C. It is preferable to mold by press-fitting at a pressure of 10 MPa to 0.50 MPa.

Since the step (iii) is a step of forming a core by press-fitting and filling a mold heated to a high temperature that defines a space for forming a core, the above-mentioned binder migration, specifically, A phenomenon occurs in which air bubbles dispersed in the kneaded material during kneading and water vapor generated from moisture in the kneaded material due to the heat of the heated mold gather in the center of the core (sand mold). Therefore, the packing density of sand, water glass, and amorphous SiO ₂ (in other words, the density of solid content) is low in the center, and conversely, the packing density of sand, water glass, and amorphous SiO ₂ (solid content) is low in the center part. The core has a high density (solid content).

In addition, as mentioned above, in the core prepared in step (iii), the amorphous _SiO2 present on the core surface has a large specific surface area and absorbs moisture (moisture absorption) instead of water glass. The moisture absorption resistance of the core can be improved.

Cores manufactured according to the present invention are used for casting various metals or alloys. Examples of the materials for the molten metal used in casting include the following. Note that the following pouring temperature refers to the temperature at which the following materials melt to an appropriate degree for pouring.
Aluminum or aluminum alloy (pouring temperature: 670°C to 700°C)
Iron or iron alloy (pouring temperature: 1300℃~1400℃)
Bronze (pouring temperature: 1100℃~1250℃)
Brass (pouring temperature: 950℃~1100℃)

Casting is performed by pouring molten metal made of the materials listed above into a core and a space in a mold, and then cooling and removing the core.

Note that the core manufactured according to the present invention can be easily removed from the casting due to the amorphous SiO ₂ on the surface of the core. Therefore, cores can be removed using low-cost and simple equipment such as vibration and air flow, and even if cores cannot be removed with simple equipment such as vibration and air flow, conventional Since it is possible to reduce the degree of complicated removal methods such as crushing treatment, heat treatment, blasting treatment, and cleaning, it is possible to realize energy saving and cost reduction in the casting process.

Additionally, in the past, the lower the temperature of the molten metal being poured, the worse the core removability tended to be.For example, in the case of aluminum castings using aluminum or aluminum alloy, the pouring temperature was relatively low. Because of this, removability tended to be worse. However, in the core manufactured according to the present invention, the amorphous SiO ₂ on the core surface allows the core to be easily removed from the casting even in the case of casting aluminum or aluminum alloy.

Hereinafter, some examples relating to the present invention will be described, but the present invention is not intended to be limited to what is shown in these examples.

1. Manufacturing of core Example group (i) Process of preparing a mixture by mixing particulate aggregate, water glass, surfactant, and amorphous SiO ₂ Molten mullite sand as particulate aggregate , No. 1 water glass (0.65% by weight based on the total weight of the granular aggregate), and sodium lauryl sulfate as a surfactant (0.03% by weight based on the total weight of the granular aggregate) and colloidal silica as amorphous SiO ₂ (0.35% by weight based on the total weight of particulate aggregate, average particle size (measured by BET method): 0.020 μm) in a homogenizer for 1 minute. A mixture was prepared by mixing.

(ii) A step of preparing a kneaded product by kneading the mixture prepared in step (i) until it becomes whipped. The mixture prepared in step (i) is kneaded for 5 minutes in a homogenizer and whipped. A kneaded product was prepared.

(iii) A step of molding the kneaded material prepared in step (ii) to prepare a core; molding the kneaded material prepared in step (ii) by injection filling into a mold at 250°C; , a core was prepared.

Comparative Example Group A sample was prepared in the same manner as the Example Group except that colloidal silica as amorphous SiO ₂ was not added in step (i) of the preparation of the Example Group.

2. Scanning Electron Microscope (SEM) Evaluation The core surface in the example group was observed using SEM. FIG. 1 shows the surface of the core of one example from the group of examples.

From FIG. 1, it was found that colloidal silica as amorphous SiO ₂ aggregated and was distributed on the surface of sand particles as particulate aggregate.

3. Evaluation of Adhesion of Cores to Aluminum Castings Aluminum castings were produced using the cores from the example group and the cores from the comparative example group. The conditions for producing aluminum castings are as follows.
- Conditions for producing aluminum castings A 30 mm diameter iron pipe was placed on top of the produced core, and molten aluminum at 680°C was poured from the top of the pipe to produce aluminum castings.

FIG. 2 shows photographs of an aluminum casting (A) produced using the core of the example and an aluminum casting (B) produced using the core of the comparative example. In FIG. 2, the central circular part is the aluminum casting, and the black part is the core sand attached to the aluminum casting.

From Figure 2, it is clear that the aluminum castings made using the cores of the examples have less core sand adhesion due to the cores than the aluminum castings made using the cores of the comparative examples. Ta. In the examples, by using colloidal silica as amorphous SiO ₂ , unevenness is formed on the surface of the core, and due to the lotus leaf effect, sand on the surface of the core adheres to the aluminum casting during aluminum casting. It is thought that it has become difficult.

4. Evaluation of bending strength by moisture absorption of cores The cores of the example group and the comparative example group were each stored at a temperature of 40° C. and a relative humidity of 70%, and changes in bending strength depending on moisture absorption time were observed.

FIG. 3 shows the relationship between the moisture absorption time and the bending strength of the cores of the example group and the comparative example group. From Figure 3, in the example group, the bending strength gradually decreases with the moisture absorption time, whereas in the comparative example group, the bending strength fluctuates greatly depending on the moisture absorption time, and after 24 hours, it rapidly decreases. was found to decrease. Therefore, colloidal silica as amorphous SiO ₂ absorbs moisture, which prevents water glass from adsorbing moisture, and as a result, decreases in strength of the core can be prevented.

5. Evaluation of mold release resistance during core molding In the manufacturing method of the example group, the amount of colloidal silica as amorphous SiO ₂ added was 0.00% by weight and 0.10% based on the total weight of the particulate aggregate. %, 0.20% by weight, and 0.35% by weight, and two cores each were prepared. The core was molded into the test piece shape shown in FIG.

FIG. 5 shows the relationship between the amount of colloidal silica added to the core and the mold release resistance. From FIG. 5, it was found that as the amount of colloidal silica added increased, the mold release resistance decreased. Therefore, if the whipped kneaded material does not contain colloidal silica in the form of amorphous SiO ₂ , the kneaded material will firmly stick to the mold and have high mold release resistance, making it easy for defects such as core cracking to occur. . By adding colloidal silica in the form of amorphous SiO ₂ to the kneaded material, mold release resistance is reduced, and thin shapes with weak strength can be easily produced.

Claims (1)

(i) A step of preparing a mixture by mixing particulate aggregate, water glass, a surfactant, and amorphous SiO ₂ having an average particle size of 0.01 μm to 0.05 μm, ,
a step in which the amorphous SiO ₂ is 0.10% to 0.35% by weight based on the weight of the particulate aggregate;
(ii) A step of kneading the mixture prepared in step (i) until it becomes whipped to prepare a kneaded material, and (iii) molding the kneaded material prepared in step (ii) to form a core. A method for manufacturing a core, the method comprising the step of preparing a core.