KR102568213B1 - Mixed sand comprising waste molding sand and method of manufacturing same - Google Patents

Abstract

Disclosed are mixed molding sand and a manufacturing method thereof. Waste molding sand containing the waste aggregate and waste cement; and molding sand containing aggregate and cement; can include The mixed molding sand and the manufacturing method of the present invention have the effect of recycling the waste molding sand by mixing and using the waste molding sand and the molding sand. In addition, the present invention can be applied to 3D printing by adjusting the mixing ratio of the waste molding sand and the molding sand, and has excellent moldability, air permeability, disintegration and strength during mold production.

Description

Mixed molding sand containing waste molding sand and its manufacturing method {MIXED SAND COMPRISING WASTE MOLDING SAND AND METHOD OF MANUFACTURING SAME}

The present invention relates to mixed molding sand and a manufacturing method thereof, and more particularly, to a mixed molding sand including waste molding sand and a manufacturing method thereof.

Molding sand is sand used for casting and must satisfy fire resistance, air permeability, and formability. Sand casting is a process of making a metal molded body of a desired shape by injecting and solidifying molten metal into an empty mold space made of casting sand, that is, sand, as a main component.

The 3D printing method using molding sand is a method that can produce a mold using 3D printing without a wooden mold or resin, which was essential for the existing casting process. Through this, mold production and product development period can be reduced to less than 50%.

Currently, research on the development of molding sand for 3D printing is being diversified, and research on the application of phenolic and furan-based organic binders, which are mainly used in general sand casting methods, is representative. In addition, methods using cement components or water glass-based inorganic binders are being studied.

However, since the casting sand for the organic binder uses special chemically coated casting sand, energy and time efficiency are reduced, and there are problems in that the working environment is deteriorated and environmental pollution is caused by the volatilization of the binder. Although the efficiency can be improved by the water glass-based liquid binder spraying method, there are problems in that it is difficult to satisfy the limitations of high-concentration liquid binder spraying and the breathability and disintegration of castings.

Korean Patent Registration No. 10-1590234 provides a material for modeling in which an aggregate and a powdery precursor, which is a binder for binding the aggregate to each other, are mixed. The modeling material uses a mixed cement having heat-resistant alumina cement as a main component and water-stop cement, which is a cement having excellent fast-hardening properties, as a sub-component. However, since the water-stop cement containing calcium silicate and calcium aluminate as main components contains gypsum, sulfurous acid gas, etc., caused by gypsum is generated at high temperatures, and this gas causes defects such as bubbles in molds or castings. there is.

Korean Patent Registration No. 10-1590234

An object of the present invention is to provide a mixed molding sand capable of recycling waste molding sand and a manufacturing method thereof by mixing and using the waste molding sand and the molding sand.

Another object of the present invention is to provide a mixed molding sand that can be applied to 3D printing by adjusting the mixing ratio of waste molding sand and molding sand and has excellent moldability, air permeability, disintegration, and strength during mold production, and a manufacturing method thereof.

In addition, an object of the present invention is to separate or reuse the waste molding sand for regeneration of the molding sand because the organic binder vaporizes and flies away during the molten metal process, whereas the cement binder, which is mostly inorganic, remains after the molten metal. To provide a mixed molding sand and a manufacturing method thereof there is

In addition, an object of the present invention is to improve profitability by significantly reducing manufacturing cost and manufacturing time, and to provide a mixed molding sand and a method for manufacturing the same that can secure eco-friendliness by reducing raw material consumption and energy consumption due to a significant reduction in the manufacturing process there is

According to one aspect of the present invention, waste molding sand containing waste aggregate and waste cement; and molding sand containing aggregate and cement; A mixed molding sand containing is provided.

The waste molding sand may be prepared by crushing a waste mold.

The waste mold may be obtained by using a mold for casting molten metal.

The aggregate includes inorganic particles, and the inorganic particles include alumina (Al ₂ O ₃ ), silica (SiO ₂ ), zirconia (ZrO ₂ ), silicate (ZrSiO ₄ ), chromium oxide (Cr ₂ O ₃ ), and magnesium oxide. (MgO), calcium oxide (CaO), phosphorus oxide (P ₂ O ₅ ), sodium oxide (Na ₂ O), iron oxide (Fe ₂ O ₃ ), potassium oxide (K ₂ O) and titanium dioxide (TiO ₂ ). It may include one or more selected from the group consisting of.

The aggregate may have a spherical shape and may have a size of 500 μm or less.

The cement is CaO·Al ₂ O ₃ (CA), 3CaO·Al ₂ O ₃ (C3A), CaO·2Al ₂ O ₃ (CA2), CaO·6Al ₂ O ₃ (CA6), 3CaO·SiO ₂ (C3S) , 2CaO·SiO ₂ (C2S), Ca ₂ Al[AlSiO ₇ ] (C2AS), and 4CaO·Al ₂ O ₃ ·Fe ₂ O ₃ (C4AF).

The mixed molding sand may include 5 to 40 parts by weight of the sum of the waste cement and cement based on 100 parts by weight of the sum of the waste aggregate and the aggregate.

The waste molding sand may further include a waste filler, and the molding sand may further include at least one selected from the group consisting of a quick filler, an organic binder, and a hardening accelerator.

The waste quick-setting agent and the quick-setting agent may each include 12CaO·7Al ₂ O ₃ (C12A7).

The mixed molding sand may include 5 to 50 parts by weight of the total waste quick-setting agent and quick-setting admixture based on 100 parts by weight of the total waste cement and the cement.

The binder is polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), dextrin, methyl cellulose (MC), hydroxypropyl methyl cellulose (HPMC), polyethylene oxide (polyethylene oxide, PEO), polyvinyl butyral (PVB), colloidal silica, and polyethylene glycol.

The curing accelerator may include at least one selected from the group consisting of lithium carbonate, lithium bromide hydroxide, lithium chloride, lithium hydrogen carbonate, lithium nitrate, lithium sulfate, lithium sulfide, lithium phosphate, lithium oxalate, and quicklime.

The mixed molding sand may include 900 parts by weight or less of the waste molding sand based on 100 parts by weight of the molding sand.

The mixed molding sand may be for use in 3D printing.

According to another aspect of the present invention, (a) preparing a waste molding sand containing waste aggregate and waste cement by crushing the waste mold; and (b) preparing a molding sand containing aggregate and cement and a mixed molding sand containing the waste molding sand; There is provided a method for producing mixed molding sand comprising a.

The method for manufacturing mixed molding sand may further include, prior to step (a), (a') obtaining a waste mold by using the mold for casting molten metal.

The casting may be performed at a temperature of 1,300 to 1,600 °C.

The manufacturing method of the mixed molding sand may further include, before step (a'), (a") manufacturing a mold by 3D printing and drying the molding sand including aggregate and cement.

The drying in step (a") may be natural drying.

A group consisting of ball milling, attrition milling, planetary milling, fine milling, and high efficiency mixer in step (a). It can be performed with any one selected from.

The mixed molding sand and the manufacturing method of the present invention have the effect of recycling the waste molding sand by mixing and using the waste molding sand and the molding sand.

In addition, the present invention can be applied to 3D printing by adjusting the mixing ratio of the waste molding sand and the molding sand, and has excellent moldability, air permeability, disintegration and strength during mold production.

In addition, the present invention has excellent strength regeneration even after a simple post-treatment and mixing process, so it is easy to mass-produce and enlarge, and there is no toxic gas generation by controlling the properties of raw material components, and excellent thermal stability.

In addition, the manufacturing method of the present invention improves profitability by significantly reducing manufacturing cost and manufacturing time, and has an effect of securing eco-friendliness by reducing raw material consumption and energy consumption according to a significant reduction in the manufacturing process.

1 is a flow chart showing a method for manufacturing mixed molding sand according to the present invention.
Figure 2a is a SEM image of waste molding sand after casting, Figure 2b is a SEM image of separately separating only cement fine powder after the ball mill process in the waste molding sand, Figure 2c is a SEM image of aggregate from which cement powder is separated and removed from the waste molding sand.
3 is a result of confirming the optimal amount of water required for hydration in Comparative Example 2-1.
4 is strength analysis according to drying time of Comparative Example 2-1.
5 is a graph of HC hardness analysis of the mixed molding sand according to Examples 1-1 to 1-9 and the molding sand according to Comparative Examples 1-1 and 1-2.
6 is a result of lamination of molded bodies of Comparative Example 2-1 and Example 2-4 manufactured using molding sand according to Comparative Example 1-1 and Example 1-4.

Since the present invention can apply various transformations and have various embodiments, specific embodiments are exemplified and described in detail in the detailed description. However, it should be understood that this is not intended to limit the present invention to specific embodiments, and includes all transformations, equivalents, and substitutes included in the spirit and scope of the present invention. In describing the present invention, if it is determined that a detailed description of related known technologies may obscure the gist of the present invention, the detailed description will be omitted.

Also, terms including ordinal numbers such as first and second to be used below may be used to describe various components, but the components are not limited by the terms. These terms are only used for the purpose of distinguishing one component from another. For example, a first element may be termed a second element, and similarly, a second element may be termed a first element, without departing from the scope of the present invention.

Also, when a component is referred to as “on another component,” “formed on another component,” “located on another component,” or “stacked on another component,” that It should be understood that although it may be directly attached to, positioned on, or stacked on the front surface or one surface of another component, other components may further exist in the middle.

Singular expressions include plural expressions unless the context clearly dictates otherwise. In this application, the terms "include" or "have" are intended to designate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, but one or more other features It should be understood that the presence or addition of numbers, steps, operations, components, parts, or combinations thereof is not precluded.

Hereinafter, the mixed molding sand of the present invention will be described.

The present invention is a waste molding sand containing waste aggregate and waste cement; and molding sand containing aggregate and cement; Provides a mixed molding sand containing a.

The waste molding sand may be prepared by crushing a waste mold.

The waste mold may be obtained by using a mold for casting molten metal.

The aggregate includes inorganic particles, and the inorganic particles include alumina (Al ₂ O ₃ ), silica (SiO ₂ ), zirconia (ZrO ₂ ), silicate (ZrSiO ₄ ), chromium oxide (Cr ₂ O ₃ ), and magnesium oxide. (MgO), calcium oxide (CaO), phosphorus oxide (P ₂ O ₅ ), sodium oxide (Na ₂ O), iron oxide (Fe ₂ O ₃ ), potassium oxide (K ₂ O) and titanium dioxide (TiO ₂ ). It may include one or more selected from the group consisting of.

The size of the inorganic particles may be 1 to 50 μm. When the size of the inorganic particles is less than 1 μm, aggregation occurs, which is not preferable, and when the size exceeds 50 μm, it is not preferable because it does not help absorb moisture sprayed during stacking of equipment. It is difficult to control the minimum particle obtained when inorganic particles are pulverized, and the size of the maximum particle is adjusted to 50 μm or less.

The aggregate may be spherical, and may have a size of 500 μm or less, preferably 1 to 500 μm. If the size of the aggregate is less than 1 μm, the amount of fine particles generated during stacking is undesirably increased, and if the size exceeds 500 μm, sufficient resolution required for casting is not satisfied, which is not preferable.

The cement is CaO·Al ₂ O ₃ (CA), 3CaO·Al ₂ O ₃ (C3A), CaO·2Al ₂ O ₃ (CA2), CaO·6Al ₂ O ₃ (CA6), 3CaO·SiO ₂ (C3S) , 2CaO·SiO ₂ (C2S), Ca ₂ Al[AlSiO ₇ ] (C2AS), and 4CaO·Al ₂ O ₃ ·Fe ₂ O ₃ (C4AF).

The mixed molding sand may include 5 to 40 parts by weight of the sum of the waste cement and cement based on 100 parts by weight of the sum of the waste aggregate and the aggregate.

The waste molding sand may further include a waste filler, and the molding sand may further include at least one selected from the group consisting of a quick filler, an organic binder, and a hardening accelerator.

The waste quick-setting agent and the quick-setting agent may each include 12CaO·7Al ₂ O ₃ (C12A7).

The mixed molding sand may include 5 to 50 parts by weight of the total waste quick-setting agent and quick-setting admixture based on 100 parts by weight of the total waste cement and the cement. If the total amount of waste quick-setting agent and quick-setting agent is less than 5 parts by weight with respect to 100 parts by weight of the waste cement and the total amount of the cement, hardening does not occur during laminate molding, and the resolution of the laminated surface is lowered due to the cohesion effect between alumina cement. Exceeding 50 parts by weight is undesirable because the amount of moisture required during actual lamination increases rapidly.

The binder is polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), dextrin, methyl cellulose (MC), hydroxypropyl methyl cellulose (HPMC), polyethylene oxide (polyethylene oxide, PEO), polyvinyl butyral (PVB), colloidal silica, and polyethylene glycol.

The curing accelerator may include at least one selected from the group consisting of lithium carbonate, lithium bromide hydroxide, lithium chloride, lithium hydrogen carbonate, lithium nitrate, lithium sulfate, lithium sulfide, lithium phosphate, lithium oxalate, and quicklime.

The mixed molding sand may include 900 parts by weight or less of the waste molding sand containing the waste aggregate and waste cement, preferably 5 to 900 parts by weight, more preferably 5 to 900 parts by weight, based on 100 parts by weight of the molding sand containing the aggregate and cement. may include 30 to 300 parts by weight, and more preferably 60 to 200 parts by weight. Less than 5 parts by weight of the waste molding sand relative to 100 parts by weight of the molding sand is not preferable in terms of recycling efficiency, and if it exceeds 900 parts by weight, sufficient strength is not satisfied, which is not preferable.

The mixed molding sand may be for use in 3D printing.

1 is a flow chart showing a method for manufacturing mixed molding sand according to the present invention. Hereinafter, with reference to FIG. 1, the manufacturing method of the mixed molding sand of the present invention will be described.

First, waste molding sand containing waste aggregate and waste cement is prepared by crushing the waste mold (step a).

A group consisting of ball milling, attrition milling, planetary milling, fine milling, and high efficiency mixer in step (a). It can be performed with any one selected from.

The method for manufacturing mixed molding sand may further include, prior to step (a), (a') obtaining a waste mold by using the mold for casting molten metal.

The casting may be performed at a temperature of 1,300 to 1,600 °C, preferably at a temperature of 1,400 to 1,500 °C.

The manufacturing method of the mixed molding sand may further include, prior to step (a'), (a") preparing a mold by 3D printing and drying the molding sand including aggregate and cement.

The drying in step (a") may be natural drying.

Finally, molding sand containing aggregate and cement and mixed molding sand including the waste molding sand are prepared (step b).

[Example]

Hereinafter, the present invention will be described in more detail by way of examples. However, this is for illustrative purposes and the scope of the present invention is not limited thereby.

Preparation Example 1: Waste molding sand

The mold obtained by 3D printing the molding sand containing aggregate and cement is naturally dried for 4 hours. The naturally dried mold is taken out after a burnout process in an oven at 200 ° C for 2 hours, and the mold is placed horizontally on the flat compacted sand. At this time, the mold is arranged so that the inlet through which the molten metal is poured faces the ceiling so that casting is possible. Casting at about 1400 to 1500 ° C is poured into the mold and cooled at room temperature for 4 hours or more. Thereafter, the cooled casting was removed and the remaining waste mold was obtained. Then, the waste mold was crushed to a size of 100 μm or less, and a ball mill process was performed for about 2 hours to obtain waste molding sand containing powdered waste aggregate and waste cement.

Example 1: Preparation of mixed molding sand

Example 1-1

Referring to Table 1 below, the waste molding sand, aggregate (refractory silica sand), cement (CA), quick-settling agent (C12A7), and additives prepared according to Preparation Example 1 under the conditions of Table 1 were mixed by a ball milling method, and plastic It was slurried on a plate and naturally dried for 5 hours to prepare mixed molding sand. At this time, the additives were used by mixing a polycarboxylic acid-based glidant (PC-based glidant, Cica Korea), an accelerator (Li ₂ CO ₃ ), and polyvinyl alcohol (PVA) to satisfy the conditions shown in Table 1 below.

Examples 1-2 to 1-9

Referring to Example 1-1 and Table 1, mixed molding sands of Examples 1-2 to 1-9 were prepared at the composition ratios shown in Table 1.

Comparative Example 1-1: Preparation of Waste Molding Sand Mixture

Referring to Example 1-1 and Table 1, a waste molding sand mixture was prepared with the composition described in Comparative Example 1-1 of Table 1.

Comparative Example 1-2: Preparation of molding sand mixture

Referring to Example 1-1 and Table 1, a molding sand mixture was prepared with the composition described in Comparative Example 1-2 of Table 1.

waste molding sand
(parts by weight) Molding sand (by weight) Additives (parts by weight) aggregate cement quick payment glidant
(polycarboxylic acid type) accelerant
(Li ₂ CO ₃ ) polyvinyl alcohol
(PVA) Example 1-1 86.4 8 1.6 4 0.2 0.2 2 Example 1-2 76.8 16 3.2 4 0.2 0.2 2 Example 1-3 67.2 24 4.8 4 0.2 0.2 2 Example 1-4 57.6 32 6.4 4 0.2 0.2 2 Example 1-5 48 40 8 4 0.2 0.2 2 Example 1-6 38.4 48 9.6 4 0.2 0.2 2 Examples 1-7 28.8 56 11.2 4 0.2 0.2 2 Examples 1-8 19.2 64 12.8 4 0.2 0.2 2 Examples 1-9 9.6 72 14.4 4 0.2 0.2 2 Comparative Example 1-1 96 0 0 4 0.2 0.2 2 Comparative Example 1-2 0 80 16 4 0.2 0.2 2

Example 2: Preparation of molded body

Example 2-1

It was laminated using a binder jetting 3D printer, z510 equipment from 3D Systems, using the mixed molding sand prepared according to Example 1-1 and ZB63 ink. At this time, the molded body was manufactured at room temperature with the system setting values shell saturation level 100% (binder/volume ratio 0.38) and core saturation level 100% (binder/volume ratio 0.19).

Example 2-2 to Example 2-9

Except for using the mixed molding sand of Examples 1-2 to 1-9 instead of using the mixed molding sand manufactured according to Example 1-1, the same method as the manufacturing method of Example 2-1 was carried out. Molded bodies of Examples 2-2 to 2-9 were respectively prepared.

Comparative Example 2-1

A molded body was manufactured in the same manner as in Example 2-1, except that the waste molding sand mixture of Comparative Example 1-1 was used instead of the mixed molding sand prepared according to Example 1-1.

Comparative Example 2-2

A molded article was manufactured in the same manner as in Example 2-1, except that the molding sand mixture of Comparative Example 1-2 was used instead of the mixed molding sand prepared according to Example 1-1.

[Test Example]

Test Example 1: SEM analysis

Figure 2a is a SEM image of waste molding sand after casting, Figure 2b is a SEM image of separately separating only cement fine powder after the ball mill process in the waste molding sand, Figure 2c is a SEM image of aggregate from which cement powder is separated and removed from the waste molding sand.

Referring to FIGS. 2A to 2C , it was found that the cement powder adhering to the surface portion could be simply separated only by a ball mill process while maintaining the original shape of the waste molding sand. This shows that the cement component is in the state of cement before hydration without binding ability. In addition, it was confirmed that the aggregate surface portion was sufficiently removed. Through this, the aggregate part and the cement part of the molding sand can be reused.

Test Example 2: Analysis of hydration strength according to the mixing ratio of waste molding sand and water

3 is a result of confirming the optimal amount of water required for hydration in Comparative Example 2-1. Strength was analyzed using a portable rubber durometer, shore c durometer (0-100HC).

Referring to FIG. 3, as an experiment to adjust the amount of water required for hydration, it was confirmed that the highest hardness was obtained when the waste molding sand mixture contained 40% of water compared to the waste molding sand mixture, and it was found that curing was possible only with the waste molding sand.

Test Example 3: Strength analysis according to drying time

4 is strength analysis according to drying time of Comparative Example 2-1. Strength was analyzed using a portable rubber durometer, shore c durometer (0-100HC).

Referring to FIG. 4, it can be seen that hardening occurs rapidly within about 30 minutes of drying time and has the highest strength after 50 minutes.

Test Example 4: HC hardness analysis according to the mixing ratio of waste molding sand

5 is a graph of HC hardness analysis of the mixed molding sand according to Examples 1-1 to 1-9 and the molding sand according to Comparative Examples 1-1 and 1-2. HC hardness was analyzed using a portable rubber durometer, shore c durometer (0-100HC).

Referring to FIG. 5, most of the HC hardness was found to be 80 or more, and it was confirmed that the HC hardness was 80 or more when the ratio of the waste molding sand to the molding sand was 80 wt% or less.

Test Example 5: Lamination suitability analysis of molded body

6 is a result of lamination of molded bodies of Comparative Example 2-1 and Example 2-4 manufactured using molding sand according to Comparative Example 1-1 and Example 1-4.

Referring to FIG. 6 , it was confirmed that a molded body could be manufactured using Comparative Example 1-1 and Example 1-4 including waste molding sand.

Test Example 6: Compressive strength analysis of molded body

Compressive strength was measured using a uniaxial pressure measuring device in accordance with the concrete compressive strength test method (KS F 2405) after drying the molded body for 4 hours.

As a result of analyzing the compressive strength by the above method, the molded article of Example 2-4 showed an average compressive strength of 4.2 MPa, Comparative Example 2-1 of 3.2 MPa, and Comparative Example 2-2 of 4.7 MPa. Through this, it was found that even when the molded body was manufactured by mixing the waste molding sand, the strength level was 80% or higher compared to the case where the molded body was manufactured using the existing molding sand.

In the above, the preferred embodiments of the present invention have been described, but those skilled in the art can add, change, delete or modify components within the scope not departing from the spirit of the present invention described in the claims. Various modifications and changes may be made to the present invention by addition or the like, which will also be included within the scope of the present invention. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as distributed may be implemented in a combined form. The scope of the present invention is indicated by the following claims rather than the detailed description above, and all changes or modifications derived from the meaning and scope of the claims and equivalent concepts should be construed as being included in the scope of the present invention. do.

Claims (20)

Waste molding sand containing waste aggregate and waste cement; and
Including; molding sand containing aggregate and cement;
The aggregate includes silica (SiO ₂ ),
The cement contains CaO·Al ₂ O ₃ (CA),
The molding sand further comprises a quick-setting material,
The quick settling material contains 12CaO 7Al ₂ O ₃ (C12A7),
The mixed molding sand comprising 5 to 900 parts by weight of the waste molding sand based on 100 parts by weight of the molding sand. According to claim 1,
The mixed molding sand, characterized in that the waste molding sand is prepared by crushing the waste mold. According to claim 2,
The mixed molding sand, characterized in that the waste mold is obtained by using the mold for casting molten metal. delete According to claim 1,
The mixed molding sand, characterized in that the aggregate is spherical and the size of the aggregate is 500 μm or less. delete According to claim 1,
The mixed molding sand, characterized in that it comprises 5 to 40 parts by weight of the sum of the waste cement and cement based on 100 parts by weight of the sum of the waste aggregate and the aggregate. According to claim 1,
The waste casting sand further includes a waste grade,
The mixed molding sand, characterized in that the molding sand further comprises at least one selected from the group consisting of an organic binder and a hardening accelerator. According to claim 8,
Mixed molding sand, characterized in that the waste filler contains 12CaO 7Al ₂ O ₃ (C12A7). According to claim 8,
The mixed molding sand, characterized in that the mixed molding sand comprises 5 to 50 parts by weight of the total waste filler and quick-setting material based on 100 parts by weight of the total sum of the waste cement and the cement. According to claim 8,
The binder is polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), dextrin, methyl cellulose (MC), hydroxypropyl methyl cellulose (HPMC), polyethylene oxide (polyethylene oxide, PEO), polyvinyl butyral (Polyvinyl butyral, PVB), colloidal silica and polyethylene glycol (polyethylene glycol) mixed molding sand characterized in that it comprises at least one selected from the group consisting of. According to claim 8,
The curing accelerator comprises at least one selected from the group consisting of lithium carbonate, lithium bromide hydroxide, lithium chloride, lithium hydrogen carbonate, lithium nitrate, lithium sulfate, lithium sulfide, lithium phosphate, lithium oxalate, and quicklime mixed molding sand. delete According to claim 1,
The mixed molding sand, characterized in that for use in 3D printing. (a) preparing waste molding sand containing waste aggregate and waste cement by crushing the waste mold; and
(b) manufacturing a mixed molding sand according to claim 1 comprising a molding sand containing aggregate and cement and the waste molding sand,
The aggregate includes silica (SiO ₂ ),
The cement contains CaO·Al ₂ O ₃ (CA),
The molding sand further comprises a quick-setting material,
The quick settling material contains 12CaO 7Al ₂ O ₃ (C12A7),
Method for producing a mixed molding sand comprising 5 to 900 parts by weight of waste molding sand based on 100 parts by weight of the molding sand. According to claim 15,
Before the manufacturing method of mixed molding sand is step (a),
(a') obtaining a waste mold by using the mold for casting molten metal; According to claim 16,
Method for producing mixed molding sand, characterized in that the casting is carried out at a temperature of 1,300 to 1,600 ℃. According to claim 16,
Before the step (a') of the manufacturing method of the mixed molding sand,
(a") manufacturing a mold by 3D printing and drying the molding sand containing aggregate and cement; manufacturing method of the mixed molding sand, characterized in that it further comprises. According to claim 18,
A method for producing mixed molding sand, characterized in that the drying in step (a") is natural drying. According to claim 15,
A group consisting of ball milling, attrition milling, planetary milling, fine milling, and high efficiency mixer in the step (a). Method for producing mixed molding sand, characterized in that carried out by any one selected from.