JP2022034338A - Artificial sand formed by melt air-granulation method, and production method thereof - Google Patents

Abstract

To provide artificial sand in the foundry industry formed by a melt air-granulation method serving as foundry sand with high grain strength that can be used semi-permanently without being crushed by stress received in a foundry process.SOLUTION: The grain strength of ceramic artificial sand is increased by controlling macroscopic internal pore defects and microscopic structural heterogeneity, which dominate fractures of the ceramic artificial sand. The artificial sand with composition of an SiO2-Al2O3 based equilibrium diagram with the primary crystal being mullite is controlled macroscopically such that the number of grains including pore defects of 10 μm or more in the cross section of the artificial sand is 25% or less, and microscopically such that the matrix has no recognizable grain boundary and no recognizable gap of 1 μm or more.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing artificial sand by a melt wind crushing method, which is a cast sand used for producing a cast product.

Casting products are manufactured around 100 million tons / year in the world and about 5 million tons / year in Japan. The majority of cast products are iron-based castings, followed by aluminum alloy castings. Mold sand, which is made by adding a binder to casting sand, requires 3 to 10 times the amount of iron-based castings to manufacture cast products, and about the same amount of aluminum alloy castings for cores. is necessary. The mold sand is regenerated and used repeatedly, but what adheres to the product in the casting finishing process is crushed by the shot process or crushed in the regenerating process that removes the binder of the mold sand. ~ 30% is dust. These are disposed of as industrial waste. In order to reduce the generation of industrial waste caused by crushing, it is difficult to crush mullite (Mohs hardness 7.5) or corundum (Mohs hardness 9) from the conventionally used quartz (Mohs hardness 7) -based silica sand. Artificial sand of the system (also called ceramic sand) has been developed.
However, artificial sand is produced by a method of manufacturing ceramics, and if there are defects or inhomogeneities inside the ceramics, the site becomes the starting point of fracture and is easily crushed. Artificial sand already on the market has many of these defects and inhomogeneities and is not always harder than silica sand. Therefore, it is an urgent task in the casting industry to improve these internal defects and inhomogeneities.

Since the casting sand is an aggregate of particles, it can be molded into a mold of any shape, it has air permeability to discharge the air and gas in the mold when pouring the molten metal into the mold, and it can withstand the heat of the molten metal. Characteristics such as having fire resistance, not causing seizure defects due to chemical reactions to various molten metal components, and having a grain shape (preferably a true sphere) that can reduce the amount of binder for using cast sand as a mold. It has a particle strength that can be repeatedly regenerated and used to reduce the environmental load, the mold has low expansion during casting and does not cause deformation problems, and the cast product can be easily taken out from the mold. Properties are required for foundry sand.

Molds are roughly divided into molds and sand molds, and casting sand is for sand molds. Most of the casting of refractory metals such as cast steel, cast iron, and copper alloys are sand molds made of cast sand. Most of the castings are produced in sand molds. Aluminum alloys, which are low melting point alloys, are mainly used for die casting and die casting called gravity casting, but sand mold cores are used.

The present invention relates to cast sand for sand molds, which has a large production volume. As the foundry sand, silica sand, which is the origin of the name of the sand mold, is most often used. Quartz (silica, SiO ₂ ) is the main mineral composition of silica sand. The secondary mineral composition is feldspar, mica, clay mineral, etc., which are Al ₂ O ₃ -SiO ₂ series minerals. In addition, as casting sand other than silica sand, olivine sand, zircon sand, chromate sand, alumina sand (crushed type), carbon sand, steel shot ball, silicon carbide sand, slag sand (ferronick, ferrochrome, blast furnace slag), , Etc.), recently developed artificial sand (Murite type, Alumina type, Zircon mix type, etc.) are used.

Casting sand is a mold material for manufacturing a cast product, and as a function, there is no casting defect at the time of casting, and as a result, a characteristic that the casting retention is high is required. There are three typical casting defects: gas defects, expansion system defects, and seizure defects. Artificial sand was developed around 1990, and these defects have been eliminated compared to quartz-based silica sand. That is, the binder could be reduced by improving the grain shape of the artificial sand, and the amount of gas generated from the mold sand was reduced, so that the gas defects were reduced. Since the linear expansion coefficient of the artificial sand is low, the expansion of the mold sand is extremely low, and the expansion system defects are reduced. Artificial sand is often less reactive with molten metal than silica sand, reducing seizure defects.
In addition, since there is an urgent need to realize an environment-adaptive society, it is desirable to have high resource conservation. In the casting process, post-treatment process, sand recovery process, etc., there is a demand for high-strength particle casting sand that can be used repeatedly and permanently without crushing the casting sand, and artificial sand has been developed in response to this.
Furthermore, it is also desired that the generation of free silicic acid, which is harmful to the human body, does not occur due to the use of quartz-containing silica sand, and in response to this, quartz-free artificial sand has been developed.

In Patent Document 1, "[Claim 1] Casting sand having an amorphous degree of 70 to 100% and a surface roughness Ra of 0.20 or less. [Claim 2] A claim having a spherical degree of 0.95 or more. The casting sand according to claim 1. [Claim 3] The claim 1 or 2 which contains Al ₂ O ₃ and SiO ₂ as main components and has an Al ₂ O ₃ / SiO ₂ weight ratio of 1 to 15. Casting sand. " In the present invention, the degree of amorphousness is not an important factor and is not particularly mentioned, but "the degree of amorphousness is 70 to 100%" may be applicable only in the case of cooling control of the present invention. be. However, it is considered that this is not the case by performing tempering in addition to controlling cooling during the manufacturing process of the cast sand according to the present invention.
Further, in Patent Document 1, in paragraph 0032 of the specification, "The cooling method can be performed by air cooling or water cooling, and it is preferable to perform rapid cooling. Since the cooling rate varies depending on the composition and particle size of the cast sand, each formulation is used. Is appropriately adjusted so that the degree of non-crystallization of the casting sand is 50 to 100%. " Although the idea is close to the cooling control of the present invention, there is no description about the specific cooling start temperature and the state of the particles at the start of cooling.
Further, in Patent Document 1, there is no concept of suppressing bubble defects and homogenizing the matrix in order to increase the particle strength. Therefore, it is clear that the technical idea which is the gist of the present invention is lacking, and the invention is based on an idea different from the present invention.

In Patent Document 2, claim 4 states that "the sand obtained by blowing air onto the raw material melt under the conditions of the melting temperature of 1600 to 2200 ° C. and the air speed of 80 to 120 m / sec. It is ... ". Patent Document 2 is a melt wind crushing method similar to that of the present invention.
However, in Patent Document 2, although there is a detailed description about the air to be blown, there is no description about the specific cooling start temperature and the state of the particles at the start of cooling.
Further, in Patent Document 2, there is no concept of suppressing bubble defects and homogenizing the matrix in order to increase the particle strength. Therefore, it is clear that the technical idea which is the gist of the present invention is lacking, and the invention is based on an idea different from the present invention.

In Patent Document 3, paragraph 0025 of the specification states, "In this embodiment, the melt scattered by the high-pressure air is configured to be naturally cooled while moving in the atmosphere. (1) may be provided with a forced cooling means using cooling water or the like. " Patent Document 3 is a melt wind crushing method similar to that of the present invention.
However, in Patent Document 3, although there is a description about the cooling method of the melt, there is no description about the specific cooling start temperature and the state of the particles at the start of cooling.
Further, in Patent Document 3, there is no concept of suppressing bubble defects and homogenizing the matrix in order to increase the particle strength. Therefore, it is clear that the technical idea which is the gist of the present invention is lacking, and the invention is based on an idea different from the present invention.

In Patent Document 4, in claim 1, "Al ₂ O ₃ and SiO ₂ are contained as raw materials, and Al ₂ O is contained in a sintered artificial sand containing a low melting point composition contained as a contaminant in the raw materials. In the ₃ -SiO ₂ phase equilibrium diagram, in the composition in which mullite crystals are crystallized as primary crystals, K2O as the low melting point composition is 0.20% or less, and there are gaps in the overlapping of crystals between the mullite crystals. It has an intercrystal structure, a bulk specific gravity of less than 1.6 g / cm ³ , an aspect ratio of 0.85 or more, and an Al ₂ O ₃ -SiO ₂ phase phase diagram showing a fire resistance within -50 ° C from the liquidus line. It is characterized by being a sintered artificial sand. " The "composition in which mullite crystals crystallize as primary crystals in the Al ₂ O ₃ -SiO ₂ phase equilibrium diagram" is the same composition as that of the present invention.
However, in Patent Document 4, although it is described as "an intercrystal structure in which there are gaps between overlapping crystals between Murite crystals", the present invention has a dense structure and there are no gaps between crystals. It is recognized as a clearly different invention.

In Patent Document 5, a method for producing mold aggregate particles according to claim 9, wherein the mold aggregate particles according to any one of claims 1 to 8 are made into particles from a melt and produced. There is a description. Further, in paragraph 0053 of the specification, "when a certain amount of water is simultaneously poured into a nozzle together with compressed air to create high-pressure water and sprayed at the same time as compressed air, the temperature of the particles is lowered at the same time as the granulation, and thereafter. It is preferable because it is easy to handle. In order to sufficiently cool the particles, the amount of cooling water is preferably 1 L / min or more, and more preferably 2 L / min or more. " Since the foundry sand according to Patent Document 5 has an Al ₂ O ₃ , ZrO ₂ , and SiO ₂ composition, the composition is different from that of the foundry sand according to the present invention. However, the place where the melt is air-crushed with compressed air is the same.
However, in Patent Document 5, only air crushing is performed with compressed air together with high-pressure water, and there is no concept of controlling the cooling start temperature and the state of particles at the start of cooling in the present invention. Furthermore, in Patent Document 5, there is no concept of suppressing bubble defects and homogenizing the matrix in order to increase the particle strength. Therefore, it is recognized that the invention is clearly different from the present invention.

Japanese Patent No. 4615370 Japanese Patent No. 3878496 Japanese Patent No. 4448945 Japanese Patent No. 6376451 Japanese Patent No. 5507262

INDUSTRIAL APPLICABILITY According to the present invention, in molten wind-crushed artificial sand having the composition of the SiO ₂ -Al ₂ O ₃ system equilibrium diagram in which the primary crystal is mullite, the bubble defects derived from the manufacturing method are minimized and the matrix inside the particles is homogeneous. The challenge is to increase the particle strength and provide cast sand that can be used semi-permanently in the casting industry. Another object of the present invention is to provide cast sand which is lightweight as a molten wind crushing artificial sand and has a good grain shape.

Still another object of the present invention is to reduce the amount of the binder added by improving the grain shape, and to achieve environmental adaptation, resource saving, and reduction of casting defects.

The present invention relates to molten wind-crushed artificial sand having the composition of the SiO ₂ -Al ₂ O ₃ system equilibrium diagram in which the primary crystal is mullite, in which particles having bubble defects with a maximum length of 10 μm or more are contained in the particle cross section. Provides cast sand with an abundance of 25% or less.
According to the melt-air crushing artificial sand according to the embodiment of the present invention, when the field of view in which the bubble defect does not exist is observed at 10000 times in the particle cross section, the maximum length is 1 μm or more in the grain boundary and inside. No gap is found. The average particle intensity is 2500 MPa or more because there are few bubble defects in the first half and no grain boundaries and gaps of 1 μm or more are observed.
Moreover, it is appropriate that the aspect ratio is 0.90 or more.
The present invention provides cast sand containing the above-mentioned molten wind crushing artificial sand.
The present invention also provides a mold containing the above-mentioned molten wind crushing artificial sand.
The present invention also provides a method for producing artificial sand by a molten wind crushing method, the gist of which is a raw material containing a composition of a SiO ₂ -Al ₂ O ₃ system equilibrium diagram in which the primary crystal is mullite. In the method of producing artificial sand by melting and wind-crushing by melting and wind-crushing, cooling is controlled during the wind-crushing process, and if necessary, tempering is performed to reduce bubble defects, micro-order inhomogeneity, and further. Provides a manufacturing method that improves the aspect ratio and the particle surface.

INDUSTRIAL APPLICABILITY The present invention has been able to provide an extremely hard spherical molten wind crushing artificial sand in which there are no defects or inhomogeneities inside the artificial sand among the artificial sands. In addition, the grain shape is good and the surface is smooth. Furthermore, it is lightweight as a molten wind crushing artificial sand. Specifically, in the SiO ₂ -Al ₂ O ₃ system equilibrium diagram, the composition in which the primary crystal is mullite is melted and then air-crushed. The time of wind crushing is controlled until the particles become spherical due to surface tension, and when the particles are spherical and have a good particle surface, they are rapidly cooled and solidified while maintaining their shape. Let me.
As a result, the stress generated in the casting process can be used repeatedly without being crushed, and can be used semi-permanently.
In addition, since the amount of the binder added can be reduced, resources can be saved and casting defects can be reduced.

Therefore, the present invention is a casting sand with high resource saving and can reduce the energy consumed when manufacturing the casting.
Further, the present invention is a molten artificial sand having a high crush resistance, a good grain shape and a particle surface shape as described above, and a relatively small specific gravity thereof, and is excellent in handleability and heavy reinforcement work. It was possible to provide molten artificial sand that can be reduced.

SiO ₂ -Al ₂ O ₃ system equilibrium diagram and artificial sand (Example, Comparative example) Graph showing the relationship between particle porosity and particle strength Graph showing comparison of aspect ratios of artificial sand Graph showing comparison of bulk specific density of artificial sand Conceptual diagram of particle strength measurement method Graph showing probability density curves of standardized stress in Examples and Comparative Examples Graph related to the area showing the pulverization rate of foundry sand

In order to solve the problem of the present invention, it is necessary to consider the following four points.
(1) Specific gravity of cast sand, which is a factor in the amount of binder added (2) Bubble defects inside artificial sand, which is a factor that reduces particle strength (3) Matrix inside artificial sand, which is a factor that reduces particle strength Heterogeneity (4) Grain shape of artificial sand that regulates mold strength and smoothness of the particle surface
Melt wind crushing method based on the SiO ₂ -Al ₂ O ₃ system equilibrium diagram Regarding the reduction of the specific density of artificial sand, SiO ₂ has a specific density of 2.65 and Al ₂ O ₃ has a specific density of 3.98, so it is manufactured on the SiO ₂ side. It can be said that it should be done. However, in the present invention, in order to use it as casting sand, it is necessary to make the grain shape spherical. In the SiO ₂ -Al ₂ O ₃ system, due to the difference in the melt viscosity of each composition, when wind-crushed, it tends to be fibrous on the SiO ₂ side and spherical on the Al ₂ O ₃ side. This is a phenomenon because the melt viscosity is high for SiO ₂ and low for Al ₂ O ₃ . The fibrous form cannot be used as casting sand.
FIG. 1 shows a SiO ₂ -Al ₂ O ₃ system equilibrium diagram and artificial sand (Examples and Comparative Examples) produced with the composition. Examples 1 to 3 and Comparative Examples 3 and 5 on the Al ₂ O ₃ side are spherical artificial sands produced by the melt wind crushing method. Comparative Examples 6 to 8 on the SiO ₂ side are spherical artificial sands produced by a granulation / sintering method. The granulation / sintering method is a manufacturing method in which a raw material made into fine powder is granulated in advance to form a spherical shape, and then fired to form ceramics. The melt wind crushing method of the present invention is a manufacturing method in which a raw material is melted in an arc furnace or the like and the surface tension of the melt is made spherical by wind crushing.
In the melt wind crushing method, fibrous and spherical shapes are generated in a certain ratio depending on the composition. Even if SiO ₂ has a composition close to 100%, spherical ones can be obtained, but most of them are fibers, and the yield is poor for casting sand. Since the examples and comparative examples of FIG. 1 are manufactured for cast sand, the composition is industrially viable in consideration of the yield. Looking at the composition of FIG. 1, it can be said that in the molten wind crushing method, Al ₂ O ₃ is the limit at which about 60% is appropriate in terms of yield.
In the present invention, since the specific gravity becomes heavier as the amount of Al ₂ O ₃ increases, the limit is about 75% of Al ₂ O ₃ in which the primary crystal becomes mullite. In addition, the lower limit is the Al ₂ O ₃ value crystallized by the primary crystal mullite excluding the composition of the primary crystal silica, which significantly deteriorates the yield.

Foam defects in artificial sand by the molten wind crushing method are those in which the volatile components in the raw material become gas and become bubbles during wind crushing, or air is caught in and becomes bubbles or scratches. In order to prevent bubble defects, it is necessary to incorporate sufficient degassing during melting and prevention of gas entrainment during wind crushing into the process. Specifically, in the present invention, it is melted in an arc furnace over a period of 1 hour or more, kept at a high temperature, and degassed. Further, since gas entrainment occurs when the wind crushing time is long, gas entrainment is prevented by quenching at the time of semi-solidification when the melt becomes spherical and the surface solidifies.
It should be noted that there is also a bubble defect in the artificial sand obtained by the granulation / sintering method, which is mainly due to the fact that the air in the gap between the fine powders when the fine powder was granulated was not completely removed during firing.
Table 1 shows the cross-sectional observation results of artificial sand with SEM (scanning electron microscope) and FE-SEM (field emission scanning electron microscope), and the measurement results of particle strength, aspect ratio, and bulk specific gravity of artificial sand.

表1 人工砂のSEM及びFE-SEM断面観察と、粒子強度、アスペクト比、かさ比重

Table 1 SEM and FE-SEM cross-sectional observation of artificial sand, particle strength, aspect ratio, bulk specific gravity

Figure 2 illustrates the relationship between particle porosity and particle strength. As the particle porosity increases, the particle strength tends to decrease, which can be approximated by the logarithmic curve shown in the figure. It is known that the fracture of ceramics is regulated by internal defects, but similar results have been obtained. However, in FIG. 2, the three points circled by the solid line tend to have low particle strength even though the porosity is low. This is Comparative Example-1, Comparative Example-3, and Comparative Example-4. In addition, the one point circled by the broken line has high particle strength even though the particle porosity is high. This is Comparative Example-5.

In the FE-SEM observation of the particle cross section in Table 1, the particle matrix is observed at 10000 times. This makes it possible to examine μm-order and sub-μm matrices. According to this, in Comparative Example 1, Comparative Example 3, and Comparative Example 4 in which the porosity is low but the particle strength is low, dendritic crystals having gaps on the order of μm are clearly crystallized. There are fine crystals of about 1 μm, and the composition image has contrast (elemental distribution is non-uniform). Therefore, it can be said that these particles have an inhomogeneous matrix, which is considered to reduce the particle strength.
On the other hand, in Comparative Example 5 having a high porosity but high particle strength, it can be said that the matrix is homogeneous as in Examples-1 to 4 having a low porosity and high particle strength. Therefore, it can be said that the particle strength is relatively high due to the homogeneity of the matrix in Comparative Example 5 even though the porosity is high.
In addition, in Comparative Example 2 other than the above, streaks and cavities on the order of μm were observed, in Comparative Examples 6 and 7, rounded gaps on the order of μm were observed, and in Comparative Examples 9 and 10, coarse mullite crystals were observed. It is considered that the particle strength is reduced because it is inhomogeneous.

[Cast strength and aspect ratio]
[aspect ratio]
The aspect ratios (minor axis / major axis) in Table 1 are shown in Fig. 3 in comparison for each artificial sand. Examples -1 to 4 and Comparative Examples -1 to 5 are melting methods. Comparative Examples 6 to 10 are sintering methods. It can be said that the melting method has an aspect ratio closer to 1 than the sintering method and has a good grain shape. Examples -1 to 4 have a good aspect ratio among the melting methods.
During wind crushing, the melt gradually becomes a sphere due to its surface tension, but if the wind crushing time (time for the melt to move in the air) is long, the sphere will collapse. Therefore, in the present invention, cooling is started so that the wind crushing time is controlled and the shape is maintained when the ball becomes a sphere. In addition, the cooling rate is also controlled to be rapidly cooled. The method is quenching by bringing particles into contact with a stainless steel plate, belt, cylinder, etc. (hereinafter referred to as a stainless steel container) having good thermal conductivity. A heat sink may be attached to the stainless steel container, or a water-cooled jacket may be attached. It may be water-quenched, but particles that break when in contact with water are generated, and the yield deteriorates. To avoid this, water may be sprayed and cooled. These control of wind crushing time and cooling are the reasons why the aspect ratio is good in Examples-1 to 4.

[Smoothness of particle surface]
As a result of controlling the above-mentioned wind crushing time, the effect of smoothing the particle surface is recognized as shown in Table 2. Table 2 shows excerpts of Example-2, Comparative Example-3, and Comparative Example-5. In Example 2, the wind crushing time is controlled. Comparative Example 3 is not controlled and moves in the air in a parabolic manner, during which it cools to a solid and then falls. Comparative Example-5 is an in-flame melting method, and since it is a downward flame, the melt falls while cooling in the direction of gravity.
As a result of controlling the wind crushing time, the particle surface of Example 2 is smooth, but in Comparative Example 3, dents caused by air resistance and crystals crystallized due to cooling in air are on the particle surface. The particle surface is not smooth. Further, in Comparative Example 5, smooth particles and particles that are not smooth due to crystals crystallized on the particle surface are mixed.

表2 粒子の表面状態

Table 2 Surface state of particles

[Umbrella density]
Figure 4 shows a comparison of the bulk specific densities of artificial sand. Examples -1 to 4 have a characteristic that the bulk specific density is light as the melt method artificial sand. As described above, in the sintering method, the bulk specific density can be reduced by increasing the ratio of SiO ₂ having a light specific gravity. However, in the melting method, when SiO ₂ is increased, it becomes fibrous. In the present invention, cooling is started in a spherical state and the shape is kept in a spherical state, so that SiO ₂ can be increased. As a result, it is lighter in the molten artificial sand.

(Necessity of particle strength)
Minerals have an index of hardness expressed by Mohs hardness for each substance. For example, typical minerals of cast sand are listed below. Corundum KAlSi ₃ O ₈ (Mohs hardness around 6), Iron Fe ₂ O ₃ (Mohs hardness around 6), Magnesium oxide MgO (Mohs hardness around 6.5), Chromium oxide Cr ₂ O ₃ (Mohs hardness 6-7), ZyrOx oxide ZrO ₂ (Mohs hardness 6-7), quartz SiO ₂ (Mohs hardness around 7), fused quartz SiO ₂ (Mohs hardness around 7), Murite ₃ Al ₂ O 3.2SiO ₂ (Mohs hardness 7.5), alumina corundum Al ₂ O ₃ (Mohs hardness 8-9).

A typical casting sand is silica sand, which is composed of quartz and feldspar, and has a Mohs hardness of around 6 to 7. Zircon sand made of zircon oxide and chromite sand made of chromium oxide are considered to be harder than silica sand in the casting industry, but their Mohs hardness is lower than that of quartz. Mullite, which is a typical artificial sand, is harder than quartz and has a Mohs hardness of about 7.5, and alumina has a Mohs hardness of 8 to 9, which is harder than quartz. Mullite and alumina have higher particle strength than the stress applied to the foundry sand during the production of casting, so they are hard to crush and can be said to be environmentally adaptable. On the other hand, silica sand is considered to be crushed by 5% to 30% from the yield in the regeneration process, and is not an environmentally adaptable type.

In this way, mullite and alumina are included in the SiO ₂ -Al ₂ O ₃ system equilibrium diagram. Therefore, by producing artificial sand according to this phase diagram, it is possible to make environmentally adaptable artificial sand that is not easily crushed. Can be done.

However, if there is a defect inside the mineral and it is not homogeneous, the Mohs hardness will not be obtained. Even if it is mullite or alumina, if there is a defect, it will be destroyed from that point, so it will not reach the original Mohs hardness and may be lower than that of silica sand. Therefore, the present invention provides a defect-free mullite-based artificial sand.

(Manufacturing method of artificial sand)
Table 3 shows the manufacturing method of artificial sand.

表3 鋳造用人工砂の製法と主な鉱物成分

Table 3 Manufacturing method of artificial sand for casting and main mineral components

(1) Granulation sintering method This is a method for producing mullite-based artificial sand produced in Japan and the United States with a production volume of approximately 50,000 tons / year. The inside of the rotary kiln is heated to 1400 ° C to 1700 ° C with a fuel burner. The heating temperature depends on the composition. A ratio of SiO ₂ with less alkaline components and Al ₂ O ₃ raw materials to mullite (3 Al ₂ O ₃・ 2SiO ₂ ), and fine powder particles are granulated to the size of casting sand. As shown in Table 3, there are three types of granulation methods, each of which has a different particle density and surface condition. In a rotary kiln, mullite is synthesized at a temperature below the melting point of mullite (about 1850 ° C). Due to specific restrictions, not all of the raw materials become mullite during synthesis and exist as amorphous. The content of mullite and other components and the amount of amorphous differ depending on the manufacturer. Mullite is 85% or more. It is desirable to do this and to make the particles dense.
In the sintering method, mullite crystals are precipitated from the granulated particles. The precipitation temperature is below the melting point of mullite.
At the time of sintering, the volatile matter in the raw material and the air in the raw material become gas and cavities are likely to occur. In addition, when the crystals are deposited, gaps are likely to occur in the crystals.

(2) Melt wind crushing method The graphite electrode contact melting method of the melt wind crushing method is a method for producing artificial sand with the highest production volume. The melt wind crushing method is also simply called the melt method. Currently, about 100,000 tons / year is mainly manufactured in China. This mineral composition is mullite + corundum. Since it is a melting method, it is necessary to melt the raw material at the liquid layer temperature shown in Fig. 1, and an arc furnace that can obtain a high temperature is used. The raw material is alum shale (Chinese bauxite containing around 75% of Al ₂ O ₃ ). The raw material is placed on a graphite electrode and melted by Joule heat. In addition, since a plasma arc is also generated, the raw material is also melted by this arc heat. The melting temperature is 2000 ° C or higher. The molten metal flows down below the graphite electrode, is discharged from the orifice, is immediately air-crushed, draws a parabola, becomes spherical particles due to the surface tension of the liquid in the air, is cooled in the atmosphere, falls into the soil, etc., and is naturally cooled. It becomes artificial sand.
Air is entrained during wind crushing, and bubble defects are likely to occur. In addition, when crystals are precipitated, inhomogeneity due to grain boundaries and transitions is likely to occur.

In the arc furnace melting method, the raw material is charged in the furnace, and the raw material is melted by the arc heat generated by the arc discharge between the graphite electrodes to form a molten metal. Immediately after the hot water is discharged, it is air-crushed, and the particles draw a parabola and are air-cooled to become artificial sand particles. The refractory material of the furnace is often self-lining, and the high refractory raw material can be melted without being affected by the melting point of the refractory material. Since the composition can be adjusted in the furnace, it is used in the manufacturing method of high refractory artificial sand with 80% Al ₂ O ₃ and 10% Zr O ₂ . Those already on the market are manufactured in China, and the production volume is estimated to be about 5,000 tons / year. It should be noted that the one on the market does not control the cooling rate and is naturally cooled.
The present invention uses this arc furnace melting method, in which a raw material whose primary crystals are murite is melted in an arc furnace, then air-crushed, a parabolic drawing is drawn, and the cooling start temperature and cooling rate are controlled. be. Further, if necessary, heat treatment such as tempering is performed to control the crystal structure of the particles. As a result, the entrainment of air is prevented and the matrix is homogenized.

(3) In-flame melting method This is also mainly produced in China, and the production volume is thought to be about 5,000 tons / year. The in-flame melting method is also simply called the melting method as well as the melting air crushing method. In a flame of about 3000 ° C using a pure oxygen combustion burner, raw material particles that have been granulated or crushed to a predetermined size in advance are put into the flame from the fuel spraying direction, and the particles are melted in the flame and spherical due to surface tension. This is a manufacturing method in which particles are formed and crystallized during cooling after passing through a flame to form spherical artificial sand. Artificial sand such as mullite, alumina, mullite + cristobalite is manufactured. Crystallization and amorphization differ depending on the state of retention in the flame and the state of cooling after passing. Those on the market are sprayed in the direction of gravity, and because the cooling time in the atmosphere is short, they are rather amorphous. Utilizing this, amorphous silica having a high refractory and a stable phase can also be produced.
Since the inside of the flame is sprayed, air bubbles are likely to be generated due to the entrainment of air, but the wind crushing time is short because it is wind crushing in the direction of gravity. Is homogenized.

(Adjusting particle size)
Since the present invention relates to cast sand, it is desirable to adjust the particles to a particle size range of 20 to 1200 μm. Generally, 106-600 μm is used as casting sand. The relatively small mass-produced castings produced in the green mold are mainly cast sand of 150 to 300 μm. Relatively large castings produced by self-hardening molds are mainly composed of 300-600 μm casting sand. The V process is around 106 μm. In addition, 20 to 106 μm is called fine sand and is used as an additive for auxiliary particle size adjustment of casting sand. 850-1200 μm is used for backup and back sand. In this way, the grain size of cast sand differs depending on the molding process.

(Casting sand and mold)
The sintered artificial sand according to the present invention is cast sand used for casting, and mold sand can be obtained by adding other substances such as a binder according to a conventional method. Then, the obtained mold sand can be molded to manufacture a mold, which is used for casting various metals. Exceptionally, there are mold sands and molds to which a binder such as depressurization or freezing is not added, but the sintered artificial sand according to the present invention can also be applied to these.

(Measurement method of bubble particle ratio)
Sift the artificial sand into single particles with an opening of 212 μm (70 mesh). The particles are arranged on a horizontal plane and filled with resin. Using a wet polishing machine, the particles are polished to 106 μm from this horizontal plane (finally mirror polishing) to form a cross section. Clean and dry the cross section to make a test piece for SEM observation. The sample was non-conductive and was SEM observed in a low vacuum mode where this could be observed.
The cross section of the particles is photographed at 40 times, and the visually recognized bubbles and scratched particles are counted and divided by the total number to obtain a percentage, which is used as the bubble particle ratio (A).
(Measuring method of porosity)
The porosity is the average of the particles selected, the particles are displayed at 250 to 300 times so that only the particles are in the observation field, and the image is binarized in black and white. The area of the black part, which is a bubble or a scratch in the particle cross-sectional area, is defined as the volume percentage (B). The porosity is the volume percentage of the voids in the average particle cross section.
(Measurement method of particle porosity)
Using these A and B, the porosity of all particles was estimated by A × B / 100, and this was taken as the particle porosity. The particle porosity is the average of the porosities present in all particles.
(Method of determining the state of the matrix)
Since FE-SEM can obtain high-resolution images at higher magnification than SEM, the state of the matrix of the particle cross section was observed at 10000 times. The sample was corroded with a nital solution for 20 minutes in order to observe the unevenness in single μm units so that the grain boundaries could be easily observed. Then, after washing and drying, platinum vapor deposition was performed so that high-resolution observation could be performed to prepare a sample for FE-SEM observation. Avoiding air bubbles and scratches as much as possible, we selected representative points and used them as the analysis field of view. The SEM image obtained after the analysis had the same contrast in general, and the grain boundaries and the like were faint, so the image processing was smoothed. The smoothing performed here is an image process that moderately emphasizes the contrast of the image and makes the part that was difficult to see until now clear.

(Measurement method of particle strength)
Figure 5 shows the appearance of the micro-strength tester and the conceptual diagram of particle strength measurement. The testing machine used is an electromagnetic force type micro-strength testing machine (hereinafter referred to as a micro-strength testing machine). The maximum load capacity was 50 N, and the load was applied under the condition of constant displacement speed of 1 mm / min. The particle strength was determined by photographing each sample with a microscope to determine the major axis and the minor axis, and then the maximum fracture load was measured using a microintensity tester.

(Measurement method of particle strength)
For the compressive strength of the artificial sand particles, a fracture test was conducted for each particle using the electromagnetic force type micro-strength tester shown in FIG. 5, and the maximum fracture load was determined.
To obtain the particle strength from the maximum fracture load, it is necessary to know the cross-sectional area of the sample particles. The cross-sectional area referred to here is the contact area between the pressure plate and the sample particles during the compression test. However, since the sample particles are irregular particles, their contact area is not always constant. Therefore, the compressive strength was measured using the following Fukumoto's formula from among several proposed formulas for calculating the compressive strength of irregular particles.
Calculation of compressive strength (Pa)
Pa = P / (A × B / 8)
Here, P: maximum fracture load, A: sample major axis, B: sample minor axis literature) Takeaki Fukumoto, Takeo Hara: Proceedings of the Civil Engineering Society, 596 / III-43 (1996), 91

(Aspect ratio measurement method)
The aspect ratio is calculated from the major axis and the minor axis, but depending on the industry, it may be major axis / minor axis or minor axis / major axis. In the present invention, the measurement is performed on the minor axis / major axis. That is, the aspect ratio in the present invention is 1 or less, and the closer it is to 1, the closer it is to a perfect circle.
The aspect ratio is generally used by industry associations, and currently the major axis / minor axis is the mainstream. However, in the foundry industry, the major / minor axis ratio is defined as the grain size factor. This is described in TIKS-302 "Grain Shape Test Method for Raw Mold Sand" established in 1982 by the Tokai Branch Inorganic Sand Mold Research Subcommittee of the Japan Foundry Association. For this reason, if the aspect ratio is the major axis / minor axis ratio, it is synonymous with the grain size coefficient. Therefore, the aspect ratio of the minor axis / major axis has been widespread in the casting industry for a long time.
(Reference) Japan Foundry Association Tokai Branch Inorganic Sand Mold Research Subcommittee: Japan Foundry Association Tokai Branch Inorganic Sand Mold Research Subcommittee Report (II) (Japan Foundry Association Tokai Branch) (1982) 95-176

(Measuring method of bulk specific density)
The bulk specific gravity is measured according to the "S-10 Casting Sand Fillability (Bulk Specific Gravity) Test Method" specified in the "Test Method for Molds and Mold Materials" issued by the Small and Medium-sized Enterprises Corporation in May 1999. Was measured. The difference is the charging container, which uses the Ford Cup # 4 specified in "S-5 Casting Sand Fluidity Test Method". That is, it is a simultaneous measurement of bulk specific gravity and fluidity.
Regarding the bulk specific density, the larger the number of voids including both the gaps derived from the crystal structure and the voids at the time of sintering, regardless of the structure of the voids, the smaller the bulk specific gravity tends to be.

(Ratio of particles with bubbles, porosity of particles, matrix state, particle strength, aspect ratio, bulk specific gravity)
Compared with other artificial sands, the molten wind crushing artificial sand of the present invention has high particle strength and is good, the aspect ratio is close to 1 and close to a perfect circle, and the bulk specific gravity is lighter than the molten artificial sand. It is described from Table 1 that there is.

The molten wind crushing artificial sand according to the embodiment of the present invention has no bubble defects inside the particles, has a uniform matrix, and has a good particle shape and particle surface. As a result, industrial waste can be reduced without crushing the particles, casting defects due to the reduction of the binder are reduced, so that the product yield is improved and the decomposition of the binder is reduced, which makes it environmentally friendly. Since it is lightweight, it has various advantages such as reduction of heavy-duty work, and this will be described below with reference to Examples and Comparative Examples of the present invention. It should not be understood in a limited way.

(Example-1)
In Example-1, the raw materials were a silica source and an alumina source, which were put into an arc furnace and melted at about 2100 ° C. The hot water was discharged by tilting the furnace body, and the air whose pressure was adjusted was blown onto the molten metal flowing down from the nozzle, and the air was crushed in a parabolic manner. When it became spherical during wind crushing, it was received in a stainless steel container to start cooling, and after drying, it was sieved to obtain a product. The main chemical components of Example-1 are SiO ₂ : 40.3%, Al ₂ O ₃ : 53.6%, and the others consist of TiO ₂ , Fe ₂ O ₃ , Na ₂ O, MgO, K ₂ O, Ca O, etc. .. The temperature at which the particles are cooled is in the range of the eutectic temperature of 1587 ° C ± 10 ° C from the liquidus temperature at which the primary crystal becomes mullite in Fig. 1. The term "nearby" refers to the fact that the reaction at the transition from high temperature to low temperature is generally below the target temperature. That is, when the temperature drops sharply, it is effective even at a temperature of 1587 ° C ± 10 ° C or less, which is the eutectic temperature. However, if the temperature is far below the eutectic temperature of 1587 ° C ± 10 ° C, the present invention has no effect.
In Example-1, since the bubble particle ratio is 19.4% and the porosity is 0.01 vol%, the particle porosity is 0.002 vol%. Also, the state of the matrix is homogeneous. As a result, the particle strength is 3263 MPa, which exceeds 2500 MPa, which is the object of the present invention. In addition, the aspect ratio is 0.956, which exceeds 0.820 to 0.941 of Comparative Examples-3 to 10 on the market. Furthermore, the bulk specific gravity is 1.656 g / cm ³ , which is lighter than 1.680 to 1.942 g / cm ³ of Comparative Examples 3 to 5 which are the artificial sands of the molten method on the market.

(Example-2)
Example-2 has the same manufacturing method as Example-1 but different components. The main chemical components of Example-2 are SiO ₂ : 34.9%, Al ₂ O ₃ : 55.7%, and the other components are TiO ₂ , Fe ₂ O ₃ , Na ₂ O, MgO, K ₂ O, Ca O, etc. Consists of.
In Example 2, since the bubble particle ratio is 21.1% and the porosity is 0.01 vol%, the particle porosity is 0.002 vol%. Also, the state of the matrix is homogeneous. As a result, the particle strength is 2732 MPa, which exceeds 2500 MPa, which is the object of the present invention. In addition, the aspect ratio is 0.965, which exceeds 0.820 to 0.941 of Comparative Examples-3 to 10 on the market. Furthermore, the bulk specific gravity is 1.662 g / cm ³ , which is lighter than 1.680 to 1.942 g / cm ³ of Comparative Examples 3 to 5 which are the artificial sands of the molten method on the market.

(Example-3)
Example 3 has the same manufacturing method as Examples 1 and 2, but the components are different. The main chemical components of Example-3 are SiO ₂ : 29.8%, Al ₂ O ₃ : 61.8%, and the other components are TiO ₂ , Fe ₂ O ₃ , Na ₂ O, MgO, K ₂ O, Ca O, etc. Consists of.
In Example 3, since the bubble particle ratio is 16.3% and the porosity is 0.08 vol%, the particle porosity is 0.013 vol%. Also, the state of the matrix is homogeneous. As a result, the particle strength is 2716 MPa, which exceeds 2500 MPa, which is the object of the present invention. In addition, the aspect ratio is 0.959, which exceeds 0.820 to 0.941 of Comparative Examples-3 to 10 on the market. Furthermore, the bulk specific gravity is 1.760 g / cm ^{3, which is the lighter weight side among these compared to 1.680 to 1.942 g / cm 3 of} Comparative Examples 3 to 5 which are the artificial sands of the molten method on the market.

(Example-4)
Example-4 had the same raw material composition as Example-1, and after being produced in the same manner, tempered at about 1200 ° C. for 1 hour. This tempering temperature may be 1587 ° C ± 10 ° C or less, which is the eutectic temperature of silica and mullite in FIG. 1, and it is necessary to lengthen the tempering time as the temperature decreases. The chemical composition of Example-4 is SiO ₂ : 39.6%, Al ₂ O ₃ : 51.4%, and the other components are TiO ₂ , Fe ₂ O ₃ , Na ₂ O, MgO, K ₂ O, Ca O, etc. ..
In Example-4, since the bubble particle ratio is 11.4% and the porosity is 0.04 vol%, the particle porosity is 0.005 vol%. Also, the state of the matrix is homogeneous. As a result, the particle strength is 4074 MPa, which exceeds 2500 MPa, which is the object of the present invention. In addition, the aspect ratio is 0.968, which exceeds 0.820 to 0.941 of Comparative Examples-3 to 10 on the market. Furthermore, the bulk specific gravity is 1.479 g / cm ³ , which is the lighter weight side among these compared to 1.680 to 1.942 g / cm ³ of Comparative Examples 3 to 5 which are the artificial sands of the molten method on the market.
Example-4 tempered Example-1, but the particle strength increased from 3263 MPa in Example-1 to 4074 MPa. This is because Example-4 has a relatively large amount of SiO ₂ , so there are two types of silica (SiO ₂ specific gravity 2.65) and mullite (3 Al ₂ O ₃・ 2SiO ₂ specific gravity 3.16) that precipitate during rewinding. The reason is that a large amount of silica, which has a light specific gravity, is deposited among the minerals to fill the gaps existing in the nm unit inside the particles and become dense particles.

(Comparative Examples-1, 2)
Comparative Example-1 had the same raw material composition as Example-2, and after being produced in the same manner, tempered at about 1200 ° C. for 1 hour. The chemical composition of Comparative Example-1 is SiO ₂ : 30.3%, Al ₂ O ₃ : 57.8%, and the other components are TiO ₂ , Fe ₂ O ₃ , Na ₂ O, MgO, K ₂ O, Ca O, etc. ..
Comparative Example-1 was tempered in the same manner as in Example 4, but had a large amount of Al ₂ O ₃ as compared with Example 4.
In Comparative Example-1, since the bubble particle ratio is 38.5% and the porosity is 1.01 vol%, the particle porosity is 0.39 vol%. The state of the matrix is inhomogeneous, and there are streak-like gaps on the order of μm. As a result, the particle strength is 1472 MPa, which does not exceed 2500 MPa, which is the object of the present invention.
Example-2 satisfied the object of the present invention, but tempered Comparative Example-1 did not. In addition, the particle strength of Example 4 tempered in the same manner was further increased, but decreased in Comparative Example-1. It is considered that these reasons are that the minerals precipitated during tempering in Comparative Example 1 have a relatively large amount of mullite having a heavy specific density. As a result, it is considered that the structure of the particles is weakened due to the formation of gaps inside the particles, the increase in the bubble particle ratio on the macro scale, and the formation of streaks on the matrix on the micro scale.

Comparative Example-2 had the same raw material composition as Example-3, and after being produced in the same manner, tempered at about 1200 ° C. for 1 hour. The chemical composition of Comparative Example-2 is SiO ₂ : 29.2%, Al ₂ O ₃ : 61.0%, and the other components are TiO ₂ , Fe ₂ O ₃ , Na ₂ O, MgO, K ₂ O, Ca O, etc. ..
Comparative Example-2 was tempered in the same manner as in Example 4, but had a large amount of Al ₂ O ₃ as compared with Example 4 and Comparative Example 2.
In Comparative Example-2, the bubble particle ratio is 31.2% and the porosity is 9.72 vol%, so that the particle porosity is 3.03 vol%. The state of the matrix is inhomogeneous, and there are streak-like gaps and cavities on the order of μm. As a result, the particle strength is 1329 MPa, which does not exceed 2500 MPa, which is the object of the present invention. The reason why the particle strength decreased due to tempering is the same as in Comparative Example-1. In Comparative Example-2, since the amount of Al ₂ O ₃ is further increased, a large amount of mullite is deposited, and the cavity in the particle is enlarged to further reduce the particle strength.

(Comparative Examples-3, 4)
Comparative Example 3 is mullite + alumina-based molten artificial sand produced by the molten air crushing method (graphite electrode contact melting method) on the market. The raw material comes into contact with the graphite electrode, and air is blown to the molten metal that has melted down instantly with a nozzle, and the particles are air-crushed in a parabolic manner, and the particles that have fallen into the soil are naturally cooled to make a product. be. The chemical composition of Comparative Example-3 is SiO ₂ : 29.8% and Al ₂ O ₃ : 61.8%. Other components consist of TiO ₂ , Fe ₂ O ₃ , Na ₂ O, MgO, K ₂ O, Ca O and the like.
In Comparative Example 3, since the bubble particle ratio is 46.2% and the porosity is 0.05 vol%, the particle porosity is 0.024 vol%. The state of the matrix is inhomogeneous and dendritic crystals are observed. As a result, the particle strength is 1433 MPa, which does not exceed 2500 MPa, which is the object of the present invention. The high number of bubble particles and the presence of dendritic crystals in the matrix may be the cause of the decrease in particle strength.

Comparative Example 4 is a commercially available molten wind crushing method (graphite electrode contact melting method) artificial sand manufactured by the same manufacturing method as Comparative Example 3. There are more impurities than Comparative Example-3. The chemical composition is SiO ₂ : 18.4% and Al ₂ O ₃ : 68.6%. The total of SiO ₂ and Al ₂ O ₃ is 90.5% in Comparative Example-3 and 87.0% in Comparative Example-4.
In Comparative Example-4, since the bubble particle ratio is 35.2% and the porosity is 0.01 vol%, the particle porosity is 0.004 vol%. The state of the matrix is homogeneous. As a result, the particle strength is 1425 MPa, which does not exceed 2500 MPa, which is the object of the present invention. The high bubble particle ratio may be the cause of hindering the particle strength.

(Comparative Example-5)
Comparative Example 5 is a mullite-based molten artificial sand produced by the in-flame melting method on the market. In an oxygen burner with a flame directed downward, raw material particles crushed to the size of cast sand in advance are put along the flame, the particles are melted by the heat of the flame, made spherical when falling, and naturally cooled. be. The chemical composition is SiO ₂ : 33.1% and Al ₂ O ₃ : 58.9%. Other components consist of TiO ₂ , Fe ₂ O ₃ , Na ₂ O, MgO, K ₂ O, Ca O and the like.
In Comparative Example 5, the bubble particle ratio is 63.9% and the porosity is 7.30 vol%, so that the particle porosity is 4.67 vol%. The state of the matrix is homogeneous. As a result, the particle strength is 1425 MPa, which does not exceed 2500 MPa, which is the object of the present invention. The high bubble particle ratio may be the cause of hindering the particle strength.

(Comparative example-6, 7)
Comparative Example 6 is mullite-based artificial sand produced by the sintering method (panmixer granulation method) that has been put on the market. The chemical composition is SiO ₂ : 51.4% and Al ₂ O ₃ : 40.7%. Other components consist of TiO ₂ , Fe ₂ O ₃ , Na ₂ O, MgO, K ₂ O, Ca O and the like.
In Comparative Example-6, the bubble particle ratio is 76.9% and the porosity is 2.60 vol%, so that the particle porosity is 2.00 vol%. The state of the matrix is inhomogeneous, with rounded irregularities on the order of μm. As a result, the particle strength is 1565 MPa, which does not exceed 2500 MPa, which is the object of the present invention. The high bubble particle ratio and the inhomogeneous matrix may be the cause of the inhibition of particle strength.

Comparative Example-7 is mullite-based artificial sand produced by the sintering method (panmixer granulation method) that has been put on the market. The chemical composition is SiO ₂ : 44.3% and Al ₂ O ₃ : 49.8%. Other components consist of TiO ₂ , Fe ₂ O ₃ , Na ₂ O, MgO, K ₂ O, Ca O and the like.
In Comparative Example-7, the bubble particle ratio is 78.6% and the porosity is 2.10vol%, so that the particle porosity is 1.65vol%. The state of the matrix is inhomogeneous, with rounded irregularities on the order of μm. As a result, the particle strength is 1671 MPa, which does not exceed 2500 MPa, which is the object of the present invention. The high bubble particle ratio and the inhomogeneous matrix may be the cause of the inhibition of particle strength.

(Comparative Example-8-10)
Comparative Example-8 is mullite-based artificial sand produced by the sintering method (spray dryer granulation method) that has been put on the market. The chemical composition is SiO ₂ : 37.5% and Al ₂ O ₃ : 55.8%. Other components consist of TiO ₂ , Fe ₂ O ₃ , Na ₂ O, MgO, K ₂ O, Ca O and the like.
In Comparative Example-8, since the bubble particle ratio is 100.0% and the porosity is 16.70vol%, the particle porosity is 16.70vol%. The state of the matrix is inhomogeneous, coarse mullite crystals are precipitated, and it is discontinuous due to grain boundaries. As a result, the particle strength is 955 MPa, which does not exceed 2500 MPa, which is the object of the present invention. The extremely high bubble particle ratio and the inhomogeneous matrix may be the cause of the inhibition of particle strength.

Comparative Example-9 is mullite-based artificial sand produced by the sintering method (spray dryer granulation method) that has been put on the market. After the same manufacturing process as in Comparative Example-8, a polishing process was added in the final process to improve the grain shape and the like. The chemical composition is SiO ₂ : 37.0% and Al ₂ O ₃ : 56.3%. Other components consist of TiO ₂ , Fe ₂ O ₃ , Na ₂ O, MgO, K ₂ O, Ca O and the like.
In Comparative Example-9, since the bubble particle ratio is 100.0% and the porosity is 9.80 vol%, the particle porosity is 9.80 vol%. The state of the matrix is inhomogeneous, coarse mullite crystals are precipitated, and it is discontinuous due to grain boundaries. As a result, the particle strength is 836 MPa, which does not exceed 2500 MPa, which is the object of the present invention. The extremely high bubble particle ratio and the inhomogeneous matrix may be the cause of the inhibition of particle strength.

Comparative Example-10 is mullite-based artificial sand produced by the sintering method (spray dryer granulation method) that has been put on the market. After the same manufacturing process as in Comparative Example-8, a polishing process different from that in Comparative Example-9 was added in the final process to improve the grain size and the like. The chemical composition is SiO ₂ : 39.8% and Al ₂ O ₃ : 57.8%. Other components consist of TiO ₂ , Fe ₂ O ₃ , Na ₂ O, MgO, K ₂ O, Ca O and the like.
In Comparative Example-10, the bubble particle ratio is 100.0% and the porosity is 9.60 vol%, so that the particle porosity is 9.60 vol%. The state of the matrix is inhomogeneous, coarse mullite crystals are precipitated, and it is discontinuous due to grain boundaries. As a result, the particle strength is 1124 MPa, which does not exceed 2500 MPa, which is the object of the present invention. The extremely high bubble particle ratio and the inhomogeneous matrix may be the cause of the inhibition of particle strength.

(Evaluation of Examples and Comparative Examples at the Micronization Rate)
Although the particle strengths of the examples and comparative examples have been described, how the difference in strength affects them in the casting line is compared by obtaining the micronization rate of the particles. The calculation method of the micronization rate is shown in the following documents by Hirata and Kurokawa et al.
Literature)
Hideyuki Hirata, Hiroshi Morimoto, Yutaka Kurokawa, Hitoshi Uebayashi: JISSAR 2003 Proceedings (2003), 149
Hideyuki Hirata, Hiroshi Morimoto, Yutaka Kurokawa, Hitoshi Uebayashi: Proceedings of the 53rd Academic Lecture Meeting of the Japan Society of Materials Science (2004), 417
H.Ameku, H.Kambayashi, Y.Kurokawa, H.Hirata, H.Miyake: AFS.Trans.114 (2006), paper06-045 (04), pdf, 1-10

First, we need to know the stress distribution that the particles receive during the casting process. Using dynamic simulation (ANSYS-LS-DYNATM), the conditions under which particles collide in the casting process are set, and the stress distribution generated at that time is obtained. The conditions are set as the velocity of particles of 5m / s, 3m / s, and 1m / s in the above document. This is the particle velocity in the regeneration process where the particles are most stressed in the casting process. It is assumed that the particles collide at these velocities. This is referred to as "stress distribution during casting".
Next, the micronization rate is calculated from the stress distribution during casting and the standardized stress obtained from the compressive strength distribution of the particles obtained in the present invention. The standardized stress is that in artificial sand, which is a ceramic, the compressive strength decreases as the particle size increases. This is because the strength of the ceramic sand depends on the volume. Therefore, it is standardized by the effective volume, and this is used as the standardized stress.
The average and deviation of both the stress distribution and the standardized stress during casting can be obtained. Therefore, the probability density curve is calculated from the mean and deviation, and is shown in Fig. 6. The integral value of the probability density curve is 1.
As shown in FIG. 7, the place where the stress distribution at the time of casting and the probability density curve of the standardized stress overlap is the place where the particles are broken, and the pulverization rate is the percentage.
Table 4 summarizes the pulverization rates of Examples-1 to 4 and Comparative Examples-1 to 10. In the examples, the micronization rate is a single-digit value, whereas in all the comparative examples, it is a double-digit value.

表4 実施例と比較例の微粉化率

Table 4 Micronization rate of Examples and Comparative Examples

(Characteristic evaluation with shell mold, furan mold, alkaline phenol mold)

(Shell mold)
Table 5 shows the characteristics of the shell mold of the molten wind crushing method artificial sand of the present invention. Examples 1 to 4 and Comparative Examples -1 to 3 from the comparative examples are shown in comparison. For each artificial sand, add 1.2% of polymer phenol resin by weight, add 15% of hexamethylenetetramine to the resin, and add 0.1% of calcium stearate to the artificial sand to make resin coated sand. And said. A test piece was prepared by heating at 280 ° C., and the bending strength and the test piece density were measured. In addition, the temperature strength, 280 ° C wall thickness, and 1000 ° C maximum expansion amount, which are generally measured, are measured.
The bending strength of Examples-1 to 4 is higher than that of Comparative Examples-1 to 3. Since Comparative Example 3 has been put on the market, the present invention has higher strength characteristics than the artificial sand sold on the market.
Although the binder was added to the weight of the sand, since the density of the test pieces depending on the bulk specific gravity is different, the bending strength data converted when the resin is added per volume is also attached. Since the volume of the mold is constant at the casting site, it is rational to keep the amount of resin per volume constant. According to this, it can be seen that the present invention has a bending strength of 1.25 to 1.40 times that of Comparative Example 3 on the market, and has sufficient strength. Therefore, it can be said that the product of the present invention is superior to those on the market in shell molds.

表5 シェル鋳型特性

Table 5 Shell mold characteristics

(Fran mold)
Table 6 shows the characteristics of the furan mold of the molten wind crushing artificial sand of the present invention. Examples 1 to 4 and Comparative Examples -1 to 3 from the comparative examples are shown in comparison. To each artificial sand, 1.2% of general-purpose furan resin was added by weight, and 40% of sulphonic acid-based curing agent was added to the resin and kneaded. Immediately after kneading, a test piece having a diameter of 28 mm and a height of 50 mm was molded, and the compressive strength was measured up to 24 hours later.
The compressive strength of Examples-1 to 4 after 24 hours was higher than that of Comparative Example-3 on the market. In addition, in terms of the compressive strength after 24 hours in terms of resin addition per volume, Examples 1 to 4 had higher compressive strength than Comparative Examples-1 to 3. Therefore, it can be said that the product of the present invention is superior to the one on the market in the furan mold.

表6 フラン鋳型特性

Table 6 Fran mold characteristics

(Alkaline phenol mold)
Table 7 shows the characteristics of the alkaline phenol template of the molten wind crushing method artificial sand of the present invention. Examples 1 to 4 and Comparative Examples -1 to 3 from the comparative examples are shown in comparison. To each artificial sand, 1.5% of alkaline phenol resin was added by weight, and 20% of ester organic acid was added to the resin and kneaded. Immediately after kneading, a test piece having a diameter of 28 mm and a height of 50 mm was molded, and the compressive strength was measured up to 24 hours later.
The compressive strength of Examples-1 to 4 after 24 hours is almost the same as that of Comparative Example 3 on the market. Further, in terms of the compressive strength after 24 hours in terms of resin addition per volume, Examples 1 to 4 have almost the same compressive strength as Comparative Examples -1 to 3. Therefore, it can be said that the product of the present invention can be used because it is similar to the one on the market.

表7 アルカリフェノール鋳型特性

Table 7 Alkaline phenol template characteristics

(Cold box mold)
Table 8 shows the characteristics of the cold box mold of the molten wind crushing artificial sand of the present invention. Examples 1 to 4 and Comparative Examples -1 to 3 from the comparative examples are shown in comparison. To each artificial sand, 0.3% of phenol resin and 0.3% of isocyanate resin were added by weight and kneaded, and the mixture was cured using amine as a catalyst. As the test piece, a test piece having a diameter of 28 mm and a height of 50 mm was molded, and the compressive strength was measured up to 24 hours later.
The compressive strength of Examples-1 to 4 after 24 hours was higher than that of Comparative Example-3 on the market. In addition, in terms of the compressive strength after 24 hours in terms of resin addition per volume, Examples 1 to 4 had higher compressive strength than Comparative Examples-1 to 3. Therefore, it can be said that the product of the present invention is superior to the one on the market in the cold box mold.

表8 コールドボックス鋳型特性

Table 8 Cold box mold characteristics

It can be used for casting sand that is repeatedly collected and used as a casting mold (sand mold). For example, it can be used as a self-hardening mold such as a furan mold or an alkaline phenol mold. It can be used for shell molds for cores, cold box molds, etc. Since the amount of the binder added is larger than that of the above-mentioned molding method, it can be naturally used for a green mold that is not easily affected by the binder. It can also be used as casting sand for the V process, which is a molding method that does not add a binder, and the lost model casting method.
These cast sands are suitable for casting cast iron, cast steel, copper alloys, aluminum alloys and other metals.
Due to its high particle strength, it can be used semi-permanently without crushing against the stress received in the casting process. As a result, resource saving of casting sand raw material is achieved, and industrial waste is eliminated, so that the casting industry becomes an environment-friendly industry.
In addition, since the grain shape and particle surface are good, the amount of the binder can be reduced, and because the artificial sand of the melting method is lightweight, the amount of the binder added is small in terms of volume, so the binder can be used. You can benefit from the reduction. The reduction merits are improvement of casting yield by reducing gas defects, improvement of environmental pollution by reduction of decomposition gas during casting, resource saving by reduction of binder amount, improvement of mold filling property by reduction of viscosity of mold sand and high-dimensional casting. Manufacturing of products, reduction of manufacturing cost of casting products, etc.
In addition, the lighter weight of the foundry sand frees the operator from heavy-duty work.

Claims (9)

In the melt wind crushing artificial sand having the composition of the SiO ₂ -Al ₂ O ₃ system equilibrium diagram in which the primary crystal is mullite, the presence of particles with bubble defects of 10 μm or more in the particle cross section is 25% or less. The molten wind crushing artificial sand according to claim 1, wherein no grain boundaries and gaps of 1 μm or more are observed when the field of view in which the bubble defects do not exist is observed at 10000 times in the particle cross section. The molten wind crushing method artificial sand according to claim 1, wherein the average particle strength is 2500 MPa or more due to the small number of bubble defects. The molten wind crushing method artificial sand according to claim 2, wherein the average particle strength is 2500 MPa or more because the crystal grain boundaries and the gaps are not observed in addition to the small number of bubble defects. The molten wind crushing method artificial sand according to any one of claims 1 to 4, wherein the aspect ratio is 0.90 or more. In the molten wind crushing artificial sand having the primary crystal of Murite and having the composition of the SiO ₂ -Al ₂ O ₃ system equilibrium diagram, Al ₂ O ₃ is 50 to 50 in the SiO ₂ -Al ₂ O ₃ system equilibrium diagram. It is 70% by mass, and the presence of particles with bubble defects of 10 μm or more in the particle cross section is 25% or less. Molten wind crushing artificial sand characterized by the homogeneity of the matrix inside the particles with no gaps of 1 μm or more, an average particle intensity of 2500 MPa or more, and an aspect ratio of 0.90 or more. Mold sand containing the molten wind crushing method artificial sand according to any one of claims 1 to 6. A mold containing the molten wind crushing method artificial sand according to any one of claims 1 to 6. In the method of producing artificial sand by melting wind crushing method by melting the raw material containing the composition of the SiO ₂ -Al ₂ O ₃ system equilibrium diagram in which the primary crystal is mullite, cooling is controlled during the wind crushing process. At the same time, a method for producing artificial sand by a molten wind crushing method that reduces bubble defects, makes micro-order inhomogeneity, and improves the aspect ratio and particle surface by performing tempering as necessary.

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