JP6367451B1 - Sintered artificial sand - Google Patents

Abstract

An object of the present invention is to provide sintered artificial sand having a function of having a high melting point and hardly reacting with molten iron in sintered artificial sand mainly composed of Al ₂ O ₃ —SiO ₂ .
SOLUTION: The type and amount of the low melting point composition is controlled (in particular, K ₂ O is controlled to 0.20% or less), and the Al ₂ O ₃ —SiO ₂ phase equilibrium diagram shows a fire resistance within −50 ° C. from the liquidus line. Sintered artificial sand constructed to show the degree. In this phase diagram, a composition in which mullite crystallizes is desirable, and a composition in which Al ₂ O ₃ is 40% to 60% is more desirable. Sintered artificial sand production method, which is preferably manufactured by sintering in a rotary kiln after pan mixer granulation. The following bulk specific gravity 1.6 g / cm ^3, especially at 1.515g / cm ³ or less of the weight, an aspect ratio of 0.85 or more spherical, hard particle strength is crushed above 1000 MPa, sintered artificial sand.
[Selection] Figure 1

Description

  The present invention relates to foundry sand used in cast products. Casting products are manufactured about 100 million tons / year worldwide, and about 500 tons / year in Japan. Most of the cast products are iron castings. Foundry sand requires 3 to 10 times the amount to produce a cast product. The foundry sand is used repeatedly, but it adheres to the product in the recovery process or is crushed in the regeneration process, resulting in a loss of 5-30%. These are discarded as industrial waste. In order to reduce loss due to crushing, artificial sand that has been difficult to crush has been developed. However, no countermeasures have been implemented for loss on products. In addition, artificial sand produced by various conventional manufacturing methods has a high bulk specific gravity, and there is a problem that it becomes a heavy muscle work when used as a mold, but no countermeasures have been taken yet.

Since casting sand is a particle aggregate, it can be molded into a mold of any shape, has air permeability to discharge air and gas in the mold when pouring the molten metal into the mold, and can withstand the heat of the molten metal Characteristics such as having fire resistance, no seizure defects due to chemical reaction to various molten metal components, and a granule shape (preferably a true sphere) that can reduce the amount of binder for casting sand as a mold Has a particle strength that can be repeatedly regenerated and used to reduce the environmental load, the mold does not expand at the time of casting, does not cause deformation problems, and the cast product can be easily removed from the mold. These characteristics are necessary for foundry sand.

Molds are roughly divided into molds and sand molds, and foundry sand is for sand molds. Most castings of refractory metals such as cast steel, cast iron and copper alloy are sand molds made of foundry sand. Most cast products are produced in sand molds. Most aluminum alloys that are low melting point alloys are die casting or die casting called gravity casting.

This patent relates to sand foundry for sand molds that have a large production volume.
As the foundry sand, dredged sand which is the origin of the name of the sand mold is most used. Quartz sand is mainly composed of quartz (silica, SiO ₂ ). As the secondary mineral composition, Al ₂ O ₃ —SiO ₂ -based minerals such as feldspar, mica, clay mineral, etc.). Other casting sands other than dredged sand include olivine sand, zircon sand, chromite sand, alumina sand (pulverized type), carbon sand, steel shot balls, silicon carbide sand, slag sand (ferronickel, ferrochrome, blast furnace slag, etc. ), Recently developed artificial sand (mullite, alumina, zircon mix, etc., also called ceramic sand) is used.

Since the foundry sand is a secondary material for producing a cast product, it is first required to be inexpensive, and as a function, it is required to have a high product yield without casting defects during casting. This is a lack of reaction between the foundry sand and the cast product. In addition, since it is an urgent need to realize an environment-adaptive society, it is desired to have high resource savings and high energy savings. Specifically, it is desired that the foundry sand that adheres to the product and is discharged out of the line can be produced, and that the energy consumed in producing the foundry sand can be reduced. Next, high-strength particles that can be regenerated and recovered and used repeatedly and permanently are desired, and it is also desired that free silicic acid generation that is harmful to the human body due to the use of quartz-based cinnabar does not occur. Of course, it is necessary to have various characteristics required for conventional foundry sand. Since the artificial sand was developed around 1990, the above has been generally improved compared to quartz sand, but for permanent use, the molten metal and foundry sand resulting from fire resistance. Measures to prevent reaction and to leak out of the line due to adhesion to the product are still insufficient. In addition, since conventional artificial sand is heavy, it is a heavy work, and measures to reduce the weight of artificial sand are urgently needed.

Patent Document 1 discloses a technique for producing spherical casting sand by sintering a mixed raw material of Al ₂ O ₃ : 20 to 70% and SiO ₂ : 80 to 30% at 1400 to 1750 ° C.
Patent Document 2 discloses a technology for producing synthetic mullite foundry sand having a composition of Al ₂ O ₃ : 40 to 90% and SiO ₂ : 60 to 10% by melting and atomizing the raw material at 1600 to 2200 ° C. Yes.

Patent Document 3 discloses an alumina crystal casting sand manufacturing technique by melting and atomizing an Al ₂ O ₃ —SiO ₂ type raw material such as calcined bauxite.
Patent Document 4 discloses a technique for producing a spherical casting sand in which powder particles are melted by a flame melting method and the weight ratio of Al ₂ O ₃ —SiO ₂ is 1 to 15.

In Patent Document 5, manufactured by a flame melting method, Al ₂ O ₃ and SiO ₂ are the main components, the content of Na ₂ O is 0.1% by weight or less, the content of K ₂ O is 0.3% by weight or less, the content of CaO The amount is 0.5 wt% or less, the MgO content is 0.1 wt% or less, the Fe ₂ O ₃ content is 2 wt% or less, the TiO ₂ content is 5 wt% or less, and the eluted alkali amount is 0.41 μmol / Production techniques are shown which are globular sands that are g or less and are used with urethane binders.

In the above-mentioned patent documents 1 to 4, although it is produced with the composition of the Al ₂ O ₃ —SiO ₂ phase diagram, the idea of controlling the influence of contaminated minerals is not recognized for the fire resistance. Moreover, the idea that the inside of the particle is rough and the particle surface is dense is not recognized. That is, conception of K ₂ O and grain structure present invention controls is not allowed.

In the above-mentioned Patent Document 5, as described in the paragraphs 0004, 0029, 0030, 0044 and the like of the specification, foundry sand that exhibits a pot life extension effect that is a problem specific to a urethane binder is proposed. More specifically, in the case of producing a mold using a urethane binder as in the cold box method, the mold is cured by mixing a phenol resin component and a polyisocyanate component and then venting a gaseous amine. There has been proposed a casting sand that solves the problem that the urethanization reaction gradually proceeds and begins to harden before aeration, and the pot life is shortened. In this Patent Document 5, it is preferable to measure the amount of the eluted alkali that greatly affects the pot life. In particular, it is pointed out that the Ca component has a large influence in the eluted alkali component, and this can be reduced. The content of Na ₂ O and K ₂ O in the casting sand composition is preferably 0.8% by weight or less, more preferably 0.5% by weight or less, and still more preferably 0.3%. It is said that it is less than wt%. In this way Patent Document 5, the relationship between pot life and contaminants, discussed bench life prolongation are urethane binder unique challenges, it is shown the influence of Ca content is large, the K ₂ O As mentioned above, the relationship between metal oxides such as Fe ₂ O ₃ , TiO ₂ , K ₂ O, and Na ₂ O and the eluted alkali is not proved about the role of individual metal oxides, It does not give any suggestion about the relationship with the degree.

In addition, since the foundry sand according to Patent Document 5 is manufactured by the flame melting method, the particles become heavy and not a lightweight particle structure.

JP-A-4-367349 JP 2003-251434 A JP 2005-193267 A Japanese Patent Laid-Open No. 2004-202577 Japanese Patent No. 4877923

An object of the present invention is to provide sintered artificial sand having a function of having a high melting point and hardly reacting with molten iron in sintered artificial sand mainly composed of Al ₂ O ₃ —SiO ₂ .
Another object of the present invention is to provide sintered artificial sand that has high resource-saving properties and excellent energy-saving properties.

Still another object of the present invention is to provide sintered artificial sand that is excellent in handling properties and can reduce heavy reinforcement work.

The present invention relates to improvement of sintered artificial sand containing Al ₂ O ₃ —SiO ₂ and a low melting point composition contained as a contaminant in the raw material, and controls the type and amount of the low melting point composition. By providing the sintered artificial sand configured so that the sintered artificial sand exhibits a fire resistance within minus 50 ° C. from the liquidus line in the Al ₂ O ₃ —SiO ₂ phase equilibrium diagram. It solves the above problems.

The present invention provides a method for producing a sintered artificial sand by sintering a raw material containing a low melting point composition contained as Al ₂ O ₃ and SiO ₂ and impurities, Al ₂ O ₃ -SiO ₂ system Providing a method for producing sintered artificial sand characterized by obtaining sintered artificial sand having a fire resistance within minus 50 ° C. from the liquidus by controlling the amount of the low melting point composition in the phase equilibrium diagram. To do.

In the present invention, the low melting point composition means a composition having a melting point lower than the casting temperature of the metal to be cast (for example, 1550 ° C. in the case of cast steel). This low-melting-point composition exists, for example, as basic oxides or weakly basic oxides as shown in Table 1 in the raw material. Specifically, Na ₂ O, K ₂ O, and FeO may be exemplified. it can.

In particular, K ₂ O has a remarkably low melting point, a large amount is contained as a contaminant in the raw material mineral, and is recognized to have a large melting point lowering effect. By controlling the amount of K ₂ O, it is extremely effective for constructing sintered artificial sand to exhibit a fire resistance within minus 50 ° C. from the liquidus in the Al ₂ O ₃ —SiO ₂ phase equilibrium diagram. The present inventor has found out that the present invention has been completed with this knowledge as a starting point.

In particular, the present invention, in the Al ₂ O ₃ —SiO ₂ phase equilibrium diagram, in the composition in which mullite crystallizes as the primary crystal, by controlling K ₂ O as the low melting point composition to 0.20% or less, Provided is a sintered artificial sand configured such that the sintered artificial sand exhibits a fire resistance within minus 50 ° C. from the liquidus line in the Al ₂ O ₃ —SiO ₂ phase equilibrium diagram.

Sintered artificial sand is characterized in that it has an intercrystalline structure in which there are gaps in the overlap of crystals between mullite crystals. Specifically, as shown in FIG. 3, the sintered artificial sand has gaps derived from the crystal structure of the overlap (alignment structure or card house structure) of columnar crystals of mullite crystals. In the present invention, sintered artificial sand having an intercrystalline structure with a gap derived from the crystal structure is an object.

On the other hand, for example, in artificial sand obtained by a melting method as shown in Patent Document 5, the surroundings of crystals such as mullite are surrounded by an amorphous state, and an amorphous state is formed between mullite crystals. It shows an intercrystalline structure in which the quality exists and there is no overlapping gap (gap derived from the crystal structure) of mullite crystals. As described above, the melt-processed artificial sand has an intercrystalline structure in which amorphous exists between mullite crystals, and thus the bulk specific gravity is increased. In particular, since it has an inter-crystal structure in which there is a gap between overlapping crystals, it can be suppressed to a bulk specific gravity of less than 1.6 g / cm ³ . In particular, by setting the bulk specific gravity to 1.515 g / cm ³ or less, it is effective in releasing from heavy muscle work.

In the Al ₂ O ₃ —SiO ₂ phase equilibrium diagram, the ratio of Al ₂ O ₃ and SiO ₂ is not particularly limited, but the composition of Al ₂ O ₃ is 40% to 60%. Considering the casting temperature of the alloy, it is particularly practical in that it exhibits sufficient heat resistance.

Furthermore, by using spherical sintered artificial sand having an aspect ratio of 0.85 or more, it is advantageous in that the specific surface area is reduced and the strength expression by the binder is increased. Further, by setting the particle strength to 1000 MPa or more, it can be used repeatedly for a long period of time and can provide foundry sand having a low environmental load from the viewpoint of protecting natural resources.

Furthermore, in carrying out the present invention, it is desirable that the particle surface has a fine structure with few voids compared to the inside of the particle. This structure can reduce the amount of binder used in combination with the high sphericity and good particle shape as described above. As a result, it is possible to construct an environment in which there is little thermal decomposition gas of the binder during casting and there is little influence on environmental pollution and the human body.

Since the sintered artificial sand according to the present invention is foundry sand used for casting, a binder is added to form foundry sand, which is molded and used as a mold. There are exceptional molds to which no binder such as reduced pressure or freezing is added, but the sintered artificial sand according to the present invention can also be applied to them.

The present invention was able to provide spherical sintered artificial sand having characteristics that hardly react with molten metal among artificial sand. Specifically, in the Al ₂ O ₃ —SiO ₂ phase equilibrium diagram, the kind and amount of the low melting point composition are controlled so that the sintered artificial sand shows a fire resistance within −50 ° C. from the liquidus. Thus, it has a function that hardly reacts with the iron-based molten metal. Thereby, after casting, it adheres to a cast product, is discharged | emitted out of a line, and the generation amount of the product adhesion sand used as industrial waste can be reduced. Furthermore, seizure defects, which are casting defects due to the reaction between the mold and the molten metal, can be prevented, and the number of casting products discarded as defects can be reduced.

Therefore, the present invention has a high resource-saving property and can reduce the energy consumed when producing the foundry sand, and can provide a sintered artificial sand excellent in energy-saving property. Is.
The present invention provides sintered artificial sand having high heat resistance as described above, and having relatively low specific gravity, excellent handling, and capable of reducing heavy work. It was made.

Further, the sintered artificial sand of the present invention exhibits an intercrystalline structure in which there are overlapping gaps of mullite crystals (gap derived from a fine crystal structure of less than 10 microns existing between crystals). Appropriate voids (voids that have little influence on the strength of the particles and do not cause a problem in practice) are present inside. In carrying out the present invention, since the particle surface can have a fine structure with less voids than the inside of the particle, the sintered artificial sand of the invention is lightweight, The present invention can be carried out even if it has high strength and is not easily crushed.

FIG. ₃ is an Al ₂ O ₃ —SiO ₂ phase equilibrium diagram showing the composition of the present invention. It is explanatory drawing of reaction with the iron-type molten metal which should be solved by this invention, and a casting_mold | template. It is a microscope picture which shows the structure of the sintered artificial sand of this invention. FIG. 2 is an external view of a microstrength tester used for measurement of Example- of the present invention and a conceptual diagram of particle strength measurement. 4 is a graph showing the effect of the effect of the present invention in Table 3 on the fire resistance of K ₂ O in the primary crystal mullite region of the Al ₂ O ₃ —SiO ₂ phase equilibrium diagram. 4 is a graph showing the influence of the effect of the present invention in Table 3 on the fire resistance of K ₂ O in the primary crystal alumina region of the Al ₂ O ₃ —SiO ₂ phase equilibrium diagram. FIG. 3 is a schematic diagram of a mold for casting test pieces (a master test type scoop test piece) for measuring the product adhesion sand used in the evaluation of Example of the present invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Al ₂ O ₃ —SiO ₂ phase equilibrium diagram composition and foundry sand)
In order to use as foundry sand, it is necessary to make it higher than the melting point of the metal to be cast. This is because when the foundry sand reaches the melting point during casting and becomes liquid, it mixes with or reacts with the metal. The metal cast into the sand mold is magnesium (651 ° C), aluminum (660 ° C), copper (1083 ° C), nickel (1455 ° C), iron (1539 ° C), chromium (1900 ° C), for example. is there. Nickel and chromium are alloys of iron as a mother alloy and are close to the melting point of iron. Cast iron is iron plus carbon and silicon, and the lowest melting point is around 1120 ° C.

During casting, the temperature is higher than the melting point to adjust the component of the metal (alloy), and after adjustment of the component, the molten metal treatment process is performed, and the molten metal is cast into the sand mold as a temperature that does not solidify during casting. . This temperature is the casting temperature. Therefore, the casting temperature is a standard for the fire resistance (melting point) required for the foundry sand. The casting temperature of cast iron with the highest production volume is approximately 1340-1440 ° C. The cast steel is approximately 1550-1650 ° C although it varies depending on the material. The aluminum alloy is about 580-680 ° C. Cast steel has the highest reactivity between the molten metal and the sand mold at the highest temperature, and it is essential that the sand mold be coated with a coating mold (fire resistant paint). This coating mold is a countermeasure against chemical seizure defects. Cast iron is basically unnecessary for sand molds that use fine-grained No. 6 sand or more, and sand molds that use coarse-grain No. 5 sand require coating. This coating mold is a countermeasure against physical seizure defects. Aluminum alloys have a low casting temperature, and coating is not necessary in principle.

Considering the casting temperature of the above alloy, it is considered that the casting sand having a melting point having the composition of the Al ₂ O ₃ —SiO ₂ phase equilibrium diagram shows sufficient heat resistance. FIG. 1 shows an Al ₂ O ₃ —SiO ₂ phase equilibrium diagram. The solidus is 1587 ° C. ± 10 ° C. for SiO ₂ + mullite and 1890 ° C. ± 10 ° C. for mullite + Al ₂ O ₃ . As described above, in the case of casting metal, it is only necessary that the mold can withstand the casting temperature of cast steel of 1550 to 1650 ° C. Since the temperature rise during casting of the mold is slightly lower than the casting temperature, Al ₂ O It can be said that the melting point of the artificial sand having the composition of the _3- SiO ₂ phase equilibrium diagram is practically sufficient. In particular, a region in which Al ₂ O ₃ has a composition of 40% to 60% is preferable in practice.
FIG. 1 is an Al ₂ O ₃ —SiO ₂ phase equilibrium diagram according to Akiyoshi Yamaguchi: Alumina-based refractories, present and future (Okayama Ceramics Technology Foundation) (2007) 3.

(Mechanism of reaction between molten metal and foundry sand)
Figure 2 shows the reaction between cast iron and cast steel melt and the mold. This explains the chemical seizure defect among the seizure defects.
First, Fe, Mn, Mg, and the like in the molten metal are oxidized by oxygen in the atmosphere, water vapor in the mold, and the like to form a liquid oxide. SiO ₂ in the mold melts due to the low fire resistance and becomes a liquid. When these oxides are mixed to form a mixed melt, amorphous slag is formed. Furthermore, when the reaction proceeds, it becomes a low-melting substance of firelite, tephrite, and forsterite. The generation of slag and low melting point material causes seizure defects that are casting defects. Also, if it is insignificant, the foundry sand adhering to the product increases and is taken out of the line, increasing industrial waste.

(A substance that lowers the fire resistance of artificial sand having the composition of Al ₂ O ₃ —SiO ₂ phase equilibrium diagram)
Artificial sand with composition of Al ₂ O ₃ -SiO ₂ phase equilibrium phase diagram is prepared by adjusting kaolinite (Al4Si4O10 (OH) 8), a silicate mineral, with alumina (Al ₂ O ₃ ), an oxide mineral. It is common to produce. Industrially, natural minerals such as silicate minerals and oxide minerals are used. Natural minerals include silicate minerals containing alkali metals (Na, K, etc.) and alkaline earth metals (Mg, Ca, etc.) as impurities, and these impurities have a purity of Al ₂ O ₃ —SiO ₂ . It is decreasing.

Table 1 shows the properties and melting points of the oxides.

Silicate minerals consist of acidic oxide silica (SiO ₂ ) and basic oxides MgO, CaO, Na ₂ O, K ₂ O and the like. In Table 1, the melting points of other oxides are also shown. According to this, the oxides lower than the casting temperature of cast steel (approximately 1550 to 1650 ° C) are Na ₂ O (1132 ° C), K ₂ O (490 ° C), and FeO (1377 ° C), especially the melting point of K ₂ O. Is remarkably low. The basic oxides and weakly basic oxides in Table 1 are low melting point compositions having a melting point depressing action in the Al ₂ O ₃ —SiO ₂ phase equilibrium diagram, and among these low melting point compositions, K ₂ O is The melting point lowering action is considered high.

(Necessity of particle strength)
Minerals have an index of hardness expressed by Mohs hardness for each substance. For example, typical minerals of foundry sand are listed below. Anorthite KAlSi ₃ O ₈ (Mohs hardness around 6), iron oxide 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), Zirconium oxide ZrO ₂ (Mohs hardness 6-7), quartz SiO ₂ (Mohs hardness around 7), fused silica SiO ₂ (Mohs hardness around 7), mullite 3Al ₂ O ₃ .2SiO ₂ (Mohs hardness 7.5), alumina corundum Al ₂ O ₃ (Mohs hardness 8-9).

The typical foundry sand is dredged sand, which is composed of quartz and feldspar, so the Mohs hardness is around 6 to around 7. Zircon sand made of zircon oxide and chromite sand made of chromium oxide are considered to be harder in the casting industry than dredged sand, but have a lower Mohs hardness than quartz. Further, typical mullite of artificial sand is harder than quartz and has a Mohs hardness of about 7.5, alumina has a Mohs hardness of 8 to 9, and is harder than quartz. Since mullite and alumina have a particle strength higher than the stress experienced by the foundry sand during the production of the casting, it is a foundry sand that is difficult to crush and is environmentally friendly. On the other hand, cinnabar sand is not environmentally friendly because it crushes 5-30%.

Thus, since mullite and alumina are included in the Al ₂ O ₃ —SiO ₂ phase equilibrium phase diagram, artificial sand is produced according to this phase diagram to make environment-friendly artificial sand that is not easily crushed. be able to.

(Manufacturing method of artificial sand)
Table 2 shows the manufacturing method of artificial sand.

(1) Sintering method This is a method for producing mullite artificial sand produced in Japan and the United States at a production rate of approximately 5 t / year. The inside of the rotary kiln is heated to 1400 ° C to 1700 ° C by a fuel burner. The heating temperature varies depending on the composition. A mixture of SiO ₂ and Al ₂ O ₃ raw materials with reduced alkali components in the ratio of mullite (3Al ₂ O ₃ · 2SiO ₂ ), and granulated fine powder to the size of foundry sand Sinter in a rotary kiln. As shown in Table 2, there are three types of granulation methods, each of which has different particle density and surface condition. In a rotary kiln, mullite is synthesized below the melting point of mullite (about 1850 ° C). Due to industrial constraints, all of the raw materials do not become mullite at the time of synthesis and exist as amorphous. The mullite content, other components, and the amount of amorphous differ depending on the manufacturer. It is desirable to make mullite 85% or more and to make dense particles.

In the sintering method, mullite crystals are precipitated from the granulated particles. The temperature for precipitation is below the melting point of mullite. In this production method, the following two types of voids exist in the particles.
Figure 3 shows two types of voids in sintered artificial sand.

FIG. 3 is a composition image taken at a magnification of 2000 using a high-resolution scanning electron microscope (SEM) for the sintered artificial sand of the present invention. The shooting location is the surface of artificial sand particles. In addition, the surface of the particle in Table 3 to be described later was taken with a low-resolution scanning electron microscope, and the space derived from the columnar mullite crystal and the crystal structure on the surface of the sintered artificial sand can be observed. Compared with this, the surface of the melt-blasted artificial sand is vitrified, and no gap derived from the crystal structure is observed.

The first type of void is a gap derived from the crystal structure described above. Specifically, it is a gap formed between the overlapping (orientation structure or card house structure) of columnar mullite crystals. Since this is a single-micron clearance, there is almost no effect on the strength of the particles, and there is no practical problem. The presence of gaps derived from this crystal structure is a factor that reduces the bulk density of the particles.

The second type of void is a void during sintering. It is a void formed in the particles during sintering due to air, moisture, raw material crystallization water, etc. in the granulated product and gaps due to insufficient compaction of the granulated product. Since the voids during the sintering are several tens of microns or more, the particle strength decreases as the voids during the sintering increase.

As described above, since there are gaps derived from the crystal structure and voids at the time of sintering in this book, the term “void” as used herein includes both gaps derived from the crystal structure and voids at the time of sintering. In the explanation, when distinguishing the two, the gap derived from the crystal structure and the gap during sintering are used properly.
In carrying out the present invention, it is advantageous to produce artificial sand by a sintering method in order to efficiently obtain artificial sand having gaps derived from the crystal structure. As for the granulation method, various granulation methods such as pan mixer granulation method and spray dryer granulation method can be adopted, but by using the pan mixer granulation method, the particle surface is compared with the inside of the particle. It is easy to have a dense structure with few voids, which is advantageous in terms of improving particle strength.

(2) Melt-blasting method The graphite-electrode contact melting method of the melt-blasting method is a method for producing artificial sand with the highest production. The melt-blasting method is also simply called a melting method. Currently, about 10 tons / year seems to be manufactured. This mineral composition is mullite + Al ₂ O ₃ . In FIG. 1, the liquid layer line is higher than that of mullite. The material is Alum Shale (Chinese bauxite containing about 75% Al ₂ O ₃ ). The raw material is put on the graphite electrode and dissolved by Joule heat. Further, since a plasma arc is also generated, the raw material is 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, and is immediately atomized (wind crushing or spray quenching). It becomes spherical particles due to the surface tension of the liquid in the air, and is rapidly cooled to artificial sand. Due to the rapid cooling, the amount that remains amorphous without being crystallized is relatively large.

In the arc furnace melting method, a raw material is charged into a furnace body, and the raw material is melted by arc heat generated by arc discharge between graphite electrodes to form a molten metal. Immediately after tapping, atomize to obtain artificial sand particles. In many cases, the refractory material of the furnace body is cell flying, and the high refractory material can be dissolved without being affected by the melting point of the refractory material. Since the components can be adjusted in the furnace, it is used for the production of artificial sand having high fire resistance of 80% Al ₂ O ₃ and 10% ZrO ₂ . Manufactured in China, production is expected to be about 0.5t / year.

In the molten air crushing method, since the temperature is higher than the liquidus line of mullite, mullite and alumina become liquid. Crystals crystallize from the liquid and become amorphous when not crystallized due to rapid cooling. Most products are surrounded by an amorphous material and there is no single-micron to sub-micron clearance between sintered crystals. Thereby, bulk specific gravity becomes large. Further, there are no voids due to gas of micron or more, or when there are bubbles, bubbles are caused by gas entrainment.

(3) In-flame melting method This is also produced in China, and the production volume is expected to be about 0.5t / year. The in-flame melting method is also simply referred to as a melting method, similar to the melt-blown method. Raw material particles granulated or crushed to a predetermined size in a flame of approximately 3000 ° C using a pure oxygen combustion burner are put into the flame from the direction of fuel spray, and the particles are melted in the flame and spherical by surface tension. It is a manufacturing method in which particles are formed into spherical artificial sand by crystallization during cooling after passing through a flame. Artificial sands such as mullite, alumina, mullite + cristobalite are manufactured. Compared to the sintering method, it is easy to produce dense particles. Crystallization and amorphization differ depending on the residence state in the flame and the cooling state after passage. If anything, it is mostly amorphous. By utilizing this, it is possible to produce amorphous silica having a high fire resistance and a stable phase.

In order to melt above the liquidus, the particles are almost identical to the melt-blown method. There is no single micron to submicron clearance between crystals. Thereby, bulk specific gravity becomes large. However, in order to spray the inside of the flame, bubbles are likely to be generated by entrainment of air, but it does not form a uniform gap as in the sintering method.

(Necessity of foundry sand with good grain shape)
Table 3 shows the grain shape and angle of repose of dredged sand and artificial sand.

Among the dredged sands, three kinds of Australian dredged sand with good grain shape, sintered artificial sand and melt-blasted artificial sand are shown in comparison. Artificial sand is compared to dredged sand and the particle shape is close to a sphere. In the sintering method, the particles are granulated and then sintered to obtain a further spherical shape. The sintered artificial sand according to the present invention preferably has a spherical shape with an aspect ratio of 0.85 or more. In the melt-blasting method, the refractory raw material is melted to form a liquid, and is made spherical by surface tension. Since it is spherical, the specific surface area is reduced, and the strength expression by the binder described later is increased. The melt-blasting method is closest to the true sphere, the particle surface is smooth, and there are no porous parts.

Sintered artificial sand has fine porous parts as shown in the SEM image of the particle surface in Table 3, which continues to the inside. The surface of the cinnabar is also observed, but this is only the surface and the inside is not porous.
In addition, the angle of repose of artificial sand decreases in the order of sintered artificial sand and melt-blasted artificial sand. Thereby, fluidity | liquidity of casting sand and the filling as a casting_mold | template become favorable.

(Coating mold for physical seizure countermeasures, coating mold for chemical seizure defects)
Whether or not to apply the coating mold is determined from two viewpoints of countermeasures for physical seizure defects and chemical seizure defects. When producing large castings, in order to replace the gas in the mold with the molten metal, the particle size is increased to ensure sand-type air permeability. At this time, the coating mold for preventing physical seizure defects prevents the molten metal from physically penetrating into the sand grain gap. Therefore, in the sintered artificial sand according to the present invention, if the particle size is increased, a coating mold for countermeasures against physical seizure defects is required.

The coating mold for seizure defects caused by the chemical reaction between the molten metal and the mold is a coating mold for preventing the reaction between the sand mold and the molten metal. In order for the sand mold and the molten metal to react, both must be liquid. The molten metal is liquid. The fact that the sand mold becomes liquid means that the foundry sand has been melted by the heat of the molten metal. Since the present invention provides casting sand made of fire-resistant sintered artificial sand that has no chemical seizure defects and does not melt even with the heat of the molten metal, a coating mold for countermeasures against chemical seizure defects becomes unnecessary. .

(Particle size adjustment)
Since the present invention is related to foundry sand, it is desirable to adjust the particle size to a particle size range of 20 to 1200 microns. Generally, 106-600 microns are used as foundry sand. The relatively small mass-produced castings produced in green molds are mainly founded in 150-300 micron foundry sand. The relatively large castings produced with self-hardening molds etc. are mainly foundry sand of 300 to 600 microns. The V process is around 106 microns. In addition, 20 to 106 microns are called fine sand and used as an additive for auxiliary particle size adjustment of foundry sand. 850-1200 microns are used for backup and back sand. In this way, foundry sand has different particle sizes used depending on the molding process.

(Casting sand and mold)
Since the sintered artificial sand according to the present invention is foundry sand used for casting, the foundry sand can be obtained by adding other substances such as a binder according to a conventional method. And the casting sand obtained can be shape | molded and a casting_mold | template can be manufactured, and it is used for casting of various metals. There are exceptional casting sands and molds to which no binder such as reduced pressure or freezing is added, but the sintered artificial sand according to the present invention can also be applied to these.

In the examples described later, evaluation as casting sand (particle strength, particle shape, fire resistance, etc.) and evaluation as a mold (product adhesion sand, presence of casting defects) are also shown. Cast products were most produced from green sand (bentonite as a binder) among the foundry sands, so the cast was evaluated as green.

(Measurement method of porosity)
As for the porosity of the particles, particles classified to 70 mesh (212 microns) were placed horizontally, and the resin was buried thereon, and the particles were polished by about 106 microns to obtain a cross section at the center of the particles. Next, a composition image was taken with a scanning electron microscope. About 10 grains of particles were divided into cavities and a particle matrix by black and white binarization, and the porosity was set to the black ratio. Note that the black on the outer periphery of the particles and the black due to noise were removed manually.

When photographing sand grains, observe about 100 particles at a magnification of 40 times to confirm the presence of voids, and for particles with average voids, take a composition image at a magnification of 250 times, and binarize the voids. The rate was determined. At 250x magnification, mullite columnar crystals cannot be photographed due to resolution. That is, in the scanning electron microscope at this magnification, it is difficult to photograph nano-unit voids, and therefore the ratio of the voids at the time of sintering among the voids derived from the crystal structure and the voids at the time of sintering becomes the void ratio. In addition, since there are particles without voids in the melting method and voids are also generated by entraining bubbles, the ratio was determined separately for “particles without voids” and “bubble entrained particles”. The porosity is not calculated because average particles could not be found due to the presence of void-free particles.

(Measurement method of bulk specific gravity)
The bulk specific gravity is measured according to the “S-10 Foundry Sand Fillability (Bulk Specific Gravity) Test Method” defined in the “Test Method for Molds and Mold Materials” issued in May 1999 by the Small and Medium Business Corporation. Measured. A different point is an input container, which uses Ford cup # 4 defined in "S-5 foundry sand fluidity test method". That is, simultaneous measurement of bulk specific gravity and fluidity.
In the bulk specific gravity, the bulk specific gravity tends to decrease as the number of voids including both the gap derived from the crystal structure and the void during sintering is increased regardless of the void structure.

(Measurement method of particle strength)
FIG. 4 shows an external view of a micro strength tester and a conceptual diagram of particle strength measurement. The tester used was an electromagnetic force type microstrength tester (hereinafter, microstrength tester). The maximum load capacity was 50N, and the load was applied at a constant displacement speed of 1mm / min. The particle strength of each sample was photographed with a microscope to determine the major axis and minor axis, and the maximum breaking load was measured using a micro strength tester.

In order to obtain the particle strength from the maximum breaking load, it is necessary to know the cross-sectional area of the sample particle. 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, the contact area is not constant. Therefore, this report uses a method of calculating the compressive strength by obtaining the cross-sectional area assuming that the sample particle is an ellipsoid. The major axis (2a) and minor axis (2b) of the foundry sand particles were measured from micrographs. The casting sand particle height (2c) and the position of the pressure plate at the time of fracture (2c-2d) are readings of the microstrength meter. The particle strength (σK) was calculated as follows.
σK = P / S
Here, σK: particle strength, P: fracture load, S: ellipsoidal cross-sectional area (estimated contact area between pressure plate and particle) at displacement d.

(Artificial sand, silica sand particle strength, aspect ratio, micrograph)
Table 4 (a) and Table 4 (b) describe that artificial sand has less industrial waste during repeated use compared to dredged sand and that the amount of binder added is good for the environment.

As described above, since the sintered foundry sand according to the embodiment of the present invention has a function that hardly reacts with the molten cast iron, the amount of product-attached sand that adheres to the cast product after casting and is discharged out of the line. Can reduce industrial waste, reduce casting defects due to reaction with molten metal, improve product yield, reduce weight, reduce heavy-bar work, and caking due to good grain shape. It has various advantages such as a reduction in the amount of additive added and a reduction in the amount of crushed and industrial waste due to its high particle strength. The present invention is described below by way of example, but the present invention should not be understood as being limited to these examples.

(Examples 1 to 5)
Examples 1 to 5 were manufactured by a sintering method (pan mixer granulation method), and were manufactured by combining high-purity kaolinite and high-purity alumina and controlling K ₂ O to 0.20% or less. is there.

Specifically, a high-purity kaolinite ore having a low K ₂ O content is used as a contaminant, finely pulverized after the beneficiation and calcination, to form a slurry, and dried and adjusted with a spray dryer to obtain particles. These particles are not dense and the surface is not smooth. Next, a fine and smooth particle size is granulated to about 100 to 300 μm with a pan mixer. Subsequently, it was fired in a predetermined range of 1350 ° C. to 1850 ° C. for 1 to 3 hours using a rotary kiln to obtain silica + mullite-based sintered artificial sand. The firing temperature and firing time are conditions for generating mullite. After cooling, the particles are classified so that they can be used for casting. In the following Examples, the ingredients are different, but the production method is the same. Since the temperature at which mullite is generated from kaolinite or the like is about 1000 ° C., the same sintered artificial sand can be produced by extending the firing time even at a temperature lower than that of this example.

The detailed chemical components of Examples-1 to 5 are shown in Table 5, but in the sintered artificial sand of Example-1, SiO ₂ : 51.4%, Al ₂ O ₃ : 40.7%, K ₂ O: 0.09% is there. As shown in Table 4 above, the porosity is 2.6%, the aspect ratio is 0.906, the bulk specific gravity is 1.502 g / cm ³ , the particle strength is 1565 MPa, and the aspect ratio is 0.91. Although it has fine voids inside, the particle surface is dense and light and extremely hard spherical sintered artificial sand.

Example -2, the content of K ₂ O with low purity kaolinite ore of Example -1, a blend of high-purity alumina flour is obtained by adjusting the Al ₂ O ₃ -SiO _2. The chemical components are shown in Table 5 and are SiO ₂ : 44.3%, Al ₂ O ₃ : 49.8%, K ₂ O: 0.11%. As shown in Table 4, it is a lightweight and extremely hard spherical artificial sand having a porosity of 2.1%, an aspect ratio of 0.886, a bulk density of 1.499 g / cm ³ , a particle strength of 1671 MPa, and an aspect ratio of 0.89.

Examples-3 to 5 were also obtained by the same production method as in Example-2, and were obtained by slightly increasing K ₂ O using alumina flour having a low purity. Table 5 shows each chemical component.

(Comparative Examples-1 to 6)
Comparative Examples-1 to 3 are sintered artificial sand as in Examples-1 and 2. Comparative Examples 4 to 6 are fused artificial sand, Comparative Examples 4 and 5 are melt pulverization methods, and Comparative Example 6 is a flame melting method. These chemical components are shown in Table 5.

Comparative Example-1 is mullite artificial sand produced by the sintering method (spray dryer granulation method) shown in Table 2, and is commercially available. The detailed chemical components of Comparative Example-1 are shown in Table 5, and are SiO ₂ : 37.5%, Al ₂ O ₃ : 55.8%, K ₂ O: 0.23%. The porosity is 16.7%, the aspect ratio is 0.834, the bulk specific gravity is 1.534 g / cm ³ , and the particle strength is 955 MPa. The porosity is high compared to Examples 1 and 2. The aspect ratio is 0.850 or less, and the particle shape is bad. Moreover, since the particle | grain surface is not precise | minute, the space | gap is open | released outside. For this reason, the particle strength is lower than in Examples 1 and 2. Moreover, despite the high porosity, the bulk specific gravity is as high as 1.534 g / cm ³ . This is considered to be due to the influence of a large specific gravity of Al ₂ O ₃ compared to SiO ₂ and the small single-micron clearance of mullite crystals.

Comparative Example-2 is mullite artificial sand produced by a sintering method (spray dryer granulation method) as in Comparative Example-1, and is commercially available. The detailed chemical components of Comparative Example-2 are shown in Table 5, and are SiO ₂ : 37.0%, Al ₂ O ₃ : 56.3%, and K ₂ O: 0.24%. The porosity is 9.8%, the aspect ratio is 0.820, the bulk specific gravity is 1.533 g / cm ³ , and the particle strength is 836 MPa. Similar to Comparative Example-1, compared with Examples 1 and 2, the particle shape is poor, the particle strength is low, and the bulk specific gravity is heavy (see Table 4).

Comparative Example-3 is the same production method as Comparative Examples-1 and 2, and the surface grinding process was added to the final process to improve the grain shape and the like. _{SiO 2: 39.8%, Al 2} O 3: 57.8%, K 2 O: 0.17%. The porosity is 9.6%, the aspect ratio is 0.867, the bulk specific gravity is 1.619 g / cm ³ , and the particle strength is 1124 MPa. Although K ₂ O is low and the fire resistance is expected to be good, the bulk specific gravity is heavy and not lightweight. Also, the particle strength is low.

Comparative Example 4 is mullite + alumina-based fused artificial sand produced by the melt-blasting method (graphite electrode contact melting method) shown in Table 2. The detailed chemical components of Comparative Example-4 are shown in Table 5, and are SiO ₂ : 19.0%, Al ₂ O ₃ : 71.5%, K ₂ O: 0.35%. As for the porosity, particles without voids and particles with voids were mixed, and the ratio was 59:41. It is a void by air entrainment and is different in shape from the void of sintered artificial sand. The porosity is not measured because it varies greatly depending on the particles. The aspect ratio is 0.925, the bulk specific gravity is 1.940 g / cm ³ , and the particle strength is 1433 MPa. The bulk specific gravity is extremely heavy because it is manufactured by the melting method.

Comparative Example-5 is mullite + alumina-based fused artificial sand produced by a melt-blasting method (graphite electrode contact melting method). The detailed chemical components of Comparative Example-5 are shown in Table 5, and are SiO ₂ : 19.4%, Al ₂ O ₃ : 68.6%, and K ₂ O: 1.16%. As for the porosity, particles without voids and particles with voids were mixed, and the ratio was 82:18. It is a void by air entrainment and is different in shape from the void of sintered artificial sand. The porosity is not measured because it varies greatly depending on the particles. The aspect ratio is 0.929, the bulk specific gravity is 1.942 g / cm ³ , and the particle strength is 1425 MPa. The bulk specific gravity is extremely heavy because it is manufactured by the melting method.

Comparative Example 6 is mullite + alumina-based fused artificial sand produced by melting in a flame. SiO ₂ : 33.1%, Al ₂ O ₃ : 58.9%, K ₂ O: 0.29%. As for the porosity, particles without voids and particles with voids were mixed, and the ratio was 38:62. It is a void by air entrainment and is different in shape from the void of sintered artificial sand. The porosity is not measured because it varies greatly depending on the particles. The in-flame melting method has more bubbles entrained particles than the melt-blown method in order to melt the particles in the combustion gas having a large gas phase. The aspect ratio is 0.941, the bulk density is 1.680 g / cm ³ , and the particle strength is 2175 MPa. Since it was manufactured by the melting method, the bulk specific gravity is 1.1 times or more heavier than the product of the present invention.

(Relationship between K ₂ O and “Difference between liquidus temperature and melting temperature”)
Although artificial sand is said to be good for the environment, it is described below that the fire resistance decreases due to the composition of artificial sand and there are bad conditions for the environment.

Table 5 shows the relationship between K ₂ O and “difference between liquidus temperature and melting temperature”. In FIG. 1, the liquidus temperature is the temperature of the liquidus at which primary silica, primary mullite, and primary alumina crystallize from the liquid phase. The liquidus temperature (Y1) of primary mullite and the corrected Al ₂ O ₃ concentration (X) were defined as equation (1). The liquidus temperature (Y2) of primary crystal alumina and the corrected Al ₂ O ₃ concentration (X) were defined as equation (2). The corrected Al ₂ O ₃ concentration is the value of Al ₂ O ₃ when other components are removed so that the total of SiO ₂ and Al ₂ O ₃ in the chemical component becomes 100. Since the Al ₂ O ₃ —SiO ₂ phase equilibrium diagram of FIG. 1 has two components, the liquidus temperature can be calculated from the corrected Al ₂ O ₃ concentration.

Y ₁ = -0.0811X ² + 11.172X + 1501.0 ... (1)
Y ₂ = -0.5307X ² + 101.87X-2745.2 ... (2)
In addition, the fire resistance test of the example and the comparative example was performed based on JIS R 2204: 1999 “Method for testing the fire resistance of refractories and refractory materials”, and the fire resistance (SK number) was measured. The melting temperature was determined from the relationship between the SK number of JIS R 8101: 1999 “Standard cone for fire resistance test” and the melting temperature.

(Difference between liquidus line temperature and melting temperature of Examples-1 to 5)
The production method of Examples-1 to 5 is the above-described sintering method (pan mixer granulation method), and produced by combining high-purity kaolinite and high-purity alumina and controlling K ₂ O to 0.20% or less. The fire resistance was measured and the melting temperature was determined. In addition, the composition of each chemical component is quantified by fluorescent X-rays, the corrected Al ₂ O ₃ concentration is calculated from the actual measured values of SiO ₂ and Al ₂ O ₃ , and the melting temperature is calculated from Equation (1) and Equation (2). Calculated. The quantitative value of fluorescent X-ray is calibrated by the quantitative value of wet analysis. In the relationship between the liquidus temperature and the melting temperature in Examples-1 to 5, the melting temperature is lower than the liquidus temperature. It can be said that this is a factor that lowers the fire resistance. However, the difference between the liquidus temperature and the melting temperature in Examples 1 to 5 is 11.3 ° C. to 38.6 ° C., and is within 50 ° C.

(Difference between liquidus line temperature and melting temperature of comparative example)
Comparative Examples 1 and 6 to 11 are mullite artificial sand produced by a sintering method (spray dryer granulation method). The composition is such that the primary crystal is mullite. In these comparative examples, K ₂ O is in the range of 0.23% to 0.80%, and the amount of K ₂ O is larger than that in the example. The melting temperature was calculated from equation (1). Compared with Example-, the melting temperature of these comparative examples is greatly lowered from the liquidus temperature, and there is a difference of 54.0 ° C to 174.9 ° C. Therefore, it can be said that the fire resistance performance predicted in the Al ₂ O ₃ —SiO ₂ phase equilibrium diagram is not expressed.

Comparative Example-2, Comparative Example-14, and Comparative Example-15 are mullite + alumina artificial sand produced by the melt-blasting method (graphite electrode contact melting method). The primary crystal is alumina. In these comparative examples, K ₂ O is in the range of 0.0.35% to 1.48%, and the amount of K ₂ O is larger than in the examples. The melting temperature was calculated by equation (2). Compared with the Examples, the melting temperature of these Comparative Examples is greatly lowered from the liquidus temperature, and a difference of 140.1 ° C. to 224.6 ° C. is generated. Therefore, it can be said that the fire resistance performance predicted in the Al ₂ O ₃ —SiO ₂ phase equilibrium diagram is not expressed.

(Influence on fire resistance of K ₂ O in primary mullite and primary alumina regions)
FIG. 5A shows a graph for clarifying the influence of K ₂ O on the fire resistance in the primary crystal mullite region and FIG. 5B in the primary crystal alumina region. The primary crystal mullite region and primary crystal alumina region are shown separately because the influence of K ₂ O is different. According to this, the liquidus temperature in the primary crystal mullite zone -熔倒temperature [Delta] Y _1, liquidus temperature in the primary crystal alumina zone - the熔倒temperature and [Delta] Y _2, when the K ₂ O content and K, respectively, It is represented by Formula (3) and Formula (4). Both are significant positive correlations with a risk factor of 1% or less. When K ₂ O increases, the difference between the liquidus temperature and the melting temperature increases, and the fire resistance decreases.
ΔY ₁ = 215.7K + 6.755 (3)
ΔY ₂ = 74.13K + 113.99 ... (4)

(Schematic diagram of mold (special test sample scoop test piece))
The effect of the present invention was determined by casting a cast iron melt with a master craft type scoop test piece shown in FIG. A flake graphite cast iron equivalent to FC250 was cast at about 1400 ° C under the conditions of a test piece weight of 6.5 kg, a casting weight of 7.5 kg, and a green mold weight of 21.5 kg. The green mold was produced by adding 8 parts of Wyoming bentonite to 100 parts of foundry sand, adding water to obtain a compactability value of approximately 40%, and kneading sand to form a green mold. The evaluation was the amount of sand adhering to the product and the presence or absence of casting defects.

Table 6 shows the results of the casting test using this casting test piece.

(Weight of sand adhering to the cast specimen)
Example-1 Example-2
In Example 1, K ₂ O was 0.09%, and the adhered sand immediately after the mold breaking was 63.1 g. The adhered sand was almost removed by the shot and remained in the product very slightly. The attached sand removed by the shot is discarded as industrial waste. As for the casting defect, the adherend was adhered to the concave portion of the product immediately after the mold breakage, but the sintered product was peeled off by the shot, and no casting defect occurred.

In Example-2, K ₂ O was 0.11%, and the adhered sand immediately after mold breaking was 22.9 g. This adhered sand was completely removed by the shot and did not remain in the product. The casting surface of the product was good and no casting defects occurred. Example -2 is given to good product casting but K ₂ O is greater than in Example 1, the high Al ₂ O _3, it is believed to contribute a high liquidus temperature.

Comparative Example-2, Comparative Example-4
In Comparative Example-2, K ₂ O was 0.24%, and the adhered sand immediately after the mold breaking was 196.5 g. The adhered sand was almost removed by the shot and remained in the product very slightly. As for the casting defect, the deposit was adhered to the concave portion of the product and its vicinity immediately after the mold breakage, but the sintered product was peeled off by the shot, and no casting defect occurred.

In Comparative Example-4, K ₂ O was 0.35%, and the adhered sand immediately after mold breaking was 121.8 g. This adhered sand was completely removed by the shot and did not remain in the product. The casting surface of the product had a slight amount of sand particles, and the casting surface was in a slightly bad state. However, it is not a casting defect.

Comparative Example-14, Comparative Example-15, Comparative Example-16
In Comparative Examples -14 to 16, cinnabar sand most frequently used as a mold was cast for comparison. These are cinnabar sand made of quartz or feldspar, and not the composition of the Al ₂ O ₃ —SiO ₂ phase equilibrium diagram. Comparative Example-14 is a high-purity cinnabar with a lot of quartz, and feldspar increases according to Comparative Examples-15 and 16. The adhering sand was 375.2 g, 284.1 g, and 415.2 g, respectively, which was much more adhering than the artificial sands of Examples-1 and 2 and Comparative Examples-2 and 4. This adhered sand was sintered and adhered to the product even after the shot. In addition, all three products were scraped and had defects.

(SEM / EDS analysis of sintered products)
In order to clarify the relationship between the amount of adhering sand and K ₂ O, the portion of the sand adhering to the product facing the product was analyzed by a scanning electron microscope (SEM / EDS) with an energy dispersive X-ray analyzer. The product side of the adhered sand is sintered into a thin sintered product. This is the result of iron diffusing into the mold layer during casting. The thickness of the sintered product is proportional to the amount of adhered sand.

K was not detected in the EDS analysis of the sintered products of Examples 1 and 2. K was detected in the EDS analysis of the sintered products of Comparative Examples-2, 4, and 16. Each analysis position is a contact point between sand grains. The melting point of the mold surface due to the heat of the cast iron melt and the diffusion of Fe from the cast iron produce the low-melting substances such as phi-flight, tephroite, and forsterite as shown in FIG. . These low-melting-point substances become a sand grain adhesive and form a sintered layer. In Examples 1 and 2 where K is not present (below the detection limit), the sintered product is thin and there is little adhered sand.

Table 7 shows the results of the casting test using this casting test piece.

(Characteristic evaluation with shell mold, furan mold, alkali phenol mold)
Tables 8 (a), (b), and (c) show the mold characteristics of the sintered artificial sand shell mold, furan mold, and alkali phenol mold of the present invention.

Although the binder was added to the sand weight, the bulk specific gravity is different, so data converted per volume is also attached. Example-1 and Example-2 are sintered artificial sand of the present invention. Comparative Example-1 is a sintered artificial sand having a high porosity that is sold in the market. Comparative Example 4 is an artificial sand obtained by the melt-blasting method. Comparative Example 14 is high-purity cinnabar, which exhibits high mold strength in cinnabar.

The flexural strength considering bulk specific gravity of the shell mold in Table 8 (a) in Example 1 Example -2, Comparative Example 1, the artificial sand of Comparative Example -4 substantially in the range of 111.4~122.2kg / cm ² It has the same strength and is stronger than the high purity cinnabar of Comparative Example-14. Therefore, it can be said that the present invention has strength characteristics equivalent to artificial sand sold in the market.

In the compressive strength after 24 hours considering the bulk specific gravity of the furan mold in Table 8 (b), Example-1 of the present invention had the highest strength, and then Example-2 had almost the same strength as Comparative Example-1. It is. Therefore, the furan mold characteristics of the product of the present invention are good. In general, sintered artificial sand adsorbs furan resin and acid hardener, which are liquid binders, and has low strength expression, but Comparative Example-1 is a sintered material developed for furan resin. Artificial sand with high strength. The same applies to the product of the present invention.

With regard to the compressive strength after 24 hours considering the bulk specific gravity of the alkali phenol mold in Table 8 (c), the melt-pulverized artificial sand of Comparative Example-4 is the best, followed by the high-purity dredged sand of Comparative Example-14. The alkali phenol resin used is for general cinnabar. Example-1 Example-2 and Comparative Example-1 of sintered artificial sand have almost the same strength, and are in the order of Example-1 Example-2 and Comparative Example-1. Sintered artificial sand has a slightly lower strength than the alkali phenol mold, but the difference is small compared to Comparative Example-4 and Comparative Example-14, and it can be sufficiently used as a mold. Moreover, since the alkali phenol resin for artificial sand is marketed, strength improvement is possible using this.

According to Tables 8 (a) to (c), the product of the present invention can be used as a casting mold (main mold) in a furan mold that is used in the second largest amount next to the green mold, and then in a large amount of alkali phenol mold. It can also be used as a shell mold that is often used as a core in a raw (main) combination.

It can be used for foundry sand that is repeatedly collected and used as a casting mold. Since it is lightweight and has high particle strength, it can be applied to all foundry sands. The most popular green molds, followed by the most self-hardening molds, are furan molds and alkali phenol molds. These molds are particularly suitable for casting the most prolific iron castings. Yes. By controlling the type and amount of the low melting point composition, such as controlling K ₂ O to 0.20% or less, there is no reaction between the molten metal and the mold, and it adheres to the product and cast sand is taken out to the shot line. Foundry sand cannot be used as foundry sand by being mixed with steel shots or metal components (castings) and is discarded as industrial waste. In the present invention, this amount is drastically reduced. In addition, the yield of products is improved by reducing chemical seizure defects due to the reaction between the molten metal and the mold. The defective product is redissolved as a return material, and this energy cost is reduced.

In addition to the fact that the mold does not react with the molten metal, the green mold, self-hardening mold, and water glass-based inorganic mold, which is expected to generate no harmful gases in the future, will contain a binder in the recovered sand recycling process. Strong mechanical polishing that peels off is necessary, and conventional foundry sand is crushed into industrial waste. It can be used without being pulverized due to the high particle strength of the present invention.

Claims (6)

In sintered artificial sand containing Al ₂ O ₃ and SiO ₂ as raw materials and containing a low melting point composition contained as a contaminant in the raw materials,
In the Al ₂ O ₃ —SiO ₂ phase equilibrium diagram, in the composition in which mullite crystals are crystallized as primary crystals, K ₂ O as the low melting point composition is 0.20% or less,
It has an intercrystal structure in which there is a gap between overlapping crystals between the mullite crystals,
Less than a bulk ratio 1.6g / cm ^3, and an aspect ratio of 0.85 or more,
Sintered artificial sand characterized by having a fire resistance of minus 50 ° C. or less from the liquidus in the Al ₂ O ₃ —SiO ₂ phase equilibrium diagram. _{2. The} sintered artificial sand according to claim 1, wherein Al ₂ O ₃ has a composition of 40% to 60% in the Al ₂ O ₃ —SiO ₂ phase equilibrium diagram. ^{3. The} sintered artificial sand according to claim 1, wherein the bulk specific gravity is 1.515 g / cm ³ or less and the particle strength is 1000 MPa or more. Casting sand containing the sintered artificial sand according to any one of claims 1 to 3. The casting_mold | template containing the sintered artificial sand in any one of Claims 1-3. In a method for producing sintered artificial sand by sintering raw materials containing Al ₂ O ₃ and SiO ₂ and a low melting point composition contained as a contaminant,
In Al ₂ O ₃ -SiO ₂ system phase diagram, the by controlling the amount of low melting point composition, sintering, characterized in that to obtain a sintered artificial sand according to any one of claims 1 to 3 A method for producing artificial sand.