JP2019089124A - 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 Al2O3-SiO2. SOLUTION: The composition and amount of the low melting point composition are controlled (particularly, K2O is controlled to 0.20% or less), and the Al2O3-SiO2 phase equilibrium diagram shows the fire resistance within minus 50 ° C from the liquidus line. To do. In this phase diagram, a composition in which mullite crystallizes is desirable, and a composition in which Al2O3 is 40% to 60% is more desirable. As a manufacturing method of sintered artificial sand, it is desirable to manufacture by sintering in a rotary kiln after granulation of pan mixer. Sintered artificial sand is lightweight with a bulk specific gravity of 1.6 g / cm3 or less, particularly 1.515 g / cm3 or less, is spherical with an aspect ratio of 0.85 or more, and has a particle strength of 1000 MPa or more and is not easily crushed. [Selection] Figure 1

Description

  The present invention relates to foundry sand used in cast products. Foundry products are produced about 100 million tons a year worldwide, and about 500 tons a year in Japan. Most of the cast products are iron castings. Foundry sand requires 3 to 10 times the amount to produce cast products. Foundry sand is used repeatedly, but it adheres to the product in the recovery process and is crushed in the regeneration process, resulting in a loss of 5 to 30%. These are discarded as industrial waste. In order to reduce the loss caused by crushing, artificial sand that is hard to be crushed has been developed. However, measures against the loss attached to the product have not been implemented. In addition, artificial sand by various conventional manufacturing methods has a large bulk specific gravity, and there is a problem that it becomes a heavy streak operation when it is used as a mold, but the countermeasure for this has not been implemented.

Foundry sand can be formed into a mold having an arbitrary shape because it is a particle aggregate, has ventilation to discharge air and gas in the mold when pouring molten metal into the mold, can withstand the heat of the molten metal Properties such as having a fire resistance, not causing seizure defects due to chemical reaction to various molten metal components, and capable of reducing the amount of caking agent for using casting sand as a mold (a true ball is desirable) Having particle strength that can reduce environmental impact by repeatedly using it repeatedly, having low mold expansion during casting and no deformation problems, easy removal of the cast product from the mold, etc. Such characteristics are necessary for casting sand.

Molds are roughly divided into molds and sand molds, and casting sand is for sand molds. The casting of high melting point metals such as cast steel, cast iron and copper alloy is mostly sand mold by casting sand. Most of the cast products are produced in sand molds. In aluminum alloys which are low melting point alloys, most of them are die casting called die casting or gravity casting.

This patent relates to casting sand for sand molds with large scale production.
Foundry sand is most often borax, from which the name of the sand mold is derived. Borax is mainly composed of quartz (silica, SiO ₂ ). As a secondary mineral composition is Al ₂ O ₃ -SiO ₂ -based mineral in which feldspar, mica, clay minerals, etc.). In addition, as casting sand other than borax, olivine sand, zircon sand, chromite sand, alumina sand (grind type), carbon sand, steel shot ball, silicon carbide sand, slag sand (ferro nickel base, ferrochrome base, blast furnace slag base etc. Recently, artificial sand (mullite type, alumina type, zircon mix type, etc., also referred to as ceramic sand), etc. are used.

Since casting sand is a secondary material for producing castings, it is first required to be inexpensive, and first of all, it is required that there is no casting defect at the time of casting and high product retention. This is that there is no reaction between the casting sand and the casting. In addition, because environmental adaptation-oriented society is urgently needed, it is desirable that the resource saving property is high and the energy saving property is high. Specifically, it is desirable to be able to deposit sand that adheres to the product and is discharged out of the line, and to reduce the energy consumed when producing the foundry sand. Then, high-strength particles that can be regenerated and recovered and used repeatedly and permanently are desired, and it is also desired that the generation of free silicic acid does not occur adversely to the human body accompanying the use of quartz-based borax. Also, of course, it is necessary to have various characteristics required for the conventional casting sand. Although artificial sand was developed around 1990, the above has generally been improved compared to quartz sand, but for permanent use it is the molten metal and casting sand due to fire resistance In addition, the measures for preventing reaction and for adhering to the product and flowing out of the line are still insufficient. In addition, since conventional artificial sand is heavy, it is necessary to perform heavy reinforcement work, and measures to reduce the weight of artificial sand are urgently needed.

In Patent Document 1, 1,400 to 1,750 ° C. in _{Al 2 O 3: 20~70%,} SiO 2: a 80 to 30% of the raw material mixture is sintered, spherical molding sand production art is shown.
In Patent Document 2, by melting and atomizing the raw material at 1600 to 2200 ° C., a synthetic mullite foundry sand manufacturing technology of a composition of Al ₂ O ₃ : 40 to 90% and SiO ₂ : 60 to 10% is shown There is.

In Patent Document 3, the alumina crystal casting sand production art is shown by atomizing by melting Al ₂ O ₃ -SiO ₂ -based material, such as calcined bauxite.
Patent Document 4 discloses a spherical casting sand production technique 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, produced by the flame fusion method, Al ₂ O ₃ and SiO ₂ is the Na ₂ O content in the main component 0.1 wt% or less, the content of K ₂ O is 0.3 wt% or less, containing CaO Content is 0.5 wt% or less, the content of MgO is 0.1 wt% or less, the content of Fe ₂ O ₃ is 2 wt% or less, the content of TiO ₂ is 5 wt% or less, and the amount of dissolved alkali is 0.41 μmol / l The production technique is shown as spherical casting sand which is less than g and is used with a urethane binder.

Are those prepared with the composition of Patent Documents 1 to 4 in Al ₂ O ₃ -SiO _2-phase phase diagram above, but is not recognized concept of controlling the effect of contaminating mineral for refractoriness. Further, the idea that the inside of the particle is rough and the surface of the particle is compact is not recognized. That is, the idea about K ₂ O or particle structure controlled by the present invention is not recognized.

In Patent Document 5 described above, as described in the specification paragraphs 0004, 0029, 0030, 0044, etc., a casting sand exhibiting a pot life extending effect which is a problem unique to urethane binders is proposed. More specifically, in the case of producing a mold using a urethane binder as in the cold box method, after mixing a phenol resin component and a polyisocyanate component, the mold is cured by aerating a gaseous amine, but the amine is The casting sand which solved the subject that a urethane-forming reaction may advance gradually and may start to harden before ventilation | gas_flowing, and the usable time will become short is proposed. In this patent document 5, it is preferable to measure the amount of eluted alkali which largely affects the usable time, and in particular, it is pointed out that the influence of Ca is large among the eluted alkali components, and this may be reduced. In addition, the content of Na ₂ O and K ₂ O in the foundry 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 weight percent. 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 Although I mention it, I have not proved the role of individual metal oxides on the relationship between metal oxides such as Fe ₂ O ₃ , TiO ₂ , K ₂ O, Na ₂ O, etc. and the elution alkali, and they are fireproof No suggestion is given as to the relationship with the degree.

Moreover, since the casting sand which concerns on patent document 5 is manufactured by the flame melting method, particle | grains become heavy and it is not a lightweight particle | grain structure.

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

The present invention, Al in ₂ O ₃ sintered artificial sand the -SiO ₂ as a main component, and aims to achieve provision of sintered artificial sand having a function of hardly reacting with high iron melt melting point.
Another object of the present invention is to provide sintered artificial sand having high resource saving property and excellent energy saving property.

Still another object of the present invention is to provide a sintered artificial sand which is excellent in handling properties and can reduce heavy streak operations.

The present invention relates to the 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 controlling the type and amount of the low melting point composition. doing, the sintered artificial sand, by providing a sintered artificial sand and configured to indicate a negative 50 ° C. within refractoriness of the liquidus in the Al ₂ O ₃ -SiO ₂ system phase diagram It solves the above-mentioned subject.

The present invention also relates to a method for producing a sintered artificial sand by sintering a raw material containing Al ₂ O ₃ , SiO ₂ and a low melting point composition contained as a contaminant, wherein the Al ₂ O ₃ -SiO ₂ system is used. In the phase equilibrium diagram, by controlling the amount of the low melting point composition, a sintered artificial sand having a fire resistance within -50 ° C. of the liquidus is obtained, and a method of producing a sintered artificial sand is provided. Do.

In the present invention, the low melting point composition means a composition having a melting point lower than the casting temperature (for example, 1550 ° C. for cast steel) of a metal to be cast. This low melting point composition exists, for example, as a basic oxide or a weak basic oxide as shown in Table 1 in the raw material, and specifically, it is possible to specifically exemplify Na ₂ O, K ₂ O, FeO it can.

In particular, it is recognized that K ₂ O has a remarkably low melting point, a large amount of impurities contained in the raw material mineral, and a composition having a large melting point lowering action. By controlling the amount of K ₂ O, it is extremely effective to construct sintered artificial sand so as to exhibit a fire resistance within -50 ° C. of the liquidus in the Al ₂ O ₃ -SiO ₂ phase equilibrium phase diagram. The present inventors have found that this is the starting point for completing the present invention.

In particular, the present invention controls the K ₂ O as the low melting point composition to be 0.20% or less in the composition in which mullite crystallizes as primary crystals in the Al ₂ O ₃ -SiO ₂ phase equilibrium phase diagram. Provided is a sintered artificial sand configured such that the sintered artificial sand exhibits a fire resistance within -50 ° C. of the liquidus in an Al ₂ O ₃ -SiO ₂ -based phase equilibrium phase diagram.

Sintered artificial sand is characterized in that it has an inter-crystal structure in which there is a gap of overlapping of crystals between mullite crystals. Specifically, as shown in FIG. 3, in the sintered artificial sand, there is a gap derived from the crystal structure of overlapping mullite crystals which are columnar crystals (oriented structure or card house structure). The present invention is directed to a sintered artificial sand provided with an inter-crystal structure in which a gap derived from a crystal structure exists.

On the other hand, in the artificial sand obtained by the melting method as shown in Patent Document 5, for example, the surrounding of crystals such as mullite is surrounded by amorphous and non-crystalline between mullite crystals. It shows an inter-crystal structure in which there is a quality and there is no overlapping gap of the mullite crystals (a gap derived from the crystal structure). As described above, the fused artificial sand has an intercrystalline structure in which amorphous is present between mullite crystals, and hence the bulk specific gravity is increased, whereas the sintered artificial sand of the present invention Since the crystal structure has an inter-crystal structure in which crystal overlapping gaps exist, the bulk specific gravity can be suppressed to 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 for release from heavy muscle work.

Further, in the Al ₂ O ₃ -SiO ₂ phase equilibrium phase diagram, the ratio of Al ₂ O ₃ to SiO ₂ is not particularly limited, but the composition of Al ₂ O ₃ is 40% to 60%. In view of 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, the specific surface area is reduced, which is advantageous in that the strength development by the caking agent is increased. In addition, by setting the particle strength to 1000 MPa or more, casting sand which can be repeatedly used for a long time and has a low environmental impact can be provided from the viewpoint of natural resource protection.

Furthermore, in the practice of the present invention, it is desirable for the particle surface to have a compact structure with fewer voids, as compared to the interior of the particle. By this structure, the amount of used caking agent can be reduced in combination with the high sphericity and the favorable particle shape as described above. As a result, there is little pyrolysis gas of the binder at the time of casting, and it is possible to construct an environment less polluting the environment and affecting the human body.

Since the sintered artificial sand according to the present invention is a foundry sand used for casting, a caking agent is added to form a foundry sand, which is molded and used as a mold. In exceptional cases, there are molds to which no caking agent such as reduced pressure or freezing is added, but the sintered artificial sand according to the present invention can be applied to these as well.

The present invention has been able to provide spherical sintered artificial sand having characteristics of being less likely to react with molten metal among artificial sands. Specifically, the kind and amount of low melting point composition are controlled as the sintered artificial sand shows the fire resistance within -50 ° C. from the liquidus in the Al ₂ O ₃ -SiO ₂ phase equilibrium phase diagram. Therefore, it has a function that hardly reacts with the iron-based molten metal. This makes it possible to reduce the amount of product-adhering sand that becomes industrial waste that adheres to the cast product and is discharged out of the line after casting. Furthermore, it is possible to prevent seizure defects, which are casting defects due to reaction between a mold and a molten metal, and to reduce the number of cast products discarded as defects.

Therefore, the present invention is able to provide a sintered artificial sand which is excellent in resource saving property, can reduce the energy consumed when producing casting sand, and is also excellent in energy saving property. It is a thing.
The present invention, of course, has high heat resistance as described above, is a sintered artificial sand having a relatively small specific gravity, is excellent in handling properties, and provides a sintered artificial sand that can reduce heavy streak work. It is made.

In addition, the sintered artificial sand of the present invention has an inter-crystal structure in which overlapping gaps of mullite crystals (gaps derived from a fine crystal structure of less than 10 microns present between crystals) are present, It has an appropriate void inside (a void that hardly affects the strength of particles and does not cause any problems in practical use). And, in the practice of the present invention, the particle surface of the particle may have a void and a dense structure as compared to the inside of the particle. It can also be carried out as having high strength and characteristics that are not easily crushed.

It is Al ₂ O ₃ -SiO ₂ system phase diagram which is the composition of the present invention. It is explanatory drawing of reaction of the iron-type molten metal and mold which should be solved by this invention. It is a microscope picture which shows the structure of the sintering artificial sand of this invention. They are an external view of the micro strength tester used for the measurement of Example of this invention, and the conceptual diagram of particle strength measurement. The effect of the present invention in Table 3 is a graph showing the effect on refractoriness of K ₂ O in the primary phase of mullite range of Al ₂ O ₃ -SiO ₂ system phase diagram. The effect of the present invention in Table 3 is a graph showing the effect on refractoriness of K ₂ O in the primary phase alumina range of Al ₂ O ₃ -SiO ₂ system phase diagram. BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram of the casting_mold | template for a casting test piece for measuring the product adhesion sand used for evaluation of the Example-of this invention (Nippon test type | mold test piece).

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Composition and casting sand of Al ₂ O ₃ -SiO ₂ phase equilibrium phase diagram)
In order to use as casting sand, it needs to be higher than the melting point of the metal to be cast. When the foundry sand reaches the melting point during casting and becomes liquid, it mixes with or reacts with metal. The metal to be cast in the sand mold is magnesium (651 ° C.), aluminum (660 ° C.), copper (1083 ° C.), nickel (1455 ° C.), iron (1539 ° C.), chromium (1900 ° C.). is there. In addition, nickel and chromium are alloys of iron as a master alloy, and are close to the melting point of iron. Further, cast iron means iron plus carbon and silicon, and the lowest melting point is around 1120 ° C.

At the time of casting, the temperature is adjusted to a high temperature above the melting point to adjust the component of the metal (alloy), and after the component is adjusted, it is cast into a sand mold as a temperature with meltability (the metal does not solidify in the middle of casting) . This temperature is the casting temperature. Therefore, the degree of fire resistance (melting point) required for casting sand is based on the casting temperature. The casting temperature of the most productive cast iron is approximately 1340-1440 ° C. Although cast steel changes with materials, it is about 1550-1650 ° C. The aluminum alloy is approximately 580-680 ° C. The cast steel is the highest temperature and the reactivity between the molten metal and the sand mold is high, and it is essential for the sand mold to apply a paint mold (refractory paint) to the sand mold. This coating is a measure against chemical burn-in defects. Cast iron is essentially unnecessary for sand molds using fine-grained No. 6 sand or more, and it is necessary for sand molds using coarse-grained No. 5 sand to be moldable. This coating is a measure against physical burn-in defects. Aluminum alloys have a low casting temperature, and in principle, coating is unnecessary.

Considering the casting temperature of the above-mentioned alloy, it is considered that the cast sand having a melting point which is the composition of the Al ₂ O ₃ -SiO ₂ phase equilibrium phase diagram has sufficient heat resistance. FIG. 1 shows an Al ₂ O ₃ —SiO ₂ phase equilibrium phase diagram. The solidus line is SiO ₂ + mullite at 1587 ° C. ± 10 ° C., and mullite + Al ₂ O ₃ at 1890 ° C. ± 10 ° C. As described above, in the casting metal, in a casting temperature is 1550-1,650 ° C. of cast steel, it is sufficient that the mold to withstand, since the slightly lower than the temperature increase casting temperature at the time of casting of the mold, Al ₂ O It can be said that the melting point of the artificial sand having the composition of the _3- SiO ₂ -based phase diagram is sufficient for practical use. In particular, a region having a composition of 40% to 60% of Al ₂ O ₃ is practically preferable.
FIG. 1 is an equilibrium diagram of Al ₂ O ₃ —SiO ₂ based phase according to Akira Yamaguchi: present state and future of alumina-based refractory (Okayama Ceramics Technology Foundation) (2007) 3.

(Mechanism of reaction between molten metal and casting sand)
The reaction between cast iron and molten cast steel and the mold is shown in FIG. This is a description of chemical burn-in defects among the burn-in defects.
First, Fe, Mn, Mg and the like in the molten metal are oxidized by oxygen in the air, water vapor in the mold, and the like to form a liquid oxide. The SiO ₂ in the mold melts to a liquid due to the low degree of fire resistance. When these oxides are mixed to form a mixed melt, it becomes amorphous slag. Further, when the reaction proceeds, it becomes low-melting substances of firelight, tefroit and forsterite. The formation of slag and low melting point substances causes seizing defects, which are casting defects. In addition, in the case of a slight amount, the amount of casting sand adhering to the product increases and it is brought out of the line, which increases industrial waste.

(A substance that lowers the fire resistance of artificial sand with the composition of Al ₂ O ₃ -SiO ₂ phase equilibrium phase diagram)
The artificial sand of the composition of the Al ₂ O ₃ -SiO ₂ phase equilibrium phase diagram is adjusted to the silicate mineral kaolinite (Al ₄ Si ₄ O 10 (OH) 8) with alumina (Al ₂ O ₃ ) which is an oxide mineral. It is common to manufacture. Industrially, natural minerals are used for both silicate minerals and oxide minerals. Natural minerals include alkali metals (Na, K, etc.) and silicate minerals including alkaline earth metals (Mg, Ca, etc.) as contaminants, and these contaminants have a purity of Al ₂ O ₃ -SiO ₂ It is decreasing.

Table 1 shows the nature of the oxide and the melting point.

The silicate mineral is composed of acid oxide silica (SiO ₂ ) and basic oxides MgO, CaO, Na ₂ O, K ₂ O and the like. Table 1 also shows the melting points of other oxides. 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), FeO (1377 ° C), especially the melting point of K ₂ O Is extremely low. The basic oxides and weakly basic oxides in Table 1 have low melting point compositions that have a melting point lowering action in the Al ₂ O ₃ -SiO ₂ phase equilibrium phase diagram, and among these low melting point compositions, K ₂ O is The melting point lowering action is considered to be high.

(Necessity of particle strength)
Minerals have an index of hardness expressed by Mohs hardness for each substance. For example, representative minerals of casting sand are listed below. Orthoclase KAlSi ₃ O ₈ (morse hardness 6 or so), iron oxide Fe ₂ O ₃ (morse hardness 6 or so), magnesium oxide MgO (morse hardness 6.5 or so), chromium oxide Cr ₂ O ₃ (morse hardness 6 to 7), Zirconium oxide ZrO ₂ (Mohs hardness 6 to 7), Quartz SiO ₂ (Mohs hardness about 7), Fused silica SiO ₂ (Mohs hardness about 7), Mullite 3Al ₂ O ₃ · 2SiO ₂ (Mohs hardness 7.5), Alumina Corundum Al ₂ O ₃ (Mohs hardness 8 to 9).

A representative foundry sand is borax and is made of quartz and feldspar, so the Mohs hardness is around 6 to around 7. Zircon sand composed of zircon oxide and chromite sand composed of chromium oxide are considered to be harder in the casting industry as compared to borax, but their Mohs hardness is lower than that of quartz. In addition, 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 higher particle strength than the stress that casting sand receives during the manufacture of casting, they are casting sand that is difficult to break, and can be said to be environmentally compatible. On the other hand, borax is not environmentally-friendly because it breaks 5% to 30%.

Thus, mullite and alumina are included in the Al ₂ O ₃ -SiO ₂ phase equilibrium phase diagram, and therefore, by producing the artificial sand according to this phase diagram, it is made an environment-adaptive artificial sand that is difficult to be broken. be able to.

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

(1) Sintering method This is a method for producing mullite artificial sand produced in Japan and the United States with a production volume 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. What mixed SiO ₂ and Al ₂ O ₃ raw materials reduced in alkali components of foreign substances at a mullite conversion ratio (3Al ₂ O ₃ · 2SiO ₂ ) and granulated fine particles into the size of casting sand Sinter in a rotary kiln. There are three types of granulation methods as shown in Table 2, and the compactness and surface state of the particles are different. Mullite is synthesized in the rotary kiln below the melting point of mullite (about 1850 ° C.). Due to industrial constraints, all of the raw materials during synthesis are not mullite but exist as amorphous. The content of mullite and other components and the amount of amorphous differ depending on the manufacturer. It is desirable to make mullite 85% or more and to make fine particles.

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

FIG. 3 shows a composition image of the sintered artificial sand of the present invention taken at a magnification of 2000 using a high resolution scanning electron microscope (SEM). The shooting site is the surface of artificial sand particles. The surface of the particles in Table 3 to be described later is photographed with a low resolution scanning electron microscope, and it is possible to cover the columnar mullite crystals on the surface of the sintered artificial sand and the gaps derived from the crystal structure. In contrast, 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 void derived from the aforementioned crystal structure. Specifically, it is a gap formed between overlapping (oriented structure or card house structure) of mullite crystals which are columnar crystals. Since this is a single micron clearance, there is almost no influence on the strength of the particles, and this is not a problem in practical use. The presence of the gaps derived from the crystal structure is a factor to reduce the bulk density of the particles.

The second type of void is a void during sintering. It is a void formed in the particles at the time of sintering due to air in the granulated material, moisture, crystal water of the raw material, or a gap due to insufficient consolidation of the granulated material. Since the voids at the time of sintering have a size of several tens of microns or more, when the voids at the time of sintering increase, the particle strength decreases.

As described above, since the voids include the void derived from the crystal structure and the void during sintering, the term "void" in the present specification includes both the void derived from the crystal structure and the void during sintering. When explaining both, it will use properly the clearance derived from crystal structure, and the space | gap at the time of sintering, when distinguishing both.
In the practice of the present invention, it is advantageous to produce the artificial sand by a sintering method in order to efficiently obtain the artificial sand provided with gaps derived from the crystal structure. With regard to the granulation method, various granulation methods such as pan mixer granulation method, spray dryer granulation method, etc. 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 show a compact structure with few voids, and is advantageous in terms of improvement of particle strength and the like.

(2) Melt blasting method The graphite electrode contact melting method of the melt blasting method is the method of producing artificial sand with the largest production volume. Melt blasting is also simply referred to as melting. It seems that about 10 t / year is currently manufactured. The mineral composition is mullite + Al ₂ O ₃ . Since the liquidus line is higher than mullite in FIG. 1, it is manufactured by the arc furnace which can obtain high temperature. It is a raw material of bald rock (Alum Shale: Chinese bauxite containing about 75% Al ₂ O ₃ ). The raw material is put on the graphite electrode and melted by Joule heat. In addition, since plasma arc is also generated, the raw material is also melted by this arc heat. The melting temperature is 2000 ° C. or more. The molten metal flows down below the graphite electrode, is discharged from the orifice, and is immediately atomized (air-blasted or spray-quenched). It becomes spherical particles by the surface tension of the liquid in the air, and it is rapidly cooled to become artificial sand. Because it is quenched, the amount of non-crystallization and remaining amorphous is relatively large.

In the arc furnace melting method, a raw material is charged in a furnace body, and the raw material is melted by arc heat due to arc discharge between graphite electrodes to form a molten metal. Perform atomization immediately after the pouring to obtain artificial sand particles. The refractory of the furnace body is often self-lined, and the high refractory material can be dissolved without being affected by the melting point of the refractory. Since the composition adjustment is possible in a furnace, it is used for the manufacturing method of the highly refractory artificial sand said that Al ₂ O ₃ is 80% and ZrO ₂ is 10%. It is manufactured in China, and the production volume seems to be about 0.5t / year.

In the melt-air-grinding method, mullite and alumina become liquid because the temperature is higher than the liquidus of mullite. Crystals crystallize out of the liquid and become amorphous if they do not crystallize out due to quenching. Most products are amorphous surrounded by crystals and there is no single micron to submicron clearance between crystals in the sintering process. This increases the bulk density. In addition, there is no air gap due to the gas of a micron or more, or if it exists, it is a bubble due to gas entrainment.

(3) In-flame melting method This is also produced in China, and the production volume seems to be about 0.5 t / year. The in-flame melting method is also referred to simply as the melting method as well as the melt-air crushing method. Raw particles pre-granulated or ground to a predetermined size are injected into the flame from a fuel spray direction into a flame of approximately 3000 ° C using a pure oxygen combustion burner, and the particles are melted in the flame to form spherical particles by surface tension. It is a manufacturing method which is made into particles and crystallized during cooling after passing through a flame to obtain spherical artificial sand. Artificial sands such as mullite, alumina, mullite + cristobalite are manufactured. It is easy to produce fine particles compared to the sintering method. The crystallization and the amorphization differ depending on the stagnation state in the flame, the cooling state after passing, and the like. If anything, it is amorphous. This can also be used to produce amorphous silica, which is a highly refractory and stable phase.

In order to melt above the liquidus, the particles are nearly identical to the melt-blown method. There is no single micron to submicron clearance between crystals. This increases the bulk density. However, in order to spray the inside of a flame, air bubbles are apt to be generated due to air entrainment, but the air gap does not become uniform as in the sintering method.

(The need for casting sand with good grain shape)
Table 3 shows the grain shapes of borax and artificial sand and the angle of repose.

Among the borax, three types of borax of good grain shape from Australian borax, sintered artificial sand and artificial sand with melt blast method are shown in comparison. Artificial sand is similar to borax and its grain shape is close to sphere. In the sintering method, particles are granulated in a spherical shape and then sintered to form a spherical shape, and 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 material is melted to be 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 caking agent described later is increased. The melt-blasting method is closest to the true sphere, the surface state of the particles is smooth, and there are no porous places.

In the sintered artificial sand, there are fine porous parts as in the SEM image of the particle surface of Table 3, and this continues to the inside. The surface of borax is also observed, but this is only the surface and not the inside.
In addition, the angle of repose of artificial sand decreases in the order of sintered artificial sand and fused artificial sand. Thereby, the fluidity of casting sand and the filling as a mold become good.

(Painting for physical seizure prevention, coating for chemical seizure prevention)
Whether or not to apply a coating is determined from two viewpoints of measures against physical burn-in defects and chemical burn-in defects. When producing large castings, the particle size is increased in order to replace the gas in the mold with the molten metal to ensure sand mold permeability. At this time, it is a paint mold for preventing physical seizure defects so as to prevent the melt from infiltrating the sand grain physically. Therefore, even in the sintered artificial sand according to the present invention, when the particle size is increased, a coating for preventing physical seizure defects is required.

The coating of the seizing defect due to the chemical reaction between the molten metal and the mold is a coating that prevents 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. Molten metal is a liquid. The fact that the sand mold is liquid means that the casting sand has been melted by the heat of the molten metal. In the present invention, since the casting sand is provided with the fire resistance sintered artificial sand which is free from chemical seizing defects and does not melt even by the heat of the molten metal, the coating for chemical seizing defects prevention becomes unnecessary. .

(Particle size adjustment)
As the present invention relates to foundry sand, it is desirable to adjust the particles to a size range of 20 to 1200 microns. Typically 106 to 600 microns are used as foundry sand. The relatively small mass-produced castings produced in green form are mainly 150 to 300 micron casting sand. The relatively large castings produced with self-hardening molds etc. are mainly found in 300-600 micron casting sand. The V process is around 106 microns. In addition, 20 to 106 microns is called fine sand and is used as an additive for auxiliary grain size adjustment of casting sand. 850 to 1200 microns are used as backup and back sand. Thus, casting sand differs in the particle size used by a molding process.

(Casting sand and mold)
Since the sintered artificial sand according to the present invention is a foundry sand used for casting, a foundry sand can be obtained by adding other materials such as a caking agent according to a conventional method. Then, the obtained casting sand can be molded to produce a mold, which is used for casting various metals. In exceptional cases, there are casting sands and molds to which no caking agent such as reduced pressure or freezing is added, but the sintered artificial sand according to the present invention can be applied to these as well.

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

(Method of measuring porosity)
The porosity of the particles was determined by placing the particles classified to 70 mesh (212 microns) horizontally, filling the resin from above, and polishing the particles for about 106 microns to obtain a cross section of the center of the particles. The composition image was then taken with a scanning electron microscope. The cavities and the particle matrix were divided by black-and-white binarization for approximately 10 particles, and the porosity was made the ratio of black. In addition, blackness due to noise and black around the periphery of the particles were removed manually.

About 100 particles are observed at a magnification of 40 times to confirm the presence of voids, and the composition image is taken at a magnification of 250 times for particles having an average void, and the void is binarized. The rate was determined. At a magnification of 250 times, mullite columnar crystals can not be photographed due to the resolution. That is, in the scanning electron microscope at this magnification, since the gaps of nano unit are hard to be photographed, the ratio of the gaps at the time of sintering among the gaps derived from the crystal structure and the gaps at the sintering becomes the porosity. In the melting method, there are particles without voids, and the voids are also generated by air bubble entrainment. Therefore, the ratio was determined by dividing into "void air free particles" and "air bubble entrainment particles". The porosity was not calculated because the average particle was not found due to the presence of void-free particles.

(Measurement method of bulk specific gravity)
The measurement of bulk specific gravity is based on the “S-10 test method for filling property (bulk specific gravity) (bulk specific gravity) test method” specified in “Testing method for mold and mold material” issued by the Small and Medium Enterprise Business Group in May 1999. Measured. The difference is in the charging vessel, which used Ford cup # 4 specified in "S-5 Test method for flowability of casting sand". In other words, simultaneous measurement of bulk density and flow rate.
With regard to bulk specific gravity, the bulk specific gravity tends to be smaller as the number of voids including both of the gap derived from the crystal structure and the void during sintering is large regardless of the structure of the void.

(Method of measuring particle strength)
Fig. 4 shows the appearance of the micro strength tester and a conceptual view of particle strength measurement. The tester used is an electromagnetic force type micro strength tester (hereinafter, micro strength tester). The maximum load capacity was 50 N, and a load was applied under the condition of a constant displacement speed of 1 mm / min. The particle strength was photographed with a microscope for each sample particle to obtain the major axis and the minor axis, and then the maximum breaking load was measured using a micro strength tester.

In order to determine 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 of the pressure plate and the sample particles at the time of the compression test. However, the contact area of the sample particles is not constant because they are irregular particles. Therefore, in this report, a method is used to calculate the compressive strength by determining the cross-sectional area on the assumption that the sample particle is an ellipsoid. The major diameter (2a) and the minor diameter (2b) of the foundry sand particles were measured from photomicrographs. The cast sand particle height (2c) and the position (2c-2d) of the pressure plate at the time of breakage are the readings of the micro strength meter. Particle strength (σK) was calculated by the following.
σ K = P / S
Here, σ K: particle strength, P: breaking load, S: ellipsoidal cross-sectional area at displacement d (estimated contact area of pressing plate and particle).

(Artificial sand, particle strength of borax, aspect ratio, photomicrograph)
Tables 4 (a) and 4 (b) show that artificial sand has less industrial waste at the time of repeated use as compared with borax and that the amount of added caking agent is small and it is good for the environment.

As described above, since the sintered foundry sand according to the embodiment of the present invention has the function of being hard to react with molten cast iron, the amount of the product deposited sand attached to the cast product after casting and discharged out of the line The industrial waste can be reduced by extremely reducing the amount of casting defects, the casting defects due to the reaction with the molten metal are reduced, the product yield is improved, the weight is reduced because of heavy weight reduction, and the particle shape is good. It has various advantages, such as reduction of the amount of additive added and reduction of the amount to be shredded into industrial waste due to high particle strength, etc. Although mentioned and explained below, the present invention should not be understood as being limited to these Examples.

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

Specifically, high purity kaolinite ore having a low K ₂ O content is used as impurities, and finely ground after beneficiary and calcination to obtain a slurry, which is dried and adjusted with a spray dryer to obtain particles. The particles are not compact and the surface is not smooth. Next, a compact and smooth particle size is granulated to about 100 to 300 μm with a pan mixer. Next, it was fired in a predetermined range of 1350 ° C. to 1850 ° C. for 1 to 3 hours using a rotary kiln to obtain a silica + mullite sintered artificial sand. The firing temperature and the firing time are conditions under which mullite is generated. After cooling, classification is performed to make the particle size usable for casting. Although the components of the raw materials are different in the following examples, the production methods are the same. The temperature at which mullite is generated from kaolinite or the like is from about 1000 ° C. Therefore, the same sintered artificial sand can be produced by prolonging the firing time also below the temperature of this embodiment.

Detailed chemical compositions of Examples 1 to 5 are shown in Table 5. 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. It is a very hard spherical sintered artificial sand that is light in weight, having fine voids inside but having a dense particle surface.

In Example 2, a high purity alumina flour is blended with the high purity kaolinite ore having a low K ₂ O content of Example 1, to prepare Al ₂ O ₃ -SiO ₂ . Chemical components shown in Table _{5, SiO 2: 44.3%,} Al 2 O 3: 49.8%, K 2 O: 0.11%. As shown in Table 4, the void ratio is 2.1%, the aspect ratio is 0.886, the bulk density is 1.499 g / cm ³ , the particle strength is 1671 MPa, the aspect ratio is 0.89, and it is lightweight and extremely hard spherical artificial sand.

Examples 3 to 5 are also obtained by the same manufacturing method as in Example 2 and slightly increase the K ₂ O using alumina flour having a low purity. The respective chemical components and the like are shown in Table 5.

(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 sands, Comparative Examples 4 and 5 are melt-pulverizing methods, and Comparative Example 6 is based on an in-flame melting method. These chemical components and the like are shown in Table 5.

Comparative Example 1 is mullite artificial sand manufactured by the sintering method (spray dryer granulation method) in Table 2 and is marketed. The detailed chemical composition of Comparative Example 1 is shown in Table 5, and is SiO ₂ : 37.5%, Al ₂ O ₃ : 55.8%, K ₂ O: 0.23%. The void ratio 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 void ratio is high as compared with Examples 1 and 2. The aspect ratio is also 0.850 or less, and the grain shape is bad. In addition, since the particle surface is not compact, the voids are open to the outside. This is probably because the particle strength is lower than in Examples 1 and 2. In addition, 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 effect due to the large amount of Al ₂ O ₃ having a heavy specific gravity compared to SiO ₂ and the small single micron clearance of mullite crystals.

Comparative Example 2 is a mullite artificial sand manufactured by the sintering method (spray dryer granulation method) in the same manner as Comparative Example 1, and is marketed. The detailed chemical composition of Comparative Example 2 is shown in Table 5, and is SiO ₂ : 37.0%, Al ₂ O ₃ : 56.3%, 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. As in Comparative Example 1, compared to 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 a method similar to Comparative Examples 1 and 2, except that the surface grinding process is added to the final step to improve the particle 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. The K ₂ O is low and the fire resistance is expected to be good, but the bulk specific gravity is heavy and not lightweight. Also, the particle strength is low.

Comparative Example 4 is a mullite + alumina-based fused artificial sand manufactured by the melt-air crushing method (graphite electrode contact melting method) in Table 2. 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%. The void ratio was a mixture of particles without voids and particles with voids, and the ratio was 59:41. It is a void due to air inclusion, and the shape is different from the void of sintered artificial sand. The porosity is not measured because it largely varies depending on particles. The aspect ratio is 0.925, the bulk specific gravity is 1.940 g / cm ³ , and the particle strength is 1433 MPa. Bulk specific gravity is extremely heavy because it is manufactured by the melting method.

Comparative Example 5 is a mullite + alumina-based fused artificial sand manufactured by a melt-air crushing 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%. The void ratio was a mixture of particles without voids and particles with voids, and the ratio was 82:18. It is a void due to air inclusion, and the shape is different from the void of sintered artificial sand. The porosity is not measured because it largely varies depending on particles. The aspect ratio is 0.929, the bulk specific gravity is 1.942 g / cm ³ , and the particle strength is 1425 MPa. Bulk specific gravity is extremely heavy because it is manufactured by the melting method.

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

(Relationship between K ₂ O and “difference between liquidus temperature and tumbling temperature”)
Although artificial sand has stated that it is good for the environment, the composition of artificial sand reduces the degree of fire resistance, and it is described below that there are adverse conditions for the environment.

Table 5 shows the relationship between K ₂ O and the “difference between liquidus temperature and tumbling temperature”. The liquidus temperature is the temperature of the liquidus at which primary silica, primary mullite, and primary alumina crystallize from the liquid phase in FIG. The liquidus temperature (Y1) of primary crystal mullite and the corrected Al ₂ O ₃ concentration (X) are set as formula (1). The liquidus temperature (Y2) of primary alumina and the corrected Al ₂ O ₃ concentration (X) were set as formula (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 components is 100. Since the Al ₂ O ₃ -SiO ₂ -based phase equilibrium diagram in FIG. 1 is binary, the liquidus temperature can be calculated from the corrected Al ₂ O ₃ concentration.

Y ₁ = −0.0811 × ² + 11.172 × + 1501.0 (1)
Y ₂ = −0.5307 X ² + 101.87 X − 2745.2 (2)
The fire resistance test of Examples and Comparative Examples was conducted based on JIS R 2204: 1999 “Test method of fire resistance of refractories and raw materials for refractories”, and fire resistance (SK number) was measured. The tumbling temperature was determined from the relationship between the SK number of JIS R 8101: 1999 "Standard cone for fire resistance test" and the tumbling temperature.

(Difference in liquidus temperature and tumbling temperature of Examples 1 to 5)
The production method of Examples 1 to 5 is the above-described sintering method (pan mixer granulation method), which is produced by combining high purity kaolinite and high purity alumina and controlling K ₂ O to 0.20% or less. The refractory temperature was measured to determine the tumbling temperature. In addition, the composition is quantified for each chemical component by X-ray fluorescence, the corrected Al ₂ O ₃ concentration is calculated from the measured values of SiO ₂ and Al ₂ O ₃ , and the temperature is calculated from the equations (1) and (2). Calculated. In addition, the quantitative value of a fluorescent X ray is calibrated by the quantitative value of wet analysis. In the relationship between the liquidus temperature and the depression temperature in Examples 1 to 5, the depression 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 tumbling temperature in Examples 1 to 5 is 11.3 ° C. to 38.6 ° C. and is within 50 ° C.

(The difference between the liquidus temperature and the tumbling temperature of the comparative example)
Comparative Example 1 and Comparative Examples 6 to 11 are mullite artificial sand produced by a sintering method (spray dryer granulation method). It is a composition in which primary crystals are mullite. In these comparative examples, K ₂ O is in the range of 0.23% to 0.80%, and there are more K ₂ O compared to the example. The tumbling temperature was calculated by equation (1). As compared to the example, the tumbling temperature of these comparative examples is much lower than the liquidus temperature, and a difference of 54.0 ° C. to 174.9 ° C. occurs. Therefore, it can be said that the performance of the fire resistance predicted by the Al ₂ O ₃ -SiO ₂ phase equilibrium phase diagram is not expressed.

Comparative Example-2, Comparative Example-14, and Comparative Example-15 are mullite + alumina artificial sands manufactured by the melt-air crushing method (graphite electrode contact melting method). It is a composition in which primary crystals are alumina. In these comparative examples, K ₂ O is in the range of 0.0.35% to 1.48%, and there are more K ₂ O compared to the examples. The tumbling temperature was calculated by the equation (2). Compared with the example, the tumbling temperature of these comparative examples is significantly lower than the liquidus temperature, and a difference of 140.1 ° C. to 224.6 ° C. is generated. Therefore, it can be said that the performance of the fire resistance predicted by the Al ₂ O ₃ -SiO ₂ phase equilibrium phase diagram is not expressed.

(Influence of K ₂ O on fire resistance in primary mullite and primary alumina regions)
FIG. 5 (a) shows a graph for clarifying the influence of K ₂ O on the fire resistance in the primary crystal mullite region and FIG. 5 (b) in the primary crystal alumina region. Since the influence of K ₂ O is different between the primary crystal mullite region and the primary crystal alumina region, they are separately shown. 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, and as K ₂ O increases, the difference between the liquidus temperature and the tumbling temperature increases and the fire resistance decreases.
ΔY ₁ = 215.7 K + 6.755 (3)
ΔY ₂ = 74.13 K + 113.99 ........ (4)

(A schematic diagram of a mold (Nippon Test-type scab specimen))
The cast iron molten metal was cast in and judged by using a standard work type scoop test piece of which the effect of the present invention is shown in FIG. Under the conditions of a test piece weight of 6.5 kg, a casting weight of 7.5 kg and a green weight of 21.5 kg, flake graphite cast iron equivalent to FC 250 was cast at about 1400 ° C. The green mold was prepared by adding 8 parts of bentonite from Wyoming to 100 parts of casting sand and adding water so as to have a compactability value of about 40% to form a kneaded sand, thereby forming a green mold. As evaluation, it was made the amount of adhesion sand to a product, and the presence or absence of a casting defect.

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

(Weight of sand attached to cast test piece)
Example 1 Example 2
In Example 1, K ₂ O was 0.09%, and the adhering sand immediately after the mold was 63.1 g. The deposited sand was almost completely removed by the shot and remained very slightly in the product. The deposited sand removed by the shot is discarded as industrial waste. With respect to casting defects, although a sintered product was adhered to the recess of the product immediately after mold disintegration, the sintered product was exfoliated by shot and casting defects were not generated.

In Example 2, K ₂ O was 0.11%, and the adhering sand immediately after the mold was 22.9 g. The adhered sand was completely removed by shot and did not remain in the product. The cast surface of the product was good and no casting defects occurred. Although Example 2 has more K ₂ O than Example 1, the good cast product seems to be due to the high Al ₂ O _{3 and the} high liquidus temperature.

Comparative Example 2 and Comparative Example 4
In Comparative Example 2, K ₂ O was 0.24%, and the adhering sand immediately after the mold was 196.5 g. The deposited sand was almost completely removed by the shot and remained very slightly in the product. With respect to casting defects, a sintered product was attached immediately after mold separation to the product recesses and the vicinity thereof, but the sintered products were separated at shots and no casting defects occurred.

In Comparative Example 4, K ₂ O was 0.35%, and the adhering sand immediately after the mold was 121.8 g. The adhered sand was completely removed by shot and did not remain in the product. Very slight sand grains were present on the cast surface of the product, and the cast surface was in a somewhat bad state. However, it is not a casting defect.

Comparative Example-14, Comparative Example-15, Comparative Example-16
In Comparative Examples 14 to 16, borax most frequently used as a mold was cast for comparison. These are borax made of quartz and feldspar and are not compositions of the Al ₂ O ₃ —SiO ₂ phase equilibrium diagram. Comparative Example 14 is a high purity borax containing a large amount of quartz, and feldspar increases in accordance with Comparative Examples 15 and 16. The adhesion sands were 375.2 g, 284.1 g and 415.2 g, respectively, which were extremely high in comparison with the artificial sands of Examples 1 and 2 and Comparative Examples 2 and 4. The adhered sand was sintered and adhered to the product even after the shot. In addition, all three products had shattering defects.

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

K was not detected in the EDS analysis of the sinter of Examples 1 and 2. In the EDS analysis of the sintered product of Comparative Example 2, 4, and 16, K was detected. Each analysis position is the point of contact 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 of phi-flight, tefloit and forsterite shown in Fig. 2. . These low melting point substances serve as an adhesive for sand particles to form a sintered layer. In Examples 1 and 2 where K does not exist (below the detection limit), the sinter is thin and the amount of adhering sand is small.

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

(Characterization of shell mold, furan mold, alkali phenol mold)
Table 8 (a) (b) (c) shows the mold characteristics of the shell mold, furan mold and alkali phenol mold of the sintered artificial sand of the present invention.

Although the caking additive was added with respect to the sand weight, since the bulk specific gravity is different, the data converted to volume is also attached. Examples 1 and 2 are the sintered artificial sand of the present invention. Comparative Example 1 is a large-porosity sintered artificial sand marketed on the market. Comparative Example 4 is an artificial sand of the melt-blasting method. Comparative Example 14 is a high purity borax, in which mold strength is highly expressed.

In the bending strength considering the bulk specific gravity of the shell mold of Table 8 (a), the artificial sand of Example 1-Example 2, Comparative Example 1 and Comparative Example 4 is approximately in the range of 111.4 to 122.2 kg / cm ² The strength is the same and higher than the high purity borax according to Comparative Example-14. Therefore, it can be said that the present invention has the same strength characteristics as artificial sand sold in the market.

In the compressive strength after 24 hours considering the bulk specific gravity of the furan mold of Table 8 (b), Example 1 of the present invention has the highest strength, and then Example 2 has almost the same strength as Comparative Example 1. It is. Therefore, the furan mold properties of the product of the present invention are good. Generally, sintered artificial sand is considered to exhibit low strength development by adsorbing furan resin as a liquid caking agent and acid curing agent, but Comparative Example 1 was developed for furan resin. It is artificial sand and its strength is high. Moreover, the present invention is also the same.

In the compressive strength after 24 hours in consideration of the bulk specific gravity of the alkali phenol mold in Table 8 (c), the melting method crushed artificial sand of Comparative Example 4 is the best, followed by the high purity borax of Comparative Example 14. The alkali phenol resin used is for general borax. Example-1 and Comparative Example-1 of sintered artificial sand have almost the same strength, and the order is Example-1 and Example-2 and Comparative example-1. Sintered artificial sand has a slightly lower strength for alkaline phenol molds, but the difference is small compared with Comparative Example 4 and Comparative Example 14 and can be used sufficiently as molds. In addition, since an alkaline phenol resin for artificial sand is commercially available, strength can be improved by using this.

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

It can be used for foundry sand which is repeatedly recovered and used as a casting mold. Because of its light weight and high particle strength, it is applicable to all foundry sands. In addition, green molds with the highest production volume, followed by self-hardening molds with the highest production volume are mainly furan molds and alkaline phenol molds, but these molds are particularly suitable for casting iron castings with the highest production volume. There is. By controlling the kind and amount of 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, adheres to the product and cast sand is taken out to the shot line, Casting sand can not be used as casting sand when it is mixed with steel shot and metal components (casting), and is discarded as industrial waste. This amount is dramatically reduced in the present invention. In addition, the reduction in chemical seizing defects caused by the reaction between the molten metal and the mold improves the product yield. In addition, since the product which became a defect is remelted as a return material, this energy cost etc. are reduced.

In addition to the above reaction between mold and molten metal, green mold, self-hardening mold and water glass inorganic mold expected not to generate harmful gas in the future, the binder is used in the process of reclaimed sand. It requires strong mechanical polishing to separate, and conventional casting sand is crushed to become industrial waste. It can be used without being crushed due to the high particle strength of the present invention.

Claims (7)

Sintered artificial sand containing Al ₂ O ₃ and SiO ₂ as a raw material and containing a low melting point composition contained as a contaminant in the raw material,
In the Al ₂ O ₃ -SiO ₂ phase equilibrium phase diagram, the kind and the amount of the low melting point composition are controlled, as the sintered artificial sand has a fire resistance within -50 ° C of the liquidus in the phase diagram. Sintered artificial sand characterized by being The method according to claim 1, characterized in that it has an intercrystalline structure in which K ₂ O as the low melting point composition is 0.20% or less, and there are crystal overlap gaps between crystals, and the aspect ratio is 0.85 or more. Sintered artificial sand. The sintered artificial sand according to claim 1 or 2, wherein the particle strength is 1000 MPa or more. In the Al ₂ O ₃ -SiO ₂ phase equilibrium phase diagram, the composition of Al ₂ O ₃ is 40% to 60%,
Sintering artificial sand according to claim 1, bulk specific gravity and less than 1.6 g / cm ^3. Casting sand containing the sintered artificial sand according to any one of claims 1 to 4. A mold containing sintered artificial sand according to any one of claims 1 to 4. In a method for producing a sintered artificial sand by sintering a raw material containing Al ₂ O ₃ , SiO ₂ and a low melting point composition contained as a contaminant,
In the Al ₂ O ₃ -SiO ₂ phase equilibrium phase diagram, a sintered artificial sand having a fire resistance within -50 ° C. of the liquidus is obtained by controlling the amount of the low melting point composition. How to make artificial sand.