JP2013043180A - Molding sand and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide molding sand which has high heat resistance, is excellent in low expansibility and low friability, is applicable to the casting of a large cast steel article having high pouring temperature, is excellent in reusability of sand, and has high production yield, and can be produced inexpensively; and to provide a method for producing the molding sand.SOLUTION: Molding sand has chemical components of, 50-85 wt.% AlO, 5-40 wt.% MgO, >0 to ≤20 wt.% SiO, wherein the total of the weight percentage of AlO, MgO and SiOis ≤100 wt.%, wherein the molding sand includes a molten spherical substance having as one kind of crystal construction, single spinel or composite of spinel with any one of alumina, mullite, cordierite and sapphirine, and wherein the molten spherical substance has a particle size distribution of 30-3,000 μm.

Description

  The present invention relates to a mold sand made of a molten sphere and a method for producing the same. Specifically, it has excellent heat resistance, low expansibility, low crushability, production yield, sand reusability, and can be applied to casting of large cast steel products with high pouring temperature, and at low manufacturing costs. The present invention relates to a molding sand and a manufacturing method thereof.

  Mold sand used in a foundry is generally formed into a predetermined shape by adding an organic or inorganic binder and curing it. A cast product is manufactured by pouring molten metal into the mold.

Known methods for producing the mold include the furan resin method, the alkali phenol resin method, the CO ₂ -water glass method, the ceramic mold method, and the ceramic shell mold method. Differences in these production methods include the binder and molding method used.

In the furan resin method, an organic acid is added to the furan resin and cured. In the alkali phenol resin method, alkali phenol is cured with an organic ester. The phenol resin method is also called an RCS method, and is a method in which a resin-coated sand (hereinafter referred to as RCS) is thermally cured to mold a mold. The CO ₂ -water glass method is a method in which carbonic acid gas is blown onto mold sand to which sodium silicate is added for hardening molding. The ceramic mold method and the ceramic shell mold method are mold making methods used for precision casting, and the mold sand is used as precision casting mold aggregate or stucco material.

  Silica sand is generally used as the mold sand. However, since quartz sand exhibits rapid thermal expansion at 573 ° C., there is a problem that casting defects are likely to occur. Moreover, since sand particles are easily destroyed by heating, there is an environmental problem in that when sand is used as mold sand, dust generation increases and a large amount of waste is generated.

Conventionally, in order to solve the above-mentioned problems, there has been proposed a molding sand obtained by baking fine powder made of a synthetic mullite raw material into a spherical shape (see Patent Document 1). That is, this mold sand is mixed with slurry (slurry) so that the chemical components are 20 to 70% by weight of Al ₂ O ₃ and 80 to 30% by weight of SiO ₂ . The agent is added and atomized with a spray dryer, and this is sintered in the vicinity of 1550 ° C. in a rotary kiln to obtain spherical mold sand.

  Such mold sand has higher strength than quartz sand, and it is effective for cost reduction by reducing waste, improving sand reuse rate, improving mold strength, and reducing the amount of binder used. Are better. However, since these mold sands sinter the fine particles obtained by spraying the slurry-like material having the above-mentioned composition, the surface of the fine particles as a sintered product exists as mullite crystals. Moreover, as shown in a scanning electron microscope (hereinafter referred to as “SEM”) photograph shown in FIG.

  In this way, if the surface of the sand particles has many irregularities, the amount of binder adsorbed on the sand particles increases, and the amount of binder used increases, resulting in higher costs and increased sand particle crushability. There is a tendency to make it. Moreover, there is a problem that heat resistance and curing characteristics are deteriorated due to an increase in residues contained in the recovered molding sand. As a result, this mold sand is not yet sufficient from the viewpoint of obtaining recyclability and stable mold characteristics in terms of strength.

Therefore, as a manufacturing method for obtaining mold sand with a smooth surface of sand particles, in addition to the above-mentioned granulating and sintering method (see Patent Document 1), an arc melt blowing method (see Patent Document 2). Has been proposed. In the arc melting blowing method, the Al ₂ O ₃ —SiO ₂ refractory raw material is melted and cooled and solidified while spraying high-pressure gas and spraying into fine particles, so that Al ₂ O ₃ is 40 to 90% by weight, This is a method for obtaining molten spherical mold sand having a crystal structure of mullite and alumina with SiO ₂ of 60% by weight or less. According to this method, sand particles having a smooth surface can be obtained as shown in the SEM photograph shown in FIG.

  The casting sand production apparatus used for the arc melting blowing method is simple as a manufacturing apparatus, has a lot of application results as a general-purpose device, and can be continuously melted. Therefore, the arc melting blowing method is implemented industrially. As a manufacturing method, it is considered as an optimum method.

Japanese Patent Publication No. 3-47943 Japanese Patent No. 3878496

However, when an Al ₂ O ₃ —SiO ₂ type raw material is melted by an arc method and blown with a high-pressure gas, for example, kaolin fibers (Al ₂ O ₃ is 45.5 wt%, SiO ₂ is 50.5 wt%) If the raw material contains many components having a high SiO ₂ weight percent, such as bauxite fiber (70% by weight of Al ₂ O _{3 and} 23% by weight of SiO ₂ ), the melting point of the raw material is lowered at the same time. The molding sand is likely to become fibrous or elliptical by spraying high pressure gas. That is, when a raw material contains a large amount of a high SiO ₂ weight% component such as kaolin fiber or bauxite fiber, it becomes difficult to produce the desired spherical sand.

In the above prior art, a raw material having a composition close to that of mullite (3Al ₂ O ₃ .2SiO ₂ ; chemical component Al ₂ O ₃ is 71.8 wt%, SiO ₂ is 28.2 wt%) and alumina Is often used. Even in that case, since the content of SiO ₂ is relatively high, the melt scattered by the high-pressure gas tends to become fibrous or elliptical particles. Therefore, spherical particles suitable for mold sand can be easily obtained. I can't. Thus, further improvement is required for efficiently obtaining spherical particle sand suitable for mold sand, and it remains as a problem.

  Further, silica separation may occur due to the reduction reaction by carbon during arc melting. When silica separation occurs, a large amount of suspended particulate dust is likely to be generated. As a result, there is a concern that the working environment is deteriorated such that the productivity of the spherical particles after spraying is inferior and the working environment is deteriorated.

  Therefore, in view of the above-mentioned problems, the object of the present invention is applicable to the casting of large cast steel products having high heat resistance, low expansion and low crushability, and high pouring temperature, and sand reusability. In addition, it is to provide a molding sand which is excellent in production and has a high yield during production. Another object is to provide a method for producing the molding sand.

In order to solve the above-mentioned problems, the molding sand according to claim 1 of the present invention has Al ₂ O ₃ of 50 to 85% by weight, MgO of 5 to 40% by weight, SiO ₂ of more than 0% by weight and 20% by weight. % Of chemical component, and the total of the weight percent of Al ₂ O ₃ , the weight percent of MgO and the weight percent of SiO ₂ is 100 wt% or less, and spinel (MgO · Al ₂ O ₃ ) A molten sphere having a crystal structure is included, and the molten sphere has a particle size distribution of 30 to 3000 μm.

Further, molding sand according to claim 2 of the present invention, a spinel _{(MgO · Al 2 O 3)} , alumina _{(α-Al 2 O 3)} , mullite _{(3Al 2 O 3 · 2SiO 2} ), cordierite ( 2MgO · 2Al ₂ O ₃ · 5SiO ₂ ) and sapphirine (4MgO · 5Al ₂ O ₃ · 2SiO ₂ ) as a kind of crystal structure, Al ₂ O ₃ is 50 to 85% by weight, MgO is 5-40 wt%, SiO ₂ containing molten spheroids having a chemical component of more than 0 wt% but not more than 20 wt%, the sum of Al ₂ O ₃ wt%, MgO wt% and SiO ₂ wt% Is 100% by weight or less, and the molten sphere has a particle size distribution of 30 to 3000 μm.

Further, the method of manufacturing molding sand according to claim 3 of the present invention are prepared from at least one of MgO source and alumina source, _Al 2 _{O 3} is 50 to 85 wt%, MgO 5 to 40 wt%, SiO ₂ A refractory raw material having a chemical component of more than 0% by weight and not more than 20% by weight, and the total of the weight percent of Al ₂ O ₃ , the weight percent of MgO and the weight percent of SiO ₂ is not more than 100% by weight After being put into the furnace, the refractory raw material is melted, and a high-pressure gas is blown to the melt formed by melting the refractory raw material to cool and solidify it as fine particles, thereby making spinel a kind of crystal structure. And a molten sphere having a particle size distribution of 30 to 3000 μm is formed.

Further, the method of manufacturing molding sand according to claim 4 of the present invention are prepared from at least one of MgO source and alumina source, _Al 2 _{O 3} is 50 to 85 wt%, MgO 5 to 40 wt%, SiO ₂ A refractory raw material having a chemical component of more than 0% by weight and not more than 20% by weight, and the total of the weight percent of Al ₂ O ₃ , the weight percent of MgO and the weight percent of SiO ₂ is not more than 100% by weight After charging into the furnace, the refractory raw material is melted, and the solid formed by melting the refractory raw material is sprayed with high pressure gas to be cooled and solidified while being dispersed in fine particles, so that spinel, alumina, mullite, A composite with either cordierite or saphirin is a kind of crystal structure, and a molten sphere having a particle size distribution of 30 to 3000 μm is formed.

Here, the “melted sphere” refers to a product obtained by making a refractory material into fine particles in a molten state and cooling and solidifying the refractory material in a spherical shape. As for the chemical composition of the molten spheres, when SiO ₂ exceeds 20% by weight, a tendency to increase the number of fibers and ellipsoids is recognized. However, in the present invention, the weight% of silica in the spinel exceeds 0% by weight and 20% by weight. When it is set to be equal to or less than%, it becomes possible to manufacture spherical objects more efficiently by spraying high-pressure gas on the melt.

  “Composite” refers to a combination of a plurality of types of crystals. The above-mentioned “composite of spinel and any one of alumina, mullite, cordierite, and sapphirine” is a combination of any one of alumina, mullite, cordierite, and saphirin combined with spinel. Means.

Al ₂ O ₃ has 50 to 85% by weight, MgO has 5 to 40% by weight, SiO ₂ has a chemical component of more than 0% and less than 20% by weight, Al ₂ O ₃ wt% and MgO wt% And a SiO ₂ weight% total of 100% by weight or less is less melted than the meltability of the Al ₂ O ₃ —SiO ₂ refractory raw material. Characteristics, work environment and productivity, and excellent fire resistance.

  Spinel, which is a kind of crystal structure of the molten sphere, has a high hardness and a high melting point (2100 ° C.). Since the melting point of this spinel is higher than 2050 ° C. of alumina and 1850 ° C. of mullite, the result is that the heat resistance is high and the low crushability is excellent.

  Moreover, as shown in FIG. 3 to FIG. 8, the surface of the molten spherical sand obtained by cooling is smooth like a glass and shows an optimum shape as mold sand. As described above, a spherical surface having an extremely smooth surface is formed as compared with the fine particles obtained by the above-mentioned conventional sintering, and an effect of preventing excessive adsorption of the binder appears.

  As described above, a molten sphere having spinel as a kind of crystal structure has high hardness. A molten sphere having a composite of any one of alumina, mullite, cordierite, and sapphirine and spinel as a crystal structure also has high hardness. The melting point of spinel is 2100 ° C, the melting point of alumina is 2050 ° C, the melting point of mullite is 1850 ° C, the melting point of saphirin is 1475 ° C, and the melting point of cordierite is 1460 ° C. Those containing a large amount of spinel, alumina and mullite are more preferable from the viewpoint of heat resistance. In other words, the heat resistance required for mold sand is as follows: the casting temperature of cast iron castings is typically 1300 ° C or higher, the casting temperature of copper alloy castings is 1100 ° C or higher, and the casting temperature of aluminum alloy castings is 700 ° C or higher. In view of the above, even when using the mold sand of the present invention partially containing sapphirine and cordierite, there is no particular problem in practical heat resistance. In addition, when applied to large cast steel with a high pouring temperature, spinel alone or a composition containing a large amount of spinel, alumina, and mullite has high heat resistance. Effective and preferred.

Furthermore, alumina, mullite, cordierite, and sapphirine are crystalline stable crystals obtained by reheating the Al ₂ O ₃ —MgO—SiO ₂ -based amorphous composition contained immediately after melting the refractory raw material at 1000 ° C. or higher. Generated by transitioning to. This is clearly shown in Table 1 below. Since these become a stable phase having heat resistance, more preferable results are obtained.

  The above-mentioned mold sand may contain a binder. Specifically, as the binder, furan resin, phenol resin, oil urethane resin, phenol urethane resin, alkali phenol resin, sodium silicate, bentonite, fireproof Examples thereof include, but are not limited to, clay, colloidal silica, and ethyl silicate hydrolyzate.

Specifically, the refractory raw material used in the above-described method for producing mold sand includes an Mg—O-based refractory raw material (referred to as “MgO source”) and an Al ₂ O ₃ —SiO ₂ -based refractory. And a raw material (referred to as “alumina source”). Examples of MgO sources include magnesia clinker, calcined magnesite, olivine, cordierite, magnesium carbonate, magnesium hydroxide, spinel, MgO. Examples of alumina sources include synthetic mullite, calcined bauxite, bauxite, fused alumina, sintered alumina, aluminum hydroxide, van earth shale, chamotte, calcined pyroxene, pyroxene, calcined flint clay, flint clay, kyanite , Sillimanite, andalusite, metakaolin, and kaolin. Of course, the MgO source and the alumina source are not limited to those exemplified. Furthermore, you may use 1 type, or 2 or more types of mixtures chosen from what was mentioned above as a MgO source, and 1 type, or 2 or more types of mixtures chosen from what was mentioned above as an alumina source. It may be used. What is used as the MgO source and what is used as the alumina source do not significantly affect the properties of the mold sand.

  Since the present invention is configured and operates as described above, the following effects (1) to (3) are obtained.

(1) Since spinel is a kind of crystal structure, the melting sphere has a high melting point, excellent heat resistance, high strength, and low expansion and low crushability. As a result, the mold formed of this mold sand has a high mold strength and a high fire resistance of SK37 (1825 ° C) or higher, and casting of a large cast steel product having a high pouring temperature of 1550 to 1650 ° C. Can be applied. In addition, since the mold formed of the mold sand has high heat resistance and high strength at high temperatures, it is possible to prevent casting defects due to mold collapse and thermal expansion of the mold at high temperatures, and high-precision castings can be manufactured.

(2) Since the sand particles are made of molten spheres, the surface of the sand particles is smooth, and the penetration of the binder into the sand particles can be reduced, so the amount of binder used is small and economical. . Further, since the amount of the binder used is small, the mold disintegration after casting is improved, and the residue contained in the sand during sand collection is reduced. Moreover, since the sand particles are spherical, the hardness is high and the friability is low. As a result, the recovery efficiency of the molding sand can be increased and the reusability is excellent. Furthermore, since the sand particles have high hardness and low crushability, the amount of dust generated can be reduced. The work environment can be improved and industrial waste can be reduced.

(3) Since the melt containing spinel as a kind of crystal structure has a low silica content, most of the molten spheres are efficiently melted with little generation of fibrosis of the composition or dust generation of floating particles by blowing high-pressure gas. Therefore, the production efficiency at the time of production is improved, and inexpensive production is possible.

It is a schematic block diagram which shows one Embodiment of the molding sand manufacturing apparatus used for manufacture of the molding sand of this invention. It is the graph which showed the relationship between the spinel X-ray intensity ratio of casting sand, a product yield, a silica depletion ratio, and a dust generation ratio. It is a SEM photograph of the molding sand which concerns on Example 1-1. It is a SEM photograph of mold sand concerning Example 2-1. It is a SEM photograph of mold sand concerning Example 3-1. It is a SEM photograph of the molding sand which concerns on Example 4-1. It is a SEM photograph of the molding sand which concerns on Example 5-1. It is a SEM photograph of the molding sand which concerns on Example 6-1. It is a SEM photograph of the molding sand concerning a prior art.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In the following explanation,
(A) Description of mold sand production apparatus used for production of mold sand of the present invention (B) Procedure for producing mold sand by mold sand production apparatus (A) (C) Explanation of Examples and Comparative Examples (D ) Description will be made according to the flow of comparison between the example and the comparative example.

(A) Description of Mold Sand Production Apparatus Used for Production of Mold Sand of the Present Invention FIG. 1 is a schematic configuration diagram showing an embodiment of a mold sand production apparatus used for production of the mold sand of the present invention. The mold sand production apparatus (1) contains a melting furnace (3) for containing and melting the refractory raw material (2), and blows out high-pressure air (as a result, the molten material (4) of the refractory raw material (2) is scattered. ) It consists of a high-pressure air spraying device (5) and a collection container (7) for collecting the molten spheres (6) scattered and solidified by cooling.

  The melting furnace (3) is an arc melting furnace and includes an electrode (8) for generating an arc for melting the refractory raw material (2), and a tap (9) through which the melt (4) flows out.

  The high pressure air blowing device (5) includes a high pressure air supply device (10), an air supply path (11), and a blowing nozzle (12) in this order. The nozzle port (13) of the blowing nozzle (12) is positioned in the horizontal direction at a position below the hot water outlet (9). And the collection container (7) is arrange | positioned in the lower position ahead of the blowing direction of this nozzle port (13).

  In this embodiment, an arc furnace is used as the melting furnace (3) for melting the refractory raw material (2). However, the melting furnace used in the present invention is not limited to a specific type. An electric furnace, an electric furnace, a reflection furnace, a vacuum melting furnace, or the like can be used. However, it is preferable to use an arc furnace as in this embodiment because it is relatively easy to operate and economical.

  As a method for allowing the melt (4) of the refractory raw material (2) to flow out from the outlet (9) of the melting furnace (3), a tilting method or an opening method can be used. Adopting this is preferable because it can easily maintain a constant outflow amount stably.

  In the present embodiment, high-pressure air is used as the high-pressure gas for scattering the melt (4) of the refractory raw material (2), and the high-pressure gas used in the present invention can be obtained at a low cost. ) Can be used in place of this high-pressure air and high-pressure steam or other types of high-pressure gas. In the present embodiment, the melt (4) scattered by the high-pressure air is naturally cooled while moving in the atmosphere. You may provide the forced cooling part using etc. Since the specific structure of such a forced cooling unit is well known, detailed description thereof will not be repeated here.

(B) Procedure for Producing Mold Sand Using Mold Sand Producing Device Next, a procedure for producing mold sand using the mold sand producing device (1) will be described.
First, the worker pulverizes at least one of the MgO source and the alumina source to an appropriate size of, for example, about 100 mm or less, and accommodates them in the melting furnace (3).

In the refractory raw material (2) used in the present embodiment, the chemical components excluding dry crystal water are 50 to 85% by weight of Al ₂ O ₃ , 5 to 40% by weight of MgO, and more than 0% by weight of SiO ₂ to 20%. What is necessary is just to prepare to weight% or less. However, the sum of the weight percent of Al ₂ O _3, the weight percent of MgO and the weight percent of SiO ₂ must be 100% by weight or less. As described above, magnesia clinker, calcined magnesite (heavy calcined magnesia, light calcined magnesia), olivine, cordierite, magnesium carbonate, magnesium hydroxide, spinel, MgO and the like are used as the MgO source. As an alumina source, synthetic mullite, calcined bauxite, bauxite, fused alumina, sintered alumina, aluminum hydroxide, van earth shale, chamotte, burned pyroclastic gemstone, calcined flint clay, flint clay, kyanite, silimanite, Andalusite, metakaolin, kaolin, etc. are used. The worker uses, as the refractory raw material (2) described above, a material prepared by drying or calcining and dehydrating at least one of the MgO source and the alumina source to have a predetermined chemical component.

The refractory raw material (2) may include at least one of Fe ₂ O ₃ , TiO ₂ , CaO, Na ₂ O, and K ₂ O in a range that does not hinder the action of the mold sand according to the present embodiment. . The ratio of the content to the total content of the mold sand is desirably 10% by weight or less.

  The operator melts the refractory material (2) accommodated in the melting furnace (3). The refractory material (2) is melted by arc heat in the melting furnace (3). Arc heat is generated by energizing the molten carbon electrode (8). The melting temperature in the furnace at this time is usually selected in the range of 1800 to 2300 ° C. A predetermined amount of the melt (4) flows out from the hot water outlet (9) of the melting furnace (3) and falls.

  The melt (4) falling from the outlet (9) is supplied from the high-pressure air supply device (10) through the air supply furnace (11) and from the nozzle port (13) of the blowing nozzle (12). High-pressure compressed air blown in a wide angle in the horizontal direction is blown. Thereby, said melt (4) is crushed and dispersed. The crushed and dispersed melt (4) is immediately spheroidized by the surface tension of the molten particles themselves, and is naturally cooled and solidified while moving in the atmosphere. As a result, a molten sphere (6) having a predetermined particle diameter is formed. The molten sphere (6) falls and accumulates in the collection container (7) and is collected.

  The particle size distribution of the molten sphere (6) includes the composition of the refractory raw material (2), the melting temperature, the spray position of high-pressure air, the pressure, the spray speed, and the shape of the nozzle port (13) of the spray nozzle (12). It can be adjusted according to the spray area (circular or plate shape, etc.), spray area, spray angle (such as horizontal or upward), and scattering distance.

  The operator cools the molten spherical material (6) collected through the above-described process by at least one of air cooling and water cooling, and then removes particles larger than 3000 μm and small particles smaller than 30 μm by sieving. . Thereby, the molding sand which consists of a molten spherical body (6) of a particle size distribution of 30-3000 micrometers is completed.

(C) Description of Examples and Comparative Examples Hereinafter, Examples 1-1 to 6-2 and Comparative Examples 1-1, 1-2, and 2 according to an embodiment of the present invention will be described.
[Example 1-1]
The operator can use fused alumina with a particle size of 10 millimeters or less and a particle size of 10 millimeters so that the weight percentage of Al ₂ O ₃ is about 70 weight percent, SiO ₂ is 1 to 2 weight percent, and MgO is about 20 weight percent. The raw material which mixed the following magnesia clinker suitably was prepared. The operator melted 15 kg of the raw material in the melting furnace (3) of the molding sand production apparatus (1) shown in FIG. 1, that is, the arc furnace (75 KVA, three carbon arc electrodes inserted from above) for 1 hour. Next, the operator discharges the molten raw material from the melting furnace (3), and sprays the high-pressure compressed air discharged from the high-pressure air supply device (10), that is, the compressor (air volume 11 m ³ / min), onto the molten raw material. It was. As a result, a melt (4) in the form of spherical particles was obtained. From this, the operator sampled one having a particle size of 600 micrometers or less to obtain mold sand. The reason why the melt (4) having a particle size of 600 micrometers or less was collected is that such a material exhibits a practical particle size distribution for use as mold sand.

[Example 1-2]
The operator obtained mold sand by re-baking the mold sand of Example 1-1 at 1500 ° C.

[Example 2-1]
The operator may use an Al ₂ O ₃ —SiO ₂ system with a particle size of 20 millimeters or less so that the weight percentage of Al ₂ O ₃ is about 55 wt%, SiO ₂ is about 10 wt%, and MgO is about 30 wt%. A raw material was prepared by appropriately mixing a refractory raw material (mullite-alumina crystal system, 75% by weight of Al ₂ O ₃ and 20% by weight of SiO ₂ ) and magnesia clinker having a particle diameter of 10 millimeters or less. Thereafter, the operator manufactured mold sand by the same method as in Example 1.

[Example 2-2]
The operator obtained mold sand by re-baking the mold sand of Example 2-1 at 1500 ° C.

[Example 3-1]
The worker should have the same Al ₂ O ₃ —SiO as Example 2-1 so that the weight percentage of Al ₂ O ₃ is about 65 wt%, SiO ₂ is about 10 wt%, and MgO is about 20 wt%. _The raw material which mixed ₂ type | system | group refractory raw material and the heavy-burning magnesia whose particle size is 10 millimeters or less suitably was prepared. Thereafter, the operator manufactured mold sand by the same method as in Example 1.

[Example 3-2]
The operator obtained mold sand by re-baking the mold sand of Example 3-1 at 1500 ° C.

[Example 4-1]
The worker should have the same Al ₂ O ₃ —SiO as in Example 2-1 so that the weight percentage of Al ₂ O ₃ is about 60 wt%, SiO ₂ is about 10 wt%, and MgO is about 15 wt%. _The raw material which mixed ₂ type | system | group refractory raw material and olivine with a particle size of 10 millimeters or less suitably was prepared. Thereafter, the operator manufactured mold sand by the same method as in Example 1.

[Example 4-2]
The operator obtained mold sand by re-baking the mold sand of Example 4-1 at 1500 ° C.

[Example 5-1]
The worker should have the same Al ₂ O ₃ —SiO as Example 2-1 so that the weight percentage of Al ₂ O ₃ is about 75 wt%, SiO ₂ is about 10 wt%, and MgO is about 10 wt%. A raw material was prepared by appropriately mixing a ₂ system refractory raw material and a magnesia clinker having a particle size of 10 mm or less. Thereafter, the operator manufactured mold sand by the same method as in Example 1.

[Example 5-2]
The operator obtained mold sand by re-baking the mold sand of Example 5-1 at 1500 ° C.

[Example 6-1]
The operator should have the same Al ₂ O ₃ —SiO as Example 2-1 so that the weight percentage of Al ₂ O ₃ is about 80 wt%, SiO ₂ is about 10 wt%, and MgO is about 5 wt%. A raw material was prepared by appropriately mixing a ₂ system refractory raw material and a magnesia clinker having a particle size of 10 mm or less. Thereafter, the operator manufactured mold sand by the same method as in Example 1.

[Example 6-2]
The operator obtained mold sand by re-baking the mold sand of Example 6-1 at 1500 ° C.

[Comparative Example 1-1]
An operator may use Al ₂ O ₃ —SiO having a particle size of 20 millimeters or less as a raw material so that the weight percentage of Al ₂ O ₃ is about 75 wt%, SiO ₂ is about 15 wt%, and MgO is 5 wt% or less. Mold sand was produced in the same manner as in Example 1 using a ₂ series refractory material (mullite-alumina crystal system, Al ₂ O ₃ 63 wt%, SiO ₂ 32 wt%).

[Comparative Example 1-2]
An operator may use Al ₂ O ₃ —SiO having a particle size of 20 mm or less as a raw material so that the weight percentage of Al ₂ O ₃ is about 80 wt%, SiO ₂ is about 10 wt%, and MgO is 5 wt% or less. Mold sand was produced in the same manner as in Example 1 using a ₂ series refractory material (mullite-alumina crystal system, 75% by weight of Al ₂ O _{3 and} 20% by weight of SiO ₂ ).

[Comparative Example 2]
Cerabeads (registered trademark) # 650, which is a commercially available synthetic mullite spherical sand, was used.

(D) Comparison between Examples and Comparative Examples [Crystal Composition]
The crystal composition of the mold sand according to Example 1-1 to Example 6-2 and the mold sand according to Comparative Examples 1-1, 1-2, and 2 was analyzed. Further, X-ray diffraction was performed on these mold sands. Table 1 shows the composition of the mold sand and the main peak intensity of X-ray diffraction.

  As is apparent from Table 1, spinel was observed in all of the molding sands according to Example 1-1 to Example 6-2. On the other hand, spinel was not recognized in any of Comparative Examples 1-1, 1-2, and 2. In the molding sand according to Comparative Examples 1-1 and 1-2, α-alumina and mullite were observed. Comparative Example 2 Mullite was observed in such casting sand. From this, it is apparent that the conventional synthetic mullite and alumina-based fused spherical particles have different crystal structures from the mold sand according to the present embodiment.

In addition, as is apparent from Table 1, the component composition from which spinel is obtained in Al ₂ O ₃ —MgO—SiO ₂ mold sand is 50 to 85 wt% Al ₂ O ₃ , 5 to 40 wt% MgO, SiO ₂ Was found to be more than 0% by weight and 20% by weight or less, and the total of these was 100% by weight or less.

Also, from the results of X-ray diffraction analysis of Example 1-2, Example 2-2, Example 3-2, Example 4-2, Example 5-2, and Example 6-2 shown in Table 1. Can be said to contain alumina, mullite, cordierite and sapphirine. This corresponds to the mold sand according to Example 1-1, the mold sand according to Example 2-1, the mold sand according to Example 3-1, the mold sand according to Example 4-1, and the example 5-1. The mold sand and the mold sand according to Example 6-1 were refired at a high temperature of 1500 ° C., so that an Al ₂ O ₃ —MgO—SiO ₂ -based amorphous material (this was the main at the time of mold sand production). This indicates that the crystalline mineral spinel) was transformed into a stable phase such as alumina, mullite, cordierite, or sapphirine. Further, it was shown that the amount of recrystallization differs depending on the amount of Al ₂ O ₃ , MgO, and SiO ₂ from these crystal transformations, and the influence of the composition is large.

[About silica depletion ratio]
When melting by arc heat, silica is separated from the melt (4) and easily pulverized, but when silica is separated and pulverized, the working environment deteriorates and the yield of molten spherical particles decreases. Accompanied by. From this, it can be inferred that the silica depletion ratio affects the production yield of the fused spherical particles, and that the silica depletion ratio is a measure for the amount of dust generated during work due to silica separation. And, the depletion ratio of silica is a measure for the amount of dust generated during the work due to the separation of silica (in other words, the depleted silica is the dust during work). This is supported by the observation results and the amount of dust collected by a locally installed dust collector. Therefore, as a method for estimating the production yield and dusting of these melts (4), the silica component before melting and the silica component after melting were measured, and the silica ratio before and after melting was obtained and calculated as the silica depletion ratio. . The index of the amount of dust generation at the time of melting is shown by quantifying as a comparison value with respect to the silica depletion ratio in the synthetic mullite system of the prior art (Comparative Examples 1-1 and 1-2).

The above measurement results are shown in Table 2 and FIG. Table 2 shows the components of the fused spherical particles of Examples 1-1, 2-1, 3-1, 4-1, 5-1, 6-1 and Comparative Examples 1-1, 1-2 according to the present embodiment. And yield (yield), depletion ratio, and dust generation ratio. FIG. 2 is a graph showing the relationship between the spinel X-ray intensity ratio of the mold sand, the product yield, the silica depletion ratio, and the dust generation ratio. The “depletion ratio” shown in Table 2 is a value represented by the following equation (1). The higher this ratio, the larger the dust generation amount SiO ₂ reduction value at the time of melting.

(Equation 1)
Depletion ratio (%) = 100- (SiO ₂ value of melt) / (SiO ₂ value of raw material) × 100 (1)

As a result of investigating the depletion ratio of SiO ₂ with respect to the raw material of the melt at the time of manufacture (see Table 2), it depends on Examples 1-1, 2-1, 3-1 In producing the spinel melt, the SiO ₂ depletion ratio tends to be significantly lower than that of the conventional mullite and alumina melts. That is, it became clear that the amount of molten spherical particles produced during melting increased (= yield improved), and the amount of dust generated was small, resulting in an excellent working environment during melting. In particular, it is clear that the yield of melted spherical particles having a particle size of 600 μm or less (value indicated as “−600 μm” in Table 2) is greatly improved as compared with those of Comparative Examples 1-1 and 1-2. It has become. Incidentally, the value shown as “+600 μm˜” in Table 2 indicates the yield of molten spherical particles having a particle diameter exceeding 600 μm.

Note that the dust generation ratio tends to decrease as the spinel X-ray intensity ratio increases when fired at 1500 ° C., and is particularly noticeable in Example 1-1 and Example 2-1. The “spinel X-ray intensity ratio” is the ratio of the X-ray diffraction intensity of the mold sand according to each example when the X-ray diffraction intensity of the foundry sand according to Example 1-1 is “1”. The component of the molding sand according to Example 1-1 is closest to “Al ₂ O ₃ /MgO=71.7/28.3” which is the theoretical value component of spinel.

[About particle size distribution]
Analysis of particle size distribution, bulk density (Japan Casting Association test method S-10), pH (Japan Casting Association test method S-3), and acid consumption for the mold sand according to Example 1-1 to Example 6-2 The quantity (Japan Foundry Association test method S-4) was measured and a test on heat resistance was carried out, and comparison was made with the molding sand according to Comparative Examples 1 and 2. Based on the result, it can be determined whether the mold sand produced in Example 1-1 to Example 6-2 can sufficiently withstand practical use or not.

  In the analysis of the particle size distribution, the particle size distribution was measured by a mold sand particle size test method (JISZ2601), and the particle size index (AFS) was calculated. That is, a standard sieve having a nominal size of 2360 μm, 1180 μm, 850 μm, 600 μm, 425 μm, 300 μm, 212 μm, 150 μm, 106 μm, 75 μm, 53 μm is selected, and 100 g of a sample is put on top of each other, and a low tap sieve is added. Sift for 15 minutes. Then, the weight remaining on each sieve is measured and displayed as a distribution ratio.

  In general, the mold sand preferably has a particle size distribution of 3000 μm or less (preferably 600 μm or less) to 30 μm on a sieve (preferably on a 45 μm sieve). The particle size distribution conforms to the method defined in JISZ2601. Particle size index AFS of 30, 40, 50, 60, 70, 100, 150 level is selected. The test results are shown in Table 3.

  From the data shown in Table 3, each of the molding sands obtained in the above examples specifically has a particle size distribution almost within the range of 75 to 600 μm and a particle size index of 46.7 to 55.3. It was observed that From these observation data, it was found that the particle size index of the mold sand is equivalent to that of the conventional mold sand, and the practicality is sufficiently obtained.

  The bulk density of the molding sand according to Example 1-1 to Example 6-2 is substantially equal to that of the molding sand according to Comparative Examples 1-1 and 1-2, and there is no practical problem. Moreover, each pH value of the molding sand obtained in the above example shows a neutral value range of 6.62 to 6.94, and the acid consumption is equivalent to that of the conventional molding sand.

  Therefore, the mold sand according to Example 1-1 to Example 6-2 had no practical problem.

[About the surface of the mold sand]
3 to 8 are photographs of sand particles obtained by scanning electron microscope (SEM) of the mold sand according to the present embodiment. FIG. 3 is a SEM photograph of the molding sand according to Example 1-1. FIG. 4 is an SEM photograph of the molding sand according to Example 2-1. FIG. 5 is an SEM photograph of the molding sand according to Example 3-1. FIG. 6 is an SEM photograph of the molding sand according to Example 4-1. FIG. 7 is an SEM photograph of the molding sand according to Example 5-1. FIG. 8 is an SEM photograph of the molding sand according to Example 6-1. FIG. 9 is an SEM photograph of the molding sand according to Comparative Examples 1-1 (a), 1-2 (b), and Comparative Example 2 (c). As apparent from the SEM photographs shown in FIGS. 3 to 8, the surface of the mold sand of the above example has a smooth spherical shape like a glass, and in particular, compared with the conspicuous uneven shape of Comparative Example 2, These are effective in improving the packing density in the case of molding a mold and improving the covering property of the binder to reduce the addition amount.

[About heat resistance test]
The mold sand according to the present embodiment contains spinel (melting point: 2100 ° C., main components: MgO and Al ₂ O ₃ ). Since the melting point of spinel is higher than the melting point of alumina crystal (2050 ° C.) and the melting point of synthetic mullite crystal (1850 ° C.), spinel is expected to have an effect on heat resistance. Of course, it is recognized that alumina and mullite have sufficient heat resistance when used as mold sand as one chemical component, and that the mold sand according to the present embodiment containing these also has sufficient heat resistance. Therefore, there is no problem even if these compositions are contained in the molding sand according to the present embodiment.

Depending on the region of the chemical composition of each crystal, in addition to spinel (MgO.Al ₂ O ₃ ; the chemical components are Al ₂ O ₃ is 71.7% by weight and MgO is 28.3% by weight), _{4MgO · 5Al 2 O 3 · 2SiO} 2; chemical component is _Al 2 _{O 3} is 64.4 wt%, MgO 20.4 wt%, SiO ₂ is 15.2 wt%), cordierite crystal (2MgO · 2Al ₂ O ₃ · 5SiO ₂ ; the chemical component may contain 34.9% by weight of Al ₂ O ₃ , 13.8% by weight of MgO and 51.3% by weight of SiO ₂ . The melting point of the sapphirine crystal is 1475 ° C., and the melting point of the cordierite crystal is 1460 ° C., but there is no particular problem when using it as the mold sand in the region showing the composition of the sand of the present invention.

  In order to confirm the above points, heat resistance was compared by carrying out the following tests.

Among the spinel fused spherical mold sands of Examples 1-1 to 6-2, spinel (MgO.Al ₂ O ₃ ), alumina (α-Al ₂ O ₃ ), mullite (3Al ₂ O ₃ · 2SiO ₂ ), Are the main composition (Al ₂ O ₃ , MgO, SiO ₂ ) and the component values of Fe ₂ O ₃ are the same level. 1 mold sand (see the components of the molten spherical particles of each example described in Table 1), Comparative Example 1-1, 1-2 mold sand (mullite, alumina-based molten spherical sand), and Comparative Example 2 The mold mold sand (synthetic mullite sintered spherical sand) and chromite sand were used to produce alkali phenol molds, which were fired at 1550 ° C. to examine heat resistance.

  About manufacture of a casting mold, 1.1-2.0 weight part of alkali phenol resin (Kobe Richemical Co., Ltd. make, brand name PHENIX 510A) was added with respect to 100 weight part (2 kg) of casting sand. The amount of resin to be used was set as shown in Table 4 in consideration of the specific gravity of each sand. Mixing is carried out with a test article river type universal mixer (manufactured by Shinagawa Kogyo Co., Ltd., 5DMR type), and an organic ester curing agent (C-10, Kobe Riken Kogyo Co., Ltd., C-10) is added in an amount of 20 wt. After adding part and mixing for 30 seconds, the resin was further added and mixed for 30 seconds to discharge sand. The mixed sand was immediately filled in a 50φ × 50 mm test piece taking wood mold, molded, left for 24 hours, and then taken out for testing. The test piece was fired at 1550 ° C. × 1 Hr in a Kanthal furnace, taken out and air-cooled, and the sample was placed in a 14 mesh low tap sieve (made by Iida Seisakusho) and shaken for 1 minute. Thereafter, the amount of sintered sand remaining on the sieve was measured and calculated as a ratio to the input sand. At this time, the comparison was made assuming that the residual ratio of the sintered sand remaining on the sieve serves as an index of heat resistance of the mold sand.

  Table 4 shows the amount of sintered residue. Incidentally, the crystal names shown in parentheses in the figure indicate crystals formed after firing at 1500 ° C. From the results shown in Table 4, as the composition of the mold sand according to the present embodiment, compositions containing spinel, spinel, α-alumina, and mullite (Example 1-1, Example 5-1, Example 6). With regard to 1), particularly, there is very little sintered residue, and it is shown that the fire resistance is particularly excellent even when compared with Comparative Examples 1-1, 1-2, and 2.

  It is conceivable that the high fire resistance is advantageous for casting defects such as mold seizure failure on a cast product, and at the same time, is advantageous for mold collapse after casting. Also in that respect, it is a feature of the mold sand according to the present embodiment.

[About binder]
The mold sand can be used after being processed in the same manner as conventional mold sand and molded into a mold using various binders. Examples of these binders include furan resin, phenol resin, oil urethane resin, phenol urethane resin, alkali phenol resin, sodium silicate, bentonite, refractory clay, colloidal silica, and ethyl silicate hydrolyzate.

  Said binder is hardened by use of the hardening | curing agent according to each use. Specifically, examples of the curing agent for furan resin include inorganic acids such as sulfuric acid, phosphoric acid, phosphoric acid ester, and pyrophosphoric acid, and organic acids such as xylene sulfonic acid, toluene sulfonic acid, and benzene sulfonic acid. Examples of the curing agent for the phenol resin include hexamethylenetetramine. Examples of the curing agent for sodium silicate include carbon dioxide gas, dical silicate, Fe-Si powder, and organic ester. Bentonite and refractory clay are used after a predetermined amount of water has been added and kneaded, or are molded by a Jolt squeeze method. Colloidal silica and ethyl silicate hydrolyzate are used in the fields of lost wax method, ceramic mold method or vanishing model casting method, and the mold sand according to this embodiment is used as these molding materials.

  The amount of these binders used is preferably as small as possible in view of the relationship with casting defects such as mold sand filling properties and gas generation during casting. When the mold sand according to the present embodiment is used, the mold strength shows a value about 1.5 times as will be described later, compared to the case of using spherical mold sand prepared by a conventional sintering method. In addition, the amount of binder used can be reduced in combination with the smooth surface of the sand particles.

  The mold molded with the above-described mold sand is not particularly limited as the target casting, and can be used for casting various castings. Specific examples include aluminum, copper, ordinary cast iron, ductile cast iron, and stainless steel. In addition, since the molding sand according to the present embodiment is nearly spherical, high filling properties and air permeability can be obtained, so that it is possible to manufacture a casting with few casting defects and gas defects due to the mold strength. Specifically, as a result of casting high chrome cast steel by applying mold sand to the skin sand of the furan mold casting method or alkali phenol mold casting method, a defect-free casting with a beautiful casting skin with good casting separation is obtained. I was able to make it.

[Crushability]
After the casting with the above-mentioned mold sand, the recovery rate of the mold sand is an important factor at the foundry site. For this recovery and regeneration rate, the quality of the crushability of the mold sand is an important decisive factor, and the lower the crushability, the better. Therefore, the superiority of the product according to the present embodiment was examined while comparing the crushability of the mold sand according to the present embodiment with the mold sand obtained by the conventional melting method and the sintering method and the general foundry sand.

  The crushability was measured by a mold sand crushing test method (JFS test method S-6). As test samples for crushing test of mold sand, spinel-based fused spherical sand according to this embodiment (Examples 1-1, 2-1, 3-1, 4-1, 5-1, 6-1), mullite Alumina-based molten spherical sand (Comparative Examples 1-1 and 1-2), spherical sand by a sintering method (Comparative Example 2), and chromite sand (Comparative Example 3) were used.

  The test method is to place 10 20 mm alumina ceramic balls and 100 g of sample in a 1 L magnetic pot mill, rotate for 30 minutes, and measure the particle size of sand before and after the treatment. The AFS particle size index was calculated from the particle size measurement result, and the crushing rate was determined by the following equation (2). Table 5 shows the measurement results of the friability.

(Equation 2)
Crushing rate (%) = (Particle size index after rotation / Particle size index of raw sand) x 100 (2)

  The crushability of the spinel-based molten spherical sand (Examples 1-1, 2-1, 3-1, 4-1, 5-1, 6-1) according to the present embodiment is the same as that of conventional mullite and alumina-based molten spherical sand. Compared to the cases of sand (Comparative Examples 1-1 and 1-2) and sintered spherical sand (Comparative Example 2), it was confirmed that the change in particle size due to crushing was small and the crushability was excellent. Furthermore, the crushability of the spinel-type molten spherical sand (Examples 1-1, 2-1, 3-1, 4-1, 5-1, 6-1) according to this embodiment is the same as that of conventional cast steel mold sand. Even when compared with the case of (chromite sand; Comparative Example 3), the result was remarkably excellent in crush resistance. From these results, even when the mold sand according to the present embodiment is used as a mold, it is compared with the mold sand produced by the conventional technique (synthetic mullite-based sintered spherical sand; Comparative Example 2) as a mold. It has become clear that it is advantageous for recovery and regeneration.

  Further, after the casting sand having the predetermined shape was actually manufactured using the casting sand according to the present embodiment, the casting sand was recovered from the used casting mold, and thus it could be easily regenerated. The method for reclaiming the mold sand from the used mold is not particularly limited, and any known method can be employed.

[Test 1: Compressive strength of furan resin mold]
Mold sand according to the present embodiment (Examples 1-1, 2-1, 3-1, 4-1, 5-1, 6-1), conventional mullite, alumina-based molten spherical sand (Comparative Example 1- 1, 1-2), synthetic mullite-based sintered spherical sand (Comparative Example 2) was used to mold a mold by a furan resin method (a mold forming method in which an organic acid is added to a furan resin and cured). The molding method is 1.0 part by weight (1.2 parts by weight in the case of synthetic mullite-based sintered spherical sand) with respect to 100 parts by weight (2 kg) of furan resin (Kao Quaker, 340B) mold sand. The acid curing agent (C-14, manufactured by Kao Quaker) was used in an amount of 50 parts by weight based on 100 parts by weight of the furan resin. The temperature during molding was 20 ° C., and the humidity was 60%. For the mixing, the above-described test article Kawa type universal mixer was used. After adding an acid curing agent to the test sand and mixing for 30 seconds, further adding a furan resin and mixing for 30 seconds, the sand was discharged. After sand removal, it was filled in a 50φ × 50 mm test piece removing wooden mold, cured for 24 hours, and extracted to obtain a test piece mold. The compressive strength and packing density for each elapsed time of the obtained test piece mold were measured with a pressure tester (Orientec, H-3000D). The results are shown in Table 6. In the “Compression strength of furan resin mold” column of Table 6, the compression strength and packing density of the furan resin mold for each of the examples and comparative examples are described.

  As a result of using the molding sand according to the present embodiment for the furan resin method from the above results, the compressive strength is extremely high as compared with the prior art (Comparative Example 2). Compared with Example 2, the strength was about 1.9 times higher. This is because the smooth surface shape and the spherical shape of the molten spherical mold sand according to this embodiment acted effectively, and for the improvement of the filling density of the mold, the improvement of the strength and the reduction of the amount of the binder. The effect was shown.

[Test 2: Compressive strength of alkali phenol resin mold]
Mold sand according to the present embodiment (Examples 1-1, 2-1, 3-1, 4-1, 5-1, 6-1), conventional mullite, alumina-based molten spherical sand (Comparative Example 1- 1, 1-2), synthetic mullite-based sintered spherical sand (Comparative Example 2) was used to mold a mold by an alkali phenol resin method (a template forming method in which an alkali phenol resin is cured with an organic ester). At the time of molding, alkali phenol resin (trade name PHENIX 510A manufactured by Kobe Riken Kogyo Co., Ltd., trade name: PHENIX 510A) is 2.0 parts by weight with respect to 100 parts by weight of mold sand (in the case of synthetic mullite type sintered spherical sand, 2.5 weights Part) and 20 parts by weight of an organic ester curing agent (C-10, manufactured by Kobe Rika Kogyo Co., Ltd.) was used with respect to 100 parts by weight of the alkali phenol resin. Moreover, the air temperature at the time of molding was 20 ° C., and the humidity was 60%. The test sand, curing agent, resin mixing method and test piece preparation method were carried out in the same manner as in [Test 1: Furan resin mold]. The compressive strength and packing density for each elapsed time of the obtained test piece mold were measured. In the column “Compression strength of alkali phenol resin mold” in Table 6, the compression strength and packing density of the alkali phenol resin mold for each of the examples and comparative examples are described.

  As is apparent from the above measurement results, when the molding sand according to the present embodiment is used for the alkali phenol resin method, a higher compressive strength is obtained than in the prior art (Comparative Example 2), and particularly after 24 hours of standing. The mold strength was 1.5 to 1.6 times higher than that of the prior art. In these cases as well as [Test 1: Furan resin mold], the smooth surface shape and spherical shape of the molten spherical mold sand according to the present embodiment acted effectively, improving the filling density of the mold, The effect was shown with respect to the improvement in strength and the reduction in the amount of binder added.

[Test 3: Thermal expansion coefficient of alkali phenol resin mold]
A test for measuring the thermal expansion coefficient by the alkali phenol resin method using the mold sand (Examples 1-1, 2-1, 3-1, 4-1, 5-1, 6-1) according to this embodiment. A piece was made. Specifically, alkali phenol resin (Kao Quaker, S661K) is used in an amount of 1.2 parts by weight based on 100 parts by weight of mold sand, and organic ester curing agent (Kao Quaker, QX140) is used in 100 wt. A test piece having a diameter of 50 mm and a height of 50 mm was prepared using 25 parts by weight of the part. The temperature during molding was 20 ° C., and the humidity was 60%. The test sand, curing agent, resin mixing method and test piece preparation method were carried out in the same manner as in [Test 1: Furan resin mold]. The test piece created by the above method was set on a direct thermal expansion meter (EOS-3, manufactured by Ozawa Science Co., Ltd.), and the coefficient of thermal expansion was measured when rapidly heated in an electric furnace maintained at 1000 ° C. . Comparison with conventional mullite, alumina-based fused spherical sand (Comparative Examples 1-1 and 1-2), synthetic mullite-based sintered spherical sand (Comparative Example 2), chromite sand and flattery quartz sand (imported quartz sand) as comparative examples And measured. The amount of resin added to each sand is listed in Table 6. The result of the thermal expansion coefficient of each example is shown in the column of “thermal expansion coefficient of alkali phenol resin mold” in Table 6. As is apparent from the results shown in Table 6, the spherical spherical sand according to this embodiment has a small coefficient of thermal expansion. Therefore, it is clear that it is more effective in preventing casting defects such as vaning, scooping and squeezing due to thermal expansion than in the past.

[Test 4: Recycled sand]
Mold sand according to this embodiment (Examples 1-1, 2-1, 3-1, 4-1, 5-1, 6-1), mullite according to the prior art, alumina-based molten spherical sand (Comparative Example 1- 1, 1-2), using synthetic mullite-based sintered spherical sand (Comparative Example 2), and molding a mold prepared according to [Test 2: Compressive strength of alkali phenol resin mold] by the alkali phenol resin method. Recycled sand was obtained using a commercially available sand regenerator. Further, these operations were repeated three times to mold a mold, and the compressive strength after standing for 24 hours was measured. The mold was prepared by adding 2.0 parts by weight of alkali phenol resin (trade name PHENIX 510A, manufactured by Kobe Riken Kogyo Co., Ltd.) to 100 parts by weight of mold sand (2.5 parts by weight in the case of synthetic mullite-based sintered spherical sand). ) And 20 parts by weight of an organic ester curing agent (C-10, manufactured by Kobe Chemical Industry Co., Ltd.) was used with respect to 100 parts by weight of the alkali phenol resin. Moreover, the air temperature at the time of molding was 20 ° C., and the humidity was 60%. The compressive strength and packing density for each elapsed time of the test piece mold using regenerated sand were measured. The results are shown in the column “Recycled sand mold strength” in Table 6. As is clear from the above measurement results, the mold strength when the mold sand according to the present embodiment is regenerated is lower in strength due to the use of the reclaimed sand compared to the mold sand of the prior art (Comparative Example 2). Few. In particular, when sand regenerated three times was used, it was found that the mold strength was about three times that of the prior art. This result shows that since the molten spherical mold sand according to this embodiment is a smooth spherical shape, there is little binder remaining on the surface of the mold sand particles, and there is no adverse effect on repeated addition of the binder. Suggests. In the case of Comparative Example 2, the surface of the mold sand is porous as apparent from the SEM photograph of the mold sand in FIG. 9B. As a result, the binder remains easily, and these are the binder. It is presumed that the effect of repeated addition was adversely affected.

[Casting test results]
Spinel-type molten sand (Examples 1-1, 2-1, 3-1, 4-1, 5-1, 6-1) manufactured according to this embodiment, mullite according to the prior art, alumina-based molten sand (Comparative Example) 1-1, 1-2), and spherical cores (Comparative Example 2) obtained by a sintering method, an alkali phenol mold core (50φ × 60H) was produced. In the upper mold, a pouring gate and a hot water (in this case, a portion for accumulating the molten metal provided in the upper part of the mold) was installed. The lower mold was provided with a 270φ × 120H cavity. The above-described 50φ × 60H core was installed at a location corresponding to the bottom of the cavity. The cores were arranged so as to keep a uniform spacing on the circumference. The lower end of the core was embedded in a portion corresponding to the bottom of the cavity. The core embedding depth was 10 mm. As a result, the size of the portion of the core that contacts the molten metal is 50φ × 50H. In this mold, a high chromium nickel steel melted in a high frequency melting furnace (pour temperature 1550 ° C., casting weight 50 kg) was poured in a ladle and the metal skin (after shot blasting) in contact with the core portion was observed. .

  The core sand is blended in an amount of 1.5% by weight of the alkali phenol resin with respect to 100 parts by weight of the molten spherical sand and 25% by weight of the hardener added to the resin. A x60H test piece removing wooden mold was filled and cured for 24 hours. In addition, a region with a paint mold and a region without a paint mold were provided in the same core. In the case of sintered spherical sand (Cerabeads (registered trademark) # 650), the amount of resin added is 2.0% by weight, the amount of hardener added to the resin is 25% by weight, and the outer mold sand is Mikawa No. 6 sand 100 It was molded by adding and kneading 6% by weight of water glass to weight% and cured with carbon dioxide gas. The results are shown in Table 7. From the results of the casting test shown in Table 7, it was clear that the core casting skin of the core produced by the melting method according to the present embodiment was good and had no problem for practical use.

  The present invention has high heat resistance and excellent low expansibility and low crushability, as well as excellent mold characteristics and sand reusability. Moreover, since the yield at the time of production is high and it can be carried out inexpensively, it can be used as mold sand used for various molds in addition to large cast steel products.

DESCRIPTION OF SYMBOLS 1 Mold sand manufacturing apparatus 2 Refractory raw material 3 Melting furnace 4 Melt 5 High pressure air spraying apparatus 6 Molten sphere 7 Collection container 8 Electrode (carbon electrode)
9 Hot water outlet 10 High-pressure air supply device 11 Air supply path 12 Blowing nozzle 13 Nozzle port

Claims (4)

Al ₂ O ₃ is 50 to 85 wt%, MgO 5 to 40 wt%, SiO ₂ has a 20% by weight of chemical components than 0 wt%, of the MgO the weight% of the _Al 2 _{O 3} A molten sphere having a total of 100% by weight or less and 100% by weight of SiO ₂ and having spinel (MgO.Al ₂ O ₃ ) as one kind of crystal structure, Mold sand characterized by having a particle size distribution of ˜3000 μm. A composite of spinel and any of alumina, mullite, cordierite, and sapphirine is a kind of crystal structure, Al ₂ O ₃ is 50 to 85% by weight, MgO is 5 to 40% by weight, and SiO ₂ is 0% by weight. A molten sphere having a chemical component of more than 20% by weight and less than 20% by weight, and the total of the weight percent of the Al ₂ O ₃ , the weight percent of the MgO and the weight percent of the SiO ₂ is 100 weight percent or less, Mold sand, wherein the molten spheres have a particle size distribution of 30 to 3000 μm. Prepared from at least one of a MgO source and an alumina source, Al ₂ O ₃ having a chemical component of 50 to 85% by weight, MgO of 5 to 40% by weight, SiO ₂ of more than 0% by weight and 20% by weight or less, A refractory material having a total of 100% by weight or less of the weight percent of Al ₂ O _3, the weight percent of MgO and the weight percent of SiO ₂ is charged into a melting furnace, and then the refractory material is melted, Melting spinel as a kind of crystal structure by spraying high-pressure gas on the melt formed by melting the refractory raw material and dispersing it into fine particles, and having a particle size distribution of 30 to 3000 μm A method for producing mold sand, characterized by forming a spherical object. Prepared from at least one of a MgO source and an alumina source, Al ₂ O ₃ having a chemical component of 50 to 85% by weight, MgO of 5 to 40% by weight, SiO ₂ of more than 0% by weight and 20% by weight or less, A refractory material having a total of 100% by weight or less of the weight percent of Al ₂ O _3, the weight percent of MgO and the weight percent of SiO ₂ is charged into a melting furnace, and then the refractory material is melted, A composite of spinel and one of alumina, mullite, cordierite, and sapphirine by spraying high-pressure gas on the melt formed by melting the refractory raw material and then cooling and solidifying it while scattering it into fine particles. And a molten sphere having a particle size distribution of 30 to 3000 μm is formed.

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