INORGANIC COATED SAND

Abstract

Inorganic coated sand in a dry state having refractory aggregate; and an inorganic binder layer formed on a surface of the refractory aggregate, in which the inorganic binder layer contains a metasilicate hydrate.

Claims

1. An inorganic coated sand in a dry state, comprising: refractory aggregate; and an inorganic binder layer formed on a surface of the refractory aggregate, wherein the inorganic binder layer comprises a metasilicate hydrate, and wherein amount of the inorganic binder layer to be applied is 0.05 parts by mass or greater and 10 parts by mass or less with respect to 100 parts by mass of the refractory aggregate.

2. The inorganic coated sand according to claim 1, wherein a water content in the inorganic binder layer is 60 parts by mass or greater and 140 parts by mass or less with respect to 100 parts by mass of the metasilicate.

3. The inorganic coated sand according to claim 1, wherein the metasilicate hydrate is at least one selected from sodium metasilicate pentahydrate and sodium metasilicate nonahydrate.

4. The inorganic coated sand according to claim 1, wherein the refractory aggregate has an amorphous degree of 30% or greater.

5. The inorganic coated sand according to claim 1, wherein a sphericity of the inorganic coated sand is 0.80 or greater.

6. The inorganic coated sand according to claim 1, wherein an average particle diameter of the inorganic coated sand is 0.05 mm or greater and 2 mm or less.

7. The inorganic coated sand according to claim 1, wherein the refractory aggregate comprises at least one selected from the group consisting of SiO.sub.2 and Al.sub.2O.sub.3.

8. The inorganic coated sand according to claim 1, further comprising inorganic fine particles at least on the inorganic binder layer or in the inorganic binder layer.

9. The inorganic coated sand according to claim 8, wherein the inorganic fine particles have an average particle diameter of 0.1 μm or greater and 2.0 μm or less.

10. The inorganic coated sand according to claim 8, wherein the inorganic fine particles comprise amorphous silica particles.

11. The inorganic coated sand according to claim 8, wherein content of the inorganic fine particles is 0.1 parts by mass or greater and 10 parts by mass or less with respect to 100 parts by mass of the refractory aggregate.

12. The inorganic coated sand according to claim 1, wherein a slump loss value measured in an environment of 25° C. and 55% relative humidity by a slump test using a slump cone having an inner diameter of 50 mm at an upper end, an inner diameter of 100 mm at a lower end, and a height of 150 mm according to JIS A 1101: 2014 is 90 mm or greater.

13. A method for manufacturing inorganic coated sand in a dry state, the inorganic coated sand having refractory aggregate and an inorganic binder layer formed on a surface of the refractory aggregate, wherein the inorganic binder layer comprises a metasilicate hydrate, and wherein amount of the inorganic binder layer to be applied is 0.05 parts by mass or greater and 10 parts by mass or less with respect to 100 parts by mass of the refractory aggregate, the method comprising: a step (1) of obtaining a mixture by mixing the refractory aggregate with the metasilicate hydrate at a temperature equal to or higher than a melting point of the metasilicate hydrate; and a step (2) of cooling the mixture to a temperature lower than the melting point of the metasilicate hydrate.

14. The method for manufacturing inorganic coated sand according to claim 13, wherein in the step (1), the metasilicate hydrate is mixed without being previously made into an aqueous solution.

15. A casting mold which is formed from the inorganic coated sand according to claim 1.

16. A method for manufacturing a casting mold comprising: a step (3) of filling a mold for providing a desired casting mold with the inorganic coated sand according to claim 1; and a step (4) of curing the inorganic coated sand by heating the mold filled with the inorganic coated sand without steam aeration.

17. An inorganic coated sand in a dry state, comprising: refractory aggregate; and an inorganic binder layer formed on a surface of the refractory aggregate, wherein the inorganic binder layer comprises at least one selected from sodium metasilicate pentahydrate and sodium metasilicate nonahydrate, wherein a water content in the inorganic binder layer is 60 parts by mass or greater and 140 parts by mass or less with respect to 100 parts by mass of the metasilicate, wherein the refractory aggregate comprises at least one selected from the group consisting of SiO.sub.2 and Al.sub.2O.sub.3, wherein amorphous degree of the refractory aggregate is 30% or greater, wherein amount of the inorganic binder layer to be applied is 0.05 parts by mass or greater and 10 parts by mass or less with respect to 100 parts by mass of the refractory aggregate, and wherein the inorganic coated sand has an average particle diameter of 0.05 mm or greater and 2 mm or less, and a sphericity of 0.80 or greater.

Description

EXAMPLES

[0175] Hereinafter, the present invention will be described with reference to examples and comparative examples, but is not limited thereto.

[0176] [1] Measurement Method

[0177] First, a measurement method in the following examples and comparative examples will be described.

[0178] (1) Average Particle Diameters of Refractory Aggregate and Inorganic Coated Sand (Or Kneaded Sand)

[0179] In a case where the sphericity obtained from a projected cross-section of a particle was 1, the diameter (mm) was measured, and in a case where the sphericity was less than 1, a major axis diameter (mm) and a minor axis diameter (mm) of the particle aligned randomly were measured to obtain (major axis diameter+minor axis diameter)/2. Values obtained for each of optional 100 particles were averaged to define the average as an average particle diameter (mm).

[0180] The major axis diameter and the minor axis diameter of the particle were obtained by taking an image (photograph) of the particle with a digital scope (model VH-8000 manufactured by KEYENCE CORPORATION) and analyzing the obtained image.

[0181] (2) Average Particle Diameter of Inorganic Fine Particles

[0182] A particle size distribution of inorganic fine particles was measured by a laser diffraction method using a laser diffraction scattering particle size distribution measurement apparatus. From the measurement results, a particle diameter (d.sub.50, average particle diameter) of the inorganic fine particles at a cumulative percentage of 50% in the weight-based cumulative distribution was obtained.

[0183] (3) Chemical Composition Ratio of Refractory Aggregate

[0184] The composition ratio of each component in the refractory aggregate was measured by a fluorescent X-ray method.

[0185] (4) Amorphous Degree of Refractory Aggregate

[0186] The refractory aggregate was pulverized in a mortar, and pressure-bonded to an X-ray glass holder of a powder X-ray diffraction apparatus for measurement. As the powder X-ray diffraction apparatus, MultiFlex (light source: CuKα ray, tube voltage: 40 kV, tube current: 40 mA) manufactured by Rigaku Corporation was used, and the measurement was performed in a range of 2θ=5° to 90° at a scanning interval of 0.01° and a scanning speed of 2°/min with slits DS 1, SS 1, RS 0.3 mm. Within a range of 2θ=10° to 50°, the X-ray intensities on the low-angle side and the high-angle side were connected by a straight line, the area below the straight line was set as a background, the crystallinity was obtained using the software attached to the apparatus and subtracted from 100, and the result was defined as the amorphous degree. Specifically, with respect to the area above the background, the amorphous peak (halo) and each crystalline component were separated by curve fitting, and areas thereof were obtained to calculate the amorphous degree (%) by the following formula.

Amorphous Degree (%)=Area of Halo/(Area of Crystalline Component+Area of Halo)×100

[0187] (5) Sphericity of Inorganic Coated Sand (Or Kneaded Sand)

[0188] The sphericities of the refractory aggregate and the inorganic coated sand (or kneaded sand) were obtained as follows: a particle image (photograph) obtained by a digital scope (model VH-8000 manufactured by KEYENCE CORPORATION) was analyzed to obtain an area of a projected cross-section of the particle and a circumferential length of the cross-section, [circumferential length (mm) of true circle having area same as that (mm.sup.2) of projected cross-section of particle]/[circumferential length (mm) of projected cross-section of particle] was calculated, and values obtained for each of optional 50 particles were averaged.

[0189] (6) Slump Loss Value and Slump Flow Value of Inorganic Coated Sand (Or Kneaded Sand)

[0190] The slump loss value and the slump flow value of the inorganic coated sand (or kneaded sand) were measured in an environment of 25° C. and 55% relative humidity by a slump test using a slump cone having an inner diameter of 50 mm at an upper end, an inner diameter of 100 mm at a lower end, and a height of 150 mm according to JIS A 1101: 2014.

[0191] (7) Dry State or Wet State of Inorganic Coated Sand or Kneaded Sand

[0192] A cylindrical transparent plastic bottle having a diameter of 76 mm and a height of 125 mm was filled with the coated sand in an amount half the volume of the bottle, held such that an axis was kept horizontal, and rotated at room temperature (25° C.) and a speed of 25 rpm around the horizontal axis. The dry state was represented as a case where a slope of the coated sand layer or the kneaded sand layer flowing in the cylinder became flat, and an angle (dynamic angle of repose) formed between the slope and the horizontal plane could be measured. The wet state was represented as a case where the coated sand or the kneaded sand did not flow in the cylinder, or the slope of the coated sand layer or the kneaded sand layer was not formed as a flat plane even when the coated sand layer or the kneaded sand layer flowed, whereby the dynamic angle of repose could not be measured.

[0193] [2] Evaluation Method

[0194] Next, evaluation methods in the following examples and comparative examples will be described.

[0195] (1) Preparation of Casting Mold

[0196] Using the inorganic coated sands (or kneaded sands) obtained in the examples and the comparative examples, casting molds were prepared by the following methods. In any method, the preparation was carried out under the condition that no steam aeration was performed.

[0197] Small Mold (Pressurization)

[0198] A horizontal mold with 5 cavities capable of molding a test piece of 10×10×60 mm, heated to 200° C., was filled with the coated sand (or kneaded sand) under pressure with a trowel, kept to heat for 10 minutes for curing, and then test pieces were obtained.

[0199] Small Mold (Pouring)

[0200] The coated sand (or kneaded sand) was poured into a horizontal mold with 5 cavities of 10×10×60 mm, heated to 200° C., kept to heat for 10 minutes to be cured, and then test pieces were obtained.

[0201] Blowing

[0202] Using a CSR-43 blow molding machine, a mold (with 5 cavities) for test pieces of 22.3×22.3×180 mm, heated to 200° C., was blow-filled in a vertical direction at a blow pressure of 0.45 MPa. Then, heating was performed for curing for 10 minutes, and test pieces were obtained.

[0203] (2) Density of Casting Mold

[0204] A weight of the test piece was measured and divided by a volume calculated by dimension measurement to calculate a density of a casting mold.

[0205] (3) Bending Strength of Casting Mold

[0206] For the test pieces obtained by using the small mold, a digital force gauge ZTS-500N was attached to a vertical electric measuring stand manufactured by Imada Co., Ltd., and the measurement was performed by a method according to JACT test method SM-1.

[0207] For the test pieces obtained by blow molding, a PBV transverse strength measuring attachment was attached to a PFG universal strength testing machine manufactured by Georg Fischer Ltd.

[0208] (4) Filling Rate

[0209] The density of the test piece obtained was divided by the bulk density of the coated sand (or kneaded sand) and multiplied by 100, and the result was defined as a filling rate.

[0210] [3] Materials

[0211] Next, materials used in the following examples and comparative examples will be described.

[0212] (1) Refractory Aggregate

[0213] Refractory Aggregate 1: silica sand (R6 manufactured by Mikawa Keiseki K.K.)

[0214] Refractory Aggregate 2: artificial sand prepared by electromelting method (ESPEARL 60L manufactured by YAMAKAWA SANGYO CO., LTD.)

[0215] Refractory Aggregate 3: spherical molten silica (prepared by spheroidizing natural silica sand by flame fusion method)

[0216] RefractoryAggregate 4: mullite-based artificial sand (LUNAMOS MS#60 manufactured by Kao Corporation)

[0217] Table 1 shows properties of the refractory aggregates 1 to 4.

TABLE-US-00001 TABLE 1 Average Chemical Composition Amorphous Particle Ratio [mass %] Degree Diameter Method SiO.sub.2 Al.sub.2O.sub.3 Fe.sub.2O.sub.3 [%] [μm] Sphericity Refractory Natural 98.6 0.4 0.2 0.2 200 0.85 Aggregate 1 Refractory Electromelting 13.7 78.8 1.7 45 241 0.97 Aggregate 2 and Air-Granulating Method Refractory Flame Fusion 98.9 0.8 0.1 >95 200 0.89 Aggregate 3 Method Refractory Flame Fusion 32 63 1 72 200 0.98 Aggregate 4 Method

[0218] (2) Inorganic Binder

[0219] Inorganic Binder 1: sodium metasilicate nonahydrate (Na.sub.2SiO.sub.3.Math.9H.sub.2O), melting point 47° C.

[0220] Inorganic Binder 2: water glass aqueous solution A (water glass aqueous solution in which sodium silicate (SiO.sub.2/Na.sub.2O=2.1) is diluted with water to give a solid content (in which water is removed from water glass aqueous solution) concentration of 35 mass %)

[0221] (3) Inorganic Fine Particles

[0222] Inorganic Fine Particles 1: amorphous silica particles (average particle diameter d.sub.50: 0.4 μm)

[0223] Inorganic fine particles 2: amorphous silica particles (average particle diameter d.sub.50: 0.6 μm)

Example 1

[0224] The refractory aggregate 1 heated to a temperature of 105° C. was put into a stirring apparatus, and then cooled to 65° C. Then, the inorganic binder 1 was added at a ratio of 5 parts by mass with respect to the refractory aggregate 1 (100 parts by mass), and kneaded while being cooled to room temperature (25° C.) to crystallize and pulverize the inorganic binder 1, and thus coated sand 1 in a dry state was obtained. The obtained coated sand 1 was evaluated as described above. The obtained results are shown in Table 2.

Examples 2 to 4

[0225] Coated sands 2 to 4 in a dry state were obtained in the same manner as in Example 1, except that the refractory aggregates 2 to 4 were used instead of the refractory aggregate 1 as the refractory aggregate. The obtained coated sands 2 to 4 were evaluated as described above. The obtained results are shown in Table 2.

Example 5

[0226] Coated sand 5 in a dry state was obtained in a manner such that the coated sand 2 (105 parts by mass) obtained in Example 2 and the inorganic fine particles 1 (1 part by mass) were put into a stirring apparatus, and then mixed by stirring at a temperature of 25° C. to apply the inorganic fine particles 1 to the inorganic binder layer of the coated sand 2. The obtained coated sand 5 was evaluated as described above. The obtained results are shown in Table 2.

Examples 6 and 7

[0227] Coated sands 6 to 7 in a dry state were obtained in the same manner as in Example 5, except that the coated sands 3 and 4 were used instead of the coated sand 2. The obtained coated sands 6 to 7 were evaluated as described above. The obtained results are shown in Table 2.

Example 8

[0228] Coated sand 8 in a dry state was obtained in the same manner as in Example 6, except that the inorganic fine particles 2 were used instead of the inorganic fine particles 1. The obtained coated sand 8 was evaluated as described above. The obtained results are shown in Table 2.

Comparative Example 1

[0229] Kneaded sand 1 in a wet state was obtained in a manner such that the refractory aggregate 1 heated to a temperature of 25° C. was put into a stirring apparatus, and then the inorganic binder 2 was added at a ratio of 1.2 parts by mass with respect to the refractory aggregate 1 (100 parts by mass) and kneaded for 1 minute. The obtained kneaded sand 1 was evaluated as described above. The obtained results are shown in Table 2.

Comparative Example 2

[0230] Kneaded sand 2 in a wet state was obtained in the same manner as in Comparative Example 1, except that the refractory aggregate 2 was used instead of the refractory aggregate 1 as the refractory aggregate. The obtained kneaded sand 2 was evaluated as described above. The obtained results are shown in Table 2.

Comparative Example 3

[0231] Coated sand 9 in a dry state was obtained in a manner such that the refractory aggregate 2 heated to a temperature of 120° C. was put into a stirring apparatus, and then the inorganic binder 2 was added at a ratio of 1.2 parts by mass with respect to the refractory aggregate 2 (100 parts by mass) and kneaded to be pulverized while being dried to remove the water in the inorganic binder 2. The obtained coated sand 9 was evaluated as described above. The obtained results are shown in Table 2.

TABLE-US-00002 TABLE 2 Small Mold (pressur- Small Mold Average ization) (pouring) Blowing Inor- State Slump Slump Particle Den- Den- Fill- Inor- ganic of Loss Flow Diam- sity Bending sity Bending ing Bending Refractory ganic Fine Coated Value Value eter (g/ Strength (g/ Strength Rate Strength Aggregate Binder Particles Sand (mm) (mm) (mm) Sphericity cm.sup.3) (MPa) cm.sup.3) (MPa) (%) (MPa) Exam- Refractory Inorganic — Dry 107 220 0.200 0.85 1.45 2.96 1.34 1.70 100 0.80 ple 1 Aggregate 1 Binder 1 Exam- Refractory Inorganic — Dry 112 290 0.241 0.97 1.81 5.12 1.72 3.60 100 2.39 ple 2 Aggregate 2 Binder 1 Exam- Refractory Inorganic — Dry 116 250 0.200 0.89 1.22 5.65 1.14 3.90 100 3.64 ple 3 Aggregate 3 Binder 1 Exam- Refractory Inorganic — Dry 110 250 0.200 0.98 1.69 4.84 1.59 3.04 100 3.24 ple 4 Aggregate 4 Binder 1 Exam- Refractory Inorganic Inorganic Dry 109 270 0.241 0.97 1.87 12.59 1.67 7.63 100 6.49 ple 5 Aggregate 2 Binder 1 Fine Particles 1 Exam- Refractory Inorganic Inorganic Dry 110 250 0.200 0.89 1.34 12.21 1.20 9.09 100 8.05 ple 6 Aggregate 3 Binder 1 Fine Particles 1 Exam- Refractory Inorganic Inorganic Dry 111 300 0.200 0.98 1.71 11.57 1.58 8.12 100 7.98 ple 7 Aggregate 4 Binder 1 Fine Particles 1 Exam- Refractory Inorganic Inorganic Dry 108 250 0.200 0.89 1.45 21.57 1.25 12.50 100 10.44 ple 8 Aggregate 3 Binder 1 Fine Particles 2 Compar- Refractory Inorganic — Wet 84 100 0.200 *1 1.27 1.43 *2 *2 94 0.61 ative Aggregate 1 Binder 2 Example 1 Compar- Refractory Inorganic — Wet 69 60 0.241 *1 1.79 *3 *2 *2 84 *3 ative Aggregate 2 Binder 2 Example 2 Compar- Refractory Inorganic — Dry 116 258 0.241 0.97 *4 *4 *4 *4 *4 *4 ative Aggregate 2 Binder 2 Example 3 *1: The measurement value was not obtained since the sand aggregates in a wet state and did not form a particle shape. *2: The measurement was not possible since the sand could not be naturally poured due to the wet state. *3: The measurement value was not obtained since the filling rate was poor and accurate comparison was not possible. *4: The measurement value was not obtained since the sand was not cured and the casting mold was not formed.

[0232] The inorganic coated sands in a dry state in Examples 1 to 8 had a higher filling rate than the kneaded sands in a wet state in Comparative Examples 1 and 2, and was thus excellent in fillability into a mold. The casting molds obtained using the inorganic coated sands in a dry state in Examples 1 to 8 had a higher bending strength than the casting molds obtained using the kneaded sands in a wet state in Comparative Examples 1 and 2, and thus had an excellent strength. The coated sand in a dry state in Comparative Example 3 was not cured under the condition that no steam aeration was performed.

[0233] As described above, it has been confirmed that the inorganic coated sand according to this embodiment makes it possible to realize an excellent fillability into a mold and a casting mold having excellent strength. It has been confirmed that the inorganic coated sand according to this embodiment is cured even under the condition that no steam aeration is performed, and thus it has been found that it is possible to achieve simplification of a facility or the like. It has been found that the inorganic coated sand according to this embodiment can be manufactured without the use of an aqueous solution of the inorganic binder, and the manufacturing of the inorganic coated sand does not require a water removing step.