Additives for green sand and green sand compositions for casting

Abstract

This invention provides an additive for green sand used in casting, which improves the performance of the sand, such as its fluidity, mixing speed, and disintegration properties. [Solution] The additive for green sand is a green sand additive comprising a surfactant, an alcohol, and water, wherein the surfactant is sodium dioctyl sulfosuccinate, the alcohol is at least one alcohol selected from propylene glycol or ethanol, and the blending ratio of the surfactant to the alcohol is 4:1 to 5:1.

Description

[[Technical Field]]

[0001] The present invention relates to an additive for green molding sand that improves performances such as filling property, fluidity, drawability and kneading completion speed of green molding sand for casting. [[Background Art]]

[0002] Casting a target product using green molding sand for casting containing silica sand as a main component is widely performed. This green molding sand for casting is required to satisfy certain standards for normal temperature properties such as sand moisture, static density, filling density, wet compressive strength and surface stability. In addition, appropriate fluidity, kneading completion speed, disintegration property and low drawing resistance are also important factors for proceeding with operations.

[0003] Commonly used green molding sand for casting has silica sand as the main component, and is formed by blending appropriate amounts of bentonite containing montmorillonite as the main mineral, coal powder, starch and water into the silica sand respectively. For the purpose of obtaining green molding sand with improved mold surface stability, the green molding sand composition described in Patent Document 1 has been proposed.

[0004] In Patent Document 1, in order to obtain a green molding sand composition with excellent surface stability, the blending ratio of sand to surfactant is preferably 0.001 to 1.0 parts by weight of surfactant relative to 100 parts by weight of sand, and the blending ratio of sand to polyhydric alcohol is preferably 0.5 to 5 parts by weight of polyhydric alcohol relative to 100 parts by weight of sand. It is stated from the examples that a ratio of surfactant to polyhydric alcohol of about 1:100 is preferable.

[0005] As the reason for the improved surface stability, Patent Document 1 describes that the surfactant increases the wettability of active clay to water, thereby improving the caking force, and the caking force is improved even when the amount of water is reduced; polyhydric alcohol can dissolve in water and well trap water, and has a high boiling point that makes it difficult to evaporate, so moisture is difficult to diffuse to the outside, allowing water to effectively wet the active clay; due to the synergistic effect of these factors, the caking force between sand particles is improved with a small amount of water, thereby improving the surface stability. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 6-154937 [Overview of the project] [Problems that the invention aims to solve]

[0007] The invention described in Patent Document 1 states that by adding polyhydric alcohol in a greater quantity than surfactant to the sand, the surface stability of the green sand mold can be improved, resulting in castings with a beautiful surface finish. However, the performance required of green sand for casting is not limited to surface stability. Other performance characteristics that contribute to improving the dimensional accuracy of cast products and improving workability include filling ability, fluidity, and mold removal ability. In particular, in aeration molding of molds, which has become popular in recent years, it is necessary to fill every corner of the mold with highly fluid green sand for casting using low-pressure compressed air. Furthermore, to improve workability, the mixing speed of the green sand for casting must quickly reach the target value during mixing. Moreover, since green sand for casting is dismantled and the sand is reused after being used as a mold, there was a problem that its disintegration ability would decrease if its surface stability and strength remained high.

[0008] Therefore, the inventors of this invention investigated an additive for green sand that improves performance such as filling properties, fluidity, mixing speed, and mold-removing properties, suppresses adhesion to equipment and contributes to improved workability, while simultaneously creating green sand for casting that maintains a certain degree of strength while also having excellent disintegration properties.

[0009] The experimental results revealed that there are suitable surfactants and alcohols for obtaining casting sand that allows for good casting operations, that there is a preferred ratio for the surfactant and at least one type of alcohol added to silica sand, and that simply increasing the amount of surfactant added to casting sand is not sufficient, as there is a limit to how much can be added for it to be effective.

[0010] The object of the present invention is to provide a green sand additive and a green sand composition for casting that can improve the fluidity of green sand for casting, allow water to penetrate quickly to reach a target mixing speed, suppress adhesion to equipment, and improve disintegrability while maintaining strength. [Means for solving the problem]

[0011] The present invention provides an additive for green sand, comprising a surfactant, an alcohol, and water, wherein the surfactant is sodium dioctyl sulfosuccinate, the alcohol is propylene glycol, and the ratio of the surfactant to the alcohol is 4:1 to 5:1.

[0012] Furthermore, the green sand composition for casting according to the present invention is characterized in that, in a green sand composition for casting to which the green sand additive is added, the surfactant is blended in a ratio of 0.0028 to 0.0112 parts by weight per 100 parts by weight of the green sand for casting.

[0013] According to this study, when preparing a green sand composition for casting, a green sand additive was pre-formed by blending sodium dioctyl sulfosuccinate and at least one type of alcohol as surfactants in a predetermined ratio. The green sand composition obtained by adding this additive to silica sand, bentonite, and water and kneading it showed improved packing density, fluidity, and mold release properties. Furthermore, the kneading speed was significantly accelerated in the initial stages of kneading. In addition, the collapse properties of the mold were significantly improved while maintaining its strength. [Effects of the Invention]

[0014] The green sand composition for casting obtained by adding the additive for green sand of the present invention exhibits improved fluidity. This allows the sand to reach even the finest details of the mold, suppressing filling defects. This reduces the defect rate of the product and improves the beauty of the casting surface. Furthermore, the surfactant's action allows water to penetrate quickly, shortening the time it takes to reach the target mixing speed. This reduces the mixing time of the green sand for casting, contributing to increased productivity. In addition, the adhesion and cohesiveness of the green sand for casting is reduced, and the mold removal resistance is also reduced, suppressing sand adhesion to equipment. This prevents problems caused by sand sheathing in the sand retention tank and suppresses adhesion to the belt conveyor, thus enabling line cleanliness. Moreover, since the collapse properties can be improved while maintaining a certain degree of strength, the recovery rate of reusable sand is also improved when the mold is dismantled after use and the green sand for casting is reused. [Brief explanation of the drawing]

[0015] [Figure 1] This figure shows the relationship between the amount of additive added and the change in packing density. [Figure 2] This figure shows the relationship between the amount of additive added and the change in wet pressure resistance. [Modes for carrying out the invention]

[0016] The following describes the casting sand composition and casting sand additive according to the present invention. The casting sand composition according to the present invention is composed of casting sand, a casting sand additive containing a surfactant, at least one type of alcohol, and water, and further water added and mixed by stirring.

[0017] Silica sand, the main base material for green casting sand, accounts for 60-90% of the total green casting sand and is mainly composed of silica. This silica sand is mixed with montmorillonite-containing bentonite, a clay mineral, as a binder. Furthermore, depending on the desired casting product, starch, coal powder, etc., may be selectively added in appropriate amounts as binders. In this invention, "silica sand" includes both silica sand alone and silica sand with appropriate amounts of additives such as starch and coal powder selectively added.

[0018] Generally, it is known that casting sand suitable for aeration molding can be obtained by mixing and kneading 100 parts by weight of silica sand with 8 parts by weight of bentonite as a binder and an appropriate amount of water (1 to 5 parts by weight). In particular, the bentonite is preferably one that contains 50% or more montmorillonite, and more preferably 70% or more.

[0019] Based on the results of tests described later, sodium dioctyl sulfosuccinate was found to be a preferred surfactant for the additive used in green sand.

[0020] Furthermore, propylene glycol or ethanol can be used as the alcohol that constitutes the additive for green sand. These alcohols are used as organic solvents to dissolve sodium dioctyl sulfosuccinate, which is a surfactant. By dissolving sodium dioctyl sulfosuccinate with alcohol, the additive for green sand can be set to a viscosity that is easy to handle. Among the alcohols, propylene glycol, a polyhydric alcohol, is particularly preferred. To lower the viscosity of the mixture of sodium dioctyl sulfosuccinate and propylene glycol and make it easier to handle, it is more preferable to compose the additive for green sand so that it contains about 15% water.

[0021] In order to find a suitable mixing ratio of the green molding sand additive for foundry green molding sand, the present inventor mixed various amounts of the green molding sand additive into foundry green molding sand obtained by mixing and kneading water with an aggregate composed of silica sand and bentonite, and confirmed properties such as packing density, wet compressive strength and drawing resistance through experiments. This experiment was carried out in accordance with the procedure specified in JIS Z 2601 "Testing Method for Foundry Sand", and the kneading time was set to 14 minutes. The green molding sand additive used consisted of 70% by mass of sodium dioctyl sulfosuccinate as a surfactant, 16% by mass of propylene glycol as an alcohol, and 14% by mass of water.

[0022] It should be noted that the method of feeding the aforementioned green molding sand additive into the kneader is not limited herein. For example, a container containing the green molding sand additive can be connected to the upstream side or the downstream side of an adjustment vessel connected to a water channel for adjusting the amount of water added to the kneader, and the additive is pushed into the water channel by a pump to be mixed with the water flow flowing through the water channel.

[0023] Experiments were conducted by varying the addition amount of the green molding sand additive relative to silica sand to 0.004 parts by weight, 0.008 parts by weight, 0.016 parts by weight, 0.032 parts by weight, 0.064 parts by weight, and 0.096 parts by weight. In these experiments, the addition amounts of sodium dioctyl sulfosuccinate relative to silica sand were 0.0028 parts by weight, 0.0056 parts by weight, 0.0112 parts by weight, 0.0224 parts by weight, 0.0448 parts by weight, and 0.0672 parts by weight, respectively.

[0024] Figure 1 is a diagram showing packing density, which illustrates the change in packing density corresponding to the change in the addition amount of the additive. Packing density indicates the sand density of a molded green mold, and affects the surface smoothness of cast products. When the addition amount of the green molding sand additive is less than 0.004 parts by weight, there is little difference in packing density compared with the case where no additive is added; however, a clear improvement is observed when the addition amount is 0.004 parts by weight or more. The packing density reaches the maximum at 0.008 parts by weight, and remains substantially constant even if the addition amount is further increased. Therefore, the addition amount of the green molding sand additive is preferably 0.004 parts by weight or more.

[0025] Figure 2 shows the wet resistance pressure, illustrating the change in wet resistance pressure in response to changes in the amount of additive. The wet resistance pressure is the value obtained by testing test pieces prepared according to a specified procedure using a uniaxial compression tester, and represents the strength index of the molded green sand mold. The wet resistance pressure is highest when the additive amount is 0, and tends to decrease with the addition of the green sand additive. This indicates that the surfactant in the green sand additive reduces the cohesive force, i.e., frictional force, between the bentonite-coated silica sand grains. On the other hand, a wet resistance pressure of 9 N / cm² or higher is required to support the metal being poured. Therefore, the amount of green sand additive added is preferably 0.016 parts by weight or less.

[0026] These experiments revealed that the optimal amount of additive for green sand, consisting of 70% sodium dioctyl sulfosuccinate, 16% propylene glycol, and 14% water, per 100 parts by weight of silica sand is between 0.004 parts by weight and 0.016 parts by weight. In other words, the optimal amount of sodium dioctyl sulfosuccinate per 100 parts by weight of silica sand is between 0.0028 parts by weight and 0.0112 parts by weight.

[0027] <Fluidity Test> Next, a test was conducted to compare the fluidity of green casting sand without green casting sand additives and green casting sand with green casting sand additives added. Hereinafter, green casting sand without green casting sand additives will be referred to as "additive-free green casting sand," green casting sand with green casting sand additives will be referred to as "green casting sand composition," and both will be referred to as "both green casting sands." 10 kg (100 parts by weight) of silica sand and an appropriate amount of distilled water (approximately 210 mL) were added to a mixer (Simpson Mixmorer) and mixed for 1 minute. 800 g (8 parts by weight) of bentonite was added to the mixed sand and mixed further. After mixing the bentonite and mixing for 14 minutes, water was added and dried as needed to achieve a compactibility of 40 ± 1%, thereby producing both types of green casting sand. The method for adding the green sand additive when preparing the green sand composition for casting involved pre-dissolving 0.8 g (0.008 parts by weight) of the green sand additive in distilled water per 10 kg of silica sand, and then adding the green sand additive at the same time as adding the distilled water. The green sand additive used in this test consisted of 70% sodium dioctyl sulfosuccinate, 16% propylene glycol, and 14% water.

[0028] The bentonite used in the production of both types of green casting sand was domestically produced sodium-exchanged bentonite and imported sodium-type bentonite. Bentonite used in green casting sand generally consists of sodium-rich sodium-type bentonite and sodium-exchanged bentonite, which has had calcium and magnesium ions artificially replaced with sodium. The montmorillonite content of these bentonites is approximately 65-75%. Green casting sand mixed with sodium-type bentonite requires a long mixing time, has moderate wet pressure resistance, and exhibits little thermal degradation, but its disintegration properties are not very good. Sodium-exchanged bentonite requires a short mixing time, has high wet pressure resistance, exhibits moderate thermal degradation, and has good disintegration properties. In the casting process, appropriate bentonite is selected and mixed with silica sand according to the casting purpose.

[0029] The static density (or sieve density) of the test specimens obtained by placing both types of green casting sand into a test cylinder specified in JIS Z 2601 "Test Method for Foundry Sand," passing them through a 6-mesh sieve, and allowing them to fall into the test cylinder under their own weight was measured. Static density is the value obtained by dividing the mass of the test specimen by the volume of the cylinder. The measurement results are shown in Table 1. The weight of each type of green casting sand is the amount that results in a test specimen height of 50 ± 0.5 mm after compaction three times in a compaction machine. This is approximately 148 g when domestically produced Na-exchanged bentonite is mixed in, and approximately 151 g when foreign-produced Na-type bentonite is mixed in.

[0030] [Table 1] As shown in Table 1 above, whether using domestically produced Na-exchanged bentonite or imported Na-type bentonite, the static density of the casting green sand composition is improved compared to green sand without additives. This is because sodium dioctyl sulfosuccinate improves or enhances the slipperiness of the sand constituting the casting green sand composition, reducing frictional resistance between the sand particles during self-weight dropping and improving fluidity. As a result, the casting green sand reaches even the finest details of the mold, suppressing filling defects and preventing the occurrence of unevenness on the surface of the casting.

[0031] <Mixing and kneading speed test> Next, the mixing speed of the mixed sand was confirmed through testing. Compactability (CB) is the shrinkage rate when green sand collected under certain conditions is compressed with a certain force, and it serves as an indicator of the mixing state. If water can be quickly penetrated by the action of a surfactant and the compactability can be quickly reached the target value, it will lead to a reduction in mixing time, thus contributing to improved productivity.

[0032] 3 kg (100 parts by weight) of silica sand, 240 g (8 parts by weight) of bentonite, and an appropriate amount of distilled water (approximately 50-70 mL) were thoroughly mixed in a small mixer (small Simpson Mixmorer), and the mixture was kneaded for 1 minute with the lid closed. The lid was opened, and approximately 250 g of each casting sand was scooped out. The compactability value was measured after 1 minute of kneading. The target compactability value was set at 40 ± 1%. The entire amount of sand whose compactability value was measured was returned to the small mixer, the lid was closed, and the mixture was kneaded for 30 seconds. The compactability value was measured after 1 minute and 30 seconds of kneading. The same procedure was repeated, and the compactability values ​​were measured after 2 minutes, 2 minutes and 30 seconds, 3 minutes, and 4 minutes of kneading. The measurement results are shown in Table 2.

[0033] The additive used for green sand consisted of 70% surfactant, 16% propylene glycol, and 14% water. (1) The case without surfactant was compared with the case with (2) sodium dioctyl sulfosuccinate, (3) polycarboxylic acid type anionic surfactant, (4) polyoxyethylene alkyl ether (nonionic surfactant), (5) polyoxyalkylene alkyl ether (nonionic surfactant), (6) lauryl amino ether (amphoteric surfactant), and (7) fluorine-based surfactant.

[0034] Furthermore, the method for adding the green sand additive when preparing the green sand composition for casting involved pre-dissolving 0.24 g (0.008 parts by weight) of the green sand additive in distilled water per 3 kg of silica sand, and then adding the green sand additive at the same time as adding the distilled water.

[0035] The mixing and kneading speed is indicated by the compactability (CB) value, and the formula for calculating it is CB(%) = (AH) / A × 100 (A: depth from the top surface of the test tube to the support stand (mm), H: height of the compacted or compressed test piece (mm)).

[0036] [Table 2] As shown in Table 2 above, the green casting sand composition in which sodium dioctyl sulfosuccinate was selected as the surfactant showed an improvement in compactability value from 26.4% to 34.1% in a mixing time of 1 minute compared to green casting sand without additives, and the rise in compactability was accelerated by 29% in the first minute of mixing. The target compactability value was reached in 3 minutes of mixing. This is presumed to be because the excellent water permeability promoting effect (penetration power) and water surface tension lowering ability of sodium dioctyl sulfosuccinate allowed water to quickly penetrate the montmorillonite contained in the bentonite, thereby promoting the binding action of the bentonite. Furthermore, when the bentonite content was 50% or more, the effect of accelerating the rise in compactability value of the green casting sand composition with added green casting sand additives was obtained, and this accelerating effect was particularly good when the montmorillonite content was 70% or more.

[0037] On the other hand, casting sand compositions using polycarboxylic acid-type anionic surfactants, polyoxyethylene alkyl ethers (nonionic surfactants), polyoxyalkylene alkyl ethers (nonionic surfactants), lauryl amino ethers (amphoteric surfactants), and fluorine-based surfactants as additives to the green sand did not show any significant difference in the rise of compactibility values ​​compared to green sand without additives.

[0038] [Table 3] Furthermore, setting the target compactability value to 30% to 55%, similar mixing rate tests were conducted using Na-type bentonite and Na-exchanged bentonite mixed with silica sand. The surfactant used as an additive for green sand was sodium dioctyl sulfosuccinate, and the mixing ratio was the same as in the aforementioned mixing rate test. In this case as well, as shown in Table 3, an improvement in compactability was observed 1 minute after the start of mixing, confirming that the rise in compactability was accelerated by 10% to 22% and the mixing time to reach the target compactability value was shortened.

[0039] Next, to find a preferred mixing ratio of sodium dioctyl sulfosuccinate and alcohol in the green sand additive, the mixing and kneading speed was checked by changing the proportion of sodium dioctyl sulfosuccinate and propylene glycol (the alcohol). For the performance test, the green sand composition for casting obtained by the same method as the mixing and kneading speed test described above was used. The amount of sodium dioctyl sulfosuccinate, the main component of the green sand additive, was fixed, and the amount of propylene glycol was varied to investigate the preferred ratio of surfactant to alcohol. Specifically, for 100 parts by weight (3000 g) of silica sand, the green sand additive was added at 0.008 parts by weight (0.24 g), and since 70% of the green sand additive was the surfactant, the weight of sodium dioctyl sulfosuccinate was set to 3000 g × 0.008% × 70% = 0.168 g. Domestically produced sodium-exchanged bentonite was used. The target compactness value was set at 40 ± 1%.

[0040] In a sample of green sand additive with a 4:1 ratio of sodium dioctyl sulfosuccinate to alcohol, the weight of propylene glycol was 0.042 g. This was mixed with an amount of distilled water equivalent to the amount of propylene glycol to form the green sand additive, which was then diluted with 79 mL of distilled water and added to a mixture of silica sand and bentonite to obtain a green sand composition for casting. In a sample of green sand additive with a 5:1 ratio of sodium dioctyl sulfosuccinate to alcohol, the weight of propylene glycol was 0.0336 g. This was mixed with an amount of distilled water equivalent to the amount of propylene glycol to form the green sand additive, which was then diluted with 75 mL of distilled water and added to a mixture of silica sand and bentonite to obtain a green sand composition for casting. In a sample of green sand additive with a 6:1 ratio of sodium dioctyl sulfosuccinate to alcohol, the weight of propylene glycol was 0.028 g. This was mixed with distilled water in an amount equivalent to propylene glycol to form a green sand additive. This additive was then diluted with 75 mL of distilled water and added to a mixture of silica sand and bentonite to obtain a green sand composition for casting.

[0041] [Table 4] Similar to the mixing speed test described above, the compactability values ​​were measured at 1 minute, 1 minute 30 seconds, 2 minutes, 2 minutes 30 seconds, 3 minutes, and 4 minutes after mixing. The measurement results are shown in Table 4.

[0042] [Table 5] Furthermore, the sand moisture content, packing density, and wet pressure resistance were measured 14 minutes after the start of mixing to evaluate the performance of the green sand composition for casting. The measurement results are shown in Table 5.

[0043] The measurement results showed no significant difference in the mixing speed when the alcohol ratio was increased (sodium dioctyl sulfosuccinate:propylene glycol = 4:1) or decreased (sodium dioctyl sulfosuccinate:propylene glycol = 6:1) compared to sodium dioctyl sulfosuccinate:propylene glycol = 5:1. However, in the case of sodium dioctyl sulfosuccinate:propylene glycol = 6:1, the sand properties after mixing (when the compactability target value was reached) were found to have a slightly lower packing density and a higher wet pressure resistance (a property representing the strength of green sand). This was thought to be due to insufficient dispersion of the surfactant. The purpose of adding alcohol is to improve the handling of the surfactant. However, when the weight of propylene glycol is less than 1 / 6 of the weight of the surfactant, the solubility of the surfactant decreases and the dispersibility deteriorates when creating an aqueous solution by adding the green sand additive to the distilled water mixed during mixing. Therefore, it was found that this could lead to a problem where the effectiveness of the surfactant is reduced, which is undesirable.

[0044] On the other hand, when the ratio of sodium dioctyl sulfosuccinate to propylene glycol was 4:1, the sand moisture content was acceptable but slightly excessive, and it was found that any further increase in the amount of propylene glycol would result in excessive sand moisture. This was thought to be due to propylene glycol inhibiting the swelling properties of bentonite. Furthermore, when the ratio of surfactant to propylene glycol was 4:1, the total amount of additives for green sand increased, and the increased amount of expensive propylene glycol resulted in increased running costs.

[0045] It was found that a ratio of 5:1 between sodium dioctyl sulfosuccinate and propylene glycol provides sufficient packing density, appropriate wet pressure resistance, improved fluidity, and prevents excessive sand moisture, resulting in an optimal blending ratio. This allows for rapid water penetration and quicker mixing, leading to reduced mixing time and improved productivity. Therefore, it was found that a blending ratio of 4:1 to 5:1 between sodium dioctyl sulfosuccinate and alcohol is preferable, with approximately 5:1 being particularly suitable. When the additive for green sand is composed of 70% sodium dioctyl sulfosuccinate, 15% propylene glycol, and 15% water, the blending ratio of sodium dioctyl sulfosuccinate to alcohol is 4.7:1. When 0.008 parts by weight of a green sand additive is added to 100 parts by weight of green sand for casting, the proportion of sodium dioctyl sulfosuccinate and the proportion of propylene glycol per 100 parts by weight of green sand for casting is 0.0056 parts by weight.

[0046] <Jenikesell shear test> Next, shear tests using the Jenikesell method were performed on test specimens of both casting sands. This test was conducted according to the procedure specified in the Japan Powder Industry Technology Association standard SAP15-13, "Method for one-sided shear testing of powders." The bentonite used in this test was imported Na-type bentonite.

[0047] [Table 6] As shown in Table 6 above, data obtained from the Jenikesel shear test were analyzed to determine the shear adhesion force (shear stress in a state without consolidation stress (state where normal stress is 0)) and the fluidity index FF (maximum principal stress / unconstrained fracture stress), confirming the adhesion and cohesiveness of both casting green sands. The casting green sand composition showed a decrease in shear adhesion force and an improvement in the fluidity index FF (maximum principal stress / unconstrained fracture stress) compared to the additive-free casting green sand.

[0048] The casting sand composition exhibits reduced adhesion compared to additive-free casting sand, thus suppressing sand adhesion to equipment and improving fluidity. Higher fluidity of casting sand improves clogging in the sand transport route at the casting site. As a result, using the casting sand composition reduces the likelihood of sand sheathing in sand retention tanks compared to additive-free casting sand. Furthermore, adhesion to equipment such as belt conveyors is reduced, preventing sand from spilling onto surrounding surfaces during transport, thus keeping the production line cleaner.

[0049] <Die-cutting resistance test> Next, the mold removal resistance of the mixed sand was confirmed by testing. Test specimens for both casting sands were prepared using a test specimen compactor specified in JIS Z 2601 "Test Methods for Foundry Sand". Test specimens for both casting sands were obtained using the same method as in the fluidity test. The weight of each casting sand was the amount required to compact the specimen three times in the compactor so that the specimen height was 50 ± 0.5 mm. This was approximately 148 g when domestically produced Na-exchanged bentonite was mixed in, and approximately 151 g when foreign-produced Na-type bentonite was mixed in. In this test, after compacting five times in the compactor, the resistance value was read when the specimen was removed from the test tube using a universal testing machine.

[0050] [Table 7] As shown in Table 7 above, when domestically produced Na-exchanged bentonite and foreign-produced Na-type bentonite were used as casting sand, the mold-removing resistance of the casting sand composition decreased by more than 100 N compared to the additive-free casting sand. The reduction in mold-removing resistance is an indicator of the suppression of adhesion of the casting sand composition to the equipment. Since the shear adhesion force in the aforementioned Jenike shear test also decreased in the casting sand composition, sand racking in the sand retention tank and adhesion to the belt conveyor are suppressed compared to the additive-free casting sand, thereby achieving cleaner equipment and production lines.

[0051] <Disintegration Test> Next, the collapse properties of both casting sands were confirmed by testing. Using a specimen compactor specified in JIS Z 2601 "Test Methods for Foundry Sand," the strength of the specimens of both casting sands was confirmed. Specimens of both casting sands were obtained using the same method as in the flowability test. The weights of both casting sands were the same as in the mold removal resistance test described above. The specimens were compacted three times using the compactor and then removed, and the wet pressure resistance (uniaxial compressive strength) was measured using a Kunitester.

[0052] [Table 8] As shown in Table 8 above, in this test, the strength was measured at three temperature ranges: room temperature, 105°C, and 600°C. Room temperature is the temperature at which both casting sands were molded, 105°C is the assumed temperature of both casting sand molds at the time molten liquid metal (iron, copper, zinc, tin, etc.) was poured into the casting sand molds, and 600°C is the assumed temperature of both casting sand molds heated by the heat conduction of the poured liquid metal. To mimic the conditions under which molds are actually used in the workplace, the strength was measured at room temperature immediately after compaction, 30 minutes and 1 hour later, 1 hour and 2 hours after the test specimen was heated to 105°C, and 15 minutes after the test specimen was heated to 600°C. Compared to additive-free casting sand, the casting sand composition had weaker strength at room temperature, but its strength in the temperature range assumed immediately after pouring the liquid metal was actually improved. Subsequently, as time passes and the temperature of the liquid metal decreases and the metal solidifies, it is preferable that the strength decreases in order to dismantle the mold, and in this case, the temperature of the mold is expected to be approximately 600°C. It was found that in this temperature range, the strength of the green casting sand composition is lower than that of green casting sand without additives.

[0053] Next, a surface stability test of the molds was conducted. The surface stability of the test specimens of both casting sands, obtained in the same manner as in the strength test described above, was measured using a rotap sieving machine at the same temperature range and elapsed time as in the strength test. The test specimens of both casting sands were rolled on a 6-mesh sieve for 1 minute, and the weight remaining on the sieve was measured. The formula for calculating surface stability is Surface Stability SSI (%) = C / B × 100 (B: weight of a 50mm diameter, 50mm height test specimen, depth from the top of the test tube to the support (mm), C: weight of the test specimen after rolling it on a 6-mesh sieve for 1 minute).

[0054] [Table 9] As shown in Table 9 above, the casting green sand composition exhibits lower surface stability at room temperature compared to additive-free casting green sand. However, at the temperature range expected when pouring the liquid metal, it achieved surface stability equivalent to that of additive-free casting green sand. Subsequently, as time passes and the temperature of the liquid metal decreases and the metal solidifies, it is preferable for the surface stability to decrease in order to dismantle the mold. In this case, the mold temperature is expected to be approximately 600°C. It was found that at this temperature range, the surface stability of the casting green sand composition is significantly lower than that of additive-free casting green sand.

[0055] From the above, it can be concluded that by adding the additive for green sand, the mold made from the green sand composition can maintain a certain degree of strength and surface stability at room temperature or the temperature range expected when pouring liquid metal. However, once the mold temperature rises to 600°C after pouring liquid metal, the strength and surface stability of the mold made from the green sand composition decrease, and its disintegration properties improve. This improved disintegration property also improves the recovery rate of sand that can be reused.

[0056] Furthermore, in actual foundries, casting sand is reused repeatedly. Therefore, when applying this to casting sand currently in use, it is preferable to check whether the ratio of surfactants remaining in the casting sand is within the aforementioned range and to replenish the confirmed deficiency of surfactants. [Industrial applicability]

[0057] The additives for green sand and the green sand compositions for casting according to the present invention can be used not only in mass production plants but also in foundries that produce a wide variety of products in small quantities.

Claims

1. An additive for green sand, consisting of a surfactant, alcohol, and water, The surfactant is sodium dioctyl sulfosuccinate. The aforementioned alcohol is propylene glycol. An additive for green sand, characterized in that the blending ratio of the surfactant to the alcohol is 4:1 to 5:

1.

2. In a casting sand composition obtained by adding the casting sand additive described in claim 1 to casting sand, A casting sand composition characterized in that the surfactant is blended in a ratio of 0.0028 to 0.0112 parts by weight per 100 parts by weight of the casting sand.

Images