Additive for green sand mold and green sand mold forming material

Abstract

To provide a carbon-neutral additive for a green sand mold used by being added to foundry sand for a green sand mold, which can be stably supplied and easily handled, and to provide a green sand mold forming material containing the additive for a green sand mold.SOLUTION: An additive for a green sand mold, which is used by being added to foundry sand for a green sand mold, contains as a main component a vegetable powder impregnated with a vegetable oil agent containing at least one of vegetable oil and an oil component derived from vegetable oil.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an additive for green sand molding that is added to green sand foundry sand, and a green sand molding material containing the additive for green sand molding. [Background technology]

[0002] Traditionally, casting has been done using green sand molds. Green sand molds are made by mixing green sand molding material, primarily consisting of green sand casting sand, and then filling a flask with the mixed green sand molding material, with a pattern set inside the flask, to accurately replicate the shape of the pattern. Molten metal is poured into the resulting green sand mold, which is then cooled and then broken down to produce the casting.

[0003] Carbon powders, such as coal powder, have been known as additives for green sand mold molding materials. The volatile matter in carbon powder gasifies due to the heat of the molten metal, forming a gas film at the interface between the molten metal and the green sand mold. Alternatively, the volatile matter thermally decomposes to form a carbon film at the interface, preventing direct contact between the molten metal and the green sand mold surface. Because the volatile matter is primarily composed of reducing substances such as carbon and hydrogen, the interface becomes a reducing atmosphere, suppressing oxide formation. This results in improved casting surface, prevention of seizure, and improved mold release. Carbon powder also acts as a cushioning material, reducing thermal stress (expansion stress) and preventing scoop-related casting defects.

[0004] Recently, biomass, a fuel derived from living organisms such as plants, has been attracting attention as a new resource that can contribute to preventing global warming and building a recycling-oriented society. When biomass is burned, carbon dioxide is produced, just like fossil fuels. However, plants absorb carbon dioxide through photosynthesis during their growth process, and when viewed over their entire life cycle, it is thought that there is no increase in carbon dioxide in the atmosphere and that the balance is zero. In this way, carbon-neutral materials that do not affect the increase or decrease of carbon dioxide are desirable.

[0005] Therefore, instead of carbon powder such as coal powder, an additive has been proposed whose main component is a by-product generated in the process of producing biodiesel fuel from edible vegetable oil (Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 4217756 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the supply of the by-products is limited, making it difficult to ensure a stable supply. Furthermore, the additive proposed in Patent Document 1 is liquid, which not only makes it impossible to use conventional equipment for adding carbon powder, but also poses a problem in handling, as it may freeze in winter.

[0008] In view of the above circumstances, an object of the present invention is to provide a carbon-neutral additive for green sand casting that can be stably supplied and is easy to handle, and a green sand casting material containing the additive. [Means for solving the problem]

[0009] The additive for green sand casting of the present invention that solves the above-mentioned object comprises: An additive for green sand molding to be added to green sand molding sand, The main component is a vegetable powder impregnated with a vegetable oil agent containing at least one of vegetable oil and an oil component derived from vegetable oil.

[0010] The green sand casting additive of the present invention generates carbon dioxide due to the heat of the molten metal, but because its main component is plant-based, it absorbs carbon dioxide through photosynthesis during its growth process, making it a carbon-neutral material that does not affect the increase or decrease of carbon dioxide. Furthermore, because it is in the form of a powder, such as a plant-based powder, it can be used with conventional carbon powder-adding equipment, there is no risk of it freezing in winter, and it is easy to handle. Furthermore, even if the supply of vegetable oil is limited, the key point is that the vegetable oil is impregnated into the vegetable powder, and the vegetable powder increases the bulk of the green sand casting additive, ensuring a stable supply.

[0011] The vegetable oil-derived oil component may be a residue generated during the process of producing biodiesel fuel from vegetable oil. The vegetable oil may be virgin oil or recycled oil (e.g., used edible vegetable oil). The vegetable oil agent may be 100% vegetable oil, 100% vegetable oil-derived oil, or both vegetable oil and vegetable oil-derived oil.

[0012] Also, The vegetable oil may be present in an amount of 5% by mass or more and 30% by mass or less relative to 100% by mass in total of the vegetable oil and the vegetable powder.

[0013] Because the proportion of the vegetable powder is higher than that of the vegetable oil, the green sand mold additive can be easily bulked while remaining a carbon-neutral material. The vegetable oil generates volatiles, gasifies, and creates a reducing atmosphere, improving the casting surface and preventing seizure. Furthermore, because the vegetable oil is oil, it improves lubrication and tends to increase mold packing density. If the vegetable oil content is less than 5% by mass, these effects are difficult to achieve. If the vegetable oil content exceeds 30% by mass, not only is the amount of vegetable oil too high, causing problems with stable supply, but the green sand mold additive itself becomes wet (i.e., sticky), reducing fluidity and making it difficult to handle as a powder. Furthermore, mold strength and moldability are reduced. Furthermore, excessive gas generation can lead to gas defects in the casting. Furthermore, the vegetable powder becomes solid carbon, which has the effect of improving demolding properties, and the green sand casting additive of the present invention can obtain the combined effect of the vegetable oil and the vegetable powder.

[0014] Also, The plant powder may have a particle size of 3 μm or more and 800 μm or less.

[0015] If the particle size of the vegetable powder is less than 3 μm, it will be bulky and difficult to handle. It will also be prone to clumping in the tank that supplies the carbon-based additive. On the other hand, if the particle size of the vegetable powder is more than 800 μm, black solid matter will appear on the surface of the mold, causing defects in the casting surface and making it more likely to cause insertion problems.

[0016] The plant-derived powder may be one or more types of powder selected from wood flour, used coffee grounds, palm husk, rice flour, wheat flour, tea leaf waste, and starch, with wood flour, used coffee grounds, palm husk, and tea leaf waste being preferred from the viewpoint of recycling. Corn-derived starch may also be used.

[0017] moreover, The moisture content may be kept to 20% or less.

[0018] As mentioned above, the plant-derived powder acts as solid carbon, improving mold release. However, its fibrous structure is thought to facilitate moisture retention in the fibrous gaps. The moisture contained in the green sand casting additive is heated by the molten metal and turns into steam, which can cause pinhole gas defects in the casting. It also reduces the viscosity of the green sand casting material, making it difficult to fill the green sand casting mold. For this reason, it is preferable to keep the moisture content of the green sand casting additive below 20.0%.

[0019] The green sand molding material of the present invention, which solves the above-mentioned object, comprises: Green sand for molding, Water and A binder; The green sand mold additive of the present invention, The green sand molding sand is characterized in that the green sand molding additive is added in an amount of 0.5% by mass to 3.0% by mass, where the green sand molding sand is taken as 100% by mass.

[0020] If the green sand casting additive is less than 0.5% by mass, it will not be effective enough. On the other hand, if the green sand casting additive is more than 3.0% by mass, the amount of water required will increase. The plant-based powder is thought to be fibrous, and moisture penetrates the gaps in the fibers, resulting in the moisture that should be supplied to the binder being absorbed by the plant-based powder, making it necessary to add more water than necessary. Excessive moisture can impair the filling ability of the green sand casting material or produce a large amount of water vapor, which can cause pinhole gas defects in the casting. For these reasons, it is preferable that the green sand casting additive be 3.0% by mass or less.

[0021] The green sand is new sand, not system sand. Examples of the green sand include silica sand. The binder may be bentonite (montmorillonite clay).

[0022] Furthermore, the timing at which the green sand molding additive of the present invention is added is not limited. For example, green sand molding sand and water may be first added and kneaded, and then the green sand molding additive of the present invention may be added together with a binder and further kneaded, or the green sand molding sand, water, and binder may be kneaded together and the green sand molding additive of the present invention may be added and further kneaded. [Effects of the Invention]

[0023] According to the present invention, it is possible to provide a carbon-neutral additive for green sand casting that can be stably supplied and is easy to handle, and a green sand casting material containing the additive for green sand casting. [Brief explanation of the drawings]

[0024] [Figure 1] (A) is a graph showing the measurement results of the moisture content, and (B) is a graph showing the measurement results of the surface stability. [Figure 2] Graph (A) shows the results of measuring air permeability, and graph (B) shows the results of measuring sand mold packing density. [Figure 3] 1 is a graph showing the measurement results of pressure resistance and shear force. [Figure 4] Graph (A) shows the measurement results of the punching resistance, and graph (B) shows the converted results of the amount of gas generated. [Figure 5] FIG. 1 is a photograph of a test piece after shot blasting. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, an embodiment of the present invention will be described.

[0026] The green sand molding material of this embodiment contains green sand, water, a binder, and a carbon-based additive. Silica sand is used as the green sand. Bentonite (montmorillonite clay) is used as the binder. The carbon-based additive is primarily made of vegetable powder impregnated with vegetable oil. With 5 kg of green sand as the mass, 400 g of binder, equivalent to 8 mass%, and 100 g of carbon-based additive, equivalent to 2 mass%, were added. A certain amount of water was added to the green sand to achieve the target compactability value (CB value). Here, water was added so that the CB value was 40±1%. The CB value is a ratio of the degree to which green sand sinks when compressed into a fixed volume having a predetermined height (A), and is 98 N / cm. 2 It is calculated from the height (H) of the green sand when compacted with a considerable amount of force. In other words, it can be calculated using the formula: CB value (%) = (AH) ÷ A × 100.

[0027] The carbon-based additive corresponds to one embodiment of the green sand mold additive of the present invention. The vegetable oil agent in this carbon-based additive may be any oil agent containing at least one of vegetable oil and an oil component derived from vegetable oil. The vegetable oil may be virgin oil or recycled oil. More specifically, it may be coconut oil, palm kernel oil, cottonseed oil, soybean oil, olive oil, or the like. Alternatively, it may be edible vegetable oil (salad oil, tempura oil) or used edible vegetable oil. Furthermore, it may be a mixture of one or more of these oil types.

[0028] The vegetable oil-derived oil component in the carbon-based additive is a residue generated during the process of producing biodiesel fuel from vegetable oil. This residue contains glycerin. More specifically, it is produced by reacting edible vegetable oil containing multiple types of glycerides with methanol in the presence of caustic potash or caustic soda to produce esters and glycerin, and then removing unreacted edible vegetable oil, glycerin, and caustic potash or caustic soda from the reaction product. That is, the residue contains unreacted edible vegetable oil and glycerin, as well as caustic potash or caustic soda.

[0029] The plant powder in the carbon-based additive contains a cellulose component, and may be one or more types of powder selected from the group consisting of wood flour, used coffee grounds, palm husk, rice flour, wheat flour, tea leaf residue, and starch. Wood flour, used coffee grounds, palm husk, and tea leaf residue are preferred from the perspective of recycling. Corn-derived starch may also be used. The particle size of the plant powder must be 3 μm or greater. Particle sizes less than 3 μm increase the bulk and reduce handleability. In particular, the particle size of the plant powder is preferably 20 μm or greater. Particle sizes less than 20 μm correspond to the fine particles in foundry sand and are treated as the total clay content. As the fine particle content increases, defects such as reduced air permeability and increased susceptibility to gas defects in the casting become more noticeable. For this reason, the particle size of the plant powder is preferably 20 μm or greater. On the other hand, the particle size of the plant powder is preferably 800 μm or less. If the particle size exceeds 800 μm, black solid matter will appear on the mold surface, causing defects in the casting surface and making it more likely that poor insertion will occur, so it is preferable that the particle size of the plant powder is 800 μm or less.

[0030] The mass % ratio of vegetable oil to vegetable powder in the carbon-based additive must be higher than that of vegetable oil. Recycled oil and residues generated during the process of producing biodiesel fuel from vegetable oil are desirable from a recycling perspective, but their supply is limited. On the other hand, vegetable powder is more readily available. The key feature of the carbon-based additive of this embodiment is that the vegetable oil is impregnated into the vegetable powder. The vegetable powder increases the volume of the carbon-based additive, ensuring a stable supply. To impregnate the vegetable powder with the vegetable oil, the vegetable oil is sprayed onto the vegetable powder and allowed to dry at room temperature for a predetermined period of time. Since the carbon-based additive of this embodiment is in the form of a powder, i.e., vegetable powder, it can be easily handled using conventional carbon powder-adding equipment, is free from the risk of freezing in winter, and is therefore easy to handle. Furthermore, although carbon dioxide is generated by the heat of the molten metal, because the primary component is plant-based, carbon dioxide is absorbed through photosynthesis during the growth process, making it a carbon-neutral material that does not affect the increase or decrease of carbon dioxide.

[0031] The impregnation amount of vegetable oil is preferably 5% by mass or more and 30% by mass or less, based on 100% by mass of the total of the vegetable oil and vegetable powder. The vegetable oil generates volatile matter, gasifies, and creates a reducing atmosphere, improving the casting surface and preventing seizure. Furthermore, because the vegetable oil is oil, it improves lubrication and tends to increase mold packing density. If the vegetable oil content is less than 5% by mass, these effects are difficult to achieve. If the vegetable oil content exceeds 30% by mass, not only will the amount of vegetable oil increase, causing problems in terms of stable supply, but the green sand casting additive itself will become wet (i.e., sticky), reducing its fluidity and making it difficult to handle as a powder. Furthermore, mold strength will decrease and moldability will also deteriorate. Furthermore, excessive gas generation will increase the likelihood of gas defects in the casting. In addition, the vegetable powder becomes solid carbon, which has the effect of improving demolding properties, and the carbon-based additive of this embodiment can obtain the combined effect of the vegetable oil and the vegetable powder.

[0032] The carbon-based additive described above is preferably added in a range of 0.5% by mass to 3.0% by mass, based on 100% by mass of the green sand. If the amount of carbon-based additive added is less than 0.5% by mass, the effect of the carbon-based additive is not fully achieved, resulting in castings prone to seizure and cracking defects. On the other hand, if the amount of carbon-based additive exceeds 3.0% by mass, the required amount of water increases. Water is added to the green sand molding material to allow the bentonite binder to absorb water, swell, and develop caking properties. Since plant-derived powder is thought to be fibrous, moisture may penetrate into the fibrous gaps, resulting in the plant-derived powder taking up the moisture that should be supplied to the binder. In this embodiment, water is added to achieve a CB value of 40±1% as described above. Therefore, if there is a shortage of moisture to supply to the binder, the amount of water added increases. The moisture that gets into the fibrous gaps in the plant powder can impair the green sand molding material's ability to fill the green sand mold, or it can turn into a large amount of water vapor, causing pinhole gas defects in the casting. For these reasons, the carbon-based additive content is preferably 3.0 mass% or less.

[0033] To prepare the green sand molding material, first add green sand and water to a kneader and knead for about 1 minute. Next, the binder bentonite and carbon-based additives are added to the kneader and kneaded for another 15 minutes or so to complete the preparation of the green sand molding material. When adding these ingredients, starch alone may also be added. This starch alone functions as a binder and contributes to improving the surface stability of the green sand mold, resulting in improved demoldability and prevention of sand inclusion. Furthermore, binders and wetting agents may also be added.

[0034] When making a green sand mold using the prepared green sand molding material, a pattern is set inside the flask, the prepared green sand molding material is manually filled into the flask, and pressure is applied to make the green sand mold. [Example]

[0035] As a carbon-based additive, we prepared wood flour impregnated with liquid residue (hereinafter referred to as vegetable residual oil) generated in the process of producing biodiesel fuel from vegetable oil. We prepared samples impregnated with 5% by mass (Example 1), 10% by mass (Example 2), and 30% by mass (Example 3) of vegetable residual oil, based on a total of 100% by mass of wood flour and vegetable residual oil.

[0036] In the comparative examples, coal powder (manufactured by Asahi Coke Engineering Co., Ltd.) (Comparative Example 1), vegetable residue oil (Comparative Example 2), and used salad oil (Comparative Example 3) were also prepared as carbonaceous additives. Note that Comparative Example 3 is an example in which wood powder is 0% by mass.

[0037] For each carbon-based additive in each example and comparative example, the values ​​(%) of "moisture," "ash," "volatile matter," "fixed carbon," and "sulfur" were determined according to JIS M 8812 (2006) proximate analysis methods for coal and coke. The results are shown in Table 1.

[0038] [Table 1] The carbon-based additives of Examples 1 to 3 contain more moisture than the coal powder of Comparative Example 1. On the other hand, the carbon-based additives of Comparative Examples 2 and 3, which contain only oil, do not contain moisture. The moisture contained in the carbon-based additives is heated by the molten metal and turns into steam, which causes pinhole gas defects in the casting. It also reduces the viscosity of the green sand molding material, worsening its ability to fill the green sand mold. Because the plant-based wood flour in each example is fibrous, it is believed to easily retain moisture in the fibrous gaps. In Examples 1 to 3, the moisture value increases as the amount of plant-based residue oil impregnation decreases, i.e., as the amount of plant-based residue wood flour increases. As described above, the plant-based powder becomes solid carbon and contributes to improving mold releasability. However, care must be taken with regard to moisture. The wood flour may be dried during the plant-based residue oil impregnation stage, or the wood flour after impregnation with the plant-based residue oil may be dried. However, it is preferable to keep the moisture content of the finished carbon-based additive below 20.0%.

[0039] Ash is cinders, and it can be seen that the carbon-based additives of Examples 1 to 3 produce less cinders than the coal powder of Comparative Example 1. The ash content of the used salad oil of Comparative Example 3 is almost zero, and in Examples 1 to 3, the ash content decreases as the amount of vegetable residue oil increases.

[0040] Volatile content represents the level of carbon-based gas (CO, CO2, hydrocarbon gases such as methane and butane) generated. It can be seen that the carbon-based additives of Examples 1 to 3 have higher volatile content than the coal powder of Comparative Example 1. Furthermore, the carbon-based additives of Comparative Examples 2 and 3, which are oils alone, also have higher volatile content. In Examples 1 to 3, the higher the amount of vegetable residue oil impregnation, the higher the volatile content. Carbon-based gas tends to improve the casting surface and reduce the occurrence of gas defects, but excessive carbon dioxide gas tends to increase the occurrence of large gas defects such as blowholes. Furthermore, a high volatile content means a high amount of vegetable residue oil impregnation, which not only makes it difficult to ensure the supply amount, but also makes the tank where the carbon-based additive is supplied sticky, making the carbon-based additive more likely to aggregate within the tank. Therefore, while a volatile content of 50% or more is necessary, it is preferable to keep it below 80%.

[0041] Fixed carbon is the carbon that remains unburned. It can be calculated as fixed carbon = 100 - (volatile matter + ash + moisture). Carbon has poor wettability with iron, and its presence on the surface of the green sand mold exerts a mold-coating effect. It can be seen that the carbon-based additives of Examples 1 to 3 have less fixed carbon than the coal powder of Comparative Example 1. On the other hand, the carbon-based additives of Comparative Examples 2 and 3, which contain oil alone, have significantly less fixed carbon, indicating that the carbon-based additives of Examples 1 to 3 are an improvement over the oil alone of Comparative Examples 2 and 3. Note that in Examples 1 to 3, the less vegetable residue oil impregnated, the more fixed carbon there is. However, when vegetable oil is impregnated into vegetable powder, a high amount of fixed carbon means that there is less vegetable oil, and the vegetable oil generates volatile matter, gasifies, or creates a reducing atmosphere, making it difficult to achieve effects such as improving the casting surface and preventing seizure. Therefore, the balance between vegetable oil and vegetable powder is important.

[0042] The less sulfur there is, the better for the spheroidization of graphite. Also, from the viewpoint of environmental measures to prevent the material from becoming a source of photochemical smog, etc., the less sulfur there is, the better. It can be seen that the carbon-based additives of Examples 1 to 3 contain less sulfur than the coal powder of Comparative Example 1. The sulfur content is preferably 0.25% or less.

[0043] From the above results, since it is necessary to keep the moisture content at 20.0% or less, it is preferable that the amount of vegetable oil impregnated into the vegetable powder be 5% by mass or more. Furthermore, in order to ensure a stable supply of vegetable oil and to obtain the combined effects of the vegetable oil and the vegetable powder, it is preferable that the volatile content be kept at 80% or less, and as a result, it is preferable that the amount of vegetable oil impregnated into the vegetable powder be 30% by mass or less.

[0044] Next, a green sand mold was made using the carbonaceous additive of Example 2 (wood flour impregnated with 10% by mass of vegetable residue oil). In both the Example and Comparative Example, 5 kg of virgin silica sand (Flattery Sand No. 6) was used as the green sand foundry sand. System sand was used because it already contained the carbonaceous additive. 400 g of bentonite (M7) was used as the binder, and water was added so that the CB value was adjusted to 40±1%. When the mass of silica sand is taken as 100 mass%, the green sand mold molding material to which the carbon-based additive of Example 2 has been added at 0.5 mass% (25 g) is Example A, the green sand mold molding material to which the carbon-based additive of Example 2 has been added at 1.0 mass% (50 g) is Example B, the green sand mold molding material to which the carbon-based additive has been added at 2.0 mass% (100 g) is Example C, the green sand mold molding material to which the carbon-based additive of Example 2 has been added at 3.0 mass% (150 g) is Example D, and the green sand mold molding material to which the carbon-based additive of Example 2 has been added at 4.0 mass% (200 g) is Example E. Furthermore, assuming the mass of silica sand to be 100 mass%, the green sand molding material to which 0.5 mass% (25 g) of the carbon-based additive (coal powder) from Comparative Example 1 was added was designated Comparative Example A, the green sand molding material to which 1.0 mass% (50 g) of the carbon-based additive was added was designated Comparative Example B, the green sand molding material to which 2.0 mass% (100 g) of the carbon-based additive was added was designated Comparative Example C, and the green sand molding material to which 4.0 mass% (200 g) of the carbon-based additive was added was designated Comparative Example D. Furthermore, the green sand molding material to which no carbon-based additive was added was designated Comparative Example E.

[0045] To prepare the green sand molding material, a 10 kg capacity Simpson sand mill was used. First, green sand and water were added to the mixer and mixed for about 1 minute. Next, bentonite and a carbon-based additive were added to the mixer and mixed for another 15 minutes to complete the preparation of the green sand molding material.

[0046] The moisture content, surface stability, air permeability, sand mold packing density, pressure resistance (compressive strength), and shear strength were measured using the methods described in "Green Sand Testing Methods," 2nd Edition, September 2017, published by the Green Sand Research Committee of the Japan Foundry Engineering Society. The measurement results are shown in graphs below, with the horizontal axis representing the amount of carbon-based additive (mass%) added when the mass of silica sand is taken as 100% by mass. The plots of the measurement results for Examples A to E and Comparative Example E are connected by straight lines, and the plots of the measurement results for Comparative Examples A to E are connected by dotted lines.

[0047] Figure 1(A) is a graph showing the results of moisture content measurements, with the vertical axis representing moisture content (%). The moisture content measured here is the amount of moisture required to achieve a CB value of 40±1% for the green sand casting material. In the case of coal powder (Comparative Examples A-D), shown by the dotted line, the moisture content remains almost constant. However, in the example using plant-derived wood flour, shown by the solid line, the moisture content increases as the amount added increases. Because wood flour is fibrous, moisture penetrates the gaps between the fibers, and moisture that should be supplied to the binder is absorbed by the wood flour, resulting in an increase in moisture content as the amount added increases. Excess moisture can impair the filling ability of the green sand casting material and increase the amount of water vapor generated, causing gas defects in the casting.

[0048] Figure 1(B) is a graph showing the results of measuring surface stability, with the vertical axis representing surface stability (%). Surface stability is an index of the mechanical strength of the surface of the green sand mold. The test piece is shaken to measure how much sand falls off. In the case of coal powder (comparative example), increasing the amount of added coal powder does not improve surface stability; in fact, it worsens. On the other hand, in the case of the examples, increasing the amount of added coal powder improves surface stability. We believe that the increase in moisture content is one of the reasons for this.

[0049] 2(A) is a graph showing the results of measuring air permeability, with the vertical axis representing air permeability. High air permeability makes insertion failure more likely, while low air permeability makes insertion failure less likely to occur but makes it more difficult for gas to escape, making gas defects more likely to occur. The examples shown by the solid line show a stronger tendency for air permeability to decrease as the amount of additive increases than the comparative examples shown by the dotted line.

[0050] Figure 2(B) is a graph showing the measurement results of the sand mold filling density, and the vertical axis is the sand mold filling density (g / cm 3 ) In the comparative example shown by the dotted line, the sand mold filling density decreased slightly when the additive was added. On the other hand, in the example shown by the solid line, the sand mold filling density increased when the additive was added. It is believed that the increased amount of vegetable oil impregnated into the vegetable powder improved the fluidity of the sand, making it easier to fill every corner. When combined with the air permeability, it is believed that the increased sand mold filling density in the example resulted in a decrease in air permeability.

[0051] Figure 3 is a graph showing the measurement results of compressive strength and shear strength, with the vertical axis representing these forces (MPa). The black graph represents compressive strength, and the gray graph represents shear strength. Compressive strength (compressive strength) and shear strength are indicators of the strength of the green sand mold. The shear strength was nearly identical between the Example and Comparative Example, and increasing the additive amount did not significantly reduce the shear strength. However, the Comparative Example reached its highest compressive strength at an additive amount of 2.0 mass%, while the Example steadily decreased as the additive amount increased. It is desirable to maintain compressive strength at 0.1 MPa or higher to prevent mold breakage during mold production. To maintain compressive strength at 0.1 MPa or higher, the amount of carbon-based additive added (mass%) must be 3.0 mass% or less, assuming that the mass of silica sand is 100 mass%.

[0052] The pull-out resistance during molding was also measured. The pull-out resistance during molding was measured by passing a cylindrical green sand mold test piece, 50 mm high and matching the inner diameter of a 120 mm high cylinder, from top to bottom using the crosshead of a universal testing machine at a speed of 5 mm / min.

[0053] 4(A) is a graph showing the measurement results of the punching resistance, with the vertical axis representing the punching resistance (N). In the comparative example, no significant change was observed even when the amount of additive was increased, but in the examples, the punching resistance decreased significantly as the amount of additive was increased. This is thought to be because the amount of vegetable oil impregnated into the vegetable powder increased, making it easier to remove.

[0054] Furthermore, the amount of gas generated by the carbon-based additive alone was also measured. In this measurement, the carbon-based additive was placed in a quartz tube with a capacity of 576.731 cc, and the gas pressure generated when heated to 1000°C in a heating furnace was measured, and the measured gas pressure was converted into the amount of gas generated (cc / g). In this measurement, the carbon-based additive of Example 2, which was impregnated with 10% by mass of vegetable residue oil, and the coal powder of Comparative Example 1 were measured.

[0055] FIG. 4(B) is a graph showing the results of conversion of the amount of gas generated, with the vertical axis representing the amount of gas generated (cc / g). The horizontal axis represents the processing time (seconds). The solid line represents the conversion result for Example 2, and the dotted line represents the conversion result for Comparative Example 1. The gas generated here includes water vapor and the like, but approximately 90% is volatile gas. It can be seen that the timing of gas generation differs between Example 2 and Comparative Example 1. Example 2 generates a larger amount of gas in a shorter period of time. It is thought that the increase in volatile gas in a short period of time creates a reducing atmosphere inside the mold, preventing oxidation of the molten metal and preventing poor seizure.

[0056] Next, Nagoya Kogyo prototype scoop test specimen molds were manually cast using the greensand molding materials of Examples A to E and the greensand molding materials of Example 2, each containing 1.5% (75 g) of carbon-based additive and 3.0% (150 g) of carbon-based additive. Also, Nagoya Kogyo prototype scoop test specimen molds (hereinafter simply referred to as molds) were manually cast using the greensand molding material of Comparative Example B, containing 1.0% (75 g) of coal powder; Comparative Example C, containing 2.0% (150 g) of coal powder; and Comparative Example E, containing no carbon-based additive. Molten metal equivalent to FC200 was poured into the completed mold. The pouring temperature (target value) was 1430°C, and the pouring time was approximately 15 seconds. After cooling sufficiently at room temperature, the specimen was removed from the frame to obtain a Meiko prototype scooped test specimen (hereinafter simply referred to as the test specimen). After removing sand from the test specimen with a gold (brass) brush, the specimen was shot with a steel ball with a diameter of 1.4 mm and a hardness of 450 HV for 5 minutes to remove the sand.

[0057] FIG. 5 is a photograph of the test piece after shot blasting.

[0058] In each of the drawings in FIG. 5, the test piece TP has a rounded groove g formed on a flat surface f.

[0059] Fig. 5(A) is a photograph of a test piece cast in a mold made using a green sand molding material containing no carbon-based additives (Comparative Example E). A "scooping" defect occurs in the round groove portion g, and a "squeezing" defect occurs in the flat portion f.

[0060] Fig. 5(B) is a photograph of a test piece cast in a mold made using the green sand molding material containing 1.0 mass% coal powder of Comparative Example B. Although not as severe as Comparative Example E, a "scooping" defect occurred in the round groove portion g, and a "squeezing" defect also occurred in the flat portion f.

[0061] Fig. 5(C) is a photograph of a test piece cast in a mold made using the green sand molding material containing 2.0 mass% of coal powder (Comparative Example C). There were almost no scooping or squeezing defects.

[0062] Fig. 5(D) is a photograph of a test piece cast in a mold made using the green sand molding material containing 1.0 mass% of Example B. Although a "scooping" defect occurs in the round groove portion g, only a slight "squeezing" defect occurs in the flat portion f.

[0063] Although a photograph of the test piece cast in the mold made using the green sand molding material of Example A containing 0.5% by mass of added fluorine is not shown, this test piece had a "scooping" defect in the round groove portion g and a "squeezing" defect in the flat portion f, although not as severe as in Comparative Example E.

[0064] Fig. 5(E) is a photograph of a test piece cast in a mold made using the green sand molding material containing 1.5 mass% of the carbon-based additive of Example 2. Neither "scooping" nor "squeezing" defects occurred.

[0065] Fig. 5(F) is a photograph of a test piece cast in a mold made using the green sand molding material containing 2.0 mass% of the additive of Example C. The same degree of scooping and squeezing defects as in Example B occurred.

[0066] Although a photograph of a test piece cast in a mold made using the green sand molding material of Example D containing 3.0% by mass of additive is not shown, this test piece had a "scooping" defect in the round groove portion g and a "squeezing" defect in the flat portion f, although not as severe as in Comparative Example E.

[0067] In the case of the mold made using the green sand molding material of Example E containing 4.0 mass % of Zn, the mold cracked during casting, and it was not possible to cast a test piece.

[0068] During casting, a moisture condensation layer forms on the surface of the green sand mold that comes into contact with the molten metal. "Scooping" and "squeezing" defects are thought to occur when cracks form in the green sand mold due to the thermal expansion of the molding sand, resulting in a decrease in mold strength due to this moisture condensation layer. For this reason, it is thought that reducing the thermal stress (expansion stress) of the green sand mold is an effective way to prevent "scooping" and "squeezing" defects.

[0069] The sand mold filling density measurement results shown in Figure 2(B) clearly show that, in the examples, increasing the addition amount up to 1.0 mass% significantly increases the sand mold filling density. As the sand mold filling density increases, thermal stress (expansion stress) also increases. On the other hand, carbon-based additives soften at 300-500°C due to tarring and other factors. This softening cushions the molding sand's expansion, preventing scooping defects caused by thermal expansion. In the case of carbon-based additives made from vegetable powder impregnated with vegetable oil, the amount of addition of 0.5 mass% or 1.0 mass% was not completely sufficient to increase the sand mold filling density, resulting in a somewhat insufficient cushioning effect, possibly resulting in scooping and squeezing defects. On the other hand, at 1.5 mass%, the cushioning effect was sufficient to offset the increase in sand mold filling density, preventing scooping and squeezing defects. Furthermore, from the measurement results of the moisture content shown in FIG. 1(A), in the examples, the moisture content increases as the amount added increases, and therefore the moisture condensation layer tends to become thicker, and it is thought that the addition of 2.0 mass % and 3.0 mass % made it easier for poor scooping and poor squeezing due to gas caused by steam generation to occur.

[0070] When the amount of carbon-based additive to vegetable powder impregnated with vegetable oil is taken as 100% by mass of green sand, the amount to be added is around 1.5% by mass (higher than 1.0% by mass and less than 2.0% by mass) to completely suppress scooping and squeezing defects, but it can be said that a certain degree of suppression effect is observed at 0.5% by mass or more and 3.0% by mass or less.

[0071] In the examples, new sand was used, but when green sand molds are made by adding new sand and carbon-based additives to recycled sand (system sand) to which carbon-based additives have been added, the carbon-based additives are added so that the amount is 0.5% by mass to 3.0% by mass, including the carbon-based additives contained in the recycled sand.

[0072] Furthermore, the surface roughness of the flat surfaces of the test pieces after shot blasting was measured in accordance with JIS B0601 (2001). As a result, the test pieces cast in molds made with a green sand molding material containing a carbon-based additive made of vegetable powder impregnated with vegetable oil had arithmetic mean roughness values ​​that were approximately the same as those of the test pieces cast in molds made with a green sand molding material containing 2.0 mass% coal powder (Comparative Example C), demonstrating an improvement in the as-cast casting surface.

[0073] Furthermore, when cross-sectional structural photographs were taken of test pieces (test pieces before shot blasting) from which sand had been removed with a gold (brass) brush, a decarburized layer without graphite was formed on the surface of the test piece cast in a mold made with the green sand molding material of Comparative Example E to which no carbon-based additives had been added. On the other hand, the test pieces cast in a mold made with the green sand molding material to which a carbon-based additive made of vegetable powder impregnated with vegetable oil had graphite present on the surface to the same extent as the test piece of Comparative Example B to which 1.0 mass% coal powder had been added, confirming the effect of suppressing decarburization of the casting surface.

[0074] To summarize what has been discussed so far, the carbon-based additives of the examples are in powder form, while maintaining the effects of improving packing density as explained using FIG. 2(B) and improving the casting surface as explained using FIG. 5. In addition, they have low punching resistance as explained using FIG. 4(A), and it has been found that the amount of carbon-based additive added can be reduced compared to coal powder.

[0075] The present invention is not limited to the embodiments and examples described above, and various modifications can be made within the scope of the claims. For example, the green sand mold additive may be 100% vegetable powder impregnated with vegetable oil, or vegetable powder impregnated with vegetable oil and further containing additives. The vegetable oil may contain one or more types of vegetable oil components. Furthermore, the vegetable powder may contain one or more types of vegetable powder.

[0076] Furthermore, the additive for green sand casting may be mainly composed of powder obtained by impregnating fumes generated by biomass power generation with vegetable oil. [Explanation of symbols]

[0077] TP test specimen f Flat part g Round groove

Claims

1. An additive for green sand molding to be added to green sand molding sand, An additive for green sand casting, characterized in that it is mainly composed of a vegetable powder impregnated with a vegetable oil agent containing at least one of vegetable oil and an oil component derived from vegetable oil.

2. 2. The additive for green sand casting according to claim 1, wherein the vegetable oil is present in an amount of 5% by mass or more and 30% by mass or less relative to 100% by mass of the total of the vegetable oil and the vegetable powder.

3. 3. The additive for green sand casting according to claim 1, wherein the vegetable powder has a particle size of 3 μm or more and 800 μm or less.

4. 3. The additive for green sand casting according to claim 1, wherein the water content is kept to 20% or less.

5. Green sand for molding, Water and A binder; The green sand mold additive of claim 1, A green sand molding material, characterized in that the green sand additive is added in an amount of 0.5% by mass to 3.0% by mass, when the green sand molding sand is taken as 100% by mass.

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