Sand casting mold coating composition

Abstract

To provide a mold coating composition for sand casting that can suppress the decrease in permeability into the sand mold even when it contains a polymer dispersant. [Solution] A mold coating composition for sand casting containing refractory aggregate, a polymer dispersant, and water, wherein the refractory aggregate includes spherical aggregate with a sphericity of 0.80 or higher.

Description

Technical Field

[0001] The present invention relates to a coating agent composition for sand casting.

Background Art

[0002] A coating agent composition for sand casting is used to protect the surface of a sand mold (casting mold) contacted by molten metal by applying or spraying (including splashing) it on the surface of the sand mold to form a coating film, and to prevent chemical reactions between the molten metal and the sand mold surface, and the occurrence of welding defects in castings.

[0003] As the coating agent composition for sand casting, an aqueous one containing water as a solvent and an alcohol-based one containing alcohol as a solvent are known (for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] An alcohol-based coating agent composition for sand casting has good volatility of the solvent and dries by catching fire, so it is excellent in the productivity of a sand mold for casting having a coating film on the surface, but there are problems in the working environment and safety. On the other hand, in an aqueous coating agent composition for sand casting, when a polymer dispersant is added to suppress an increase in viscosity, the penetration into the sand mold tends to become shallow when applied to the sand mold, so there is room for improvement in terms of the productivity of the sand mold for casting.

[0006] The present invention provides a coating agent composition for sand casting that can suppress a decrease in permeability into a sand mold even when a polymer dispersant is contained. [Means for solving the problem]

[0007] The present invention relates to a mold coating composition for sand casting containing a refractory aggregate, a polymer dispersant, and water. The aforementioned fire-resistant aggregate is a mold coating composition for sand casting, which includes spherical aggregate with a sphericity of 0.80 or higher. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a mold coating composition for sand casting that can suppress a decrease in penetration into the sand mold even when a polymer dispersant is included. [Modes for carrying out the invention]

[0009] <Composition for sand casting mold coatings> The mold casting coating composition of this embodiment (hereinafter also simply referred to as the mold casting composition) is a mold casting composition containing refractory aggregate, a polymer dispersant, and water, wherein the refractory aggregate includes spherical aggregate with a sphericity of 0.80 or higher. According to the mold casting composition of this embodiment, even if a polymer dispersant is included, a decrease in penetration into the sand mold can be suppressed.

[0010] Solvents are added to adjust the viscosity of the mold coating composition to improve workability such as application. However, if the water content as the solvent is high, workability improves, but drying takes longer. The mold coating composition of this embodiment contains a polymer dispersant, which suppresses the increase in viscosity even when the amount of water in the solvent is reduced, resulting in excellent workability. However, it was found that when a mold coating composition with a polymer dispersant is applied to a sand mold, the penetration into the sand mold tends to be shallow. Casting using a sand mold with shallow penetration of the mold coating composition may result in smear defects and other problems in the casting, potentially degrading the quality of the casting. The mold coating composition of this embodiment uses spherical aggregate with a sphericity of 0.80 or higher as refractory aggregate, which has been shown to suppress the decrease in penetration into the sand mold even when the mold coating composition contains a polymer dispersant, thereby suppressing the degradation of casting quality due to smear defects and other problems.

[0011] [Polymer dispersant] Various compounds can be used as the polymer dispersant, but from the viewpoint of reducing the amount of solvent required when applying the coating agent and improving the drying properties of the coating agent composition, a polycarboxylic acid-based polymer dispersant having multiple carboxyl groups in the molecule is preferred. Examples of the polycarboxylic acid-based polymer dispersant include poly(meth)acrylic acid and its derivatives. Specific examples of its derivatives include copolymers of (meth)acrylic acid and (meth)acrylic acid esters, copolymers of (meth)acrylic acid and maleic anhydride, as well as their amidates and esters, copolymers of (meth)acrylic acid and maleic acid, and comb-type polymers having (meth)acrylic acid units. In this specification, (meth)acrylic acid refers to acrylic acid or methacrylic acid.

[0012] The polycarboxylic acid-based polymer dispersant may be neutralized. The neutralization rate of the polycarboxylic acid-based polymer dispersant can be arbitrarily adjusted between 0 and 100%. From the viewpoint of improving the drying properties of the coating composition, 30 to 100% is preferred, 50 to 100% is more preferred, and 80 to 100% is even more preferred. When the polycarboxylic acid-based polymer dispersant is neutralized, the base constituting the salt is preferably an alkali metal, more preferably one or more selected from the group consisting of lithium, sodium, and potassium, even more preferably one or more selected from the group consisting of sodium and potassium, and even more preferably sodium.

[0013] The weight-average molecular weight of the polymer dispersant is preferably 1000 or more, more preferably 2000 or more, and even more preferably 3000 or more, from the viewpoint of reducing the amount of solvent and improving the drying properties of the coating agent composition. The weight-average molecular weight of the polymer dispersant is preferably 100,000 or less, more preferably 70,000 or less, and even more preferably 50,000 or less, from the same viewpoint. In this specification, the weight-average molecular weight of the polymer dispersant is measured by the method described in the examples.

[0014] The content of the polymer dispersant is preferably more than 0.1 parts by mass, and more preferably 0.3 parts by mass or more, per 100 parts by mass of the refractory aggregate, from the viewpoint of suppressing a decrease in the permeability of the mold coating composition containing the polymer dispersant into the sand mold.

[0015] From the viewpoint of reducing the amount of solvent and improving the drying properties of the coating composition, the content of the polymer dispersant is preferably 0.03 parts by mass or more, more preferably 0.07 parts by mass or more, per 100 parts by mass of the refractory aggregate. From the viewpoint of maintaining the smoothness of the coating film, the content of the polymer dispersant is preferably 1.00 parts by mass or less, more preferably 0.80 parts by mass or less, per 100 parts by mass of the refractory aggregate.

[0016] [Fire-resistant aggregate] The refractory aggregate is not particularly limited, but from the viewpoint of refractory properties, economy, and reactivity with molten metal, it is preferably at least one selected from the group consisting of mullite, silica, alumina, magnesia, zircon, aluminasilicate, graphite, obsidian, olivine, talc, and mica; more preferably at least one selected from the group consisting of silica, obsidian, mica, mullite, and graphite (especially scaly graphite); and even more preferably at least one selected from the group consisting of silica, obsidian, and mica.

[0017] The aforementioned refractory aggregate includes spherical aggregate with a sphericity of 0.80 or higher, preferably 0.84 or higher, and more preferably 0.90 or higher, from the viewpoint of suppressing a decrease in the permeability of the mold coating composition containing a polymer dispersant into the sand mold. In this specification, the sphericity of the refractory aggregate is measured by the method described in the examples.

[0018] From the viewpoint of suppressing a decrease in the penetration of the mold coating composition containing a polymer dispersant into the sand mold, the spherical aggregate preferably has a mode diameter smaller than 10 μm, more preferably smaller than 7 μm, even more preferably smaller than 5 μm, and even more preferably smaller than 3 μm. In this specification, the mode diameter of the refractory aggregate is measured by the method described in the examples.

[0019] From the perspective of suppressing the decrease in the permeability of the coating agent composition containing the polymer dispersant to the sand mold, the content of the spherical aggregate in the refractory aggregate is preferably 50% by mass or more, more preferably 60% by mass or more. From the perspective of maintaining the structural viscosity of the coating agent composition, the content of the spherical aggregate in the refractory aggregate is preferably 90% by mass or less, more preferably 80% by mass or less.

[0020] From the perspective of improving the coating workability, the average particle size of the refractory aggregate is preferably 0.5 to 200 μm, more preferably 1 to 100 μm, and still more preferably 2 to 40 μm. When two or more kinds of refractory aggregates are mixed and used, from the perspective of improving the coating workability, the average particle size of the mixture of refractory aggregates is preferably 0.5 to 200 μm, more preferably 1 to 100 μm, and still more preferably 2 to 60 μm. In this specification, the average particle size of the refractory aggregate is measured by the method described in the examples.

[0021] 〔Solvent〕 The coating agent composition contains water as a solvent. It may contain solvents other than water, but from the perspectives of safety and economy, the water content in the solvent is preferably 98% by mass or more, more preferably 99% by mass or more, still more preferably substantially 100% by mass, and even more preferably 100% by mass. In this specification, substantially 100% by mass means a state containing unavoidably trace amounts of impurities and the like.

[0022] Examples of solvents other than water include alcohols such as methanol, ethanol, propanol, butanol, and hexanol.

[0023] From the perspectives of maintaining the thickness of the coating film within an appropriate range and workability, the water content of the coating agent composition is preferably 20% by mass or more, more preferably 30% by mass or more. From the perspective of shortening the time required for drying and improving the productivity of the sand mold for casting, the water content of the coating agent composition is preferably 49% by mass or less, more preferably 47% by mass or less.

[0024] [Binder] The binder may contain gums such as gum arabic and polysaccharides that can form a strong coating film at room temperature, organic binders such as phenol, rosin, and petroleum resins, and inorganic binders such as ethyl silicate and sodium silicate for increasing the hot strength of the coating film during casting. These binders may be used in combination depending on the conditions. From the perspective of improving the coating film strength, the content of the binder in the coating agent composition is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, based on 100 parts by mass of the refractory aggregate. From the perspective of reducing the amount of pyrolysis gas, the content of the binder in the coating agent composition is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, based on 100 parts by mass of the refractory aggregate.

[0025] [Other Components] As other components that can be incorporated into the coating agent composition, thickeners such as attapulgite and bentonite, colorants such as pigments and dyes, rheology modifiers for improving coating workability, anti-settling agents, and additives such as surfactants can be used. Also, additives such as thickeners and preservatives, such as cellulose derivatives like hydroxyalkylated cellulose, polyvinyl alcohol, and sodium alginate, can be used. The content of the other components in the coating agent composition is generally 0.1 parts by mass or more and 15 parts by mass or less based on 100 parts by mass of the refractory aggregate.

[0026] Also, generally, the coating agent composition is kept as a composition with a low solvent concentration (high solid content concentration) during storage (storage composition), and is diluted with a solvent for use so as to obtain an appropriate viscosity during use. The composition with the above high solid content concentration (storage composition) may usually have a penetration of about 200 by adjusting the amount of solvent and the like. The appropriate specific gravity during use is 30 - 80 degrees Baumé. The specific gravity expressed in degrees Baumé can collectively represent the factors of the viscosity and concentration of the coating agent composition, and serves as a guide when applying the coating agent to the sand mold.

[0027] [Method for Manufacturing Castings] The casting method of this embodiment is a casting method that uses a casting sand mold in which the mold coating composition is applied to the surface of the sand mold. In the casting method of this embodiment, aside from the use of the mold coating composition, a conventional manufacturing process can be adopted.

[0028] The foundry sand used in the aforementioned sand mold may be silica sand, which is mainly composed of quartz, or new sand such as zircon sand, chromite sand, or synthetic mullite sand, or recycled sand thereof. The foundry sand may be used without adding the binder, in which case the filling properties will be good. However, if high sand mold strength is required, it is preferable to add a binder and harden it with a hardening agent.

[0029] Generally, the aforementioned sand mold is obtained by mixing an organic binder such as furan resin or alkali phenolic resin, or an inorganic binder such as water glass, with foundry sand, filling the mixture around a wooden mold of the same shape as the product (casting), and then allowing it to harden and be removed.

[0030] The method for applying the aforementioned mold coating composition to the sand mold (casting mold) is not particularly limited, and conventionally known methods such as pouring, dipping, brushing, and spraying can be used.

[0031] The casting sand mold is obtained by applying the mold coating composition to the surface of the sand mold and then drying the mold coating composition to form a mold film. That is, the casting sand mold comprises the sand mold and a mold film obtained by drying the mold coating composition on the surface of the sand mold. A known method can be used to dry the mold coating composition. The particle size index (AFS) of the foundry sand used in the casting sand mold is preferably 30 or higher, more preferably 40 or higher, from the viewpoint of obtaining the effects of the present invention due to the mold coating composition. The particle size index (AFS) of the foundry sand used in the casting sand mold is preferably 100 or lower, more preferably 60 or lower, from the same viewpoint.

[0032] From the viewpoint of allowing the coating agent to exert its intended function, the thickness of the aforementioned coating film is preferably 50 to 300 μm, more preferably 60 to 150 μm, and even more preferably 70 to 120 μm. [Examples]

[0033] The following describes specific examples illustrating the present invention. <Measurement method> [Weight-average molecular weight of polymer dispersants] The weight-average molecular weight of the polymer dispersant was measured using gel permeation chromatography (GPC) under the following measurement conditions. • Columns (G4000PWXL + G2500PWXL) • Eluent (0.2 ml / L phosphate buffer / CH3CN;9 / 1) ·Flow rate (1.0ml / min) • Column temperature (40°C) • Detectors (CH1: RID, CH2: UVD) • Conversion molecular weight standard (polyethylene glycol)

[0034] [Sphericality of fire-resistant aggregates] Images of primary particles of refractory aggregate were captured using a scanning electron microscope (SEM), and the area (cross-sectional area) of the primary particles was obtained by analyzing them using JEOL's analysis software (granulometry) under the following conditions. Image analysis conditions Preprocessing: Gaussian Blur This process: Fixed Threshold Post-processing: Edge Cut In this specification, sphericity is calculated by determining [the diameter of a perfect circle with the same area as the cross-sectional area of ​​the primary particle / the diameter of the smallest circumscribed perfect circle of the primary particle] and averaging this value over 30 randomly selected primary particles of fire-resistant aggregate.

[0035] [Mode diameter of fire-resistant aggregate] The mode diameter is the mode system measured using a laser diffraction particle size distribution analyzer (LA-960V2, Horiba, Ltd.). The measurement conditions are as follows: • Measurement method: Flow method • Dispersion medium: Ion-exchanged water • Dispersion method: stirring, built-in ultrasonic for 3 minutes • Sample concentration: 10mg~1g / 180cc

[0036] [Average particle size of fire-resistant aggregate] The average particle size was measured using a laser diffraction particle size distribution analyzer (LA-960V2, Horiba, Ltd.). The measurement conditions are as follows: • Measurement method: Flow method • Dispersion medium: Ion-exchanged water • Dispersion method: stirring, built-in ultrasonic for 3 minutes • Sample concentration: 10mg~1g / 180cc

[0037] <Preparation of coating agent composition> [Examples 1-5, and Comparative Examples 1 and 2] Under conditions of 25°C, 100 parts by mass of the refractory aggregate shown in Table 1 were mixed with the amounts of polymer dispersant, thickener, other additives, and water shown in Table 1, and kneaded in a twin-shaft mixer until uniformly homogeneous by visual inspection to obtain the coating compositions for each example and comparative example.

[0038] The contents of the raw materials listed in Table 1 are as follows. • Spherical silica (sphericity 0.84, mode diameter 1 μm, average particle size 3 μm): "SF-AN" manufactured by Tomoe Engineering Co., Ltd. • Spherical silica (sphericity 0.90, mode diameter 5 μm, average particle size 7 μm): Denka Corporation's fused silica "FB-5D" • Irregularly shaped silica (sphericity 0.77, mode diameter 1 μm, average particle size 3 μm): "Silsic PL" manufactured by Yamamori Tsuchimoto Mining Co., Ltd. • Irregularly shaped silica (sphericity 0.65, mode diameter 5 μm, average particle size 6 μm): "K2-4" manufactured by Yamamori Tsuchimoto Mining Co., Ltd. Obsidian (sphericity 0.59, mode diameter 187 μm, average particle size 152 μm): "AJ Remove" manufactured by Ajimu Perlite Industry Co., Ltd. • Mica (sphericity 0.59, mode diameter 83 μm, average particle size 85 μm): Kirara Co., Ltd. muscovite "KC200" • Sodium polyacrylate: Kao Corporation's "Poise 530" (weight-average molecular weight: 17000) • Bentonite: Kunimine Industries Co., Ltd. "Kunigel VA" • Attapulgite: BASF "Atagel 50" Other additives: A mixture of a thickening agent (polyamine-based cationic surfactant: "Softex K-370" manufactured by Kitahiro Chemical Co., Ltd.), a preservative ("Biohope" manufactured by Kei-I Kasei Co., Ltd.), and a pigment ("Binamon Green 600734" manufactured by Heubach Colour Pvt. Ltd.) in a mass ratio of 5 parts thickening agent, 0.1 parts pigment, and 0.3 parts preservative.

[0039] <Evaluation Method> [Drying test (evaluation of drying properties)] To 100 parts by mass of recycled furan sand (AFS46~47), 0.9 parts by mass of Kao Quaker furan resin (EF-1112) was added. Furthermore, 50 parts by mass of a mixture of Kao Quaker hardeners (TK-1) and (C-25) in a 1:1 ratio was added to 100 parts by mass of furan resin. The resulting mixed sand was kneaded and placed into a mold to create a plate-shaped sand mold measuring 300 mm in length, 100 mm in width, and 15 mm in thickness. This sand mold was placed with its side facing down against a 60-degree inclined wall. Each coating agent composition was diluted with water so that the wet film thickness of the coating film when poured was 75~100 μm. The coating was then poured onto the lower part of the sand mold (a range of 200 mm in length and 100 mm in width) starting 100 mm below the top edge. Then, 5 seconds after pouring the coating, the sand mold was tilted 75 degrees towards the user, and after another 5 seconds, the coated surface of the sand mold was placed on a horizontal surface. After waiting about 5 minutes for the surface gloss to diminish, a gas burner was applied to the sand mold from a distance of 30 cm to dry it. The time it took for the surface to dry was measured and evaluated on a 3-point scale according to the evaluation criteria below. The evaluation results are shown in Table 1. ○: The time it takes for the surface to dry is less than 1 minute and 30 seconds. △: The time it takes for the surface to dry is 1 minute 30 seconds or more, but less than 2 minutes 30 seconds. ×: The surface takes more than 2 minutes and 30 seconds to dry.

[0040] [Water content (mass%) of the mold coating composition when applied to a sand mold with a constant film thickness] In the drying test described above, 10 g of each mold coating composition, diluted to be applied to the sand mold to a constant film thickness, was placed in an aluminum petri dish and dried in a hot air dryer at 105°C for 1 hour. The amount of evaporated water (g) was then measured. The formula [100 × Amount of evaporated water (g) / 10 (g)] was calculated, and this value was taken as the water content (mass%) of the mold coating composition when applied to the sand mold to a constant film thickness.

[0041] [Wet film thickness of the mold coating] The measurement was performed using an Elcometer rotary wet film thickness gauge (model number: ELCOMETER3230). The gauge was rotated over the wet coating, and the reading was taken at the point where the central wheel touched the film. This value represents the wet film thickness (μm).

[0042] [Evaluation of permeability into sand molds] In the drying test described above, the plate-shaped sand mold after drying was cut in half at the 100mm mark in the area where the mold coating composition was applied (a range of 200mm vertically x 100mm horizontally). The depth (mm) to which the mold coating penetrated the cross-section was measured and evaluated in three stages according to the evaluation criteria below. The results are shown in Table 1. 〇: Over 2mm △: Over 1mm, 2mm or less ×: 1mm or less

[0043] [Seizure test] For the lower mold, a sand mold with a recess measuring 600mm in length, 450mm in width, and 150mm in depth was prepared, and a core (200mm in length, 108mm in width, and 100mm in height) coated with mold coating agent was set on its bottom surface. The upper mold was placed on top of the lower mold so as to align with it, and the molds for the sprue and riser were placed on top of that to create a sand mold with a head height of 1200mm. 250kg of molten metal of FCD450 material, with a casting temperature of 1400℃, was poured into this sand mold to produce a casting measuring 600mm in length, 450mm in width, and 150mm in height, with a recess for the core. After applying shot blasting for 10 minutes, the surface of the recess for the core was observed and evaluated visually in two stages according to the evaluation criteria below. ○: Almost no baking defects. ×: Has a baking defect.

[0044] [Table 1]

Claims

1. A mold coating composition for sand casting containing refractory aggregate, polymer dispersant, and water, A mold coating composition for sand casting, wherein the refractory aggregate includes spherical aggregate with a sphericity of 0.80 or higher.

2. The sand casting mold coating composition according to claim 1, wherein the mode diameter of the spherical aggregate is less than 10 μm.

3. The sand casting mold coating composition according to claim 1, wherein the content of the polymer dispersant is 0.03 parts by mass or more and 1.00 parts by mass or less per 100 parts by mass of the refractory aggregate.

4. The mold coating composition for sand casting according to claim 1, wherein the water content of the mold coating composition is 20% by mass or more and 49% by mass or less.

5. A method for manufacturing a casting using a casting sand mold in which a mold coating composition is applied to the surface of the sand mold, A method for manufacturing a casting, wherein the mold coating composition is the mold coating composition for sand casting described in any one of claims 1 to 4.

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