JP3170897B2 - Sand core manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a sand core having excellent pressure resistance and excellent coating properties for use in high pressure die casting of a casting having an undercut portion, such as a closed deck type automobile engine. It is about. More specifically, when shaping a sand core prototype by the shell mold method, the same coating agent can be coated thickly only once by adding an organic acid salt, and is also suitable for high-pressure casting. The present invention relates to a method for manufacturing a child. Here, the excellent coating property means that when the coating agent is coated on the sand core prototype, the coating agent does not penetrate deeply in a thin liquid state and spread inside the sand core prototype, or It is formed to a uniform thickness with a predetermined thickness, uniformly, reliably and easily without being repelled from the surface of the sand core prototype, and over the entire surface layer of the sand core prototype. That is, it can sufficiently withstand the high casting pressure during casting.

[0002]

2. Description of the Related Art Conventionally, for example, when a closed deck type automobile engine block or other castings such as aluminum alloys and magnesium alloys having an undercut portion are manufactured by die casting, a collapsible sand core is used. Die-casting is performed using the same. In order to obtain a collapsible sand core, first, the sand is hardened to a desired shape, and then a coating agent is applied to the surface of the hardened sand core prototype. To prevent the breakage of the core or the molten metal from entering the sand core.
After casting, attempts have been made to disintegrate the sand core with little force so that it can be easily taken out and that the sand can be taken out to every corner. Of course, in this case, various attempts have been made on the components of the sand core prototype, the method of hardening the sand, the components of the coating agent, the coating method, etc., but no satisfactory one has been obtained. It is.

[0003] Among them, the hardening method, warm box method,
There are a shell mold method, a cold box method and the like.
As the Hardox method, for example, Japanese Patent Publication No. 64-989
The technique described in Japanese Patent Publication No. 8 is known. In this method, the sand core prototype is composed of a binder mainly composed of sand, an acid-curable resin and an oxidizing agent.
Cured by sulfur dioxide.

[0004]

In the above-mentioned Hardox method, when sand formed into a desired shape is hardened to obtain a sand core prototype, it is hardened using sulfur dioxide, that is, sulfurous acid gas. Therefore, because sulfur dioxide is used,
The working environment is poor, and Japanese factories do not like the use of gases that can harm the human body. Also, even if sulfurous acid gas is used, it is very difficult to install ancillary equipment to prevent adverse effects on the human body and the working environment from deteriorating. Are also subject to laws and regulations.

[0005] Therefore, the present inventor has reviewed the merits of the shell mold method using a binder instead of the oxidizing agent and the sulfurous acid gas. In the shell mold method, a mixture of sand and a binder is hardened to obtain a sand core prototype without using sulfurous acid gas. For example, a resin-coated sand (RCS) previously coated with a phenolic synthetic resin such as phenolic resin is used. ) Is blown into the mold for sand core prototype molding with compressed air, and is heated and cured to form a mold. However, in this case, even if the same coating agent as the coating agent which had been performed quite well in the above-mentioned Hardox method was applied to the sand core prototype, the coating agent was repelled without getting wet, which did not work.

[0006]

According to the present invention, RC is used.
A step of molding a sand core prototype using S and an organic acid salt;
A step of coating the surface of the molded sand core prototype with a slurry-like coating agent comprising a neutral aqueous dispersion mainly composed of a powdered refractory, and drying the coated sand core. The process yields a sand core with an excellent coating. In addition, the organic acid salt that is mixed when the sand core prototype is formed refers to a salt formed between an organic acid and an inorganic ion. Formic acid, acetic acid, propionic acid, acrylic acid, methacrylic acid, oxalic acid, Organic acids such as fumaric acid, maleic acid, succinic acid, tartaric acid, citric acid, carboxylic acid such as butanetetracarboxylic acid, benzoic acid, phthalic acid, terephthalic acid, trimellitic acid, benzenesulfonic acid, and toluenesulfonic acid, and sulfonic acid. Anion and L
i ⁺ , Na ⁺ , K ⁺ , Cs ⁺ , Cu ⁺ , Cu ²⁺ , Mg
²⁺ , Ca ²⁺ , Ba ²⁺ , Zn ²⁺ , Al ³⁺ , Mn
²⁺ , Fe ²⁺ , Fe ³⁺ , Co ²⁺ , Ni ²⁺ , NH
₄ ⁺ and inorganic cations such refers to generating a form for neutralizing the electric charge. Examples include potassium acetate, sodium acetate, magnesium acetate, calcium acetate, zinc acetate, barium acetate, magnesium acrylate, calcium acrylate, zinc acrylate, aluminum acrylate, sodium benzoate and the like. In addition, when molding a sand core prototype containing an organic acid salt, for example, the RCS
After compounding an organic acid salt or an organic acid salt solution such as powdered calcium acetate or an aqueous solution thereof, this is mixed with compressed air in a sand core prototype molding mold heated to, for example, 200 to 300 ° C. Blow and heat cure.

[0007]

In the present invention, first, for example, RCS
After mixing an organic acid salt or an organic acid salt solution such as powdered calcium acetate or an aqueous solution thereof, the composition is heated and cured as described above to form a sand core prototype containing the organic acid salt. . Next, the surface of the sand core prototype thus obtained is coated with a slurry-like coating agent comprising a neutral aqueous dispersion mainly composed of a powdered refractory.

[0008] By applying a slurry-like coating agent comprising a neutral aqueous dispersion mainly composed of powdered refractory to a sand core prototype obtained by blending an organic acid salt with such RCS, The organic acid salt present on and near the surface of the sand core prototype causes the coating agent to be instantly agglomerated and not to be repelled on the surface of the sand core prototype, but to be coated on the surface of the sand core prototype thickly. it can. Thereafter, when this is dried, a homogeneous coating layer having a desired thickness is formed.

In this way, even with the shell mold method, the sand core prototype can be hardened, and the surface of the sand core prototype can be coated easily and reliably with a coating agent in a desired state. When the coated sand core obtained by the present invention is used, the sand core is not broken or cracked at the time of casting the molten metal under high pressure as in the case of high-pressure die casting, and the molten metal is used as the sand core. No intrusion.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS To manufacture a sand core prototype containing an organic acid salt, first, a resin-coated sand (RC) in which a phenolic synthetic resin such as phenolic resin is coated on sand.
S) is prepared. RCS is manufactured by the cold method, semi-hot method, and dry-hot method based on kneading temperature and properties of phenolic synthetic resin such as phenolic resin.
The dry hot method is preferred in terms of cost. That is,
After the solid resin is melt-coated on sand heated to 130-160 ° C by a mixer, a hexamine aqueous solution of a hardener is used for novolak resin, and only water is added for resol resin. A wax such as calcium stearate is dispersed at the time when the fixation of the sand grains is reduced while quenching, to obtain an RCS that is dry and free-flowing. As the sand, use is made of silica sand, zircon sand, chromite sand, cerabeads or their regenerated sand.

Examples of the organic acid salts include organic acid salts such as calcium acetate, zinc acetate, and aluminum acrylate. These organic acid salts are blended in at least 0.1 part by weight based on 100 parts by weight of sand. When the amount is less than 0.1 parts by weight, the coating agent is repelled on the surface of the sand core prototype, and a thick coating layer is not formed on the surface of the sand core prototype. These organic acid salts can be added in a large amount exceeding 0.1 parts by weight or more with respect to 100 parts by weight of the sand, as long as it does not hinder the molding of the sand core prototype.

The above-mentioned organic acid salt may be blended as a solid such as powder, or may be blended in the form of a solution such as an aqueous solution or a dispersion in a suitable dispersant. As the solvent or dispersant used in the latter case, a solvent or a dispersant that does not impair the storage stability and heat-curability (molding property) of the RCS is appropriately selected. The concentration and the amount of the organic acid salt solution or dispersion are appropriately selected so as to be at least 0.1 parts by weight or more per 100 parts by weight of the sand in terms of the organic acid salt alone. You.

A mixture of these components of RCS and an organic acid salt is blown together with pressurized air into a mold having a predetermined sand core-shaped cavity, so-called shell molding method. The sand core prototype was molded.
In this case, the heating temperature of the core molding die is, for example, 200.
To 300 ° C, preferably 230 to 270 ° C,
By heating for about 30 seconds to 2 minutes, the sand core prototype was hardened to a predetermined strength. For example, a sand core prototype having a bending strength of 20 to 50 kg was obtained.

Next, the surface of the sand core prototype formed as described above is coated with a coating agent. In this case, the sand core prototype may be dipped in the coating agent, or the surface of the sand core prototype may be brushed or sprayed with the coating agent. The coating agent was a slurry having a solid content of 50 to 90% by weight containing fine powder silica and fine powder alumina as main components and a small amount of colloidal silica. If the solid content is less than 50% by weight, the thickness of the coating layer becomes thin, and if it exceeds 90% by weight, it becomes extremely difficult to stir the slurry. If the pH of the coating agent is not maintained at 7.0 ± 1.0, precipitation and solidification may occur even under stirring.

As the coating agent, other coating agents can be used. For example, about 30 to 80% by weight of an inorganic refractory material such as graphite, mica, fused silica, alumina, magnesia, carbon black and zircon powder, and about 1 inorganic binder such as colloidal silica, alumina sol, clay and amine-treated bentonite. It is also possible to use water consisting of up to 25% by weight and water. In this case, more preferred are fused silica and colloidal silica. In addition, about 10% by volume of methanol and kaolin may be added.

A sand core prototype molded with an organic acid salt is immersed in the coating agent for several seconds, and then dried by heating. Drying conditions are about 120 ° C. and about 10 minutes. When the organic acid salt is not blended, the coating is repelled from the surface of the sand core prototype and hardly painted, but is sufficiently thick and has less penetration into the sand core prototype. The coating is firm. Coating layer is 1
Layers may be used, but two layers are more preferable in order to improve the releasability between the product and the coating layer. As a coating agent for forming the second coating layer, for example, 1 liter of a 3% aqueous phenol resin solution,
500 g of mica powder, 10 g of sodium dodecylbenzenesulfonate as a wetting agent, and 1 g of octyl alcohol as an antifoaming agent can be used by well stirring and mixing. This coating is performed by immersing the sand core prototype after the first layer coating in the second layer coating agent, or brushing or spraying the second layer coating agent on the surface of the sand core prototype. , Formed by drying.

An experimental example will be described below as a more detailed example. (Experimental Examples 1 to 3 and Comparative Example) An RCS in which 100 parts of flat sand was coated with 2 parts of a phenol resin (including a hardening agent hexamine) was used.
0.1 parts, 0.2 parts or 0.5 parts of calcium acetate powder was mixed as an organic acid salt, and a sand core prototype for an engine block weighing about 2 kg was formed by a shell mold method. Molding conditions: mold temperature 250 ° C, blow pressure 0.8k
g / cm ² and heating time was 90 seconds. A sand core prototype containing no organic acid salt was molded in the same manner and coated in the same manner as in this experimental example. The results are shown in Table 1 below as a comparative example.

The sand core prototypes which were not blended with the calcium acetate powder and which were molded by blending a predetermined amount of calcium acetate powder respectively were mixed with the same coating agent by 1 to 2 times.
After immersion for 2 seconds, it was dried in a circulating hot air heating furnace at 120 ° C. for 10 minutes. The composition of the coating agent is fine powder silica 5
0 parts and 30 parts of fine alumina powder were prepared by suspending 3 parts of colloidal silica in 20 parts of water, and the pH was adjusted to 7.2. In the case of the comparative example, the coating agent was repelled on the surface of the sand core prototype and the coating was poor, whereas in the case of experimental examples 1 to 3, the coating was good.

After finishing the first layer coating, a second layer coating was next performed. As a coating agent for the second layer, 500 g of mica powder, 10 g of sodium dodecylbenzenesulfonate as a wetting agent, and 1 g of octyl alcohol as an antifoaming agent were thoroughly mixed with 1 liter of a 3% aqueous phenol resin solution. Was used. That is, the sand core prototype having been coated with the first layer is added to the second layer coating agent by 1 to 2 times.
After immersion for 2 seconds, it was dried in a circulating hot air heating furnace at 120 ° C. for 10 minutes.

[0020]

[Table 1]

The sand core obtained as described above is set in a mold, and an aluminum alloy ADC10 is cast at a casting pressure of 600 k.
g / cm ² , Gate speed 200 mm / sec, Pouring temperature 7
High pressure casting was performed at 60 ° C. 3 at 350 ° C after casting
After the heat treatment for 0 minutes, sand removal was performed with a normal core knockout machine. In the case of Experimental Examples 1 to 3, the core sand was completely removed, and an excellent cast product was obtained. In the case of the comparative example, the molten metal was inserted into the sand core prototype, and the removal of the core sand was poor. The results are summarized in Table 1.

(Experimental Examples 4 to 6, and Comparative Example) In place of the calcium acetate powder of Experimental Examples 1 to 3, 1 part, 2 parts or 5 parts of a 20% aqueous solution of aluminum acrylate was used, respectively. After processing and operating in the same way,
Excellent results were obtained as with the calcium acetate powder. Table 2 shows the results.

[0023]

[Table 2]

[0024]

As described above, in the present invention, a step of molding a sand core prototype using a resin-coated sand (RCS) coated with a carbonated synthetic resin and an organic acid salt, and a step of molding the sand core prototype A step of coating the surface of the prototype with a slurry-like coating agent consisting of a neutral aqueous dispersion mainly composed of a powdery refractory, and a step of drying the sand core obtained by the coating. Since the core is manufactured, when coating with the coating agent, the coating agent does not repel on the surface of the sand core prototype and does not penetrate into the sand core prototype. To form a coating layer. Therefore, the sand core can sufficiently withstand high casting pressure during casting.

That is, when high-pressure casting such as die casting is performed using the sand core obtained in the present invention, the molten metal is not inserted into the sand core, and the product after the sand is discharged is cast. There is no sand left on the skin and it is very smooth. Therefore, such a sand core is used, for example, in the cooling jacket portion of a closed deck type engine block.
Even when used for casting a product having a very complicated shape, a sufficiently satisfactory working state and the product can be obtained easily and reliably.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-171245 (JP, A) JP-A-59-70438 (JP, A) JP-A-58-68446 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) B22C 1 / 22,3 / 00 B22C 9 / 10,13 / 08

Claims (1)

(57) [Claims] 1. A step of molding a sand core prototype using a resin-coated sand coated with a carboxylate synthetic resin and an organic acid salt, and comprising a powdered refractory material on the surface of the molded sand core prototype. A method for producing a sand core, comprising: a step of coating a slurry-like coating agent comprising a neutral aqueous dispersion; and a step of drying the sand core obtained by coating.