JPH06585A - Production of sand core - Google Patents

Abstract

PURPOSE:To obtain a sand core which withstands high-pressure casting and has a good collapsing property by molding a sand core prototype by a shell molding method using RCS and treating this prototype with an org. acid salt, then drying the prototype, applying a coating material thereon and drying the coating. CONSTITUTION:The resin coated sand(RCS) formed by coating silica sand, etc., with a coal acid resin is prepd. and the sand core prototype is produced by the shell molding method of blowing this sand into heated molds. This prototype is immersed into an aq. org. acid soln. of calcium acetate, etc., and is then dried for about 30 minutes at 120 deg.C. The surface thereof is then coated with the slurry-like coating material consisting of a neutral aq. dispersion essentially consisting of powdery refractories and is dried. As a result, the coating material is instantaneously flocculated by the org. acid salt existing on the surface and near the surface of the sand core prototype and the surface of the sand core prototype is thickly coated with this material without spilling on the surface.

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 property 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, by treating the sand core mold produced by the shell mold method with an organic acid salt, the same coating agent can be thickly coated only once, and a sand core suitable for high pressure casting can be manufactured. It is about the method. Here, the excellent coating property means that when the sand core prototype is coated with the coating agent, the coating agent is a thin liquid and does not penetrate deeply inside the sand core prototype, or It is not repelled from the surface of the sand core prototype, but is formed only on the surface layer of the sand core prototype uniformly over the entire surface with a predetermined thickness uniformly and surely easily and firmly so that it does not come off. That is, it is possible to sufficiently withstand the high casting pressure during casting.

[0002]

2. Description of the Related Art Conventionally, when a die-cast casting is used to produce a cast product such as a closed-deck type automobile engine block or other aluminum alloy or magnesium alloy having an undercut portion, a collapsible sand core is used. Die casting is performed by using. When a collapsible sand core is to be obtained, the sand is first solidified into the desired shape, then the coating agent is applied to the surface of the solid sand core prototype, and when the molten metal is cast under high pressure Prevent the child from being damaged and the molten metal from entering the sand core.
After casting, it has been attempted to disintegrate the sand core with little force so that the sand core can be easily taken out, and the sand can be fully taken out to every corner. Of course, in that case, various attempts have been made in the past, such as the components of the sand core prototype, the method of hardening the sand, the components of the coating agent, the method of coating, etc., but the ones that are not sufficiently satisfactory have not yet been obtained. Is.

Among them, as a method of solidifying sand to obtain a sand core prototype, a hard-box method, a warm box method,
Shell mold method, cold box method, etc. are available.
As the Hardox method, for example, Japanese Patent Publication No. Sho 64-989.
The technique described in Japanese Patent No. 8 is known. In this method, the sand core prototype is composed of sand, an acid-curable resin and a binder whose main component is an oxidant,
Hardened by sulfur dioxide.

[0004]

In the above-mentioned Hardox method, when the sand core prototype is obtained by hardening the sand shaped into a desired shape, it is hardened by using sulfur dioxide, that is, sulfurous acid gas. Therefore, since sulfur dioxide is used,
Due to the poor working environment, the use of gas that adversely affects the human body is not preferred in Japanese factories. Moreover, even if sulfurous acid gas is used, it is difficult to install auxiliary equipment for that purpose in order to prevent the human body from being adversely affected and the working environment from being deteriorated. Also subject to legal restrictions.

Therefore, the present inventor has decided to reconsider the goodness of the shell mold method using a binder instead of an oxidizing agent and sulfurous acid gas. In the shell mold method, instead of using sulfurous acid gas to solidify a mixture of sand and a binder to obtain a sand core prototype, resin coated sand (RCS) coated beforehand with a phenolic resin-based synthetic resin such as phenolic resin is used. , Sand core mold is blown with compressed air into a mold for molding and heat-cured to mold. But in this case,
Even when the same coating agent that was used quite well in the above-mentioned Hardox method was applied to the sand core prototype, the coating agent was not wet because the coating agent did not get wet.

[0006]

In the present invention, RC
A step of molding a sand core prototype using S, a step of treating the sand core prototype with an organic acid salt, a step of drying the sand core prototype treated with the organic acid salt, and the dried sand Excellent in the process of coating the surface of the core mold with a slurry-like coating agent composed of a powdery refractory-based water dispersion, and drying the sand core obtained by this coating. A sand core with a coating is obtained. Incidentally, the organic acid salt for treating the sand core prototype is a salt formed between an organic acid and an inorganic ion, such as formic acid, acetic acid, propionic acid, acrylic acid, methacrylic acid, oxalic acid,
Fumaric acid, maleic acid, succinic acid, tartaric acid, citric acid,
Anions of organic acids such as carboxylic acids such as butanetetracarboxylic acid, benzoic acid, phthalic acid, terephthalic acid, trimellitic acid, benzenesulfonic acid, toluenesulfonic acid, sulfonic acids, and Li ⁺ , Na ⁺ , K ⁺ , Cs ⁺ , Cu ⁺ ,
Cu ²⁺ , Mg ²⁺ , Ca ²⁺ , Ba ²⁺ , Zn ²⁺ ,
Al ³⁺ , Mn ²⁺ , Fe ²⁺ , Fe ³⁺ , Co ²⁺ ,
Inorganic cations such as Ni ²⁺ and NH ₄ ⁺ are generated in the form of neutralizing charges. For example, potassium acetate,
Sodium acetate, magnesium acetate, calcium acetate,
Examples thereof include zinc acetate, barium acetate, magnesium acrylate, calcium acrylate, zinc acrylate, aluminum acrylate, sodium benzoate and the like. Also,
When the sand core prototype is treated with an organic acid salt, for example, it is immersed in an organic acid salt solution such as an aqueous solution of calcium acetate, or the organic acid salt solution is brushed on the surface of the sand core prototype or blown. Put it on or sprinkle it with a fine powder of organic acid salt.

[0007]

In the present invention, first, for example, as described above, a sand core prototype is formed by using RCS, and then the sand core prototype is immersed in an organic acid salt solution such as a calcium acetate aqueous solution. The organic salt is soaked into the sand core mold, and then the sand core mold is dried. Next, the surface of this sand core prototype obtained by treating with an organic acid salt and then drying is coated with a slurry-like coating agent composed of a neutral water dispersion whose main component is a powdery refractory. In this case, before coating the molded sand core prototype,
For example, when immersed in an aqueous solution of an organic acid salt such as an aqueous solution of calcium acetate, the organic acid salt adheres to or penetrates into the surface layer portion of the sand core prototype. After the sand core prototype is pulled out of the dipping tank and dried at 80 to 200 ° C. for several minutes to 2 hours, the powder of the organic acid salt uniformly adheres to the surface layer portion of the sand core prototype.

On the other hand, if a sand core prototype obtained through such organic acid salt treatment and drying is applied with a slurry-like coating agent composed of a neutral water dispersion containing powdery refractory as a main component, The surface of the sand core prototype is thickly coated on the surface of the sand core prototype without the coating agent being instantaneously aggregated by the organic acid salt present on the surface of the sand core prototype and being repelled by the surface of the sand core prototype. it can. Then, it is dried to form a uniform coating layer having a desired thickness.

[0009] In this way, the sand core mold can be solidified even by the shell mold method, and the surface of the sand core mold can be coated with the coating agent easily and surely in a desired state. When the coated sand core obtained by the present invention is used, the molten core is not damaged or cracked when the molten core is cast under high pressure like high pressure die casting, and the molten core is There is no intrusion.

[0010]

EXAMPLES When manufacturing a sand core prototype, first, resin coated sand (RCS) is prepared by coating a sand with a carboxylic acid-based synthetic resin such as phenolic resin. RC
S is produced by a cold method, a semi-hot method, or a dry hot method depending on the kneading temperature and the properties of a phenolic resin such as a phenol resin. The dry hot method is preferable in terms of productivity, stability and cost. That is, after the solid resin is melt-coated with a mixer on sand heated to 130 to 160 ° C., a hexamine aqueous solution of a curing agent is added in the case of a novolac resin, and only water is added in the case of a resole resin to evaporate latent heat of water. Then, while rapidly cooling by aeration, a wax such as calcium stearate is dispersed at the time when the sticking of sand grains is reduced, and dry free-flowing RCS is obtained.

As the sand, silica sand, zircon sand, chromite sand, cera beads, etc. or recycled sand thereof is used. This RCS is blown together with pressurized air into a mold having a predetermined sand core-shaped cavity,
A sand core prototype was molded by a method called a shell mold method. In this case, the heating temperature of the core molding die is, for example, 200 to 300 ° C., preferably 230 to 270 ° C., and the sand core prototype is cured to a predetermined strength by heating for 30 seconds to 2 minutes. Let For example, a sand core prototype having a transverse rupture strength of 20 to 50 kg was obtained.

Next, the sand core mold thus formed is treated with an aqueous solution of an organic acid salt. Examples of the organic acid salt include calcium acetate, zinc acetate, aluminum acrylate and the like. The sand core prototype is immersed in an aqueous solution of these organic acid salts, absorbed in the sand core prototype, and then heated and dried. The concentration of the aqueous solution is within 200 times the dilution ratio.
If the dilution ratio exceeds 200 times, the coating thickness will be thin and the treatment effect will be lost. The immersion time is from a short time of 0.5 seconds to about 5 minutes, although it varies depending on the concentration of the treatment liquid and the affinity between the sand core prototype and the turtle shell liquid.

If the sand core prototype is difficult to wet with the treatment liquid, the sand core prototype is immersed in a hydrophilic organic solvent such as methanol for a short time in advance and then immersed in the treatment liquid, or the above-mentioned hydrophilic formation is applied to the treatment liquid. The organic solvent is mixed until the sand core prototype becomes wet with the treatment liquid, and then treated. The heat-drying of the sand core mold that has been subjected to the immersion treatment takes shorter time as the temperature becomes higher, and it is about 30 minutes at 120 ° C. as a guide. The organic acid salt may be used as it is without being diluted, and the sand core prototype is sprinkled with the organic acid salt fine powder and the excess organic acid salt fine powder is wiped off. As described above, when a solution having a low concentration such as an aqueous solution of calcium acetate is used, drying is necessary to evaporate water, but when it is not diluted with water, it is not necessary to perform drying.

Next, the surface of the sand core prototype treated as described above is coated with a coating agent. In this case, the sand core master may be dipped in the coating agent, or the surface of the sand core master 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. When the solid content is 50% by weight or less, the thickness of the coating layer becomes thin, and when it is 90% by weight or more, it becomes extremely difficult to stir the slurry. If the pH of this coating agent is not maintained at 7.0 ± 1.0, precipitation and solidification may occur even under stirring.

Other coating agents may be used as the coating agent. 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% of an inorganic binder such as colloidal silica, alumina sol, clay and amine-treated bentonite. It is also possible to use water consisting of ˜25% by weight. In this case, more preferred are fused silica and colloidal silica. Incidentally, about 10% by volume of methanol and kaolin may be added thereto.

The sand core prototype, which has been treated with an organic acid salt and then heated and dried, is immersed in the coating agent for a few seconds, and then dried by heating. Drying conditions are 120 ° C. and about 10 minutes. The thickness of the coating is almost free from the sand core prototype when it is not treated with an organic acid salt, whereas it is thick enough to penetrate the sand core prototype, and the coating film is It is solid. The coating layer may be one layer, but two layers are more preferable in order to improve the mold release between the product and the coating layer. The coating agent for forming the second coating layer is, for example, 1 liter of a 3% aqueous phenol resin solution,
It is possible to use, for example, 500 g of mica powder, 10 g of sodium dodecylbenzenesulfonate as a wetting agent, and 1 g of octyl alcohol as an antifoaming agent, which are well mixed with stirring. This coating is carried out by immersing the sand core prototype that has been subjected to 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 template. , Dry to form.

As a more detailed example, an experimental example will be shown below. (Experimental Examples 1 to 4 and Comparative Example) Using RCS in which 2 parts of a phenol resin (including a curing agent hexamine) is coated on 100 parts of frittary sand, a weight of about 2 kg
A plurality of sand core prototypes for engine blocks were molded by the shell molding method. The molding conditions were a mold cavity 250 ° C., a blowing pressure of 0.8 Kg / cm ² , and a heating time of 90 seconds. The transverse rupture strength of the sand core prototype after standing for 1 day was 38 kg.
One of them was subjected to the same coating as that of the present experimental example without any treatment with an organic acid salt described later, and therefore is shown in Table 1 as a comparative example.

1 part of calcium acetate and 9 parts of water and 49 parts of water, respectively
Parts, 99 parts, 199 parts mixed, dilution ratio 10, 50,
A 100 and 200 times aqueous solution was prepared, respectively. The sand core prototype was immersed in this aqueous solution for 1 to 2 seconds, and then dried in a circulating hot air heating furnace at 120 ° C for 30 minutes. (Experimental example 1
4)

1 to 1 of the same sanding agent prototypes of sand cores which were treated with calcium acetate by liquids having different concentrations from those not treated with calcium acetate
After immersing for 2 seconds, use a circulating hot air oven at 120 ° C for 10
Dry for minutes. The composition of the coating agent was such that 50 parts of fine powder silica and 30 parts of fine powder alumina and 3 parts of colloidal silica were suspended in 20 parts of water, and the pH was adjusted to 7.2. In the comparative example and the experimental example 4, the coating was poor or good. From this, it was estimated that the calcium acetate dilution ratio should be 150 to 200 times or less.

After finishing the above-mentioned first layer coating, a second layer coating was then carried out. As the 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 a defoaming agent were mixed well with 1 liter of a 3% aqueous phenol resin solution. I used one. That is, the sand core prototype that has been subjected to the first layer coating is added to the second layer coating agent in an amount of 1 to 2
After soaking for 2 seconds, it was dried for 10 minutes in a circulating hot air heating oven at 120 ° C.

[0021]

[Table 1]

The sand core obtained as described above is set in a mold and the aluminum alloy ADC10 is cast at a pressure of 600 k.
g / cm ² , spout speed 200 mm / sec, pouring temperature 7
High pressure casting was performed under the condition of 60 ° C. 3 at 350 ℃ after casting
After heat treatment for 0 minutes, the sand was removed by a normal core knockout machine. In the cases of Experimental Examples 1 to 3, the core sand was completely removed, and an excellent cast product was obtained. Experimental example 4
In the case of No. 2, the removal of the core sand was slightly good, but in the case of the Comparative Example, the removal of the core sand was poor because the molten metal was inserted into the sand core prototype. Collectively, the results are shown in Table 1.

Experimental Examples 5 to 8 and Comparative Example Experimental Example 1
When aluminum acrylate was used in place of the calcium acetate of ~ 4, and the other treatments and operations were performed in the same manner, the same excellent results as in the case of calcium acetate were obtained. The results are shown in Table 2.

[0024]

[Table 2]

[0025]

As described above, in the present invention, a step of molding a sand core prototype using a resin coated sand coated with a carboxylic acid-based synthetic resin, and a step of treating the sand core prototype with an organic acid salt And a step of drying the sand core prototype treated with this organic acid salt, and a slurry-like coating comprising a neutral water dispersion containing powdery refractory as a main component on the surface of the dry sand core prototype. Since the coated sand core is manufactured by the step of coating the agent and the step of drying the sand core obtained by the coating, when coating with the coating agent, the coating agent is a sand core prototype. A coating layer of uniform and appropriate thickness is formed without being repelled on the surface or soaking into the sand core prototype. Therefore, the sand core can sufficiently withstand a 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 does not enter the sand core and the product is cast after the sand is discharged. No sand remains on the skin surface and it is very smooth. Therefore, such a sand core, for example, like the cooling jacket portion of a closed deck type engine block,
Even when it is used for casting a product having a very complicated shape, it is possible to obtain a sufficiently satisfactory working condition and the product easily.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Morie Kotani 1980 Okiyama, Ogushi, Obe, Ube, Yamaguchi Prefecture Ube Machinery Co., Ltd.

Claims (1)

[Claims] 1. A step of molding a sand core prototype using a resin coated sand coated with a carboxylic acid synthetic resin, a step of treating the sand core prototype with an organic acid salt, and a treatment with the organic acid salt. The process of dry-explosion the sand core prototype, the step of coating the surface of the dry sand core prototype with a slurry-like coating agent consisting of a neutral water dispersion containing powdery refractory as the main component, A method for producing a sand core, which comprises a step of drying a sand core obtained by coating.