JP2952870B2 - 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, by treating the sand core prototype formed by the warm box method with an organic acid salt, the same coating agent can be coated thickly only once, and the production of a sand core suitable for high-pressure casting is also possible. It is about the method. 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.

Among them, the hardening method, the two-worm 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 warm box method in which a curing agent is used instead of the oxidizing agent and the sulfurous acid gas. In the warm box method, sulfur dioxide gas is not used to solidify a mixture of sand and a binder to obtain a sand core prototype, but, for example, in a mold for a sand core prototype heated to 90 to 240 ° C. Then, a mixture of sand and a binder is blown with compressed air to be heated and cured to form a mold. However,
In this case, even if the same coating agent as the coating agent, which has been performed fairly well in the above-mentioned Hardox method, is applied to the sand core, the coating agent penetrates into the sand core prototype and has a sufficient thickness. No coating layer was obtained.

[0006]

According to the present invention, sand,
A step of molding a sand core prototype using a furan-based resin and a curing agent for the resin heat curing, a step of treating the sand core prototype with an organic acid salt, and a step of processing the sand core prototype with the organic acid salt Drying, and coating the surface of the dried sand core prototype with a slurry-like coating agent composed of a neutral aqueous dispersion containing powdered refractory as a main component. The step of drying the sand core results in a sand core having an excellent coating. The organic acid salt used for treating the sand core prototype is a salt formed between an organic acid and an inorganic ion. Formic acid, acetic acid, propionic acid, acrylic acid, methacrylic acid, oxalic acid, fumaric acid, maleic acid Acid, succinic acid, tartaric acid, citric acid, butanetetracarboxylic acid, benzoic acid, phthalic acid, terephthalic acid, trimellitic acid, carboxylic acid such as benzenesulfonic acid, toluenesulfonic acid, etc. 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. When treating the sand core prototype with an organic acid salt, for example, immersing it in an organic acid salt solution such as an aqueous solution of calcium acetate, brushing the organic salt solution on the surface of the sand core prototype, , Spraying,
Sprinkle fine powder of organic acid salt.

[0007]

In the present invention, for example, a sand core prototype is first formed as described above, and then the sand core prototype is immersed in an organic acid salt aqueous solution such as a calcium acetate aqueous solution. The organic acid salt is impregnated inside the prototype,
The sand core prototype is dried. Next, the surface of the sand core prototype obtained by treating with an organic acid salt and then drying is coated with a slurry-like coating agent comprising a neutral aqueous dispersion mainly composed of a powdered refractory. In this case, if the molded sand core prototype is immersed in an aqueous solution of an organic acid salt such as an aqueous solution of calcium acetate before coating, the organic acid salt may adhere to the surface layer of or inside the sand core prototype. And soak. After lifting this sand core prototype from the immersion tank,
When dried at 200 ° C. for several minutes to 2 hours, the organic acid salt powder uniformly adheres to the surface layer of the sand core prototype.

On the other hand, a slurry-like coating agent composed of a neutral aqueous dispersion containing a powdered refractory as a main component is applied to a sand core prototype obtained through such an organic acid salt treatment and drying. The coating agent is instantaneously agglomerated by the organic acid salt present on and near the surface of the sand core prototype, and does not penetrate deep into the sand core prototype, but is applied to the surface of the sand core prototype. Can be coated thickly. Thereafter, when this is dried, a homogeneous coating layer having a desired thickness is formed.

In this way, even with the warm box method, the sand core prototype can be hardened, and the surface of the sand core prototype can be coated easily and in a desired state with a coating agent. 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 When a sand core prototype is manufactured, first, a furan resin and a curing agent for heat curing the resin are mixed with sand core aggregate such as core sand. Sand core aggregate is silica sand, zircon sand, chromite sand, cerabeads, etc. Furfuryl-based resin is furfuryl alcohol / formaldehyde resin, furfuryl alcohol / urea / formaldehyde resin, furfuryl alcohol / phenol / formaldehyde Resin, furfuryl alcohol / phenol /
A so-called warm box furan resin such as urea / formaldehyde resin is used. In addition, as a curing agent for heat curing of the resin, benzene sulfonic acid, phenol sulfonic acid, toluene sulfonic acid, xylene sulfonic acid,
Use is made of a salt of at least one of lower alkyl sulfonic acids and at least one of aluminum, copper, zinc, iron and ammonium. Further, a small amount of copper chloride, zinc chloride, iron chloride or the like may be used in combination as a curing accelerator.

A mixture of these components is blown together with pressurized air into a mold having a predetermined sand core-shaped cavity, for example, by a method called a warm box method. Was molded. In this case, the heating hot seat of the mold for core molding is, for example, 90 to 240 ° C., preferably about 90 to 200 ° C., and is heated for about 1 minute to harden the sand core prototype to a predetermined strength. Was. For example, bending force 2
A sand core prototype of 0 to 50 kg was obtained.

Next, the sand core prototype thus formed is treated with an aqueous solution of an organic acid salt. Examples of the organic acid salt include calcium acetate, zinc acetate, and aluminum acrylate. The sand core prototype is immersed in an aqueous solution of these organic acid salts, absorbed by the sand core prototype, and then dried by heating. The concentration of the aqueous solution is within 200 times the dilution ratio.
When the dilution ratio exceeds 200 times, the coating thickness becomes thin, and the treatment effect is lost. The immersion time varies depending on the concentration of the treatment liquid and the affinity between the sand core prototype and the treatment liquid, but is as short as 0.5 seconds to about 5 minutes.

If the sand core prototype is difficult to get wet with the processing liquid, the sand core prototype may be immersed in the processing liquid after being immersed in a hydrophilic organic solvent such as methanol in advance for a short time, or the sand core prototype may be dipped in the processing liquid. The organic solvent is mixed until the sand core prototype becomes wet with the processing solution, and then the processing is performed. Drying of the immersion-treated sand core prototype requires a shorter time as the temperature is higher, and is approximately 30 minutes at 120 ° C. as a guide. The organic acid salt may be used as it is without diluting, and the fine powder of the organic acid salt is applied to the sand core prototype, and 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 required to evaporate water. However, when the solution is not diluted with water, drying is not necessary.

Next, the surface of the sand core prototype treated 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 powdered silica and fine powdered alumina as a medium component 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.

The sand core prototype, which has been treated with an organic acid salt and then dried by heating, is immersed in the coating agent for several seconds, and then heated and dried. Drying conditions are about 120 ° C. and about 10 minutes. If the organic acid salt treatment is not performed, the coating thickness is almost 0 m soaked in the sand core prototype.
m, it is sufficiently thick and has little penetration into the sand core prototype, and the coating film is firm. One coating layer 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, a mixture of 500 g of mica powder, 10 g of sodium dodecylbenzenesulfonate as a wetting agent, and 1 g of octyl alcohol as a defoaming agent per 1 liter of a 3% aqueous phenol resin solution can be used. . This coating is performed by dipping 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 1-4, and Comparative Example) 100 parts of flat sand as an aggregate, 1.5 parts of a furan resin as an organic binder, and a commercially available curing agent mainly containing paratoluenesulfonic acid salt as a curing agent for the furan resin ( Kao Quaker Product FC-1
00, the main component is paratoluenesulfonic acid copper salt) 0.6 part,
And commercially available additives (Kao Quaker Products J-20,
0.06 parts of main component silane compound)
A plurality of g prototype sand cores for engine blocks were formed by a warm box method. Molding conditions were a mold temperature of 120 ° C., a blowing pressure of 4.5 kg / cm ² , and a heating time of 90 seconds.
After standing for one day, the sand core prototype had a transverse rupture strength of 35 kg. One of these was coated with the same coating as in this experimental example without performing any of the later-described organic acid salt treatments.
The results are shown in Table 1 below as comparative examples.

9 parts of water and 49 parts of 1 part of calcium acetate
Parts, 99 parts, and 199 parts, and the dilution ratio was 10,50,
100 and 200 times aqueous solutions were 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 Examples 1 to
4)

The non-calcium acetate-treated sand core prototypes treated with calcium acetate by liquids having different concentrations from each other were applied to the same coating agent in the same coating agent.
After immersion for 2 seconds, 10 minutes in a circulating hot air heating furnace at 120 ° C.
Dried for minutes. The composition of the coating agent was prepared by suspending 3 parts of colloidal silica in 20 parts of water in 50 parts of fine powder silica and 30 parts of fine powder alumina, and the pH was adjusted to 7.2. In the case of the comparative example and the case of the experimental example 4, the coating was defective or slightly good. Thus, it was estimated that the dilution ratio of calcium acetate was preferably 150 to 200 times or less.

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 a defoaming 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.

[0021]

[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. After casting, sand removal was performed with a normal core knockout machine.
In the case of No. 3, the core sand was completely removed, and an excellent cast product was obtained. In the case of Experimental Example 4, the removal of the core sand was somewhat good, but 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 5 to 8) When aluminum acrylate was used in place of calcium acetate in Experimental Examples 1 to 4 and the other treatment and operation were performed in exactly the same manner, excellent results were obtained as in the case of calcium acetate. was gotten. Table 2 shows the results.

[0024]

[Table 2]

[0025]

As described above, according to the present invention, a step of molding a sand core prototype using sand, a furan-based resin, and a curing agent for heat curing the resin, and the step of molding the sand core prototype with an organic acid salt. Treating, drying the sand core prototype treated with this organic acid salt, and forming a slurry comprising a powdered refractory-based neutral water dispersion on the surface of the dried sand core prototype. The coated core is manufactured by the step of coating the coated core and the step of drying the sand core prototype obtained from the coating. A uniform and appropriate thickness coating layer is formed without penetrating into the core prototype. Therefore, sand core
During casting, it can withstand high casting pressure.

That is, when high-pressure casting such as die-casting is performed using the collapsible sand core obtained in the present invention, the molten metal is not inserted into the sand core, and the product after sand is discharged. No sand remains on the casting surface of the steel, and it is very smooth.
In addition, the sand core after casting has good disintegration properties, and sand can be easily discharged. Therefore, even if such a sand core is used for casting a product having a very complicated shape, for example, a cooling jacket portion of a closed-deck type engine block, a sufficiently satisfactory working condition is obtained. And the product can be obtained easily and reliably.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-309350 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B22C 9/10, 3 / 00,1 / twenty two

Claims (1)

(57) [Claims] 1. A step of molding a sand core prototype using sand, a furan-based resin, and a curing agent for heat curing the resin, a step of treating the sand core prototype with an organic acid salt, Drying the sand core prototype treated with the above, and coating the surface of the dried sand core prototype with a slurry-like coating agent comprising a neutral aqueous dispersion mainly composed of a powdered refractory. And a step of drying the sand core obtained by the coating.