JP2935390B2 - Method for producing collapsible sand core - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to disintegration having good pressure resistance and good coating properties and easy disintegration for use in high pressure die casting of a casting having an undercut portion, such as a closed deck type automobile engine. The present invention relates to a method for manufacturing a sand core. More specifically, the sand core prototype formed by the warm box method is treated with a mineral acid, then washed with water, and then treated with an organic acid salt, so that the coating agent can be thickly coated only once, and after casting. The present invention relates to a method for producing a sand core which is suitable for high-pressure casting and has excellent collapse properties. here,
Good coating property means that the coating agent does not penetrate deep into the sand core prototype when it is coated with the coating agent on the sand core prototype. It shall be uniformly and securely formed to a predetermined thickness on the entire surface layer of the sand core prototype, without being repelled from the surface of the child prototype, and to be easily and firmly coated so as not to come off. 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 solidified into a desired shape, and then a coating agent is applied to the surface of the solidified sand core prototype. To prevent breakage of the molten metal and penetration of the molten metal into 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. As the coating agent, for example, as described in JP-A-63-40639, a first coating agent composed of a powdery refractory and a metal oxide, and a A second coating agent containing scale-like aluminum powder, mica, or the like, which is applied to the substrate, is used.

[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 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.

On the other hand, the inventor of the present invention formed a sand core prototype by using a warm box method using sand core aggregate such as silica sand or zircon sand and an organic binder such as furan resin. After treating the core prototype with a mineral acid such as dilute sulfuric acid, phosphoric acid, etc., it is dried on a sand core prototype to form a slurry-like slurry consisting of a neutral aqueous dispersion mainly composed of powdered refractory. A method for obtaining a collapsible sand core by coating a coating agent and drying it was invented and applied for a patent. Although the collapsible sand core obtained by this method is effective to some extent, in order to more surely prevent the molten metal from being inserted into the collapsible sand core during high-pressure die-casting, the first coating is used. An attempt was made to coat a second coating agent containing aluminum powder as described in JP-A-63-40639 on the surface of the coating layer. However, no good coating was obtained with this combination. That is, the acid remaining near the surface of the sand core prototype permeates through the first coating layer and oozes out to the second coating layer, and reacts with the aluminum powder which is a component in the second coating agent. . As a result, the second coating layer is bald or peeled.

[0007]

According to the present invention, sand,
A step of molding a sand core prototype using a furan-based resin and a curing agent for heat curing the resin, a step of treating the sand core prototype with an acid, and a step of drying the sand core prototype treated with the acid A step of washing the dried sand core prototype with water, a step of treating the washed sand core prototype with an organic acid salt, and a step of drying the sand core prototype treated with the organic acid salt; A step of 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 drying the coated sand core. The process yields a collapsible sand core.

As an acid for treating the sand core prototype, for example, a mineral acid such as sulfuric acid or phosphoric acid is used. When treating the sand core prototype with an acid, for example, the sand core prototype is immersed in an acidic solution such as dilute sulfuric acid, or the surface of the sand core prototype is brushed or sprayed with the acidic solution. Next, the sand core prototype treated with this acid is dried. Thereafter, the dried sand core prototype is washed with water, which simply involves immersing the sand core prototype in water or spraying water on the sand core prototype. Thereafter, the washed sand core prototype is treated with an organic acid salt.

[0009] The organic acid salt used for treating the sand core prototype is as follows.
Salts formed between organic acids and inorganic ions. Formic acid,
Acetic acid, propionic acid, acrylic acid, methacrylic acid, oxalic acid, fumaric acid, maleic acid, succinic acid, tartaric acid, citric acid, butanetetracarboxylic acid, benzoic acid, phthalic acid, terephthalic acid, trimellitic acid, benzenesulfonic acid Anions of carboxylic acids such as sulfonic acid, toluenesulfonic acid and the like and organic acids such as sulfonic acid and Li ⁺ , Na ⁺ , K ⁺ , C
s ⁺ , Cu ⁺ , Cu ²⁺ , Mg ²⁺ , Ca ²⁺ , Ba
²⁺ , Zn ²⁺ , Al ³⁺ , Mn ²⁺ , Fe ²⁺ , Fe
^{3+, Co 2+, Ni 2 +} , and the inorganic cations such as _NH ^{4 +} 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, or brush-coating the organic salt solution onto the surface of the sand core prototype is applied. Spraying or dusting with fine powder of organic acid salt.

[0010]

In the present invention, first, as described above, a sand core prototype is formed using sand, a furan-based resin, and a curing agent for heat curing the resin, and then the sand core prototype is diluted with sulfuric acid or the like. Then, the mineral acid is impregnated into the sand core prototype by immersing it in a mineral acid solution, and then the sand core prototype is dried.
In this case, if the molded sand core prototype (ocher, brown to dark green) is immersed in a mineral acid solution such as a dilute sulfuric acid solution, the mineral acid adheres to the surface layer and inside of the sand core prototype. Or soak. When this sand core prototype is pulled out of the dipping tank and dried at 80 to 200 ° C. for several minutes to 2 hours, the sand core prototype turns black. This is because the hardened furan resin that bound the sand was dehydrated and carbonized by the mineral acid that had adhered to or penetrated the sand core prototype. That is, the cured furan resin that connects the sand to each other accelerates the carbonolysis reaction by the heat during drying. This gives
Blackening and strength decrease. This decrease in strength is sufficient to withstand the pressing force during casting. Naturally, the hardened furan resin is thermally degraded by the heat of the molten metal during casting. However, if the strength is reduced in advance as described above, the sand core can be removed from the cast product removed from the mold after casting. The sand core can be removed very easily and easily.

When a slurry-like first coating agent composed of a neutral aqueous dispersion mainly composed of a powdery refractory is applied to the sand core prototype obtained through such acid treatment and drying, The surface of the sand core prototype is instantaneously agglomerated by the mineral acid present on and near the surface of the sand core prototype, and does not penetrate deep inside the sand core prototype. When the first coating layer having a desired thickness is formed, a uniform first coating layer having a desired thickness can be formed. By the way, as described above, the slurry-like second slurry containing aluminum powder is formed on the first coating layer.
When the coating is applied, the acid remaining near the surface of the sand core prototype permeates through the first coating layer and oozes out to the second coating layer, and aluminum as a component in the second coating agent is removed. Reacts with powder. as a result,
The second coating layer balds or peels. Therefore, the sand core prototype obtained through the above-described acid treatment and drying is immersed in water for several seconds to several minutes, for example, to remove the acid existing near the surface of the sand core.

By the way, even if an attempt is made to apply a slurry-like first coating agent comprising a neutral aqueous dispersion mainly composed of a powdery refractory in a state where the acid near the surface is removed, an acid treatment is required. As in the case where no sand core is used, the first coating agent penetrates into the sand core prototype and cannot be coated thickly on the surface of the sand core prototype. Thus, the sand core prototype washed with water as described above is immersed in an organic acid salt aqueous solution such as an aqueous solution of calcium acetate to infiltrate the organic acid salt into the sand core prototype. Dry the prototype. Next, a slurry-like coating agent composed of a neutral aqueous dispersion mainly composed of a powdery refractory is coated on the surface of the sand core prototype obtained by treating with an organic acid salt and then drying. To go. In this case, if the sand core prototype washed with water as described above is immersed in an organic acid salt aqueous solution such as a calcium acetate aqueous solution before coating,
Organic salt adheres or penetrates into and out of the surface layer of the sand core prototype. When the sand core prototype is pulled out of the immersion tank and then dried at 80 to 200 ° C. for several minutes to 2 hours, the organic acid salt powder uniformly adheres to the surface layer of the sand core prototype.

A slurry coating made of a neutral aqueous dispersion mainly composed of a powdery refractory is applied to the sand core prototype obtained through such acid treatment, drying, water washing, organic acid salt treatment and drying. When the agent is applied, the coating agent instantaneously agglomerates due to 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, and the Thick coating on the surface of the child prototype. Thereafter, when this is dried, a homogeneous coating layer having a desired thickness is formed.

[0014] In this manner, the slurry-like second coating agent containing aluminum powder can be coated on the sand core prototype having the coating layer formed thereon. In that case, then at room temperature to 200 ° C for several minutes to
After drying for 2 hours, a second coating layer containing aluminum powder is uniformly formed on the first coating layer. The second coating layer thus formed is stable for a long period of time without leaving the aluminum powder of the component no longer attacked by the acid even when left in the high humidity atmosphere as well as in the air. is there.

By doing so, the sand core prototype can be solidified even by the warm box method, and a slurry made of a neutral water dispersion mainly composed of powdered refractory is formed on the surface of the sand core prototype. Can easily and reliably be coated in a desired state. When the collapsible sand core obtained according to 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 can be sanded. There is no intrusion into the core. In addition, when the molten metal solidifies after casting and the cast product is removed from the mold, the sand core is collapsed and removed, and the sand core can be easily collapsed and removed with little force. The sand can be sufficiently and reliably taken out to all corners without leaving sand at the corners of the casting surface. In other words, the acid treatment step and the subsequent drying step contribute to the dehydration and carbonization of the hardened furan resin in which the sand is bound by the acid soaked in the sand core.
The organic acid salt treatment step and the subsequent drying step contribute to assuredly and firmly forming a slurry-like coating composed of a neutral aqueous dispersion mainly composed of a powdery refractory.

[0016]

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 the resin heat curing, benzenesulfonic acid, phenolsulfonic acid, toluenesulfonic acid, xylenesulfonic 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 temperature of the core molding die 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. . 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 acid solution. Examples of the acid include mineral acids such as sulfuric acid and phosphoric acid. The sand core prototype is immersed in an aqueous solution of these acids, absorbed by the sand core prototype, and then dried by heating. The concentration of the aqueous solution is within 200 times the dilution ratio (98% concentrated sulfuric acid, 89% phosphoric acid dilution ratio). 20 dilution ratio
If it exceeds 0 times, the disintegration of the sand core after casting is reduced and the treatment effect is lost. The immersion time varies depending on the concentration of the treatment solution and the affinity between the sand core prototype and the treatment solution.
From a short time of seconds to about 5 minutes.

If the sand core prototype is difficult to get wet with the processing solution, the sand core prototype is immersed in a hydrophilic organic solvent such as methanol for a short time and then immersed in the processing solution, or the above-mentioned hydrophilicity is added to the processing solution. The organic solvent is mixed until the sand core prototype becomes wet with the processing solution before processing. 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 acid may be used as it is without diluting it. If the acid is a liquid such as concentrated sulfuric acid (98%) or phosphoric acid (89%), it is only necessary to immerse and remove the sand core prototype. As described above, when a solution with a low concentration such as dilute sulfuric acid is used, drying is necessary to evaporate water. However, when not diluted with water, such as concentrated sulfuric acid, drying is not necessary. . The treated sand core prototype turns black, and its bending strength decreases in proportion to the treatment concentration.
The decrease in strength is considered to be due to the progress of carbonization degradation by acid in the case of sulfuric acid or phosphoric acid.

Next, the sand core prototype that has been acid-treated and dried as described above is washed with water. In the water washing, the sand core prototype may be immersed in water, or water may be sprayed on the sand core prototype, but the former is simple and reliable. That is, the sand core prototype is immersed in water such as tap water for several seconds to several minutes and then taken out. The washed sand core prototype may or may not be dried, but is then treated with an aqueous solution of an organic acid salt.

As the organic acid salt, calcium acetate,
Examples include zinc acetate and aluminum acrylate. The washed 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. Dilution ratio is 2
If it exceeds 00 times, the coating thickness is too thin and the processing effect is lost. The immersion time varies depending on the concentration of the treatment solution and the affinity between the washed sand core prototype and the treatment solution.
From a short time of 5 seconds to about 5 minutes.

If the sand core prototype is difficult to wet with the processing solution, the sand core prototype is immersed in a hydrophilic organic solvent such as methanol for a short time and then immersed in the processing solution. The hydrophilic organic solvent is mixed and processed until the sand core prototype becomes wet with the processing solution. The drying of the sand core prototype subjected to the immersion treatment requires less time as the temperature is higher, and it is about 30 minutes at 120 ° C. as a guide. The organic acid salt may be used as it is without diluting. The fine powder of the organic acid salt is applied to the washed 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 immersed in a coating agent, or the surface of the sand core prototype may be brushed or sprayed with a 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. In addition, p of this coating agent
If H is not maintained at 7.0 ± 1.0, precipitation and solidification may occur even under stirring.

It should be noted that other coating agents can 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 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 subjected to an acid treatment, heat drying, washing with water, an organic acid salt treatment and then heat drying, is immersed in the above coating agent for several seconds, and then heated and dried. Drying conditions are about 120 ° C. for about 10 minutes. In the case where the organic acid salt treatment is not performed, the thickness of the coating is almost 0 mm because it almost penetrates into the sand core prototype, but is sufficiently thick and has little penetration into the sand core prototype. Moreover, the coating film is firm. The coating layer may be a single layer, but the product and the coating
In order to improve the releasability from the tinting layer, two layers are more preferable. As a coating agent for forming the second coating layer, for example, 500 g of mica powder per liter of a 3% aqueous phenol resin solution, and sodium dodecylbenzenesulfonate 10 g as a lubricant As an antifoaming agent, octyl alcohol (1 g) obtained by well stirring and mixing can be used. This coating is performed by immersing the sand core prototype after finishing the first layer coating in the second layer coating agent, or brushing the surface of the sand core prototype with the second layer coating agent. After painting or spraying, it is dried to form.

As another example of the coating agent of the second layer, for example, 1 liter of a 3% aqueous phenol resin solution, 500 g of flaky aluminum powder, 10 g of sodium dodecylbenzenesulfonate as a wetting agent, 1 g of octyl alcohol as a defoaming agent, mixed well, mixed with mica, carbon black,
What mixed zircon powder etc. can be used. This second layer coating is performed by immersing the sand core prototype after the first layer coating in the second layer coating agent, or brushing the surface of the sand core prototype with the second layer coating agent. After dripping or spraying, dry to form. Drying conditions are about 120 ° C. and about 10 minutes.

An experimental example will be described below as a more detailed example. (Experimental Examples 1-4, and Comparative Examples 1-4) 100 parts of flat sand as an aggregate and 1.5 parts of furan resin as an organic binder
, A commercially available curing agent containing paratoluenesulfonate as the main curing agent for furan resin (Kao Quaker product F
C-100, copper p-toluenesulfonic acid salt).
6 parts and a commercially available additive (Kao Quaker Product J-
20, a main component silane compound) were mixed, and a plurality of sand core prototypes for an engine block weighing about 2 kg were formed by a warm box method. Molding conditions are mold temperature 120
° C, the blowing pressure was 4.5 kg / cm ² , and the heating time was 90 seconds. After leaving for one day, the sand core prototype has a transverse rupture strength of 35 kg.
Met.

Next, 39 parts of water was added to 1 part of 98% concentrated sulfuric acid.
And 79 parts were mixed to prepare aqueous solutions having a dilution ratio of 40 and 80 times, respectively. After the sand core prototype was immersed in this treatment liquid for 1 minute, it was dried in a circulating hot air heating furnace at 120 ° C. for 30 minutes. At this stage, the same first and second coatings as in the present experimental example were performed without performing any subsequent water washing and organic acid salt treatment, and are shown in Table 1 below as Comparative Examples 1 and 3. . Then, the diluted sand core prototype which had been treated with the diluted sulfuric acid was immersed in tap water for 10 seconds and washed with water. Similarly, at this stage, the same first and second coatings as those of the present experimental example were performed without any subsequent treatment with an organic acid salt, and the results are shown in Table 1 below as Comparative Examples 2 and 4. .

Thereafter, the washed sand core prototype was taken out, and 9 parts, 49 parts, and 19 parts of water were added to 1 part of calcium acetate, respectively.
It was immersed in an aqueous solution having a dilution ratio of 10, 50 or 200 parts obtained by mixing 9 parts 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 samples not subjected to the water washing treatment or later (Comparative Examples 1 and 3), the samples not subjected to the treatment after calcium acetate (Comparative Examples 2 and 4), and the sand core prototypes treated with calcium acetate and dried. With the same first code
After being immersed for 1 to 2 seconds in a heating agent, it was dried in a circulating hot air heating furnace at 120 ° C. for 10 minutes. The composition of the first coating agent is obtained 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.
The pH was adjusted to 7.2. The bending strength of the dried sand core is shown in Table 1.

[0031]

[Table 1]

After finishing the first layer coating, a second layer coating was next performed. As the coating agent for the second layer, 500 g of flaky aluminum 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. A mixture was used. That is, the sand core prototype coated with the first layer was immersed in the second layer coating agent for 1 to 2 seconds, and then dried in a circulating hot air heating furnace at 120 ° C. for 10 minutes. The sand core prototype obtained as described above was kept at a temperature of 33 ° C. and a relative humidity of 90%. It was left in a thermo-hygrostat for 7 days. Table 1 shows the state of the second coating layer after 7 days.

The sand core obtained as described above was set in a mold, and the aluminum alloy ADC10 was 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 was removed using a conventional core knockout machine.
In cases 2 and 4, the core sand was completely removed, and an excellent cast product was obtained. In the case of Experimental Example 3, the removal of the core sand was slightly good, but in the case of Comparative Examples 1 to 4, the removal of the core sand was poor. The results are summarized in Table 1. When aluminum acrylate was used as the organic acid salt instead of calcium acetate, and the other treatment and operation were performed in exactly the same manner, excellent results were obtained as in the case of calcium acetate.

[0034]

As described above, in the present invention, the step of molding a sand core prototype using sand, a furan-based resin, and a curing agent for curing the resin, and treating the sand core prototype with an acid. A step of drying the sand core prototype treated with the acid,
A step of washing the dried sand core prototype with water, a step of treating the washed sand core prototype with an organic acid salt, a step of drying the sand core prototype treated with the organic acid salt, and A step of coating the surface of the sand core prototype with a slurry-like coating agent comprising a neutral aqueous dispersion mainly composed of a powdered refractory, and a sand core obtained by the coating. Was dried to produce a collapsible sand core by the process, so the sand core prototype was previously reduced to the desired strength,
Further, when coating with a coating agent, the coating agent forms a uniform and appropriate thickness coating layer without infiltrating into the sand core prototype or being repelled from the surface. . When the first coating layer is coated with a second coating agent containing aluminum powder, the second coating layer maintains a stable state even under high humidity for a long time. maintain. Therefore, the sand core withstands a high casting pressure during casting, and has good disintegration properties after casting.

That is, when high-pressure casting such as die-casting is performed using the collapsible sand core obtained in the present invention, no molten metal is inserted into the sand core, and after the casting, the product is removed from the product. When discharging sand, because of the good disintegration of the sand core,
Sand can be discharged easily, reliably and completely. Of course, no sand remains on the casting surface of the product after the sand is discharged, and the product is very smooth. 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-52-125416 (JP, A) JP-A-58-68448 (JP, A) JP-A-63-309350 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) B22C 9 / 10,1 / 22,3 / 00

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 acid, and a step of treating the sand with the acid. A step of drying the core prototype, a step of washing the dried sand core prototype, a step of treating the washed sand core prototype with an organic acid salt, and a step of treating the organic core salt with a sand core prototype 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. A method for producing a disintegratable sand core, comprising a step of drying the sand core.