JPH05277632A - Manufacture of collapsible sand core - Google Patents

Abstract

PURPOSE:To obtain a sand core which can be coated sufficiently and is superior in collapsibility, even when it is an original mold of the sand core solidified by means of the warm box process. CONSTITUTION:The original mold of the sand core, which is made by heating and solidifying sand together with furan resin and a hardening agent for heating and hardening the resin, is alkali-treated in such a manner as being immersed in a water solution of caustic soda, etc. This original mold of the sand core is rinsed with water after being heated and dried. Then, after it is treated with inorganic salt and dried, a uniform first coating is applied on the surface of the original mold of the sand core by immersing in the first coating liquid, etc. Then, a second coating is applied on the first coating in such a manner as immersing the mold in the second coating liquid containing aluminum powder. After it is dried again, a collapsible sand core is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure-resistant material used for high-pressure die casting of a casting having an undercut portion, such as a closed-deck type automobile engine, and good disintegrating property with good coating property and easy disintegration. The present invention relates to a method for manufacturing a sand core. More specifically, the sand core prototype made by the warm box method is treated with an alkali, then washed with water, and further treated with an inorganic salt, so that the first coating agent can be thickly coated only once, and The present invention relates to a sand core manufacturing method suitable for high pressure casting, in which the same coating layer can be solidified even when coated with a second coating agent containing aluminum powder and which is excellent in disintegration after casting and suitable for high pressure casting. is there. Here, good 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 into the sand core prototype, or It is not repelled from the surface of the sand core mold, and is formed only on the surface layer of the sand core mold uniformly over the entire surface with a predetermined thickness uniformly and surely easily and firmly so that it does not come off. Is that
It is to be able to withstand a high casting pressure during casting.

[0002]

2. Description of the Related Art Conventionally, for example, 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 breaking 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 to allow the sand to be taken out to every corner. Of course, in that case, various attempts have been made in the past such as sand core prototype components, sand compaction, coating agent components, coating methods, etc., but the current situation is that no satisfactory results have been obtained. Is. As the coating agent, for example, as described in JP-A-63-40639, a powdery refractory, a first coating agent composed of a metal oxide, and a first coating agent A second coating agent or the like containing scale-like aluminum powder or mica to be applied to is used.

Among them, as a method for 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.
The technique described in Japanese Patent Publication 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 Hardox method, when a sand core prototype is obtained by hardening sand molded into a desired shape, sulfur dioxide, that is, sulfurous acid gas is used for hardening. 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. Further, 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 to be deteriorated. Also subject to legal restrictions.

Therefore, the present inventor has decided to reexamine the merit 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, instead of using sulfurous acid gas to solidify a mixture of sand and a binder to obtain a sand core mold, for example, in a mold for sand core mold molding heated to 90 to 240 ° C. The mixture of sand and binder is blown with compressed air and heat-cured to mold. However,
In this case, even if the same coating agent as was used in the Hardox method was applied to the sand core, the coating agent would penetrate into the sand core prototype, resulting in a sufficient thickness. No coating layer was obtained.

On the other hand, the inventor of the present invention uses a sand core aggregate such as silica sand or zircon sand and an organic binder such as furan resin to mold a sand core prototype using the warm box method. Slurry coating agent consisting of neutral water dispersion containing powdered refractory as the main component on the surface of sand core prototype, which is obtained by treating core prototype with alkaline aqueous solution such as caustic soda solution We invented a method to obtain a collapsible sand core by coating the above and drying it, and applied for a patent. The collapsible sand core obtained by this method is reasonably effective, but in order to more reliably eliminate the insertion of the molten metal into the collapsible sand core during high pressure die casting, A coating layer was formed on the surface of the coating layer described in JP-A-63-40639.
An attempt was made to coat a second coating agent containing aluminum powder as disclosed in Japanese Patent Laid-Open Publication No. However, good coating was not obtained with this combination. That is, the alkali remaining near the surface of the sand core prototype permeates the first coating layer, 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 off.

[0007]

In the present invention, sand,
A step of molding a sand core prototype using a furan-based resin and a curing agent for heat curing of the resin, a step of treating the sand core prototype with an alkali, and a step of drying the sand core prototype treated with the alkali And a step of washing the dried sand core prototype with water, a step of treating the washed sand core prototype with an inorganic salt, a step of drying the sand core prototype treated with the inorganic salt, and a drying step The step of coating the surface of the sand core prototype with the first coating agent in the form of a slurry consisting of a neutral water dispersion containing a powdery refractory as a main component, and drying the sand core obtained by this coating. A disintegrating sand core is obtained by a step, a step of coating the coated sand core with a second coating agent in the form of a slurry containing aluminum powder, and a step of drying the sand core obtained by the coating. .

As the alkali for treating the sand core prototype,
For example, alkali such as caustic soda is used. Also, sand
When treating the core prototype with alkali, for example,
Immersed in an inorganic alkaline solution such as soda solution
Then, the alkaline solution was brushed on the surface of the sand core prototype.
And spray. Then treated with this alkali
Dry the sand core prototype. After that, this dried sand core
The prototype is washed with water, but this is simply immersing the sand core prototype in water.
Or spray water on the sand core prototype. After that,
The sand core prototype washed with water is treated with an inorganic salt. Nothing in this case
Machine salt is Li⁺, Na⁺, K⁺, Cs⁺, Cu⁺, Cu
²⁺, Mg²⁺, Ca²⁺, Ba²⁺, Zn²⁺, A1
³⁺, Mn²⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni
^{2+, NH}Four ⁺Positive ions such as F⁻, Cl⁻, Br
⁻, I⁻, NO_Three ⁻, CO_Three ^2-, SO_Four ^2-, PO_Four
^3-Anions such as generated in the form of neutralizing the charge
Say. For example, Na_TwoSO_Four, K_TwoCO_Three, MgCl
_Two, Ba_Three(PO_Four)_Two, Al_Two(SO_Four)_Three, MnC
l_Two, FeSO_Four, NH_FourNO_ThreeEtc. Well
In addition, the sand core prototype obtained as described above is treated with an inorganic salt.
For example, BaCl_Two, Al_Two(SO^Four)_Threewater
Soak in an inorganic salt solution such as
Brush or spray on the surface of the sand core prototype, inorganic
Finely sprinkle with a fine powder of salt.

[0009]

In the present invention, first, for example, as described above, a sand core prototype is formed using sand, a furan-based resin, and a curing agent for heat curing of the resin, and then the sand core prototype is formed into a caustic soda solution or the like. The sand core prototype is dried by immersing the alkali in the sand core prototype, for example, by immersing it in the alkaline solution. In this case, if the sand core prototype (ocher color, brown to dark green) that has been molded is dipped in an alkaline solution such as caustic soda aqueous solution, alkali will be attached or dipped into the surface layer part or inside of the sand core prototype. To look in. After pulling out this sand core prototype from the immersion tank,
The sand core prototype turns light brown when dried at ℃ for several minutes to 2 hours. This is because the hardened furan resin, which bound the sands, was oxidatively decomposed by the alkali that adhered to the sand core prototype and soaked into it. In other words, the oxidative decomposition reaction of the hardened furan resin that connects the sands to each other is accelerated by the heat during the drying. This thermal oxidative decomposition reaction seems to be the formation of hydroperoxide structure in the methylene group and methine group of the cured furan resin and the subsequent decomposition of this unstable hydroperoxide structure. This also reduces the strength. This decrease in strength can sufficiently withstand the pressure applied during casting. During casting, the heat of the molten metal naturally deteriorates the hardened furan resin, but if the strength is lowered in advance as described above, the sand core will be removed from the cast product taken out from the mold after casting. When taking out the sand core, it is extremely easy and easy to take out.

If a sand core prototype obtained through such alkali treatment and drying is coated with a slurry-like first coating agent comprising a neutral water dispersion containing a powdery refractory as a main component, The first coating agent does not instantaneously aggregate due to the alkali existing on the surface of the sand core mold and near the surface of the sand core mold, and does not penetrate deep into the sand core mold to the surface of the sand core mold. A thick coating can be obtained and then dried to form a homogeneous first coating layer of the desired thickness. By the way, as mentioned above, this first
When a second slurry-like coating containing aluminum powder is applied on the coating layer of No. 1, the alkali remaining near the surface of the sand core prototype permeates the first coating layer and the second coating layer It oozes out to the second
Reacts with aluminum powder, which is a component in the coating agent. As a result, the second coating layer is bald or peeled off. Therefore, the sand core prototype obtained through the above-mentioned alkali treatment and drying is immersed in, for example, water for several seconds to several minutes to remove the alkali existing near the sand core surface.

In the meantime, when the alkali treatment is not performed even when the first coating agent in the form of a slurry made of a neutral water dispersion containing a powdery refractory as a main component is applied in a state where the alkali near the surface is removed. Like the above, the first coating agent penetrates even into the inside of the sand core prototype, so that the surface of the sand core prototype cannot be thickly coated. Therefore, as described above, the sand core prototype washed with water is immersed in an aqueous solution of an inorganic salt such as an aqueous solution of BaCl ₂ , Al ₂ (SO ₄ ) ₃ to infiltrate the inorganic salt into the vicinity of the surface of the sand core prototype. No, then dry this sand core mold. Next, the surface of the sand core prototype obtained by performing such a treatment and then drying is coated with a slurry-like first coating agent composed of a neutral water dispersion containing powdery refractory as a main component. To do. In this case, if the sand core prototype washed with water as described above is dipped in an inorganic salt aqueous solution such as a BaCl ₂ aqueous solution before coating, the inorganic salt adheres to the surface layer of the sand core prototype. And soak. 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 inorganic salt powder is uniformly attached to the surface layer of the sand core prototype.

The sand core prototype obtained through such alkali treatment, drying, washing with water, inorganic salt treatment, and drying has a slurry-like first composition consisting of a neutral water dispersion containing powdery refractory as a main component.
When the coating agent is applied, the inorganic salt existing on and near the surface of the sand core prototype does not cause the coating agent to instantaneously agglomerate and penetrate deep into the sand core prototype. The core mold surface can be thickly coated. Then, if this is dried, a homogeneous first layer of the desired thickness is obtained.
Coating layer is formed.

In this way, the sand core prototype having the first coating layer formed thereon is coated with the second slurry-like coating agent containing aluminum powder. Then, by drying at room temperature to 200 ° C. for several minutes to 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 when the aluminum powder as its component is no longer attacked by alkali, even when left in the air or in a high humidity atmosphere. Is.

In this way, the sand core prototype can be hardened even by the warm box method, and the surface of the sand core prototype is made of a slurry of neutral water dispersion containing powdery refractory as a main component. The first coating agent can be surely and easily coated in a desired state, and the slurry-like second coating agent containing aluminum powder on the first coating layer can be surely and easily coated in a desired state. The second coating layer can be stably maintained for a long period of time.

When the collapsible sand core obtained according to the present invention is used, the sand core is not damaged or cracked when the molten metal is cast under high pressure like high pressure die casting. The molten metal does not enter the sand core. In addition, after the molten metal is solidified after casting and the cast product is taken out of the mold, the sand core is disintegrated and taken out, and the sand core can be disintegrated and taken out easily with almost no force applied. The sand does not remain in the corners of the casting surface, and the sand can be fully and reliably taken out to every corner. In other words, the alkali treatment step and the subsequent drying step contribute to the oxidative decomposition of the hardened furan resin, in which the alkali that has permeated the sand core binds the sand comrades, to the water washing step and the inorganic salt treatment step. The subsequent drying step ensures that a slurry-like first coating consisting of a powdery refractory-based neutral water dispersion and a slurry-like second coating containing aluminum powder are firmly formed. Contribute to.

[0016]

EXAMPLE When manufacturing a sand core prototype, first, a furan-based resin and a curing agent for heat curing the same are mixed with a sand core aggregate such as core sand. As sand core aggregate, silica sand, zircon sand, chromite sand, cera beads are used, and as furan resin, furfuryl alcohol / formaldehyde resin, furfuryl alcohol / urea / formaldehyde resin, furfuryl alcohol / phenol / formaldehyde. Resin, furfuryl alcohol / phenol
Furan resin for so-called warm boxes such as urea / formaldehyde resin is used. As the curing agent for heat curing of the resin, at least one of benzene sulfonic acid, phenol sulfonic acid, toluene sulfonic acid, xylene sulfonic acid and lower alkyl sulfonic acid, and at least 1 of aluminum, copper, zinc, iron and ammonium.
The one consisting of a salt with the seed is used. Also, a small amount of copper chloride, zinc chloride, iron chloride or the like may be used together 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, and, for example, a sand core mold is formed 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 the sand core mold is cured to a predetermined strength by heating for about 1 minute. .. For example, transverse strength 2
A sand core prototype of 0 to 50 kg was obtained.

Next, the sand core mold thus formed is treated with an alkaline aqueous solution. Examples of the alkali include inorganic alkalis such as caustic soda and caustic. The sand core prototype is dipped in an aqueous solution of these alkalis, absorbed in the sand core prototype, and then dried by heating. The concentration of the aqueous solution is within 200 times the dilution ratio. If the dilution ratio exceeds 200 times, the collapsibility of the sand core after casting will decrease,
The processing effect is lost. The immersion time depends on the concentration of the treatment solution and the affinity between the sand core prototype and the treatment solution.
It is from a short time of 0.5 seconds to about 5 minutes.

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 hydrophilicity is added to the treatment liquid. The organic solvent is mixed until the sand core prototype becomes wet with the treatment liquid, and then treated. The higher the temperature, the shorter the time required for drying the sand core prototype that has been subjected to the immersion treatment, and as a guide, it is about 30 minutes at 120 ° C. The alkali may be used as it is without being diluted. If the alkali is a fine powder such as caustic soda or causticari, sprinkle the sand core prototype with the powder and wipe off the excess powder. As described above, when a solution having a low concentration such as caustic soda aqueous solution is used, it is necessary to dry to evaporate water, but if it is not diluted with water, it is not necessary to dry. The bending strength of the treated sand core prototype decreases in proportion to the treated concentration.

Next, the sand core prototype that has been alkali-treated and dried as described above is washed with water. For washing with water, 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 a few seconds to a few minutes and then taken out. This washed sand core prototype may or may not be dried, but is then treated with an aqueous solution of an inorganic salt. As the inorganic salt, BaCl ₂ , Al
An inorganic salt such as ₂ (SO ₄ ) ₃ can be used.

The sand core prototype that has been washed with water is dipped in an aqueous solution of these inorganic salts, absorbed near the surface of 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 of the first coating agent is thin 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 washed with water and the treatment solution, but is from a short time of 0.5 seconds to about 5 minutes. The higher the temperature, the shorter the time required to dry the sand core prototype that has been subjected to the immersion treatment, and the time is about 30 minutes at 120 ° C. as a guide. The inorganic salt may be used as it is without being diluted, and the sand core prototype washed with water is sprinkled with the inorganic salt fine powder and the excess inorganic salt fine powder is wiped off.
As described above, when a solution having a low concentration such as a BaCl ₂ aqueous solution is used, drying is necessary to evaporate water. However, when the solution is not diluted with water, it is not necessary to perform drying.

Next, the surface of the sand core master treated as described above is coated with the first coating agent.
In this case, the sand core master may be dipped in the first coating agent, or the surface of the sand core master may be brushed or sprayed with the first coating agent. The first coating agent is composed of fine powder silica and fine powder alumina as main components, and a solid content of 5 with a small amount of colloidal silica added.
The slurry was 0 to 90% by weight. When the solid content is 50% by weight or less, the thickness of the first coating layer becomes thin, and when it is 90% by weight or more, it becomes extremely difficult to stir the slurry. The pH of the first coating agent is 7.0 ±
If not maintained at 1.0, precipitation and solidification may occur even under stirring.

Other coating agents can also be used as the first 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 subjected to alkali treatment, heat drying, water washing, inorganic salt treatment, and heat drying in this order, is immersed in the first coating agent for a few seconds, and then,
Heat drying. The drying conditions are 120 ° C. and about 10 minutes. The thickness of the first coating is almost 0 m when it is not soaked in the sand core prototype without inorganic salt treatment.
In contrast to m, it is thick enough and has little penetration into the sand core prototype, and the coating film is solid.

After finishing the first coating, a slurry-like second coating agent containing aluminum powder is coated. As the second coating agent, for example, 1 liter of a 3% aqueous phenol resin solution, 500 g of scale-like aluminum powder, 10 g of sodium dodecylbenzenesulfonate as a wetting agent, and 1 g of octyl alcohol as a defoaming agent are used. It is possible to use a well-mixed mixture or a mixture of mica, carbon black, zircon powder, and the like.
The second coating is performed by immersing the sand core prototype that has been subjected to the first coating in a second coating agent, brushing or spraying the surface of the sand core prototype with the second coating agent. After drying, it is formed by drying. The drying conditions are 120 ° C. and about 10 minutes.

As a more detailed example, an experimental example will be shown below. (Experimental Examples 1 to 4 and Comparative Examples 1 to 4) Fratari Sand 10
0 part, 1.5 parts of furan resin, a commercially available curing agent containing paratoluenesulfonate as a main component for furan resin (Kao Quaker FC-100, main component paratoluenesulfonic acid copper salt) 0.6 Parts and commercially available additives (Kao Quaker product J-20, main component silane compound)
By mixing 0.06 parts, a plurality of sand core molds for engine blocks having a weight of about 2 kg were molded by the warm box method.
Molding conditions are mold temperature 120 ℃, blow pressure 4.5 kg / c
It was m ² and the heating time was 90 seconds. The transverse rupture strength of the sand core prototype after standing for 1 day was 35 kg.

Next, water is added to 1 part of caustic soda.
Parts and 99 parts were mixed to prepare aqueous solutions with dilution ratios of 50 and 100 times, respectively. After immersing the sand core prototype in this aqueous solution 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 those of the present experimental example were performed without performing the subsequent washing with water and inorganic salt treatment, and therefore, Tables 1 and 2 below show Comparative Examples 1 and 3. Next, this caustic soda aqueous solution treatment and the dried sand core prototype were 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 inorganic salt treatment, and therefore, Tables 1 and 2 below show Comparative Examples 2 and 4.

Thereafter, the sand core prototype washed with water was taken out, and 1 part of MgCl ₂ was mixed with 9 parts, 49 parts, and 199 parts of water, respectively, to obtain an aqueous solution having a dilution ratio of 10, 50, and 200 parts by 1-2. After soaking for 2 seconds, it was dried in a circulating hot air heating oven at 120 ° C. for 30 minutes. (Experimental Examples 1 to 4)

Those which were not subjected to the water washing treatment (Comparative Examples 1 and 3) and those which were not subjected to the inorganic salt treatment (Comparative Examples 2 and 4) and the sand core prototypes which were subjected to the inorganic salt treatment and drying To the same first coating agent
After dipping for 2 seconds, circulate in a hot air oven at 120 ° C for 10
Dry for minutes. The composition of the first coating agent was such that 50 parts of fine powder silica and 30 parts of fine powder alumina were suspended in 3 parts of colloidal silica in 20 parts of water, and the pH was adjusted to 7.2. .. Table 1 shows the transverse rupture strength of sand cores after drying.
Shown in.

[0030]

[Table 1]

After finishing the above-mentioned first layer coating, a second layer coating was performed next. As the coating agent for the second layer, 1 liter of 3% water-soluble phenol resin solution, 500 g of scale-like aluminum powder, 10 g of sodium dodecylbenzenesulfonate as a wetting agent, and 1 g of octyl alcohol as a defoaming agent were well stirred. The 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 oven at 120 ° C for 10 minutes. The sand core prototype obtained as described above was left for 7 days in a thermo-hygrostat maintained at a temperature of 33 ° C. and a relative humidity of 90%. Table 1 shows the state of the second coating layer after 7 days.

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. After casting, sand was removed using a normal core knockout machine.
In cases 2 and 4, the core sand was completely removed, and excellent cast products were obtained. In the case of Experimental Example 3, the removal of the core sand was slightly good, but in the cases of Comparative Examples 1 to 4, the removal of the core sand was poor. Collectively, the results are shown in Table 1.

[0033]

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 of the resin, and the sand core prototype is treated with an alkali. A step of drying the sand core prototype treated with the alkali, a step of washing the dried sand core prototype with water, a step of treating the washed sand core prototype with an inorganic salt, and the inorganic salt The step of drying the sand core prototype treated with the above, and the surface of the dry sand core prototype is coated with a slurry-like first coating agent consisting of a neutral water dispersion containing powdery refractory as a main component. And a step of drying the sand core obtained by the coating, a step of coating the slurry-like second coating agent containing aluminum powder on the coated sand core, Sand Since the collapsible sand core is manufactured by the step of drying the core, the sand core prototype is reduced to a desired strength in advance, and when the core is coated with the first coating agent, the first coating agent is used. Forms a first coating layer having a uniform and appropriate thickness without penetrating into the sand core prototype. When the second coating agent containing aluminum powder is coated on the first coating layer, the second coating layer maintains a stable state for a long time even under high humidity. Therefore, the sand core withstands high pouring pressure during casting and has good disintegration after casting.

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 does not enter the sand core, and When the sand is discharged, the sand core has a good collapsibility, so
The sand can be discharged easily, reliably and completely. Of course, no sand remains at all on the casting surface of the product after the sand is discharged, and it is very smooth. Therefore, even if such a sand core is used for casting a product having a very complicated shape such as a cooling jacket portion of a closed deck type engine block, the working condition is sufficiently satisfactory. And the product can be obtained reliably and easily.

Claims (1)

[Claims] 1. A step of molding a sand core prototype using sand, a furan resin, and a curing agent for heat curing of the resin, a step of treating the sand core prototype with an alkali, and a sand treated with the alkali The step of drying the core prototype, the step of washing the dried sand core prototype with water, the step of treating the washed sand core prototype with an inorganic salt, and the sand core prototype treated with this inorganic salt And a step of coating the surface of the dried sand core prototype with a slurry-like first coating agent composed of a neutral water dispersion containing powdery refractory as a main component, The step of drying the sand core, the step of coating the coated sand core with the second coating agent in the form of a slurry containing aluminum powder, and the step of drying the sand core obtained by the coating. Become collapse Method for manufacturing sand core.