JPH06190501A - Production of sand core - Google Patents

Abstract

PURPOSE:To provide the sand core which sufficiently withstands a high-casting pressure at the time of casting by molding a sand core prototype by using sand, a furan resin and a hardener for curing the resin by heating, then by subjecting the sand core prototype to a treatment with a liquid org. compd. having a specific value or above of the surface tension with a coating material consisting of a medium dispersion, etc. CONSTITUTION:The sand core prototype is molded by using the sand, the furan resin and the hardener for curing the resin by heating. This sand core prototype is treated with the liquid org. compd. having at least >=2.0mN/m surface tension with the slurry coating material consisting of the medium aq. dispersion consisting essentially of powdery refractories. This process for production consists of stages for drying the treated sand core prototype, treating the dried sand core prototype with an alkali, drying the treated sand core prototype, coating the surface of the dried sand core prototype with the coating material and drying the sand core obtd. by the coating. As a result, the penetration of molten metal into the sand core does not arise and the sand does not remain at the casting surfaces. The smooth surfaces are thus obtd.

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, the sand core prototype produced by the warm box method is treated with a liquid organic compound having an interfacial tension with the coating agent of at least 2.0 mN / m or more, and further treated with an alkali to obtain a sand core prototype. The present invention relates to a method for producing a sand core, which enables the same coating agent to be thickly coated on the surface only once and is also suitable for high pressure casting.

Here, the excellent coating property means that when the sand core prototype is coated with the coating agent, the coating agent does not penetrate deeply into the sand core prototype as a thin liquid spreading inside the sand core prototype. , Or, without being repelled from the surface of the sand core prototype, only the surface layer of the sand core prototype is uniformly and firmly formed with a predetermined thickness, and easily and firmly so that it does not peel off. That is, it is to be sufficiently coated to withstand the high casting pressure during casting.

[0003]

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 obtaining a collapsible sand core, first,
The sand is hardened into the desired shape, and then the coating agent is applied to the surface of the hardened sand core prototype. When the molten metal is poured under high pressure, the sand core is damaged or the molten metal is put inside the sand core. It has been attempted to prevent infiltration, to disintegrate the sand core with little force after casting so that the sand core can be easily removed, and to allow the sand to be fully removed 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 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. 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.

[0006]

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 reexamine the merit of the warm box method using a curing agent 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 prototype, for example, in a mold for sand core prototype molding heated to 90 to 240 ° C. Then, a mixture of sand and a binder is blown with compressed air and heat-cured to mold the mixture. 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.

[0008]

In the present invention, sand,
A process of molding a sand core prototype using a furan-based resin and a curing agent for heat-curing the resin, and a slurry-like prototype composed of a neutral water dispersion whose main component is a powdery refractory. A step of treating with a liquid organic compound having an interfacial tension with the coating agent of at least 2.0 mN / m, a step of drying the sand core prototype treated with this liquid organic compound, and an alkali of the dried sand core prototype. And a step of drying the sand core prototype treated with the alkali, a step of coating the surface of the dried sand core prototype with the coating agent, and a sand core obtained by the coating. The drying step results in a sand core with a good coating.

The liquid organic compounds for treating the sand core prototype are phthalic acid ester, trimellitic acid ester, aliphatic monobasic acid ester, aliphatic dibasic acid ester, phosphoric acid ester, epoxy fatty acid ester, polyester,
It is selected from a dihydric alcohol ester and an oxyacid ester, and examples thereof include dibutyl phthalate, di2-ethylhexyl phthalate, di2-ethylhexyl adipate, and di2-ethylhexyl sebacate. When the sand core prototype is treated with a liquid organic compound, for example, it is immersed in an organic solvent solution such as an acetone solution of dibutyl phthalate, or the organic solvent solution is brushed on the surface of the sand core prototype. Or spray it. Then, the sand core prototype treated with the liquid organic compound is dried. Then, the dried sand core prototype is treated with alkali.

As the alkali for treating the sand core prototype, for example, caustic soda, caustic potash or the like is used.
When the sand core prototype is treated with alkali, for example, it is immersed in an inorganic alkaline solution such as caustic soda aqueous solution, or the alkaline solution is brushed or sprayed on the surface of the sand core prototype.

[0011]

In the present invention, first, as described above, sand,
After molding a sand core prototype using a furan-based resin and a curing agent for heat-curing the same, a slurry-like coating consisting of a neutral water dispersion whose main component is a powdery refractory The liquid organic compound is immersed in the sand core prototype by immersing it in a liquid organic compound such as dibutyl phthalate having an interfacial tension with the agent of at least 2.0 mN / m,
Then, the sand core mold is dried.

In this case, if the sand core prototype thus formed is immersed in a liquid organic compound solution such as an acetone solution of dibutyl phthalate, the liquid organic compound adheres to the surface layer portion or inside of the sand core prototype. And soak. After pulling this sand core mold out of the dipping tank, it is heated at 80 to 200 ° C for several minutes
When dried for 2 hours, the liquid organic compound is uniformly attached to the surface layer of the sand core prototype.

The sand core prototype obtained through such liquid organic compound treatment and drying is dipped in an alkaline solution such as caustic soda aqueous solution to allow the alkali to soak into the sand core prototype. ， Dry this sand core prototype. Next, the surface of the sand core prototype obtained by treating with an alkali and then drying is coated with a slurry-like coating agent composed of a neutral water dispersion containing powdery refractory as a main component.

In this case, if the sand core prototype obtained through the treatment with a liquid organic compound and drying is dipped in an alkaline solution such as caustic soda aqueous solution before coating, the sand core prototype has a surface layer portion and a core portion. Alkali adheres to or soaks into. 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 alkali uniformly adheres to the surface layer of the sand core prototype.

On the sand core prototype obtained through such treatment with liquid organic compound, drying, alkali treatment, and drying, a slurry-like coating agent comprising a neutral water dispersion containing powdery refractory as a main component is added. When applied, the liquid organic compound having a specific interfacial tension attached to the surface of the sand core mold prevents the coating agent from penetrating into the sand core mold. The alkali adhered to the surface allows the coating agent to be thickly coated on the surface of the sand core prototype without instantaneously aggregating and penetrating deep inside the sand core prototype.

Therefore, by pre-treating the sand core prototype with the liquid organic compound, the coating agent does not penetrate deep into the sand core prototype even if the concentration of the solution for alkali treatment is low. It will be possible to coat thickly. That is, by using the liquid organic compound treatment and the alkali treatment together, the solution concentration in the case of the alkali treatment can be lowered. Thereafter, the sand core mold is dried to form a uniform coating layer having a desired thickness.

In this way, the sand core prototype can be hardened even by the warm box method, and the surface of the sand core prototype can be coated with the coating agent reliably and easily in a desired state. When the coated sand core obtained according to the present invention is used, the molten metal is not damaged or cracked in the sand core during casting of the molten metal under high pressure like high pressure die casting. It does not infiltrate.

[0018]

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, etc. are used, and as furan resin, 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.

Further, as the curing agent for heat curing the resin,
At least one of benzene sulfonic acid, phenol sulfonic acid, toluene sulfonic acid, xylene sulfonic acid, lower alkyl sulfonic acid, aluminum, copper, zinc,
Use is made of a salt with at least one of iron and ammonium. Also, as a curing accelerator, copper chloride, zinc chloride,
A small amount of iron chloride or the like may be used together.

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 produced 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 2 minutes. . 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 a solvent solution in which a liquid organic compound is mixed. The liquid organic compounds include dibutyl phthalate, di2-ethylhexyl phthalate, isononyl phthalate, butyl oleate, dibutyl adipate, dibutyl sebacate, tricresyl phosphate, epoxidized soybean oil, diethylene glycol dibenzoate, butylphthalyl. Butyl glycolate and the like can be mentioned. Further, examples of the solvent for mixing the liquid organic compound include low boiling point organic solvents such as acetone and methanol. The sand core prototype is immersed in a solvent solution of these liquid organic compounds, absorbed in the sand core prototype, and then dried by heating.

The concentration of the organic solvent solution is a dilution ratio of 10 to 10
It is 0 times. If the dilution ratio is greater than 100 times, the coating agent will penetrate deep into the sand core mold,
A thick coating layer is not formed on the surface of the sand core mold, and the treatment effect is lost. Further, if the dilution ratio is less than 10 times, the coating agent will be repelled on the surface of the sand core prototype, and 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 depends on the concentration of the processing solution and the affinity between the sand core prototype and the processing solution. The higher the temperature, the shorter the time required to dry the sand core prototype that has been subjected to the immersion treatment.
It's about a minute.

Next, liquid organic compound treatment as described above,
The dried sand core prototype is treated with an aqueous alkali solution. Examples of the alkali include inorganic alkalis such as caustic soda and caustic. The sand core prototype is immersed in an aqueous solution of these alkalis, absorbed in the sand core prototype, and then heated and dried. The concentration of the aqueous solution is 500
Within twice. If the dilution ratio exceeds 500 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 processing liquid and the affinity between the sand core prototype and the processing liquid. The higher the temperature, the shorter the time required to dry the sand core prototype that has been subjected to the immersion treatment, and as a guide, it takes 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 mentioned above,
When a dilute solution such as caustic soda solution is used, drying is necessary to evaporate water, but when it is not diluted with water, it is not necessary to dry.

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.

A sand core prototype that has been treated with a liquid organic compound, dried by heating, treated with an alkali and then dried by heating is dipped in the coating agent for several seconds, and then dried by heating. The drying conditions are 120 ° C. and about 10 minutes. The coating thickness is almost 0 m when it is almost immersed in the sand core prototype when neither liquid organic compound treatment nor alkali treatment is performed.
In contrast to m, it is thick enough to penetrate into the sand core prototype, and the coating is strong.

The coating layer may be one layer, but two layers are more preferable in order to improve the releasing property between the product and the coating layer. As a coating agent for forming the second coating layer, for example, 1 liter of a 3% aqueous phenol resin solution, 500 g of mica powder,
Sodium dodecylbenzene sulfonate as a wetting agent 1
It is possible to use, for example, a mixture of 0 g and 1 g of octyl alcohol as an antifoaming agent with good stirring and mixing. 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 3 and Comparative Examples 1 to 4] 100 parts of flat sand as an aggregate, and a furan resin of 1.5 as an organic binder.
, A commercially available curing agent containing paratoluene sulfonate as a main component as a curing agent for furan resin (Kao Quaker Product F
C-100, main component paratoluenesulfonic acid copper salt) 0.
6 parts and commercially available additives (Kao Quaker Product J-
(20, main component silane compound) was mixed, and a sand core prototype for an engine block having a weight of about 2 kg was molded by the warm box method. The 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.
The transverse rupture strength of the sand core prototype after standing for 1 day was 30 kg. One of them was subjected to the same coating as that of the present experimental example without performing the liquid organic compound treatment and the alkali treatment described later, and therefore is shown in Table 1 as Comparative Example 1.
In addition, since the other three were not subjected to the liquid organic compound treatment described later, only the alkali treatment was performed and the same coating as that of the present experimental example was performed, the results are shown in Table 1 as Comparative Examples 2 to 4.

[0030]

[Table 1]

Next, 49 parts of acetone was mixed with 1 part of dibutyl phthalate (DBP) to prepare an acetone solution having a dilution ratio of 50 times. The sand core prototype was immersed in this treatment solution for 1 to 2 seconds, and then dried in a circulating hot air heating oven at 120 ° C for 10 minutes. The interfacial tension between DBP and the following coating agent was 6.8 mN / m.

Then, the dried sand core prototype was dipped in an aqueous solution having a dilution ratio of 200, 300, 500 times obtained by mixing 1 part of caustic soda with 199 parts, 299 parts and 499 parts of water for 1 to 2 seconds. After that, it was dried in a circulating hot air heating furnace at 120 ° C. for 30 minutes. (Experimental Examples 1 to 3)

Those which were not subjected to these dibutyl phthalate treatment and caustic soda treatment (Comparative Example 1) and those which were not treated with dibutyl phthalate (Comparative Examples 2 to 2)
4), the dibutyl phthalate-treated and caustic soda-treated and dried sand core prototypes were immersed in the same coating agent for 1 to 2 seconds and then dried in a circulating hot air heating oven at 120 ° C for 10 minutes. The composition of the coating agent was such that 50 parts of fine powder silica and 30 parts of fine powder alumina, 3 parts of colloidal silica were suspended in 20 parts of water, and the pH was adjusted to 7.0.

Comparative Examples 1, 3, 4 and Comparative Example 2,
In Experimental Example 3, the coating was poor or slightly defective. In other words, the concentration of caustic soda treatment solution that provides good coating was within 200 times the dilution ratio without dibutyl phthalate treatment, and within 500 times the dilution ratio with dibutyl phthalate treatment. . This confirmed that the combined use of dibutyl phthalate treatment and caustic soda treatment was effective.

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.

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. When sand was removed using a normal core knockout machine after casting, in the case of Experimental Examples 1 and 2, the core sand was completely removed, and an excellent cast product was obtained. In the case of Experimental Example 3 and Comparative Example 2, the removal of the core sand was somewhat good, but in the case of Comparative Examples 1, 3 and 4, the molten metal was inserted into the sand core prototype and Removal was poor. Collectively, the results are shown in Table 1.

[Experimental Examples 4 to 6] In Experimental Examples 1 to 3,
When di2-ethylhexyl phthalate (DOP) was used as the liquid organic compound instead of dibutyl phthalate, and the same treatment and operation were performed except for that, excellent results were obtained as with dibutyl phthalate. It was The results are shown in Table 2. The interfacial tension between the DOP and the coating agent was 10.0 mN / m.

[0038]

[Table 2]

[Experimental Examples 7 to 9 and Comparative Examples 5 to 8] In Experimental Examples 1 to 3 and Comparative Examples 1 to 4, as the alkali, causticari was used in place of caustic soda, and the other treatments were performed in exactly the same manner. When operated, the same excellent effect as that of caustic soda was obtained. The results are shown in Table 3.
Shown in.

[0040]

[Table 3]

[Experimental Examples 10 to 12] In Experimental Examples 1 to 3, di2-ethylhexyl phthalate was used as the liquid organic compound in place of dibutyl phthalate, and causticari was used in place of caustic soda as the alkali. Other than that, when treated and operated in the same manner, excellent results were obtained as in the case of dibutyl phthalate and caustic soda. The results are shown in Table 4.

[0042]

[Table 4]

[0043]

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 are powdered fireproof. Process with a liquid organic compound having an interfacial tension of at least 2.0 mN / m or more with a slurry-like coating agent composed of a neutral water dispersion containing as a main component, and a sand core treated with this liquid organic compound A step of drying the prototype, a step of treating the dry sand core prototype with an alkali, a step of drying the sand core prototype treated with the alkali, and the above-mentioned coating 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 prototype obtained by the coating, when coating with the coating agent Ingu agent without Komu penetrates into the sand core prototype, forming a coating layer of uniform and appropriate thickness. 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 collapsible sand core obtained in the present invention, the molten metal does not enter the sand core, and the product after the sand is discharged No sand remains on the surface of the cast surface and the surface is extremely smooth.
In addition, the sand core after casting has good disintegration properties, and sand removal is easy. 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 you can get the product surely and easily.

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[Procedure amendment]

[Submission date] May 12, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction content]

Next, the sand core mold thus formed is treated with a solvent solution mixed with a liquid organic compound. The liquid organic compounds include dibutyl phthalate, di2-ethylhexyl phthalate, isononyl phthalate, butyl oleate, dibutyl adipate, dibutyl sebacate, tricresyl phosphate, epoxidized soybean oil, diethylene glycol dibenzoate, butyl. Examples thereof include phthalyl butyl glycolate. Examples of the solvent for mixing the liquid organic compound include low boiling point organic solvents such as acetone and methanol. The sand core prototype is immersed in a solvent solution of these liquid organic compounds, absorbed in the sand core prototype, and then dried by heating.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0039

[Correction method] Change

[Correction content]

[Experimental Examples 7 to 9 and Comparative Examples 5 to 8]
In Experimental Examples 1 to 3 and Comparative Examples 1 to 4, as an alkali, Kaseikari was used in place of Kaseiso-da,
Other than that, when the treatment and operation were carried out in exactly the same manner, excellent results were obtained as in the case of Kaseiso-da. The results are shown in Table 3.

Front page continued (72) Kenji Kawanishi 3-10 Nakamiyakitamachi, Hirakata-shi, Osaka Ube Industries Ltd. Hirakata Research Laboratory (72) Inventor Hideyuki Iitani 3-10 Nakamiyakitamachi, Hirakata-shi, Osaka Ube Industries Ltd. Hirakata In the laboratory

Claims (1)

[Claims] 1. 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 neutral water containing the sand core prototype as a main component of a powdery refractory material. A step of treating with a liquid organic compound having an interfacial tension with a slurry-like coating agent composed of a dispersion of at least 2.0 mN / m, a step of drying a sand core prototype treated with this liquid organic compound, and a step of drying this The step of treating the sand core prototype with an alkali, the step of drying the sand core prototype treated with the alkali, the step of coating the surface of the dried sand core prototype with the above-mentioned coating agent, and the step of coating A method for producing a sand core, which comprises the step of drying the sand core obtained in the above.