JPH06182482A - Production of sand core - Google Patents

Abstract

PURPOSE:To provide the sand core having excellent coatability by treating a sand core prototype with a mineral acid even if the sand core prototype is solidified by using a worm box method. CONSTITUTION:The sand core prototype is obtd. by compounding phthalic acid esters, such as dibutyl phthalate, or fatty acid esters at the time of molding the sand core. This sand core prototype is treated with the mineral acid, such as dilute sulfuric acid soln., and is subjected to immersion into a coating agent, etc., by which the surface of the sand core prototype is uniformly coated and is dried. The sand core having the excellent coatability is 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, by blending a liquid organic compound having an interfacial tension of at least 2.0 mN / m or more with the coating agent at the time of molding by the warm box method, the same coating agent can be thickened only once on the surface of the sand core mold. The present invention relates to a method for producing a sand core that can be coated 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 a collapsible sand core is to be obtained, the sand is first solidified into the desired shape, then the coating agent is applied to the surface of the solid sand core prototype, and when the molten metal is cast under high pressure Prevent the child from being damaged and the molten metal from entering the sand core.
After casting, it has been attempted to disintegrate the sand core with little force so that the sand core can be easily taken out, and the sand can be fully taken out to every corner. Of course, in that case, various attempts have been made in the past, such as the components of the sand core prototype, the method of hardening the sand, the components of the coating agent, the method of coating, etc., but the ones that are not sufficiently satisfactory have not yet been obtained. Is.

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

[0005]

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 review 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 above Hardox method was applied to the sand core prototype, the coating agent would penetrate into the sand core prototype, resulting in a sufficient No thick coating layer was obtained.

[0007]

In the present invention, sand,
The interfacial tension between the furan resin, the curing agent for heat curing of the resin, and the slurry-like coating agent composed of a powdery refractory-based neutral water dispersion is at least 2.0 mN / m or more, and they are dissolved in each other. In addition, a step of molding a sand core prototype with a liquid organic compound having a boiling point higher than the molding temperature, a step of treating the sand core prototype with a mineral acid, and a step of drying the sand core prototype. ， By the process of coating the surface of this sand core prototype with the above coating agent, a sand core having an excellent coating is obtained.

The liquid organic compounds are phthalic acid ester, trimellitic acid ester, aliphatic monobasic acid ester, aliphatic dibasic acid ester, phosphoric acid ester, epoxy fatty acid ester, polyester, dihydric alcohol ester, oxy ester. It is selected from acid esters, and examples thereof include dibutyl phthalate, di2-ethylhexyl phthalate, di2-ethylhexyl adipate, and di2-ethylhexyl sebacate. When a sand core prototype containing the liquid organic compound is formed, sand, furan-based resin,
For example, dibutyl phthalate or its solvent diluting solution is mixed with the curing agent for heat curing of the resin, and then this is heated in a mold for sand core prototype molding heated to 90 to 240 ° C. with compressed air. Blow in to dry and heat cure.

Next, for example, sulfuric acid, phosphoric acid or the like is used as the mineral acid for treating the sand core prototype molded as described above. When the sand core prototype is treated with a mineral acid, for example, it is immersed in a mineral acid solution such as dilute sulfuric acid, or the surface of the sand core prototype is brushed or sprayed with the mineral acid solution. To do.

[0010]

In the present invention, first, the interfacial tension between sand, furan resin, a curing agent for heat curing of the resin, and a slurry-like coating agent composed of a neutral water dispersion containing a powdery refractory as a main component. Is mixed with a liquid organic compound of at least 2.0 mN / m to form a sand core mold, and then the sand core mold is treated by immersing it in the above-mentioned mineral acid solution. Then, soak the mineral acid in, and dry the sand core prototype.

By applying a slurry-like coating agent composed of a neutral water dispersion containing a powdery refractory as a main component to the sand core prototype obtained through such acid treatment and drying,
The mineral acid attached to the surface of the sand core mold and the liquid organic compound having a specific interfacial tension allow the coating agent to be thickly coated on the surface of the sand core mold without penetrating the inside of the sand core mold. Thereafter, this is dried to form a uniform coating layer having a desired thickness.

By blending the liquid organic compound, the coating agent does not penetrate into the sand core mold even if the concentration of the mineral acid solution to be treated after molding is low. 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 easily and surely in a desired state. When the coated sand core obtained by the present invention is used, the molten metal is not broken or cracked in the molten sand core during the molten metal casting under high pressure like high pressure die casting. There is no intrusion.

[0013]

EXAMPLES When manufacturing a sand core prototype containing a liquid organic compound according to the claims, first, a sand core aggregate such as core sand, a furan-based resin, a curing agent for heat-curing the resin, and the above Mix the liquid organic compound. 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, furfur-based resin for so-called warm box such as furfuryl alcohol, phenol, 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. Phthalates,
Liquid organic compounds such as aliphatic monobasic acid esters include dibutyl phthalate, di2-ethylhexyl phthalate, isononyl phthalate, butyl oleate, dibutyl adipate, dibutyl sebacate, tricresyl phosphate, epoxidized soybean oil. , Diethylene glycol dibenzoate, butyl phthalyl butyl glycolate, etc. are used.

The liquid organic compound is mixed in an amount of 0.05 to 0.5 parts by weight with respect to 100 parts by weight of sand. Compounding amount is 0.05
If it is less than the weight part, the coating agent penetrates deep into the sand core prototype, and a thick coating layer is not formed on the surface of the sand core prototype. On the other hand, if the blending amount is more than 0.5 parts by weight, the coating agent is repelled on the surface of the sand core prototype, and the coating layer is not formed. Also,
The above-mentioned liquid organic compound may be blended as it is as a stock solution, or may be blended by dissolving it in an appropriate low boiling point solvent. The solvent used in the latter case is appropriately selected as long as it does not impair the storage stability and heat curability (molding property) of the composition comprising the sand core aggregate, the furan resin, and the curing agent for heat curing. . Therefore, the concentration and blending amount of the above-mentioned liquid organic compound solution are converted to the liquid organic compound only and the sand 1
It is appropriately selected so as to be 0.05 to 0.5 parts by weight with respect to 00 parts by weight.

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 prepared 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 prototype thus formed is treated with an aqueous solution of mineral acid.

Examples of the mineral acid include sulfuric acid and phosphoric acid. Immerse the sand core prototype in an aqueous solution of these mineral acids,
After being absorbed into the sand core prototype, it is heated and dried. With respect to the concentration of the aqueous solution, the dilution ratio (dilution ratio of 98% concentrated sulfuric acid, 89% phosphoric acid) is 20 in the system containing no liquid organic compound.
It is within 0 times. However, when the liquid organic compound and mineral acid are used in combination, the dilution ratio is within 500 times. When the dilution ratio exceeds 500 times, the mineral acid treatment effect is 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 heat-drying of the sand core mold that has been subjected to the immersion treatment takes shorter time as the temperature becomes higher, and it is about 30 minutes at 120 ° C. as a guide.

Next, the surface of the sand core master formed 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 containing a liquid organic compound having an interfacial tension with the coating agent of at least 2.0 mN / m is treated with a mineral acid, heated and dried, and then immersed in the coating agent for several seconds. After that, heat drying is performed. The drying conditions are 120 ° C. and about 10 minutes.

The coating layer may be one layer, but two layers are more preferable in order to improve the releasability between the product and the coating layer. As a coating agent for forming the second coating layer, for example, 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 Example 1) 100 parts by weight of flat sand as an aggregate, 1.5 parts by weight of a furan resin, and a commercially available curing agent mainly containing paratoluenesulfonate as a curing agent for the furan resin (FC-100, Kao Quaker product, 0.6 parts by weight of main component paratoluenesulfonic acid copper salt, and a commercially available additive (K-20, Kao Quaker product, main component silane compound).
06 parts by weight and 0.17 parts by weight of dibutyl phthalate (DBP) were mixed, and a sand core prototype for an engine block having a weight of about 2 kg was formed by the warm box method. The interfacial tension between DBP and the following coating agent was 6.8 mN / m. Molding conditions are mold temperature 120 ° C, blow pressure 4.5k
The heating time was g / cm ² and the heating time was 90 seconds. The transverse rupture strength of the sand core prototype after standing for 1 day was 31 kg. This sand core prototype was diluted 500 times (1 part of 98% concentrated sulfuric acid with 49 parts water).
Immerse in dilute sulfuric acid (mixed with 9 parts) for 1 to 2 seconds at 120 ° C for 30
It was dried in a split circulation hot air heating furnace.

The sand core prototype was dipped in a slurry-like coating agent composed of a neutral water dispersion containing a powdery refractory as a main component for 1 to 2 seconds, and then 10 times in a circulating hot air heating furnace at 120 ° C. Min dried. 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.

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, the core sand was completely removed, and an excellent cast product was obtained. The results are shown in Table 1.
Shown in.

[0026]

[Table 1]

(Comparative Example 1) 100 flat sand as an aggregate
Part, 1.5 parts of furan resin, 0.6 part of commercially available hardener containing para-toluene sulfonate as a hardener for furan resin (Kao Quaker FC-100, main component para-toluene sulfonic acid copper salt) , And commercially available additives (Kao Quaker product J-20, main component silane compound)
0.06 parts were mixed, and a sand core prototype for an engine block having a weight of about 2 kg was formed by the warm box method. Molding conditions are a mold temperature of 120 ° C., a blowing pressure of 4.5 kg / cm ² ,
The heating time was 90 seconds. The transverse rupture strength of the sand core prototype after standing for 1 day was 30 kg. Using this sand core prototype, the same treatment and operation as in Experimental Example 1 were performed. After removing the sand with a normal core knockout machine after casting,
The molten metal was inserted into the sand core mold and removal of the core sand was poor. The results are shown in Table 1.

Comparative Example 2 Using the composition of Comparative Example 1, a sand core prototype for engine blocks 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. 1
The transverse rupture strength of the sand core prototype after standing for 30 days was 30 kg. This sand core prototype was treated with diluted sulfuric acid having a dilution ratio of 500 times and dried at 120 ° C. for 30 minutes. Using this sand core prototype, the same treatment and operation as in Experimental Example 1 were performed. When sand was removed using a normal core knockout machine after casting, the molten metal was inserted into the sand core prototype and removal of core sand was poor. The results are shown in Table 1.

(Experimental Example 2) Instead of dibutyl phthalate (DBP) in Experimental Example 1, di2-ethylhexyl phthalate (D) was used.
OP) was used and treated and operated in the same manner except for the above, and excellent results were obtained as in the case of dibutyl phthalate. The interfacial tension between DOP and the coating agent was 10.0 mN / m. The results are shown in Table 1.

(Experimental Example 3) When phosphoric acid was used in place of the sulfuric acid of Experimental Example 1 and the other treatments and operations were carried out in the same manner, the same excellent results as in the case of sulfuric acid were obtained. The results are shown in Table 1.

Experimental Example 4 Instead of dibutyl phthalate (DBP) in Experimental Example 3, di2-ethylhexyl phthalate (D) was used.
OP) was used and treated and operated in the same manner except for the above, and excellent results were obtained as in the case of dibutyl phthalate. The results are shown in Table 1.

[0032]

As described above, according to the present invention, a slurry-like coating agent comprising sand, a furan resin, a curing agent for heat curing of the resin, and a neutral water dispersion containing a powdery refractory as a main component. A step of molding a sand core prototype using a liquid organic compound having an interfacial tension of at least 2.0 mN / m or more, which does not dissolve with each other and has a boiling point higher than the molding temperature; , A step of drying the sand core prototype treated with the mineral acid, a step of coating the surface of the sand core prototype with the coating agent, and a sand core prototype obtained by the coating. Since the coated sand core is manufactured by the process of drying the, when coating the coating agent, the coating agent does not penetrate into the sand core prototype,
A coating layer having a uniform and appropriate thickness is formed. Therefore, the sand core can sufficiently withstand a high casting pressure during casting.

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[Procedure amendment]

[Submission date] May 12, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0001

[Correction method] Change

[Correction content]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sand 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. The present invention relates to a core manufacturing method. More specifically, the sand core prototype containing a liquid organic compound having an interfacial tension with a coating agent of at least 2.0 mN / m during molding by the warm box method is treated with a mineral acid to produce a sand core. The present invention relates to a method for producing a sand core, which is capable of thickly coating the same coating agent once on the surface of a child mold and is also suitable for high pressure casting.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction content]

Further, as a curing agent for heat curing the same resin,
At least one of benzene sulfonic acid, phenol sulfonic acid, toluene sulfonic acid, xylene sulfonic acid, lower alkyl sulfonic acid, and aluminum, copper, zinc,
A salt consisting of at least one of iron and ammonium is used. Further, a small amount of copper chloride, zinc chloride, iron chloride or the like may be used together as a curing accelerator. Liquid organic compounds such as phthalic acid esters and aliphatic monobasic acid esters include dibutyl phthalate, di-2-ethylhexyl phthalate, isononyl phthalate, butyl oleate, dibutyl adipate, dibutyl sebacate, tricresyl phosphate. , Epoxidized soybean oil, diethylene glycol dibenzoate, butylphthalyl butyl glycolate and the like are used.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenji Kawanishi 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 Hirakata Research Institute Co., Ltd.

Claims (1)

[Claims] 1. The interfacial tension between sand, a furan resin, a curing agent for heat curing of the resin, and a slurry-like coating agent composed of a neutral water dispersion containing a powdery refractory as a main component is at least 2. A step of molding a sand core prototype using a liquid organic compound having a melting point of 0 mN / m or more and having a boiling point higher than the molding temperature; a step of treating the sand core prototype with a mineral acid; The sand core mold is composed of a step of drying the sand core prototype treated with an acid, a step of coating the surface of the sand core prototype with the coating agent, and a step of drying the sand core obtained by the coating. Production method.