JPH06142832A - Production of sand core - Google Patents

Abstract

PURPOSE:To produce the sand core prototype with which the working environment is good and which is used for high-pressure casting by forming a core of core sand mixed with a furan resin hardener and coating the core with a coating material consisting essentially of powdery refractories. CONSTITUTION:The furan resin, the hardener for thermal curing of the resin and a liquid org. compd. are first compd. with the core sand constituting sand core aggregate at 0.05 to 0.5 pts.wt. per 100 pts. sand. The sand core prototype having a prescribed shape is molded by using such sand and is heated to prescribed strength. The sand core prototype is then coated. The coating material consists essentially of fine powder silica and fine powder alumina which are added with a small amt. of colloidal silica and is made into a slurry of about 50 to 90wt.% solid content. The sand core prototype compounded with the liquid org. compd. having at least >=2.0mN/m interfacial tension with this coating material is immersed for several seconds in the coating material and then dried by heating. The sand core which has the sufficiently large thickness of the coating and withstands high-pressure casting is 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 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 the sand core from entering and to make it easy to remove the sand core after casting by collapsing the sand core with little force, and to fully remove the sand in 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,
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 sand core having an excellent coating by the step of molding a sand core by blending a liquid organic compound having a boiling point higher than the molding temperature and the step of coating the surface of the sand core prototype with the above-mentioned coating agent To get

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.

[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 at least 2.0 mN / m or more of a liquid organic compound to form a sand core prototype. Next, the surface of the sand core prototype is coated with the above coating agent. The sand core prototype obtained by blending the liquid organic compound as described above is coated with a slurry-like coating agent composed of a neutral water dispersion containing powdery refractory as a main component. The liquid organic compound having an interfacial tension attached to the surface of the master mold allows the coating agent to be thickly coated on the master surface of the sand core without penetrating into the master mold. Thereafter, this 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 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.

[0012]

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 part with respect to 100 parts by weight of sand. If the blending amount is less than 0.05 parts by weight, the coating agent penetrates deep into the sand core mold, and a thick coating layer is not formed on the surface of the sand core mold. 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.

The above 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 solution of the above-mentioned liquid organic compound are 0.05 to 0.
It is appropriately selected so as to be 5 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 surface of the sand core mold 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 dipped in the coating agent for a few seconds, and then heated and dried. Drying condition is 120 ℃, 1
It takes about 0 minutes. When the liquid organic compound is not added, the coating thickness is almost 0 mm when it is almost immersed in the sand core prototype, whereas it is sufficiently thick and the penetration into the sand core prototype is small and the coating film Is solid.

(Example 1) 100 of flat sand as 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 and 0.17 parts 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 ℃, blow pressure 4.5kg.
/ Cm ² , and the heating time was 90 seconds. The transverse rupture strength of the sand core prototype after standing for 1 day was 32 kg.

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 minutes in a circulating heating furnace at 120 ° C.
Min dried. The composition of the coating agent is finely divided silica 5
It was prepared by suspending 3 parts of colloidal silica in 0 part and 30 parts of finely powdered alumina 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.

[0024]

[Table 1]

(Comparative Example) 100 flat sand as 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 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 prototype and removal of the sand core was poor. The results are shown in Table 1.

Example 2 Instead of dibutyl phthalate (DBP) in Example 1, di2-ethylhexyl phthalate (D) was used.
OP) was used and the other treatments and operations were performed in exactly the same manner, 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 / It was m. The results are shown in Table 1.

Example 3 Diisodecyl phthalate (DIDP) was used instead of dibutyl phthalate (DBP) in Example 1.
The same result was obtained as in the case of dibutyl phthalate, except that the interfacial tension between DIDP and the coating agent was 11.5 mN / m. there were. The results are shown in Table 1.

(Example 4) Dibutyl phthalate (DBP) in Example 1 was replaced with di-2-ethylhexyl adipate (DOA), and otherwise the same treatment and operation were carried out. As in the case, excellent results were obtained, and the interfacial tension between DOA and the coating agent was 6.3 mN / m. The results are shown in Table 1.

(Example 5) Dibutyl phthalate (DBP) in Example 1 was replaced with di-2-ethylhexyl sebacate (DOS), and otherwise the same treatment and operation were carried out. Similar excellent results were obtained as in the case, and the interfacial tension between DOS and the coating agent was 7.1 mN / m. The results are shown in Table 1.

[0030]

As described above, according to the present invention, a slurry-like composition comprising sand, a furan-based resin, a curing agent for heat curing of the resin and a neutral water dispersion containing powdery refractory as a main component Interfacial tension with coating agent is at least 2.0mN /
a step of molding a sand core mold using a liquid organic compound having a boiling point of m or more, which does not dissolve each other and has a boiling point higher than the molding temperature; and a step of coating the surface of the sand core mold with the above-mentioned coating agent, Since the coated sand core is manufactured by the process of drying the sand core prototype obtained by coating, the coating agent does not penetrate into the sand core prototype when coated with the coating agent. Form a uniform and appropriate thickness coating layer. 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] 0013

[Correction method] Change

[Correction content]

Further, 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, 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.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction content]

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 g 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 gram and 1 gram of octyl alcohol as an antifoaming agent with good stirring. This coating is performed by immersing the sand core prototype after finishing the first layer coating in a second layer coating agent, or by brushing the second layer coating agent on the surface of the sand core prototype. After being applied or sprayed, it is dried to form. (Experimental Example 1) 100 parts of flat sand as an aggregate, 1.5 parts of a furan resin, and a commercially available curing agent containing paratoluenesulfonate as a main component for a furan resin (Kao Quaker Product FC-100). , 0.6 parts of main component paratoluenesulfonic acid copper salt, and a commercially available additive (Kao Quaker)
Product J-20, main component silane compound) 0.06 part, and dibutyl phthalate (DBP) 0.17 part are mixed, and the weight is about 2
A kg sand core prototype for an engine block was molded by the warm box method. The interfacial tension between DBP and the following coating agent was 6.8 mN / m. 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 32 kg.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction content]

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 in a circulating heating furnace at 120 ° C. 10
Min dried. The composition of the coating agent is finely divided silica 5
It was prepared by suspending 3 parts of colloidal silica in 0 part and 30 parts of finely powdered alumina in 20 parts of water and adjusting the pH to 7.0.

 ─────────────────────────────────────────────────── ─── 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 using a liquid organic compound having a boiling point higher than the molding temperature, which is 0 mN / m or more and does not dissolve each other; and a step of coating the surface of the sand core prototype with the coating agent, A method for producing a sand core, which comprises a step of drying the sand core obtained by coating.