JPH05237596A - Production of sand core - Google Patents

Abstract

PURPOSE:To obtain the sand core having excellent coatability even with a sand core prototype solidified by using a worm box method. CONSTITUTION:The sand core prototype is obtd. by subjecting the sand core prototype formed by solidifying sand to an inorg. salt treatment by immersing of this prototype into an aq. soln. of Na2SO4, etc., and after this sand core prototype is dried by heating, the prototype is immersed into a coating liquid, by which a uniform coating is applied on the surface of the sand core prototype. The prototype is then dried, by which the sand core having the excellent coating 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 treating the sand core prototype molded by the warm box method with an inorganic salt, the same coating agent can be thickly coated only once, and a sand core manufacturing method suitable for high pressure casting is also provided. It is about. Here, the excellent 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. That is, it is possible to fully withstand the 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 undercut aluminum alloy or magnesium alloy, 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.

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 the mixture of sand and 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. In addition, even if the same coating agent is applied using a core obtained by solidifying resin coated sand (RCS) in which sand is coated with a phenolic resin such as phenolic resin beforehand by the so-called shell mold method, the coating agent gets wet. It didn't work because it was flipped.

[0006]

In the present invention, a step of forming a sand core prototype using an organic binder, a step of treating the sand core prototype with an inorganic salt, and a sand treated with the inorganic salt The step of drying the core mold, the step of coating the surface of the dried sand core mold with a slurry-like coating agent composed of a neutral water dispersion containing powdery refractory as a main component, and the coating A sand core having an excellent coating is obtained by a step of drying the sand core thus obtained. The inorganic salt used to treat the sand core prototype is Li ⁺ , N
a ⁺ , K ⁺ , Cs ⁺ , Cu ⁺ , Cu ²⁺ , Mg ²⁺ , C
a ²⁺ , Ba ²⁺ , Zn ²⁺ , Al ³⁺ , Mn ²⁺ , F
^{e 2+, Fe 3+, Co 2+} , Ni 2+, and cations such as _{^{NH 4 +, F -, Cl}} -, Br -, I -, N
An anion such as O ₃ ⁻ , CO ₃ ²⁻ , SO ₄ ²⁻ , PO ₄ ³⁻ is generated in the form of neutralizing the electric charge. For example, Na ₂ SO ₄ , K ₂ CO ₃ , MgCl ₂ , Ba
₃ (PO ₄ ) ₂ , Al ₂ (SO ₄ ) ₃ , MnCl ₂ , F
eSO ₄ , NH ₄ NO _{3 and the} like can be mentioned. When the sand core prototype is treated with an inorganic salt, for example, Na ₂ SO _{4 is used.}
It is dipped in an inorganic salt solution such as an aqueous solution, brushed with the inorganic salt solution on the surface of the sand core mold, sprayed, or dusted with a fine powder of the inorganic salt.

[0007]

In the present invention, first, for example, a sand core prototype is formed as described above, and then the sand core prototype is formed with Na ₂
The inorganic core is soaked in an aqueous solution of an inorganic salt such as an SO ₄ aqueous solution so that the inorganic core is soaked in the sand core prototype, and then the sand core prototype is dried. Next, the surface of the sand core prototype obtained by treating with an inorganic salt 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, the molded sand core prototype is
If it is dipped in an aqueous solution of an inorganic salt such as an aqueous solution of Na ₂ SO ₄ before coating, the inorganic salt will adhere to or soak into the surface layer part of the sand core prototype. 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.

On the other hand, if a sand core prototype obtained through such inorganic salt treatment and drying is applied with a slurry-like coating agent composed of a neutral water dispersion containing powdery refractory as a main component, The inorganic salt present on the surface of the sand core prototype 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. it can. After that, it 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 core is not damaged or cracked when the molten core is cast under high pressure like high pressure die casting, and the molten core is not melted. There is no intrusion.

[0010]

[Example] When manufacturing a sand core prototype, first, an organic binder is mixed with a sand core aggregate such as core sand. Sand core aggregates include silica sand, zircon sand, chromite sand,
A so-called warm-box binder such as furan resin is used as the organic binder, and the mixture of these components is pressed into a mold having a predetermined sand core-shaped cavity. It was blown together with air and, for example, a sand core prototype was molded by a method called the warm box method. In this case, the heating temperature of the core molding die is, for example, 90 to 240 ° C., preferably 90.
The sand core prototype was cured to a predetermined strength by heating at about 200 ° C for about 1 minute. For example, transverse rupture strength of 20 to 50
A kg sand core prototype was obtained.

Next, the sand core mold thus formed is treated with an aqueous solution of an inorganic salt. As this inorganic salt,
Examples thereof include inorganic salts such as Na ₂ SO ₄ and MgCl ₂ . The sand core prototype is immersed in an aqueous solution of these inorganic salts, 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 coating thickness will be thin and the treatment effect will be lost.
The immersion time varies depending on the concentration of the treatment liquid and the affinity between the sand core prototype and the treatment liquid, but from a short time of 0.5 seconds to 5
It's about a minute.

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 in advance for a short time 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 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 diluting it, and the sand core prototype 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 Na ₂ SO ₄ aqueous solution is used, it is necessary to dry to evaporate water, but when it is not diluted with water, it is not necessary to dry it. Absent.

Next, the surface of the sand core master 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 containing fine powder silica and fine powder alumina as main components, and a small amount of colloidal silica, and having a solid content of 50 to 90% by weight. 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, it may precipitate and solidify even under stirring.

Other coating agents may be used as the coating agent. For example, about 30 to 80% by weight of inorganic refractory material such as graphite, mica, fused silica, alumina, magnesia, carbon black and zircon powder, and about 1% of 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.

An inorganic salt treatment followed by heating and drying of a sand core prototype is dipped in the coating agent for a few seconds, and then,
Heat drying. The drying conditions are 120 ° C. and about 10 minutes. When the inorganic salt treatment is not applied, the thickness of the coating is almost 0 mm when it is almost immersed in the sand core prototype, whereas it is sufficiently thick that the penetration into the sand core prototype is small and the coating The membrane is solid. 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. The coating agent for forming the second coating layer is, for example, 1 liter of a 3% aqueous phenol resin solution,
It is possible to use, for example, 500 g of mica powder, 10 g of sodium dodecylbenzenesulfonate as a wetting agent, and 1 g of octyl alcohol as an antifoaming agent, which are well mixed with stirring. This coating is carried out by immersing the sand core prototype after 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 prototype. , Dry to form.

As a more detailed example, an experimental example will be shown below. (Experimental Examples 1 to 4 and Comparative Example) 100 parts of flat sand as an aggregate, 1.5 parts of a furan resin as an organic binder, and a commercially available hardener containing paratoluenesulfonate as a hardener for a furan resin ( Kao Quaker product FC-1
00, main component paratoluenesulfonic acid copper salt) 0.6 part,
And commercially available additives (Kao Quaker product J-20,
Main component silane compound) 0.06 parts mixed, weight approx. 2k
A plurality of sand core prototypes for engine block g were 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 35 kg. One of them was subjected to the same coating as that of the present experimental example without any treatment with an inorganic salt described later, and therefore is shown in Table 1 as a comparative example.

Water was added to 1 part of Na ₂ SO ₄ , 9 parts and 49 parts, respectively.
Parts, 99 parts, 199 parts mixed, dilution ratio 10, 50,
A 100 and 200 times aqueous solution was prepared, respectively. The sand core prototype was dipped in this aqueous solution for 1 to 2 seconds, and then dried in a circulating hot air heating furnace at 120 ° C. for 30 minutes. (Experimental example 1
4)

After dipping the Na ₂ SO ₄ -treated sand core prototypes in the same coating agent for 1 to 2 seconds with a solution having a different concentration from those not treated with Na ₂ SO _4, the solution was kept at 120 ° C. It was dried for 10 minutes in a circulating hot air heating furnace. The composition of the coating agent is 50
And 30 parts of finely powdered alumina, 3 parts of colloidal silica and 2 parts of water
It was suspended in 0 part and the pH was adjusted to 7.2. In the comparative example and the experimental example 4, the coating was poor or good. From this, it was estimated that the Na ₂ SO ₄ dilution ratio should be 150 to 200 times or less.

After the above-mentioned first layer coating was completed, 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 an antifoaming agent were well mixed with 1 liter of a 3% aqueous phenol resin solution. I used one. That is, 1 to 2 of the sand core prototype that has been subjected to the first layer coating is added to the second layer coating agent.
After soaking for 2 seconds, it was dried for 10 minutes in a circulating hot air heating oven at 120 ° C.

[0020]

[Table 1]

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. 3 at 350 ℃ after casting
After heat treatment for 0 minutes, the sand was removed by a normal core knockout machine. In the cases of Experimental Examples 1 to 3, the core sand was completely removed, and an excellent cast product was obtained. Experimental example 4
In the case of, the removal of the core sand was slightly good, but in the case of the comparative example, the removal of the core sand was poor. Collectively, the results are shown in Table 1.

Experimental Examples 5 to 8 Na ₂ S of Experimental Examples 1 to 4
When MgCl ₂ was used in place of O ₄ , and the same treatment and operation were otherwise performed, the same excellent results as in the case of Na ₂ SO ₄ were obtained. The results are shown in Table 2.

[0023]

[Table 2]

[0024]

As described above, according to the present invention, a step of molding a sand core prototype using an organic binder, a step of treating the sand core prototype with an inorganic salt, and a sand treated with the inorganic salt. The step of drying the core mold, the step of coating the surface of the dried sand core mold with a slurry-like coating agent composed of a neutral water dispersion containing powdery refractory as a main component, and the coating Since the sand core coated by the process of drying the obtained sand core prototype is manufactured, when coating with the coating agent, the coating agent does not penetrate into the sand core prototype and is uniform. A coating layer having an appropriate thickness is formed. Therefore, the sand core can 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.
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.

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] January 5, 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 The present invention is, for example, a closed-circuit device.
Undercut parts, such as a kick-type automobile engine
Pressure resistance of high pressure die casting of cast products
And method for producing sand core having excellent coating property
It is about. For more details,
By treating the sand core prototype made by the
Thick coating with the same coating agent only once
A method for producing a sand core that can be done and is also suitable for high pressure casting
It is about. Here, with excellent coating
When coating the sand core prototype with a coating agent
In addition, the coating agent is a thin liquid inside the sand core prototype.
Without spreading deeply in the spread state, or sand core prototype
Only the surface layer of the sand core prototype is not repelled from the surface of
On the front, uniform with a certain thickness, and securely and easily
Formed into Reference number = P92TH-5
(2) And coated to prevent it from peeling
And that it can withstand the high casting pressure during casting.
Is.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0025

[Correction method] Change

[Correction content]

The sand core obtained by the present invention has good disintegration property after casting. Therefore, when performing high-pressure casting such as die casting using the sand core obtained in the present invention, the molten metal does not insert into the sand core,
No sand remains on the casting surface of the product after discharging the sand,
It is very smooth. Therefore, a sand core like this
For example, even when used for casting a product having a very complicated shape such as a cooling jacket portion of a closed deck type engine block, it is possible to reliably and easily obtain a sufficiently satisfactory working condition. it can. ─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] January 8, 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, by treating a sand core prototype molded by the warm box method with an inorganic salt, the same coating agent can be thickly coated only once, and it is also suitable for high pressure casting. The present invention relates to a method for manufacturing a sand core. Here, the excellent coating property means that when the coating agent is coated on the sand core prototype, the coating agent is a thin liquid and spreads deep inside the sand core prototype. Without impregnation, or without being repelled from the surface of the sand core prototype, only in the surface layer of the sand core prototype and on the front surface, uniformly with a predetermined thickness, and firmly and firmly formed, It is coated so that it does not come off, and it can withstand a high casting pressure during casting.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Morie Kotani, Morie Koyama, Ube City, Yamaguchi Prefecture 1980 Okiyama Oki, Obe Machine Manufacturing Co., Ltd.

Claims (1)

[Claims] 1. A step of molding a sand core mold using an organic binder, a step of treating the sand core mold with an inorganic salt, and a step of drying the sand core mold treated with the inorganic salt. The step of coating the surface of this dried sand core prototype with a slurry-like coating agent composed of a powdery refractory-based neutral water dispersion, and drying the sand core obtained by this coating A method for manufacturing a sand core, which comprises steps.