JPH06106294A - Production of collapsible sand core - Google Patents

Abstract

PURPOSE:To provide collapsible sand core for a shell mold method capable of withstanding high-pressure die casting and having a favorable collapsing property after casting. CONSTITUTION:This sand core is obtd. by adding 0.1-5wt.% double salts consisting of aluminum sulfate and the sulfate of univalent ions of alkaline metal or ammonium, etc., and/or the sulfate of aluminum sulfate and bivalent metal ions to RCS consisting of aggregate for molding the sand core coated with a phenolic resin to coat the RCS with the double salts of the aluminum sulfate and molding the sand core with the RCS coated with the double salts of the aluminum sulfate, then coating the sand core and drying the core.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a collapsible sand having pressure resistance and good coating property and good disintegration property, which is used 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 and its manufacturing method. Here, good coating property means that when the sand core prototype is coated with the coating agent, the coating agent spreads in a thin liquid state inside the sand core prototype without deeply immersing it, or Without being repelled from the surface of the sand core prototype,
It is a strong and uniform coating of a predetermined thickness that is formed only on the entire surface of the sand core mold, and is formed so that it does not come off easily. It must be able to withstand the applied pressure. In addition, good collapse quality means that the sand core does not collapse during casting, but after the cast product is removed from the mold after casting, the sand core in the cast product collapses smoothly with a slight impact, and Is something that can be taken out easily without being left in every corner of the undercut part.

[0002]

2. Description of the Related Art Conventionally, for example, when a cast product such as a closed deck type automobile engine block or other aluminum alloy or magnesium alloy having an undercut portion is produced by die casting, a collapsible sand core is used. Die casting is performed by using. When molding a collapsible sand core, first, the sand core molding aggregate is molded into a desired shape using an organic binder, and then the surface of the molded sand core is coated with a coating liquid. To prevent the sand core from being damaged or the molten metal to enter the sand core during die casting, and
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 fully taken out to every corner.

Of course, in this case, various attempts have been made in the past, such as the components of the sand core molding aggregate, the method of molding the sand core, the components of the coating liquid, and the coating method, but they are fully satisfactory. The current situation is that no has been obtained. Among them, there are a hard-box method, a warm box method, a shell mold method, a cold box method, etc. as a method for solidifying the sand core molding aggregate to mold the sand core. As the Hardox method, for example, Japanese Patent Publication No.
The technology described in Japanese Patent Publication No. 9898 is known. In this method, the sand core is composed of sand core modeling aggregate, furan-based resin, and compounded sand containing an organic peroxide, and is hardened by sulfurous acid gas.

[0004]

In the above-mentioned Hardox method, the sand-core-forming aggregate is mixed with a furan resin and an organic peroxide which is a curing catalyst for the furan resin, and the kneaded sand is kneaded into a desired shape. When molding the sand core by filling it in the mold, sulfurous acid gas is used to cure the furan resin and mold the sand core. Therefore, since sulfur dioxide is used for sand core molding, the working environment is poor, and it is not preferred to use gas that adversely affects the human body in Japan. 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 to be deteriorated. Also receive.

Therefore, the present inventor has decided to reconsider the merit of the shell mold method using a phenol resin as a binder, instead of the Hardox method in which a furan resin is cured with an organic peroxide and sulfur dioxide. In the shell mold method, sulfurous acid gas is not used to mold the sand core by hardening the mixture of the core-forming aggregate and the binder. For example, a resin coated beforehand with a phenolic resin such as phenol resin is used. Coated sand (RCS) is blown into a sand core molding die with compressed air and heat-cured to mold it. However, in this case, in the sand core molded by the Hardox method, even if the same coating liquid as the coating that was performed quite well is coated on the surface of the sand core molded by the shell mold method, the coating liquid remains The surface of the sand core was not repelled and did not form a coating layer at all.

[0006]

In the present invention, in sand
Resinco coated with phenolic resin on the surface of the aggregate for child modeling
Aluminum sulphate on the coated sand (RCS)
Sulfuric acid of monovalent ion such as Lucari metal or ammonium
Double salt M consisting of salt₁ Al (SO_Four )₂ [M₁ = Na,
K, Rb, Cs, NH_Four At least one or more], and
Or aluminum sulfate and divalent metal ion sulfate
Double salt consisting of M₂ SO_Four ・ Al₂ (SO_Four ) ₃ , [M₂ =
At least one kind of Cu, Fe, Mg, Zn]
0.1 to 5 wt% is added to the RCS and the above-mentioned al sulfate is added.
The process of coating the double salt of minium and the aluminum sulfate
The process of molding the sand core with RCS coated with double salt,
Mainly made of fine powder refractory on the sand core surface
Slurry coating liquid consisting of neutral water dispersion
The coating process and the result of this coating
A disintegrating sand core is obtained by the process of drying the sand core.

[0007]

In the present invention, first, for example, as described above, a sand core is formed by RCS mixed with aluminum sulfate double salt, and then a fine powdery refractory material is used as a main component on the surface of the sand core. A slurry-like coating liquid consisting of a neutral water dispersion is coated to prevent the molten metal from entering the sand core during die casting. In this case, the coating liquid composed of a neutral water dispersion containing a fine powder refractory as a main component contains hydrophobic colloidal particles, and the hydrophobic colloidal particles are in contact with water as a dispersion medium. always on the surface of the hydrophobic colloidal particles -OH ^-
It absorbs ions and is electrically negatively charged. However,
Since the solution of the hydrophobic colloidal particles dispersed in water is electrically neutral as a whole, the charge with the opposite positive sign that is charged in the hydrophobic colloidal particles is transferred to the dispersion medium, water. It exists and is in a stable state by forming an electric double layer similar to a parallel capacitor when viewed microscopically.

The above-mentioned coating liquid
When the sand core modeled by the
Positively charged metal ion opposite the coating solution, eg
For example, M ₁ Ions (Na, K, Rb, Cs, NH_Four ), M
₂ Ions (Cu, Fe, Mg, Zn) Al ions are eluted
As these ions come in, the
Neutralize and destroy the electric double layer present at the Lloyd's particle interface
Therefore, the colloidal particles lose their charge and become electrochemically uneasy.
And the gelling reaction occurs on the sand core surface
It becomes a macromolecule and aggregates. As a result, on the sand core surface
Is, for example, a coating layer having a thickness of 0.2 to 0.3 mm
Are uniformly formed.

By doing so, even if the sand core molded by the shell mold method and the same coating solution as the sand core molded by the Hardox method are used, the surface of the sand core is appropriately wetted, so that the coating solution is repelled. The coating layer is also formed on the surface of the sand core, and the surface of the sand core can be easily and surely coated with a desired thickness. When the collapsible sand core obtained by the present invention is used, the sand core is not damaged or the coating layer is not cracked when the molten metal is cast under high pressure as in high pressure die casting. Therefore, the molten metal does not enter the sand core. Also, after the molten metal is solidified after casting and the cast product is taken out from the mold, when the sand core is disintegrated and taken out, the sand core can be disintegrated and easily taken out with little force applied. The sand can be fully and reliably taken out to every corner without the sand remaining in the corners of the cast product.

[0010]

[Examples] RCS is produced by a cold method, a semi-hot method, or a dry-hot method depending on the kneading temperature and the properties of a phenolic resin such as phenol resin.
The dry hot method is preferable in terms of cost. As a first example of coating RCS with a double salt of aluminum sulfate, a double salt of aluminum sulfate and a sulfate of a monovalent ion of an alkali metal was used. In this case, 130-1
Phenol resin 1.5 wt%, sodium aluminum sulfate NaAl (SO ₄ ) ₂ 0.1-5 wt%, hexamine solution 0.15 wt%, calcium stearate 0.1 wt, relative to the flattery sand heated to 60 ° C.
% Of aluminum sulfate NaAl (SO
₄ ) ₂ coated RCS was obtained. In this case, it is better to use an aqueous solution of sodium aluminum sulfate added.
Its concentration is 10 to 35 wt%, preferably 30 to 35
wt% is good.

In the second embodiment, aluminum sulfate is used.
A double salt composed of a sulfate of um and a divalent metal ion was used.
In this case, the flattery heated to 130-160 ℃
Phenol resin 1.5wt%, sulfuric acid to the sand
Iron aluminum FeSO_Four ・ Al₂ (SO_Four ) ₃ 0.1
~ 5wt%, Hexamine solution 0.15wt%, Steari
Mix and knead with 0.1 wt% of calcium carbonate,
Um FeSO_Four ・ Al₂ (SO_Four )₃ Coated RCS
Got In this case, the added aluminum aluminum sulfate is water-soluble.
It is better to use liquid, and its concentration is 10 ~ 20wt%,
It is preferably 15 to 20 wt%. Both of the above two examples
, Aluminum sulfate double salt was added during RCS production
However, adding these aluminum sulfate double salts to commercially available RCS
You may use it after adding and drying. And this aluminum sulfate
No effect is obtained if the amount of the added double salt is 0.1 wt% or less.
In particular, the range of 0.3 to 2.5 wt% was particularly good.

The RCS coated with the aluminum sulfate double salt thus obtained is blown together with pressurized air into a mold having a predetermined sand core-shaped cavity, which is a so-called shell mold method. The sand core was modeled by the method.
In this case, the heating temperature of the sand core molding die is, for example,
The sand core was heated to 200 to 300 ° C., preferably 230 to 270 ° C. for 30 seconds to 1 minute in the mold to cure the sand core to a predetermined strength. For example, a sand core having a crushing force of 20 to 50 kg was obtained. Next, the surface of the sand core molded as described above is coated with a coating agent. In this case, the sand core may be dipped in the coating agent, or the surface of the sand core may be brushed or sprayed with the coating agent.

When the coating is dipped in a coating solution containing colloidal silica, the reaction as described in the above action occurs at the portion where the colloidal silica comes into contact with the surface of the sand core, resulting in gelation. Agglomerate on the core surface to increase the viscosity and become a sand core with the desired coating layer. Of course, the penetration of the coating liquid into the sand core is suppressed, and a uniform coating layer is formed on the surface of the sand core. As the coating liquid, for example, 3 parts of finely-divided fuse silica and 1 part of fine-powder alumina are mixed, and 100 parts thereof are mixed with 30 parts.
% Colloidal silica 10 parts and water 20 parts were added, and the mixture was kneaded all day and night with a ball mill to obtain a solid content of 70-75.
% Slurry was used as prepared. If the pH of this coating agent is not maintained at 6.5 to 7.5, it may precipitate and solidify even under stirring.

The coating layer formed on the surface of the sand core may be a one-layer coating or a two-layer coating, but in order to improve the releasability between the surface of the casting and the coating layer, the two-layer coating is preferable. preferable. The coating solution for two-layer coating is, for example, 1 liter of 3% aqueous phenol resin solution and 50 parts of natural mica.
0 g, 10 g of anionic surfactant sodium dodecylbenzenesulfonate as a wetting agent, and 1 g of octyl alcohol as an antifoaming agent were added and well mixed with stirring.

The sand core molded as described above is dipped in the first layer coating solution to coat the surface of the sand core and dried at 90 to 100 ° C. for 10 minutes. Then, subsequently, the second layer coating solution is applied onto the first layer coating layer, and then the core is dried. As a result, the coating layer coated on the surface of the sand core was 0.10 to 0.30 mm in the first layer and 0.01 to 0.05 in the second layer.
mm coating film is formed. On the other hand, in the sand core molded by RCS without addition of sodium aluminum sulfate or aluminum iron sulfate, the coating liquid was repelled without getting wet on the core surface, and the coating layer was hardly formed on the sand core surface. If this state is used for casting, the molten metal will be inserted into the sand.

The sand core molded and coated by the above method is set in the cavity of the mold, and the casting pressure is 700 kg / cm ² , the plunger speed is 0.2 m / sec, and the casting temperature is 700 ° C. Under aluminum alloy (ADC-
12) was cast. When sand was removed using a normal core knockout machine after casting, the sand core in the product had completely collapsed, and sand could be easily and completely discharged. In addition, the casting surface of the obtained cast product was smooth and no molten aluminum was inserted, and a sound product could be obtained.

However, in the shell mold method sand core made of RCS which is not coated with sodium aluminum sulfate or aluminum iron sulfate, the coating liquid is repelled without getting wet on the sand core surface. Since a predetermined coating layer is not formed on the surface of the child, a large amount of molten aluminum is inserted into the sand core during casting, resulting in poor sand seizure and sand disintegration in the product. In addition, the casting surface was not smooth even in the part where the molten metal was not inserted into the sand core, and irregularities were seen as if the surface shape of the sand core body was transferred. Although the examples of sodium aluminum sulfate and aluminum iron sulfate have been described above as examples, similar effects can be obtained by using other double salts of aluminum sulfate. Even if a single salt is mixed in the same composition as the aluminum sulfate double salt, the same effect as in the above example can be obtained.

[0018]

As described above, according to the present invention, the RCS obtained by coating the sand core forming aggregate with the phenol resin, the double salt containing aluminum sulfate and a sulfate of a monovalent ion such as an alkali metal or ammonium. , And / or a double salt composed of aluminum sulfate and a sulfate of a divalent metal ion,
A step of adding 0.1 to 5 wt% of RCS to coat the aluminum sulfate double salt described above, a step of molding a sand core with the RCS coated with the aluminum sulfate double salt, and a step of molding the molded sand core The process of coating a slurry-like coating liquid consisting of a neutral water dispersion containing powdered refractory as the main component on the surface and the process of drying the sand core obtained by this coating Since the sand cores were manufactured, when the sand cores were immersed in a coating solution containing colloidal silica, the gel ions were instantaneously gelled at the parts where the colloidal silica contacted the sand core surface due to the metal ions in the sand cores. As a result, the coating liquid thickens, so that the insertion of the coating liquid into the sand core is suppressed and a coating layer having a uniform thickness is formed.

Therefore, when high-pressure casting such as die casting is performed using the collapsible core obtained in the present invention, the sand is discharged from the product after casting without the molten metal being inserted into the sand core. In this case as well, the sand core can be easily and surely and completely discharged because the sand core has a good disintegration property. Of course, no sand remains on the casting surface of the cast product after the sand has been discharged, and the surface is very smooth. Therefore, such a sand core is, 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 and cast product.

Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location B22D 17/22 H 8926-4E

Claims (1)

[Claims] 1. A phenol resin is coated on a sand core modeling aggregate.
For the coated resin sand (RCS) overlaid,
Aluminum acid and alkali metal or ammonium
Double salt M consisting of sulfate of monovalent ion such as₁ Al (SO
_Four )₂ [M₁ = Na, K, Rb, Cs, NH_Four Less
More than one type] and / or aluminum sulfate and divalent
Double salt M consisting of metal ion sulfate₂ SO_Four ・ Al₂ 
(SO_Four ) ₃ , [M₂ = Less Cu, Fe, Mg, Zn
0.1% to 5% by weight of RCS
To the step of coating the double salt of aluminum sulfate described above
And RCS coated with this aluminum sulfate double salt in sand
The process of molding the child and the fine powder on the sand core surface
Slurries consisting of neutral water dispersions mainly composed of fire-shaped refractories
And the process of coating the coating liquid
It consists of the process of drying the sand core obtained by coating.
A method for producing a collapsible sand core.