JP2673860B2 - Method for producing collapsible sand core - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a collapsible sand having good pressure resistance and good coating properties and good collapsibility 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 a manufacturing method thereof. 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 the sand core 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, in the case of producing a closed deck type automobile engine block or other castings such as aluminum alloys and magnesium alloys having an undercut portion by die casting, a collapsible sand core is used. Die-casting is performed using the same. When molding a disintegratable sand core, first, the aggregate for sand core molding 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 during the die casting and the molten metal from entering the sand core.
After casting, attempts have been made to disintegrate the sand core with little force so that it can be easily taken out, and to allow the sand to be taken out to every corner.

[0003] Of course, in this case, various attempts have been made on the components of the aggregate for sand core molding, the molding method of the sand core, the components of the coating liquid, the coating method, and the like, but they are satisfactory. Has not been obtained yet. Among them, as a method of solidifying an aggregate for sand core molding to form a sand core, there are a hardox method, a warm box method, a shell mold method, a cold box method and the like. As the Hardox method, for example,
A technique described in JP-A-9898 is known. In this method, the sand core is made of a sand containing a sand core molding aggregate, a furan resin and an organic peroxide, and is hardened by sulfur dioxide gas.

[0004]

In the above-mentioned Hardox method, a furan resin and an organic peroxide which is a curing catalyst for the furan resin are blended with an aggregate for sand core molding and kneaded, and the blended sand having a desired shape is mixed. When a sand core is formed by filling in a mold, a furan resin is cured using sulfurous acid gas to form a sand core. Therefore, since sulfurous acid gas is used for sand core molding, the working environment is poor, and the use of gas that adversely affects the human body is not preferred 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.

[0005] For this reason, the present inventor has decided to review the merits 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, instead of using a sulfur dioxide gas to mold a mixture of a core molding aggregate and a binder to form a sand core, for example,
Resin coated sand (RCS) coated with a phenolic resin such as phenolic resin in advance is blown into a sand core molding die with compressed air to be heat-cured and molded. However, in this case, in the case of the sand core formed by the above-mentioned Hardox method, even if the same coating liquid as that of the coating which has been performed fairly well is coated on the surface of the sand core formed by the shell mold method, the coating liquid is not The surface of the sand core repelled and did not wet, and no coating layer was formed.

[0006]

SUMMARY OF THE INVENTION In the present invention, a resin coated sand (RCS) having a sand core molding aggregate surface coated with a phenol resin is used to prepare iron sulfate and monovalent ions such as alkali metal or ammonium. A step of adding 0.1 to 5 wt% of a double salt composed of sulfate to coat RCS with a double salt of iron sulfate, a step of molding a sand core with RCS coated with this double salt, and a step of molding the sand Disintegration by coating the surface of the core with a slurry-like coating liquid consisting of a neutral water dispersion containing fine powder refractory as the main component, and drying the sand core obtained by this coating. Get a sex sand core.

[0007]

In the present invention, first, for example, as described above, a sand core is molded by RCS mixed with a double salt of iron sulfate, and then a fine powdery refractory 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 applied to prevent the molten metal from entering the sand core during die casting. In this case, the coating liquid composed of a neutral aqueous dispersion mainly composed of a refractory in the form of fine powder contains hydrophobic colloidal particles, and the hydrophobic colloidal particles come into contact with water as a dispersion medium. The surface of the hydrophobic colloidal particles always adsorbs -OH ^- ions and is electrically negatively charged. However, since the solution of 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 the water of the dispersion medium. Microscopically, it is in a stable state by forming an electric double layer similar to a parallel capacitor.

When the sand core molded by the above-mentioned method is dipped in such a coating solution, the positively charged iron ion Fe ⁺³ opposite to the coating solution elutes from the surface of the sand core. This ion neutralizes and destroys the electric double layer existing at the interface of the hydrophobic colloidal particles of the coating solution, so that the colloidal particles lose their charge and become electrochemically unstable, and then gelate on the sand core surface. It reacts to form macromolecules and aggregates. As a result, a coating layer having a thickness of, for example, 0.2 to 0.3 mm is uniformly formed on the surface of the sand core.

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. In addition, when the molten metal solidifies after casting and the cast product is removed from the mold, the sand core is collapsed and removed, and the sand core can be easily collapsed and removed with little force. The sand can be sufficiently and reliably taken out to every corner without leaving sand in the corners of the cast product.

[0010]

The RCS is manufactured by a cold method, a semi-hot method, or a dry-hot method from the properties of phenolic resin such as phenolic resin and kneading temperature.
The dry hot method is preferred in terms of cost. As an example of coating the RCS with a double salt of iron sulfate, a double salt of iron sulfate and a sulfate of a monovalent ion of ammonium was used. Then, 1.5 wt% of a phenol resin and 0.1 to 5 wt% of ammonium iron sulfate were added to the fratarisand heated to 130 to 160 ° C., and 0.15 wt% of a hexamine solution and 0.1 wt% of calcium stearate as a curing agent. RC with addition of ammonium iron sulfate
S was obtained. Although ammonium iron sulfate was added when producing RCS, commercially available RCS ammonium ammonium sulfate may be added and dried before use. The concentration of ammonium iron sulfate added is, for example, 10 to 30 wt.
%, Preferably 20 to 30 wt%.

The iron sulfate ammonium-coated RCS thus produced was blown together with pressurized air into a mold having a predetermined sand core-shaped cavity by a so-called shell mold method. I made a sand core. In this case, the heating temperature of the sand core mold is, for example, 2
The sand core was hardened to a predetermined strength by heating in a mold for 30 seconds to 1 minute at a temperature of 00 to 300 ° C, preferably about 230 to 270 ° C. For example, a sand core having a borrowing 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 immersed 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, 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 the coating agent is not maintained at 6.5 to 7.5, precipitation and solidification may occur even under stirring.

The coating layer formed on the surface of the sand core may be a single layer or a double layer coating, but in order to improve the mold release property between the surface of the casting and the coating layer, a double layer coating is preferred. 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 formed as described above is immersed 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, the core is dried after applying the second layer coating liquid on the first layer coating layer. 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 modeled by RCS without addition of ammonium 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 used for casting, the molten metal will be inserted into the sand.

The sand core molded and coated by the above method is placed in the cavity of the mold, and the conditions are as follows: casting pressure 700 kg / cm ² , plunger speed 0.2 m / sec, casting temperature 700 ° C. Under the aluminum alloy (ADC-
12) was cast. After casting, the sand core in the product was completely disintegrated, and the 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 molded by RCS whose surface is not coated with ammonium ferrous sulfate, the coating solution is splashed without getting wet on the surface of the sand core, so that the surface of the sand core is not covered. Since a predetermined coating layer is not formed, sand is seized on the product due to many molten aluminum inserts in the sand core during casting.
Poor sand disintegration. In addition, the casting surface was not smooth even in a portion 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 example of ammonium iron sulfate has been described above, the same effect can be obtained by using a double salt composed of iron sulfate and a sulfate of a monovalent ion of an alkali metal.

[0017]

As described above, according to the present invention, an iron sulfate double salt M ₁ Fe comprising iron sulfate and a monovalent ion such as an alkali metal or ammonium is added to RCS obtained by coating a sand core molding aggregate with a phenol resin. (SO ₄ ) ₂ [M ₁ = K, N
H ₄ , Rb, Cs of at least one or more]
Step of coating 5% by weight of RCS with iron sulfate double salt, step of molding sand core with RCS coated with iron sulfate double salt, and powdery refractory on the surface of the molded sand core A collapsible sand core was manufactured by coating a slurry-like coating liquid composed of a neutral aqueous dispersion containing strontium as a main component and drying the sand core obtained by this coating. Therefore, when this sand core is immersed in a coating solution containing colloidal silica, iron ions Fe ^{+3 in the} sand core cause gelation instantaneously at the part where the colloidal silica comes into contact with the surface of the sand core. Since the liquid thickens, the pouring 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. At this time, the sand core can be easily and completely discharged completely because of the good disintegration of the sand core. Of course, no sand remains on the casting surface of the cast product after the sand is discharged, and it is very smooth. Therefore, such a sand core, for example,
Even when a product having a very complicated shape is cast, such as a cooling jacket portion of a closed deck type engine block, a sufficiently satisfactory working state and a cast product can be obtained easily and reliably.

Claims (1)

(57) [Claims] 1. A resin coated sand (RCS) obtained by coating a sand core molding aggregate with a phenol resin, and iron sulfate.
Double salt M ₁ Fe (SO ₄ ) ₂ [M ₁ = K, N consisting of sulfate of monovalent ion such as alkali metal or ammonium
H ₄ , Rb, Cs of at least one or more]
Adding 5 wt% of RCS to coat the double salt of iron sulfate, molding the sand core with RCS coated with this iron sulfate double salt, and refining the powder sand on the surface of the sand core A method for producing a collapsible sand core, which comprises a step of coating a slurry-like coating liquid composed of a neutral aqueous dispersion containing a substance as a main component, and a step of drying the sand core obtained by this coating.