JPH0647489A - Production of collapsible sand core - Google Patents

Abstract

PURPOSE:To improve the coating property of the collapsible sand core by subjecting the surface of a sand core prototype made of resin coated sand coated with metal salts of org. acids having specific compsns. to coating, then drying the prototype. CONSTITUTION:The process for production of the collapsible core is constituted of a stage for compounding 0.5 to 5% at least one kind of metal salts of org. acid among sodium salt, potassium salt and calcium salt of the org. acids into the resin coated sand formed by coating aggregate for molding the sand core prototype with a phenolic resin, and kneading the compound thereby coating the resin coated sand with the metal salts of the org. acids, a stage for producing the sand core phototype with the resin coated sand, a stage for coating the surface of this prototype with a slurry-like coating liquid consisting of an aq. neutral dispersion essentially consisting of fine powdery refractories and drying the coating. The collapsible sand mold having the excellent coating property 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 disintegrating property such as pressure resistance and good coating property and good disintegrating property, which are 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 sand 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 is a thin liquid and does not penetrate deeply inside the sand core prototype, or It is not repelled from the surface of the sand core prototype, but is formed only on the surface layer of the sand core prototype 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 sufficiently withstand the high casting pressure during casting.

[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, a sand core prototype molding aggregate is molded into a desired shape using an organic binder, and then a coating liquid is applied to the surface of the molded sand core prototype. To prevent the sand core from being damaged or the molten metal entering into the sand core during die casting, and after casting, the sand core is collapsed with little force after casting to allow easy removal. It has been attempted to ensure that the sand is removed from all corners. Of course, in that case, various attempts have been made in the past, such as the components of the sand core prototype molding material, the method of molding the sand core prototype, the components of the coating solution, and the coating method.
At present, there is no product that is fully satisfactory.

Among them, as a method for solidifying the sand core prototype molding aggregate to mold the sand core prototype, the Hardox method,
There are warm box method, shell mold method, cold box method, and the like. As the Hardox method, for example, the technique described in JP-B-64-9898 is known. In this method, the sand core prototype is
The sand core is made of sand for prototyping, furan-based resin, and blended sand containing a peroxide, and is hardened by sulfurous acid gas.

[0004]

In the above-mentioned Hardox method, a compound sand having a desired shape is obtained by adding a furan resin and an organic peroxide which is a furan resin curing catalyst to a sand core prototype molding aggregate. When the sand core prototype is filled by filling the inside, the furan resin is cured using sulfurous acid gas to mold the sand core prototype. Therefore, since the sulfur dioxide gas is used for the sand core prototype molding, the working environment is bad, and in the Japanese factory,
The use of gas that has a harmful effect on the human body is not preferred.
Moreover, even if sulfur dioxide 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 work environment to be deteriorated. It is also subject to legal restrictions.

For this reason, the present inventor has decided to review the merit of the shell molding method using a phenol resin as a binder, instead of curing the furan resin, which is a binder of an aggregate, with an organic peroxide and sulfur dioxide. did. In the shell mold method, sulfurous acid gas is not used to mold the sand core mold by solidifying the mixture of the core mold forming aggregate and the binder. For example, phenolic resin or other carboxylic acid-based synthetic resin is coated beforehand. Resin coated sand (R
CS) is blown into the sand core prototype molding die with compressed air and heat-cured to mold it. However, in this case, in the sand core prototype molded by the Hardox method, the same coating solution as the coating solution that was performed fairly well was coated on the surface of the sand core prototype molded by the shell mold method. However, the coating liquid was repelled on the surface of the sand core prototype without getting wet, and the coating layer was not successfully formed on the surface of the core prototype.

[0006]

In the present invention, a resin coated sand (RCS) having a sand core prototype molding surface coated with a phenol resin is used to form sodium salts, potassium salts, magnesium salts, calcium salts of organic acids. Alternatively, a step of coating at least one metal salt of an organic acid of a zinc salt, a step of molding a sand core prototype using the coated RCS, and a step of forming a fine powder on the surface of the sand core prototype A collapsible sand core is obtained by a step of coating a slurry-like coating liquid composed of a neutral water dispersion containing a refractory as a middle component and a step of drying the sand core obtained by this coating.

[0007]

In the present invention, first, for example, as described above, a sand core prototype is formed by RCS mixed with a metal salt of an organic acid, and then a fine powder refractory material is formed on the surface of the sand core prototype. A slurry-like coating liquid consisting of a neutral water dispersion as the main component is coated to prevent the molten metal from entering the sand core under high pressure during 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. On the surface of the colloidal particles, -OH ^- ions are always adsorbed and electrically negatively charged. However, since the solution of the hydrophobic colloidal particles dispersed in water is electrically neutral as a whole, the opposite positive charge on the colloidal particles causes the charge of water, which is 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 prototype molded by the above-mentioned method is immersed in this coating solution, positively charged metal ions opposite to the coating solution elute from the surface of the sand core prototype. Neutralizes and destroys the electric double layer existing at the interface of the colloidal particles of the coating solution, causing the colloidal particles to lose their charge and become electrochemically unstable, and to cause gelation on the surface of the sand core prototype. It awakens to become a macromolecule 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 master. In this way, the surface of the sand core mold is appropriately wetted even if the same sand core mold made by the shell mold method or the sand core mold made by the Hardox method is used. It won't be repelled. As a result, a coating layer is also formed on the surface of the sand core master formed by the shell molding method, and the surface of the sand core master can be surely and easily coated with a desired thickness.

When the disintegratable sand core obtained by the present invention is used, the sand core is damaged or the coating layer is cracked when the molten metal is cast under high pressure like high pressure die casting. Since there is no problem, the molten metal does not enter the sand core. In addition, 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 taken out easily with almost no 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. So 1
To RCS heated to 30 to 160 ° C, 30% calcium acetate was added in an amount of 0.1 to 3% and phenol resin was added in an amount of 1.5% to RCS, and a hexamine solution and calcium stearate were further added as a curing agent. Then, RCS coated with calcium acetate was obtained. In addition, calcium acetate is R
Although it was added when manufacturing CS, it is a commercially available RC
The same amount of calcium acetate may be added to S and dried before use.

The RCS produced in this manner is blown together with pressurized air into a mold having a cavity having a predetermined sand core prototype shape, and the sand core prototype is produced by a so-called shell mold method. Was molded. In this case, the heating temperature of the mold for the sand core master mold is, for example, 200 to 300.
℃, preferably about 230 ~ 270 ℃, 30 seconds ~
The sand core mold was heated to a predetermined strength by heating in the mold for 2 minutes. For example, a sand core prototype having a crushing force of 20 to 50 kg was obtained.

Next, a coating agent is coated on the surface of the sand core master formed as described above. In this case, the sand core master may be dipped in the coating agent, or the surface of the sand core master may be brush coated 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 part where the colloidal silica contacts the surface of the sand core prototype, causing gelation. Aggregates on the surface of the child mold to increase the viscosity and becomes a sand core having a desired coating layer. Of course, the penetration of the coating solution into the sand core is also suppressed, and a uniform coating layer is formed on the surface of the sand core.

As the coating liquid, for example, 3 parts of fine powdered fuse silica and 1 part of fine powdered alumina are mixed, and to 100 parts thereof, 10 parts of 30% colloidal silica and 20 parts of water are added. Then, the mixture was kneaded for one day in a ball mill to prepare a slurry having a solid content of 70 to 75%. The pH of this coating agent is 6.5
If not maintained at 7.5, precipitation and solidification may occur even under stirring. And, the coating layer formed on the surface of the sand core prototype may be one layer or two layers,
In order to improve the mold release property between the surface of the casting and the coating layer, the two-layer coating is preferable. The coating solution for two-layer coating is, for example, 1 liter of a 3% aqueous phenol resin solution and 5 parts of natural mica.
00 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 mold thus produced is dipped in the first layer coating solution to coat the surface of the sand core mold, 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 sand core prototype is dried. As a result, the coating layer coated on the surface of the sand core prototype has a first layer of 0.10 to 0.30 mm,
A coating film having a second layer of 0.01 to 0.05 mm is formed. On the other hand, RC without addition of calcium acetate
In the sand core prototype made in S, the coating liquid was repelled without getting wet on the surface of the sand core prototype, and the coating layer was hardly formed on the surface of the sand core prototype. If you do so, 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, R which did not coat the surface with calcium acetate
In the shell mold method sand core prototype made by CS, the coating liquid is splashed without getting wet on the surface of the sand core prototype, so a predetermined coating layer is not formed on the surface of the sand core prototype. At this time, a large amount of molten aluminum was inserted into the sand core, so the product had poor seizure and sand disintegration properties. 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.

[0016]

As described above, according to the present invention, at least one of the sodium salt, potassium salt, magnesium salt, calcium salt or zinc salt of an organic acid is added to the RCS obtained by coating the sand core prototype molding aggregate with a phenol resin. RCS by adding 0.1 to 5% of metal salt of organic acid to RCS
A step of coating a metal salt of an organic acid with the coated RC
The step of forming a sand core prototype using S, and coating the surface of this sand core prototype with a slurry-like coating liquid consisting of a neutral water dispersion containing fine powder refractory as a main component Since the collapsible sand core was manufactured by the steps and the step of drying the sand core prototype obtained by the coating, the sand core prototype was prepared by immersing it in a coating solution containing colloidal silica. The aluminum ion in the core mold causes the gelling of the colloidal silica to occur instantaneously at the portion where the colloidal silica contacts the surface of the sand core mold, increasing the viscosity of the coating liquid. 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 sand core obtained in the present invention, even when the sand is discharged from the product after casting without the molten metal being inserted into the sand core. ， The sand core is easy to disintegrate, so sand can be discharged easily, reliably and completely.
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, 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 the cast product can be obtained reliably and easily.

Claims (1)

[Claims] 1. A resin coated sand obtained by coating a sand core prototyping aggregate with a phenol resin, and at least one metal salt of an organic acid of sodium salt, potassium salt, magnesium salt, calcium salt, or zinc salt of an organic acid. 0.5 to 5% of a salt is mixed and kneaded to coat a metal salt of an organic acid on a resin coated sand, and a step of molding a sand core prototype with the resin coated sand coated with this organic metal salt, The step of coating the surface of the molded sand core prototype with a slurry-like coating liquid composed of a neutral water dispersion containing fine powdery refractory as a main component, and the sand core obtained by this coating A method for producing a collapsible sand core, which comprises a step of drying.