JP2673857B2 - 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 disintegration having good pressure resistance and good coating properties and good disintegration 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 method for producing the same. 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.

[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 prototype molding is molded into a desired shape using an organic binder, and then the 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 from entering the sand core during die casting. After casting, the sand core collapses with little force and is easily removed. Attempts have been made to ensure that the sand is removed to every corner. Of course, in this case, various attempts have been made in the past, such as the components of the sand core prototype molding aggregate, the molding method of the sand core prototype, the components of the coating solution, and the coating method.
At present, there is no satisfactory product.

[0003] Among them, the Hardox method, a method of solidifying the sand core prototype molding aggregate and molding the sand core prototype is known.
There are a warm box method, a shell mold method, a cold box method and the like. As the Hardx method, for example, a technique described in Japanese Patent Publication No. 64-9898 is known. In this method, the sand core prototype is composed of sand sand prototype molding aggregate, furan-based resin and compounded sand containing an organic peroxide, and is hardened by sulfurous acid gas.

[0004]

In the Hardox method, the sand core prototyping aggregate is blended with a furan resin and an organic peroxide which is a curing catalyst for the furan resin, and the blended sand is kneaded into a desired shape. When molding the sand core mold by filling it in the mold, the sulfur core gas is used to cure the furan resin to mold the sand core mold. Therefore, since sulfurous acid gas is used for sand core prototype molding, the working environment is bad, and the use of gas that adversely affects the human body is not preferred in Japanese factories. Moreover, even if sulfurous acid gas is used, in order to prevent the human body from being adversely affected and the working environment from being deteriorated, it is difficult to install auxiliary equipment for that purpose.
It is also subject to legal regulations for its installation and operation.

Therefore, the present inventor has decided to reconsider the goodness of the shell molding method using a phenol resin as a binder instead of curing the furan resin with an organic peroxide and sulfur dioxide. In the shell mold method, sulfur dioxide is not used to mold the sand core mold by solidifying the mixture of the core mold forming aggregate and the binder, and for example, coating a phenolic resin or other carboxylic acid synthetic resin in advance. The resin coated sand (RCS) is blown into a sand core prototype molding die with compressed air to be heat-cured and molded. However, in this case, in the sand core prototype molded by the above-mentioned Hardox method, even if the same coating solution as the coating performed fairly well is coated on the surface of the sand core prototype molded by the shell mold method, The liquid did not repel the surface of the sand core prototype and did not get wet, and no coating layer was formed.

[0006]

SUMMARY OF THE INVENTION In the present invention, a resin coated sand (RCS) in which a phenol resin is coated on the surface of a sand core prototype aggregate is coated with aluminum sulfate.
A step of coating 1 to 5% of RCS with aluminum sulfate, a step of molding a sand core prototype with this RCS coated with aluminum sulfate, and a surface of the molded sand core prototype with fine powder particles A disintegrating 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 main 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 aluminum sulfate, and then a fine powder refractory material is used as a main component on the surface of the sand core prototype. 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 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. Be sure to use -O on the surface of the hydrophobic colloidal particles.
It absorbs H ⁻ 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 oppositely charged charge on the hydrophobic colloidal particles is the water of the dispersion medium. When viewed microscopically, the state is stabilized 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 such a coating solution, positively charged aluminum ions opposite to the coating solution elute from the surface of the sand core prototype. Since these ions neutralize and destroy the electric double layer existing at the interface of the hydrophobic colloidal particles of the coating liquid, the colloidal particles lose their charge and become electrochemically unstable, and at the surface of the sand core prototype. A gelation reaction occurs to form macromolecules that aggregate. As a result, on the surface of the sand core prototype, for example, 0.2 to 0.
A coating layer having a thickness of 3 mm is uniformly formed. 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 is not repelled, a coating layer is formed on the surface of the sand core prototype, and the surface of the sand core prototype 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 broken or the coating layer is cracked at the time of casting the molten metal under high pressure as in high-pressure die casting. Since it does not occur, 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 easily disintegrated and 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]

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. So, 1
1.5% phenol resin and 0.1-3% aluminum sulfate in the flattery sand heated to 30-160 ℃
Hexamine solution and calcium stearate were added as a curing agent to obtain aluminum sulfate-coated RCS. Aluminum sulfate was added when RCS was manufactured. You may use after adding and drying. The concentration of aluminum sulfate added is, for example, 10 to 45.
%, Preferably 35 to 45%.

The aluminum sulfate-coated RCS thus produced is blown together with pressurized air into a mold having a predetermined sand core mold-shaped cavity by a so-called shell mold method. A sand core prototype was created. In this case, the heating temperature of the mold for sand core mold making is
For example, 200 to 300 ° C., preferably 230 to 27
The sand core mold was hardened to a predetermined strength by heating it in the mold for 30 seconds to 1 minute at about 0 ° C. For example, digging force 20 ~
50 kg of sand core prototype was obtained.

Next, the surface of the sand core prototype formed as described above is coated with a coating agent. In this case, the sand core prototype may be immersed in the coating agent, or the surface of the sand core prototype may be brushed or sprayed with the coating agent. When the coating is immersed in a coating solution containing colloidal silica, the reaction described in the above section takes place in the area where the colloidal silica comes into contact with the surface of the sand core prototype, and gelation occurs. Agglomerates on the surface of the child prototype to increase the viscosity, resulting in a sand core having a 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 a coating liquid, for example, 3 parts of fine powder fuse silica and 1 part of fine powder alumina are mixed, and 10 parts of 30% colloidal silica and 20 parts of water are added to 100 parts thereof. The mixture was kneaded with a ball mill for 24 hours, and a slurry having a solid content of 70 to 75% was prepared and used. The pH of this coating agent is 6.5
If not maintained at 7.5, precipitation and solidification may occur even under stirring. One or two coating layers may be formed on the surface of the sand core prototype.
In order to improve the releasability between the surface of the casting and the coating layer, two-layer coating is preferred. The coating liquid for two-layer coating is, for example, 1 m of a 3% water-soluble phenol resin solution per 5 m of natural mica.
Then, 100 g, 10 g of sodium dodecylbenzenesulfonate as an anionic surfactant as a wetting agent, and 1 g of octyl alcohol as an antifoaming agent were added and mixed well.

The sand core prototype formed as described above is immersed in the first layer coating solution to coat the surface of the sand core prototype, and dried at 90 to 100 ° C. for 10 minutes. Then, after the second layer coating liquid is applied on the first layer coating layer, 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, R without addition of aluminum sulfate
In the sand core mold made by CS, the coating liquid was repelled without getting wet on the surface of the sand core mold, and the coating layer was hardly formed on the surface of the sand core mold. If you use it, 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 sand core prototype made by RCS that did not cover the surface with aluminum sulfate, the coating liquid was splashed without getting wet on the surface of the sand core prototype, so the surface of the sand core prototype was repelled. Since a predetermined coating layer is not formed on the product, a large amount of molten aluminum is inserted into the sand core during casting, resulting in poor seizure and sand disintegration of the product. In addition, the casting surface was not smooth even in the 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.

[0016]

As described above, in the present invention, the step of coating the RCS with aluminum sulfate by adding 0.1 to 5% of aluminum sulfate to the RCS obtained by coating the sand core prototype molding material with the phenol resin. And a step of molding a sand core prototype with this RCS coated with aluminum sulfate, and a slurry form consisting of a neutral water dispersion containing powdery refractory as the main component on the surface of the sand core prototype Since the collapsible sand core is manufactured by the step of coating the coating solution of 1. and the step of drying the sand core obtained by the coating, the sand core prototype is a coating solution containing colloidal silica. When soaked, the aluminum ions in the sand core mold cause the gelling to occur instantaneously in the area where the colloidal silica contacts the surface of the sand core mold, and the coating solution Since the viscosity is suppressed insertion of the coating liquid into the interior of the sand core prototype, the 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 is 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)

(57) [Claims] 1. A step of adding 0.1 to 5% of aluminum sulfate to a resin coated sand obtained by coating a sand core prototyping aggregate with a phenol resin and coating the resin coated sand with aluminum sulfate, and the aluminum sulfate. Molding of sand core mold with resin coated sand coated with sand, and slurry-like coating of neutral water dispersion containing fine powdery refractory as the main component on the surface of this sand core mold A method for producing a collapsible sand core, which comprises a step of coating a liquid and a step of drying the sand core obtained by the coating.