JP2929586B2 - 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 method for manufacturing a sand core.

[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, an organic binder is mixed with the aggregate for sand core molding to form a sand core of a desired shape, and a coating liquid is applied to the surface of the molded sand core. Coating to prevent the sand core from being broken 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 fully removed to every corner.

[0003] Of course, in this case, various attempts have been made on the components of the sand core, the molding method of the sand core, the components of the coating solution, the coating method, and the like, but those which are sufficiently satisfactory have not been obtained. It is not currently done. Among them, as a method of hardening 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, Japanese Patent Publication No. 64-9
The technique described in JP-A-898 is known. In this method, the composition of the sand core is composed of sand for molding a sand core, a mixed sand of a furan resin and an organic peroxide, and is hardened by sulfur dioxide gas.

[0004]

In the above-mentioned Hardox method, a sand mixture is prepared by mixing and kneading an aggregate for sand core molding with a furan resin as an organic binder and an organic peroxide as a curing catalyst for the furan resin. The mold is filled into a mold, and sulfuric acid gas is flowed through the mold to cure the furan resin and form a sand core. Therefore, the hardox method uses sulfur dioxide gas during sand core molding, so the working environment is poor, and in Japan, the use of a gas that adversely affects the human body is not preferred. Also, even if sulfurous acid gas is used, it is difficult to install ancillary equipment to prevent adverse effects on the human body and the working environment from deteriorating.
It is also subject to laws and regulations for its installation and operation.

Therefore, the present inventors have developed a warm box method using a curing agent containing an organic acid salt as a main component, instead of the Hardox method of curing a furan resin with an organic peroxide and sulfur dioxide gas. I decided to review it. In the warm box method, instead of using sulfurous acid gas to harden the mixed sand of the core molding aggregate and the furan resin to form a sand core, for example, a sand core heated to 90 to 200 ° C. A sand core is formed by mixing a sand core molding aggregate, a furan-based resin, and a curing agent of the resin into a molding die and blowing the kneaded mixed sand with compressed air to heat and cure. However, in this case, in the case of the sand core molded by the above-mentioned Hardox method, even if the same coating liquid as that of the coating that has been performed fairly well is applied to the surface of the sand core molded by the warm box method, the coating liquid is not The surface of the sand core only penetrated into the inside, and the sand core surface could not have a sufficiently thick coating layer.

[0006]

To mold a sand core, first, 0.1 to 10% of aluminum sulfate is added to 100 parts by weight of aggregate for sand core molding to form a sand core. A step of coating the aggregate with aluminum sulfate; adding a furan resin as a binder for a warm box and a curing agent for the furan resin to the aluminum sulfate-coated aggregate; A step of adding 0.01 to 0.5% of a coupling agent to each mixture and kneading to obtain a mixed sand for a warm box; A step of forming a core, a step of coating the surface of the formed sand core with a slurry-like coating solution composed of a neutral aqueous dispersion containing a refractory in the form of fine powder as a main component, Obtaining a disintegrating sand core by drying the sand core which is.

[0007]

In the present invention, first, for example,
Method, phthalate was added to the sand composition of the warm box method.
Acid ester, titanate coupling agent, and sulfuric acid
Filling is performed using compounded sand mixed with aluminum.
After molding a sand core with a degree of 60% or more, this sand core surface
From a neutral aqueous dispersion mainly composed of a refractory in the form of fine powder
With a slurry-like coating solution
Do not allow molten metal under high pressure during ingot casting to enter the sand core.
I prevent it. In this case, fine powder refractories
For coating liquids consisting of neutral aqueous dispersions as the main component
Contains hydrophobic colloidal particles.
Since the dull particles come into contact with the dispersion medium, water, their colloids
The surface of the particles must be hydroxyl ion OH ^- To absorb electricity
It is negatively charged. However, hydrophobicity dispersed in water
The solution of colloidal particles is totally electrically neutral
With the opposite sign charged to the hydrophobic colloidal particles
Charged charges are present in the water, which is the dispersion medium.
Visually, it forms an electric double layer similar to a parallel capacitor
It is in a stabilized state.

When a sand core formed by the above-described method is immersed in such a coating solution, positively charged aluminum ions Al ⁺³ opposite to the hydrophobic colloidal particles are eluted from the surface of the sand core. This aluminum ion neutralizes and destroys the electric double layer present at the interface of the hydrophobic colloid particles in the coating solution, and as a result, the hydrophobic colloid particles lose their charge and become electrochemically unstable,
Then, gelation occurs on the surface of the sand core, and the colloid particles aggregate to form macromolecules. At this time, if the phthalate ester is contained in the sand core, the aggregation of the hydrophobic colloid particles becomes extremely fine and dense. For example, when no phthalate is contained, the aggregated particle size is about 15 μm
On the other hand, when a small amount of phthalate is added, the particle size becomes about 1 μm. The coating formed on the surface of the sand core by adding a small amount of phthalate to the sand for molding sand cores The film layer becomes very dense. As a result, for example, a very dense coating film layer is uniformly formed on the surface of the sand core to a thickness of 0.20 to 0.30 mm.

Further, when a small amount of a titanate-based coupling agent is added to the compounded sand, the strength of the sand core is improved, so that a sound sand core can be formed even when a sand core having a high filling density is formed. On the other hand, the warm-box method sand core made of aggregates not coated with aluminum sulfate has a very low cation concentration eluted. Therefore, when this warm-box sand core is immersed in the coating solution, gel Since no chemical reaction occurs, a coating layer is not formed, and therefore, the coating liquid permeates into the sand core due to capillary action and soaks. As described above, if aluminum sulfate is coated on the sand core molding aggregate so that the cations are eluted during coating, the sand core molded by the warm box method can be used in the sand molded by the Hardox method. Even if the same coating liquid as that of the core is used, the sand core does not seep into the coating liquid, and the surface can be easily and reliably coated with a desired thickness.

[0010] If the collapsible sand core having a packing density of 60% or more obtained by the present invention is used, the deformation of the sand core during casting of the molten metal is small even under high pressure such as the high pressure die casting method. Since the sand core is not damaged or the coating layer is not cracked, 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 is collapsed with little force and can be easily removed. Sand can be sufficiently and reliably taken out to every corner without leaving sand in the corners of the cast product.

[0011]

EXAMPLE As the aggregate for sand core molding, flattery sand used as ordinary foundry sand was used. Then, in forming the sand core, first, 0.1 to 3 parts by weight of 10 to 45% of aluminum sulfate dissolved in a paste with water in 100% by weight of sand is added to the flattery sand. The mixture was well kneaded, and the surface of the sand was coated with aluminum sulfate. Here, the strength of aluminum sulfate is 10 to 45%
The reason for this is that if it is less than 10%, it becomes messed up and it is necessary to dry more, and if it exceeds 45%, it becomes a solid and exceeds the limit of the aqueous solution.

Although an aqueous solution of anhydrous aluminum sulfate was used for the addition of aluminum sulfate, similar effects can be obtained by using aluminum sulfate of 16 to 18 hydrates. In addition, the solid powder may be added as it is, but in order to uniformly coat the aggregate, it is preferable to add the aqueous solution. And the addition amount of aluminum sulfate is 0.1
%, There is almost no effect, and if it exceeds 10%, the effect does not increase. Therefore, in the present invention, 0.1 to
10%. However, the range of 0.3 to 2.5% is particularly good.

In this case, when aluminum sulfate is added as a solid powder, drying is not necessary. However, when aluminum sulfate is added as an aqueous solution, the aggregate for sand core molding has a lot of excess moisture. Therefore, when the sand core is formed, the flowability of the sand is poor and the sand core having a packing density of 60% cannot be formed. Therefore, after adding an aluminum sulfate solution to the flattery sand, which is an aggregate, kneading and mixing at 100 ° C. ×
Dry for 30 minutes. Next, an organic binder is mixed with the flattery sand thus coated with aluminum sulfate. As the organic binder, a binder for a so-called warm box method such as a furan resin was used.

That is, 1.5 parts of a furan resin (701 manufactured by Kao Quaker) as an organic binder and paratoluenesulfonate as a curing agent for the furan resin are added to 100 parts of the flattery sand surface-coated with aluminum sulfate. Commercially available curing agent (Kao Quaker product FC-31
0, copper paratoluenesulfonate, cupric chloride)
0.6 parts and a commercially available additive (Kao Quaker Product J
-20, a main component silane compound) was mixed and kneaded, and dimethyl phthalate, a phthalate ester,
Diethyl phthalate, dibutyl phthalate, di-2-phthalate
At least one phthalate ester selected from ethylhexyl and diisodecyl phthalate, and (RO) _a
Ti (OCOOR) _b , provided that 0.01 to 0.5% of a titanate-based coupling agent having a chemical structure of a + b = 4, for example, C-151 manufactured by Nippon Soda is added for sand core molding. Was kneaded.

When the added amount of the phthalic acid ester and the titanate coupling agent is less than 0.01% and more than 0.5%, the expected effect cannot be obtained so much. That is, if it is more than 0.5%, the sand is wet and cannot be filled in the mold.
The core cannot be formed, and if it is less than 0.01%, the core is cracked and molding cannot be performed, but if it is 0.01 to 0.5%, the core can be molded well. Get out of well. A better result was obtained with the addition of 0.05 to 0.3%.

The mixed sand kneaded as described above is blown together with compressed air into a mold having a predetermined sand core-shaped cavity, and the sand core is removed by, for example, a method called a warm box method. Molded. In this case, the heating temperature of the mold for sand core molding is, for example, about 90 to 200 ° C., preferably about 120 to 180 ° C., and the sand core is heated to a predetermined strength by heating in the mold for about 1 minute. Cured to a packing density of 60
% Of sand cores were molded. Next, a coating agent is coated on the surface of the warm box sand core formed as described above.

As the coating solution, for example, 3 parts of fine powder fuse silica and 1 part of fine powder alumina are mixed, and 100 parts thereof are mixed with 30% colloidal silica 5%.
And 15 parts of water, kneaded and crushed with a ball mill for 50 hours, and used a slurry having a solid content of 80 to 85%. The pH of the coating agent was 6.5 to 7.5.
Otherwise, precipitation and solidification may occur even with stirring.

One or two coating layers may be formed on the surface of the sand core. However, in order to improve the releasability between the surface of the casting and the coating layer, the two-layer coating is preferred. Is preferred. The coating solution for two-layer coating is, for example, 1 g of a 3% aqueous phenol resin solution, 500 g of natural mica, and 10 g of sodium dodecylbenzenesulfonate as a wetting agent.
g, 1 g of octyl alcohol was added as a defoaming agent, and the mixture was well stirred and used.

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 90-100 ° C. for 10 minutes. Then, after the second layer coating solution is applied on the first layer coating layer, the core is dried. As a result, the coating layer coated on the surface of the sand core has a first layer of 0.10 to 0.30 mm and a second layer of 0.01 to 0.00 mm.
A 5 mm coating film was formed.

On the other hand, in the case of a sand core simply formed with a flat sand that has not been treated with aluminum sulfate, the coating liquid penetrates into the sand core, and a coating layer is hardly formed on the surface of the sand core. ， The entire surface of the sand core became uneven. A warm box method sand core molded and coated by the above method is placed in a cavity of a mold, and a casting pressure of 700 kg / cm ² ,
An aluminum alloy (ADC-12) was cast under the conditions of a plunger speed of 0.2 m / sec and a casting temperature of 700 ° C. Tables 1 and 2 show examples of the experimental results. Table 2 shows the results of experiments using an aqueous solution of aluminum sulfate with and without drying.

[0021]

[Table 1] Phthalate ester: DBP Dibutyl phthalate DIDP Diisodecyl phthalate Moldability: × Poor △ Slightly good ○ Good Sand baking resistance: × Poor ○ Good

[0022]

[Table 2] Phthalate ester: DBP Dibutyl phthalate DIDP Diisodecyl phthalate Moldability: × Poor ○ Good Sanding resistance: × Poor ○ Good

After casting, sand removal was performed using a conventional core knockout machine. Nos. 6 to 9 and NO. The sand cores in the products Nos. 15 to 17 were completely disintegrated, and the sand could be easily and completely discharged. In addition, the casting surface of the obtained cast product was smooth and there was no insertion of molten aluminum, and a sound product was obtained. However, no aluminum sulfate was added, no phthalic acid ester was added, no titanate coupling agent was added, and the sand density was 60% or less. In the core, during casting, a large amount of molten aluminum is inserted into the sand core, so that the product has poor seizure of sand and poor disintegration of sand. 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.

[0024]

As described above, according to the present invention, in forming a sand core, first, 0.1 to 10% of aluminum sulfate is added to 100 parts by weight of the sand core forming aggregate. A process for coating the aggregate for sand core molding with aluminum sulfate, and adding a furan resin and a hardening agent as a binder for a warm box to the aggregate coated with aluminum sulfate,
A step of adding 0.01 to 0.5% of each of the phthalic acid ester and the titanate-based coupling agent and kneading to obtain a compound sand for a warm box; and using the compound sand, a packing density of 60% or more. A step of forming a sand core, a step of coating the surface of the formed sand core with a slurry-like coating liquid composed of a neutral aqueous dispersion mainly composed of a refractory in the form of fine powder, and In the process of drying the obtained sand core, a collapsible sand core is produced. When the sand core is immersed in a coating liquid containing colloidal silica, it elutes on the surface of the sand core. Incoming aluminum ion causes the colloidal silica in the coating solution to instantaneously cause a gelling reaction at the part where it contacts the surface of the sand core, causing the coating solution to thicken. Penetration of the coating solution is suppressed,
A very dense coating layer with a uniform thickness is formed on the sand core surface.

Therefore, when high-pressure casting such as die-casting is performed using the high-filling-density collapsible core obtained in the present invention, the deformation of the sand core is small, so that the molten metal is different in the sand core. When the sand is discharged from the cast product after casting, the sand core can be easily and reliably and completely discharged due to 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, even when such a sand core is used for casting a product having a very complicated shape, for example, a cooling jacket portion of a closed deck type engine block, a sufficiently satisfactory working condition is obtained. Cast products can be obtained easily and reliably.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-53-91014 (JP, A) JP-A-50-9524 (JP, A) JP-B 64-9898 (JP, B2) (58) Field (Int.Cl. ⁶ , DB name) B22C 9 / 10,1 / 22,3 / 00

Claims (1)

(57) [Claims] 1. In molding a sand core, first, 0.1 to 10% of aluminum sulfate is added to 100 parts by weight of the sand core molding aggregate to add sulfuric acid to the sand core molding aggregate. A process of coating aluminum, adding a furan resin as a binder for a warm box and a curing agent for a furan resin to the aggregate coated with aluminum sulfate, and adding a phthalate ester and a titanate coupling agent. 0.0 each
A step of adding 1 to 0.5% and kneading to obtain a compound sand for a warm box;
%, And a step of coating the surface of the molded sand core with a slurry-like coating liquid composed of a neutral aqueous dispersion mainly composed of a fine powdered refractory. And a method for producing a disintegratable sand core comprising a step of drying the sand core obtained by coating.