JP3170896B2 - Sand core manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a sand core having excellent pressure resistance and excellent coating properties for use in high pressure die casting of a casting having an undercut portion, such as a closed deck type automobile engine. It is about. In more detail, when molding a sand core prototype by the warm box method, the same coating agent can be coated thickly only once by blending an organic acid salt, and it is also suitable for high-pressure casting. The present invention relates to a method for manufacturing a child. Here, the excellent coating property means that when the coating agent is coated on the sand core prototype, the coating agent does not penetrate deeply in a thin liquid state and spread inside the sand core prototype, or It is formed to a uniform thickness with a predetermined thickness, uniformly, reliably and easily without being repelled from the surface of the sand core prototype, and over the entire surface layer of the sand core prototype. That is, it can sufficiently withstand the high casting pressure during casting.

[0002]

2. Description of the Related Art Conventionally, for example, when a closed deck type automobile engine block or other castings such as aluminum alloys and magnesium alloys having an undercut portion are manufactured by die casting, a collapsible sand core is used. Die-casting is performed using the same. In order to obtain a collapsible sand core, first, the sand is hardened to a desired shape, and then a coating agent is applied to the surface of the hardened sand core prototype. To prevent the breakage of the core or 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 that the sand can be taken out to every corner. Of course, in this case, various attempts have been made on the components of the sand core prototype, the method of hardening the sand, the components of the coating agent, the coating method, etc., but no satisfactory one has been obtained. It is.

[0003] Among them, the hardening method, warm box method,
There are a shell mold method, a cold box method and the like.
As the Hardox method, for example, Japanese Patent Publication No. 64-989
The technique described in Japanese Patent Publication No. 8 is known. In this method, the sand core prototype is composed of a binder mainly composed of sand, an acid-curable resin and an oxidizing agent.
Cured by sulfur dioxide.

[0004]

In the above-mentioned Hardox method, when sand formed into a desired shape is hardened to obtain a sand core prototype, it is hardened using sulfur dioxide, that is, sulfurous acid gas. Therefore, because sulfur dioxide is used,
The working environment is poor, and Japanese factories do not like the use of gases that can harm the human body. Also, even if sulfurous acid gas is used, it is very difficult to install ancillary equipment to prevent adverse effects on the human body and the working environment from deteriorating. Are also subject to laws and regulations.

[0005] Therefore, the present inventor has reviewed the merits of the warm box method in which a curing agent is used instead of the oxidizing agent and the sulfurous acid gas. In the warm box method, sulfur dioxide gas is not used to solidify a mixture of sand and a binder to obtain a sand core prototype, but, for example, in a mold for a sand core prototype heated to 90 to 240 ° C. Then, a mixture of sand and a binder is blown with compressed air to be heated and cured to form a mold. However,
In this case, even if the same coating agent as the coating agent, which has been performed fairly well in the above-mentioned Hardox method, is applied to the sand core, the coating agent penetrates into the sand core prototype and has a sufficient thickness. No coating layer was obtained.

[0006]

According to the present invention, sand,
The process of molding a sand core prototype using a furan-based resin, a curing agent for heat curing the resin, and an organic acid salt, and the process of forming a powdered refractory as a main component on the surface of the molded sand core prototype. A step of coating a slurry-like coating agent composed of an aqueous dispersion, and a step of drying the sand core obtained by the coating provide a sand core having an excellent coating. In addition, the organic acid salt to be mixed when molding the sand core prototype is a salt formed between an organic acid and an inorganic ion.
Formic acid, acetic acid, propionic acid, acrylic acid, methacrylic acid, oxalic acid, fumaric acid, maleic acid, succinic acid, tartaric acid, citric acid, butanetetracarboxylic acid, benzoic acid, phthalic acid, terephthalic acid, trimellitic acid, benzene Anions of carboxylic acids such as sulfonic acid and toluenesulfonic acid, and organic acids such as sulfonic acid, and Li ⁺ , Na ⁺ , K ⁺ , and C
s ⁺ , Cu ⁺ , Cu ²⁺ , Mg ²⁺ , Ca ²⁺ , Ba
²⁺ , Zn ²⁺ , Al ³⁺ , Mn ²⁺ , Fe ²⁺ , Fe
^{It is formed} by inorganic cations such as ³⁺ , Co ²⁺ , Ni ²⁺ , and NH ₄ ^{+ in} such a form as to neutralize electric charge. Examples include potassium acetate, sodium acetate, magnesium acetate, calcium acetate, zinc acetate, barium acetate, magnesium acrylate, calcium acrylate, zinc acrylate, aluminum acrylate, sodium benzoate and the like. When a sand core prototype containing an organic acid salt is formed, sand, a furan-based resin, and a curing agent for heat curing the resin may be, for example, an organic acid salt such as powdered calcium acetate or an aqueous solution thereof, or an organic acid salt. After compounding the acid salt solution, it is heated and cured by blowing it with compressed air into a mold for sand core prototype molding heated to, for example, 90 to 240 ° C.

[0007]

In the present invention, first, sand, furan resin,
An organic acid salt or an organic acid salt solution such as powdered calcium acetate or an aqueous solution thereof is mixed with the curing agent for heat curing of the resin, and the composition is heated and cured as described above to form an organic acid. A sand core prototype containing salt is formed. Next, the surface of the sand core prototype thus obtained is coated with a slurry-like coating agent comprising a neutral aqueous dispersion mainly composed of a powdered refractory.

[0008] By applying a slurry-like coating agent comprising a neutral aqueous dispersion containing a powdered refractory as a main component to a sand core prototype obtained by blending such an organic acid salt, The coating agent is instantaneously agglomerated by the organic acid salt present on and near the surface of the core core prototype, and is coated on the surface of the sand core prototype thickly without penetrating deep inside the sand core prototype. it can. Thereafter, when this is dried, a homogeneous coating layer having a desired thickness is formed.

In this way, even with the warm box method, the sand core prototype can be hardened, and the surface of the sand core prototype can be coated easily and in a desired state with a coating agent. When the coated sand core obtained by the present invention is used, the sand core is not broken or cracked at the time of casting the molten metal under high pressure as in the case of high-pressure die casting, and the molten metal is used as the sand core. No intrusion.

[0010]

EXAMPLE When manufacturing a sand core prototype containing an organic acid salt, first, a furan resin, a curing agent for heat curing the resin, and an organic acid salt are mixed with a sand core aggregate such as a core sand. I do. Sand core aggregate is silica sand, zircon sand, chromite sand, cerabeads, etc. Furfuryl-based resin is furfuryl alcohol / formaldehyde resin, furfuryl alcohol / urea / formaldehyde resin, furfuryl alcohol / phenol / formaldehyde A so-called furan resin for a warm box such as a resin, furfuryl alcohol, phenol, urea, and formaldehyde resin is used. As the curing agent for heat curing the resin, at least one of benzenesulfonic acid, phenolsulfonic acid, toluenesulfonic acid, xylenesulfonic acid and lower alkylsulfonic acid, and aluminum, copper, zinc, iron,
Use is made of a salt with at least one kind of ammonium. Further, a small amount of copper chloride, zinc chloride, iron chloride or the like may be used in combination as a curing accelerator.

Examples of the organic acid salts include organic acid salts such as calcium acetate, zinc acetate, and aluminum acrylate. These organic acid salts are blended in at least 0.1 part by weight based on 100 parts by weight of sand. If the amount is less than 0.1 part by weight, the coating agent penetrates deep inside the sand core prototype, and a thick coating layer is not formed on the surface of the sand core prototype. These organic acid salts can be added in a large amount exceeding 0.1 parts by weight or more with respect to 100 parts by weight of the sand, as long as it does not hinder the molding of the sand core prototype.

The above-mentioned organic acid salt may be blended as a solid such as powder, or may be blended in the form of a solution such as an aqueous solution or a dispersion in a suitable dispersant. The solvent or dispersant used in the latter case does not impair the storage stability and heat curability (moldability) of the composition comprising the sand core aggregate, the furan-based resin, and the resin curing agent for heat curing. Are appropriately selected. The concentration and the amount of the solution or dispersion of the organic acid salt described above should be at least 0.1 parts by weight based on 100 parts by weight of sand in terms of the organic acid salt alone.
It is selected appropriately so as to be at least part by weight.

A mixture of these components is blown together with pressurized air into a mold having a predetermined sand core-shaped cavity, and a sand core prototype is formed by a method called a warm box method. did. In this case, the heating temperature of the core molding die is, for example, 90 to 240 ° C., preferably 90 ° C.
The temperature was set to about 200 ° C. and heated for about 1 minute to harden the sand core prototype to a predetermined strength. For example, bending strength 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 dipped in the coating agent, or the surface of the sand core prototype may be brushed or sprayed with the coating agent. The coating agent was a slurry having a solid content of 50 to 90% by weight containing fine powder silica and fine powder alumina as main components and a small amount of colloidal silica. If the solid content is less than 50% by weight, the thickness of the coating layer becomes thin, and if it exceeds 90% by weight, it becomes extremely difficult to stir the slurry. If the pH of the coating agent is not maintained at 7.0 ± 1.0, precipitation and solidification may occur even under stirring.

As the coating agent, other coating agents can be used. For example, about 30 to 80% by weight of an inorganic refractory material such as graphite, mica, fused silica, alumina, magnesia, carbon black and zircon powder, and about 1 inorganic binder such as colloidal silica, alumina sol, clay and amine-treated bentonite. It is also possible to use water consisting of up to 25% by weight and water. In this case, more preferred are fused silica and colloidal silica. In addition, about 10% by volume of methanol and kaolin may be added.

A sand core prototype molded with an organic acid salt is immersed in the coating agent for several seconds, and then dried by heating. Drying conditions are about 120 ° C. and about 10 minutes. When the organic acid salt is not blended, the thickness of the coating is almost 0 mm because it almost penetrates into the sand core prototype, whereas it is sufficiently thick and has little penetration into the sand core prototype. ， The coating is firm. Coating layer is 1
Layers may be used, but two layers are more preferable in order to improve the releasability between the product and the coating layer. As a coating agent for forming the second coating layer, for example, 1 liter of a 3% aqueous phenol resin solution,
500 g of mica powder, 10 g of sodium dodecylbenzenesulfonate as a wetting agent, and 1 g of octyl alcohol as an antifoaming agent can be used by well stirring and mixing. This coating is performed by immersing the sand core prototype after the first layer coating in the second layer coating agent, or brushing or spraying the second layer coating agent on the surface of the sand core prototype. , Formed by drying.

An experimental example will be described below as a more detailed example. (Experimental Examples 1 to 3 and Comparative Example) 100 parts of flat sand as an aggregate, 1.5 parts of furan resin as an organic binder,
Commercially available curing agent containing para-toluenesulfonate as the main curing agent for furan resin (Kao Quaker product FC-
100, main component copper salt of paratoluenesulfonic acid) 0.6
Parts, 0.06 part of a commercially available additive (Kao Quaker product J-20, main component silane compound), and 0.1 part, 0.2 part or 0.5 part of calcium acetate powder as an organic acid salt
The respective parts were mixed, and a sand core prototype for an engine block weighing about 2 kg was formed by a warm box method. Molding conditions were a mold temperature of 120 ° C., a blowing pressure of 4.5 kg / cm ² ,
The heating time was 90 seconds. A sand core prototype containing no organic acid salt was molded in the same manner and coated in the same manner as in this experimental example. The results are shown in Table 1 below as a comparative example.

The sand core prototypes which were not blended with the calcium acetate powder and which were molded by blending a predetermined amount of calcium acetate powder respectively were mixed with the same coating agent by 1 to 2 times.
After immersion for 2 seconds, it was dried in a circulating hot air heating furnace at 120 ° C. for 10 minutes. The composition of the coating agent is fine powder silica 5
0 parts and 30 parts of fine alumina powder were prepared by suspending 3 parts of colloidal silica in 20 parts of water, and the pH was adjusted to 7.2. In the case of the comparative example, the coating agent penetrated into the interior of the sand core prototype, and the coating was poor, whereas in the case of Experimental Examples 1 to 3, the coating was good.

After finishing the first layer coating, a second layer coating was next performed. As the coating agent for the second layer, 500 g of mica powder, 10 g of sodium dodecylbenzenesulfonate as a wetting agent, and 1 g of octyl alcohol as an antifoaming agent were thoroughly mixed with 1 liter of a 3% aqueous phenol resin solution. Was used. That is, the sand core prototype having been coated with the first layer is added to the second layer coating agent by 1 to 2 times.
After immersion for 2 seconds, it was dried in a circulating hot air heating furnace at 120 ° C. for 10 minutes.

[0020]

[Table 1]

The sand core obtained as described above is set in a mold, and an aluminum alloy ADC10 is cast at a casting pressure of 600 k.
g / cm ² , Gate speed 200 mm / sec, Pouring temperature 7
High pressure casting was performed at 60 ° C. After casting, sand removal was performed with a normal core knockout machine.
In the case of No. 3, the core sand was completely removed, and an excellent cast product was obtained. In the case of the comparative example, the molten metal was inserted into the sand core prototype, and the removal of the core sand was poor. The results are summarized in Table 1.

(Experimental Examples 4 to 6, and Comparative Example) In place of the calcium acetate powder of Experimental Examples 1 to 3, 1 part, 2 parts or 5 parts of a 20% aqueous solution of aluminum acrylate was used, respectively. After processing and operating in the same way,
Excellent results were obtained as with the calcium acetate powder. Table 2 shows the results.

[0023]

[Table 2]

[0024]

As described above, according to the present invention, a step of molding a sand core prototype using sand, a furan-based resin, a curing agent for heat curing the resin and an organic acid salt, and a step of molding the sand core prototype A step of coating the surface of the prototype with a slurry-like coating agent consisting of a neutral aqueous dispersion mainly composed of a powdery refractory, and a step of drying the sand core obtained by the coating. Since the core is manufactured, when coating with the coating agent, the coating agent forms a uniform and appropriate thickness coating layer without infiltrating into the sand core prototype. Therefore, the sand core can sufficiently withstand high casting pressure during casting.

That is, when high-pressure casting such as die casting is performed using the sand core obtained in the present invention, the molten metal is not inserted into the sand core, and the product after the sand is discharged is cast. There is no sand left on the skin and it is very smooth. Also,
The sand core after casting has good disintegration properties and sand is easy to get out.
Therefore, even if 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. And the product can be obtained easily and reliably.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-309350 (JP, A) JP-A-62-40949 (JP, A) JP-A-63-303645 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) B22C 9 / 10,3 / 00,1 / 22

Claims (1)

(57) [Claims] 1. A step of molding a sand core prototype using sand, a furan-based resin, a curing agent for heat curing of the resin, and an organic acid salt, and a powdered refractory on the surface of the molded sand core prototype. A method for producing a sand core, comprising a step of coating a slurry-like coating agent comprising a neutral aqueous dispersion mainly composed of: and a step of drying the sand core obtained by coating.