JP2930165B2 - 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. More specifically, the same coating agent can be thickly coated only once by forming a semi-permeable membrane made of calcium alginate on a sand core prototype formed by the shell mold method, and it is also suitable for high-pressure casting. The present invention relates to a method for manufacturing a sand core. Here, excellent coating property means that the coating agent is used to coat the sand core prototype with the coating agent.
The specified thickness is applied only to the entire surface layer of the sand core prototype without penetrating deeply in a thin liquid state and spreading inside the sand core prototype, or without being repelled from the surface of the sand core prototype. Thus, it is formed uniformly and firmly easily and firmly, and is coated so as not to peel off, and sufficiently withstands a high casting pressure at the time of 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 shell mold method using a binder instead of the oxidizing agent and the sulfurous acid gas. In the shell mold method, instead of using a sulfur dioxide gas to solidify a mixture of sand and a binder to obtain a sand core prototype, a resin coated sand (RCS) previously coated with a phenolic synthetic resin such as phenolic resin is used. Then, it is blown with compressed air into a mold for sand core prototype molding, and is heated and cured to form a mold. However, in this case,
Even if the same coating agent that had been performed fairly well in the above-mentioned Hardox method was applied to the sand core prototype, the coating agent was repelled without getting wet, which did not work.

[0006]

According to the present invention, RC is used.
A step of forming a sand core prototype using S, a step of forming a semi-permeable membrane of calcium alginate on the sand core prototype, and a step of forming a semi-permeable membrane of calcium alginate on the sand core prototype. A step of drying, a step of coating the surface of the dried sand core prototype with a slurry-like coating agent comprising a neutral aqueous dispersion mainly composed of a powdered refractory, and a step of coating the sand obtained by the coating. The step of drying the core results in a sand core having an excellent coating. In order to form a semipermeable membrane made of calcium alginate on the sand core prototype, the sand core prototype must first be prepared by adding an inorganic calcium salt aqueous solution such as calcium chloride, calcium sulfate, calcium carbonate, or calcium acetate, acrylic It is immersed in an aqueous solution of an organic calcium salt such as calcium acid. Next, the sand core prototypes treated in these inorganic or organic calcium salt aqueous solutions were converted to sodium alginate,
It is immersed in an alginate solution other than calcium alginate such as ammonium alginate and potassium alginate.

As another method of forming a semipermeable membrane made of calcium alginate on a sand core prototype, a sand core prototype is first immersed in an alginate aqueous solution such as a sodium alginate aqueous solution. Thereafter, for example, immersion in an inorganic or organic calcium salt aqueous solution such as an aqueous solution of calcium chloride or calcium acetate. The sand core prototype is mixed with an inorganic or organic calcium salt such as, for example, calcium chloride or calcium acetate. Immersion in a mixed aqueous solution of alginate such as sodium alginate.

[0008]

In the present invention, first, for example, a sand core prototype is formed using RCS as described above, and the sand core prototype is then placed in an aqueous solution of an inorganic calcium salt such as an aqueous solution of calcium chloride or an aqueous solution of calcium acetate. Etc., and then immersed in an alginate aqueous solution other than calcium alginate such as sodium alginate aqueous solution to form a semi-permeable membrane made of calcium alginate on the sand core prototype, The sand core prototype is dried. Next, a slurry coating consisting of a neutral aqueous dispersion mainly composed of powdered refractory is applied to the surface of the sand core prototype obtained by forming and drying a semi-permeable membrane made of calcium alginate. Coating.

In this case, if the molded sand core prototype is immersed in an aqueous solution of an inorganic calcium salt such as an aqueous solution of calcium chloride or an aqueous solution of an organic calcium salt such as an aqueous solution of calcium acetate before coating, the sand core can be immersed in the sand. Inorganic or organic calcium salts adhere to or penetrate into the surface layer of the prototype. After this sand core prototype is pulled up from the immersion tank, it is then immersed in an alginate aqueous solution other than calcium alginate such as sodium alginate aqueous solution, and the alginate adheres to the surface layer and inside of the sand core prototype. Or soak. As a result, Ca ²⁺ reacts with the alginate to form a semi-permeable membrane made of water-insoluble calcium alginate. When this sand core prototype is pulled up from the immersion tank and dried at 80 to 200 ° C. for several minutes to 2 hours, a semi-permeable membrane made of calcium alginate is uniformly formed on the sand core prototype.

On the other hand, a slurry-like coating agent composed of a neutral aqueous dispersion mainly composed of powdered refractory is applied to the sand core prototype on which the semi-permeable membrane composed of calcium alginate is formed. Then, the coating agent is thickly coated on the surface of the sand core prototype by the hydrophilic semipermeable membrane made of calcium alginate formed on the sand core prototype without being repelled on the surface of the sand core prototype. it can. That is, among the constituents of the coating agent, only water permeates the semipermeable membrane, and does not transmit the powdered refractory. Thereafter, when this is dried, a homogeneous coating layer having a desired thickness is formed.

In this way, even in the shell mold method, the sand core prototype can be hardened, and the surface of the sand core prototype can be coated easily and reliably 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.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS To manufacture a sand core prototype, first, a resin-coated sand (RCS) in which phenolic resin such as phenolic resin is coated on sand is prepared. RC
S is produced by a cold method, a semi-hot method, or a dry hot method based on the kneading temperature and properties of a phenolic resin such as a phenol resin, but the dry hot method is preferred in terms of productivity, stability, and cost. That is, after a solid resin is melt-coated on sand heated to 130 to 160 ° C. by a mixer, a hexamine aqueous solution as a curing agent for novolak resin, and only water for resol resin, are charged to evaporate latent heat of water and A wax such as calcium stearate is dispersed when the adhesion of the sand particles is reduced while rapidly cooling by aeration, thereby obtaining a dry, free-flowing RCS.

As the sand, silica sand, zircon sand, chromite sand, cerabeads or the like or their regenerated sand is used. The RCS is blown together with pressurized air into a mold having a predetermined sand core-shaped cavity.
A sand core prototype was molded by a method called a shell mold method. In this case, the heating temperature of the mold for core molding is, for example, about 200 to 300 ° C., preferably about 230 to 270 ° C., and heating is performed for about 30 seconds to 2 minutes to harden the sand core prototype to a predetermined strength. I let it. For example, a sand core prototype having a bending strength of 20 to 50 kg was obtained.

Next, the sand core prototype thus formed is treated with an aqueous solution of an inorganic or organic calcium salt. Examples of the inorganic calcium salt include calcium chloride, calcium sulfate, calcium carbonate, and the like, and examples of the organic calcium salt include calcium acetate, calcium acrylate, and the like. The sand core prototype is immersed in an aqueous solution of these inorganic or organic calcium salts, absorbed by the sand core prototype, and then dried by heating. In this case, heat drying may or may not be performed, but heat drying is more preferable. Thereafter, the sand core prototype treated in an aqueous solution of an inorganic or organic calcium salt is then treated with an aqueous solution of an alginate other than calcium alginate.

Examples of the alginate include sodium alginate, ammonium alginate, potassium alginate and the like. The sand core prototype treated in an aqueous solution of an inorganic or organic calcium salt is immersed in an aqueous solution of an alginate other than these calcium alginate, absorbed by the sand core prototype, and then dried by heating. The respective concentrations of the inorganic or organic calcium salt aqueous solution and the alginate aqueous solution other than calcium alginate are determined by the dilution factor of 50.
It is within 0 times. If each dilution ratio exceeds 500 times, a semipermeable membrane made of calcium alginate will not be formed, or even if the semipermeable membrane is thin, the coating thickness will be thin and the treatment effect will be lost. The immersion time varies depending on the concentration of the treatment liquid and the affinity between the sand core prototype and the treatment liquid, but is as short as 0.5 seconds to about 5 minutes.

If the sand core prototype is difficult to get wet with the processing solution, the sand core prototype is immersed in a hydrophilic organic solvent such as methanol for a short time and then immersed in the processing solution, or The organic solvent is mixed until the sand core prototype becomes wet with the processing solution before processing. Heat drying of the immersion-treated sand core prototype requires a shorter time as the temperature is higher, and is approximately 30 minutes at 120 ° C. as a guide.

Next, the surface of the sand core prototype treated 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.

It should be noted that other coating agents can be used as the coating agent. 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 treatment for forming a semi-permeable membrane made of calcium alginate is then immersed in the coating agent for several seconds, followed by immersing the heat-dried sand core prototype for several seconds, followed by heat drying. Drying conditions are about 120 ° C. and about 10 minutes.
The thickness of the coating is almost unpainted because it is repelled from the sand core prototype if no treatment is performed to form a semipermeable membrane composed of calcium alginate.
It is sufficiently thick, has little penetration into the sand core prototype, and has a solid coating. One coating layer 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 g of a 3% aqueous phenol resin solution, 500 g of mica powder, 10 g of sodium dodecylbenzenesulfonate as a wetting agent, and a defoaming agent One obtained by well stirring and mixing 1 gram of octyl alcohol can be used. This coating is performed by dipping 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 9 and Comparative Example) Using RCS coated with 2 parts of phenolic resin (including the curing agent hexamine) for 100 parts of flat sand, weight of about 2 kg
A plurality of sand core prototypes for the engine block were molded by the shell mold method. Molding conditions were a mold temperature of 250 ° C., a blowing pressure of 0.8 kg / cm ² , and a heating time of 90 seconds. The bending strength of the sand core prototype after being left for one day was 38 kg.
One of them was subjected to the same coating as that of the present experimental example without any treatment for forming a semi-permeable membrane made of calcium alginate described later, and is shown in Table 1 described later as a comparative example.

299 parts of water are added to 1 part of calcium chloride,
399 parts, 499 parts mixed, dilution ratio 300, 40
A 0,500-fold aqueous solution was prepared. After the sand core prototype was immersed in this aqueous solution for 1 to 2 seconds, it was dried in a hot air circulating heating furnace at 120 ° C. for 30 minutes. Next, 1 part of sodium alginate was mixed with 299 parts, 399 parts, and 499 times of water, respectively, to prepare aqueous solutions having dilution ratios of 300, 400, and 500 times, respectively. The sand core prototype treated with the aqueous calcium chloride solution was immersed in the aqueous solution for 1 to 2 seconds, and then dried in a hot air circulating heating furnace at 120 ° C. for 30 minutes.
(Experimental Examples 1 to 9)

The sand core prototypes treated with calcium chloride and then sodium alginate with liquids having different concentrations from those not subjected to the calcium chloride treatment and then the sodium alginate treatment are immersed in the same coating agent for 1 to 2 seconds. After that, it was dried in a circulating hot air heating furnace at 120 ° C. for 10 minutes. The composition of the coating agent was prepared by suspending 3 parts of colloidal silica in 20 parts of water in 50 parts of fine powder silica and 30 parts of fine powder alumina, and the pH was adjusted to 7.2. The coatings of the comparative examples and those of Experimental Examples 5 to 9 had poor or slightly good coating. As a result, the dilution ratio of calcium chloride and sodium alginate was 450 to 5 respectively.
It was estimated that 00 times or less was good.

After the completion of the first layer coating, a second layer coating was next performed. As a 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 a defoaming 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. (Hereinafter, margin)

[0024]

[Table 1]

The sand core obtained as described above is set in a mold, and the 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. 3 at 350 ° C after casting
After the heat treatment for 0 minutes, sand removal was performed with a normal core knockout machine. In the case of Experimental Examples 1 to 4, the core sand was completely removed, and an excellent cast product was obtained. Experimental example 5
In the case of ~ 9, the removal of the core sand was somewhat good, but 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 10 to 18 and Comparative Example) Calcium acetate was used in place of calcium chloride in Experimental Examples 1 to 9, and the other treatment and operation were performed in exactly the same manner. Excellent results were obtained. Table 2 shows the results. (Hereinafter, margin)

[0027]

[Table 2]

(Experimental Examples 19 to 27) When ammonium alginate was used in place of sodium alginate in Experimental Examples 1 to 9 and the other treatment and operation were carried out in exactly the same manner, excellent results were obtained as in the case of sodium alginate. Obtained. Table 3 shows the results. (Hereinafter, margin)

[0029]

[Table 3]

(Experimental Examples 28 to 36) When calcium acetate was used instead of calcium chloride and ammonium alginate was used instead of sodium alginate in Experimental Examples 1 to 9, except that the treatment and operation were performed in exactly the same manner. Excellent results were obtained as with calcium and sodium alginate. Table 4 shows the results. (Hereinafter, margin)

[0031]

[Table 4]

[0032]

As described above, in the present invention, a step of molding a sand core prototype using a resin-coated sand coated with a carboxylate synthetic resin, and a semi-permeable process comprising calcium alginate on the sand core prototype. A step of forming a film, a step of drying the sand core prototype having a semipermeable membrane made of calcium alginate, and a step of forming a powder-based refractory as a main component on the surface of the dried sand core prototype. The process of coating a slurry-like coating agent composed of an aqueous dispersion and the process of drying the obtained sand core produce a coated sand core. , The coating agent does not repel on the surface of the sand core prototype and does not penetrate into the sand core prototype. To form a grayed layer. Therefore,
The sand core can 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. Therefore, such a sand core is used, for example, in the cooling jacket portion of a closed deck type engine block.
Even when used for casting a product having a very complicated shape, a sufficiently satisfactory working state and the product can be obtained easily and reliably.

Claims (1)

(57) [Claims] 1. A step of forming a sand core prototype using a resin-coated sand coated with a phenolic synthetic resin, a step of forming a semi-permeable membrane made of calcium alginate on the sand core prototype, and A step of drying the sand core prototype having a semipermeable membrane made of calcium, and a slurry-like coating made of a powdered refractory-based neutral water dispersion on the surface of the dried sand core prototype A method for producing a sand core, comprising a step of coating an agent and a step of drying the sand core obtained by coating.