JP3090294B2 - 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, by treating a sand core prototype molded by the shell mold method with a non-thermosetting water-soluble synthetic polymer, the same coating agent can be coated thickly only once, and it is also suitable for high-pressure casting. The present invention relates to a method for producing a sand core. Here, excellent coating properties mean that when coating the coating on the sand core prototype, the coating agent does not penetrate deeply in a thin liquid state while spreading inside the sand core prototype.
Alternatively, it is formed firmly and easily with a predetermined thickness uniformly and securely on the surface layer of the sand core prototype without being repelled from the surface of the sand core prototype. That is, it must be able to 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 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
A step of molding a sand core prototype using S, a step of treating the sand core prototype with a non-thermosetting water-soluble synthetic polymer, and a step of treating the sand core prototype with the non-thermosetting water-soluble synthetic polymer. A step of drying the child prototype; and a step of coating a slurry-like coating agent comprising a neutral aqueous dispersion containing a powdered refractory as a main component on the surface of the dried sand core prototype, By drying the sand core obtained by this coating, a sand core having an excellent coating is obtained. The non-thermosetting water-soluble synthetic polymer for treating the sand core has a molecular structure of one or more of an acrylic group, a methacrylic group, a vinyl group, an ether group, and maleic anhydride. Most of them have a water-soluble substituent on the side chain. Examples of the water-soluble substituent include a sulfonic acid group, a carboxyl group and its anhydride, a hydroxyl group, an amide group, an amino group,
Examples include ether groups, pyrrolidone groups, ethyleneimine groups, and water-soluble glycidyl ether groups. Specific examples of the non-thermosetting water-soluble synthetic polymer include polyacrylic acid, polyvinyl alcohol, polyethylene glycol, polypropylene glycol, polyacrylamide, polyvinylpyrrolidone, water-soluble alkyd, polyvinyl ether, and maleic. Acid copolymers and the like can be mentioned. When the sand core prototype is treated with a non-thermosetting water-soluble synthetic polymer, for example, it may be immersed in a non-thermosetting water-soluble synthetic polymer solution such as a polyacrylic acid aqueous solution, or may be non-thermosetting. A water-soluble synthetic polymer solution is brushed or sprayed on the surface of the sand core prototype.

[0007]

According to the present invention, first, a sand core prototype is formed by using RCS as described above, and then the sand core prototype is subjected to a non-thermosetting water-soluble synthetic polymer such as an aqueous solution of polyacrylic acid. Infiltrate the non-thermosetting water-soluble synthetic polymer into the sand core prototype by immersing it in an aqueous solution, and then
The sand core prototype is dried. Next, after treating with a non-thermosetting water-soluble synthetic polymer and drying, the surface of this sand core prototype is coated with a slurry-like neutral water dispersion mainly composed of powdered refractory. Coating a coating agent. In this case, if the molded sand core prototype is immersed in a non-thermosetting water-soluble synthetic polymer aqueous solution such as a polyacrylic acid aqueous solution before coating, the sand core prototype becomes in the surface layer or inside of the sand core prototype. Non-thermosetting water-soluble synthetic polymer adheres or penetrates. When the sand core prototype is pulled out of the dipping tank and dried at 80 to 200 ° C. for several minutes to 2 hours, a non-thermosetting water-soluble synthetic polymer film is uniformly formed on the surface of the sand core prototype. The voids (capillaries) on the surface of the sand core prototype are clogged, and the surface of the sand core prototype is hydrophilized.

On the other hand, a sand core prototype obtained through such a non-thermosetting water-soluble synthetic polymer treatment and drying is added to a slurry-like neutral water dispersion mainly composed of a powdery refractory. When a coating agent is applied, the voids on the surface of the sand core prototype are clogged by the non-thermosetting water-soluble synthetic polymer film formed on and near the surface of the sand core prototype, and the surface of the sand core prototype is Is uniformly hydrophilized, so that the coating agent can be thickly coated on the surface of the sand core prototype without being repelled by the surface of the sand core prototype. Thereafter, when this is dried, a homogeneous coating layer having a desired thickness is formed.

In this way, even with 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 with a coating agent in a desired state. 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]

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 a non-thermosetting water-soluble synthetic polymer.
Examples of the non-thermosetting water-soluble synthetic polymer include polyacrylic acid, polyvinyl alcohol, and polyacrylamide. The sand core prototype is immersed in an aqueous solution of these non-thermosetting water-soluble synthetic polymers, absorbed by the sand core prototype, and then dried by heating. The concentration of the aqueous solution is within 200 times the dilution ratio. If the dilution ratio exceeds 200 times, the coating thickness is too thin and the treatment effect is 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 before being 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.

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 non-thermosetting water-soluble synthetic polymer treatment and a heat-dried sand core prototype are immersed in the coating agent for several seconds, and then heat-dried. Drying condition is 1
20 ° C., about 10 minutes. If the coating is not treated with a non-thermosetting water-soluble synthetic polymer, the coating is repelled from the sand core prototype and hardly painted, but is sufficiently thick and has little penetration into the sand core prototype. Moreover, the coating film is firm. 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 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 1-4, and Comparative Example) Using a RCS obtained by coating 2 parts of a phenolic resin (including a hardener hexamine) with 100 parts of flat sand, a sand core prototype for an engine block weighing about 2 kg was used. A plurality of pieces were formed by a shell mold method. Molding conditions were: mold temperature 250 ° C., blowing pressure 0.8 kg / cm 2, heating time 9
It was 0 seconds. The bending strength of the sand core prototype after standing for one day was 38 kg. One of them was coated with the same coating as that of the present experimental example without any treatment of a non-thermosetting water-soluble synthetic polymer described later, and is shown in Table 1 below as a comparative example.

9 parts, 49 parts, 99 parts and 199 parts of water were mixed with 1 part of polyacrylic acid (degree of polymerization: 3000),
Aqueous solutions having a dilution ratio of 10, 50, 100, and 200 times were prepared. The sand core prototype was immersed in this aqueous solution for 1 to 2 seconds, and then dried in a circulating hot air heating furnace at 120 ° C. for 30 minutes. (Experimental Examples 1-4)

The non-polyacrylic acid-treated sand core prototypes treated with polyacrylic acid by liquids having different concentrations from each other were applied to the same coating agent in the same coating agent.
After immersion for 2 seconds, 10 minutes in a circulating hot air heating furnace at 120 ° C.
Dried for 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. In the case of the comparative example and the case of the experimental example 4, the coating was defective or slightly good. Thus, it was estimated that the dilution ratio of polyacrylic acid was preferably 150 to 200 times or less.

After finishing 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.

[0021]

[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. 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 3, the core sand was completely removed, and an excellent cast product was obtained. Experimental example 4
In the case of (1), the removal of the core sand was slightly 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 5 to 8 and Comparative Example) Experimental Example 1
Polyvinyl alcohol (degree of polymerization: 2000) was used in place of polyacrylic acid of Nos. 4 to 4, and the same treatment and operation were performed except for the above, and excellent results were obtained as in the case of polyacrylic acid. Table 2 shows the results.

[0024]

[Table 2]

[0025]

As described above, according to the present invention, a step of molding a sand core prototype using a resin-coated sand coated with a carboxylate-based synthetic resin, and a step of synthesizing the sand core prototype with a non-thermosetting water-soluble synthetic resin A step of treating with a polymer, a step of drying the sand core prototype treated with the non-thermosetting water-soluble synthetic polymer, and a step of coating the surface of the dried sand core prototype with a powdered refractory as a main component. The coated core is manufactured by the step of coating a slurry-like coating agent composed of a neutral aqueous dispersion and the step of drying the core obtained by coating. When coating, the coating agent forms a uniform and appropriate thickness coating layer without being repelled on the surface of the sand core prototype or penetrating 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. 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 molding a sand core prototype using a resin-coated sand coated with a carboxylate synthetic resin, a step of treating the sand core prototype with a non-thermosetting water-soluble synthetic polymer, and A step of drying the sand core prototype treated with the non-thermosetting water-soluble synthetic polymer, and a slurry comprising a powdered refractory-based neutral water dispersion on the surface of the dried sand core prototype. A method for producing a sand core, comprising the steps of: coating a coating agent in a shape; and drying the sand core obtained by coating.