JP3092750B2 - 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, the same coating agent can be thickly coated only once by heating the sand core prototype formed by the shell mold method.
Moreover, the present invention relates to a method for producing a sand core suitable for high-pressure casting. Here, the disturbed 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 while spreading inside the sand core prototype, or It is formed on the surface layer of the sand core prototype only and uniformly over the entire surface layer without being repelled from the surface 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 shell mold method using a binder instead of the oxidizing agent and the sulfurous acid gas. In the shell mold method, a mixture of sand and a binder is hardened to obtain a sand core prototype without using sulfurous acid gas. For example, a resin-coated sand (RCS) previously coated with a phenolic synthetic resin such as phenolic resin is used. ) Is blown with compressed air into a mold for forming a sand core prototype heated to 90 to 240 ° C., and is cured by heating. However, in this case, even if the same coating agent as the coating agent which had been performed quite 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.
When the sand core prototype is formed using S, the sand core prototype is heat-treated at 70 to 400 ° C., and then the powdered refractory is formed on the surface of the hot sand core prototype after the heat treatment. Is coated with a slurry-like coating agent composed of a neutral aqueous dispersion containing as a main component, and then a sand core having an excellent coating for drying the obtained sand core is obtained.

[0007]

[Effects] First, a shell mold for heat treatment using RCS.
A sand core prototype is formed by using a welding method, and then the hot sand core prototype is coated. In order to form a good coating layer on the surface of the sand core prototype, the coating agent penetrates into the sand core prototype during the time until the solvent evaporates from the coating agent to dry and solidify. It is a necessary condition that they do not do it. Since the time dependency of the penetration depth of the liquid into the porous material is proportional to the square root of the reciprocal of the viscosity as in the sand core prototype, it is possible to suppress the penetration by increasing the viscosity of the coating agent. . However, it is desirable that the coating agent has a low viscosity from the viewpoint of storage maintenance. Therefore, a viscosity is low before coating, and a coating agent or mechanism which increases the viscosity with coating is required. In the present invention, the sand core prototype to be coated is used as it is while it is hot immediately after the heat treatment in the previous step, or it is heated and used beforehand once the temperature is lowered. To promote the evaporation of the solvent from the coating agent, thereby increasing the viscosity of the coating agent and to form a good coating layer.

[0008] That is, after forming a sand core prototype by heating at 70 to 400 ° C, the sand core prototype once cooled to near room temperature may be reheated to 70 to 400 ° C. , Instead of performing such reheating treatment
The same effect can be obtained by coating the surface of the sand core prototype with a slurry-like coating agent composed of a neutral aqueous dispersion mainly composed of a powdery refractory in a still hot state immediately after molding at 70 to 400 ° C. Is obtained. The present invention makes it possible to coat even those that cannot be coated by conventional methods, while keeping the viscosity of the coating agent itself low. Further, since no additives are used at the time of coating, it is possible to obtain an extremely good coating layer. The present invention can be used for controlling the core strength by previously measuring the change in strength of the sand core prototype with respect to the heating temperature and time.

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 hardening agent is used for a novolak resin, and only water is added for a resol resin. Also, when the adhesion of the sand particles is reduced while rapidly cooling by aeration, a wax such as calcium stearate is dispersed to obtain a dry free-flowing RCS. As the sand, use is made of silica sand, zircon sand, chromite sand, cerabeads or their regenerated sand.

The RCS was blown into a mold having a cavity of a predetermined sand core shape together with pressurized air, and a sand core prototype was formed by a so-called shell mold method. In this case, the heating temperature of the mold for core molding is, for example, 70 to 400 ° C., preferably about 90 to 300 ° 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. The sand core prototype immediately after removal from the mold is hot. The sand core prototype may be temporarily cooled after being taken out of the mold and allowed to cool to room temperature.
Reheat to 0 ° C. to get hot.

Next, a coating agent is coated on the surface of the hot sand core prototype after the heat treatment at the time of molding. 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 consists of fine powder silica and fine powder alumina as the main components, and a solid content of 50 to 50 to which a small amount of colloidal silica is added.
A 90% by weight slurry was obtained. 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. In addition,
If the pH of this coating agent is not maintained at 7.0 ± 1.0, precipitation and solidification may occur even under stirring.

Incidentally, 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 sand core prototype in a hot state is immersed in the coating agent for a few seconds, and then heated and dried.
Drying conditions are about 120 ° C. for about 10 minutes. If the coating is not in a hot state, the coating is repelled from the surface of the sand core prototype and can hardly be painted. Is solid. The coating layer may be a single layer, but the product and the coating
In order to improve the releasability from the tinting layer, two layers are more preferable. The coating agent for forming the second coating layer is, for example, 500 g of mica powder per liter of a 3% aqueous phenol resin solution, and sodium dodecylbenzenesulfonate 10 g as a lubricant. As an antifoaming agent, octyl alcohol (1 g) which is well mixed with stirring 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 the surface of the sand core prototype with the second layer coating agent. After painting or spraying, it is dried to form.

An experimental example will be described below as a more detailed example. (Experimental Examples 1-4 and Comparative Example) Using RCS coated with 2 parts of phenolic resin (including the hardener hexamine) on 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. After standing at room temperature for one day, the bending strength of the sand core prototype was 38 kg. One of them was subjected to the same coating as that of the present experimental example without any heat treatment described later, and is shown in Table 1 described later as a comparative example. The above sand core prototypes were heat-treated for 10 minutes in a circulating hot air heating furnace set at 70 ° C, 120 ° C, 180 ° C, and 250 ° C, respectively (Experimental Example 1).
4).

The hot core sand core heat-treated at different temperatures from those not subjected to the heat treatment was immersed in the same coating agent for 1 to 2 seconds.
It was dried in a circulating hot air heating furnace at 20 ° 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 was adjusted to pH 7.2. In the case of the comparative example, the coating agent was repelled from the surface of the sand core prototype and the coating was poor, whereas in the case of Experimental Examples 1 to 4, the coating was good.

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.

[0018]

[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. After casting, sand removal was performed with a normal core knockout machine.
In the case of No. 4, 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 5 and 6) Using the same raw material composition as in Experimental Examples 1 to 4, a sand core prototype for an engine block weighing about 2 kg was used as a shell mold.
It was molded by the Ludo method. Molding conditions were: mold temperature 200 ° C. or 300 ° C., blowing pressure 0.8 kg / cm ² , heating time 9
It was 0 seconds. The hot sand core prototype immediately after being taken out after molding was immersed in the same coating agent in the same manner as in Experimental Examples 1 to 4, and then dried in the same manner. All of the sand core prototypes had good coatings. Thereafter, the same operation as in Experimental Examples 1 to 4 was performed to complete the second layer coating, and high-pressure casting was performed as in Experimental Examples 1 to 4. After casting,
When sand removal was performed in the same manner as in Experimental Examples 1 to 4, in each case, the sand core was completely removed, and an excellent cast product was obtained.

[0021]

As described above, according to the present invention, when a sand core prototype is formed using a resin-coated sand coated with a carboxylate synthetic resin, the sand core prototype is heated at 70 to 400 ° C. After the heat treatment, the surface of the hot sand core prototype after the heat treatment is coated with a slurry-like coating agent comprising a neutral aqueous dispersion mainly composed of a powdery refractory. Then, the coated sand core was dried by drying the sand core prototype, so that the coated core was coated with a coating agent.
When coating, the coating agent forms a coating layer of uniform and appropriate thickness without being repelled from the surface of 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. When a sand core prototype is formed using a resin-coated sand coated with a phenolic synthetic resin, the sand core prototype is subjected to a heat treatment at 70 to 400 ° C. The surface of the hot sand core prototype is coated with a slurry-like coating agent consisting of a powdered refractory-based neutral aqueous dispersion, and then the coated sand core is dried. Method for producing a sand core.