JP2930163B2 - 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 the sand core prototype molded by the warm box method with poly (meth) acrylate, the same coating agent can be coated thickly only once, and is also suitable for high-pressure casting. The present invention relates to a method for manufacturing a 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 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 and a curing agent for heat curing the resin, and the process of forming the sand core prototype into poly (meth)
A step of treating with an acrylate, a step of drying the sand core prototype treated with the poly (meth) acrylate, and a step of mainly using a powdered refractory on the surface of the dried sand core prototype. A step of coating a slurry-like coating agent composed of a neutral aqueous dispersion and a step of drying the sand core obtained by the coating provide a sand core having an excellent coating. The poly (meth) acrylate used for treating the sand core prototype is polyacrylic acid or a salt formed between polymethacrylic acid and inorganic ions, and the poly (meth) acrylic acid anion and Li ⁺ , Na ⁺ , K
⁺ , Cs ⁺ , Cu ⁺ , Cu ²⁺ , Mg ²⁺ , Ca ²⁺ , B
a ²⁺ , Zn ²⁺ , Al ³⁺ , Mn ²⁺ , Fe ²⁺ , Fe ³⁺ , Co
An inorganic cation such as ²⁺ , Ni ²⁺ , and NH ₄ ⁺ is generated in a form that neutralizes electric charge. Examples thereof include potassium poly (meth) acrylate, calcium poly (meth) acrylate, magnesium poly (meth) acrylate, and ammonium poly (meth) acrylate. When the sand core prototype is treated with poly (meth) acrylate, it may be immersed in a poly (meth) acrylate solution such as an aqueous solution of ammonium polyacrylate, or may be treated with poly (meth) acrylic acid. Brush or spray the salt solution onto the surface of the sand core prototype.

[0007]

In the present invention, for example, after a sand core prototype is formed as described above, the sand core prototype is immersed in an aqueous solution of poly (meth) acrylate such as an aqueous solution of ammonium polyacrylate. For example, the poly (meth) acrylate is impregnated into the sand core prototype, and then the sand core prototype is dried. Next, after treating with a poly (meth) acrylate, the surface of the sand core prototype obtained by drying is coated with a slurry-like core made of a neutral aqueous dispersion mainly composed of a powdery refractory. The coating agent is coated. In this case, if the sand core prototype obtained by molding is immersed in a poly (meth) acrylate solution such as an ammonium polyacrylate aqueous solution before coating, the surface layer of the sand core prototype is obtained. Poly (meth) acrylate adheres to or penetrates parts or inside. When this sand core prototype is pulled out of the dipping tank and dried at 80 to 200 ° C. for several minutes to 2 hours, a poly (meth) acrylate film is uniformly formed on the surface layer of the sand core prototype, The voids (capillaries) on the surface of the sand core prototype are clogged, and the poly (meth) acrylate, which is a polymer electrolyte, is uniformly present on and near the surface of the sand core prototype.

On the other hand, a sand core prototype obtained through such poly (meth) acrylate treatment and drying is coated with a slurry-like coating agent comprising a neutral aqueous dispersion mainly composed of a powdery refractory. Is applied, the coating agent does not penetrate deep into the sand core prototype due to the poly (meth) acrylate film formed on and near the surface of the sand core prototype, and The coating agent is instantaneously aggregated by the poly (meth) acrylate, which is a polymer electrolyte existing on and near the surface of the child prototype, so that the surface of the sand core prototype can be thickly coated. 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, first, a furan-based resin and a curing agent for heat curing the resin are mixed with a sand core aggregate such as a core sand. As the sand core aggregate, silica sand, zircon sand, chromite sand, celavies, etc. are used, and as the furan resin, furfuryl alcohol / formaldehyde resin, furfuryl alcohol / urea / formaldehyde resin, fullerene Furyl alcohol phenol formaldehyde resin, furfuryl alcohol phenol
A furan resin for so-called wormmox such as urea-formaldehyde resin is used. Further, as the curing agent for heat curing of the resin, benzenesulfonic acid, phenolsulfonic acid, toluenesulfonic acid, xylenesulfonic acid,
Use is made of a salt of at least one of lower alkyl sulfonic acids and at least one of aluminum, copper, zinc, iron and ammonium. In addition, as a curing accelerator,
A small amount of copper chloride, zinc chloride, iron chloride or the like may be used in combination.

A mixture of these components is blown together with pressurized air into a mold having a predetermined sand core-shaped cavity, for example, by a method called a warm box method. Was molded. In this case, the heating temperature of the core molding die is, for example, 90 to 240 ° C., preferably about 90 to 200 ° C., and is heated for about 1 minute to harden the sand core prototype to a predetermined strength. . For example, bending force 2
A sand core prototype of 0 to 50 kg was obtained.

Next, the sand core prototype thus formed is treated with an aqueous solution of poly (meth) acrylate. Examples of the poly (meth) acrylate include ammonium polyacrylate, calcium polyacrylate, sodium polymethacrylate, and the like. The sand core prototype is immersed in an aqueous solution of these poly (meth) acrylates, absorbed by the sand core prototype, and then dried by heating. The concentration of the aqueous solution is within 200 times the dilution ratio. When the dilution ratio exceeds 200 times, the coating thickness becomes 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. 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.

The sand core prototype, which has been treated with poly (meth) acrylate and then heated and dried, is immersed in the coating agent for several seconds, and then heated and dried. Drying conditions are 12
0 ° C., about 10 minutes. When the coating is not treated with poly (meth) acrylate, the thickness of the coating is almost 0 mm because it almost penetrates the sand core prototype.
It is thick enough, 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 1-4, and Comparative Example) 100 parts of flat sand as an aggregate, 1.5 parts of a furan resin as an organic binder, and a commercially available curing agent mainly containing paratoluenesulfonic acid salt as a curing agent for the furan resin ( Kao Quaker Product FC-1
00, the main component is paratoluenesulfonic acid copper salt) 0.6 part,
And commercially available additives (Kao Quaker Products J-20,
0.06 parts of main component silane compound)
A plurality of g prototype sand cores for engine blocks were formed by a warm box method. Molding conditions were a mold temperature of 120 ° C., a blowing pressure of 4.5 kg / cm ² , and a heating time of 90 seconds.
After standing for one day, the sand core prototype had a transverse rupture strength of 35 kg. One of these was coated with the same coating as that of the present experimental example without performing any poly (meth) acrylate treatment described later, and is shown in Table 1 described later as a comparative example.

9 parts, 49 parts, 99 parts, and 1 part of water were added to 1 part of ammonium polyacrylate (average molecular weight: 67.2 thousand).
99 parts were mixed and dilution ratio was 10,50,100,200
Two-fold aqueous solutions 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 sand core molds treated with ammonium polyacrylate and having different concentrations were immersed in the same coating agent for 1 to 2 seconds at a temperature different from those not treated with ammonium polyacrylate.
In a circulating hot air heating furnace for 10 minutes. The composition of the coating agent is 50 parts of fine powder silica and 30 parts of fine powder alumina.
In which 3 parts of colloidal silica were suspended in 20 parts of water, 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 ammonium polyacrylate 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. (Hereinafter, the next page)

[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. 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 Experimental Example 4, 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 5 to 8) In place of ammonium polyacrylate of Experimental Examples 1 to 4, calcium polyacrylate (average molecular weight: 570,000) was used, and the other parts were treated and operated in exactly the same manner. Excellent results were obtained as in the case of ammonium polyacrylate. 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 sand, a furan-based resin, and a curing agent for the resin heat curing, and a step of molding the sand core prototype into poly (meth) A step of treating with an acrylate, a step of drying the sand core prototype treated with the poly (meth) acrylate, and a step of mainly using a powdered refractory on the surface of the dried sand core prototype. The process of coating a slurry-like coating agent consisting of a neutral aqueous dispersion and the step of drying the sand core prototype obtained by this coating produce a coated sand core. When coating, the coating agent does not penetrate into the sand core mold, but forms a uniform and appropriate thickness coating layer. 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 collapsible sand core obtained in the present invention, the molten metal is not inserted into the sand core, and the product after sand is discharged. No sand remains on the casting surface of the steel, and it is very smooth.
In addition, the sand core after casting has good disintegration properties, and sand can be easily discharged. 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.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-64-48638 (JP, A) JP-A-53-91014 (JP, A) JP-A-4-123835 (JP, A) (58) Field (Int. Cl. ⁶ , DB name) B22C 9/10, 3/00

Claims (1)

(57) [Claims] 1. A step of molding a sand core prototype using sand, a furan-based resin, and a curing agent for heat curing the resin, and a step of treating the sand core prototype with a poly (meth) acrylate. Drying the sand core prototype treated with the poly (meth) acrylate, and forming a slurry on the surface of the dried sand core prototype from a neutral aqueous dispersion mainly composed of powdered refractory. A method for producing a sand core, comprising the steps of: coating a coating agent; and drying the sand core obtained by coating.