JPH0679405A - Production of sand core - Google Patents

Abstract

PURPOSE:To provide the sand core having excellent coatability by using a sand core prototype solidified by using a worm box method. CONSTITUTION:The sand core prototype subjected to a water-soluble synthetic high polymer treatment is obtd. by immersing the sand core prototype formed by solidifying sand into an aq. polyacrylic acid soln., etc. Such sand core prototype is dried by heating and is then immersed into a coating liquid, by which the surface of the sand core prototype is uniformly coated. The sand core prototype is then dried and the sand core having the excellent coating is obtd.

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 property 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 a water-soluble synthetic polymer, the same coating agent can be thickly coated only once, and is also suitable for high pressure casting. The present invention relates to a manufacturing method of. Here, the excellent coating property means that when the sand core prototype is coated with the coating agent, the coating agent is a thin liquid and does not penetrate deeply inside the sand core prototype, or
It is not repelled from the surface of the sand core prototype, but is formed only on the surface layer of the sand core prototype uniformly over the entire surface with a predetermined thickness uniformly and surely easily and firmly so that it does not come off. That is, it is possible to sufficiently withstand the high casting pressure during casting.

[0002]

2. Description of the Related Art Conventionally, when a die-cast casting is used to produce a cast product such as a closed-deck type automobile engine block or other aluminum alloy or magnesium alloy having an undercut portion, a collapsible sand core is used. Die casting is performed by using. When a collapsible sand core is to be obtained, the sand is first solidified into the desired shape, then the coating agent is applied to the surface of the solid sand core prototype, and when the molten metal is cast under high pressure Prevent the child from being damaged and the molten metal from entering the sand core.
After casting, it has been attempted to disintegrate the sand core with little force so that the sand core can be easily taken out, and the sand can be fully taken out to every corner. Of course, in that case, various attempts have been made in the past, such as the components of the sand core prototype, the method of hardening the sand, the components of the coating agent, the method of coating, etc., but the ones that are not sufficiently satisfactory have not yet been obtained. Is.

Among them, as a method of solidifying sand to obtain a sand core prototype, a hard-box method, a warm box method,
Shell mold method, cold box method, etc. are available.
As the Hardox method, for example, Japanese Patent Publication No. Sho 64-989.
The technique described in Japanese Patent No. 8 is known. In this method, the sand core prototype is composed of sand, an acid-curable resin, and a binder whose main component is an oxidant,
Hardened by sulfur dioxide.

[0004]

In the above-mentioned Hardox method, when the sand core prototype is obtained by hardening the sand shaped into a desired shape, it is hardened by using sulfur dioxide, that is, sulfurous acid gas. Therefore, since sulfur dioxide is used,
Due to the poor working environment, the use of gas that adversely affects the human body is not preferred in Japanese factories. Moreover, even if sulfurous acid gas is used, it is difficult to install auxiliary equipment for that purpose in order to prevent the human body from being adversely affected and the working environment from being deteriorated. Also subject to legal restrictions.

Therefore, the present inventor has decided to reexamine the merit of the warm box method using a curing agent instead of the oxidizing agent and the sulfurous acid gas. In the warm box method, instead of using sulfurous acid gas to solidify a mixture of sand and a binder to obtain a sand core prototype, for example, in a mold for sand core prototype molding heated to 90 to 240 ° C. Then, a mixture of sand and a binder is blown with compressed air and heat-cured to mold the mixture. However,
In this case, even if the same coating agent as was used in the Hardox method was applied to the sand core, the coating agent would penetrate into the sand core prototype, resulting in a sufficient thickness. No coating layer was obtained.

[0006]

In the present invention, sand,
A step of molding a sand core prototype using a furan-based resin and a curing agent for heat curing of the resin, a step of treating this sand core prototype with a water-soluble synthetic polymer, and a treatment with this water-soluble synthetic polymer A step of drying the sand core prototype, a step of coating the surface of the dry sand core prototype with a slurry-like coating agent composed of a neutral water dispersion containing powdery refractory as a main component, and the coating A sand core having an excellent coating is obtained by a step of drying the sand core obtained in the above. The water-soluble synthetic polymer that processes sand cores has a molecular structure composed of one or more main chains of acrylic acid, methacrylic acid, vinyl acid, ether acid, and maleic anhydride. The majority have water-soluble substituents in the chain. Water-soluble substituents include sulfonate groups,
Carboxyl group and its anhydride, hydroxyl group, amide group, amino group, ether group, pyrrolidone group, ethyleneimine group,
There are water-soluble glycidyl ether groups and the like. Specific examples of the water-soluble polymer include polyacrylic acid, polyvinyl alcohol, polyethylene glycol, polypropylene glycol, polyacrylamide, polyvinylpyrrolidone, water-soluble alkyd, polyvinyl ether, and maleic acid copolymer. When the sand core prototype is treated with a water-soluble synthetic polymer, for example, it is immersed in a water-soluble synthetic polymer solution such as an aqueous polyacrylic acid solution, or the water-soluble synthetic polymer solution is used as a sand core prototype. Brush or spray on the surface of.

[0007]

In the present invention, first, for example, as described above, a sand core prototype is formed, and then the sand core prototype is immersed in a water-soluble synthetic polymer aqueous solution such as a polyacrylic acid aqueous solution. The water-soluble synthetic polymer is impregnated into the sand core prototype, and then the sand core prototype is dried. Next, the surface of the sand core prototype obtained by treating with a water-soluble synthetic polymer and then drying is coated with a slurry-like coating agent composed of a neutral water dispersion containing powdery refractory as a main component. .
In this case, if the formed sand core prototype is immersed in an aqueous solution of a water-soluble synthetic polymer, such as an aqueous solution of polyacrylic acid, before coating, the water-soluble synthetic high-level material may be formed in the surface layer portion or inside of the sand core prototype. Molecules attach and soak. After pulling this sand core prototype out of the dipping tank and drying it at 80 to 200 ° C for several minutes to 2 hours, a film of water-soluble synthetic polymer is uniformly formed on the surface layer of the sand core prototype, and the sand core is formed. The voids (capillaries) on the prototype surface are filled.

On the other hand, a slurry-like coating agent composed of a neutral water dispersion containing a powdery refractory as a main component is applied to a sand core prototype obtained through such treatment with a water-soluble synthetic polymer and drying. By doing so, the surface of the sand core prototype and the film of the water-soluble synthetic polymer formed near the surface of the sand core prototype fill the voids on the surface of the sand core prototype, and the coating agent penetrates deep inside the sand core prototype. The surface of the sand core prototype can be thickly coated without being embedded. Then if you dry it,
A homogeneous coating layer of desired thickness is formed.

In this way, the sand core prototype can be solidified even by the warm box method, and the surface of the sand core prototype can be coated with the coating agent easily and surely in a desired state. When the coated sand core obtained by the present invention is used, the molten core is not damaged or cracked when the molten core is cast under high pressure like high pressure die casting, and the molten core is There is no intrusion.

[0010]

EXAMPLE When manufacturing a sand core prototype, first, a furan-based resin and a curing agent for heat curing the same are mixed with a sand core aggregate such as core sand. As sand core aggregate, silica sand, zircon sand, chromite sand, cera beads, etc. are used, and as furan resin, furfuryl alcohol / formaldehyde resin, furfuryl alcohol / urea / formaldehyde resin, furfuryl alcohol / phenol / formaldehyde. Resin, furfuryl alcohol / phenol
A so-called warm box furan resin such as urea / formaldehyde resin is used. Further, as a curing agent for the resin heat curing, benzene sulfonic acid, phenol sulfonic acid, toluene sulfonic acid, xylene sulfonic acid,
A salt of at least one lower alkyl sulfonic acid and at least one of aluminum, copper, zinc, iron and ammonium is used. Further, a small amount of copper chloride, zinc chloride, iron chloride or the like may be used together as a curing accelerator.

A mixture of these components is blown together with pressurized air into a mold having a predetermined sand core-shaped cavity, and, for example, a sand core mold is formed 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 the sand core prototype is cured to a predetermined strength by heating for about 1 minute. . For example, transverse strength 2
A sand core prototype of 0 to 50 kg was obtained.

Next, the sand core prototype thus molded is treated with an aqueous solution of a water-soluble synthetic polymer. Examples of the water-soluble synthetic polymer include polyacrylic acid, polyvinyl alcohol, polyacrylamide and the like. The sand core prototype is immersed in an aqueous solution of these water-soluble synthetic polymers, absorbed in 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 will be thin and the treatment effect will be lost. The immersion time is from a short time of 0.5 seconds to about 5 minutes, although it depends on the concentration of the processing solution and the affinity between the sand core prototype and the processing solution.

If the sand core prototype is difficult to be wet with the treatment liquid, the sand core prototype is immersed in a hydrophilic organic solvent such as methanol for a short time in advance and then immersed in the treatment liquid, or the above-mentioned hydrophilicity is added to the treatment liquid. The organic solvent is mixed until the sand core prototype becomes wet with the treatment liquid, and then treated. The higher the temperature, the shorter the time required to dry the sand core prototype that has been subjected to the immersion treatment, and as a guide, it takes about 30 minutes at 120 ° C.

Next, the surface of the sand core prototype treated as described above is coated with a coating agent. In this case, the sand core master may be dipped in the coating agent, or the surface of the sand core master 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. When the solid content is 50% by weight or less, the thickness of the coating layer becomes thin, and when it is 90% by weight or more, it becomes extremely difficult to stir the slurry. If the pH of this coating agent is not maintained at 7.0 ± 1.0, precipitation and solidification may occur even under stirring.

Other coating agents may 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% of an inorganic binder such as colloidal silica, alumina sol, clay and amine-treated bentonite. It is also possible to use water consisting of ˜25% by weight. In this case, more preferred are fused silica and colloidal silica. Incidentally, about 10% by volume of methanol and kaolin may be added thereto.

The sand core prototype, which has been treated with a water-soluble synthetic polymer and then heated and dried, is dipped in the coating agent for several seconds, and then heated and dried. The drying conditions are 120 ℃,
It takes about 10 minutes. When the water-soluble synthetic polymer treatment is not applied, the thickness of the coating is almost 0 mm when it is almost immersed in the sand core prototype, whereas it is sufficiently thick and the penetration into the sand core prototype is small. Moreover, the coating film is solid. The coating layer may be one layer, but two layers are more preferable in order to improve the releasing property between the product and the coating layer. Examples of the coating agent for forming the second coating layer include, 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 a defoaming agent. It is possible to use a material in which 1 gram of octyl alcohol is well stirred and mixed. This coating is carried out by immersing the sand core prototype that has been subjected to 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 template. , Dry to form.

As a more detailed example, an experimental example will be shown below. (Experimental Examples 1 to 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 containing paratoluenesulfonate as a curing agent for a furan resin ( Kao Quaker product FC-1
00, main component paratoluenesulfonic acid copper salt) 0.6 part,
And commercially available additives (Kao Quaker product J-20,
Main component silane compound) 0.06 parts mixed, weight approx. 2k
A plurality of sand core prototypes for engine block of g were molded by the warm box method. The 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.
The transverse rupture strength of the sand core prototype after standing for 1 day was 35 kg. One of them was subjected to the same coating as that of the present experimental example without any treatment of the water-soluble synthetic polymer described below, and therefore is shown in Table 1 below as a comparative example.

Water was mixed with 1 part of polyacrylic acid (degree of polymerization: 3000), 9 parts, 49 parts, 99 parts and 199 parts, respectively,
Aqueous solutions having dilution ratios of 10, 50, 100 and 200 were prepared, respectively. 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 to 4)

The sand core prototypes treated with polyacrylic acid by liquids having different concentrations from those not treated with polyacrylic acid were added to the same coating agent as 1 to
After dipping for 2 seconds, circulate in a hot air oven at 120 ° C for 10
Dry for minutes. The composition of the coating agent was such that 50 parts of fine powder silica and 30 parts of fine powder alumina and 3 parts of colloidal silica were suspended in 20 parts of water, and the pH was adjusted to 7.2. In the comparative example and the experimental example 4, the coating was poor or good. From this, it was estimated that the polyacrylic acid dilution ratio should be 150 to 200 times or less.

After finishing the above-mentioned first layer coating, a second layer coating was then carried out. 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 a defoaming agent were mixed well with 1 liter of a 3% aqueous phenol resin solution. I used one. That is, the sand core prototype that has been subjected to the first layer coating is added to the second layer coating agent in an amount of 1 to 2
After soaking for 2 seconds, it was dried for 10 minutes in a circulating hot air heating oven at 120 ° C.

[0021]

[Table 1]

The sand core obtained as described above is set in a mold and the aluminum alloy ADC10 is cast at a pressure of 600 k.
g / cm ² , spout speed 200 mm / sec, pouring temperature 7
High pressure casting was performed under the condition of 60 ° C. When sand was removed using a normal core knockout machine after casting, Experimental Examples 1 to
In the case of 3, 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 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. Collectively, the results are shown in Table 1.

(Experimental Examples 5 to 8) Instead of the polyacrylic acid of Experimental Examples 1 to 4, polyvinyl alcohol (degree of polymerization: 200) was used.
When 0) was used and the other treatments and operations were performed in the same manner, excellent results were obtained as in the case of polyacrylic acid. The results are shown in Table 2.

[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 heat curing of the resin, and the sand core prototype are treated with a water-soluble synthetic resin. A step of treating with a molecule, a step of drying a sand core prototype treated with this water-soluble synthetic polymer, and a neutral water dispersion containing powdery refractory as a main component on the surface of this dry sand core prototype. Since the coated sand core is manufactured by the step of coating the slurry-like coating agent consisting of the body and the step of drying the sand core prototype obtained by this coating, when coating with the coating agent, The coating agent does not penetrate into the sand core mold and forms a coating layer of uniform and appropriate thickness. Therefore, the sand core can sufficiently withstand a 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 does not enter the sand core, and the product after the sand is discharged No sand remains on the surface of the cast surface and the surface is extremely smooth.
In addition, the sand core after casting has good disintegration properties, and sand removal is easy. Therefore, even if such a sand core is used for casting a product having a very complicated shape such as a cooling jacket portion of a closed deck type engine block, the working condition is sufficiently satisfactory. And you can get the product surely and easily.

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[Procedure amendment]

[Submission date] May 12, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction content]

[0006]

In the present invention, sand,
A step of molding a sand core prototype using a furan-based resin and a curing agent for heat curing of the resin, a step of treating the sand core prototype with a water-soluble synthetic polymer, and a treatment with this water-soluble synthetic polymer A step of drying the sand core prototype, and a step of coating a slurry-like coating agent composed of a neutral water dispersion containing powdery refractory as a main component on the surface of the dried sand core prototype Then, a sand core having excellent coating is obtained by the step of drying the sand core obtained by this coating. The water-soluble synthetic polymer for treating the sand core has a molecular structure composed of one or more main chains of an acrylic group, a methacrylic group, a vinyl group, an ether group and maleic anhydride. The majority have water-soluble substituents on their side chains. As the water-soluble substituent, a sulfonate group,
Carboxyl group and its anhydride, hydroxyl group, amide group, amino group, ether group, pyrrolidone group, ethyleneimine group,
There are water-soluble glycidyl ether groups and the like. Specific examples of the water-soluble synthetic polymer include polyacrylic acid, polyvinyl alcohol, polyethylene glycol, polypropylene glycol, polyacrylamide, polyvinylpyrrolidone,
Examples thereof include water-soluble alkyd, polyvinyl ether, and maleic acid copolymer. When the sand core prototype is treated with a water-soluble synthetic polymer, for example, it is immersed in a water-soluble synthetic polymer solution such as an aqueous solution of polyacrylic acid, or the water-soluble synthetic polymer solution is used as a sand core prototype. Brush or spray on the surface of.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction content]

[0010]

EXAMPLES When manufacturing a sand core prototype, first, a furan resin and a curing agent for heat curing the same are mixed with a sand core aggregate such as core sand. As the sand core aggregate, silica sand, zircon sand, chromite sand, ceravise, etc. are used, and as the furan resin, furfuryl alcohol formaldehyde resin, furfuryl alcohol urea urea formaldehyde resin, full Furyl alcohol phenol formaldehyde resin, full frill alcohol phenol phenol
A furan resin for so-called warm mox such as urea / formaldehyde resin is used. Further, as the curing agent for heating and curing the resin, benzenesulfonic acid, phenolsulfonic acid, toluenesulfonic acid, xylenesulfonic acid,
A salt of at least one of lower alkyl sulfonic acid and at least one of aluminum, copper, zinc, iron and ammonium is used. Also, as a curing accelerator,
A small amount of copper chloride, zinc chloride, iron chloride or the like may be used together.

Claims (1)

[Claims] 1. A step of molding a sand core prototype using sand, a furan-based resin, and a curing agent for heat curing of the resin, a step of treating the sand core prototype with a water-soluble synthetic polymer, and Of a sand core prototype treated with a water-soluble synthetic polymer, and a slurry-like coating agent consisting of a neutral water dispersion containing powdery refractory as the main component on the surface of the dry sand core prototype. A method for producing a sand core, comprising a coating step and a step of drying the sand core obtained by the coating.