JPH06182490A - Production of sand core - Google Patents

Abstract

PURPOSE:To form a coating layer capable of withstanding a casting pressure at a uniform and adequate thickness by coating the surface of a sand core prototype formed by compounding a furan resin, a hardener for curing the resin by heating and polyaluminum chloride and solidifying sand with a slurry coating material essentially consisting of refractories. CONSTITUTION:The sand core prototype contg. the polyaluminum chloride is produced by compounding the polyaluminum chloride with the sand, the furan resin and the hardener for curing the resin by heating, then curing the compsn. by heating. The surface of the resulted sand core prototype is then coated with the slurry coating material consisting of a neutral aq. dispersion consisting essentially of powdery refractories. Then, the solidifying of the sand core prototype even by the worm box method is possible and the surface of the sand core prototype is surely and easily coated with the coating material in a desired state. The failure or crack of the sand core at the time of pouring of the molten metal under a high pressure does not arise and the molten metal does not infiltrate into the inside of the sand core.

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, when a sand core prototype is formed by the warm box method, by blending polyaluminum chloride, the same coating agent can be thickly coated only once, and it is also suitable for high-pressure casting. The present invention relates to a child manufacturing method.

Here, the excellent coating property means that when the sand core prototype is coated with the coating agent, the coating agent does not penetrate deeply into the sand core prototype as a thin liquid spreading inside the sand core prototype. , Or, without being repelled from the surface of the sand core prototype, only the surface layer of the sand core prototype is uniformly and firmly formed with a predetermined thickness, and easily and firmly so that it does not peel off. That is, it is to be sufficiently coated to withstand the high casting pressure during casting.

[0003]

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.

[0005]

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 review 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 above Hardox method was applied to the sand core prototype, the coating agent would penetrate into the sand core prototype, resulting in a sufficient No thick coating layer was obtained.

[0007]

In the present invention, sand,
A process of molding a sand core prototype using a furan-based resin, a curing agent for heat-curing the resin, and polyaluminum chloride, and a neutrality mainly composed of powdery refractory on the surface of the sand core prototype. A sand core having an excellent coating is obtained by a step of coating a slurry-like coating agent comprising an aqueous dispersion and a step of drying the sand core obtained by the coating. The polyaluminum chloride compounded when the sand core mold is molded is marketed by Nippon Light Metal Co., Ltd. (Nikkei pack), and is used for water treatment for water supply, paper sizing agent, and the like. Also, when making a sand core prototype containing polyaluminum chloride,
After compounding polyaluminum chloride with sand, furan-based resin, and a curing agent for heat curing of the resin, the mixture is mixed with, for example,
It is heated and hardened by blowing it into a mold for molding a sand core prototype heated to 40 ° C. with compressed air.

[0008]

In the present invention, first, sand, furan resin,
After polyaluminum chloride is added to the curing agent for heat curing of the resin, the composition is heat-cured as described above to form a sand core prototype containing polyaluminum chloride. Next, the surface of the sand core prototype thus obtained is coated with a slurry-like coating agent composed of a neutral water dispersion containing a powdery refractory as a main component.

When a sand core prototype obtained by blending such polyaluminum chloride is coated with a slurry coating agent composed of a neutral water dispersion containing a powdery refractory material as a main component, the sand core is obtained. Polyaluminum chloride existing on the surface of the core mold and near the surface of the core mold does not cause the coating agent to instantaneously agglomerate and penetrate deep into the core mold of the sand core. it can. Then, it is dried to form a uniform coating layer having a desired thickness.

In this way, the sand core prototype can be hardened 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.

[0011]

[Examples] When manufacturing a sand core prototype containing polyaluminum chloride, first, a furan resin, a curing agent for heat curing of the resin and polyaluminum chloride are mixed with a sand core aggregate such as core sand. To do. 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, furfur-based resin for so-called warm box such as furfuryl alcohol, phenol, urea, formaldehyde resin is used. As the curing agent for heat curing of the resin, at least one of benzene sulfonic acid, phenol sulfonic acid, toluene sulfonic acid, xylene sulfonic acid and lower alkyl sulfonic acid, and at least 1 of aluminum, copper, zinc, iron and ammonium.
The one consisting of a salt with the seed is used. Further, a small amount of copper chloride, zinc chloride, iron chloride or the like may be used together as a curing accelerator.

Examples of polyaluminum chloride include Nikkei Pack manufactured by Nippon Light Metal Co., Ltd. Polyaluminum chloride should be at least 0.1 per 100 parts by weight of sand.
Add more than part by weight. If the amount is less than 0.1 parts by weight,
The coating agent penetrates deep inside the sand core mold, and a thick coating layer does not form on the surface of the sand core mold. In addition, polyaluminum chloride can be added in a large amount in excess of 0.1 parts by weight or more with respect to 100 parts by weight of sand as long as it does not hinder the molding of the sand core prototype.

A mixture of these components is blown into a mold having a predetermined sand core-shaped cavity together with pressurized air, and a sand core prototype is formed by a method called a warm box method. did. In this case, the heating temperature of the core molding die is, for example, 90 to 240 ° C., preferably 90.
The sand core prototype was cured to a predetermined strength by heating at about 200 ° C for about 1 minute. For example, transverse rupture strength of 20 to 50
A kg sand core prototype was obtained.

Next, the surface of the sand core mold produced 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.

A sand core prototype molded by blending polyaluminum chloride in the above coating agent is dipped for several seconds, and then heated and dried. The drying conditions are 120 ℃,
It takes about 10 minutes. The thickness of the coating is almost 0 mm when it is not soaked in the sand core prototype when polyaluminum chloride is not blended, whereas it is sufficiently thick and has little penetration into the sand core prototype. ， The coating film is solid.

The coating layer may be one layer, 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 liter of a 3% aqueous phenol resin solution, 500 g of mica powder,
Sodium dodecylbenzene sulfonate as a wetting agent 1
It is possible to use, for example, a mixture of 0 g and 1 g of octyl alcohol as an antifoaming agent with good stirring and mixing. 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 3 and Comparative Example] 100 parts of flat sand as an aggregate, 1.5 parts of furan resin as an organic binder,
As a curing agent for furan resin, a commercially available curing agent whose main component is paratoluene sulfonate (Kao Quaker FC-
100, main component paratoluenesulfonic acid copper salt) 0.6
Part, commercially available additive (Kao Quaker product J-20, main component silane compound) 0.06 part, and Nikkei pack (manufactured by Nippon Light Metal Co., Ltd., polyaluminum chloride) 0.1 part,
Mix 0.2 parts or 0.5 parts respectively and weigh about 2
A kg sand core prototype for an engine block was 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. In addition, a sand core prototype containing no polyaluminum chloride was formed in the same manner, and the same coating as that of the present experimental example was applied.

[0019]

[Table 1]

The same coating agent was prepared by using the same sanding core prototype which was prepared by blending a prescribed amount of polyaluminum chloride and one not blended with polyaluminum chloride.
After dipping for ~ 2 seconds, 1 cycle in a circulating hot air oven at 120 ° C
Dry for 0 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 examples, the coating agent penetrated into the sand core mold and the coating was poor, whereas in the experimental examples 1 to 3, the coating was good.

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.

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 the comparative example, the molten metal was inserted into the sand core prototype and removal of the core sand was poor. Collectively, the results are shown in Table 1.

[0023]

As described above, according to the present invention, a step of molding a sand core prototype using sand, a furan-based resin, a curing agent for heat curing of the resin, and polyaluminum chloride, and the sand core thus molded The sand coated by the step of coating the surface of the prototype with a slurry-like coating agent composed of a neutral water dispersion containing powdered refractory as a main component and the step of drying the sand core obtained by this coating Since the core is manufactured, when the coating agent is applied, the coating agent does not penetrate into the sand core prototype and forms a coating layer having a 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 sand core obtained in the present invention, the molten metal does not enter the sand core and the product is cast after the sand is discharged. No sand remains on the skin surface and it is very smooth. Therefore, such a sand core, for example, like the cooling jacket portion of a closed deck type engine block,
Even when it is used for casting a product having a very complicated shape, it is possible to obtain a sufficiently satisfactory working condition and the product easily.

Claims (1)

[Claims] 1. A step of molding a sand core prototype using sand, a furan-based resin, a curing agent for heat curing of the resin, and polyaluminum chloride, and a powdery refractory material on the surface of the sand core prototype. A method for producing a sand core, which comprises a step of coating a slurry-like coating agent composed of a neutral water dispersion containing as a main component, and a step of drying the sand core obtained by the coating.