JPH05185180A - Manufacture of collapsible sand core - Google Patents

Abstract

PURPOSE:To sufficiently execute coating even in the case of a sand core original mold hardened by using a warm box method and obtain the sand core having excellent collapsibility. CONSTITUTION:The sand core original mold hardening the sand is dipped into dilute sulfuric acid solution, etc., to obtain the chemically treated sand core original mold. After heating and drying this sand core original mold, by dipping into the coating liquid, etc., the uniform coating application is executed on the surface of the sand core original mold and successively, drying is executed to obtain the collapsible sand core.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure-resistant material used for high-pressure die casting of a cast product having an undercut portion, such as a closed-deck type automobile engine, and a disintegrating property having good coating property and easy disintegration. The present invention relates to a method for manufacturing a sand core. More specifically, the same coating agent can be thickly coated only once by chemically treating the molded sand core prototype.
Moreover, the present invention relates to a method for producing a sand core which has excellent disintegration properties after casting and is suitable for high pressure casting.

[0002]

2. Description of the Related Art Conventionally, for example, when a die-cast casting is used to produce a cast product such as a closed deck type automobile engine block or other undercut aluminum alloy or magnesium alloy, 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 breaking 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 to allow the sand to be taken out to every corner. Of course, in that case, various attempts have been made in the past such as sand core prototype components, sand compaction, coating agent components, coating methods, etc., but the current situation is that no satisfactory results have been obtained. Is.

Among them, as a method for 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.
The technique described in Japanese Patent Publication 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,
It is oxidized by sulfur dioxide.

[0004]

In the above Hardox method, when a sand core prototype is obtained by hardening sand molded into a desired shape, sulfur dioxide, that is, sulfurous acid gas is used for hardening. 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. Further, 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 to be deteriorated. Also subject to legal restrictions.

Therefore, the present inventor has decided to reexamine the merit 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, instead of using sulfurous acid gas to solidify the mixture of sand and binder to obtain a sand core mold, for example, in a mold for sand core mold molding heated to 90 to 240 ° C. The mixture of sand and binder is blown with compressed air and heat-cured to mold. 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. In addition, even if the same coating agent is applied using resin coated sand (RCS), which is a so-called shell mold method in which sand is coated with a phenolic resin or other synthetic resin in advance, the coating agent does not get wet. It was repelled and it didn't work.

[0006]

In the present invention, a step of molding a sand core prototype using an organic binder, a step of treating the sand core prototype with a chemical, and a sand core treated with the chemical The step of drying the prototype, the step of coating the surface of the dried sand core prototype with a slurry-like coating agent consisting of a neutral water dispersion containing powdery refractory as a main component, and the coating A disintegrating sand core is obtained by the process of drying the sand core. As the chemical agent for treating the sand core prototype, for example, a mineral acid such as sulfuric acid or phosphoric acid is used. When the sand core prototype is treated with a chemical, for example, the sand core prototype is immersed in an acidic solution such as dilute sulfuric acid, or the acidic solution is brushed or sprayed on the surface of the sand core prototype.

[0007]

In the present invention, first, for example, as described above, a sand core prototype is formed, and then the sand core prototype is dipped in a mineral acid solution such as dilute sulfuric acid. The mineral acid is impregnated inside, and then the sand core prototype is dried. Next, the surface of the sand core prototype obtained by treating with a chemical such as mineral acid 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 (ocher color, brown to dark green) is dipped in a mineral acid solution such as dilute sulfuric acid solution before coating, the sand core prototype surface layer or core Mineral acid adheres to or soaks into. When this sand core prototype is pulled out of the dipping tank and then dried at 80 to 200 ° C. for several minutes to 2 hours, the sand core prototype turns black.
This is because the hardened furan resin that bound the sands was dehydrated and carbonized by the mineral acid that adhered to the sand core prototype and soaked in it. That is, in the hardened furan resin that connects sands to each other, the carbonization reaction is accelerated by the heat during the drying. As a result, blackening occurs and the strength also decreases. This decrease in strength can sufficiently withstand the pressure applied during casting. During casting, the heat of the molten metal naturally deteriorates the hardened furan resin, but if the strength is lowered in advance as described above, the sand core will be removed from the cast product taken out from the mold after casting. When taking out the sand core, it is extremely easy and easy to take out.

On the other hand, if a sand core prototype obtained through such chemical treatment and drying is coated with a slurry coating agent composed of a neutral water dispersion containing powdery refractory as a main component, The surface of the sand core mold can be thickly coated without the coating agent instantaneously agglomerating due to the mineral acid existing on the surface of the sand core mold and penetrating deep inside the sand core mold. .. After that, 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 collapsible sand core obtained by the present invention is used, the melt core is not damaged or cracked at the time of pouring the melt under high pressure like high pressure die casting, and the melt is sanded. It does not enter the core. In addition, after the molten metal is solidified after casting and the cast product is taken out from the mold, when the sand core is disintegrated and taken out, the sand core can be disintegrated and taken out easily with almost no force applied. The sand does not remain in the corners of the casting surface, and the sand can be fully and reliably taken out to every corner.

[0010]

[Example] When manufacturing a sand core prototype, first, an organic binder is mixed with a sand core aggregate such as core sand. Sand core aggregates include silica sand, zircon sand, chromite sand,
A so-called warm-box binder such as furan resin is used as the organic binder, and the mixture of these components is pressed into a mold having a predetermined sand core-shaped cavity. It was blown together with air and, for example, a sand core prototype was molded by a method called the warm box method. 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 sand core mold thus formed is treated with an aqueous solution of various chemicals. As for this medicine,
Mineral acids such as sulfuric acid and phosphoric acid may be mentioned. The sand core prototype is immersed in an aqueous solution of these chemicals, absorbed in the sand core prototype, and then heated and dried. The concentration of the aqueous solution is the dilution ratio (98%
Dilution ratio of concentrated sulfuric acid and 89% phosphoric acid is within 200 times. If the dilution ratio exceeds 200 times, the coating thickness will be thin, and the disintegration property of the sand core after casting will be reduced, and the treatment effect will be lost. The immersion time is from a short time of 0.5 seconds to about 5 minutes, depending 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 wet with the treatment liquid, the sand core prototype is immersed in an organic solvent such as methanol or acetone for a short time in advance and then immersed in the treatment liquid, or the above-mentioned organic solvent is added to the treatment liquid. Mix until the sand core prototype becomes wet with the processing solution before processing. The higher the temperature, the shorter the time required to dry the sand core prototype that has been subjected to the immersion treatment, and the time is about 20 minutes at 120 ° C. as a guide. The chemical may be used as it is without being diluted. If the chemical is a liquid such as concentrated sulfuric acid (98%) or phosphoric acid (89%), the sand core prototype is dipped to remove the fine powder of acid. As in the case of fine powder, sprinkle the powder on the sand core prototype and wipe off the excess powder. As mentioned above, when a solution with a low concentration such as dilute sulfuric acid is used, it is necessary to dry it to evaporate water, but if it is not diluted with water like concentrated sulfuric acid, it is not necessary to dry it. .. The treated sand core prototype turned black and its transverse rupture strength decreased in proportion to the treatment concentration, but the decrease in strength is considered to be due to the progress of carbonization deterioration due to acid in the case of sulfuric acid or phosphoric acid.

Next, the surface of the sand core master treated as described above is coated with a coating agent. In this case, the sand core prototype may be immersed 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 containing fine powder silica and fine powder alumina as main components, and a small amount of colloidal silica, and having a solid content of 50 to 90% by weight. 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. In addition, p of this coating agent
If H 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 inorganic refractory material such as graphite, mica, fused silica, alumina, magnesia, carbon black and zircon powder, and about 1% of 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 that has been chemically treated and then heat-dried is dipped in the coating agent for several seconds, and then heat-dried. The drying conditions are 120 ° C. and about 10 minutes. The thickness of the coating is almost 0 mm when it is almost immersed in the sand core prototype without chemical treatment, 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. As a coating agent for forming the second coating layer, for example, 3
% Liter of a water-soluble phenol resin solution, 500 g of mica powder, 10 g of sodium dodecylbenzenesulfonate as a wetting agent, and 1 g of octyl alcohol as a defoaming agent, which are well stirred and mixed, can be used. This coating is carried out 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. , Dry to form.

As a more detailed example, an experimental example will be shown below. (Experimental Examples 1 to 5) 100 parts of flat sand as an aggregate, 1.5 parts of a furan resin as an organic binder, and a commercially available hardener mainly containing paratoluenesulfonate as a hardener for furan resin (Kao Quaker product FC -100, a main component paratoluene sulfonic acid copper salt) 0.6 part, and a commercially available additive (Kao Quaker product J-20, main component silane compound) 0.06 part are mixed, and an engine block weighing about 2 kg. A plurality of sand core molds were made by the warm box method. Molding conditions are mold temperature 120 ° C, blow pressure 4.5k
The heating time was g / cm ² and the heating time was 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 the present experimental example without performing any chemical treatment described later, and therefore it is shown in Table 1 below as a comparative example.

This sand core prototype was immersed in 98% concentrated sulfuric acid for 1 to 2 seconds. (Experimental Example 1) Next, 1 part of 98% concentrated sulfuric acid was mixed with 9 parts, 49 parts and 99 parts of water, respectively.
Parts, 199 parts mixed, dilution ratio 10, 50, 100,
A 200-fold aqueous solution was prepared. The sand core prototype was dipped in this treatment solution for 1 to 2 seconds, and then dried in a circulating hot air heating furnace at 120 ° C. for 30 minutes. (Experimental Examples 2-5)

The sand core prototypes treated with sulfuric acid by the liquids having different concentrations from those not treated with the chemicals were immersed in the same coating agent for 1 to 2 seconds, and then 1
It was dried for 10 minutes in a circulating hot air heating oven at 20 ° C. 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. As shown in Table 1, the transverse rupture strength of the sand core after drying decreased in proportion to the dilution ratio. The coatings of Comparative Example and Experimental Example 5 had poor or rather good coating,
Moreover, the transverse rupture strength was also large. From this, it was estimated that the sulfuric acid dilution ratio should be 200 times or less.

[0019]

[Table 1]

The sand core was set in a mold, and aluminum alloy ADC10 was high-pressure cast under the conditions of a casting pressure of 600 kg / cm ² , a spout speed of 200 mm / sec, and a pouring temperature of 760 ° C. When sand was removed using a normal core knockout machine after casting, in the case of Experimental Examples 1 to 4, the core sand was completely removed, and an excellent cast product was obtained. In the case of Experimental Example 5, the removal of the core sand was slightly good, but in the case of the Comparative Example, the removal of the core sand was poor. Collectively, the results are shown in Table 1.

Phosphoric acid (89
%) And other treatments and operations were performed in the same manner, and excellent results were obtained as in the case of sulfuric acid. The results are shown in Table 2.

[0022]

[Table 2]

[0023]

As described above, according to the present invention, a step of molding a sand core prototype using an organic binder, a step of treating the sand core prototype with a chemical, and a sand core treated with the chemical. The step of drying the prototype, the step of coating the surface of the dried sand core prototype with a slurry-like coating agent consisting of a neutral water dispersion containing powdery refractory as a main component, and the coating Since the disintegrating sand core is manufactured by the process of drying the sand core, the sand core prototype is reduced to a desired strength in advance, and when the sand core is coated with the coating agent, the coating agent is A uniform and appropriate thickness coating layer is formed without penetrating into the child prototype. Therefore, the sand core withstands high pouring pressure during casting and has good disintegration after 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 after casting, When the sand is discharged, the sand core has a good collapsibility, so
The sand can be discharged easily, reliably and completely. Of course, no sand remains at all on the casting surface of the product after the sand is discharged, and it is very smooth. 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] October 27, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0003

[Correction method] Change

[Correction content]

Among them, as a method of solidifying sand to obtain a sand core prototype, a hard-box method, a warm box method,
There are a shell mold method, a cold box method and the like.
As the hard-dox method, for example, Japanese Examined Patent Publication No. Sho 64-989.
The technique described in Japanese Patent Publication No. 8 is known. In this method, the sand core prototype is composed of sand, an acid-curable resin and a binder containing an oxidizing agent as a main component, and is hardened by sulfur dioxide.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0005

[Correction method] Change

[Correction content]

Therefore, the present inventor has decided to reconsider the goodness of the warm box method using a curing agent instead of an oxidizing agent and sulfurous acid gas. In the warm box method, sulfurous acid gas is not used to obtain a sand core prototype by solidifying a mixture of sand and a binder. For example, a metal for sand core prototype molding heated to 90 to 240 ° C. is used. A mixture of sand and a binder is blown into the mold with compressed air and heat-cured to mold the mold. However, in this case, even if the same coating agent as the coating agent that has been used quite well in the above-mentioned hard-dox method is applied to the sand core prototype, the coating agent is not the sand core prototype. It penetrated into the inside, and a coating layer having a sufficient thickness could not be obtained. Further, the same coating agent is applied to the sand by using a core obtained by solidifying resin coated sand (RCS) obtained by coating a synthetic resin such as phenolic resin with a phenolic resin by a so-called shell mold method. Even
The coating agent didn't get wet and was repelled and didn't work.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction content]

If the sand core prototype is difficult to 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. The hydrophilic 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 for drying the sand core prototype that has been subjected to the immersion treatment, and as a guide, it is about 30 minutes at 120 ° C. The chemical may be used as it is without being diluted, and the chemical may be concentrated sulfuric acid (98
%) Or phosphoric acid (89%), in the case of a liquid, dip the sand core prototype, and in the case of fine powder such as a fine powder of acid, sprinkle the powder on the sand core prototype to remove excess powder. Wipe off. As mentioned above, when a solution with a low concentration such as dilute sulfuric acid is used, it is necessary to dry it to evaporate water, but when it is not diluted with water like concentrated sulfuric acid, it is not necessary to dry it. ..
The treated sand core prototype turned black and its transverse rupture strength decreased in proportion to the treatment concentration, but the decrease in strength is considered to be due to the progress of carbonization deterioration due to acid in the case of sulfuric acid or phosphoric acid.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction content]

(Experimental Examples 6 to 10) Phosphoric acid (89%) was used in place of the sulfuric acid of Experimental Examples 1 to 5, and the same treatment and operation were performed except for the above, and the same excellent effect as in the case of sulfuric acid was obtained. was gotten. The results are shown in Table 2.

[Procedure correction 6]

[Document name to be amended] Statement

[Name of item to be corrected] 0022

[Correction method] Change

[Correction content]

[0022]

[Table 2]

Claims (1)

[Claims] 1. A step of molding a sand core prototype using an organic binder, and a step of treating the sand core prototype with a chemical,
Drying the sand core prototype treated with this chemical, and coating the surface of the dry sand core prototype with a slurry-like coating agent consisting of a powdery refractory-based neutral water dispersion A method for producing a collapsible sand core, which comprises a step and a step of drying the sand core obtained by coating.