JP2929584B2 - 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 forming a semi-permeable membrane made of calcium alginate on a sand core prototype formed by the warm box method, 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 method for manufacturing a sand core.
Here, the excellent 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 and spread inside the sand core prototype, or It is formed to a uniform thickness with a predetermined thickness, uniformly, reliably and easily without being repelled from the surface of the sand core prototype, and over the entire surface layer 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 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,
A step of molding a sand core prototype using a furan resin and a curing agent for heat curing the resin, a step of forming a semi-permeable membrane of calcium alginate on the sand core prototype, and a step of forming a semi-permeable membrane of calcium alginate. Drying the sand core prototype with the permeable membrane, and coating the surface of the dried sand core prototype with a slurry-like coating agent composed of a neutral aqueous dispersion mainly composed of a powdered refractory. A sand core having an excellent coating is obtained by the step of drying the sand core obtained by coating. In order to form a semipermeable membrane made of calcium alginate on the sand core prototype, the sand core prototype must first be prepared by adding an inorganic calcium salt aqueous solution such as calcium chloride, calcium sulfate, calcium carbonate, or calcium acetate, acrylic It is immersed in an aqueous solution of an organic calcium salt such as calcium acid. Next, the sand core prototype treated in the aqueous solution of an inorganic or organic calcium salt is immersed in an aqueous solution of alginate other than calcium alginate, such as sodium alginate, ammonium alginate, and potassium alginate.

As another method of forming a semipermeable membrane made of calcium alginate on a sand core prototype, a sand core prototype is first immersed in an alginate aqueous solution such as a sodium alginate aqueous solution. Thereafter, for example, immersion in an inorganic or organic calcium salt aqueous solution such as an aqueous solution of calcium chloride or calcium acetate. The sand core prototype is mixed with an inorganic or organic calcium salt such as, for example, calcium chloride or calcium acetate. Immersion in a mixed aqueous solution of alginate such as sodium alginate.

[0008]

In the present invention, for example, after a sand core prototype is formed as described above, the sand core prototype is placed in an inorganic calcium salt aqueous solution such as a calcium chloride aqueous solution or an organic calcium salt aqueous solution such as a calcium acetate aqueous solution. Immersed in an aqueous solution of calcium salt, then immersed in an aqueous solution of alginate other than calcium alginate, such as an aqueous solution of sodium alginate, to form a semipermeable membrane of calcium alginate on the sand core prototype, and then Dry the prototype. Next, a slurry coating consisting of a neutral aqueous dispersion mainly composed of powdered refractory is applied to the surface of the sand core prototype obtained by forming and drying a semi-permeable membrane made of calcium alginate. Coating.

In this case, if the molded sand core prototype is immersed in an aqueous solution of an inorganic calcium salt such as an aqueous solution of calcium chloride or an aqueous solution of an organic calcium salt such as an aqueous solution of calcium acetate before coating, the sand core can be immersed in the sand. Inorganic or organic calcium salts adhere to or penetrate into the surface layer of the prototype. After this sand core prototype is pulled up from the immersion tank, it is then immersed in an alginate aqueous solution other than calcium alginate such as sodium alginate aqueous solution, and the alginate adheres to the surface layer and inside of the sand core prototype. Or soak. As a result, Ca ²⁺ reacts with the alginate to form a semi-permeable membrane made of water-insoluble calcium alginate. When this sand core prototype is pulled up from the immersion tank and dried at 80 to 200 ° C. for several minutes to 2 hours, a semi-permeable membrane made of calcium alginate is uniformly formed on the sand core prototype.

On the other hand, a slurry-like coating agent composed of a neutral aqueous dispersion mainly composed of a powdered refractory is applied to the sand core prototype on which the semi-permeable membrane composed of calcium alginate is formed. Then, the hydrophilic semi-permeable membrane made of calcium alginate formed on the sand core prototype can prevent the coating agent from penetrating deep inside the sand core prototype, and can be applied to the surface of the sand core prototype. Can be coated thickly. That is, among the constituents of the coating agent, only water permeates the semipermeable membrane, and does not transmit the powdered refractory. Thereafter, when this is dried, a homogeneous coating layer having a desired thickness is formed.

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 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.

[0012]

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 an inorganic or organic calcium salt. Examples of the inorganic calcium salt include calcium chloride, calcium sulfate, calcium carbonate, and the like, and examples of the organic calcium salt include calcium acetate, calcium acrylate, and the like. The sand core prototype is immersed in an aqueous solution of these inorganic or organic calcium salts, absorbed by the sand core prototype, and then dried by heating. In this case, heat drying may or may not be performed, but heat drying is more preferable. Thereafter, the sand core prototype treated in an aqueous solution of an inorganic or organic calcium salt is then treated with an aqueous solution of an alginate other than calcium alginate.

Examples of the alginate include sodium alginate, ammonium alginate, potassium alginate and the like. The sand core prototype treated in an aqueous solution of an inorganic or organic calcium salt is immersed in an aqueous solution of an alginate other than these calcium alginate, absorbed by the sand core prototype, and then dried by heating. The respective concentrations of the inorganic or organic calcium salt aqueous solution and the alginate aqueous solution other than calcium alginate are determined by the dilution factor of 50.
It is within 0 times. If each dilution ratio exceeds 500 times, a semipermeable membrane made of calcium alginate will not be formed, or even if the semipermeable membrane is thin, the coating thickness will be thin and the treatment effect will be 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 and then 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.

It should be noted that 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 treatment for forming a semi-permeable membrane made of calcium alginate is then immersed in the coating agent for several seconds, followed by immersing the heat-dried sand core prototype for several seconds, followed by heat drying. Drying conditions are about 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 when no treatment for forming a semi-permeable membrane made of calcium alginate is performed, whereas it is sufficiently thick. There is no penetration into the child prototype, and the coating is firm. The coating layer may be one layer, but in order to improve the releasability between the product and the coating layer,
Two layers are more preferred. As a coating agent for forming the second coating layer, for example, mica powder 50 per 1 liter of a 3% aqueous phenol resin solution is used.
0 g, 10 g of sodium dodecylbenzenesulfonate as a wetting agent, and 1 g of octyl alcohol as a defoaming agent are well stirred and mixed. This coating can be performed by dipping the sand core prototype after the first layer coating in the second layer coating agent,
A second layer coating agent is brushed or sprayed on the surface of the sand core prototype, and then dried to form a coating.

An experimental example will be described below as a more detailed example. (Experimental Examples 1 to 9 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 p-toluenesulfonic 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 them was prepared without performing any treatment for forming a semipermeable membrane composed of calcium alginate described below.
Since the same coating as that in this experimental example was performed, the results are shown in Table 1 below as a comparative example.

299 parts of water are added to 1 part of calcium chloride,
399 parts, 499 parts mixed, dilution ratio 300, 40
A 0,500-fold aqueous solution was prepared. After the sand core prototype was immersed in this aqueous solution for 1 to 2 seconds, it was dried in a hot air circulating heating furnace at 120 ° C. for 30 minutes. Next, 1 part of sodium alginate was mixed with 299 parts, 399 parts, and 499 times of water, respectively, to prepare aqueous solutions having dilution ratios of 300, 400, and 500 times, respectively. The sand core prototype treated with the aqueous calcium chloride solution was immersed in the aqueous solution for 1 to 2 seconds, and then dried in a hot air circulating heating furnace at 120 ° C. for 30 minutes.
(Experimental Examples 1 to 9)

The sand core prototypes treated with calcium chloride and then sodium alginate with liquids having different concentrations from those not subjected to the calcium chloride treatment and then the sodium alginate treatment are immersed in the same coating agent for 1 to 2 seconds. After that, it was dried in a circulating hot air heating furnace at 120 ° 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 the pH was adjusted to 7.2. The coatings of the comparative examples and those of Experimental Examples 5 to 9 had poor or slightly good coating. As a result, the dilution ratio of calcium chloride and sodium alginate was 450 to 5 respectively.
It was estimated that 00 times or less was good.

After the completion of 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, margin)

[0024]

[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 Experimental Examples 5 to 9, 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 10 to 18) When calcium acetate was used in place of calcium chloride in Experimental Examples 1 to 9 and the other treatment and operation were performed in exactly the same manner, excellent results were obtained as in the case of calcium chloride. Obtained. Table 2 shows the results. (Hereinafter, margin)

[0027]

[Table 2]

(Experimental Examples 19 to 27) When ammonium alginate was used in place of sodium alginate in Experimental Examples 1 to 9 and the other treatment and operation were carried out in exactly the same manner, excellent results were obtained as in the case of sodium alginate. Obtained. Table 3 shows the results. (Hereinafter, margin)

[0029]

[Table 3]

(Experimental Examples 28 to 36) When calcium acetate was used instead of calcium chloride and ammonium alginate was used instead of sodium alginate in Experimental Examples 1 to 9, except that the treatment and operation were performed in exactly the same manner. Excellent results were obtained as with calcium and sodium alginate. Table 4 shows the results. (Hereinafter, margin)

[0031]

[Table 4]

[0032]

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 the resin, and a step of forming calcium alginate on the sand core prototype. Forming a semipermeable membrane, drying the sand core prototype having the calcium alginate semipermeable membrane formed thereon, and using a powdered refractory as a main component on the surface of the dried sand core prototype. The coated sand core is manufactured by a step of coating a slurry-like coating agent composed of a neutral aqueous dispersion to be dried and a step of drying the sand core prototype obtained by coating. When coating with, the coating agent does not penetrate into the sand core prototype, but forms a coating layer of uniform and appropriate thickness. 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 the 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.

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 forming a semi-permeable membrane made of calcium alginate on the sand core prototype. Drying the sand core prototype on which the semipermeable membrane made of calcium alginate is formed, and a slurry comprising a powdered refractory-based neutral aqueous dispersion on the surface of the dried sand core prototype. A method for producing a sand core, comprising the steps of: coating a coating agent in a shape; and drying the sand core obtained by coating.