JPH06190496A - Production of sand core - Google Patents

Abstract

PURPOSE:To prevent the penetration of molten metal by molding a sand core prototype by using sand, a furan resin and a hardener for curing this resin by heating, then coating this sand core prototype with a slurry coating material of a water or other dispersion essentially consisting of refractories of coarse- grain size particles and fine-grain size particles. CONSTITUTION:The sand core prototype is molded by using the sand, the furan resin and the hardener for curing this resin by heating. This sand core prototype is coated with the coating material in the slurry form consisting of the water or alcohol dispersion essentially consisting of the relatively coarse powdery refractories having an average grain size of >=15% of the average grain size of the sand of the sand core and the fine powdery refractories of 20 to 100%, by weight, of these coarse powdery refractories. The sand core is produced by drying the sand core obtd. by such coating. As a result, the resulted sand core prevents the penetration of the molten metal into the sand core and the parting of the coasting material from the product after casting is facilitated.

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 coating with a coating agent obtained by mixing a coating agent with a relatively coarse particle size and a coating agent in the form of a fine powder on a sand core prototype molded by the warm box method, high pressure casting is possible. Also relates to a suitable method for producing a sand core.

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 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.

[0007]

In the present invention, sand,
A sand core prototype is molded using a furan-based resin and a curing agent for heat-curing the resin, and the average particle size on the sand core prototype is 15% or more of the average particle size of the sand in the sand core. 20% to 10% by weight of the coarse powdery refractory material and the coarse powdery refractory material.
A sand core obtained by coating with a slurry-like coating agent consisting of a water or alcohol dispersion containing 0% of a fine powdery refractory mixture having an average particle size of several μm or less as a main component. To obtain a sand core with an excellent coating.

Now, the particle size of 10 which is generally used for sand cores
The diameter of the sand core between the sand particles is 0 to 400 μm, which is made by the warm box method using sand such as natural silica sand, zircon sand or artificial sand such as Cera beads.
Voids corresponding to 5 to 60 μm are formed and are connected from the surface to the inside. In the sand core prototype with such voids,
If you try to coat a coating agent with a small particle size that can make a good coating on the sand core molded by the Hardox method, the coating agent penetrates inside the sand core and the coating agent on the surface may be a little. However, only a very thin coat can be obtained.

Therefore, it is considered that coating can be performed if the coating agent can be prevented from penetrating into the sand core prototype. That is, a coating agent obtained by mixing a coating agent (1) having a coarse particle diameter and a coating agent (2) having a small particle diameter is coated, and the voids of the sand core prototype are clogged with the coarse particle particles. If so, a sand core with an excellent coating can be obtained.

The particle size of the refractory particles necessary for filling the voids of the sand core prototype needs to be larger than the voids of the sand core prototype, and therefore the coating agent (1) is relatively composed. The average particle size of the coarse powder refractory material should be 15% or more of the average particle size of the sand core prototype sand. It is possible to draw a circumscribing sphere corresponding to 15% of the diameter of the sand when the sand is considered as a sphere in the void formed in the sand core prototype. ~ 6
This is because a void corresponding to 0 μm will be formed. Therefore, if a coating agent containing at least 15% or more of the average particle diameter of the sand core particles is used, the coating agent can be prevented from penetrating into the sand core.

The average particle size of the fine powdery refractory material constituting the coating material (2) mixed with the coating agent (1) composed of coarse powdery refractory material is several μm or less, for example, 5 μm or less.
Below μm and above 0.1 μm, coating agent (1)
The mixing ratio of coating agent (2) and
It was set to 100: 20-100. When the average particle diameter of the refractory material in the form of fine powder of the coating agent (2) becomes too large, the entire coating agent becomes too coarse, and the molten metal is inserted during casting.

A relatively coarse coating agent (1)
If the proportion of the coating agent (2) in the form of fine powder is too small, the overall particle diameter will be large and the coating material will be rough, so that the surface of the coating film may be a little rough when coated. , The coating film becomes loose, the coating film becomes less dense, the holes in the coating film become larger, the molten metal easily enters during pouring, sand sticking occurs, and the sand removal property deteriorates.

On the other hand, if the ratio of the coating agent (2) to the coating agent (1) is too large, the particle size of the entire coating agent will be small. It penetrates into the inside, the coating film is only thin and it is easy to be broken,
Therefore, when casting at high pressure, the coating film breaks and molten metal easily enters. Therefore, the mixing ratio of the coating agent (1) and the coating agent (2) is 10% by weight.
It was set to 0:20 to 100. The coating is performed by immersing the sand core prototype in the coating agent for several seconds.

The sand core coated with the coating agent as described above is then dried. The drying temperature is 90 to 150 ° C. and the drying time is about 5 to 30 minutes. May be short.

After being coated with the above coating agent, the dried sand core can be subsequently coated with a second coating agent. This coating and the subsequent drying can be performed according to the case of the above-mentioned coating.

[0016]

In this way, if the sand core prototype is coated with the coating agent containing the coating agent (1) and the coating agent (2) as the main components, the coarse particle size component in the coating agent becomes the sand core prototype. Since the voids are filled, the coating agent does not penetrate into the sand core and a thick coat layer can be obtained. Since the fine particle size component is present in this coat layer, the infiltration of the molten metal by high pressure casting is prevented, and the sand core having an excellent coating can be obtained. The second coating agent improves the mold release between the casting surface and the previous coat layer.

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 reliably and easily in a desired state. When the coated sand core obtained according to the present invention is used, the molten core is not damaged or cracked when the molten core is poured under high pressure like high pressure die casting, and the molten core is It does not infiltrate the child.

[0018]

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 mold for core molding is, for example, 90 to 240 ° C., preferably about 90 to 200 ° C., and it is heated for about 1 minute to cure the sand core mold to a predetermined strength. . For example, transverse strength 2
A sand core prototype of 0 to 50 kg was obtained.

Next, the surface of the sand core prototype 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 first coating agent containing the coating agents (1) and (2) as a main component is prepared by mixing the coating agent (1) having a relatively coarse particle size and the coating agent (2) having a fine particle size. . The coating agent (1) having a relatively coarse particle size has an average particle size of 15 μm or more,
This is a slurry composed of an aqueous dispersion containing powder silica and alumina of 50 μm or less as main components and having a solid content of 30 to 90% by weight.

On the other hand, the coating agent (2) having a fine particle size has an average particle size of several μm, for example, 0.1 to 5 μm.
This is a slurry of an aqueous dispersion containing 30 to 90% by weight of solid content, which is composed mainly of finely divided silica and finely divided alumina, and to which a small amount of colloidal silica is added. The mixing ratio of the coating agent (1) having a coarse particle diameter and the coating agent (2) having a fine particle diameter is 100 parts by weight of the former and 20 to 20% for the latter.
It is 100% by weight. If it is less than 20% by weight, the coarse particle size component increases, so that the molten iron is inserted into the sand core,
On the other hand, if it exceeds 100% by weight, the amount of fine components increases, so that the penetration of the coating agent into the sand core prototype increases,
A thick coat layer cannot be obtained.

Other coating agents may be used as the coating agent (2) having a fine particle size. 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,
An inorganic binder such as colloidal silica, alumina sol, clay and amine-treated bentonite may be used, which is composed of about 1 to 25% by weight of water and water. 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 second coating agent was an isopropanol slurry containing scaly aluminum powder having a particle size of 5 μm as a main component and sodium dodecylbenzenesulfonate as a wetting agent, and the solid content was 5 to 20% by weight. When the solid content is less than 5% by weight, the coating layer becomes thin,
If it exceeds 20% by weight, the coat thickness becomes unnecessarily thick.

The second coating agent is, for example, 1 liter of a 3% water-soluble phenol resin solution, 500 g of mica powder, 10 g of sodium dodecylbenzenesulfonate as a wetting agent, and 1 octyl alcohol as a defoaming agent. It is also possible to use a mixture in which gram is well stirred and mixed. This coating is performed by immersing the sand core prototype after finishing the first layer coating in a second coating agent, brushing or spraying the second coating agent on the surface of the sand core prototype, and then drying. To form.

As a more detailed example, an experimental example will be shown below. [Experimental Examples 1 to 4 and Comparative Examples 1 to 3] 100 parts of flat sand as an aggregate, and a furan resin of 1.5 as an organic binder.
, A commercially available curing agent containing paratoluene sulfonate as a main component as a curing agent for furan resin (Kao Quaker Product F
C-100, main component paratoluenesulfonic acid copper salt) 0.
6 parts and commercially available additives (Kao Quaker Product J-
20, main component silane compound) 0.06 parts were mixed, and a plurality of sand core molds for engine blocks having a weight of about 2 kg were molded by the warm box method. Molding conditions are mold temperature 120
The temperature was 90 ° C., the blowing pressure was 4.5 kg / cm ² , and the heating time was 90 seconds. The bending strength of the sand core prototype after standing for 1 day is 35 kg.
Met.

The first coating agent was a coating agent (1) having a relatively coarse particle diameter, which contained powder silica and alumina as main components (average particle diameter: 20 μm), and an aqueous dispersion having a solid content of 70% by weight. , Fine powder silica and fine powder alumina as main components (average particle diameter: 1.4 μm) as a coating agent (2) having a fine particle diameter, and solid content of 85% by weight
20 parts of the latter with respect to 100 parts by weight of the former.
It was prepared by blending 100% by weight.

The second coating agent has an average particle size of 5 μm
Isopropanol slurry containing the scaly aluminum powder of No. 3 as a main component and sodium dodecylbenzenesulfonate as a wetting agent, and the solid content was 15% by weight.

The coating is performed by first immersing the sand core prototype in the first coating agent for 2 to 3 seconds, pulling it up, and
It was dried in a hot air drying oven at 20 ° C. for 5 minutes. Then, the second
After being immersed in the coating agent of No. 2 for 2 to 3 seconds, it was pulled out and left in the room to be dried (Experimental Examples 1 to 4).

On the other hand, as the first coating agent, only the coating agent (1) having a coarse particle size, 100% by weight of the coating agent (1) having a coarse particle size and 110% by weight of the coating agent (2) having a fine particle size are mixed. The individual sand core prototypes were coated with only the coating agent prepared in step 1 and the fine coating agent (2), and after drying, the second
Was coated and dried (Comparative Examples 1, 2, 3).

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 4, the core sand was completely removed and an excellent cast product was obtained. However, in Comparative Examples 1, 2, and 3, the sand removal property was poor, and seizure of sand occurred. The results are shown in Table 1.

[0031]

[Table 1] Note) Coating agent (1): coating agent having an average particle size of 20 μm Coating agent (2): coating agent having an average particle size of 1.4 μm The mixing ratio of coating agent (1) and coating agent (2) is% by weight. Good, △ Some problem, × Bad

[0032]

As described above, according to the present invention, a sand core prototype is formed using sand, a furan-based resin, and a curing agent for heat curing of the resin, and an average particle size is formed on the sand core prototype. The weight% of the relatively coarse powdery refractory having a mean particle size of 15% or more of the sand core sand and the coarse powdery refractory is 20 to 100.
% Of a fine powder refractory material as a main component is coated with a slurry-like coating agent consisting of a water or alcohol dispersion, and the sand core obtained by this coating is dried. Since the coating is performed, a sand core having an excellent coating can be obtained. 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 iron 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 18, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0015

[Correction method] Change

[Correction content]

After being coated with the above coating agent, the dried sand core can be subsequently coated with a second coating agent composed of scaly aluminum, mica powder or the like. This coating and the subsequent drying can be carried out according to the above-mentioned coating.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction content]

[0018]

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-based resin, furfuryl alcohol-formaldehyde resin, furfuryl alcohol-urea-formaldehyde resin, full-furyl alcohol. 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.

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] 0029

[Correction method] Change

[Correction content]

On the other hand, as the first coating agent, only the coating agent having a coarse particle size (1) or the coating agent having a coarse particle size (1) 100% by weight is used as the fine coating agent. (2) An individual sand core prototype is coated using only the coating agent prepared by blending 130% by weight and the coating agent (2) having a fine particle size, and after drying,
A second coating was performed and dried (Comparative Examples 1, 2,
3).

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0031

[Correction method] Change

[Correction content]

[0031]

[Table 1] Note) Coating agent (1): coating agent having an average particle size of 20 μm Coating agent (2): coating agent having an average particle size of 1.4 μm Coating agent (1) and coating agent The mixing ratio of the coating agent (2) is% by weight. ○ Good, △ Slightly problematic, × Poor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsu Kunimura 3-10 Nakamiyakitamachi, Hirakata-shi, Osaka Ube Industries Ltd. Hirakata Research Laboratory

Claims (1)

[Claims] 1. A sand core prototype is formed using sand, a furan-based resin, and a curing agent for heat curing of the resin, and an average particle size of sand having an average particle size of sand is found on the sand core prototype. Of 15% or more of a relatively coarse powdered refractory and a fine powdered refractory mixture of 20% to 100% by weight of the coarse powdered refractory as a main component of water or alcohol dispersion A method for producing a sand core, which comprises coating a slurry-like coating agent comprising, and drying the sand core obtained by the coating.