JP7121580B2 - Mold manufacturing method - Google Patents

Description

The present invention relates to a mold manufacturing method.

A mold is required to produce a casting. There are normal molds and special molds for molds, and there are green molds and dry molds for normal molds. On the other hand, special molds include thermosetting molds, self-hardening molds, and gas-hardening molds. For example, bentonite-based green molds are generally used for mass production of castings, and shell molds, which are thermosetting molds, are generally used for cores used when manufacturing castings with hollow parts or internal structures. Adopted. Self-hardening molds and gas hardening molds are mainly used for high-mix low-volume production.

Refractory granular material such as silica sand is used as the material for the mold, but because the refractory granular material alone tends to crumble when dried, a binder is added to prevent crumbling.
Clays such as bentonite are commonly used as binders in molds. On the other hand, for special molds, organic binders such as phenol resin, furan resin, and urethane resin, and inorganic binders such as water glass are used.

A liquid obtained by melting a metal such as iron, copper, or aluminum at a high temperature is poured into a mold manufactured by various methods to obtain a casting. The casting is removed by dismantling the mold. It is also common to reclaim the refractory particulate material from dismantled molds and reuse it in the manufacture of molds.
Organic binders are excellent in handleability and easy to mold. Moreover, the mold using the organic binder is excellent in collapsibility at the time of dismantling. However, the organic binder tends to thermally decompose during pouring to generate gas (thermal decomposition gas), which tends to cause defects in castings and worsen the working environment.

On the other hand, in a mold using an inorganic binder, the inorganic binder is less likely to be thermally decomposed, so that the thermal decomposition gas of the binder is less likely to be generated during pouring. However, inorganic binders are inferior to organic binders in handleability and are not easy to mold. In addition, a mold using an inorganic binder is less likely to decrease in strength after pouring and is less likely to collapse (becomes inferior in disintegration), and thus is more difficult to dismantle than a mold using an organic binder.

As a method for improving the collapsibility of a mold using an inorganic binder, a method using both water glass and an organic binder has been proposed (Patent Document 1).
A method using a binder-coated refractory in which a coating layer is formed on the surface of a refractory granular material has also been proposed (Patent Document 2). The coating layer contains a water-soluble inorganic compound as a binder.
Furthermore, a method of producing a salt core by pouring heat-melted salt into an iron mold and solidifying the salt in the mold has been proposed (Patent Document 3).

JP-A-4-59148 Japanese Patent No. 5933169 Japanese Patent No. 4000106

However, the method of using both water glass and an organic binder as described in Patent Document 1 has not sufficiently improved the collapsibility of the mold after casting.
In the binder-coated refractory described in Patent Document 2, the strength of the mold itself is insufficient.
In the method described in Patent Document 3, it is necessary to use a metal mold such as an iron mold as a mold that can withstand heat-melted salt, and there are restrictions on mold making molds.

The present invention has been made in view of the above circumstances. An object of the present invention is to provide a manufacturing method without being restricted by molds for mold making.

The present invention has the following aspects.
[1] A primary molded body which is a cured product of a mixture containing a refractory granular material and an organic binder, and which contains a water-soluble inorganic salt. A method for manufacturing a mold, which is fired at a decomposition temperature or higher.
[2] The mixture includes a refractory granular material, the organic binder, and the water-soluble inorganic salt. The mold manufacturing method according to [1], wherein a primary compact is obtained.
[3] The mixture is filled in a mold for molding, the organic binder is cured to obtain the cured product, and the obtained cured product is impregnated with the water-soluble inorganic salt to form the primary compact. The method for producing a mold according to [1], wherein
[4] The method for producing a mold according to any one of [1] to [3], wherein the water-soluble inorganic salt is at least one of an alkali metal salt and an alkaline earth metal salt.
[5] When the total content of the refractory granular material and the water-soluble inorganic salt is 100% by mass, the content of the water-soluble inorganic salt is 3 to 30% by mass, [1]- [4] A method for manufacturing a mold according to any one of [4].

According to the mold manufacturing method of the present invention, a mold that maintains sufficient strength until casting, is excellent in collapsibility after casting, and is less likely to generate pyrolysis gas of the binder during casting is produced. It can be manufactured without being restricted by the type of application.

[Mold manufacturing method]
In the method for producing a casting mold of the present invention, a casting mold is obtained by firing a primary compact which is a cured mixture containing a refractory granular material and an organic binder and which contains a water-soluble inorganic salt (firing step). .
A curing agent may be used in combination with the refractory granular material, the organic binder and the water-soluble inorganic salt when manufacturing the mold.
In addition, the primary compact may contain components (optional components) other than the refractory granular material, the organic binder, the water-soluble inorganic salt and the curing agent, if necessary.

<Refractory granular material>
As the refractory granular material, conventionally known materials such as natural sand such as silica sand, chromite sand, zircon sand, olivine sand, alumina sand and mullite sand; artificial sand and the like can be used. In addition, used refractory granular material recovered (recovered sand) or reclaimed (reclaimed sand) can also be used.
These refractory granular materials may be used singly or in combination of two or more.

<Organic binder>
Examples of organic binders include binders used when manufacturing molds by the shell mold method, binders used when manufacturing molds by the amine cold box method, alkali phenol resins, and acid-curable binders. etc.
These organic binders may be used individually by 1 type, and may be used in combination of 2 or more types.

Examples of binders used in producing molds by the shell molding method include novolac-type phenolic resins and resol-type phenolic resins.
Novolak-type phenolic resins are obtained by reacting phenols and aldehydes in the presence of an acidic catalyst, and are usually solid.
Examples of phenols include phenol, o-cresol, m-cresol, p-cresol, 2,3-xylenol, 3,5-xylenol, m-ethylphenol, m-propylphenol, m-butylphenol, p-butylphenol, o-butylphenol, resorcinol, hydroquinone, catechol, 3-methoxyphenol, 4-methoxyphenol, 3-methylcatechol, 4-methylcatechol, methylhydroquinone, 2-methylresorcinol, 2,3-dimethylhydroquinone, 2,5-dimethyl resorcinol, 2-ethoxyphenol, 4-ethoxyphenol, 4-ethylresorcinol, 3-ethoxy-4-methoxyphenol, 2-propenylphenol, 2-isopropylphenol, 3-isopropylphenol, 4-isopropylphenol, 3,4, 5-trimethylphenol, 2-isopropoxyphenol, 4-pyropoxyphenol, 2-allylphenol, 3,4,5-trimethoxyphenol, 4-isopropyl-3-methylphenol, pyrogallol, phloroglicinol, 1,2 , 4-benzenetriol, 5-isopropyl-3-methylphenol, 4-butoxyphenol, 4-t-butylcatechol, t-butylhydroquinone, 4-t-pentylphenol, 2-t-butyl-5-methylphenol, 2-phenylphenol, 3-phenylphenol, 4-phenylphenol, 3-phenoxyphenol, 4-phenoxyphenol, 4-hexyloxyphenol, 4-hexanoylresorcinol, 3,5-diisopropylcatechol, 4-hexylresorcinol, 4-heptyloxyphenol, 3,5-di-t-butylphenol, 3,5-di-t-butylcatechol, 2,5-di-t-butylhydroquinone, di-sec-butylphenol, 4-cumylphenol, nonylphenol, 2-cyclopentylphenol, 4-cyclopentylphenol, bisphenol A, bisphenol F and the like. These phenols may be used singly or in combination of two or more.

Examples of aldehydes include formaldehyde, trioxane, furfural, paraformaldehyde, benzaldehyde, methylhemiformal, ethylhemiformal, propylhemiformal, salicylaldehyde, glyoxal, butylhemiformal, phenylhemiformal, acetaldehyde, propylaldehyde, phenylacetaldehyde, α-phenylpropylaldehyde, β-phenylpropylaldehyde, o-hydroxybenzaldehyde, m-hydroxybenzaldehyde, p-hydroxybenzaldehyde, o-chlorobenzaldehyde, o-nitrobenzaldehyde, m-nitrobenzaldehyde, p-nitrobenzaldehyde, o-methyl benzaldehyde, m-methylbenzaldehyde, p-methylbenzaldehyde, p-ethylbenzaldehyde, pn-butylbenzaldehyde and the like. These aldehydes may be used individually by 1 type, and may use 2 or more types together.
Examples of acidic catalysts include hydrochloric acid, sulfuric acid, phosphoric acid, formic acid, acetic acid, oxalic acid, butyric acid, lactic acid, benzenesulfonic acid, p-toluenesulfonic acid and boric acid. These acidic catalysts may be used singly or in combination of two or more. Metal salts such as zinc chloride or zinc acetate may also be used, or used in combination with an acidic catalyst.

A silane coupling agent is often added to the novolac-type phenolic resin during the manufacturing process of the novolac-type phenolic resin for the purpose of improving the mold strength. If the silane coupling agent is not blended in the manufacturing process, the novolak phenolic resin and the silane coupling agent may be used together.
Silane coupling agents include, for example, γ-aminopropyltriethoxysilane and γ-glycidoxypropyltrimethoxysilane.

A resol-type phenolic resin is obtained by reacting phenols and aldehydes in the presence of a basic catalyst.
Phenols and aldehydes include the phenols and aldehydes exemplified above in the description of the novolak-type phenolic resin.
Examples of basic catalysts include sodium hydroxide, potassium hydroxide, ammonia, hexamine, and amines. These basic catalysts may be used singly or in combination of two or more.

A resol-type phenolic resin is usually obtained in a state of being dispersed in a solvent such as water (hereinafter, a resol-type phenolic resin in this state is referred to as a "liquid resol-type phenolic resin").
The resol-type phenolic resin may be used in a liquid state, or the liquid resol-type phenolic resin may be subjected to a dehydration treatment or the like to remove the solvent, and dried at room temperature to be used in a solid state.
A silane coupling agent is often added to the resol-type phenolic resin during the manufacturing process of the resol-type phenolic resin for the purpose of improving mold strength. If the silane coupling agent is not blended in the manufacturing process, the resol-type phenolic resin and the silane coupling agent may be used together.

Examples of the binder used in producing a mold by the amine cold box method include a two-liquid binder composed of a phenol resin solution and a polyisocyanate solution using an organic solvent as a solvent.

The alkali phenol resin is prepared by a conventional method in the presence of an alkali metal hydroxide, with one or more selected from the group consisting of phenols and bisphenols (hereinafter referred to as "phenol compounds") and aldehydes. is obtained by reacting in an aqueous system.
Phenols and aldehydes include the phenols and aldehydes exemplified above in the description of the novolak-type phenolic resin.
Examples of bisphenols include bisphenol A, bisphenol F, bisphenol C, bisphenol S, bisphenol Z and the like.

As the phenolic compound, either one of phenols and bisphenols may be used alone, or a mixture of phenols and bisphenols may be used.

Examples of alkali metal hydroxides include sodium hydroxide, potassium hydroxide, and lithium hydroxide. Among these, sodium hydroxide and potassium hydroxide are preferred. These alkali metal hydroxides may be used singly or in combination of two or more.

In addition, when reacting the phenol-based compound and the aldehydes, a monomer capable of condensing with the aldehyde (for example, urea, cyclohexanone, melamine, etc.) may be added to the reaction system. Alternatively, the obtained alkali phenol resin may be diluted with a monohydric alcohol (eg, methanol, ethanol, propanol, etc.) to a desired concentration.

Examples of acid-curable resins include furfuryl alcohol and furan resin. Moreover, you may use the resol type phenol resin illustrated previously as an acid hardening resin.
Among these, furan resin is preferred.
The furan resin is a resin mainly composed of furfuryl alcohol, urea, phenols, formaldehyde, etc., and is cured by polycondensation while being dehydrated with an acid.
Furan resins include one or more selected from the group consisting of furfuryl alcohol, phenols and urea, and one or more condensates or cocondensates of aldehydes, and furfuryl alcohol. It is preferable to use those containing.
Phenols and aldehydes include the phenols and aldehydes exemplified above in the description of the novolak-type phenolic resin.

The following four are mentioned as particularly preferable aspects of the acid-curable resin. In addition, the (co)condensate below means at least one of a condensate and a cocondensate.
i) A (co)condensate obtained by condensing urea, furfuryl alcohol and aldehydes, and a mixture of furfuryl alcohol.
ii) A mixture of condensates of urea and aldehydes and furfuryl alcohol.
iii) mixtures of (co)condensates obtained by condensing urea, furfuryl alcohol and aldehydes, condensates of phenols and aldehydes, and furfuryl alcohol.
iv) mixtures of condensates of phenols and aldehydes and furfuryl alcohol.
When the acid-curable binder is in the above aspects i) to iv), the pot life can be set more easily and the mold strength can be further improved.

An acid-hardening binder can be obtained by a general manufacturing method. An example is shown below.
First, raw materials for acid-curable resins (furfuryl alcohol, aldehydes, urea, phenols, etc.) are mixed, an aqueous solution of a basic catalyst is added, and the pH of the mixture is adjusted to 9-11 to make it alkaline. Next, the mixture is heated to cause an addition reaction between urea and aldehydes to produce a reaction product (first step). An acidic catalyst is added to the obtained reaction solution to adjust the pH of the reaction solution to 2 to 5 to make it acidic, and the condensation reaction of the addition reaction product of urea and aldehydes proceeds (second step). After that, an aqueous solution of a basic catalyst is added to the reaction solution, the pH of the reaction solution is adjusted to 7 to 10 to make it alkaline, additives are mixed and reacted (third step), and additives are added as necessary. A further addition results in a reaction product containing an acid-curable resin.

Examples of the basic catalyst include the basic catalysts exemplified above in the description of the resol-type phenolic resin.
The acidic catalyst includes, for example, the acidic catalysts exemplified above in the description of the novolac-type phenolic resin. Since the amount of the acid catalyst added is small, the curing reaction does not proceed.
Examples of additives include silane coupling agents and formaldehyde reducing agents.
Examples of the silane coupling agent include the silane coupling agents exemplified above in the description of the novolak-type phenol resin.
The formaldehyde reducing agent is for reducing formaldehyde generated during mold making. Formaldehyde reducing agents include urea, resorcinol, gallic acid, pyrogallol, and the like.

<Water-soluble inorganic salt>
Water-soluble inorganic salts act as inorganic binders.
In the present invention, "water-soluble" means that the solubility in water at 20°C is 2 g/100 mL or more.
Examples of water-soluble inorganic salts include alkali metal salts and alkaline earth metal salts. These water-soluble inorganic salts may be used singly or in combination of two or more.

Alkali metal salts include, for example, sodium chloride, potassium chloride, sodium tetraborate, sodium sulfate, sodium carbonate, potassium carbonate, sodium phosphate and the like. These alkali metal salts may be used singly or in combination of two or more.
Alkaline earth metal salts include, for example, magnesium chloride, calcium chloride, and magnesium phosphate. These alkaline earth metal salts may be used singly or in combination of two or more.
Among these, as the water-soluble inorganic salt, it is preferable to use a water-soluble inorganic salt having a thermal decomposition temperature higher than that of the organic binder. Chlorides such as calcium chloride are more preferred. Among these, sodium chloride and potassium chloride are particularly preferred in terms of low deliquescence and easy handling.

<Curing agent>
The curing agent may be selected from known curing agents according to the type of organic binder and curing method.
For example, in the case of using a binder that is used in manufacturing a mold by the shell mold method as the organic binder, hexamethylenetetramine is preferred as the curing agent.
When using the binder used when producing a mold by the amine cold box method as the organic binder, the curing agent is preferably an amine gas such as triethylamine or diethylamine. These curing agents may be used singly or in combination of two or more.
When an alkali phenol resin is used as an organic binder, curing agents include methyl formate, ethyl formate, triacetin, diacetin, monoacetin, ethylene glycol diacetate, ethylene glycol monoacetate, γ-butyrolactone, Propiolactone, ε-caprolactone and the like are preferred. In the gas curing mold making method, highly volatile esters are preferred, and methyl formate and the like are more preferred.
When an acid-curable resin is used as the organic binder, inorganic acids such as sulfuric acid, phosphoric acid, and hydrochloric acid are used as the curing agent; etc.), carboxylic acids (eg, formic acid, acetic acid, oxalic acid, lactic acid, maleic acid, malic acid, citric acid, tartaric acid, malonic acid, succinic acid, benzoic acid, etc.). These curing agents may be used singly or in combination of two or more.

When a mold is produced by a thermosetting mold making method or a self-hardening mold making method, the curing agent can be used in the form of an aqueous solution, that is, as an aqueous curing agent solution.
The content of the curing agent with respect to the total mass of the aqueous curing agent solution is preferably 20 to 75% by mass, more preferably 30 to 70% by mass.
The water content is preferably 25 to 80% by mass, more preferably 30 to 70% by mass, relative to the total mass of the aqueous curing agent solution.
The aqueous curing agent solution may contain a solvent (another solvent) other than water, and examples of other solvents include alcohols such as methanol, ethanol, and butanol.

<Optional component>
Optional components include, for example, silane coupling agents, lubricants, disintegrants, and curing accelerators.
Examples of the silane coupling agent include the silane coupling agents exemplified above in the description of the novolak-type phenol resin.
Examples of lubricants include fatty acid amides and calcium stearate.
Disintegrants include, for example, nitrates.
Examples of hardening accelerators include benzoic acid and salicylic acid.

<Primary compact>
The primary molding is a hardened mixture containing a refractory granular material and an organic binder, and contains a water-soluble inorganic salt. The primary molded article may further contain optional components.
The primary molding is an intermediate body of the mold, in which refractory granular materials are adhered together by a cured organic binder.
Examples of the method for producing the primary molded body include the methods shown below.

(First aspect)
A method for producing a primary compact according to the first aspect includes a mixture (hereinafter referred to as "mixture (A)") containing a refractory granular material, an organic binder, a water-soluble inorganic salt, and optionally optional ingredients. ) is filled into a casting mold and the organic binder is cured.
The mold for casting is not particularly limited, and any of wooden molds, resin molds and metal molds may be used.

The content of the organic binder in the mixture (A) is preferably 0.1 to 5 parts by mass, and 0.5 to 3.5 parts by mass is more preferable. If the content of the organic binder is at least the above lower limit, sufficient strength can be maintained until the primary compact is fired. If the content of the organic binder is equal to or less than the above upper limit, the organic binder is thermally decomposed and gasified in a short time of baking, and hardly remains in the mold, although the details will be described later.
The content of the water-soluble inorganic salt in the mixture (A) is 3 to 30% by mass when the total content of the refractory granular material and the water-soluble inorganic salt is 100% by mass. %, more preferably 10 to 20% by mass. If the content of the water-soluble inorganic salt is at least the above lower limit, a mold with higher strength can be easily obtained. If the content of the water-soluble inorganic salt is equal to or less than the above upper limit, the disintegrability of the mold after casting can be maintained satisfactorily.

Mixture (A) can be prepared, for example, by mixing a refractory particulate material, a water-soluble inorganic salt, an organic binder and optional ingredients. The mixture (A) thus obtained is also called "kneaded sand".
Alternatively, for example, a refractory granular material is heated to a predetermined temperature, and the heated refractory granular material, a water-soluble inorganic salt, an organic binder, and optionally optional ingredients are mixed to obtain The mixture (a1) may be cooled to produce the mixture (A). Optional ingredients may be added after cooling the mixture (a1). The heating temperature of the refractory granular material is preferably higher than the melting point of the organic binder, usually 100-150°C. By preheating the refractory granular material, the organic binder melts when mixed with the organic binder, and the surfaces of the refractory granular material and the water-soluble inorganic salt are coated with the organic binder. . The mixture (A) thus obtained is also called "coated sand".

Methods for curing the organic binder include heat curing, normal temperature curing, gas curing and the like. Here, "normal temperature curing" means curing at normal temperature without external heating or gas ventilation.
When the organic binder is cured by thermosetting or normal temperature curing, that is, when the mold is produced by a thermosetting mold making method or a self-hardening mold making method, the mixture (A) preferably contains a curing agent. Hereinafter, the mixture (A) containing the curing agent is also particularly referred to as "mixture (A1)".
The content of the curing agent in the mixture (A1) is preferably 0.1 to 0.5 parts by mass, and 0.2 to 0 .4 parts by weight is more preferred. If the content of the curing agent is within the above range, a mold with higher strength can be easily obtained.

The mixture (A1) can be produced using an aqueous curing agent solution, for example, as follows.
When the mixture (A1) is kneaded sand, the mixture ( A1) is obtained.
When the mixture (A1) is coated sand, for example, an aqueous hardening agent solution is added to the mixture (a1) described above, and the resulting mass (a2) is cooled to disintegrate into granules to obtain the mixture (A1). The optional component may be added at the same timing as the aqueous curing agent solution is added to the mixture (a1), or may be added after the aggregate (a2) is disintegrated into granules by cooling.

When the organic binder is cured by gas curing, that is, when the mold is produced by the gas curing mold making method, the mixture (A) is filled in the mold for making the mold, and the gaseous curing agent is passed through to form the organic binder. Allow the binder to harden.
The aeration flow rate and aeration time of the gaseous curing agent are not particularly limited as long as they are within the ranges of the aeration flow rate and aeration time in a normal gas curing mold making method.

By curing the organic binder by a method such as heat curing, room temperature curing, gas curing, etc., a primary molded body composed of the cured product of the mixture (A) can be obtained. The cured product of the mixture (A) is a cured product of a mixture containing a refractory granular material and an organic binder, and contains a water-soluble inorganic salt.
The obtained primary compact is taken out from the casting mold. Since the primary molded body can maintain its shape due to the cured organic binder, it does not easily collapse even when it is removed from the casting mold.

According to the method for producing the primary compact of the first aspect, a large amount of water-soluble inorganic salt can be blended into the primary compact. Therefore, the method for producing a primary molded body according to the first aspect is particularly suitable for producing a primary molded body having a relatively high water-soluble inorganic salt content.

(Second aspect)
In the method for producing a primary molded body of the second aspect, a mixture (hereinafter also referred to as “mixture (B)”) containing a refractory granular material, an organic binder, and optionally optional ingredients is prepared into a mold. It is a method of filling a molding die, curing the organic binder to obtain a cured product of the mixture (B), and then impregnating the obtained cured product with a water-soluble inorganic salt.
The mold for casting is not particularly limited, and any of wooden molds, resin molds and metal molds may be used.
The content of the organic binder in the mixture (B) is the same as in the mixture (A).
The mixture (B) may or may not contain a water-soluble inorganic salt, but from the viewpoint of production costs, the mixture (B) preferably does not contain a water-soluble inorganic salt.

Mixture (B) can be prepared, for example, by mixing a refractory particulate material, an organic binder and optional ingredients. The mixture (B) thus obtained is also called "kneaded sand".
Alternatively, for example, a refractory granular material is heated to a predetermined temperature, and the heated refractory granular material, an organic binder, and optionally optional components are mixed, and the resulting mixture (b1) is Mixture (B) may be produced by cooling. Optional ingredients may be added after cooling the mixture (b1). The heating temperature of the refractory granular material is preferably higher than the melting point of the organic binder, usually 100-150°C. By preheating the refractory granular material, the organic binder melts when mixed with the organic binder, and the surface of the refractory granular material is coated with the organic binder. The mixture (B) thus obtained is also called "coated sand".

Methods for curing the organic binder include heat curing, normal temperature curing, gas curing and the like.
When the organic binder is cured by heat curing or normal temperature curing, the mixture (B) preferably contains a curing agent. Hereinafter, the mixture (B) containing the curing agent is also particularly referred to as "mixture (B1)".
The content of the curing agent in the mixture (B1) is the same as in the mixture (A1).

The mixture (B1) can be produced using an aqueous curing agent solution, for example, as follows.
When the mixture (B1) is kneaded sand, the mixture (B1) is obtained by mixing, for example, a refractory granular material, an organic binder, an aqueous hardening agent solution, and optional ingredients.
When the mixture (B1) is coated sand, for example, an aqueous hardening agent solution is added to the mixture (b1) described above, and the obtained lumps (b2) are cooled to disintegrate into granules to obtain the mixture (B1). The optional component may be added at the same timing as the aqueous curing agent solution is added to the mixture (b1), or may be added after the aggregate (b2) is cooled to disintegrate into granules.

When the organic binder is cured by gas curing, the mixture (B) is filled into the mold for molding, and the gaseous curing agent is passed through to cure the organic binder.
The aeration flow rate and aeration time of the gaseous curing agent are the same as in the first embodiment.

A cured product of the mixture (B) can be obtained by curing the organic binder by a method such as heat curing, normal temperature curing, or gas curing.
Next, the resulting cured product is impregnated with a water-soluble inorganic salt. Specifically, the cured product is impregnated with an aqueous solution of a water-soluble inorganic salt.
The impregnation amount of the water-soluble inorganic salt is preferably an amount such that the content of the water-soluble inorganic salt is 3 to 30% by mass when the total content of the refractory granular material and the water-soluble inorganic salt is 100% by mass. , more preferably 10 to 20% by mass.

By impregnating the cured product with the water-soluble inorganic salt, a primary molded product that is the cured product of the mixture (B) and contains the water-soluble inorganic salt is obtained.
The obtained primary compact is taken out from the casting mold. Since the primary molded body can maintain its shape due to the cured organic binder, it does not easily collapse even when it is removed from the casting mold.

According to the method for producing the primary compact of the second aspect, the water-soluble inorganic salt can be more uniformly dispersed in the primary compact. Therefore, in the case of producing a primary compact in which the water-soluble inorganic salt is more uniformly dispersed, the method for producing the primary compact according to the second embodiment is particularly suitable.

(Other embodiments)
The method for producing the primary molded body is not limited to the above-described methods. You may manufacture a primary molded object by the lamination-molding method. In addition, after obtaining a three-dimensional laminate-molded article by a three-dimensional laminate-molding method using a refractory granular material, an organic binder, and optionally a curing agent and optional components, the three-dimensional laminate-molded article is dissolved in water. A primary molded body may be produced by impregnating the molded body with an organic inorganic salt.

<Baking process>
The sintering step is a step of sintering the primary compact.
In the firing step, the primary molded body is fired at a temperature higher than the melting point of the water-soluble inorganic salt contained in the primary molded body and higher than the decomposition temperature of the organic binder.
By firing the primary compact at a temperature higher than the melting point of the water-soluble inorganic salt and higher than the decomposition temperature of the organic binder, the organic binder is thermally decomposed and gasified, and is removed from the primary compact as thermal decomposition gas. . On the other hand, the water-soluble inorganic salt melts.

In the firing step, firing is preferably performed at a temperature lower than the decomposition temperature of the water-soluble inorganic salt contained in the primary compact. By firing the primary compact at a temperature lower than the decomposition temperature of the water-soluble inorganic salt, the strength of the mold can be maintained satisfactorily. In particular, when chloride is used as the water-soluble inorganic salt, the generation of chlorine odor can be suppressed because the water-soluble inorganic salt is difficult to thermally decompose.

The firing temperature may be determined according to the type of water-soluble inorganic salt and organic binder contained in the primary compact. For example, when chloride is used as the water-soluble inorganic salt, the firing temperature is 350 to 1000°C. Preferably, 500 to 900°C is more preferable. If the baking temperature is at least the above lower limit, the water-soluble inorganic salt is sufficiently melted while the organic binder is sufficiently thermally decomposed. If the firing temperature is equal to or lower than the above upper limit, the water-soluble inorganic salt is less likely to be thermally decomposed.
The baking time is not particularly limited as long as the organic binder contained in the primary compact is sufficiently thermally decomposed and the water-soluble inorganic salt is sufficiently melted, but for example, 1 to 30 minutes is preferable.
A known method can be employed as a method for sintering the primary compact, and examples thereof include a method using an electric furnace and an oven.

A fired product obtained by firing the primary compact is cooled to room temperature (25° C.) to obtain a mold. The melted water-soluble inorganic salt is solidified by cooling the baked product. By solidifying the water-soluble inorganic salt that has once been melted in this manner, a mold that maintains sufficient strength until casting can be obtained.
As a method for cooling the fired product, a known method can be employed, and examples thereof include a method of natural cooling at room temperature, a method of forced cooling using air blowing, and the like.

<Effect>
According to the mold manufacturing method of the present invention described above, two types of binding agents, organic and inorganic, are used. obtain. Since the organic binder is excellent in handleability and can be easily formed into a mold, the primary compact can be easily produced with good handleability according to the present invention. Moreover, as the casting mold used for manufacturing the primary compact, a casting mold used for manufacturing a normal casting mold can be used, so there is no restriction on the casting mold.
Then, the primary compact is fired at a predetermined temperature. By firing the primary compact at a predetermined temperature, the organic binder is thermally decomposed and gasified, and is removed from the primary compact as thermal decomposition gas. On the other hand, the water-soluble inorganic salt is melted, and the melted water-soluble inorganic salt is solidified by cooling the fired product of the primary compact, and a mold that maintains sufficient strength until casting is obtained.

In the casting mold thus obtained, the organic binder is sufficiently removed by the firing process, so that the pyrolysis gas of the organic binder is less likely to be generated during casting. Therefore, the working environment during casting is favorable, and defects in castings caused by pyrolysis gas can be suppressed. In addition, the mold maintains its shape and strength due to the water-soluble inorganic salt, but since the water-soluble inorganic salt easily dissolves in water, the mold can easily collapse by pouring water over it after casting. do. Furthermore, since the water-soluble inorganic salt dissolves in water, the refractory particulate material can be easily regenerated from dismantled molds.

As described above, according to the present invention, the function of the organic binder is used up to the production of the primary compact, and thereafter the function of the water-soluble inorganic salt, which is the inorganic binder, is used to produce the mold. That is, the binder is switched from organic to inorganic during mold manufacture.
Therefore, according to the mold manufacturing method of the present invention, it is possible to obtain a mold that maintains sufficient strength until casting, is excellent in collapsibility after casting, and is less likely to generate pyrolysis gas of the binder during casting. It can be manufactured without being restricted by molds for mold making. In addition, the mold manufacturing method of the present invention can maintain the handling property and moldability that are characteristics of the organic binder.

As described above, if the mold obtained by the present invention is used, the pyrolysis gas of the organic binder is less likely to be generated during casting. Since the organic binder is thermally decomposed, thermal decomposition gas is generated.
However, since the firing of the primary molded body is performed in a narrow space such as an electric furnace or an oven, it is easy to exhaust the pyrolysis gas. In addition, in the firing of the primary molded body, heat and oxygen are sufficiently distributed throughout the primary molded body, so that the organic binder is likely to burn completely. Therefore, the pyrolysis gas generated during firing is mainly water vapor and carbon dioxide.
On the other hand, since casting is performed in a large space such as a factory, when pyrolysis gas of the organic binder is generated, it is difficult to exhaust compared to a narrow space, and the space is easily filled with the gas, which deteriorates the working environment. Also, defects may occur in the casting. Furthermore, in casting, it is difficult for heat and oxygen to spread sufficiently throughout the mold, and it is difficult for the organic binder to burn completely. Therefore, the pyrolysis gas generated during casting is mainly an organic gas. For example, when an organic binder made from phenols is used, a pyrolysis gas having a phenol group is generated.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these. The refractory granular material, water-soluble inorganic salt, organic binder, curing agent and lubricant used in each example are shown below. Various measurement methods and evaluation methods are as follows.
Examples 14 to 16 are reference examples.

<Refractory granular material>
As the refractory granular material, the following materials were used.
Refractory granular material (i): Artificial sand obtained by a sintering method (manufactured by Itochu Ceratec Co., Ltd., "Cerabeads #1450").
• Refractory granular material (ii): Flattery silica sand.
Refractory granular material (iii): 50 parts by mass of artificial sand obtained by a sintering method ("Cerabeads #1450" manufactured by ITOCHU CERATEC Co., Ltd.) and artificial sand obtained by a sintering method (ITOCHU CERATEC Co., Ltd.) (manufactured by Cerabeads #1700)) and a mixture with 50 parts by mass.
Refractory granular material (iv): Artificial sand obtained by a melting method (manufactured by Ito Kiko Co., Ltd., "Arsand #1000").

<Inorganic binder>
As the inorganic binder, the following was used.
- NaCl: sodium chloride (manufactured by Kanto Kagaku Co., Ltd., special grade reagent, melting point 801°C, thermal decomposition temperature 1413°C).
- KCl: Potassium chloride (manufactured by Kanto Kagaku Co., Ltd., special grade reagent, melting point 770°C, thermal decomposition temperature 1420°C).
· Na ₂ CO ₃ : Sodium carbonate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent, melting point 851°C, thermal decomposition temperature 1600°C).
· B ₄ Na ₂ O ₇ : Sodium tetraborate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent, melting point 741°C, thermal decomposition temperature 1575°C).
· Na ₂ SO ₄ : sodium sulfate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent, melting point 883°C, thermal decomposition temperature 1429°C).
Water glass: aqueous solution of sodium silicate (Fuji Chemical Co., Ltd., molar ratio (SiO ₂ /Na ₂ O) 2.1, Baume degree 25 (20° C.)).

<Shell mold method>
The following organic binders, hardeners and lubricants were used for mold production using the shell mold method.
A novolac-type phenolic resin ("PSM-5419B" manufactured by Gun Ei Chemical Industry Co., Ltd., thermal decomposition temperature of about 350° C.) was used as an organic binder.
Hexamethylenetetramine (manufactured by Mitsubishi Gas Chemical Company, Inc.) was used as a curing agent.
Calcium stearate (manufactured by ADEKA Corporation) was used as a lubricant.

<Self-hardening property of alkali phenol>
The following organic binders and hardening agents were used in producing molds utilizing the self-hardening property of alkali phenol.
A resol-type phenolic resin (manufactured by Gun Ei Chemical Industry Co., Ltd., resin for alpha system "AR-170", thermal decomposition temperature of about 350° C.) was used as an organic binder.
An organic ester (Alpha System Curing Agent “AH-530” manufactured by Gun Ei Chemical Industry Co., Ltd.) was used as a curing agent.

<Furan self-hardening property>
The following organic binders and hardening agents were used in the production of molds utilizing the self-hardening property of furan.
A furan resin (N-furan resin "GFA-160" manufactured by Gun Ei Chemical Industry Co., Ltd., thermal decomposition temperature: about 200° C.) was used as an organic binder.
60 parts by mass of a sulfonic acid aqueous solution (manufactured by Gunei Chemical Industry Co., Ltd., Nfuran curing agent "GH-20") as a curing agent, and a sulfonic acid aqueous solution (manufactured by Gunei Chemical Industry Co., Ltd., Nfurane curing agent "GH-70"). A mixture with 40 parts by mass was used.

<Amine cold box method>
The following organic binders and curing agents were used in the mold production using the amine cold box method.
Phenol urethane resin ("New Cold Box 96" manufactured by Okazaki Huttenas Albertas Kasei Co., Ltd.) as an organic binder; 1 part by mass of a two-liquid binder) was used.
Triethylamine (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) was used as a curing agent.

<Measurement/Evaluation>
(Measurement of gas generation amount)
The mold was heat-treated in an atmosphere of 700° C. for 3 minutes, exposing the mold to the same atmosphere as when producing castings. The amount of gas generated during the heat treatment was measured according to JACT test method M-5 "Method for measuring the amount of gas generated".

(Measurement of residual strength)
The mold was heat-treated in an atmosphere of 500° C. for 15 minutes, exposing the mold to the same atmosphere as when producing castings. After heat treatment, the mold was cooled to 25°C. The bending strength of the mold after cooling was measured according to JIS K 6910. This bending strength is defined as the residual strength of the mold. A higher residual strength means that a higher strength is maintained during casting.

(Evaluation of collapsibility)
After measuring the residual strength, the mold was submerged in water to visually confirm whether or not the mold collapsed, and the evaluation was made according to the following evaluation criteria.
○: The mold collapsed to the extent that it could be ground with a finger.
x: The mold did not collapse and maintained its shape.

(Measurement of cold strength)
The bending strength of the primary compact or mold cooled to 25° C. was measured according to JIS K 6910. This bending strength is defined as the cold strength of the primary compact or mold.

[Example 1]
Using the shell mold method, a mold was manufactured as follows.
An aqueous curing agent solution was prepared by dissolving 4.5 g of hexamethylenetetramine as a curing agent in 30 g of cooling water.
Into a speed mixer, 1350 g of the refractory granular material (i) heated to 150° C., 150 g of NaCl which is a water-soluble inorganic salt as an inorganic binder, and 30 g of a novolak-type phenolic resin as an organic binder are charged, Knead for 60 seconds. Next, 34.5 g of an aqueous hardening agent solution is added, and the resulting mass is disintegrated into granules by air cooling, and then 1.5 g of calcium stearate is added as a lubricant and mixed for 10 seconds to form coated sand (A1-1). ).
The content of the organic binder in the resulting coated sand (A1-1) was 2.0 parts by mass per 100 parts by mass of the total content of the refractory granular material and the water-soluble inorganic salt. The content of the water-soluble inorganic salt was 10% by mass when the total content of the refractory granular material and the water-soluble inorganic salt was 100% by mass. The content of the curing agent was 0.3 parts by mass with respect to 100 parts by mass of the total content of the refractory granular material and the water-soluble inorganic salt.

The mold was heated to 250° C., filled with the previously obtained coated sand (A1-1), left to stand for 1 minute to harden the organic binder, and a primary compact was obtained. The obtained primary compact was taken out from the mold, placed in an electric furnace and fired at 850° C. for 15 minutes to obtain a fired product. The fired product obtained was cooled to 25° C. to obtain a mold.
The cold strength of the primary compact and mold was measured. In addition, the amount of gas generated and the residual strength of the mold were measured to evaluate the collapsibility. Tables 1 and 2 show the results.

[Example 2]
Using the self-hardening property of alkali phenol, a mold was produced as follows.
1350 g of refractory granular material (i) and 150 g of NaCl, which is a water-soluble inorganic salt as an inorganic binder, are mixed, and 100 parts by mass of the resulting mixture is added with 1 resol-type phenolic resin as an organic binder. .5 parts by mass and 0.3 parts by mass of an organic ester as a curing agent are added at the same time, and kneaded with a Shinagawa type universal stirrer (manufactured by Shinagawa Kogyosho Co., Ltd., MIXER) to obtain kneaded sand (A1-2). rice field.
The content of the organic binder in the resulting kneaded sand (A1-2) was 1.5 parts by mass per 100 parts by mass of the total content of the refractory granular material and the water-soluble inorganic salt. The content of the water-soluble inorganic salt was 10% by mass when the total content of the refractory granular material and the water-soluble inorganic salt was 100% by mass. The content of the curing agent was 0.3 parts by mass with respect to 100 parts by mass of the total content of the refractory granular material and the water-soluble inorganic salt.

The obtained kneaded sand (A1-2) was filled in a wooden mold under conditions of a temperature of 25° C. and a humidity of 60%, and left to stand for 24 hours to harden the organic binder to obtain a primary compact. The obtained primary compact was taken out from the mold, placed in an electric furnace and fired at 850° C. for 15 minutes to obtain a fired product. The fired product obtained was cooled to 25° C. to obtain a mold.
The cold strength of the primary compact and mold was measured. In addition, the amount of gas generated and the residual strength of the mold were measured to evaluate the collapsibility. Table 1 shows the results.

[Example 3]
Using the self-hardening property of furan, a mold was manufactured as follows.
1350 g of the refractory granular material (i) and 150 g of NaCl, which is a water-soluble inorganic salt as an inorganic binder, are mixed, and 0.8 part of a furan resin as an organic binder is added to 100 parts by mass of the resulting mixture. Parts by mass and 0.32 parts by mass of an aqueous sulfonic acid solution (a mixture of 60 parts by mass of "GH-20" and 40 parts by mass of "GH-70") as a curing agent were added at the same time, and a Shinagawa type universal stirrer (stock MIXER manufactured by Shinagawa Kogyosho Co., Ltd. to obtain kneaded sand (A1-3).
The content of the organic binder in the resulting kneaded sand (A1-3) was 0.8 parts by mass per 100 parts by mass of the total content of the refractory granular material and the water-soluble inorganic salt. The content of the water-soluble inorganic salt was 10% by mass when the total content of the refractory granular material and the water-soluble inorganic salt was 100% by mass. The content of the curing agent was 0.32 parts by mass with respect to 100 parts by mass of the total content of the refractory granular material and the water-soluble inorganic salt. The content of the curing agent as an active ingredient was 0.18 parts by mass in terms of solid content with respect to 100 parts by mass of the total content of the refractory granular material and the water-soluble inorganic salt.

A mold was produced in the same manner as in Example 2, except that the mixed sand (A1-3) was used instead of the mixed sand (A1-2).
The cold strength of the primary compact and mold was measured. In addition, the amount of gas generated and the residual strength of the mold were measured to evaluate the collapsibility. Table 1 shows the results.

[Example 4]
Using the self-hardening property of furan, a mold was manufactured as follows.
With respect to 100 parts by mass of the refractory granular material (i), 2.0 parts by mass of furan resin as an organic binder and an aqueous sulfonic acid solution as a curing agent (60 parts by mass of "GH-20" and "GH-70" 0.32 parts by mass of a mixture with 40 parts by mass) was added at the same time, and kneaded with a Shinagawa type universal stirrer (manufactured by Shinagawa Kogyosho Co., Ltd., MIXER) to obtain kneaded sand (B1-1).
The content of the organic binder in the resulting kneaded sand (B1-1) was 2.0 parts by mass per 100 parts by mass of the total content of the refractory granular material and the water-soluble inorganic salt. The content of water-soluble inorganic salt was 0% by mass. The content of the curing agent was 0.32 parts by mass with respect to 100 parts by mass of the total content of the refractory granular material and the water-soluble inorganic salt. The content of the curing agent as an active ingredient was 0.18 parts by mass in terms of solid content with respect to 100 parts by mass of the total content of the refractory granular material and the water-soluble inorganic salt.

The obtained kneaded sand (B1-1) was filled in a wooden mold under conditions of a temperature of 25° C. and a humidity of 60%, and allowed to stand for 24 hours to harden the organic binder. The resulting cured product was removed from the wooden mold and impregnated with 2.2 mL of a 20% by mass aqueous solution of NaCl, which is a water-soluble inorganic salt, as an inorganic binder to obtain a primary compact. The impregnation amount of the water-soluble inorganic salt was 4.3% by mass when the total content of the refractory granular material and the water-soluble inorganic salt was 100% by mass.
The obtained primary compact was placed in an electric furnace and fired at 850° C. for 15 minutes to obtain a fired product. The fired product obtained was cooled to 25° C. to obtain a mold.
The cold strength of the primary compact and mold was measured. In addition, the amount of gas generated and the residual strength of the mold were measured to evaluate the collapsibility. Table 1 shows the results.

[Example 5]
Using the amine cold box method, molds were prepared as follows.
1350 g of the refractory granular material (i) and 150 g of NaCl, which is a water-soluble inorganic salt as an inorganic binder, are mixed, and 100 parts by mass of the resulting mixture is added with a phenol urethane resin (phenol 2.0 parts by mass of a two-liquid caking agent composed of 1 part by mass of a resin solution and 1 part by mass of a polyisocyanate solution) is added and kneaded with a Shinagawa universal stirrer (manufactured by Shinagawa Kogyosho Co., Ltd., MIXER). Then, kneaded sand (A1-4) was obtained.
The content of the organic binder in the resulting kneaded sand (A1-4) was 2.0 parts by mass per 100 parts by mass of the total content of the refractory granular material and the water-soluble inorganic salt. The content of the water-soluble inorganic salt was 10% by mass when the total content of the refractory granular material and the water-soluble inorganic salt was 100% by mass.

The kneaded sand (A1-4) thus obtained was filled in a wooden mold under conditions of a temperature of 25° C. and a humidity of 60%, and triethylamine as a curing agent was aerated with compressed air for 1 minute at an air flow rate of 10 L/min. The binder was cured to obtain a primary compact. The obtained primary compact was taken out from the mold, placed in an electric furnace and fired at 850° C. for 15 minutes to obtain a fired product. The fired product obtained was cooled to 25° C. to obtain a mold.
The cold strength of the primary compact and mold was measured. In addition, the amount of gas generated and the residual strength of the mold were measured to evaluate the collapsibility. Table 1 shows the results.

[Comparative Example 1]
Using the shell mold method, a mold was manufactured as follows.
An aqueous curing agent solution was prepared by dissolving 4.5 g of hexamethylenetetramine as a curing agent in 30 g of cooling water.
1500 g of the refractory granular material (i) heated to 150° C. and 22.5 g of a novolac-type phenolic resin as an organic binder were put into a speed mixer and kneaded for 60 seconds. Next, 34.5 g of an aqueous hardening agent solution is added, and the resulting mass is disintegrated into granules by air cooling. 1.5 g of calcium stearate is added as a lubricant, and mixed for 10 seconds to form coated sand (B1-2). ).
The content of the organic binder in the resulting coated sand (B1-2) was 1.5 parts by mass per 100 parts by mass of the total content of the refractory granular material and the water-soluble inorganic salt. The content of water-soluble inorganic salt was 0% by mass. The content of the curing agent was 0.3 parts by mass with respect to 100 parts by mass of the total content of the refractory granular material and the water-soluble inorganic salt.

The mold was heated to 250° C., filled with the previously obtained coated sand (B1-2), and left for 1 minute to cure the organic binder. The resulting cured product (primary molded product) was removed from the mold and used as a mold.
The cold strength of the primary compact was measured. In addition, the amount of gas generated and the residual strength of the mold were measured to evaluate the collapsibility. Table 1 shows the results.

[Comparative Example 2]
Into a speed mixer, 1500 g of refractory granular material (i), 30 g of water glass as an inorganic binder, and 15 g of amorphous silica as a curing agent for water glass are charged and kneaded for 60 seconds to form kneading sand (C- 1) was obtained.
The content of the organic binder in the resulting kneaded sand (C-1) was 0 parts by mass. The content of water glass was 0.5% by mass when the total content of the refractory granular material and water glass was 100% by mass. The content of amorphous silica was 1.0 parts by mass with respect to 100 parts by mass of the refractory granular material.

The mold was heated to 150° C., filled with the previously obtained kneaded sand (C-1), and allowed to stand for 10 minutes to harden the water glass. The resulting cured product (primary molded product) was removed from the mold and used as a mold.
The resulting mold was measured for the amount of gas generated and evaluated for collapsibility. Table 1 shows the results.

[Comparative Example 3]
Using the shell mold method, a mold was manufactured as follows.
An aqueous curing agent solution was prepared by dissolving 4.5 g of hexamethylenetetramine as a curing agent in 30 g of cooling water.
1500 g of the refractory granular material (i) heated to 150° C. and 30 g of a novolak-type phenolic resin as an organic binder were put into a speed mixer and kneaded for 60 seconds. Next, 34.5 g of an aqueous hardening agent solution is added, and the resulting mass is disintegrated into granules by air cooling. 1.5 g of calcium stearate is added as a lubricant, and mixed for 10 seconds to form coated sand (B1-3). ).
The content of the organic binder in the resulting coated sand (B1-3) was 2.0 parts by mass per 100 parts by mass of the total content of the refractory granular material and the water-soluble inorganic salt. The content of water-soluble inorganic salt was 0% by mass. The content of the curing agent was 0.3 parts by mass with respect to 100 parts by mass of the total content of the refractory granular material and the water-soluble inorganic salt.

The mold was heated to 250° C., filled with the previously obtained coated sand (B1-3) and left for 1 minute to cure the organic binder. The resulting cured product was removed from the mold, cooled to 25° C., and impregnated with water glass as an inorganic binder to obtain a primary molded product. The impregnated amount of water glass was 8% by mass when the total content of the refractory granular material and water glass was taken as 100% by mass.
The obtained primary compact was placed in an electric furnace and fired at 850° C. for 15 minutes to obtain a fired product. The fired product obtained was cooled to 25° C. to obtain a mold.
The cold strength of the primary compact and mold was measured. In addition, the amount of gas generated and the residual strength of the mold were measured to evaluate the collapsibility. Table 1 shows the results.

[Comparative Example 4]
Coated sand (A1-1) was obtained in the same manner as in Example 1.
The mold was heated to 250° C., filled with the previously obtained coated sand (A1-1), left to stand for 1 minute to harden the organic binder, and a primary compact was obtained. The obtained primary compact was removed from the mold and used as a mold.
The cold strength of the primary compact was measured. In addition, the amount of gas generated and the residual strength of the mold were measured to evaluate the collapsibility. Table 1 shows the results.

In Table 1, "amount of inorganic binder" is the inorganic binder when the total content of the refractory granular material and the inorganic binder (water-soluble inorganic salt or water glass) is 100% by mass. It is the amount (% by mass) of (water-soluble inorganic salt or water glass). The "amount of the organic binder" is the amount (parts by mass) of the organic binder with respect to the total 100 parts by mass of the contents of the refractory granular material and the water-soluble inorganic salt.

The results in Table 1 show that the mold obtained in each example has moderately high cold strength and residual strength, and can maintain sufficient strength until casting. In addition, the amount of gas generated was small, and the disintegration property was also excellent.
On the other hand, the mold obtained in Comparative Example 1 generated a large amount of gas. In addition, it was difficult to disintegrate even when water was applied, and was inferior in disintegration properties.
The mold obtained in Comparative Example 2 generated a large amount of gas. In addition, it was difficult to disintegrate even when water was applied, and was inferior in disintegration properties.
The mold obtained in Comparative Example 3 had an excessively high residual strength, was difficult to collapse even when water was applied, and was inferior in disintegration properties.
The mold obtained in Comparative Example 4 generated a large amount of gas. In addition, it was difficult to disintegrate even when water was applied, and was inferior in disintegration properties.
The gases generated in Comparative Examples 1 and 4 are mainly pyrolysis gases of the organic binder. The gas generated in Comparative Example 2 is mainly water vapor.

[Examples 6 to 25, Comparative Examples 5 to 7]
Type of refractory granular material, type of water-soluble inorganic salt used as an inorganic binder, total content of refractory granular material and inorganic binder (water-soluble inorganic salt), when the total content is 100% by mass The amount of the inorganic binder (water-soluble inorganic salt), the amount of the organic binder (novolac-type phenolic resin) per 100 parts by mass of the total content of the refractory granular material and the water-soluble inorganic salt, and the baking conditions are shown. A mold was manufactured in the same manner as in Example 1, except for changing as shown in 2.
The cold strength of the primary compact and mold was measured. In addition, the amount of gas generated was measured to evaluate the disintegrability. Table 2 shows the results.

In Table 2, the "amount of inorganic binder" is the inorganic binder (water-soluble inorganic salt) amount (% by mass). The "amount of the organic binder" is the amount (parts by mass) of the organic binder with respect to the total 100 parts by mass of the contents of the refractory granular material and the water-soluble inorganic salt.

The results in Table 2 show that the molds obtained in each example have moderately high cold strength and residual strength, and can maintain sufficient strength until casting. In addition, the amount of gas generated was small, and the disintegration property was also excellent.
On the other hand, the molds obtained in Comparative Examples 5 to 7 had low residual strength and could not maintain sufficient strength until casting.

Claims (3)

A primary molded body which is a cured product of a mixture containing a refractory granular material and an organic binder and which contains a water-soluble inorganic salt is heated to a temperature higher than the melting point of the water-soluble inorganic salt and higher than the decomposition temperature of the organic binder. A method for manufacturing a mold to be fired at
the water-soluble inorganic salt is at least one of an alkali metal salt and an alkaline earth metal salt;
A method for producing a mold , wherein the content of the water-soluble inorganic salt is 3 to 30% by mass when the total content of the refractory granular material and the water-soluble inorganic salt is 100% by mass . The mixture includes a refractory granular material, the organic binder, and the water-soluble inorganic salt. The mixture is filled into a mold for molding, and the organic binder is cured to form the primary compact. The method for manufacturing a mold according to claim 1, wherein After filling the mixture into a casting mold and curing the organic binder to obtain the cured product, the obtained cured product is impregnated with the water-soluble inorganic salt to obtain the primary molded body. A method for manufacturing the mold according to claim 1 .