JP2663617B2 - Method for producing calcia self-hardening mold - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a calcia self-hardening mold, and particularly to a calcia which can easily produce a calcia self-hardening firing mold having sufficiently high strength before firing. The present invention relates to a method for producing a self-hardening mold.

[Prior art] Conventionally, casting molds include zirconia, mullite,
Generally, graphite is used as an aggregate, and a self-hardening mold obtained by molding these aggregates using a binder such as urethane, PVA (polyvinyl alcohol), or rubber is known. Conventional self-hardening molds are usually used without firing. (JP-B 43-4841, JP-B 45-32820, JP-B-4
8-25431, 49-17141, 49-37486) That is, conventionally, when the molten metal is poured into the mold, the binder of the mold burns and the disintegration of the mold is improved.

However, such a mold using zirconia or the like as an aggregate has a problem of molten metal contamination because zirconia or the like easily reacts with an active metal. In order to prevent the molten metal from being contaminated by such an aggregate, a mold using chemically stable calcia as an aggregate can be considered.

The use of calcia as an aggregate can prevent the molten metal from being contaminated by the aggregate, but the conventional mold has the following disadvantages. That is, since the conventional mold is not fired, casting defects (mainly pinholes) tend to occur due to the burning of the binder at the time of pouring the molten metal, and the reaction between the binder and the molten metal tends to occur. Contamination and casting defects may occur. Moreover, in vacuum casting,
Due to the presence of the binder, there is a drawback that evacuation is not easy and it takes a long time to obtain a predetermined degree of vacuum.

For this reason, when a conventional self-hardening mold is used for an active metal, particularly as a mold for vacuum casting, it is necessary to completely remove the binder by firing the mold in advance.

[Problems to be Solved by the Invention] However, when the binder is removed by firing, it cannot be used as a mold because the high-temperature strength of the mold is insufficient. In addition, removing the self-hardening binder by firing requires firing for a long period of time, and also has the disadvantage that the gas generated during firing significantly damages the heater (such as Kanthal Super) of the heat treatment furnace.

In particular, with the use of calcia as an aggregate, urethane, PVA, and self-hardening molds using rubber-based binders, although the strength before firing is excellent, the binder burns during firing, especially at 400 to 800 ° C, There has been a problem that cracks and shape breaks due to firing occur, and it becomes impossible to use.
In addition, since the binder is burned off by firing, high-temperature firing (1400 to 1600 ° C.) is required for firing so that strength is obtained by calcia sintering.

In addition, the calcia mold has a disadvantage that it is inferior in digestion resistance.

An object of the present invention is to solve the above-mentioned conventional problems and to provide a method for producing a calcia self-hardening mold having extremely high strength before, during, or after firing.

[Means for Solving the Problems] The method for producing a calcia self-hardening mold of the present invention has a particle diameter of 5 mm.
Hereinafter, a calcia powder having a CaO content of 95% by weight or more and a urethane-based self-hardening binder composition of 0.1 to 15% by weight with respect to the calcia powder are mixed and then molded. After impregnating with calcium and alcohol,
It is characterized by firing and firing at 800-1300 ° C.

 Hereinafter, the present invention will be described in detail.

In the method for producing a calcia self-hardening mold of the present invention,
As the aggregate, calcia powder having a particle size of 5 mm or less and a CaO content of 95% by weight or more is used.

If the calcia powder used has a particle size of more than 5 mm, sufficient moldability cannot be obtained, and air permeability and disintegration after casting will be poor. Therefore, the particle size of the calcia powder is
5 mm or less, preferably 2 mm or less.

On the other hand, if the CaO content of the calcia powder is less than 95% by weight, a mold having sufficient stability for active metals and having no problem of molten metal contamination cannot be obtained. Therefore, calcia powder
The CaO content is at least 95% by weight, preferably at least 98% by weight.

In the present invention, the self-hardening binder composition is not particularly limited, and any one can be used as long as it generates a urethane reaction and becomes a self-hardening binder. Specifically, those containing the following resin I or II and a curing agent can be used.

That is, in No. I, an NCO group of an isocyanate is reacted with an OH group of a phenol, and a urethane resin is formed by a polymerization addition reaction to obtain strength.

In No. II, urethane resin is formed by reacting the NCO group of isocyanate with the OH or COOH group of the alkyd to obtain strength, and the strength is further increased by the polymerization reaction of the drying oil by air oxidation polymerization. It is to let.

In No. I, the phenolic resin is a resin formed by the condensation of a phenolic compound and an aldehyde, and useful phenolic compounds include phenols represented by the following general formula in which the ortho position is unsubstituted. Is mentioned.

(X, Y and Z in the formula represent a hydrogen atom, a hydrocarbon group, an oxyhydrocarbon group or a halogen atom) Specifically, m-cresol, p-cresol, 3,5
-Xylenol, 3,4-xylenol, 2,3,4-trimethylphenol, 3-ethylphenol, 3,5-diethylphenol, p-butylphenol, 3,5-dibutylphenol, p-amylphenol, p-cyclohexylphenol , P-octylphenol, 3,5-dicyclohexylphenol, p-phenylphenol, p-crotylphenol, 3,5-di-methoxyphenol, 3,5
4,5-trimethoxyphenol, p-ethoxyphenol, p-butoxyphenol, 3-methyl-4-methoxyphenol, and p-phenoxyphenol.

On the other hand, as the aldehyde, an aldehyde represented by the following general formula R'CHO (where R 'represents a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms), specifically, formaldehyde, acetaldehyde , Propionaldehyde, furfuraldehyde, benzaldehyde and the like can be used. The most preferred aldehyde is formaldehyde.

These phenolic compounds and aldehydes are preferably reacted in the usual manner in the range of aldehyde: phenolic compound = 1: 1 or more (molar ratio), more preferably aldehyde: phenolic compound = 1.5: 1 to 3: 1. By doing so, a phenolic resin can be easily obtained.

On the other hand, the No. II oil-modified Alkit resin is preferably composed of the following three components.

Polyhydric alcohols having at least three oxygens. For example, glycerin, pentaerythritol, tolmethylolpropane and the like. Particularly, pentaerythritol is preferred. These can be used as a mixture.

Polycarboxylic acids (or their anhydrides) such as maleic acid, fumaric acid, phthalic acid, phthalic anhydride and isophthalic acid; chlorendic acid; Of these, particularly preferred are inphthalic acid and phthalic anhydride. These can be used as a mixture.

Soybean oil, linseed oil, cottonseed oil, castor oil, dehydrated castor oil, tall oil, tung oil, fish oil, etc. Mixtures of oils can also be used. Of these, linseed oil is particularly preferred. Alkyd resins made from a mixture of linseed oil and castor oil containing at least 25% by weight of linseed oil are particularly preferred.

As the polyisocyanate used in No. I and No. II, aliphatic having 2 to 5 isocyanate groups,
Alicyclic or aromatic polyisocyanates are preferred. These can be used as a mixture if desired. Specifically, aliphatic polyisocyanates such as hexamethylene diisocyanate, alicyclic polyisocyanates such as 4 ', 4'-dicyclohexylmethane diisocyanate, 3,4- and 2,6-toluene diisocyanate, diphenylmethyl diisocyanate or There are aromatic polyisocyanates such as the dimethyl derivative.
In addition, 1,5-naphthalene diisocyanate, triphenylmethane triisocyanate, xylylene diisocyanate and its methyl derivative, polymethylene polyphenol isocyanate, chlorophenylene-2,4-diisocyanate and the like can also be used. Of these, diphenylmethane diisocyanate, triphenylmethane triisocyanate and mixtures thereof are particularly preferred.

In No. I and No. II, the resin component and the polyisocyanate of the curing agent are NCO group of isocyanate and OH of resin.
It is mixed and used according to the reaction equivalent with the group (or COOH group).

In the present invention, when the oil-modified alkyd resin of No. II is used as a resin component of the urethane-based self-hardening binder composition, the binder composition causes a curing reaction by reaction with atmospheric moisture. Therefore, the digestion resistance of the template can be improved.

An oxidation reaction of the drying oil when the alkyd resin and the drying oil are mixed has an effect of further improving the mold strength.

In the present invention, the urethane-based self-hardening binder composition containing such a resin and a curing agent is stirred and mixed at 0.1 to 15% by weight, preferably 1 to 5% by weight, based on the weight of the calcia powder. The mixing method is preferably mechanical stirring and mixing by a kneader.

The resulting mixture is molded by a method such as stamping, rubber pressing, and slurry method, using a mold composed of inner molds such as molds, wooden molds, and rubber molds and outer molds of various refractory materials or SUS-based alloys. After that, the mixture is left for 10 minutes to 10 hours, preferably 1 to 2 hours to be naturally cured, and then removed from the mold to obtain a molded article.

Next, the obtained molded body is impregnated with calcium chloride and alcohol, for example, by immersing it in an alcohol solution containing calcium chloride, preferably an ethanol solution containing calcium chloride. The calcium chloride-containing ethanol solution to be used is preferably ethanol containing 0.1 to 15% by weight, particularly 0.5 to 5% by weight of calcium chloride. The immersion time is preferably 1 to 30 minutes, particularly preferably about 3 to 5 minutes. In the present invention, by such treatment, 0.1 to 5% by weight of calcium chloride and 2-2 to 2
Preferably, it is impregnated with 0% by weight of ethanol.

If the impregnation amount of calcium chloride is less than 0.1% by weight, sufficient sintering strength cannot be obtained, and if it exceeds 5% by weight, shrinkage due to sintering is large and cracks are easily generated in the mold. If the amount of ethanol impregnated is less than 2% by weight, the burning of the urethane-based self-hardening binder by ignition cannot be performed sufficiently, and the
Above this, there is no effect on binder combustion.

After such impregnation treatment, the molded body is ignited, and preferably the self-hardening binder is sufficiently removed by calcining at a temperature of about 300 to 500 ° C. for 1 to 12 hours, and then 800 to 1300 ° C.
For preferably 1 to 10 hours, more preferably 900 to 1200 ° C
For 1 to 4 hours. By firing at such a relatively low temperature, a mold having excellent air permeability and disintegration properties can be obtained.

In the method of the present invention, since basic calcia is used as an aggregate, it is not particularly necessary to use a catalyst in the urethane-based self-hardening binder composition, but an appropriate catalyst is added to the reaction system as needed. You may.

[Action] In the present invention, the following action and effect are exerted.

Since calcia, which is thermodynamically stable, is used as an aggregate, the reactivity is low with respect to active metals, and there is no problem of molten metal contamination.

The strength before firing can be obtained with a urethane-based self-hardening binder, and the strength of firing can be maintained by adding calcium chloride.
Moreover, since calcia does not need to be sintered, there is no need for high-temperature firing.

Since ignition is performed after impregnation with calcium chloride and ethanol after molding, most of the self-hardening binder burns at the time of ignition, so that firing is short.

The self-hardening binder is organic and can improve the digestion resistance of calcia.

Since a basic calcia is used for the aggregate, a catalyst for a self-hardening binder is not required.

[Examples] Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

Examples 1 to 4 A calcia powder having a particle size of 3 to 0.1 mm and a CaO content of 99% by weight, and a urethane-based self-hardening binder composition having the composition shown in Table 1 were mixed in the composition shown in Table 1 and mixed by a stamping method. After being molded for 2 hours, it was left for 2 hours to cure naturally, and then released.

The obtained molded body was immersed in an ethanol solution containing 5% by weight of CaCl ₂ for 5 minutes. The impregnated amount of CaCl _{2 to} the molded body was 0.4% by weight, and the impregnated amount of ethanol was 8% by weight. Next, the compact was ignited and calcined at 400 ° C. for 6 hours.
Calcination was performed at 0 ° C. for 2 hours to obtain a calcia self-hardening mold.

The strength of the molded body after demolding and the strength of the mold after firing were measured by the following methods, and the results are shown in Table 1.

Strength Measuring Method A test piece of 25 × 25 × 205 mm was manufactured, and the bending strength was measured by a bending tester.

Comparative Examples 1 and ₂ Molds were produced in the same manner as in Examples 1 and 3, except that the immersion treatment of CaCl ₂ and ethanol was not performed. In this case, in the firing, 12
It took time.

The strength of the molded body before firing and the strength of the obtained mold
It is shown in the table.

Comparative Example 3 A mold was produced by the following method using calcium chloride as a binder.

That is, 10% by weight of a 5% by weight CaCl ₂ -containing ethanol solution is added to a calcia powder having a particle size of 2 to 0.1 mm and a CaO content of 99% by weight, molded by a stamping method, and calcined at 1100 ° C. for 2 hours. A mold was obtained.

 Table 1 shows the strength of the molded body and the firing mold before firing.

From Table 1, it is clear that in the present invention, a mold having high strength before and after firing can be produced.

[Effects of the Invention] As described in detail above, according to the method for producing a calcia self-hardening mold of the present invention, a mold using calcia as an aggregate that is stable even to an active metal, and the strength of the molded body before firing In addition, a mold having high strength during and after firing can be easily manufactured at a low cost in a short time without causing loss or the like of the heat treatment furnace.

Thus, since the molded body before firing has sufficient strength and the firing strength is high, it is fired without causing such firing defects, and a fired mold suitable for vacuum casting of active metal is provided. It is possible to do.

Claims (1)

(57) [Claims] 1. A mixture of a calcia powder having a particle size of 5 mm or less and a CaO content of 95 wt% or more and a urethane-based self-hardening binder composition of 0.1 to 15 wt% based on the calcia powder. A method for producing a calcia self-hardening mold, comprising impregnating the obtained molded body with calcium chloride and alcohol, igniting and firing at 800 to 1300 ° C.