JPH1080744A - Locally esterified phenol resin binder for casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide binder-covered sand for a shell mold excellent in mold strength and collapsibility by using the binder in which the phenol hydroxide group of the phenol resin is substituted by the ester group for the binder of the casting sand. SOLUTION: The partially esterifled phenol resin binder for casting having the structure in which a part of the phenol hydroxide group is substituted by the ester group is manufactured. The partially esterified phenol resin is obtained, for example, by reacting the phenol with the aldehyde using the acid catalyst to form the condensation product first, and by reacting it with the esterified agent such as carboxylate anhydride or by performing the condensation reaction of carbonic acid phenyl ester with the aldehyde. A mold molded using the binder is of the mold strength equivalent to that made of the conventional binder- covered sand, and collapsibility of the mold after the molten metal is poured is excellent even when no collapse promoting agent causing corrosion of a die is used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binder-coated sand for shell molds which is suitable for casting of light alloys such as aluminum having a lower melting point than cast iron, and has good mold disintegration properties after casting. It is.

[0002]

2. Description of the Related Art In response to recent demands for lighter automobiles, there has been a remarkable replacement of conventional cast iron-related parts with aluminum (alloy) cast parts, and it is expected that the demand will continue to increase.

[0003] As a casting method of these parts, a shell molding method using coated sand obtained by coating silica sand mainly with a phenolic resin binder is generally used. However, in casting of light alloys such as aluminum having a lower melting point than cast iron, since the pouring temperature is lower than in the case of cast iron, thermal decomposition of the phenolic resin binder becomes insufficient, and after pouring, The disintegration of the mold and the core is poor, making it difficult to remove the sand. Therefore, after casting, heat treatment is performed at 400 to 500 ° C. for several hours, and then the core is disintegrated by applying a physical impact by core knocking to discharge sand as sand particles.
A lot of money and effort is spent for that.

On the other hand, as a method for improving the disintegration property, use of a binder (unsaturated polyester resin or the like) having a bond easily decomposed at a low temperature promotes decomposition of the phenolic resin binder at a low temperature. Addition of disintegration accelerators (halogen-containing organic compounds, inorganic halogen compounds, phosphoric esters), and a method of using the above-mentioned low-temperature decomposable binder and disintegration accelerator together have been proposed.

For example, the method disclosed in Japanese Patent Application Laid-Open No. 57-187142 uses an unsaturated polyester resin which easily undergoes a thermal decomposition reaction at a low temperature as a binder, and the method disclosed in Japanese Patent Publication No. 3-37817 discloses a polyester resin, A phenolic resin modified with a vinyl acetate resin, an acrylic resin, or the like is used as a binder. Although these methods improve disintegration as compared with conventional phenolic resin binders, they are unsuitable for cores having complicated shapes due to low mold strength.

On the other hand, Japanese Patent Publication No. 58-12094 discloses a method using a halogen-containing organic compound as a disintegration accelerator. This method has the effect of improving the disintegration without reducing the mold strength, but involves the problem of mold corrosion due to the generation of hydrogen halide gas. When the inorganic halogen compounds disclosed in JP-A-58-84636 and JP-A-60-64744 are added, although the disintegration improving effect is high, a mold such as a mold and a core mold (casting process) is used. (Including the main mold used in the present invention) and the problem of deterioration of the mold strength. Further, when the phosphoric acid esters disclosed in Japanese Patent Publication No. 61-2454 are used, the problems of strength reduction and mold corrosion are eliminated, but the disintegration improving effect is insufficient. Further, a method obtained by improving the above-mentioned prior art is disclosed in JP-A-63-248.
540, Japanese Patent Publication No. 44443/1994,
Japanese Patent Application No. -10897 has been proposed. However, these are not always practically satisfactory in terms of disintegration and mold corrosion problems.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to overcome the above-mentioned problems and to improve the disintegration of a mold without using a disintegration accelerator or the like which causes problems such as a reduction in mold strength and mold corrosion. It is an object of the present invention to provide a resin binder for a light alloy casting sand excellent in heat resistance and its coated sand.

[0008]

Means for Solving the Problems The present inventors have made intensive studies on a method for improving the disintegration of a template by thermal decomposition of a phenolic resin, and as a result, have accomplished the present invention. The present invention is characterized in that a phenolic hydroxyl group of a phenolic resin is substituted with an ester group for use as a binder for molding sand, and molding is performed using the binder-coated sand. Found that the mold had a mold strength comparable to that of conventional binder-coated sand, and that the mold disintegration after pouring was good even without using a disintegration accelerator accompanied by mold corrosion. . The present invention can provide an adhesive-coated sand for shell mold having excellent mold strength and disintegration.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The partially esterified phenolic resin of the present invention is obtained, for example, by reacting a phenol with an aldehyde using an acidic catalyst, first forming a condensation product, and then forming a carboxylic acid anhydride or the like. Or a condensation reaction of carboxylic acid phenyl esters and aldehydes.

Phenols used as raw materials include phenol, cresol, xylenol, resorcin, catechol, hydroquinone, bisphenol A,
Examples include bisphenol F, bisphenol S and phenolic residues such as resorcinol residue, catechol residue, cresol residue and xylenol residue which are by-produced during the production of phenols, and carboxylic acid phenyl esters of these phenols. Preferable ones are appropriately selected according to various conditions of properties required for the material (binder). Considering the reactivity and the complexity of the reaction process,
Phenols are preferred (rather than carboxylic acid phenyl esters). Two or more phenols can be combined.

The aldehydes include formaldehyde, paraformaldehyde, trioxane, polyacetal, hexamethylenetetramine, acetaldehyde,
Glyoxal, furfural, benzaldehyde and the like can be used. Preferred aldehydes can be appropriately selected according to various conditions required for the binder, and generally, formaldehyde (formalin), paraformaldehyde and the like are used. Two or more aldehydes can be combined.

The ratio of phenols to aldehydes is about 0.6 to 1 mol, preferably about 0.7 to 0.9 mol, of aldehydes per mol of phenols.

Examples of the acidic catalyst include inorganic acids such as hydrochloric acid and sulfuric acid; organic acids such as oxalic acid and paratoluenesulfonic acid; Mn salts such as carboxylic acid, naphthenic acid and boric acid; Zn salts;
There are divalent metal salts such as salts and Lewis acids.

First, they are reacted and subjected to dehydration condensation. The reaction may be performed according to a known method.
The reaction may be carried out at a temperature of about 0 ° C. to a reflux temperature for 1 to 5 hours, followed by dehydration and concentration under reduced pressure or the like.

As the esterifying agent, acetic acid, propionic acid, butyric acid, valeric acid, succinic acid, maleic acid, etc.
It is possible to use up to about 5 aliphatic carboxylic acid anhydrides and carboxylic acid chlorides or a combination thereof. From the viewpoint of removing carboxylic acid by-produced after the esterification reaction, the boiling point of the by-produced carboxylic acid can be reduced. However, it is desirable that acetic acid and propionic acid be as low as possible. An anhydride is more preferable than an acid chloride in that a corrosive gas such as hydrogen chloride is generated.

The amount of the carboxylic anhydride to be used is selected within the range of 0.1 to 0.9 mol, preferably 0.2 to 0.7 mol, per mol of the phenolic hydroxyl group. If it is less than 0.1 mol, the effect of improving disintegration is small, and if it is more than 0.9 mol, the resin curing speed is extremely impaired, and the softening point of the condensate produced is undesirably lowered. The same applies to the case of carboxylic acid chloride.

The reaction between the phenolic hydroxyl group and the aliphatic carboxylic acid anhydride is usually carried out at 100 to 200 ° C., preferably at 13 ° C.
The reaction is performed at 0 to 180 ° C for 1 to 5 hours. The same applies to the case of carboxylic acid chloride.

Thereafter, the reaction by-products and unreacted substances are removed under reduced pressure or the like to obtain a partially esterified phenolic resin.

The partially esterified phenolic resin thus obtained has a number-average molecular weight of about 500 to 1,000, and usually varies from 600 to 500, although it varies depending on various conditions of properties required for the binder.
It is about 900, and the esterification ratio of the phenolic hydroxyl group is usually about 0.1 to 0.6.

As the binder, this partially esterified phenolic resin may be used alone, or the resin may be used in combination with a novolak-type or resol-type phenolic resin, or modified with a bisphenol A, urea, aniline, furan, melamine, or the like. It may be a mixture with a modified phenolic resin or the like.
In the case of a mixture, the content of the partially esterified phenolic resin is at least 40% by weight or more, preferably 60% by weight or more.

The molding sand to be coated with the binder may be a known one, and silica sand, olivine sand, chromite sand, zircon sand, alumina sand, river sand, sea sand and the like can be used. The particle size is appropriately selected depending on the purpose of use, but is usually in the range of 40 to 80 in average particle size index (AFS index).

The average particle size index (AFS) is determined as follows. That is, 50 g of a sample was set on a low-tap type sieve with a 28-280 mesh sieve of a Tyler standard combination, sieved for 15 minutes, and the amount of sand remaining on each sieve face was measured. Calculate the percentage. From the results, the average particle size index is obtained by dividing by 100 the sum of the percentages of the weight of the sand particles obtained by screening and multiplied by the particle size coefficient.
The particle size coefficients are as follows.

[0023]

[Table 1]

The amount of the binder to be added to the molding sand is not limited, but is usually 0.2 to 100 parts by weight of the molding sand.
10 to 10 parts by weight, preferably 0.5 to 5 parts by weight.

The coating method may be the same as the conventional method of coating a binder with a molding sand, and the binder and the molding sand may be sufficiently kneaded in a molten state of the binder.

In the binder-coated sand of the present invention, conventionally used compounding agents such as ethylene bisstearic acid amide, oxystearic acid amide, and stearic acid amide within a range not impairing the essential effects of the present invention. Such as lubricants, aminosilanes, vinylsilanes, silane coupling agents such as epoxysilanes, benzoic acid, salicylic acid,
A curing accelerator such as adipic acid can be blended. It can be appropriately selected according to various conditions such as the characteristics of the material used and the characteristics required for the binder, and is generally 0.1 to 10% by weight, preferably 0.5 to 5% by weight based on the molding sand. %.

In the production of the binder-coated sand in the present invention, the method of blending the above-mentioned various additives is as follows. It may be used at the time of coating.

[0028]

EXAMPLES In the following Examples and Comparative Examples, "parts" and "%" are all "parts by weight" and "% by weight".
Is shown.

Example 1 Phenol 9 was placed in a reaction vessel equipped with a reflux condenser and a stirrer.
Forty parts, 567 parts of 37% formalin, 5 parts of salicylic acid and 90 parts of a 5% oxalic acid aqueous solution were charged and reacted under reflux for 2.5 hours. Subsequently, dehydration concentration was performed under reduced pressure to obtain a phenol-formalin condensate. Further, 300 parts of acetic anhydride was added to the condensate and reacted at 130 to 135 ° C. for 1 hour. Then, acetic acid and acetic anhydride were distilled off under reduced pressure to obtain 970 parts of a partially esterified phenol resin binder. .

The obtained partially esterified phenol resin had a number average molecular weight of 810 and an esterification ratio of phenolic hydroxyl groups of 0.22.

8000 parts of No. 6 silica sand heated to a temperature of 150 to 160 ° C. was charged into a speed kneader, and then 168 parts of the above partially esterified phenolic resin binder were added and kneaded for 60 seconds. Next, an aqueous solution of hexamethylenetetramine in which 25 parts of hexamethylenetetramine was dissolved in 126 parts of water was added, and after the aggregates were loosened, 8 parts of calcium stearate was added. A binder-coated sand was obtained.

Example 2 Phenol 9 was added to a reaction vessel equipped with a reflux condenser and a stirrer.
Forty parts, 567 parts of 37% formalin, 5 parts of salicylic acid and 90 parts of a 5% oxalic acid aqueous solution were charged and reacted under reflux for 2.5 hours. Next, dehydration and concentration were performed under reduced pressure to obtain a phenol-formalin conjugate. Further, 450 parts of acetic anhydride was added to the condensate and reacted at 130 to 135 ° C. for 1 hour. Then, acetic acid and acetic anhydride were distilled off under reduced pressure to obtain 1014 parts of a partially esterified phenolic resin binder. Was.

The obtained partially esterified phenol resin had a number average molecular weight of 840 and an esterification ratio of phenolic hydroxyl groups of 0.34.

A binder-coated sand was obtained in the same manner as in Example 1 except that the above resin binder was used.

Example 3 Phenol 9 was added to a reaction vessel equipped with a reflux condenser and a stirrer.
Forty parts, 567 parts of 37% formalin, 5 parts of salicylic acid and 90 parts of a 5% oxalic acid aqueous solution were charged and reacted under reflux for 2.5 hours. Subsequently, dehydration concentration was performed under reduced pressure to obtain a phenol-formalin condensate. Further, 334 parts of propionic anhydride was added to the condensate, and the mixture was reacted at 160 to 165 ° C. for 1 hour. Then, propionic acid and propionic anhydride were distilled off under reduced pressure to obtain a partially esterified phenolic resin binder. 986 parts were obtained.

The obtained partially esterified phenol resin had a number average molecular weight of 870 and an esterification ratio of phenolic hydroxyl groups of 0.20.

A binder-coated sand was obtained in the same manner as in Example 1 except that the above resin binder was used.

Comparative Example 1 Phenol 9 was added to a reaction vessel equipped with a reflux condenser and a stirrer.
40 parts, 567 parts of 37% formalin, 5 parts of salicylic acid and 90 parts of a 5% oxalic acid aqueous solution were charged and reacted under reflux for 2.5 hours, and then dehydrated and concentrated under reduced pressure to obtain 871 parts of a phenol-formalin condensate. Was.

A binder-coated sand was obtained in the same manner as in Example 1 except that the above condensate was used.

COMPARATIVE EXAMPLE 2 8000 parts of No. 6 silica sand heated to a temperature of 150 to 160 ° C. was charged into a speed mill, and then the same condensate 168 as in Comparative Example 1 was prepared.
And kneaded for 60 seconds. Next, 25 parts of hexamethylenetetramine and 3.4 parts of zinc chloride were added to 126 parts of water.
Hexamethylenetetramine aqueous solution to which
After the mass was loosened, 8 parts of calcium stearate was added, and after 60 seconds, the mixture was discharged, aerated and sieved to obtain a binder-coated sand.

Using the binder-coated sand obtained in Examples 1, 2, and 3 and Comparative Examples 1 and 2, the strength at room temperature and the strength after heat treatment were measured.

The test method is as described below. Room temperature: JACT test method SM-1 Strength after heat treatment: A test piece having the same bending strength as room temperature was wrapped in aluminum foil, placed in a circulating hot air drying oven set at a temperature of 500 ° C., taken out after 10 and 20 minutes, and taken out at room temperature. After cooling to room temperature, the strength after the heat treatment was measured in the same manner as the normal temperature strength.

Table 2 shows the test results. Further, the strength deterioration rate in the table was calculated by the following equation.

Strength degradation rate (%) = (normal temperature strength−strength after heat treatment) / normal temperature strength × 100

[0045]

[Table 2]

[0046]

As is clear from the results of the examples and comparative examples, according to the present invention, a disintegration accelerator such as a halogen-containing compound such as zinc chloride can be used without impairing the strength reduction to an extent that causes a practical problem. It was recognized that the disintegration was improved without adding any of them. This indicates that the problem of corrosion of the mold and the core mold due to the halogen compound can be eliminated.

Claims (2)

[Claims] 1. A partially esterified phenolic resin binder for castings having a structure in which a part of a phenolic hydroxyl group is substituted by an ester group. 2. A binder-coated sand for casting, wherein the surface of the silica sand of the casting is coated with the binder of claim 1.