JPH0890151A - Resin coated sand composition for shell mold - Google Patents

Abstract

PURPOSE: To enhance the strength of a shell mold by resin coated sand by incorporating a polyamide resin into a phenolic resin and specifying the melt viscosity at a specific temp. to a specific poise. CONSTITUTION: The resin coated sand is formed by coating a refractory material for castings having the moisture adsorbability of the refractory material of >=0.6% with the phenolic resin. The phenolic resin contg. the polyamide resin and having the melt viscosity of 5 to 20 poises at 150 deg.C is used. The amt. of the polyamide resin to be incorporated into the phenolic resin is specified to 1 to 20wt.%. The phenolic resin contg. the polyamide resin is effective for the refractory material having the high moisture adsorbability. The phenolic resin is a solid phenolic resin obtd. by bringing phenols and aldehydes into reaction in the presence of a catalyst. As a result, this resin coated sand compsn. is adequate for production of the resin coated sand for industrial shell molds.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin coated sand composition for shell molds used when molding a casting mold, and relates to a resin coated sand composition for shell molds having a high mold strength. .

[0002]

2. Description of the Related Art Generally, silica sand, chromite sand, olivine sand, zircon sand or recycled sand of these are used as a refractory material for foundry sand. In some cases, the water adsorption capacity is high. This tendency is particularly remarkable in the reclaimed sand that is recovered by the reclaimer method or the heat treatment method using a fluidized bed after collecting the discharged sand after casting. The resin coated sand for shell molds, which uses a refractory material having a high water adsorption capacity, has a drawback that the strength of the mold is low. This is probably because the phenolic resin used as a binder is absorbed by the pores and cracks on the surface of the refractory material during molding of the mold, and the amount of effective resin that can contribute to the bond between sand particles decreases. ing. In order to solve this drawback, there has been attempted a method of performing preliminary coating with a low-viscosity resin and then performing this coating, but it was not sufficient to improve the strength of the mold.

[0003]

DISCLOSURE OF THE INVENTION The present invention overcomes the drawback that the strength of the mold is low in the resin coated sand for shell molds, which uses a refractory material having a high water adsorption capacity.
Moreover, as a result of diligent research aimed at obtaining a phenol resin which does not deteriorate workability at the time of manufacturing the resin coated sand and curability and workability at the time of molding, a melt viscosity at 150 ° C. including a polyamide resin is 5 to 20 poises. It has been found that very good properties are obtained by using a limited phenolic resin which is

[0004]

DISCLOSURE OF THE INVENTION The present invention provides a resin coated sand coated with a refractory material for castings, which has a water adsorption capacity of 0.6% or more, and the phenol resin contains a polyamide resin. It was found that a resin coated sand composition having extremely good properties can be obtained by using a limited phenol resin having a melt viscosity of 5 to 20 poises at 150 ° C. and completed the present invention.

The water adsorption capacity of the refractory material is a characteristic value related to the surface condition of the refractory material, and the test method is JAC.
T test method: S-8 is described in detail. That is, the refractory material is sufficiently immersed in water and then centrifuged to separate excess water. It is a value obtained by dividing the amount of water adsorbed on the refractory material after the drying treatment by the sample amount of the dried refractory material. Normal fresh sand or regenerated sand whose sand surface has been sufficiently polished has a water adsorption capacity of 0.5% or less. However, if the polishing treatment is insufficient and spongy impurities are adhered to the sand surface, or if the removal of fine powder is insufficient, the water adsorption capacity tends to increase.

The phenol resin containing the polyamide resin of the present invention is effective as a refractory material having a high water adsorption capacity. In the present invention, the phenol resin is a solid phenol resin obtained by reacting phenols and aldehydes in the presence of a catalyst. Phenols used as a raw material are phenol, cresol, xylenol and the like, but those in which bisphenols, urea, melamine and the like are allowed to coexist can also be used. As the aldehyde, formalin, paraformaldehyde, trioxane or the like which can be an aldehyde source can be used. The reaction catalyst is oxalic acid, sulfuric acid,
It is an acidic substance such as hydrochloric acid. The polyamide resin is nylon 6, nylon 66, nylon 610, nylon 11, nylon 12, and mixtures thereof.

The method of incorporating the polyamide resin into the phenol resin may be either a method of dissolving the polyamide resin in phenol before the reaction of the phenol resin or a method of melt mixing the polyamide resin after the reaction of the phenol resin. The amount of polyamide resin contained in the phenol resin is 1 to 20% by weight. If the amount of polyamide resin is less than 1% by weight, the effect of inclusion in the resin is poor and the mold strength is not improved. When the amount of the polyamide resin exceeds 20% by weight, the compatibility with the phenol resin becomes poor and the melt viscosity becomes high so that the mold strength cannot be improved.

The melt viscosity of a phenol resin containing a polyamide resin at 150 ° C. is 5 to 20 poise.
If the melt viscosity is less than 5 poise, the resin is absorbed by the pores and cracks on the surface of the refractory material during the molding of the mold, so that the mold strength cannot be improved. When it exceeds 20 poise, the coating property of the resin on the sand surface is deteriorated and the mold strength is deteriorated. The melt viscosity can be adjusted by selecting the molecular weight of the phenol resin, adjusting the content of the polyamide resin, and adding a phenolic monomer.

In order to further improve the strength of the mold by the resin coated sand which uses the phenol resin containing the polyamide resin in the present invention, it is not necessary to add the lubricant and the silane coupling agent at the time of producing the resin. It is possible. As the lubricant, ethylene bis-stearic acid amide, methylene bis-stearic acid amide, oxystearic acid amide, stearic acid amide, methylol stearic acid amide, etc. are used, and as the silane coupling agent, aminosilane, epoxysilane,
Vinylsilane or the like is used. The dry hot coat method is recommended as the method for producing the resin coated sand employed in the present invention.

[0010]

In the present invention, the reason why the resin coated sand using the phenol resin containing the polyamide resin improves the mold strength is that the polyamide resin having good compatibility with the phenol resin does not impair other properties. It is presumed that the amount of resin adsorbed on the sand surface can be reduced by improving the adhesiveness between the resin component and the resin component and by optimizing the melt viscosity.

[0011]

EXAMPLES The present invention will be described below with reference to examples. However, the present invention is not limited to these examples. Further, "parts" and "%" described in Production Examples, Examples and Comparative Examples all represent "parts by weight" and "% by weight".

[Production Example 1] 1000 parts of phenol was charged into a reaction vessel equipped with a condenser and a stirrer, heated to 120 ± 10 ° C., and while stirring, 6 parts of nylon 6 was gradually added and dissolved. Next, after 10 parts of oxalic acid was charged, 518 parts of 37% formalin was added over 60 minutes, and the state of reflux was further maintained for 60 minutes. Next, dehydration reaction was performed under vacuum, and when the temperature reached 180 ° C., 12 parts of ethylenebisstearic acid amide and 5 parts of γ-aminotriethoxysilane were added and mixed. Then, it was discharged from the reaction vessel and rapidly cooled to obtain 1040 parts of a phenol resin containing a polyamide resin. The melt viscosity of this resin at 150 ° C. was 8 poises.

[Production Example 2] Nylon 6 in Production Example 1
In place of Nylon 66, 650 parts of a phenol resin containing a polyamide resin was obtained by the same reaction method.
The melt viscosity of this resin at 150 ° C. was 12 poise.

[Production Example 3] A reaction vessel equipped with a condenser and a stirrer was charged with 1000 parts of phenol and 10 parts of oxalic acid, and 98
After heating to 0 ° C., 518 parts of 37% formalin was added over 60 minutes, and the state of reflux was further maintained for 60 minutes. Then, the dehydration reaction is performed under vacuum, and when the temperature reaches 180 ° C., the dehydration reaction is terminated, and nylon 6, 80 parts is gradually added to
Nylon 6 was melt-mixed by heating to 30 ° C. After cooling the content to 160 ° C., 12 parts of ethylenebisstearic acid amide and 5 parts of γ-aminotriethoxysilane were added and mixed. Then, it was discharged from the reaction vessel and rapidly cooled to obtain 1020 parts of a phenol resin containing a polyamide resin. The melt viscosity of this resin at 150 ° C. was 15 poise.

Production Example 4 (Comparative Example) 1000 parts of phenol and 10 parts of oxalic acid were placed in a reaction vessel equipped with a condenser and a stirrer, heated to 98 ° C. and then 37% formalin 518.
Parts were added over 60 minutes and maintained at reflux for an additional 60 minutes. Next, dehydration reaction is performed under vacuum, and when the temperature reaches 180 ° C., the dehydration reaction is terminated and the content is cooled to 160 ° C., then 12 parts of ethylenebisstearic acid amide, γ-
5 parts of aminotriethoxysilane was added and mixed. Then, 960 parts of a phenol resin which was discharged from the reaction vessel and rapidly cooled was obtained. The melt viscosity of this resin at 150 ° C. was 4 poises.

Production Example 5 (Comparative Example) 1000 parts of phenol and 10 parts of oxalic acid were placed in a reaction vessel equipped with a condenser and a stirrer, heated to 98 ° C. and then 37% formalin 647.
Parts were added over 60 minutes and maintained at reflux for an additional 60 minutes. Next, dehydration reaction is performed under vacuum, and when the temperature reaches 180 ° C., the dehydration reaction is terminated and the content is cooled to 160 ° C., then 12 parts of ethylenebisstearic acid amide, γ-
5 parts of aminotriethoxysilane was added and mixed. Then, 1050 parts of a phenol resin which was discharged from the reaction vessel and rapidly cooled was obtained. The melt viscosity of this resin at 150 ° C. was 10 poise.

Example 1 8000 parts of regenerated silica sand having a water adsorption capacity of 1.0% heated to a temperature of 140 to 150 ° C. was charged into a whirl mixer, and the phenol resin containing the polyamide resin obtained in Production Example 1 was included. 45 after adding 200 parts
Knead for 2 seconds. Next, an aqueous hexamethylenetetramine solution prepared by dissolving 30 parts of hexamethylenetetramine in 88 parts of water was added, and the mixture was kneaded while air cooling until the coated sand collapsed, and further 8 parts of calcium stearate was added.
After kneading for 0 seconds, the mixture was discharged from the mixer to obtain a resin coated sand.

Example 2 A phenol resin containing the polyamide resin obtained in Production Example 2 was prepared by charging 8000 parts of synthetic new sand having a water adsorption capacity of 0.8% heated to a temperature of 140 to 150 ° C. into the whirl mixer. 45 after adding 200 parts
Knead for 2 seconds. Next, an aqueous hexamethylenetetramine solution prepared by dissolving 30 parts of hexamethylenetetramine in 88 parts of water was added, and the mixture was kneaded while air cooling until the coated sand collapsed, and further 8 parts of calcium stearate was added.
After kneading for 0 seconds, the mixture was discharged from the mixer to obtain a resin coated sand.

Example 3 A phenol resin containing the polyamide resin obtained in Production Example 3 was prepared by charging 8000 parts of regenerated silica sand having a water adsorption capacity of 1.8% heated to a temperature of 140 to 150 ° C. 45 after adding 200 parts
Knead for 2 seconds. Next, an aqueous hexamethylenetetramine solution prepared by dissolving 30 parts of hexamethylenetetramine in 88 parts of water was added, and the mixture was kneaded while air cooling until the coated sand collapsed, and further 8 parts of calcium stearate was added.
After kneading for 0 seconds, the mixture was discharged from the mixer to obtain a resin coated sand.

Comparative Example 1 8000 parts of regenerated silica sand having a water adsorption capacity of 1.0% heated to a temperature of 140 to 150 ° C. was charged into a whirl mixer, and 200 parts of the phenol resin obtained in Production Comparative Example 1 was added. After that, the mixture was kneaded for 45 seconds. Then, an aqueous solution of hexamethylenetetramine in which 30 parts of hexamethylenetetramine is dissolved in 88 parts of water is added, and the mixture is kneaded while being air-cooled until the coated sand collapses. Further, 8 parts of calcium stearate is added and kneaded for 20 seconds,
It was discharged from the mixer to obtain resin coated sand.

Comparative Example 2 8000 parts of regenerated silica sand having a water adsorption capacity of 1.8% heated to a temperature of 140 to 150 ° C. was charged into a whirl mixer, and 200 parts of the phenol resin obtained in Production Comparative Example 2 was added. After that, the mixture was kneaded for 45 seconds. Then, an aqueous solution of hexamethylenetetramine in which 30 parts of hexamethylenetetramine is dissolved in 88 parts of water is added, and the mixture is kneaded while being air-cooled until the coated sand collapses. Further, 8 parts of calcium stearate is added and kneaded for 20 seconds,
It was discharged from the mixer to obtain resin coated sand.

The characteristic values of the resin coated sands obtained in Example 1.2.3 and Comparative Example 1.2 are shown in Table 1. The test method is as follows. 1. Cold bending strength: According to JACT test method SM-1. Firing condition: 250 ° C., 60 seconds 2. Hot tensile strength: According to JACT test method SM-10. Firing condition: 250 ° C, 30 seconds

[0023]

[Table 1]

[0024]

According to the present invention, since it is possible to increase the strength of the shell mold by the resin coated sand for shell mold using the refractory material having a high water adsorption capacity, which has been impossible in the past, the industrial shell mold can be made. It is suitable for manufacturing resin coated sand for use.

Claims (2)

[Claims] 1. A resin-coated sand obtained by coating a refractory material for castings having a water adsorption capacity of 0.6% or more with a phenol resin, wherein the phenol resin contains a polyamide resin and the melt viscosity at 150 ° C. is 5. A resin coated sand composition for a shell mold, wherein the resin coated sand composition is 20 poise. 2. The resin coated sand composition for shell mold according to claim 1, wherein the amount of the polyamide resin contained in the phenol resin is 1 to 20% by weight.