JPH09239486A - Resin coated sand for shell mold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide resin coated sand for shell molds having the higher normal strength than the normal strength of conventional coated sand and the excellent collapsing property of casting molds after pouring. SOLUTION: This resin coated sand for the shell molds is produced by coating the sand with a novolak type phenol-triazine cocondensation resin obtd. by bringing a mixture composed in a range of a molar ratio (P/T)=4.0 to 19.0 of phenols (P) and triazine compd. (T) and molar ratio F/(P+T)}=0.45 to 0.90 of formaldehydes (F), phenols (P) and triazine compd. (T) into reaction at pH<=4.0 by an acidic catalyst.

Description

Detailed Description of the Invention [Object of the invention]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin-coated sand for a shell mold, and more particularly to a resin-coated sand for a shell mold which has high normal strength and improved disintegration of a mold after pouring.

2. Description of the Related Art Conventionally, as a phenol resin used for producing a resin-coated sand for shell mold, formaldehydes (F) and phenols (P) are generally used in a molar ratio (F / P) = 0.4- A solid novolac type phenolic resin obtained by reacting in the presence of an acidic catalyst at a ratio of 0.9 is used as a binder, hexamethylenetetramine (hereinafter hexamine) is used as a curing agent, and these are mixed with heated silica sand. A method of producing a resin-coated sand by using the above-mentioned method and manufacturing a mold using the resin-coated sand is widely used. However, in these conventional phenolic resins, in order to provide high strength, the curing density of the resin must be increased or the amount of resin added must be increased, which inevitably improves the heat resistance, resulting in a mold core after pouring. The disintegration of the part that is not treated at high temperature is bad,
Sand removal was very difficult. It has been known to add a triazine compound / formaldehyde condensation resin to a novolac type phenol resin by blending or at the time of kneading with silica sand. However, sufficient strength cannot be obtained, or a fusion point is lowered to cause blocking. The current situation is that it has not been put to practical use because it has the drawback of inducing
Also, sufficient disintegration cannot be obtained.

DISCLOSURE OF THE INVENTION The present invention uses a novolac-type phenol-triazine co-condensation resin, which has excellent disintegration after pouring and has higher strength than conventional coated sand. The purpose is to provide coated sand.

Configuration of the Invention

Means for Solving the Problems As a result of intensive studies conducted by the present inventors in order to achieve the above objects, sand coated with a resin obtained by co-condensing a triazine compound in the production of a phenol resin for a shell mold It was found that the use of the above-mentioned material disturbs a part of the three-dimensional network structure having high heat resistance and lowers the thermal decomposition temperature, while maintaining high strength at room temperature and remarkably improving the disintegration property after pouring. The novolac-type phenol-triazine co-condensation resin of the present invention has a molar ratio (P / T) of phenols (P) to triazine compound (T) of 4.0 to 19.0, formaldehydes (F) and phenol (P). ) And the molar ratio of the triazine compound (T) {F / (P + T)} = 0.45 to 0.9
A mixture composed of a range of 0 to pH 4.
It is obtained by adjusting to 0 or less and reacting. The phenols used in the present invention are phenols or alkylphenols such as o-cresol, m-cresol, p-cresols, bisphenols and mixtures of these phenols. Examples of the triazine compound used in the present invention include compounds having a triazine ring such as melamine, acetoguanamine, and benzoguanamine, and mixtures of these triazine compounds. Formaldehyde used in the present invention,
Examples include formalin or paraformaldehyde, trioxane, polyoxymethylene, tetraoxymethylene, and mixtures of these formaldehyde polymers. The acidic catalyst used in the present invention may be either an inorganic acid (sulfuric acid, hydrochloric acid, etc.), an organic acid (paratoluenesulfonic acid, oxalic acid, etc.), or a mixture thereof. The novolac-type phenol-triazine co-condensation resin used in the present invention is synthesized by using the above raw materials. First, phenols and triazine compounds were charged into a reaction vessel so that their molar ratio (P / T) was 4.0 to 19.0. Then, formaldehydes were added to these in a molar ratio {F / (P + T )} = 0.45-0.
Prepare so that it becomes 90. Then, the catalyst is added so that the pH becomes 4 or less, and the temperature is gradually raised to atmospheric pressure, 1
After reacting at 00 ° C. for 2 to 8 hours from the start of reflux, then 200
Dehydration is performed while raising the temperature to 0 ° C, and when the temperature reaches 200 ° C, the water content and unreacted phenol are further removed by vacuum concentration to obtain the target resin. An internal lubricant (ethylene bisstearamide, etc.) and a silane coupling agent (γ-aminopropyltriethoxysilane, etc.) are added to the resin obtained by the above method. Although the resin obtained by the above-mentioned method has a long gel time, the bend value is almost the same as that of the comparative example as shown in the section of Examples, and the work is not hindered. It is expected that the gel state, that is, the three-dimensional network structure, is different from that of phenol alone. This novolac-type phenol-triazine co-condensation resin was previously
Add to kneaded sand heated to 0 to 180 ° C., knead, add an aqueous solution of hexamine in which hexamine is dissolved in water, knead until the resin-coated sand disintegrates, and then add a lubricant such as calcium stearate or zinc stearate. Obtain resin coated sand. The amount of resin added is 0.5 to 6.0%, preferably 1.0 to 3.0%, based on the sand. Hexamine is added to the resin in an amount of 5 to 25%, preferably 10 to 20%
It is. The kneading may be carried out by an ordinary method, and as the casting sand, other than silica sand, zircon sand, chromite sand, olivine sand, alumina sand, mullite sand and the like can be applied in exactly the same manner as in the prior art. The resin-coated sand thus obtained has high strength and is excellent in mold disintegration after pouring.

EXAMPLES The present invention will now be described in detail with reference to examples, but the present invention is not limited to the examples. In addition,
Parts or% in the examples are parts by weight unless otherwise specified. Example 1 A reaction vessel was charged with 678 parts of phenol, 101 parts of melamine and 192 parts of 50% formalin. Then, 27 parts of oxalic acid was charged, and the temperature was gradually raised to 100 ° C.
After the temperature reached, the reaction was refluxed for 4 hours. Then 200 ° C
The dehydration reaction is carried out while the temperature is raised to 200 ° C., and when the temperature reaches 200 ° C., the pressure is reduced to 14.2 Pa and the water content and
After removing unreacted phenol, an internal lubricant / silane coupling agent was added and taken out in a cooling vat to obtain 492 parts of a novolac-type phenol / melamine co-condensed resin which was solid at room temperature. 160 parts of this novolac-type phenol / melamine co-condensation resin was added to 8000 parts of silica sand preheated to 140 to 150 ° C., and kneaded for 60 seconds with a speed muller manufactured by Enshu Tekko Co., Ltd.
A hexamine aqueous solution dissolved in 1 part was kneaded until the resin-coated sand was disintegrated, then 8 parts of calcium stearate was added and mixed for 10 seconds to obtain a resin-coated sand. Example 2 A reaction vessel was charged with 715 parts of phenol, 50 parts of melamine, and 288 parts of 50% formalin. Next, 29 parts of oxalic acid was charged, the temperature was gradually raised, and after reaching 100 ° C., a reflux reaction was carried out for 4 hours. Then, dehydration reaction was carried out while raising the temperature to 200 ° C. When the temperature reached 200 ° C., the pressure was reduced to 14.2 Pa to further remove the water content and unreacted phenol, and then an internal lubricant / silane coupling agent was added. Then, it was taken out in a cooling vat to obtain 672 parts of a novolac-type phenol / melamine co-condensed resin which was solid at room temperature. 160 parts of this novolac type phenol / melamine co-condensation resin was kneaded in the same manner as in Example 1 to obtain resin-coated sand. Example 3 A reactor was charged with 447 parts of phenol, 28 parts of benzoguanamine, and 180 parts of 50% formalin. Then, add 18 parts of oxalic acid, gradually raise the temperature,
After reaching 100 ° C., a reflux reaction was carried out for 4 hours. Then, dehydration reaction was performed while raising the temperature to 200 ° C., and when the temperature reached 200 ° C., the content of water and unreacted phenol were further reduced by reducing the pressure to 14.2 Pa, and then an internal lubricant / silane coupling agent was added. Then, it was taken out in a cooling vat to obtain 416 parts of a novolac-type phenol / guanamine co-condensation resin which was solid at room temperature. 160 parts of this novolac-type phenol-guanamine co-condensation resin was used in Example 1.
Kneading was carried out in the same manner as above to obtain resin-coated sand. Comparative Example 1 A reaction vessel was charged with 400 parts of phenol and 179 parts of 50% formalin. Then, 2 parts of 10% hydrochloric acid was charged, the temperature was gradually raised, and after reaching 100 ° C., a reflux reaction was carried out for 4 hours. Next, dehydration reaction was performed while raising the temperature to 200 ° C., and when reaching 200 ° C., 14.2 Pa
When the water content and the unreacted phenol were further removed by depressurizing, the internal lubricant / silane coupling agent was added and taken out into a cooling vat to obtain 395 parts of a novolac type phenol resin solid at room temperature. 160 parts of this novolac type phenol resin was kneaded in the same manner as in Example 1 to obtain resin-coated sand. [Comparative Example 2] 260 parts of phenol, 140 parts of bisphenol A, and 109 parts of 50% formalin were charged into a reaction vessel. Then, 2 parts of 10% hydrochloric acid was charged, and the temperature was gradually raised to 1
After reaching 00 ° C, a reflux reaction was carried out for 4 hours. Then 2
The dehydration reaction was carried out while the temperature was raised to 00 ° C, and when the temperature reached 200 ° C, the pressure was reduced to 14.2 Pa to further remove the water content and unreacted phenol.
A silane coupling agent was added, and the mixture was taken out in a cooling vat to obtain 338 parts of a novolac type phenol resin which was solid at room temperature. 160 parts of this novolac type phenol resin
Kneading was performed in the same manner as in Example 1 to obtain resin-coated sand. Comparative Example 3 5 parts of melamine was melt-mixed with the resin 95 of Comparative Example 1. 160 parts of this novolac-type phenol resin / melamine mixture was kneaded in the same manner as in Example 1 to obtain resin-coated sand.

[Test example]

-Resin test method Cold bending strength: According to JIS K6910. Fusion point: According to JACT test method C-1.

[Table 1] Resin properties

[Table 2] Characteristics of resin-coated sand

EFFECTS OF THE INVENTION By using the novolac-type phenol / triazine compound co-condensation resin for a mold obtained according to the present invention, a resin-coated sand for shell mold having high strength and excellent in collapsibility of the mold after pouring is obtained. be able to. As a result, it can be widely used as a binder for a mold in the shell molding method, which is excellent in workability during molding.

Claims (1)

[Claims] 1. A molar ratio (P / T) of phenols (P) to a compound having a triazine ring (T) (hereinafter referred to as a triazine compound) = 4.0 to 19.0, formaldehydes (F) to phenols, and A novolac-type phenol-triazine co-condensation resin obtained by reacting a mixture composed of a triazine compound in a molar ratio {F / (P + T)} of 0.45 to 0.90 with an acidic catalyst at a pH of 4.0 or less. A resin-coated sand for a high-strength, easily disintegrating shell mold, which is characterized by being coated with sand.