JPS6261375B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a mold, and in particular to a method for manufacturing a mold that significantly improves the collapsibility of the mold after casting, which is mainly used for castings with relatively low casting temperatures such as aluminum castings and alloy castings. . Conventionally, there are various processes for manufacturing molds, but among them, the shell molding method using phenolic resin is widely used, mainly in the automobile industry, because it has excellent mold dimensional stability, has a good mold surface, and has a fast curing speed. ing. However, when used in a mold with a low pouring temperature such as aluminum casting, the mold has poor collapsibility and requires heat treatment for 6 to 12 hours at a high temperature of about 500°C, making it extremely difficult to remove sand after casting. It requires a lot of cost and effort. Therefore, in order to improve the disintegration properties of the mold, a method was developed in which polyisocyanate and polyol were mixed with foundry sand and cured with amine gas, but this method had problems with the toxicity of amine gas and in countermeasures against odor. A self-hardening mold manufacturing method has also been developed in which foundry sand is blended with polyisocyanate and amine polyol, but there is a problem in that it takes a long time to harden. Therefore, there is a strong demand in the foundry industry for the development of a mold manufacturing method that can perform operations similar to the shell molding method and has excellent mold disintegration properties. The inventor of the present invention has conducted intensive studies on a method for manufacturing a mold that requires less heat treatment after casting, disintegrates easily, and can perform the same work as the current shell mold method. By manufacturing a mold by hardening the coated sand coated with the containing composition by heating, the collapsibility after casting is significantly improved, and the work is equivalent to the current shell mold method (sand fluidity, hardening speed) I discovered that it can be done. That is, according to the present invention, when the above resin-coated foundry sand is filled into a mold heated to 150°C and 350°C, the blocking agent of the blocking isocyanate compound dissociates, and the generated isocyanate compound and resol type phenolic resin are separated. Methylol groups, hydroxyl groups, etc. react and the urethane bonds make the mold strong enough to allow it to be removed. Furthermore, the disintegration properties of the mold are significantly improved. This seems to be due to the use of urethane bonding in forming the template. As the blocking isocyanate compound in the composition used in the present invention, an addition reaction product of a polyisocyanate compound and an isocyanate blocking agent is used. As the polyisocyanate compound, any conventionally known isocyanate compound having two or more isocyanate groups can be used, and these polyisocyanate compounds and ethylene glycol, propylene glycol, trimethylolpropane, glycerin, and polyether polyols can be used. A terminal isocyanate group-containing compound obtained by reacting with an active hydrogen compound such as the following may also be used. As the isocyanate blocking agent, any conventionally used one can be used, including phenols such as phenol, cresol, xylenol, and nonylphenol, tertiary alcohols such as t-butyl alcohol, acetylacetone, and malon. Active methylene compounds such as acid diesters, aromatic amines such as methylaniline and diphenylamine, imides such as phthalic acid imide, lactams such as ε-caprolactam, imines such as ethyleneimine, ureas, oximes, bisulfite These include salts and boric acids. The blocked isocyanate compound used in the present invention can be obtained by reacting the above-mentioned isocyanate compound with an isocyanate blocking agent by a conventionally known method. Further, the resol type phenolic resin used in the present invention is preferably a resol resin using bisphenols in order to maintain the dryness of sand, and more preferably one that is solid at room temperature. As the resol type phenol resin, any phenol resin having a methylol group can be used, and the synthesis of the resol type phenol resin is not particularly limited, but phenol, cresol, bisphenol A, bisphenol S, bisphenol Phenols such as phenol F and formaldehyde are mixed with NaOH and Ba.
It is obtained by a conventionally known method by reaction using a synthetic catalyst such as (OH) ₂ , ammonia, or trimethylamine. As a resol type bisphenol resin,
A resin obtained by reacting bisphenols such as bisphenol A, bisphenol S, and bisphenol F with formaldehyde using a catalyst such as NaOH, Ba(OH) ₂ ammonia, or trimethylamine is used. As a resol type bisphenol resin, formaldehyde is 1.5 to 1 mole of bisphenol A.
A resin obtained by reacting 4.0 mol is preferably used. If the amount of formaldehyde is less than 1.5 mol, the number of methylol groups will decrease and the curing rate will be slow, and if the amount of formaldehyde exceeds 4.0 mol, the odor of formaldehyde will become strong during heat curing of the sand mold, which is not preferable. The resin-coated sand for foundries used in the present invention has a
It is obtained by stirring and mixing a solid or solution blocked isocyanate compound and a resol type phenol resin in foundry sand heated to 180°C, and evaporating the solvent as necessary during this mixing process. When the temperature of the foundry sand exceeds 180° C., the blocked isocyanate compound begins to dissociate, which not only shortens the life of the foundry resin-coated sand but also reduces the strength of the sand mold, which is undesirable. Further, if the temperature is less than 90°C, the resin coating becomes insufficient or the solvent evaporates insufficiently, which lowers the melting point of the resin-coated sand for foundries and causes blocking, which is not preferable. Also, the blending ratio (weight ratio) of the blocking isocyanate compound and resol type phenol resin to be used is
Used in the range of 95:5 to 5:95, preferably
Used in the range of 85:15 to 30:70. If the blocking isocyanate compound is too large, curing will be delayed, and if the resol type phenolic resin is too large, the disintegrability of the sand mold will be poor. Also, the heating temperature when manufacturing the mold is 150℃~350℃
It is. If the temperature is less than 150°C, the curing of the mold will be slow, and if it exceeds 350°C, there will be disadvantages such as a decrease in the strength of the mold or a worsening of the surface of the mold. The total amount of the blocked isocyanate compound and the resol type phenolic resin in the composition to be mixed with the sand and coated is 7.0 to 0.3% by weight, preferably 3.0 to 0.5% by weight, based on the foundry sand. If the total amount of resin added exceeds 7%, it is not good because it not only causes gas defects during casting manufacturing but also increases the price. or
If it is less than 0.3%, the strength of the sand mold will be too low to be of practical use. Furthermore, any of the conventionally known dissociation catalysts for blocked isocyanate compounds can be used for the foundry resin-coated sand obtained in the present invention, such as dibutyl tin dilaurate,
Tinnic chloride, cobalt naphthenate, etc. may be added, and the amount of catalyst added is 0.01 to 0.01 to the resin solid content.
It is 1.0% by weight. In addition, a lubricant such as calcium stearate used in the shell molding method may be added to resin-coated sand for foundries to improve fluidity.
The amount of lubricant added is 0.05 to 0.2% by weight based on foundry sand. In addition, when producing resin-coated sand for foundries, the method of mixing the blocked isocyanate compound and the resol type phenolic resin is not particularly limited, and even if both components are mixed in advance before stirring and mixing with the sand, They may be added separately during mixing. Further, the foundry sand used in the present invention may be any of those commonly used for foundries, and zircon sand and olivine sand can also be used. Examples of the present invention will be shown below. Example 1 (Synthesis of resol type phenolic resin) 2280 g of bisphenol A and 1620 g of 37% formalin were put into a four-necked flask equipped with a reflux condenser, 40 g of 20% NaOH aqueous solution was added, and the mixture was reacted at reflux temperature for 2 hours, followed by dehydration and concentration. A solid resin was obtained. (Production method of resin-coated sand for foundries) 8 kg of flattery silica sand heated to 160℃ in a kneader
Add 120 g of Coronate AP Stable (manufactured by Nippon Polyurethane Co., Ltd., phenol-masked isocyanate compound, softening point: approximately 10°C) and 40 g of the resol type phenolic resin obtained above, and stir and mix until the sand disintegrates. Thereafter, 8 g of calcium stearate was added and mixed for an additional 20 seconds to obtain resin-coated foundry sand. Table 1 shows the characteristics of the sand mold. Example 2 8 kg of flattery silica sand heated to 110°C in a kneader
100g of Coronate AP Stable and 60g of acetone
A solution consisting of 100 g of the resol type phenolic resin obtained in Example 1 and 60 g of acetone was added and mixed with stirring until the sand disintegrated. Thereafter, 8 g of calcium stearate was added and mixed for an additional 20 seconds to obtain resin-coated foundry sand. Table 1 shows the characteristics of the sand mold. Example 3 8 kg of flattery silica sand heated to 160°C in a kneader
Clelan Cross Linking Agent UT
(Manufactured by Sumitomo Bayer Urethane Co., Ltd., isocyanate compound masked with ε-caprolactam, softening point approximately 100°C) After adding 100g and stirring and mixing for 40 seconds, the resol-type phenolic resin obtained in Example 1 (60g) and methanol (30g) were added. Add the solution and mix until the sand is broken down. Thereafter, 8 g of calcium stearate was added and mixed for an additional 20 seconds to obtain resin-coated foundry sand. Table 1 shows the characteristics of the sand mold. Example 4 Resin-coated sand for foundries was obtained in the same manner as in Example 3, except that 1.6 g of dibutyltin dilaurate was added. Table 1 shows the characteristics of the sand mold. Comparative Example 1 (Manufacture of novolac type phenolic resin) 1880 g of phenol, 244 g of 37% formalin, and 488 g of 80% paraformaldehyde were put into a four-necked flask equipped with a reflux condenser, 4 g of oxalic acid was added, and the mixture was reacted at reflux temperature for 3 hours. After this, a solid resin was obtained by dehydration and concentration. (Manufacture of resin-coated sand for foundries) 8 kg of flattery silica sand heated to 160℃ in a kneader
The novolak type phenolic resin obtained above
After adding 160 g and stirring and mixing for 40 seconds, add a solution consisting of 24 g of hexamethylenetetramine and 80 g of water and stirring and mixing until the sand disintegrates. Thereafter, 8 g of calcium stearate was added and mixed for an additional 20 seconds to obtain resin-coated foundry sand. Table 1 shows the characteristics of the sand mold. Comparative Example 2 8 kg of flattery silica sand heated to 160℃ in a kneader
100 g of Coronate AP Stable and 60 g of the novolak type phenolic resin obtained in Comparative Example 1 were added to the mixture, and the mixture was stirred and mixed until the sand disintegrated. Thereafter, 8 g of calcium stearate was added and mixed for an additional 20 seconds to obtain resin-coated foundry sand. Table 1 shows the characteristics of the sand mold. Comparative Example 3 8 kg of flattery silica sand heated to 110℃ in a kneader
100g of Coronate AP Stable and 60g of acetone
A solution consisting of Sannix HS-207 (manufactured by Sanyo Chemical Industries, Ltd., Sucrose polyol with a viscosity of approx.
A solution consisting of 60g of 70P/25°C) and 30g of acetone was added and mixed for 3 minutes, then 8g of calcium stearate was added and mixed for a further 20 seconds to obtain resin-coated sand for foundry use. Table 1 shows the characteristics of the sand mold.

[Table] By using the method for producing a mold according to the present invention, a mold can be obtained which has sand fluidity equivalent to that of the Shell mode method, a sand mold hardening speed, and excellent mold disintegrability.

Claims (1)

[Scope of Claims] 1. A method for producing a mold, which comprises curing resin-coated foundry sand by heating, which is obtained by coating foundry sand with a composition containing a blocked isocyanate compound and a resol type phenolic resin. 2. The method for manufacturing a mold according to claim 1, wherein the resol type phenolic resin is a resol type bisphenol resin. 3. The method for producing a mold according to claim 1 or 2, wherein the resol type bisphenol resin is a resin obtained by reacting 1.5 to 4.0 moles of formaldehyde with 1 mole of bisphenol A. . 4. The mold manufacturing method according to claim 1, wherein the heating temperature is 150°C to 350°C.