JPH0337817B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to resin-coated sand for shell molds,
In particular, the present invention relates to resin-coated sand for shell molds, which is used for castings made of materials such as aluminum alloy castings or light alloy castings, where the pouring temperature is relatively low at 700 to 800°C, and improves the collapsibility of the mold after casting. [Prior Art] Generally, the mainstream method for molding mold cores for mass production is the shell molding method, which uses coated sand in which foundry sand is coated with phenolic resin. However, the pouring temperature for phenolic resins, like aluminum alloys, is low.
For materials with a temperature of 700 to 800℃, which is lower than iron's temperature of 1300 to 1400℃, the mold core has poor collapsibility after pouring because it is not treated at high temperatures, making it extremely difficult to remove sand. Therefore, the current situation is to have a separate sand removal process and spend a lot of money and effort to remove the sand. As the weight of automobiles decreases, the amount of light alloys used tends to increase, and there is a strong demand for improved resins that have the physical properties necessary for shell molds and are more easily disintegrated than conventional phenolic resins because they thermally decompose at lower temperatures. ing. The first method to improve disintegration properties is to use resins with bonds that easily undergo thermal decomposition reactions at low temperatures;
JP-A No. 55-165252 uses unsaturated polyester resin as a binder, and focuses on the fact that it has ester bonds that are essentially more easily thermally decomposed at low temperatures than phenol resins, and it does not disintegrate. Although the properties are improved, the strength of the core is low and it is not suitable for cores with complex shapes. Furthermore, although it has excellent disintegration properties at low temperatures, thermal decomposition of the binder is accelerated during molding of the core and pouring, which causes bad odors and worsens the working environment, which has a negative impact on the human body and is a cause of industrial pollution. That's a problem. The second method to improve the disintegration property is to add a thermal decomposition accelerator to the phenolic resin, but Japanese Patent Application Laid-open No. 149043/1983 discloses that a bromine-containing organic compound is used as a substance that promotes oxidative decomposition. Heating splits Br or Br compounds, oxidizes and decomposes the phenolic resin and improves the disintegration of the mold. However, it generates a harmful odor during core molding and pouring, and causes metallurgical damage. Since it is highly corrosive to molds and machines, a disintegration promoter for molds after molding that satisfies these conditions has not yet been completed. A third method for improving the disintegration property is to modify the conventional phenolic resin with a polymeric substance or resin that exhibits thermal decomposition at low temperatures, and many methods have been proposed in the past. JP-A No. 56-114546 proposes a resin in which phenols, synthetic organic fibers, and formaldehyde are reacted under an acidic or alkaline catalyst when producing phenolic resin, but in order to improve disintegration, it is necessary to use a resin at low temperatures. Fibrous polymers that cause thermal decomposition have too much molecular weight and are shaped like cores, and thermal decomposition is delayed in areas where heat is difficult to conduct, making it unsatisfactory to provide sufficient disintegration properties. . [Problems to be Solved by the Invention] The purpose of the present invention is to eliminate the above-mentioned drawbacks of the conventional techniques, to eliminate the need for large costs and labor, and to solve the problems of the conventional coated sand and the poor mold strength. and molding properties, and the pouring temperature is excellent for disintegration after pouring.
The object of the present invention is to provide resin-coated sand for shell molds, which is suitable for casting of low-temperature materials of 700 to 800°C. [Means for solving the problem] As a result of intensive research, the present inventors found that ε-
Coated sand coated with a resin obtained by modifying or mixing phenolic resin with one or more compounds and/or resins selected from caprolactam, nylon oligomer, polyvinyl acetate resin, polyester resin, and acrylic resin can be used. We have completed the present invention by discovering that the characteristics of chain polymers are utilized, the crosslinking density during curing is relaxed, the thermal decomposition temperature is lowered, and the disintegration properties after pouring are significantly improved. The present invention comprises phenols, ε-caprolactam, nylon oligomer, polyvinyl acetate resin,
1 selected from polyester resin and acrylic resin
This is resin-coated sand for shell molds, characterized in that the sand is coated with a resin obtained by reacting at least one type of compound and/or resin and formaldehyde under an acidic or alkaline catalyst. In carrying out the present invention, for example, phenols and formaldehyde are reacted under an acidic or alkaline catalyst to first form an initial product of phenolic resin, and then ε-caprolactam, nylon oligomer, polyvinyl acetate resin, etc. Resin-coated sand for shell molds can be obtained by coating sand with a resin obtained by reacting with one or more compounds selected from polyester resins and acrylic resins and/or resins. The phenols used in the present invention are phenol, m-cresol, p-cresol, 3-cresol,
Meta- or para-alkyl phenols such as 4-xylenol, 3-5-xylenol, and mixtures of these phenols. Formaldehydes used in the present invention include formalin, paraformaldehyde, trioxane, polyoxymethylene, tetraoxymethylene, and mixtures of these formaldehyde polymers. The amount of formaldehyde used is preferably in the range of 0.5 to 2.5 moles per mole of phenols. The amount of one or more compounds and/or resin selected from ε-caprolactam, nylon oligomer, polyvinyl acetate resin, polyester resin, and acrylic resin used in the present invention mixed into the total resin and reacted is 5 to 40% by weight. % range is preferable; if it is less than 5% by weight, the effect will be small, and if it is more than 40% by weight, the disintegration property after pouring will be improved, but the curing property during core molding will be slow and the practicality will be reduced. [Example] The present invention will be explained below with reference to Examples. Since the resin-coated sand for shell molds of the present invention is coated in the same manner as conventional phenolic resin-coated sand, a phenolic resin modified with an organic compound or resin exhibiting low-temperature thermal decomposition will be described. Percentage depends on weight. Example 1 940 g of phenol, 100 g of ε-caprolactam,
465 g of 50% formalin and 6.6 g of oxalic acid were charged into a reaction vessel equipped with a reflux condenser and reacted under reflux for 3.0 hours, and then dehydrated and concentrated under reduced pressure to reach a softening point of 85.
A ε-caprolactam modified phenolic resin was obtained. Example 2 Nylon oligomer was used in place of ε-caprolactam in Example 1. A nylon oligomer-modified phenolic resin having a softening point of 86° C. was obtained in the same manner as in Example 1 except for the above. Example 3 Polyvinyl acetate resin was used in place of ε-caprolactam in Example 1. A polyvinyl acetate resin-modified phenolic resin having a softening point of 84° C. was obtained in the same manner as in Example 1 except for the above. Example 4 Polyester resin was used in place of ε-caprolactam in Example 1. A polyester resin-modified phenolic resin having a softening point of 88° C. was obtained in the same manner as in Example 1 except for the above. Example 5 Acrylic resin was used in place of ε-caprolactam in Example 1. An acrylic resin-modified phenolic resin having a softening point of 85° C. was obtained in the same manner as in Example 1 except for the above. Example 6 Phenol 940g, 50% formalin 450g, oxalic acid
After charging 6.6 g into a reactor equipped with a reflux condenser and performing a reflux reaction under reflux until emulsification, 300 g of ε-caprolactam was added, and the mixture was allowed to reflux under reflux for 2.0 hours, followed by dehydration and concentration under reduced pressure. ,
An ε-caprolactam modified phenolic resin with a softening point of 85°C was obtained. Example 7 In place of ε-caprolactam in Example 6, 400 g of nylon oligomer was used. A nylon oligomer-modified phenol resin having a softening point of 80° C. was obtained in the same manner as in Example 6 except for the above. Example 8 In place of ε-caprolactam in Example 6, 350 g of polyvinyl acetate resin was used. Otherwise, a polyvinyl acetate resin-modified phenol resin having a softening point of 82° C. was obtained in the same manner as in Example 6. Example 9 In place of ε-caprolactam in Example 6, 500 g of polyester resin was used. A polyester resin-modified phenolic resin having a softening point of 80° C. was obtained in the same manner as in Example 6 except for the above. Example 10 In place of ε-caprolactam in Example 6, 600 g of acrylic resin was used. An acrylic resin-modified phenolic resin having a softening point of 80° C. was obtained in the same manner as in Example 6 except for the above. Example 11 940 g of phenol and 100 g of nylon oligomer were placed in a reaction vessel equipped with a reflux condenser and dissolved by heating, followed by 1200 g of 50% formalin and 25% aqueous ammonia.
122g was charged and reacted at 80°C for 1.5 hours, then the temperature was gradually raised to 90°C while removing moisture under reduced pressure, and when it reached 95°C, it was immediately removed from the reactor and rapidly cooled to a softening point of 80°C. A nylon oligomer modified resol type solid phenolic resin was obtained. Example 12 In place of the nylon oligomer in Example 11, 100 g of polyester resin was used. Other examples are examples
A polyester-modified resol type solid phenolic resin having a softening point of 82°C was obtained in the same manner as in Example 11. Comparative example 1 940g of phenol, 450g of 50% formalin, oxalic acid
6.6 g was charged into a reactor equipped with a reflux condenser and reacted under reflux for 3.0 hours, followed by dehydration and concentration under reduced pressure to obtain a novolak type phenolic resin with a softening point of 81°C. Comparative Example 2 Phenol 940g, 50% formalin 1080g, 35
Pour 122g of ammonia water into a reaction vessel and heat to 80℃1.0
The temperature was gradually raised to 90°C while removing moisture under reduced pressure, and when it reached 95°C, it was immediately removed from the reactor and the softening point was 78.
A resol-type solid phenolic resin at ℃ was obtained. Test Example Table 1 shows the results of testing the properties of the resin-coated sand for shell molds of the present invention, which was obtained by coating molding sand with the resins obtained in the Examples and Comparative Examples. Put 10 kg of silica sand heated to 140℃ and 0.2 kg of resin into a speed mixer for kneading foundry sand, and knead for 60 seconds. Next, add hexane water in which 0.03 kg of hexane is dissolved in 0.1 kg of water, and continue kneading for about 60 seconds. Thereafter, calcium stearate was added and kneaded for a further 20 seconds to obtain resin-coated sand for shell molds of the present invention. The characteristics of this resin-coated sand are shown, however, hexamine is not required for resol-type resin.

【table】

〔Effect of the invention〕

As is clear from the table of Examples, it was observed that the disintegration properties of the cores treated at 500°C were significantly improved.

Claims (1)

[Claims] 1. One or more compounds and/or resins selected from phenols, ε-caprolactam, nylon oligomers, polyvinyl acetate resins, polyester resins, and acrylic resins, and formaldehyde,
The amount of formaldehyde used is 1 phenol.
The amount of the organic compound or resin exhibiting low temperature thermal decomposition mixed into the resin and reacted is in the range of 5 to 40% by weight under an acidic or alkaline catalyst. 1. Resin-coated sand for shell molding, characterized in that sand is coated with a resin obtained by reaction.