JPS6240949A - Resin composition for coated sand - Google Patents

Abstract

PURPOSE:To obtain a resin compsn. for coated sand for a shell mold method which has a good collapsing property of a core during low-temp. casting and obviates the generation of casting defects arising from the generation of gaseous nitrogen in a casting stage by using a furan resin having specific structure as an essential component. CONSTITUTION:The resin compsn. for coated sand for a casting essentially consisting of the furan resin including >=2, more preferably 2-4 furan rings in one molecule adequately contains 30-100wt% above-mentioned furan resin. The above-mentioned furan resin is obtd. by polymerizing furfuryl alcohol alone or furfuryl alcohol and aldehyde in the presence of an acidic catalyst such as phosphoric acid or xylene sulfonic acid. The above-mentioned resin compsn. is thrown into the heated molding sand at about 0.8-8wt% by 100pts.wt. molding sand and the mixture is thoroughly agitated by a mixer to uniformly stick the resin compsn. on the surface of the molding sand. The coated sand is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a resin composition for coated sand used in shell molding.

Conventional technology Conventionally, resin compositions for coated sand generally used in the shell molding method are composed of a novolac type phenolic resin obtained by reacting phenols and formaldehydes in the presence of a catalyst, and hegisamidetetramine as a curing agent. Compositions are known and this mixture is mixed with foundry sand grains to make resin-coated sand for shell molds.

However, shell molds made from coated sand using conventional phenolic resin have the disadvantage that hexamethylenetetramine decomposes during firing during J1 molding and generates an ammonia odor, which worsens the working environment. There is also the drawback that nitrogen gas generated by thermal decomposition of hexamethylenetetramine has an adverse effect on castings even when hot water is used.

Furthermore, when casting high-melting point metals such as iron, using coated sandshell molds made of phenolic resin,
The mold is exposed to high temperatures, the phenolic resin thermally decomposes, and the mold collapses. However, when a light metal with a low melting point such as aluminum is poured, the internal temperature of the shell mold remains at a low temperature of 300 to 500°C. For this reason,
Thermal decomposition of the phenolic resin may be insufficient, resulting in poor collapsibility, and it may be extremely difficult to remove the core from the casting. For this reason, in order to remove the shell core, a method is used in which the casting is heated in a kiln for a long period of time in a so-called sand firing process to cause the core to collapse. This leads to wasted energy and reduced productivity, and improvements are desired.

On the other hand, a filtrate-like initial cured product (usually called furan resin) is obtained by polymerizing furfural or furfuryl alcohol as a main component with urea, formaldehyde, phenol, etc. using an acid catalyst. ) is used as a foundry Sunagawa binder for pot boxes, etc.

However, these resins whose main component is furfuryl alcohol are liquid at room temperature because furfuryl alcohol is a monomer or a low-molecular substance containing only one furan ring in the molecule, and cannot be mixed with foundry sand grains. However, the coated sand remains wet and smooth and fluid coated sand for shell molding cannot be obtained.

Japanese Patent Publication No. 40-28443 proposes the use of an initial condensate of furfuryl alcohol-modified urea formaldehyde resin as a binder for shell molds. Since it was unsuitable for obtaining coating sand for shell molds, it was made with ureid to increase its viscosity and make it harden quickly. Not suggested at all.

Problems to be Solved by the Invention The present invention addresses the drawbacks of phenolic resins conventionally used as binders for coated sand for shell molds, such as poor decomposition of cores during low-temperature casting such as aluminum molds, and hardening agents. To provide a resin composition for coated sand that does not cause casting defects due to ammonium odor caused by (hexamedylenetetramine) and nitrogen gas generated by thermal decomposition.

Means for Solving the Problems - 3~ The present invention relates to a resin composition for coated sand for foundries, the main component of which is a furan resin containing two or more furan rings in one molecule.

The furan resin used in the present invention is obtained by reacting furfuryl alcohol or furfuryl alcohol with an aldehyde in the presence of an acid catalyst and has a polymerization degree of 2 to IO1, particularly 2 to 4.
It is a resin.

Acidic catalysts for reacting furfuryl alcohol alone or with furfuryl alcohol and aldehydes include inorganic acid aqueous solutions such as phosphoric acid, sulfuric acid, and hydrochloric acid, as well as xylene sulfonic acid, toluene sulfonic acid, benzenesulfonic acid, oxalic acid, Organic acids such as lactic acid can also be used. After the reaction, dehydration is performed under reduced pressure to neutralize the reaction solution and remove unreacted furfuryl alcohol, unreacted aldehydes, and condensed water, and the polymerization reaction is performed so that one molecule contains two or more furan rings. proceed. The reaction product may be washed with water and then dehydrated.

In the present invention, formaldehyde, acetaldehyde, a portion of glyoxa, etc. can be used as aldehydes. Although the present invention does not necessarily require the use of aldehydes, the reaction of the resin can generally proceed more quickly than when aldehydes are not used.

As the resin component of the present invention, a portion of phenols such as phenol, cresol, bisphenol, etc. may be blended, but when these are blended, the resin viscosity generally decreases.

The resin composition of the present invention is generally solid at room temperature, but it can be made to adhere uniformly to the surface of the foundry sand by pulverizing it or putting it into heated foundry sand in the form of a lump, and thoroughly stirring it with a mixer. .

0.8 to 100 parts by weight of the resin composition of the present invention per 100 parts by weight of foundry sand
8 parts by weight, especially 1 to 5 parts by weight.

The resin composition of the present invention may contain a coupling agent (for example, dimethoxysilane), a lubricant (calcium stearate), etc., if necessary.

Furthermore, in a method of producing coated sand by mixing the resin composition for coated sand according to the present invention with foundry sand grains, fatty acid amides, fatty acid calcium, and waxes are added as lubricants to improve fluidity. May be improved. These may be used by being added internally to the resin composition in advance. In addition, a silane compound may be added internally to the resin composition as a strength improver, or may be added at the time of producing the J-coated sand.

As a more effective conditioning method of the present invention, when producing coated sand, an acid that is solid at room temperature such as oxalic acid, salicylic acid, maleic acid, boric acid, paratoluene sulfonic acid, etc. is added to the resin composition. By adding 05 to 10% by weight, the firing temperature of coated sand can be lowered,
Firing time can be shortened.

The present invention will be explained below with reference to Examples.

Concentration %j+ 300g furfuryl alcohol, 1 water in a four-eye flask
50g, 4g of 20% phosphoric acid was added as a reaction catalyst, and 1
)T(2,0. Gradually raise the temperature until the reaction temperature is 9.
The reaction was carried out at 5°C for 9 hours.

After the reaction, the reaction solution was neutralized with a 20% aqueous sodium hydroxide solution to obtain 1) H6.5. After that, the degree of decompression is -600
The resin was dehydrated at mmHg until the resin temperature reached 05°C.

Next, 4 kg of Flatarisand heated to 200°C was put into the Speed Migizer, and the resin composition 12 of "2.
When the mixture started blocking, 4 g of calcium stearate was added and cooled to prepare coated sand. A fluid coated sand was obtained. The transverse rupture strength of this coated sand was measured. The results are shown in Table 1.

Furthermore, when an aluminum casting AC-40 was cast using a shell mold using this coated sand, the collapsibility was very good compared to a shell mold using a phenol resin.

Example 2 Example 1 was repeated using the synthesis method of Example 1 except that 80 g of 37% formalin was added. When the transverse rupture strength was measured using this coated sand, the results shown in Table 1 were obtained.

Furthermore, when an aluminum casting AC1C was cast using a shell mold using this coated sand, the collapsibility was very good compared to a shell mold using a phenol resin.

Week 4 - Dimethoxynolan was added to the resin synthesized in Example 2 in an amount of 0.5% by weight based on the resin.

Coated sand was prepared in the same manner as in Example 1 using the resin described in "2".

Table I shows the test results of sand molds obtained using the coated sand.

Example 4 To the resin synthesized in Example 2, methylene bisstearic acid amide was added in an amount of 3% based on the resin.

Coated sand was produced using the above resin in the same manner as in Example 1.

Table 1 shows the test results of sand molds obtained from the coated sand mentioned above.

Example 5 A solid acidic substance (salicylic acid) was added as a hardening accelerator to the Francoated sand produced in Example 1 to foundry sand.
．． 1% by weight was added.

Table 1 shows the test results of sand molds using Franco-coated sand produced in Examples 1 to 5.

Table-1 [Unit: Kg/cm', mold holding time 60 seconds]
[Bending strength: Measured according to JIS K6910] Effects of the invention The foundry sand coated with the resin composition for coated sand of the present invention is used for low-temperature casting of aluminum etc. (internal temperature 300-500
When used in cores for 300 °C), the cores easily disintegrate and can be easily removed after casting. Therefore, unlike conventional phenolic resins, high-temperature sand firing is not required, which simplifies the casting process and shortens the time. Furthermore, since a hardening agent such as hexamethylenetetramine is not required, no nitrogen gas is generated during the casting process, and therefore no casting defects due to nitrogen gas occur.

Claims (1)

[Claims] 1. A resin composition for coated sand for foundries, the main component of which is a furan resin containing two or more furan rings in each molecule. 2. The resin composition according to item 1, wherein the furan resin is a homopolymer of furfuryl alcohol. 3. The resin composition according to item 1, wherein the furan resin is a polymer of furfuryl alcohol and aldehyde. 4. The resin composition according to item 1, having 2 to 4 furan rings in one molecule. 5. The resin composition according to item 1, containing 30 to 100% by weight of furan resin.