JPH0259138A - Resin coated sand for shell mold - Google Patents

Abstract

PURPOSE:To enable the effect of lowering odor and the improvement of mold strength by forming resin coated sand composing of molding sand, phenol resin and ferrous salt. CONSTITUTION:At the time of executing the molding by using the resin coated sand using the phenol resin, after coating the molding sand with novolak type phenol resin (novolak), at the time of using hexamethylene tetramine (hwxamine) as curing agent, this hexamine is heat-decomposed and offensive odor components of ammonia, formaldehyde, etc., are generated. In the case of using solid resol type phenol resin (resol) without using the hexamine, the offensive ordor component of the ammonia, etc., is generated only at a little quantity. By containing the ferrous salt reacting with these offensive odor component in the resin coated sand, the offensive odor is caught, and the working environment is improved, and not only the effect of lowering the odor, but also the improvement of mold strength are served.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to resin-coated sand grains used in shell molding. In particular, the present invention relates to resin-coated sand grains used in shell molding to reduce odor during molding.

[Prior art] Conventional resin-coated sand grains for shell molds are made by coating molding sand with a novolac-type phenolic resin (hereinafter referred to as novolac), and then using hexamethylenetetramine (as a hardening agent).
It is produced by adding about 15 parts by weight of hexazine (hereinafter referred to as hexazine) to novolac, and further adding calcium stearate as a lubricant.

These resin-coated sand grains generate foul-smelling gases such as ammonia 1 and formaldehyde due to thermal decomposition of hexamine, a hardening agent, during mold making, which not only deteriorates the working environment but also causes pollution.

In order to reduce the generation of these foul-smelling gases and reduce the odor, solid resol-type phenolic resin (hereinafter referred to as resol) is used as a phenol resin that does not use the curing agent hexamine, especially the presence of a catalyst mainly based on ammonia. Resin-coated sand grains using a resol obtained by the condensation reaction described below have been proposed (Japanese Patent Publication No. 12658/1983).

Another method is to apply a deodorizing agent (for example, International Market Development) to Norhexazine or Rawhexazine sand grains, which are a mixture of sand grains coated with resol and sand grains coated with novolac, and which retain volatile matter even after firing. A molding material containing the product name "5top 0dor" manufactured by Group Inc. has been proposed (Japanese Unexamined Patent Publication No. 55-94751).
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[Problems to be Solved by the Invention] However, resin-coated sand grains containing resol alone or in combination are an effective method for reducing odor, since hexamine, which is a curing agent for novolac, is not used or is reduced. There is a strong need to improve productivity, as the mold strength, especially during low-temperature curing, is slow and the strength immediately after mold molding is low.

Furthermore, the deodorizing agent "St, op 0dor" used in Japanese Patent Application Laid-open No. 55-94751 has a strong odor itself, and an odorless deodorizing agent is required.

[Means for Solving the Problems] An object of the present invention is to solve the above problems and provide resin-coated sand grains for shell molds that can improve mold physical properties such as mold strength and reduce odor during molding. It's about doing.

That is, the present invention uses foundry sand, phenolic resin and first
This is a resin-coated sand grain for shell molding characterized by being made of iron salt.

The phenolic resin of the present invention includes, for example, phenol, xylenol, cresol, catechol, bisphenol A
1 mole of phenols such as formalin, less than 1 mole of formaldehyde such as formalin and paraformaldehyde, and an acid such as hydrochloric acid, sulfuric acid, oxalic acid, para-toluenesulfonic acid, or an acetate of a divalent metal such as zinc acetate or magnesium borate, A novolak obtained by condensation reaction using a borate as a catalyst and concentrated hydrophilicity is used together with a curing agent such as hexamine. Alternatively, a resol containing 1 mole of the above phenol and 1 mole or more of formaldehyde as a main catalyst of ammonia, a primary amine, a secondary amine or hexazine is used.

The above-mentioned novolak and resol phenolic resins can also be modified with oil, acrylic, by-products from the production of bisphenol A, etc., as appropriate. Furthermore, various additives such as silane coupling agents such as aminosilane and epoxysilane, organic acids such as salicylic acid and benzoic acid, and lubricants such as zinc stearate and ethylene bisamide can be added.

The ferrous salt used in the present invention is, for example, an inorganic ferrous salt such as ferrous sulfate, ferrous nitrate, ferrous phosphate, or ferrous carbonate, or ferrous acetate, or ferrous oxalate. , ferrous citrate, or a mixture of organic ferrous salts such as ferrous citrate.

The blending ratio of this ferrous salt is 5 to 30 parts by weight, preferably 10 to 2 parts by weight, per 100 parts of phenolic resin.
This is a huge disappointment.

[Operations and Effects of the Invention] When molding is performed using resin-coated sand grains using phenolic resin, in the case of novolac, the hardening agent hexamine is thermally decomposed and generates malodorous components such as ammonia and formaldehyde. .

In addition, in the case of ammonia aresol, -(: H
When a nitrogen-containing compound such as -N-G H□- forms a methylene bond, it generates a small amount of malodorous components such as ammonia and formaldehyde, similar to novolak.

The resin-coated sand grains for shell molds of the present invention contain ferrous salts that react with these malodorous components, so they can supplement the malodorous components generated during mold making, reduce the amount of malodorous components generated, and improve the workability. Change the environment. This deodorizing mechanism is based on the following reaction. Fc"+6NH3-+ [
In addition, the resin-coated sand grains for shell molds of the present invention not only have the effect of reducing odor, but also improve mold strength.
It is also useful for

[Example] Examples of the present invention will be shown below, but the present invention is not limited thereto.

[Production method for resin A] 100 parts by weight of phenol and 80 parts by weight of 37% formalin were placed in a reaction vessel equipped with a thermometer and a condenser, 1.5 parts by weight of oxalic acid was added to the colander, and the condensation reaction was carried out under reflux until the bubble viscosity was reduced. Proceed to "Z" in total, then -60 to -70cmH
Dehydration is carried out to 200° C. under a reduced pressure of 100 g. Furthermore, while stirring was continued, 1.7 parts by weight of ethylene bisamide and 0.9 parts by weight of salicylic acid were added and dissolved to obtain 88 parts by weight of novolac (referred to as resin A).

[Example 1] Sand grains heated to a temperature of 150 to 160°C were charged into a speed mixer, and 2.0 parts of resin A was added to 100 parts by weight of silica sand.
Parts by weight were added and kneaded for 20 seconds. In addition, hexamine 0.3
parts by weight and 0.2 parts by weight of ferrous sulfate are dissolved in 1.5 parts by weight of cooling water, and then 0.2 parts by weight of calcium stearate is added.
After adding 1 part by weight and kneading for 20 seconds, the sand was removed and cooled to obtain resin-coated sand grains for shell molds.

[Example 2] Resin-coated sand grains for shell molding were obtained in the same manner as in Example 1, except that 0.2 parts by weight of ferrous cosulfate was replaced with 0.4 parts by weight of ferrous sulfate.

[Production method of resin B] 100 parts by weight of phenol, 12 parts by weight of 86% formaldehyde, and 25 parts by weight of 37% formalin were placed in a reaction vessel equipped with a thermometer and a condenser, and 1 part by weight of zinc acetate was added. Linearization reaction was carried out at 105°C for 4 hours, and then dehydration was carried out for 17 hours under reduced pressure of -65 to 70 crnHg.
The temperature was raised to 0°C, and 2.0 parts by weight of ethylene bisamide and 3 parts by weight of aminosilane were added and dissolved.
Parts by weight of novolak (referred to as Resin B) were obtained.

[Example 3] Resin-coated sand grains for shell molding were obtained in the same manner as in Example 1 except that resin A was replaced with resin B.

[Example 4] Resin-coated sand grains for shell molds were produced in the same manner as in Example 1, except that resin A was replaced with resin B and 0.2 parts by weight of ferrous sulfate was replaced with 0.4 parts by weight of ferrous sulfate. I got it.

[Production method for resin C] 100 parts by weight of phenol and 56 parts by weight of 86% paraformaldehyde were placed in a reaction vessel equipped with a thermometer and a condenser, 1.0 part by weight of a 50% aqueous sodium hydroxide solution was added, and the mixture was heated at 90 to 95°C. The reaction was carried out for 60 minutes, then cooled to 50°C, 18 parts by weight of a 28% ammonia aqueous solution was gradually added while cooling, and the rX-
Even YJ reacts.

Subsequently, dehydration was performed at 70°C under a reduced pressure of -65 to -70 cmHg.
Then, 40 parts by weight of methanol was added at normal pressure and mixed uniformly while cooling. This resin methanol solution was granulated and dried with warm air at 190 to 200°C using a spray dryer to obtain a granular resol. This resol 10
3.0 parts by weight of calcium stearate was added and mixed to 0 parts by weight to obtain a granular resol (referred to as resin C) having a particle size of 400 to 600 μm.

[Example 5] Silica sand heated to a temperature of 140 to 150° C. was charged into a speed mixer, and 2.0 parts by weight of resin C was added to 100 parts by weight of silica sand and kneaded for 30 seconds. Then ferrous sulfate was added to 0.
Add 2 parts by weight dissolved in 1.5 parts by weight of cooling water, knead until the sand grains disintegrate, further add 0.1ii part of calcium stearate, knead for 20 seconds, remove the sand and cool. Resin-coated sand grains for shell molding were obtained.

[Example 6] Resin-coated sand grains for a shell mold were obtained in the same manner as in Example 5, except that 0.2 parts by weight of ferrous sulfate was replaced with 0.4 parts by weight of ferrous sulfate.

[Comparative Example 1] Silica sand heated to a temperature of 150 to 160°C was charged into a speed mixer, and 2 parts of resin A were added to 1001.17 parts of silica sand.
．． Added 0 parts by weight and kneaded for 20 seconds, then added 0.3 parts by weight of hexamine.
Part by weight was dissolved in 1.5 parts by weight of cooling water and added, and kneaded until the sand grains disintegrated. Thereafter, 0.1 part by weight of calcium stearate was added and kneaded for 20 seconds. The sand was removed and cooled to obtain resin-coated sand grains for shell molding.

[Comparative Example 2] Resin-coated sand grains for shell molding were obtained in the same manner as in Comparative Example 1, except that resin A was replaced with resin B.

[Comparative Example 3] Silica sand heated to a temperature of 140 to 150°C was charged into a speed mixer, 2.0 parts by weight of resin C was added to 100 parts by weight of silica sand, kneaded for 30 seconds, and 1.5 parts by weight of cooling water was added. After kneading until the sand grains disintegrate, 0.1 part by weight of calcium stearate is added and kneaded for 20 seconds. The sand was removed and cooled to obtain resin-coated sand grains for shell molding.

The resin-coated sand grains for shell molds obtained in Examples 1 to 6 and Comparative Examples 1 to 3 were tested and evaluated for fusion point, normal temperature bending strength, warm bending strength, and ammonia concentration, and the results are shown in the table.

Table Test results (3) Warm bending strength: Based on JACT test method 5M-5 (4) Ammonia concentration: Accurately place 1 g of resin-coated sand grains into a combustion boat. This combustion boat was placed in the center of a tubular electric furnace maintained at 300°C, dry air was passed through at a flow rate of in/min, and the generated gas was collected using a sampling bag for 10 minutes. Immediately measure the ammonia concentration using a kita-type detector tube.

According to the test results in this table, the resin-coated sand grains for shell molds of Examples 1 to 6 have higher room temperature strength and warm strength due to the addition of ferrous sulfate, and have higher ammonia concentration than Comparative Examples 1 to 3. It can be seen that this has been reduced.

Test method (1) Fusion point: Based on JACT test method C-1 (2) Room temperature bending strength: Based on JIS K-6910 Patent applicant Haruo Miyaji, representative of Aisin Kako Co., Ltd.

Claims (1)

[Claims] 1. Resin-coated sand grains for shell molds, characterized by comprising foundry sand, phenolic resin, and ferrous salt.