JP2002263787A - Method of manufacturing resin coated sand for shell mold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve casting quality by preventing the occurrence of the casting defect occurring in the casting mold damage and casting mold surface damage by the lack of the heat resistance of a shell casting mold and to improve the yield of products. SOLUTION: The method of manufacturing the resin coated sand for the shell mold by adding and mixing a phenolic resin and boric acid to and with aggregate comprises adding the phenolic resin at 1 to 5 wt.% to the aggregate and the boric acid at 80 to 150 deg.C of the aggregate at 0.5 to 10 wt.% to the phenolic resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a resin-coated sand for shell molding obtained by coating a heated aggregate such as silica sand with a phenol resin. More specifically, the present invention provides a resin-coated sand suitable for producing a mold having excellent heat resistance.

[0002]

2. Description of the Related Art As a binder used for producing a resin coated sand for shell molding, there are usually a combination of a novolak type phenol resin and hexamine, a solid resol alone, or a combination of a novolak resin and a solid resol. A phenolic resin is added to the heated aggregate, coated, cooled, and added with calcium stearate or the like, whereby a resin-coated sand having good fluidity can be obtained. The shell mold molding method is a method in which a mold can be molded in a very short time by firing resin-coated sand in a mold at 250 to 300 ° C. The obtained shell mold is widely used as a mold manufacturing method such as casting of automobile parts because of its high strength, good dimensional stability, and good productivity. However, although the heat resistance of phenolic resin is good, in the case of mold parts where the flow of molten metal is fast, or in the case of cast steel or stainless steel with a high casting temperature, damage to the mold due to the molten metal may occur, which may cause seizure defects in the casting. There is. In order to prevent this seizure defect, a coating process using a zircon powder with good heat resistance or a slurry of a binder is applied, or a special aggregate such as zircon sand with high heat resistance is used instead of general silica sand. Is dealt with by applying However, the coating process requires heat energy for coating and drying and heating and drying.
In addition, special aggregates are limited in terms of resources, and are very expensive compared to silica sand. Therefore, a solution by an alternative technology is required from the viewpoint of economy.

[0003]

The damage of the mold due to the molten metal is caused by the phenolic resin in the mold which is bound in a mesh form, due to the thermal energy of the molten metal and the oxidative decomposition by some oxygen in the air. As a result of studying various modifiers to suppress the decomposition and improve the heat resistance, it was found that the compounding of boric acid was extremely practical and effective. This is probably because boric acid forms a strong bond with the hydroxyl group in the resin. However, when added at the melting temperature of the resin during the production of the resin, the melting point increases, the fluidity decreases, and it is difficult to obtain a high-strength mold. It was difficult.

The inventor of the present invention has studied the resin coated sand for a shell mold which can improve the heat resistance of the mold without impairing the characteristics of the mold at normal temperature, and has reached the present invention. The present invention provides a mold having excellent heat resistance by mixing boric acid at a specific ratio with respect to a phenol resin and adding boric acid at a temperature of 80 ° C to 150 ° C during the production process of the resin coated sand for shell mold. An object of the present invention is to provide a resin coated sand for shell mold that can be manufactured.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a method for producing a resin-coated sand for shell molding in which a phenol resin and boric acid are added to and mixed with an aggregate. % And the aggregate temperature 8
A method for producing a resin-coated sand for shell molding, comprising adding 0.5 to 10% by weight of boric acid to a phenol resin at 0 to 150 ° C.

In the present invention, the phenol resin used is a novolak resin obtained using an acidic substance as a catalyst, a solid resol resin obtained using an alkaline substance as a catalyst,
Alternatively, a mixture of both can be used. In the case of a novolak resin, hexamethylenetetramine is used in combination as a curing agent. The amount of phenolic resin added to the aggregate is the same as in the case of resin coated sand for normal shell mold,
1 to 5% by weight. If the amount is less than 1% by weight, the strength of the obtained mold is low and it is difficult to handle. If the amount exceeds 5% by weight, the strength is too high, the disintegration of the mold after casting is poor, and the amount of gas generated increases, and the workability and casting quality are increased. Decrease. The amount of boric acid added to the aggregate is 0.5 to 10% by weight based on the phenol resin. If it is less than 0.5% by weight, the effect of improving the heat resistance due to the addition of boric acid is small and not practical. If it exceeds 10% by weight, the strength of the mold is reduced, and handling of the mold is hindered.

In the process of producing resin-coated sand, a phenol resin is added to an aggregate such as silica sand, which is usually heated to about 130 to 150 ° C. The resin is mixed while being melted to cover the surface of the aggregate, and then cooled with added water and cold air to solidify the phenol resin. In the present invention, boric acid is added at a temperature of 80 ° C. or more and 150 ° C. or less until the phenol resin is added to the heated aggregate and melted and solidified. When boric acid is added at a low temperature of less than 80 ° C. in the resin-coated sand manufacturing process, uniform dispersion and uniform mixing with a phenol resin are likely to be insufficient, and a mold having excellent heat resistance is stabilized. May not be available. The boric acid may be added in the form of a powder at the same time as the addition of the phenol resin, or when the phenol resin is in a molten state, or when adding water as an aqueous solution. Since the heating temperature of the aggregate does not substantially exceed 150 ° C., the temperature at which boric acid is added is also 150 ° C. or less. On the other hand, if the temperature exceeds 150 ° C., the reaction between the phenolic resin and the phenolic resin and boric acid proceeds excessively during kneading, so that trouble occurs during shell molding. Preferably, it is 100-130 degreeC from a point of uniform kneading and prevention of a reaction.

[0008] Silica sand is generally used as the aggregate used for the resin-coated sand for shell molding, but it is also possible to mix or use a special sand such as zircon sand or artificial mullite sand.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to embodiments. However, the present invention is not limited to the embodiments. All “%” described in the text indicate “% by weight”.

Production Example 1 Phenol 1000 was placed in a reaction vessel equipped with a cooler and a stirrer.
g, 10 g of oxalic acid, and 621 g of 37% formalin. After the temperature was gradually raised and the reaction was carried out at 95 to 100 ° C. for 4 hours, the mixture was dehydrated by heating at atmospheric pressure and decomposed for 140
After the temperature in the reaction system reached 180 ° C., ethylene bisstearic acid amide was added and mixed, and then discharged from the reaction vessel to a cooling vessel.
055 g of a novolak type phenol resin was obtained.

Production Example 2 Phenol 100 was prepared using the reaction vessel used in Production Example 1.
0 g, 37% formalin 1840 g, followed by 28% ammonia water 120 g, 50% sodium hydroxide aqueous solution 5
0 g was added. After the temperature was gradually raised and the temperature reached 96 ° C., and a reflux reaction was performed for 25 minutes, 50 g of ethylene bisstearic acid amide was added, and the pressure was gradually reduced to 30 KPa. After reaching 105 ° C., the mixture was discharged from the reaction vessel and rapidly cooled to obtain 1150 g of a solid resol resin having a melting point of 70 ° C.

Example 1 8 kg of flattery sand heated to 130 ° C. was charged into a mixer, and 160 g of the resin obtained in Production Example 1 and boric acid 2.4 were added.
g was added and kneaded for 45 seconds, and then an aqueous solution in which 80 g of hexamethylenetetramine was dissolved in 100 g of water was added. After cooling with air to solidify the phenolic resin and obtain sandy fluidity, 8 g of calcium stearate was added and mixed to prepare a resin-coated sand. The bending strength, fusion point, and bend (bending amount) of the obtained resin-coated sand were measured. Further, the bending strength of the mold after the exposure and heat treatment was measured as an index of heat resistance, and the residual ratio of the strength to the strength before the treatment was determined.

Example 2 8 kg of flattery sand heated to 130 ° C. was charged into a mixer, and then 64 g of the novolak resin of Production Example 1 and Production Example 2
Were simultaneously added and kneaded for 45 seconds, and then 100 g of water was added. After cooling with air to solidify the phenolic resin and obtain a sandy fluidity, 8 g of calcium stearate was added and mixed to prepare a resin-coated sand.

Example 3 Regenerated sand No. 6 silica sand heated to 130 ° C. (AFS particle size index: 6
5.0) After charging 8 kg to the mixer, the resin 16 of Production Example 1 was added.
After adding 0 g and kneading for 45 seconds, an aqueous solution in which 80 g of hexamethylenetetramine and 8 g of boric acid were dissolved in 100 g of water was added. The temperature of the mixture in the mixer at the time of addition is 110 ° C
Met. After cooling with air to solidify the phenolic resin and obtain sandy fluidity, 8 g of calcium stearate was added and mixed to prepare a resin-coated sand.

Comparative Example 1 A resin-coated sand was prepared according to the procedure for preparing the resin-coated sand of Example 1, but without adding boric acid.

Comparative Example 2 8 kg of flattery sand heated to 130 ° C. was charged into a mixer, and 160 g of the resin obtained in Production Example 1 was added.
After kneading for 5 seconds, 80 g of hexamethylenetetramine was added for 10 minutes.
An aqueous solution dissolved in 0 g of water was added. After cooling with air to solidify the phenolic resin and obtain a sandy fluidity, 8 g of calcium stearate and 2.4 g of boric acid were obtained.
Was added and mixed to prepare a resin-coated sand. The temperature during the addition and mixing of boric acid was 74 ° C.

Table 1 shows the resin-coated sand compounding conditions and the characteristic measurement results.

[Table 1]

As is clear from Table 1, the resin-coated sands obtained in Examples 1 to 3 have a flexural strength after exposure and heat treatment of the mold without impairing the characteristics of the resin-coated sands as compared with Comparative Examples 1 and 2. It is clear that the residual ratio of the strength to the strength before the treatment is high.

(Measurement method) (1) Flexural strength: According to JIS-K6910. The firing conditions are 250 ° C. and 60 seconds. (2) Fusing point: Measured by the Japan Casting Technology Association Test Method C-1. (3) Bend (bending amount): Japan Casting Technology Association Test Method S
M-3. A 5 * 40 * 180 mm plate-shaped test piece is fired at 250 ° C. for 30 seconds, and after 10 seconds, a predetermined load is applied and the amount of deflection is read. The larger the value, the larger the deformation after molding and the slower the curing. (4) Residual bending strength: A test piece was prepared in accordance with JIS-K6910, aluminum foil was double-wrapped, heat-treated for 15 minutes in an electric furnace heated to 550 ° C., taken out, cooled to room temperature, and then subjected to bending strength. Was measured. (5) Residual strength: residual bending strength ((4) above) / bending strength ((1) above) × 100

[0020]

The resin coated sand for shell molding obtained by the present invention can produce a mold excellent in heat resistance while maintaining properties such as bending strength and fusion point. ADVANTAGE OF THE INVENTION According to this invention, it is economically useful since the resin coated sand for shell molds can be industrially manufactured without requiring complicated steps.

Claims (1)

[Claims] 1. A method for producing a resin coated sand for shell molding, comprising adding and mixing a phenol resin and boric acid to an aggregate, wherein the phenol resin is added to the aggregate in an amount of 1 to 5 parts.
A method for producing a resin-coated sand for shell molds, comprising adding 0.5 to 10% by weight of boric acid to a phenol resin at an aggregate temperature of 80 to 150 ° C.