JP3123029B2 - Coating agent for green mold - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating agent for green molds which is applied to the surface of a green mold to improve the surface stability of the green mold.

[0002]

2. Description of the Related Art Heretofore, green molds have been produced by kneading a green sand composition for producing a casting, comprising sand, clay and water, and solidifying the composition in a desired mold. In addition, other than clay, carbide components such as coal powder and pitch for improving the casting surface and adhesive components such as starch for improving the binding force between sands are added to sand to produce castings. It has also been practiced to produce a green sand composition.

[0003] The binding force between sands is improved by using water to some extent by the cohesive force of the clay component and the adhesive force of starch or the like, and a high-strength green mold can be obtained. However, even though the strength was high as a whole, the binding force between the sands on the green mold surface did not readily improve. The reason for this is that water evaporates on the green mold surface, and thus the binding power of sand decreases. Therefore, in such a green mold, sand on the surface tends to fall off (blown), the green mold surface is eroded or washed, and the surface stability is poor, and the obtained casting surface is beautiful. There was a drawback that it could not be finished.

For this reason, it has been attempted to apply a silicone compound such as dimethyl silicone oil to the surface of a green mold (JP-A-51-124626).
That is, by applying a silicone compound to the green mold surface, the evaporation of water on the green mold surface is prevented, and the surface stability of the green mold is improved. However, since silicone compounds have high viscosity and poor solubility in water, they need to be diluted and sprayed with a large amount of water.

[0005]

Therefore, the present inventors have sought a coating agent to be applied to the surface of a green mold, which has a low viscosity and contributes to the improvement of the surface stability of the green mold. Various studies were performed. As a result, it has been found that, by applying a polyhydric alcohol having a relatively low viscosity to the surface of the green mold, evaporation of water on the green mold surface can be prevented, and the surface stability of the green mold is improved. It was done.

[0006]

That is, the present invention relates to a green mold coating composition comprising a polyhydric alcohol.

The polyhydric alcohol used in the present invention includes ethylene glycol, propylene glycol,
Trimethylene glycol, tetramethylene glycol,
Pentamethylene glycol, hexamethylene glycol, diethylene glycol, triethylene glycol,
Tetraethylene glycol, polyethylene glycol,
Dihydric alcohols such as dipropylene glycol and polypropylene glycol, trihydric alcohols such as glycerin, trimethylolethane, and trimethylolpropane, and tetrahydric alcohols such as diglycerin and pentaerythrit can be used. In particular, ethylene glycol,
It is preferable to use glycerin and diglycerin.

[0008] The polyhydric alcohol is applied to the surface of a green mold which is mixed with sand, clay or the like and solidified. The coating amount of the polyhydric alcohol, the raw type surface 1 m ² per 10~60g
It is preferred that The application amount of polyhydric alcohol is 10 g /
If it is less than m ² , there is a tendency that evaporation of water on the green mold surface cannot be sufficiently prevented. Conversely, even if the application amount of the polyhydric alcohol exceeds 60 g / m ² , the prevention of evaporation of water on the green mold surface becomes saturated, and the use of the polyhydric alcohol tends to be uneconomical. As a method for applying the polyhydric alcohol, brush coating may be used, or the polyhydric alcohol may be sprayed on the green mold surface with a spray gun or the like.

[0009]

【Example】

Examples 1 to 5, Comparative Examples 1 and 2 7 parts by weight of bentonite, 3 parts by weight of coal powder, 2 parts by weight of α-starch, and the amount of water shown in Table 1 were added to 100 parts by weight of Australian silica sand. Then, the mixture was kneaded with a kneading machine (Simpleson type mill) for 12 minutes. Using the green sand composition for producing a casting thus obtained, a cylinder of 50 mmφ × 50 mm was produced based on the JIS Z-2604 method. In this cylinder,
Polyhydric alcohols of the types and amounts shown in Table 1 were applied by a spray method. The amount of polyhydric alcohol applied is
It was represented by the weight (g) of polyhydric alcohol per 1 cm ^{2 of the} green mold surface. After the application, the substrate was left in a constant temperature room at 25 ° C. × 55% RH, and the weight Bg of the cylindrical body was measured at each elapsed time. Then, assuming that the weight of the initially obtained cylindrical body was Ag, the water reduction rate (%) was calculated by the following equation. Moisture reduction rate (%) =
[(A−B / A)] × 100. The results are shown in Table 1.

[0010]

[Table 1]

As is clear from a comparison between the examples and the comparative examples, when a polyhydric alcohol is applied to the green mold surface, the water reduction rate can be suppressed to a low level, and the surface stability of the green mold is reduced. Can be improved.

[0012]

As described above, if the coating agent for green mold according to the present invention is applied to the green mold surface, the polyhydric alcohol has excellent affinity with water on the green mold surface. The water on the green mold surface is grasped and the evaporation of the water is prevented.
Therefore, water on the green mold surface is less likely to evaporate, sand on the green mold surface can be prevented from falling off, and stability of the green mold surface can be improved. Therefore, if the green mold additive according to the present invention is applied to the green mold surface to produce a casting, the green mold surface can be prevented from being eroded or washed, and the obtained casting surface has defects. This has the effect of preventing the occurrence of.

Further, since the polyhydric alcohol of the green mold coating agent according to the present invention is an organic substance, it is easily evaporated and decomposed by the heat of the molten metal after being applied to the green mold surface to produce a casting.
Less likely to remain in green sand. Therefore, even if the green mold after use is broken and reuse of the green sand is repeated, there is an effect that the residual airborne properties and strength of the green mold are hardly adversely affected due to the remaining foreign components.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B22C 3/00

Claims (2)

(57) [Claims] 1. A green mold coating composition comprising a polyhydric alcohol. 2. The coating composition for green mold according to claim 1, wherein the polyhydric alcohol is glycerin.