JP2660186B2 - Binder for foundry sand - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binder for molding sand, which improves the disintegration of a mold such as a core without impairing the properties such as strength to the extent that it poses a practical problem.

[0002]

2. Description of the Related Art A binder for molding sand mainly composed of a phenolic thermosetting resin useful in the field of the production of cast iron castings is also used in the production of light alloy castings such as aluminum. Because the melt temperature is low and the heat capacity is small,
The disintegration of the mold after pouring is poor, and its improvement is demanded in the field.

As a solution to such a problem, there has been proposed a method in which a substance having a high coefficient of thermal expansion is added to a binder, or a disintegrating agent such as a bromine compound or a disintegrating aid is added. There is a drawback that characteristics such as the free flowing property of the sand and the strength of the mold are reduced. In addition, the bromine compound generates bromine gas generated by thermal decomposition, which promotes carbonization of the resin and improves the disintegration property of the mold, but has the disadvantage of corroding the mold at the same time. Further, a method of using a binder obtained by blending an organic peroxide with an unsaturated polyester resin or an aliphatic acrylic resin is also known, but the rate of thermal decomposition of the resin is too fast, so that the molten metal is solidified. Gas is generated beforehand, and there is a problem that not only a gas defect occurs in the casting, but also a slight change in the mold temperature at the time of molding causes deterioration of the strength of the mold, resulting in brittleness.

[0004]

SUMMARY OF THE INVENTION In view of such circumstances in the field, the present invention is not only concerned with the free flowability of molding sand, but also with the practical problems such as the strength and the like of the mold such as a core. The purpose of the present invention is to make it possible to greatly improve the disintegration of the template without impairing the degree to a certain extent. Further, the problem of mold corrosion caused by a bromine compound is also to be solved at the same time.

[0005]

That is, a phthalyl-based polymerizable substance is used in an amount of 0.1 to 20 with respect to a phenol-based thermosetting resin.
Molding sand comprising 0.002 to 1.4% by weight of a radical polymerization accelerator which starts to act at 140 ° C. to 160 ° C. and 1 to 10% by weight of a bromine-containing organic compound which generates a bromine gas by heating For binders for use.

As the phenolic thermosetting resin, those conventionally used in the art, such as novolak type phenolic resin for shell mold, resol type phenolic resin, and a mixture thereof may be appropriately used. In this case, hexamethylenetetramine or the like may be appropriately used as a curing agent. For example, in the case of a novolak type phenol resin, hexamethylenetetramine is generally used as a curing agent in an amount of 10 to 20% by weight based on the resin.

Examples of the phthalyl polymerizable substance used in the present invention include a homopolymer of diallyl orthophthalate or diallyl isophthalate and a copolymer of a monomer such as diallyl orthophthalate and another radical polymerizable monomer. Homopolymers of orthophthalate or diallyl isophthalate are particularly preferred. The molecular weight of these polymers is 10,000
0-100,000, preferably 30,000-50,
000. This kind of phthalyl-based polymerizable substance is compared with conventionally used acrylic resin binders, etc.
Because the rate of thermal decomposition is moderately slow, the gas generated before the molten metal solidifies causes gas defects to be formed in the casting, and slight changes in the mold temperature during molding,
The problem that the strength of the mold deteriorates is suppressed as much as possible.

The amount of the phthalyl-based polymerizable substance may be appropriately selected according to the type of the sand to be treated, the type of the casting metal, the type of the mold, the workability, and the like. 0.1 to 20% by weight, preferably 2 to 10% by weight, based on the weight of the resin, if less than 0.1% by weight, the initial object of the present invention is difficult to achieve, When the amount is too large, the amount of generated gas increases, which not only causes gas defects but also increases the cost, which is not practical.

The binder for foundry sand according to the present invention further comprises:
A radical polymerization accelerator is blended. Organic peroxides such as t-butyl perbenzoate, benzoyl peroxide, lauryl peroxide, cumene hydroperoxide and dicumyl peroxide are known as radical polymerization accelerators, all of which are relatively low temperatures. Since it starts to work, the phthalyl-based polymerizable substance is already cured in the coating step. Furthermore, these organic peroxides significantly inhibit the curability of a curing agent for a phenolic thermosetting resin, for example, hexamethylenetetramine, and make molding difficult. From this viewpoint, in the present invention, 140 ° C. to 16 ° C.
A radical polymerization accelerator which starts working at 0 ° C. is used. Examples of this type of radical polymerization accelerator include biscumyl and bissimol, and from the above viewpoint, biscumyl is particularly preferred. The amount of the radical polymerization accelerator of this type may be appropriately selected according to the type of the phthalyl-based polymerizable substance or the radical polymerization accelerator, and is usually determined with respect to the phthalyl-based polymerizable substance. 2.0 to 7.0% by weight, preferably 3.0 to 5.0% by weight.
When the amount is less than 10% by weight, the phthalyl-based polymerizable substance cannot be sufficiently cured. When the amount is more than 7.0% by weight, the strength of the mold deteriorates.

[0010] The binder for foundry sands according to the present invention further contains a bromine-containing organic compound. A method of using a bromine-containing organic compound as a heat disintegrating agent has already been proposed (see, for example, Japanese Patent Publication No. 58-12094). Even with the compounding amount, mold corrosion cannot be avoided. On the other hand, in the present invention, since the phthalyl-based polymerizable substance is used in combination, not only can the heat disintegration property of the mold be significantly improved, but also the problem of mold corrosion due to bromine gas can be suppressed at the same time. Examples of this type of bromine-containing organic compound include aryl bromides such as tetrabromobisphenol A, bisaryl ether tetrabromobisphenol A, and bis (dibromopropyl ether) tetrabromobisphenol A. The compounding amount of the bromine-containing organic compound is 1 to 10% by weight, and preferably 3 to 6% by weight, based on the phenolic thermosetting resin. If it is worse, and if it exceeds 10% by weight, it becomes difficult to suppress mold corrosion.

The binder according to the present invention includes, in addition to the above components, other conventional compounding agents known in the art, for example, moisture-proof and lubricating properties of silane coupling agents, bisamide amide, calcium stearate and the like. You may mix | blend a property improver etc. suitably.

[0012] The main raw material of molding sand such as silica sand and the above-mentioned binder according to the present invention are kneaded in a conventional manner, silica sand and the like are coated with the binder, and the coated sand is subjected to a drying treatment to form a mold. A molding sand capable of greatly improving the disintegration of a mold can be obtained without impairing properties such as strength to such an extent that it becomes practically problematic. The amount of the binder added to silica sand or the like is usually 1.
2 to 3.5% by weight. It is not preferable to use too much of the binder because the disintegration of the mold is impaired due to the phenol resin.

[0013]

The present invention will be described below with reference to examples. Example 1 Novolac type phenol resin 170 for shell mold
g, 10 g of diallyl orthophthalate prepolymer (molecular weight: 20,000 to 30,000), 0.3 g of biscumyl and 10 g of tetrabromobisphenol A are uniformly mixed at room temperature to obtain a binder for core sand according to the present invention. 1 was prepared. Into a small speed muller preheated to about 80 ° C., 10 kg of flattery sand (AFS No. 60) previously heated to 200 ° C. was charged, and rotated several times. When the temperature of the charged sand reached 170 ° C., After adding the whole amount of the binder 1 and kneading for 50 seconds, 25.5 g of hexamethylenetetramine was added to 100 parts of water.
An aqueous solution dissolved in cc was added, and kneading was continued. When the mass kneaded material in the small speed maller began to unravel, after further adding 10 g of calcium stearate and kneading, the kneaded material in the small speed maller was taken out on a 20-mesh sieve and cooled to room temperature. Core sand 1 was produced. Angle of repose, softening point, room temperature bending strength (bending strength of a test piece prepared at 250 ° C. for 60 seconds after air cooling to room temperature) and hot bending strength (250 ° C.) of the obtained core sand 1 The bending strength of the test piece immediately after being prepared under the conditions of 60 seconds) was measured according to a conventional method,
The results are shown in Table 1 below. The dimensions of the test piece are 1 inch × 4 inches × 0.25 inch.

[0014]

[Table 1]

The disintegration of the core sand 1 was measured using the disintegration tester shown in FIG. 1, and the results are shown in Table 1. In FIG. 1, (1) shows an inner diameter of 27 mm, an outer diameter of 34 mm and a length of 1 mm.
A 50 mm iron pipe is naturally filled with core sand 1,
After baking for 30 minutes at 500 ° C. and further for 20 minutes at 500 ° C., a sample filling tube taken out of the baking furnace and gradually cooled to room temperature is shown.
1 shows a hammer with a 0 g head. Hammer (2)
Is freely rotated in the direction of the arrow in the figure to strike the sample filling tube (1), thereby discharging the core sand in the sample filling tube. The number of hammer hits until the core sand in the sample filling tube is completely discharged and the number of vibrations of the sieve until the discharged core sand completely passes through the 4.2 mesh sieve Scale.

Example 2 and Comparative Example 1 Core sand 2 was obtained in the same manner as in Example 1 except that the blends and the amounts thereof were changed. As a comparative example,
According to the formulation of Example 1, core sand 1 'was prepared except diallyl orthophthalate, tetrabromobisphenol-A, and biscumyl. Angle of repose, softening point, room temperature bending strength, hot bending strength of core sand 2 and core sand 1 ',
And the disintegration was measured in the same manner as in Example 1, and the results are shown in Table 1.

As is clear from the results of the examples and comparative examples, the core sand of the present invention exhibits excellent free-flowing properties in a dry state, and the angle of repose is completely inferior to that of the conventional core sand. There is no. Therefore, it can be used to manufacture cores of complex shapes,
Further, the collapsibility is excellent although the room temperature bending strength and the hot bending strength are higher than those of the conventional core sand.

[0018]

According to the present invention, the disintegration of a mold can be greatly improved without impairing the properties of a mold such as a core at room temperature bending strength and hot bending strength to such a degree that they become practically problematic. can do. Further, as is apparent from the physical properties of the core sand 4, the disintegration properties are excellent by using a phthalyl-based polymerizable substance in combination, despite the small amount of bromide added. This also shows that the problem of mold corrosion caused by bromide can be greatly improved. In addition, when the binder according to the present invention is used, the gas generated before the molten metal solidifies causes a problem that gas defects are formed in the casting and a slight change in the mold temperature during molding. The problem that the strength of the mold deteriorates is suppressed as much as possible. Furthermore, the use of the binder according to the present invention does not impair other basic properties that the molding sand should have, such as moldability, air permeability, smoothness, shrinkability and reusability. . The binder according to the present invention can be generally used as a binder for foundry sands. In particular, from the viewpoint of improvement of engine performance, etc., light alloy automobile castings whose thickness has become more complicated and thinner are further advanced. It is suitable as a binder for core sand used for casting.

[Brief description of the drawings]

FIG. 1 is a schematic side view of a collapsible tester.

[Explanation of symbols]

 1: Sample filling tube 2: Hammer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location C08L 61/06 LMY C08L 61/06 LMY

Claims (6)

(57) [Claims] 1. A phthalyl-based polymerizable substance in an amount of 0.1 to 20% by weight, based on a phenol-based thermosetting resin, at 140 ° C. to 1%.
Radical polymerization accelerator starting to act at 60 ° C 0.002
A binder for molding sand, comprising 1.4% by weight and 1 to 10% by weight of a bromine-containing organic compound which generates a bromine gas when heated. 2. The binder according to claim 1, wherein the phenolic thermosetting resin is a novolak type phenol resin and / or a resol type phenol resin. 3. The binder according to claim 1, wherein the phthalyl polymerizable substance is a homopolymer of diallyl orthophthalate or diallyl isophthalate. 4. The binder according to claim 1, wherein the radical polymerization accelerator is biscumyl. 5. The bromine-containing organic compound is an aryl bromide such as tetrabromobisphenol A.
5. The binder according to any one of items 1 to 4. 6. Foundry sand obtained by subjecting raw material sand coated with the binder according to claim 1 to a drying treatment.