JPH11309544A - Coating agent - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a casting of excellent quality capable of demonstrating an excellent pin hole preventive effect, and free from any defective pin holes even when the temperature of molten metal is lower than 1300 deg.C. SOLUTION: Casting is achieved after applying on the cavity surface of a mold a coating agent containing at least one kind to be selected among gilsonite, engine oil and phenol resin which are substances to generate hydrocarbon gas through pyrolysis at a temperature lower than 1300 deg.C. These substances generate hydrocarbon gas at temperatures around 200 deg.C, reduces water contained in the mold, and changes it into stable molecular hydrogen. Water in the mold is brought into direct contact with the molten metal to prevent hydrogen absorption to cause generation of pin holes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating composition used in a mold for casting a cast iron casting, and more particularly to a coating composition effective for preventing casting defects when a molten metal is filled at a temperature lower than 1300 ° C. With regard to molds.

[0002]

2. Description of the Related Art When casting a cast iron casting using a green sand mold, there is a problem that a defect called a pinhole occurs near a casting surface. At the casting site, when the incidence of pinhole defects increases, the defect incidence is reduced by reviewing and improving the composition, inoculation, compounding material, mold composition, casting method, etc. of the casting material. However, at present, the cause of the occurrence of the pinhole defect has not been clarified, and no method for reliably preventing this has been known.

Hitherto, various methods have been proposed for improving the quality of cast iron castings (Japanese Patent Laid-Open No. Hei 7-1005).
No. 81, Japanese Patent Application Laid-Open No. 54-41226, etc.). As a relatively effective method for preventing pinhole defects, there is a method of applying bengara (Fe ₂ O ₃ ) to the surface of a green sand mold or into green sand. , Addition of carbonate, and addition of coal powder to green sand are known.

Although the mechanism of preventing pinholes by these methods and these methods is not necessarily elucidated, the molten metal reacts with the moisture in the raw sand in the mold (formula (1)), and the molten metal [M] + H ₂ O → MO + 2H (1) Since it is considered that a large amount of hydrogen is absorbed, it is considered that a pinhole is generated due to a difference in hydrogen solubility between the liquid phase and the solid phase in the molten cast iron molten metal. Under the assumption, it is inferred as follows. First, in the red iron oxide, oxygen released by thermal decomposition oxidizes atomic hydrogen (formulas (2) and (3)), and 3Fe ₂ O ₃ → 2Fe ₃ O ₄ + O (2) 2H + O → H ₂ O (3) It is considered to prevent the dissolution of hydrogen in the molten metal or reduce the equilibrium hydrogen solubility by dissolving the released oxygen. In addition, the addition of carbonates and coal powders causes the decomposition of C in the mold by the thermal decomposition of these additives.
It is considered that the generation of hydrogen is suppressed because the gas pressure of O and CO ₂ increases and the reducing atmosphere becomes strong.

[0005] However, the addition of red iron oxide has been confirmed to be effective when the pouring temperature is relatively high. However, when the pouring temperature is set low or when the temperature of the molten metal in the mold is large, the effect is large. The effect is reduced. Specifically, when the temperature of the molten metal falls below 1300 ° C., the effect of preventing pinholes is almost lost. This is because the thermal decomposition temperature of Bengala is around 1300 ° C., and it is considered that the reaction does not proceed below that temperature. Also,
The additive has a lower thermal decomposition temperature than Bengala, so that there is no problem like Bengala in the temperature range of cast iron casting conditions. However, the effect of preventing pinholes is insufficient as compared with the case of Bengala, and it is difficult to sufficiently reduce the incidence of pinhole defects.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide an excellent pinhole prevention effect even at a temperature lower than 1300 ° C. It is to provide a means for obtaining a quality casting.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies in view of the above-mentioned circumstances, and as a substance which is thermally decomposed at a temperature lower than 1300 ° C. to generate a hydrocarbon gas, gilsonite, engine oil, It has been found that the use of a mold wash containing at least one selected from phenolic resin and phenolic resin has a remarkable effect in reducing pinhole defects (claim 1).

[0008] Substances such as Gilsonite, engine oil and phenolic resin generate hydrocarbon gases at a temperature of about 200 ° C. This hydrocarbon-based gas has an action of reducing water contained in the mold to change it into stable molecular hydrogen. Therefore, if a mold is applied to a mold surface using a mold wash containing these substances, it is possible to prevent the water in the mold from directly contacting the molten metal and absorbing hydrogen, which causes pinholes. Can be. Therefore, pouring temperature is 1
Exhibits an excellent pinhole prevention effect not only when the temperature is 300 ° C. or higher but also when the temperature is lower than 1300 ° C.
The generation of pinholes can be prevented in a wider range of casting conditions, and the quality of the casting can be greatly improved.

In the present invention, a coating composition containing a low-melting glass, which is applied to the surface of a mold to prevent casting defects in a casting, melts at a temperature lower than 1300 ° C. to form a low-melting film on the surface of the mold. The same effect of preventing pinholes can be obtained by using a mold agent (claim 2).

The low melting glass melts at a temperature lower than 1300 ° C. and forms a glassy film on the surface of the mold. The low-melting-point coating prevents the water in the mold from directly contacting the molten metal to cause an oxidation reaction, thereby preventing absorption of hydrogen, which causes pinholes. Therefore, even when the pouring temperature is lower than 1300 ° C., an excellent pinhole prevention effect is exhibited, and a high-quality casting free of pinhole defects can be obtained in a wider range of casting conditions.

According to the present invention, a low melting point reaction product film is formed on the surface of a mold by reacting with a component in the mold at a temperature lower than 1300 ° C. as a coating agent applied to the surface of the mold to prevent casting defects. CuO, KMn, which are substances to be formed
A mold wash containing at least one selected from O ₄ , Ag ₂ O, NiO, and ZnO can be used, and the same effect of preventing pinholes can be obtained (claim 3).

CuO, KMnO ₄ , Ag ₂ O, NiO,
ZnO reacts with SiO ₂ contained in the mold to form a low-melting reaction product film on the mold surface. This allows
Moisture in the mold comes into direct contact with the molten metal, causing an oxidation reaction,
It is possible to prevent the absorption of hydrogen that causes pinholes. Therefore, even when the pouring temperature is lower than 1300 ° C., an excellent pinhole preventing effect is exhibited,
In a wider range of casting conditions, a high quality casting without pinhole defects can be obtained.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The mold wash of the present invention is applied to the surface of a casting mold for casting a cast iron casting or the like to prevent casting defects in the casting, and is thermally decomposed at a temperature lower than 1300 ° C. It contains a substance that generates a hydrocarbon gas, for example, at least one selected from gilsonite, engine oil, and phenolic resin. These substances have an action of reducing the moisture in the mold serving as a hydrogen absorption source and preventing the generation of pinholes. Examples of the mold to which the mold wash of the present invention can be applied include a green sand mold generally used for casting. The green sand mold is formed by adding and kneading bentonite, coal powder, moisture and the like to mineral sand as a base material, for example, silica sand.

Here, Gilsonite is naturally produced as so-called natural asphalt, and its main composition is 86% carbon, 0.3% sulfur, 1.5% nitrogen.
It is characterized by high volatile content in%. Analysis of the gas composition of the volatile matter shows that a large amount of hydrocarbon-based substances such as methane and tar are generated at a low temperature of about 400 ° C., and a small amount of hydrogen is generated at a high temperature.

[0015] As the engine oil, any engine oil generally used as an engine oil for automobiles can be used. These engine oils
Usually, various additives such as an antioxidant and a detergent-dispersant are added to a mineral oil-based or synthetic base oil, and are thermally decomposed during casting to generate a hydrocarbon-based gas. Preferably, an engine oil that is thermally decomposed at a low temperature and generates a large amount of hydrocarbon-based gas is used.

The phenol resin volatilizes at a low temperature and generates a hydrocarbon-based gas. Specifically, a phenol novolak resin is preferably used.

These Gilsonite, engine oil and phenolic resin may be used alone or in combination of two or more to constitute the coating composition of the present invention. The mold wash of the present invention containing one or more of these gilsonites, engine oils and phenolic resins is usually made into a liquid form using a solvent such as alcohol or water, and is applied to the cavity surface of the mold. The coating method can be appropriately selected according to the properties of the coating agent. For example, a liquid engine oil can be applied as it is. Gilsonite is usually finely divided,
What was made into a solution by mixing with an alcohol-based coating agent may be applied by a spray gun or brush coating. The phenolic resin is usually in the form of granules, and the phenolic resin may be sprayed on the surface of the mold and then pressed. Alternatively, it can be added to and mixed with the mineral sand constituting the mold. The mold is
Usually, it is performed prior to casting, and when the application amount of the coating agent to the mold is 0.01 g / cm ² or more and 0.1 g / cm ² or less, the effect of preventing pinhole defects is large.

Further, in the present invention, in addition to a mold wash containing a substance that generates a hydrocarbon-based gas that reduces moisture in the mold, such as the above-mentioned Gilsonite, a low-melting coating is formed on the mold surface to form molten metal and water. A mold wash containing a substance that prevents contact with the mold can also be used. Examples of such a substance include a low-melting glass that melts at a temperature lower than 1300 ° C. and forms a low-melting coating on the surface of a mold, and by using a mold wash containing the low-melting glass, A similar effect of preventing pinholes can be obtained. Here, as a usable low melting point glass, for example, a bottle glass to which about 20% of borax is added can be mentioned. The main component is S
iO ₂ : 75%, CaO: 8%, Na ₂ O: 13%,
The melting point is about 1200 ° C.

Alternatively, Si contained in the mold at the time of casting
A mold wash containing a substance that reacts with O ₂ to form a low-melting-point reaction product film on the mold surface can also be used. Such materials include CuO, KMnO ₄ , Ag ₂ O, N
The same effect can be obtained by using a mold wash containing at least one selected from iO and ZnO.

Similarly, when using a mold wash containing a substance that forms a low melting point film, a mold made from a liquid using a solvent such as alcohol or water may be sprayed with a spray gun or brush or the like to form a mold. It may be applied to the cavity surface.

The above various substances constituting the coating composition of the present invention may be used alone or in combination of two or more. In addition, a substance that generates a hydrocarbon-based gas and a substance that forms a low-melting point coating can be used in combination. At this time, by using a substance that reduces water in the mold to convert it into molecular hydrogen and a substance that forms a vitreous film and prevents direct contact between the molten metal and water,
The effect of more reliably suppressing the hydrogen absorption of the molten metal can be expected. It can also contain other coating agents, additives and the like.

The casting is carried out by a usual method, and the mold coated with the coating composition of the present invention is heated and held in accordance with the metal to be cast, and the molten metal which has been heated and melted is solidified. During the process of raising the temperature of the mold, the pyrolysis of gilsonite, engine oil, or phenolic resin contained in the mold wash of the present invention generates hydrocarbon-based gas and prevents pinhole defects. Alternatively, pinhole defects are prevented by the action of the low melting point coating. This operation will be described below.

In a cast iron casting, a change in the amount of hydrogen in the molten metal in the melting and casting process was traced and analyzed.
About 5 to 6 ppm of hydrogen was dissolved, and it was confirmed that the pinhole defect generation rate was high. Further, even a normal molten metal dissolves about 2 ppm of hydrogen, and this molten metal dissolves and absorbs about 1 to 2 ppm of hydrogen in the mold, and finally becomes about 3 to 4 ppm of hydrogen. On the other hand, green sand types commonly used include bentonite and coal powder along with 2 to 2.
It is considered that about 4% of water is added, and this water serves as a hydrogen absorption source of the molten metal and causes pinholes.

The mold wash of the present invention has an effect of reducing the absorption of hydrogen by the water, and the water (H ₂ O)
To reduce pinhole defects by reducing hydrogen to molecular hydrogen (H ₂ ) or by forming a vitreous film on the surface of the mold (green sand) to prevent direct contact between molten metal and water. It is. That is, when the poured high-temperature molten metal heats the mold by the calorific value, the water added in the mold becomes steam and fills between the mold sand particles. At this time, if there is no mold on the surface of the mold, steam directly contacts the molten metal to cause an oxidation reaction represented by the formula (1), and active hydrogen (H) in the nascent phase is dissolved in the molten metal. Molten metal [M] + H ₂ O → MO + 2H ... (1)

On the other hand, the coating agent is water vapor (H ₂
O) has gilsonite, engine oil, and phenolic resin as reducing substances. These substances generate hydrocarbon-based gas at a temperature of about 200 ° C. and react between the sand grains of the mold as shown in equation (4) to produce steam. (H ₂ O) is converted into stable molecular hydrogen (H ₂ ). H ₂ O + CH → CO + 2H ₂ (4)

The mold wash agent softens or melts at a temperature lower than 1300 ° C. to form a glassy film on the surface of the mold, or reacts with silica sand (SiO ₂ ) in the mold to form a low-melting reaction. An object film is formed. Such materials include low melting glass powder, or CuO, KMnO ₄ ,
There are Ag ₂ O, NiO, and ZnO, which can prevent the molten metal from coming into direct contact with water vapor and causing an oxidation reaction, thereby reducing hydrogen absorption.

[0027]

EXAMPLES (Examples 1 to 9 and Comparative Examples 1 to 3) Cast iron castings were cast using the test mold shown in FIG. 1 to evaluate the degree of pinhole occurrence. The mold used for the test was a sand mold prepared by adding 5.5% of bentonite, 3% of coal powder, and 3% of water to silica sand and kneading the same, and can cast a disk-shaped casting having a thickness of 20 mm and a diameter of 110 mm. . Prior to casting, various mold wash agents shown as Examples 1 to 9 in FIG. 2 were applied to the cavity surface of the green sand mold. 2.5 g of each of these coating agents was weighed, diluted with an alcohol-based coating solution, and brush-coated on the surface of a green sand mold. In the case of a liquid substance, it was applied as it was. Here, the resin of Example 3 was a phenol novolak resin, and the glass powder of Example 9 was a low melting point glass bottle to which about 20% borax was added.

As the molten metal, a normal cast iron molten metal at 1400 ° C. and 1280 ° C. was used in which the amount of hydrogen was increased to 5 ppm and pinholes were easily generated. The molten metal was poured from the gate of the test mold shown in FIG. 1 coated with various coating agents, and cast to prepare a test piece. Upper surface 1 of the obtained cast iron casting
The number of pinholes having a diameter of 0.5 mm or more generated by cutting mm was examined, and the results are shown in FIGS. 2 (a) and 2 (b).

As Comparative Example 1, the case where no mold wash was used (without mold wash) was further compared with Comparative Examples 2 and 3.
As a conventionally used coating agent, bengara and C
In the case of using aCO ₃ , a test piece was prepared in the same manner, and the degree of pinhole generation was examined. The result
2 (a) and 2 (b).

As apparent from FIGS. 2 (a) and 2 (b), when there was no coating in Comparative Example 1, the melt temperature was 1280.degree.
At 200 ° C., about 200 pinholes were generated. On the other hand, when gilsonite, engine oil, and phenolic resin were applied at a melt temperature of 1280 ° C., the number of pinholes was significantly reduced to 10 to 30, and the effect of the coating agent to prevent pinholes was observed. Was. Almost the same effect can be observed when the temperature of the molten metal is 1400 ° C.

Further, low melting glass powder, CuO, K
When MnO ₄ , Ag ₂ O, NiO, and ZnO are applied,
At a molten metal temperature of 1280 ° C., the number of pinholes is 5 to 20, and the effect of preventing pinholes is great. Melt temperature 1400 ° C
The same was true for the case.

On the other hand, when Bengala, a conventional coating agent, was applied (Comparative Example 3), a pinhole prevention effect was observed at a molten metal temperature of 1400 ° C.
The effect of preventing pinholes at 0 ° C. is significantly reduced. When CaCO ₃ was used (Comparative Example 2),
None of the molten metal temperatures of 1280 ° C. and 1400 ° C. exhibited a sufficient pinhole preventing effect.

Example 10 and Comparative Example 4 The effect of the mold wash of the present invention was examined by applying it to a casting apparatus for automobile castings immediately after furnace repair. Refractories used in melting and holding furnaces of casting equipment are usually replaced once every several years. Immediately after the furnace repair, it is known that the amount of hydrogen contained in the molten metal increases from the time of normal operation, and the pinhole generation rate increases. Therefore, CuO was used as a mold wash agent of the present invention, and this was dissolved in an alcohol-based mold wash solution.
Immediately after the furnace repair, spray casting was applied to a portion of the casting apparatus where pinholes are likely to occur, and casting was performed. When the number of castings: N = 300, the defective rate generated on the machined surface of the casting for automobiles was determined in a steady state and immediately after furnace repair without using a mold wash (Comparative Example 4).
The results are shown in Table 1 below.

[0034]

[Table 1]

As is evident from Table 1, when the mold wash of the present invention was used, the defect rate was almost the same as in the steady state, and the pinhole defect was smaller than when the mold wash was not used. It was confirmed that it had a high effect on prevention.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a test mold used in an embodiment.

FIGS. 2A and 2B show the relationship between the mold wash and the incidence of pinhole defects. FIG. 2A shows a case where the molten metal temperature is 1400 ° C., and FIG. 2B shows a case where the molten metal temperature is 1280 ° C.

Continuing from the front page (72) Inventor Yoji Awano 41, Chuchu-Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture Inside Toyota Central Research Institute, Inc. No. 1 Toyota Central Research Institute, Inc. (72) Inventor Hitoshi Onishi 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Kazuo Nishidate 1 Toyota Town Toyota City, Toyota City Toyota Motor Stock In company

Claims (3)

[Claims] 1. A coating agent applied to the surface of a mold to prevent casting defects in a casting, wherein the substance which is thermally decomposed at a temperature lower than 1300 ° C. to generate a hydrocarbon-based gas includes gilsonite, engine oil, And at least one selected from phenolic resins. 2. A mold-coating agent which is applied to the surface of a mold to prevent casting defects in a casting, and contains a low-melting glass which melts at a temperature lower than 1300 ° C. to form a low-melting film on the surface of the mold. Coating agent characterized by the following. 3. A mold-coating agent applied to a surface of a mold to prevent casting defects in a casting, and reacts with components in the mold at a temperature lower than 1300 ° C. to form a low-melting reaction product film on the surface of the mold. CuO, KMnO ₄ , Ag ₂
A mold wash containing at least one selected from O, NiO, and ZnO.