JPH10296385A - Production of spherical graphite cast iron casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a producing method of a sound spherical graphite casing having no defect of shrinkage hole, etc. SOLUTION: Temp. variations at two points of an one point in the inner part of the casting and an one point near the surface, are compared and casting is executed by changing the casting shape and/or casting plan so that the ratio of an eutectic solidified completing time at the one point near the surface to that at the one point in the inner part becomes <=0.8, preferably <=0.7 decision factor. As the other way, the temp. variations in two points at an one point in the inner part of the casting and an one point near the surface, are compared and casting is executed by changing the casting shape and/or the casting plan so that the ratio of the time from the eutectic solidified start at the one point in the inner part to the eutectic solidified completion at the one point near the surface to that at the one point in the inner part becomes <=0.7, preferably <=0.6 decision factor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of producing a sound spheroidal graphite cast iron casting free from defects such as shrinkage cavities in the casting of spheroidal graphite cast iron.

[0002]

2. Description of the Related Art One of the general methods for producing a metal shaped material.
There is a casting method. The molten metal is poured into a mold cavity having a required shape, and is removed from the mold after solidification. The mold is formed from casting sand mixed with a binder and usually has cavities, weirs, runners and risers. In general, the molten metal injected into the cavity shrinks with a decrease in temperature, so that there is a possibility that a sink defect may occur inside the casting. Therefore, it is desirable to predict the presence or absence of shrinkage cavities in advance and design a casting plan. Usually, as a method for predicting the sink mark, the “hot spot method” by coagulation simulation is used.
Is used. This is because, during the solidification process, when an island of molten metal (an unsolidified metal island surrounded by solidified metal and called a “hot spot”) is formed in the cavity, the unsolidified metal is completely surrounded by the solidified metal. This method focuses on the fact that molten metal cannot be supplied and voids are formed, and determines whether or not a hot spot is formed, thereby determining the quality of the casting method.

As methods for judging sinkability of molten metal, Japanese Patent Application Laid-Open No. Hei 5-96365, "Title of Invention: Method for Determining Metal Shrinkability", and Japanese Patent Publication No. 6-504322, "Title of Invention: CV Graphite" Cast Iron Manufacturing Method ”, there is a method of comparing the cooling curves of the container center portion and the container inner wall portion. These focus on the fact that the solidification form differs between the inside of the casting and the surface due to differences in the properties of the molten metal, and are used in advance to determine the molten metal in which sink cavities are likely to occur.

[0004]

SUMMARY OF THE INVENTION In the case of spheroidal graphite cast iron,
During solidification, there is a volume expansion accompanying graphite crystallization. For this reason, it is said that it is very difficult to directly predict the occurrence of shrinkage nests. The hot spot method is effective for metals such as cast steel and aluminum that undergo considerable shrinkage upon solidification. However, for metals such as ordinary cast iron and spheroidal graphite cast iron in which crystallization of graphite is observed during eutectic solidification, shrinkage cavities may not be formed even when hot spots are formed.
This is because the spheroidal graphite cast iron is not only shrunk but also expands when solidified, and it has the specialty that it is a massy solidification in which the entire solidification proceeds at the same time. It has not been clarified.
As described above, in spheroidal graphite cast iron, the occurrence of shrinkage cavities cannot be accurately predicted by the hot spot method, and the size of the riser is not economically calculated.

[0005] Furthermore, depending on the shape of the casting, there is a case where a sink mark is formed and a case where the same molten metal is not formed.
However, the method described in JP-A-5-96365 measures the temperature of the inside and the surface of a single container, and predicts the occurrence of sink marks due to the difference in the molten metal. Although possible, casting shapes and casting schemes cannot be determined. Tokuhyo Hei 6-50432
No. 2 relates to CV cast iron,
This is different from the spheroidal graphite cast iron of interest here, but so is the same. An object of the present invention is to obtain a sound spheroidal graphite cast iron by accurately predicting the occurrence of shrinkage porosity defects in various casting shapes, and utilizing the prediction for design of casting plans and examination of casting shapes.

[0006]

Means for Solving the Problems The inventor conducted intensive research and examined the relationship between the cooling conditions of various castings and shrinkage cavities. As a result, the ending time of eutectic solidification on the casting surface was found to be eutectic solidification inside the casting. It was found that shrinkage cavities disappeared relatively earlier than the end time. Therefore, it has been found that it is possible to predict the occurrence of shrinkage porosity defects by grasping and comparing the temperature difference between the casting surface and the inside of the casting. That is, in the method of manufacturing a spheroidal graphite cast iron casting, the temperature change at two points, one point inside the casting and one point near the surface, is compared, and the time at the one point near the surface relative to the eutectic solidification end time at the one point inside is compared. Casting is performed by changing the casting shape and / or the casting plan so that the ratio of the eutectic solidification end time is equal to or less than the determination coefficient. The determination coefficient is 0.8 or less, preferably 0.7 or less. Alternatively, the ratio of the time from the start of the eutectic solidification of one internal point to the end of the eutectic solidification of one point near the surface to the time from the start of the eutectic solidification of the one internal point to the end of the eutectic solidification is equal to or less than the determination coefficient. The casting is performed by changing the casting shape and / or the casting plan so that The determination coefficient in this case is 0.7 or less, preferably 0.6 or less. By using this manufacturing method of the present invention, shrinkage nests can be reduced.

That is, a position where the eutectic solidification end time is relatively late in the casting as shown in FIG. 1 (a part inside the casting).
1, and near the surface (the part of the surface of the casting)
2, as shown in FIG. 2, the occurrence of shrinkage cavities is predicted by obtaining respective cooling curves and comparing the eutectic solidification end time from the cooling curves. In FIG. 2, Ta indicates the eutectic solidification start time in the casting, Tb indicates the eutectic solidification end time in the casting, and Tc indicates the eutectic solidification end time in the casting surface.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) FIG. 3 shows Embodiment 1 of the present invention. In the first embodiment, actual measurement using a thermocouple and simulation calculation using a computer can be used. Study casting shape and plan. In the casting shape, one point inside the casting, where solidification is considered to be relatively slow, and one point near the casting surface are set as observation points. Measure or calculate the cooling curve at each observation point. (See FIG. 2) The eutectic solidification end time (Tb) inside the casting is determined. Here, Tb means the time (second) from the pouring to the end of eutectic solidification at one point inside the casting. The eutectic solidification end time (Tc) of the casting surface is determined. Here, Tc means the time (second) from the pouring to the end of eutectic solidification at one point on the casting surface. The coagulation end time ratio Tc / Tb is calculated. When the eutectic solidification end time ratio is larger than the determination coefficient 0.8 (more preferably 0.7), it is determined that there is a sink mark,
Return to and review the casting shape or plan. This step is repeated as necessary, and when the coagulation end time ratio becomes smaller than the determination coefficient, it is determined that there is no sink mark, and actual production is performed.

(Embodiment 2) Alternatively, the solidification state inside the casting when the surface of the casting has completed eutectic solidification can be obtained and compared with a judgment coefficient. This embodiment 2 is shown in FIG. . The second embodiment is performed in the following steps (1) to (4). Study casting shape and plan. In the casting shape, one point inside the casting, where solidification is considered to be relatively slow, and one point near the casting surface are set as observation points. Measure or calculate the cooling curve at each observation point. (See FIG. 2) The eutectic solidification start time (Ta) inside the casting and the eutectic solidification end time (Tb) inside the casting are determined. The eutectic solidification end time (Tc) of the casting surface is determined. The internal solid fraction (Tc-Ta) / (Tb-Ta) is calculated. Here, the numerator (Tc-Ta) of this equation is the time (second) from the start of eutectic solidification inside the casting to the end of eutectic solidification on the casting surface, and the denominator (Tb-Ta) of this equation is inside the casting. Is the time (sec) from the start of eutectic solidification to the end of eutectic solidification. When the internal solid phase ratio is larger than the determination coefficient 0.7, it is determined that there is a sink mark, and the process returns to the step to reconsider the casting shape or the plan. This step is repeated as necessary, and when the coagulation end time ratio becomes smaller than the determination coefficient, it is determined that there is no sink mark and actual production is performed.

Table 1 shows the results of applying the present invention to castings of various shapes and judging the presence or absence of sink marks in comparison with the actual casting results and the hot spot method. That is,
The shape of the casting is shown in FIG. 5, FIG. 7 and FIG.
1 is a cylinder with a flange, FIG. 10 is a cylinder, FIG.
Is a sphere.

[0011]

[Table 1]

For example, in the case of determining a shrinkage cavity using the above-mentioned eutectic solidification time ratio for a casting having a plate thickness of 30 mm shown in FIG. 5, cooling curves of the casting surface portion B and the casting interior A are obtained by simulation calculation. Is as shown in FIG.
Here, when the solidification time ratio is calculated, it becomes 0.88 (see the description in the column of FIG. 5 of the casting shape in Table 1), and when casting is actually performed with this shape, shrinkage cavities occur. Therefore,
As shown in FIG. 7, the plate thickness is increased to 50 mm, and a cooling curve is obtained by simulation calculation. This cooling curve is shown in FIG. Here, when the solidification time ratio was calculated, it was 0.72 (Table 1).
In the casting, see the description in the column of FIG. 7), and no shrinkage cavities occur even in actual casting.

[0013]

As is clear from the above description, since the present invention can predict the occurrence of shrinkage cavities with high accuracy, it is possible to minimize the size of the feeder in designing a casting plan and examining a casting shape. This has the effect of reducing the defective rate. This makes it possible to efficiently manufacture a spheroidal graphite cast iron casting at low cost.

[Brief description of the drawings]

FIG. 1 is a view showing a cylindrical-shaped casting with a flange.

FIG. 2 is a diagram showing a cooling curve of the casting of FIG. 1;

FIG. 3 is a diagram showing steps in the first embodiment.

FIG. 4 is a diagram showing steps in the second embodiment.

FIG. 5 is a view showing a casting having a rectangular parallelepiped shape.

FIG. 6 is a diagram showing a cooling curve of the casting of FIG. 5;

FIG. 7 is a view showing a casting having a rectangular parallelepiped shape.

FIG. 8 is a diagram showing a cooling curve of the casting of FIG. 7;

FIG. 9 is a view showing a casting having a rectangular parallelepiped shape.

FIG. 10 is a view showing a casting having a stepped cylindrical shape.

FIG. 11 is a view showing a casting having a spherical shape.

[Explanation of symbols]

 Reference Signs List 1 Casting interior 2 Casting surface 3 Casting 4 Feeder Ta Eutectic solidification start time inside cast Tb Eutectic solidification end time inside cast Tc Eutectic solidification end time inside cast surface

Claims (6)

[Claims] 1. A method for producing a spheroidal graphite cast iron casting, comprising:
The temperature change at two points, one point inside the casting and one point near the surface, is compared, and the ratio of the eutectic solidification end time at one point near the surface to the eutectic solidification end time at one point inside the casting is equal to or less than the determination coefficient. A method for producing a spheroidal graphite cast iron casting, wherein the casting is changed while changing the shape of the casting and / or the casting plan so that 2. The method for producing a spheroidal graphite cast iron casting according to claim 1, wherein the determination coefficient is 0.8 or less. 3. The method for producing a spheroidal graphite cast iron casting according to claim 1, wherein said determination coefficient is preferably 0.7 or less. 4. A method for producing a spheroidal graphite cast iron casting, comprising:
The temperature changes at two points, one point inside the casting and one point near the surface, are compared, and the time from the start of the eutectic solidification of the inside one point to the end of the eutectic solidification, from the start of the eutectic solidification of the inside one point to the time A method for producing a spheroidal graphite cast iron casting, wherein casting is performed by changing a casting shape and / or a casting plan so that a ratio of time until completion of eutectic solidification at one point near a surface is equal to or less than a determination coefficient. 5. The method for producing a spheroidal graphite cast iron casting according to claim 4, wherein the determination coefficient is 0.7 or less. 6. The method for producing a spheroidal graphite cast iron casting according to claim 4, wherein said determination coefficient is preferably 0.6 or less.