JPH0596365A - Method for deciding shrinkage property of molten metal - Google Patents

Abstract

PURPOSE:To decide solidified condition of molten metal and to prevent the development of internal defect of shrinkage hole, etc., by measuring temps. and times of the solidification start and the solidification completion of the molten metal with a temp. detecting means arranged at plural points of a cavity in a mold in the different thicknesses. CONSTITUTION:The thermocouples 1, 2, 3 for measuring the temps. are arranged at the positions having the different thicknesses in the mold 5 and the solidification temp.-time is measured with the temp. measuring instrument connected with these thermocouples. By gradient ratio of the solidification starting diagram and gradient ratio of the solidification completing diagram of the different thicknesses at plural points and the gradient difference between the solidification starting diagram and the solidification completing diagram, the solidification condition of the molten metal can be obtd., and the shrinkage property related to some specific component in the molten metal can be decided as the concrete value. Therefore, this method is greatly available to the molten metal control and the casting designing for manufacturing the sound casting without shrinkage hole.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for determining the properties of molten metal for producing a sound casting having no internal defects such as shrinkage cavities.

[0002]

2. Description of the Related Art There are several methods of installing a thermocouple in a mold, measuring the temperature after pouring a molten metal, and obtaining information on the molten metal from the measurement result. For example, one thermocouple 23 is installed in the center of a cylindrical mold 22 as shown in FIG. 10, a molten metal is poured into this, and the temperature after pouring is input to a measuring device 24 for measurement, The CE value of the cast iron (carbon equivalent: C% + 1/3) was obtained from the primary crystal temperature of the cooling diagram obtained as a result.
A method for determining the component concentration of Si%) or a specific element has been put to practical use. Further, as shown in FIG. 11, a thermocouple 23 is installed at the center and the surface of the mold 22, the molten metal is poured, the temperature is measured, and the solidification morphology is determined by comparing the differences in the cooling diagrams. There is a way to do it.

[0003]

However, the former can determine the CE value and the component concentration of a specific element, but cannot determine the solidified form of the molten metal.

On the other hand, in the latter case, the eutectic solidification times of the casting surface and the center are determined from the cooling diagrams, and the solidification morphology is determined from the ratio of the eutectic solidification time at the center to the difference in the eutectic solidification start time between the surface and the center. This is a judgment method, and this method is simply a comparison between two points on the surface of the casting, and the difference in wall thickness is not taken into consideration in the judgment of solidification morphology. There is a problem in that the temperature measurement result of the same place must be used. Such temperature measurement on the casting surface is not accurate because it is affected by the mold and the coating mold applied to the mold surface. Further, in the temperature measurement at two points including the surface, only the difference between the solidification start times at the two points and the eutectic solidification time at the central portion are taken into consideration, and a large error may occur if the solidification morphology is determined from this result. Yes,
It is not possible to compare the solidification morphologies of melts with slightly different components. That is, in addition to this, considering how solidification proceeds and completes inside the casting, the difference between the time of solidification start and the end of solidification will be different if the thickness of the cast product changes, so It is necessary to link it with the difference and use it as a criterion for judgment.

As described above, most of the conventional methods simply check the CE value and the concentration of a specific component. There is a method to determine the solidification morphology from the temperature measurement results between two points,
There are some factors that have not been taken into consideration in this, and since only two points can be compared, an accurate judgment cannot be made.

According to the present invention, the solidified morphology of the metal is known from the times of solidification and completion of solidification of the molten metal within a plurality of different wall thicknesses, and internal defects such as shrinkage cavities are predicted to produce a sound casting. It is an object of the present invention to provide a method for determining a molten metal property for manufacturing.

[0007]

In order to achieve the above object, the present invention provides a temperature detecting means at a plurality of different wall thicknesses in a mold cavity, and pours a molten metal into the mold to obtain the temperature detecting means. By measuring the temperature and time of solidification start and solidification completion of the molten metal, the ratio of the gradient of the solidification start diagram with different wall thicknesses of the multiple points, the ratio of the gradient of the solidification end diagram and the solidification start diagram and the completion of solidification It is characterized in that the solidification morphology of the molten metal is determined from the difference in the gradients of the diagrams.

In the present invention, the temperature of the casting surface is not measured, but the temperature is measured inside a plurality of castings having different wall thicknesses. Since the judgment factor also includes the wall thickness, no matter what shape the casting is used in, the temperature of the molten metal is measured using a mold equipped with multiple thermocouples, and solidification is performed from the obtained cooling diagram and wall thickness. It is possible to know the form.

The present invention will be described in detail below. Figure 1
A thermocouple for temperature measurement is provided in the mold 5 at different thicknesses,
It is a top view showing the method of solidification temperature-time measurement connected to the temperature measuring device from the thermocouple. In FIG. 1, 1-3
Is a thermocouple, 4 is a runner that also serves as a feeder, 5 is a mold, and 6 is a solidification temperature measuring device. The shape of the casting shown in FIG. 1 may be any shape as long as the thickness of each part of the casting is different. For example, a stepped casting as shown in FIG. 2 may be used. Install all thermocouples in the center of the casting, and do not measure near the surface where measurement error is large. In FIG. 1, molten metal is poured into the mold 5 from the runner 4 which also serves as a feeder, and the thermocouples 1, 2, 3,
The temperature change of the molten metal is measured and recorded by the temperature measuring device 6.

FIG. 4 is an example of a measured temperature change diagram. 14 is a temperature change diagram of a thin portion of the cast product, and 16 is a temperature change diagram of a thick portion of the cast product.

In the temperature change diagram, 12 is the primary crystal temperature, 1
3 is the lowest point of supercooling, and 15 is the solidification completion temperature. Also, 1
7 is the eutectic solidification start time, and 18 to 20 is 14 to 1
It is the eutectic solidification completion time for each of the 6 thick parts. FIG. 5 shows the primary crystal time, the eutectic solidification start time, and the eutectic solidification completion time at each thickness point read from FIG. 4, with the horizontal axis representing time and the vertical axis representing wall thickness. This FIG. 5 is called a coagulation progress diagram.

FIG. 7 shows the solidification state inside the casting at the time t from the solidification progress diagram of FIG. Figure 7
The closer the solid-liquid coexisting portion is, the closer it is to the skin formation solidification (smooth solidification), and the solidification progresses sequentially from the thin-walled portion to the thick-walled portion of the casting, and a sound casting without shrinkage cavities is likely to be formed. On the other hand, the larger the solid-liquid coexisting part, the closer it is to Massy solidification (itchy solidification). That is, the more the diagram of the eutectic solidification start time and the eutectic solidification completion time in FIG. In this form of massy solidification, the casting does not directionally solidify, and at the same time the solidification tends to progress,
The final solidified portion remains inside the casting, and shrinkage cavities are likely to occur.
Also, the larger the gradient of the eutectic solidification start time diagram, the stronger the tendency of the entire casting to simultaneously solidify,
The larger the gradient of the eutectic solidification completion time diagram, the stronger the tendency that the solidification of the entire casting is completed at the same time. That is,
It can be said that the larger the difference in gradient between the temperature-time diagram at the start of solidification and the temperature-time diagram at the end of solidification, the closer it is to massy-solidification.

FIG. 6 shows three points, a, b, and
The eutectic solidification start time and the eutectic solidification completion time in c were measured,
These three points are connected by a straight line with the vertical axis. Here, regarding the diagram of the eutectic solidification start time of FIG.
The ratio of the gradient in the section 2 between (a and b) to the gradient in the section 1 between c) is represented by the equation 1. Further, the ratio of the gradient in the section 2 to the gradient in the section 1 in the diagram of the completion time of the eutectic solidification is represented by Formula 2. In addition, the ratio of the eutectic solidification end time difference Δt1 from the eutectic solidification start time at point a, which is the thin portion, to the eutectic solidification end time difference Δt3 from the eutectic solidification start time at point c, which is the thick portion, It is expressed by Equation 3.

[0014]

## EQU1 ## α = (d2 / Δs2) / (d1 / Δs1) where, d1: difference in thickness between points a and b d2: difference in thickness between points b and c Δs1: difference between points a and b Difference in eutectic solidification start time Δs2: Difference in eutectic solidification start time at points b and c.

[0015]

[Formula 2] β = (d2 / Δe2) / (d1 / Δe1) where, d1: difference in thickness between points a and b d2: difference in thickness between points b and c Δe1: difference between points a and b Difference in end time of eutectic solidification Δe2: Difference in end time of eutectic solidification at points b and c.

[0016]

[Mathematical formula-see original document] γ = Δt1 / Δt3 where, d1: difference in wall thickness at points a and b d2: difference in wall thickness at points b and c Δt1: eutectic solidification time at point a Att3: at point c Eutectic solidification time.

The larger the values of the parameters (α, β) of the equations 1 and 2, the larger the difference in the gradient between the solidification start temperature and the solidification end temperature diagram, and the larger the massy solidification. Close to. Moreover, the larger the parameter (γ) of the equation 3 is,
This shows that the difference in the solidification time due to the wall thickness is small, and is closer to the massy solidification.

From the above, a product obtained by multiplying the equations 1, 2, and 3 was used as a parameter for determining the degree of Massy coagulation and named as Massy coagulation degree determination parameter (P). This is expressed by Equation 4.

[0019]

[Formula 4] P = α · β · γ = (Δt1 · Δs1 · Δe1 · d22) / (Δt3 · Δs2 · Δe2 · d12) As described above, the castings of the present invention have different thicknesses. Using the results of measuring the temperature and time of the start of eutectic solidification and the end of eutectic solidification of the metal melt, the difference in the Massie-solidification degree due to slight changes in the melt components can be found as a specific numerical value. Since the possibility of shrinkage cavities increases as the Massy-coagulation degree increases, it can be used for the determination of shrinkage cavities.

[0020]

EXAMPLE An example of the present invention will be described in detail below. FIG. 1 is a plan view of a stepped cylindrical casting used in an example and a measuring device, and FIG. 2 is a front view of a stepped casting. The spheroidal graphite cast iron was cast in the molds shown in FIGS. 1 and 2 by changing the chemical composition, and the eutectic solidification start time and the eutectic solidification end time after casting and the wall thickness at the measurement points were measured. Main elements such as carbon (C) and silicon (Si) are kept constant, molybdenum (Mo) and bismuth (Bi), which are said to promote shrinkage cavity generation, are added, and shrinkage cavity generation is reduced. The experiment was conducted by increasing the amount of sulfur (S) added. The value of the Massey-coagulation degree determination parameter was determined from the obtained results. Table 1 shows the standard component values of spheroidal graphite cast iron. Table 2 shows the values of the Massey-coagulation degree determination parameters measured by changing the components.

[0021]

[Table 1] Standard chemical composition of spheroidal graphite cast iron (% by weight) C Si Mn P Cr Cu Mg Mg S Mo Bi 3.60 2.10 0.30 0.020 0.03 0.03 0.035 0.004--

[0022]

[Table 2] Chemical composition weight% parameter value of stepped cast material with varied stepped cylindrical casting Parameter value Standard value 0.287 0.152 Mo 0.50 0.410 0.180 S 0.015 0.174 0.012 Bi 0.01 1.500 0.574

It can be seen from Table 2 that the value of the parameter is particularly large when the bismuth (Bi) is increased in both the stepped cylindrical casting and the stepped casting. Moreover, the value of the parameter when the sulfur (S) is increased is the smallest.

In this way, it is possible to determine the occurrence of shrinkage cavities regardless of what element changes. The critical value of the parameter can be determined by examining the massiness-coagulation degree parameter and the occurrence of shrinkage cavities when the components are changed little by little.

As shown in Table 2, the values of the parameters differ if the shapes of the test castings differ even if they have the same composition. It is necessary to use a specific casting for which the critical value of shrinkage cavity generation is known in advance in order to judge the massiness degree in an actual foundry. For example, it is assumed that the critical value of the test casting as shown in FIG. 8 is P = 0.7. Then, for example, the casting "A" has a shape in which shrinkage cavities easily occur, or the acceptance criteria of the product is strict. on the other hand,
It is assumed that the casting B has a shape with few shrinkage cavities or has a high acceptance criterion. In such a case, the parameter value of the molten metal when casting the casting A is made sufficiently lower than the critical value, for example, P = 0.5 or less. For casting B, the parameter value is close to the critical value, or may exceed the critical value a little, so P =
It may be 0.7 to 0.8 or less.

FIG. 9 shows the massiness / solidification degree determining parameters and shrinkage cavities of spheroidal graphite cast iron when the amount of sulfur (S) was changed using the stepped casting shown in FIG. It is a thing. Comparing the two with different sulfur (S), when the amount of sulfur (S) is small, shrinkage cavities have occurred and the mass-
The value of the coagulation degree determination parameter (P) is also large. On the other hand, when the amount of sulfur (S) is large, shrinkage cavities do not occur, and the value of the Massey-coagulation degree determination parameter (P) is small. The parameter critical value of this test casting is the parameter of both.
You can see that it lies between the values. FIG. 3 shows a block diagram of the method for determining the shrinkability of the molten metal of the present invention.

[0027]

As described above, according to the present invention, the temperature and time of solidification start and solidification completion are measured for a plurality of different wall thicknesses, and the temperature-time line of solidification start and solidification end with respect to the change in wall thickness. It is possible to determine the solidification morphology of the molten metal from the ratio or difference of the gradients in the figure, and it becomes possible to determine the shrinkage of a certain molten metal component as a specific numerical value, and to obtain a sound casting without shrinkage cavities. It is very useful for molten metal management and plan design for manufacturing.

[Brief description of drawings]

FIG. 1 is a plan view in which a stepped cylindrical casting according to an embodiment of the present invention and a measuring device are provided.

FIG. 2 is a front view of a stepped casting according to another embodiment of the present invention.

FIG. 3 is a block diagram of molten metal management using the shrinkability determination method of the present invention.

FIG. 4 is an example of a measured temperature change diagram.

FIG. 5 is a coagulation progress chart in which the horizontal axis represents time and the vertical axis represents wall thickness.

FIG. 6 is a diagram of a eutectic solidification start time and a eutectic solidification end time at different points in the thickness of the casting.

FIG. 7 is a diagram showing the solidification state in the casting at time t from the solidification progress diagram of FIG.

FIG. 8 is a diagram showing a casting method and determination of shrinkability thereof as a Massy-solidification degree determination parameter using the present invention.

FIG. 9: Sulfur (S) per step cast using the present invention.
It is a figure which shows one Example which improved the molten metal property by changing the generation | occurrence | production state of the shrinkage cavity and the parameter value of a Massey-coagulation degree judgment when changing the amount of.

FIG. 10 is a diagram showing a conventional test apparatus for determining the concentration of a component or the concentration of a specific element.

FIG. 11 is a diagram showing a conventional test apparatus for determining solidification morphology in which thermocouples are provided at two points on the surface of a mold.

[Explanation of symbols]

 1, 2 and 3 Thermocouple 4 Runway 5 Mold 6 Temperature measuring device 7 Casting product part 8 Hot water 9 Hot water route 10 Gate 9 Mold 12 Initial crystal temperature 13 Supercooling lowest point 14 Temperature diagram of thin part 15 Solidification completed Temperature 16 Temperature diagram of thick part 17 Eutectic solidification start time 18-20 Eutectic solidification completion time of each thick part 21 Shrinkage cavity 22 Mold 23 Thermocouple 24 Measuring device

Claims (1)

[Claims] 1. A temperature detecting means is provided at a plurality of different wall thicknesses in a mold cavity, molten metal is poured into the mold, and the temperature and time for solidification start and completion of solidification of the molten metal are measured by the temperature detecting means. Measure and determine the solidification morphology of the molten metal from the ratio of the gradients of the solidification start diagram with different thicknesses at the above-mentioned multiple points, the ratio of the gradients of the solidification end diagram and the difference of the gradients of the solidification start diagram and the solidification end diagram Method for determining shrinkage of molten metal characterized by