JPH09201664A - Casting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an expensive and easy casting method to obtain the objective quality of a cast product, by supplying electricity to electrodes in contact with a position in molten metal which forms a thin thickness part to give positive calory and controlling cooling speed of the molten metal. SOLUTION: The molten metal is poured into a cavity C in sand molds 1, 2. After the molten metal comes into contact with both electrodes 3a, 3b, the electricity is supplied to both electrodes 3a, 3b from an electric source 4, and the positive calory is given to the position of the molten metal which forms the thin thickness part. In this case, since the heating and the insulating are positively executed while naturally cooling a suspension arm to about room temp., the wasteful consumption of the energy is not executed and the production cost is reduced.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a casting method,
More specifically, the present invention relates to a casting method capable of reliably and easily achieving the desired quality of the whole or a part of the cast product.

[0002]

2. Description of the Related Art When a cast product having a certain shape is cast, the cast product immediately after casting may not have a desired quality, that is, a metal structure or mechanical properties such as impact value and elongation. In this case, the alloy composition of the molten metal and the shape of the mold may be changed, but since such a change is close to trial and error, generally, the cast product immediately after casting is subjected to heat treatment such as annealing and normalizing. Is done. As the cast product thus obtained, for example, austempered spheroidal graphite cast iron product (J
ISG5503), heat-resistant cast steel products (JISG5122)
There is.

Further, in the field of aluminum casting, there is known an aluminum casting pot in which the entire mold can be heated by a flame torch. When performing aluminum casting with this aluminum casting kettle, before injecting the molten metal into the cavity of the mold, the entire mold is heated by the flame torch, thereby slowing down the cooling rate of the entire molten metal and obtaining a predetermined aluminum cast product. it can.

Further, in the field of cast iron, a casting mold is known in which a chill made of a metal having a high thermal conductivity is provided at a desired portion of the mold (for example, Japanese Patent Laid-Open No. 61-60252).
JP-A-61-78548). When performing cast iron casting with this casting mold, after injecting the molten metal into the cavity of the mold, the chill structure (cementite (Fe ₃ C)) is increased by accelerating the cooling rate of the molten metal at the desired site with a cooling metal. It is possible to obtain cast iron products having

In addition, a heat insulating insert for delaying the cooling rate of the thin portion of the casting is formed in the portion of the mold forming the thin portion of the casting, and the thick portion of the casting is formed in the portion of the casting forming the thick portion of the casting. There is also known a casting mold provided with a cooling insert that speeds up the cooling rate of (No. 2-13).
No. 8056). When casting with this casting mold, after injecting the molten metal into the cavity of the mold, the heat retention insert and cooling insert enable directional solidification of the melt to obtain a cast product without shrinkage cavities. You can

[0006]

However, in the above-mentioned general method of heat treatment immediately after casting, the cast product once cooled to room temperature has to be reheated, resulting in wasteful consumption of energy, resulting in manufacturing cost. Becomes higher. Further, in this method, since the entire cast product is reheated by the batch furnace or the continuous furnace, it is not possible to obtain the desired quality for only a part of the cast product. Even in the above-mentioned aluminum casting kettle in which the entire mold is heated by the flame torch, it is not possible to achieve the desired quality for only a part of the cast product.

On the other hand, in the above-mentioned casting mold in which a chill, a heat retaining insert or a cooling insert is provided at a desired portion such as a specific portion of the mold, only a part of the cast product should have a desired quality. Although it is possible for a while, since the cooling rate of the molten metal is accelerated or delayed depending on the internal characteristics of the chiller itself, the cooling rate tends to vary, and its quality is uncertain or difficult to achieve. .

The present invention has been made in view of the above-mentioned conventional circumstances, and the whole or a part of a cast product can be made to have a desired quality, and it is inexpensive, reliable and easy. The problem to be solved is to provide a casting method.

[0009]

[Means for Solving the Problems]

(1) The casting method according to claim 1 controls the cooling rate of the molten metal in the desired portion by injecting the molten metal into the cavity of the mold and then applying an externally controllable amount of heat to the desired portion of the molten metal. It is characterized by According to the casting method of claim 1, after the molten metal is injected into the cavity of the mold, heat is applied to a desired portion of the molten metal. Here, not applying the amount of heat is passive natural cooling, whereas applying the amount of heat is positive, as in the casting method of claim 1. Applying a positive amount of heat is heating or heat retention, and applying a negative amount of heat is cooling.

Thus, in the casting method according to the first aspect, since the cast product is naturally cooled to about room temperature and is actively heated, kept warm or cooled, the cast product cooled to about room temperature is not reheated. do not do. So this method
There is no waste of energy and manufacturing costs are low. Further, while the thin portion of the cast product is naturally cooled at a high cooling rate, the thick portion of the cast product is naturally cooled at a low cooling rate. Therefore, in this case, it is difficult to obtain the desired quality of the entire cast product. Further, in this case, the thin portion is solidified before the thick portion, and impurities and contained gas in the molten metal are aggregated in the vicinity of the thick portion, which makes it difficult to effectively perform degassing and riser, making it a cast product. It was prone to shrinkage.

On the other hand, in the casting method according to the first aspect, by setting the desired portion in accordance with the shape of the cavity, the quality of the entire cast product can be obtained, or a part of the cast product can be obtained. Can be quality. Further, it is possible to effectively perform degassing and hot water, and to prevent shrinkage cavities from occurring. In addition, since the amount of heat that can be externally controlled is adopted during these periods, the cooling rate of the molten metal at the desired portion is stably controlled, and the quality of the cast product is surely and easily realized.

As means for applying a positive amount of heat that can be externally controlled, in addition to the means according to claim 2, a molten material or a resistor made of a material different from the molten metal and having a large electric resistance is embedded in a desired portion of the mold, Means for energizing this resistor can be adopted. If graphite lumps are used as the resistor embedded in the molten metal, the function as a carburizing material can be exhibited at the same time. Further, as the externally controllable means for applying a negative heat quantity, a means such as burying a cooling pipe in a desired portion of the mold and flowing a heat-absorbable refrigerant into the cooling pipe can be employed.

(2) The casting method according to claim 2 is the casting method according to claim 1, in which a pair of electrodes is brought into contact with the molten metal at a desired portion, and a positive amount of heat is applied by energizing both electrodes. It is characterized by Since energization can be easily controlled externally, according to the casting method of claim 2, the cooling rate of the molten metal at a desired portion of the cast product can be reliably and stably controlled, and the quality of the cast product is further ensured. And it will be easy. As a method for externally controlling the energization, in addition to the means according to claim 3, it is possible to employ means for energizing with a power pattern previously obtained by a preliminary test using the same mold and the same molten metal.

Further, embedding a resistor made of a material different from that of the molten metal in a desired portion of the molten metal also functions as a carburizing material in view of the desired quality of the cast product in which the resistor is in-molded. It is often impossible except for a graphite rod or a lump of graphite that can perform. On the other hand, in the casting method of claim 2, since the heat generated by the electric resistance obtained by energizing the molten metal itself is used as a positive amount of heat, the resistor is not in-molded in the cast product, It does not impair the desired quality of. If you do not embed, but if you use a material different from the molten metal as the electrode that comes into contact with the molten metal, the desired quality of the cast product, unless it is a graphite rod that can also function as a carburizing material. Moreover, it is necessary to cut off the electrode after casting. On the other hand, if cast iron welding rods are used for casting, aluminum rods are used for aluminum casting, and electrodes of the same or similar material as the molten metal are used, cutting after casting is minimized. Also, maintenance-free is realized and the manufacturing cost is reduced. Further, in a graphite rod that is embedded in or in contact with the molten metal and can be adopted as a resistor or an electrode made of a material different from that of the molten metal, cracks easily occur due to heat shock during pouring, thereby changing the electrical resistance, External controllability is impaired due to changes in the amount of heat generated. On the other hand, if an electrode made of the same material as or a material similar to that of the molten metal is used, cracks are less likely to occur due to heat shock during pouring, and external controllability is not impaired. However, if a graphite lump that hardly causes cracks is adopted as the resistor, the problem of external controllability can be solved.

(3) The casting method according to claim 3 is the casting method according to claim 2, in which the electric resistance is obtained from the voltage applied to both electrodes and the current flowing through a desired portion of the molten metal, and based on the obtained electric resistance. Then, the temperature of the desired portion is obtained, and the voltage applied to both electrodes is feedback-controlled so that the obtained temperature becomes the target temperature. In the casting method of claim 3, since the voltage applied to both electrodes is feedback-controlled so that the temperature of the desired portion of the molten metal reaches the target temperature, the cooling rate of the molten metal at the desired portion of the cast product is more reliably and stably controlled. The realization of the quality of cast products becomes even more reliable and easier.

Further, in order to detect the temperature of a desired portion of the molten metal, it is conceivable to provide a detecting means such as a thermocouple made of Pt-PtRh at a desired portion of the molten metal or the mold. And
It is also possible to provide a heat generating means such as a resistor at a desired portion of the mold and externally control this heat generating means. However, when the detecting means is provided in the mold, the temperature of the molten metal cannot be directly detected. Further, when the heat generating means is provided in the mold, the temperature of the molten metal cannot be controlled directly. Therefore, in these cases, the external controllability is impaired. In addition, the thermocouple has a small amount of heat generation and can hardly be used as a positive amount of heat, and a separate heat generating means is required, which is inefficient.
On the other hand, in the casting method of claim 3, the electric resistance is obtained from the voltage applied to the electrode in contact with the molten metal and the current flowing through the molten metal, and the temperature of the desired portion is obtained based on the obtained electric resistance. Since the temperature of the molten metal is directly detected, the temperature of the molten metal is directly controlled, and the external controllability is excellent. Further, in the casting method of the third aspect, the heat generated by the electric resistance obtained by energizing the molten metal itself is used as a positive amount of heat, and a separate heat generating means is not required, which is efficient.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments 1 and 2 embodying the invention of each claim will be described below with reference to the drawings. In the first and second embodiments, the cast iron suspension arm shown in FIG. 1 is cast. When casting such a suspension arm, the thin portion n is naturally cooled at a high cooling rate, while the thick portion k is naturally cooled at a low cooling rate. For this reason, in this case, it is difficult to achieve the desired quality for the entire suspension arm. In this case, the thin portion n
Is solidified earlier than the thick portion k, and impurities and contained gas in the molten metal are condensed in the vicinity of the thick portion k, so it is difficult to effectively degas and raise the molten metal, and shrinkage cavities are likely to occur in the suspension arm. It was

(Embodiment 1) In Embodiment 1, claim 1
2 is embodied. First, as shown in FIG. 2, sand molds 1 and 2 as a mold having a suspension arm-shaped cavity C are prepared (FIG. 2 is a sectional view taken along the line II-II in FIG. 1). Electrodes 3a and 3b made of the same material as the molten metal to be poured into the cavity C are provided at the site where the thin portion n of the sand mold 1 is formed.

A power source 4 is connected to both electrodes 3a, 3b,
A constant voltage control circuit 5 is connected to the power supply 4. The constant voltage control circuit 5 uses the power pattern P shown in the lower diagram of FIG.
Energizes both electrodes 3a, 3b. The power pattern P is obtained in advance by a preliminary test using the same sand molds 1 and 2 and the same molten metal. That is, in the preliminary test, when the electrodes 3a and 3b are not energized, the molten metal of 1400 (° C.) made of FCD400 is naturally cooled in the thin portion n by the curve A ₁ shown by the solid line in the upper diagram of FIG. In part k, the curve A shown by the broken line in the figure
It was naturally cooled by ₂ . In addition, in FIG.
(° C) is the solidification temperature of the molten metal. The suspension arm obtained in the preliminary test had a matrix of pearlite in the thin portion n, and had a relatively hard and brittle metallic structure in which spheroidal graphite was scattered.
In the thick portion k, pearlite and ferrite were mixed to form a matrix, and a spherically dispersed graphite was dispersed therein to form a relatively soft and flexible metal structure. In such a suspension arm, brittle fracture is likely to occur in the thin portion n, so the thin portion n needs to have the same metallographic structure as the thick part k or a metallographic structure in which ferrite forms a matrix. For this purpose, the molten metal needs to be cooled in the thin portion n by the curve A ₃ shown by the chain line in the figure. The curve A ₃ is characterized by having an isothermal transformation period T in the range of 250 to 450 (° C).

Therefore, the integrated value of the portion surrounded by the curves A ₁ and A ₃ is calculated as the heat quantity W (cal) to be given. This heat quantity causes the current flowing through the thin portion n to be I
(A), electric resistance of thin portion n is R (Ω), time is t
(Seconds) is approximately represented by W = 0.24I ² Rt. The heat quantity W is converted into electric power, and the electric power pattern P shown in the lower diagram of FIG. 3 is set.

Then, as shown in the upper diagram of FIG. 3, the same molten metal is poured into the cavities C of the sand molds 1 and 2. After the molten metal comes into contact with both electrodes 3a, 3b, by energizing both electrodes 3a, 3b from the power source 4 with the power pattern P shown in the lower diagram of FIG. 3, a positive amount of heat W is applied to the portion forming the thin portion n of the molten metal. Is granted. Thus, in the casting method according to the first embodiment, the suspension arm is naturally cooled to about room temperature, and is actively heated and kept warm. Therefore, the suspension arm cooled to about room temperature is not reheated. Therefore, in this method, there is no waste of energy and the manufacturing cost is low.

In addition, in this method, the portions where the electrodes 3a and 3b are provided are set to the thin portion n to effectively perform gas venting and hot water to prevent shrinkage cavities and to reduce the thin portion n. Since the metal structure is the same as that of the thick portion k or the metal structure of which ferrite forms a matrix, the quality of the entire suspension arm can be improved. Since the amount of heat W is applied by the externally controlled electric power pattern P during these periods, the cooling rate of the molten metal in the thin portion n is reliably and stably controlled, and the quality of the suspension arm is surely and easily realized. Become.

Further, in this method, since the heat generated by the electric resistance obtained by energizing the molten metal itself is utilized as the positive heat quantity W, the resistor is not in-molded on the suspension arm, and the desired suspension arm is obtained. It does not impair the quality of. Further, in this method, the electrodes 3a and 3b that come into contact with the molten metal are made of the same material as the molten metal.
Therefore, cutting after casting is minimized, maintenance-free is realized, and manufacturing cost is reduced. Also, cracks are less likely to occur due to heat shock during pouring, and external controllability is not impaired.

Therefore, if this method is adopted, the quality of the suspension arm as a whole can be made to be the desired quality, and it is inexpensive, reliable and easy. (Second Embodiment) In the second embodiment, claims 1 to 3 are embodied.

First, as shown in FIG. 4, electrodes 3a and 3b are formed.
Prepare sand molds 1 and 2 with. A current detection circuit 6 is connected to both electrodes 3a and 3b, and a power supply 7 with a built-in constant voltage control circuit is connected to the current detection circuit 6. The constant voltage control circuit of the power supply 7 performs DC / AC chopper control. A comparison circuit 8 is connected to the current detection circuit 6, and a power supply 7
A programmable controller 9 is connected to the constant voltage control circuit and the comparison circuit 8. The programmable controller 9 stores various programs and the curve A _{3 of} FIG. 3 described above. Other configurations are the same as the first embodiment.

Then, as in the first embodiment, the molten metal is poured into the cavities C of the sand molds 1 and 2, and the molten metal comes into contact with both electrodes 3a and 3b.
And the current i flowing through the thin portion n is detected by the current detection circuit 6. Here, the electrodes 3a, the voltage applied to 3b E, the electric resistance of the molten metal R _1, if the internal resistance R _2, since there is a relation of _{R 1 = E / i-R} 2, the molten metal electrical The resistance R ₁ is calculated in real time. Then, according to the shape of the cavity C, the electrical resistivity ρ is calculated from the calculated electrical resistance R ₁ . These have been revealed by preliminary tests.

During this period, it has been known that the electrical resistivity ρ of the molten metal decreases as the temperature drops. Here, the relationship between the temperature t and the electrical resistivity ρ is that the melting point of the molten metal is 1536.
When pure iron of (° C.) is adopted, the chain line D in FIG. 5 is obtained. The curve D is ρ = −2.4 + 3.65 × 10 ⁻² t + 0.65 × 10 ⁻⁶
It is represented by t ³ . The electrical resistivity ρ of the molten alloy is determined by ρ = ρ ₀ + α c, where ρ _{0 is} the resistivity of pure metal, α is the residual resistance per percentage, and c is the weight% of impurities. Therefore, it can be seen that the electric resistance ρ of the molten metal used decreases as the temperature drops, as indicated by the curve B shown by the solid line in FIG. The curve B shown by the broken line in FIG.
₁ and B ₂ represent the relationship between the temperature and the electrical resistivity ρ within the composition range of cast iron. Further, when pure aluminum is used as the molten metal, the curve E of the two-dot chain line in FIG. 5 is obtained.

Therefore, the temperature of the thin portion n can be grasped based on the calculated electrical resistivity ρ. Then, the applied voltage E to both electrodes 3a and 3b is feedback-controlled so that the grasped temperature becomes the target temperature on the curve A _{3 in} FIG.
Thus, according to the casting method of the second embodiment, the cooling rate of the molten metal in the thin portion n of the suspension arm is reliably and stably controlled, and the quality of the cast product is surely and easily realized.

Further, in this method, the electric resistance R ₁ is obtained from the voltage E applied to the electrodes 3a, 3b in contact with the molten metal and the current i flowing through the molten metal, and the thin portion n is calculated based on the obtained electric resistance R _1. Since the temperature of the molten metal is obtained, the temperature of the molten metal is directly detected, and the temperature of the molten metal is directly controlled, and the external controllability is excellent. Furthermore, this method is efficient because the heat generated by the electric resistance R ₁ obtained by energizing the molten metal itself is used as a positive amount of heat and no additional heat generating means is required.

Therefore, if this method is adopted, the quality of the suspension arm as a whole can be made to be the desired quality, and it is cheaper, more reliable and easier than in the first embodiment. In Embodiments 1 and 2 above, the metal structure after transformation can be bainite. Further, as described above, the present invention can be applied to a case where a part of a cast product has a desired quality. In this case, if a high-frequency current is adopted as the current to be passed through the electrodes 3a and 3b, only the surface of the cast product that is energized can be heated due to the skin effect of the high-frequency current, so that only the mechanical properties of the surface of the cast product are maintained. It can also be modified.
Needless to say, the invention of each claim is not limited to the method of casting the suspension arm.

[0031]

As described in detail above, by adopting the casting method described in each claim, the whole or a part of the cast product can be made to have a desired quality, and it is inexpensive and reliable. And it will be easy.

[Brief description of drawings]

FIG. 1 is a perspective view of a cast iron suspension arm according to first and second embodiments.

FIG. 2 is a cross-sectional view taken along the line II-II of FIG. 1 and a configuration diagram of an apparatus according to the first embodiment.

FIG. 3 is a graph showing a relationship between time, temperature, and electric power according to the first embodiment.

FIG. 4 is a sectional view taken along the line IV-IV in FIG. 1 and a configuration diagram of the apparatus according to the second embodiment.

FIG. 5 is a graph showing a relationship between temperature and electrical resistivity according to the second embodiment.

[Explanation of symbols]

 1, 2 ... Sand mold (mold) C ... Cavity n ... Thin portion 3a, 3b ... Electrode

Claims (3)

[Claims] 1. A casting characterized by controlling the cooling rate of the molten metal in the desired portion by injecting the molten metal into the cavity of the mold and then applying an externally controllable amount of heat to the desired portion of the molten metal. Method. 2. The casting method according to claim 1, wherein a pair of electrodes is brought into contact with the molten metal at a desired portion and a positive amount of heat is applied by energizing both electrodes. 3. The electric resistance is obtained from the voltage applied to both electrodes and the current flowing through the desired portion of the molten metal, the temperature of the desired portion is obtained based on the obtained electric resistance, and the obtained temperature becomes the target temperature. The casting method according to claim 2, wherein the voltage applied to both electrodes is feedback-controlled.