JPH1133703A - Casting method for cast iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new casting method which has no casting defects such as shrinkage cavity and the like and in which the core burning, filtering, mold flash and so forth seldom take place in casting the cast iron. SOLUTION: This method comprises a fire-resisting pipe 1 vertically connected to a mold cavity 4 to have the molten metal poured into at the same time of causing of the cast iron, and an induction heating coil 6 arranged outside the pipe 1, to induction-heat and keep the molten metal in a molten condition on one hand and to cool the molten metal in the mold on the other hand. By selecting a proper timing to stop the induction heating so that the desired degree of molten condition in the fire-resisting pipe 1 is kept for a desired length of time after the start of euctic consolidation till its end, the generation of casting defects such as shrinkage cavities in the cast metal, filtrate of molten metal into the core, and flash in the outside mold can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for casting iron, which significantly reduces the amount of riser and shrinkage porosity of cast metal.
The present invention relates to a casting method capable of suppressing insertion of a molten metal into a core and mold tension of an outer mold.

[0002]

2. Description of the Related Art A feeder is indispensable for preventing casting defects such as shrinkage cavities in the production of metal castings regardless of whether they are ferrous or non-ferrous. Standard cast iron requires 20-40% of the original casting, ductile iron requires 20-60%, cast steel 30-70%, and pure copper casting requires 30-70% riser. In other words, in order to make a casting with a weight of 1, it is necessary to create a waste of 0.2 to 0.7 weight, because of the presence of the feeder, such as metal melting costs, molding costs, mold separation, and cutting work of the feeder section. Inexpensive and wasted costs are spent. In particular, the cutting of the feeder is performed by fusing the neck, saw cutting, grinder cutting, hammering, or a combination of these, all of which are forced in a harsh working environment. This is a typical work that is disliked as 3K. How to reduce the size of the riser and how to streamline the work of cutting the riser are crucial issues in the casting industry.

Against this background, attempts have been made in the past to reduce the riser height by using induction heating. JP-A-55-
No. 64958 describes that an induction coil is buried in the upper part of the mold and induction heating of the molten metal is performed. However, since the induction coil is embedded in the mold, after casting and ingot casting,
When the mold is broken and the casting is taken out, the refractory in which the induction coil is embedded is also broken. In other words, the work of burying the induction coil with the refractory and the work of breaking the buried refractory and taking out the coil are indispensable for each ingot, which is too laborious and costly. Furthermore, at the time of casting, if the molten metal comes into direct contact with the coil due to scattering of the molten metal or damage to the lining material, melting of the coil and interlayer short-circuiting occur.
There are drawbacks such as the danger of steam explosion due to coil cooling water. Further, this method can be applied to large-sized, simple-shaped castings such as steel ingots, but is difficult to apply to ordinary castings having various shapes. In addition, the present invention does not raise any problem regarding the cutting of the riser after ingot formation.

In view of such a problem, the present inventors can freely and economically cope with various shapes, sizes, small to large amounts, and a wide variety of production forms, and at the same time, remarkably improve the cutting operation of the feeder section. We have invented a new casting method which brings about various effects and filed an application (Japanese Patent Application No. 8-152930).

[0005]

SUMMARY OF THE INVENTION According to the present invention, there is no casting defect such as shrinkage cavities when applying the invention filed in the prior application to cast iron, and it is difficult for the core to be baked or inserted. It is an object of the present invention to provide a new casting method that hardly causes mold tensioning.

[0006]

The above problems are solved by the following casting method. 1. During casting of a cast iron casting, a refractory pipe is erected so as to communicate with the mold cavity, molten metal is injected into the mold and the refractory pipe, and an induction heating coil is arranged outside the refractory pipe. A casting method is employed in which the molten metal in the pipe is cooled while the molten metal in the pipe is induction-heated to keep the molten metal in the molten state. By selecting the timing of stopping the induction heating so that it is maintained until the desired time within the time from the start to the end of crystal solidification, shrinkage cavities of cast metal, insertion of molten metal into core and A method of casting cast iron, characterized in that the outer mold is kept from being stretched. 2. The shrinkage porosity defect of the cast metal is mainly controlled by maintaining the molten state in the refractory pipe until a desired point in the first half of the eutectic solidification.
The casting method of the cast iron according to the paragraph. 3. Maintaining the molten state in the refractory pipe until a desired point in the second half of the eutectic solidification, thereby mainly suppressing insertion into the core of the cast metal and molding of the outer mold. 2. The method for casting cast iron according to the above item 1, wherein 4. The method for casting a cast iron according to any one of the above items 1 to 3, wherein a transition from the start to the end of the eutectic solidification is estimated from a change in the level of the molten metal in the refractory pipe. 5. The method of claim 4, wherein the change in the level of the molten metal is detected by floating a refractory float on the molten metal in the refractory pipe and detecting the displacement of the float. 6. The method of claim 4, wherein the change in the level of the molten metal is detected by a change in the electromagnetic characteristics of an induction heating coil disposed outside the refractory pipe. 7. The method for casting a cast iron according to any one of the above items 4 to 6, wherein the operation of the induction heating is controlled in conjunction with the signal of the change in the molten metal level.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION

[Fire-Resistant Pipe] The fire-resistant pipe 1 is erected at a place where a riser of the mold body is installed so as to communicate with the cavity 3 of the mold body 2 as illustrated in FIG. The standing position of the pipe 1 may be determined based on the same concept as the conventional design of a feeder for castings. That is, it may be arranged preferentially in a thick portion where shrinkage cavities easily occur. At the time of standing, the pipe 1 prepared in advance may be embedded and fixed in the standing position of the mold. Alternatively, since the mold wall 4 where the pipe 1 is erected is thin, the mold wall 4 may be broken when the pipe is embedded. Therefore, the mold wall 4 where the pipe 1 is erected is partially cut out and cut off. Alternatively, the mold wall 4 and the pipe 1 may be combined and made into an integral type, and this may be fitted into the mold and set. The cast metal in the portion surrounded by the mold wall 4 where the pipe 1 is erected cools down quickly and the heating efficiency of induction heating is poor, so that depending on the conditions, this portion tends to solidify quickly. To prevent this and improve the efficiency of induction heating, it is preferable to make the mold wall 4 where the pipe 1 is erected thinner. For this purpose, a reinforcing core material 5 is preferably inserted in the mold wall.

FIG. 2 shows a structure in which a mold wall 4 and a refractory pipe 1 are integrally formed, and a reinforcing core material 5 is put in the mold.
This is inserted and set in a mold so that a cassette is inserted. The refractory pipe 1 and the mold wall 4 may be made of different materials and integrated, or may be made of the same material and integrally. The mold wall 4 is not limited to the same material as the mold material constituting the mold body 2 and may be made of the same fire-resistant material as the fire-resistant pipe 1. The core material 5 is a reinforcing material made of steel wire, ceramic fiber or the like, and is preferably inserted when the strength of the mold wall is insufficient.

The material of the refractory pipe 1 is
In any case, alone or in one piece with the mold wall 4, any material can be used as long as it is a refractory material and a shape that can withstand at least the molten metal to be cast. That is, the refractory pipe 1 is formed from a mold material commonly used in the production of ordinary castings such as shell molds, or a pipe 1 and a mold wall 4 are integrated, and this is set in a mold. Is also good. The pipe 1 is formed of a normal refractory other than the above examples, for example, alumina, silica, zirconia, chromia, magnesia, mullite, cordierite, zircon, titania, chromite, chamotte refractory, or graphite refractory. Can be used irrespective of the type, such as those made from refractories, or those made from amorphous refractories, or sintered bodies such as nitrides and carbide ceramics.
It is not limited to the shape. Further, a high refractory powder may be applied (molded) to the inner surface of the pipe and the inner surface of the mold wall as needed in order to increase the fire resistance.

The present invention is effective in any case, without being limited to a specific object or structure such as a method of setting the refractory pipe 1 in a mold or a structure of a mold of a set portion. An induction coil 6 is fitted to the outside of the pipe. As long as the structure, shape, and arrangement of the molten metal in the pipe 1 can be effectively induction-heated, any shape, structure, and arrangement of the induction coil 6 can be used effectively.

The periphery of the induction coil 6 is protected with a refractory so as not to damage the coil even if the pipe breaks during casting.
Further, it is preferable that the coil can be removed at any time. For example, the induction coil 6 is loosely fitted so that it can be quickly removed from the refractory pipe 1,
Alternatively, the structure of the refractory pipe 1 may be a double-structured pipe in which the outer pipe 1b is fitted outside the inner pipe 1a, or at least the refractory is lined on the inner surface and the bottom surface of the induction coil 6 to form a molten metal. It is preferable to adopt a structure that does not cause erosion even when contacted.

The molten metal is filled into the refractory pipe 1 and the molten metal in the pipe is induction-heated to solidify and cool the cast metal in the mold while maintaining the molten state in the molten state. The molten metal in the molten pipe serves as a feeder during normal casting, and the molten metal is replenished without hindrance to the shrinkage cavities formed by solidification and cooling of the cast metal in the mold. As described above, the molten state is maintained at least within the temperature and time at which shrinkage cavities are formed in the cast metal. When the molten metal is replenished using a riser, the molten metal needs to be about 10 to 20 times the volume of the pipe.

In general, in the solidification of metal, the volume shrinks during solidification, but in cast iron, the volume expands conversely when eutectic solidification starts. In particular, in the case of spheroidal graphite cast iron and CV graphite cast iron, a solidified skin is formed in the mold, and the inside takes a solidified form in which the inside is solidified, and the volume expansion during eutectic solidification is particularly remarkable.
In the case of the method of the present invention, the liquid level of the molten metal in the pipe is greatly pushed up. However, at some point during eutectic solidification, induction heating is stopped and the molten metal in the pipe is solidified to restrain the volume expansion of the cast metal.After that, the volume expansion loses its escape route, and the volume expansion is This is converted into a force for compressing the metal cast structure, and the cast structure is densified.

On the other hand, when the volume expansion is converted into a force for compressing the casting structure of the cast metal by the restraint of the volume expansion, the molten metal is pressurized and penetrates into the core sand to cause seizure of the sand. In the worst case, the molten metal may enter the core and short-circuit the sand with the molten metal. In addition, as a result of closing the escape path for volume expansion, the outer mold may be stretched in which the casting expands outward and the outer mold of the mold projects.

As described above, it is difficult to easily achieve the trade-offs between densification of the casting structure and suppression of the insertion of the molten metal into the core sand and the molding of the outer mold. Or the timing of stopping the induction heating so that the molten metal in the pipe is solidified at a well-balanced time within a range that does not sacrifice the other problem, while focusing on the important problem depending on the shape and size of the mold It is important to select

For example, in cast iron having a flaky graphite structure, C
Low-alloy cast iron to which alloying elements such as r, Mo, P, Cu, Sn, and Sb are added tends to have a structure with many shrinkage cavities and is difficult to cast. In the present invention, such a cast iron has a sound structure when the molten metal in the pipe is maintained in a molten state and is sufficiently replenished just before or until the end of the eutectic solidification. Cr: 0 to 2%, Mo: 0 to 0%
2%, Ni: 0 to 2%, Co: 0 to 1%, P: 0 to 1
%, Cu: 0 to 2%, Sn: 0 to 0.1%, Sb: 0 to 0.1%
For example, low alloy flake graphite cast iron having an alloying element such as%.

When it is desired to mainly suppress shrinkage porosity defects such as the above-mentioned spheroidal graphite and CV graphite cast iron, the inside of the pipe is maintained in a molten state from the start of eutectic solidification to a specific point in time in the first half of the first half. The timing at which induction heating is stopped may be selected, and the starting point or immediately after the start of eutectic solidification may be a suitable timing for stopping heating. If you want to suppress seizures and insertions, you can select the timing to stop induction heating so that the inside of the pipe is maintained in a molten state until a specific point in the second half of eutectic solidification. The appropriate timing may be just before or after the end of coagulation, or even after the end, that is, when the end of coagulation is confirmed.
The above-described stoppage of the heating in the latter half of the length of the core is also advantageous in preventing seizure of the core, insertion of the molten metal into the core, and prevention of shrinkage cavity defects. The first half of the above-mentioned eutectic solidification is from the start of solidification to the time when solidification has progressed halfway, and the latter half has a rough meaning from the time when the solidification has progressed halfway to after solidification has ended. Although it is a thing, it may be considered that the first half and the second half which are temporally divided substantially match.

Here, it is important to know how to actually start and end the eutectic solidification of the casting. Eutectic solidification can be clearly understood by inserting a thermocouple into the casting and performing a thermal analysis of the molten metal. However, this is often not allowed because a hole in which the thermocouple is inserted remains in the casting. Therefore, it is preferable to identify the start and end of the eutectic solidification by a substitute characteristic value other than the temperature. For example, a method of detecting the change in the level of the molten metal in the refractory pipe is recommended.

That is, shrinkage of the molten metal itself in the mold or
The level of the molten metal in the refractory pipe falls as the mold is cast after pouring. Next, when the eutectic solidification starts, the lowering of the molten metal level temporarily stops because the volume expands, and then the rising of the molten metal level starts. This descent stop in the transition of the descent of the metal surface → stop of descent → elevation of the molten metal is a sign of the start of the eutectic solidification, and it is possible to know the start of the eutectic solidification.
At the end of the eutectic solidification, the rise in the molten metal level gradually stops and then stops, so that the end of the eutectic solidification can be known. The start time and end time of the eutectic solidification may be determined in advance, and the casting according to the method of the present invention may be performed on the basis thereof, or the method of the present invention may be performed while detecting the above-mentioned time during the casting operation. May be.

The change in the level of the liquid level in the pipe can be detected by using a non-contact type liquid level sensor using ultrasonic waves or the like or a liquid level sensor directly contacted as appropriate. It is recommended to use a method in which a refractory float is floated and the displacement is detected.

Further, a method of detecting by a change in an electric or magnetic characteristic value is also simple. For example, when the level of the molten metal in the pipe surrounded by the induction heating coil changes, the inductance of the coil changes. Therefore, the correlation between the change pattern of the inductance and the solidification pattern indicates the start and end of the eutectic solidification. Can be detected. In either case, a circuit for controlling the operation such as activation and stop of the induction heating in conjunction with the detected signal indicating the change in the level of the molten metal level can be provided for automation and further for program control.

In the present invention, cast iron is flaky graphite cast iron,
Spheroidal graphite cast iron, CV graphite cast iron, etc., including graphite crystallization cast iron, etc.
In particular, the method of the present invention is effective for spheroidal graphite cast iron, CV graphite cast iron, and low alloy flake graphite cast iron.
Most suitable for casting V graphite cast iron.

[0023]

【Example】

Example 1 A comparison was made between the conventional casting method and the casting method of the present invention. In the method of the present invention, the mold shown in FIG. 1 was used, and in the conventional method, the heating feeder mold shown in FIG. <Mold of the Present Invention (FIG. 1)> Mold cavity size: 131 × 131 × 131 mm Mold size: 200 × 200 × 250 mm The mold cavity was formed by a CO ₂ process. Fire-resistant pipe: Double pipe of inner pipe and outer pipe adopted Inner pipe dimensions: Inner diameter 20mm, outer diameter 30mm, length 200mm Inner pipe material: chamotte quality Outer pipe dimensions: inner diameter 60mm, outer diameter 75mm, length Material of outer tube: Outer tube material: Chamotte material of the same material as the inner tube The inner tube and the outer tube were inserted from the top of the mold as shown in Fig. 1 and erected. In order to measure the temperature of the cast metal in the mold, a thermocouple 7 was inserted to the center of the mold and fixed as shown in FIG. <Conventional mold> Mold: Same as the mold in FIG. Mold making method: Molding by the same CO ₂ process as the mold in FIG. A bell-shaped heat insulating material 8 as shown in FIG.
(Manufactured by Foseco Japan). The bell-shaped part of the heat insulation part is about 10% of the mold cavity volume. <Molten metal composition> Spheroidal graphite cast iron of the following composition, which is generally made of FCD-450, was used. The component composition is as follows (% by weight): C Si Mn P S Mg 3.65 2.39 0.22 0.031 0.009 0.034 <Casting conditions> Melting temperature: 1510 ° C Spheroidizing temperature: 1480 ° C Pouring temperature: 1400 ° C Spheroidizing: Spheroidizing OGRC3: 1.4% added By ladle placing and injection <Induction heating> After pouring, an induction coil is inserted into a refractory pipe, heating is started at a frequency of 20 kHz and an output of 9 kW, and the temperature of the molten metal is inserted by a thermocouple inserted into a mold. The induction heating was stopped when the eutectic solidification started. In addition, the thing of the conventional mold was cooled as it was in the mold. [Results] <Method of the Present Invention> After cooling, the mold was taken out from the mold, cut and examined for shrinkage. In the case of the present invention, no shrinkage was observed in any of the metal inside the refractory pipe and the metal inside the mold cavity. The metal inside the refractory pipe could be removed in just two minutes. Microstructure: The casting was cut into two, and the microstructure of the cut surface was observed. The tissue was dense and no micro-shrinkage cavities were observed. <Conventional method> Heating feeder mold: There was no contraction in any of the metal and the feeder in the cavity of the casting mold. However, it took 12 minutes to cut and remove the riser. Microstructure: The casting was cut into two parts, and the microstructure of the cut surface was observed. No microshrinkage was observed. From the above test, it was confirmed that the method of the present invention has the same feeder effect as a conventional large feeder. In addition, the work of removing the feeder part (metal inside the refractory pipe) after removing the mold can be performed in a much shorter time than conventional feeder, and the amount of feeder can be reduced to several hundredths. Labor saving,
It was confirmed that energy saving was extremely effective. It was also confirmed that the casting structure could be densified by stopping the induction heating at the start of the eutectic solidification.

Embodiment 2 (Example of using a sand core) A cooling water circulation path as narrow as a maze passes through the cylinder head. The narrow circuit is cast with a fine sand core.
Core sand is burned in, and core sand cannot be removed due to the insertion into the core of the molten metal. This example tests a cylinder head of a diesel engine. CV graphite cast iron was used as the material. The jacket core is set in a mold cavity of approximately 420 (L) x 350 (W) x 200 (H) mm. The narrowest part is φ12 mm and length 25 mm. The material and manufacturing method of the sand core are shell sand used for the water jacket core (phenol resin: 3.2%), and CO ₂ for the intake and exhaust port cores.
Sand (water glass: 5.5%, CO ₂ gas: 9%) Tightening bolt core and squeezing core use furan sand (furan range: 0.7%, catalyst: 40% compared to resin) <Mold of the present invention> Manufacturing method: Molding with the self-hardening sand process of furan Refractory pipe: Adopt inner pipe, outer pipe double pipe method Inner pipe dimensions: Inner diameter 30mm, outer diameter 40mm, length 200mm Inner pipe material: Chamotte quality Outer pipe dimensions : Inner diameter 60 mm, outer diameter 75 mm, length 200 mm Outer pipe material: Chamotte inner pipe and outer pipe were inserted from above the mold and erected. <Conventional mold> Heating feeder mold is used. An exothermic heat insulating material (manufactured by Foseco Japan) was placed on the upper part of the mold. <Molten metal composition> CV graphite cast iron was cast with the following composition. (Weight%) C Si Mn PS Mg 3.75 2.52 0.26 0.028 0.018 0.012 <Casting conditions> Melting temperature: 1520 ° C CV conversion temperature: 1520 ° C Casting temperature: 1400 ° C CV graphitization: 0.95% added (CV alloy: Osaka Made by Tokuyo Gokin Co., Ltd.) <Induction heating> After pouring, the induction coil is inserted into a refractory pipe, heating is started at a frequency of 20 kHz and an output of 12 kW, the temperature of the molten metal is measured with a thermocouple inserted just below the pipe of the mold, and eutectic solidification is completed. After confirming that the heating was completed, the induction heating was stopped.
In addition, the thing of the conventional mold was cooled as it was in the mold. [Result] Twenty cases were repeatedly cast by this method. There was no seizure of the sand in the core, and no case was found in which the molten metal had been inserted into the core so that it could not be remedied. Also, no external mold tension was observed. It was confirmed that this method was extremely effective in preventing seizure, insertion of molten metal, and prevention of mold closing of the outer mold. By the way, in the conventional method, seizure and insertion of molten metal are 10
Approximately 10 of the 0 cases were recognized, and a few were discarded without any relief specifications.

Example 3 (Example of low alloy gray cast iron) A comparison was made between the conventional casting method and the casting method of the present invention. The method of the present invention is a mold shown in FIG. In the conventional method, a heating feeder mold shown in FIG. 4 was used. <Mold of the Present Invention> Mold cavity size: 131 × 131 × 131 mm Mold size: 200 × 200 × 250 mm The mold cavity was formed by a CO ₂ process. Fire-resistant pipe: Double pipe of inner pipe and outer pipe adopted Inner pipe dimensions: Inner diameter 20mm, outer diameter 30mm, length 200mm Inner pipe material: chamotte quality Outer pipe dimensions: inner diameter 60mm, outer diameter 75mm, length Material of outer tube: Outer tube material: Chamotte material of the same material as the inner tube The inner tube and the outer tube were inserted from the top of the mold as shown in Fig. 1 and erected. To measure the temperature of the cast metal in the mold, a thermocouple was inserted into the center of the mold as shown in the figure and fixed. <Conventional mold> Mold: Same as the mold in FIG. Mold production method: Molding by the same CO ₂ process as the mold in FIG. A bell-shaped heat insulating material 8 as shown in FIG.
(Manufactured by Foseco Japan). The bell-shaped part of the heat insulation part is about 10% of the mold cavity volume. <Molten composition> Low alloy flake graphite cast iron The composition of the components is as follows: C Si Mn PS Cu Cr 3.03 1.93 0.62 0.33 0.063 0.008 0.34 <Casting conditions> Melting temperature: 1530 ° C Pouring temperature: 1395 ° C <Induction heating> Note After the hot water, the induction coil was inserted into a refractory pipe, heating was started at a frequency of 20 kHz and an output of 9 kW, the temperature of the molten metal was measured with a thermocouple inserted into a mold, and the induction heating was stopped at the end of the eutectic solidification. In addition, the thing of the conventional mold was cooled as it was in the mold. [Results] <Method of the Present Invention> After cooling, the mold was taken out from the mold, cut and examined for shrinkage. In the case of the present invention, no shrinkage was observed in any of the metal inside the refractory pipe and the metal inside the mold cavity. Microstructure: The casting was cut into two, and the microstructure of the cut surface was observed. The tissue was dense and no microscopic shrinkage cavities were observed. <Conventional method> Heating feeder mold: A shrinkage cavity was found in the metal in the mold cavity and the feeder section. Microstructure: The casting was cut into two, and the microstructure of the cut surface was observed. Micro shrinkage cavities were observed on a part of the cut surface. From the above test, it was confirmed that the method of the present invention was very effective in preventing shrinkage cavities and minute shrinkage cavities even in low alloy gray cast iron.

Embodiment 4 (Example of Cylinder Head) In this embodiment, the present invention is applied to the casting of a cylinder head for a diesel engine. Product dimensions: 570 (L) x 750 (W) x 445 (H) mm Weight: 784 kg Material: CV graphite cast iron Sand used in the mold: Furan sand (resin 0.8%, catalyst (against resin) 40%) CV conversion Processing temperature: 1510 ° C CV agent addition amount: Vermic Alloy (brand name) 0.95
% Inoculant: Fe-Si 0.8% Dimensions of refractory pipe: inner diameter 40 mm, length 7 mm FIG. 4 shows the structure around the refractory pipe erected on the mold used in the present example. <Molten metal composition> CV graphite cast iron was cast with the following composition. (Weight%) C Si Mn P S Mg 3.75 2.52 0.26 0.028 0.018 0.013 <Induction heating> After pouring, the induction coil was loosely fitted into the refractory pipe and heated at a frequency of 20 kHz and an output of 4 to 6 kW. In about 25 minutes, the liquid level in the pot sleeve began to rise, indicating the onset of eutectic solidification. 4 minutes and 30 seconds after the start of ascent, 70 mm
The heating was stopped at the time of the rise. [Results] There was no burning of the core sand and no insertion of the molten metal. No outer mold was found. The finish cleaning time after casting is about 50 minutes. By the way, when casting with a conventional type of hot water using a bell-shaped heat insulating material, sand seizure occurred on a part of the tightening bolt core (φ57 mm) and a part of the starting valve core (φ30 mm), and one piece It took 4 to 5 hours for finishing and polishing. In this example, it was possible to reduce the cost by about 1/5 of the conventional method.

[0027]

【The invention's effect】

1. It has a great effect on densification of the structure of spheroidal graphite cast iron and CV graphite cast iron. 2. It has a great effect on preventing core sand from seizing, preventing molten metal from being inserted into the core, and preventing the outer mold from being closed. 3. It has a great effect in preventing the occurrence of casting defects in low alloy flake graphite alloy cast iron. 4. The feeder part can be minimized, and the casting yield can be greatly improved. 5. The working time required for cutting the riser can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view for explaining an example of the structure of a mold used in an embodiment of the present invention.

FIG. 2 is a perspective view for explaining a structure in which a part of a mold and a refractory pipe are integrated.

FIG. 3 is a cross-sectional view for explaining a main part of a mold used in an example of the present invention.

FIG. 4 is a cross-sectional view for explaining the structure of a mold used for conventional casting.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Refractory pipe 2 Mold main body 3 Cavity 4 Mold wall 5 Core material for reinforcement 6 Induction coil

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takahiro Sugiyama 2400, Kansai-oki-cho, Izumo-shi, Shimane Inside Daihatsu Metal Industry Co., Ltd. No. 8 Daiichi Kogyo Kogyo Co., Ltd. (72) Inventor Kotaro Hirayama 2-17-8 Tonomachi, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture

Claims (7)

[Claims] 1. A cast iron casting, in which a refractory pipe is erected so as to communicate with a mold cavity, molten metal is injected into the mold and the refractory pipe, and an induction heating coil is disposed outside the refractory pipe. A casting method in which the molten metal in the pipe is cooled while the molten metal in the pipe is induction-heated and kept in a molten state while cooling the molten metal in the mold is adopted. By selecting the timing of stopping the induction heating so that it is maintained until the desired time within the time from the start to the end of eutectic solidification, shrinkage porosity defects in the cast metal and insertion of the molten metal into the core And a method for casting cast iron, characterized by suppressing mold tension of an outer mold. 2. The molten state in the refractory pipe is maintained until a desired point in the first half of the eutectic solidification,
2. The method for casting cast iron according to claim 1, wherein shrinkage cavities of the cast metal are mainly suppressed. 3. The molten state in the refractory pipe is maintained until a desired point in the latter half of the eutectic solidification,
The method for casting a cast iron according to claim 1, wherein insertion of a cast metal into a core and mold tension of an outer mold are mainly suppressed. 4. The method according to claim 1, wherein a transition from the start to the end of the eutectic solidification is estimated from a change in the level of the molten metal in the refractory pipe. 5. The method according to claim 4, wherein the change in the level of the molten metal is detected by floating a refractory float on the molten metal in the refractory pipe and detecting the displacement of the float. 6. The method according to claim 4, wherein the change in the level of the molten metal is detected by a change in the electromagnetic characteristics of an induction heating coil disposed outside the refractory pipe. 7. The method for casting cast iron according to claim 4, wherein the operation of induction heating is controlled in conjunction with the signal of the change in the molten metal level.