JP2010105023A - Vacuum suction casting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a casting method which can effectively suppress the carburizing of the surface layer in a casting even without adding a special process to the conventional casting process. <P>SOLUTION: A casting die 16 molded using an organic binder is arranged at the inside of an evacuation chamber 22, the evacuation chamber 22 is vacuum-sucked in such a state that suction inlets 20 are immersed into the molten metal W of a steel so as to suck up the molten metal W to a cavity 18 in the casting die 16, the vacuum suction is continued for a prescribed time in a pulling up state of the casting die 16 even after casting, and the forced inhalation of the outer air into the casting die 16 and the forced exhaust of gas in the casting die 16 are performed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a vacuum suction casting method in which a molten steel is vacuum sucked into a mold for casting, and more particularly to a method characterized by technical means for preventing carburization of a surface layer of a cast product.

Conventionally, in casting of molten steel using a mold containing an organic binder (a mold formed using an organic binder as a binder), it has been regarded as a problem that the surface layer of the cast product causes carburization.
For example, the following patent document 1, patent document 2, patent document 3 and the like point out such problems.

This carburization phenomenon is caused by pyrolysis when the organic binder contained in the mold is exposed to high heat during casting, and a large amount of hydrocarbon gas such as CO gas, CO ₂ gas and methane, that is, carburizing gas. It is a phenomenon that occurs when it enters the surface layer of the molten metal or casting and diffuses.

  In general, in the case of cast steel having a C content of 1% (mass%) or less, such as ferritic stainless cast steel, when such carburizing phenomenon occurs, corrosion resistance is lowered and this causes volume expansion due to martensitic transformation. May cause cracks.

  In order to avoid a harmful phenomenon caused by carburizing the surface layer of a cast product, the surface layer is conventionally shaved and removed with a grinder, but in this case, it takes a lot of labor and man-hours.

  As another countermeasure, a coating mold is applied to the inner surface of the mold, and the carburizing gas generated inside the mold is blocked by the coating mold to prevent the carburizing gas from entering the cast product surface layer. In this case, a material cost for the coating mold is required, and a process for applying the coating mold is required. Arise.

Further, depending on the cast product, there is a case where such a countermeasure by coating application cannot be adopted.
For example, if the cast product is a thin and thin product with strict dimensional tolerance, the product thickness will be uneven due to uneven application of the coating mold, and the dimensional accuracy may not be satisfied, or the thickness may be partially The changed part may be a starting point of cracking.
Therefore, it is not possible to adopt a countermeasure by applying a coating mold for such a cast product.

In Patent Document 1, as a means for solving the problem of carburization phenomenon on the surface layer of a cast product, a coating agent containing chromite flower and Fe ₂ O ₃ + 2CaO · SiO ₂ or olivine flower as a base material on the surface of an organic self-hardening mold. To form a first coating layer, and then, on the first coating layer, based on one or more selected from the group consisting of zircon flower, mullite flower, alumina flower, and syamot flower. The point which provides the 2nd coating type layer by apply | coating the template agent contained as a material is disclosed.
However, the one disclosed in Patent Document 1 is different from the present invention in the solution means.

On the other hand, as means for solving the carburization problem in Patent Document At 2 casting surface, MgO quartz _{sand: 27~33%, SiO 2: 48~58} %, Al 2 O 3: 1~3%, FeO: 5~ The point which uses what added 15 to 70 weight% of the ferronickel ore smelting iron slag which consists of 11%, CaO: 4 to 6%, and remainder unavoidable impurities is disclosed as casting sand for shell molds.
However, the one disclosed in Patent Document 2 is also different from the present invention with a different solution.

On the other hand, in Patent Document 3, as a means for solving the same problem, chromite having a small particle diameter is used for the skin sand that comes into contact with the casting, and 1.2 to 2.2 mm is used for the back sand of other portions. It is disclosed that a cast steel mold is manufactured using a mullite ceramic having a large particle size (good air permeability), and gas generated in the mold is easily released into the atmosphere outside the mold.
However, the one disclosed in Patent Document 3 is also different from the present invention in terms of solution means.

JP-A-61-293625 JP-A-62-263842 JP-A-8-257678

  In view of the above circumstances, the present invention aims to provide a casting method capable of effectively suppressing carburization of the surface layer of a cast product without adding a special process to the conventional casting process. It was made.

  Thus, according to the casting method of claim 1, a mold molded using an organic binder is placed in a vacuum chamber, and the vacuum chamber is suctioned under reduced pressure while the suction port is immersed in the molten steel, so that the molten metal is contained in the vacuum chamber. In a vacuum suction casting method in which the mold cavity is sucked up and filled into the mold cavity and cast, after the molten metal is filled into the cavity and solidified, the mold is pulled up, and the suction port is separated from the molten metal The decompression suction is continued for a predetermined time, and the outside air is forcibly sucked into the mold and the gas in the mold is forcibly discharged.

Effects and effects of the invention

  As described above, the present invention is arranged such that a mold containing an organic binder is disposed in a decompression chamber, and the decompression chamber is suctioned under reduced pressure to suck up the molten metal, fill the mold cavity, and solidify it to cast a cast product, And even after the end of the casting operation due to the suction of the molten metal at the time of casting, that is, the molten metal is filled in the cavity and solidified to pull up the mold, and the suction port is separated from the molten metal, and the vacuum suction is continued for a predetermined time, The forced intake of outside air into the mold and the forced discharge of gas in the mold are performed.

  Compared to the normal casting method in which the molten metal is poured into the mold cavity from above and filled into the cavity by gravity, the vacuum suction casting method is used even when casting a thin cast product with a thin wall thickness. This is a casting method that has been conventionally known as a casting method in which a molten metal can be introduced and filled well.

  In the present invention, such a vacuum suction casting method utilizes the air permeability of the porous mold, and focuses on the point that the vacuum of the decompression chamber, that is, the negative pressure, acts on the cavity of the mold to suck up and cast the molten metal. Even after the casting operation is finished, in detail, after filling the cavity with the molten metal and solidifying it, the mold is pulled up, and after the suction port is separated from the molten metal, the vacuum suction is continued in the outside air, The outside air is forcibly sucked into the mold by vacuum suction and the gas in the mold is forcibly discharged.

As described above, the carburization phenomenon described above is caused by the organic binder contained in the mold being exposed to the high-temperature heat of the molten metal to decompose and generate carburizing gas, which penetrates into the molten metal or cast product surface layer and diffuses. However, in the present invention, vacuum suction is continued even after the casting operation is completed, and the forced air is sucked into the mold and the gas in the mold is forcibly discharged. The carburizing gas, particularly the carburizing gas supplied to the interface between the inner surface of the mold and the cast product, can be quickly discharged out of the mold by replacing it with the outside air.
Thereby, the phenomenon of carburizing due to the contact between the carburizing gas generated inside the mold and the molten metal or the cast product surface layer can be effectively prevented or suppressed.

  According to the present invention, even if the pre-treatment such as coating the inner surface of the mold is not performed as in the prior art, the vacuum suction in the conventional vacuum suction casting is simply performed after the casting operation is completed, It is only necessary to continue for a predetermined time under the state of cutting the edge, and the carburization phenomenon of the casting surface layer, which has been regarded as a problem in the past, can be prevented or suppressed without any special process, and it is inexpensive and requires less man-hours. It becomes possible to manufacture a cast product which is prevented from carburizing.

The carburization phenomenon described above is a phenomenon that occurs when the cast product is at a high temperature of a certain temperature or higher, and such a carburization phenomenon does not occur particularly after the temperature of the cast product has dropped.
Therefore, it is sufficient to continue the vacuum suction after the mold is pulled from the molten metal in the present invention to a temperature at which carburization does not occur, and there is no need to continue the vacuum suction thereafter.
This means that the vacuum suction is continued for a predetermined time.
However, since the temperature at which carburization does not occur varies depending on factors such as the shape of the cast product and casting equipment, the suction duration time is appropriately determined according to the respective conditions.

Next, embodiments of the present invention will be described in detail with reference to the drawings.
In FIG. 1, reference numeral 10 denotes a furnace disposed inside the container 12, in which a molten steel W is held.
14 is a decompression chamber, and 22 is a decompression chamber formed inside thereof. In the decompression chamber 22, a porous mold 16 is formed which is formed by solidifying molding sand with an organic binder as a binder. Here, the mold 16 is suspended in the decompression chamber 14.

A cavity 18 having a shape corresponding to the shape of the cast product is formed in the mold 16. Further, the mold 16 is formed with a plurality of suction ports 20 extending downward from the cavities 18 in the figure and opening at the bottom thereof.
A decompression suction tube 24 extends from the decompression chamber 14, and the decompression chamber 22 is decompressed by the decompression suction through the decompression suction tube 24.

In this embodiment, in a state where the lower part of the mold 16 is immersed in the molten metal W, more specifically, in a state where the suction port 20 is immersed in the molten metal W, the internal pressure of the vacuum chamber 14 (the vacuum chamber) is reduced by vacuum suction through the vacuum suction pipe 24. 22) is depressurized. The molten metal W is sucked up through the suction port 20 by the reduced pressure, that is, by the negative pressure, and filled in each cavity 18.
When the molten metal W filled in the cavity 18 is solidified (the molten metal W in the cavity 18 is solidified in about 20 seconds), the mold 16 is pulled upward together with the vacuum chamber 14 while continuing the vacuum suction. The melt W is cut off. That is, the suction port 20 is separated upward from the molten metal W.

In this embodiment, the vacuum suction is continued even after the molten metal W is solidified and the mold 16 is pulled up from the molten metal W in the furnace 10.
Specifically, the mold 16 and the decompression chamber 14 are taken out from the inside of the container 12 while continuing the decompression and suction, and are held in the outside air outside the container 12 for a predetermined time. )

Due to the vacuum suction during this time, outside air is forcibly sucked into the porous mold 16 having air permeability, in particular, into the mold 16 through the suction port 20.
Further, the gas generated in the mold 16, that is, the carburizing gas generated by the decomposition of the organic binder at a high temperature is replaced by the outside air forcedly sucked, and the decompression chamber 22 and the decompression suction pipe 24 are further provided outside the mold 16. Through the system.

That is, the carburizing gas generated by the decomposition of the organic binder is brought into contact with the molten metal W filled in the cavity 18 or the surface layer of the cast product 26 after solidification (see FIG. 1) to cause carburization to generate a mold by vacuum suction. 16 is discharged from the inside.
When the vacuum suction state is maintained for a predetermined time, the mold 16 is placed on the conveyor 28 and sent to the subsequent process.

Phenol resin (using Gas Hearts 6348 manufactured by Okazaki Huttenus Albertas Kasei Co., Ltd.) and a curing agent (using activator 6324 manufactured by Okazaki) were used as the organic binder. (Cerabead # 650) is added to 1.6% by mass (% by mass based on foundry sand) to form a mold, and a turbocharger turbine housing for an automobile is shown in FIG. Cast in
This turbine housing is ferritic heat-resistant stainless steel cast with a steel material composition of 0.05C-19Cr-2W-1Nb-residual Fe (the numerical value is contained mass%) and has a mass of 3.5 kg and a wall thickness of 2.5 mm It is.

  Here, as shown in FIG. 2, the pressure in the decompression chamber 22 inside the decompression chamber 14 is reduced to a pressure at which the pressure difference from the atmospheric pressure becomes 30 kPa over 3 seconds from the start of decompression, and then the same pressure is maintained for 30 seconds. The molten metal W was sucked and filled into the cavity 18 of the mold 16 and solidified, that is, the molten metal W was cast (the molten metal temperature at the time of casting was 1570 ° C.).

After the above casting operation is completed, the mold 16 is pulled up together with the decompression chamber 14 while continuing vacuum suction, and is cut off from the molten metal W in the furnace 10, and thereafter, the mold 16 is removed from the container 12 while maintaining vacuum suction. 1 and held in the outside air as shown in FIG. 1, and the forced intake of the outside air into the mold 16 and the forced discharge of the gas in the mold 16 were continued.
When the relationship between the suction duration time at that time and the thickness of the carburized layer of the surface layer of the cast product 26 was examined, the result shown in FIG. 3 was obtained. Here, the thickness of the surface layer portion where the C concentration is higher than that of the base material is measured as the thickness of the carburized layer.
In FIG. 3, the horizontal axis represents the forced suction time after casting, and the vertical axis represents the thickness of the carburized layer.
In FIG. 3, the plot of forced suction time 0 after casting is when no forced suction is performed.

  From the results of FIG. 3, it can be seen that the carburization of the surface layer of the cast product is suppressed by forced suction of the outside air by continuing the vacuum suction, and that the suppression of the carburization is more effective as the forced suction time becomes longer. In this case, it can be seen that the carburized layer on the surface of the cast product is not substantially formed by continuing the forced suction for 5 minutes.

  According to the present embodiment as described above, the vacuum suction in the conventional vacuum suction casting is simply performed after the casting operation is completed, without performing a pretreatment such as coating the inner surface of the mold as in the past. It is only necessary to continue for a predetermined time in a state where the mold 16 is cut off from the molten metal W, and the carburization phenomenon of the surface layer of the cast product 26, which has been regarded as a problem, can be prevented or suppressed without adding a special process. Thus, it is possible to manufacture the cast product 26 which is carburized and prevented at low cost and with a small number of man-hours.

  FIG. 4 shows another embodiment. Here, when the mold 16 is taken out from the container 12, a hood 30 with a vacuum suction pipe 24 is immediately attached to the mold 16 in place of the vacuum chamber 14, and cast. The vacuum suction after the operation is switched to vacuum suction through the vacuum suction tube 24 of the hood 30, and the mold 16 is sent to the subsequent process by the conveyor 28 while continuing the vacuum suction.

  In this way, holding of the vacuum suction for a predetermined time until the mold 16 taken out from the container 12 is placed on the conveyor 28 is omitted, and the vacuum suction is continued while the mold 16 is sent to the subsequent process by the conveyor 28. Therefore, the time required for manufacturing the cast product 26 can be shortened.

  Although the embodiment of the present invention has been described in detail above, this is merely an example, and the present invention can be implemented in variously modified forms without departing from the spirit of the present invention.

It is explanatory drawing of the vacuum suction casting method of one Embodiment of this invention. It is the figure which showed the pressure change of the decompression chamber at the time of casting operation. It is the figure which showed the relationship between the forced suction time after casting and a carburized layer thickness. It is explanatory drawing of other embodiment of this invention.

Explanation of symbols

14 Depressurization chamber 16 Mold 18 Cavity 20 Suction port 22 Decompression chamber 26 Cast product W Molten metal

Claims (1)

A mold molded using an organic binder is placed in a vacuum chamber, and the vacuum chamber is suctioned under reduced pressure while the suction port is immersed in a molten steel, so that the molten metal is sucked up through the suction port and filled into the mold cavity. In the vacuum suction casting method in which casting is performed, the vacuum suction is continued for a predetermined time after the molten metal is filled into the cavity and solidified to pull up the mold, and the suction port is separated from the molten metal. A vacuum suction casting method characterized in that the outside air is forcibly sucked and the gas in the mold is forcibly discharged.

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