JPS6359787B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a precision casting method, and particularly relates to a method for inexpensively casting large precision castings that partially require high dimensional accuracy and smooth casting surfaces, such as pump parts such as impellers, differential users, and casings. Regarding how to.

Precision casting methods have been developed as a method for casting products that require high dimensional accuracy and extremely smooth casting surfaces and have complex shapes. This precision casting method involves assembling a vanishing model made of wax, urea resin, etc., immersing the vanishing model in slurry to form a slurry coating layer, and sprinkling stucco material before the coating layer dries. This is a method in which the desired metal is cast into the ceramic shell mold at a high temperature obtained by repeating this several times, drying it, and then disappearing the disappearing model to form a hollow mold, which is then fired.

Such a precision casting method requires the above-mentioned complicated steps and is therefore disadvantageous in terms of cost compared to a method using a normal sand mold. In addition, when relatively large parts are cast using the precision casting method described above, the strength of the model is low, so distortion is likely to occur in the model when assembling the model.As a result, it is necessary to maintain high dimensional accuracy of the resulting cast product. The problem arises that it is not possible. Moreover, there is also the problem that cracks are likely to occur in the mold when the model disappears.

Incidentally, pump parts such as impellers require high dimensional accuracy and smooth casting surfaces, and have complex shapes, so the precision casting method described above should be applied, but from a cost standpoint, and relatively large Particularly for parts, it is difficult to apply the precision casting method as is because of the various problems mentioned above.

However, for pump parts such as impellers, high dimensional accuracy and smooth casting surfaces are required for the crown and blades, while the outer part of the shroud has a simple shape and requires post-processing. Because of the large number of cast members, high dimensional accuracy and smooth casting surfaces are not required.

Therefore, when casting the above-mentioned impeller, the present inventor used a ceramic shell mold only for the crown part, the inner side of the shroud part, and the part corresponding to the blade part (the core part in the normal casting method).
It has been found that it is better to use a metal mold for the other main mold parts, that is, it is better to use a composite mold.

The present invention has been made based on this knowledge, and an object of the present invention is to provide a method for inexpensively casting large precision castings that partially require high dimensional accuracy and smooth casting surfaces.

The precision casting method according to the present invention uses a composite mold in which the main mold part is formed of a mold whose required surface is coated with a mold coating agent in advance, and the core part is formed of a ceramic shell mold. Composite mold temperature is 200℃
It is characterized by casting the metal while being heated and maintained at a temperature above.

The present invention will now be described in detail with reference to the accompanying drawings. FIG. 1 is a longitudinal sectional view showing a pump impeller being cast by the method of the present invention. In the figure, 1 is a ring-shaped mold forming the main mold part, and the surface where it is necessary to form a coating film is coated with refractory powder to prevent surface defects such as burning and penetration. A mold coating agent such as the following is applied in advance. As a method for applying the mold, it is preferable to heat the mold 1 to 100 to 300°C and apply the mold by brushing or spraying. The surface (inner circumferential surface of the mold 1) on which this mold coating agent is applied in advance corresponds to a portion that will form the outside of the shroud portion 3c when casting the molten metal 3 to cast an impeller.

Ceramic shell mold 2 is made by molding a disappearing model made of wax, urea resin, etc., and then making the model disappear and firing at a firing temperature of 800 to 1200°C. Molten metal 3 is poured into the mold to cast an impeller. In this case, a mold forming the crown part 3a and a plurality of wing parts 3b...3b attached at equal intervals around the crown part 3a, and a feeder opening that guides the molten metal 3 to the middle ring feeder part 3e and the outer ring feeder part 3d. It is equivalent.

Ceramic shell mold 2 and mold 1 as described above
A composite mold is formed by mold setting, and by pouring the molten metal 3 into the composite mold while heating and maintaining the composite mold at a temperature of 200°C or higher, a plurality of wing parts 3b...3b are formed. is the shroud part 3c
It is also possible to cast a sealed impeller in which the front and rear are integrally connected at the crown portion 3a.

In addition, when the ceramic shell mold 2 and the metal mold 1 are placed together, they are simply brought into contact with each other, and there is no forced connection between them. Therefore, the difference in thermal expansion coefficient between the ceramic shell mold 2 and the mold 1 does not substantially pose a problem. In addition, the reason why we decided to pour the molten metal 3 into the composite mold, which is a combination of the ceramic shell mold 2 and the metal mold 1, while heating and maintaining it at a temperature of 200°C or higher, is because the composite mold is heated to a temperature of 200°C or higher.
If the melt is poured in a state below the melt temperature, the binder of the ceramic shell mold 2 (usually colloidal silica or ethyl silicate) has crystallization water, which will react with the molten metal 3 and cause casting defects such as blowholes. It is heated to over 200℃,
By maintaining the heated state until the metal casting starts, it is possible to prevent casting defects caused by crystal water, and by applying the heating to the entire mold including the mold, ceramic shell molds can be heated. Differences in solidification rate, thermal stress, etc. that occur in the cast product near the boundary between the mold and the mold are alleviated, and a cast product with less distortion and deformation without cracking can be obtained.

When manufacturing a cast product using the method of the present invention as described above, the ceramic shell mold 2 is used only in areas where high dimensional accuracy and smooth casting surface are required.
Since the mold 1, which can be used as a durable mold, is used for the other parts, precision casting products can be manufactured at relatively low cost. In addition, since we use a composite mold that combines mold 1 and Sierra Mitsushiel mold 2, the strength of the mold is high and the model can be easily removed, making it easier to produce large precision castings. It becomes possible. Furthermore, while the ceramic shell mold 2 has high heat insulation properties, the mold 1 has a large cooling capacity, so when using the method of the present invention using a composite mold that combines both, directional solidification is promoted and a sound casting can be obtained. easy. In addition, ceramic shell mold 2 requires heating and holding the mold at a temperature of 200°C or higher before pouring due to the problem of crystallization water. Since the surface condition of the mold is stable in this state, it can be said that the above-mentioned composite mold in which the ceramic shell mold 2 and the mold 1 are combined is extremely excellent. Furthermore, since both the ceramic shell mold 2 and the mold 1 generate very little gas during casting compared to other molds, the method of the present invention for casting metal using the above-mentioned composite mold makes it possible to obtain a sound cast product. It can be said that this is a casting method that allows for

The above explanation is for casting pump impellers, but it is also applicable to casting products that partially require precision casting elements, such as pump parts such as diffusers and casings, turbine blades, and fans. It goes without saying that the method of the present invention can be applied to many other manufacturing processes.

Further, in the method of the present invention, cast steel is most suitable as the metal to be cast, but of course cast iron, aluminum, aluminum bronze, copper, etc. may also be used.

As detailed above, the present invention uses a composite mold that combines a metal mold and a ceramic shell mold,
This is a precision casting method in which metal is cast while the composite mold is heated and maintained at a temperature of 200°C or higher. Ceramic shell molds are used in areas where high dimensional accuracy and smooth casting surfaces are required, and other molds are used. If the method of the present invention is carried out by using a highly durable and strong mold for the part, it is possible to inexpensively manufacture a large precision casting product that requires high dimensional accuracy and a smooth casting surface in some parts. I can do it. In this manner, the present invention provides an extremely effective means for precision casting metals.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view showing a pump impeller being cast by the method of the present invention. 1: Mold, 2: Ceramic shell mold, 3: Molten metal, 3d: Outer ring feeder section, 3e: Middle ring feeder section.

Claims (1)

[Claims] 1 Using a composite mold in which the main mold part consists of a mold whose required surfaces are coated with a mold coating agent in advance, and the core part is formed of a ceramic shell mold,
A precision casting method characterized by casting metal into the composite mold while being heated and maintained at a temperature of 200°C or higher.