JPS6057417B2 - Casting method for gas turbine blades - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas turbine blade with a large cooling effect, and more particularly to a precision casting method for a gas turbine blade that is leached cooled.

The thermal efficiency of gas turbine engines is improved by increasing the gas turbine inlet temperature, which is accomplished by increasing the heat resistance of the materials of construction and the cooling effectiveness of the components.

When the gas turbine inlet temperature is high, it is necessary to use a superalloy such as a Co-based or Ni-based alloy with high high-temperature strength to create a structure that allows blade cooling. In order to make this difficult-to-process material into a hollow structure, blades are generally manufactured by precision casting. In a gas turbine blade, the blade part is high temperature and has low stress, so it is necessary to have a large cooling effect, and impingement cooling and film cooling, which have a relatively large cooling effect, are used for the leading edge and trailing edge.

The tabdil part (implanted part) is subject to medium temperature and high stress, so high strength and toughness are required rather than a cooling effect. A relatively effective cooling method for blade cooling is film cooling, which reduces /J on the blade surface.
There is a method to reduce the rise in surface temperature of the wing by blowing air out from the wing L and creating a film of air on the wing surface.

A cooling method that has an even greater cooling effect is known as leaching cooling. However, the reason why the leaching cooling method cannot be put to practical use is because conventional manufacturing methods cannot produce blades that are sufficiently satisfactory in terms of cooling effect and material strength. As shown in FIG. 1, the exudation cooling blade has a hollow blade whose surface is made of a porous layer containing non-linear micropores. The refrigerant is forced into the hollow part 1 from the blade root, and this percolates into the porous surface layer 2 and reaches the blade surface. This structure creates a uniform film of refrigerant over the entire blade surface, and a small amount of refrigerant prevents the temperature of the blade surface from rising.
The temperature drop in gas temperature is small, and the cooling effect and thermal efficiency are superior to film cooling. One of the conventional manufacturing methods for leaching cooling blades is to manufacture hollow blades by precision casting.
The surface layer is micro-processed using plasma beams, electron beams, etc. to create many smaller holes than the film cooling holes, and the other method is to compression mold metal powder using a powder or metal method to make it porous. In this method, the hollow portion is generally perforated by electrolytic machining, electric discharge machining, etc. after molding.

However, in the former manufacturing method, it is necessary to drill small-diameter leaching holes over the entire surface of the blade, resulting in poor workability.Since the leaching holes are straight holes, a large amount of refrigerant is used, resulting in a large decrease in thermal efficiency. It is difficult to drill deep small-diameter holes, and the porosity of the surface layer increases, resulting in a significant decrease in the strength of the blade.

On the other hand, the powder and metal methods enable non-linear fine leaching holes and have a large cooling effect, but because the powder is compression molded, the grain bonding in the interior is more incomplete than in the surface layer, resulting in a significant decrease in the strength of the blade. . In particular, the strength of the dovetail portion, which requires surface cooling and which requires high strength and high toughness, is greatly reduced.
Furthermore, since the internal hollow holes are post-processed, they are limited to simple shapes, making it difficult to process complex shapes up to the top of the blade to accommodate the twisting of the blade. An object of the present invention is to provide a new manufacturing method that does not have the disadvantages of the conventional manufacturing method of exudation-cooled blades, such as the reduction in cooling effect and strength, and the shape limitations of hollow holes.

The method for manufacturing the leaching cooling blade of the present invention will be described in detail below.

The blade manufacturing method of the present invention is to manufacture a leaching-cooled blade by a precision casting method. That is, a ceramic shell mold is manufactured by a precision casting method called the stwax method (investment method), and metal powder or grains are charged into the mold at the same time as or prior to the injection of molten metal. According to the present invention, the molten metal completes pseudo-solidification after filling the spaces between the metal powders. It is a characteristic. In the present invention, in order to fill the spaces between the metal powder particles in an unmelted state with molten metal, it is necessary that the melting point of the metal particles be higher than the injection temperature of the molten metal.

Also, when injecting molten metal, there is a risk of damage between the metal grains! To aid infiltration, hot molds are preferably applied, similar to conventional precision casting. In a high-temperature mold, solidification is not completed immediately after the molten metal is injected, so some component diffusion occurs between the metal grains and the molten metal, and bonding between the grains progresses. Solidification from a state in which molten metal exists between solid metal particles can leave fine shrinkage pores between the metal particles. In conventional precision casting, the temperature gradient is applied to replenish the molten metal to prevent the generation of voids due to the physical shrinkage caused by solidification, but in the present invention, since solid metal particles are present,
Even if there is a slight temperature gradient, the supply path for the molten metal is cut off and solid metal particles solidify adiabatically before solidification, leaving fine solidification shrinkage holes. The present invention focuses on this point and provides a gas turbine blade in which fine contraction holes are used as seepage cooling holes. Embodiment An embodiment of the present invention is shown in FIG.

The mold 3 made by the Investmefund method has a ceramic core 4
was installed for the hollow hole in the center of the blade, and the entire mold was heated at a high temperature of 122σC in a vacuum furnace. The dimensions of the mold and the overall structure of the mold are as follows. In other words, the dimensions of the mold are: the blade length from the top part 11 of the turbine blade to the blade root part 12 gates is 96Tm1, the average wall thickness of the blade A, that is, the average distance between the mold inner surface and the core surface is about 3.5m, and the average blade length is 96Tm. Chord length B is 617m
It is. The turbine blade in FIG. 1 shows a sectional view taken along line I-1 in FIG. 2. The mold is made from the blade top part 11 to the blade root part 12.
It is composed of a wing part up to the top, a shank 13 above the blade root, a dovetail 14 located at the top of the shank, and a riser 15.The height of the shank and tabtail are both 25 meters, and the height of the riser is is 70 m.The metal powder 5 is
It is frozen crushed grains of cobalt (CO)-based ×45 alloy,
Its composition is 0.23% carbon and 24% chromium by weight.
5% nickel, 10% nickel, 7.5% tungsten, 0.01% boron, and the remainder cobalt.

The particle size of the powder is about 100 μm or less. The metal powder 5 is filled in advance (approximately 20 cc) to a height equivalent to about 1/2 of the height from the blade top portion 11 to the blade root portion 12 in the mold, and then the metal powder 5 in the hopper 6 is filled. It was charged into the mold at the same time as molten metal 7. Approximately 27 cc of metal powder 5 was charged so as to fill it up to the height of the blade root portion 12. Molten metal 7
is a nickel (Ni)-based alloy 1N738, whose composition in weight percent is 0.17% carbon, 16.2% chromium, 8.5% cobalt, 2.6% tungsten, and 1% molybdenum.
．． 75% niobium, 0.9% niobium, 3.43% titanium, 3.45% aluminum, 1.75% tantalum, 0.1% zirconium, 0.01% boron, and the remainder nickel.
The amount of molten metal 7 is 2.3k9, and it is poured up to the riser part! 7. The injection temperature of the molten metal 7 was 1300° C., which was lower than the melting point of the metal powder 5. The blade cross section after solidification and cooling has a thickness of 10 to 5 μm.
It was confirmed that the micropores were uniformly distributed. Also, since the density of the metal powder 5 (approximately 8.6y/c!l) is greater than the density of the molten metal 7 (density at room temperature is approximately 8.1f/cfl), the tabtail portion located above the blade root portion The metal powder 5 was not present in the sample, and it was in a healthy state with no shrinkage pores. As described above, according to the casting method of the present invention, a porous layer containing non-linear micropores is formed on the blade surface, ensuring the integrity of the dovetail portion where the surface is not cooled, and eliminating constraints on the shape of the hollow hole. Therefore, it is possible to manufacture a seepage cooling blade with a large cooling effect, high material strength, and a suitable hollow hole shape.

For the application of the invention, it is useful to take the following auxiliary measures.

In other words, in order to fill the spaces between the metal particles with molten metal, pressure is applied after pouring, vibration is applied to the mold, and the metal is melted and solidified by heating in a vacuum. These actions ensure the bond between the metal particles. There is.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the structure of a seepage cooling blade, and FIG. 2 is a diagram showing an embodiment of the present invention. 1... Hollow part, 2... Porous surface layer,
3...Mold, 4...Ceramic core,
5...Metal powder, 6...Hopper, 7.
...Molten metal.

Claims (1)

[Claims] 1. In the casting of gas turbine blades with a structure in which the blade surface is cooled by introducing a refrigerant into the blade, metal particles having a melting point higher than the injection temperature of the molten metal are charged into the high-temperature mold in advance or simultaneously with the molten metal. A method for casting a gas turbine blade, characterized in that a porous layer containing fine pores is provided between metal particles by injection.