RU2302923C1 - Turbine blades casting plant with use of directed crystallization process - Google Patents

Abstract

FIELD: foundry, possibly manufacture of blades of aircraft gas turbine small-size engines and of engines of ground mounted aggregates.

SUBSTANCE: plant includes ceramic mold having starting cavity, blade cavities and seed cavity communicated with starting cavity. System of horizontal and vertical gating having relation of their cross section areas in range 1 : (1 - 2) provides smooth melt supply to each blade cavity.

EFFECT: improved quality of cast blades, less loss of yield by structure of cast blades, enhanced efficiency of process.

2 cl, 1 dwg, 3 ex

Description

The invention relates to the field of foundry and can be used to obtain castings from heat-resistant and intermetallic alloys based on nickel with directional and single-crystal structure, in particular castings of blades of aircraft gas turbine small engines and engines of ground installations.

Known devices for producing castings by directional crystallization, in which the ceramic mold contains a starting cavity, a cavity of a casting and a crystal sampler in the form of a helicoid (US Pat. Nos. 4,133,368, 4,453,588), designed to produce castings with an orientation of [001] with an accuracy of 10-15 °, as well as devices containing a seed cavity with a single crystal seed placed therein to produce castings with a crystallographic orientation other than [001] (US Pat. Nos. 4,714,101, 4,475,582, 4,469,161).

The disadvantage of these devices, made with an open bottom installed directly on the refrigerator, is the low yield when casting the blades due to the difficulty of hermetically securing the molds directly on the mold-refrigerator.

Known devices consisting of several ceramic molds for simultaneous production of several castings of blades with directional and single-crystal structure, placed and fixed on the mold-plate around the circumference and poured through a common casting bowl (US patent No. 4133371, 3888301), as well as a device representing These are ceramic blade blocks obtained by the method of layer-by-layer application of a ceramic suspension, containing several blade cavities, united by a common gate system (EP 0059550 B1).

However, due to their low productivity, it is not economically feasible to use them for casting the blades of a small engine.

Upon receipt of blades with directional and single-crystal structure from heat-resistant alloys of a small engine in order to increase productivity in mass production, it is advisable to use devices for casting in multi-tiered blocks.

Closest to the claimed is a device for producing castings by directional crystallization, containing a ceramic mold with a casting bowl, including the starting cavity and the cavity of the blades located one above the other coaxially relative to the vertical axis. The starting cavity contains a crystal sample in the form of a helicoid, mounted directly on the refrigerator-crystallizer (UK patent No. 2322584)

The disadvantage of this device is the inability to obtain blades with a directional and single-crystal structure of any crystallographic orientation, except [001] with an accuracy of 12-15 °, low productivity of the process due to the difficulty of tightly fastening the bottom-open form to the mold plate, the inability to use the device with automated the process, in particular in foundries with liquid metal cooling, as well as the inability to compensate for foundry stresses due to the difference in thermal expansion coefficients (KTP) of ceramic form and heat-resistant alloy, leading to castings marriage.

The technical task of the invention is to obtain turbine blades from nickel casting heat-resistant alloys with a single crystal structure of the desired crystallographic orientation or directional structure in plants with a liquid metal cooler, improving the quality of castings and structural yield, improving process performance, especially when casting small turbine blades.

To implement the technical task, a device for producing turbine blades by directional crystallization is proposed, containing a ceramic mold with a casting bowl, including a starting cavity and cavity of the blades, located one above the other coaxially relative to the vertical axis, which additionally contains a system of vertical and horizontal sprue channels separating the cavity of the blades and located between the starting cavity and the casting bowl, and the seed cavity, which is directly connected to the start second cavity, wherein the ratio of cross-sectional areas of horizontal and vertical runner is 1: (1-2).

To obtain single crystal castings, the seed cavity is made with a closed lower part, on the inner surface of which is a refractory single crystal seed of a given orientation.

To clarify the invention, the drawing shows a schematic illustration of a device for casting small-sized GTE blades with a single-crystal structure, where:

1 - cavity 2 turbine blades;

2 - starting cavity;

3 - seed cavity;

4 - horizontal and vertical sprue channels;

5 - casting bowl;

6 - single crystal seed.

In the ceramic block, the cavity of the blades (1) are located one above the other coaxially relative to the vertical axis. The cavity of the lower blade in turn is directly connected in the lower part of the block to the starting cavity (2) and the seed cavity (3) closed from below, into which the single-crystal seed (6) is installed.

The cavities of each blade are separated from each other by the gates of the gate horizontal and vertical channels (4) located between the casting bowl (5) and the starting cavity (2) of the device.

The system of horizontal and vertical sprue channels provides a smooth supply of melt into each blade cavity from below to avoid rod breakage and reduce blockage by blockages, as well as to compensate for stresses that usually arise due to the significant difference in the KTP values of the mold and cast materials, leading to cracking and tears on the thin edges of the blades after completion of the crystallization process. In this case, the diameters of the horizontal and vertical gating channels are selected depending on the size of the castings obtained, but in such a way as to ensure the optimal ratio of the cross-sectional areas of the horizontal and vertical channels, which is within 1: (1-2).

If the ratio of the cross-sectional areas of the horizontal and vertical channels is less than 1: 1, then a heat storage unit can be created in the horizontal channel, which does not contribute to the process of directed crystallization of the blade unit, and the ratio of these areas of more than 1: 2 creates thermal nodes in the vertical channel. Going beyond the optimal ratio leads to an increase in marriage in structure.

To obtain single-crystal castings with predetermined properties, there is a seed cavity at the top of the starting cavity in which a refractory single-crystal seed of the desired crystallographic orientation is placed.

The crystallographic orientation from the single-crystal seed through the starting cavity is transmitted to the lower blade of the block, and from it to all subsequent blades located coaxially above it. This allows you to increase the productivity of the casting process, reduce the cost of expensive refractory seeds for one melt.

Examples of implementation

Example 1. A shell ceramic mold was made by layer-by-layer application of a ceramic suspension on a model block consisting of 12 models of small blades placed in 2 tiers parallel to the vertical axis one above the other and forming 6 sections of blades mounted on one casting bowl. Each section had an individual starting and starting part. The system of horizontal and vertical elements of the sprue system located between the casting bowl and the start part and separating the blades serves to form sprue channels in ceramic form, which will provide melt supply to the blades from below. The sprue system provides an increase in the strength of the block structure, which prevents the formation of tears in the castings of the blades after crystallization is completed. The manufactured shell molds were dried, the model mass was heated and calcined at a furnace T = 1100 ° C. The ratio of the cross-sectional areas of the horizontal and vertical gating channels is selected as 1: 1 (Diameters of the vertical and horizontal gating channels = 10 mm). Before the melting, single crystal refractory orientation seeds [111] were installed in the open seed cavity of each blade section before melting and sealed with an electrocorundum suspension.

The mold on a special suspension was placed in the installation for directional crystallization with a UVK-9 liquid metal cooler, where it was heated to operating temperature, the VKNA-4U intermetallic alloy alloy billet was melted in a crucible, and it was poured into a casting bowl of a spatula-shaped ceramic block at a temperature of 150 ° above Tlick . alloy. After that, directional crystallization was performed by immersing the ceramic mold with the melt from the heater into a liquid metal cooler. After crystallization, the blades were freed from ceramics, the sprue system and subjected to etching on the macrostructure. As shown by visual and X-ray control, 90% of the castings had a single crystal [111] orientation structure with a deviation of up to 10 °. Cracks and damage to the shoulder blades were not detected.

Example 2. A shell ceramic mold was made analogously to example 1, but the diameters of the sprue channels were chosen so that the ratio of the cross-sectional areas of the horizontal and vertical sprue channels was 1: 2. The open seed cavity of each section of the blades before melting was sealed with a suspension based on electrocorundum without installing a refractory seed. The mold was placed in an installation for directional crystallization with a UVK-9 liquid metal cooler and casting and directional crystallization were performed, as shown in Example 1. For one melt, 24 suitable blades with directional structure were obtained.

Example 3, made by the prototype method.

Shell ceramic blade shape was made according to the prototype method and was filled with a melt of heat-resistant nickel alloy. About 30% of the blades obtained had tears on the side of the outlet edge after removal of the ceramics as a result of uncompensated metal shrinkage. Visual and x-ray control of the blades after etching showed that part of the castings of the blades had foreign crystals sprouted from the junction of the mold and the refrigerator, and the monocrystalline structure had 50% of the obtained blades with a deviation from the [001] direction of 5-20 °.

Testing of the proposed device in serial production for casting single-crystal turbine blades of a small engine has shown that it provides high performance in obtaining blades of the desired crystallographic orientation with a yield of up to 90% in structure and 99-100% with directional structure.

Claims (2)

1. A device for producing turbine blades by directional crystallization, containing a ceramic mold with a casting bowl, including a starting cavity and cavity of the blades, located one above the other coaxially along the vertical axis, characterized in that the device is equipped with a system of vertical and horizontal sprue channels separating the cavity of the blades and located between the starting cavity and the casting bowl, and the seed cavity, which is directly connected to the starting cavity, the ratio of the areas cross sectional horizontal and vertical runner is 1: (1-2). 2. The device according to claim 1, characterized in that the seed cavity is made with a closed lower part, on the inner surface of which is a refractory single-crystal seed of a given orientation.