RU2597491C2 - Device and the ceramic shell for producing castings with monocrystalline and directed structure - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy and can be used for casting with monocrystalline and directed structure from heat-resistant nickel alloys. Device comprises transfer chamber, vacuum chamber, furnace heating of ceramic shells, located in a vacuum chamber and containing heat-insulating walls 23, top heater, bottom heater 27, bottom screen, separating zones of cooling and heating, top screen 22 and suspension system for movement of ceramic shells. Ceramic shell contains located in one row forms 1 of the cast details with starting and profitable parts, which form a channel with a nozzle for pouring of the melt. At the ends of the channel are located brackets 4 embracing suspensions 10. Under the furnace the refrigerator 29 is placed. Shells is installed on crossbar 9 with suspensions 10. Melt through the funnel 21 and manifold 15 is poured into molds shells and shells are moved into cooling zone through openings of the bottom screen and between zigzags of coil of bottom heater. Increase in quantity of details molded in one process cycle, increase of accuracy of geometry of casts and quality of their surface is provided.

EFFECT: increase in a efficiency of casting alloy is reached.

3 cl, 9 dwg, 1 tbl

Description

The invention relates to foundry and can be used for casting castings with a single-crystal and directional structure from heat-resistant nickel alloys, for example, parts of a hot tract of gas turbine engines (GTE), in particular rotor blades, nozzle flaps, as well as for producing single-crystal blanks from Ni- alloy W for the manufacture of seeds, samples for testing alloys for strength.

A device is known for producing castings with directional and single-crystal structure, comprising a heating zone with a heater, a cooling zone with movable and stationary water-cooled refrigerators, a heat-insulating screen separating the heating zone and the cooling zone, the stationary refrigerator and the screen being made with coaxial holes, the stationary refrigerator is installed under screen, while casting the blanks, a ceramic shell, consisting of several forms, is installed on a movable refrigerator, and filled with the molds are moved from the heating zone to the cooling zone through holes in the screen and holes in a stationary refrigerator (RF patent No. 2258578, CL. B22D 27/04, publ. 08/20/2005).

The disadvantage of this device is that in the initial position, the starting sections of the molds are located on a movable refrigerator and are surrounded by the cold surfaces of a stationary refrigerator. Under such conditions, it is practically impossible to heat the Ni-W alloy seeds to at least 1300 ° C in order to transfer the given single-crystal structure to the castings. In addition, due to the presence of a stationary refrigerator with holes, it is problematic to use a lock chamber in the device. Therefore, the operation of the device is characterized by low productivity and is designed only for castings with directional structure.

Also known is a device for producing castings with directional and single-crystal structure, containing a vertical vacuum chamber, inside which there is a melting furnace, a shape heating furnace (PPF) of a rectangular shape in horizontal section with two heaters of the upper and lower zones, a ceramic mold moving mechanism, a sliding screen, separating the heating zone and the cooling zone, a container for crystallization of castings with a liquid metal cooler, on the surface of which there is a heat shield, moreover, shapes and sizes measures the top of the container corresponds to the dimensions of the outer wall of the PPF and the dimensions of its lower part - the dimensions of the inner wall PPF (RF Patent №2398653, Cl B22D 27/04, published on 10.09.2010..).

The disadvantages of this device are as follows.

During the crystallization process, the sliding screen can only shield the shapes of the cast parts that are located in the plane of symmetry of the PPF, so the number of parts cast in one technological cycle is limited by the length of the PPF. In addition, the sliding screen requires providing large gaps with the lower zone heater and the heat shield, which increases the distance between the heating and cooling zones and affects the quality of the castings.

Most of the side surface of the tank with liquid metal cooler is surrounded by heating elements. Despite the fact that the heating elements accelerate the melting of the cooler, during crystallization they shield the tank and prevent radiant heat removal from it, which can lead to an unacceptable increase in the temperature of the cooler, a decrease in the temperature gradient and deterioration of the structure of castings.

Closest to the claimed (prototype) device is a device for producing castings with directional and monocrystalline structure, containing an oven for heating ceramic shells with heat-insulated walls placed inside a vacuum chamber, and an upper heater in the form of two parallel plates made of two parallel plates made of ceramic shells along its side walls composite material and a lower heater with a front U-shaped jumper, while the furnace for heating ceramic shells is closed on top with a groove for the passage of suspensions and funnels, under a heating furnace for ceramic shells, a container with a liquid metal cooler is located on a lifting water-cooled table, heat insulators are located between the tank and the heat-insulating screen, for moving ceramic shells from the heating zone to the cooling zone, a vertical ceramic movement mechanism is installed shells, while the sprue bowls of the shells are located on the crossbars suspended on the pendants, and the shapes of cast parts are found in it Xia in limbo (RF patent No. 2267380, Cl. B22D 27/04, publ. 01/10/2006).

The disadvantages of the prototype include a significant distance between the lower heater and the surface of the liquid metal cooler - about 70 ... 100 mm, due to the edge of the tank located above the cooler, the presence of insulators and a screen between it and the heater. As a result, a significant part of the height of the castings crystallizes even before the cooler touches. In fact, heat is removed in this device mainly due to the heat radiation of ceramic shells. In this case, the surface of the liquid metal cooler, the upper edge of the tank, heat insulators and the lower screen, surrounding ceramic shells and receiving a radiant heat flux from them, can be heated to 700 ... 1200 ° C. In such an environment, the heat removal from the ceramic shells necessary to obtain high-quality castings is not as significant as is commonly believed when using a liquid metal crystallizer.

During heat shrinkage of the crystallized casting, the ceramic shell slightly crackes. In this case, the cooler can penetrate the cracks of the ceramic shell and come into contact with the casting, followed by dissolution of its surface layer and the formation of defects on it. Since the cooler atoms for heat-resistant alloys, as a rule, are harmful impurities, with the exception of aluminum, castings with the indicated defects are not to be disposed of. In addition, in the case of breakdown of the shell, the melt flows into the cooler, dissolves in it, and the resulting alloy is not disposed of.

The use of liquid aluminum as a cooler is problematic due to its high activity. In particular, when using a cast-iron tank, aluminum slightly dissolves its walls, especially near its upper edge. In this case, a hard alloy layer is formed at its bottom with a decrease in the depth of immersion. The depth also decreases due to the deposition at the bottom of aluminum oxides formed on its surface. Its cleaning from oxides, as a rule, is carried out in conditions hazardous to health - with an open melting chamber and at a furnace temperature of heating ceramic shells and aluminum of the order of 700 ... 800 ° C. After 45 ... 55 heats, the walls of the cast-iron bath at the aluminum mirror level are thinned to 5 mm, and the immersion depth of the ceramic shells does not exceed several centimeters. The use of a graphite container, the most inert to aluminum, is too expensive for mass production and, in addition, graphite is a relatively fragile material. Reinforcing graphite capacity with a heat-resistant alloy shell weakens heat dissipation.

It should also be noted that during heating, aluminum can unpredictably boil in the form of rising aluminum foam and disable the heating of the ceramic shells.

Suspension of ceramic shells makes it necessary to provide supporting gates under the sprue bowl so that when immersed filled shells in aluminum, the graphite pendant earrings do not cut into carbon heat insulators and do not cause them to touch aluminum with subsequent boiling. This circumstance forces us to increase the height of the supporting elements up to 70-80 mm so that at the end of the dive we guarantee a gap between the earring and insulators of the order of 2-3 cm.

The gating “forest” together with the bowl, having a height of the order of 120 ... 130 mm, shields the lower forms of the molded parts, slows down the achievement of thermal equilibrium during heating and creates the conditions for the formation of an inhomogeneous thermal field, the occurrence of thermal stresses, cracks and breakdown of ceramic shells during pouring. This also contributes to the mutual shielding of the shapes of the blades. In the cooling zone, mutual shielding weakens the radiant heat dissipation, helps to reduce the quality of the macrostructure. In this regard, the device uses ceramic shells made with no more than two rows of molds of molded parts so that at least one side of the mold faces the heater. This limits the degree of congestion in the furnace space and the number of parts cast in one production cycle.

A ceramic shell is known that contains a sprue bowl and feeders for working cavities, while at the bottom of the bowl a closed groove is made in the form of a flat frame that communicates with the feeders and has an annular, triangular or rectangular shape, and the feeders (sprues) under the sprue bowl are made in the form of U- shaped channels, each of which in pairs combines the inputs of the molds of molded parts (RF Patent No. 114282, CL. B22D 27/04, publ. 20.03.2012).

Despite the fact that this embodiment of the ceramic shell somewhat reduces the consumption of the alloy, however, the presence of a bowl and supporting elements in it does not significantly reduce the consumption of the cast alloy.

Closest to the claimed ceramic shell (prototype) is a ceramic shell for producing small-sized turbine blades by the method of directed crystallization, containing molds of molded blades, arranged one above the other coaxially in several tiers, and the molds contain starting cavities with seed pockets, in addition, the shell contains a sprue bowl , a system of vertical and horizontal sprue channels with a ratio of cross-sectional areas 1: (1-2) located between the starting cavity and h Yours (RF Patent 2302923, Cl. B22D 27/04, publ. 20.07.2007).

The disadvantage of this ceramic shell is that the tops of the "cones" on the upper tiers are located on the castle parts of the shape of the scapula of the lower tier; since the alloy at the top of the “cone” cools faster than in the lower located massive castle part, the transfer of the structure from the castle to the “cone” is not stable and, as a rule, at low crystallization rates, no more than 6 ... 8 mm / min. Therefore, when using such a ceramic shell, the yield on the macrostructure is relatively low and obtaining a finely dispersed dendritic structure to increase fatigue strength is problematic. The ceramic shell is made in no more than two tiers, since the immersion depth in liquid aluminum after each smelting decreases, so the increase in the number of parts cast in one technological cycle is not so significant. Vertical gates between the starting cavity and the bowl are made primarily to provide rigidity and strength of the ceramic shell. Therefore, the diameters of their channels are at least 10 mm. Accordingly, the utilization rate of the cast alloy is relatively low.

The technical result of the claimed device is an increase in the number of parts cast in one technological cycle, increasing the accuracy of the geometry of the castings and the quality of their surface, reducing the temperature of heating the shells and reducing material costs.

The technical result of the claimed ceramic shell is an increase in the utilization rate of the cast alloy.

A device for producing castings with a single-crystal and directional structure from heat-resistant nickel alloys, containing a lock chamber, a vacuum chamber, a ceramic shell heating furnace located in a vacuum chamber and containing heat-insulated walls, a lid, lower and upper heaters, a lower screen separating the cooling zone and the zone heating, the upper screen placed on the heating furnace, a funnel for pouring the melt into the form of a ceramic shell mounted on the upper screen, and a suspension system for moving eramicheskih shells. A device for producing castings with a single-crystal and directional structure from heat-resistant nickel alloys is also equipped with a water-cooled refrigerator located under the heating furnace, a collector located on ceramic shells and made with holes in the number of ceramic shells. In this case, the water-cooled refrigerator and the lower heater are made in the form of coils, and the suspension system contains crossbars connected to the suspensions for installing ceramic shells and is configured to allow the movement of ceramic shells during crystallization of the melt in the cooling zone through windows made in the lower screen and between the zigzags of the lower a heater and a water-cooled refrigerator.

These symptoms are significant.

Replacing the tank with a liquid metal cooler with a water-cooled refrigerator eliminates the need after 50 heats to make an iron bath and fill it with aluminum, and then after several heats also clean its surface from oxides. Placing the refrigerator under the ceramic shell heating furnace allows the lower screen to be located on the water-cooled surface of the refrigerator, which makes it possible to bring the heating and cooling zones closer, increase the temperature gradient and improve the structure of single-crystal casting.

The implementation of the lower heater in the form of a coil ensures uniform distribution of the radiant heat flux emanating from the lower heater along the perimeters of the shapes of the parts during crystallization; without decreasing the heating power, it is possible to reduce the temperature of the shells, increase the thermal insulation resource, reduce the simple melting plant associated with replacing worn thermal insulation, and also reduce the transverse temperature gradients, thermal stresses in the rods and their warpage, and also improve the accuracy of the castings geometry and the quality of their surface.

The standing position of the ceramic shells and the location of the collector on them with holes for each shell under the funnel allows to eliminate the sprue bowls and supporting sprues in the shells. This in turn allows to reduce metal consumption and increase the utilization rate of the cast alloy. In addition, this design of the suspension system provides it with increased flexibility. If you accidentally touch a moving down shell of any surface, for example, the lower screen, it can relatively easily and accidentally shift to the side and continue its movement. The absence of a bowl and gating “forest” under it facilitates heating of the shells from above, which in turn reduces thermal stresses and reduces the risk of breakdown of the shells in the gating system.

The smaller the gaps between the curved surfaces of the lower heater and the refrigerator, respectively, the steeper the heat front and the narrower the rows of shapes of the molded parts in ceramic shells.

The ceramic shell for producing castings with a single-crystal and directional structure from heat-resistant nickel alloys contains molds of cast parts with starting and profitable parts. In this case, the shapes of the cast parts are arranged in a row in the shell, and their profitable parts form a channel on which a nozzle for pouring the melt is placed, and brackets for connecting to the suspension system are located on the ends of the channel.

These symptoms are significant. The arrangement of forms in a ceramic shell in one row, in which their profitable parts form a channel with brackets at the ends, provides each shell with a stable vertical position on the crossbar of the suspension system and allows it to move through the narrow gaps of the heater, refrigerator and narrow windows of the lower screen and crystallize apart from other shells, as well as loading the furnace space with three or more rows of parts shapes and, thus, casting more castings in one production cycle.

Molds of cast parts can be located in a ceramic shell with the smallest row width, which allows to reduce the gaps between the curved surfaces of the lower heater and the refrigerator and, thereby, increase the temperature gradient of the heat front.

If there are wide transverse sections in the cast parts, for example, retaining shelves in the GTE blades, the shapes of the cast parts in the ceramic shell can be located in the row plane at an angle to the vertical, and there are profit cavities on the raised edges of the transverse sections, which increases the density in these sections and quality structure.

In FIG. 1 shows the ceramic shell of the GTE blades (longitudinal section);

in FIG. 2 - ceramic shell of GTE blades (front view with cuts in the starting part and bracket);

in FIG. 3 - ceramic shell, in which the shapes of the molded parts are inclined in the plane of the row;

in FIG. 4 - ceramic collector (longitudinal section);

in FIG. 5 is a section AA of FIG. four;

in FIG. 6 - suspension system (side view);

in FIG. 7 - a furnace for heating ceramic shells (longitudinal section);

in FIG. 8 - lower heater in the form of a coil and three rows of projections of cross sections of the shapes of the molded blades;

in FIG. 9 - refrigerator in the form of a water-cooled coil.

The ceramic shell used in the proposed device (Fig. 1, 2) contains, for example, molds 1 of cast GTE blades with retaining shelves arranged in a row with the smallest width (Fig. 7). Profitable parts of the forms form channel 2 in the form of a tube elongated along the length and in the plane of the row. On the walls of the channel 2, a pipe 3 is placed on top, on the ends - brackets 4 and washers 5 to remove the model mass and to extract the reinforcement from the shell. The external diameter of the channel 2 and pipe 3 does not exceed the thickness of a number of forms 1. The starting part of the forms (Figs. 1 and 2) consists of cavities of a “cone” with “scarves” 6 and a semiconical seed pocket 7, the cavity of which communicates with the top of the cavity of the “cone” capillary in the form of a sinusoid (Fig. 2).

If the cast GTE blades have wide retaining shelves, then the shapes of the cast blades are placed in the row plane at an angle to the vertical (Fig. 3). Moreover, on the edges of the retaining shelves raised due to the inclination, there are cavities of profits 8.

In the suspension system of the proposed device (Fig. 6 and 7), each ceramic shell stands on its crossbar 9 in the form of a molybdenum rod. The crossbar 9 itself is suspended on two carbon pendants 10 encircled by brackets 4. All carbon pendants 10 hang on two pendants consisting of molybdenum rods 11 with screwed earrings 12 and axles 13. To prevent staples 4 from hanging 10 on the last strung tungsten-rhenium "Springs" 14.

For pouring three ceramic shells, a collector 15 is located on top of their nozzles 3 (Figs. 5 and 6). The collector 15 (Figs. 4 and 5) consists of a channel 16 and a nozzle 17. There are three holes along the length of the channel with a step of τ — two side 18 and one central 19.

The diameters of the reservoir cavities are determined from the equality:

(h / d _{March ²⁾} = (h / d _{April ²} + (τ-d _2/2) / d ₁ ^{of 2),}

where d ₁ , d ₂ , d ₃ , d ₄ are the diameters of the channel 16, the pipe 17, the Central hole 19 and the side hole 18, respectively; h is the height of the holes 18 and 19.

To ensure a stable position, supports 20 are provided in the collector 15. A funnel 21 located on the upper screen 22 is used to fill the melt into the molds. The drain end of the funnel is located in the nozzle 17 of the collector 15.

The furnace for heating ceramic shells (Fig. 7) contains thermally insulated walls 23, a cover 24, an upper heater 25 with current leads 26, a lower heater 27 and a lower screen 28 with windows located on a water-cooled refrigerator 29.

The lower heater 27 and the water-cooled refrigerator 29 (Figs. 8 and 9) are made in plan in the form of zigzag coils. The gaps between the curved surfaces (zigzags) and the windows in the lower screen 28 provide the ability to move the flooded ceramic shells during crystallization. Moreover, the step τ of the indicated gaps and the location of the ceramic shells, as well as the holes in the collector 15 and the windows in the lower screen 28, is the same (Figs. 4, 7, 8, and 9). In the drawings are indicated: ceramic plugs - 30, semiconical seeds - 31 (Fig. 6).

The work of the proposed device is considered on the example of the manufacture of castings with a single crystal structure for GTE blades.

According to the existing technology, three ceramic casings are made by investment casting, each of which consists of nine forms 1 of GTE blades arranged in a row with the smallest width and a profitable part in the form of channel 2 with brackets 4 at the ends and pipe 3. Moreover, form 1 in shells They are made with starting parts with kerchiefs 6 and a semiconical seed pocket 7. (Blade height - 87 mm, length - 38 mm, width - 16 mm.) One collector 15 and one funnel 21 are made into three shells according to the lost wax models.

Next, prepare ceramic shells for pouring. Ceramic plugs 30 are inserted into the washbasins 5, and half-conic seeds 31 of Ni-W alloy with axial orientation [001] and azimuth [010] are parallel to the row plane into the seed pockets 7.

Prepare a smelter type UVNK. A water-cooled refrigerator 29 is installed. A lower screen 28 of carbon material of the TUM-1 brand is installed on it in the form of a plate with a thickness of 25 mm and with three windows 380 × 34 mm, located with a step of τ = 66 mm. The side walls 23 are insulated in a heating furnace for ceramic shells (hereinafter referred to as “the oven”) by thermal insulation, the upper heater 25 is installed. The lower heater 27 is installed in the form of a graphite coil 50 mm high, 18 mm thick with intervals between zigzags 48 mm and pitch τ = 66 mm - and the cover 24.

The suspension system is prepared: 11 graphite earrings 12 are screwed to molybdenum rods 12, on the axis 13 of which three pendants 10 are suspended in the form of technical carbon cords with a diameter of 8 mm with filling (TU 1916-003-18070047-98) with strung springs "14. Molybdenum crossbars 8 - ⌀ 20 mm, length 350 mm, are suspended from pendants 10. The prepared three shells are placed on the crossbars 9, clasping the pendants 10 with brackets 4. On top of the pipes 3 of the ceramic shells, a collector 15 with three holes located at a pitch of 66 mm is installed. On the earrings 12 put the upper screen 22 and install the funnel 21, deepening its lower drain end into the pipe 17 of the manifold 15.

The prepared suspension system is introduced into the lock chamber (not shown), vacuum it, open the vacuum shutter and the door of the furnace for heating ceramic shells. The suspension system is moved to a vacuum melting chamber (not shown) and introduced into the furnace. It is closed and lowered to a level at which the ends of the seed pockets 7 are 3 ... 5 mm higher than the lower plane of the lower heater 27. Ceramic shells are heated under vacuum of 5 · 10 ^-2 mm Hg. and at a temperature on the upper and lower heaters 1530 ° C. Simultaneously with the heating of the ceramic shells, a measured charge billet of an alloy like ZhS with a mass of 4.3 kg is melted. All shells are filled with melt through a funnel 21 and collector 15, heated to 1550 ° C, and at a temperature between shells of 1530 ° C. After pouring - incubated for 0.5 minutes. The filled shells are immersed in the cooling zone at a variable speed, with each shell passing through its heat front at the beginning - at a speed of (3 ± 0.5) mm / min. After 20 ... 30 mm immersion, the speed of movement was gradually increased to (10 + 2) mm / min. The poured ceramic shells are moved down 130 mm, after which the furnace is de-energized and when the temperature on the heaters drops below 900 ° C, they are raised to the initial level.

Further, according to the existing technology, castings are moved to the lock chamber, kept for 5 minutes, removed from the lock chamber, ceramics are beaten, the blades are cut from the LPS, and they are blown with electrocorundum. After etching, the blades are monitored for macrostructure and X-rayed.

Next, “cones” are cut from the blades, followed by deep etching. By the method of X-ray diffraction analysis of the etched “cones”, the deviations of the longitudinal axes from a given crystallographic orientation are determined. After heat treatment, the blades are sent to a capillary luminescent control.

The table shows the results of melting single-crystal vanes in the claimed device and the prototype. (According to the capillary luminescent control, X-ray diffraction analysis, the yield both by the proposed method and by prototypes (to the device and the sheath) was almost the same and amounted to 96 - 98% of the fit for the macrostructure.)

According to the prototypes, two ceramic shells were poured in one technological cycle, each of which had a two-tiered arrangement of blade shapes and two rows on one shell. The macrostructure of the prototype is mainly due to the nucleation of “parasitic” crystals on the “cones”, the tops of which began from the massive locks of the blades of the first tier.

On the blades cast on the proposed device, there was no grayish-pink coating characteristic of the blades cast on the prototype.

The table shows that the proposed device with a ceramic shell allows you to increase the yield by macrostructure by 10.9% and the utilization rate of the cast alloy is doubled.

It has been experimentally observed that with a decrease in the temperature of heating the shells to 1530 ° C, the thermal insulation resource increases to approximately 87-90 heats.

In the process of pouring in the proposed device there was no breakdown of the ceramic shell. When pouring in the device according to the prototype, one breakdown occurred.

Thus, the use of the proposed device and ceramic shell will allow casting high-quality single-crystal GTE blades with an increased yield without the use of a liquid metal mold, with a low consumption of cast alloy and thermal insulation, reduce equipment downtime and improve the working conditions of the smelter and, as a result, reduce the cost of manufacturing single-crystal blades GTE.

Claims (3)

1. A device for producing castings with a single-crystal and directional structure from heat-resistant nickel alloys, containing a lock chamber, a vacuum chamber, ceramic shells, a ceramic shell heating furnace located in a vacuum chamber and containing heat-insulated walls, a cover, a lower and upper heaters, a lower screen, separating the cooling zone and the heating zone, the upper screen placed on the heating furnace, a funnel for pouring the melt into ceramic shells mounted on the upper screen, and a hanging a system for moving ceramic shells, characterized in that it is equipped with a water-cooled refrigerator located under the heating furnace, a collector located on the nozzles of the ceramic shells and made with holes in the number of ceramic shells, while the water-cooled refrigerator and the lower heater are made in the form of coils, and the suspension the system comprises crossbars connected to the suspensions for installing ceramic shells and is configured to allow the movement of ceramic shells during melt crystallization in the cooling zone through a window formed in the lower screen and zigzag between the lower heater and the water-cooled cooler. 2. A ceramic shell for producing castings with a single-crystal and directional structure made of heat-resistant nickel alloys, containing molds of cast parts with starting and profitable parts, characterized in that the shapes of cast parts are arranged in a row in the shell, and their profitable parts form a channel on which is placed a nozzle for pouring the melt, and at the ends of the channel there are brackets for connecting the shell to the suspension system. 3. The ceramic shell according to claim 2, characterized in that when casting the blades of gas turbine engines, the shapes in the row plane are located at an angle to the vertical, while the profits cavities are made on the retaining shelves of the castings of the blades.

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