KR20000016339A - Method and apparatus for making directional solidification castings - Google Patents

Abstract

PURPOSE: A manufacturing method for a large, directionally solidified cast article is provided to have a cast height higher than 300 millimeters. CONSTITUTION: A method and apparatus for producing large, directionally solidified cast articles having a cast height greater than 200 mm, and preferably greater than 300 mm is described. The casting mold reliability, as well as the casting equipment, is improved by proportioned pouring of a molten super alloy into a casting mold where the mold is protected by suspender elements. The cast articles made by the inventive method are of particular interest to aircraft and power generation equipment, and include, but are not limited to, components such as blades, airfoils, buckets, nozzles, and the like.

Description

Method and apparatus for producing directional solidified casting

It is known that the properties of superalloys can be improved by directional casting techniques to produce unidirectional columnar granular or monocrystalline products. Single crystal products differ greatly from conventional polycrystalline products by the absence of boundaries between various arbitrarily oriented crystals. Recently, it is desirable to have the option of monocrystalline directional solidified casting products or polycrystalline directional solidified casting products for industries utilizing superalloy cast products, such as the aircraft and land based gas turbine turbine industries.

The directional solidification casting with monocrystals and polycrystals is by a unidirectional solidification process in which a casting shell mold containing molten superalloy material is withdrawn from a heated furnace. The molten alloy gradually solidifies from the bottom of the casting mold to the top. For single crystal castings, crystal seeds with crystallographic orientations such as < 01 1 > are injected at the base of the casting mold.

One process for producing a directional solidified casting is to inject molten metal into a mold in a heating table, the base of the mold is cooled by a chill plate, and the crystallization of the molten metal is continued by gradually removing the mold from the heating table. By appearing, the bottom of the mold is cooled upward by convective radiation to solidify the casting product. This process is disclosed in US Pat. No. 3,857,436. Another method of making a directional solidified casting product is to inject a molten metal into a superheated mold disposed in a superheater, and to exit the mold from the furnace into a liquid coolant bath, where the coolant bath is lower than the solidus temperature of the casting metal. Has a temperature. This process is disclosed in US Pat. No. 3,915,761. Various variations of these methods are disclosed in Russian Federation Republic Patent No. 201010 and Russian Proof of Work USSR N1061926.

The aforementioned method is defective in that the casting product produced has a limited length size and cross section. This is due in part to the lack of reliability of the casting molds during the casting process. For large casting molds, i.e., casting molds of 200 mm or more in length, hydrostatic forces act on the casting mold when molten alloy is injected into the mold and the mold continues to cool. These forces tend to surround the casting mold and the resulting casting product outline. The mold itself is often broken in the casting of large products. Thus, there is a need for a method and apparatus for producing large casting products, ie large casting products of about 20 mm or more in length, where the casting molds are reliable throughout the casting process.

Summary of the Invention

The present invention satisfies the above-mentioned needs by providing a method for producing a directional solidified casting product characterized by an improvement in the reliability of the casting mold, the method comprising the steps of heating the casting mold of the heating table of the casting furnace to a predetermined temperature; ; Injecting the molten superalloy into the casting mold of the heating zone in an initial amount sufficient to maintain the molten superalloy height up to the solidified front top of the foundry product so as not to interfere with crystal growth of the directional solidified casting product; Injecting the molten superalloy into the casting mold at a rate such that the molten superalloy is directionally solidified simultaneously in the casting mold and the height of the molten superalloy is maintained above the solidification front by withdrawing the mold from the heating stand to the cooling stand; And terminating the injection of the molten superalloy such that the height of the solidified portion of the cast product is at least half of the total height of the cast product.

In another aspect of the invention, a suspender system is provided that improves the reliability of the mold during the casting process. The suspender system consists of a horizontal load-bearing beam or rod which is enclosed close to the casting mold in the casting furnace. Another embodiment of the suspender system includes coupling the beam or rod to a manufacturing apparatus of the mold itself. This is accomplished by forming a pattern from wax or resin material depending on the shape of the mold.

In another embodiment of the invention, an injection riser is provided that is attached to the mold along the height of the vertical side of the mold. The injection riser has at least one passage, preferably one or more passages into the inner cavity of the mold, and a fixed injection cup is telescope coupled to the injection riser. The infusion cup is placed near the top of the furnace.

The following figures and detailed description further illustrate the invention.

TECHNICAL FIELD The present invention relates to a method and apparatus for producing a directional solidified casting, and more particularly to a product produced therefrom. The invention also relates to a method and apparatus for improving the reliability of ceramic molds used in casting processes for products.

1 is a schematic diagram of a ceramic shell mold for a cast product blade with its base raised in a suspender system, FIG.

2 is a schematic diagram of a ceramic shell mold for a cast product blade with its base facing downwards in a suspender system,

3 is a schematic side view of a ceramic shell mold for a cast product blade at point A-A of FIGS. 1 and 2;

4 is a schematic view of a ceramic shell mold having an injection riser, at least one passage into the cavity of the mold and a fixed injection cup,

5 is a schematic diagram of a casting pattern of a shell mold, a skeleton design of a mold having a suspender system coupled into a mold pattern, a suspender system flange and a starter flange in the mold during initiation of directional solidification of the molten superalloy.

The present invention relates to a method and apparatus for producing large, directional solidified casting products having a casting height of at least 200 mm, preferably at least 300 mm. As a result of the present invention, not only the casting apparatus but also the casting mold reliability is improved. Casting products made by the method are particularly important for aircraft and power generating devices, including but not limited to components such as blades, airfoils, buckets, nozzles, and the like.

In general, the present invention may be described as heating molds, shells, shell molds, and casting molds, and these terms herein refer to molds that normally receive ceramic waters at a predetermined temperature in the heating zone of the casting presbyopia.

The predetermined temperature is the temperature of the mold sufficient to accommodate the molten superalloy material before the crystallization or solidification of the superalloy begins. Preheating temperatures are recommended for molds above the superalloy melting temperature. The casting furnace atmosphere is generally kept in a vacuum. The mold will have starter crystal seeds in its cavity to initiate growth of the desired crystallographic oriented single crystal product. As a result, the mold can be designed as a polycrystalline or monocrystalline cast product.

After heating the mold to a predetermined temperature, a molten superalloy (also referred to herein as a melt) is injected into the mold. The superalloy metal will be heated and melted in individual compartments or in individual furnaces of the casting furnace. The temperature of the molten superalloy (melt) at the moment of injection into the mold will be about 100 ° C. to about 120 ° C. higher than the temperature corresponding to the initial stage of crystallization, but somewhat lower than the temperature of the mold.

The process according to the invention is initiated after the directional solidification of the molten superalloy is initiated after a sufficient amount of molten superalloy has been injected into the mold so that the level or height of the molten superalloy on top of the solidification front does not obstruct or difficult crystal formation during the directional solidification process. Suitable for A sufficient initial amount of molten superalloy injected into the mold can be from about 10% to about 40% of the mold volume, preferably from about 20% to about 30% of the mold volume. When a sufficient amount of molten superalloy is injected into the mold, the directional solidification of the molten superalloy begins by withdrawing the mold from the heating stand to the cooling stand. The cooling stand may be a chill plate or a liquid metal cooling bath, and other suitable cooling means. In the present specification, the present invention will be described as a cooling stand which is a liquid metal cooling bath such as liquid tin or aluminum. It is also noted that when directionally solidifying the casting product, a baffle may be present between the heating and cooling stages which further increases the temperature gradient.

When initially injecting a sufficient amount of molten superalloy from about 20% to about 30% by volume into the mold, additional injection of molten superalloy into the mold is then performed simultaneously with the directional solidification process through the porous cup. Desired levels of molten superalloy may be provided on the solidification front of the cast superalloy metal so as not to interfere with crystal growth of the cast product.

Parasitic grain growth can occur in various crystallographic directions if the initial volume of molten superalloy injected into the mold is not sufficient before the start of the solidification process. Therefore, those skilled in the art will be able to determine the desired amount of molten superalloy metal injected into the mold to promote monocrystalline or polycrystalline unidirectional solidification of the casting product. As mentioned above, about 20% to 30% of the mold volume is preferred as the initial amount of molten superalloy injected.

In the present invention, when the injection of the melt is finished, the height of the solidified portion of the casting product should be at least 1/2 of the total casting height of the product. This also serves to reduce the mechanical load on the ceramic mold. In order to produce a good acceptable casting, the height of the molten supermetal above the solidification front is of sufficient height so that turbulence does not affect the solidification of the casting product. The suggested height can be from about 30 mm to about 70 mm. Again, those skilled in the art can determine the appropriate height without overtesting according to mold size and shape.

Another component of the present invention that also improves the reliability of the mold is a particular suspender system. The shell mold may be positioned into the suspender system in the casting furnace before the start of the casting process, or the suspender system may form part of the actual shell mold during the pattern step of making the shell mold. In a first embodiment, the suspender system comprises a suspender component that constitutes a horizontal load-bearing beam that closely surrounds or wraps around the shell mold at a point or location about one quarter of the mold height spaced apart; Contains ingredients. The beam supports its static pressure when molten superalloy is injected into the mold. The beam or rod consists of molybdenum, graphite, graphite based component materials, and mixtures thereof. Referring to FIG. 1, the shell mold 1 is suspended in two upper horizontal load-bearing beams 2 located in the opening of the upper graphite insert 3. The next pair of horizontal beams 4 is then placed in position. The beam closely surrounds the mold side surface and is secured with a wedge of graphite, molybdenum, graphite-based compositions and mixtures thereof to place the fixed position of the shell mold in the suspender system. The amount of beam used depends on the height, width and cross-sectional size of the mold. For example, when the width of the casting is less than 200 mm, the horizontal beam should be located about every 100 ± 50 mm. Those skilled in the art can use basic mechanical theory to adjust the amount of beam and travel distance to wrap and support the mold during casting. This suspender system is suspended in a casting furnace by two vertical hangers of molybdenum, graphite, graphite-based composition material and mixtures thereof. The mold is then fixed in the suspender system. In FIG. 2, the cell mold 5 is suspended on two upper horizontal load-bearing beams 6 located in the upper graphite insertion opening 7. 3 is a cross-sectional view of FIGS. 1 and 2. The shell mold is suspended on two upper vertical load-bearing beams 10 located in the upper graphite insertion opening 11. The next pair of horizontal beams 12 is disposed at the next location.

In another embodiment of the suspender system, there is provided a suspender component or component such as a beam, bar and rod, which itself is joined as part of a mold. Suspender components or components are disposed in the mold pattern of the mold on the outside of the mold. The mold is first manufactured from a wax or plastic pattern that will later receive a ceramic slurry coating to produce a ceramic mold for casting of the product. In the initial stage of forming the wax or plastic pattern, the horizontal beam and the vertical support beam are placed as a framework in the mold casting pattern. For example, the framework is in the shape of a cylindrical member having a flange at the impact end on the outer surface or the outer surface of the mold. The frame cross section for the suspender component forms an outer cavity on the mold. When the mold is made with slurry castings, suspender components, molybdenum, graphite, graphite-based compositions and mixtures thereof according to methods known in the art, the rods or beams are placed inside the framework on the mold and the impingement ends of the framework Sealed with ceramic slurry. The framework members are disposed above the start of the mold top and are evenly distributed along the entire height of the mold. As described above in the method according to the invention, the mold is placed on the hanger of the casting presbyopia to be heated to a predetermined temperature. FIG. 5 shows the pattern of the framework 20 with the casting pattern 19 and the flange 21 and the starting stage 22.

In addition to the suspender element according to the invention, another feature of the invention is provided with an injection cup and an injection riser. The injection cup is placed in a mold in the heating zone of the casting furnace. In order to eliminate the spread of molten superalloy upon injection into the mold, the injection cup has an elongated side that is introduced at the base of the mold if there is no internal core in the mold. If the inner core is in the mold, the cup is introduced into the particular injection channel. In yet another embodiment of the present invention, an injection riser is disposed on one transverse side of the mold to eliminate turbulence due to molten superalloy injection above the solidification line. This consists of a casting pattern for the mold. The injection risers are connected along the entire height of the pattern and are joined along the inclined passageway at an angle of -70 ° to + 70 ° with respect to the horizontal plane. In order to also serve as filtration when molten superalloy is injected into the mold, the cross section of each passage should be about 1 mm to 3 mm. Thus, when a pattern for a mold is produced, both the injection and suspender systems can be combined into a pattern, which will eventually become part of the final mold. Referring to FIG. 4, the ceramic shell mold 13 has an injection riser 14 disposed on the transverse side of the mold in a passage 15 having a small cross section. The infusion cup 16 is fixed and placed near the top of the furnace. Also shown is a fixed cup 17 that simultaneously injects molten superalloy into two clusters of a mold.

In the present invention, the molten superalloy is injected into the mold through a fixed cup disposed on the top surface of the furnace. The cup is telescoped into the injection riser. When wishing to inject molten superalloy into two or more clusters at the same time, a fixed infusion cup is used having an injection member for each injection riser.

As mentioned above, the molten superalloy injected horizontally through the passages inclined at the proper angle from the riser provides a smooth movement of the molten superalloy without any turbulent streams that can cause parasitic granular growth of the casting product. In addition, passages with sufficiently small cross sections help to reduce the formation of nonmetal depressions in the casting product.

The following examples further serve to illustrate the scope of protection of the present invention, but are not limited thereto.

Example 1

Casting furnaces with a liquid cooling bath (Russian commercial model unit UVNK-8P) are used to produce large castings according to the invention. The shell mold is for a large airfoil having a height of 400 mm, a cord cross-sectional area of 180 mm and a width dimension of the base of 200 mm. The shell mold had a thickness of about 8 mm to 10 mm, the base of which solidified upwards. The mold had a single crystal seed in the starting cavity and disposed inside a particular suspender, as shown in the figures of FIGS. 1 and 3. The suspender system included two vertical molybdenum hangers consisting of rods of about 20 mm diameter and was joined by a graphite insert (wedge) with two openings. The distance between the openings is approximately equal to the thickness of the shell mold.

The load is transferred to the horizontal beam of the suspender in order to reduce mold deformation due to its own weight and the influence of the molten superalloy static pressure. These beams wrap around the mold and effectively prevent its deformation. The horizontal load-bearing beam is made of molybdenum and has a cross section of 10 mm x 20 mm.

The injection cup has a gauge hole and is disposed inside the mold cavity in such a way that the injection hole is placed about 200 mm high from the top edge of the mold.

The corrosion-resistant nickel-based superalloy of the Russian type ZhSKS was melted in an induction furnace having a crucible volume of about 20 to 25 kilograms. The mold was preheated to a temperature of 80-100 ° C. above the melting temperature of the superalloy. The temperature of the superalloy in the crucible was raised to about 1560 ± 20 ° and molten superalloy was injected into the mold through the injection cup. Once 4 to 5 kilograms (about 20% of the mold volume) of the molten superalloy were injected into the mold, the directional solidification process started by lowering the mold from the heating zone to the cooling zone, and the molten superalloy was inducted when the mold was removed from the cooling zone. From the mold at the same time.

When the injection of the molten superalloy into the mold had ended, about half of the mold had already dropped to the cooling flux. The mold continued to descend until the mold was completely immersed in the cooling zone with the superalloy. The solidified casting is removed from the suspender and from the ceramic mold to reveal the microstructure of the casting product. The use of single crystal seeds in the starting cones, crystal orientation selection and directional solidification processes provided casting products having a single crystal structure in a desired direction depending on the overall height of the casting.

Example 2

In this embodiment the base of the airfoil solidified downward. The method of positioning in the suspender system is shown in FIG. Horizontal load-bearing beams were made of sintered graphite. In this example, the directional solidification process was filled with about 30% of the mold volume (about 7 to 7.5 kilograms of molten superalloy) with a nickel-based superalloy, Russian type ZhS. The method of assigning control of the injection of the molten superalloy and the directional solidification process is as shown in Example 1. The large airfoil castings thus produced had single crystal structures along the entire height.

At the same time, the use of an assigned injection step of molten superalloy with a directional solidification process and the use of a specific mold suspender system improves the reliability of the shell mold and the casting apparatus. The efficiency of the directional solidification process is further improved and allows for high quality large profile and blade casings of 200 mm or more in height, preferably at least about 300 mm. This applies to monocrystalline casting products and polycrystalline casting products.

Example 3

This embodiment further illustrates the present invention. One of the transverse sides of the large airfoil (blade) pattern is inclined about 70 ° with respect to the horizontal plane and has an injection riser coupled with the casting cavity along its entire height by about eight passages 2 mm in diameter. Frames of suspender components are prepared, where the frames have flanges on the impact ends.

After the pattern was made, the ceramic cell was prepared according to slurry dipping techniques known in the art and complexed to 1250 ° C. for about 4 hours. The molybdenum suspender component was positioned in a cooling bath inside the ceramic frame. The frame impact end was then sealed with a ceramic slurry. The mold and suspenders were placed in a casting furnace, the Russian commercial model UVNK-8P, and the heating chamber was evacuated to 1 x 10 ^-3 mm mc. Superalloy of Russian type ZhS was melted in induced presbyopia. Molten superalloy was injected into the mold via a sloped passage through a fixed cup. A fixed cup was telescoped into the injection riser. The injection process was performed in two steps. First, about 20% of the molten superalloy of the mold volume was injected into the mold, and solidification began by dropping the mold into the refrigerant at a rate of 10 mm / min. After solidification began in the beginning of the mold, the injection of the molten superalloy continued, while the injection of the molten superalloy continued while the exit of the mold from the heating zone of the mold continued. At the moment when the molten superalloy molten metal was injected, the mold was evacuated to about half the height of the mold. The mold with the molten superalloy dropped completely until it was completely immersed into the liquid metal cooling bath.

After the solidification process was terminated and the preheater was shut off, the mold was separated from the coolant to separate the solidified casting from the suspender and the ceramic to separate the microstructure of the cast product. The cast product was 450 mm in height and had a single crystal structure in the [0 0 1] direction over the entire height. In the course of the directional solidification process, the ceramic mold is absolutely free of deformation. Suspender components were protected with a coolant metal bath.

This process was repeated using a passage of about 3 mm inclined at an angle of about + 70 °. When the diameter of the passage is more than 3 mm, the passage does not act as a filter and coarse nonmetallic inclusions can pass through the casting. It may be difficult to produce passages of diameter up to 1 mm.

The method according to the invention allows castings, monocrystalline and polycrystalline castings of large articles with the desired geometric size. Suspender components are reusable for the directional solidification process.

Claims (22)

In the manufacturing method of the directional solidification casting product which the improvement of the casting mold or the reliability of a mold exhibits, Heating the casting mold to a predetermined temperature in a heating zone of the casting presbyopia, Injecting the molten superalloy into the casting mold of the heating zone by an initial amount sufficient to maintain the level of the molten superalloy on the solidified front top of the casting product such that crystal growth of the directional solidified casting product is not hindered; Directional solidifying the molten superalloy simultaneously by withdrawing the mold from the heating zone while further injecting the molten superalloy into the foundry mold at a rate capable of maintaining the molten superalloy level above the solidified front; Injecting the molten superalloy into the casting mold to terminate injection of the molten superalloy into the casting mold such that the height of the solidified portion of the cast product is greater than ½ of the total height of the cast product. The method of claim 1, And wherein the aromatic solidified casting product is a monocrystalline or polycrystalline product. The method of claim 1, And the casting mold is heated above the melting temperature of the molten superalloy. The method of claim 1, A method for producing a oriented solidified product, wherein the initial amount of molten superalloy injected into the mold is 20% to 30% of the mold volume. The method of claim 1, And wherein the molten superalloy level above the solidification front is about 30 mm to 70 mm high. The method of claim 1, And said cooling zone comprises a liquid metal bath. The method of claim 1, And the cooling stage comprises a chill plate and a space without auxiliary heating. The method of claim 1, Wherein said casting mold comprises one or more internal cavities for producing a plurality of casting products. The method of claim 1, Wherein said casting mold is suspended vertically in said furnace, said mold being wrapped by a suspender system. The method of claim 9, The suspender system comprises a horizontal and vertical suspension component. The method of claim 10, Wherein said suspension component is made of a material selected from molybdenum, graphite, graphite-based compositions and mixtures thereof. The method of claim 1, Wherein said casting mold is produced in a pattern having a suspender frame. The method of claim 12, Wherein said suspender frame has a suspender element disposed in an outer mold cavity and the end of the suspension element is sealed with a ceramic slurry. The method of claim 1, Wherein the mold has at least one passage introduced into the interior cavity of the mold and has an injection riser attached on its lateral side end. The method of claim 14, Wherein the mold has at least one inner cavity and each cavity is at least one passage from an injection riser introduced into the inner cavity. The method of claim 15, Wherein said passageway has an angle between about + 70 ° and -70 ° relative to a horizontal plane. The method of claim 16, Wherein said passageway has a diameter of at least about 1 millimeter. The method of claim 14, And the infusion riser has a fixed infusion cup introduced telescopically. A product made according to the method of claim 1. The product according to claim 14, which is a single crystal. In the apparatus for casting a directional solidified product, Induction furnace for heating metal, heating means coupled to induction furnace for heating metal, heating means for preheating the mold and chamber, injection means for induction furnace for injecting heated metal into the preheated mold, chamber for preheating the mold Apparatus for casting a directional solidified product having injection means therein, mold suspender means in a chamber for preheating the mold, a cooling chamber and means for maintaining a controlled atmosphere in each chamber. A casting mold having an inner casting cavity having a size for a casting product and an outer cavity for the suspender element.