JP2007090434A - Method and apparatus for attaching metallic casting core to ceramic casting core - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for attaching a refractory metal casting core to a ceramic casting core by investment casting. <P>SOLUTION: A fixture 204 in a casting core assembly has a function of fixing a ceramic casting core 210 and a refractory metal core 212 to be engaged therewith. The fixture 204 comprises a plurality of tooling balls 222 for fixing the refractory metal core 212, a clamp 224 and a pivotal retaining bar 230, and comprises a clamp 240 for supporting the refractory metal core 212. After the fixing of the core, a slurry comprising zircon and aqueous colloidal silica is introduced into the joint between the cores, and the slurry is infiltrated into the joint by the vibration of a vibration stand to which the fixture is attached. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to investment casting. More particularly, the present invention relates to investment casting core assemblies.

  Investment casting is commonly used in the aerospace industry. Various examples relate to the casting of gas turbine engine components. Examples of parts include various blades, vanes, seals, and combustion chamber panels. Many of these parts are cast cooling paths. The path can be formed by a sacrificial casting core.

  Examples of cores include ceramic cores, refractory metal cores (RMC), and combinations thereof. In one example combination, the ceramic core forms a supply path, while the refractory metal core forms a cooling path that extends from the supply path through the inner wall of the part. The cores can be assembled together and secured with a ceramic adhesive. An example ceramic adhesive is alumina-based. For example, the adhesive may comprise a binder such as alumina powder and colloidal silica.

After the initial casting of the part (eg, from a nickel or cobalt based superalloy), the cast shell or core is removed in a broken fashion. The removal of an example shell is primarily mechanical. The removal of an example core is primarily chemical. For example, the core is removed by chemical leaching. One example leaching involves the use of an alkaline solution in an autoclave. Examples of leaching techniques are disclosed in US Pat.
US Pat. No. 4,141,781 US Pat. No. 6,241,000 US Pat. No. 6,739,380

  Accordingly, one aspect of the present invention includes a method of attaching a metal cast core to a ceramic cast core. The insertion site of the metal casting core is inserted into the insertion site of the ceramic casting core. A slurry is introduced between the metal casting core and the ceramic casting core.

  In various embodiments, the metal casting core can include a refractory metal-based substrate (eg, optionally coated). This method is used to form a turbine blade core assembly or a turbine vane core assembly. Heated to cure the slurry. Metal and ceramic casting cores are vibrated during the introduction of the slurry. The part is inserted when the ceramic casting core is not fired. The slurry comprises zircon and water soluble colloidal silica.

  Another aspect of the invention includes an apparatus for manufacturing a cast core assembly. The apparatus has means for fixing the ceramic casting core. The apparatus has means for securing a metal cast core having an insertion site inserted into a receiving site of the ceramic cast core. The apparatus has means for vibrating the ceramic and metal casting cores.

  In various embodiments, the means for securing includes means for adjusting the relative position of the ceramic and metal casting cores.

  In various manufacturing situations, ceramic adhesive binders can exhibit rejection with additional components such as refractory metal cores. As another method, a special slurry has been developed to fix the core based on the slurry used for shelling. The example slurry consists essentially of a combination of 79:21 zircon by weight, water-soluble colloidal silica, a surfactant, and sufficient added water to achieve the desired viscosity. Example ranges for the ratio of zircon to colloidal silica are 70:30 to 80:20.

The example surfactants are essentially linear alcohol based surfactants available under the trademark ANTAROX BL225 from Solvay Chemicals, Inc. of Houston, Texas. The amount of surfactant in the examples is 0.05-0.15% (volume%), more strictly less than 0.1%, for example 0.07-0.09%. Optional additives are small amounts (eg, 0.005 to 0.015% by volume) of polydimethylsiloxane (available under the trademark BURST RSD-10 from Hydrolabs, Wayne, NJ), Helps to destroy bubbles. The example slurry has a density in the range of 2.87-2.96 g / cm ³ . The slurry of the example has a hydrogen ion concentration in the range of 9.0 to 10.5 (pH). The example slurry has a viscosity of 25 ± 2 centipoise (cP). However, other viscosities (eg, 18-25 centipoise) are suitable for certain situations, particularly thinner slurries.

  FIG. 1 illustrates a method 20 of an investment casting mold embodiment. Other methods are possible, including various prior art methods and methods that have not yet been developed. One or more metal core members are formed (step 22) (eg, made of a refractory metal such as molybdenum or niobium, stamped from sheet metal or otherwise cut) and coated (step 24). Suitable coating materials include silica, alumina, zirconia, chromia, mullite and hafnia. Desirably, the refractory metal and the coating have approximately the same coefficient of thermal expansion (CTE). The coating is applied by any suitable visual (line-of-sight technique) or non-visual (non-line-of-sight technique) (eg chemical vapor deposition (CVD), physical vapor deposition (PVD)). ), Plasma spraying, electrophoresis, and sol-gel methods). Individual layers are typically 0.1 to 1 mil thick. Metal cores to protect layers from layers of Pt, other precious metals, Cr, Si, W, Al, or other non-metallic materials in combination with a ceramic coating to protect against erosion and dissolution by molten metal In some cases, the member may be coated.

  One or more ceramic cores are also formed (step 26) (e.g., by forming and firing processes, or by including silica in this process). One or more coated metal core members (hereinafter referred to as refractory metal cores (RMC)) are combined into one or more ceramic cores (step 28). As noted above, the assembly also includes the use of a ceramic slurry as described below. The core assembly is then overmolded with a sacrificial material, such as natural or synthetic wax (step 30) (eg, placing the assembly in a mold (wax mold) and molding the wax around it) By doing). Multiple assemblies may be included in one specific mold (brazing mold).

  The overmolded core assembly (or group of assemblies) forms a casting pattern (model) having an external shape that corresponds primarily to the internal shape of the part being cast. This pattern is then attached to the shelling fixture (step 32) (eg, by brazing between the fixture end plates). The pattern is then shelled (step 34) (eg, by one or more stages such as slurry immersion, slurry spray, etc.). After the shell is formed, it is dried (step 36). Drying provides the shell with at least sufficient strength or other physical integrity characteristics to allow subsequent processing. For example, the shell containing the investment casting core assembly is completely or partially removed from the shelling fixture (step 38) and sent to a dewaxing device (eg, a steam autoclave) (step 40). In the dewaxing device, the vapor dewaxing process (step 42) removes most of the wax, leaving a core assembly secured within the shell. The shell and core assembly mostly forms the final mold. However, the dewaxing process usually leaves wax and by-product hydrocarbon residues inside the shell and on the core assembly.

  After dewaxing, the shell is sent to a furnace (eg, containing air or other oxidizing atmosphere) (step 44) where it is heated (step 46) to strengthen the shell and remove any wax residue. The hydrocarbon residue is converted to carbon (eg, by evaporation). Oxygen in the atmosphere reacts with carbon to produce carbon dioxide. Carbon removal is beneficial in reducing or eliminating the formation of harmful carbides in metal casting. The removal of carbon provides the additional benefit of reducing the possibility of clogging the vacuum pump used in the next stage of work.

  The mold is removed from the atmosphere furnace, cooled and inspected (step 48). The mold is seeded by placing a metal crystal seed in the mold (step 50) to set the final crystal structure of unidirectional solidification casting or single crystal casting. Other techniques may be applied to other unidirectional solidification and single crystal casting techniques (for example, the shell shape serves as a means for selecting crystal grains) or other fine structure castings. The mold is sent to a casting furnace (eg, placed on a chill plate in the furnace) (step 52). The casting furnace is filled with a vacuum or a non-oxidizing atmosphere (eg, inert gas) (step 54) to prevent oxidation of the cast alloy. The casting furnace is heated (step 56) to preheat the mold. This preheating serves two purposes. That is, to further harden and strengthen the shell and to preheat the shell for molten alloy castings to prevent thermal shock and premature solidification of the alloy.

  While the pressure is still reduced after preheating, the molten alloy is cast into a mold (step 58), and the mold is cooled to solidify the alloy (step 60) (eg, removed from the high temperature zone of the furnace). rear). After solidification, the reduced pressure is released (step 62), and the chilled mold is removed from the casting furnace (step 64). The shell is removed in a shell removal process (step 66) (eg, mechanical destruction of the shell).

  The core assembly is removed in a decore process (step 68), leaving a cast (eg, the final part metal prototype). The multi-stage decore process according to the present invention is shown below. The casting is machined (step 70), processed by chemical or thermal processing (step 72), and coated (step 74) to form the final part. Some or all of machining or chemical or thermal treatment is performed prior to decore.

  FIG. 2 shows details of the core assembly apparatus 200. The apparatus includes a shaking table 202 that vibrates the assembly. Each assembly is secured by a fixture 204 on the shaking table. The exemplary assembly (FIG. 3) is comprised of a cast ceramic feedcore 210 and a refractory metal core 212 in a trailing edge slot made of refractory sheet metal. FIG. 3 further shows details of the fixture 204 of the embodiment. The fixture includes a base 220 that attaches to the shaking table.

  The fixture includes the function of fixing the associated feed core 210. These functions include a plurality of tooling balls 222 that are precisely fixed to the base to engage the feed core 210. The clamp 224 is attached to the base to engage the feed core after it is placed on the tooling ball. The rotary fixing bar 230 is arranged to engage with the base of the feed core in order to fix the feed core in place.

  The fixture includes the function of fixing the corresponding refractory metal core 212 to the feed core. In the fixing of the embodiment, the tip portion of the refractory metal core is inserted into the groove of the leg portion on the rear edge side of the feed core. The function of supporting the refractory metal core includes a clamp 240 that grips the rear end portion of the refractory metal core. The clamp is attached to the gantry structure 242. The example gantry structure is slidably mounted for movement along direction 500. The position of the gantry (and hence the refractory metal core) is adjusted by the micrometer device 250. The micrometer device of the embodiment presses the gantry against the root of the feed core to make a precise adjustment of the position of the refractory metal core along the feed core.

  After core attachment and positioning (step 300) (FIG. 4), a slurry bead is applied to the joint (step 302). Slurry permeates the coupling portion by vibration of the shaking table (step 304). After infiltration, the slurry is dried (step 306). The slurry is applied when the feed core is not fired. The core assembly is then removed (step 308) and fired to cure the feed core (step 310). Moreover, the slurry is further hardened by firing to bond the cores more strongly. The firing may be performed separately or simultaneously with the shell firing described above.

  Conveniently, the slurry has an effective viscosity to facilitate the penetration of the slurry into the joint promoted by vibration. However, shrinkage due to drying should not be so great as to cause mechanical failure. The coefficient of thermal expansion should also be effective to maintain bonding during the heating associated with firing and casting. The characteristics and configurations of the above examples are believed to be particularly effective.

The flowchart which shows the investment casting process of an Example. The perspective view of a core assembly apparatus. FIG. 3 is a perspective view of a fixture of one of the devices of FIG. 2 that secures the investment casting core during joining. The flowchart which shows the core coupling | bonding process of an Example.

Explanation of symbols

204 ... Fixing tool 210 ... Ceramic casting core 212 ... Refractory metal casting core 222 ... Tooling ball 224 ... Clamp 230 ... Rotary fixing bar 240 ... Clamp

Claims (16)

Insert the insertion part of the metal casting core into the receiving part of the ceramic casting core,
A method of joining a metal cast core to a ceramic cast core, comprising introducing a slurry between the metal cast core and the ceramic cast core.   The joining method according to claim 1, wherein the metal casting core includes a refractory metal base.   The method according to claim 1, wherein the method is used for manufacturing a turbine blade core assembly or a turbine vane core assembly.   The method of claim 1, further comprising heating the slurry to cure the slurry.   The joining method according to claim 1, further comprising vibrating the metal casting core and the ceramic casting core during the introduction.   The bonding method according to claim 1, wherein the insertion is performed when the ceramic casting core is not fired.   The bonding method according to claim 1, wherein the slurry comprises zircon and water-soluble colloidal silica.   The bonding method according to claim 6, wherein the slurry contains water-soluble colloidal silica having 20 to 30% (wt%) of the zircon content.   The bonding method according to claim 1, wherein the slurry comprises a surfactant. The slurry is
A density of 2.87-2.96 g / cm ³ ;
A hydrogen ion concentration of 9 to 10.5 (pH);
A viscosity of 25 ± 2 centipoise (cP);
The coupling method according to claim 1, wherein: The slurry is
A density of 2.87-2.96 g / cm ³ ;
A hydrogen ion concentration of 9 to 10.5 (pH);
A viscosity of 18-27 centipoise (cP);
The coupling method according to claim 1, wherein:   A bonding method comprising using a slurry comprising zircon and water-soluble colloidal silica to secure a metal casting core to a ceramic casting core.   The method of claim 12, further comprising heating the slurry to cure the slurry. Means for supporting the ceramic casting core;
Means for supporting a metal casting core having an insertion site inserted into a receiving site of the ceramic casting core;
Means for vibrating the ceramic casting core and the metal casting core;
A device comprising: The ceramic casting core;
The metal casting core;
A slurry comprising zircon and water-soluble colloidal silica between the metal casting core and the ceramic casting core, wherein the slurry is vibrated by vibration means;
The device according to claim 14, which is a combination of the above.   The apparatus of claim 14, wherein the means for supporting the metal cast core comprises means for adjusting the relative position of the ceramic cast core and the metal cast core.

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