EP0347344B1 - Ceramic shell mold for investment casting and method of making the same - Google Patents

Ceramic shell mold for investment casting and method of making the same Download PDF

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Publication number
EP0347344B1
EP0347344B1 EP19890420208 EP89420208A EP0347344B1 EP 0347344 B1 EP0347344 B1 EP 0347344B1 EP 19890420208 EP19890420208 EP 19890420208 EP 89420208 A EP89420208 A EP 89420208A EP 0347344 B1 EP0347344 B1 EP 0347344B1
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EP
European Patent Office
Prior art keywords
ceramic
shell mold
ceramic material
alumina
layers
Prior art date
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Expired - Lifetime
Application number
EP19890420208
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German (de)
English (en)
French (fr)
Other versions
EP0347344A3 (en
EP0347344A2 (en
Inventor
Paul Randolph Johnson
Eliot Scott Lassow
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Howmet Corp
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Howmet Corp
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Publication date
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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22C—FOUNDRY MOULDING
    • B22C9/00—Moulds or cores; Moulding processes
    • B22C9/06—Permanent moulds for shaped castings
    • B22C9/061—Materials which make up the mould

Definitions

  • the invention relates to investment casting and, more particularly, to a ceramic shell mold for investment casting high melting point metals and alloys and a method for forming the ceramic shell mold according to the preambles of claims 10 and 1, respectively.
  • silica bonded ceramic shell molds In the investment casting of high melting point metals and alloys, silica bonded ceramic shell molds conventionally have been used to contain and shape the molten material. Bulging and cracking of conventional silica bonded ceramic shell molds have been experienced in the investment casting of recently developed high melting point alloys at casting temperatures above 1480° C because of the low flexural strength and low creep resistance of such shell molds at the higher casting temperatures. When the ceramic shell mold bulges, the dimensions of the resultant casting are not accurate. Significant cracking can result in failure of the ceramic shell mold and runout of the molten material.
  • ceramic shell molds having an alumina, mullite, or other highly refractory oxide bond have been used. These bond materials normally are incorporated into the shell molds via slurries or suspensions of the ceramic material. Ceramic shell molds bonded with highly refractory oxides, however, suffer from one or more of the following disadvantages.
  • the required ceramic slurries typically are difficult to control with respect to suspension stability, viscosity, and drainage. Further, the slurry coatings are difficult to dry and cure.
  • These shell molds must be fired to a high temperature to achieve adequate sintering or chemical bonding.
  • the shell molds also may be too strong during post-cast cooling, thereby inducing hot tears and/for recrystallization in the cast metal. In addition, such shell molds can be too strong and chemically inert at room temperature to be easily removed from the casting.
  • the British Patent 1577836 which corresponds to DE-A-27 16 342, upon which the preambles of claims 1 and 10 are based, discloses a process for manufacturing a ceramic shell mold by dipping the meltable pattern in a slurry of a first ceramic material, made of silica and calcia, applying repeatedly a stucco of dry ceramic particles to the wet slurry coated surface and drying until the required mold thickness is obtained.
  • This multilayer but homogeneous coating forming a high viscosity glass-like phase during the firing step, provides a surface which is non-reactive with molten superalloys, allowing a better dimensional control and a better surface finish of the casting part, but the mechanical strength and the creep resistance are not sufficient for casting the newly developed high melting point superalloys.
  • Another objective of the invention is to provide a ceramic shell mold which facilitates improved control of casting dimensions and which can be easily removed from the casting.
  • a further objective of the invention is to provide a method for making a ceramic shell mold having improved mechanical properties at high temperatures.
  • the ceramic shell mold of the present invention includes a facecoat layer comprised of a first ceramic material.
  • a plurality of alternating layers overlay the facecoat layer.
  • the alternating layers are comprised of a second ceramic material and a third ceramic material, the third ceramic material having thermophysical properties different than the second ceramic material.
  • a cover layer overlaying the alternating layers may be provided.
  • the resultant ceramic shell mold has a greater high temperature creep resistance than a shell mold formed solely from the second ceramic material or solely from the third ceramic material.
  • a pattern having the shape of the desired casting is provided.
  • a facecoat layer is formed by applying a first ceramic material on the pattern, preferably by dipping the pattern into a slurry comprised of the first ceramic material.
  • a plurality of alternating layers overlaying the facecoat layer then are formed.
  • the alternating layers are formed by alternately applying a second ceramic material and a third ceramic material on the coated pattern, the third ceramic material having thermophysical properties different than the second ceramic material.
  • the alternating layers are formed by alternately dipping the coated pattern into slurries comprised of the second ceramic material and the third ceramic material, respectively.
  • Each dipping step is followed by the step of applying a ceramic stucco on the ceramic slurry layer and drying.
  • the method may include the step of forming a cover layer overlaying the alternating layers.
  • Fig. 1 is a transmitted light photomicrograph of the interface between an alumina-based layer and a zircon-based layer in a ceramic shell mold formed in accordance with the invention.
  • a pattern having the shape of the desired casting is provided.
  • the pattern may be made of wax, plastic, frozen mercury, or other materials suitable for use in "lost wax” casting processes.
  • a facecoat layer then is formed on the pattern by applying a first ceramic material.
  • the ceramic material is preferably an alumina-based or zircon-based material.
  • the facecoat layer preferably is formed by dipping the pattern into a first slurry comprised of the first ceramic material. After allowing excess slurry to drain from the coated pattern, ceramic stucco is applied.
  • the ceramic stucco may be coarse alumina (120 mesh or coarser) or other suitable refractory material.
  • the facecoat layer is allowed to dry prior to the application of additional layers.
  • a plurality of alternating layers overlaying the facecoat layer are formed by alternately applying a second ceramic material and a third ceramic material on the coated pattern.
  • a sequence of "alternating" layers is any sequence of layers including at least one layer of the second ceramic material and at least one layer of the third ceramic material.
  • A represents the second ceramic material
  • B represents the third ceramic material
  • sequences of layers such as ABABAB, AAABAA, AABBAA, and BBBABB are all sequences of alternating layers.
  • the second and third ceramic materials are preferably applied by alternately dipping the coated pattern into a second ceramic slurry comprised of the second ceramic material and a third ceramic slurry comprised of the third ceramic material. Each dipping step is followed by the step of applying a ceramic stucco on the ceramic slurry layer and drying. While not preferred, it is possible to omit applying ceramic stucco on either the facecoat layer or any of the alternating layers.
  • the alternating layers, as well as the facecoat layer may be applied by spray coating or flow coating.
  • the layers are applied by spray coating or flow coating, the ceramic slurry is thinned, if necessary, with an appropriate solvent to provide for suitable handling.
  • the third ceramic material has thermophysical properties different than the second ceramic material.
  • a ceramic shell mold formed of alternating layers of ceramic materials having different thermophysical properties has better high temperature properties than a ceramic shell mold formed solely from either individual ceramic material.
  • thermophysical properties refer to the physical characteristics of a material at elevated temperatures. While not fully understood, it is believed that a mismatch in a physical characteristic such as strength or creep resistance between the alternating layers causes the shell mold to act as a composite material, with the layers of one material reinforcing the layers of the other material.
  • Suitable materials having different thermophysical properties include, but are not limited to, alumina, mullite, zirconia, yttria, thoria, zircon, silica, an alumino-silicate containing less than 72 wt% alumina, and compounds, mixtures, or alloys thereof.
  • the ceramic material used to form the facecoat layer may be substantially the same as either of the second or third ceramic materials used in forming the alternating layers.
  • ceramic materials that are “substantially the same” are ceramic materials that are identical or differ in that one ceramic material contains additional components that do not materially affect the properties of the other ceramic material.
  • the alternating layers are formed by alternately dipping the coated pattern into an alumina-based slurry containing a silica binder and a zircon-based slurry containing a silica binder.
  • the number of alternating layers required for adequate shell mold build-up depends on the nature of the casting operation in which the shell mold is to be used.
  • Examples of shell mold constructions for a nine-layer shell mold, where the alternating layers are formed from an alumina-based material (represented by A) and a zircon-based material (represented by Z), include: ZZZAZAZAZ, ZAZAZAZAZ, AZAZAZAZA, ZZAZZZZZZ, ZZZZZZZA, ZAAZAAZAA, ZZAZAZZA, ZZAZAZZZZ, ZZAZZZZAA, and ZZZAAAZZZ.
  • seven alternating layers overlaying the facecoat layer are formed.
  • the first, second, fourth, and sixth layers are formed by dipping the pattern into the zircon-based slurry.
  • the third, fifth, and seventh layers are formed by dipping the pattern into the alumina-based slurry.
  • ceramic stucco is preferably applied after each dipping step.
  • a cover or seal layer may be formed overlaying the plurality of alternating layers. No stucco is applied to a cover layer.
  • the cover layer may be formed of either the first, second, or third ceramic material, or a different ceramic material.
  • a plurality of cover dips also may be applied.
  • the shell mold is built-up to the desired number of layers, it is thoroughly dried and the pattern is removed therefrom. Conventional techniques, such as melting, dissolution, and/or ignition may be used to remove the pattern from the shell mold. Following pattern removal, it is desirable to fire the shell mold at a temperature of approximately 980°C for approximately one hour in an oxidizing, reducing, or inert atmosphere.
  • the fired shell mold is ready for use in the investment casting of metals and alloys, including high melting point metals and alloys.
  • the shell mold Prior to casting, however, the shell mold may be preheated to a temperature in the range of 90°C to 1540°C to insure that it is effectively free from moisture and to promote good filling of the molten material in all locations of the shell mold.
  • Equiaxed, directionally solidified, and single crystal castings of high melting point alloys, in particular nickel-based superalloys, may be produced in accordance with conventional investment casting techniques using the ceramic shell mold of the invention. After the molten material has cooled, the casting, which assumes the shape of the original wax pattern, is removed and finished using conventional methods.
  • Shell plates (152,4 mm x 25,4mm) were fabricated on wax patterns in accordance with conventional dipping and stuccoing techniques.
  • the shell molds were dried, dewaxed in a steam autoclave, and fired at 1010°C for 1 hour in an air atmosphere. The shell molds then were trimmed to the desired test specimen size via diamond saw cutting.
  • Four-point modulus of rupture (MOR) and cantilever slump (also known as creep or sag) were measured at 1540°C in an air atmosphere for each shell mold. MOR testing was conducted on "flat,” 87,63mm x 19,05 mm specimens loaded with 25,4 mm upper span and 50,8 mm lower span. The crosshead speed was 5,08 mm/minute.
  • shell mold No. 3 having the alternating layer construction of the invention demonstrated higher strength than shell mold No. 1 (formed solely from zircon-based material), advantageously lower strength than shell mold No. 2 (formed solely from alumina-based material), and less slump than either shell mold No. 1 or No. 2.
  • Such surprising slump performance results would not have been predicted via a rule-of-mixtures model.
  • Fig. 1 which is a photomicrograph of the interface between an alumina-based layer and a zircon-based layer, there is no apparent reaction or new phase formation to account for the improvement in mechanical properties for the shell mold of the invention. This observation is further supported by X-ray diffraction analyses which revealed no new phase formation.
  • the bottom half of the photomicrograph is the zircon-based layer.
  • the top half is the alumina-based layer.
  • the large white grain in the upper left hand corner is an alumina stucco grain.

Landscapes

  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Molds, Cores, And Manufacturing Methods Thereof (AREA)
EP19890420208 1988-06-13 1989-06-12 Ceramic shell mold for investment casting and method of making the same Expired - Lifetime EP0347344B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US205731 1980-11-10
US20573188A 1988-06-13 1988-06-13

Publications (3)

Publication Number Publication Date
EP0347344A2 EP0347344A2 (en) 1989-12-20
EP0347344A3 EP0347344A3 (en) 1991-02-27
EP0347344B1 true EP0347344B1 (en) 1994-06-08

Family

ID=22763405

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19890420208 Expired - Lifetime EP0347344B1 (en) 1988-06-13 1989-06-12 Ceramic shell mold for investment casting and method of making the same

Country Status (3)

Country Link
EP (1) EP0347344B1 (ja)
JP (1) JPH0675744B2 (ja)
DE (1) DE68915861T2 (ja)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2225329B (en) * 1988-11-21 1992-03-18 Rolls Royce Plc Shell moulds for casting metals
GB9104728D0 (en) * 1991-03-06 1991-04-17 Ae Turbine Components Casting mould
EP0789109A1 (fr) * 1996-02-06 1997-08-13 Scheuchzer S.A. Machine pour le reprofilage des rails
JP6055963B2 (ja) * 2012-08-31 2017-01-11 株式会社Ｐｃｓジャパン 鋳型製造方法
DE102020108196B4 (de) 2020-03-25 2024-05-16 Technische Universität Bergakademie Freiberg Verfahren zur Herstellung einer keramischen, silikatfreien Feingussform für die Herstellung von Feingussteilen aus höherschmelzenden Metallen und Verwendung einer keramischen, silikatfreien Feingussform für die Herstellung von Feingussteilen aus höherschmelzenden Metallen

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4040845A (en) * 1976-03-04 1977-08-09 The Garrett Corporation Ceramic composition and crucibles and molds formed therefrom
SE7704162L (sv) * 1976-04-22 1977-10-23 United Technologies Corp Kalciumoxidmodifierat keramiskt skalformsystem
US4244743A (en) * 1979-04-23 1981-01-13 United Technologies Corporation Sulfur containing refractory for resisting reactive molten metals

Also Published As

Publication number Publication date
DE68915861D1 (de) 1994-07-14
JPH02112848A (ja) 1990-04-25
DE68915861T2 (de) 1995-01-19
EP0347344A3 (en) 1991-02-27
JPH0675744B2 (ja) 1994-09-28
EP0347344A2 (en) 1989-12-20

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