Precision Castparts Corp.

Other

Pcc Structurals, Inc.

William W Kemp

David H Sturgis

Mehrdad Yasrebi

Douglas Gene Nikolas

Mark E Springgate

Ted R Crego

Thomas J Kelly, Iii

Gary L Wright

Ilhan A Aksay

Renee Van Ginhoven

Hamazo Nakagawa

Methods and compositions for forming shells for investment casting and methods for casting metal articles using the shells are described. One embodiment of the method comprises serially immersing a pattern in at least one, and perhaps several different slurries, each of which slurries comprises refractory material and from about 0 to about 30 volume percent inorganic binder. This forms a facecoat and plural refractory backup layers about the pattern, the facecoat and at least one backup layer defining a shell. The facecoat and/or the shell is then infiltrated with a binder. Infiltrating the shell with a binder is a key feature of the present invention. Infiltration refers to any process whereby a binder can be introduced into the facecoat and/or the subsequent layers built up about the shell. One method of infiltrating the facecoat and/or layers with binder comprises immersing the pattern having refractory material into a slurry comprising a binder, including inorganic binders, organic binders, and mixtures thereof. The pattern then is separated from the shell, forming a shell having an internal void in the shape of an article to be cast. Molten metal is then introduced into the void and allowed to solidify.

Infiltration method for producing shells useful for investment casting

Time-stable yttria slurries, and a method for forming such yttria slurries and articles therefrom are described. The method involves forming an intimate mixture comprising yttria and at least about 0.1 weight percent of a dopant material. An aqueous slurry is then formed comprising from about 1 weight percent to about 95 weight percent of the intimate mixture. The intimate mixture may be formed by heating the mixture to a temperature sufficient to calcine the mixture. Alternatively, the intimate mixture may be formed by heating the mixture to a temperature sufficient to fuse the mixture. The dopant also may be provided as a surface coating on the yttria particles. The dopant material comprises an oxide or hydroxide, or combinations thereof, or compounds that form such oxides or hydroxides upon further processing, wherein the metal oxides or hydroxides are of metals selected from the group consisting of aluminum, titanium, niobium, tantalum, silicon, hafnium, tin, gallium, indium, beryllium, thorium, boron, scandium, vanadium, chromium, ruthenium, rhodium, iridium, palladium, platinum, copper, germanium, bismuth, tellurium, erbium, thulium, ytterbium, lutetium, neptunium, plutonium, and combinations thereof. The aqueous suspension may further comprise other materials, such as other ceramic or metallic particles, co-solvents, dispersing agents, surfactants, inorganic binders, or organic binders.

Method for stabilizing ceramic suspensions

A method for dispersing and reducing the rate of dissolution and/or hydration of colloidal ceramic suspensions is described. The method comprises adding to a ceramic suspension a non-polymeric hydroxylated organic compound. The organic compound has at least one hydroxyl group, preferably at least two hydroxyl groups. The organic compound also includes a functional group selected from the group consisting of a carboxyl, a carboxylate, a sulfonic acid, a sulfonate, a phosphoric acid, a phosphate, an amine, and a quaternary ammonium salt. The ceramic suspension typically comprises a colloidal suspension of a metal oxide, wherein the metal of the metal oxide is an alkali metal, alkaline-earth metal or a rare-earth metal, but preferably is magnesium, calcium or a rare-earth metal. The non-polymeric organic compound is added to the suspension in an amount effective to substantially disperse and reduce the rate of dissolution of the ceramic particles, such as from about 0.01 weight percent to about 5.0 weight percent.

The disclosure describes an aqueous ceramic slurry having from about 70-weight percent to about 85 weight-percent of a fused yttria-zirconia material. The weight percent of zirconia in the fused yttria-zirconia preferably varies from about 1.0 weight percent to about 10.0 weight percent. Fused slurries may comprise, in addition to fused yttria-zirconia, an inorganic binder (preferably silica), an organic binder (preferably a latex binder), a surfactant (preferably a sodium dioctyl sulfosuccinate), an antifoaming agent (preferably a water-dilutable active silicone defoamer) and titanium dioxide. The slurries of the present invention are used to form ceramic mold facecoatings for casting reactive materials. These slurries are less sensitive to pH fluctuations than are slurries made from 100 percent yttria (yttria slurries). Moreover, slurries as described in the disclosure do not gel prematurely, and exhibit substantially the same formation of oxygen-enriched titanium (alpha case) than do yttria slurries.

Yttria-zirconia slurries and mold facecoats for casting reactive metals

Y.sub.2 O.sub.3 is recovered from investment casting shell molds by introducing used mold materials into a dissolution reactor preferably consisting of a rotating vessel having an interior lining of acid and abrasion resistant material. An acid is combined with the materials in the reactor and agitated for a selected time period. Thereafter, the liquid remaining in the reactor is separated from the residual solids and removed. The liquid contains dissolved Y.sub.2 O.sub.3 which is precipitated, preferably using oxalic acid to produce yttrium oxalate [Y.sub.2 (C.sub.2 O.sub.4).sub.3.9H.sub.2 O]. The Y.sub.2 (C.sub.2 O.sub.4).sub.3.9H.sub.2 O is ultimately removed from the solution and calcined to produce high purity Y.sub.2 O.sub.3.

Method for recovering casting refractory compositions from investment

A highly efficient method for recovering Y.sub.2 O.sub.3 from casting slurries and cores containing Y.sub.2 O.sub.3 in combination with a binder is disclosed. The slurry is first treated with a gelling agent which causes the slurry to gel. The gelled slurry is then ignited in order to remove residual organic compounds. After ignition, the product is crushed and pulverized to form a powder. Thereafter, the powder is calcined at a temperature sufficient to crystallize the silica binder in the powder. The calcined product is subsequently dissolved in a heated acid solution for a selected time period. The resulting solution contains dissolved Y.sub.2 O.sub.3 and undissolved binder residue, which is filtered and removed. The Y.sub.2 O.sub.3 in the solution is then diluted with deionized water, and precipitated, preferably using oxalic acid to produce yttrium oxalate. The yttrium oxalate is ultimately removed from the solution and calcined to produce high purity Y.sub.2 O.sub.3. Cores are processed in a similar manner.

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Milwaukie, OR, United States of America

William W Kemp