CN106232261B

CN106232261B - Investment casting compositions, molds, and related methods

Info

Publication number: CN106232261B
Application number: CN201580022255.0A
Authority: CN
Inventors: 克里斯托佛·A·怀特豪斯; 小威廉·S·斯奈德
Original assignee: 3M Innovative Properties Co
Current assignee: 3M Innovative Properties Co
Priority date: 2014-05-02
Filing date: 2015-04-29
Publication date: 2020-07-21
Anticipated expiration: 2035-04-29
Also published as: CA2947695A1; CN106232261A; WO2015168233A1; EP3137244A1; MX2016014279A; US20170043390A1

Abstract

The invention provides a slurry composition and a method for preparing an investment casting mold. These compositions comprise a fire resistant material, a binder, a solvent, and a thixotropic agent comprising a polymer emulsion. The practice of these slurry compositions enables a reduction in the number of backing layers in investment casting shells while maintaining similar viscosity characteristics and similar or higher strength characteristics in the finished investment mold.

Description

Investment casting compositions, molds, and related methods

Technical Field

The present invention provides compositions for investment casting and related articles and methods. The composition more particularly includes additives that facilitate the preparation of investment casting molds.

Background

Investment casting, sometimes referred to as the "lost wax" process, is a well-known method of manufacturing parts having intricate and complex shapes. The process is used in a variety of different large and small scale applications, from the manufacture of superalloy turbine engine components to tiny custom orthodontic appliances.

Investment casting processes typically first produce a sacrificial wax pattern having a size and shape similar to the size and shape of the device to be fabricated. The wax pattern may be prepared by molding (rapid prototyping process) or any other method. The pattern is then subjected to a shelling process in which the pattern is sequentially dipped into a tank containing a coating material, typically a ceramic slurry. Each layer of coating material is allowed to dry for a certain time before the next impregnation. Additionally, dry fire-resistant granules or stucco may be applied between impregnations to improve the structural integrity of the shell. This process is repeated multiple times to gradually form a shell having multiple ceramic layers.

Thus, after the shell is formed, the pattern is heated, typically using a flash furnace or steam autoclave, to melt the wax and extract the mold from the mold. Finally, a mold having a hollow cavity is obtained, and the mold exactly reproduces the shape of the pattern. At this time, the strength of the mold can be further improved by firing. The molten metal alloy may then be injected into the mold cavity to cast the desired part. Finally, after the alloy has cooled sufficiently, the mold may be broken mechanically or chemically to separate the cast part from the mold.

In a conventional investment casting process, the finished shell comprises six or more layers, each of which may include two or more layers of a slurry or stucco. The first layer, referred to as the primer coating, is applied directly to the wax pattern. The primer coating typically includes both a fire resistant size and a fire resistant stucco. The next layer, referred to as an intermediate coating, is applied to the primer coating and also includes a fire resistant size and a fire resistant stucco. After the primer coating and intermediate coating are applied, typically three or more backing coatings are applied to form the thickness of the shell. Each backing coating also typically includes a fire resistant size and a fire resistant stucco. In many cases, a final seal coating is then applied to the final backing coating to prevent stucco from detaching from the shell during further processing of the shell.

Disclosure of Invention

A lot of time is required to form the aforementioned shell layer. The substantial amount of time required not only involves the dipping process for applying the individual component slurry and/or stucco layers, but also involves a drying step after each major layer is coated. The large number of steps in the manufacturing process also increases the overall risk of accidentally causing a trap or causing damage to the housing.

It has been found that incorporating a thixotropic agent derived from a polymer emulsion, such as an acrylic polymer emulsion, into the slurry composition enables the slurry to significantly and substantially increase the yield stress of the slurry when disposed on the investment pattern. This enables the pattern to maintain a thicker slurry layer than was previously possible using conventional investment casting slurries and additives, even those containing thixotropic agents. Thus, the use of the modified investment slurry enables the number of backing layers in an investment casting shell to be reduced from four to one while maintaining acceptable slurry viscosity, conformability and similar or greater strength characteristics in the final investment mold after firing.

It has also been observed that the aforementioned slurry compositions are capable of avoiding settling over a long period of time, thereby providing a "shippable" slurry that can be mixed in advance by the manufacturer before delivery to the end user. Advantageously, the slurry composition can be prepared on a large scale under precisely controlled conditions to obtain a more predictable, consistent slurry composition. Such consistency is critical to the end user as variations in the slurry composition are known to cause shell performance problems and increase waste rates. Both effects have a detrimental effect on the fidelity of the final manufactured product.

In one aspect, a slurry composition for investment casting is provided. The slurry composition comprises: a refractory material; a binder; a solvent; and a thixotropic agent comprising a polymer emulsion.

In another aspect, a method of preparing an investment casting mold is provided. The method comprises the following steps: coating a primer layer comprising a first fire resistant slurry and a first fire resistant stucco over the sacrificial pattern; at least partially hardening the primer layer; coating an intermediate layer comprising a second fire resistant slurry and a second fire resistant stucco over the primer layer; at least partially hardening the intermediate layer; applying a backing layer comprising a thixotropic agent to the intermediate layer, the thixotropic agent comprising a polymer emulsion; and at least partially hardening the backing layer.

Drawings

FIG. 1 is a cross-sectional view of a multi-layer investment casting mold according to a prior art embodiment.

FIG. 2 is an enlarged fragmentary cross-sectional view of an insert portion of the investment casting mold of FIG. 1.

Fig. 3-5 are cross-sectional views of multi-layer investment casting molds according to various exemplary embodiments of the present invention.

FIG. 6 is a graph showing experimental data for slurry viscosity as a function of shear rate.

FIG. 7 is a graph showing experimental data for slurry shear stress as a function of shear rate.

Definition of

As used herein:

"refractory" refers to refractory ceramic materials;

"slurry" refers to a fluid mixture of solid particles and a liquid;

"stucco" refers to solid particles having a particle size generally no greater than a30 mesh U.S. standard sieve screen;

"thixotropic" refers to shear thinning properties in which a gel or liquid becomes less viscous when shaken, stirred, or otherwise stressed;

"wax" refers to a polymeric substance that is capable of melting at relatively low temperatures to produce a low viscosity liquid;

"zircon" means zirconium silicate having the formula ZrSiO₄。

Detailed Description

As used herein, the terms "preferred" and "preferably" refer to embodiments described herein that may provide certain benefits under certain circumstances. Other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude other embodiments from the scope of the invention.

As used herein and in the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a" or "the" component can include one or more components or equivalents thereof known to those skilled in the art. Additionally, the term "and/or" means one or all of the listed elements or a combination of any two or more of the listed elements.

It is noted that the term "comprises" and its variants, when appearing in the appended description, have no limiting meaning. Furthermore, "a," "an," "the," "at least one," and "one or more" are used interchangeably herein.

Reference throughout this specification to "one embodiment," "certain embodiments," "one or more embodiments," or "an embodiment" means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, appearances of the phrases such as "in one or more embodiments," "in certain embodiments," "in one embodiment," or "in an embodiment" in various places throughout this specification are not necessarily referring to the same embodiment of the invention. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments.

The present disclosure describes, by way of illustration and example, a slurry composition for preparing an investment casting mold. The patterns and associated nozzles shown are exemplary, not drawn to scale, and may vary widely in size and shape depending on the application. It should also be understood that the refractory materials, solvents, and binders described herein are exemplary and may be substituted or modified according to the knowledge of one skilled in the art.

While the compositions and associated methods described herein enable one of ordinary skill in the art to make and use investment casting molds having certain advantageous properties, it will be recognized that these compositions and methods may also incorporate additives or reinforcing agents not shown herein. For example, the slurry composition may also include a gaseous or solvent-based gelling agent, a chemically treated refractory material, and a slurry binder system that interact with each other.

Fig. 1 shows a cross-section of a conventional investment casting mold, designated by the numeral 100. In this figure, the mold 100 is shown encapsulating a substantial portion of a sacrificial pattern 102 having a tree-like structure comprising a centrally located trunk 103 and a plurality of branches 105 extending outwardly from the trunk 103. The pattern 102 is exemplary, and there is no particular limitation in size and shape thereof.

In a preferred embodiment, pattern 102 is made of wax, polymeric resin, or other suitable pattern material that is subsequently capable of melting, evaporating, burning, or dissolving, leaving cavities (with minimal residue) that conform to the outer contours of pattern 102.

As shown, mold 100 includes a series of continuous layers formed by dipping pattern 102 into a vessel of refractory slurry. After each dip, pattern 102 is extracted, and excess slurry/stucco is drained. Optionally, the pattern 102 is manipulated manually or mechanically to promote uniform coverage. The fire resistant granules or stucco are then applied to the wet slurry coating. Here, the combination of the slurry and stucco comprises a single major layer which is dried and at least partially hardened before the next coating layer is applied. By repeating this process, the walls of the mold 100 are progressively formed layer by layer until the entire mold 100 has sufficient strength to withstand the physical handling forces caused by the metal casting. Mold 100, starting with the innermost layer and ending with the outermost layer, includes primer layer 104, intermediate layer 110, first backing layer 116, second backing layer 122, third backing layer 128, and sealing layer 134.

Although the mold 100 of fig. 1 is of a six-layer construction, more or fewer layers may be used depending on the nature of the application. For example, factors such as the molten metal head pressure and the size of the casting to be poured from the final mold can affect the amount of backing layer used. Common commercially available investment casting shells typically use four backing layers.

Each of the six layers enumerated above is described in more detail with reference to fig. 2. Undercoat layer 104 is the innermost layer that extends across and contacts pattern 102. The purpose of primer layer 104 is to directly contact the molten metal after dewaxing and firing of finished mold 100. As shown, primer layer 104 includes two sublayers, namely an inner layer 106 of a refractory mortar and an outer layer 108 of refractory stucco. In mold 100 shown in FIG. 2, both refractory slurry 106 and refractory stucco 108 include zircon particles (shown here as round particles), but this is not necessarily so. In certain embodiments, one or more additional primer layers may be used. This may be the case, for example, where there is no intermediate slurry layer.

Referring again to fig. 2, the intermediate layer 110 and continuous backing layers 116, 122, 128 also each include two sub-layers, namely a

refractory mortar layer

112, 118, 124, 130 and an adjacent

refractory stucco layer

114, 120, 126, 132, respectively. The refractory slurry for these layers may comprise fused silica, aluminosilicates, zircon, alumina, or mixtures thereof. Similarly, the refractory stucco (shown as particles with jagged edges in the figure) may also include fused silica, aluminosilicate, zircon, alumina, or mixtures thereof. Stucco may be applied by spraying through a manual or rainfall sander onto the freshly coated slurry or by immersion into a fluidized bed of stucco. In some embodiments, stucco particles generally increase in size from the inside to the outside of mold 100.

Optionally and as shown, a sealing layer 134 is located at the outermost periphery of the mold 100. Sealing layer 134 serves to prevent stucco of backing layer 128 from loosening during subsequent processing of finished mold 100 and may have the same or similar composition as the intermediate or backing slurry. In an exemplary embodiment, sealing layer 134 comprises fused silica, aluminosilicates, zircon, alumina, or mixtures thereof.

In one exemplary method, the resulting structure as shown in fig. 1 and 2 may then be completely dried and heated to melt the pattern 102, and then the pattern 102 is removed from the finished investment casting mold 100. To improve strength, the finished mold 100 may be fired in a curing oven at a temperature of about 980 ℃.

An improved investment casting mold 200 according to an exemplary embodiment is shown in fig. 3. Some of the characteristics of the mold 200 are the same as the mold 100. For example, similar to mold 100, mold 200 includes a primer layer 204 disposed on a wax pattern 202 and an intermediate layer 210 disposed on primer layer 204. Pattern 202, primer layer 204, and intermediate layer 210 generally have the aforementioned features, options, and advantages described with respect to mold 100. Here, the primer layer 204 includes an inner zircon-containing slurry coating 206 and an outer zircon stucco layer 208. In the illustrated embodiment, the intermediate layer 210 includes an inner refractory slurry coating 212 and an outer refractory stucco coating 214. The intermediate slurry layer 210 may also comprise a zircon refractory material.

Referring again to fig. 3, a single backing layer 240 is disposed on the intermediate layer 210. As shown, the backing layer 240 has a spatial thickness that is much greater than the thickness of the primer 204 or the intermediate layer 210. Advantageously and as shown, the backing layer 240 may fill the open undercuts and cavities represented by the branches of the pattern 202, thereby simplifying the subsequent coating process. As another major advantage, the configuration of the mold 200 eliminates the need for multiple backing layers in common investment casting applications. As shown, backing layer 240 includes a refractory mortar inner coating 242 and a refractory stucco coating 244. Finally, the sealing layer 234 is disposed on the backing layer 240, the two

layers

234 and 240 being in direct contact with each other. The sealing layer 234, which is used for the same purpose as the sealing layer 134, may also be omitted if desired.

In the above method, each slurry layer is optionally disposed on a pattern or underlying layer using a dipping process. When using an impregnation process, it is advantageous that the slurry has a viscosity high enough to remain on the pattern or underlying layer for an acceptable working time, while still having a fluidity high enough to fill substantially all the voids of the impregnated component, thereby maintaining a high fidelity of the mould shape. Acceptable working times generally range from about 12 seconds to about 60 seconds. The working time required for the slurry depends on the process and the casting, but is generally the time required for moving the slurry from the above slurry tank into the stucco application area after the discharge of the slurry is stopped. Using the prior art method, this time period is about 2-3 minutes. These conflicting properties can be achieved simultaneously using an investment casting mold and the method described below.

In the exemplary embodiment, investment casting mold 200 is fabricated using a layer-by-layer build-up process similar to that used to fabricate investment casting mold 100, with certain differences as described below. Generally, differences from prior art methods include differences in the refractory slurry composition used for the backing layer and, advantageously, a reduction in the number of processing steps required to prepare the finished investment casting mold 200.

The composition of fire-resistant paste 242 includes a fire-resistant material, a binder, a solvent, and a thixotropic agent that includes a polymer emulsion.

Refractory material, refractory powder or powder is the first major component of the refractory slurry 242. A common refractory powder used in the investment casting industry is zircon (ZrSiO)₄) Fused and Silica (SiO)₂) Alumina (Al)₂O₃) Zirconium oxide (ZrO)₂) And aluminosilicates (Al)₂O₃And SiO₂Various combinations of (a), typically firing at high temperatures). Preferred refractory materials for slurry 242 and/or stucco 244 include fused silica, aluminosilicates, zircon, alumina, and mixtures thereof. Although not critical, the refractory powder can have a broad particle size distribution, including particle sizes up to 30 mesh as well as sub-micron particle sizes.

The binder may be a second major component of the refractory slurry 242 for purposes described herein, the binder may include a refractory binder, an organic binder, or a combination of both, the refractory binder that may be included in the refractory slurry 242 includes various ceramic materials including silicates, alkali metal silicates, silica sols, aluminum chlorohydrate, aluminum phosphate, gypsum-silica mixtures, cements, and mixtures thereof.

The solvent is generally the same as the liquid dispersant used for the binder. In the exemplary embodiments herein, water is the preferred solvent. However, many other solvents may be used, including other polar solvents such as mineral acids, alcohols such as methanol, ethanol, isopropanol, and butanol, glycols and glycol ethers, and mixtures thereof. Commercial binders are usually provided in solution, and therefore a separate addition of solvent may not be necessary.

The composition of fire-resistant paste 242 also includes a thixotropic agent (or shear diluent) based on the polymer emulsion. In a preferred embodiment, the polymer emulsion is an acrylic polymer emulsion. More preferably, the polymer emulsion is an acrylic polymer emulsion dissolved in water.

Polymers suitable for use in the present application can be prepared using a variety of different synthetic routes. The alkali-swellable polymers are synthesized, for example, by copolymerizing different monomers, at least one of which contains a carboxyl (-COOH) functional group. These polymers may have a linear, branched structure or be crosslinked to form a network structure. The use of these polymers as thickeners is described, for example, in U.S. Pat. No.4,226,754(Whitton et al) which discloses a polymer prepared by reacting an acrylic acid ester, methacrylic acid and a vinyl ester of a saturated aliphatic carboxylic acid. These thickeners are generally referred to as alkali swellable thickeners because the carboxylic acid groups are sufficient to render the polymer soluble in water when neutralized with a suitable base.

In other preferred embodiments, the slurry composition comprises a hydrophobic entity covalently bonded to the polymer backbone. For example, the polymer may be formed by reacting an ethylenically unsaturated carboxylic acid monomer, a nonionic vinyl monomer, and a vinyl surfactant ester, such as alkyl phenoxy (ethyleneoxy) ethyl acrylate terminated at one end with an alkyl phenyl group. Another example is derived from the reaction product of an unsaturated carboxylic acid, an alkyl (meth) acrylate, and an alkyl phenyl-containing ester, the alkyl group having from 8 to 20 carbon atoms. These water-soluble polymers modified with hydrophobic moieties are described in U.S. Pat. Nos. 4,384,096(Sonnabend) and 4,138,381(Chang et al).

In some embodiments, the syrup compositions comprise an acrylic emulsion copolymer prepared using emulsion copolymerization of monomers in three of four classes of monomers, namely, (meth) acrylic acid, alkyl (meth) acrylates, ethoxy (meth) acrylates having hydrophobic groups, and optionally, polyethylenically unsaturated monomers. In other embodiments, the slurry composition comprises an emulsion copolymer based on the reaction product of monomers comprising methacrylic acid, ethyl acrylate, optionally defined copolymerizable ethylenically unsaturated monomers, and a weight percent of smaller multi-ethylenically unsaturated monomers. Advantageously, the addition of various surfactants to the aqueous system containing the copolymer can enhance the thickening effect on the composition when neutralizing the emulsion copolymer. The aforementioned copolymers are also described in European patent No.13,836(Chang et al) and U.S. patent No.4,421,902(Chang et al).

In another embodiment, the alkali-swellable copolymer is synthesized as the reaction product of an ethylenically unsaturated carboxylic acid, a surface-active unsaturated ester, a methacrylate or acrylate ester of an aliphatic alcohol, and optionally one or more other ethylenically unsaturated monomers, a polyethylenically unsaturated compound, and a molecular weight regulator. One end of the surface active ester is terminated with an aliphatic group which may be a straight or branched chain, monoalkyl, dialkyl or trialkyl phenyl group containing from 4 to 12 carbon atoms or a block copolymeric group. Upon partial or complete neutralization, the copolymers become water soluble or colloidally dispersible and can be used as thickeners. These copolymers are also described in U.S. Pat. No.4,668,410(Engel et al).

One particularly advantageous thixotropic agent that may be used in fire-resistant paste 242 is a polymer emulsion based on a hydrophobically modified ester of methacrylic acid, which polymer solution is available under the trade designation RHEO L ATE from Elementis Specialties (Hightstown, NJ) of Haizyton, N.J.A. the process for preparing such polymer emulsions is described in detail in U.S. Pat. No.6,069,217(Nae et al).

Another advantageous thixotropic agent is available from the same manufacturer under the same trade name, based on a water-soluble hydrophobically modified alkali-soluble emulsion derived from an acrylic polymer and having about 30 weight percent solids. Typically, the acrylic emulsion has a pH of less than about 5.

The polymer emulsion is preferably present in an amount that increases the yield stress of the refractory slurry to such an extent that the strength of the investment casting mold is maintained using only a single backing layer. In some embodiments, the polymer emulsion is present in an amount of at least 0.02 wt%, at least 0.03 wt%, at least 0.05 wt%, at least 0.06 wt%, or at least 0.07 wt%, based on the total weight of the composition. In some embodiments, the polymer emulsion is present in an amount of up to 1 weight percent, up to 0.9 weight percent, up to 0.8 weight percent, up to 0.75 weight percent, or up to 0.7 weight percent, based on the total weight of the composition.

Advantageously, the use of a polymer emulsion as a thixotropic agent enables the refractory slurry to operate at shear stress conditions much lower than the prior art while achieving similar investment casting operating viscosities. In some embodiments, the slurry composition exhibits a working viscosity of about 20 poise when subjected to a shear stress of at least 1 dyne per square centimeter, at least 5 dynes per square centimeter, at least 10 dynes per square centimeter, at least 20 dynes per square centimeter, at least 50 dynes per square centimeter, at least 100 dynes per square centimeter, at least 200 dynes per square centimeter, or at least 400 dynes per square centimeter, as measured using the methods described in the examples.

In some embodiments, the same composition exhibits a working viscosity of about 20 poise when subjected to a shear stress of at most 1000 dynes per square centimeter, at most 950 dynes per square centimeter, at most 900 dynes per square centimeter, at most 850 dynes per square centimeter, or at most 800 dynes per square centimeter.

As a result of the stucco process, investment cast shells typically have a large porosity which may adversely affect strength. For the strength to be considered suitable for a given application, it must be able to withstand the internal pressures and thermal stresses that can be high, especially during dewaxing and when pouring the metal into a separate ceramic shell. When the stress on the mold is greater than the modulus of rupture of the mold material, cracking may occur. In some embodiments, the investment casting mold has a non-sintered fracture modulus of at least 150psi, at least 175psi, at least 200psi, at least 225psi, or at least 250psi after fully hardening. In some embodiments, the investment casting mold has a non-sintered fracture modulus of at most 750psi, at most 735psi, at most 725psi, at most 710psi, or at most 700psi after being fully hardened.

In some embodiments, the composition of refractory slurry 242 also includes a layered aluminosilicate clay. In some embodiments, the layered aluminosilicate clay is present in a weight ratio relative to the polymer emulsion in a range of at least 1: 15, at least 1: 10, at least 1: 8, at least 1: 7, or at least 1: 6. In some embodiments, the layered aluminosilicate clay is present in an amount in a weight ratio range of up to 6: 1, up to 5: 1, or up to 4:1 relative to the polymer emulsion.

It has been observed that combining a thixotropic thickener comprising a polymer emulsion, particularly an acrylic emulsion, with a layered aluminosilicate clay provides some synergistic enhancement in an investment mold. For example, it has been observed that the inclusion of both a polymer emulsion thickener and a layered aluminosilicate clay in a backing slurry composition greatly extends the working time of the slurry compared to a slurry containing only a layered aluminosilicate as the thickener. When the layered aluminosilicate clay is used independently, the backing slurry is easily discharged from the pattern. In addition, the inclusion of both a polymer emulsion and a layered aluminosilicate clay is preferred over the inclusion of only a polymer emulsion, as the latter tends to produce slurries with excessive viscosity. Such high viscosity in turn can lead to cracking or breaking of the fragile pattern when inserted into the slurry. In summary, the combination of the polymer emulsion thickener and the layered aluminosilicate clay provides an unexpected and advantageous balance of mobile phase and long working time.

The total solids present in the refractory slurry 242 are not particularly limited, but the index should fall within a range sufficient to obtain a stable colloidal suspension and produce a robust final investment casting mold 200. In some embodiments, the refractory slurry 242 has a total solids content of at least 45 wt%, at least 50 wt%, or at least 55 wt%, based on the total weight of the composition. In some embodiments, refractory slurry 242 has a total solids content of at most 85 wt%, at most 80 wt%, or at most 75 wt%, based on the total weight of the composition.

Alternative embodiments are shown in fig. 4 and 5. FIG. 4 shows an investment casting mold 300 according to another embodiment, wherein the outermost sealing layer is omitted. The three-layer construction includes primer layer 304 extending across and contacting sacrificial pattern 302, intermediate layer 310 extending across and contacting primer layer 304, and single backing layer 340 extending across and contacting intermediate layer 310. As with the previously described embodiments, each of the

layers

304, 310, 340 includes an inner sub-layer of a refractory mortar adjacent to an outer sub-layer of refractory stucco.

There is no outermost sealing layer in the mold 300; in fig. 4, the layered construction ends with fire resistant stucco for backing layer 340. Although having most of the same functional characteristics as the mold 200, the mold 300 requires fewer processing steps to manufacture.

FIG. 5 shows an investment casting mold 400 according to another embodiment. The mold 400 is significantly further simplified in its two-layer construction compared to the previous embodiments. Showing only primer layer 404 and backing layer 440 disposed over pattern 402, mold 400 may advantageously be prepared using only two impregnations for

layers

404 and 440, respectively. Other aspects of the mold 400 and its constituent layers are substantially the same as described with respect to the three-layer and four-layer embodiments described above.

Ideally, investment casting slurry compositions exhibit a yield stress sufficient to prevent excess slurry from being drained from the pattern as it is drawn from the slurry bath. However, this property should be adjusted by its fluidity, which essentially refers to the ability of the slurry to flow into and around complex pattern geometries (including narrow cavities) as the pattern is immersed in the slurry. The slurry compositions provided herein operate in a solid-like state at low shear rates associated with gravity, but operate in a liquid-like state at higher shear rates associated with immersion of the pattern into the slurry bath. By minimizing gravity-induced drainage while achieving good flow during infusion, the provided compositions reduce the number of infusions required while still maintaining the fidelity of the final molded product.

In some embodiments, the slurry composition has a yield stress of at least 0.2 dynes/cm²At least 0.5 dyne/cm²At least 1 dyne/cm²At least 5 dynes/cm²Or at least 10 dynes/cm². In the same or alternative embodiments, the yield stress of the slurry composition can be up to 200 dynes/cm²At most 250 dynes/cm²At most 500 dynes/cm²At most 750 dynes/cm²Or up to 1000 dynes/cm². Exemplary slurry compositions may exhibit a viscosity of at least 50 poise, at least 100 poise, at least 200 poise, at least 500 poise, or at least 1000 poise at initial flow. In the same or alternative embodiments, the viscosity of the slurry composition at initial flow may be at most 7000 poise, at most 8000 poise, at most 9000 poise, at most 10000 poise, or at most 12000 poise.

The technical features and advantages of the invention are further illustrated by, but not necessarily limited to, the embodiments a-AI enumerated below:

A. a slurry composition for investment casting, the composition comprising: a refractory material; a binder; a solvent; and a thixotropic agent comprising a polymer emulsion.

B. The composition of embodiment a, wherein the polymer emulsion is an aqueous emulsion.

C. The composition of embodiment a or embodiment B wherein the polymer emulsion comprises an alkali-swellable polymer.

D. The composition of embodiment C, wherein the alkali-swellable polymer comprises a hydrophobically modified methacrylate.

E. The composition of any of embodiments a-D, further comprising a layered aluminosilicate clay.

F. The composition of embodiment E, wherein the layered aluminosilicate clay is present in a weight ratio relative to the polymer emulsion in an amount in a range of 1: 15 to 6: 1.

G. The composition of embodiment E, wherein the layered aluminosilicate clay is present in a weight ratio relative to the polymer emulsion in an amount in a range of 1: 8 to 4: 1.

H. The composition of embodiment G, wherein the layered aluminosilicate clay is present in a weight ratio relative to the polymer emulsion in an amount in a range of 1:6 to 4: 1.

I. The composition of any of embodiments a-H, wherein the polymer emulsion is present in an amount ranging from 0.02 wt% to 1 wt%, based on the total weight of the composition.

J. The composition of embodiment I, wherein the polymer emulsion is present in an amount ranging from 0.05% to 1% by weight, based on the total weight of the composition.

K. The composition of embodiment J, wherein the polymer emulsion is present in an amount ranging from 0.07 wt% to 0.75 wt% based on the total weight of the composition.

L the composition of any one of embodiments A-K, wherein the composition has a total solids content in the range of from 45 wt% to 80 wt%, based on the total weight of the composition.

M. the composition of embodiment L, wherein the composition has a total solids content ranging from 45% to 75% by weight, based on the total weight of the composition.

The composition of embodiment M, wherein the composition has a total solids content ranging from 50 wt% to 75 wt%, based on the total weight of the composition.

O. the composition of any one of embodiments a-N, wherein the solvent is water.

P. the composition of any of embodiments a-O, wherein the binder comprises colloidal silica.

Q. the composition of any of embodiments a-P, wherein the composition is subjected to 25 dynes/cm²To 1000 dynes/cm²Exhibits a working viscosity of about 20 poise at yield stress.

R. the composition of embodiment Q, wherein the composition is subjected to 25 dynes/cm²To 900 dynes/cm²Exhibits a working viscosity of 20 poise at yield stress.

S. the composition of embodiment R, wherein the composition is subjected to 25 dynes/cm²To 800 dyne/cm²Exhibits a working viscosity of 20 poise at yield stress。

T. the composition of any of embodiments a-S, wherein the binder comprises styrene-butadiene latex.

U. the composition of any of embodiments a-S, wherein the binder comprises a polyvinyl butyral resin.

V. an investment casting mold prepared using the composition of any of embodiments a-U.

W. a method of preparing an investment casting mold, the method comprising: coating a primer layer comprising a first fire resistant slurry and a first fire resistant stucco over the sacrificial pattern; at least partially hardening the primer layer; coating an intermediate layer comprising a second fire resistant slurry and a second fire resistant stucco over the primer layer; at least partially hardening the intermediate layer; applying a backing layer comprising a thixotropic agent to the intermediate layer, the thixotropic agent comprising a polymer emulsion; and at least partially hardening the backing layer.

X. the method of embodiment W, wherein the first refractory slurry comprises zircon.

Y. the method of embodiment W or X, wherein the first refractory stucco comprises zircon.

The method of any of embodiments W-Y, wherein the second refractory slurry comprises fused silica, alumina, aluminosilicate, or mixtures thereof.

The method of any of embodiments W-Z wherein the second refractory stucco comprises fused silica, alumina, aluminosilicate, or mixtures thereof.

The method of any one of embodiments W-AA, further comprising: coating a sealing layer comprising a third refractory slurry on the backing layer, wherein the sealing layer is in direct contact with the backing layer; and at least partially hardening the sealing layer.

The method of embodiment AB, wherein the third refractory slurry comprises a fused silica slurry, an aluminosilicate slurry, or a mixture thereof.

AD. the method according to any of embodiments W-AC, wherein the investment casting mold has a non-sintered fracture modulus in the range of 150psi to 750psi after fully hardening.

AE. the method of embodiment AD wherein the investment casting mold has a non-sintered fracture modulus in the range of 200psi to 700psi after fully hardening.

The method of embodiment AE, wherein the investment casting mold has a non-sintered fracture modulus in the range of 250psi to 700psi after fully hardened.

The method of any one of embodiments W-AF, further comprising applying heat to remove a pattern on an investment casting mold.

AH. the method according to any one of embodiments W-AG wherein the second refractory stucco has a size in the range of 10 mesh U.S. Standard Sieve to 100 mesh U.S. Standard Sieve.

The method of any of embodiments W-AH, wherein the backing layer further comprises flame resistant stucco having a size in the range of 30 mesh, U.S. standard screen, to 100 mesh.

Examples

Material

"WDS II", a fused silica available under the trade designation "WDS II" from 3M Midway, Midway, TN of Midway, USA.

"WDS 3", a fused silica available under the trade designation "WDS 3" from 3M Midway, Midway, TN of Midway, USA.

"Min-Sil 120F", a fused silica, available under the trade designation "Min-Sil 120F" from 3M Midway, Midway, TN of Midwei, Tennessee, USA.

"NA L CO 1130", a silica sol, 30% by weight SiO₂Particle size 8 nm, available from Nepperwell Nakangaku Chemical Company, Ill., U.S.A. (Nalco Chemical Company, Naperville, I L) under the trade designation "NA L CO 1130".

"NA L CO 6300", a styrene-butadiene latex polymer, 50% by weight solids, available under the trade designation "NA L CO 6300" from Nepperwell Nalco Chemical Company, Ill., U.S.A. (Nalco Chemical Company, Naperville, I L).

"Minco HP", a styrene-butadiene latex polymer, 50 wt.% solids, available as "MincoHP" from 3M Midway, Midway, TN of Midway, USA.

"NA L CO 2305," an anti-foaming additive comprising a blend of silicone resin and polyglycol dissolved in a hydrocarbon solvent, is available under the trade designation "NA L CO 2305" from Nepperwell Nalci chemical Company, Nalco chemical Company, Naperville, I L, Ill.

"NA L CO 8815," a wetting agent, available under the trade designation "NA L CO 8815" from Nepperwell Narco Chemical Company, Ill., USA (Nalco Chemical Company, Naperville, I L).

"Bentone EW", a highly synergistic readily dispersible powdered clay thickener available under the trade designation "Bentone EW" from Haimass specialty Chemicals, Inc., of Haizton, N.J. (Elementis, Specialties, Inc., Hightstown, N.J.).

"RHEO L ATE 420", an alkali swellable thickener, available under the trade designation "RHEO L ATE 420" from Haimass specialty Chemicals, Inc., of Haizdun, N.J. (Elementis, Specialties, Inc., Hightstown, N.J.).

"RHEO L ATE 288," a high performance polyether polyurethane associative thickener available under the trade designation "RHEO L ATE 288," from Haimass specialty Chemicals, Inc., of Haizdun, N.J. (Elementis, Specialties, Inc., Hightstown, N.J.).

"RHEO L ATE 1", an acrylic thickener with high thickening efficiency, available under the trade designation "RHEO L ATE 1" from Haimass specialty Chemicals, Inc., of Hazendon, N.J. (Elementis, Specialties, Inc., Hightstown, N.J.).

"RHEO L ATE 278", a high performance polyether polyurethane associative thickener available under the trade designation "RHEO L ATE 278" from Haimass specialty Chemicals, Inc., of Haizdun, N.J. (Elementis, Specialties, Inc., Hightstown, N.J.).

"SO L THIX A300", an alkali swellable thickener, available under the trade designation "SO L THIX A300" from Luborun Advanced Materials, Brokeville, Ohio (L, Britrizol Advanced Materials, Inc., Brecksville, OH).

"SO L THIX A100", an alkali swellable thickener, available under the trade designation "SO L THIX A100" from Luborun Advanced Materials, Brokeville, Ohio (L, Britrizol Advanced Materials, Inc., Brecksville, OH).

"THIXATRO L P L US," an active, anti-seeding organic rheological additive, available under the trade designation "THIXATRO L P L US" from hainskian specialty chemicals, alzheimer, NJ, usa.

Fused silica, 50 × 100 mesh (finer than 50 mesh U.S. standard sieve, but coarser than 100 mesh U.S. standard sieve), was purchased from 3M Midway, TN of Midway, tennessee, usa.

Fused silica, 30 × 50 mesh (finer than 30 mesh U.S. standard sieve, but coarser than 50 mesh U.S. standard sieve), was purchased from 3M Midway, TN of Midway, tennessee, usa.

General method for preparing primer pastes, intermediate pastes and backing pastes

Deionized (DI) water and NA L CO1130 silica sol are added to a sufficiently large volume container during mixing using an INDCO model HS120T mixer (2 horsepower, 220V, single phase motor set at 2050rpm), the desired amount of silica gel powder, additives such as polymeric binders (e.g., styrene-butadiene latex), defoamers, and/or wetting agents are added and mixing is continued until all lumps are dispersed.

General method of preparing investment casting molds

The method includes the steps of preparing a investment casting mold using a multi-step process, first, providing a wax pattern having the shape of the final investment cast part, sequentially forming a series of shells (i.e., layers) on top of the wax pattern, thereby forming the investment casting mold, in a first step, coating the wax pattern with a "primer layer" comprising an initial coating of a primer slurry layer, and further coating the initial coating with a primer stucco layer, dipping the wax pattern into the primer slurry for about 20 seconds while rotating and moving the wax pattern to maximize the uniformity of the primer slurry layer, thereby forming the primer slurry layer, then exposing the wax pattern including the primer slurry layer thereon to a 50 mesh zircon particle fluidized bed, depositing the primer stucco layer onto the wet primer slurry layer, then drying the wax pattern including the primer stucco layer at 21 ℃ for about 2 hours, thereafter coating the wax pattern including the dried primer layer with a "middle layer" in a manner substantially the same as, except that the intermediate slurry and stucco layers are dried and dried using 3650 c.36100 c. the intermediate slurry is dried to form a primary pattern with a primary stucco slurry layer, and then the same or a secondary backing layer.

The example and comparative investment casting molds prepared according to the above-described method are characterized as having a "green" state and/or a post-fired state.

Viscosity measuring method

Viscosity and shear stress data of the slurry were measured using an AR G2 stress controlled rheometer (TA Instruments, New Castle, DE) equipped with parallel plate clamps of 40mm diameter. The measurements were carried out using a gap of 1mm and an operating temperature of 23 ℃.

The slurry was tested using a continuous flow shear rate scan. When performing the test using 10^-3s^-1To 100s^-1Increasing shear rate of (2) and then using as low as 10^-3s^-1A decreasing shear rate. The yield stress of various slurries was determined by the following method: plotting shear stress as a function of the total strain at increasing shear rate, identifying fluid-like and solid-like behavior along the plot, fitting the power law for each state, and then determining the shear stress at the intersection between these fit results. The viscosity at the beginning of flow is also determined based on the viscosity measured when the yield stress is first reached.

Method for measuring bending strength

To prepare the strength Test samples, the investment casting shells were covered with a standard stainless steel strip of 1 inch × 0.25 inch × 13 inch (2.54cm × 0.64cm × 33cm) and the shells were made from the slurry used in the examples and comparative examples in the same manner as the investment casting molds were prepared as described above, prior to coating the investment casting shells, the steel strip was first coated with wax (mushy wax from minister corporation, commercially available from minister corporation of lancin, wisconsin & Sons, inc., Racine, WI) in the United states, the resulting shells were separated from the steel plate and used for flexural strength testing, the strength of the shell samples were tested using a universal tester (model SSTM-1, from United testing machines, huntington bidge, usa (United states, huntington, inc., CA), the strength of the shell samples was measured using a 0.05 inch (0.13cm) speed and 2 inch (5 inch) fracture position, the Test results of the samples were measured along with the average modulus of the Test results of the Test of the respective Test sample, and the results of the tensile strength of the Test samples were measured for each of the average crack strength of the samples under the conditions of the Test of the tensile modulus of the Test and the Test of the respective Test of the tensile strength of the respective Test of the respective Test sample, and the Test of the respective Test sample, and the respective Test of the respective Test of.

Permeability andfracture testing method

In this test, a case was manufactured on a polyvinyl chloride (PVC) Schedule 40 cold pipe by using the slurry prepared according to the examples and comparative examples to prepare a sample. The PVC pipe had an inner diameter of 0.75 inches (1.09cm), an outer diameter of 1.05 inches (2.77cm) and a length of 13 inches (33 cm). The tube is first coated with wax (a pasty wax from the minister company). After the case was formed, the resulting sample was cut into 6-inch (15.2cm) long portions for testing. "a novel combination Shell Strength and Permeability Test" published at the 51 th annual meeting of the American society for investment casting, using Snyder, B, and Snow, J, 2003, 11: pages 1-25 (published by the american society for investment casting). Each example and comparative example was tested for 10 sections (i.e., samples).

Comparative example 1(CE-1)

The compositions of the middle layer, backing layer and sealer slurry layer used to make the CE-1 investment casting mold were all the same, and slurries were made using the general methods described above for making the primer slurry, middle slurry and backing slurry, 13705g of WDS II silica powder, 4516g of NA L CO1130, 934g of deionized water, 498g of Minco HP latex binder and 21g of NA L CO 2305 defoamer additive were mixed during the preparation.

The CE-1 investment casting molds were fired at 2000 ℃ F. (1093 ℃ C.) for 2 hours prior to use.

Comparative example 2(CE-2)

The compositions of the middle layer, backing layer, and sealing slurry layers used to make the CE-2 investment casting mold were all the same, and slurries were made using the general methods described above for making the primer slurry, middle slurry, and backing slurry, with 13305g WDS 3 silica powder 6259g NA L CO1130, 545g NA L CO6300, 285g deionized water, 10g NA L CO 2305 antifoam additive, and 10g NA L CO 8815 wetting additive mixed during preparation.

The CE-2 investment casting molds were fired at 2000 ℃ F. (1093 ℃ C.) for 2 hours prior to use.

Example 3(EX-3)

The general procedure described above for making investment casting molds was used to make an EX-3 investment casting mold, except that no primer layer was applied, and the EX-3 investment casting mold included only one backing layer the composition of the intermediate layer and the sealing slurry layer was the same as that described above for making a CE-1 investment casting mold.the slurry for the EX-3 backing layer had a unique composition that could be made into a single usable backing layer the general procedure described above for making the primer slurry, intermediate slurry and backing slurry was used to make an EX-3 backing slurry, during which 6750g Min-Sil 120F fused silica powder, 3362g NA L CO1130, 476g deionized water, 164g styrene-butadiene latex binder and 15g RHOE L ATE 420 rheology additive (thixotropic agent) were mixed.

The EX-3 investment casting molds were fired at 2000 ℃ F. (1093 ℃ C.) for 2 hours prior to use.

Sufficient quantities of permeability, rupture and strength test specimens were prepared using the CE-1, CE-2 and EX-3 formulations to perform the tests under various test conditions as described below. Sample preparation and testing was performed using the procedure described above. The test results obtained are as follows.

Thickness of the shell

The thickness of the shells from which each formulation was constructed was determined using the CE-1, CE-2 and EX-3 samples used for the strength test and permeability test. The shell thickness data is summarized in table 1 below.

TABLE 1

Table 2 below summarizes permeability and rupture test data for CE-1, CE-2, and EX-3 obtained using the above-described methods.

TABLE 2

Table 3 below summarizes green strength test data for CE-1, CE-2, and EX-3 obtained using the methods described above.

TABLE 3

Table 4 below summarizes the hot/wet strength test data (e.g., "hot/wet" status) after boiling in water for 15 minutes. CE-1, CE-2 and EX-3 were obtained using the methods described above.

TABLE 4

Table 5 below summarizes the post-firing (after cooling to room temperature) strength test data for CE-1, CE-2, and EX-3 obtained using the methods described above.

TABLE 5

Table 6 below summarizes the post-firing (test at elevated temperature) strength test data for CE-1, CE-2, and EX-3 prepared using the methods described above.

TABLE 6

Examples 5-22(EX-5 to EX-22) and comparative example 4(CE-4)

Comparative example CE-4 and examples EX-5 to EX-19 were prepared to demonstrate the variation in rheological properties of the backing slurry available with the amount and type of various rheological additives CE-4 was prepared in the same manner as EX-3 except that CE-4 did not contain any rheological additives EX-5 to EX-22 were prepared in the same manner as EX-3 except that the rheological additive RHEO L ATE 420 was replaced with the various rheological additives as summarized in table 7 below.

TABLE 7

Examples 24-26(EX-24 to EX-26) and comparative example 23(CE-23)

EX-24 to EX-26 and CE-23 were prepared in the laboratory using a "Magic Bullet" high intensity mixer according to the recipe shown in Table 8 below, first, NA L CO1130 colloidal liquid, Minco HP styrene-butadiene latex and deionized water were mixed by hand, then Min-Sil 120F fused silica powder was added and mixed with a high intensity mixer for 1 minute, after which time CE-23 was prepared.

For EX-24 and EX-25, BENTONE EW was added to the batch, gently mixed by hand to wet the clay, then mixed in a high intensity mixer for 30 seconds, then RHEO L ATE 420 was added to the batch and mixed at high intensity for 1 minute, all slurries were tested over a 24 hour recipe to determine their rheological properties.

TABLE 8

The yield stress and viscosity at the initial flow of each example/comparative example listed in table 8 above were obtained. The results are summarized in table 9 below.

TABLE 9

Examples 27-32(EX-27 to EX-32) and comparative examples 24-25(CE-24 to CE-25)

The general method for preparing the investment casting molds described above was used to prepare EX-27 to EX-32 investment casting molds, except that for each example of EX-27 to EX-32, in a first step, a wax pattern was coated with a "primer layer" comprising an initial coating of a primer slurry layer, and the initial coating was further coated with a primer stucco layer, the wax pattern was immersed in the primer slurry (the same composition as used in CE-1) for about 20 seconds while rotating and moving the wax pattern to maximize the uniformity of the primer slurry layer, thereby forming a primer slurry layer, then the wax pattern comprising the primer slurry layer thereon was exposed to a 50 × 100 mesh zircon particle fluidized bed, the primer stucco layer was deposited onto the wet primer slurry layer, then the wax pattern comprising the primer stucco layer was dried at 21 ℃ for about 2 hours, after which the wax pattern with the dry primer slurry was coated with the corresponding exemplary slurry, then fused silica particles with a particle size of 30 × 50 mesh was used to form a stucco layer, the wax pattern for each example of EX-27 to EX-32 was dried to a unique composition that was also capable of being applied to the EX-32 as a single sealing layer, after the unique sealing layer coating slurry was dried.

General procedure for making primer, intermediate and backing pastes as described above EX-27 paste was prepared by mixing 13500g Min-Sil 120F fused silica powder, 15g BENTONE EW, 6724g NA L CO1130, 952g deionized water, 328g styrene-butadiene latex binder and 60g RHEO L ATE 475 rheology additive (thixotropic agent) during the preparation.

The EX-28 slurry was the same as the EX-27 slurry except that it was aged for 1 month prior to use.

The EX-29 slurry was the same as the EX-27 slurry, except that it contained 30g of BENTONE EW.

The EX-30 slurry was the same as the EX-29 slurry except that it was aged for 1 month prior to use.

The EX-31 slurry was identical to the EX-27 slurry, except that it contained 120g of RHEO L ATE 475.

The EX-32 slurry was identical to the EX-31 slurry except that it was aged for 1 month prior to use.

CE-24 and CE-25 are identical to CE-1 and CE-2, respectively.

Sufficient quantities of permeability, rupture and strength test specimens were prepared using the CE-24, CE-25 and EX-27 to EX-32 formulations to perform the tests under various test conditions as described below. Sample preparation and testing was performed using the procedure described above. The test results obtained are summarized below.

The thickness of the shell from which each formulation was constructed was determined using CE-24, CE-25 and EX-27 to EX-32 samples prepared for strength testing (24 samples per example) and permeability testing (10 samples per example). The shell thickness data is summarized in table 10 below.

Watch 10

Table 11 below summarizes permeability and rupture test data for CE-24, CE-25, and EX-27 through EX-32 obtained using the methods described above.

TABLE 11

Table 12 below summarizes green strength test data for CE-24, CE-25, and EX-27 through EX-32 obtained using the methods described above.

TABLE 12

Table 13 below summarizes the hot/wet strength test data (e.g., "hot/wet" status) after boiling in water for 15 minutes. CE-24, CE-25 and EX-27 to EX-32 were obtained using the methods described above.

Watch 13

Table 14 below summarizes the post-firing (after cooling to room temperature) strength test data for CE-24, CE-25, and EX-27 through EX-32 obtained using the methods described above.

TABLE 14

Table 15 below summarizes the post-firing (tested at elevated temperatures) strength test data for CE-24, CE-25, and EX-27 through EX-32 prepared using the methods described above.

Watch 15

All patents and patent applications mentioned above are expressly incorporated herein by reference. Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It will be apparent to those skilled in the art that various modifications and variations can be made in the method and apparatus of the present invention without departing from the spirit and scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the following claims and their equivalents.

Claims

1. A slurry composition for investment casting, the slurry composition comprising:

a refractory material;

a binder;

a solvent; and

a thixotropic agent comprising a polymer emulsion, wherein the polymer emulsion comprises an alkali-swellable polymer;

wherein the composition is subjected to a temperature of 25 dynes/cm²To 800 dyne/cm²Yield stress in the range exhibits a working viscosity of 20 poise.

2. The composition of claim 1, wherein the polymer emulsion is an aqueous emulsion.

3. The composition of claim 1 or 2, wherein the alkali-swellable polymer comprises a hydrophobically modified methacrylate.

4. The composition of claim 1 or 2, further comprising a layered aluminosilicate clay.

5. The composition of claim 4, wherein the layered aluminosilicate clay is present in an amount in a weight ratio relative to the polymer emulsion ranging from 1:6 to 4: 1.

6. The composition of claim 1 or 2, wherein the polymer emulsion is present in an amount ranging from 0.07 wt% to 0.75 wt% based on the total weight of the composition.

7. The composition of claim 1 or 2, wherein the composition has a total solids content ranging from 50 wt% to 75 wt%, based on the total weight of the composition.

8. The composition of claim 1 or 2, wherein the binder comprises colloidal silica.

9. The composition of claim 1 or 2, wherein the binder comprises a styrene-butadiene latex.

10. The composition of claim 1 or 2, wherein the binder comprises a polyvinyl butyral resin.

11. An investment casting mold prepared using the composition of any one of claims 1-10.

12. A method of preparing an investment casting mold, the method comprising:

coating a primer layer comprising a first fire resistant slurry and a first fire resistant stucco over the sacrificial pattern;

at least partially hardening the primer layer;

coating an intermediate layer comprising a second fire resistant slurry and a second fire resistant stucco on the primer layer;

at least partially hardening the intermediate layer;

applying a backing layer comprising a thixotropic agent comprising a polymer emulsion on the intermediate layer; and

allowing the backing layer to at least partially harden,

wherein the first refractory slurry and the second refractory slurry each comprise the slurry composition of any one of claims 1-10.

13. The method of claim 12, wherein the investment casting mold has a non-sintered fracture modulus in the range of 250psi to 700psi after fully hardening.