JP2772090B2 - Ceramic shell mold and core for reactive metal casting - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a ceramic shell mold for casting a metal such as titanium and a method for producing the mold. More particularly, the present invention relates to a slurry comprising a yttria refractory for use as a casting composition for forming a shell mold, and a method of making the same. More particularly, the present invention relates to a slurry comprising a yttria refractory, an acid and an organic solvent for making a ceramic shell mold for casting reactive metals such as titanium and titanium alloys. The compositions of the present invention are characterized by having a favorable shell life and improved stability. The mold manufactured according to the present invention,
It is particularly useful as it allows for the casting of reactive metals with minimal or substantially no alpha skin formation.

In yet another aspect, the invention relates to the ceramics and cast cores used to make them.

BACKGROUND OF THE INVENTION Much effort has been made over the last 25 years to provide compositions and methods for casting reactive metals, particularly titanium and its alloys, in ceramic molds. Interest in such developments and this potential has been stimulated by activities in the nuclear and aviation industries that require strong, lightweight metals. Due to the high strength to weight ratio, titanium is in great demand in the aviation industry and its use is increasing.

Metallic titanium has a melting point near 3100 ° F and reacts with most refractory materials under melting conditions. Early attempts to cast titanium into ordinary casting molds have been unsuccessful due to undesired chemical reactions between the hot metal and the surfaces it contacts. For example, a violent reaction site occurs on the casting surface due to the reducing action of silica present in this type of casting mold.
In the industry, this reaction layer is called the “alpha case”
And the problems involved in this are well described in the literature.

Cut and formed graphite molds have been used commercially to make titanium castings. This type of mold can be made to minimize the alpha skin layer. The U.S. Department of Mines has supported research on refractory metal casting for almost 25 years. Therefore, there is a constant effort to study new materials and methods to reduce or eliminate alpha epidermis.

The use of graphite in precision molds is fully described in U.S. Pat.
3,241,200, 3,243,733, 3,256,574, 3,266,106
No. 3,296,666 and 3,321,005, the technique is disclosed. Graphite powder and "stucco"
The conventional technology showing a carbonaceous mold surface using finely pulverized inorganic powder, referred to as Opahole (Op
erhall, US Patent No. 3,257,692, Zusman
et al., U.S. Patent No. 3,485,288 and Morozov (Mo
Rozov) et al., US Patent No. 3,389,743. These documents describe various methods for obtaining carbonaceous mold surfaces, including graphite and stucco, colloidal silica, colloidal graphite,
Various organic and inorganic binder systems, synthetic resins intended to reduce carbon during burnout, and carbon-coated refractory mold surfaces have been adopted. These methods need to omit oxygen during combustion,
It has been found that there is a disadvantage that the reaction temperature of titanium and carbon is formed on the casting surface due to the limitation of the mold temperature.

To further advance this, a development involving various deformations of the casting mold is described in US Pat. No. 3,802,902 by Turner et al.
In this case, graphite or olivine combined with sodium silicate is used and then coated with a relatively less reactive coating such as alumina. However, this method still did not produce a contamination-free coating surface.

U.S. Patent No. 3,581,6 to Schneider
No. 58 discloses a mold having low reactivity to steel and alloy steel having a high content of chromium, titanium and aluminum, and a magnesium oxide forsterite composition is used on a mold surface.

In the past, numerous attempts have been made to coat graphite and ceramic molds with materials that do not appear to react with the reactive metal being cast. For example, metal powders such as tantalum, molybdenum, niobium, and tungsten, and also thorium oxide have been used as non-reactive mold surfaces with certain oxide binders.
(Brown, U.S. Patent No. 3,442,880;
537,949 and 3,994,346).

U.S. Pat. No. 2,806,271 to Operhall shows a coating in which a patterned material having a continuous layer of metal to be cast is lined with a metal of high thermal conductivity and burned into a mold material.

U.S. Pat. No. 4,135,030 to Basche shows a method of impregnating a standard ceramic shell mold with a tungsten compound and firing in a reducing atmosphere such as hydrogen to convert the tungsten compound to metallic tungsten or tungsten oxide. I have. Although these molds are said to be less reactive with molten tungsten, they still have oxide problems associated with them.

U.S. Pat. No. 4,057,433 to Brown uses fluorides and oxyfluorides of metals of Group IIIa of the Periodic Table and lanthanides and actinides of Group IIIb as components of the mold surface to minimize reaction with molten titanium. How to make it public. This document also shows the incorporation of metal particles of one or more refractory metal powders into a heat sink material. However, this procedure still has some alpha skin problems.

A development by General Electric has included a refractory oxide barrier layer in a Silica bonded mold to cast alloys containing significant amounts of reactive metals. (Gigliotti
i) et al., U.S. Patent Nos. 3,955,616, 3,972,367 and
U.S. Pat. No. 4,240,828 to Huseby shows a method of doping a nickel and cobalt alloy with a rare earth metal and casting it into a ceramic mold.

In the 1960s, Wright Air D
The evelopment center) has produced crucibles for forming molten titanium from titanium-enriched zirconium oxide crucibles that have less reaction to molten titanium than pure zirconia.

US Patent No. 4,040,8 by Richerson
No. 45 shows a crucible and mold ceramic composition that is mostly yttria and contains a small amount of heavy rare earth mixed oxide. This type of method, including the production of titanium-enriched yttria, is a tedious and expensive technique that requires many steps,
It was just part of the success.

Molybdenum casting molds made from calcia-stabilized zirconia combined with zirconium acetate were manufactured by the Mining Department.

U.S. Pat. No. 4,415,673 to Feagin discloses a zirconia binder which is an active refractory containing stabilized zirconia.
liquid zirconia sol used as a binder for ory), which causes the reaction and gelation of the sol. A solid mold was made to cast depleted uranium. The present invention distinguishes between "active" refractory and relatively inert refractory. The composition of the Fegan is intended to include at least some active refractory material. See also U.S. Patent No. 4,504,591 to Fiegan.

For adhesive plasters made from a suspension of oxide powders such as yttrium oxide and acid, see Wholecom (Ho
lcomb) et al. in U.S. Pat. No. 4,087,573. These compositions cure naturally and are useful for forming a coated surface or cast. Of particular interest is the coating of graphite crucibles used in uranium melting operations.

It is generally recognized in the industry that castings obtained by any of the commercial processes produce some alpha skin. Its thickness ranges from 0.005 inches to 0.04 inches, depending on the manufacturing process and the size of the casting. The alpha skin must be scraped by chemical or other means until a satisfactory casting is obtained. The extra cost of a chemical milling operation is disadvantageous and a significant problem in terms of dimensional accuracy. Typically, tooling is performed taking into account the chemical attrition that will be cut away to produce a dimensionally accurate casting. However, since the casting conditions change, the alpha skin on the surface also changes depending on the location. In other words, there is a considerable problem regarding the change in dimensions.

The wax pattern (wax patte) is reduced by a special method, such as reducing the alpha epidermis and spraying.
rn), several refractory compositions have been developed that can be coated to successfully produce production line castings. However, the pot life of certain refractory mixtures is not long, and the problem with the correct composition is that it gels quickly and accidentally with only a few minutes of stirring. In this regard, see Holcombe U.S. Pat. No. 4,087,573.

Therefore, it is highly advantageous to have a slurry that is stable for at least several days, and preferably several weeks, so that patterns of the desired shape can be immersed in the slurry according to current production practices.

The present invention is a ceramic shell mold
The invention relates to a composition of a slurry of yttria, in particular yttrium oxide refractory, an acid and an inert organic solvent used to make the same. The yttria refractory can be dissolved or undissolved and can be present alone or, if desired, with other refractories. Preferably, the yttria is dissolved and ground to a suitable fine powder, but undissolved or sintered yttria can also be used. The use of a dissolved refractory material allows for a somewhat denser filler filling to reduce the tendency to microcracking during sintering. Melted or unmelted yttria can be blended with other refractory materials such as zirconia and used to make mold coatings.

The present invention further relates to a reactive composition of yttria refractory, along with other optional refractory materials, and mold coatings and castings made therefrom. The invention also relates to a method of making the coating composition and a method of making the mold. The invention is of particular interest for the casting of titanium and titanium alloys such as Ti6A14V.

As yet another aspect of the present invention, the present invention may include coating cores and molds, casting cores for ceramic and metal casting, and various other refractory materials, metal powders and fibers having good stability. It relates to the use of a slurry of yttria which is suitable for various uses and purposes.

SUMMARY OF THE INVENTION One object of the present invention is to provide a stable composition suitable for producing a mold coating having low reactivity with titanium and a titanium alloy during casting.

It is another object of the present invention to provide a less reactive mold coating characterized by good stability to reactive metal castings.

It is still another object of the present invention to provide a ceramic mold having a casting surface with low reactivity with reactive metals.

It is yet another object of the present invention to provide a method of making an investment casting mold having low reactivity with reactive metals.

It is yet another object of the present invention to provide a relatively non-reactive ceramic shell mold into which metal is injected.

Still another object of the present invention is to provide a castable composition having good stability using a slurry of yttria and a ceramic body made therefrom.

Yet another object of the present invention is to provide a process for producing a precision cast mold with low reactivity with molten titanium, titanium alloys, zirconium and zirconium alloys.

It is a further object of the present invention to spray or apply to casting molds, ceramic cores for casting, melting crucibles, ladle or pouring basins to further withstand reactive metals. It is an object of the present invention to provide a coating composition suitable for the above.

It is a still further object of the present invention to provide a ceramic casting core using yttria slurry.

(Means for solving the problem) "Reactive metal" used here
The term silica, alumina, aluminosilicate,
Poured into a conventional investment casting mold having a mold surface containing one or more of the refractory materials of zirconium silicate (zircon) or other oxides and mixed oxides commonly used in investment casting molds. Metals and alloys that will react or produce a relatively rough mold surface when exposed. Examples of these reactive metals include titanium, titanium alloys such as Ti6A14V, zirconium, zirconium alloys, high carbon steels, eutectic alloys (including substantial amounts of tungsten, hafnium, carbon, nickel, cobalt, etc.), aluminum Lithium alloys, nickel-based alloys containing significant amounts of titanium, aluminum, hafnium and tungsten. Reactive metals are well known in the art, the most reactive of all being titanium.

According to the present invention, there is provided a slurry or suspension type composition comprising as a main component molten or non-yttria in finely divided form. Any finely ground refractory compatible with this can be blended with yttrium oxide. Refractory materials particularly suitable for this purpose include zirconia, molten zirconia, cubic zirconia, calcium oxide and magnesium oxide as stabilizers,
Melt stabilized zirconia with yttrium oxide, lanthanum oxide, dysprosium oxide and other rare earth oxides,
And melt blends of zirconium with other rare earth oxides, and mixtures of any of the foregoing. Generally, when mixed with the other refractory materials described above, yttria is present as the main refractory component. The term "rare earth" as used herein refers to an element having an atomic number of 57 to 71 in the periodic table.

In yet another aspect, the present invention provides a stable slurry composition or suspension of a yttria refractory, an organic solvent and an acid, applying the slurry to a pattern, and applying the coated pattern to water under appropriate conditions. For producing an investment casting mold with low reactivity with reactive metals, comprising facilitating the formation of a "green bond" by exposing to light and then firing to form a fired bond. There is.

Yet another feature of the present invention is that the outside of the pattern is coated with a slurry of yttria, an acid, a solvent and any of the optional refractory materials described above, dried and heated to produce the intended shell mold, as described above. In the way. An alternative procedure is to add a finely ground refractory material called "stucco" to the coating before it dries. The "stucco" technique is well known. After "stucco", the coating is air dried, the shell is removed from the pattern and fired at a sufficiently high temperature to fire the refractory material together.

Still further, as a feature of the present invention, a method of casting a reactive metal in a mold having low reactivity with the reactive metal, comprising a stable suspension of yttria, an organic solvent and an acid, and optionally other refractory materials. Prepare the coating composition with the materials and some water, apply this coating composition to the pattern made into the desired shape, react the coating with moisture to gel, and fully convert the resulting coated pattern Baking at a high temperature to melt the coating composition into a desired shape, and then casting the metal into the desired mold.

A further feature of the present invention is a process for making a core that is coated with a suitable core mold with a slurry of yttria, an acid and an organic solvent. After coating, while the coating is still wet, stucco with a suitable refractory material such as, for example, molten yttria, and then air dry. After drying, a castable mixture of any compatible refractory material is added to the core mold,
The mixture is gelled by applying a coating. After gelling, the finished core can be formed by removing the core from the mold and firing to adhere the coating to the backing casting.

EXAMPLES The compositions of the present invention are characterized by a suspension comprising a yttria refractory, an inert organic solvent and a suitable acid.
Small amounts of water have been found to be acceptable for these compositions. Typical acids used for the purposes of the present invention, such as, for example, HCl and HNO ₃ , contain significant amounts of water even when small amounts of acid are used relative to the total amount of the slurry. In practicing the present invention, care must be taken in water regulation as more water is present, the shorter the shelf life ("pot" life) of the slurry. Under ideal conditions, no water should be added to extend the shelf life of the slurry, i.e. to keep it stable for several months. However, the slurries of the present invention can withstand some water, especially if it is desired to use the slurries quickly. Factors such as the amount of exposure to the atmosphere, the particle size of the yttria refractory, the amount of acid used, and whether or not a rapidly curable slurry is desired also affect the water content. The slurry must be used as quickly as spraying or drying, and more water must be added if some hardening occurs during the drying operation and the dependence on the humidity conditions of the atmosphere is less. These matters will become apparent to those skilled in the art upon reading this specification.

The yttria slurry is prepared by mixing the ingredients in any suitable manner using conventional equipment.
Yttria is a finely ground state, sometimes called "flour". The term "fines" commonly used in the foundry industry refers to finely ground refractory materials commonly used to prepare slurry compositions. The size of the particles can vary considerably, but can still be used to their fullest extent. However, in investment casting, the particle size is typically 150
Means sub-micron, sometimes as small as 1 to 10 microns. The common fines used in the industry are fines that contain particles that are substantially 75% finer than 325 mesh (44 microns), and typically have a wide range of variation. Regarding the size of the "mesh", the US standard mesh series (USStanda
rd Screen Series).

Another size commonly used in the industry is commonly referred to as 325 mesh, which is understood to mean that at least 95% of the particles pass through a U.S. standard 325 mesh. In this case, 95% of the fine powder particles are 44
Finer than micron. Commonly used fines are 150 mesh, 200 mesh and 325 mesh, which is understood to mean that the particles are finely ground and at least 96% pass through the specified mesh. The particle size distribution is not generally available, but can be determined by methods known in the art. Manufacturers of this type of flour make all lots "typical" (typica
l) While there is no guarantee that the results will be the same or match the "batch" analysis, it is well known that certain "representative" grades are indicated by mesh analysis. It is important for the purposes of the present invention to produce a smooth mold surface with sufficiently fine particle size.

During the preparation of the slurry, the component acid reacts with yttria to form the yttrium salt of the acid. This salt then reacts with some of the yttria and reacts like the surface of calcium when exposed to moisture, forming a hydrated salt that forms a "green bond" when exposed to a moist atmosphere I do. This hydrate is then dehydrated by firing to form yttrium oxide and becomes a fired bond.

For the purposes of the present invention, refractory powders or aggregates suitable for addition to yttria for mold compositions and coatings include monoclinic zirconia, yttrium oxide, cubic zirconia, molten yttrium oxide, molten zirconium oxide, As a stabilizer, selected from the group consisting of calcium oxide, magnesium oxide, yttrium oxide, scandium oxide, lanthanum series elements of the periodic table, for example, lanthanum, cerium, dysprosium, praseodymium, neodymium, samarium, oxides, and other rare earth oxides. Melt stabilized zirconium oxide, a mixture of zirconium oxide and yttrium oxide or a mixture of other components of this group, and a molten mixture of zirconium oxide and / or yttrium oxide with other rare earth oxides. Door can be. These can be used with yttria in the slurry, or a mixture of one or more of these can be used.

According to the invention, the slurry also contains an acid as an essential component. As the acid to be used, any acid which reacts with yttria under ordinary room temperature conditions to form a salt which eventually becomes a hydrate can be used. Preferably, the salt is completely soluble in the solvent, but it may be partially soluble. The acid must also be inherently soluble in the solvent and relatively stable under ambient conditions except for reaction with the yttria refractory. To give examples of suitable acids,
There are saturated organic acids having mono- and polycarboxyl groups such as formic, acetic, propionic, citric, succinic, oxalic, tricarballyllic, phthalic, maleic and tartaric acids. Other acids can also be used. The concentration of acid must not be so high as to significantly dissolve yttria or other refractory materials, and must not be diluted with water so that water contributes too much to the system.

Preferably, the solvent present in the slurry according to the present invention does not have a high vapor pressure at room temperature so as to cause cooling and not to break the wax pattern when applying the slurry. In addition, the vapor pressure must not be extremely low such that it takes several days to dry on the wax pattern. The solvent should preferably be water-soluble or semi-water-soluble to facilitate the curing of the coating. Solvents that can be used in accordance with the present invention are generally inert organic solvents and include, but are not limited to, ketones, alkanols, and esters as listed below. That is, acetone, methyl isobutyl ketone, methanol, ethanol, butanol, isobutanol, n-propanol, isopropanol,
Hexanol, methyl ethyl ketone, ethyl acetate, methyl acetate, isopropyl acetate, 1,4-dioxane, ethoxyethanol (cellosolve), methoxyethanol (methyl cellosolve), methoxyisopropanol, and others. Solvent blends can also be used. Higher boiling organic acids such as propylene glycol monomethyl ether and carbitol can be used in whole or in part, but will increase the drying time of the coating.

Yttrium salts have the property of forming hydrated salts or hydroxy salts in the presence of water. (New Yttria Plasters, CE
Holcombe et al., US Department of Energy, Report No. Y-2104, January 1978). For example, yttria that is mixed with a dilute acid such as nitric acid to form a slurry generally gels in a short time of several minutes to form a hardened state.

Since the yttrium salt reacts with the water and shortens the pot life, the H ₂ is adjusted so that the slurry is stable for days or weeks.
It is preferable to use a solvent containing no or minimal O. When water is used as the suspending medium, the slurry gels and hardens in a very short time of several minutes or several hours, and is not suitable for some purposes. The wax pattern may be immersed in the slurry and then exposed to an atmosphere containing some moisture. Atmospheric moisture enters the reaction with the formed yttrium salt to form a hydrated salt, which hardens the coating on the pattern. Rather than exposing the dipped pattern to moisture, it is preferable to expose it to a controlled high-humidity atmosphere and then dry it because a stronger coating can be formed and better production control can be performed. This technique allows the use of a stable slurry for immersion of the pattern and the curing of the coating on the pattern after immersion and stuccoing.

It may be advantageous to include certain other materials in the slurry, such as plastic latex, film formers, soluble plastic materials, organic and inorganic fibers, and other refractory fillers. Minimizing or preventing penetration of the backside slurry medium through the first coating;
It is desirable to include some film former or plastic material to minimize crushing and cracking during final ceramic shell dewaxing. Such additives and adjuvants for this purpose are well known in the art.

In another embodiment of the present invention, it is desirable to include an yttrium salt in the slurry so that the curing effect of the coating can be adjusted more. The yttrium salt must be soluble in the solvent and can be used in place of the yttria and acid combination. Thus, the yttrium salt can be used in whole or in part in place of yttria and acid in the composition of the slurry. The mixing of yttrium salts is as described above, which can react with moisture to form hydrated salts. These salts are, for example, acetates, nitrates, chlorides, sulphates and other salts which can form water and hydrates.

A number of slurries were made experimentally to determine the shelf life of the slurries. These are the first
The results are shown in Table 2 and Table 2. Many types of solvents and acids are used in these tables. Unmelted Y ₂ O ₃ powder (made by precipitation and drying) and sintered Y ₂ O ₃ powder were also used. The effect of the addition of water on the shell life was observed. The presence of water shortens the shell life, so the amount of water must be adjusted as described above.

For the yttria powder used in these examples, two types of powder were used. One is a manufacturer's product,
Used according to manufacturer's instructions. The other is a highly sintered powder adjacent to a molten yttrium oxide ingot. The sintered powder is densified as obtained from the manufacturer but is not as dense as the molten product. A molten ingot was made, crushed and crushed to a size suitable for later experiments. For the purposes of the present invention, any suitable commercially available yttria powder can be used.

Many slurries are deposited on a sheet of wax, excess slurry is washed off, humidity more than 50%, often
It was exposed to a high humidity atmosphere of 75-80. These were dried overnight before examining the strength of the coating. The # 37,38,39,41,17 slurries produced some abrasion resistant coatings, but
Number 5,39,41 was quite hard and strong. No. 60 and 61
The coating from the turn required a long drying time to gain strength. Nos. 75, 76 and 77 were fairly strong and as abrasion resistant as Nos. 81 and 82. The coatings from Nos. 88 and 89 were very hard and strong after complete drying.

The coating was deposited on the wax using a number of slurries and immediately after deposition the sample with the coating was transferred to a container above the water source of the high humidity atmosphere. After drying, these coatings became considerably harder.

For the production of casting molds in Ti6Al4V alloy, a number of pattern wax bars of about 1/2 inch to 5/8 inch diameter have to be about 4 inches long (finger). ) And prepared. To apply the coating, the fingers were dipped into the slurry or the wax fingers were sprayed with a coating material leaving about 1/2 inch of the fingers. After soaking and draining,
The wet coating was stuccoed with coarse molten yttrium oxide of about -40 + 140 mesh size. The coating was then air dried in an atmosphere with a relative humidity of 50% or more. After drying, the pattern was sealed in a central wax sprue with some other experimental coated fingers. The uncoated wax sprue was then coated with molten pure oxidized yttria in colloidal yttria and stuccoed with molten yttria. This was air-dried and immersed in a backup slurry for stucco treatment. Backup (ba
The ck-up) slurry was 325 mesh Ramasi (Ramasi).
l) Mix with 60, 25 seconds # 4 Zahn cup (25seconds # 4 Z
It consists of a 30% liquid silica sol with a viscosity of ahn cup). Seven back-up coats were applied. The coating was allowed to air cure and then recoated with the same slurry, followed by stucco treatment with Ramasil 60, 50 mesh particle size. This was repeated until all the coatings had been applied to the pattern with stucco of 50 mesh particle size. The last coating was not stucco treated. After all coatings were applied, the molds were completely dried for several days before dewaxing, but increasing the drying time is not a requirement. Ramsil 60 in Chadwix, New York
cks) of about 60% of the Remet company
Alumino of Al ₂ O ₃ - is a silicate refractory material.

After the final coating was applied, the final coating was not stuccoed and the mold was left to dry at room temperature. This was then soaked in hot motor oil to remove the wax and leave a shell mold. The resulting shell mold was baked at 2500 ° F for 2 hours and then cooled to room temperature.

One of a variety of facecoats, to form a continuous film, to improve wax adhesion and to prevent the silica binder from penetrating the mold surface during dipping of the backing coating, It seems that vinyl acrylate latex should be added. Several known latexes can be used provided they are compatible with the slurry.

The refractory and other materials that can be used to prepare the slurry according to the present invention can be expressed as follows.

1. Some sources, such as Air Products
oducts), a commercially available vinyl-acrylic latex having improved film-forming properties to the slurry and used to prevent subsequent penetration of liquid from the film into the mold surface.

2. A low-foaming wetting agent such as Sterox from Monsanto Chemical can be used.

3. A commercially available chemical, 2-ethylhexanol, can be used as a defoamer.

4. Standard commercial product, glacial acetic acid.

5.99.9% Y ₂ O ₃ powder electrically melted 1.9% + 200 fused yttrium oxide made by grinding 200 mesh powder showing a mesh.

6. Yttria stucco is the same product as in 5, but the particle size is -40 + 100 mesh.

Each mold is then turned into a centrifugal casting machine (centrifuga
l Attached to the sprue connector of the casting box that is coupled to the casting machine. Foundry sand with a trace amount of sodium silicate binder
Is packed around the mold in the box. After drying, the box is placed under vacuum in a large chamber, degassed, and a commercially available molten 6Al4V titanium alloy is poured into the mold under vacuum.

After casting, cool the mold, remove the fingers,
Divide into sections, embed in plastic, etch until the alpha skin appears, and examine the alpha skin with a microscope.

Table 3 shows the preparation of the slurry used for the mold surface for each pattern casting.

Table 4 shows the measured average values of the alpha skin on each finger casting. These values are very low for alpha epidermis.

With respect to Table 4, it is noted that the samples SA, SK and SL have very low alpha skin values. SB, SC and SJ
Is good, but the value of alpha epidermis is somewhat higher. The high value of the sample SD seems to be due to the effect of the treatment, but the cause is unknown at present.

Regarding the ratio of refractory material in the yttria slurry, for relatively "inert" refractory materials such as monoclinic zirconia, plate-like alumina, fused silica and zircon, the particle size distribution and the specific gravity of the refractory material , Injection molding, casting, compression or dipping and mixing, etc. Generally, when preparing a slurry for dipping an investment casting pattern having a molten yttria refractory flour of about 325 mesh, a ratio of at least 1 part yttria flower to 1 part carrier. Two parts of refractory may be used to make a thick slurry coating. These various ratios can be determined by the particular result desired.

Further, it is advantageous to add refractory fibers to the yttria slurry to produce a high temperature refractory material. These fibers include silicon carbide, silicon nitride, carbon fibers, alumina fibers and the like.

If a gelling agent or active refractory is used with the yttria slurry, many compositions made from the yttria slurry refractory fiber system can be used for special coatings and shape casting.

Separate slurries made of yttria powder, zircon, alumina and fused silica were deposited on a wax pattern and allowed to air dry. The resulting coating resisted knife scratching. Protective coatings can be applied to ceramics, metals, cast molds, and many types of surfaces for applications in the electronics field. For example, a slurry of citric acid, isopropanol, and molten yttria can be sprayed or coated on a refractory melting crucible to minimize the reaction between the metal and the crucible. In addition, weir (po
uring basin and ladle can be coated to minimize the reaction. In particular, for protection when casting an active metal such as titanium into a mold, a thin inert layer is sprayed onto the upper and lower molds of the casting mold and dried to form a strong inert coating. Usually, one layer is sufficient to obtain a good protection effect.

A suitable preform suitable for titanium casting casting molds, for example, by coating the inside of the core mold with a slurry made of molten yttria, citric acid and isopropanol and having a viscosity of about 20 seconds in a # 4 Zahn cup. A molded ceramic casting core was made. A few drops of a non-ionic wetting agent, Sterox NJ, was added to facilitate wetting the surface of the mold.

While the coating is still wet,
Stucco treatment was performed with +100 mesh molten yttria particles. Thereafter, the coating may be air dried at room temperature. After drying the heavy castable mixture of pre-hydrolyzed ethyl silicate binder containing a fused silica refractory and 20% SiO ₂ in various particle sizes under 20 mesh, the core mold having said coating a mixture of Some ammonium carbonate gelling agents can be added to the mixture to allow it to gel spontaneously. After gelling, the core can be removed from the mold. This is then fired at a sufficiently high temperature to bond both the coating and the casting backing to form a finished core ready for casting.

The mixture of refractory material suitable as the body of the core can be any mixture compatible with the coating, and is primarily used to line or support the coating or core surface. If titanium or other reactive metal is poured into the core, the refractory may be yttria.
If the metal is less reactive than titanium, alumina, zirconia or other refractory materials can be used.

Ceramic cores suitable for the casting of reactive metals, and especially titanium, can be made from yttria-type or other refractory materials and cast, injection molded or compressed into a suitable mold to allow the finished slurry to naturally gel. it can. The gelled article can then be dried and fired and used as a casting core.

Other changes and modifications will be apparent to those skilled in the art from the foregoing description and are encompassed by the following claims.

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Claims (30)

(57) [Claims] 1. A refractory composition comprising a slurry of yttria, an acid and an inert organic solvent, wherein yttria is present as a main component in the slurry. 2. A finely ground yttrium oxide refractory, an acid, an inert organic solvent, and a mixture of yttrium oxide, zirconium oxide, molten yttrium oxide, molten zirconium oxide, melt-stabilized zirconium oxide, yttrium oxide and zirconium oxide. A coating production composition comprising a refractory material selected from the group consisting of a molten homogeneous mixture, wherein yttria is the main component of the slurry and a higher component of the refractory material. Composition. 3. The composition according to claim 2, comprising a small amount of water. 4. The composition of claim 1 further comprising a sufficient amount of added refractory. 5. The additive refractory material is monoclinic zirconium oxide,
5. The method according to claim 4, wherein the material is selected from the group consisting of yttrium oxide, cubic zirconium oxide, molten yttrium oxide, molten zirconium oxide, and melt-stabilized zirconium oxide.
A composition as described. 6. The melt-stabilized zirconium oxide is selected from the group consisting of calcium oxide, magnesium oxide, yttrium oxide, lanthanum oxide, dysprosium oxide, and atomic numbers in the periodic table.
Oxides of other rare earth elements from 57 to 71, mixtures of zirconium oxide and yttrium oxide or mixtures of other components of this group, and zirconium oxide and / or yttrium oxide with atomic numbers from 57 in the periodic table
6. The composition according to claim 5, which has, as a stabilizer, one selected from the group consisting of a molten mixture with oxides of other rare earth elements up to 71. 7. The composition according to claim 2, wherein the acid is an organic acid or an inorganic acid, and the acid can react with yttria in the slurry to form a salt that hydrates in the presence of moisture. 8. The composition according to claim 2, wherein the solvent is one of alkanols or ketones. 9. A group comprising finely ground yttria, an acid, and an organic solvent, comprising yttrium oxide, zirconium oxide, molten yttrium oxide, molten zirconium oxide, melt-stabilized zirconium oxide, a molten homogeneous mixture of yttrium oxide and zirconium oxide. A method for producing a coating composition, which comprises mixing a mixture containing a refractory material selected from the group consisting of: 10. A finely ground yttrium oxide,
In acids and organic solvents, having a stabilizer selected from monoclinic zirconium oxide, cubic zirconium oxide, and calcium oxide, magnesium oxide, yttrium oxide, lanthanum oxide, dysprosium oxide, and other rare earth oxides A method for producing a coating composition comprising mixing an additional refractory material selected from the group consisting of melt-stabilized zirconium oxide. 11. A surface coating comprising finely ground yttria, an acid, an inert organic solvent, and an added refractory. 12. The additive refractory material is selected from the group consisting of monoclinic zirconium oxide, cubic zirconium oxide, and calcium oxide, yttrium oxide, lanthanum oxide, dysprosium oxide, and other rare earth oxides. 12. The coating according to claim 11, wherein the coating is selected from the group consisting of melt-stabilized zirconium oxide having a stabilizer. 13. The additive refractory material is selected from the group consisting of yttrium oxide, zirconium oxide, molten yttrium oxide, molten zirconium oxide, melt-stabilized zirconium oxide, and a molten homogeneous mixture of yttrium oxide and zirconium oxide. The coating as described. 14. A refractory made from the composition of claim 1. 15. The refractory according to claim 14, which is a mold. 16. The refractory according to claim 14, which is a core. 17. The refractory according to claim 14, which is a mold. 18. The refractory according to claim 14, which is a core. 19. A sufficient amount of finely ground yttria, acid, organic solvent, and yttrium oxide, zirconium oxide, molten yttrium oxide, molten zirconium oxide, melt-stabilized zirconium oxide, and the melting of yttrium oxide and zirconium oxide A formed mold made from a composition comprising an added refractory selected from the group consisting of a homogeneous mixture. 20. A sufficient amount of finely ground yttrium oxide, an acid, an organic solvent, and monoclinic zirconium oxide, cubic zirconium oxide, and calcium oxide, magnesium oxide, yttrium oxide, lanthanum oxide, oxide A mold formed from an additional refractory material selected from the group consisting of melt-stabilized zirconium oxide having as a stabilizer a member selected from the group of dysprosium and other rare earth oxides. 21. A molded core comprising a molded refractory having a coating formed from the composition of claim 1. 22. A finely ground yttria is prepared, the powder is mixed with a solvent and an organic acid to form a coating composition, and the coating composition is applied to a pattern formed into a desired form. Drying and hardening the composition, heating the completed coated pattern to a sufficiently high temperature and sintering the composition into a desired shape; and forming an investment casting mold having low reactivity with the reactive metal. Production method. 23. Yttrium oxide, zirconium oxide,
23. A coating composition comprising adding an additional refractory material selected from the group consisting of molten yttrium oxide, molten zirconium oxide, melt-stabilized zirconium oxide, and a molten homogeneous mixture of yttrium oxide and zirconium oxide. Manufacturing method. 24. The method according to claim 22, comprising applying a plurality of coatings to the pattern. 25. The coating composition is applied to a pattern or mold, the coating is dried, and the dried coating is subjected to a plurality of identical or different coatings to form a neat mold or core, wherein the coating composition is yttria. A method for producing a ceramic mold or core comprising a slurry, an acid and an inert organic solvent. 26. An additive refractory material wherein the coating composition is selected from the group consisting of yttrium oxide, zirconium oxide, molten yttrium oxide, molten zirconium oxide, melt-stabilized zirconium oxide, a molten homogeneous mixture of yttrium oxide and zirconium oxide. Claims including
25. The manufacturing method according to 25. 27. A mold or a core manufactured by the manufacturing method according to claim 25. 28. A mold or a core manufactured by the manufacturing method according to claim 26. 29. The core mold is coated with a slurry of yttria, an acid and an organic solvent sufficient to wet the surface of the core mold, and then the gellable castable refractory composition is applied to the core mold. 26. The production method according to claim 25, further comprising: forming a core by gelling the refractory composition; removing the core from the mold; and firing; and bonding the yttria-containing coating to the refractory composition. 30. The method of claim 29, further comprising applying stucco to the surface of the yttria-coated core mold prior to adding the refractory composition.