US 3305358 A
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Description (OCR text may contain errors)
Feb. 21, 1967 3,305,358
METHOD N. G. LIRONES FOR SHAPING BERYLLIUM AND OTHER AAAAAAAAAAAAAAA CS INVENTOR.
Nick 6'. Drones United States ?atent C) ice 3,305,358 METHOD FOR SHAPING BERYLLIUM AND OTHER METALS AND CERAMICS Nick G. Lirones, North Muskegon, Mich, assignor to Howrnet Corporation, a corporation of Delaware Filed Sept. 20, 1963, Ser. No. 310,433 6 Claims. (Cl. 75211) This invention relates to the art of producing shaped products of sintered powders and its relates more particularly to molds and compositions and methods for producing same and in the use of such molds for the fabrication of powders into products of defined and predetermined shapes.
As used herein, the term powders is meant to include metals, alloys of metals and ceramics and the like in finely divided form and preferably such metals, alloys of metals and ceramics which, alone or in combination with a binder, are capable of being formed into composites of high strength responsive to sintering at elevated temperature.
Of particular interest are such powders as are formed of beryllium, tantalum, titanium, zirconium, tungsten, chromium, columbium, molybdenum, and other high melting point or refractory metals and their oxides and metallides from which it is difficult if not heretofore impractical to produce shaped products by the conventional techniques of casting the metal, while in a molten state, into suitable refractory molds. Included also are the other high melting point metals and alloys or the oxide dispersed family of metals and ceramics, such as quartz, glass, porcelain and the like, as will hereinafter be described.
With reference to beryllium, beryllium oxide or beryllides (beryllium compounds such as beryllium sulfides and others of the ides), for example, widespread acceptance has not been achieved of such beryllium metals, oxides or beryllides because of the high costs incurred in the fabrication of the various of the shapes desired for use. For example, this exotic metal finds widespread use in the field of nuclear reactors, missiles and other parts because of the extremely low specific gravity of the metal, its high strength and its rigidity at high temperatures, just to name a few of the many desirable properties of the metal.
When it is desired to make use of the metal as a shaped body, or when it has been desirable to make shaped products of the metal, it has been the practice to reduce the metal to a powdered state. The powder is then loaded into a housing of uniform cylindrical or rectangular shape for compression between platens to densify the powder whereafter the entire assembly is raised to elevated temperature for sintering to form large composite rectangular or cylindrical blocks of the sintered metal.
When it is desired to form shaped parts, the blocks are cut into rough segments which are thereafter carefully machined to the desired shape. Such amounts of material are lost in machining, such care is required in machining, and such precatious are required for protection of the operators from the beryllium dust that considerable time is expended in the fabrication of the shaped part and the cost for the machining of the part from the previously formed block has often times been many multiples of the cost of the material itself thereby materially to limit the uses capable of being made of this type of metal.
The foregoing experience with beryllium is only typicay of the beryllium oxides, beryllides and other metals and metal oxides and metallides, such as of tantalum, ti-
Patented Feb. 21, 1967 tanium, TD nickel, tungsten and the oxide dispersed family of metals.
It is an object of this invention to provide a new and improved process and composition and elements for use in said process wherein shaped products approximately conforming to the desired shape can be molded of such metals, metal oxides and metallides or ceramics by a relatively low cost forming process to produce products of the desired shape and it is a related object to provide a process of the type described which can be carried out to produce high yields at minimum expense and in minimum time without the need for highly skilled labor or highly specialized and expensive equipment and in which a product of the desired physical and mechanical properties can be made available at relatively low cost.
These and other objects and advantages of this invention will hereinafter appear and for purposes of illustration, but not of limitation, an embodiment of the invention is shown in the accompanying drawings, in which- FIG. 1 is a cross-sectional view of a mold part prepared in accordance with the practice of this invention;
FIG. 2 is a sectional view similar to that of FIG. 1 showing the mold part filled with powdered beryllium metal; and
FIG. 3 is a sectional view of the beryllium metal part molded in accordance with the practice of this invention.
The concepts of this invention reside in the use of the metal, metal alloy, metal oxide, metallide or ceramic in finely divided form formulated either into a fluid or preferably aqueous slip composition or as apourable powder for introduction into mold cavities of molds specially fabricated of selected materials to provide support for such powders or slips for the shaping thereof and for the maintenance of such shapes until the composite is heated to sintering temperature to bond the powders to the desired shaped product without permitting undesirable alterations of the heated metal but while permitting the sintered product simply and easily to be removed for release of the product shaped of the beryllium, beryllium oxide, beryllide or other metal, metal alloy, or ceramic of the type described.
The concept of this invention can be divided into two phases, the first of which relates to the fabrication of special molds and the compositions employed in the fabrication of same, hereinafter referred to as the mold phase, and the other of which relates to the special formulation and techniques for the production of shaped products in the prepared molds, hereinafter referred to as the production phase.
In accordance with the practice of this invention, in the mold phase at least the inner portion and preferably the entire cross-section of a mold is of graphitic material formed on the surface of a heat or otherwise disposable pattern by series of integrated layers of dip coats and stucco coats but in which the essential solids of the dip coat composition and the stucco, including the binder, forming at least the inner portions of the mold, are all graphitic, as will hereinafter be described.
The mold phase will be described with reference to compositions employed and the methods of manufacture in a representative process illustrating the practice of this phase of the invention.
In the following description, the terms pattern and cluster will be used interchangeably to refer to the wax or plastic pattern 10 or a cluster formed of a multiplicity of such individual patterns. It will be understood that changes may be made in the details of formulation, materials and methods employed without departing from the spirit of the invention.
3 EXAMPLE 1 Preparation of wax pattern and cluster The pattern 10 is formed of conventional materials disposable by heat or chemicals, as in the well known investment casting processes. In the illustrated modification, the pattern is molded under pressure in suitable metal molds by injection of molten wax to fill the mold and set the pattern. thermoplastic, synthetic resinous material or combinations of such plastics and wax.
If the mold is to be formed about more than one pattern, the plurality of patterns are connected by runners for communication with a pouring spout to form a completed cluster, as described in the Operhall et al. Patent No. 2,961,751. Where, as in the instant process, the cluster is to be repeatedly dipped into a slurry, identified as a dip coat, it is desirable to provide a hanger rod for carrying the cluster and for suspending the cluster for drying and the like.
7 EXAMPLE 2 Dip coat composition 2.77 percent by weight solids of colloidal graphite (22% solids in aqueous medium) 37.8 percent by weight solids of graphite flour (less than 200 mesh) 0.174 percent by weight emulsifying agent (gum tragacanth) 0.00325 percent by weight anionic wetting agent (sodium heptadecyl sulphate) Remainder water As the colloidal graphite, it is preferred to make use of colloidal particles of graphite of less than 1 micron. For the purpose of reducing cost, use can be made of a combination of such colloidal graphite mixed with up to 50 percent by weight and preferably up to only 30 percent by weight of semi-colloidal graphite having a particle size of between 120 microns.
The amount of colloidal graphite in the dip coat composition may vary but it is desirable to make use of an amount greater than 0.5 percent by weight but less than 5 percent by weight and preferably an amount within the range of 1 to 3.0 percent by weight.
In the dip coat compositions represented by the above formulation, the emulsifying agents and the anionic wetting agents are preferred but not essential. Instead of gum tragacanth, use can be made of other hydrophilic colloids such as the gums, gelatins, alginates and the like, wherein, when used, such emulsifying agents are employed in an amount within the range of 0.01 to 0.5 percent by weight. Instead of the sodium heptadecyl sulphate wetting agent, other anionic surface active agents may be employed such as the allyl sulphates and the allyl aryl sulfonates and their salts. When employed, the amount of such surface active agent may range from 0.01 to 0.5 percent by weight of the composition.
The dip coat composition will have a pH within the range of 8.8 to 9.4 and a viscosity measured by the cup of Patent No. 3,011,986 of between 2535 seconds.
The solids content, insofar as the colloidal or semicolloidal graphite and graphite flour is concerned, can be varied quite widely, it being necessary only to formulate for a viscosity that can be handled to coat the pattern and to make use of colloidal or semi-colloidal graphite in an amount sufficient to achieve the desired bonding action. For this purpose, it is deemed sufficient if the latter is present in an amount to make up more than 1.5 percent by weight of the graphite solids of the dip coat composition and it is usually undesirable and uneconomical to make use of an amount of colloidal or semi-colloidal graphite greater than percent by weight of the graphite in the dip coat composition. It will be understood, however, that the essentially 100% graphite making up the Instead, the pattern can be formed of a,
solids in the dip coat composition can be achieved by the use of colloidal or colloidal and semi-colloidal graphite alone.
Application of dip coat composition The wax pattern or cluster is first inspected to remove dirt, fiakes and other objects which may have adhered to the surfaces of the wax patterns and which, if allowed to remain, would impair the preparation of a good mold and lead to an imperfect casting. The cleaned cluster is immersed into the dip coat composition, while being stirred, to cover all of the surfaces of the cluster with the exception of the lip of the pouring spout. To pro= mote the elimination of air pockets, it is desirable to rotate the cluster while immersing in the dip coat corn-position. Instead of immersing the pattern in the stirred slurry of the dip coat composition for coverage of the surfaces of the pattern, the dip coat composition can be applied to achieve the desired coverage by spraying the the dip coat composition onto the surfaces of the pattern. By this latter spraying technique the casting weight of the dip coat composition can be increased or decreased, as desired, by comparison with the amount of coating retained on the surfaces of immersion.
When fully coated, the pattern or cluster is suspended to drain excess dip coat composition. During drainage, the cluster can be inspected to detect air pockets which can be eliminated by addressing a stream of air onto the uncoated portions and thereafter allowing the slurry of the dip coat composition to flow onto the uncovered areas. While the cluster is being drained, it should be held in different planes designed to achieve uniform coating on all surfaces. In general, drainage should be completed within a few minutes but, in any event, in less time than would allow the dip coat composition to gel or dry whereby the surface would not retain stucco in the desired uniform arrangement.
EXAMPLE 3 Stuccoing After the cluster has been allowed to drain for a short time and while the surface is still wet with the dip coat composition, the surface is stuccoed with particles of graphite having the following particle size distribution:
Tyler screen size: Percent retained on screen 65 62 29 '7 200 11 Pan 1 The graphite will hereinafter be referred to as having a particle size of more than 150 mesh but less than 35 mesh. The particles of graphite are caused to flow over the surface of the pattern until the wet surface is substan tially completely covered.
Application of stucco coat After the uniformity of coating has been achieved with the dip coat composition, the stucco is sprinkled onto the wet surface While constantly changing the position of the cluster substantially uniformly to cover the dip coating with a layer of stucco, while at the same time minimizing flow of the dip coat composition whereby non-uniformities might otherwise develop. In practice, the graphite particles are rained down from above through a screening member which is constantly fed from a vibratory conveyor. The particles of graphite adhere to the wet coating and become partially embedded therein to become integrated with the coating formed on the wax patterns.
If the dip coat composition is adjusted to enable gellation to take place within a very short period of time, the stuccoed cluster need not be set aside for drying. However, it is preferred to slow the gellation of the dip coat so that sufficient leeway is available for the desired drainage and stucco application. Thus it is desirable to provide for an air dry for a time ranging from -25 minutes. It will be understood that the drying time may be extended indefinitely beyond the times described without harm to the structure. If desired, drying of the combined coatings can be accelerated in a humidity controlled air circulating chamber heated to a temperature up to about 100 F.
The particle size of the graphite stucco is not critical since the particle size of the graphite can be varied over a fairly wide range. However, for best practice of this invention, it is preferred to make use of graphite having a particle size greater than 150 mesh and less than 20 mesh.
The operation is repeated, that is the pattern is again dipped into the dip coat composition and covered with fine particles of graphite to build up a second composite layer. In the preferred practice of this invention, it is desired, though not essential, to precede the immersion of the coated pattern in the dip coat composition with a prewetting step in which the prewetting composition employs substantially the same formulation as the dip coat composition with the exception that a lower viscosity is employed occasioned by the formulation to include additional amounts of water suflicient to reduce the total solids to about 2575% of the solids in the dip coat composition. Thus the coated pattern is first submerged in the prewet composition more completely to penetrate and wet out the coated surface followed almost immediately by submersion in the dip coat composition after which the steps of drainage, stuccoing with the fine particles of graphite, and drying are carried out. Thus the layers become better integrated one with the other to produce a strong and composite structure.
The steps of prewetting, if uesd, dip coating, stuccoing with the dry particles of graphite and drying can be repeated several times until a mold 12 of the desired thickness and strength has been built up about the disposable pattern or cluster.
While a mold of higher strength will be secured if the graphite particles of the type having a mesh size within the range of more than 150 but less than 20 are used throughout to build up the mold, it is preferred to make use of particles of graphite of larger dimension for use as the stucco after the second coat and preferably after the fifth coat. For such outer layers or coatings, graphite having the following particle size distribution may be employed:
Percent retained Tyler screen size: on screen 8 1 10 14 20 65 35 18 65 1 Pan l The foregoing will hereinafter be referred to as having a particle size greater than 35 mesh but less than 8 mesh.
Instead of fabricating the mold entirely of graphitic material, the inner portion of the mold immediately adjacent the disposable pattern may be fabricated substantially entirely of graphitic materials while the major cross section, forming the outer portion of the mold, is formulated of the conventional ceramic materials in the dip coats and stucco coats, or of dip coats formulated to contain colloidal graphite as the binder component along with conventional ceramic flours, as will hereinafter be described, with the stucco comprising ceramic materials, such as zircon, alumina, silica and the like.
The steps of prewetting, if used, dip coating and stuccoing with the described graphite systems can be repeated one or more times but, in accordance with the further modification, after about the second, third or fourth cycle, the remainder forming the major cross section of the shell is built up by the use of dip coat compositions and stuccos of the inorganic or ceramic type. The following will illus- 6 trate dip coat compositions and stucco which may be used to build up the remainder of the shell mold:
EXAMPLE 4 Dip coat composition 8000 cc. colloidal silica (30% grade-specific gravity 1.198) 165 pounds zircon (99% through 325 mesh) 6150 cc. water grams sodium fluoride EXAMPLE 5 Stuccoing composition: tabular alumina in the form of coarse particles greater than 14 mesh with less than 10% through 50 mes/1 Instead of making use of a dip coat composition formed substantially entirely of 'the ceramic materials or inorganic materials as dmcribed in Example 4, certain advantages are derived, as will hereinafter be pointed out, by the use of a dip coat composition for the subsequent coats wherein colloidal graphite is retained as a component in combination with ceramic inorganic materials conventionally employed as the flour and the like in the dip coat composi tion. The following will represent a dip coat composition of the type described:
EXAMPLE 6 11 pounds distilled water 8.8 pounds of a 22% dispersion of colloidal graphite in water 88 pounds zirconia of less than 325 mesh 200 cc. of anionic wetting agent (sodium heptadecyl sulphate) The foregoing dip coat compositions of Examples 4 and 6 and the stucco of Example 5 can be built up onto the previously formed layers of the graphitic materials by procedures as previously described.
A mold 12 having a wall thickness of from A1 to /2-inch is usually sufficient for the slip casting, pressureless forming, and the like, although molds of greater wall thickness can be formed where greater strengths are desired for use in the molding of larger castings. The normal wall thickness of mold can be achieved with the compositions described with from 5l0 cycles of dip coating, stuccoing, and drying. Where the inner portions are to be formed of graphite and the outer portions with ceramic materials in accordance with the described modification, the normal wall thickness of the mold can be achieved with the compositions described including from two to four cycles of dip coating, stuccoing and aging with the graphite systems of Examples 2 and 3 and with from three to eight additional coatings of the ceramic systems of Examples 4 to 6. Instead of alumina as a stucco, use can be made of Alundum, zircon, silica and the like.
EXAMPLE 7 Dewaxing After the composite mold has been produced, the disposable pattern is removed to leave a mold cavity in which the material to be molded may be cast. Pattern removal, hereinafter referred to as dewaxing, can be achieved in a number of ways:
(a) Use can be made of flash dewaxing wherein the composite is heated to an elevated temperature far above the melting point temperature of the wax or plastic. In a preferred process of flash dewaxing, the composite is heated to a temperature above 800 F. and preferably to a temperature within the range of 8002200 F. for a time sufficient to eliminate the wax and to fire the mold. When the mold is exposed to a temperature in excess of 800 F. during dewaxing or firing, it is desirable to enclose the mold within a reducing or non-oxidizing atmosphere, otherwise the graphite binder will be burned out.
(b) Dewaxing can be carried out by a process referred to as hot sand dewaxing wherein sand heated to a temperature of 400800 F. is arranged to surround the composite for intimate contact with the outer surfaces thereof whereby rapid heat transfer is achieved into the interior to melt out the wax. The hot sand can be poured about the mold or the mold can be buried in the hot sand. Instead of sand, use can be made of a metal or alloy system of low melting point such as the cerro alloys, low eutectic alloys, and the like.
(-c) Dewaxing can be carried out with steam when the wax patterns are formed of a material having a melting point range below 200 F. For such purpose, the composite can be housed within a steam chamber or autoclave or else steam at relatively high pressure can be addressed onto the composite while it is suspended with the spout extending downwardly for drainage of the molten wax.
(d) Dewaxing can be carried out in an oven heated to a temperature above the melting point temperature of the wax but below the oxidizing temperature of the graphite, or preferably at a temperature within the range of 250850 F. in a process referred to as slow temperature dewaxing, without the need to maintain a reducing atmosphere.
The mold is thereafter fired by heating to a temperature above 800 F. and preferably to a temperature within the range of 800-2200 F. Firing can be achieved by exposure of the mold to firing temperature for 15 or more minutes but it is preferred to fire the mold at a temperature within the range of 8002200 F. for a time within the range of l5120 minutes. Firing can be carried out concurrently with dewaxing when use is made of a high temperature dewaxing method as described in (a) above. Since graphite will be consumed when heated to a temperature above 800 F. in an oxidizing atmosphere, high temperature dew-axing and firing are carried out in an inert atmosphere and preferably in a reducing atmosphere. For this purpose, use can be made of hydrogen or an atmosphere composed of carbon monoxide.
Because of the thinness of the walls of the mold and the high heat conductivity of the graphite, heat penetrates rapidly through the mold to cause the wax portion of the pattern immediately adjacent the interior surfaces of the mold to be reduced to a molten state even before the remainder of the pattern has been heated to elevated temperature. Thus the liquefied portion leaves suflicient room to permit expansion of the remainder of the wax pattern when the cross section of the pattern is heated to elevated temperature thereby to eliminate strain on the mold which might otherwise lead to breakage.
The fired mold is cooled from firing temperature to a safe temperature below 800 F. before exposure to atmospheric conditions for continued cooling or for further processing.
To the present, description has been made of the mold phase wherein the inner portions of the mold coming into contact with the cast met-a] are formed entirely of graphite including colloid-a1 graphite, graphite flour from the dip coat composition and graphite particles from the stucco, while the outer portions of the mold, out of contact with the cast metal, are formed of graphite or of conventional ceramic materials to back up and reinforce the graphite layers.
The description will hereafter be made to the production phase of this invention wherein use is made of the new and novel mold in the fabrication of shaped products by such means as slip casting, pressureless casting, and the like, of metals, ceramics and the like materials, many of which have not been capable of being formed into shaped cast parts by rocesses and with materials heretofore available.
An important concept of the invention is unique to the type of mold that is produced. The graphite mold of this invention is capable of being cleanly and substantially completely removed to leave a clean shaped product merely by exposure to high temperature in an oxidizing atmosphere, as by heating in air, whereby graphite is consumed. The entire mold can be caused to be consumed at a temperature above 800 F. in an oxidizing atmosphere but it has been found to be sufficient only partially to burn out the graphite since the remainder can thereafter be easily pulled off for clean removal from the product.
The use of such dispensable graphite mold contributes materially to the adaptability of such molds for the slip casting or pressureless forming of such materials as ceramics, cermets, glass and the like, which may not have the strengths sufficient to enable mold release by conventional impacting techniques but from which the mold can be quickly and efficiently removed by the described burning out procedures to free the element. Under such circumstances, the graphite mold acts as a support for the ceramic shape'until such time as the graphite is oxidized off. The ceramic or other casting becomes self-supporting by the time that the graphite is consumed.
The graphite mold of this invention also embodies a combination of characteristics which enables new and novel use in the forming of shaped products by the slip casting techniques formulated of materials which have heretofore been difficult to mold into shapes, such for example as with molds of the type TD nickel, nickel, tungsten, beryllium, tantalum, titanium, the oxide dispersed family of metals, and ceramics.
Slips of such metals and ceramics can be poured into the mold cavity of the graphite mold to form cast elements employing the concepts of slip casting, but wherein the porous graphite body of the high strength graphite mold effects removal of sufiicient of the liquid carrier to set the slip in the mold.
The following are illustrative of metal slip casting compositions:
EXAMPLE 8 Nickel 0.88 gram colloidal graphite 440 grams less than 325 mesh nickel 36 grams distilled water EXAMPLE 9 316 stainless steel 1.1 grams colloidal graphite 680 grams less than 325 mesh 316 stainless steel 50 grams distilled water Procedure The slip compositions are poured into the fired mold in amounts suflicient to fill the mold cavity and prefera'bly in an amount to replace the volume of material absorbed from the slip into the adjacent porous walls of the graphite mold. Moisture is absorbed from the cast slip composition into the capillaries and pores of the graphite walls of the mold rapidly to set the slip in the mold cavity. After the cavity has been filled and the casting set, with one or more additions of slip composition, if necessary, the composite is dried at elevated temperature, such as at a temperature of up to 225- 350 F.
In the case of the metal slips of Examples 7 and 8, the composite is heated to the sintering temperature for the metal while still being supported in the graphite mold. The sintering temperature will vary depending on the metal and composition thereof, i.e., whether a binder metal of lower melting point is also present. For example, for the nickel composition of Example 8 or the stainless steel of Example 9, the time and tem- 9 perature for sintering is selected within the range of 2200-2500 F. for from /2 to several hours. It is preferred to carry out such sintering in vacuum or in an inert or reducing atmosphere.
As for the ceramic composition of Example 10, the composite can be heated to sintering temperature.
The system described in Example provides a unique combination wherein the colloidal graphite functions as an interim binder which can be easily burned out when heated to elevated temperature to produce a molded product of pure silica or the like. This concept is especially beneficial in core formation where it is desirable to produce a core of a pure high melting point material such as of silica, aluminum oxide, and the like. Thus for this concept, it will be understood that ceramic materials other than quartz or silicon oxide can be used in substitution for the silica in Example 10, such for example as aluminum oxide, zirconium oxide and the like, to produce a pure ceramic molding or core.
After sintering, and after the casting has been cooled, the mold is broken away to release the casting. If it is desired to consume graphite binder for easier release of the casting, the heated mold may be exposed to oxidizing atmosphere while at a temperature above 800 F.
When colloidal graphite is used, the amount of col loidal graphite in the slip cast composition may be varied but it is desirable to make use of an amount at least as great as 0.25% by weight and it is undesirable to make use of an amount in excess of about 3% by weight. The preferred range for graphite binder in the slip cast composition is within the range of 0.5 to 1.5% by weight. With steels, such as stainless steel, graphite of the binder may enter into the steel composition at the sintering temperature to produce a new and improved product. Temperatures above or below the range of 2200-2500 F. can be employed in sintering depending somewhat upon the materials that are being molded and depending also on the presence of binder metals or eutectoids of lower melting point,
An important concept of this invention resides in the method and means by which beryllium shapes can be produced with the graphite molds of the type produced in accordance with the practice of this invention.
In the preparation of a shaped beryllium part, the graphite mold is produced from a pattern having the shape of the part desired plus the tolerances calculated to compensate for the amount of shrinkage which will take place when the beryllium metal is cooled from sintering temperature to ambient temperature. After the graphite mold has been produced and fired, the mold cavity is filled with beryllium, reduced to a finely divided state, perferably less than about 20 mesh and more preferably less than about 100 mesh. The powder fiows rather freely into the mold cavity to fill the mold cavity but to insure filling and to maximize densification, it is desirable to impact or vibrate the mold. After the metal powder is packed in the mold, the mold is located within a vacuum chamber and heated under high vacuum to sintering temperature. For beryllium the sintering temperature may be within the range of 21902240 F. and heating is carried out for a time sufficient to heat through the metal casting and to form a sintered metal product which may approach 90% or more of theoretical density. The assembly is allowed to cool down under vacuum until a temperature below 800 F. is reached. Thereafter the assembly may be allowed to cool to ambient temperature within the vacuum chamber or without the vacuum chamber.
Because of the high shrinkage of the beryllium, the molded product may break the mold during the cooling down period to free the casting from the mold or separation can be easily effected after the casting has cooled to about ambient temperature. The graphite adjacent the surface of the metal and the vacuum conditions operate to protect the metal at elevated temperature and the graphite mold is capable of supporting the cast material at the extremely high temperature for sintering. Further, the graphite mold is characterized by a strength sufficient to support the cast material during the formative stages of sintering and cooling but insufficient to cause tearing of the formed metal product by reason of differential con traction during the cool-down stage.
Thus a molded product can be formed of beryllium, beryllium oxide and beryllides and similar metals, such as tantalum, titanium, TD nickel and the like, wherein the product which is of the desired intricate shape or which so closely approaches the desired shape as to require little if any machining, is secured. The shaped product is produced with a minimum of material and with minimum waste and with a marked savings in finishing time thereby not only effectively to reduce the cost of the shaped product but also to enable production of shaped products which have heretofore been incapable of production.
It will be apparent from the foregoing that I have provided a method and means for the production of shaped metal products at low cost and at high yield and a method and means for producing shaped products of materials which have otherwise been incapable of being produced or otherwise incapable of being produced at low cost.
It will be understood that changes may be made in the details of construction, arrangement and operation without departing from the spirit of the invention, especially as defined in the following claims.
1. In the molding of cast shapes of beryllium, the steps of providing a mold formed of graphite in cross-section through at least the inner portion of the mold about the mold cavity including layers of colloidal graphite and graphite flour alternating with layers of graphite stucco, filling the mold cavity with beryllium powder in finely divided form, impacting the mold to density the beryllium in the mold cavity, heating the assembly to a temperature above sintering temperature for the beryllium powder to sinter the beryllium powder cast into the mold, and maintaining a non-oxidizing atmosphere during the heating to sintering and subsequent cooling.
2. The molding method as claimed in claim 1 in which the assembly is heated to sintering temperature above 2100 F. for a time ranging from /2 to several hours.
3. The molding method as claimed in claim 1 in which the mold is formed of graphite material through a portion of the cross-section of the mold while the remainder of the cross-section forming the walls of the mold is formed of ceramic materials.
4. In the molding of cast shapes of beryllium, beryllium oxide and beryllides, the steps of providing a mold formed of graphite in cross-section through at least the inner portion of the mold defining the mold cavity including layers of colloidal graphite and graphite flour alternating with layers of graphite stucco, filling the mold cavity with the finely divided powders of the beryllium selected from the group consisting of beryllium metal, beryllium oxide and beryllide, impacting the mold to density the powder in the mold cavity heating the assembly to sinter the beryllium cast into the mold, and maintaining a non-oxidizing atmosphere during heating to sintering and subsequent cooling.
5. In the molding of cast shapes of a metal selected from the group consisting of tungsten, beryllium, tantalum and titanium, the steps of providing a mold formed of graphite in cross-section through at least the inner portion of the mold about the mold cavity including layers of colloidal graphite and graphite flour alternating with layers of graphite stucco, filling the mold cavity with the metal in finely divided particulate form, impacting the mold to density the metal particles in the mold cavity,
1 1 1 2 heating the assembly to a temperature above the sinter- 2,862,826 12/1958 Hohn et al. 22-2165 ing temperature for the particles of metal to sinter the 2,886,869 5/1959 Webb et al. 22216.5 metal particles cast into the mold, and maintaining a non- 2,979,401 4/ 1961 Szym aszek 752v2i3 oxidizing atmosphere during the heating to sintering and 3,115,698 12/1963 St. Pierre 29-182 subsequent cooling. 5 3,153,826 10/1964 Horton 22216.5
6. The method as claimed in claim 5 in which the D mold is formed of graphite material through the inner OTHER ERENCES portion of the cross-section of the mold while the re- Leszynski, Powder y, Interscience Publishers, mainder of the cross-section forming the walls of the New York, 1961, PP- 463, 466, 9 93 mold is formed of ceramic materials. 10 and 01- References Cited by th E a i CARL D. QUARFORTH, Primary Examiner.
UNITED STATES PATENTS REUBEN EPSTEIN, Examiner.
2,151,874 3/1939 Simons 75-223 LEON D. ROSDOL, R. L. GOLDBERG, R. L.
2,698,990 1/1955 Conant et al. 75-211 15 G-RUDZIECKI, Assistant Examiners.