US3263957A - Apparatus for the production of ceramic, cermet, and metal components - Google Patents

Description

63,957 TIoN oF CERAMIC, CERMET, AND L coMPoNENTs G. LIRONES APPARATUS FOR THE PRODUG META Filed Feb. 9. 1961 2 Sheets-Sheet 1 ABSORBENT MATEmALs l l l l I. I .l x I MQW/g y* Vacazzm Aug. 2, 1966 N. G. I lRoNEs 3,253,957

APPARATUS FOR THE PRODUCTION OF CERAMIC, CERMET, AND METAL COMPONENTS Filed Feb. 9. 1961 2 Sheets-Sheet 2 FIG. 5

United States Patent O APPARATUS FOR TIIE PRODUCTION OF CE- RAMIC, CERMET, AND METAL COMPONENTS Nick G. Lirones, North Muskegon, Mich., assignor to Howe Sound Company, N ew York, N.Y., a corporation of Delaware Fiied Feb. 9, 1961, Ser. No. 88,046 1 Claim. (Cl. 249-134) This invention relates to an apparatus for the production of components composed of ceramic, cermet, and metal, and combinations thereof. The process and corresponding apparatus is particularly adapted for the formation of components of complex shape, with or without extremely thin sections, and is further peculiarly adaptable for the production of complex core members of the above materials where dimensional tolerances are critical.-

lt has been found impractical to employ known methods for the production of core members `and like parts where a complex design was necessary. This has been found to be particularly true in the case where the parts are to be subjected to stress at elevated temperatures, as is the c-ase when casting metal about such cores. In addition, the production of these parts on a commercially feasible basis has not been satisfactorily accomplished heretofore.

Known ceramic and powder metallurgical techniques have failed to give a satisfactory solution to existing problems in making cores of high dimensional stability where difficult sizes and shapes are involved. The preparation of cores for the production `of cored vanes for use in aircraft engines, for example, necessitates that the cores be accurate within a few thousandths of an inch to comply with the strictly observed wall tolerances of the v-anes. The casting of high melting point materials which make up the vanes also requires that the cores have exceptional strength and durability. These requirements are magnified when the cores lare of complex design, for example, when it is necessary to provide holes in the cores, thus resulting in vanes with cooling passages therein.

T-he apparatus to be hereinafter described provides a system of a relatively simple nature which enables the production of complex components on an economical basis and a particularly Iadvantageous feature includes ready adaptation to production processing.

The process of this invention consists broadly of providing a slip of a ceramic, cermet, or metal base and introducing this slip into a mold of the desired configuration. The mold is provided with selected portions of porous material which will absorb the liquid portion of the slip. The solid portion of the slip will proceed to build up in a manner conforming precisely to the contiguration of the mold, however complex this may be. The conventional steps of drying and firing will result in an article with the desired strength and durability and which requires no final machining.

It is van object to provide an apparatus of a relatively simple nature which will permit accurate and repeated manufacture `of these components on a production basis and at 'relatively lowcost.

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- FIGURE 1 represents a component which may be produced in accordance with the disclosed invention;

FIGURE 2 is a split mold which is designed to correspond to the configuration of the component shown in FIGURE 1;

FIGURE 3 represents an adaptation of the disclosed process to a production basis;

FIGURE 4 is an exploded perspective view of a special mold design in accordance with the concepts of this invention;

FIGURE 5 is a horizontal cross-section of an assembled mold of the type shown in FIGURE 4; and

FIGURE 6 is a front elevation view of a mold assembly embodying special concepts of this invention.

Referring to the drawings, there is shown in FIGURE 1 a core element 10 of particularly complex design which has passages 20 formed therein. These cores are employed in the manufacture of turbine blades or vanes which require air-cooling passages for most eicient operation. Components m-ade according to this invention may be composed of materials such as silica, alumina, zircon, zirconium, nickel Vand chromium. Other well-known ceramic, cermet or metal compositions are equally well adapted. The materials can be blended into a slip individually or in combinations by any one or all of the conventional blending processes. The characteristics that all the 'base materials that make up the slip have in cornmon are particle size approximately 325 mesh, and particle structure, `best described as microcrystalline. A p-articular .advantage of this process resides in the fact that a component such as that shown in FIGURE 1 may be produced from ceramic or metallic materials, whereas prior-art systems have ordinarily been limited to one or the other type of material.

The mold employed in one particular embodiment of the invention is shown in FIGURE 2. The mold 11 is composed of split mold parts 12 and 13. There are shown within the mold part 13 appropriate core elements 14 which correspond to the passages 20vin the core element 10. Guide means 2-1 are adapted to assure accurate positioning of the mold parts. These molds, or molds of similar nature, may be composed of such materials as plastic, wax, rubber or metal, the essential characteristic being that they be composed of essentially non-absorbent materials. It has been established, however, that plastic molds are superior from a quality standpoint as well as from an economical standpoint being particularly suitable for providing Ia smooth surface finish.

FIGURE 3 pictures an assembly of molds substantially of the type shown in FIGURE 2. The molds 11 are secured together by mold-clamping means 15. They are disposed upon a slab 16, the function of whichwill be shortly disclosed. A ladle 17 is shown in the pouring'position while a slip 18 is shown being introduced intothe mold 11. A vacuum means 19 is shown associated with the slab 16. The nature of the slab 16 is that of an absorbent material and it is produced from such materials as plaster, ceramic, or -other suitable absorbent materials. Although an absorbent slab 16 has been shown associated with the mold assembly in FIGURE 3, an absorbent plug may be inserted at 22 to provide an absorbent base, which plug may be used with or without the slab 16. A cover.23 is shown above filled molds in the assembled construction shown inFIGURE 3. This cover is employed to prevent the evaporation to the atmosphere of liquid portions of the slip 18 after it has been poured into the mold.

The special mold design shown in FIGURES 4, 5, and 6 consists of a split mold 31 having one-half composed of an absorbent material 33 and a non-absorbent material 3S, with the other half consisting of a non-absorbent section 34. Various size openings 36 are provided in the section 35 and the absorbent material 33 extends within the openings 36 to provide a smooth forming surface. The section 34 is .completely solid and provides the opposite forming surface for the split mold 31. Absorbent base portion 16 and cover member 23 are associated with the molds 31 in the same manner as heretofore described.

By way of a specific embodiment, and in order to explain the operation of the aforementioned apparatus, the production of a core element 10, as shown in FIG- URE 1, will be described. A plaster slab 16 is prepared by mixing 50 parts by weight of water with 50 parts by weight of plaster. A series of molds 11 is placed upon the slab as shown in FIGURE 3. A slip composed of about 75% silica having 4a particle size of approximately B25-mesh and about 25% water is ladled into a mold 11. Cover 23 is then placed over the mold opening to prevent evaporation to the atmosphere. As the slip 18 progresses to the bottom of the mold adjacent the slab 16, there is a uniform unidirectional build-up of the solid material portion of the slip. The build-up is permitted to continue until substantially all of the liquid portion of the slip is absorbed through the builtup portion into the base 16. The build-up of solid material results in a core element of the desired dimensions, .and the structure of the element is in the nature of interlocked particles. Subsequent drying and ring of the ceramic core element will result in a dimensionally accurate core capable of producing a passage in a cast vane or turbine blade within the required tolerance ranges.

The use of the mold shown in FIGURES 4-6 is substantially the same as described with reference to the preceding mold construction. However, in this instance, the openings 36 and associated portions of absorbent material 33 provide additional absorbing surfaces with respect to the liquid portions of the slip material 18. These selected additional absorbing portions are employed in order to achieve uniformity of absorption which has been found necessary where large components are being formed, particularly where the large components have relatively thin sections. The use of the selected absorbing portions arises due tothe fact that a slight volume decrease occurs during the build-up of the solid material portion of the slip. T-here is a tendency for voids to form due to the volume decrease, and therefore absorption must be permitted to progress to relatively thin areas where the tendency to form voids is the greatest. In other words, the positioning of the absorbent portions in the thin sections permits a progressive build-up of the solid material portion of the slip, thus resulting inI an interlocked structure even in the thin portions.

By Way of a specific example, the mold shown in FIG- URES 4-6 will produce a core having -a length of about 51/2 inches, with thicknesses varying from 5/16 of an inch -to approximately .010 inch. The openings 36 vary from about fe inch in diameter in the thicker sections of the mold, and near the bottom of the mold, to about 1/s inch in diameter in the thinnest sections of the mold, and near the top of the mold. The mold during use should be covered, as shown in FIGURE 6, by means 23 as otherwise evaporation to the atmosphere will make it difficult to provide controlled build-up of Ithe solid material portion lof the slip.

It will be obvious when viewing FIGURE 3 that the aforementioned series of steps is readily `adapted to a production process by simply changing the position of the ladle 17 and repeating the process steps in the adjacent molds.

In the case of silica slips, firing of the molded "cores will take place at temperatures between 1600-2100 F., with a preferred temperature of about 1900 F. In order to provide sufficient owability of the slips employed in this invention, a water content of less than about 20% should not be employed. The firing conditions and minimum Water content will, of course, vary with the different slip compositions which are employed. However, the fine particle size heretofore referred to has been found critical to the formation of the desired interlocked structure which permits exact conformance to the particular mold configurations.

The operation of the vacuum means 19 is such that the absorption rate may be accelerated, and this feature is adaptable to all the various liquid-absorbing portions of the molds of this invention. In addition, the absorption rate may be varied by changing the character of the absorbing mold portions. For example, a plaster slab prepared by mixing 25 parts of water with 75 parts of plaster will be less absorbent than the aforementioned slab. Where ceramic slabs are employed, the absorption rate can be controlled by the temperature of firing of the slab. For example, a silica slab fired at 2000 F. will be less porous and less absorbent than the same slab fired to a temperature of 1200 F.

With regard to the mold construction shown in FIG- URES 4-6, it will be understood that the specific mold design, placement of openings 36, and the size of these openings is not to be considered limiting. It may generally be stated that the magnitude of absorbing areas will vary progressively from the thinner sections to the thicker sections of a given core mold, and from the bottom to the top of the mold. Although the openings 36 are shown only in one-half of the split mold 31, this likewise is not to be considered limiting and openings in selected areas of all core-forming surfaces are contemplated.

It will be obvious that other variations of the material will result in variations in the absorption rate, and furthermore, other well-known mechanical means may be employed to control or :accelerate the absorption rate.

It will be understood that changes may ybe made in the above-disclosed process and apparatus in a manner to provide the characteristics of this invention without departing from the spirit thereof, especially as defined in the following claim.

\I claim:

A mold for the production of articles of ceramic, metal and cermet materials from slip compositions, the articles to be formed including thin sections extending to progressively thicker sections whereby the mold includes thin sections extending to progressively larger thicker sections, said mold comprising a substantially horizontally disposed base portion and a substantially vertically disposed mold section situated on top of said base portion and extending upwardly therefrom, said mold section comprising first and second opposed side walls defining the configuration of the article to be formed therebetween, said base portion being formed of absorbent material adapted to absorb the liquid portion of said slip compositions, said side walls defining forming surfaces comprised of areas of absorbent material and non-absorbent material, whereby the mold is adapted to absorb liquid through said base portion and through absorbent areas of said mold section, said first side wall being formed of substantially non-absorbent material, and said second side wall being formed of selectively alternating absorbent and non-absorbent areas, the absorbent areas in said second side wall being dimensioned to be progressively larger from the thinnest sections of said mold to the thicker sections thereof and from the top of the mold to the bottom thereof.

(References on following page) References Cited by the Examiner UNTED STATES PATENTS Ramsome et al.

6 FOREIGN PATENTS 1,214,464 11/ 1959 France.

OTHER REFERENCES gills/irma 264 31 5 Kingery, W. D.: Ceramic Fabrication Processes, N.Y.,

Lawrence t al St. Pierre, Slip Casting Nonclay Ceramics.

Rand 26%86 Rempes et al.: Slip Casting of Metals, Ceramics and C Cermets, Ceramic Bulletin, vol. 37, No. 7 (July 1958),

asselman 264-87 lo pp 334 339 Curtis.

Demflf- ROBERT F. WHITE, Primary Examiner.

Hemphill 264-219 Wadman 26,1 86 MICHAEL V. BRTNDISI, ALEXANDER H. BROD- Gaved 25 129 15 MERKEL, Exammers.

Pall 264-127 A. O. MAKI, S. I. COHEN, R. B. MOFFITT,

Lambie 25-129 Assistant Examiners.

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