RADIAL BLADE TYPE CERAMIC ROTOR AND METHOD OF PRODUCING THE SAME

Abstract: A radial blade type ceramic rotor consists of a ceramic blade body 1 and a ceramic shaft body 4 joined to each other. To improve the properties of the rotor, the blade body 1 is formed in one piece with a shaft portion 3 which is joined to the shaft body 4, so that the joint is located in the shaft in a zone subjected to a relatively low stress when rotating. To make the rotor a molded ceramic blade body 1 having a shaft portion 3 in one-piece therewith and a molded ceramic shaft body 4 are urged against each other at joint surfaces in the shaft, and hydrostatic pressure is applied to make the bodies dense. The bodies are then sintered to form a high strength unitary rotor suitable for use in gas turbine engines or internal combustion engines.

Description: RADIAL BLADE TYPE CERAMIC ROTOR AND METHOD OF PRODUCING THE SAME This invention relates to a radial blade type ceramic rotor, suitable for use for example in gas turbines or internal combustion engines, which comprises a ceramic blade portion and a ceramic shaft portion joined to each other, and further relates to a method of producing such a rotor. Recently, silicon ceramic materials such as silicon nitride, silicon carbide, sialon and the like have been proposed as structural materials for parts of engines as gas turbines, internal combustion engines and the like, because of their superior resistance to heat and thermal shock. Some engine parts are however very complicated in shape. It is very difficult to make such parts only by one-step molding. On the other hand, since such an engine part is generally required to have different strengths at each location in the part, it has been proposed to manufacture such an engine part by joining together separate parts made of materials meeting the respective strength requirements for the various locations. For example, Japanese Patent Application Publication No. 38,722/78 discloses an axial type turbine rotor manufactured by the steps of making a blade portion from reaction-sintered silicon nitride, putting the blade portion in dies in a hot press and then forming a rotor portion in the dies adjacent the blade portion to form a unitary rotor. However, this process is expensive and not suitable for massproduction. Japanese Laid-open Patent Application No. 57-88,201 shows a rotor, illustrated in Fig. 2 of the present drawing, comprising a rotor blade portion 6 formed with a frustoconical fitting recess 7 and a rotor shaft 8 having one end fitted and jointed into the recess. The joint in the recess in the blade portion tends to reduce its strength because the joint portion lies in a highly stressed zone of the rotor when rotating, and cavities at the fitted end of the rotor shaft are likely to result. It is an object of the invention to provide an improved radial type ceramic rotor which reduces or eliminates the above disadvantages of the prior art. It is another object of the invention to provide a method of producing a radial type ceramic rotor which has a joint in a zone subjected to comparatively low stresses and sufficiently dense to achieve good strength. The radial type ceramic rotor according to the invention comprises a ceramic blade body integrally formed with at least part of a shaft and a ceramic shaft body joined to each other at said part of said shaft so as to form a unitary rotor. The method according to the invention comprises the steps of molding a ceramic blade body integrally formed with at least part of a shaft, separately molding a ceramic shaft body, urging said blade and shaft bodies together at said part of the shaft, applying hydrostatic pressure to said blade and shaft bodies, and sintering said blade and shaft bodies to form a unitary rotor. Embodiments of the invention will be described below, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a sectional view illustrating a ceramic rotor according to the invention; and Fig. 2 is a sectional view showing the ceramic rotor of the prior art, discussed above. A rotor according to the invention may be made of an oxide such as alumina or zirconia or of silicon nitride, silicon carbide or sialon or of a combination of two or more of these materials or substances producing these materials by sintering. The starting material preferably includes at least one sintering aid such as Y2 0 3' Ae O3, MgO At203 MgO, SrO and CeO2 in case of silicon nitride or sialon, and such as B, C and ASN in case of silicon carbide, and should be sufficiently mixed. Thereafter, the material including the sintering aid may be mixed with a plasticizer such as a resin, wax or the like to obtain a raw material for molding. This raw materials may then be injection-molded to form the desired shaped molded blade body of the rotor formed in one piece with at least part of a shaft. The same raw material prepared in the same way may be separately injection-molded to obtain the molded shaft body of the rotor. As an alternative a raw material not containing the plasticizer may be formed into the shaft body of the rotor by slip casting, extruding, die pressing or another process conventionally used in ceramic forming. In this case, the materials of the blade and shaft bodies may not be the same. However, use of the same materia is preferable in order to minimise the difference in thermal expansion. Referring to Fig. 1 illustrating one embodiment of the invention, a molded blade body 1 comprises radial blades 2 and a part 3 of a shaft formed in one piece therewith, and is closely joined to a molded shaft body 4 at a close contact portion 5. To join the molded bodies 1 and 4, after the contact surfaces of the close contact portion 5 have been made smooth, the molded bodies 1 and 4 may be simply contacted or urged directly against each other or with a binder of heat meltable ceramic such as glass interposed between them. Most preferably, the molded bodies 1 and 4 are urged against each other with an interposed slurry or paste binder which is of the same material as at least one of the molded bodies 1 and 4. Although the contact surfaces are preferably flat, they may be curved or a combination of flat and curved surfaces. The joining of the molded bodies is generally preferably effected between the raw molded bodies. However, at least one of the bodies may be presintered. When using a binder of heat meltable ceramic, sintered bodies may be jointed. When using an interposed binder, the binder is preferably coated onto the surfaces so as to form a bond layer having a thickness less than 200 pm after sintering. After the above treatment, the molded bodies closely contacted or urged against each other are covered by an elastic membrane and then subjected to hydrostatic pressure such that the molded or presintered bodies are shrunk in length, e.g. by an amount in the range 0.5-5%. The pressure applied is usually in the range 500-5,000 kg/cm2. The shrunk bodies are then sintered at a temperature in an atmosphere which is optimum for the molded bodies or binder to join the molded bodies into a unitary body. The joint 5 of the unitary rotor is preferably located a distance from the rear surface of the blades (i.e. the end faces of the blades towards the shaft part of the rotor as seen in Fig. 1) which distance is in the range 10-100%, more preferably 30-100%, most preferably 30%-70% of the maximum blade diameter. If this distance is less than 308 of the maximum blade diameter, the joint may be too near to the blades, so as to be within a highly stressed zone of the rotor, tending to result in rupture at the joint portion when rotating. If this, distance is more than 100% of the maximum blade diameter the joint is so remote from the blades that it may be difficult to achieve flow of the material into the shaft part of the blade body in the injection molding, resulting in comparatively large voids or poor uniformity in density in that part which reduce its strength. A particular example of the invention will now be described. A raw material for injection molding was prepared which contained 77 parts by weight of powder Si3N4 having an average particle diameter 0.5 pm, 2 parts by weight of SrO, 4 parts of MgO and 2 parts of CeO2 as sintering aids and 15 parts of paraffin wax. The raw material was injection molded to form molded blade bodies for radial ceramic rotors, each having a maximum blade diameter of 50 mm (after firing) and having a shaft part of length 25 mm extending from the rear surface of the blades. A raw material similar with the exception of having no paraffin wax was molded by a die press to form cylindrical molded shaft bodies each having an outer diameter 10 mm and a length 50 mm. After the molded blade bodies had been slowly heated to 5500C to remove the paraffin wax, the molded blade and shaft bodies were presintered by heating at 1,1000C for 30 minutes and the surf aces of these bodies to be joined were machined on a lathe to make them smooth. A powder consisting of Si3N4, SrO, MgO and CeO2 whose proportions were the same as in the starting material of the molded bodies, i.e. 77:2:4:2 was mixed with methyl cellulose (38 by weight) and water (80% by weight) to form a slip having substantially the same composition as the starting material of the molded bodies. The slip was coated on the smooth surfaces of the molded bodies so as to obtain coated bonding layers having in each case a total thickness of 100 pm after sintering. After the molded blade and shaft bodies had been urged against each other at the smooth surfaces and dried, they were subjected to hydrostatic pressure of 1,500 kg/cm2 to join them. Thereafter, the joined molded bodies were sintered in a nitrogen atmosphere at 1,7000C for one hour to obtain radial ceramic rotors completely joined in shaft regions according to the invention. A rotor according to the invention thus formed was inspected by X-ray radiography. There were no defects inside the joint portion of the rotor. The ceramic rotors thus made according to the invention did not rupture even at rotating speeds as high as 15,000 RPM in spin tests. -Thus by the invention there can be made a rotor in which the joint is not located in a highly stressed zone and yet is sufficiently dense. The rotor is thus completely unitary part and can be of very high strength. It can be suitable as a turbo-charger rotor or gas turbine rotor. The term "radial blade type rotor" includes cases where the blades of the rotor deviate from truly radial.

Claims: CLAIMS: 1. A radial blade type ceramic rotor comprising a ceramic blade body (1) and a ceramic shaft body (4) joined to each other so as to form a unitary rotor characterised in that the blade body (1) is formed in one piece,with a shaft portion (3), which is joined to the said shaft body (4). 2. A rotor according to claim 1, wherein the joint (5) is at a distance which is in the range 10 to 100% of the maximum blade diameter from the surface of the blades of the blade body on the shaft side thereof. 3. A rotor according to claim 2, wherein the said distance is in the range 30% to 100% of the maximum blade diameter. 4. A rotor according to claim 3, wherein the said distance is in the range 30 to 70% of the maximum blade diameter. 5. A rotor according to apy one of the preceding claims wherein the surfaces of the bodies (1,4) at the joint are flat. 6. A method of producing a radial blade type ceramic rotor according to any one of the preceding claims comprising the steps of molding the ceramic blade body (1) in one piece with a shaft portion (3), separately molding the ceramic shaft body (4), urging the shaft portion (3) of the blade body and the shaft body together, applying hydrostatic pressure to the blade and shaft bodies, and sintering the blade and shaft bodies to form the unitary rotor. 7. A method according to claim 6, wherein before said blade and shaft bodies are urged together, a binder is applied between the surfaces of the bodies to be jointed. 8. A method according to claim 7, wherein said binder is a heat-meltable ceramic such as glass. 9. A method according to claim 7, wherein said binder is of the same material as at least one of the blade and shaft bodies. 10. A method according to any one of claims 7 to 9, wherein said binder is coated on said surfaces to be joined to form a bond layer having a thickness of less than 200pm after sintering. 11. A method according to claim 14, wherein the thickness of said bond layer is approximately 100 pm. 12. A method according to any one of claims 6 to 11, wherein said hydrostatic pressure is applied to an extent such that said blade and shaft bodies (1,4) are shrunk in length by an amount in the range 0.5-5%.

Inventors: HAYAKAWA, ISSEI
Applicants: NGK INSULATORS, LTD.
Application year: 1983
Main classification: F01D5
IPC codes: F01D5, C04B37