Ceramic bearing

Abstract: The ceramic product of this invention is characterized in that the ceramic bearing constructed by being allowed to contact the ceramic outer ring (2) slidably with the ceramic inner ring (1) is provided with a latching member (3) to prevent the transfer of the ceramic inner ring (1) in the axial direction at the inner or the outer ring (2) of said ceramic product. The bearing constructed by the sliding contact of the ceramic inner ring (1) with the ceramic outer ring (2) can prevent the occurrence of the transfer of the inner ring (1) in the axial direction with respect to the outer ring (2) by providing a latching member (3) which prevents the transfer of the inner ring (1) in the axial direction at the inner or outer ring (2). Accordingly, there is no anxiety of separation of the outer ring (2) from the inner ring (1).

Description: This invention relates to a ceramic bearing constructed by combining a ceramic inner ring and a ceramic outer ring, particularly to a ceramic bearing wherein relative movement between the ceramic inner ring and the ceramic outer ring in an axial direction is prevented. It is generally known to use a sliding bearing or a rolling bearing in a case of attaching an axis of rotation to a machine frame. As a rolling bearing, such kinds of a ball bearing, a roller bearing and a needle bearing having a rotary member such as balls, rollers and needles is situated between the inner ring and the outer ring. Further, there exist bearings such as radial bearings, thrust bearing and the like according to a supporting system of a load which acts on an axis engaged with the inner ring. A deep-groove type bearing, an angular type bearing, and a tapered roller bearing and so on are known as the bearing enabling to support the shaft to which a radial load and a thrust load are simultaneously applied. These many rolling bearings are standardised. Accordingly, on designing a machine, the most suitable one is selected and employed. The above sliding bearings are made or constructed of a metal supporter made of steel, cast iron, copper or the like, with a white metal layer laminated thereon or an oil including alloy laminated thereon or embedded therein. Further, some sliding bearings are made or constructed by gun metal, synthetic resin and the like formed to a sleeve shape. Generally, in conventional sliding bearings, a bearing which supports a radial load and a bearing which supports a thrust load are separately standardised. The above rolling bearing and the sliding bearing have peculiar characteristics respectively. Accordingly, in employment the most suitable one is used considering these characteristics. However, even the above rolling bearings and the sliding bearings have troubles. Namely, in the rolling bearing flaking phenomenon due to rolling fatigue occurs which limits its life. By this, because the thermal resistance is low and the number of constructing parts thereof increases, the cost of the product becomes high. Further, in the above sliding bearing the friction loss increases due to the sliding contact of the outer periphery of the axis with the inner periphery. By this, there occurs such problem as the necessity of applying a reinforced lubrication or a self lubrication to the contact surface of the axis with the bearing. On the other hand, ceramics having high compressive strength, friction resistance and small friction coefficient, have been developed recently. Further, a prior art disclosed in US-A-4 634 300 relates to a rolling bearing constructed by using a ceramic roller as a rolling body. According to this technique, it is possible to constitute a rolling bearing having heat resistance and anti-corrosion properties, but the number of parts which constitute the bearing increases. In order to solve the above problems, the applicant of this invention has developed many kinds of ceramic bearings and submitted patent applications, e.g. EP-A-0 376 647 which was published after the priority date of the application (Japanese Patent Application No. 63-325933). Further, GB-A-1 437 532 discloses a ceramic bearing according to the preamble of claim 1. Summary of the Invention: The main object of this invention is to provide a ceramic bearing to solve the above problems, particularly a ceramic bearing constructed by the sliding contact of the inner ring of ceramic product with the outer ring of ceramic product, said ceramic bearing being able to prevent to move the inner ring of the ceramic product in an axial direction with respect to the outer ring of the ceramic product. Another object of this invention is to provide a bearing having small numbers of parts by constructing the inner and outer rings by means of ceramics. Accordingly, the invention provides a ceramic bearing comprising a ceramic inner ring defining an axis, an internal bore for engagement by an interference fit on a rotatable shaft, and an outer sliding surface; and a coaxial ceramic outer ring defining an inner sliding surface dimensioned for sliding contact with the outer sliding surface of the inner ring; characterised in that latching means are provided to prevent relative axial movement of the rings in the form of at least one ceramic pin secured in the outer ring and extending into an annular groove in the inner ring. Brief description of the drawings: Fig. 1 is an assembling explanatory view of the bearing in an embodiment of this invention; Fig. 2 is a sectional explanatory view along the line II-II of Fig. 1; Fig. 3 is an explanatory view of a guide pin in the embodiment of Figs 1 and 2. Detailed description of the Preferred Embodiment: In Fig. 1 to Fig. 3, the bearing A comprises an inner ring 1 to be engaged with the axis, an outer ring 2 to be attached to a machine frame or a casing and a plurality of guide pins 3 fitted to the outer ring 2. The inner ring 1 is formed by press-forming an oxide ceramics material of a material such as PSZ (partially stabilised Zirconia) or alumina etc., by filling it in a mold and then sintering the molded product at 1500°C to 1600°C. An axial hole 4 for engaging the axis is formed so as to have a fixed engaging allowance according to a diameter of the axis to be engaged with the axial hole 4. The numeral 5 refers to an axial centre of the axial hole and corresponds to the axial centre of the bearing A. A sliding surface 1a is formed on the outer periphery of the inner ring 1 in parallel to the axial centre 5. The sliding surface 1a transmits a radial load applied on the axis to the outer ring 2 by the sliding contact with the sliding surface 2a formed at the outer ring 2 described hereinafter. For this purpose, the sliding surface 1a must be parallel to the axial centre 5 correctly. At the approximately middle portion of the sliding surface 1a formed on the outer periphery of the inner ring 1, an annular groove 6 is formed all around the inner ring 1. The groove 6 constrains the inner ring 1 to move in a rotational direction by latching with guide pin 3. The outer ring 2 is also formed by press-forming filling an oxide ceramics material such as PSZ or alumina etc. in a mold in the same way as for the inner ring 1 and then sintering it at 1500°C to 1600°C. At the interior of the outer ring 2, a sliding surface 2a is formed so as to have a fixed allowance with respect to the sliding surface 1a formed on the outer periphery of the inner ring 1. The sliding surface 2a is formed so as to have an approximately equivalent length to the sliding surface 1a of the inner ring and contacts with the sliding surface 1a slidably whereby a radial load applied on the axis is transmitted through the inner ring 1. For this purpose, the sliding surface 2a is constructed by a parallel surface to the axial centre 5. A plurality of holes 7 for engaging guide pins 3 are formed at approximately the middle portion in the axial direction of the outer ring 2 and at positions corresponding to the groove 6 in the inner ring 1. The shape of the hole 7 is that of the guide pin 3, namely a circular shape or a polygon and the dimensions thereof is formed to be approximately equivalent to that of the guide pin 3. The outer periphery 2b of the outer ring 2 is formed to be a cylindrical shape parallel to the axial centre 5. Both end surfaces 2c of the outer ring 2 are constructed as a rectangular plane against the axial centre 5. The outer periphery 2b and the end surface 2c become engaged portions when they are attached to a machine frame or a casing (not shown). The guide pin 3 is formed by press-forming an oxide ceramics material such as PSZ and alumina etc. filling it in a mold and sintering a molded product thereof at approximately 1500°C to 1600°C. The guide pin 3 may be a straight pin or a taper pin. Further, the shape of guide pin 3 (3a to 3c) may be a cylindrical pin 3a as shown in Fig. 3(A) or may be a square pin 3b as shown in Fig. 3(B). Further, a pin 3c having a flange at the end portion as shown in Fig. 3(C) may be used. In this embodiment, the cylindrical pin 3a is used as guide pin 3. The guide pin 3 is formed to be equal to the width dimension of the groove 6 in the inner ring 1 or to be somewhat smaller. Accordingly, there is no anxiety of occurrence of play between the guide pin 3 and the groove 6. Further, the number of guide pins 3 is preferably 3 or more than 3. This is due to the fact that when the number of guide pins is small and a load in a thrust direction applies on the axis of the inner ring 1, there is anxiety that a bending stress applies to the guide pin 3 due to said load. The axial hole 4, the sliding surface 1a, the groove 6 in the inner ring 1 and the sliding surface 2a, the outer periphery 2b, the end surface 2c and the hole 7 etc., in the outer ring 2a are formed simultaneously when the inner and outer rings are press-formed. In the above press forming, the dimension accuracies of the inner ring 1 and the outer ring 2 can obtain approximately ±0.005mm in accuracy against designed dimension of each part. Further, surface roughness can be secured about RA 0.8. In order to construct the bearing A using the inner ring 1, outer ring 2 and guide pin 3 constructed as shown in the above, the sliding surface 2a is allowed to contact with the sliding surface 1a slidably by engaging the inner ring 1 with the outer ring 2. The groove 6 formed in the inner ring 1 is opposed to the holes 7 formed in the outer ring 2 and a guide pin 3 is inserted into each hole 7, the top end of said guide pin 3 being allowed to latch with groove 6. At this time, the guide pins 3 can be fixed to the outer ring 2 by applying an adhesive to the corresponding part with the hole 7 of the guide pin 3 and engaging said pin 3 with hole 7. Further, the guide pins 3 can be fixed to the outer ring 2 by expanding the hole 7 by heating the outer ring 2 and engaging the guide pin 3 in normal temperature state to the hole 7, so called thermal insert. Furthermore, the guide pin 3 can be fixed to the outer ring 2 by cooling the guide pin 3 to shrink by means of a cold agent such as liquid nitrogen etc. and engaging said pin 3 to the outer ring 2 which is at a normal temperature, so called cooling insert. It is desirable to perform a grinding process on the sliding surface 1a, the groove 6 of the inner ring 1, and the sliding surface 2a and the pin 3 of the outer ring 2 separately which constitute the bearing A according to the accuracy required for said bearing A. Further, the lapping of the contact surface of the sliding surface 2a with the sliding surface 1a, the guide pin 3 and the groove 6 is also possible after engaging the inner ring 1 to the outer ring 2. The lapping can be practised by giving an abrasive agent such as diamond powders etc. to each contact surface and a relative rotation thereto. The rotation of the bearing A becomes smooth by grinding the inner and outer rings and guide pin 3 and groove 6 respectively or lapping them. In the bearing A constructed as described above, the top end portion of the guide pin 3 fixed to the outer ring 2 is inserted into the groove 6 formed in the inner ring 1. By this, the inner ring 1 is constrained so as only to perform a rotary movement against the outer ring 2. Namely, the inner ring 1 is constrained against movement in the axial direction with respect to the outer ring 2. Accordingly, when the outer ring 2 is, for instance, attached to a machine frame (not illustrated herein) and the axis is inserted into the axial hole 4 of the inner ring 1, the axis does not transfer in the axial direction with respect to the machine frame. In the bearing A of this embodiment, the movement of the inner ring 1 in the axial direction with respect to the outer ring 2 is prevented. In the above bearing, since the inner and outer rings are both made of ceramics, the friction coefficient becomes small thereby decreasing the friction loss thereof. By this, there is no need of the lubrication against the sliding surface. Further, even when the heat is generated due to the sliding, there occurs no excess of the thermal stress due to the thermal expansion of the inner and outer rings because the coefficient of the thermal expansion is about 8 to 11x10⁻⁶/°C. Further, since the heat temperature resistance of the ceramics is about 600°C to 1000°C, there is no fear of deterioration of the inner and outer rings due to the heat generation.

Claims: A ceramic bearing comprising a ceramic inner ring (1) defining an axis, an internal bore (4) for engagement by an interference fit on a rotatable shaft, and an outer sliding surface (1a); and a coaxial ceramic outer ring (2) defining an inner sliding surface (2a) dimensioned for sliding contact with the outer sliding surface (1a) of the inner ring (1); characterised in that latching means are provided to prevent relative axial movement of the rings (1,2) in the form of at least one ceramic pin (3) secured in the outer ring (2) and extending into an annular groove (6) in the inner ring (1). A ceramic bearing according to Claim 1, in which the pin is held in a hole (7) which extends from an outer peripheral surface (2b) to the inner peripheral surface (2a) of the outer ring (2) and is axially aligned with said groove (6). A ceramic bearing according to Claim 1, in which three or more ceramic pins (3) engage in said groove (6). A ceramic bearing according to any preceding claim, in which the or each pin (3) is straight. A ceramic bearing according to any of Claims 1 to 3, in which the or each pin (3) is tapered. A ceramic bearing according to any preceding claim, in which the or each pin (3c) is provided with a flanged head. A ceramic bearing according to any preceding claim, in which the or each pin (3) has a cross-section which is circular (3a) or square (3b).

Inventors: MOMOSE TERUNOBU, MOMOSE, TERUNOBU
Applicants: WING HIGHCERA KK, WING HIGHCERA CO., LTD.
Application year: 1990
Main classification: F16C33
IPC codes: F16C17, F16C33