JPH0473422A - Ball bearing made of ceramics - Google Patents

Abstract

PURPOSE:To reduce abrasion by forming a stress relaxation part having a prescribed width so as to include the center part in the longer axis direction of an elliptical initial contact surface which is generated in the case when a radial load is applied on the raceway track of a bearing ring made of ceramics. CONSTITUTION:A stress relaxation part 4 consisting of an arcuate annular fine recessed part having the less radius of curvature than a raceway groove 2a of an outer ring 2 is formed so as to include the center part in the longer axis X direction of an elliptical initial contact surface F which is generated in the case when a radial load is applied on the raceway groove 2a of the outer ring 2. For instance, the annular fine recessed part has a width of 500mum or less and a depth of 5mum or less. When the outer ring 2 and a ball 3 are applied with a radial load, both are put into surface contact, and a circular initial contact surface F is formed. The outer ring 2 and the ball 3 contact on the whole of the initial contact surface including the stress relaxation part 4. Accordingly, the max. shear stress reduces, and abrasion reduces. Further, the deterioration of the rolling performance is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a ceramic ball bearing in which both inner and outer rings and balls are made of ceramic.

Problems with conventional technology and invention In cases where heat resistance and corrosion resistance are required for rolling bearings,
When a rolling bearing is used in a vacuum, a ceramic ball bearing is used in which both the inner and outer wheels and the balls serving as the rolling elements are made of ceramic, such as silicon nitride.

When ceramic ball bearings are used in special environments such as those mentioned above, liquid lubricants such as oil and grease cannot be used, so solid lubricants such as graphite, molybdenum disulfide, and tungsten disulfide are used.

However, ceramic ball bearings have the following problems. In other words, it is a contact between ceramics with a large Young's modulus, and when a solid lubricant is used, there is no wedge action lubrication like when a liquid lubricant is used, so the maximum contact pressure becomes large. ,
Fatigue peeling of the inner and outer rings is likely to occur, shortening the service life.

In addition, wear when the contact surface is in sliding motion is generally
Although the wear is much greater than that during pure rolling motion, even in ball bearings, as the length of the contact surface in the longitudinal direction increases, the distance from the center of rotation of the ball to each part of the contact surface increases. Heathcote (Heathcote)
resulting in differential slippage and excessive wear. Furthermore, since the solid lubricant baked on the contact surface is directly subjected to high pressure, it scatters as wear powder in a short period of time and ceases to perform its function.

An object of the present invention is to provide a ceramic ball bearing that solves the above problems.

Means for Solving the Problems A ceramic ball bearing according to the present invention has the following features: A ceramic ball bearing in which at least one of the inner and outer rings and the balls are each made of ceramic, the ceramic ball bearing having a predetermined curvature. A stress relaxation part of a predetermined width is formed in the raceway so as to include the center in the long axis direction of the elliptical initial contact surface that occurs when receiving a radial load, and is located within the contact surface. .

In addition, in the above ceramic ball bearing, the stress relaxation part
It may be a minute annular recess. In this case, a solid lubricant may be filled in the minute recesses.

The inventors of the present invention have conducted various studies to investigate the causes of the above-mentioned problems, and as a result, they have discovered the following facts and completed the present invention. That is, using a rolling wear testing device previously filed by the present applicant (see Japanese Patent Application No. 1-245734), rolling wear tests were carried out on ceramic balls and cylinders under a vertical load of 40 ON and without lubrication. When the cross-sectional shapes of the ball and cylinder were measured at the total number of rotations, the results shown in FIG. 5 were obtained.

Figures (a) to (C) are the cross-sectional shapes of the balls, and Figure (d) is the cross-sectional shape of the ball.
~(r) is the cross-sectional shape of the cylinder. The cross-sectional shape of the cylinder (11) is not as shown by the broken line in FIG. 6 as expected from the shape of the ball (10), but is exaggerated as shown by the solid line in the same figure. This is because the cylinder (11) is worn out and rolling grooves (11, a) are formed, as shown in Figure 7.
When the radius (RG) of the cross section of the groove (lla) approaches the radius (17B) of the ball (lO), the long axis (
Each point (A) on its long axis (T) becomes longer than the length of T)
(B) The difference in distance (rA) (rB) (rC) from the rotation center axis (0) of the ball (10) in (C) will be large, so even if it is purely rolling at point (B) , point (A)
This is because in (C), rolling occurs with Heath-Scott differential slip. In other words, the wear in sliding contact is much larger than the wear in rolling contact, so there is not much wear at the point (B) where pure rolling occurs, and there is severe wear at points (A) and (C) where rolling with sliding occurs. It wears out, resulting in a shape as shown by the solid line in FIG. It was also found that the pressure distribution on the long axis (T) of the contact surface (S) changes as shown in FIG. 8 as the total number of rotations increases. According to Fig. 8, at the initial stage of rotation, the contact pressure on the long axis (T) of the elliptical initial contact surface [S] takes a maximum value (P3) at its center, and the total number of rotations increases. As a result, the length of the long axis (T) of the contact surface (S) increases, and the contact pressure reaches its maximum value at two positions sandwiching the center on the long axis (T).
It can be seen that the value gradually becomes smaller than the maximum value (P3) of the contact pressure at the center of the long axis (T) of the initial contact surface (S). The present inventors have completed the present invention by discovering that if the maximum value (P3) of the initial contact pressure is large, fatigue peeling is more likely to occur and the amount of wear increases.

Function: A raceway of a ceramic bearing ring having a predetermined curvature has a predetermined width located within the contact surface so as to include the center in the long axis direction of the elliptical initial contact surface that occurs when a radial load is applied. If a stress relief part is formed, the initial contact pressure between the ball and the raceway when receiving a radial load in the part where the stress relief part is formed will be higher than the initial contact pressure when the stress relief part is not formed. becomes smaller.

Moreover, compared to the case where no stress relaxation part is formed,
The contact surface expands and the initial contact pressure is distributed over a wide range.

Therefore, the maximum shear stress generated under the contact surface is reduced and the amount of wear is reduced.

In addition, if the stress relaxation part consists of a minute annular recess and solid lubricant is filled in this minute annular recess, the wear of the solid lubricant progresses slowly because the contact pressure in this part is small. Solid lubricant functionality is maintained over a long period of time. Furthermore, as the wear progresses, the solid lubricant comes out of the micro recesses and invades other parts of the contact surface.
It also contributes to lubrication across the entire contact surface.

Example Embodiments of the invention will be described below with reference to the drawings.

In addition, FIG. 2 and FIG. 3 show the difference in curvature between the raceway groove of the outer ring and the ball to be larger than it actually is.

In the following description, the same parts and parts are denoted by the same reference numerals throughout the drawings, and the description thereof will be omitted.

FIG. 1 shows both the inner and outer rings and balls of a deep groove type ceramic ball bearing according to the present invention. In FIG. 1, the ceramic ball bearing consists of both inner and outer rings (1) and (2) and a plurality of balls (3) arranged between them. The ball (3) is held by a holder (not shown). Both inner and outer wheels (1) (2
) and the plurality of balls (3) are each made of ceramics such as silicon nitride. Both inner and outer wheels (
1) and (2) each have a raceway groove (la) with a predetermined curvature.
(2a) is formed.

Figure 2 shows that both the inner and outer wheels (1) (2) and the ball (3) are
Outer ring (2) and balls (3) when receiving a load in the radial direction
) is shown in an enlarged view. Raceway groove (2) of outer ring (2)
a) has a radius of curvature smaller than, for example, the raceway groove (2a) so as to include the center in the long axis (X) direction of the elliptical initial contact surface (P) that occurs when receiving a radial load. A stress relaxation portion (4) is formed which is an arcuate annular minute recess.

For example, the width of the annular micro-concave portion is approximately 500 μm or less, and the depth is approximately 5 μm or less at its maximum portion.

The width, depth, etc. of the minute recesses may be appropriately determined based on the graph shown in FIG. 8, taking into consideration the performance required of the bearing, etc., so that the initial contact pressure is the optimum value. The inside of the stress relaxation part (4) consisting of four annular minute parts is filled and baked with a solid lubricant (as shown) made of graphite, molybdenum disulfide, tungsten disulfide, or the like.

When both the inner and outer rings (1), (2) and the ball (3) receive a load in the radial direction, the circumferential surface of the raceway groove (2a) of the outer ring (2) and the ball (3) elastically deform, causing surface contact between the two. This results in an elliptical initial contact surface (F). And outer ring (2) and ball (3)
and the entire initial contact surface (P) including the stress relaxation part (4). Although not shown, the raceway groove (1) of the inner ring (1)
In a), a stress relaxation section is also formed, which is an annular micro-concavity with a predetermined width, so as to include the center in the longitudinal direction of the elliptical initial contact surface that occurs when a radial load is applied. Solid lubricant is filled and baked inside.

Then, as in the case of the outer ring (2), when a radial load is applied, the circumferential surface of the raceway groove (1a) and the balls (3) are elastically deformed, and the two come into surface contact and form an elliptical initial contact. A surface appears.

The initial contact pressure distribution between the inner and outer wheels (1), (2) and the ball (3) on the long axis (X) of the elliptical initial contact surface (P) at the initial stage of rotation is shown by the solid line (M) in Fig. 4. The maximum value (
Pl) is the maximum value (P
3) will be smaller than. As the total number of rotations increases, the contact surface (F) expands at an early stage and its long axis (
As X) becomes longer, the contact pressure distribution on the long axis (X) becomes as shown by the solid line (N) in the figure. In other words, the contact pressure between the inner and outer wheels (1) (2) and the ball (3) is
The maximum value (P2) on both sides of the stress relaxation part (4) in P)
), and gradually decreases toward the outside in the left and right direction.

This value (P2) is even smaller than the maximum value (Pl) of the initial contact pressure. Therefore, the maximum shear stress generated under the contact surface (F) is reduced, and fatigue peeling due to this shear stress is less likely to occur, extending the service life and reducing the amount of wear.

In addition, since the solid lubricant is filled and baked into the stress relaxation part (4), which is a micro-concave part where the contact pressure is small, the wear of the solid lubricant progresses slowly and the degree of deterioration of the lubrication performance is reduced. The solid lubricant function is maintained over a long period of time. Furthermore, as the wear progresses, the solid lubricant leaves the stress relaxation part (4) and enters other parts of the contact surface (F), so it also contributes to lubrication of the entire contact surface (F).

In this embodiment, the stress relaxation section (4) is an annular micro-concave section with an arcuate cross section having a curvature larger than that of the raceway groove, but the shape is not limited to this, and its shape is To maximize lubricant retention time,
Determined by experiment or theoretical calculation.

FIG. 3 is a view corresponding to FIG. 2 showing another embodiment of the ceramic ball bearing of the present invention. In Figure 4, outer ring (2)
The raceway groove (2a) of the raceway groove (2a) has a stress relief structure consisting of an annular micro-concavity of a predetermined width so as to include both ends in the long axis (X) direction of the elliptical initial contact surface (F) that occurs when receiving a radial load. A part (6) is formed, and inside this stress relaxation part (6),
It is filled and baked with a solid lubricant made of graphite, molybdenum disulfide, tungsten disulfide, etc.

When both the inner and outer wheels (1') (2) and the ball (3) receive a load in the radial direction, the outer ring (2)
The circumferential surface of the raceway groove (2a) and the ball (3) are elastically deformed, and the two come into surface contact to form an elliptical initial contact surface (F). The outer ring (2) and the balls (3) have both stress relaxation parts (4) (B
), contact is made over the entire initial contact surface (F).

On the long axis (X) of the initial contact surface (F) at the beginning of rotation,
The initial contact pressure between the inner and outer wheels (L) (2) and the ball (3) is also smaller at the outer stress relief portion (6) than if it were not present. Although not shown, the inner ring (1
) is also formed with a stress relaxation part consisting of four annular minute parts of a predetermined width, so as to include the center in the long axis direction of the circular initial contact surface generated when receiving a radial load. A solid lubricant is filled and baked inside this.

Then, as in the case of the outer ring (2), when a radial load is applied, the circumferential surface of the raceway groove (1a) and the balls (3) are elastically deformed, and the two come into surface contact and form an elliptical initial contact. A surface appears.

Although the above two embodiments are applied to deep groove ball bearings with cages, they are also applicable to full ball bearings. Moreover, either one of the inner and outer rings may be formed of bearing steel, heat-resistant steel such as Al5I M2O, or stainless steel instead of ceramics.

Effects of the Invention According to the ceramic ball bearing of the present invention, as described above,
Compared to conventional ceramic ball bearings, the maximum shear core force generated at the bottom of the contact surface is smaller, making it less likely that fatigue flaking will occur and extending the service life. Furthermore, since the amount of wear is reduced, the amount of abrasion powder generated is also reduced, and deterioration of rolling performance due to this is prevented.

Furthermore, since the function of the solid lubricant is maintained for a long period of time and deterioration of the lubricating performance can be prevented, the life of the solid lubricant can be further significantly extended and the amount of wear can be further reduced.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing both the inner and outer rings and balls of a ceramic ball bearing according to the present invention, Fig. 2 is an enlarged view showing the state of the contact portion between the outer ring and the balls when subjected to a radial load, and Fig. 3
Figure 2 shows another embodiment of the ceramic ball bearing of this invention.
Figure 4 is a graph showing the contact pressure distribution on the long axis of the contact surface when the ceramic ball bearing of the present invention receives a load in the radial direction, and Figure 5 is a graph showing the rolling of the ceramic cylinder and balls. A graph showing the measurement results of the cross-sectional shape of the worn surfaces of the cylinder and balls during the wear test. Figure 6 is a diagram showing the cross-sectional shape of the rolling groove of the cylinder. Figure 7 is the cross-sectional shape of the cylinder under radial load. FIG. 8 is a graph showing the contact pressure distribution on the long axis of the contact surface when the cylinder and the ball are subjected to a load in the radial direction. ...Inner ring, outer ring, ...ball, stress relief part, (F) ...contact surface, (X) ...long axis. That's all for the 21st book. Figure 3a Figure 1 Figure 4 Figure 6

Claims (1)

[Claims] 1. In a ceramic ball bearing in which at least one of the inner and outer rings and balls are each made of ceramic, the raceway of the ceramic raceway having a predetermined curvature is subjected to a radial load. A ceramic ball bearing in which a stress relaxation portion of a predetermined width is formed within the contact surface so as to include the center portion in the longitudinal direction of the elliptical initial contact surface that occurs at the contact surface. 2. Claim 1, wherein the stress relaxation part is a minute annular recess.
Ceramic ball bearings listed. 3. The ceramic ball bearing according to claim 2, wherein the annular recess is filled with a solid lubricant.