JP2012246976A - Rolling bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further extend the life of a rolling bearing which is excellent in electrolytic corrosion prevention effect and uses a rolling element made from silicon nitride.SOLUTION: The rolling bearing includes an inner ring, an outer ring, a rolling element, and a holder. The rolling element is made from silicon nitride being made dense by a filtering aid. The maximum diameter of segregation substances of the sintering aid on the surface is 20 μm or less. The thickness of a remaining sintering effect layer is 1.0% or less relative to the radius of the rolling element.

Description

  The present invention relates to a rolling bearing, and more particularly to a rolling bearing suitable for a device such as a fan motor or a servo motor of an air conditioner where electric corrosion is likely to occur.

  In applications where high-frequency current flows such as a fan motor or a servo motor of an air conditioner, ceramic rolling elements may be used because there is a risk of electric corrosion occurring on the rolling bearing that supports the rotating shaft. Silicon nitride is widely used as ceramics, and Patent Document 1 attempts to extend the life by defining the diameter of micropores that form a pattern observed as a white dendritic surface. Moreover, in patent document 2, it is aiming at lifetime extension by using the rolling element which has the effect which suppresses the impact from a track member rather than silicon nitride and which is excellent in beta sialon.

JP-A-6-329472 Japanese Patent No. 2010-1995

  However, further improvement in the life is inevitable, and an object of the present invention is to further extend the life of the rolling bearing using the rolling element made of silicon nitride and having an excellent effect of preventing electrolytic corrosion.

  As a result of examining the peeling of the rolling elements made of silicon nitride, the present inventors have found that the segregation of the sintering aid is the starting point, and thus the separation occurs. The inventors have found that a long life can be achieved by suppressing peeling, and the present invention has been completed.

  That is, the present invention relates to a rolling bearing comprising an inner ring, an outer ring, a rolling element, and a cage, wherein the rolling element is made of silicon nitride densified with a sintering aid, and a surface sintering aid. A rolling bearing characterized in that the segregated material has a maximum diameter of 20 μm or less and a residual sintering-affected layer thickness of 1.0% or less with respect to the radius of the rolling element.

  The rolling bearing of the present invention is excellent in the effect of preventing electrolytic corrosion and has a longer life because the peeling of the rolling elements is suppressed.

It is sectional drawing which shows the ball bearing which is an example of the rolling bearing which concerns on this invention. It is a figure which shows the SEM photograph of the surface of a ball | bowl in a life test. It is a figure for demonstrating how to obtain | require the maximum diameter of the segregation thing of a sintering auxiliary agent. It is a graph which shows the relationship between the maximum diameter of a segregation thing of a sintering auxiliary agent, and a life ratio. It is a figure which shows the SEM photograph of the cross section of the ball | bowl immediately after sintering. It is a figure which shows the density | concentration distribution of the sintering auxiliary agent in a rolling element. It is a schematic diagram which shows the relationship between the method of grinding | polishing and a completed sphere. It is a graph which shows the relationship between a residual sintering influence layer / finished sphere radius, and a life ratio. It is a graph which shows the relationship between the residual sintering influence layer / finished sphere radius and lifetime ratio which were obtained in the Example. It is a graph which shows the relationship between the maximum diameter and lifetime ratio of the segregation thing of the sintering aid obtained in the Example.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a cross-sectional view showing a ball bearing which is an example of a rolling bearing used for a fan motor of an air conditioner. As shown in the figure, the ball bearing 1 includes a plurality of balls 13 rotatably held by a cage 12 between an inner ring 10 and an outer ring 11, and a grease composition ( (Not shown) is sealed with a seal 14. The inner ring 10 and the outer ring 12 are made of a generally used steel material (for example, stainless steel or bearing steel). In the present invention, the balls 13 are made of silicon nitride for the purpose of preventing electrolytic corrosion.

  The balls 13 made of silicon nitride include particles of a sintering aid made of a metal oxide such as alumina, yttria, magnesia, etc., in order to improve the adhesion between the silicon nitride particles and the silicon nitride particles. About 1 to 5 mol% is mixed, sintered, and polished. In the present invention, the type and content of the sintering aid are not limited.

  The ball 13 is excluded by a strict inspection because if the surface has defects such as foreign matter and scratches, the ball 13 peels off and has a short life. However, it has been found that, in addition to defects such as foreign matter and scratches, separation occurs due to segregation of the sintering aid, and the larger the segregation product of the sintering aid, the easier the separation and the shorter the life.

Then, the following (life test) was performed in order to investigate the relationship between the size of the segregation material of the sintering aid and the life.
(Life test)
Silicon nitride particles, alumina particles, and yttria particles were mixed, molded, sintered, and polished to produce 3/16 inch balls. Twelve of these balls were incorporated in a bearing “No. 51305” (inner ring / outer ring: SUJ2) manufactured by NSK Ltd. to obtain a test bearing. The test bearing was rotated with oil bath lubrication (lubricant: R068) at a load of 1176 N and a rotation speed of 1000 min ⁻¹ , the life was measured, and the life ratio (actual life / calculated life) was obtained. In addition, after the test, the test bearing was disassembled, the peeled part of the ball was observed with SEM (2000 times), and the size of the segregation product (confirmed as containing Al, Y, O by analysis) of the sintering aid was measured. did. FIG. 2 is a view showing an SEM photograph of the surface of the ball, and the area that appears white is the peeled portion. The segregation product of the sintering aid was approximated by a circle or an ellipse as shown in FIG. 3, and the length of the longest portion a was measured. The results are shown in Table 1 and FIG. 4, and it can be seen that when the maximum diameter of the segregation material of the sintering aid is 20 μm or less, the life ratio is around 2, and the life is extended.

  Further, the sintering aid moves from the inside to the surface during the sintering and is concentrated, and a surface layer portion that is turned black is formed on the elementary sphere immediately after sintering. FIG. 5 is a view showing an SEM photograph of a cross section of the elementary sphere, and the region from the surface to a depth of about 100 μm is changed to black. In the following description, the black-discolored area is referred to as “black layer”. This black layer contains many defects and causes peeling. Therefore, it was thought that the life would be extended if the black layer was completely removed by polishing the ball, but when the above (life test) was performed using the ball from which the black layer was removed, the actual life was calculated. It often happens that the effect of improving the life is not seen.

  Therefore, when the cross section of the elementary sphere was examined in detail, it was found that the concentration distribution as shown in FIG. 6 was obtained. Here, the concentrations of the Al component, the Y component, and the O component are shown as traces of the sintering aid. As shown in the figure, the sintering aid is present at a high concentration from the surface to a certain depth (point A), forming a region corresponding to the black layer. In addition, after passing point A, the concentration of the sintering aid decreases rapidly, and the concentration decreases toward the inside, and the concentration of each component becomes constant at a certain depth (point B). In the following description, an area from point A to point B is referred to as “harmful layer”, and an area deeper than point B is referred to as “harmless layer”. Accordingly, the black layer and the harmful layer are collectively referred to as a “sintering effect layer”.

  Therefore, the harmful layer remains only by removing the black layer, and it is considered that the sintering aid contained in the harmful layer at a relatively high concentration causes peeling. That is, as shown in FIG. 7, even if the basic sphere shown in (a) is polished and the black layer is completely removed, a harmful layer remains as shown in (b). It is necessary to remove even the harmful layer.

  Therefore, as shown in Table 2, silicon nitride particles, alumina particles, and yttria particles are mixed, molded and sintered to produce an elementary ball, and a single-sided allowance (see FIG. 7) is adjusted during polishing to obtain a ball ( Finished sphere) was prepared, and the above (life test) was performed to determine the life ratio. Then, the relationship between the thickness of the remaining sintering-affected layer and the radius of the completed sphere was examined. The thickness of the residual sintering-affected layer is determined by conducting a chemical analysis on the cross section of the finished sphere to determine the relationship between the depth from the surface and the concentrations of the Al component, Y component, and O component. The depth to the position. Further, the cross section of the elementary sphere was observed with SEM (2000 times), and the thickness of the black layer was determined. The results are shown in Table 2 and FIG.

  It can be seen that by setting the ratio of (residual sintering-affected layer / finished sphere radius) to 1% or less, the life ratio is doubled and the effect of improving the life is great.

  The balls 13 are obtained by mixing silicon nitride particles and a sintering aid such as alumina particles and yttria particles, and molding, sintering, and polishing. However, the silicon nitride particles and the sintering aid have few impurities. It is preferable. In particular, silicon nitride having a low purity as in the direct nitriding method is inferior in sinterability compared to a high purity as in the imide decomposition method, requires a large amount of sintering aid, and has a sintering-affected layer. It is formed thick.

  Further, both the silicon nitride particles and the sintering aid are preferably fine powders, and are preferably fine powders having an average particle size of 1 μm or less. By using fine powder, particularly fine powder having an average particle size of 1 μm or less, the crystal grains of silicon nitride after sintering become fine, and even when peeled, the peeled area is small and the unevenness is also small.

  To remove the sintering-affected layer as described above, it can be carried out by increasing the amount of polishing. Brings rise. In addition, the sintering-affected layer may be formed by entering into the inside along the crack generated when the gas generated from the inside of the elementary sphere at the time of deoiling breaks through the hard dense layer on the surface. It may not be removed only by polishing. Therefore, it is also effective to optimize the sintering conditions (degreasing process) so as to suppress the generation of cracks.

  The molding is preferably CIP molding (cold hydraulic molding), and after sintering, HIP treatment (hot isostatic pressing) is preferably performed.

  Although there is no restriction | limiting in the grease enclosed with the rolling bearing of this invention, For example, when the affinity with the ball | bowl 13 is considered, it is preferable to use ester-type lubricating oil which has polarity for a base oil. When it is necessary to reduce the torque, a low viscosity base oil is used.

  Examples The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited thereby.

(Examples 1-3, Comparative Examples 1-9)
Silicon nitride particles and sintering aids (alumina particles and yttria particles) are mixed, CIP-molded and sintered, HIP-treated to produce a base ball, and further lapped to a ball having the diameter shown in Table 3 (Completed sphere) was produced. And said (life test) was performed using the produced ball | bowl, and the life ratio was calculated | required. In addition, after the test, the test bearing was disassembled and the surface of the ball was observed, and the large diameter was determined in the case of the segregation product of the sintering aid that was the starting point of the peeling.

  Moreover, about the ball produced from the same rod, the cross section was chemically analyzed and the thickness of the residual sintering influence layer was calculated | required.

  The results are shown in Table 3, FIG. 9 and FIG. 10. As in Examples 1 to 3, the maximum diameter of the segregation product of the sintering aid is 20 μm or less, (residual sintering-affected layer / finished sphere radius) ratio. If is 1% or less, it can be seen that the life ratio is doubled or more, and an excellent effect of improving the life is obtained.

  On the other hand, when the ratio (residual sintering-affected layer / finished sphere radius) exceeds 1% as in Comparative Examples 1 to 6, or the maximum diameter of the segregation product of the sintering aid as in Comparative Examples 7 to 9 When the thickness exceeds 20 μm, the effect of improving the life is small, and in some cases, it is shorter than the calculated life.

DESCRIPTION OF SYMBOLS 1 Ball bearing 10 Inner ring 11 Outer ring 12 Cage 13 Ball 14 Seal

Claims (1)

In a rolling bearing comprising an inner ring, an outer ring, a rolling element, and a cage,
The rolling element is made of silicon nitride densified with a sintering aid, the maximum diameter of the segregation product of the sintering aid on the surface is 20 μm or less, and the thickness of the residual sintering-affected layer is A rolling bearing characterized by being 1.0% or less with respect to the radius of the rolling element.