JP2010002012A - Rotary bearing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rotary bearing whose weight is reduced, and in which sliding abrasion and fretting damage are suppressed in a contact part between an rolling element and a bearing ring. <P>SOLUTION: This rotary bearing has an inner ring 1, an outer ring 2, and a plurality of rolling elements 3 freely rolling between respective raceway surfaces 1a, 1b, 2a and 2b of these inner-outer rings 1 and 2. The rolling elements 3 are made of ceramic strong against impact resistance. The ceramic is constituted of a sintered body containing β sialon as main component and a residual part of an impurity, or a sintered body containing β sialon as main component, a residual part of a sintering aid and an impurity. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a large-size or ultra-large size slewing bearing used for a slewing portion of, for example, a wind power generator.

  7 and 8 show an example of a wind power generator. This wind power generator 11 is provided with a nacelle 13 on a support base 12 so as to be able to turn horizontally, and a main shaft 15 is rotatably supported in a casing 14 of the nacelle 13, and at one end of the main shaft 15 protruding outside the casing 14. The blade 16 which is a swirl wing is attached. The other end of the main shaft 15 is connected to the speed increaser 17, and the output shaft 18 of the speed increaser 17 is coupled to the rotor shaft of the generator 19.

  The wind power generation apparatus is very large, and the length of one blade 16 is several tens of meters, and some of them exceed 100 meters. Therefore, when the blade 16 rotates about the main shaft 15, the wind speed of the wind received by the blade 16 differs depending on the rotation position, for example, the position above the main shaft 15 and the position below the main shaft 15. While the blade 16 rotates, the angle of each blade 16 toward the wind is adjusted according to the wind speed so that each blade 16 receives the same load even if the wind speed is different. Further, the direction of the nacelle 13 is changed according to the change of the wind direction so that each blade 16 receives wind from the front (yaw). If the wind speed is too high and a large load may be received, the direction of the nacelle 13 may be reversed to allow the wind to escape.

Thus, in the wind turbine generator, it is necessary to change the angle of the blade 16 and the direction of the nacelle 13 at any time according to the wind condition, so that the blade 16 and the nacelle 13 are rotatably supported by the slewing bearings 21 and 22, respectively. Rotation is performed by driving means (not shown). The characteristics of the slewing bearing of the wind power generator include that the dimensions are very large, the swing angle of the slewing is relatively small, and a variable load is received.
Regarding the dimensions, the outer ring outer diameter is 1000 to 3000 mm for blades and 1500 to 3500 mm for yaw. The swing angle is about 90 ° at the maximum for blades and 360 ° at the maximum for yaw. As for the fluctuating load, both the blade and the yaw are subjected to a fluctuating load, but the blade is often subjected to a sudden fluctuating load.

In a wide range of fields such as construction machines and machine tools, four-point contact ball bearings are used as slewing bearings (for example, Patent Documents 1 and 2). The four-point contact ball bearing is formed by forming each raceway surface of the inner ring and the outer ring with two curved surfaces, and interposing a plurality of balls so as to roll freely between these raceway surfaces. A large load capacity can be obtained with a simple configuration because the inner and outer rings are firmly clamped between the raceway surfaces and the rigidity of the inner and outer rings is high.
JP 2002-339981 A JP 2003-13963 A

Therefore, we decided to consider the use of four-point contact ball bearings for slewing bearings of wind power generators that are large or very large and require a large load capacity. According to JIS B 0104-1991, a large bearing is defined as having an outer ring outer diameter of 180 to 800 mm.
As described above, the slewing bearing of the wind turbine generator frequently oscillates within a relatively narrow slewing range due to a fluctuating load, so that fretting is likely to occur. In order to prevent fretting, it is effective to suppress slippage between the rolling elements and the raceway by making the internal clearance negative. However, if the four-point contact ball bearing has a negative clearance, there is a problem that sliding wear occurs due to the ball rolling in the four-point contact state. Even with a negative clearance, it is difficult to completely prevent fretting due to fluctuating loads. Therefore, reducing fretting damage as much as possible remains an important issue. Furthermore, in the slewing bearing of a large or very large wind power generator, weight reduction of the bearing is also an important issue. These problems and problems are not limited to the case of a four-point contact ball bearing, but can be applied to other types of bearings. For example, a three-row cylindrical roller bearing that combines a cylindrical roller that receives an axial load and a cylindrical roller that receives a radial load.

  Conventionally, countermeasures against the above-mentioned sliding wear and fretting damage have been taken by adjusting the amount of grease sealed in the bearing or adding an additive such as molybdenum dioxide to the grease. These methods can be expected to have a certain effect, but more fundamental solutions are required.

  An object of the present invention is to provide a slewing bearing in which sliding wear and fretting damage at a contact portion between a rolling element and a bearing ring are suppressed, and the weight of the bearing can be reduced.

  The slewing bearing according to the present invention comprises an inner ring, an outer ring, and a plurality of rolling elements that can roll between the raceway surfaces of the inner and outer rings, and the rolling elements are made of ceramics having high impact resistance. Features.

If the rolling element is made of ceramics, the following effects can be obtained.
・ Ceramics that are sintered bodies have good oil retention. For this reason, the oil impregnated in the rolling elements oozes out between the raceways of the rolling elements and the inner and outer rings and acts as lubricating oil, and both sliding wear and fretting damage are suppressed.
-Ceramics have a lower density than steel. For this reason, the weight of the rolling element can be reduced, and the weight of the entire bearing can be reduced.
・ Ceramics have high corrosion resistance and insulation. For this reason, it can suppress that a rolling element is damaged by corrosion or electrolytic corrosion.

The ceramics may be composed of a sintered body containing β sialon as a main component and the remaining impurities. In that case, the ceramic _is represented by a composition formula of _{Si 6-Z Al Z O Z} N 8-Z, as a main component β-sialon satisfying 0.1 ≦ z ≦ 3.5, sintering the balance being impurities It is preferable that the Young's modulus is 180 GPa or more and 270 GPa or less.
Further, the ceramic may be composed of a sintered body containing β sialon as a main component and the remaining sintering aid and impurities. In this case, the ceramic is mainly composed of β sialon represented by a composition formula of Si _6-Z Al _Z O _Z N _8-Z and satisfying 0.1 ≦ z ≦ 3.5, and the remaining sintering aid and It is preferably composed of a sintered body made of impurities and has a Young's modulus of 180 GPa or more and 270 GPa or less.
Hereinafter, these sintered bodies containing β sialon as a main component are referred to as “sialon sintered bodies”.

  The inventor of this invention investigated in detail the relationship between the rolling fatigue life of the rolling element which consists of a sialon sintered compact, and the structure of a rolling element. As a result, the following knowledge was obtained and the present invention was conceived.

  That is, the above-described β sialon can be produced with various compositions in which the value of z (hereinafter referred to as z value) is 0.1 or more by employing a production process including combustion synthesis. is there. And the hardness which has a big influence on a general rolling fatigue life hardly changes in the range of z value 4.0 or less which is easy to manufacture. However, when the relationship between the rolling fatigue life and z value of a rolling element made of a sintered body containing β sialon as a main component is investigated in detail, if the z value exceeds 3.5, the rolling fatigue life of the rolling element is obtained. Was found to drop significantly.

  More specifically, when the z value is in the range of 0.1 to 3.5, the rolling fatigue life is substantially the same. When the operation time of the slewing bearing exceeds a predetermined time, the surface of the rolling element is peeled off. Occurs and breaks. On the other hand, when the z value exceeds 3.5, the rolling elements are likely to be worn, and the rolling fatigue life is significantly reduced due to this. In other words, the failure mode of the rolling element made of a sialon sintered body changes with the composition having a z value of 3.5 as a boundary, and when the z value exceeds 3.5, the rolling fatigue life is greatly reduced. Became clear. Therefore, in order to ensure a stable and sufficient life in a rolling element made of a sialon sintered body, the z value needs to be 3.5 or less.

  On the other hand, as described above, β sialon can be manufactured at a low cost by being manufactured by a manufacturing process including combustion synthesis. However, it has been found that when the z value is less than 0.1, it is difficult to perform the combustion synthesis. Therefore, in order to manufacture a rolling element made of a sialon sintered body at a low cost, the z value needs to be 0.1 or more.

  Moreover, when the Young's modulus of a rolling element becomes high, it exists in the tendency for the intensity | strength of the raw material which comprises a rolling element to rise. However, when the Young's modulus of the rolling element is increased, the rolling element is less likely to be elastically deformed, so that the contact area between the rolling element and the raceway is reduced and the contact surface pressure is increased. As a result, when the load applied increases rapidly, the rolling elements are likely to be damaged. On the other hand, when the Young's modulus of the rolling element is lowered, the rolling element is easily elastically deformed, so that the contact area between the rolling element and the raceway is increased, and the contact surface pressure is reduced. However, on the other hand, when the Young's modulus of the rolling element becomes low, the strength of the material constituting the rolling element tends to decrease. For this reason, the Young's modulus of the rolling element needs to be within a range that can ensure a balance between the strength of the material constituting the rolling element and the reduction of the contact surface pressure between the rolling element and the race.

  More specifically, when the Young's modulus of the rolling element made of a sialon sintered body is less than 180 GPa, the influence of the strength reduction of the material constituting the rolling element exceeds the effect of reducing the contact surface pressure, and the rolling element rolls. Fatigue life is reduced. In addition, as the contact area between the rolling element and the raceway increases, the frictional force acting between the rolling element and the raceway increases, causing a problem that the bearing torque increases. Therefore, the Young's modulus of the rolling element made of a sialon sintered body needs to be 180 GPa or more.

  On the other hand, when the Young's modulus of the rolling element made of a sialon sintered body exceeds 270 GPa, the influence of the increase in the contact surface pressure exceeds the effect of increasing the strength of the material constituting the rolling element, and the applied load increases. Damage such as deformation is likely to occur on the rolling contact surface that is in contact with the race. As a result, the rolling fatigue life of the rolling element made of a sialon sintered body is reduced. Therefore, when it is used for an application in which the load applied changes rapidly, the Young's modulus of the rolling element made of the sialon sintered body needs to be 270 GPa or less.

On the other hand, the rolling element according to one aspect of the present invention is mainly composed of β sialon represented by a composition formula of Si _6-Z Al _Z O _Z N _8-Z and satisfying 0.1 ≦ z ≦ 3.5. In addition, since the Young's modulus is 180 GPa or more and 270 GPa or less because the Young's modulus is 180 GPa or less and 270 GPa or less, it is possible to stably ensure sufficient durability while being inexpensive. It can be used for applications in which the applied load changes rapidly. For example, it is suitable for a rolling element of a slewing bearing of a wind power generator.

  In addition, when using for the application with a comparatively big load, it is desirable that the Young's modulus of a rolling element is 220 GPa or more. On the other hand, the Young's modulus of the rolling element is preferably 260 GPa or less when used in an environment where the change in applied load is particularly large, such as when an external impact is applied.

  In addition, the rolling element according to another aspect of the present invention basically has the same configuration as the rolling element according to one aspect of the present invention, and exhibits the same effects. However, the rolling element according to another aspect of the present invention is different from the rolling element according to one aspect of the present invention in that it includes a sintering aid in consideration of the use of the rolling element. The rolling element according to another aspect of the present invention can easily reduce the porosity of the sialon sintered body by adopting the sintering aid, and can ensure sufficient durability stably.

  As the sintering aid, at least one of magnesium (Mg), aluminum (Al), silicon (Si), titanium (Ti), rare earth element oxide, nitride, and oxynitride is employed. be able to. Further, the sintering aid is desirably 20% by mass or less in the sintered body.

Since the sialon sintered body is sintered under a low pressure, for example, a pressure of 1 MPa or less, a general ceramic that is pressure-sintered under a pressure of 10 MPa or more, for example, a sintered body mainly composed of silicon nitride (hereinafter referred to as a sintered body) , “The silicon nitride sintered body”), the manufacturing cost can be kept low.
The sialon sintered body has a smaller Young's modulus than the silicon nitride sintered body. The Young's modulus of the silicon nitride sintered body is 310 GPa, whereas the Young's modulus of the sialon sintered body is 180 GPa or more and 270 GPa or less as described above. Therefore, a rolling element made of a sialon sintered body has a larger area where the rolling element comes into contact with the raceway surface of the inner and outer rings when a load is applied, and has a larger load capacity than a rolling element made of a silicon nitride sintered body. In addition, since the rolling element made of a sialon sintered body is in contact with the raceway surface of the inner and outer rings over a wide area, the aggression against the raceway surface is small and the raceway surface is hardly damaged.

In the rolling element, a dense layer, which is a layer having a higher density than the inside, is preferably formed in a region including a rolling surface which is a surface in contact with the inner and outer rings.
In a rolling element made of a sialon sintered body, the denseness greatly affects the rolling fatigue life, which is one of the most important durability of the rolling element. As described above, a rolling element in which a dense layer is formed in a region including a rolling surface has an improved rolling fatigue life and can stably ensure sufficient durability.

  Here, the high-density layer is a layer having a low porosity (high density) in the sintered body and can be investigated as follows, for example. First, the rolling element is cut in a cross section perpendicular to the surface of the rolling element, and the cross section is mirror-wrapped. After that, the mirror-wrapped cross section is photographed with oblique light (dark field) of an optical microscope at, for example, about 50 to 100 times, and recorded as an image of 300 DPI (Dot Per Inch) or more. At this time, the white region observed as a white region corresponds to a region with high porosity (low density). Therefore, a region where the area ratio of the white region is low is denser than a region where the area ratio is high. Then, after binarizing the image recorded using the image processing device with the luminance threshold, the area ratio of the white area is measured, and the denseness of the photographed area can be known from the area ratio.

  That is, in the rolling element of the slewing bearing of the present invention, a dense layer, which is a layer having a lower area ratio of the white region than the inside, is formed in the region including the rolling surface. In addition, it is preferable to perform the said imaging | photography at 5 or more places at random, and to evaluate the said area ratio by the average value. Moreover, the area ratio of the said white area | region inside a rolling element is 15% or more, for example. Further, in order to further improve the rolling fatigue life of the rolling element, the dense layer preferably has a thickness of 100 μm or more.

When the cross section of the dense layer is observed with oblique light from an optical microscope, the area ratio of the white region observed as a white region is preferably 7% or less.
By improving the denseness of the dense layer to such an extent that the area ratio of the white region is 7% or less, the rolling fatigue life of the rolling element is further improved. Therefore, with the above configuration, the rolling fatigue life of the rolling elements can be further improved.

In the region including the surface of the dense layer, it is more preferable that a highly dense layer which is a layer having a higher denseness than other regions in the dense layer is formed.
By forming the denser layer having a higher density in the region including the surface of the dense layer, the durability against rolling fatigue of the rolling elements is further improved, and the rolling fatigue life is further improved.

When the cross section of the highly dense layer is observed with oblique light from an optical microscope, the area ratio of the white region observed as a white region is preferably 3.5% or less.
By improving the denseness of the highly dense layer to such an extent that the area ratio of the white region is 3.5% or less, the rolling fatigue life of the rolling element is further improved. Therefore, with the above configuration, the rolling fatigue life of the rolling elements can be further improved.

  Since the slewing bearing of the present invention can obtain the above-described effects, the blade of the wind power generator is supported so as to be pivotable about the axis substantially perpendicular to the main shaft axis with respect to the main shaft. The nacelle can be suitably used for pivotally supporting the nacelle.

  The slewing bearing according to the present invention includes an inner ring, an outer ring, and a plurality of rolling elements that are freely rollable between the raceway surfaces of the inner and outer rings, and the rolling elements are made of ceramics having high impact resistance. Sliding wear and fretting damage at the contact portion between the moving body and the race are suppressed, and the weight of the bearing can be reduced. In particular, when the ceramic is a sialon sintered body, the manufacturing cost can be kept low and the raceway surface is hardly damaged.

  An embodiment of the present invention will be described with reference to FIG. This slewing bearing is, for example, a bearing that supports a blade of a wind turbine generator so that it can pivot about an axis substantially perpendicular to the spindle axis, or a nacelle of a wind turbine generator, with respect to a support base. Used as a bearing to support

  The slewing bearing is composed of an inner ring 1, an outer ring 2, and rolling elements 3 including a plurality of balls in each row interposed between the raceways 1 a, 1 b, 2 a, and 2 b of the inner and outer rings 1 and 2, respectively. And a cage 4 that holds the rolling elements 3 in each row separately in the pocket 4a.

  Each of the raceway surfaces 1a, 1b, 2a, 2b of the inner and outer rings 1, 2 is composed of two curved surfaces 1aa, 1ab, 1ba, 1bb, 2aa, 2ab, 2ba, 2bb. Each of these two curved surfaces has a circular arc shape having a radius of curvature larger than that of the rolling element 3 and different centers of curvature. Between a pair of curved surfaces constituting each track surface 1a, 1b, 2a, 2b, groove portions 1ac, 1bc, 2ac, 2bc are formed. Each rolling element 3 comes into contact at four points with its rolling surface 3a in contact with the curved surfaces of the inner ring raceway surfaces 1a and 1b and the outer ring raceway surfaces 2a and 2b. That is, this slewing bearing is configured as a four-point contact double row ball bearing.

  The inner ring 1 and the outer ring 2 are provided with mounting bolt holes 5 and 6, respectively. Grease is filled in the bearing space between the inner and outer rings 1 and 2, and both ends in the axial direction of the bearing space are sealed with seal members 7.

  The rolling element 3 is composed of a sialon sintered body. The sialon sintered body refers to a sintered body mainly composed of β sialon and composed of the remaining impurities, or a sintered body composed mainly of β sialon and composed of the remaining sintering aid and impurities.

β sialon is a kind of ceramics and is a substance represented by a composition formula of Si _6-Z Al _Z O _Z N _8-Z and satisfying 0.1 ≦ z ≦ 3.5. Impurities include inevitable impurities including those derived from raw materials or those mixed in the manufacturing process. As the sintering aid, at least one of magnesium (Mg), aluminum (Al), silicon (Si), titanium (Ti), rare earth element oxide, nitride, and oxynitride may be employed. it can. Note that the sintering aid is desirably 20% by mass or less in the sintered body.

In FIG. 2, the manufacturing method of the rolling element 3 which consists of a sialon sintered compact is shown.
The β sialon powder preparation step S1 is a step of preparing β sialon powder. For example, by employing a combustion synthesis method, β sialon powder can be produced at low cost.

  The mixing step S2 is a step of adding and mixing a sintering aid to the β sialon powder prepared in the β sialon powder preparation step S1. If no sintering aid is added, this step can be omitted.

  The forming step S <b> 3 is a step of forming β sialon powder or a mixture of β sialon powder and a sintering aid into a schematic shape of the rolling element 3. Specifically, by applying a molding technique such as press molding, cast molding, extrusion molding, rolling granulation, etc. to a β sialon powder or a mixture of β sialon powder and a sintering aid, a rolling element 3 is produced.

  The pre-sintering processing step S4 is a step in which the molded body is subjected to surface processing so that the molded body has a shape closer to the desired shape of the rolling element 3 after sintering. Specifically, by applying a processing method such as green body processing, the molded body is molded so as to have a shape closer to the shape of the rolling element 3 after sintering. This pre-sintering processing step S4 can be omitted when a shape close to the shape of the desired rolling element 3 is obtained after sintering at the stage where the molded body is formed in the forming step S3. .

  Sintering process S5 is a process of sintering the said molded object under the pressure of 1 Mpa or less. Specifically, a sintered body having a schematic shape of the rolling element 3 is produced by heating and sintering the molded body by a heating method such as heating with a heater or radio wave heating using microwaves or millimeter waves. .

  The finishing step S6 is a step of completing the rolling element 3 by performing a finishing process on the sintered body produced in the sintering step S5. Specifically, the rolling element 3 is completed by polishing the surface of the sintered body produced in the sintering step S5.

  Here, due to the sintering in the sintering step S5, a region having a thickness of about 500 μm from the surface of the sintered body is denser than the inside, and when the cross section is observed by oblique light of an optical microscope, A dense layer in which the area ratio of the white region observed as the region is 7% or less is formed. Furthermore, in the region of about 150 μm thickness from the surface of the sintered body, the denseness is higher than other regions in the dense layer, and when the cross section is observed with oblique light of an optical microscope, it is observed as a white region. A high-density layer in which the area ratio of the white region is 3.5% or less is formed. Therefore, in the finishing step S6, it is preferable that the thickness of the sintered body to be removed is 150 μm or less, particularly in a region to be a rolling surface. Thereby, a highly dense layer can remain in the region including the rolling surface 3a of the rolling element 3, and the rolling fatigue life of the rolling element 3 can be improved.

  The sintering step S5 is preferably performed under a pressure of 0.01 MPa or higher in order to suppress the decomposition of β sialon, and more preferably performed under a pressure of atmospheric pressure or higher in consideration of cost reduction. Moreover, in order to form a dense layer while suppressing manufacturing costs, the sintering step S5 is preferably performed under a pressure of 1 MPa or less. Further, in order to adjust the Young's modulus of the produced rolling element 3 to a desired value of 180 GPa or more and 270 GPa or less, for example, the z value of β sialon powder prepared in β sialon powder preparation step S1 is set to 0.1 ≦ z Adjustment may be made within a range of ≦ 3.5. More specifically, the Young's modulus of the produced rolling element can be reduced by increasing the z value.

  In general ceramic sintering, sintering by a pressure sintering method such as a hot isostatic sintering (HIP) method, a gas pressure sintering (GPS) method, or the like is employed. Since these pressure sintering methods usually sinter under a pressure of 10 MPa or more, the production cost is high. On the other hand, since the manufacturing method of the product which consists of a sialon sintered compact sinters under the pressure of 1 Mpa or less as mentioned above, manufacturing cost can be restrained low, for example to about 1/10. Therefore, the rolling element 3 can be manufactured at low cost.

  The materials of the inner and outer rings 1 and 2 and the cage 4 are not particularly limited. For example, the inner and outer rings 1 and 2 can employ steel, specifically, bearing steel such as JIS standard SUJ2, or carburized steel such as SCR420 and SCM420. The cage 4 can use resin in addition to steel. In some cases, a sialon sintered body may be used for the inner and outer rings 1 and 2 and the cage 4 as well as the rolling element 3.

  In this slewing bearing, the bearing type is a four-point contact ball bearing and the rolling elements 3 are arranged in a double row, so that the rated load is large while the configuration is simple. In the simple calculation, the static load rating is twice that of the single-row case. If the rolling elements 3 are in a double row, the axial width of the cage 4 will be widened, but will not be doubled compared to a single row. Therefore, the rated load can be increased without increasing the axial width of the cage 4 too much. Since the rolling elements 3 are securely held by the cage 4, the rolling elements 3 are not scattered due to the advance and delay of the rolling elements 3, and the rolling elements 3 can always be held at equal intervals.

  Table 1 compares the characteristics of a sialon sintered body, a silicon nitride sintered body, and bearing steel (SUJ2).

By configuring the rolling element 3 with a sialon sintered body, the following effects can be obtained.
・ Sialon sintered body has many holes and good oil retention. For this reason, the oil impregnated in the rolling element 3 oozes out between the rolling surface of the rolling element 3 and the raceway surfaces 1a, 1b, 2a, 2b of the inner and outer rings 1, 2 and acts as lubricating oil, Both sliding wear and fretting damage are suppressed.
・ The density of sialon sintered compact is smaller than that of steel. For this reason, the rolling element 3 can be reduced in weight, and the entire bearing can be reduced in weight.
・ Sialon sintered body has high corrosion resistance and insulation. For this reason, it can suppress that the rolling element 3 is damaged by corrosion or electrolytic corrosion.

Each of the above effects can be said when the rolling element 3 is another ceramic, for example, a silicon nitride sintered body. When the sialon sintered body is compared with the silicon nitride sintered body, the sialon sintered body has a characteristic that Young's modulus is smaller than that of the silicon nitride sintered body. For this reason, the rolling element 3 made of a sialon sintered body has a raceway surface 1a, 1b, 2a, 2b of the inner and outer rings 1 and 2 when subjected to a load, rather than the rolling element made of a silicon nitride sintered body. Large contact area with large load capacity. Moreover, since the rolling element 3 made of a sialon sintered body is in contact with the raceway surfaces 1a, 1b, 2a, and 2b of the inner and outer rings 1 and 2 in a wide area, the aggressiveness against the raceway surfaces 1a, 1b, 2a, and 2b is small. The raceway surfaces 1a, 1b, 2a, 2b are hardly damaged.
Furthermore, as described above, the sialon sintered body has an advantage that the cost is lower than other ceramics.

  As described above, this slewing bearing has a simple configuration, a large rated load, excellent durability, and is unlikely to cause fretting. Therefore, the slewing bearing 21 for supporting the blades of the wind power generator (FIG. 7) or Suitable for the nacelle yaw support slewing bearing 22 (FIG. 8). Other than wind power generators, it can be applied to construction machines such as hydraulic excavators and cranes, rotary tables of machine tools, parabolic antennas, and the like.

  In the said embodiment, although the rolling element 3 was made into the double row, a single row may be sufficient.

  FIG. 3 shows a different embodiment of the invention. This slewing bearing has a three-row cylindrical roller bearing type, and includes an inner ring 31, an outer ring 32 made up of a pair of upper and lower outer ring members 32A, 32B, and rolling elements 33A, 33B, 33C made up of three rows of cylindrical rollers. Is provided. The rolling elements 33A and 33B have raceway surfaces 31aa and 31ab formed on both upper and lower surfaces of the outer diameter side protrusion 31a of the inner ring 31, and raceway surfaces 32aa formed on the inner diameter side protrusions 32aA and 32aB of the outer ring members 32A and 32B. , 32ab to be freely rollable and receive an axial load. The rolling element 33C can freely roll between a raceway surface 31ac formed on the outer diameter surface of the outer diameter side protruding portion 31a of the inner ring 31 and a raceway surface 32c formed on the inner diameter surface of the upper outer ring member 32A. To receive a radial load. Each of the rolling elements 33A, 33B, 33C is composed of the same sialon sintered body as described above.

  The inner ring 31 and the outer ring 32 are provided with mounting bolt holes 35 and 36, respectively. Grease is filled in the bearing space between the inner and outer rings 31 and 32, and both ends in the axial direction of the bearing space are sealed with seal members 37.

  Since this slewing bearing is configured to receive an axial load by rolling elements 33A and 33B made of double-row cylindrical rollers, the rated load is large. Further, the slewing bearing in which the bearing type is a three-row cylindrical roller bearing is also a slewing bearing in which the rolling elements 33A, 33B, and 33C are formed of sialon sintered bodies, and the bearing type is a four-point contact ball bearing. The same effect as described in the column can be obtained. Therefore, it is particularly suitable for a yaw bearing that supports a nacelle of a wind turbine generator.

  A plurality of slewing bearings each provided with rolling elements made of sialon sintered bodies having different z values were prepared, and a test was conducted to investigate the relationship between the z value and the rolling fatigue life (durability). In addition, although this test was done about the rolling element of a general slewing bearing, it is applicable also to the rolling element of the slewing bearing of a wind power generator. In this test, the rolling elements were balls, but it is expected that similar test results can be obtained when the rolling elements are rollers. The test procedure is as follows.

  First, a method for producing a test bearing to be tested will be described. First, β sialon powder prepared by the combustion synthesis method in the range of z value and 0.1 to 4 is prepared, and the z value is 0.1 to 0.1 in the same method as the rolling element manufacturing method shown in FIG. A rolling element 4 was produced. A specific manufacturing method is as follows. First, β sialon powder refined to submicron, aluminum oxide (manufactured by Sumitomo Chemical Co., Ltd., AKP30) and yttrium oxide (manufactured by HC Starck Co., Ltd., Yttrium oxide grade C) as a ball mill Were mixed by wet mixing. Then, granulation was performed with a spray dryer to produce granulated powder. The granulated powder was molded into a spherical shape with a mold and further pressurized by cold isostatic pressing (CIP) to obtain a spherical molded body.

  Subsequently, after performing normal pressure sintering as the primary sintering for the molded body, the sintered sphere is obtained by performing HIP (Hot Isostatic Press) in a nitrogen atmosphere at a pressure of 200 MPa. Manufactured. Next, lapping was performed on the sintered spheres to obtain 3/8 inch ceramic spheres (JIS grade G5). And the bearing of the JIS standard 6206 model number was produced in combination with the bearing ring made from bearing steel (JIS standard SUJ2) prepared separately. (Examples A to H and comparative examples B and C). For comparison, a rolling element made of a silicon nitride sintered body, that is, a rolling element having a z value of 0 was produced in the same manner as the rolling element made of the sialon sintered body, and assembled in the same manner. (Comparative Example A).

  Next, test conditions will be described. For the bearing of JIS standard 6206 model number produced as described above, maximum contact surface pressure Pmax: 3.2 GPa, bearing rotation speed: 2000 rpm, lubrication: circulating oil supply of turbine oil VG68 (clean oil), test temperature: room temperature, A fatigue test was conducted under the conditions of The vibration of the bearing during operation is monitored by the vibration detection device, and the test is stopped when the rolling element is damaged and the vibration of the bearing exceeds a predetermined value. Recorded as bearing life. In addition, after the test was stopped, the bearing was disassembled to confirm the damaged state of the rolling elements.

  Table 2 shows the test results. In Table 2, the life in each Example and Comparative Example is expressed as a life ratio with the life in Comparative Example A (silicon nitride sintered body) as 1. The damage form is described as “peeling” when peeling occurs on the surface of the rolling element, and “wearing” when the surface is worn without peeling and the test is stopped.

  Referring to Table 2, in Examples A to H of the present invention in which the z value is 0.1 or more and less than 3.5, the lifetime is comparable to that of the silicon nitride sintered body (Comparative Example A). Have. Further, the damage form is “peeling” as in the case of the silicon nitride sintered body. On the other hand, in Comparative Example B in which the z value exceeds 3.5 and is outside the scope of the present invention, the life is significantly reduced and wear is observed on the rolling elements. That is, in the comparative example in which the z value is 3.8, although the rolling element is finally peeled off, it is considered that the life of the rolling element is greatly reduced due to the wear of the rolling element. Further, in Comparative Example C where the z value is 4, the wear of the rolling elements proceeds in a very short time, and the durability of the bearing is significantly reduced.

  As described above, in the range where the z value is 0.1 or more and 3.5 or less, the durability of the bearing provided with the rolling element made of the sialon sintered body is provided with the rolling element made of the silicon nitride sintered body. It is almost equivalent to a bearing. On the other hand, when the z value exceeds 3.5, the rolling elements are likely to be worn, and the rolling fatigue life is significantly reduced due to this. Furthermore, it became clear that when the z value was increased, the cause of breakage of the rolling element made of a sialon sintered body was changed from “peeling” to “wear”, and the rolling fatigue life was significantly reduced. Thus, by setting the z value to 0.1 or more and 3.5 or less, it is possible to provide a bearing made of a sialon sintered body that is inexpensive and can stably ensure sufficient durability. It was confirmed that there was.

  Referring to Table 2, in Example H in which the z value exceeds 3.5, a slight amount of wear occurs in the rolling elements, and the service life also decreases compared to Examples A to G. ing. From this, it can be said that the z value is desirably 3 or less in order to ensure sufficient durability more stably.

  Further, from the above experimental results, in order to obtain durability (life) equal to or greater than that of a rolling element made of a silicon nitride sintered body, the z value is preferably 2 or less, and 1.5 or less. More preferred. On the other hand, in view of the ease of production of β sialon powder by a production process employing combustion synthesis, it is preferable to set the z value to 0.5 or more, at which a reaction due to self-heating is sufficiently expected.

  A test was conducted to investigate the formation state of the dense layer and the highly dense layer in the cross section of the sialon sintered body. The test procedure is as follows.

First, a β sialon powder (product name: Melamix, manufactured by Isman Jay Co., Ltd.) having a composition produced by combustion synthesis method of Si ₅ AlON ₇ is prepared, and the same method as the method of manufacturing the rolling element shown in FIG. Thus, a cubic test piece having a side of about 10 mm was produced. A specific manufacturing method is as follows. First, a β sialon powder refined to submicron, aluminum oxide (manufactured by Sumitomo Chemical Co., Ltd., AKP30) and yttrium oxide (manufactured by HC Starck Co., Ltd., Yttrium oxide grade C) as a ball mill Were mixed by wet mixing. Then, granulation was performed with a spray dryer to produce granulated powder. The granulated powder was molded into a predetermined shape with a mold, and further pressed by cold isostatic pressing (CIP) to obtain a molded body. Subsequently, the molded body test piece was manufactured by heating and sintering the molded body at 1650 ° C. in a nitrogen atmosphere at a pressure of 0.4 MPa.

  Thereafter, the test piece was cut, and the cut surface was lapped with a diamond lapping machine, and then mirror lapping with a chromium oxide lapping machine was performed to form a cross section for observation including the center of the cube. And the said cross section was observed with the oblique light of the optical microscope (the Nikon Co., Ltd. make, microphoto-FAX), and the instant photograph (FP-100B made by Fuji Film Co., Ltd.) of 50 times magnification was image | photographed. Thereafter, the obtained photographic image was taken into a personal computer using a scanner (resolution 300 DP1). And the binarization process by a brightness | luminance threshold value was performed using image processing software (Mitani Corporation WinROOF) (binarization threshold value in this test: 140), and the area ratio of the white area | region was measured.

  Next, test results will be described. FIG. 4 is a photograph of the cross section for observation of the test piece taken with oblique light from an optical microscope. FIG. 5 is an example showing a state in which the image of the photograph of FIG. 4 is binarized by a luminance threshold using image processing software. FIG. 6 is a diagram showing a region (evaluation region) where image processing is performed when the image of the photograph of FIG. 4 is binarized using a luminance threshold value using image processing software. In FIG. 4, the upper side of the photograph is the processing side of the test piece, and the upper end is the surface.

  4 and 5, the test piece created by the same method as the rolling element manufacturing method shown in FIG. 2 has a layer with a white area smaller than the inside in the area including the surface. I understand. And, as shown in FIG. 6, the photographed photograph image is divided into three regions according to the distance from the outermost surface of the test piece (the region having a distance from the outermost surface within 150 μm, the region exceeding 150 μm and within 500 μm, When the area ratio of the white region was calculated by performing image analysis for each region, the results shown in Table 2 were obtained. In Table 2, the average value and the maximum value of the area ratio of the white area in five fields of view obtained from five photographs taken at random are shown with each field shown in FIG. 6 as one field of view. Yes.

  Referring to Table 3, the area ratio of the white region in the test piece was 18.5% inside, while 3.7% in the region having a depth of 500 μm or less from the surface, from the surface. In the region where the depth of 150 μm or less was 1.2%. From this, the test piece produced by the same method as the rolling element manufacturing method shown in FIG. 2 has a dense layer and a highly dense layer having a white region less than the inside in the region including the surface. confirmed.

  A test was conducted to confirm the rolling fatigue life of the rolling element of the slewing bearing according to the present invention. In addition, although this test was done about the rolling element of a general slewing bearing, it is applicable also to the rolling element of the slewing bearing of a wind power generator. The test procedure is as follows.

First, a method for producing a test bearing to be tested will be described. First, a β sialon powder (product name: Melamix, manufactured by Isman Jay Co., Ltd.) having a composition produced by combustion synthesis method of Si ₅ AlON ₇ is prepared, and the same method as the method of manufacturing the rolling element shown in FIG. Thus, a 3/8 inch ceramic sphere having a diameter of 9.525 mm was produced. A specific manufacturing method is as follows. First, a β sialon powder refined to submicron, aluminum oxide (manufactured by Sumitomo Chemical Co., Ltd., AKP30) and yttrium oxide (manufactured by HC Starck Co., Ltd., Yttrium oxide grade C) as a ball mill Were mixed by wet mixing. Then, granulation was performed with a spray dryer to produce granulated powder. The granulated powder was molded into a sphere with a mold and further pressurized by cold isostatic pressing (CIP) to obtain a spherical molded body.

  Next, the green body is green processed so that the machining allowance after sintering becomes a predetermined dimension, and the sintered body is subsequently heated to 1650 ° C. in a nitrogen atmosphere at a pressure of 0.4 MPa. By sintering, sintered spheres were produced. Next, lapping was performed on the sintered spheres to obtain 3/8 inch ceramic spheres (rolling elements; JIS grade G5). And the bearing of the JIS standard 6206 model number was created combining with the bearing ring made from bearing steel (JIS standard SUJ2) prepared separately. Here, the thickness (processing allowance) of the sintered sphere removed by the lapping process on the sintered sphere was changed in eight stages, and eight types of bearings were produced (Examples A to H). On the other hand, for comparison, lapping is performed on sintered spheres (EC 141 manufactured by Nippon Special Ceramics Co., Ltd.) sintered by pressure sintering using raw material powders composed of silicon nitride and a sintering aid in the same manner as described above. Processing was performed and a bearing of JIS standard 6206 model number was fabricated in combination with a separately prepared bearing ring made of bearing steel (JIS standard SUJ2) (Comparative Example A). The machining allowance for lapping was 0.25 mm.

Next, test conditions will be described. For the bearing of JIS standard 6206 model number produced as described above, maximum contact surface pressure Pmax: 3.2 GPa, bearing rotation speed: 2000 rpm, lubrication: circulating oil supply of turbine oil VG68 (clean oil), test temperature: room temperature, A fatigue test was conducted under the conditions of The vibration of the bearing during operation is monitored by the vibration detection device, and the test is stopped when the rolling element is damaged and the vibration of the bearing exceeds a predetermined value. Recorded as bearing life. The number of tests was 15 in each of the examples and the comparative examples, and after calculating the L ₁₀ life, the durability was evaluated by the life ratio with respect to Comparative Example A.

  Table 4 shows the test results of this test. Referring to Table 4, it can be said that the life of the bearings of the examples is all good considering the manufacturing cost and the like. The life of the bearings of Examples D to G in which the dense layer remains on the surface of the rolling element by setting the machining allowance to 0.5 mm or less is about 1.5 to 2 times the life of Comparative Example A. It was. Furthermore, the life of the bearings of Examples A to C in which the high-density layer remained on the surface of the rolling element by setting the machining allowance to 0.15 mm or less was about three times the life of Comparative Example A. From this, it was confirmed that the slewing bearing provided with the rolling element made of the sialon sintered body is excellent in durability. And the slewing bearing provided with the rolling element made of the sialon sintered body has a working life of the rolling element of 0.5 mm or less, the life is improved by leaving a dense layer on the surface, and the machining allowance of the rolling element is reduced to 0. It was found that the lifetime was further improved by leaving the highly dense layer on the surface at a thickness of .15 mm or less.

It is sectional drawing of the slewing bearing concerning embodiment of this invention. It is a figure which shows the outline of the manufacturing method of the holder | retainer of the slewing bearing. It is sectional drawing of the slewing bearing concerning different embodiment of this invention. It is the photograph which image | photographed the cross section for observation of a test piece with the oblique light of the optical microscope. It is an example which shows the state which binarized the image of the photograph of FIG. 4 with the brightness | luminance threshold value using image processing software. FIG. 5 is a diagram showing a region (evaluation region) where image processing is performed when the image of the photograph of FIG. 4 is binarized using a luminance threshold value using image processing software. It is the perspective view which notched and represented a part of example of the wind power generator. It is a fracture side view of the wind power generator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,31 ... Inner ring 1a, 1b, 31aa, 31ab ... Inner ring raceway surface 2, 32 ... Outer ring 2a, 2b, 32aa, 32ab ... Outer ring raceway surface 3, 33A, 33B, 33C ... Rolling element 3a ... Rolling surface 4 ... Holding 21, 22 ... slewing bearing

Claims (11)

  A slewing bearing comprising an inner ring, an outer ring, and a plurality of rolling elements capable of rolling between the raceways of the inner and outer rings, wherein the rolling elements are made of ceramics having high impact resistance.   2. The slewing bearing according to claim 1, wherein the ceramic is composed of a sintered body containing β sialon as a main component and remaining impurities. According to claim 2, wherein the ceramic _is represented by a composition formula of _{Si 6-Z Al Z O Z} N 8-Z, as a main component β-sialon satisfying 0.1 ≦ z ≦ 3.5, the balance being impurities A slewing bearing made of a sintered body and having a Young's modulus of 180 GPa or more and 270 GPa or less.   2. The slewing bearing according to claim 1, wherein the ceramic is composed of a sintered body containing β sialon as a main component and the remaining sintering aid and impurities. According to claim 4, wherein the ceramic _is represented by a composition formula of _{Si 6-Z Al Z O Z} N 8-Z, as a main component β-sialon satisfying 0.1 ≦ z ≦ 3.5, the balance sintered Yuisuke A slewing bearing comprising a sintered body made of an agent and impurities and having a Young's modulus of 180 GPa or more and 270 GPa or less.   6. The dense layer according to claim 1, wherein the rolling element includes a dense layer that is a denser layer than the inside in a region including a rolling surface that is a surface in contact with the inner and outer rings. Slewing bearings.   The slewing bearing according to claim 6, wherein when the cross section of the dense layer is observed with oblique light of an optical microscope, the area ratio of the white region observed as a white region is 7% or less.   8. The slewing bearing according to claim 6, wherein a high-density layer that is a layer having higher density than the other areas in the dense layer is formed in a region including the surface of the dense layer.   The slewing bearing according to claim 8, wherein the area ratio of the white region observed as a white region is 3.5% or less when the cross section of the high-density layer is observed with oblique light of an optical microscope.   The slewing bearing according to claim 1, wherein the blade of the wind power generator is supported so as to be pivotable about an axis substantially perpendicular to the spindle axis with respect to the spindle.   The slewing bearing according to any one of claims 1 to 9, wherein the slewing bearing supports the nacelle of the wind power generator so as to be pivotable with respect to the support base.

Images