JP2010000241A - Roll bearing for ct scanner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a roll bearing for CT scanner which can achieve the elongation of the service life while suppressing the generation of poor sounds resulting from vibrations or impacts. <P>SOLUTION: A ball 13 which constitutes a four-point contact ball bearing 1 freely rotatably supports a rotary stand, on which the X-ray protection section of a CT scanner is installed, with respect to a fixed stand which is arranged to be confronted with the rotary stand. The ball 13 is constituted of a sintered body having a β sialon which is represented by a nominal composition of Si<SB>6-Z</SB>Al<SB>Z</SB>O<SB>Z</SB>N<SB>8-Z</SB>and satisfies 0.1≤z≤3.5 as the major component, and consisting of a remainder impurity. The Young's modulus of the ball 13 is 180 GPa or more and 270 GPa or less. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a rolling bearing for a CT scanner, and more particularly to a rolling bearing for a CT scanner provided with a component made of a sintered body containing β sialon as a main component.

A CT scanner (Computed Tomography Scanner) irradiates a human body or an object as an object with X-rays from an X-ray irradiation unit, and receives X-rays that have passed through the subject with a detector. The detector is configured to be rotatable around the subject. Then, by analyzing the data obtained in the detector with a computer, a cross-sectional image of the subject can be output. Here, the X-ray irradiation unit and the detector are installed on a rotating gantry that can rotate with respect to the stationary gantry. A CT scanner rolling bearing that is a rolling bearing that rotatably supports the rotating mount with respect to the fixed mount is disposed between the fixed mount and the rotating mount. For this CT scanner rolling bearing, improvement has been studied from various viewpoints such as reduction of orbital torque, improvement of durability, and improvement of ease of assembly, and many proposals have been made (for example, Patent Document 1). To 3).
JP-A-2005-3152 JP 2007-278332 A JP2007-155028A

  On the other hand, in recent years, with the demand for improvement in inspection efficiency and the like, the rotational speed of the rotating gantry in the CT scanner tends to increase. For this reason, the rotational speed of the rolling bearing for the CT scanner that supports the rotary mount is also increasing. In addition, there is a demand for maintenance-free for rolling bearings for CT scanners. Under such circumstances, the rolling bearing for the CT scanner is used at a high rotational speed for a long time without receiving maintenance. For this reason, a longer life is required for rolling bearings for CT scanners than for general rolling bearings.

  On the other hand, a rolling element made of silicon nitride may be employed as a rolling element for a rolling bearing for a CT scanner. Silicon nitride has higher durability than steel generally used as a material for rolling elements, and can meet the demand for longer life of the rolling bearing for CT scanner.

  On the other hand, a rolling bearing for a CT scanner is often a large bearing having an outer diameter of 800 mm or more. For this reason, it is not always easy to carry the bearing and handle the CT scanner, and there is a risk that an impact will be given accidentally. Further, during the operation of the CT scanner, the gantry to which the CT scanner rolling bearing is attached may vibrate, and a relatively large vibration due to resonance may act on the CT scanner rolling bearing. Here, silicon nitride has a characteristic that it has a Young's modulus larger than that of steel and is less likely to be elastically deformed. For this reason, the contact area between the rolling element made of silicon nitride and the raceway member is smaller than the rolling element made of steel, and the contact surface pressure tends to increase. Accordingly, when a rolling element made of silicon nitride is employed as a rolling element for a CT scanner rolling bearing, damage such as indentation is likely to occur in the raceway member when vibration or impact is applied. And when damages, such as an indentation, generate | occur | produce in a track member, there exists a possibility that the driving | running | working sound of a rolling bearing may become loud (acoustic defect generation | occurrence | production) or a lifetime may fall. In particular, in a medical CT scanner having a subject as a human body, the occurrence of acoustic defects becomes a serious problem.

  Accordingly, an object of the present invention is to provide a rolling bearing for a CT scanner capable of achieving a long life while suppressing the occurrence of acoustic defects due to vibration and impact.

  A rolling bearing for a CT scanner according to the present invention is a CT scanner that rotatably supports a rotating gantry on which an X-ray irradiation unit of a CT scanner is installed with respect to a fixed gantry arranged to face the rotating gantry. This is a rolling bearing. This rolling bearing for a CT scanner includes a race member and a rolling element that contacts the race member and is disposed on an annular raceway. And the rolling element consists of ceramics which can suppress the impact with respect to a track member compared with the case where it consists of silicon nitride. More specifically, for example, the rolling element is made of ceramics having a Young's modulus smaller than that of silicon nitride.

  According to the rolling bearing for the CT scanner of the present invention, since damage to the raceway member is suppressed even when an impact is applied, it is possible to achieve a long life while suppressing the occurrence of acoustic defects due to vibration and impact. Therefore, it is possible to provide a rolling bearing for a CT scanner capable of satisfying the requirements.

  A rolling bearing for a CT scanner according to one aspect of the present invention rotatably supports a rotating gantry on which an X-ray irradiation unit of a CT scanner is installed with respect to a fixed gantry arranged to face the rotating gantry. This is a rolling bearing for CT scanner. This rolling bearing for a CT scanner includes a race member and a rolling element that contacts the race member and is disposed on an annular raceway. And a rolling element is comprised from the sintered compact which has (beta) sialon as a main component and consists of remainder impurities.

  A rolling bearing for a CT scanner according to another aspect of the present invention rotatably supports a rotating gantry on which an X-ray irradiation unit of a CT scanner is installed with respect to a fixed gantry arranged to face the rotating gantry. This is a rolling bearing for CT scanner. This rolling bearing for a CT scanner includes a race member and a rolling element that contacts the race member and is disposed on an annular raceway. And a rolling element is comprised from the sintered compact which has (beta) sialon as a main component and consists of a remainder sintering auxiliary agent and an impurity.

In the rolling bearing for a CT scanner according to one aspect of the present invention, a β sialon sintered body (sintered body containing β sialon as a main component), which is a highly durable ceramic, is employed for the rolling element. For this reason, the life of the CT scanner rolling bearing is extended. Further, the β sialon sintered body has a Young's modulus smaller than a sintered body made of a general ceramic such as silicon nitride (Si ₃ N ₄ ) or alumina (Al ₂ O ₃ ). Therefore, damage to the track member due to vibration and impact due to a high Young's modulus can be suppressed, and occurrence of acoustic defects can be suppressed. As described above, according to the rolling bearing for a CT scanner in one aspect of the present invention, the rolling for a CT scanner capable of achieving a long life while suppressing the occurrence of acoustic defects due to vibration and impact. A bearing can be provided.

  A CT scanner rolling bearing according to another aspect of the present invention basically has the same configuration as the CT scanner rolling bearing according to one aspect of the present invention, and exhibits the same effects. However, the rolling bearing for CT scanner according to another aspect of the present invention is different from the rolling bearing for CT scanner according to one aspect of the present invention in that the sintered body contains a sintering aid. According to the rolling bearing for the CT scanner in another aspect of the present invention, the adoption of the sintering aid makes it easy to lower the porosity of the sintered body, and can ensure sufficient durability stably. A rolling bearing for a CT scanner can be easily provided.

  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. In addition, in order to achieve the same effect as the CT scanner rolling bearing according to one aspect of the present invention, the sintering aid is desirably 20% by mass or less of the sintered body.

In the CT scanner rolling bearing, preferably, the β sialon is represented by a composition formula of Si _6-Z Al _Z O _Z N _8-Z and satisfies 0.1 ≦ z ≦ 3.5.

  The inventor has investigated in detail the relationship between the rolling fatigue life of a rolling element made of a β sialon sintered body and the composition of β sialon. As a result, the following knowledge was obtained. By adopting a production process including combustion synthesis, β sialon can be produced inexpensively with various compositions having a value of z (hereinafter referred to as z value) of 0.1 or more. In general, the hardness that greatly affects the rolling fatigue life hardly changes in the range of the z value of 4.0 or less that is easy to manufacture. However, when the relationship between the rolling fatigue life of the rolling element made of β sialon sintered body and the z value is investigated in detail, when the z value exceeds 3.5, the rolling fatigue life of the rolling element may decrease. I understood.

  More specifically, when the z value is in the range of 0.1 or more and 3.5 or less, the rolling fatigue life is substantially the same, and if the operation time of the rolling bearing exceeds a predetermined time, the surface of the rolling element is peeled off. Occurs and breaks. On the other hand, if the z value exceeds 3.5, the rolling elements are likely to be worn, resulting in a decrease in the rolling fatigue life. That is, it becomes clear that the failure mode of the rolling element made of β sialon changes with the composition having the z value of 3.5 as a boundary, and the rolling fatigue life decreases when the z value exceeds 3.5. It was. Therefore, in the rolling element made of β sialon sintered body, the z value is preferably set to 3.5 or less in order to ensure a stable and sufficient life. As described above, when the β sialon satisfies 0.1 ≦ z ≦ 3.5, it is possible to provide a rolling bearing for a CT scanner that is inexpensive and excellent in durability.

In the CT scanner rolling bearing, preferably, the β sialon is represented by a composition formula of Si _6-Z Al _Z O _Z N _8-Z and satisfies 0.5 ≦ z ≦ 3.0.

  Thereby, durability of the rolling bearing for CT scanner when a vibration and an impact act can be improved further.

  In the rolling bearing for CT scanner, preferably, the Young's modulus of the rolling element is not less than 180 GPa and not more than 270 GPa.

  When the Young's modulus of the rolling element increases, the strength of the material (β sialon sintered body) constituting the rolling element tends to increase. 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 with the raceway member is reduced and the contact surface pressure is increased. As a result, the track member is likely to be damaged. On the other hand, when the Young's modulus of the rolling element becomes low, the rolling element is easily elastically deformed, so that the contact area with the raceway member increases and the contact surface pressure decreases. 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 in which a balance between the strength of the material constituting the rolling element and the reduction of the contact surface pressure between the race members can be secured.

  More specifically, when the Young's modulus of the rolling element made of β 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 rolling Dynamic fatigue life is reduced. In addition, as the contact area with the raceway member increases, the frictional force acting between the raceway member and the bearing torque increases. Therefore, the Young's modulus of the rolling element made of the β sialon sintered body is preferably 180 GPa or more, and more preferably 220 GPa or more.

  On the other hand, if the Young's modulus of the rolling element made of β sialon sintered body exceeds 270 GPa, the effect of increasing the contact surface pressure exceeds the effect of increasing the strength of the material constituting the rolling element, and the indentation is formed on the rolling surface of the race member. Damage is likely to occur. Therefore, the Young's modulus of the rolling element made of the β sialon sintered body is preferably 270 GPa or less, and preferably 260 GPa or less.

  In the CT scanner rolling bearing, the raceway member may be made of steel. In this case, the surface hardness of the track member is preferably HV680 or more. Thereby, damage to the track member when vibration or impact is applied can be suppressed.

  Preferably, in the rolling bearing for the CT scanner, the rolling element has a dense layer that is a layer having a higher density than the inside in a region including a rolling surface that is a surface in contact with the race member.

  In the rolling element made of the above-described β sialon sintered body, the denseness greatly affects the rolling fatigue life. On the other hand, according to the said structure, a rolling fatigue life improves because the dense layer which is a layer denser than the inside is formed in the area | region containing a rolling surface. As a result, it is possible to provide a rolling bearing for a CT scanner capable of stably ensuring 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 made of β sialon sintered body, and the cross section is mirror-wrapped. Thereafter, 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. The recorded image is binarized using a luminance threshold using an image processing apparatus, and then the area ratio of the white area is measured, and the density of the photographed area can be known from the area ratio. .

  That is, in the rolling bearing for the CT scanner, preferably, the sintered body is formed with a dense layer that is a layer having a lower area ratio in the white region than 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 the said sintered compact is 15% or more, for example. In order to further improve the rolling fatigue life of the rolling element made of β sialon sintered body, the dense layer preferably has a thickness of 100 μm or more.

  In the rolling bearing for CT scanner, preferably, 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.

  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 made of the β sialon sintered body is further improved. Therefore, the durability of the rolling bearing for CT scanner of the present invention can be further improved by the above configuration.

  In the rolling bearing for a CT scanner, preferably, a high-density layer that is a layer having higher density than other areas in the dense layer is formed in a region including the surface of the dense layer.

  By forming a dense layer with higher density in the region including the surface of the dense layer, the durability of the rolling element made of β sialon sintered body against rolling fatigue is further improved, and the rolling bearing for CT scanner is improved. The lifetime can be further improved.

  In the rolling bearing for CT scanner, preferably, when the cross section of the high-density layer is observed with oblique light of an optical microscope, the area ratio of the white region observed as a white region is 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 made of the β sialon sintered body is further improved. Therefore, the durability of the rolling bearing for CT scanner of the present invention can be further improved by the above configuration.

  As is apparent from the above description, according to the rolling bearing for CT scanner of the present invention, it is possible to achieve a long life while suppressing the occurrence of acoustic defects due to vibration and impact. A bearing can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

  FIG. 1 is a schematic cross-sectional view showing a configuration of a CT scanner provided with a rolling bearing for CT scanner according to an embodiment of the present invention. Hereinafter, a CT scanner according to an embodiment of the present invention will be described with reference to FIG. 1 by taking as an example a case where a four-point contact ball bearing which is a rolling bearing for a CT scanner is provided.

  Referring to FIG. 1, a CT scanner 90 according to the present embodiment includes a fixed base 96 having a cylindrical opening 96 </ b> A and an annular shape disposed so as to face the outer peripheral surface of the opening 96 </ b> A of the fixed base 96. A four-point contact ball bearing 1 disposed between the fixed frame 96 and the fixed frame 96, and rotatably supporting the rotary frame 95 with respect to the fixed frame 96. Between the X-ray irradiating unit 91 and the X-ray irradiating unit 91 that is configured to be able to enter the X-ray irradiating unit 91. A wedge filter 92 installed on the rotary mount 95, and a slit 93 installed on the rotary mount 95 so as to be positioned between the wedge filter 92 and a region inside the rotary mount 95 into which the mounting table 97 enters. , And a detector 94 installed in the rotating gantry 95 so as to face the slit 93.

  The X-ray irradiation unit 91 includes an X-ray source that generates X-rays, and has a function of irradiating the detector 94 with X-rays. The wedge filter 92 has a function of making the intensity distribution of the X-rays irradiated from the X-ray irradiation unit 91 uniform. The slit 93 has a function of limiting the intensity distribution of the X-rays irradiated from the X-ray irradiation unit 91. The mounting table 97 has a function of holding the subject 81 and carrying the subject 81 between the X-ray irradiation unit 91 and the detector 94. The detector 94 has a function of detecting X-rays irradiated from the X-ray irradiation unit 91 and passing through the subject 81. Further, the four-point contact ball bearing 1 rotatably supports the rotating mount 95 on which the X-ray irradiation unit 91 of the CT scanner 90 is installed, with respect to the fixed mount 96 disposed so as to face the rotating mount 95. This is a rolling bearing for CT scanner.

  Next, the operation of the CT scanner 90 will be described. First, the mounting table 97 on which the subject 81 is placed enters the inside of the rotary mount 95 so that a desired examination site of the subject 81 is located between the slit 93 and the detector 94. Next, when X-rays are emitted from the X-ray irradiation unit 91, the intensity distribution of the X-rays is flattened in the wedge filter 92, and the intensity distribution is limited in the slit 93. Then, the subject 81 is irradiated with X-rays that have passed through the wedge filter 92 and the slit 93. The X-rays irradiated to the subject 81 pass through a desired examination site of the subject 81 and reach the detector 94. Further, the rotary base 95 rotates with respect to the fixed base 96 while being supported by the four-point contact ball bearing 1. Accordingly, the X-ray irradiation unit 91, the wedge filter 92, the slit 93, and the detector 94 rotate around the subject 81 while maintaining a positional relationship in which they face each other. As a result, X-rays that have passed through the subject 81 can be received by the detector 94 while changing the X-ray incident position on the subject 81. Then, the X-ray intensity detected by the detector 94 is analyzed by an analysis device (not shown) including a computer connected to the detector, and is output as a cross-sectional image of the examination site of the subject 81.

  Next, the 4-point contact ball bearing 1 will be described. FIG. 2A is a schematic cross-sectional view showing a configuration of a four-point contact ball bearing as a rolling bearing for a CT scanner according to an embodiment of the present invention. FIG. 3A is a schematic partial cross-sectional view showing an enlarged main part of FIG. In the CT scanner 90, instead of the four-point contact ball bearing 1, for example, a combined double-row angular ball bearing 100 can be employed. FIG.2 (b) is a schematic sectional drawing which shows the structure of the combination double row angular contact ball bearing as a rolling bearing for CT scanners in one embodiment of this invention. FIG. 3B is a schematic partial cross-sectional view showing an enlarged main part of FIG. The four-point contact ball bearing 1 and the combined double-row angular ball bearing 100 differ only in the type of bearing, and basically have the same configuration and the same effect. Here, the four-point contact ball bearing 1 will be described, and for the combined double-row angular contact ball bearing 100, 100 is added to the reference number of the corresponding part of the four-point contact ball bearing 1, and FIG. It is illustrated in b) and its description is omitted.

  2A and 3A, a four-point contact ball bearing 1 includes an outer ring 11 as a first race member, an inner ring 12 as a second race member, and a plurality of rolling elements. A ball 13 and a cage 14 are provided. An outer ring rolling surface 11 </ b> A as an annular first rolling surface is formed on the inner peripheral surface of the outer ring 11. On the outer peripheral surface of the inner ring 12, an inner ring rolling surface 12A as an annular second rolling surface facing the outer ring rolling surface 11A is formed. In addition, a plurality of balls 13 is formed with a ball rolling surface 13A (the surface of the ball 13) as a rolling element rolling surface. The balls 13 are in contact with each of the outer ring rolling surface 11A and the inner ring rolling surface 12A at the ball rolling surface 13A, and are arranged at a predetermined pitch in the circumferential direction by an annular retainer 14. It is rotatably held on an annular track.

  Here, the outer ring rolling surface 11A and the inner ring rolling surface 12A are formed so as to be able to contact the ball 13 at two points. As a result, the ball 13 and the track member can be contacted at four points. With the above configuration, the outer ring 11 and the inner ring 12 can rotate relative to each other, and the four-point contact ball bearing 1 can receive an axial load in both directions.

Then, balls 13 serving as rolling elements in this embodiment _is represented by a composition formula of _{Si 6-Z Al Z O Z} N 8-Z, composed mainly of β-sialon satisfying 0.1 ≦ z ≦ 3.5 And the Young's modulus is 180 GPa or more and 270 GPa or less.

  Further, referring to FIG. 3A, a ball dense layer 13B, which is a layer having a higher density than the inside 13C, is formed in a region including the ball rolling surface 13A that is the rolling surface of the ball 13. Yes. When the cross section of the dense ball layer 13B is observed with oblique light from an optical microscope, the area ratio of the white region observed as a white region is 7% or less. Therefore, the four-point contact ball bearing 1 according to the present embodiment is a rolling bearing for a CT scanner that can achieve a long life while suppressing the occurrence of acoustic defects due to vibration and impact. The impurities include inevitable impurities including those derived from raw materials or those mixed in the manufacturing process.

  Furthermore, referring to FIG. 3A, the region including the ball rolling surface 13A, which is the surface of the ball dense layer 13B, is a layer having a higher density than the other regions in the ball dense layer 13B. A ball height dense layer 13D is formed. When the cross section of the ball height dense layer 13D is observed with oblique light from an optical microscope, the area ratio of the white region observed as a white region is 3.5% or less. Thereby, the durability with respect to rolling fatigue of the ball 13 is further improved, and the durability of the four-point contact ball bearing 1 is further improved.

  In the present embodiment, the balls 13 constituting the four-point contact ball bearing 1 may be composed of a sintered body containing β sialon as a main component and the remaining sintering aid and impurities. By including a sintering aid, the porosity of the sintered body can be easily reduced, and the four-point contact ball bearing 1 that can stably ensure sufficient durability can be easily provided. . The impurities include inevitable impurities including those derived from raw materials or those mixed in the manufacturing process.

  Next, the manufacturing method of the rolling bearing for CT scanner in this Embodiment is demonstrated. FIG. 4 is a diagram showing an outline of a method for manufacturing a rolling bearing for a CT scanner in one embodiment of the present invention. Moreover, FIG. 5 is a figure which shows the outline of the manufacturing method of the rolling element which consists of (beta) sialon sintered compact in one embodiment of this invention.

  Referring to FIG. 4, in the method of manufacturing a rolling bearing for CT scanner in the present embodiment, first, a track member manufacturing process for manufacturing a track member and a rolling element manufacturing process for manufacturing a rolling element are performed. . Specifically, in the race member manufacturing process, the outer ring 11, the inner ring 12, and the like are manufactured. On the other hand, in the rolling element manufacturing process, balls 13 and the like are manufactured.

  And the assembly process which assembles the rolling bearing for CT scanner is implemented by combining the track member manufactured in the track member manufacturing process, and the rolling element manufactured in the rolling element manufacturing process. Specifically, the four-point contact ball bearing 1 is assembled by combining the outer ring 11 and the inner ring 12 and the ball 13, for example. And a rolling element manufacturing process is implemented using the manufacturing method of the rolling element which consists of the following (beta) sialon sintered compact, for example.

  Referring to FIG. 5, in the method for manufacturing a rolling element made of a β sialon sintered body in the present embodiment, first, a β sialon powder preparation step of preparing β sialon powder is performed. In the β sialon powder preparation step, β sialon powder can be produced at low cost by, for example, a production step employing a combustion synthesis method.

  Next, a mixing step is performed in which a sintering aid is added to and mixed with the β sialon powder prepared in the β sialon powder preparation step. This mixing step can be omitted if no sintering aid is added.

  Next, referring to FIG. 5, a forming step of forming the β sialon powder or the mixture of the β sialon powder and the sintering aid into a schematic shape of the rolling element is performed. Specifically, by applying a molding technique such as press molding, cast molding, extrusion molding, rolling granulation, or the like to the above β sialon powder or a mixture of β sialon powder and a sintering aid, the ball 13 Thus, a molded body formed into a general shape such as is produced.

  Next, a pre-sintering processing step is performed in which the surface of the molded body is processed so that the molded body is shaped to be closer to the shape of the desired rolling element after sintering. Specifically, by applying a processing method such as green body processing, the molded body is processed to have a shape closer to the shape of the ball 13 or the like after sintering. This pre-sintering processing step can be omitted if the shape is sufficiently close to the shape of the desired rolling element after sintering at the stage where the molded body is formed in the forming step.

  Next, referring to FIG. 5, a sintering step is performed in which the molded body is sintered. Specifically, for example, the molded body is heated and sintered by a heating method such as heating with an electromagnetic wave using microwaves or millimeter waves under a pressure of 1 MPa or less, so that the rough shape of the ball 13 or the like is obtained. A sintered body having the same is produced. Sintering is performed by heating the molded body to a temperature range of 1550 ° C. or higher and 1800 ° C. or lower in an inert gas atmosphere or a mixed gas atmosphere of nitrogen and oxygen. As the inert gas, helium, neon, argon, nitrogen, or the like can be employed, but nitrogen is preferably employed from the viewpoint of reducing manufacturing costs.

  Next, a finishing process for completing the rolling elements is performed by performing a finishing process in which the surface of the sintered body produced in the sintering process is processed and a region including the surface is removed. Specifically, the balls 13 as rolling elements are completed by polishing the surface of the sintered body produced in the sintering step. Through the above steps, the rolling element made of the β sialon sintered body in the present embodiment is completed.

  Here, as a result of sintering in the above-described sintering step, 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 with oblique light of an optical microscope, a white region is obtained. A dense layer in which the area ratio of the observed white region is 7% or less is formed. Furthermore, the region having a thickness of about 150 μm from the surface of the sintered body has a higher density than the other regions in the dense layer, and is observed as a white region when the cross section is observed with an oblique light of an optical microscope. A highly dense layer in which the area ratio of the white region is 3.5% or less is formed. Therefore, in the finishing step, 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 ball rolling surface 13A, and the rolling fatigue life of the ball 13 can be improved.

  The sintering step 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 process is preferably performed under a pressure of 1 MPa or less. Further, in order to adjust the Young's modulus of the rolling element made of the β sialon sintered body to a desired value of 180 GPa or more and 270 GPa or less, for example, the z value of the β sialon powder prepared in the β sialon powder preparation step is set to 0. What is necessary is just to adjust in the range of 1 <= z <= 3.5. More specifically, the Young's modulus of the β sialon sintered body can be decreased by increasing the z value.

  Further, as the material of the outer ring 11 and the inner ring 12 in the above embodiment, for example, high carbon chromium bearing steel such as JIS standard SUJ2, alloy steel for machine structure such as SCM420, steel such as carbon steel for machine structure such as S53C, and the like. Can be adopted.

  In the above embodiment, a four-point contact ball bearing and a combined double-row angular ball bearing have been described as examples of the CT scanner rolling bearing of the present invention. However, the CT scanner rolling bearing of the present invention is not limited to these, and deep grooves It can be employed in various types of rolling bearings such as ball bearings. In the above embodiment, the case where the outer ring and the inner ring are employed as the race members of the rolling bearing of the present invention has been described. However, the race member is a shaft used so that the rolling elements roll on the surface. Or a member such as a housing. That is, the raceway member should just be a member in which the rolling surface for a rolling element to roll was formed.

  Embodiment 1 of the present invention will be described below. Rolling bearings having rolling elements made of β sialon sintered bodies having various z values were produced, and tests for investigating the relationship between the z value and the rolling fatigue life (durability) were conducted. 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 a combustion synthesis method with a z value in the range of 0.1 to 4 is prepared, and is basically the same as the rolling element manufacturing method described in the above embodiment based on FIG. The rolling element whose z value is 0.1-4 by the method 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 sphere with a mold and further pressurized by cold isostatic pressing (CIP) to obtain a spherical molded body.

  Subsequently, after performing atmospheric pressure sintering as primary sintering for the molded body, the sintered spheres are 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 (Example AJ). For comparison, a rolling element made of silicon nitride, that is, a rolling element having a z value of 0 was also produced in the same manner as the rolling element made of β sialon, and similarly assembled to a bearing (Comparative Example A).

Next, test conditions will be described. Maximum contact surface pressure P _max : 3.2 GPa, bearing rotational speed: 2000 rpm, lubrication: circulating oil supply of turbine oil VG68 (clean oil), test temperature: room temperature for the JIS standard 6206 model bearing manufactured as described above A fatigue test was performed 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 1 shows the test results of this example. In Table 1, the life in each Example and Comparative Example is expressed as a life ratio with the life in Comparative Example A (silicon nitride) 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 1, Examples A to H of the present invention in which the z value is 0.1 or more and 3.5 or less have a life comparable to that of silicon nitride (Comparative Example A). Yes. Further, the form of breakage is “peeling” as in the case of silicon nitride. On the other hand, in Example I in which the z value exceeds 3.5, the life is shortened and wear is observed on the rolling elements. That is, in Example I in which the z value is 3.8, it is considered that although the rolling element finally peeled off, the life of the rolling element was affected by the wear of the rolling element. Furthermore, in Example J in which the z value is 4, the wear of the rolling elements proceeds in a short time, and the durability of the rolling bearing is further reduced.

  As described above, when the z value is in the range of 0.1 to 3.5, the rolling bearing provided with the rolling element made of β sialon sintered body has the durability of the rolling element made of the silicon nitride sintered body. It is almost equivalent to a rolling bearing with On the other hand, if the z value exceeds 3.5, the rolling elements are likely to be worn, resulting in a decrease in the rolling fatigue life. Furthermore, it has been clarified that when the z value increases, the cause of breakage of the rolling element made of β sialon changes from “peeling” to “wear”, and the rolling fatigue life is further reduced. Thus, it was confirmed that a rolling element made of a β sialon sintered body that is inexpensive and excellent in durability can be obtained by setting the z value to 0.1 or more and 3.5 or less.

  In addition, with reference to Table 1, in Example H in which the z value exceeds 3.5, a slight amount of wear has occurred in the rolling elements, and the service life has also decreased 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.

  From the above experimental results, the z value is preferably 2 or less, and more preferably 1.5 or less, in order to obtain durability (life) equal to or greater than that of a rolling element made of silicon nitride. 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 employ a z value of 0.5 or more at which a reaction due to self-heating can be sufficiently expected.

  Embodiment 2 of the present invention will be described below. A test for producing a rolling bearing having rolling elements made of β-sialon sintered bodies having various z values and investigating the relationship between the z value and the rolling fatigue life in an environment in which an impact is applied to the rolling bearing. Was done. 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 a combustion synthesis method with a z value in the range of 0.1 to 3.5 is prepared, and the z value is 0.1 to 3.5 by the same method as in Example 1 above. A rolling element was produced. And the bearing of the JIS standard 6206 model number was produced in combination with the bearing ring produced using the various steel materials prepared separately as a raw material (Examples AJ). As steel constituting the race, JIS standards SUJ2, SCM420, SCr420, S53C, S45C, S40C and AISI standard M50 were adopted. For comparison, a rolling element made of silicon nitride, that is, a rolling element having a z value of 0 was also produced in the same manner as the rolling element made of β sialon, and similarly assembled to a bearing (Comparative Example A).

Next, test conditions will be described. For the bearing of the JIS standard 6206 model number manufactured as described above, the maximum contact surface pressure P _max : 2.5 GPa, the bearing rotation speed: 500 rpm, lubrication: turbine oil VG68 circulating oil supply, vibration conditions: 2500 N (50 Hz), Test temperature: An excitation shock fatigue test was performed under the condition of room temperature. The vibration of the bearing during operation is monitored by the vibration detection device, and the test is stopped when the bearing is damaged and the vibration of the bearing exceeds a predetermined value. Recorded as the lifetime of. In addition, after the test was stopped, the bearing was disassembled to confirm the damaged state of the bearing.

  Table 2 shows the test results of this example. In Table 2, the life in each example and comparative example is shown in the upper part of each column as a life ratio with the life of Comparative Example A (silicon nitride) as 1 when the material of the bearing ring is SUJ2. Yes. Moreover, the damaged part (bearing ring or ball) of the bearing is described in the lower part of each column.

  Referring to Table 2, Examples C to H of the present invention having a z value of 0.5 or more and 3.0 or less clearly have a longer life than silicon nitride (Comparative Example A). Yes. Here, as shown in Table 2, the damaged part was a track member (track ring) as in the case of silicon nitride, and the damaged form was delamination. On the other hand, in Examples I and J in which the z value exceeds 3.0, the life is shortened and the rolling element (ball) is damaged (peeled) first. That is, in Example I in which the z value is 3.25, it is considered that the bearing part (ball) made of the β sialon sintered body is damaged due to the impact and the life is shortened. Furthermore, in Example J in which the z value is 3.5, the rolling elements are peeled off in a shorter time, and the durability of the rolling bearing is further reduced.

  On the other hand, in Examples A and B in which the z value is smaller than 0.5, the lifetime is reduced to substantially the same level as in Comparative Example A, and the raceway member is preceded by breakage (peeling). That is, in Example B in which the z value is 0.25, the difference in physical properties from Comparative Example A in which the z value is 0 (silicon nitride) is reduced. Therefore, the collision between the ball made of the β sialon sintered body and the race member facing the ball unilaterally causes damage on the race member side, and the same as Comparative Example A employing the ball made of the silicon nitride sintered body. It is thought that the lifetime was reduced to

  Furthermore, referring to Table 2, even when the z value is 0.5 or more and 3.0 or less, when the hardness (surface hardness) of the opposite bearing ring is less than HV680, The life tends to be shorter than when the hardness is HV680 or higher. This is thought to be because when the hardness of the raceway is low, damage to the raceway member is likely to occur due to the collision between the ball made of β sialon sintered body and the raceway member facing the ball.

  As described above, when the z value exceeds 3.0, the bearing part itself made of the β sialon sintered body is easily damaged, whereas when the z value is less than 0.5, the contact surface pressure between the mating member is low. It increases, and damage to the mating member is likely to occur. And by making z value 0.5 or more and 3.0 or less, the balance of the intensity | strength of the raw material which comprises a rolling element and the reduction of the contact surface pressure between track members is ensured. As a result, it was confirmed that the life of a rolling bearing including a rolling element made of a β sialon sintered body is improved in an environment in which an impact is applied to the bearing. In particular, when the race member is made of steel, the physical properties of the race member and the physical properties of the rolling elements are well matched, and the occurrence of damage due to impact, vibration, or the like can be suppressed. Thus, it was confirmed that the durability of the rolling bearing when vibration or impact is applied can be improved by setting the z value of β sialon constituting the rolling element to 0.5 or more and 3.0 or less. It was.

  In addition, when the race member is made of steel, it was confirmed that the surface hardness of the race member is preferably HV680 or more in order to suppress damage to the race member.

  Embodiment 3 of the present invention will be described below. A test was conducted to investigate the formation state of the dense layer and the highly dense layer of the rolling element made of β sialon constituting the rolling bearing for the CT scanner of the present invention. The test procedure is as follows.

First, a β sialon powder (product name: Melamix, manufactured by Isman Jay Co., Ltd.) having a composition of Si ₅ AlON ₇ prepared by a combustion synthesis method was prepared, and the rolling element described in the above embodiment based on FIG. A cubic test piece having a side of about 10 mm was produced in the same manner as in the manufacturing method. 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 cube test piece was manufactured by heating and sintering the molded body at 1650 ° C. in a nitrogen atmosphere having a pressure of 0.4 MPa (atmospheric pressure sintering).

  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 Corporation make, Microphoto-FXA), and the 50-times-magnification instant photograph (Fujifilm Corporation FP-100B) was image | photographed. Thereafter, the obtained photographic image was taken into a personal computer using a scanner (resolution: 300 DPI). And the binarization process by a brightness | luminance threshold value was performed using the image processing software (Mitani Corporation WinROOF) (binarization separation threshold value in a present Example: 140), and the area ratio of the white area | region was measured.

  Next, test results will be described. FIG. 6 is a photograph obtained by photographing the observation cross section of the test piece with oblique light from an optical microscope. FIG. 7 is an example showing a state in which the image of the photograph in FIG. 6 is binarized using a luminance threshold using image processing software. Further, FIG. 8 shows a region (evaluation region) where image processing is performed when the image of the photograph of FIG. 6 is binarized by the luminance threshold using image processing software and the area ratio of the white region is measured. FIG. In FIG. 6, the upper side of the photograph is the surface side of the test piece, and the upper end is the surface.

  With reference to FIGS. 6 and 7, the test piece in this example manufactured by the same manufacturing method as in the above embodiment has a layer having a white area smaller than the inside in the area including the surface. I understand. Then, as shown in FIG. 8, 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 of 150 μm or less from the outermost surface, the region exceeding 150 μm and within 500 μm, When the area ratio of the white area was calculated by performing image analysis for each area and obtaining the area ratio of the white area, the results shown in Table 3 were obtained. In Table 3, 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. 8 as one field of view. Yes.

  Referring to Table 3, the area ratio of the white region in the present example was 18.5% inside, whereas it was 3.7% in the region having a depth of 500 μm or less from the surface. It was 1.2% in the region where the depth from the region was 150 μm or less. From this, in the test piece in the present example produced by the above manufacturing method similar to the above embodiment, a dense layer and a highly dense layer having a white region less than the inside are formed in the region including the surface. It was confirmed.

  Embodiment 4 of the present invention will be described below. A test was conducted to confirm the rolling fatigue life of the rolling element made of a β sialon sintered body constituting the rolling bearing for the CT scanner of the present invention. 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 of Si ₅ AlON ₇ prepared by a combustion synthesis method was prepared, and the rolling element described in the above embodiment based on FIG. A 3/8 inch ceramic sphere having a diameter of 9.525 mm was produced in the same manner as the production method described above. 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 processed so that the processing allowance after sintering becomes a predetermined dimension, and the green 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 produced in combination 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 manufactured in combination with a bearing ring (JIS standard SUJ2) prepared separately (Comparative Example A). The machining allowance for lapping was 0.25 mm.

Next, test conditions will be described. Maximum contact surface pressure P _max : 3.2 GPa, bearing rotational speed: 2000 rpm, lubrication: circulating oil supply of turbine oil VG68 (clean oil), test temperature: room temperature for the JIS standard 6206 model bearing manufactured as described above A fatigue test was performed 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 example. 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 rolling bearing for CT scanner of this invention is excellent in durability. In the rolling bearing for CT scanner of the present invention, the machining cost of the rolling element made of β sialon sintered body is set to 0.5 mm or less, and the life is improved by leaving the dense layer on the surface. It was found that the lifetime was further improved by leaving the highly dense layer on the surface at 15 mm or less.

  The embodiments and examples disclosed herein are illustrative in all respects and should not be construed as being restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  The rolling bearing for CT scanner of the present invention can be applied particularly advantageously to a rolling bearing for CT scanner that requires a long life.

It is a schematic sectional drawing which shows the structure of CT scanner provided with the rolling bearing for CT scanner in one embodiment of this invention. (A) is a schematic sectional drawing which shows the structure of the 4-point contact ball bearing in one embodiment of this invention. (B) is a schematic sectional drawing which shows the structure of the combination double row angular contact ball bearing in one embodiment of this invention. (A) is the general | schematic fragmentary sectional view which expanded and showed the principal part of Fig.2 (a). FIG. 3B is a schematic partial cross-sectional view showing an enlarged main part of FIG. It is a figure which shows the outline of the manufacturing method of the rolling bearing for CT scanners in one embodiment of this invention. It is a figure which shows the outline of the manufacturing method of the rolling element which consists of (beta) sialon sintered compact in one 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. 6 with the brightness | luminance threshold value using image processing software. It is a figure which shows the area | region (evaluation area | region) which performs image processing.

Explanation of symbols

  1 4 point contact ball bearing, 11, 111 outer ring, 11A, 111A outer ring rolling surface, 12, 112 inner ring, 12A, 112 inner ring rolling surface, 13, 113 ball, 13A, 113A ball rolling surface, 13B, 113B ball Dense layer, 13C, 113C inside, 13D, 113D Ball height dense layer, 14, 114 holder, 81 subject, 90 CT scanner, 91 X-ray irradiation unit, 92 wedge filter, 93 slit, 94 detector, 95 rotating stand , 96 fixed base, 96A opening, 97 mounting base, 100 combination double-row angular contact ball bearing.

Claims (12)

A CT scanner rolling bearing that rotatably supports a rotating frame on which an X-ray irradiation unit of a CT scanner is installed, with respect to a fixed frame arranged to face the rotating frame,
A track member;
A rolling element that contacts the raceway member and is disposed on an annular raceway,
The rolling element for a CT scanner, wherein the rolling element is made of a ceramic capable of suppressing an impact on the raceway member as compared with a case where the rolling element is made of silicon nitride.   2. The rolling bearing for a CT scanner according to claim 1, wherein the rolling element is composed of a sintered body mainly composed of β sialon and composed of remaining impurities.   2. The rolling bearing for a CT scanner according to claim 1, wherein the rolling element is composed of a sintered body mainly composed of β sialon and comprising a remaining sintering aid and impurities. The β-sialon _is represented by the composition formula of _{Si 6-Z Al Z O Z} N 8-Z, satisfy 0.1 ≦ z ≦ 3.5, the rolling bearing CT scanner according to claim 2 or 3. The β-sialon _is represented by the composition formula of _{Si 6-Z Al Z O Z} N 8-Z, satisfy 0.5 ≦ z ≦ 3.0, the rolling bearing CT scanner according to claim 2 or 3.   The rolling bearing for a CT scanner according to claim 1, wherein the rolling element has a Young's modulus of 180 GPa or more and 270 GPa or less.   The rolling bearing for a CT scanner according to claim 1, wherein the rolling element has a Young's modulus of 220 GPa to 260 GPa. The track member is made of steel,
The rolling bearing for a CT scanner according to any one of claims 1 to 7, wherein the raceway member has a surface hardness of HV680 or more.   9. The rolling element according to claim 1, wherein the rolling element has a dense layer, which is a dense layer than the inside, in a region including a rolling surface that is a surface in contact with the raceway member. Rolling bearings for CT scanners as described in 1.   The rolling bearing for a CT scanner according to claim 9, wherein an area ratio of a white region observed as a white region is 7% or less when a cross section of the dense layer is observed with oblique light of an optical microscope.   The rolling for a CT scanner according to claim 9 or 10, wherein a high-density layer, which is a layer having a higher density than other areas in the dense layer, is formed in a region including the surface of the dense layer. bearing.   The rolling bearing for a CT scanner according to claim 11, wherein 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 3.5% or less.