Patent Publication Number: US-2021187452-A1

Title: Rotating member, kneading machine member, and kneading machine using same, bearing and bearing unit using same

Description:
TECHNICAL FIELD 
     The present invention relates to a kneading machine member to knead paste or the like used for toner materials, electronic component materials, and electrode materials for lithium-ion secondary batteries and a kneading machine using the same or a large bearing used in steel facilities, construction machinery, industrial machinery, or the like and a bearing unit using the same. 
     BACKGROUND 
     Conventionally, when producing an electrode paint or the like of a lithium-ion secondary battery, a twin-screw extruder in which two kneading shafts are arranged in parallel is used. In order to improve the quality of a lithium-ion secondary battery, for example, in Patent Document 1, a twin-screw kneading machine is suggested in which a kneading machine member (paddle, screw) in contact with raw materials is formed of ceramics to prevent contamination of metal impurities. 
     In addition, in Patent Document 2, a kneading extruder is suggested in which an edge part of a key inserted between a paddle made of ceramics and a rotating shaft mounted on the paddle is a curved surface and an edge part of a key groove formed in the paddle is a curved surface corresponding to the edge part of the key. 
     Moreover, a bearing with high wear resistance, friction vibration suppression function, and impact resistance is required, and in Patent Document 3, a bearing is suggested in which a friction body having a lubricating effect is disposed in engaging grooves provided at equal intervals along the circumferential direction on the inner peripheral surface side of an outer ring supporting a rotating shaft. 
     RELATED ART DOCUMENTS 
     Patent Documents 
     
         
         Patent Document 1: Japanese Unexamined Patent Publication No. 2012-129126 
         Patent Document 2: Japanese Unexamined Utility Model Publication No. H5-78504 
         Patent Document 3: Japanese Unexamined Patent Publication No. H11-153138 
       
    
     SUMMARY 
     A rotating member of the present invention mainly includes ceramics and includes a first through-hole into which a shaft is inserted and a second through-hole into which a key protruding from an outer peripheral surface of the shaft or a solid lubricant in direct or indirect sliding contact with the outer peripheral surface of the shaft is inserted. The second through-hole is a polygonal shape if viewed in an axial direction of the first through-hole and includes a notch part extending along the axial direction at at least one corner. 
     A kneading machine member of the present invention is composed of the above rotating member. 
     A kneading machine of the present invention includes the above kneading machine member, a shaft inserted into the first through-hole, and a key protruding from the outer peripheral surface of the shaft and inserted into the second through-hole. 
     A first bearing of the present invention is composed of the above rotating member. 
     A second bearing of the present invention includes an outer ring which is composed of the above rotating member and an inner ring which is located in the first through-hole, is composed of an annular body coaxial with the first through-hole, and is rotatable with respect to the outer ring. 
     A bearing unit of the present invention includes the above first bearing, a shaft inserted into the first through-hole, and a solid lubricant inserted into the second through-hole and sliding contact with the shaft. 
     A bearing unit of the present invention includes the above second bearing, a shaft inserted into the inner ring, and a solid lubricant inserted into the second through-hole and sliding contact with the inner ring. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an example of a kneading machine member of the present disclosure, where (a) is a front view, (b) is a perspective view, and (c) is a perspective view showing a state in which a shaft is inserted into the kneading machine member. 
         FIG. 2  shows another example of a kneading machine member of the present disclosure, where (a) is a perspective view, (b) is a side view, and (c) is a sectional view of (a). 
         FIG. 3  is a perspective view showing another example of a kneading machine member of the present disclosure. 
         FIG. 4( a )  is a schematic diagram of a cross section perpendicular to the axial direction, and  FIG. 4( b )  is a schematic diagram of a cross section including the axis, inside a cylinder used in a kneading machine of the present disclosure. 
         FIG. 5( a )  is a main part enlarged view of a kneading machine member of  FIG. 1 , and  FIG. 5( b )  shows a state in which a key is inserted into the kneading machine member of  FIG. 5( a ) . 
         FIG. 6( a )  is a main part enlarged view showing another example of a kneading machine member of the present disclosure, and  FIG. 6( b )  shows a state in which a key is inserted into the kneading machine member of  FIG. 6( a ) . 
         FIG. 7( a )  is a main part enlarged view showing another example of a kneading machine member of the present disclosure, and  FIG. 7( b )  shows a state in which a key is inserted into the kneading machine member of  FIG. 7( a ) . 
         FIG. 8  shows an example of a bearing unit of the present disclosure, where (a) is a front view, (b) is a sectional view at AA′ line showing a state in which a side plate is mounted on the bearing unit of (a), and (c) is a front view showing a state in which a side plate is mounted on the bearing unit of (a). 
         FIG. 9  shows another example of a bearing unit of the present disclosure, where (a) is a front view, (b) is a sectional view at BB′ line showing a state in which a side plate is mounted on the bearing unit of (a), and (c) is a front view showing a state in which a side plate is mounted on the bearing unit of (a). 
     
    
    
     EMBODIMENTS 
     Hereinafter, the present invention is explained with reference to the accompanying drawings. The following embodiment is one Example that embodies the present invention and is not intended to limit the technical scope of the present invention. 
       FIG. 1  shows an example of a kneading machine member if a rotating member of the present disclosure is used as a kneading machine member, where (a) is a front view, (b) is a perspective view, and (c) is a perspective view showing a state in which a shaft is inserted into the kneading machine member. 
       FIG. 2  shows another example of a kneading machine member if a rotating member of the present disclosure is used as a kneading machine member, where (a) is a perspective view, (b) is a side view, and (c) is a sectional view of (a). 
       FIG. 3  is a perspective view showing another example of a kneading machine member if a rotating member is used as a kneading machine member. 
     The kneading machine member shown in  FIG. 1  is a shear paddle  10  mounted on a rotating shaft  2 , having a substantially triangular-shaped cross section perpendicular to the shaft  2 , and used to efficiently knead a mixture (paste). 
     The kneading machine member shown in  FIG. 2  is a screw  20  including a helical triple thread mounted to a rotating shaft  2  and used to send a mixture from the supply direction toward the discharge direction. The screw  20  shown in  FIG. 2  is a shape with a triple thread, but it may also be a shape with a double thread. The outer periphery of the screw  20  may also be opposite from the direction of the helix shown in  FIG. 2 . In that case, the mixture can be returned from the discharge direction to the supply direction. The direction of the helix can be opposite depending on the direction of rotation of the shaft  2 . 
     Then, the kneading machine member shown in  FIG. 3  is a resistance paddle  30  mounted on a rotating shaft  2  and has a flange shape. This shape blocks a kneading space of a cylinder  1  and acts as a resistance to the progress of the mixture, which can control the moving speed of the mixture in the cylinder  1 . 
     In any case, the shaft  2  is made of metal. 
     Kneading machine members  10 ,  20 , and  30  of the present disclosure mainly include ceramics and include a first through-hole  11  into which a shaft  2  is inserted and a second through-hole  12  into which a key  3  protruding from the outer peripheral surface of the shaft  2  is inserted, in which the second through-hole  12  is a polygonal shape if viewed in the axial direction of the first through-hole  11  and includes a notch part  13  extending along the axial direction at at least one corner. 
     By including the notch part  13 , it is possible to provide a space that is not in contact with the key  3 . This space can decrease stress concentration received from the vicinity of an edge part of the key  3 , relieve the load of tensile stress in a stress part of the second through-hole  12  which serves as a key groove in torque transmission from the shaft  2 , and reduce the risk of damage. 
       FIG. 5( a )  shows a main part enlarged view of a kneading machine member  10  in  FIG. 1 . As shown in  FIG. 5( a ) , the second through-hole  12  includes multiple planes P 1  to P 3  parallel to the axis of the first through-hole  11 . By these planes, the second through-hole  12  has a quadrangle shape if viewed in the axial direction of the first through-hole  11 . The second through-hole  12  is not limited to such a quadrangle shape but may be any other polygonal shape such as a pentagonal or hexagonal shape. 
     In addition, the kneading machine member  10  includes the notch parts  13  ( 13   a ,  13   b ) that connect with the second through-hole  12  at a corner where adjacent planes intersect with each other. In.  FIG. 5( a ) , a notch part  13   a  is located at a corner where a plane P 1  intersects with a plane P 2 , and a notch part  13   b  is located at a corner where a plane P 2  intersects with a plane P 3 . 
     In the kneading machine member  10 , the notch part  13   a  is located so as to notch both the adjacent plane P 1  and plane P 2 . In other words, in  FIG. 5( a ) , a part where the adjacent plane P 1  and plane P 2  intersect is an intersection part C 1 , but an end part of the plane P 1  and an end part of the plane P 2  are both notched by the notch part  13   a . Similarly, the notch part  13   b  is located so as to notch both the adjacent plane P 3  and plane P 2 . That is, in  FIG. 5( a ) , a part where the adjacent plane P 3  and plane P 2  intersect is an intersection part C 2 , but an end part of the plane P 3  and the end part of the plane P 2  are both notched by the notch part  13   b.    
     By this structure, the stress concentration received from the key  3  can be reduced more effectively. That is, as shown in  FIG. 5( b ) , when the key  3  is inserted into the second through-hole  12 , the space is located so as to surround a corner of the key  3  where stress concentration tends to occur, and the damage to the kneading machine member  10  can be further reduced. 
     As shown in  FIG. 5( a ) , the notch part  13   a  may include a width L 1  starting at the intersection part C 1  in the plane P 2  that is larger than a width L 2  starting at the intersection part C 1  in the plane P 1 . In this case, the stress applied to the kneading machine member  10  can be reduced, and torque can be efficiently applied to the kneading machine member  10  from the key  3 . In other words, since a large amount of torque is applied from the side surface of the key  3  when the kneading machine member  10  rotates, torque can be efficiently applied to the kneading machine member  10  by increasing a contact area between the side surface of the key  3  and the plane P 1 . In addition, by increasing a space region between a tip surface of the key  3  and the plane P 2 , stress concentration can also be reduced. Similar to the above for the notch part  13   b , a width starting at the intersection part C 2  in the plane P 2  may be larger than a width starting at the intersection part C 2  in the plane P 3 . 
     For the notch part  13   a , the above width L 1  may be twice or more and three times or less than the width L 2 . The above width L 1  may also be 0.25 times or more and 0.35 times or less than a width of the second through-hole  12  (a distance between the plane P 1  and the plane P 3 ). The notch part  13   b  may also have a similar relationship as above. 
     In addition, as another example of a kneading machine member if the rotating member of the present disclosure is used as a kneading machine member, a kneading machine member  40  shown in  FIG. 6( a )  may be used. The kneading machine member  40  is different from the kneading machine member  10  in the disposition of notch parts  43  ( 43   a ,  43   b ) in a second through-hole  42 . A notch part  43   a  includes the intersection part C 1  and is located so as to notch only the plane P 2  out of the adjacent plane P 1  and plane P 2 . In other words, in  FIG. 6 ( a ) , a part where the adjacent plane P 1  and plane P 2  intersect is the intersection part C 1 , but only the end part of the plane P 2  is notched by the notch part  43   a . Similarly, a notch part  43   b  includes the intersection C 2  and is located so as to notch only the plane P 2  out of the adjacent plane P 3  and plane P 2 . That is, in  FIG. 6( a ) , a part where the adjacent plane P 3  and plane P 2  intersect is the intersection part C 2 , but only the end part of the plane P 2  is notched by the notch part  43   b.    
       FIG. 6( b )  shows a state when the key  3  is inserted into the second through-hole  42  of the kneading machine member  40 . In  FIG. 6( b ) , a space is located between the kneading machine member  40  and a part of the tip surface of the key  3 , and a contact area of the side surface of the key  3  with the plane P 1  and a contact area with the plane P 3  are larger than the kneading machine member  10 . By this structure, torque from the key  3  can be more efficiently applied to the kneading machine member  10  while reducing stress concentration received from the key  3 . 
     For the notch part  43   a , a width L 3  (that is, a width of the notch part  43   a ) starting at the intersection part C 1  in the plane P 2  may be 0.25 times or more and 0.35 times or less than a width of the second through-hole  42  (a distance between the plane P 1  and the plane P 3 ). The notch part  43   b  may also have a similar relationship as above. 
     In the case that only the plane P 2  includes notches as shown in  FIG. 6 , the notches can be formed accurately by cutting. In order to reduce play during rotation of the shaft  2 , it is important to make a smaller fitting between the second through hole  42  and the key  3 . For this purpose, it is effective to perform the grinding process of the second through-hole  42  with a diamond tool using a machining center or the like, however, in order to obtain the notch parts  43  with a small width, the diameter of a grinding wheel part of the diamond tool must be small, and a shank that holds the grinding wheel part must be even smaller in diameter than the grinding wheel part. In such a case, the rigidity of the diamond tool becomes low, and processing becomes difficult. If the kneading machine member  40  is made of a difficult-to-cut material such as a zirconia ceramics, the processing resistance is high, and the diamond tool escapes, which makes it impossible to finish with the targeted processing accuracy and requires a great deal of processing time. However, if the width of the notch parts  43  is 0.25 times or more than the width of the second through-hole  42 , the diamond tool that forms the second through-hole  42  can be selected with a larger outer diameter for both the grinding wheel part and the shank, and the rigidity of the diamond tool becomes higher. Therefore, it is possible to shorten the processing time. On the other hand, if the width of the notch parts  43  is 0.35 times or less than the width of the second through-hole  42 , the contact area of the key  3  to the inner surface of the second through-hole  42  increases, and play during rotation of the shaft  2  can be reduced. 
     As another example of a kneading machine member if the rotating member of the present disclosure is used as a kneading machine member, a kneading machine member  50  shown in  FIG. 7( a )  may be used. The kneading machine member  50  is different from the kneading machine member  10  in the disposition of notch parts  53  ( 53   a ,  53   b ) in a second through-hole  52 . A notch part  53   a  includes the intersection C 1  and is located so as to notch only the plane P 1  out of the adjacent plane P 1  and plane P 2 . This means that, in  FIG. 7 ( a ) , a part where the adjacent plane P 1  and plane P 2  intersect is the intersection C 1 , but only the end part of the plane P 1  is notched by the notch part  53   a . Similarly, a notch part  53   b  includes the intersection C 2  and is located so as to notch only the plane P 3  out of the adjacent plane P 3  and plane P 2 . That is, in  FIG. 7( a ) , a part where the adjacent plane P 3  and plane P 2  intersect is the intersection C 2 , but only an end part of the plane P 3  is notched by the notch part  53   b.    
       FIG. 7( b )  shows a state when the key  3  is inserted into the second through-hole  52  of the kneading machine member  50 . In  FIG. 7 ( b ) , a space is located between the kneading machine member  50  and a part of the side surface of the key  3 , and a contact area of the tip surface of the key  3  with the plane P 2  is larger than the kneading machine member  10 . By this structure, it is possible to further improve the fitting between the second through-hole  52  and the key  3  and reduce play during rotation of the shaft  2  while reducing stress concentration received from the key  3 . 
     For the notch part  53   a , a width L 4  (that is, a width of the notch part  53   a ) starting at the intersection part C 1  in the plane P 1  may be 0.25 times or more and 0.35 times or less than a depth of the second through-hole  52  (a distance from the intersection part C 3  of the plane P 1  and the first through-hole  11  to the intersection part C 1 ). The notch part  53   b  may also have a similar relationship as above. 
       FIG. 8  shows an example of the bearing unit of the present disclosure, where (a) is a front view, (b) is a sectional view at AA′ line showing a state in which the side plate is mounted on the bearing unit of (a), and (c) is a front view showing a state in which the side plate is mounted on the bearing unit of (a). 
     The bearing unit shown in  FIG. 8  is a bearing unit  60  that includes a bearing  61 , a shaft  63 , and a solid lubricant  64 . 
     The bearing unit  61  includes an outer ring  61   b  and an inner ring  61   a . The outer ring  61   b  is composed of the rotating member of the present disclosure, and a similar structure to the rotating member used as a kneading machine member described above is used. The inner ring  61   a  is located in a first through-hole  62  and is composed of an annular body coaxial with the first through-hole  62 . The inner ring  61   a  is supported by the outer ring  61   b  through the solid lubricant  64  and is rotatable with respect to the outer ring  61   b . As the material of the inner ring  61   a , ceramics, metal, or the like are used. 
     The shaft  63  is inserted into the inner ring  61   a  and rotates with the inner ring  61   a.    
     The solid lubricant  64 , for example, is made of rectangular-shaped woody porous carbon material and is inserted into a second through-hole  65 , indirectly sliding contact with the outer peripheral surface of the shaft  63  through the inner ring  61   a.    
       FIG. 9  shows another example of the bearing unit of the present disclosure, where (a) is a front view, (b) is a sectional view at BB′ line showing a state in which the side plate is mounted on the bearing unit of (a), and (c) is a front view showing a state in which the side plate is mounted on the bearing unit of (a). 
     The bearing unit shown in  FIG. 9  is a bearing unit  70  that includes the bearing  61  composed of the rotating member of the present disclosure, the shaft  63  inserted into the first through-hole  62 , and the solid lubricant  64  in direct sliding contact with the outer peripheral surface of the shaft  63  inserted into the first through-hole  62 . The solid lubricant  64 , for example, is made of the rectangular-shaped woody porous carbon material and is inserted into the second through-hole  65 , directly sliding contact with the outer peripheral surface of the shaft  63 . 
     In both the bearing units  60  and  70 , the second through-hole  65  is polygonal shape if viewed in the axial direction of the first through-hole  62  and includes a notch part  65   a  extending along the axial direction at at least one corner. In addition, the second through-hole  65  is disposed at equal intervals every 90 degrees along the circumferential direction. 
     An annular side plate  67  including an insertion hole  66  to pass the shaft  63  through is fixed to both sides of the bearing  61  by inserting screws  69  into screw holes  68  of the bearing  61 . By fixing the side plate  67 , the movement of an inner ring  63   a  in the axial direction due to lateral swing and the intrusion of foreign substances into a gap between the inner ring  63   a  or the shaft  63  and the solid lubricant  64  are suppressed, and therefore, the smoothness of rotation can be maintained over a long period of time. 
     By including the notch part  65   a , both the bearing units  60  and  70  can provide a space that is not in contact with the solid lubricant  64 . This space can decrease the stress concentration received from the vicinity of an edge part of the solid lubricant  64 , relieve the load of tensile stress in the stress part of the second through-hole  65  in torque transmission from the shaft  63 , and reduce the risk of damage. 
     The ceramics used in each of the rotating members (including the kneading machine members and the bearings) described above are, for example, ceramics composed mainly of at least any of zirconia, silicon nitride, sialon, silicon carbide, alumina, and ZTA (zirconia-toughened alumina). 
     The main component in ceramics means the component that accounts for 80% by mass or more out of 100% by mass of all components that compose the ceramics. 
     The components of ceramics are first identified by checking the results, which are obtained by measurement using an X-ray diffractometer (XRD), against the JCPDS card. Next, it is the main component if the content, which is determined by converting it into the identified compound from the value obtained by measurement using an X-ray fluorescence analyzer (XRF) or an ICP (Inductively Coupled Plasma) emission spectrometer (ICP), is 80% by mass or more. Specifically, the ceramics is mainly composed of zirconia if it is confirmed that ZrO 2  is included from the measurement by XRD, and the value (content) that converts the value of Zr obtained by ICP into ZrO 2  is 80% by mass or more. 
     The ceramics whose main component is zirconia may also contain, for example, silicon oxide and aluminum oxide as components other than the main component. The ceramics whose main component is silicon nitride or sialon may contain, for example, at least one of aluminum oxide and rare earth metal oxide as a component other than the main component. The ceramics whose main component is alumina may contain, for example, at least one of silicon oxide, calcium oxide, and magnesium oxide as a component other than the main component. 
     In addition, a rotating member that mainly includes ceramics refers to a rotating member in which the ceramics accounts for 90% by mass or more out of 100% by mass of all components that compose the rotating member, and an amorphous hard carbon film may be formed on any surface of the rotating member. 
     In the kneading machine members  10 ,  20 , and  30  of the present disclosure, the inner surface of the notch part  13  may include a larger cutting level difference (Rδc) in a roughness curve, which represents the difference between the cutting level at 25% of the load length ratio in the roughness curve and the cutting level at 75% of the load length ratio in the roughness curve, than the inner surface inscribed in the key  3 . 
     Similarly, in the bearings  60  and  70  of the present disclosure, the inner surface of the notch part  65   a  may include a larger cutting level difference (Rδc) in the roughness curve, which represents the difference between the cutting level at 25% of the load length ratio in the roughness curve and the cutting level at 75% of the load length ratio in the roughness curve, than the inner surface inscribed in the solid lubricant  64 . 
     To make such a structure, the notch parts  13  and  65   a  are not grounded with the diamond tool but formed by cutting in the pre-sintering stage. In that case, the cutting level difference (Rδc) of the inner surfaces of the notch parts  13  and  65   a  is larger than the cutting level difference (Rδc) of the inner surfaces inscribed respectively in the key  3  and the solid lubricant  64 . The inner surfaces of the notch parts  13  and  65   a  have fewer microcracks due to the grinding process, making it more difficult to break even when stress is concentrated. 
     In the kneading machine members  10 ,  20 , and  30  of the present disclosure, the arithmetic mean roughness (Ra) of the inner surface of the notch part  13  may be larger than the arithmetic mean roughness (Ra) of the inner surface inscribed in the key  3 . 
     Similarly, in the bearings  40  and  50  of the present disclosure, the arithmetic mean roughness (Ra) of the inner surface of the notch part  65   a  may be larger than the arithmetic mean roughness (Ra) of the inner surface inscribed in the solid lubricant  64 . To make such a structure, the notch parts  13  and  65   a  are not ground with the diamond tool but are formed by cutting in the pre-sintering stage. In that case, the arithmetic mean roughness (Ra) of the inner surfaces of the notch parts  13  and  65   a  is larger than the arithmetic mean roughness (Ra) of the inner surfaces inscribed in the key  3  and the solid lubricant  64 , respectively. The inner surfaces of the notch parts  13  and  65   a  have fewer microcracks due to the grinding process, making it more difficult to break when stress is concentrated. For example, the arithmetic mean roughness (Ra) of the inner surfaces of the notch parts  13  and  65   a  is set to 3.2 μm or more and 6.3 μm or less, and the arithmetic mean roughness (Ra) of the inner surface inscribed in the key  3  or the solid lubricant  64  is set to 0.8 μm or more and 1.6 μm or less. It is suitable for the inscribed inner surface of the key  3  to have a low arithmetic mean roughness (Ra) value in order to avoid damaging the key  3  when it is inserted into the second through-hole  12 . For the inner surface inscribed in the solid lubricant  64 , it is also suitable to have a similarly low arithmetic mean roughness (Ra) value. 
     Each of the cutting level difference (Rδc) and the arithmetic mean roughness (Ra) of the inner surfaces of the notch parts  13  and  65   a  and the inner surfaces inscribed respectively in the key  3  and the solid lubricant  64  can be measured using a surface roughness measuring instrument (Surfcorder (SE500A or its successor model) manufactured by Kosaka Laboratory Ltd.) in accordance with JIS B 0601-1982. For the measurement conditions, the radius of the probe may be 5 μm, the material of the probe may be diamond, the measurement length may be 2.5 mm (in the axial direction of the first through-holes  11  and  62 ), the cutoff value may be 0.8 mm, and the scanning speed may be 0.1 mm per second. 
     The inner surface where the key  3  or the solid lubricant  64  is inscribed includes a first side surface P 1  and a second side surface P 3  opposed to each other across the second through-holes  12 ,  42 ,  52 ,  65  and the upper surface P 2  which connects the first side surface P 1  and the second side surface P 3 , and the maximum grain size of the crystal grains on the first side surface P 1  and the second side surface P 3  may be smaller than the maximum grain size of the crystal grains on the upper surface P 2 . 
     With this structure, the crystal grains in the vicinity of the first side surface P 1  and the second side surface P 3 , which are located in the vicinity of the shafts  2  and  63 , have a higher compressive stress between them than the crystal grains in the vicinity of the upper surface P 2 , so that even if the key  3  and the solid lubricant  64  are repeatedly detached, it is possible to suppress de-graining from the vicinity of the first side surface P 1  and the second side surface P 3  and prevent damage to the shafts  2  and  63 . 
     The difference between the maximum grain size of the crystal grains on the first side surface P 1  and the second side surface P 3  and the maximum grain size of the crystal grains on the upper surface P 2  may be 0.2 μm or more. 
     If the difference from the maximum grain size of the crystal grains is in this range, damage to the shafts  2  and  63  can be further suppressed. For the measurement of the maximum grain size of the crystal grains on the first side surface P 1 , the second side surface P 3 , and the upper surface P 2 , the surface to be measured is first heat-treated at a temperature 50° C. to 100° C. lower than the sintering temperature until the crystal grains can be distinguished from the grain boundary layers. The heat treatment is performed for approximately 30 minutes, for example. If the ceramics that composes the rotating member is a zirconia ceramics, the temperature of the heat treatment is, for example, 1300° C. to 1650° C. 
     Then, the heat-treated surface is photographed using a scanning electron microscope (SEM) with a magnification of 10000×, and the range to be measured is set to, for example, a length of 12 μm in the horizontal direction and a length of 9 μm in the vertical direction. Next, the maximum grain size can be obtained by setting the measurement range from the captured image and analyzing it using an image analysis software (for example, Win ROOF manufactured by Mitani Corporation). For the analysis, the threshold of the grain size is set to 0.21 μm, and a grain size of less than 0.21 μm is not included in the calculation of the maximum grain size. 
     The ceramics may also be the zirconia ceramics. The zirconia ceramics refers to ceramics composed mainly of zirconia, and if the rotating member is a kneading machine member made of the zirconia ceramics, for example, if it is a paste (mixture) used to form the positive electrode of a lithium-ion battery, an alkaline solvent is used as the solvent, but it can be made into a kneading machine member that has high corrosion resistance due to the absence of a liquid phase that becomes glassy and is difficult to break due to its high mechanical strength. Furthermore, by using the zirconia ceramics, it is possible to reduce the difference in the thermal expansion coefficient from a shaft made of metal, thus reducing the effect of heat. Because the zirconia ceramics has low rigidity, it is effective in relieving stress by slightly deforming against a slurry pressure generated by kneading. 
     In addition, the zirconia ceramics may contain 2 to 5 mol % of yttria. If the zirconia ceramics contains 2 to 5 mol % of yttria, it becomes a stable zirconia ceramics, which can increase the mechanical strength and make it difficult to break. It is also possible to obtain the rotating members  10 ,  20 ,  30 ,  40 ,  50 ,  60 , and  70  that are difficult to chip. 
     The zirconia ceramics may also contain 10 to 40 mol % of a monoclinic zirconia crystal. It suppresses the transformation of the crystal phase at a high temperature, and the slurry can be handled even at a high temperature of 100° C. or higher. If the ratio of the monoclinic zirconia crystal is within the above range, the zirconia ceramics is less likely to undergo a phase transformation when heat is supplied, and the volume change caused by this phase transformation is less likely to occur, so mechanical properties such as the strength of the rotating members  10 ,  20 ,  30 ,  40 ,  50 ,  60 ,  70  are less likely to deteriorate even after repeated heating and cooling. 
     The ratio of the monoclinic zirconia crystal in the zirconia ceramics can be indicated as the monoclinic ratio. The monoclinic ratio X may be calculated from the area of each peak intensity I of the zirconia crystals obtained from the measurement results by X-ray diffractometer using the following formula. 
         X =( Im (111)+ Im (11-1))/( Im (111)+ Im (11-1)+ It (111)+ Ic (111)) 
     In this case, Im (111) is a peak intensity of a monoclinic (111) plane, Im (11-1) is a peak intensity of a monoclinic (11-1) plane, It (111) is a peak intensity of a tetragonal (111) plane, and Ic (111) is a peak intensity of a cubic (111) plane. 
     Then, as shown in  FIG. 2( c ) , a part of the inner surface of the first through-hole  11  may include a central part in the axial direction that is more depressed than the vicinity of an opening. By using a bridge structure, in which the central part is more depressed than the vicinity of the opening, the area in contact with the side surface of the long key  3  can be reduced, so that distortions during rotation of the shaft  2  can be absorbed by the depressed central part, which reduces the risk of damage. In addition, a part of the second through-hole  12  to be processed can be made smaller, which can reduce costs. 
     The kneading machine of the present disclosure includes any of the above-described kneading machine members  10 ,  20 ,  30 ,  40 , and  50 , the shaft  2  inserted into the first through-hole  11 , and the key  3  protruding from the outer peripheral surface of the shaft  2  and inserted into the second through-hole  12 . The kneading machine of the present disclosure can be used for a long period of time because the kneading machine member having less risk of being damaged is used in this way. Similarly, the bearing units  60  and  70  of the present disclosure include any of the above-described bearings  61 , the shaft  63  inserted into the first through-hole  62 , and the solid lubricant  64  in sliding contact with the shaft  63  or the inner ring  61   a  supporting the shaft  63 . The bearing unit of the present disclosure can be used for a long period of time because the bearing having less risk of being damaged is used in this way. 
       FIG. 4  is a schematic diagram of the inside of the cylinder used in the kneading machine of the present disclosure, where (a) is a cross section perpendicular to the axial direction and (b) is a cross section including the axis. 
     The kneading machine  40  shown in  FIG. 4  includes the cylinder  1  providing a kneading space for the mixture, the two shafts  2  disposed in parallel in the cylinder  1 , the shear paddles  10  for kneading the mixture around the shaft  2 , and a screw  20  for feeding the mixture from the supply direction to the discharge direction, and a minute gap is set between the inner peripheral surface of the cylinder  1  and the outer peripheral surface of the shear paddles  10 . The precursor of the mixture is supplied from one end of the cylinder  1 , heated by a heater (not shown) to be a molten state, kneaded by rotation of the shear paddles  10 , and discharged from the other end of the cylinder  1  by rotation of the screw  20 . In this way, the kneading machine  40  where a plurality of the shafts  2  is disposed in parallel can efficiently knead the mixture by the shear paddles  10  which are rotatably provided adjacent to each other. 
     In addition, a heater and a water-cooling jacket (both not shown) are provided in the cylinder  1  in a belt-like form along the axial direction, and the cylinder  1  and the shear paddles  10  can be maintained at a temperature suitable for kneading by repeating the on and off control. The two shafts  2  are controlled to rotate in the same direction but may be rotated in the opposite direction by changing the pitch shape of the screw  20 . 
     The shear paddles  10  are constituted in combination and always rotating out of phase so as to rub, with one edge part in close proximity to the other. 
     Next, an example of the manufacturing method for the rotating member of the present disclosure is explained. 
     If the rotating member is made of the zirconia ceramics, first, zirconia powder which is the main component, magnesia powder as a stabilizer, dispersant to disperse zirconia powder if necessary, and binder such as polyvinyl alcohol are wet-mixed for 40 to 50 hours by a barrel mill, rotation mill, vibration mill, bead mill, sand mill, and agitator mill to make the slurry. 
     The average grain size (D 50 ) of the zirconia powder is 0.1 μm or more and 2.2 μm or less, and the content of the magnesia powder in the total 100% by mass of the above powders is 2.0% by mass or more and 4.0% by mass or less. 
     If the rotating member is made of the zirconia ceramics containing 2 to 5 mol % of yttria, the magnesia powder may be substituted for the yttria powder. The content of the yttria powder in the total 100% by mass of the zirconia powder and the yttria powder is 3.6% by mass or more and 8.8% by mass or less. 
     Next, organic binders such as paraffin wax, PVA (polyvinyl alcohol), and PEG (polyethylene glycol) are weighed in predetermined amounts and added to the slurry. In addition, a thickening stabilizer, dispersant, pH adjuster, defoaming agent, and the like may be added. 
     The slurry is then spray dried to obtain granules. Next, it is molded using a hydrostatic pressure device or a uniaxial pressure device, and the molding pressure is set to 80 MPa or more and 200 MPa or less, for example, to obtain a ring-shaped or cylindrical molded body. The molded body is then cut and finished into a near net shape. Then, a sintered body can be obtained by keeping the sintering temperature at 1400° C. or higher and 1700° C. or lower, preferably 1600° C. or higher and 1700° C. or lower, for 1 hour or more and 3 hours or less. Then, by applying the grinding process to the sintered body as necessary, the rotating members shown in  FIGS. 1 to 9  can be obtained. 
     If obtaining the rotating member that mainly includes the zirconia ceramics including 10 to 40 mol % of the monoclinic zirconia crystal, first, the content of the magnesia powder in the total 100% by mass of the zirconia powder and the magnesia powder is set to 3.0% by mass or more and 3.8% by mass to obtain the molded body by the method described above. Then, the molded body may be held at the sintering temperature of 1600° C. or higher and 1700° C. or lower for 1 hour or more and 3 hours or less and cooled at the temperature drop rate of 80° C. or higher and 150° C. or lower per hour. 
     It is possible to increase the mechanical strength of the rotating members such as the kneading machine members and the bearings obtained by the manufacturing method described above. Therefore, the kneading machine including the kneading machine member, the shaft inserted into the first through-hole, and the key protruding from the outer peripheral surface of the shaft and inserted into the second through-hole can be used for a long period of time because it uses a kneading machine member that is less likely to be damaged. Similarly, the bearing unit that includes the bearing, the shaft inserted into the first through-hole, and the solid lubricant inserted into the second through-hole and in direct or indirect sliding contact with the outer peripheral surface of the shaft can be used for a long period of time because it uses a bearing that is less likely to be damaged. 
     DESCRIPTION OF THE REFERENCE NUMERALS 
     
         
         
           
               1  Cylinder 
               2  Shaft 
               3  Key 
               10 ,  40 ,  50  Kneading Machine Member (Shear Paddle) 
               11  First Through-Hole 
               12 ,  42 ,  52  Second Through-Hole 
               13  Notch Part 
               20  Kneading Machine Member (Screw) 
               30  Kneading Machine Member (Resistance Paddle) 
               60  Bearing Unit 
               61  Bearing 
               62  First Through-Hole 
               63  Shaft 
               64  Solid Lubricant 
               65  Second Through-Hole 
               65   a  Notch Part 
               66  Insertion Hole 
               67  Side Plate 
               68  Screw Hole 
               69  Screw 
               70  Bearing Unit