第 3 章 グリースの再供給と軸受トルク
3.5 本章のまとめ
外輪をガラス製としたモデル軸受を用いてリングとボールの接触面を動的に直接観察し，
接触面の入口におけるグリースの入口距離を指標として，軸受トルクおよびグリースの物 性との相関性を，グリース封入量を少なくした条件で調査した．この結果，以下の知見が 得られた．
・接触面の周囲で発生する軸受トルクは入口距離の影響を受け，混和ちょう度が低く，降 伏応力や見掛けの粘度が高いグリースは，入口距離の減少とともに低くなる傾向が強い．
・入口距離は回転初期に大きく減少し，その後，安定する傾向を有する．
・回転初期は入口距離が長く，接触面の周囲で発生する起動トルクは，見掛けの粘度およ びヒステリシスループ面積の増大とともに大きくなる影響を示す．
・定常状態では入口距離が短くなり，接触面の周囲で発生する回転トルクへのグリースの 流動特性の影響は小さい．
・潤滑油の動粘度が低い方が入口距離が長く，また軸受トルクが低くなる傾向を有する．
・入口距離はグリースの見掛けの粘度が低いほど，もしくはヒステリシスループ面積が小 さいほど，回転による，減少の程度が小さい．
・接触面へのグリースの再供給は，主に保持器ポケット部を通過した，ボールの転動面に 付着したグリースによって行われると推定される．
・定常状態での入口距離へのグリースの封入量の影響は軽微である．
本章ではモデル軸受を用い，再供給により接触面の周囲で発生する軸受トルクを評価し た．実用を想定した条件での軸受トルクの評価は第5章において行う．
Table 3-1 Properties of test greases
Grease E10OH22 E10OH29 E10St22 E10St28
Base oil Ester oil
Kinematic viscosity of
base oil at 313 K, mm2/s 100
Thickener Lithium 12-hydroxystearate Lithium stearate
Thickener concentration, wt% 10 8 22 17
Worked penetration 219 290 220 284
Yield stress, Pa 2990 970 1020 440
Hysteresis loop area, kPa/s 682 114 776 141
Table 3-2 Bearing test condition
Bearing type 6306 (Inner diameter 30 mm, Outer diameter 72 mm, Width 19 mm) 8) Rotating speed 100 - 1800 min-1
Axial load 29.4 N
Temperature Room temperature Amount of lubricant 0.5, 3, 5 g
Flame rate 8000 fps (85 frames per a ball passage)
Test bearing Cross section of a test bearing Fig. 3-1 A schematic image of a test bearing
Cr semi-reflective film
Outer ring (BK7)
Fig. 3-2 A schematic image of a bearing test apparatus
EHD contact contact
Fig. 3-3 The position of filled grease in a test bearing
Fig. 3-4 An image of fracture
Fig. 3-5 An image of hysteresis loop area Down curve Up curve
Hysteresis loop area Fracture
Fig. 3-6 A contact area image of a ball and an outer ring using E10OH22
Fig. 3-7 Fluctuation of inlet distance of continuous balls 500μm
Inlet
Interface Grease Air
Kinematic
viscosity of oil 2 revolutions of a ball 4632 revolutions of a ball
30 mm2/s
100 mm2/s
417 mm2/s
Fig. 3-8 Contact area images of oils at different times 2285 μm
1040 μm
160 μm
440 μm
0 m 400 μm
Fig. 3-9 Changes in the inlet distance of oils with revolution times mm2/s
mm2/s mm2/s
Lubricants 2 revolutions of a ball 4632 revolutions of a ball
E10 (base oil)
E10OH22
E10OH29
E10St22
E10St28
Fig. 3-10 The inlet distance of the greases at different times
Fig. 3-11 Changes in the inlet distance of greases and base oil with revolution times
Fig. 3-12 Decrease of inlet distance of greases and base oil
2 revolutions of a ball 4632 revolutions of a ball
0.5 g
3 g
5 g
Fig. 3-13 Contact area images of E10OH29 with different grease filled volume
> 2500 μm 960 μm
> 2500 μm 1340 m
1450 m 1050 m
Fig. 3-14 Change in the inlet distance of E10OH29 with grease filled volume and revolution times
(a) 100 min-1 (b) 500 min-1
(c) 1000 min-1 (d) 1800 min-1
Fig. 3-15 Change in the inlet distance of E10OH29 with rotating speed, grease filled volume and revolution times, (a) 100 min-1, (b) 500 min-1, (c) 1000 min-1, (d) 1800 min-1
Fig. 3-16 Change of the inlet distance at 180 sec of E10OH29 with grease filled volume and rotating speed
Fig. 3-17 Changes in bearing torque with revolution times
Fig. 3-18 Variation in bearing torque of oils with revolution times
Fig. 3-19 Starting torque and running torque of bearing torque of greases and base oil
Fig. 3-20 Decrease of bearing torque of greases and base oil
Fig. 3-21 Changes in bearing torque of E10OH29 with grease filled volume and revolution times
Fig. 3-22 Variation in bearing torque of E10OH29 with grease filled volume and revolution times
(a) 100 min-1 (b) 500 min-1
(c) 1000 min-1 (d) 1800 min-1
Fig. 3-23 Change in bearing torque of E10OH29 with rotating speed, grease filled volume and revolution times, (a) 100 min-1, (b) 500 min-1, (c) 1000 min-1, (d) 1800 min-1
Fig. 3-24 Increase of bearing torque with rotating speed of E10OH29 min-1 min-1 min-1
(a) 3 s
(b) 180 s
Fig. 3-25 Variation in bearing torque at 3 s and 180 s of E10OH29 with grease filled volume and rotating speed
Fig. 3-26 Worked penetration of test greases
Fig. 3-27 Yield stress of test greases
(a) Li(12OH)St thickener
(b) LiSt thickener
Fig. 3-28 Hysteresis loop test results of test greases, (a) Li(12OH)St thickener, (b) LiSt thickener E10OH22
E10OH29
E10St22
E10St28
Fig. 3-29 Apparent viscosity at 100 s-1 of test greases
Fig. 3-30 Hysteresis loop area test results of test greases
(a) E10OH22 (b) E10OH29
(c) E10St22 (d) E10St28
Fig. 3-31 SEM images of test greases
Fig. 3-32 Correlation between the inlet distance and bearing torque of test oils mm2/s
mm2/s mm2/s
(a) 2 times
(b) 4632 times
Fig. 3-33 Correlation between the inlet distance and bearing torque with grease filled volume of 0.5 g, (a) at 2 times, (b) at 4632 times
(a) E10OH22
(b) E10OH29
Fig. 3-34 Correlation between the inlet distance and bearing torque with grease filled volume of 0.5 g, (a) E10OH22, (b) E10OH29
R2=0.83
R2=0.31
Fig. 3-35 Correlation between the inlet distance and bearing torque with grease filled volume of 0.5 g
Fig. 3-36 Correlation between the inlet distance and bearing torque of E10OH29 with different grease filled volume at 100 min-1
(a) E10OH22
(b) E10OH29
Fig. 3-37 Images of a tested bearing at 100 min-1 and 0.5 g (a) E10OH22, (b) E10OH29
Attached grease
Attached grease
Attached grease Attached grease
Cage pocket
Cage pocket
(a) Grease volume of 3 g
(b) Grease volume of 5 g
Fig. 3-38 Images of a tested bearing with E10OH29 at 100 min-1 (a) grease filled volume of 3 g, (b) grease filled volume of 5 g
(a) Soon after the test
(b) 1 hr after the test
Fig. 3-39 Static images of contact area with E10OH22 after 4632 times at 100 min-1 (a) soon after the test, (b) 1 hr after the test
Interface
Interface
(a) Inlet distance after 2 times
(b) Inlet distance after 4632 times
Fig. 3-40 Correlation between yield stress and the inlet distance (a) inlet distance after 2 times, (b) inlet distance after 4632 times
(a) Inlet distance after 2 times
(b) Inlet distance after 4632 times
Fig. 3-41 Correlation between apparent viscosity at 100 s-1 and the inlet distance (a) inlet distance after 2 times, (b) inlet distance after 4632 times
(a) Inlet distance after 2 times
(b) Inlet distance after 4632 times
Fig. 3-42 Correlation between hysteresis loop area and the inlet distance (a) inlet distance after 2 times, (b) inlet distance after 4632 times
Fig. 3-43 Correlation between yield stress and bearing torque
Fig. 3-44 Correlation between apparent viscosity and bearing torque
Fig. 3-45 Correlation between hysteresis loop area and bearing torque