strategies for optimizing greases to mitigate fretting wear
TRANSCRIPT
Strategies for Optimizing Greases
to Mitigate Fretting Wear
Juan Bosch Giner and G. L. Doll
Mechanical Engineering Department,
The University of Akron
September 2021
Outline
• Project Definition and Motivation
• Experimental Methods
• Lube Tests
• Tribotests
• Results
• Rotational Fretting
• Translational Fretting
• Summary of Conclusions
2
Project Definition and Motivation
3
• Greases are ubiquitously utilized in sealed rolling element bearings.
• When the bearings experience continuous rotational motion, adequate
lubricant films are usually generated between the rolling elements and the
raceways.
• However, during periods when rotational motion is interrupted, intimate
contact between the asperities on the rolling elements and the raceways
can occur.
• If the bearing is subjected to vibrations or low amplitude oscillations during
these non-rotational periods, fretting-type wear of the raceways can occur.
Fretting wear on the
inner raceway of a
deep-groove ball
bearing (left) and
tapered roller
bearing (right)
Project Definition and Motivation
4
• Previous research performed in our laboratories has revealed that the
success of these approaches greatly depends on the type of fretting
motion experienced by the bearing or other mechanical component [*].
• Our research has found that if fretting results from linear oscillations,
solid additives such as boric acid or molybdenum disulfide may be more
effective than bleed rate in mitigating fretting-type wear.
• On the other hand, bleed rate may be more effective than solid additives
if the fretting wear resulted from rotational oscillations.
* Saatchi, A., 2019. The Effect of Grease Composition on Fretting Wear (Doctoral
dissertation, University of Akron).
Experimental Methods
5
• Materials
▪ Greases: Lithium complex 100, 220, and 460 cSt.
▪ Oils: 1 and 5 wt.% Synthetic base oil 100, 220,
and 460 cSt.
▪ Solid Additives: 1 wt.% CuO, ZrO2, and ZrO
nanoparticles.
Experimental Methods
6
• Experiments
• Grease Characterizations:
• Bleed Rate - ASTM D6185
• Consistency - ASTM D1403
• Rheology
• Fretting Tests:
• Translational: HFRR - ASTM D7594
• Rotational: Modified Fafnir
• Wear Analysis:
• Wear Volume: Zygo
• Mass Loss
Experimental Methods: Grease characterization
7
Test Parameters: ASTM D1403
50 g of worked grease
25 ℃One half size equipment
Cone penetration
Test Parameters: ASTM D6184
100 ℃ oven for 30 hours
Bleed rate
Experimental Methods: Rheology
8
Oscillatory stress sweep parameters:
10-6
10-5
10-4
10-3
10-5
10-4
10-3
10-2
10-1
Modulu
s (
MP
a)
Oscillation Stress (MPa)
Storage modulus
Loss modulus
-20
-10
0
10
20
Tan(delta)
Tan(d
elta)
Parameter Value
Pre-shear 3.259 Pa for 1 min
Frequency (Hz) 1
Stress sweep (Pa) 1 - 1000
Grease (mL) 2
Temperature (℃) 40 and 80
Experimental Methods: HFRR
9
Test Parameters:
0 10000 20000 30000 40000
0.2
0.4
Friction c
oeff
icie
nt
Cycles
Parameter Value
Stroke length (µm) 40
Frequency (Hz) 25
Load (N) 10
Grease (mL) 2
Number of cycles 45,000
Experimental Methods: Modified Fafnir
10
Test Parameters:Parameter Value
Load (kN) 18
Frequency (Hz) 8
Rotation (degrees) 3
Grease (mL) 2
Number of cycles 720,000
Experimental Methods: Zygo
11
Grease Characterization
12
Grease Addition
Penetration
distance ½ size
testing
NLGI grade
100 cSt
As-received 141.8 ± 1.8 2
1% CuO 135.3 ± 0.8 2
1% ZrO2 138.4 ± 1.7 2
1% ZrO 134.3 ± 1.5 2
1% Base oil 138 ± 1.3 2
5% Base oil 141.9 ± 0.9 2
220 cSt
As-received 143.4 ± 0.5 2
1% CuO 143 ± 0.7 2
1% ZrO2 137.5 ± 1.3 2
1% ZrO 141.8 ± 1.1 2
1% Base oil 139.3 ± 1.4 2
5% Base oil 143.2 ± 1.3 2
460 cSt
As-received 140.8 ± 2.1 2
1% CuO 138.5 ± 1.8 2
1% ZrO2 142.5 ± 1.6 2
1% ZrO 141.7 ± 0.8 2
1% Base oil 142 ± 1.2 2
5% Base oil 143.3 ± 0.5 2
Consistency results
Grease Characterization
13
460
cSt B
ase
460
+ 1%
CuO
460
+ Zr
O2
460
+ 1%
ZrO
460
+ 1%
BO
460
+ 5%
BO
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Weig
ht
loss (
g)
Grease
220
cSt B
ase
220
+ 1%
CuO
220
+ Zr
O2
220
+ 1%
ZrO
220
+ 1%
BO
220
+ 5%
BO
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Weig
ht
loss (
g)
Grease
100
cSt B
ase
100
+ 1%
CuO
100
+ Zr
O2
100
+ 1%
ZrO
100
+ 1%
BO
100
+ 5%
BO
0.00
0.05
0.10
0.15
0.20
0.25
0.30
Weig
ht
loss (
g)
460 Grease 220 Grease 100 Grease
Bleed rate results
Results: Rheology
14
Crossover Modulus
220
cSt B
ase
220
+ 1%
CuO
2
220
+ Zr
O2
220
+ 1%
ZrO
220
+ 1%
BO
220
+ 5%
BO
0.002
0.004
0.006
0.008
0.010
0.012C
rossover
modulu
s (
MP
a)
Grease
Flow point 40C
Flow point 80C
100
Base
100
+ CuO
100
+ Zr
O2
100
+ Zr
O
100
+ 1%
BO
100
+ 5%
BO
0.001
0.002
0.003
0.004
0.005
0.006
Cro
ssover
modulu
s (
MP
a)
Grease
Flow point 40C
Flow point 80C
460
cSt B
ase
460
+ Zr
O2
460
+ 1%
CuO
2
460
+ 1%
ZrO
460
+ 1%
BO
460
+ 5%
BO
0.002
0.004
0.006
0.008
0.010
Cro
ssover
modulu
s (
MP
a)
Grease
Flow point 40C
Flow point 80C
460 Grease 220 Grease 100 Grease
Results: Rheology
15
460 Grease 220 Grease 100 Grease
Crossover Stress
460
cSt B
ase
460
+ Zr
O2
460
+ 1%
CuO
2
460
+ 1%
ZrO
460
+ 1%
BO
460
+ 5%
BO
0.0000
0.0002
0.0004
0.0006
0.0008
0.0010
Cro
ssover
poin
t (M
Pa)
Grease
Crossover point 40C (40C)
Crossover point 80C (80C)
220
cSt B
ase
220
+ 1%
CuO
2
220
+ Zr
O2
220
+ 1%
ZrO
220
+ 1%
BO
220
+ 5%
BO
0.00010
0.00012
0.00014
0.00016
0.00018
0.00020
0.00022
0.00024
0.00026
0.00028C
rossover
poin
t (M
Pa)
Grease
Crossover point 40C (40C)
Crossover point 80C (80C)
100
Base
100
+ CuO
100
+ Zr
O2
100
+ Zr
O
100
+ 1%
BO
100
+ 5%
BO
0.00016
0.00018
0.00020
0.00022
0.00024
0.00026
0.00028
0.00030
0.00032
0.00034
0.00036
0.00038
Cro
ssover
poin
t (M
Pa)
Grease
Crossover point 40C
Crossover point 80C
Translational Fretting Results
16
220
cSt B
ase
220
cSt C
uO
220
cSt Z
rO2
220
cSt Z
rO
220
cSt 1
% B
O
220
cSt 5
% B
O
16000
20000
24000
28000
32000
36000
Volu
me d
ow
n (m
3)
Grease
Volume down
100
cSt B
ase
100
cSt C
uO
100
cSt Z
rO2
100
cSt Z
rO
100
cSt 1
% B
O
100
cSt 5
% B
O
16000
20000
24000
28000
32000
36000
Volu
me d
ow
n (m
3)
Grease
Volume down
460 Grease 220 Grease 100 Grease
HFRR data after Zygo analysis
Volume down plots
460
cSt B
ase
460
cSt C
uO
460
cSt Z
rO2
460
cSt Z
rO
460
cSt 1
% B
O
460
cSt 5
% B
O
16000
20000
24000
28000
32000
36000
40000
Volu
me d
ow
n (m
3)
Grease
Volume down
Translational Fretting Results
17
460 Grease 220 Grease 100 Grease
HFRR data after Zygo analysis
Pit depth plots
220
cSt B
ase
220
cSt C
uO
220
cSt Z
rO2
220
cSt Z
rO
220
cSt 1
% B
O
220
cSt 5
% B
O
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0M
ax d
epth
(m
)
Grease
Max Scar depth
100
cSt B
ase
100
cSt C
uO
100
cSt Z
rO2
100
cSt Z
rO
100
cSt 1
% B
O
100
cSt 5
% B
O
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
Max d
epth
(m
)Grease
Max Scar depth
460
cSt B
ase
460
cSt C
uO
460
cSt Z
rO2
460
cSt Z
rO
460
cSt 1
% B
O
460
cSt 5
% B
O
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
Max d
epth
(m
)
Grease
Max Scar depth
460
cSt B
ase
460
+ 1%
CuO
460
+ Zr
O2
460
+ 1%
ZrO
460
+ 1%
BO
460
+ 5%
BO
0
5
10
15
20
25
Weig
ht
loss (
mg)
Grease
220
cSt B
ase
220
+ 1%
CuO
220
+ Zr
O2
220
+ 1%
ZrO
220
+ 1%
BO
220
+ 5%
BO
0
1
2
3
4W
eig
ht
loss (
mg)
Grease
Rotational Fretting Results
18
100
cSt B
ase
100
+ 1%
CuO
100
+ Zr
O2
100+
ZrO
100
+ 1%
BO
100
+ 5%
BO
0
2
4
6
Weig
ht
loss (
mg)
460 Grease 220 Grease 100 Grease
Modified Fafnir results
Summary and Conclusions
19
• All greases displayed the same consistency NLGI grade 2.
• Bleed rate was mitigated by ZrO.
• CuO and ZrO2 also mitigate fretting wear from tangential motion.
• ZrO promoted more fretting wear from tangential motion.
• Deeper pit depths were promoted by oil bleed (460 and 220) and powders, being
the worst ZrO.
• ZrO and ZrO2 promotes more fretting wear on rotational motion.
• CuO mitigates fretting wear on rotational motion.
• Low oil bleed (1 wt.%) do not significantly affect fretting from rotational motion,
sometimes promoting it. However, higher oil bleeds (5 wt.%) showed enhanced
protection.
Acknowledgements
20
TESL Students and Staff
NLGI Project Mentor: Dr. Kuldeep Mistry (The Timken Company)
NLGI Research Grant