NLGI
Effect of Water on Grease Performance and
Lubrication for Life in Sealed Bearings
Hocine Faci, John Haspert, Castrol Industrial, St. White Cloud, Michigan, USA
Presented at NLGI’s 80th Annual Meeting, June, 2013, Tucson, Arizona, USA
(EOF), that will be further processed into a final shape.
Continuous casting methods are common practice
where molten steel is directly poured into semi-finished
shapes. After the steel shell is solidified in its mold, the
cast continues to flow toward the latter segments and
is guided to the Run-Out table. Continued shaping is
performed with hot forming or cold forming. Hot form
ing is the process used to make slabs, bars, strips or
plates. Heated steel is passed between two Work Rolls
a given number of times until it reaches its desired
thickness. Cold forming is used to produce tubes,
wires, sheets. The steel is passed between two Work
Rolls without heating to reduce its thickness. The steel
is then heated in an annealing furnace to improve the
ductile properties, Cold rolling is more time consuming,
but is more frequently used because the products have
better mechanical properties, improved workability, and
can be more easily shaped into special sizes, thinner
gauges, etc. Once rolling is complete, the steel pieces
are finished to prevent corrosion and improve metal
properties. The rolling section utilizes a large number of
rolls, where each roll has at least 2 bearings. These are
vital parts of the steel making process.
The lubricating compounds are commonly chal
lenged by hostile environments and adverse conditions:
excessive loads and shock loading, high volumes of
aggressive process water, massive clouds of steam
and mill scale. Conventional bearings require significant
amounts of replacement grease to compensate the
large amounts of grease that has been washed out by
cooling water. More recently, sealed bearings used in
these types of applications, have positively contributed
to the process improvement. This paper covers a case
study conducted in a cold rolling section at a steel
mill plant on sealed roll neck bearings, operated in an
aggressive environment. An advanced grease technol
ogy will be covered in this work as well as extensive lab
evaluation and field testing.
Introduction
L
comprised
ubricating greases
of 3 groups
are semi-fluid
of components:
compounds
base oils,
thickeners and additives. These materials are designed
to effectively meet specific lubrication requirements.
The base oils could be mineral, synthetic, vegetable
oils or blends, and usually make up to 70 to 95% of
the finished grease. The thickener provides the gel-like
structure that holds the base oils and liquid additives in
place. Additives, that could be liquid or solid or combi
nations, are used to improve certain properties of the
grease such as friction, anti-wear, extreme pressure,
oxidation, corrosion, water resistance, odor or other
properties. The required performance targeted deter
mines the selection of these components as well as
their proportions in the finished greases [1 -4].
Greases can be classified based on a variety of crite
ria: synthetic or mineral based, biodegradable or nonbiodegradable, high temperature or low temperature,
or according to the product thickening systems: simple
metallic soaps such as calcium, lithium, sodium, barium
based, or complex metallic soaps such as lithium
complex, aluminum complex and calcium complex.
Greases can also be non-metallic soaps such as poly
urea, bentonite, silica, PTFE or any other polymer type
material with oil adsorbing properties.
These thickening systems may be associated with all
types of base oils covering a wide range of viscosities
depending on conditions of application (temperature,
load, rpms, humidity level, etc.). The most commonly
used greases in the steel industry are those based on
aluminum complex, lithium complex and calcium sulfo
nate complexes.
Grease is the lubricant of choice in the steel mill
plant bearings. Typical steel manufacturing begins with
molten metal from the basic oxygen furnace (BOF),
electrical arc furnace (EAF) or energy optimized furnace
—8—
VOLUME 77, NUMBER 6
NLGII
Grease samples were taken from various spots on the
bearhgs and submitted to the lab for analysis”.
Work background
The purpose of this project was to develop a grease for
a major bearing company to be used in sealed Work
Roll bearings. The grease is applied differently in sealed
bearings compared to current bearing lubricating tech
nology, in that, the grease remains in the bearing during
the entire campaign (10-12 months). Existing Lubricant
Technologies needed enhancement to allow extended
service life under the harsh conditions of the steel mill
environment.
From other correspondence, the report reads:
“Everyone from the Plant was impressed and so was
the Bearing Manufacturer” and “Looks great, everyone
was very impressed”
Operator side Bearings Inspection Report (Extract)
for bearings disassembled on October 16, 2008
“We disassembled the second set of bearings this
morning. We saw similar results to the first set. NO
SIGNS OF CORROSION. We were all pleased with the
results.
Most of the bearings we looked at were
already 5 years old. The grease Th the top and bottom
bearing 509 was black in color with water present, while
the Thrust bearThg held its color Neither showed any
sign of corrosion, We were also very pleased on how
easy the grease was to remove. Removal is one of the
problems the plant is facing with the current grease”.
Technology
.
An advanced technology based on a unique thickening
system coupled with an enhanced additive package
was used to make a finished grease with improved
wear, EP properties, corrosion resistance, and water
resistance, which are critical parameters for sealed
bearing lubrication. Laboratory evaluation results are
regrouped in Table 1.
.
.
Used Grease Lab Evaluation
Six samples were collected from the Drive Side bear
ings (4 from the first bearing, 2 from the second bear
ing) and 4 samples were collected from the Operator
side bearings (2 from each bearing). These samples
have been subjected to the following tests:
Field Testing & Preliminary Inspection
Reports
The grease was filled in 2 sets of sealed roll bearings.
The first set, comprising 2 bearings, has been mounted
on the drive side while the second set of 2 bearings
has been mounted on the Operator side of the lower
work roll chock. The bearings were in operation for a
total of 11 months.
• Visual inspection (consistency, color change,
apparent water, etc.)
• Worked penetration (ASTM D 1403)
Inspection Reports
• Water content
Drive Side Bearings Inspection Report (Extract) for
bearings disassembled on October 08, 2008
• EP/Anti wear and friction for samples available in
sufficient quantities
“The first bearing was easily slipped out of the
housing…. The 2 sets of bearings and races were
removed.
Grease appearance was smooth and
had a slight cream color.
There was no evidence
of free water in the bearThgs.
The second bearing
was dismantled the same way and when it was laid
on the table there was free water exiting the bottom
of the bearhg.
Further Thspection of the bearing
races showed no signs of corrosion, Th fact there was
a thin film of grease on the rollers and bearhg race that
appears to have provided the necessary protection.
• Metal content (spectral analysis)
…
.
.
Visual Inspection
.
Pictures of Figures 1 and 2 display the actual color of
the grease samples (S-i to S-6) shown side by side
with the original product (designated with “Seal”)
…
.
.
.
From the drive side / Tapered roil bearhg I:
Sample 1: Bottom Work Roll, Top edge/outer
Sample 2: Bottom Work Roll, Bearing surface, outer
—9—
NLGI SPOKESMAN, JANUARY/FEBRUARY 2014
NLGI
_______________________
Sample 3: Bottom Work Roll, Below top bearing,
middle
Sample 4: Bottom Work Roll, Inside bearing surface,
and
From tapered roll bearing II:
Sample 5: Bottom Work Roll, outer
Sample 6: Bottom Work Roll, outer
Table 1
Seal Grease Laboratory Evaluation
Test Method
Benchmark Product
Seal Grease
—
Light Brown/Smooth
Light Amber!
Base Oil Viscosity, cSt
ASTM D 445
170
200
Penetration, 1/10 mm @77°F
Unworked
Worked, 60 strokes
100 K strokes, % change
ASTM D 217
270
296
327 (+10.5%) +31 pts
300
300
305 (+1.7%) +5 pts
Water Sprayoff, % loss
ASTM D 4049
70.5
14.4
Water Washout, % loss
ASTM D 1264
5.4
2.4
Dropping Point, F
ASTM D 2265
470
529
Oil Separation, % loss
ASTM D 1742
1.5
0.5
Dry Roll Stability, % change
ASTM D 1831
+5.0%
+5.0%
Wet Roll Stability,
(77°F, 2 hrs, 10% Process Water), % change
ASTM D 1831
+3.8%
+4.9%
Four Ball EP, kg weld
ASTM D 2596
400
400
Oxidation Stability, psi drop (99°C, 100 hrs)
ASTM D 942
5.0
5,0
Rust Test,
Distilled water (48 hrs, 52°C)
Process water (48 hrs)
Process Water (48 hrs)
Process Water (96 hrs)
ASTM D 1743
Pass
Fail
Pass
Fail
Pass
Pass
Pass
Pass
Emcor Rust Test, rating
Distilled water (7 days, RT)
Process Water (7 days)
Process Water (14 days)
Process Water (14 days)
ASTM D 6138
0 (ball tracks)
0 (ball tracks)
2
0-1 (deep ball tracks)
0
0
0
0
Water Washout, 1 75°F, Process Water, % loss
ASTM Dl 264
7.4
3.0
Dry Roll Stability @ 90°C, % change
ASTM D 1831
6~3
3.9
Wet Roll Stability © 90°C,
10% Process Water, % change
ASTM D 1831
-10.8
+6.2
Rust Test, Process Water
24 hrs © 90°C
48 hrs © 90°C
~
ASTM D 5969
Pass
Pass
Pass
Pass
Characteristic
Color/Appearance
—10—
VOLUME 77, NUMBER 6
NLGI
7
From the Operator side:
Thrust Bearing
Sample A: Bottom Operator GE 108, 390 thrust bearing
Sample B: Top Operator GE 108, 390 thrust bearing
Tapered Roll Bearing:
Visually, the scraped grease samples appeared darker
in color than the original sample and the intensity of the
color varies in function of the area (or part) from where
the grease was scraped and the amount of absorbed
water. The darkest samples are those collected from
the tapered roll bearing from the Operator side.
Sample C: Bottom Operator, GA 579, 509
Sample D: Top Operator 509, HD 655
Figure 1
—
6 samples of grease from drive side bearings (surrounding a
fresh sample of SEAL grease)
Figure 2 —4 samples of grease from Operator side bearings (surrounding
a fresh sample of Seal grease
Table 2
Worked Penetration (WP of fresh Seal grease: 290)
Worked Penetration
Percentage
Sample
Penetration change
Water content,
% w.
‘~#1
#2
339
Insufficient amount
16~9
—
27.0
21 .0
#3
339
16~9
25.1
#4
343
18.3
25.7
#5
328
13.1
15.7
#6
335
15.5
25.0
A
B
335
343
15.5
18.3
42.9
22.7
~C
407
40.3
31.0
3.3
4.8
380
— 11 —
NLGI SPOKESMAN, JANUARY/FEBRUARY
2014
NLGH
Worked Penetration
Quarter scale worked penetration test (ASTM D 1403)
has been conducted on all samples at ambient tem
perature. Table 2 shows worked penetration data and
percentage of worked penetration change in compari
son with worked penetration of the original product.
A slight softening (1 3-1 8% change in worked pen
etration) was observed on all samples where water was
present in moderate to large quantities (15 to 43%)
such as in samples 1 to 6 and Samples A and B.
By contrast, a significant softening has been noticed
on samples C and D (respectively 40 and 31 % worked
penetration change) where small amounts of water
were detected (3.3 and 4.8% respectively).
It appears that water, adsorbed by the grease while
in service, has positive effect on the mechanical
(shear) stability of the grease. It minimizes the softening
phenomenon. Thus, the amount of grease running out
from the bearing, if any, is minimal.
a
Water Content
Samples of approximately 4 grams of grease have been
placed in an oven at 100°C. After 24 hours, samples
were removed, cooled and weighed. The percentage
of evaporated water in each sample was determined.
Under these conditions a fresh sample did show a
loss of 0.2% only, which is regarded as typical for a
stable grease manufactured in a dry environment.
Percentages of water content on the studied samples
are displayed in the right column of Table 2.
Results show a wide range of water content even
within the samples collected from the same bearing,
probably due to different exposure angles of water
ingress.
Typically, there is a direct correlation between the
amount of water absorbed and softening of the grease
for a given range of water. This suggests that as more
water is absorbed, the softer the grease will become.
We cannot extrapolate this correlation to the lower
water content in Samples C and D which show an
intense softening with infinitesimal amounts of water.
Probably, in this case, there are other variables that
need to be taken into account such as quality of the
seal achieved, age of the bearing, temperature, etc.
Friction, Wear and Extreme Pressure
(EP) properties
Instead of the conventional Four-Ball EP and FourBall Wear testing, we selected to run the SRV tests to
evaluate these properties due to limited amounts of
grease available for testing. Ball on disk (point contact)
configuration was chosen for this test.
Friction and wear
Testing was completed per ASTM D 5707 using the
following conditions: running-in 50 Newtons (N) for
30 seconds, testing load: 400 N, temperature 50°C,
frequency 50 Hz, amplitude: 1 .00 mm, test duration:
2 hours.
The dynamic Coefficient of Friction (COF) is recorded
during the entire run time and at the end of the run, the
ball scar diameter is measured in mm.
Tests were conducted on a fresh sample of SEAL
grease and on some samples (wet and dry) from the
Drive Side and Operator side.
EP test
Testing was completed per ASTM D 5706 using the
following conditions: temperature 50°C, oscillation
frequency: 50 Hz, oscillation amplitude: 1 .00 mm,
running-in 50 N for 30 seconds and then loading will
be increased by increments of 100 N for a duration
of 2 minutes. Test is run until failure (or stalling of the
machine);. Failure Load is reported.
Tests were conducted on a fresh sample of SEAL
grease and on at least one sample from each bearing.
Table 2 summarizes all the results obtained on the
SRV test rig. The Coefficient of Friction (COF) reported
are those obtained at the end of the 2 hour run time.
Figures 3, 4, 5 and 6 show the dynamic coefficient of
friction during the entire run.
From this study we can draw the following conclusions:
COF: Used samples displayed slightly better coefficient of
friction than SEAL grease (0.110 0.120 for used sam
ples vs. 0.140 for fresh sample) and is consistent with all
used samples regardless of their water content, consis
tency, color intensity or even the wear metal content.
—12—
VOLUME 77, NUMBER 6
–
NLG~
Wear: Ball scar diameter measurements display values
in the range of 0.55 to 0.80 mm for the wet samples
and 0.57 to 0.80 mm for the dry samples. The fresh
sample showed 0.63 mm.
Sn
tee
445 ~544455$
eee$,e
~
—
EP: The failure loads obtained on used samples var
ied between 1000 and 1400 N. The failure load of
the SEAL was 1500 N. Failure loads in this range are
regarded as extremely high for this type of application.
Greases based on conventional thickening systems
tnt, Jet ted.
—n
~n
ste
fin,
~ ~
w,qneq~nqeeqsøflflw~eq~~eqflfl-n’qw — W~~Wflflflfl5SeWflt5te~fl55nfl~
~
Figure 3 — coefficient of friction obtained on SEAL grease, Samples 1, 2, 3 and 4 (Tapered Roll Bearing I, Drive side)
Sn
ThS~
Sc.
ted.
tests.
4445 SfleWeS
eeflS
‘tee
.ee~fl eq
At, ass.
~
4Sn’eq’flas~eq5~AcAtqeqAflflflSfl
~te~afleq~eqnaseq~
net
~
Figure 4 — coefficient of friction obtained on SEAL Grease, Samples 5 and 6 (Tapered Roll Bearing II, drive side)
Sn
5efl~ Jet cede
cent.
$445 tetAnus it.,q,e
~
sq~,3,
4$.
fin4
~as-ns.u~u-n
~nj-sq~~s.s.~sqeqqneqt.uneta
~as~cea~a
Figure 5 — coefficient of friction obtained on SEAL Grease, Samples A and B (Thrust Bearing, Operator side)
en ~nfl
Se. ted.
Tenet
sue us ness’
ee,$e
~e,
—
fine sees
Figure 6
—
coefficient of friction obtained on SEAL Grease, Samples C and D (Tapered Roll Bearing, Operator side)
—13—
NLGI SPOKESMAN, JANUARY/FEBRUARY 2014
NLGI
the test results obtained on Samples, 4, 6, B and D,
(see Table 4)
Elements such as Fe, Cu, Al and Cr which are com
monly detected in used lubricants can be used to
assess the wear degree of a component. Except for
Sample B that shows a relatively high iron content, the
other metal levels are considered typical for bearing
lubrication. The COF as well as wear and EP measured
on Sample B were not affected by the iron content in
this sample. Possibly, this was due to the age of the
bearing rather than to the lubrication performance.
Mg and Na are part of the process water that comes
in contact with the grease in service. Lower amount of
Na in Sample D correlates to some extent the lower
content of water in this sample as determined by the
evaporation test.
reach failure loads that remain often below 800-900 N
in many comparable high performance greases. SEAL
Grease, after 11 months of service in these sealed
bearings still exhibits outstanding results in this perfor
mance evaluation.
In conclusion, the EP, Wear and Friction character
istics evaluated with the SRV test rig indicate that the
grease, after 11 months in service in a sealed Work Roll
bearings, still exhibits much of the original performance
characteristics.
Spectral Analysis
These analyses were conducted to determine the
amount of wear by measuring the metal content that
is not part of the grease composition. Following are
Table 3
Friction, wear and EP test results
Side
Bearing
Sample
j #1
#2
) #3
#4
#5
#6
A
B
C
D
Wet Sample
COF @
Ball Scar
diameter, mm
0.76
0.112
0.120
0.70
0.121
0.75
0.120
0.78
0,120
0.78
0.120
0.80
0.113
0.82
0.55
0.102
0.60
0.120
0.58
0.111
NA
NA
Sample
Ball Scar
EP test, Failure COF @
2 hours
diameter, mm
load, N
1200
—
1400
0.119
0.78
0.110
0.113
0.105
0.120
0.111
0.140
0.76
0.80
057
0.56
0.57
0.63
—
1000
—
1000
1000
1500
Table 4
Spectral analysis results, ppm
Side
Bearing
~
Sample
~#4
Fe
2200
3200
5800
1460
0
Cu
21
9
16
6
0
—14—
VOLUME 77, NUMBER 6
Al
222
233
63
87
14
Cr
32
25
15
19
0
Mg
47
53
36
41
47
Na
351
421
463
225
105
NLGI
Conclusions
The lab evaluation of used SEAL grease collected from
sealed bearings in service for 11 months in a steel mill
application indicates the following:
• The grease color changed from light amber to a
wide spectrum of colors varying from moderate
cream to intense dark.
• The grease has absorbed moderate to large
amounts of water varying between 15 and 43%
weight in both bearings on the drive side and in
the thrust bearing on the Operator side. Small
amount of water (around 3-5%) were present in
the grease collected from the tapered roll bearing
on the Operator side.
• The grease has softened from NLGI 1 .5 to soft or
slightly softer than NLGI 1 for all samples contain
ing moderate to large amounts of water (both
drive side bearings and Operator side thrust bear
ing). There is though a significant softening of the
grease from NLGI 1 .5 to NLGI 0-00 for samples
containing small amounts of water (tapered roll
bearing of the Operator side).
• There was no effect to minor effect on wear and
EP performance characteristics of the grease after
service. However, there was improvement of the
frictional properties that would lead to lower oper
ating temperature, therefore longer service life.
performance will certainly have a positive impact on the
bearing service life leading to lower maintenance costs
and enhanced productivity.
Bibliography:
1.0. White, Lubrication, Vol. 77, No. 1, 1991
2. NLGI Lubricating Grease Guide, Second Edition, 1989
3. J. Schlobohm Sr., H. Faci, B. Cisler, Steel Mill Greases.
Evaluation and Analysis, NLGI Spokesman, Vol. 69,
No. 8, November 2005
4. A.E Cichelli, Grease Lubrication in Steel Mills with
Emphasis on Roll Neck Bearings, NLGI Spokesman,
April 1980
5. H. Faci, B. Cisler, A. Medrano, M. Inns, When
Performance and Biodegradability Converge.
A Superior Product in a Demanding Environment,
NLGI Spokesman, Volume 70, No 1, April 2006
6. R.E Rush, Greases for Steel Mill Lubrication, Journal of
the Society of Tribologists and Lubrication Engineers,
August 1993
7. Namiki, M. Kagoshima, T. Development of Grease
for Continuous Casting Machines Achievement in
Bearing Life Extension, NLGI Spokesman, Vol. 71;
No. 6, 2007
–
ABOUT THE AUTHORS
Hocine Faci
BP/Castrol Hocine
received his BS, Doctorate in Chemical
~ Engineering from the Institute of Petro
leum and Gas, Romania. He has been
very active in Petroleum Refining and
I Lubricants for over 25 years, 17 of them
with Castrol. Today Faci is an Expert
Technologist for Castro! Industrial Global
I Technology. Hocine received the NLGI
Fellow Award in 2007.
—
• The elemental analysis of the grease did show low
content of metals in the used samples suggesting
that the grease has superior corrosion inhibition
and considerably improved wear protection.
Based on the field reports and lab evaluation test
results that, after 11 months of service with no
re-lubrication of these sealed Work Roll bearings,
operating in an environment where load is high, shock
loading is frequent, temperatures are elevated and
water is abundant and aggressive, that the SEAL
grease has met all the requirements for which it has
been designed. The grease effectively showed excel
lent mechanical stability, outstanding water resistance,
extraordinary wear protection, improved friction reduc
tion and extended protection against corrosion. This
—
John Haspert, CLS BP/Castrol
Photo unavailable at
time of press. John is currently a Senior Corporate Engineer!
Application Engineer with Castrol Industrial, a division of BP,
after a career spanning 36 years in Product Development, QC/
QA Manager, Customer Service Lab Manager and Marketing
and Engineering. Haspert earned his BS Chemistry from
California State University in Los Angeles. He is a Certified
Oil Monitoring Analyst, member of NLGI and Association
of Iron & Steel Technologists.
—
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NLGI SPOKESMAN, JANUARY/FEBRUARY 2014
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