JUL LUBRICATIoN:
i~i~ease Performance
Jer Be~r~ng S,~rvice Life
Castro! Industrial
Abstract
Calcium Sulfonate Grease has been in use in the steel
mill industry for more than 15 years. Its success in these
applications is mainly due to a set of performances
associated with the thickening material itself, which
provides a decent carrying capacity and wear protection,
good water resistance, corrosion resistance and thermal
stability. Experience has demonstrated however that
this technology as currently offered, does not meet the
totality of the end users expectations, namely on load
carrying capacity, thermal stability and mobility, crucial
properties for long service life of the bearings.
The objective of this project was to build on the existing
technology of Calcium Sulfonate greases, a more robust
product that would boost the load carrying capacity /
antiwar properties to higher levels, while keeping the
current corrosion inhibition, water resistance, thermal
stability, and grease mobility at least at the current level
of performance, if not better.
An extensive benchmarking program that involved over
9 different commercially available products has been
conducted in the laboratory testing phase where more
simulative tests have been performed. This work has
led to the development of a product that has met all the
specification requirements. The load carrying capacity
has been improved as well as the wear protection, the
water resistance (under both the sprayoff and washout
test conditions), and mechanical stability in the presence
of various still mill process waters.
Since undergoing trial in a steel mill caster section,
this product has shown great mobility, outstanding
thermo-oxidation stability; excellent mechanical stability,
excellent grease coverage of the bearing, and more
importantly all these benefits were achieved with lower
grease consumption. The service life of the bearing
was extended from 3 to 4 years, and could be extended
further. The detailed work will be compiled in this paper.
Introduction
Prior to the introduction of continuous casting in the
1940/1950s, steel was poured in individual molds to form
ingots. Since then, the steel manufacturing has improved
drastically. Continuous casting became the process of
choice in steel, aluminium and copper industry.
Within the steelmaking process, the steel is cooled to
form a semi-finished product in the continuous caster
area. In a typical installation, molten steel is tapped from
ladles on the ladle turret and fills a mold before entering
a continuous caster. The mold is cooled externally and
an outer skin is formed around the liquid metal core;
this will remain liquid until near the end of the casting
process (known as the metallurgical length).
The caster consists of rollers that are in contact with
the cast steel, and these are generally cooled internally
with process water. Bearings are installed to allow the
rollers to rotate, and these are also water cooled in most
casters. The steel is spray cooled at a determined rate, to
maintain the metallurgical length. Bearings and rollers
are also water cooled in the runout table directly after the
caster; at this stage, the cast steel can still be in the region
of 800°C.
If the internal water cooling system or pipe work fails,
18 VOLUME 79, NUMBER 1
roller and bearing temperatures will rise rapidly. The
cast steel is very soft and malleable at this stage, and
surface damage can occur that cannot be rectified further
downstream in the steelmaking process. This can result
in scrap costs, as well as downtime to repair the affected
ma~hinery including bearings, rollers and cooling water
pipe work.
Specialty greases are available to lubricate high
temperature applications in the hot areas of a steel mill,
and water resistant greases are available for areas where
large volumes of water are used. It is not common to
find products that are effective in both high temperatures
and extreme conditions such as large volumes of process
water.
Balancing the mix of oil, thickener and additives to
match the type of application can result in a significant
increase in performance compared to conventional
greases.
This paper discusses the evaluation, benchmarking
and field trial of single grease specifically designed for
performing under the harsh and varied conditions found
in casting sections in steel mill plants.
Background
The most used greases in the steel industry are those
based on aluminium complex, lithium complex and
calcium sulfonates. References [1, 2, 3, 4, 5 and 6] cover
a comprehensive description of some of the steel mill
plants, the typical greases used in these plants and their
conditions of application.
Recently a good number of papers have been presented
at ELGI and NLGI outlining the benefits of calcium
sulfonates or calcium sulfonate complexes; Reference [7]
indicates that the calcium sulfonate greases remain the
fastest growing grease thickener system, a main reason
being that it does not change its characteristics even
in the presence of large amounts of water. Reference
[8] emphasizes on what makes the calcium sulfonate
greases different to the other greases from the structure
to the manufacturing process. Reference [9] studies the
effect of water on various types of thickening systems,
and different types of base oils are evaluated for a good
number of characteristics by various test methods. This
reference joins the other papers to confirm that calcium
sulfonate greases outperform the other greases under
high load and high temperature applications. Reference
[10] outlines the impact of other advanced thickening
systems on the bearing service life.
This study takes into consideration all the work that
has been covered earlier using the calcium sulfonate
grease technology, and will identify the key advantages of
this technology. The laboratory work as well as the field
testing approaches will be covered.
Laboratory Development Work
Definition of required tests
The caster section bearings in a steel mill plant as
described above require grease with good number of
properties in order to withstand the harsh conditions
of the application, namely: (1) high load carrying
capacity; (2) improved wear protection, (3) excellent
mechanical stability; (4) outstanding water resistance,
and (5) excellent corrosion inhibition. To evaluate these
properties, the following test methods were used:
1. Load Carrying Capacity:
One of the most popular tests for determining the load
carrying capacity is Four Ball EP (ASTM D 2596, DIN
5 1350-4). This test consists of 4 balls arranged in the
form of an equilateral tetrahedron. The basic elements
of the tetrahedron are 3 balls held stationary in a pot to
form a cradle in which the fourth upper ball is rotated
around a vertical axis under pre-selected conditions of
loads. The rotating speed is 1770 +1- 60 rpm. A series
of 10-second runs are made at successively higher loads
until welding of the 4th ball occurs (Figure 1).
– 19 NLGI SPOKESMAN, MARCH/APRIL 2015
Figure 1: Four Ball EP set up
Wear:
Wear protection is measured by Four Ball Wear
method. The test (ASTM D 2266, DIN 5 1350-5) can be
run at a specified rotational speed under a prescribed
load at a controlled temperature. The test duration
standard is 1 hour. The diameters of the wear scars on the
stationary balls are measured after completion of the test
(Figure 2).
Figure 4:
Grease Worker
Roll Stability Test: ASTM D 1831
In the Roll Stability Test, a small sample (50 grams) of
grease is rolled at 165 rpm for a specified period of time
under a given temperature. The difference in worked
penetration measured with 1/4 scale penetrometer before
and after rolling is reported (Figures 5 and 6).
Figure 2: Four Ball Wear set up
Figure 5:
Rolls
Mechanical / Shear Stability:
Shear stability is the ability of grease to resist changes
in consistency when subjected to mechanical work. The
most common laboratory tests used to evaluate shear
stability are described below:
Worked Penetration (extended worked stability):
ASTM D 217, DIN 51804
It consists of subjecting the grease in a standard
penetration cup in a grease worker to a number of double
strokes (1 k, 10 k, 100 k, etc…). The difference between
worked penetration before the test and the worked
penetration after the test determines the shear stability
and is reported
as the change
from the original
figure (Figures 3
and 4).
Figure 6: Roll
Stability Tester
Water Resistance:
This can be evaluated by using three different
procedures that complement each other. The following
test methods were used in this study:
Water Washout Test: ASTM D 1264
Method consists of a standardized bearing with front
and rear shields having a specific clearance. The bearing
is packed with 4 grams of grease and rotated at 600 rpm
Figure 3:
Penetrometer
20 VOLUME 79, NUMBER 1
–
under a jet of water at a given temperature for one hour.
At the end of the hour, the bearing is removed, dried and
weighed. The weight loss is reported (Figure 7).
Wet Roll Stability: ASTM D 1831 (modified)
Method consists of running the roll stability test, but in
the presence of water. Process water may be used instead
of distilled water. Visual inspection of the grease and its
penetration change after the roll, along with the presence
of free water and its quantity; are determining factors for
the water resistance characteristics of the grease.
Corrosion Resistance:
In wet applications such as those in steel mill
environments, greases are expected to assure protection
against steel rusting. Two tests are considered in this
program:
Rust Test: ASTM D 1743
Method consists of running a tapered roller bearing
packed with 2 grams of the grease. The bearing is rotated
under a given thrust load for 60 seconds to distribute
the grease uniformly. The bearing is then immersed in
distilled water without breaking contact between cup and
cone and stored at 52°C and 100% humidity for 48 hours.
At the end of the 48 hours, the bearing is removed,
cleaned and inspected for rusting. A corrosion spot of 1.0
mm or longer is an indication of failure. Only pass or fail
ratings are used. Run in the presence of process water,
this test gives an accurate indication of the corrosion
resistance characteristics of lubricating grease (Figure 9).
Figure 7: Water Washout Tester
Water Spray-off Test: ASTM D 4049
This test method consists of subjecting a layer of grease
at a given thickness on a stainless steel panel to water
spray off. The grease is sprayed with 40 psi water at a
given temperature for 5 minutes. The panel is then dried
and weighed. Spray off resistance is reported as the
percentage weight of grease removed by the water spray
(Figure 8).
Figure 9: Bearing Spinnerfor ASTM D 1743
Figure 8: Water Sprayoff Tester
21 NLGI SPOKESMAN, MARCH/APRIL 2015
–
NLGI
EmcorRust Test: ASTM D 6138, DIN 51802
This test method is used to assess the ability of grease to prevent corrosion in rolling bearings
operated in the presence of distilled or process water. It consists of packing a pair of double row
ball bearings with grease and mounting them on a shaft in a housing where a specified amount
of water is added. The bearings are subject to 8 hours run and 16 hours off for three days and
after that they are left for 4 days. The bearings are disassembled and the bearing race is rated for
corrosion (0 to 5: no corrosion to highly corroded surface), (Figures 10 and 11)
Figure 11: Emcor Test housing and bearing
Figure 10: Emcor Test Unit
Table 1: Initial Specification Target
Based on field
experience and after
consultation with a
good number of end
users and OEMs, the
following targets have
been selected (Table 1):
Test
Method
Units
Requirements
Thickening System
—
—
Calcium Sulfonate
Base Oil
-~
—
Mineral
Base Oil Viscosity
ASTM D 445
cSt
460 +1- 46
Worked Penetration,
60 strokes @ 25°C177°F
ASTM D 217
DIN 51804
1110mm
285- 320
kgf
500 minimum
ASTM D 2596
Four Ball EP, Weld Load
DIN 5 1350-4
Four Ball Wear Test, Ball Scar Diameter
DIN 5 1350-5
mm
0.60 max.
Worked Stability (100 k), 25C,
Change from 60 strokes, 1/10 mm
ASTM D 217
% change
+1-10 max.
Roll Stability, RT, 3 h,
Penetration change,
ASTM D 1831
% Change
+1- 10 max.
Roll StabHity, RT, 3 h, 10% water
(distilled), Penetration change
ASTM D 1831
% change
+1- 10 max.
Water Washout, 79C/1 7SF
ASTM D 1264
% Change
5.0 max
Water Spray-off, 100°F, 5 mm
ASTM D 4049
% Loss
35,0 max.
Rust Test, 48 hrs ~ 52°Cl126°F
ASTM 0 1743
Rating
Pass / Fail
Pass
Emoor Test
ASTM D 6138
DIN 51802
Rating
011 max.
ASTM D 2266
– 22 VOLUME 79, NUMBER 1
NLGI
Evaluation of Commercially Available Products:
Nine commercially available products based on different thickening systems have been
subjected to a series of tests including water washout, water spray-off, roll stability in
presence of process water and rust test as per ASTM D 1743. Different process waters
are considered in this program. The results for the nine greases and calcium sulfonate
grease prototype, P5606 are displayed in Table 2 below:
Table 2: Evaluation of commercially available products vs. prototype (Process Waters)
Process Water I (Steel Mill Plant I)
Product
P5606
CAP 1
CAP 2
CAP 3
CAP 4
CAPS
CAP 6
CAP 7
CAP 8
CAP 9
26.93
42.88
78.97
72.66
64.56
74.66
56.11
21.02
46.27
74.60
% Loss
0.47
8.73
0.00
1.30
1.25
7.94
0.91
0.91
0.61
4,93
Rust, D1743
Pass? Fail
Pass
Pass
Pass
Pass
Pass
Pass
Fail
Pass
Fail
Roll Stab. D 1831, 3
hrs,RT,%change
-1.6
-2.7
-0.3
-1.4
11.0
-13.6
-4.8
6.2
-8.10
5.1
WSO, D 4049
% loss
WWO, D 1264
1j
I
j
Pass
Pro~ssWater2 (Steel MIII Plant2)
WSO~ D404S
% toss
29.0W
64.17
B1~3
79.70
8333
78.69
6732
22.74
~2.73
6326
% Loss
1,43
726
•21.82~
4A4
1,14
0.59
9.07
2A2
1A3
6.44
Rust. 01743
Passf~Fal1
Pass
Pass
Pass
F44~
Faff
Pass
Fall
Pass
PalE
RoIL S(ab. 0 1831, 3 ft
R1 % oIiange
~4~8
~t5
4~
~-2,8
4~4
4.1
112
~16$~
4.6
WWO~ ~ 1264
Pass
40,0
~
~
P5606: Prototype
CAP 1, 2,….’ Commercially Available
Product 1, 2,….
WSO: Water Sprayoff
WWO: Water Washout
The graphs of Figures 12, 13 and 14 reproduce the
above results, showing the effect of process water on
each product. The results showed that none of the
commercial greases met all three performance targets set
for measuring water resistance and mechanical stability.
On the other hand, calcium sulfonate prototype easily
met the targets and specification limits were made more
stringent as shown in Table 3.
–
23
–
NLGI SPOKESMAN, MARCH/APRIL 2015
Figure 12: Water SprayoffData obtained on Commercially Available Products
Water Spray Off
J
~r
~
I~)
1
R
2
W3tr~ ~I
1~
~
A
zl
~
I
PriL
L
W~trr
JI’
27
14(A
1
612h
2
I
~t
1
1
441
ti~ S~ec~fca~ion
F oi Sc~ic~don
~‘
Figure 13: Water Washout Data obtained on Commercially Available Products:
Water Wash Out
1400
1100
1000
~00
I
ii
600
4~00
100
~2.00
I
~ Process Water 1
P~600
CA?
CAPI
833
(AP2
0.00
CAP3
1.30
CA~4
135
CAP1~
734
CAP6
0.91
CAP~7
0.91
CAP8
0,61
CAP9
4.93
~ Process WaLer 2
1A3
735
-2134
1.44
1.14
0.59
5.07
2.42
1A3
6,44
~ Process Water 3
1,9
26.0
22.2
0.2
12.1
1.4
0.2
5.0
0.2
t6
Figure 14: Wet Roll Stability Data obtained on Commercially Available Products:
Roll Stability
12.00
10.00
3.00
1
6.00
I
200
I
—
-4.00
-6.00
-8.00
-10.00
-12.00
PS606
(API
(.AP2
(AP3
(AP4
(AP6
(API
CAP3
~ Proce~ Water 1
160
2,70
-0.30
-L40
1t00
-13.60
-4.80
6.20
8.10
5,10
~ Process Water 2
hA Process Water 3
-1.60
-1.50
400
-2.80
-lAO
-10(X)
-3.10
11.30
-10,30
4.30
1,90
8 00
1 60
340
1010
8 30
340
11,30
450
3.30
Method
Units
Requirements
Prototype
P5606
Thickening System
—
—
Calcium
Sulfonate
Calcium
Sulfonate
Base Oil
—
—
Mineral
Mineral
Base Oil Viscosity
ASTM D 445
cSt
460 ÷1-46
460
Worked Penetration,
60 strokes @ 25~C/77~F
ASTM D 217
1/10 mm
285-320
304
Four Ball EP, Weld Load,
ASTM D 2596
Kgf
500 minimum
800
Four Ball Wear Test, Ball Scar
Diameter,
ASTM D 2266
mm
0.60 max
0,46
Worked Stability (100 k), 25C,
Change from 60 strokes, 1/10
mm,
ASTM D 217
% change
+/-10 max
+
Roll Stability, RT, 3 h,
Penetration change,
ASTM D 1831
% Change
+1- 10 max
+4.8
Roll Stability, RT, 3 h, 10% water
(distilled), Penetration change,
ASTM D 1831
% change
2.0 max (for 10
initially set)
-1.9
ASTM D 1264
% Change
2,0 max (for
5.0 initially set)
1.9
Water Washout, 79C/175F,
28.4
Pass
Test
Final Spec~fication
Target:
Based on the data
obtained above, a new
specification target has
been established for the
prototype grease in terms
of water and corrosion
resistance. Table 3
regroups these data as well
as the results obtained on
the prototype:
Table 3: Final
Speqfication
Requirement
and Prototype
Characteristics
(AP9
Water Spray-off, 100~F, 5 mm,
ASTM D 4049
% Loss
30.0 max (for
35.0 initially
set)
Rust Test, 48 hrs ~ 52°C/126°F
ASTM D 1743
Rating
Pass
ASTM D
6138,
DIN 51802
Rating
Oil max
EmcorTest
5.3
0/0
NLGI
The above results indicate that the prototype meets
all of the revised requirements. It displays outstanding
results in terms of load carrying capacity, wear, water
resistance, mechanical stability as well as corrosion
resistance.
Field trial
A trial has been conducted for 12 months in the process
downstream of the curved section of a six strand bifiet
caster. This covers the extractors, straightener section,
runout table to cutting torches, runout table to cooling
bed, lifters, cooling bed, walking bed pivots and transfer
car.
Mechanical Stability & Water Resistance
Although the grease consumption has been significantly
reduced at the start of the trial, a generous amount of
grease still remains in the bearing 12 months later. This
indicates excellent mechanical stability, advanced water
resistance and extremely good tackiness to keep the
grease in place.
Pumpability, Dispensability, and Mobility
The above picture as well as the field inspection
reports indicate that the grease was present in large
amounts in all the bearings inspected, demonstrating a
good pumpability through the dispensing systems and
mobility in the bearing.
This demonstrates the flexibility of the grease; one
product can be used in many areas, consolidating stock
and making lubrication tasks a lot simpler.
Field Trial Results
Grease Consumption
Using the evaluation data in comparison with the
performance of a previous grease in application, it was
possible to reduce the grease consumption by 50%. This
reduction in consumption resulted mainly from the
improved mechanical stability as well as water resistance.
Further reductions were possible, but the centralised
grease system was not flexible enough to further
optimize grease consumption without risking the damage
of critical components lubricated by the system. This
level of consumption set up was maintained until the
lubrication system constraints are over-hauled.
This reduction in grease consumption has resulted in
a lower pumping rate through the lubrication system
pipe work, eliminating the risks of blocking the line, and
therefore assuring permanently the dispensing of grease
to the bearings. Figure 15 shows the condition of the
grease inside a bearing housing before cleaning ready for
inspection.
4*
Figure 15: Bearing, Pre Inspection
Noise Reduction
The specificity of the calcium sulfonate greases, which
by definition contain a much larger amount of thickening
system in comparison with the conventional greases and
when also enforced with solid lubricants, this grease will
have the capacity of assuring the presence of a strong
film between the lubricated surfaces. This film will
contribute to the amortization of the shock loading and
therefore reducing or eliminating the noise. Effectively
the operators have reported that in the walking beam
area, where the plain metal bearings of the pivots used to
be very noisy, due to metal on metal contact under high
temperatures and low speeds, after using the prototype
product, no noises were noticed. During the final
inspection after 12 months trial, the end user confirmed
26 VOLUME 79, NUMBER 1
NLGI
that the prototype grease had prevented damage within
these critical bearings.
elements, and the grease did not form hard deposits
High Temperature Performance
On two occasions during the trial period, pipe work
for the internal cooling of the continuous caster roller
bearings failed.
This can be quite a common occurrence with flexible
pipe work, and failures mean that bearing temperatures
will raise very quickly, leading to seized bearings. This
causes production quality issues, as the billet surface
finish will be affected by sliding instead of rolling over the
rollers.
Figure 16: Bearing in normal conditions
The bearing housing and grease pipe work in the
immediate vicinity will also be subjected to extreme heat;
some greases will form hard deposits in this situation and
will require pipe work and bearing housing replacement
as well as a bearing change.
During the trial with the prototype grease, the end
user reported that cooling water supply to one roller had
failed for a period of between 24 and 48 hours. It was
not possible to stop production, so the affected bearings
had to remain in place after the cooling water system was
repaired. Cast product quality was monitored, and no
quality issues were reported.
At the next available maintenance opporthnity the
bearings were removed from their housings and changed;
however, upon further inspection they were found to
be in a serviceable condition. Furthermore, grease pipe
work did not need to be replaced. Grease within the
bearing housings also remained mobile, significantly
reducing maintenance time after the cooling water failure.
Pictures of a used bearing running in normal
conditions, and one subjected to extreme heat, are shown
below (Figures 16, 17).
Discolouration of the brass cage can clearly be seen on
the heated bearing, but all roller elements remained free
to rotate and clearances were measured and found to be
within tolerances defined by the end user.
No scoring marks could be seen on the bearing
Figure 17: Heated Bearing
Bearing Life
A selection of bearings were inspected jointly with the
end user, and the remainder were inspected by the end
user’s maintenance team. All bearings were found to
be within a specified tolerance and deemed suitable for
further use.
Historically, bearings have been replaced every three
years as a preventive measure to avoid unplanned
downtime. Bearings reaching three year life were
also found to be suitable for further use, minimizing
bearing replacement costs across the whole of the caster
installation. It is fully expected that these three year old
bearings will not require replacing during the next 12
monthly maintenance period.
NLGI
Even when considering a minimum of 25% life
extension then the reduction in spare parts alone is
significant, but the end user is confident that bearing life
can be extended even further. This will be confirmed
after the next 12 month maintenance period.
Corrosion Resistance
No staining or corrosion was visible in any of the
bearings inspected during the maintenance period,
indicating that the grease performs extremely well
in being able to resist corrosion from the chemical
aggressiveness of process waters in use in the plant
Conclusion
Key parameters selected to prove the capabilities of
the product were high temperature performance, load
carrying capability, performance in wet environments
and extended component life.
Taking the performance of greases with a similar
technology platform, an initial specification was shaped
to benchmark a new development product, targeting
high load performance, water resistance, corrosion
prevention and mechanical stability (also in the presence
of process water).
A continuous caster was selected for a field trial. This
application is well known to be a critical area requiring
high performance in lubrication to avoid costly
breakdowns and increased maintenance.
After the 12 month trial period, the performance was
evaluated with the end user and the following benefits
were observed:
• Grease consumption reduced by 50%
• Grease still appears to have the same consistency as
the new product
• No signs of corrosion or surface staining
• Bearing tolerances remained within specification
• Bearing life extended from thtee to four years, most
likely longer
In addition to the points listed above, the grease did
not block pipe work when subjected to extreme heat,
giving the added advantage of minimising associated
maintenance work.
Acknowledgements
Authors would like to thank Luis Blazquez, Soman
Dhar, and the customer for the valued contribution to
the product field testing
References
1. C. White, Lubrication, Vol. 77, Nr 1, 1991
2. NLGI Lubricating Grease Guide, Second Edition,
1989
3. A.E. Cichelli, Evaluation of Greases For Steel Mill
Service, NLGI Spokesman, August 1973
4. A.E. Cichelli, Grease Lubrication in Steel Mills
with Emphasis on Roll Neck Bearings, NLGI
Spokesman, April 1980
5. J. Schlobohm Sr., H. Faci, B. Cisler, Steel Mill
Greases: Evaluation and Analysis,
presented
at the 71st NLGI annual meeting, Dana Point, CA,
2004
6. P. Booker, H. Faci, M. Totten, M. Maass “Advanced
Lubrication of Steel Mill Components. Long term
solution for Extreme Conditions”, Presented at the
26th ELGI Meeting, April 26-29, 2014
7. Gareth Fish, William C. Ward, Calcium Sulfonate
Answers to Water Issues, presented at the ELGI
25th Annual Meeting, Amsterdam, April 20-23,
2013
8. David Autier and al. Calcium Sulfonate Greases. A
solution to Water Resistance, presented at the ELGI
25th Annual Meeting, Amsterdam, April 20-23,
2013
9. Johan Leckner, Water + Grease: Fatal Attraction,
presented at the ELGI 25th Annual Meeting,
Amsterdam, April 22-23, 2013
10. Hocine Faci, John Haspert, Effect of Water on
Grease Performance and Lubrication for life in
sealed bearings, presented at the NLGI 80th Annual
Meeting, Tucson, AZ, June 15-18, 2013.
– 28 VOLUME 79, NUMBER 1