Water Washout Resistant property-an outlook - (NLGI)

Water Washout Resistant property-an outlook - (NLGI)
Water Resistance Property of Greases – An Outlook
B S Nagarkoti
E-mail: bhagwat@hpcl.co.in
A K Jain, C S Krishnaswamy
Hindustan Petroleum Corporation Limited, R&D Centre, Plot D - 500,
T T C Industrial Area, Turbhe, Navi Mumbai - 400 703 , India
Abstract
In rolling mills of steel plants, cold rolling oil emulsion is used as coolant and lubricant for
rollers. Normally simple Lithium soap, mixed soap (Lithium and Calcium) based and Lithium
Complex greases are used for lubrication of bearings. In recent time Overbased Calcium
Sulfonate complex based grease is also being used predominantly as lubricant in the bearings
supporting the rollers. But due to continuous high ingress of water/emulsion, in some cases this
grease also gets emulsified due to absorption of water and looses its structure. Due to drop in
consistency, the grease is washed away from the bearings. As a result frequent re-lubrication is
required in bearings which causes production loss and high production cost. In order to maintain
its structure, the grease is required to have good water repellency in addition to water tolerance
property. By making grease water repellent, the water tolerance/resistance limit can be extended
and resultant water washout and water spray-off property can be improved. Thus life of grease
and bearings can be increased substantially. We have attempted to study the water washout
resistant property of four different soap based greases by incorporating two different types of
polymers viz. high molecular weight polymer and specially designed hydrocarbon resin polymer
in these greases. The water washout and water spray off tests were conducted of these greases
with these polymers. The water washout and water spray off tests were also conducted in base
greases (without these additives). Other performance enhancing additives like EP/Antiwear,
antioxidant and rust and corrosion inhibitor were also incorporated to meet requirement of high
performance grease. These greases were tested for all other test parameters also. Lot of
improvement was achieved in water washout resistant and water spray-off properties in these
greases. The grease specimen has enhanced high temperature thermal/oxidation stability, rust
and corrosion inhibition property, good shear/ mechanical stability and high load carrying
capacity as expected.
Introduction
The present work relates to study the water washout resistance and water spray-off resistant
properties of two different types of polymers in four different soap type greases. The greases
used in steel plants are more susceptible to water washout due to heavy water ingress in hot &
cold rolling mills. Therefore selection of proper grease is very important for successful running
of rolling mills. Normally simple Lithium soap, mixed soap (Lithium and Calcium) based and
Lithium Complex greases are used. These greases are emulsified with huge quantity of water
thus not able to withstand the force of water sprayed on bearing and washed away from the
bearing. Therefore Overbased Calcium Sulfonate complex based grease is introduced and being
used predominantly. But due to continuous high ingress of water/emulsion it absorbs lot of
water and grease gets emulsified and deterioration of grease structure takes place. Normally 300
and 400 BN calcium sulfonate is used for making calcium sulfonate complex greases. Total
Base Number (TBN) of calcium sulfonate used for making Calcium sulfonate complex grease,
also play a crucial role in water resistant and water spray-off resistant property. Higher the TBN
of Calcium sulfonate about 400, better the water wash out and spray-off resistant property,
whereas, the calcium sulfonate with 300 TBN have less water resistance and tolerance than 400
TBN calcium sulfonate. Though the Calcium Sulfonate complex grease has good water
absorption and water tolerance property at lower consistency and retaining its structure, but this
tolerance limit decreases at higher consistency side, as a result break down of grease structure
takes place and grease is washed away due to continuous spray/ingress of water. As a result
frequent re-lubrication is required in bearings. Additionally, the water washout property and
water spray off property is also related with consistency of grease and the viscosity of base oil
used for making grease. Lower the consistency and higher the base oil viscosity, better the
washout and spray-off resistance property. Grease in NLGI 3 range is not suitable for centralized
lubrication system. But in rolling mills, the grease made with high viscosity oils also not able to
withstand force of water and rolling oil emulsion. Since in steel plants bearings are lubricated
through centralized lubrication system, the consistency need to be adjusted at higher side i.e.
between NLGI 2 and NLGI 1.5 consistency range having high water resistant and water sprayoff property, good structure/shear stability and the mechanical stability even in the presence of
water ingress. In order to maintain its structure and remain inside the bearings, the grease is
required to have good water repellency in addition to water tolerance property. By making grease
water repellent, the water tolerance/resistance limit can be extended and resultant water washout
and water spray-off property can be improved. This can be achieved by use of high molecular
weight polyisobutylene and specially designed hydrocarbon resin polymer (neopolymer) in these
greases. The greate advantage of hydrocarbon resin is they are very good water repellant, highly
hydrophobic and shear stable. Due to better water repellency, they will not soften and washed
away even in hot water. Thus the grease will remain in bearing and the life of grease and
bearings can be enhanced substantially. They are more water repellant than polymers and
penetration of water will be less in grease and retention of grease structure and water resistant
will be higher. This hydrocarbon resin gives extra tackiness and embodiment to grease. Due to
these characteristics they are preferably used in water resistant paint for longer life. The
Performance of the grease was bench marked with respect to water wash out resistant, water
spray-off resistant properties, the structure/shear stability and load carrying properties.
Experimental Details
Four different soap type greases were prepared by conventional method. The fatty acids for all
the three types of greases were kept same. In first experiment the base oil viscosity of all the
three grease types was kept in ISO VG 150, whereas of calcium sulfonate complex grease it was
kept ISO VG 180. The consistency of all the four types different soap types greases was kept in
NLGI 3 consistency range between 244 to 246. The water washout tests were conducted on these
four greases. In second experiment the consistency was raised from NLGI 3 to NLGI 2 with
consistency range between 274 to 276. Water washout test was conducted for these greases. In
third experiment the base oil viscosity was further increased from ISO VG 250 to ISO VG 220
but consistency of the greases was maintained between 274 to 276. Water washout test was
conducted for these greases. In fourth experiment the base oil viscosity was further increased
from ISO VG 220 to ISO VG 320 but consistency of the greases was maintained between 274 to
276. Water washout test was conducted for these greases. In fifth experiment water wash out test
was conducted for greases having different base number of over based calcium sulfonates used
for making calcium sulfonate complex greases. Because Total Base Number (TBN) of calcium
sulfonate used for making Calcium sulfonate complex grease, also play a crucial role in water
resistant and water spray-off resistant properties. The base oil viscosity of both the greases was
maintained in ISO VG 320 and consistency in NLGI 2 at 275. Since in steel plants water ingress
is very high, the grease need to have very good water washout and water spray-off resistant
properties, therefore the losses due to water washout and water spray should be minimal. In order
to achieve these two different types of polymers viz. high molecular weight polymer and
specially designed hydrocarbon resin polymer were tried at same treat level in these greases to
enhance the water washout resistance and water spray-off resistant properties. Again water
washout tests were conducted in all four different soap types greases. Other performance
enhancing additives like EP/Antiwear, antioxidant and rust and corrosion inhibitor were also
incorporated to meet requirement of high performance grease. These greases were tested for all
other test parameters in addition to water washout resistance and water spray-off resistant tests.
The water resistant properties were checked for all the four grease specimens before addition of
these polymers. The details of types of greases are as under.
1.
2.
3.
4.
Simple Lithium soap grease
Lithium/Calcium mixed soap grease
Lithium Complex grease
Calcium Sulfonate complex grease
Results and Discussion
The test results of water washout and water spray-off properties of base greases prepared in
NLGI 3 are provided in Table 1. The water washout value of simple lithium grease,
Lithium/calcium mixed soap, lithium complex greases are about 5 to 6%, whereas in case of
calcium sulfonate complex grease it is 3.6%. With rise in consistency of all the greases the loss
due to water washout has almost doubled in all the greases. The results are provided in Table 2.
It is clear that with increase in consistency the water wash out loss increase due to less adhesive
property of grease as water can penetrates easily in thinner grease. However, when viscosity of
base oil in grease is increased from ISO VG 150 to 220, the losses due to water wash out can be
improved about 15 to 20%. The results are provided in Table 3 when the base oil viscosity was
further increased from ISO VG 220 to ISO VG 320, the losses due to water wash out could be
further reduced from 16 to 20% in different soap type greases. The results are provided in Table
4. In recent time, Overbased Calcium Sulfonate complex based grease is also being used
predominantly in steel plants. As the Total Base Number (TBN) of calcium sulfonate used for
making Calcium sulfonate complex grease plays a crucial role in water resistant and water sprayoff resistant properties. The Water washout test was conducted of two calcium sulfonate complex
greases having 300 and 400 TBN. The results are provided in table 5. It can be observed that
calcium sulfonate used for making grease having high base number i.e. 400 TBN has shown
better water washout resistant property than lower base number i.e. 300 TBN calcium sulfonate.
The grease having 400 TBN has water washout loss 4.28% whereas grease is having 300 TBN
has shown water washout loss 5.33%. But these losses are also very high. And grease will be
washed away from the bearing shortly. Therefore this limit need to be reduced minimal level. In
order to make grease more water washout and water spray-of resistant two different types of
polymers viz. high molecular weight polymer and specially designed hydrocarbon resin polymer
were tried at equal treat level in these greases to enhance the water washout resistance and water
spray-off resistant properties. The water washout resistances of simple lithium soap grease come
down from 8% to 5% with both the polymers. In lithium calcium mixed soap grease from 6.4%
to 2% and 2.1% with polymers with P1 and P2 respectively. In lithium complex from 6.5% to
4.4% and 4.5% with polymer P1 and P2 respectively. And in calcium sulfonate complex grease it
has come down from 4.29% to 1.97% with polymer P1 and 2.1 with polymer P2. The results are
provided in table 6.
Conclusions
The water washout loss of greases increases with increase in penetration/consistency of grease.
The water washout loss of greases reduces with increase of mineral oil viscosity used for making
greases. The base number of over based calcium sulfonate used for making calcium sulfonate
complex grease also plays a role in improvement in water washout and water spray-off resistance
properties. Higher the base number of calcium sulfonate used for making grease lower the losses
of grease due to water washout. Use of water repellent is essential for making grease more water
washout resistant and water spray-off resistant. By making grease water repellant water tolerance
limit of greases can be extended thus greases will be most water resistant. The hydrocarbon resin
polymer used for making water resistant grease has also comparable water washout resistant
properties with high molecular weight polymer used currently.
Table 1. Test Results of water washout properties of base greases (grease
consistency NLGI 3)
Grease type
Grease consistency
60 X (NLGI 3)
Base oil viscosity
@ 40°C (cSt)
Water Washout,
ASTM D1264
79°C % loss
Simple Lithium soap
Lithium/calcium
mixed soap
Lithium Complex
Calcium sulfonate
complex
245
244
150
150
6
5
246
245
150
180
5
3.6
Table 2. Test Results of water washout properties of base greases (grease
consistency NLGI 2)
Grease type
Simple Lithium soap
Lithium/calcium
mixed soap
Lithium Complex
Calcium sulfonate
complex
Grease
consistency
60 X (NLGI 2)
Base oil viscosity @ 40°C
(cSt)
Water Washout,
ASTM D1264
79°C % loss
274
276
150
150
12
10
275
276
150
180
10
6.8
Table 3. Test Results of water washout tests of base greases with higher
viscosity base Oil (ISO VG 220 )
Grease type
Simple Lithium soap
Lithium/calcium
mixed soap
Lithium Complex
Calcium sulfonate
complex
Grease
consistency
60 X (NLGI 2)
Base oil viscosity @40°C
(cSt)
Water Washout,
ASTM D1264
79°C % loss
274
276
220
220
9.5
8
275
276
220
220
8
5.1
Table 4 Test Results of water washout properties with higher base oil viscosity
(ISO VG 320)
Grease type
Simple Lithium soap
Lithium/calcium
mixed soap
Lithium Complex
Calcium sulfonate
complex
Grease consistency
60 X (NLGI 2)
Base oil Viscosity @40°C
(cSt)
Water Washout,
ASTM D1264
79°C % loss
274
276
320
320
8
6.4
275
276
320
320
6.5
4.29
Table 5. Test Results of water washout properties of Calcium sulfonate grease
with different base number without polymer
Grease type
Grease consistency,
60 X
Base oil Vis @40°C
(cSt)
Calcium sulfonate
complex
275
320
Water Washout,
ASTM D1264
79°C % loss
300 BN
400 BN
5.33
4.28
Table 6. Test Results of water washout tests of greases (with two different
polymers)
Type of polymers
1. Hiigh Molecular Weight polymer (P1)
2. Hydrocarbon resin polymer (P2)
Grease type
Grease consistency
60X (NLGI 2)
Base oil Vis @40°C
(cSt)
Water Washout,
ASTM D1264
79°C % loss
P1
P2
Simple Lithium
Soap
Lithium/calcium
mixed soap
Lithium Complex
Calcium sulfonate
complex
274
320
5
5
276
320
2
2.1
275
278
320
320
4.4
1.97
4.5
2.1
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