Lubrication

왎 General principals of lubrication 122

Choosing the type of lubrication 122

Grease lubrication 123

왎 Characteristics of greases 123
왎 Greasing recommendations 124
왎 Choice of grease according to the application 125
왎 Quantity 128

Oil lubrication 131

왎 Lubrication systems 132
왎 Quantity of oil 134
 Lubrication

General principals of lubrication

Lubrication is essential for optimum bearing

performance. direction
70% of bearing failures are due to lubrication of rotation
load
problems.

thickness
The aim of lubrication is to provide a film of
of lubricant
lubricant (oil film) between the rolling elements film
and the raceway of the bearing in order to
prevent wear and seizure of the components in
contact. Pressure diagram

The lubricant also provides protection against s1

oxidation and external contamination, and s2
can have a cooling effect in the case of
recirculating oil.

The service life of the bearing is directly related to the efficiency of the lubricant film, which
depends on:
• the nature of the lubricant and its speed and temperature capabilities...
• the load and speed of rotation of the bearing
The influence of lubrication on the bearing life can be determined page 77.

 Choosing the type of lubrication

Oil lubrication Grease lubrication

◗ Good penetration in the bearing ◗ Cleanliness of the mechanism
◗ Good physical and chemical stability ◗ Sealing easier to secure
◗ Cooling possibility ◗ Protection barrier
Advantages ◗ Easy monitoring of the lubricant: condition ◗ Assembly simplicity
and levels ◗ Ease of manipulation
◗ Reduction or elimination of relubrication
◗ Possibility of using pre-greased bearings

◗ Necessary to effectively seal the assembly ◗ Higher friction coefficient than for oil
◗ Poor protection against oxidation ◗ Poorer dissipation of heat
and moisture in case of long stops ◗ Replacement (if necessary) requires dismounting
Disadvantages ◗ Starting delay when circulation and washing of the bearing
of oil is necessary prior to rotation ◗ No possibility of checking the level of grease,
therefore it requires reliable grease retention
or periodic addition to compensate for leaks,
contamination or ageing

122
Grease lubrication
Characteristics of greases

왎 Grease is a product whose consistency ranges from semi-fluid to solid and which is
obtained by dispersing a thickening agent (soap) in a liquid lubricant (mineral or synthetic oil).
Additives can be included to bring certain specific properties.
The increasing use of grease-lubricated bearings combined with the development of the
life-lubrication concept, has made grease an integral component of the bearing. The service
life of the bearing and its behaviour in diverse environments are largely determined by the
properties of the grease.

왎 Physical and chemical characteristics:

NLGI Kneaded Consistency
Consistency grades penetration
◗ NLGI (National Lubrication Grease Institute) 0 385 - 355 Semi-fluid
grades correspond to a value of penetration 1 340 - 310 Very soft
in the kneaded grease (per test specification 2 295 - 265 Soft
ASTM/D217). 3 250 - 220 Moderate
◗ The consistency generally chosen for 4 205 - 175 Semi-hard
bearings is grade 2.
Viscosity of the basic oil: usually defined in cSt (mm2/s) at 40°C (104°F).
Density: 0.9 approx.
Drop point: temperature at which the first drop of a grease falls from a sample.
Approximate temperature: 180°C (356°F) to 260°C (500°F) depending on the constituents of
the grease. The maximum service temperature of the grease is always far below the drop
point.

왎 Functional characteristics
The conditions under which the lubricant works (rolling, kneading) require special bearing
greases that cannot be selected only on the basis of the physical and chemical characteristics.
The SNR Research and Test Centre constantly performs qualification tests on bearings that
enables us to give advice on the recommended grease for the application.
The qualification specification concerns the following basic criteria:
• endurance in ball bearings • adherence when exposed to centrifugal
• endurance in roller bearings forces
• water resistance • vibration resistance (false Brinell effect)
• high and low temperature resistance • high speed adequacy, etc.

These criteria may be met in order to satisfy the customer’s goal. The selection for an
application is a compromise between the required specifications and the available


greases.

123
 Lubrication
Grease lubrication (continued)

Greasing recommendations

Sealed and shielded bearings are fitted with grease before packing. With the other bearings,
the grease must be added with great care in order not to reduce bearing performance.

왎 Method to apply the grease

Cleanliness is essential
Any foreign body in the grease can cause the premature destruction of the bearing.
• Thoroughly clean the area around the bearing
• Protect the grease containers against contamination
• The use of a grease gun provides a guarantee of cleanliness

The grease must be applied as close as possible to the active parts of the bearing (race-
ways and rolling elements)
Insert the grease between the cage and the raceway of the inner ring, especially where
angular-contact or spherical or self-aligning bearings are concerned.

For each assembly, record the date of past and future lubrications, and the type and weight
of grease
◗ Assemblies and bearings with lubrication devices
• Clean the lubricator head
• Get rid of all foreign particles
• Check and clean the spout of the grease gun
• Introduce the grease
• Pay particular attention to the quantity introduced
• Remove the old grease at every 4th or 5th relubrication
• When relubrication is very frequent, provide a system for removing the old grease

◗ Assemblies and bearings without a greasing device

Carefully clean the assembly before opening it
• Remove the old grease with a non-metallic spatula
• Introduce the grease between the rolling elements on both sides
• Grease the shields and seals

124
왎 Greasing devices

Manual packing Lubrication with a grease gun SNR Automatic Lubricator

Grease fitting

Choice of grease according to the application

왎 The choice of grease is based on the knowledge of the operating conditions, which must be
carefully considered: temperature, rotation speed, load, environment, vibration, application-
specific constraints.
Ask your SNR ROULEMENTS contact for assistance in choosing the grease for your application.
The table on the following page will help to make an initial choice.

왎 There are two types of operation

Normal operating conditions
SNR recommends two types of greases:
◗ SNR LUB MS: for assemblies on machines, agricultural machinery, electric motors, handling
equipment, pumps
◗ SNR LUB EP: for heavily-loaded bearings (iron and steel industry, civil engineering)
Special operating conditions
The application specifications will be studied in close cooperation with SNR ROULEMENTS in
the following cases:
• Continuous operating temperature above • Centrifugal forces (outer ring rotating)
+100°C (212°F) or below –30°C (-22°F) or vibration
• Speed greater than 80% of the bearing • Low torque
maximum speed • Presence of hydrocarbons
• Moist environment • Nuclear radiation, etc.

The viscosity of the base oil is of great importance for lubrication efficiency. The diagram on
page 78 can be used to check lubrication efficiency for your application.
The majority of general-purpose greases can be mixed with one another. However, to obtain
the best result avoid mixing greases (the mixing of certain special application greases is
forbidden).
SNR can supply sealed and shielded bearing pre-greased with a type of grease that is appro-
priate for the application (see technical range bearings or check minimum order quantity).

125
 Lubrication


Choice of grease according to the application

Predominant Service limits Examples of SNR LUB

operating General recommendation
Temp. °C (°F) Speed applications recommendation
conditions
◗ Mineral oil ◗ Automobiles
◗ Traditional soap (lithium, calcium…) ◗ Agricultural
◗ Consistency: usually grade 2, grade 3 machinery
- 30 (-22) < max.
Standard for large bearings or bearings with ◗ Common
up to speed of LUB MS
use particular operating characteristics mechanisms
+120 (+248) bearing
◗ Drop in performance above 80°C (+176°F) ◗ Handling
in continuous operation, certain applications equipment
can require a better suited grease ◗ Electric tools

-30 (-22) < 2/3 max. ◗ Iron and steel

High ◗ Similar to standard greases industry
up to speed of LUB EP
load with extreme pressure additive ◗ Civil engineering
+110 (+230) bearing
equipment
-30 (-22) < 2/3 max. ◗ Class-E electric
up to speed of motors
+130 (+266) bearing ◗ Traditional soap with high-viscosity
◗ Class-F electric LUB HT
mineral-base or synthetic oil
-20 (-4) up to motors
+150 (+302) ◗ Alternators
◗ Furnace
High -20 (-4) ≤ 1/3 max. ◗ Entirely synthetic greases equipment
temperature up to speed of ◗ Greases with silicone-base oil have ◗ Class-H electric LUB THT
+200 (+428) bearing reduced resistance to loads motors
◗ Couplers
◗ Synthetic products in solid or paste ◗ Furnace
-20 (-4) to < 1/5 max. Consult
form equipment
+250 (+482) speed of SNR
bearing ◗ Poorly miscible products ◗ Kiln cars

≤ 2/3 max. ◗ Basic oil of very low viscosity ◗ Aviation

Low up to
speed of Marginal retention of grease ◗ Special
temperature - 50 (-58)
bearing if temperature above 80°C (+176°F) machines

≤ 4/3 max.
◗ Machine-tool LUB GV+
-20 (-4) spindles
High
up to speed of ◗ Oil of very low viscosity ◗ Wood-working
speed
+120 (+248) bearing machines
◗ Textile spindles
-30 (-22) ≤ 2/3 max.
◗ Conventional grease heavily treated ◗ Washing LUB MS
Moisture up to speed of
with anti-corrosion additives machines LUB EP
+120 (+248) bearing
Centrifugal
≤ 2/3 v2/3
◗ Alternators
forces/ -20 (-4)
◗ Grease with strong adherence ◗ Civil engineering
Vibration/ up to max. speed LUB VX
consistency (grade 2) equipment
Outer ring +130 (+266) of bearing
◗ Loose pulleys
rotating
-30 (-22) ≤ 2/3 max.
Food ◗ Compatible with food processing ◗ Food-processing
up to speed of LUB AL1
industry applications industry
+120 (+248) bearing
High load ◗ Heavy industry :
-5(+23) up to ◗ Suitable for very low speed operation
and
+140 (+284) under very high loads Steel Industry, paper LUB FV
low speed mill Industry, Quarries
Note : The grease must be chosen in collaboration with SNR.

126
 
Characteristics of the SNR LUB product range

MS EP HT GV+ VX THT AL1 FV

Colour Light Light Transparent
Amber Amber Blonde White yellowish
brown yellow
◗ Mineral ◗ Mineral ◗ Synthetic ◗ Di-ester ◗ Mineral ◗ ◗ Mineral ◗ Mineral
oil oil oil oil paraffinic Thickening paraffinic oil
Composition ◗ Lithium ◗ Extreme ◗ Barium ◗ Lithium oil perfluorin oil ◗ Lithium
soap pressure soap soap ◗ Lithium fluid ◗ Complex + calcium
◗ Lithium soap ◗ Teflon aluminium
soap soap
Viscosity of base oil 105 105 150 15 310 390 200 950

Consistance Grade NLGI 2 2 2 2 2 2 2 2

Service -30 (-22), -30 (-22), -30 (-22), -50 (-58), -20 (-4), -20 -20 -30 (-22), -5 (-23)
+120 +110 +150 +120 +130 +120 +140
temperature °C (°F) (+248) (+230) (+302) (+248) (+266) +220 +250* (+248) (+284)
Moderate loads VG G G G VG
P<C/5 G G G
High load NR VG NR NR VG VG NR G VG
P>C/5
Low speed G
N.Dm < 100000 G NR NR VG VG G VG
High speed
N.Dm > 100000 G G G VG NR G G G NR
Moisture,
Presence of water VG VG G VG G G G G
Low amplitude
oscillations G G VG G VG VG G G
Vibration when
stationary NR NR NR VG NR NR NR NR

Adherence G G VG G VG VG G VG

Low torque G G G VG NR NR G NR

Low Noise G G G VG NR NR NR NR
Anti-corrosion VG VG G VG G G G G
protection
Resistance NR NR NR NR NR VG NR NR
to chemical agents
Pump wise VG VG VG VG VG VG VG G
◗ Service ◗ Pay ◗ Approved by
life of special US Food and
grease attention to: Drug
is linked - quantity Administration
Remarks with - shaft - as H1 class
working position
temperature - close active
parts
- grease
retention

N.Dm : Product of the RPM times the mean diameter * Under low load, the THT grease sustains up to +250°C (+482)
VG : Very good performance – G : Good performance Under higher load, thermal strength is limited to +220°C (+428)
NR : Not recommended
127
 Lubrication
Grease lubrication (continued)

Quantity

왎 Initial greasing
The quantity of grease necessary for optimum operation of a bearing must be equal to 20 to
30% of its free internal volume.

Approximate amount of grease

to be introduced into an open bearing G = 0.005 D . B

G: Quantity of grease in g or cm3

D: Outside diameter of bearing in mm
B: Bearing width in mm.

The quantity of grease may be increased by 20% for assemblies provided with a hole for
drainage of the old grease.
A bearing that rotates at very low speed can be fully packed with grease, which favours its
protection in highly contaminated environments (conveyor rollers, etc. )

It is very important that this quantity should be maintained inside the bearing. Check that the
adjacent parts (seals, shields) are capable of limiting the transfer of grease. If there is an
adjacent free space, fill it to 50% with grease.

One can verify that the quantity of grease is adequate if the bearing temperature stays at a level
of 10°C (50°F) to 30°C (86°F) above the room temperature, after a transient state of less than one
hour during which the temperature has peaked at a higher level.

128
왎 Relubrication
Relubrication frequency
The following table can be used to establish the basic frequency in hours according to the type
of bearing and speed of rotation.

Basic frequency (in hours)

Ball bearings

Cylindrical roller
bearings

Tapered roller
bearings

Spherical roller
bearings

Operating speed
Maximum speed

왎 Correction of relubrication frequency

The basic frequency (Fb) must be corrected using factors taken from the table below, accord-
ing to the particular operating conditions of the mechanism, using the relation:

Fc = Fb . Te . Ta . Tt

Factor Conditions Level Value of factor

Environment
- dust - moderate 0.8
Te
- humidity - high 0.5
- condensation - very high 0.3
Application
- with impacts - moderate 0.8
Ta
- with vibration - high 0.5
- with vertical shaft - very high 0.3
75°C 0.8
75° à 85°C With standard With high
0.5 0.8
Tt Temperatures 85° à 120°C 0.3
grease
0.5 temperature
120° à 170°C 0.3 grease

129
 Lubrication
Grease lubrication (continued)

왎 Weight of grease
The opposite table can be used to determine the factor c to be applied, depending on the
corrected frequency in hours to obtain the weight of grease to be added from the relation.

P=DxBxc

Corrected frequency (in hours)

276

0,0028
Coefficient c

Example
A 22212 EA bearing lubricated with a standard grease and rotating at 1,500 RPM in a dusty
environment at 90°C (194°F) with no other application constraints:
22212 – Spherical roller bearing
Service speed/Maximum speed = 1,500 rpm / 3,900 rpm = 0.38
hence the basic frequency: Fb = 2,300 hours (see table of the preceding page)
c = 0,028
Coefficients Diameter D = 110
Te = 0.5 dust Width B = 28
Ta = 0.8 normal Weight of grease:
Tt = 0.3 90°C (194°F) P = 110 . 28 . 0.0028 = 9 grams


Corrected
Fréquencefrequency:
corrigée : Fc
Fc =
= Fb
Fb .. Te
Te .. Ta
Ta .. Tt
Tt =
= 2,300
23,00 .. 0.5
0,5 .. 0.8
0,8 .. 0.3
0,3 =
= 276
276 hours
Heures

130
Oil lubrication
Oil lubrication is generally used when the bearing is adapted in a mechanism that is already
lubricated (gear reducer, gearbox) or else when it can benefit from a central lubrication system
where the oil is also used as a coolant.

왎 Type of oil
Principal oil types used to lubricate bearings.

Synthetic oils
Mineral oils
ester perfluoroalkilether
Special use, usually at high
Comments Standard use
or low temperature
Density 0,9 0,9 1,9
Index 80 - 100 130 - 180 60 - 130
Viscosity
Variation low
high low
with temperature
Freezing point -40 up to -15°C -70 up to -30°C -70 up to -30°C
(-40 up to 5°F) (-94 up to -22 °F) (-94 up to -22 °F)
Flash point < 240° C (464°F) 200 up to 240°C non inflammable
( 392 up to 464°F)
Resistance to oxidation average good excellent
Thermal stability average good excellent
Compatibility with elastomers good to be checked good
Price level 1 3 - 10 500

왎 Viscosity
The choice of the oil viscosity is very important for the efficiency of lubrication. The choice can
be made using the diagram in page 78.
It can be seen from this diagram that life duration increases with the viscosity of the lubricant.
This advantage is nevertheless limited because a more viscous lubricant raises the operating
temperature of the bearing.

왎 Additives
The most commonly used additives are the Extreme Pressure, anti-wear and anti-corrosion
additives. Great care must be used in choosing an additive. One must check with the lubricant
manufacturer to check the influence of the additive on the bearing performance.

Extreme pressure
• Protects metal surfaces against micro-welding
• Necessary when the bearing is highly loaded P>C/5

131
 Lubrication
Oil lubrication (continued)

Anti-wear
Reduces the wear of the metal surfaces by forming a protective surface layer

Anti-corrosion
Protects metal surfaces against corrosive attacks

왎 Contamination
The lubrication oil must be clean.

왎 Special lubricants
In certain assemblies the bearing can be lubricated by the liquid carried in the assembly
(hydraulic fluid, diesel fuel).
In such cases, and for all the lubrication problems mentioned here, check with SNR.

Lubrication systems

왎 Oil bath
Used in closed and sealed mechanisms.
Oil level at the level of the lowest rolling element of the lowest
bearing.
Moderate rotation speed as heat dissipation is limited.

왎 One time usage oil

Shaft rotating at high speed.
Necessary evacuation of the old oil.

132
왎 Dripping and splashing
Oil usually thrown up by the gears.
The oil can be directed to the bearing by channels.

왎 Oil circulation
A pump ensures a constant flow, a reserve compen-
sates for the priming delay starting.
The oil can be filtered and cooled in a heat exchanger to
give better performance.
Oil circulation can sometimes be intermittent.

왎 Oil spray
This is also a low-consumption method of one time
usage lubrication. The oil under pressure spray reaches
all parts of the bearing, prevents the entry of foreign
bodies and acts as a coolant.
Used for high precision bearings rotating at very high
speed.
Consult the SNR catalogue of high precision bearings
for machine-tool spindles.

Important: Most oil lubrication systems do not secure an adequate film during


the first few rotations of the bearing. It is therefore strongly recommended to

oil new bearings after installation.

133
 Lubrication
Oil lubrication (continued)

Quantity of oil

The diagram below gives an idea of the minimum safe flow rate under normal service condi-
tions for bearings.

Minimum quantity of oil

(in cm3/min.) 300

200

100

50
40

30

20

10

1
10 20 50 100 200 500

Mean bearing diameter (mm).

134