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Grease
A solid to semi-fluid product of a
thickening agent in a liquid lubricant.
Other ingredients imparting general
properties may be included
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Grease
• Advantages • Disadvantages
Convenience Low Cooling Rate
Resistance Contamination
Protection Performance
Cleanliness Limitations
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Grease Composition
Base Oil Thickener Additives
70 - 95% 10 - 20% 5 - 10%
Grease
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Lubricating Greases - Basics and Applications
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Components Used in Grease Formulation
Base oils Thickeners Additives
Mineral oils Sodium soap Anti-oxidants
Synthetic mineral oils Calcium soap Anti-wear additives
Di-esters Lithium soap EP additives
Silicones Aluminium soap Corrosion inhibitors
Phospate esters Barium soap Friction modifiers
Fluorocarbon Aluminium complex Metal deactivators
Fluorinated silicone Lithium complex VI improvers
Chlorinated silicone Bentonite clay Pour-point depressants
Silica Tackiness additives
Carbon/graphite Water repellants
Polyurea Dyes
PTFE Structure modifiers
Polyethylene
Indanthrene dye
Phthalocyanine dye
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Typical Oils Used in Lubricating Greases
• Petroleum
Paraffinic – good VI and thermal stability to 350oF max. temp.
Naphthenic – good low temperature performance to –65oF min
• Synthetic
Nominal Serviceable Temp. Range. oF
Diester - 100 to 400
Fluorosilicone - 50 to 450
Hydrocarbon - 80 to 350
Polyalkylene glycol - 40 to 350
Polyol ester - 50 to 400
Silicone - 100 to 450
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Base Oil For Grease
• Depends on required characteristics of grease.
Flow, viscosity, temp. range and speed.
• Paraffinic and napthenic mineral oils
• Synthetics used for special applications – very
low/very high temp.
• Base oil function is to lubricate
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Thickener Influences
• Act as a carrier
To release fluid
• Water Resistance
1. Washout Resistance - the ability of the lubricant to stay in the bearing
while operating partially or fully submerged (ASTM D1264).
2. Water Absorption - the ability of the grease to deal with the presence of
water by either absorbing or resisting the washing and diluting action of
the water.
3. Spray Resistance - the ability of the grease to resist displacement from a
direct impingement of the water on the greased surface (ASTM D4049).
• Heat Resistance
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Grease Additives
• Anti-Wear/Extreme Pressure Agents
Zinc dialkyIdithiophosphates
Dithiocarbamates (Zn, Sb, Pb)
Phosphate esters
Sulfurized fatty acids
Sulfurized hydrocarbons
Chlorinated hydrocarbons
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Grease Additives
• Anti-oxidants
Aryl amines
Zinc dialkyldithiophosphates
Hinderes phenols
Zinc and amine dithiocarbamates
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Grease Additives
• Rust and Corrosion Inhibitors
Sulfonates (Ca, Ba, Li, Mg, Na, Pb, amine salts)
Napthenates (Zn, Ba, Pb)
Carboxylic acid derivatives
Triazoles
Sodium Nitrite
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Grease Additives
• Friction Modifiers
Molybdenum disulfide
Graphite
PTFE
Powdered fluorocarbons
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Grease Additives
• Adhesion Promoters
Polyolefins and olefin copolymers
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Penetration
The depth, in tenths of a millimeter, that a standard cone sinks into a
material under prescribed conditions of weight, time and temperature.
This depth is described as NLGI numbers.
NLGI Number ASTM Worked Penetration
000 445-475
00 400-430
0 355-385
1 310-340
2 265-295
3 220-250
4 175-205
5 130-160
6 85-115
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Factors In Deciding NLGI Grades
• Speed
The higher the speed the harder the grease, so for high
speeds use no. 3. The maximum outer race speed for grease-
lubricated rolling bearings is about 15 m/s (3000 ft/min)
• Bearing size
Use a harder grease in a large bearing, No.3 or even no.4
• Sealing
If there is a particular need for effective sealing, use a harder
grease, No.3 or No.4
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Factors In Deciding NLGI Grades
• Shock loads or vibration
Shock load or vibration tends to cause grease to slump into
the moving components causing churning. A harder grease
minimizes the problem, so use No.3 or No.4. (Note that normal
steady loading does not strongly influence the grade)
• Temperature
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Grease Selection
Some basic rules:
Low speeds Greases with high base oil viscosity
and high loads and EP and / or solid lubricants
like Graphite or MoS2
High speeds Greases with low base oil viscosity
Oscill. movement Greases with white solid lubricants
High or low Greases with synthetic base oils
temperatures
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Important factors on Grease selection
1. Bearing design
2. Bearing speed
3. Load
4. Temperature
5. Environmental conditions
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Grease Incompatibility
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Calculation of lubricant consumption
Effective lubrication is the combination of a suitable
lubricant, right re-lubrication intervals and the optimum re-
lubrication quantity.
„The more, the better“ is (nearly) always wrong. Over-
lubrication leads to preliminary bearing failure and causes
additional costs.
Frequent re-lubrication with small quantities is better than
seldom re-lubrication in huge quantities. Optimization is
necessary, because frequent re-lubrication needs more
time.
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Calculation of lubricant consumption:
When calculating the optimum grease quantity, the free
volume in the bearing as well as free space in the housing
has to be considered.
First fill of bearing:
Fill the bearing completely, fill free space in the housing
only with a quantity which allows, that grease coming out of
the bearing during operation can remain in the housing to
avoid undesired heating of the grease and the bearing.
Sometimes sealing discs can be helpful.
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Calculation of lubricant consumption
Exceptions:
very high speeds:
fill bearing and housing only to one third to avoid
ineffective working of the grease
very low speeds:
fill bearing and housing completely to ensure
lubrication of all parts. In this case inner friction of the
grease can be neglected.
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Calculation of lubricant consumption
Calculation of the free bearing volume:
Calculation can be done with the dimensions and weights
given by the suppliers of the bearings with the following
formula:
V ≈ π/4 . B . (D² - d²) . 10-3 - G . 1000 / 7,8 [cm³]
V - free bearing volume in cm³ d - Inner diameter in mm
B - Bearing width in mm G - Weight in kg
D - Outer diameter in mm
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Calculation of lubricant consumption
Basic quantities when using grease guns:
One stroke with a
conventional (DIN) or
with
SYSTEM REINER-
Grease Gun gives ca. 1,5
- 2 ccm of grease.
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Calculation of lubricant consumption
Re-lubrication quantities and -intervals depend very much on the real
operating conditions. Therefore, exact calculation is extremely difficult.
In the past data of practical applications were collected which were used
as a data base for calculations for specific application fields. These
calculations use factors for special operating conditions which were found
by studying numerous similar applications.
Difficulties arise from the determination of these correction factors as well
as from the use of specialised greases with a performance being much
higher than that of conventional Li-soap-mineral-oil greases.
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Calculation of lubricant consumption
Correction factors for re-lubrication intervals
f1 - Dust and moisture (0.1 ... 0.9)
f2 - Shocks, vibrations (0.1 ... 0.9)
f3 - Temperature higher than 70°C (0.1 ... 0.9)
f4 - High load (0.1 ... 1.0)
f5 - Air flow through the bearing (0.1 ... 0.7)
The reduced re-lubrication interval is then calculated by multiplying all
these single factors:
tfq = f1 . f2 . f3 . f4 . f5 . tf
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Mechanical dynamic testing of lubricating greases
FE 8-bearings Timken-machine with specimen
FBT-balls
Emcor-machines
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Classification
Lubricating Greases
Properties:
Consistency (NLGI-grade)
Temperature range
EP-properties Classification (DIN 51502):
Base oil viscosity and type e.g. K P F 2 K -20
Thickener
Solid lubricants
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Grease Troubleshooting Guide
Application Symptom Possible Cause Check For
Bearings Rolling Noise Condition of bearing Worn or brinelled bearing
contact
High bearing temp. Over greasing Too frequent application
Bearing packed too full
Excessive grease charge
Starvation Insufficient application frequency
Incorrect product Wrong base oil viscosity
Excessive leakage Seals Mechanical damage
Incorrect installation
Over greasing Too frequent application
Excessive amount applied
Incorrect product Too soft for application or softening in
service
Incompatibility of grease Admixture of grease
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Grease Troubleshooting Guide
Application Symptom Possible Cause Check For
Bearings Rolling Frequent bearing Excessive wear Deficient load carrying (EP)
contact replacement
Starvation
Contamination (dirt,dust)
Bearing life exceeded
Improper installation
Grease too stiff (channeling)
High temperature High operating temperature
Misalignment Correct alignment
Bearings Plain Overheating Improper distribution Grease too stiff
Incorrect grooving
Starvation Infrequent application
Defective lubricator
Incorrect grease Mechanical stability
Excessive wear Starvation Infrequent application
Defective lubricator
Incorrect grease Load carrying (EP)
Temperature range
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Grease Troubleshooting Guide
Application Symptom Possible Cause Check For
Gears Enclosed Excessive leakage Grease too soft Product penetration
Milling down of product
Incompatibility of greases Admixture of greases
Noisy gearbox Lack of lubrication Improper lubricant level
Grease to stiff
Overheating Lack of lubrication Improper lubricant level
Grease too stiff
Churning High grease level
Grease too stiff
Tooth breakage Not usually lubricant related
Pitting Mostly poor design and fatigue related While not generally lubricant related, a heavier grease or
base oil may retard progression of pitting
Wear and scoring Lack of lubrication Improper lubricant level
Grease too stiff
Incorrect product used Consistency, EP, quality and base oil viscosity
Abbrasive wear Lubricant contamination
Alignment Not lubricant related
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Grease Troubleshooting Guide
Application Symptom Possible Cause Check For
Gears Open Gear wear Lack of lubrication Incorrect lubricant
Incorrect application frequency
Build up on gears or in roots Excessive lubricant Application frequency
Lubricant type
Airborne dirt
Sliding Surfaces Non-uniform motion Lack of lubrication Application frequency
Proper grease type
Universal Joints Excessive wear Insufficient lubrication Lubricant EP, temperature quality
Application frequency
Grease slumpability
Electric Motors Electric malfunction Excessive grease leakage Application frequency and quantity
High temperature
Couplings Dry coupling Excessive grease leakage Damaged seals
Grease consistency
Keyway openings
Initial fill
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