Grease basic knowledge_nk0906

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1


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 Types

•Metal soaps
Lithium, calcium, sodium, barium, aluminium, etc
Complex (I.e. Lithium complex, alumunium complex, Calcium
complex)
• Inorganics/non soap
Clays, megalite, montmorilonite, hectorites, bentonites
• Organics
Polyurea
• Fluoro Organic
PTFE

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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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Base fluid compatibility

Mineralöl Polyalfa- Poly- Ester, Natives Öl Alkoxy- Silikonöl
Öl-
olefin glykol synth. fluoröl
Typ

Mineralöl
+ + - + + - -
Polyalfa-
olefin + + - + + - -
Polyglykol - - + - - - -
Ester,
synth. + + - + + - -
Natives Öl + + - + + - -
Alkoxy-
fluoröl - - - - - + -
Silikonöl - - - - - - +

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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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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 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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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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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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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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ASTM Grease Tests

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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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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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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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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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Thank you

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Grease basic knowledge_nk0906

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