Introduction to

Tribology
MODULE 1
Contents
• Definition of “Tribology”
• Historical background
• Importance
• Application
• Lubricants
◦ Types and specific field of applications
◦ Properties of lubricants, viscosity, its measurement
◦ Effect of temperature and pressure on viscosity
◦ Lubrication types
◦ Standard grades of lubricants
◦ Selection of lubricants
Introduction
Tribology comes from the Greek word, “tribos”, meaning “rubbing” or “to rub”

And from the suffix, “ology” means “the study of”

Therefore, Tribology is the study of rubbing, or… “the study of things that rub”.

This includes the fields of

• Friction
• Lubrication
• Wear
Historical background

The use of a sledge to transport a heavy statue by the Egyptians, 1880 BC

One man, standing on the sledge supporting the statue, is seen pouring a liquid (most

likely water) into the path of motion; he was one of the earliest lubrication engineers

During and after the Roman Empire, military engineers rose to prominence by devising

both war machinery and methods of fortification, using tribological principles

Renaissance engineer-artist Leonardo da Vinci celebrated in his day for his

genius in military construction as well as for his painting and sculpture, who first

postulated a scientific approach to friction

Da Vinci deduced the rules governing the motion of a rectangular block sliding over a flat surface.

He introduced the concept of the coefficient of friction as the ratio of the friction force to normal
load.

Essential laws of viscous flow were postulated by Sir Isaac Newton in 1668

In 1699, the French physicist Guillaume Amontons re-discovered the rules of friction after he studied
dry sliding between two flat surfaces

In 1785, these observations were verified by the French physicist Charles-Augustin Coulomb
The Industrial Revolution (AD 1750–1850) is recognized as the period of rapid and impressive development
of the machinery of production. The use of steam power and the subsequent development of the railways
in the 1830s, automobiles in the early 1900s and aircraft in the 1940s led to the need for reliable machine
components.

Since the beginning of the twentieth century, from enormous industrial growth leading to demand for
better tribology, knowledge in all areas of tribology has expanded
September 1964 -- Conference on Lubrication in Iron and Steel Works in Cardiff (UK) :
Realization of considerable losses due to lack of knowledge related friction and wear of machine
components.

Formation of committee by UK Minister of State for science to investigate the questions of

lubrication education, research and need of industry.
Conclusions of Committee: Interdisciplinary approach embracing solid & fluid mechanics,
chemistry, and material science is essential to address lubrication related problems. New name
“Tribology” was coined in 1966.
Coined by Dr. H. Peter Jost in England in 1966
“The Jost Report”, provided to the British Parliament – Ministry for Education and Science, indicate
“Potential savings of over £515 million per year ($800 million) for industry by better application of
tribological principles and practices.”
1981: Development of “Scanning tunneling microscope” and systematic theory based on
“Contact mechanics”.
1985: Development of Atomic Force Microscope
◦ Measurement of surface topography & friction force of all engineering surfaces.
◦ Studies of adhesion, scratching, wear, lubrication, surface temperatures and measurements of elastic/plastic
mechanical properties.
Why ?????
Friction, wear and lubrication have been taught in science and engineering classes, but at a
basic level.

Inherently complicated and interconnected origins of most tribological phenomena.

Integration of knowledge from multifaceted disciplines.

Importance
Tribology is the art of applying operational analysis to problems of great economic significance,
namely, reliability, maintenance, and wear of technical equipment, ranging from spacecraft to
household appliances.

It encompasses the interdisciplinary science and technology of interacting surfaces in relative
motion and associated subjects and practices.
Economic Benefits
Successful implementation of tribological knowledge in INDIA can save 1 to 1.5% of GNP ($ 3.4
Trillion) Rs. 1500 million.

If 50% of this cost needs to be invested in unsuccessful trials and fruitless hypotheses, still INDIA
will gain from practicing tribology.
Tribology in conservation of energy ?
The knowledge of tribology is useful in reducing the unnecessary friction and wear
between two rubbings surfaces (tribo-pair).

Using tribology appropriate lubricant and lubrication mechanism can be adopted to minimize
the friction and eliminate wear which would reduce the wastage of energy and enhance working
life of tribo-pair.
Tribology in increasing efficiency
The tribology knowledge can be utilized by lubricating all the joints and moving/rubbing pairs in the
mechanical system which would not only reduce friction, wear, corrosion etc.

It would also make the system much more efficient and reliable by reducing mechanical wear.

Due to reduced friction, wear and corrosion the longevity of the system would improve.

The tribology knowledge would also help in identifying the right kind of lubricant and lubrication
mechanism for the system.

It is difficult to achieve 100% efficiency for any system but the use of tribology knowledge would
definitely help in improving the efficiency level
 Application
In Applications from Simple to Complex and Scales from Small to Large components

1. Individual Components

2. Assemblies or Products

3. Manufacturing Processes

4. Construction/Exploration

5. Natural Phenomena
Individual Components
Assemblies or Products
Manufacturing Processes
Construction/Exploration
Natural Phenomena
Other Applications
1. Aerospace
2. Agriculture
3. Automotive
I. Engine: Piston ring/cylinder, Bearings, valve seats, injectors
II. Brakes/clutch
III. Tooling/Machining/Sheet metal forming

4. Coatings Providers
I. Low Friction
II. Wear Resistant What do All These Diverse Fields
and Applications have in
Common?
1. Cosmetics/Personal Care
2. Dental Implants
3. Energy
I. Nuclear
II. Wind
III. Fossil
IV. Solar
4. Fabric/Clothing
5. Flooring What do All These Diverse Fields
6. Food Processing and Applications have in
Common?
7. Highway/Transportation
1. Lubricant Manufacturers
2. Medical Diagnostics
3. Medical Implants
4. Military
5. Pharmaceutical
6. Shoe Manufacturers
7. Sports Equipment Companies
What do All These Diverse Fields
and Applications have in
Common?
 What do All These Diverse Fields and
Applications have in Common?

What do we need to think about as

engineers and scientists when we design
products or friction/wear experiments?
 Every Application has:
Surfaces in Contact, and is in Relative Motion

Friction comes into play and causes wear in most of the

cases, hence lubrication is necessary
LUBRICANTS
1. Types and specific field of
applications

2. Properties of lubricants,
viscosity, its measurement

3. Effect of temperature and

pressure on viscosity

4. Lubrication types

5. Standard grades of lubricants

6. Selection of lubricants
WHAT ?????? are lubricant(s)ion
Lubrication is the control of friction and wear by the introduction of a friction-reducing film
between moving surfaces in contact.

A lubricant is a substance, introduced to reduce friction between surfaces in mutual contact,

which ultimately reduces the heat generated when the surfaces move.
WHY ?????? are they used
1. Keep parts moving
2. Reduce friction
3. Transfer heat
4. Carry away contaminants
5. Transmit power (hydraulics)
6. Prevent wear
7. Protect the equipment from corrosion
8. Provide a fluid seal
Keep Parts Moving
Lubricants are typically used to separate moving parts in a system.
This separation has the benefit of reducing friction, wear and surface fatigue, together with
reduced heat generation, operating noise and vibrations
Reduce friction
Typically the lubricant-to-surface friction is much less than surface-to-surface friction in a
system without any lubrication
Thus use of a lubricant reduces the overall system friction
Reduced friction has the benefit of reducing heat generation and reduced formation of wear
particles as well as improved efficiency
Transfer Heat

Both gas and liquid lubricants can transfer heat.

Liquid lubricants are much more effective on account of their high specific heat capacity.

Circulating flow also determines the amount of heat that is carried away in any given unit of
time

Non-flowing lubricants such as greases and pastes are not effective at heat transfer although
they do contribute by reducing the generation of heat in the first place.
Carry away contaminants and debris

Benefit of carrying away internally generated debris and external contaminants that get
introduced into the system to a filter where they can be removed.
Protect against wear

Lubricants prevent wear by keeping the moving parts apart.

Lubricants may also contain anti-wear or extreme pressure additives to boost their performance
against wear and fatigue.
Transmit power

Lubricants known as hydraulic fluid are used as the working fluid in hydrostatic power
transmission
Prevent corrosion

Many lubricants are formulated with additives that form chemical bonds with surfaces or that
exclude moisture, to prevent corrosion and rust
Seal for gases

Lubricants will occupy the clearance between moving parts through the capillary force, thus
sealing the clearance.
WHERE ?????? are they used
1. Automotives
I. Engine oil
II. Gearbox
III. Brake fluids
IV. Automatic transmission fluids
2. Industry
I. Compressors
II. Hydraulics press
III. Bearings
IV. Turbines
3. Aviation
4. Marine
Additives
Additives are chemicals, nearly always organic or organometallic, that are added to oils in quantities of
a few weight percent to improve the lubricating capacity and durability of the oil.
Specific purposes of lubricant additives are
1. Improving the wear & friction characteristics
2. Improving the oxidation resistance
3. Control of corrosion
4. Control of contamination by reaction products, wear particles and other debris
5. Reducing excessive decrease of lubricant viscosity at high temperatures
6. Enhancing lubricant characteristics by reducing the pour point
7. Inhibiting the generation of foam.
 HOW ??? are they classified
Lubricants = majority of base oil + variety of additives  impart desirable characteristics.
Classification

Liquid Lubricants Semi Solid Solid Lubricants Aqueous Lubricants

Mineral Oils Synthetic Oils

Mineral Oils
Mineral oils are the most commonly used lubricants.

They are manufactured from crude oil which is

mined in various parts of the world.

Source : mineral oils are the result of decomposition

of animal & plant matter in salt water

Crude oil exhibits a complex structure which is

separated into a number of fractions by a distillation
process which is called fractional distillation.
Mineral oils differ from each other depending on the source of crude oil and refining process.

Mineral oils are classified based on

1. Chemical forms
a. Paraffinic

b. Napthalenic

c. Aromatic

2. Sulphur content

3. Viscosity
 Drawbacks of mineral oils
Despite availability and relatively low cost, mineral oils also have several serious defects

Oxidation and viscosity loss at high temperatures

Combustion or explosion in the presence of strong oxidizing agents and solidification at low temperatures.

These effects are prohibitive in some specialized applications such as gas turbine engines

In food processing and the pharmaceutical industry low toxicity lubricant is required

 In recent years the strongest demand has been for high performance lubricants, especially for applications in the
aviation industry

This led to the development of synthetic lubricants

 Synthetic Oils
Synthetic lubricants were originally developed early this century by countries lacking a reliable supply of
mineral oil.

These lubricants were expensive and initially did not gain general acceptance.

Synthetic hydrocarbon lubricants are produced from the 'cracking' of petroleum

Through the application of high pressures and catalysts large complex molecules present in the oil are
decomposed to more simple, smaller and more uniform molecules.

The low molecular weight hydrocarbons are then polymerized under carefully controlled conditions to
produce fluids with the required low volatility and high viscosity.
Polyalpha-olefin (PAO)

Synthetic esters

Polyalkylene glycols (PAG)

Phosphate esters

Alkylated naphthalenes (AN)

Silicate esters

Multiply alkylated cyclopentanes (MAC)

Solid Lubricants
Solid lubricants are used where
 Operating conditions are such that a lubricating film cannot be secured by use of lubricating oils or
greases

 Contamination (by the entry of dust or grit particles) of lubricating oil or grease is unacceptable

 The operating temperatures or load is too high even for a semi-solid lubricant to remain in position

 Combustible lubricants must be avoided.

The two most usual solid lubricants employed are
1. Graphite
2. Molybdenum disulphide

Applied by spraying, dipping (less expensive), brushing

Surface preparation is very important to remove contaminants

Other substances like soapstone, talc, mica, PTFE, Nylon etc. are also used as
solid lubricants
ADVANTAGES DISADVANTAGES

1. More effective at high loads compared to 1. Poor self healing properties

fluid lubricants
2. Poor heat dissipation (low value of thermal
2. Resistance to deterioration (progressively conductivity)
worse)
3. Higher co-efficient of friction and wear
3. Stable in extreme temperature and
reactive environments
4. Simpler and no external force required as
compared to liquid lubricants (can be
applied as coatings or in the form of
powder)
Aqueous Lubricants
Emulsions are produced by mixing water and oil with an emulsifier.

By continuous rapid exchange of bound water with other free water molecules, these polymer
films keep the surfaces separated while maintaining a high fluidity, thus leading to a very low
coefficient of friction.

Emulsions and aqueous solutions are mostly used as cutting fluids in the metal working Industry

As fire resistant lubricants in the mining industry.

Semi Solid Lubricants
Mixtures of lubricating oils and thickeners. The thickeners are dispersed in lubricating oils in
order to produce a stable colloidal structure or gel.

A grease consists of oil constrained by minute thickener. Since the oil is constrained and unable
to flow it provides semi-permanent lubrication.

Greases are widely used, despite certain limitations in performance.

Widespread application of greases is as low-maintenance, semi-permanent lubricants in rolling

contact bearings and some gears.
Greases have to meet the same requirements as
lubricating oils but with one extra condition

The grease must remain as a semi-solid mass

despite high service temperatures.

If the grease liquefies and flows away from the

contact then the likelihood of lubrication failure
rapidly increases.

 Mineral oils are most often used as the base stock in grease formulation. About 99% of greases are
made with mineral oils.
Gas Lubricants
Gases like nitrogen and helium are used as lubricants in applications where film thickness
between tribo-pair is ultra small

The advantages of using gas lubricants are large temperature range, no sealing required for
lubrication

Very low friction due to low viscosity, no vaporization, no solidification, and no decomposition.

The downsides of using gas lubricants are low load capacity

Bio-Lubricant
Bio-lubricants are derived from vegetable oils and other renewable sources.

They usually are triglyceride esters (fats obtained from plants and animals)

 For lubricant base oil use, the vegetable derived materials are preferred.

Whale oil was a historically important lubricant, with some uses up to the latter part of the 20th
century
 Properties of Lubricants
A good lubricant generally possesses the following characteristics:

1. A high boiling point & low freezing point (in order to stay liquid within a wide range of temperature)

2. A high viscosity index

3. Thermal stability (no change at micro-structural level)

4. Hydraulic stability (ability of a lubricant to resist chemical decomposition with H2O)

5. Demulsibility (ability of oil to separate from H2O)

6. Corrosion prevention

7. A high resistance to oxidation

Viscosity
Physical property - resistance to flow.
This resistance is mainly due to internal friction and is a molecular phenomenon.

Where,

µ = dynamic viscosity/absolute viscosity

du/dy = velocity gradient

Dynamic viscosity – poise
 1P = 0.1 Pa-s

 1 cP = 0.01 P

Kinematic viscosity (ƞ= µ / ρ) – stokes

 1 S = 1 cm2/s

 1 cS = 1 mm2/s
Effect of Temperature on µ
With increase in temperature, the molecules move apart and
intermolecular forces decrease
Thus, viscosity of oil decreases with increasing temperature
The change of viscosity due to change in temperature is different
for different oils
Thus, two oils having the same viscosity at some temperature may
have different viscosity at another temperature
There is no unique way to represent the variation with temperature
The simple equation is ln µ = A + ( B / T)
 where A & B are constants, and T is absolute temperature
Viscosity Index (V.I)
Two oils having the same viscosity at some temperature may have different viscosity at another
temperature
In order to show the effect of temperature change on viscosity of oil, viscosity index (V.I) is used
To find V.I, its temperature – viscosity relation is compared with that of two standard oils
Thus, V.I = (L-U)*100 / (L-H)
Where, U = viscosity at 100ºF of oil whose VI is to be calculated
L = viscosity at 100ºF of an oil of 0 V.I having same V.I at 210ºF as the oil whose V.I is to be
calculated
H = viscosity at 100ºF of an oil of 100 V.I
Two groups of oil is used: Pennsylvania oil (V.I = 100) and Gulf coast oil (V.I = 0)
Effect of Pressure on µ
As pressure of an oil is increased, the molecules are forced to come closer, thereby increasing
intermolecular forces.
This increases the viscosity.
Thus, the viscosity of lubricating oil increases with the increase in pressure and relatively slowly
at low pressure
As pressure is further increased, the viscosity increases until they become plastic solids.
There is no unique way to represent the variation with pressure
µ = µo exp (αP)
Where, µo = absolute viscosity at atmospheric pressure
 α = pressure coefficient of viscosity
Lubrication Types (mechanism)
Mainly 3 types of lubrication
 Boundary lubrication
(thin film lubrication)
 Mixed lubrication
(partial contact)
 Full film lubrication
(Hydrodynamic lubrication)
Stribeck Curve
Coefficient of friction vs bearing number
Bearing number = Sliding speed * (lubricant viscosity / Unit load)
No continuity at the beginning, that means no lubrication when there is no sliding
Initially its boundary lubrication.
Elastic hydrodynamic lubrication in between mixed and hydrodynamic lubrication
Always, try to operate on right-side of the line.
Boundary lubrication
Exists when the operating condition are such that it is not possible to establish a full fluid
condition, particularly at low relative speeds between the moving or sliding surfaces.
Found where there are frequent starts and stops, and where shock-loading conditions are
present
The oil film thickness may be reduced to such a degree that metal to metal contact occurs
between the moving surfaces.
Boundary lubrication happens when a shaft starts moving from rest. The speed is very low, the
load is very high.
Mixed Lubrication
Possibility of boundary and liquid lubrication. Contact at few locations only.
The combination maybe anything, ie
 Boundary lubrication + Elasto-hydrodynamic lubrication + Fluid Lubrication

Wear also is a combination of all the lubrication mechanisms

Elasto-Hydrodynamic lubrication
In rolling contact elements, fluid film is minutely small and slightly greater than irregularities of
the surface
They serve much longer than predicted by mixed lubrication theories
Under loads, every surface deforms. The applied lubricant gets dragged into interface and builds
pressure
Full film lubrication (hydrodynamic lubrication)

Hydrodynamic lubrication occurs when two surfaces in sliding motion (relative to each other)
are fully separated by a film of fluid

Very low friction (0.01 – 0.001)

Lower the viscosity of the oil, lower the friction

In ideal case, there is no wear of the moving parts.

 Societies and Industry Bodies
1. Society of Automotive Engineers (SAE)
2. American Petroleum Institute (API)
3. American Gear Manufacturers Association (AGMA)
4. International Standards Organization (ISO)
5. Japanese Automotive Standards Organization (JASO)
6. European Automobile Manufacturers Association (ACEA)
7. Society of Tribologists and Lubrication Engineers (STLE)
8. Petroleum Packaging Council (PPC)
9. Independent Lubricant Manufacturer Association (ILMA)
10. National Lubricating Grease Institute (NLGI)
Standard Grades of Lubricants
The viscosity grade of a lubricant is determined by the Society of Automotive Engineers (SAE).
Oils can be separated into multi-grade oils and mono-grade oils
Multi-grade oils must fulfill two viscosity specifications, their viscosity grade consists of two numbers,
e.g. 10W-40
 10W refers to the low-temperature viscosity ("Winter"), The lower the number here, the less it thickens in the
cold. So 5W-30 viscosity engine oil thickens less in the cold than a 10W-30, but more than a 0W-30. An engine
in a colder climate, where motor oil tends to thicken because of lower temperatures, would benefit from 0W
or 5W viscosity.
 40 refers to the high-temperature viscosity ("Summer"). ). This number represents the oil's resistance to
thinning at high temperatures. For example, 10W-30 oil will thin out at higher temperatures faster than 10W-
40 will.
Currently, most automotive engine oils are multi-grade oils
Mono-grade oils such as SAE 30, 40 or 50 are no longer used in latest automotive engines, but may be
required for use in some vintage and antique engines, lawn movers
 Selection of Lubricants
Manufacturer recommendations
1. Lubricants are normally tested by subjecting them to various types of physical stress. However,
these tests do not completely indicate how a lubricant will perform in service. Experience has
probably played a larger role, machine manufacturers have learned which classes of lubricants will
perform well in their products.
2. Professional societies have established specifications and classifications for lubricants to be used
in a given mechanical application. For example, AGMA has established standard specifications for
enclosed and open-gear systems. These specifications have been developed from the experience
of the association’s membership for a wide range of applications.
3. Individual manufacturers may have different opinions based on their experience and equipment
design. The concept of “best” lubricant is ambiguous because it is based on opinion. The
manufacturer is probably in the best position to recommend a lubricant. This recommendation
should be followed unless the lubricant fails to perform satisfactorily.
4. Although some manufacturers may recommend a specific brand name, they can usually provide a
list of alternative lubricants that also meet the operating requirements for their equipment.
Lubricant producer recommendations
1. When manufacturers recommend lubricants for their products in terms of specifications or
required qualities rather than particular brand names, the user must identify brands that
meet the requirements. When a user is uncertain, lubricant producers should be consulted.
2. Lubricant producers employ product engineers to assist users in selecting lubricants and to
answer technical questions. Given a manufacturer's product description, operating
characteristics, unusual operating requirements, and lubricant specification, product
engineers can identify lubricants that meet the manufacturer's specifications.
3. Viscosity should be the equipment manufacturer’s recommended grade. If a
recommendation seems unreasonable, the user should ask for verification or consult a
different lubricant producer for a recommendation. This will help prevent the unnecessary
purchase of high-priced premium quality lubricants when they are not required.
User selection
1. The user should ensure that applicable criteria are met regardless of who makes the
lubricant selection. Selection should be in the class recommended by the machinery
manufacturer and be in the same base stock category (paraffinic, naphthenic, or synthetic).
2. Furthermore, physical and chemical properties should be equal to or exceed those specified
by the manufacturer. Generally, the user should follow the manufacturer's specification.
3. If the manufacturer’s specifications are not available, determine what lubricant is currently
in use. If it is performing satisfactorily, continue to use the same brand.
4. If the brand is not available, select a brand with specifications equal to or exceeding the
brand previously used. If the lubricant is performing poorly, obtain the recommendation of a
product engineer.
Viscometers
•For any application requiring a fluid to perform a task, it is imperative to know the viscosity of the
fluid.

•Various industries rely on viscosity checks of their products to produce a product with consistent
texture.

•Many important parameters for the production control of materials and also for the development of
new products are directly related to the product’s viscosity.

•In nearly all production stages the viscosity of the material has a great impact, e.g. in the mixing
process and while pumping liquids through pipes.

•Incoming liquid raw materials also have to be checked using viscosity measurements.
Capillary Viscometer
•Capillary Viscometer / Ostwald
Viscometer / U tube Viscometer

•For Newtonian Fluids

•Not applicable for highly viscous fluid

 Zahn Cup
• A Zahn cup is a viscosity measurement device widely used in the paint industry.

• It is commonly a stainless steel cup with a tiny hole drilled in the center of the bottom of the cup. There is also a long
handle attached to the sides.

• There are five cup specifications, labeled Zahn cup #x, where x is the number from one through five.

• Large number cup sizes are used when viscosity is high, while low number cup sizes are used when viscosity is low.

• To determine the viscosity of a liquid, the cup is dipped and completely filled with the substance.

• After lifting the cup out of the substance the user measures the time until the liquid streaming out of it breaks up, this is
the corresponding "efflux time".

• On paint standard specifications, one denotes viscosity in this manner: efflux time, Zahn cup number.
One can convert efflux time to kinematic viscosity by using an equation for each cup
specification number, where t is the efflux time and ν is the kinematic viscosity in centistokes.
1. Zahn Cup #1: ν = 1.1(t − 29)

2. Zahn Cup #2: ν = 3.5(t − 14)

3. Zahn Cup #3: ν = 11.7(t − 7.5)

4. Zahn Cup #4: ν = 14.8(t − 5)

5. Zahn Cup #5: ν = 23t

 Falling Sphere Viscometer
• The principle of the viscometer is to determine the falling time of a sphere with known density and diameter within a fluid filled
inside glass tube.

• The viscosity of the fluid sample is related to the time taken by the sphere to pass between two specified lines on the cylindrical
tube.

• Velocity of the sphere which is falling through the tube is dependent on the viscosity of the fluid.

• When a sphere is placed in an incompressible Newtonian fluid, it initially accelerates due to gravity.

• The forces acting are :

1. gravity (FG)
2. buoyancy (FB)
3. fluid drag (FD)
•For the velocity to be steady, Newton’s second law requires that the net forces acting on the
sphere is zero
•FG-FB-FD = 0
Rotational Viscometer
•Rotational viscometers are relatively easy to use

•Common version has two coaxial cylinders with the fluid to be measured
contained between them.

•One cylinder is driven at a constant angular velocity by a motor and the

other is suspended by torsion wire.

•After the driven cylinder starts from rest, the suspended cylinder rotates
until an equilibrium position is reached, where the force due to the torsion
wire is just balanced by the viscous force transmitted through the liquid.
 Vibration Viscometer
•Vibrational viscometers operates by measuring the damping of an
oscillating electromechanical resonator immersed in a fluid whose
viscosity is to be determined.

•The resonator generally oscillates in torsion. The higher the viscosity,

the larger the damping imposed on the resonator.

•The resonator's damping may be measured by one of several methods:

• Measuring the power input necessary to keep the oscillator vibrating at a
constant amplitude. The higher the viscosity, the more power is needed to
maintain the amplitude of oscillation.

• Measuring the decay time of the oscillation once the excitation is switched
off. The higher the viscosity, the faster the signal decays.
Saybolt Viscometer
•Works on the principle of Hagen Poiseuille law, similar to capillary tube viscometer

•Saybolt Viscometer has a vertical cylindrical chamber filled with liquid whose viscosity is to be
measured

•It is surrounded by a constant temperature bath and a capillary tube and a capillary tube is attached
at the bottom of the chamber

•For measurement of viscosity, the stopper at the bottom is removed and time for liquid to flow for
60ml is noted which is named as saybolt seconds

•The kinematic viscosity can be calculated using

Saybolt vs Redwood Viscometer
SAYBOLT VISCOMETER REDWOOD VISCOMETER

1. The experiment is held and a 60ml of oil is 1. In this experiment is held and a 50ml of oil
passed through a standard orifice. The is passed through a standard orifice. The
total time duration is then noted. total time duration is then noted.

2. A stopper is provided at the bottom of the 2. The stopper is replaced with a ball valve
tube for the liquid not to flow. It is released and orifice.
during the experiment.
Further Learning
1. https://www.lubricants.total.com/help-support
2. https://www.farmoyl.com/resources/sae-viscosity-grades
3. https://www.farmoyl.com/resources/glossary-of-terms