LESSON 2 Flashcards
are the most commonly used lubricants.
Mineral Oils
They are manufactured from crude oil which is
mined in various parts of the world.
Mineral Oils
The commonly accepted hypothesis about the origins of mineral oils is the
fossil fuel theory
The theory states that the mineral oils are the result of decomposition of animal and plant
matter in salt water. According to the theory the remains of dead plants and animals were
collected in sedimentary basins, especially in places where the rivers dump silt into the sea.
Over time they were buried and compressed.
fossil fuel theory.
Under these conditions the organic matter
transformed into tar-like molecules
kerogen.
The fundamental differences between mineral oils are based on:
chemical forms,
sulfur content,
viscosity
There are three basic chemical forms of mineral oil:
paraffinic,
naphthenic,
aromatic.
It has been demonstrated, for example, that between _____ of
natural sulphur content ensures reduced wear.
0.1% and 1%
The sulphur
content varies with the source of crude oil and the range of concentration lies between
0% and 8%.
Mineral oils can also be classified by _____, which depends on the degree of refining.
viscosity,
cS means?
centistoke
that can withstand high temperatures without
decomposing and at the same time will provide a reduced fire hazard.
synthetic lubricants
In most cases synthetic hydrocarbon lubricants are produced from low molecular weight
hydrocarbons which are derived from the
_____ of petroleum
‘cracking’
____ by itself is a very poor lubricant but
when mixed with oils to form emulsions or when mixed with water-soluble hydrocarbons to
produce an aqueous solution, some useful lubricants can be developed.
Water
____ are produced by mixing water and oil with an emulsifier.
Emulsions
The ____ emulsions are used as fire resistant hydraulic
‘W/O’
while the ____ emulsions are suitable as metalworking coolants.
‘O/W’
Emulsions and aqueous solutions are mostly used as _____ and as ______
cutting fluids in the metal working
industry and fire resistant lubricants in the mining industry
They are in fact mixtures of lubricating oils and
thickeners.
Grease
What does grease provide?
semi-permanent lubrication
The most widespread application of greases is
as
low-maintenance, semipermanent lubricants in rolling contact bearings and some gears.
_______ are also
suitable candidates for grease lubrication.
Low maintenance items
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.
it is not effective as a cooling agent.
Grease
It also cannot be used at speeds as high as oil because frictional drag would cause overheating.
Grease
Greases are manufactured by adding _________ to a quantity of oil:
alkali and fatty acid
Greases always contain three basic active ingredients:
base mineral or synthetic oil, additives
and thickener.
Thickeners used in grease?
metal soaps and clays
What plays the most important role in determining the grease performance?
mineral oil
Different types of lubricants
- Mineral Oils
- Synthetic Oils
- Emulsions and Aqueous Lubricants
- Grease
The parameter that plays a fundamental role in lubrication
oil viscosity.
oil viscosity changes with
temperature,
shear rate and pressure and the
thickness of the generated oil film is usually proportional to
oil velocity
Knowing the
temperature at which the oil is expected to operate is critical as oil viscosity is extremely
temperature
dependent.
-is defined as the property of a fluid which offers a resistance to the movement of one layer of fluid
over another layer of fluid, thus, it is the resisting property of a fluid to shearing force.
Dynamic Viscosity
is important in engineering calculations and sometimes offers a simple way of identifying lubricants.
Lubricant density
is often used to characterize crude
oils.
Density or specific gravity
is defined as the ratio of
the mass of a given volume of oil at temperature ‘t1’to the mass of an equal volume of pure water
at temperature ‘t2’.
Specific gravity
is the mass per unit volume of oil
[kg/m3].
Density,
API
(American Petroleum Institute)
- Another standard commonly associated with brine.
Baume Gravity Unit, °Baume’ or °
Be’
The most important thermal properties of lubricants are
specific heat, thermal conductivity
and thermal diffusivity.
varies linearly with temperature and increases with increasing polarity or hydrogen bonding of the molecules.
Specific heat
also varies linearly with temperature and is affected by polarity and
hydrogen bonding of the molecules. The
Thermal conductivity
-is defined as the property of a fluid which offers a
resistance to the movement of one
layer of fluid over another layer of
fluid, thus, it is the resisting property
of a fluid to shearing force.
Dynamic Viscosity
the ratio of dynamic viscosity to the density of
the fluid
Kinematic Viscosity
is th e parameter describing the temperature propagation into the solids
Thermal Diffusivity
On the other hand, too much sulphur is
detrimental to the performance of the machinery,it may accelerate the corrosion of seals.
The sulphur
content varies with the source of crude oil and the range of concentration lies between
0%
and 8%.
For commonly used mineral oils, viscosity varies from about
5 [cS] to 700 [cS].
spindle oil
20 [cS],
engine oil
between 30 and 300 [cS],
bright stock
about 600 [cS],
mineral oils also have several serious defects, such as
oxidation and viscosity loss at high temperatures,
combustion or explosion in the presence of strong oxidizing agents and solidification at low
temperatures.
Mineral oils advantage
availability and relatively low cost,
A prime example of this method of lubricant synthesis is the production of a
polyolefin synthetic lubricant oil from olefins (alkenes).
Why water is an attractive extender of lubricating oils?
cheap, good heat transfer characteristics
and non-flammability are all useful attributes.
Disadvantage of emulsions
The most severe limitation of these lubricants is the temperature range at which they can successfully be applied. They are limited to the
temperature range of water, which lies between the melting point of ice and the boiling point
of water.
Enumerate the Physical Properties of Lubricants
- Oil Viscosity
- Lubricant Density and Specific Gravity
Enumerate the Thermal Properties of Lubricants
- Specific Heat
- Thermal Conductivity
- Thermal Diffusivity
