Lubrication
is the process, or technique employed to reduce wear between moving surfaces,
by interposing a substance called lubricant between the
surfaces to help carry the load between the opposing surfaces.(google article)
Or it can be defined as the use of a material to improve the smoothness or
movement of one surface over another; the material which is used is called a
lubricant. A lubricant is a substance introduced to reduce friction between moving
surfaces
Basic types of lubricant
Lubricants are usually divided into four basic
classes.
¨ Oils:
A general term used to cover all liquid lubricants, whether they are mineral
oils, natural oils, synthetics, emulsions, or even process fluids.
¨ Greases:
Technically these are oils, which contain a thickening agent to make them
semi-solid. It is convenient, however, to include the anti-seize pastes and the
semi-fluid greases under the same heading.
¨ Dry
lubricants: These include any lubricants, which are used in solid form, and may
be bulky solids, paint-like coatings, or loose powders.
¨ Gases:
The gas usually used in gas bearings is air, but any gas can be used which will
not attack the bearings, or itself decompose.
PROPERTIES OF LUBRICANTS
¨ A
good lubricant possesses the following characteristics:
¨ High
boiling point
¨ Low
freezing point
¨ High
viscosity index
¨ Thermal
stability
¨ Hydraulic
Stability
¨ Demulsibility
¨ Corrosion
prevention
High resistance to oxidation
DETAILS ON TYPES OF LUBRICANT
1. MINERAL OILS
•
Mineral oils are easily the most widely
used lubricating oils. Consequently, they are often the standard with which
other oils are compared.
•
Mineral oils generally mean oils
obtained from petroleum, although they can also be obtained from similar
sources, such as oil shales and tar-stands.
The chemical compounds, which
comprise mineral oils, are mainly hydrocarbons, which contain only carbon and
hydrogen. These are of three basic types depending on the prevailing
compositions:
Paraffinic
Naphthenic
aromatic
- NATURAL
OIL
These
include vegetable oils and animal fats. They are usually excellent boundary
lubricants, but they are much less stable than mineral oils, and tend to break
down to give sticky deposits. Rapeseed oil is till used by itself or as an
additive to mineral oils to give improved boundary lubrication.
A
recent development is an increase in use of castor oil and palm oil in
manufacture of bio-degradable and food industry grade lubricants
3. SYNTHETIC
OILS
There
are many types of synthetic oils and are manufactured from various feedstocks
by chemical processes. There are different types of synthetic oil and are very
different from each other in their performance and properties.
The
widely-used synthetic oils include hydrocarbons, di-esters, polyol esters,
phosphate ester, silicones, polyglycols, and- to a much smaller extent-
polyphenyl ethers and perfluoroalkyl polyethers.
¨ Synthetic
Hydrocarbons
The
most important are branched-chain paraffins, which are known as
polyalphaolefins (PAO). Their properties and performance are very similar to
some of the most highly refined mineral oils. Polyalphaolefins are one of the
most important classes of synthetic oil, yet they resemble mineral oils. Their
inherent oxidation resistance is quite good and their boundary lubrication not
very good, like those of the highly refined mineral oils
Di-esters and polyol esters
In
terms of the total volume used, di-esters and polyol esters comprise the most
important class of synthetic oils, as they are almost universally used for
aircraft gas turbine engine lubrication.
Di-esters are a class of �carboxylic
esters�,
containing the carboxylic group �O-C=O.Poly
esters are carboxylic esters with better thermal stability. Di-esters are used
as base oils for high-temperature applications in industry, such as hot-rolling
oils in steel rolling. They can be used at higher temperatures than mineral
oils, have very good lubricating characteristics, and are readily available in
a variety of viscosities.
Polyol esters are now extensively used in aircraft
jet engines and are readily available in a few different viscosity grades.
Apart from their good high-temperature properties, they also have very good
lubricating characteristics.
4 Emulsions
¨ This
is usually a mixture of oil and water. It is been used in manufacturing
industries like machine shops during cutting or shearing operations
the other lubricants
such as greese, solid lubricants and gases are outside the scope of this
training.
¨ Further
talks on key qualities of oil and grades of oil with their usefulness based on
car and engine capacicity will be discussed in subsequent training.
¨ STAY
TUNED, DON’T TOUCH THE DIAL
This was researched and produced by
MADUKA Anthony
ooshaynaz@gmail.com
REFERENCES
wikkipedia
google search
No comments:
Post a Comment