Block diagram reduction techniques in control systems.ppt
Lubrication
1.
2. Lubrication:
It is the process or technique employed to reduce
the friction between the moving parts of a
machine.
Lubricants
The substances which is employed in the process
of lubrication .Eg: petroleum oil, animal or
vegetable oil .
3. It act as coolant because it reduces the
production of heat between the moving parts
of the machine in contact.
It avoid the damage of the moving parts of
machines by minimizing the production of
heat.
It reduces the wear and tear of by keeping the
moving parts of machines apart.
It reduces the maintenance and running cost
of machine.
4. It increases the efficiency of machine by
reducing the loss of energy.
It can also act as corrosion preventers.
It act as a seal as in piston.
5. Three types of lubrication are :
Hydrodynamic or Fluid film or Thick film
lubrication
Boundary or Thin film lubrication
Extreme pressure lubrication
6. Also called complete or full flow.
Occurs when two surfaces are completely
separated by a fluid film. { Thickness of fluid
film is at least 1000 Å } .
In this method ,the lubricant fills the grooves
and forms a thick layer in between them so
that there is no direct contact between the
sliding surfaces.
In this way ,the lubricant reduces the wear
and tear by reducing the frictional resistance
produced by movement of sliding parts.
7.
8. It is a semi-solid, consisting of a metallic
soap dispersed throughout a liquid
lubricating oil . The liquid lubricant maybe
petroleum oil or synthetic oil and it may
contain additives also.
These are prepared by saponification of fat {
fatty acid, vegetable oils } with alkali [like
lime,caustic soda ] followed by adding hot
lubricating oil while under agitation.
Sodium,calcium,lithium soaps are used as
gelling agents.
9.
10. To improve the heat resistance of grease ,
inorganic solid thickening gents like finely
divided clay,belonite,carbon black etc..
11. They have high shear or frictional resistance
than oils ,can support much heavier loads at
lower speeds .
Normally grease can sustain temperature
upto 180 degree.
They have a tendency to separate into oils
and soaps.
12. In situations where oil cannot remain in place
due to high load,low speed,sudden jerks etc..
I. FOR EXAMPLE :In rail axle boxes;
In bearing and gears that work at high T
In situations where bearing neeeds to be
sealed against entry of dust,dirt,moisture
because greases are less liable to
contamination by these.
In situations where dripping of oil is
undesirable , because unlike oils,greases if
used do not splash over articles being
prepared by the machine.For
eg:paper,textile industrial machines.
13. The main function of soap is thickening agent
so that grease sticks firmly to the metal
surface.
Temperature upto which the grease can be
used.
Its consistency.
Its water and oxidation resistance.
14. CALCIUM BASED GREASES:
Emulsion of petroleum oils with calcium
soaps.
Cheapest and most commonly used
Insoluble in water.
Used at low temperature ,because above 80°C
oil and soaps begin to separate.
USED for :Tractors, lubricating water pumps.
15. Thickened by mixing sodium soaps.
Not a water resistant.Since it slightly soluble
in water.
However , they can be used upto 175°C .
Used in ball bearings.
Dropping point is very high
16. It is prepared by the saponification of vegetal
oils with lithium hydroxide.
It is thickened by adding adding lithium
soaps.
Water resistant
Suitable to use at low temperature [15°C]
only.
Used for lubricating engines.
17.
18. It is prepared by adding lime to resins and
fatty oils.Fillers like talc and mica are also
added to them.
Water resistant.
Very cheap resin-grease.
Suitable for less delicate equipments working
under high load and low speed’
19. Used where :
1) Operating conditions and load is too high
2) Where contamination of lubricating oil or
greases is unacceptable.
3) Combustible lubricants must be avoided
4) Operating condition are such that a
lubricating film cannot be secured by use of
oils or greases.
