Friction and Lubrication
Some times there is screeching sound while using a pulley or hand
pump. Friction is a force. Whatever work we do, friction works opposite
to our force. When we apply a force to move something, the friction
opposes our force and there is no motion. When our force is greater than
the friction force, the object starts moving. The parts where there is
friction, they wear out fast.
A smooth surface shows lots of uneven and rough surface under a
microscope. When these rough parts rub on each other, it results in
friction.
Oiling and greasing reduces friction and wear & tear of parts. When
there is dust or foreign particles in the area of contact, friction and
wear & tear are high and rapid. To prevent this, we must first clean
the friction area and put oil or grease there.
Friction is not always bad. Sometimes we require friction.
For
example:
1) While walking friction helps us. If we put oil on the floor, we will
fall down due to slippery floor. We need friction to be able to walk.
2) It is commonly seen that in muddy area the wheel of a truck slips
round and round because there is no friction between the tyres and
ground.
3) Flour mill works because of friction between belt and wheel.
4) Bicycle can be stopped by putting on a brake, which works because
there is friction.
5) When we tie a knot in a rope, it is the friction which holds the
knot.
Thus friction is useful to some extent but it will reduce the efficiency
of work.
Factors affecting friction
The intensity of friction depends on following factors:
i) The area involved in friction.
ii) The pressure applied on the surfaces.
Force = Pressure ´
Area
Frictional force will increase, if the area of contact will increase or if pressure applied on the surface increased.
Methods to reduce friction
i) Polish the contact surface.
ii) Put oil or grease so that it fills in the small gaps of the flat parts.
iii) Use ball bearings to reduce area of contact between rotating parts.
Lubrication
Following methods can be used to reduce friction:
Oil is either thin or viscous. It depends upon SAE No. of oil. (SAE means Society of Automotive Engineers). If we use very viscous oil, it does not reach all the parts. Very thin oil will flows away easily and gets wasted. Grease is used in such cases. It is generally used around ball-bearing. Normal grease or oil is never used where there is high pressure, high temperature and high speed. Special lubricants are used in such cases. In cold season the oil becomes thick and in hot season it becomes thin. Therefore selection of lubrication also depends on the season. It is always advisable to refer operating manual of the equipment before selecting the lubricant.
