\(\small \bullet\) When a solid surface is rubbed/slided against another surface, a force is created between the two solids which acts in the opposite direction of motion, this force is called frictional force. This phenomenon is called friction.
\(\small \bullet\) This happens due to roughness of the two surfaces.
\(\small \bullet\) Friction is the force of resistance offered to motion, experienced by bodies which are in contact.
Types of friction
Static friction: The friction between two solid objects when at rest is called static friction. Static friction can prevent an object from sliding down on a sloped surface.
Limiting friction: When the frictional force (F) is equal to the applied pulling force (P) then the friction between two surfaces is known as limiting friction. (i.e F=P)
Dynamic friction: It is the friction between two objects, when are in motion is called dynamic friction. It is also called kinetic friction.
Sliding friction: It is the friction experienced by an object when it slides over another object. Sliding friction is always less than limiting friction.
Rolling friction: It is the friction that occurs when a circular object rolls on a flat surface. Rolling friction is less than sliding friction. (ball or roller bearing)
\(\small \bullet\) Weight of the block acting vertically downward (W)
\(\small \bullet\) The normal reaction which acts upwards (R)
\(\small \bullet\) The applied pulling force (P)
\(\small \bullet\) The frictional force (F)
\(\small \bullet\) When the body is about to move W=R, F=P
\(\small \bullet\) When pulling force is increased the body starts to move.
Laws of friction
\(\small \bullet\) Frictional force is directly proportional to the normal reaction between contacting surfaces.
\(\small \bullet\) Frictional force acts opposite to the direction of motion.
\(\small \bullet\) Frictional force depends on the nature of contacting surfaces.
\(\small \bullet\) Frictional force is independent over the area and shape of contacting surfaces.
Coefficient of friction
\(\small \bullet\) It is a ratio between the frictional force to the normal reaction when the body is just about to move but at equilibrium. It is represented by symbol μ.
$\displaystyle \small \mu =\frac{Limiting\, friction\, or \, Force}{Normal\, reaction\, or \, Weight}$
$\displaystyle \small \mu =\frac{F}{R}=\frac{P}{W}$
Angle of friction
\(\small \bullet\) The forces acting on a body when it is just about to move by the application of a pulling force are W, R, P and F.
\(\small \bullet\) The forces 'R' and 'F' are compounded and we get the resultant force 'S'.
\(\small \bullet\) The angle formed by 'S' with 'R' is the angle of friction.
$\displaystyle \small \tan \theta =\frac{F}{R}$
$\displaystyle \small \tan \theta =\mu$
Angle of repose
\(\small \bullet\) A body placed on an inclined surface remains at rest till the angle of inclination equals the angle of friction.
\(\small \bullet\) When it exceeds the body starts sliding down. This is known as angle of repose.
Coefficient of friction = Tangent of angle of repose
$\displaystyle \small \mu =\tan \phi$
∴ $\displaystyle \small \theta =\phi$
R=Wcosθ
P=F+Wsinθ
$\displaystyle \small P=W\left [ \frac{\sin (\theta +\phi )}{\cos \phi } \right ]$
Advantages of friction
\(\small \bullet\) Helps us to walk without slipping
\(\small \bullet\) Used to stop vehicles when brakes are applied.
\(\small \bullet\) Movement of vehicles due to friction between revolving wheels with tyres and the road.
\(\small \bullet\) Power transmission using gear drive or belt pulley drive.
\(\small \bullet\) Using friction we can sharp any object and also to hold it.
\(\small \bullet\) Nails and screws are held in wood by friction.
\(\small \bullet\) Heat is produced when two rough surfaces are rubbed against each other.
Disadvantages of friction
\(\small \bullet\) It causes wear and tear of the machine parts.
\(\small \bullet\) It produces heat and may cause melting of machine parts. To avoid production of heat using of coolant is necessary.
\(\small \bullet\) It reduces efficiency of a machine.
\(\small \bullet\) It reduces speed of the moving object. ex. spindle, shaft, piston etc.
Friction can be reduced
\(\small \bullet\) By using suitable lubricants (oil, grease) between the moving parts.
\(\small \bullet\) By polishing the surface to make them smooth.
\(\small \bullet\) By using ball bearings and roller bearings.
\(\small \bullet\) By the use of wheel
Lubrication
\(\small \bullet\) When two parts of a machine rub against each other while operating, friction and heat are generated due to which the machine operates noisily and heavily.
\(\small \bullet\) Lubrication is a process in which problems arising out of friction are reduced by applying oil or grease or engine oil between moving parts.
\(\small \bullet\) Substance used for lubrication is known as lubricant.
Advantages of Lubrication
\(\small \bullet\) Life of the machine increases
\(\small \bullet\) Speed of the machine increases
\(\small \bullet\) Efficiency of the machine increases
\(\small \bullet\) Accuracy of the machine is maintained
\(\small \bullet\) Machine becomes non-corrosive
\(\small \bullet\) Parts are protected from getting heated
\(\small \bullet\) Saves electricity bill
Types of Lubrication System
Gravity feed
The gravity feed principle is employed in oil holes, oil cups and wick feed lubricators provided on the machines
Force feed/Pressure feed
Oil, grease gun and grease cups
By pressing the nose of the gun against the oil hole or grease point leading to each bearing, the lubricant is forced to the bearing. Greases are also force fed using grease cup
Splash lubrication
In this method a ring oiler is attached to the shaft and it dips into the oil and a stream of lubricant continuously splashes around the parts, as the shaft rotates. The rotation of the shaft causes the ring to turn and the oil adhering to it is brought up and fed into the bearing, and the oil is then led back into the reservoir. This is also known as ring oiling.
Types of grease guns
Cutting Fluids
Cutting fluids are the substances used for efficient cutting while cutting operations take place.
Functions of Cutting Fluids
1. to cool the tool as well as the work-piece
2. to reduce the friction between the chip and the tool face by lubricating
3. to prevent the chip from getting welded to the tool cutting edge
4. to flush away the chips
5. to prevent corrosion of the work and the machine
Properties of Cutting Fluids
1. A good cutting fluid should be sufficiently viscous.
2. At cutting temperature, the coolant should not catch fire.
3. It should have a low evaporation rate.
4. It should not corrode the work-piece or machine.
5. It must be stable and should not foam or fume.
6. It should not create any skin problems to the operator.
7. Should be transparent
Types of Cutting Fluids
Straight mineral oil: coolants which can be used undiluted
Chemical solution: chemicals in dilute solution with water
Compounded oil: used in automatic lathes. These are cheaper and more fluid
Fatty oils: lard oil and vegetable oil.
Soluble oil: soluble oil is added to water which gets non corrosive effect with water in the ratio of about 1:20. Soluble oil is an oil blend mixed with an emulsifier (soft soap, caustic soda).
\(\small \bullet\) This happens due to roughness of the two surfaces.
\(\small \bullet\) Friction is the force of resistance offered to motion, experienced by bodies which are in contact.
Types of friction
Static friction: The friction between two solid objects when at rest is called static friction. Static friction can prevent an object from sliding down on a sloped surface.
Limiting friction: When the frictional force (F) is equal to the applied pulling force (P) then the friction between two surfaces is known as limiting friction. (i.e F=P)
Dynamic friction: It is the friction between two objects, when are in motion is called dynamic friction. It is also called kinetic friction.
Sliding friction: It is the friction experienced by an object when it slides over another object. Sliding friction is always less than limiting friction.
Rolling friction: It is the friction that occurs when a circular object rolls on a flat surface. Rolling friction is less than sliding friction. (ball or roller bearing)
\(\small \bullet\) The normal reaction which acts upwards (R)
\(\small \bullet\) The applied pulling force (P)
\(\small \bullet\) The frictional force (F)
\(\small \bullet\) When the body is about to move W=R, F=P
\(\small \bullet\) When pulling force is increased the body starts to move.
Laws of friction
\(\small \bullet\) Frictional force is directly proportional to the normal reaction between contacting surfaces.
\(\small \bullet\) Frictional force acts opposite to the direction of motion.
\(\small \bullet\) Frictional force depends on the nature of contacting surfaces.
\(\small \bullet\) Frictional force is independent over the area and shape of contacting surfaces.
Coefficient of friction
\(\small \bullet\) It is a ratio between the frictional force to the normal reaction when the body is just about to move but at equilibrium. It is represented by symbol μ.
$\displaystyle \small \mu =\frac{Limiting\, friction\, or \, Force}{Normal\, reaction\, or \, Weight}$
$\displaystyle \small \mu =\frac{F}{R}=\frac{P}{W}$
Angle of friction
\(\small \bullet\) The forces 'R' and 'F' are compounded and we get the resultant force 'S'.
\(\small \bullet\) The angle formed by 'S' with 'R' is the angle of friction.
$\displaystyle \small \tan \theta =\frac{F}{R}$
$\displaystyle \small \tan \theta =\mu$
Angle of repose
\(\small \bullet\) When it exceeds the body starts sliding down. This is known as angle of repose.
Coefficient of friction = Tangent of angle of repose
$\displaystyle \small \mu =\tan \phi$
∴ $\displaystyle \small \theta =\phi$
R=Wcosθ
P=F+Wsinθ
$\displaystyle \small P=W\left [ \frac{\sin (\theta +\phi )}{\cos \phi } \right ]$
Advantages of friction
\(\small \bullet\) Helps us to walk without slipping
\(\small \bullet\) Used to stop vehicles when brakes are applied.
\(\small \bullet\) Movement of vehicles due to friction between revolving wheels with tyres and the road.
\(\small \bullet\) Power transmission using gear drive or belt pulley drive.
\(\small \bullet\) Using friction we can sharp any object and also to hold it.
\(\small \bullet\) Nails and screws are held in wood by friction.
\(\small \bullet\) Heat is produced when two rough surfaces are rubbed against each other.
Disadvantages of friction
\(\small \bullet\) It causes wear and tear of the machine parts.
\(\small \bullet\) It produces heat and may cause melting of machine parts. To avoid production of heat using of coolant is necessary.
\(\small \bullet\) It reduces efficiency of a machine.
\(\small \bullet\) It reduces speed of the moving object. ex. spindle, shaft, piston etc.
Friction can be reduced
\(\small \bullet\) By using suitable lubricants (oil, grease) between the moving parts.
\(\small \bullet\) By polishing the surface to make them smooth.
\(\small \bullet\) By using ball bearings and roller bearings.
\(\small \bullet\) By the use of wheel
Lubrication
\(\small \bullet\) When two parts of a machine rub against each other while operating, friction and heat are generated due to which the machine operates noisily and heavily.
\(\small \bullet\) Lubrication is a process in which problems arising out of friction are reduced by applying oil or grease or engine oil between moving parts.
\(\small \bullet\) Substance used for lubrication is known as lubricant.
Advantages of Lubrication
\(\small \bullet\) Life of the machine increases
\(\small \bullet\) Speed of the machine increases
\(\small \bullet\) Efficiency of the machine increases
\(\small \bullet\) Accuracy of the machine is maintained
\(\small \bullet\) Machine becomes non-corrosive
\(\small \bullet\) Parts are protected from getting heated
\(\small \bullet\) Saves electricity bill
Types of Lubrication System
Gravity feed
The gravity feed principle is employed in oil holes, oil cups and wick feed lubricators provided on the machines
Oil, grease gun and grease cups
By pressing the nose of the gun against the oil hole or grease point leading to each bearing, the lubricant is forced to the bearing. Greases are also force fed using grease cup
Splash lubrication
In this method a ring oiler is attached to the shaft and it dips into the oil and a stream of lubricant continuously splashes around the parts, as the shaft rotates. The rotation of the shaft causes the ring to turn and the oil adhering to it is brought up and fed into the bearing, and the oil is then led back into the reservoir. This is also known as ring oiling.
Types of grease guns
Cutting Fluids
Cutting fluids are the substances used for efficient cutting while cutting operations take place.
Functions of Cutting Fluids
1. to cool the tool as well as the work-piece
2. to reduce the friction between the chip and the tool face by lubricating
3. to prevent the chip from getting welded to the tool cutting edge
4. to flush away the chips
5. to prevent corrosion of the work and the machine
Properties of Cutting Fluids
1. A good cutting fluid should be sufficiently viscous.
2. At cutting temperature, the coolant should not catch fire.
3. It should have a low evaporation rate.
4. It should not corrode the work-piece or machine.
5. It must be stable and should not foam or fume.
6. It should not create any skin problems to the operator.
7. Should be transparent
Types of Cutting Fluids
Straight mineral oil: coolants which can be used undiluted
Chemical solution: chemicals in dilute solution with water
Compounded oil: used in automatic lathes. These are cheaper and more fluid
Fatty oils: lard oil and vegetable oil.
Soluble oil: soluble oil is added to water which gets non corrosive effect with water in the ratio of about 1:20. Soluble oil is an oil blend mixed with an emulsifier (soft soap, caustic soda).
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