Basic Mechanical Engineering -Mechanical Elements

Unit 1
Introduction to Mechanical Engg.
Prof. S.R.Thorat
Mechanical Engg. Department
Sanjivani Collge of Engineering, Kopargaon
1
1. Mechanical Elements
S.R. Thorat/BME/Unit-1/Mechanical Elements

Transmission Shaft
2S.R. Thorat/BME/Unit-1/Mechanical Elements

Machine Shaft
Crankshaft
Spindle

2.Axle
• It is used to support rotating element pulleys,
brakes.
• It does not transmits torque but subjected to
bending moment only.

3.Key
• A key is a mechanical element inserted between
the shaft and hub or boss of the pulley to
connect these together in order to prevent
relative motion between them.
• It is always inserted parallel to the axis of the
shaft.
• Keys are used as temporary fastenings and are
subjected to considerable crushing
and shearing stresses
• material – Plain carbon steel
• Material used for key is lesser
strength than shaft material. 5S.R. Thorat/BME/Unit-1/Mechanical Elements

Classification-
1.Sunk keys 5. Kennedy Key
2. Saddle key 6. Tangent key
3. Round keys
4.Splines.
1.Sunk Key-
The sunk keys are provided half in the keyway
of the shaft and half in the keyway of the hub
• Types of Sunk key
1 Rectangular sunk key
2. Square sunk key
3. Parallel sunk key
4. Gib-head key 6S.R. Thorat/BME/Unit-1/Mechanical Elements

1 Rectangular sunk key
2. Square sunk key 3.Gib-head key

2.Saddle keys
• The saddle keys completely fits in key way
provided in hub of rotating element.
• Types-
1. Flat saddle key
2. Hollow saddle
key
8

3.Splines
4.Kennedy Key
9

4.Coupling
Coupling is used to connect two shafts or to couple
driving shaft with driven shaft.
Functions-
1. To provide the connection of shafts of different
units such as a motor and generator and to
provide disconnection for repairs or
alternations.
2.To reduce the transmission of shock loads from
one shaft to another.
3.To introduce protection against overloads.

Requirements of a Good Coupling-
1.It should be easy to connect or disconnect.
2. It should transmit the full power from one
shaft to the other shaft without losses.
3.It should hold the shafts
in perfect alignment.

1.Rigid coupling
2. Flexible coupling
1.Flange coupling
2.Sleeve or muff coupling.
1.Universal coupling or Hooks Joint
2. Oldham coupling

1.Flange coupling
13
Applications- Connection of electric motor to pump or
compressor S.R. Thorat/BME/Unit-1/Mechanical Elements

2.Sleeve or muff coupling

1.Oldham coupling
2.Universal coupling or Hooks Joint

5.Bearing
• It is machine element supports moving element .
• Function-
1.To provide support to the shaft
2. To permit free rotation of shaft with minimum
friction.
Classification –
1.Sliding contact Bearing
i. Journal Bearing
ii. Thrust Bearing
2. Rolling Contact Bearing
i.Ball Bearing
ii.Roller Bearing 16

1.Sliding Contact Bearing
i. Journal Bearing
ii. Thrust Bearing-

2. Rolling Contact Bearing
i. Ball Bearing-
ii. Roller Bearing-

Ball Bearing
19

6. clutch
• Clutch is mechanism used to transmit rotary
motion from driving shaft to driven shaft as
when required without stopping the driver
shaft.
• Function-
i. When engaged transmit max power from
engine shaft to gearbox i/p shaft .
ii. When disengaged , allow driver to shift the
transmission in various gear positions.
iii. When disengaged, engine shaft should freely
rotate without transmitting drive to wheels. 20
S.R. Thorat/BME/Unit-1/Mechanical
Elements

Single Plate clutch

7.Brakes
• Brake is device with help of which artificial
frictional resistance is applied to moving
machine member in order to stop or retard the
motion of a machine.
• While performing this operation , brakes absorb
kinetic energy of moving member .
• Energy absorbed by brake is dissipated in the
form of heat in surrounding air, so that excessive
heating of brake lining does not takes place.

Disc Brake
23

Unit 1
Introduction to Mechanical Engg.
Prof. S.R.Thorat
1
2. Power Transmission Devices
(Belt and Chain Drive)
S.R. Thorat/BME/Unit-1/Belt and Chain Drive

Power Transmission Devices
• Drives- It is mechanism used to transmit
power and speed from prime mover to
machine.
• Flexible drive-Belt , rope, chain
• Rigid Drive-Gears, cams, Clutch, coupling,
2
S.R. Thorat/BME/Unit-1/Belt and Chain
Drive

1. Belt Drive
• Used to transmit power from one shaft to another by means of
pulleys which rotates at the same speed or different.
• Power is transmitted by virtue of friction between belt and pulley
surface
• Power Transmitted depends on
1. Velocity of belt
2. Tension under which belt is placed on
pulleys.
3. The arc of contact between
the belt and smaller pulley.
. .
n D D t
s p
N d d t
+
= = =
+ 3
Drive

Flat Belt V Belt
 V Belt: The belt is having
trapezoidal c/s.
 Used to transmit large
amount of power when two
pulleys are close to each
other.
 Wedging action. Compact in
construction.
 Multiple V drives - very
large power.
 High speed reduction. Upto
7.
 Negligible Sleep, quiet in
operation.
 Limitations:Low efficiency
80-96%, costlier.
 Applications: Blowers,
compressors, drilling m/c, IC
Engines
 Flat Belt: The belt is having
rectangular c/s.
• Used to transmit Moderate
amount of power.
• Puller distance is not more
than 8m apart.
• Pulley are provided with
crowning to avoid coming off
of the belt.
• Relatively cheap and easy to
maintain.
• Efficiency about 98%
• Limitations: Slip, Occupy
more space, Not suitable for
transmitting very high power,
cannot used for short
distances.
• App: Industrial Applications –
Floor mills, Stone crushers,
pumps. 4
Drive

• Circular Belt or Rope Drive:
• Circular in c/s.
• Transmits large amount of power , Pulley dist 5m.
• Pulleys are provided with grooves.
 Timing Belts: It is a toothed belt transmits
power by means of teeth. Hence no slip.
 It uses toothed wheels or sprocket.
 Transmits power at constant speed ratio,
Light weight, High efficiency 97-99%,
Quieter in operation.
 Limitations: costlier, cannot transmit large
power.
 Applications: To drive cam shaft from crank
shaft, to position drives in machine tools,
steeper motor drives. 5
Drive

Types of belt drives
 Open Belt Drive:
 Shafts are parallel and rotate in same direction.
 Lower side – Tight side and upper side – slack side.
6
Drive

• Cross Belt Drive:
• Shafts are parallel and rotates in opposite
direction.
• Gives more angle of contact hence more
frictional grip.
• However at a point where belt crosses, it rubs
against each other and causes wear and tear
of belt thus reducing life.
7
Drive

• Compound Belt Drive:
• Used when power is transmitted from one shaft to
another through number of intermediate pulleys.
• High reduction ratio.
8
Drive

Open Belt with Idler Pulley:
 It is used when shaft are parallel.
 Used when open belt cannot used due to small
angle of contact on smaller pulley.
 It is used to obtain high velocity ratio.
 Tension can be adjusted by changing the position of
the idler pulley.
9
Drive

• Multiple Belt Drive:
• Used when power is transmitted from one shaft
to the number of parallel shafts.
10
Drive

• Chain Drive: Consists of an endless chain
wrapped around two sprockets wheels.
• It consists of number of links connected with pin
joint, while sprockets are toothed wheels.
• Intermediate between gear and belt drives.
2. Chain Drive
11
Drive

Types of chain Drive
1.Hoisting Chain (Cranes)
2. Conveyer Chain
3.Power Transmitting Chain
12
Drive

Unit 1
Introduction to Mechanical
Engg.
Prof. S.R.Thorat
1
2. Power Transmission Devices
(Gears)
S.R. Thorat/BME/Unit-1/Gears

GEAR
• Gear is toothed wheel which can transmit power
and motion from one shaft to another shaft by
means of successive engagement of teeth.
• A gear is a component within a transmission
device that transmits rotational force to another
gear or device
• Gear consist two wheels –
Small –Pinion , large -Gear
2S.R. Thorat/BME/Unit-1/Gears

TYPES OF GEARS
1. According to the position of axes of the
shafts.
a. Parallel Axes Gear
1.Spur Gear
2.Helical Gear
3.Herring bone Gear
b. Intersecting Axes Gear
Bevel Gear
c. Non-intersecting and Non-parallel Axes Gear
worm and worm gears

Spur Gear
• Teeth is parallel to axis
of rotation
• Transmit power from
one shaft to another
parallel shaft
• Applications- Machine
tool gear box ,
Automobile gearbox,
Watches

Helical Gear
• The teeth on helical gears are cut at an angle
to the face of the gear .
• This gradual engagement makes helical gears
operate much more smoothly and quietly than
spur gears .

Herringbone gears
• To avoid axial thrust, two
helical gears of opposite
hand can be mounted side
by side, to cancel resulting
thrust forces
• Herringbone gears are
mostly used on heavy
machinery.

Rack and pinion
• Rack and pinion gears
are used to convert
rotation (From the
pinion) into linear
motion (of the rack)
• Application- steering
system on many cars

Bevel gears
• Bevel gears are useful when the direction of a
shaft's rotation needs to be changed
• They are usually mounted on shafts that are
90 degrees apart, but can be designed to work
at other angles as well.
• The teeth on bevel gears can be straight,
spiral or hypoid
• Applications- locomotives, automobiles,
printing presses, railway track inspection
machines, etc.

Straight and Spiral Bevel Gears

WORM AND WORM GEAR
• Worm gears are used when large gear reductions
are needed.
• It is common for worm gears to have reductions
of 20:1, and even up to 300:1 or greater
• The worm can easily turn the gear, but the gear
cannot turn the worm.
• Applications- material handling and
transportation machinery, machine tools,
automobiles etc

WORM AND WORM GEAR

GEAR TRAINS
• A gear train is combination of two or more gear
which are used to transmit power and speed .
• It is necessary when large speed reduction is
required in small space.
• it is used in watches ,
automobiles.
Types-
1.Simple gear train
2.Compound gear train
3.Planetary gear train
g g p
p p g
Z D n
i
Z d n
= = =

1.Simple Gear Train
• The most common of the gear train is the gear pair
connecting parallel shafts.
• Only one gear may rotate about a single axis
• Number of intermediate gears odd , motion of driver
and driven gear is same.
• Number of intermediate gears even , motion of driver
and driven gear is opposite.
15
S.R. Thorat/BME/Unit-1/Gears

2.Compound Gear Train
• For large velocities, compound arrangement is
preferred
• Two or more gears may rotate about a single
axis

Planetary Gear Train (Epicyclic Gear Train)

Basic Mechanical Engineering -Mechanical Elements

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