Study of Gears

1. “Study Of Different types Of Gears”
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2015
H.T
[Companyname]
4/17/2015
Basics Mechanics OF Machines
Study OF Different types Of
Gears
Assignment: Study Of Different types OF Gears
Submitted To: Mam Mehroz Sana
Submitted By: Syed Mesum Raza Naqvi
Roll No: 2013-Bt-Mech-116
Date: 16/April/2015
Lab No: 2 Study OF Different types Of Gears

2. Objective:
“Study OF Different types Of Gears”
What is Gear:
A gear is a component with in transmission device that transmits rotational force to another gear
or device, gear is different form a pulley in that gear is round wheel which has linkage (teeth) that
mesh with other gear teeth, allowing force to be fully transferred without any kind of slippage.
Depending upon their construction and arrangement gear devices can transmit force at different
speeds, torques in a different directions from the power source, the most common situation is for
a gear to mesh with another gear most important features is that the gears of unequal sizes
combined with each other to get a maximum mechanical advantage so that the rotational speed
and torque of second gear is different from the first one, gears are as shown in the figure below.
Fig (2.1) Fig (2.2)
Power Transmission by Gears:
Power transmission can be defined as the movement of energy from its place of generation to a
location where it is applied to performing useful work as shown in figure.
Fig (2.3) Fig (2.4)

3. Types OF Gears:
According to the position of axes of the shafts:
a) Parallel
1) Spur Gears
2) Helical Gears
3) Rack and Pinion
b) Intersecting (non-parallel)
1) Bevel Gears
c) Non-Intersecting and Non-Parallel
1) Worm and Worm Gears
“According to the position of axis of the shaft”
Spur Gears:
In spur gears the teeth are parallel to the axis of rotation and they transfer power from one shaft to
another parallel shaft, in this case the two parallel and co-planar shafts are connected to each other
by the help of spur gears and the arrangement is known as spur gearing because they have teeth
parallel to the axis of the wheel, spur gears are shown in the figures below.
Uses:
a) Used in electric Screw Drivers
b) Oscillating Sprinkler
c) Windup Alarm Clock
d) Washing Machine
e) Clothes Dryer
Fig (2.5) Fig (2.6)

4. Helical Gears:
Another name given to the spur gearing is helical gearing in which the teeth ate inclined to the axis
of the wheel, in simple word 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. One interesting thing about helical gears is that if the angles of the gears are correct, they
can be mounted on perpendicular shafts adjusting the rotation angle by 90 degrees, the load on
helical gears is distributed to the several teeth resulting in reduce wear.
Fig (2.7) Fig (2.8)
Uses:
a) These are highly used in transmission because they are quieter even at higher speed.
b) Helical gears are durable and used in cars.
c) Helical gears are used in textile industries.
d) Helical gears are also used in rolling mills, elevators, sugar industries, conveyors belts.
e) Helical gears are also used in compressors and in oil industries.
Advantages:
a) Can transmit power b/w parallel or right angle shafts.
b) Helical gears are highly durable and ideal for high load applications.
Disadvantages:
a) There is greater degree of sliding friction b/w the meshing teeth due to the
resultant thrust along the axis of the gears.
b) Efficiency of helical gear is less because helical gear trains have sliding contact
b/w teeth which produce axial thrust of gears.

5. Herringbone Gears:
Helical gears may be double or single, the double helical gears are known as Herringbone gears
in which a pair of gears is kinematically equivalent to a pair of cylindrical disc which attached to
the parallel shaft and having a line contact, to avoid axial thrust, two helical gears of opposite
hand can be mounted side by side, to cancel the resulting thrust forces.
Fig (2.9) Fig (2.10)
Uses:
a) These gears are increasingly use in external gears pumps.
b) These are used for applications that required high pressure.
Advantages:
a) Quite and pulse free flow.
b) Improved load carrying ability.
c) Greater strength.
d) Minimum hydraulic shock
e) Made up of cast iron for wear resistance
Disadvantages:
a) The manufacturing cost is very high due to special shape.
b) During assembly a gear box, aligning is to be given special attention.

6. Rack and Pinion:
Sometimes the gears of the shaft mashes externally and internally with the gears in straight line
such type of gear is known as Rack and Pinion gears, the straight line gear is called as Rack and
the circular is called as Pinion a little consideration will show that with the help of rack and
pinion we can convert linear motion to rotatory motion and vice versa.
Fig (2.11) Fig (2.12)
Uses:
The rack and pinion system assists in power steering of many vehicles including cars and some
trucks.
Advantages:
a) Rack and Pinion give easier and more compact control over the vehicle.
b) Easiest way to convert rotation motion to linear motion.
c) It is cheap.
d) It is compact.
e) It is robust.
Disadvantages:
a) The most adverse advantages of rack and pinion would also be due to the inherent
friction due to this friction it is under a constant wear possibly needing after a certain
time.
b) The rack and pinion can only work with certain levels of friction

7. Bevel Gears:
The two non-parallel but coplanar shafts connected by gears are known as Bevel Gears and the
arrangement is known as bevel gearing, it may also have their teeth inclined to the face of the
bevel in this case these are called as helical bevel gearing.
Fig (2.13) Fig (2.14)
Uses:
a) Bevel gears are used when the direction of a shafts needs to be changed.
b) They are usually mounted on shafts that are 90 degrees apart, but can be designed to
work at other angles as well.
c) These are used in locomotive marine applications and in railway tracks and in inspection
machines.
Advantages:
f) This gear make it possible to change the operating angle.
g) Differing number of teeth on each wheel allows mechanical advantage to be changed.
Disadvantages:
c) One wheel of such gear is designed to work with its complementary wheel and no
other.
d) Must be precisely mounted.
e) The shafts bearings must be capable of supporting significant forces.

8. Worm and Worm Gear:
Boston Gear's worms and worm gears provide an effective answer for power transmission
applications requiring high-ratio speed reduction in a limited space using right angle (90°), non-
intersecting shafts. When properly applied, worms and worm gears provide the smoothest,
quietest form of gearing. Because the efficiency of a worm gear drive depends on the lead angle
and number of starts on the worm - and because increased efficiency is always a goal, the ratio
should be kept as low as possible. To run properly, worms and worm gears used together must
have the same diameter pitch and threads.
Fig (2.15) Fig (2.16)
Uses:
d) Worm gears are used when large gear reductions needed.
e) Many worms gear have interesting property that no other gear set, the worm can
easily turn the gear.
f) Worm gears are widely used in material handling and transportation machinery,
machine tools and automobiles.
g) Advantages:
h) Worms gear drives operates smoothly.
i) They are self-locking.
j) They occupy less space.
k) They have good meshing effectiveness.
l) They can be used to reduce the speed.
m) High velocity ratio cab be obtained.
Disadvantages:
f) Worms gears materials are expensive.
g) Worm drives have high power loss.
h) They produce a lot of heat.
i) A disadvantages is the potential for considerable sliding action leading to low
efficiency.

9. “The Gears According to the Peripheral Velocity”
a) Low Velocity
b) Medium Velocity
c) High Velocity
Low Velocity Gears:
Low velocity gears can be defined has the gears having velocity less than 3m/s are termed as
low velocity gears.
Medium Velocity Gears:
High velocity gears cab be defined as the gears having velocity between 3m/s to 15m/s are called
medium velocity gears.
High Velocity Gears:
The velocity gears can be defined as the gears having velocity more than 15m/s is known as high
velocity gears.
“The Gears According to the type Of Gearing”
a) External Gears
b) Internal Gears
c) Rack and pinion
External Gearing:
In external gearing the gears of two shafts mesh externally with each and the other the larger of
these two wheel is called Spur wheel and the smaller one is called Pinion.
Internal Gearing:
The gears of two shafts mesh internally, the larger one wheel is called Anular and the smaller is
called Pinion, in internal gearing the motion of two wheels are always in same direction.
Rack and Pinion:
Sometimes the gears of the shaft mashes externally and internally with the gears in straight line
such type of gear is known as Rack and Pinion gears, the straight line gear is called as Rack and
the circular is called as Pinion a little consideration will show that with the help of rack and
pinion we can convert linear motion to rotatory motion and vice versa.

10. “The Gears According to the position of teeth on Gears surfaces”
a) Straight
b) Inclined
c) Curved
The spur gears have straight teeth whereas the helical gears have inclined teeth and in case of
spiral gears the teeth are curved over the rim.
Gear Trains:
a) A gear train is two or more gear working together meshing their teeth and turning each
other in a system to generate power and speed.
b) It reduces speed and increases torque.
c) Electric motors are used with the gear system to reduce the speed and increase the torque.
Fig (2.17) Fig (2.18)

11. Types Of gear trains:
a) Simple gear train
b) Compound gear train
c) Planetary gear train
Simple Gear Train:
The most common of the gear train is the gear pair connecting parallel shafts, the teeth of this
type can be spur, helical or herringbone.
Fig (2.19) Fig (2.20)
Compound Gear Train:
a) Compound gear train used for large velocities.
b) Two or more gears may rotate about a single axis .
Fig (2.21) Fig (2.22)