1.1 introduction of gear

Sanjivani Rural Education Society’s
Sanjivani College of Engineering, Kopargaon-423603
( An Autonomous Institute Affiliated to Savitribai Phule Pune University, Pune)
NAAC ‘A’ Grade Accredited, ISO 9001:2015 Certified
Subject :- Theory of Machines II
T.E. Mechanical (302043)
Unit 1
1.1 Introduction of Gears
By
Prof. K. N. Wakchaure(Asst Professor)
Department of Mechanical Engineering
Sanjivani College of Engineering
(An Autonomous Institute)
Kopargaon, Maharashtra
Email: wakchaurekiranmech@Sanjivani.org.in Mobile:- +91-7588025393

GEAR
Power transmission is the movement of energy from its place of generation
to a location where it is applied to performing useful work
A gear is a component within a transmission device that transmits
rotational force to another gear or device.
2Subject :- Theory of Machines II

PRIMITIVE GEARS

GEAR MATERIALS
 The materials used for the manufacture of gears depends upon the strength and service conditions like
wear, noise etc.
 The gears may be manufactured from metallic or non-metallic materials. The metallic gears with cut teeth
are commercially obtainable in cast iron, steel and bronze.
 The non-metallic materials like wood, rawhide, compressed paper and synthetic resins like nylon are
used for gears, especially for reducing noise.
 The cast iron is widely used for the manufacture of gears due to its good wearing properties, excellent
machinability and ease of producing complicated shapes by casting method. The cast iron gears with
cut teeth may be employed, where smooth action is not important.
 The steel is used for high strength gears and steel may be plain carbon steel or alloy steel. The steel gears
are usually heat treated in order to combine properly the toughness and tooth hardness.
 The phosphor bronze is widely used for worms gears in order to reduce wear of the worms which will be
excessive with cast iron or steel.

TYPES OF GEARS
1. According to the position of axes of the shafts.
a. Parallel
1.Spur Gear
2.Helical Gear
3.Rack and Pinion
b. Intersecting
Bevel Gear
c. Non-intersecting and Non-parallel
Worm and worm gears
6PROF. K N WAKCHAURE

TYPES OF GEARS
2. According to the peripheral velocity of the gears.
(a)Low velocity : less than 3 m/s
(b) Medium velocity: between 3 and 15 m/s
(c) High velocity: more than 15 m/s
7

TYPES OF GEARS
3. According to the type of gearing.
(a) External gearing,
(b) Internal gearing, and
(c) Rack and pinion.
8

SPUR GEAR
 Teeth is parallel to axis of rotation
 Transmit power from one shaft to another parallel
shaft
 Used in Electric screwdriver, oscillating sprinkler,
windup alarm clock, washing machine and clothes
dryer

 Advantages
 They offer constant velocity ratio
 Spur gears are highly reliable
 Spur gears are simplest, hence easiest to design and manufacture
 A spur gear is more efficient if you compare it with helical gear of same size
 Spur gear teeth are parallel to its axis. Hence, spur gear train does not produce axial thrust. So the gear shafts can
be mounted easily using ball bearings.
 They can be used to transmit large amount of power (of the order of 50,000 kW)
 Disadvantages
 Spur gear are slow-speed gears
 Gear teeth experience a large amount of stress
 They cannot transfer power between non-parallel shafts
 They cannot be used for long distance power transmission.
 Spur gears produce a lot of noise when operating at high speeds.
 when compared with other types of gears, they are not as strong as them.
SPUR GEAR

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
 One interesting thing about helical gears is that if the angles of the gear teeth are correct, they can be
mounted on perpendicular shafts, adjusting the rotation angle by 90 degrees.

 Advantages
 The angled teeth engage more gradually than do spur gear teeth causing them to run more smoothly and
quietly
 Helical gears are highly durable and are ideal for high load applications.
 At any given time their load is distributed over several teeth, resulting in less wear
 Can transmit motion and power between either parallel or right angle shafts
 Disadvantages
 An obvious disadvantage of the helical gears is a resultant thrust along the axis of the gear, which needs to
be accommodated by appropriate thrust bearings, and a greater degree of sliding friction between the
meshing teeth, often addressed with additives in the lubricant.
 Thus we can say that helical gears cause losses due to the unique geometry along the axis of the helical
gear’s shaft.
 Efficiency of helical gear is less because helical gear trains have sliding contacts between the teeth
which in turns produce axial thrust of gear shafts and generate more heat. So, more power loss and less
efficiency
HELICAL GEAR

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.
13PROF. K N WAKCHAURESubject :- Theory of Machines II

RACK AND PINION
 Rack and pinion gears are used to convert rotation (From the pinion)
into linear motion (of the rack)
 A perfect example of this is the steering system on many cars.
14PROF. K N WAKCHAURESubject :- Theory of Machines II

 Advantages
 Cheap
 Compact
 Robust
 Easiest way to convert rotation
motion into linear motion
 Rack and pinion gives easier and
more compact control over the
vehicle
 Disadvantages
 The rack and pinion can only work with certain levels of
friction. Too high a friction and the mechanism will be
subject to wear more than usual and will require more
force to operate.
 The most adverse disadvantage of rack and pinion
would also be due to the inherent friction, the same
force that actually makes things work in the mechanism.
Due to the friction, it is under a constant wear, possibly
needing replacement after a certain time
RACK AND PINION

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, marine applications, automobiles, printing presses, cooling
towers, power plants, steel plants, railway track inspection machines, etc.
16

STRAIGHT AND SPIRAL BEVEL GEARS

BEVEL GEARS
Disadvantages
•High costs.
•Bevel gears are manufactured in pairs. For
maintenance and repair, both gears must be replaced.
•In order to achieve high efficiency, bevel gear sets
must be positioned exactly, so the shafts must be
adjusted very precisely.
•Limited translation range. Maximum ratio of 6:1 per
bevel gear set. Spur gear stages are necessary in order
to achieve a higher overall gear ratio.
•Bevel gears are not recommended for high-speed
reduction. At high speed, a bevel gear unit generates
noise.
Advantages
•Quiet Operating noise (Quiet operation is
particularly advantageous in environments
such as theatres or airports.)
•Increased torque capacity compared to worm
gears of the same size.
•High efficiency (rolling of bevel gears is very
efficient compared to the sliding effect of worm
gears (98.5%). The metal bevel gear teeth never
come into direct contact with an oil film.)
•Hollow shaft possible

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
 Many worm gears have an interesting property that no other gear set has: the worm can easily turn
the gear, but the gear cannot turn the worm
 Worm gears are used widely in material handling and transportation machinery, machine
tools, automobiles etc
Worm Wheel
Worm

 Advantages
 Worm gear drives operate silently and smoothly.
 They are self-locking.
 They occupy less space.
 They have good meshing effectiveness.
 They can be used for reducing speed and increasing torque.
 High velocity ratio of the order of 100 can be obtained in a single step
 Disadvantages
 Worm gear materials are expensive.
 Worm drives have high power losses
 A disadvantage is the potential for considerable sliding action, leading to low efficiency
 They produce a lot of heat.
WORM AND WORM GEAR

GEAR APPLICATIONS
•Automobiles
•Toy’s Industry
•Factory automation
•Packaging machine
•Industrial robots
•Food processing machine
•Car production machine
•Machine tool industry
•Material handling
•Printing machine
•Automatic cutting / welding machine
•Machine for medical/cosmetic field
•Construction machine
•Wood / Glass processing machine
•Agricultural machinery https://khkgears.net/new/gear_application.html

1.1 introduction of gear

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