A presentation on spur gear

Department of Mechanical Engineering
Don Bosco College of Engineering and Technology, ADBU
Dipjyoti Deka- DC2015BTE0167
Prepared By
A presentation on
Spur gears: design and applications
SPUR GEARS: DESIGN AND APPLICATIONS 1

1) Introduction: Spur gear Terminology
2) Beam strength of spur gear
3) Tangential load on gear tooth
4) Service factor
5) Design for dynamic load
6) Bukingham’s load equation
7) Design for wear
8) Gear tooth failures
9) Force analysis
10) Tooth involute system
11) Proportions of standard involute teeth
12) Advantages and Disadvantages
13) Applications of Spur Gear
14) Conclusion
15) References
Contents

 Spur gears are used to transmit power and rotary motion between
parallel shafts.
 If teeth of the gear wheels are parallel to the axis of wheel, the
gears are called spur gears.
 It is used when axes of the driving and driven shafts are parallel
and co-planar.
 The smaller of the two gears in mesh is called the pinion, and the
larger is designated as the gear.
Introduction

Fundamental Law of Gearing: This law may be stated as "The
shape of the teeth of a gear must be such that the common normal
at the point of contact between two teeth must always pass
through a fixed point on the line of centers”.
Fundamental Law of Gearing
Fig No: 1. Fundamental Law of Gearing

Gear ratio : The ratio of the number of teeth of the
wheel (gear) to that of the pinion is called gear
ratio.
Transmission ratio : The ratio of the angular speed
of the first driving gear of a train of gears to that of
the last driven gear is called transmission ratio.
Cycloid: A plane curve described by a point on a
circle (generating circle), which rolls without slip
on a fixed line (base line) is known as cycloid.
Involute: A plane curve described by a point on a
straight line which rolls without slip
on a fixed circle is known as involute.
Face width: The width over the toothed part of a
gear, measured along a straight line generator of the
reference cylinder is known as face width.
Gear Nomenclature
Fig No: 2. Gear Nomenclature

Base circle: In an involute cylindrical gear, the
base circle of the involutes of the tooth profiles
is known as base circle.
Circular pitch (p): The distance on the pitch
circle from a point on a tooth to the
corresponding point of the adjacent tooth.
Diametric pitch (P): It is defined as the
number of teeth of the gear divided by the pitch
circle diameter.
Module (m): It is defined as the pitch circle
diameter per unit number of teeth, i.e,
Gear Nomenclature contd..

Pressure angle (ɸ): The angle between the line of
action (a line through the pitch point and tangential
to the base circles) and a line perpendicular to the
line of centers at the pitch point is known as
pressure angle.
Centre distance (C): The distance between the
centers of the two gears in mesh is known as
center distance.
Backlash: The difference between tooth space
and tooth width is known as backlash.
Clearance: The difference between the dedendum
of one gear and the addendum of
the mating gear is known as clearance.
Gear Nomenclature contd..

The analysis of bending stresses in gear tooth was
done by Wilfred. In the Lewis analysis, the gear
tooth is treated as a cantilever beam as shown in Fig.
The tangential component (Pt) causes the bending
moment about the base of the tooth. The Lewis
equation is based on the following assumptions:
(i) The effect of the radial component (Pr), which
induces compressive stresses, is neglected.
(ii) It is assumed that the tangential component (Pt)
is uniformly distributed over the face width of the
gear. This is possible when the gears are rigid and
accurately machined.
(iii) The effect of stress concentration is
neglected.
(iv) It is assumed that at any time, only one pair of
teeth is in contact and takes the total load.
Beam strength of spur gear teeth (Design for Static Load)
Fig No: 3 Gear Tooth as Cantilever
Fig No: 4. Gear Tooth as Parabolic Beam

In the above equation, Y is called the Lewis form
factor.
Beam strength of spur gear teeth (Design for Static
Load) contd..
Fig No: 3 Gear Tooth as Cantilever
Fig No: 4. Gear Tooth as Parabolic Beam

The two basic modes for gear tooth failure are:
1. Breakage of the tooth due to static and dynamic loads,
2. Surface destruction.
Breakage of Tooth: The complete breakage of the tooth can
be avoided by adjusting module and face width so that the
beam strength of the gear tooth is more than the sum of
static and dynamic loads.
Surface Destruction: The wear of gear tooth takes place due
to the combined action of rolling and sliding. Rolling causes
contact stresses and sliding causes rubbing action. Pinion is
subjected to more rubbing action as it rotates faster than the
gear.
The principal types of gear tooth wear are:
1. abrasive wear
2. corrosive wear
3. pitting
4. scoring
Gear tooth failures
Fig No: 5. Gear tooth failures

Velocity Factor

The service factor accounts for increase in the tangential force due to fluctuation of the
torque developed by the prime mover and the torque required to run the machine. It
depends upon the prime mover and the driven machine.
Tangential Load on tooth
Service Factor, Cs

The dynamic force is introduced in the gear teeth due to the
following factors:
1. Inaccuracies of the tooth profile,
2. Errors in tooth spacing,
3. Misalignment between bearings
4. Elasticity of parts, and
5. Inertia of rotating masses
Design for dynamic load

Force analysis
The force (Fn) is resolved into two
components, tangential, (Ft), and
radial component, (Fr) which are
related to the pressure angle as
Fig No: 6 Force analysis of gear tooth

All standard systems prescribe the
involute profile for gear tooth. The
reasons are as follows:
(i) The involute profile satisfies the
fundamental law of gearing at any
center distance.
(ii) All involute gears of a given module
and pressure angle are completely
interchangeable.
(iii) All involute gears of a given
module and pressure angle can be
machined from one single tool.
(iv) The basic rack of an involute
profile has straight sides. It is
comparatively easy to machine straight
sides. Further, straight sides can be
more accurately machined compared
with a curved surface.
Tooth involute system
Fig No: 7 Tooth involute system

Proportions of standard involute teeth
Fig No: 8

Advantages of Spur Gear:
1. Spur gears have high power transmission efficiency.
2. They are compact and easy to install.
3. They offer constant velocity ratio.
4. Unlike belt drives, spur gear drives have no slip.
5. Spur gears are highly reliable.
They can be used to transmit large amount of power (of the
order of 50,000 kW).
Disadvantages of Spur Gear:
1. Spur gear drives are costly when compared to belt drives. They have a
limited center distance. This is because in a spur gear drive, the gears
should be meshed and they should be in direct contact with each other.
2. Spur gears produce a lot of noise when operating at high
speeds.
Advantages and Disadvantages

Spur gears have a wide range of applications. They are used in:
1. Metal cutting machines
2. Power plants
3. Marine engines
4. Mechanical clocks and watches
5. Fuel pumps
6. Washing Machines
7. Gear motors and gear pumps
8. Rack and pinion mechanisms
9. Material handling equipment's
10. Automobile gear boxes
11. Steel mills
12. Rolling mills
Applications of Spur Gear

In this presentation we have studied about Spur gear, its design,
working and its applications. The usage of this type of gears in various
units like automobile, industrial and many other such units helps to
regulate amount the speed and prevents in wear. Spur gears are, now, a
very vital part of any factories, industries and technical sectors based on
their types and its application aspects.
Conclusion

Friday, January 18, 2019 20
Internet websites
Wikipedia
NPTEL
Calvin.edu
Mechanicalksk.com
E-Book
Spur gear design Prof. K.gopinath & Prof.M.mayuram
Gear design by Sunil g. janiyani
Book
Design of Machine elements by V.B Bhandari
References

A presentation on spur gear

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