Technical Presentation on External Gear PPT Introduction A gear or cogwheel is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part to transmit torque. Geared devices can change the speed, torque, and direction of a power source. Gears almost always produce a change in torque, creating a mechanical advantage, through their gear ratio, and thus may be considered a simple machine. The teeth on the two meshing gears all have the same shape. Two or more meshing gears, working in a sequence, are called a gear train or a transmission. A gear can mesh with a linear toothed part, called a rack, thereby producing translation instead of rotation. The gears in a transmission are analogous to the wheels in a crossed belt pulley system. An advantage of gears is that the teeth of a gear prevent slippage.

1. Technical Presentation
External Gears & its Application
Presented By:
Prathamesh Deshpande

2. Introduction
A gear or cogwheel is a rotating machine part having
cut teeth, or cogs, which mesh with another toothed
part to transmit torque.
Geared devices can change the speed, torque, and
direction of a power source.
Gears almost always produce a change in torque,
creating a mechanical advantage, through their gear
ratio, and thus may be considered a simple machine.
The teeth on the two meshing gears all have the same
shape. Two or more meshing gears, working in a
sequence, are called a gear train or a transmission.
A gear can mesh with a linear toothed part, called a
rack, thereby producing translation instead of rotation.
The gears in a transmission are analogous to the
wheels in a crossed belt pulley system. An advantage
of gears is that the teeth of a gear prevent slippage.

3. History of Gear
Early examples of gears date from the 4th century BCE
in China, which have been preserved at the Luoyang
Museum of Henan Province, China.
The earliest gears in Europe were circa CE 50 by Hero
of Alexandria, but they can be traced back to
the Greek mechanics of the Alexandrian school in the
3rd century BCE and were greatly developed by the
Greek polymath Archimedes.

4. Comparison with drive mechanisms
The definite velocity ratio that teeth give gears
provides an advantage over other drives in precision
machines such as watches that depend upon an
exact velocity ratio.
In cases where driver and follower are proximal,
gears also have an advantage over other drives in
the reduced number of parts required; the downside
is that gears are more expensive to manufacture and
their lubrication requirements may impose a higher
operating cost per hour.
Single stage gear reducer

5. Gear Nomenclature

6. Types of Gear

7. External & Internal Gear
An external gear is one with the teeth formed on the
outer surface of a cylinder or cone.
Conversely, an internal gear is one with the teeth
formed on the inner surface of a cylinder or cone.
For bevel gears, an internal gear is one with
the pitch angle exceeding 90 degrees. Internal gears
do not cause output shaft direction reversal.
External Gear Internal Gear

8. External Gear Pump
An external gear pump uses two external gears that
displace non-lubricating fluids.
The mechanism is usually driven by one of the toothed
gears, which in turn drives the other.
Three factors are involved in the regulation of flow:
volume of cavity between the teeth, speed of gears,
and the amount of fluid that slips back to the inlet via
the mechanism.
There are three main types of external gears: spur,
helical and herringbone.
Helical and herringbone deliver more flow at higher
pressure while also being quieter, but may require a
greater inlet pressure than spur.

9. Internal Gear Pump
An internal gear pump uses internal and external
gears. The gears themselves are lubricated by the
fluid, which is of a lubricating nature.
The internal design is seen as being reliable, easy to
operate and maintain due to only two moving parts
being present.
Only one drive gear is required for the mechanism to
function but it is possible to use two.
The design can also be modified to include
a crescent shaped portion that improves
performance when pumping high viscosity fluids.
Internal gear pumps have relatively low speed and
inlet pressure requirements.

10. External & Internal Gear Pump
External Gear Pump Internal Gear Pump

11. Application

12. References Links
http://processprinciples.com/2012/07/gear-pumps/
http://www.slideshare.net/Nishalkadli/introduction-
to-gears-15838360?next_slideshow=1
https://en.wikipedia.org/wiki/Gear
http://mechanicalmania.blogspot.in/2011/07/types-
of-gear.html
http://www.engineersedge.com/gear_design.htm