Design & Construction of a Pair of Bevel gear A report submitted to the Department of Mechanical Engineering, Khulna University of Engineering & Technology in partial fulfillment of the requirements for the “Course of ME 3218” Supervised by Submitted by Dr. Mohammad Mashud Md. Shariful Islam Professor Roll: 1205004 Department of Mechanical Engineering Section: A Khulna University of Engineering & Technology January 2016 Department of Mechanical Engineering Khulna University of Engineering & Technology Khulna 9203, Bangladesh
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Design & Construction of a Pair of Bevel gear
A report submitted to the Department of Mechanical Engineering, Khulna University of
Engineering & Technology in partial fulfillment of the requirements for the
“Course of ME 3218”
Supervised by Submitted by
Dr. Mohammad Mashud Md. Shariful Islam
Professor Roll: 1205004
Department of Mechanical Engineering Section: A
Khulna University of Engineering & Technology
January 2016
Department of Mechanical Engineering
Khulna University of Engineering & Technology
Khulna 9203, Bangladesh
i
Acknowledgements
All the praises to the almighty who makes author capable to complete this Special
work successfully. The author is very much indebted to his course teacher
Dr. Mohammad Mashud, professor of Department of Mechanical Engineering, Khulna
University of Engineering & Technology, Bangladesh, for his wise inspiration to do such
extraordinary work. The author expresses the heart- felt respect to him for his proper
guidance and all kind of support to perform and complete this special study.
The author is extremely grateful to Prof. Dr. Nawsher Ali Moral ,Head of the department of
Mechanical Engineering Khulna University of Engineering & Technology, Bangladesh,
to provide such a good opportunity to do the project work and for providing all other
supports.
May ALLAH bless the course teacher.
“Author”
ii
Abstract
A gear, simply put, is an extension of the wheel. A gear is a rotating machine part having
cut teeth, which mesh with another toothed part to transmit torque. The main function of a
gear is to transmit power of rotating shaft.
Bevel gears are used to connect intersecting shafts, usually but not necessarily at 900. Bevel
gears are most often mounted on shafts that are 90 degrees apart, but can be designed to work
at other angles as well. The pitch surface of bevel gears is a cone.
In this project work a couple of bevel gear(gear & pinion) was designed, and number of
teeth, pitch, face, material of gear and finally heat treatment of gear material also determined.
Finally the Gears were made by Mild Steel, which is low cost and available in every
Figure-1.1 Some typical bevel gear ……………………………………….......................2
Figure-2.2 Nomenclature of a simple gear ……………….………………………………5
Figure-2.2 Schematic arrangement of (a)External (b)Internal Gear …….………………..6
Figure-2.3 Typical view of spur,bevel,skew,helical and worm gear sequentially …..…..6
Figure-3.1 Designed of dimension of gear ……………………………………………....14
Figure-3.2 Designed of dimension of pinion………………………………………….….14
Figure-3.3 CAD Design of Gear and pinion sequentially …………………….………….…..15
Figure-3.4 Rendered view of designed gear…………………….………………….….…..15
Figure-4.1 Developed pair of bevel gear (Gear & Pinion) ……………….………...……19
1
Introduction
Objectives
Chapter I
2
1.1 Introduction
A gear or cogwheel is a rotating machine part having cut teeth, or cogs, which mesh with another
toothed part to transmit torque, in most cases with teeth on the one gear being of identical shape,
and often also with that shape on the other gear. Two or more gears working in a sequence (train)
are called a gear train or, in many cases, a transmission. such gear arrangements can produce
a mechanical advantage through a gear ratio and thus may be considered a simple machine.
Geared devices can change the speed, torque, and direction of a power source. The most
common situation is for a gear to mesh with another gear; however, a gear can also mesh with a
linear toothed part, called a rack, thereby producing translation instead of rotation.
Bevel gears are gears where the axes of the two shafts intersect and the tooth-bearing faces of the
gears themselves are conically shaped. Bevel gears are most often mounted on shafts that are 90
degrees apart, but can be designed to work at other angles as well. The pitch surface of bevel
gears is a cone.
Fig 1.1: Some typical bevel gear
The most common gear-cutting processes include hobbing, broaching, milling, and grinding.
Gears are commonly made from metal, plastic, and wood.
1.2 Objectives:
The main objectives of this project work are-
I. To solve a problem related to Bevel Gear
II. To design that Bevel Gear
III. To develop the selected Gear
3
Historical Background
What is Gear?
Types Of Gears
Bevel Gear
Field of Applications of Bevel gear
Advantages of Bevel Gear
Dis-advantages of Bevel Gear
Chapter II
4
2.1 Historical Background
Early examples of gears date from the 4th century BCE in China (Zhan Guo times - Late
East Zhou dynasty), 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 (287–212 BCE).
Examples of further development include:
Ma Jun (c. 200–265 CE) used gears as part of a south-pointing chariot.
The Antikythera mechanism is an example of a very early and intricate geared device,
designed to calculateastronomical positions. Its time of construction is now estimated
between 150 and 100 BCE.
The water-powered grain-mill, the water-powered saw mill, fulling mill, and other
applications of watermill often used gears.
The first mechanical clocks were built in CE 725.
The 1386 Salisbury cathedral clock may be the world's oldest working mechanical clock.
2.2 What is Gear ?:
A gear, simply put, is an extension of the wheel. The extension is the teeth on the outer rim of
the wheel, which allows them to be meshed together with other gears for the purpose of
transferring drive from a motor. In a very basic driveshaft, there are three types of gears:
The driver, the idler, and the driven. Due to the laws of motion, coupling two gears together
causes them to rotate in opposite directions. When two gears mesh, and one gear is bigger than
the other (even though the size of the teeth must match), a mechanical advantage is produced,
with the rotational speeds and the torques of the two gears differing in an inverse relationship.
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Fig 2.1: Nomenclature of a simple gear
2.2.1 Basic Purpose Of Use Of Gears
Gears are widely used in various mechanisms and devices to transmit power and motion
positively (without slip) between parallel, intersecting (axis) or non-intersecting non parallel
shafts,
without change in the direction of rotation
with change in the direction of rotation
without change of speed (of rotation)
with change in speed at any desired ratio
Often some gearing system (rack – and – pinion) is also used to transform rotary motion into
linear motion and vice-versa.
2.2.2 General Applications Of Gears
Gears of various type, size and material are widely used in several machines and systems
requiring positive and stepped drive. The major applications are:
Speed gear box, feed gear box and some other kinematic units of machine tools
Speed drives in textile, jute and similar machineries
Gear boxes of automobiles
Speed and / or feed drives of several metal forming machines
Machineries for mining, tea processing etc.
Large and heavy duty gear boxes used in cement industries, sugar industries, cranes,
conveyors etc.
Precision equipments, clocks and watches
Industrial robots and toys.
2.2.3 Types Of Gears
2.1.4.1 According to configuration
External gear
Internal gear
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Fig 2.2: Schematic arrangement of (a)External (b)Internal Gear
2.1.4.2 According to axes of transmission
Spur gears
Bevel gears
Helical gears
Skew gears
Worm gears
Fig 2.3: Typical view of spur,bevel,skew,helical and worm gear sequentially
2.1.4.3 According to pattern of motion
Rotation to rotation
Rotation to translation or vice versa – e.g. rack and pinion
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2.3 Bevel Gear:
2.3.1 Types of Bevel Gear:
Bevel gears are classified in different types according to geometry:
Straight bevel gears have conical pitch surface and teeth are straight and tapering
towards apex.
Spiral bevel gears have curved teeth at an angle allowing tooth contact to be gradual and
smooth.
Zerol bevel gears are very similar to a bevel gear only exception is the teeth are curved:
the ends of each tooth are coplanar with the axis, but the middle of each tooth is swept
circumferentially around the gear. Zerol bevel gears can be thought of as spiral bevel
gears, which also have curved teeth, but with a spiral angle of zero, so the ends of the
teeth align with the axis. Hypoid bevel gears are similar to spiral bevel but the pitch surfaces are hyperbolic and
not conical. Pinion can be offset above, or below,the gear centre, thus allowing larger
pinion diameter, and longer life and smoother mesh, with additional ratios e.g., 6:1, 8:1,
10:1. In a limiting case of making the "bevel" surface parallel with the axis of rotation,
this configuration resembles a worm drive. Hypoid gears were widely used in automobile
rear axles.
2.3.2 Field of Applications of Bevel gear
The bevel gear has many diverse applications such as locomotives, marine applications, automobiles, printing presses, cooling towers, power plants, steel plants, railway track inspection machines, etc.
For examples, see the following articles on:
Bevel gears are used in differential drives, which can transmit power to two axles spinning at different speeds, such as those on a cornering automobile.
Bevel gears are used as the main mechanism for a hand drill. As the handle of the
drill is turned in a vertical direction, the bevel gears change the rotation of the chuck
to a horizontal rotation. The bevel gears in a hand drill have the added advantage of
increasing the speed of rotation of the chuck and this makes it possible to drill a range
of materials.
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The gears in a bevel gear planer permit minor adjustment during assembly and allow
for some displacement due to deflection under operating loads without concentrating
the load on the end of the tooth.
Spiral bevel gears are important components on rotorcraft drive systems. These
components are required to operate at high speeds, high loads, and for a large number
of load cycles. In this application, spiral bevel gears are used to redirect the shaft
from the horizontal gas turbine engine to the vertical rotor.
2.3.3 Advantages of Bevel Gear This gear makes it possible to change the operating angle.
Differing of the number of teeth (effectively diameter) on each wheel
allows mechanical advantage to be changed. By increasing or decreasing the ratio
of teeth between the drive and driven wheels one may change the ratio of
rotations between the two, meaning that the rotational drive and torque of the
second wheel can be changed in relation to the first, with speed increasing and
torque decreasing, or speed decreasing and torque increasing.
2.3.4 Dis-advantages of Bevel Gear One wheel of such gear is designed to work with its complementary wheel and no
other.
Must be precisely mounted.
The shafts' bearings must be capable of supporting significant forces.
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Problem
Solution
Our Designed Dimension
CAD Design & Rendered View
Specification Of Gears
Gear materials
Selected Material
Chapter III
10
3.1 Problem
Decide upon the pitch, face, Ng , material, and heat treatment of a pair of straight
Bevel gears to transmit continuously and indefinitely a uniform loading of 5 hp at
900 rpm of the pinion, reasonable operating temperature, high reliability;