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

workshop.

iii

CONTENTS

Page

Acknowledgement………………………………………………………….…………….…i

Abstract……………………………………………………………………….….….………ii

List of Figures………………………………………………………………………………..v

CHAPTER-І: INTRODUCTION

1.1 Introduction……………………………………………………………………………..2

1.2 Objectives……………………………………………………….……………………….2

CHAPTER-ІІ: LITERATURE REVIEW

2.1 Historical Background………………………………………………………...................4

2.2 What is Gear?…………….….………….………………………………………….…….4

2.2.1 Basic Purpose Of Use Of Gears.…….……………………………………..…..5

2.2.2 General Applications Of Gears.………………………………………………..5

2.2.3 Types Of Gears……………………………………………………………..…..5

2.3 Bevel Gear ……………….……………………………………………………………….7

2.3.1 Types of Bevel Gear …………………………………………………..……..…7

2.3.2 Field of Applications of Bevel gear………………………………………….…7

2.3.3 Advantages of Bevel Gear……………………………………………..……….8

2.3.4 Dis-advantages of Bevel Gear…………………………..………………………8

iv

CHAPTER-III

3.1 Problem……………………………..……………………………………………………10

3.2 Solution…………………………………………………………………………………..10

3.3 Our Designed Dimension………………………………………...………………………13

3.4 CAD Design & Rendered View………………………………………………………….14

3.5 Specification Of Gears…………………………………………………………………...15

3.6 Gear materials………………………………………………………………..…………..15

3.7 Selected Material………………………………………………………………………...16

CHAPTER-ІV

4.1 Manufacture Of Gears ………….………………………………………….……………18

4.2 Manufacture of bevel gear………..…….………………………………………….……18

4.3 Finishing of Gear Teeth………..…….………………………………….……….………18

4.4 Final Project…………………………………………………………………….….….…19

CHAPTER- V

5.1 Discussion ………………………………………………………………………..……..21

5.2 Conclusion ………………………………………………………………………………21

References………………………………………………………………………….………..22

v

LIST OF FIGURES

Figure Title Page

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.

5

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

6

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

7

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.

8

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.

9

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;

mg≈1.75 ; Dp ≈ 3.333in. Pinion overhangs, gear is straddle mounted.

3.2 Solution

L=(rp2+rg

2)1/2

tanᵞp =1/mg=1/1.75

ᵞp=29.7º

L sinᵞp=rp

L sin29.7º=3.333/2

L=3.358in

Ft=(33,000hp/vm) lb

vm=(π*Dp *np/12)=(π*3.33*900/12)=785.1 fpm

Ft=(33,000*5/785.1)=210lb

Fd=(VF)*Nsf *Km *Ft

VF=(50+vm1/2)/50=(50+785.41/2)/50

One gear straddle, one not

Km=1.2

Table 15.2, for uniform loading

Nsf=1.0

11

Dynamic load

Fd=(1.56)*(1.0)*(1.2)*(210)=393lb

Wear load

Fw=Dp *b*I *(scd2/C2)*(Cl/Kt*Cr)

2

Dp=3.333in

b = 0.3L=0.3(3.358)=1.0in

Temperature factor

Kt=1.0, reasonable operating temperature

Life factor for wear

Ct=1.0 for indefinite life

Reliability factor for wear

Cr=1.25 high reliability

Geometry factor for wear, Fig. 15.7

Assume I=0.080

Elastic coefficient (Table 15.4)

Steel on steel, Ce =2800

Fw=Fd

(3.333)*(1.0)*(0.08)*{(scd)2/(2800)2}*[1.0/(1.0)*(1.25)]2=393

scd= 134,370 psi

12

Table 15.3, use Steel, (300)

scd= 135ksi

Strength of bevel gears

Fs=(sbbj/Pd)*{Kt/(Ks *Kt*Kr)}

Size factor, assumeKs=0.71

Life factor for strength

Kl=1, for indefinite life

Temperature factor,

Kt=1, good operating condition

Reliability factor

Kr=1.5 high reliability

Geometry factor for strength (Fig. 15.5)

Assume J=0.240

b =1.0in

sd = design flexural stress

Min. BHN = 300

sd =19ksi

Fs=Fd

(19,000)*(1.0)*(0.240)/Pd*[1/{(0.71)*(1)*(1.5)}]=393

13

Pd=110

Say Pd=10

So that b =10/Pd=10/10=1.0in

Dg=DP*mg=(3.333)*(1.75)=5.833in

Ng=Pd *Dg= (10)*(5.833)=58.33

Say Ng=58

Use Pd =10, b=1.0 in, Ng= 58

Material = steel, minm BHN = 300

3.3 Our Designed Dimension

Answer:

Ng=58 Pd =10

b=1.0 in BHN = 300

Material: steel (Mild)

14

Fig 3.1:Designed of dimension of gear

Fig 3.2:Designed of dimension of pinion

3.4 CAD Design & Rendered View

15

Fig 3.4: Rendered view of designed gear

3.5 Specification Of Gears

Fig 3.3: CAD Design of Gear and pinion sequentially

16

Gears are generally specified by their

Type; e.g. spur, bevel, spiral etc.

Material

Size or dimensions

Geometry

Special features, if any.

3.6 Gear materials

The material for any gear is selected based on,

The working condition ie, power, speed and torque to be transmitted

Working environment, i.e., temperature, vibration, chemical etc.

Ease of manufacture

Overall cost of material and manufacture

The materials generally used for making gears are :

Ferrous metals – for high loads

Grey cast iron – preferred for reasonable strength and wear resistance, ease of

casting and machining and low cost

Forged or rolled high carbon steels and alloy steels (Ni-Cr, Mo etc.) which are

either fully hardened or surface hardened for use under high stresses and speed.

Non ferrous metals – for light load

Aluminum, bronze and brass are used for making gears having fine teeth and

working at very light load – e.g., in equipments, toys etc. or against hard steel mating

gears.

Aluminum alloys like aluminum bronze, Zinc – Al. alloy etc.

Non-metals – widely used for light load, non-precision and noiseless operation.

Polymers (plastics) : both thermoplastic and thermosetting type and various

composites (metals, graphite, wood dust or ceramic powders dispersed in

thermosetting plastics).

3.7 Selected Material

Considering cost, strength, ease of access taken into account the selected material for this design

is MILD STEEL.

17

Manufacture Of Gears

Manufacture of bevel gears

Finishing of Gear Teeth

Final Project

Chapter IV

18

4.1 Manufacture Of Gears

Manufacture of gears needs several processing operations in sequential stages depending upon

the material and type of the gears and quality desired. Those stages generally are :

Performing the blank without or with teeth

Annealing of the blank, if required, as in case of forged or cast steels

Preparation of the gear blank to the required dimensions by machining

Producing teeth or finishing the preformed teeth by machining

Full or surface hardening of the machined gear (teeth), if required

Finishing teeth, if required, by shaving, grinding etc.

Inspection of the finished gears.

4.2 Manufacture of bevel gears

In manufacture Straight toothed bevel gear

Forming by milling cutter – low productivity and quality hence employed for

production requiring less volume and precision

Generation – high accuracy and finish, hence applied for batch to mass

production.

Production of gear teeth by form milling are characterised by :

use of HSS form milling cutters

use of ordinary milling machines

low production rate for

⎯ Need of indexing after machining each tooth gap

⎯ slow speed and feed

low accuracy and surface finish

Inventory problem – due to need of a set of eight cutters for each module –

pressure angle combination.

End mill type cutters are used for teeth of large gears and / or module.

4.3 Finishing of Gear Teeth

For smooth running, good performance and long service life, the gears need

to be accurate in dimensions and forms

to have high surface finish and

to be hard and wear resistive at their tooth flanks

Common methods of gear teeth finishing

Gear teeth, after preforming and machining, are finished generally by:

19

for soft and unhardened gears

gear shaving

gear rolling or burnishing

for hard and hardened gears

grinding

lapping

for soft but precision gears

shaving followed by surface hardening and then lapping

4.4 Final Project

Fig 4.1: Developed pair of bevel gear (Gear & Pinion)

20

Discussion

Conclusion

Chapter V

21

5.1 Discuusion

Gears have a principal use in the transformation of power of rotating shaft. This project work

includes design and development of a problem from text book of machine design.Our problem

was related to bevel gear. According to the instruction the bevel gear of selected problem was

designed then developed. Considering cost, strength, ease of access taken into account the

selected material for this design as MILD STEEL.

5.2 Conclusion

Mechanical design is a complex undertaking, requiring many skills. Design and fabrication of a

Pair of bevel was done in this project work. In designing problem number of gear teeth was

determined. The pitch, face, material and heat treatment of gear material were also determined.

The application of bevel gears also studied in this project work.

22

References:

[1]: www.nptel.ac.in/courses/112105127/pdf/LM-31.pdf

[2]: http://www.merriam-webster.com/dictionary/gear

[3]: http://www.myoops.org