High applications, low gear ratios Continuous contact, quite

High transmission efficiency, noisy
operation, simple tooth profile and easy manufacturing, medium life span.

 

Parallel shafts, Medium to high speed and torques
applications, low gear ratios

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Continuous contact, quite operation, complex tooth profile,
tedious manufacturing, high

 

Continuous contact, quite operation, complex tooth profile,
tedious manufacturing, high

 

Continuous contact, quite operation, complex tooth profile,
tedious manufacturing, high

 

Parallel shafts, high speed and torque applications, low
gear ratios (used as gear trains to achieve high gear ratios).

 

efficiency (less than spur gear)

 

Efficiency less than spur and helical gears, continuous
contact and relatively quiet operation, complex tooth profile

 

Efficiency at par with helical and spur, high loads

 

 

 

 

 

 

 

 

 

 

INTRODUCTION

1.1      
Background and Problem Statements

Gears are part of our everyday machines. They
are used to transfer motion and power from one place to another and used to
manipulate torque and speed and motion direction at the output. When a number
of gears are used together in a confined environment with proper arrangement of
shafts, bearings, seals and a housing converting the whole assembly, it is
called a gearbox. With the advancement of technology, there are many types of
gearboxes which include variable transmission ratio gearboxes as well.

The problem statement involves design of a
gearbox with selection of appropriate gear train to transmit power from an
input motor shaft running at 1440 rpm to an output shaft running at 480 rpm. The
torque at the output shaft is 100 N-m. The gearbox will operate for 5 hours
continuous in working days and the user require gearbox to have a life of at
least 5 years.

1.2      
.Project Goals
and Limitations

1.2.1    
Goals:

·      Selection
of appropriate gear type and size to be used in gearbox.

·      Sizing
of the gear and pinion as per the speed ratio and forces being transmitted.

·      Selection
of appropriate material for gear and pinion.

·      Design
of input and output gear shaft with appropriate coupling scheme and suitable
material.

·      Selections
of bearings from a manufacturer’s catalogue keeping in view the strength and
life requirements.

·      Selection
of lubricant seals from a manufacturer’s catalogue.

·      Selection
of motor for input with appropriate power rating (torque and speed).

·      Manufacturing
and fabrication drawings for all the components including BOM and costing.

1.2.2    
Limitations:

·      Input
shaft speed is 1440 rpm

·      Output
shaft speed is 480 rpm

·      Gearbox
minimum life is 5 years (4 hours of duty cycle in working days).

·      Torque
at output shaft is 100 N-m.

1.3      
Quality Assurance International Standards

The
quality of report and design both have been in accordance with the project
report instructions provided. All the contents have been verified and reviewed
twice.

All
the figures, tables, have been checked for errors. Reports have been proof read
for grammatical mistakes, spelling errors and formatting abnormalities.
References have been cross checked.

The
design process of gearbox and functional requirements are strictly as per the
project report template. All the limitations mentioned in project report
template have been taken into account during the design process of gearbox.
Safety factors are taken into account, fatigue factor and dynamic loading
factors have been considered while doing the calculations. Safety standards and
design standards used for gearbox have been taken into account during the
design process of gearbox.

1.4      
Symbols and Terminology

All the symbols, abbreviations and nomenclatures
used in this report have been summarized in following table.

                                                          Table 1 List of Symbols

 

2      
BASIC CALCULATIONS AND DESIGN SELECTION

In this chapter, following topics will be covered.

·      
Selection of gear type

·      
Speed and torque calculations

·      
Design of input and output shafts

·      
Design of gears

·      
Selection of seals and bearings

2.1      
Selection of Gear Type

There are four major types of gears that are Spur gears,
helical gears, worm gears and bevel gears majorly used in gearboxes for speed
reduction and power transmission. Following table shows the characteristics of
each type of gear and its application.                                             

Table 2 Types of gears and their application

Speed ratio of the gearbox intended to be designed is
calculated as

Since the speed ratio for the desired gearbox is small and
the operating speeds are also low-medium range. A single stage spur gear is
suitable for the selected gearbox. The detailed design of the gear and pinion
will be done in following sections.

2.2      
Speed and Torque Calculations

The speed ratio of gearbox is

The torque ratios in a single stage gearbox are given by
following formula

The torque ratios are calculated considering the
transmission efficiency to be 100% and neglecting any frictional or thermal
losses for simplicity.

2.3      
Design of Input and Output Shafts

The input and output shafts of a gearbox are key components
to consider in the design process. The torque from motor is transmitted to the
input shaft which in turn transmits the torque to the pinion. This torque is
amplified at the gear wheel and transmitted to the output shaft on which gear
wheel is mounted. The increase in the output torque is at the cost of reduction
in the speed since overall power in the system remains constant. The shaft
design consists of following steps;

·      
Material Selection

·      
Sizing Calculation

·      
Stress and Deflection

Shafts undergoes phenomenon called twisting when torque is
transmitted through. So they must be designed to withstand the torque at
certain factor of safety.

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