Design & Construction of a Flanged Coupling

Supervised by:-

Engr. Md. Rasedul Islam,

Lecturer,

Khulna University of Engineering & Technology.

Submitted by:-

Al Aman

Roll No.: 1105032

Ashraful Alam Shiplu

Roll No.: 1105033

Tausif Rafid Ahmed

Roll No.: 1105034

Md. Habib Ullah Khan

Roll No.: 1105035

Md. Asiful Islam

Roll No.: 1105036

A report submitted to the department of Mechanical Engineering , Khulna University of Enfineering & Technology in partial fulfillment of the requirements for the

“Course of ME-3118”

September-2014Department of Mechanical Engineering

Khulna University of Engineering & TechnologyKhulna-9203,Bangladesh

Thanks to almighty Allah for enabling and helping the authors to carry out this project work.

The authors would like express deep and sincere gratitude to their supervisor Md. Rasedul Islam, Lecturer,Department of Mechanical Engineering, KUET, for his consultion and discussion which were essential to carry out this work. His perpetual energy and enthusiasm in research had motivated the authors through his advices a lot. In addition, he was always accessible and willing to help them to carry out this project.

They want to express their sincere gratitude to Prof. Dr. Mohammad Ariful Islam, Head, Department of Mechanical Engineering, KUET, who gave them permission to work in machine shop, welding shop and heat engine laboratory.

Also thanks to all the lab assistants who helped the authors in order to achieve the project goal.

“Authors”

ACKNOWLEDGEMENT

I

A rigid coupling is a unit of hardware used to join two shafts within a motor or mechanical system. It may be used to connect two separate systems, such as a motor and a generator, or to repair a connection within a single system. A rigid coupling may also be added between shafts to reduce shock and wear at the point where the shafts meet.

Flanged coupling is a type of rigid coupling in which two co-linear shafts are connected by the flanges. The coupling enables torque transmission between the shafts & prevents relative rotation between them.

In the project work a flanged coupling was made by local material available & the analysis of various stresses & safety factor was also performed.

The outcome of analysis is there’s no danger of failure by pure shear, even if a fatigue strength reduction factor is included, but this same section may have severe & undefinable bending stresses on it if the flanges are imperfectly aligned, and they surely will be. The bolts bending was neglected since they were too small compared to the result outcome.

Finally, the computed factor of safety of the flanges suggest that it would withstand repeated bending if the misalignment is small.

ABSTRACT

II

TABLE OF CONTENTS

Acknowledgement I Abstract

II Table of Contents III List of Figures

V List of Tables VI

Nomenclature VII

Page

CHAPTER-1: INTRODUCTION1.1 Introduction

1 1.2 Objectives

3CHAPTER-2: LITERATURE REVIEW

2.1 Historical Background 4

2.2 Safety Factor4

2.3 Importance of Safety Factor 5

2.4 Shear stress & Compression Stress 5

2.5 Unit of Safety Factor 6

2.6 Units of Stress 6

2.7 Description 7

2.8 Function 7

2.9 Advantages & Disadvantages8

2.10 Drawbacks8

CHAPTER-3: DESIGN

III

3.1 Introduction9

3.2 Problem 10

3.3 Solution 11

3.4 Dimensions 13

3.5 Solidwork Design & Keyshot Renderings 14

3.6 Material 15

3.7 Key Feature of the Design 15

3.8 Selection 15

CHAPTER-4: CONSTRUCTION

4.1 Machines & Apparatus Required 16

4.2 Machining Processes 16

4.3 Methodology 18

4.4 Final Project 18

IV

CHAPTER-5: CONCLUSION

5.1 Result & Discussion19

5.2 Conclusion19

REFERENCES20

LIST OF FIGURES

Figure Title Page

Figure 1.1 Muff Coupling 1

Figure 1.2 Types of misalignments in shafts 2

Figure 1.3 A typical flange coupling 2

Figure 1.4 Application of Flanged Coupling 2

Figure 2.1 Single Shear 5

Figure 2.2 Double Shear 6

Figure 2.3 Compressive stress 6

Figure 2.4 Key 7

Figure 2.5 Keyway & Keyseat in flange & shaft 7

Figure 3.1 Dimension Reference 10

Figure 3.2 Flange 1 (Male Part) Dimension in (mm) 13

Figure 3.3 Flange 2 (Female Part) Dimension in (mm) 13

Figure 3.4 Solidwork Design of Flanged Coupling 14

Figure 3.5 Facing 16

Figure 3.6 Turning 17

Figure 3.7 Boring 17

Figure 3.8 Chamfering 17

Figure 3.9 Drilling 18

Figure 3.10 Final Project 18

V

LIST OF TABLES

Table Title Page

Table 2.1 Advantages & Disadvantages of Flanged Coupling 8

VI

NOMENCLATURE

Symbol Description

NDesign FactorFForceAResisting AreaτStressSd

Design StressSy

Yeild StressDDiameterHHeightLLengthTTorqueSys

Yeild StresssSs

Shearing Stress

VII

CHAPTER 1

INTRODUCTION OBJECTIVES

A coupling is a device used to connect two shafts together at their ends for the purpose of transmitting power. Couplings do not normally allow disconnection of shafts during operation, however there are torque limiting couplings which can slip or disconnect when some torque limit is exceeded.

The primary purpose of couplings is to join two pieces of rotating equipment while permitting some degree of misalignment or end movement or both. By careful selection, installation and maintenance of couplings, substantial savings can be made in reduced maintenance costs and downtime.

Couplings are used to connect two shafts for torque transmission in varied applications. It may be to connect two units such as a motor and a generator or it may be to form a long line shaft by connecting shafts of standard lengths say 6-8m by couplings. Coupling may be rigid or they may provide flexibility and compensate for misalignment. They may also reduce shock loading and vibration. A wide variety of commercial shaft couplings are available ranging from a simple keyed coupling to one which requires a complex design procedure using gears or fluid drives etc.

However there are two main types of couplings:

a. Rigid couplings

b. Flexible couplings

a) Rigid Coupling

Rigid Couplings are mainly used in areas where the two shafts are coaxial to each other. There are many types of couplings that fall under the rigid couplings category. They are

Rigid Sleeve or Muff Couplings- 

This is the basic type of coupling. This consists of a pipe whose bore is finished to the required tolerance based on the shaft size. Based on the usage of the coupling a keyway in made in the bore in order to transmit the torque by means of the key. Two threaded holes are provided in order to lock the coupling in position. The photo shows a type of the rigid sleeve or muff coupling.

1.1 INTRODUCTION:

Fig. 1.1 : Muff coupling

b) Flexible Coupling

Flexible couplings are used to transmit torque from one shaft to another when the two shafts are slightly misaligned. Flexible couplings can accommodate varying degrees of misalignment up to 3° and some parallel misalignment. In addition, they can also be used for vibration damping or noise reduction. The material used to manufacture the beam coupling also affects its performance and suitability for specific applications such as food, medical and aerospace. Materials are typically aluminum alloy and stainless steel, but they can also be made in acetal, maraging steeland titanium. The most common applications are attaching encoders to shafts and motion control for robotics.

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Fig.1.2 Types of misalignments in shafts

Flange Coupling

It is a very widely used rigid coupling and consists of two flanges keyed to the shafts and bolted.

Fig. 1.3 A typical flange coupling

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Application:1. Designed for heavy load & industrial

equipment.

2. In various machines.

3. Can be used in a driveshaft of a car or truck.( A drive shaft, driveshaft, driving shaft, propeller shaft (prop shaft), or Cardan shaft is a mechanical component for transmitting torque and rotation )

Fig. 1.4: Application of Flanged Coupling

I. To solve a problem

II. To design that problem

III. To calculate factor of safety

IV. To know about couplings function

V. To know about its application

1.2 OBJECTIVES:

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CHAPTER 2

HISTORICAL BACKGROUND SAFETY FACTOR IMPORTANCE OF SAFETY FACTOR SHEAR STRESS & COMPRESSION STRESS UNIT OF SAFETY FACTOR UNIT OF STRESS DESCRIPTION FUNCTION ADVANTAGES & DISADVANTAGES DRAWBACKS

In 1545, Italian mathematician Girolamo Cardano theorized that the principal of gimbals could be used to transmit rotary motion through an angled connection, which was developed into the Cardan Shaft, which was said to deliver a smoother ride, along with being more efficient and less prone to breakdowns because the shaft was always at a 90 degree angle to the axle. This new concept was actually first seen in 1548 on the carriage of the Holy Roman Emperor Charles the 5th.

Then in 1676, Robert Hooke revisited Cardano’s idea and used it to make an instrument that would allow for a safer way to study the sun. This new instrument used a new type of joint that allowed for twisting motion in one shaft to be passed on to another, no matter how the two shafts were oriented. It would take another 240 years for Clarence W. Spicer to come along and apply this idea to the automotive and industrial industries. Spicer received a patent for the universal joint in 1903 and demonstrated his new patent in a self-designed car, which did not have a troublesome chain & sprocket nor did it have chain and geared adaptions. Spicer would then begin manufacturing in 1904.

Human invented the transformation of energy. Soon they learnt to transfer it using shaft. But in many cases they were unable to transfer power by shafts due to misalignment, length of the shaft & its bending property. So they tried hard & invented the way of transmitting power by shafts in all possible situations. The mechanical joint they invented was named coupling.

2.1 Historical Background:

2.2 Safety Factor- Design Factor:

Factor of safety (FoS) or safety factor (SF) is ordinarily a number obtained that is divided into a criterion of strength in order to obtain a design criterion. In the literal meaning of this words, factor of safety would indicate by what factor the design is safe, but as actually used this is not true. Since its meaning does not accord with the true meaning of the words, it would be better to call it design factor. We shall use the design factor N to define a design stress.

sd=

Factor of safety=

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2.3 Importace of Safety Factor:

Factor of safety is required to bring the structure from the state of collapse to a usable state.It has following significances:1. The structure shouls be able to withstand the variations in expected loading up to some extent. Factor of safety covers uncertainties in forces or loads.2. At service load, deflection should be small.3. When the material used is under strength, factor of safety covers uncertainties in material strength.4. It covers, poor workmanship.5. It covers unexpected behavior of the structure.6. It covers natural disasters.7. During fabrication and erection due to storage of materials, movement of machinery and labor. Stresses are produced which may be very high. Factor of safety may take care of these loads during construction.8. Presence of residual stresses and stress concentrations beyond the level theoretically expected.

2.4 Shear stress & Compression stress:

Stress caused by the forces acting parallel to the area resisting the forces is termed as shear stress.

A shearing stress is produced whenever the applied loads cause one section of a body to tend to slide past its adjacent section

Fig. 2.1: Single Shear

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Fig.2.2: Double Shear

Compression stress is frequently called normal stress.

2.5 Unit of Safety Factor:

Fig.2.3 : Compressive stress

Safety factor is a ratio of the same type of properies & hence it has no unit.

2.6 Unit of Stress:Unit of stress is N/m2 or Pa

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2.7 Description:

The RIGID FLANGE COUPLING is especially designed and developed for horizontal shaft mounted geared unit applications. These applications require a rigid link between the low speed shaft of the gear unit and the machine, such as for conveyor drive, bucket elevator, travel drive applications etc.The coupling consist of a male and female half couplings made from high quality steel 070 M55 (EN9). The range consists of two basic designs, a single taper configuration on smaller sizes and a double taper configuration on larger sizes.The two half couplings are assembled with standardised hardware in compliance with DIN standards. The range of couplings includes 11 sizes with nominal torques ranging from 25 kNm to 1310 kNm. ……[2]

The main parts are :

1) Key

2) Key Hole

3) Bolts & Nuts

The Function of these parts are described below-

2.8 Function:

1) Key is a device used to connect a rotating machine element to a shaft. The key prevents relative rotation between the two parts and may enable torque  transmission.

Fig.2.4: Key

2) For a key to function, the shaft and rotating machine element must have a keyway and a keyseat, which is a slot and pocket in which the key fits.

3) Bolts & nuts holds firmly the two flanges.

Fig.2.5: Keyway & Keyseat in flange & shaft

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2.10 Drawbacks:Drawbacks of flanged coupling are as following-

Flanged coupling can’t transmit power between two non linear shaft.

Advantages Disadvantages

It is cheap Can’t be de-engaged in motion

Simple

Effective

No maintanance

2.9 Advantages & Disadvantages:

Table 2.1 Advantages & Disadvantages of Flanged Coupling

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CHAPTER 3

INTRODUCTION PROBLEM SOLUTION OUR DESIGNED DIMENSION SOLIDWORK DESIGN & KEYSHOT RENDERINGS MATERIAL KEY FEATURES OF THE DESIGN SELECTION

Design of machine components from first principles requires to be able to discriminate between critical and non-critical stress (or strains).

Critical stresses (or strains) are those that essentially determine the required dimensions of a feature or component. These stresses or strains need to be calculated. For example, in coupling design, the key and keyway involve critical stress and the dimensions of the keyway are based on the allowable stress in the key and keyway.

Non-critical stresses (or strains) are those that have a low value and do not influence dimensions. The dimensions in this case are determined by appearance or some other functional requirement other than stress or strain. For example, in a coupling, the width of the outer flange is a non-critical dimension and is usually determined by appearance/safety considerations (giving adequate protection from the protruding bolts and nuts).

Where critical stresses are involved, the analysis can be done by calculation using formulas. This is the approach adopted here. It is important to realise that this approach involves some "guesstimation" because certain assumptions and approximations are usually necessary. This is where experience and skill of a mechanical design engineer is required, to know what assumptions to make and to have a feel for the types of stresses involved and to be able to discriminate between those that are critical and those that are not.

Another method of stress and strain analysis is using finite element method (FEA) using a computer. This is a more accurate method but involves study in its own right.

3.1 Introduction:

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The vast majority of cases, when a coupling is needed, it is more cost effective to purchase an off-the-shelf coupling than to design and manufacture a custom coupling. However, from the point of view of mechanical design, the design of a rigid coupling from first principles is a good exercise to familiarise with the process of machine element design.

The project work is an outcome of a flanged coupling. At first it was designed & thenConstructed.

3.2 Problem:A manufacturer’s catalog gives the following dimensions in inches for a flange coupling, Fig. 10.19: d=3, D=5, L=4, h=, H=8, g=1. Let the shaft be made of cold-finished C 1035, the bolts and square keys of cold drawn C 1020, and flanges of as-rolled C 1035. There are Nb =4 bolts equally spaced. Let a design factor of N=3.5 based on the shearing yield strength cover the effect of stress concentration and determine the torque capacity of the shaft in pure torsion. Then, for this torque applied to other parts of the connection, compute the nominal factors of safety based on yield strengths for each conventional method of failure.

Fig. 3.1 : Dimension Reference

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3.3 Solution:

The yield strengths of the materials are ( sy for tension and compression; sys=.6sy )

From table AT 7, Cold-drawn C 1020, sy= 66 ksi; sys= 39.6 ksi;

From table AT 7, As-rolled C 1020, sy= 55 ksi; sys= 33 ksi;

From table AT 10, Cold-drawn C 1035, sy= 78 ksi; sys= 46.8 ksi;

Now,

Torque Capacity of the shaft is, T=ss = =71 in-kips

For 4 bolts, Area offering resistance = 4A1 =4* = (0.75)2 = 1.767 in2

Corresponding resistance force, ssA = ss(0.75)2

Moment arm of this resistance is, r = H/2 = 8.25/2 =4.125 in , Fig 10.19

Hence the torque T is

T= Fr = ss(0.75)2(4.125) = 71 in-kips,

Hence, ss= 9.73 ksi. The factor of safety is

N= = 4.07

Compression area per bolt = hg;

For four bolts, Ae= 4hg = (4)(0.75)(1.0625) = 3.1875

Corresponding resistance force, scA = sc(3.1875),

Whose moment arm is r = H/2 = 4.125

Hence the torque is, T = Fr =sc(3.1875)(4.125) = 71 in-kips,

From which sc = 5.4 ksi.

With the flange strength governing ( 55<66 ),

N = = 10.2, compression of bolts

and flange.

The flange may shear at the outside hub diameter.

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The resisting area is cylindrical, Dg ;

The resistance force is ssDg = ss(5.375)(1.0625); and,

Moment arm of r = D/2= 5.375/2 = 2.6875, the resisting torque is

T = Fr = ss(5.375)(1.0625)(2.6875) = 71 in-kips

From which ss = 1.47 ksi

Nominal factor of safety is

N= = 22.4 , shear of flange.

There is no danger here of failure by pure shear, even if a fatigue strength reduction factor were included but this same section may have severe and undefinable bending stresses on it if the flanges are imperfectly aligned, and they surely will be.

The bolts will also subjected to some bending.

Let, the side of square key be b= inch Table AT 19; let it’s length be the hub length, L=4.75 in Then the Factor of safety of the key are

N= = == 2.98 [shear]

N= = == 2.07 [ compression ]

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Fig. 3.2 Flange 1 (Male Part) Dimension in (mm)

Fig. 3.3 Flange 2 (Female Part) Dimension in (mm)

3.4 Our Designed Dimension in (mm):

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3.5 Solidworks Design & Keyshot Renderings:

Fig. 3.4: Solidwork Design of Flanged Coupling

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3.6 Material:

In our project work we used cast iron material. Since it is a dummy design & we didn’t need the actual strength, we used it. Besides AISI materials aren’t available in our workshop.

3.7 Key Features of the Design:

Even clamping force on application shaft.Limiting stress raisers on application shaft.Easy assembly / disassembly without damage to components.Can be assembled on keyed shaft.The reduced key increases the coupling torque capability and limits damage to components by preventing relative movement between components. ………[2]

3.8 Selection:

The nominal torque of the coupling is tabulated. We recommend the use of a service factor of two (SF=2) on the nominal torque. The maximum applied torque should therefore be equal to less than half the tabulated torque value.Applied Torque [kNm] = 9.55 x Applied Power [kW] ÷ Speed [rpm] ½ Nominal Torque [kNm]

The coupling can be supplied with an optional reduced key connection. The reduced key connection has not been taken into consideration in calculating the nominal torque rating of the coupling. The purpose of this key connection is to prevent relative movement between the coupling and application shafts due to shock loading.

Axial forces can be accommodated. If the coupling is used with exceptionally high axial forces, the torque capability must be de-rated proportionally. For additional safety, a backing plate can be fitted.

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CHAPTER 4

Machines & Apparatus Required Machining Processes Methodology Final Project

4.1 Machines & Apparatus Required:

The following machines were required in performing the machining processes-

1. Lathe Machine2. Drilling Machine3. Die & Tapsi. Grinding Machine Turning Boring Chamfering Drilling

4.2 Machining Processes:

i. Facing:Facing is the process of removing metal from the end of a workpiece to produce a flat surface. Most often, the workpiece is cylindrical.When a lathe cutting tool removes metal it applies considerable tangential (i.e. lateral or sideways) force to the workpiece. To safely perform a facing operation the end of the workpiece must be positioned close to the jaws of the chuck. The workpiece should not extend more than 2-3 times its diameter from the chuck jaws unless a steady rest is used to support the free end.

Fig. 3.5 Facing

Turning is a machining process in which a cutting tool, typically a non-rotary tool bit, describes a helical toolpath by moving more or less linearly while the workpiece rotates. The tool's axes of movement may be literally a straight line, or they may be along some set of curves or angles, but they are essentially linear. Usually the term "turning" is reserved for the generation of external surfaces by this cutting action, whereas this same essential cutting action when applied to internal surfaces (that is, holes, of one kind or another) is called "boring". Thus the phrase "turning and boring" categorizes the larger family of (essentially similar) processes. The cutting of faces on the workpiece (that is, surfaces perpendicular to its rotating axis), whether with a turning or boring tool, is called "facing", and may be lumped into either category as a subset.

ii. Turning

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Fig. 3.6: Turning

In machining, boring is the process of enlarging a hole that has already been drilled (or cast), by means of a single-point cutting tool (or of a boring head containing several such tools), for example as in boring a gun barrel or an engine cylinder. Boring is used to achieve greater accuracy of the diameter of a hole, and can be used to cut a tapered hole. Boring can be viewed as the internal-diameter counterpart to turning, which cuts external diameters.

iii. Boring

Fig. 3.7: Boring

iv. Chamfering

Chamfering is the operation of beveling the extreme end of a workpiece. This is done to remove the burrs, to protect the end of the workpiece from being damaged and to have a better look. The operation may be performed after knurling, rough turning, boring, drilling. Chamfering is an essential operation before thread cutting so that the nut may pass freely on the threaded workpiece. 

Fig. 3.8: Chamfering

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Various Machines were used for several machining processes:-

I. Lathe machine was used for facing, turning, boring, chamfering

II. Drilling machine was used for drilling & boring

III. Grinding machine was used for surface finishing

IV. Internal die & External die was used for internal thread cutting of nuts & external thread cutting of bolts

4.2Methodology:

v. Drilling

Drilling is a cutting process that uses a drill bit to cut or enlarge a hole of circular cross-section in solid materials. The drill bit is a rotary cutting tool, often multipoint. The bit is pressed against the workpiece and rotated at rates from hundreds to thousands of revolutions per minute.

Fig. 3.9: Drilling

Fig. 3.10: Final Project

4.3 Final Project:

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CHAPTER 5

RESULT & DISCUSSION CONCLUSION

5.1 Result & Discussion:

If the shafts can not be maintained in good alignment and if the loading induces relatively high stresses fatigue failure occurs. If the flanges are nearer to the bearings the smaller will be the deflection of the shaft at the point and the smaller the stresses included in the flanges by this deflection. So the design will be safe from failure.

5.0 CONCLUSION:

5.2 Conclusion:

By performing this project we had learnt the design of a flanged coupling, analysis of a flanged coupling, calculating safety factor of it & the safe arrangement of it. In future it will be helpful for us to choose the right coupling among various types of couplings.

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REFERENCES

[1] FAIRES VIRGIL MORING, “DESIGN OF MACHINE ELEMENTS”, 4th edition, The Macmillan Company, New York/Collier-Macmillan Limited, London

[2] Jain R.K., “ Production Technology”, 16th edition, 2-B, Nath Market, Nai Sarak, Delhi-110006

[3] http://www.hansen.co.za/hansen_rigid_flange_couplings.html

[4] Mechanical Design Data Manual Chapter 15

References:

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