daniel nyathi n0093824n(grinding mill)

8/7/2019 Daniel Nyathi N0093824N(Grinding mill)

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Department of industrial and manufacturing

engineering

AUTHOR DANIEL T NYATHI

STUDENT NUMBER N0093824N

PROJECT TITLE DESIGN OF A GRINDING MILL

SUPERVISOR MR ZIMWARA

DATE OF SUBMISSION 02 MARCH 2011


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Dedication

This project is dedicated to all my friends and family. Thank you for your support.


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ACKNOWLEDGEMENTS

The author would like to acknowledge the following for their help and insight in

completion of this assignment.

The staff in the Department of Industrial and Manufacturing Engineering and my classmates

Mr. Mugwagwa for his supervision

God almighty lord


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Table of contents

DEDICATIONS

ACKNOWLEDGEMENT

ABSTRACT

CHAPTER 1: INTRODUCTORY CHAPTER

1.1: Introduction

1.2: Aim

1.3: Objectives

1.4: Definitions of critical terms in the design title

1.5: Scope of the project

1.6: Background to the problem

1.7: Conclusion

CHAPTER 2: LITERATURE REVIEW

2.0: Introduction

2.1.1: Belts

2.1.2: Shafts

2.1.3: Bearing

2.1.4: Key design

CHAPTER THREE: DESIGN CALCULATION

3.0: Introduction

3.1:Belt

3.2: Shaft


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CHAPTER FOUR: RESULTS

4.0: Introductions

4.1: Results

4.2: Conclusion

REFERENCES


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CHAPTER ONE: INTRODUCTORY CHAPTER

1.0: Introduction

The author is undertaking a blade crushing system design which is to be used mostly on farms in and

around Zimbabwe. The author will focus on the design of the shaft, pulley and the v-belt which will grind

grain.

1.1: Aim

To design a grinding system to be used on farm

1.2: Objectives

y To design the shaft

y To design the v-belt

y To select the bearing

y To design the blades

1.3: Justification.

In these economic people are finding it hard to acquire mealie meal. Also the production of maize on

farms will make it easier for people to sustain themselves.

1.4 Definitions of critical terms

Design: Aprocess that involves the correct determination of sizes of components to withstandthe

maximum stress due to combinations of direct, bending and shear loads.

Grinding: A powdering or pulverizing process.

1.5 Scope of the project

The design will focus on the capability to grind agricultural produce given the appropriate power

that will produce the appropriate torque for grinding seed.


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1.6 Background information

People need equipment to process their agricultural produce into edible products. People are travelling

longer distances on foot so as to get such services therefore it would make it easier as the service would

be available locally.

1.7 Conclusion

This chapter is served to define the problem, state the aims and objectives and the possible solution to

the design problem. It is also served to launch the design project.


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CHAPTER TWO: LITERATURE REVIEW

2.0 Introduction

Literature review focused on the design of an electrical driven grinding mill. The author will focus mainly

on v-belts, shafts and bearings.

2.1 V-belt design


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The cross-sectional dimensions of V belts have been standardized by manufacturers, with each section

designated by a letter of the alphabet for sizes in inch dimensions. Metric sizes are designated in

numbers. V-belts have significant advantages over other types.

i) Advantages

lowmaintenance ability towithstand shocks and vibration.

easy to manufacture

produce considerablylow/no noise

ii) Disadvantages

cannot be repairedwhen deformed

can break at any time

Fig. 2.1: V-belt geometry

Shigleys MechanicalEngineering Design, Eighth Edition McGrawHill

d = 2 sin-1

.................................................. equation2.1


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Where D = diameter of large pulley (sheave)

d = diameter of small pulley (sheave)

C = centre distance

= angle of contact

L= [4C2

(D-d)2]

0.5+0.5 (D d + d d).............................equation 2.2

Where L = length of belt

V= (*d*n) / 60....................equation2.3

Where V= peripheral speed

n = number of revolutions per minute

Lp = L + Lc.........................................................................equation2.4

Where Lp = pitch length

Lc = pitch conversion length

........................................................................................equation2.5

......................................................equation2.6

Where Ha = allowable power per belt

K1 = angle of wrap correction factor

K2= belt length correction factor


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.........................................................equation2.7

Where Hd = design power

Hnorm = nominal power

Ks = service factor

nd = design factor

...........................equation2.8

Where nb = number of belts

..................................................equation2.9

Where Fc = centrifugal tension

Kc = V belt parameter

............................................equation2.10

Where

....................................equation2.11

Where F1 = largest tension

= angle of wrap

f = coefficient of friction


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..................................................equation2.12

Where F2 = least tension

.........................................equation2.13

Where Fi =

................................................equation2.14

Where nfs = factor of safety

.........................equation2.15

Where T1 = tension in tight side

T2 = tension in loose side

...................equation2.16

[Miner rule for belt life]

................................................equation2.17

Where t = lifetime in hours


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2.2 Shaft design

A shaft is normally designed to transfer torque from a driving device to a driven device. If the shaft is

rotating, it is transferring power and if the shaft operating without rotary motion it is simply

transmitting torque and is probably resisting the transfer of power. A shaft is normally supported on

bearings. The torque is normally transmitted to the mounted components using pins, keys, clampingbushes; press fits and bonded joint.

A shaft is a rotary member; it may be either solid or hollow, may be either horizontal, vertical or be

positioned at an angle (inclined).

Formulas to consider in shaft design:

Ta = torque on pinion shaft (Nm) =

pp nH=

n

H

.2.

609.550...[2.21]

Tb = torque on gear shaft ( Nm ) = H60

2. . ng

..[2.22]

N.B Selection of shaft diameter should be due to significant bending loads considering both torque

and loads.

Shigleys MechanicalEngineering Design 1986

=W

rOverhangWa Rm .... [2.23]

Where overhang falls in the range 9mm to 10mm.

bending moment due to tangential load

= Mw

= Wtoverhang

....... [2.30]

Resulting bending moment = M = 222

1 M+M ...... [2.24]

Twisting moment Tm due to M and T =22

TK+MKtb

.....[2.25]

Where K b = bending moment factor

K t = torsion moment factor

diameter of pinion shaft = d p3=

16 Te

s

Thus: = 316

s

e

p

T=d ... [2.26]


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Where Ws = allowable shear stress for the material of the pinion shaft

Allowable deflection = H =64 Fl

3

48 Ed4

Thus: shaft length = l= 364

48 4

F

Ed.... [2.27]

2.3 BEARINGS

A bearing is a mechanical device that supports the moving parts of a machine to reduce friction thereby

aligning parts. The speed the shaft rotates, conditions under which they work and amount of load the

bearing can support determine the type of bearings to be used.

2.4 Key selection

Keys are used in shafts to secure rotating elements. One third of thickness of the key is let into the shaft,

the remainder in the wheel. The key at its root or thick end should be square in section. Newnes

Engineering Practice col.D.J Smith

Keys for ordinary work are as follows:

Width of key diameter of shaft up to 4ins (101.6mm)

1/5 diameter of shaft up to 4ins(101.6mm) to 8ins(203.2mm) 1/6 diameter of shaft up to 8 ins(203.2mm) to 12ins (304.8mm)


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CHAPTER THREE: CALCULATIONS

3:1 Introduction

To come up with the necessary dimensions for components of the grinding mill, the author

introduces to you this chapter where calculations will be performed. The calculations are goingto be for V-belts, shaft diameter, pulley and the forces required to spin crush the load/waste

and rotate the shaft with or against the load.

Given information

i) Power = 18.7KW

ii) electric motor = 340Viii) Velocity ratio of the pulley = 1:4

iv) speed of motor=1000rpm

3:2 V-BELTS

Assuming a leather belt of maximum allowable stress=2,4MPa

Density=970kg/m^3.

Width of belt=250mm, thickness=10mm

Diameter of large pulley=300mm

Smaller pulley diameter=75mm

=3.029rad

Let for each pulley be 0.3

For the smaller pulley ------ = = 2.4810For the larger pulley -------


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Smaller pulley governs.

+

Mass of belt = btp

= (0.0010)(0.250)(970)

= 2.4 kg/m

For the velocity (v)

V =

V =

V = 15.707m/s

For the tensions

= (2.4MPa)(0.0010)(0.250)

= 2.4810

power capacity = ( = 50.7kW

3.3 SHAFT

Using the general twisting equation,

Where T Torque

G modulus of rigidity

llength of shaft

r radius of shaft


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power = torque * angular velocity

J =


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CHAPTER FOUR: RESULTS

4.0 Introductions

In this chapter the author gives a summary of the results obtained during calculations performed in

chapter 3.

4.1 Results

Table 1 a table of results

QUANTITY RESULT

angle ofwrapof driverpulley 3.029rad

angle ofwrapof driven pulley 3.025rad

centre distance C 2m

diameteroflargerpulley 30cm

diameterof smallerpulley 7.5cm

beltlength 4.07m

tension on the tighter side 6kN

tension on the slack side 2.772Kn

beltpower capacity 50.7Kn

shaft diameter(driven) 45mm

shaft diameter(driver) 45mm

4.2 Conclusions

The author summarised the specifications of the grinding mill.


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daniel nyathi n0093824n(grinding mill)

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