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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